A454/R-93-011
[States
Environmental Protection
Agency
Office of Air Quality
Planning and Standards
Research Triangle Park. NC 27711
EPA-454/R-93-011
April 1993
VEFA
LOCATING AND ESTIMATING
Am EMISSIONS
FROM SOURCES OF
STYRENE
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EPA-454/R-93-011
LOCATING AND ESTIMATING
AIR EMISSIONS
FROM SOURCES OF
STYRENE
Office Of Air Quality Planning And Standards
Office Of Air And Radiation
U. S. Environmental Protection Agency
Research Triangle Park, NC 27711
April 1993
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This report has been reviewed by the Office Of Air Quality Planning And Standards, U. S. Environmental
Protection Agency, and has been approved for publication. Any mention of trade names or commercial
products is not intended to constitute endorsement or recommendation for use.
EPA-454/R-93-011
n
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TABLE OF CONTENTS
Section Page
PREFACE iii
1 Purpose of Document 1
References for Section 1 4
2 Overview of Document Contents 5
3 Background 7
Nature of Pollutant 7
Overview of Production and Use 9
References for Section 3 20
4 Emissions from Styrene Production 22
Process Description 22
Emissions 31
References for Section 4 40
5 Emissions from Major Uses of Styrene 42
Polystyrene Production 42
Styrene-Butadiene Copolymer Production 53
Styrene-Acrylonitrile Production 64
Acrylonitrile-Butadiene-Styrene Copolymer
Production 72
Unsaturated Polyester Resin Production 81
Miscellaneous Styrene Copolymer Production .... 90
References for Section 5 93
6 Emissions from the Use of Styrene-Containing Materials . 96
Thermodegradation of Styrene-Containing Materials . 98
Acrylonitrile-Butadiene-Styrene Compounding .... 100
Unsaturated Polyester Resin Use 108
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3/9/93
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TABLE OF CONTENTS (Continued)
Section page
Polystyrene Foam 137
References for Section 6 148
7 Source Test Procedures 151
EPA Reference Method 18 151
NIOSH Method 1501 153
EPA Method 5040 154
Compendium Method TO-14 156
EPA Reference Method 8270 157
References for Section 7 158
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3/9/93 TV
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LIST OF TABLES
Table Page
1 Chemical and Physical Properties of Styrene 8
2 End-Uses of Styrene 12
3 Potential Source Categories of Styrene Emissions .... 13
4 Styrene Production Locations and Capacities 23
5 Styrene Storage and Secondary Emission Factors 33
6 Average Emission Factors for Fugitive Emissions .... 35
7 Control Techniques and Efficiencies Applicable to
Equipment Leak Emissions 37
8 Polystyrene Production Facilities 44
9 Emission Factors for Polystyrene Production 54
10 Styrene-Butadiene Elastomer Production Facilities ... 56
11 Styrene-Butadiene Latex Production Facilities 57
12 Typical Recipe for Emulsion SBR - 60
13 Emission Factors for Styrene-Butadiene Production ... 65
14 Styrene-Acrylonitrile Production Facilities 66
15 Acrylonitrile-Butadiene-Styrene Production
Facilities 74
16 Typical Components Used to Form Unsaturated
Polyester Resins 82
17 Producers of Unsaturated Polyester Resins 85
18 Emission Factors for Styrene from UPR Production .... 89
19 Miscellaneous Uses for Styrene in Chemical Production . 91
20 Prevalence of Styrenic Resin Fabricators 97
21 Styrene Emitted from Thermooxidative Degradation .... 99
22 Summary of Source Testing Data for an ABS Compounding
Facility Uncontrolled and with Temporary Controls . . . 104
23 Summary of ABS Compounding Facility Source Test
Data After Installation of Permanent Controls .... 107
24 Styrene Emission Factors for Cultured Marble and
Sink Manufacturing Operations 119
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3/9/93
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LIST OF TABLES (Continued)
Table Page
25 Geographic Distribution of the Fiberglass Boat Industry
by Number of Facilities 127
26 VOC Emission Factors for Polyester Resin Product
Fabrication Processes 131
27 Monomer-Based Emission Factors for Polyester
Resin/Fiberglass Operations 132
28 Factors Affecting Styrene Emissions from Lamination . .135
29 Domestic Consumption of Polystyrene Foam by End Uses . .138
30 Distribution of PSF Producers by State 139
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3/9/93 VI
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LIST OF FIGURES
Figure Page
1 Chemical Use Tree for Styrene 11
2 Locations of Plants Manufacturing Styrene 24
3 Process Flow Diagram for Styrene Production by
Ethylbenzene Dehydrogenation 26
4 Process Flow Diagram for Styrene Production by
Ethylbenzene Hydroperoxidation 28
5 Process Flow Diagram for Styrene Production by
Isothermal Processing 30
6 Polystyrene Production by Suspension Polymerization . . 48
7 Polystyrene Production by Mass Polymerization 49
8 Polystyrene Production by Solution Polymerization ... 51
9 S-B/SBR Production by Emulsion Polymerization 58
10 SBR Production by Solution Polymerization 62
11 Production of SAN by Emulsion Polymerization 68
12 Production of SAN by Suspension Polymerization 70
13 Production of SAN by Continuous Mass Polymerization . . 71
14 Production of ABS/SAN by Emulsion Polymerization .... 76
15 Production of ABS by Suspension Polymerization 78
16 Production of ABS by Continuous Mass Polymerization . . 80
17 Typical Reactions for Unsaturated Polyester and
Polyester Resin Formation 84
18 Unsaturated Polyester Resin Production 88
19 Original Vacuum and Vent System at an ABS
Compounding Facility 101
20 Permanent VOC Controls at an ABS Compounding Facility . 106
21 Typical Filament Winding Process 112
22 Typical Continuous Lamination Production Process .... 114
23 Small, Custom Operation Production Area 117
24 Large Operation Production Area 121
25 Geographic Distribution of Fiberglass Boat Manufacturing
Facilities for States with More than Ten Facilities . . 128
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VII
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LIST OF FIGURES (Continued)
Figure page
26 Fiberglass Boat Production Process 129
27 Flow Diagram of Typical Polystyrene Foam Sheet
Manufacturing Process 141
28 Flow Diagram of a Typical Polystyrene Foam Board
Manufacturing Process ......... 143
29 Flow Diagram of a Typical EPS Bead Process 145
30 Integrated Bag Sampling Train 152
31 Schematic Diagram of Trap Desorption/Analysis System . . 155
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3/9/93 viii
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SECTION 1
PURPOSE OF DOCUMENT
The Environmental Protection Agency (EPA) and State and
local air pollution control agencies are becoming increasingly
aware of the presence of substances in the ambient air that may
be toxic at certain concentrations. This awareness, in turn, has
led to attempts to identify source/receptor relationships for
these substances and to develop control programs to regulate
emissions. Unfortunately, very little information is available
on the ambient air concentrations of these substances or on the
sources that may be discharging them to the atmosphere.
To assist groups interested in inventorying air emissions of
various potentially toxic substances, EPA is preparing a series
of documents such as this that compiles available information on
sources and emissions of these substances. Prior documents in
the series are listed below:
Substance
EPA Publication Number
Acrylonitrile
Carbon Tetrachloride
Chloroform
Ethylene Dichloride
Formaldehyde (Revised)
Nickel
Chromium
Manganese
Phosgene
Epichlorohydrin
Vinyl Chloride
Ethylene Oxide
Chlorobenzenes
Polychlorinated Biphenyls (PCBs)
Polycyclic Organic Matter (POM)
Benzene
Organic Liquid Storage Tanks
Coal and Oil Combustion Sources
Municipal Waste Combustors
Perchloroethylene and Trichloroethylene
EPA-450/4-84-007a
EPA-450/4-84-007b
EPA-450/4-84-007C
EPA-450/4-84-007d
EPA-450/2-91-012
EPA-450/4-84-007f
EPA-450/4-84-007g
EPA-450/4-84-007h
EPA-450/4-84-007i
EPA-450/4-84-007J
EPA-450/4-84-007k
EPA-450/4-84-0071
EPA-450/4-84-007m
EPA-450/4-84-007n
EPA-450/4-84-007p
EPA-450/4-84-007q
EPA-450/4-88-004
EPA-450/2-89-001
EPA-450/2-89-006
EPA-450/2-90-013
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1,3-Butadiene EPA-450/2-89-021
Chromium (supplement) EPA-450/2-89-002
Sewage Sludge EPA-450/2-90-009
This document deals specifically with styrene. Its intended
audience includes Federal, State and local air pollution
personnel and others who are interested in locating potential
emitters of styrene, and making gross estimates of air emissions
therefrom.
Because of the limited amounts of data available on some
potential sources of styrene emissions, and since the
configurations of many sources will not be the same as those
described here, this document is best used as a primer to inform
air pollution personnel about (1) the types of sources that may
emit styrene, (2) process variations and release points that may
be expected within these sources, and (3) available emissions
information indicating the potential for styrene to be released
into the air from each operation.
The reader is strongly cautioned against using the emissions
information contained in this document to try to develop an exact
assessment of emissions from any particular facility. Because
insufficient data are available to develop statistical estimates
of the accuracy of these emission factors, no estimate can be
made of the error that could result when these factors are used
to calculate emissions from any given facility. It is possible,
in some extreme cases, that order-of-magnitude differences could
result between actual and calculated emissions, depending on
differences in source configurations, control equipment, and
operating practices. Thus, in situations where an accurate
assessment of styrene emissions is necessary, source-specific
information should be obtained to confirm the existence of
particular emitting operations, the types and effectiveness of
control measures, and the impact of operating practices. A
source test and/or material balance should be considered as the
best means to determine air emissions directly from an operation.
In addition to the information presented in this document,
another potential source of emissions data for styrene is the
Toxic Chemical Release Inventory (TRI) form required by Section
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313 of Title III of the Superfund Amendments and Reauthorization
Act of 1986 (SARA 313).1 SARA 313 requires owners and operators
of certain facilities that manufacture, import, process or
otherwise use certain toxic chemicals to report annually their
releases of these chemicals to any environmental media. As part
of SARA 313, EPA provides public access to the annual emissions
data. The TRI data include general facility information,
chemical information, and emissions data. Air emissions data are
reported as total facility release estimates, broken out into
fugitive and point components. No individual process or stack
data are provided to EPA. The TRI requires the use of available
stack monitoring or measurement of emissions to comply with SARA
313. If monitoring data are unavailable, emissions are to be
quantified based on best estimates of releases to the
environment.
The reader is cautioned that the TRI will not likely provide
facility, emissions, and chemical release data sufficient for
conducting detailed exposure modeling and risk assessment. In
many cases, the TRI data are based on annual estimates of
emissions (i.e., on emission factors, material balances,
engineering judgment). The reader is urged to obtain TRI data in
addition to information provided in this document to locate
potential emitters of styrene, and to make preliminary estimates
of air emissions from these facilities. To obtain an exact
assessment of air emissions from processes at a specific
facility, source tests or detailed material balance calculations
should be conducted, and detailed plant site information should
be compiled.
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REFERENCES FOR SECTION 1
1. Toxic Chemical Release Reporting: Community Right-To-Know.
Federal Register 52(107): 21152-21208. June 4, 1987.
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SECTION 2
OVERVIEW OF DOCUMENT CONTENTS
As noted in Section 1, the purpose of this document is to
assist Federal, State and local air pollution agencies and others
who are interested in locating potential air emitters of styrene
and making gross estimates of air emissions therefrom. Because
of the limited background data available, the information
summarized in this document does not and should not be assumed to
represent the source configuration or emissions associated with
any particular facility.
This section provides an overview of the contents of this
document. It briefly outlines the nature, extent, and format of
the material presented in the remaining sections of this report.
Section 3 of this document briefly summarizes the physical
and chemical characteristics of styrene, and provides an overview
of its production and use. This background section may be useful
to someone who needs to develop a general perspective on the
nature of this substance and how it is manufactured and consumed.
Sections 4, 5, and 6 of this document focus on major source
categories that may discharge styrene air emissions. Section 4
discusses emissions from the production of styrene; Section 5
discusses emissions from the major uses of styrene; and Section 6
addresses emissions from the use of styrene-containing materials.
For each major industrial source category described in
Sections 4, 5, and 6, example process descriptions and flow
diagrams are given, potential emission points are identified, and
available emission factor estimates are presented that show the
potential for styrene emissions before and after controls are
employed by industry. Individual companies are named that are
reported to be involved with either the production or use of
styrene based primarily on information from trade publications.
The final section of this document summarizes available
procedures for source sampling and analysis of styrene. Details
are not prescribed nor is any EPA endorsement given or implied to
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any of these sampling and analysis procedures. At this time, EPA
has not generally evaluated these methods. Consequently, this
document merely provides an overview of applicable source
sampling procedures, citing references for those interested in
conducting source tests.
This document does not contain any discussion of health or
other environmental effects of styrene, nor does it include any
discussion of ambient air levels or ambient air monitoring
techniques.
Comments on the contents or usefulness of this document are
welcomed, as is any information on process descriptions,
operating practices, control measures and emissions information
that would enable EPA to improve its contents. All comments
should be sent to:
Chief, Emission Factor and Methodologies Section
Emission Inventory Branch (MD-14)
U. S. Environmental Protection Agency
Research Triangle Park, North Carolina 27711
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SECTION 3
BACKGROUND
NATURE OF POLLUTANT
Styrene (CAS No. 100-42-5) is an unsaturated aromatic
monomer that is widely used in the production of plastics,
resins, and elastomers. In the past century production and use
of styrene have increased rapidly because it can be polymerized
and copolymerized easily to produce a wide variety of products.
Styrene was the twenty-first highest-volume chemical produced in
the United States in 1988.1
Styrene's molecular formula is represented as:
Table 1 shows the chemical and physical properties of
styrene. Because of styrene's flammability and its ease of
polymerization, an inhibitor (10-15 ppm tert-butylcatechol) must
be added during storage and high temperatures must be avoided.2
Styrene is released to the atmosphere during its manufacture
and from the use of styrene-containing materials. Styrene has
also been detected in small amounts in automobile emissions3 and
from publicly owned treatment works/ The combustion of styrene-
based products is another potential source of styrene emissions.5
Styrene is very reactive in the air, reacting readily with
hydroxyl radicals and ozone.6 Styrene readily undergoes
oxidation by ozone to produce formaldehyde, benzaldehyde, benzoic
acid, and traces of formic acid. The styrene half-life resulting
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TABLE 1. CHEMICAL AND PHYSICAL PROPERTIES OF STYRENE
Synonyms:
Chemical Abstracts
Registry Number:
Molecular Formula:
Molecular Weight:
Ambient State:
Boiling Point:
(760 mm Hg)
Freezing Point:
Density:
Solubility:
Flammable (explosive)
Limits:
Flashpoint:
Autoignition Temperature:
Vapor Pressure:
Concentration in
Saturated Air:
Odor Threshold:
Conversion Factors:
(25°C, 760 mm Hg)
Cinnamene, cinnamenol, cinnamol,
ethenylbenzene, monotryrene,
phenthylene, phenlethene,
phylethylene, styrole, styrolene,
styron, styropol, styropor,
vinylbenzene, vinylbenzol
100-42-5
C6H5CH=CH2
104.16
Colorless volatile liquid
145.2°C (293.4°F)
-30.6°C (-23.1°F)
0.9018 g/cm3 (25"C)
Soluble in ethyl ether, benzene,
methanol, toluene, ethanol,
acetone, n-heptane, carbon
tetrachloride, carbon disulfide;
slightly soluble in water (about
25 mg/100 g water at 25°C)
1.1-6.1% by volume in air
34.4°C (94°F) Tag closed cup
36.7°C (98°F) Tag open cup
490°C (914°F)
50
68
77
86
104
(10)
(20)
(25)
(30)
(40)
mm Hg
2.34
4.50
6.45
8.21
14.30
fkPa)
(0.31)
(0.60)
(0.86)
(1.09)
(1.91)
8,500 ppm (25°C)
0.05 - 0.15 ppm
1 ppm = 4.26 mg/rn3
1 mg/m = 0.235 ppm
Source: References 7 and 8.
8
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from its oxidation by ozone is estimated to be at least 9 hours.6
The oxidation of hydroxyl radicals yields benzaldehyde. The
estimated half-life of styrene from this oxidation is 3 hours.6
Styrene released to water is expected to have an evaporative
half-life of 23.8 hours, assuming a water depth of 1 meter (3.28
feet). In addition, styrene may be oxidized by some common water
treatment compounds. Epichlorohydrin is formed in the presence
of styrene and aqueous chlorine (hypochlorous acid).3
Liquid styrene exposed to air results in polymerization of
styrene initiated by ozone. As it polymerizes, styrene becomes
increasingly viscous until a clear, glossy solid is formed.9
OVERVIEW OF PRODUCTION AND USE
The total annual capacity of styrene manufacturing
facilities in the United States was 4,075,142 Mg (8984 MM Ibs) in
1989.10 The majority of styrene is produced by dehydrogenation
of ethylbenzene, with about 15 percent produced by
hydroperoxidation of ethylbenzene. Propylene is a coproduct in
the hydroperoxidation process. In 1989, eight companies at nine
locations produced styrene in the United States. One additional
facility has been on standby since 1985.10 The ethylbenzene used
to manufacture styrene is produced by alkylation of benzene or
extraction from mixed xylenes.11 Most ethylbenzene production
processes are for captive styrene uses rather than for sale of
the monomer. °
Styrene is manufactured as an intermediate for the
production of polystyrene (68%), styrene-butadiene (SBR)
elastomers (6%), latexes (SBR latexes containing <45% styrene and
styrene-butadiene latexes containing >45% styrene) (7%),
acrylonitrile-butadiene styrene (ABS) resins and styrene-
acrylonitrile (SAN) (9%), unsaturated polyester resins (7%), and
for miscellaneous products and export (3%).12 Seven of the eight
styrene production facilities have some captive consumption of
styrene monomer. Captively consumed monomer is mainly used for
manufacturing polystyrene, but it is also used to a lesser extent
to produce ABS, SAN, and styrene-butadiene copolymer latexes.12
Figure 1 and Table 2 show some of the end products from styrene.
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These products and some of their production processes will be
covered in detail in Sections 5 and 6. Table 3 lists the
potential source categories of styrene emissions by Standard
Industrial Classification (SIC) code. It is important to note
that these source categories do not necessarily denote
significant sources of styrene emissions.
10
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Production Method
Use
Percent
Ethylbenzene
Dehydrogenation (85%)
Ethylbenzene
Hydroperoxidation (15%)
Polystyrene
— Styrene butadiene
(SBR) elastomer
Styrene butadiene
(SBR) latex (contains <45%
styrene) and styrene-butadiene
latex (contains >45% styrene)
Unsaturated polyester resins
— Acrylonftrile-butadiene-styrene
resins and styrene-acrylonitrile
Miscellaneous and export
Figure 1. Chemical Use Tree for Styrene12
68
6
7
9
100
11
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TABLE 2. END USES OF STYRENE
Polystyrene
Styrene butadiene
rubber (SBR)
elastomers and
latexes
Styrene-butadiene
(S-B) latexes
Aerylonitrile-
butadiene-styrene
(ABS)
Styrene-
acrylonitrile
(SAN)
Unsaturated
polyester
resins(reinforced
plastics/
composites)
Insulation board, loose-fill packaging,
disposable dinnerware, food containers,
toys, games, hobby kits, housings for
room air conditioners and small handheld
appliances, television cabinets, shower
doors, drain pipes, tubing, light
diffusers, audio and video tape
cassettes, combs, brushes, eyeglasses,
picnic coolers, molded shutters,
furniture parts, watering cans, soap
dishes, room dividers
Passenger car tires, industrial hoses,
conveyer belts, appliance parts, wire
and cable insulation, footwear, coated
fabrics, car bumpers and weatherstrips,
additive in cements and adhesives
Tufted carpet and upholstery
backcoatings, binder for paper coatings,
binder for felt base of vinyl floor
tile, cement additive, component of
latex paints
Piping (drain, waste, and vent),
conduit, pipefittings, automotive
components (instrument panels, consoles,
front radiator grilles, headlight
housings, etc.)/ refrigerator doorliners
and food compartments, telephones,
luggage and cases, toys, hobby kits,
shower stalls and bathroom fixtures for
mobile homes, margarine rubs, radio
chassis
Drinking tumblers, blender jars and
covers, dishes, instrument panel lenses,
battery cases
Fiberglass reinforced boats, storage
tanks, tub, spa, and shower units, truck
camper tops, recreational vehicles, wall
panels, cultured marble products,
automotive parts, appliance/electrical
components, and many other products.
Source: Reference 8
12
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TABLE 3. POTENTIAL SOURCE CATEGORIES OF STYRENE EMISSIONS
SIC SOURCE DESCRIPTION
CODE*
1331 Crude petroleum and natural gas
1321 Natural gas liquids
1711 Plumbing, heating, air-conditioning
1743 Terrazzo, tile, marble, mosaic work
2221 Broadwoven fabric mills, manmade
2262 Finishing plants, manmade
2295 Coated fabrics, not rubberized
2431 Millwork
2434 Wood kitchen cabinets
2492 Reconstituted wood products
2499 Wood products, not elsewhere classified
2511 Wood household furniture
2517 Wood TV and radio cabinets
2519 Household furniture not elsewhere classified
2522 Office furniture, except wood
2531 Public building and related furniture
2599 Furniture and fixtures, not elsewhere classified
265 PAPER AND ALLIED PRODUCTS
2621 Paper mills
2631 Paperboard mills
265 Paperboard containers and boxes
2655 Fiber cans, drums, and similar products
2657 Folding paperboard boxes
267 Miscellaneous converted paper products
2672 Paper, coated and laminated, not elsewhere classified
28 CHEMICALS AND ALLIED PRODUCTS
281 Industrial gases
2812 Inorganic pigments
2813 Industrial inorganic chemicals, not elsewhere
classified
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TABLE 3. (Continued)
2816 Industrial pigments
2819 Industrial inorganic chemicals, not elsewhere
classified
282 Plastics materials and synthetics
2821 Plastics materials and resins
2823 Cellulosic manmade fibers
2833 Medicinals and botanicals
2834 Pharmaceutical preparations
2835 Diagnostic substances
2836 Biological products (excluding diagnostic)
2841 Soap and other detergents
2842 ' Polishes and sanitation goods
2843 Surface active agents
2844 Toilet preparations
2851 Paints and allied products
286 Industrial organic chemicals
2861 Gum and wood chemicals
2865 Cyclic crudes and intermediates
2869 Industrial organic chemicals, not elsewhere
classified
2873 Nitrogenous fertilizers
2874 Phosphatic fertilizers
2879 Agricultural chemicals, not elsewhere classified
2891 Adhesive and sealants
2892 Explosives
2899 Chemical preparations, not elsewhere classified
29 PETROLEUM AMD COAL PRODUCTS
2911 Petroleum refining
2951 Asphalt paving mixtures and blocks
2992 Lubricating oils and greases
2999 Petroleum and coal products, not elsewhere classified
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TABLE 3. (Continued)
30 RUBBER AND MISCELLANEOUS PLASTICS PRODUCTS
3011 Tires and inner tubes
3021 Rubber and plastics footware
3052 Rubber and plastics hose and belting
3069 Fabricated rubber products, not elsewhere classified
308 Miscellaneous plastics products, not elsewhere
classified
3081 . Unsupported plastics film and sheet
3082 Unsupported plastics profile shapes
3083 Laminated plastics plate and sheet
3084 Plastics pipe
3086 Plastics foam products
3087 Custom compound purchased resins
3088 Plastic plumbing fixtures
3089 Plastics products, not elsewhere classified
3142 House slippers
3229 Pressed and blown glass, not elsewhere classified
3241 Cement, hydraulic
3261 Vitreous plumbing fixtures
3271 Concrete block and brick
3272 Concrete products, not elsewhere classified
3274 Lime
3281 Cut stone and stone products
3291 Abrasive products
329 Mineral wool
3299 Non-metallic mineral products, not elsewhere
classified
3312 Blast furnaces and steel mills
3313 Electrometallurgical products
316 Cold finishing of steel shapes
3321 Gray and ductile iron foundries
3324 Steel investment foundries
15
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TABLE 3. (Continued)
3325 Steel foundries, not elsewhere classified
3339 Primary nonferrous metals, not elsewhere classified
3341 Secondary nonferrous metals
3363 Aluminum die-casting
3364 Nonferrous die-casting, excluding aluminum
3365 Aluminum foundries
3366 Copper foundries
3369 Nonferrous foundries, not elsewhere classified
34 FABRICATED METAL PRODUCTS
3423 Hand and edge tools, not elsewhere classified
343 Plumbing and heating, except electric
3431 Metal sanitary ware
344 Fabricated structural metal products
3441 . Fabricated structural metal
3442 Metal doors, sash, and trim
3343 Fabricated plate work (boiler shops)
3444 Sheet metal work
3446 Architectural metal work
3451 Screw machine products
3479 Metal coating and allied services
3498 Fabricated pipe and fittings
3499 Fabricated metal products, not elsewhere classified
3511 Turbines and turbine generator sets
3519 Internal combustion engines, not elsewhere classified
352 Farm and garden machinery
3523 Farm machinery and equipment
3533 Oil and gas field machinery
3541 Machine tools, metal cutting types
3546 Power-driven handtools
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TABLE 3. (Continued)
3548 Welding apparatus
3561 Pumps and pumping equipment
3563 Air and gas compressors
3564 Blowers and fans
3575 Computer terminals
3585 Refrigeration and heating equipment
3599 Industrial machinery, not elsewhere classified
3612 Transformers, except electronic
3613 Switchgear and switchboard apparatus
3621 Motors and generators
3624 Carbon and graphite products
3625 Relays and industrial controls
3643 Current-carrying wiring devices
3644 Noncurrent-carrying wiring devices
3647 Vehicular lighting equipment
3661 Telephone and telegraph apparatus
3663 Radio and TV communications equipment
367 Electric components and accessories
3671 Electron tubes
3674 Semiconductors and related devices
3679 Electronic components, not elsewhere classified
3694 Engine electrical equipment
37 TRANSPORTATION EQUIPMENT
371 Motor vehicles and equipment
3711 Motor vehicles and car bodies
3713 Truck and bus bodies
3714 Motor vehicles parts and accessories
3715 Truck trailers
3716 Motor homes
17
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TABLE 3. (Continued)
3721 Aircraft
373 Ship and boat building and repairing
3731 Ship building and repairing
3732 Boat building and repairing
3792 Travel trailers and campers
3799 Transportation equipment, not elsewhere classified
3812 Search and navigation equipment
3821 Laboratory apparatus and furniture
3826 Analytical instruments
3829 Measuring and controlling devices, not elsewhere
classified
3842 Surgical appliances and supplies
3844 X-ray apparatus and tubes
3861 Photographic equipment and supplies
39 MISCELLANEOUS MANUFACTURING INDUSTRIES
3931 Musical instruments
394 Toys and sporting goods
3944 Games, toys, and children's vehicles
3949 Sporting and athletic goods, not elsewhere classified
3965 Fasteners, buttons, needles, and pins
3999 Manufacturing industries, not elsewhere classified
4225 General warehousing and storage
4226 Special warehousing and storage, not elsewhere
classified
4231 Trucking terminal facilities
4991 Marine cargo handling
4612 Crude petroleum pipelines
4953 Refuse systems
4961 Steam and air-conditioning supply
5091 Sporting and recreational goods
18
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TABLE 3. (Continued)
516 Chemicals and allied products
5171 Petroleum bulk stations and terminals
6512 Nonresidential building operators
6514 Dwelling operators, excluding apartments
7389 Business services, not elsewhere classified
7999 Amusement and recreation, not elsewhere classified
8062 General medial and surgical hospitals
8731 Commercial physical research
8999 Services, not elsewhere classified
*SIC Code is listed as a potential source in the EPA "Crosswalk"
document.13 The data in Crosswalk were obtained primarily from
permitting and source test information contained in the 1986
National Air Toxics Information Clearinghouse (NATICH) data base.
Additional data were gathered from the Organic Chemical
Producers' Data Base and Air Emissions Species Data Manual
(Volume I, Volatile Organic Compound Species profiles), and SARA
313 Toxic Release Inventory.13
19
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REFERENCES FOR SECTION 3
1. Chemical and Engineering News. Facts and Figures for the
Chemical Industry at a Glance, pp. 36-45. June 1989.
2. National Research Council. The Alkyl Benzenes. Committee
on Alkyl Benzene Derivatives; Board on Toxicology and
Environmental Health Hazards; Assembly of Life Science.
National Academy Press. 1981.
3. Santodonato, J., et al. Investigation of Selected Potential
Environmental Contaminants: Styrene, Ethylbenzene, and
Related Compounds. EPA-560/11-80-018. U. S. Environmental
Protection Agency, Washington, D.C. 1980.
4. Pope, A. A., et al. Toxic Air Pollutant Emission Factors -
A Compilation for Selected Air Toxic Compounds and Sources.
EPA-450/2-88-006. U. S. Environmental Protection Agency,
Research Triangle Park, North Carolina. 1988.
5. Pfaffli, P., et al. Thermal Degradation Products of
Homopolymer Polystyrene in Air. Scand. J. Work Environ, and
Health. Suppl. 2:22-27. 1978.
6. Alexander, M. The Environmental Fate of Styrene. The SIRC
Review, pp. 33-42. April 1990.
7. Kirk-Othmer Encyclopedia of Chemical Technology. 3rd ed.
Styrene. Volume 21. John Wiley and Sons. New York, New
York. pp. 770-801. 1983.
8. U. S. Department of Health and Human Services. Criteria for
a Recommended Standard. Occupational Exposure to Styrene.
DHHS (NIOSH) Publication No. 83-119. National Institute for
Occupational Safety and Health, Cincinnati, Ohio. 1983.
9. Lowenheim, F. A. and M. K. Moran. Styrene. In: Faith,
Keyes, and Clark's Industrial Chemicals. John Wiley and
Sons. New York, New York. pp. 779-785. 1975.
10. SRI International. 1989 Directory of Chemical Producers,
United States of America. Menlo Park, California. 1989.
11. U. S. Environmental Protection Agency. Benzene Emissions
from the Ethylbenzene/Styrene Industry - Background
Information for Proposed Standards. EPA-450/3-70-035a.
Research Triangle Park, North Carolina. 1980.
12. A. T. Kearney. Impact Analysis of the EPA Office of
Drinking Water Proposal to Regulate Styrene. Styrene
Information Research Center. 1989.
20
-------
13. Pope, A. A., et al. Toxic Air Pollutant/Source Crosswalk
A Screening Tool for Locating Possible Sources Emitting
Toxic Air Pollutants, Second Edition. EPA-450/2-89-017.
U. S. Environmental Protection Agency, Research Triangle
ParJc, North Carolina. 1989.
21
-------
SECTION 4
EMISSIONS FROM STYRENE PRODUCTION
Styrene production and the associated air emissions are
described in this section. Process flow diagrams are included as
appropriate, with specific streams or vents in the figures
labeled to correspond with the discussion in the text. Emission
factors for the production processes are presented when
available, and control technologies are described. The reader
should contact the specific facility to verify the nature of the
process used, production volume, and controls in place before
applying any of the emission factors presented.
Styrene is currently produced by eight companies at nine
locations in the United States. One additional facility has been
on standby since 1985 and is not currently manufacturing styrene.
The production locations and capacities are presented in Table 4.
The total annual capacity for all styrene manufacturing
facilities is 4,075,142 Mg (8984 MM Ibs) (not including the plant
on standby),1 with facilities operating at 98 percent of
capacity.2 As shown in Figure 2, the majority of styrene-
manufacturing facilities are located on the Gulf Coast.
All but one plant manufactures styrene by dehydrogenation of
ethylbenzene. The other facility uses hydroperoxidation of
ethylbenzene to produce propylene, with styrene as a by-product.
PROCESS DESCRIPTION
Ethylbenzene Dehydrogenation
The majority of styrene produced in the United States is
produced by the dehydrogenation of ethylbenzene. Seven
facilities have the capacity to produce an annual total of
3,480,926 Mg (7674 MM Ibs).
22
-------
TABLE 4. STYRENE PRODUCTION LOCATIONS AND CAPACITIES
Facility
Location
Annual Capacity
MM
Mq/yr Ib/yr
Amoco Corporation
ARCO Chemical Co.
Chevron Corporation
Cos-Mar, Inc.
Dow chemical
Huntsman Chemical Corp.
Rexene Products Co.
Sterling Chemicals, Inc.
Texas City, TX
Channelview, TX*
Monaca, PA
St. James, LA
Carville, LA
Freeport, TX
Midland, MI
Bayport, TX
Odessa, TX
Texas City, TX
362,880
800
594,216
99,792
272,160
680,400
639,576
146,966
453,600
145,152
680,400
1310
220
600
1500
1410
324
1000
320
1500
4,075,142
8984
*Ethylbenzene hydroperoxidation process.
bPlant has been on standby since 1985 (not included in total
capacity).
NOTE: This listing is subject to change as market conditions
change, facility ownership changes, plants are closed down, etc.
The reader should verify the existence of particular facilities
by consulting current listings and/or the plants themselves. The
level of styrene emissions from any given facility is a function
of variables such as capacity, throughput, and control measures,
and should be determined through direct contacts with plant
personnel. These operating plants and locations were current as
of January 1990.
Source: Reference 1
23
-------
LEGEND OF PLANT NAMES AND LOCATIONS
1. ARCO, Monaca, PA
2. Chevron, St. James, LA
3. Huntsman Chemical, Bayport, TX
4. Cos-Mar, Carville, LA
5. Dow, Freeport, TX
6. Dow, Midland, Ml
7. Rexene Products Co., Odessa, TX
8. Amoco Corporation, Texas City, TX
9. ARCO, Channelview, TX
10. Sterling Chemicals, Texas City, TX
Figure 2. Locations of Plants Manufacturing Styrene
24
-------
Styrene manufacture by ethylbenzene dehydrogenation is shown by
the reaction:
CH-CH,
Ethylb«nzena
Styrena
Hydrogvn
Figure 3 illustrates the process of ethylbenzene
dehydrogenation. Purified ethylbenzene is preheated in a heat
exchanger (Step 1), and the resultant vapor is mixed continuously
with steam at 710°C in the dehydrogenation reactor (Step 2) that
contains one of several catalysts such as zinc, aluminum,
chromium, iron, or magnesium oxide. The reaction product exits
through the heat exchanger and is further cooled in a condenser
where water and crude styrene vapors are condensed (Step 3). The
hydrogen-rich process gas is recovered and used as a fuel (Step
4) and the process water is purified in a stripper (Step 5) and
recycled to the boiler. The remaining crude liquid styrene goes
to a storage tank (Step 6). The liquid consists of styrene
(37%), ethylbenzene (61%), toluene (1%), benzene (0.7%) and tars
(0.3%). Benzene and toluene are removed from the crude styrene
in the benzene/toluene column (Step 7). They are then typically
separated by distillation. The toluene is sold and the benzene
is returned to the ethylbenzene production section or sold.
Next, the ethylbenzene column removes ethylbenzene that is
directly recycled (Step 8). Tars are removed and the styrene
product emerges from the styrene finishing column (Step 9). In
some facilities, an ethylbenzene/benzene/toluene stream is
separated from the crude styrene initially and processed
separately.
Ethylbenzene Hydroperoxidation
Styrene is currently manufactured by ethylbenzene
hydroperoxidation at only one facility in the United States.
25
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This process, shown in Figure 4, is described below. Styrene
manufacture by ethylbenzene hydroperoxidation is shown by the
reaction:
°» ~t~ I I -h CH'CH-CH, ~ I I -4- HC-CH-CH, 4- HO
« I I I I 3 2 I I I 2 \ / 3 I 2
o
Oxygen Bhylberaen* Propylerw Styrtn* Propylen* Oxide Water
Ethylbenzene is oxidized with air to produce ethylene
hydroperoxide and small amounts of methylbenzylalcohol and
acetophenone (Step 1). The exit gas (principally nitrogen) is
cooled and scrubbed to recover aromatics before venting.
Unreacted ethylbenzene and low-boiling contaminants are removed
in an evaporator (Step 2). Ethylbenzene is then sent to the
recovery section to be treated before reuse (Step 3).
The mixed stream of methylbenzylalcohol and acetophenone is
then dehydrated over a solid catalyst to produce styrene
(Step 4). Residual catalyst solids and high-boiling impurities
are separated and collected for disposal. The crude styrene goes
to a series of distillation columns where the pure styrene
monomer product is recovered (Step 5). The residual organic
stream contains crude acetophenone, catalyst residue, and various
impurities. This mixture is treated under pressure with hydrogen
to convert the acetophenone to methylbenzylalcohol (Step 6).
Catalyst waste is separate from the methylbenzylalcohol which is
returned to the recovery section for processing and reuse.
Hydrogen and organic vapors are recovered for use as fuel.
Ethylbenzene hydroperoxide is combined with propylene over a
catalyst mixture under .high pressure to produce propylene oxide
and acetophenone (Step 7). Pressure is then reduced and residual
propylene and other low-boiling compounds are separated by
distillation (Step 8). The vent stream containing propane and
some propylene can be used as a fuel. Propylene is recycled to
the epoxidation reactor. The crude epoxidate is treated to
27
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remove acidic impurities and residual catalyst material (Step 9)
and the resultant epoxidate stream is distilled (Step 10) to
separate the propylene oxide product for storage. Residual water
and propylene are recycled to the process train and liquid
distillate is recovered as a fuel. The organic layer is routed
to the ethylbenzene and methylbenzylalcohol recovery section.
Isothermal Processing
An isothermal process for producing styrene from
ethylbenzene was patented in the United States in 1981.5 This
process is not currently used in the United States, but it is
used in several European countries.
As shown in Figure 5, liquid ethylbenzene is vaporized by
condensing steam in a heat exchanger (Step 1). Process steam is
then introduced into the ethylbenzene stream and the feed mixture
is superheated before it enters the molten-salt reactor (Step 2).
In the reactor, the ethylbenzene/steam mixture passes
through tubes where it comes into contact with the catalyst and
is dehydrogenated. Heat for the dehydrogenation reaction is
supplied by molten salt (preferably a mixture of sodium
carbonate, lithium carbonate, and potassium carbonate)
surrounding the tubes. The reactor is maintained at a uniform
wall temperature by circulating the molten-salt mixture through
the heat exchanger of a fired heater.
The reaction products are cooled and condensed in a
separator (Step 3). The liquid phase is a mixture of organic
products: styrene, unreacted ethylbenzene, and small quantities
of benzene, toluene, and high-boiling compounds. Styrene is
separated from the other liquid constituents, which are then
recovered and recycled.
29
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The gas phase from the condensation step in the separator
consists mainly of hydrogen, with small quantities of carbon
dioxide, carbon monoxide, and methane. After these gases are
compressed, they are cooled. Condensable products from this
final cooling stage are then recovered and recycled to the
separator. When hydrogen-rich off gas is used as fuel for the
heater of the molten-salt reactor, the fuel requirement for this
stage of the process is zero.
EMISSIONS
Most air emissions associated with styrene production arise
from loading operations, styrene monomer storage, and equipment
leaks. Process vents may also contribute to air emissions in
addition to secondary sources (such as waste treatment and
disposal facilities) .
ssions
Figure 3 shows that during styrene production by
ethylbenzene dehydrogenation, process vent discharges (A) of
styrene occur primarily from the vacuum column vents. The
hydrogen separation vent is only used during startup, shutdown,
and during recovery section outages.4 The vacuum column vents
remove air that leaks into the column, as well as light
hydrocarbons and hydrogen that form during dehydrogenation,
noncombustibles dissolved in the column feed, and any entrained
aromatics. The majority of styrene emissions occur at the first
column, the benzene-toluene column, in the distillation train.
Although no specific information on controls was available,
process vents that have the potential to emit benzene may be
controlled to prevent occupational exposure.
Other sources of process emissions from ethylbenzene
dehydrogenation are less likely because of the need to operate
most processes under a vacuum and because of the heating value of
31
-------
the gases. No emission estimates for styrene production
processes were located in the literature. Also, little
information was found on emission controls. One type of control
option is incineration, which can reduce styrene emissions by as
much as 98 percent.4
No information was located in the literature that discussed
process emission sources from styrene production by ethylbenzene
hydroperoxidation or the isothermal production process. Styrene
emissions may occur during the styrene refining process for each
of these production processes.
Storage Emissions
Other possible sources of styrene emissions are storage tank
losses (B) and handling losses (C) that occur during product
loading into drums, tank trucks, tank cars, barges, or ships.
Styrene production plants typically have from 2 to 12 small,
fixed-roof monomer storage tanks. Storage tank losses are either
working losses that occur while filling the tank, or breathing
losses due to expansion from temperature changes. Both can be
estimated using equations for storage tank emissions given in the
U. S. Environmental Protection Agency's "Estimating Air Toxic
Emissions from Organic Liquid Storage Tanks" report.6 In the
absence of specific data on the storage tank, two emission
factors were identified in the literature.7 Shown in Table 5,
both are for uncontrolled emissions. No facilities are known to
currently control emissions with floating roof tanks or
incineration, although several use condensing units to recover
styrene.2
Equipment Leak Emissions
Emissions occur from process equipment components whenever
the liquid or gas streams leak from the equipment. Equipment
leaks can occur from the following components: pump seals,
32
-------
TABLE 5. STYRENE STORAGE AND SECONDARY EMISSION FACTORS
Emission Source
Estimated Emission Factor
Storage
Breathing Loss*
Working Loss*
Secondary
Wastewater Treatment11
0.18 g/L (1.5 lbs/10 Ibs) storage
capacity
0.02 g/L (0.17 lbs/10 Ibs) gallons
throughput
0.50 g/g (0.50 Ib/lb) styrene in
wastewater
"Source: Reference 7.
Source: Reference 8.
33
-------
process valves, compressor safety relief valves, flanges, open-
ended lines, and sampling connections. Fugitive emissions will
be primarily limited to the streams containing no benzene because
of the National Emission Standard for Hazardous Air Pollutants
(NESHAP) that applies to equipment in benzene service. This
NESHAP addresses all equipment components handling process
streams containing 10 percent by weight or greater benzene.
Emission estimates can be calculated in the five ways described
in the EPA publication "Protocols for Generating Unit-Specific
Emission Estimates."9 The methods differ in complexity; however,
the more complex, the better the emission estimate.
The simplest method requires that the number of each
component type be known. Furthermore, for every component the
styrene content of the stream and the time the component is in
service is needed. This information is then multiplied by the
EPA's average emission factors for the Synthetic Organic Chemical
Manufacturing Industries (SOCMI) shown in Table 6. This method
should only be used if no other data are available, as it
probably results in an overestimation of actual equipment leak
emissions. For each component, estimated emissions are:
No. of
equipment
components
Weight %
styrene in the
stream
lomponent-specific
emission factor
No. hrs/yr in
styrene service
To obtain better equipment leak emission estimates, one of
*
the more complex estimation methods should be used. These other
four methods require that some level of emission measurement for
the facility's equipment components be collected. These are
described briefly, and the reader is referred to the Protocols
document for the calculation details.
34
-------
TABLE 6. AVERAGE EMISSION FACTORS FOR FUGITIVE EMISSIONS
Equipment
Valves
Pump Seals
Compressor Seals
Pressure Relief
Seals
Flanges
Open-Ended Lines
Sampling Connections
Service
Gas
Light Liquid
Heavy Liquid
Light Liquid
Heavy Liquid
Gas /Vapor
Gas /Vapor
All
All
All
Emission
(Kg/hr/
Source)
0.0056
0.0071
0.00023
0.0494
0.0214
0.228
0.104
0.00083
0.0017
0.0150
Factor
(Lb/hr/
Source)
0.012
0.016
0.00051
0.109
0.472
0.503
0.229
0.0018
0.0037
0.033
Source: Reference 9.
35
-------
The leak/no leak approach is based on a determination of the
number of leaking and non-leaking components. These values are
then multiplied by two different sets of EPA-derived emission
factors. The third method groups screening results into three
ranges: 0-1,000 ppmv; 1,001-10,000 ppmv; and greater than 10,000
ppmv. The number of each component falling in a particular range
is multiplied by the component-specific emission factor for that
range. These emission factors have also been developed by EPA.
The fourth procedure uses screening data in correlation equations
derived from earlier work by EPA.
The fifth method gives the facility the option to develop
its own correlation equations but requires more rigorous testing,
bagging and analyzing of equipment leaks to determine mass
emission rates.
Although no specific information on controls used by the
industry was identified, equipment components in benzene service
will have some controls in place. Generally, control of fugitive
emissions will require the use of sealless or double mechanical
seal pumps, an inspection and maintenance program, as well as
replacement or leaking valves and fittings. Typical controls for
equipment leaks are listed in Table 7. Additionally, some
leakless equipment is available such as leakless valves10 and
sealless pumps.2
Secondary Emissions
Secondary emissions occur at both on-site and off-site
facilities that treat and dispose of wastewater, liquid waste, or
solid waste. Waste streams may be generated for any of the
operations shown in Figures 3, 4, and 5.
For secondary emissions resulting from treatment of
wastewater containing styrene, one reference estimated that
approximately 50 percent of the styrene present in the water may
36
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be released during processing at a publicly owned treatment works
(POTW) facility.11 This emission factor is given in Table 5. No
information was available on the styrene content in the
wastewater. Furthermore, handling and processing practices will
differ with each facility; therefore, the emission factor should
be reviewed as providing an order-of-magnitude estimate at best.
39
-------
REFERENCES FOR SECTION 4
1. SRI International. 1990 Directory of Chemical Producers,
United States of America. Menlo Park, California. 1990.
2. A. T. Kearney. Impact Analysis of the EPA Office of
Drinking Water Proposal to Regulate Styrene. Styrene
Information Research Center. 1989.
3. U. S. Environmental Protection Agency. Benzene Emissions
from the Ethylbenzene/Styrene Industry - Background
Information for Proposed Standards. EPA-450/3-70-035a.
U. S. Environmental Protection Agency, Research Triangle
Park, North Carolina. 1980.
4. Cruse, P. A. Locating and Estimating Air Emissions from
Sources of Benzene. EPA-450/4-84-007q. U. S. Environmental
Protection Agency, Research Triangle Park, North Carolina.
1988.
5. Short, H. C. and L. Bolton. New Styrene Process Pares
Production Costs. Chemical Engineering. August: 30-31.
1985.
6. Murphy, P. Estimating Air Toxics Emissions From Organic
Liquid Storage Tanks. EPA-450/4-88-004. U. S.
Environmental Protection Agency, Research Triangle Park,
North Carolina. 1988.
7. Stockton, M. B. and J. H. E. Stelling. Criteria Pollutant
Emission Factors for the 1985 NAPAP Emissions Inventory.
EPA-600/7-87-015. U. S. Environmental Protection Agency,
Washington, D.C. p. 134. 1987.
8. Pope, A. A., et al. Toxic Air Pollutant Emission Factors -
A Compilation for Selected Air Toxic Compounds and Sources.
EPA-450/2-88-006. U. S. Environmental Protection Agency,
Research Triangle Park, North Carolina. 1988.
9. U. S. Environmental Protection Agency. Protocols for
Generating Unit-Specific Emission Estimates for Equipment
Leaks of VOC and VHAP. EPA-450/3-88-010. U. S.
Environmental Protection Agency, Research Triangle Park,
North Carolina. 1988.
10. U. S. Environmental Protection Agency. Fugitive Emission
Sources of Organic Compounds—Additional Information on
Emissions, Emission Reductions, and Costs. EPA-450/3-82-
010. U. S. Environmental Protection Agency, Research
Triangle Park, North Carolina. April 1982.
40
-------
11. White, T. S. Volatile Organic Compound Emissions from
Hazardous Waste Treatment Facilities at Downstream POTW.
Prepared for the U. S. Environmental Protection Agency,
Research Triangle Park, North Carolina, pp. 5-6. 1987.
41
-------
SECTION 5
EMISSIONS FROM MAJOR USES OF STYRENE
This section discusses emissions from major industrial
processes that use styrene as a feedstock. The processes
described are production of polystyrene (PS) polymer, styrene-
butadiene copolymers (S-B, SBR), styrene-acrylonitrile copolymer
(SAN), acrylonitrile-butadiene-styrene copolymer (ABS), and
unsaturated polyester resins (UPR). In addition, product and
process descriptions are provided for the miscellaneous styrene
copolymers: styrene-butadiene-vinylpyridine (SBV) latex, methyl
methacrylate-butadiene-styrene (MBS) resins, and methyl
methacrylate-acrylonitrile-butadiene-styrene (MABS) polymer.
Process flow diagrams are included as appropriate, with specific
streams or vents in the figures labeled to correspond with the
discussion in the text.
Emissions of styrene are expected from all facilities that
produce the above listed resins. However, insufficient
information is available to develop emission factors for
fugitives or process emission sources. Available information is
provided in each subsection. The reader is encouraged to contact
State or local air pollution control agencies, the toxic release
inventory, and specific production facilities for information on
styrene emissions and control technologies.
POLYSTYRENE PRODUCTION
Polystyrene is produced by the polymerization of styrene
monomer. The polymer is available in a wide range of
formulations including crystal, high impact and expandable (EPS).
Crystal PS is the general purpose grade. It is a clear, rigid
plastic with excellent electrical and insulation properties and
low impact resistance.1 To increase the toughness of the
polystyrene plastic, rubber particles (usually polybutadiene) may
42
-------
be incorporated into the polymer matrix. This rubber-modified
form is known as high impact PS.2 Expandable polystyrene is
produced by the addition of a volatile blowing agent to the
polystyrene which causes the polymer to expand when heated. The
blowing agent may be added during the polymerization process or
during the fabrication process.3
Polystyrene is used in injection and extrusion processes to
produce a wide variety of products. The major end use for PS is
in packaging. The resin also finds applications in the building,
electronics, furniture, housewares, and recreational marketing
areas. Polystyrene is the leading resin used for making toys.
Injection molding is used to make products such as tumblers,
tooth brush handles, computer disk reels, pill bottles, and toys.
Extrusion is used to make egg cartons, meat/poultry trays, and
fast-food packages. Crystal PS is used to make fast-food
packages and egg cartons. High impact PS is used to produce
fast-food cups, lids, and containers, toys, containers for food,
fruit juices, and dairy products, kitchen housewares, and small
appliances. Expandable PS, which is easy to process, is used to
make disposable drinking cups, loose fill packaging, insulation,
and packaging shapes. Polystyrene is commonly marketed in bead
or pellet form; however, some is captively converted to film,
sheet, or foam.4
Polystyrene is currently produced by 17 companies at 34
facilities in 16 States. These facilities and their 1990
production capacities are listed in Table 8.5 Manufacture of
polystyrene is the major end use of styrene monomer, consuming
approximately 68 percent of the styrene produced in the United
States.6
Process Description
Polystyrene may be produced by the suspension, mass (bulk),
solution, and emulsion processes. The suspension process is
43
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operated in a batch mode, whereas the mass and solution processes
are operated in the continuous mode. The mass and suspension
methods are commercially significant. Use of the emulsion
process for PS production has decreased significantly since the
mid-1940's.8 It is not used for the production of crystal PS
because the soap solution (emulsifier) adversely affects the
clarity and electrical-insulation characteristics of the
product.3 Therefore, the emulsion process will not be discussed
here.
To produce impact grade polystyrene, the rubber component
may be incorporated by mechanical means after styrene
polymerization or it may be added to the polymerization reactor
along with the styrene monomer. If mechanical means are used,
rubber latex may be added to polystyrene latex followed by
coagulation and drying, or dry rubber can be milled with dry
polystyrene. Alternatively, chopped preformed unsaturated rubber
can be dissolved into styrene monomer and then the mixture can
undergo polymerization by any of the three processes described
below.3 Most impact PS is produced by suspension
polymerization.3
Expandable polystyrene is produced by modifying the batch
suspension process. A blowing agent, such as n-pentane, may be
added to the reactor before or after polymerization and is
absorbed by the polystyrene. The post-impregnation process is
more commonly used.8 In this method the finished polystyrene
product bead from the suspension process is fed through a second
suspension process train where the blowing agent is impregnated
into the product beads through the use of temperature and applied
pressure.
46
-------
Suspension Process—
The suspension process (Figure 6) is a batch polymerization
process that may be used to produce crystal, impact or expandable
polystyrene beads. In this process, polymerization is carried
out in an aqueous medium to permit removal of the heat of there
action.1 The polystyrene polymer is formed in small beads which
are easily separated from the aqueous phase.
Styrene monomer from storage is first washed to remove any
inhibitors of the polymerization reaction (Step 1). The washed
styrene is transferred to a mixing tank where it is combined with
a free radical initiator (Step 2). The styrene is then fed into
an agitated reactor along with water, initiator, a monomer
soluble suspending agent and suspension stabilizer (Step 3). A
blowing agent or rubber may be added at this time for the
production of expandable PS or high impact PS respectively. Both
the blowing agent and the rubber may also be added later as part
of a post polymerization process. Following polymerization, the
polymer beads are transferred to a wash tank where they are
washed with acid to remove initiators and suspension stabilizers
(Step 4). The wet beads are sent to a centrifuge (Step 5) and
then a dryer (Step 6) for dewatering and drying. The beads are
passed to a devolatilization extruder for recovery of unreacted
styrene monomer (Step 7). Recovered monomer is recycled into the
polymerization reactor. The purified polymer beads are dried and
sent to product storage.3
Mass Process—
The mass process uses no water or organic solvents and is
the simplest process for producing polystyrene. As shown in
Figure 7, there are four major stages in the mass process:
prepolymerization, polymerization, devolatilization, and
extrusion. Styrene monomer is stripped of inhibitors in a steam
stripper (Step 1) then pumped into a stirred prepolymerization
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reactor equipped with a reflux condenser operating under reduced
pressure (Step 2). Reaction temperature is controlled by
removing some of the monomer vapor, condensing it, and then
returning the liquid monomer to the reactor. Polymerization may
be initiated either thermally or through the use of chemical
initiators. In this reactor monomer conversion proceeds to 25 to
35 percent. The polymer melt is then fed through a series of
stirred reflux reactors (Step 3). The reaction temperature is
continually raised to promote polymerization and reduce the
viscosity of the polymer mass. Final temperatures typically
range from 150 to 200°C. The polymer melt is transferred to a
static devolatilizer (Step 4) where unreacted monomer and low
molecular weight polymers are flashed off distilled and recycled
(Step 5). The stripped polymer is fed through a vent extruder
and palletized (Step 6).3
Solution Process—
A block diagram of the polystyrene solution process is
presented in Figure 8. In this process, polymerization proceeds
in a solvent medium. In Step 1, styrene monomer is steam
stripped to remove any inhibitors of the polymerization reaction.
The washed styrene monomer is mixed with a solvent (such as
ethylbenzene) and an initiator, then fed through a series of
agitated reactors (Step 2). The initial ethylbenzene
concentration may range from 5 to 25 percent. Following
polymerization the polymer mix is sent to a flash tank for the
removal of unreacted styrene and solvent (Step 3). Recovered
styrene and solvent are recycled with the reactor feed. The
purified polymer is fed through an extruder and chopped into
pellets (Step 4).3
Emissions
Typical emission sources at a polystyrene plant include
process vents, storage tanks, equipment leaks, secondary sources,
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and transfer and handling operations. Styrene may also be
emitted during accidental or emergency releases.3
Styrene may be emitted from reactor vents, mixing tanks,
wash tanks, devolatilizer condenser vents, styrene recovery unit
condenser vents, and during polymer drying and finishing stages.3
The monomer storage tank, the mixing/dissolving tanks, and the
reactor feed tank typically have fixed roofs. Emissions from
these sources are relatively small and are due to normal
breathing and filling of the tanks.4 Vapor balance use on
working condenser is the largest styrene emission source in a
polystyrene plant; however, the quantity of emissions is not
particularly large.*'9 Following the devolatilization step,
residual styrene monomer in the polymer is typically less than
one percent.3 The extruder pelletizer vent is potentially the
second largest styrene emission source.4
Vent emissions may be controlled by routing the process
streams to a flare or a blowdown tank.6 Conservation valves can
be installed on holding and mixing tanks.4 Vapor return lines to
tank cars or trucks can be installed to reduce styrene losses
during storage tank filling.
Fugitive emissions result from leaks in flanges, valves,
pumps, open drains, and other equipment components. Control of
these emissions may be accomplished through a regular inspection
and maintenance program as well as by equipment modification.
The mode of operation also influences emissions. Batch
processes generally have high conversion efficiencies, leaving
only small amounts of unreacted styrene to be emitted if the
reactor is purged or opened between batches.8 In continuous
processes a lower percentage of styrene is converted to
polystyrene, and thus larger amounts of unreacted styrene may be
emitted.8
52
-------
Facilities using batch processes may manufacture a wide
variety of polystyrene products. Styrene emissions vary with the
product grade with higher emissions expected during the
manufacture of lower molecular weight products.10 Typical
emission factor ranges suggested by the Chemical Manufacturers
Association (CMA) for three batch process vents are presented in
Table 9.
For plants using the continuous process, a wide range of
emission rates have been found, depending in part on the type of
vacuum system used.8 The shift from the use of steam eductors to
vacuum pumps results in lower emission factors.10 Table 9
presents VOC emission factors given by CMA for the continuous
polystyrene plants. Emission factors for the same vents based on
information from other industry sources are also presented in
Table 9.9
STYRENE-BUTADIENE COPOLYMER PRODUCTION
Styrene-butadiene copolymers are composed of monomer units
of styrene and butadiene. The copolymers may be categorized into
two general types: styrene-butadiene rubber (SBR) and
styrene-butadiene latex (S-B latex), based on percent styrene
composition. However, the exact nomenclature for the different
types of styrene-butadiene copolymers is often used differently
between the plastics and rubber industry.
SBR copolymers contain less than 45 percent styrene and have
rubber-like qualities. They are characterized by processability,
heat aging, and abrasion resistance. SBR can be in a solid
(elastomer) or latex (elastomer emulsion) form. The solid form
of the copolymer is also known as crumb.
As the styrene content is increased above 45 percent,
copolymers become more plastic-like and are in latex form. They
may be referred to as S-B latex. S-B latex is characterized by
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excellent resistance to water and very good electrical insulation
qualities.
Styrene-butadiene copolymers account for 13 percent of
national styrene consumption.6 SB copolymers are produced by 13
companies at 23 facilities in 12 states. Elastomer and latex
production facilities are listed in Tables 10 and 11,
respectively. The U. S. annual production capacity of SB
copolymers for 1990 is estimated to be 1,575,691 Mg
(3474 MM Ibs), 61 percent elastomer and 39 percent latex.5 Most
SBR elastomer is used to manufacture automobile tires and related
automotive products. In the United States, SBR has the highest
production rate of all synthetic rubbers. However, due to the
longer life of tires and the use of smaller tires, U. S. demand
for SBR is declining. Other automotive uses of SBR include
belts, hoses, gaskets, and seals. Non-automotive uses of SBR
include cable insulation, hoses, tubes, conveyor belts, floor
tiles, shoe soles, adhesives, and sporting goods. Over
80 percent of styrene-butadiene latexes are used in the
carpet/upholstery backing and paper coating industries.3
Process Description
Styrene-butadiene elastomer is manufactured by two types of
polymerization processes: (1) the emulsion process, in which the
monomers are dispersed in water, and (2) the solution process, in
which the monomers are dissolved in a solvent. The emulsion
process is more commonly used. Styrene-butadiene latex is
produced by the emulsion process in a similar manner to SBR,
except that the emulsion breaking (coagulation) and drying steps
are omitted.
Emulsion Process—
A flow diagram of the emulsion process for SBR elastomer
production is shown in Figure 9. In Step 1, fresh styrene and
55
-------
TABLE 10. SBR ELASTOMER PRODUCTION FACILITIES
Annual Capacity
Company Location (Mg/yr) (MM Ib/yr)
Ameripol
Copolymer
Firestone
General Tire
Goodyear
Port Neches, TX
Baton Rouge, LA
Lake Charles, LA
Odessa , TX
Beaumont, TX
Houston, TX
TOTAL
336,000
125,000
120,000
90,000
20,000a
305,000
996,000
741
276
265
198
44
672
2,196
"For captive use.
NOTE: This listing is subject to change as market conditions
change, facility ownership changes, plants are closed down, etc.
The reader should verify the existence of particular facilities
by consulting current listings and/or the plants themselves. The
level of styrene emissions from any given facility is a function
of variables such as capacity, throughput, and control measures,
and should be determined through direct contact with plant
personnel. These operating plants and locations were current as
of January 1990.
Source: Reference 5.
56
-------
TABLE 11. STYRENE-BUTADIENE LATEX PRODUCTION FACILITIES
Annual Capacity
Company
SBR LATEX*
BASF
B.F. Goodrich
GenCorp
Goodyear
S-B LATEX*
BASF
B.F. Goodrich
Colloids
Dow Chemical
GenCorp
Goodyear
Reichhold
W.R. Grace
Unocal
Location
Chattanooga , TN
Akron, OH
Mogador e , OH
Akron , OH
Calhoun, GA
Houston, TX
. TOTAL
Chattanooga , TN
Monaca , PA
Akron, OH
Gastonia , GA
Dalton, GA
Freeport , TX
Gales Ferry, CT •
Midland, MI
Pittsburg, CA
Mogador e, OH
Calhoun, GA
Cheswold , DE
Kensington, GA
Owensburg, KY
Charlotte, NC
La Mirada, CA
TOTAL
(Mg/yr)
9,030
907b
6,804b
3,175;
5,443
22.680
68,039
49,895
24,948
907
15,876
181,437
84,822
39,916
69,853
4,536
27,216
12.247
511,652"
(MM Ib/yr)
64
2
15
7
12
50
150
110
55
2
35
400
187
88
154
10
60
27
1,128
b<45% styrene
Capacity includes s-b-vinylpryidine latex.
^Capacity is all s-b-vinylpyridine latex.
>45% styrene
"Numbers do not total due to rounding.
NOTE: This listing is subject to change as market conditions
change, facility ownership changes, plants are closed down, etc.
The reader should verify the existence of particular facilities
by consulting current listings and/or the plants themselves. The
level of styrene emission from any given facility is a function
of variables such as capacity, throughput, and control measures,
and should be determined through the direct contact with plant
personnel. These operating plants and locations were current as
of January 1990.
Source: Reference 5.
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butadiene monomers are washed to remove inhibitors which may have
been added to prevent premature polymerization. The washed
monomers are mixed with recycled monomers, modifiers, activators,
soap solution (emulsifier), and catalyst and charged into a
polymerization reactor (Step 2). A typical recipe for emulsion
SBR is presented in Table 12. Polymerization proceeds in a
stepwise fashion through a chain of reactors that allow the
facility a high degree of flexibility in producing different
grades of SBR. Either a hot (50°C) or a cold (4°C) process may
be used. The reaction is normally carried out to a 60 percent
monomer conversion after which a shortstop solution is added to
prevent further polymerization. The latex reaction mixture is
sent to a vacuum flash tank for recovery of unreacted butadiene
and then to a steam stripping unit for the recovery of unreacted
styrene (Step 3). After the monomer is removed, the latex may
take one of two routes. In one route, SBR elastomer is formed
through emulsion breaking and drying steps. The stripped latex
is transferred to a blending and storage tank where an
antioxidant is added to prevent the polymer from reacting with
oxygen or ozone (Step 4). The latex stream is then pumped into
coagulation tanks where the emulsion is broken (Step 5). An
acid-brine mixture (aluminum sulfate) is added which causes the
rubber (known as crumb) to precipitate out. The rubber copolymer
is then sent to a washing and drying section (Step 6) and pressed
into bales.11'12
The second route, which produces styrene butadiene latex as
the end product, includes the same steps as the elastomer
production except for the latex coagulation and final rinsing,
drying and baling. However, in some instances the latex
polymerization reaction may be continued to a 98 or 99 percent
conversion—as opposed to 60 percent conversion for emulsion
crumb rubber. Therefore, in these instances, the monomer
recovery steps are omitted. The latex product is also passed
59
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TABLE 12. TYPICAL RECIPE FOR EMULSION SBR
Components Weight Percent
Butadiene
Styrene
d-Isopropyl Benzene
Hydroperoxide
'Ferrous Sulfate
Tert-Dodecyl Mercaptan
Potassium Pyrophosphate
Rosin Acid Soap
Water
25
10
<0
<0
0.
0.
1.
63
.0
.0
.1
.1
1
1
4
.0
Function
Monomer
Monomer
Catalyst
Activator
Modifier
Buffer
Emulsif ier
Source: Reference 11.
60
-------
through a series of screen filters (Step 7) to remove large
solids before it is sent to the blending tank for storage (Step
8).11'12
Solution Process—
A flow diagram for the solution process is shown in
Figure 10. In this process, polymerization takes place in an
organic solvent medium, usually hexane. Freshly washed (Step 1)
and recycled styrene and butadiene monomers and the organic
solvent are pumped through dryers to remove any water (Step 2),
then blended together to form the mixed feed. The feed may be
sent to a dryer as well (Step 3) to remove any residual traces of
water. The mixture is added to the polymerization reactor along
with a catalyst (Step 4). Polymerization takes place through a
series of reactors and proceeds to greater than 90 percent
conversion. A shortstop solution is added to halt further
polymerization. The reaction product is in the form of rubber
cement. It is pumped to product storage (Step 5) where it is
washed to remove catalyst and then an antioxidant and other
desired chemicals such as oils and fillers are added. The rubber
cement is pumped to a coagulator (Step 6) where the rubber is
precipitated in crumb form. Unreacted monomers and solvent are
recovered by steam stripping. The stripped rubber cement slurry
is sent to a washing and drying section (Step 7) where it is
separated, washed, and then passed through an extruder for
dewatering and drying. The dried rubber is baled and stored.11'13
The emission sources at an SB copolymer facility are typical
of those common to chemical production facilities: process
vents, open process equipment, equipment leaks, storage tanks and
transfer operations and secondary emissions from the handling and
disposal of wastes. Styrene may also be emitted during
accidental or emergency releases.
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Emissions from process vents and open equipment occur from
reactors, recovery columns, blend and coagulation tanks, filter
screens, dryers and other process vessels. They may occur
continuously (from a continuous process) or intermittently (from
a batch process). Polymerization reactors for both emulsion and
solution processes are normally sealed using rupture discs, with
venting to a flare during rare, extreme upset conditions. Most
of the styrene emitted during the emulsion crumb process occurs
by evaporation from open blend and coagulation tanks and from
dryer vents. An estimated 78 percent of total VOC emissions
(mostly styrene) from the emulsion crumb process are emitted
during the copolymer drying steps.1* An emission factor for the
drying step in SBR emulsion polymerization is given in Table 13.
Emission data for other process sources are not available.13 In
the SB latex production process, the latex is stripped of
unreacted monomers and passed through shaker screens to remove
large agglomerated solids. These screens are open to the
atmosphere, but emissions are estimated to be very low.
Concentrations of 25 ppm styrene (and 39 ppm butadiene) have been
measured above the screens, but the air flow rate could not be
determined.16
To control process vent emissions, the process streams can
be routed to a flare or blowdown tank. Recovered styrene
emissions from the vacuum distillation column are recycled with
the reactor feed stream. Where feasible, open equipment may be
enclosed.6
Sources of fugitive emissions are listed in Section 4. Also
provided is a description of the procedure for estimating
emissions and a table of control options and efficiencies.
At these facilities the major source of air emissions of
styrene occurs from styrene transfer during the unloading of
trucks, tank cars and barges and the filling of the monomer
storage tanks. No SB copolymer facilities are known to have
63
-------
installed control devices to reduce or capture these emissions.6
Losses of styrene from storage tanks also occur due to normal
tank breathing processes. Uncontrolled emission factors for
breathing and fugitive losses of styrene from storage tanks are
presented in Table 13.ls
STYRENE-ACRYLONITRILE PRODUCTION
Styrene-acrylonitrile copolymers are noncrystalline, linear
resins. They are characterized by good hardness, rigidity,
dimensional stability, high heat deflection temperatures, and
chemical resistance.1 Acrylonitrile provides the chemical
resistance and heat stability, and styrene provides rigidity and
processing ease. A diversity of SAN specialty grades, including
UV-stabilized, antistat, barrier, and weatherable grades are
available.17 The styrene content of SAN ranges from 65 to
85 per cent.8>17>18
The majority of SAN manufactured is used captively to
produce acrylonitrile-butadiene-styrene resins. SAN also has a
wide range of applications in the automotive, housewares,
electronics, appliances, and packaging marketing areas. SAN is
used in automotive trim, marine instruments, tractor components,
coffee filter funnels, instrument panels on appliances and
automobiles, boat hulls, swimming pool components, cassette
parts, syringes, dentures, toothbrush handles, blender bowls, and
vacuum cleaner parts. Most of the SAN sold in the United States
is used for injection molding as a replacement for polystyrene.19
Only two companies produce SAN exclusively for sale on the
market. These facilities and their annual capacities are listed
in Table 14. SAN is also produced at all ABS facilities, as a
step in the manufacture of ABS. Less than four percent of
styrene production in the United states is used in the
manufacture of SAN for direct sale.20
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TABLE 14. STYRENE-ACRYLONITRILE PRODUCTION FACILITIES
Annual Capacity
Company* Location (Mg/yr) (MM Ib/yr)
DOW
Monsanto
Midland, MI
Addyston , OH
TOTAL
31,751
22.679
54,431b
70
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120
*Only those producers who manufacture SAN for sale on the
merchant market are listed. All ABS resins producers have SAN
resin production capacity.
bNumbers do not total due to rounding.
NOTE: This listing is subject to change as market conditions
change, facility ownership changes, plants are closed down, etc.
The reader should verify the existence of particular facilities
by consulting current listings and/or the plants themselves. The
level of styrene emissions from any given facility is a function
of variables such as'capacity, throughput, and control measures,
and should be determined through direct contact with plant
personnel. These operating plants and locations were current as
of January 1990.
Source: Reference 5.
66
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Process Descriptions
SAN resins may be produced by emulsion, suspension, or
continuous mass polymerization. The majority of SAN for captive
use is produced using emulsion polymerization. SAN for sale in
the marketplace is most often produced by mass polymerization.21
Emulsion Process—
SAN production by emulsion polymerization, shown in
Figure 11, may be conducted in either a batch or a continuous
mode.2'11'18 The batch process is more commonly used.20 In both
processes, styrene and acrylonitrile monomers are pumped into a
monomer-makeup tank along with recovered acrylonitrile and
chemical additives (Step 1). The monomer mix is fed into the
polymerization reactor with emulsifier, initiator, chain-transfer
agent and deionized water (Step 2). Copolymerization is carried
out in the temperature range of 70-100°C (160-212°F) and proceeds
to 90-98 percent conversion.21 The polymerization temperature
may be reduced to as low as 38 °C (100°F) if redox catalysis
systems are used. After a suitable retention time in the
reactor, the SAN copolymer melt (latex) is pumped to a steam
stripper for recovery of unreacted monomers (Step 3). The
copolymer latex may be used directly in the production of ABS
resin, or it may be sent to a coagulation and flocculation
section (Step 4). The polymer is filtered (Step 5) then washed,
and dried (Step 6) to produce the solid SAN copolymer.2 Dyes,
antioxidants and other additives may be mechanically blended into
the copolymer using extruders and rolling mills (Step 7).
Polymer sheets from these operations are then pelletized and
packaged.
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Suspension Process—
SAN production by suspension polymerization may be conducted
in either batch or continuous mode.2'11'18 A block flow diagram
for the suspension process is given in Figure 12. Styrene and
acrylonitrile monomers are fed into a pressure reactor and
mechanically dispersed in water containing catalysts and
suspending agents (Step 1). The water functions to remove heat
and control particle size. Equal amounts of monomer and water
are used.19 While suspended by agitation, the monomer droplets
copolymerize forming insoluble beads of polymer. The temperature
of the polymerization reactor ranges from 60-150°C (140-300°F).
A monomer conversion of 95 percent is normally achieved. The
polymer slurry is pumped to a centrifuge for washing and
dewatering (Step 2). The polymer is sent to a flash tank and
steam or vacuum stripper for recovery of unreacted monomers
(Step 3). The solid and liquid phases of the polymer slurry are
separated by centrifugation and/or filtration (Step 4). The
solid phase is then dried in a rotary dryer (Step 5). The dried
SAN is finished by mechanically blending in dyes, antioxidants
and other additives. The polymer sheets are then pallatized and
packaged (Step 6).7'8 This suspension process is simpler than the
emulsion process as no coagulation and flocculation steps are
required.
Continuous Mass Process—
The continuous mass process, shown in Figure 13, is a self-
contained system that does not require emulsifiers, suspending
agents, salts, or water. Solvents are used to control the
viscosity. In Step one, styrene and acrylonitrile monomers are
heated together with modifier-solvent and pumped continuously
into the agitated polymerization reactor maintained at about
275 kPa (40 psia) and 100-200«C (212-390°F). Catalyst is added
and reaction proceeds to 20 percent conversion. The polymer is
passed through a series of devolatilizers to remove unreacted
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monomers and modifier-solvent (Step 2) . Devolatilization occurs
under vacuum at a temperature ranging from 120-260°C (248-500°F) .
Inerts, unreacted monomers and modifier-solvent are removed
overhead from the devolatilizers. The overheads are the
condensed and passed through a refrigerated styrene scrubber to
recover monomers and modifier-solvent which are recycled to the
feed tanks. The bottoms from the final devolatilizer are almost
pure polymer melt. The polymer melt is pumped through an
extruder, cooled and chopped into pellets (Step 3) .2>11>18
Facilities manufacturing SAN emit styrene from process
equipment vents, open process equipment, equipment leaks, storage
tank vents, secondary sources, and transfer and handling
operations. No emissions data for any of these sources are
available.
Process equipment sources include monomer make-up tanks,
polymerization reactors, monomer strippers, devolatilizers,
coagulation/flocculation stages, dewater ing/dry ing stages, and
blending/ compounding operations. The emissions will vary
according to the type of polymerization process used and the
exact monomer mix.
As described under styrene-butadiene copolymer production,
process vent emissions may be controlled by routing the streams
to a flare or blowdown. Currently, neither SAN facility has
controls to capture or prevent styrene emissions from transfer
operations .
ACRYLONITRILE-BUTADIENE-STYRENE COPOLYMER PRODUCTION
Acrylonitrile-butadiene-styrene resins are produced by
grafting styrene-acrylonitrile copolymer onto a rubber and then
blending the grafted rubber with SAN.23 Polybutadiene is
72
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normally used as the backbone or substrate rubber, but nitrile
rubbers and SBR are also used. The resulting polymer has three
phases: continuous matrix of SAN, dispersed phase of
polybutadiene or other rubber, and boundary layer of SAN graft.22
The SAN grafted rubber provides adhesion between SAN and the
rubber which would have been incompatible.
ABS possesses the useful properties of SAN, such as rigidity
and resistance to chemicals and solvents, while the rubber
additive imparts impact resistance.2 ABS resins are produced
with a wide range of properties that are tailored to specific
applications. The differences in application are achieved by
changing the relative concentrations of the three monomers and by
using additives. Over 75 grades of ABS are available, including
glass reinforced, UV-resistant, flame retardant, foamable, and
electroplating grades.23'2*'25 The resins are marketed in powder
form or as natural and precolored pellets.22
ABS resins are used to make plastic components for a variety
of products such as automotive parts, pipes and fittings,
appliances, telephones, business machines, toys and sporting
goods. The major use for ABS is in the automotive industry,
where the resins are injection molded to make interior trim
components, consoles, instrument panel trim grills and wheel
covers.
Currently ABS resins are produced by three companies at ten
locations in eight States. These facilities and their production
capacities are listed in Table 15. These ten facilities also
produce SAN as a step in the manufacture of ABS. Industry-wide
ABS capacity for 1990 is about 790,158 Mg/yr (1742 MM Ibs).3
Manufacture of ABS and SAN resins consumes 9 percent of U. S.
styrene production.
73
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TABLE 15. ACRYLONITRILE-BUTADIENE-STYRENE PRODUCTION FACILITIES
Annual Capacity
Company
Diamond Polymers
Dow
General Electric
Monsanto
Location
Akron, OH
Gales Ferry, CT
Ironton , OH
Midland, MI
Torrance , CA
Bay St. Louis, MS
Ottawa , IL
Washington, WV
Addyston, OH
Muscatine, IA
(Mg/yr)
9,979
27,215
36,287
68,039
18,144
95,254
136,078
158,757
145,150
95,254
(MM Ib/yr)
22
60
80
150
40
210
300
350
320
210
TOTAL
790,158
1,742
NOTE: This listing is subject to change as market conditions
change, facility ownership changes, plants are closed down, etc.
The reader should verify the existence of particular facilities
by consulting current listings and/or the plants themselves. The
level of styrene emissions from any given facility is a function
of variables such as capacity, throughput, and control measures,
and should be determined through direct contact with plant
personnel. These operating plants and locations were current as
of January 1990.
Source: Reference 5.
74
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Process Descriptions
ABS resins may be synthesized by emulsion, suspension, and
continuous mass (bulk) polymerization. The majority of
production is by batch emulsion. Specialized resins are produced
by suspension polymerization. Emulsion and suspension
polymerizations are based on an aqueous-phase reaction. In
contrast, the continuous mass process, the newest technology,
does not proceed in water. Therefore, dewatering and polymer
drying are not required and wastewater treatment is minimized.23
Emulsion Process—
A block diagram showing two routes by which ABS is produced
using the emulsion process is presented in Figure 14. This
process is referred to as the ABS/SAN process because SAN is
prepared in a side step and mixed with graft ABS.
The emulsion process involves three distinct
polymerizations:
• polymerization of butadiene to form polybutadiene;
• grafting of styrene and acrylonitrile monomers to the
polybutadiene substrate; and
• copolymerization of styrene-acrylonitrile.
Butadiene monomer is converted to polybutadiene latex
(Step 1) and then pumped into the ABS reactor with styrene,
acrylonitrile, emulsifiers and initiators (Step 2). The styrene
and acrylonitrile monomers are grafted to the polybutadiene latex
substrate in either a batch or continuous process. Reaction
conversion is 90 to 95 percent. Vapors from the reactor are
usually vented to an acrylonitrile absorber. The absorber
emissions are usually vented to the atmosphere or incinerated.
The graft ABS is then transferred to a coagulator (Step 3). SAN
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copolymer is prepared in a separate side step (Step 8) (see
process descriptions under SAN copolymers in this section). The
graft ABS and the SAN may be mixed together at either of two
points in the emulsion process. The SAN latex may added to the
graft ABS latex in the ABS coagulator (Step 3). The agglomerated
polymer is dewatered by screening (Step 4), centrifuging
(Step 5), and vacuum filtration (Step 6). No drying step is
required. However, some facilities employ a dryer in place of
the centrifuge and vacuum filter. The ABS is sent to a finishing
section where dyes, antioxidants, and other additives are
mechanically blended in (Step 7). Alternatively, the SAN latex
may be pumped into an SAN coagulator (Step 8) and sent to a
dewatering section (Step 10) separately. The solid SAN is then
mechanically mixed with solid graft ABS at the finishing stage
(Step 7). The polymer sheets are cut into pellets and packaged
(Step II).2'11'18
In a third route (not shown) SAN graft and styrene-
acrylonitrile copolymerization occur in the same reaction vessel.
The resulting ABS latex is coagulated, washed, filtered and
dried.
Suspension Process—
A block flow diagram of the suspension ABS process is shown
in Figure 15. This process begins with polybutadiene rubber
which is so lightly cross linked that it is soluble in the
acrylonitrile and styrene monomers. The polybutadiene is first
dissolved in styrene and acrylonitrile monomers to produce a
solution free of crosslinked rubber gels (Step 1). The solution
is pumped into a prepolymerizer where a free-radical initiator is
added along with chain-transfer agents in a prepolymerizer
(Step 2). After 25 to 35 percent monomer conversion, the polymer
syrup is transferred to a suspension reactor where it is
dispersed in water by agitation (Step 3).
77
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After achieving the desired monomer conversion, the products
are transferred to a washing/devatering system (Step 4), usually
a continuous centrifuge. The polymer beads are then sent to a
hot air dryer (Step 5). The dried finished beads are transferred
to product storage (Step 6) .2>11'18
Continuous Mass Process—
A block flow diagram for the continuous mass ABS process is
shown in Figure 16.19 Unlike emulsion and suspension
polymerization, this polymerization process does not proceed in
water. A lightly cross-linked, monomer-soluble form of
polybutadiene is dissolved in styrene and acrylonitrile monomers,
along with initiators and modifiers (Step 1). The mixed feed is
pumped into a prepolymerizer, in which a conversion reaction
causes the ABS rubber to precipitate out of solution (Step 2).
When monomer conversion reaches about 30 percent, the resulting
syrup is transferred to the bulk polymerizer where monomer
conversion is continued to between 50 to 80 percent (Step 3).
The polymer melt is sent to a devolatizer (Step 4) where
unreacted monomer is removed under vacuum. The monomer vapors
are condensed and recycled to the prepolymerizer. The ABS
polymer is then passed through an extruder, cooled in a water
bath (Step 5), and chopped into pellets (Step 6) .2lll>18
Emissions
Information is available on acrylonitrile and butadiene
emissions from 10 ABS production facilities. Although styrene
emissions were not reported separately by any of the facilities,
three facilities listed "other VOC" emission estimates, of which
the major component is likely to be styrene. These VOC emissions
were attributed to process vents from polymerization reactors,
coagulation/washing steps, dewatering, intermediate process
tanks, and compounding.23 Significant styrene emissions result
primarily from unloading styrene from tank trucks and barges and
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filling the storage tank.6 In addition, some emissions are
possible from secondary sources and emergency and accidental
releases. Insufficient information is available to develop
emission factors for fugitives or process emission sources.
The emission points vary depending upon the type of
polymerization process used. The emulsion process has the
highest emissions while the continuous mass process has
inherently low emissions. In addition, styrene emissions may
vary from plant to plant depending on product mix.
Manufacturers of ABS resins have taken two basic approaches
to control some of the AN process vents: high monomer conversion
technology (HMCT) and thermal oxidation. These techniques would
also control styrene emissions. The high monomer conversion is
achieved using a second reactor the same size as the first
reactor where conversion is increased to around 98 percent. The
HMCT requires that the second reactor and an absorber be
installed at the polymer filter step. Thermal oxidation is
applicable to all types of ABS processes. In this approach
emission vents are tied into one or more combustion devices.
These devices may be parts of steam generators, incinerators or
flares.
UNSATURATED POLYESTER RESIN PRODUCTION
Thermoset polyester resins are complex polymers resulting
from the cross-linking reaction of a liquid unsaturated polyester
with a vinyl type monomer, most often styrene. The unsaturated
polyester is formed from the condensation reaction of an
unsaturated dibasic acid or anhydride, a saturated dibasic acid
or anhydride, and a polyfunctional alcohol. Table 16 lists the
most common compounds used for each component of the polyester
"backbone," along with the principal cross-linking monomer
styrene. The chemical reactions that form both the unsaturated
81
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TABLE 16. TYPICAL COMPONENTS USED TO FORM
UNSATURATED POLYESTER RESINS
Unsaturated
Acids
Saturated
Acids
Polyfunctional
Alcohols
Cross-Linked
Agent
(Monomer)
Maleic Phthalic Propylene Styrene
anhydride anhydride glycol
Fumaric acid Isophthalic Ethylene glycol
acid Diethylene
Adipic acid glycol
Dipropylene
glycol
Neopentyl
glycol
Pentaerythritol
Source: Reference 27.
82
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polyester and the cross-linked polyester resin are shown in
Figure 17.21
In order to be used in the fabrication of products, the
liquid resin must be mixed with a catalyst to initiate
polymerization into a solid thermoset. Catalyst concentrations
generally range from 1 to 2 percent by original weight of resin;
within certain limits, the higher the catalyst concentration, the
faster the cross-linking reaction proceeds. Common catalysts are
organic peroxides, typically methyl ethyl ketone peroxide or
benzoyl peroxide. Resins may contain inhibitors, to avoid self
curing during resin storage, and promoters, to allow
polymerization to occur at lower temperatures.27
Unsaturated polyester resins (UPR) are produced by 23
companies at 56 locations in the United States as shown in
Table 17. Production capacity for these facilities was not found
in the literature. .Although styrene is not the only monomer that
may be used as a cross-linking agent, it is the most common. In
1988, total UPR production in the United States was 768,852 Mg
(1695 MM Ibs) .6 UPR is a thermoset resin used in construction
(tubs and showers), marine and marine accessories (boats, boat
accessories), casting (cultured marble and onyx), transportation
(distributor caps, auto body parts), consumer goods (appliances),
gel coatings, surface protective coatings, bonding/adhesives,
electrical components, and business machines.
Process Description
Unsaturated polyester resins can be produced by a fusion or
a solvent process. There is no published information on their
relative capacities, however. In the fusion process, an inert
gas (typically nitrogen) is used to remove water that is
generated during the production process. The solvent process
uses azeotropic distillation.4 Both of these are batch
processes. The fusion process consists of the reacting
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TABLE 17. PRODUCERS OF UNSATURATED POLYESTER RESINS
Facility
Location(s)
The Alpha Corporation
American Cyanamid Company
Aristech Chemical Corporation
Ashland Chemical Inc.
Barton Chemical Corporation
BASF Corporation
Bayer USA Inc.
BP America, Inc.
Cargill, Inc.
Cook Composites
Dow Chemical U.S.A.
Emhart Corporation
The P.D. George Company
High J. - Resins Company
ICI American Holdings, Inc.
(The Gliden Company)
Insulating Materials Inc.
Collierville, TN
Kathleen, FL
Perris, CA
Wallingford, CT
Bartow, FL
CoIton, CA
Jacksonville, AR
Neville Island, PA
Ashtabula, OH
Calumet City, IL
Los Angeles, CA
Philadelphia, PA
Bartow, FL
Chicago, IL
Detroit, MI
Houston, TX
Covington, KY
Hawthorne., CA
Atlanta, GA
Parpentersville, IL
Ennis, TX
Forest Park, GA
Lynwood, CA
Bethlehem, PA
North Kansas City, MO
Catham, VA
Marshall, TX
Saukville, Wl
Joliet, IL
Middleton, MA
St. Louis, MO
Long Beach, CA
Columbus, GA
Reading, PA
Schenectady, NY
85
-------
TABLE 17. (Continued)
Facility
Location(s)
Interplastic Corporation
The O'Brien Corporation
Owen's Corning Fiberglas Corp.
Reichhold Chemicals, Inc.
Sherex Chemical Company
Trinova Corporation
Valspar Corporation
(McWhorter, Inc., subsidiary)
Minneapolis, MN
Pryor, OK
South Bend, IN
Anderson, SC
Valparaiso, IN
Azusa, CA
Bridgeville, PA
Houston, TX
Jacksonville, FL
Morris, IL
Oxnard, CA
Lakeland, FL
Auburn, ME
Chicago, IL
Rochester, PA
Baltimore, MO
Carpenstersville, IL
Kankakee, IL
Los Angeles, CA
Philadelphia, PA
Portland, OR
NOTE: This listing is subject to change as market conditions
change, facility ownership changes, plants are closed down, etc.
The reader should verify the existence of particular facilities
by consulting current listings and/or the plants themselves.
These operating plants and locations were current as of January
1990.
Source: Reference 5.
86
-------
(polyesterification) and thinning stages (Figure 18). During
polyesterification, dibasic acids such as maleic and phthalic
anhydrides, isophthalic acids, and glycols such as ethylene and
propylene glycol are combined to form a soluble resin. This
condensation reaction is carried out in an insulated stainless
steel or glass-lined kettle. The mixture is then heated to about
•
200 C and held for 10 to 20 hours, and water (by-product) is
continuously removed by bubbling an inert gas through the
mixture.4'28 When the desired degree of condensation is reached,
the product is cooled, blended with additives if necessary, and
transferred to the thinning tank. In the thinning tank, styrene
monomer is combined with the cooling unsaturated resin from the
polyesterification tank (Step 2). The final product is then
transferred to a storage tank (Step 3).
The solvent process is similar to the fusion process except
that instead of bubbling an inert gas through the mixture to
remove water, xylene is added. A xylene-water azeotrope is
formed. The azeotrope enhances the separation of water vapor
by-product. The xylene in the condensed azeotrope is separated
from the water and is recycled using a decanter and two
receivers.
Emissions
The following information is taken directly from a 1979
report prepared for the U. S. Environmental Protection Agency
that estimated and ranked VOC emissions for the plastics
industry. Data were gathered through literature surveys,
calculations, site visits, and questionnaire responses.4 For UPR
production (both the fusion and the solvent processes), one
source of styrene emissions is the thinning tank vent (A).
Overhead vapors from the thinning operation are usually
controlled by a cooling-water condensor; otherwise they remain
uncontrolled. The emission factor developed for the UPR thinning
tank is shown in Table 18. The authors of Reference 4 estimate
87
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TABLE 18. EMISSION FACTORS FOR STYRENE
FROM UPR PRODUCTION
Emission
Source
Thinning tank
Blending tank
Product storage
Monomer storage
Estimated Emission Factor"
(Kg/Mg Resin) (Lb/Ton Resin)
0.08
0.05
0.05
0.02
0.16
0.10
0.10
0.04
"The emission factors are for fusion and solvent processes (while
reactor is operating).
Source: References 4 and 28.
89
-------
that the use of a refrigerated brine condenser on the thinning
tank vent could reduce emissions by 80 percent. Industry experts
indicate that this method is no longer practiced and that Thermal
Oxidation is the preferred method today.28
Also shown in Table 18 are styrene emission factors for UPR
product storage (C) and styrene monomer storage (B). The
emission factor shown for UPR product storage assumes that the
tanks are equipped with fixed-roof tanks. Monomer storage tanks
are also assumed to be equipped with fixed-roof tanks, with a
50 percent reduction in styrene emissions achievable with
floating-roof tanks and/or refrigerated vent condensers.
MISCELLANEOUS STYRENE COPOLYMER PRODUCTION
In addition to the sources of styrene emissions previously
discussed, styrene is also used in the production of
miscellaneous products such as styrene-butadiene-vinylpyridine
(SBV) latex, methyl methacrylate-butadiene-styrene (MBS) resins,
and methyl methacrylate-acrylonitrile-butadiene-styrene (MASS)
polymer. Table 19 summarizes the location of these facilities
and their estimated production capacities.
Available details of the production processes will be
provided, where known. Often these details are incomplete;
therefore, readers should contact the facilities directly for the
most accurate information. No information was found in the
literature about styrene emissions from these facilities.
Styrene-Butadiene-Vinylpyridine Latex
No information on the production process or use of styrene-
butadiene-vinylpyridine latex is available. As a copolymer, the
production is likely to be similar to that of other copolymers.
90
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Methvl Methacrylate-Butadiene-Styrene Terpolymers
Methyl methacrylate-butadiene-styrene terpolymers are
produced in resin form by four companies at four locations. This
resin is used as an impact modifier in rigid polyvinyl chloride
products for applications in packaging, building, and
construction. Production of MBS terpolymers is achieved using an
emulsion process in which methyl methacrylate and styrene are
grafted onto a styrene-butadiene rubber. The product is a two-
phase polymer.11
Methvl Methacrylate-Acrylonitrile-Butadiene-Styrene Polymers
Methyl methacrylate-acrylonitrile-butadiene-styrene polymers
are produced by Standard Oil Company under the trade name Barex*.
The MABS copolymers are prepared by dissolving or dispersing
polybutadiene rubber in a mixture of methyl methacrylate-
acrylonitrile-styrene and butadiene monomer. The graft
copolymerization is carried out by a bulk or a suspension
process. The final polymer is two phase, with the continuous
phase terpolymer of methyl methacrylate, acrylonitrile, and
styrene grafted onto the dispersed polybutadiene phase.11
These polymers are used in the plastics industry in
applications requiring a tough, transparent, highly impact-
resistant, and thermally forroable material. Except for their
transparency, the MABS polymers are similar to the opaque
acrylonitrile-butadiene-styrene plastics. The primary function
of methyl methacrylate is to match the refractive indices of the
two phases, thereby imparting transparency.11
92
-------
-------
REFERENCES FOR SECTION 5
1. Swett, R. M. Polystyrene. Modern Plastics Encyclopedia.
63:74-78. 1986-1987.
2. Kirk-Othmer Encyclopedia of Chemical Technology. 3rd
Edition. Styrene Plastics. John Wiley and Sons. New York,
New York. Vol. 1, pp. 427-441, Vol. 21, pp. 801-811. 1978.
3. Industrial Process Profiles for Environmental Use. Chapter
10 - The Plastics and Resins Production Industry, pp. 74-
93, 465-518, 641-657.
4. Click, C. N. and D. K. Webber. Polymer Industry Ranking by
VOC Emissions Reduction That Would Occur From New Source
Performance Standards. Prepared for U. S. Environmental
Protection Agency, Research Triangle Park, North Carolina.
pp. 187-198, 227, 233-236. 1979.
5. SRI International. 1990 Directory of Chemical Producers -
U.S.A. Menlo Park, California.
6. A. T. Kearney. Impact Analysis of the EPA Office of
Drinking Water Proposal to Regulate Styrene. Styrene
Information Research Center. 1989.
7. Chemical Product Synopsis. Polystyrene. April 1988.
8. U. S. Environmental Protection Agency. Polymer
Manufacturing Industry - Background Information for Proposed
Standards. Draft EIS. EPA-450/3-83-019a. U. S.
Environmental Protection Agency, pp. 3-40 to 3-53. 1985.
9. U. S. Environmental Protection Agency. Guideline Series -
Control of Volatile Organic Compound Emissions from
Manufacture of High-Density Polyethylene, Polypropylene, and
Polystyrene Resins. EPA-450/3-83-008. U. S. Environmental
Protection Agency, pp. 2-18 to 2-25. 1983.
10. Letter from J. S. Matey, Chemical Manufacturers Association,
to E. J. Vincent, U. S. Environmental Protection •Agency.
October 19, 1981.
11. Buchanan, S. K. Locating and Estimating Air Emissions from
Sources of 1,3-Butadiene. EPA-450/2-89-021. U. S.
Environmental Protection Agency, Research Triangle Park,
North Carolina, pp. 44-45, 71-79. 1989.
12. Chi, C. T. et al. Source Assessment: Rubber Processing,
State of the Art. EPA-600/2-78-004J. U. S. Environmental
Protection Agency, pp. 12-21. 1978.
93
-------
13. Chemical and Process Technology Encyclopedia, pp. 387-392.
1974.
14. U. S. Environmental Protection Agency. Guideline Series -
Control of Volatile Organic Compound Emissions from
Manufacture of Styrene-Butadiene Copolymers. U. S.
Environmental Protection Agency, Research Triangle Park,
North Carolina. Preliminary Draft, pp. 2-12. 1981.
15. Pope, A. A. et al. Toxic Air Pollutant Emission Factors - A
Compilation for Selected Air Toxic Compounds and Sources.
EPA-450/2-88-006. U. S. Environmental Protection Agency,
Research Triangle Park, North Carolina, p. 4-216. 1988.
16. Rubber Products Styrene-Butadiene Rubber Manufacture.
Emission Test Report General Tire and Rubber Company,
Mogadore Chemical Plant, Mogadore, Ohio. U. S.
Environmental Protection Agency, Research Triangle Park,
North Carolina. EMB Report No. 79-RBM-4.
17. Shay, J. J. Styrene-Acrylonitrile. Modern Plastics
Encyclopedia. 63:88-89.
18. Energy and Environmental Analysis, Inc. Source Category
Survey for the Acrylonitrile Industry - Draft Report.
Prepared for U. S. Environmental Protection Agency, pp. 3-
10, 3-30 to 3-37. 1981.
19. Click, C. N. and D. O. Moore. Emission, Process and Control
Technology Study of the ABS/SAN, Acrylic Fiber, and NBR
Industries. Prepared for U. S. Environmental Protection
Agency. Pullman Kellog. Houston, Texas, pp. 18, 33.
1979.
20. Chemical Profile: Styrene. Chemical Marketing Reporter.
pp. 49, 50. August 14, 1989.
21. U. S. Environmental Protection Agency. Locating and
Estimating Air Emissions From Sources of Acrylonitrile.
EPA-450/4-84-007a. U. S. Environmental Protection Agency,
Research Triangle Park, North Carolina, pp. 34-45. 1984.
22. Hensley, D.S. and C.A. Johnson. ABS and Related
Multipolymers. Modern Plastics Encyclopedia, pp. 6-7.
1985-1986.
23. Memorandum from R. Burt and R. Howie, Radian Corporation, to
L.B. Evans, EPA/Chemicals and Petroleum Branch, January 29,
1986. Estimates of Acrylonitrile, Butadiene, and Other VOC
Emissions and Controls for ABS and NBR Facilities.
94
-------
24. Lantz, J. H. ABS and Related Multipolymers. Modern
Plastics Encyclopedia, pp. 6,8. 1986-1987.
25. Considine, D. M. ed. Acrylonitrile-Butadiene-Styrene
Resins. Chemical and Process Technology Encyclopedia.
McGraw-Hill Publishing Co., Los Angeles, California, pp.
32-34. 1974.
26. Rolston, J. A. Fiberglass Composite Materials and
Fabrication Processes. Chemical Engineering, January 28:
96-110. 1980.
27. U. S. Environmental Protection Agency. Compilation of Air
Pollutant Emission Factors. EPA-AP-42. U. S. Environmental
Protection Agency, Research Triangle Park, North Carolina.
pp. 4.12-1 to 4.12-3. September 1985.
28. Letter from Randazzo, C., SPI Composites Institute.
Comments on draft "Locating and Estimating Air Emissions
from Sources of Styrene" document. December 1990.
95
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SECTION 6
EMISSIONS FROM THE USE OF STYRENE-CONTAINING MATERIALS
As discussed in Section 3, styrene-based resins are present
in many materials, including packaging, appliances, building
materials, furniture, electrical materials, housewares, rubber
products, paints, adhesives, and automotive and recreational
equipment parts. Sections 4 and 5 evaluate the potential for
styrene emissions from styrene production and from the major
intermediate styrene processors. Often these processors sell the
resins as pellets, granules, powders, or liquids.1 These resins
may then be combined with colorants and fillers before they are
transferred to the fabricator for manufacture of the final
product. Alternately, the resin may be sold to a separate
compounding facility for this treatment. The fabricators then
extrude, inject, or spray styrene-based resins to make the final
products.
To provide some idea of the prevalence of styrene-containing
product manufacture, Table 20 presents an estimate of the total
number of some of the styrenic resin fabricators in the United
States. In addition to the resin producers listed in Sections 4
and 5, an additional 200 distributors and compounders sell
styrenic resins to fabricators in the United States.1
The production process descriptions and emissions data
presented in this section cover some of the most common processes
and products. Because of styrene's widespread use, all processes
cannot be included here. Furthermore, emissions data were
limited. Individuals are encouraged to examine the lists of
final products in Section 3 to identify specific facilities to
contact for emissions information.
This section also describes the results of industrial
hygiene measurements of the release of styrene from the
Jlh.126
3/9/93 96
-------
TABLE 20. PREVALENCE OF STYRENIC RESIN FABRICATORS
Type of Facility
Number
UPR fabricators, cultured marble
UPR fabricators, marine
UPR compounders (bulk and sheet molding)
UPR fabricators, tubs, showers, spas, and
hot tubs
Tire and inner tube manufacturers (SBR use)
Crystal and/or IPS
Polystyrene foam producers
1,600
977
28
197
56
29
237
Source: References 1 and 2.
97
-------
thermodegradation of styrene-containing thermoplastics. In
addition, three categories of styrene emission sources are
described. The first is styrene emissions from an
acrylonitrile-butadiene-styrene (ABS) compounding facility that
receives ABS granules and adds colorants. The second category is
styrene emissions from unsaturated polyester resins (UPR) use in
different molding processes. Finally, the process descriptions
for the manufacture of polystyrene foam products for drinking
cups, loose fill, and other products are provided; no emissions
data are available for this category.
THERMODEGRADATION OF STYRENE-CONTAINING MATERIALS
One less obvious source of styrene emissions is the
thermodegradation of styrene-containing materials to form the
final product. Because the processing of these materials
typically involves high temperatures, varying amounts of occluded
styrene monomer may be released. Styrene-containing
thermoplastics are extruded or molded (by injection, compression,
or blowing) at temperatures that range from 150 to 320°C. The
following information on the release of styrene monomer during
the processing of PS, impact (IPS), ABS, and SAN is based on
industrial hygiene investigations conducted in Sweden and
Finland.3'*
In general, the thermostability of these materials is
dependent on their molecular weight, mode of polymerization, and
composition.4 Table 21 shows the range of styrene monomer
released during the thermooxidative degradation of styrene-
containing materials. The temperatures used and the oxygen
content during combustion were intended to represent those
encountered in industrial process situations. For PS, typical
processing temperatures are 150 to 280°C for extrusion and
injection molding and 190 to 235°C for blow molding.4
.Jlh.126
3/9/93 98
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Polystyrene is the most thermostable of the styrene-containing
materials studied, and is considered stable during commercial
molding and extruding at temperatures below 275°C.
ACRYLONITRILE-BUTADIENE-STYRENE COMPOUNDING
The following material was provided by a State air pollution
control office following source testing of an ABS compounding
facility.3 Uncontrolled styrene emissions for this facility are
presented under two different scenarios and the facility's
original control system, a water spray scrubber, was evaluated
for its effectiveness in reducing styrene emissions. The
facility operators and State representatives then installed and
tested an interim control measure of two packed columns in series
in an effort to temporarily reduce styrene emissions while
designing a permanent control system. Once installed, the
permanent control system was found to be 99.5 percent effective
in reducing total styrene emissions. The applicability of this
information to other facilities is not known, nor is there any
information on the number or location of similar facilities.
Process Description
The ABS compounding facility receives granulated ABS resin,
mixes the resin with dyes and additives, and extrudes the final
product (Step 1) into pellets for shipment (Figure 19). The
plant operates six extruders; all of the extruder vacuum vents
are pumped to one water ring vacuum pump (Step 2). All die vents
are also pumped to a common vent and a common blower. The
gaseous components are pulled into the vent system, while the
water is discharged to the oil-water separation sump (Step 3).
The discharge from the oil-water separation sump (Step 4) is then
sent through a basket strainer and baffled to separate the oil
from the water. The oil is hand skimmed and the water is sent to
a rotating biological contactor (RBC) for biological treatment.
Jlh.126
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The RBC sump and the outlet from the RBC are also piped into the
die vent system.
Emission Measurements
The emissions from the die and vacuum pump streams were
tested under a variety of control situations and are discussed
below. In addition, styrene emissions were monitored to compare
the emissions when the oil-water separation tank was enclosed and
when it was open. The emissions were measured by gas
chromatograph (GC) analyses and delta nonaqueous volatile (NAV)
mass balance.
The extruder vacuum pump and die vent emissions were tested
under four scenarios: uncontrolled with the oil-water separation
tank open and enclosed, and controlled with a water spray
scrubber with the oil-water separation tank open and enclosed.
The vacuum pump discharge from the separator was also
disconnected from the main stack to measure its emissions
separately. Gas chromatograph styrene measurements were also
taken around the oil-water separation sump.
Of the total emissions, the majority were from the vacuum
pump discharge, with the remainder coming from the die vent.
Stack emissions increased 20 percent when the oil-water
separation sump was enclosed due to the reduction in fugitive
losses. The results showed that the water spray scrubber was
only 25 percent efficient in reducing styrene emissions, and in
one measurement the controlled emissions were actually higher
than uncontrolled emissions. Attempts to reduce vacuum pump
emissions with a water spray in the outlet line were only
12 percent effective in overall emission reduction.
Emission estimates derived from GC analysis were then
compared with estimates from NAV. The NAV is a mass balance
estimate determined by monitoring resin content of the ABS resin,
Jlh.126
3/9/93 102
-------
pellets produced, vent oil sludge, and vacuum pump discharge
water. In general, GC and NAV were found to agree within 21
percent.
Because the water spray scrubber does not adequately control
styrene emissions, design of a better system was proposed. In
the interim, two packed columns in series vented to a temporary
carbon adsorption system were installed. The water/gas mixture
discharged from the vacuum pump was first sent to an air-water
separator, and the air leaving the separator was scrubbed in two
columns. Water was fed to the columns from a recirculation tank.
A total of 40 gallons per minute (gpm) were circulated through
each column. About 6 gpm was drained from the recirculation tank
for treatment in the RBC. The air leaving the second column was
heated to raise the relative humidity above 50 percent and sent
to a Calgon unit for carbon adsorption of the styrene. After
passing through the carbon adsorption bed, the vacuum pump air
stream combined with the die vent stream. This air stream then
passed through the water spray scrubber system. Test results
showed a total styrene emission reduction from the vacuum pump
exhaust and die vent of 96.4 percent. Table 22 presents the
emission factors developed from these data.
Permanent VOC controls were installed on this ABS
compounding facility at a later date (Figure 20). The air from
the air-water separator (about 200 standard cubic feet per minute
(scfm)) is scrubbed in two columns. The outlet of the second
scrubber passes through a heat exchanger. The air then passes
through two small carbon beds (2,000 pounds each) and the outlet
of the second bed is joined with the outlet of the die vent
system blower. This air then passes through two large carbon
beds (4,000 Ibs each). Follow-up source testing indicated that
emissions were reduced by more than 99.5 percent for total
reactive organic compounds. Table 23 presents the emissions
information for styrene at the outlet of the first large carbon
Jlh.126
3/9/93 103
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TABLE 23. SUMMARY OF ABS COMPOUNDING FACILITY SOURCE TEST
DATA AFTER INSTALLATION OF PERMANENT CONTROLS8
Emission Source
Styrene Emission
Factor
Comments
Outlet of first large
carbon bed
Outlet of first large
carbon bed
Vacuum pump outlet
Vacuum pump outlet
Outlet of second
small carbon bed
Outlet of first small
carbon bed
Outlet of second
small carbon bed
0.0012
0.0017
1.5157
1.6507
0.0012
0.0017
0.0017
Six lines running
(max. production
rate)
Five lines running
Six lines running
Five lines running
Six lines running
after change of small
carbon bed
Five lines running
after change of small
carbon bed
Five lines running
after change of small
carbon bed
"Measured by gas chromatograph.
blbs/103 Ib product or kg/Mg product,
107
-------
bed (a worst case scenario if operating on only one bed), and at
the outlet of the second large carbon bed.
UNSATURATED POLYESTER RESIN USE
Styrene-containing UPR is used in the manufacture of boats,
vehicle components, bowling balls, bathroom fixtures, gasoline
storage tanks and other products.
Unsaturated polyester resins can be used in reinforced or
non-reinforced applications. Eighty percent of UPR is
reinforced, usually with glass fibers, and extended with various
inorganic filler materials such as calcium carbonate, talc, mica
or small glass spheres.6'7 These composite materials are often
referred to as fiberglass reinforced plastic (FRP), or simply
fiberglass.* The Society of the Plastics Industry designates
these materials as "reinforced plastic/composites" (RP/C). Also,
advanced reinforced plastic products are now formulated with
fibers other than glass, such as carbon, aramid and aramid/carbon
hybrids.7 Reinforced UPR is used to make boats and marine
accessories, tub and shower stalls, transportation components and
recreational vehicle components.6 Nonreinforced UPR is used in
casting processes to make simulated marble products, cast
furniture parts, buttons, and bowling balls.
Molding processes are either closed or open. Closed molding
techniques are compression, injection, pultrusion, continuous
lamination, marble casting, bag molding, and resin transfer.
Open molding processes are hand layup, filament winding, and
spray layup. Selection of closed or open molding depends on the
size and volume of the product to be manufactured. Open molding
As used in this report, "fiberglass" means glass fibers or
fiberglass reinforced plastic. The term does not necessarily
mean "Fiberglas7*," trademark of Owens/Corning Fiberglas
Corporation, Toledo, Ohio.
Jib.128
3/9/93 108
-------
is used for large parts such as boats and recreational vehicle
structures. Open molding processes of spray layup and hand layup
offer advantages for firms that produce a limited number of units
for each mold, require rapid startup, and operate with restricted
capital for tooling. Because of limited production and/or unique
designs, many fabricators will continue to rely on open mold
fabrication.
In descending order of resin use, the UPR molding processes
are:7
• Spray layup (sprayup);
• Hand layup;
• Continuous lamination;
• Press molding;
• Marble casting;
• Pultrusion;
• Filament winding;
• Resin transfer molding; and
• Bag molding.
Process descriptions for these molding processes are given below.
Open Molding
Most open mold fabricators use similar processes to produce
products with varying composition, sizes, and shapes. For
products with a smooth, durable surface, a smooth and highly
polished mold is required. For many products, a catalyzed gel
coat is applied as the initial step. The resins are generally
either hand rolled or sprayed into the fiberglass reinforcement.
Some hand rolling is essential even when the resin is sprayed,
for removing voids and ensuring proper compaction of resin and
reinforcing material.
Most open mold fabrication facilities consist of one or more
open production areas. In these open areas, a large number of
exhaust fan outlets are provided. Emissions can be reduced by
jlh.126
3/9/93 109
-------
using airless spray guns, spray booths for gel coating and resin
application, isolated work bay operations, and air filtration.
Spray Layup—
In UPR spray layup, the mold defines the shape of the outer
surface, and the mold itself is usually made of reinforced
plastic. The mold is first coated with a wax to ensure removal
after curing. A layer of gel coat is then sprayed on to the mold
to form the outermost surface of the products. Gel coats are
highly pigmented unsaturated polyester resins that provide a
smooth, colored surface that gives the appearance of a painted
part.8 The gel coat is allowed to cure for several hours but
remains tacky so subsequent resin layers adhere better. The
polyester resin is applied with a spray gun that has a glass
chopper attachment. This allows simultaneous spraying of resin
and chopped glass onto the mold. The spray gun has separate
resin and catalyst streams which mix as they exit the gun. Air
spray guns require a large volume of air flow at high pressures.
This provides good control over spray patterns; however, this
type of spraying contributes to excessive fogging, overspray, and
bounce back, resulting in increased emissions and material loss.
To reduce styrene emissions, air-assisted airless spray guns can
be used to apply gel coats and resins. Because high pressure is
not needed at the nozzle, air-assisted airless spraying results
in lower emissions and less material loss. Unsaturated polyester
resins designed for use in spray layup are promoted for cure at
room temperature and usually are catalyzed with a liquid peroxide
such as methyl ethyl ketone peroxide (MEKP).9
Hand Layup—
Hand layup involves the same initial steps (up through
application of the gel coat) as used in spray layup. Following
gel coat application, alternate layers of catalyzed polyester
resin and reinforcement material are applied. The ratio of resin
Jlh.126
3/9/93 110
-------
to glass is usually 60 to 40 by weight, but varies by product.
Each reinforcement layer is "wetted out" with resin, and then
rolled out to remove air pockets. The process continues until
the desired thickness is achieved. Hand layup is also a room
temperature curing process.
Filament Winding—
Filament winding, shown in Figure 21, is the process of
laying a band of resin impregnated fibers onto a rotating mandrel
surface in a precise geometric pattern, and curing them to form
the product. This is an efficient method of producing
cylindrical parts with optimum strength characteristics suited to
the specific design and application. Glass fiber is most often
used for the filament, but aramid, graphite, and sometimes boron
and various metal wires may be used. The filament can be wetted
during fabrication, or previously impregnated filament
("prepreg") can be used. The three most common winding patterns
are circumferential, helical, and polar winding. The various
winding patterns can be used alone or in combination to achieve
the desired strength and shape characteristics. Mandrels are
made of a wide variety of materials and, in some applications,
remain inside the finished product as a liner or core. Example
products are storage tanks, fuselages, wind turbine and
helicopter blades, and tubing and pipe.7
Closed Molding
Closed molding systems reduce styrene emissions by
eliminating the requirement for atomization of the resin. The
most common closed molding processes are press molding, marble
casting, pultrusion, continuous lamination, resin transfer
molding, and bag molding, of these, the two largest categories
are press molding and marble casting.
JUi.126
3/9/93 111
-------
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Press Molding—
Press molding includes compression, injection and transfer
molding, and requires a large hydraulic press typically ranging
from 454 to 4536 Mg (500 to 5000 tons) in capacity. Press
molding uses either bulk molding or sheet molding compounds of
resin and reinforcing materials.8
Bulk molding compounds are produced in rope or solid bulk
form, and sheet molding compounds are produced in sheet form.
Generally the UPR compounders have indoor UPR tanks containing
less than 37,853 liters (10,000 gallons) each. The UPR is pumped
from the storage tanks to a mixing tank where fillers (primarily
calcium carbonate, clay or alumina) and catalysts are added. To
make sheet molding compounds, the resulting paste is reinforced
with glass fibers and formed into sheets on a continuous basis.
To make bulk molding compounds, the paste is placed in a mixer
with glass fibers. After compounding, the product is extruded
into rope form or packaged in bulk form. Air emissions arise
from storage tanks, mixing tanks, and mixing rooms.
Compression molding uses sheet molding compound where the
sheet is compressed between heated molds and cured. Injection
and transfer molding use bulk molding compound. The molding
compound is forced through a small opening into a closed heated
mold and cured.0
Continuous Lamination—
Garage doors, truck bed liners, patio covers, skylights, and
solar collectors are some of the products made with unsaturated
polyester resins using the continuous lamination process.
As shown in Figure 22, the polyester resin is first applied
to a film on an impregnation table on a conveyor belt. The film
forms the bottom surface of the product. This film can be made
Jib. 120
3/0/83 113
-------
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-------
of polyester, cellophane, or nylon. The resin usually contains
additives such as calcium carbonate or aluminum trihydrate to
increase weather and flame resistance. Chopped glass is then
added to the wet coat of resin, and a top layer of film is added
and the layers are pulled through rollers to remove air bubbles.
The conveyor belt then carries the laminate to a curing oven
(200°C). After exiting the oven the films are removed and the
laminate is trimmed to the desired size. Impregnation ensures a
high degree of control of fiber/resin ratio and catalyst/resin
ratio. Styrene emissions are reduced as compared to air
sprayers.
Marble Casting—
The polyester resin used in synthetic marble casting usually
has higher viscosity and lower monomer levels than the resins
used for laminating and gel coats. Fillers and colorants are
mixed with the resin in large vats. To achieve the marbled
effect, the colorants are often hand stirred. The mixed resin is
then hand poured into partially closed molds. The resin is cured
at room temperature and, after curing, the mold is removed. Gel
coats may also be used, in which case, they are applied to the
mold surface before pouring in the resin. Sources of styrene
emissions include equipment leaks, UPR storage tanks, process
operations, and transfer and handling operations. The major
sources of process operation emissions are the gel coat area and
casting areas, where UPR is mixed and poured into molds.
Recently, the Emissions Measurements Branch of the
U.S. Environmental Protection Agency contracted an environmental
consulting firm to perform source testing at two cultured marble
and sink manufacturing facilities. The primary purpose of the
testing was to determine the emission rate of styrene during
normal production activities at each facility. One of the
facilities, characterized as a small, custom operation
manufactures products consisting of bathtubs, bathroom counter
Jlh.126
3/9/93 115
-------
tops, bathroom sinks, showers, wall panels, and window sills.10
The other facility, characterized as a large production
operation, manufactures products consisting almost entirely of
bathroom sinks.11 In addition to determining emission rates of
styrene, particulate matter emissions were assessed at both
facilities. Only styrene emissions are discussed in this report.
The reader should refer to References 10 and 11 for information
on particulate matter emissions from these facilities. Data
gathered during the emissions testing were used to calculate
styrene emission factors. A discussion of the production process
and associated styrene emissions is presented below for each
facility.
Process Description - Custom Operation10
The following discussion describes the production process at
the small, custom facility. Figure 23 presents a schematic of
the plant production area. The resin and gel coat are purchased
in bulk liquid form in 55 gallon drums with no vapor suppressor
added. The styrene content of the resin is 23 to 35 percent by
weight, and 45 to 55 percent of the gel coat.
Several steps are taken to complete the finished product.
The first step involves mold preparation. Molds are hand made,
often using standard forms. After a mold is formed it is
cleaned, waxed, and transported to a spray booth where a thin
layer of gel coat is applied. After gel coating, molds proceed
to the casting process which takes place in the mixing room.
Resin, crushed marble filler, and catalyst are mixed in a closed
process and applied to the molds which are then mechanically
vibrated to remove bubbles and allow the resin to settle. The
filled open molds are allowed to cure and harden in the curing
area. After the resin has hardened, the molds are polished and
sanded in the grinding room. Lastly, the finished product is
taken to the warehouse for packaging and shipment.
jlh.126
3/9/93 116
-------
§,
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Figure 23. Small, Custom Operation Production Area
117
-------
The entire production operation is contained in a large
single room with the exception of the grinding and sanding area.
This segment of the process is contained in a separate, enclosed
area within a large manufacturing room. Work place air is vented
to the outside through three exhaust fans. One fan exhausts air
from the spray booth. A second exhaust fan and a floor level
vent connected to a rooftop fan remove air from the resin mixing
and casting area. A high efficiency filtration system controls
particulate matter generated during the grinding and polishing
area. Filtered air from this system is returned to the work
place and not vented to the outside of the building. The only
control devices used are the grinding room filtration system and
a bank of filters at the spray booth.
Emission Measurements~~Custom Operation
Styrene emissions originate from several points located
within the building. Vapors are primarily generated in the spray
booth during gel coating. Vapors are also generated from the
automatic resin/catalyst/filler mixer.
Styrene emissions were measured from the spray booth/
mixing room vent, and the mixing room exhaust using testing
procedures meeting minimum EPA Method 1 requirements. Data from
emission measurements and materials usage were used to calculate
styrene emission factors. Emission factors were developed for
the entire production operation. The emission factor calculated
for the entire process incorporates emission rates measured from
the mixing room vent, mixing room exhaust, and the spray booth.
Table 24 presents this emission factor, along with the emission
factor derived for the large production facility, which is
discussed below.
Although emission factors cannot be developed for the
individual operations, the results of the emission measurements
indicate that spray booth emissions had a higher concentration of
Jlh. 126
3/9/93 118
-------
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styrene than emissions from the mixing room vent and mixing room
exhaust. Likewise, the emission rates measured from the spray
booth were considerably higher than the rates measured from the
mixing room vent and exhaust. These results may reflect the fact
that the gel coat (used in the spray booth) has a higher
concentration of styrene than the resin.
Process Description - Large Operation
The second facility tested is a large production operation
manufacturing products consisting almost entirely of bathroom
sinks. Figure 24 is a diagram of the plant production area.
The facility purchases resin and gel coat in bulk liquid
form. The styrene content of the resin ranges from 23 to
35 percent and from 45 to 55 percent for the gel coat. The resin
is stored on site in four 4000 gallon tanks which are housed in a
separate room attached to the main manufacturing area. The gel
coat is purchased in 55 gallon drums. With the exception of the
resin storage tanks which are contained in a separate room, the
entire manufacturing operation is housed in a single large room.
Each day, resin is mixed with crushed marble filler in three
large open top mixing vats. Each vat will hold 1200 pounds of
mix of which 23 percent by weight is resin. From these large
vats, smaller 120 pound "working" batches are removed as needed.
Catalyst is then added to the working batch before the mixture is
poured onto molds.
The manufacturing process begins with the cleaning and
waxing of molds. These molds then proceed to the spray booth,
where a thin layer of gel coat resin is applied. A conveyer
takes the gel coated molds through a gel coat drying oven. After
drying, a premixed composition of resin, filler, and catalyst is
manually applied to the molds using hand held trowels (pouring
area). The back of the mold is then clamped into place and the
assembly is mechanically vibrated in the shaker to remove bubbles
jlh.126
3/9/93 120
-------
Exhaust Fans
Grinding
Sanding
Area
Polishing
Area
Package
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Area
Office
Curing
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Shaker
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Figure 24. Large Operation Production Area
121
-------
and allow the resin to settle. The molds remain on the conveyor
and pass through a curing oven before proceeding to the grinding
and sanding area and polishing area. Lastly, finished products
are taken to the warehouse area for packaging and shipment.
Various exhaust fans are used to vent workplace air to the
outside of the building. Both the gel coat oven and the curing
oven have two ducts each that extend through the roof. The spray
booth has a single duct extending through the roof. The tank
room has a floor level intake vent that exhausts through a
louvered fan mounted on an outside wall. Each of the four
storage tanks is equipped with a two inch static vent pipe that
extends through an outside wall. A high efficiency filtration
system controls particulate from the grinding and sanding
operations as shown in the dashed lines in Figure 24. Filtered
air is returned to the work place and not vented to the outside
of the building. Five louvered exhaust fans mounted close to the
ceiling on the back of the outside wall provide general building
exhaust. These fans tend to be operated only in the warmer
months of the year.
Emission Measurements - Large Operation
Styrene emissions originate from several points within the
building housing the entire operation. The adjacent tank room is
also a source of styrene vapors. Styrene is emitted from the
spray booth during gel coat application, the gel coat curing oven
and the curing oven. The mixing vats and working batches are
also sources of styrene vapors.
Styrene emissions were measured from the spray booth, gel
coat oven, curing oven and tank room. Tank room styrene
emissions were measured from the tank room floor level vent and
from tank head space. Emission rates were calculated for the
tank room vent, curing oven inlet and outlet, gel coat oven inlet
and outlet, and the spray booth. The results indicate that the
jlh.126
3/9/93 122
-------
curing oven inlet has the highest emission rate of styrene,
followed by the spray booth, gel coat oven outlet, tank room
vent, curing oven outlet, and lastly the gel coat oven inlet.
Table 24 presents the emission factor developed for this
operation. A styrene emission factor was also developed for tank
loading. Table 24 presents this emission factor.
Pultrusion—
Pultrusion, which can be thought of as extrusion by pulling,
is used to produce continuous cross-sectional lineals similar to
those made by extruding metals such as aluminum. Reinforcing
fibers are pulled through a liquid resin mix bath and into a long
machined steel die, where heat initiates an exothermic reaction
to polymerize the thermosetting resin matrix. The composite
emerges from the die as a hot, constant cross-sectional profile
that cools sufficiently to be fed into a clamping and pulling
mechanism. The product can then be cut to desired lengths.7 The
final pultruded product is typically at least 70 percent
reinforcement by weight. These products are used in the
electrical and building industries.
Resin Transfer Molding—
Resin transfer molding is a low pressure closed molding
process which is normally carried out at room temperature. In
the process, continuous or chopped strand glass fiber mats are
placed in a mold, with catalyzed resin injected after the mold is
closed. Because no resin surfaces are exposed to air during
curing, styrene emissions from this molding process are greatly
reduced as more styrene is retained in the mixture and added to
the polymer as it cures, instead of volatilizing out of the
mixture. Gel coats, which are often used with resin transfer
molding, are applied to the molds (which may be reinforced
plastic). After the gel coat cures, glass reinforcement is
placed in the mold and resin is injected. This molding process
jlh.126
3/9/93 123
-------
is best used for intermediate volume production of small to mid-
sized components such as restaurant seats, hatches, doors,
automotive parts, tubs, and shower units.8
Pultrusion—
Pultrusion, which can be thought of as extrusion by pulling,
is used to produce continuous cross-sectional lineals similar to
those made by extruding metals such as aluminum. Reinforcing
fibers are pulled through a liquid resin mix bath and into a long
machined steel die, where heat initiates an exothermic reaction
to polymerize the thermosetting resin matrix. The composite
emerges from the die as a hot, constant cross-sectional profile
that cools sufficiently to be fed into a clamping and pulling
mechanism. The product can then be cut to desired lengths. The
final pultruded product is typically at least 70 percent
reinforcement by weight. These products are used in the
electrical and building industries.
Resin Transfer Molding—
Resin transfer molding is a low pressure closed molding
process which is normally carried out at room temperature. In
the process, continuous or chopped strand glass fiber mats are
placed in a mold, with catalyzed resin injected after the mold is
closed. Because no resin surfaces are exposed to air during
curing, styrene emissions from this molding process are greatly
reduced as more styrene is retained in the mixture and added to
the polymer as it cures, instead of volatilizing out of the
mixture. Gel coats, which are often used with resin transfer
molding, are applied to the molds (which may be reinforced
plastic). After the gel coat cures, glass reinforcement is
placed in the mold and resin is injected. This molding process
is best used for intermediate volume production of small to mid-
sized components such as restaurant seats, hatches, doors,
automotive parts, tubs, and shower units.8
Jlh.126
3/9/93 124
-------
Bag Molding—
Bag molding is best used to produce an intermediate volume
of small to mid-size components such as seats, boat hatches, boat
deck structures, and other items with shallow draft molds. Bag
molding is conducted in sealed molds at room temperature. The
process is initiated with gel coat applied to the surface of the
mold. Glass reinforcing fibers and other materials are carefully
cut to fit the mold and placed over it. Catalyzed resin is
sprayed, pumped or poured over the layup. Once the layup
materials are in place, the exposed area is covered with special
layers of plastic which are sealed to the edges of the mold.
Styrene emissions occur primarily from gel coat layup, UPR
storage, and handling operations. The bag molding process uses a
bag or flexible membrane to apply pressure during molding;
usually in conjunction with an autoclave.12 A reinforced
laminate is layed up by hand or sprayed and pressure is applied
by drawing a vacuum under a cellophane, vinyl, or nylon bag
covering it. This assembly is then heated under pressure in an
autoclave. The use of bag molding allows the final product to
have a higher fiberglass to resin ratio.9
Spas/Tubs/Showers—
Open mold processes (spray layup) are used to fabricate
spas, tubs, and showers. The process consists of gel coat
sprayup and laminating operations. The polyester resin is hand
rolled to build successive layers of reinforced plastic. The
product is usually cured at room temperature. Significant
sources of emissions are from UPR storage, transfer operations,
and open mold operations.
Fiberglass Boat Production—
The fiberglass boat industry is a large consumer of UPR,
with facilities scattered throughout the United States. The
jib.126
3/9/03 125
-------
production process is discussed separately here because no one
Q
specific process is used.
Currently, there are over 900 fiberglass boat plants in the
United States. The distribution of large fiberglass boat
manufacturing facilities in 1987 by number in each State is shown
in Table 25. Only 16 States do not have any fiberglass boat
manufacturing establishments. Furthermore, 10 States have more
than 10 boat manufacturing facilities and represent 65 percent of
the facilities: California, Florida, Illinois, Indiana,
Michigan, North Carolina, South Carolina, Tennessee, Texas, and
Washington. The geographic distribution of major fiberglass boat
manufacturing facilities by State is presented in Figure 25.
Points that represent more than one establishment in a given city
are assigned a numerical value. In general, the major locations
of fiberglass boat manufacturing facilities are centered near
lakes, rivers, and coastal areas.9
The styrene concentration of UPR used in fiberglass boat
manufacture is usually 35 to 45 percent, and the styrene content
of the gel coat is typically 45 to 50 percent. The most common
fiberglass boat production process is contact molding, both spray
layup and hand layup (Figure 26).12 Concave female molds are
preferred for boat hulls and decks as they leave smooth outer
surfaces (male molds leave smooth inner surfaces). As discussed
in the spray layup description, an airless spray gun is normally
preferred. Gel coat application typically takes place in a
ventilated spray area in boat manufacturing facilities. Hand and
spray layup, as well as automated fabrication techniques, can be
used in the manufacture of fiberglass boats. Often the first
layer is allowed to cure to the touch before subsequent layers
are applied to the desired thickness. Automated layup of large
hull boats involves the simultaneous mechanical application of
resin and reinforcement material, and may still require hand
rolling to remove air bubbles. Spray layup is used for small
parts, hulls, and decks. Hand rollers are also used to remove
Jib. 128
3/9/93 126
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TABLE 25.
GEOGRAPHIC DISTRIBUTION OF THE FIBERGLASS BOAT
INDUSTRY BY NUMBER OF FACILITIES
Florida
Tennessee
California
Texas
Michigan
South Carolina
Indiana
Illinois
Washington
North Carolina
Arkansas
Massachusetts
Missouri
Louisiana
Georgia
Maryland
Minnesota
Rhode Island
Maine
Wisconsin
New Jersey
Ohio
Alabama
Arizona
Kansas
Oklahoma
Oregon
Connecticut
Kentucky
Mississippi
New York
Pennsylvania
Iowa
Nebraska
Utah
Virginia
TOTAL:
77
40
23
21
14
14
13
12
11
10
9
9
9
9
8
8
8
7
7
6
5
5
4
4
4
4
4
3
3
3
3
2
1
1
1
1
363
Source: Reference 13.
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air bubbles. Small parts are usually produced in a ventilated
booth in the molding area. A separate assembly room is used for
sanding parts and assembling the entire craft. Carpet and other
fixtures are also installed in the assembly area.9
A less common molding method for the fiberglass boat
manufacturing industry is the resin transfer molding process
typically used to manufacture small parts such as boat seats,
hatch covers, and bait boxes.14
Emission Measurements by Molding Process
The U. S. Environmental Protection Agency has published
emission factors for fabrication processes using styrene as the
monomer.7 These emission factors, shown in Table 26, are
presented as pound VOC per pound monomer used. Styrene is by far
the most common monomer used.7 Table 26 includes emission
factors for vapor-suppressed (VS) resins, which can be used to
reduce VOC emissions in place of nonvapor-suppressed (NVS)
resins. Discussions with industry representatives indicate,
however, that VS gel coats are not used, nor are VS resins used
in closed molding processes.15
The California Air Resources Board (GARB) has also developed
emission factors for UPR by molding process.1*'18 These emission
factors are shown in Table 27, and are based on resin monomer
content, layup process, and microenvironmental conditions (such
as temperature, indoor versus outdoor processes, and
ventilation). It should be noted that the CARS emission factors
are given in pounds of monomer emitted per pound of monomer used.
The emission factors published by EPA and CARB are similar
for many of the processes shown in Tables 26 and 27. Notable
exceptions are the emission factors for hand layup. The EPA
emission factors are much lower than CARB's emission factors.
jlh.126
3/8/93 130
-------
TABLE 26. VOC EMISSION FACTORS FOR POLYESTER RESIN PRODUCT
FABRICATION PROCESS3
(Pound VOC emitted/pound monomer used)
Process
Hand Layup
Spray Layup
Continuous
Lamination
Pultrusiond
Filament Winding"
Marble Casting
Closed Molding9
Resin
NVS
0.
0.
0.
0.
0.
0.
0.
05-0.
09-0.
04-0.
04-0.
05-0.
01-0.
01-0.
10
13
07
07
10
03
03
0.
0.
0.
0.
0.
0.
0.
vsb
02-0.
03-0.
01-0.
01-0.
02-0.
01-0.
01-0.
07
09
05
05
07
02
02
Gel Coat
NVS VSb
0.26-0.35
0.26-0.35
c
c
c
f
c
0.08-0.
0.08-0.
c
c
c
f
c
25
25
8Ranges represent the variability of processes and sensitivity of emissions
to process parameters, single value factors should be selected with
caution. NVS = nonvapor-suppressed resin. VS = vapor-suppressed resin.
Factors are 30-70% of those for nonvapor-suppressed resins.
cGel coat is not normally used in this process.
Resin factors for the continuous lamination process are assumed to apply.
eResin factors for the hand layup process are assumed to apply.
Factors unavailable. However, when case parts are subsequently sprayed
with gel coat, hand and spray layup gel coat factors are assumed to apply.
9Resin factors for marble casting, a semiclosed process, are assumed to
apply.
Source: Reference 7.
jlh:c 131
-------
TABLE 27. MONOMER-BASED EMISSION FACTORS FOR POLYESTER
RESIN/FIBERGLASS OPERATIONS
(Pound monomer emitted/pound monomer used)
Process
Hand Layup Only
Spray Layup Only
Hand and Spray
Marble Casting
Continuous
Lamination
Pultrusion
Filament Winding
Closed Molding
Resin
NVS VS
0.16-0.35
0.09-0.13
0.11-0.19
0.01-0.03
0.06-0.13
0.06-0.13
0.06-0.13
0.01-0.03
0.14-0.20
0.05-0.09
0.06-0.13
0.01-0.03
0.06-0.13
0.06-0.13
0.03-0.09
0.01-0.03
Gel Coat
NVS VS
0.47
0.16-0.35
0.31-0.38
0.26-0.35
NA
NA
0.26-0.35
NA
0.24-0.33
0.13-0.25
0.16-0.27
0.13-0.25
NA
NA
0.13-0.25
NA
NA - Not applicable; gel coat normally not used for these processes.
Source: References 14 and 16.
-------
Sample Calculation Using EPA Emission Factors7—
A fiberglass boat building facility consumes an average of
500 Ib per day of styrene-containing resins using a combination
of hand layup (65%) and spray layup (35%) techniques. The
laminating resins for hand and spray layup contain 41.0 and
42.5 percent, respectively, of styrene. The resin used for hand
layup contains a vapor-suppressing agent.
From Table 26, the factor for hand layup using a vapor-
suppressed resin is 0.02 - 0.07 pounds VOC per pound monomer
used. The factor for spray layup is 0.09 - 0.13 pounds VOC per
pound monomer used (NVS). Assuming the midpoints of these
emission factor ranges, and assuming that all VOC emissions are
styrene, total styrene emissions are:
(500 Ib) X [(0.41)(0.04) (0.65) + (0.425) (0.11) (0.35)] .
=13.5 Ib/day.
The emission factor ranges shown for marble casting in both
tables include emissions for both gel coat spraying and casting.
In general, the styrene emissions from synthetic marble casting
are expected to be lower than those from other processes because
of the closed mold nature of the process. Emissions vary with
the amount of time the resin is exposed to air, and the majority
of emissions were due to gel coat spraying.
For continuous lamination, exposure of the resin surface to
air at the impregnation table is a source of styrene emissions.
In addition, the ovens and the final sawing operations release
some uncured resin to the atmosphere. The emissions from
pultrusion operations are assumed to be the same as continuous
lamination.
The prevalence of emission control use in the UPR industry
is not known. The 1982 California study found that VS resins
jlh.126
3/9/93 133
-------
were used for 26 percent of resin and gel coat application.
Vapor suppressants are typically paraffin waxes that reduce
styrene emissions by migrating to the surface and reducing
volatilization of styrene. In laminating resins, the vapor
suppressant content can range from 0.3 to 0.6 percent by weight.
Other vapor suppressants in use are thermoplastics and fatty acid
esters.
Other ways to reduce styrene emissions would be to change
from open to closed molding, reduce rollout times, and in general
improve housekeeping. In addition, the amount of polyester
resin used can be reduced by redesigning products, adding more
fillers, and improving spray gun efficiency. Reformulation of
UPR could also be used to reduce the monomer content in the
resin.
Emission Measurements for Fiberglass Boat Manufacture
Styrene can be emitted during storage and transfer of the
polyester resin and from the lamination area. Resin is typically
stored in outdoor temperature-controlled tanks and transferred to
55-galIon drums for spray application. Emissions from these
sources are expected to be small compared to the process
emissions.9
As discussed previously, styrene emissions occur during gel
coat and resin application and from resin curing. Gel coats are
typically sprayed on and the resins are applied either by hand or
spray layup. The emission factors from hand and spray layup are
shown in Tables 26 and 27.
Several factors influence the styrene process emissions
during fiberglass boat manufacture. These include resin
temperature, air temperature, air velocity in the lamination
area, mold surface area, and spray gun transfer efficiency
(Table 28). The reader is encouraged to contact the fiberglass
Jlh.128
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TABLE 28. FACTORS AFFECTING STYRENE EMISSIONS FROM LAMINATION
Factors
Effect on Emissions
Resin temperatures
Air temperatures
Spray gun
pressure/equipment
atomization
Air velocity in lamination
area
Mold surface area
Resin/gel coat styrene
content
Emissions increase as temperature
rises
Emission increase as temperature
rises
Greater pressure increases the
atomization which increases the
overspray
Greater air flow may increase
evaporation resulting in increased
emissions and decreased
concentration
Greater surface area allows more
vaporization in terms of total mass
Increase emissions from increased
styrene monomer content
Source: Reference 9.
135
-------
boat manufacturing facility to obtain specific information on the
layup process used and environmental conditions in the lamination
area in order to better estimate styrene emissions.
Control of styrene emission from fiberglass boat
manufacturing can be accomplished with several of the options
Q
described above for UPR use including:
• Reduction of styrene content in resin;
• Improved transfer efficiency of spray guns;
• Use VS resins; and
• Use of add-on controls.
The use of low styrene resins (35 percent styrene versus
43 percent) can potentially reduce total styrene emission by
19 percent from resin application and curing. Problems with
application may occur as viscosity increases, and curing problems
may result in structural defects. By improving the transfer
efficiencies of the spray guns used to apply gel coat and resin,
styrene emissions due to overspray can be reduced to 42 percent
for gel coat and 33 percent for resin spray layup. • Another
option is the use of VS resins which may reduce styrene emissions
by 30 to 50 percent during curing. However, the resins form a
wax layer during curing which must be thoroughly removed between
each laminate application to ensure interlaminate bonding. If
maximum strength is not required, reducing the curing time
between laminate applications can partially address the wax layer
buildup problem.14 Because of the difficulty in removing the wax
layer, VS resins are only suitable for selected applications.
Add-on controls that have been evaluated for use by the
fiberglass boat manufacturing industry include incineration,
adsorption (mass transfer) systems, and absorption (wet scrubber)
systems. None of these add-on controls are currently used,
however.13 Problems (primarily economic) with the use of add-on
jib. 126
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controls by the fiberglass boat manufacturing industry are due to
the high flow rates and low VOC concentrations in the exhaust.
POLYSTYRENE FOAM
Polystyrene foam (PSF) products consist of foam sheet, foam
board, and expandable beads. These products are manufactured by
either extrusion or expandable bead blowing. The density,
strength, formability, and insulating qualities of PSF make it an
ideal material for packing "peanuts," hamburger boxes, and hot or
cold drink cups, and many other products. A 1988 estimate of end
uses for polystyrene resin indicates that foam packaging accounts
for 26 percent, disposables account for 16 percent, consumer and
institutional products account for 16 percent, and expandable
polystyrene (EPS) beads account for 11 percent of total United
States polystyrene production. The remainder goes into
electronics, compounding, furniture manufacturing, and
17 *
construction. Most extruded PSF products are manufactured by
polystyrene producers. Blowing agent is incorporated into the
polystyrene as it is extruded. Expanded polystyrene products,
however, are made from polystyrene beads which contain an
inactive blowing agent. These beads are usually produced by the
large chemical companies, but they are expanded and molded at
different facilities. Although no information on styrene
emissions from the manufacture of polystyrene foam was found in
the literature, process descriptions and facility locations are
provided. Table 29 lists the major end uses of PS foam board and
sheet and presents total United States consumption of PS foam
products in 1988. Table 30 indicates the number of PSF producers
in the United States by State.
Process Description
Polystyrene is foamed through the use of physical blowing
agents that are gases or liquids that are soluble in the molten
polymer under pressure. Under depressurization, the blowing
Jlh.126
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TABLE 29. DOMESTIC CONSUMPTION OF POLYSTYRENE FOAM BY END USES
1988 1988
End Use (Mg) (MM Ib)
Extruded Foam
Board 66,679 147
Sheet
Single Service Containers 156,038 344
Stock Food Trays 86,184 190
Egg Cartons 36,288 80
Other Foamed Sheet 15.876 35
Total Foamed Sheet 361,065 796
Expandable Beads
Building and Construction3
Cups and Containers
Packaging
Loose Fill
Other EPS Products
Total EPS Bead Products
77,112
75,298
48.082
27,216
25.401
253,109
170
166
106
60
56
558
Values include construction uses other than insulation, such as
wall and ceiling coverings and concrete filler.
Source: Reference 18.
138
-------
TABLE 30. DISTRIBUTION OF PSF PRODUCERS BY STATE
Sheet, Film, Board, and Block Producers
Including Foam Blowers and Extruders
State Number of
Facilities
California 23
Pennsylvania 19
Michigan 14
Mississippi 14
New York 14
Ohio 14
Illinois 12
Massachusetts 12
Georgia 11
Missouri 9
New Jersey 9
Texas 8
Arkansas 7
Connecticut 7
Florida 6
Washington 6
Indiana 5
Wisconsin 5
Colorado 4
Kentucky 4
North Carolina 4
Virginia 4
Maryland 3
Minnesota 3
Tennessee 3
Alabama 2
Iowa 2
Nebraska 2
Rhode Island 2
South Carolina 2
Arizona 1
Hawaii 1
Idaho 1
Kansas 1
New Hampshire 1
Oklahoma 1
TOTAL: 237
Source: References 19, 20, and 27,
139
-------
agent volatilizes, causing the polymer to foam through the
formation of gas cells.
Polystyrene Foam Sheet—
The formation of PSF sheet is an extrusion process, commonly
using two extruders in series or one extruder with two sections.
The process produces foam sheets 1 to 7 mm thick, with densities
of 32 to 160 kg/m3.22 A typical extruded PSF foam sheet
manufacturing process flow diagram is shown in Figure 27.
Polystyrene pellets are mixed with a small amount (0.2 to
2 percent) of powdered nucleating agent such as talc, or a
combination of citric acid and bicarbonate of soda (Step 1),22
This mixture is fed into the primary extruder (Step 2). The
extruder is heated to provide an increasing temperature profile
along its length, so that the polystyrene melts. The blowing
agent is injected as a liquid, under high pressure, into the
primary extruder where it mixes with the molten polystyrene. A
screen is used to remove impurities from the molten polystyrene
before it enters the secondary extruder. The secondary extruder
introduces a cooling profile that increases the mixture's
viscosity and give it enough strength to contain the blowing
agent as it expands (Step 3). As the viscous polystyrene mix
leaves the second extruder through a die, it foams and partially
solidifies. The blowing agent bubbles attach to the nucleating
agent and a cellular structure is formed.
An annular extrusion die is used in extruded polystyrene
sheet production, resulting in attubular form (Step 4). Foaming
initiates near the die outlet where the pressure rapidly
decreases, allowing the blowing agent to volatilize. As the
foamed polystyrene passes through the die, compressed air is
applied, forming a skin on the outer surfaces. Additional
foaming occurs outside the die as the polystyrene tube passes
over a forming mandrel, which determines the final circumference
of the foam tube .(Step 5} . At the end of the mandrel the tube is
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split lengthwise, flattened out, and an S-wrap, or sheet wrapping
unit, winds the sheet into a roll (Step 6). The PSF sheet is
then stored for two to five days. During this time, a portion of
the blowing agent diffuses out of the foam cells and is replaced
with air. This results in an optimum ratio of air to blowing
agent within the foam cells, which will allow for postexpansion
of the PSF during thermoforming.
Thermoforming is a process in which the extruded PSF sheet
is reheated, then pressed between the two halves of a metal mold
to form the desired end product such as fast-food containers
(Step 7). After thermoforming, the molded shape is trimmed,
sometimes printed, and packaged. Resulting scraps are ground and
sent to scrap storage silos. This scrap is introduced into the
primary extruder with virgin polystyrene. Polystyrene scrap
typically makes up 35 percent of the total polystyrene fed to the
primary extruder.
Extruded Polystyrene Foam Board—
Polystyrene foam board ranges from 1.25 to 15 cm thick, with
densities of 27 to 66 kg/m . The extrusion of PS foam boards is
identical to that of PS foam sheets (Step 1: mixing PS pellets
with necleating agent, Step 2: primary extrusion, Step 3:
secondary extrusion), with the exception that a simple slit
aperture die is used instead of an annular die so that board is
extruded as slabs rather than a tube (Step 4). Following cooling
of the PS board, it is trimmed to size and packaged. A typical
PSF board manufacturing process flow diagram is shown in
Figure 28. Some board is laminated with facing materials that
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act as a vapor barrier or aid in the retention of low
conductivity gas.23
Expandable Polystyrene—
Expandable polystyrene is produced from spherical
polystyrene beads which have been impregnated with a volatile
hydrocarbon such as n-pentene or CFC-12. The polystyrene beads
are produced by polymerizing styrene in a water suspension and
adding it to a volatile liquid such as n-pentane. That serves as
the blowing agent. The beads typically contain 5 to 7 weight
percent of blowing agent. Prior to use, the beads are stored at
temperatures below 21°C (70°F) to inhibit premature expansion.2*
A typical EPS bead manufacturing process flow diagram is
shown in Figure 29. Normally, the beads are expanded in one step
and molded in another. The beads are first expanded to achieve
the desired molding density (Step 1). Expansion is promoted by
exposing the beads to a continuous flow of steam of hot air at
temperatures of 212 to 220°F within a process unit called a pre-
expander. The amount of expansion is controlled by steam
pressure and temperature and the bead feed rate.23 Both batch
and continuous processes are common. The transfer of heat
vaporizes the volatile hydrocarbon trapped in the polystyrene
matrix. As the volatiles are released from the matrix, the beads
foam and expand.
Following the expansion process, the excess moisture
acquired during the steaming is eliminated with hot air and the
beads are transported to storage silos constructed of large mesh
bags, where they are allowed to cool (Step 2)." The beads are
allowed to age for 2 to 72 hours, during which time a portion of
the remaining trapped volatile compounds evaporates and is
replaced with air that diffuses into the beads. Air may be
pumped through the beads to accelerate the aging process.
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Once aged, the beads are placed in molds and steam is used
to expand the beads (Step 3). There are three types of molding:
24
shape, block, and cup molding. In shape molding, a premeasured
amount of expanded beads is fed to a preheated split cavity mold.
The beads are exposed to steam through small holes in the mold.
The beads undergo further expansion, become soft and molten due
to the transfer of heat from the steam, and fuse together under
these conditions to form a single polymer mass. Following the
expansion and fusing process, the mold and PSF part are cooled by
circulating water through the mold. The mold is then opened, and
the molded part is ejected by compressed air, mechanical pins, or
manually. Shape-molded polystyrene foam products have densities
ranging from 1.0 to 2.5 lb/ft3.25
•
In block molding, pre-expanded beads are molded into large
blocks of densities from 0.8 to 1.0 lb/ft3.25 Following cooling
and intermediate storage, blocks are sliced into sheets or custom
fabricated shapes. Cup molding uses smaller beads and lower
blowing agent content than block or shape molding. Cup density
is over 3.5 lb/ft3.24 Cups are molded at a moderate temperature;
the final product is packaged in plastic and boxed for shipping.
Post molding operations of aging (Step 4) and fabrication
(Step 5) are the final steps before printing and shipping of the
product.
Polystyrene Loose Fill Packaging—
Polystyrene loose fill packaging is manufactured with a
combination of extrusion and bead expansion. Recycled and new
polystyrene are mixed with a nucleating agent and melted, as for
extrusion. The blowing agent is injected under pressure, and the
viscous mix is extruded, foaming as the blowing agent evaporates,
and forming hollow strands as it exits through the die. The
hollow strands are cut into 3/4-inch pieces. The strands are
then steamed for further expansion, as are EPS beads.
Jlh.126
3/9/93 146
-------
Intermediate aging follows, and then the strands are further
steam expanded, dried in ovens, and aged. The density of loose
fill is about 0.2 Ib/ft3.23
Emissions from Polystyrene Foam Production
No information was located in the literature on styrene
emissions associated with these processes. The reader is
encouraged to contact individual facilities in question to obtain
styrene emissions data.
Jlh.126
3/9/93 147
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REFERENCES FOR SECTION 6
1. A. T. Kearney. Impact Analysis of the EPA Office of
Drinking Water Proposal to Regulate styrene. Styrene
Information Research Center. 1989.
2. Clark, R., et al. Potential Environmental Impact of
Compounding and Fabricating Industries: A Preliminary
Assessment. EPA-600/2-77-160. U. S. Environmental
Protection Agency, Cincinnati, Ohio. 1977.
3. Pfaffi, P., et al. Degradation Products of Homopolymer
Polystyrene in Air. Scand. J. Work Environ. Health 4
(suppl. 2): pp. 22-27. 1987.
4. Hoff, A., et al. Degradation Products of Plastics:
Polyethylene and Styrene - Containing Thermoplastics -
Analytical, Occupational and Toxicologic Aspects. Scand. J.
Work Environ. Health 8 (suppl 2):
p. 60. 1982.
5. Letter and enclosure from Terri Thomas, Ventura County
Resource Management Agency, California, to D. Campbell,
Radian Corporation.
June 27, 1989.
6. Sprow, T. K. Unsaturated Polyester. Modern Plastics
Encyclopedia, pp. 48-50. 1986-1987.
7. U. S. Environmental Protection Agency. Compilation of Air
Pollutant Emission Factors. AP-42. U. S. Environmental
Protection Agency, Research Triangle Park, North Carolina.
p. 4.12-1 - 4.12-12.
8. Randazzo, C., SPI Composites Institute. Comments on draft
"Locating and Estimating Air Emissions from Sources of
Styrene" document. December 1990.
9. Stockton, M. B. and I. R. Kuo. Assessment of VOC Emissions
from Fiberglass Boat Manufacturing. EPA-600/2-90-0019.
U. S. Environmental Protection Agency, Research Triangle
Park, North Carolina. 1990.
10. Radian Corporation. Determination of Styrene Emissions from
the Cultured Marble and Sink Manufacturing Industry.
Venetian Marble, Richmond, Virginia. Prepared for the
U. S. Environmental Protection Agency, Research Triangle
Park, North Carolina. April 1992.
jlh.126
3/9/93 148
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11. Radian Corporation. Determination of Styrene Emissions from
the Cultured Marble and Sink Manufacturing Industry.
General Marble, Lincolnton, North Carolina. Prepared for
the Emission Measurement Branch, U. S. Environmental
Protection Agency, Research Triangle Park, North Carolina.
August 1992.
12. Gibbs and Cox, Inc. Marine Design Manual for Fiberglass
Reinforced Plastics. McGraw-Hill Book Company, New York,
New York. pp. 4-16. 1960.
13. Thomas Register of American Manufacturers. Thomas
Publishing Company, New York, New York. 1987.
14. Rogozen, M. B. Control Techniques for Organic Gas Emissions
from Fiberglass Impregnation and Fabrication Processes.
California Air Resources Board Report No. ARB/R-82/165.
1982.
15. Randazzo, C., SPI Composites Institute. Comments on draft
"Locating and Estimating Air Emissions from Sources of
Styrene" document. August 1991.
16. Rogozen, M. B. Development of an Inventory of Styrene
Emissions from Polyester Resin/Fiberglass Fabrication in
California. In: The Air Pollution Control Association, ed.
A Specialty Conference on Emission Inventories and Air
Quality Management. April 27-30, Kansas city, Missouri.
pp. 363-378. 1982.
17. Chemical Profile; Polystyrene. Chemical Marketing Reporter,
June 20:52. 1988.
18. Resin Report 1989. Journal of Modern Plastics, January,
1989.
19. Society of the Plastics Industry. Membership Directory,
1989.
20. U. S. Environmental Protection Agency. Industrial Process
Profiles for Environmental Use: Chapter 10. Prepared by
Radian Corporation, 1987.
21. Thomas Register of American Manufacturers. Thomas
Publishing Company, New York, New York. 1988.
22. Kirk-Othmer Encyclopedia of Chemical Technology. 3rd ed. '
Styrene Polymers. Volume 16. John Wiley and Sons. New
York, New York. pp. 148-245. 1979.
23. Foundation Design Handbook: Volume 1. Undercurrent Design
Research. Underground Space Center, University of
Minnesota.
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24. Rodriguez, P. Principles of Polymer Systems. McGraw-Hill,
Inc., New York, New York, 1970.
25. Tsitsopoulas, L. and M. Mills. Staff Report, Proposed Rule
1175: Control of Emissions from the Manufacture of
Polymeric Cellular Products (Foam). South Coast Air Quality
Management District; Rule Development Division, September,
1989.
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SECTION 7
SOURCE TEST PROCEDURES
Styrene emissions can be measured by several methods, five
of which are: (1) EPA Reference Method 18, which was announced
in the Federal Register on October 18, 1983^ (2) NIOSH
Analytical Method 1501 published in the NIOSH Manual of
Analytical Methods on February 15, 1984;2 (3) EPA Method 5040
which was published in EPA Report No. SW-846 in November 1986;3
(4) Compendium Method TO-14, determination of volatile organic
compounds (VOCs) in ambient air using canister sampling;4 and
(5) EPA Reference Method 827O.5
EPA Reference Method 18 applies to the sampling and analysis
of approximately 90 percent of the total gaseous organics emitted
from an industrial source; whereas NIOSH Method 1501 applies only
to the collection and analysis of ten specific aromatic
hydrocarbons. A method similar to the NIOSH Method 1501 is the
American Society for Testing and Materials (ASTM) D 3686-84
method (published on June 29, 1984) .6 EPA Method 5040 applies to
the analysis of TENAX* and TENAX®/charcoal cartridges used to
collect volatile principal organic hazardous constituents (POHCs)
from wet stag gas effluents. Compendium Method TO-14 is
applicable to specific VOCs that have been tested and determined
to be stable when stored in pressurized and sub-atmospheric
pressure canister.8 EPA Method 8270 is used to determine the
concentration of semivolatile organic compounds using gas
chromatography/mass spectrometry (GC/MS).
EPA REFERENCE METHOD 18
In Method 18, a sample of the exhaust gas to be analyzed is
drawn into a Tedlar« or aluminized Mylar® bag as shown in
Figure 30. The bag is placed inside a rigid, leakproof container
and evacuated. The bag is then connected by a Teflon* sampling
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line to a sampling probe (stainless steel, Pyrex® glass, or
Teflon®) at the center of the stack. The sample is drawn into
the bag by pumping air out of the rigid container.
The sample is then analyzed by gas chromatography (GC)
coupled with flame ionization detection (FID). Based on field
and laboratory studies, the recommended time limit for analysis
is within 30 days of sample collection.7'8 The GC operator should
select the column and GC conditions that provide good resolution
and minimum analysis time for styrene. Zero helium or nitrogen
should be used as the carrier gas at a flow rate that optimizes
the resolution.
The peak areas corresponding to the retention times of
styrene are measured and compared to peak areas for a set of
standard gas mixtures to determine the styrene concentrations.
The detection limit of this method ranges from about 1 part per
million (ppm) to an upper limit governed by the FID saturation or
column overloading. However, the upper limit can be extended by
diluting the stack gases with the inert gas or by using smaller
gas sampling loops.
When access to the sampling location is difficult, an
alternative sampling method described in Section 7.4 of EPA
Reference Method 18 may be preferred.9
NIOSH METHOD 1501
This method has limited application. The method applies
only to ten specific aromatic hydrocarbons. Several necessary
modifications are recommended if this method is to be used.9
In the NIOSH method, samples are collected with solid
sorbent tubes containing coconut shell charcoal. Five to 14-
liter air samples are collected with the use of a personal
sampling pump at a known flow rate of < 1 L/minute.2
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Samples are desorbed with carbon disulfide and analyzed by
GC equipped with an FID and a column capable of resolving styrene
from the solvent front and other interferences. The column
specified in NIOSH Method 1501 isa3.0mx2mm glass or
stainless steel, 10% OV-275 on 100/120 mesh Chromosorb* W-AW, or
equivalent.2
The amount of styrene in a sample is obtained from the
calibration curve in units of milligrams per sample, storage
stability has not been assessed for this method, thus, analysis
should occur as soon as possible following sample collection.
Styrene can dimerize during handling and storage. The rate of
dimerization is a function of temperature, increasing as the
temperature increases. Consequently, samples should be stored at
low temperatures.
This procedure is applicable for monitoring styrene air
concentrations ranging from 2.17 to 8.49 mg. The GC column and
operating conditions should provide good resolution and minimum
analysis time.
EPA METHOD 5040
In Method 5040, a sample of stack gas is collected on TENAX®
and TENAX®/charcoal sorbent cartridges using a volatile organic
sampling train, (VOST).3 Because the majority of gas streams
sampled using VOST will contain a high concentration of water,
the analytical method is based on the quantitative thermal
desorption of volatile POHCs from the TENAX* and TENAX*/charcoal
traps. The analysis is by purge-and-trap 6C/MS.
A schematic diagram of the analytical system is shown in
Figure 31. The contents of the sorbent cartridges are spiked
with an internal standard, thermally desorbed, and trapped on an
analytical adsorbent trap directed into the GC/MS. The volatile
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POHCs are separated by temperature-programmed GC and detected by
low-resolution mass spectrometry.
The concentrations of volatile POHCs are calculated using
the internal standard technique. Sample trains obtained from the
VOST should be analyzed within two to six weeks of sample
collection. The desired target detection limit of this method is
0.1 ng/L (20 ng on a single pair of traps). Industry experience
has found this method to be difficult to use and easily
overloaded when the analyte concentration is in the high parts
per billion (ppb) to ppm range.10 In addition, the cost
associated with this method is higher than other analytical
methods.9
COMPENDIUM METHOD TO-14
Method TO-14 is based on collection of whole air samples in
SUMMA* passivated stainless steel canisters for analysis of
volatile organic compounds (VOCs) in ambient air. A sample of
ambient air is drawn through a sampling train composed of
components that regulate the rate and duration of sampling into a
pre-evacuated SUMMA* passivated canister.
The VOCs are separated by GC and measured by mass-selective
detectors or multidetector techniques. The recommended time
limit for analysis is within 14 days of sample collection.10 The
column specified in Compendium Method TO-14 is a Hewlett OV-1
capillary column, 0.32 mm I.D. x 50 m with 0.88 urn cross-linked
methyl silicone coating, or equivalent/ The wider J & W
Scientific Company Megabore® column (i.e., 0.53 mm I.D.) can be
used as long as the system meets user needs..4 Compounds have
been successfully measured at the parts per billion by volume
(ppbv) level using this method.
This method is designed for ambient, not source monitoring.
Few laboratories offer it and it is quite costly. It is
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reportedly difficult to use and the sample may be easily
contaminated by the system. Recovery rates for reactive
compounds tend to be very low.9
EPA REFERENCE METHOD 8270
Method 8270 describes conditions for GC/MS and is used to
determine the concentration of semivolatile organic compounds in
extracts prepared from all types of solid waste matrices, soils,
and ground water. The analytical methodology will be equally
applicable to an extract from sorbent media used in conjunction
with EPA Method 0010 to sample stationary sources. The sorbent
for Method 0010 is XAD-2« resin which is a styrene-divinylbenzene
copolymer. Styrene monomer may also be present in the resin and
may result in interferences. A different sorbent should be
substituted for XAD-2®. Two possible candidates are TENAX®,
which would require extraction with pentane or hexane, and XAD-7®
which is an acrylic resin. Extraction efficiencies would need to
be validated before these modifications are accepted.
Styrene is within the boiling point range for analysis by
Method 8270, but is sufficiently volatile. Care must be taken in
sample concentration to avoid loss. An adjustment in
chromatographic conditions will be required to resolve the
relatively volatile styrene from the solvent.
The practical guantitation limit for Method 8270 is
approximately 50 ug/mL of extract. The entire sorbent module
with filter is typically extracted and concentrated to a final
volume of 1 mL. This final extract volume represents the entire
volume of gas sampled.
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REFERENCES FOR SECTION 7
1. 40 CFR Part 60, Appendix A, Method 18: Measurement of
Gaseous Organic Compound Emissions by Gas Chromatography,
pp. 868, 873-878, 886, 889, 895. July 1, 1989.
2. U. S. Department of Health, Education, and Welfare. NIOSH
Manual of Analytical Methods, 3rd ed., Volume 2. National
Institute for Occupational Safety and Health, Cincinnati,
Ohio. pp. 1501-1 to 1501-7. 1984.
3. Method 5040: Protocol for Analysis of Sorbent Cartridges
from Volatile Organic Sampling Train. Test Methods for
Evaluating Solid Waste, 3rd ed., Vol. IB: Laboratory
Manual, Physical/Chemical Methods. EPA Report No. SW-846.
November 1986.
4. Compendium Method TO-14: The Determination of Volatile
Organic Compounds (VOCs) in Ambient Air Using Summa*
Passivated Canister Sampling and Gas Chromatographic
Analyses. Quality Assurance Division. Atmospheric Research
and Exposure Assessment Laboratory, U. S. Environmental
Protection Agency, Research Triangle Park, North Carolina.
pp. 1-15, 18,19, 21-23. May 1988.
5. U. S. Environmental Protection Agency, Office of Solid Waste
and Emergency Response. Method 8270: Gas Chromatography/
Mass Spectrometry for Semivolatile Organics: Capillary
Column Technique. Test Methods for Evaluating Solid Waste,
3rd ed. Report No. SW-846. Washington, D.C. 1986.
6. ASTM D3686-84. Annual Book of ASTM Standards, Volume 11.03.
1984.
7. Personal Communication. Moody, T. K., Radian Corporation,
with Hartman, M., Radian Corporation, October 9, 1989.
Discussion of styrene/butadiene stack sampling and analysis.
8. Personal Communication. Moody, T. K., Radian Corporation
with Pau, J., U. S. Environmental Protection Agency,
Atmospheric Research and Exposure Assessment Laboratory,
October 10, 1989. Discussion of EPA Reference Method 18 in
relation to styrene stack sampling.
9. Randazzo, C., SPI Composites Institute. Comments on draft
"Locating and Estimating Air Emissions from Sources of
Styrene" document. December 1990.
10. Personal Communication. Moody, T. K., Radian Corporation,
with Rice, J., Radian Corporation, February 7, 1990.
Discussion of Compendium Method TO-14.
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA 454/R-93-011
4. TITLE AND SUBTITLE
Locating and Estimating Ai
of Styrene
2.
r Emissions From Sources
7. AUTHOfl(S)
Darcy Campbell
9. PERFORMING ORGANIZATION NAME M
Radian Corporation
Post Office Box 13000
Research Triangle Park, NC
(919) 541-9100
12. SPONSORING AGENCY NAME AND ADC
U. S. Environmental Protec
OAR, OAQPS, TSD (MD-14)
Research Triangle Park, NC
(919) 541-5371
40 ADDRESS
27709
>RESS
tion Agency
27711
3. RECIPIENT'S ACCESSION NO.
5. REPORT DATE
April 1993
6. PERFORMING ORGANIZATION CODE
8. PERFORMING ORGANIZATION REPORT NO.
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
13. TYPE OF REPORT AND PERIOD COVERED
Final
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
EPA Project Manager: Dallas Safriet
16. ABSTRACT
To assist groups interested in inventorying air emissions of various potentially
toxic substances, EPA is preparing a series of documents such as this to compile
available information on sources and emission of these substances. This document
deals specifically with styrene. Its intended audience includes Federal, State
and local air pollution personnel and others interested in locating potential
emitters of styrene and in making gross estimates of air emissions therefrom.
This document presents information on (1) the types of sources that may emit
styrene, (2) process variations and release points that may be emitted within these
sources, and (3) available emissions information indicating the potential for
styrene releases into the air from each operation.
This document updates a previous interim document published in October, 1991. This
document contains information and styrene emission factors that were not available
in the interim report for two cultured marble and sink manufacturing operations.
7. KEY WORDS AND DOCUMENT ANALYSIS
I. DESCRIPTORS
Styrene
Air Emissions Sources
Locating Air Emissions Sources
Toxic Substances
8. DISTRIBUTION STATEMENT
Unlimited
b.lDENTIFIERS/OPEN ENDED TERMS
19. SECURITY CLASS {Tins Report/
Unclassified
20. SECURITY CLASS / Tins page )
Unclassified
c. COSATl Field/Croup
21 NO OF PAGES
164
22. PRICE
PA Form 2220-1 (R«v. 4-77) PREVIOUS EDITION is OBSOLETE
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