v>EPA
United States
Environmental Protection
Agency
Risk Reduction
Engineering Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/S-92/004 May 1992
ENVIRONMENTAL
RESEARCH BRIEF
Waste Minimization Assessment for a Manufacturer of Chemicals
Gwen P. Looby and Phylissa S. Miller*
Abstract
The U.S. Environmental Protection Agency (EPA) has funded
a pilot project to assist small- and medium-size manufacturers
who want to minimize their generation of waste but who lack
the expertise to do so. In an effort to assist these manufactur-
ers, Waste Minimization Assessment Centers (WMACs) were
established at selected universities and procedures were
adapted from the EPA Waste Minimization Opportunity As-
sessment Manual (EPA/625/7-88/003, July 1988). The WMAC
team at the University of Tennessee performed an assessment
at a plant manufacturing acrylic emulsions, low molecular weight
resins, herbicides, and specialty chemicals-approximately 300
million Ib/yr. In general, monomers, additives, activators, and
catalysts are metered and mixed in tanks then pumped se-
quentially into reactor vessels. Once the product is formed, the
solution is pumped into a blend tank where more chemicals,
such as binders, emulsifiers, and thickeners, are added. From
the blend tank the product is passed through filters for clump
removal then pumped into either storage tanks or drums for
shipping. The team's report, detailing findings and recommen-
dations, indicated that the majority of waste was generated in
the wastewater treatment system and that the greatest savings
could be obtained by installing a natural gas-fired dry-off oven
in the wastewater treatment system to reduce (by 81%) the
amount of sludge removed to the landfill.
This Research Brief was developed by the principal investiga-
tors and EPA's Risk Reduction Engineering Laboratory, Cincin-
nati, OH, to announce key findings of an ongoing research
project. This brief provides only summary information and is
•University City Science Center, Philadelphia, PA 19104.
not intended for use as a thorough analysis. A fully docu-
mented report of the same title is available from the authors.
Introduction
The amount of waste generated by industrial plants has be-
come an increasingly costly problem for manufacturers and an
additional stress on the environment. One solution to the prob-
lem of waste is to reduce or eliminate the waste at its source.
University City Science Center (Philadelphia, PA) has begun a
pilot project to assist small- and medium-size manufacturers
who want to minimize their formation of waste but who lack the
in-house expertise to do so. Under agreement with EPA's Risk
Reduction Engineering Laboratory, the Science Center has
established three WMACs. This assessment was done by
engineering faculty and students at the University of
Tennessee's (Knoxville) WMAC. The assessment teams have
considerable direct experience with process operations in manu-
facturing plants and also have the knowledge and skills needed
to minimize waste generation.
The waste minimization assessments are done for small- and
medium-size manufacturers at no out-of-pocket cost to the
client. To qualify for the assessment, each client must fall
within Standard Industrial Classification Code 20-39, have gross
annual sales not exceeding $50 million, employ no more than
500 persons, and lack in-house expertise in waste minimiza-
tion.
The potential benefits of the pilot project include minimization
of the amount of waste generated by manufacturers and reduc-
tion of waste treatment and disposal costs for participating
plants. In addition, the project provides valuable experience for
graduate and undergraduate students who participate in the
program and a cleaner environment without more regulations
and higher costs for manufacturers.
Printed on Recycled Paper
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Methodology of Assessments
The waste minimization assessments require several site visits
to each client served. In general, the WMACs follow the proce-
dures outlined in the EPA Waste Minimization Opportunity
Assessment Manual (EPA/625/7-88/003, July 1988). The WMAC
staff locates the sources of waste in the plant and identifies the
current disposal or treatment methods and their associated
costs. They then identify and analyze a variety of ways to
reduce or eliminate the waste. Specific measures to achieve
that goal are recommended and the essential supporting tech-
nological and economic information is developed. Finally, a
confidential report that details the WMAC's findings and recom-
mendations (including cost savings, implementation costs, and
payback times) is prepared for each client.
Plant Background
This plant manufactures acrylic emulsions, low molecular weight
resins, herbicides, and other specialty chemicals. The plant
operates 8,400 hr/yr to produce approximately 300 million
pounds of chemicals.
Manufacturing Process
The processes are complex and vary extensively in the exact
methods used in order to produce the final product. The pro-
duction of one particular low molecular weight dispersant prod-
uct generates significant quantities of wastes and therefore will
be considered a separate process in this evaluation. The pro-
cess lines are described below in detail.
Acrylic Emulsion Production
Approximately 400 different acrylic emulsion formulations are
produced by this plant. The actual sequence of steps required
varies greatly from product to product. However, the overall
process sequence is similar in most cases and is described
below. Raw materials for the emulsion line include monomers,
additives, activators, and catalysts in either liquid or solid form.
Some monomers have been pre-mixed with inhibitors for stabi-
lization. Catalysts are used to activate the monomers and
initiate the desired reactions. Activators increase the activity
level of the catalysts and allow reactions to overcome the
effects of the inhibitors. Additives include detergents, disper-
sants, and pH-adjustment ingredients.
Monomers are pumped from tanker trucks to monomer tanks
for storage. From the storage tanks, monomers are pumped to
holding/premixing tanks, and in some cases to the additive,
activator, and catalyst holding tanks where mixing occurs. The
additives, activators, and catalysts may be added directly to
the reactors without being mixed with monomers in their re-
spective holding tanks.
From the holding tanks, raw materials are mixed together using
certain proprietary recipes in one of three temperature- and
pressure-regulated reactors where polymers are formed. Chemi-
cal reactions are initiated by addition of catalysts and are
regulated with additives or by pressure and temperature ad-
justment.
Next, the resulting acrylic emulsion polymers are pumped to
blend tanks where other ingredients are added. At this point
approximately 40% to 60% of the emulsion is water. Formalde-
hyde is added as a preservative to control bacteria and mold
growth, and ammonia is added to approximately half of the
product for pH adjustment. Another pH-adjustment chemical
that is added in the blend tanks is sodium hydroxide. Other
ingredients such as emulsions, emulsifiers, surfactants, bind-
ers, and thickeners are added to modify monomer viscosity, to
stabilize the polymers, and to hold the polymers in suspension.
De-ionized water is added to lower the solids content. After
each polymer batch is processed, the blend tanks are flushed
with de-ionized water that is then pumped to the plant's waste-
water treatment system.
Wastes generated up to this point in the process include
composited absorbed monomers, burnable liquids, and off-
grade methylolacrylamide/acrylamide. Most of the composited
absorbed monomer waste generated occurs from spillage dur-
ing loading and unloading of the railcars or from batch spills
and reactor clean-ups. Burnable liquids waste results from off-
spec mixtures or reactions resulting from incorrect tempera-
tures or incorrect batch weights of solutions in the feed tanks
and reactors. Some of the burnable liquids waste from the off-
spec batches are recovered and mixed with good batches. Off-
grade methylolacrylamide/acrylamide results from bad batches
of a particular commercial product. In addition, some waste is
generated because of a product's relatively short shelf life.
Equipment and/or operator error also accounts for a portion of
off-grade material.
From the blend tanks, the acrylic emulsion polymers are pumped
through tightly woven cloth filters that separate unwanted clumps
of product from the water phase. The used filters, which con-
tain clumps of product, are shipped offs'rte to a landfill. (An
estimated 0.25% of actual product is trapped in the filters.)
After filtering, the emulsions are pumped either to storage
tanks or directly into drums for shipping.
Low Molecular Weight Resin Production
Production processes and raw materials for the low molecular
weight (LMW) resins are identical to those of the acrylic emul-
sions until the product is pumped into the blend tanks.
Following batch polymerization in the reactor vessels, the LMW
resin product is pumped to one of six blend tanks where
different additives including water, sodium hydroxide, ammo-
nia, detergents, and emulsifiers are added. These additives
provide pH adjustment, solids adjustment, and preservation of
the product. From the blend tanks, the LMW resin polymers
are pumped either to storage tanks for future shipping or
directly to drums for immediate shipping.
One waste generated from this production line is an unsalable
product, which is shipped offsite as a hazardous waste. Addi-
tional waste generated by this line is a result of off-grade
batches.
Other wastes generated in this process are similar to those in
the emulsion line and include composited absorbed mono-
mers, burnable liquids, and off-grade methylolacrylamide/
acrylamide. These wastes are generated in the same manner
mentioned above. An abbreviated flow diagram for acrylic
emulsion and the LMW resin process is shown in Figure 1.
Dispersant Process
The production of one particular low molecular weight resin
product (a proprietary dispersant) results in the generation of
two significant waste streams and will be considered here as a
separate process description.
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Burnable
Compopijfy
Absorbed:, ,
Monomers
- v- 4
Miscellaneous
Other
Chemicals
Depending on
the Product
Acrylic
Emulsion
Used Filters,
Clumps, Waste water
Storage Tanks or
Drums
Unsalable Product
Figure 1. Abbreviated flow diagram for the acrylic emulsion and LMW resin process.
Xylene, diisobutylene (DIB), and other monomers and addi-
tives are pumped to the reactors in the LMW resin production
line. In a batch production, polymers are formed in the reac-
tors. The product is pumped to a separation tank where the
unwanted heavier DIB settles to the bottom of the tank and the
lighter-fraction product is decanted from the top. An emulsion-
like interface composed of DIB and product is formed between
the product and the DIB layers and is removed from the tank
and shipped offsite as a hazardous waste. Some of the DIB
solvent from the separation tank is drained to a storage tank
where further separation by settling occurs. Product/DIB inter-
face is removed from this storage tank and is shipped offsite as
hazardous waste. The DIB wet solvent from this tank is pumped
to the boiler and burned. Recovered xylene/DIB mixture from
the separation tank is returned to the reactor.
From the separation tank, the upper layer product fraction is
decanted into another separation tank. Water is separated
from the product and pumped to the plant's water treatment
system. The product is pumped to a blend tank from which
more DIB wet solvent is removed and burned in the boiler. The
product is then pumped either to storage tanks or to drums for
shipping. An abbreviated flow diagram for the dispersant pro-
cess is shown in Figure 2.
Herbicide/Specialty Chemical Production
Ingredients are mixed together in a pressure- and temperature-
regulated reactor where a specified reaction occurs. Absorbed
propionic acid waste is generated from the loading and unload-
ing of material. High- and low-acidic content propionic acid
wastes are generated by the reactions. Highly acidic propionic
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Raw Material
Reactors
Separation Tank
pH and Solids
Adjustment
/Excess DIB\
Blend Tank
Decanted DIB
Storage Tanks
or Drums
Figure 2. Abbreviated flow diagram for the dispersant process.
acid is recycled back into the reactors for use in further pro-
cessing. The low-acidic content propionic acid is pumped to
the wastewater treatment system where it is used to neutralize
caustic wastewater from other plant operations.
From the reactor, the product is pumped to a blend tank to
which other chemicals and emulsifiers are added; these sub-
stances reduce the viscosity of the product. Several wastes are
generated from the annual cleaning of the reactor and blend
tank including wastewater that is pumped to the wastewater
treatment system, herbicide residue, and herbicide articles
(contaminated employee clothing). From the blend tank, the
products are loaded onto railcars and shipped. An abbreviated
flow diagram for the herbicide/specialty chemical process is
shown in Figure 3.
Pollution Abatement (PA) System
This plant uses a pollution abatement system to remove va-
pors from various areas of the plant including the monomer
storage area, tanks in the resin production area, and the
reactors and holding/premixing tanks in the emulsion produc-
tion line. This system was installed mainly to remove vapors
with persistent irritating odor from the plant.
A blower located down the line creates a pressure difference
and pulls fresh air over the tanks mentioned above. Vapors
collected from the monomer storage area and resin area tanks
are blown to separate liquid knock-out tanks. These tanks act
as condensers and use ambient air cooling to condense a
portion of the vapors. The resulting condensate from these
tanks is directed to the water treatment facility. From the
knock-out tanks, the vapors are ducted through separate lower
explosive limit (LEL) monitors that evaluate the flammability of
the vapors. From the monitors, the vapors are directed through
backfire preventers that act as safety valves and prevent va-
pors from being drawn back through the system.
Vapors from the reactors and feed tanks in the emulsion line
follow a similar route through the PA system; however, they
are first ducted through a caustic scrubber. Caustic solution is
added to this scrubber as well as 150 gal/min of water to
remove particulates from the fumes. This solution is dumped to
the water treatment system every 11 days. The vapors are
then directed through a liquid knock-out tank (from which water
is pumped to water treatment), through a backfire preventer,
and then through an LEL monitor.
From that monitor, the vapors pass through a blower, another
backfire preventer, and finally most of the vapors (99.97%)
enter a natural gas-fired thermal oxidizer at MOOT.
Wastewater Treatment System
Another onsite waste treatment facility this plant has installed
is its wastewater treatment system. Wastewater from the emul-
sion line and the resin line, laboratory wastewater, and air
compressor and other cooling water are directed to this facility
for treatment. All incoming water passes through a roto-strainer
that removes suspended solid particulates. The solid waste
falls into two hoppers and is eventually hauled offsite to a
landfill.
From the roto-strainer, the water enters a neutralization tank
where carbon dioxide and low acidic propionic acid from the
herbicide line are added for neutralization. The water then
enters a second neutralization tank where the water is agitated
to promote further neutralization. Next, the wastewater enters
three open-air mixing basins in which sludge is allowed to
settle to the bottom. Sludge is removed quarterly to landfill.
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Excess
High
Strength
Propionic
Acid
Excess Low
Strength
Propionic Acid
to Wastewater
Treatment
Figure 3. Abbreviated flow diagram for the herbicide/speciality chemical process.
The effluent wastewater is released to the municipal sewer.
Total water discharged from the plant on an annual basis is
approximately 126 million gal/yr.
Existing Waste Management Practices
• A pollution abatement system removes noxious and odor-
ous vapors from the plant and incinerates them.
• Off-grade monomers and polymers are reused in an effort
to produce salable products.
• Diisobutylene wet solvent is burned in an onsfte boiler.
Waste Minimization Opportunities
The type of waste currently generated by the plant, the source
of the waste, the quantity of the waste, and the annual treat-
ment and disposal costs are given in Table 1.
Table 2 shows the opportunities for waste minimization that the
WMAC team recommended for the plant. The type of waste,
the minimization opportunity, the possible waste reduction and
associated savings, and the implementation cost along with the
payback time are given in the table. The quantities of waste
currently generated by the plant and possible waste reduction
depend on the production level of the plant. All values should
be considered in that context.
It should be noted that, in most cases, the economic savings of
the minimization opportunities result from the need for less raw
material and from reduced present and future costs associated
with waste treatment and disposal. Other savings not quantifi-
able by this study include a wide variety of possible future
costs related to changing emissions standards, liability, and
employee health. It should also be noted that the savings given
for each opportunity reflect the savings achievable when imple-
menting each waste minimization opportunity independently
and do not reflect duplication of sayings that would result when
the opportunities are implemented in a package.
This research brief summarizes a part of the work done under
Cooperative Agreement No. CR-814903 by the University City
Science Center under the sponsorship of the U.S. Environmen-
tal Protection Agency. The EPA Project Officer was Emma Lou
George. ;
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Tsble 1. Summary of Waste Generation
Waste Generated
Source of Waste
Annual Quantity Annual Waste
Generated Management Cost ($)
Burnable liquids
Composited absorbed monomers
Off-grade methylolacrylamide/
acrylamlde
Used filters and trapped product
Unsalable low molecular weight
resins
Diisobutylene (DIB) wet solvent
Off-grade mixtures and bad reactions in the
acrylic emulsion and low molecular weight resin
production lines.
Spillage and clean-up of reactors in the
acrylic emulsion and low molecular weight resin
production lines.
Off-grade batches of product in the acrylic
emulsion and low molecular weight resin
production lines
Filtering process in the acrylic emulsion
production line.
Expired products and off-grade batches of products
in the low molecular weight resin production line.
Spent solvent from the dispersant production line.
DIB wet solvent is sent to an onsite thermal
oxidizer.
15,400 Ib
15.400 Ib
5,100 Ib
44,800 Ib
20,880 Ib
316,220 Ib
77,110
77,110
40,760
33,080
116,200
24,500
Product/DIB Interface
Absorbed proplonic acid
Contaminated employee clothing
Herbicide residue
Cold stack gases (noxious,
odorous, and organic vapors
drawn from monomer storage
area, tanks in resin line, and resin
reactors and tanks)
Wastewater sludge
Wastewater
Separation tank in the dispersant production line.
Spillage in the herbicide/specialty chemical
production line.
Herbicide/specialty chemical production line.
Cleaning of the reactor and blend tank in the
herbicide/specialty chemical production line.
Thermal oxidizer and heat exchanger in the
Pollution Abatement System.
Onsite wastewater treatment system.
Onsite wastewater treatment system.
25,750 Ib
6,000 Ib
*
1,000lb
394,200 ff
300,000 Ib
126,000,000 gal
79,860
13,510
*
24,150
0"
456,800
2,121,700
'New waste; no data available.
"There are no direct costs reported for handling evaporative waste.
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Table 2. Summary of Waste Minimization Opportunities
acrylamide
Unsalable product
Annual Waste Reduction
Net Annual Implementation Payback
Waste Generated
Burnable liquids
Composited absorbed
monomers
Off-grade
methylolacrylamide/
Minimization Opportunity
Upgrade the redundant
sensing and control
devices on the reactor
raw material lines to
reduce the amount of off-
specification product
batches.
Quantity
7 1,550 to
2,890 Ib
3,480 to
Percent
75
19
71
Savings ($) Cost ($)
139,810 365,480
Years
2.6
3,130 Ib
15
Wastewater sludge
Install a natural gas-fired
dry-off oven in the waste-
water treatment system to
reduce the amount of
sludge removed to the
landfill.
244,030 Ib
81
92,730
70,320
0.8
•&U.S. GOVERNMENT PRINTING OFFICE: 1992 - 648-080/40271
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United States
Environmental Protection
Agency
Center for Environmental
Research Information
Cincinnati, OH 45268
BULK RATE
POSTAGE & FEES PAID
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EPA/600/S-92/004
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