Evaluation of Benzene-Related Petroleum Processing Operations


&EFA
            United States
            Environmental Protection
            Agency
           Office of Air Quality
           Planning and Standards
           Research Triangle Park NC 27711
EPA-450/3-79-022
October 1978
            Air
Evaluation of Benzene-
Related  Petroleum
Processing  Operations

-------
                                     EPA-450/3-79-022
  Evaluation of  Benzene-Related
Petroleum Processing Operations
                        by

               Dr. Terry Briggs and Vijay P. Patel

                 PEDCo Environmental, Inc.
                   11499 Chester Road
                  Cincinnati, Ohio 45246
                 Contract No. 68-02-2603
                     Project No. 20
              EPA Project Officer: Kent C. Hustvedt
                     Prepared for

           U.S. ENVIRONMENTAL PROTECTION AGENCY
               Office of Air, Noise, and Radiation
            Office of Air Quality Planning and Standards
           Research Triangle Park, North Carolina 27711

                     October 1978

-------
This report is issued by the Environmental Protection Agency to report
 technical data of interest to a limited number of readers.  Copies are
 available free of charge to Federal employees, current contractors and
 grantees, and nonprofit organizations - in limited quantities - from  the
 Library Services Office (MD-35), U.S. Environmental Protection Agency,
 Research Triangle Park, North Carolina 27711; or for a nominal fee,
 from the National Technical Information Service, 5285 Port Royal Road,
 Springfield,Virginia 22I6I.
 This report was furnished to the Environmental Protection Agency by
 PEDCo Environmental, Inc.,  11499 Chester Road, Cincinnati, Ohio 45246,
 in fulfillment of Contract No. 68-02-2603. The contents of this report are
 reproduced herein as received from PEDCo Environmental, Inc.  The opinions,
 findings, and conclusions expressed are those of the author and not necessarily
 those of the Environmental Protection Agency.  Mention of company or product
 names"is not to be considered as an endorsement by the Environmental Protection
 Agency.
                        Publication No. EPA-450/3-79-022

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                            CONTENTS

                                                            Page

Figures                                                      iv
Tables                                                       iv
Acknowledgment                                               vi

1.   Introduction                                             1

2.   Survey of Benzene-related Petroleum Processing
     Operations                                               2
     2.1  Survey Results                                      2
     2.2  Generalized Process Descriptions                    7

3.   Process Descriptions                                    16
     3.1  Glycol BTX Process                                 16
     3.2  Sulfolane Process                                  24
     3.3  Other Aromatic Solvent Extraction Processes        29
     3.4  Toluene Dealkylation Processes                     29
     3.5  Toluene Disproportionation Processes               36

4.   Model Plant Development                                 40

Appendix

A.   Estimation of Benzene Emission From Receiver Vents      50
                               111

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                             FIGURES


No.                                                         Page

2-1  Refinery block flow diagram showing location of
     solvent extraction and toluene dealkylation units        9

2-2  Simplified process flow diagram of a sulfolane unit    10

2-3  Simplified process flow diagram of a glycol BTX unit   12

2-4  Simplified process flow diagram of BTX fractionation   12

2-5  Simplified process flow diagram of a toluene
     dealkylation unit                                      14

3-1  Flow diagram of a glycol BTX unit process              19

3-2  Sulfolane unit process flow diagram                    25

3-3  Process flow diagram of a toluene hydrodealkylation
     unit                                                   31



                             TABLES

No.                                                         Page

2-1  Results of Survey of Refinery Benzene Processes         3

2-2  Analysis of Reformate Aromatics                        11

3-1  Properties of Selected Solvents                        18

3-2  Glycol BTX Unit Material Balance                       22

3-3  Typical Operating Conditions of a Glycol BTX Unit       23

3-4  Sulfolane Unit Material Balance                        27
                               IV

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                       TABLES (continued)

No.                                                         Page

3-5  Sulfolane Unit Operating Conditions                     28

3-6  Toluene Dealkylation Unit Material Balance               33

3-7  Comparison of Toluene Dealkylation Yields Based  on
     Different Feed Compositions                             34
                                     t
3-8  Toluene Dealkylation Unit Operating Conditions           35

4-1  Sulfolane Unit Pump Listing                             41

4-2  Listing of Valves in Sulfolane Units                    42

4-3  Relief Valves on Sulfolane Unit Listing                 42

4-4  Sulfolane Unit Sample Connection Listing                43

4-5  Glycol BTX Unit Pump Listing                            44

4-6  Glycol BTX Unit Valve Listing                           45

4-7  Glycol BTX Unit Relief Valve Listing                    45

4-8  Glycol BTX Unit Sample Connections Listing               46

4-9  Toluene Dealkylation Unit Pump Seal Listing             46

4-10 Toluene Dealkylation Unit Valve Listing                 47

4-11 Toluene Dealkylation Unit Relief Valve Listing           47

4-12 Connection for Toluene Dealkylation Unit Sample
     Valve Listing                                           48
                               v

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                         ACKNOWLEDGMENT






     This report was prepared by PEDCo Environmental,  Inc.,  under



the direction of Mr. Richard W. Gerstle.  The PEDCo Project



Manager was Dr. Terry Briggs.  Dr. Briggs and Mr.  Vijay P.  Patel



were the principal authors.  Mr. Kent C. Hustvedt was  the Project



Officer for the Office of Air Quality Planning and Standards.
                               VI

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                            SECTION 1



                          INTRODUCTION






     The classification of benzene as a hazardous air pollutant



prompted an investigation by the Environmental Protection Agency



(EPA) regarding the need for hazardous air pollutant standards



under Section 112 of the Clean Air Act.  This assessment of



benzene emissions from petroleum-based operations that process



liquids with high concentrations of benzene is part of this



effort.  The refinery processes included in the assessment are



aromatics solvent extraction, toluene hydrodealkylation, toluene



disproportionation, and benzene-toluene-xylene (BTX) fractiona-



tion.



     Section 2 presents the results of a survey of all domestic



petroleum-based producers of benzene and identifies the relevant



processes and their capacities  (when they are known).  Section 3



describes all the major operations identified and presents



typical operating characteristics and simplified material bal-



ances, focusing particular attention on the benzene concentration



in each process flow stream.  Section 4 identifies model plants



for sulfolane, glycol BTX, and toluene deal kylation processes,



and includes a listing of major equipment.

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                            SECTION 2

    SURVEY OF BENZENE-RELATED PETROLEUM PROCESSING OPERATIONS


     All domestic petroleum refineries producing benzene were

surveyed to collect information on benzene-producing processes.

This information was needed to assure that all relevant processes

would be identified and described in this report.  These proc-

esses are also introduced with brief process descriptions.


2.1  SURVEY RESULTS

     Table 2-1 presents the results of the survey of refinery

chemical plants.  It lists all the plants that process petroleum

or petroleum fractions and produce benzene for sale or inter-

mediate use.  Whenever possible, data were obtained from the

literature, '   from EPA files, or through personal contact with

EPA State and Regional officials.  When no data were available,

specific refineries were contacted directly.  A few plants had

still not responded as of the date of this report.

     All but 5 of the 45 plants reported to have solvent extrac-

tion processes had glycol* or Sulfolane solvent processes.  The

remaining five had the Aromex process (one plant uses two units,
*
 The specific gylcol solvent is listed when known; otherwise the
 term UDEX is employed.  Throughout the report the term glycol
 BTX process will be used to describe solvent extraction proc-
 esses containing glycol solvents.

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                 TABLE 2-1.  RESULTS OF  SURVEY OF REFINERY BENZENE  PROCESSES
State
California


Delaware
Illinois

Kansas
Kentucky
Louisiana


Company
Atlantic
Richfield
Chevron
Chevron
Getty
Shell Oil
Union Oil
Skelly Oil
(Getty)
Ashland Oil
Cities
Service
Exxon
Gulf Oil
City
Wilmington
El Segundo
Richmond
Delaware
City
Wood River
Lemon t
El Dorado
Ashland
Lake
Charles
Baton Rouge
Alliance
Solvent extraction
Process
TEGC
solvent
Phenol
UDEXC
UDEXC
Sulfolanec
UDEXC
UDEXC
Sulfolanec
Lurgic
UDEXC
Sulfolanec
Throughput,
103 bbl/day

4.0C
1.2C
8.1e
34C
11. 4C
4.8C
4.0e
12. Oc
15C
11. le
TDAa
Process







HDA


THDC
Throughput,
103 bbl/day







2.5a


5.4e
Benzene
produced ,
10 3 bbl/day
0.78d
1.5c'd

0.75C
2.7b - 2.9d
l.ld
0.85d
4.1d
1.5 - 1.6C
1.6C
4.6d
4.6d
Comments

Phenol used in
an azeotropic
process
Produces a BTX
mixture
Vapor recovery
at loading
area and on
tank vents



Relief valves
vented to flares
Process vents to
flares are monitor-
ing benzene;
N-methyl per-
ibidone solvent
used

Closed drains and
sump system
U)
    (continued)

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TABLE 2-1. (continued)
State
Louisiana
(continued)

Michigan
Mississippi
New Jersey
New York
Ohio
Oklahoma
Pennsyl-
vania

Company
Penzoil
United
(Atlas
Refinery)
Tenneco
Union
Carbide
Dow Chem.
Chevron
Texaco
Ashland
Oil
Sun Oil
Sun Oil
Gulf Oil
Sohio
(BP oil)
Sun Oil
City
Shrcvepor t
Chalmette
Taft
Bay City
Pascagoula
Westville
North
Tonawanda
Toledo
Tulsa
Philadelphia
Marcus Hook
Marcus Hook
Solvent extraction
Process
Phono lc
Sulfolanec
TEGC

Sulfolanec
Sulfolanec
Sulfolanec
TEGC
UDEXC
TEGC
UDEX
TEGC
Throughput,
103 bbl/day

14e

12C

7.6C
14. 7C
5.5C
14. OC

14. Oc
TDAa
Process

HDAC
Hydeal0
THDC

TDPC
Throuahput ,
103 bbl/day

4.2C
0.95C
2.2C

3.6C
Benzene
produced,
103 bbl/day
1.0C
0.6C
0.65C
4.6^
1.96d

2.3-J
0.8C
1.54
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TABLE 2-1. (continued)
State
Puerto
Rico

Texas

Company
Commonwealth
Oil
Phillips
American
Retrof ina
(Cosden Oil)
Amoco

Atlantic
Richfield

Champlin
(Union
Pacific)
Charter
Interna-
tional
Crown
Central
Petroleum
Coastal
States

Dow Chem.
Exxon
Gulf Oil

City
Ponce

Guayama
Big Spring

Texas City

Houston

Corpus
Christi

Houston

Corpus
Christi

Free port
Baytown
Port Arthur

Solvent extraction
Process
Sulfolanec

Aromexc
(Two units)

Sulfolane
(Two units)
Sulfolane0

UDFX and
Sulfolane

UDEXC

Sulfolane0

Sulfolane
TEC0

Throughput,
103 bbl/day
12. 5C

5.0°

48.8, 17.0°

10. 6e

8.0°

2.2°

50. 0C
24. 0C

TDAa
Process

HDA°
HDAC

Dispro-
portiona-
tion unit

Detol0

Hydealc

Throughput,
103 bbl/day

7.2°
4.0C

6.0e

Benzene
produced,
103 bbl/day
12. 1^

7.2d
2.9C
3.6
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TABLE 2-1 (continued)
State
Texas

Virgin
Islands
Company
Howe 11

Independent
Refining
Marathon
Oil
Mobil
Monsanto

Phillips

Quintana
Howe 11
Shell Oil
Shell Oil
South-
western
Sun Oil

Texaco
Union Oil
Amer.
Petrof ina
Americal
Petrofina
Amerada
Hess
City
San Antonio

Winnie

Texas City

Beaumont
Chocolate
Bayou
Sweeney

Corpus
Christi
Deer Park
Odessa
Corpus
Christi
Corpus
Christi
Port Arthur
Beaumont

Port Arthur

St. Croix

Solvent extraction
Process
Arosorb

UDEXC

TEGC

Sulfolane

Sulfolane0
UDEXC
Sulfolane

UDEXC

UDEXC
UDEXC

Sulfolane
(Two units)
Throughput,
103 bbl/day
0.75C

0.4e

6.3C

7.9C

7.2C

10. 5C

16. Oe
0.8C
1.1

11. 0C

5.4C

50. Oc

TDA3
Process

HDAC

Hydeal0

HDAC

Throughput ,
103 bbl/day

8.16

0.8d

1.8C

1.04°

Benzene
produced ,
103 bbl/day

0.20

Q.55d
0.39d (1978)
3.9d
5.5°'d

1.4d - 0.65d
(1978)
0.8d - 5.87d
(1978)
5.87d

1.8d
2.3C (1978)
2.93d
1.4d

1.3d
0.8C
4.24d

Comments
Does not produce
pure benzene

No information
Most benzene
production is from
pyrolysis gasoline"

No information
Flare off-gases

TDA = Toluene Dealkylation.

Where specific glycol solvent is known, it is presented; otherwise, glycol
BTX process is designated as UDEX.

c Data from telephone or written conversation with EPA Regional officials,
EPA state officials, or direct plant contacts.

d SRI Chemical Directory 1978.

' Data taken from The Oil and Gas Journal Annual Refining Survey, March 20, 1978.
-------
two use a solvent extraction process using phenol with an

azeotropic separation, one uses the Arosorb process, and the

remaining plant uses the Lurgi process, which uses n-methyl

peribidone as the solvent. Feed rates were reported for 17 of 18

Sulfolane units and 18 of 23 glycol BTX units. Based on these

data the mean Sulfolane unit feed rate is 2576 m /day (16,200

barrels/day) and the median rate is 1908 m /day (12,000 barrels/

day) '. The corresponding glycol BTX unit mean is 1522 m /day

(9300 barrels/day) and the median is 1244 m /day (7600 barrels/

day). Of the units with a feed rate greater than 2455 m /day

(15,000 barrels/day), five used the Sulfolane process and one

used glycol BTX.

Although fewer plants use toluene dealkylation units, the

variety of processes was greater. As shown in Table 2-1, 14

plants have toluene dealkylation units and two plants have a

toluene disproportionation process. Plants having toluene deal-

kylation units reported the following processes: Hydeal, Detol,

Hydrodealkylation (HDA), and Thermal Hydrodealkylation (THD).

Based on the 12 plants that reported the feed rates of their

toluene dealkylation process, the mean feed rate is 573 m /day

(3500 barrels/day) and the median feed rate is 540 m /day (3300

barrels/day).

2.2 GENERALIZED PROCESS DESCRIPTIONS

The operating processes of interest are solvent extraction,

toluene dealkylation, and toluene disproportionation. These

processes are briefly introduced in this section, primarily to

describe how they fit into the overall refinery processing
-------
picture. Figure 2-1 presents a block flow diagram of an inte-

grated modern petroleum refinery. As the figure indicates, feed

to the solvent extraction (shown as BTX extraction) unit is in

the gasoline-blending-stock boiling range (60 to 204°C or 140° to

400°F). Feed is normally prefractionated to remove low- and

high-boiling-range components.

2.2.1 Solvent Extraction

Solvent extraction selectively separates aromatics from the

remaining paraffins in the hydrocarbon feed stream. The high-

purity aromatics are then fractionated to produce individual

aromatic products. Reformate, the major solvent extraction

feedstock, is formed by the catalytic reforming of the naphtha-

boiling-range hydrocarbons (93° to 190°C or 200° to 375°F) from

crude oil. Reforming provides the refiner with the flexibility

to meet motor fuel and aromatics production needs. Operating

conditions can be varied over relatively narrow limits so that

increased severity of catalyst operating conditions reduces yield

while increasing the reformate octane number. This is usually

accomplished by simultaneously increasing aromatic yield and

decreasing the concentration of heavy paraffins. The typical

aromatics concentration in high-octane reformates is 45 to 70

4
volume percent. While severity adjustments account for a por-

tion of this variation, the chemical composition of the naphtha

feed is the major factor affecting aromatics content. Table 2-2

presents a breakdown of the aromatics in different reformates.

The high-octane blending values shown for these aromatics

8
-------
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Figure 2-1. Refinery block flow diagram showing location of solvent extraction
and toluene dealkylation units.3
-------
EXTRACT
RECOVERY
EXTRACTOR
CHARGE
EXTRACTIVE! "ly COLUMNJT
. STRIPPER A D p^
w»
I
r
RAFFINATE
RAFFINATE
WATER
WASH
J
•^ 6
Figure 2-2. Simplified process flow diagram of a Sulfolane unit.
-------
indicate their value in raising the octane ratings of a motor

gasoline pool. Other feed streams to solvent extraction units

are pyrolysis gasoline (primarily from ethylene plants) and other

refinery hydrocarbon streams containing light aromatics.

Solvent extraction feed is normally prefractionated to

remove light ends (C5 hydrocarbons) and also heavy ends (C_

hydrocarbons). Some plants also remove C_ and/or C0 hydrocar-
/ o

bons, resulting in a C, or C,-C_ feed stream for benzene and

toluene production only.

Table 2-2. ANALYSIS OF REFORMATS AROMATICS
Source
Benzene
Toluene
Ethylbenzene
P-xylene
M-xylene
O-xylene
Cg aromatics
Volume % of reformate
A4
5
24
4
4
9
5
4
B5
3.5
13.9
3.6
4.5
10.1
5.2
31.4
c6
2.2
17.3
7

28.6
18.8
Octane blending
values4
0 g Pb
108
112
113
114
114
100
103
3 g Pb
112
115
116
115
116
96
107
Figure 2-2 presents a simplified flow diagram of a Sulfolane

unit handling.a reformate charge, and Figure 2-3 shows a similar

diagram for a glycol BTX unit. Extract refers to the aromatics

stream, and the raffinate refers to the remaining paraffin stream

separated from the reformate. After it is treated, raffinate is

normally used for gasoline blending or olefin plant feedstock.

As shown in Figure 2-4, the extract from glycol BTX or sulfolane

units is fractionated into individual components.
11
-------
EXTRACTOR
STRIPPER
LEAN SOLVENT"
FEEDSTOCK
START —«
REFLUX
RICH SOLVENT
RAFFINATE
WATER WASH
RAFFINATE
AROMATICS
WATER WASH
PRODUCT
. . 6
Figure 2-3. Simplified process flow diagram of a glycol BTX unit.
START
EXTRACT
FEED
CLAY
TOWERS
tvl
CD

I
I
L
XYLENES

•-TOLUENE

•-BENZENE
Figure 2-4.
Simplified process flow diagram of BTX
fractionation.4
12
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2.2.2 Toluene Dealkylation

Toluene dealkylation processes are used to increase benzene

production by the conversion of toluene to benzene. The attrac-

tiveness of this process depends on the price difference between

benzene and toluene. Because this price differential fluctuates,

the process is sometimes operated on an intermittent basis.

Process feed toluene normally comes from a solvent extraction

unit or is purchased. The feed stream is normally either pure

toluene or a toluene-rich hydrocarbon.

Figure 2-5 presents a simplified process flow diagram of a

Hydeal unit. The process flow of other toluene dealkylation

units is similar. These cracking processes use heat and a

hydrogen atmosphere to convert toluene and other higher aromatics

to benzene and methane. Some processes use a fixed-bed catalyst;

the rest are thermal processes. Unreacted toluene in the reactor

effluent is recycled back to the feed after fractionation.

Although at least three toluene disproportionation processes

are available, only one unit was reported to be in operation in

the United States. The process flow of these processes is sim-

ilar to toluene dealkylation; however, these catalyzed processes

convert toluene to benzene and xylenes. The yield ratio of

4
benzene to xylene is variable.
13
-------
HEATER REACTOR
SEPARATOR STABILIZER
BENZENE
COLUMN
MAKEUP
GAS
A
A P
ALKYLBENZENE
Figure 2-5. Simplified process flow diagram of a toluene
dealkylation unit (Hydeal unit shown).7
-------
REFERENCES FOR SECTION 2
1. Ailleen Cantrell. Annual Refining Survey. The Oil and Gas
Journal, Vol. 76, March 20, 1978. pp. 108-140.

2. Stanford Research Institute Directory of Chemical Producers.
Menlo Park, California, 1978.

3. Maclean, W.D. Construction site selection - A U.S. view-
point. Hydrocarbon Processing, June 1977. pp. 111-116.

4. Mager, E.M. Aromatics Production. In: U.S. Petrochem-
icals, A.M. Brownstein, ed., Petroleum Publishing Co.,
Tulsa, Oklahoma, 1972.

5. Pollitzer, E.L., J.C. Hayes, and V. Haensel. The Chemistry
of Aromatics Production via Catalytic Reforming in Refining
Petroleum for Chemicals. In: America Chemical Soc. Advances
in Chemistry, L.J. Spillane and H.P. Lefton, eds, Series 97,
Washington, D.C., 1970.

6. Refining Handbook. Hydrocarbon Processing, 55(9), September
1976. pp. 216-217.

7. Refining Handbook. Hydrocarbon Process, 47(9), September
1968. p. 189.
15
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SECTION 3

PROCESS DESCRIPTIONS

This section presents detailed process descriptions of

solvent extraction, toluene dealkylation, and BTX fractionation,

and identifies potential atmospheric emission sources. It also

serves as a basis for the information on atmospheric emissions

presented in Sections 4, 5, and 6. The Sulfolane, glycol BTX,

and toluene dealkylation processes are addressed separately. The

fractionation associated with each process is included in each

process description.

3.1 GLYCOL BTX PROCESS

Glycol BTX processes rely on the greater solubility of

aromatic hydrocarbons in a glycol solvent compared with that of

the paraffinic components of a feed stream. Several glycol

solutions have been used in these processes, including a solution

of diethylene glycol and water, diethylene and dipropylene

glycols, and water and tetraethylene glycol .(TEG) . The tendency

in the refining and chemical industry is to use higher-molecular-

weight glycols to increase the benzene-producing capacity and

simultaneously recovering more of the higher-molecular-weight

1 2
hydrocarbons and reducing operating costs. ' Glycol solvent

systems can be changed by minor equipment modifications that in-

volve no change in royalty status; therefore it is not uncommon

16
-------
2
for refineries and chemical plants to switch solvents. This

report is restricted to a glycol BTX unit using TEG solvent

because TEG is commonly used by refiners and because it is the

solvent used at all four refineries with glycol BTX units visited

by PEDCo in conjunction with this project. Although plant oper-

ation is similar when different solvents are used, flow ratios

vary. (See Table 3-1.) Table 3-1 also shows solvent properties,

including those for Sulfolane.

The glycol BTX unit feed stream is normally reformate;

however with proper feed treatment, other refinery feed streams

containing aromatics can be used. Reformate used for aromatic

extraction is normally prefractionated to give a Cfi-Cp fraction

for BTX production or a Cg-C7 fraction when only benzene and

toluene are recovered. To obtain these "heart-cut" reformate

fractions, reformate is first depentanized to remove C5 paraffins

then a second fractionator removes hydrocarbons with higher

boiling points.

Figure 3-1 presents a process flow diagram of a typical

glycol BTX unit using a TEG solvent. The drawing has been sim-

plified, particularly with regard to the heat exchangers and

control loops on control valves. Aromatics are separated from

the feed by the solvent in the trayed rotating disc extractor or

sieve tray extractor by the liquid-liquid solvent extraction

method. Aromatics-free raffinate leaves the top of the extractor,

while the solvent containing dissolved aromatics (rich solvent)

leaves the bottom. The light hydrocarbon reflux strips paraffins

from the rich solvent. The rich solvent goes to the stripper,

17
-------
TABLE 3-1. PROPERTIES OF SELECTED SOLVENTS'
Solvent name
Molecular weight
Specific gravity 20/20'C
Normal boiling point, "C ("F)
Freeze point, "C (°F)
Viscosity, cst at 50°C
cst at 20°C
Flash point, open cup °C (°F)
Specific heat at 300°F, Btu/lb
Pure solvent
Solvent + 10% water
Latent heat or vaporization
(Btu/lb) J/g
Extraction temperature, °C (°F)
Recovery column bottom
Temperature, °C (°F)
Pressure, psig (mmHg)
Water, wt. »
Solvent/feed vol. ratios
Reflux/feed vol. ratios
Price, $/kg (S/lb)
Diglycolamine
105
1.06
221(430)
-9.4 (15)
8
30
127 (260)

0.68
0.72

510 (220)
121-149 (250-300)

149-177(300-350)
6
3-10
3-4
0.6-0.9
0.605(0.275)
Diethylene
glycol
106
1.12
246 (474)
-7.8 (18)
10
32
143 (290)

0.65
0.71

557 (240)
132-154 (270-310)

149-154 (300-310)
6
8-10
6-8
1.0-1.4
0.209(0.095)
Depropylene
glycol
134
1.02
231 (448)
Super cools
10
90
127 (260)

0.58

TEG
194
1.13
Decomp.
-3.9 (25)

55
182 (360)

0.52

132-154(270-310)

149-154(300-310)
6
5-10
4-5
0.7-1.0
0.363(0.165)
Sulfolane
120
1.27
Decomp .

0.43

93 (200)

177 (350)
(500)
0.5
2-3.5
0.5
1.38(0.63)
CD
Note: Some of these properties and data are rough estimates.
-------
UHs "*
FC riOM CH«PT

1C LEVEL CONTROL

PC PRESSURE CONTROL
Figure 3-1. Flow diagram of a glycol BTX unit process.
3,4,5
-------
where the extract is steam-stripped from solvent and light ends.

A significant amount of extract purification (nonaromatics

separation) also takes place in the stripper. The stripper feed

goes through a two-stage flash to remove the light ends and

water, which go to the stripper receiver. The stripper separates

hydrocarbons from the solvent and strips nonaromatics from the

extract. The extract is removed as a side-cut, and the lean

solvent is the bottom fraction. Both the extract and raffinate

are water-washed to remove any dissolved solvent before they go

to fractionation and gasoline blending. After the extract is

heated, it flows through a clay tower that removes any olefins

present. The pure benzene, toluene, and xylenes are separated by

conventional fractionation. Benzene is sometimes drawn off as a

side-cut near the top of the benzene column to remove paraffinic

and water impurities. The toluene product normally contains

considerably less than 1 percent benzene.

The solvent regenerator and solvent filters, which remove

liquid and solid impurities (primarily due to solvent degrada-

tion) in the solvent, are operated on an intermittent basis

456
and/or as a small slip stream. ' ' Some plants have replaced

5 8
the solvent regenerator with a charcoal filter bed. ' The water

still, which removes solvent from the recirculation water, can

also be operated on an intermittent basis. '
20
-------
Table 3-2 presents a simplified materials balance for a

glycol BTX unit (based on a Cg-C., feed).* Table 3-3 gives the

operating conditions of some of the major process streams.

3.1.1 Glycol BTX Unit Emission Sources

Benzene and total hydrocarbon emission sources in glycol BTX

units (as well as Sulfolane and toluene dealkylation units) can

be classified into two groups: process vents and fugitive

emissions. Categories of potential onsite fugitive emissions

that are common to each process are control, process, and relief

valve leaks; pump seal leaks; sampling connections; wastewater

sump; and flange leaks. Although some glycol BTX units do not
4 5
vent receivers to the atmosphere, ' others vent certain ones,

notably the stripper overhead receiver and benzene column re-

ceiver. In some instances extract and toluene column receivers

are also vented to the atmosphere. A natural gas sweep is com-

monly used on the process receivers to keep their pressure from

going negative.

No data are available on emission rates. Estimates are

shown in Appendix A. Vent rates depend on receiver liquid com-

position, gas-sweep rate and composition, and receiver pressure.

Because most volatile fractions in the feed (C^'s) that dissolve

in the solvent go to the stripper overhead receiver, its vent

would have the highest off-gas rate. These atmospheric emissions

can be eliminated by reducing C5's in the feed and routing these
*
The material balances presented in Section 3 (for glycol BTX,
Sulfolane, and toluene dealkylation units) do not represent
operating conditions in any specific unit. Engineering judge-
ment was used where data were lacking.
21
-------
tv)
TABLE 3-2. GLYCOL BTX UNIT MATERIAL BALANCE2'4'5'6'7
(Basis 7500 bbl/day feed)

Extractor - Feed
- Lean solvent
- Rich solvent
- Raffinate
- Light HC reflux
Stripper-Extract
to benzene column
Benzene product
Toluene column feed
Toluene product
Toluene column bottoms
Composition, wt *
, Flow Rate
m /d (bbl/day)
1193 (7,500)
4771 (30,000)
5144 (32,350)
819 (5,150)
1193 (7,500)

382 (2,400)
163 (1,025)
219 (1,375)
195 (1,225)
24 (150)
Benz
14.0

3.2
0.5
45.0

42.7
99.9
0.1
0.1

Tol
17.0

3.8
1.0
30.0

51.1
0.1
99.0
99.9
0.5
Xyl
2.0

0.5

6.2

98.0
C_Arom
0.1

1.5
Paraf
67.0

97.5
25.0

Solv

90.0
92.5
1.0

"2°

10.0

-------
to
U)
TABLE 3-3. TYPICAL OPERATING CONDITIONS OF A GLYCOL

BTX UNIT4'5'6'7
Extractor - top
Stripper - top flash drum
Stripper - second flash
drum
Stripper receiver, extract
receiver
Benzenes toluene column
receivers
Solvent regenerator
receiver
Temperature,
°C (°F)
135-149 (275-300)

38 (100)

38 (100)
Pressure,
kPa (psig)
689-827 (100-120)
172-345 (25-50)

34-69 (5-10)

3.4 (0.5)

68.9 (~10)
-------
vents to flare headers or using hot-vapor bypass or comparable

pressure-control systems.

3.2 SULFOLANE PROCESS

The Sulfolane process, a more recent development than the

glycol BTX unit, has come into common use because the solvent

2
properties of Sulfolane are superior to any of the glycols. As

shown in Table 2-1, all but one of the solvent extraction units

with a feed capacity greater than 15,000 barrels/day use the

Sulfolane process. Major factors preventing refineries from

switching to Sulfolane on existing glycol BTX units are the major

2
equipment changes and high royalty rates involved. Tetrahydro-

thiophene dioxide (the solvent used in the Sulfolane process) is

highly polar, permitting reduced solvent-to-feed ratios in the

extractor while increasing the total recovery of xylenes and

9
heavy aromatics.

Feed sources and preparation for Sulfolane units are similar

to glycol BTX units. Sulfolane feed is normally C^-CQ or C,-C~ ,

whereas the process feed to glycol BTX units often consists only

of Cg-C_ fractions.

A flow diagram of a Sulfolane unit (Figure 3-2) shows that

the process flow is similar to that of a glycol BTX unit; how-

ever, unlike the glycol BTX processes (which separate the rich

solvent in one distillation step in the stripper) the Sulfolane

unit requires two steps. First, rich solvent from the extractor

enters the extractive stripper, where partial stripping of the

hydrocarbon takes place. In this column light hydrocarbons,

24
-------
K)
SOLVENT
REGENERATOR
CONDENSER OR COOLER

HEATER OR REBOILER

o PW
FC FLOU CHART

LC LEVEL CONTROL

PC PRESSURE CONTROL
CLAY
TREATERS
BENZENE
COLUMN
TOLUENE
COLUMN
XYLENE
COLUMN
Figure 3-2. Sulfolane unit process flow diagram.
10,11
-------
including some benzene, are removed overhead and recycled to the

extractor. The extractive stripper bottoms, consisting of sol-

vent, aromatics, and a few nonaromatics, enter the extract re-

covery column, which is operated under vacuum. Here the extract

is separated from the solvent, which is recycled to the extractor

as lean solvent. Solvent cleanup is accomplished by sending a

small slip stream of lean solvent to a solvent regenerator and

filters for removal of solvent degradation products. The solvent

regenerator is usually operated under a vacuum, and steam jet

ejectors are normally used to maintain a vacuum in the two vacuum

columns.

Some variations in the water circulation loops occur among

Sulfolane units. ' Raffinate from the extractor is contacted

with water to remove dissolved Sulfolane, and the resulting rich

water is either returned to the extract recovery column or to a

water stripper to reclaim the Sulfolane content.

The fractionation section of the Sulfolane unit, which is

preceded by clay treaters to remove olefins, is similar to a

glycol BTX unit.

Table 3-4 presents the material balance for a typical

Sulfolane unit, based on 2455 m /day (15,000 bbl/day). Table

3-5 presents operating conditions of selected process streams.

3.2.1 Sulfolane Unit Emission Sources

Most emission sources in Sulfolane units are similar to

those in glycol BTX units. Other potential sources are the

vacuum system on the recovery columns and solvent regenerators
26
-------
TABLE 3-4. SULFOLANE UNIT MATERIAL BALANCE2'10'11
[Based on feed of 2385 m /day (15,000 bbl/day)]
ro

Extractor - feed
- Lean solvent
- Rich solvent
- Raffinate
- Light HC reflux
Extractive stripper bottom
- Extract
Solvent Regenerator Feed
Nash water from raffinate wash
Benzene Product
Toluene column feed
Toluene product
Xylene column feed
Xylene product
Xylene column bottoms
Composition, wt. %
Flow Rate
mJ/day (bbl/day)
2385 (15,000)
4771 (30,000)
6118 (38,470)
1059 (6,660)
954 (6,000)

1347 (8,470)
31.8 (200)
318 (2,000)
200 (1,255)
1126 (7,055)
712 (4,480)
410 (2,575)
355 (2,230)
55 (345)
Benz
8.5

3.3

15.0

100.0
0.3
0.5

Tol
30.0

13.3

25.0

53.2

63.1
99.0
0.7
0.8

Xyl
15.0

26.6

31.1

85.0
97.0
7.0
C,-A
2.5

4.4

4.7

13.0
1.1
90.0
Paraf
44.0

0.2
98.0
60.0

0.8

99.0

0.8
0.5
1.3
1.1
3.0
Solv

100
80
2.0

99.0
1.0

-------
to
co
TABLE 3-5. SULFOLANE UNIT OPERATING CONDITIONS2'10'11
Temperature
°C (°F)
Pressure
Kpa-gauge psig
Raffinate
Extractive stripper-top
Recovery column-top
Recovery column-bottoms
Water stripper (if used)
Solvent regenerator-top
93 (200)
127-135(260-275)

177 (350)
110-121(230-250)
166 (330)
276-345 (40-50)
34.5-48.3 (5-7)
-75.8 (-11)

55.1 (8-20)
-96.5 (-14)
-------
that can be vented to the atmosphere. Process receivers could be

vented to the atmosphere; however, no available information indi-

cates that this is done.

3.3 OTHER AROMATIC SOLVENT EXTRACTION PROCESSES

Other solvent extraction processes have been commercially

developed, but not as many of these have been installed. The

configurations of such processes, Formex (which uses n-form-

glmorpholine as the solvent) and Aromex (which uses diglycol-

2 12
amine) are very similar to glycol BTX and Sulfolane processes. '

As shown in Table 3-1, the solvent properties of diglycolamine

are similar to other commonly used solvents. Therefore, the

emission characteristics of the Aromex process are likely to be

similar to those from glycol BTX and Sulfolane units.

3.4 TOLUENE DEALKYLATION PROCESSES

Naphtha reformers yield two to three times more toluene than

benzene; however, because the demand for benzene continues to be

substantially greater than that for toluene, some refiners have

installed toluene dealkylation units to convert toluene to

9
benzene. For this process to be feasible, the price differen-

tial between benzene and toluene must be large. The generally

low price differential over the past 15 years has caused some

refiners to shut these units down or to run them on an inter-

9
mittent basis.

There are a number of commercially available toluene deal-

kylation processes, all of which have similar process flow

29
-------
configurations. The processes can be divided into two groups,

thermal and catalytic. The survey results (shown on Table 2-1)

identified four processes in domestic operation:

1. Hydeal - catalytic process licensed by UOP

2. Detol - catalytic process licensed by Houdry

3. HDA - thermal process licensed by Atlantic Richfield
and HRI

4. THD - thermal process licensed by Gulf Oil

Other commercialized processes are Shell's Bextol process (cata-

lytic) and Mitsubishi's MHC process (thermal). Pure toluene or

toluene mixed with other aromatics and paraffins can be used.

The reactions take place in a hydrogen atmosphere at 540° to

760°C (1000° to 1400°F) and 3445 to 4820 kPa (500 to 700 psig).

The catalytic processes typically operate at 200° to 300°F lower

9
temperature, but they are more sensitive to coke laydown.

Toluene conversion per pass is 70 to 80 percent, and the overall

yield is about 97 percent of theoretical. The major reactions

are the dealkylation of alkylbenzenes to benzene and cracking of

essentially all nonaromatics to methane and ethane.

Figure 3-3 presents the process flow diagram of a typical

toluene dealkylation unit. Because the dealkylation reaction is

highly exothermic, cold hydrogen is used in some designs as a

9
quench for temperature control in the reactor system." The

reported overall mole ratio range of hydrogen-to-feed is 3:1 to

459
8:1. ' ' Recycle hydrogen purity is maintained above 50 mol

percent to minimize coking and for economic reasons. Among the

various configurations used to maintain recycle gas hydrogen

30
-------
RECYCLE GAS
COMPRESSOR
U)
—WJ FC
Ugfo^a^
o
I BENZENE
PRODUCT
DRAG STREAK
Figure 3-3. Process flow diagram of a toluene hydrodealkylation unit.4'5'14'15
-------
purity above a minimum level are purification of makeup gas,

which is normally reformer hydrogen; adding hydrogen from a

hydrogen unit; and purification of recycle gas. Purification is

normally accomplished by compression, cooling, and absorption or

with a cryogenics unit. A condensate rich in benzene is re-

covered by these processes. Other process variations are the use

of a low-pressure (LP) separator after the high-pressure (HP)

separator to flash off a methane-rich gas, ' the recycling of a

light liquid stream from the stripper overhead receiver, and

the use of a recycle column after the fractionator (or benzene

column) to separate toluene overhead for recycle from a bottoms

drag stream.

Table 3-6 presents the material balance of a toluene dealky-

lation unit based on 2500 barrels/day of toluene feed. The

amount of toluene recycle is dependent upon process economics.

Table 3-7 compares the yields of different feed compositions. A

pure toluene feed results in the lowest process flow rate per

unit of benzene produced. Net gas rates are noticeably lower.

Table 3-8 shows typical unit operating conditions.

3.4.1 Toluene Dealkylation Unit Emission Sources

Potential benzene and hydrocarbon emission sources are the

fractionator receiver vents and the same general leak sources as

listed for glycol BTX units (in Section 3.1.1). The fired-charge

heater, which uses fuel gas or fuel oil, is a source of hydro-

carbon emissions. The recycle gas compressor seals are also

potential sources of benzene and hydrocarbon leaks. The

32
-------
TABLE 3-6. TOLUENE DEALKYLATION UNIT MATERIAL BALANCE
4,5,11,13,14,15,16,17

Toluene feed
Makeup hydrogen.
Recycle hydrogen
HP separation net gas
HP separator liquid
Stripper off-gas
Fractionator feed
Benzene product
Recycle toluene
Drag stream
Composition, %
Flow Rate
m-Vday (bbl/day)
397.6 (2500)
0.12 (4.4)
0.64 (22.8) ,
1.4 x 103 (5.2x10°)
459.8 (2891)
2435 (86,000)
453.2 (2850)
318.1 (2000)
132.0 (830)
3.2 (20)
Basis
wt
vol
vol

wt
vol
wt
wt
wt
wt
Benz

0.1

0.1
70.2
100

Tol
100

0.1

29.1

100

Other
Arom

0.7

100
Non-
arom

10
45

90
55

OJ
CO
Assumptions: 80 weight percent overall conversion of toluene to benzene
75 percent conversion per pass
Purification of makeup water to 90 volume percent
Recycle gas rate is 4 mol H2/mol of toluene in the feed.
-------
TABLE 3-7.
COMPARISON OF TOLUENE DEALKYLATION YIELDS BASED ON
DIFFERENT FEED COMPOSITIONS17
u>

Feed

Net
- Toluene, wt . %
Benzene, wt . %
Nonaromatics, wt.%
Total feed m /day (bbl/day)
Gg/day (103 Ib/day)
H2 consumed m /day (10 x sdf/day)
Products benzene, Gg/day (10 Ib/day)

Tar, Mg/day (103 Ib/day)
Net off-gas, m /day (10 scf/day)
Case A
59.0
20.5
20.5
517.8 (3256)
0.36 (792)
0.15 (5.22)
0.25 (548)
4.2 (9.3)
0.16 (5.62)
Case B
65.0
10.0
25.0
560.6 (3525)
0.39 (852)
0.17 (6.11)
0.25 (548)
4.5 (9.9)
0.19 (6.61)
Case C
100.0
0
0
415.5 (2613)
0.30 (660)
0.10 (3.66)
0.25 (548)
3.6 (7.9)
0.10 (3.66)
-------
TABLE 3-8. TOLUENE DEALKYLATION UNIT
OPERATING CONDITIONS4'5'13'14'16
Reactor inlet
Temperature, °C (°F)
Pressure, MPa (psig)

Hj-to-feed molar ratio
H
- purity of recycle gas, %
HP separator
Temperature, °C (°F)
Pressure, MPa (psig)

Recycle compressor discharge
Pressure, MPa (psig)

Stripped overhead
Pressure, MPa (psig)

Fractionator overhead
Temperature, °C (°F)
Pressure, MPa (psig)

Recycle column overhead
Temperature, °C (°F)
Pressure, MPa (psig)

Recycle column bottoms
Temperature, °C (°F)
537-704 (1000-1300)
3.1-4.8 (450-700)

3:1-8:1

50-60
38 (100)
2.4-3.8 (350-550)
3.4-5.2 (500-750)
1.4-1.7 (200-250)
93 (200)
0.007-0.04 (1-6)
121 (250)
0.03-0.07 (5-10)
199 (390)
-------
off-gases from the HP separator (and LP separator, if used) and

stripper are of sufficient value to be used for fuel and, in some

cases, for recovery of heavier fractions for further processing.

3.5 TOLUENE DISPROPORTIONATE ON PROCESSES

Because of the marginal economics associated with toluene

dealkylation, processes have been developed for disproportioning

toluene into benzene and xylene. The disproportionation of

toluene can be represented as follows:
Toluene Benzene Xylenes

Since only one operating toluene disproportionation is listed in

Table 2-1, the process does not merit detailed description.

Three available commercial processes are low temperature

disproportionation (LTD), licensed by Mobil Oil; Tatoray, li-

censed by UOP; and Xylenes-Plus, licensed by Atlantic-Richfield.

All are catalytic processes. When the feed is 100 percent

toluene, 37 percent benzene and 55 percent xylene are obtained

rather than 50 percent each as the basic toluene disproportiona-

9
tion reaction would predict. The Xylene-Plus process also can

be used to transalkylate some Cq aromatics in the feed by re-

9
acting them with toluene to form more xylenes. As a result in

this process the benzene-to-xylene ratio can be varied from 1.5:1

9
to 10:1 depending upon the amount of Cq aromatics in the feed.

36
-------
The Tatoray and LTD processes use a hydrogen atmosphere (but

consume less hydrogen than the toluene dealkylation process) to

9 18 19
prevent coke layover on the catalyst. ' ' Although the

process flows are similar, the operating conditions are less

severe than those for toluene dealkylation. The process flow

diagram for a typical toluene dealkylation unit (Figure 3-3) is

also representative of toluene disproportionation. The major

differences are an LP separator can be used after the HP sepa-

rator, a xylene column and possibly a Cg column are used,

hydrogen purification generally is not needed, and (for the

Xylene-Plus process) no makeup hydrogen is needed. The off-gases

from the HP and LP separators and stripper go to fuel; however,

flow rates should be considerably lower than the corresponding

rates for toluene dealkylation units because far less cracking

18
takes place (reported aromatic ring yield is 97 to 97.5%) . The

reactor operates at lower temperatures than those used in dealky-

lation, and the conversion per pass (typically about 45 per-

/- I Q

cent) ' is also considerably lower, thus requiring more toluene

recirculation. Reactor operating conditions are as follows:

temperature 260° to 540°C (500° to 1000°F) and 3445 to 4480 kPa

(500 to 650 psig).18'19

Emission sources are similar to those of toluene dealkyla-

tion units.
37
-------
REFERENCES FOR SECTION 3
1. Somekh, G.S. Part 1: Ethylene Glycols; How to Improve
Aromatics Extraction. Hydrocarbon Processing and Petroleum
Refiners, 42(7), July 1963. pp. 161-164.

2. Jones, W.T., and V. Payne. New Solvent to Extract Aro-
matics. Hydrocarbon Processing, 52(3), March 1973. pp. 91-
92.

3. Somekh, G.S. New Union Carbide Aromatics Extraction Proc-
ess. In: International Solvent Extraction Conference,
Paper 65, The Hague, Netherlands, Society of Chemical
Industry, London, U.K., 1976. pp. 323-328.

4. Trip report by T.M. Briggs. PEDCo, Covering visit to Gulf
Oil Refinery, Philadelphia, August 1978.

5. Trip report by T.M. Briggs. PEDCo, on a visit to Sun Petro-
leum, Toledo, Ohio Refinery, September 19, 1978.

6. Trip report by T.M. Briggs. PEDCo, Covering visit to Sun
Petroleum Refinery, Marcus Hook, Pennsylvania, September 18,
1978.

7. Somekh, G.S., and B.I. Friedlander. TETRA Best Aromatics
Extractant. Hydrocarbon Processing, December 1969. pp.
127-130.

8. Trip report by T.M. Briggs. PEDCo, Covering visit to
Phillips Petroleum, Sweeney, Texas Refinery, August 1978.

9. Mager, E.M. Aromatics Production. In: U.S. Petrochemicals,
A.M. Brownstein, ed., Petroleum Publishing Co., Tulsa,
Oklahoma, 1972.

10. Broughton, D.B., and G.F. Asselin. Production of High
Purity Aromatics by the Sulfolane Process, Vol. 4. In:
Seventh World Petroleum Congress Proceedings, 1967. pp.
65-73.

11. Trip report by T.M. Briggs. PEDCo, Covering visit to Exxon
Chemical plant, Baytown, Texas. August 1978.
38
-------
12. Cinelli, E., S. Noe, and G. Paret. Extract Aromatics with
FM. Hydrocarbon Processing, 51(4), April 1972. pp. 141-
144.

13. Fowle, M.J., and P.M. Pitts. Thermal Hydrodealkylation.
Chemical Engineering Progress, 58(4), April 1962. pp. 37-
40.

14. Asselin, G.F., and R.A. Erickson. Benzene and Naphthalene
from Petroleum by the Hydeal Process. Chemical Engineering
Progress, 58(4), April 1962. pp. 47-52.

15. Benzene from Toluene by Detol Process. Hydrocarbon Proc-
essing, 40(6), June 1961. pp. 228-229.

16. New process Makes Benzene from Toluene (Bextol). Hydro-
carbon Processing, 42(3), March 1963. pp. 121-124.

17. Masamune, S., et al. A Hydrodealkylation (MHC) Process or
Production of Benzene and/or Naphthalene. In: Symposium on
Foreign Developments in Petrochemicals, Presented before the
Division of Petroleum Chemistry, inc., American Chemical
Society, Atlantic City, September 8-13, 1968. pp. A7-A21.

18. Erandlo, et al. Toluene for Benzene and Xylenes. Hydro-
carbon Processing, 51(8), August 1972. pp. 85-86.

19. Otam, S., et al. Tatoray Process - a New Transalkylation
Process of Aromatics Developed by Toray. Japan Chemical
Quarterly, 4, 6(16), 1968. pp. 16-18.
39
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SECTION 4

MODEL PLANT DEVELOPMENT

Model plant equipment listings are developed, based on the

median plant sizes determined for glycol BTX, sulfolane, and

toluene dealkylation units in Section 2. Equipment itemized are

pumps and compressors, process valves, relief valves, and sample

connections. Generally the total number of each type of equip-

ment is insensitive to plant size. Equipment listings were

developed from plant trip report data and equipment listings from

refinery plot plans (Pacific Environmental Services [PES]). The

toluene dealkylation reactor section equipment listing was taken
2
from a detailed equipment listing (Pullman Kellogg). A ratio

of 337 process valves per process pump, except for the toluene

dealkylation reactor section, was used.

Tables 4-1 to 4-4 present equipment listings for the sul-

folane unit; Tables 4-5 and 4-8, the glycol BTX unit; and Tables

4-9 to 4-13, the toluene dealkylation unit. The model plant

sizes are presented below:

Feed rate,
m-Vday (barrels/days)

Sulfolane 1,908 (12,000)
Glycol BTX 1,244 ( 7,600)
Toluene dealkylation 540 ( 3,300)
40
-------
TABLE 4-1. SULFOLANE UNIT PUMP LISTING1'3
Service
Extractor feed
Extractor reflux
Raffinate product
Raffinate water
wash recycle
Water stripper
tower charge
Bottoms-solvent
recovery tower
Bottoms water
stripper
Raffinate from
water wash
Extract to
fractionation
Feed to benzene/
toluene column
Benzene product
Toluene product
Feed to xylene
column
Xylene product
Heavy aromatic
product
41
-------
TABLE 4-2. LISTING OF VALVES IN SULFOLANE UNITS
Service
Extractor
Stripper
Recovery column
Raf f inate
Water stripper
Clay treater
Benzene column
Toluene column
Xylene column
Total
No. of
valves
132
66
66
99
132
66
132
132
198
1023
TABLE 4-3. RELIEF VALVES ON SULFOLANE UNIT LISTING
Service
Extractor
Stripper
Recovery column
Raf f inate
Water stripper
Clay treater
Benzene column
Toluene column
Xylene column
Solvent regeneration
Rundowns
Totals
No. of
valves
3
2
3
3
1
2
2
2
2
3
3
26
42
-------
TABLE 4-4. SULFOLANE UNIT SAMPLE CONNECTION LISTING
Service
Extractor
Stripper
Recovery column
Raffinate water wash
Water stripper
Clay treater
Benzene column
Toluene column
Xylene column
Solvent system
Water system
Total
No. of
connections
5
2
2
2
1
3
3
2
2
6
3
31
43
-------
TABLE 4-5. GLYCOL BTX UNIT PUMP LISTING
1,3
NO.
2
2

2
2

2
2
2

2
2
1
Service
Extractor feed
Extractor overhead
(raf f inate)
Solvent column feed
Solvent column reflux
and product
Solvent column bottoms
to extractor
Benzene column tops
Benzene column bottoms
Toluene column tops
Toluene column bottoms
Hot oil
Miscellaneous pumps for
solvent, acid, soda
and water
Fractionator feed
Extractor reflux
Stripper extractor
RVP class*
C

C
C

-
C
C
C
C
D

C
C
C
b
Pump type
C

C
C

C
C
C
C

R
C
C
C
Seal type
M

M
M

M
M
M
M

P
M
M
M
C « Liquid vapor pressure « <5 psi (average loss
D = Hot oil service (low vapor pressure).

C « Centrifugal pump.
R « Rotary pump
0.14 Ib/day)
M « Mechanical seal.
P * Packed seal.
-------
TABLE 4-6. GLYCOL BTX UNIT VALVE LISTING
Service
Extractor
Stripped
Clay treaters
Benzene column
Toluene column
Solvent system
Total
No. of
valves
192
66
66
132
132
192
780
TABLE 4-7. GLYCOL BTX UNIT RELIEF VALVE LISTING
Service
Extractor
Stripper and receiver
Solvent cleanup
Water wash
Clay treaters
Fractionation
Total
No. of
valves
2
3
2
1
2
4
14
45
-------
TABLE 4-8. GLYCOL BTX UNIT SAMPLE CONNECTIONS LISTING
Service
No. of
connections
Extractor

Stripper

Water wash

Water still

Clay treater

Benzene column

Toluene column

Solvent system
3

3
TABLE 4-9. TOLUENE DEALKYLATION UNIT PUMP SEAL LISTING
Service
Toluene feed
Stabilizer reflux
Benzene column
reflux
Toluene recycle
Heavy aromatics to
storage
No. of
pumps
2
2
2
2
1
RVP3
class
C
C
C
C
C
*RVP Class C - 3.4-34 kPa (0.5-5.0 psi)

RVP Class D - 3.4 kPa (0.5 psi).
46
-------
TABLE 4-10. TOLUENE DEALKYLATION UNIT VALVE LISTING
Service
Compression
Furnace
Reactor
Separator
Enrichment
Benzene column
Recycle column
Total
No. of
valves
48V, 7L
24V, 25L
3V, 2L
19V, 13L
15V, 41L
132
132
261
TABLE 4-11. TOLUENE DEALKYLATION UNIT RELIEF VALVE LISTING
Service
Compression
Furnace
Separation
Enrichment
Clay treaters
Stabilizer
Fractionator
Total
No. of
relief valves
4V
IV
2V
2V, 2L
2L
1L, IV
IV, IV
17
47
-------
TABLE 4-12. CONNECTION FOR TOLUENE DEALKYLATION
UNIT SAMPLE VALVE LISTING
Service
Compression
Furnace
Reactor
Separation
Enrichment
Stabilizer
Fractionator
Total
No. of
samples
IV
IV
2V
2V
IV
1L
3L
11
48
-------
REFERENCES FOR SECTION 4
1. Powell, D., et al. Development of Petroleum Refinery Plot
Plans. EPA-450/3-78-025. June 1978.

2. Cader, G.A., and B.B. Horton. Equipment Component Analysis
for Identification of Potential Fugitive Emission Sources.
U.S. Environmental Protection Agency, Research Triangle
Park, North Carolina. Contract No. 68-02-2619, Task 5.
June 1978.

3. Booz, Allen and Hamilton, Inc., Foster D. Snell Division.
Benzene Emission Control Costs in Selected Segments of the
Chemical Industry. Florham Park, New Jersey. June 1978.
49
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APPENDIX A

ESTIMATION OF BENZENE EMISSION FROM RECEIVER VENTS

Uncontrolled receivers in glycol BTX, Sulfolane, and toluene

dealkylation units typically operate with a purge gas to keep the

receiver pressure positive and vent the net gas to the atmosphere.

The simplest receiver system is the overhead receiver on the

benzene column, which contains essentially pure benzene. This

system is analyzed below and can be used to make estimates of

emission potential from process vents in all similar operations.

Benzene column overhead receiver:
37.8°C, 0.057
(100°F, 2 acfm)
CTC2
37.8°C, 0.07 mVmin
(100°F, 190 gal/m1n)
37.8°C, 0.07 m3/min (100°F, 190 gal/m1n)-*-
50
-------
Assumptions

0 Benzene production is 238 m /day (1500 bbl/day) and
column reflux is 795 m3 (5000 bbl/day). Total benzene
flow is 1033 m3 (6500 bbl/day) or 0.072 m3 (190 gal/min).

0 Bleed gas rate is (5 acfm) at 37.8°C (100°F) and
contains methane and ethane; no benzene.

0 Receiver operates at 117 kPa (17 psia).

o Vessel dimensions are 3.05 m (10 ft) diameter (D),
4.57 m (15 ft) long (L).

0 Vessel operates 50 percent full.

The dynamic benzene material balance is:

pMgas ' Q ' x0 + kg • A • (x£ - x) - PMga£. . Q .x = P_Mgas . v . ||

where
3 3
p = molar density of purge gas, kg mole/m (Ib mole/ft )
JXlCf cl S
V = volume of gas in the receiver, m (ft )

x = benzene mole fraction in the inlet air = 0
o
k_ = mass transfer coefficient, kg molar/m min (Ib molar/
0 min ft )

x = benzene mole fraction in exit gas

x_ = equilibrium mole fraciton of benzene
£j

Q = gas flow rate, 0.142 m /min (5 acfm) = 8.50 m /h (300
acfh)

Solving the above equation, gives
M , -Nt
X = N i - e
where
k
M = —
V PMgas
/kG • A \
N = ^ + Q A
\pMgas /

t = time, h
51
-------
Calculation of M and N

, . GM
kG = f ' 2-

Receiver vapor space x - area
2
A' = ^§- = 39.27 ft2
o

GM = Q • 60
359 x 560 _,
^—— • A
460 A

= 5 • 60
359 x 560 .
460 ^'^'

= 0.0173 Ib mole/h • ft2

D - receiver vapor space adjusted diameter

= 2 ( A; . = ,np2/8. = D = •
wetted perimeter' vJID/2 ; 2

_ Q _ 5 x 60
V ~ A5" ~ 39.27

=7.64 ft/h

ND = Reynold's number
Ke

D ' v ' pgas _ 5 x 7.64 x 0.05
y'gas 0.0266
= 71.7
= 0.223 x 0.0173
Li • /

2
V = ^§- L = 589 ft3
o
assume bleed gas MW = 22

M = kG x A x XE
V x pMgas

= 1.93 x 10~3 x 10' x 15' x 0.219

589 x 2.65 x 10~3
= 4.06 x 10~2 iT
52
-------
N =( k. A
+ Q
/V
Mgas
-3
= 1.93 x 10 x 150 + 300 /589
= 0.695 h
M ,
= — 1 —
N
= 0.058
2.65 x 10

-1
-3
-Nt
1 - e
-.695t
Residence time, t = V =
Q
589 ft"

5 x 60 f\
= 1.96 h
x = 0.043

Thus 4.3 mole percent of the vent gas is benzene, assuming

vapor-liquid equilibrium

Benzene emission = 0.36 SNm /h (12.9 acfh)
= 1.20 kg (2.65 Ib/h)

Because no data are available on actual receiver purge gas

flow rates, the effect of varying the purge gas on benzene

emissions is shown below.
Q
Purge gas
flow,
m^/min (acfm)
0.06 (2)
0.14 (5)
0.28 (10)
0.57 (20)
t
Gas residence
time,
h
4.91
1.96
0.98
0.49
x
Vent gas
benzene,
mole- fraction
0.0886
0.043
0.0236
0.0121
Benzene emission
rate,
kg/h (Ib/h)
0.994 (2.19)
1.20 (2.65)
1.32 (2.91)
1.36 (2.99)
Thus, the benzene emission rate from the benzene column

receiver is expected to be in the range of 0.91201.36 kg (2 to 3

Ib/h). Other vented receivers all contain far lower percentages

of benzene in the liquid and are expected to result in lower

benzene emissions.
53
-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-450/3-79-022
2.
3. RECIPIENT'S ACCESSION NO.
4. TITLE ANDSUBTITLE
Evaluation of Benzene-Related Petroleum Processing
Operations
5. REPORT DATE
October 1978
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
8. PERFORMING ORGANIZATION REPORT NO.
Dr. Terry Briggs
Vijay P. Patel
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Pedco Environmental, Inc.
11499 Chester Road
Cincinnati, Ohio 45246
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
68-02-2603 - Task 20
12. SPONSORING AGENCY NAME AND ADDRESS
13. TYPE OF REPORT AND PERIOD COVERED
U.S. Environmental Protection Agency
Office of Air Quality Planning and Standards
Emission Standards and Engineering Division
Research Triangle Park. North Carolina 27711
Final
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
EPA Project Officer: Kent C. Hustvedt
16. ABSTRACT
This report describes refinery processing of liquids with high benzene
concentrations. Processes which are addressed include aromatics extraction
(both sulfolane and glycol solvent processes), toluene dealkylation, and
toluene disproportionation. Each process is described and modeled. In
addition, a list and characterization of the 45 plants in the United States
processing liquids with high benzene concentrations is presented.
Characteristics include, where possible, company name, plant location,
benzene process, and benzene production rate.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
COSATl Held/Group
Petroleum Refining
Hydrocarbons
Benzene
Pump and Compressor Seals
Valves
Pressure Relief Valves
Sulfolane Toluene Dealkylation
Air Pollution Control
Stationary Sources
134
07C
18. DISTRIBUTION STATEMENT
Unlimited
19. SECURITY CLASS (ThisReport)
Unclassified
21. NO. OF PAGES
60
2O. SECURITY CLASS (This page)
Unclassified
22. PRICE
EPA Form 2220-1 (Rev. 4-77)
PREVIOUS EDITION is OBSOLETE
54
-------
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Environmental Protection
Agency
Office of Air, Noise, and Radiation
Office of Air Quality Planning and Standards
Research Triangle Park NC 27711
Official Business
Penalty for Private Use
$300
Publication No. EPA-450/3-79-022
Postage and
Fees Paid
Environmental
Protection
Agency
EPA 335
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