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WATER QUALITY REQUIREMENTS OF THE ORGANIC
CHEMICALS INDUSTRY FOR RECYCLUREUSE APPLICATIONS
Preliminary Draft Submitted by
Walk, Haydel & Associates, Inc. (For Ethylene Oxide and Ethylene Glycol Only)
Work Assignment No. 4 Contract No. 68-0 1-6024
October, I 980
,
Section I
Section I I
TABLE OF CONTENTS
Ethylene Oxide
Ethylene Glycol
- I -
SECTION I
ETHYLENE OXIDE
Introduction
This Section is an evaluation of the potential for increased recycle/reuse for
process water in the ethylene oxide (EO) industry. Water flows indirectly associated
with the process, such as conventional cooling tower blowdown, seal water, wash-
down, run off, etc. a r e not addressed since this information was not generally
available. Many of these waters a re subject to possible reductions using good
management practices.
Section I I evaluates the recycle/reuse potential for water from the ethylene
glycol (EG) process which is closely associated with the ethylene oxide process.
Conc I us i on s
o Extensive water recycle/reuse is currently practiced in the ethylene
oxide industry.
Potential exists for increasing recycle/reuse, including reuse of strip-
per bottoms purge and dehydrator bottoms by employing in-process
t rea tment and by-product glycol recovery.
o
o A potential exists in some facilities for segregation and reuse of
s t ream condensate by employing a reboiler instead of direct s team
injection for s team stripper operations. *
o Published EPA da ta indicate total water discharged from ethylene
oxide facilities amounts t o an average of 2800 L/1000 kg product. On
an industry wide basis, this represents 4200 gpm for all ethylene oxide
production.
- 2 -
o Average flows for process wastewater alone a r e estimated to be 1200
L/1000 kg product or 1800 gpm for t he en t i re ethylene oxide industry.
o Maximum recyc leheuse and employing close integration of water
flows between ethylene oxide and ethylene glycol operations could
reduce process wastewater flow further, to an estimated lower limit
of 750 gpm for t h e en t i re combined ethylene oxide and ethylene glycol
industry.
o Increased recycle/reuse will:
I .
2.
3.
Reduce organic concentrations in the final wastewater.
Increase salt concentration in the wastewater.
Increase secondary t rea tment holdup time, possibly improving
end-of-pipe t rea tment
o In-process t rea tment for reuse is favored over end-of-pipe t rea tment
and reuse.
For a median size plant, order of magnitude capital costs for in-
process t rea tment a r e estimated at $900,000. Operating costs a r e
estimated at roughly $ I .55/ IO00 kg ethylene oxide product.
o
- 3 -
Industry Profile
Ethylene oxide has been produced by the following processes:
1.
2.
3.
The first two processes account for essentially all of the ethylene oxide
produced in this country. The chlorohydrin route is practically extinct. A single
plant (Dow, Freeport , Texas) is capable of producing ethylene oxide via t h e
chlorohydrin process. This plant is not currently making ethylene oxide and will not
in the foreseeable future. When operational, the chlorohydrin process generates large
quantities of wastewater and, in fact, would have a significant impact on the total
industry discharge. However, str ides have been made to reduce this facility's total
wastewater discharge.
Vapor phase oxidation of ethylene using oxygen.
Vapor phase oxidation of ethylene using air.
Aqueous phase ethylene chlorohydrin process.
Ethylene oxide production is about evenly split between the oxygen and air
total
A list of
oxidation processes. There a r e presently I2 producers of ethylene oxide with a
annual capacity of approximately 3000 gigagrams (6.58 billion pounds).
producers and capacit ies is given in Table I (SR I , 1980).
- 4 -
TABLE 1 . U.S. ETHYLENE OXIDE CAPACITY
Manufacturer Location Annual Capacity
BASF Wyandotte Corp. Geimsar, La. 154.7
Celanese Corp. Clear Lake, Tx. 192.8 Dow Chem. U.S.A. Freeport, Tx. * 119.9
Plaquemine, La. 204.1 Eastman Kodak Co. Longview, Tx 88.5 Northern Natural G a s Co. Morris, II. 104.3
PPG Indust., Inc. Beaumont, Tx. 68.0 Shell Chem. Co. Geismar, La. 317.5
Jefferson Chem. Co., Inc. (Subsid of Texaco) Port Neches, Tx 315.2
Union Carbide Corp. Seadrift, Tx 417.3 Taft. La. 539.8
(gigagrams)
Calcasieu Chem. Corp. Lake Charles, La. 102. I
Olin Corp. Brandenburg, Ky. 49.9
Sun Olin Chem. Co. Claymont, Del. 45.4
Pendeias, P.R. Total
267.6 2,987.1
( 6 , 5 8 0 ~ I O6 Ibs)
*Approximately 90.7 gigagrams per year of additional capacity can be obtained from a unit using the chlorohydrin process.
About 60% of ethylene oxide production is used to make ethylene glycol and
nearly all ethylene oxide plants are integrated with ethylene glycol plants. Ethylene
oxide is also used in the production of surface active agents, glycol ethers and other
che mica I s.
For ethylene oxide that goes into ethylene glycol production, there exists
two major glycol grades. These grades impact how the oxide is processed. Fiber
grade, or high purity ethylene glycol, must be free of trace impurities generated in
the EO/EG processes. Commercial grade (antifreeze quality) represents about 40%
of the market and requires less stringent processing. Removal of impurities impacts
the water usage requirements.
I ' - 5 -
Future Trends
Although significant excess capacity currently exists, future plant expan-
sions and debottlenecking should continue to increase ethylene oxide production
capability. In 1979, approximately 2400 gigagrams ( 5290 million pounds) of ethylene
oxide were produced. However, 1980 production is expected to decline t o 2300
gigagrams or 5,070 million pounds (C & EN, 1980).
Ethylene oxide should continue to be produced by vapor phase oxidation of
ethylene. Selection of the oxygen or air oxidation process is dependent on many
factors. Local conditions for a plant may determine which route is selected. The
oxygen process is generally preferable and future expansions are expected to use this
process (Yen, 1977).
Characterist ics of Ethylene Oxide
Chemical names of ethylene oxide include epoxyethane, oxirane, and
Ethylene oxide has a boiling point of 10.7OC, a specific gravity dimethylene oxide.
of 0.89 at 7OC and is completely soluble in water.
Chemistry
The catalyt ic oxidation of ethylene to ethylene oxide is shown below:
C2H4 + 112 0 2 + C2H40
The reaction is highly exothermic with a heat of reaction of about -104
kJ/mol. A supported silver catalyst is used in all commercial production. The
reaction is carried out in the vapor phase, using either pure oxygen or a i r as the
oxygen source. Reaction temperatures and pressures vary depending on the process
(oxygen or air). Reaction temperatures range from 250 to 27OoC, and pressures range
from I800 to 2 IO0 kPa (260-305 psi).
By-products and Impurities
By-products of the ethylene oxide reaction include carbon dioxide and
water, the combustion products of ethylene.
- 6 -
During processing in the ethylene oxide plant, ethylene glycol by-product is
This ethylene glycol by-product is formed by the hydration of ethylene oxide.
frequently recovered in an associated ethylene glycol plant.
Small amounts of aldehydes (acetaldehyde/formaldehyde) and acids
(primarily ace t ic and carbonic) a r e formed in the process. The acids a r e neutralized
with caustic to form salts. These salts and aldehydes a r e impurities which must be
removed from the process.
Another impurity in the process is ethane, which may be present in the
ethylene feed.
Ethylene dichloride and other compounds a re of ten added in small amounts
as inhibitors or moderators of the reaction and must be removed.
Process Description
Discussed below a r e operations based on the oxygen process. Those include
I) operations based primarily on patent l i terature, which represent minimum
recycle/reuse; and 2) operations based on industrial input for an EO/EG operation
using extensive recycIe/reuse.
The l i terature has limited useful information about the air process and
contacts with major producers employing this route failed to yield detailed informa-
tion (for proprietary reasons) regarding current practices. There a r e many similari-
ties between the two technologies. Differences a r e discussed in the f i rs t process
description to follow.
Fiqure I Process (Literature Based Design)
A typical flowsheet for ethylene oxide production via the oxygen process is
given in Figure I which emphasizes water flows in the process. The major process
sequence is reaction, absorption, recovery and refining.
TUBULAR REACTOR
LIGHT ENDS REFINING COLUMN COLUMN
i *
ABSORBER REABSORBER DEHYDRATOR STR I PPER
OXYGEN
REMOVAL
I - F I
1
I VENT
FIGtJRE 1 .
ETHYLENE OXIDE
*
* HEAVY ENDS (DISPOSAL)
ETHYL-ENE OXIDE P R O D U C T I O N (OXYGEN PROCESS1 BASIS : PATENT LITERATURE
- 7 -
Ethylene, oxygen and recycle gases are combined, heated and fed to a
tubular reactor containing silver catalyst. Reaction takes place in the gas phase. A
heat transfer medium removes the heat of reaction and produces steam in a steam
generator.
The main reaction produces ethylene oxide and the parallel combustion
reaction produces carbon dioxide and water (stream I). Reactor product gases are
cooled and then absorbed in water consisting of fresh make-up (stream 2) and stripper
bottoms recycle (stream 4). Nearly all of the ethylene oxide is removed from the
reactor gases in the water absorber. Trace amounts of acid formed in the process are
neutralized with caustic forming salts which must eventually be removed from the
system. The absorber tail gases are recycled to the ethylene oxide reactor. A side
stream of the ta i l gas is sent to a carbon dioxide removal unit. Carbon dioxide
absorption and desorption is effected with a recirculating solution such as potassium
carbonate (not shown). The carbon dioxide generated in the process i s either vented
or recovered as a by-product.
The absorber bottoms are heated and sent to a steam stripper. Direct steam
injection (stream 3) is shown for stripper boil-up. Some plants use a reboiler for this
purpose. The overhead from the stripper contains ethylene oxide, C02, aldehydes and
inert gases. The aqueous bottoms stream is cooled and recycled to the ethylene oxide
. absorber (stream 4). This stream contains steam condensate, ethylene glycol,
aldehydes and other impurities. To prevent buildup of these components a purge
(stream 5) i s removed from the stripper bottoms recycle. The purge results in the
major wastewater flow from the process. .
The stripper overhead is sent to a reabsorber, where the ethylene oxide
product is recovered. Water is added to the reabsorber (stream 6 ) , producing a r ich
ethylene oxide solution. The reabsorber tail gases containing ethylene, ethane,
carbon dioxide and inerts, are sent to a disposal unit such as an incinerator.
- a -
Reabsorber bottoms a r e sent to a dehydrator, where crude ethylene oxide is
recovered overhead. Dehydrator bottoms (stream 71, containing small concentrations
of organics such as ethylene glycol and aldehydes, a r e discharged as wastewater.
However, in some plants they a r e recycled to the reabsorber to replace added water
(stream 6 ) . In other integrated ethylene oxide-ethylene glycol facilities, part of t he
reabsorber bottoms are sent to the glycol plant.
The dehydrator overhead is condensed and sent to a light ends column. Light
ends are ei ther recycled to the reactor or sent to vapors disposal. The bottoms from
the light ends column go to a refining column. Overhead from this column is
condensed and stored as ethylene oxide product. Bottoms residue from the refining
column containing impurities such as aldehydes is sent to disposal (e.g. contract
hauling or incineration).
Although the air oxidation process is very similar to the oxygen process for
making ethylene oxide, there are few a differences due to the source of oxygen. In
the a i r process it is necessary to maintain a low ethylene concentration in the reactor
off gas to minimize ethylene losses in the vent. A second (purge) reactor is added in
series with the main reactor in the air process. In large plants, three reactors in
series may be used. Each reactor requires a water absorber to recover product from
the. reactor gases. Some of the tail gases from the absorber a r e recycled, but a large
portion, containing ethylene and other organics, is vented or incinerated. Although
multiple absorbers are used in the air process, the water purge r a t e should be about
the same as in the oxygen process. t
The carbon dioxide removal system is used only in the oxygen process. It
can affect wastewater quality through losses o r drainage of absorption liquid
(potassium carbonate solution) into the water system.
The product recovery and purification sections of the air process are
essentially the same as those of the oxygen process. Water usage and wastewater
- 9 -
production in the two processes a r e similar (Gans, 1976). A slightly higher water
consumption can be expected in the air process due to greater water vapor losses in
the high tail gas vent rate.
Fiqure 2 Process (Industry Based Design)
This description highlights major differences affecting the water balance
between the previous l i terature based process and a typical industrial operation.
The major differences between this process and the Figure I process a r e as
follows: I) the ethylene oxide and ethylene glycol processes a r e integrated, 2)
ethylene oxide feed to ethylene glycol is wet rather than anhydrous, 3) it is primarily
geared toward making commercial grade ethylene glycol 4) a process cooling tower
rather than surface coolers is used on the stripper bottoms, 5) the dehydrator column
is eliminated, and 6 ) water recycle between the ethylene oxide and ethylene glycol
units is practiced.
The reactor operation is the same as discussed previously. Significant
evaporation losses occur from t h e process cooling tower (s t ream 8) reducing the
wastewater discharge. Additionally, water containing glycol and salts leaves the
system as stripper bottoms purge (s t ream 7) and is t rea ted to remove these impurities
prior to transfer to the ethylene glycol unit (as s t ream 9 ) for glycol recovery.
Wastewater s t ream I O from this t rea tment is discharged.
Water from the cooling tower is used in the absorber and reabsorber as lean
Demineralized water make-up and C02 removal unit condensate a r e absorbent.
added to the cooling tower (stream 3). This is comparable to adding w a t q directly
to the absorber and reabsorber in the process shown in Figure 1 . The ethylene glycol
unit provides the balance of water sent to the ethylene oxide cooling tower (stream
2).
The stripper overhead product is partially condensed. The vapor goes to the
This combined reabsorber and the condensate mixes with the reabsorber bottoms.
>. d
t
0
I
3 4
T
- IO-
s t ream feeds the light ends column where it is split. Pa r t goes t o the refining column
to make anhydrous ethylene oxide product. The remaining aqueous ethylene oxide
portion goes to the ethylene glycol unit.
A separate dehydrator column is not necessary because the refining column
serves the dual purpose of dehydrating and purifing ethylene oxide product. The
refining column bottoms a re recycled to the stripper feed.
Water Balance
Fiqure I Process (Literature Based Design)
A water balance for t h e typical ethylene oxidation process using pure
oxygen and producing anhydrous ethylene oxide is given in Table 2 (based on patent
literature as described by Yen, 1977).
- 1 1 -
TABLE 2. WATER BALANCE FOR ETHYLENE OXIDE PRODUCTION (FIGURE I PROCESS)
~~
Figure I Streams Quantity* L/lOOOkg EO
Input
I. Water of Reaction 260
2 Absorber Make-up
3. Steam to Stripper
6 . Reabsorber Water
TOTAL
350
I230
I10 - I950
Effluent To Waste Treatment
5. Stripper Bottoms Purge Wastewater 1200
750 6 . Dehydrator Bottoms Wastewater -
TOTAL I950
*L/ I OOOkg = kg/ I OOOkg = Ib/ I OOOlb
Referring to Figure 1 and Table 2, water en ters the process as water of
reaction (stream I), absorber make-up (stream 2), s team to the stripper (stream 3)
and water to the reabsorber (stream 6) . A significant amount of water is'recycled
from the stripper bottoms to the absorber (stream 4, not included in Table 2). The
recycle ra t io is 20/1 based on absorber make-up.
Water leaves the process as stripper bottoms purge (s t ream 5) and dehy-
drator bottoms (stream 7). These s t reams a r e the two major wastewater sources.
Total wastewater flow determined by the water balance is 1950 L/1000kg. Miscella-
- 1 2 -
neous non-process wastewater sources (washings, etc.) are not included because
information on these specific sources was not available.
Fiqure 2 Process (Industry h s e d Design)
Since most ethylene oxide plants a r e integrated with ethylene glycol plants,
some facilities, especially those producing commercial grade ethylene glycol, feed
aqueous ethylene oxide product t o the glycol plant. The Figure 2 process is primarily
geared toward production of commercial grade ethylene glycol which tends to reduce
the water quality requirements and increase recycle potential. Its water balance was
derived from industrial contac ts and confidential EPA information and is not specific
for a single plant.
The water balance for this process depends on the quantity of wet ethylene
oxide production sent to the ethylene glycol unit. The Table 3 water balance is based
on 60% of the ethylene oxide product going to ethylene glycol production and 40%
going to anhydrous ethylene oxide product, a split representative of major end use
patterns. The wet ethylene oxide feed to ethylene glycol is approximately 50%
water.
.
- 1 3 -
TABLE 3. WATER BALANCE FOR ETHYLENE OXIDE PRODUCTION (FIGURE 2 PROCESS)
Figure 2 Streams Quantity" L/ I OOOkg
Input
1 . Water of Reaction
2.
3.
4. Steam to Stripper
5. Steam to C02 System
EG Water Recycle to EO
Demineralized Water to Cooling Tower
TOTAL
Effluent
6.
8. Cooling Tower Evaporation Losses
9.
IO. Wastewater
Water with EO feed to EG
Water to EG unit for glycol recovery
TOTAL
260
500
200
2000
1000
3960
-
700
2360
400
500 -
3960
* L/lOOOkg = kg/1000kg - Ib/1000 Ib
The major differences between the Figure I balance and this balan,ce a r e as
follows: I) cooling tower evaporation losses (stream 8) a r e present, 2) water (stream
6 ) is recycled to the ethylene glycol unit as part of the wet ethylene oxide feed, 3)
water recycle from the ethylene glycol unit en te rs the oxide unit as s t ream 2, 4)
stripper bottoms purge (stream 7) is treated resulting in s t ream 9 and IO. Stream 9 is
recycled to t h e ethylene glycol unit and s t ream IO is discharged to wastewater.
- 1 4 -
Make-up includes the C 0 2 removal steam condensate (stream 5) and demineralized
water make-up (stream 3).
Much of the water leaving the unit is reused in the ethylene glycol unit or is
lost to the atmosphere via the cooling tower. The stripper bottoms purge is treated
to remove impurities (primarily salts and aldehydes) prior to use in the ethylene
glycol unit. Wastewater from this treatment of about 5OOL/I OOOkg ethylene oxide
is discharged to the general plant effluent. Alternately, these wastes, in a more
concentrated form, might be incinerated. As another option, the stripper bottoms
purge can be used directly in the ethylene glycol unit without the treatment i f glycol
product quality is maintained by special product treatment (Scheeline, I971 1.
Reported Wastewater Flows
Several wastewater flows have been reported for ethylene oxide plants.
These are given in Table 4. One industry source found reported flows related to their
operation unrealistically high due to the inclusion of non-process related waters.
Such waters include conventional cooling tower blowdown, pump packing gland water,
washdown, runoff, etc. Based on these comments, it is likely that other reported
flows include both process and non-process related wastewaters
TABLE 4. REPORTED WASTEWATER FLOWS FOR ETHYLENE OXIDE PRODUCTlON
Wastewater Flow Survey Range Average Number Number L/ I OOOkg L/ I OOOkg of Plants Reference .
I 150- I090 620 2 USEPA ( 1974)
2 150-72 I 0 2 350 10 USEPA ( I 978)
3 - 2790 14 USEPA ( 1980)
- 15 -
Make-up Water Quality
In order to ensure product quality and minimize mpur i ty bui ldup n recycle
water, demineralized (condensate quality) make-up water i s used in the manufacture
of EO/EG. For the oxygen process, Figure I shows make-up to the absorber and
reabsorber, whereas Figure 2 shows make-up to the process cooling tower only.
Additional water make-up is from live steam injection for column heating.
Wastewater Quality
Referring to Figure I and Table 2, streams 5 and 7 make up the total
wastewater flow from the ethylene oxide process. Components in the wastewater
include ethylene glycol, aldehydes, ethylene dichloride and other impurities. Pollu-
tant concentration is much higher in the stripper bottoms purge (stream 5) than in the
dehydrator water (stream 7). In the industry stream 5 is called "the lean water cycle
stream". This stream contains from I to 3 6 ethylene glycol, which is the major
organic component. Since this stream would represent a significant loss, ethylene
glycol recovery can be expected at most installations.
Impurities which are ultra-violet light absorbers build up in the ethylene
oxide water and make reuse of the water difficult. These impurities contaminate
both the ethylene oxide and ethylene glycol product, making the final ethylene glycol
unsuitable as fiber-grade material. For this reason, water purges may not always be
.further processed for by-product recovery or water reuse. The ultra-violet light
absorbers can be removed in a process developed by PPG Industries ( I 975).
Referring to Figure 2 and Table 3, stripper bottoms purge (strFam 7) is
processed for ethylene glycol recovery rather than being discharged directly as
wastewater. A portion of the water is recovered with the remaining portion
discharged to wastewater.
Wastewater quality data from plant surveys are shown in Table 5. The
extent of ethylene glycol by-product recovery from ethylene oxide wastewater was
not reported.
- 1 6 -
TABLE 5. REPORTED WASTEWATER QUALITY FOR ETHYLENE OXIDE PRODUCTION*
Flow** Avg. COD Avg. BOD L/ I OOOkg kg/ I OOOkg mg/L kg/ I OOOkg mg/L Reference
I50 7.7 52,000 0.7 I 4,800 USEPA, 1974 IO90 5.3 4,800 0.7 I 650 USEPA, 1974 430 - - 2. I 4,840 USEPA, 1978
I920 9.2 4,800 7.1 3,680 USEPA, 1978
*Quality data per 1000 kg product or per l iter of wastewater. **Data available for lower flow facilities only.
Current Iy Practiced Wastewater Treatment
Most ethylene oxide production occurs in large multiproduct plants. Waste-
water from various product/processes are combined for treatment. USEPA ( 1980)
indicates that 1 I out of 14 plants surveyed have biological treatment. Activated
sludge and aerated lagoons are used for secondary treatment. USEPA (1978)
indicates good secondary treatment of wastewaters from sites which include ethylene
oxide production.
Potential for Recycle/Reuse
The potential for recycle/reuse was examined in some detail for the oxygen
In order to bracket the wastewater flow, two process, based on Shell technology.
extremes were considered to represent current operations. The f i r s t is based on
patent literature for anhydrous ethylene oxide production and the second is based on
informat ion from industrial sources employing recycle/reuse practices in an inte-
grated EO/EG facility. Discharges are estimated to be between the values'based on
these two extremes.
Reuse potential for the air oxidation process for producing ethylene oxide is
not discussed in detail because information necessary for this evaluation was
insufficient . Ethylene oxide production already makes extensive use of water recycling.
- 1 7 -
Purges necessary to remove ethylene glycol and impurities can be sent to an ethylene
glycol plant for by-product ethylene glycol recovery. Water removed in the ethylene
glycol plant can be recycled to the ethylene oxide plant to achieve high water
recycle. Based on current da ta (Table 41, average wastewater flow can be as high as
2800 L/lOOOkg of ethylene oxide. Based on a current annual production capacity of
3000 gigagrams (6.58 billion pounds), this equates to a total industry flow of 4200
gpm. From a study of Figure I and 2 operations, t he average flow of process
wastewater is probably closer to 1200 L/lOOOkg (1800 gpm for the en t i re ethylene
oxide industry). Additional recycle/reuse operations across the industry could bring
the average discharge down to about 750gpm for the combined EO/EG industry.
PPG Industries (1975) developed a patented process for removal of recycle
impurities. Application of this in-process t reatment or others might contribute to
the lower water usage discussed above. The PPG process consists of ion exchange,
degassing and activated carbon adsorption. Ion exchange is used to remove salts from
the wastewater and degassing removes carbon dioxide and other volatile components.
Activated carbon adsorption removes ultra-violet light absorbers which cause product
quality problems. Yen (1977) describes a typical design tha t utilizes this process.
Based on inquiries, industry responses to the ion exchange s tep of this process were
negative because ion exchange units in such wastewater service are generally
difficult to operate due to fouling problems and frequent regeneration . Evaporation
is used in some instances instead of an ion exchange system (Anonymous, 1980).
Although evaporator s team consumption would be high, significant quantit ies of
ethylene glycol can be recovered.
Wastewater which is discharged to secondary t reatment units from the
manufacture of ethylene oxide might, in some cases, be upgraded to reuse quality by
ter t iary treatment. However, this would offer no advantage over in-process
treatment.
I - 1 8 -
Replacing live steam stripping with indirect heat exchange (reboiler)
increases the potential for reducing the system purge and water consumption. The
minimum system purge is set by the by-product production of ethylene glycol and
contaminants. Actual purge rates may not always be at the minimum rate required
for product quality, but can instead be set based on steam condensate removal
requirements to satisfy a water balance. Where this is true, capital investment in a
reboiler wil l reduce water purges while recovering condensate for reuse. Both direct
steam injection and reboilers are used in ethylene oxide plants for stripping product
from absorber bottoms. Some fouling problems can be expected when using reboilers.
Replacing existing process cooling towers with surface coolers and conven-
tional cooling towers offers some potential for reducing stripper bottoms purge and
for increasing water reuse. Organic oxidat ion contaminants (aldehydes and acids) can
be expected to form in process cooling towers requiring extra stripper bottoms purge
for their removal. Additionally, conventional cooling tower make-up water would be
of a lower quality than the condensate now required for the process cooling tower,
thereby increasing the reuse potential of available wastewater streams. It is doubtful
that additional surface coolers and conversion to conventional towers can be
economically justified.
Economic Evaluation for In-Process Treatment
The economic study in this section is based on installation of the wastewater
treatment system shown in Figure 3. It serves as a basis for order of magnitude
costs for improved recycle/reuse realizing it wil l require modification for individual
installations. Wastewater from the stripping and dehydration columns passes through
a holding tank and enters a cation exchanger. This ion exchanger is fil led with
styrene divinyl benzene cation resin. Effluent from the cation exchanger enters the
degasser column which is packed with Raschig rings. The degassed stream enters the
anion exchanger which is packed with styrene divinyl benzene anion resin.
%
CATION DEGASSER AHIOH EXCHAMGER CQLIJM N EXCHANGER
ACTIVATE D TREATED
FILTER TANK WATER HOLD1 Nt CARBON
WASTE WATER HOLDING TANK
EO JASTE WATER
Ec IT
FIGURE 3. ETHYLENE 0x1 DE WASTEWATER TREATMENT.
- 19-
The last t reatment s tage is carbon adsorption. There a re two adsorption
vessels each packed with act ivated carbon. The parallel columns a r e a l ternated
between service and regeneration which prevents downtime. The t reated water is
stored in a holding tank.
Economics are based on equipment sized for a median sized U.S. ethylene
oxide, oxygen process plant ( I 54 gigagrams/yr). The equipment was scaled up from
published design da ta (Yen, 19771, then cost estimated and escalated to a March 1980
leve I.
Table 6 assumes the following:
1.
2.
3.
4.
5.
6 .
No additional on-site operating labor or overhead expenses.
Units Cost($) e lectr ic i ty .04/kw hr act ivated carbon .36/Ib anion resin 3.65 / I b cation resin 4.75/1 b raschig rings I4.20/f t
Negligible deterioration and regeneration losses a r e assumed for ion
exchange resin. Regeneration capital costs a r e included with ion
exchanger costs. Stainless steel construction is assumed for the resin
bed vessels.
Regeneration acid and caustic costs are included in raw material
costs.
The carbon bed not in service is s team stripped to regenerate the
carbon. It is assumed tha t the carbon will need to be replaced 4 t imes
each year. s
Capital recovery costs a r e based on recovery over a IO year period and
10% interest.
- 20 -
TABLE 6. CAPITAL AND INCREMENTAL OPERATING COSTS Wastewater Treatment: Ethylene Oxide, Oxygen Process
Basis: 154 gigagrams/yr (340 million Ibs/yr)
Capital Costs ( $ I ?OOO Instal led)
Ion Exchanger (including resins & regeneration facilities) 456 Carbon beds (including carbon) 92 Degass i f ica t ion Column (i nc 1 ud ing packing) I08 Tanks I67
26 Piping to a rea Total Capital Cost 900
Pumps 51 -
Incremental Operating Costs, ( $ 1 ,OOO/yr)
Direct Costs
U t i I it ies Materials (includes acid, base for regeneration) Maintenance
5 50 20
Total Direct Costs
Indirect Costs
Taxes and Insurance Capital Recovery
Total Indirect Costs
Net Annual Incremental Operating Cost ( $ 1 ,000/yr)
Net Incremental Operating Unit Cost
75
18 I46 - I64
239
$1.55/1000 kg EO
.
- 2 1 -
REFERENCES
1 . Anonymous, Industria
2.
3.
4.
5.
6.
7.
9.
IO.
I I .
Contacts, September, I980
C & EN, Ethylene Oxide, Chemical and Engineering News, June 16, 1980.
Gans, M. and B.J. Ozero, For EO: Air or Oxygen? Hydrocarbon Processing, March 1976, ppg. 73-77.
PPG Industries. Process for Preparing Monoethylene Glycol and Ethylene Oxide, U.S. Patent 3,904,656, 1975.
SRI, I980 Directory of Chemical Producers, Stanford Research Institute, Menlo Park, California.
USEPA, Development Document for Effluent Limitation Guidelines and New Source Performance Standards for t he Major Organic Products Segment of Organic Chemical Manufacturing, EPA-440/ I -74-009-a, April 1974.
USEPA, Draft , BPT Evaluation of Organic Chemical and Plastics and Synthetics, Vol. I l l , EPA Effluent Guidelines Division, November 1978.
USEPA, Draft , "Briefing Package for Organic Chemicals Phase I", Preliminary Plant Survey Data, Feb., 1980.
Scheeline, H.W., Ethylene Glycol, Process Economics Program Report, No. 70, Stanford Research Institute, Menlo Park, Ca., I97 I .
Yen, Y.C. Propylene Oxide and Ethylene Oxide, Report No. 2C, Process Economics Program, Stanford Research Institute, Menlo Park, California, April, 1977.
I - 22 -
Section II
ETHYLENE GLYCOL
Introduction
Process waters from ethylene glycol manufacture are evaluated for
recycle/reuse potential. This evaluation is tied to the companion ethylene oxide
report (Section I ) which, for better understanding, should be read prior to this report.
Only waters directly associated with the process were evaluated, as discussed in the
Introduction to the oxide report.
Conclusions
0
0
0
0
0
0
Extensive water recycle/reuse is currently practiced in the ethylene
glycol industry.
Potential exists for increasing recycle/reuse for evaporator overhead
following in-process treatment.
Potential exists for wastewater elimination by substitution of vacuum
pumps and surface condensers for barometric condensers and steam
jets.
Published EPA data indicate total water discharged from ethylene
glycol facilities amount to an average of 2500 L/1000 kg product. On
an industry wide basis, this represents 3100 gpm for all ethylene glycol
product ion.
Average flows for process wastewater alone are estimated to be 1200
L/lOOO kg product, or I500 gpm for the entire ethylene glycol
industry . Maximum recycle/reuse and employing close integration of water
flows between ethylene oxide and ethylene glycol operations could
reduce process wastewater flow further, to an estimated lower l imi t
*
- 2 3 -
of 750 gpm for the ent i re combined ethylene oxide and ethylene glycol
industry.
o Increased recycle/reuse will:
I.
2. Increase secondary t rea tment holdup time, possibly improving
Reduce organic concentrations in the final wastewater.
end-of-pipe treatment.
o In-process t rea tment for reuse is favored over end-of-pipe t rea tment
and reuse.
o For a median size plant, order of magnitude capital costs for in-
Operation costs a r e process t rea tment are estimated a t $280,000.
estimated at roughly $.50/1000 kg ethylene glycol product.
Industry Profile
Ethylene glycol has been produced commercially by the following processes:
1.
2.
3.
4.
5. Ethylene chlorohydrin hydrolysis
6. Vapor-phase propane oxidation
7.
High temperature and pressure hydration of ethylene oxide.
Acid-catalyzed hydration of ethylene oxide.
Hydrolysis of glycol es te rs from ethylene
Formaldehyde and carbon monoxide synthesis
Hydrogenat ion and hydrogenolysis of molasses
The first two processes, each based on hydration of ethylene oxide, account
for all of ethylene glycol produced in this country (Considine, 1974). The new
Oxirane plant (Channelview, Texas) utilizes the glycol es te r hydrolysis route.
However, this plant is shut down indefinitely due to operating difficulties. The
remaining four processes a r e no longer used commercially in this country (Scheeline,
1978).
- 24 -
Ethylene glycol is produced in large volume with an annual capacity of 14
plants of about 2450 gigagrams (5.4 billion pounds). A list of producers and capacit ies
is given in Table 1 (SR I , 1980).
TABLE I . U.S. ETHYLENE GLYCOL CAPACITY
Manufacturer Location
BASF Wyandotte Corp. Calcasieu Chem. Corp. Celanese Corp. Dow Chem. U.S.A.
Eastman Kodak Co. Northern Natural Gas Co. Olin Corp.
Geimsar, La. Lake Charles, La. Clear Lake, Tx. Freeport, Tx. Plaquemine, La. Longview, Tx Morris, I I . Brandenburg, Ky.
Oxirane Internal1 Channelview, Tx PPG Indust., Inc. Beaumont, Tx. Shell Chem. Co. Geismar, La. Jefferson Chem. Co., Inc.
(Subsid of Texaco) Union Carbide Corp. Seadrift, Tx
Port Neches, Tx
Taft , La. Penuelas, P.R.
Total
Annual Capacity (gigagrams)
1 13.4 81.6
226.9 115.7 158.8 81.6 90.7 22.8
* 81.6
154.2
149.7 340.2 567 .O 272.2
2,456.4
( 5 , 4 1 0 ~ 1 0 ~ Ibs)
*This is a 362.9 Gg capacity plant on standby.
As discussed in the companion ethylene oxide report, two major ethylene
glycol product grades a re primarily produced. Fiber grade or high purity ethylene
glycol constituting 50% of the market, must be f ree of t race impurities generated in
t he EO/EG processes. Removal of these impurities impacts t h e water usage
requirements. Commercial grade (antifreeze quality) representing about 40% of the
- 25 -
market is lower purity and requires less stringent processing.
glycol plants a r e integrated with ethylene oxide plants.
Nearly all ethylene
Two high temperature and pressure hydration operations were examined in
detail. These represent ex t reme cases with regard to water recycle/reuse and a re
discussed in the process description to follow. The acid catalyzed hydration process
was not examined in detail. It is expected this route will b e discontinued in the
future due to corrosion and acid residue problems. Except for t h e reaction itself,
the acid catalyzed process is nearly the same as the high temperature and pressure
process. Product yields, product distribution, and purification are similar. There is
some difference in wastewater quality due to acid residues in the acid catalyzed
process.
Future Trends
The conventional process for ethylene glycol production is the high tempera-
t u re and pressure hydration of ethylene oxide. As previously mentioned, t h e older
acid catalyzed ethylene oxide hydration process is expected to eventually b e
discontinued as a commercial route to ethylene glycol.
Two new processes show promise for the future; the glycol e s t e r hydrolysis
process and the process for direct ca ta ly t ic oxidation of ethylene with simultaneous
. hydration to ethylene glycol. Both processes have higher ethylene glycol yields. The
future of glycol es te r technology is uncertain.The f i rs t plant utilizing this route
(Oxirane at Channelview, Texas) is shut down indefinitely because of start-up/opera-
tional problems. The direct catalytic oxidation route has not yet been
commercialized.
Although both of these new processes employ technologies not yet proven,
as ethylene prices increase economics for these higher yield processes will become
more favorable and increase incentive to develop these technologies. Short term,
- 26 -
new process development efforts may be slowed by the current excess ethylene glycol
production capacity.
Characteristics of Ethylene Glycol
The term ethylene glycol ususally refers to a group of compounds. The ones
of commercial importance are the mono-, di-, and triethylene glycols. Other names
for ethylene glycol include glycol, ethylene dihydrate, I, 2-dihydroxyethane, I, 2-
ethanediol, and ethylene alcohol. Ethylene glycols are stable, water-white liquids
with practically no odor. Their density, viscosity and boiling points are higher than
that of water. A l i s t of their physical properties i s given in Table. 2.
TABLE 2. PHYSICAL PROPERTIES OF ETHYLENE GLYCOLS
Property
Molecular Wt. Boiling point a t 7609m Hg, OC Vapor pressure at 2% C, mom Hg Specific gravity (20 C/20 C) Water so I ub i I i t y
Ethylene Diethylene Tr iet hy lene Glycol Glycol Glycol
62.07 106.12 150.17 197.6 245.0 287.4
0.06 0.0 I 0.0 I 1.1 155 1.1 I84 . I. I254
Complete Complete Comp let e
- 27 -
MW:
Ethylene Oxide Hydration Chemistry
The simplest glycol, ethylene glycol, is formed by the hydration of ethylene
oxide at high temperature and pressure.
L kPa L
ethylene oxide water ethylene glycol MW 44.05 18.02 62.07
The higher homologs a r e formed by t h e addition of ethylene oxide to the
mono or diethylene glycol.
MW:
CH2\ + I / CH2
ethylene oxide 44.05
fH2- 0 + CH2’
ethylene oxide 44.05
CH20H I - CH20H
ethylene glycol 62.07
diethylene g I ycol 106.12
t H 2 0 H
diet hy lene g I yco I tr ie t hy lene g I yco I 106.12 150.17
The hydration reaction is strongly exothermic, t he hea t of reaction being
-74.5kJ/moI at 18OoC. An excess of water is required to favor the first reaction
tha t produces monoethylene glycol. As t he market generally d ic ta tes a preference
for this compound, commercial production entails large excesses of water. The
reaction is generally considered to be first order with ethylene oxide concentration.
The high temperature and pressure conditions of the conventional process eliminate
t h e need for a catalyst. Representative conditions include a temperature of 2OO0C
.- A
- 20 -
and a pressure of 1500 kPa, with a reaction t ime of I hour. Neither temperature nor
pressure have an appreciable effect on the distribution of mono-, di- and triethylene
glycol.
A typical total product yield is 95% of theory. For a 20/1 water/ethylene
oxide molar ratio, product distribution is estimated as follows (Scheeline, 1978):
Product %(wt) ,
Ethylene glycol 88. I Diethylene glcyol 9.4 Tr iet hy l e n e g I ycol 2.5
100.0
By-Products
Losses in the typical ethylene glycol process discussed below a r e about 5%
of theoretical ethylene glycol production. About one-half of these losses are
estimated to be due to formation of heavy ends, the remainder being ethylene oxide
leakage and other miscellaneous losses. The ethylene oxide feed may contain t r a c e
impurities such as acetaldehyde and acetic acid.
Process Description
Two ethylene glycol operations using the high temperature and pressure
ethylene oxide hydration route a r e described below. The first is based primarily on
patent literature, which represents minimum recycle/reuse within the ethylene glycol
unit and between the ethylene oxide and ethylene glycol units. The second is based
on industrial input for an integrated EO/EG facility using extensive recycle/reuse in
each unit and between units.
Fiqure I Process (Literature Based Design)
This design is based on Sheeline ( I 978) using anhydrous ethylene oxide feed.
A typical flowsheet for glycol production emphasizing water flows is given
HYDRAT I ON FIRST S E C W THIRD RWCTOR STAGE STAGE STAGE
EVAPORATOR EVAPORATOR EVWORATOR
WATER MG DG TG REMOVAL PRODUCT PRODUCT PRODUCT COLUMN COLUMN COLUMN COLUMN
RECYCLE WATER@
A
WATER PURGE
FIGURE 1, ETHYLENE OXIDE HYDRATION TO ETHYLENE GLYCOL.
cw
t HE3VY ENDS
(DTSPOSAL)
- 29 -
in Figure 1. Make-up condensate (stream I) and recycled water (stream 7) are mixed
to form the total dilution water stream (2). Ethylene oxide is added to the water
stream to form the total reactor feed stream (41, which is preheated. The ethylene
oxide is hydrated in the liquid-phase reactor, where water is consumed (stream 8).
The reactor effluent (stream 5 ) contains large quantities of water which are removed
overhead in the evaporators. The evaporators are typically triple effect and operate
at pressures greater than atmospheric, removing most of the water. The f i r s t effect
overhead water (stream 6 ) containing ethylene oxide, ethylene glycol, and light
impurities (aldehydes) i s purged to wastewater. This is the major wastewater stream
in the process. Water from the second and third effects and the water removal
column is recycled to the hydration reactor (steam 7). The dehydrated product
stream is distilled under vacuum in three separate product columns. The mono-, di-,
and triethylene glycols are removed as overheads in each of these columns. Heavy
ends from the triethylene glycol column are sent to disposal. Vacuum operation of
the water removal column and product columns usually entails use of steam je t
ejectors (not shown) which results in a small additional wastewater flow.
The extent of vacuum operation in ethylene glycol plants varies. In the
Figure I process, the evaporators are run under pressure while the columns are run
under vacuum. Steam eductors were assumed for vacuum and surface condensers for
cbndensation. Some plants make more extensive use of steam eductors with
barometric condensers.
Fiqure 2 Process (Industrial Based Design)
This description highlights the major differences between the previous
literature based process and a typical industrial operation shown in Figure 2.
Q
\- .
If
-
, 1
-30-
Major differences between this process, and Figure I a r e as follows: 1 ) The
ethylene oxide and ethylene glycol facilities are integrated, 2) ethylene oxide feed to
the ethylene glycol plant is wet, rather than anhydrous, 3) the process is geared
toward making commercial grade ethylene glycol, 4) t reated stripper bottoms purge
from the oxide unit is reused in the glycol unit, 5) A barometric condenser and
cooling tower are used in vacuum generation, 6 ) Water from the barometric system is
recycled to the ethylene oxide unit, 7) A small aldehyde purge (flash) is taken from
t h e first effect overhead, 8) The third effect overhead is removed from the system
as condensate for reuse, 9 ) Reactor feed make-up water is added as s team to provide -
preheat.
Water leaves the glycol unit via the evaporator, but is not discharged as
wastewater. Overhead gases a r e separated from condensate in t h e first and second
effluent evaporator overhead. The gas is vented and the condensate recycled to the
reactor. The third effect evaporator overhead (stream 5) is removed as condensate
quality water for reuse application. Residual water in the third effect bottoms is
removed in the water removal column.
'The barometric condenser system provides vacuum for the water removal
column. A cooling tower provides necessary cooling for extensive recycle of this
water. Water enters cooling tower system from the water removal column overhead
. and from the demineralized water make-up (stream 7). Water exits as cooling tower
evaporation losses (stream 8) and as recycle water to the ethylene oxide plant
(stream 9) . In this way, s t ream 9 provides needed water for t he oxide plant and a t
the same t ime serves as a purge for the process cooling tower. .
- 31 -
Water Balance
Fiqure I Process (Literature Based Design)
A typical water balance for ethylene glycol production is shown in Table 3
(based on Scheeline, 1978). Referring to Figure I and Table 3, water enters the
process as make-up condensate (s t ream I ) .
Water is consumed in the hydration reaction (stream 8) and leaves the
process in the purge (stream 6 ) . A large amount of water is recycled in the process
(stream 7). The ratio of recycle water to influent water (stream I ) is about 2/1.
TABLE 3. WATER BALANCE FOR ETHYLENE OXIDE HYDRATION TO ETHYLENE GLYCOL
~~~ ~~~
Quantity" L/ IO00 kg Figure I Streams
Input
I . Make-up Condensate
Effluent
6. Purge Water (wastewater)
Consumption
8. Hydration Reaction
Recycle
7. Recycle Water
2000
I700
300
41 00
*L/lOOO kg = kg/1000 kg = lb/1000 Ib
Water associated with vacuum steam eductors is relatively small and is
not included in the water balance.
- 32 - * '
Fiqure 2 Process (Industry Based Design)
The Figure 2 process is geared toward production of commercial grade
ethylene glycol which tends to reduce the water quality requirement and increase
the recycle/reuse potential. As a consequence, water is recycled between the EO/EG
units to achieve optimum recycle/reuse.
The water balance shown in Table 4 was derived from industrial contacts
and confidential EPA information and is not specific to any plant.
Water input to the Figure 2 process is much higher than for the Figure
1 Process (as shown in the Table 4 balance) and wastewater discharge is seemingly
non-existant. However, an undefined port ion of the ethylene oxide unit wastewater
results from glycol production.
- 33- E
TABLE 4. WATER BALANCE FOR ETHYLENE GLYCOL (FIGURE 2 PROCESS)
Figure 2 Streams \
Quantity L/ IO00 kg EG
lnpu t
1. Make-up Water 700
2. Wet oxide feed 900
3. Water from EO Unit 600
I100
TOTAL 3300
7. Cooling Tower Make-up -
Consu mpt ion
i 1. Water of Reaction 300
Effluent
4. Evaporator overhead purge
to vent IO0
5. Evaporator overhead
condensate removal 800
8 Cooling Tower
evaporation losses I400
700 9 Barometric water to the oxide plant - TOTAL 3000
a
, - 3 4 -
The primary reasons for higher water input are I )excess evaporator overhead
(stream 5) removed as condensate quality water for reuse, 2) significant water lost
to the atmosphere (stream 8) from cooling tower evaporation and 3) water recycled
between the oxide and glycol plants.
Unlike the Figure I process, oxide plant glycol by-product and associated
water are recovered in the glycol plant.
Reported Waste wa t er F I ow s
Table 5 gives reported wastewater flows for ethylene glycol plants. As
mentioned in the ethylene oxide report, industry sources found these flows to be
unrealistically high. The inclusion of non-process related waters such as cooling
tower blowdown, washdown, runoff and others in reported wastewater flows could
make them excessively high.
TABLE 5. REPORTED WASTEWATER FLOWS FROM ETHYLENE GLYCOL PLANTS
Wastewater Flow Range Average Number
L/ IOOO kq L/ IOOO k q of Plants Reference
- 4,870 - USEPA, 1974
80-2970 9 20 7 USEPA, 1978
- 2,480 14 USEPA, 1980
Make-uD Water Quali tv
In order to ensure product quality and minimize impurity buildup in recycle
water, condensate quality make-up water is used in EO/EG manufacture. In Figure
I & 2 operations make-up is to the recycle water entering the hydration reactor.
In the Figure 2, make-up water in also added to the cooling tower.
- 35 - 8 .
r
Waste Water Quality
Table 6 presents survey study results for an investigation of wastewater
quality from ethylene glycol production.
Referring to Figure I and Table 3, the purge water (stream 6 ) is the only
source of wastewater in the process. It contains unreacted ethylene oxide, ethylene
glycol and light impurities present in the overhead from the first effect evaporator.
Purge water does not contain any non-volatile compounds (salts, etc). The major
contaminant is ethylene glycol. Any ethylene oxide present in the wastewater would
probably hydrate to ethylene glycol given sufficient time.
For Figure 2 the only direct discharge from the ethylene glycol plant is
distillation column heavy ends. This s t ream can be furfher processed for polyglycol
recovery, or disposed of (e.g. incineration).
Plant survey da ta have been reported on the end-of-pipe wastewater from
ethylene glycol production. Reported wastewater quality da t a are given in Table 6 .
TABLE 6 . REPORTED WASTEWATER QUALITY* FOR ETHYLENE GLYCOL PRODUCTION
Flow Avg COD Avg BODS L/ IO00 kq kg/1000 kg mg/L kg/1000 k g mq/L
4,870 8.77 1,800 0.34 69"" USEPA, I974
920 6.2 6,700 3.0 3,300 USEPA, 1978
~~
"Quality da t a per 1000 kg product or liter of wastewater
**This is unusually low
Current Iy Practiced Wastewater Treatment
Most ethylene glycol production occurs in large multiproduct plants where
wastewaters from t h e various plants on-site a r e combined for treatment. Biological
-36- I
t reatment of these combined wastewaters was
oxide.
The Potential for Recycle/Reuse
discussed in the section on ethylene
Ethylene glycol production already makes extensive use of recycle/reuse in
the glycol unit and between units. The potential for further recycle/reuse was
examined in some detail for t he high temperature and pressure hydration process.
The two operations discussed earlier a r e considered to represent extremes in current
operations. The first is based on patent l i terature and represents minimum water
recycle/reuse within the glycol unit and between EO/EG units. The second operation,
based on industrial sources and confidential EPA information, is geared toward
making commercial grade glycol in an integrated EO/EG facility with water
extensively recycled.
Based on current da t a (Table 5), average wastewater flow may be as high as
2500 L/1000kg. Considering a current annual capacity of 2456 gigagramdyear, this is
a total glycol industry flow of 3100 gpm. An independent es t imate of the average
volume of process wastewater associated with the manufacture of ethylene glycol is
1200 L/1000 kg EG; which is equivalent to 1500 gpm for the ent i re industry operating
at capacity. Additional industry wide recycle/reuse could reduce this average *
process wastewater figure further and a combined process water discharge from
EO/EG operations could reach a lower limit of approximately 750 gpm for t h e en t i re
EO/EG industry operating at capacity.
As a variation of the Figure 2 operation, the PPG Industry (1975) patent
discussed in the oxide report for removal of impurities in wastewater could be
modified in some facil i t ies as a t rea tment of the glycol plant evaporator purge. The
absence of non-volatile salts would eliminate the need for t he ion exchange.
.
Also, as in the oxide operations, wastewater which is discharged to
secondary t reatment units in multiproduct plants producing ethylene glycol might b e
- 37 -
upgraded to reuse quality by ter t iary treatment.
advantage over in-process treatment.
However, this would offer no
Water usages may be decreased by replacing barometric condensers and
s team je t s with surface condensers and vacuum pumps.
Economic Eva I u a t ion
For estimating purposes only, a carbon adsorption t rea tment system for
organic impurity removal was considered. Economic bases and details a r e described
in the ethylene oxide report. Order-of-magnitude capital costs for recycle/reuse in
the glycol plant alone were est imated at $280,000 (Table 7). Operating costs were
estimated to be about $0.53/1000 kg EG. For an integrated EO/EG plant employing
this type t reatment , a combined system for t he EO/EG units would be more likely.
I
- 3 a -
TABLE 7. CAPITAL AND INCREMENTAL OPERATING COSTS
Wastewater Treatment Ethylene Glycol
Basis: I50 gigagramdyr (330 million pounds/yr)
Capital Costs ( $ I ,000 Installed)
Carbon filters (carbon included) Tanks Pumps Piping
Total Capital Cost
Incremental Operatinq Costs ( $ 1 ,OOO/yr)
Di rec t Costs
Utilities Materials Maintenance
Total Direct Cost
Indirect Cost
Taxes and Insurance Capital Recovery
Total Indirect Costs
Net Annual Incremental Operating Cost ($1,00O/yr)
Net Incremental Operating Unit Cost
8 3 I 49 31 17 -
280
t 3 18 8 -
29
6 45
51
-
80
$0.53/ 1000 kg EG
, r - 39 -
REFERENCES
I . Considine, D.M. (ed.), Ethylene Glycol, Chemical and Process Technology Encyclopedia,
2. PPG Industries, U.S. Patent 3,904, 656, Process for Preparing Monoethylene Glycol
McGraw-Hill Ebok Company, New York, 1974, pp. 439-442.
and Ethylene Oxide, September 9, 1975.
3. Scheeline, H.W. and H. Naka, Ethylene Glycol Process Economics Program, Report No. 70, 70A, 708, SRI International, Menlo Park, California, 1978.
4. SRI, 1980 Directory of Chemical Producers, United States of America, SRI International, Menlo Park, California, 1980.
5. USEPA, Development Document for Effluent Limitations Guidelines and New Source Performance Standards for t h e Major Organic Products Segment of t h e Organic Chemicals ManufacturingPoint Category, U.S. EPA, 440/1-74-009a, 1974.
6 . USEPA, Draft, BPT Evaluation of Organic Chemicals and Plastics and Synthetics, Vol. I l l , EPA Effluent Guidelines Division, November, 1978.
7. USEPA, Draft, "Briefing Package for Organic Chemicals Phase I", Preliminary Plant Survey Data, February, 1980.
