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Preventing Industrial Pollution at its Source
A Final Report of the Michigan Source Reduction Initiative


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Appendix 2: Detailed Description of MSRI Reduction Products


PROCESS: METHOCEL®

Background/Process Description

The METHOCEL® process is part of the Global Specialty Chemicals business within Dow. There are three manufacturing sites including the Midland site, Plaquemine, Louisiana and Stade, Germany. METHOCEL® is Dow's trade name for a line of methylcellulose and hydroxypropyl methylcellulose water-soluble polymers. These products are used for their water retention, viscosity modification and other properties in a wide variety of markets including food, pharmaceutical, ceramics, construction and other uses.

Cellulose from wood or cotton is used as a primary raw material and is modified by reaction with sodium hydroxide, chloromethane and propylene oxide. First, the cellulose is treated with the sodium hydroxide to activate the cellulose as alkali cellulose. Then, the chloromethane is used in an alkylation reaction to form the final product.


Diagram


Sources and Baseline Conditions

The largest source of MSRI waste from the process is the vent gas from the reactors. Chloromethane is the only MSRI chemical within this waste stream and is generated as an unreacted raw material. The vent gas also contains non-MSRI chemicals including dimethyl ether, a byproduct formed in the chemical reaction.


Pollution Prevention Options and Reductions

There were no pollution prevention options implemented during the course of MSRI.


Non Pollution Prevention Reductions

Three options were examined for the vent gas stream. 1) On-site recovery of chloromethane followed by purification and sale of other stream constituents. 2) On-site recovery of chloromethane followed by shipment of other stream constituents to the Plaquemine site for conversion to chloromethane; and 3) Off-site recovery of chloromethane at the Plaquemine site followed by conversion of other stream constituents to chloromethane. These three alternatives were examined for technical risk, market risk, capital requirements and economic value. After considering all factors, the business chose to implement the off-site recovery and conversion option (3). This waste-to-product option does not fit the MSRI definition of pollution prevention and so is not counted toward the MSRI goals. It is, however, an improvement to the current management option, incineration.


Financial Savings Costs

The waste to product project is expected to reduce total wastes by approximately 4.2 million pounds and have a payback period of approximately 4 years.



PROCESS: ION EXCHANGE

Process Description and Sources

The Ion Exchange process is part of the Liquid Separations business within Dow's Global Specialty Chemical business. The Ion Exchange process produces a range of DOWEX® anion and cation exchange resins. These resins are used in various water treatment applications for industrial and residential uses.

The primary raw materials in the ion exchange process are methanol, formaldehyde, HCl, catalyst and a polymer, which is produced at the Midland site in another process. The chemical reaction in the ion exchange process creates a substituted polymer with a functional group, which is used as an exchange site to capture unwanted cations and anions from water as it passes through the resin.

There are two primary sources of wastes in the process. The first is vent gas from the reactors, which is burned in a vent gas incinerator. Chloromethane, which is produced as a byproduct of the chemical reaction, is the primary chemical within this waste stream. The second source is generated in the recovery system and consists of accumulated tars and raw materials that are not recovered. The tars created in the reaction prevent the recovery of additional raw materials and reducing tar formation was the focus of pollution prevention investigations.


Diagram


Pollution Prevention Options and Reductions

Several pollution prevention options were developed as part of extensive studies of the basic chemistry of the reaction looking for the underlying causes for waste generation.

Four options focused on reducing tar formation and increasing the recovery of raw materials. The first option reduced the solvent content of the polymer used as a raw material feedstock in the process. Dow discovered that reducing residual solvent in the polymer reduced the generation of tar and allowed more raw materials to be recovered from the tar for reuse. The second option changed catalyst use within the reaction, which also resulted in less tar and increased recovery. The third option changed reaction conditions, increasing yield and thus sending fewer raw materials to the recovery system. With these changes in waste generation within the reaction, Dow was then able to implement the fourth option, which involved changing the operation of the raw material recovery system to increase recovery. When fully implemented, these four options will almost completely eliminate the loss of raw materials to the wastewater treatment plant.

In addition to the options to reduce tars and improve raw material recovery, Dow also modified reaction conditions to reduce the formation of Chloromethane vented from reactors to the vent incinerator.


SourceChemicalEstimated Release Reduction (pounds)Estimated Waste Reduction (pounds)
Vent gas to vent incineratorChloromethane798800,000
Tars and Raw Materials to WWTPFormaldehyde63,6211,300,000


Financial Savings Costs

Equipment changes needed to decrease solvent in the polymer and change reaction conditions cost approximately $330,000. Other changes detailed above did not require capital. The investment will reduce the cost of lost raw materials and waste treatment by approximately $3.3 million per year.


Source/projectQuantity (lbs)Lost Raw Material Savings/YearWaste Treatment Savings/YearProject Cost
Vent gas to vent incinerator800,000$66,000$62,000$330,000
Tars and Raw Materials to WWTP4,900,000$1,400,000$1,800,000



PROCESS: STYRENE-BUTADIENE LATEX (SB LATEX)

Process Description and Sources

The Styrene-Butadiene Latex (SB Latex) process is part of Dow's Global Emulsion Polymers Business. The SB Latex product is used in coatings for coated paper and paperboard. It is also used in adhesives in the carpet industry and as binders in a variety of other applications.

Styrene and butadiene are the primary raw materials that are used in the presence of an initiator to produce emulsion polymers. During the reaction process, a fraction of the raw materials are converted into finished products. The uncon- verted monomers are sent to a recovery system with any excess disposed of by incineration.

An impurity in the butadiene, a "dimer" which is formed when butadiene reacts with itself, plays a critical roll in waste generation and its presence dictates what quantities of styrene and butadiene are generated as waste. As the dimer builds up in the recovery system, it must be periodically purged for incineration at the on-site RCRA incinerator.


Diagram


Pollution Prevention Options and Reductions

Two pollution prevention options are being pursued: modified recovery techniques, and reducing dimer levels in purchased butadiene. The first option, which was implemented during the MSRI timeframe, modifies Dow's production schedules and improves the method for recovering raw materials. In combination, these techniques reduce the quantity of the purge stream sent to the incinerator. Dow rearranged existing handling systems to make this possible.

The second pollution prevention option focuses on reducing dimer levels in the incoming butadiene. Dimer formation is directly related to time and temperature. The higher the temperature and the longer the storage time the more dimer is formed. Dow conducted extensive analysis of the dimer levels "as shipped" by their suppliers, "as received" at the plant, transit time, and storage temperatures. Dow developed a model to predict dimer levels. From these studies, Dow believes additional reductions of 300,000 to 400,000 pounds of MSRI waste can be achieved if their suppliers load butadiene at lower temperatures. Dow has begun discussions with its principal butadiene supplier to discuss reducing the temperature of butadiene at the time of loading. Almost all users of butadiene, no matter what the product they make or in what country they are operating, have wastes that are a consequence of dimer in butadiene. Dow will attempt to convince its supplier that a competitive advantage can be gained by supplying its customer with lower dimer-content butadiene by loading colder.


SourceChemicalEstimated Release Reduction (pounds)Estimated Waste Reduction (pounds)
Purge stream from recovery systemStyrene0208,000
Butadiene044,000


Financial Savings Costs

Pollution prevention techniques reduced total wastes by approximately 30 %, saving $105,000 per year in lost raw materials and waste treatment costs.


SourceQuantity reduced (lbs.)Lost Raw Material Savings/yearWaste Treatment Savings/YearProject Cost
Purge stream from recovery system252,000$80,000$25,000$ 50,000


The capital needed to modify the current process to achieve these results amounted to $50,000. However, this expenditure reflects the fact that Dow had an existing handling system and other equipment in place at the Midland site. If this equipment had not been available, the project would have cost an estimated $500,000. At this level, the project may not have been funded. Dow is not pursuing this option at other sites at this time because it does not have the necessary spare equipment. However, the cold loading agreement is being pursued with suppliers. If suppliers load butadiene into rail cars at lower temperatures, styrene and butadiene waste will be reduced at both Midland and other Dow SB Latex plants in North America.



PROCESS: BULK PHARMACEUTICAL (PHARMA)

Process Description and Sources

Dow produces pharmaceutical products under contract for another company. These products are part of the Contract Manufacturing Services unit of Dow's Global Specialty Chemicals business. The federal Food and Drug Administration (FDA) approves the products and production processes used in manufacturing.

In the process examined for MSRI, methylene chloride is used as a chemical processing aid to keep raw materials and intermediates in solution as they react to form the final product. Methylene chloride is first distilled during the product reaction and then again during the quench reaction. The methylene chloride is then burned in the on-site RCRA incinerators.


Diagram


Pollution Prevention Options and Reductions

Because of the difficulty of qualifying a new process through the Food and Drug Administration (FDA), a change of solvents was not examined. This led Dow to consider in-process recycling options. Process changes to incorporate these options required approval from the FDA, which is sometimes cited as a disincentive for making pollution prevention changes in the pharmaceutical industry. Of particular concern was the potential build up of impurities in the system and the impact of these impurities, if present, on the product. However, since Dow had included an option for in-process recycling in its original FDA application, approval could be expedited.

Methylene chloride from the quench reaction separation step contains water. Water would complicate the operation of a recovery system and Dow opted not to explore options for this step first. The pollution prevention option pursued was recovering the methylene chloride from the product reaction distillation step. Dow conducted pilot trials to determine any impacts on product quality and to develop technical data for the design of the final system. To conduct the trials, Dow installed temporary piping systems to recycle the methylene chloride to produce a sufficient number of batches. The product was tested in Dow's quality assurance labs to ensure no impurities were present.


SourceChemicalEstimated Release Reduction (pounds)Estimated Waste Reduction (pounds)
Distillation tarsMethylene Chloride0273,000


Initially, Dow recycled approximately 50 % of the methylene chloride for quality assurance testing. Subsequently the number of times solvent is recycled before incineration has slowly been extended. Test results show no impact on product quality to date, and Dow's goal is to recycle about 95% of all of the methylene chloride from the product reaction distillation step. This will result in in-process recycling of 75% of the total methylene chloride waste from the process. After the recycling of distillation wastes has been fully implemented, Dow plans to begin work on the quench reaction distillation waste. Both quench reaction distillation improvements and in-process recycling will be pursued.


Financial Savings Costs

The construction of a permanent recovery system is estimated to cost approximately $140,000 and save approximately $ 450,000 per year in raw material costs and waste treatment costs.


SourceQuantity reduced (lbs.)Lost Raw Material Savings/YearWaste Treatment Savings/YearProject Cost
Distillation tars273,000$ 350,000 $100,000$ 140,000



PROCESS: DURSBAN* (CHLORPYRIFOS)

Process Description and Sources

Dursban*, or chlorpyrifos, is a pesticide manufactured at the Midland site by Dow AgroSciences LLC. Dursban*, an organophosphate pesticide, is the most widely used insecticide on Earth. It is used in a variety of applications such as combating termites, fleas and other household pests as well as agricultural uses.

The process uses two primary raw materials: "symtet" (symmetrical tetrachloropyridine) and "DEPCT" (diethyl phosphorochloridothioate) along with sodium hydroxide, surfactants and catalysts. First, sodium hydroxide is reacted with symtet to form an intermediate. This intermediate is then reacted with DEPCT to form the final product. The reaction mixture containing the final product then goes through a series of separation and refining steps to isolate the final product.

In the reaction, byproducts containing sulfur are created. Because humans can detect organic sulfur compounds at extremely low levels, these byproducts are vented to air controls including a thermal oxidizer and a "soil bed" of bacteria that metabolize sulfur compounds. The process also generates solids and sludge containing intermediates and final product as waste. Pollution prevention investigations focused on recovering product and an intermediate from these wastes.


Diagram


Pollution Prevention Options and Reductions

Dursban staff developed several pollution prevention options, which can be grouped into three areas. The first option focused on recovering and reusing the product recycle reject. This waste stream is now in-process recycled back through the purification system to recover the remaining product. The second group of pollution prevention options included a series of small process changes such as improved monitoring of process conditions and surfactant usage. Finally, changes to the reactors were made to improve the yield of product, decreasing the formation of unwanted byproducts.


SourceChemicalEstimated Release Reduction (pounds)Estimated Waste Reduction (pounds)
Product Recycle RejectFinal Product BCl-40125,000
Process changesFinal Product BCl-40162,000
Intermediate product BCl-40 12,000
Guard filters/reactor yieldFinal Product BCl-4032,000
Intermediate product BCl-40 19,000


Financial Savings Costs

The savings from lost raw materials and avoided waste treatment costs totaled approximately $157,000. It cost approximately $43,000 to implement these projects.


SourceQuantity reduced (lbs.)Lost Raw Material Savings/yearWaste Treatment Savings/YearProject Cost
Product Recycle Reject125,000$45,000$12,000$20,000
Process changes174,000$63,000$17,000Procedure changes
Guard filters/reactor yield51,000$15,000$5,000$23,000

Another pollution prevention project was still in the design phase in April 1999. This project would recover finished product by adding new distillation and filtration equipment. Capital needed is estimated to be $300,000. An additional 100,000 pounds of finished product, which is now wasted, would be recovered. If these estimates are correct, the project will be implemented. However, because capital was not approved by April 1999, this potential reduction of an MSRI chemical has not been counted toward the project goal.

* Trademark of Dow AgroSciences



PROCESS: DICHLOROPHENOXY ACETIC ACID (2,4D)

Process Description and Sources

Dow AgroSciences LLC produces 2,4-Dichlorophenoxy Acetic Acid (2,4D), a member of the phenoxy family of herbicides. 2,4D is used for the control of broadleaf weeds in grain and other crops. It is also used on rangelands and for residential lawn and garden applications.

The primary raw materials used in the process are monochloroacetic acid and 2,4-dichlorophenol, both of which are produced at the Midland site. (See process descriptions for CAC and 2,4 dichlorophenol.) Sodium hydroxide, hydrochloric acid and tetrachloroethylene are also used in the process.

Monochloroacetic acid, 2,4-dichlorophenol and sodium hydroxide are batch reacted to produce sodium 2,4-dichlorophenoxyacetate. The reaction mixture is extracted with tetrachloroethylene to remove and recover unreacted 2,4-dichlorophenol. The tetrachloroethylene is then distilled for reuse. A portion of the tetrachloroethylene is carried forward where it is stripped from the product mixture for recovery. Hydrochloric acid is then added to convert the sodium salt of 2,4D to the acid form, the final product.


Diagram


The largest source of MSRI waste in the 2,4D process is tetrachloroethylene from the 2,4-dichlorophenol-recovery process. This waste is burned in an on-site RCRA incinerator. Most vents from the reaction step are treated in a scrubber and sent to an incinerator. There are also fugitive emissions of tetrachloroethylene and HCl from numerous seals, pipes, flanges, pumps and other devices.


Pollution Prevention Options and Reductions

Pollution prevention options focused on reducing the tetrachloroethylene waste generated in the recovery step. Dow found a way to do a better job of reducing the formation of and breaking a difficult emulsion formed in this step. As a result more tetrachloroethylene is recovered. During 1999 and 2000 Dow will continue to investigate additional ways to reduce tetrachloroethylene losses from the recovery, although reductions will not be counted toward the MSRI goal because funding was not in place by April 1999.


SourceChemicalEstimated Release Reduction (pounds)Estimated Waste Reduction (pounds)
Distillation tarsTetrachloroethylene0984,000

Citizen and NGO participants of the MSRI team expressed concern over the timing and the manner in which this pollution prevention option was developed. Dow developed the option early in the MSRI project before Dow Elanco (the predecessor of Dow AgroSciences) had officially agreed to participate, but after MSRI's pollution prevention consultant had begun a dialog with the plant. The idea was reported to the group "after the fact" and did not follow the participatory process used for other processes. In a more fully participatory process, citizen and NGO participants would likely have asked 2,4D staff more fundamental questions about the use and generation of toxic substances. These questions may have led to different options being considered. For example, why was tetrachloroethylene used as the solvent? Are substitutes available? In the past, Dursban was able to change process chemistry eliminating the use of methylene chloride in a new water-based process. Are similar opportunities available for 2,4D? Tetrachloroethylene is used to recover unreacted raw material. Can the yield of the process be improved to reduce the quantity of unreacted raw material? These kinds of questions were pursued with other businesses, but not with 2,4D.


Financial Savings Costs

The emulsion project cost approximately $140,000 and resulted in a total saving of approximately $525,000 annually.


SourceQuantity reduced (lbs.)Lost Raw Material Savings/yearWaste Treatment Savings/YearProject Cost
Distillation tars984,000$215,000$310,700$140,000



PROCESS: CHLOROPHENOL (2,4-DICHLOROPHENOL)

Process Description and Sources

Dow AgroSciences LLC produces 2,4-dichlorophenol (DCP) at the Midland site. All of the DCP produced is used on-site as a raw material for the manufacture of 2,4D.

The process uses phenol and chlorine as raw materials. The chlorination reaction produces DCP and byproduct hydrochloric acid, which is used in other processes on-site. The DCP is then purified by distillation prior to storage.


Diagram


The chlorination reaction also creates byproducts, which are the principal wastes generated in the process. One byproduct is 2,4,6-trichlorophenol, which is generated by the addition of a third, unwanted chlorine to the phenol molecule. Another chlorinated waste stream, identified for MSRI purposes as Cyclic Process Tar BCl-2, is generated by the addition of chlorine to other unintended sites on the phenol molecule. These wastes are separated from DCP by distillation and burned in an on-site RCRA incinerator. Some DCP distills over with these wastes and is also incinerated.


Pollution Prevention Options and Reductions

No pollution prevention options were developed during the course of MSRI. A working relationship between the plant's improvement leader and the independent pollution prevention assessor was not established until December 1998.

DCP process staff will focus pollution prevention efforts in 1999 and 2000 on improving the "selectivity" of the chlorination reaction. This would improve the yield of 2,4 dichlorophenol production and decrease formation of the 2,4,6-trichlorophenol and other unintended byproducts. A study of the kinetics of chlorine addition indicates that a reduction of approximately 40 % in 2,4,6 TCP and Cyclic Process Tar BCl-2 wastes is possible. Another future pollution prevention option that will be considered is improved separation of the product in the distillation step. A 50 % recovery of DCP from the waste is possible. Dow will continue to pursue these options, although reductions will not be counted toward the MSRI goal because funding was not in place by April 1999.



PROCESS: CHLORO ACETYL CHLORIDE (CAC)

Process Description and Sources

The Chloro Acetyl Chloride (CAC) process is part of the Global Chlorinated Organics business within Dow. The Midland site is Dow's only operating CAC plant. CAC is used primarily as an intermediate in the manufacture of monochloroacetic acid (MCAA). Most of the MCAA is sold. However, some is used as an intermediate at Midland to manufacture the pesticide 2,4 Dichlorophenoxy acetic acid, more commonly known as 24D.

Vinylidene Chloride and oxygen are the primary raw materials used to produce CAC. The oxidation reaction is highly exothermic, generating significant heat. Currently, the reactor is cooled with water from a cooling tower system.

The source of all wastes in CAC is the formation of byproducts in the reactor. These wastes exit the process at two primary sources: vent gases from the reactors and overhead tars from distillation. Waste from these two sources account for about 18 % of all MSRI wastes.


Diagram


Pollution Prevention Options and Reductions

Several pollution prevention options were explored including improved cooling, distillation column optimization and in-process recycling. The pollution prevention option of choice focused on the fundamentals of the chemical reaction to improve the overall efficiency through improved cooling. All the wastes from the process are generated as byproducts through inefficiencies in the reaction. Lower reaction temperature would decrease the formation of these unintended byproducts and increase yield of CAC product. Dow determined that additional cooling could be provided through refrigeration instead of the existing cooling towers. Improved refrigeration was estimated to reduce the generation of byproduct wastes by approximately 1.8 million pounds, 1.3 million of which is MSRI chemicals.


SourceMSRI ChemicalEstimated Release Reduction (pounds)Estimated Waste Reduction (pounds)
Vent Gas to IncineratorHCl0480,000
Phosgene0156,000
Vinylidene Chloride048,000
Overhead TarsNon-TRI chlorinated
Organics (aliphatic tar BCl-1) 0500,000
CAC (finished product BCl-1)010,000
MCAA distillation tars1,1,1,2tetrachloroethane0120,000


Financial Savings Costs

The avoided cost of lost raw materials and waste treatment from CAC was estimated to be $475,000 per year.


SourceQuantity (lbs.)Lost Raw Material Savings/YearWaste Treatment Savings/YearProject Cost
Reaction1,800,000$ 225,000$250,000$300,000


Initially, Dow prepared a "Project Definition," a package of technical and financial information used in Dow's internal funding approval process, based on purchasing new refrigeration equipment. New equipment was estimated to cost $500,000. In addition, $20,000 was requested so technical staff could conduct more detailed technical analysis for the project. At this early stage in the funding approval process, the project was considered only marginally attractive. . However, it was clear that if Dow followed this "typical" project development and approval process, it would be a challenge to obtain funding approval before the end of April.

In an effort to improve the economics of the project, Dow CAC staff contacted brokers of used refrigeration equipment. A suitable refrigeration unit was identified which improved the Discounted Cash Flow from 25 % to 48 %. CAC staff then contacted the business leaders who make funding decisions to discuss the new information. Funding was approved in less than one week. A search is now underway for idle refrigeration equipment within Dow which, if found, will improve project economics even further. The project will also increase production capacity. However, financial benefits from increased production were not part of the economic justification for the project because Dow evaluation rules require the increased production to be pre-sold before its value can be counted.

Detailed technical review of the equipment is expected to be complete by mid summer and installed and operational by April 2000.



PROCESS: ETHOCEL®

Process Description and Sources

The ETHOCEL® process is part of Dow's Global Specialty Chemicals business. The manufacturing plant has been in operation at the Midland site for over 60 years. ETHOCEL® is used in pharmaceutical applications.


Diagram


Air releases of toluene and chloroethane are the largest source of MSRI waste from the process. Vents from the reaction and recovery vessels are collected and passed through a refrigerated toluene scrubber. Any solvent not recovered by the time product leaves the solvent recovery step is lost as vent releases during the washing and drying steps.


Pollution Prevention Options and Reductions

Two pollution prevention options were implemented. The first included constructing a solvent recovery unit that uses steam to remove organic compounds from the product stream as it leaves the reaction train. The second pollution prevention project was the installation of another refrigerated condenser for recovery of toluene and chloroethane. This system was attached to the vent of the existing chilled toluene recovery system. The new refrigerated condenser was then connected to an existing on-site vent gas incinerator because one of the reaction byproducts, ethylene, cannot be condensed without expending a large amount of energy.


SourceChemicalEstimated Release Reduction (pounds)Estimated Waste Reduction (pounds)
Vent losses from reaction and recoveryToluene243,000243,000
Chloroethane114,000114,000


Financial Savings Costs

At $1.8 million, these were the highest cost projects in MSRI. They accounted for almost 60% of the total expenditure of $3 million. The raw materials recovered are inexpensive, so the savings gained by these investments were small. However, ETHOCEL® was by far the largest emitter of TRI chemicals at the Midland site. The initial driving force behind implementation of the projects was the magnitude of the TRI chemical releases relative to the corporate environmental philosophy However, the MSRI effort provided the impetus for a concerted effort to focus on the quick start-up and opimization of these unit operations.


SourceQuantity (lbs.)Lost Raw Material Savings/YearWaste Treatment Savings/YearProject Cost
Vent losses from reaction and recovery357,000$54,000$0 (formerly released)$1,785,000


Non-Pollution Prevention Reductions

Ethylene and a small amount of entrained raw materials were routed to an existing on-site incinerator. Incinerating these materials will reduce net releases by an additional 269,000 pounds per year: 30,000 pounds of MSRI chemicals (28,000 chloroethane and 2,000 toluene) and 239,000 pounds of non-MSRI chemicals (233,000 ethylene). The incineration of these materials, and the 9,000 pounds incinerated by engineering plastics, are the only treatment associated with the MSRI project. Materials incinerated are not counted in MSRI release reductions.



PROCESS: SARAN*

Process Description and Sources

The SARAN* process is part of Dow's Global Polyethylene business. There are three general types of SARAN* resins produced at the Midland site, each having vinylidene chloride (1,1-dichloroethylene, or VDC) as a principal raw material. SARAN* products are used for their barrier protection properties that prevent transmission of gases, water and odors in various food packaging and other applications.

While there are differences between the three processes, a single general description is used for the process. The first step in the process involves purification and storage of VDC monomer. Next, the other raw materials are added to initiate the polymerization reaction. The reaction mixture is then stripped to remove unreacted raw materials. A portion of these materials are recovered and reused. After stripping, the resin slurry is dewatered and dried prior to storage and packaging of the product.


Diagram


There are four primary sources of MSRI waste within the SARAN* processes. The first source is a vent from the raw material storage tanks connected to a vent incinerator. This waste is the result of vapor losses during filling and transfer of vinylidene chloride. The second source is also a vent to the vent incinerator. This loss is from the recovery of unreacted monomers in the SARAN*B process and consists primarily of vinyl chloride monomer. The third source is a liquid waste generated in the recovery process for the VDC/MA copolymer. This waste is burned in the on-site RCRA incinerator. The last source is a vent release to the air from the slurry storage and drying steps.


Pollution Prevention Options and Reductions

One pollution prevention option was implemented in this process. The change reduced vent losses from the raw material storage step by instituting new vapor balance procedures for transfers between tanks. Previously, Dow transferred raw material once per day to one of two tanks. Following the new procedures, there are two transfers per day and the tanks are not filled completely. This allows vapors displaced during filling to be vented into the headspace of the other tank instead of vented to the incinerator.

Dow studied recovery options for the vinyl chloride monomer vent losses from the recovery system in the SARAN*B process. Options considered for recovery include Pressure Swing Adsorption (PSA), increased pressure/condensation, and membrane separation. Dow has budgeted $50,000 to pilot test new technologies during the summer of 1999. The focus of these tests is on the use of PSA. Expecting that these tests will prove recovery is feasible, Dow has budgeted capital for implementation in 2000. Since the commitment of capital is dependent on tests to be conducted after the April 1999 deadline, these reductions are not counted. PSA tests run on similar streams at other Dow sites indicate that a 95% recovery rate of vinyl chloride can be expected.

Dow also looked at options for reducing the liquid waste from the VDC/MA process. Options considered for reducing this stream included in-process recycling and improving yield through changes in reaction chemistry. Concerns about the effect of MA recycle on product quality make it likely that the focus of future investigations will be on changes in chemistry. There are no firm plans for pursuing either of these options at this time.


SourceChemicalEstimated Release Reduction (pounds)Estimated Waste Reduction (pounds)
Vent from storage tanks to vent incineratorVinylidene Chloride034,000


Financial Savings Costs

The pollution prevention option in the storage step will save $13,000 annually. Instituting the new procedures did not require any capital expenditure.


SourceQuantity reduced (lbs.)Lost Raw Material Savings/YearWaste Treatment Savings/YearProject Cost
Vent from storage tanks to vent incinerator34,000$10,000$3,000Procedure change only

* A trademark of The Dow Chemical Company



PROCESS: HIGH IMPACT POLYSTYRENE (HIPS)

Process Description and Sources

The high impact polystyrene (HIPS) process is part of Dow's Global Polystyrene Business. The process produces STYRON® resins that are used in a variety of injection molding and extruded applications. STYRON® HIPS is used to manufacture products such as toys, appliance parts, packaging and furniture.

The process uses styrene and rubber as the primary raw materials. Styrene is used as a reactant for the polymerization reaction and rubber is added to increase strength and dent-resistance. In addition to these primary raw materials, an initiator is needed to start the polymerization reaction. This initiator is received in liquid form diluted with ethylbenzene. Once the polymer is produced, unreacted styrene and ethylbenzene remaining in the product is removed through stripping and condensing. This styrene is then reused in the process.

The primary by-product generated in the process is a purge stream from the recovery and reuse of styrene. A portion of the material in the recycle loop must be removed to prevent the buildup of ethylbenzene, which is un-reactive, in the system. Styrene is lost along with the ethylbenzene. The ethylbenzene comes from two sources: as an impurity in the styrene and as the initiator diluent. The by-product is sent to another Dow facility and is used as a raw material to produce styrene.


Diagram


Pollution Prevention Options and Reductions

A new concentrated form of the initiator was introduced. The concentrated form contains much less ethylbenzene diluent. This reduction in ethylbenzene inputs enabled Dow to reduce the amount of purge from the recycle system. Lower purge volumes mean lower styrene loss.


SourceChemicalEstimated Release Reduction (pounds)Estimated Waste Reduction (pounds)
Polystyrene Bypass Recycle (PBR)Styrene0456,000
Ethylbenzene0364,800


Financial Savings Costs

Equipment changes needed to use the concentrated catalyst cost approximately $300,000. This investment saved approximately $270,000 per year in lost raw material cost.


SourceQuantity reduced (lbs.)Lost Raw Material Savings/YearWaste Treatment Savings/YearProject Cost
Polystyrene Bypass Recycle (PBR)820,800$270,000
$300,000



PROCESS: ENGINEERING PLASTICS

Process Description and Sources

Three families of plastics are produced at the Midland site as part of the Global Engineering Plastics business. These plastics include TYRIL® (Styrene-Acrylonitrile or SAN), Mass ABS and Emulsion ABS/SAN. These plastics can be formulated to give a wide range of physical properties. Typical applications include housewares, packaging, auto parts, appliances, and piping.

Styrene is the raw material common to each of these engineering plastics. TYRIL® uses acrylonitrile to create a styrene-acrylonitrile copolymer. Mass ABS and Emulsion ABS also add polybutadiene rubber to enhance strength and other performance properties.

The TRYIL® and Mass ABS processes use similar steps. Raw materials react to form the polymer. The polymer is then stripped to remove unreacted, volatile raw materials. Most of these raw materials are recovered through condensation and returned to the process. After stripping, the polymer is pelletized prior to storage in large silos.


Diagram


The largest sources of wastes from the process are generated in the recovery of volatile raw materials. Two separate waste streams, one of low molecular weight compounds and a second of higher molecular weight compounds, are generated and sent to the RCRA incinerator. A smaller source of waste is generated from the equipment cleaning operations that use methylene chloride to clean heat exchangers.

The Emulsion process uses different processing steps. Here, latex ABS is produced. In addition to the latex ABS, a portion of the Mass ABS and TYRIL® are used as intermediates to manufacture different forms of the polymer.


Diagram


No liquid or solid MSRI wastes are generated in the recovery of raw materials. Vent air losses are the primary losses from the emulsion/latex process.


Pollution Prevention Options and Reductions

One pollution prevention option was developed in the Mass ABS process. Methylene chloride was used to clean process equipment (heat exchangers). Dow is replacing methylene chloride with a new cleaning process. Currently, two options are being considered. One option uses N-methyl pyrrolidone (NMP) for cleaning. Initial tests results demonstrated that NMP is a better and less volatile cleaner. In winter months, however, the cleaning tank will have to be heated. The second option uses a non-TRI substance in a new cleaning process currently being tested at another Dow site. Because six months elapse before the heat exchangers are re-installed, both options will be pursued during the summer of 1999. The NMP process works, but the other process is attractive because it does not use a TRI chemical (process uses heat and a high boiling point, recycled petroleum solvent) and the cleaning would be done by one of Dow's contractors.

Dow is also pursuing an additional pollution prevention option that was not fully developed within the 2-year time period for MSRI. This option involves switching from a dry form of initiator to a liquid form. Additional research and trial runs are needed and Dow plans to continue these efforts.


SourceChemicalEstimated Release Reduction (pounds)Estimated Waste Reduction (pounds)
Cleaning solventMethylene chloride33910,000


Financial Savings Costs

The new cleaning process is expected cost approximately $1,000 and save approximately $1,000 per year.


SourceQuantity reduced (lbs.)Lost Raw Material Savings/YearWaste Treatment Savings/YearProject Cost
Heat exchanger cleaning10,000$0$1,000$1,000


Non Pollution Prevention Reductions

During the MSRI project, Dow implemented additional treatment of vent air losses. Dow installed additional collection and piping to capture and send vent losses from the finishing step to an existing vent incinerator. This additional treatment is expected to reduce styrene vent releases by 9,000 pounds per year.

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