v>EPA United States Environmental Protection Agency Risk Reduction Engineering Laboratory Cincinnati OH 45268 Research and Development EPA/600/S-92/004 May 1992 ENVIRONMENTAL RESEARCH BRIEF Waste Minimization Assessment for a Manufacturer of Chemicals Gwen P. Looby and Phylissa S. Miller* Abstract The U.S. Environmental Protection Agency (EPA) has funded a pilot project to assist small- and medium-size manufacturers who want to minimize their generation of waste but who lack the expertise to do so. In an effort to assist these manufactur- ers, Waste Minimization Assessment Centers (WMACs) were established at selected universities and procedures were adapted from the EPA Waste Minimization Opportunity As- sessment Manual (EPA/625/7-88/003, July 1988). The WMAC team at the University of Tennessee performed an assessment at a plant manufacturing acrylic emulsions, low molecular weight resins, herbicides, and specialty chemicals-approximately 300 million Ib/yr. In general, monomers, additives, activators, and catalysts are metered and mixed in tanks then pumped se- quentially into reactor vessels. Once the product is formed, the solution is pumped into a blend tank where more chemicals, such as binders, emulsifiers, and thickeners, are added. From the blend tank the product is passed through filters for clump removal then pumped into either storage tanks or drums for shipping. The team's report, detailing findings and recommen- dations, indicated that the majority of waste was generated in the wastewater treatment system and that the greatest savings could be obtained by installing a natural gas-fired dry-off oven in the wastewater treatment system to reduce (by 81%) the amount of sludge removed to the landfill. This Research Brief was developed by the principal investiga- tors and EPA's Risk Reduction Engineering Laboratory, Cincin- nati, OH, to announce key findings of an ongoing research project. This brief provides only summary information and is •University City Science Center, Philadelphia, PA 19104. not intended for use as a thorough analysis. A fully docu- mented report of the same title is available from the authors. Introduction The amount of waste generated by industrial plants has be- come an increasingly costly problem for manufacturers and an additional stress on the environment. One solution to the prob- lem of waste is to reduce or eliminate the waste at its source. University City Science Center (Philadelphia, PA) has begun a pilot project to assist small- and medium-size manufacturers who want to minimize their formation of waste but who lack the in-house expertise to do so. Under agreement with EPA's Risk Reduction Engineering Laboratory, the Science Center has established three WMACs. This assessment was done by engineering faculty and students at the University of Tennessee's (Knoxville) WMAC. The assessment teams have considerable direct experience with process operations in manu- facturing plants and also have the knowledge and skills needed to minimize waste generation. The waste minimization assessments are done for small- and medium-size manufacturers at no out-of-pocket cost to the client. To qualify for the assessment, each client must fall within Standard Industrial Classification Code 20-39, have gross annual sales not exceeding $50 million, employ no more than 500 persons, and lack in-house expertise in waste minimiza- tion. The potential benefits of the pilot project include minimization of the amount of waste generated by manufacturers and reduc- tion of waste treatment and disposal costs for participating plants. In addition, the project provides valuable experience for graduate and undergraduate students who participate in the program and a cleaner environment without more regulations and higher costs for manufacturers. Printed on Recycled Paper ------- Methodology of Assessments The waste minimization assessments require several site visits to each client served. In general, the WMACs follow the proce- dures outlined in the EPA Waste Minimization Opportunity Assessment Manual (EPA/625/7-88/003, July 1988). The WMAC staff locates the sources of waste in the plant and identifies the current disposal or treatment methods and their associated costs. They then identify and analyze a variety of ways to reduce or eliminate the waste. Specific measures to achieve that goal are recommended and the essential supporting tech- nological and economic information is developed. Finally, a confidential report that details the WMAC's findings and recom- mendations (including cost savings, implementation costs, and payback times) is prepared for each client. Plant Background This plant manufactures acrylic emulsions, low molecular weight resins, herbicides, and other specialty chemicals. The plant operates 8,400 hr/yr to produce approximately 300 million pounds of chemicals. Manufacturing Process The processes are complex and vary extensively in the exact methods used in order to produce the final product. The pro- duction of one particular low molecular weight dispersant prod- uct generates significant quantities of wastes and therefore will be considered a separate process in this evaluation. The pro- cess lines are described below in detail. Acrylic Emulsion Production Approximately 400 different acrylic emulsion formulations are produced by this plant. The actual sequence of steps required varies greatly from product to product. However, the overall process sequence is similar in most cases and is described below. Raw materials for the emulsion line include monomers, additives, activators, and catalysts in either liquid or solid form. Some monomers have been pre-mixed with inhibitors for stabi- lization. Catalysts are used to activate the monomers and initiate the desired reactions. Activators increase the activity level of the catalysts and allow reactions to overcome the effects of the inhibitors. Additives include detergents, disper- sants, and pH-adjustment ingredients. Monomers are pumped from tanker trucks to monomer tanks for storage. From the storage tanks, monomers are pumped to holding/premixing tanks, and in some cases to the additive, activator, and catalyst holding tanks where mixing occurs. The additives, activators, and catalysts may be added directly to the reactors without being mixed with monomers in their re- spective holding tanks. From the holding tanks, raw materials are mixed together using certain proprietary recipes in one of three temperature- and pressure-regulated reactors where polymers are formed. Chemi- cal reactions are initiated by addition of catalysts and are regulated with additives or by pressure and temperature ad- justment. Next, the resulting acrylic emulsion polymers are pumped to blend tanks where other ingredients are added. At this point approximately 40% to 60% of the emulsion is water. Formalde- hyde is added as a preservative to control bacteria and mold growth, and ammonia is added to approximately half of the product for pH adjustment. Another pH-adjustment chemical that is added in the blend tanks is sodium hydroxide. Other ingredients such as emulsions, emulsifiers, surfactants, bind- ers, and thickeners are added to modify monomer viscosity, to stabilize the polymers, and to hold the polymers in suspension. De-ionized water is added to lower the solids content. After each polymer batch is processed, the blend tanks are flushed with de-ionized water that is then pumped to the plant's waste- water treatment system. Wastes generated up to this point in the process include composited absorbed monomers, burnable liquids, and off- grade methylolacrylamide/acrylamide. Most of the composited absorbed monomer waste generated occurs from spillage dur- ing loading and unloading of the railcars or from batch spills and reactor clean-ups. Burnable liquids waste results from off- spec mixtures or reactions resulting from incorrect tempera- tures or incorrect batch weights of solutions in the feed tanks and reactors. Some of the burnable liquids waste from the off- spec batches are recovered and mixed with good batches. Off- grade methylolacrylamide/acrylamide results from bad batches of a particular commercial product. In addition, some waste is generated because of a product's relatively short shelf life. Equipment and/or operator error also accounts for a portion of off-grade material. From the blend tanks, the acrylic emulsion polymers are pumped through tightly woven cloth filters that separate unwanted clumps of product from the water phase. The used filters, which con- tain clumps of product, are shipped offs'rte to a landfill. (An estimated 0.25% of actual product is trapped in the filters.) After filtering, the emulsions are pumped either to storage tanks or directly into drums for shipping. Low Molecular Weight Resin Production Production processes and raw materials for the low molecular weight (LMW) resins are identical to those of the acrylic emul- sions until the product is pumped into the blend tanks. Following batch polymerization in the reactor vessels, the LMW resin product is pumped to one of six blend tanks where different additives including water, sodium hydroxide, ammo- nia, detergents, and emulsifiers are added. These additives provide pH adjustment, solids adjustment, and preservation of the product. From the blend tanks, the LMW resin polymers are pumped either to storage tanks for future shipping or directly to drums for immediate shipping. One waste generated from this production line is an unsalable product, which is shipped offsite as a hazardous waste. Addi- tional waste generated by this line is a result of off-grade batches. Other wastes generated in this process are similar to those in the emulsion line and include composited absorbed mono- mers, burnable liquids, and off-grade methylolacrylamide/ acrylamide. These wastes are generated in the same manner mentioned above. An abbreviated flow diagram for acrylic emulsion and the LMW resin process is shown in Figure 1. Dispersant Process The production of one particular low molecular weight resin product (a proprietary dispersant) results in the generation of two significant waste streams and will be considered here as a separate process description. ------- Burnable Compopijfy Absorbed:, , Monomers - v- 4 Miscellaneous Other Chemicals Depending on the Product Acrylic Emulsion Used Filters, Clumps, Waste water Storage Tanks or Drums Unsalable Product Figure 1. Abbreviated flow diagram for the acrylic emulsion and LMW resin process. Xylene, diisobutylene (DIB), and other monomers and addi- tives are pumped to the reactors in the LMW resin production line. In a batch production, polymers are formed in the reac- tors. The product is pumped to a separation tank where the unwanted heavier DIB settles to the bottom of the tank and the lighter-fraction product is decanted from the top. An emulsion- like interface composed of DIB and product is formed between the product and the DIB layers and is removed from the tank and shipped offsite as a hazardous waste. Some of the DIB solvent from the separation tank is drained to a storage tank where further separation by settling occurs. Product/DIB inter- face is removed from this storage tank and is shipped offsite as hazardous waste. The DIB wet solvent from this tank is pumped to the boiler and burned. Recovered xylene/DIB mixture from the separation tank is returned to the reactor. From the separation tank, the upper layer product fraction is decanted into another separation tank. Water is separated from the product and pumped to the plant's water treatment system. The product is pumped to a blend tank from which more DIB wet solvent is removed and burned in the boiler. The product is then pumped either to storage tanks or to drums for shipping. An abbreviated flow diagram for the dispersant pro- cess is shown in Figure 2. Herbicide/Specialty Chemical Production Ingredients are mixed together in a pressure- and temperature- regulated reactor where a specified reaction occurs. Absorbed propionic acid waste is generated from the loading and unload- ing of material. High- and low-acidic content propionic acid wastes are generated by the reactions. Highly acidic propionic ------- Raw Material Reactors Separation Tank pH and Solids Adjustment /Excess DIB\ Blend Tank Decanted DIB Storage Tanks or Drums Figure 2. Abbreviated flow diagram for the dispersant process. acid is recycled back into the reactors for use in further pro- cessing. The low-acidic content propionic acid is pumped to the wastewater treatment system where it is used to neutralize caustic wastewater from other plant operations. From the reactor, the product is pumped to a blend tank to which other chemicals and emulsifiers are added; these sub- stances reduce the viscosity of the product. Several wastes are generated from the annual cleaning of the reactor and blend tank including wastewater that is pumped to the wastewater treatment system, herbicide residue, and herbicide articles (contaminated employee clothing). From the blend tank, the products are loaded onto railcars and shipped. An abbreviated flow diagram for the herbicide/specialty chemical process is shown in Figure 3. Pollution Abatement (PA) System This plant uses a pollution abatement system to remove va- pors from various areas of the plant including the monomer storage area, tanks in the resin production area, and the reactors and holding/premixing tanks in the emulsion produc- tion line. This system was installed mainly to remove vapors with persistent irritating odor from the plant. A blower located down the line creates a pressure difference and pulls fresh air over the tanks mentioned above. Vapors collected from the monomer storage area and resin area tanks are blown to separate liquid knock-out tanks. These tanks act as condensers and use ambient air cooling to condense a portion of the vapors. The resulting condensate from these tanks is directed to the water treatment facility. From the knock-out tanks, the vapors are ducted through separate lower explosive limit (LEL) monitors that evaluate the flammability of the vapors. From the monitors, the vapors are directed through backfire preventers that act as safety valves and prevent va- pors from being drawn back through the system. Vapors from the reactors and feed tanks in the emulsion line follow a similar route through the PA system; however, they are first ducted through a caustic scrubber. Caustic solution is added to this scrubber as well as 150 gal/min of water to remove particulates from the fumes. This solution is dumped to the water treatment system every 11 days. The vapors are then directed through a liquid knock-out tank (from which water is pumped to water treatment), through a backfire preventer, and then through an LEL monitor. From that monitor, the vapors pass through a blower, another backfire preventer, and finally most of the vapors (99.97%) enter a natural gas-fired thermal oxidizer at MOOT. Wastewater Treatment System Another onsite waste treatment facility this plant has installed is its wastewater treatment system. Wastewater from the emul- sion line and the resin line, laboratory wastewater, and air compressor and other cooling water are directed to this facility for treatment. All incoming water passes through a roto-strainer that removes suspended solid particulates. The solid waste falls into two hoppers and is eventually hauled offsite to a landfill. From the roto-strainer, the water enters a neutralization tank where carbon dioxide and low acidic propionic acid from the herbicide line are added for neutralization. The water then enters a second neutralization tank where the water is agitated to promote further neutralization. Next, the wastewater enters three open-air mixing basins in which sludge is allowed to settle to the bottom. Sludge is removed quarterly to landfill. ------- Excess High Strength Propionic Acid Excess Low Strength Propionic Acid to Wastewater Treatment Figure 3. Abbreviated flow diagram for the herbicide/speciality chemical process. The effluent wastewater is released to the municipal sewer. Total water discharged from the plant on an annual basis is approximately 126 million gal/yr. Existing Waste Management Practices • A pollution abatement system removes noxious and odor- ous vapors from the plant and incinerates them. • Off-grade monomers and polymers are reused in an effort to produce salable products. • Diisobutylene wet solvent is burned in an onsfte boiler. Waste Minimization Opportunities The type of waste currently generated by the plant, the source of the waste, the quantity of the waste, and the annual treat- ment and disposal costs are given in Table 1. Table 2 shows the opportunities for waste minimization that the WMAC team recommended for the plant. The type of waste, the minimization opportunity, the possible waste reduction and associated savings, and the implementation cost along with the payback time are given in the table. The quantities of waste currently generated by the plant and possible waste reduction depend on the production level of the plant. All values should be considered in that context. It should be noted that, in most cases, the economic savings of the minimization opportunities result from the need for less raw material and from reduced present and future costs associated with waste treatment and disposal. Other savings not quantifi- able by this study include a wide variety of possible future costs related to changing emissions standards, liability, and employee health. It should also be noted that the savings given for each opportunity reflect the savings achievable when imple- menting each waste minimization opportunity independently and do not reflect duplication of sayings that would result when the opportunities are implemented in a package. This research brief summarizes a part of the work done under Cooperative Agreement No. CR-814903 by the University City Science Center under the sponsorship of the U.S. Environmen- tal Protection Agency. The EPA Project Officer was Emma Lou George. ; ------- Tsble 1. Summary of Waste Generation Waste Generated Source of Waste Annual Quantity Annual Waste Generated Management Cost ($) Burnable liquids Composited absorbed monomers Off-grade methylolacrylamide/ acrylamlde Used filters and trapped product Unsalable low molecular weight resins Diisobutylene (DIB) wet solvent Off-grade mixtures and bad reactions in the acrylic emulsion and low molecular weight resin production lines. Spillage and clean-up of reactors in the acrylic emulsion and low molecular weight resin production lines. Off-grade batches of product in the acrylic emulsion and low molecular weight resin production lines Filtering process in the acrylic emulsion production line. Expired products and off-grade batches of products in the low molecular weight resin production line. Spent solvent from the dispersant production line. DIB wet solvent is sent to an onsite thermal oxidizer. 15,400 Ib 15.400 Ib 5,100 Ib 44,800 Ib 20,880 Ib 316,220 Ib 77,110 77,110 40,760 33,080 116,200 24,500 Product/DIB Interface Absorbed proplonic acid Contaminated employee clothing Herbicide residue Cold stack gases (noxious, odorous, and organic vapors drawn from monomer storage area, tanks in resin line, and resin reactors and tanks) Wastewater sludge Wastewater Separation tank in the dispersant production line. Spillage in the herbicide/specialty chemical production line. Herbicide/specialty chemical production line. Cleaning of the reactor and blend tank in the herbicide/specialty chemical production line. Thermal oxidizer and heat exchanger in the Pollution Abatement System. Onsite wastewater treatment system. Onsite wastewater treatment system. 25,750 Ib 6,000 Ib * 1,000lb 394,200 ff 300,000 Ib 126,000,000 gal 79,860 13,510 * 24,150 0" 456,800 2,121,700 'New waste; no data available. "There are no direct costs reported for handling evaporative waste. ------- Table 2. Summary of Waste Minimization Opportunities acrylamide Unsalable product Annual Waste Reduction Net Annual Implementation Payback Waste Generated Burnable liquids Composited absorbed monomers Off-grade methylolacrylamide/ Minimization Opportunity Upgrade the redundant sensing and control devices on the reactor raw material lines to reduce the amount of off- specification product batches. Quantity 7 1,550 to 2,890 Ib 3,480 to Percent 75 19 71 Savings ($) Cost ($) 139,810 365,480 Years 2.6 3,130 Ib 15 Wastewater sludge Install a natural gas-fired dry-off oven in the waste- water treatment system to reduce the amount of sludge removed to the landfill. 244,030 Ib 81 92,730 70,320 0.8 •&U.S. GOVERNMENT PRINTING OFFICE: 1992 - 648-080/40271 ------- United States Environmental Protection Agency Center for Environmental Research Information Cincinnati, OH 45268 BULK RATE POSTAGE & FEES PAID EPA PERMIT NO. G-35 Official Business Penalty for Private Use $300 EPA/600/S-92/004 ------- |