DOWEX OPTIPORE Adsorbents DOWEX OPTIPORE Adsorbent Cuts Costs of Cleaning Solvent from Soil Vapor Extraction Off-Gas

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1 Case History DOWEX OPTIPORE Adsorbents DOWEX OPTIPORE Adsorbent Cuts Costs of Cleaning Solvent from Soil Vapor Extraction Off-Gas Site Information Location Connecticut, USA Purpose Lower cost alternative to thermal oxidation and adsorption by activated carbon for vent air treatment. Comparative Performance 99% overall removal efficiency Cost per year of $2,732 plus $0.06/lb of recovered solvent, compared to $104,000 for thermal oxidation and $739,000 for activated carbon Thermal oxidation and activated carbon have been used for many years to treat air contaminated with solvents. However, when the Allyn s Point site of The Dow Chemical Company needed a treatment system for air vented from their soil vapor extraction process, they turned to a relatively new product, DOWEX* OPTIPORE* V493 adsorbent. Introduction The Dow Chemical Company operates a solvent processing facility at Allyn s Point, CT. This facility uses a soil vapor extraction (SVE) process to decontaminate a wide variety of chlorinated and nonchlorinated solvents from soil. Air passes through contaminated soil to transfer the solvents from the soil to the air so the air must be treated before it can be discharged. Although there are established methods for vent air treatment, such as thermal oxidation and adsorption by activated carbon, such methods can be expensive. A lower cost alternative uses DOWEX* OPTIPORE* V493 adsorbent. Background Accidental spills and improper disposal of industrial chemicals can result in contamination of soils. Normally the chemical will diffuse through the soil to the water table and migrate away from the contamination site with the underground water flow. The spread of contaminated groundwater is contained with interdiction wells that pump the contaminated water to the surface where it can be treated. Page 1 of 5 * Trademark of The Dow Chemical Company Form No

2 Background, cont. Unfortunately, with pump and treat systems, the soil above the water table is still contaminated with the spill chemicals. Dow employs an SVE system to draw air through the soil to extract the spilled chemical. Because the concentration of the chemical can be significant, the air produced by the SVE process must be treated. Dow considered three alternatives for treating the vent air: thermal oxidation, adsorption with activated carbon and disposal, and adsorption using a regenerable adsorbent with solvent recovery. Conventional Options Thermal oxidation of chlorinated solvents will certainly destroy these wastes. However, this process requires natural gas as fuel and produces HCl as the combustion by-product, which must be scrubbed from the air with a caustic scrubber. The scrubber needs to be maintained at ph 8.2 (minimum) to effectively remove HCl, but CO 2 produced by combustion also places a demand for caustic in the scrubber. Estimates for a thermal oxidation system to treat a 271 ft 3 /min stream with an oxidizer and scrubber were $130,000 in capital cost and $104,000 in annual operating costs. 1 Activated carbon has been widely used to remove a variety of organic and chlorinated compounds from air streams. However, the capacity of activated carbon is reduced by the high humidity of the SVE air stream. Activated carbon is also voluminous and must still be disposed at a cost that is often more than the original purchase price of the activated carbon. In this example, where 150 lb/day of mixed organic and chlorinated chemicals are involved, the operational treatment cost was estimated to be $739,000 per year. 2 An Alternative Treatment A lower cost alternative to disposable activated carbon is DOWEX OPTIPORE V493 polymeric adsorbent. This engineered, synthetic adsorbent has been designed for on-site regeneration. On-site regeneration means rapid regeneration and reuse of the adsorbent, small inventories of adsorbent, and lower overall treatment costs. Key features of the adsorbent include Highly crosslinked polymer matrix Unique pore size distribution High surface area Improved capacity for organic compounds Hydrophobic adsorbent surface Noncatalytic activity Spherical beads with good physical strength SVE Process Characteristics The SVE air stream at the Allyn s Point site has a flow rate of 271 ft 3 /min, relative humidity of 98%, and ambient temperature. The SVE vent is first directed through a water and dirt trap, then directed to a bed of DOWEX OPTIPORE V493 polymeric adsorbent (Figure 1). The adsorbent beds contain 9 ft 3 each (191 lb) of V493 with an empty bed contact time of 2 s. The two beds of OPTIPORE alternate with one bed in service while the second is in regeneration. Page 2 of 5 * Trademark of The Dow Chemical Company Form No

3 SVE Process Characteristics, cont. Figure 1. Treatment system for vent from SVE process. Clean Air Organic Vapors Water and Dirt Trap Adsorbent Bed Adsorbent Bed Regeneration Loop Blower Condensing System External Condensate Tank Regeneration of the solvent-loaded adsorbent is performed by conductively heating the media to 125 C. A vacuum is applied while a low volume of sweep gas crosses the adsorbent to carry the solvent-laden gas to the condenser section. Because chlorinated solvents are involved, the potential for corrosion exists, so the vent gas is bubbled through an acid trap prior to condensation. The condensed solvents are transferred to a supply tank for later destruction by incineration. At the end of the heating cycle, the adsorbent is cooled back to ambient temperature in preparation for the next loading cycle. System Performance Table 1 lists the 44 chlorinated and nonchlorinated solvents that were monitored in this particular vent stream. The capture efficiency of DOWEX OPTIPORE V493 for any particular solvent was >97% and the overall removal efficiency for the composite solvent was >99%. Operating costs for the treatment system from the electricity to run the blowers, vacuum pumps, valves, condensers, and internal cooling systems are typically $0.06/lb of recovered solvent. This figure does not include the cost of incineration of the recovered mixed solvent. The adsorbent is replaced about every 5 years. Capital costs for this type of system will vary with the specific needs of the individual air stream and site requirements. A typical purchase price for a completely automated system will range from $120,000 to $160,000. Page 3 of 5 * Trademark of The Dow Chemical Company Form No

4 Table 1. Capture efficiency of DOWEX OPTIPORE V493 for various contaminants. Concentration (ppbv) Comp6und Before treatment After treatment Percent removed Dichlorodifluoromethane Chloromethane Chloroethane 7, Trichlorofluoromethane , 1-Dichloroethene , 2-Dichloropropane Methylene chloride 7, , 1-Dichloroethane 6, , 2-Dichloroethane 1, Chloroform 88, , 1, 1-Trichloroethane 45, Carbon tetrachloride 816,000 3, Benzene Toluene Tetrachloroethene 1, Ethlybenzene 10, Ethyltoluene (2-, 3-, 4-) m & p Xylene 1, o-xylene 1, Trichloroethene 1, , 3-Butadiene n-butane Butene/Isobutene 6, cis-2-butene 4, trans-2-butene 6, Cyclohexane Cyclopentane 3, Cyclopentene Dichlorobenzene (1, 2 & 1, 4) Dimethylbutane (2, 2 & 2, 3) , 4-Dimethylpentane n-heptane n-hexane Isobutane Isopropylbenzene 3, Methylbutane Methylcyclohexane n-octane/tetrachloroethene n-pentane n-propylbenzene 1, Trimethylpentane Page 4 of 5 * Trademark of The Dow Chemical Company Form No

5 Conclusions A regenerable adsorbent like DOWEX OPTIPORE V493, when used in an on-site regeneration system, can achieve a very high capture efficiency of >99% for a wide variety of chlorinated and non-chlorinated solvents. This type of system can be purchased and operated at a lower cost than the alternatives of disposable activated carbon or thermal oxidation. Notes 1. Natural gas use was estimated at 73,000 BTU/h and, at $3/million BTU, natural gas would cost about $2,000 per year. Estimates based on 0.5 lb/h of HCl are that 7 lb of NaOH/h would be required. If the cost of NaOH is $1.70/lb, annual costs would be $104,000/year. 2. Daily consumption of activated carbon was estimated to be 1,500 lb/day (based on a wt/wt% loading capacity). For these calculations, a purchase price of $0.65/lb and disposal cost of $0.70/lb (without freight included) were used. For more information about DOWEX resins, call the Dow Liquid Separations business: North America: Latin America: (+55) Europe: (+32) Pacific (ex. China): China: Notice: Oxidizing agents such as nitric acid attack organic ion exchange resins under certain conditions. This could lead to anything from slight resin degradation to a violent exothermic reaction (explosion). Before using strong oxidizing agents, consult sources knowledgeable in handling such materials. Notice: No freedom from any patent owned by Seller or others is to be inferred. Because use conditions and applicable laws may differ from one location to another and may change with time, Customer is responsible for determining whether products and the information in this document are appropriate for Customer s use and for ensuring that Customer s workplace and disposal practices are in compliance with applicable laws and other governmental enactments. Seller assumes no obligation or liability for the information in this document. NO WARRANTIES ARE GIVEN; ALL IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE ARE EXPRESSLY EXCLUDED. Page 5 of 5 *Trademark of The Dow Chemical Company Form No