Installation and Operation of Sorbathene Solvent Vapor Recovery Units to Recover and Recycle Volatile Organic Compounds at Operating Sites within the Dow Chemical Company

Abstract

In 1988, the Separation Technologies Lab of The Dow Chemical Company in Michigan developed and patented a modified vacuum swing adsorption machine that captures, concentrates, and condenses the organic contaminants from the vent stream, returning a liquid mixture of the chemicals present in the inlet stream. Designed and installed under The Dow Chemical Company environmental program "Waste Reduction Always Pays," the SORBATHENE units recover and recycle thousands of pounds of chemicals every year that incineration equipment would otherwise destroy as waste. The recovered chemicals are valuable to the company and the recycling option avoids the costs of downstream waste processing associated with thermal destruction. The Dow Chemical Company developed the SORBATHENE vacuum swing adsorption as an economical alternative for the recovery of volatile organic compounds (VOC's) from storage, loading, and process vents streams. This paper discusses the application of the technology on nineteen units to collect hydrocarbons, chlorofluorocarbons (CFC's), chlorinated solvents, aromatics, and monomers. SORBATHENE units are now meeting air permit requirements for the abatement of VOC's such as benzene, acetone, trichloroethylene, trichlorofluoromethane, carbon tetrachloride, and styrene monomer. In operation, the SORBATHENE process conserves the heat generated during adsorption and utilizes this heat and depressurization with backpurge for batch regeneration of the adsorbent in a subsequent vacuum desorption step. Proprietary Dow research data is used in the selection of the optimum adsorbent mixture. The adsorption and desorption steps are batch processes that occur simultaneously in alternating twin beds to maintain steady state operation of the SORBATHENE unit. The unit is self-regenerating with no need for offsite regeneration or disposal of the adsorbent. The unit requires minimum operator interface and minimum maintenance. As a rule of thumb, the power to operate the unit is approximately one-tenth of a horsepower per each actual cubic feet per minute of the vent stream.