Tenneco develops economic process to recover ethylene from waste streams

A COMMERCIALLY viable method of recovering polymer-grade ethylene from waste gas streams has been ded o p e d by TeMeCO Chemicals. Called the ESEP process, it is based on the cuprous aluminum tetrachloride technoIogy previously applied by Tenneco to the recovery of carbon monoxide from dilute gas streams, Cosorb. (ESEP and Cosorb are trademarks.) The ESEP effort, as described by Arthur P. Gutierrez and Donald J. Haase during the 85th National Meeting of the American Institute of Chemical Engineers (Philadelphia, June 481, began in mid-1974. Vapor-liquid equilibrium data were developed, followed by bench-scale process simulation studies. These data were then utilized as a basis for pilot-plant d e sign. The pilot plant, with a production capacity of 500,OOO lb/year of ethylene, has been operated for about 2 years. Initially designed to demonstrate the separability of ethylene from carbon monoxide, it was subsequently tested on other gaseous mixtures. Process description. The process selectively and reversibly absorbs ethylene from gas mixtures by reaction with a cuprous aluminum tetrachloride ( CUAICla) complex dissolved in an aromatic base. Although the solvent complex exhibits a high selectivity for ethylene, a relatively weak bond is formed between the ethylene molecule and the solvent complex. Desorption can be accomplished at mild stripping conditions. In designing an ESEP plant, several important possible side reactions must be eliminated or at least minimized. Water, if present in significant quantity, will react irreversibly with the solvent, destroying its complexing properties. For this reason, a feed gas specification of less than 1 ppm of water must be maintained. Other side reactions can take place if certain sulfur compounds, namely hydrogen sulfide (HzS) and sulfur dioxide (SOz), are present. These reactions also affect the complexing properties of the solvent. Concentrations of H2S and SOz in the feed gas should be maintained at less than 1 PP" Olefins such as ethylene react with aromatic solvents in the presence of aluminum chloride to produce alkylated aromatic compounds. If this reaction were allowed to occur, the aromatic solvent base would become highly alkylated. A major proprietary innovation of the process involves the suppression of ethylene alkylation