HIGH-PURITY ISOBUTENE PRODUCTION FROM MTBE

Under suitable conditions, methyl-tert-butyl ether (MTBE) is decomposed into isobutene (C4H8) and methanol (CH3OH). This decomposition is a reversible endothermic chemical reaction (DELTA-H298-degrees = 15.6 kcal/mol in the gas phase). When this reaction is situated downstream from MTBE synthesis from a C4 cut, this results in the separation of the different isomers in this cut by a less costly method than the one now used, which consists of concentrated sulfuric-acid extraction. The isobutene obtained by MTBE decomposition is very pure and meets the specifications required for subsequent polymerization into butyl rubber or methyl methacrylate. The MTBE decomposition reaction is accompanied by secondary reactions such as the oligomerization of isobutene (mainly the formation of dimers), the dehydration of methanol into dimethylether, and the hydration of isobutene into tert-butyl alcohol. MTBE decomposition is catalyzed by solids with an acid nature. It has mainly been examined on catalysts of the sulfonic-resin type, but solid acid catalysts have recently appeared (zeolites, silica-alumina, supported phosphoric acid, etc.). The different types of catalysts used are examined for the principal reaction and secondary reactions.