GB875346A - Production of isoprene - Google Patents

Abstract

Isoprene is produced by combining with a mixed C5 olefinic hydrocarbon fraction, from which any cyclic C5 hydrocarbons have been removed, at least an equal part by weight of a lower boiling hydrocarbon fraction containing not more than 20% by weight isobutylene, adding to the mixture at least an equimolar amount of steam, dehydrogenating under alkaline conditions in the presence of a water-gas-active dehydrogenation catalyst and fractionating the product to separate an isoprene-containing C5 fraction. The feed, both C5 and the lower boiling fraction, may be obtained, by fractionation of an olefinic, catalytically cracked gasoline. The lower boiling fraction is preferably C3-C4 and is used in amounts of 2-12 times the weight of the C5 fraction. The mixture is dehydrogenated at 550-650 DEG C. in the presence of 1-20 moles of steam in the presence of a catalyst promoted with an alkaline salt of potassium or calcium, e.g. potassium carbonate, such as the catalysts described in Specifications 596,616, 597,993, 649,444, and 746,611 and U.S.A. Specifications 2,395,875, 2,414,585, and 2,866,790. In the examples the catalyst comprises approximately equal amounts of potassium carbonate and iron oxide, in one case stabilized with chromium oxide. The isoprene may be recovered by extractive distillation with acetone-water, acetonitrile-water or sulpholane.