GB571736A - Dehydrogenation of butenes to butadiene - Google Patents

Abstract

In the manufacture of butadiene by thermal non-catalytic dehydrogenation of a butene, a hydrocarbon mixture comprising predominantly C4 hydrocarbons and containing a substantial amount of a normal butene is heated to a dehydrogenating temperature by mixing with a separately heated inert gas having a temperature substantially above that of dehydrogenation, and rapidly quenching the resulting product. A suitable feed may be prepared by dehydration of butyl alcohol, dehydrohalogenation of chlorbutane or, preferably, by treating a C4 fraction of cracked gas with cold sulphuric acid to remove isobutene, contacting with warm acid to isomerize butene-1 to butene-2, and separating the olefin from paraffins by extractive distillation. The butene feed is preheated to below about 550, preferably 450-550 DEG C., an inert gas such as hydrogen, methane, ethane, steam, carbon dioxide or nitrogen is heated to about 700-1200, generally 800-1000 DEG C., and mixed rapidly therewith to give a temperature above 600, preferably 650-850 DEG C. The time of reaction varies and is chosen to give a conversion of 5-85 per cent of the butene in the feed. Contact with ferrous metals or iron oxides is avoided, heated surfaces preferably being of copper alloys or ceramics. Pressures are about atmospheric or below, preferably not substantially above 100-150 lbs./sq. in. The products are rapidly quenched by admixture with a cold fluid such as water or hydrocarbon which is inert and easily separable to lower the temperature to below 450, preferably 400-300 DEG C. Butadiene and, if desired, a butene fraction for recycling may be separated from the products. Butene-1 may be isomerized to butene-2 before recycling.