GB867296A - A process for the production of butadiene and isoprene - Google Patents

Abstract

<PICT:0867296/IV (b)/1> Butadiene and isoprene are obtained by catalytic dehydrogenation of a mixture of n-butylene and tert.-amylenes, separating lighter and heavier materials to recover a mono-and di-olefinic C4/C5 fraction, fractionating to separate C4 hydrocarbons from C5 hydrocarbons and separately recovering butadiene and isoprene. Referring to Fig. 1, a butane stream 10 is dehydrogenated at 12 and separated at 15 into butane, which is recycled, and butylene and butadiene. The separation may be by extractive distillation, e.g. with acetonitrile/water. The solvent is stripped and butadiene then recovered by solution, e.g. in cuprous ammonium acetate, furfural, acetone/water or acetonitrile/water in unit 19. Part of the butylene stream 23 is treated at 24 for removal of isobutylene, e.g. by treatment with sulphuric acid (which may contain ethyl alcohol) or a supported phosphoric acid catalyst, or by extractive distillation or by fractionation to separate butene-2. Tertiary amylenes are separated from amylene stream 25 at 27 by sulphuric acid treatment or selective formation of alcohol or ether, which is then decomposed. The amylenes and butylenes are mixed, heated, mixed with an equimolar quantity of steam and dehydrogenated (at 550-680 DEG C. and less than 50 p.s.i.a., over iron oxide promoted with chromium oxide and potassium carbonate, or nickel and calcium phosphates containing chromium oxide). The resultant stream 35 is passed to stripper-scrubber 37 fed at the top with a hydrocarbon oil, e.g. a heavy catalytically cracked gas oil fraction boiling in the range 260-370 DEG C., which dissolves out heavy polymeric material, and at the bottom with high pressure steam, which strips light hydrocarbons from the oil. The gas is cooled to liquefy water, which is separated in separator 41, then cooled with liquid ammonia to separate C2 and lower boiling materials, which are contacted in tower 48 with oil from the stripper-scrubber 37 to dissolve C3 and heavier hydrocarbons, which are then recovered in the stripper-scrubber. The liquid from separator 45 is depropanised in tower 51 and separated in C4 and C5 hydrocarbons in tower 53. The C4 hydrocarbons pass by line 55 for butadiene recovery and butylene recycle, at least part being returned to unit 15 to prevent build up of butane. The C5 hydrocarbons are extractively distilled at 56 with acetonitrile/water to recover dienes, which are separated at 61 into isoprene and piperylene and amylenes, which are recycled to the dehydrogenation. Specifications 593,849, 649,444 and 679,082 are referred to.