GB959744A - Process for the combined production of butadiene and isoprene - Google Patents

Abstract

Butadiene and isoprene are obtained from a C4 hydrocarbon feed containing both normal and branched chain hydrocarbons by subjecting the feed to dehydrogenation, separating and recovering butadiene, subjecting at least part of the residue to reaction with formaldehyde to convert not more than 99% of the isobutene into isoprene and/or 4,4-dimethyl metadioxane which is subsequently converted into isoprene, recovering isoprene and separating and recycling to the dehydrogenation unreacted hydrocarbons. The feed containing at least one of isobutane and isobutene and at least one of n-butane and n-butenes is dehydrogenated conventionally, e.g. over a mixed oxides catalyst. The effluent is preferably fractionated to separate a C4 stream and butadiene is selectively dissolved in cuprous ammonium acetate or subjected to extractive distillation with furfural. The residue is preferably distilled or subjected to solvent extraction to separate an isobutene-rich fraction. the remainder being recycled direct to the dehydrogenation. Reaction with formaldehyde is effected over an acid on a support to produce isoprene or passed into an acid containing formaldehyde polymer to form 4,4-dimethylmetadioxane which is subsequently decomposed into isoprene. Unreacted hydrocarbons are recycled. In modifications a further C4 feed is introduced, e.g. a steam cracking product is introduced immediately before the recovery of butadiene or a catalytic cracking product after the recovery of butadiene.