METHOD OF PREPARING ISOPRENE BY LIQUID PHASE REACTION OF ISOBUTENE AND FORMALDEHYDE Russian patent published in 1999 - IPC

FIELD: chemical industry. SUBSTANCE: method of preparing isoprene by liquid phase reaction of isobutene and/or isobutene-containing hydrocarbon mixture and/or tert-butanol with aqueous solution of formaldehyde in the presence of acid catalysts in succession at least in two reaction zones. In one of zones semiproducts are synthesized and in the last one semiproducts are decomposed at higher temperature and at least isoprene and, isobutene are subsequently isolated from reaction products and at least greater portion of isobutene and optionally acid catalyst solution are recycled to synthesis zone. Temperature, amount of catalyst and contact time in semiproduct decomposition zone are maintained so as to afford conversion of at least 90%, preferably at least 95% of methyl butadiol being admitted and not higher than 80% of 4,4-dimethyl-1,3-dioxane being admitted, and unreacted 4,4-dimethyl-1,3-dioxane is recycled individually or/and in admixture with tert-butanol or/and in admixture with by-products into first reaction zone. EFFECT: improved purity of the desired product. 6 cl, 4 ex, 1 tbl