| 摘要 |
1,195,648. Isoprene. JAPANESE GEON CO. Ltd. 11 Nov., 1968 [11 Nov., 1967; 15 July, 1968], No. 53361/68. Heading C5E. Isoprene is freed from cyclopentadiene, e.g. in the recovery of isoprene from C 5 fractions, by extractive distillation under anhydrous conditions using as solvent an N-alkyl fatty acid amide, e.g. dimethyl formamide, so as to extract cyclopentadiene into the solvent, the solvent then being regenerated by heatstripping in one or more zones, of which the or at least the last such zone is operated under subatmospheric pressure at a temperature below 140‹ C. Two stripping zones are preferably employed, the first under atmospheric pressure and the second under said subatmospheric pressure. If the feed is a C 5 mixture it may, before treatment as above, be subjected to (a) a first extractive distillation using a similar solvent so as to extract isoprene and hydrocarbons more soluble than isoprene from less soluble hydrocarbons such as pentenes and pentanes, followed by (b) ordinary distillation of the extracted isoprene to remove a major proportion of cyclopentadiene and other higher boiling hydrocarbons therefrom. Isoprene product may be further fractionated to remove isopropyl acetylene and butyne-2. In an example, a process comprising all of the above steps results in isoprene of 98À18 mol. per cent purity, the main impurity being 1À42% 2-methyl butene-2.
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