GB831357A - Purification of isoprene - Google Patents

Abstract

Isoprene is freed of straight chain acetylene contaminants by contacting the impure isoprene with a molecular sieve having a channel diameter of about 5 . The usual contaminants are 1-pentyne and 2-butyne in amounts up to about 5% by weight and these can be removed to leave less than 0.1%. The sieve may be any natural or synthetic zeolite of the required pore size. In small-scale operations the isoprene can be stirred with a powdered sieve in an amount of 200-400 grams per mol. of acetylene contaminant. In larger scale operations the isoprene is contacted in the vapour and/or liquid phase at - 20 DEG to 150 DEG F. and 1-250 p.s.i.a., preferably ambient conditions, with fixed or moving beds of sieves at space velocities of 0.3-20 vol/vol/hr. The isoprene is preferably predried since water is preferentially adsorbed on the sieves. The sieve may also be dried by heating to 250-650 DEG F. The sieves may be regenerated by burning off the acetylene contaminants with an oxygen-containing gas at 900-1100 DEG F. To prevent the temperature rising too high the oxidizing gas is normally air diluted, e.g. with nitrogen. The sieve is cooled by passing through it a dry inert gas. The isoprene freed from acetylenes is suitable for polymerization. Dienes may also be removed if desired, e.g. by adding maleic anhydride and flash distilling.