GB811629A - Improved isomerization process - Google Patents

Abstract

In a combination hydrocarbon separation and isomerisation process a naphtha boiling in the range C5-180 DEG F. and containing normal pentane and hexane is upgraded by passing in the vapour phase through an adsorption zone where normal hydrocarbons are adsorbed, cyclic and branched chain hydrocarbons being unadsorbed, desorbing the adsorbed hydrocarbons and passing to an isomerization zone, passing the isomerizate with fresh feed to the adsorption zone and fractionating the unadsorbed hydrocarbons firstly to separate cyclic from non-cyclic hydrocarbons and secondly to separate the latter into (a) isopentane and dimethyl butanes and (b) methyl pentanes. The methyl pentanes are preferably passed to the isomerization zone. The feed may be a virgin naphtha or reformate, olefines are preferably removed. The adsorption zone preferably contains a 5<\>r molecular sieve, e.g. a zeolite, and is operated at 200-400 DEG F. with flow rates of 0.1-2 vol./vol./hr. and pressures of 0-100 p.s.i.g. Desorption is effected by heating to 450-800 DEG F. with or without addition of carbon dioxide, methane or ammonia or reduction of pressure, or by passing propylene or a propylene-containing refinery gas through the sieve. Activated carbons having 5<\>r pore openings can be used instead of the sieve. The isomerisation is preferably performed in the liquid phase using a FriedelCrafts catalyst such as aluminium chloride which may be supported on porous alumina at temperatures of 100-275 DEG F., pressures of 100-450 p.s.i.g. and space velocities of 0.3-3 vol./vol./hr. with 0.1-6 per cent by weight of hydrogen chloride promoter based on hydrocarbon charge and a hydrogen partial pressure of 0.1-3 mol. per cent. A small amount, below 0.5 per cent of a cyclic hydrocarbon, may also be added to the feed to the isomerisation zone; such cyclic hydrocarbon may be benzene, methylcyclopentane or cyclohexane and may be obtained from the cyclic hydrocarbon product from the process. Vapour phase isomerisation can also be used.