GB817126A - Isomerization process and preparation of feed stream therefor - Google Patents

Abstract

In a combination hydrocarbon separation and isomerization process a light naphtha boiling within the range 60-180 DEG F. containing aromatic and normal paraffinic hydrocarbons is passed through a contacting zone containing an adsorbent which selectively adsorbs aromatic hydrocarbons, at least a portion of the aromatic free naphtha is subjected to isomerization to form high octane isoparaffins and at least a portion of such isoparaffins is used to desorb aromatic hydrocarbons from the adsorbent to give a stream of a mixture of isoparaffinic and aromatic hydrocarbons. The naphtha feed is preferably depentonised. The adsorbent used may be a suitable char but is preferably a molecular sieve having 6-15 pore openings. The feed is preferably vaporized and conditions of 180-400 DEG F. and 0-100 p.s.i.g. are used with flow rates of 0.05-5 vol./vol./hr. over fixed, moving or fluidized beds of adsorbent. The raffinate may then be fractionated to remove naphthenes and highly branched isoparaffins, only straight chain paraffins or paraffins with single branches passing to the isomerization. This is preferably a liquid phase process over a Friedel-Crafts catalyst such as aluminium chloride supported on "Porocel." Olefines should not be present in amounts more than 0.2 per cent, but 0.2-0.5 volume per cent of benzene may be present and 5-20 volume per cent of naphthenes. Temperatures of 100-275 DEG F., pressures of 100-450 p.s.i.g. and flow rates of 0.3-3 vol./vol./hr. are used. Hydrogen chloride may be present in the feed as an activator in amounts of 0.1-6.0 weight per cent and 0.1-3 mol. per cent of hydrogen may be added. The isomerisate is then fed to the fractionator before the isomeriser to remove highly branched isoparaffins and recycle other materials. This fractionator may be placed after the isomeriser if the feed contains little isoparaffins and in another alternative is placed before the contacting zone. The highly branched product is passed through the adsorbent in the vapour phase at 140-500 DEG F. Extraneous desorbents may be used in conjunction with the isomerisate such as heavier paraffins and naphthenes or purge gases.