GB575797A - Improvements relating to the isomerisation and alkylation of hydrocarbons - Google Patents

Abstract

In the catalytic isomerization of normal paraffins or hydrocarbon mixtures consisting mainly thereof, the feed, before passing to the isomerizer is freed from olefins and moisture by contacting with sulphuric acid, initially of not less than 98 per cent concentration, and not less than 96 per cent after absorbing the olefins. The process is applicable to the isomerization of butane or pentane cuts with aluminium chloride, alone or on a carrier, such as bauxite, the purification preferably being effected by liquid phase counter-current flow. The acid solution may be used for alkylating isoparaffins. A treated butane feed, after removing acid, may be isomerized in the vapour phase at 250-350 DEG F. and 100-400 lbs./sq. in. using aluminium chloride promoted with hydrogen chloride. The isoparaffins produced may be fed with the used acid and additional olefines as required to an alkylation stage. The molar ratio of isobutane to butenes is from 3 to 10 : 1, preferably 5 : 1, with a volume of acid to hydrocarbon feed of 1 : 1, a temperature of 25-80 DEG , preferably 35 DEG F., and a time of contact of 20-200, preferably 60 mins. Butane containing isobutane, butenes, moisture and other impurities is liquefied and washed in counter-current with 98 per cent or more sulphuric acid, part of which may be recycled. The purified feed passes through an acid separator and preheater to an isomerizer, if necessary after removal of isoparaffin. The product is stripped of HC1, washed, and treated to separate isobutane which is fed to an alkylation stage, n-butane being recycled. Acid containing absorbed olefins, isobutane, additional butenes and fresh acid are fed to an alkylator. The product, after acid separation, is fractionated in stages to recover alkylate, iso- and n-butanes. Comparative figures are given for the isomerization of untreated and acid-treated n-pentane containing pentenes which is given two batch treatments each for 1 hour with 5 per cent by volume of 98 per cent sulphuric acid prior to liquid phase isomerization with 100 per cent by weight of aluminium chloride and 22 per cent hydrogen chloride for 2 hours at 75 DEG F. and 200-220 lbs./sq. in. Specifications 538,307 and 553,334 are referred to.