GB876730A - Production of branched-chain aliphatic hydrocarbons - Google Patents

Abstract

The proportion of branched chain isomers in a paraffinic feed stock is increased by isomerising in the presence of hydrogen, distilling the the product to obtain an overhead comprising hydrogen and normally gaseous hydrocarbons and bottoms comprising normal and branched chain paraffins, which are separated by contact with a molecular sieve, the effluent comprising branched chain isomers collected as product, and desorbing the normal paraffins from the sieve by means of the overhead, the resulting mixture being recycled to the isomerisation. The feed stock may be a single hydrocarbon or a mixture of hydrocarbons in the C4-C12 range. Isomerisation catalysts may be employed such as inorganic mineral acids, metal halides, sulphates of zinc, aluminium or tin, calcined silica-alumina, phosphoric acid on kieselguhr and composites of a hydrogenating component, particularly Group VIII metals, on a refractory oxide such as alumina containing combined chlorine and/or fluorine. Using metal salts temperatures of -30 to 100 DEG C. and pressures of to 1000 p.s.i. are used while processes involving metal-oxide composites employ 80-500 DEG C. and up to 1500 p.s.i. Desorption of the molecular sieve may be effected at 50-400 DEG C., preferably at or near the sorption temperature and at least as high as the boiling point of the highest boiling adsorbed material at the existing pressure. The volume of desorbing agent passed through a sieve is 1-40 times the combined volume of void spaces between the sieve particles and the pore volume.