Patent GB-1015211-A (GB)
Title: Improvements relating to the isomerization of paraffin hydrocarbons
IPC: B01J23/28
Filed: 1962-05-16
Abstract: C4 and higher paraffin hydrocarbons boiling in the gasoline boiling range are isomerized by contacting said hydrocarbons at elevated temperature and pressure in the presence of hydrogen and hydrogen chloride or a compound decomposable to hydrogen chloride under the isomerization conditions, at a temperature of below 400 DEG  F., with a solid catalyst comprising alumina and combined chlorine, separating in hydrogen rich gas containing hydrogen chloride from the product in a high pressure separator at substantially the isomerization pressure and recycling this gas to the isomerization zone, separating further hydrogen <PICT:1015211/C4-C5/1> <PICT:1015211/C4-C5/2> chloride from the product after the first separation of hydrogen rich gas containing hydrogen chloride by distillation at substantially the isomerization pressure and recycling this hydrogen chloride to the isomerization zone, and recovering a normally liquid product of increased iso-paraffin content.  In preferred embodiments: (1) the further hydrogen chloride is separated from the product as hydrogen chloride in an overhead stream from the distillation substantially free from C2 and higher hydrocarbons; (2) the further hydrogen chloride is recycled to the isomerization zone by (a) adding said gas to the hydrogen rich gas recycle stream containing hydrogen chloride, (b) adding said gas to the gasoline feed stream to the isomerization zone and (3) the further hydrogen chloride and the gasoline feed stream are passed counter-current through a stripper so that hydrogen chloride is taken up by the gasoline.  An additional amount of 0.01 to 5% weight, preferably 0.01 to 1.0% weight based on the feedstock of the hydrogen chloride or decomposable chlorine containing material may be added.  The isomerization is carried out in either liquid or vapour phase at 50 DEG  to 400 DEG  F., at atmospheric to 2,000 p.s.i.g. with a space velocity of 0.05 to 10 v/v/hr. and a hydrogen: hydrocarbon mole ratio of from 0.01 : 1 to 20 : 1.  The feedstock contains a major proportion of pentanes, hexanes or mixtures thereof and may also contain up to 0.5% weight of aromatics without appreciable loss of catalyst activity.  The feedstock is, advantageously free of sulphur and water and has a low content of naphthenes and may also be pretreated as described in Specifications 899,378 and 987,238. Specified chlorine containing compounds are chloro-substituted derivatives of C1 to C4 aliphatic hydrocarbons, e.g. carbon tetrachloride, chloroform, methylene chloride and tertiary butyl chloride.  The catalyst used is prepared by contacting alumina with a compound of general formula <FORM:1015211/C4-C5/1> (wherein X and Y may be the same or different and are H, Cl, Br, F or SCl, or X and Y together may be oxygen or sulphur) under non-reducing conditions at a temperature such that chlorine is taken up by the alumina without the production of free aluminium chloride. Preferably the alumina contains less than 25% weight of a metal or compound thereof having hydrogenating activity selected from Group VIa and VIII, e.g. a platinum group metal.  Preferably the catalyst contains from 1 to 15% wt. of chlorine in amounts of 2.0 x 10-4 to 3.5 x 10-4 gms./sq. metre of alumina surface.  As shown in Fig. 1, feedstock is pretreated by passing through furnace 1, desulphurization reactor 2, stabilizer 3, dearomatization reactor 4 and then to high-pressure separator 18 from which the feedstock is withdrawn through line 22 to isomerization reactor 5 wherein it reacts with hydrogen rich recycle gas containing hydrogen chloride added from line 25 to line 22 and any additional amounts added via line 23, the isomerized products passing to high-pressure separator 27 from which hydrogen rich gas and hydrogen chloride are withdrawn for recycle, the isomerized products passing through line 28 to stripper 6.  Hydrogen chloride substantially free from C2 and higher hydrocarbons is then taken off through line 29 to line 25 and product is withdrawn via pipe 30.  Alternatively, line 29 may pass to a scrubber (not shown) in which the hydrogen chloride meets gasoline in counter-current flow, the gasoline being subsequently passed to the isomerization reactor 5.  Fig. 2 shows an alternative feed pretreatment system in which desulphurization and dearomatization are carried out in a single reactor 36 which contains two catalyst beds.