Patent GB-566062-A (GB)
Title: Improved process for the isomerisation of paraffinic hydrocarbons
IPC: C07C5/27
Filed: 1943-01-01
Abstract: <PICT:0566062/IV/1> A normal paraffin containing at least four carbon atoms is contacted with an aluminium halide under isomerizing and refluxing conditions to obtain a simultaneous isomerization and distillation of the isomerized products from the catalyst zone while separately removing therefrom the heavy degradation products substantially as formed.  Halogen-containing promoters and hydrogen may be present.  Hydrocarbons predominating in normal paraffins are fed continuously in liquid or liquid-vapour phase to a fractionating column having a central catalyst zone filled with aluminium halide, alone or on a sorbent carrier, with a space above and below which may contain bubble caps or the like for aiding fractionation.  The catalyst may also be bounded top and bottom by layers of carrier alone and packed in open mesh baskets. The isomerized product is vaporized as formed and taken off as overhead, condensed, and part-returned as reflux condensate, while the bottoms containing unreacted feed only returned.  The feed may be introduced at a point higher up or lower down the column according to whether it contains substantial amounts of light products or of heavier degradation products.  In a modification, a slurry of powdered catalyst suspended in the feed or recycled condensate flows down the column from about the mid-point over baffles and is drawn off at the base to a filter press or centrifuge, the bottoms passing therethrough being fractionated, and the unreacted feed used as back-wash to reform a slurry for recycling.  A plurality of reaction-fractionation columns may be used, particularly with mixtures of C5-C6 paraffins or straight run naphthas either in series or parallel operation. Ordinary fractionators may be placed between successive columns. Thus a C5-C6 paraffin feed is treated using combination columns A and C with a simple fractionator B interposed.  Part of the reflux condensate from A is fed to B, and uncondensed overhead from A comprising C5 paraffins is either returned to the feed line to A or fed with the overhead from B to C.  Iso-C6 paraffin is taken as a side stream from B, n-C6 withdrawn as bottoms and recycled to A, and overhead from B is fed with that from A to column C. Part of the recycle reflux condensate of C is withdrawn and fractionated to separate isopentane from n-pentane which is recycled to C.  Bottoms from C is separated into n-C5 for recycling and heavier which is withdrawn.  Known reaction conditions are employed, for butane generally 75-350 DEG  F. with a catalyst concentration of 10-200 per cent by weight of the butane present, a hydrogen halide concentration of 1-20 per cent, and a contact time of 1/2 -25 hrs.  For pentane, corresponding figures are 40-125 DEG  F., 10-200 per cent, 1-22 per cent, and 1/2 -9\ba1/2 hrs.  Pressure is adjusted to give the desired fractionation.  For butane, a pressure of 240 lbs./sq. in. at 200 DEG F. is suitable.  The feed is introduced by line 2 into column 4 having the solid catalyst 5, for example, aluminium chloride in such amount that it is tenaciously held by the porous carrier, and plates or packing 6.  Hydrogen chloride enters by line 52 and leaves by line 7 with the overhead comprising substantially only isoparaffin.  Part of the condensed overhead is recycled by line 12 and the rest passed by line 26 to fractionator 22 where isoparaffin separates as bottoms while overhead is released or recycled through line 33. Non-condensed reaction products pass by line 14 to low temperature cooler 16 to separate propane and/or butane from hydrogen chloride and hydrogen which are returned by line 20.  Bottoms from column 4 are in part circulated through reboiler 41 and part continuously fed by line 44 to fractionator 46 where unreacted normal paraffin is separated and returned by line 49 to feed line 2 while heavier hydrocarbons are removed as bottoms.  In a modification, Fig. 2 (not shown), a slurry of catalyst suspended in n-pentane is circulated between the lower part of the column and a reboiler, the pentane feed being introduced into the centre of the column through the reboiler, and promoter introduced near the base.  The overhead passes to a fractionator where isopentane is separated, part being recycled as reflux condensate.  Part of the bottoms are freed from catalyst and fractionated to separate heavy products from unreacted pentane which is returned after picking up the separated catalyst.  A solution of aluminium bromide may be used as catalyst in substantially the same apparatus.  In examples, pentane is isomerized using aluminium chloride on porous alumina, containing 17 per cent of the former, and hydrogen chloride, the temperature being about 90 DEG  F.  Aluminium chloride suspended by means of a turbo-mixer may be used under similar conditions.