Patent GB-564198-A (GB)
Title: Improved process for the isomerization of normal paraffins
IPC: C07C5/27
Filed: 1942-12-30
Abstract: <PICT:0564198/IV/1> Normal paraffins of at least four carbon atoms are intermixed in the presence of a Friedel-Crafts' catalyst and a normally gaseous halogen-containing promoter boiling below propane or decomposing under the isomerization reaction conditions to produce hydrogen chloride or bromide, the reaction products being passed to a stripping tower wherein the temperature and pressure are maintained at predetermined values such that all of the promoter, together with a substantially constant proportion of the normally gaseous decomposition products, is separated as overhead and recycled to the isomerization zone, the remainder of the gaseous decomposition products being removed with the bottoms from the tower.  The feedstock, such as normal butane, pentane, hexane or heptane, casinghead gasoline or straight run naphtha may be isomerized in liquid phase at about 75-150 DEG  F. or vapour phase at about 250-400 DEG  F.  The isomerization of butane in vapour phase using aluminium chloride-impregnated "Porocel" (Registered Trade Mark), or other partially dehydrated bauxite and hydrogen chloride as promoter is effected in reactor 5, preferably at 300-350 DEG  F. and 200 lbs./sq. in., butane being fed by line 2 through heater 3 and mixed with 2-12 per cent of hydrogen chloride fed from line 32.  The time of contact with the catalyst, in which aluminium chloride is preferably about 8-12 per cent of the carrier, is about 50-250 secs.  The products are liquefied in cooler 9 and passed to stripper 23 usually at the same pressure as the isomerizer, and having a reboiler 36 for reheating the bottoms to about 150-300 DEG  F.  Vapours are withdrawn by line 25 through cooler 26 and returned to the stripper by line 27 above the partition 24.  Liquid remains in the stripper, the seal 31 providing for return of excess just below the partition, while vapour is re-cycled by line 32 to the feed.  The composition of the vapour is varied by varying the temperature of cooler 26.  An overhead temperature of about 50 DEG  F., a bottom temperature of about 250 DEG  F., and a pressure about 350 lbs./sq. in. are typical for removal of the hydrogen chloride together with a constant proportion of the propane produced.  For pentane isomerization, corresponding temperatures are 150 and 390 DEG  F. at the top and bottom respectively.  The liquid reaction products are fed to the stripper at a point nearer the top the higher the content of hydrogen chloride.  Three lines 21, 17, 19 are shown.  The hydrogen chloride-free mixture leaves the stripper by line 39, is washed with aqueous caustic soda in mixer 40, and fed through settler 42 to fractionator 53, where propane or other gaseous decomposition products are removed, and then to fractionator 58 where isobutane is separated as overhead from n-butane which may be dried and re-cycled to the reactor 5.  Free hydrogen chloride may be added through line 33 to replace losses.  In an example, a catalyst containing 88 per cent dehydrated "Porocel" (Registered Trade Mark) and 12 per cent aluminium chloride is used at 302-305 DEG  F. for isomerizing a 93.4 per cent by volume isobutane mixture to which 6 per cent hydrogen chloride is added in the form of a mixture which is 70 per cent by volume hydrogen chloride, 22 per cent propane, and the rest isobutane, obtained as overhead in the stripping operation performed on the reaction product with an overhead temperature of 50 DEG  F. and a bottoms temperature of 200 DEG  F.