GB801646A - Alkylation with effluent refrigeration and flashed vapor absorption - Google Patents

Abstract

<PICT:0801646/IV (b)/1> In a process for alkylating isobutane, by reacting a molar excess of isobutane with an olefinic feed stock containing some propane in the liquid phase in the presence of a nonvolatile liquid alkylation catalyst which generates volatile acidic degradation products under the reaction conditions, the resulting reaction mixture is separated into a catalyst and a liquid hydrocarbon phase which latter is flashed to evaporate isobutane, propane and volatile acidic products and chill the remaining hydrocarbon liquid, part of which is used as a cooling medium in controlling the temperature in the alkylation zone, the flashed vapours are compressed to condense isobutane and the remaining vapours containing volatile acidic products and propane are absorbed at elevated pressure in the remaining chilled hydrocarbon liquid from the flash zone and the liquid and vapours are neutralized. The absorption of the vapours may take place before, during or after the addition of alkali to the hydrocarbon liquid. Specified liquid catalysts are sulphuric acid and aluminium chloride-hydrocarbon complex. In a preferred embodiment using an alkylation reactor of the internal recirculation type an olefine feed such as a cracked gas fraction containing butanes and butylenes is introduced by line 10, make-up isobutane by line 11 and recycle isobutane by line 12 and the feed is cooled in heat exchanger 13. Water is separated in separator 15 and after mixing with a chilled liquid recycle from line 46 the feed is passed to the reactor 19. Sulphuric acid enters by line 22. The catalyst : hydrocarbon liquid ratio is maintained at about 1 : 1, the acid strength at 88-98 per cent and the mol. ratio of isobutane to olefin between 1 : 1 and 10 : 1. After an average contact time of 10-15 minutes the reaction product is withdrawn by line 20, catalyst separated in separator 21 and recycled and hydrocarbon passed to the flash drum 25 where the pressure drops from 25-40 p.s.i.a. to atmospheric or below due to the suction of pump 39. Unevaporated liquid at about 35 DEG F. is in part taken by line 27 through cooling coils in the reactor 19 and returned by line 29. Liquid is also withdrawn by line 30 and used as the cooling medium in heat exchanger 13. Vapours pass to the compressor trap 35 through the pump 39, where the pressure is raised to 52-55 p.s.i.g., and condenser 41 into a second flash drum 43. The condensate passes to a third flash drum 103 where the pressure is reduced to atmospheric, vapours passing to the trap 35 and chilled liquid being recycled by line 46 to the reactor. Vapours from flash drum 43 contain volatile acidic products such as SO2 and propane and pass into the absorber 48 where they are absorbed at 30-100 p.s.i.g. in condensate from the flash drum 26 fed by lines 30 and 33 through heat exchanger 13. The resulting liquid is pumped to the caustic washer 52 where it is mixed with 5 per cent aqueous caustic soda. The hydrocarbon layer is separated in separator 55, washed with water in mixer 62 and separated therefrom in separator 64. The resulting product is fractionated to obtain propane, isobutane which is recycled by line 12, butane, alkylate product and heavier alkylate bottoms.