Improvements in or relating to process for isobutane-olefin alkylation

摘要

A process for isobutane-olefin alkylation comprises contacting a molar excess of isobutane and olefins containing propane, in liquid phase with a liquid alkylation catalyst under alkylating conditions. The reaction mixture is separated into a liquid catalyst phase, and a liquid hydrocarbon phase which is passed to a first flash zone of lower pressure wherein isobutane and propane are evaporated off and at least part of the remaining hydrocarbon liquid thus chilled used as a heat exchange medium to control the temperature in the alkylation zone. The isobutane and propane from the first flash zone are compressed and condensed and fractionated to evaporate the propane, leaving liquid isobutane which is passed to a second flash zone of lower pressure; part of the isobutane is vaporized and the thus chilled liquid isobutane recycled to the alkylation zone. Vaporized isobutane from the second flash zone may be mixed with vaporized hydrocarbons from the first flash zone. In the drawing, an olefin feed stream is introduced by line 10, make-up isobutane from line 11 and recycled isobutane from line 12, and the mixture chilled in heat exchanger 13 and introduced by line 14 into recycle line 15 of the pump and time tank alkylation reaction system consisting of recycle pump 16, chiller 17 and tank 19. A portion of the circulating emulsion is removed by line 22 to settler 23. A major proportion of the liquid catalyst layer is recycled via line 24; the hydrocarbon layer is passed to flash drum 31 wherein the pressure is dropped from 25-40 p.s.i. to about atmospheric. Isobutane and propane are thus vaporized and the remaining liquid hydrocarbons chilled to about 35 DEG F. Part of the chilled hydrocarbons are passed to chiller 17 to chill the alkylation zone, and part passed to heat exchanger 13 to prechill the feed to the alkylation zone, and then, via line 39, to caustic alkali washing zone 70 and waterwashing zone 71. The washed product is passed to debutanizer 73 wherein isobutane is vaporized, and after condensation recycled to the alkylation zone via line 12; then to debutanizer 83 wherein n-butane is vaporized; and finally to fractionator 91 to obtain the desired alkylate fractions. Vaporized isobutane and propane from the flash drum 31 pass via lines 35 and 33 to the compressor 32 which raises the pressure to about 75-85 p.s.i., and then through condenser 46 via lines 47, 49 and 52 to depropanizer 53. Propane vapour removed by line 55 is condensed in line 56 and isobutane is passed by line 62 and partially cooled by passing through heat exchanger 51 and then through line 63 to cooler 64 to flash drum 65 where the pressure is reduced to about atmospheric. Part of the isobutane is thus vaporized and the vapours combined with those from the first flash drum; the liquid isobutane, chilled to about 15-20 DEG F., is passed by line 69 to line 14 where it is mixed with the feed to the alkylation zone. Alkylation catalysts referred to are 88-98 per cent sulphuric acid and aluminium chloride-hydrocarbon complex. The olefin feed stream may be a C4 gas fraction containing butanes and butylene, or mixed C3-C4 olefins containing butanes and butylenes. In the example, the olefin feedstock contains propane and lighter hydrocarbons, isobutane, n-butane, butylenes and C5 hydrocarbons. The contact time in the alkylation zone may be 25-45 minutes, and the temperature therein may be below 70 DEG F.