zone 200 are disclosed in e g u s pat no 4 348 544 the depropanizer column 240 can provide an overhead stream 260 a side stream 270 and a bottom stream 280 usually the side stream 270 can include or be rich in one or more hydrocarbons such as c3 c5 hydrocarbons more typically c4 hydrocarbons the bottom stream 280 can include or be rich in c4 hydrocarbons typically an alkylate product the overhead stream 260 can include or be rich in one or more c4 u2212 hydrocarbons and an alkylation catalyst typically an acid such as hydrogen fluoride the overhead stream 260 can be received within a receiver 300 forming a boot 304 the boot 304 can collect an alkylation catalyst and provide an alkylation catalyst stream 308 that can be recycled to the acid alkylation zone 140 the receiver 300 can also provide a hydrocarbon product in a stream 262 that can be split into a reflux stream 264 sent back to the depropanizer column 240 and an overhead product stream 266 typically including propane in addition the receiver 300 can form a vent condenser or a stack 310 that can provide a vent stream 314 including c2 u2212 hydrocarbons with a reduced level of an acid alkylation catalyst the vent stream 314 can be provided to a scrubber 380 to provide a scrubber effluent stream 384 that can be sent to any suitable destination such as fuel gas or the flare typically the receiver 300 can be at a pressure of no more than about 1 720 kpa in the vent condenser 310 one or more cooling coils 320 can be provided to cool the vent stream 314 prior to exiting the vent condenser 310 to partially recover propane and the acid.