Appts. comprises a fractionator (12) with a feed inlet (14), overhead outlet, bottoms outlet (18) and reflux inlet (20). There is a first conduit connected to the bottoms outlet for conveying fractionator bottoms, and a second conduit connected to the feed inlet. A condenser (28) has an inlet and outlet, with a third conduit connected between the overhead outlet and the condenser inlet. An overhead accumulator (34) has three sections. An inlet and first outlet are connected to the middle section (36). There are other outlets for the top (42) and bottom (46) sections. A fourth conduit connects the condenser outlet and the inlet of the overhead accumulator. There is a stripping column with inlet, overhead and bottoms outlets, which has a suction inlet and discharge outlet. A fifth conduit connects the first outlet of the accumulator and the suction inlet. A sixth conduit connects the discharge outlet and the stripper inlet, and a seventh connects the stripper overhead outlet and the condenser inlet. Stripper bottoms are conveyed in an eighth conduit, and a ninth connects the previous conduit with the suction inlet. A tenth conduit transports HF acid phase from the overhead accumulator to the second outlet of the accumulator, and an eleventh conduit conveys ethane and lighter gases from the overhead accumulator to the third outlet of the accumulator.    The process is controlled by a number of parameters and control valves in certain conduits. The control parameters include: maintaining a predetermined level in the middle section of the overhead accumulator; maintaining a predetermined level in the stripping column; maintaining a predetermined pressure in the stripping column; maintaining a predetermined level of HF acid phase in the bottoms section; maintaining a predetermined flow rate of reflux; and maintaining a predetermined level in the fractionator.    USE/ADVANTAGE -   Appts. is used in an HF alkylation process for the removal of HF acid from a hydrocarbon product. Propane is recovered that is substantially free of HF acid. The operation is improved by the use of an HF alkylation propane stripper which utilises a bottoms recycle stream.