Abstract: A vapor fraction containing hydrogen and at least one hydrocarbon selected from the group consisting of C.sub.1 to C.sub.4 hydrocarbons is separated from a hydrogen-rich refinery off-gas feed to give a liquid product fraction. The refinery off-gas is fed to and compressed in a compressor/expander having compressor means and expander means mounted and driven on a common shaft, and then cooled and partially condensed to form a two-phase fluid in a heat exchanger followed by separation of the vapor and liquid product phases of the fluid in a separator or a separator/fractionation column stabilizer unit. The separated vapor phase is transmitted to the compressor/expander unit wherein the vapor is depressurized and partially condensed, thereby driving the compressor.

Abstract: A vapor fraction containing hydrogen and at least one hydrocarbon selected from the group consisting of C.sub.1 to C.sub.4 hydrocarbons is separated from a hydrogen-rich refinery off-gas feed to give a liquid product fraction. The refinery off-gas is fed to and compressed in a compressor/expander having compressor means and expander means mounted and driven on a common shaft, and then cooled and partially condensed to form a two-phase fluid in a heat exchanger followed by separation of the vapor and liquid product phases of the fluid in a separator or a separator/fractionation column stabilizer unit. The separated vapor phase is transmitted to the compressor/expander unit wherein the vapor is depressurized and partially condensed, thereby driving the compressor.