A method and apparatus for separating a component from a multi-component feed gas stream has a flow conduit (14) having a semi-permeable section (15) that permeates the component to be separated from feed gas stream (12). A sweep gas is provided at a first velocity on the permeate sides of flow conduit (14) and the velocity of sweep gas (13) is accelerated so that the velocity of sweep gas (13) along at least a portion of the permeate side of flow conduit (14) is greater than the first velocity. The mixture of permeate and sweep gas (13) is then decelerated by diffuser (20), thereby recovering as pressure a portion of the energy of feed gas stream (12).