Traditional systems for olefin/paraffin separation, like low-temperature distillation, are expensive and energy-consuming, and therefore, alternative separation methods are desired. The conceptual design of a new propylene/ propane separation process (300 kton/yr at 99.9 wt % propene purity) by means of a gas/liquid membrane contactor and a selective silver salt solution is presented. It involves the selection of an absorption liquid (AgBF4), its concentration (5.5 M, assumed loading of 90%), and the operating conditions of the membrane contactor and the desorber. Subsequently, modeling of the gas/liquid membrane contactor is carried out. The calculated membrane area required for the process is approximately 80 000 m(2). The influence of the assumptions made during the conceptual design and modeling stage is evaluated with a sensitivity analysis. Finally, a preliminary design is presented, resulting in a process flow sheet with equipment sized on standard design criteria. A brief economic evaluation shows that the marginal difference between the feed and product prices should be at least 175 $/ton to make the proposed propylene/propane separation process economically feasible.