Abstract: In this study, the hollow fibers replace conventional trays and/or structured packing. Using a column less than 40 cm long, an ~ 8% enrichment of propylene from a 30% propane/70%propylene mixture was achieved. An HTU as low as 8.8 cm was obtained. Such a low HTU has not been previously reported for propane/propylene separations. The mass transfer time was less than one second. Introduction: Ethylene and propylene are two of the largest commodity chemicals in the U.S. and are major building blocks for the petrochemicals industry. These olefins are currently separated by cryogenic distillation, which demands extremely low temperatures and high pressures. Over 75 billion pounds of ethylene and propylene are distilled annually in the U.S. at an estimated energy requirement of 400 trillion BTU'