Permeation performances of pure and mixed nitrogen, ethylene, ethane, propylene and propane were investigated using a polydimethylsiloxane (PDMS) coated polysulfone composite membrane in the temperature range of -20 to 40 degrees C. The permeances and selectivities strongly depended on the temperature and feed composition at a constant pressure. Propylene and propane plasticized the PDMS coating with decreasing temperature and increasing hydrocarbon concentrations, which led to significantly high permeances for all mixed hydrocarbons. It also caused positive coupling effects for ethane, ethylene and nitro.-en in the presence of propylene and propane. Moreover, pure nitrogen permeances or nitrogen permeance as a mixture component always decreased considerably by lowering the temperature. Consequently, all selectivities for the hydrocarbons to nitrogen increased significantly with the decrease of temperature and increase of total hydrocarbon concentration in feed. A systematic analysis of apparent activation energies to verify the experimental results was also presented. Crown Copyright (c) 2006 Published by Elsevier B.V. All rights reserved.