: The removal of heavy hydrocarbons from natural gas becomes necessary to facilitate its pipeline traort and distribution, and for applications in conventional gas burners and co-generation engines. Polyurethanes are the group of polymers that are considered as a membrane in the different separation fields because of their good Mechanical, Chemical and Thermal properties. In this research the effects of changes of the polyol, disocyanate, chain extender and ratio of them on the gas permeability of polyurethane membrane were investigated. The membranes used in this study were prepared by PTMG, PPG and CaPa as the polyol, IPDI, HDI and TDI as the diisocyanate and BDO and BDA as the chain extender. Obtain results indicate that the more condensable gas, the higher permeability and by increasing the microphase separation of hard and soft segments, the rubbery behavior and permeability of condensable gases increase as well as their selectivity. Polymers based on PPG show maximum permeability, because of their high phase separation. Results obtained by Fourier Transform Infrared Spectrometer (FTIR) and Differential Scanning Caloremetry (DSC) confirm more hard and soft segment connections in polymers based on TDI. For this reason polymers based on TDI shows minimum permeability. The effects of silica nano particles on the gas permeation of polyesther and polyether based polyurethane membranes has been investigated. Polyesther based polyurethane was synthesized by using Polycaprolactone (CaPa225)/Hexamethylene diisocyanate/ 1, 4-Butane diol as well as Polyether based polyurethane that was synthesized by using Polypropylene glycol (PPG) /Hexamethylene diisocyanate/ 1, 4-Butane diol in 1/3/2 mole fraction. Silica particles were prepared via the sol-gel method through the hydrolysis of Tetra ethoxy silane (TEOS). PU and PU-silica hybrid membranes were prepared by dry phase inversion method. Six PU/silica hybrid membranes prepared which contain silica particles up to 30 wt% silica in polymer. The obtained SEM micrographs and FT-IR spectras confirmed the nano-scale distribution of silica particles in the polymer matrix. Permeations of CH 4 , C 2 H 6 and C 3 H 8 at 25?C and at 2 bar for pure poly urethane membrane and 2, 4 and 6 bars for polyurethane-nano particle membrane were investigated by time lag method. The results of the gas permeability experiments indicates that additional of silica particles in polyether based polyurethane firstly increase then decreases the permeability. The reduction of permeability by increasing silica content may refer to introduce of tortuous paths in membrane and
