Nitrogen Removal From Natural Gas by Membrane Separation

Abstract

Canada is globally the third largest natural gas producer with a total production of 13.9 billion ft3/day. Natural gas is a naturally occurring mixture consisting of mainly CH4 and varying amounts of other gases such as nitrogen. N2 is difficult to remove from natural gas. Cryogenic distillation is energy intensive and costly, while pressure swing adsorption only applies to very limited cases. Membrane separation is expected to offer a promising alternative process for nitrogen removal from natural gas. In this research, a series of Poly(ether block amide) (PEBA) and Poly(dimethyl siloxane) (PDMS) membranes were employed to separate nitrogen from methane under different pressures and temperatures. These rubbery polymers have a higher methane permeability than nitrogen, and the selectivity is presented as the permeability ratio of methane over nitrogen. The study involved pure gas permeation tests by using different PEBA membranes (PEBA 2533, PEBA 1074, PEBA 1657 and PEBA 3000) and PDMS. Based on the gas permeability data, PEBA 2533 and PEBA 1074 were chosen for further studies. Polymer blending was employed to combine the beneficial properties of the two materials. A series of blend polymers of PEBA 2533/1074 were used to prepare the membranes for gas permeability tests with pure and mixture gas at different operating conditions. At 0.813 MPa and -200C, a blend membrane with the blend ratio of PEBA 2533/1074 (50/50) showed a CH4/N2 permeability ratio greater than 6, which is better than the conventional membrane reported in the literature.