Influence of coating conditions on the H2 separation performance from H2/CH4 gas mixtures by the PDMS/PEI composite membrane

•Composite asymmetric PDMS/PEI membranes were prepared and characterized for H2/CH4 separation.•The effect of different coating methods on the selectivity and permeance was studied.•The effect of coating condition on the performance of the composite membrane was studied.•Single and mixed gases experiments were conducted.•A high selectivity for H2 was obtained about 96 for single gas and 70 for mixed gas experiments.

In the present study, the composite polyetherimide (PEI) membrane coated with poly dimethyl siloxane (PDMS) was synthesized and optimum conditions of coating were obtained for separation of hydrogen from methane. Three coating techniques “pouring solution inclined by 45°”, “film casting” and “dip-coating” were used. The effect of sequential coating for different methods on permselectivity of the membranes was investigated. In addition, the influences of coating conditions including coating solution concentration, coating and curing temperatures were examined. The results showed that when the concentration of PDMS coating solution was increased; the permeance of H2 was initially declined rapidly and was then gradually leveled off. The optimum concentration of coating solution was 15 wt.%. The examination of the curing and coating temperatures showed no significant effect on H2 permeance and selectivity. In the “dip coating” method, two times coating showed superior permeance and selectivity and in “film casting”, the performance of triple coating was promising. Higher selectivities for the composite membrane prepared by “dip-coating” introduced this method as the best method. The sequential dip-coating with different PDMS concentrations was applied and the selectivity was enhanced significantly from 26 to 96 for pure gases and from 22 to 70 for the binary gas mixture. Finally, the influence of pressure on the separation performance of the fabricated membrane was investigated.