Hydrophobic modification and silver doping of silica membranes for H2/CO2 separation

•Preparation of T-SiO2, M-SiO2 and Ag/M-SiO2 membranes by sol–gel method.•The effect of CH3 modification and Ag-doping on the material structures was studied.•Permeance measurements of the three silica membranes were performed and compared.•Apparent activation energies of the three silica membranes for H2 were calculated.•The hydrothermal stability of the three silica membranes were examined and compared.

Pure hydrophilic silica (T-SiO2), methyl-modified silica (M-SiO2) and Ag-doped methyl-modified silica (Ag/M-SiO2) membranes have been prepared by sol–gel method. The added hydrophobic precursor methyltriethoxysilane has successfully introduced CH3 groups into the M-SiO2 and Ag/M-SiO2 materials. The formed metallic silver results from the transformation of AgNO3. The methyl ligands and Ag-doped can make the mean pore size and total pore volume of silica membranes larger. The apparent activation energy for H2 permeance in T-SiO2, M-SiO2 and Ag/M-SiO2 membranes were 3.65 ± 0.10, 3.64 ± 0.08 and 3.05 ± 0.08 kJ mol−1, respectively. Compared with the T-SiO2 membrane, the H2 permeation rates of the M-SiO2 and Ag/M-SiO2 membranes increase by 34.25% and 148.34%, respectively, and the H2/CO2 permselectivity of M-SiO2 membrane decreases by 10.93% while that of Ag/M-SiO2 membrane increases by 10.61%, when operated at 200 °C and a pressure difference of 0.35 MPa. After steam treatment and thermal regeneration, Ag/M-SiO2 membranes show a much smaller change to their original values in H2 permeance and H2/CO2 permselectivity than the T-SiO2 and M-SiO2 membranes.

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