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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