Zirconia-Doped Methylated Silica Membranes via Sol-Gel Process: Microstructure and Hydrogen Permselectivity

In order to obtain a steam-stable hydrogen permselectivity membrane, with tetraethylorthosilicate (TEOS) as the silicon source, zirconium nitrate pentahydrate (Zr(NO₃)₄·5H₂O) as the zirconium source, and methyltriethoxysilane (MTES) as the hydrophobic modifier, the methyl-modified ZrO₂-SiO₂ (ZrO₂-MSiO₂) membranes were prepared via the sol-gel method. The microstructure and gas permeance of the ZrO₂-MSiO₂ membranes were studied. The physical-chemical properties of the membranes were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscope (SEM), and N₂ adsorption-desorption analysis. The hydrogen permselectivity of ZrO₂-MSiO₂ membranes was evaluated with Zr content, temperature, pressure difference, drying control chemical additive (glycerol) content, and hydrothermal stability as the inferred factors. XRD and pore structure analysis revealed that, as n_Zr increased, the MSiO₂ peak gradually shifted to a higher 2θ value, and the intensity gradually decreased. The study found that the permeation mechanism of H₂ and other gases is mainly based on the activation-diffusion mechanism. The separation of H₂ is facilitated by an increase in temperature. The ZrO₂-MSiO₂ membrane with n_Zr = 0.15 has a better pore structure and a suitable ratio of micropores to mesopores, which improved the gas permselectivities. At 200 °C, the H₂ permeance of MSiO₂ and ZrO₂-MSiO₂ membranes was 3.66 × 10^-6 and 6.46 × 10^-6 mol·m^-2·s^-1·Pa^-1, respectively. Compared with the MSiO₂ membrane, the H₂/CO₂ and H₂/N₂ permselectivities of the ZrO₂-MSiO₂ membrane were improved by 79.18% and 26.75%, respectively. The added amount of glycerol as the drying control chemical additive increased from 20% to 30%, the permeance of H₂ decreased by 11.55%, and the permselectivities of H₂/CO₂ and H₂/N₂ rose by 2.14% and 0.28%, respectively. The final results demonstrate that the ZrO₂-MSiO₂ membrane possesses excellent hydrothermal stability and regeneration capability.