Kinetic effects of methane on binary mixture separation on methyltriethoxysilane templated silica membranes

2019/6/16

Separation characteristics and dynamic behavior of two binary mixtures, CO2/CH4 (50:50, vol%) and CH4/N2 (50:50, vol%), on Methyltriethoxysilane templated silica (MTES) membrane were studied experimentally and theoretically. The permeation of the binary mixtures was compared with that of pure CO2, CH4, and N2 at 323–473?K and 300–600?kPa. The permeation flux of pure CO2, which has the strong adsorption affinity, was much higher than that of CH4. However, the permeation flux of the CO2/CH4 mixture was hindered by CH4 with large kinetic diameter. Although the permeation flux of pure N2 was higher than that of pure CH4, the permeation flux of CH4 in the CH4/N2 mixture was greater than that of N2 owing to the disturbance of N2 permeation by CH4 and the relatively weak adsorption affinity of N2. Because the molecular interactions, adsorption affinity, and kinetic diameter and structure of each component contributed to the separation, compared to the separation factors, the permselectivity was overestimated in the CO2/CH4 mixture, but somewhat underestimated in the CH4/N2 mixture. Due to its kinetic effects, the diffusion mechanism of CH4 needs to be investigated thoroughly in pore-controlled silica-based membranes. The transient permeation and separation behaviors of the binary mixtures on MTES membranes were successfully predicted by the generalized Maxwell–Stefan model, which incorporated the dusty gas model and Langmuir isotherm model.