Boehmite-phenolic resin carbon molecular sieve membranes-Permeation and adsorption studies

Composite carbon molecular sieve membranes (c-CMSM) were prepared in a single dipping-drying-carbonization step from phenolic resin solutions (12.5-15wt.%) loaded with boehmite nanoparticles (0.5-1.2wt.%). A carbon matrix with well-dispersed Al₂O₃ nanowires was formed from the decomposition of the resin and dehydroxylation of boehmite. The effect of the carbon/Al₂O₃ ratio on the porous structure of the c-CMSM was accessed based on the pore size distribution and gas permeation toward N₂, O₂, CO₂, He, H₂, C₃H₆ and C₃H₈. c-CMSM with higher carbon/Al₂O₃ ratios had a more open porous structure, exhibiting higher permeabilities and lower permselectivities. c-CMSM performance was above the upper bound curves for polymeric membranes for several gas pairs, particularly for C₃H₆/C₃H₈ (permeability toward C₃H₆ of 420 barrer and permselectivity of 18.1 for a c-CMSM with carbon/Al₂O₃ ratio of 4.4).Unsupported films were also prepared (carbon/Al₂O₃ ratio 7.3) and crushed into small flakes. Equilibrium isotherms of H₂, N₂, O₂, CO₂, C₃H₈ and C₃H₆ at 293K were determined on these flakes to obtain the kinetic and adsorption selectivities toward gas pairs of interest; obtained adsorption and diffusion coefficients accurately predicted the permeabilities of all studied gases except CO₂ (experimental and predicted permeabilities of 1148 and 154 barrer, respectively).