(788e) Silicalite Adsorbent Membranes for Separation of CO2 and N2 Gases

Silicalite-1/ceramic composite membranes were prepared on the inner surface of zirconium oxide and/or titanium oxide tubular supports by pore plugging hydrothermal synthesis. The effect of support pore size on the membrane’s morphology and permeation performance was investigated. Five supports with different pore sizes in the range of 0.14 – 1.4 mm were studied. The synthesized membranes were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), electron diffraction spectrometer (EDS), and permeation experiments with pure and mixed CO₂ and N₂ gases.

The SEM of the membranes revealed a dense and continuous surface morphology with a highest crystal size of around 3.0 mm on the surface of all supports. SEM micrographs also showed a continuous layer grown over four supports out of five, with different pore sizes, that were investigated, with no layer observed on the support with 1.4 mm pore size. The uniformity of the zeolite layer was increasing with decreasing pore size of the support, except for the membrane synthesized using the support that has a pore size of 0.14 mm. SEM micrographs also showed that the surface coverage with zeolite crystals decreased by increased pore size of the support except for the membrane with 0.45 mm support which showed a complete surface coverage. The EDS analysis confirmed the formation of pure silicalite-1 layer at the top as well as inside the pores of all supports. The silicalite-1 crystals penetration increased with increased pore size of the support.

Pure gas permeation experiments with CO₂ and N₂ gases at 293 K revealed that the permeance values for N₂ were constant with pressure difference across all the membranes while the CO₂ values were decreasing with the increasing pressure difference across all the membranes prepared with supports with different pore sizes. The highest ideal selectivity was around 2.7 for the membrane with the support that had a pore size of 0.45 mm. The mixed gas permeation tests with CO₂ and N₂ (50/50 mixture) performed at different feed total pressures showed that increasing the feed pressure decreases the permselectivity for all supports. The highest permselectivities of around 24 were observed for the membranes prepared using the supports with 0.2 and 1.4 mm pore sizes. The highest CO₂ permeances of around 6.4 x 10^-6 (mol/m² Pa s) were obtained for the membranes with the 0.45 and 0.8 mm pore size supports and the lowest CO₂ permeances of around 1.1 x 10^-6 (mol/m² Pa s) were obtained for the membrane with the 0.2 mm pore size support. The very high permeances did not allow the testing of the membranes for pressures higher than 3 atm. Despite these very high permeances, the membranes prepared provided reasonably high selectivity. The membranes with the 0.45 pore size supports showed the best reproducibility among all membranes studied.