Separation of Hydrogen from Carbon Dioxide through Porous Ceramics

The gas permeability of alpha-alumina, yttria-stabilized zirconia (YSZ), and silicon carbide porous ceramics toward H-2, CO2, and H-2-CO2 mixtures were investigated at room temperature. The permeation of H-2 and CO2 single gases occurred above a critical pressure gradient, which was smaller for H-2 gas than for CO2 gas. When the Knudsen number (lambda/r ratio, lambda: molecular mean free path, r: pore radius) of a single gas was larger than unity, Knudsen flow became the dominant gas transportation process. The H-2 fraction for the mixed gas of (20%-80%) H-2-(80%-20%) CO2 through porous Al2O3, YSZ, and SiC approached unity with decreasing pressure gradient. The high fraction of H-2 gas was closely related to the difference in the critical pressure gradient values of H-2 and CO2 single gas, the inlet mixed gas composition, and the gas flow mechanism of the mixed gas. Moisture in the atmosphere adsorbed easily on the porous ceramics and affected the critical pressure gradient, leading to the increased selectivity of H-2 gas.