Microporous silica xerogel membrane with high selectivity and high permeance for carbon dioxide separation

The asymmetric microporous silica xerogel membrane was prepared by sol-gel method. A multi-layer (asymmetric) structure was obtained by silica xerogel layer on top of mesoporous silica layer (mean pore diameter of 4 nm), supported by porous alumina tube (mean pore diameter of 0.1 mum). The ratio of the permeances, CO2/N-2 for this membrane attained more than 60 at 298 K. This value is considerably higher than the theoretical Knudsen value (CO2/N-2 = 0.8). The gas permeances of this membrane were about 5-10 times higher than the previous membrane. Application of the membrane to an enrichment of CO2 from air was also investigated. CO2 in the air (about 300 ppm) was concentrated to more than 1000 ppm by using the membrane at 298 K.