Development of inorganic membranes by sol-gel method for CO2 separation

We have developed ceramic membranes exhibiting high perm-selectivity of CO2. The membrane is composed of microporous silica formed on the outer side of a porous substrate of Al2O3 We have developed a technique controlling the diameter of micropores and simultaneously modifying the surface of the micropores by using an organic template. At room temperature, by using existence of water, we could separate CO2 and N-2, whose kinetic diameters are almost the same in size. The membranes of SiO2 have high perm-selectivity at room temperature, the perm-selectivity of PCO2/PN2 is over 100. On the other hand, the membranes of SiO2-ZrO2 have high perm-selectivity even at 150 degrees C, the permselectivity of PCO2/PN2 is almost 10 at 150 degrees C. These high perm-selectivities of PCO2/PN2 result from sols combined with tetraethoxysilane(TEOS) and tetra-n-propylammonium bromide (TPABr). In case of SiO2 membranes, TPABr has the affinity with water, which enables the permeation of CO2 and prevents the permeation of N-2. On the other hand, in case of Si-4-ZrO2 membranes, the micropores have been formed by the removal of TPABr, which has the effects as template. The micropores formed have the diameter less than 1nm, and the gases transport through the micropores by molecular sieving now. The controlled pore size and the adsorption with CO2 are essential for separation of CO2 and N-2. The perm-selectivities of PCO2/PN2 for SiO2 and SiO2-ZrO2 membranes depend on humidity. Humidity is seriously related with water at the micropore surface. Water enables permeation of CO2 and prevents permeation of N-2. The high perm-selectivity of PCO2/PN2 results from the existence of water.