In the previous work1} a method was proposed to make a thin ceramic membranefor gas separation. Later it was found that the membrane could be improved by keeping it in hot humid air for a few days after being treated with a dilute aqueous solution of sodium silicate, and that this kind of membrane is fairly good for alcohol/water separation. The separation factor was found in the previous work2) to be dependent on the alcohol concentration, and the smallest value was about 5 for methanol/water, 8 for ethanol/water and 1 1 for isopropanol/water gaseous mixture.The previous results anticipated a possibility of gas separation by a mechanismsomewhatlike molecular sieving with this kind of ceramic membrane. It was found that the previous, rather small separation factor at high alcohol concentrations was mainly due to some large pinholes left in the membrane. In this work an improvement was made to the membrane, which was used for separation of gaseous alcohol/ water mixtures to obtain relatively large separation factors.1. Experimental Ceramic membraneA coarse porous ceramic cylinder (Multipoaron supplied by Mitsui Grinding Wheel Company) was used as the substrate to support a thin ceramic membraneon its outer surface. The ceramic cylinder was cut to 150-mm length. One end of the substrate was connected to a glass tube and the other was closed with alumina cement. As mentioned in the previous work,1} the substrate was dipped in an alumina sol and was dried at 80°C. Then it was fired at around 450°C for about 20 minutes. These procedures were repeated several times to form a quite thin alumina membraneof about 10 /mi in thickness.Then aluminum isopropoxide dissolved in an organic solvent was used to makethe pores smaller. It was finally treated with sodium silicate aqueous Received July 3, 1985. Correspondence concerning this article should be addressed to M. Asaeda.84 solution, which gave stability to the membrane.Most of the membrane is made of bohmite, but the surface of pores can be considered to have a structure of silica-alumina, though this could not be clearly detected by an X-ray analyzer. One of the most important steps in these procedures was found to be the first simple step of making a porous thin alumina membrane.Somelarger pinholes after this step were found to have a large effect on the performance of the final membrane. These relatively large pinholes were filled by pressuring the alumina sol into the membrane module through the glass tube while it was dried from outside.