Separation of gaseous mixtures of CO2 and CH4 using a composite microporous glass membrane on ceramic tubing

Abstract Separation of a gaseous mixture of CO 2 and CH 4 was carried out using a microporous, thin glass membrane coated on the surface of a porous ceramic tubing. The glass membrane was prepared by repeating the following procedure: dipping the ceramic tubing into a metal alkoxide solution containing B 2 O 3 , followed by drying, heating and leaching in HCl solution. The thickness of the membrane was in the range of 5-23 μm, depending upon the number of dips. The structure of the membrane was investigated by means of a scanning electron microscope. The mean pore diameter estimated was in the range of 4–64 nm. The maximum separation factor of 1.48 was obtained with the composite membranes which were coated over 15 times with a casting solution in which the ratio of B 2 O 3 : SiO 2 was 0.25:1. Composite membranes with less than 5 coatings showed no ability to separate. When decreasing the content of B 2 O 3 , carbon dioxide seemed to permeate through the composite membrane by the surface diffusion mechanism in the pores.