Separation of gases with an A-type zeolite membrane

A highly hydrophilic A-type zeolite membrane was prepared by a hydrothermal synthesis on the outer surface of a porous alpha-alumina tube. Increasing and decreasing the permeation temperature between 308 and 473 K over 40 cycles in a period of 4 months did not damage the membrane. Permeation tests with a variety of permeates showed that the membrane possessed two types of pores: zeolitic pores of 0.4-0.43 nm diameter and nonzeolitic pores. Molecules larger than C2H6 were not able to permeate through the zeolitic pores. The separation factors of the membrane were dependent on molecular size, affinity to the pore walls, and hydrophobicity of the permeating molecules. The combination of permeants also affected the permeation rates. H2O molecules could be concentrated in the zeolitic and nonzeolitic pores, thus reducing the permeation of the hydrophobic permeants. The H2O/H-2 separation factor was larger than 160 at permeation temperatures of 303-473 K.