日本ゼオライト学会　刊行物 Publication of Japan Zeolite Association

Metal-organic frameworks (MOFs) have been recognized as a new candidate for gas separation membranes based on their characteristic pore size and adsorption properties. Mixed matrix membranes have been proposed so far for the easy preparation of the MOF-based membranes using polymer matrix; however, their gas permeation properties are the combination of MOF particles and polymer matrix. Recently, pure-MOF membranes have been reported using the in-situ growth method and the secondary growth method, which prepare the pure MOF separation layer. another preparation method is the counter-diffusion method, which supply the solution of the metal salt and the organic ligand from both sides of the porous support. Some varieties of MOF-based membranes were prepared so far, and the molecular sieve gas permeation properties have been reported. Among several varieties of MOFs, ZIF-8 is one of the most focused materials for separation membranes, which is effective for propylene/propane separation based on their small difference in molecular size. As an example, we prepared the ZIF-8 membrane using the counter-diffusion method with selective ZIF-8 layer prepared within the porous support. The contribution of diffusive separation for propylene/propane was clarified from the analysis of diffusivity and solubility. In this review, the preparation methods and the typical gas permeation properties of the MOF-based membranes, especially the preparation and the characterization of the latest ZIF-8 membranes for propylene/propane separation are presented.