Effect of Temperature on Synthesis of ZIF-8 Membranes for Propylene/propane Separation by Counter Diffusion Method

The counter diffusion method is a promising approach for the preparation of zeolitic imidazolate framework-8 (Z1F-8) membranes for propylene/propane separation. The effects of the reaction temperature on the structure and permeation properties of ZIF-8 membranes were evaluated to explore the mechanism of membrane formation. ZIF-8 membranes were prepared by the counter diffusion method using dimethylformamide as a solvent in order to control the reaction temperature within the range 25-125 degrees C. The ZIF-8 formation reaction and interdiffusion of the solutes are facilitated at higher reaction temperatures; the opposing effects of these factors strongly influence the membrane structure and permeation properties. The thickness of the ZIF-8 layer formed in the outermost section of the resultant ZIF-8 membranes decreased from 70 to 40 mu m and was characterized by a definite layer structures with increasing reaction temperature. A propylene permeance of 2.2 X 10(-9) mol m(-2) s(-1) Pa-1 with a propylene propane selectivity of around 10 was obtained in the binary gas permeation analysis of the ZIF-8 membrane prepared at 100 degrees C. The structure of the membranes and the effect of the total feed pressure, propylene fraction in the feed, and temperature dependence on the binary permeation properties were thoroughly characterized.