ZIF-8 tubular membrane for propylene purification: Effect of surface curvature and zinc salts on separation performance

A continuous and defect-free ZIF-8 membrane was successfully grown on a positive surface curvature of a porous tubular alumina support that was prepared from zinc nitrate precursor solution at 120 degrees C for 4 h of synthesis time. The membrane produced the highest propylene permeation of 198 x 10(-10) mol.m(-2).s(-1).Pa-1 and moderate separation factor of 48. Despite its modest level of separation factor, the membrane was able to enrich propylene from 50 vol%. to 98 vol% from a binary feed mixture containing equal flowrate of propylene and propane. The high purity however came with low propylene recovery of merely 5% because there was a trade-off between the separation factor and permeance as a result of an inversed relationship between the two.