Pervaporation of Water-Alcohol Mixtures on Cation-Exchanged LTA Zeolite Membranes

Na-LTA membranes have been synthesized on porous nickel supports by in situ crystallization from a true solution. K-LTA and Ca-LTA membranes have been prepared from Na-LTA membranes by ion exchange in 1 M KCl and CaCl2 solutions, respectively. The formation of the LTA structure, its preservation during ion exchange, and achievement of nearly 100% replacement in the near-surface layer of the zeolite membranes have been proven by means of XPD and SEM-EDX. All the zeolite membranes synthesized have been tested in pervaporation of isopropanol-water, ethanol-water, and methanol-water mixtures containing 10 wt % water. It has been found that the mass flux of alcohol does not depend on the nature of alcohol or zeolite cation if the kinetic diameter of alcohol molecule is greater the effective diameter of zeolite pores. A new method for evaluating of the mass flux through nonzeolite pores based on pervaporation data has been proposed. The estimated mass flux through nonzeolite pores for all the zeolite membranes tested is 15 +/- 3 g m(-2) h(-1) which is 1.6 to 7.6% of the total transmembrane mass flux depending on the alcohol chosen.