Recent progress in polycrystalline zeolite membrane research

Zeolite membranes possess a highly defined microporous structure which is capable of very unique separation principally based around molecular size exclusion, adsorption, and diffusion. Polycrystalline membranes of different zeolites have been prepared in the laboratory. These zeolite membranes show excellent separation performance for mixture with a strongly adsorbing component. These unique properties have let to industrial application of zeolite membranes for pervaporation separation of liquid mixtures. However, zeolite membranes exhibit somewhat lower diffusion-controlled selectivity for gas mixtures or unstable separation characteristics due to adsorption induced microstructural changes. These problems together with high membrane costs have hindered industrial applications of zeolite membranes for gas separations. Recent research has been directed toward synthesis of zeolite membranes by more efficient methods or on more cost-effective supports and microstructural engineering of the zeolite membranes. These efforts include understanding the formation of the non-zeolitic pores, developing methods to seal these defects, and synthesis of thin oriented zeolite membranes for improving separation performance. Research was also conducted to extend applications of zeolite membranes from gas and liquid separation to nanofiltration or desalination.