Challenges in the Separation of Xylene Isomers by means of Zeolite Membranes

In the view of wide applications and high capability of zeolite materials in separation processes, membrane and micro reactors, gas sensors, zeolitic catalysis, hollow fibers, etc., a large number of studies during the past 25 years have been focused on the preparation of zeolite type films and membranes. Zeolite membranes have high potentials to be used in many separation processes, mostly due to the differences in the diffusivity of various molecules (even of similar kinetic diameters) in the uniform and molecular-size zeolitic pores. The latter property results in the selective adsorption and separation of molecules. MFI type zeolite membranes grown on the porous supports, including silicalite and ZSM-5, have been the most studied zeolitic materials for separation processes. The average pore size of MFI which is similar to the kinetic diameter of many organic molecules is one of the desirable characteristics of this type of zeolite. Moreover, MFI type zeolite possesses higher thermal and chemical stability, and adsorption property based on the hydrophilic/hydrophobic interactions. Fractionation of xylene isomers is one of the important separation processes in petrochemical industries, due to the various industrial applications of these isomers. The recovery of xylenes in the industrial scale is currently achieved either by crystallization or adsorption processes. However, these techniques are very complex and energy intensive. Thus membrane-based separation processes have been considered as an alternative for such separations. MFI type zeolite membrane has been synthesized in the laboratory scale by a number of research groups to separate xylene isomers. In this study, various synthesis methods of zeolite membranes and their effective parameters have been reviewed. Results reported by different research groups represent the effective factors on membrane preparation as well as the optimum operating conditions viable for xylenes separation. The discussions provided here can assist improving and optimizing membrane separation techniques for xylene recovery.

کلیدواژه ها:

Zeolite ، Membrane ، Xylene ، Silicalite-1 ، ZSM-5 ، Pervaporation ، Vapor Permeation