CHARACTERIZATION OF MFI ZEOLITE MEMBRANES BY MEANS OF PERMEABILITY DETERMINATION OF NEAR CRITICAL AND SUPERCRITICAL C0(2)

Abstract

Zeolites are inorganic materials with intrinsic microporous properties. Basically they are aluminasilicates constituted from a three dimensional network of SiO 4 and AlO 4 tetrahedra. This type of materials may have very interesting applications like adsorbents or molecular sieves. In this study, mass transfer properties of supported MFI zeolite membranes at high pressure are established using a new experimental methodology. The aim of this study was the analysis of the mass transfer of a compressed carbon dioxide through microporous zeolite membranes in order to characterize its structural parameters, identifying mass transfer mechanisms under high pressure conditions. This type of materials can be used like molecular sieves, since they present a crystalline structure with interstitial micropores of a mean pore diameter of 0.55 nm. For this purpose, we studied the mass transfer of high pressure CO 2 through microporous MFI zeolite membranes using a new experimental methodology in order to determine the permeance of carbon dioxide using an original apparatus operating in transient state. Carbon dioxide is used in experiments taking into account several applications reported in the literature coupling recovery or separation of this compound from gaseous solutions with inorganic molecular sieves. Values of flux (mol m-2 s-1) and permeance (mol m-2 s-1 Pa-1) have been obtained experimentally. This new experimental device allows estimating permeance values between 3.59 * 10-9 and 7.51 * 10-7 mol m-2 s-1 Pa-1) when the values of feed pressure are ranged between 3 and 14 MPa and the temperature varies between 25 and 100oC. These values are coherent with the microscopic nature of pores, showing that the zeolite layer deposed on the macroporous support was synthesized without macroporous defaults. An activated diffusion through the micropores might be identified in the gas phase, but under supercritical conditions (P > P c , T > T c ) an irreversible modification of transport properties was observed. This behavior was explained by a limited mechanical resistance of the membrane at high pressure conditions. In supercritical conditions, mass transfer could be controlled by a combination of diffusion through mesoscopic and microscopic porosity.