Développement de membranes inorganiques à partir de minéraux tubulaires, lamellaires et zéolitiques.

Abstract

A new approach to prepare inorganic membranes has been developed. Those inorganic membranes are used in cation exchange, gas separation and in ultrafiltration processes. Clay and zeolite materials are used in the preparation of the inorganic membranes. First organic polymers are intercalated in kaolinite in order to improve the flexibility and to reduce cracks in the membranes. Sepiolite which is a natural hydrated magnesium silicate mineral with an interesting fibrous and porous morphology gives crack free membranes. The thickness of those unsupported membranes was 100-150$\mu$m. The main objective of this work was to prepare membranes with high percentages of microporosity in order to ensure a high selectivity in gas separation. For this purpose, zeolite was incorporated in the membrane together with sepiolite. The new inorganic membranes were tested and characterized using BET by adsorption-desorption of nitrogen to determine the microporosity, average pore diameter and pore size distribution. The porosity of these membranes were found to give a high surface area dominated by micropores. The membranes showed a good mechanical and thermal resistance. The liquid phase operation with microporous zeolitic materials is affected by the low diffusion rates of the liquids through the micropores. In cation exchange we have the diffusion through preferential pathways. Nevertheless, gas separation tests showed that although zeolitic membranes contained some connecting-through large pores, the relative fast diffusion of gaseous molecules through the zeolite micropores prevented their search for preferential diffusion pathways as in the case of liquid diffusing molecules.