Novel inorganic membranes.

Abstract

Membrane forming properties of two natural, microporous clay minerals, montmorillonite and sepiolite, were investigated. The research presented in this work was exploratory in nature and had two distinct parts: montmorillonite as a gas separation membrane material and sepiolite as an ultrafiltration membrane material. The pore size of montmorillonite was modified by pillaring with an aluminum hydroxy cation; sepiolite was only purified from its natural state. By employing the sol-gel method, with various amounts of the inorganic polymer boehmite as a binder, unsupported membranes were cast, calcined and tested under different configurations and permeating species. The membranes made of 60% pillared montmorillonite and 40% boehmite showed permeability ratios higher than 200 between gases with small molecular size (helium, hydrogen) and gases with bulkier molecules (propane, nitrogen). Preparation of composite membranes consisting of a thin layer of pillared clay/boehmite mixture on inorganic supports with different pore sizes was also attempted. The sepiolite membranes displayed a sharp pore size distribution centered around 9.3 nm radius and good results in ultrafiltration experiments using dilute aqueous solutions of macromolecules of various molecular weights. A mathematical model was attempted for the sepiolite membrane, linking pore size distribution with the experimental permeation data.