PILLARED CLAYS AS A NEW CLASS OF SORBENTS FOR GAS SEPARATION

High-surface-area, Zr-pillared, layered clays are synthesized and characterized for their adsorption properties. Although large free interlayer spacings are claimed in the literature (as also found in this work, 14.3 angstrom), the limiting pore size is the narrow interpillar spacing. The distribution of interpillar spacing is determined by molecular probing and adsorption data along with a theoretical framework available from the literature. Interpillar spacing can be tailored by controlling the number density of pillars inserted during the ion exchange (oligomer inserting) step. The following variables in the ion exchange solution result in lowering the pillar density: higher pH, lower oligomer concentration, and introduction of competitive cations. By changing these variables, peak interpillar spacing is shifted by nearly 2 angstrom (from 5 to 7 angstrom). The versatility of pillared clays as sorbents for kinetic separation (i.e., separation based on diffusivity differences) has been demonstrated by the separations of air and xylene isomers.