Preparation and Testing of Microporous Glass Membranes for Gas Separations

California Institute Of Technology, Pasadena CA

Investigators

Abstract

CTS-0085480 Preparation and Testing of Microporous Glass Membranes for Gas Separations George R. Gavalas California Institute of Technology Abstract Supported glass membranes suitable for gas separations are developed using phase-separated-glass casting techniques. Membranes are made by first dip-coating flat or tubular porous alumina supports in a suspension of the glass components (Na2O-B2O3-SiO2-Al2O3). The particle coating is then heated to react the components into a continuous glass film 5-10 mm thick. Upon cooling, the glass separates into two intertwined phases, one soluble in acid and the other insoluble. Leaching in acid removes the solid phase, leaving behind the insoluble phase as a porous film with pore sizes varying from below 1 nm to 10 nm depending on the initial composition as well as on the processing conditions. To achieve high membrane selectivity it is essential to identify compositions that give pore size below 1 nm. For this purpose membrane specimens are being prepared over a broad range of glass compositions. Such an effort is prohibitive using conventional membrane-preparation techniques. In this project parallel processing is used to explore quickly and thoroughly a large multicomponent composition space. Specifically, arrays of several small circular membranes, each of different composition, are deposited simultaneously on a single alumina disk. After thermal treatment and leaching the membranes are characterized by scanning electron microscopy and tested for permeance and selectivity with various gas mixtures, including CO2-CH4 and combinations of C1-C4 hydrocarbons. The permeation testing is carried out serially using a mass spectrometer probe. Approximately fifty disks, each containing upwards of thirty membranes, are being processed in the course of this project. Inorganic membranes offer a practical and energy-efficient technology for gas separations needed in industrial processing of materials such as natural gas and petrochemicals and in fuel cells. One type of such durable membranes consists of thin microporous glass films supported on porous ceramic plates or tubes. To achieve good membrane properties it is necessary to bring the pore sizes down to molecular dimensions, and for this purpose it is necessary to test a wide range of preparation conditions. This necessarily extensive experimental effort would be extremely time consuming by conventional techniques. In this project techniques for simultaneously depositing and testing a number of membrane formulations on a single support disk is being developed. The increased productivity afforded by this parallel, or combinatorial, processing permits evaluation of over one thousand membrane compositions in order to optimize their separation properties. Such optimized membranes will contribute to improved efficiency and economy in separations pertaining to the natural-gas and petroleum industries.