Structural and mechanical characterizations of microporous silica-boron membranes for gas separation

This paper presents structural and mechanical characterizations of microporous silica membranes for gas separation. The membrane separative layer is made of microporous silica-B2O3 produced via a sol-gel process. This layer of about 200 nm of thickness is deposited on the internal surface of a tubular asymmetric gamma-alumina/alpha-alumina support. FTIR and Raman analyses indicate the presence of the boron in the silica net and the above methods in conjunction with B-11 MAS NMR analyses of the samples indicate that boron is located mainly in the tetrahedral framework position. Such membranes present interesting gas separation properties at temperatures up to 500 degrees C and transmembrane pressures lower than 8 bar. He permeance values close to 10(-10) kmol m(-2) s(-1) Pa-1 are obtained, associated with ideal selectivity alpha(He/CO2) which can reach 55. Mechanical properties of separative silica-modified layers are measured by nanoindentation and the coefficient of thermal expansion is obtained from pure material. (C) 2008 Elsevier B.V. All rights reserved.