Experimental and modeling study of gas transport through composite ceramic membranes

Abstract

Concerning the gas transport through ceramic membranes, insufficient attention is paid to concentration polarization (mass transfer) in the measuring cell or module used and to support effects. Therefore, the aim of this study is to demonstrate these effects based on a combined experimental and modeling study of two types of membranes. The gas permeation through a graded ceramic microporous membrane consisting of α-Al2O3/γ-Al2O3/silica was well simulated with the “Binary-Friction-Model” (α-Al2O3/γ-Al2O3 substrate) and the Maxwell–Stefan model (silica top-layer), respectively. For both the α-Al2O3 support and γ-Al2O3 interlayer, the geometric factors, such as the pore radius (r), and the ratio of porosity versus tortuosity (ε/τ) obtained from single gas permeation agree well with physical characterizations. Knudsen diffusion is the dominant transport mechanism through both the α-Al2O3 support and γ-Al2O3 interlayer and the support effect cannot be neglected due to significant contributions of transport resistance.For the asymmetric BSCF membrane the comparison of experimental data and gas transport simulation using the “Binary-Friction-Model” and the “Wagner equation” coupled to a 2D fluent simulation to account for the local variations of oxygen concentration and gas velocities profiles show a deviation by a factor of ca. 2. The oxygen concentration profile and the gas velocity profile derived from 2D fluent clearly pointed out the concentration polarization effect, which resulted in a permeation reduction up to ca. 20.3%. The porous support exerts a great influence on the gas transport through the asymmetric BSCF membrane. With increasing sweep flow rates, the effect of concentration polarization is less pronounced, while the gas transport through dense and support layer become more important.