Mass Transfer Characteristics through Alumina Membranes with Different Pores Sizes and Porosity

Abstract

Different membranes covering the macroporous to nano-pororous range and having different porosities have been used to study the mass transfer of methane and carbon dioxide single gases. The effect of flow parameters on the transport mechanisms through porous membranes were reviewed in detail. The characteristics of gas transport through the macroporous, microporous, and nano-porous membranes were investigated with several gas diffusion models in the range of 20–100 ◦C and at pressure differences ranging from 0.2 to 3 bar. The experimental gas permeation data of the membranes were analyzed using the Darcy flow model. The results clearly showed good agreement between the model analysis and the experimental data. The experimental data showed that the permeation followed a parallel flow model in which the behavior of gases was governed by viscous and Knudsen diffusion, although to varied degrees. Permeation of the gases through each membrane varies considering the viscosity of the gases at the same temperature. Furthermore, the membranes followed the configurational diffusion model in which the permeance increased with increasing pressure and decreasing temperature. For the gas flow measurements through macroporous and nano-porous membranes with diameters ranging from 6000nm to 15nm, the results indicate that the experimental flux agrees well with the calculated (model) flux through which gas flows from the bulk stream in the shell side to the membrane outer surface where viscous flow and Knudsen diffusion coexist. The study shows that experimental flux is larger than Knudsen diffusion, and the contribution of Knudsen diffusion to the experimental flux increases with the decrease in the diameter. On the other hand, the effects of gas slippage are considerable as gas velocity near the wall is higher than zero. The slip length effects are inversely proportional to pore size and with driving pressure.