Experimental and Theoretical Study of Enhanced Vapor Transport through Nanochannels of Anodic Alumina Membranes in a Capillary Condensation Regime

The pressure-driven flow of condensable and permanent gases was studied experimentally for anodic alumina membranes with channel diameters ranging from 20 to 90 nm depending on feed and permeate pressures. A substantial permeability rise for condensable gases was detected under capillary condensation conditions. A self consistent theoretical model for mixed liquid gas transport through the nanopore was suggested based on the obtained experimental results. The model was used for the evaluation of the pressure drop in a liquid defined by menisci curvatures and determination of the optimal conditions to enhance the membrane performance. The highest pressure difference in a liquid can be obtained by decreasing the entrance meniscus curvature with a simultaneous increase in the curvature of the evaporating meniscus. This case was realized in asymmetric membranes with multiple branching of channels into 5 nm nanocapillaries, resulting in up to 10x enhancement of isobutane permeability (up to 450 m(3)/(m(2).bar.h)) in the capillary condensation regime. Combined with a serious selectivity rise for condensable and permanent components of gas mixtures, this enables mesoporous membranes to be successfully utilized in the self-controlled removal of water and hydrocarbon vapors for the conditioning of natural and associated petroleum gas.