Modeling ideal selectivity variation in nanoporous membranes

Abstract

A parallel resistance transport model has been developed to describe variations in separation ability (quality) of nanoporous carbon membranes. The model considers transport through high-selectivity, high-resistance nanopores in combination with low-selectivity, low-resistance defect pores. Although few in number or small as a percentage of membrane area, these low-selectivity pores exert a disproportionate influence on permeation. The predictive qualities of the model are demonstrated using permeation data from the literature. Using flux ratios of oxygen to nitrogen, we can predict the area fraction ( α) of defect pores. At an area fraction of only 10 −9 defect pores, the oxygen-to-nitrogen ratio falls to near unity—indicating no selectivity for oxygen. Although developed for nanoporous carbon membranes, the approach will work for zeolitic and other forms of nanoporous membranes.