Electrical field enhanced CO2 permeation through a carbon molecular sieve membrane: A combined density functional based tight binding and computational fluid dynamics study

Abstract

An important challenge in membrane technology for gas separation is to simultaneously improve their permeability and selectivity. Often, the increase in one performance leads to the decline of the other. This study presents a solution to that problem by utilizing electrical field coupling to improve CO2 permeation through a nitrile-containing poly (arylene-ether-ketone) (PEK-C(CN)) carbon molecular sieve membrane. Density functional based tight binding simulations of CO2, CH4, and N2 adsorption on PEK-C(CN) monolayer were conducted without and with electric field. The findings revealed that the electric field strength and orientation affected the molecules bond lengths, atomic charges, and bond angles. Investigation of their adsorption energy dominantly favored CO2 adsorption. Analysis of the partial density of states confirmed that adsorption interactions with the membrane were due to CO2 responses to the applied electric field. It additionally proved the electrical stability of PEK-C(CN) membrane. Computational fluid dynamics simulations of gas permeation through PEK-C(CN) membrane were performed without and with electric field. Results indicated an average pore distribution around 0.5 nm. The velocity flow distribution aided locate the interconnected pores, bringing to the fore the dominant transportation paths of gas molecules. It was uncovered that although the application of an electric field significantly improved the membrane gas permeability, it was not necessarily beneficial to its selectivity. −5 V was determined to be the optimum potential for an improvement of CO2 permeability from 57.32 Barrer (no field) to 15924.91 Barrer, while also enhancing the selectivity. This work demonstrates the benefits of the electric field and its promising application in gas separation processes.