Exceptionally high performance of charged carbon nanotube arrays for CO2 separation from flue gas

Abstract

We use grand canonical Monte Carlo simulation to investigate the adsorption of a CO2/N2 mixture in neutral and charged (7, 7) carbon nanotube (CNT) arrays. It is found that both the adsorption of CO2, and the CO2/N2 selectivity are either enhanced or reduced when the charges are positive or negative. The CO2/N2 selectivity in a CNT bundle carrying +0.05e charge with intertube distance of 0.335 nm exceeds 1000 for pressures up to 15 bar, which is remarkably high. It is seen that strong electrostatic interactions from neighbouring CNTs enhance the adsorption of CO2 over N2, and while the adsorption of CO2 has complex dependence on intertube distance, the CO2/N2 selectivity decreases with intertube spacing. We propose a quantitative performance coefficient as an aid to assessing the efficiency of CNT bundles to separate CO2 from flue gas, and show that a +0.05e charged bundle with intertube distance of 0.335 nm provides the best performance. Further, it is found that water vapor in flue gas imposes negligible effect on the adsorption of CO2 and its selectivity over N2 in the neutral and positively charged (7, 7) CNT bundles, but dramatically reduces the adsorption of CO2 and N2 in negatively charged bundles.