Improving the equilibrium performance of active carbons for separation processes by co-adsorption with low pressure solvent: application to carbon capture

Abstract

The equilibrium performance of a novel gas separation process described quite recently (Sweatman in Chem. Eng. Sci. 65:3907, 2010) called ‘pressure-swing wetting layer absorption’ here is investigated by means of molecular Monte-Carlo simulation. This process is very similar to pressure-swing adsorption except that solvent, in the form of low pressure vapour, is added to the gas to be separated in order to improve equilibrium performance. Earlier work, based on relatively simple density functional theory models, suggests that this process could be significantly more efficient than the analogous pressure-swing adsorption process when tetrahydrofuran (THF) is used as the solvent, although this conclusion is based only on equilibrium behaviour and does not take into account the effect of any dynamical processes. The aim of this work is to provide more detailed molecular simulation results to help understand this behaviour and guide experiments towards suitable solvents and conditions so that the process can experimentally tested. It is found that using acetonitrile as the solvent could be over nine times more effective than THF, which was modelled in previous work, for the particular carbon capture application studied here. These simulation results also demonstrate that, due to the effect of confinement on fluid structure, bulk solubility data cannot be used to reliably predict equilibrium performance in this context, and that the equilibrium performance is especially enhanced for pores that exhibit a bilayer phase transition.