Molecular simulation of swelling and structure for Na-Wyoming montmorillonite in supercritical CO ₂

Abstract

Gibbs ensemble Monte Carlo (GEMC) simulations were used to study the swelling stability and interlayer structures of Na-montmorillonite clay in supercritical CO2 (scCO2). From the GEMC simulation, it was found that there exist several stable mechanical spacings for Na-Wyoming montmorillonite immersed in scCO2, which are larger than the stable spacing in vacuum condition. The swelling behaviour of Na-montmorillonite clay in scCO2 fluid is thermodynamically favourable. However, it was also observed that the clay swelling is inhibited when in contact with CO2 gas at atmospheric pressure. The interlayer structures were applied to investigate the mechanism of swelling. In the case of stable spacings, the interlayer sodium cations are not only well solvated with the surrounding CO2 molecules but also show stronger tendency to adhere to the clay surface.