Molecular simulation of swelling and structure for Na-Wyoming montmorillonite in supercritical CO₂

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.

Keywords:

• montmorillonite clay
• supercritical CO₂
• molecular simulation
• swelling
• structure

Acknowledgements

This work was supported by the Natural Science Foundation of China under Grant Nos. 20776066 and 20976079, and by the Natural Science Foundation from Jiangsu Province (BK2009359).