Molecular simulations of water and paracresol in MFI zeolite--a Monte Carlo study.

Paracresol is a protein-bound toxin that is not efficiently eliminated by the hemodialysis method. Monte Carlo simulations in grand-canonical (GCMC) and canonical ensembles were performed to investigate the adsorption of paracresol and water in silicalite-1 zeolite. GCMC simulations using a configurational-biased algorithm show that four paracresol molecules are adsorbed at the channel intersections per unit cell of silicalite-1. The adsorption isotherms of water with and without the presence of paracresol at the intersections were investigated. A cooperative phenomenon in the process of coadsorption has been observed: at very low chemical potential, paracresol facilitates the penetration of water into silicalite-1. This mechanism is interpreted in terms of the properties of the zeolite and paracresol molecules. A thermodynamic cycle is used to calculate the adsorption energy of paracresol in silicalite-1. The calculated adsorption energy reasonably agrees with the experimental data.