Grand canonical Monte Carlo simulation on the metal-doped zeolite for enhancing separation of organic sulfur

Content

In this study, the effects of metal doping (Al, Cu, Fe) on the performance of MFI for adsorption and removal of organic sulfur (carbonyl sulfide (COS), methyl sulfide (CH₃SH), carbon disulfide (CS₂), and ethyl mercaptan (C₂H₅SH)) were systematically investigated. The mechanisms of metal doping on the adsorption sites and the competing adsorption behaviors were revealed. Under the independent adsorption conditions, Al doping resulted in an enhancement in the adsorption of COS and CS₂. Cu doping led to a preferential enhancement in the adsorption of COS, while concurrently inhibiting the adsorption of other molecules. Fe doping results in a slight reduction in the amount of adsorption. However, it concomitantly leads to a decrease in the stable adsorption escape from 607.43 to 470.32 kPa. Under the simultaneous adsorption conditions, Fe-MFI demonstrated optimal industrial adaptability, characterized by a low adsorption fugacity demand (130.87 kPa) and effective separation of the four molecules through a variable pressure process. Furthermore, the variation of organic sulfur concentration exerts a significant effect on the migration of the respective adsorption sites and the alteration of the adsorption configurations. The present study provides a theoretical basis for the application of metal-modified MFI zeolites in the field of organic sulfur removal and variable pressure adsorption separation.

Methods

The theoretical study is based on the density functional theory (DFT) method for geometric structure optimization and the grand canonical Monte Carlo (GCMC) method for simulation of adsorption properties. This geometric structure (MFI, metal-doped MFI, COS, CS₂, CH₃SH, and C₂H₅SH) optimization is carried out using the Dmol³ module in the Material Studio 2017. In this study, the GGA/PBE method was employed in conjunction with the DNP basis set, a spin-polarized set, and a DFT-D correction. The translational and rotational partition functions of the gas-phase molecules have been taken into account. This sorption behaviors of COS, CS₂, CH₃SH, and C₂H₅SH on MFI and metal-doped MFI are carried out using the Sorption module in the Material Studio 2017. The fugacity range is from 101.33 to 1013.25 kPa, and the temperature is 298 K.