CS2 Removal from C5 Distillates by Reactive Molecular Dynamics Simulations

Abstract

With the expansion of the world’s ethylene industry, the production of carbon five (C5) distillates has also gradually increased. C5 can be used to produce a series of high-value-added chemical products; however, it contains carbon disulfide (CS2), which is not conducive to subsequent processing. This requires the use of highly efficient catalysts for the deep desulfurization of C5 fractions. Analyzing the desulfurization mechanisms from a microscopic perspective might be the key to prepare an efficient catalyst. This work uses molecular dynamics (MD) and density functional theory (DFT) to simulate and calculate the removal process of CS2. A reactive force field was used to simulate the kinetics and explore possible reactions of the desulfurization process. It is found that CS2 reacts with a hydroxyl group instead of water, mainly including the C–O and S–O paths. The main reaction is the C–O path two-step mechanism, and it is also observed that few C atoms can adsorb two hydroxyl groups in the one-step mechanism. Then, a DFT analysis at the B3PW91/Aug-cc-pVTZ level of theory is performed to calculate the reaction paths and relative energies of the one- and two-step mechanisms of the C–O and S–O paths. It is found that the adsorption of CS2 and hydroxyl in the two-step mechanism of the C–O path is an exothermic reaction with an activation energy of only 18.0 kcal mol–1. However, the one-step mechanisms of the C–O and S–O paths require more than 30 kcal mol–1 to obtain their corresponding products. Therefore, the two-step mechanism of the C–O path is the most likely to occur, which is consistent with the results from the MD simulations.