Molecular modeling insights in the extraction of benzene from hydrocarbon stream using deep eutectic solvent

Abstract

The present study aims to elucidate the molecular insights into the extraction of benzene from hydrocarbon mixture using a phosphonium based deep eutectic solvent (DES). The prepared DES consists of the hydrogen bond acceptor (HBA; methyltriphenylphosphonium bromide, MTPB) and hydrogen bond donor (HBD; ethylene glycol) at a molar ratio of 1:4. The atomic-level classical molecular dynamic (MD) simulation technique is then employed to investigate the equilibrium phase behaviour of the DES + benzene + hexane ternary system with respect to solvent rich and hydrocarbon-rich phases. To observe the effect of feed concentration, three different concentrations were considered from the reported experimental runs, which gave high selectivity and distribution coefficient values. The non-bonded interaction energies of different species and the structural properties such as radial distribution functions, spatial distribution functions (SDFs), and the average number of hydrogen bonds are then computed. It is found that the cation within the HBA, namely, MTP, initiates interactions with benzene when compared to HBD or its anion (Br). MTP and ethylene glycol both are seen to contribute to the hydrogen bonding with benzene, which results in a higher experimental solubility value. The calculations of SDFs further reveal the fact that the benzene molecules are evenly distributed around the active sites of the MTP molecule, whereas hexane molecules are found to be distributed around the non-active sites of the DES. In order to validate the simulation procedure, the concentration in both the phases was compared with the existing LLE experimental results. In the penultimate part, 2D 1H-13C Heteronuclear Multiple Bond Correlation (HMBC) NMR is performed for investigating and confirming the hydrogen bonding interactions among components of DES and benzene.