Optimizing Waste Motor Oil Recycling into Diesel Using Novel Deep Eutectic Solvents: An Atomistic Study

Abstract

The optimization of recycling processes for waste motor oil (WMO) into diesel fuel is crucial for sustainable waste management and resource recovery. This study explores the application of novel deep eutectic solvents (DES), specifically methyltriphenylphosphonium chloride (MTPPCl) and ethylene glycol (EGL)-based DES, for the efficient removal of naphthalene from WMO. Density functional theory (DFT) calculations and classical all-atom molecular dynamics (MD) simulations were employed to investigate the intermolecular interactions between DES components and WMO constituents, with naphthalene and octane serving as model components. Significant changes in molecular electrostatic maps, highest occupied molecular orbital and lowest unoccupied molecular orbital (HOMO-LUMO) distribution and energies, interaction energies, and hydrogen bonding networks were observed upon mixing DES with WMO. Notably, the interaction energy between naphthalene and DES components, such as the electrostatic interaction energies, was relatively higher for chloride (-2.19 kJ/mol). Moreover, MTPP (-1.06 kJ/mol), EGL (-1.21 kJ/mol) and chloride (-1.23 kJ/mol), revealed strong interactions, particularly from van der Waals forces, that facilitate effective contaminant removal. The HOMO-LUMO energy gap for the DES-naphthalene system was found to be 1.22 eV, indicating moderate electronic stability. These findings highlight the DES's capability to disrupt naphthalene-octane interactions, enhance naphthalene solubilization, and suggest its potential for improving the purification of WMO.