Dearomatization Insights with Phosphonium-Based Deep Eutectic Solvent: Liquid–Liquid Equilibria Experiments and Predictions

Abstract

In a challenge to develop a process that meets the criteria of being “green” in the extraction of aromatics, deep eutectic solvents (DESs) are currently gaining importance as separation media. This work reports a phosphonium-based DES for the dearomatization of model diesel components at 25 °C and p = 1 bar. The DES comprising a hydrogen bond acceptor, namely, methyltriphenylphosphonium bromide, along with ethylene glycol as a hydrogen bond donor, was formulated with a molar ratio of 1:4. The DES was then used to extract benzene from representative diesel fuel components, a mixture of n-decane, n-dodecane, and n-hexadecane. Ternary liquid–liquid equilibrium experiments were then performed at ambient conditions with different benzene concentrations with the feed varying from 2 to 20 wt %. An absence of the solvent in the raffinate phase was found in all the tie lines, suggesting limited solvent recovery costs. Besides, it was also found that all three ternary systems show type I phase activity with positive slopes, indicating that the desired removal of benzene requires a small amount of solvent. The quantum chemical-based COSMO-SAC model was then used to predict the tie lines giving an average root mean square deviation value of 1.2%. The mechanism of the extraction process was also extensively studied with the help of quantitative 1H NMR and Fourier transform infrared spectroscopy. Higher benzene extraction efficiencies were observed due to the strong noncovalent interaction between the DES and benzene.