Abstract
The economic feasibility of biodiesel depends on the proper removal of glycerol, a main byproduct that decreases gasoline quality. Current purification processes can be energy-intensive or produce secondary waste, necessitating the creation of new, efficient solvents. This study uses Density Functional Theory (DFT) at the B3LYP/6-311G++(d,p) level, along with D3(BJ) dispersion correction, to assess a butanoic acid/thymol-based deep eutectic solvent (DES) for glycerol extraction. The glycerol-DES complex underwent quantum-chemical computations, which included geometry optimization, natural population analysis, and frontier orbital characterisation. The examination of contact energies, electrostatic potential maps, and molecular orbitals reveals that the interaction is exothermic (ΔH_int = -20.3 kJ/mol). However, the positive change in Gibbs free energy (+21.9 kJ/mol) and the large negative entropy change (-142.1 J mol⁻¹ K⁻¹) suggest the non-spontaneous character of the interaction at ambient conditions, which is predominantly driven by enthalpy. The findings provide fundamental atomistic-scale insights into the interaction mechanisms, demonstrating the efficacy of DFT for selecting DES candidates. While the exact butanoic acid/thymol combination is theoretically unsuitable for spontaneous glycerol removal, this study provides a strong computational basis.