Comparative study on organic solvents and green solvents in separation of aromatic hydrocarbons/low-carbon alcohols azeotrope by structure–activity relationship

Abstract

Organic solvents, deep eutectic solvents, low transition temperature mixtures and ionic liquids show excellent performance in the separation of azeotropes by extractive distillation. However, the functions and characteristics of four kind of solvents in azeotropic system are not clear. The interaction between solvent molecules and p-xylene and pentanol was studied by quantum chemical calculation, and the separation mechanism was studied at the molecular level. Electrostatic interaction and van der Waals interaction are the key interactions in the complexes. They are quantitatively studied based on the energy decomposition analysis of molecular force field. The electron density difference is used to explain the weak interaction generated by electrostatic interaction. On this basis, the van der Waals potential between solvent and azeotrope molecules is intuitively displayed by using van der Waals potential. The van der Waals potential is suitable for the molecular configuration in which van der Waals interaction plays a key role, which can be regarded as a supplement to the analysis of electrostatic interaction. In addition, since the optimal molecular structure is bound to be accompanied by orbital overlap, the orbital interaction is analyzed by using Natural Bond Orbital; Use the Interaction Region Indicator function to clearly show all types of interactions in one picture. The results of quantum chemical calculation show that the introduction of solvent has a significant effect on the molecular interaction of azeotropes, which is the main factor for the solvent to reduce the relative volatility between azeotropes. This study provides important information for understanding the role of organic solvents, deep eutectic solvents, low transition temperature mixtures and ionic liquids in the separation of azeotropic systems, and has important reference value for the development of new solvents.