Separation mechanism and thermodynamic phase behavior of n-propanol/p-xylene azeotrope from petrochemical wastewater by green solvents

Abstract

P-xylene, n-propanol and water are widely present in the petroleum production process, so the effective separation of these substances is of great significance to environmental protection and resource conservation. In this study, deep-eutectic solvents (DESs) were used to separate the n-propanol/p-xylene/water ternary azeotrope system for the first time and compared with the commonly used solvents. The difficulty of forming hydrogen bonds and the interaction between the extractants and the system to be separated were determined by quantum chemical calculations. Quantitative analysis was performed using σ-profile, interaction energy and electrostatic potential (ESP) energy. The order of interaction strength was N-formylmorpholine (NFM) > cyclohexanol, (DL-Menthol/Lauric acid)2:1 (DES1) > (DL-Menthol/Decanoic acid)1:1 (DES2). Qualitative analyses were performed using interaction region indicator (IRI) and independent gradient model based on Hirshfeld partition (IGMH). It can be visually shown that the H atoms on the hydroxyl groups of n-propanol play a major role in the interaction, and all form hydrogen bonds with the O atoms of the entrainers. Finally, phase equilibria data for entrainers and azeotropes were supplemented with the improved new Rose VLE kettle. A series of relevant calculations and experimental data show that the selected four extractants can achieve component separation. Among them, NFM and DES1 are the best extractants. This study provides a solvents screening process through quantum chemical calculations and phase equilibrium experimental multi-scale studies, which provide guidance for the application of solvents screening and DESs in extractive distillation separation processes.