Process Design and Optimization of an Acetic Acid Recovery System in Terephthalic Acid Production via Hybrid Extraction Distillation Using a Novel Mixed Solvent

An extraction and distillation hybrid process using a novel mixed solvent was proposed for enhancing acetic acid recovery during terephthalic acid production. Feasible hybrid extraction distillation schemes were designed, simulated, and optimized for two mixed solvents, p-xylene + methyl acetate, and p-xylene + ethyl acetate, based on liquid-liquid equilibrium data for a quaternary system containing methyl acetate or ethyl acetate with p-xylene, acetic acid, and water. A hybrid process using the p-xylene + methyl acetate mixed solvent was found to generate the desired purity of acetic acid with a lower energy consumption and higher product yield than conventional extraction processes. Results showed that the proposed hybrid extraction distillation process improves the process economics remarkably: the hybrid process using the p-xylene + methyl acetate and p-xylene + ethyl acetate mixed solvent reduced a total annual cost by 14% and 6%, respectively, compared with the conventional hybrid process using the ethyl acetate single solvent. With the important advantage of p-xylene and methyl acetate as internally existing components, the proposed mixed solvent is promising for safe and cost-effective recovery of acetic acid, particularly during terephthalic acid production.