(390c) Optimal Hybrid Extraction–Distillation Process Design for Bio-Acetic Acid Recovery

Acetic acid (HAc) is a key platform chemical widely used across industries, but its conventional production via methanol carbonylation results in substantial greenhouse gas emissions. Gas fermentation has emerged as a sustainable alternative, converting carbon monoxide in industrial off-gases into HAc through the Wood-Ljungdahl pathway. However, the resulting fermentation broth contains low HAc concentrations (~40 g/L) and butyric acid as a byproduct, posing significant challenges for downstream separation. To address this, we propose two hybrid extraction-distillation (HED) processes using ethyl acetate (EA) and tri-n-octylamine (TOA) with 1-octanol as a extractant.

Process models were developed in Aspen Plus for both systems. To simulate the TOA-based process, we conducted LLE experiments and developed a Pitzer activity coefficient model, which was used to accurately predict extraction performance in the presence of carboxylic acids.

Key design variables, including solvent-to-feed ratio, reflux ratio, and distillation column configurations, were optimized to minimize separation cost (USD/kg-HAc). The TOA-based process demonstrated lower reboiler duty and solvent consumption, leading to improved energy efficiency. Despite TOA's higher price, its stronger extractive performance and reduced energy demand resulted in a competitive economic profile compared to the EA-based process.

This study highlights the critical role of solvent selection and thermodynamic modeling in designing cost- and energy-efficient downstream processes for bio-based HAc production, supporting the broader transition to low-carbon chemical manufacturing.