Distillation-based treatment of unsaturated polyester resin wastewater for propylene glycol recovery

This study evaluates distillation as an integrated treatment and resource recovery approach for wastewater generated from unsaturated polyester resin (UPR) production. An integrated experimental and modelling approach was developed to evaluate separation performance and support industrial process design. Laboratory experiments were conducted using a packed distillation column under different operating conditions, and a thermodynamic model based on vapour-liquid equilibrium data was developed and validated against experimental results. A continuous two-column distillation process was subsequently simulated and optimized using actual industrial UPR wastewater, with the total annualized cost as the optimization criterion. The system recovered water at 99.7% purity with a yield of 95%, while PG was obtained at 99.1% purity and 83.5% recovery efficiency at the lab scale. Recommended conditions for water separation were atmospheric pressure, 0.20 kW heat duty, and a reflux ratio of 0.25, whereas PG recovery achieved the highest performance under reduced pressure (<0.1 bar) with a reflux ratio of 1.8-2.0. The optimized industrial process achieved 86.63% overall valuable-chemical recovery using 9 and 22 theoretical stages for the water and phenol separation columns, respectively. The results demonstrate the feasibility of integrating validated process simulation with laboratory experiments for industrial wastewater treatment and resource recovery.