Combined Experiment, Simulation, and Ex-ante LCA Approach for Sustainable Cl Recovery from NaCl/Ethylene Glycol by Electrodialysis

The dechlorination (de-Cl) process for polyvinyl chloride wastes not only removes chlorine (Cl) that is undesired in the subsequent thermal treatment but also potentially establishes a Cl cycle that avoids NaCl production. Because the de-Cl process utilizes a mixture of sodium hydroxide (NaOH) and ethylene glycol (EG), the recovery of both Cl ions and EG is practically necessary for economic and environmental reasons. Designing an electrodialysis (ED) process that can recover Cl ions and EG from their mixture requires an understanding of the expected trade-off among the extent of recovery, energy consumption, and other unforeseen factors prior to the experiments. Here, the trade-off is assessed by combining laboratory-scale experiments, simulation for scale-up, and ex-ante life cycle assessment (LCA). Laboratory-scale ED experiments were performed by varying NaCl concentration in EG, NaCl concentration in water, and electrode voltage. In experiments, a Cl yield over 90% was achieved with an electrode voltage at 2.5 V, and treatment was still possible when the NaCl/H2O solution was concentrated to saturation. Based on the experiments, a commercial-scale ED process was simulated to provide LCA with inventory data under different ED operation conditions. The results revealed high environmental impacts caused by the solvent penetration reported in our previous study. To reduce the environmental impacts, a high NaCl concentration in EG is preferable, while the membranes and the electrode voltage need to be optimized to balance Cl recovery efficiency and environmental impacts, which are suggested for the future direction of research and development.