From complex mixtures to high purity: Modeling and optimization of electrodialysis for electro-refinery

This study delivers a comprehensive assessment of a selective electrodialysis system designed to isolate oxalic acid from an equimolar mixture of four organic acids: oxalic, formic, acetic, and propionic. The separation approach exploits the distinct ionization behavior of these acids under strongly acidic conditions. Operating at a controlled pH of 1.3 ensures oxalic acid remains predominantly ionized, while the other acids largely retain their neutral form, enabling targeted migration of oxalate ions through ion-exchange membranes. Experimental results revealed a significant improvement in oxalic acid purity within the recovered stream, rising from 25% to 50%. This outcome confirms the effectiveness of pH manipulation as a driving force for selective transport in electrodialysis systems handling complex carboxylate mixtures. To optimize the process, a detailed mathematical model was developed, allowing estimation of diffusion and migration constants for each species and providing a robust characterization of system dynamics. The model's predictive capability proved essential for designing multistage electrodialysis configurations aimed at achieving higher purities. Simulations based on the validated framework indicate that three sequential stages under consistent operating conditions can achieve an oxalic acid purity of approximately 90%, while experimental results reach about 95%, offering a scalable solution for industrial applications. Overall, this work integrates experimental validation with theoretical modeling to advance the selective separation of organic acids. The findings underscore the critical role of acid dissociation dynamics in membrane-based purification and provide actionable insights for future process development. This combined approach establishes a blueprint for optimizing electrodialysis systems for targeted recovery of chemically similar compounds. • Electrodialysis enables selective oxalic acid separation from mixed acids. • Operating at pH 1.3 ensures oxalic acid ionization and preferential migration. • Oxalic acid purity improved from 25% to 50% in single-stage experiments. • Developed a predictive model accurately simulating ion transport dynamics. • Three extra stages can achieve >95% oxalic acid purity in multistage design.