Efficient and Sustainable Electrochemical System for Alkali Ion Recovery from Alkaline Polyester Waste Hydrolysis

Alkali-catalyzed hydrolysis effectively depolymerizes waste polyesters and recovers high-purity monomers. Nonetheless, the conventional acid-based neutralization process (ABNP) for polyesters recycling faces economic and efficiency challenges due to substantial alkali consumption. To address these challenges, this study developed an electrochemical recovery and separation system (ERSS), a three-chamber electrolyzer separated by cation exchange membranes (CEM), with an ion separation module (ISM) situated between the anode and cathode of a water electrolysis system. Through water electrolysis, the system can efficiently recover excess KOH from polyester hydrolysates by leveraging directed ion migration under an electric field. Experimentally, the system achieves outstanding performance in real PET hydrolysates, with a KOH Faraday efficiency of 96.4%, yielding 88.4% for ethylene glycol (EG) and 89.3% for p-phthalic acid (PTA). The system operates stably and continuously for 100 h, processing ≈6 liters of hydrolysate. Additionally, it has exceptional KOH recovery across multiple polyester hydrolysates. A techno-economic analysis (TEA) shows that compared to the traditional ABNP, the ERSS significantly reduces chemical input costs in the hydrolysis unit, achieving savings of up to 62.5%. This study provides an efficient and cost-effective solution for the alkaline hydrolysis recycling of waste polyesters, effectively mitigating the economic drawbacks of excessive KOH usage.