Quaternary ammonium hydroxide-catalyzed methanolysis of bisphenol–A polycarbonate: performance, mechanism, and scale-up

Abstract

Polycarbonate (PC) is extensively utilized in various industrial applications; however, its environmental persistence and inherent difficulties associated with its recycling have raised significant concerns. To address these issues and promote a circular economy, it is crucial to develop efficient and sustainable depolymerization methods. In this study, tetramethylammonium hydroxide (TMAOH) was used as an efficient depolymerization catalyst, exhibiting excellent catalytic activity and selectivity, with satisfactory chromatic properties and eliminating the need for additional catalyst removal. Real-time visual observations, complemented by GPC and DSC analyses, revealed a degradation process marked by a gradual particle size reduction and a decrease in molecular weight. Mechanistic studies using FT-IR, NMR, and GC analyses uncovered two coexisting pathways, each involving distinct carbonate bond cleavage mechanisms. Owing to its advantages such as mild reaction conditions, high activity, and decomposability without residues, the catalytic system was seamlessly implemented at the pilot scale. The process proved scalable (5 kg per batch) and effective for processing waste PC. The recovered bisphenol–A met industrial purity standards (≥99.85%), and the repolymerization from the recovered monomer could offer commercial-grade PC. Life cycle assessment revealed that this process reduces carbon emissions by 63% compared to conventional fossil-based routes, while generating an economic benefit of $911 per ton of PC processed, providing an environmentally and economically sustainable solution for the closed-loop recycling of PC.