Reactive Crystallization via Metal-Organic-Framework Formation Enables Separation of Terephthalic Acid from Textile Impurities

Polyethylene terephthalate (PET) fibers are among the largest plastics in production. Used commonly in textiles, PET fibers are often blended with non-PET components such as cotton, dyes, and additives. As these non-PET components generate impurities during depolymerization, extracting high-purity terephthalic acid (TPA) monomer from the chemical recycling of textiles is challenging. Here, we demonstrate the extraction of high-quality TPA from the impure crude digestion mixtures containing depolymerized PET fibers and non-PET components. Our approach uses reactive crystallization to turn TPA into a metal-organic framework (MOF). As TPA is the only component in the mixture capable of forming an extended, crystalline structure, TPA monomers are separated from impurities as MOF crystallizes. We demonstrate this concept on recycled TPA (rTPA) extracted from a polyester-cotton blend textile through alkaline hydrolysis, where the impure rTPA was used as an organic linker to prepare MOF MIL-53(Ga). This MOF crystallization removed the trapped impurities. After MOF disassembly, colorless TPA, reminiscent of virgin-grade monomer, was obtained. These results demonstrate self-assembly-induced crystallization as a new strategy to selectively recover monomers from complex mixtures.