Benign and ecofriendly depolymerization of polycarbonate wastes into valuable diols using micro- and nano-TiO2 as the solid supports

Abstract

Hydroglycolysis of polycarbonate (PC) wastes received from optical (CDs) and digital optical discs (DVDs) to the diols derivatives of bisphenol-A (BPA), namely, bis(4-hydroxybutyl hydrogen carbonate) of BPA (DHB–BPA), mono(4-hydroxybutyl hydrogen carbonate) of BPA (MHB–BPA), and BPA itself as the major and oligomeric minor products were developed under mild and convenient conditions. Experiments were performed with the mixture of green solvents, including 1,4-butanediol and water in the presence of nanoparticles TiO2 (NPs-TiO2) and microparticles TiO2 (MPs-TiO2) as the solid supports, and sodium hydroxide as the catalyst under simple heating method and the obtained results were compared with together. In the developed procedure, DHB–BPA achieved and selectively converted into the MHB–BPA and BPA, respectively, when left in the moisturized environment. In these reactions, the effects of various parameters such as concentration of sodium hydroxide, the role of water as co-solvent, and nano-solid support on reaction progress are considered. The obtained results showed that by increasing the amount of water (0 up to 30 pbw based on total solvent weights) and catalyst as well (0 up to 2 pbw based on total solvents and PC wastes weights), the depolymerizing reaction was performed in high yields. In the meantime, DHB–BPA was recovered in 80% yield, using NPs-TiO2 as the solid support in the 30 pbw aqueous 1,4-butanediol. The depolymerization reaction time shortened in using NPs-TiO2 as the solid support when the data compared with the experiments performed by MPs-TiO2. Finally, the recyclability and efficiency of the NPs-TiO2 were studied and the data showed the usability of this solid support for four cycles. The recovered products were characterized using 1H NMR, 13C NMR, Fourier-transform-infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and gas chromatography–mass spectrometry (GC–MS) methods.