Comparative FTIR Analysis of Liquid By-products from PET Hydrolysis Using Methanol and Ethylene Glycol

Polyethylene terephthalate (PET) hydrolysis is a promising pathway for recycling plastic waste into valuable chemical feedstocks. In this work, the focus is shifted from the solid terephthalic acid product to the liquid by-products generated using two different solvents: ethylene glycol and methanol. Hydrolysis was conducted under controlled conditions using sodium hydroxide as the catalyst, followed by neutralization with sulfuric acid. Fourier Transform Infrared (FTIR) spectroscopy was employed to characterize the liquid fractions. Results indicated that the spectra of ethylene glycol-based hydrolysis products closely resembled that of pure ethylene glycol, with minor deviations due to impurities, while methanol-derived samples exhibited significant spectral differences compared to pure methanol. The broad absorption peaks between 3200–3500 cm⁻¹ confirmed the presence of hydroxyl groups in all liquid samples. This study highlights the critical role of solvent selection in determining the quality and reusability of the liquid by-products during PET hydrolysis.