γ-Valerolactone-Enabled Mild Methanolysis of Waste Polyethylene Terephthalate for Efficient Chemical Recycling.

To tackle growing resource and environmental challenges, closed-loop chemical recycling of waste PET is gaining significant attention. Methanolysis demonstrates significant industrial potential due to the ease of separation and purification of its depolymerization product, dimethyl terephthalate (DMT). However, conventional methanolysis processes for PET typically require harsh conditions (>200 °C and 2-4 MPa), highlighting the need for more efficient and milder methods. In this work, leveraging Hansen's solubility parameter theory, a bio-based solvent gamma-valerolactone (GVL) was introduced to construct a binary mixed solvent system, enabling highly efficient depolymerization of PET. Through systematic optimization of reaction conditions, an in-depth analysis of the effects of various factors on depolymerization efficiency and kinetics was conducted. The incorporation of GVL markedly enhanced the compatibility between the solvent and PET, thereby significantly improving depolymerization efficiency while effectively lowering the reaction temperature and pressure. Complete depolymerization of PET can be achieved within 2 h at 150 °C under a pressure of 0.9 MPa, with a DMT yield of up to 97.8%. This GVL/methanol depolymerization system exhibits higher efficiency, milder reaction conditions, and substantial advantages in terms of environmental impact and energy consumption indicators. By using the renewable bio-based solvent GVL, this technology aligns with the core principles of green chemistry and provides an efficient, feasible, and innovative pathway for sustainable closed-loop PET recycling.