Upcycling of waste polyethylene terephthalate to dimethyl terephthalate over solid acids under mild conditions

Abstract

Abandoned plastics have become a serious hazard to the environment and ecology both on land and in oceans; among them, waste polyethylene terephthalate (PET) accounts for up to 13.9% of all waste plastics. The recycling of these hazardous materials has attracted the attention of many scientists. In this work, an efficient strategy of catalytic upcycling of waste PET to dimethyl terephthalate (DMT) was performed over environmentally friendly Ti_xSi_1−xO₂ solid acids. Characterization studies disclosed that Lewis acid sites in Ti_xSi_1−xO₂ catalysts were extremely active for the alcoholysis of PET with methanol under mild conditions. In particular, the yield of DMT over Ti_0.5Si_0.5O₂ (2.5 wt% added PET) reached 98.2% with complete degradation of PET in 2 h at 160 °C. Ti_0.5Si_0.5O₂ could be recycled at least five times without obvious loss of activity. The best specific activity of each acid site in Ti_0.5Si_0.5O₂ reached 708.3 h⁻¹, and it was also capable of upcycling waste bottles and polyester yarn. The degradation mechanism of PET over Ti_0.5Si_0.5O₂ was validated via matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, scanning electron microscopy and gel permeation chromatography. The Ti_0.5Si_0.5O₂-catalyzed alcoholysis method provides a green pathway for upcycling waste PET.