Investigating and modeling PET methanolysis under supercritical conditions by response surface methodology approach

• Interaction effects were investigated in PET supercritical methanolysis process.
• RSM was used to develop mathematical model and analysis for process.
• A modified square root transformation model was used in RSM for better prediction.
• Terms including MeOH to PET mass ratio are uninfluential among experiment conditions.
• The optimum DMT yield was much closer to the extent of the complete reaction.

Polyethylene terephthalate (PET) is one of the most widely used raw materials in chemical industry. Chemical recycling of the waste PET is a sustainable way not only considering the economic benefit but also the environmental goals. This paper focused on the effects among three foremost variables (methanolysis temperature, time, and mass ratio of methanol (MeOH) to PET), established a mathematical model depicted the complete effects of the parameters on the process, and sought the optimal solution of this PET methanolysis reaction. Response surface methodology (RSM) was used to model and analysis the recycling process of dimethyl terephthalate (DMT) from waste PET under supercritical methanol conditions. Methanolysis temperature and time could increase the DMT yield. Mass ratio of MeOH to PET hardly affected DMT yield when the methanol is excess. Different operation parameters including reaction temperature (240–320 °C), reaction time (15–120 min), and MeOH to PET mass ratio (6:1–10:1) were modeled and optimized using RSM. The quadratic equation with mathematical transformation (square root) modified was established for predicting the DMT yield and evaluated the validity on the basic of analysis of variance (ANOVA). The result indicated that the MeOH to PET mass ratio and relative term exhibit a less significant influence on the response surface in comparison to reaction temperature and time in the range of the experiment conditions. Prediction made by the developed model was in reasonably good agreement with the test runs. Under the optimal condition, the yield of DMT reached 99.79% which was much closer to the extent of the complete reaction.