Benzoic acid recovery via waste poly(ethylene terephthalate) (PET) catalytic pyrolysis using sulphated zirconia catalyst

摘要

Polyethylene terephthalate (PET) is one of the main plastics used in food packaging products, which have a very short life and are rapidly transformed into waste, and accounts for 7 wt% of the total plastic waste generated. Current PET waste management, mainly via mechanical recycling and glycolysis, have encountered a number of issues: negative impact on the environment, segregation of waste and product separation/purification. Therefore other versatile alternatives such as pyrolysis should be employed to recover value-added products from waste. Benzoic acid a precursor in the food and beverage industry, derived from PET via thermochemical conversion opposed to the current manufacturing process from fossil fuel-based feedstock is considered as a promising approach. In this study, the effect of operating conditions i.e. temperature, catalyst to plastic mass ratio and volatiles residence time and their interactions on product yields and properties were studied. Sulphated zirconia (SZ) was first time used for catalytic pyrolysis of PET due to its high acidity and environmentally friendly synthesis. Results showed that up to 27-32 wt% benzoic acid could be recovered through PET pyrolysis at 450-600 degrees C at 20 s residence time. By increasing the catalyst:plastic ratio to 10 wt% only 26 wt% of benzoic acid was recovered in the wax but it increased the amount of other valuable products i.e. light hydrocarbons (C-1-C-3) recovered in the gas.