(229d) Catalytic Co-Pyrolysis of Ldpe and PET with HZSM-5, H-Beta, and HY: Experiments and Kinetic Modeling

The disposal of plastics is a global issue as it has been shown that plastics are responsible for 60- 80% of total marine debris which have led to the formation of the great pacific garbage patch with an estimated surface area of 1.6 million square kilometers. Pyrolysis is a process of thermal degradation of feedstocks in inert ambience. It is an attractive alternative to mechanical recycling for the processing of plastic waste, as it can process both single streams of plastics in addition to mixtures of plastics at large volumes. The catalytic pyrolysis of plastics can help to tailor product distribution to increase the production of chemicals and fuels depending on the type of catalyst used.

In this study, the catalytic pyrolysis of low-density polyethylene (LDPE), polyethylene terephthalate (PET) and their mixture (1:1 wt./wt.) with three zeolite catalysts (HZSM-5, H-Beta, HY) was investigated using a thermogravimetric analyzer (TGA) and a Pyroprobe® micro-reactor coupled to a gas chromatograph mass spectrometer (Py-GC/MS). The TGA results demonstrated that during pyrolysis at 10 °C/min, on average, zeolite catalysts decreased the maximum decomposition temperature by 149 °C for LDPE while only decreasing by 8 °C for PET. The derivative thermogravimetric (DTG) curve evidenced interactions when the two polymers were catalytically co-pyrolyzed for all the three catalysts. A lumped nth order reaction scheme was able to accurately model both non-catalytic and catalytic pyrolysis and co-pyrolysis by using least squares fitting approach for determining the kinetic parameters. The kinetic model was able to model well the interaction effects observed during catalytic co-pyrolysis of LDPE and PET with HZSM-5, H-Beta, and HY (Fit%Wt% > 96%, Fit%DTG > 93%). Py-GC/MS experiments for the catalytic fast pyrolysis of LDPE, PET and a mixture of PET and LDPE allowed us to provide further insight into the product distribution.