Thermal behavior, synergistic effect and thermodynamic parameter evaluations of biomass/plastics co-pyrolysis in a concentrating photothermal TGA

The heating rate would significantly impact the pyrolysis process, especially for the reactions containing synergistic effects between two different feedstocks. Co-pyrolysis of two widely available biomass (CC-corncob and PS-peanut shell) with plastic (PET-polyethylene terephthalate and PVC-polyvinyl chloride) was studied in a concentrating photothermal thermogravimetric analysis (CP-TGA) system at three heating rates (100, 500, 1000 degrees C/min). The TG and DTG curves of CC and PS differ due to their polymeric components (holocellulose and lignin); two pronounced levels at 100 and 500 degrees C/min heating rates were present in PVC. With increasing heating rate, the lateral shift towards higher temperature regions in the TG and DTG curves exceeded 100 degrees C. The synergistic effects on the blend samples were concentrated in the main decomposition region (250-580 degrees C) due to rapid volatiles release, and the discrepancy values further stabilized at the final decomposition stages. The activation energy (Ea) was assessed using a comparative study of isoconversional methods, namely Kissinger-Akahira-Sunose (KAS), Flynn-Wall-Ozawa (FWO), and Starink. The isoconversional methods demonstrated that the co-pyrolysis process required about 30 % less activation energy than the pyrolysis of plastic (PET/PVC) alone. Coats-Redfern' s (CR) model-fitting approach was used to identify the kinetic triplet of the devolatilization stage. The CR models revealed that biomass-PET blends belong to two to four-dimensional diffusion models, whereas biomass-PVC blends are dominated by chemical reactions of 1.5 and 2 orders. The energy barrier between activation energy (Ea) and change in enthalpy (Delta H) for all the blend samples was lower (similar to 5-6 kJmol(-1)), which slightly increased at higher heating rate.