Kinetic and thermodynamic studies of co-pyrolysis of babool sawdust blended with high-density polyethylene using model-free isoconversional methods

Commercial exploitation of biomass and waste plastic for the production of value-added fuels and chemicals is of paramount importance considering pollution mitigation and waste management issues. So, in the present manuscript, co-pyrolysis kinetics of babool (Acacia nilotica) sawdust (BSD) blended with high-density polyethylene (HDPE) was carried out in a nitrogen environment at the heating rates of 5, 10, and 15 degrees C/min. The findings provide crucial insights into adjusting the blend composition and pyrolysis parameters to improve decomposition efficiency, minimize activation energy, and produce greater synergistic effects contributing to energy sustainability and waste valorization. Three blends of biomass and plastic were pyrolyzed, i.e., B:P (3:1) (75 wt% BSD and 25 wt% HDPE), B:P (1:1), and B:P (1:3). The kinetic parameters were obtained using isoconversional models like KAS, FWO, and Starink. The calculated average activation energy for BSD emerged to be 117.55, 122.41, and 117.07 kJ mol-1 following KAS, FWO, and Starink models, respectively. However, for B:P (3:1) average activation energy is 104.61, 108.30, and 104.15 kJ mol-1 using these models. This emphasizes that addition of HDPE helps to enhance the rate of decomposition. However, addition of further plastic was not beneficial as for B:P (1:1) or B:P (1:3) activation energy increased thereby reducing the rate of decomposition. This is to be noted that the activation energy dropped by about 11% for B:P (3:1) as compared to BSD. Synergistic effect during co-pyrolysis of biomass and plastic blends B:P (3:1), B:P (1:1), and B:P (1:3) through TGA analysis was carried out at 10 degrees C/min. The synergistic effect was the most evident in the B:P(1:1) at a temperature of 400 degrees C. Comprehensive pyrolysis index (CPI) was also estimated to understand the performance of pyrolysis of raw biomass and its blend with HDPE. Criado's Z-master plots indicated a multistep reaction mechanism for the blends, with the B:P(3:1) exhibiting diffusion and power-law models at lower conversion rates while phase boundary-controlled reactions were observed at higher conversion rates.