Thermal behavior, thermodynamics and kinetics of co-pyrolysis of binary and ternary mixtures of biomass through thermogravimetric analysis

The present study aims to investigate the co-pyrolysis behaviors, kinetics and thermodynamics of spirulina microalgae, sugarcane bagasse and waste fire, and their mixtures, by means of thermogravimetric analysis. Various Isoconversional methods, specifically Flynn-Wall-Ozawa (FWO), Kissinger-AkahiraSunose (KAS), Starink (STK) and Vyazovkin (VYA), the compensation effect and master plots were implemented to evaluate the kinetic parameters. Furthermore, by comparing experimental and theoretical values of mass loss, it was concluded that for the microalgae-bagasse mixture, the interaction is synergistic. In other cases, inhibitive interaction has been observed. Due to fire composition and its tough structure, the fire had the highest activation energy and the addition of fire to the binary mixture increased the activation energy of ternary mixtures. The average activation energy obtained for Spirulina, bagasse and scrap fires is around 200, 90 and 230 kJ mol(-1), respectively. However, the average activation energy of their ternary mixture is approximately 165 kJ mol(-1). Thermodynamic parameters (Delta G, Delta H and Delta S) were estimated based on kinetic data using the thermogravimetric relations. The endothermic character of the pyrolysis process was proved by the positive values of Delta H, obtaining an average value of 160.5 kJ mol(-1) for the ternary mixture. The Gibbs free energy Delta G of the ternary mixture is quite uniform with the conversion, varying slightly between 173 and 176 kJ mol(-1). In contrast, Delta S depends strongly on the pyrolysis conversion, obtaining negative values for conversions below 0.4 for the ternary mixture, whereas positive values are attained for conversions above 0.6.