Thermal behavior analysis and biochar formation through co-pyrolysis of de-oiled microalgae biomass and wood sawdust for ecofriendly resource utilization

The co-pyrolysis of biomass wastes is of great importance for the integration of waste management and renewable energy sources, and the achievement of sustainable development goals. In this context, this study aimed to understand the reaction mechanisms and their behavior by examining the co-pyrolysis reactions of de-oiled microalgae and wood sawdust wastes. In this scope, the co-pyrolytic behavior of wood sawdust – de-oiled microalgae blends was determined by the thermogravimetric method, and co-pyrolysis kinetics and thermodynamics were calculated using model-free methods. In addition, biochar was produced from these blends under the conditions of 600 °C temperature and 20 °C min⁻¹ heating rate, and the characterization of biochars was performed. According to the obtained results, it was observed that the degradation time of de-oiled microalgae was longer than that of wood sawdust, depending on the complexity of its structure. The main decomposition of wood sawdust occurred in a single step within the temperature range of approximately 200–400 °C, whereas the main decomposition of de-oiled microalgae occurred in multiple steps within the temperature range of approximately 200–550 °C. The calculated pyrolysis activation energy values for the biomasses ranged from approximately 149 to 180 kJ mol⁻¹, while for the blends, these values ranged from approximately 159 to 203 kJ mol⁻¹. Additionally, the higher HHV values of the biochars produced from the blends (approximately 10 MJ kg⁻¹ higher than the others) increased their potential as a fuel. Based on these results, biochars produced via co-pyrolysis can be considered as a suitable option to be used as a fuel in terms of energy efficiency.