Thermal analysis of St. John's Wort wastes and biochars: A study of combustion characteristics and kinetics

Abstract

St. John's wort, extensively utilized in industries such as food, medicine, and cosmetics, generates substantial biomass waste. Utilizing these wastes is crucial to reducing environmental harm and making an economic contribution. This study aimed to determine the potential of St. John's wort wastes and biochar forms produced from these wastes to be used as solid fuel. In this context, the combustion behavior of the biomass and biochar were determined by thermogravimetric analysis method. Additionally, the Kissenger-Akahira-Sunosa and Flynn-Wall-Ozawa techniques were used to compute the combustion activation energies of these samples. According to the analysis, biomass combustion commenced at approximately 250°C and occurred in two stages, whereas biochar combustion initiated at around 400°C and proceeded in a single stage. Furthermore, over 90% of the mass from both samples was observed to decompose during combustion, with average combustion activation energies ranging between 70.08 and 203.86 kJ/mol for biomass and biochar, respectively. These findings suggest that biomass exhibits more readily combustible characteristics compared to biochar but is less energy efficient. In conclusion, optimizing the biochar production process could enhance its energy efficiency and potentially narrow the performance gap between biomass and biochar. Additionally, further research into alternative methods or additives to improve the energy efficiency of biomass combustion is warranted.