The invasive Egeria densa macrophyte and its potential as a new renewable energy source: A study of degradation kinetics and thermodynamic parameters

The increase in global demand, along with environmental concerns, has led to the need for new sources that can supply the energy needed for socioeconomic development while reducing pollutant emissions. Aquatic biomasses, especially those of invasive aquatic macrophytes, can be potential energy sources, and this study evaluated the thermal degradation of the invasive Egeria densa macrophytes (EDM) in an inert environment at four heating rates to evaluate its potential as a low-cost biomass and bioenergy source. Pyrolysis experiments were performed using a thermogravimetric analyzer. The thermal profile of invasive EDM has three main events (multiple stages). Stages (i) and (ii) occur at a temperature range of 125-395 °C and represent the decomposition of carbohydrates such as hemicellulose and cellulose. Stage (iii) occurs between 395 and 500 °C and mainly relates to the decomposition of lignin. Thermal data have been used to analyze kinetic parameters through isoconversional methods, and the activation energy (Ea) value of EDM showed variation at different conversion points. The highest Ea values were observed for conversion rates of 0.3-0.6 due to the increased energy required to break down the lignocellulosic chains during decomposition. The small difference between the enthalpy change and Ea values for the different isoconversional methods can be due to a small potential energy barrier, which reflects the feasibility that the reaction can occur under the expected conditions. Gibbs free energy (137-145 kJ mol-1) and high heating value (13.40 MJ/kg) revealed a significant bioenergy potential for EDM biomass.