Kinetics and thermodynamics parameters evaluation of pyrolysis of invasive aquatic macrophytes to determine their bioenergy potentials

Abstract

In the present study, the bioenergy potential of two invasive aquatic macrophytes, water hyacinth (Eichhornia crassipes) and yellow velvetleaf (Limnocharis flava), were investigated through thermochemical characterization, kinetic study and thermodynamic analysis. Thermochemical characterization indicated that the two study specimens have a good potential for use as abundant low-cost biomass to solid biofuel. Pyrolysis experiments were performed in a thermogravimetric analyzer under an inert environment at six low heating rates (5, 10, 20, 30, 40 and 50 °C min−1). The thermal degradation of two invasive aquatic macrophytes exhibited a similar behavior, which occurs in multi-step events. Non-isothermal experimental data were used to analyze kinetic parameters through isoconversional methods: Friedman (FR), Flynn-Wall-Ozawa (FWO), Kissinger-Akahira-Sunose (KAS), Starink (STK) and Vyazovkin (VYA). The KAS, STK and VYA methods showed a similar value of Ea for water hyacinth and yellow velvetleaf (Ea(Stage1) = 92.58 and 160.66 kJ mol−1, Ea(Stage2) = 119.56 and 105.55 kJ mol−1, Ea(Stage3) = 229.07 and 160.99 kJ mol−1, respectively) due to the approximation equations have the lowest relative errors. The endothermic and non-spontaneous process occurred for the invasive aquatic macrophytes due to the positive ΔH, positive ΔG, and negative ΔS values. This study provides useful data for future simulation, design, optimization and scale-up of reactors for pyrolysis processes of invasive aquatic macrophytes. Sustainable, abundant and low-cost invasive aquatic macrophytes have considerable bioenergy potential comparable to established bioenergy feedstock for bioenergy production, and at the same time, acting as a solution to the problems caused by these invasive plants.