Pyrolysis characteristics, kinetic, and thermodynamic analysis of camel dung, date stone, and their blend using thermogravimetric analysis

Understanding the co-pyrolytic thermal behaviour and kinetics of feedstocks is important for the design of pyrolysers. In this study, the pyrolytic degradation of camel dung, date stones, and their blend (1:1 wt.%) has been investigated under non-isothermal conditions using a thermogravimetric analyser. The Coats-Redfern (CR) and distributed activation energy model (DAEM) methods were used to investigate the pyrolytic kinetics of feedstocks. While applying the CR method, different solid-state reaction mechanisms were employed, and the mechanisms with the best fit were identified. The kinetic data of both models were used to estimate thermodynamic properties such as enthalpy change, Gibbs free energy change, and entropy change. In the case of the CR method, the best-fitting models were found to be those based on first and second-order reaction mechanisms. The activation energy values using the DAEM for the whole conversion were estimated to be 171, 324, and 215 kJ/mol for camel dung, date stone, and camel dung-date stone blend, respectively. The Delta H values were calculated to be 166, 319, and 210 kJ/mol for camel dung, date stone, and camel dung-date stone blend, respectively. A slight difference (5 kJ/mol) between the activation energy and enthalpy values indicated that pyrolysis of the selected feedstocks is feasible. The Delta G values for the individual and blend feedstocks were similar (160-164 kJ/mol), implying that co-pyrolysis will require the same amount of energy as individual pyrolysis. The low Delta S values of the feedstocks (0.0116-0.2808 kJ/mol K) indicate that the system is in a state proximate to thermodynamic equilibrium.