Title : A model fitting approach for the investigation of thermo kinetic parameters of rice straw – A viable renewable energy resource in Bangladesh.
Abstract:
The depletion of fossil-fuel resources coupled with the growing environmental issues related to the burning of agricultural wastes have pushed the quest to find alternative sources of energy that is more sustainable. The agricultural wastes especially rice straw have a good potential as renewable and sustainable feedstock in generation of energy. Rice straw burning is a major contributor of air pollutants and greenhouse gases, and thus leads to environmental degradation in many rice-producing countries, particularly those in the Asia and African regions. Pyrolysis is a thermochemical conversion type of transforming rice straw into value products of biochar, bio-oil, and syngas. The research is aimed at analytically investigating the pyrolysis behavior of rice straw by applying thermogravimetric analysis and model-based kinetic interpretation to determine the practicability of the material as an alternative energy source. A heating rate of 50C min-1 in an inert nitrogen atmosphere was used to define the thermogravimetric study from ambient temperature to 900 0C and kinetic parameters were derived through the Coats-Redfern method.
The findings showed that there are three characteristic steps of biomass thermal degradation and they were: (i) moisture evaporation at temperatures between 300C and 1500C, (ii) major devolatilization at temperatures (2000C to 400 0 C) involved in the degradation of hemicellulose and cellulose, and (iii) progressive lignin degradation at high temperatures (600 0 C and higher) and the formation of char. The decomposition range of 230 0C to 400 0C was found to be the ideal pyrolysis temperature range, which can be explained by the maximum level of devolatilization. The results showed that the F1.5 chemical reaction order model has the highest regression coefficient of 0.9709 compared to other models, indicating its better reliability compared to other models, while diffusion model D3 also demonstrated strong reliability. The activation energy value varied between 16.86 kJ/mol and 78.12 kJ/mol, indicating that the reactivity of the biomass is relatively high with favourable conversion characteristics compared to other lignocellulosic biomass materials. The thermodynamic analysis indicated positive values of enthalpy change ranging from 12 to 74 kJ/mol, which confirmed the endothermic process of rice straw pyrolysis and the requirement of heat supply to the process. The positive values of Gibbs free energy change ranging from 70 to 170 kJ/mol indicated non-spontaneity of the reaction process, while the negative values of entropy change indicated increased order of the product formed through the process of pyrolysis.
The analysis of the results obtained through the process of pyrolysis with the existing literature indicated that the values of activation energy were consistent with the values obtained through other lignocellulosic biomass-based studies. The results obtained through the process of pyrolysis have confirmed that the process of rice straw pyrolysis is technically viable and environmentally sound for the production of valuable biofuels such as biochar, bio-oils, and syngas from agricultural waste. The study contributes to sustainable energy transition efforts by supporting agro-residue-based decentralized energy systems and enhancing resource recovery pathways in developing regions.
Keywords: Rice straw pyrolysis; Thermogravimetric analysis; Coats–Redfern kinetics; Activation energy; Thermodynamic analysis; Bioenergy; Agricultural waste valorization; Circular economy.
