Investigation of thermal behaviour and kinetic analysis of Pakistani biomass: Rice husk, sugarcane bagasse and wheat straw using thermogravimetric analysis

Sugarcane bagasse, wheat straw and rice husk are amongst the most abundantly available agriculture residues in Pakistan. Constant supply and huge quantities of these residues make them favourable option to replace the fossil fuels. Thermal degradation of these three samples was studied using TGA at three different heating rates of 5 °C min^-1, 20 °C min^-1 and 40 °C min^-1. The three samples were heated from 25 °C to 900 °C and the influence of heating rate was investigated. Coats-Redfern method was applied to calculate the apparent kinetic parameters. The results showed that the apparent kinetic energy varies from 28.27 kJ mol^-1 to 31.98 kJ mol^-1, 38.39 kJ mol^-1 to 70.22 kJ mol^-1 and 25.05 kJ mol^-1 to 30.42 kJ mol^-1 for bagasse, wheat straw and rice husk respectively. A clear linear fit was obtained using the Coats-Redfern method with above 0.96 coefficient of regression for wheat straw and above 0.97 for sugarcane bagasse and wheat straw respectively. For wheat straw at 40 °C min^-1 heating rate and for the first peak in DTG thermogram of sugarcane bagasse at 5 °C min^-1, the order of reaction was found to be 2.0 and for all three samples, order of reaction was found to be 0.5 for rest of the heating rates. Higher heating rates caused the lateral shift in the TGA thermograms of all three biomass samples but the amount of residual char and ash were unaffected. It was observed that the higher heating rate caused the sudden release of volatile matter from the sample merging the different weight loss peaks, as were evident at lower heating rate in the DTG thermogram of sugarcane bagasse. The values of pre-exponential factor were found to be varied from 12.77-111.08 min^-1, 117.92-1.17×10⁶ min^-1 and 21.45-5.92×10⁴ min^-1 for rice husk, wheat straw and sugarcane bagasse respectively. For order of reaction of 0.5 at 20 °C min^-1 heating rate, three biomass samples can be arranged in terms of activation energy: wheat straw > sugarcane bagasse > rice husk.