Pyrolysis of Soybean Residue for Bioenergy Valorization: Kinetic Parameters and Environmental Benefits

For the thermochemical valorization of okara (soybean residue), pyrolysis fixed-bed experiments and its kinetic analysis were conducted. Okara exhibited a major mass loss between 200 and 500 °C with observed derivative thermogravimetry curves corresponding to hemicellulose and cellulose, which was also confirmed by real time FTIR. From the fixed-bed pyrolysis experiments, the resulting pyrolysis oil, gas and char achieved average yields of 42 ± 1.4%, 32 ± 2.6%, and 26 ± 1.7%, respectively. The components of pyrolysis oil are primarily derived from hemicellulose and cellulose, with acids > furans > ketones > alcohols being the most abundant in that order. The most abundant compounds among them were acetic acid and furfuryl alcohol, with maximums of 38.59% and 7.86%, respectively. In the kinetic analysis, okara showed high R² values of 0.15−0.65 for the conversion rate, corresponding to the pyrolysis of hemicellulose and cellulose. The activation energy (E_α) values were found to be in the ranges of 136−503 kJ/mol. The pre-exponential factor (A) values were mostly A ≥ 1E + 09, indicating a ‘loose’ complex mechanism. The master plot showed that okara pyrolysis is similar to the power law mechanism of the nucleation model.