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Apparent kinetic and thermodynamic calculation for thermal degradation of stearic acid and its esterification derivants through thermogravimetric analysis

Niu, Shengli, Yu, Hewei, Zhao, Shuang, Zhang, Xiangyu, Li, Ximing, Han, Kuihua, Lu, Chunmei, Wang, Yongzheng
Renewable energy 2019 v.133 pp. 373-381
Gibbs free energy, activation energy, alcohols, biodiesel, enthalpy, entropy, esterification, stearic acid, temperature, thermal degradation, thermogravimetry
Thermal degradation properties of stearic acid and its esterification derivants of methyl stearate and ethyl stearate are investigated through thermogravimetric analysis. Based on experiments, which are conducted at the temperature heated rates of 10, 15 and 20 K min−1, the iso-conversional methods of Kissinger-Akahira-Sunose and Flynn-Wall-Ozawa are used to calculate the apparent activation energy. Further, the Avrami theory is used to estimate the apparent reaction order. Apparent thermodynamic parameters of the apparent enthalpy change, apparent Gibbs free energy change and apparent entropy change are calculated. Calculations of apparent kinetic and thermodynamic parameters illustrate that thermal activity of stearic acid is distinctly heightened after esterification and the derived derivants are more easily activated. Meanwhile, influences of alcohol type on esterification products are weak. Conclusions from this study make more comprehensive understanding of the thermal events of biodiesel to be favor for its commercial application.