Thermal degradation of carbohydrates, proteins and lipids in microalgae analyzed by evolutionary computation

Abstract

The kinetics of microalgae pyrolysis is investigated to analyze the thermal degradation of carbohydrates, proteins and lipids in different species of microalgae. The pyrolysis processes of microalgae Chlorella vulgaris ESP-31, Nannochloropsis oceanica CY2, and Chlamydomonas sp. JSC4 are examined by thermogravimetric analysis (TGA), and independent parallel reaction (IPR) model is adopted to approach the pyrolysis kinetics. To maximize the fit quality between the established kinetic models and experimental data, particle swarm optimization (PSO), a kind of evolutionary computation, is employed. The thermal degradation characteristics of the three microalgal species are compared with each other. The results suggest that the thermal degradation curves of the three microalgae can be predicted with a fit quality of at least 97.9%. The activation energies of carbohydrates, proteins, and lipids in the microalgae are in the ranges of 53.28–53.30, 142.61–188.35, and 40.21–59.23 kJ mol−1, respectively, while the thermal degradation of carbohydrates, proteins, and lipids are in temperature ranges of 164–497, 209–309, and 200–635 °C, respectively. It is proved in this work that the IPR model and the calculation of the PSO can be used to predict the pyrolysis kinetics of microalgae to a good level of fitness.