Kinetic Study of the Pyrolysis of Microalgae-Spirulina and Macroalgae-porphyra under Nitrogen and Carbon Dioxide Atmosphere

The pyrolysis behaviour and the kinetic characteristics of representative microalgae, i.e.-spirulina and macroalgae, i.e.-porphyra, pyrolyzed under nitrogen and carbon dioxide were investigated in this study. Pyrolysis of spirulina and porphyra algae were carried out non-isothermally via conventional electrical heating in a thermogravimetric analyser (TGA, NETZSCH STA449F3, Germany). Four linear heating rates of 5, 10, 20 and 50°C/min were used to heat 2±0.5 mg of samples from 50°C to 900°C, in 20mL/min of pure nitrogen or carbon dioxide. The iso-conversional method, Kissinger-Akahira-Sunose (KAS) was employed based on the Arrhenius Law to determine activation energy and pre-exponential factor from the weight loss profiles. On the other hand, the model fitting Coats-Redfern method was used to calculate the kinetic parameters and determine the order and mechanism of reaction. Upon comparison of the activation energy derived from the pyrolysis processes, spirulina required lower amount of energy (160 kJ/mol) to initiate pyrolysis under N2. Moreover, the time required to complete the pyrolysis under CO2 atmosphere was shorter compared to N2 atmosphere which indicated that CO2 could assist in the pyrolysis of both algae.