Apparent Kinetics of Fast Pyrolysis of Four Different Microalgae and Product Analyses Using Pyrolysis-FTIR and Pyrolysis-GC/MS

This study reports an experimental technique to obtain the isothermal mass loss profiles of four different microalgae (Chlorella vulgaris, Nannochlorpsis oculata, Schizochytrium limacinum, and Arthrospira platensis) under fast pyrolysis conditions in the temperature range of 400-700 °C at short residence times of 2-60 s using an analytical pyrolyzer. The microalgae investigated in this study vary significantly, based on elemental and biochemical composition. The apparent kinetic parameters of fast pyrolysis of the algae were evaluated using first-order and multidimensional diffusion models. The apparent activation energy and pre-exponential factor evaluated under fast heating rate conditions were lower compared to those reported under slow pyrolysis conditions, which is attributed to the diffusion effects. The rate parameters were validated by constructing a kinetic compensation plot, which showed that ln(A) = 0.19Ea + 0.43. The product time evolution at short time scales was studied using in situ Fourier transform infrared spectroscopy, and a majority of the functional groups evolved in the range of 5-12 s. The evolution of C=O and aliphatic C-H stretching vibrations for lipid-rich algae was slow, compared to that for protein-rich algae. The pyrolysates were characterized using gas chromatography/mass spectrometry, and the yield of nitrogen-containing organics followed a linear trend with the elemental nitrogen content in the algae.