Comparative study of different algae pyrolysis using photoionization mass spectrometry and gas chromatography/mass spectrometry

•Pyrolysis pathways of microalgae were described based on different algae.•Pyrolysis of individual algae constituents and interactions between them were studied.•Lipids and carbohydrate have different effects on pyrolysis of protein.•Suggestions for industrial applications of algae pyrolysis were proposed. Pyrolysis of three algae, i.e. Nannochloropsis, Spirulina, and Sargassum was investigated by the combination of fixed bed pyrolysis with gas chromatography/mass spectrometry and pyrolysis photoionization mass spectrometry (py-PIMS) methods. Lipid, protein, and carbohydrate are the dominant components of the three algae, respectively. Mass spectrum profiles at different temperatures (400 °C, 500 °C, 600 °C, and 700 °C), temperature-programmed and time-evolved profiles of major products were measured. The decomposition reaction of fatty acids led to the formation of alkanes and alkenes. Aromatic compounds came from the nitrogen-containing compounds derived from protein and dehydrogenation of cyclic alkanes and alkenes through the Diels–Alder reaction from unsaturated fatty acids. Polycyclic nitrogenous compounds can be generated by the ring condensation reactions of monocyclic N-heterocyclic compounds. Lipids may interfere with the decomposition of protein. The presence of carbohydrates facilitates the formation of N-heterocyclic compounds. Two formation pathways of 1,4:3,6-dianhydro-α-d-glucopyranose and 2,4-dimethylfuran from hemicellulose and cellulose at different temperatures were observed.