Pyrolysis characteristics and pathways of protein, lipid and carbohydrate isolated from microalgae Nannochloropsis sp.

•Protein, lipid and carbohydrate were isolated for microalgal component pyrolysis.•Relationship between DTG curves of microalgae and their isolated components.•Experimental N was 0.6776, 0.3861 and 0.2856 for lipid, protein and carbohydrate.•Recommended pyrolysis pathways by biocrude composition of isolated algal components.•Steroids and lipopolysaccharides increased hydrocarbon content in bio-crude.

Microalgal components were isolated gradually to get lipid-rich, protein-rich and carbohydrate-rich components. The aim of this work was to study pyrolysis mechanism of microalgae by real isolated real algae components. Thermogrametric analysis (DTG) curve of microalgae was fitted by single pyrolysis curves of protein, lipid and carbohydrate except special zones, which likely affected by cell disruption and hydrolysis mass loss. Experimental microalgae liquefaction without water index N was 0.6776, 0.3861 and 0.2856 for isolated lipid, protein and carbohydrate. Pyrolysis pathways of lipid are decarboxylation, decarbonylation, fragmentation of glycerin moieties and steroid to form hydrocarbons, carboxylic acids and esters. Pyrolysis pathways of protein are decarboxylation, deamination, hydrocarbon residue fragmentation, dimerization and fragmentation of peptide bonds to form amide/amines/nitriles, esters, hydrocarbons and N-heterocyclic compounds, especially diketopiperazines (DKPs). Pyrolysis pathways of carbohydrate are dehydrated reactions and further fragmentation to form ketones and aldehyde, decomposition of lignin to form phenols, and fragmentation of lipopolysaccharides.