Pyrolysis of microalgae residual biomass derived from Dunaliella tertiolecta after lipid extraction and carbohydrate saccharification

• Dunaliella tertiolecta residual biomass was further utilized by pyrolysis as a biorefinery concept.
• Effects of pyrolysis temperature and time on product distributions were investigated.
• The product bio-oil from pyrolysis of the biomass residue was analyzed by GC–MS.
• The pyrolysis reaction mechanism was studied using the lumped kinetic model.

Microalgae (Dunaliella tertiolecta) are considered potential feedstock for production of biodiesel and bioethanol due to their high lipid and carbohydrate contents. To achieve complete utilization of microalgae in a microalgae biorefinery, residual biomass after conversion of lipids and carbohydrates into biodiesel and bioethanol can be converted into bio-oils by pyrolysis. D. tertiolecta residual biomass decomposed mainly between 200 °C and 550 °C at heating rates of 5–20 °C/min. The apparent activation energy increased from 163.12 kJ mol−1 to 670.24 kJ mol−1 with increasing pyrolysis conversion. Experimental results were consistent with the proposed lumped kinetic model, and the kinetic rate constant for D. tertiolecta residual → bio-oil (k2) was the highest. This result indicates that the predominant reaction pathway of D. tertiolecta residual was A (D. tertiolecta residual) to B (bio-oil), rather than A (D. tertiolecta residual) to C (gas; C1–C4, CO, CO2, H2) or B (bio-oil) to C (gas; C1–C4, CO, CO2, H2).