Energetic and economic evaluation of Chlamydomonas reinhardtii hydrothermal liquefaction and pyrolysis through thermochemical models

Renewable diesel productions through HTL (hydrothermal liquefaction) and pyrolysis of Chlamydomonas reinhardtii were compared based on energetic and economic evaluation. The whole biofuel production pathway was simulated, from the microalgae cultivation step to the upgrading of the bio-oil. Alternative dewatering technologies were evaluated to decrease the energy consumption and the bio-diesel cost. Thermochemical models were developed for both HTL and pyrolysis of C. reinhardtii based on experimental results. The pathways using heat exchangers between the inlet and outlet of the HTL reactor were the only scenarios to be net energy producers. The other pathways consumed more energy than they produced. The costs of production of renewable diesel from HTL or pyrolysis were significantly higher than petroleum diesel (average of 70.4 €/GJ). The most expensive step was the microalgae cultivation (nutrients cost and raceway capital cost). - Highlights: • HTL and pyrolysis processes were evaluated. • Energetic and economic evaluations were performed. • Thermochemical models for HTL and pyrolysis were developed. • Pathway with HTL and heat exchanger was the sole net energy producer. • Pyrolysis pathways consumed more energy than they produced.