Hydrothermal Liquefaction of Microalgae in a Continuous Stirred-Tank Reactor

The microalgae species Nannochloropsis gaditana (N. gaditana, marine) and Scenedesmus almeriensis (S. almeriensis, freshwater) were subjected to hydrothermal liquefaction (HTL; 350 °C; residence time of 15 min) in a continuous stirred-tank reactor (190 mL) at microalgae loadings of 9.1 and 18.2 wt % in the feed. The results indicate that the high loading of biomass in the feed promotes the formation of biocrude oil, with a maximum yield of 54.8 ± 3.4 wt % for N. gaditana. A similar type of biocrude was obtained with both species. Its nitrogen and carbon contents increased at the high biomass loading, as well as the higher heating value. The HTL product yields varied from those reported for batch experiments carried out at the same reaction conditions. Most of the nutrients initially present in the feedstock were recovered to some extent in bioavailable forms in the aqueous phase, especially in the case of N. gaditana.