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This paper reviews the literature on upgrading of biocrude oil obtained by hydrothermal liquefaction of microalgae. It analyses the influence of several parameters (e.g., temperature, operation mode, reaction time, catalyst) on the yields and properties of the upgraded product. Some own experiments are performed based on the review outcomes, comparing for the first time the application of heterogeneous catalysis to biocrude oil obtained from two different algae species: Scenedesmus almeriensis (freshwater) and Nannochloropsis gaditana (marine). The conditions applied were 4 to 8MPa hydrogen atmosphere in 10mL microautoclaves at 400°C and 4h. The influence of two catalysts (Pt/Al2O3 and HZSM-5) and the effect of water addition to the reaction medium were investigated. Many of the effects were found to be caused by the temperature applied, rather than by the catalyst. The conditions applied improved the quality of the algal biocrude oil, viz. by reducing its amount of heteroatoms, saturating and cracking its molecules, and increasing its volatility. The degree of upgrading to a transportation biofuel in the experiments herewith reported, as well as in the literature studies, is however still insufficient and demands further developments of the upgrading techniques.
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•A literature review on upgrading of HTL biocrude oil from microalgae is presented.•The performance of heterogeneous catalytic oil upgrading is species-dependent.•The use of hot compressed water did not enable using lower H2 pressures.