Comparative dynamic optimization study of batch hydrothermal liquefaction of two microalgal strains for economic bio-oil production

[Display omitted] •Dynamic optimization problems for hydrothermal liquefaction of two microalgae strains.•Reactor temperature profiles are optimized using direct collocation.•11% and 6.18% increase in biocrude yields for Aurantiochytrium sp. KRS101 and Nannochloropsis sp. using optimized policy.•78.2% and 61.66% decrease in batch times for the microalgae with higher lipids and protein content.•26% and 28% savings in reactor thermal energies compared to biocrude maximization. This work presents dynamic optimization strategies of batch hydrothermal liquefaction of two microalgal species, Aurantiochytrium sp. KRS101 and Nannochloropsis sp. to optimize the reactor temperature profiles. Three dynamic optimization problems are solved to maximize the endpoint biocrude yield, minimize the final time, and minimize the reactor thermal energy. The biocrude maximization and time minimization problems demonstrated 11% and 6.18% increment in the optimal biocrude yields and reduction of 78.2% and 61.66% in batch times compared to the base cases for the microalgae with higher lipid and protein fractions, respectively. The energy minimization problem revealed a significant reduction in the reactor thermal energies to generate the targeted biocrude yields compared to the biocrude maximization. Therefore, the identified optimal temperature trajectories outperformed the conventional fixed temperature profiles and could improve the overall economics of the batch bio-oil production from the algal-based biorefineries by significantly enhancing the reactor performance.