Catalytic and Solvent Hydrothermal Liquefaction of Microalgae: A Strategy for Recovering Fine Chemicals

Abstract

The study investigates the influence of various catalysts (Ni/TiO₂, Co/TiO₂, and Zeolite) on the hydrothermal liquefaction of microalgae and explores the effect of co-solvents (acetone, methanol, and toluene) on biocrude yield from different microalgae three species namely Nannochloropsis oculata, Chlorella vulgaris, and Spirulina maxima. Catalyst characterization using FE-SEM, XRD, and BET analysis revealed distinct properties. Under Co-TiO₂, Nannochloropsis oculata and Chlorella vulgaris yield 56.21% and 57.6% biocrude at 5% loading; Spirulina maxima yields 45.3% at 2.5% loading. With Ni-TiO₂, Nannochloropsis oculata yields 52.4% at 2.5% loading; Chlorella vulgaris yields 44.7% at 5%; Spirulina maxima yields 44% at 2.5% loading. Zeolite yields: Spirulina maxima and Chlorella vulgaris yield 53.8% and 52.1% at 2.5%; Nannochloropsis oculata yields 48.3% at 7.5% loading. Co-solvent addition significantly boosts biocrude yield; methanol and toluene yield 53.7% and 49.2% for Chlorella vulgaris and Spirulina maxima, respectively, while acetone yields 57.6% for Nannochloropsis oculata. Different solvents extract diverse functional groups such as alkanes, halides, aromatics, and aldehydes which has wide industrial applications.