Microalgae Dunaliella tertiolecta were studied for production of bio-oil through a sub- and supercritical water liquefaction process. The effects of liquefaction temperature, holding time, and feedstock ratio on the yields of the products were investigated. The maximum bio-oil yield is about 36.9%, obtained at a reaction temperature of 360 °C and a holding time of 30 min, with a feedstock ratio of materials to water of 1 : 10. The various physical and chemical characteristics of bio-oil obtained under the most suitable conditions were determined, and detailed chemical compositional analysis of bio-oil was performed using an elemental analyzer, Fourier transform infrared spectroscopy, and gas chromatography–mass spectrometry. The empirical formula of bio-oil with a heating value of 26.62 MJ kg⁻¹ was established as CH_1.38O_0.43N_0.07, and bio-oil was composed of hexadecanoic acid, palmitamide, and fatty acid methyl ester. Overall, the bio-oil obtained from microalgae Dunaliella tertiolecta were presented as a potentially valuable and environmentally friendly feedstock candidate for biofuels and chemicals.

Upgrading of bio-oil over metal/zeolite bi-functional catalysts, is of high necessity and popularity in converting biomass to high-quality hydrocarbons (transportation fuels and petrochemicals) to reduce the overall CO ₂ emissions of fossil based materials.

This critical review provides an investigation elaborated by recent references on conversion of low-lipid microalgae into bio-oil via pyrolysis and hydrothermal liquefaction, and the catalytic upgrading of algal-derived bio-oil was examined.