Hydrothermal liquefaction of microalga with and without seawater: Effects of reaction temperature on yield and hydrocarbon species distribution in biocrude

A halophytic microalga Tetraselmis sp. biomass diluted with deionized water and seawater was converted to biocrude with the hydrothermal liquefaction (HTL) process in a batch reactor at 310, 330, 350, and 370°C, 15 min with $\approx 20$ %w/w solids. The biocrude yield, carbon, and energy recovery in biocrude and hydrocarbon species distribution from deionized water base HTL (DW HTL) and seawater base HTL (SW HTL) were evaluated. The results revealed that irrespective of reaction medium, the yield in biocrude increased with an increase in temperature, reaching a maximum of 50–56 wt% at 350°C, characterized by a higher heating value of up to 35.6 MJ/kg. The carbon and energy recovery at 350°C were 85% and 89% respectively, for SW HTL, while the DW HTL stream was 10% and 12% lower. Also, the GC MS analysis of biocrude obtained from both streams contains a complex mixture of compounds such as hydrocarbons, phenolics, and large amounts of nitrogenated and oxygenated compounds. The metallic constituents in biocrudes derived from both steams showed no substantial variations. The study showed a marginal increase in biocrude yield and its HHV with a reduction in oxygen and nitrogen contents from the SW HTL stream, suggesting the potential of seawater as a reaction medium.