Hydrothermal liquefaction of macroalgae over various solids, basic or acidic oxides and metal salt catalyst: Products distribution and characterization

Hydrothermal liquefaction (HTL) of macroalgae Ulva prolifera (UP) over various solids, basic, or acidic oxide and metal salt catalysts at different reaction temperature (260, 280 and 300 degrees C), reaction holding time (15, 30 and 45 min.) and solvents (water, ethanol and methanol) were investigated. The maximum bio-oil yield (35.1 wt %) was obtained with metal MgO catalyst with water solvent compared to the acidic (Al2O3, ZrO2, and CeO2), salt (MgCl2, FeCl3, and CuCl2) and other basic (CaO and CaCO3) catalyst. When alcoholic solvent (ethanol and methanol) used, the bio-oil yield increased extensively, and highest bio-oil yield (50.6 wt%) was observed with MgO catalyst in ethanol solvent. GC-MS, FT-IR, NMR, TGA, and CHNS were used for bio-oil characterization. The higher selectively ester compound 62.2 % was obtained with MgO under ethanol solvent. The higher carbon (60.8-66.2 %) and higher heating value (HHV) (30.2-34.2 MJ/kg) was observed in the case of catalytic liquefaction bio-oil compared to the non-catalytic reaction bio-oil. The results suggest that catalytic liquefaction has potential for quality bio-oil production. Also, the reusability of the optimum catalyst (MgO) was examined in this study.