Effect of process parameters on hydrothermal liquefaction of oil palm biomass for bio-oil production and its life cycle assessment

• Water is used as a clean solvent to liquefy palm biomass to bio-oil.
• The optimum liquefaction condition of oil palm biomass is 390 °C and 25 MPa.
• Optimum reaction time for liquefaction of empty fruit bunch and palm mesocarp fiber is 120 min.
• Optimum reaction time for liquefaction of palm kernel shell is 240 min.
• From the life cycle assessment, a net 2.29 kg CO2 equivalent is generated per kg of bio-oil produced.

This paper presents the studies on the effect of three process parameters; temperature, pressure and reaction time on the subcritical and supercritical hydrothermal liquefaction of oil palm empty fruit bunch, palm mesocarp fiber and palm kernel shell. The effect of temperature (330–390 °C), pressure (25–35 MPa) and reaction time (30–240 min) on bio-oil yields were investigated using a Inconel batch reactor. The optimum liquefaction condition for empty fruit bunch, palm mesocarp fiber and palm kernel shell was at supercritical condition of water; 390 °C and 25 MPa. For the effect of reaction time, bio-oil from empty fruit bunch and palm mesocarp fiber attained maximum yields at 120 min, whereas bio-oil yield from palm kernel shell continued to increase at reaction time of 240 min. Lastly, a life cycle assessment based on a conceptual biomass hydrothermal liquefaction process for bio-oil production was constructed and presented.