Effects of transition metals on hydrothermal liquefaction of empty fruit bunches (EFB) for conversion to biofuel and valuable chemicals

Hydrothermal liquefaction(HTL) of empty fruit bunches(EFB) was performed with an autoclave reactor at various temperatures (240, 270, 300, and 330 °C) in the presence of transition metal chlorides(ZnCl2, CuCl2, and NiCl2) under high pressure(∼22 MPa) and N2 atmosphere. Main HTL products including hydrochar, gas, water-soluble fraction (WSF), and crude-like HTL oil were investigated. The yield of HTL oil gradually increased with increasing temperature, and the highest oil yield of 22.8 wt% was obtained at 300 °C. When transition metal chlorides (2.5-10.0% (w/w sample)) were added to the reaction, mass distributions of the four fractions were clearly modified based on the type of transition metal chloride as well as their concentration. In general, the yield of HTL oil decreased with an increase in transition metal concentration up to 10.0%, the water content increased and the chemical compounds decreased with an increase in the amount of metal. γ-Valerolactone (GVL) and levulinic acid (LA) were detected in the catalytic HTL oil, due to the presence of transition metal ion and high acidity. Unlike other metal chlorides, the presence of CuCl2 resulted in relatively low GVL and high LA concentration, which may inactivate the route from LA to GVL under acidic hydrothermal conditions.