Synthesis of hydrochar from empty fruit bunches (EFB) and oil palm trunks (OPT) Via wet torrefaction: A parametric study

With the rising popularity of the oil palm industry driven by global demand, an abundance of oil palm biomass waste is expected. Wet torrefaction is an appealing method for converting oil palm biomass waste into fuel. Empty fruit bunches (EFB) with a particle size range of 0.5 to 1.0 mm were treated via wet torrefaction at 180 to 220 °C with 20 °C intervals and 3 to 9 hours with 3 hours intervals. The wet torrefied EFB, termed EFB hydrochar, was evaluated for its mass yield and higher heating value (HHV). The energy yield of the hydrochar was assessed as well, as it represents the fuel potential of the hydrochar. Ensuring that the mass yield is relatively high whilst HHV is favourable is desirable. The HHV of hydrochar increased with increasing temperature and residence times whilst mass yield followed an opposite trend. For instance, hydrochar obtained at 220 °C and 9 hours had the highest HHV and the lowest mass yield, at 23.74 MJ kg−1 and 42.86 wt. %, respectively. Despite its highest HHV, its energy yield was relatively low, at only 60 %. On the contrary, hydrochar obtained at 180 °C and 3 hours had the lowest HHV (17.37 MJ kg−1) among all treated EFB; however, it had the highest energy yield, at 76 %. The higher value of energy yield was due to its relatively higher mass yield when compared to the hydrochar with the highest HHV (i.e. 73.78 wt. % to 42.86 wt. %, respectively). Similar trends were observed for OPT hydrochar subjected to the same wet torrefaction condition. Nevertheless, EFB hydrochar generally had a higher mass yield and HHV, offering a higher energy yield than OPT hydrochar. This disparity is likely attributed to the higher lignin content in EFB compared to OPT.