Organic acid-assisted catalytic wet torrefaction of oil palm trunks (OPT)

Abstract

Oil palm trunks (OPT) are attractive bio-fuel sources given their abundant availability. Nonetheless, the inherent properties of these biomass can lead to their inefficient use as bio-fuel directly. This work utilizes four organic acids (i.e., acetic, formic, levulinic, and citric acid) as catalyst in wet torrefaction to enhance the fuel properties of OPT hydrochar. In this study, the effects of different catalysts, catalyst concentrations, and residence times on the fuel properties of OPT hydrochar are analyzed. To study the effect of residence time, 0.2M of acid concentration was used for all four acids at 220 °C for 3 hr and 24 hr. Meanwhile, study on the effect of catalyst concentration was performed at 220 °C for 24 hr at 0.2M and 1.0M for all four acids. Increasing the residence time decreased the solid yield of OPT hydrochar treated in deionized water, acetic, formic, and levulinic acid, while wet torrefaction in citric acid results in close solid yield value in both residence time. The energy yield was observed to decrease in all liquid medium with increasing residence time except for formic acid and citric acid. On the other hand, increasing the acid concentration increased the OPT hydrochar solid yield in all acids except formic acid and the highest energy yield of 77.08% was obtained from wet torrefaction in 1.0M of citric acid at 220 °C for 24 hr. In summary, citric acid is an environmentally friendly acid to be used as catalyst to enhance the fuel properties of OPT hydrochar. Further study on the reaction mechanisms that governs such fuel properties enhancement with citric acid is warranted.