Hydrothermal liquefaction of Elaeis guineensis trunks: Lessons learned from a case study in Guatemala

The oil palm industry has been under public scrutiny during the last decades due to environmental and social issues related to its practices. Oil palm (Elaeis guineensis Jacq.) trunks (OPTs) are of special interest as they are left idle in the field after the replanting process which is performed every 25 years. This common practice results in harvesting challenges, phytosanitary risks, and a loss of bioenergy potential. Due to their high moisture content and fibrous nature, OPTs present a problem for traditional conversion processes that require a dry and homogeneous material. This study evaluates the feasibility of converting OPTs into a bio-crude oil and biochar to increase the sustainability of the oil palm sector. To date, research efforts have primarily focused on hydrothermal liquefaction (HTL) of OPT without catalysts, resulting in a limited understanding of the potential of OPTs. Thus, the main novelty of this work is the evaluation of the effects of catalyst dosage (0-5 wt%) on the bio-oil yield, reaction temperature (260-300 degrees C), and residence time (15-60 min) using a half-fraction experimental design methodology. For this, OPTs extracted from two plantations in Guatemala were used. The maximum biooil yield (26.77 +/- 3.60 wt%) was found at 260 degrees C for 15 min and 5 wt% catalyst with a high heating value (HHV) of 19.29 +/- 1.33 MJ kg(-1). Nonetheless, the bio-oils produced without a catalyst at 300 degrees C and 15 min have higher HHV (27.63 +/- 1.35 MJ kg(-1)) and are similar to Diesel fuel based on their H/C and O/C ratio. These results indicate that there is a potential trade-off between the bio-crude oil mass yield and HHV when using the catalyst.