Use of an alkaline catalyst with ethanol-water as a co-solvent in the hydrothermal liquefaction of the Korean native kenaf: An analysis of the light oil and heavy oil characteristics

Hydrothermal liquefaction of the Korean native kenaf, with ethanol–water as a co-solvent at 275–350 °C for 30 min with and without 1 wt% of the alkaline catalysts Ca(OH)2, Na2CO3, K2CO3, and KOH, was investigated to identify the effect of the alkaline catalyst addition on the characteristics of the light and heavy oil produced. Component, elemental, ICP-ASE, and GC-MS analyses were conducted to determine the characteristics of the light oil, heavy oil, and solid residue. The highest bio-crude oil yield of 61.81% at 275 °C was found using ethanol–water without an alkaline catalyst. The addition of alkaline catalysts prompted the decomposition of both the heavy oil and light oil fractions, and re-polymerization reactions were suppressed. In addition, there were increases in the area percentages of ketone and phenolics derived from holocellulose and monolignols, respectively. Calcium ion was mainly detected in the aqueous phase, while sodium and potassium existed as solids in the solid residue. The results show that the addition of a calcium-based alkaline catalyst in the hydrothermal liquefaction of kenaf can enhance the energy recovery ratio to 58% and calorific value to 32.27 MJ/kg of the light oil at 350 °C. •Alkali-catalyzed HTL of kenaf in co-solvent improved light oil yield and characteristics.•Alkaline catalyst, ethanol, and high temperature enhance the carbon content and HHV.•Calcium-based alkaline catalyst increase the energy recovery ratio to 58%.•Elemental calcium was mainly detected in the aqueous phase.•Sodium and calcium compounds were detected in the bio-crude oil and solid residue.