Hydrothermal liquefaction of sugarcane bagasse to bio-oils: Effect of liquefaction solvents on bio-oil stability

Abstract

Bio-oil produced from the hydrothermal liquefaction (HTL) of biomass is unstable and cannot be transported over long distances to a refinery for upgrading to transportation fuel. This study examined the effect of the liquefaction solvent on the stability of bio-oils derived from the HTL of sugarcane bagasse. The accelerated aging test (0–8 days at 80 °C) was used to assess the stability of these oils with the aid of indicators such as water content, molecular weight range, functional groups present, phase separation, thermal stability, and the amount of residue after thermal analysis of the oils. The HTL solvent mixture of ethanol/water was found to produce the most stable bio-oil when compared to crude glycerol/water or water on its own. The light oils fractionated by solvent extraction were more stable than their corresponding bio-oils. The higher heating values (HHVs) of the light oils during the agiging process were relatively stable and were between 33 and 35 MJ/kg. The maximum boiling temperature of the first peak in the DTG thermogram of the aged light oil derived from ethanol/water is 147 °C (cf. diesel of 157 °C), while that of crude glycerol/water light oil is up to 190 °C. The stabilities of the oils derived from either ethanol or crude glycerol are related to alkylation, esterification, and acetalization reactions. This study has demonstrated that the HTL of sugarcane bagasse in the presence of ethanol/water produces oils of good quality that have long shelf-lives and have been projected to be stored for up to 8 years with minor compositional and structural changes.