Non-catalytic upgrading of fast pyrolysis bio-oil in supercritical ethanol and combustion behavior of the upgraded oil

Fast pyrolysis bio-oil derived from empty palm fruit bunch was upgraded in supercritical ethanol (scEtOH) without using external catalysts and molecular hydrogen. The effects of the reaction temperature and time on the product yield and the quality of the upgraded oil based on parameters like the elemental content, total acid number (TAN), water content, high heating value (HHV), and viscosity were examined. At 400 °C, almost all of the organic species in the fast pyrolysis bio-oil were converted to the liquid and gas phase in 30 min, resulting in a high yield of the upgraded oil (83.0 wt%) with an enhanced HHV of 34.1 MJ kg^-1 and very low values of TAN (4.8 mg KOH g^-1) and water (1.6 wt%) when compared to the fast pyrolysis bio-oil (HHV, 24.3 MJ kg^-1; TAN, 69.4 mg KOH g^-1; water, 14.0 wt%). The major chemical species in the upgraded oil were alcohols, esters, phenols, hydrocarbons, and aromatics. After aging at 80 °C for one week, a marginal increase in the viscosity of the upgraded bio-oil was observed, indicating a significant improvement in the stability of the bio-oil. Computational fluid dynamics (CFD) analysis of the process performed in a commercial boiler demonstrated that the upgraded oil firing exhibited high gas temperature profiles, a high firing peak of 1599 °C, and a high total heat transfer rate of 121.81 MW_th. These results are comparable to the performance parameters of conventional heavy oil-firing processes.