Upgrading of the Acid-Rich Fraction of Bio-oil by Catalytic Hydrogenation-Esterification

The complex composition, high degree of unsaturation, and strong corrosiveness of bio-oil make direct catalytic upgrading problematic due to coking and device corrosion, and therefore, proper pretreatment is required. In this study, catalytic hydrogenation-esterification was identified as an efficient pretreatment method for bio-oil upgrading, and the hydrogenation-esterification behavior of typical compounds found in the acid-rich fraction of bio-oil over Cu/ SBA-15 catalyst was investigated. It was found that furfural, hydroxyacetone, and guaiacol could be synergistically transformed with acetic acid (AcOH) during hydrogenation-esterification. Meanwhile, a higher reaction temperature promoted AcOH conversion and increased the degree of hydrogenation. On the basis of the quantification of the main products, the reaction pathways in the presence of furfural, hydroxyacetone, or guaiacol were proposed. Finally, the hydrogenation-esterification of simulated bio-oil was performed at 300 degrees C. The results showed that furfural, hydroxyacetone, and guaiacol were efficiently hydrogenated, and AcOH was almost completely converted into ethanol and esters, with the fraction of acid compounds drastically declining from 25.0 wt % to 0.4 wt %. Thus, a high quality pretreated bio-oil fraction, mainly consisting of alcohols and esters and ready for subsequent upgrading, was obtained in a long-term test.