Upgrading the oil-soluble fraction of bio-oil by solvent extraction coupling with chemical conversion

Upgrading the oil-soluble fraction, which was obtained by water extraction of bio-oil from fast pyrolysis of rice husk, was investigated with simultaneous esterification and acetalation in butanol with online solvent extraction (SEAWOSE). The results show that almost all of the acids, aldehydes and ketones in the oil-soluble fraction can be converted to the corresponding esters, hemiacetals and acetals by SEAWOSE. In comparing with direct esterification and acetalation without extraction, the char formation is significantly suppressed. Meanwhile, the upgraded oil has very low acidity and moisture content, but high heating value and good volatility. The effect of oxidation and reduction pretreatment of the oil-soluble fraction before SEAWOSE was also investigated. By hydrogen peroxide oxidation, the aldehydes are firstly converted into acids and subsequently esterified to esters, consequently without char formation. The upgraded oil is high quality, less than 4% in moisture, higher than 30 MJ/kg in heating value and less than 2 KOH mg/g in acidity.