Upgrading of Bio-oil by Removing Carboxylic Acids in Supercritical Ethanol

摘要

In this work, the effects of the ratio of ethanol to bio-oil, and reaction time on the removing of these carboxylic acids were studied as well as the addition of external acid such as H2SO4, H3PO4 or zeolite. The results showed that carboxylic acids in crude bio-oil could easily esterified with ethanol in the supercritical system, and the formation of esters was affected greatly by the reaction parameters. Ethyl acetate was generated obviously at higher volume ratio of ethanol to bio-oil and reached the selectivity of 100% at the volume ratio of ethanol to bio-oil of 5:1 after 2 h reaction, whereas more side reactions were carried out in lower or higher ratio of ethanol to bio-oil. The addition of external acid would decrease distinctly the formation of esters due to more side reactions, indicating that these carboxylic acids could be effectively removed under the acidic system arising from the internal ionization of ethanol.