Upgrading Bio-oil Using Microwave Heating By Catalytic Esterification

Bio-oil, a liquid product from biomass via liquefaction or pyrolysis, is regarded as a promising renewable energy source. The bio-oil is a complicated oxygenated mixture which generally contains a wide variety of acids, aldehydes, ketones, phenols and sugars, and as a result, bio-oil exhibits some undesired properties such as high viscosity, acidity and high water. High water and oxygen content in the bio-oil leads to its low heating value compared with that of fossil fuels. Consequently, crude bio-oil needs to be upgraded to remove organic acids before its application.Catalytic upgrading of bio-oil using microwave heating was carried out in order to transform varieties of acids to esters. In this process, ethanol, as solvent and reactant, was added to bio-oil system. First, model reaction of acetic acid and ethanol under microwave heating condition was carried out to choose proper solid acid catalyst which owns high esterification activity and water tolerance. And then, upgrading of bio-oil using microwave heating was processed by this solid acid catalyst. For the bio-oil system, the appropriate power of microwave heating fitted was between 100 and 300W.At present, the research report about catalytic esterification of bio-oil under microwave condition is very little, so the study in this paper combining catalytic esterification of bio-oil and microwave heating deserves great value and realistic significance.Esterification reactions of acetic acid with ethanol under microwave heating were carried out using three types of solid acid catalysts. The results showed that the activity of the heterogeneous catalysts decreased in the following order:Amberlite > SO42-ZrO2> HZSM-5. Due to the significant amount of water content in bio-oil, the water tolerance properties of catalysts were also investigated using different levels of water added to the reaction system. The catalytic activities of SO42-/ZrO2 decreased obviously with increasing water concentration in the reaction mixture. However, the catalytic activity of cation exchange resin present in water was still higher. The catalytic upgrading of crude bio-oil was carried out under microwave heating using cation exchange resin as catalyst. Compared with the result of upgraded bio-oil under conventional heating, the upgrading process under microwave heating performed effectively and the components of upgraded bio-oil were optimized. Most of organic acids were converted into various esters through esterification in the existence of ethanol with the acid of cation exchange resin.