Bio-oil upgrading by means of ethyl ester production in reactive distillation to remove water and to improve storage and fuel characteristics

Several solid acids (SO42−/MxOy) were prepared and compared in upgrading bio-oil using ethanol and bio-oil as raw materials through reactive rectification. Two kinds of upgraded bio-oil were obtained in the upgrading process. The densities of two kinds of upgraded bio-oil were reduced from 1.16 to 0.91 and 0.95 g cm−3, and the gross calorific value increased from 14.3 to 21.5 and 24.5 MJ kg−1 and the acidity of upgraded bio-oil was also alleviated from 2.82 to 7.06 and 5.35, respectively. The results of 1H NMR, gas chromatography-mass spectrometry (GC–MS) and FT-IR analysis showed that the ester reaction in the bio-oil was promoted by solid acid catalysts. The stability of upgraded bio-oil was investigated by storing at room temperature. After 3 months of aging, the upgraded bio-oil did not show much viscosity increase.