An in situ reduction approach for bio-oil hydroprocessing

An in situ reduction treatment, combination of reduction and esterification, was investigated to refine bio-oil. Over Raney Ni and zeolites-supported noble metal (Pd and Ru) catalysts, the reductant formic acid decomposed into hydrogen and carbon dioxide, and then hydrogen reduced the bio-oil while compressible CO2 dissolved in methanol to form a CO2–CH3OH expanded liquid. The results showed that Raney Ni and zeolites-supported Ru were highly active in this heterogeneous catalytic system. The reactions preformed at 150–230 °C for 5–7 h would give a better upgraded bio-oil with a high yield of 80–90 wt.%. The unsaturated components in bio-oil were reduced substantially without obvious coke formation, and the oxygen content was lowered by ca. 5 wt.%. Organic acids were converted into esters through the esterification with methanol, and the properties of hydrogenated bio-oil were improved: the pH value increased from 2.17 to ca. 4.5; the higher heating value approached to 22 MJ/kg, and the viscosity decreased from 5.31 to ca. 4.0 mm2/s.