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The direct deoxygenation effect of CaO on bio-oil during biomass pyrolysis in a fluidized-bed reactor was studied. Bio-oils were produced from white pine in the presence and absence of CaO at 520 °C and a carrier gas flow rate of 50 L/min (standard temperature and pressure). The results showed that the oxygen content of the organic components in the bio-oils was 39, 39, 39, 36, 32, and 31 wt % for white pine alone and white pine accompanied with CaO at CaO/biomass mass ratios of 1, 2, 3, 4 and 5, respectively. At a CaO mass ratio of 5, the relative reduction of oxygen content in the bio-oil reached 21%. Detailed gas chromatography−mass spectrometry analysis showed that the relative abundances of high oxygen content laevoglucose, formic acid, and acetic acid were highly reduced by CaO, indicating direct fixation of “the active quasi-CO2 intermediates” produced during biomass pyrolysis. Furthermore, the relative abundances of furfural, furfuryl alcohol, etc., mainly derived from dehydration reactions, all increased, showing that CaO addition could also catalyze dehydration reactions. X-ray diffraction and Fourier transform infrared analyses of the solid residues prepared by a thermal balance confirmed the direct fixation of the active quasi-CO2 intermediates and showed that some organic calcium salts appeared at 350 °C, which would decompose below 400 °C to form easily regenerated CaCO3. This further confirmed the feasibility of CaO recycling for in situ deoxygenation of bio-oil.
Lin et al. (Tue,) studied this question.