Experimental Investigation On Biomass Fast Pyrolysis In The Presence Of CaO For In-situ Deoxygenation Of Bio-oil

Compared with other usages of biomass, pyrolysis to produce bio-oil is now considered to be an advanced and promising methodology. However, raw bio-oil usually has very poor fuel properties, such as high oxygen content, high instability, low calorific value, high viscosity and high corrosiveness. Refining and subsequent purification of the raw oil increase the production cost and greatly reduces the efficiency of energy utilization. Under the supports of the National Natural Science Foundation of China --?Deoxygenation in bio-oil-making by biomass fast pyrolysis with CaO chemical-looping replacement?and the overview of the biomass utilization technology and biomass pyrolysis mechanism, experiment investigations on biomass pyrolysis in the presence of CaO was performed, for further research and eventually developing a new scheme for the production of high quality bio-oil by direct deoxygenation in bio-oil production. The main study methods and conclusions are as follows:A preliminary study on the pyrolysis of red pine and rice straw with CaO was carried out in a thermal balance, indicating that some intermediates called“the active quasi-CO₂ intermediates”generated in the pyrolysis process might be directly fixed by CaO. There was an optimum range for the CaO/biomass mass ratio for the CaO to CaCO₃ conversion rates. Red pine was more adaptable for the raw biomass to be pyrolyzed than rice straw.A small drop tube pyrolyzer test at a range of CaO/cellulose mass ratios was carried out to explore deoxygenation effect of CaO addition on cellulose pyrolysis to bio-oil. Compared with the original value of the bio-oil from cellulose alone, 44.4 wt%, the oxygen content of the organic components of the bio-oil from pyrolysis decreased to 40.7 wt% for a CaO/cellulose mass ratio R=2. i.e. a relative variation of -8.4%. With addition of CaO, The active oxygen-rich groups, so called“active quasi-CO₂ intermediates”, can be fixed directly as some organic calcium salts such as calcium carboxylates , which will function as a‘chemical sink', and cause the dominant shift of the parallel competitive reactions to decomposition and reforming. In addition, CaO addition can also promote dehydration reactions.A small fluidized bed test was carried out to explore the deoxygenation effect on the pyrolysis of white pine to bio-oil. Compared with the original value of the bio-oil from white pine powder alone, 39 wt%, the oxygen content of the organic components of the bio-oil from pyrolysis decreased to 31 wt% for a CaO/white pine mass ratio R=5. i.e. a relative change of -21%. The results further confirmed the existence of the route of direct fixation of“the active quasi-CO₂ intermediates”with the appearance of some organic calcium salts such as some calcium salts of uronic acid. In addition, CaO addition can also promote the trend of the side-chain-detachment reaction pathway for the pyrolysis of white pine lignin, and also promote dehydration reactions.X-ray diffraction (XRD), Fourier transform infrared (FTIR) and X-ray Photoelectron Spectroscopy (XPS) analyses of the solid residues from biomass pyrolysis with CaO in a thermal balance were carried out. The results indicated that some organic calcium salts appeared greatly in the solid residues at the temperature of 300³50oC, which decomposed apparently before 400oC.