Effect of Selective Condensation on the Characterization of Bio-oil from Pine Sawdust Fast Pyrolysis Using a Fluidized-Bed Reactor

To maximize selective condensation of organics that are of known higher commercial value and to investigate the effects of selective condensation on bio-oil characterization, pine sawdust was pyrolyzed in a 1-5 kg/h bench-scale fluidized-bed reactor. In the experiments, the selective condensers and electrostatic precipitator were used to condense the pyrolysis vapors. In addition, the characterization of bio-oils, gases, and biochar was investigated. The results showed that the total bio-oil, gases, and char yields were 41.5, 43.3, and 15.2%, respectively, and 86.2 wt % water steam was condensed in condenser 1. The bio-oil condensed in the later condensers has a lower water content, higher pH value, higher heating value, and higher kinetic viscosity compared to the first one. Analysis of the 1, 4, and 5 bio-oils with gas chromatography mass spectrometry (GC-MS) showed that 102 types of chemical compounds were detected and most of the compounds were condensed at different condensers. Therefore, the selective condensation is useful to separate the water and chemical compounds from bio-oil compared to direct contacting condensing. The gas products were mainly CO, H-2, CO2, CH4, and C-2-C-4. Char characteristics were determined by ultimate analysis, Fourier transform infrared (FTIR) spectrometry, and scanning electron microscopy (SEM) methods. A lot of bonds, such as -NH-, CH, -C=C-, -CH3, and -C-O-C-, were found in the char samples. It was observed that the surface morphology of the pine particle changed after pyrolysis, and it became thinner and shrank. The thermal decomposition of chemical bonds and the melting of some compounds can break the chemical bonds of the original material, and the chemical bonds with lower bond energies break with priority. The research has provided a useful reference for biomass fast pyrolysis.