Comparative study on the evolution of physicochemical properties of tar obtained from heavy fraction of bio-oil at different heating rates

摘要

The effects of heating rate on the evolution of tar obtained from heavy fraction of bio-oil (HB) were revealed by the change of elements, functional groups and chemical compounds. The results showed that slow heating rate had a negligible effect on the physicochemical properties of HB from 400 to 800 degrees C. By contrast, decomposition, radical recombination and polymerization reactions could occur at fast heating rate. A clear trend of increasing tar yields was monitored from 300 - 500 degrees C. However, a significant decrease was observed at high temperature (600 - 800 degrees C). Through elemental analyzer, C content in tar expanded with the temperature increasing, whereas N content remained unchanged. Nuclear magnetic resonance (NMR) spectroscopy results indicated that the carboxyl functional groups would be destroyed at high temperature. Furthermore, the concentrations of aromatics showed a trend to increase accompanied by a simultaneous decrease in phenols with the temperature rising according to gas chromatography/mass spectrometer (GC/MS) analysis.