Pyrolysis characteristics of bio-oil fractions separated by molecular distillation

Molecular distillation was used to separate bio-oil into a light fraction, a middle fraction and a heavy fraction. The chemical composition of the three fractions and the crude bio-oil was analyzed by gas chromatography coupled with mass spectrometry (GC–MS). The diversity of the components reflected the complexity of the bio-oil and the necessity for fractionation. The pyrolysis characteristics of the bio-oil fractions were determined with a thermogravimetric analyzer coupled with Fourier transform infrared spectroscopy (TG–FTIR). The weight loss of components was in agreement with the chemical composition. The light fraction evaporated fastest with the formation of water, CO2, hydrocarbons and alcohols. The heavy fraction had the slowest rate of decomposition and the highest char residue yield due to the presence of phenols and saccharides, and the pyrolysis products included CO2 and alcohols or phenols, which was similar to the middle fraction except the formation of water and formic acid. The release of CO or methane, evidence of a secondary reaction, began at ∼450 °C in the pyrolysis of the light and middle fractions.