COMPARISON BETWEEN SLOW AND FLASH PYROLYSIS OILS FROM BIOMASS

This paper presents the results obtained in the characterization of different pyrolysis oils, five oils produced by carbonization and one by flash pyrolysis. Chemical and physical properties such as density, viscosity, elemental composition, char content, water content, solubility and heating value were first determined, then an in-depth chemical characterization was carried out by liquid-liquid fractionation. A diagram indicating the separation procedure, providing four fractions (acids, bases, polars and hydrocarbons), is presented. Polar molecules which were retained in the aqueous layer ('aqueous' fraction) are recuperated. Each fraction was subsequently analysed by gas chromatography-mass spectrometry (g.c.-m.s.) and Fourier transform infrared spectroscopy (FT-i.r.). The acidic fraction was the most abundant and contained essentially phenolic structures. However, phenols were differently substituted in the two types of oils: alkyl and methoxy groups in the carbonization oils; methoxy, acidic, aldehydic and ketonic functions in the flash pyrolysis oil. The other fractions present a similar composition for all oils. The basic fraction was always very small; some aromatic N-containing compounds were identified. The 'polar' neutral fraction was also small and its characterization was very difficult. The hydrocarbon fraction, especially, was constituted of aromatics and cyclics, and some aliphatics were also identified. The 'aqueous' fraction contained mainly carboxylic esters, alcohols and ethers.