COMPARISON BETWEEN SLOW AND FLASH PYROLYSIS OILS FROM BIOMASS

This paper presents the results obtained in the characterization of di fferent pyrolysis oils, five oils produced by carbonization and one by flash pyrolysis. Chemical and physical properties such as density, vi scosity, elemental composition, char content, water content, solubilit y and heating value were first determined, then an in-depth chemical c haracterization was carried out by liquid-liquid fractionation. A diag ram indicating the separation procedure, providing four fractions (aci ds, bases, polars and hydrocarbons), is presented. Polar molecules whi ch were retained in the aqueous layer ('aqueous' fraction) are recuper ated. Each fraction was subsequently analysed by gas chromatography-ma ss spectrometry (g.c.-m.s.) and Fourier transform infrared spectroscop y (FT-i.r.). The acidic fraction was the most abundant and contained e ssentially phenolic structures. However, phenols were differently subs tituted in the two types of oils: alkyl and methoxy groups in the carb onization oils; methoxy, acidic, aldehydic and ketonic functions in th e flash pyrolysis oil. The other fractions present a similar compositi on for all oils. The basic fraction was always very small; some aromat ic N-containing compounds were identified. The 'polar' neutral fractio n was also small and its characterization was very difficult. The hydr ocarbon fraction, especially, was constituted of aromatics and cyclics , and some aliphatics were also identified. The 'aqueous' fraction con tained mainly carboxylic esters, alcohols and ethers.