Chemical Characterization of Hydrocarbons Produced by Vacuum Pyrolysis of Aspen Poplar Wood Chips

Abstract

Vacuum pyrolysis of aspen poplar wood chips was performed in a Process Development Unit multiple hearth furnace. Various pyrolysis oils were collected in a series of cooling traps installed in parallel at the reactor outlets (Primary Condensation Train, H-I to H-VI). Aqueous phase with about 45% water (96% of the total pyrolysis water) was collected separately in a Secondary Condensation Train (C-1 to C-4) and contained high volatile and partially soluble organic matter. Liquid-liquid and liquid-solid chromatographic techniques were developed to separate aliphatic and aromatic hydrocarbons. Preliminary characterization of the aliphatic and aromatic hydrocarbons was performed by gas chromatography. Aliphatic hydrocarbons comprised between 0.08 to 0.44% of the oil phase and 0.01 to 0.02% of the aqueous phase. The aliphatic hydrocarbon fraction of the H-VI was surprisingly dominated with n-alkanes in the range of n-C13 to n-C28 and n-alkenes in the range of n-C19 to n-C26. Aromatic hydrocarbons contributed between 0.06 to 0.24% of the organic phase and were detected only in trace amounts in the aqueous phase. FTNMR and FTIR spectroscopic analyses of the aromatic fractions showed a complex mixture of highly branched aromatic hydrocarbons. Due to the highly branched nature of the aromatic fractions, both organic and aqueous phases were believed not to have any significant environmental and toxicological impact. Efficiency of the separation technique was also tested on tar sample from a 10 t h-1 wood gasifier which contained over 50% polycyclic aromatic hydrocarbons.