HYDROCARBON CONTENT OF LIQUID PRODUCTS AND TAR FROM PYROLYSIS AND GASIFICATION OF WOOD

Vacuum pyrolysis of aspen poplar wood chips was performed in a multiple hearth furnace process development unit. Various pyrolysis oils were collected in a series of cooling traps installed in parallel at the reactor outlets (primary condensing unit, H-I to H-VI). An aqueous phase containing about 45% water (96% of the total pyrolysis water) was collected separately in a secondary condensing unit (C-1 to C-3) which contained high-volatile and partially water 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 and mass spectrometry (GC/MS). Aliphatic hydrocarbons represented between 0.08 and 0.44% of the oil phase and 0.01 and 0.02% of the aqueous phase. The aliphatic hydrocarbon fraction of the H-VI oil was dominated by n-alkanes in the range of n-C19 to n-C26. Aromatic hydrocarbons contributed between 0.06 and 0.24% of the oil 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 their aromatic fractions, neither phase is believed to have significant environmental and toxicological impact. The efficiency of the hydrocarbon separation technique was also tested on a tar sample from a 10 t/h wood gasifier which contained over 50% polycyclic aromatic hydrocarbons. Of this tar sample 85% was characterized by GC/MS.