Sources of polyaromatic hydrocarbons (PAH)
Aromatic hydrocarbons including PAH compounds are thermally and chemically very stable compounds and are formed by gasifications/pyrolysis of biomass. With reference to the tar compounds present in the produced gas from updraft gasifieres the sources responsible for the formation of naphtalene and poly-aromatic hydrocarbons have been investigated.
Naphthalene and poly-aromatic hydrocarbons (PAH) are thermally and chemically very stable compounds. They are formed by gasification/pyrolysis of biomass at moderate temperatures (800 deg.C) and are found in minor amount in the produced gas from an updraft gasifier. The purpose of the project is to identify the tar compounds being responsible for the sources to the formation of the PAH compounds. Special emphasis will be paid to the tar compounds formed in updraft gasifiers. Thus, the focus will be on thermal and oxidative conversions of compounds derived from the lignin structure. The investigations will be performed using Risø's laboratory ovens and by application of analytical pyrolysis. A significant international effort has been directed to the transformation of naphthalene and PAH compounds by thermal, partial oxidative and catalytic methods. Opposite, the studies of the formation of PAH compounds are much more limited. It is expected that the present investigation will give results which can facilitate the determination of the optimum conditions for updraft gasifiers including a reduction of the PAH formation
The focus has been on thermal and oxidative conversions of compounds related to the lignin building blocks. Thus, phenols, 2-methoxy-phenols and 4-substituted-2-methoxy-phenols were investigated by introducing water solutions of the compounds into a continuos flow system operating in the temperature range 600-850 deg. C. The pyrolysis products were identified by GC/MS. The tar compounds reveal a well-defined and characteristic thermal transformation. Phenol is a strong source to naphthalene and indenes while 2-methoxyphenols are sources to aromatic oxo-compounds such as cinnamaldehyde. More complex systems are sources to higher PAH compounds. Thus, oligomers of phenol and 2-methoxyphenol give dibenzofuran and oligomers of isoeugenol are important sources to acenaphthylene. It is characteristic that the simple tar compounds investigated undergo loss of CO and hereby loss of the aromatic structure. The intermediary compounds are reactive cyclo-pentadiens entering Diels-Alder reactions. The later products are transformed to aromatic compounds. The results may facilitate the determination of optimum conditions for updraft gasifiers and hence a reduction of PAH formation
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Participants
| Partner | Subsidy | Auto financing |
|---|---|---|
| Danmarks Tekniske Universitet (DTU) |
Contact
P.O. Box 49
DK-4000 Roskilde, Denmark
Egsgaard, Helge (Ph.D., civ.ing.); Projektleder: Larsen, Elfinn (civ.ing.), 46775450, elfinn.larsen@risoe.dk
Øvr. Partnere: Danmarks Tekniske Universitet
