Polychlorinated dioxins and furans (PCDD/PCDF or PCDD/F) are a group of
highly toxic components. They are found to be a consequence of the de novo synthesis
in the temperature range within 180°C and 500°C . Carbon, chlorine,
catalysts (Cu) and oxygen are necessary for the formation of PCDD/F, so PCDD/F
can be formed in very small amounts from all biomass fuels containing chlorine.
The emissions of PCDD/F are highly dependent on the conditions under which
combustion and flue gas cooling take place; therefore, wide variations are found
in practice. Although herbaceous biomass fuels have high chlorine contents, their
PCDD/F emissions are usually very low. This may be explained by their high
alkali content, which leads to the formation of salts (KCl, NaCl) and thus to a
lower level of gaseous chlorine for the de novo synthesis. Because of the many
factors influencing PCDD/F formation, wide variations may appear even within
the same biomass combustion installation, but in general, the PCDD/F emission
level from biomass combustion applications using virgin wood as a fuel is well
below the health risk limit.
Platinum and palladium may catalyze chlorination of PCDD/Fs via the Deacon reaction or an oxidation process.