Comparison of observed and predicted equilibrium PAH concentrations in coke oven emissions: I. Relative abundances of carbon-hydrogen PAH.

The relationship between the equilibrium concentrations of the carbon-hydrogen species in polycyclic aromatic hydrocarbons (PAH) found in coke oven emissions by Kirton et al and those which they measured has been investigated. A thermodynamic database for the species involved for use with the MTDATA computational package has been constructed and used to predict concentrations for local equilibrium between the group of PAH species at varied temperature. The temperature at which the concentration of each species observed would be in equilibrium with representative methane and hydrogen concentrations in coke oven gases has also been calculated. In each case the most satisfactory agreement between equilibrium and observed concentrations occurs above 1100K. In the group calculation, the higher PAH are over-predicted and this is consistent with the known kinetic restriction on soot formation. Some substituted benzenes and the biphenyl series are seriously under-predicted within the PAH group, and in the calculations for the model coke oven gas, do not equilibrate with methane and hydrogen at temperatures representative of coke ovens: this is consistent with their formation by reaction during quenching. The predicted equilibrium concentrations of the majority of species are within an order of magnitude of group equilibrium concentration at 1150K.