Here is a recent publication from our group on this subject.
The micro-structures of atmospheric pressure, laminar, premixed flames of CH3Cl/CH4 and CH4 have been studied under similar fuel-rich (equivalence ratio = 2.5) and carbon density (1.9x10-5 mole/cc) conditions using both heated micro-probe and cold trap sampling, followed by analysis by gas chromatography/ mass spectrometry (GC/MS). The mole fraction profiles of a large number species, including aromatic and polycyclic aromatic hydrocarbons (PAH) has been determined. In addition, the temperature and relative soot profiles were obtained using thermocouples and He-Ne laser light extinction measurements, respectively. These experiments indicated that although the CH3Cl/CH4 flame was more sooting, the levels of all the aromatics and PAH were significantly lower, some by as much as a factor of 10 than the CH4 flame in the post flame zones. This is a surprising result that contradicts the generally held belief that increased soot formation is associated with higher PAH levels. These measurements also provide new information on flame chemistry and suffest that the major effect of chlorine is the rapid incorporation of PAH into soot.
The pre-combustion composition and parameters as well as mole
fraction profiles are given below.
Parameters of Flames Studied |
||||
|---|---|---|---|---|
| Parameters | Methane | Methane/Chloromethane | ||
| Equivalence Ratio | 2.5 | 2.5 | ||
| Cold Gas Velocity (cm/sec) | 6.33 | 5.25 | ||
| C/O Ratio | 0.63 | 0.75 | ||
| Carbon Density (mole/cc) @298 K | 1.9x10-5 | 1.9x10-5 | ||
| Feed Mole Percentage | ||||
| Argon | 14.7 | 19.0 | ||
| O2 | 37.9 | 31.7 | ||
| CH4 | 47.4 | 23.8 | ||
| CH3Cl | --- | 23.8 | ||
It was found that, starting from benzene, PAH levels of the chloromethane/methane flame were lower than those of the methane flame by a factor of about 2-5, although the former was more sooting than the later flame.
This is a surprising and important observation, which provides new information about the effects of Cl on hazardous air pollutants formed in the incineration of chlorinated hydrocarbons and on the flame chemistry, e.g. reaction pathways of PAH formation.
Results on PAH formation in Methane and Chloromethane/Methane Flames are provided in images below.
Major Species in Cl flames
Aromatic Formation
in Premixed Chlorinated Flames
PAH profiles
in Premixed Chorinated Flames
Here is a recent publication from our group on this subject.
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