Effects of organic chlorine on the chemical composition and carbon number distribution of pyrolysis tars

In order to quantify the effects of chlorine on the composition and distribution of tar products, droplets containing varying amounts of toluene and chlorinated hydrocarbon additives were pyrolyzed in nitrogen. Three chlorinated organics were studied: o-dichlorobenzene, 1,2-dichloroethane, and trichloroethylene. It was found that the pyrolysis of chloro-organics results in the sequestration of hydrogen, leading to (1) a higher propensity for soot formation, (2) a higher degree of ring fusion of the aromatic compounds produced, and (3) little chlorination of arenes at low Cl H molar ratios. More specifically, little aryl chlorine was found in tars from pyrolysis at high temperatures with Cl H < 0.3 , and most of the aryl chlorine that was detected was bound to unfused benzene rings. Pyrolysis of fuels with higher chlorine content ( 0.3 < Cl H < 0.6 ) produced tars containing significant quantities of monochlorinated and dichlorinated aromatics; in these tars, the extent of chlorine substitution decreased as aromatic carbon number increased. At a very high fuel chlorine level ( Cl H = 3 ), perchloroaromatics of low carbon number were formed almost exclusively. With regard to aromatic structure, the formation of peri-fused aromatics, including cyclopenta[cd]pyrene, and soot was favored with increasing fuel chlorine content. These results demonstrate that the role of organic chlorine in pyrolysis is governed by its preferential incorporation into HCl due to the relative instability of carbonchlorine and chlorinechlorine bonds at high temperatures.