The effect of chlorinated hydrocarbons on the formation of positively charged polycyclic aromatic hydrocarbons and fullerenes with masses up to 1300 U in benzene and butane flames

Abstract

The influence of chlorine-containing hydrocarbons on the formation of large polycyclic aromatic hydrocarbons (PAHs) in low-pressure flat flames of benzene and butane premixed with oxygen was studied. Because of the close relation between neutral and positively charged PAHs, flame ions were investigated. The ions were withdrawn through a molecular beam system and analyzed with a reflectron time-of-flight mass spectrometer. Monochlorobenzene (maximum 20% of the fuel) and chloroform (maximum 8.3%) were added to benzene flames and 10% 1-chlorobutane to the butane flame. Large PAH ions in the seeded flames were qualitatively the same as in the pure flames (i.e., they did not contain chlorine). All additives caused a delay in PAH formation in the cooler portion of the flame near the burner and suppressed the formation of very hydrogen-rich PAHs. In the hotter part of the oxidation zone, PAH formation was accelerated. Very large PAHs were formed because of a faster decrease of the lower- and medium-mass PAHs, however, with only a slight increase of the total amount of carbon in the PAHs. At maximum flame temperature, PAHs+ were decomposed and fullerene ions appeared. The latter were absent in the butane flame without additive.