The flux of polycyclic aromatic hydrocarbons and of insoluble material in pre-mixed acetylene-oxygen flames

Abstract

The mass flux of (a) total polymeric material, (b) soluble material, (c) insoluble material, and (d) polycyclic aromatic hydrocarbons has been determined at different heights above a flatflame burner on which acetylene-oxygen flames were stabilized at 20 mm mercury pressure. The acetylene-oxygen ratios used were 1.2, 1.5, and 1.8, respectively. The flux of each of the above reaches a maximum early in the flame just beyond the bluegreen zone and then undergoes an initially rapid decline; the flux of insoluble material becoming constant while that of p.c.a.h. shows an appreciable increase higher in the flame. The physical appearance of the material collected from the flame by isokinetic sampling through a water-cooled stainless-steel funnel suggests that a polymer-like material is first formed which then undergoes carbonization with dehydrogenation higher in the flame. The p.c.a.h. are formed in two distinct regions of the flame: (i) in a region where the temperature is rising (they are then destroyed to an appreciable extent in the highest temperature region); (ii) in a secondary zone much higher in the flame where the temperature is falling over the approximate range 900°–650°C, presumably by pyrolysis of residual acetylene. The majority of the p.c.a.h. (identified by programmed temperature gas chromatography combined with uv spectrophotometry) are devoid of side-chains-e.g., methyl group—and are probably the relatively unreactive ones.