Pyrolysis of ethylene – ammonia mixture: Formation of soot, gases and PAH

The effect of inlet concentration of NH 3 (0, 30000, 60000, and 100000 ppm) and temperature (1275, 1375, and 1475 K) on the formation of soot, gases and polycyclic aromatic hydrocarbons (PAH) from the pyrolysis of C 2 H 4 /NH 3 mixtures with constant concentration of C 2 H 4 (30000 ppm) was analyzed. Light gases were quantified through gas chromatography, while soot was collected in a fiber filter, at the reactor outlet, and the particle diameter was analyzed. The PAH were analyzed through gas chromatograph coupled to mass spectrometer by considering the 16 PAH reported by Environmental Protection Agency (EPA) as priority pollutants. The main results show that the higher the presence of NH 3 in the NH 3 /C 2 H 4 mixture, the lower the soot formation. This decrease of soot is accompanied by an increase of HCN and a decrease in C 2 H 2 , indicating that the carbon has been removed from the typical soot reaction pathways. In all conditions tested, PAH formed follow the typical trend observed in earlier works with respect to temperature, i.e. as the temperature increases, the formation of PAH decreases. At 1275 K, the presence of high NH₃ levels increases PAH concentrations, likely due to suppression of soot formation routes, which prevents PAH consumption and allows aromatic intermediates to accumulate rather than proceed to particle growth. The increase in NH 3 concentrations at the inlet reduces the toxicity expressed as benzo[ a ]pyrene equivalent concentration (B[ a ]P-eq), under all conditions studied. Analysis of the particle distribution diameter reveals that the NH 3 presence reduces diameter variations and predominantly results in smaller soot particles.