On the Mechanism of Soot Formation in a Vertical Flow Reactor

Abstract

The formation process of carbonaceous material (soot) has been experimentally studied in order 10 explain the role of polynuclear aromatic hydrocarbons (PCAH) in that process; in particular the research has been directed to see if PCAH are byproducts or intermediate compounds.The experimental work was carried out in a vertical reactor, where the fuel was fed after mixing with oxygen and nitrogen at atmospheric pressure. The flow rate and the composition of the mixtures were such that a yellow flame was present in the reactor.The flue gas was sampled along the axis in order to determinate concentration profiles of several PCAH and of perinaphthenyl radical, which is strictly correlated to PCAH in the formation process. The soot was collected from the gas at five locations: every sample was extracted with solvent, obtaining one insoluble fraction, that was called "carbon" and a soluble one, called "tar".The concentration profiles of all the analyzed PCAH and of the perinaphthenyl radical show a maximum, which is characteristic of intermediate products: the content of soot in the flue gas increases along the reactor axis, however,if the two fractions are taken into account one can see that only the tar increases, while the carbon has a flat profile. The interpretation of those concentration profiles suggest that the PCAH and the perinaphthenyl radical certainly are intermediates in the formation process of the soluble fraction of soot (tar), which still plays a secondary role in the production mechanism of the insoluble part (carbon).