Alicia Callejas

Reactivity Towards O2 and NO of the Soot Formed from Ethylene Pyrolysis at Different Temperatures

The influence of temperature on the formation of soot from ethylene pyrolysis has been studied. Pyrolysis experiments were carried out in a quartz reactor in the 1000-1200 °C temperature range, for an inlet C2H4 concentration of 50000 ppmv and a gas residence time of 4552/T(K) seconds. Outlet gases were analyzed by gas chromatography and the amount of soot produced measured. The reactivity of the soot samples obtained towards O2 and NO was also studied. Results show that the higher the formation temperature, the less reactive the soot. The soot samples were further characterized using elemental analysis, scanning electron microscopy and Raman spectroscopy, in order to study their structural properties, and relate them to their reactivity. Additionally, a comparison of the reactivity towards NO between acetylene and ethylene soot samples obtained under similar conditions has been carried out. The soot samples obtained from ethylene pyrolysis present higher reactivity towards NO than the soot samples formed from acetylene.

Formation and Characterization of Polyaromatic Hydrocarbons

Issues concerning polycyclic aromatic hydrocarbons (PAH) carcinogenicity, and their important role in formation of dangerous pollutants, such as soot, have motivated their study under a wide range of laboratory conditions and for several kinds of thermochemical processes. Every experimental system, depending on the operating conditions, demands a specific protocol for PAH determination. This chapter aims to contribute to the knowledge of different procedures for PAH quantification both at the gas phase and when they are associated with soot particles. Different kinds of experimental set-ups for PAH formation together with the collection systems to capture them are explained here. Besides, some sample extraction techniques are reviewed, mainly focused on Soxhlet extraction because of its inexpensive equipment and overall simplicity to be applied by staff with limited analytical experience. Chromatographic techniques are also considered, paying special attention to gas chromatography coupled to mass spectrometry (GC–MS), popular in PAH analysis.