The impact of chlorine on hexavalent chromium emissions from a laminar diffusion flame
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Measurements of total chromium and hexavalent chromium have been obtained in a laminar hydrocarbon/air diffusion flame. Chlorine was added to the fuel as methyl chloride gas. A probe sampled the emissions from the flame. Particles were collected on a filter and vapor phase species were collected in impingers. Hexavalent chromium was measured with a spectrophotometric method. Total chromium added to the flame was determined by gravimetric analysis of the chromium source, chromium hexacarbonyl. The fraction of hexavalent chromium increased significantly as small amounts of chlorine were added. Partitioning between phases was also altered - much more hexavalent chromium was found in the impingers as the chlorine loading increased. Differential mobility analysis of the particles showed that the mean particle size was always in the range of 25-30 nm, whether chlorine was added or not. However, particle concentrations decreased when chlorine was present. Equilibrium calculations showed strong sensitivity to the thermochemical properties of the included species, particularly CrO2Cl2.
