Formation of PCDD/F catalysed by chromium chloride: experiments and PCDD/F signatures

Although chromium chloride has been known as a potential catalyst for formation of chlorinated aromatics including polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F), its promoting effect on these compounds has hardly been experimentally verified. In this study, model fly ash (MFA) incorporating CrCl3 was tested for PCDD/F formation at different temperatures, oxygen contents in the reaction atmosphere and reaction time. Besides the output, the fingerprint or signature of homologue and isomer was also systematically analysed, to investigate the formation mechanisms of PCDD/F from the perspective of reaction products. Maximum outputs of PCDD/F were reached at conditions of 350 celcius and 10% O2 content, respectively. A single test was conducted for 240 min and distinction was made between the gas evolving during six successive intervals of reaction time, and the residue. The formation/desorption reaction was intense in the first 90 min and then slowed down; the solid residue kept most of the PCDD/F (85.5%). A complete isomer-specific analysis was established for all samples in this study and the other two catalytic systems (CuCl2 and FeCl3). Special attention was paid to the 2,3,7,8-substituted congeners, to the chlorophenols route PCDD/F and to their behaviour at different conditions.