Experimental And Modeling Study On The Role Of Water In De Novo Synthesis Of Polychlorinated Dibenzo-p-dioxins And Dibenzofurans

Water plays an important role in the formation of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs). A series of experiments were conducted on a fixed bed incinerator to investigate the effect of water on non-catalyzed and catalyzed de novo synthesis of PCDD/Fs. Moreover, experimental and modeling study was carried on a Entrained Flow Reactor (EFR) to study the de novo formation of PCDD/Fs.The result on the fixed bed incinerator indicated that water could activate fly ash to promote the formation of PCDD/Fs. Due to the selectivity of catalyst, the promotion of water did not change the pattern of PCDD/F formation but enforced the original pattern. This pathway was proved to be the dominant one. The second potential pathway was to change the equilibrium of certain key reaction such as Deacon reaction to reduce the concentration of chlorine gas in atmosphere. But this effect could only be presented when water content reached 18%. This effect confirmed the view that chlorine concentration was correlated to PCDD/F formation only when chlorine concentration was very low in atmosphere. The third effect of water was to provide oxygen for PCDD/F formation when there was no addition oxygen source in atmosphere. But this will reduce the effect of activating fly ash. The fourth effect of water was to inhibit the catalyst of de novo synthesis such as CuCl₂. However, this inhibition was limited due to the overall promotion of water on PCDD/F formation.De novo formation of PCDDs and PCDFs has been studied in an entrained-flow reactor (EFR) to simulate waste combustion. The role of sulfur dioxide (SQ2) in de novo formation was isolated for investigation. A chlorination model based on conditional probability was employed to evaluate the homologue patterns of PCDDs and PCDFs. The experimental result revealed that the presence of SO₂ did not change the formation pathway although SO₂ had various inhibition effects on dioxin formation. The model evaluation of PCDFs had a good agreement with the experimental data, which could be referred from a high correlation value of 0.95. However, the prediction...