Quantum Chemical and Kinetic Study on Dioxin Formation from the 2,4,6-TCP and 2,4-DCP Precursors

Abstract

This study focuses on the homogeneous gas-phase formation of polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) from the 2,4,6-trichlorophenol (2,4,6-TCP) and 2,4-dichlorophenol (2,4-DCP) precursors, which were found both in the gas phase and in the fly ash samples as the dominating chlorophenol congeners in municipal waste incinerators (MWIs). Molecular orbital theory calculations have been performed for the formation mechanism. The geometrical parameters and vibrational frequencies of all the stationary points were calculated at the MPWB1K level with the 6-31+G(d,p) basis set. Single-point energy calculations were carried out at the MPWB1K/6-311+G(3df,2p) level of theory. Canonical variational transition-state (CVT) theory with small curvature tunneling (SCT) contribution was used to predict the rate constants of crucial elementary steps over the temperature range of interest (600-1200 K). The rate-temperature formulas were fitted for the first time. The pre-exponential factor, the activation energy, and the rate constants are reported. This study shows that at least one chlorine substituent in the ortho position is needed for the formation of PCDDs from the condensation of chlorophenols. The results presented here should help to clarify and detail the formation mechanism of PCDD/PCDFs (PCDD/Fs for short) from chlorophenol precursors in real waste combustion.

Formation of dibenzofuran, dibenzo-p-dioxin and their hydroxylated derivatives from catechol

“…13,14,16,25 We find that the presence of two OH substituents at ortho positions does not influence this high ) and lead to the formation of preDF structures. To the best of our knowledge, our discussed C-C ring-closure reactions have never been proposed as pathways for the formation of substituted DF molecules.…”

“…The currently suggested mechanisms for the synthesis of DD and DF rely on the wellestablished analogous pathways that operate in chlorophenol systems. 3,[12][13][14][15][16] As the opening step in these mechanisms, formation of DD and DF arises from the conversion of CT into phenol. Conversely, these mechanisms do not incorporate a plausible role for the two ortho OH groups in mediating the occurrence of crucial reaction steps, such as ring-closure and water elimination.…”

Electrosynthesis of blue-light-emitting oligo(1-bromopyrene) with favorable solubility

“…Electric charge (11) 0.115551 C (13) 0.122169 C (15) −0.002373 (12) 0.131134 C (14) 0.127249 Quantum chemical calculations can provide some theoretical information on the chemical structure and property [35][36][37]. For more information on the structure of polymers and the polymerization mechanism, we calculated the atomic electron-density population ( Table 1) and proportion of the frontier orbitals (Scheme 2) of the BrP monomers using the B3LYP/6-31G(d,p) level of Gaussian 03 software.…”

Comparison of bioaugmented EGSB and GAC–FBB reactors and their combination with aerobic SBR for the abatement of chlorophenols

“…Therefore, it has been included in the List of Priority Pollutants of the US-EPA and it is also listed in the European Directive 2006/ 11/EC on pollution caused by certain dangerous substances discharged into the aquatic environment of the Community (List I, organohalogen compounds). Besides its own high toxicity it is recognized as a precursor in the formation of some polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) [4].…”