The effect of sulfur dioxide （SO2） on the formation of polychlorinated dibenzo-p-dioxins （PCDDs） and polychlorinated dibenzofurans （PCDFs） has been studied in an entrained-flow reactor （EFR） under simulated wa...The effect of sulfur dioxide （SO2） on the formation of polychlorinated dibenzo-p-dioxins （PCDDs） and polychlorinated dibenzofurans （PCDFs） has been studied in an entrained-flow reactor （EFR） under simulated waste combustion conditions. A chlorination model based on conditional probability was employed to evaluate the homologue patterns of PCDDs and PCDFs. Results revealed that the presence of SO2 did not alter the formation pathway although SO2 suppressed PCDD/F formation. The prediction model of PCDF showed good agreement with the experimental data （R--0.95）, whereas the prediction for PCDDs did not correlate well with the experimental data. This may be explained because potential chlorination pathways play a significant role in PCDF formation, whereas PCDDs are mainly formed through condensation reactions. Furthermore, the result indicated that the steric hindrance during formation has more effects on PCDD than on PCDF due to the symmetric molecular structures of PCDDs.展开更多
Numerous thermal processes （e.g. waste incineration, steel and nonferrous industry, wastes recycling plants, hot dip galvanizing etc. ） have been identified as emission sources of PolyChlorinated Dibenzo-p-Dioxins ...Numerous thermal processes （e.g. waste incineration, steel and nonferrous industry, wastes recycling plants, hot dip galvanizing etc. ） have been identified as emission sources of PolyChlorinated Dibenzo-p-Dioxins （PCDD） and PolyChlorinated DibenzoFurans （PCDF）, which are named in brief ＂dioxins＂ The processes by which such dioxins （PCDD/F） are formed are still incompletely understood and probably proceed catalytically by multiple and parallel pathways. However, two major pathways of formation have been identified during final stages of the combustion process： The first one is the precursor route, i.e. the formation of PCDD/F from related structures, such as simple or chlorinated benzenes, phenols, biphenyls, and polycyclic aromatic hydrocarbons （PAH）, and the second one is the de novo synthesis of PCDD/F from macromolecular solid carbon （ or other structures unrelated to dioxins）, organic and inorganic chlorine, oxygen, etc. Knowledge of the relevant thermodynamic parameters is essential for predicting possible stability domains of PCDD/F during combustion processes and their equilibrium distribution at emission sources. In the previous study, thermodynamic parameters of PCDDi predicted with density functional theory （DFF） method have been reported. A comprehensive thermodynamic database of the standard entropy （ S^0 ）, specific heat （Cp）, enthalpy of formation （ΔfH^0） and Gibbs free energy of formation （ΔfG^0） for 135 gaseous PCDF （including dibenzofuran） was studied. From the enthalpies of formation the order of stability of individual congeners is reported. Additionally, the results obtained in this study are compared with values determined by other electronic structural methods.展开更多
Optimized calculation of dibenzofuran （DF） and 135 polychlorinated dibenzofurans （PCDFs） was carried out at the B3LYP/6-31G＊ level in GAUSSIAN 98 program. Based on the theoretical linear solvation energy relation...Optimized calculation of dibenzofuran （DF） and 135 polychlorinated dibenzofurans （PCDFs） was carried out at the B3LYP/6-31G＊ level in GAUSSIAN 98 program. Based on the theoretical linear solvation energy relationship （TLSER） model, the obtained structural parameters were taken as theoretical descriptors to establish the novel quantitative structureproperty relationship （QSPR） model for predicting n-octanol/water partition coefficients （lgKow） of PCDFs. The new model of lgKow achieved in this work contains three variables： energy of the highest occupied molecular orbital （EHOMO）, the most negative atomic partial charge （q^-） and average molecular polarizability （a）, of which R^2= 0.9011 and SD = 0,17 with larger t values. In addition, the variation inflation factors （VIF） of variables in the present model are all less than 5.5, suggesting high accuracy of the lgKow model. And the results of cross-validation test （q^2 = 0.8688） and method validation also show this model exhibits optimum stability and better predictive power than semi-empirical method. At the same time, it is found that the aqueous solubility （-lgSw） has high relative correlation with constant volume molar heat capacity （Cv^0）, of which R^2 = 0.9777 and SD = 0.22. Moreover, lgKow and -lgSw values of all PCDF congeners were predicted respectively.展开更多
基金Project supported by the China Scholarship Council Foundation (2003) the National Natural Science Foundation of China (No. 50576082).
文摘The effect of sulfur dioxide （SO2） on the formation of polychlorinated dibenzo-p-dioxins （PCDDs） and polychlorinated dibenzofurans （PCDFs） has been studied in an entrained-flow reactor （EFR） under simulated waste combustion conditions. A chlorination model based on conditional probability was employed to evaluate the homologue patterns of PCDDs and PCDFs. Results revealed that the presence of SO2 did not alter the formation pathway although SO2 suppressed PCDD/F formation. The prediction model of PCDF showed good agreement with the experimental data （R--0.95）, whereas the prediction for PCDDs did not correlate well with the experimental data. This may be explained because potential chlorination pathways play a significant role in PCDF formation, whereas PCDDs are mainly formed through condensation reactions. Furthermore, the result indicated that the steric hindrance during formation has more effects on PCDD than on PCDF due to the symmetric molecular structures of PCDDs.
文摘Numerous thermal processes （e.g. waste incineration, steel and nonferrous industry, wastes recycling plants, hot dip galvanizing etc. ） have been identified as emission sources of PolyChlorinated Dibenzo-p-Dioxins （PCDD） and PolyChlorinated DibenzoFurans （PCDF）, which are named in brief ＂dioxins＂ The processes by which such dioxins （PCDD/F） are formed are still incompletely understood and probably proceed catalytically by multiple and parallel pathways. However, two major pathways of formation have been identified during final stages of the combustion process： The first one is the precursor route, i.e. the formation of PCDD/F from related structures, such as simple or chlorinated benzenes, phenols, biphenyls, and polycyclic aromatic hydrocarbons （PAH）, and the second one is the de novo synthesis of PCDD/F from macromolecular solid carbon （ or other structures unrelated to dioxins）, organic and inorganic chlorine, oxygen, etc. Knowledge of the relevant thermodynamic parameters is essential for predicting possible stability domains of PCDD/F during combustion processes and their equilibrium distribution at emission sources. In the previous study, thermodynamic parameters of PCDDi predicted with density functional theory （DFF） method have been reported. A comprehensive thermodynamic database of the standard entropy （ S^0 ）, specific heat （Cp）, enthalpy of formation （ΔfH^0） and Gibbs free energy of formation （ΔfG^0） for 135 gaseous PCDF （including dibenzofuran） was studied. From the enthalpies of formation the order of stability of individual congeners is reported. Additionally, the results obtained in this study are compared with values determined by other electronic structural methods.
基金This work was supported by the China Postdoctoral Science Foundation (No. 2003033486)
文摘Optimized calculation of dibenzofuran （DF） and 135 polychlorinated dibenzofurans （PCDFs） was carried out at the B3LYP/6-31G＊ level in GAUSSIAN 98 program. Based on the theoretical linear solvation energy relationship （TLSER） model, the obtained structural parameters were taken as theoretical descriptors to establish the novel quantitative structureproperty relationship （QSPR） model for predicting n-octanol/water partition coefficients （lgKow） of PCDFs. The new model of lgKow achieved in this work contains three variables： energy of the highest occupied molecular orbital （EHOMO）, the most negative atomic partial charge （q^-） and average molecular polarizability （a）, of which R^2= 0.9011 and SD = 0,17 with larger t values. In addition, the variation inflation factors （VIF） of variables in the present model are all less than 5.5, suggesting high accuracy of the lgKow model. And the results of cross-validation test （q^2 = 0.8688） and method validation also show this model exhibits optimum stability and better predictive power than semi-empirical method. At the same time, it is found that the aqueous solubility （-lgSw） has high relative correlation with constant volume molar heat capacity （Cv^0）, of which R^2 = 0.9777 and SD = 0.22. Moreover, lgKow and -lgSw values of all PCDF congeners were predicted respectively.
