Vaporization of zinc during thermal treatment of ZnO with tetrabromobisphenol A (TBBPA).

In the present work we investigate the vaporization of zinc or its compounds during thermal treatment of ZnO with tetrabromobisphenol A. Samples of 2g of ZnO:TBBPA (3.34:1) were isothermally heated in a laboratory-scale furnace at temperatures from 490 °C to 950 °C, and the solid, condensed and gaseous products formed were analyzed by X-ray diffraction analysis, electron probe microanalysis, inductively coupled plasma analysis, ion chromatography, and gas chromatography coupled with mass spectrometry. The results obtained indicate that the vaporization of ZnBr(2) formed strongly depends on heating time and temperature, yet is restrained by char, if formed with sufficient yield (above 15 wt%). Starting from 850 °C, this char commences carbothermic reduction of any remaining ZnO, which from then begins to evaporate as zinc metal vapor. Volatilization of zinc is completed at 950 °C. The presence of 5 vol.% of oxygen has no significant effect on the vaporization of formed ZnBr(2), the carbothermic reduction or the volatilization of metallic zinc. Strongly oxidizing conditions (20 vol.% of oxygen), however, boost the oxidation of char and thus the vaporization of ZnBr(2), but prevent carbothermic reduction of any un-reacted ZnO by depleting this char.

Influence of temperature and heating time on bromination of zinc oxide during thermal treatment with tetrabromobisphenol A.

Our prior research indicates that hydrogen bromide (HBr) evolved during thermal decomposition of tetrabromobisphenol A (TBBPA) can be utilized as a reagent for selective bromination and evaporation of zinc oxide. The present work investigated dependency of the bromination reaction on time at selected temperatures using a laboratory-scale furnace. The formed solid, condensed, and gaseous products were analyzed by X-ray diffraction analysis, electron probe microanalysis, inductively coupled plasma analysis, ion chromatography, and gas chromatography coupled with mass spectrometry. Results indicate that the bromination rate is strongly dependent on heating time. This dependency is a direct consequence of progress in the decomposition of TBBPA, which provides inorganic bromine suitable for the reaction. The bromination rate increases with time until the bromine source is depleted. The process is shorter at higher applied temperatures and appears instantaneous at 310 degrees C and above. However, the maximum bromination yield is independent of the applied conditions and ranges from 64 to 70%. Additionally, the influence of oxidizing conditions on the bromination reaction and the effect of ZnO on decomposition of TBBPA were investigated in this study.

Studies on bromination and evaporation of zinc oxide during thermal treatment with TBBPA.

Thermodynamic considerations indicate that base metal oxides such as ZnO, PbO, Cu2O, etc. should easily react with HBr, the main gaseous product from the thermal decomposition of tetrabromobisphenol A (TBBPA), to form low boiling point metallic bromides suitable for volatile separation. In this work a differential scanning calorimeter and laboratory-scale furnace was used to investigate the scope and conditions for the bromination of ZnO by the thermal decomposition of TBBPA. The formed solid, condensed, and gaseous products were analyzed by X-ray diffraction analysis, electron probe microanalysis, inductively coupled plasma analysis, ion chromatography, and gas chromatography coupled with mass spectrometry. The results obtained in this study indicate that the bromination of ZnO occurred at 272 degrees C (DSC) and above 290 degrees C (furnace) with an effectiveness of 41, 64, and 81% dependent on the experimental conditions. Volatilization of the formed ZnBr2 began at 340 degrees C and had a 45% yield at 650 degrees C. This yield corresponded to 28-36% of the original zinc content in the mixture under the present experimental conditions.

Fate of PCDD/PCDF during mechanical-biological sludge treatment.

In this preliminary study the seventeen 2,3,7,8-substituted congeners of PCDD/PCDF were analyzed at the inlet and outlet water and for three sewage sludge samples taken from different treatment stages to check behaviours of PCDD/PCDF at a municipal wastewater treatment plant (MWTP) in Poland. At the inlet (untreated sewage) water dominated PCDD congeners, whereas in the outlet (treated water) dominated the PCDF congeners. The octaCDD, 1,2,3,4,6,7,8-heptaCDD/CDF and octaCDF congeners dominated in all of the sludge samples. The total toxicity load gradually increased in the series excess, digested and dewatered sludge and amounted to 12.2, 14.4 and 16.9ngI-TEQkg(-1).

Application of the conductor-like screening model for real solvents for prediction of the aqueous solubility of chlorobenzenes depending on temperature and salinity.

The conductor-like screening model for real solvents (COSMO-RS) is applied to the prediction of the aqueous solubility of chlorobenzenes (CBZs) in a liquid-liquid and liquid-solid equilibrium. The solubilities of CBZs at temperatures ranging from 5 to 60 degrees C are reported, and the enthalpies of solution are derived from van't Hoff plots. The salting effect of 12 chlorobenzenes is determined for sodium, potassium, and calcium solutions at concentrations ranging from 0.01 to 3.5 mol/L. A new experimental aqueous solubility value is given for the isotopic labeled 1,2,4-trichlorobenzene determined at 25 degrees C by the generator column procedure. The COSMO-RS method presented in this study can be useful to estimate the magnitude of the salt effect and temperature influence on the behavior of any chlorobezene under environmental conditions.