Three thermodynamic databases of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), derived using the Group Additivity approach and two computational molecular modeling methods, Modified Neglect of Diatomic Overlap (MNDO) and Parametrized Model 3 (PM3), respectively, combined with the Scientific Group Thermodata Europe (SGTE) database have been used to model the formation of PCDD/Fs in thermal processes, such as iron ore sintering process. The predictions using the three different databases are compared, and similar thermodynamic conditions of PCDD/Fs formation are found. The comparison of the calculated values with measured results obtained from industrial iron ore sinter plant indicates that the PCDDs and PCDFs found in practice are not in equilibrium with each other. While within each dioxin and furan homologue equilibrium between the isomers appears to be established in industrial processes, reactions between dioxins and furans seem to be kinetically inhibited. This view has been supported by assuming no reaction at all between PCDFs and PCDDs in the simulation. With this assumption, both PCDFs and PCDDs reached partial pressures between 600 and 800 K in the order of magnitude actually found in practice. Taking this restriction into account, the conditions for PCDD/Fs formation were calculated as a function of oxygen partial pressure; temperature; concentrations of carbon, hydrogen, and chlorine; and C/H ratio.

A thermodynamic model has been developed to predict the distribution behavior of Ni, Cu, Co, Fe, S, As, Sb, and Bi in the Outokumpu flash-smelting process, the Outokumpu direct high-grade matte smelting process, and the INCO flash-smelting process. In this model, as many as 16 elements (Ni, Cu, Co, Fe, As, Sb, Bi, S, O, Al, Ca, Mg, Si, N, C, and H) are considered, and two nickel sulfide species are used to allow for modeling of sulfur-deficient mattes. The compositions of the matte, slag, and gaseous phases in equilibrium are calculated using Gibbs free energies of formation and the activity coefficients of the components derived from the experimental data. The model predictions are compared with the known industrial data from the Kalgoorlie Nickel Smelter (Kalgoorlie, Australia), the Outokumpu Harjavalta Nickel Smelter (Harjavalta, Finland), the INCO Metals Company (Sudbury, Canada), and from a number of experimental data. An excellent agreement is obtained. It was found that the distribution behaviors of Ni, Co, Cu, Fe, S, As, Sb, and Bi in the nickel smelting furnace depend on process parameters such as the smelting temperature, matte grade, and partial pressure of oxygen in the process.

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For a specific set of conditions applied in experimental hot-wall reactor investigations for depositing ␣-Al 2 O 3 from precursor gas mixtures containing AlCl 3 , kinetic modelling of the gas-phase reactions was carried out on the basis of rate parameters collected or estimated by Catoire and Swihart. Calculations are presented for upward flow rates of 200, 20, 0.41, and 0.08 slh, a vertical tube reactor ͑27 mm id͒ with a 450 mm isothermal zone ͑1050°C͒ and with varying concentrations of AlCl 3 , CO 2 , H 2 , and HCl in the feed gas at a total pressure of 0.1 bar. The residence times of the gas in the isothermal zone were 0.1, 1, 48, and 250 s. The results show that AlCl 3 decomposes by reacting with CO 2 and H 2 to form AlOCl as the major intermediate species. The water-gas shift reaction, CO 2 + H 2 = CO + H 2 O, is found to take place very slowly at short residence times and much faster at higher ones. The H 2 O generation increases with the AlOCl content in the gas phase. A comparison of the kinetic values with calculated equilibrium compositions shows that for residence times typically used in technical equipment for chemical vapor deposition ͑CVD͒, the gas-phase reactions are kinetically controlled at the temperature and pressure selected. The results may be helpful in understanding the complex reaction mechanisms involved in high-temperature CVD of alumina.