Starting from the relationship between Gibbs free energy and equilibrium constant of a chemical reaction (ECCR) and taking into account its temperature dependence according to Kirchhoff, Eq. (12), we arrive at the three-parametric Eq. (26). In going this way, we employ the relationship between the ECCR and the degree of conversion of the solid phase using Eqs. (20) and (21). We find that there is a compensating effect between the coefficients of the equation (i.e., a 1 ; a 2 ) in the form of a linear equation, which has been attributed to the enthalpy-entropy compensation. According to current state of knowledge, this result applies both to the chemical reactions resulting in individual chemical bond formation as well as in thermal decomposition. When the heat capacity of such chemical reactions decreases linearly along with temperature, it can adopt the value of the (arithmetic mean) average, and the negative sign determines the elements of the functional equations valid for theoretical (Eq. 26) and experimentally fit (Eq. 32) states. For calcite, several possibilities arising from equilibrium changes in the conversion rate vs. temperature are compared by taking into account the CDV L'vov theory.
List of symbols AbstractThe adsorption process at near ambient temperatures indicated that the EEC (enthalpy-entropy compensation) is affected by three basic thermodynamic values: ∆H, ∆S and T. The consequence is that it is possible to determine an isosteric straight (symbol H − S) without experimental studies based on the slope coefficient T iso , which is the constant arising from the expected temperature range (about 0-60 °C). Therefore, EEC curves can be obtained by appropriate modification of the temperature range. In the case of entropy of adsorption, the decisive influence is the entropy of gas. For visualization and characterization of this impact, we proposed resolute pointer µ (Eq. 25), through which it is observed that for small values of the equilibrium vapor pressure, as P → 0, there are significant deviations from the isosteric straight H − S. The case where P → P 0 followed a gradual grouping of experimental data in accordance with the relationship with H − S. We used the three-parameter equation for exothermic processes. For the extrapolated conditions, the so-called point of zero adsorption represented the enthalpy and entropy of adsorption, whose values are analogous to previous results in the literature, which can be considered an appropriate analytical method to determine these two thermodynamic values.
The thermodynamic aspects of the methods commonly used in thermogravimetric analysis, that is, isothermal and dynamic, are presented. Models for isoconversional variants of dynamic methods are accepted. For the thermal dissociation of the solid phase, the free enthalpy of the system, called the Gibbs free energy state, and the stoichiometric principles according to de Donder's extent of reaction, were proposed as the starting point, binding the dissociative pressure in the gas phase with the rate of solid phase conversion. It was found that the isothermal methods and, surprisingly, the dynamic methods, occur in one system group, although with different energetic activity, whereas isoconversional variants of dynamic methods represent opposite effects in this range. Off-distance, which is formally defined as D = ΔΔ G, was proposed for the quantification of each analyzed case. According to the presented considerations, the isothermal and dynamic methods are dominated by enthalpy, whereas isoconversional methods are dominated by entropy.
A coke oven battery is not considered as a significant source of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) emissions; however, due to small amounts of chlorine in coal dioxins, dibenzofurans may be formed. The paper presents the attempts to determine the level of emission of PCDDs/PCDFs from the COB underfiring system and to confront the obtained results with the calculations based on the mass balance of chlorine in the coking process and reactions of both chlorophenols formation and PCDDs and PCDFs formation from mono-and polychlorophenols. There were PCDDs/PCDFs concentrations measured in flue gases from the underfiring system of two COBs at a Polish coking plant. The measurements included both an old and a new battery. The obtained concentrations of PCDDs/ PCDFs were lower than reported in the literature (0.5-1.7 ng I-TEQ/Mg coke ), while the results for old COB were on average 3 times higher than for the new one. It was found that PCDDs/PCDFs emission from COB underfiring system is insignificant and that PCDDs/PCDFs formation during coal coking should consider the mechanisms of their formation from mono-and polychlorophenols, as well as the influence of process parameters on the synthesis.
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