Thermodynamic databases

Equilibrium combustion product compositions and properties may be readily calculated using thermochemical computer codes which minimize the Gibbs free energy and use thermodynamic databases... 

The field of chemical reaction engineering (CRE) is intimately and uniquely connected with the design and scale-up of chemical reacting systems. To achieve the latter, two essential elements must be combined. First, a detailed knowledge of the possible chemical transformations that can occur in the system is required. This information is represented in the form of chemical kinetic schemes, kinetic rate parameters, and thermodynamic databases. In recent years, considerable progress has been made in this area using computational chemistry and carefully... 

The example reactions considered in this section all have the property that the number of reactions is less than or equal to the number of chemical species. Thus, they are examples of so-called simple chemistry (Fox, 2003) for which it is always possible to rewrite the transport equations in terms of the mixture fraction and a set of reaction-progress variables where each reaction-progress variablereaction-progress variable —> depends on only one reaction. For chemical mechanisms where the number of reactions is larger than the number of species, it is still possible to decompose the concentration vector into three subspaces (i) conserved-constant scalars (whose values are null everywhere), (ii) a mixture-fraction vector, and (iii) a reaction-progress vector. Nevertheless, most commercial CFD codes do not use such decompositions and, instead, solve directly for the mass fractions of the chemical species. We will thus look next at methods for treating detailed chemistry expressed in terms of a set of elementary reaction steps, a thermodynamic database for the species, and chemical rate expressions for each reaction step (Fox, 2003). 

Once we have calculated the distribution of species in the fluid, we can determine the degree to which it is undersaturated or supersaturated with respect to the many minerals in the thermodynamic database. Only a few of the minerals can exist in equilibrium with the fluid, which is therefore undersaturated or supersaturated with respect to each of the rest. For any mineral A , we can write a reaction,... 

Using the modified thermodynamic database, we simulate reaction over 300 minutes in a fluid buffered to a pH of 7. We prescribe a redox disequilibrium model by disabling redox couples for chromium and sulfur. We set 10 mmolal NaCl as the background electrolyte, initial concentrations of 200 (imolal for CrVI and 800 innolal for H2S, and small initial masses of Cr2C>3 and S(aq). Finally, we set Equation 17.29 as the rate law and specify that pH be held constant over the simulation. 

We can expect the sulfide produced by the bacteria to react with the iron in solution to form mackinawite (FeS), a precursor to pyrite (FeS2). The mineral is not in the default thermodynamic database, so we add to the file the reaction... 

Before running the model, we need to include lactate ion in the thermodynamic database. To do so, we add a redox couple,... 

The simulated C02 fugacity matches the initial reservoir C02 content and indicates that the pH is buffered by C02-calcite equilibrium. Further modelling was carried out using the Geochemists Workbench React and Tact modules with the thermodynamic database modified to reflect the elevated P conditions and kinetic rate parameters consistent with the Waarre C mineralogy. The Waarre C shows low reactivity and short-term predictive modelling of the system under elevated C02 content changes little with time (Fig. 1). 

The existing thermodynamic database focuses on the commodity chemicals sector. Only limited information is available for the ingredients in... 

Thermo-Calc (Sundman et al. 1985, Andersson et al. 2002). ft features a wide spectrum of thermodynamic models, databases and modules making it possible to perform calculations on most problems involving phase equilibria (phase transformation, stable and metastable equilibria, etc.). The calculations are performed using databases produced by an expert evaluation of experimental data. There are thermodynamic databases available for many different systems and applications. 

In the data above, the first line provides the chemical name, a comment, the elemental composition, the phase, and the temperature range over which the data are reported. In lines 2 through 4, the high-temperature coefficients ah..., a7 are presented first followed by the low temperature coefficients. For more information, refer to Kee et al. (Kee, R. J., Rupley, F. M and Miller, J. A., The Chemkin Thermodynamic Database, Sandia Report, SAND87-8215B, reprinted March 1991). 

Thermochemical data are also available from the Internet. Some examples are the NIST Chemical Kinetics Model Database (http //kinetics.nist. gov/CKMech/), the Third Millennium Ideal Gas and Condensed Phase Thermochemical Database for Combustion (A. Burcat and B. Ruscic, ftp //ftp. technion.ac.il/pub/supported/aetdd/thermodynamics/), and the Sandia National Laboratory high-temperature thermodynamic database (http //www.ca.sandia. gov/HiTempThermo/). 

CHEMRev The Comparison of Detailed Chemical Kinetic Mechanisms Forward Versus Reverse Rates with CHEMRev, Rolland, S. and Simmie, J. M. Int. J. Chem. Kinet. 37(3), 119-125 (2005). This program makes use of CHEMKIN input files and computes the reverse rate constant, kit), from the forward rate constant and the equilibrium constant at a specific temperature and the corresponding Arrhenius equation is statistically fitted, either over a user-supplied temperature range or, else over temperatures defined by the range of temperatures in the thermodynamic database for the relevant species. Refer to the website http //www.nuigalway.ie/chem/c3/software.htm for more information. 

Equilibrium combustion product compositions and properties may be readily calculated using thermochemical computer codes which minimize the Gibbs free energy and use thermodynamic databases containing polynomial curve-fits of physical properties. Two widely used versions are those developed at NASA Lewis (Gordon and McBride, NASA SP-273, 1971) and at Stanford University (Reynolds, STANJAN Chemical Equilibrium Solver, Stanford University, 1987). 

IVIINEQL+ uses a thermodynamic database that contains the entire USEPA IVIINTEQA2 database plus data for chemical components that the EPA did not include, so all calculations will produce results compatible with EPA specifications. 

Key material properties for SOFC, such as the ionic conductivity as a function of temperature, are available in refs 36—39. In addition, Todd and Young ° compiled extensive data and presented estimation methods for the calculation of diffusion coefficients, thermal conductivities, and viscosities for both pure components and mixtures of a wide variety of gases commonly encountered in SOFCs. Another excellent source of transport properties for gases and mixtures involved in a SOFC is the CHEMKIN thermodynamic database. ... 

Kee, R. J., F.M. Ruply, and J. A. Miller. 1987. The Chemkin thermodynamic database. Sandia Report SAND987-8215 (Reprinted April 1994). 

The main areas of application for more generalised models have, until recently, been restricted to binary and ternary systems or limited to ideal industrial materials where only major elements were included. The key to general application of CALPHAD methods in multi-component systems is the development of sound, validated thermodynamic databases which can be accessed by the computing software and, until recently, there has been a dearth of such databases. 

STABCAL was also used to construct pE-pH stability fields for chloropyromorphite, hinsdalite, plumbogummite, tricadmium diphosphate, tricopper diphosphate, and hopeite (Fig. 7). These diagrams allow for estimation of stability with respect to pH and to the presence of insoluble sulphides. The NBS thermodynamic database (Wagman et al. 1982) was used as a source of thermodynamic data. The total concentrations chosen for each metal were selected to produce a stability region for the metal phosphate solid. In some cases, this was a very low total concentration (e.g., CTPb =1 x 10 10 M for Pb). In other cases, the total metals concentration was high (e.g., C r.cd— 1 x 10 3 M for Cd). The modelling exercise used typical equilibrium concentrations for MSW bottom ash leachates as shown in Table 2. 

Fig. 10. Uranium dioxide solubility data obtained under nominally reducing conditions, corresponding to values extracted from the literature as given in the figure. Thermodynamic database for uranium from Grenthe et al. (1992) and Bruno Puigdomenech (1989).

Bruno, J. Puigdomenech, I. 1989. Validation of the SKBU1 Uranium thermodynamic database for its use in geochemical calculations with EQ3/6. Materials Research Society Symposium Proceedings, 127, 887-896. 

Kulik, D. A. 2002. Minimising uncertainty induced by temperature extrapolations of thermodynamic data A pragmatic view on the integration of thermodynamic databases into geochemical computer codes. Proceedings of the Workshop on The Use of Thermodynamic Databases in Performance Assessment , 29-30 May 2001, Barcelona, Spain. Organisation for Economic Cooperation and Development OECD, Paris, France, 125-137. 

TCLP TDB TDF THC TBP TEM TLM TM-AFM TOC TRLFS TRU TSP TST TVS Toxicity characteristics leaching procedure Thermodynamic database Tyre-derived fuel Total hydrocarbon Tri-n-butyl phosphate Transmission electron microscopy Triple layer model Tapping mode atomic force microscopy Total organic carbon Time-resolved laser fluorescence spectroscopy Transuranic Total suspended particles Transition state theory Transportable vitrification system... 

The first step in any problem is to run the Chemkin Interpreter, which reads the user s description of a gas-phase reaction mechanism. The CHEMKIN Interpreter also draws on a Thermodynamic Database containing polynomial fits to individual species specific heats,... 

For a problem involving surface chemistry, the next step is to execute the Surface Chemkin Interpreter, which reads the user s symbolic description of the surface-reaction mechanism. Required thermodynamic data can come from the same Thermodynamic Database used by Chemkin or from a separate Thermodynamic Database compiled for surface species. Both Interpreters provide the capability to add to or override the data in the database by user input in the reaction description. The Surface Chemkin Interpreter extracts all needed information about gas-phase species from the Chemkin Linking File. (Thus the Chemkin Interpreter must be executed before the Surface Chemkin Interpreter.) Like the Chemkin Interpreter, the Surface Chemkin Interpreter also provides a printed output and a Linking File. Again, the Surface Linking File is read by an initialization subroutine in the Surface Subroutine Library that makes the surface-reaction mechanism information available to all other subroutines in the Library. 

Table 16.6 Thermodynamic database for the effect of nearest-neighbor interactions on...

Once formed, H2S° would partially dissociate into HS- and H+. A small amount of H2As03 and H+ would form from the dissociation of H3As03°. Some H3As03° and H2S° could also react to produce thioarsenic species, such as AsS(OH)HS (see also Section 2.7.3). Depending on the accuracy and completeness of their thermodynamic databases, geochemical computer models may be able to identify the major reactions and estimate the activities of their products. 

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