Thermodynamic equilibrium calculations

Shikazono (1976) attempted to interpret this Na-K-Ca geothermometer based on thermodynamic equilibrium calculation. 

The processing of hydrocarbons always has the potential to form coke (soot). If the fuel processor is not properly designed or operated, coking is likely to occur (3). Carbon deposition not only represents a loss of carbon for the reaction but more importantly also results in deactivation of catalysts in the processor and the fuel cell, due to deposition at the active sites. Thermodynamic equilibrium calculations provide a first approximation of the potential for coke formation. The governing equations are ... 

We also made thermodynamic equilibrium calculations to see how much methane could be formed by methanation of carbon oxides. These calculations show that, for all conditions within the reactor tube, it is possible (thermodynamically) to form methane in quantities even greater than those observed. 

One such difficulty is that, while it appears that [Sn2 ] levels may be as high as 400 /iM in some hypoxic environments, the precise number (n) of sulfur atoms in these polysulfide species, or even the range of n, is uncertain. Bouleague (16) discusses some of the thermodynamic equilibrium calculations which may be used to estimate the distribution of s[Sn2 ] among the various polysulfide species. Another difficulty with these data is that the structures of the thiols (RSH) detected are not well known. Mopper and Taylor (14) identified 13 different thiols in slurries of intertidal sediments from Biscayne Bay (FL), and found at least 20 more thiols whose structures could not be determined. Their observations (Table III) indicate that thiols encountered in natural waters will probably exhibit a broad variety of structures in any one location, but that a relatively small number of compounds may dominate the mixture. 

For non-ideal multicomponent mixtures the multiphase flow calculation can be combined with a more rigorous thermodynamic equilibrium calculation to determine the mixture properties at the interface as discussed by [81, 69, 117]. 

This reaction is in direct competition with the partial oxidation to synthesis gas, complete combustion, and carbon formation on the surface with the olefin essentially and intermediate en route to more stable products. Thermodynamic equilibrium calculations under these severe reaction conditions, predict the formation of carbon, CO, and H2, and only trace amounts of C2H4. Clearly, thermodynamic equilibrium is not obtained since the system is kinetically... 

Acetone is to be scrubbed from dry air into water at 30°C and 1.0 atm. The acetone concentration is 2.60 vol-%. For the condition of thermodynamic equilibrium, calculate the following ... 

Volcanic gases contain sulfur in the form of S02 and H2S. Thermodynamic equilibrium calculations by Heald et al. (1963) indicate that in the anoxic environment of the magma S02 is dominant at high temperatures, whereas H2S is preferred at low temperatures. Accordingly, most active volcanoes... 

Thermodynamic questions often were discussed in connection with the reaction mechanism of the synthesis (102). Montgomery and Weinberger (103) report that the distribution of paraffins obtained at normal-pressure synthesis on cobalt is similar to that predicted by thermodynamic equilibrium calculations. 

Thermodynamic equilibrium calculations are often employed to investigate solubi-... 

Repetition of the calculations for graphitic carbon gives a similar result with shifted boundaries (we need a lower C H2O ratio of approximately 1 2 to eliminate C at 700°C). Thermodynamic equilibrium calculations carried out for very high pressures and temperatures [40] are consistent with our calculations. 

Both reactions R3 and R4 are exothermic, suggesting that methanation is thermodynamically favored at low temperature (typically, 300-400 C) moreover, the large decrease in mole number suggests that high CH4 yield is predicted at high pressure. Figure 8.3 shows the thermodynamic equilibrium calculation for the system of reactions R2-R3 at different temperature and pressure. The software CHEMCAD 6.3.1.4168 has been used for the calculation. 

The reforming properties were also examined in view of thermodynamic equilibrium calculation. Figure 17.12 shows equilibrium gas composition under the condition of S/C = 0.88 at 900 °C as a function of O2/CH4 ratio. Actual O2/CH4 ratio was estimated to be 0.264 from CH4 input and oxygen permeation flux values shown in Table 17.1. The observed gas composition seems to show a good agreement with thermodynamically calculated values. A small deviation of H2 concentration seems to originate from an accuracy of the Q-mass spectrometer. 

Thermodynamic equilibrium calculations of gas-phase composition asfunction of the oxygen ratio (OR) where OR =1 describes full combustion to CO2 and H2O, OR = 0.25 corresponds to the stoichiometric point for partial oxidation to 00 and H2. and at OR = 0 methane decomposition to C and H2 occurs. 

There are in general several steps of refinement to model a gasification system. Zero-dimensional models show the lowest complexity, and rely on empirical correlations or thermodynamic equilibrium calculations. The next step is a onedimensional model that usually requires kinetic expressions either to resolve the space or time coordinate using idealized chemical reactor models. Approaching two- or three-dimensional calculations provokes the use of computational fluid dynamics (CFD) that may incorporate either equiUbriiun or kinetics-based turbulence chemistry interactions. Each step of modeling adds significant complexity and calculation time. 

A review of the literature and thermodynamic calculation procedures for such systems are available in McHugh and Krukonis (1986). The same reference may he studied for thermodynamic equilibrium calculations for the solute distribution between a liquid and a supercritical fluid solvent. 

For non-ideal multicomponent mixtures the multiphase flow calculation can be combined with a more rigorous thermodynamic equilibrium calculation to determine the mixture properties at the interface as discussed by [60, 70, 98]. However, describing the chemical reactor performance under industrial operation conditions the heat balance is normally dominated by the heat of reaction term, the transport terms and the external heating/cooling boundary conditions, hence for chemical processes in which the phase change rates are relatively small the latent heat term is often neglected. 

Lothenbach, B. (2010). Thermodynamic equilibrium calculations in cementitious systems . Materials and Structures 43(10) 1413-1433. 

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