Methane thermodynamic properties

The process gas of ethylene plants and methyl tertiary butyl ether plants is normally a hydrogen/ methane mixture. The molecular weight of the gas in such processes ranges from 3.5 to 14. The tliermodynamic behavior of hydrogen/methane mixtures has been and continues to be extensively researched. The gas dynamic design of turboexpanders, which are extensively used in such plants, depends on the equations of state of the process gas. Optimum performance of the turboexpander and associated equipment demands accurate thermodynamic properties for a wide range of process gas conditions. 

The thermodynamic properties of a chemical substance are dependent upon its state and, therefore, it is important to indicate conditions when writing chemical reactions. For example, in the burning of methane to form carbon dioxide and water, it is important to specify whether each reactant and product are solid, liquid, or gaseous since different changes in the thermodynamic property will occur depending upon the state of each substance. Thus, different volume and energy changes occur in the reactions... 

Benedict, M., Webb, G.B., and Rubin, L.C. An Empirical Equation for Thermodynamic Properties of Light Hydrocarbons and Their Mixtures, I. Methane, Ethane, Propane and n-Butane, J. Chem. Phys. (April 1940) 8, 334-345. 

The critical properties of hydrazine and nitro-methane 7 are available in the literature. Thermodynamic properties for hydrazine, A arc available from 27 C to 727T. Thermodynamic properties of niirrancihanc are also available.161 The other critical properties have been estimated by the me thod ol Lvdersen.1... 

We conclude that the proximal radial distribution function (Fig. 1.11) provides an effective deblurring of this interfacial profile (Fig. 1.9), and the deblurred structure is similar to that structure known from small molecule hydration results. The subtle differences of the ( ) for carbon-(water)hydrogen exhibited in Fig. 1.11 suggest how the thermodynamic properties of this interface, fully addressed, can differ from those obtained by simple analogy from a small molecular solute like methane such distinctions should be kept in mind together to form a correct physical understanding of these systems. 

The third largest class of enzymes is the oxidoreductases, which transfer electrons. Oxidoreductase reactions are different from other reactions in that they can be divided into two or more half reactions. Usually there are only two half reactions, but the methane monooxygenase reaction can be divided into three "half reactions." Each chemical half reaction makes an independent contribution to the equilibrium constant E for a chemical redox reaction. For chemical reactions the standard reduction potentials ° can be determined for half reactions by using electrochemical cells, and these measurements have provided most of the information on standard chemical thermodynamic properties of ions. This research has been restricted to rather simple reactions for which electrode reactions are reversible on platinized platinum or other metal electrodes. 

There are no reported experimental studies leading to the heat of formation of SlH2F(g). We estimate this value via a linear interpolation between the established A H°(298.15 K) values of SiH (g) and SiF (g) (1 ). The reasonableness of this approach has been demonstrated by Lapidus et al. (2 ), Hunt and Sirtl (3 ), and Seiter and Sirtl (4). Lapidus et al. (2 ) examined the trends in the thermodynamic properties of halogenated silanes and methanes. Hunt and Sirtl (3 ) and Seiter and Sirtl (4) studied the chlorinated silanes and proposed a linear relationship within the sequence SiH (g) to SiCl (g). 

In order to examine the effect of the Kihara parameters on the predicted hydrate equilibrium pressures, a sensitivity analysis was carried out (see also Cao et al. ). In this study we report results for methane (si hydrate former) and propane (sll hydrate former). The Kihara parameter values, as well as the thermodynamic property values, reported by Sloan were taken as the base-reference case and hydrate equilibrium pressures were calculated by perturbing the reference values in the range +(1%-10%). On the other hand, the reported thermodynamic parameters zl// and Ah have a wider range, but as it is going to be discussed later, have a less significant effect on the predictions. 

Figure 1 Sensitivity analysis of the Kihara parameters and the thermodynamic properties for methane. Effect on the predicted equilibrium pressure of (a) energy parameter, e/k, (b) distance parameter, a, and (c) reference chemical potential difference, Ap ...

A sensitivity analysis was performed to examine the effect of the thermodynamic properties and the Kihara parameters on the hydrate equilibrium calculations. It was demonstrated that the Kihara parameters (s/k and a) had a more significant effect on hydrate equilibrium predictions than the thermodynamic properties (Ap and Ah ) for the cases of methane and propane that were examined in this work. It was observed that parameters obtained from one set of experiments could not always be used in correlating successfully other hydrate experimental data sets. This problem was more pronounced in cases that the fitted parameters were to be used for other properties such as virial coefficients or viscosities. Finally, issues such as satisfactory predictions at very high pressures and multiple cage occupancy need to be considered. 

Handa, Y.P. Stupin, D. Thermodynamic properties and dissociation characteristics of methane and propane hydrates in 70-A-radius silica gel pores. J. Phys. Chem. 1992, 96, 8599-8606. 

Setzmann U, Wagner W. A new equation of state and tables of thermodynamic properties for methane covering the range from the melting line to 625 K at pressures up to 1000 MPa. J Phys Chem Ref Data 1991 20 1061. 

Figure 5.1-3 Pressure-enthalpy diagram for methane. [Source W. C. Reynolds, Thermodynamic Properties in SI, Depanment of Mechanical Engineering, Stanford University, Stanford, CA, 1979. Used with permission.)...

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