Methane water system

Fig. 9.4. Pa (e) and (e) as a function of the binding energy. The simulations treated 216 water molecules, utilizing the SPC/E water model, and the Lennard-Jones parameters for methane were from [63]. The number density for both the systems is fixed at 0.03333 A 3, and T = 298 K established by velocity rescaling. These calculations used the NAMD program (www.ks.uiuc.edu/namd). After equilibration, the production run comprised 200 ps in the case of the pure water simulation and 500 ps in the case of the methane-water system. Configurations were saved every 0.5 ps for analysis...

Figure 2. Comparison of predicted and experimental phase solubilities for methane-water systems (phase liquid—(%) ( 7) vapor—(O) ( 1) (A) (21,22) (-)...

Methane - Water System. Interaction parameters were generated for the vapor phase and the aqueous liquid phase for the methane -... 

A constant interaction parameter was capable of representing the mole fraction of water in the vapor phase within experimental uncertainty over the temperature range from 100°F to 460°F. As with the methane - water system, the temperature - dependent interaction parameter is also a monotonically increasing function of temperature. However, at each specified temperature, the interaction parameter for this system is numerically greater than that for the methane - water system. Although it is possible for this binary to form a three-phase equilibrium locus, no experimental data on this effect have been reported. 

Figure 5. Experimental and predicted vapor and liquid phase compositions for methane-water system at 250°C ((----) P-R prediction (A) (IT) (A) (IS))...

Ohmura, R. Matsuda, S. Itoh, S. Ebinuma, T. Narita, H. (2005d). Clathrate Hydrate Crystal Growth in Liquid Water Saturated with a Guest Substance Observations in a Methane + Water System. Crystal Growth Design, 5(3), 953-957. 

However, for a multicomponent natural gas mixture, at 5-20 MPa, the subcooling was found to significantly underestimate the driving force (the pure methane-water system showed a far better match between driving force and subcooling). However, above 20 MPa, the driving force was matched well by... 

Figure 5.12 Pressure vs. temperature diagram for methane + water system.

Figure 5.12 is the pressure versus temperature phase diagram for the methane+ water system. Note that excess water is present so that, as hydrates form, all gas is incorporated into the hydrate phase. The phase equilibria of methane hydrates is well predicted as can be seen by a comparison of the prediction and data in Figure 5.12 note that the predicted hydrate formation pressure for methane hydrates at 277.6 K is 40.6 bar. 

Glew DN (1962) Aqueous solubility and the gas hydrates. The methane-water system. J Phys Chem 66 605 - 609... 

Olds, R.H., B.H. Sage, and W.N. Lacey. 1942. Phase equilibria in hydrocarbon systems. Composition of dew-point gas in methane-water system. Ind. Eng. Chem. 34 1223-1227. 

A. Laaksonen and P. Stilbs, Molecular Dynamics and NMR Study of Methane-Water Systems, Mol. Phys., 74 (1991), 747. 

D. P. Beggs and F. H. Field, Reversible reactions of gaseous ions. I. Methane-water system, J. Am. Chem. Soc. 93, 1567-1575 (1971). 

Bercic and Pintar [40] measured gas-liquid mass transfer in a single channel for a wide range of superficial gas and liquid velocities (Figure 11.4). Their experimental set-up allowed the independent variation of bubble and slug length, but most of their experiments were performed under conditions where > tp. They correlated their data for a methane-water system as... 

Figure 24 Potential energy and F order parameter for the methane-water system over the course of the molecular dynamics simulation. The reference value (—0.04) for a fully melted hydrate (horizontal blue line) identifies the beginning of nucleation at 1.2 ps. Snapshots (a) through (f) show the system evolution during the simulation. Adapted from Ref. 119. (For a color version of this figure, please see plate 9 in color plate section.)...

Early computer simulation work on the methane-water system was reported by Dashevsky and Sarkisov. Recent theoretical studies of the methane-water system are the initio molecular orbital calculations of the methane-water pairwise interaction energy by Ungemach and Schaefer and the Monte Carlo computer simulation on the dilute aqueous solution in the isotherroal-isobaric ensemble by Owickl and Scheraga. 

In Approach 1, experimental equilibrium three-phase dissociation pressure data compiled by Sloan (57), consisting of 97 points for the methane-water system from 148.8 to 320.1 K, were used in the parameter optimization. Although the fits were satisfactory, the intermolecular parameters fitted from the experimental data did not have much physical meaning (9). We also found that none of the simple potentials, including Lennard-Jones 12-6, Kihara, and optimized potential from liquid simulation (OPLS), were able to predict both... 

Via this approach, we were able to obtain the reference properties directly from the ab initio potential and methane hydrate P-T equilibrium. Without the need of the composition data, we incorporated 97 data points for the methane-water system (5 in our fitting procedure. The result is shown in Figure 7. The fitted reference properties (A/i =1236 J/mol, A// =1703 J/mol) are within... 

For a methane water system, the impact of the interaction coefficient can be established through regression analysis. The following multiplication factor (f) can be used as a correction factor for the interaction coefficient ... 

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