Methane in water

Previous research by our groiqD [6] has confirmed literature reports [1,2] that it is possible to photolyze methane, saturated with water vapcff, to produce methanol and hydrogen. In a modification of the above ejq)eriment, we were also able to photolyze methane sparged throu a photochemical reactor filled with water. Recently, we began investigating the photocatalytic conversion of methane in water. 

Lekvam, K. Bishnoi, P.R. (1997). Dissolution of methane in water at low temperatures and intermediate pressures. Fluid Phase Equilibria, 131, 297-309. 

The mole fraction of methane in water under equilibrium at a partial pressure of 0.20 atm is... 

Culberson, O.L. and McKetta, J.J., Jr. Phase Equilibria in Hydrocarbon-Water Systems III—The Solubility of Methane in Water at Pressures to 10,000 psia, Trans., AIME (1951) 192, 223-226. 

A reaction closely related to acetal formation is the polymerization of aldehydes. Both linear and cyclic polymers are obtained. For example, methanal in water solution polymerizes to a solid long-chain polymer called paraformaldehyde or polyoxymethylene ... 

Exercise 16-20 Write a reasonable mechanism for the polymerization of methanal in water solution under the influence of a basic catalyst. Would you expect base catalysis to produce any 1,3,5-trioxacyclohexane Why ... 

There are only few data sets of aqueous solubility for systems with hydrates (1) methane and ethane solubility in water as a function of temperature ramping rate (Song et al. 1997), (2) carbon dioxide solubility in water by Yamane and Aya (1995), (3) methane in water and in seawater (Besnard et al., 1997), (4) methane in water in Lw-H region [see Servio and Englezos (2002) and Chou and Burruss, Personal Communication, December 18,2006, Chapter 6], As a standard for comparison, Handa s (1990) calculations for aqueous methane solubility are reported in Table 4.3. 

The aerobic oxidation of methane in water catalyzed by [Pt(Mebipym)Cl2] [PV2Mo1004o]5 (Mebipym = N-methy-2,2 -bipyrimidine) complex supported on Si02 was reported [149]. The conjugation of [PV2Mo1004o]5 to a known Pt2 + -bipyrimidine complex by electrostatic interaction could fadlitate the oxidation of the Pt2 + intermediate to a Pt4 + intermediate by 02, resulting in the catalytic aerobic oxidation of methane to methanol in water and then surprisingly further to acetaldehyde via a carbon-carbon coupling reaction. 

Table I. The Solubility of Methane in Water and in Organic Solvents at 77°F and at Pressures up to 140 Atmospheres...

The unfavorable Gibbs energy (AG° > 0) for the dissolution of methane in water is the result of a strongly negative entropy of solution (AA° 0), which prevails over... 

The proximal radial distribution functions for carbon-oxygen and carbon-(water)hydrogen in the example are shown in Fig. 1.11. The proximal radial distribution function for carbon-oxygen is significantly more structured than the interfacial profile (Fig. 1.9), showing a maximum value of 2. This proximal radial distribution function agrees closely with the carbon-oxygen radial distribution function for methane in water, determined from simulation of a solitary methane molecule in water. While more structured than expected from the... 

Surprisingly, the low solubility of small-sized particles does not stem from a weak interaction of particles with their surrounding water environment (77). For example, the heat of solvation of methane in water at ambient temperature is of similar magnitude as the heat of vaporization of pure liquid methane (80). The positive solvation free energy of small apolar particles at low temperatures is the consequence of negative solvation entropy, which overcompensates for the negative solvation enthalpy. It is widely believed that this entropy penalty is caused by the orientation order introduced to the hydration-shell water molecules as they try to maintain an intact hydrogen bond network (77). Parallel to the entropy decrease observed for low... 

Fig. 3 Calculated energies of solvation v. experimental values for (from left to right) water, ethanol, methanol, and methane in water. The diagonal line gives perfect agreement, the open circles results with the joint density-functional theory for electronic structure of solvated systems, and the other symbols results from different continuum approaches. Reproduced with permission from ref. 54. 

Haas J. A. (1978) An empirical equation with tables of smoothed solubilities of methane in water and aqueous sodium chloride solutions up to 25 weight percent, 360 °C, and 138 MPa. US Geological Survey Open-File Report 78-1004. 

Culberson, O. L. McKetta, J. J. Phase equilibria in hydrocarbon-water systems. 111. The solubility of methane in water at pressures to 10,000 psia. Pet. Technol. 1951, 3, 223-226. 

Three systems were selected for examination, namely the solubilities of oxygen, carbon dioxide, and methane in water -1- sodium chloride. An accurate semiempirical equation [64] was used to express the composition dependence of the osmotic coefficient in water-r sodium chloride. The results of the calculations are presented in Fig. 1 and Table 1. One can see that Eq. (26) provides an accurate correlation for the gas solubility in solutions of strong electrolytes. In addition, the fluctuation theory allows one to use the experimental solubility data to examine the hydration in water (l)-gas (2)-cosolvent (3) mixtures. 

In the present paper, the method which the authors employed previously to derive an expression for the solubility of various proteins in aqueous solutions, has been extended to the solubility of gases in mixtures of water + strong electrolytes. One parameter equation for the solubility of gases has been derived, which was used to represent the solubilities of oxygen, carbon dioxide and methane in water -i- sodium chloride. In additions, the developed theory could be used to examine the local composition of the solvent around a gas molecule. The results revealed that the oxygen, carbon dioxide and methane molecules are preferentially hydrated in water-i-sodium chloride mixtures. A similar result was obtained for the water -i- methane -i- sodium chloride by molecular dynamics simulations [72]. 

One of the typical minimized clusters 1 (methane) 10 (waters) is presented in Figure la,b. They show that the methane molecule is enclosed in a cavity formed by water molecules. The two spheres centered on a methane molecule, with radii of 3.6 and 5.35 A, correspond to the first maximum and the first minimum in the radial distribution function goo = goo(roc) in dilute mixtures of methane in water. It is worth noting that... 

Figure 3.9 Solubility of methane in water (after Bonham, 1978. Reprinted by permission of the American Association of Petroleum Geologists).

The American Association of Petroleum Geologists Bulletin, Vol. 72, no. 1, pp. 21-32 Bonham, L.C., 1978. Solubility of methane in water at elevated temperatures and pressures. 

In figure 8.11, we also plot the values of G 4 for a series of linear alcohols CH3(CH2) iOH as a function of n at t = 0 °C. We also show the value of G ]ww at the same temperature. Note that the value G( nv is quite near the value that can be extrapolated from the linear plot of G (n) at n = 0 (n = 1 corresponds to methanol, n = 2 to ethanol, and n = 0 correspond to an extrapolated alcohol with no methyl group). This is an important observation and it might indicate that the value of G( vw is not very sensitive to the extent of the structure of water. This is in sharp contrast to the behavior of the entropy of solvation of inert gases in water, and in a series of alcohols. It is known (Ben-Naim 1987) that the value of A6 4 of say, argon or methane in water, is far more negative than the value that one can extrapolate from the solvation entropy in a series of alcohols. 

There is another, very important and large repository of methane methane hydrates (also known as gas hydrates or clathrates Kvenvolden 1988).They comprise ice in which the interstices of the lattice house small molecules, such as methane, ethane, carbon dioxide and hydrogen sulphide. In fact, enough gas needs to be present to fill 90% of the interstices in order for the hydrate to form, and it has a different crystal structure from normal ice (Sloan 1990). If fully saturated, the most common crystalline structure can hold one molecule of methane for every 5.75 molecules of water, so lm3 of hydrate can contain 164 m3 of methane at STP (see Box 4.8).The solubility of methane in water is insufficient to account for hydrate formation, and a major nearby source is required, typically methanogenesis, based on the dominance of methane (99%) and its very light isotopic composition (813C generally <—60%o see Section 5.8.2). 

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