Methane water versus

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. 

Figure 5.15 is the pseudo-binary pressure versus excess water composition diagram for the methane+propane+water system at a temperature of 277.6 K. At 277.6 K the hydrate formation pressures are 4.3 and 40.6 bar for pure propane (sll) and pure methane (si) hydrates, respectively, as shown at the excess water composition extremes in Figure 5.15. As methane is added to pure propane, there will be a composition at which the incipient hydrate structure changes from sll to si as seen in the inset of Figure 5.15, this composition is predicted to be 0.9995 mole fraction methane in the vapor—a very small amount of propane added to a methane+water mixture will form sll hydrates.

Learning of chemical concepts is assessed through two tests and homework assignments. Many of the questions on the tests require students to connect chemical concepts to issues relevant to chemical evolution or chemical processes important for life. For example, questions look at the possibility of life on Titan and the potential for successful life on Titan. This requires students to address this possibility in terms of energy sources, temperature, chemical processes given Titan s atmosphere, and the differences in chemical and physical processes in a liquid methane environment versus water. 

Fischer-Tropsch activity, selectivity and deactivation data obtained in fixed bed reaction tests of Co/Si02 catalysts are summarized in Table 1. The turnover frequencies (TOFs) or site time yields based on H2 uptake and on rate measured after 20 hours of reaction agree within a factor of two with those reported for other cobalt catalysts [2, 3, 25-27]. CO conversion and methane selectivity versus time for Cab-O-Sil supported cobalt at both low and high space velocities are shown in Figure 1. It can be seen that at high conversion the catalyst deactivates rapidly while at low conversion the catalyst appears to be stable. The conversion is proportional to the water partial pressure thus water could be causing this deactivation. 

Natural gas enrichment (CO2/CH4 membrane separation) is employed to remove CO2 from natural gas streams as well as for recovering CO2 in enhanced oil recovery processes. Methane recovery from landfill sources is an additional application. Membranes are employed for hydrogen recovery in ammonia ptuge gas, H2/CO ratio adjustments in hydrogen production (HYCO process), in hydrocracker and hydrotreater ptuge gas, and in catalytic reformer off-gas. With the very high permeability of water versus common gases, membranes have fotmd applications for air dehydration and natural gas dehydration. Additional applications include helium recovery and H2S removal from natural gas. 

Waters have measured relative rates of p-toluenesulfonyl radical addition to substituted styrenes, deducing from the value of p — 0.50 in the Hammett plot that the sulfonyl radical has an electrophilic character (equation 21). Further indications that sulfonyl radicals are strongly electrophilic have been obtained by Takahara and coworkers , who measured relative reactivities for the addition reactions of benzenesulfonyl radicals to various vinyl monomers and plotted rate constants versus Hammett s <7p and Alfrey-Price s e values these relative rates are spread over a wide range, for example, acrylonitrile (0.006), methyl methacrylate (0.08), styrene (1.00) and a-methylstyrene (3.21). The relative rates for the addition reaction of p-methylstyrene to styrene towards methane- and p-substituted benzenesulfonyl radicals are almost the same in accord with their cr-type structure discussed earlier in this chapter. 

To evaluate the phase equilibria of binary gas mixtures in contact with water, consider phase diagrams showing pressure versus pseudo-binary hydrocarbon composition. Water is present in excess throughout the phase diagrams and so the compositions of each phase is relative only to the hydrocarbon content. This type of analysis is particularly useful for hydrate phase equilibria since the distribution of the guests is of most importance. This section will discuss one diagram of each binary hydrate mixture of methane, ethane, and propane at a temperature of 277.6 K. 

Figure 5.16 is the pseudo-binary pressure versus excess water composition diagram for the methane + ethane + water system at a temperature of 277.6 K. In the diagram, pure ethane and pure methane both form si hydrates in the presence of water at pressures of 8.2 and 40.6 bar, respectively. Note that between the compositions of 0.74 and 0.994 mole fraction methane, sll hydrates form at the incipient formation pressure. Similar to the methane + propane + water system, only a small amount of ethane added to pure methane will form sll hydrates. 

Therefore, key advantages of the QCM method are that much smaller samples (one drop of water) and hence shorter times (15 min/temperature step versus several hours for conventional methods) are required for these hydrate phase equilibria measurements. The authors applied this system to measure dissociation temperatures of gas hydrates, such as methane, nitrogen, and oxygen hydrates. 

The biologically active surface (to 10 cm depth) has a methane flux that varies between 1 and 100 mmC/m2 per day. The hydrate results from free gas and gas dissolved in water. Two types of hydrate fabric result (1) porous hydrates, from accumulation of bubbles of free gas and (2) massive hydrates, with twice the density of porous hydrates (0.9 g/L versus 0.4 g/L). In the recent Raman spectroscopy, southern Hydrate Ridge experiments by the MBARI (Hester et al., 2005), the near-surface hydrate Raman specta contained significant amounts of free gas as well as hydrates, with only a trace of hydrogen sulfide in the methane gas. 

Figure 2 Is a plot of 6 D-H2O versus 6 D-CH for samples obtained from littoral zone sediments of several freshwater lakes and from several shallow (1 m or less water depth) areas of the Tampa Bay estuary. Also shown on Figure 2 are lines that describe predicted 6D-H2O/6D-CH Isotopic pairs resulting from varying the relative contributions to methane production of the acetate dissimilation and CO2 reduction pathways. This model was originally proposed by Woltemate et al. (22) and used In that study to estimate that methyl group transfer (from acetate or other methyl group donors such as methanol) was responsible for about 76% of total methane production In the sediments of Wurmsee, a shallow lake near Hannover, FRG.

Fig. 14.2 Guest molecules versus hydrate cage size range (from Sloan 1998). Left line shows the size of typical hydrateforming guest molecules. The number of water molecules in gas hydrates shown, corresponds to single guest gas occupants listed on the left. The related type of structures formed are listed on the left. As an example, methane has a typical hydration number of 5V and occupies both cages of structure I.

Arts. Water and methane are very nearly the same molecular mass 16 versus 18). The difference in boiling points is due to the large difference in the intermolecular attractions present in the two compounds. Methane has only the weak attractions of dispersion forces. Water has the strongly polar 0—H... 

Solvent water s ability to accommodate a solute s dipolarity appears to be more localized than one might expect. This is somewhat disappointing, because the simple dipole moment is easily available by measurement or calculation. This failure of simple dipole moment is evidenced by the fact that measured log P values for o-dichlorobenzene and p-dichlorobenzene are indistinguishable experimentally (3.43 versus 3.44) while their dipole moments are quite different (2.3D and OD). Note that the difference in solvent-accessible-surface-area (SASA), if pertinent, should also make log P for the ortho isomer appreciably lower (SASA ortho = 2 2.52 para = 285.60). Furthermore, the sequential chlorination of methane gives evidence that it is the localized bond dipoles that lower log P, and that in multiples they may shield each other. See Figure 7.1. 

If the feed mole ratio of water to methane is X, and if equilibrium is achieved at reactor effluent conditions of 1073 K and 200 psia, determine the composition of the effluent gas for values of X from 1 to 10. Prepare plots of the extents of reactions (I) and (II), as well as plots of the fractions of the original CH4 that are converted to CO and CO2 versus X. 

The aforementioned tendency does not hold here. On the contrary, many very selective polymers also have a very high permeability Numerous polymers are available v ith water vapor selectivities of 5000 and more. For the following calculation a two-component water vapor/methane mixture has been assumed with 0.2% water vapor. The membrane unit shall reduce this water content by one order of magnitude i.e. the retentate water concentration has been set to 0.02%. The simple equation (10) cannot be applied, the equations first derived by Weller and Steiner [322] have been used for the calculation of methane loss and the equation of Saltonstall [323] for calculation of membrane area. The methane loss is simply defined by methane permeate stream divided by methane feed stream times 100. In Fig. 7.14 the methane loss is plotted versus membrane selectivity for two different pressure ratios. 

A long-chain fatty alcohol of molecular mass 242 Da is ionized via positive-ion chemical ionization with methane, isobutane, hydrogen, water, or methanol as the reagent gas. The two major ions in the spectrum are miz 243 and 225 (the loss of water from the protonated molecule). Predict how the ratio of ion abundances of m/z 243 versus m/z 225 will change with those different reagent gases. Rationalize your answers with a reasonable explanation. The proton affinity of this alcohol is 200 kcalmoD ... 

Figure 3.28 Adiabatic temperature rise (termed exotherm here) of reformate containing 53.1 vol.% hydrogen, 7.7 voL% carbon monoxide, 7.5 vol.% carbon dioxide, 31.4 vol.% steam and 0.3 vol.% methane versus carbon monoxide conversion by water-gas shift [57. ...

FIG. 4.4 The surface conditions of different places in the solar system plotted on a phase diagram of temperature versus pressure. Note how the Earth sits in the liquid water region and Titan sits in the liquid methane region, but other places fall outside these regions and do not maintain surface oceans. 

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