Methane binary systems

The use of the K-factor charts represents pure components and pseudo binary systems of a light hydrocarbon plus a calculated pseudo heavy component in a mixture, when several components are present. It is necessary to determine the average molecular weight of the system on a methane-free basis, and then interpolate the K-value between the two binarys whose heavy component lies on either side of the pseudo-components. If nitrogen is present by more than 3-5 mol%, the accuracy becomes poor. See Reference 79 to obtain more detailed explanation and a more complete set of charts. 

The dilated van Laar model is readily generalized to the multicomponent case, as discussed in detail elsewhere (C3, C4). The important technical advantage of the generalization is that it permits good estimates to be made of multicomponent phase behavior using only experimental data obtained for binary systems. For example, Fig. 14 presents a comparison of calculated and observed -factors for the methane-propane-n-pentane system at conditions close to the critical.7... 

Data for the hydrogen sulfide-water and the methane-n-hexane binary systems were considered. The first is a type III system in the binary phase diagram classification scheme of van Konynenburg and Scott. Experimental data from Selleck et al. (1952) were used. Carroll and Mather (1989a b) presented a new interpretation of these data and also new three phase data. In this work, only those VLE data from Selleck et al. (1952) that are consistent with the new data were used. Data for the methane-n-hexane system are available from Poston and McKetta (1966) and Lin et al. (1977). This is a type V system. 

Although comparisons for the steam-methane system have been presented, similar trends were noted for the other binary systems previously published by Wormald, namely mixtures of steam with nitrogen, carbon dioxide, n-hexane, and benzene. 

The interaction parameters for binary systems containing water with methane, ethane, propane, n-butane, n-pentane, n-hexane, n-octane, and benzene have been determined using data from the literature. The phase behavior of the paraffin - water systems can be represented very well using the modified procedure. However, the aromatic - water system can not be correlated satisfactorily. Possibly a differetn type of mixing rule will be required for the aromatic - water systems, although this has not as yet been explored. 

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. 

Pluto, with a diameter of 2300 km, has now been demoted from the smallest planet to one of the largest Kuiper belt objects. Pluto and its satellite Charon could be considered a binary system because they are closer in size than any other known celestial pair in the solar system and the barycenter of their orbits does not lie within either body. There are also two smaller moons, Nix and Hydra. All four bodies are likely KBOs with similar compositions. Pluto has a thin atmosphere containing N2, with minor CH4, CO, and Ar. Curiously, the face of Pluto oriented towards Charon contains more methane ice, and the opposite face contains more nitrogen and carbon monoxide ice. 

About the same time as the initial measurements of sH with methane and adamantane in the Colorado School of Mines (CSM) laboratory by Lederhos et al. (1992), Becke et al. (1992) surmised that they measured the sH equilibrium for methane + methylcyclohexane. Structure H phase equilibria data were reported for binary systems with methane as the help gas (Mehta and Sloan, 1993, 1994, 1996 Thomas and Behar, 1994), with methane and nitrogen as the help gas (Danesh et al., 1994), and binary systems with salt (Hutz and Englezos, 1995). 

Robinson and Bailey (1957) and Robinson et al. (1959) studied the VLE in the ternary mixtures of hydrogen sulfide + carbon dioxide + methane. These investigations also included a few points for the binary system H2S + C02. The points for the binary mixtures were at temperatures between 4° and 71 °C and at pressures from 4 to 8 MPa. 

Chen, R.J.J. Chappelear, P.S. Kobayashi, R. Dew-point loci for methane-hexane and methane-heptane binary systems. J. Chem. Eng. Data 1976, 21 (2), 213-219. 

In Figure 3.4,1 the results for the methane and n-pentane (Knapp et al. 1982) binary system are presented. This is a typical mixture for which the van der Waals one-fluid mixing rules with a single constant binary interaction parameter performs very well... 

Figure 3.4.1. VLE correlation of the methane and n-pentane binary system at 310, 377, and 444 K with the IPVDW mixing rule and the PRSV equation of state. The lines represent VLE results calculated with the binary interaction parameter ki2 = 0.0215. (Data are from the DECHEMA Chemistry Series, Gmehling, and Onken 1977, Vol. 6, p. 445 data files for this system on the accompanying disk are C1C5310.DAT, C1C5377.DAT, and C1C5444.DAT.)...

The correlation of data for the methane and pentane binary system is shown in Figure 4.2.1. In this case the van Laar excess Gibbs free-energy model has been used in the HVO model the two model parameters were fitted to VLE data on the 277 K isotherm, and the vapor-liquid equilibria at higher temperatures were predicted with the same temperature-independent parameters. The results are very good in this case and similar to those obtained with the IPVDW and 2PVDW models. 

Figure 5.3.1. VLB predictions for the methane and heptane binary system using the HVOS (solid lines) and LCVM (dashed lines) models. See text for details. (Measured data (O, and , ) reported in the DECHEMA Chemistry Data Series, Knapp et al.

It has been established from these studies that the different catalytic properties of transition metal oxides (chromium, cobalt) on zirconium dioxide are attributed to their different acidic properties determined by TPDA and IR-spectroscopy. The most active catalyst is characterized by strong acidic Bronsted centers. The cobalt oxide deposited by precipitation on the zirconium-containing pentasils has a considerable oxidative activity in the reaction N0+02 N02, and for SCR-activity the definite surface acidity is necessary for methane activation. Among the binary systems, 10% CoO/(65% H-Zeolite - 35% Z1O2)... 

Figure 3.21 Examples of binary solid-supercritical fluid systems with a temperature minimum in the SLV line (a) carbon dioxide-solid systems (McHugh and Yogan, 1984) (b) methane-naphthalene system (van Hest and Diepen, 1963).

Figure 5.1 A comparison of calculated (lines) and experimental (symbols) data for the methane-ethane binary system. For these calculations k) is 0.02 (Igel, 1985). (14.504 psi = 1 bar)...

The fit of the last binary pair, the methane-octane system, is shown in figure 5.3. This fit was obtained with a value of kij equal to 0.01. A few words of caution are warranted in this case. As noted in chapter 3, methane-hydrocarbon mixtures are expected to deviate from type-I behavior if the methane-solute carbon ratio is greater than 5. The P-x data shown in figure 5.3 are far above the temperatures where a three-phase LLV line is expected for this binary system. However, a three-phase LLV line is predicted near the critical point of methane using A ,y equal to 0.01. 

Radically different binary phase behavior is found for the methane-TMB and the methane-methanol systems. This suggests that TMB can be extracted from methanol. To verify this conjecture experimental information was obtained on the TMB-methanol-methane system to ascertain whether the weak TMB-methanol complex can be broken by nonpolar methane. Interestingly, carbon dioxide, ethane, and ethylene, all much better supercritical solvents than methane, dissolve both methanol and TMB to such a large extent that they are not selective for either component. But with methane, the interactions between methane and TMB are strong enough to maintain a constant concentration of TMB in the extract phase as TMB is removed from the methanol-rich liquid phase. This means that the distribution coefficient for TMB increases as the concentration in the liquid phase decreases. We know of no other system that exhibits this type of distribution coefficient behavior. 

Kohn, J. P. 1967. Volumetric and phase equilibria of methane-hydrocarbon binary systems at low temperatures and high pressures. Chem. Eng. Progr. Symp. Ser. 63 57. 

Four binary systems of methane are included in Table III. The use of a zero value of v is tested on three of them and found to give about the same results as the best nonzero value. It appears that v = 0 for all these systems, and only one interaction constant, c, needs to be deter-... 

Another system for which success is better than might be expected is the C02-methane binary shown in Figure 2. Here very accurate data over a wide range of conditions have recently become available (23,24), for which Professors Kidnay and Kobayashi and their students deserve special praise. This system is very nonideal (owing to the C02 quadru-pole), and is shown on a very expanded scale rms errors in K-value at each temperature, except for the lowest, were less than 3%, and the smooth trend in Ct exhibited for data from two different sources demonstrates really remarkable consistency of results between two laboratories. The points below — 89°C are essentially for C02 well below its triple point near infinite dilution in methane. Although C02 liquid properties were extrapolated carefully into this region to obtain RKJZ parameters, the apparent S-curve in Cij may be an artifact of the extrapolation. 

There is one kind of limitation which, although difficult to summarize concisely, should be mentioned, since it might come as an unpleasant surprise to the uninitiated. That is that the RKJZ or Soave models cannot represent certain details of light hydrocarbon systems at subambient temperatures to anything close to experimental accuracy. This kind of limitation was difficult to distinguish from systematic experimental error before the development of more accurate experimental techniques, notably by Kobayashi and co-workers and Kahre, who have measured low-temperature phase behavior for methane binaries (32,33,34, 35,36). 

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