Hexane/methane system

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. 

MOLECULAR DIFFUSION COEFFICIENTS IN BINARY GASEOUS SYSTEMS AT ONE ATMOSPHERE PRESSURE. N-HEXANE-METHANE AND 3-METHYLPENTANE-METHANE SYSTEMS. 

As discussed in Sec. 4, the icomplex function of temperature, pressure, and equilibrium vapor- and hquid-phase compositions. However, for mixtures of compounds of similar molecular structure and size, the K value depends mainly on temperature and pressure. For example, several major graphical ilight-hydrocarbon systems. The easiest to use are the DePriester charts [Chem. Eng. Prog. Symp. Ser 7, 49, 1 (1953)], which cover 12 hydrocarbons (methane, ethylene, ethane, propylene, propane, isobutane, isobutylene, /i-butane, isopentane, /1-pentane, /i-hexane, and /i-heptane). These charts are a simplification of the Kellogg charts [Liquid-Vapor Equilibiia in Mixtures of Light Hydrocarbons, MWK Equilibnum Con.stants, Polyco Data, (1950)] and include additional experimental data. The Kellogg charts, and hence the DePriester charts, are based primarily on the Benedict-Webb-Rubin equation of state [Chem. Eng. Prog., 47,419 (1951) 47, 449 (1951)], which can represent both the liquid and the vapor phases and can predict K values quite accurately when the equation constants are available for the components in question. 

The proposed methodology was also followed and the best parameter estimates for the various types of data are shown in Table 14.7 for the methane-n-hexane system. As seen, the parameter set (ka, kd) was found to be the best to correlate the VL2E, the LiL2E and the VL2LtE data and another (k , kb) for the VL E data. 

Table 14.7 Parameter Estimates for the Methane-n-Hexane System...

Using the estimated interaction parameters phase equilibrium computations were performed. It was found that the EoS is able to represent the VL2E behavior of the methane-n-hexane system in the temperature range of 198.05 to 444.25 K reasonably well. Typical results together with the experimental data at 273.16 and 444.25 K are shown in Figures 14.14 and 14.15 respectively. However, the EoS was found to be unable to correlate the entire phase behavior in the temperature range of 195.91 K (Upper Critical Solution Temperature) and 182.46K (Lower Critical Solution Temperature). 

VLE data and calculated phase diagram for the methane-n-hexane system [reprinted from Industrial Engineering Chemistry Research with permission from the American Chemical Society],... 

Figure 14.15 LE data and calculated phase diagram for the methane -n-hexane system.

Five critical points for the methane-n-hexane system in the temperature range of 198 to 273 K measured by Lin et al. (1977) are available. By employing the Trebble-Bishnoi EoS in our critical point regression least squares estimation method, the parameter set (k , kb) was found to be the optimal one. Convergence from an initial guess of (ka,kb=0.001, -0.001) was achieved in six iterations. The estimated values are given in Table 14.8. 

Poston, R.S. McKetta, J. "Vapor-Liquid Equilibrium in the Methane-n-Hexane System", J. Chem. Eng. Data, 11,362-363 (1966). 

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 variety of solvents have higher boiling points than that of water but do not have polar structures. The most accessible of these are the hydrocarbons, which come in a series from the smallest (methane) to higher homologs (ethane, propane, butane, and so on) and are abundant in the solar system. Methane, ethane, propane, butane, pentane, and hexane have boiling points of about 109, 184, 231, 273, 309, and 349 K, respectively, at standard terran pressure. Thus, at a mean surface temperature of 95 K, methane (which freezes at 90 K) would be liquid, implying that oceans of methane could cover the surface of Titan. 

The alkane mixtures provide the prototypical examples of type I type V behavior. Methane + hexane (and higher alkanes), ethane + octadecane, and propane + pentatriacontane are all type V. The upper LL regions of these systems are noteworthy in that the temperature difference between the UCEP and the LCEP seems to monotonically increase with increasing carbon number. Ultimately, this trend must reverse as type III behavior sets in, but no indication of this reversal has been observed experimentally. Mixtures of methane with hexane isomers provide unusual examples of type V phase behavior. Type V behavior is exhibited for all isomers except 2,2-dimethyl butane. Ternary mixtures of methane with the 2,2 and 2,3-isomers provide a rare example of tri-critical behavior. Turning to another example, the type V LLV locus becomes extremely short as the asymmetry of the mixture increases to the point where transition to type III behavior is approached. Ethane + p-dichlorobenzene provides an example of this phenomenon, with an LLV locus extending over a mere 0.6K.[ Such an odd effect may seem to have little practical significance, unless one considers the impact of an unexpected precipitation on a critical pipeline. 

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. 

Merrill, R. C., K. D. Luks, and J. P. Kohn. 1983. Three phase liquid-liquid-vapor equilibria in the methane -f n-pentane + M-octane, methane + n-hexane + n-octane, and methane + n-hexane + carbon dioxide systems. J. Chem. Eng. Data 28 210. 

The mixture was concentrated to one third of the original volumn. Hexane (25 mL) was added to the mixture for precipitation of the product. Recrystalli-sation was undertaken repeatedly in the system of toluene/hexane or dichloro-methane/hexane. The isolated product was 0.34 g (74% yield). 

Using the estimated interaction parameters phase equilibrium computations were performed. It was found that the EoS is able to represent the VL2E behavior of the methane-n-hexane system in the temperature range of 198.05 to... 

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