Methane-hydrocarbon binaries

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. 

The kij9s for Methane-Hydrocarbon Binaries. As noted earlier, most of the fey values available in the literature are for binaries of inorganic gases and hydrocarbons with up to 8 carbon atoms. New determinations of optimum fey values for methane-hydrocarbon binaries are listed in Table I. These and Chueh s results make a total of 26 fey values (for 25 binaries two different fey s were included for the naphthalene binary) over the carbon-number range of 2 to 30 for /. This is the most... 

Table I. Optimum y Values for Methane-Hydrocarbon Binaries...

Figure 1. Optimum ky values for methane-hydrocarbon binaries (-----), Equation 13 (O) Kaul and...

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. 

Equation 11 was much less satisfactory, even when the coefficient was adjusted to minimize the deviation. The optimum value of the coefficient was 0.18, in agreement with Lin s conclusion for rare-gas mixtures, but the root-mean-square deviation of k j was 0.08. Any relationship involving I, the first ionization potential, is doomed to failure when applied to heavy hydrocarbon mixtures because I, for a given homologous series, is very weakly dependent on carbon number. For example, the I of n-decane is 10.19 eV, only 0.24 eV less than that of n-hexane, while that of n-eicosane should be about 10.04 eV. Thus, a correlation of kijs for methane-paraffin binaries based solely on ionization potentials would give the same result for all Ci0+ paraffins. 

Equation 12b works surprisingly well. Although it is inferior to Equation 11 when applied to the paraffin binaries (average deviation of 0.03 vs. 0.02), it comes out better when all hydrocarbon binaries are considered (average deviation of 0.04 vs. 0.05). Equation 12b is also satisfactory for the binaries of methane with Ar, Kr, N2, and H2S (average deviation of 0.01 vs. 0.03 with Equation 10), but is very poor for methane-H2. 

Many simple systems that could be expected to form ideal Hquid mixtures are reasonably predicted by extending pure-species adsorption equiUbrium data to a multicomponent equation. The potential theory has been extended to binary mixtures of several hydrocarbons on activated carbon by assuming an ideal mixture (99) and to hydrocarbons on activated carbon and carbon molecular sieves, and to O2 and N2 on 5A and lOX zeoHtes (100). Mixture isotherms predicted by lAST agree with experimental data for methane + ethane and for ethylene + CO2 on activated carbon, and for CO + O2 and for propane + propylene on siUca gel (36). A statistical thermodynamic model has been successfully appHed to equiUbrium isotherms of several nonpolar species on 5A zeoHte, to predict multicomponent sorption equiUbria from the Henry constants for the pure components (26). A set of equations that incorporate surface heterogeneity into the lAST model provides a means for predicting multicomponent equiUbria, but the agreement is only good up to 50% surface saturation (9). 

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. 

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. 

All the binary Cu/ZnO catalysts were found highly selective toward methanol without DME, methane, or higher alcohols and hydrocarbons detected in the product by sensitive gas chromatographic methods (59). Several of the composites were also found to be very active when subjected to a standard test with synthesis gas C0/C02/H2 = 24/6/70 at gas hourly space velocity of 5000 hr- pressure 75 atm, and temperature 250°C. The activities, expressed as carbon conversions and yields, are summarized in Table VIII. The end members of the series, pure copper and pure zinc oxide, were inactive under these testing conditions, and maximum activity was obtained for the composition Cu/ZnO = 30/70. The yields per unit weight, per unit area of the catalyst or the individual components, turnover rates per site titratable by irreversible oxygen and by irreversible carbon monoxide, are graphically... 

Hydrocarbon molecules are abundant constituents of planetary atmospheres and major compounds in combustible gas mixtures and in fusion edge plasmas [7-11]. Methane is the simplest of these hydrocarbon molecules. Acetylene, C2H2, is the simplest hydrocarbon molecule that contains 2 carbon atoms. Thus absolute total and partial photon [24-27] and electron [15,28-34] ionization cross-sections and nascent fragment ion energy distributions [19,20,28,36-40] have been studied extensively for these molecules. For the deuterated methane molecule electron impact ionization and dissociative ionization cross-sections were determined for the CD (x=l—4) molecule and radicals applying a fast neutral beam technique [41]. Electron impact total ionization cross-sections have been determined also theoretically applying the BEB (Binary-Encounter-Bethe) model [42], the DM (Deutsch-Mark) method [43] and the JK (Jain-Khare) method [44], Partial electron impact ionization cross-sections were calculated for methane [45,46] as well as total electron impact cross-sections for various CH radicals [47]. The dissocia-... 

Thermal Properties, Silanes have less thermal stabflity than hydrocarbon analogues. The C—H bond eneigy in methane is 414 kj / mol (98.9 kcal/mol) the Si—H bond energy in silane is 3781 /mol (90.3 kcal/mol) (10). Silane, however, is one of the most thermally stable inoiganic silanes. Decomposition occurs at 500 0 in the absence of catalytic surfaces, at 300°C in glass vessels, and at 180°C in the presence of charcoal (11). Disilanes and other members of the binary series are less stable. Halogen-substituted silanes are subject to disproportionation reactions at higher temperatures (12). 

Gas permeabUities of isotropic PDMS films were determined over a temperature range of 35°C to 20°C for pure gases and a series of binary n-butane/methane and multicomponent hydrocarbons/hydrogen mixtures [38]. Pure-gas permeabUities in PDMS as a function of reciprocal temperature are presented in Figure 9.15. It can be seen that the decrease in temperature... 

Calculations were carried out for the solubilities of mixtures of hydrocarbons (methane—ethane and methane—n-butane) and for the mixture methane—carbon dioxide in water, because experimental data regarding the solubilities of binary gas mixtures and individual gases are available for these mixtures. ... 

The analysis of critical phenomena, such as hysteresis and self-oscillations, gives valuable information about the intrinsic mechanism of catalytic reactions [1,2], Recently we have observed a synergistic behavior and kinetic oscillations during methane oxidation in a binary catalytic bed containing oxide and metal components [3]. Whereas the oxide component (10% Nd/MgO) itself is very efficient as a catalyst for oxidative coupling of methane (OCM) to higher hydrocarbons, in the presence of an inactive low-surface area metal filament (Ni-based alloy) a sharp increase in the rate of reaction accompanied by a selectivity shift towards CO and H2 takes place and the oscillatory behavior arises. In the present work the following aspects of these phenomena have been studied ... 

LLV behavior near the critical point of methane T = —82.5°C, Pj. = 46.4 bar) occurs when the ratio of carbon atoms between methane and the second component exceeds 5.0. For binary ethane-hydrocarbon mixtures, LLV behavior occurs near the critical point of ethane T = 32.3°C, Pc = 48.8 bar) when the ratio of carbon atoms between ethane and the second component exceeds 9.5. And for binary propane-hydrocarbon mixtures LLV behavior occurs near the critical point of propane T = 96.7 C, Pc = 42.5 bar)... 

Table III. Binary Interaction Parameters for Methane (First Component) with Heavier Hydrocarbons...

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