Pressure for methane

Figure 5.10 shows a plot of Vm/Vm versus pressure for methane at 25°C. Up to about 150 atm, methane shows a steadily increasing negative deviation from ideality, as might be expected on the basis of attractive forces. At 150 atm, Vm is only about 70% of V ,. 

Figure 6-5 Maximum pressure for methane combustion in a 20-L sphere. The flammability limits are defined at 1 psig maximum pressure. Data from C. V. Mashuga and D. A. Crowl, Process Safety Progress (1998), 17(3) 176-183 and J. M. Kuchta, Investigation of Fire and Explosion Accidents in the Chemical, Mining, and Fuel-Related Industries A Manual, US Bureau of Mines Report 680 (Washington, DC US Bureau of Mines, 1985).

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. 

Taking p(H20) = 3 x 10-2, p(C02) = 3x 10-4, p(H2) = 5 x 10-5, we find an equilibrium pressure for methane of 100 bar. The calculation ignores the fact that the supply of hydrogen is limited and the methane pressure cannot exceed the initial pressure of hydrogen, but the result demonstrates the... 

Hence, TOFitk is a function mainly of [ H] (or partial pressure of hydrogen) in addition to temperature and the nature of the active sites. Xp has, in fact, been shown to vary with H2 partial pressure for methanation on Ru [12] and Co [13]. Thus, for the simple reaction of methanation given above, TOFitk has, in general, less of a dependency on surface concentrations (and hence partial pressures of reactants) than TOFchem-The relationships of TOFchem, TOFitk, and true site TOF are as follows ... 

At -175°F and 25 psia, the experimental -values for methane and propane in a binary mixture are 8.3 and 0.0066, respectively. Assuming that the vapor forms an ideal solution, estimate the liquid-phase activity coefficients for methane and propane. Do not assume that the gas phase obeys the ideal gas law. At - 175°F, the vapor pressures for methane and propane are 220 and 0.097 psia, respectively. 

Fig. 3.2. The dependence of the compressibility factor z upon pressure for methane at various temperatures including the Boyle temperature Tg.

Browarzik et al calculated asphaltenes flocculation at high pressures for methane + crude oil - - 2,2,4-trimethylpentane [i-octane] using continuous thermodynamics where 2,2,4-trimethylpentane acts as a precipitant. The asphaltene flocculation was considered to be a liquid -b liquid equilibrium. Browarzik et al applied the van der Waals equation of state. The polydispersity of the crude oil was considered to be described by the solubility parameter of the Scatchard-Hildebrand theory. Within this distribution the asphaltenes represent the species with the highest solubility parameters. The calculated results were compared to experimental data. For oils with a very low content of asphaltenes the model describes the experimental flocculation data reasonably well. However, on contrary to the experimental results, the model predicts the asphaltenes to show a higher flocculation tendency with increasing asphaltenes content of the crude oil. Based on these comparisons further work was undertaken by Browarzik et al and the associates formed... 

We describe proeedures, based on the slit pore model and Monte Carlo simulation, for predicting the adsorption of pure gases in active carbons given only a single carbon dioxide probe adsorption isotherm. Predictions are made at ambient temperature up to quite high pressure for methane, ethene, ethane, propene and propane. The key development in our work concerns our method for calibrating gas - surface interactions, i.e. we calibrate these interactions to a reference active carbon rather than a low surface area carbon as in most other work of this type. Our predictions highlight limitations in our surface model and experiments. 

Figure 9. K-values vs. pressure for methane-ethane mixtures corresponding-states method of MoUerup and Rowlinson...

Figures 8 and 9 illustrate the type of agreement that was obtained for the water content and the hydrocarbon distribution in both the hydrocarbon liquid and vapor phases for the methane n-butane-water system. It can be seen from Figure 8 that the predictions reproduce the water content very well at all temperatures. Figure 9 shows that the agreement between experimental and predicted hydrocarbon concentrations in the vapor and liquid phases is good at 100 F, although the agreements does not seem to be as good at 2220 F. The experimental data for 220 F may be open to question since the critical pressure for methane-n-butane mixtures at 220 F is reported to be about 1350 psia by Roberts et al (11). The experimental data of these authors on the methane-n-butane system at 220 F are Included for comparison. It seems doubtful that the presence of water in this system would increase the critical pressure to about 1550 psia as indicated by the three component data. In view of this, the predicted results are thought to be just as good at 220 F as at 100°F.

Solution. By definition, the vapor pressure of each component is equal to the partial pressure at saturation conditions. By using Eq. (6.76) and Table 6.8, the partial pressures for methane and ethane may be determined. At 67 K and 101.325 kPa... 

Figure 8.5 Variation of z with reduced pressure for methane (and argon) and n-decane at — 1.05.

Cmde gas leaves from the top of the gasifier at 288—593°C depending on the type of coal used. The composition of gas also depends on the type of coal and is notable for the relatively high methane content when contrasted to gases produced at lower pressures or higher temperatures. These gas products can be used as produced for electric power production or can be treated to remove carbon dioxide and hydrocarbons to provide synthesis gas for ammonia, methanol, and synthetic oil production. The gas is made suitable for methanation, to produce synthetic natural gas, by a partial shift and carbon dioxide and sulfur removal. 

Methane is also used for the production of several halogenated products, principally the chloromethanes. Due to environmental pressures, this outlet for methane is decreasing rapidly. 

If the substitute fuel is of the same general type, eg, propane for methane, the problem reduces to control of the primary equivalence ratio. For nonaspiring burners, ie, those in which the air and fuel suppHes are essentially independent, it is further reduced to control of the fuel dow, since the air dow usually constitutes most of the mass dow and this is fixed. For a given fuel supply pressure and fixed dow resistance of the feed system, the volume dow rate of the fuel is inversely proportional to. ypJ. The same total heat input rate or enthalpy dow to the dame simply requires satisfactory reproduction of the product of the lower heating value of the fuel and its dow rate, so that WI = l- / remains the same. WI is the Wobbe Index of the fuel gas, and... 

Ethylene oxide storage tanks ate pressurized with inert gas to keep the vapor space in a nonexplosive region and prevent the potential for decomposition of the ethylene oxide vapor. The total pressure that should be maintained in a storage tank increases with Hquid temperature, since the partial pressure of ethylene oxide will also increase. Figure 5 shows the recommended minimum storage pressures for Hquid ethylene oxide under nitrogen or methane blanketing gas. 

Fig. 5. Recommended safe storage pressures for liquid ethylene oxide under nitrogen (—) or methane ( ) blanketiag (9). To convert kPa to psi, multiply...

Gases For pure eomponent, low pressure (<350 kPa) hydro-earbon gases, Misic and Thodos recommend the following equations. For methane and eyelie eompounds below reduced temperatures of 1.0 ... 

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. 

When one of the elements is solid, as in tire case of carbon in the calculation of the partial pressures of tire gaseous species in the reaction between methane and air, CO(g) can be used as a basic element together widr hydrogen and oxygen molecules, and thus the calculation of the final partial pressure of methane must be evaluated using the equilibrium constant for CH4 formation... 

A tube 10 m long and 2.5 m inside diameter was used for experiments with methane (Moen et al. 1982) and propane (Hjertager et al. 1984). These often-cited experiments showed that very intense gas explosions were possible in this tube, which had an aspect ratio of only 4 but which contained internal obstructions. Pressures of up to 4.0 bar for methane and 13.9 bar for propane were reported. Obstruction parameters, for example, blockage ratio and pitch, were varied. As with cylindrical geometry, explosions became more severe with increasing obstacle density. 

Figure 7-46. Ignitibiiity curve and limits of flammability for methane-air mixtures at atmospheric pressure and 26°C. By permission, U.S. Bureau of Mines, Bulletin 627 [43].

Recommend applying only for methane, propane, and solvent vapors due to insufficient data and for a static activation pressure of the relief device of Ps,ai =0.1 bar (see reference [54]). 

Figure 8-3B. Pressure vs. K for methane at convergence pressure of 800 psia. Used by pennission, Gas Processors Suppliers Association Data Book, 9th Ed. V. 1 and 2 (1972-1987), Tulsa, Okla.

Critical temperature and pressure for pure liquid methane. 

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