Methane behavior

The same workers (234) also studied the methanation behavior of bimetallic clusters of Ru/Ni and Ru/Cu in zeolite Y. Such clusters can be formed by metals, such as ruthenium and copper which are immiscible as bulk metals (235, 236). The turnover numbers versus bimetallic cluster composition are shown in Fig. 22. Dilution of ruthenium with copper clearly causes a marked decrease in specific activity. This decrease in activity is also accompanied by a decrease in methanation selectivity. This was attributed to an inhibiting effect of copper on the ruthenium hydrogenolysis activity. 

Using activation energies for CO dissociation and carbon hydrogenation reported in the literature (i.e., 230 and 145 kJ/mol, respectively), calculations showed that changes in heats of adsorption of the reactants H, and CO on Ni significantly alter methanation behavior. Turnover frequencies for the Ni and TiOx/Ni surfaces are plotted in an Arrhenius fashion in Figure 9 for a total pressure of 120 Torr and an H,/C0 ratio of 4. The plots show that... 

It is noteworthy that the above rule connects two quite different values, because the temperature dependence of is governed by the rate constant of incoherent processes, while A characterizes coherent tunneling. In actual fact, A is not measured directly, but it is calculated from the barrier height, extracted from the Arrhenius dependence k T). This dependence should level off to a low-temperature plateau at 7 < This non-Arrhenius behavior of has actually been observed by Punnkinen [1980] in methane crystals (see fig. 1). A similar dependence, also depicted in fig. 1, has been observed by Geoffroy et al. [1979] for the radical... 

The process gas of ethylene plants and methyl tertiary butyl ether plants is normally a hydrogen/ methane mixture. The molecular weight of the gas in such processes ranges from 3.5 to 14. The tliermodynamic behavior of hydrogen/methane mixtures has been and continues to be extensively researched. The gas dynamic design of turboexpanders, which are extensively used in such plants, depends on the equations of state of the process gas. Optimum performance of the turboexpander and associated equipment demands accurate thermodynamic properties for a wide range of process gas conditions. 

The azo compounds A and B were prepared and the thermal and photochemical behavior of these materials was investigated. The results are summarized in the equations below. Discuss how these results m relate to the photochemical di-rc-methane rearrangement. (See Section 12.1.4 for some indications of the reactivity of... 

The influence of hemispherical wire mesh screens (obstacles) on the behavior of hemispherical flames was studied by Dorge et al. (1976) on a laboratory scale. The dimensions of the wire mesh screens were varied. Maximum flame speeds for methane, propane, and acetylene are given in Table 4.1b. 

All vapor bum tests were performed with LNG except for one with liquid methane. The tests were carried out to study the nature and behavior of the burning... 

Deviation of methane gas from ideal gas behavior. Below about 350 atm, attractive forces between methane (CH4) molecules cause the observed molar volume at 25°C to be less than that calculated from the ideal gas law. At 350 atm, the effect of the attractive forces is just balanced by that of the finite volume of CH4 molecules, and the gas appears to behave ideally. Above 350 atm, the effect of finite molecular volume predominates and V, > 1C... 

A comparison of the electron impact (El) and chemical ionization (Cl-methane) mass spectra of 1//-azepine-1-carboxylates and l-(arylsulfonyl)-l//-azepines reveals that in the El spectra at low temperature the azepines retain their 8 -electron ring structure prior to fragmentation, whereas the Cl spectra are complicated by high temperature thermal decompositions.90 It has been concluded that Cl mass spectrometry is not an efficient technique for studying azepines, and that there is no apparent correlation between the thermal and photo-induced rearrangements of 1//-azepines and their mass spectral behavior. 

Carson and Katz5 studied another part of the methane-propane-water system. These authors investigated its behavior when an aqueous liquid, a hydrocarbon liquid, a gas, and some solid were present. It was found that the system was univariant so that the solid consisted of a single phase only. This phase is a hydrate which proved to contain methane and propane in various ratios. They then concluded that these hydrates behaved as solid solutions. It is clear that Carson and Katz measured a part of the four-phase line HllL1L2G. 

For a clearer understanding of the behavior of syngases in a shift converter, we established another set of carbon isotherms when considering the shift reaction only (without methanation) in addition to the carbon-forming reactions. Figure 6 shows isotherms at a partial pressure of 270 psia for all components of a gas mixture, but excluding methane. 

B.H. Sage, Phase Behavior in Binary and Multi-component Systems at Elevated Pressures n-Pentane and Methane-m-Pentane , NSRDS-NBS 32 (1970) 20)A.S. Mal tseva et al,... 

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... 

It is obvious that one can use the basic ideas concerning the effect of alkali promoters on hydrogen and CO chemisorption (section 2.5.1) to explain their effect on the catalytic activity and selectivity of the CO hydrogenation reaction. For typical methanation catalysts, such as Ni, where the selectivity to CH4 can be as high as 95% or higher (at 500 to 550 K), the modification of the catalyst by alkali metals increases the rate of heavier hydrocarbon production and decreases the rate of methane formation.128 Promotion in this way makes the alkali promoted nickel surface to behave like an unpromoted iron surface for this catalytic action. The same behavior has been observed in model studies of the methanation reaction on Ni single crystals.129... 

The influence of electronegative additives on the CO hydrogenation reaction corresponds mainly to a reduction in the overall catalyst activity.131 This is shown for example in Fig. 2.42 which compares the steady-state methanation activities of Ni, Co, Fe and Ru catalysts relative to their fresh, unpoisoned activities as a function of gas phase H2S concentration. The distribution of the reaction products is also affected, leading to an increase in the relative amount of higher unsaturated hydrocarbons at the expense of methane formation.6 Model kinetic studies of the effect of sulfur on the methanation reaction on Ni(lOO)132,135 and Ru(OOl)133,134 at near atmospheric pressure attribute this behavior to the inhibition effect of sulfur to the dissociative adsorption rate of hydrogen but also to the drastic decrease in the... 

Kinetic examination of the methane yield shows behavior quite similar to that of methyl radical a pressure dependent yield of 0.406 molecule/100 e.v., a pressure independent yield of 0.126 molecule/100 e.v., and a rate constant ratio of kq/kf = 1.5 X 106 mole-1 cc. for the competing steps. 

Solution Ideal gas behavior is a reasonable approximation for the feed stream. The inlet concentrations are 287mol/m of methane and 15mol/m of carbon dioxide. The column pressure drop is mainly due to the liquid head on the trays and will be negligible compared with 8 atm unless there are an enormous number of trays. Thus, the gas flow rate F will be approximately constant for the column as a whole. With fast reaction and a controlling gas-side resistance, c = 0. The gas-phase balance gives everything that is necessary to solve the problem ... 

It is presumed that the global-quenching criteria of premixed flames can be characterized by turbulent shaining (effect of Ka), equivalence ratio (effect of 4>), and heat-loss effects. Based on these aforemenhoned data, it is obvious that the lean methane flames (Le < 1) are much more difficult to be quenched globally by turbulence than the rich methane flames (Le > 1). This may be explained by the premixed flame shucture proposed by Peters [13], for which the premixed flame consisted of a chemically inert preheat zone, a chemically reacting inner layer, and an oxidation layer. Rich methane flames have only the inert preheat layer and the inner layer without the oxidation layers, while the lean methane flames have all the three layers. Since the behavior of the inner layer is responsible for the fuel consumption that... 

Figure 6.2.5 also shows the effect of RHL, which has an influence on the global quenching of lean methane/ air flames based on the behaviors between N2- and CO2-diluted flames of the same Sl lOcm/s. The larger the RHL is, the smaller is the value of Ka, . For example, Ka, = 26.1 for N2-diluted flames (small RHL), while Ka, = 20.4 for C02-diluted flames (large RHL) when (j> 0.64. It is found that for lean mefhane/air flames of constant Sl, the values of Ka, increased with for both N2- and C02-diluted flames, and fhe difference in the values of Ka, befween these two different diluted flames also increased with (f>, as shown in Figure 6.2.5. On the other hand, the effects of RHL did not have influence on the global quenching of rich methane/air flames, because Ka, 8.4 for both N2- and C02-diluted flames (values of Ka are in a log plof in Figure 6.2.5).

Tec and rn decrease when the carbon adsorption energy increases. Volcano-type behavior of the selectivity to coke formation is found when the activation energy of C-C bond formation decreases faster with increasing metal-carbon bond energy than with the rate of methane formation. Equation (1.16b) indicates that the rate of the nonselective C-C bond forming reaction is slow when Oc is high and when the metal-carbon bond is so strong that methane formation exceeds the carbon-carbon bond formation. The other extreme is the case of very slow CO dissociation, where 0c is so small that the rate of C-C bond formation is minimized. 

A number of theoretical (5), (19-23). experimental (24-28) and computational (2), (23), (29-32). studies of premixed flames in a stagnation point flow have appeared recently in the literature. In many of these papers it was found that the Lewis number of the deficient reactant played an important role in the behavior of the flames near extinction. In particular, in the absence of downstream heat loss, it was shown that extinction of strained premixed laminar flames can be accomplished via one of the following two mechanisms. If the Lewis number (the ratio of the thermal diffusivity to the mass diffusivity) of the deficient reactant is greater than a critical value, Lee > 1 then extinction can be achieved by flame stretch alone. In such flames (e.g., rich methane-air and lean propane-air flames) extinction occurs at a finite distance from the plane of symmetry. However, if the Lewis number of the deficient reactant is less than this value (e.g., lean hydrogen-air and lean methane-air flames), then extinction occurs from a combination of flame stretch and incomplete chemical reaction. Based upon these results we anticipate that the Lewis number of hydrogen will play an important role in the extinction process. 

The gas composition at the outlet of the reactor was determined using gas chromatography. The selectivity of methane was almost 100%. We directly observed the fluidization behavior and photographed it using a video camera with recording onto a videotape. We also measured the expansion of the emulsion by the bed collapse method [10] during the reaction. 

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