Methane reaction data

An examination of some laboratory runs with diluted C150-1-02 catalyst can illustrate this problem. In one run with 304°C at inlet, 314 °C at exit, and 97,297 outlet dry gas space velocity, the following results were obtained after minor corrections for analytical errors. Of the CO present (out of an inlet 2.04 mole % ), 99.9885% disappeared in reaction while the C02 present (from an initial 1.96%) increased by over 30%. Equilibrium carbon oxides for both methanation reactions were essentially zero whereas the equilibrium CO based on the water-gas shift reaction at the exit composition was about one-third the actual CO exit of 0.03 mole %. From these data, activities for the various reactions may be estimated on the basis of various assumptions (see Table XIX for the effect of two different assumptions). 

For the first assumption, the value of Kw for the shift appears to be too high. It must be this high because it is necessary to make C02 appear while both C02 and CO are being consumed rapidly by methanation. The data may be tested to see if the indicated rate appears unreasonable from the standpoint of mass transfer to the gross catalyst surface. Regardless of the rate of diffusion in catalyst pores or the surface reaction rate, it is unlikely that the reaction can proceed more rapidly than material can reach the gross pill surface unless the reaction is a homogeneous one that is catalyzed by free radicals strewn from the catalyst into the gas stream. 

Reaction between carbon monoxide and dihydrogen. The catalysts used were the Pd/Si02 samples described earlier in this paper. The steady-state reaction was first studied at atmospheric pressure in a flow system (Table II). Under the conditions of this work, selectivity was 100% to methane with all catalysts. The site time yield for methanation, STY, is defined as the number of CH molecules produced per second per site where the total number of sites is measured by dihydrogen chemisorption at RT before use, assuming H/Pd = 1. The values of STY increased almost three times as the particle size decreased. The data obtained by Vannice et al. (11,12) are included in Table II and we can see that the methanation reaction on palladium is structure-sensitive. It must also be noted that no increase of STY occurred by adding methanol to the feed stream which indicates that methane did not come from methanol. 

The single crystal results are compared in Fig. 2 with three sets of data taken from Ref. 13 for nickel supported on alumina, a high surface area catalyst. This comparison shows extraordinary similarities in kinetic data taken under nearly identical conditions. Thus, for the Hj-CO reaction over nickel, there is no significant variation in the specific reaction rates or the activation energy as the catalyst changes from small metal particles to bulk single crystals. These data provide convincing evidence that the methanation reaction rate is indeed structure insensitive on nickel catalysts. 

The batch reactor, above described, permits both to operate at quasi-zero conversion per pass and to evaluate the cat ytic activity at finite values of the reagents conversion. A typical test performed on Si02 catalyst at 600°C is presented in Figure 1. It is remarkable how in our approach the product selectivity is unaffected by the methane conversion. A special care was taken to avoid oxygen-limiting conditions and, hence, methane conversion data obtained for oxygen conversions below 20% only have been used for the calculation of reaction rates. 

Arrhenius parameters for the methanation reaction on alumina-supported Group VIII metals (227b) were close to the line for cracking reactions on several metals (Table III, A). Activity was based on the numbers of surface metal atoms and a compensation relation was described from these data we calculate c = 0.1185 0.0117, B = 15.216 1.068, and oL = 0.491. 

A detailed study of the oxidation of alkenes by O on MgO at 300 K indicated a stoichiometry of one alkene reacted for each O ion (114). With all three alkenes, the initial reaction appears to be the abstraction of a hydrogen atom by the O ion in line with the gas-phase data (100). The reaction of ethylene and propylene with O" gave no gaseous products at 25°C, but heating the sample above 450°C gave mainly methane. Reaction of 1-butene with O gives butadiene as the main product on thermal desorption, and the formation of alkoxide ions was proposed as the intermediate step. The reaction of ethylene is assumed to go through the intermediate H2C=C HO which reacts further with surface oxide ions to form carboxylate ions in Eq. (23),... 

Lefebvre et al. (170) have conducted the high pressure CO + H2 reaction (30 atm, 503-523 K) over Rh-NaY catalysts. Whatever the rhodium precursors [e.g., Rh -NaY and Rh (CO)2-NaY], the reaction data were similar. This is in agreement with the fact that all the precursors were ultimately converted to Rh6(CO),6 under catalytic conditions. The external Rh crystals deposited on the zeolite surface exhibit significant activity for hydrocarbons, mainly methane, whereas the carbonyl clusters gave lower conversion to hydrocarbons with a small amount of oxygenates such as methanol and ethanol. 

Fig. 12.19 Methane oxidation reaction data for microreactor ACT-G2-4 channel B with a feed gas flow rate of 10.1 ml min". The feed composition was 14.9% methane, 10.3% oxygen, 39.8% nitrogen, and balance helium. This microreactor was placed in Reactor Board 2. Error bars represent the 95% confidence interval of each value.

In Figure 7 an Arrhenius plot of the H atom-carbon reaction data is presented based on the methane yields given in Table III. Three distinct reaction regions are indicated. A least-squares fit on the data resulted in activation energies for the production of methane of 4.5 1.2, 0.15 =t 0.05, and 0.94 0.20 kcal/mole in the high, medium, and low temperature regions, respectively. The precision limits are the standard deviations... 

Table 3 shows methane conversion data for the both catalysts and the increase of the activity for (Ni-I) after submitting the carbon deposition to the H2/N2 flow. These results indicate that some of the carbon deposits are eliminated during the hydrogen treatment, since, as shown by TPH, they are hydrogenable at temperature lower than those in which the reaction is performed and eliminated in the reaction medium. 

Table 2.6 Methane conversion data for methane dry reforming reaction...

TABLE 20.4 Thermodynamic Data for Methanation Reactions Temperature Reaction ... 

The rate of substitution correlates with the electron density at the aromatic nucleus. Several quantum mechanical calculations (CNDO [1] and AM 1 [52], where CNDO stands for Complete Neglect of Differential Overlap and AMI stands for Austin Model 1) show that the position of the methylol group on the ring influences electron density. The position reactivities determined by Freeman and Lewis [75] were later confirmed by Zsavitsas [76], who did extensive gas chromatography studies on the separation of the substituted phenols formed. Also, the pK -value of these compounds correlates closely with the kinetic data determined. Another group studied the influence of the metal ion in the metal hydroxide catalyst on kinetics and product stmcture [73]. The rate constants evaluated for the phenol methanal reaction under alkaline... 

For gaseous flows a huge amount of chemical reaction data is available. Therefore the concentration was focused on combustion problems as a field for examining the coupling of chemical reaction and turbulence. The detailed system of methane-air-combustion has been automatically reduced in order to establish a chemical database for a PDF-approach. The PDF-algorithm has been applied to a combustion problem which is close to realistic flow configurations and the results are compared with experimental data and an other combustion-model. 

Numerical Modeling of Transient Isotope Responses On the first step, the authors analyzed in detail five possible heterogeneous methanation models based on two gas phase (CO, CH4) and three surface components (COads, Ca,ads, and Cp,ads) that follow from qualitative analysis of CO labeling data [19,21]. These models contained either a buffer step or parallel routes of methane formation. The homogeneous model having one type of methane intermediate was also considered. A methanation reaction was modeled separately from the entire set of reactions included in the Fischer-Tropsch ... 

Because the transient data for methanation reaction are more accurate than those for C2-C5 hydrocarbons. By decoupling the methanation reaction, rate coefficients for the initial part of the mechanism can be fixed, followed by correct account of readsorption of reactive olefins during subsequent modeling based on a plug-flow reactor model. 

Table 8.1. Main reactions involved in catalytic combustion and catalytic partial oxidation of methane (thermodynamic data from Ref. 4).

---