Carbon monoxide reactions, methanation reaction

As is indicated in Figure 1, the heat liberated in the conversion of carbon monoxide to methane is 52,730 cal/mole CO under expected reaction conditions. Also, the heat liberated in the conversion of carbon dioxide is 43,680 cal/mole C02. Such high heat releases strongly affect the process design of the methanation plant since it is necessary to prevent excessively high temperatures in order to avoid catalyst deactivation and carbon laydown. Several approaches have been proposed. 

In a later publication, Kolbel et al. (K16) have proposed a less empirical model based on the assumption that the rate-determining steps for a slurry process are the catalytic reaction and the mass transfer across the gas-liquid interface. When used for the hydrogenation of carbon monoxide to methane, the process rate is expressed as moles carbon monoxide consumed per hour and per cubic meter of slurry ... 

This overview is organized into several major sections. The first is a description of the cluster source, reactor, and the general mechanisms used to describe the reaction kinetics that will be studied. The next two sections describe the relatively simple reactions of hydrogen, nitrogen, methane, carbon monoxide, and oxygen reactions with a variety of metal clusters, followed by the more complicated dehydrogenation reactions of hydrocarbons with platinum clusters. The last section develops a model to rationalize the observed chemical behavior and describes several predictions that can be made from the model. 

In related studies, Cp2ZrCl2 has been found to catalyze at room temperature an aluminum hydride (i-Bu2AlH) reduction of CO to linear Ci-C5 alcohols (430). The system involves reaction of complex 55 with CO, which precipitates the starting zirconium(IV) complex and leaves a yellow solution, that on hydrolysis yields the alcohols. Toluene solutions of Cp2Ti(CO)2 complex under H2/CO effect Eq.(69), i.e., a homogeneous stoichiometric hydrogenation of carbon monoxide to methane (426). 

Not all C-H activation chemistry is mediated by transition metal catalysts. Many of the research groups involved in transition metal catalysis for C-H activation have opted for alternative means of catalysis. The activation of methane and ethane in water by the hexaoxo-/i-peroxodisulfate(2—) ion (S2O82) was studied and proceeds by hydrogen abstraction via an oxo radical. Methane gave rise to acetic acid in the absence of external carbon monoxide, suggesting a reaction of a methyl radical with CO formed in situ. Moreover, the addition of (external) CO to the reaction mixture led to an increase in yield of the acid product (Equation (ll)).20... 

To study the effect of the Ru/Al Oj catalyst on hydrogen yield for refomung of glucose in supercritical water, the experiments were compared to reactions with and without catalytic runs imder identical conditions. Typical product distributions are shown in Table 6.9 for experiments with and without a Ru/Al Oj catalyst at 973 K with 1 wt.% glucose feed (Byrd et al., 2007). There was a significant reduction in carbon monoxide and methane yields in the presence of the catalyst. The main products of the reaction were hydrogen, methane, carbon dioxide, and carbon monoxide. The low carbon monoxide yield (0.1% by vol.) indicates that the water-gas shift reaction approaches completion. 

It was observed that the water content does not influence ethylene formation. When 5% Rh is added to alumina, the main steam reforming reaction occurs above 460 °C and the products include hydrogen, carbon dioxide, carbon monoxide and methane. 

This reaction sequence is similar to that described for acetaldehyde decomposition to methane and carbon monoxide Reactions that produce stable products actually occur only... 

The SMR process consists of two steps. The first is the reformation process in which methane mixed with steam is passed over a catalyst bed at high temperature and pressure to form a mixture of hydrogen and carbon monoxide (reaction 1.1), called syngas. The second step is the shift reaction in which carbon monoxide from the first stage reacts with additional steam to release carbon dioxide and more hydrogen (reaction 1.2). 

The photochemistry of biacetyl has been extensively studied, both in the vapor phase and in solution. In the vapor phase the products include carbon monoxide, ethane, methane, acetone, ketene, and 2,3-pentanedione. It has been shown that the primary process is cleavage of the carbon-carbon bond between the two carbonyl groups to yield acyl radicals, which on further reaction give the observed products.14,43... 

Figures 1 to 3 present calculated equilibrium molar ratios of products to reactants as a function of temperature and total pressure of 1 and 100 atm. for the gas-carbon reactions (4), (7), and (5), (6), (4), (7), respectively. Up to 100 atm. over the temperature range involved, the fugacity coefficients of the gases are close to 1 therefore, pressures can be calculated directly from the equilibrium constant. From Fig. 1, it is seen that at temperatures above 1200°K. and at atmospheric pressure, the conversion of carbon dioxide to carbon monoxide by the reaction C - - COj 2CO essentially is unrestricted by equilibrium considerations. At elevated pressures, the possible conversion markedly decreases hence, high pressure has little utility for this reaction, since increased reaction rate can easily be obtained by increasing reaction temperature. On the other hand, for the reaction C -t- 2H2 CH4, the production of methane is seriously limited at one atmosphere pressure and practical operating temperatures, as seen in Fig. 2. Obviously, this reaction must be conducted at elevated pressures to realize a satisfactory yield of methane. For the carbon-steam reaction.

High Temperature Reaction. Reaction in the high temperature regime produces carbon monoxide, water, methane, formaldehyde, and methanol (8) the two higher ketones also form ethylene (I). The intermediate responsible for chain branching appears to be formaldehyde. The concentration of formaldehyde and the rate of reaction run parallel over the whole of the reaction, as shown in Figure 4 for diethyl ketone. 

Reactions R1 - RIO are also key reactions in determining OH distribution in the troposphere and lower stratosphere. The key point here is that increases in ozone and nitrogen oxides enhances the OH distribution through reactions R1 and RIO, while enhanced carbon monoxide and methane reduces OH through reactions R4 and R6. Furthermore, reactions with OH (R4 and R6) represent the main loss of CO and methane. 

Coke oven gas consists mainly of a mixture of carbon monoxide, hydrogen, methane, and carbon dioxide. It is contaminated with a variety of organic and inorganic compounds that have to be separated in absorption columns before its further use as a synthesis gas. The selective absorption of coke plant gas contamination results from a complex system of parallel liquid-phase reactions. Instantaneous reversible reactions ... 

Carbon may be formed from carbon monoxide and methane by the following reversible reactions [6,12,18],... 

The presence of methane in the decomposition products together with the fifty per cent of carbon monoxide indicates a reaction more complicated than (1) or (4) and favors reaction (2) or (5). Rice and Herzfeld32 have proposed a series of chain reactions for the thermal decomposition of acetone which would give both methane and ethane. The recombination of CH3 and CH3CO according to (2) might account for the low quantum yield. 

This is probably because 0 atoms produced in primary process (45) react much more rapidly with C2H6 than with N20. Several products are formed including ethylene, butane, carbon monoxide, hydrogen, methane, and probably ethanol and acetaldehyde. More ethylene is formed than one would expect from the amount of butane. It was found that 0 atoms react rapidly with ethylene, which is one of the photolytic products. The reaction-rate constant of O atoms with ethylene is estimated to be about 330 times as rapid as that with ethane.82 Complete elucidation of the mechanism of O-atom reaction with ethane is complicated because of the rapid reaction of O atoms with one or more of the products. 

Lanthanides as modifiers to other oxides in aluminas In zirconias In iron oxide Lanthanide oxides in mixed oxides With aluminas With iron oxides With other transition metal oxides To maintain surface area To increase oxidation rates To increase methanation rates For conduction in electrocatalysis For ammonia synthesis promotion To provide sulfur oxides (SO.,) control For dehydrogenation in carbon monoxide reactions For oxidation... 

The pairing of copper with platinum and nickel with palladium was reminiscent of the work of Taylor and McKinney (3) who pointed out that copper and platinum were relatively poor catalysts for the hydrogenation of carbon monoxide to methane, while nickel and palladium were active catalysts for this reaction. Although this pattern could be coincidental, it is more reasonable and productive to assume a relationship between the spectroscopic results and the catalytic activities and to conclude that metals which chemisorb carbon monoxide in... 

Ketene, H,C = C = 0, has been obtained by the pyrolysis of many compounds containing the CHjCO—group. However, its preparation from acetone has been the most successful from the standpoint of the laboratory and is carried out by passing the vapors through a combustion furnace at 650° (30%) or over a hot Chromel A wire filament at 700-750° (90%). The product is contaminated with ethylene, carbon monoxide, and methane. It may be purified by dimerization followed by depolymerization (cf. method 246). More often than not, since ketene dimerizes readily, it is passed directly from the generator into a reaction vessel for immediate consumption. 

The removal of hydroxyl from the atmosphere occurs most frequently as a result of reactions with carbon monoxide or methane ... 

Carbon Monoxide-Hydrogen. - The reactions between CO and H2have been reviewed in the present series and previously by Vannice, who noted the paucity of studies with well defined alloys, although in both reviews it was possible to include CO adsorption/desorption and i.r. measurements involving alloys and bimetallic catalysts. The intrinsic importance of the catalyzed reaction makes it likely that much more work with bimetallic catalysts will be reported as indicated by the latest literature. The supported metals differ considerably in terms of product formation (which is also dependent on reaction conditions), methane (Ni), olefins (Ru, Co, and Ir), > C4 products (Co, Fe), and paraffin waxes (Ru), and it is tempting to suppose that bimetallics would combine desirable properties. 

As an example of the use of concentration measures other than that of moles per unit volume consider the gas reaction A —> B + C, say the decomposition of acetaldehyde vapor into methane and carbon monoxide. If the reaction proceeds at constant volume and temperature, it may be followed by the increase in pressure. Suppose TVo moles of A are introduced into a volume V at temperature T so that the initial pressure is Pq = MRTyr. When the gross extent of reaction is X there will be (M + X) total moles present and the pressure will be P = (TVo + X)Rr/ V, Hence y = (P — Pq) V/ RP. If the reaction is second order and so proportional to the square of the concentration (Aq — X)/ K, we have... 

In this reaction scheme, CH4 is produced by two steps of radiative association with slow rate constants. Because the destruction of C by electron capture (radiative) is four orders of magnitude slower than the destruction of a molecular ion by dissociative recombination, there is not a rapid loss of C , allowing production of a saturated hydrocarbon. We recall that chemical equilibrium arguments predict preponderant conversion of carbon monoxide to methane and water. There is little evidence for this, as stated earlier. The gas-phase production of CH4 from CO and H2 then proceeds by a very high-energy kinetic path, namely He + CO = C +... 

Heterogeneous catalysis is activated when the catalyst slides against itself or other materials, e.g. ceramics. Oxidation reactions of hydrogen, carbon monoxide and methane were demonstrated as being enhanced by rubbing platinum, palladium and silver, respectively [29-31], and the reduction of carbon dioxide is enhanced by the rubbing of iron oxide [32],... 

In the conversion of coal to gaseous compounds, many reactions are occurring in series and parallel. All the reactions shown in the methane reforming section (Reactions 2.1—2.10) play a role in the gasification process. The important additional coal reactions are shown in Reactions 2.17—2.20. Reaction 2.17 is the partial combustion of coal to form carbon monoxide. Reaction 2.18 is the heterogeneous steam gasification to form carbon monoxide and hydrogen. Reaction 2.19 is the complete oxidation of carbon, while Reaction 2.20 is the methanation of coal. 

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