Methane syntheses with

Ventura, S. C., Hum, G.P. and Narang, S.C., Novel Strategies for the Synthesis of Methane Adsorbents with Controlled Porosity and High Surface Area", Gas Research Institute Report GRl-93/0018, 1993... 

As mentioned in Chapter 2, methane is a one-carhon paraffinic hydrocarbon that is not very reactive under normal conditions. Only a few chemicals can he produced directly from methane under relatively severe conditions. Chlorination of methane is only possible by thermal or photochemical initiation. Methane can be partially oxidized with a limited amount of oxygen or in presence of steam to a synthesis gas mixture. Many chemicals can be produced from methane via the more reactive synthesis gas mixture. Synthesis gas is the precursor for two major chemicals, ammonia and methanol. Both compounds are the hosts for many important petrochemical products. Figure 5-1 shows the important chemicals based on methane, synthesis gas, methanol, and ammonia. ... 

The preceeding discussion was confined mostly to the carbon deposition curves as a function of temperature, pressure, and initial composition. Also of interest, especially for methane synthesis, is the composition and heating value of the equilibrium gas mixture. It is desirable to produce a gas with a high heating value which implies a high concentration of CH4 and low concentrations of the other species. Of particular interest are the concentrations of H2 and CO since these are generally the valuable raw materials. Also, by custom it is desirable to maintain a CO concentration of less than 0.1%. The calculated heating values are reported as is customary in the gas industry on the basis of one cubic foot at 30 in. Hg and 15.6°C (60°F) when saturated with water vapor (II). Furthermore, calculations are made and reported for a C02- and H20-free gas since these components may be removed from the mixture after the final chemical reaction. Concentrations of CH4, CO, and H2 are also reported on a C02 and H20-free basis. 

The scheme of commercial methane synthesis includes a multistage reaction system and recycle of product gas. Adiabatic reactors connected with waste heat boilers are used to remove the heat in the form of high pressure steam. In designing the pilot plants, major emphasis was placed on the design of the catalytic reactor system. Thermodynamic parameters (composition of feed gas, temperature, temperature rise, pressure, etc.) as well as hydrodynamic parameters (bed depth, linear velocity, catalyst pellet size, etc.) are identical to those in a commercial methana-tion plant. This permits direct upscaling of test results to commercial size reactors because radial gradients are not present in an adiabatic shift reactor. 

For SNG manufacture, it is necessary to reduce the residual hydrogen to a minimum in order to achieve a high calorific value. This is best realized if the synthesis gas, instead of having a stoichiometric composition, contains a surplus of C02 which can be utilized to reduce the H2 content by the C02 methanation reaction to less than 1% according to equilibrium conditions. The surplus C02 must be removed at the end of the process sequence. It is, of course, also possible to operate a methanation plant with synthesis gas of stoichiometric composition then there is no need for a final C02 removal system. The residual H2 content will be higher, and therefore the heating value will be lower (cf. the two long term runs in Table II). 

Methane reforming with carbon dioxide to synthesis gas over Mg-promoted Ni/HY catalyst... 

FIGURE 9.18 Influence of pressure on reaction rate, olefin content in the C3 fraction, and methane selectivity with cobalt as the catalyst for FT synthesis. Catalyst 100Co-18Th02-100 Si02 (Kieselguhr), H2/CO = 1.8, 175°C. 

Figure 10.1 A comparison of the rate of methane synthesis overtwo different nickel single-crystal catalysts and supported Ni/alumina catalysts at 120 torr total reactant pressure. (Reprinted from Goodman, D.W., J. Vac. Sci. Technol., 20, 522-526, 1982. With permission from the American Institute of Physics.)...

Fig. 22. A comparison of the rate of methane synthesis over a clean single crystal Ni(100) catalyst with the corresponding rate over a potassium-doped catalyst. Total reactant pressure is 120 torr, Hj/CO = 4/1. (From Ref. 148.)...

Enamines and Formamidines. Enamines, prepared from methylpyridines, methyl-pyridazines, methylpyrimidines or methyltriazine, and A, A -dimethylformamide dimethylacetal or ferf-butoxybis(dimethylamino)methane, react with 2-phenyl-5(4//)-oxazolone 146 to afford the unsaturated 5(477)-oxazolones 199 and 201 that are intermediates in the synthesis of fused pyridones 200 and pyridotriazi-nones 202, respectively (Scheme 7.61). ... 

Methanation, that is, the transformation of CO to methane222 270-272 [Eq. (3.1), reverse process], was developed in the 1950s as a purification method in ammonia synthesis. To prevent poisoning of the catalyst, even low levels of residual CO must be removed from hydrogen. This is done by methanation combined with the water-gas shift reaction.214,273,274 In the 1970s the oil crises spurred research efforts to develop methods for substitute natural-gas production from petroleum or coal via the methanation of synthesis gas. ... 

Table 14.2 Synthesis of carbides and nitrides by reaction of a (bcc) metal film with CH4/H2 (10% methane) or with pure ammonia in a furnace... 

The activation of methane [1] is also included as one of the most desired yet not technically viable reactions. Abundant amounts of methane occur with crude oil and as gas in remote locations it is also produced in large quantities during hydrocarbon processing. A large fraction of this methane is flared, because economical use or transportation is not possible. This gas and the abundant resources of methane gas hydrates would make a very suitable feedstock for higher hydrocarbons, if its activation to produce molecules other than synthesis gas were feasible. Despite enormous fundamental and practical efforts [1-5], no applicable method has yet been found for creation of ethylene, methanol, or formaldehyde from methane. 

One synthesis of a dihydrophosphinine 155 was achieved by reaction of a dilithiated bis(3-indolyl)methane 156 with dichlorophenylphosphine <20050M37> (Scheme 6). The dimethylaminomethyl groups on nitrogen of 157, which serve both to protect the nitrogen atoms and direct metallation to the indolyl 2-positions, could be removed using NaBH4. 

In a trivial application of this method, one could consider the synthesis of carbon dioxide from methane as a combustion synthesis. This trivial example provides some framework for additional insights into the solid-state case. The balanced reaction for methane reacting with oxygen is... 

Metriol trinitrate can be prepared by nitration of methyltrimethylol-methane (Metriol) with mixed acid. Metriol is prepared by condensation of propanal with formaldehyde in a manner similar to that employed in the synthesis of pentaerythrol. 

Methane reacts with elemental sutfur above 700 C or at lower temperatures in the presence of a catalyst to give good yields of CS2, a reaction that has been used for the commercial synthesis of the disulfide.n-Butane, however, gives alkenes, dienes and thiophene under similar conditions. 

Usually not considered as Fischct-Tropsch processes are the methanol synthesis with oxidic chromium/zinc catalysts (c.f. the chapter on Methanol Building Block for Chemicals ) or the higli-pressure-high-temperature synthesis of higher alcohols over alkalized methanol catalysts or thorium catalysts (isobutyl synthesis). Tliese reactions, as well as the methanation reactions, are not covered in this contribution. 

This general method of synthesis has been applied to each member of the methane series with the result that each hydrocarbon has been proven to be the methyl substitution product of another hydrocarbon containing one less carbon atom. We have then for the successive members of the series a continually elongating chain of carbon groups, each group being a residue of methane. For the first six members the formulas are as follows ... 

The first completely synthetic ion exchange resins were prepared by B. A. Adams and E. L. Holmes in 1935. The basis of their synthesis was the condensation polymerization of methanal (formaldehyde) with phenol or polysubstituted benzene compounds to give, after... 

After desulfurization, steam is added and the mixture heated to 480 to 550°C before it is fed into the primary reformer. The gas leaving the primary reformer contains between 7 and 10% methane. This is removed in so-called secondary reformers in which the gas leaving the primary reformer is partially burnt with air in nickel catalyst-filled shaft furnaces (autothermal process), whereupon the temperature increases to ca. 1000°C. Under these conditions the methane reacts with the steam reducing the methane content in the synthesis gas to ca. 0.5 mole %. The quantity of air is adjusted to give the nitrogen to hydrogen ratio required for the stoichiometry of the ammonia synthesis. 

Methane reacts with steam in the presence of a supported nickel catalyst to produce a mixture of CO and H2, also known as synthesis gas or syngas as represented by Equation 2.1. This reaction is also referred to as steam methane reforming (SMR) and is a widely practiced technology for industrial production of H2. However, the SMR is not really just one reaction as indicated in Equation 2.1 but involves contributions from several different catalyzed reactions such as water-gas shift... 

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