Methane from carbon monoxide and

Tn the synthesis of methane from carbon monoxide and hydrogen, it is desired to operate the reactor or reactors in such a way as to avoid carbon deposition on catalyst surfaces and to produce high quality product gas. Since gas compositions entering the reactor may vary considerably because of the use of diluents and recycle gas in a technical operation, it is desirable to estimate the effects of initial gas composition on the subsequent operation. Pressure and temperature are additional variables. 

The reactions studied were the catalytic formation of methane from carbon monoxide and hydrogen (according to Sabatier (34), normal pressure), the catalytic hydrogenation of unsaturated hydrocarbons and also of unsaturated fatty acids ( fat hardening according to Normann (35)). Here again, a certain analogy was established between... 

The formation of methane from carbon monoxide and hydrogen using a nickel catalyst was studied by Parsley. The reaction... 

Following earlier work in which the intermediate in the formation of methane from carbon monoxide and hydrogen was found to be carbon, McCarty and Wise carried out a thorough study of the system. Four types of carbon were found to be formed from carbon monoxide on nickel at 550 50K. Chemisorbed carbon atoms reacted readily with hydrogen as did the initial layers of nickel carbide. Further deposits of the carbide, amorphous carbon, and crystalline elemental carbon were much less reactive and the kinetics of the reaction should be described by the established rate laws. Conversion of the more active to the less active forms of carbon occurred above approximately 600 K. 

In 1902 Sabatier and Senderens (5) reported the synthesis of methane from carbon monoxide and hydrogen in the presence of nickel and cobalt catalysts. 

Several important chemical reactions for the conversion of coal to methane are shown in Table 2. Steam conversion involves the reaction of coal with steam to produce hydrogen and carbon monoxide. Hydrogen conversion is a reaction in which coal and hydrogen react to form methane. Oxygen conversion produces hydrogen and carbon monoxide by partial oxidation of coal. Methan-ation involves a reaction in which methane and water are produced from carbon monoxide and hydrogen. The water gas shift reaction between carbon monoxide and steam produces carbon dioxide and hydrogen. 

Another important use of methane is its conversion into synthesis gas (or syn-gas), a mixture of hydrogen gas and carbon monoxide as shown in Figure 17.1. Syn-gas can also be derived from coal. When this occurs, it is called water gas. Interestingly, the reaction of methane giving carbon monoxide and hydrogen can be reversed so that methane can be produced from coal through this route. 

In this regard, it is well to remember the role which the wall plays on the nature of the products obtained from gas phase oxidation. There is certainly common agreement that walls and wall reactions are important in this respect. For example, Hay et al. (11) have shown the importance of the walls in determining the nature and composition of the oxygenated products from 2-butane + 02 at 270°C. Cohens study on the photo-oxidation of acetone also illustrates this point (10). He found that if acetone is photolyzed by itself in a quartz vessel, the normal products—methane, ethane, carbon monoxide, and methyl ethyl ketone— are produced. 

Methanol can also be produced through a two-step process comprising of steam reforming of methane and methanol synthesis from carbon monoxide and hydrogen. The first step of steam reforming of methane consists of the following two reactions ... 

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

Acyl cations are formed in the reversible addition of carbon monoxide to carbonium ions (Balaban and Nenitzescu, 1959 Koch and Haaf, 1958a, b 1961). The formation of the acetyl cation 193 from carbon monoxide and methane in SbF6 has been directly observed by XH n.m.r. 

Fig. 2.19. Standard free energies of formation of hydrocarbons and alcohols from carbon monoxide and hydrogen with water as by-roduct. A, ethanol B, methanol C, acetylene D, benzene E, propylene F, ethylene G, propane H, ethane I, methane [7].

Derivation (1) By high-pressure catalytic synthesis from carbon monoxide and hydrogen (2) partial oxidation of natural gas hydrocarbons (3) several processes for making methanol by gasification of wood, peat, and lignite have been developed but have not yet proved out commercially (4) from methane with molybdenum catalyst (experimental). 

Other gas permeation applications include separation of hydrogen from methane, hydrogen from carbon monoxide, and removal of components such as carbon dioxide, helium, moisture, and organic solvents from gas streams. Gas permeation for such operations may provide a more economical and more practical alternative than conventional separation processes such as cryogenic distillation, absorption, or adsorption. 

Table I.—Formation of Methane and Hydrogen from Carbon Monoxide and Steam. Inlet gas practically pure carbou monoxide plus steam.

Qi et al. [32] tested autothermal reforming of n-octane over a ruthenium catalyst, which was composed of 0.5 wt.% ruthenium stabilized by ceria and potassium on y-alumina. It showed full conversion of n-octane for 800 h. However, the selectivity moved from carbon dioxide and methane toward carbon monoxide and light hydrocarbons, which has to be regarded as an indication of catalyst degradation during long-term tests despite the fact that full conversion was achieved. After 800 h the catalyst consequently showed incomplete conversion. Tests performed on the spent catalyst revealed losses of specific surface area and of 33 wt.% of the noble metal. 

Although all reactions may describe specific operating conditions, only two out of the first four reactions are independent from a thermodynamic point of view, since die other two can be established as linear combinations of the two selected ones. Catalytic studies indicate that it is steam reforming of methane to carbon monoxide and the water-gas-shift reactions that are the independent reactions in addition to the steam reforming of higher hydrocarbons as the last reaction. This set of reactions (Rl, R4, and R5 in Table 1.2) will consequently be used in the following. 

The equilibrium conversion in the steam reforming of methane to carbon monoxide and hydrogen is determined from the two equilibrum expressions shown in Example 1.1. In this second example a large hydrogen plant making 100,000 Nm /h of H2 is considered. 

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