Reaction of Methane with Steam

Interaction of methane with steam on a nickel surface is the basis of the natural gas reforming process. The process is used as a source of hydrogen for ammonia production and methanol synthesis and, therefore, finds a large-scale industrial application. 

At high temperatures, such as 900°C, the effect of entropy increase in reaction (272) resulting from the increase in the number of gas molecules outweighs the effect of enthalpy increase due to the reaction consequently, the reaction can proceed in the forward direction to its end under atmospheric pressure, or even at pressures of some tens of atmospheres. At lower temperatures (e.g., 300°C) the reaction under atmospheric pressure can go completely in the reverse direction. In the intermediate temperature range and at pressures near 1 atm, the substances entering (272) coexist at equilibrium in comparable amounts. 

The stoichiometry of the reaction of methane with steam on nickel is described by (272) together with the equation of the water-gas shift reaction  

We studied methane reforming kinetics at atmospheric pressure. The utilization of circulation flow systems made it possible to use nickel foil as 

At 900°C the rate of the reaction as measured by the amount of CH4 consumed, r, is satisfactorily described by a simple first-order equation (82)  

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Let us write such a model for the catalytic reaction of methane with steam on a nickel catalyst. Its detailed mechanism has been given above. 

Hydrogen is produced commercially by the reaction of methane with steam ... 

Catalyst-based technologies were introduced in the second half of the 19th century. The Deacon process (2HC1 -I- O2 + — H2O + CI2) was discovered in 1860, and the oxidation of SO2 to SO3 by platinum was discovered by Messel in 1875. Mond introduced the nickel-catalyzed reaction of methane with steam (CH4... 

A chemist examining the conversion of methane to other fuels was investigating the following reaction describing the reaction of methane with steam at 1200 K ... 

Nitrogen gas, from the air, is mixed with hydrogen gas, obtained from the reaction of methane with steam (steam re-forming). The nitrogen and hydrogen are fed into the main reaction vessel in the ratio of 1 3 by volume. 

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. 

To exemplify a complex mechanism of a heterogeneous catalytic reaction, we will consider the interaction of methane with steam on a nickel surface. Stoichiometric equations for this reaction are... 

In practice, gas mixtures containing carbon monoxide (CO) as well as carbon dioxide (C02) and unconverted methane (CH4) are produced and require further processing. The reaction of CO with steam (water-gas shift) over a catalyst produces additional hydrogen and C02, and after purification, high-purity hydrogen (H2) is recovered. In most cases,... 

C. is necessary for its practical completion. The decomposition of methane with steam goes quantitatively at 1300° C. to form hydrogen and carbon monoxide. It is possible, however, by using an excess of steam to force the reaction to the right and thus to obtain good conversion to... 

Nickel on an acidic support, such as that used for methane reforming, will promote the desired naphtha decomposition reaction, but it also promotes the cracking and polymerization reactions that are the basis for carbon formation. ICI has solved this problem by incorporating an alkali metal into their catalyst [7]. The alkali accelerates the reaction of carbon with steam (the primary carbon removal reaction) and at the same time neutralizes acidity in the support inhibiting the cracking and polymerization reactions (other carbon-forming reactions). The most effective alkali is K2OH (potash). Most naphtha reformers use the alkalized catalyst developed by ICI [7]. 

Ammonia is synthesised from its elements nitrogen and hydrogen. The nitrogen is obtained by the fractional distillation of liquid air. The hydrogen is obtained by the reaction of methane (from natural gas) with steam. 

The direct reaction of methane partial oxidation always competes with total oxidation reactions, which are also responsible for O2 consumption, whereas steam and dry reforming and C-forming reactions are also to be considered. All reactions are catalyzed by the materials which are active in partial oxidation, but different scales of reactivity for the catalysts can be estimated from the experimental data. Total oxidation prevails at the light-off of the fuel-rich stream over most catalysts, but precious metals are more active than transition metals. 

Methane is an important starting material for numerous other chemicals. The most important of these are ammonia, methanol, acetylene, synthesis gas, formaldehyde, chlorinated methanes, and chlorofluorocarbons. Methane is used in the petrochemical industry to produce synthesis gas or syn gas, which is then used as a feedstock in other reactions. Synthesis gas is a mixture of hydrogen and carbon monoxide. It is produced through steam-methane reforming by reacting methane with steam at approximately 900°C in the presence of a metal catalyst CH4 + H20 —> CO + 3H2. Alternately, methane is partially oxidized and the energy from its partial combustion is used to produce syn gas ... 

The Use of Other Metals for Methanation and Steam Reforming. - The review by Vannice133 gives a good description of work in the reactions of CO with hydrogen over metals such as Fe, Ru, Co, and other Group VIII metals. Hence, only a few selected references will be discussed here. 

Munster and Grabke196 have studied the kinetics of the steam reforming of methane with iron, nickel, and iron-nickel alloys. The concluded that the steam reforming of methane is a sequence of two reactions ... 

Some research groups working on the modeling of MCFC include the reforming reactions in their process models in different ways. He and Chen [1] and Yoshiba et al. [2] only consider the water-gas shift reaction in a spatially distributed anode channel. Due to its high rate, they assume the shift reaction to be in chemical equilibrium. Lukas and Lee [3] and Park et al. [4] also describe the water-gas shift reaction in equilibrium, but in addition they include the steam reforming reaction of methane as an irreversible reaction with a finite reaction rate. In particular, Park... 

C. Soaking Phase. The soaking phase takes place in the rest of the reactor, where the gas is at high temperature. Minor changes in gas composition occur due to secondary reactions of methane and carbon. As the reaction rates are relatively low, the methane content is higher than would be expected from equilibrium. During the soaking phase, a portion of the carbon also disappears by reactions with CO2 and steam. However, some carbon is always present in the product gas from the reactor in a quantity equivalent to about 1-3% wt of the oil feed. Natural gas feedstock produces only a very small amount of residual carbon i.e., about 0.02% wt of the gas feedstock. 

The catalytic reaction of steam with methane at elevated temperatures (300-400 + C) over various catalysts copper or nickel/molybde-num oxide/alumina—can be made to yield CO and H2 in desired ratios. The generalized reaction for hydrocarbons with steam is ... 

The steam reforming reaction of methane is endothermic and proceeds with an increase in volume. In Figures 30 and 31 [1487] the relationship between equilibrium methane concentration (a measure for the theoretical possible conversion) and temperature, steam-to-carbon ratio S/C, and reforming pressure are plotted for the range relevant for the reaction in the primary reformer. 

In a real coal gasification reactor, sulfur in the coal would form hydrogen sulfide in the product gas. nitrogen in the coal would form N2. some of the carbon monoxide formed in the first reaction would react with steam to form carbon dioxide and more hydrogen, and some of the carbon in the coal would react with hydrogen to form methane. For simplicity, we are ignoring these reactions. 

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