CO methanation

Gaseous vent streams from the different unit operations may contain traces (or more) of HCl, CO, methane, ethylene, chlorine, and vinyl chloride. These can sometimes be treated chemically, or a specific chemical value can be recovered by scmbbing, sorption, or other method when economically justified. Eor objectionable components in the vent streams, however, the common treatment method is either incineration or catalytic combustion, followed by removal of HCl from the effluent gas. 

Significant differences were observed when S/G was varied from 0.15 to 0.40. At the lower S/G ratios there is no CO shift conversion whereas there is CO shift conversion at the higher S/G ratios. When the data are evaluated and activity constants for CO and C02 methanation and CO shift conversion are determined, the activity for methanation remains the same regardless of the S/G. However, with high S/G, shift conversion occurs at about 25% of the rate of CO methanation. At low S/G, no shift conversion is observed. 

In the early phases of this study, temperature surveys were run on various catalysts in order to determine the threshold temperature for CO methanation. The data in Table XVII, calculated for 0.25-in. C150-1-02 catalyst, are rather typical. 

It is concluded that a fully satisfactory system for calculating simultaneous reactions of CO and COo with H2 and H20 will require a schedule of the effect of CO on C02 methanation as a function of temperature. This effect will probably be different with different particle sizes. From a commercial standpoint, the particle size range may be too small to require much difference in the treatment of the data, but in the laboratory very small particle size may lower the CO methanation rate. A simple kinetics system such as that derived from Equation 3 may be satisfactory for all the reactions. It is unlikely that reliable data will be collected soon for the shift reaction (since it is of a somewhat secondary nature and difficult to study by itself), and therefore a more complicated treatment is not justified. 

For CO methanation, one of the simple literature kinetic systems (2, 3) should be as reliable or better than the one used in this study. With C02 methanation, it is less certain that a simple system is indicated. It is probably of more urgency to elucidate the quantiative effect of CO on C02 methanation than to find a complex kinetic expression for the C02-H2 reaction itself. 

It is expected that the actual rate of CO methanation will always be high, at least under industrial conditions, whereas the C02 methanation rate will vary from about the same as that for CO down to zero, depending on operating pressure, temperature, CO content of the gas, and catalyst particle size. Meanwhile a water-gas shift (or reverse shift) reaction will be occurring at all times at a fairly high rate. 

Noble metal dispersions and surface areas Table 2 lists the apparent dispersions obtained from the CO methanation technique. No correlation is observed between dispersion and catalyst performance as measured by the CO/NOx crossover efficiencies. The C2 and C3 Pd-only TWCs, despite their extremely high CO/NOx crossover efficiencies, gave apparent dispersions of 3.5 and 3.0% after 75 and 120 h aging versus higher values of 5.9% for the Pd/Rh catalyst (E) and 4.3% for the Pt/Rh catalyst (G). both of which displayed low CO/NOx crossover efficiencies. Even between the two Pd/Rh catalysts, catalyst E h2is an apparent dispersion more than four times that of catalyst F, yet the two are nearly identical in their CO/NOx crossover efficiencies. 

Catalysts were prepared by impregnation using cobalt (ii) nitrate. Co/A1203 was the most the active and selective catalyst. Suppresses the ethanol decomposition and CO methanation reactions... 

The ability of bimetallic systems to enhance various reactions, by increasing the activity, selectivity, or both, has produced a great deal of interest in understanding the different roles and relative importance of ensemble and electronic effects. Deposition of one metal onto the single-crystal face of another provides an advantage by which the electronic and chemical properties of a well-defined bimetallic surface can be correlated with the atomic structure.5 22 23 Besenbacher et al.24 used this method to study steam reforming (the reverse of the CO methanation process) on Ni(l 11) surfaces... 

Fig. 19. A plot of the rate of CO methanation as a function of sulfur and phosphorous coverage over a Ni(100) catalyst at 120 torr and a H /CO ratio equal to 4. (From R. 4.)...

Gasoline has many advantages over methanol, but conversion to H2 requires temperatures in excess of 650°C and produces greater amounts of CO, methane (CH4), and possibly coke. 

They reported that the catalyst exhibits very high selectivity to hydrogen and carbon dioxide. The CO methanation and ethanol decomposition are considerably reduced. In addition, coke formation is strongly depressed because of the benefits induced by the use of the basic support, which modify positively the electronic properties of Ni. 

Palladium dichloride is a starting material for preparing several palladium compounds. It also is used for detection of carbon monoxide. For such detection, a paper is soaked in very dilute solution of PdCb which is decolorized by CO, methane and other reducing substances. It also is used in toning and electroplating solutions and in photography for porcelain pictures. 

A global rate expression for CO methanation over a nickel catalyst is given by Lee (1973) and Vatcha (1976). They report that a Langmuir-Hinshelwood rate law of the form... 

Figure 4.43. Energy diagram for CO methanation over Ni. Adapted from [140].

Figure 4.44. Contracted energy diagrams for CO methanation over Ni, Ru, and Re (Left). BEP-relation for CO dissociation over transition metal surfaces (right-top) and the corresponding volcano-relation for the turnover frequency (right-bottom). Adapted from [55,140].

The chemistry of the major processes of the petrochemical industry, including cracking, reforming, isomerization, and alkylation, is covered in Chapters 2, 4, and 5, respectively. The increasingly important Ci chemistry—that of one-carbon compounds (C02, CO, methane, and its derivatives)—is discussed in Chapter 3 (Synthesis from Ci sources). 

The results are consistent with the fact that carbidic carbon Cs is formed on Ni while heated either in clean CO or in H2 + CO, but with H2 the CO dissociation proceeds much faster (2, 110). It is also of relevance that in the FT-IRAS study of the CO methanation on Ru(001), which is very similar to the methanation on Ni surfaces (112), Hoffmann and Robbins (112) suggested the formation of the H CO complex to reconcile all experimental findings. 

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