Catalyst methanation

Most commercial methanator catalysts contain nickel, supported on alumina, kaolin, or calcium aluminate cement. Sulfur and arsenic are poisons to the catalyst, which can also be fouled by carry-over of solvent from the CO2 removal system. 

Remaining trace quantities of CO (which would poison the iron catalyst during ammonia synthesis) are converted back to CH4 by passing the damp gas from the scmbbers over a Ni methanation catalyst at 325° CO -t- 3H2, CRt -t- H2O. This reaction is the reverse of that occurring in the primary steam reformer. The synthesis gas now emerging has the approximate composition H2 74.3%, N2 24.7%, CH4 0.8%, Ar 0.3%, CO 1 -2ppm. It is compressed in three stages from 25 atm to 200 atm and then passed over a promoted iron catalyst at 380-450°C ... 

Nickel. As a methanation catalyst, nickel is presently preeminent. It is relatively cheap, it is very active, and it is the most selective to methane of all the metals. Its main drawback is that it is easily poisoned by sulfur, a fault common to all the known active methanation catalysts. The nickel content of commercial nickel catalysts is 25-77 wt %. Nickel is dispersed on a high-surface-area, refractory support such as alumina or kieselguhr. Some supports inhibit the formation of carbon by Reaction 4. Chromia-supported nickel has been studied by Czechoslovakian and Russian investigators. 

Catalyst Poisons. Hausberger, Atwood, and Knight (33) reported that nickel catalysts are extremely sensitive to sulfides and chlorides. If all materials which adversely affect the performance of a catalyst were classified as poisons, then carbon laydown and, under extreme conditions, water vapor would be included as nickel methanation catalyst poisons. 

The catalyst losses in either system are moderate and not excessively costly when inexpensive iron catalyst is used (as for production of liquid hydrocarbons). It is questionable, however, whether comparable losses of expensive nickel catalysts (for methanation) could be tolerated. For this reason, it is quite likely that the fluidized catalyst system will be used for methanation only after a cheap methanation catalyst is developed. 

Development of Methanation Catalysts for the Synthetic Natural Gas Processes... 

A good methanation catalyst is one which is physically strong, is reducible at 300°C (570°F) and has high activity. In order to provide a long life, it must retain these properties in use. Lives of 3-5 years are commonly obtained from charges of Imperial Chemical Industries, Ltd. (ICI) catalyst 11-3, depending on the temperature of operation and the presence of poisons in the synthesis gas, factors which are discussed below. These properties can be obtained by careful attention to the formulation and manufacture of the catalyst. 

Intimate mixing of the components can lead to the formation of compounds or of solid solutions of the components which are difficult to reduce at 300°C but which, when reduced, contain well dispersed and well stabilized nickel. Methanation catalysts in practice therefore are compromises which combine optimum reducibility with activity and stability. As an example of compound formation, alumina readily forms with nickel... 

In summary, therefore, we have found it beneficial to include a small amount of MgO (2-3% ) in ICI methanation catalyst 11-3. This provides the ideal compromise between ease of reducibility and sintering resistance. By this means, a catalyst is produced which is readily reduced at 300°-350°C (572°-662°F) loss of activity caused by sintering is not a problem... 

The poisons most likely to be encountered in an ammonia plant are those originating in the C02-removal system which precedes the metha-nator. Carry-over of a small amount of liquid into the methanator, which is almost inevitable, is not normally serious. Plant malfunction, however, can sometimes result in large quantities of C02-removal liquor being pumped over the catalyst, and this can be very deleterious. Table I lists the effects of common C02-removal liquors on methanation catalyst activity. 

Benfield process aqueous potassium carbonate blocking of pores of methanation catalyst by evaporation of potassium carbonate solution... 

In summary, therefore, we can say that methanation catalysts for these applications are very satisfactory in terms of activity, strength, and stability. In the absence of detrimental malfunctions, one can expect favorable operating experience, and we have demonstrated a simple and convenient method by which the future useful life of an on-line catalyst can be estimated. 

All tests reported here were performed with a special methanation catalyst developed by BASF, Ludwigshafen, for the process. The catalyst had a relatively high nickel content on a carrier. It was charged to reactors D2 and D3 in unreduced form and had to be activated by reduction with hydrogen. 

The selection of optimum reactor inlet and outlet temperatures is affected by catalyst activity, and catalyst stability, and the need to minimize operating and investment costs. When the special BASF methanation catalyst is used, inlet temperatures of 260°-300°C or even lower are quite acceptable (see Table II). The final decision on design inlet temperature is affected by engineering requirements. 

Catalyst Section. The design criteria for the HYGAS plant methanation section were developed in the late 1960 s (10). At that time, three commercially available nickel methanation catalysts and one ruthenium... 

Shift Conversion. The shift reaction and methanation proceed concurrently without interference over bulk methanation catalyst thereby eliminating the need for a separate shift conversion operation. 

Bench-Scale Reactor. The bench-scale reactor is 0.81 in. i.d. and 48 in. long. The nominal feed gas rate for this unit is 30 standard cubic feet per hour (scfh) the feed gas is supplied from premixed, high-pressure gas cylinders. Except for reaction temperature, the bench-scale unit is substantially manually operated and controlled. The catalysts used in these studies were standard commercial methanation catalysts ground to a 16-20 mesh size which is compatible with the small reactor diameter. 

Dr. Woodward I tried to indicate in my paper that in ammonia-hydrogen plant operation, in comparison with several other catalysts in such plants, the methanation catalyst situation is really well under control. Speaking for our company, and I would guess others, it s not a particularly active research area because we have higher priorities in catalyst development. As regards methanation catalysts for SNG, I did not discuss that today and perhaps I should let some other fellows answer first. Sulfur tolerance is one area for future development. 

Anonymous What else can we say about the poisoning of methanation catalysts by materials other than sulfur, e.g., any information in... 

A. Hausberger As we mentioned earlier, the light hydrocarbons do not seem to affect catalyst activity, and they do reform into methane. However, you can increase the hydrocarbon content to levels where they do depress the methanation activity. If the hydrocarbons are high enough in unsaturation, they will form carbon when they get to a certain level. As far as hydrogen cyanide and ammonia are concerned, we don t expect them to affect the nickel methanation catalyst. 

Dr. Moeller We have done this, and we compared an iron catalyst used for the Fischer-Tropsch plant and a nickel catalyst used in the methanation plant. By the same x-ray techniques, we found no nickel carbide on the used methanation catalyst, but we did find iron carbide on the used Fischer-Tropsch catalyst. 

Anonymous Can such a system remove sulfur to the low levels required for present day methanation catalysts ... 

Dr. Blum As a further comment on pressure optimization, and as it relates to our system, I think the response of the slurry methanation system to pressure is somewhat different from that of dry methanation. It relates to the ability of the catalyst to methanate a given amount of gas. In our system, the effective pressure is the total pressure minus the vapor pressure of the liquid phase. This doesn t hold for the standard methanation catalyst in the dry system. There is a different pressure relationship so the optimum just might not work quite the same way. 

Synthetic natural gas processes, development of methanation catalysts for the. 47... 

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