Carbon monoxide, shift

Ammonia production from natural gas includes the following processes desulfurization of the feedstock primary and secondary reforming carbon monoxide shift conversion and removal of carbon dioxide, which can be used for urea manufacture methanation and ammonia synthesis. Catalysts used in the process may include cobalt, molybdenum, nickel, iron oxide/chromium oxide, copper oxide/zinc oxide, and iron. 

It was shown in laboratory studies that methanation activity increases with increasing nickel content of the catalyst but decreases with increasing catalyst particle size. Increasing the steam-to-gas ratio of the feed gas results in increased carbon monoxide shift conversion but does not affect the rate of methanation. Trace impurities in the process gas such as H2S and HCl poison the catalyst. The poisoning mechanism differs because the sulfur remains on the catalyst while the chloride does not. Hydrocarbons at low concentrations do not affect methanation activity significantly, and they reform into methane at higher levels, hydrocarbons inhibit methanation and can result in carbon deposition. A pore diffusion kinetic system was adopted which correlates the laboratory data and defines the rate of reaction. 

The success of the correlation of catalytic behavior with bulk Mossbauer parameters by Skalkina et al. is also reflected in the work of Tops0e and Boudart (96). As discussed earlier, these authors found a decrease in the isomer shift of the octahedral iron ions in a lead-promoted Cr-Fe304 carbon monoxide shift catalyst, indicative of an increased covalency of these ions. Schwab et al. (203) have proposed a correlation of the activity for CO oxidation by ferrites with the octahedral ions in these materials, and the electron transfer required for this catalytic process may be facilitated by an increased covalency of the metal ions (204). In view of these suggestions, the lead-promoted catalyst is expected to possess a higher catalytic activity for the CO shift reaction than an unpromoted catalyst, as evidenced by the Mossbauer parameters of these two samples. This has in fact been shown experimentally to be the case (96). For the reverse CO shift reaction over supported europium (176), the success of the correlation between catalytic activity and the Mossbauer parameters (in this case the reducibility) has already been noted in Section III, A, 4. 

Carbon monoxide shift (high temp.) Fe203/Cr203... 

As shown in Figure 5.4 and Figure 5.17 and as described for each of the major processes that produce synthesis gas, the Water Gas Shift Conversion or the Carbon Monoxide Shift reaction is one of the traditional purification steps that will still be found in many ammonia plants. The CO must be removed because it acts as a poison to the catalyst that is used in ammonia synthesis. 

The Carbon Monoxide Shift removes most of the carbon monoxide (CO) from the synthesis gas, and [as shown by Eq. (5.2)] it also produces more hydrogen. 

The carbon monoxide shift removes most of or if C02 is present, any of these compounds the CO from the synthesis gas and also pro- will be a poison for many catalysts and will duces more hydrogen. partly or completely inhibit catalyst activity. 

The steam-methane reforming process produces ammonia by steam reforming natural or refinery gas under pressure, followed by carbon monoxide shift, purification of raw synthesis gas, and ammonia synthesis. In the process, saturated and unsaturated hydrocarbons are decomposed by steam according to the basic equation ... 

It has been already mentioned briefly, that compared to the synthesis section itself, where of course some progress has been made in converter design and optimization of heat recovery, the more fundamental changes over the years have occurred in synthesis gas preparation and gas compression. It is therefore appropriate to discuss the various methods for the synthesis gas generation, carbon monoxide shift conversion, and gas purification in some detail. Figure 29 shows schematically the options for the process steps for ammonia production. 

On account of the striking analogy with the selectivity of the alcohol decomposition, however, this does not seem so probable, but it is worth while to consider this possibility in the case of the decomposition of formic acid on those catalysts which are known to accelerate the carbon monoxide shift reaction i,e., Fe304 and MgO. 

For Eq. (5.7), the carbon monoxide shift conversion (which in nearly every case has to be considered), the equilibrium composition of the shift conversion is not influenced by the total pressure, because the number of molecules (reactants) on... 

H. Uchida, N. Isogai, M. Oba, T. Hasegawa, The zinc oxide-copper catalyst for carbon monoxide-shift conversion. I. The dependency of the catalytic activity on the chemical composition of the catalyst, Bull. Chem. Soc. Jpn. 40 (1967) 1981-1986. 

In fact, moisture appears to play a more integral role in the combustion of hydrogen-deficient carbonaceous fuels (such as coal) than has been generally recognized. The carbon-steam reaction to produce carbon monoxide and hydrogen (which are then oxidized to the final products) is an important stage in the combustion sequence as is the carbon monoxide shift reaction to yield carbon dioxide and hydrogen ... 

Table 3.7 Equilibrium constant for the carbon monoxide shift reaction...

Heat exchange in multi-bed direct heat exchange reactor is by directly adding a cold gas to the reaction gas to lower the reaction temperature this is the so-called cold-quench . If the quenching gas is the feed gas, it is called feedgas quench , such as the Topspe S-100 type ammonia converter, and ICI cold-quencher ammonia synthesis converter. If the quenching gas is not the feed gas, it is called non-feedgas quench , such as the steam cold-quench carbon monoxide shift reactor. 

The reaction rate of the whole process in some reversible exothermic reactions, such as the carbon monoxide shift reaction, can be considerable. The heat needed to be extracted from unit volume of catalyst at the beginning and the ending stages of the reaction may vary by 10 times or more. These reactions require multi-stage heat exchange reactors. Other reactions, such as the ammonia synthesis... 

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