Carbon monoxide conversion activity

A 10 Ndm3 min-1 feed composed of 75.0% H2, 0.7% CO and balance C02 with air for oxidation was fed into the relatively large test reactor carrying 230 cm3 catalyst microsperes of 1 mm diameter. Of the non-precious metal catalysts, that composed of hopcalite showed the highest activity, achieving almost full conversion in the temperature range 130-160 °C. The minimum CO output achieved was 40 ppm. A minimum 02/CO ratio of 2.5 was determined for this catalyst to achieve a carbon monoxide conversion exceeding 90%. The catalysts tested are summarized in Table 2.7. 

As noted above, the reaction mixture most often used contains only the amount of oxygen required to oxidise either the carbon monoxide or some of the hydrogen, or a modest excess. This, together with knowledge of the relative activation energies (Figure 7.1) helps to explain the temperature profile of conversions and selectivity, as shown in a typical case in Figure 7.2. The maximum in the carbon monoxide conversion arises because... 

Generally, in a conventional WGS system a two-step shift is used to obtain high CO conversion rates. In the first high-temperature shift reactor the major part of the CO is converted at high activity, whereas in the second shift reactor the rest of the CO (closely up to the thermodynamic equilibrium) is converted at low temperature and also low activity. Steam to carbon monoxide ratios above the stoichiometric ratio (higher than 2) are generally being used to attain the desired carbon monoxide conversion, but also to suppress carbon formation on certain catalysts. 

Carbon monoxide oxidation activity of various catalysts are represented as percentage conversion of carbon monoxide to carbon... 

Figure 13A shows the progress of carbon monoxide conversion (standard cobalt catalyst, fixed catalyst bed, 100 vol. synthesis gas throughput per volume of catalyst per hour) at different points of the gas inlet on the first day of operation. The freshly reduced Co catalyst is very active. Carbon monoxide conversion was 75% in the first 10% of the catalyst bed. 

Dofour et al. [17] investigated the influence of synthesis method, precursor and effect of Cu addition on the WGS activity of Fe-Cr-Co catalysts. They prepared FeCr, FeCrCu, FeCrCo and FeCrCuCo formulations by oxidation precipitation method, using chloride (Cl) and sulphate (S) metal precursors. The catalytic activity results of FeCrCo and FeCrCuCo catalysts are presented in Figure 2.2. All the materials prepared from sulphate precursor showed higher carbon monoxide conversion than those synthesized with chloride. As expected Cu-promoted catalysts show better activity than Fe-Cr-Co catalysts. For the catalysts synthesized by chloride precursor, in the case of cobalt, incorporation of this metal into the magnetite lattice could improve the covalency of Fe and... 

A catalytic activity test of the MOjC-coated powder revealed that at 275°C, it had comparable activity to commercial bulk MOjC after 1 h on stream. At these conditions Ihe carbon monoxide conversion with the MAFBS-prepared... 

In modem, single stream ammonia plants there is little scope in the design to make significant changes to the operating conditions in any of the individual catalyst reactors. Operating conditions for the carbon monoxide conversion reaction are shown in Table 9.14. The only practical variable is operating temperature which can be slowly increased as catalyst loses activity. 

An LTS catalyst should be sufficiently active to give a high conversion for a given volume of catalyst at the minimum practicable temperature. It should also be thermally stable and operate for the design period with maximum carbon monoxide conversion. With proper design and good upstream poisons removal, a typical catalyst lifetime is about three years. 

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 space velocity was varied from 2539 to 9130 scf/hr ft3 catalyst. Carbon monoxide and ethane were at equilibrium conversion at all space velocities however, some carbon dioxide breakthrough was noticed at the higher space velocities. A bed of activated carbon and zinc oxide at 149 °C reduced the sulfur content of the feed gas from about 2 ppm to less than 0.1 ppm in order to avoid catalyst deactivation by sulfur poisoning. Subsequent tests have indicated that the catalyst is equally effective for feed gases containing up to 1 mole % benzene and 0.5 ppm sulfur (5). These are the maximum concentrations of impurities that can be present in methanation section feed gases. 

GP 9] [R 16] The reaction rate and activation energy of metal catalysts (Rh, Pt or Pd) supported on alumina particles ( 3 mg 53-71 pm) were determined for conversions of 10% or less at steady state (1% carbon monoxide 1% oxygen, balance helium 20-60 seem up to 260 °C) [7, 78]. The catalyst particles were inserted into a meso-channel as a mini fixed bed, fed by a bifurcation cascade of micro-channels. For 0.3% Pd/Al203 (35% dispersion), TOF (about 0.5-5 molecules per site... 

A somewhat related process, the cobalt-mediated synthesis of symmetrical benzo-phenones from aryl iodides and dicobalt octacarbonyl, is shown in Scheme 6.49 [100]. Here, dicobalt octacarbonyl is used as a combined Ar-I bond activator and carbon monoxide source. Employing acetonitrile as solvent, a variety of aryl iodides with different steric and electronic properties underwent the carbonylative coupling in excellent yields. Remarkably, in several cases, microwave irradiation for just 6 s was sufficient to achieve full conversion An inert atmosphere, a base or other additives were all unnecessary. No conversion occurred in the absence of heating, regardless of the reaction time. However, equally high yields could be achieved by heating the reaction mixture in an oil bath for 2 min. 

Conversly, the Fe3(C0)12 NaY adduct is active for syngas conversion. A non-decomposed sample exhibits a significant activity at 230°C whereas the catalytic efficiency for the decar-bonylated one already appears at 200°C. Infrared experiments show an increase in the stability of the Fe3(C0)- 2 units upon thermal treatment under CO atmosphere so that total carbon monoxide evolution only takes place at 230°C thus suggesting that the catalyst is certainly not Fe3(C0)- 2. This cluster has to be transformed into higher nuclearity species which bind less strongly with carbon monoxide upon CO re-adsorption (1 7). 

Recently, Shibata et al. reported on the successful conversion of al-lenynes [49]. By employing [IrCl(CO)(PPh3)2] as active catalyst (Eq. 5), reactions were carried out under a very low pressure of carbon monoxide affording yields up to 91%. 

In many applications acetic acid is used as the anhydride and the synthesis of the latter is therefore equally important. In the 1970 s Halcon (now Eastman) and Hoechst (now Celanese) developed a process for the conversion of methyl acetate and carbon monoxide to acetic anhydride. The process has been on stream since 1983 and with an annual production of several 100,000 tons, together with some 10-20% acetic acid. The reaction is carried out under similar conditions as the Monsanto process, and also uses methyl iodide as the "activator" for the methyl group. 

However, in contrast to the human His25Ala HO-l heme complex, which has no detectable activity in the absence of imidazole (78), the His20Ala Hmu O rheme complex in the presence of NAD PH and NADPH-cytochrome P450 reductase was foimd to catalyze the initial meso-hydroxylation of the heme (151). The product of the reaction was Fe verdoheme, as judged by the electronic absorption spectrum and the detection of carbon monoxide as a product of the reaction. Hydrolytic conversion of the verdoheme product to biliverdin and subsequent HPLC analysis confirmed that the oxidative cleavage of the porphyrin macrocycle was specific for the a-meso-carbon. 

Alkanes can also be activated by oxidative addition of coordinatively unsaturated organo-metallic reagents. In the presence of carbon monoxide, C—C bond formation can ensue, e.g., the conversion of pentane to hexanal7. Note that this method, highly selective for primary sites, is complementary to the radical-based chemistry outlined above. 

The previous extension of solvent mixtures involved solvent interfaces. This organic-water interfacial technique has been successfully extended to the synthesis of phenylacetic and phenylenediacetic acids based on the use of surface-active palla-dium-(4-dimethylaminophenyl)diphenylphosphine complex in conjunction with dode-cyl sodium sulfate to effect the carbonylation of benzyl chloride and dichloro-p-xylene in a toluene-aqueous sodium hydroxide mixture. The product yields at 60°C and 1 atm are essentially quantitative based on the substrate conversions, although carbon monoxide also undergoes a slow hydrolysis reaction along with the carbonylation reactions. The side reaction produces formic acid and is catalyzed by aqueous base but not by palladium. The phosphine ligand is stable to the carbonylation reactions and the palladium can be recovered quantitatively as a compact emulsion between the organic and aqueous phases after the reaction, but the catalytic activity of the recovered palladium is about a third of its initial activity due to product inhibition (Zhong et al., 1996). 

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