Carbon monoxide selective methanation

To further reduce the carbon monoxide, a preferential oxidation reactor or a carbon monoxide selective methanation reactor is used. The term selective oxidation is also used for preferential oxi-... 

Non-noble metal catalysts, particularly those containing nickel, have also been investigated extensively since 1990. Lunsford et al. (107) examined a 25 wt% Ni/Al203 catalyst in the temperature range 723-1173 K. Carbon monoxide selectivities approaching 95% and virtually complete conversion of the methane were achieved at temperatures above 973 K. The authors observed that, under their operating conditions, the calcined catalyst bed consisted of... 

Coke oven gas consists mainly of a mixture of carbon monoxide, hydrogen, methane, and carbon dioxide. It is contaminated with a variety of organic and inorganic compounds that have to be separated in absorption columns before its further use as a synthesis gas. The selective absorption of coke plant gas contamination results from a complex system of parallel liquid-phase reactions. Instantaneous reversible reactions ... 

Catalyst testing was performed in packed beds at a S/C ratio of three and reaction temperatures between 527 and 750 °C. The feed was composed of 12.5 vol.% methane and 37.5 vol.% steam, balance argon. At 700 °C reaction temperature and a space velocity of 32 h-1, conversion rates close to the thermodynamic equilibrium could be achieved. With increasing WHSV, the point of equal carbon dioxide to carbon monoxide selectivity was shifted to higher temperatures (Figure 2.17). In other words, C02/CO ratio of one was always achieved at about 90% conversion. During 96 h of operation, the catalyst showed no detectable deactivation, in contrast to its commercial nickel-based counterpart. 

At about 1 140 °C reaction temperature, full oxygen conversion was always achieved when the CH4/02 ratio was decreased from 2 to 1.5, but methane conversion increased from 45 to 96%. Carbon monoxide selectivity remained almost unchanged at 90%, but hydrogen selectivity increased from 75 to 83%. These effects were assumed to stem from the increased heat generation by enhanced methane combustion leading to a hot-spot at the reactor inlet. 

A feed of 100 Ncm3 min-1 methane and 50 Ncm3 min-1 oxygen was introduced into the reactor at a pressure loss of < 2.5 mbar. The residence time of the reaction was 50 ms. 60% conversion was achieved along with a high carbon monoxide selectivity of 70% at 700 °C reaction temperature. Owing to the short residence times applied, no coke formation was observed and carbon monoxide selectivity was higher than expected from the thermodynamic equilibrium [46],... 

Synthesis gas production from combined CO2 reforming and partial oxidation of natural gas Maximization of both methane conversion and carbon monoxide selectivity while maintaining tiie hydrogen to carbon monoxide ratio close to 1. Real-coded NSGA with blend crossover Empirical models were used for optimization. Mohanty (2006)... 

C and the selectivity toward aromatics increased from 4.9% to 16.4% at 380 C and from 3.6% to 18.9% at 500 C as the SiOj/AljOj ratio was raised. GAPO-5 and FeAPO-5 yielded mainly dimethylether. Carbon monoxide and methane were the principal products on VAPO-5. The highest selectivity to hydrocarbons was obtained on BeAPO-5. Hydrocarbon fractions containing 69.8% to 73.6% of olefins were obtained between 380 and 500 C with a BeO/AljOj ratio of 0.25. The conversion of methanol varied from 93.3% to 98.9% for the seune range of temperature. 

Figure 2. Methane and carbon monoxide selectivity over potassium promoted iron FTS catalyst...

In 1824, Henry reported the first example of poisoning. Ethylene inhibited the reaction between hydrogen and oxygen on platinum. He also noted selective oxidation in the reaction between oxygen and a mixture of hydrogen, carbon monoxide, and methane. 

The maximum absolute methane conversion of 21% was obtained at the temperature of 500 °C, while the maximum carbon dioxide conversion of 23% was achieved at 400—450 °C. Moreover, carbon monoxide selectivity was always higher than hydrogen selectivity, and this was read as an empirical proof of the effect of reverse water gas shift reaction and Boudouard reaction (Paturzo et al., 2003). 

Wanat et al. investigated methanol partial oxidation over various rhodium containing catalysts on ceramic monoliths, namely rhodium/alumina, rhodium/ceria, rhodium/ruthenium and rhodium/cobalt catalysts [195]. The rhodium/ceria sample performed best. Full methanol conversion was achieved at reaction temperatures exceeding 550 °C and with O/C ratios of from 0.66 to 1.0. Owing to the high reaction temperature, carbon monoxide selectivity was high, exceeding 70%. No by-products were observed except for methane. 

Figure 4.8 Methane conversion, hydrogen selectivity and carbon monoxide selectivity versus gas hourly space velocity as determined by Hohn and Schmidt [223] (symbols) and calculated by Bizzi et al. [224] (straight lines) for short contact time partial oxidation of methane in fixed beds ofdifferent particle diameters (a) 0.4 mm (b) 0.8 mm (c) 1.2 mm (d) 3.2 mm. 

A flow diagram for the system is shown in Figure 5. Feed gas is dried, and ammonia and sulfur compounds are removed to prevent the irreversible buildup of insoluble salts in the system. Water and soHds formed by trace ammonia and sulfur compounds are removed in the solvent maintenance section (96). The pretreated carbon monoxide feed gas enters the absorber where it is selectively absorbed by a countercurrent flow of solvent to form a carbon monoxide complex with the active copper salt. The carbon monoxide-rich solution flows from the bottom of the absorber to a flash vessel where physically absorbed gas species such as hydrogen, nitrogen, and methane are removed. The solution is then sent to the stripper where the carbon monoxide is released from the complex by heating and pressure reduction to about 0.15 MPa (1.5 atm). The solvent is stripped of residual carbon monoxide, heat-exchanged with the stripper feed, and pumped to the top of the absorber to complete the cycle. 

It is highly active but easily poisoned by sulfur and not particularly selective to methane. Oddly enough, carbon monoxide appears to inhibit the rate of methane formation. 

Selective transformations Selective styrene ring opening [103] One-pot domino process for regioselective synthesis of a-carbonyl furans [104] Tandem process for synthesis of quinoxalines [105] Atmospheric oxidation of toluene [106] Cyclohexane oxidation [107] Synthesis of imines from alcohols [108] Synthesis of 2-aminodiphenylamine [109] 9H-Fluorene oxidation [110] Dehydrogenation of ethane in the presence of C02 [111] Decomposition of methane [112] Carbon monoxide oxidation [113]... 

Another way to eliminate the oxygen plant is to react a metal oxide with methane to yield the synthesis gas in a fluidized-bed reactor (83-86). Experiments have shown that copper oxide readily oxidizes methane to carbon monoxide and hydrogen with high selectivity at a temperature of about 1200 K and that the reduced CuO can be reoxidized with air. Lewis et al. (83-86)... 

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