Hydrogen and Carbon Dioxide

Steam reformation can also be carried out with a heavy fraction of crude oil or coal. Note that coal also has an appreciable amount of inorganic material and sometimes water. If the organic part of coal, a highly complex mixture of mainly polycyclic aromatic rings, is represented as C H, then reaction 1.6.4.2 represents the basic reaction of coal gasification. 

As shown by reaction 1.6.4.3, depending on the requirement for hydrogen, carbon monoxide could be further reacted with water to yield more hydrogen. This reaction is called water gas shift reaction and is of relevance in homogeneous catalyst-based carbonylation reactions (see Section 4.7.1). The heterogeneous industrial catalyst for water gas shift reaction contains copper and zinc oxide on alumina. By the standards of heterogeneous catalysis, it operates at a relatively low temperature ( 230°C). 

In a hydrogenation reaction with a soluble catalyst there are Uquid and gaseous phases present. Why then is the reaction called homogeneous rather than heterogeneous  

Ans The reaction takes place between the dissolved gas, the catalyst, and the substrate, i.e., aU in one phase with discrete molecular structures. 

The chances of success are greater if one tries to develop a homogeneous water gas shift catalyst rather than a steam reformation catalyst. Why Ans Both are endothermic reactions but the former less so, making the thermodynamics less unfavorable at temperatures at which a homogeneous catalyst is stable. 

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These equations are based on the thermodynamically stable species. Further research is needed to clarify the actual intermediate formed during overcharge. In reahty, the oxygen cycle can not be fully balanced because of other side reactions, that include gtid corrosion, formation of residual lead oxides in the positive electrode, and oxidation of organic materials in the cell. As a result, some gases, primarily hydrogen and carbon dioxide (53), are vented. 

Only recently has a mechanism been proposed for the copper-cataly2ed reaction that is completely satisfactory (58). It had been known for many years that a small amount of carbon dioxide in the feed to the reactor is necessary for optimum yield, but most workers in the field beHeved that the main reaction in the formation of methanol was the hydrogenation of carbon monoxide. Now, convincing evidence has been assembled to indicate that methanol is actually formed with >99% selectivity by the reaction of dissociated, adsorbed hydrogen and carbon dioxide on the metallic copper surface in two steps ... 

The modern natural-gas industry has its origins in the nineteenth centuiy as urban gas works that distributed synthesis gas (a mixture of carbon monoxide, hydrogen and carbon dioxide made by the incomplete combustion of coal, oil, or organic wastes in the presence of steam). Gas works illuminated London streets even before 1800, and subsequently... 

Combining Equation 1 and Equation 2, one can generate hydrogen and carbon dioxide ... 

Effects of Cold Gas Recycle and Approach to Equilibrium. Product gases resulting from various CGR ratios were analyzed (Table XI). For the experiments tabulated, a decrease in the cold recycle ratio resulted consistently in increases in the product gas concentrations of water vapor, hydrogen, and carbon dioxide and a decrease in methane concentration. These trends may be noted in experiment HGR-12 as the CGR ratio decreased from 8.7 1 to 1.2 1, in experiment HGR-13 as it increased from 1.0 1 to 9.1 1, and in experiment HGR-14 as it decreased from 3.0 1 to 1.0 1. These trends indicate that the water-gas shift reaction (CO + H20 —> C02 + H2) was sustained to some degree. Except for the 462-hr period in experiment HGR-14, the apparent mass action constants for the water-gas shift reaction (based on the product gas compositions in Table XI) remained fairly constant at 0.57-1.6. These values are much lower than the value of 11.7 for equilibrium conversion at 400°C. In... 

The catalytic steam-reforming process of methanol on Cu/ZnO/Ab03 catalyst primarily produces hydrogen and carbon dioxide. In addition, the minor quantities of carbon monoxide are also produced. This mechanism is explained in terms of parallel reactions [11]. 

Poisoning of platinum fuel cell catalysts by CO is undoubtedly one of the most severe problems in fuel cell anode catalysis. As shown in Fig. 6.1, CO is a strongly bonded intermediate in methanol (and ethanol) oxidation. It is also a side product in the reformation of hydrocarbons to hydrogen and carbon dioxide, and as such blocks platinum sites for hydrogen oxidation. Not surprisingly, CO electrooxidation is one of the most intensively smdied electrocatalytic reactions, and there is a continued search for CO-tolerant anode materials that are able to either bind CO weakly but still oxidize hydrogen, or that oxidize CO at significantly reduced overpotential. 

Rate expressions of this type have been proposed to correlate the data for the reaction between hydrogen and carbon dioxide on tungsten. 

In conventional production of hydrogen from coal, as described earlier, coal is converted to hydrogen and carbon monoxide (CO) through the water-carbon reaction as shown in reactions 3.9 through 3.11. CO is then converted to hydrogen and carbon dioxide by the water-gas shift reaction as shown in reaction 3.12. 

Schulien S., Sandstede G., Hahn H.W., Hydrogen and carbon dioxide as raw materials for an ecological energy-technology, Int.. Hydrogen Energ., 24, 299-303, 1999. 

Damle, A.S., Separation of Hydrogen and Carbon Dioxide in Advanced Fossil Energy Conversion Processes using a Membrane Reactor, 2002 Pittsburgh Coal Conference, Pittsburgh, PA, September 2002. 

Bugante, E.C. et al, Methane production from hydrogen and carbon dioxide and monoxide in a column bioreactor of thermophilic methanogens by gas recirculation, /. Perm. Bioeng., 67(6), 419,1989. 

The contaminants oxygen, nitrogen, hydrogen, and carbon dioxide are considered in this chapter. 

The Vision 21 program is focused on new concepts for coal-based energy production where modular plants could be configured to produce a variety of fuels and chemicals depending on market needs with virtually no environmental impact outside the plant s footprint. Membranes would be used to separate oxygen from air for the gasification process and to separate hydrogen and carbon dioxide from coal gas. 

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