Removal of carbon monoxide

Decarbonylations can occur by either an ionic or a radical mechanism. The former mechanism is involved in reactions catalysed by acids, Lewis acids, or bases, and the latter in chain reactions induced thermally, photo-lytically, or by some other radical-forming process. 

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This reaction serves for removal of carbon monoxide from gas mixtures and is usually carried out over supported metal catalysts. In reforming techniques, carbon monoxide, poisonous for the catalyst in fuel cells, is removed in such a way. It is also applied in automobiles for reducing the exhaust gas carbon monoxide to an environmentally acceptable level. 

High-carbon ferrochromium alloys are made by the reduction of chromite ore with carbon in an arc furnace. On the other hand, low-carbon ferrochromium is obtained by silicon reduction of the ore. The carbon content of ferrochromium can be reduced further by heating high-carbon alloys with ground quartzite or by oxidation in vacuum and removal of carbon monoxide formed. Ferrochromium alloys are used in the manufacture of stainless steel. 

A second type of substitution occurs in the form of substitutions of subprocesses within a particular process. For example, one step in the steam reforming process for ammonia production is the removal of carbon monoxide and carbon dioxide from the synthesis gas. A number of processes, which differ somewhat in energy and capital requirements, have been developed for this purpose. 

Removal of carbon monoxide from the —CHO group of the aldol leaving a secondary alcohol. 

However, the removal of carbon monoxide by water-gas shift to a low level still demands its selective oxidation to the minimum concentration possible. Much research and development has been conducted during the past decades to find a gold catalyst that can do this the target is usually described by the acronym PROX (preferential oxidation), but sometimes as SCO (selective catalytic oxidation). The task is somewhat simplified by the constraints that are externally imposed the preferred feed gas, often termed idealised reformate, has the composition 1.0% CO, 1.0% 02, 75.0% H2, balance nitrogen or other inert gas, and while of course variations to this composition can be made to explore the kinetics and mechanism, and the effects of the products water and carbon dioxide can be added to observe their effects, the successful catalyst must remove almost all the carbon monoxide (to <10 ppm) and less than 0.5% hydrogen. This requirement is expressed as a selectivity based on the percentage of the oxygen consumed that is taken by the carbon monoxide this should exceed 50%, under conditions where the conversion of carbon monoxide is above 99.5%.5... 

Another important application is the removal of carbon monoxide from the valuable hydrogen produced in steam reformed natural gas. 

Li P, Miser DE, Rabiei S, Yadav RT, Hajaligol MR (2003) The removal of carbon monoxide by iron oxide nanoparticles. Appl Catal B Environ 43 151... 

This reaction, or the hydrocarbon reforming reactions noted above, can generate sufficient carbon monoxide to poison the catalysts used for hydrogen-based fuel cells that are used to generate electricity. Thus, carbon monoxide is a trace component of concern, and as the hydrogen economy is further developed and reformation reactions may become more important in the development of hydrogen fuels, technologies for the efficient removal of carbon monoxide must be developed. 

Where the Fischer-Tropsch process has been used on an industrial scale, iron or cobalt are the essential catalyst components. Technical catalysts also contain oxidic promoters, such as alumina and potassium oxide. Ruthenium and nickel are most attractive for academic research since they produce the simplest product packages. Nickel is used for methanation (production of substitute natural gas and removal of carbon monoxide impurities from hydrogen). 

The extent to which each of the main reactions contributes to the removal of carbon monoxide, hydrocarbons and nitrogen oxides depends on the catalyst formulation and the catalyst operating conditions. Detailed kinetic data for these reactions are rarely found in the literature. Some fundamental data do exist for the oxidation of carbon monoxide, reaction 11, and some overall kinetic data exist for the other reactions [15-19],... 

The first concept is the closed-loop-controlled three-way catalyst. In this, one type of catalyst, which is placed in the exhaust gas stream, is able to promote all the main reactions that lead to the simultaneous removal of carbon monoxide, hydrocarbons and nitrogen oxides. To balance the extent of the oxidation and the reduction reactions, the composition of the engine-out exhaust gas is maintained at or around stoichiometry. This is achieved by a closed-loop engine operation control, in which the oxygen content of the engine-out exhaust gas is measured up-stream of the catalyst with an electrochemical oxygen sensor, also called lambda sensor. 

The third concept is the dual-bed emission control catalyst. In this, the catalytic converter is made of two different types of catalyst. The first is either a multifunctional catalyst or at least one capable of promoting NO.v reduction reactions. The engine is calibrated so as to guarantee a net reducing exhaust gas composition. Under these conditions, the first catalyst will lead to an elimination of the nitrogen oxides. The second catalyst is an oxidation catalyst. Extra air is injected in front of the second catalyst to assist the removal of carbon monoxide and hydrocarbons. The secondary air can be added either by mechanically or by electrically driven air pumps. 

Secondary purification—further removing of carbon monoxide... 

Figure 11. Performance of virgin TWC-1 catalyst for removal of carbon monoxide, hydrocarbons, and nitric oxide from a synthetic exhaust...

Grant, S.J. Catalytic and non-catalytic additives for the removal of carbon monoxide from cigarette smoke ... 

Reynolds, J.H. IV and M.N. Andrews Removal of carbon monoxide from cigarette smoke. II. Development and application of a rapid method for screening prospective carbon monoxide removal agents RDR, 1971, No. 16, July 29, see www.ijrtdocs.com 514902024 -2043. Reynolds, J.H. IV and B.R Hege Experiments in removal of carbon monoxide from cigarette smoke. IB. Successful catalytic removal of carbon monoxide from smoke RDM, 1973, No. 120, March 19, see www.ijrt-docs.com 508566003 -6012. 

The mean global CO concentration in the atmosphere, determined on the basis of data obtained over the Pacific, is approximately 0.125 mg m [42]. The estimates of the residence time in the atmosphere again differ from each other. The actual residence time can be considered to range between 0.1 and 0.3 years [40, 41) it depends on the rate of removal of carbon monoxide from the atmosphere. The process probably occurs through the oxidation of CO by certain components present in the atmosphere, e.g. OH radicals ... 

In this direct propylene-oxidation process, catalyst life is maintained at high levels by periodically interrupting or lowering the flow of oxygen without changing other conditions. Removal of carbon monoxide from the... 

These reactions occur at a very slow rate on pure platinum and this has resulted in a large research effort to discover more active electrocatalysts. At present, platinum—ruthenium offers the best performance. Ruthenium adsorbs water more readily than platinum and the resulting species, Ru—OHads, assists the removal of carbon monoxide from neighbouring platinum sites. Despite this beneficial effect of ruthenium, still more efficient electrocatalysts are required to enhance the power delivered by DMFCs, especially if the system is to compete favourably with hydrogen—air PEMFCs. 

Igarashi H., Uchida H., Suzuki M., Sasaki Y. and Watanabe M. 1997. Removal of carbon monoxide from hydrogen-rich fuels by selective oxidation over platinum catalyst supported on zeolite, Appl. Catal. A, 159, 159-169. 

This reaction can only proceed if the carbon monoxide reaction product can escape through the scale. In general, porous scales are produced, particularly under industrial conditions, and removal of carbon monoxide is not a problem. However, it has been shown that very careful heating can produce a non-porous scale or a scale of greatly reduced permeability to carbon monoxide. As a result, instead of showing a decarburized surface, the steel shows carbon enrichment at the surface. This clearly demonstrates that removal of the carbon monoxide gas is vital for decarburization to occur. 

Takenaka, S., Shimizu, T. and Otsuka, K. (2004) Complete removal of carbon monoxide in hydrogen-rich gas stream through methanation over supported metal catalysts. International Journal of Hydrogen Energy, 29, 1065-1073. 

Removal of carbon monoxide which would poison any fuel cell. 

Pressure swing adsorption (PSA) is a gas purification process, which consists of the removal of impurities on adsorbent beds. The usual adsorbents and gases adsorbed thereon are molecular sieves for carbon monoxide, activated carbon for carbon dioxide, activated alumina or silica gel. lyuke et td. reported that the addition of tin onto activated carbon improved the efficiency of the adsorptive removal of carbon monoxide from hydrogen [420]. 

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