Carbon deposition on iron

In the case of high-temperature, fluidized-bed reactors operation at higher pressures has an additional benefit in that the rate of carbon deposition on iron catalysts is proportional to Pgg/P H2 (ref. 2). As the partial pressures increase, the carbon deposition rate decreases. Because the deposited carbon has a high area and acts like a sponge for retaining wax, the rate of wax accumulation on the catalyst also decreases with increasing pressure (ref. 2). The benefit of this is that the catalyst particles are less likely to become "sticky" and result in defluidization of the bed. The CFB reactors at Sasol Two and Three operate at higher pressures than the older units at Sasol One, and the lower deposition rates of carbon and wax on... 

V. Carbide Formation and Carbon Deposition on Iron Catal3rsts... 

Park, C., and Baker, R. T. K. (1998). Carbon deposition on iron-nickel during interaction with ethylene-hydrogen mixtures. J. Catal. 179, 361-374. 

The phase transformations in the catalyst play an important role in determining the activity, attrition resistance, and deactivation of this catalyst. Activation of this precipitated catalyst transforms single crystals of hematite to smaller crystallites of carbide. While the transformation from hematite to magnetite is extremely rapid, the magnetite to carbide transition is much slower under the conditions of temperature and pressure employed in this study. As carbon deposits on the carbide particles, it serves to further prise the carbide particles apart. In a commercial slurry phase reactor the carbide particles break away leading to catalyst attrition. The implication of this work for the attrition resistance of iron FT catalysts is explored in detail elsewhere.18... 

Many investigations of the molecular structure of thin films formed by y-APS deposited onto inorganic substrates from aqueous solutions have been carried out. Ondrus and Boerio [2] used reflection-absorption infrared spectroscopy (RAIR) to determine the structure of y-APS films deposited on iron, 1100 aluminum, 2024 aluminum, and copper substrates from aqueous solutions at pH 10.4. They found that the as-formed films absorbed carbon dioxide and water vapor to form amine bicarbonate salts which were characterized by absorption bands near 1330, 1470, 1570, and 1640 cm-1. y-APS films had to be heated to temperatures above about 90°C in order to dissociate the bicarbonates, presumably to free amine, carbon dioxide, and water. Since the amine bicarbonates failed to react with epoxies, the strength of adhesive joints prepared... 

In general, the addition of alkaline promoters gives similar results to the use of syngas mixtures rich in CO. and also the waicrgas shift reaction is enhanced. The carbon deposition on potassium-promoted iron has recently been investigated using X-ray phoioemission spectroscopy (XPS) [57]. Measurements on the K 2p levels showed that the potassium compound is not covered by the deposited carbon but rather sits on top of the carbon layer. 

Comparison of the behavior of alcohol in the presence of an iron catalyst at ordinary pressures and at high pressures showed that in the former case the reaction occurs at a lower temperature and also that for any given temperature the velocity of reaction is much greater.59 That is, pressure appeared to decrease the decomposition. At ordinary pressures in the presence of an iron catalyst, alcohol decomposes rapidly at temperatures between 510° and 525° C. to give principally acetaldehyde and gases rich in hydrogen. Above 525° C. increases in temperature are accompanied by corresponding decreases in aldehyde production and increases in the quantity of solid carbon deposited on the iron reactor walls. 

Figure 7. SEM photograph of carbon deposited on an iron foil showing filamentary growth. Magnification is 9,350x ...

Hofer, L.J.E. Sterling, E. and McCartney, J.T. "Structure of the Carbon Deposited from Carbon Monoxide on Iron, Cobalt, and Nickel" J. Phys. Chem. 1955, 59, 1153. 

Boron-carbon-nitride ceramic is deposited on iron-based sliding parts by chemical vapor deposition (CVD) it is used as rotary compressor shafts, in order to improve the wear resistance [1 to 5]. Such B-C-N coatings have also been applied to dynamic pressure air bearings [6]. In gas-cooled nuclear reactors, °B-enriched B-C-N can be deposited by CVD in the fluid channels of the fuel elements for permanent deactivation in case of an emergency [7]. Radiofrequency or microwave-enhanced CVD is employed in order to deposit a diamond carbon and (3-BN superlattice structure [8]. 

Carbon Deposition during the FT Synthesis. Under normal HTFT conditions, elemental carbon, as distinct from coke, is deposited on iron catalysts. The main source is the Boudouard reaction ... 

Carbonyl iron or carbonyl iron powder is metallic iron of extreme purity, produced as microscopic spherical particles by the reaction of carbon monoxide on iron ore. This reaction gives a liquid, called iron carbonyl Fe(CO), that is vaporized and deposited as a powder. Carbonyl iron is mainly used for magnetic cores for high-frequency equipment and for pharmaceutical application of iron. 

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