Oxidation in steam

Fig. 7.32 Metal wastage of several steels due to oxidation in steam at various temperatures, (a) Mild steel, (b) Fe-2Cr-0-25Mo, (c) Fe-12Cr -I- Mo -I- V, (d) A.l.S.I. 316 and (e) Fe-18Cr-12Ni-lNb. T,oi,i = Ssutface -I- / penetration (after King el at.)...

Other methods of formation are the addition of sodium carbonate to a solution of cupric sulphate and sodium chloride reduced with sulphurous acid,9 and that of an alkaline solution of sodium potassium tartrate to a solution of cuprous chloride and sodium chloride.10 At temperatures below 350° C. copper reacts with nitrous oxide to form cuprous oxide above this temperature the product is cupric oxide.u Cuprous oxide is also formed at the anode in the electrolysis of a solution of cupric sulphate,12 and by heating cupric oxide in steam. 

PZC/IEP of 1 pm Thick Layer of Silica on Silicon Obtained by Oxidation in Steam... 

Growth of an oxide involves both consumption and addition of material but is listed in table 3.7 as an additive process since its result is a new material. Oxidation involves heating the wafer in a wet or dry oxygen stream at elevated temperatures (between 600 and 1250 °C). Wet oxidation in steam is much faster than dry oxidation but the quality of the oxide is somewhat lower. 

The steam-carbon dioxide-hydrocarbon conversion is conducted over a catalyst such as nickel (oxide) on alumina. This type of catalyst can be purchased in quite similar composition from a number of catalyst vendors. In the case in which the feed stock is processed over a catalyst as in steam-hydrocarbon reforming, it is essential that the gas be purified, at least to some extent, prior to its passage over the reforming catalyst, particularly if the catalyst is of the typical composition of supported and promoted nickel (oxide). In steam hydrocarbon reforming, the methane (natural gas) is usually detoxified using an adsorbent such as carbon on which is impregnated suitable chemical adsorbents such as elemental iron or copper. There are at least two of these metallized carbon desulfurizers in parallel with one on... 

Additional analysis may have to take into account another mechanism of cladding damage, i.e. the acceleration of the steam-zirconium reaction at temperatures above 800°C. At 1000°C and above, the heat release from zirconium oxidation in steam becomes commensurate with the residual heat release in the fuel. 

Sulphur may be removed by oxidation in steam under controlled conditions [377]. As illustrated in Figure 5.44, no improvement is observed when increasing the H2O/H2 ratio, as also expected fi-om equilibrium studies (refer to Section 5.4.2). 

Given the following data, determine which metal has the greater probability of oxidation in steam at 827°C (1100 K) and 1 atm pressure... 

Experimental investigations modifying the inner surface of tubes of 9% Cr steel via CVD with silicon containing precursors have been performed to provide improved protection against high temperature oxidation in steam atmosphere. 

In more recent studies, in order to interpret the observed accelerated steel oxidation in steam in the range of 400-900°C for power plant applications, various possibilities of water , oxygen and hydrogen transports through the oxide scales were again considered [47], but no conclusion was made as to which species was the predominant one and responsible for the observed oxidation rates and scale structures developed. 

C. W. Tuck, Possible mechanisms of oxidation in steam-bearing atmospheres . Internal Report 933, 1967, GKN Group Research Centre, UK. 

Colourless liquid with a strong peppermintlike odour b.p. 155" C. Manufactured by passing cyclohexanol vapour over a heated copper catalyst. Volatile in steam. Oxidized to adipic acid. Used in the manufacture of caprolactam. Nylon, adipic acid, nitrocellulose lacquers, celluloid, artificial leather and printing inks. 

Prepare a mixture of 30 ml, of aniline, 8 g. of o-chloro-benzoic acid, 8 g. of anhydrous potassium carbonate and 0 4 g. of copper oxide in a 500 ml. round-bottomed flask fitted with an air-condenser, and then boil the mixture under reflux for 1 5 hours the mixture tends to foam during the earlier part of the heating owing to the evolution of carbon dioxide, and hence the large flask is used. When the heating has been completed, fit the flask with a steam-distillation head, and stcam-distil the crude product until all the excess of aniline has been removed. The residual solution now contains the potassium. V-phenylanthrani-late add ca. 2 g. of animal charcoal to this solution, boil for about 5 minutes, and filter hot. Add dilute hydrochloric acid (1 1 by volume) to the filtrate until no further precipitation occurs, and then cool in ice-water with stirring. Filter otT the. V-phcnylanthranilic acid at the pump, wash with water, drain and dry. Yield, 9-9 5 g. I he acid may be recrystallised from aqueous ethanol, or methylated spirit, with addition of charcoal if necessary, and is obtained as colourless crystals, m.p. 185-186°. 

Activated carbons are made by first preparing a carbonaceous char with low surface area followed by controlled oxidation in air, carbon dioxide, or steam. The pore-size distributions of the resulting products are highly dependent on both the raw materials and the conditions used in their manufacture, as maybe seen in Figure 7 (42). 

Chromium is the most effective addition to improve the resistance of steels to corrosion and oxidation at elevated temperatures, and the chromium—molybdenum steels are an important class of alloys for use in steam (qv) power plants, petroleum (qv) refineries, and chemical-process equipment. The chromium content in these steels varies from 0.5 to 10%. As a group, the low carbon chromium—molybdenum steels have similar creep—mpture strengths, regardless of the chromium content, but corrosion and oxidation resistance increase progressively with chromium content. 

The first-stage catalysts for the oxidation to methacrolein are based on complex mixed metal oxides of molybdenum, bismuth, and iron, often with the addition of cobalt, nickel, antimony, tungsten, and an alkaU metal. Process optimization continues to be in the form of incremental improvements in catalyst yield and lifetime. Typically, a dilute stream, 5—10% of isobutylene tert-huty alcohol) in steam (10%) and air, is passed over the catalyst at 300—420°C. Conversion is often nearly quantitative, with selectivities to methacrolein ranging from 85% to better than 95% (114—118). Often there is accompanying selectivity to methacrylic acid of an additional 2—5%. A patent by Mitsui Toatsu Chemicals reports selectivity to methacrolein of better than 97% at conversions of 98.7% for a yield of methacrolein of nearly 96% (119). 

Equilibiium is achieved in steam leforming equilibiium is approached for partial oxidation process. 

Tubular Fixed-Bed Reactors. Bundles of downflow reactor tubes filled with catalyst and surrounded by heat-transfer media are tubular fixed-bed reactors. Such reactors are used most notably in steam reforming and phthaUc anhydride manufacture. Steam reforming is the reaction of light hydrocarbons, preferably natural gas or naphthas, with steam over a nickel-supported catalyst to form synthesis gas, which is primarily and CO with some CO2 and CH. Additional conversion to the primary products can be obtained by iron oxide-catalyzed water gas shift reactions, but these are carried out ia large-diameter, fixed-bed reactors rather than ia small-diameter tubes (65). The physical arrangement of a multitubular steam reformer ia a box-shaped furnace has been described (1). 

Fig. 12. Ray diagram of carryover coefficients of salts and metal oxide contaminants in steam (6). To convert MPa to psi, multiply by 145.

Conventional Transportation Fuels. Synthesis gas produced from coal gasification or from natural gas by partial oxidation or steam reforming can be converted into a variety of transportation fuels, such as gasoline, aviation turbine fuel (see Aviation and other gas turbine fuels), and diesel fuel. A widely known process used for this appHcation is the Eischer-Tropsch process which converts synthesis gas into largely aHphatic hydrocarbons over an iron or cobalt catalyst. The process was operated successfully in Germany during World War II and is being used commercially at the Sasol plants in South Africa. 

---