Oxidation, velocities

The governing equations are nondimensionalized using the fuel slot width, D, the difference between the inlet fuel and oxidizer velocities, AU, and Tq-The jet Reynolds number. Re = DAUpo/po, where po and po are the reference density and viscosity, respectively, is chosen as 5000. The nondimensional Damkohler (Da = DpoAf/(AUMWq)), Zel dovich (Ze = Ea/ RT)o), and heat... 

However, in molecules where the axial alcohol is subject to very severe steric interactions, the release of steric tension may become the major factor affecting DDQ oxidation velocity. For example, the 3 -acetoxy-6 —hydroxy-5a-cholest-7-ene (92) is oxidized faster than the corresponding 6a isomer (93). 

As we have already seen, the current density is the regulator of the electrically obtainable concentration conditions for the discharged ions, and thereby becomes codeterminative of the velocity of reaction. The obtainable phase of an oxidation or reduction is intimately related to the velocity of reaction, for as soon as the reaction velocity of the liberation of reducing or oxidizing ions greatly exceeds the reduction or oxidation velocity with the depolarizer, the reduction or oxidation stops. Thus the obtainable phase, i.e. the quality of the reaction, occurs also as a function of the reaction velocity. 

The absorption of oxygen in the presence of ROO—CHD has a very characteristic course. The oxidation velocity retards after the rapid initial phase. Judging from the known characteristics of products of the thermal transformation of ROO-CHD, some of them having the benzoquinone character, this retardation of oxidation can be ascribed just to the products of subsequent transformations which gradually accumulate in the oxidized mixture. This explanation is in agreement with the experimentally found retardation effect of the mixture of thermolytic products of LXXXV, which was independently prepared and added to oxidized tetrahydronaphtalene. The induction period of oxidation was very short also in polypropylene which contained LXXXV or LXXXVI at 180 °C, but it was followed by a phase with the perceptible weak retardation effect of thermolysis products116. ... 

C. Gensch, K. Hauffe, Oxidation velocity of zinc alloys, Z. Phys. Chem. 196 (1951) 427-437. 

The oxidation velocity, which is at a maximum between pH 7 and 8.5, then decreases and reaches another maximum from pH 11 to 12 (exactly where spent caustic is located). 

For concentrations of <300 mg l , the oxidation velocity is said to be at a chemical rate, since it is limited by the reaction and not by the oxygen transfer. 

Herskowitz et al [26] and Tsukamoto et al [78] also used batch recycle reactors for their studies of trickle beds in cyclohexene hydrogenation and glucose oxidation, respectively. In the cyclohexene hydrogenation studies, liquid velocities as high as 2 cm/s were used. In glucose oxidation, velocities up to 0.35 cm/s were used. 

MA polymerization solvent, 244, 245, 250, 257 MA raw material, 17-30 oxidation mechanism, 21-33 oxidation rates, 31, 32, 38 oxidation to MA, 22-28, 31-33, 38 oxidation velocity constant, 38 triplet(excited)form, 241... 

The Beckstead-Derr-Price model (Fig. 1) considers both the gas-phase and condensed-phase reactions. It assumes heat release from the condensed phase, an oxidizer flame, a primary diffusion flame between the fuel and oxidizer decomposition products, and a final diffusion flame between the fuel decomposition products and the products of the oxidizer flame. Examination of the physical phenomena reveals an irregular surface on top of the unheated bulk of the propellant that consists of the binder undergoing pyrolysis, decomposing oxidizer particles, and an agglomeration of metallic particles. The oxidizer and fuel decomposition products mix and react exothermically in the three-dimensional zone above the surface for a distance that depends on the propellant composition, its microstmcture, and the ambient pressure and gas velocity. If aluminum is present, additional heat is subsequently produced at a comparatively large distance from the surface. Only small aluminum particles ignite and bum close enough to the surface to influence the propellant bum rate. The temperature of the surface is ca 500 to 1000°C compared to ca 300°C for double-base propellants. 

Aluminum-containing propellants deflver less than the calculated impulse because of two-phase flow losses in the nozzle caused by aluminum oxide particles. Combustion of the aluminum must occur in the residence time in the chamber to meet impulse expectations. As the residence time increases, the unbumed metal decreases, and the specific impulse increases. The soHd reaction products also show a velocity lag during nozzle expansion, and may fail to attain thermal equiUbrium with the gas exhaust. An overall efficiency loss of 5 to 8% from theoretical may result from these phenomena. However, these losses are more than offset by the increase in energy produced by metal oxidation (85—87). 

Tracer Type. A discrete quantity of a foreign substance is injected momentarily into the flow stream and the time interval for this substance to reach a detection point, or pass between detection points, is measured. From this time, the average velocity can be computed. Among the tracers that have historically been used are salt, anhydrous ammonia, nitrous oxide, dyes, and radioactive isotopes. The most common appHcation area for tracer methods is in gas pipelines where tracers are used to check existing metered sections and to spot-check unmetered sections. 

Computer Models, The actual residence time for waste destmction can be quite different from the superficial value calculated by dividing the chamber volume by the volumetric flow rate. The large activation energies for chemical reaction, and the sensitivity of reaction rates to oxidant concentration, mean that the presence of cold spots or oxidant deficient zones render such subvolumes ineffective. Poor flow patterns, ie, dead zones and bypassing, can also contribute to loss of effective volume. The tools of computational fluid dynamics (qv) are useful in assessing the extent to which the actual profiles of velocity, temperature, and oxidant concentration deviate from the ideal (40). 

The equiHbrium approach should not be used for species that are highly sensitive to variations in residence time, oxidant concentration, or temperature, or for species which clearly do not reach equiHbrium. There are at least three classes of compounds that cannot be estimated weU by assuming equiHbrium CO, products of incomplete combustion (PlCs), and NO. Under most incineration conditions, chemical equiHbrium results in virtually no CO or PlCs, as required by regulations. Thus success depends on achieving a nearly complete approach to equiHbrium. Calculations depend on detailed knowledge of the reaction network, its kinetics, the mixing patterns, and the temperature, oxidant, and velocity profiles. 

Sodium is a soft, malleable soHd readily cut with a knife or extmded as wire. It is commonly coated with a layer of white sodium monoxide, carbonate, or hydroxide, depending on the degree and kind of atmospheric exposure. In a strictiy anhydrous iaert atmosphere, the freshly cut surface has a faintiy pink, bright metallic luster. Liquid sodium ia such an atmosphere looks much like mercury. Both Hquid and soHd oxidize ia air, but traces of moisture appear to be required for the reaction to proceed. Oxidation of the Hquid is accelerated by an iacrease ia temperature, or by iacreased velocity of sodium through an air or oxygen environment. 

Extensive research has been conducted on catalysts that promote the methane—sulfur reaction to carbon disulfide. Data are pubhshed for sihca gel (49), alurnina-based materials (50—59), magnesia (60,61), charcoal (62), various metal compounds (63,64), and metal salts, oxides, or sulfides (65—71). Eor a sihca gel catalyst the rate constant for temperatures of 500—700°C and various space velocities is (72)... 

In the second stage, a more active 2inc oxide—copper oxide catalyst is used. This higher catalytic activity permits operation at lower exit temperatures than the first-stage reactor, and the resulting product has as low as 0.2% carbon monoxide. For space velocities of 2000-4000 h , exit carbon monoxide... 

Oxidation. Carbon monoxide can be oxidized without a catalyst or at a controlled rate with a catalyst (eq. 4) (26). Carbon monoxide oxidation proceeds explosively if the gases are mixed stoichiometticaHy and then ignited. Surface burning will continue at temperatures above 1173 K, but the reaction is slow below 923 K without a catalyst. HopcaUte, a mixture of manganese and copper oxides, catalyzes carbon monoxide oxidation at room temperature it was used in gas masks during World War I to destroy low levels of carbon monoxide. Catalysts prepared from platinum and palladium are particularly effective for carbon monoxide oxidation at 323 K and at space velocities of 50 to 10, 000 h . Such catalysts are used in catalytic converters on automobiles (27) (see Exhaust CONTHOL, automotive). 

High pressure processes P > 150 atm) are catalyzed by copper chromite catalysts. The most widely used process, however, is the low pressure methanol process that is conducted at 503—523 K, 5—10 MPa (50—100 atm), space velocities of 20, 000-60,000 h , and H2-to-CO ratios of 3. The reaction is catalyzed by a copper—zinc oxide catalyst using promoters such as alumina (31,32). This catalyst is more easily poisoned than the older copper chromite catalysts and requites the use of sulfiir-free synthesis gas. 

---