Extent of oxidation reaction

With only two locally distributed states in the model, it is possible to illustrate all results in a phase diagram. In this diagram, the space coordinate is eliminated by plotting one state versus the second. Figure 2.4 shows the extent of the reforming reaction on the horizontal axis and the extent of oxidation reaction on the vertical axis. 

Consistent with the above observations is the recently proposed order of the intermolecular reaction rates in polyethylene oxide amorphous > interfacial > crystalline [Zhang et al., 1992]. The role of oxygen diffusion during the radiation-induced degradation was also brought out by the work of Burillo et al. [1992], who found that, because of the reduced diffusion of oxygen, the extent of oxidative reactions was lower in compressed PVC samples (P < 880 MPa) than in uncompressed ones. 

The primary photolytic reactions postulated are not themselves self-propagating, but provide the variety of radical species involved in subsequent oxidation and chain scission reactions characteristic of PET. The extent of oxidation reaction will depend in part on the balance of scission reactions in the initial process. Once established, the autoxidation cycle has a very long kinetic chain length, and will result in a rapid build-up of hydroperoxide in the polyester. 

Gear lubricants In addition to the usual oxidation and corrosion inhibitors, lubricants for heavily loaded gears almost always contain EP additives containing sulphur, chlorine or phosphorus. In order to function, these additives must react locally with the metal surfaces, and yet the extent of the reaction should not be such that it could be described as corrosive, or promote fatigue pitting . These EP additives may be quite safe with ferrous metal surfaces, but may cause severe corrosion on copper alloys, e.g. on bronze worm wheels if for any reason excessive temperatures arise. 

At least for ethylene hydrogenation, catalysis appears to be simpler over oxides than over metals. Even if we were to assume that Eqs. (1) and (2) told the whole story, this would be true. In these terms over oxides the hydrocarbon surface species in the addition of deuterium to ethylene would be limited to C2H4 and C2H4D, whereas over metals a multiplicity of species of the form CzH D and CsHs-jD, would be expected. Adsorption (18) and IR studies (19) reveal that even with ethylene alone, metals are complex. When a metal surface is exposed to ethylene, selfhydrogenation and dimerization occur. These are surface reactions, not catalysis in other words, the extent of these reactions is determined by the amount of surface available as a reactant. The over-all result is that a metal surface exposed to an olefin forms a variety of carbonaceous species of variable stoichiometry. The presence of this variety of relatively inert species confounds attempts to use physical techniques such as IR to char-... 

The extent of oxidation, when determined by the reaction of the product with phenylhydrazine, is 85%. Hydrolysis of the oxidized xylan should produce approximately equimolar quantities of D-glyceraldehyde and glyoxal. Experimental determination of glyceraldehyde indicates 67 % of the theoretical when the oxidized xylan is distilled with sulfuric acid and the evolved methylglyoxal measured as the phenylosazone. Glyoxal is isolated in 63% yield, when separated as the phenylosazone or as the dioxime. Aldehyde groups in the oxidized xylan may be further... 

In Table 5.4 the contributions of the individual weathering reactions were assigned and combined in such a way as to yield the concentrations of Ca2+, Mg2+, Na+, K+, and H+ measured in these lakes the amounts of silicic acid and aluminum hydroxide produced and the hydrogen ions consumed were calculated stoichiometrically from the quantity of minerals assumed to have reacted. Corrections must be made for biological processes, such as ammonium assimilation and nitrification and the uptake of silicic acid by diatoms. Some of the H4Si04 was apparently lost by adsorption on aluminum hydroxide and Fe(III)(hydr)oxides, but the extent of these reactions was difficult to assess. 

Many investigators have used different techniques to study the electrochemical behavior of different sulphide mineral electrodes in solutions of different compositions. Linear potential sweep voltammetry (LPSV), and cyclic voltammetry (CV) have been perhaps, used most extensively and applied successfully to the investigation of reactions of sulphide minerals with aqueous systems. These techniques have provided valuable information on the extent of oxidation as a function of potential for various solution conditions and have allowed the identity of the surface products to be deduced. 

Other indices measure a secondary stage of oxidation, such as the anisidine value (ANV), pointing to formation of carbonyl compounds, capable of undergoing condensation reactions with p-anisidine, and the thiobarbituric acid reactive substance (TBARS) pointing to the presence of malondialdehyde (MDA) in particular. In biological systems, TBARS is of widespread use as a measure for the extent of oxidation damage. Another test for stability of oils to oxidation is based on the development of acidity as secondary product, for example, standards using the Rancimat equipment or a similar setup. 

TJecent research has established that the medium has an important effect on the rates and routes of oxidation reactions (4, 5, 10, 12). Chain oxidation reactions occur via peroxy radicals. The mechanism of liquid-phase oxidation at low extents of conversion is known to involve the following elementary reactions ... 

When immersed in aqueous solutions, the surfaces of metal oxides are expected to be hydroxylated (see Section 3.1). However, metal oxides may also react with aqueous solutions leading to dissolution, which can effectively be thought of as mass transfer from the solid to aqueous phase. The rate and extent of dissolution reactions depend on a number of factors, including solution pH, acid-base properties of oxo groups on the metal oxide surface, types of ligands present in solution, metal... 

In the collectors used, R is generally in the C2 to C6 range. Xanthates are readily oxidized to dixanthogens, and the extent of this reaction may have a big effect on the efficiency of the collector. 

Methane loss was usually small (5-20% ) for reasonable amounts of water formation (AP = 5-20 mm. Hg), so that the initial ratio —d[RH]/ d[H20] could be taken as A[RH]/A[H20] with sufficient accuracy for the analytical treatment discussed below. With computer interpretation, increased accuracy is possible if the initial concentrations of the various reactants are replaced by their mean concentrations during the reaction period. Because it was not considered sufficiently accurate to measure small differences by gas chromatography, the extent of oxidation was determined by oxidizing all the products to carbon dioxide, which was then measured (6). Because of the absence of any significant effect of methane on the rate, concentrations of methane up to 3% were sometimes used instead of the normal 1%. 

Several methods have been introduced which express the degree of oxidation deterioration in terms of hydroperoxides per unit weight of fat. The modified Stamm method (Hamm et at 1965), the most sensitive of the peroxide determinations, is based on the reaction of oxidized fat and 1,5-diphenyl-carbohydrazide to yield a red color. The Lea method (American Oil Chemists Society 1971) depends on the liberation of iodine from potassium iodide, wherein the amount of iodine liberated by the hydroperoxides is used as the measure of the extent of oxidative deterioration. The colorimetric ferric thiocyanate procedure adapted to dairy products by Loftus Hills and Thiel (1946), with modifications by various workers (Pont 1955 Stine et at 1954), involves conversion of the ferrous ion to the ferric state in the presence of ammonium thiocyanate, presumably by the hydroperoxides present, to yield the red pigment ferric thiocyanate. Newstead and Headifen (1981), who reexamined this method, recommend that the extraction of the fat from whole milk powder be carried out in complete darkness to avoid elevated peroxide values. Hamm and Hammond (1967) have shown that the results of these three methods can be interrelated by the use of the proper correction factors. However, those methods based on the direct or indirect determination of hydroperoxides which do not consider previous dismutations of these primary reaction products are not necessarily indicative of the extent of the reaction, nor do they correlate well with the degree of off-flavors in the product (Kliman et at. 1962). 

The minimum removal of TOC indicates the losses of H202 and shows the importance of Equation (6.124). No removal of TOC was observed during the first 30 min due to lower Fe2+ concentrations and thus limited hydroxyl radical is available for oxidation of organics. In the presence of oxygen, the rate of degradation and extent of oxidation increased dramatically, but no major difference was observed in the removal of TOC and COD. The reaction was also run at three different temperatures (21,30, and 40°C), with all other conditions constant. Figure 6.15 shows that temperature affects the reaction rate considerably. 

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