Transfer, oxygen

2 Oxygen Transfer- Evidence for metallaoxetane involvement in metalloporphyrins is contained in a review, ) ) as are approaches to fine chemicals by oxidation.) ) ) The combination of a metal acac complex and an aldehyde constitutes a new and powerful method for alkene 

In heterogeneous catalytic oxidation, the reaction is always between a molecule to be oxidized (in adsorbed form or not) and oxygen which is attached to, or is part of, the surface. 

A number of different oxygen species is possible, ranging from free oxygen molecules to oxygen anions. The species in between can be represented by the scheme 

From left to right, the oxidizing power will decrease. Which of the different oxygen species are active on a catalyst is determined by 

It is generally assumed that, in the group of transition metal oxides, the intermediates between 02 (gas) and O2- (surface) do not come into the picture. O2- (surface) is considered to be the reactive oxygen species. 

Another way to avoid the need for a sacrificial reductant is to use a reduced form of dioxygen, e.g. H202 or R02H, as a single oxygen donor. Such a reaction is referred to as a catalytic oxygen transfer and can be described by the general equation shown in Fig. 4.9. 

XOY = H202, R02H, R3NO, NaOCl, KHSO5, etc. Fig. 4.9 Catalytic oxygen transfer. 

Heterolytic oxygen transfer processes can be divided into two categories based on the nature of the active oxidant an oxometal or a peroxometal species (Fig. 4.10). Catalysis by early transition metals (Mo, W, Re, V, Ti, Zr) generally involves high-valent peroxometal complexes whereas later transition metals (Ru, Os), particularly first row elements (Cr, Mn, Fe) mediate oxygen transfer via oxometal species. Some elements, e.g. vanadium, can operate via either mechanism, depending on the substrate. Although the pathways outlined in Fig. 4.10 

For the sake of completeness we also note that oxygen transfer processes can be mediated by organic catalysts which can be categorized on the same basis as metal catalysts. For example, ketones catalyze a variety of oxidations with mono-peroxysulfate (KHS05) [14]. The active oxidant is the corresponding dkmrane and, hence, the reaction can be construed as involving a peroxometal pathway. Similarly, TEMPO-catalyzed oxidations of alcohols with hypochlorite [15, 16] involve an oxoammonium salt as the active oxidant, i.e. an oxometal pathway. 

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Peroxy acid and alkene Transition state for oxygen transfer from the OH group of the peroxy acid to the alkene Acetic acid and epoxide ... 

Oxygen solubility Oxygen tents Oxygen transfer Oxygen transfer rate Oxygen transport Oxyhalide Oxyhemoglobin... 

From equation 23, it can be seen that the higher the power input per unit volume, the lower the oxygen transfer efficiency. Therefore, devices should be compared at equal transfer rates. AH devices become less energy efficient as rates of transfer increase (3). 

The most basic oxygen transfer equation (6) states that the amount of diffusion is proportional to the surface of the interface (6,20) ... 

Aerator type Materials of constmction Oxygen transfer efficiency, OTE, % Oxygen transfer rate, OTR, g/(W-h)... 

Oxygen transfer rate (OTR) is estimated by the foUowiag standard procedure (12), where the rate of mass transfer per unit volume of Hquid is taken to be directly proportional to the driving force of the system... 

The oxygen transfer rate for aerators is normally reported at standard conditions. Thus, ia order to make meaningful comparisons, the ORT under working or field conditions should be adjusted to standard conditions oxygen requirement for treatment (SORT) by means of... 

Table 2. Altitude Correction Factors for Oxygen Transfer...

The SORT value when divided by the standard conditions oxygen transfer rate (OTR) given for a mechanical aerator yields the oxygen concentration required for treatment. 

The mechanism of this reaction involves an activation of the ammonia and hydrogen peroxide because these compounds do not themselves react (118—121). It appears that acetamide functions as an oxygen transfer agent, possibly as the iminoperacetic acid (41) which then oxidizes the transient Schiff base formed between MEK and ammonia (40) to give the oxaziridine (42), with regeneration of acetamide ... 

For the oxygen migration test for oxirene participation to be valid, it must be shown (80ZN(B)1040) that intermolecular oxygen transfer does not occur, and that oxygen scrambling... 

E] Based on oxygen transfer from water to air 77 F. Liquid film resistance controls. (Dwnei- 77 F = 2.4 X 10 ). Equation is dimensional. Data was for thin-waUed polyethylene Raschig rings. Correlation also fit data for spheres. Fit 25%. See Reiss for graph. 

Interfacial Phenomena These can significantly affect overall mass transfer. In fermentation reactors, small quantities of surface-active agents (especially antifoaming agents) can drastically reduce overall oxygen transfer (Aiba et al., op. cit., pp. 153, 154), and in aerobic... 

The need for highly cost-efficient oxygen transfer in fermentations such as those with hydrocarbon feedstocks has led to air-hft fermenters as shown in Fig. 24-4. The worlds largest industrial fermenter was... 

As the oxygen transfer rate under steady-state conditions must equal oxygen uptake, K a may be calculated ... 

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