Oxygen pressure oxide system

Oxidation of Hydrocarbons. Ethanol is one of a variety of oxygen-containing compounds produced by the oxidation of hydrocarbons. Ethanol is reported to be obtained in a yield of 51% by the slow combustion of ethane (158,159). When propane is oxidi2ed at 350°C under a pressure of 17.2 MPa (170 atm) (160,161), 8% of the oxygen is converted to ethanol. Lower conversions to ethanol are obtained by oxidi2ing butane. Other oxidation systems used to produce ethanol and acetaldehyde (162—164) and methods for separating the products have been described in the patent Hterature. 

Therefore at constant temperature of 300°C and 7.5 psig of pressure, the system uses air that has 500 PPM TCE in it. Complete oxidation of 500 PPM TCE would consume only 750 PPM of oxygen as can be seen from the stoichiometric reaction. This is not a significant change from the oxygen content of air. 

Over the years, Pourbaix and his co-workers in the CEBELCOR Institute, founded under his direction, extended these diagrams by including lines for metastable compounds. Figure 7.66 illustrates such a presentation for the Fe-O system over the temperature range 830-2200 K. Pourbaix used these diagrams as a basis for a discussion of the stability of metallic iron (solid, liquid and vapour phases), the oxides of iron as a function of oxygen pressure and temperature from which he explained the protection of iron at high temperature by immunity and passivation. He also pointed out the... 

Solid particle-gaseous oxidizer systems have been studied because of applications to propints and expls (Refs 5 14), and hazards due to dust explns (Refs 1,3, 4, 6, 7, 10 15). Strauss (Ref 9) reported on a heterogeneous detonation in a solid particle and gaseous oxidizer mixt the study concerned A1 powder and pure oxygen in a tube. Detonations initiated, by a weak source were obtained in mixts contg 45-60% fuel by mass. Measured characteristics of the detonations agreed with theoretical calcns within about 10%, and detonation pressures of up to 31 atms were observed. With regard to solid particle-air mixts, detonations have not been reported only conditions for expln have been studied (Ref 2)... 

It appears that the presence of U6+, for which there is no counterpart in the Pu/O system, is responsible for preventing the oxygen pressures from increasing as rapidly in the mixed-oxide system as in the plutonia system. These results (39J indicate that the oxygen partial pressures in equilibrium with the mixed oxide will not differ drastically from those in equilibrium with urania. 

Both of the above chemical studies point towards the increased importance of the burning process at 285°C in determining the initial rate of heat production. The role of water as yet remains undefined other than at the higher temperature of 285°C it appears to have the opposite effect on the bitumen sample compared to the process at 225°C i.e., it appears that water vapor encourages pathways by which the various components of bitumen react with oxygen. Preliminary calculations of the total heats evolved during the wet oxidation of bitumen sands indicate that they are independent of the partial pressure of oxygen in the system at... 

The first case is the one dealt with by Fujita and Kwan (15), Barry (16), and Terenin and Solonitzin (17) who studied a ZnO-02 system, and also by Kennedy et al. (18,19) who worked with a Ti02-02 system On oxidation of the specimen photodesorption was replaced by photoadsorption. Here also belong the papers by Romero-Rossi and Stone (11,12) (ZnO-02) and by Kwan (18) (Ti02-02) who observed, at high temperatures (above 400°C), the replacement of photodesorption by photoadsorption with increasing oxygen pressure (i.e., as the degree of oxidation of the specimen increased). 

At a fixed temperature, AGr is constant, and so the equilibrium oxygen partial pressure, po2, will also be constant. This oxygen pressure is called the decomposition pressure or dissociation pressure of the oxide and depends only upon the temperature of the system. 

A. Muan, The Effect of Oxygen Pressure on Phase Relations in Oxide Systems, Am. J. Sci, 256, 171-207 (1958). 

Examples 24-27 are for oxidation reactions, three of hydrocarbons and one of CH3OH. Examples 24 and 25 are for the same reaction, with Example 24 for high oxygen pressure and coverage and Example 25 at low oxygen pressure and coverage. For the low-pressure case, Korchak and Tretyakov (98) postulated for their system that the surface-active oxygen is atomic ... 

With decreasing temperature, as we have seen, the intrinsic defect population decreases exponentially and, at low T, extrinsic disorder becomes dominant. Moreover, extrinsic disorder for oxygen-based minerals (such as silicates and oxides) is significantly alfected by the partial pressure of oxygen in the system (see section 4.4) and, in the region of intrinsic pressure, by the concentration of point impurities. In this new region, term Qj does not embody the enthalpy of defect formation, but simply the enthalpy of migration of the defect—i.e.,... 

W-O system. At lower temperatures, the W surface is always covered with some kind of oxide. Above 725°C, at relatively low oxygen pressure, only W and WO2 are present. Because WO2 is volatile, a metal W surface is generated. (After Promi.scl, 1964.)... 

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