Thermodynamics oxygen concentrations

If results are required at very high temperatures, as in experiments related to steel making, even short-term survival makes severe demands on the construction of the cell (Komarek and Ipser 1984). However, oxygen concentration cells have been employed with molten ionic slags to determine the thermodynamics of oxide formation in iron between 1500-1600°C (Kay 1979). Other applications include the use of YSZ for studies of semiconducting systems (Sears and Anderson 1989, Lee et al. 1992). 

The first step is relevant to the start-up phase, which in this particular case we chose to extend for up to 1 h in order to verify the reactor stability also in these conditions, where water is not present and while there is a higher oxygen concentration in the feed gas with respect to the ATR conditions. By lowering the 02 CH4 ratio, the H2 concentration at the reactor outlet increases, approaching the value expected by thermodynamic evaluation and CH4 conversion is still complete. A further decrease in the 02 CH4 feed ratio to values lower than 1.16 corresponds to an abrupt decrease in temperature in the lower section and a simultaneous temperature increase in the catalytic reforming section. 

For this calculation, a synthetic gasoline is used, consisting of 35% n-Ce, 25% hexene, and 40% xylene. As expected, the results show that as the oxygen concentration ( air ratio ) increases, the thermodynamic driving force for coke formation decreases. Increasing the S/R ratio from zero i.e., POX) to 0.7 also decreases coke formation. Coke is not thermodynamically favored at air ratios above 0.3, which corresponds to temperatures above 850°C. 

These phenomena principally govern the performance of a bioreactor. The first and second of these phenomena are independent of scale. Neither a typical thermodynamic property (e.g., the solubility of oxygen in a broth) nor microkinetic properties (e.g., the growth and product formation by the microorganism) are dependent on the scale of the bioreactors. However, the actual oxygen concentrations and the kinetic behavior of microorganisms in a bioreactor are dependent on... 

In a recent study (4) kinetic measurements in a CSTR were combined with simultaneous in situ measurement of the thermodynamic activity of oxygen adsorbed on the catalyst by using the technique of solid electrolyte potentiometry (SEP). The technique originally proposed by C. Wagner (1) utilizes a solid electrolyte oxygen concentration cell with one electrode also serving as the catalyst for the reaction under study. It has already been used to study the oxidation of ethylene on Ag (5) and on Pt (6). 

TABLE 7.1 Thermodynamic Equilibrium Concentrations of Nitric Oxide from Equimolar Amounts of Nitrogen and Oxygen ... 

This thermodynamic coupling between oxygen and carbon dioxide exhibited in water will also occur between any two gases in any solvent. A physiological example of this is the solubility of oxygen and carbon dioxide in blood, where it is found that increasing the partial pressure of Oo at fixed CO2 partial pressure results in an increased oxygen concentration in blood and decreased carbon dioxide concentration. Also, the situation is reversed if the CO2 partial pressure is increased at fixed O2 partial pressure. This phenomenon was first experimentally observed in 1914 and is referred to as the Bohr effect. 

In waters with high values of Eh, many more biotic and abiotic oxidation reactions become thermodynamically probable (though not necessarily feasible from a kinetic perspective). Similarly, a low oxygen concentration or Eh makes reductive processes more likely. 

The two parameters that control corrosivity of soft waters are the pH and the dissolved oxygen concentration. In hard waters, however, the natural deposition on the metal surface of a thin diffusion-barrier film composed largely of calcium carbonate (CaCOs) protects the underlying metal. This film retards diffusion of dissolved oxygen to cathodic areas, supplementing the natural corrosion barrier of Fe(OH)2 mentioned earlier (Section 7.2.3). In soft water, no such protective film of CaCOs can form. But hardness alone is not the only factor that determines whether a protective film is possible. Ability of CaCOs to precipitate on the metal surface also depends on total acidity or alkalinity, pH, and concentration of dissolved solids in the water. For given values of hardness, alkalinity, and total dissolved salt concentration, a value of pH, given the symbol pHs, exists at which the water is in equilibrium with solid CaCOs. When pH > pHs, the deposition of CaCOs is thermodynamically possible. 

These calculations are the basic of potentio-metric sensors which are applied in broad field of industry and traffic. Main fields of application are the fast measuring of oxygen concentration in gases and liquid metals such as flue gases of combustion in steam boilers, in glass and ceramic making industries. By combination of sensor signals with stoichiometric and thermodynamic relations, a complex characterization of gas phases under equilibrium conditions is possible. 

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