Partial pressures of CO2 and

The corrosion rate of steel in carbonic acid is faster than in hydrochloric acid Correlations are available to predict the rate of steel corrosion for different partial pressures of CO2 and different temperatures. At high temperatures the iron carbonate forms a film of protective scale on the steel s surface, but this is easily washed away at lower temperatures (again a corrosion nomogram is available to predict the impact of the scale on the corrosion rate at various CO2 partial pressures and temperatures). 

Because of the relative instabiUty of FeO, the reduction to metallic Fe occurs at a much lower temperature and appreciable CO2 is present in the product gas. The high temperature required for the reaction of MnO and C results in the formation of essentially pure CO the partial pressures of CO2 and Mn are <0.1 kPa (1 X 10 atm). The product of this reaction is manganese carbide (7 3) [12076-37-8J, Mn C, containing 8.56% carbon. Assuming immiscibility of the metal and carbide, Mn should be obtainable by the reaction of MnO and Mn C at 1607°C. However, at this temperature and activity of Mn, the partial pressure of Mn vapor is approximately 10 kPa (0.1 atm) which would lead to large manganese losses. 

Thennodynamic inhibitors are complexing and chelating agents, suitable for specific scales. For example, for scale inhibition of barium sulfate, common chemicals are ethylenediaminetetraacetic acid (EDTA) andnitrilotriacetic acid. The solubility of calcium carbonate can be influenced by varying the pH or the partial pressure of carbon dioxide (CO2). The solubility increases with decreasing pH and increasing partial pressure of CO2, and it decreases with temperature. 

In an MCFC power system, increased pressure can result in increased cathode corrosion. Cathode corrosion is related to the acidity of the cell, which increases with the partial pressure of CO2, and therefore with the cell pressure. Such corrosion is typified by cathode dissolution and nickel precipitation, which can ultimately result in a shorted cell, causing cell failure (37). Thus, the chosen pressure of the MCFC has a direct link to the cell life, economics, and commercial viability. 

The solubility of some gases, such as CO2, is complicated by their chemical reaction with water. In the case of CO2, these reactions tend to reach equilibrimn rapidly, making the equilibrium concentration of CO2 a function of temperature, salinity, the atmospheric partial pressure of CO2, and pH. The last determines the degree to which CO2 is converted into the other inorganic species, H2C03(aq), HCO3 (aq), and COj Caq). Other gases that react with water include H2S and NH3. Note that these hydrolysis and acid dissociation reactions act to enhance the solubility of the parent gas. 

The radiation heat fluxes are exchanged between the internal and external surfaces of the cell slice and the surrounding surfaces. Moreover, fuel should not be considered as a transparent gas because of the significant partial pressures of CO2 and H2O. This means that radiation heat fluxes are exchanged between the external surface of the cell slice and the fuel volumes. The total net flux exiting the ith cell slice can be expressed as (see Figure 7.21) ... 

The thermodynamic criterion for the equilibria CaCO, ) = Ca0(,) + C02 (,) is AG ° = -RT n Kp, where AG° is the change in Gibbs free energy of the reactants and products in their standard state, R is the gas constant, and Kp is the equilibrium constant. For this equilibria, A p = pco, for pressure in units of atmospheres. Values for AG are tabulated in the form AG° = a+ bT combining these expressions yields an exponential relationship between the partial pressure of CO2 and temperature for the above equilibria. Complete derivations and discussion of these equations may be found in physical chemistry textbooks such as references [13] and [14]. 

Clearly, H2CO3 is now a constant for a fixed partial pressure of CO2 and is independent of pH, i.e. H2CO3 = KhPcoi- This means that H2CO3 is also constant over the entire pH range. 

Analysis The volumetric analysis of a gas mixture gives the mole fractions y of the components, vrhich are equivalent to pressure fractions for an ideal gas mixture. Therefore, the partial pressures of CO2 and H2O are... 

PC02 Pcoi ind Cj — Cf, Pcoi and correspond to any previous CO2 partial pressure and total inorganic carbon in seawater, respectively. For example, they might represent the preindustrial partial pressure of CO2 and the preindustrial total inorganic carbon in seawater. If the atmospheric p o creases by X percent, the C7 increases by X/rj percent. 

A 0.422-g sample of pentane, CjHj2, is placed in a 4.00-L reaction vessel with excess O2. The mixture is then ignited and the sample burns with complete combustion. What will be the partial pressures of CO2 and of H20(g) in the reaction vessel if the final temperature is 300.°C ... 

The effect of the partial pressure of carbon dioxide on the ethane dehydrogenation over oxidized diamond-supported Cr203 catalyst was examined. The results are shown in Fig. 4. Ethane conversion and ethylene yield markedly increased at a low partial pressure of CO2, and increased with increasing partial pressure. However, the ethylene selectivity slightly decreased with increasing partial pressure. The following reaction with CO2, in the dehydrogenation of ethane, would be possible ... 

Zhai WD, Dai MH, Cai WJ, Wang YC, Wang ZH (2005) High partial pressure of CO2 and its maintaining mechanism in a subtropical estuary The Pearl River Estuary, China. Max Chem 93(l) 21-32... 

If it is assumed that the partial pressures of CO2 and H2O in the atmosphere derived from fuel combustion are about 10 kPa, then the partial pressures of CO2 and H2O in a pore near the metal surface will be about 2.8 kPa and 3.7 kPa, respectively. These values will be higher in pores that are further from the metal surface, at sites where the activity of iron is lower, eventually tending to 10 kPa at the scale-gas interface. 

Respiratory chemoreceptors exist peripherally in the aortic arch and carotic bodies and centrally in the ventral medulla oblongata of the brain. These receptors are sensitive to partial pressures of CO2 and O2 and to blood pH. 

Check The units are correct for solubility, and the answer has two significant figures consistent with both the partial pressure of CO2 and the value of Henry s constant. 

The final properties of hardened cement may be modified by caibonation that takes place upon curing in an atmosphere of CO2, especially at hi humidity. The rate of carbonation depends on the partial pressure of CO2, and fairly high CO2 concentrations are required to attain an acceptable reaction rate. As there is always a steep gradient in the degree of carbonation, depending on the distance from the surface, the procedure is suitable only for thin-wall concrete/mortar elements. 

Revelle factor A dimensionless number that expresses the relative sensitivity of the partial pressure of CO2 and total dissolved inorganic carbon in a solution to the incremental additional or removal of CO2, bicarbonate or carbonate ions. 

---