Ammonia partial pressure dependence

The complex dependency of the yield of combustion products on the ammonia partial pressure indicates that various factors are influencing the rate of formation of this product class. If ammonia is only inhibiting the adsorption of propene, then the yield of combustion products is expected to follow the same trend as the yield of the partial (amm)oxidation products. Ammonia is not only consumed for the formation of acrylonitrile, but can also reduce the surface under the formation of e g. N2. This will change the degree of reduction of the surface, and hence the composition of the pool of oxygen species. If ammonia cannot... 

Effects of Potassium on the Adsorption of Ammonia on Iron Under Ammonia Synthesis Conditions The changes in the apparent reaction order dependence in ammonia partial pressure suggest that to elucidate the effects of potassium on both iron single crystals and the industrial catalyst, it is necessary to understand the readsorption of gas-phase ammonia on the catalyst surface during ammonia synthesis The fact that the rate of ammonia synthesis is negative order in ammonia synthesis. Once adsorbed, the ammonia has a certain residence time (t) on the catalyst which is determined by its adsorption energy on iron [t cx tq exp (AH /RT)]... 

Because the ammonia synthesis reaction is an equiUbrium, the quantity of ammonia depends on temperature, pressure, and the H2 to-N2 ratio. At 500°C and 20.3 MPa (200 atm), the equiUbrium mixture contains 17.6% ammonia. The ammonia formed is removed from the exit gases by condensation at about —20° C, and the gases are recirculated with fresh synthesis gas into the reactor. The ammonia must be removed continually as its presence decreases both the equiUbrium yield and the reaction rate by reducing the partial pressure of the N2—H2 mixture. 

The choice of a specific CO2 removal system depends on the overall ammonia plant design and process integration. Important considerations include CO2 sHp required, CO2 partial pressure in the synthesis gas, presence or lack of sulfur, process energy demands, investment cost, availabiUty of solvent, and CO2 recovery requirements. Carbon dioxide is normally recovered for use in the manufacture of urea, in the carbonated beverage industry, or for enhanced oil recovery by miscible flooding. 

Therefore, the ISE potential depends on the CO2 partial pressure with Nernstian slope. Contemporary microporous hydrophobic membranes permitted the construction of a number of gas probes, developed mainly by the Orion Research Company (for a survey see [143]. The most important among these sensors is the ammonia electrode, in which ammonia diffusing through the membrane affects the pH at a glass electrode. Other electrodes based on similar principles respond to SO2, HCN, H2S (with an internal S ISE), etc. The ammonia probe has a better detection limit than the ammonium ion ISE based on the non-actin ionophore. The response time of gas probes depends mostly on the rate of diffusion of the test gas through the microporous medium [77,143]. 

Sour water strippers are designed primarily for the removal of sulfides and can be expected to achieve 85-99% removal. If acid is not required to enhance sulfide stripping, ammonia will also be stripped, the percentage varying widely with stripping pH and temperature. Depending on pH, temperature, and contaminant partial pressure, phenols and cyanides can also be stripped with removal as high as 30%. 

That the entropy change is unfavourable could be confidently predicted, given the presence of two moles of gas on the left-hand side. As the temperature is increased, the TAS" term becomes more important neglecting the small temperature dependence of AH° and A5°, it can be easily shown that AG° will become zero at about 850 K, at which temperature the decomposition of the complex should be complete. Such decomposition can be achieved at lower temperatures if the partial pressure of ammonia is kept low, by pumping. Most thermal decompositions-which are often the reverse of acid-base reactions (see Section 9.2) - are entropy-driven. All substances containing chemical bonds can be decomposed by heating to a sufficiently high temperature. 

The reactor can operate with either a liquid-phase reaction or a gas-phase reaction. In both types, temperature is very important. With a gas-phase reaction, the operating pressure is also a critical design variable because the kinetic reaction rates in most gas-phase reactions depend on partial pressures of reactants and products. For example, in ammonia synthesis (N2 + 3H2 O 2NH3), the gas-phase reactor is operated at high pressure because of LeChatelier s principle, namely that reactions with a net decrease in moles should be mn at high pressure. The same principle leads to the conclusion that the steam-methane reforming reaction to form synthesis gas (CH4 + H20 O CO + 3 H2) should be conducted at low pressure. 

The only homogeneous catalyst that has been systematically studied for the reaction of silanes with ammonia is Cp2TiMe2.147 This catalyst is effective for tertiary, secondary, and primary organosilanes, but the products from secondary and primary organosilanes are quite complex and strongly dependent on the reaction conditions. Reasonable rates were achieved at temperatures of 70 to 100°C, at partial pressures of 1 to 2 atm NH3, and at a catalyst concentration of ca. 1 mol % relative to silane. Some typical results are shown in Table V. 

A frequent reason for the dependence of catalyst structure on the chemical potential in the gas phase containing all the reactants is the incorporation of molecules or atoms from the reaction mixture into the catalyst phases. Formation of subphases, often only in the near-surface region of the solid, fails to create phases with individual reflections but modifies the reflections of the starting precatalyst phase notably (see previous sections). This complication presents a massive problem in the analysis of working catalysts when significant partial pressures of products are important to the phase formation and when the necessary conversions cannot be reached in the experimental cell. The investigation of ammonia synthesis catalysts when insufficient partial pressures of the product ammonia prevent the formation of the relevant nitride phases is a prominent example of this limitation (Herzog et al., 1996 Walker et al., 1989). 

Contradictory data on the kinetics of ammonia synthesis, especially in the earlier literature, in some circumstances may reflect a lack of attention to the influence of impurities in the gas. If oxygen compounds are present in the synthesis gas, reversible poisoning of the adsorbing areas, in accordance with an equilibrium depending on the temperature and the water vapor-hydrogen partial pressure ratio, must be taken into account when developing rate equations (see also Section 3.6.1.5). 

Recently, however, a correlation has been found between the pH-dependent (gaseous) partial pressure of the arterial NH3 and the clinical degree of HE. (54) A recent study showed that ammonia levels (arterial and venous) as well as arterial and venous partial pressure of ammonia correlate with the severity of HE. It was hereby demonstrated that venous sampling is adequate for ammonia measurement. (75) Another study suggests there is no significant difference between arterial and venous ammonia levels or partial pressure of ammonia no correlation of these three ammonia values with HE was found. (71)... 

By studying the pressure dependence of the hydrogen evolution reaction on Hg at pH 1 they obtained a negative volume of activation (—3.4 ml. mole"1), which, they argued, was not in accord with any H-atom process but could result from the emission and hydration of metallic electrons as the rate-determining step. This interpretation thus invokes the formation of e aq even at pH 1. (This value of —3.4 agrees well with the partial molal volume of e m (—5.5 to —1.1 mole 1) obtained indirectly in a radiation chemical system (45). It is interesting to note the difference in V for e aq and e ( ammonia >, where the value is —60 ml. mole 1 (49)). 

Note that the concentration product of nitric acid and ammonia in equilibrium with a mixed sulfate-nitrate solution having a value of T = 0.5 is about one-half as high as that in equilibrium with a pure ammonium nitrate solution. The temperature dependence of the partial-pressure product for the aqueous mixed-salt case is similar to that of the pure salt. 

The amount of a gas which will dissolve in a liquid chiefly depends upon the gas pressure—the greater the gas pressure, the greater its solubility. Gas solubility will be even greater if the gas reacts with the solvent, e.g., ammonia and carbon dioxide in water. Gas solubility is quantitatively described by Henry s law, which states that the amount of a gas dissolved in a liquid at a fixed temperature depends only upon the gas pressure. This is true for both pure gases and mixtures of gases. The solubilities of gases in a mixture depend upon the pressure each gas would exert if it were present alone, i.e., its partial pressure. In quantitative terms, Henry s law states... 

The mechanism and kinetics of adsorption in this case is quite complex in view of the fact that the two interfaces, viz. vapour/organic liquid and organic liquid/aqueous solution interfaces are involved. Kinetics of adsorption in such types of complicated cases have been investigated recently involving kinetics at fluid-fluid interface, nonionic surfactant solution and surfactant mixtures [54, 55], Taking a simplistic view, the extent of adsorption would depend on partial pressure of ammonia, which would depend on the concentration of NHj/amine in the vapour phase and also on the distance and the cotton-soaked solution in the glass tube from the interface. 

However, Murakami et al. (2005) suggested that the ammonia synthesis rate may not depend on only electrolysis potential. Other factors such as catalytic activity of electrode material, partial pressure of gaseous reactants, and temperature are cmcial parameters for the kinetics of ammonia synthesis (Mamellos, Zisekas, Stoukides, 2000 Skodra Stoukides, 2009). 

The manner in which the concentrations of H2, N2, and NH3 vary with time is shown in Figure 15.6(a) . The situation is analogous to the one shown in Figure 15.3(a). The relative amounts of N2, H2, and NH3 present at equilibrium do not depend on the amount of catalyst present. However, they do depend on the relative amounts of H2 and N2 at the beginning of the reaction. Furthermore, if only ammonia is placed in the tank under the same reaction conditions, an equilibrium mixture of N2, H2, and NH3 will form. The variations in partial pressures as a function of time for this situation are shown in Figure 15.6(b). At equilibrium the relative partial pressures of H2, N2, and NH3 are Ihe same, regardless of whether the starting mixture was a 3 1 molar ratio of H2 and N2 or pure NH3. The equilibrium condition can he reached from either direction. 

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