Pressure ammonia

The observed rate law depends on the type of catalyst used with promoted iron catalysts a rather complex dependence on nitrogen, hydrogen, and ammonia pressures is observed, and it has been difficult to obtain any definitive form from experimental data (although note Eq. XVIII-20). A useful alternative approach... 

Insoluble Ammonium Polyphosphate. When ammonium phosphates are heated ia the presence of urea (qv), or by themselves under ammonia pressure, relatively water-iasoluble ammonium polyphosphate [68333-79-9] is produced (49). There are several crystal forms and the commercial products, avaUable from Monsanto, Albright WUson, or Hoechst-Celanese, differ ia molecular weight, particle size, solubUity, and surface coating. Insoluble ammonium polyphosphate consists of long chains of repeating 0P(0)(0NH units. 

Manufacture. Dicyandiamide is converted into melamine by heating. Simple pyrolysis above the melting point leads to an exothermic reaction however, deammoniation occurs, forming products containing two or three triazine rings as well as melamine. After it was discovered in 1940 that deammoniation can be counteracted by conducting the reaction under ammonia pressure, various methods were developed to control the exothermic reaction on an industrial scale. 

Figure B-4. Ammonia pressure-enthalpy diagram. (From Short, Kent and Walls, Pressure-Enthalpy Charts for Selected Fn i neering Substances, Gulf Publishing Company, Houston, TX, 1970.)...

Synthesis of B-monosubstituted Borazine Derivatives. The photolytic reaction of borazine with a second reagent is a convenient method for synthesizing a number of B-monosubstituted borazine derivatives. B-monoaminoborazine, produced in the gas phase photolysis of borazine ammonia mixtures with 184.9 nm radiation, was first synthesized by Lee and Porter in 1967. This is the only method currenfly known for generating this compound. A detailed study of the photochemical reaction, under varying conditions of borazine and ammonia pressures, was reported by Neiss and Porter in 1972. The quantum yield for the production of H2 according to the overall Eq. (19) varies from 0.27 and 1.17 when the initial NH3 pressures are varied from 0.1 to 7.0 Torr and the borazine pressure is maintained at 5.0 Torr (Fig. 11). 

Figure 3 Fractional surface coverage 0. determined using Eq. (3), as a function of ammonia pressure for (a) an etched w-CdSe crystal and (b) a n-CdSe crystal coated with an ammonia-imprinted PAA film. The insets show the same data as double reciprocal plots, yielding equilibrium constants for (a) and (b) of 750 250 and 1000 500...

From the reaction mechanism above, derive an expression for the adsorbed ammonia site fraction, 6 = [NH3(ad)]/T. Make the simplifying assumption that kip(NH3) + k-1 >> 2[Si(s)] this is equivalent to assuming that reaction 1 is at equilibrium, and that reaction 2 makes a negligible difference in the adsorbed ammonia concentration. Determine the NH3(ad) site fraction for an ammonia pressure of 124 Pa. 

The surface nitrogen concentration [N(s)] was measured as a function of time for ammonia pressures of 124 and 1400 Pa. Calculate [N(s>] (atoms/cm2) as a function of time for these two pressures, and compare with experimental values from Ref. [425] (data can be found in the file SiNitridation, csv). Plot theory and experiment on the same graph. Take k2 = 1.5 x 10 4 s 1. 

At the present time, there has been too little experimental forming done at intermediate ammonia pressures. 

When sulfur dioxide is introduced through the nozzle and the amount of ammonia behind the annular opening varies from 6 to 50 torr, the extent of ammonia incorporation into the clusters dramatically increases with increasing ammonia pressure. Up to two ammonia molecules were observed to be incorporated into the clusters with 20 torr of ammonia behind the annular opening. With 40 torr, up to four NH3 molecules were observed in the clusters. 

Steam, ammonia Pressure lOkN/m Abs, no DoncondensaUes 8000-12000 0-1x10 ... 

The application of ammonia pressure leaching as a method of refining nickel-cobalt matte has been studied (Bll, P3) and is considered an economically attractive process. Nickel-copper mattes with low cobalt content have been found to be readily leached with ammonia (P3). A high-nickel matte with a composition of 77% Ni, 0.1% Cu, 1.8% Co, 0.7% Fe, and 20% S is amenable to both acid and ammonia leach, but the sulfur deficiency can be made up more economically by circulation of ammonium sulfate solution within the process than by providing the sulfur through addition of sulfuric acid. 

An objection to this view was made by Laidler (3), who found that the rate of the exchange reaction between deuterium and ammonia on a promoted iron catalyst passed through a maximum with increase of the ammonia pressure, contrary to the zero-order kinetics with respect to ammonia reported by Farkas (4). 

In most cases the color of the ammonia-treated wood is darker and approaches a walnut color. Some color streaking is a drawback with certain wood species. In addition, the ammonia vapor reacts with some of the wood components to produce a liquid that drains from the wood upon release of the ammonia pressure. This process is not in commercial use at the present time. 

For low-temperature N2 production, Pignet and Schmidt conclude that, since the reaction rate increases with a decrease in ammonia pressure in the ammonia-rich regime, there must be competitive adsorption operating. This effect was more pronounced for NH3/O2 reactants than for NH3/NO reactants. Their equation for the rate of N2 production below 800 °C is ... 

The detailed variation in reaction rate with reactant pressures and surface composition has been examined at 200 and at 400 °C. The production of N 2 coincided quantitatively with the intensity of the AES N (390 V) peak the NO production rate correlated well with the intensity of the AES O (510 V) peak. At 200 °C the rate of nitrogen formation was first order in oxygen pressure but independent of NH3 pressure. Conversely at 400 °C the nitric oxide formation rate was first order in ammonia pressure above 4 x 10 Torr. Desorption experiments during the reaction proved the surface species were N atoms and O atoms respectively. 

In some factories it is added to the feed make-up prior to digestion. The disadvantage of this method is that, during heating, an ammonia pressure is built up that prevents one to reach the desired temperature by steam injection. An intermediate venting of the autoclave is necessary, resulting in loss of time and in increased steam demand. The advantage is the proper separation of all impurities. 

In the calculation of P, however, the Dutch workers used P h, the exit of the catalyst bed. In other words, the ammonia pressure over the catalyst was postulated to be equal to that at the exit. In the flow system P h, a.t the entrance of the catalyst bed is zero. Without knowing, consequently, the distribution of ammonia pressure throughout the catalyst bed, the calculation of P is subject to error, especially since P is proportional to the square of P h,-... 

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