Ammonia conversion nitric oxide production

When a metal-catalyzed reaction is so fast that external mass transfer controls, several layers of fine wire screen can be used as the catalyst bed. The catalytic oxidation of ammonia to nitric oxide, which is the first step in nitric acid production, is carried out with screens (called gauzes) of Pt/Rh alloy, and very high ammonia conversions are obtained. Similar gauzes are used in the Andrussov process for manufacture of HCN from CH4, NH3, and O2. Wire screens are also used for catalytic incineration of pollutants and in improving combustion efficiency in gas burners. 

Dual-Pressure Process. Dual-pressure processes have a medium pressure (ca 0.3—0.6 MPa) front end for ammonia oxidation and a high pressure (1.1—1.5 MPa) tail end for absorption. Some older plants still use atmospheric pressure for ammonia conversion. Compared to high monopressure plants, the lower oxidation pressure improves ammonia yield and catalyst performance. Platinum losses are significantiy lower and production mns are extended by a longer catalyst life. Reduced pressure also results in weaker nitric acid condensate from the cooler condenser, which helps to improve absorber performance. Due to the spHt in operating conditions, the dual-pressure process requires a specialized stainless steel NO compressor. 

Today, solid-catalyzed gas reactions are executed to an extent of several billions of tonnes per annum. To name only a few important examples Steam reforming of methane-rich natural gas to synthesis gas (H2 + CO), conversion of CO with H20 to C02 + H2, conversion of CO with H2 to methane, ammonia synthesis, oxidation of S02 to S03 (sulphuric acid production), oxidation of NH3 to NO (nitric acid production). The world production of ammonia in 1995 amounted to 90 m tonnes and... 

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 this method, large amounts of acetonitrile, CH3CN, occur as a by-product. Catalysis is by vanadium oxide on AI2O3, or borophosphate, titanium phosphate, or bismuth phosphomolybdate on silica acid. The mechanism is still unestablished. On the one hand, acrolein does not appear to be an intermediate product, since it is not formed in the absence of ammonia. On the other hand, acrylonitrile can also be obtained from acrolein with ammonia and oxygen, and molybdenum oxide as catalyst. In another variation, the conversion is not made with ammonia and air, but with nitric oxide ... 

Many times, the conversion of a reactor depends on the operating temperature. Even if isothermal operation is recommended, sometimes it is not easy to remove the energy generated during the reaction, or because it can be an asset for the process, the reactor operates under adiabatic conditions. The example that we are trying to solve now presents the features of this last type. In the production of nitric acid from ammonia, the converter oxidizes NHj into NO. The conversion of that reactor varies with temperature and the conversion profile may be obtained from experimental data in the Ullmann s Encyclopedia [9]. 

Industrial fertilizer synthesis starts from ammonia synthesis, and ammonia is then easily oxidized in a separate reactor to nitric oxide over PtRh wire gauze catalyst. Formation of nitric acid requires further oxidation of nitric oxide to nitrogen dioxide (NO2) and absorption of the nitrogen dioxide in water. Overall, three different chemical process plants are used for the synthesis of nitric acid. The ammonia synthesis reaction takes place in a high-tem-perature, high-pressure reactor that requires recycling of products due to the thermodynamic limitations of chanical conversion. The ammonia oxidation reaction is very fast and takes place over a very small reactor length. Finally, nitric acid synthesis takes place in absorption columns. 

A basic problem for the production of nitric acid from ammonia can be found in [1,7]. However, typically dual processes have become preferred in order to take advantage of the physicochemical principles so that it is possible to enhance the conversion of ammonia oxidation at low pressure and improve the gases absorption downstream at a higher pressure. The problem that we address is presented as follows. The production of HNO3 fro ammonia starts with atmospheric air. The ratio between oxygen and ammonia to be fed to the converter must be 2.11, and the... 

At about the same time, industrial ammonia production became possible by catalytic conversion of nitrogen and hydrogen (Haber-Bosch process, Section 6.1), at first based on coal and later on natural gas or heavy crude oil fractions. This opened up the modern route to nitric acid by catalytic oxidation of ammonia, which is examined here in detail. 

The NH3 into NO conversion efficiency increases with decreasing pressure, whereas the conversion of NO into NO2 and the subsequent absorption is favored by high pressures. Thus, modern nitric acid piants are duai pressure processes, that is, the product gas of ammonia oxidation (at 6 bar) is compressed to 12 bar and then fed to the absorption tower for NO oxidation and for NO2 absorption. 

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