Ammonia temperature distribution

Probably due to higher temperatures the contents of sulfur and carbon were lower at the inlet of the bed when the sulfur content in the gas was higher (Table 1). The interaction of adsorbed sulfur and carbon formation could also have influenced the carbon content. The higher ammonia conversions obtained at higher sulfur levels in the gas may have been partly due to the temperature distribution. However, this carmot be the main reason as there was no temperature gi ent in the bed during atmospheric experiments. Nevertheless, the uneven distribution of the poison as a function of location in the fixed bed complicated fundamental interpretation of experimental data. 

Egyhazi, J., Scholtz, J., 1983a, Simulation of the operation of the new and partially deactivated ammonia synthesis catalyst, part 2 Calculation of the concentration and temperature distributions, Hungarian chemical Soc., Hung, Vol.2,13. 

The mature Haber-Bosch technology is unlikely to change substantiaHy in the foreseeable future. The centers for commercial ammonia production may, however, relocate to sites where large quantities of natural gas are flared from cmde oil production, eg, Saudi Arabia or Venezuela. Relocation would not offset the problems for agriculture of high transportation and storage costs for ammonia production and distribution. Whereas the development of improved lower temperature and pressure catalysts is feasible, none is on the horizon as of this writing. 

Moderately Volatile Ma.teria.ls, For moderately volatile materials, such as the amines commonly used in feedwater and boiler water chemical treatment, the distribution ratios vary from 0.1 to 30 for gases, the ratios are much higher. The distribution ratios of amines and organic acids are generally temperature-dependent. The distribution ratios for ammonia [7664-41-7] morpholine [110-91-8] and acetic acid [64-19-7] are shown in Figure 16 as examples. 

In the SCR process, ammonia, usually diluted with air or steam, is injected through a grid system into the flue/exhaust stream upstream of a catalyst bed (37). The effectiveness of the SCR process is also dependent on the NH to NO ratio. The ammonia injection rate and distribution must be controlled to yield an approximately 1 1 molar ratio. At a given temperature and space velocity, as the molar ratio increases to approximately 1 1, the NO reduction increases. At operations above 1 1, however, the amount of ammonia passing through the system increases (38). This ammonia sHp can be caused by catalyst deterioration, by poor velocity distribution, or inhomogeneous ammonia distribution in the bed. 

Isopiestic or isothermal distillation. This technique can be useful for the preparation of metal-free solutions of volatile acids and bases for use in trace metal studies. The procedure involves placing two beakers, one of distilled water and the other of a solution of the material to be purified, in a desiccator. The desiccator is sealed and left to stand at room temperature for several days. The volatile components distribute themselves between the two beakers whereas the non-volatile contaminants remain in the original beaker. This technique has afforded metal-free pure solutions of ammonia, hydrochloric acid and hydrogen fluoride. 

Figure 4-8 shows a continuous reactor used for bubbling gaseous reactants through a liquid catalyst. This reactor allows for close temperature control. The fixed-bed (packed-bed) reactor is a tubular reactor that is packed with solid catalyst particles. The catalyst of the reactor may be placed in one or more fixed beds (i.e., layers across the reactor) or may be distributed in a series of parallel long tubes. The latter type of fixed-bed reactor is widely used in industry (e.g., ammonia synthesis) and offers several advantages over other forms of fixed beds. 

Various amines find application for pH control. The most commonly used are ammonia, morpholine, cyclohexylamine, and, more recently AMP (2-amino-2-methyl-l-propanol). The amount of each needed to produce a given pH depends upon the basicity constant, and values of this are given in Table 17.4. The volatility also influences their utility and their selection for any particular application. Like other substances, amines tend towards equilibrium concentrations in each phase of the steam/water mixture, the equilibrium being temperature dependent. Values of the distribution coefficient, Kp, are also given in Table 17.4. These factors need to be taken into account when estimating the pH attainable at any given point in a circuit so as to provide appropriate protection for each location. 

Brown et al. [494] developed a method for the production of hydrated niobium or tantalum pentoxide from fluoride-containing solutions. The essence of the method is that the fluorotantalic or oxyfluoroniobic acid solution is mixed in stages with aqueous ammonia at controlled pH, temperature, and precipitation time. The above conditions enable to produce tantalum or niobium hydroxides with a narrow particle size distribution. The precipitated hydroxides are calcinated at temperatures above 790°C, yielding tantalum oxide powder that is characterized by a pack density of approximately 3 g/cm3. Niobium oxide is obtained by thermal treatment of niobium hydroxide at temperatures above 650°C. The product obtained has a pack density of approximately 1.8 g/cm3. The specific surface area of tantalum oxide and niobium oxide is nominally about 3 or 2 m2/g, respectively. 

However, it was Maxwell in 1848 who showed that molecules have a distribution of velocities and that they do not travel in a direct line. One experimental method used to show this was that ammonia molecules are not detected in the time expected, as derived from their calculated velocity, but arrive much later. This arises l om the fact that the ammonia molecules tnterdiffuse among the air moixules by intermolecular collisions. The molecular velocity calculated for N-ls molecules from the work done by Joule in 1843 was 5.0 xl02 meters/sec. at room temperature. This implied that the odor of ammonia ought to be detected in 4 millisec at a distance of 2.0 meters from the source. Since Maxwell observed that it took several minutes, it was fuUy obvious that the molecules did not travel in a direct path. 

Propylene, ammonia, steam and air are fed to a vapour-phase catalytic reactor (item A). The feedstream composition (molar per cent) is propylene 7 ammonia 8 steam 20 air 65. A fixed-bed reactor is employed using a molybdenum-based catalyst at a temperature of 450°C, a pressure of 3 bar absolute, and a residence time of 4 seconds. Based upon a pure propylene feed, the carbon distribution by weight in the product from the reactor is ... 

Ammonia TPD is very simple and versatile. The use of propylamine as a probe molecule is starting to gain some popularity since it decomposes at the acid site to form ammonia and propene directly. This eliminates issues with surface adsorption observed with ammonia. The conversion of the TPD data into acid strength distribution can be influenced by the heating rate and can be subjective based on the selection of desorption temperatures for categorizing acid strength. Since basic molecules can adsorb on both Bronsted and Lewis acid sites, the TPD data may not necessarily be relevant for the specific catalytic reaction of interest because of the inability to distinguish between Bronsted and Lewis acid sites. 

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