Ammonia synthesis nitrogen

Figure 4.2 In the reactor for ammonia synthesis, nitrogen and hydrogen gases are used. (Courtesy of Solutia Inc., Luling, LA)...

Nearly all commercial nitrogen fertilizer is derived from synthetic ammonia. However, prior to the introduction of ammonia synthesis processes in the early 1900s dependence was entirely on other sources. These sources are stdl utilized, but their relative importance has diminished. 

Resources for Nitrogen Fertilizers. The production of more than 95% of all nitrogen fertilizer begins with the synthesis of ammonia, thus it is the raw materials for ammonia synthesis that are of prime interest. Required feed to the synthesis process (synthesis gas) consists of an approximately 3 1 mixture (by volume) of hydrogen and nitrogen. 

Ammonia Synthesis and Recovery. The purified synthesis gas consists of hydrogen and nitrogen in about 3 1 molar ratio, having residual inerts (CH Ar, sometimes He). The fresh make-up gas is mixed with the loop recycle and compressed to synthesis pressures. AH modern synthesis loops recycle the unreacted gases because of equiUbrium limitations to attain high overall conversions. The loop configurations differ in terms of the pressure used and the point at which ammonia is recovered. 

Removing Carbon Oxides from Ammonia Synthesis Gas," Nitrogen 180, 20—30 (July-Aug. 1989). 

Direct synthesis from nitrogen and finely divided titanium metal can be achieved at temperatures of >ca 1200° C (4). Typically, titanium sponge or powder is heated in an ammonia- or nitrogen-filled furnace and the product is subsequently milled and classified. 

These pioneers understood the interplay between chemical equiUbrium and reaction kinetics indeed, Haber s research, motivated by the development of a commercial process, helped to spur the development of the principles of physical chemistry that account for the effects of temperature and pressure on chemical equiUbrium and kinetics. The ammonia synthesis reaction is strongly equiUbrium limited. The equiUbrium conversion to ammonia is favored by high pressure and low temperature. Haber therefore recognized that the key to a successful process for making ammonia from hydrogen and nitrogen was a catalyst with a high activity to allow operation at low temperatures where the equiUbrium is relatively favorable. 

Ammonia Synthesis. Ammonia (qv) has been manufactured by the hydrogenolysis of the N-N bond in nitrogen over an iron-based catalyst since the beginning of the twentieth century (46) ... 

The reverse reaction to ammonia synthesis, the decomposition to nitrogen and hydrogen, is used in die nitriding of iron and canied out industiially at temperatures around 800 K and atmospheric pressure to produce surfacehardening. This dissolution reaction must also play a part in the synthesis of ammonia by the industiial process. The attempt to ninide non by reaction with nin ogen gas is vety slow under atmospheric pressure, presumably due to the stability of the nitrogen molecule. 

Figure 3 illustrates the shift and methanation conversion. The resulting methane is inert and the water is condensed. Thus purified, the hydrogen-nitrogen mixture with the ratio of 3H2 pressed to the pressure selected for ammonia synthesis. 

The compressed synthesis gas is dried, mixed with a recycle stream, and introduced into the synthesis reactor after the recycle compressor. The gas mixture is chilled and liquid ammonia is removed from the secondary separator. The vapor is heated and passed into the ammonia converter. The feed is preheated inside the converter prior to entering the catalyst bed. The reaction occurs at 450-600°C over an iron oxide catalyst. The ammonia synthesis reaction between nitrogen, N2, and hydrogen, Hj, is... 

Ammonium nitrate is manufactured by reacting ammonia with nitric acid. Consider the process shown by Fig. 9.19. First, namral gas is reformed and converted into hydrogen, nitrogen and carbon dioxide. Hydrogen and nitrogen are separated an fed to the ammonia synthesis plant. A fraction of the produced ammonia is employed in nitric acid formation. Ammonia is first oxidized with compressed air then absorbed in water to form nitric acid. Finally nitric acid is reacted with anunonia to oduce ammonium nitrate. 

An even more effective homogeneous hydrogenation catalyst is the complex [RhClfPPhsfs] which permits rapid reduction of alkenes, alkynes and other unsaturated compounds in benzene solution at 25°C and 1 atm pressure (p. 1134). The Haber process, which uses iron metal catalysts for the direct synthesis of ammonia from nitrogen and hydrogen at high temperatures and pressures, is a further example (p. 421). 

For producing hydrogen for ammonia synthesis, however, further treatment steps are needed. First, the required amount of nitrogen for ammonia must he obtained from atmospheric air. This is done hy partially oxidizing unreacted methane in the exit gas mixture from the first reactor in another reactor (secondary reforming). 

Graphite compounds have been described as catalysts for ammonia synthesis from nitrogen and hydrogen (14, Pll), for Fischer-Tropsch chemistry M13, R14), for paraffin isomerization iR15), and for Friedel-Crafts chemistry (07). 

Metal complexes as inorganic nitrogen-fixing systems Fixation of molecular nitrogen and ammonia synthesis Complexes of dinitrogen... 

To solve a quantitative limiting reactant problem, we identify the limiting reactant by working with amounts in moles and the stoichiometric coefficients from the balanced equation. For the ammonia synthesis, if we start with 84.0 g of molecular nitrogen and 24.2 g of molecular hydrogen, what mass of ammonia can be prepared First, convert from... 

Figure 7.21 shows the results for the ammonia synthesis on real catalysts in a reactor. The surface is predominantly covered by atomic nitrogen and by NH intermediates. This actually limits the rate of the reaction as soon as an appreciable partial pressure of ammonia has built up. In fact, ammonia poisons the reaction. 

Ammonia synthesis is the second largest chemical process, after the production of sulfuric acid (see also Chapter 1). It accounts for about 1 % of the total human-related energy consumption. Roughly 80 % of the ammonia produced is used for fertilizers (either as liquid ammonia or as more easily handled salts such as ammonium nitrate, ammonium phosphate, etc.) and, as such, ammonia synthesis is indispensable for our society. Other applications of ammonia are nitrogen-containing... 

---