High-pressure synthesis of ammonia

On 2 July 1909 two representatives of BASF visited Haber s laboratory at Karlsruhe. Their brief was to evaluate Haber s apparatus for the high pressure synthesis of ammonia from its elements. Even under optimum conditions the yield was low, around 5 per cent, but Haber had arranged for unreacted hydrogen and nitrogen to be recirculated. Though exothermic, the reaction was carried out at 600°C in order to increase the rate. The preferred catalyst was osmium or uranium. 

See in particular Roy MacLeod s contribution to this volume. For French attempts to imitate German processes in the immediate post-war period see Lothar Meinzer s paper. Compare also Rolf Petri s description of the situation in Italy, where notable progress was made in the high pressure synthesis of ammonia. Unlike most other contributors to this volume, I place the greatest emphasis on products and... 

Three years after Bosch s 1910 high-pressure laboratory synthesis of ammonia, BASF inaugurated the high-pressure chemical industry. On September 9,1913 in the nearby village of Oppau it completed construction of the world s first plant for the high-pressure synthesis of ammonia. With... 

Carl Bosch, 1874-1940, German industrial chemist, developed the Haber-Bosch process for high-pressure synthesis of ammonia. Bosch shared with Friedrich Bergius the 1931 Nobel Prize for chemistry for their contribution to the invention and development of chemical high pressure methods. ... 

Furthermore, we have extended the high-pressure polycondensation to the synthesis of condensation polymers other than polyimides. A successful example was the high-pressure synthesis of polybenzoxazoles starting from the bis-o-aminophenol (or its hydrochloride) and aliphatic dinitriles (Eq. 8) [35]. The polycondensation readily proceeded under high pressure in a closed reaction vessel with the elimination of the by-product of ammonia (or ammonium chloride). 

This reaction is used for the synthesis of nitric acid in the Ostwald process (see Section 7.8.1). Without catalysts, and at higher temperatures, ammonia bums in an oxygen atmosphere with a pale yellow flame forming the thermodynamically favorable products dinitrogen and water (AH = -1267kJmol ). At high pressures, mixtures of ammonia and oxygen are explosive. 

P. Stoltze and J.K. Norskov, An interpretation of the high-pressure kinetics of ammonia synthesis based on a microscopic model. /. Catal. 110,1 (1988). 

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). 

The catalytic synthesis of ammonia from its elements via the Haber-Bosch process is of major industrial importance. The high pressure synthesis is catalyzed by Fe promoted with K20, CaO and A1203. 

FIGURE 9.14 One of the high-pressure vessels used for the catalytic synthesis of ammonia. The vessel must be able to withstand internal pressures of greater than 250 atm. 

Haber process (Haber-Bosch process) The catalyzed synthesis of ammonia at high pressure, half-cell One compartment of an electrochemical cell consisting of an electrode and an electrolyte, half-life (f1/2) (1) In chemical kinetics, the time needed for... 

High pressures are required for many commercial chemical processes. For example, the synthesis of ammonia is carried out at reactor pressures of up to 1000 bar, and high-density polyethylene processes operate up to 1500 bar. 

The synthesis of ammonia, N2 + 3H2 = 2NH3, like the oxidation of SO, (Section 1.5.4 and Figure 1.4), is an exothermic, reversible, catalytic reaction carried out in a multistage tubular flow reactor in which each stage consists of a (fixed) bed of catalyst particles. Unlike SO, oxidation, it is a high-pressure reaction (150-350 bar, at an average temperature of about 450°C). The usual catalyst is metallic Fe. 

Iron has a rich surface coordination chemistry that forms the basis of its important catalytic properties. There are many catalytic applications in which metallic iron or its oxides play a vital part, and the best known are associated with the synthesis of ammonia from hydrogen and nitrogen at high pressure (Haber-Bosch Process), and in hydrocarbon synthesis from CO/C02/hydrogen mixtures (Fischer-Tropsch synthesis). The surface species present in the former includes hydrides and nitrides as well as NH, NH2, and coordinated NH3 itself. Many intermediates have been proposed for hydrogenation of carbon oxides during Fischer-Tropsch synthesis that include growing hydrocarbon chains. 

With the technical development achieved in the last 30 years, pressure has become a common variable in several chemical and biochemical laboratories. In addition to temperature, concentration, pH, solvent, ionic strength, etc., it helps provide a better understanding of structures and reactions in chemical, biochemical, catalytic-mechanistic studies and industrial applications. Two of the first industrial examples of the effect of pressure on reactions are the Haber process for the synthesis of ammonia and the conversion of carbon to diamond. The production of NH3 and synthetic diamonds illustrate completely different fields of use of high pressures the first application concerns reactions involving pressurized gases and the second deals with the effect of very high hydrostatic pressure on chemical reactions. High pressure analytical techniques have been developed for the majority of the physicochemical methods (spectroscopies e. g. NMR, IR, UV-visible and electrochemistry, flow methods, etc.). 

Some particular processes can require very high pressures for special applications (i.e. in explosive welding and plating), but pressures between 100 and 1000 bar can be found easily in different industrial processes. Typical examples are the synthesis of ammonia, the synthesis of methanol and the production of low-density polyethylene, but also analytical techniques as high-pressure liquid chromatography. Other important implications are for the storage and transportation of fluids and enhanced oil recovery. 

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