Iron industrial synthesis

Soon it was recognized that the iron-alumina-potash combination was the best suitable catalyst for the large scale industrial synthesis. Again and again, it was proved that this particular catalyst gave the most dependable yields both in the pilot plants and in large scale operation. 

Tab. 19.3 Industrial synthesis reactions involving iron oxide catalysts.

In the early 1900s, the German chemist Fritz Haber discovered that a catalyst consisting of iron mixed with certain metal oxides causes the reaction to occur at a satisfactory rate at temperatures where the equilibrium concentration of NH3 is reasonably favorable. The yield of NH3 can be improved further by running the reaction at high pressures. Typical reaction conditions for the industrial synthesis of ammonia are 400-500°C and 130-300 atm. 

The transition metals iron and copper have been known since antiquity and have played an important role in the development of civilization. Iron, the main constituent of steel, is still important as a structural material. Worldwide production of steel amounts to some 800 million tons per year. In newer technologies, other transition elements are useful. For example, the strong, lightweight metal titanium is a major component in modern jet aircraft. Transition metals are also used as heterogeneous catalysts in automobile catalytic converters and in the industrial synthesis of essential chemicals such as sulfuric acid, nitric acid, and ammonia. 

It should be noted that the results for the formic acid decomposition donor reaction have no bearing for ammonia synthesis. On the contrary, if that synthesis is indeed governed by nitrogen chemisorption forming a nitride anion, it should behave like an acceptor reaction. Consistent with this view, the apparent activation energy is increased from 10 kcal/mole for the simply promoted catalyst (iron on alumina) to 13-15 kcal/mole by addition of K20. Despite the fact that it retards the reaction, potassium is added to stabilize industrial synthesis catalysts. It has been shown that potassium addition stabilizes the disorder equilibrium of alumina and thus retards its self-diffusion. This, in turn, increases the resistance of the iron/alumina catalyst system to sintering and loss of active surface during use. 

Sulfur, Phosphorus, and Arsenic Compounds. Sulfur, occasionally present in synthesis gases from coal or heavy fuel oil, is more tightly bound on iron catalysts than oxygen. For example, catalysts partially poisoned with hydrogen sulfide cannot be regenerated under the conditions of industrial ammonia synthesis. Compounds of phosphorus and arsenic are poisons but are not generally present in industrial synthesis gas. There are... 

The NH3 can then be further converted into nitrate or nitrite or directly used in the synthesis of amino acids and other essential compounds. This reaction takes place at 0.8 atm N2 pressure and ambient temperatures in Rhizobium bacteria in nodules on the roots of legumes such as peas and beans, as well as in other independent bacteria. In contrast to these mild conditions, industrial synthesis of ammonia requires high temperatures and pressures with iron oxide catalysts, and even then yields only 15% to 20% conversion of the nitrogen to ammonia. Intensive efforts to determine the bacterial mechanism and to improve the efficiency of the industrial process have so far been only moderately successful the goal of approaching enzymatic efficiency on an industrial scale is still only a goal. 

Nitration of an aromatic ring is a particularly important reaction 5 the nitro-substituted product can be reduced by reagents such as iron metal or SnCl2 to yield an arylamine, ArNHg. Attachment of a nitrogen to an aromatic rii by the two-step nitration/reduction sequence is a key part of the industrial synthesis of dyes and many pharmaceutica agents. We ll discuss this and other reactions of aromatic nitrogen compounds in Chapter 24. 

Despite that it is named as such quite often in the literature, the radical -scission or -cleavage is not a fragmentation in the sense considered in this chapter. The flrst example of a macrolide synthesis through such a reaction type was achieved by Ohloff ° and resulted in an industrial synthesis of exal-tolide (134 Scheme 70). Schteiber has described iron-copper-promoted fragmentation reactions of a-al-koxy hydroperoxides as a route to macrolides. Two recent informative publications which cover the prior literature have been written by Suginome and Macdonald. ... 

Perfluoroaromatic compounds can be obtained by reductive aromatization of readily accessible perfluorocycloaliphatic precursors [73]. Defluorination can be accomplished by contact with hot (500 °C) iron or iron oxide. After reducing the per-fluoroaliphatic compound the metal surface can be regenerated by passage of hydrogen gas. This method has been scaled up to a continuous flow process for industrial synthesis of a variety of perfluorinated aromatic compounds (Scheme 2.27). 

Citral a doubly unsaturated monoterpene aldehyde, M, 152.24. A mixture of cis and Irons isomers is a component of many essential oils. C.A (trans-C., geranial) b.p.,2 110-112 "C, P20 0.8898, n J 1.4894. CB (cis-C., neral) b.p.12 102-104°C, pjo 0.8888, /Id 1.4891. C. is a component of complex insect pheromone mixtures. When heated, it is converted to isocitral, and it undergoes photocyclization to photocitral A. Conversion of C. to pseudoionone with acetone is important as the first step in the industrial synthesis of vitamin A. In the perfume and food industries C. is the most important of the aliphatic monoterpenes. 

A similar insertion of ethylene into a C—M bond of a w-butenyl complex seems to occur in the industrial synthesis of hexadienes from butadiene and ethylene, at least with rhodium and nickel compounds. These catalysts give tra f-l,4-hexadiene as the initial product 178). Cobalt and iron catalysts give the cis isomer 179,180), probably by a different mechanism. 

Finally, the chapters by Schlogl and Somorjai deal with the effects of water on the action of the promoters, in particular alumina, with an oxidized iron surface. The structure and catalytic properties obtained by the iron surface after reduction appear to be affected significantly by previous exposure to water vapor (and hydrogen) at high temperatures. The small amount of alumina present in industrial synthesis catalysts renders assessment of the interaction of the excess oxidized iron with the alumina difficult. We therefore will review some results obtained on iron catalysts supported on alumina at a much lower iron content. 

The industrial catalysts for ammonia synthesis consist of far more than the catalyticaHy active iron (74). There are textural promoters, alumina and calcium oxide, that minimise sintering of the iron and a chemical promoter, potassium (about 1 wt % of the catalyst), and possibly present as K2O the potassium is beheved to be present on the iron surface and to donate electrons to the iron, increasing its activity for the dissociative adsorption of N2. The primary iron particles are about 30 nm in size, and the surface area is about 15 m /g. These catalysts last for years. 

C.G. Yiokari, G.E. Pitselis, D.G. Polydoros, A.D. Katsaounis, and C.G. Vayenas, High pressure electrochemical promotion of ammonia synthesis over an industrial iron catalyst, /. Phys. Chem. 104, 10600-10602 (2000). 

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