Ammonia oxidation modem process

The modem process for manufacturing nitric acid depends on the catalytic oxidation of NH3 over heated Pt to give NO in preference to other thermodynamically more favour products (p. 423). The reaction was first systematically studied in 1901 by W. Ostwald (Nobel Prize 1909) and by 1908 a commercial plant near Bochum. Germany, was producing 3 tonnes/day. However, significant expansion in production depended on the economical availability of synthetic ammonia by the Haber-Bosch process (p. 421). The reactions occurring, and the enthalpy changes per mole of N atoms at 25 C are ... 

Although the earlier processes for the commercial production of hydrazine used urea as a raw material, modem processes employ direct ammonia oxidation. In one such process, reactions occur in two steps ... 

Manufacture. Historically, ammonium nitrate was manufactured by a double decomposition method using sodium nitrate and either ammonium sulfate or ammonium chloride. Modem commercial processes, however, rely almost exclusively on the neutralization of nitric acid (qv), produced from ammonia through catalyzed oxidation, with ammonia. Manufacturers commonly use onsite ammonia although some ammonium nitrate is made from purchased ammonia. SoHd product used as fertilizer has been the predominant form produced. However, sale of ammonium nitrate as a component in urea—ammonium nitrate Hquid fertilizer has grown to where about half the ammonium nitrate produced is actually marketed as a solution. 

Nitric acid is one of the three major acids of the modem chemical industiy and has been known as a corrosive solvent for metals since alchemical times in the thirteenth centuiy. " " It is now invariably made by the catalytic oxidation of ammonia under conditions which promote the formation of NO rather than the thermodynamically more favoured products N2 or N2O (p. 423). The NO is then further oxidized to NO2 and the gases absorbed in water to yield a concentrated aqueous solution of the acid. The vast scale of production requires the optimization of all the reaction conditions and present-day operations are based on the intricate interaction of fundamental thermodynamics, modem catalyst technology, advanced reactor design, and chemical engineering aspects of process control (see Panel). Production in the USA alone now exceeds 7 million tonnes annually, of which the greater part is used to produce nitrates for fertilizers, explosives and other purposes (see Panel). 

Much research has been carried out into direct amination of aromatic substrates, typified by the direct conversion of benzene to aniline using ammonia and a catalyst. Although there have been many patented routes conversions, are normally low, making them uneconomic. Modem catalysts based on rhodium and iridium, together with nickel oxide (which becomes reduced), have proved more active,and such is the research activity in this area that it is only a matter of time before such processes become widely used. 

Ostwald The basis of the modem family of processes for making nitric acid by the catalytic oxidation of ammonia. 

The Ostwald process is the basis for the modem family of processes that make nitric acid by the catalytic oxidation of ammonia. Wilhelm Ostwald, a German physical chemist, discovered it in 1900. The process was used by Germany during World War I to make explosives after the Allied blockade cut off the regular German supply of nitrites from Chile and other places96. 

Ostwald The basis of the modem family of processes for making nitric acid by the oxidation of ammonia over a platinum catalyst. Named after the eminent German physical chemist Friedrich Wilhelm Ostwald (1853 to 1932). His invention was patented in the United States in 1902, but the patent was not granted in Germany, where the process had to be operated in secret. Ostwald received the Nobel Prize for this work in 1909. 

Most of the modem manufacture of nitric acid is done by the catalytic oxidation of ammonia (Ostwald process). Other now outdated processes include the reaction of sodium nitrate with sulfuric acid and direct synthesis from N2 and 02 by the arc process at temperatures in excess of 2,000°C. Once cheap ammonia became available these processes were no longer economical. 

Ammonia has been produced commercially from its component elements since 1909, when Fritz Haber first demonstrated the viability of this process. Bosch, Mittasch and co-workers discovered an excellent promoted Fe catalyst in 1909 that was composed of iron with aluminium oxide, calcium oxide and potassium oxide as promoters. Surprisingly, modem ammonia synthesis catalysts are nearly identical to that first promoted iron catalyst. The reaction is somewhat exothermic and is favoured at high pressures and low temperatures, although, to keep reaction rates high, moderate temperatures are generally used. Typical industrial reaction conditions for ammonia synthesis are 650-750 K and 150-300 atm. Given the technological importance of the... 

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