What is the name of NH 3
Elements and molecules, school book
82 5 LARGE TECHNICAL CHEMICAL 5.2 PRODUCTION OF INORGANIC BASIC CHEMICALS Ammonia • Nitric acid • Sulfuric acid • Soda • Sodium hydroxide • Chlorine Ammonia The synthesis of ammonia from the elements was developed by Fritz Haber and Carl Bosch in Germany shortly before the outbreak of the First World War. The aim at that time was to find access to the nitrogen compounds based on atmospheric nitrogen in order to be independent of the import of Chile nitrate (sodium nitrate, NaNO 3). The production of nitric acid from ammonia made it possible to manufacture explosives that were essential for the war effort. Ammonia then turned out to be the key to nitrogen fertilizers and, it is no exaggeration to say, the basis of world nutrition. The discovery was awarded the Nobel Prize in 1918 (Fritz Haber, 1868–1934). Carl Bosch (1874–1940) also received the Nobel Prize in 1931 for the technical implementation. The worldwide production of ammonia is currently around 125 million tons per year. To obtain ammonia, the starting gas mixture, a mixture of nitrogen and hydrogen in a molar ratio of 1: 3, must first be prepared. Today the raw material for this is almost exclusively natural gas (CH 4). It is first desulphurized, then compressed and thus reacted with steam. This “natural gas fission” is an endothermic reaction, ie the higher the temperature, the more favorable the equilibrium situation. The reaction takes place technically in externally heated tubes at around 800 ° C. Around 90% of the methane is converted in the process. In order to split the remaining methane, the temperature has to be increased to over 1000 ° C. This is done by adding air, in which the combustible gases in the mixture burn in a strongly exothermic manner. So much air is supplied that the nitrogen content of the gas mixture is sufficient for the ammonia synthesis. Now there is a gas mixture of hydrogen, nitrogen and carbon monoxide. In the next step, carbon monoxide is reacted with additional water vapor. This weakly exothermic reaction must take place at the lowest possible temperature according to the principle of the least constraint. Catalysts are therefore required. Almost complete conversion is achieved in two stages over iron and chromium oxide at 350–400 ° C and over copper at 200 ° C. The reaction is called “converting”, as one mole of H 2 is obtained for every mole of CO, ie CO is “converted” into H 2. The resulting carbon dioxide is now dissolved in organic solvents and hot potassium carbonate solution and thus removed from the gas mixture (hot potash process). By reducing the pressure and using hot steam, the resulting potassium hydrogen carbonate is converted back into potassium carbonate (steam stripping). Residues of carbon monoxide still have to be removed from the gas mixture, which is now basically ready for ammonia synthesis, since these act as catalyst poisons during ammonia synthesis. This is done by reversing the first reaction using catalysts (methanation). The traces of methane affect the ammonia synthesis catalysts only slightly. Ammonia is now synthesized as it was developed by Haber and Bosch. It has remained the same to this day, apart from a few improvements in detail (Fig. 82.2). Nitrogen (N 2) is a molecule with a very high binding energy. This is the reason for its sluggishness. All reactions involving elemental nitrogen require a high activation energy. At low temperatures, the equilibrium position for the weakly exothermic reaction is favorable, but the reaction is almost infinitely slow. At a high temperature, at which the reaction would be fast enough, the starting materials are in equilibrium. So you need a catalyst. With the iron and aluminum oxide catalysts used today, the reaction temperature can be reduced to 380 ° C, but the equilibrium position is still unfavorable even at this temperature. The change in the number of moles is therefore used in the reaction. According to the law, the starting materials (4 mol) have 3 H 2 + N 2 2 NH 3 CH 4 + H 2 O CO + 3 H 2 ∆ H = +206.2 kJ natural gas splitting CO + H 2 O CO 2 + H 2 ∆ H = –41.2 kJ conversion K 2 CO 3 + H 2 O + CO 2 2 KHCO 3 binding of carbon dioxide CO + 3 H 2 CH 4 + H 2 O ∆ H = –206.2 kJ removal of the residual CO N 2 + 3 H 2 2 NH 3 ∆ H = –92.2 kJ ammonia synthesis Fig. 82.2: Reactions of ammonia production Fixed point –77.7 ° C Boiling point –33.0 ° C • Toxic (MAK value: 50 ppm) • Stinging Odor • Easily soluble in water 1 L water dissolves 675 L NH 3 at 20 ° C • Aqueous solution is called ammonia spirit • Aqueous solution has a basic reaction • Commercial form: 25% aqueous solution Fig. 82.1: Properties of ammonia NH 3 Fig. 82.3: Historical ammonia synthesis Apparatus For testing purposes only - property of the publisher öbv
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