Industrial Chemistry 1: Chapter 4 - Ammonia Production PDF

Industrial Chemistry 1 Chapter 4 Ammonia Production Dr. OSAMAH ALGHAZWAT 1  Properties of Ammonia Molecular weight : 17 gm/mol Boiling point : -33.34 ˚C Freezing point : -77.7 ˚C Standard heat of formation: -46 222 KJ...

Industrial Chemistry 1 Chapter 4 Ammonia Production Dr. OSAMAH ALGHAZWAT 1  Properties of Ammonia Molecular weight : 17 gm/mol Boiling point : -33.34 ˚C Freezing point : -77.7 ˚C Standard heat of formation: -46 222 KJ/Kmol Solubility : Soluble In chloroform, ether, ethanol Density : 0.769 Kg/3𝑚 At STP 2  Refrigerant Medicine & Industry Cosmetics Uses of Solvent Preservative Ammonia of 𝐻2 Lab Transport reagent Metal treatment 3 Uses of Ammonia In Industries Fertilizer Industry Petroleum Industry Mining Industry Rubber Industry Paper Industry Leather 4  MANUFACTURING PROCESSES The synthesis gas for manufacture of Ammonia is produced by steam reforming or partial oxidation of Hydrocarbon feed. The variousprocesses usedcommercially in industries for production of Ammonia are : 1. Haber–Bosch Process 2. Braun Purifier Process 5  1. Haber – Bosch Process The Haber–Bosch process, is the industrial implementation of the reaction of nitrogen gas and hydrogen gas. It is the main industrial procedure to produce ammonia: N2 + 3 H2 → 2 NH3 (ΔH = −92.4 kJ·mol−1) 6 A Flow Scheme of Haber Process 7 Process flow Diagram 8  Parameters Temperature: 450˚C, moderately high. Using a lower temperature would increase yield at equilibrium, but the reactions would be too slow. Pressure: 200-1000 atm. Pressure is beneficial in terms of rate and position of equilibrium, so a very high pressure is used.. Catalyst: Iron, As the rates are increased, the temperature used need not be so high as that which would be required in the absence of a catalyst. By allowing a lower temperature to be used, the position of equilibrium is more favorable as the Haber process is exothermic in the forward direction. 1 2 N2 2 NH3 N2 + 3 H2 = 2 NH3 +Heat 3 H2 Heat 9  Major Engineering Problems Reaction kinetics and equilibrium : As per Le Chatelier principle for exothermic reaction lower temp favour the forward reaction and for decreasing moles the higher pressure is favourable. From graph (1) & (2) the equilibrium yield of NH3 is increased by increase in pressure and decrease in temperature. 10  Catalyst : All catalyst based on FeO. Nowadays promoters like oxides of Al, Zr, K are added to make the catalyst more porous and to withstand the high temperature. 11  2. Braun Purifier Process In this process Synthetic ammonia (NH ) refers to ammonia 3 that has been synthesized from natural gas. Natural gas molecules are reduced to carbon and hydrogen. The hydrogen is then purified and reacted with nitrogen to produce ammonia. 12 Chemical Processes 13 Simple Block Diagram 14 15  The first stage is purification where impurities, mainly sulphur compounds, are removed from the gas stream. Steam reforming is performed in two stages. In the primary stage, the endothermic reactions take place at pressures around 30 bar and temperatures of 800°C or higher. This is followed by an exothermic secondary reformer where air is added to the partially reformed gas stream. The carbon monoxide in the gas leaving the secondary reformer is converted to carbon dioxide in the shift reactors and then removed by scrubbing from the gas stream. Any residual carbon oxides are then converted back to methane by methanation before compression of the hydrogen and nitrogen to ammonia synthesis pressure. The final reaction stage is ammonia synthesis where the hydrogen and nitrogen combine to form ammonia. This reaction stage takes place at high pressure (100-350 bar) and is highly exothermic. 16 Reactor for Ammonia Synthesis 17 18