Haber Process, Energy Considerations and Heat Exchange - Assignment Example

Haber Process Q1. Raw materials used and their sources The raw materials used in the manufacture of ammonia are nitrogen and hydrogen. Hydrogen isobtained by reacting methane with steam and thus creating carbon dioxide and hydrogen. The nitrogen is obtained from the air by fractional distillation, since the mixture of air consists of approximately 78% nitrogen. Q2. Equations and reactions involved The basic equation for the overall reaction is: N2(g) + 3H2(g) 2NH3(g) nitrogen + hydrogen at heat, pressure, catalyst = ammonia H = -92.4 kJ mol These other reactions take place to take out Hydrogen and Nitrogen. Hydrogen is produced by reforming light petroleum fractions or natural gas (methane, CH4) by adding steam: Ni catalyst CH4(g) + H2O(g) CO(g) + 3H2(g) 700C Enough steam is used to react with about 45% of the methane (CH4), the rest of the methane is reacted with air: Ni catalyst 2CH4(g) + O2(g) + 4N2(g)2CO(g) + 4H2(g) + 4N2(g) All the carbon monoxide (CO) in the mixture is oxidised to CO2 using steam and an iron oxide catalyst: iron oxide catalyst CO(g) + H2O(g) H2(g) + CO2(g) The carbon dioxide (CO2) is removed using a suitable base so that only the nitrogen gas (N2) and hydrogen gas (H2) remain and are used in the production of ammonia (NH3). Q3. Optimum conditions chosen with detailed explanation of the principle involved Proportions: The mixture of nitrogen and hydrogen going into the reactor is in the ratio of 1 volume of nitrogen to 3 volumes of hydrogen. Avogadro's Law says that equal volumes of gases at the same temperature and pressure contain equal numbers of molecules. That means that the gases are going into the reactor in the ratio of 1 molecule of nitrogen to 3 of hydrogen. Temperature: You need to shift the position of the equilibrium as far as possible to the right in order to produce the maximum possible amount of ammonia in the equilibrium mixture. The forward reaction (the production of ammonia) is exothermic. According to Le Chatelier's Principle, this will be favored if you lower the temperature. The system will respond by moving the position of equilibrium to counteract this - in other words by producing more heat. In order to get as much ammonia as possible in the equilibrium mixture, you need as low a temperature as possible. The lower the temperature you use, the slower the reaction becomes. A manufacturer is trying to produce as much ammonia as possible per day. It makes no sense to try to achieve an equilibrium mixture which contains a very high proportion of ammonia if it takes several years for the reaction to reach that equilibrium. You need the gases to reach equilibrium within the very short time that they will be in contact with the catalyst in the reactor. Therefore 400 - 450C is a compromise temperature producing a reasonably high proportion of ammonia in the equilibrium mixture (even if it is only 15%), but in a very short time. Pressure: According to Le Chatelier's Principle, if you increase the pressure the system will respond by favoring the reaction which produces fewer molecules. That will cause the pressure to fall again. In order to get as much ammonia as possible in the equilibrium mixture, you need as high a pressure as possible. 200 atmospheres is a high pressure. Increasing the pressure brings the molecules closer together. In this particular instance, it will increase their chances of hitting and sticking to the surface of the catalyst where they can react. The higher the pressure the better in terms of the rate of a gas reaction. 200 atmospheres is a compromise pressure chosen on economic grounds. If the pressure used is too high, the cost of generating it exceeds the price you can get for the extra ammonia produced. Catalyst: It is explained below. Q4. Catalyst (with theory about its mechanism) The catalyst has no affect whatsoever on the position of the equilibrium. Adding a catalyst doesn't produce any greater percentage of ammonia in the equilibrium mixture. Its only function is to speed up the reaction. In the absence of a catalyst the reaction is so slow that virtually no reaction happens in any sensible time. The catalyst ensures that the reaction is fast enough for a dynamic equilibrium to be set up within the very short time that the gases are actually in the reactor. The catalyst is actually slightly more complicated than pure iron. It has potassium hydroxide added to it as a promoter - a substance that increases its efficiency. Q5. Plant layout and design The plant must be huge to support the distillation plant for nitrogen and then combination of hydrogen with nitrogen to produce ammonia. Q6. Energy considerations and heat exchange The process of making ammonia is a reversible one. Heat is exchanged when shifting from one state to another. The reaction includes a temperature of about 400-450 C, meaning that the particles have more energy, so the rate of reaction will increase, so the ammonia will be made more quickly. The catalyst such as an iron catalyst is used to speed up the reaction by lowering the activation energy so that the N2 bonds and H2 bonds can be more readily broken. Q7. Uses and major products Industry Use Fertilizer production of: ammonium sulfate, (NH4)2SO4 ammonium phosphate, (NH4)3PO4 ammonium nitrate, NH4NO3 urea, (NH2)2CO,also used in the production of barbiturates (sedatives), is made by the reaction of ammonia with carbon dioxide Chemicals synthesis of: nitric acid, HNO3, which is used in making explosives such as TNT (2,4,6-trinitrotoluene), nitroglycerine which is also used as a vasodilator (a substance that dilates blood vessels) and PETN (pentaerythritol nitrate). sodium hydrogen carbonate (sodium bicarbonate), NaHCO3 sodium carbonate, Na2CO3 hydrogen cyanide (hydrocyanic acid), HCN hydrazine, N2H4 (used in rocket propulsion systems) Fibers & Plastics nylon, -[(CH2)4-CO-NH-(CH2)6-NH-CO]-,and other polyamides Refrigeration used for making ice, large scale refrigeration plants, air-conditioning units in buildings and plants Pharmaceuticals used in the manufacture of drugs such as sulfonamide which inhibit the growth and multiplication of bacteria that require p-aminobenzoic acid (PABA) for the biosynthesis of folic acids, anti-malarials and vitamins such as the B vitamins nicotinamide (niacinamide) and thiamine. Pulp & Paper ammonium hydrogen sulfite, NH4HSO3, enables some hardwoods to be used Mining & Metallurgy used in nitriding (bright annealing) steel, used in zinc and nickel extraction Cleaning ammonia in solution is used as a cleaning agent such as in 'cloudy ammonia' Q8. Analysis of reasons why industrial process run under non-equilibrium conditions During industrial production of ammonia, the reaction never reaches equilibrium as the gas mixture leaving the reactor is cooled to liquefy and remove the ammonia. Also to lower the costs, a compromise value for temperature, pressure and the type of catalyst is used thus setting a non-equilibrium situation. Q9. Social, economic and environmental considerations (ammonia and its products) The benefits of using a nitrogenous fertilizers is obvious because the crops grow taller, and are healthier therefore yielding a higher crop and therefore cheaper, more plentiful food. There are always disadvantages. These are after applying the fertilizer and it rains or too much fertilizer is used it gets into the steams or rivers and pollutes them. In the rivers, the fertilizer does the same as it would on land, the river plants grow and algae grow rapidly because of the abundant food supply. The algae then die in large numbers. The bacteria feeding on the dead plant material use up the oxygen in the water. Fish may then die because of the lack of oxygen in the water. Also too high of nitrates in the drinking water is a health hazard, particularly with infants. Nitrates can interfere with the oxygen flow in the blood stream. Works Cited 1. Ausetute. (2000). Haber Process for the Production of Ammonia. Retrieved February 5, 2008, from Ausetute: http://www.ausetute.com.au/haberpro.html 2. Clark, J. (2002). THE HABER PROCESS. Retrieved February 5, 2008, from Chem Guide: http://www.chemguide.co.uk/physical/equilibria/haber.html 3. Haber Process Research Site . (n.d.). Retrieved February 5, 2008, from http://haberchemistry.tripod.com/ 4. Synetix. (2008). Overall Layout of a Steam Reforming Plant for Ammonia Synthesis. Retrieved February 5, 2008, from Chemistry Resources: http://www.cheresources.com/ammonia.shtml Read More