Chemistry Lab: Haber’s Process (A Computer Simulation) Cherno Okafor Mr. Huang SCH4U7 October 8th, 2012 Introduction The Haber process is the process by which ammonia (NH3) is produced. The equation for this reaction is… The symbol shown in the middle means it is a reversible reaction so the product can decompose back into the reactants. Therefore, optimum conditions must be selected to get the greatest yield. When the forward and backward reactions are the same, it is said to be in a state of dynamic equilibrium.
The position of this dynamic equilibrium can be moved forward by changing the conditions the reaction is done in. This follows Le Chatelier’s Principle which says changes to a system in equilibrium will move it in an opposite direction. Condition (Dependent Variables)| Effect (Independent Variables)-Yield, Equilibrium Time, Net Profit| Pressure| Increasing this will improve the yield because the forward reaction reduces pressure. However, putting up the pressure too far is impractical and becomes too expensive. Temperature| A higher yield can be obtained by using a low temperature since the forward reaction produces heat, but this also will make the reaction slower, and less profitable. | Catalyst| The Haber process makes use of catalysts like iron, tungsten, and platinum to speed up the reaction, however this does not improve the yield. | Note: The conditions of the Haber process must be finely balanced to reach a combination of highest yield and fastest reaction, this is very important because getting this right will make sure this industrial process is as profitable as possible.
Data Collection and Processing (Raw Data): Variables| Results (No Catalyst)| Results (No Catalyst)| Results (No Catalyst)| Results (No Catalyst)| Results (No Catalyst)| Temperature (°C)| 658| 660| 663| 677| 680| Pressure (Atm. )| 464| 482| 510| 658| 694| Time to Equilibrate (Min)| 10. 16| 10. 17| 10. 17| 10. 15| 10. 15| Yield (%) | 15. 8| 16. 3| 17. 1| 21. 2| 22. 2| Amount ($) per day| 36,454. 36| 36,413. 56 | 36,380. 36 | 36, 361. 71| 36,321. 0| RESULTS: * After this first trial using no catalysts, it is evident that the equilibrium time is extremely slow and unfortunately, only produces a small yield yet with a large amount of net profit per day. * Another thing was the temperature. The net profit and yield seemed to be at its highest when the temperatures were set at around the 600-700°C range. With an extremely low temperature though, the time to equilibrate was close to a million years, so temperature had to be fairly high * In terms of the pressure, it had to be between the 400-700 Atm. ange (not too high so that it would yield a high cost and not too low so that it would yield a low percentage and net profit) but just in the middle * I wanted to find balance in my profit and yield, so with no catalyst, I adjusted the bars so that the temperature value was fairly close to the pressure value and the results were a greater net profit, with a reasonable equilibrium time of reaction Variables| Results (With Iron Catalyst) | Results (With Iron Catalyst)| Results (With Iron Catalyst)| Results (With Iron Catalyst)| Results (With Iron Catalyst)| Temperature (°C)| 468| 475| 472| 473| 479| Pressure (Atm. | 721| 881| 809| 832| 989| Time to Equilibrate (Min)| 10. 18| 10. 16| 10. 17| 10. 16| 10. 18| Yield (%) | 58. 8| 63. 9| 61. 7| 62. 4| 66. 9| Amount ($) per day| 33, 793. 48| 33, 909. 39| 33, 805. 15| 33,893. 81| 33, 753. 80| RESULTS: * After this second trial, I used the catalyst of iron. Iron was by far the most profitable catalyst to use as it was not that expensive as the others (Tungsten and Platinum), and it produced a high yield with a pretty high amount as well * In terms of the temperature, it was a very typical 400-500°C range which is also a very high temperature and the yield of ammonia would be high and my net profit as well. For pressure, I increased its value to the 700-900atm range and this in conjunction with my high temperature range produced the best results as I produced high yields from 50-70% with the exact same time frame it took for the non-catalyst reaction to equilibrate * So obviously with the addition of the iron catalyst, I did not have to take more or less time for the equilibrium reaction to take place, I instead produced a higher yield of ammonia with a fairly large net profit, which was my goal in the first place Variables| Results (With Tungsten Catalyst)| Results (With Tungsten Catalyst)| Temperature (°C)| 429| 435|
Pressure (Atm. )| 346| 418| Time to Equilibrate (Min)| 10. 46| 10. 16| Yield (%) | 50. 4| 49. 9| Amount ($) per day| 19, 506. 24| 19, 495. 86| RESULTS: * Finally, for this last third trial, I used Tungsten catalyst. This Tungsten catalyst was not as efficient as the iron catalyst, and it also cost more. * In terms of temperature, the 400-450°C range which was average because increasing the temperature would have created more economic problems such as higher costs of energy/production, etc. With iron, it was fairly easy to play around with the temperature, but for Tungsten it was more challenging. I also had to lower the pressures, but not too low so that the equilibrium time would be slow, but not too high either so that I would be losing a lot of profit because of the economic costs * As a result, this adjustments yielded only a little less than what I yielded with iron, however still a fairly high yield. The only decrease was in the net profit, because of the expenses of Tungsten. * The Temperature-Equilibrium Considerations: * One must 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 of the production of ammonia is exothermic. Therefore according to Le Chatelier’s Principle, this will be favoured if one lowers the temperature. The system will respond by moving the position of equilibrium to counteract this-producing more heat. In order to get as much ammonia as possible in the equilibrium mixture, one needs as low a temperature as possible. * The Temperature-Rate Considerations: * The lower the temperature one uses, the slower the reaction becomes. In this case though as a manufacturer, I am trying to produce as much ammonia as possible per day.
It makes no sense to try and achieve an equilibrium mixture which contains a very high proportion of ammonia if it takes several years for the reaction to reach that equilibrium. Therefore, one needs the gases to reach equilibrium within the very short time that they will be in contact with the catalyst (or without) in the reactor. * During my experiment lab, I noticed that the temperature range of 400-700°C is a compromise temperature, producing a reasonably high proportion of ammonia in the equilibrium mixture, but also in a very short time. * The Pressure-Equilibrium Considerations:
There are only 4 molecules on the left-hand side of the equation, but only 2 on the right. According to Le Chatelier’s Principle, if you increase the pressure the system will respond by favouring 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, one needs as high a pressure as possible. * The Pressure-Rate Considerations: * 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. * Economic Considerations: * Very high pressures are extremely expensive to produce on two accounts: * One has to build extremely strong pipes to withstand the very high pressure. * Also, high pressures cost a lot to produce and even maintain. That means that the running costs of your manufacture are very high for you. * During my lab, I noticed that 200 atm is a reasonable choice of pressure. If the pressure used is too high however, the cost of generating it exceeds the price you can get for the extra ammonia produced. The Catalyst-Equilibrium Considerations: * The Catalyst actually has no affect whatsoever on the position of the equilibrium. Adding a catalyst does not produce any greater percentage of ammonia in the equilibrium mixture. Its only function is to speed up the reaction. * The Catalyst-Rate Considerations: * 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.
Conclusion: To sum up, the objective of this computer simulation lab was to produce a high yield of ammonia with as high a net profit as possible, while considering the economic factors such as energy cost, and production cost, and even catalyst costs. It turned out that I was prohibited from using platinum as a catalyst because it was too expensive. Out of the remaining catalysts: Iron, and Tungsten, Iron was the most efficient and profitable one as it is less expensive and yielded a great amount of ammonia while I was able to make a large profit as well.
The Tungsten catalyst did yield a fairly high amount of ammonia, however not a very high net profit was made from it and this is again due to the economic implications of energy and production as mentioned. When I did not use any catalysts, the problem was that the time to equilibrate the reactions was atrocious, and very slow. With the criteria “highest yield and fastest reaction” in mind, the most optimal combination to produce ammonia was the 400-500°C (479°C) temperature range, with the 900-1000 Atm range (989atm). and along with the iron catalyst produced 66. % of ammonia, and at least $33, 000 in net profit. I chose this result as the best one because of the balance of the dependent variables of time, yield, and net profit. I could not find my way up to at least $34, 000 or above in net profit with the iron catalyst. I only managed to exceed that profit when I did not use any catalysts, but again the reaction time is way too slow and hence senseless. I probably could have kept on going to gradually adjust the temperature and pressure one by one to look for an even higher yield and net profit, but time is an issue and I would have to sit for a long time doing this.
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