Sunday 9 October 2016

Production of Ammonia : The Haber-Bosch Process

Fig 1. Haber-Bosch Process Diagram
Fig 2. Operating conditions in Haber-Bosch Process

the preceding diagrams (Fig 1 and Fig 2) explain the Haber-Bosch process which is a common process for producing ammonia. the overall process is rather cyclic and consists of 2 main stages or units, they are the reacting unit (reactor) and the condensing unit (the condenser).

firstly, the feed containing nitrogen and hydrogen with volumetric ratio of 1 : 3 are pumped to the reactor by a compressor. in the reactor, the gases are reacted at high temperature at 400 to 450 centigrade and high pressure at 200 atm, using an iron catalyst. the reaction occurs as follows:

from the equation, it is clear that the reaction occurs in equilibrium state and the rightwards one occurs exothermically. therefore, according to Le Chatelier's principle to maximize the product (ammonia) the temperature has to be reduced as an increase causes the reaction to move to the endothermic side which is the leftwards reaction. but consequently, with the reduction of temperature the reaction rate will be decreased as well. so there are several alternatives to optimize the process:
1. by using catalyst. it is well-known that catalyst helps increase reaction rate by decreasing the activation energy of a particular reaction.
2. by providing high pressure. according to Le Chatelier's principle also, an increase in pressure can change orientation of a gaseous reaction to the less reaction coefficient. therefore, by providing high pressure to the system, the reaction will move rightwards.
3. by taking ammonia from the reaction system. also, according to Le Chatelier, concentration of the reactant(s) also has impact to the reaction orientation and rates. by taking ammonia from the system, the concentration of ammonia will be depleted, causing concentration of nitrogen and hydrogen to be dominant. thus, the reaction will go rightwards.

in the subsequent process, the yield of the reaction is pumped to the condensing unit. the produced ammonia, alongside with unreacted hydrogen and nitrogen are pumped to a heat exchanger. this will reduce the contained heat in the flow. as the temperature of the flow is reduced, it is then compressed to a condenser for further cooling using cooling water as coolant. consequently, the refrigerated ammonia will separate from cool hydrogen and nitrogen which are still in their gaseous states. the cool gases are then recycled to the reactor but heated first in the heat exchanger, utilizing the heat from the reaction yield. and the process continues.

Yogyakarta, October 9th 2016
still, practicing IELTS writing task 1 : process diagram.
will be taking the official exam on November 5th
what do you think? share in the comment section below.

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