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13 Dec 2019

1. Nitric acid is commonly produced from ammonia. The first step in the process is combustion of the ammonia according to the reaction:

4NH3(g) + 5O2(g) −→ 4NO(g) + 6H2O(g)

Determine:

a) the standard heat of reaction at 25◦C.

b) the adiabatic flame temperature for this reaction when the reactants are at

25◦ C.

(Note: For H2O(g) assume 〈CP 〉H /R = 4.80. For NO(g) assume 〈CP 〉H /R = 3.94.)

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Beverley Smith
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17 Dec 2019

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Related questions

In the first step of the Ostwald process for the synthesis of nitric acid, ammonia is converted to nitric oxide by the high-temperature reaction
4NH3(g)+5O2(g)→4NO(g)+6H2O(g)

Part A: How is the rate of consumption of O2 related to the rate of consumption of NH3?

Part B: How is the rate of formation of NO related to the rate of consumption of NH3?

Part C: How is the rates of formation of H2O related to the rate of consumption of NH3?

In the first step of the Ostwald process for the synthesis of nitric acid, ammonia is converted to nitric oxide by the high-temperature reaction 4NH3 (g) + 5O2 (g) --> 4NO (g) + 6H2O (g). (a) How is the rate of consumption of O2 related to the rate of consumption of NH3? (b) How is the rate of formation of NO related to the rate of consumption of NH3? (c) How is the rate of formation of H2O related to the rate of consumption of NH3?

Nitric acid may be produced by oxidizing ammonia to nitric oxide over a platinum-rhodium catalyst, then oxidizing the nitric oxide to nitrogen dioxide in a separate unit where it is absorbed in water to form an aqueous solution of nitric acid. The three key reactions in the synthesis are the oxidation of the ammonia to nitric oxide and of nitric oxide to nitrogen dioxide, followed by dissolution of the NO2 in water:

4NH3(g)+ 5O2(g)→ 4NO(g)+ 6H2O(g)

2NO(g) + O2(g) → 2NO2(g)

4NO2 (g)+ 2H2O(l) + O2(g) → 4HNO3(aq)

In this problem, you may neglect side reactions that would lower the product yield. This would include the side reaction in which ammonia is oxidized to form nitrogen and water which can lower product yield.

4NH3 + 3O2 → 2N2 + 6H2O

Thus, for this project the overall reaction may be represented from the three key reactions above as:

NH3 + 2O2 → H2O + HNO3

Ammonia vapor at 275oC and 8 atm is mixed with air, also at 275oC and 8 atm, and the combined stream is fed to a converter. Fresh air entering the system at 30oC and 1 atm with a relative humidity of 50% is compressed to 100oC and 8 atm, and the compressed air then exchanges heat with the product gas leaving the converter. The quantity of oxygen in the feed to the converter is 20% in excess of the amount theoretically required to convert all the ammonia to HNO3. The entire process after the compressor may be taken to operate at a constant pressure of 8 atm.

In the converter, the ammonia is completely oxidized, with a negligible amount of NO2 formed. The product gas leaves the converter at 850oC and exchanges heat with the air leaving the system as described earlier. The product gas is then fed to a waste-heat boiler that produces superheated steam at 200oC and 10 bar from liquid water at 35oC. The product gas leaving the waste-heat boiler is cooled further to 35oC and fed to an absorption column in which the NO is completely oxidized to NO2 which in turn combines with water (some of which is present in the product gas). Water is fed to the absorber at 25oC, at a rate sufficient to form a 55 wt% aqueous nitric acid solution. Any NO formed in the reaction of NO2 to produce HNO3 is oxidized and the NO2 produced is hydrated to form still more HNO3. The off-gas from the process may be taken to contain only N2 and O2 and at 25oC and 1 atm.

b). Taking a basis of 100 kmol of ammonia fed to the process

(i) kmol of water fed to the absorber

(ii). Temperature of the product gas after it has exchanged heat with the air, assuming no heat is transferred between the heat exchanger and the surroundings

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