Ammonia (NH3) is produced from hydrogen and nitrogen according to the following

Question

Ammonia (NH3) is produced from hydrogen and nitrogen according to the following reaction: 3H2 + N2 arrow 2NH3 The fresh feed to the process contains hydrogen, nitrogen, and argon. The reactor effluent contains 300 mol H2/s, 150 mol N2/s, 75 mol NH3/s, and 1 mol Ar/s. After the reactor, all of the ammonia is condensed and all of the gases (H2, N2, and Ar) leave the top stream from the condenser. 5% of this stream is purged from the process and the rest is recycled and mixed with the fresh feed. Use the Atomic Species Balance method to solve this problem. a) Determine the molar flow rate of each component in the reactor feed. b) Calculate the single-pass conversion of the limiting reactant. c) Determine the composition of the purge stream. d) Determine the molar flow rate of each component in the process feed. e) Calculate the overall conversions of both hydrogen and nitrogen.

Explanation / Answer

Moles of ammonai produced= 75 mol/s

This is removed in the separator and balance containing 300mo/s H2, 150 mol.s N2 and 1 mol/s aron is sent for recyle as well as purge,

Total moles = 300+150+1 =451 mol/s

Mole fractions ( compositon of purge)

H2 = 300/451 =0.6651

N2= 150/451 =0.332594

Ar= 1/451 = 0.002217

This composition is same in recycle as welll as purge.

5% of the stream is purged and rest recycled

Moles purged= (5/100)* 451= 22.55 mol/s

Moled recycled = 451-22.55= 428.45 mol/s

Let F be the fresh feed

Inerts in purge =1 mol/s

Making overall hydrogen balance

Moles of hydrogen entering = moles of hydrogen consumed for ammonia production + hydrogen in purge

Moles of hydrogen entering = 75*3/2 + 300 * 5/100= 112.5+15=127.5 mol/s

Similar moles of nitrogen entering = 75/2+ 150*5/100= 45 mol/s

Argon in the purge= 1 mol/s =argon in feed

Fresh feed ( mol/s) Recycle ( mol/s)   

H2 127.5 300*95100= 285

N2 45 150*95100= 142.5

Ar 1 0.95

Making a balance across the reacor F= M+R

F is fresh feed, M is mixed feed and R is recycle

H2 entering the reactor = 285+127.5= 412.5 mol/s

N2= 45+142.5 mol/s = 187.5 mol.s

Ar= 1+0.95 mo/s =1.95 mol/s

Argon in purge= 1 mol/s

Ratio of Hydrogen and nitrogen at the inlet to reactor = 412.5/187.5 =2.2

Stioichiometric requirement= 3/1 =3

Nitrogen is excess reactant and hydrogen is the limting reactant

Entering hydrogen= 412.5 mol/s

Leaving hydrogen = 300 mol/s

hence sinble pass conversion= {(412.5-300)/412.5}*100=27.27%

Ammonia formed = 75 mol/s

Hyrogen required ( or reacted)= 75*3/2= 112.5 mol/s and nitrogen required ( or reacted)= 75/2= 37.5 mol.s

hydrogen entering the reactor= 412.5 mol/s and nitrogen entering = 187.5 mol/s

Hydrogen in fresh feed= 127.5 mol.s and Nitrogen in fresh feed= 45 mol/s

Conversion of hydrogen = (112.5/127.5)*100= 88.23 and conversion of nitrogen= {37.5/ 45}*100= 83.3%

  

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