o. Methanol is synthesized from carbon monoxide and hydrogen in a reactor. The f

Question

o. Methanol is synthesized from carbon monoxide and hydrogen in a reactor. The fresh feed to the process contains 32.0 mole% CO, 64.0% H2,and 4.0% stream is stream in a ratio 5 mol recycle/1 mol fresh feed to produce the feed to the reactor, which contain 130 mole% N2. A low conversion is attained in the reactor. The reactor effluent goes to a condenser from which two streams emerge: a liquid product stream containing essentially all the methanol formed in the reactor, and a gas stream containing all the CO, H2,and N2 leaving the reactor. The gas stream is split into two fractions: one is removed from the process as a purge stream. and the other is the recycle stream that combines with the fresh to the reactor.

Explanation / Answer

CO + 2H2 ---> CH3OH

Fresh feed has CO= 32 mol %

H2 = 64 mol %

N2 = 4 mol %

CO and H2 remain in the ratio 1:2 as seen through the reaction

In the reactor

CO = X

H2 = 2X

N2 = 0.13

Recycle = 500 mol/h

After recycle,

Let N2 =y mol

CO =z mol

H2 =2z mol

Number of moles just before recycle are CO= n1, H2=2n1, N2=n2, Ch3OH=n3(product).

Perge = np mol/h

At mixing point

2x+x+0.13 =1

X =0.29

for, N2

4+500y =0.13 x 600

y = 0.148 mol/h

for recycle,

y+z+2z =1

0.148 +3z =1

z = 0.284 mol/h

Overall system atomic balance

C : 32 = n3+(0.284)np

N2 : 4 =(0.148)np

np = 24.0 mol/h

n3 = 24.3 mol/h

Overall conversion

24.3/32 = 0.76

Single pass conversion

24.3/0.29X600 = 0.14

Purge composition

np = 27.0 mol/h

N2 (y) = 0.148 mol

CO (z) = 0.284mol

H2 (2z) =0.568 mol

B) the recycle stream is included in the process to overall increase the conversion of the equilibrium reaction (ii) purge stream throws of some of the unreacted portions.

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