Sunflower oil contains 0.070 mol palmitic acid (CBH32O2)/mol, 0.060 mol stearic

Question

Sunflower oil contains 0.070 mol palmitic acid (CBH32O2)/mol, 0.060 mol stearic acid (C18H36O2)/mol, 0.31 To create margarine from sunflower oil, the liquid oleic and linoleic acids are hydrogenated in the presence of a metal catalyst to form solid stearic acid. C18H340, H At a margarine production facility, a stream of 310.0 mol sunflower oil/hr is fed into a reactor. The fresh hydrogen source available is a mixture containing 0.98 mol H2/mol and 0.020 mol N2/mol. (N2 is inert in this process. To insure complete hydrogenation, the hydrogen gas mixture is introduced into the reactor in 60.0% excess. All reaction products leave the reactor and proceed to a separator where palmitic and stearic acids are separated from the hydrogen gas mixture. The hydrogen gas mixture is recycled to the fresh feed stream, and 115.0 mol gashr of this recycle stream is purged to prevent the buildup of nitrogen gas. What is the molar flow rate of the fresh hydrogen and nitrogen gas mixture to the process? Number mol gas/hr What is the composition of the purge stream? Number mol H, ol

Explanation / Answer

Oleic acid in the feed= 310*0.31 moles=96 moles/hr, linoleic acid in the feed = 310*0.56= 185 moles/hr

Palmitic acid = 0.070*310=22 moles/hr and stearic acid=310-96-185-22= 7 moles/hr

As per the reaction, 1 mole of oleic acid requires 1 mole of hydrogen and hence 96 moles of oleic acid requires 96 moles of hydrogen. Similarly, moles of Hydrogen for conversion of linoleic acid= 185*2= 370 moles. Total moles of hydrogen required= 370+96=426 moles/hr. Moles of Nitrogen in the fresh feed= 426*0.02= 9 moles/hr. This nitrogen is removed from purge. Moles of Purge= 115 moles/hr, moles of hydrogen in the purge= 115-9=106 moles/hr

Composition of purge ( as well as recycle) : H2 : 106/115=0.92 and N2= 9/115= 0.08

Writing hydrogen gas balance for the system

Hydrogen in the fresh feed= Hydrogen consumed + hydorgen in the purge

F*0.98= 426+115x, where x= mole fraction of hydrogen in the purge (1)

F= 426/0.98+115/0.98x= 435+117x (1)

Writing nitrogen balance

F*0.02= 115*(1-x), F= (1-x)*115/0.02= 5750*(1-x)   (2)

Comparing Eq.1 and Eq.2 435+117x= 5750-5750x

Hence x*(5750+117)= 5750-435, x=0.91 mole fraction of nitrogen in the purge= 1-0.91=0.0. This is also the compositio of recycle as well as purge.

Flow rate of fresh feed= 435+117*0.91= 541.5 moles/hr. Flow rate of hydrogen in the feed= 541.5*0.98 =531 moles/hr and nitrogen in the fresh feed= 541.5-531= 10.5 moles/hr

Let R= recycle flow rate, flow rate of hydrogen = R*0.91

Flow rate of hydrogen in the fresh feed= 531 moles/hr

Total hydorgen = R*0.91+531

But hydrogen supplies is 60% excess. So hydrogen entering the reactor

(R*0.91+531)*1.6

Hydrogen consumed= 426

Unreacted hydrogen is purged as well as recycled

Hence hydrogen unreacted

(R*0.91+531)*1.6-426= (115+R)*0.91+R

1.5R +850-426= 105+1.91R

850-426-105= 0.41R

Hence 0.41R= 319, R= 319/0.41= 778 moles/hr

Flow of gas leaving the separator = 778(recycle)+ purge (115)= 893 moles/hr

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