Question

Membranes are used to separate gases since membranes tend to pass smaller molecules through them at a higher rate than larger molecules. In a separation process, air (A) is the feed. Two streams leave the process: a product stream (P) and a waste stream (W). The product stream, which does not pass through the membrane, is equal to 20% of the feed stream, and has a molar composition of 25% O2 and 75% N2 representing increased O2 concentration. Determine the composition of the waste stream that passes through the membrane

Note: Take the air composition to be 21 mol% O2 and the rest is N2

Answer 1

Let F= 100 moes/ hr of air

it contains 21 mole % O2 and 79 mole %N2 .Moles of Oxygen =21 and moles of N2= 79 in air

F= P+W

P= 20% of feed stream = 100*0.2= 20 moles/hr

W= 100-20= 80 moles/hr

This P contains 25% O2 and 75%N2, moles of O2= 20*0.25= 5 and moles of N2= 20*0.75= 15

Since the balance N2 and O2 will have to be in Waste stream

W= 100-20 =80 moles/ hr it contains =21-5 =16 moles/ hr of Oxygen and 79-15= 64 moles/hr of Nitrogen

composition : O2= 16/80=0.2 and N2= 64/80= 0.8