Question

The fresh feed to an ammonia synthesis reactor contains nitrogen, hydrogen and 2.0 mole per cent inerts. The molar ratio of H2:N2 is 3:1. The product stream consists of pure ammonia. Since conversion in the reactor is only 15%, a recycle stream is used and in order to avoid build-up of inerts, a purge stream is withdrawn. The rate of purge stream is adjusted to keep inert concentration in the recycle stream at 8 mole per cent. For a fresh feed rate of 100 moles/hr. Note that recycle stream contains only nitrogen, hydrogen and inerts. The N2:H2 ratio of 1:3 is maintained in every process stream, and calculate the moles of nitrogen entering the reactor and in the recycle stream?

(a) 125 moles/hr, 100.50 moles

(b) 135 moles/hr, 50 moles

(c) 125 moles/hr, 50 moles

(d) 185 moles/hr, 100.50 moles

I had been asked this question by my college director while I was bunking the class.

The query is from Material Balances with Recycle, By topic in portion Material Balance of Bioprocess Engineering

Answer 1

The correct answer is (a) 125 moles/hr, 100.50 moles

The best I can explain: Moles of nitrogen entering the reactor = (37.50/2)/0.15 = 125 moles/hr

Therefore there are 125 – 24.50 = 100.50 moles of nitrogen in the recycle stream.