Question

Membranes represent a relatively new technology for commercial gas separation. Among the various applications they have, one that has caught the attention of the industrial sector is the separation of nitrogen and oxygen from the air. Suppose you pass through a separation membrane an air stream with the known molar compositions of oxygen and nitrogen, 21 and 79% respectively, and two streams come out of the membrane: a) The product stream whose composition is 25 mol% oxygen and 75% mol nitrogen, and b) The waste stream whose composition is unknown, but which contains 80% of the moles that enter the membrane. Choose where to set a calculation basis and use matter balances to determine the composition of the waste stream.

Answer 1

Product O2 = 25% N₂=75 % Separation Basis Feed = 100 mole O2 = 21% N2 = 79% Waste Unknown composition given that Waste Storam D is 80% of mole & feed than, molas flow Rate & Waste 80 x Feed X100 = 80 mole 100 overal mole Balance Mole Feed = mole in Product & mole in Waste Mole in Product mole in waste Mole in Product 20 mole mole Balance son of O₂ O in feed O in Product to in Waste 21 Xloo 25 x 20 + O₂ in Waste O₂ in Waste = 21 25 x 20 - 21-5 = 16 mole

than N₂ in Waste molar flow of waste O in Waste doo 16 64 mole => composition of Waste Stream % Nz mole 64 xloo = 80 % 80 % O₂ mole 20 % 16 xloo 80