An adiabatic membrane separation unit is used to dry (remove water vapor from) a gas

Chapter 8, Problem 8.34

(choose chapter or problem)

An adiabatic membrane separation unit is used to dry (remove water vapor from) a gas mixture containing 10.0 mole% \(\mathrm{H}_{2} \mathrm{O}(\mathrm{v})\), 10.0 mole% CO, and the balance \(\mathrm{CO}_{2}\). The gas enters the unit at \(30°C\) and flows past a semipermeable membrane. Water vapor permeates through the membrane into an air stream. The dried gas leaves the separator at \(30°C\) containing 2.0 mole% \(\mathrm{H}_{2} \mathrm{O}(\mathrm{v})\) and the balance CO and \(\mathrm{CO}_{2}\). Air enters the separator at \(50°C\) with an absolute humidity of 0.002 kg \(\mathrm{H}_{2} \mathrm{O} / \mathrm{kg}\) dry air and leaves at \(48°C\). Negligible quantities of \(\mathrm{CO},\mathrm{\ CO}_2,\mathrm{\ O}_2\), and \(\mathrm{N}_{2}\) permeate through the membrane. All gas streams are at approximately 1 atm.

(a) Draw and label a flowchart of the process and carry out a degree-of-freedom analysis to verify that you can determine all unknown quantities on the chart.

(b) Calculate (i) the ratio of entering air to entering gas (kg humid air/mol gas) and (ii) the relative humidity of the exiting air.

(c) List several desirable properties of the membrane. (Think about more than just what it allows and does not allow to permeate.)