A purification system with recycle is used to recover the solvent dimethyl formamide (DMF) from a gas containing 55 mole% DMF in air. The purification unit removes two thirds of the DMF in the combined feed to the unit. The off gas has only 10 mole% DMF in the waste stream. A schematic is shown below.
Draw and label a flowchart and using a degree-of-freedom approach solve for all flowrates and compositions. Calculate the recycle fraction, where the recycle fraction is here defined as the ratio of the molar flowrate of the recycle stream to the molar flowrate of the pure DMF stream leaving the purification unit.