20. 
21. In the PFD given below components A (CH₃OH), B (C₂H₅OH) and C (C₃H₇OH) are separated in a distillation column.

1. How many molecular species are there?
2. How many unknowns are there?
3. How many equations relating the unknown variables are there?
4. How many degrees of freedom are there?
5. If Stream 2 is specified to have a mass fraction of 0.49 kg CH₃OH/kg of mixture you can now prepare a balanced flow sheet. Why?
6. Solve for all of the unknowns.
7. Convert the mass fractions of stream 4 to mole fractions. ( Please write clearly )

F (kg A/h) 2000 (kg/h) 0.03 kg B/kg 0.97 kg /kg N 1200 kg/h 0.70 kg A/kg 5300 kg/h Y4 (kg B/kg) z (kg C/kg) *, (kg A/kg) Yz (kg B/kg) F (kg/h) 0.60 kg B/kg 0.40 kg C/kg