Problem 5    Due 2/2/01

An important design variable in designing an extraction
system is determining the number of contactors (equilibrium
stages).  You are asked to design a system which can extract
99.9% of a toxic organic solute from a waste stream, reducing
its concentration to the point where it can be discharged into
an ordinary waste treatment facility.  You are to use hexane
as the stripper phase due to its high volatility:  residual hexane
dissolved in the water stream can be easily stripped out after
the toxic organic is removed by an air stripper (not part of the
problem).  So:

If the water flow rate is 10 gal/min, the stripper phase (hexane) 
flow rate is 1 gal/min, and the solute partition coefficient 
(Henry's Law coefficient) is 100:1 on a molar basis, what is the 
required number of contactors?  What is the minimum solvent
flow rate for which the extraction can be performed for an
infinite number of stages?

You will find today's example helpful in solving this problem!