The operation of a fractionating column is circumscribed by two limiting reflux ratios: one corresponding to the use of an infinite number of plates and the other a total reflux, or infinite reflux, ratio. Consider a rectifying column fed at the bottom with a constant flow of a binary vapor having a constant composition, and assume also that the column has an infinite number of plates.

(a) What happens in such a column operating at total reflux?

(b) Assume that a product is withdrawn at a constant rate from the top of this column. What happens as more and more product is withdrawn in successive steps if each step achieves steady state between changes?