When the distillation column is operating at full reflux, it is farthest from equilibrium and has the greatest mass transfer driving force – does this refer to the largest concentration difference?
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Why is the mass transfer driving force greater the larger the concentration difference? What is being compared when referring to a concentration difference? How does the concentration difference change when switching from a normal reflux ratio to full reflux?
It refers to the concentration difference of the same medium at different heights within the tower; the greater the concentration difference, the greater the driving force for mass transfer. When switching from a normal reflux ratio to full reflux, the concentration difference decreases accordingly.
Why is the concentration difference under full reflux smaller than normal? The concentration difference should be large; with full reflux, the number of theoretical plates is minimal, and the separation of substances is most thorough, so the concentration difference should be greatest, resulting in the highest mass transfer driving force!