Mass Transfer
For a binary mixture with low relative volatility, continuous rectification to get pure products will require

Small cross-section column
Less number of trays
High reflux ratio
Low reflux ratio

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Mass Transfer
Fenske's equation for determining the minimum number of theoretical stages in distillation column holds good, when the

Mixture (to be separated) shows positive deviation from ideality
Relative volatility is reasonably constant
Multicomponent distillation is involved
Mixture (to be separated) shows negative deviation from ideality

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