$13.$ What factors influence the determination of the minimum reflux ratio in a distillation column?

$14.$ Why are multiple feeds and side streams used in a distillation column, and what challenges do they present?

$15.$ How does relative volatility affect the choice between using simple distillation versus fractional distillation for a mixture?

$16.$ What are the key considerations when determining the optimal feed stage location in a distillation column?