What happens when the reflux is increased in a distillation column?

When more overhead liquid product is refluxed in a distillation column the liquid rate in the column increases. This may or may not be an optimal change in the column. Too little reflux will not have the proper vapor-liquid contact to promote separation and the overhead product will may meet the desired concentration specification. Too much reflux will flood the column and lead to wasted energy and cooling utilities associated with condensing more vapor than necessary. On a McCabe Thiele diagram for a binary distillation, increasing the reflux will decrease the slope of the stripping operating line. Typically the optimum reflux ratio (overhead product sent back to the column divided by distillate removed) is the theoretical minimum reflux ratio multiplied by a factor of 1.2-1.5.