Packed towers, separations distillation example

As the potentialities of liquid extraction as a separation method were developed, the need for efficient, continuously operated, multistage equipment became apparent. It was natural therefore to turn to devices which had been so successful in other similar fluid-contacting operations, such as the bubble-tray tower and the packed tower of distillation. These devices have proved to be disappointing in liquid-extraction service, however for example, bubble-tray towers provide tray efficiencies in liquid-extraction operations of less than 5% (S7), and conventional packed towers show heights of transfer units of 10 to 20 ft. or more (T3). 

Example 12.4-1 Benzene-toluene distillation in a packed tower You want to separate a saturated liquid feed of 3500 mol/hr containing 40% benzene into a distillate containing 98% benzene and a bottoms with 2% benzene. The reflux ratio should be 1.5 times the minimum the packing has an HTU of 0.2 m. 

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