Ethanol is often used as a fuel additive, but to function in most engines, the ethanol must be very pure and contain little water. It is difficult to distill ethanol and water above 90 mole percent ethanol because at this concentration, the vapor and the liquid phases of this mixture have the same composition. To get around this effect, benzene is often added to the mixture. The distillation column then separates the mixture into a very nearly pure ethanol stream and a mixture of benzene and water. The benzene may be separated from the water and then recycled to use again in the ethanolwater distillation. A company wishes to distill a 0.860 mole fraction ethanol (0.140 mole fraction water) solution. To aid in the distillation process, a 0.960 mole fraction benzene (0.040 mole fraction water) mixture containing fresh benzene and a recovered benzene solution is added. The plant wishes to produce 84.0 mol/hr of a 0.999 mole fraction ethanol (0.001 mole fraction benzene) mixture from a distillation column. The other product from the distillation is a water and benzene mixture. This mixture is sent to a separator which produces a 9.77 mol/hr stream of water, and a 0.9300 mole fraction benzene (0.0700 mole fraction water) mixture, some of which is recycled back to the fresh benzene stream.

A. Label the process flow diagram. Label any quantities as unknown if a calculation is needed to obtain the numeric value. Be sure to identify all of the components. Note that "et" is short for ethanol, "b" is short for benzene, and "w" is short for water.

B. What flow rate of the ethanol and water feed stream is needed to provide 84.0 mol/hr84.0 mol/hr of the 0.999 mole fraction ethanol stream? flow rate: ________________ mol/hr

C. What flow rate of fresh benzene is required? flow rate: ________ mol benzene/hr

D. What is the flow rate of the recycle line? flow rate: ________ mol/hr

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