Question

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 % 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 ethanol-water distillation. A company wishes to distill a 0.880 mole fraction ethanol (0.120 mole fraction water) solution. To aid in the distillation process, a 0.950 mole fraction benzene (0.050 mole fraction water) mixture containing fresh benzene and a recovered benzene solution is added. The plant wishes to produce 86.0 moles/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 7.12 mol/hr stream of water, and a 0.9000 mole fraction benzene (0.1000 mole fraction water) mixture, some of which is recycled back to the fresh benzene stream.

Label the process flow diagram below, Label any quantites as "unknown" if you have to perform a calculation to obtain the numeric value. DO NOT LEAVE ANY ANSWER SPACE BLANK. "el" is short for ethanol, "b" is short for benzene, and w is short for waten molihr mol b mol w mol bvhr mol b mol mol w mol b mol mol w mol mol/hr mol etimol mol whr mol wimol mol etmol 0.10000.001 unkwn mol b/imol 0.90000.999 0.880 0.050 86.0 7.12 0.950 0.120 What flow rate of the ethancl and water feed stream is needed to provide 86.0 moWhr of the 0.999 mole fraction ethanol stream? Number mol/hr What flow rate of fresh benzene is required? Number mol benzene/ hr What is the Tlow rate of the recycle line? Number mol/hr

Answer 1

Given

molhr 0.9 mol b 0.1 mol w mol mol molhr mol bwhr mol/hr 0.95 jmol mol b 0.9 ma 3 bimol 0.9 0.05 mol 0.1 wimcl istillat lumn mol b mol Separat mol w mol/hr 0.88 mol etmol 7.12 mol whr 0.12mol wimol 86 molhr 0.999 mol etmol 0.001 mol blmol 0.10000.001 unknown 0.90000.999 0880 0.050 86.0 7.12 0.9500.120

o8.ou 09 00 Bottom p.ochut of dahuoon 1000 11.00 12.00 01.00 Plou 02.00 03.00 4.00 o elao male Rnzant 0 ud

wakoni Shem 9 = 4.5956 a 0 08.00 09.00 0.00 41 116 Rinzeno ry

41.446 molhr 0.9 mol b 0.1 mol w mol 41.446mol bwhr 45.95糸01hr mol mo hr 0.95 mol 0.9 mal 3 mo/hr mal 0.05 mol 0.1 wmd istillat lumn mol b mol Separat mol w 97. 63 mol/hr 0.88 mol etlmol 0.12mol wimol 7.12 mol w/hr 86 molhr 0.999 mol et/mol 0.001 mol blmol 0.10000.00 unknown 0.90000.999 0.880 0.050 86.0 7.12 0.9500.120 1