problem 1: Ethanol is frequently used as a fuel additive, but to function in most engines, the ethanol should be very pure and contain little water. It is difficult to distill ethanol and water above 90 mol% ethanol as at this concentration the vapor and the liquid phases of this mixture have similar composition. To get around this effect, benzene is frequently 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.

The company wishes to distill a 0.870 mole fraction ethanol solution (the balance is water). To aid in the distillation process, a mixture of benzene and water is added to the distillation column. This benzene or water mixture is made by combining a fresh feed of 0.97 mol fraction benzene in water with a recovered benzene solution. The plant wishes to produce 73.0 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 the separator which produces a 10.70 mol/hr stream of pure water, and a 0.93 mol fraction benzene mixture in water; from this benzene mixture a small amount is purged and the remaining 90.00 mol/hr is recycled back to the fresh benzene stream to form the feed into the column.

a) Draw the process flow diagram. On the flow chart, label all the variables and unknowns.

b) What is the basis of calculation for the process?

c) Compute the total degrees of freedom over the entire process. Next, compute the degrees of freedom around each unit operation. Label all the calculations.

d) List all the algebraic equations for the material balances and the order for which you would solve for all of the unknowns. If the problem is underdetermined list which unknowns you can solve for. DO NO CALCULATIONS.

problem 2: Streptomycin is an antibiotic generally used to fight bacterial diseases in humans. Streptomycin is produced by the microbial strain Streptomyces griseus by fermentation on glucose and soybean meal. After fermentation, the biomass is separated from liquid and Streptomycin is recovered by adsorption on activated charcoal followed by extraction with an organic solvent in a continuous extraction process. For the given problem, ignore the other details of the process and consider just the overall extraction process: 200 L/h of an aqueous solution containing 10 g Streptomycin per L (SG 1.00) is contacted with 10 L/hr of an organic solvent (SG 0.600). Two streams leave the extraction procedure: an aqueous solution of 0.2 g Streptomycin per L and an organic solvent containing an unknown concentration of Streptomycin.

a) Draw the process flow diagram. On flow chart, label all the variables and unknowns.

b) What is the basis of calculation for the process?

c) Compute the degrees of freedom for the overall process. Label all the calculations.

d) List all the material balances and the order for which you would resolve for all of the unknowns. If the problem is underdetermined list which unknowns you can solve for. If the problem can be solved give the concentration of Streptomycin in the output stream in units [g/L].

problem 3: MTBE (methyl tert-butyl ether) is added to the gasoline (SG 0.72) to raise the oxygen content of the gasoline. MTBE (SG 0.74) is soluble in water to certain extent and becomes a contaminant when the gasoline gets into surface or underground water. The gasoline used by boats has an MTBE content of 10 vol%. The boats operate in a well-mixed flood control pond having dimensions 3 km long, 1 km wide, and 3 m deep on average. Assume that each of the 10 boats on the pond spills 0.5 L of gasoline throughout the 12 h of daylight. The flow of water (which contains no MTBE) into the pond is 10 m3/hr, however no water leaves the spillway as the water level is below the spillway of the pond. Also suppose that no water or MTBE leaves due to evaporation.

a) Draw the process flow diagram. On flow chart, label all the variables and unknowns.

b) What is the mass fraction of MTBE in the pond after the end of 12 hr of boating? Express your answer in parts per billion. Suppose no MTBE is initially in the pond.