Single Equilibrium Stages and Flash Calculations

1. Single Equilibrium Stages and Flash Calculations Chapter5 Exercises

2. Exercise5.1 • An aqueous acetic acid solution containing 6.0 moles of acid per liter is to be extracted in the laboratory with chloroform at 25°C to recover the acid (B) from chloroform-insoluble impurities present in the water. The water (A) and chloroform (C) are essentially immiscible. If 10 liters of solution are to be extracted at 25CC, calculate the percent extraction of acid obtained with 10 liters of chloroform under the following conditions: • (a) Using the entire quantity of solvent in a single batch ex­traction • (b) Using three batch extractions with one-third of the total solvent used in each batch • (c) Using three batch extractions with 5 liters of solvent in the first, 3 liters in the second, and 2 liters in the third batch Assume that the volumetric amounts of the feed and solvent • do not change during extraction. Also, assume the distribu­tion coefficient for the acid, K"n = (ck)c/(cb)a - 2.8, where (cb)c ~ concentration of acid in chloroform and (cH)A — concentration of acid in water, both in moles per liter.

3. Exercise5.2 • A 20 wt'7r solution of uranyl nitrate (UN) in water is to be treated with tributyl phosphate (TBP) to remove 90% of the uranyl nitrate. All operations are to be batchwise equilibrium contacts. Assuming that water and TBP are mu­tually insoluble, how much TBP is required for 100 g of solution if at equilibrium (g UN/g TBP) = 5.5(g UN/g H2O) and: • (a) All the TBP is used at once in one stage? • (b) Half is used in each of two consecutive stages? • (c) Two countercurrent stages are used? • (d) An infinite number of crosscurrent stages is used? • (e) An infinite number of countercurrent stages is used?

4. Exercise5.3 • A stripper operating at 50 psia with three equilibrium stages is used to strip 1,000 kmol/h of liquid at 300°F having the following molar composition: 0.03% C,, 0.22% C2, 1.82% G,, 4.47% «C4, 8.59% «C5, 84.87% nC,0. The stripping agent is 1,000 kmol/h of superheated steam at 300°F and 50 psia. Use the Kremser equation to estimate the compositions and flow rates of the stripped liquid and exiting rich gas. • Assume a /C-value for CK) of 0.20 and assume that no steam is absorbed. However, calculate the dew-point temper- • ature of the exiting rich gas at 50 psia. If that temperature is above 300°F, what would you suggest be done?

5. Exercise5.4 • Verity the values given in Table 5.1 for AV, A7/.;, and ;V/, tor a partial reboiler and a total condenser.

6. Exercise5.5 • A mixture of maleic anhydride and benzoic acid contaming 10 molf/r acid is a product of the manufacture of phthalic anhydride. The mixture is to be distilled continuously in a column with a total condenser and a partial reboiler at a pressure of 13.2 kPa (100 torr) with a reflux ratio of 1.2 times the minimum value to give a product of 99.5 mol% maleic anhydride and a bottoms of 0.5 mol% anhydride. Is this problem completely specified

7. Exercise5.6 • Verify A//> for the following unit operations in Table 12: (ft), (t), and (#). How would WD change if two feeds were used instead of one?

8. Exercise5.7 • The following are not listed as design variables for the i distillation unit operations in Table 5.2: jfa) Condenser heat duty jfb) Stage temperature ifc) Intermediate-stage vapor rate Id) Reboiler heat load Under what conditions might these become design variables?If so, which variables listed in Table 5.2 would you eliminate?