ch05 - Exercise 5.1 Subject: Three-column interlinked...

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Unformatted text preview: Exercise 5.1 Subject: Three-column interlinked cascade for a four-component system. Given: Configuration for a two-column interlinked cascade for a three-component system Find: Devise the three-column cascade. Analysis: The system is shown in the sketch below . Assume that the feed is comprised of components A, B, C, and D in the order of decreasing volatility. Starting from the feed end at the left-hand side, Column 1 performs a sloppy split to separate the feed into an overhead of A, part of B, and part of C; and a bottoms of part of B, part of C, and D. In the second column, the overhead is A and part of B, the middle sidestream is part of B and part of C, while the bottoms is D and part of C. In the third column, the four products are removed in nearly pure states. Exercise 5.2 Subject: Batch cascades for liquid-liquid extraction Given: Batch process in Fig. 5.19 Find: (a) Cascade diagram for Fig. 5.19. (b) Type of cascade in Part (a). (c) Comparison of process in Fig. 5.19 to a single stage process. (d) Modification to achieve a countercurrent cascade. Analysis: (a) A cascade diagram representing Fig. 5.19 is the following: Exercise 5.2 (continued) (b) The above cascade is a two-dimensional triangular cascade of the crosscurrent type. (c) For a single batch extraction using just the feed and one portion of the solvent, i.e. 100 ml of organic solvent and 100 ml of water containing 100 mg each of A and B, the resulting products are: Extract containing 100 ml solvent, 66.7 mg A, and 33.3 mg B. Raffinate containing 100 ml water, 33.3 mg A, and 66.7 mg B. If all 4 extracts and all 4 raffinates for the Fig. 5.19 are combined, we find: Extract containing 400 ml solvent, 66.7 mg A, and 33.3 mg B. Raffinate containing 400 ml water, 33.3 mg A, and 66.7 mg B. The process in Fig. 5.19 does produce extracts of varying purity, but overall, it is not effective. (d) The cascade above in Part (a) can be modified to give a more countercurrent process by reversing the flows of the solvents as shown in the following diagram. However, it is not possible to carry this out batchwise. Exercise 5.3 Subject: Two-stage membrane cascades for removal of nitrogen from methane by gas permeation. Given: Glassy polymer membrane that is selective for nitrogen. Assumptions: Desired degree of separation can not be achieved with one stage. Find: Two different two-stage cascades. Analysis : The two cascades are shown below. In both cases, the retentate is methane- rich and the permeate is nitrogen-rich. In the first cascade, the permeate from Stage 2 is recycled to the feed to obtain a more pure methane retentate. In the second cascade, the retentate from Stage 2 is recycled to the feed to obtain a more pure nitrogen permeate. Exercise 5. 4 Subject: Leaching of oil from soybeans with benzene using countercurrent-flow cascades....
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ch05 - Exercise 5.1 Subject: Three-column interlinked...

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