Study Questions for
“Separation Process Principles” by
J. D. Seader and Ernest J. Henley
Chapter 14
1. What is a membrane and how does it effect the separation of a mixture? Can the feed mixture be either liquid or gas?
2. What are the two products from a membrane separation called? What is a sweep?
3. What kinds of materials are membranes made from? Can a membrane be porous or nonporous?
4. How does a membrane separation differ from distillation?
5. What were the major breakthroughs that led to widespread use of membrane separations following World War II?
6. What are the eight most common membrane separation processes? Give an industrial application of each one.
Section 14.1:
7. Is it true that almost all industrial membrane processes use natural or synthetic polymers? Give an example of each kind of polymer.
8. What is the difference between a thermoplastic and a thermosetting polymer? What is the difference between a glassy and a crystalline polymer? What does amorphous mean?
9. What is the glass-transition temperature? To what kind of polymer does it apply? To what kind of a polymer does the melting point apply? What is a rubbery polymer? Give one example each of glassy, crystalline, and rubbery polymers.
10. What is the basic equation for computing the rate of mass transfer through a membrane? Explain each of the four factors in the equation and how they can be exploited to obtain necessary high rates of mass transfer.
11. What is the difference between the permeability and the permeance? How are they analogous to the diffusivity and the mass-transfer coefficient?
Section 14.2:
13. For a membrane separation, is it usually possible to achieve both a high permeability and a large separation factor?
14. What are the four most common membrane shapes? Which two are the most widely used? Why?
15. What are the six most common membrane modules? Which three are most widely used?
16. Under what conditions would a hollow-fiber module be a poor choice?
Section 14.3:
17. What are the three mechanisms for mass transfer through a porous membrane? Which two are the best for making a separation? Why?
18. What is the mechanism for mass transfer through a dense (nonporous) membrane? Why is it called solution-diffusion? Does this mechanism work if the polymer is
completely crystalline? Explain.
19. For bulk flow through a porous membrane, is the flow almost always laminar or turbulent? Explain.
20. What equation can be used to calculate the rate of bulk flow through a porous membrane?
21. What mass transfer law can be applied to liquid diffusion through a membrane? How must this law be modified when the size of the diffusing molecules is of the order of the pore diameter? What is Knudsen diffusion?
22. How do the solution-diffusion equations differ for liquid transport and gas transport? How is Henry's law used for solution-diffusion for gas transport?
Why are the film resistances to mass transfer on either side of the membrane often negligible?
23. For the solution-diffusion mechanism, how can the permeability be computed from the membrane diffusivity and the membrane solubility of the species?
24. How is the separation factor defined for a membrane separation? How does the definition differ from the relative volatility for distillation?
25. What assumption is used to obtain the definition of the ideal separation factor for a gas separation?
27. What are the four idealized flow patterns in membrane modules? Which is the most effective? Which is the most difficult to calculate?
28. What is meant by the cut, ?
29. Why are membrane cascades sometimes used? What are the most common cascades?
30. What is concentration polarization? When should it be taken into account?
Section 14.4:
31. What is dialysis? What are some of its major applications?
32. What is electrodialysis? What is it used for?
Section 14.5:
33. What is osmosis? Can it be used to separate a liquid mixture?
34. What is reverse osmosis? How is it used to purify water? What is the preferred membrane material?
35. What is the osmotic pressure? Is it a thermodynamic quantity? How is it measured and calculated?
36. What is the Merten equation for mass transfer of a solvent through a membrane that is used for reverse osmosis?
37. Why does water have to be pumped to a high pressure in order to purify it by reverse osmosis?
38. What is meant by salt passage? How is it used in calculating reverse osmosis?
Section 14.6:
39. Can a near perfect separation be made with gas permeation? If not, why not?
40. What are the major applications of gas permeation?
Section 14.7:
41. What is pervaporation?
42. What are the major applications of pervaporation?
