Page 312 - Pressure Swing Adsorption

11
288 PRESSURE SWING ADSORPTION
CHAPTER
_ C. N. Kenney, m "Separation of Gases," Proceedings of the ~tli BOC Priestley Conference,
7
h
.
B1rmmg am UK (1984) Roval Societv. of Chemislry, Special PuD. No. 80, PP· 273-86 8
,
. .
(1990).
_ R. Y,tng, Gas Separatmn by Adsorption Processes, p. 263, Butterworths, Stoneham, MA
8
(1987).
9. R. L. Jones, G. E. Keller, and R. C. Wells, U.S. Patent 4,194,892 (1980), to Union Carbide. Membrane Processes:
10. a. E. Keller and R. L. Jones, Am. Chem. Soc. Symp. Ser. 135,275 (1980). l,
Comparison with PSA
l l. R. L. Jones and G. E. Keller, J. Sep. Process Technology 2(3), 17 (1981).
12. S. J, Doong and R. T. Yang, A/ChE Symp. Ser. 84(264), 145 (1988).
13. E. A\pay, C. N. Kenney, and D. M. Scott, Chem. Eng. Sci. m press.

Although pressure swmg adsorption and membrane· oerrneatton processes
operate on quite different prmc1ples, they offer economically competitive
alternatives for many small- and medium-scale gas separations. The focus of
this book 1s on pressure swing systems, but 1t seems appropriate to mclude a
brief mtroduction to membrane processes ro orovide the reader with the
background needed to assess the comparative merits of the membrane
alternative. From an overall standoomt pressure swing and membrane pro-
cesses are similar in that they are both best suited to producing a pure
raffinate (retentate) product. Although either orocess can be adapted to yield
a pure extract (permeate) product this cannot be accomolished without a
significant loss of efficiency. In both classes of process- the main operating
cost is the power reautred to compress the feed stream; so a first estimate of
comparative performance can be obtained simply by considenng the power
! , requirements.

8.1 Permeability and Separation Factor

The concept of a membrane orocess 1s straightforward (Figure 8.1). The
separation depends on the difference m permeation rates through a perm-
selective membrane, and the process efficiency 1s largely dependent on the
se!ect1v1ty and permeability of the membrane matcnai. The permeability ( ,r;),
which provides a quant1tat1ve measure of the ease with which a particular