Page 35 - Pressure Swing Adsorption

CHAPTER
2

Fundamentals of Adsorption

To understand the design and operation of PSA ptocess reauires at ieast an
elementary knowledge of Lhc pnnc1plcs of adsorption and the dynamic
behavior of an adsorption column. A brief review of these subjects is
therefore included m this chapter. More detailed mformat1on can be found
2
1
m the books of Ruthven, Yang, and Suzuki. 3
The overall performance of a PSA process depends on both equilibnum
and kinetic factors, but the relative 1moortance of these factors vanes greatiy
for different systems. The maJonty of PSA orocesses are "equilibrium dnven"
m the sense that the se!ect1v1ty clepends on differences in the equilibrmm
affinities. In such processes mass transfer resistance generally has a dcictcn-
ous effect and reduces the performance relative lo an ideal (equilibrium)
system. There are, however, several processes in which the selectivity is
entirely kinetic (i.e .. the separation depends on differences m adsorot1on rate
rather than on differences m equilibrium affinity). In such systems the roie
played by mass transfer resistance 1s dearly pivotal, and a more fundamentai
understanding of kinci1c effecrs 1s needed in order .io understand and model
this class of process.

2.1 Adsorbents
2.1.1 Forces of Adsorption

A gas molecule near u solid surface exoenences a reduction m potential
energy as a consequence of interaction with the atbms (or moiecules) m the

11