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270 Adsorption (Chemical Engineering)

TABLE IV Commercial Sorbex Processes a
Name Feed Extract Raffinate Process details
Parex Mixed C 8 aromatics 98–99% PX OX, MX, EB K–BaY + toluene as
Sr–BaX + PDEB or
K–BaX + PDEB
Ebex Mixed C 8 aromatics OX, MX, PX 99% EB NaY or Sr–KX + toluene
Molex n-Alkanes, branched alkanes, n-Paraffins Branched and cyclic 5A Sieve + light paraffin
and cycloalkanes isomers desorbent
Olex Olefins + paraffins Olefins Mixed paraffins Probably CaX or SrX
Sarex Corn syrup Fructose Other sugars Aqueous system CaY
a Abbreviations: OX, o-xylene; MX, m-xylene; PX, p-xylene; EB, ethylbenzene; PDEB, p-diethylbenzene.

where, as a result of the very low concentrations of parameters. The analysis for a nonlinear system is more
the contaminants, the LUB is large, so that very large complicated and requires numerical simulation of the
beds would be needed for a conventional cyclic batch system.
process. Detailed reviews of the modeling and optimization of
such processes have been given by Ruthven and Ching
(1989) and by Morbidelli et al. (1989, 1995) (see refer-
B. The Sorbex Process
ences given in the bibliography).
A more sophisticated development of the same general Large-scale Sorbex processes have been developed for
principle is the Sorbex process, developed by UOP, which a variety of different bulk separations; a brief summary is
is illustrated in Fig. 14. In this system a single fixed ad- given in Table IV. In recent years, the same principle has
sorbent bed is divided into a number of discrete sections, been applied also to a wide range of chiral separations and
and the feed, desorbent, raffinate, and extract lines are other “difficult” separations that are important in the phar-
switched through the bed by a rotary valve. The process maceutical industry. Several novel system configurations
operates essentially isothermally with regeneration of the have been developed. In one system, a carousel of 12 small
adsorbent by displacement desorption. There are four dis- columns rotates between two stationary circular headers,
tinct zones in the bed, with changes in liquid flow rate which act as the switch valve, thus effectively incorporat-
between zones. Each zone consists of several sections ing the adsorption and the flow switching functions within
(Fig. 14). a single unit.
The operation is most easily understood by reference
to the equivalent true countercurrent system (Fig. 15).
If we consider a feed containing two species A and B, SEE ALSO THE FOLLOWING ARTICLES
with A the more strongly adsorbed, and a desorbent C,
then in order to obtain separation the net flow directions • ABSORPTION (CHEMICAL ENGINEERING) • CHEMICAL
in each section must be as indicated. With the equilib- THERMODYNAMICS • CHROMATOGRAPHY • DISTILL-
rium isotherms and the feed composition and flow rate ATION • KINETICS (CHEMISTRY) • PETROLEUM REFIN-
specified, this requirement in effect fixes all flow rates ING • SOLVENT EXTRACTION • ZEOLITES,SYNTHESIS
throughout the system as well as the adsorbent recircu- AND PROPERTIES
lation rate or switch time. From simple theoretical con-
siderations it can be easily shown that the affinity of the
adsorbent for the desorbent should be intermediate be- BIBLIOGRAPHY
tween that for the strongly and weakly adsorbed feed
compounds (i.e., α AC > 1.0, α BC < 1.0). The heights of the Barrer,R.M.(1978).“ZeolitesandClayMineralsasSorbentsandMolec-
individualized bed sections are then determined by the re- ular Sieves,” Academic Press, New York.
quirement that each section contain sufficient “theoretical Basmadjian, D. (1997). “The Little Adsorption Book,” CRC Press, Boca
plates” to achieve the required purity of raffinate and ex- Raton, FL.
Breck, D. W. (1974). “Zeolite Molecular Sieves,” John Wiley & Sons,
tract products. For a linear system the analysis is straight-
New York.
forward since simple expressions for the concentration Do, D. D. (1998). “Adsorption Analysis: Kinetics and Equilibria,” Im-
profile are available in terms of the kinetic and equilibrium perial College Press, London.