3. Zone III between feed injection and raffinate withdrawal: adsorption of the more
strongly adsorbed component
4. Zone IV between raffinate withdrawal and desorbent injection: adsorption of the
less adsorbed component
The countercurrent motion of the solid phase with respect to the liquid phase is
achieved by synchronously advancing the injections and withdrawals of the system
in the direction of the liquid flow. The two main technical solutions commercially
implemented are the UOP rotary valve and the more recent system of multiple on-off
valves commercialized by AXENS. The latter offers a high level of operation
flexibility since it allows the modification of the chromatographic beds distribution
associated with the different zones.
As illustrated, in spite of its very high efficiency, the complexity of the SMB
operation is often restrained to difficult separations involving highly valuable products. In addition to the complexity of this process, the choice of an adsorbent
selective for paraxylene is the critical point.
4.7 Other Industrial Separations Involving Zeolites
Besides the previously introduced applications, other less central ones can be found.
When referring to countercurrent liquid-phase separations, the SMB concept has
been extended to a variety of similar isomeric separations comprising the separation
of ethylbenzene, cymene, or cresol. The concept is also applied to other systems such
sugars separation where the technology has evolved from the use of zeolitic adsorbents to ion-exchange resins [27]. In the past commercial processes involving X, Y,
and L zeolites were available [28].
These processes initially applied in the field of the food industry are actually
inspiring the development of separation applications processes in the context of the
biorefinery.
Finally, a variety of applications can be found for the purpose of purification.
Among them, one can mention natural gas drying, sulfur compounds capture, or
ethylene purification.
5 Industrial Zeolite Development and Improvement
The following sections are devoted to the development and improvement of adsorbents for industrial separations. A collection of selected examples is devoted to
illustrate different theoretical and experimental approaches linking (in qualitatively
or quantitative ways) the main properties of a given adsorbent and the industrial
performances.
212
J. Pérez-Pellitero and G. D. Pirngruber
strongly adsorbed component
4. Zone IV between raffinate withdrawal and desorbent injection: adsorption of the
less adsorbed component
The countercurrent motion of the solid phase with respect to the liquid phase is
achieved by synchronously advancing the injections and withdrawals of the system
in the direction of the liquid flow. The two main technical solutions commercially
implemented are the UOP rotary valve and the more recent system of multiple on-off
valves commercialized by AXENS. The latter offers a high level of operation
flexibility since it allows the modification of the chromatographic beds distribution
associated with the different zones.
As illustrated, in spite of its very high efficiency, the complexity of the SMB
operation is often restrained to difficult separations involving highly valuable products. In addition to the complexity of this process, the choice of an adsorbent
selective for paraxylene is the critical point.
4.7 Other Industrial Separations Involving Zeolites
Besides the previously introduced applications, other less central ones can be found.
When referring to countercurrent liquid-phase separations, the SMB concept has
been extended to a variety of similar isomeric separations comprising the separation
of ethylbenzene, cymene, or cresol. The concept is also applied to other systems such
sugars separation where the technology has evolved from the use of zeolitic adsorbents to ion-exchange resins [27]. In the past commercial processes involving X, Y,
and L zeolites were available [28].
These processes initially applied in the field of the food industry are actually
inspiring the development of separation applications processes in the context of the
biorefinery.
Finally, a variety of applications can be found for the purpose of purification.
Among them, one can mention natural gas drying, sulfur compounds capture, or
ethylene purification.
5 Industrial Zeolite Development and Improvement
The following sections are devoted to the development and improvement of adsorbents for industrial separations. A collection of selected examples is devoted to
illustrate different theoretical and experimental approaches linking (in qualitatively
or quantitative ways) the main properties of a given adsorbent and the industrial
performances.
212
J. Pérez-Pellitero and G. D. Pirngruber