Operating diagram adsorption

FIGURE 8 Schematic diagram showing the two basic modes of operating an adsorption separation process (a) cyclic batch two-bed system (b) continuous countercurrent system with adsorbent recirculation. Concentration profiles through the adsorbent bed are indicated. Component A is more strongly adsorbed than B. (Reprinted with permission from Ruthven, D. M. (1984). Principles of Adsorption and Adsorption Processes, copyright John Wiley Sons, New York.)... 

As an example the procedure for determining the operating diagram is explained for the EMD53986 system (Appendix B). The adsorption equilibrium of this system can be described by the multi-Langmuir isotherm (Eq. 7.63). 

Fig. 9.4-1 Scheme of a one-stage unit and illustration in a diagram with an equilibrium curve and an operating line (adsorption)... 

Fig. 4-15. Operating diagram of a three stage cross-flow adsorption.

Operating diagram for single-stage equilibrium adsorption. 

Illustration 7.1 Single-Stage Adsorption The Rectangular Operating Diagram... 

Operating diagram for a two-stage crosscurrent adsorption process using fresh adsorbent. 

Operating diagram for countercurrent cascades (a) adsorption (b) absorption. 

When both components of a binary gas or vapor mixture are separately adsorbed to roughly the same extent, the amount of either one adsorbed from the mixture will be affected by the presence of the other. Since such systems are composed of three components when the adsorbent is included, the equilibrium data are conveniently shown in the maimer used for ternary liquid equilibria in Chap. 10. For this purpose it is convenient to consider the solid adsorbent as being analogous to liquid solvent in extraction operations. However, adsorption is greatly influenced by both temperature and pressure, unlike liquid solubility, which is scarcely affected by pressure under ordinary circumstances. Equilibrium diagrams are consequently best plotted at constant temperature and constant total pressure, and they are therefore simultaneously isotherms and isobars. 

The resulting operating diagram is shown in Figure 7.4b. It shows us, at a glance, that an increase in the extracting medium B will increase the slope of the operating line and hence solute recovery (Yp - Yp)/Yp, just as it did for adsorption, but that this will be at the expense of a more dilute extract. Various other consequences can be read off with equal ease. 

Figure 7.13 Removal of a single component contaminant from a feed continuous countercurrent adsorption system and McCabe-Thiele operating diagram (source Ruthven and Ching 1989).

The graphical construction of an extraction isotherm, an operating line, and the stepwise evaluation of the number of stages in this manner is known as a McCabe-Thiele diagram. Flistorically, it found great application in a variety of mass transfer operations, from gas adsorption through distillation to solvent extraction. Flowever, the advent of modern computational techniques has made it largely redundant, as it is often easier and certainly more accurate to calculate the cascade directly. 

Figure 10 Carbon adsorption flow diagram. The carbon columns are operated in series backwash water is provided by a pump (from Ref. 11).

The improved process utilizes CO2 to extract ethylene oxide from water in a flow scheme which is similar to the other liquid extractions described previously. A block diagram in the patent depicts operation of the process. Ethylene oxidation and adsorption of the ethylene oxide in an absorber are carried out in the traditional manner, but the water stream from the absorber is then sent to a stripper where CO2 strip extracts the ethylene oxide from the water solution. The CO2 stream containing the ethylene oxide is lowered in pressure and sent to a high pressure distillation column called the ethylene oxide purifier. CO2 is vaporized, and as previously described throughout this book, vapor CO2 exhibits little dissolving power. Almost pure CO2 vapor is distilled and condensed in the column and a concentrated ethylene oxide stream containing some CO2 is obtained. 

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