Adsorbents, design

Additional information may be found by referring to the appropriate sections of this handbook. A comprehensive treatment of adsorber design principles is given in Bnonicore and Theodore, Industrial Control Equipment for Gaseous Pollutants, vol. 1, 2d ed., CRC press, Boca Raton, Florida, 1992. 

References 110 through 123 provide additional information on adsorbers, design, and scale-up principles, as well as operational guidance. 

Figure 10.8 Different contacting arrangements for adsorber design.

The necessity of forming zeolite powders into larger particles or other structures stems from a combination of pressure drop, reactor/adsorber design and mass transfer considerahons. For an adsorption or catalytic process to be productive, the molecules of interest need to diffuse to adsorption/catalytic sites as quickly as possible, while some trade-off may be necessary in cases of shape- or size-selective reactions. A schematic diagram of the principal resistances to mass transfer in a packed-bed zeolite adsorbent or catalyst system is shown in Figure 3.1 [69]. 

The process sketched out in this section can be used to create an adsorber design. There are often times when one wants to examine the performance of an existing unit. When performance analysis is needed there are several alternatives. Depending on the specifics of the problem there may be an analytical solution for the adsorption problem and that may enable the creation of a satisfactory descrip-hon of the process to use in understanding phenomena that are observed in operation. 

This paper Is concerned with a broad range of gas-adsorption processes as practiced In the organic-chemical, petroleum, natural-gas and allied Industries Emphasis will be on a description of processes rather than a review of adsorber design... 

The scope of the following chapter will be an attempt to identify system parameters limiting the efficiency of fluidized bed adsorption and to define operating parameters, e.g. adsorbent design, flow rate, column geometry, and... 

During transport, both external and intraparticle mass transfer resistances play a role to a varying degree. A first step in adsorber design is to predict or... 

The growth in both variety and scale of gas-pliase adsorption separation processes, particularly since 1970, is due in part to continuing discoveries of new, porous, high-surface-area adsorbent materials (particularly molecular sieve zeolites) and, especially, to improvements in the design and modification of adsorbents. These advances have encouraged parallel inventions of new process concepts. Increasingly, the development of new applications requires close cooperation in adsorbent design and process cycle development and optimization. 

Wang, C. K. and S. E. Lee (1997). Evaluation of granular activated carbon adsorber design criteria for removal of organics based on pilot and small-scale studies. Water Science Technol., Proc. 1996 1st Int. Specialized Conf. Adsorption in the Water Environment and Treatment Processes, Nov. 5-8,1996, Shirahama, Japan, 35,7, 227-234. Elsevier Science Ltd., Oxford, England. 

Conventional adsorber designs include vertical (length/diameter >1) or horizontal (lengdi/diameter <1) packed beds. The maximum permissible gas flow rates throug)i these vessels is governed by pressure drop and the possibility of local fluidization and channeling [11]. Some of these problems are solved by novel designs such as (a) radial bed and (b) rotary bed adsorbers. 

K. S. Knaebel, The basics of adsorber design, Chem. Eng., 92-103 (April 1999). 

An understanding of the above principles and their interrelationship is imperative for cost-effective adsorber design and operation. For instance, the bulk transport step can be readily manipulated (e.g., by mixing) so that it does not control... 

Most experimental kinetic curves are rather smooth, i.e, the concentration of adsorbate in solution monotonically decreases, but some kinetic curves reported in the literature have multiple minima and maxima, which are rather unlikely to be reproducible. Such minima and maxima represent probably the scatter of results due to insufficient control over the experimental conditions. For instance use of a specific type of shaker or stirrer at constant speed and amplitude does not necessarily assure reproducible conditions of mass transfer. Some publications report only kinetic data—results of experiments aimed merely at establishing the sufficient equilibration time in equilibrium experiments. Other authors studied adherence of the experimentally observed kinetic behavior to theoretical kinetic equations derived from different models describing the transport of the adsorbate. Design of a kinetic experiment aimed at testing kinetic models is much more demanding, and full control over all parameters that potentially affect the sorption kinetics is hardly possible. 

Biochemical product recovery, affinity adsorbent design, 123-32 Biological activity, largomycin F-II, 133... 

In Chapter 2, we discussed the fundamentals of adsorption equilibria for pure component, and in Chapter 3 we presented various empirical equations, practical for the calculation of adsorption kinetics and adsorber design, the BET theory and its varieties for the description of multilayer adsorption used as the yardstick for the surface area determination, and the capillary condensation for the pore size distribution determination. Here, we present another important adsorption mechanism applicable for microporous solids only, called micropore filling. In this class of solids, micropore walls are in proximity to each other, providing an enhanced adsorption potential within the micropores. This strong potential is due to the dispersive forces. Theories based on this force include that of Polanyi and particularly that of Dubinin, who coined the term micropore filling. This Dubinin theory forms the basis for many equations which are currently used for the description of equilibria in microporous solids. 

Even this simple geometry of the example illustrates the influence of the adsorber design on self-heating. But beside the inlet region there are some additional critical regions in real adsorbers. The next example emphasizes the effect of the adsorber geometry on the self-heating process much more. 

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