Fluidized bed adsorption process

Table 22.2.1. Application data. Activated carbon fluidized bed adsorption process...

The literature contains many references to the use of fluidized bed adsorption processes. Applications have included the removal of organic compounds from air and vent streams (Avery and Tracey 1968, Rowson 1963) and the drying of air with silica gel (Ermenc 1%1, Cox 1958). Fluidized beds are attractive because, when fully fluidized, the pressure drop is independent of flowrate and heat and mass transfer processes external to the adsorbent particles are very good. The main problems lie, as with many moving bed processes, with the mechanical strength of the adsorbent particles. 

The commercialization by Kureha Chemical Co. of Japan of a new, highly attrition-resistant, activated-carbon adsorbent as Beaded Activated Carbon (BAC) allowed development of a process employing fluidized-bed adsorption and moving-bed desorption for removal of volatile organic carbon compounds from air. The process has been marketed as GASTAK in Japan and as PURASIV HR (91) in the United States, and is now marketed as SOLD ACS by Daikin Industries, Ltd. 

Figure 4.19 Continuous feed of substrate and removal of products synthesis of 3-phenylcatechol from 2-phenylphenol applying a fed batch process with fluidized bed adsorption followed recrystallization...

As in fluidized bed adsorption, proteins are bound to porous particles as well, these parameters will remain important and must be considered when describing protein adsorption to fluidized beds. As mentioned above, fluidizing the adsorbent allows free movement of the particles within the adsorbent bed, so dispersion in the solid phase is another component determining process performance. 

Fig. 4. System and operating parameters influencing process performance of fluidized bed adsorption...

For the fluidized bed process the bed expansion as a consequence of an increase in linear flow rate has to be considered. In a simplified picture diffusive transport takes place in a boundary layer around the matrix particle which is frequently renewed, this frequency being dependent on velocity and voidage, as long as convective effects, e.g. the movement of particles are neglected. Rowe [74] has included these considerations into his correlation for kf in fluidized beds, which is applicable for a wide range of Reynolds numbers, including the laminar flow regime where fluidized bed adsorption of proteins takes place (Eq. 19). The exponent m is set to 1 for a liquid fluidized bed, a represents the proportionality factor in the correlation for packed beds (Eq. 18) and is assumed as 1.45. 

Finally, in a concluding paper Dr. Jorg Thommes considers enzyme recovery in Fluidized Bed Adsorption as a Primary Recovery Step in Protein Purification . As important as it is to track down new enzymes and selectively modify them, it remains equally important to actually make them available in the flask on the bench in adequate quantities at low cost with sufficient purity. Recovery is of central significance in this respect. Fluidized bed adsorption combines the process steps of cell separation, concentration and primary cleaning in recovery work. The procedure can also be excellently transferred from the laboratory to the pilot scale. 

The procedure for the scale-up of an expanded-bed-adsorption process is relatively straightforward and the principles are similar to those used for a packed-bed process. It is important that the length of the laboratory column be equal to the pilot-plant column. If the pilot-plant equipment is not specifically designed for expanded-bed-adsorption procedures, it should be modified as described in the previous section on laboratory equipment. To verify that the expanded-bed flow patterns are similar for the lab and pilot-plant columns, pulse tests using NaCl solution should be carried out. The adsorbent used, whole-broth-solvent ratio, bed height, and linear velocity, should not be changed on scale-up. The volumetric flow should be increased m proportion to the mcrease in the cross-sectional area of the two columns. Thus, the superficial velocity will be maintained and the adsorption and the fluidization properties will be constant. 

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