Packed Bed Columns

A significant advantage of immobilized enzymes is the total absence of catalytic activity in the product. Moreover, the degree of substrate-to-product conversion can be controlled during processing, eg, by adjusting the flow rate through a packed-bed column reactor of immobilized enzyme. 

The recycle reactor is shown schematically in Figure 1. It consists of a catalytic or electrocatalytic reactor unit with a bypass loop, a recycle pump and a molecular sieve trap unit. The latter comprises one or two packed bed columns in parallel each containing 2-10 g of Linde 5A molecular sieve pellets. On line gas chromatography (Shimadzu 14A) was used for the analysis of CH4, O2, CO, CO2, C2H4 and C2H6 in the reactants and products. 

Figure 5.4-7. Empty bubble column. Figure 5.4-8. Packed-bed column reactors.

The gas liquid contact in a packed bed column is continuous, not stage-wise, as in a plate column. The liquid flows down the column over the packing surface and the gas or vapour, counter-currently, up the column. In some gas-absorption columns co-current flow is used. The performance of a packed column is very dependent on the maintenance of good liquid and gas distribution throughout the packed bed, and this is an important consideration in packed-column design. 

B has a negligible vapor pressure, hence does not go into the gas phase. We plan to do this absorption in either a packed bed column, or an agitated tank contactor. 

Researchers at Lehigh University have investigated the ability of ground tire rubber to sorb organic compounds such as benzene, toluene, ethylbenzene, and xylene (BTEX) to determine the feasibility of using the rubber as the sorbent media in reactive permeable barrier systems. Thus far, no field-scale work has been performed on this technology. Both batch and packed-bed column tests have been conducted. All information is from the researchers and has not been independently verified. 

Cultor Ltd. (Finland) and Tuchenhagen(Germany) have developed a process, where yeast cells are adsorbed on the surface of the carrier developed for glucose isomerase (Spezyme, Table 6.1). The high volumetric productivity of the immobilized yeast cells make a conversion of dr-acetolactate to acetoin possible with only a few hours residence time in the packed bed columns. 

Another type of mass transfer equipment, shown in Figure 6.2d, is normally referred to as the packed- (fixed-) bed. Unlike the packed column for gas-liquid mass transfer, the packed-bed column is used for mass transfer between the surface of packed solid particles (e.g., catalyst particles or immobilized enzyme particles) and a single-phase liquid or gas. This type of equipment, which is widely used as reactors, adsorption columns, chromatography columns, and so on, is discussed in greater detail in Chapters 7 and 11. 

Fig. 6.21 Column fermenters (a) bubble column, (b) tapered bubble column, (c) sieve-tray bubble column, (d) sieve-tray column with external pumping, and (e) packed-bed column with external pumping.

In contrast to continuous packed bed columns, each stage, whether cocurrent or countercurrent, can be considered to be at equilibrium for many multi-phase mass-transfer processes such as distillation, absorption, extraction etc. Such stages are usually called ideal stages . 

Westerhoff, P., Highfield, D., Badruzzaman, M. and Yoon, Y. (2005) Rapid small-scale column tests for arsenate removal in iron oxide packed bed columns. Journal of Environmental Engineering, 131(2), 262-71. 

The Munakata study utilized an upflow packed bed column filled with 0.1-2.0 g of 1% w/w Pd/alumina catalyst crushed to a 0.3-0.8 mm size fraction. (Munakata et al. 1998) The influent water stream consisted of deionized water containing 1.5-25 mg/L ofTCE. Hydrogen was supplied by purging the influent water supply with hydrogen gas and pressurizing it to 0.5 atm. As in the Yu study, a plug flow model was used and an apparent first order rate constant with respect to TCE was calculated. 

In order to reduce the duration of aging, Qureshi and Tamhane (1986) used a two-packed bed column reactors in series, separately containing immobilized H. anomala (yeast strain able to produce ethyl acetate) and immobilized S. cerevisiae. They also found that the rate of ethanol production was higher in a double column reactors in series than in a single column reactor with both yeast species coimmobilized. 

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