Countercurrent multistage fluidized bed reactor for immobilized biocatalysts: III. Hydrodynamic aspects
In Parts I and II of this series we described the modelling, design, and operation of a multistage fluidized bed reactor (MFBR) for immobilized biocatalysts. This article deals with those aspects of the MFBR which are different from single‐stage fluidized beds which are operated in batch mode with respect to the solids. The semicontinuous transport of the particles requires perfect mixing of the particles in the reactor compartments, because particles are mainly transported from the bottom of these compartments. A large spread in the physical properties of the biocatalyst particles, especially of both size and density, may cause the particles to segregate into layers with different diameter and/or density. This affects the efficient use of the biocatalyst. The properties of the particles are dependent on the immobilization method. The suitability of different methods for possible future application in the MFBR is therefore compared. Because of segregation, successful use of a biofilm catalyst with a nonuniform thickness of the biofilm is doubtful. Experiments in a small scale reactor (± 0.1 m diameter) demonstrated that perfect particle mixing is possible using commercially available biocatalyst particles of uniform density. Co‐immobilization of the biocatalyst with glass powder in a gel is a simple and effective method of increasing gel density. High density particles allow high liquid flow rates, and thus an improved external mass transfer can be achieved.
A comparative study of the activity of free and immobilized enzymes and its application to glucose isomerase
We have made an experimental study of the isomerization of fructose and glucose by glucose isomerase in two forms: one soluble and the other immobilized by being fixed in a gel matrix. For the latter technique we used a fixed-bed differential reeirculation reactor, which allowed us to obtain comparable results to those we got with the enzyme dissolved within a batch reactor. We propose a simple method of comparing the results obtained in both systems, which permits us to determine the relative activity of each enzyme and also the effective diffusivity in the immobilized enzyme. The values obtained for the latter indicate a tortuosity factor of 2.04, which is lower than that generally found in porous solids but consistent with the results published in the literature for diffusion in gel particles. The application of our method to the results arrived at with the two systems studied confirms the validity of the kinetic model for glucose-fructose isomerization and has lead to our being able to determine both the kinetic constants for the reaction and their variation according to temperature. Copyright © 1996 Elsevier Science Ltd
General expression for the density effect for the ionization loss of charged particles
The equations for the density-effect correction $\ensuremath{\delta}(X)$ for the ionization loss as given in a previous paper have been extended to the case where $\ensuremath{\delta}({X}_{0})\ensuremath{\equiv}{\ensuremath{\delta}}_{0}g0$. Here ${X}_{0}$ is the lower limit of the range ${X}_{0}lXl{X}_{1}$, where a particularly simple expression for $\ensuremath{\delta}(X)$ applies; $X={log}_{10}(\frac{p}{{m}_{0}c})$, where $p$ is the momentum and ${m}_{0}$ is the mass of the incident particle. The case ${\ensuremath{\delta}}_{0}g0$ applies directly to the calculation of $\ensuremath{\delta}(X)$ for conductors (metals).