Fibers dense membrane reactor

A schematic diagram of a typical hollow fiber dense membrane reactor is shown in Figure 37.5a. The hollow fibers (Figure 37.5b) are manufactured by a phase inversion process (OD = l.1-1.5 mm ID = 0.75-1 mm) [63,64]. The oxidant gas (O2, H2O, CO2, N2O) mixture is fed to the core side, while a fuel (CH4, CO, or H2) mixture is fed to the shell side. A catalyst can be packed on the shell side. Both exit hnes are continuously monitored by onhne gas chromatography or mass spectrometry. 

Figure 37.S (a) Schematic diagram of a hollow fiber dense membrane reactor. (Reproduced from Ref. [60] with permission from Elsevier.) (b) SEM image of the cross...

Highly efficient enzyme membrane reactors can be also produced by immobilizing enzymes in membranes or in hollow fibers. For example, enzymes can be confined in the porous support matrix of an asymmetric capillary membrane, while substrate-containing solution flows through the fiber lumen. The dense skin layer at the lumen wall should be impermeable to the enzyme molecules. The latter diffuse through the inner wall of the fiber to the enzyme into the spongy part, where the conversion takes place. Applied transmembrane pressure and axial flow rate are parameters that contribute to control of the reactor performance. 

There are three main types of dense ceramic membranes disk/flat sheet, tubular, and hollow fibers. The disk/flat sheet membranes are applied mostly in research work because they can be fabricated easily in laboratories with a small amount of membrane material. Comparatively, the hollow fiber membranes can provide the largest membrane area per volume but low mechanical strength, while the tubular membranes possess a satisfactory specific membrane area, high mechanical strength, and are easy to assemble in membrane reactors. Dense ceramic MRs can be constructed and operated in either packed bed MR or catalytic MR configurations. 

Some of the efforts, so far, to model such membrane bioreactors seem to not have considered the complications that may result from the presence of the biomass. Tharakan and Chau [5.101], for example, developed a model and carried out numerical simulations to describe a radial flow, hollow fiber membrane bioreactor, in which the biocatalyst consisted of a mammalian cell culture placed in the annular volume between the reactor cell and the hollow fibers. Their model utilizes the appropriate non-linear kinetics to describe the substrate consumption however, the flow patterns assumed for the model were based on those obtained with an empty reactor, and would probably be inappropriate, when the annular volume is substantially filled with microorganisms. A model to describe a hollow-fiber perfusion system utilizing mouse adrenal tumor cells as biocatalysts was developed by Cima et al [5.102]. In contrast, to the model of Tharakan and Chau [5.101], this model took into account the effect of the biomass, and the flow pattern distribution in the annular volume. These effects are of key importance for conditions encountered in long-term cell cultures, when the cell mass is very dense and small voids can completely distort the flow patterns. However, the model calculations of Cima et al. [5.102] did not take into account the dynamic evolution of the cell culture due to growth, and its influence on the permeate flow rate. Their model is appropriate for constant biocatalyst concentration. 

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