Shell-and-tube configuration

Ultrafiltration hollow-fiber modules are usually made with a shell and tube configuration. The fibers are potted at both ends of the module with the fiber lumen open for recirculation of the process stream (Figure 21). Naturally, strainers or prefilters must be utilized to eliminate plugging of the fibers. At Nude-pore, it has been shown that larger diameter hollow fibers, 1.5 to 3mm in i.d., are much less prone to fouling. Fortunately, all UF hollow fiber systems can be back-washed and are amenable to a number of cleaning techniques. 

These reactors are of shell-and-tube configuration and mostly have the catalyst in the tubes, although some ammonia converters have the... 

Thermal Effects in Membrane Reactors - The problem of how to supply or remove heat from membrane reactors is an important practical concern. In a shell-and-tube configuration, the catalyst can be put on the shell side, which can then be encased in yet another shell containing a heat-transfer fluid. It is likely that other geometries will, in fact, be used. For example, the burner unit of Ohta et al. is shown schematically in Figure 10. 

A porous matrix is sandwiched between two membranes. The matrix supports a liquid-phase catalyst. For the reaction A -> B, membrane 1 passes A but resists B, and membrane 2 passes both freely the function of membrane 2 is to encapsulate the catalyst solution. Reactant A is fed external to membrane 1 the concentration of A drops across the catalyst as it is consumed by reaction, due to diffusional resistance. The product diffuses to the right, reactant A does not. The benefits of this reactor are the liquid phase is encapsulated, the catalyst is separated from the product stream, the product is separated from the reactant, it provides a higher gas-liquid interfacial area, and a product is removed from an equilibrium-limited reaction. The authors suggested that the system be implemented as a shell-and-tube configuration using two different hollow-fiber membranes. 

The use of configurations employing multiple beds of catalyst usually arises because of the need to maintain adequate temperature control within the system. Other constraints leading to the use of multiple beds include those of pressure drop or adequate fluid distribution. In addition to the shell-and-tube configuration, some of the possibilities... 

Other bioreactor configurations have been developed specifically for immobilized enzymes and cells. Enzymes immobilized within polymeric membranes are used in hollow fiber (Fig. 16) and spiral membrane bioreactors (Fig. 17). In the hollow fiber device, many fibers are held in a shell-and-tube configuration (Fig. 16) and the reactant solution (or feed) flows inside the hollow fibers. The permeate that has passed through the porous walls of the fibers is collected on the shell side and contains the product of the enzymatic reaction. Also, instead of being immobilized in the fiber wall, enzymes bound to a soluble inert polymer may be held in solution that flows inside the hollow fiber. The soluble product of the reaction then passes through the fiber wall and is collected on the shell side the enzyme molecule, sometimes linked to a soluble polymer, is too large to pass through the fiber wall. 

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