Hollow fiber modules operation

Fig. 14. Schematic drawing of hollow-fiber module operations.

Hollow fiber refers to a membrane tube of very small diameter (e.g., 200 pm). Such small diameters enable a large membrane area per unit volume of device, as well as operation at somewhat elevated pressures. Hollow-fiber modules are widely used in medical devices such as blood oxygenators and hemodialyzers. The general geometry of the most commonly used hollow-fiber module is similar to that of the tubular membrane, but hollow fibers are used instead of tubular membranes. Both ends of the hollow fibers are supported by header plates and are connected to the header rooms, one of which serves as the feed entrance and the other as the retentate exit. Another type of hollow-fiber module uses a bundle of hollow fibers wound spirally around a core. 

Figure 19.6. Gas permeation equipment and performance, (a) Cutaway of a Monsanto Prism hollow fiber module for gas separation by permeation, (b) Flowsketch of a continuous column membrane gas separator, (c) Composition profiles of a mixture of C02 and Oz in a column 5 m long operated at total reflux [Thorman and Hwang in ( Turbak, Ed.), Synthetic Membranes II, American Chemical Society, Washington DC, 1981, pp. 259-279],...

Referring to the membrane module design, it has a big influence on the membrane-contactor efficiency, because it affects the pressure drops of the streams (and, thus, the operating pressures and flowrates), and their fluidodynamic (which means the mass and heat transport resistances of the phases). Furthermore, for hollow-fiber modules it is essential to ensure a uniform packing, in order to have... 

Lanthanide-actinide separation was also attempted by HFSLM (operated in the nondispersive extraction mode) method using diphenyldithiophosphinic acid derivatives. Geist et al. have employed a synergistic mixture of bis(chlorophenyl)-dithiophosphinic acid and TOPO in a hollow fiber module for the lanthanide-actinide separation [168]. About 99.99% Am... 

The choice between the two concepts is mainly based on some parameters such as operation pressure, pressure drop, or type of membrane available. The fiber wall has a structure of the asymmetric membrane, and the active skin layer being placed to the feed side. The hollow-fiber module is featured by a very high packing density, which can reach values of 30,000 vtPlm . 

Fig. 4 Schematic of the axial view of a hollow fiber module featuring (A) shell-side ports and (B) operating from out-to-in the...

While several niche applications for OD have been identified, the commercial acceptance of the technology has been hampered by the nonavailability of a suitable membrane-membrane module combination. Fluoropolymer membranes, such as PTFE and PVDF, have been shown to provide superior flux performance, but are still unavailable in hollow fiber form with a suitable thickness for use in OD applications. The inherently low flux of OD requires fhaf membranepacking density be maximized for effective operation, and hence the available flat-sheet form of perfluoro-carbon membranes is unsuitable for commercial use. Four-port hollow fiber modules that provide excellent fluid dynamics are currently available, but only low-flux polypropylene membranes are utilized. 

Hollow fiber membrane modules have minimum hold-up volumes and can operate without blockage of the fibers if the l.d. of the fiber is substantially larger than the maximum cell aggregate. Until recently, hollow fiber modules were only available with UF membranes. The advent of polysulfone MF hollow fibers makes possible cleaning with acid and base and even autoclaving at 121° in some instances. Since MF membranes are prone to internal pore fouling, membrane cleanability with flux recovery is particularly important. 

This reactor can be operated in two ways. When the substrate is fed to the shell side of the hollow fiber module ("back flush mode"), the substrate comes in contact with the enzyme in the fiber wall and product passes into the lumen of the fiber from which it exits the module. When the substrate is fed to the lumen of the fibers (with all permeate ports closed), it will pass from the lumen to the shell side where it contacts the enzyme and products will recycle back to the lumen ("recycle mode") (see Figure 3.72). The "recycle mode" has the advantage over the "back flush mode" in that the substrate does not have to be free of suspended matter. In the "back flush mode", particles in the substrate would plug the sponge wall. 

Consider the air separation problem of Example 9.2. In this case, the separation will be performed in a hollow-fiber module using the same PEMA membrane and operating in a crossflow mode. For the operating pressures considered in Example 9.2, calculate the cut, composited permeate concentration, and membrane area required to produce a retentate oxygen concentration of 7%. Compare these results to those obtained for perfect mixing in Example 9.2. 

Immobilized Liquid Membranes. A pilot plant study of the recovery of ethylene and propylene from a polypropylene reactor off-gas stream was presented by Hughes et al. (23). Aqueous solutions of Ag Ion were Immobilized In the pore structure of commercial reverse osmosis hollow fiber modules. The pilot plant operated at feed pressures of 414-827 kPa, feed flow rates of 1.42-4.25 m /h at STP, and sweep flow rates of 3.79 10" - 0.114 m /h hexane. Permeate streams with propylene concentrations In excess of 98 mole % were observed in pilot plant operation with modules containing 22.3 to 37.2 m membrane area. 

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