Hollow fibers, operating modes

Mass Transfer MoDEtiNC in Different Hollow Fiber Operating Modes... 

Parameter Stirred-tank bioreactors operated in batch and fed-batch mode Stirred-tank bioreactors operated in perfusion mode Heterogeneous bioreactors (packed-bed or hollow-fiber) operated in perfusion mode... 

A mathematical formulation for the gas separation by hollow fibers operating in a cocurrent mode was developed by Pan [264], [265]. The assumptions made in his model were... 

A typical UF pilot plant has been used in this study. Examples of application for these membranes can be found in the literature [40, 58]. The UF unit woks in deadend mode (2.5 m h ) and it can be operated in filtration, backwash and chemically enhanced backwash (CEB) modes as described in the literature for similar UF systems [40]. The specifications of the hollow fiber UF modules and the operating conditions are summarized in Table 5. 

Trtic, T.M., Vladisavljevic, G.T. and Comor, J.J. (2001) Single-stage and 2-stage solvent-extraction of Tl(III) in hollow-fiber contactors under recirculation mode of operation. Separation Science and Technology, 36, 295. 

The use of membrane introduction mass spectrometry (MIMS) was first reported in 1963 by Hoch and Kok for measuring oxygen and carbon dioxide in the kinetic studies of photosynthesis [46], The membrane module used in this work was a flat membrane fitted on the tip of a probe and was operated in the MIS mode. The permeated anaytes were drawn by the vacuum in the MS through a long transfer line. Similar devices were later used for the analysis of organic compounds in blood [47], Memory effects and poor reproducibility plagued these earlier systems. In 1974, the use of hollow-fiber membranes in MIMS was reported, which was also operated in the MIS mode [48], Lower detection limits were achieved thanks to the larger surface area provided by hollow fibers. However, memory effects caused by analyte condensation on the wall of the vacuum transfer line remained a problem. 

Figure 9.19 shows typical cell concentrations reached in the main industrial bioreactors and a comparison of these values with those found in microbial fermentations. As can be observed, batch and fed-batch cultivations attain dry biomass values comparable to those of continuous cultures of microorganisms, so that mass and heat transfer capacities are not limited for these operation modes. However, high cell density cultivation in heterogeneous bioreactors, such as hollow-fiber devices, reaches dry biomass values similar to the maxima observed in microbial cultures. 

Transport of Pu(lV) from 3 M HNO3 solutions across Ahquat-336/ Solvesso-100 by HFSLM was studied. Permeability of Pu(IV) through a bundle of hollow fibers made up with 20 lumens, of 67 cm surface area, 9 cm length, and operated at a flow rate of 10 m /s on recycle mode was examined. More than 80% Pu from oxalate bearing wastes generated during reconversion process could be transported through 10% Aliquat-336/Solvesso-100 into hydroxylamine hydrochloride strippant in about three runs [167]. 

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... 

FIGURE 33.9 Schematic view of hollow fiber membrane contactor operated in recycling mode for U(VI) recovery from aqueous acidic waste (1) HFC module, (2) feed, (3) extractant, and (4) peristaltic pumps. 

Chen and Lee [24] studied lactic acid production from dilute acid pretreated a-cellulose and switchgrass by L. delbruckii NRRL-B445 in the presence of a fungal cellulase in a fermentor extractor employing a microporous hollow fiber membrane (MHF). This reactor system was operated in a fed-batch mode with continuous removal of lactic acid by in situ extraction. A tertiary amine (alamine... 

Identification of the individual mass-transfer coefficients depends on the construction of the module (material and structure of fibers in both bundles) and on its mode of operation. For the laminar flow inside hollow fibers, the following correlation can be used [84] ... 

If die hollow fiber is made of glassy polymers, only small fiber deformation is tolerable over the possible operating pressure range to avoid rupture of the fiber wall. Since the selective dense layer ou the outside region of die hollow fiber is normally very thin (less than 1300 A), it is understandable that the shell-feed mode, where the fiber is pressurized externally, is of most commercial interest since the dense layer may be ruptured by dilation if die fiber is pressurized internally. 

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. 

Figure 7.46 Long term stability of a hollow fiber fermenter in single pass mode processing whey permeate. Initial cell concentration is 100 g/C. Dilution rate (D ) is changed from 2.7 to 1.3 C/h after 80 hours of operation. ( ) lactose, (A) ethanol, ( ) productivity.85...

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. 

By the use of hollow-fiber membranes, the ideal module comprises short fibers with a wide bore to avoid a high pressure drop in the flow direction thereby disturbing the uniform radial flow pattern and creating channeling. The membranes should also possess thick porous walls with small pore size and a high ligand density. The hollow-fiber modules can be operated in cross-flow mode that makes them especially suitable in the treatment of solutions containing particulate material. 

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