Membranes and Membrane Configurations

Solute feed concentration usually 1 ppm to 0.1 % with some applications up to 10%. [10 to 10 mol]. The bulk/film volume ratio, d = 1. 

Surface concentration 1 to 5 (imol/m bubble area. Height to diameter 5 1 to 15 1. Usual liquid feed superficial velocity 0.1 to 1 L/s m. Bubble diameter = 0.8 to 1 mm. Volumetric feedrate ratio of inlet gas to liquid flowrates 4 to 7.5 dm gas/L liquid. Volumetric ratio of gas in foam to overhead liquid in draining foam 100 to 250 1. Liquid in the foam/liquid in the feed = 6 to 12 % y/x draining foam density 0.003 Mg/m. Superficial gas velocity for foam drainage section 3 to 250 drrf/s m. Scaleup based on constant superficial gas velocity. 

To remove ions, consider adding ionic surfactant. 

Consider first the membranes materials of construction, pore sizes and surface properties. Then consider options for operating membranes and the configurations for membranes hollow fibers, tubes, flat sheets and spirals. 

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The earhest reverse osmosis and ultrafiltration units were based on flat membrane sheets ia arrangements similar to that of a plate and frame filter press. Siace then, mote efficient membrane configurations, ie, tubular, spiral wound, and hoUow fiber, have emerged (96—98). 

RO membrane performance in the utility industry is a function of two major factors the membrane material and the configuration of the membrane module. Most utility applications use either spiral-wound or hollow-fiber elements. Hollow-fiber elements are particularly prone to fouling and, once fouled, are hard to clean. Thus, applications that employ these fibers require a great deal of pretreatment to remove all suspended and colloidal material in the feed stream. Spiral-wound modules (refer to Figure 50), due to their relative resistance to fouling, have a broader range of applications. A major advantage of the hollow-fiber modules, however, is the fact that they can pack 5000 ft of surface area in a 1 ft volume, while a spiral wound module can only contain 300 ftVff. 

Phillips, RJ Deen, WM Brady, JF, Hindered Transport in Fibrous Membranes and Gels Effect of Solute Size and Fiber Configuration, Journal of Colloid and Interface Science 139,363, 1990. 

Makriyannis A, Banijamali A, Van der Schyf C, Jarrell H. The role of cannabinoid stereochemistry and absolute configuration and the orientation of A9-THC in the membrane bilayer. Structure-activity relationships of cannabinoids. In Rapaka RS, Makriyannis A, eds. Interactions of Cannabinoids with Membranes. National Institute on Drug Abuse Research Monograph 79. Rockville, MD US Department of Health and Human Services, 1987. 

The combined features of structural adaptation in a specific hybrid nanospace and of a dynamic supramolecular selection process make the dynamic-site membranes, presented in the third part, of general interest for the development of a specific approach toward nanomembranes of increasing structural selectivity. From the conceptual point of view these membranes express a synergistic adaptative behavior the addition of the most suitable alkali ion drives a constitutional evolution of the membrane toward the selection and amplification of a specific transport crown-ether superstructure in the presence of the solute that promoted its generation in the first place. It embodies a constitutional selfreorganization (self-adaptation) of the membrane configuration producing an adaptative response in the presence of its solute. This is the first example of dynamic smart membranes where a solute induces the preparation of its own selective membrane. 

Absorption evaluation from luminal disappearance of drugs has been widely employed as a simple and easy method. Although the appearance of drugs in the mesenteric blood can provide a more sensitive way that enables to detect lower levels of absorption, it is technically more complicated, especially due to the colon s anatomical and morphological configuration. Another alternative for absorption evaluation is to measure drugs that appear in the systemic circulation, although this method cannot provide a direct measure of membrane permeability. 

The emulsion liquid membrane (Fig. 15.1b) is a modification of the single drop membrane configuration presented by Li [2] in order to improve the stability of the membrane and to increase the interfacial area. The membrane phase contains surfactants or other additives that stabilize the emulsion. 

The development of the Loeb-Sourlrajan asymmetric cellulose acetate membrane (1) has been followed by numerous attempts to obtain a similar membrane configuration from virtually any available polymer. The presumably simplistic structure of this cellulose acetate membrane - a dense, ultrathln skin resting on a porous structure - has been investigated by transmission and scanning electron microscopy since the 1960s (2,3). The discovery of macrovoids ( ), a nodular intermediate layer, and a bottom skin have contributed to the question of the mechanism by which a polymer solution is coagulated to yield an asymmetric membrane. 

It should be obvious from the above that fluid-management techniques which Improve the mass-transfer coefficient (k) with minimum power consumption are most desirable. However, in some cases, low-cost membrane configurations with inefficient fluid management may be more cost effective. In any case, it is important to understand quantitatively how tangential velocity and mem-brane/hardware geometry affects the mass-transfer coefficient. 

To generate this kind of field, that is, the cross-flow, the channel walls must be made semiperme-able, and a membrane must act as an accumulation wall so that carrier liquid is allowed to pass but not the analyte. Cross-flow FFF can be broken down into symmetric, asymmetric, and cylindrical configurations (see Figure 12.8). 

TABLE 5.3 Variation in Membrane Configuration and Pore Size Based on Five Different Manufacturers... 

The fundamentals of these technologies are described, including membrane polymers and device configurations, as well as complete system design considerations. 

In order for membranes to be used in a commercial separation system they must be packaged in a manner that supports the membrane and facilitates handling of the two product gas streams. These packages are generally referred to as elements or bundles. The most common types of membrane elements in use today include the spiral-wound, hollow fiber, tubular, and plate and frame configurations. The systems currently being marketed for gas separation are of the spiral-wound type, such as the SEPAREX and Delsep processes, and the hollow-fiber type such as the Prism separator and the Cynara Company process. 

To design or optimize an ED process several parameters are to be taken into account, namely stack construction and spacer configuration, operation mode, membrane perm-selectivity, feed and product concentration, flow velocities, current density and voltage applied to the electrodes, recovery... 

Microporous membrane liquid-liquid extraction (MMLLE) is a two-phase extraction setup. In MMLLE procedures, the membrane material and format (FS and HF), extraction units, and system configurations are identical to those described in SLM (Section 4.4.1.2).63 The two-phase HF-MMLLE system is identical to that used in Section 4.4.3, although sometimes with minor differences. In contrast to three-phase SLM extraction, MMLLE employs a microporous membrane as a miniaturized barrier between two different phases (aqueous and organic). One of the phases is organic, filling both the membrane pores (thus making the membrane nonporous) and the compartment on one side of the membrane (acceptor side). The other phase is the aqueous sample on the other side of the membrane (donor side). In this way, the two-phase MMLLE system is highly suited to the extraction of hydrophobic compounds (log Ko/w > 4) and can thus be considered a technique complimentary to SLM in which polar analytes (2 < log Ko/w < 4) can be extracted. 

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