Types membranes

Fig. 1. Water flux and NaCl rejection of several membrane types (10), where (D) represents seawater membranes, which operate at 5.5 MPa and 25°C ...

Gleaning. Fouling films are removed from the membrane surface by chemical and mechanical methods. Chemicals and procedures vary with the process, membrane type, system configuration, and materials of constmction. The equipment manufacturer recommends cleaning methods for specific apphcations. A system is considered clean when it has returned to >75% of its original water flux. 

The second major membrane type is a composite. Starting with a loose asymmetric membrane, usually a UF membrane, a coating is applied which is polymerized in situ to become the salt rejecflng membrane. This process is used for most high-performance flat-sheet RO membranes, as well as for many commercial nanofiltration membranes. The chemistry of the leading RO membranes is known, but... 

Crossflow Filters - These are usually membrane-type filters used for ultrafiltration. In the field of biotechnology these types of filters are used in ultrafiltration devices used in concentrating solutions, and performing buffer exchanges. 

Process Retentate Permeate Common range of feed pressure (atm) Membrane type Typical iqrplications/ species... 

In supported liquid membranes, a chiral liquid is immobilized in the pores of a membrane by capillary and interfacial tension forces. The immobilized film can keep apart two miscible liquids that do not wet the porous membrane. Vaidya et al. [10] reported the effects of membrane type (structure and wettability) on the stability of solvents in the pores of the membrane. Examples of chiral separation by a supported liquid membrane are extraction of chiral ammonium cations by a supported (micro-porous polypropylene film) membrane [11] and the enantiomeric separation of propranolol (2) and bupranolol (3) by a nitrate membrane with a A/ -hexadecyl-L-hydroxy proline carrier [12]. 

Resistance to puncture is another type of loading. It is of particular interest in applications involving sheet and film as well as thin-walled tubing or molding and other membrane type loaded structures. Hie surface skins of sandwich panels are another area where it is important. A localized force is applied by a relatively sharp object perpendicular to the plane of the sheet of material being stressed. If the material is thick compared to the area of application of the stress, it is effectively a localized compression stress with some shear effects as the material is deformed below the surface of the sheet. 

MA M10 M10.014 Membrane-type matrix m etallo pe pt id ase-1 Potential drug target for tumor cell invasion... 

The liquid-liquid patition systems discussed above are in fact very similar to various membrane-type interfaces and may serve as a model for them.A good example is, for instance, the distribution of a dissociated salt between an aqueous solution and a permeable organic polmer. ... 

Membrane-type fuel cells. The electrolyte is a polymeric ion-exchange membrane the working temperatures are 60 to 100°C. Such systems were first used in Gemini spaceships. These fuel cells subsequently saw a rather broad development and are known as (solid) polymer electrolyte or proton-exchange membrane fuel cells (PEMFCs). 

In the design of membrane-type fuel cell stacks (batteries), membrane-electrode assemblies (MEAs) are used, which consist of a sheet of membrane and of the two electrodes (positive and negative) pressed onto it from either side. 

In the first membrane-type fuel cells, the dispersed platinum catalyst was pure metal because of its large consumption. Smaller consumption and a much more efficient utilization of the platinum catalyst were attained by depositing the metal on a highly disperse carbon carrier. The best results were attained by using Vulcan XC-72 furnace... 

Traditional octanol-water distribuhon coefficients are shll widely used in quan-titahve structure-achvity relationship (QSAR) and in ADM E/PK studies. However, alternahve solvent systems have been proposed [80]. To cover the variabihty in biophysical characterishcs of different membrane types a set of four solvents has been suggested, somehmes called the critical quartet [81]. The 1,2-dichloroeth-ane-water system has been promoted as a good alternative to alkane-water due to its far better dissolution properties [82, 83], but may find little applicahon because of its carcinogenic properties. 

Membrane Types Key membrane properties include their size rating, selectivity, permeability, mechanical robustness (to allow module fabrication and withstand operating conditions), chemical robustness (to fabrication materials, process fluids, cleaners, and sanitizers), low extractibles, low fouling characteristics, high capacity, low cost, and consistency. 

Another device that finds frequent use is the stirred cell shown in Fig. 20-54. This device uses a membrane coupon at the bottom of the reservoir with a magnetic stir bar. Stirred cells use low fluid volumes and can be used in screening and R D studies to evaluate membrane types and membrane properties. The velocity profiles have been well defined (Schlichting, Boundary Layer Theory, 6th ed., McGraw-Hill, New York, 1968, pp. 93-99). 

Liquid membrane type ion-seleetive electrodes (ISEs) provide one of the most versatile sensing methods because it is possible to customize the sensory elements to suit the structure of the analyte. A wealth of different synthetic and natural ionophores has been developed, in the past 30 years, for use in liquid membrane type ISEs for various inorganic and organic ions [1], In extensive studies [2-4], the response mechanism of these ISEs has been interpreted in terms of thermodynamics and kinetics. However, there have been few achievements in the characterization of the processes occurring at the surface of ISEs at molecular level. 

Two aqueous phases separated by a liquid membrane, EM, of nitrobenzene, NB, were layered in a glass tube, which was equipped with Pt counterelectrodes in W1 and W2 and reference electrodes in three phases as in Eq. (1). Reference electrodes set in W1 and W2 were Ag/AgCl electrodes, SSE, and those in LM were two tetraphenylborate ion selective electrodes [26,27], TPhBE, of liquid membrane type. The membrane current, /wi-w2 was applied using two Pt electrodes. The membrane potential, AFwi-wi recorded as the potential of SSE in W2 vs. that in W1. When a constant current of 25 /aA cm was applied from W1 to W2 in the cell given as Eq. (1), the oscillation of membrane potential was observed as shown in curve 1 of Fig. 1. The oscillation of AFwi-wi continued for 40 to 60 min, and finally settled at ca. —0.40 V. 

Together with active metal electrodes, the membrane electrodes represent the best known ion-selective electrodes (ISEs) however, the membrane type has the advantages of insensitivity to redox agents and surface poisons. As the... 

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