Membrane crystallization

Low resolution models (20-30 A) based on diffraction analysis of membrane crystals of Na,K-ATPase [34,35,39] and Ca-ATPase [40,41] show that the cytoplasmic protrusions of the proteins are remarkably similar. A notable difference is a 10-20 A... 

As documented in Chapter 5, zeolites are very powerful adsorbents used to separate many products from industrial process steams. In many cases, adsorption is the only separation tool when other conventional separation techniques such as distillation, extraction, membranes, crystallization and absorption are not applicable. For example, adsorption is the only process that can separate a mixture of C10-C14 olefins from a mixture of C10-C14 hydrocarbons. It has also been found that in certain processes, adsorption has many technological and economical advantages over conventional processes. This was seen, for example, when the separation of m-xylene from other Cg-aromatics by the HF-BF3 extraction process was replaced by adsorption using the UOP MX Sorbex process. Although zeolite separations have many advantages, there are some disadvantages such as complexity in the separation chemistry and the need to recover and recycle desorbents. 

Adsorptive separation is a powerful technology in industrial separations. In many cases, adsorption is the only technology available to separate products from industrial process streams when other conventional separation tools fail, such as distillation, absorption, membrane, crystallization and extraction. Itis also demonstrated that zeolites are unique as an adsorbent in adsorptive separation processes. This is because zeolites are crystalline soUds that are composed of many framework structures. Zeolites also have uniform pore openings, ion exchange abiUty and a variety of chemical compositions and crystal particle sizes. With the features mentioned, the degree of zeoUte adsorption is almost infinite. It is also noted that because of the unique characteristics of zeoHtes, such as various pore openings, chemical compositions and structures, many adsorption mechanisms are in existence and are practiced commercially. 

In 2002, Drioli and coworkers (304) investigated a process for obtaining protein crystals by means of membrane crystallization, which actually combines membrane distillation and crystallization techniques. The solvent evaporates at the membrane interface, migrates through the pores of the membrane, and condenses on the opposite side of the membrane. The reported preliminary results indicate interesting potentialities of this new method with respect to macromole-cular crystallization. 

Lisitzin, D., Hasson, D. and Semiat, R.(June 2006) Membrane crystallizer for increased desalination recovery, ECI -Advanced Membranes Technology III. Membrane Engineering for Process Intensification, Cetraro, Calabria, Italy. Awerbuch, L. (1997) Dual purpose power desalination/hybrid systems/energy and economics. IDA Desalination Seminar, Cairo, Egypt. 

Membrane crystallization (MCr) has been recently proposed as one of the most interesting and promising extensions of the MD concept [13]. 

Figure 12.3 Flow sheet of an integrated desalination system utilizing membrane crystallization units (IS5, Ref. 10).

Figure 20.7 NaCI crystals obtained in a membrane crystallizer (magnification xlO) (From Ref. [26].)...

Table 5.10 summarizes the presently available electrodes categorized as glass, ion-exchange membrane, crystal membrane, and liquid membrane. These electrodes can be used either for direct potentiometric measurements of ionic activity after calibration of the Nemst expression for the particular electrode or to monitor a potentiometric titration when a selected reaction that involves the monitored ion is available. Table 5.10 also indicates the common interfering ions. Several instrument companies are endeavoring to develop potentiometric-membrane electrodes to monitor directly ions in body fluids. 

Figure 12. Three-dimensional structures of Na+-K+-ATPase and Ca2+-ATPase based on image reconstruction analysis of electron microscopic data obtained from two-dimensional membrane crystals, (a). Na+-K+-ATPase molecule consisting of one a-subunit and one p-subunit. The horizontal arrows indicate a tentative location of the membrane surfaces (upper arrow cytoplasmic surface lower arrow extracellular surface suggested membrane thickness 39 A). Data from Hebert et al., 1988. (b). Ca2+-ATPase molecule consisting only of a catalytic subunit. A tentative location of the transmembrane helices (M1-M10) is indicated. The cytoplasmic part (head) is pointing upwards. In this study, the membrane (sarcoplasmic reticulum) was found to be only 32 A thick (surfaces indicated by shaded areas). Modified from Toyoshima et al., 1993. 

Hebert, H Skriver, E., Soderholm, M., Maunsbach, A.B. (1988). Three-dimensional structure of renal Na,K-ATPase determined from two-dimensional membrane crystals of the pi form. J. Ultrastruct. Mol. Struct. Res. 100, 86-93. 

Hovm ller, S., Leonard, K., and Weiss, H., 1981, Membrane crystals of a subunit complex of mitochondrial cytochrome reductase containing the cytochromes b and cl, FEBS Lett. 123 118nl22. 

Karlsson, B., Hovmoller, S., Weiss, H., and Leonard, K., 1983, Structural studies of cytochrome reductase. Subunit topography determined by electron microscopy of membrane crystals of a subcomplex, J. Mol. Biol. 165 2878302. 

A novel idea for the production of water is by the combination of MD and membrane crystallization [ 139], where the salt is concentrated on the feed side to a point close to super-samration, thereby inducing nucleation of crystals. Recently Gryta and Morawski [140] performed experiments using polypropylene capillary membranes with pore diameters ranging between 0.2 and 0.6 p.m, and 70% porosity. They found crystallization to occur at the membrane surface, but by increasing the distillate temperature to 328 K, the problem was eliminated and stable flux restored. 

Membrane contactors (MCs) represent another interesting frontier in the application of membrane technology in seawater desalination. Gas-liquid application for addition/extraction of selected gasses or operation like membrane crystallization has been recognized in some new experimental works, as important ways for improve efficiency and get some advantages for the overall desalination processes [5,6]. 

An innovative potential application of membrane technology in catalysis and in CMRs might be the possibility to produce catalytic crystals with a well-dehned size, size distribution, and shape by membrane crystallization [19,20] (Figure 43.5). Membrane crystallization is particularly attractive for the preparation of heat-sensitive catalysts such as enzymes. 

Membrane crystallizers, membrane emulsifiers, membrane strippers and scrubbers, membrane distillation systems, membrane extractors, etc. can be devised and integrated in the production lines together with the other existing membranes operations for advanced molecular separation, and chemical transformations conducted using selective membranes and membrane reactors, overcoming existing limits of the more traditional membrane processes (e.g., the osmotic effect of concentration by reverse osmosis). 

Di Profio, G., Curcio, E., and Drioh, E., Membrane crystallization of lysoz3mie Kinetic aspects, J. Cryst. Growth, 257, 359, 2003. 

Membrane Crystals—Aurantii Dulcis Cortex, Limonis Cortex, Condurango. 

Membrane crystals are monoclinic prisms, each of which is surrounded by a wall or membrane. In the process of formation a crystal first is formed in the cell sap and then numerous oil globules make their appearance in the protoplasm surrounding it later some of the walls of the cell grow around the crystal and completely envelop it. 

Fig, 6. Graphical representation of two types of membrane-protein crystals. Type 1 crystal consists of stacks of two-dimensional crystalline membranes ordered in the third dimension to form the "membrane crystal. Type 11 crystals are formed by membrane proteins with the hydrocarbon tails of detergent molecules bound to their hydrophobic surfaces. The hydrophilic surfaces of the protein are indicated by dotted boundaries. Figure source Michel (1983) Crystallization of membrane proteins. Trends Biochem... 

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