Nanofilters

Nanofilters incorporate negative membrane charge for higher anion rejection. High feed salinities can passivate these charges and reduce anion retention. 

Northeastern University has worked on a high-density storage system based on the absorption powers of carbon nanofilters. This form of storage could make direct-hydrogen cars practical. The National University in Singapore has had some encouraging results in this area. 

Fig. 10. The application of 7c as catalyst for the Kharasch addition of methyl methylacrylate and carbon tetrachloride in a CFMR using a SelRO-MPF-50 nanofiltation membrane. (Residence time (or cycle) is 43 min) (26).

Chloride, sulfate, and other anions may affect the removal of arsenic by nanofiltration. The effects often depend on the composition of the nanofilter. Specifically, increasing NaCl concentrations actually improves arsenic removals with polyamide thin-film composite filters. On the other hand, NaCl solutions may interfere with the removal of arsenic with sulfonated polysulfone thin-film composite nanofilters (Shih,... 

Nanofilters are used to purity groundwater in Manitoba, Canada Digital videodisk recorders (DVRs) are introduced IBM develops the smallest light-emitting transmitter, comprised of carbon nano tubes (CNTs)... 

The preparation of the required microporous ceramic layers is possible by the sol-gel route from stable colloidal dispersions with individual nanoparticles of less than 10 nm. Different types of ceramic nanofilters have been prepared from such aqueous or organic sols of the following oxides y-alumina, zirconia, ° hafnia," and titania. ... 

Due to the amphoteric behavior of the used oxides, the separative properties of these ceramic nanofilters for ionic solutes in aqueous solutions will depend on both sieving and electrical effects. Complex electrokinetic phenomena occur during the forced flow of the ionic solutions through the confined volume of the micropores because the thickness of the double layer formed on the charged pore surface and the pore size have the same order of magnitude. Figure 25.3 illustrates... 

FIGURE 25.2 Electron microscope images of a zirconia nanofilter, (a) SEM cross-section view of the multilayer asymmetric structure with the thin zirconia top layer, (b) Transmission electron microscope (TEM) surface view of the sintered packing of 5 nm to 10... 

FIGURE 25.3 (a) HfOj electrophoretic mobility vs. pH in ICH M Na2S04 and CaCl2 solntions (b) Na2S04 and CaClj rejections versns pH nsing a hafnia nanofilter. (From Blanc, R, Larbot, A., Palmeri, J., Lopez, M., and Cot, L., J. Membr. Set, 149, 151, 1998.)... 

The porous structure of ceramic supports and membranes can be first described using the lUPAC classification on porous materials. Thus, macroporous ceramic membranes (pore diameter >50 nm) deposited on ceramic, carbon, or metallic porous supports are used for cross-flow microfiltration. These membranes are obtained by two successive ceramic processing techniques extrusion of ceramic pastes to produce cylindrical-shaped macroporous supports and slip-casting of ceramic powder slurries to obtain the supported microfiltration layer [2]. For ultrafiltration membranes, an additional mesoporous ceramic layer (2 nm<pore diameter <50 nm) is deposited, most often by the solgel process [11]. Ceramic nanofilters are produced in the same way by depositing a very thin microporous membrane (pore diameter <2 nm) on the ultrafiltration layer [4]. Two categories of micropores are distinguished the supermicropores >0.7 nm and the ultramicropores <0.7 nm. 

As the newest development of the liquid filtration family, nanofiltration (NF) is capable of retaining small molecules from 200 to 1000 Da, and multivalent ions. The main current applications of NF polymeric membranes are dealing with the production of drinking and process water, the sulphate removal of seawater or the desalination of cheese whey. Ceramic nanofilters were... 

Lefebvre X, Palmeri J, Sandeaux J, Sandeaux R, David P, Maleyre B, Guizard C, Amblard P, Diaz J-F, and Lamaze B. Nanofiltration modelling A comparative study of the salt filtration performance of a charged ceramic membrane and an organic nanofilter using the computer simulation program NANOFLUX. Sep. Purif. Technol. 2003 32(1-3) 117-126. 

Inorganic membranes are very resistant and quite stable at hard-operating conditions. Several materials are available. Different membranes have been successfully tested for separations involving supercritical fluids such as tubular carbon membranes [ 1 ], mbular silica membranes [2-5], silica hollow fibber membranes [6], zeolite membranes [7-10], titane-nafion membranes [11], polycarbonate membrane [12], nanofilter having a thin layer of Zr02-Ti02 [12], and silicalite membranes [4]. 

Transfer mechanisms involved in SC CO2 permeation through such porous membranes can be convection (Poiseuille law), diffusion (Knudsen flow), and surface membrane interaction by adsorption, capillary condensation, etc. [11]. Mechanisms have been specifically investigated for nanofiltration and zeolite membranes. With a nanofilter presenting a pore diameter of about 1 nm, Sarrade [11] mentioned a Poiseuille flow associated with an irreversible CO2 adsorption on the micropore wall. Transfer... 

FIGURE 7.2 Caffeine rejection rate (o) and permeability constant ( ) obtained during caffeine/SC CO2 separation on a nanofilter having a thin layer of Zr02-Ti02 ( = 308 K, transmembrane pressure = 0.2 MPa). Values of estimated cluster size for each experimental point are indicated. (Adapted from Chiu, Y.-W. and Tan, C.-S., J. Supercrit. Fluids, 21, 81, 2001.)... 

FIGURE 35.2 Size and charge effects on the retention of various lump parameters when paper miU total effluent was nanofiltered (Desal-5 DK membrane) at different pH. (Adapted from Manttari, M., Nuortila-Jokinen, J., and Nystrdm, M., J. Membr. Sci., 137, 187, 1997.)... 

Diafiltration Diafiltration [17] is a step in addition to nanofiltration wherein the retentate is further diluted with water and re-nanofiltered to reduce further the soluble components and concentrate further the retained components. 

Schulman S, Wallensten R, White B, Smith OP. Efficacy of a high purity, chemically treated and nanofiltered factor IX concentrate for continuous infusion in haemophilia patients undergoing surgery. Haemophilia 1999 5(2) 96-100. 

Finally, microfilters are described as part of the microchannel system in order to assist sample preparation. Channels with diameters less than 30 /rm can easily be blocked by particulates in the sample, or crystals formed in solutions held in a micro-reservoir. While prefiltration outside of the microchannel system can separate most particles out of the sample solution prior to addition to the biosensor system, volumes required for macrofiltration are much larger than the volume finally applied to the biosensor. In addition, crystal or aggregate formation inside the channel cannot be avoided. Thus, the use of microfilters inside the microchannel system will be an important element in miniaturized biosensors. Filters have been described for trapping cells from blood [53], percolation filters for filtering solvents containing particulate materials ranging from dust to cells [54], and nanofilters that can separate particles as small as 44 nm [55]. 

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