Rejection characteristics

B. Production and Rejection Characteristics of S-Layer Ultrafiltration Membranes (SUMs)... 

TABLE 3 Rejection Characteristics of SUMs Prepared of S-Layer-Carrying Cell Wall Fragments from B. sphaericus CCM 2120... 

Thanuttamavong M., K. Yamamoto, J.I. Oh, K.H. Choo, and S.J. Choi (2002). Rejection characteristics of organic and inorganic pollutants by ultra low-pressure nanoliltration of surface water for drinking water treatment. Desalination 145 257-264. 

The model successfully explained the permeation characteristics of the membrane. The rejection curves calculated on the base of the model are presented in Fig. 24. As can be seen, when temperature changes from 25 to 45 °C, the calculated rejection curve shifts to the same extent in molecular weight as the experimental rejection curve. Thus it was verified that the change in the pore structure in the gel controlled the rejection characteristics of the membrane. 

Also, the dense PBI membrane is slow (99%). Although this membrane exhibited, in general, the best rejection characteristics, the very low flux observed is a definite drawback of such dense membranes. 

Another indication of the somewhat complex initial few hours of interaction between membrane and the solutes in the feed solution, that is, the earlier part of the RO run, can be found in Table VII. Here, the rejection characteristics of the membranes after 90 min of permeation are compared with a final value obtained for the feed solution at the end of the RO run. In most cases, the membranes have not reached a saturation or complete equilibration value even after 10-20 mL of solution has been allowed to permeate the membranes. Although the mechanics of interaction between the membrane and the solute requires sufficient time, and such equilibrations may not be significant for extended runs for several weeks, these details should be considered in exploratory work on the RO process. 

PVP has very low systemic toxicity, shows no immime rejection characteristics, and is easily excreted by the kidneys at molecular weights up to 100,000 Da. The pKj of the conjugate acid (PVP H+) is between 0 and 1, and the viscosity of PVP does not change until near pH 1, when it doubles. Therefore the ionic character of the PVP chain should not be appreciable at pharmaceutical or physiologic pH values. However, with ionic cosolutes, anions are bound much more readily than are cations by PVP. 

Both calculations by Perry and Schirg have been performed to describe and to predict the rejection characteristics of organic nanofiltration membranes when ionic and charged molecular solute mixtures are used in the feed solution. Recently experiments were carried out with ceramic nanofilters [67] which showed that similar properties can be obtained. As an example, results concerning the rejection of a dye/electrolyte mixture at pH = 9 through a zirconia nanofilter are reported in Table 12.5. 

In contrast to the polymeric materials for RO and NF membranes, for which the macromolecular structures have much to do with their permeation properties such as salt rejection characteristics, the choice of membrane material for UF does not depend on the material s influence on the permeation properties. Membrane permeation properties are largely governed by the pore sizes and the pore size distributions of UF membranes. Rather, the thermal, chemical, mechanical, and biological stability is considered of greater importance. 

Together, fractional rejection curve (Rjj.) and traditional cut off curve will give more information on the rejection characteristics of ultrafiltration membranes. 

Replacing the ultrafiltration, nanofiltration pretreatment and reverse osmosis by BAHLM processes in desalination industry is the main idea of this proposal. Rejection characteristics of natural organic matters and inorganic salts in a low pressure nanofiltration (e.g., >99% at 1.5 MPa [115]) and capacity of polyanions to complex monovalent and especially bivalent cations [92, 95, 115-117] make this idea promising. 

Thanuttamavong M, Oh JI, Yamamoto K, and Urase T, Comparison between rejection characteristics of natural organic matters and inorganic salts in ultra low pressure nanofiltration for drinking water production. Proceedings of the Conference on Membranes in Drinking and Industrial Water Production. Paris, Prance, October 2000 Desalination Publications, L Aquila, Italy, 2000 Vol. 1, pp. 269-282. 

Before discussing the rejection characteristics of membrane with gel layer, the property of membrane without gel layer should be determined. Various transport equations have been used, some of which are based on the particular mechanism, the others are based on the phenomenology. According to the latter the following equations are presented ( ). 

Rejection characteristics of ultrafiltration membrane were analysed and method to determine the transport coefficients is developed. Also the rejection characteristics of membrane with gel layer were analysed and it is found that the transport coefficients of gel layer have a definite relation with the gel layer resistance, and perhaps with gel layer thickness. 

We believe that for reverse osmosis new membranes with high chemical stability, high temperature resistance, and improved performance rates in respect to rejection characteristics and flux rates are coming on the market very soon in the form of improved thin-film composite membranes. 

Graft copolymers of starch with acrylonitrile and 2-acrylamido-2-methylpropanesulfonic acid, after saponification, were claimed to be good sorbents.3092 A composite of saponified acrylonitrile-starch-copolymer with vinyl formal polymers showed very good salt-rejection characteristics and served as membranes.3093 The same material prepared with poly(vinyl chloride) has been used in gaskets for concrete pipes.3057 Saponified acrylonitrile-starch graft copolymers blended with C12-C16 alcohols provided excellent water-retention characteristics.3094... 

Fabrication of a thin film composite membrane is typically a more expensive route to reverse osmosis membranes because it involves a two-step process versus the one-step nature of the phase inversion film casting method. However, it offers the possibility of each individual layer being tailor-made for maximum performance. The semipermeable coating can be optimized for water flux and solute rejection characteristics. The microporous sublayer can be optimized for porosity, compression resistance and strength. Both layers can be optimized for chemical resistance. In nearly all thin film composite reverse osmosis membranes, the chemical composition of the surface barrier layer is radically different from the chemical composition of the microporous sublayer. This is a common result of the thin film composite approach. 

When furfuryl alcohol was added as a comonomer to the THEIC, water fluxes were increased tenfold. In addition, the extremely high salt rejections characteristic of NS-200 were obtained, while the high organic rejections characteristic of the isocyanurate moiety were retained. A typical patent example of membrane fabrication uses a water solution of 1 2 2 1 weight percent THEIC fur-furyl alcohol sulfuric acid dodecyl sodium sulfate, deposited on microporous polysulfone and cured at 150°C for 15 minutes. This membrane, possessing a thin active layer 100 to 300 angstroms thick, showed 99.9% rejection and 12 gfd flux under seawater test conditions at 1,000 psi. 

Sulfonation of aromatic polymers has been explored as a method to produce hydrophilic polymers with water permeability and salt rejection characteristics. These have been of interest because of their potentially high degree of chlorine resistance. The use of sulfonated aromatic polymers for reverse osmosis membranes began in the late 1960 s with the work of Plummer, Kimura and LaConti of General Electric Company.82 Polyphenylene oxide [poly(2,6-di-... 

These organic rejections, while greatly exceeding the capabilities of cellulose acetate membranes, are not appreciably different than rejection levels exhibited by aromatic polyamide membranes (FT-30, Permasep B-9). Nor do they match the organic rejection characteristics of the PEC-1000 membrane. The Solrox membrane is not resistant to chlorine, and its water flux is somewhat low (about 25 gfd at 650 psi net driving pressure). Consequently, it has not become a significant competitive membrane in the world marketplace. 

If the surface is permeable to the flow as, for example, with a membrane, then there is also a finite flux normal to the surface. The extent to which the species permeates will depend on the rejection characteristics of the membrane, and we shall discuss this boundary condition later in connection with membrane filtration. Here, we suppose the surface to be impermeable so that u = 0, in which case at the reaction surface... 

MF of colloids smaller than the pores and colloid-organic systems Rejection characteristics of fouled membranes... 

It t as found that the flux decline, even at critical fouling conditions is completely avoided by addition of ferric chloride. For large dosages (100 mgL FeCh), an osmotic pressure builds up and this reduces flux reversibly. The positive ferric hydroxide colloids deposit on the membrane and their charge appears to govern rejection. Cation rejection increases considerably, while the rejection of organics decreases. This demonstrates that the deposit on a fouled membrane can change rejection characteristics. 

The Permutit Liberator 1 reverse osmosis unit contains two spiral wound modules of 0.96 m each with Filmtec BW30 membranes, a crosslinked aromatic polyamide. These were selected based on low adsorption and high rejection characteristics. 

Peeters J.M.M., Mulder M.H.V., Keizer K., Strathmann H. (1995), Relation between membrane charge and rejection characteristics of nanofiltration membranes, Proc. of Euromembrane 95, Vol I, 107-112. 

Rios G.M., Sarrade S.J., Carles M. (1995), Rejection characteristics of nanofiltration for small organic and ionic compounds, Proc. of Euromembrane 95, Vol 1,113-118. 

Dobrak A, Verrecht B, Van den Dungen H, Buekenhoudt A, Vankelecom IFJ, and Van der Bruggen B. Solvent flux behavior and rejection characteristics of hydrophihe and hydrophobic mesoporons and microporous TiOj and Zr02 membranes. 7. Membr. Sci. 2010 346 344-352. 

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