Nanofiltration concentrates

TZW nanofiltration concentrate and tap water appeared to be very corrosive waters for copper with concentrations exceeding 3 mg/1 after 2-hours stagnation. fith these waters, contamination by copper quickly increased in the first months of operation and then stabilised or started to decrease. 

Very high zinc concentrations (>4 to 9 mg/1) were observed after 8 hours stagnation with TZW waters (nanofiltration concentrate, filtrate and tap water) but contamination quickly decreased in the first weeks of operation, th other waters, concentrations were lower and did not exceed 1 mg/1 even for 8-hours stagnation. In order of decreasing corrosivity, ranking of waters was as follows TZW concentrate TZW tap > TZW filtrate > Kiwa LHRSP CRECEP > WRC. 

Except with TZW nanofiltration concentrate, zinc concentrations alw s decreased with operating time, the curves being typically of type 1 (exponential decrease to a minimiun value). The maximum levels of contamination occurred... 

The shape of the ageing curves ([Zn] = /(operating time)) was different with TZW nanofiltration concentrate and cannot be described by a simple shape (type 1, 2 or 3). Figure 4.13 shows a comparison between the evolution of zinc concentration (after 8 hours stagnation) and pH of water. Parallel evolution can be seen an increase in pH corresponds to a decrease in zinc. Thus, it appears very likely that variations in zinc concentration is due essentially to changes in water quality (pH, but probably also temperature, oxygen or other parameters) and not (only ) to ageing of the material. 

Figure 4.13 Comparison of zinc and pH evolution with operating time for galvanized steel rig with TZW nanofiltration concentrate water...

Stainless steel Chromium, nickel and iron have been analysed. For iron, all results were very low and most of them are near detection limits or do not significantly differ from the noise (iron in the test waters). For chromium, all results were below the detection limits of the analytical methods except for one 25 igl after 1 hour s stagnation on d 637. These were both with TZW nanofiltration concentrate. 

For nickel, only two results exceeded 10 igl 16 (xg/1 after 30 minutes stagnation on d 69,37 (xg/1 after 1 hour s stagnation on d 637, both with TZW nanofiltration concentrate. These isolated points cannot be interpreted as real contamination from the material, as all other results were below 5 igl. ... 

Nanofiltration concentrating ammonium succinate and removing low-molecular-weight nonionic and monovalent impurities (e.g., sugars and acetate)... 

Atkinson S. Nanofiltration concentrates coloured wastewater and produces potable water. Membr Technol 2002 2002(7) ll-2. 

The individual membrane filtration processes are defined chiefly by pore size although there is some overlap. The smallest membrane pore size is used in reverse osmosis (0.0005—0.002 microns), followed by nanofiltration (0.001—0.01 microns), ultrafHtration (0.002—0.1 microns), and microfiltration (0.1—1.0 microns). Electro dialysis uses electric current to transport ionic species across a membrane. Micro- and ultrafHtration rely on pore size for material separation, reverse osmosis on pore size and diffusion, and electro dialysis on diffusion. Separation efficiency does not reach 100% for any of these membrane processes. For example, when used to desalinate—soften water for industrial processes, the concentrated salt stream (reject) from reverse osmosis can be 20% of the total flow. These concentrated, yet stiH dilute streams, may require additional treatment or special disposal methods. 

Whey concentration, both of whole whey and ultrafiltration permeate, is practiced successfully, but the solubility of lactose hmits the practical concentration of whey to about 20 percent total sohds, about a 4x concentration fac tor. (Membranes do not tolerate sohds forming on their surface.) Nanofiltration is used to soften water and clean up streams where complete removal of monovalent ions is either unnecessary or undesirable. Because of the ionic character of most NF membranes, they reject polyvalent ions much more readily than monovalent ions. NF is used to treat salt whey, the whey expressed after NaCl is added to curd. Nanofiltration permits the NaCl to permeate while retaining the other whey components, which may then be blended with ordinaiy whey. NF is also used to deacidify whey produced by the addition of HCl to milk in the production of casein. 

Membrane Characterization Membranes are always rated for flux and rejection. NaCl is always used as one measure of rejection, and for a veiy good RO membrane, it will be 99.7 percent or more. Nanofiltration membranes are also tested on a larger solute, commonly MgS04. Test results are veiy much a function of how the test is run, and membrane suppliers are usually specific on the test conditions. Salt concentration will be specified as some average of feed and exit concentration, but both are bulk values. Salt concentration at the membrane governs performance. Flux, pressure, membrane geome-tiy, and cross-flow velocity all influence polarization and the other variables shown in Fig. 22-63. 

The separation of homogeneous catalysts by means of membrane filtration has been pioneered by Wandrey and Kragl. Based on the enzyme-membrane-reactor (EMR),[3,4] that Wandrey developed and Degussa nowadays applies for the production of amino acids, they started to use polymer-bound ligands for homogeneous catalysis in a chemical membrane reactor (CMR).[5] For large enzymes, concentration polarization is less of an issue, as the dimension of an enzyme is well above the pore-size of a nanofiltration membrane. 

The first SRS unit was built as a demonstration plant and has been in operation since September 1997. The basic principle of operation is that a solution of sodium chloride and sodium sulphate in contact with a nanofiltration membrane at high pressure, will separate into a sulphate-lean permeate stream and a sulphate-rich concentrate stream. 

It was expected that sulphate removal from sodium bromide solutions would be very similar to sulphate removal from sodium chloride. Experimentation was carried out to determine sulphate rejection, membrane permeability and membrane stability in concentrated sodium bromide. The experimental work determined that nanofiltration is a useful process for separating these materials. 

Twardowski, Z. (1996) Nanofiltration of Concentrated Salt Solutions. United States Patent No. 5,587,083. 

Dendritic catalysts can be recycled by using techniques similar to those applied with their monomeric analogues, such as precipitation, two-phase catalysis, and immobilization on insoluble supports. Furthermore, the large size and the globular structure of the dendrimer can be utilized to facilitate catalyst-product separation by means of nanofiltration. Nanofiltration can be performed batch wise or in a continuous-flow membrane reactor (CFMR). The latter offers significant advantages the conditions such as reactant concentrations and reactant residence time can be controlled accurately. These advantages are especially important in reactions in which the product can react further with the catalytically active center to form side products. 

There are reports of numerous examples of dendritic transition metal catalysts incorporating various dendritic backbones functionalized at various locations. Dendritic effects in catalysis include increased or decreased activity, selectivity, and stability. It is clear from the contributions of many research groups that dendrimers are suitable supports for recyclable transition metal catalysts. Separation and/or recycle of the catalysts are possible with these functionalized dendrimers for example, separation results from precipitation of the dendrimer from the product liquid two-phase catalysis allows separation and recycle of the catalyst when the products and catalyst are concentrated in two immiscible liquid phases and immobilization of the dendrimer in an insoluble support (such as crosslinked polystyrene or silica) allows use of a fixed-bed reactor holding the catalyst and excluding it from the product stream. Furthermore, the large size and the globular structure of the dendrimers enable efficient separation by nanofiltration techniques. Nanofiltration can be performed either batch wise or in a continuous-flow membrane reactor (CFMR). 

Nanofiltration membranes usually have good rejections of organic compounds having molecular weights above 200—500 (114,115). NF provides the possibility of selective separation of certain organics from concentrated monovalent salt solutions such as NaCl. The most important nanofiltration membranes are composite membranes made by interfacial polymerization. Polyamides made from piperazine and aromatic acyl chlorides are examples of widely used nanofiltration membrane. Nanofiltration has been used in several commercial applications, among which are demineralization, oiganic removal, heavy-metal removal, and color removal (116). 

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,... 

As an example, by referring to an IE or ED de-ashing unit with an overall capacity of 45 m3/day of nanofiltrated whey (three times concentrated and partially desalted), Greiter et al (2002) estimated that the cumulative energy... 

Many nanofiltration membranes follow these rules, but oftentimes the behavior is more complex. Nanofiltration membranes frequently combine both size and Donnan exclusion effects to minimize the rejection of all salts and solutes. These so-called low-pressure reverse osmosis membranes have very high rejections and high permeances of salt at low salt concentrations, but lose their selectivity at salt concentrations above 1000 or 2000 ppm salt in the feed water. The membranes are therefore used to remove low levels of salt from already relatively clean water. The membranes are usually operated at very low pressures of 50-200 psig. 

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