Nanofiltration applications

Figure 5.8 Membranes based on sulfonated polysulfone and substituted poly(vinyl alcohol) are produced by Hydranautics (Nitto) for nanofiltration applications...

FIGURE 30 Performance of some commercial reverse osmosis membranes for (a) seawater desalination (test conditions 56 bar 25°C 3.5% NaCI feed) (b) low-pressure desalination (15 bar 25°C 1500 mg/liter NaCI feed) and (c) ultralow-pressure nanofiltration applications (7.5 bar, 25°C 500 mg/liter NaCI feed). 

M. Pontie, H. Buisson, C.K. Diawara, H. Essis-Tome, Studies of halide ions mass transfer in nanofiltration - application to selective defluorination of brackish water, Desalination 157 (2003) 127-134. 

A. Lhassani, M. Rumeau, D. Benjelloun, M. Pontie, Selective demineralisation of water by nanofiltration application to the defluoridation of brackish water, Water Res. 

Membranes having effective pore sizes between 0.001 and 0.01 pm are used in nanofiltration. NF is placed between reverse osmosis and ultrafiltration, and because of that it is sometimes considered as loose reverse osmosis. Typical operating pressures for NF are 0.3-1.4 MPa. The process allows to separate monovalent ions from multivalent ions, which are retained by NF membrane. The process can be used for separation of organic compounds of moderate molecular weight from the solution of monovalent salts. The very well-known application in nuclear industry is boric acid recovery from contaminated cooling water in nuclear reactor. There are some examples of nanofiltration applications and studies done with the aim of implementation in nuclear centers described in literature. Some of them are listed in the Table 30.4. 

Nanohybrid materials have been furthermore used for ultra-/nanofiltration applications. Nanofiltration is a pressure-driven membrane separation process and can be used for the production of drinking water as well as for the treatment of process and waste waters. Some apphcations are desalination of brackish water, water softening, removal of micropollutants, and retention of dyes. Ultrafiltration membranes based on polysulfones filled with zirconia nanoparticles are usually prepared via a phase-inversion technique and have been used since 1990 [328]. Various studies were done in order to assess the effect of the addition of Zr02 to polysulfone-based ultrafiltration membranes [329] and the influence of filler loading on the compaction and filtration properties of membranes. The results indicate that the elastic strain of the nanohybrid membranes decreases and the time-dependent strain... 

Lhassani, L., Rumeau, M., Benjelloun, D. Pontie, M. (2001) Selective demineralization of water by nanofiltration application to the defluorination of brackish water. Water Research, 35, 3260-3264. 

T. Courtois, U Nanofiltration Applications Workshop, Shawinigan, Canada, (1997), 60. 

Aromatic Polyamides as Reverse Osmosis and Nanofiltration Application... 

This chapter is concluded therefore with the following statement. Although membranes with electric charges are well established in reverse osmosis and nanofiltration applications, the fundamental aspects of membrane formation and membrane transport are still in its infant stage. 

One of the main applications of dendrimers is in catalysis allowing easy recycling of the homogeneous catalyst by means of nanofiltration. Carbosilane dendrimers functionalized with diphenylphosphine groups at the periphery have been synthesized and characterized. Palladium complexes of these dendrimers have been used as catalysts in the allylic alkylation reaction. These dendrimeric catalysts can be used in a continuous process using a membrane reactor.509... 

Commercial dead-end filtration cells are available from Millipore [12] suitable for ultrafiltration (Figure 4.4, e.g. model 8003 and 8010) and from Schleicher Schuell [13] (Figure 4.5) applicable for ultra- and nanofiltration. 

In the field of membrane filtration, a distinction is made based upon the size of the particles, which are retained by the membrane. That is micro-, ultra-, nanofiltration and reverse osmosis. Figure 4.8 shows a schematic picture of the classification of membrane processes. The areas of importance for application with homogeneous catalysts are ultra- and nanofiltration, depicted in gray. 

In Table 4.3, a selection of inorganic membrane suppliers is given. Very little data are available on applications in catalysis so far. The membranes can be used for separation in the ultra- or nanofiltration range. 

Reverse osmosis membrane process, 27 637 Reverse osmosis membrane cleaning citric acid application, 6 647 Reverse-osmosis membranes, 75 811, 825 development of, 75 797 Reverse osmosis models, 27 638-639 Reverse osmosis permeators, 76 19 Reverse osmosis seawater desalination process, 26 85 Reverse osmosis systems blending in, 26 80-81 brackish and nanofiltration, 26 80-83 Reverse osmosis technology... 

In the recent years, many researchers have devoted attention to the development of membrane science and technology. Different important types of membranes, such as these for nanofiltration, ultrafiltration, microfiltration, separation of gases and inorganic membranes, facilitated or liquid membranes, catalytic and conducting membranes, and their applications and processes, such as wastewater purification and bio-processing have been developed [303], In fact, almost 40 % of the sales from membrane production market are for purifying wastewaters. 

We will discuss here applications of polyelectrolyte-modified electrodes, with particular emphasis on layer-by-layer self-assembled redox polyelectrolyte multilayers. The method offers a series of advantages over traditional technologies to construct integrated electrochemical devices with technological applications in biosensors, electrochromic, electrocatalysis, corrosion prevention, nanofiltration, fuel-cell membranes, and so on. 

In the search to develop new materials for immobilization of homogeneous transition metal catalyst to facilitate catalyst-product separation and catalyst recychng, the study of dendrimers and hyperbranched polymers for application in catalysis has become a subject of intense research in the last five years [68], because they have excellent solubility and a high number of easily accessible active sites. Moreover, the pseudo-spherical structure with nanometer dimensions opens the possibility of separation and recycling by nanofiltration methods. Although dendrimers allow for controlled incorporation of transition metal catalysts in the core [69] as well as at the surface [70], a serious drawback of this approach is the tedious preparation of functionalized dendrimers by multi-step synthesis. 

Generally, a distinction can be made between membrane bioreactors based on cells performing a desired conversion and processes based on enzymes. In ceU-based processes, bacteria, plant and mammalian cells are used for the production of (fine) chemicals, pharmaceuticals and food additives or for the treatment of waste streams. Enzyme-based membrane bioreactors are typically used for the degradation of natural polymeric materials Hke starch, cellulose or proteins or for the resolution of optically active components in the pharmaceutical, agrochemical, food and chemical industry [50, 51]. In general, only ultrafiltration (UF) or microfiltration (MF)-based processes have been reported and little is known on the application of reverse osmosis (RO) or nanofiltration (NF) in membrane bioreactors. Additionally, membrane contactor systems have been developed, based on micro-porous polyolefin or teflon membranes [52-55]. 

Xu P, Drewes JE, Bellona C, Amy G, Kim T-U, Adam M, Heberer T (2005) Rejection of emerging organic micropollutants in nanofiltration-reverse osmosis membrane applications. 

M. Pontie, C. Diawara, A. Lhassani, H. Dach, M. Rumeau, H. Buisson, J.C. Schrotter, Water defluoridation processes A review. Application Nanofiltration (NF) for future large-scale pilot plants, in A. Tressaud (Ed.), Advances in Fluorine Science, Vol. 2, Elsevier, Amsterdam, 2006, pp. 49-80. 

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). 

Dendrimers, among other applications, are generating interest as soluble supports thanks to the following intrinsic characteristics (i) the well-defined molecular composition of a dendrimer provides a support with a precisely defined arrangement of the reactive sites, (ii) a high loading of reactive sites is achieved on the dendrimer surface and (iii) nanofiltration techniques are available to separate the dendritic support from products. Dendrimer 143, based on a carbosilane core, possesses 12 ester functionalities on... 

Researchers at Degussa AG focused on an alternative means towards commercial application of the Julia-Colonna epoxidation [41]. Successful development was based on design of a continuous process in a chemzyme membrane reactor (CMR reactor). In this the epoxide and unconverted chalcone and oxidation reagent pass through the membrane whereas the polymer-enlarged organocatalyst is retained in the reactor by means of a nanofiltration membrane. The equipment used for this type of continuous epoxidation reaction is shown in Scheme 14.5 [41]. The chemzyme membrane reactor is based on the same continuous process concept as the efficient enzyme membrane reactor, which is already used for enzymatic a-amino acid resolution on an industrial scale at a production level of hundreds of tons per year [42]. 

Dynamically formed membranes were pursued for many years for reverse osmosis because of their high water fluxes and relatively good salt rejection, especially with brackish water feeds. However, the membranes proved to be unstable and difficult to reproduce reliably and consistently. For these reasons, and because high-performance interfacial composite membranes were developed in the meantime, dynamically formed reverse osmosis membranes fell out of favor. A small application niche in high-temperature nanofiltration and ultrafiltration remains, and Rhone Poulenc continues their production. The principal application is poly(vinyl alcohol) recovery from hot wash water produced in textile dyeing operations. 

Dijkstra, H.P., Ronde, N., van Klink, G.P.M., Vogt, D. and van Koten, G. (2003) Application of a homogeneous dodecakis (NCN—Pd11) catalyst in a nanofiltration membrane reactor under continuous reaction conditions. Adv. Synth. Catal., 345, 364. 

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