Reverse osmosis thin-film composite

GagHatdo P., Adham S., Tmssell R. (1997), Water purification using reverse osmosis thin film composite versus cellulose acetate membranes, Proc. AWW A Membrane Technolog Conference, New Orleans, Feb. 97, 597-608. 

Z.V.P. Murthy, S.K. Gupta, Sodium cyanide separation and parameter estimation for reverse osmosis thin-film composite polyamide membrane,... 

Nataraj, S.K., Hosamani, K.M. and Aminabhavi, T.M. 2009. Nanofiltration and reverse osmosis thin film composite membrane module for the removal of dye and salts from the simulated mixtures, 249 12-17. 

Cellulose acetate, the earhest reverse osmosis membrane, is still widely used. Asymmetric polyamide and thin-film composites of polyamide and several other polymers have also made gains in recent years whereas polysulfone is the most practical membrane material in ultrafiltration appHcations. 

The structure of the so-called "composite" membranes used in reverse osmosis is also much more complex than the conventional, simplistic description of the ultrathin semipermeable film deposited on and supported by a porous substrate. Most of these membranes which exhibit high flux and separation are composed of an anisotropic, porous substrate topped by an anisotropic, ultrathin permselective dense layer which is either highly crosslinked, or exhibits a progressively decreased hydrophilicity toward the surface. The basic difference between the conventional anisotropic (asymmetric) membrane and the thin film composite is that the latter might be... 

Thin-Film Composite Reverse-Osmosis Membranes Origin, Development, and Recent Advances... 

The origin of thin-film-composite reverse osmosis membranes began with a newly formed research institute and one of its first employees, Peter S. Francis. North Star Research and Development Institute was formed in Minneapolis during 1963 to fill a need for a nonprofit contract research institute in the Upper Midwest. Francis was given the mission of developing the chemistry division through support, in part, by federal research contracts. At this time the Initial discoveries by Reid and Breton ( ) on the desalination capability of dense cellulose acetate membranes and by Loeb and Sourlrajan (,2) on asymmetric cellulose acetate membranes had recently been published. Francis speculated that improved membrane performance could be achieved, if the ultrathin, dense barrier layer and the porous substructure of the asymmetric... 

A significant advance was made in the art of thin-film-composite membranes by Cadotte in 1970 with the advent of the NS-lOO membrane ( 5). This reverse osmosis membrane contained an ultrathin aryl-alkyl polyurea formed Insltu on a mlcroporous polysul-... 

In 1977 the North Star membrane research group was spun off by Midwest Research Institute, forming FilmTec Corporation. Two new thin-film-composite reverse osmosis membranes have been under development at FilmTec Corporation since that time, the NS-300 and the FT-30 membranes. 

This thin-film-composite membrane has been found to have appreciable resistance to degradation by chlorine in the feed-water. Figure 2 illustrates the effect of chlorine in tap water at different pH values. Chlorine (100 ppm) was added to the tap water in the form of sodium hypochlorite (two equivalents of hypochlorite ion per stated equivalent of chlorine). Membrane exposure to chlorine was by the so-called "static" method, in which membrane specimens were immersed in the aqueous media inside closed, dark glass jars for known periods. Specimens were then removed and tested in a reverse osmosis loop under seawater test conditions. At alkaline pH values, the FT-30 membrane showed effects of chlorine attack within four to five days. In acidic solutions (pH 1 and 5), chlorine attack was far slower. Only a one to two percent decline in salt rejection was noted, for example, after 20 days exposure to 100 ppm chlorine in water at pH 5. The FT-30 tests at pH 1 were necessarily terminated after the fourth day of exposure because the microporous polysul-fone substrate had itself become totally embrittled by chlorine attack. 

Y. Kamiyama, N. Yoshioka, K. Matsui and E. Nakagome, New Thin-film Composite Reverse Osmosis Membranes and Spiral Wound Modules, Desalination 51, 79... 

R.J. Petersen and J.E. Cadotte, Thin Film Composite Reverse Osmosis Membranes, in Handbook of Industrial Membrane Technology, M.C. Porter (ed.), Noyes Publications, Park Ridge, NJ, pp. 307-348 (1990). 

R.L. Riley, C.E. Milstead, A.L. Lloyd, M.W. Seroy and M. Takami, Spiral-wound Thin Film Composite Membrane Systems for Brackish and Seawater Desalination by Reverse Osmosis, Desalination 23, 331 (1977). 

Nonporous anisotropic, thin-film composite Pervaporation Reverse Osmosis Nanofiltration ... 

The membranes under study are thin-film composite membranes composed of two layers as illustrated in Fig. 3 a thin polyamide film as active layer and a large mesoporous polysulphone as the support layer. The three studied membranes are 2 NF membranes, noted NF90, NF270 and a low-polarization reverse osmosis (LPRO) membrane, noted BW30. All membranes were purchased from Filmtec (DOW, USA) the specifications of the membranes are given in Table 2. The chemical structures of the support and active layer materials are reported in Fig. 4 [86], Polyamide material is the more used but some authors have reported results... 

Fig. 12. A spkal-wound reverse osmosis membrane element (a) schematic depiction (b) cross section of a spiral-wound thin-film composite RO Fikntec...

Universal Oil Products (UOP) developed reverse osmosis equipment for demineralization of brackish and seawater using composite membranes with a polyamide as the functional coating. The UOP products carry a "TFC" registered trademark. Another good example of a thin-film composite membrane involving a thin film of polyamide as the functional coating is the FilmTec FT-30 membrane for RO (21). 

The list of polymer membrane materials is virtually endless insofar as possiljle chemical varieties are concerned (37 ). However, the number of fundamental physical structures into which they may be formed is much more limited. For present purposes, a distinction is made between skinned and skinless membranes. However, in view of the substantial and growing evidence cited above for the existence of pores in RO and UF membranes, even this is done with trepidation. Further subdivision results in three types of skinned membrane integrally-skinned ultragel3 integrally-skinned miorogels and nonintegrally-skinned miarogele (that Is, thin film composite membranes). Such skinned membranes are utilized in gas separations, reverse osmosis and ultrafiltration. 

M., "Recent Developments in Thin-Film Composite Reverse Osmosis Membrane Systems." Desalination. 1981, 36, 207-233. 

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. 

The thin film composite membrane exhibited superior overall rejection performance in these tests, with ammonia and nitrate rejection showing an outstanding improvement. It has also been reported that silica rejection by the thin film composite membranes is superior to that of cellulose acetate. While the above data indicates a marginal improvement in the rejection of chemical oxygen demand (COD), which is an indication of organic content, other tests conducted by membrane manufacturers show that the polyurea and polyamide membrane barrier layers exhibit an organic rejection that is clearly superior to that of cellulose acetate. Reverse osmosis element manufacturers should be contacted for rejection data on specific organic compounds. ... 

Thin Film Composite Reverse Osmosis Membranes... 

A thin film composite reverse osmosis membrane can be defined as a multilayer membrane in which an ultrathin semipermeable membrane layer is deposited on a preformed, finely microporous support structure. This contrasts with asymmetric reverse osmosis membranes in which both the barrier layer and the porous substructure are formed in a single-step phase inversion process and are integrally bonded. 

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. 

The term "thin film composite" has the connotation that the barrier layer is extremely thin, and hence quite fragile. Indeed, the barrier layer may be quite thin, varying to as low as 200 angstroms depending on the nature of the particular reverse osmosis membrane and its method of manufacture. But this does not necessarily result in fragility. Some of these membranes may be considerably... 

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