Osmosis properties

A. Yarshuk, E. Staude. Charged membranes for low pressure reverse osmosis properties and applications. Desalination 55 115, 1992. 

In summary, the NS-300 membrane system actually comprises a family of membranes, with reverse osmosis properties determined by the isophthallc trimesic ratio. Exceptionally high fluxes are possible at high retentivity levels for dissolved salts containing polyvalent anions. This membrane type may find applications in the desalination of brackish sulfate ground waters or industrial... 

McKinney et al. 49,50) described the reverse osmosis properties of asymmetric membranes prepared from the following polyamides and polyamide-hydrazides (7, 8, or 9). 

Reverse osmosis properties of the membranes composed of cellulose acetate phthalate and PVPo are summarized in Table 18484. Table 18 reveals the rejection decreases as the values of solubility parameters (<5) of the membrane and of the solute approach one another. 

It can also be done by analysis of reverse osmosis properties of a membrane as a function of the effective driving pressure according to the relationship developed by Yasuda and Lamaze [11]. Salt rejection is a result of transport depletion of salt in... 

Following a brief review of the development of dynamic membranes and an overview of the current state of the art, Spencer (10) discusses dynamic polyblend membranes. In particular, he looks at the Influence that polymer selection and membrane preparation procedures have on membrane performance. Dynamic membranes composed of a poly(acrylic acid)/basic polyamine blend deposited on a ZOSS (hydrous zirconium oxide on stainless steel) ultrafiltration membrane are discussed. Their hyperfiltration or reverse osmosis properties are compared to the more traditional ZOPA (zirconium oxide plus poly(acrylic acid)) membrane. 

Table 5.5 Reverse Osmosis Properties of Interfacial Membranes Formed of Piperazine Oligomers and Isophthaloyl Chloride...

Yasuda obtained membranes with good reverse osmosis properties by polymerizing gas plasma mixtures of acetylene/water/nitrogen and acetylene/wa-ter/carbon monoxide.92 9J Elemental analysis of the acetylene/water/nitrogen membrane was not given, but it was likely approximately equivalent to the allyl-amine-derived composition. Yasuda has observed membrane performance levels as high as 99% salt rejection and 38 gfd, tested on 3.5% sodium chloride at 1,500 psi. 

Grafting and reverse osmosis properties of styrene 2-vinylpyridine-grafted cellulose acetate... 

The reverse osmosis properties of the grafted films are presented in Tables I and II and in Figures 3 and 4. The results are most interesting in that the flux could be increased considerably, up to ten fold in the best case, while maintaining the salt rejection at a similar level to that of unmodified dense cellulose acetate. This was accomplished by the copolymerization of 2-vinyl pyridine and styrene or methyl methacrylate followed by quatemization. The full development of these findings would need the additional development of assymetric or ultra thin membranes from these materials. 

Fig. 3. Reverse osmosis properties of styrene-2-vinyl pyridine grafted cellulose acetate membranes as i function of the 2-vinyl pyridine content. Approximately 30% graft. 0.5% NcCl - 800 psi.

Reverse osmosis properties of grafted polyvinyl chloride films... 

SEM photomicrograph of a four-layer TiOj membrane. Thin layer on left i.s a ceramic skin with ullrafiltration and reverse osmosis properties. The other three layers form a microfillraiion system. From Haggin [2491 reporting on membranes prepared by Uhlhorn. 

Chem. Analysis 44.5-45.5% total solids, 42% act. solids Uses Scale inhibitor, dispersant for silica and magnesium silicate scale control for cooling water treatment, boiler treatment, geothermal wells, reverse osmosis Properties Dk. yel. to brn. cl. sol n. mild odor m.w. 5000 sp.gr. 1.2 dens. 10 lb/ gal vise. 400 cps pH 2.1-2.6... 

In other areas, POD has been used to improve the wear resistance of a mbber latex binder by incorporation of 25% of Oksalon fibers. Heat-resistant laminate films, made by coating a polyester film with POD, have been used as electrical insulators and show good resistance to abrasion and are capable of 126% elongation. In some instances, thin sheets of PODs have been used as mold release agents. For this appHcation a resin is placed between the two sheets of POD, which is then pressed in a mold, and the sheets simply peel off from the object and mold after the resin has cured. POD-based membranes exhibit salt rejection properties and hence find potential as reverse osmosis membranes in the purification of seawater. PODs have also been used in the manufacturing of electrophotographic plates as binders between the toner and plate. These improved binders produce sharper images than were possible before. 

Although these composite fibers were developed for reverse osmosis their acceptance in the desalination industry has been limited due to insufficient selectivity and oxidative stabiUty. The concept, however, is extremely viable composite membrane fiat films made from interfacial polymerisation (20) have gained wide industry approval. HoUow fibers using this technique to give equivalent properties and life, yet to be developed, should be market tested during the 1990s. 

Membranes and Osmosis. Membranes based on PEI can be used for the dehydration of organic solvents such as 2-propanol, methyl ethyl ketone, and toluene (451), and for concentrating seawater (452—454). On exposure to ultrasound waves, aqueous PEI salt solutions and brominated poly(2,6-dimethylphenylene oxide) form stable emulsions from which it is possible to cast membranes in which submicrometer capsules of the salt solution ate embedded (455). The rate of release of the salt solution can be altered by surface—active substances. In membranes, PEI can act as a proton source in the generation of a photocurrent (456). The formation of a PEI coating on ion-exchange membranes modifies the transport properties and results in permanent selectivity of the membrane (457). The electrochemical testing of salts (458) is another possible appHcation of PEI. 

Nonporous Dense Membranes. Nonporous, dense membranes consist of a dense film through which permeants are transported by diffusion under the driving force of a pressure, concentration, or electrical potential gradient. The separation of various components of a solution is related directiy to their relative transport rate within the membrane, which is determined by their diffusivity and solubiUty ia the membrane material. An important property of nonporous, dense membranes is that even permeants of similar size may be separated when their concentration ia the membrane material (ie, their solubiUty) differs significantly. Most gas separation, pervaporation, and reverse osmosis membranes use dense membranes to perform the separation. However, these membranes usually have an asymmetric stmcture to improve the flux. 

Cellulose acetate Loeb-Sourirajan reverse osmosis membranes were introduced commercially in the 1960s. Since then, many other polymers have been made into asymmetric membranes in attempts to improve membrane properties. In the reverse osmosis area, these attempts have had limited success, the only significant example being Du Font s polyamide membrane. For gas separation and ultrafUtration, a number of membranes with useful properties have been made. However, the early work on asymmetric membranes has spawned numerous other techniques in which a microporous membrane is used as a support to carry another thin, dense separating layer. 

Reverse osmosis membrane separations are governed by the properties of the membrane used in the process. These properties depend on the chemical nature of the membrane material, which is almost always a polymer, as well as its physical stmcture. Properties for the ideal RO membrane include low cost, resistance to chemical and microbial attack, mechanical and stmctural stabiHty over long operating periods and wide temperature ranges, and the desired separation characteristics for each particular system. However, few membranes satisfy all these criteria and so compromises must be made to select the best RO membrane available for each appHcation. Excellent discussions of RO membrane materials, preparation methods, and stmctures are available (8,13,16-21). 

Reverse Osmosis. A reverse osmosis (RO) process has been developed to remove alcohol from distilled spirits without affecting the sensory properties (14). It consists of passing barrel-strength whiskey through a permeable membrane at high pressure, causing the alcohol to permeate the membrane and concentrating the flavor components in the retentate. 

Behavior. Diffusion, Brownian motion, electrophoresis, osmosis, rheology, mechanics, and optical and electrical properties are among the general physical properties and phenomena that are primarily important in coUoidal systems (21,24—27). Of course, chemical reactivity and adsorption often play important, if not dominant, roles. Any physical and chemical feature may ultimately govern a specific industrial process and determine final product characteristics. 

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