Cellulose acetate membranes development

Asymmetric cellulose acetate membrane developed Loeb and Sourirajan -1962... 

The first commercial brackish water RO(BWRO) was on line at the Raintree facility in Coalinga, California. Tubular cellulose acetate membranes developed and prepared at UCLA were used in the facility. Additionally, the hardware for the system was fabricated at UCLA and transported piecemeal to the facility.9... 

Cellulose acetate membranes developed by Loeb and Sourirajan for the purpose of seawater desalination continue to be useful in various membrane applications, despite the development of new membrane materials and new membrane preparation techniques. Because of its historical importance, the casting method of the first successful reverse osmosis membrane is described below in detail. 

Reverse Osmosis. This was the first membrane-based separation process to be commercialized on a significant scale. The breakthrough discovery that made reverse osmosis (qv) possible was the development of the Loeb-Sourirajan asymmetric cellulose acetate membrane. This membrane made desalination by reverse osmosis practical within a few years commercial plants were installed. The total worldwide market for reverse osmosis membrane modules is about 200 million /yr, spHt approximately between 25% hoUow-ftber and 75% spiral-wound modules. The general trend of the industry is toward spiral-wound modules for this appHcation, and the market share of the hoUow-ftber products is gradually falling (72). 

Our Investigation on durability and membrane characteristics changes under adverse conditions have much contributed to development of RO applications. Among these applications are those for ultra-pure water in electronic and pharmaceutical industries. Even under the circumstance of pH 7 and with 2 to 4 times per year of sterilization by H2O2 of as high as 1 %, the cellulose acetate membrane proved to show membrane life of more than 3 years. 

Thomas, D.G., and Mixon, W.R., "Effect of Axial Velocity and Initial Flux on Flux Decline of Cellulose Acetate Membrane in Hyperfiltration of Primary Sewage Effluents," I EC Process Design and Development 11, 339-343 (1972). 

The development of the Loeb-Sourlrajan asymmetric cellulose acetate membrane (1) has been followed by numerous attempts to obtain a similar membrane configuration from virtually any available polymer. The presumably simplistic structure of this cellulose acetate membrane - a dense, ultrathln skin resting on a porous structure - has been investigated by transmission and scanning electron microscopy since the 1960s (2,3). The discovery of macrovoids ( ), a nodular intermediate layer, and a bottom skin have contributed to the question of the mechanism by which a polymer solution is coagulated to yield an asymmetric membrane. 

The successful development of asymmetric cellulose acetate membranes by Loeb and Sourirajan in the early sixties, at the University of California, Los Angeles, has been primarily responsible for the rapid development of Reverse Osmosis (RO) technology for brack sh/sea water desalination. Reverse Osmosis approaches a reversible process when the pressure barely exceeds the osmotic pressure and hence the energy costs are quite low. Theenergy requirement to purify one litre of water by RO is only O.OO3 KW as against 0,7 KV required just to supply the vaporisation energy to change the phase of one litre of water from liquid to vapour by evaporation. Thus RO has an inherent capability to convert brackish water to potable water at economic cost and thus contribute effectively to the health and prosperity of all humanity. 

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... 

In 1966, Cadotte developed a method for casting mlcroporous support film from polysulfone, polycarbonate, and polyphenylene oxide plastics ( ). Of these, polysulfone (Union Carbide Corporation, Udel P-3500) proved to have the best combination of compaction resistance and surface microporosity. Use of the mlcroporous sheet as a support for ultrathin cellulose acetate membranes produced fluxes of 10 to 15 gfd, an increase of about five-fold over that of the original mlcroporous asymmetric cellulose acetate support. Since that time, mlcroporous polysulfone has been widely adopted as the material of choice for the support film in composite membranes, while finding use itself in many ultrafiltration processes. 

Asymmetric cellulose acetate membranes were developed in the early 1960s by Loeb and Sourirajan (2). For more than a decade, cellulose acetate and its blends were the only commercially available RO membranes. Improved membranes (with respect to operating pH, biodegradation, compaction, and organic compound rejection) were developed in the early 1970s (3). These membranes used aromatic... 

Seawater has a salt concentration of 3.2-4.0%, depending on the region of the world. Because of this high salinity, only membranes with salt rejections of 99.3 % or more can produce potable water in a single pass. Application to seawater desalination of the first-generation cellulose acetate membranes, with rejections of 97-99 %, was limited. With the development of the polyamide hollow fine fibers and interfacial composites, suitable seawater membranes became available, and many plants have been installed. In general, membranes are not... 

The process shown in Figure 9.21 was first developed by Separex, using cellulose acetate membranes. The separation factor for methanol from MTBE is high (>1000) because the membrane material, cellulose acetate, is relatively glassy and hydrophilic. Thus, both the mobility selectivity term and the sorption term in Equation (9.5) significantly favor permeation of the smaller molecule, methanol, because methanol is more polar than MTBE or isobutene, the other feed components. These membranes are reported to work well for feed methanol concentrations up to 6%. Above this concentration, the membrane is plasticized, and selectivity is lost. More recently, Sulzer (GFT) has also studied this separation using their plasma-polymerized membrane [56],... 

A decade after Dr. Hassler s efforts, Sidney Loeb and Srinivasa Sourirajan at UCLA attempted an approach to osmosis and reverse osmosis that differed from that of Dr. Hassler. Their approach consisted of pressurizing a solution directly against a flat, plastic film.3 Their work led to the development of the first asymmetric cellulose acetate membrane in 1960 (see Chapter 4.2.1).2 This membrane made RO a commercial viability due to the significantly... 

E. 1960 - Loeb and Sourirajan develop asymmetric cellulose acetate membrane at UCLA... 

The high sensitivity of ETA—AAS for Cu has stimulated the development of methods to measure concentrations of the Cu carrier species in biological fluids. Delves [7] analysed the Cu content of the protein fractions separated from 2 pi volumes of serum by cellulose acetate membrane (CAM) electrophoresis. The separated protein bands were cut from the CAM and placed directly into the ETA via a 6 mm x 1 mm hole cut in the wall of the graphite tube. Calibration was achieved by adding 2 pi volumes of aqueous standards to 8 mm x 6 mm strips of CAM. Background correction was essential. Approximately 94% of the Cu was located in the a2 band, where carulo-plasmin would run, whereas other fractions contained less than 5% of the total serum Cu. The recovery of Cu after electrophoresis was quantitative, 99%, and the RSD was 0.086 at 1.74 ng Cu. This method was applied to studies of Cu changes in patients with Menkes Syndrome receiving intramuscular injections of copper as the EDTA complex, and in children with acute lymphoblastic leukaemia. 

The development of asymmetric membrane technology in the 1960 s was a critical point in the history of gas separations. These asymmetric structures consist of a thin (0.1 utol n) dense skin supported on a coarse open-cell foam stmcture. A mmetric membranes composed of the polyimides discussed above can provide extremely high fluxes throuj the thin dense skin, and still possess the inherently hij separation factors of the basic glassy polymers from which they are made. In the early 1960 s, Loeb and Sourirajan described techniques for producing asymmetric cellulose acetate membranes suitable for separation operations. The processes involved in membrane formation are complex. It is believed that the thin dense skin forms at the... 

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