Cellulose membrane technology

Cellulose acetate films, specially cast to have a dense surface and a porous substmcture, are used in reverse osmosis to purify brackish water (138—141) in hollow fibers for purification of blood (artificial kidney) (142), and for purifying fmit juices (143,144) (see Membrane technology). 

Membranes (Technology)—Congresses. I. Loeb, Sidney. II. Sourirajan, S. III. Turbak, Albin F., 1929-. IV. American Chemical Society. Cellulose,... 

Dialysis operates by the diffusion of selected solutes across a nonporous membrane from high to low concentration. An early industrial application of dialysis was caustic soda recovery from rayon manufacturing. It had been a viable process because inexpensive but alkali-resistant cellulose membranes were available that were capable of removing polymeric impurities from the caustic. Gradually however, dialysis is being replaced by dynamic membrane technology for caustic soda recovery because of the latter s much higher productivity. 

Hjartstam, J. (1998), Ethyl Cellulose Membranes Used in Modified Release Formulations, Chalmers University of Technology, Goteborg, Sweden. 

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... 

There have been many studies on the application of membrane technology to food Industries. Few have, however, reached a commercial success except those of dairy processes (1) DAICEL has been studying since 1971 the application of its cellulose acetate RO membranes and polyacrylonitrile UF membranes to food, pharmaceutical, medical, paper and other industries. As to the use of membranes in food industries other than dairy processes, only two cases were developed to a semicommercial scale, that is, grape juice concentration for wine must and tomato juice concentration for processing and storage of the juice till next harvest. 

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. 

The high yield and hence higher purity of sugar obtained by strong acid hydrolysis of cellulose makes it an attractive process, but the lack of a recovery system for strong acid complicates the outlook. The improvement of membrane technology will probably proceed because of potential applications to many problems. Application to cellulose hydrolysis adds justification for intensified work in the field. 

NMMO technology can be utilized to make cellulose membranes and films [37]. 

New materials with improved CO2/CH4 separation selectivity and membrane stability under realistic NG conditions have been developed however, even after three decades of development, only three membrane material types have been commercialized cellulose acetate-based Separex (Honeywell s UOP), Cynara (Cameron) membranes, polyimide-based membranes from Medal (Air Liquide) and Ube, and per-fluoropolymer-based Z-top membranes from Membrane Technology and Research, Inc. (MTR). The key reasons for the selection of the desired polymer for commercialization are the cost of material, ease of fabrication into commercially viable form, effect of impurities on membrane performance, and gas selectivity under realistic feed conditions. 

Membrane technology has often been mentioned as the next technological generation for the prtrification of natural gases. Indeed, membrane systems are operated successfully for gas sweetening for decades. The best known examples include CO2 selective membranes that are based on pure polymers, e.g., cellulose acetate (Cynara membranes by Natco or Separex membranes by UOP) and polyimide (Ube). Despite their popularity, their performance at high pressures deteriorates as a result of CO2 induced plasticization. 

Pandey L.K., Saxena C., Dubey V, Studies on pervaporative characteristics of bacterial cellulose membrane. Separation and Purification Technology, 42, 2005, 213. 

The current knowledge related to the structure and chemistry of cellulose, and the development of innovative cellulose derivatives for different applications (coatings, films, membranes, building materials, pharmaceuticals, foodstuffs), as well as the new perspectives, including environmentally-friendly cellulose fiber technologies, bacterial cellulose biomaterials, in-vitro syntheses of cellulose, and cellulose-based biocomposites were highlighted in several important works [30-34]. 

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