Membrane cellulose acetate

Fig. 9. SEM photographs of cellulose acetate membranes cast from a solution of acetone (volatile solvent) and 2-meth5l-2,4-pentanediol (nonvolatile solvent). The evaporation time before the stmcture is fixed by immersion ia water is shown (24).

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). 

The life of membranes is affected by gradual chemical decomposition or change. For example, cellulose acetate membranes hydrolyze with time. 

FIG. 22-76 Constant -cost lines as a function of permeability and selectivity for CO2/CH4, Cellulose-acetate membrane mscf is one thousand standard cubic feet, CouHesy VP R. Grace.)... 

FIG. 22-77 Influence of feed purity on total membrane area when the residue gas at fixed purity is the product, Feed-gas volume is constant, CO2/CH4 cellulose-acetate membrane, (X = 21, Courtesy VP R. Grace.)... 

Two common types of membrane materials used are cellulose acetate and aromatic polyamide membranes. Cellulose acetate membrane performance is particularly susceptible to annealing temperature, with lower flux and higher rejection rates at higher temperatures. Such membranes are prone to hydrolysis at extreme pH, are subject to compaction at operating pressures, and are sensitive to free chlorine above 1.0 ppm. These membranes generally have a useful life of 2 to 3 years. Aromatic polyamide membranes are prone to compaction. These fibers are more resistant to hydrolysis than are cellulose acetate membranes. 

Hydrolysis of cellulose acetate membranes is another operational problem and occurs whenever the feed is too acid or alkaline that is, the pH deviates beyond designed range limits. As may readily happen, whenever C02 passes through the... 

The enzyme is used in an enzyme electrode in which a tube is sealed at its lower end with a cellulose acetate membrane. An outer membrane of collagen is also attached to the end of the electrode tube and glucose oxidase enzyme is contained in the space between the two diaphragms. 

NOTE The above applies to composite polyamide and polyvinyl derivative membranes. Do NOT use chlorine, which is suitable only for cellulose acetate membranes. 

Commercial interest in RO began with the first high-flux, high-NaCl-retention Loeb-Sourirajan anisotropic cellulose acetate membrane. Practical application began with the thin film composite (TFC) membrane and implementation for seawater desalination at Jeddah, Saudi Arabia [Muhurji et ak. Desalination, 76, 75 (1975)]. 

Air (particulate lead) Collection of particulate matter onto cellulose acetate membrane filter wet ashing with HN03 / HCI04 ICP/AES (Method P CAM 7300) 5 pg/m3 95-105 NIOSH 1984... 

All polymers utilized in this investigation have been listed in Table 2, along with their supplier and the concentration range over which they were tested. Polymers were either used as received or purified by filtration through a 0.22 or 0.45-pm MiUipore cellulose acetate membrane. For aseptic applications autoclaving was carried out for 20 min at a temperature of 121 °C. Qualitative properties of each polymer are listed in Table 3. For polymers supplied as solutions, dialysis was carried out in membranes (Spectrum Medical Industries, Houston, TX) with a MWCO of 10,000 daltons. 

Astroquartz, fiber reinforcement for ceramic- matrix composite, 5 558t Asymmetric allylboration, 13 669-671 Asymmetric cellulose acetate membranes, 21 633... 

PERFORMANCE OF HOMOGENEOUS AND ASYMMETRIC CELLULOSE ACETATE MEMBRANES... 

For purposes of illustration, the following discussion, unless otherwise specified, is limited to single-solute aqueous feed solutions, cellulose acetate membranes, and reverse osmosis systems for which osmotic pressure effects are essentially negligible. 

Figure 2a. Experimental data on the effect of operating pressure, average pore size on membrane surface, and feed concentration on solute separation and product rate for the reverse osmosis system cellulose acetate membrane-sodium chloride-...

The preferential sorption-capillary flow mechanism of reverse osmosis does that. In the NaCl-H20-cellulose acetate membrane system, water is preferentially sorbed at the membrane-solution Interface due to electrostatic repulsion of ions in the vicinity of materials of low dielectric constant (13) and also due to the polar character of the cellulose acetate membrane material. In the p-chlorophenol-water-cellulose acetate membrane system, solute is preferentially sorbed at the interface due to higher acidity (proton donating ability) of p-chlorophenol compared to that of water and the net proton acceptor (basic) character of the polar part of cellulose acetate membrane material. In the benzene-water-cellulose acetate membrane, and cumene-water-cellulose acetate membrane systems, again solute is preferentially sorbed at the interface due to nonpolar... 

Figure 3. Potential functions for surface ( and friction ( forces as a function of the distance d front cellulose acetate membrane material for different solution...

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