Cellulose Acetate Ultrafiltration Membranes Research Articles

Alkaline saponification and its effect on the properties of cellulose acetate ultrafiltration membranes

The kinetics of the saponification of cellulose acetate ultrafiltration membranes and its effect on their transport characteristics and certain physicochemical properties are studied. It is established that the rate and effective activation energy of the saponification process are inversely related to the pore size, and that on passing from large pore to fine pore membranes the saponification process passes from the diffusional into the kinetic region. It is shown that on asymmetric hydrolysis of the membranes the process takes place in the presence of a moving boundary of reacted layer with a markedly diffuse front. Specification of the membranes is accompanied by a change in their transport characteristics and the state of the water in the membrane pores.

Influence of casting solution concentration on structure and performance of cellulose acetate membranes

On the basis of separation curves, the pore size and pore size distribution of cellulose acetate ultrafiltration membranes are determined. Quantitative conclusions are drawn as to the influence of casting solution concentration on membrane structure and performance. The polymer concentration in the casting solution was varied between 17.5 and 21% wt.

Annealing effect in porous cellulose acetate membranes

On the basis of separation curves the pore size and pore dize distribution of cellulose acetate ultrafiltration membranes are determined. The change of these parameters by annealing is discussed and from the correlation between pore size and annealing temperature up to 75°C conclusions are drawn as to the structure of salt rejecting membranes annealed at 90°C.

Annealing effect in porous cellulose acetate membranes

On the basis of separation curves the pore size and pore dize distribution of cellulose acetate ultrafiltration membranes are determined. The change of these parameters by annealing is discussed and from the correlation between pore size and annealing temperature up to 75°C conclusions are drawn as to the structure of salt rejecting membranes annealed at 90° C.

Analysis of solutes rejection in ultrafiltration.

To establish an effective method of quantitative analysis in ultrafiltration, the rejection of six solutions of various molecular weights by cellulose acetate ultrafiltration membranes was studied. At first, the effects of concentration polarization were corrected. Mass transfer coefficients determined by the velocity variation method agreed very well with the Deissler correlation. Next, by using Spiegler and Kedem equations, transport of solute through ultrafiltration membrane was analyzed. A method of curve-fitting was found effective to determine two parameters, i.e. solute permeability P and reflection coefficient σ. Finally, these parameters obtained from experiments for various solutes were analyzed using the modified theory, and were correlated with the ratio of the radius of solute and pore and with the effective pore length. Structure of the membrane was estimated from these results.

High flux cellulose acetate ultrafiltration membranes

Conditions for casting high flux tubular and flat cellulose acetate ultra-filtration membranes are given. The usefulness of some of the tubular membranes cast under the above conditions for ultrafiltration applications in industrial water purification and reuse is illustrated. Using ethanol-water mixture as the gelation medium in the temperature range-20° to 30°C, ultrafiltration membranes giving water fluxes in the range <4 to >400 m 3/m 2 day at the operating pressure of 689.5 × 10 3 Pa (100 psig) have been obtained.

Effect of ethanol–water mixture as gelation medium during formation of cellulose acetate reverse osmosis membranes

AbstractBy using ethanol–water mixtures in a wide range of alcohol concentrations and temperatures, cellulose acetate membranes with a wide range of surface porosities can be obtained. Two different casting solution compositions were used, involving cellulose acetate, acetone, and aqueous magnesium perchlorate (composition I) or formamide (composition II). All reverse osmosis experiments were carried out at 250 psig using a 3500 ppm NaCl–H2O feed solution at laboratory temperature. The effective area of film surface was 12 cm2 in all cases. With composition I, with pure water gelation medium at 0°C, the resulting membrane gave a solute separation of 5% and product rate of 220 g/hr, whereas with 95% alcohol as gelation medium, the resulting membrane gave a solute separation of ∼1% and product rate of 1240 g/hr under otherwise identical experimental conditions. With composition II membranes, the maximum product rate of 360 g/hr with the corresponding minimum solute separation of ∼1% was obtained with 71.2% alcohol–water gelation medium at 0°C. Increase in the temperature of the gelation medium in the range 12° −25°C tends to increase the average size of pores on the membrane surface. These results offer a basis for the development of cellulose acetate ultrafiltration membranes.

An approach to the development of cellulose acetate ultrafiltration membranes

The film-casting solution consisted of a mixture of cellulose acetate, acetone, and aqueous magnesium perchlorate [Mg(ClO4)2:H2O = 1:8.5], designated as polymer P, solvent S, and nonsolvent N, respectively. Using the composition P:S:N = 17: 69.2: 13.8 as reference, films were obtained from 19 different casting solutions in which the weight ratios S/P, N/S, and N/P were varied in different directions. The casting solution temperature was 0°C, and solvent evaporation period during film formation was minimum in most cases. The effects of variations of casting solution temperature and solvent evaporation period were also briefly studied. Reverse osmosis experiments with resulting membranes were carried out at 100 psig using 200 ppm NaCl–H2O as the feed solution. Decrease in S/P, increase in N/S, and increase in N/P in the casting solution, decrease in temperature of the casting solution, and increase in solvent evaporation period tend to increase the size of pores on the surface of resulting membranes in the ascast condition. Increase in S/P in the casting solution, and increase in the temperature of the casting solution tend to increase the effective number of pores on the membrane surface. These results offer definitive physicochemical criteria in terms on solution structure–evaporation rate concept for developing useful cellulose acetate ultrafiltration membranes.

On the preparation of highly permeable cellulose acetate ultrafiltration membranes

On the preparation of highly permeable cellulose acetate ultrafiltration membranes

Protein Concentrate from Cheese Whey by Ultrafiltration

A concentrate containing up to 65% protein in the solids was recovered from cheese whey by the use of tubular cellulose acetate ultrafiltration membranes designed to reject solutes larger than 20,000 molecular weight. Removal of 90% of the water as permeate resulted in a concentrate containing 20% solids with 35 to 37% protein and 50 to 52% lactose in the solids. By diluting and recycling, a concentrate containing 60 to 65% protein and 30 to 35% lactose in the solids was obtained. for 90% reduction in volume, fractionation averaged 12 gallons per square foot of membrane surface per day

Recovery of biological materials through ultrafiltration.

AbstractExperiments were performed on a cellulose acetate ultrafiltration membrane (HF‐200, ABCOR Inc., Cambridge, Mass.) to test its efficacy in concentrating and purifying a crude enzyme (trypsin) preparation. Studies were also made to determine the influence of inorganic salts, pressure, and temperature on the rate of ultrafiltration for this membrane. The results showed reductions in the rates will be encountered due to the presence of inorganic salts. However, the reduced rates were still sufficiently high to make this method extremely attractive. Operating at filtration pressures above 75 psi at, 20 to 30°C for this membrane does not show any beneficial effect in terms of ultrafiltration rates. However, at 10°C there were continual increases in the filtration rates up to 100 psi. Concentration and purification studies with trypsin yielded a concentration factor of 8.35 and a purification factor 2.35. It was shown concretely that the purification of the enzyme was due to the passage of low molecular weight proteins (below 20,000) through the membrane. Enzyme activity slightly greater than 90% was obtained: 70% was found in the concentrate and 20% in the filtrate. It is concluded that membrane ultrafiltration is an ideal simple, rapid, and economical method for the recovery of biological active substances.