DE2419930A1 - ULTRAFILTRATION MEMBRANE AND METHOD OF MANUFACTURING THEREOF - Google Patents

Description

Dr. Hans-Heinrich Willrath t - 62 Wiesbaden April 24, 1974

Dr Dieter Weber ρ ^ λληώ / i / _ep

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PATENT LAWYERS

Case G 1907

Dorr-Oliver Incorporated

77 Havemeyer Lane, Stamford / Connecticut 06904

United States

ultrafiltration membrane and method for the same

Manufacturing

Priority; v. April 30, 1973 in USA Serial No .: 355 726

The invention relates to hydrophilic ultrafiltration membranes and a method for their production. Ultrafiltration membranes are used in appropriate cells to separate particles of molecular sizes from a fluid, wherein the particles are dispersed. Such membranes can lead to separation processes in cheese whey, waste water and electrophoretic Colors are used by way of example. Separations of electrophoretic color polymers are performed to the valuable polymers returned to the dye bath, while the carrier and contaminants are removed for reuse or disposal.

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PostschMfc: Frankfurt / Main 67 63-602 Bank: Dresdner Bank AG, Wiesbaden, account no. 276807

The electrophoretic colors, so far most common,
have been used are anionic in nature, and anisotropic microporous polymer membranes of the type described in U.S. Patent 3,615,024 dated Oct. 26, 1971, Art
work very well with such colors. In the industry, however, there is a tendency to switch to cationic electrophoretic paints because the hue of the deposited paint is easier to control, oxidation of the deposited film is avoided, a superior one
Corrosion protection of the substrate is achieved and some
cathodic systems tolerate a wide pH range. A difficulty has arisen due to the fact that such cationic inks tend to foul hydrophobic ultrafiltration membranes of the type described in the aforementioned patent
and drastically reduce the flow. There is therefore a real need for a hydrophilic ultrafiltration membrane that can be used in filterable media which is cationic
Contain polymers, work well.

The object of the invention is therefore to create an improved hydrophilic membrane and a method for its production.

In principle, the invention relates to a method for production a hydrophilic ultrafiltration membrane, which consists of a modified cellulose acetate, whereby one first an ultrafiltration membrane made from a cellulose acetate manufactures and then deace-

^tylated ·. 409845/0873 " ³ "

241993Q

In detail, the invention consists in first producing a cellulose acetate ultrafiltration membrane on a suitable support, such as paper, in a predetermined configuration, ie as hollow cylinders or tubes, flat plates or the like. The cellulose acetate membranes are then combined to form their support structure, for example by forming a cartridge for an ultrafiltration system. The structure is then immersed in a caustic deacetylating agent, such as triethanolamine, or the membrane surfaces are flooded with it. Over a period of time, hydrolysis or deacetylation occurs and a modified cellulose acetate membrane remains which generally retains the porosity properties of the previously formed cellulose acetate membrane, although there is some slight modification of the pore structure due to shrinkage and other phenomena. Cellulose triacetate is a suitable membrane precursor, but up to 90% or slightly more of the triacetate can be replaced with cellulose diacetate. The acetate bound in these precursor materials can be from as little as 20% to over 50%, and a bound acetate of 30% has been found to work well and be readily available commercially. Although triethyl ethanol is a satisfactory deacetylating agent, other caustic reagents including diethyleneamine, triethyleneamine, and sodium hydroxide can be used. Certain caustic agents, such as NH ₄ OH, can in some cases have a tendency to attack the cellulose skeleton of the membrane. Such an attack can be made through careful selection

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the concentration of the reagent, the reaction time and other reaction conditions can be largely reduced.

The time required for deacetylation can range from a few minutes to several days or even a week or more, depending on the temperature at which the reaction is carried out, the concentration of the deacetylating agent, the composition of the acetate, etc., vary. An extended long deacetylation is not necessarily a large one Disadvantage, since membranes such as those used for ultrafiltration purposes are always shipped in a moist state must be, - and usually be immersed in water during storage until shipping. In this case it is only necessary to remove the deacetylating agent when the reaction time is over, and remove it with water to replace.

Although the reaction has been termed "deacetylation" and in some cases to complete deacetylation In other cases, the reaction need not be carried out to completion. in the in general, the degree of deatretylation is at least about 10% Make out surface acetylation.

The following examples serve to explain the advantages of the invention:

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example 1

Cellulose acetate solutions are poured onto a glass support. The solutions contain various types of cellulose triacetate Solvents. The solutions consist of 10 to 20 parts of cellulose triacetate and residual solvent. The solvents used are acetone in dimethylformamide, formamide with dimethylformamide, or dimethylformamide alone. The precipitation of the cellulose acetate membrane is achieved by preferably one side of the poured solution with brings a water phase into contact, as described in the aforementioned US Pat. No. 3,615,024. Cellulose acetate ultrafiltration membranes from about 0.1 to 0.3 mm (4 to 12 mils) in diameter are made in this manner. The membranes are then immersed in a solution of the deacetylating agent. After 48 hours of dwell in a 5% strength In diethylenamine solution, the membranes are completely deacetylated. The mechanical properties are good. When testing with a fluid containing protein of molecular weight 12,400, the membranes show protein repulsion of 70%.

Example 2

A commercially available cartridge with cellulose acetate membranes, which is made from a solution of 12% cellulose triacetate in dimethyl · formamide has been poured and knocked down in

■ v

deacetylated a solution with a concentration of 119 cm triethanolamine in 1000 cm water. The pH of the deacetylation solution is 10.5. The cartridge is left in the solution for 5 days

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leave, whereupon it is almost completely deacetylated. When tested with a protein with a molecular weight of 12,500 containing fluids, the membrane exhibited a protein rejection of 65%.

Example 3

A modified cellulose acetate cartridge produced by the method of Example 2 is combined with a cellulose acetate cartridge and a commercial cartridge (designation XP-24) currently used for anionic paint compared to ultrafiltration of cationic paint. the XP-24 membranes are made from Dynel (an acrilonitrile-vinyl chloride copolymer). The cationic paint is made from a modified epoxy resin, well blended with deionized Water, and certain additives to regulate the properties of the resin in dispersion. The molecular weight of the Resin is about 1000. The cartridges are a working pressure

2
of about 2.1 kg / cm (30 psi) and a flow rate of about 3000 liters (80 gallons) per minute. The flow rates in the steady state are determined on the cartridges by periodic flow measurement. After 19 hours of operation, the modified cellulose acetate cartridge has a flow rate of about 339 liters / 0.09 m ² / day (89.6 gallons / square foot / day) which has not changed significantly (less than 1% decrease) over 10 hours. The cellulose acetate cartridge reached

Liter 2, a steady state flow rate of about 184 / 0.09 m / Day (48.7 gallons / square foot / day) at 19 hours. The XP-24

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Cartridge was tested in a similar manner and showed a

2 Flow rate in a steady state of only around 42 liters / 0.09 m / Day (11 gallons / square foot / day). These attempts show the clear superiority of the modified cellulose acetate detected against cellulose acetate and polymer membranes of the non-cellulose type.

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Claims (11)

Claims 1.) Process for the production of hydrophilic ultrafiltration membranes, characterized in that a solution containing cellulose acetate is placed in a thin layer on a base pours, the cellulose acetate precipitates out of the solution to form an ultrafiltration membrane and the membrane deacetylated with an organic or inorganic wetting agent. 2.) The method according to claim 1, characterized in that the precipitation of the membrane takes place in that one side brings the cellulose acetate solution into contact with a water phase. 3.) The method according to claim 2, characterized in that the etchant of triethanolamine, triethyleneamine, diethylenamine or NaOH. 4.) The method according to claim 3, characterized in that the cellulose acetate consists of cellulose triacetate. 5.) The method according to claim 3, characterized in that the cellulose acetate consists of at least about 10% cellulose triacetate and the remainder consists essentially of cellulose diacetate. - 9 409845/0873 6.) Method according to claim 4, characterized in that the cellulose triacetate is essentially completely deacetylated. 7.) The method according to claim 4, characterized in that the cellulose triacetate during the reaction to at least about 10% is deacetylated. 8.) The method according to claim 5, characterized in that the cellulose acetates are essentially completely deacetylated. 9.) The method according to claim 5, characterized in that the Cellulose acetates are deacetylated to at least about 10% during the reaction. 10.) The method according to claim 3, characterized in that the Cellulose acetate from cellulose triacetate and the deacetylating agent consist of triethanolamine and the reaction up to Consummation is carried out. 11.) Hydrophilic, anisotropic microporous ultrafiltration membrane, consisting of a deacetylated cellulose acetate. 409845/0873