DE2835890A1 - Reverse osmosis membrane comprising cellulose deriv. - obtd. from soln. contg. e.g. cellulose acetate (butyrate) methyl or ethyl cellulose, organic solvent and tetra-carboxylic acid - Google Patents

Abstract

The membrane consists of a cellulose derivative 0.2 piece/0.844 mm2 void coefficient and 3x10-10 g3/cm7.atm3 A3/B wher A is water permeating constant (g/cm2.sec. atm), and B is salt permeating constant (cm/sec.). The membrane is obtd. from a membrane producing solution of a cellulose derivative, organic solvent, and tetracarboxylic acid of formula R-(CO2H)4, where R is tetravalent aliphatic or alicyclic organic group of 2-10C. The cellulose derivative is cellulose acetate, cellulose acetate butyrate, methyl cellulose, or ethyl cellulose. The organic solvent is acetone, DMC, dioxane, DMSO acetic acid, diethylene glycol, diacetone alcohol, acetonitrile, or nitromethane. The acid is butane tetracarboxylic acid, ethylene tetracarboxylic acid, dicyclobutane, tetracarboxylic acid, cyclopentane tetracarboxylic acid or cyclopropane tetracarboxylic acid.

Description

Reverse osmosis membrane, process for its manufacture

and casting solution for carrying out the method. The invention relates to an improved reverse osmosis membrane and method of manufacture the same from a cellulose derivative. The invention also relates to a casting solution to make this membrane and a casting solution additive that is used to make a reverse osmosis membrane.

Phenomena such as spontaneous transition from pure water to aqueous Solution or from a less concentrated aqueous solution to a more concentrated one aqueous solution, if these are separated from one another by a semipermeable membrane are generally referred to as "direct osmosis".

On the other hand, the passage of pure water is reversed Direction, i.e. the movement of pure water or a pure solvent a more concentrated solution into a less concentrated one through a semipermeable one Membrane passes under an external force that is greater than the osmotic pressure is, this force being exerted on the more concentrated solution than "reverse" Osmosis ".

Reverse osmosis is now widely used for many purposes, such as for desalination of salt water or brackish water, for Pollution control, for water recovery, food processing and many others Separation, concentration and recovery processes.

Since Loeb et al a method for the production of asymmetric membranes Developed for reverse osmosis in 1961, many research programs have been pertaining to Reverse osmosis membranes were very actively promoted. 1966 developed Manjikian et al discloses a reverse osmosis membrane which has found practical use.

Many studies on better membranes have been actively carried out, and numerous better membranes have been proposed. These better membranes are for example made of cellulose derivatives (especially cellulose acetate) in the Form of casting solutions made from solvents for cellulose derivatives and additives such as perchlorate salts (U.S. Pat. No. 3,133 132), from water-soluble liquid amides (US Pat. No. 3,344,214), from mineral acids (U.S. Patent 3,444,286), from organic amine salts (U.S. Patent 3,522,335), from dibasic or tribasic aliphatic acids (U.S. Patent 3,673,084), from water (U.S. Patent 3,917 777) and / or from maleic acid monomethyl ester (Japanese Patent Laid-Open No.

35074/75).

Membranes of the type indicated above have a (upper) skin layer and a (lower) porous layer. As is known to those skilled in the art, it is to membranes with optimal performance both regarding salt repellency as well in terms of water permeability, required on the membrane fine structure to provide a layer of skin that is as thin as possible. This requirement leads however, to decrease the durability of the membrane and, more specifically, cause the following other difficulties: 1. The speed of water permeability takes due to the compaction of the membrane during operation under high pressure away.

2. The salt concentration of the permeated water increases gradually during prolonged operation, as the top layer (skin layer) of the membrane breaks and stretch. This is caused by voids or imperfections, such as membrane defects in the form of large cell-shaped finger-like cavities, caused in the lower layer (porous layer) of the membrane during the gelation stage of membrane manufacture appear.

A decrease in water permeability or water permeability can be switched off to a certain extent by adjusting the heating temperature controls during the heat treatment step in the membrane manufacturing process. By increasing the heating temperature, the unfavorable influence of membrane compaction becomes reduced. The latter difficulty (gradual increase in However, salt concentration) is quite difficult to overcome. Voids tend to to occur when the membrane separation properties are improved. When the membrane is made to have high separation properties by changing the membrane manufacturing conditions controls, the void number tends to increase in general. If the membrane manufacturing conditions continue be selected in such a way that the membrane is prevented from having such voids owning the entire membrane property, especially the combination of Salt repellency and water permeability, greatly reduced.

Accordingly, it is an object of the present invention to provide an improved membrane for reverse osmosis with good balance of membrane separation properties, speed the water permeability and salt repellency, with a minimum of voids and with high durability and an additive for the membrane casting solution to obtain from which such a membrane can be made.

The new reverse osmosis membrane made from a cellulose derivative according to the invention has no less than about 3 x 10 10 g3 / cm7 second² atmosphere³, preferably not less than about 7 x 10-10 g³ / cm7 7th second²th atmosphere³ of A3 / B and no more than about 0.2, preferably no more than about 0.1 voids 0.844 mm2 each. According to the definition above, A is the water penetration coefficient (g / cm2. second atmosphere) and is defined as follows: A = F1 / (# P - ##), where F1 is the rate of product water flow 2 through the Membrane (g / cm2.second), the applied pressure difference (atmosphere) and tff the osmotic pressure difference (atmospheres).

According to the further definition here, B is the salt penetration coefficient (cm / second) calculated according to the following equation: B = F2 / (c1-C2), where F2 is the Salt penetration through the membrane (g / cm2 sec.), 3 C1 the salt concentration in the concentrate (g / cm3) and C2 the salt concentration in the product water (g / cm3) is.

The term cavity or flaw here means a membrane defect, such as an inclusion, a bubble, a pore defect or a line-shaped and / or finger-like cavity or other cavity, all in the lower layer (porous layer) of the membrane during the gelation stage of membrane manufacture appear. The meaning of "void" or void is given by C.W. Salton stable in Office of Sahne Water ", Res. Develop. Prog.Rept. No. 434, 1969, fully explained.

The number of cavities is conveniently determined with the help of a microscope measured.

The new reverse osmosis membrane can be made from a casting solution which are a cellulose derivative, an organic solvent therefor and a Tetracarboxylic acid of the general formula R- (C02H) 4, in which R is a substituted one or unsubstituted tetrafunctional aliphatic or alicyclic organic Means a remainder with 2 to 10 raw material atoms.

Examples of the cellulose derivative used in the process of the present invention Invention used are cellulose acetate, cellulose propionate, cellulose acetate propionate, Cellulose acetate butyrate, methyl cellulose and ethyl cellulose. Most preferred are the cellulose acetate compounds, such as cellulose acetate, cellulose diacetate, cellulose triacetate, Mixtures of cellulose diacetate and cellulose triacetate, as well as cellulose, the is acetylated to an extent between the diacetate and the triacetate.

The practical acetyl content of cellulose acetate, based on cellulose acetate, is from about 39.8 to about 43.2 weight percent, and the range from about 40.5 to about 42.5 wt% is preferred in order to use an improved reverse osmosis membrane to maintain excellent properties of water penetration and salt repellency.

Examples of the organic solvent used in the process of Invention used are acetone, tetrahydrofuran, dimethylformamide, dioxane, Dimethyl sulfoxide, acetic acid, diethylene glycol, diacetone alcohol, acetonitrile, nitromethane and mixtures thereof.

Examples of tetracarboxylic acid are butanetetracarboxylic acid, ethylene tetracarboxylic acid, Cyclopropane tetracarboxylic acid, cyclobutane tetracarboxylic acid, cyclopentane tetracarboxylic acid and furantetracarboxylic acid. The preferred form is a butanetetracarboxylic acid such as 1,2,3,4-butanetetracarboxylic acid.

The casting solution can be prepared as follows, for example: The cellulose derivative is dissolved in an organic solvent. The solution typically consists of 20 parts by weight of cellulose derivative and about 30 to about 180 parts by weight, preferably about 50 to 80 parts by weight, of organic solvent.

About 2 to 49 parts by weight, preferably about 2 to 20 parts by weight of tetracarboxylic acid were added.

Conveniently, the tetracarboxylic acid can be used as a solution in water, Methanol, acetone or another solvent for tetracarboxylic acid added will. Methanol is preferred.

In addition to the tetracarboxylic acid, the use of another additive a monovalent and / or divalent carboxylic acid, good results. The monobasic or dibasic carboxylic acids are, for example, the following: glycolic acid, Oxalic acid, maletic acid, maleic acid monomethyl ester, malonic acid, glutaric acid, formic acid and citric acid.

Most preferred is maleic acid.

The mole fraction of the monobasic and / or dibasic carboxylic acid is generally no more than 0.55, preferably from about 0.20 to about 0.55, particularly preferred about 0.20 to 0.40 based on the total amount of additive, i.e. H. of tetracarboxylic acid and monobasic and / or dibasic carboxylic acid.

The above-described casting solution can be carried out in the following process steps to a membrane with improved performance, fewer voids, and high durability are processed: 1. Casting stage: The casting solution is applied to a substrate, such as a Cast glass plate or a woven or non-woven fabric.

2nd evaporation stage: The organic solvent is partially evaporates.

3rd coagulation stage: the cast membrane is immersed in water.

4th heating stage: the resulting membrane is heated.

In practicing the present invention, however, is the coagulation bath temperature not limited to a range of 0 to 5 ° C or below, which is the usual Is condition that is applied in the manufacture of cellulose membranes.

In contrast, temperatures from about 15 to 20 ° C can be used which means that cooling devices can be omitted.

By modifying the manufacturing conditions, it is possible to create a obtain highly water permeable membrane that is effective as an ultrafiltration membrane can be used.

In the following examples and comparative examples, the performances were of the membranes measured under the following conditions: salt concentration: 2500 ppm NaCl Driving pressure: 30 kg / cm2 Flow velocity: 1.0 m / sec.

Flow temperature: 25 OC The m-value became as follows calculated: m = log (F / FO) / log (T / To), where F is the water permeability at the time T and Fo means the water permeability at time To (T = typically 200 Hours, To = typically 1 hour.) The mean value of the voids was after ten observation series in an area of 0.844 mm2 calculated in the microscope.

The elongation at break was measured with a Tensilon Universal Tester (Type UPM-3, Toyo Borudowin Inc.) using the following method: membrane strip 5 mm wide were held at a distance of 4 cm and at a speed of 2 cm per min.

drawn. The elongation at break was determined by the up to one Fracture stretched length divided by 4 cm length.

Example 1 Cellulose triacetate with 43.2% by weight acetyl content (Eastman Cellulose Triacetate A-432-130B) and cellulose diacetate with 39.8% by weight acetyl content (Eastman Cellulose Diacetate E-398-3) were used in this example.

A casting solution was made from 8 g of cellulose triacetate, 12 g of cellulose diacetate, 40 g of 1,4-dioxane, 27 g of acetone and 3 grams of 9,2,3,4, -butanetetracarboxylic acid, dissolved in 10 grams of methanol, hetpAnAlt The casting solution was on a glass plate Poured at 30 C using a doctor blade to make a film 0.2 mm thick to obtain. After partial evaporation of the solvent for 1 minute, the Film coagulated in cold water held at 5 ° C for 10 minutes.

During the coagulation process, the film came off the glass plate washed off and heated in cold water at 75 ° C for 5 minutes to create a membrane to surrender.

The membrane properties were as follows: Flow rate: 0.8 m3 / m2 day Salt repellency: 97 e m value: greater than -0.01 voids: no elongation at break: approx 13%.

Another membrane that was heated to 80 ° C instead of 75 ° C, had the following properties: flow rate: 0.6 m3 / m2 day salt repellency: 98% m-value: about zero voids: no elongation at break: about 11%.

The salt rejection of the membrane increased from 98.0% to 98.5% after 2 hours Test.

Example 2 A casting solution was made from 20 g of cellulose diacetate at 39.8 g % By weight acetyl content, 40 g acetone, 15 g 1,4-dioxane, 12 g acetonitrile, 10 g methanol and 3 g of 1,2,3,4-butanetetracarboxylic acid.

A membrane was made from this casting solution under the same conditions as obtained in example 1. The heating took place at 75 ° C. for 5 minutes. the Properties of the membrane were as follows: 32 Flow rate: 1.5 m / m day Salt repellency: 87 e m value: - 0.02 cavities: no elongation b ~ at break: 10%.

Example 3 A casting solution was made from 10 g of cellulose triacetate with 43.2% by weight of acetyl content, 50 g of 1,4-dioxane, 10 g of acetone, 12 g of dimethyl sulfoxide, 3 g of 1,2,3,4-butanetetracarboxylic acid and 15 g of methanol were prepared.

A membrane was made from this casting solution under the same conditions as obtained in example 2. The properties of the membrane are as follows: Flow rate: 3 m³ / m² day salt repellency: 11% voids: no elongation at break: 10%.

Example 4 Cyclopentanetetracarboxylic acid was used in place of 1,2,3,4-butanetetracarboxylic acid of Example 1 is used. The heating took place at 75 ° C. for 5 minutes. the The properties of the membrane were as follows: Flow rate: 0.7 m3 / m2 day Salt repellency: 96% voids: no elongation at break: 12%.

Example 5 A casting solution was prepared using 2 g of 1,2,3,4-butanetetracarboxylic acid and 1 g of t-maleic acid instead of 3 g of 1,2,3,4-butanetetracarboxylic acid as in Example 1 manufactured. The heating step was carried out at 75 ° C. for 5 minutes. The properties the membrane were as follows; Flow rate: 0.8 m 32 day salt rejection: 97% voids: no elongation at break: 12%.

Example 6 1 g of glycolic acid was used instead of maleic acid as in Example 5 used. The properties of the membrane obtained were as follows: Flow rate: 0.75 m3 / m2 day salt repellency: 97% voids: no elongation at break: 11.5%.

Example 7 A membrane was produced according to Example 1, however with the exception that the coagulation step was carried out at 15 ° C. for 10 minutes became. The heating stage was carried out at 75 ° C for 5 minutes. The properties the Msmbran were as follows: flow rate: 0.75 m3 / m2 day salt repellency: 97% voids: no elongation at break: 12 t.

Example 8 A membrane was produced according to Example 5, however with the exception that the coagulation stage at 15 ° C for 10 in.

was carried out. The heating step was carried out at 75 ° C for 5 minutes. The properties of the membrane were as follows: Flow rate: 0.6 m3 / m2 day Salt repellency: 98% voids: none.

Example 9 In Example 7, there was 2.4 g of 1,2,3,4-butanetetracarboxylic acid and Q, 6 g of maleic acid used instead of 3 g of 1,2,3,4-butanetetracarboxylic acid. The properties of the membrane were as follows: Flow rate: 0.65 m3 / m 2 day Salt rejection: 98% voids: none.

Example 10 A membrane was made according to Example 9 using of 2.5 g of 1,2,3,4-butanetetracarboxylic acid and 0.5 g of maleic acid instead of 2.4 g of 1,2,3,4-butanetetracarboxylic acid and 0.6 g of maleic acid.

The properties of the membrane were as follows: Flow rate: 0.7 m³ / m² day Salt repellency: 98% Voids: none.

Example 11 A membrane was made according to Example 9 using of 2.6 g of 1,2,3,4-butanetetracarboxylic acid and 0.4 g of maleic acid instead of 2.4 g of 1,2,3,4-butanetetracarboxylic acid and 0.6 g of maleic acid.

The properties of the membrane were as follows: Flow rate: 0.65 m3 / m2 Day salt repellency: 98% voids: none.

Comparative Example 1 A membrane was produced by the same method, used in Example 1, with the exception that 3 g of oxalic acid instead of 3 g of 1,2,3,4-butanetetracarboxylic acid were used. The heating stage was carried out at 75 ° C for five minutes. The properties of the membrane were the following: flow rate: 0.8 m3 / m2 day salt repellency: 96% m-value: - 0.03 number of cavities: 450 per 0.844 mm2 elongation at break: 5%.

The salt repellency decreased to 94% after a 200 hour test.

Comparative Example 2 A membrane was made by the same procedure Prepared as in Comparative Example 1, with the exception that pyromalic acid £ was used in place of oxalic acid. The membrane properties were as follows: Flow rate: 0.43 m3 / m2 day Salt repellency: 54% Numerous cavities were observed.

Comparative Example 3 A membrane was prepared according to the same procedure, as used in Comparative Example 1, but with the exception that acetic acid was used instead of oxalic acid. The membrane properties were the following: flow rate: 0.6 m3 / m2 day salt repellency: 93% number of cavities: approx 500 per 0.844 mm2 elongation at break: 6%.

Comparative Example 4 A membrane was made according to Example 9 using of 3 g of maleic acid instead of 2.4 g of 1,2 ~, 3,4-butanetetracarboxylic acid and 0.6 g maleic acid. The membrane properties were as follows: Flow rate: 0.45 m3 / m2 day salt repellency: 98.5% number of voids: 1.2 per 0.844 mm2.

Claims (17)

Reverse osmosis membrane, process for its manufacture and Casting solution for performing the method Claims 1. A membrane Cellulose derivative for reverse osmosis with no less than about 3 x 10-10 g3 / cm7 Sec. 2 atmosphere³ of A³ / B and no more than about 0.2 voids per 0.844 mm, where A is the water penetration coefficient (g / cm2 sec atmosphere) and equals F1 / (# P -tt, where F1 is the product water flow through the membrane (g / cm2 second), A P is the applied pressure difference (atmosphere) and ## AT is the osmotic pressure difference (Atmosphere), and B is the salt permeation coefficient (cm / second) and F2 / (C1-C2) where F2 is the salt penetration through the membrane (g / cm2 x second), C1 the salt concentration in the concentrate (g / cm³) and C2 the salt concentration in the product water (g / cm3). 2. membrane for reverse osmosis according to claim 1, characterized in that that the cellulose derivative is a cellulose acetate with an acetyl content of about 39.8 is up to about 43.2% by weight. 3. Method of making a reverse osmosis membrane according to Claim 1 and 2, characterized in that a solution of a cellulose derivative is used in a solvent, a tetracarboxylic acid is added to the solution, the solution pours onto a substrate, and the solvent partially evaporates, the resulting Membrane coagulates and then heated. 4. The method according to claim 3, characterized in that as Tetracarboxylic acid of the general formula R- (CO 2 H) 4 is used, in which R a tetravalent aliphatic or ahcyclic organic radical with 2 to 10 Means carbon atoms. 5. The method according to claim 3 and 4, characterized in that one add a monobasic and / or dibasic carboxylic acid to the solution before pouring clogs. 6. The method according to claim 3 to 5, characterized in that one as a cellulose derivative, a cellulose acetate, in which the acetyl content is about 39.8 to 43.2 % By weight is approximately 30 to 180 Parts of solvent, based to 20 parts by weight of the cellulose acetate. 7. The method according to claim 3 to 6, characterized in that one about 2 to 40 parts by weight of tetracarboxylic acid, based on 20 parts by weight of the cellulose acetate, clogs. 8. The method according to claim 5 to 7, characterized in that one a mole fraction of 0.20 to 0.55 of a monobasic and / or dibasic carboxylic acid added to the solution, the mole fraction being based on the total amount of tetracarboxylic acid plus monobasic and / or dibasic carboxylic acid. 9. casting solution for performing the method according to claim 3 to 8, characterized in that it is a cellulose derivative, an organic solvent therefor and a tetracarboxylic acid of the general formula R- (C02H) 4, wherein R is a tetravalent aliphatic or alicyclic organic radical with 2 to 10 carbon atoms means contains. 10. Casting solution according to claim 9, characterized in that its cellulose derivative Cellulose acetate, cellulose acetate propionate, cellulose acetate butyrate, methyl cellulose and / or Eth # lcellulose. 11. Casting solution according to claim 9 and 10, characterized in that its cellulose derivative is a cellulose acetate. 12. Casting solution according to claim 9 to 11, characterized in that they use the tetracarboxylic acid in an amount of about 1 to 20 parts by weight per 10 wt. - Contains parts of the cellulose derivative. 13. Casting solution according to claim 9 to 12, characterized in that they as tetracarboxylic acid butane tetracarboxylic acid, ethylene tetracarboxylic acid, cyclopropane tetracarboxylic acid, Cyclobutanetetracarboxylic acid, cyclopentanetetracarboxylic acid and / or furantetracarboxylic acid contains. 14. Casting solution according to claim 9 to 13, characterized in that it contains 1,2,3,4-butanetetracarboxylic acid as tetracarboxylic acid. 15. Casting solution according to claim 9 to 14, characterized in that they also have a monocarboxylic acid and / or dicarboxylic acid. contains acid. 16. Casting solution according to claim 15, characterized in that; that the mole fraction of the monocarboxylic acid and / or dicarboxylic acid, based on the total number of moles of these Acids plus tetracarboxylic acid in the casting solution no more than about 0.55, preferably is about 0.20 to about 0.40. 17. Casting solution according to claim 15 and 15, characterized in that it contains maleic acid as the dicarboxylic acid.