JPS5924647B2 - Manufacturing method of composite membrane for reverse osmosis - Google Patents

Description

Detailed Description of the Invention The present invention uses a porous membrane made of polysulfone as a support,
The present invention relates to a method for producing a composite membrane for reverse osmosis, which comprises forming a barrier layer made of a polymer different from the polysulfone on the surface of the support.

Conventionally, various reverse osmosis membranes have been proposed as liquid separation membranes that apply the principle of reverse osmosis, but among them, they are more porous than membranes with asymmetric structures made of the same polymer, such as cellulose acetate membranes. Composite membranes with a dense barrier layer formed on the surface of the support can greatly improve membrane performance by independently selecting the type, combination, or membrane structure of the polymers constituting the support and barrier layer. It is attracting attention because it has many merits, such as improved performance and the ability to manufacture membranes tailored to specific uses and purposes.

The manufacturing method for this composite membrane for reverse osmosis can be roughly divided into a method in which a membrane-forming polymer is coated on the microporous support membrane and solidified to manufacture a composite membrane (hereinafter referred to as polymer-coated type). (hereinafter referred to as "monomer coating type"), and a method in which an in-situ polymerization type reaction component such as a monomer, oligomer, or an initial reaction product thereof is coated on the support film and a polymerization reaction is performed to form a film (hereinafter referred to as monomer coating type). However, the manufacturing method of these composite membranes, especially the monomer-coated type, has an industrial problem in that the membrane performance of the resulting composite membrane tends to fluctuate, making it difficult to obtain a membrane with stable quality and performance with good reproducibility. There is a problem. For example, P.B.RepOrt
No. 2,34198, as described in U.S. Pat.
In the production of the monomer-coated composite membrane disclosed in No. 926,798, the water permeability, which is the basic performance of a reverse osmosis membrane, is said to vary by about 2 to 3 times. Therefore, there is a strong demand for the production of membranes with stable quality and performance without such fluctuations in membrane properties.

The inventors of the present invention have focused on these problems and have conducted extensive research to discover the present invention.

That is, an object of the present invention is to provide an industrially advantageous manufacturing method that maintains the inherent membrane properties of a composite membrane for reverse osmosis and significantly reduces fluctuations in membrane performance. The object of the present invention is to provide a solution containing in-situ polymerizable reaction components such as initial reactants such as film-forming monomers and/or oligomers on a support film made of polysulfone. applied and heated to about 140℃
After drying at a temperature of at least 10°C above that temperature
This can be achieved by heat treatment under high temperature conditions ~ As the support membrane made of polysulfone used in the present invention, a known microporous polysulfone membrane such as a dimethylformamide solution of polysulfone can be used. The polysulfone is cast into a film and introduced into a medium that is a non-solvent for the polysulfone and is miscible with dimethylformamide, such as water, to gel (solidify) the polysulfone.

A microporous membrane obtained by a wet membrane forming method can be exemplified. The polysulfone support membrane is dried, especially at 100%
When drying under heating above ℃, the membrane surface and internal pore size may change due to thermal contraction of the membrane itself, which may change membrane properties such as water permeability. Alternatively, it is better to keep it in a hydrated state. The in-situ polymerization type reaction components such as monomer oligomers or initial reaction products coated on the polysulfone support film are non-solvents for the polysulfone and include the following A. B. C. A material containing D and/or E as a main component is used.

A. Furfuryl alcohol B. A compound represented by the following general formula (Rl, R2, R3 are hydrogen or an organic group having 2 to 5 carbon atoms, and at least two of them are organic groups having 2 to 5 carbon atoms having a hydroxyl group or a glycidyl group) ,C. D. an intermolecular condensate of the compound of B. Compound B and carbon number 2-
3 epoxy compound, polyhydric alcohol having 2 to 8 carbon atoms,
A mixture with at least one selected from polyethylene oxide or formaldehyde; E. Intermolecular condensate of B, polyhydric alcohol having 2 to 8 carbon atoms, and 2 to 17 carbon atoms
at least one selected from polycarboxylic acids, furfuryl alcohol, and tetrahydrofurfuryl alcohol
Specific examples of the compound B above as a mixture with seeds include 1,3
, 5-tris(2/-hydroxyethyl)isocyanuric acid (hereinafter abbreviated as THEIC), bis(2-hydroxypropyl)isocyanuric acid, 1,3,5-tris(glycidyl)isocyanuric acid, etc. Especially T
HEIC is preferably used.

The intermolecular condensate of B can be easily obtained from the compound of B by a known method. For example, when THEIC is used, a small amount of water is added to THEIC and heated to form a paste, and as an acid catalyst. An intermolecular condensate of THEIC is obtained by adding sulfuric acid, heating at 140° C. for 10 minutes, and then removing water in the system, including produced water, under reduced pressure. Specific examples of the epoxy compound, which is one of the starting materials, include ethylene oxide and propylene oxide, and specific examples of the polyhydric alcohol include ethylene glycol, glycerin, sorbitol, and inositol.

In addition, polycarboxylic acids include oxalic acid, maleic acid,
Water-soluble ones such as 1,2,3,4-benzenetetracarboxylic acid and butanetetracarboxylic acid are used. As the acid catalyst, sulfuric acid is most preferred, but other examples include methanesulfonic acid, benzenesulfonic acid, toluenesulfonic acid,
Phosphoric acid, hydrochloric acid, etc. can also be used.

The weight ratio of the reaction component and the acid catalyst is preferably optimized depending on the combination, but it is 20:1 when only the compound B is used, and 1:1 when other reaction components are used.
The ratio is preferably about 0.5 to 1:1. In addition to the above-mentioned reaction components, acid catalyst, water or water-soluble organic solvent, the coating solution contains a solvent that does not deteriorate the support (for polysulfone support, methanol, Koshool, propanol, isopropanol, etc.). In addition, a surfactant (for example, an anionic surfactant or a nonionic surfactant) may be added to improve the wettability of the support surface so that the coating solution can be applied uniformly.

The concentration of the barrier layer forming solution varies depending on the type of reaction components such as monomers, oligomers and/or initial reaction products contained in the solution, but is preferably in the range of 1.0 to 10.0% by weight. It is best to use one prepared in the following manner.

In addition, the thickness of coating on the support membrane varies depending on the type of reaction components such as monomers, oligomers and/or initial reaction products, and the membrane performance required of the resulting composite membrane, but it is usually applied on the surface of the support. The thickness of the barrier layer is preferably 0.01 to 0.10 microns. In the present invention, the method of coating the polysulfone support membrane with the coating liquid for forming a barrier layer may be any known method and is not particularly limited. For example, a method of coating or spraying the coating liquid, a method of immersing the polysulfone support film in the coating liquid, etc. can be applied. As mentioned above, a water-containing polysulfone support membrane is used, and a coating liquid that is a non-solvent for polysulfone but miscible with water, that is, a solvent such as water or isopropyl alcohol, is used. This replaces the water in the support film with the solvent of the coating solution, improving the adhesion of the coating solution to the surface of the support film.

In particular, the immersion method is more effective in replacing the water contained in the film with the solvent than coating or spraying, resulting in a composite film with uniform coating thickness, uniform film thickness, and good film performance. It's easy to get caught. Thus, the support film coated with the coating solution for forming a barrier layer is, if desired, kept vertical or tilted to drain the liquid, and then the coating solution layer is polymerized. Incidentally, fluctuations in membrane performance can be reduced by keeping the temperature, humidity, atmosphere, angle, time, etc. during draining constant. Next, in the present invention, the coating solution coated on the support film as described above, that is, the monomer, oligomer, and/or initial reaction product as reaction components, is reacted to coat the support film on the support film. Although it is necessary to form an integrated barrier layer, in the present invention, after drying at a temperature of 140° C. or less,
It is characterized in that it is then heat-treated at a temperature that is about 10° C. or more higher than the drying temperature.

That is, as described above, in order to form a barrier layer from a coating solution containing the monomer, oligomer and/or initial reaction product, the solvent in the coating solution is removed and the monomer, oligomer and/or initial reaction product is removed. It is necessary to polymerize the reaction product and remove water in the support membrane, and in this barrier layer forming step, slight variations in conditions can lead to wide variations in membrane properties. For example, as the film thickness and water content of the polysulfone support film change, the amount of coating fluid applied also changes.
Along with this, it is thought that the drying rate of moisture, the solvent, and the reaction rate of the reaction components also change. However, as in the present invention, when first drying at a temperature of about 140°C or lower and then heat-treating at a temperature of about 10°C or higher than this drying temperature, a composite membrane having constant performance and quality with significantly less fluctuation in membrane performance can be obtained. It can be manufactured with good reproducibility.

The reason for this is not fully clear, but perhaps in the first drying step, priority is given to removing the moisture contained in the support film and the solvent of the coating solution, and in particular, as mentioned above, heat shrinkage of the polysulfone support film is avoided. However, in the present invention, during the drying process, the reactive components in the coating liquid that entered the pores existing in the surface layer of the polysulfone support membrane partially polymerized, and the resulting polymer This is thought to suppress shrinkage of the support membrane because it is less susceptible to thermal deformation. In addition, as a dryer used in the drying process, a hot air type using a steam heater is preferable in consideration of drying efficiency, explosion of organic solvent vapor, and impact on the human body. However, as a dryer used in the heat treatment process, it is practically Since the solvent has been removed, various heat treatment equipment, preferably a hot air type, can be used.

According to the present invention, (1) the performance of the composite membrane for reverse osmosis, especially the fluctuation in desalination performance such as water permeability and solute exclusion rate, is extremely small, for example, the coefficient of variation of each performance is 0.10 and 0.0010 or less; It is possible to produce a composite membrane with good desalination performance with good reproducibility.

(2) Composite membrane performance is improved; for example, when desalinating seawater at a pressure of 56 Kq and a temperature of 25° C., the water permeation rate is 0.30 w1/i and the supernatant rejection rate is 99.

7% can be easily obtained.

Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example 1 20? X3O? Shioputa is made of rectangular polyester fibers with a size of
7 pieces/inch, thickness 160μ) were fixed on a glass plate,
On top of that, polysulfone (U made by Union Carbide)
delP-3,500) in dimethylformamide (DMF) to a thickness of 200μ at room temperature (15~3
The fiber-reinforced polysulfone carrier (hereinafter referred to as It is abbreviated as FR-PS support.

). This FR-PS support *holder (thickness 200
The pure water permeability coefficient of μ) is 0.01 to 0.0209/CwL-Sec when measured at a pressure of 1 Kg and a starting temperature of 25°C. atm
It is. THEICl wt%, furfuryl alcohol 2
% by weight, 2% by weight of sulfuric acid, 1% by weight of sodium dodecyl sulfate, and 20% by weight of isopropyl alcohol.
Soak the PS support for 5 minutes at room temperature.

Next, take out the FR-PS support and tie both ends of the long side by 2
After hanging between iron plates (150g/sheet) of my width and hanging them vertically at room temperature for 1 minute, drying them in a hot air dryer for 3 minutes at 140℃, and then drying them at 150℃ for 5 minutes.
Perform heat treatment for a minute. Films were formed four times using the above method and conditions, and the three-point reverse osmosis performance of each film was measured. The measurement conditions and measurement results are shown in Table-1. Comparative Example 1 The same procedure as in Example 1 was carried out except that drying and heat treatment were performed once at 150° C. for 8 minutes.

The measurement results are shown in Table-1. Examples 2 and 3 Films were formed in the same manner as in Example 1 except that the drying temperature was changed, and the reverse osmosis performance was measured at one point each (4 points in total) for each film formed.

The measurement results are shown in Table-2. Comparative Examples 2 to 5 Table 2 shows the cases in which drying and heat treatment were performed once at different temperatures in Examples 2 and 3, and the cases where drying and heat treatment were performed twice at the same temperature.

Examples 4 and 5 In Example 1, an aqueous solution consisting of 2% by weight of furfuryl alcohol, 2% by weight of sulfuric acid, 0.7% by weight of sodium dodecyl sulfate and 20% by weight of isopropyl alcohol is used as the coating liquid, and the drying temperature is changed. The membranes were formed in the same manner except for the above, and the reverse osmosis performance was measured at one point each (4 points in total) for each membrane formed.

The measurement results are shown in Table-3. Comparative Examples 6 to 9 Table 3 shows the cases in which drying and heat treatment were performed once at different temperatures in Examples 4 and 5, and the cases where drying and heat treatment were performed twice at the same temperature.

Measurement conditions: Same as Table 1, upper column is range, lower column is average value Examples 6, 7 Film formation was performed in the same manner as in Example 1 except that sorbitol was used instead of THEIC and the drying temperature was changed. Reverse osmosis performance was measured for each film formed at one point each (4 points in total).

The measurement results are shown in Table-4. Comparative Examples 10 to 13 Table 4 shows the cases in which drying and heat treatment were performed once at different temperatures in Examples 6 and 7, and the cases where drying and heat treatment were performed twice at the same temperature.

Claims (1)

[Scope of Claims] 1. A film-forming in-situ polymerization reaction containing the following A, B, C, D and/or E as a main component, which is a non-solvent for the polysulfone, on a porous support membrane made of polysulfone. A method for producing a composite membrane for reverse osmosis, comprising applying a solution containing the components, drying at a temperature of about 140° C. or lower, and then heat-treating at a temperature at least 10° C. higher than the drying temperature. A, furfuryl alcohol B, a compound represented by the following general formula ▲ Numerical formula, chemical formula, table, etc. ▼ (R_1, R_2, R_3 are hydrogen or an organic group having 2 to 5 carbon atoms, and at least two of them are It is an organic group having 2 to 5 carbon atoms and having a hydroxyl group or a glycidyl group.) C, an intermolecular condensate D of the compound B above, an epoxy compound having 2 to 3 carbon atoms and the compound B above, and 2 to 8 carbon atoms. and at least one selected from polyhydric alcohol, polyethylene oxide, and formaldehyde. F, a mixture of the intermolecular condensate of B and at least one selected from polyhydric alcohols having 2 to 8 carbon atoms, polycarboxylic acids having 2 to 17 carbon atoms, furfuryl alcohol, and tetrahydrofurfuryl alcohol; 2. A method for producing a composite membrane for reverse osmosis according to claim 1, characterized in that a porous support membrane made of polysulfone is maintained in a water-containing state.