JPS5837842B2 - Manufacturing method of ultrafiltration membrane - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a selectively permeable membrane, and more particularly to an aromatic polyamide selectively permeable membrane that can be suitably used as an ultrafilter membrane.

In general, membranes that selectively permeate specific components in liquid mixtures such as solutions, emulsions, and suspensions are called selectively permeable membranes. Since it is possible to separate the detergent medium and dispersion medium from solutions and emulsions containing polymeric substances and organisms, it is useful for purification in the fields of industrial wastewater treatment, sewage purification, food, medicine, brewing, fermentation, etc. Used in the concentration process.

Conventionally, such selective permeable membranes are mainly made of cellulose acetate, which has a high permeation rate and rejection rate, but they have poor heat resistance, chemical resistance, mechanical strength, etc. Since these are not necessarily sufficient, selectively permeable membranes made of aromatic polyamides, which are superior in these respects, have recently been proposed.

Generally, in order for a selectively permeable membrane to be put to practical use in membrane separation treatment, the permeable membrane must have a high permeation rate for solvents and dispersion media and a high rejection rate for solutes and dispersoids. However, there is a contradictory relationship between the permeation rate and the rejection rate, and in order to increase the rejection rate, the permeation rate must be sacrificed to some extent.

Therefore, none of the aromatic polyamide membranes that have been proposed so far have both a high permeation rate and a high rejection rate, and there are also difficulties in putting them into practical use.

In particular, conventional aromatic polyamide membranes have a wide pore size distribution in the membrane surface layer, the so-called skin layer, and low ambivalence with respect to the molecular weight of the solute, which is the reason why it is not possible to increase the rejection rate without impairing the permeation rate. I can say that.

The present inventors have conducted intensive research to solve the above-mentioned problems in aromatic polyamide membranes. As a result, in the production of aromatic polyamide membranes, conventionally, a membrane forming solution (hereinafter referred to as dope) containing this polymer has been used.

) (hereinafter referred to as dope solvent).

dimethyl sulfoxide (hereinafter referred to as DMSO), which is only considered as one of the

) is understood as a kind of additive or modifier to the dope due to its remarkable influence on the physical properties of the dope, and by making it exist in the dope in a specified amount for the aromatic polyamide, a high permeation rate can be maintained. In addition, the present inventors have discovered that it is possible to produce an aromatic polyamide membrane with an increased rejection rate, leading to the present invention.

The method for producing a selectively permeable membrane according to the present invention is carried out using the general formula (wherein R1 and R2 each independently represent a divalent aromatic group, and X and X2 each independently represent an amide bond.

) and an inorganic swelling agent selected from alkali metal and alkali metal halides, nitrates, sulfates, and mixtures of two or more thereof, based on 100 parts by weight of this polyamide. l
5 to 90 parts by weight, 280 to 1200 parts by weight of DMSO based on 100 parts by weight of the above polyamide, and N-methyl-2
- A dope consisting of an organic solvent selected from pyrrolidone, dimethylacetamide, dimethylformamide, hexamethylene phosphoramide and mixtures of two or more thereof is applied to a suitable supporting substrate, and then water or water as the main component is applied. The method is characterized in that the above polyamide is coagulated in a brewing agent to form a film.

The aromatic polyamide used in the present invention consists of repeating units represented by the above general formula, and examples of R1 and R2 include 1,3-phenylene, 1,4-phenylene, 3,3'-biphenylene, 4,4' -biphenylene,
1,4-naphthylene, 1,5-naphthylene, 1,6-naphthylene, 4,4'-oxadiphenylene, 4,4'-
Examples include methylene diphenylene, 4,4'-monocarbonyl diphenylene, 3,3'-sulfonyl diphenylene, etc., and these aromatic groups have a portion of their hydrogen atoms converted into halogen atoms, amino groups, nitro groups, etc. may be substituted with a group, a carboxyl group, a sulfonic acid group, a lower alkyl group, etc.

Among these aromatic polyamides, those consisting essentially of repeating units represented by the following formula are preferably used in the present invention, and in particular, among the total 7 enylene groups, 7 m-phenylene groups are used.
Those containing 0 mol % or more and 30 mol % or less of p-phenylene groups are preferably used.

The above-mentioned aromatic polyamides are, for example,
It can be produced by the method disclosed in Japanese Patent Publication No. 13247 and Japanese Patent Publication No. 35-14399.

Usually, a dicarboxylic acid chloride and a diamine are condensed and polymerized in a solvent such as dimethylacetamide at a low depth.

The aromatic polyamide obtained in this way differs depending on the starting materials, reaction conditions, etc., but generally has a limiting viscosity (solvent N-methyl-2-pyrrolidone,
Hereinafter referred to as NMP.

) is about 0.3 to 2.0. In the present invention, 0.0.
Aromatic polyamides having an intrinsic viscosity of 9 to 2.0 are preferably used.

In the present invention, the doping solvent used is NMP or dimethylformamide (hereinafter referred to as DMP), which dissolves the aromatic polyamide and is compatible with water.

λ dimethylacetamide (hereinafter referred to as DMAO).

), hexamethylene phosphoramide, or a mixture of two or more of these are used, and the aromatic polyamide concentration in the dope (hereinafter referred to as dope concentration) is used.

) is usually 5 to 30% by weight, preferably 8 to 20% by weight.

If the dope concentration is too low, the resulting permeable membrane will have poor selective separation ability, while if the dope concentration is too high,
This is because not only is it difficult to uniformly coat the support substrate, but also the permeation rate of the resulting permeable membrane becomes low.

In relation to the dope concentration, the viscosity of the dope when applied to the support substrate is usually adjusted to 20 to 5000 poise (20°C), preferably 50 to 1000 poise (20°C).

In the present invention, an inorganic swelling agent and DMSO are used as additives constituting the dope.

The inorganic contrast agent is selected from alkali metals and alkali metals, preferably lithium, potassium, sodium, calcium and magnesium chlorides, especially chlorides and bromides, nitrates, sulfates and mixtures of two or more thereof. It will be done.

Specific examples include lithium chloride, potassium chloride, calcium chloride, lithium bromide, potassium bromide, lithium nitrate, potassium nitrate, and magnesium sulfate.

The amount of these inorganic salt swelling agents used varies depending on the dope solvent and dope concentration, but is generally 15 to 90 parts by weight, preferably 30 to 80 parts by weight, per 100 parts by weight of the aromatic polyamide in the dope. be.

If the amount of inorganic salt swelling agent used is too large, the dissolution state of the dope tends to deteriorate, and the resulting membrane becomes inferior in selective separation ability.On the other hand, if the amount of the inorganic salt swelling agent is too small, The solubility in the solvent decreases,
This is because not only is membrane formation difficult, but also the permeation rate of the resulting permeable membrane tends to be low.

DMSO is aromatic polyamide 100 that constitutes the dope.
280 to 1200 parts by weight, preferably 300 to 1200 parts by weight
800 parts by weight are used.

Surprisingly, it has been found that DMSO has a significant effect on the coagulability of aromatic polyamides when the doped support substrate is immersed in a coagulation solvent.

That is, it has been found that when DMSO is used in the above-mentioned range for aromatic polyamide, the aromatic polyamide is rapidly coagulated in the coagulating thickener.

In other words, the aromatic polyamide rapidly solidifies while remaining relatively dissolved in the dope, and in terms of membrane structure, the surface layer is quickly and uniformly formed. .

As a result, according to the method of the present invention, the skin layer has a pore-like structure with a significantly narrow pore size distribution, and therefore has high ambivalence with respect to the molecular weight of the solute, and therefore has a high rejection rate for solutes of a certain size or more. This makes it possible to obtain ultrafilter membranes with high filtration.

On the other hand, when the amount of DMSO added is too small or when it is not used as an additive, the coagulation rate of the aromatic polyamide in the immersion medium is slow, and the surface layer of the film may have an uneven structure during the coagulation process. Therefore, only a membrane having a skin layer with a wide pore size distribution can be obtained.

Generally, the solubility of aromatic polyamide in dope solvent is
It depends not only on the type of solvent but also on the content of inorganic swelling agent in the dope.

If the amount of DMSO added is too large, the state of dope dissolution will deteriorate when the amount is increased enough to be suitable for forming a film with a high dope concentration.

Therefore, if the amount of the inorganic lubricant that helps dissolve the aromatic polyamide in the dope is increased more than necessary, the above-mentioned disadvantages will occur.

Therefore, in the method of the present invention, the amounts of the additive DMSO and the inorganic swelling agent are mutually critical.

By providing a certain balance to the dope composition, the method of the present invention, as described above, does not impair the permeation rate of the resulting permeable membrane, but rather improves it, while significantly increasing its fractionation. This method was successful in obtaining a permeable membrane with a high rejection rate.

As is clear from a comparison of Examples and Comparative Examples, which will be explained later, for example, when a polyethylene glycol aqueous solution with a molecular weight of 20,000 is treated, the ultrafurnace filtered membrane obtained with a dope that does not contain DMSO as an additive is at best 85-87%
whereas the membranes obtained according to the invention have a rejection rate of more than 90%, preferably about 94%.
It has a high rejection rate.

This difference in rejection rate is extremely important in practical marginalization.

Moreover, since the membrane according to the present invention is also superior in terms of water permeation rate, the superiority of the membrane according to the present invention is clear.

The dope is usually applied to the support substrate in a mixed room at a temperature of about 15 to 35°C.

The doped support substrate is contacted with the coagulation solvent, typically within a few minutes, such as within 5 minutes, after application.

This is because if the membrane is left for too long after dope application, the resulting permeable membrane will be inferior in selective separation ability.

The coagulating solvent must not dissolve the aromatic polyamide, be compatible with the dope solvent and DM80, and be capable of dissolving the inorganic swelling agent.

Water is most preferably used as the coagulating solvent, but methanol, ethanol, acetone, ethylene glycol, and mixed solvents of these with water can also be used.

Coagulation or mixing is not particularly limited, but is generally carried out at a temperature below the boiling point of the coagulation solvent.

When water is used as a coagulating solvent, the temperature is usually 0 to 80°C, preferably 0 to 50°C.

The time required for coagulation varies depending on the coagulation solvent and its mixture, but is usually 1 to 10 hours.

The supporting base material to which the dope is applied is not particularly limited.

glass, stainless steel, aluminum, polypropylene,
When a plate or tube with a smooth surface, such as polyethylene, is used as a supporting substrate, the aromatic polyamide is easily peeled off from these supporting substrates after coagulating in a coagulating solvent, so each sheet is Shape and tubular permeable membranes are obtained.

In addition, by using sheet-like or tubular support materials of woven or non-woven fabrics made of organic fibers such as polyester fibers and acrylic fibers, and inorganic fibers such as glass fibers and carbon fibers, these support materials can be A composite permeable membrane can be obtained integrally formed thereon.

Furthermore, a hollow fiber-like permeable membrane can also be obtained by extruding the dope from a hollow spinneret into a coagulating solvent.

In the method of the present invention, for the purpose of improving the mechanical toughness at high temperatures of the selectively permeable membrane obtained as described above, it is possible to The heat treatment can be performed for about 5 seconds to 30 minutes.

This treatment is carried out by placing the permeable membrane in heated air or by immersing it in heated water or glycerin.

The treatment time may be short if the treatment temperature is high, and long if the treatment temperature is low.

The present invention will be explained in more detail with reference to Examples below, but the present invention is not limited to these Examples in any way.

Similarly, in the following examples, the film properties were evaluated as follows.

That is, the permeable membrane was attached to a pressurized filter holder, and in the case of pure water, "11/c4", polyethylene glycol (hereinafter referred to as PEG) was applied under a nitrogen atmosphere.

) 4 in the case of an aqueous solution (concentration 5000 ppm)
Each was supplied at an operating pressure of kg/cd, and the permeation rate and rejection rate defined by the following equations were determined.

In addition, the porosity of the permeable membrane was determined from the water content of the membrane.

Example 1 A homogeneous solution consisting of parts by weight of dope solvent DMAOIO, 1 parts by weight of feeding agent DMS07 and 7 parts by weight of lithium chloride was
It consists of repeating units represented by the above general formula, m-phenylene group is 70 mol%, p-phenylene group is 30 mol%, and the intrinsic viscosity of the NMP solution at 30°C is 1,
83 aromatic polyamide (hereinafter referred to as PA).

) was added and completely dissolved to prepare a dope.

This dope was cast onto a glass plate at room temperature, immediately poured into 20°C water, immersed for 24 hours, and the thickness was 150 μm.
, an ultrafilter membrane with a porosity of 89% was obtained.

The physical properties of the membrane are shown in the table below.

Examples 2 to 6 Using DMAO as a dope solvent, various ultrafilter films were obtained from dopes having different dope compositions in exactly the same manner as in Example 1.

The dope composition and physical properties of the obtained film are shown in the table below.

Example 7 A film was formed in exactly the same manner as in Example 1, except that NMP was used as the dope solvent and a set of doves shown in the table below was used.

The physical properties of the obtained membrane are shown in the table below. Example 8 A film was formed in exactly the same manner as in Example 1, except that DMF was used as the dope buty agent and one of the dopes shown in the table below was used.

The physical properties of the obtained membrane are shown in the table below. Comparative Example I A dope was prepared by completely dissolving 12 parts by weight of PA in a solution consisting of 050 parts by weight of DMA, 3 parts by weight of DM, and 5 parts by weight of lithium chloride. An ultrafiltration membrane having the following properties was obtained.

It is clear that the pure water permeation rate and rejection rate for PEG having a molecular weight of 20,000 are inferior compared to the ultrafilter membrane according to the present invention.

Comparative Example 2 A dope was prepared by completely dissolving 12 parts by weight of PA in a solution consisting of 081 parts by weight of DMA and 7 parts by weight of lithium chloride, and an ultrafurnace having the physical properties shown in the table was prepared in exactly the same manner as in Example 1. A membrane was obtained.

Comparative Examples 3 to 4 Ultrafurnace membranes having the physical properties shown in the table were obtained in exactly the same manner as in Comparative Example 1, except that NMP and DMF were used as dope solvents, respectively.

Example 9 The ultrafilter membrane obtained in Example 1 was examined for its permeation rate and rejection rate for PEG aqueous solutions with various molecular weights.

In addition to the membrane obtained in Comparative Example 2, Figures 1 and 2 respectively
As shown in the figure.

The solid line shows the film produced by the method of the present invention, and the dotted line shows the film of the comparative example.

It is clear that the membrane according to the invention has excellent compatibility with respect to the molecular weight of the solute and a high water permeation rate.

[Brief explanation of the drawing]

Figures 1 and 2 show the water permeation rate and rejection rate when polyethylene glycol aqueous solutions of various molecular weights were treated, the solid line shows the ultrafilter membrane obtained by the method of the present invention, and the dotted line shows the comparative This is an example.

Claims (1)

[Claims] 1 Consists of repeating units represented by the general formula (wherein R and R2 each independently represent a divalent aromatic group, and X and X2 each independently represent an amide bond) an aromatic polyamide, and 15 to 90 parts by weight of an inorganic swelling agent selected from alkali metals and alkali metal halogenides, nitrates, sulfates, and mixtures of two or more thereof, based on 100 parts by weight of the polyamide. , 280 to 1200 parts by weight of dimethyl sulfoxide based on 10 parts by weight of the polyamide;
N-methyl-2-pyrrolidone, dimethylacetamide,
A dope consisting of dimethylformamide, hexamethylene phosphoramide, and an organic acid selected from mixtures of two or more thereof is applied to a suitable support substrate, and then dimethyl sulfoxide and the above solvent are doped without substantially evaporating. A method for producing an ultrafiltration membrane, which comprises coagulating the above polyamide in water or a solvent mainly containing water to form a membrane. 2. The aromatic polyamide consists essentially of repeats represented by the formula, and the proportion of 5-m-phenylene groups of all phenylene groups is 70 mol% or more, and the proportion of p-phenylene groups is 30 mol% or less A method for producing an ultrafiltration membrane according to claim 1.