JPS61209054A - Treatment of aqueous solution - Google Patents

Abstract

PURPOSE:To enhance separation capacity, in separating the neutral solute and charged solute contained in an aqueous solution, by using a composite semipermeable membrane equipped with a skin layer with a specific thickness having a specific amount of a sulfonic acid group. CONSTITUTION:A semipermeable membrane having a sulfonic acid group comprises a polymer wherein a sulfonic acid group is 70% or more based on all of ion exchange groups and the residual ion exchange group is one other than the sulfonic acid group, for example, a carboxylic acid group. As mentioned above, if the polysulfone composite semipermeable membrane having the sulfonic acid group and provided with a skin layer having separation capacity comprising sulfonated polysulfone and integrally laminated to a support membrane with a thickness of 10mum or less is used, the neutral substance in an aqueous solution to be treated can be conc. in the membrane transmitted solution and the charged solute therein can be effectively separated therein.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method for treating an aqueous solution, and more specifically, a method for treating an aqueous solution containing an electrically substantially neutral solute and a charged solute. and a method for separating these solutes.

(Prior art) Conventionally, a substantially electrically neutral solute (
(hereinafter referred to as neutral solute) and charged solute (hereinafter referred to as
It is called a charged solute. ), it is possible to use an ion exchange membrane as a semipermeable membrane and treat the aqueous solution under pressure, but since ion exchange membranes are generally thick, depending on this method, Water permeation rate is low,
This is difficult to adopt as a practical treatment method. In addition, a method of separating sucrose and sodium chloride in an aqueous solution by reverse osmosis using a cellulose acetate membrane is already well known, but the cellulose acetate membrane has pEI resistance, chlorine resistance,
Due to its poor heat resistance, it cannot be applied, for example, to the treatment of aqueous solutions containing acids or alkalis as solutes.
Furthermore, it cannot be applied to fields that require processing at high temperatures.

On the other hand, ultrafiltration membranes made of polysulfone are known as semipermeable membranes with excellent pi resistance, chlorine resistance, heat resistance, etc. However, all conventional polysulfone ultrafiltration membranes have a molecular weight cutoff. Because of their large size, they are unsuitable for treating aqueous solutions containing solutes with relatively small molecular weights, and furthermore, when their molecular weights are approximately the same, it is difficult to separate neutral solutes from charged solutes.

(Purpose of the Invention) Therefore, as a result of intensive research on the separation of neutral solutes and charged solutes contained in aqueous solutions, the present inventors found that the thickness of the skin layer, which has sulfonic acid groups and has separation performance, is 1.
When an aqueous solution containing the neutral solute and a charged solute is subjected to pressure treatment using a semipermeable membrane having a diameter of 0.8 m or less, the semipermeable membrane removes the neutral solute at a nearly constant level over a wide concentration range. On the other hand, for charged solutes, we discovered a phenomenon in which the removal rate decreases as the concentration increases.
In addition, the semipermeable membrane has a practical water permeation rate and can be used over a wide pH range and temperature range, so it can be applied to the treatment of various aqueous solutions containing neutral solutes and charged solutes. The present invention was achieved based on the discovery that charged solutes can be concentrated in a membrane permeate and charged solutes can be separated in a membrane permeate.

(Structure of the Invention) The method for treating an aqueous solution according to the present invention involves separating a substantially electrically neutral solute and a charged solute using a semipermeable membrane having sulfonic acid groups in a proportion of 70% or more of the total ion exchange groups. The method is characterized in that a substantially neutral solute is concentrated in a membrane non-permeable liquid, and a charged solute is separated in a membrane permeable liquid.

In the present invention, examples of neutral solutes include sugars, alcohols and derivatives thereof, amino acids and proteins at isoelectric points, dyes, and pigments. In the present invention, the phrase "the neutral solute is substantially electrically neutral" means that the solute is made electrically neutral by adjusting the pH.

Charged solutes refer to solutes that dissociate in water, and include organic salts, inorganic salts, alkalis, and acids. Specific examples include charged amino acids, proteins, sodium chloride, and potassium chloride. etc. can be mentioned.

In the method of the present invention, the concentration of the neutral solute and the charged solute in the aqueous solution to be treated is not particularly limited, but the higher the concentration of the charged solute, the lower the removal rate. , is effective in treating an aqueous solution with a high concentration of charged solutes, concentrating neutral solutes in the membrane permeate, and separating charged solutes in the membrane permeate. However, if the solute concentration is too high, the aqueous solution may have a high viscosity, making smooth processing difficult. is preferred.

The semipermeable membrane having sulfonic acid groups used in the method of the present invention is a semipermeable membrane made of a polymer in which sulfonic acid groups account for most of the total ion exchange groups, preferably 70% or more, particularly preferably 90% or more. be.

As long as the sulfonic acid group is within the above range among all ion exchange groups, the remaining ion exchange group may be an ion exchange group other than the sulfonic acid group, for example, a carboxylic acid group.

In the present invention, as a semipermeable membrane having a sulfonic acid group that can be particularly suitably used, Japanese Patent Application No. 59-12404
8 and Japanese Patent Application No. 59-124049, sulfonated polysulfone obtained by sulfonating a polysulfone consisting of repeating unit A, or a linear polysulfone copolymer consisting of repeating unit A and repeating unit B described above. One example is a composite semipermeable membrane in which a skin layer made of sulfonated polysulfone is integrally laminated on an ultrafiltration membrane as a support membrane.

Such a composite semipermeable membrane is preferably prepared by sulfonating a polysulfone consisting of the above-mentioned repeating unit A or a linear polysulfone copolymer consisting of the above-mentioned repeating unit A and repeating unit B to prepare a sulfonated polysulfone'. is dissolved in an alkylene glycol alkyl ether such as ethylene glycol monomethyl ether which may contain a small amount of an aprotic polar organic solvent to prepare a membrane forming solution, and an alkanediol having 2 to 4 carbon atoms, for example 1. After immersing in an aqueous solution of a plugging agent such as 4-butanediol or hydroxycarboxylic acid, such as lactic acid, the above membrane forming solution is applied onto the dried ultrafiltration membrane, and then the solvent is removed from the applied membrane forming solution. It can be obtained by evaporation.

In particular, in the above method, the sulfonated polysulfone is mixed with 0.5 g of N-methyl-2-pyrrolidone 1
It is desirable that the logarithmic viscosity measured at a temperature of 30° C. for a solution dissolved in 00 ml is 0.2 or more, and that the ion exchange group is 2.3 milliequivalents/g or less.

When the amount of ion exchange groups exceeds 2.3 milliequivalents/g, the sulfonated polysulfone becomes water-soluble and is unsuitable as a material for semipermeable membranes for treating aqueous solutions, and the logarithmic viscosity is 0. This is because when it is smaller than .2, it is difficult to form a uniform skin layer without defects such as pinholes.

In addition, when forming a skin layer using sulfonated polysulfone obtained by sulfonating the linear polysulfone copolymer, the linear polysulfone copolymer contains 10 mol% or more of repeating unit A and 90 mol % of the repeating unit A. % or less of repeating units B.

The sulfonated polysulfone composite semipermeable membrane also contains sulfonated polysulfone, an alkylene glycol alkyl ether that may contain a small amount of an aprotic polar organic solvent, and a water-soluble and low-volatility organic solvent as an additive. It can also be obtained by applying a film-forming solution containing a compound or an inorganic salt as an additive onto a dried support film, and then evaporating the organic solvent from this film-forming solution.

In the above method, the ultrafiltration membrane used as a support membrane for applying the membrane forming solution is not particularly limited, but preferably an ultrafiltration membrane made of polysulfone, for example, an ultrafiltration membrane made of a repeating unit of the following formula C. A filtration membrane is preferably used. The ultrafiltration membrane preferably has a molecular weight cut-off in the range of 1,000 to 200,000, particularly preferably about 100,000.

In this way, the thickness is usually 10 μm or less,
A polysulfone composite semipermeable membrane can be obtained in which a skin layer having sulfonic acid groups and separation performance is made of sulfonated polysulfone, and this skin layer is integrally laminated on a support membrane.

In the method of the present invention, the conditions for treating the aqueous solution are appropriately selected taking into account the nature of the semipermeable membrane used as well as the type and concentration of the solute. It can be easily selected.

(Effects of the Invention) As described above, according to the method of the present invention, a semipermeable membrane having a sulfonic acid group, particularly a composite semipermeable membrane having a skin layer made of sulfonated polysulfone, is used to remove neutral solutes. When treating an aqueous solution containing a charged solute and a neutral solute, the semipermeable membrane has a nearly constant removal rate over a wide range of concentrations, whereas for a charged solute the concentration is As it increases, the removal rate decreases so that neutral solutes can be concentrated in the membrane retentate and charged solutes can be separated in the membrane permeate.

Therefore, the method of the present invention is not particularly limited in its mode of application, but includes, for example, the separation of sucrose and inorganic salts in an aqueous solution containing them, or the separation of sucrose and inorganic salts in a substantially neutral solution at the isoelectric point. It can be suitably applied to the separation of charged amino acids and charged amino acids.

(Examples) The present invention will be described below with reference to Examples, but the present invention is not limited to these Examples in any way. In the Examples, the solute removal rate and water permeation rate of the obtained composite semipermeable membrane were determined by the following equations.

Reference Example 1 (1) Production of polysulfone A polysulfone having a repeating unit of formula A1 was produced according to the method described in Japanese Patent Publication No. 46-21458.

That is, 13.2 g (0.12 mol) of hydroquinone was placed in a flask equipped with a stirrer, a nitrogen gas inlet tube, a water drain tube, and a thermometer, and 100 ml of sulfolane and 50 ml of xylene were added thereto. Refluxing was carried out at 150° C. for 1 hour while stirring while heating with a mantle heater, and at this time, 3 ml of fishing rod was taken out.

Then, the temperature was lowered to 110°C, and 34.5 g (0.12 mol) of 4.4"-dichlorodiphenylsulfone and 20.7 g (0.15 mol) of potassium carbonate were added to start the polymerization reaction. 155°C After refluxing for 50 minutes, the temperature was raised to 200°C while removing water for 50 minutes, and then refluxed for 20 minutes.
Refluxing was continued for 30 minutes at 00-215°C. The amount of water drawn off during this reaction was 3.6 ml.

After confirming that a film could be formed when a portion of the reaction solution was applied to a glass plate and immersed in water, 80 ml of sulfolane was added to the reaction solution, the temperature was lowered to 100° C., and 20 ml of dichloromethane was added.

The reaction mixture thus obtained was poured into pure water to solidify the polysulfone, and the mixture was allowed to stand overnight. This was separated, pulverized with a mixer, washed with pure water and isopropyl alcohol, and then dried at a temperature of 80° C. for 6 hours.

The polysulfone thus obtained is a reddish-colored granular material, and its logarithmic viscosity (hereinafter referred to as the logarithmic viscosity of polysulfone) was measured at 47°C as a solution of 0.4 g of this polymer dissolved in 100 ml of p-chlorophenol. The measurement conditions were the same.) was 1°40.

(2) Production of sulfonated polysulfone 10 g of the polysulfone obtained as described above was added to 80 ml of 97% concentrated sulfuric acid and reacted with gentle stirring at room temperature for 4 hours to obtain a dark brown viscous reaction liquid.

This was placed in a water bath to solidify the sulfonated polysulfone. After washing with water, it was left overnight in 800 ml of a 0.5N aqueous sodium hydroxide solution. Next, the polymer was washed until the washing solution became neutral, and then vacuum-dried at 30° C. for 7 hours. The pale yellow granular sulfonated polysulfone thus obtained had a logarithmic viscosity of 3.00, sulfonic acid groups accounted for 100% of the total ion exchange groups, and the ion exchange groups were 1.92 milliequivalents/g. Ta.

(3) Manufacture of composite semipermeable membrane Consisting of repeating units of the above formula C, average molecular weight 20,000
An anisotropic ultrafiltration membrane with a removal rate of 10% for polyethylene glycol and a molecular weight cut-off of 100,000 was heat-treated by immersing it in hot water at a temperature of 80°C for 1 hour, and then heated at 25°C. immersed in a 10% aqueous 1,4-butanediol solution for 1 hour at a temperature of
A dry ultrafiltration membrane was obtained by standing for a minute.

The above sulfonated polysulfone was dissolved in ethylene glycol monomethyl ether to prepare a 1.0% by weight polymer solution, which was applied onto the above dry ultrafiltration membrane and left at room temperature to completely remove almost all of the sulfonated polysulfone. After removing the solvent by evaporation, it was heated at a temperature of 60° C. for 5 minutes to obtain a composite semipermeable membrane. This composite semipermeable membrane had a molecular weight cutoff of 10,000.

In addition, the molecular weight cut-off here refers to 0.05% aqueous solutions of polyethylene glycols with different molecular weights at 25°C, 20 kg/
It refers to the dextran-equivalent molecular weight of the polyethylene glycol measured by GPC when the removal rate is about 90% when treated under cffl conditions.

Reference Example 2 +1) Production of polysulfone copolymer In Reference Example 1, 15.0 g (0.06 mol) of 4.4'-dihydroxydiphenylsulfone and 8.8 g (0.08 mol) of hydroquinone were used instead of hydroquinone. The formula A was prepared in the same manner as in Reference Example 1.

A linear polysulfone copolymer consisting of 57 mol% of repeating units of 2B and 43 mol% of repeating units of 2B was produced.

The polysulfone copolymer thus obtained was pale yellow granular and had an logarithmic viscosity of 0.84.

(2) Production of sulfonated polysulfone copolymer 10 g of the polysulfone copolymer obtained as described above was dissolved in 80 ml of 97% concentrated sulfuric acid, stirred at room temperature for 4 hours, and a blackish brown viscous A reaction solution was obtained. This was placed in a water bath to pseudo-solidify the sulfonated polysulfone copolymer. After washing with water, it was left overnight in 800 ml of a 0.5N sulfur-IJium hydroxide aqueous solution. Next, the polymer was washed until the washing solution became neutral, and then vacuum-dried at 60° C. for 5 hours.

The sulfonated polysulfone copolymer thus obtained had a logarithmic viscosity of 0.84, sulfonic acid groups accounted for 100% of the total ion exchange groups, and the ion exchange groups were 1.2 meq/g. .

(3) Production of composite semipermeable membrane The same polysulfone anisotropic ultrafiltration membrane used in Reference Example 1 was heat-treated by immersing it in hot water at a temperature of 80°C for 1 hour, and then heated at a temperature of 25°C. The membrane was immersed in a 10% aqueous 1,4-butanediol solution for 1 hour, and then left in a drying layer at about 60° C. for 5 minutes to obtain a dry ultrafiltration membrane.

The above sulfonated polysulfone was dissolved in ethylene glycol monomethyl ether to prepare a 1.0% by weight polymer solution, which was applied onto the above dry ultrafiltration membrane and left at room temperature to completely remove almost all of the sulfonated polysulfone. After removing the solvent by evaporation, it was heated at a temperature of 60° C. for 5 minutes to obtain a composite semipermeable membrane. This composite semipermeable membrane had a molecular weight cutoff of 700.

Reference Example 3 In the same manner as in Reference Example 2, a linear polysulfone copolymer consisting of 43 mol% of the repeating units of the formula AI and 57 mol% of the repeating units of NiB was prepared and sulfonated in the same manner. Obtained polysulfone. The logarithmic viscosity of this sulfonated polysulfone was 0°87, and the ion exchange group was 1.3 mm/IJk/g.

Thereafter, in the same manner as in Reference Example 2, a composite semipermeable membrane having a molecular weight cut off of 200 was obtained.

Example 1 Using the composite semipermeable membrane obtained in Reference Example 1, a mixed aqueous solution containing sodium chloride and sucrose each at a concentration of 5% was treated at a treatment temperature of 25° C. and a treatment pressure of 20 kg/cnf. The water permeation rate is 1.39 m”/d·day, and the removal rate is 9.7% for sodium chloride and 63% for sucrose.
It was 5%. It is understood that sodium chloride and sucrose can be efficiently separated.

Example 2 Using the composite semipermeable membrane obtained in Reference Example 2, a sodium chloride aqueous solution and a sucrose aqueous solution were treated, respectively. Results first
Shown in the table. In addition, the processing temperature is 50°C and the processing pressure is 20°C.
The relationship between solute concentration and removal rate when kg/CIA is expressed as
As shown in the figure.

Example 3 Using the composite semipermeable membrane obtained in Reference Example 3, a sodium chloride aqueous solution and a sucrose aqueous solution were treated, respectively. Second result
Shown in the table. In addition, the processing temperature was 50°C and the processing pressure was 2.0°C.
Figure 2 shows the relationship between solute concentration and removal rate in kg/cJ.

Example 4 Using the composite semipermeable membranes obtained in Reference Examples 2 and 3, a mixed aqueous solution containing sodium chloride and sucrose at a concentration of 10% was treated. The results are shown in Table 3. It is clear that sodium chloride and sucrose can be efficiently separated.

Example 5 Using the composite semipermeable membrane obtained in Reference Example 3, aspartic acid, which is an acidic amino acid, inleucine, which is a neutral amino acid,
and the basic amino acid ornithine, each containing 500
An amino acid mixed aqueous solution containing ppm and having an ionic strength adjusted to 0.1M was treated at 25° C. and 10 kg/cnt. FIG. 3 shows the relationship between the pH of the aqueous solution and the removal rate of each amino acid.

Therefore, for example, by adjusting the pH to a range of about 5 to 8, aspartic acid can be concentrated in the submembrane permeate, and ρI
By setting I in the range of about 8 to 10, ornithine can be concentrated in the membrane permeate.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between solute concentration and removal rate when a sodium chloride aqueous solution and a sucrose aqueous solution are treated using the composite semipermeable membrane obtained in Reference Example 2, and FIG.
Figure 3 is a graph showing the relationship between solute concentration and removal rate when a sodium chloride aqueous solution and a sucrose aqueous solution were treated using the composite semipermeable membrane obtained in Reference Example 3. p of the aqueous solution when an amino acid mixed aqueous solution is treated using
It is a graph showing the relationship between H and the removal rate of each amino acid. Fig. 1 Concentration (wt%) Fig. 2 Jino Cliff (wt%)

Claims (1)

[Claims] (1) Treating an aqueous solution containing a substantially electrically neutral solute and a charged solute with a semipermeable membrane having 70% or more of the total ion exchange groups has sulfonic acid groups. 1. A method for treating an aqueous solution, which comprises concentrating neutral solutes in a membrane non-permeable liquid and separating charged solutes in a membrane permeable liquid.