JPH047254B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for separating water from an organic aqueous solution or an organic matter/water mixed vapor. For more details,
The present invention relates to a membrane for separating and concentrating an aqueous solution of organic matter by pervaporation or a mixed vapor of organic matter/water by vapor permeation. (Prior Art) Regarding the concentration and separation of organic substance aqueous solutions using membranes, reverse osmosis has been put to practical use for concentrating some low-concentration organic substance aqueous solutions. However, reverse osmosis requires applying pressure to the liquid to be separated that is higher than the osmotic pressure of the separation liquid, so it cannot be applied to highly concentrated aqueous solutions where the osmotic pressure is high, and therefore the concentration of the solution that can be separated is There are limits to In contrast, pervaporation and vapor permeation methods are attracting attention as new separation methods that are not affected by osmotic pressure. What is pervaporation method?
This is a method in which the separated substance is passed through the membrane in gaseous form by supplying a separated liquid to the primary side of the membrane and reducing the pressure on the secondary side (permeation side) of the membrane, or by passing a carrier gas through the membrane. The permeation method differs from the pervaporation method in that mixed vapor is supplied to the primary side of the membrane. The membrane-permeable substance can be collected by cooling and condensing the permeated vapor. Many research examples have been reported so far regarding the pervaporation method. For example, regarding the separation of aqueous ethanol solutions, there are examples of a cellulose acetate homogeneous membrane in US Pat. No. 2,953,502 and a polyvinyl alcohol membrane in US Pat. No. 3,035,060. In both cases, the separation coefficient is low. In addition, JP-A-59-109204 discloses a composite membrane with a skin layer of cellulose acetate membrane or polyvinyl alcohol-based membrane.
No. 55305 discloses polyethyleneimine-based crosslinked composite membranes, but all of them had low permeation rates or separation coefficients. Here, the composite membrane refers to a membrane formed by coating or laminating a dense thin film layer to provide a predetermined separation function on the surface layer of a porous support membrane that does not have the desired separation function. Further, the term "crosslinked composite membrane" refers to a case where the dense thin film layer is made of a crosslinked polymer. JP-A-60-129104 describes membranes made from anionic polysaccharides. The thin material described in the examples of this patent has a low membrane durability against aqueous solutions of organic substances at low concentrations due to the water-soluble polymer. Therefore, although not mentioned in the Examples, the patent also describes crosslinking in an amount sufficient to render the membrane insoluble in water. However, when a crosslinking treatment is normally performed, the permeation rate decreases although the separation coefficient increases as described in the comparative example in the Examples section of the present invention. (Object of the Invention) As mentioned above, the separation membranes to be used in the conventional pervaporation method or vapor permeation method have a low permeation rate, so a large-area membrane is required, or
Due to the low separation coefficient, it was necessary to circulate the highly concentrated permeate in order to concentrate the separated liquid to the desired concentration. These have been disadvantageous in increasing the equipment price or operating cost. The permeation rate in the present invention is the amount of permeated mixture per unit membrane area/unit time, expressed in units of Kg/m ² ·hr. On the other hand, the separation coefficient (α) is the ratio of water and organic matter in the permeate gas to the ratio of water and organic matter in the feed liquid or feed vapor. That is, α=
(X/Y)p/(X/Y)f. Here, X,
Y represents the respective compositions of water and organic matter in a two-component system, and p and f represent permeation and supply. The purpose of the present invention is to provide sufficient durability, high permeation rate, and separation for a wide concentration range of organic matter in the separation of organic matter aqueous solutions or mixed vapors of organic matter and water by pervaporation and vapor permeation methods. The objective is to obtain a separation membrane having a coefficient of (Structure of the Invention) As a result of intensive study on the above points, it has been found that the above problems can be solved by the following method. (1) Sulfonic acid base and/or
Or a crosslinked composite membrane having water selective permeability, in which a skin layer is composed of a crosslinked reaction product consisting of a water-soluble polysaccharide having a sulfonic acid group and a polyfunctional melamine compound. (2) The crosslinked composite membrane according to item 1, wherein the skin layer is composed of a crosslinked reactant having a water content of 50% to 300% and a thickness of 3 μm or less. (3) The crosslinked composite membrane according to item 1 or 2, wherein the water-soluble polysaccharide is sulfoethylcellulose or an alkali salt thereof. (4) The crosslinked composite membrane according to item 1 or 2, wherein the polyfunctional melamine compound is n-methoxymethylmelamine (n is di-hexa). In order to selectively permeate water from an organic aqueous solution or an organic matter/water vapor mixture, it is preferable to introduce into the membrane a functional group that has a large ability to coordinate water. The water coordinated in these membranes is called bound water in contrast to the free water of the bulk liquid. Matsuura et al.
Science and Technology Vol. 17, p. 821 (1982) states that cellulose has a significantly lower solubility of organic matter in bound water than other polymers. However, cellulose membranes do not provide a high separation coefficient for water/organic matter separation. Therefore, the present inventors attempted to introduce an anionic group having a high ability to coordinate water into a polysaccharide in order to improve water permeability and separation performance for organic substances. However, polysaccharides into which anionic groups have been introduced become water-soluble depending on the degree of substitution. Although these materials are resistant to aqueous organic matter solutions of high concentration, they dissolve or swell to aqueous solutions of organic matter of low concentration, and their function as a membrane is significantly reduced.
Therefore, by covalently bonding polysaccharides having these anionic groups to form a three-dimensional structure, it is possible to enhance the resistance to separated liquids having a wide range of organic substance aqueous solution concentrations. However, when a membrane is normally crosslinked, the separation coefficient increases, but the permeation rate tends to decrease. As a result of various studies on polysaccharides having anionic groups and crosslinking agents, the present inventors found that a membrane consisting of a polysaccharide having a sulfonic acid group and/or a sulfonic acid group and a melamine crosslinking agent was found to be different from a conventional crosslinked membrane. In contrast, it has been found that crosslinking increases the separation coefficient and also increases the permeation rate. The present invention will be explained in more detail below. The polysaccharide containing sulfonic acid groups and/or sulfonic acid groups is preferably sulfoethylcellulose. After adjusting the pH of the mixed aqueous solution of the sulfonic acid group and/or sulfonic acid group-containing polysaccharide and melamine to 6 or less, preferably 4 or less, it is cast onto a porous support membrane, for example, an ultrafiltration membrane. Both mineral acids and organic acids may be used to adjust the pH of the mixed aqueous solution. Also, for polysaccharides with sulfonic acid groups, countercations include alkali metals, alkaline earth metals, transition metals and the form R ₄ N ⁺
(wherein R is hydrogen or alkyl), preferably an alkali metal, more preferably a sodium ion. The weight fraction of the crosslinking agent with respect to the sulfonate group and/or sulfonate group-containing polysaccharide is 3% by weight.
-60% by weight, preferably 10% - 40% by weight. If the amount of crosslinking agent is small, resistance to water is lacking, and if it is large, the film becomes hard and brittle, making it difficult to obtain a film that can withstand membrane performance evaluation. The skin layer made of a crosslinkable thin film is preferably a long and thin layer that can be formed without pinholes. The thickness of the skin layer is preferably from 0.03 μm to 3 μm.
It is 0.05 μm to 0.5 μm. Crosslinked thin films of 1 μm or less are difficult to handle alone. Usually, a mixed aqueous solution of a sulfonic acid group and/or a sulfonic acid group-containing polysaccharide and a melamine crosslinking agent is applied onto a porous support and crosslinked to form a composite membrane. The support is a support having micropores of tens to thousands of angstroms on its surface, and known materials made of polysulfone, polyethersulfone, polyacrylonitrile, cellulose ester, polycarbonate, polyvinylidene fluoride, etc. Includes: In addition, as a polyfunctional melamine compound used as a crosslinking agent, n-methylolated melamine (n is di-hexane) is suitable, and furthermore, n-methoxymethylmelamine (where n is di-hexane) is methylated. ) is preferred. In order to reduce the thickness of the skin layer of the composite membrane, the solid content concentration of the mixed solution coated on the porous support is lowered, or the coating thickness is reduced. The membrane of the present invention can be a flat membrane, a tube membrane, or a hollow fiber membrane. Flat membranes can be laminated as they are, or they can be formed into pleats or spirals to form modules. The membrane produced in this way can be used to contain water/organic mixtures such as alcohols such as methanol, ethanol, 1-propanol, 2-propanol, n-butanol, ketones such as acetone and methyl ethyl ketone, ethers such as tetrahydrofuran and dioxane, etc. Organic acids such as formic acid and acetic acid, aldehydes,
1 or 2 consisting of aldehydes such as propionaldehyde and amines such as pyridine and picoline
It is used to separate aqueous solutions containing the above compounds or vapor mixtures with water. (Effect of the invention) A composite film having a skin layer of a crosslinked thin film made of a polysaccharide containing a sulfonic acid group and/or a sulfonic acid group and a melamine crosslinking agent has an uncrosslinked sulfonic acid group and/or a sulfonic acid group. Not only is it superior in water resistance and heat resistance to membranes made from polysaccharides, but it is also more effective in separating water/organic mixtures than membranes made from other crosslinking agents such as polyepoxies and aldehydes. , both the permeation rate and separation coefficient are large. Reference Example 1 Synthesis of sulfoethylcellulose 42.6 g of linter is dispersed in 480 g of isopropanol. Add 45g of 40% caustic soda aqueous solution,
Heat to 70°C. 2-bromoethanesulfonic acid
Add 14.9g and reflux for 30 minutes. Further, 14.9 g of 2-bromoethanesulfonic acid is added and the mixture is refluxed for 60 minutes. Add 8.4 g of 90% acetic acid aqueous solution to neutralize the reaction solution. The reaction product was washed and filtered twice with 75% aqueous methanol solution. Vacuum drying was performed at 60°C for 24 hours. The degree of substitution introduced into the glucose ring by the sulfonic acid group was 0.3. Example 1 (1) Preparation of crosslinked composite membrane A mixed solution consisting of 90 parts by weight of a 2% aqueous solution of sulfoethylcellulose synthesized in Reference Example 1 and 10 parts by weight of a 2% aqueous solution of hexamethoxymethylmelamine was mixed with 10% by weight hydrochloric acid. The pH was adjusted to 4. This mixed solution was applied to a polyether sulfone ultrafiltration membrane (DUS40 manufactured by Daicel Chemical Co., Ltd.) at a thickness of 250 µm.
The coating was performed using a doctor blade having a slit thickness of m. Then, heat treatment was performed at 100°C for 1 hour. (2) Evaluation of membrane performance Primary side (skin layer) of the membrane obtained in (1) above
A mixed vapor of ethanol/water (95/5 weight ratio) at a temperature of 83℃ and a gauge pressure of 0.3Kg/ ^cm3 was supplied to the
The pressure on the secondary side of the membrane was reduced to 3 mmHg. membrane 2
When the next side is made into a closed system, this system has a pressure of 6 mm due to the mixed vapor of ethanol/water passing through the membrane.
It rose to Hg. The total number of moles of the mixed vapor permeating through the membrane was calculated from the volume of the closed system and the time required for the pressure to rise. Note that the temperature of this closed system was maintained at 80°C. In addition, the permeation rate and separation coefficient were calculated by analyzing the composition of the supply and the mixed vapor of this closed system by gas chromatography. The values of the permeation rate and separation coefficient thus obtained coincided with the values of the permeation rate and separation coefficient calculated from the weight and composition ratio analysis of the permeated mixed vapor trapped in liquid nitrogen. (3) Membrane performance results are shown in Table 1. Examples 2 to 4 The same procedure as in Example 1 was carried out except that (1) of Example 1 was changed in the composition ratio of sulfoethylcellulose and hexamethoxymethylmelamine. The results are summarized in Table 1. Comparative Examples 1 to 6 In (1) of Example 1, the water-soluble polymer shown in Table 2 was used instead of sulfoethylcellulose, and the weight parts of sulfoethylcellulose and hexamethoxymethylmelamine were replaced with those shown in Table 2. Example 1 was carried out in the same manner as in Example 1, except that the respective weight parts shown were used. As the composition ratio of hexamethoxymethylmelamine increased, both the permeation rate and separation coefficient decreased in the case of carboxymethylcellulose, and in the case of polyvinyl alcohol, the separation coefficient increased but the permeation rate decreased. Example 5 The same procedure as in Example 1 was carried out except that in (1) of Example 1, trimethoxymethylmelamine was used instead of hexamethoxymethylmelamine. Transmission rate
It was 0.20Kg/m ² ·hr, and the separation coefficient was 1250.

【table】

【table】

[Table] Comparative Examples 8 to 9 The same procedure as in Example 1 was carried out except that in (1) of Example 1, the crosslinking agent shown in Table 3 was used instead of hexamethylmethoxymethylmelamine. As shown in Table 3, the results showed that there was no significant change in the transient speed, but the separation coefficient decreased. Examples 6-7 Sulfoethyl cellulose with a degree of substitution of 0.91 was synthesized by repeating the sulfoethylation reaction on cellulose in the same manner as in Reference Example 1. The obtained 2% aqueous sulfoethylcellulose solution and 2% aqueous hexamethoxymethylmelamine solution were mixed in the proportions shown in Table 4. The pH of the mixed solution was adjusted to 3.5 using hydrochloric acid, and it was applied onto a polyethersulfone ultrafiltration membrane (DUS-40, manufactured by Daicel Chemical Industries, Ltd.) using a wire bar wound with a wire of 0.2 mm. Immediately after coating, it was placed in a dust-free constant temperature bath at 100°C and dried by heating for 8 minutes. This coating and drying process was repeated three more times for a total of four coatings, and then heat treated at 100° C. for 30 minutes. The membrane performance of the obtained membrane was evaluated by the vapor permeation method in the same manner as in Example 1, and the results shown in Table 4 were obtained.

[Table] Comparative Example 10 A composite membrane was prepared in the same manner as in Example 6, except that hexamethoxymethylmelamine was not used to form a crosslinked membrane. The membrane performance of this membrane was examined in the same manner as in Example 1, and the results are shown in Table 4. The membrane has lower permeation rate and separation coefficient than melamine crosslinked membranes, and the effect of melamine crosslinking is clear.

Claims (1)

[Claims] 1. On a porous support membrane, a sulfonic acid group and/or
Or a crosslinked composite membrane having water selective permeability, in which a skin layer is composed of a crosslinked reaction product consisting of a water-soluble polysaccharide having a sulfonic acid group and a polyfunctional melamine compound. 2. The crosslinked composite membrane according to claim 1, wherein the skin layer is composed of a crosslinked reactant having a water content of 50 to 300% and a thickness of 3 μm or less. 3. The crosslinked composite membrane according to claim 1 or 2, wherein the water-soluble polysaccharide is sulfoethylcellulose or an alkali salt thereof. 4. The crosslinked composite membrane according to claim 1 or 2, wherein the polyfunctional melamine compound is n-methoxymethylmelamine (n is di-hexa).