JPH0568292B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a membrane that separates water from an organic aqueous solution or a water/organic mixed vapor. More specifically, the present invention relates to a membrane for separating and concentrating an organic aqueous solution by pervaporation or a water/organic mixed vapor by vapor permeation. (Prior art) Regarding the concentration and separation of organic substance aqueous solutions using membranes, for the concentration of some low concentration organic substance aqueous solutions,
Reverse osmosis has been put into practical use. However, since the reverse osmosis method requires applying a pressure higher than the osmotic pressure of the separating liquid to the liquid to be separated, it is not applicable to highly concentrated aqueous solutions where the osmotic pressure is high.
There is a limit to the concentration of solutions that can be separated. In contrast, pervaporation and vapor permeation methods are attracting attention as new separation methods that are not affected by osmotic pressure. In the pervaporation method, a separated liquid is supplied to the primary side of the membrane, and the secondary side (permeation side) of the membrane is
This is a method in which the separated substance is passed through the membrane in a gaseous state by reducing the pressure or passing a carrier gas through the membrane.The vapor permeation method is characterized by the fact that mixed vapor is supplied to the primary side of the membrane. This is different from the pervaporation method. The membrane-permeable substance can be collected by cooling and condensing the permeated vapor. Regarding the pervaporation method, many research examples have been reported so far. For example, regarding the separation of aqueous ethanol solutions, there are examples of cellulose acetate homogeneous membranes in US Pat. No. 2,953,502 and polyvinyl alcohol in US Pat. No. 3,035,060. Also, Special Publication No. 54-10548, No. 54-10549 and Special Publication No.
No. 59-49041 reports an experimental example in which a water-organic liquid mixture was separated using a synthetic polymer membrane into which ionic groups were introduced. (Problem to be solved by the invention) Based on the theory that membrane permeation of liquids and vapors is controlled by dissolution and diffusion, an attempt was made to use a membrane with a small free volume to perform separation based on the size difference of permeating molecules. Attempts have been made to do so. However, membranes with a small free volume have a large separation coefficient but have the disadvantage of a low permeation rate. For this reason, attempts have been made to utilize the difference in solubility of substances in order to increase the permeation rate and further increase the selectivity. For example, JP-A-56-24007 discloses a permeable membrane with improved water permeation rate by introducing sulfone groups into the molecular chain of aromatic polyamideimide, but as the amount of sulfone groups in the polymer increases, Therefore, the membrane-forming ability is poor, and the resulting membrane has the disadvantage that its mechanical strength decreases and the selectivity based on molecular size is lost due to swelling, resulting in a loss of selectivity in separating water and organic matter. In addition, JP-A-60-129104 describes a membrane made from anionic polysaccharide, but it has problems with heat resistance, chemical resistance, etc., and cannot be said to be suitable for separating a wide range of organic substances. . Therefore, an object of the present invention is to provide sufficient durability for various organic substances and a wide range of concentration ranges in the separation of organic substance aqueous solutions or mixed vapors of organic substances and water by pervaporation and vapor permeation methods. The object of the present invention is to obtain a separation membrane having heat resistance, high permeation rate, and separation coefficient. (Means for Solving the Problems) As a result of intensive study on the above points, the present invention has been arrived at. That is, the present invention is capable of removing water from a water/organic substance mixture that has a plurality of anionic groups and cationic groups in the same molecule, whose main chain is mainly composed of an aromatic polymer, and which has a crosslinked structure by covalent bonds. This is an amphoteric polymer electrolyte separation membrane for pervaporation and vapor permeation that allows selective permeation. In order to selectively permeate water from an aqueous organic solution or a water/organic vapor mixture, it is preferable to introduce into the membrane a functional group that has a large ability to coordinate water.
Therefore, the present inventors attempted to introduce an anionic group having a high ability to coordinate water into an aromatic polymer in order to improve water permeability and separation performance for organic substances. However, when a large amount of anionic groups are introduced into the polymer chain, not only the membrane forming ability becomes poor, but also the selective separation property of the membrane is significantly reduced. Therefore, by introducing cationic groups together with anionic groups into mainly aromatic polymers, a separation membrane with high selectivity and high permeability was obtained. Furthermore, with these amphoteric polymer membranes and crosslinking agents, 3
By increasing the dimensionality, we were able to strengthen the resistance to a wide range of organic mixtures. The present invention will be explained in more detail below. In the present invention, the anionic group is not particularly limited as long as it can form a salt, but for practical purposes, sulfonic acid residues and carboxylic acid residues are preferably used. Further, the cationic group is not particularly limited as long as it can form a salt, but for practical purposes,
Various primary to quaternary amino groups and pyridine residues are preferably used. These anionic groups and cationic groups may be used alone, or two or more types may be mixed, depending on the target separation target. Such anionic groups and cationic groups can be achieved by copolymerizing monomers containing them, or by introducing anionic groups and cationic groups by a known method after polymerization or after film formation. be done. The ratio of cationic groups and anionic groups is not particularly limited, but is preferably 1/20<A/C<20 (A: amount meq/g of anionic groups in the polymer chain, C: amount of anionic groups in the polymer chain). The amount of cationic groups (meq/g) is within the range of In addition, the ratio of anionic groups and cationic groups in the repeating unit is m/n in general formula (1).
100/0 to 5/95, preferably 100/0 to 20/80. (-X _Aaod/prc ) _n --(-X _p ) _o --(1) [In the above aromatic polymer, X _Aaod/prc is a repeating unit containing an anionic group and/or a cationic group, X _p is a repeating unit containing neither an anionic group nor a cationic group. ] In the amphoteric polymer electrolyte, the anionic group and the cationic group may be present in a single molecule chain in a random, block form, or as a graft, and the repeating unit may contain both an anionic group and a cationic group. It's okay to stay. The aromatic polymer in the present invention is one whose main chain is mainly composed of an aromatic compound, and examples include, but are not limited to, polyamide, polyamideimide, polyimide, polyurea, polyurethane, polysulfone, and polyether. I can do it. Further, in the present invention, it may be blended, blocked, or grafted with other polymers that are compatible with the membrane without departing from the spirit of the present invention. The polymers used in these blends, blocks and grafts do not necessarily have to contain anionic and/or cationic groups. The separation membrane according to the present invention is preferably crosslinked to form a three-dimensional structure in order to improve membrane strength and separation performance. When a covalent bond is used for this purpose, for example, a polymer compound having active hydrogen such as a hydroxyl group, a primary amino group, or a secondary amino group and an epoxy, acid chloride, or melamine compound,
Crosslinking can be carried out using a combination of compounds having functional groups that react with active hydrogen, such as isocyanates, aldehydes, and acid anhydrides. Furthermore, crosslinking can also be achieved by ultraviolet irradiation, electron beam irradiation, plasma treatment, or the like. In such a crosslinking bridge, a molecular molecular that can be a multi -molecules that can be a crosslinking point, co -polygap, as well as a monomer that can be a crosslinking point, as well as an anion or an anionic group. After synthesizing (urea bond of polyurea), a crosslinking agent may be added or impregnated during film formation or after film formation, and heat treatment, ultraviolet treatment, etc. may be performed.
These crosslinking methods may be performed alone or in combination. In addition, cross-linking by hydrogen bonding can also be used. The membrane prepared in this way can contain water/organic mixtures, such as organic acids such as formic acid, acetic acid, propionic acid, butyric acid, alcohols such as methanol, ethanol, 1-propanol, 2-propanol, n-butanol, etc. An aqueous solution containing one or more compounds from the group of ketones such as acetone and methyl ethyl ketone, ethers such as tetrahydrofuran and dioxane, aldehydes such as aldehyde and propionaldehyde, and amines such as pyridine and picoline, or aqueous solution containing one or more compounds from the group of amines such as pyridine and picoline. Used for separation of vapor mixtures. The ampholyte polymer electrolyte separation membrane can also be used as a selectively permeable membrane for a wide variety of water, ion, and gas treatments. This includes dialysis membranes, reverse dialysis membranes, ultrafiltration membranes, etc. The membrane of the present invention can be a flat membrane, a tube membrane, or a hollow fiber membrane. The flat membranes can be laminated as they are, or can be formed into a module by pleating or spiraling. In addition, by coating it on a porous support as a composite membrane, the film thickness can be reduced to 0.1μ.
It is possible to make it as thin as possible. (Effects of the Invention) The aromatic polymer membrane containing anionic groups and cationic groups according to the present invention has a higher water resistance than membranes containing no such groups and membranes containing only anionic groups or only cationic groups. / It shows excellent performance in both permeation rate and separation coefficient for separation of mixtures of organic substances, and also has excellent solvent resistance and heat resistance. (Example) Next, the present invention will be described in more detail using examples. Example 1 Sodium 2,5-diaminobenzenesulfonate (0.01 mol) and 4,4'-diaminodiphenylamine (0.01 mol) were dissolved in 50 ml of dimethylacetamide (DMAC), and triethylamine (0.02 mol) was used as an acid scavenger. Add trimellitic anhydride chloride (0.02 mol) while cooling.
was added all at once and stirring was continued for 3 hours to obtain a precursor polyamic acid. After refining this, 10% trifunctional epoxy "Tepik" (manufactured by Nissan Chemical Industries, Ltd.) was added to the polymer, cast on a glass plate, dried at 100℃ for 2 hours, peeled off from the glass plate, A uniform polyamide-imide film was obtained by vacuum drying at 200° C. overnight and then for 6 hours at 200° C. The separation performance of the membrane was measured by pervaporation at 70°C using 80% acetic acid as the feed liquid. The results obtained are shown in Table 1. Comparative Example 1 A polyamideimide membrane was obtained which was the same as in Example 1 except that 4,4'-diaminodiphenylamine was 3,5 diaminobenzoic acid. Table 1 shows the measurement results of the separation performance of the membrane. Comparative Example 2 In Example 1, the diamine monomer was 2,5
Sodium diaminobenzenesulfonate (0.015
A polyamide-imide membrane was obtained which was identical except that 2,4 diaminophenol (0.005 mole) and 2,4 diaminophenol (0.005 mole) were used. Table 1 shows the measurement results of the separation performance of the membrane. Example 2 Sodium 2,5 diaminobenzenesulfonate (0.008 mol), 2,6 diaminopyridine (0.008 mol), and 3,5 diaminobenzoic acid (0.004 mol)
After dissolving in 50 ml of DMAc, add pyromellitic anhydride (0.02 mol) at once and continue stirring for 3 hours.
A precursor polyamic acid was obtained. A uniform polyimide film was obtained in the same manner as in Example 1. Table 1 shows the separation performance of the membrane. Comparative Example 3 In Example 2, the diamine monomer was 4,
A homogeneous polyimide film was obtained which was identical except that it consisted only of 4'-diaminodiphelamine. Table 1 shows the separation performance of the membrane.

【table】

【table】

Claims (1)

[Scope of Claims] 1. Having a plurality of anionic groups and cationic groups in the same molecule, the main chain mainly consisting of an aromatic polymer, and having a crosslinked structure by covalent bonds.
Ampholytic polymer electrolyte separation membrane for pervaporation and vapor permeation that selectively permeates water from a water/organic mixture. 2. The ampholytic polymer electrolyte separation membrane according to claim 1, wherein the anionic group is a sulfonic acid residue, a carboxylic acid residue, or a mixture of these groups. 3. The ampholytic polymer electrolyte separation membrane according to claim 1, wherein the cationic group is a primary to quaternary amino group, a pyridine residue, or a mixture of these groups. 4. Claim 1, wherein the aromatic polymer is at least one selected from the group consisting of polyamide, polyamideimide, polyimide, polyurea, polyurethane, polysulfone, and polyether.
The ampholytic polymer electrolyte separation membrane according to item 1, 2, or 3.