JPH0556179B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for separating water from an organic substance aqueous solution. More specifically, the present invention relates to a separation membrane for separating water from a water-organic liquid mixture by a pervaporation method. (Prior Art) Distillation has long been known as a method for separating a water-organic liquid mixture or an organic liquid mixture of two or more components. However, it is extremely difficult to separate azeotropic mixtures, near-boiling point mixtures, and compounds that are easily denatured by heat using distillation, and even for mixtures that can be separated by distillation, a large amount of energy is consumed. Separation technology using membranes is expected to solve these problems. Among separation techniques using membranes, pervaporation is considered to be particularly effective for separating water-organic liquid mixtures. This pervaporation method is
By supplying a mixed liquid for the purpose of separation to one side of a polymer membrane and applying a vacuum, reduced pressure, or flowing a carrier gas to the other side, a vapor pressure difference is created to allow specific substances to preferentially permeate through the membrane. This is a method of separation. In other words, the pervaporation method differs greatly from other membrane separation methods such as the reverse osmosis method and the gas separation method in that it causes a phase change through a membrane. Furthermore, because the pressure on the permeate side of the membrane is extremely low, the gradient of the chemical potential, which is the driving force for the permeation of substances through the membrane, is extremely large, making it possible to separate the entire concentration range compared to other membranes. This is a feature not found in separation methods. Therefore, this pervaporation method can also be applied to the separation of organic liquid mixtures, which is difficult to perform using reverse osmosis due to its operating pressure. Another feature of the pervaporation method is that it is an energy-saving process because it can separate, concentrate, or purify azeotropic mixtures, near-boiling point mixtures, and thermally decomposable mixtures that were difficult to separate using conventional distillation methods. can give. As described above, the pervaporation method has many characteristics that other separation methods do not have, and is one of the separation methods most suitable for separating organic liquid mixtures. In recent years, research on pervaporation methods in particular has been actively conducted, and there have been many reports regarding the polymer membranes used. For example, regarding water-ethanol separation, an acetylcellulose homogeneous membrane is proposed in US Pat. No. 2,953,502, and a hydrolyzed polyvinyl acetate membrane is proposed in US Pat. No. 3,035,060. In addition, JP-A-59-109204 discloses a composite membrane having a cellulose acetate membrane or a polyvinyl alcohol-based membrane as a skin layer.
55304 and JP-A-59-55305 disclose polyethyleneimine-based crosslinked composite membranes;
Publication No. 281138 proposes an acrylic acid group-containing polymer-based crosslinked composite membrane. Journal of
In Membrane Science 1 (1976) 271-287, a membrane made of polytetrafluoroethylene grafted with poly(N-vinylpyrrolidone) was published in the Journal
of Membrane Science 9 (1981) 191-196 reports a membrane in which styrene is grafted onto polytetrafluoroethylene. However, although many polymer membranes for pervaporation have been proposed, this pervaporation method has not been put to practical use. This is because many of the polymer membranes proposed to date for pervaporation have insufficient separation performance or permeation performance, or have problems with membrane formability or membrane durability. ing. Moreover, as a general tendency, separation performance and permeation performance are contradictory, and it is said that it is difficult to maintain both at a high level. In order to put pervaporation membranes into practical use, it is necessary to solve these problems. In other words, if the separation performance is poor, it will not be possible to concentrate or separate to the desired concentration even if it passes through the polymer membrane once. Therefore, multi-stage separation operations will be required, making it difficult to combine with other separation methods. This poses many practical problems, such as increasing the size of the equipment and excessive equipment costs. In addition, if the permeability coefficient (expressed as the permeation amount per unit membrane area, unit membrane thickness, or unit time) of water or organic compounds permeating through a polymer membrane is small, the membrane area must be made very large or the membrane thickness must be made extremely large. In either case, it is necessary to make the film thinner or use a composite film.
This poses practical problems such as reduced durability. In the case of a flat membrane, the permeation rate referred to in the present invention is the amount of permeated mixture per unit membrane area, unit time, and membrane thickness of 1 μm, and is expressed in units of Kg·μm/m ² ·hr. In the case of a hollow membrane, it is expressed by unit membrane area and amount of permeated mixture per unit time. On the other hand, the separation coefficient (α) is the concentration ratio of water and organic matter in the permeate gas to the concentration ratio of water and organic matter in the feed liquid. That is, α ^X _Y = (X/
P) _P /(X/Y) _f . Here, X and Y represent the respective concentrations of water and organic matter in a two-component system, and P and f represent the permeate gas and the feed liquid. (Problems to be Solved by the Invention) The purpose of the present invention is to separate water from a water-organic liquid mixture by a pervaporation method, and to solve the problem that conventional membranes cannot simultaneously increase permeation rate and separation coefficient. The present invention provides a polymer membrane that solves the above problems and has excellent durability. (Means for Solving the Problems) The present inventors have worked diligently to develop a pervaporation separation membrane that has high separation performance and large permeability while maintaining good membrane formability, membrane strength, and durability of membrane performance. As a result of research, it was found that the following separation membrane achieves this purpose. Here, in order to explain the content of the present invention in more detail, a liquid separation mechanism using a pervaporation method will be explained. That is, it is explained that the liquid separation mechanism by pervaporation is based on the dissolution and diffusion of the liquid in the membrane. In general, the separation coefficient α A B is calculated by dividing the concentration ratio of component ^A to component _B after permeation by the concentration ratio of component A to component B before permeation. It is expressed as the product of the ratio of diffusion rates at . In order to increase the separation coefficient α ^A _B , it is necessary to increase either or both of the solubility ratio and the diffusion rate ratio of the A component and the B component. Solubility is primarily determined by the intermolecular interaction (chemical compatibility) between the permeable molecules and the membrane. The solubility parameter has been taken up as a measure of chemical compatibility between membrane materials and the separation target. When selecting a membrane material, it is best to choose a substance that has high chemical compatibility with the membrane material and the permeable molecules, or a membrane material with similar polarity, so that the separation object (permeable molecule) in the feed liquid is hydrophilic. In this case, a membrane material with a large solubility parameter and high polarity is said to be suitable, while in the case of hydrophobicity, the opposite membrane material is said to be suitable. In other words, the former membrane material is suitable for water-ethanol separation. However, many of these materials dissolve or swell in the supply liquid, and when such materials are used alone, problems arise in terms of membrane durability and the like. Therefore, after film formation, durability is often imparted by introducing a crosslinked structure through ionic bonding, electron beam or plasma irradiation, creating a block structure with a non-polar material, or forming a composite film. Diffusion rate depends on the shape, size, and
It depends on the agglomeration state and the free volume of the membrane. In order to increase the separation factor α ^A _B , the shapes of the permeating molecules in the feed liquid must be significantly different. Generally, molecules with smaller shapes have higher diffusion rates. On the other hand, the free volume of a membrane is not defined by macroscopic pores, but by molecular gaps on a molecular scale. In a membrane with a large free volume, the difference in diffusion rate due to the difference in the size of the permeating molecules is small, and in a membrane with a small free volume, the difference in the diffusion rate due to the difference in the size of the permeating molecules is large. In order to increase the separation coefficient by utilizing the size of permeable molecules, it is necessary to reduce the free volume of the membrane. In order to reduce the free volume of a film, methods have been used to introduce a cross-linked structure or a crystal structure to form a dense three-dimensional network structure. The present inventors investigated the separation performance of various polymer membranes for aqueous solutions containing water-soluble organic substances, especially alcohols, using the pervaporation method. A copolymer of aromatic polyamide with a diamine component and an isophthalic acid component as the main acid component has good film formability and high separation coefficient and permeation rate as a single material without introducing a crosslinked structure or forming a composite film. I found out. The present invention will be explained in more detail below. The diamines used in the aromatic polyamide polymers of the present invention are bis(3-aminophenyl)sulfone and metaphenylenediamine as the low molecular weight diamine component. The amount of metaphenylenediamine used is 20 to 20% of the total amount of all diamine components.
It is 70 mol%. If it is more than 70 mol%, the solubility of the polymer will be significantly reduced, the solvent conditions for forming the membrane structure into an asymmetric membrane will be severely limited, and it will be difficult to obtain a good separation membrane. Further, if the amount is less than 20 mol%, good separation performance cannot be obtained. When the metaphenylenediamine component is in the range of 20 to 70 mol%, both separation coefficient and solubility performance are excellent. As the acid component, an isophthalic acid component is mainly used, but an aromatic dicarboxylic acid component can also be used. The amount used is preferably 20 mol% or less based on the total acid components. The polymer is obtained by reacting a diamine with a dicarboxylic acid chloride. A solution polymerization method or an interfacial polymerization method is used for the reaction. The shape of the separation membrane obtained from the polymer is not particularly limited to a flat membrane, spiral type, or hollow type, but in order to improve separation performance, particularly permeation rate, it is desirable that the membrane has an asymmetric structure. The polymer is N-methylpyrrolidone, N,
It is dissolved in a suitable polar solvent such as N'-dimethylformamide or N,N'-dimethylacetamide. In addition, to form an asymmetric structure, a film-forming stock solution in which the polymer is dissolved is cast onto a glass plate using a doctor knife, left to stand for a certain period of time to evaporate part of the solvent, and then a film forming solution containing the polymer dissolved therein is cast onto a glass plate. Just immerse it in the polymer's non-solvent. In addition, when forming a hollow fiber membrane,
After the membrane-forming stock solution is spun into a hollow fiber using a spinneret, a portion of the solvent may be evaporated in an inert gas for a certain period of time, followed by immersion in a coagulation bath. When forming an asymmetric structure, a slow coagulating agent such as glycols may be dissolved in the membrane forming stock solution. The separation membrane produced in this way mainly consists of water/
Organic substances, mixtures such as methanol, ethanol, 1-propanol, 2-propanol, n-
Alcohols such as butanol, ketones such as acetone and methyl ethyl ketone, ethers such as tetrahydrofuran and dioxane, organic acids such as formic acid and acetic acid, formaldehyde, acetaldehyde,
1 or 2 consisting of aldehydes such as propionaldehyde and amines such as pyridine and picoline
Although it is used to separate aqueous solutions containing the above compounds by pervaporation, it can also be used to separate a vapor mixture of water and the organic substance by vapor permeation. (Function) Since the film obtained from the polymer of the present invention is an aromatic polyamide, it is thermally stable, has excellent chemical resistance, and has good film formability. The reasons for the high separation coefficient and permeation rate of this membrane are not clear, but the moderate flexibility and hydrogen bonding in the aromatic polyamide molecular structure create a molecular gap (free volume) suitable for separating water and organic matter. It is presumed that it has been formed. In addition, aromatic polyamide contains hydrophilic amide bonds, carboxylic acid groups, amino groups, etc., and has a high affinity for water in the feed solution, so the water permeation rate is higher than the permeation rate of organic matter. This is thought to be due to its large size. (Example) The present invention will be specifically explained below using Examples.
The present invention is not limited thereby. (1) Film forming method To form a flat film, dissolve 3 g of polymer in 12 g of N,N'-dimethylacetamide (DMAC), cast onto a glass plate using a doctor knife, and heat at 80°C. After drying, the film was peeled off from the glass plate to obtain a homogeneous film. Sandwich the membrane between filter paper,
Drying was carried out under reduced pressure at 160°C for 16 hours. Furthermore,
Heat treatment was performed at 250°C for 1 hour. The hollow fiber membrane manufacturing method uses a polymer of N,
The polymer was dissolved in N'-dimethylacetamide solvent at a concentration of 30% by weight. This solution is extruded at a constant flow rate from a spinneret for manufacturing hollow fibers, and at the same time propylene glycol is extruded as a core liquid at a constant flow rate. While withdrawing the mixture, it was introduced into a coagulation bath at 25°C consisting of an aqueous solution containing 30% by weight of N,N'-dimethylacetamide, and further,
It was washed by soaking it in water all day and night. Thereafter, it was immersed in isopropyl alcohol and hexane for 1 hour each, and then air-dried overnight. The obtained hollow fibers were heated and dried at 160° C. under reduced pressure all day and night. (2) Method for measuring pervaporation performance To measure pervaporation performance, we created a Seikagaku-style pervaporation measuring device. The following pervaporation experiment was conducted under atmospheric pressure on the feed side of the water/aqueous organic compound mixture and under reduced pressure of 0.3 mmHg or less on the permeate side. The feed solution was added onto the membrane surface and stirred at a constant temperature. The effective area of the membrane at this time was 19.6 cm ² . Water and organic compounds that passed through the membrane were condensed with liquid nitrogen and collected. N-propanol was added to the permeate as an internal standard, and the permeation rate and separation coefficient were determined by TCD-gas chromatography. The separation coefficient α ^H20 _EtOH of water with respect to ethanol is defined as follows. _α ^H20 _{EtOH =} Y _H20 /Y _EtOH /Y _H20 /Y _EtOH However, in the above formula, _{X EtOH} , Expresses weight %. In the case of a flat membrane, the permeation rate (Q) is expressed as the amount of permeated mixture per unit membrane area, unit time, and membrane thickness of 1 μm.
Expressed in m/ ^m2・hr. In the case of hollow fiber membranes, the amount of permeated mixture per unit membrane area and unit time is Kg/ ^m2・
Expressed in hr. Example 1 42.5 g (0.17 ml) of bis(3-aminophenyl)sulfone and 7.9 g (0.07 ml) of metaphenylenediamine were placed in a four-neck flask equipped with a stirrer, temperature system, nitrogen inlet tube, and sample inlet. and introduce nitrogen gas. Dehydrated N-methylpyrrolidone
Add 500ml and stir. After completely melting, cool in an ice bath until the internal temperature reaches 4°C. From the sample inlet, 49.5 g of isophthalic acid dichloride powder (0.24
ml) and stirred for 1 hour while cooling in a bath. Thereafter, the mixture was reacted at room temperature for 2 hours, and then poured into methanol (Step 3) to obtain a polymer solid. The polymer was repeatedly pulverized using a mixer and washed with water, and then dried under reduced pressure. A flat film was formed from the obtained polymer according to the above film forming method,
The pervaporation performance was measured. The pervaporation performance was measured by supplying a 95% ethanol aqueous solution to the membrane surface and leaving it at 60℃ for 100 hours, taking into account the durability of the membrane. ^H20 _EtOH ) 1050, permeation rate is 0.31 (Kg・μ
m・m ²・h). Example 2 A hollow fiber membrane was formed from the polymer obtained in the same manner as in Example 1 according to the method described above, and further heat-treated at the temperature shown in Table 1 for 1 hour. The pervaporation performance of the hollow fiber membrane thus obtained was measured. Measuring pervaporation performance takes into account the durability of the membrane.
After supplying 95% ethanol aqueous solution to the membrane surface, 60℃
After being left for 100 hours, the permeability performance was measured.

[Table] Comparative Example 1 In the same manner as in Example 1, 55.0 g (0.22 mol) of bis(3-aminophenyl)sulfone was used as the diamine component, and 45.0 g of isophthalic acid dichloride was added.
Polymerization was carried out using (0.22 mol) as the acid component. The resulting polymer was formed into a film according to the method described above, and its pervaporation performance was measured. Measurement of pervaporation performance is
Taking into consideration the durability of the membrane, a 95% ethanol aqueous solution was supplied to the membrane surface, and after being left at 60°C for 100 hours, the pervaporation performance was measured. The separation coefficient between water and ethanol (α ^H20 _EtOH ) is 53, and the permeation rate is 0.73 (Kg・μm/
^m2・h). Comparative Example 2 68.1 g (0.16 mol) of bis[4-(3-aminophenoxy)phenyl]sulfone was prepared in the same manner as in Example 1.
isophthalic acid dichloride with diamine component.
Polymerization was carried out using 31.9 g (0.16 mol) as the acid component.
The resulting polymer was formed into a film according to the method described above, and its pervaporation performance was measured. The pervaporation performance was measured by supplying a 95% ethanol aqueous solution to the membrane surface and leaving it at 60°C for 100 hours, considering the durability of the membrane.
The pervaporation performance was measured. The separation coefficient between water and ethanol (α ^H20 _EtOH ) is 40, and the permeation rate is 0.84 (Kg・μm/
^m2・h). (Effects of the Invention) By using the membrane of the present invention, organic liquid mixtures can be efficiently separated by pervaporation at a higher permeation rate while maintaining a higher separation coefficient than in separation methods using conventional membranes. I can do it. Further, it is possible to form a film using a single material without performing a crosslinking reaction or forming a composite film. Therefore, the separation system can be made more compact, more rational, the processing capacity can be increased, and the cost can be lowered, and the present invention is effective in shortening separation and purification processes in the chemical industry, etc., and in practical application of membrane separation methods to save energy. Therefore, it has extremely great industrial utility.

Claims (1)

[Claims] 1 Consisting of an aromatic polyamide copolymer containing 30 mol% to 80 mol% of bis(3-aminophenyl) sulfone and 70 mol% to 20 mol% of metaphenylenediamine as a diamine component and an isophthalic acid component as the main acid component. A separation membrane for pervaporation characterized by: