JPH0516287B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a separation membrane that preferentially permeates water from a mixed solution of water and alcohol and concentrates alcohol, and a method for producing the same.
Alcohol separation membranes can be used to concentrate alcohol from biomass fermentation liquid and to recover and purify alcohol from aqueous alcohol in various manufacturing and processing processes. BACKGROUND ART Distillation has conventionally been used to separate and purify solutions, including water-alcohol mixed solutions. However, this distillation involves heating and vaporizing a liquid and then utilizing the difference in boiling point to separate substances. The amount of energy consumed for heating at this stage is enormous. On the other hand, a refrigerant such as water is also required to cool and liquefy the vaporized substance. In recent years, great expectations have been placed on the use of membranes as an alternative process to such distillation. Separation and purification using membranes has a wide range of applications, and processes such as dialysis using membranes for artificial kidneys, desalination of seawater using reverse osmosis membranes, and production of pure water are already in practical use today. Furthermore, it is well known that some gas separation membranes such as oxygen enrichment membranes have been put into practical use and are being incorporated into medical applications and separation processes in chemical manufacturing processes. However, examples of membrane separation of organic substances such as alcohols are currently extremely rare. This is because membrane materials suitable for this purpose have not yet been developed, and efforts are currently being made to achieve this goal. If such membranes are put into practical use and membrane separation becomes possible, it is expected to replace distillation, etc., and contribute to energy savings, simplify and speed up production processes, and make a major contribution to various fields. . Separation through the membrane is performed using the difference in the degree of dissolution and diffusion of the substance to be permeated into the membrane. In other words, so that permeable substances can pass through with higher priority,
Selective permeation separation can be achieved by constructing a structure with high affinity in the membrane. For example, in order to selectively permeate water from a mixed solution of water and a water-soluble organic substance, The membrane may be composed of more hydrophilic groups. From this point of view, the following membranes, for example, have been studied as membranes that selectively permeate and separate water from a water-alcohol mixed solution. Cellulose acetate membrane [Journal of Membrane Science, Vol. 1, p. 271, (1976)] Polyphenylene oxide membrane [Membrane, Vol. 8, No.
177 pages, (1983)] Acrylic acid-acrylonitrile copolymer membrane [Journal of Polymer Science, edited by Polymer Letters, Vol. 22, No. 473, (1984)] N-substituted polyimide-containing copolymer membrane [ polymer·
Journal, Volume 17, Page 363, (1985);
Vol. 16, p. 653, (1984)] Chitosan membrane [Kobunshi Papers, Vol. 42, p. 139,
(1985); same journal, vol. 43, p. 449, (1986)] Nafion membrane [Journal of Membrane Science, vol. 24, p. 101, (1985)] When these membranes are used, water- Since water can be permeated and removed from an alcohol mixed solution, alcohol can be concentrated. Problems to be Solved by the Invention The membranes described above are all homogeneous membranes, and the permeation rate is generally low. In addition, in these separation membranes, the micropores that are formed in the membrane due to swelling when it comes into contact with a solution become passageways for substance permeation, and selective separation occurs here, but with homogeneous membranes, the degree of swelling Degeneration and rupture of the membrane may also occur. If this happens, it becomes a practical problem as a separation membrane. That is, it goes without saying that a practical separation membrane must have both separation performance and mechanical stability. An object of the present invention is to overcome these problems and obtain a separation membrane with higher selective separation performance. Means to solve the problem To this end, we selected a porous polymer membrane made of a material that is stable against water and alcohol as a substrate, grafted acrylamide onto it, and then converted it into methylol. Therefore, this objective was achieved by constructing a membrane in which this layer had a more hydrophilic -CONHCH ₂ OH structure. First, a method for graft polymerizing acrylamide onto a porous polymer membrane was disclosed in Japanese Patent Application No. 60-269951.
I am familiar with Porous polymer membrane materials that are substantially unaffected by water and alcohol include polyethylene, polypropylene, polyvinyl chloride, polyvinylidene fluoride, polytetrafluoroethylene, nylon,
Examples include cellulose derivatives. There are several methods for graft polymerizing acrylamide onto these porous polymer membranes. For example, there is a method of activating with excited species such as light, plasma, and radiation. Although each method has its advantages and disadvantages, graft polymerization via plasma activation can be cited as a means for forming a separation membrane suitable for the present invention. This is because the action of the plasma is limited to the very surface of the polymer, thereby preventing deterioration of the mechanical properties of the porous polymer membrane as a bulk. Furthermore, plasma is effective for initiating graft polymerization for a wider range of polymer membrane materials. For the same reason, graft polymerization initiated by vacuum ultraviolet light is also effective. Graft polymerization via plasma surface treatment will be described below. Graft polymerization via plasma surface treatment involves two steps: (1) radical activation of the polymer surface by plasma irradiation, and (2) graft polymerization by monomer contact. First, the process of radical activation of the polymer surface is no different from ordinary plasma surface treatment. A low-temperature plasma process using glow discharge is already well known. for example,
He is familiar with "Techniques and Applications of Plasma Chemistry" edited by JR Horan and AT Bell, Wiley, New York (1974). To briefly explain plasma surface treatment,
Polymer materials are irradiated using glow discharge obtained by electrical discharge, and various reactions occur at the very surface layer of the material exposed to plasma. In other words, as soon as carbon-carbon bonds, carbon-hydrogen bonds, etc. that make up a polymer are cleaved by the action of plasma, polymer radicals are formed, and these radicals subsequently react to form crosslinks and unsaturation. A bond or a new polar group will be introduced. It is well known that when a polymer is irradiated with plasma, there is a considerable amount of polymer radicals that cannot participate in crosslinking or unsaturated bond formation reactions. Plasma graft polymerization utilizes these polymer radicals as starting points for polymerization. Separation membranes obtained by plasma graft polymerization that take advantage of the surface-specific characteristics of plasma treatment have the advantage of utilizing the respective functions of the substrate polymer and the graft polymer layer, and are superior to other grafting methods. As a method of generating glow discharge plasma, several K
Audio waves on the order of Hz to several tens of kilohertz, or microwaves with short wavelengths on the order of GHz,
13.56MHz radio waves are available. The appropriate plasma surface treatment conditions for the porous polymer membrane are irradiation treatment at a gas pressure of 0.01 to 1.0 Torr and an output of 5 to 100 watts for 5 seconds to 10 minutes. Suitable plasma gases include rare gases such as argon and helium, which do not cause deterioration or etching of the porous polymer membrane substrate, or non-polymerizable nitrogen gases or residual inorganic gases. It is not preferable to use oxygen or air as a plasma gas because it oxidizes and etches the substrate polymer film. In particular, polypropylene is deteriorated by air plasma or oxygen plasma and the strength of the film is significantly reduced, so it is better to avoid it. Next, the method of graft polymerization will be described.
Graft polymerization is a process in which an activated surface is chemically treated.
Although it may be damaged in some cases, it has the advantage that a regular polymer layer can be introduced by chain polymerization. Furthermore, since the newly formed graft polymer layer is chemically bonded to the substrate through covalent bonds, it does not come off and has excellent mechanical and chemical stability. Plasma graft polymerization methods include: (1) Graft polymerization in which a plasma-activated porous polymer membrane is brought into direct contact with a monomer gas or its solution in a vacuum without being taken out into the atmosphere as polymer radicals (2). ) There are two types of graft polymerization: a plasma-activated porous polymer membrane is brought into contact with air or oxygen gas to form a peroxide, and this is thermally decomposed to generate oxy radicals. However, either method can be used to create the grafted separation membrane. Next, methylolization of the acrylamide graft polymerized membrane thus obtained will be explained. Methylolation of polyacrylamide homopolymers is known; for example, methylol can be converted with high efficiency by the method described in Journal of Polymer Science, A-1, Vol. 7, p. 409 (1969). It is possible to obtain a reaction product.
A polyacrylamide layer graft-polymerized on a porous polymer membrane can also be methylolized in exactly the same manner. That is, paraformaldehyde is dissolved in a weak alkaline aqueous solution prepared to 10 or 12N using sodium hydroxide, potassium hydroxide, or lithium hydroxide to make a 2 to 10% solution, and a polyacrylamide graft polymerized membrane is added to this solution. This can be achieved by immersing it in water and allowing it to react at room temperature for 0.5 to 3 hours. The infrared absorption spectrum shows that the blast-polymerized acrylamide layer is almost completely methylolized ^.
This is clear from the fact that strong absorption is observed over 1030 cm ^-1 . This absorption is caused by the C-
This is due to O stretching vibration. Next, the means of separation will be described. A pervaporation method is suitable as a means for water-alcohol separation. This method involves bringing the mixed solution to be separated into contact with one side of the membrane.
The other side is evacuated or an inert gas is sent to collect the permeate. Regarding the actual situation, please refer to Membrane, Vol. 6, p. 168 (1981).
Familiar with literature such as Pervaporation is
It is said to be an effective method for separating azeotropic mixtures and separating isomer mixtures that are difficult to separate by distillation alone. A practical example of separation by pervaporation is shown below. Mount the membrane sample in the filtration holder and place the solution mixture in the holder. The lower part of the holder, that is, the side of the membrane not in contact with the permeate, is connected to a vacuum line to reduce the pressure. The vacuum is maintained for several to 10 minutes, and after the system pressure becomes constant and membrane permeation reaches equilibrium, the permeate is collected using a liquid nitrogen trap. After a certain period of time, the sample is weighed and subjected to gas chromatography to determine the concentration of water and alcohol from the intensity of the peaks. As an index showing separability, a separation coefficient (α) is given by the following method. Let us now consider permeation separation of component B from a mixed solution of two components A and B. When the concentrations of A and B components on the supply side through the membrane are respectively Af and Bf, and the concentrations on the permeate side are Ap and Bp, respectively, the separation coefficient α _B/A of B is expressed by the following equation. α _B/A = Bp/Ap/Bf/Af That is, it is given as the ratio of the concentration ratio of each component on both sides of the supply permeation. The larger the value of this separation coefficient, the higher the selectivity in permeation. In the methylolation-treated membrane of the present invention, when a separation operation is performed using a 0 to 90% ethanol aqueous solution by this pervaporation method, the ethanol concentration in the permeate decreases significantly, and water selection It was observed that it showed transparency. Effects of the Invention Next, the effects exhibited by the separation membrane of the present invention will be explained in more detail with reference to the accompanying drawings. The figure shows the selective permeation of water through a separation membrane having a methylolated layer of polyacrylamide on a porous polypropylene membrane, expressed as a separation coefficient, and its dependence on the grafting rate. Here, an example is shown in which a 70% ethanol aqueous solution is used as the supply liquid. Comparing this with the method described in Japanese Patent Application No. 60-269951, that is, using an acrylamide graft polymerized membrane before methylolization, the separation coefficient has significantly increased from 4-10 to 40-170, and the water- Ethanol separation is significantly improved. That is, it can be seen that the methylol treatment is effective. This improvement in water selective permeability is due to the fact that the amide group -CONH ₂ in polyacrylamide takes on the structure of -CONHCH ₂ OH through methylolation treatment, that is, a new hydroxyl group is added to the amide group, and the hydrophilic component in the separation active layer is improved. This is due to increased density, etc. Effects of the invention The separation membrane of the present invention has an alcohol concentration of 0-90%.
It is possible to selectively permeate water and separate water and alcohol from a wide range of water-alcohol mixed solutions. Therefore, it can be used, for example, to remove water from a biomass fermentation liquid and concentrate alcohol. Examples Next, the present invention will be explained in more detail with reference to examples. Example 1 Using a porous polypropylene membrane (Jyuragard), it was treated under a residual gas condition of 0.02 Torr at 10 Watts for 60 minutes, and then 30 ml of a 5% acrylamide aqueous solution that had been previously vacuum degassed was added.
The reaction was allowed to proceed for 2 hours at 60° C. under vacuum. After the reaction, unreacted monomers and homopolymers were removed by washing with water to obtain an acrylamide graft polymer membrane. Add 3.0 ml of rose formaldehyde to 30 ml of alkaline aqueous solution made 11N with sodium hydroxide.
gram was added to form a solution, and the mixture was reacted at room temperature for 3 hours. The weight increase after washing and drying was 4.96 mg/cm ² . Perform pervaporation using this membrane,
The following results were obtained at 30°C.

【table】 In addition, the following results were obtained at 40°C.

【table】 In addition, the following results were obtained at 50°C.

[Table] Example 2 A porous polypropylene film was subjected to plasma treatment in the same manner as in Example 1, and then exposed to the atmosphere for 10 minutes. This was subjected to graft polymerization of acrylamide and methylolization treatment under the same conditions as before to obtain a membrane with a graft ratio of 0.83 mg/cm ² . Perform pervaporation using this membrane,
The following results were obtained at 40°C.

[Table] Example 3 After a polypropylene porous film was subjected to plasma treatment in the same manner as in Example 1, the film was exposed to the atmosphere for 60 minutes. This was subjected to acrylamide graft polymerization and methylolization treatment under the same conditions as before to obtain a membrane with a graft ratio of 0.625 mg/cm ² . Perform pervaporation using this membrane,
The following results were obtained at 40°C.

[Table] Comparative Example 1 A separation experiment was conducted at 40°C using the acrylamide grafted membrane of Example 1 before methylolization, and the results were as follows.

【table】 [Brief explanation of the drawing]

The figure shows the separation coefficient of water-alcohol separation by the separation membrane 1 of the present invention as a dependence on the grafting rate, and is compared with that of the acrylamide grafted membrane 2 before methylolization treatment.

Claims (1)

[Scope of Claims] 1. Water consisting of a methylolated product of a porous polymer membrane substrate obtained by graft polymerization of acrylamide.
Alcohol separation membrane 2 A method for producing a water-alcohol separation membrane characterized by graft polymerizing acrylamide onto the surface of a porous polymer membrane substrate and then subjecting it to methylolization treatment.