JPH049577B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an electroosmotic dehydration method and an electroosmotic dehydration apparatus for efficiently electrically dehydrating a water-containing material using the electroosmotic force of a microporous membrane, and more specifically, to an electroosmotic dehydration apparatus and an electroosmotic dehydration apparatus for efficiently dehydrating a water-containing material using the electroosmotic force of a microporous membrane. The present invention relates to an electroosmotic dehydration method and an electroosmotic dehydration device that efficiently dehydrate with the degree of water decomposition being as small as possible by using a semipermeable membrane having a specific cation transport number. In general, dehydration of aqueous solutions, colloids, pastes, or gels (hereinafter referred to as hydrated materials) containing hydrophilic substances is considered to be relatively difficult, and if these dehydration steps are included in the manufacturing process, a large amount of money will be added to the process. Usually, it costs about 100 yen. Particularly in the case of hydrated materials containing highly hydrophilic polymeric substances, there is a strong demand for a particularly efficient dehydration method because hydrated materials often have a significantly high water content due to the characteristics of the polymeric substances. Conventionally, various methods have been implemented or proposed for dehydrating a hydrous material containing a polymeric substance, depending on the various characteristics of the polymeric substance. For example, for low viscosity solutions, membrane filtration methods such as reverse osmosis and ultrafiltration that utilize membranes that allow water to pass through without allowing polymer substances to pass through; for high viscosity solutions, reprecipitation methods such as alcohol precipitation; Alternatively, for agar that gels at room temperature and hydrated carrageenan, there are pressing methods such as gel press and rubber press. Reverse osmosis and ultrafiltration methods are efficient dehydration methods, but
It can only be applied to water-containing substances that have low solution viscosity and are difficult to form gels or pastes, and there is a limit to the decrease in the viscosity of the target object due to temperature rise due to the durability of the membrane, so the range of application is narrow and the concentration ratio is limited. It also has the disadvantage of being small. On the other hand, the alcohol precipitation method, which is often applied to aqueous polymer solutions, generally requires a large amount of alcohol compared to the polymer material, and therefore has the drawback of high costs for recovering the alcohol. Proposals regarding the method of dehydrating high viscosity substances by electroosmosis include Japanese Patent Publication No. 56-25167 and Japanese Patent Publication No. 57-251, as an efficient method for dehydrating gels or pastes.
36004 and Special Publication No. 58-36605. These are methods for electrically dehydrating artificially formed gels or pastes, in which case a cation exchange membrane with high electroosmotic power is used on the cathode side and an anion exchange membrane on the anode side. This is an attempt to electrically dewater objects without applying much mechanical pressure. Furthermore, by providing at least one drainage chamber separated by a membrane on both sides in the middle part that does not directly contact both electrodes, the purpose is to prevent contamination of the target object and to supply ions to the target object. The remaining sample chambers are separated by multiple diaphragms to improve efficiency. However, ion exchange membranes are generally made of a homogeneous and dense material and have a small amount of electroosmosis, so they cannot be expected to provide efficient dewatering performance when dehydrating hydrated materials whose electroosmosis is low. . The inventors of the present invention attempted to expand the number of objects to be dehydrated and increase the dehydration efficiency, and as a result of various studies, they discovered a new dehydration method, and filed a patent application in 1983.
-227062, patent application No. 58-18126, and patent application No. 58-18949. To briefly describe these methods, in these methods, a microporous membrane is newly placed on the anode side of the cathode side diaphragm of a sample chamber separated by a diaphragm, and furthermore, a microporous membrane is placed between the cathode side diaphragm and the microporous membrane. By providing a water outlet in the provided partial gap and applying electricity between both electrodes, the hydrated substance in the sample chamber is dehydrated and water is separated from the system through the water outlet. The main driving force for dehydration in the above method is the electroosmotic force of the microporous membrane, and the cation exchange membrane suitable as the cathode side diaphragm functions as a membrane with low electroosmosis. These methods are extremely useful as they enable electroosmotic dehydration with excellent power efficiency and dehydration speed even from aqueous solutions and dispersions, which were difficult to dehydrate using conventional electroosmotic methods. In the above method, among cation exchange membranes that are particularly suitable as semipermeable membranes for separating sample chambers, a cation exchange membrane with a higher transport number has a characteristic that it has better dehydration efficiency. However, it has a high cation transfer number (e.g.
0.98 to 0.99) When a cation exchange membrane is used, there is a problem in that water decomposition tends to occur between the cathode side diaphragm and the micropores under practical current density conditions. In other words, when water decomposition occurs, the alkali is discharged from the system together with the separated water, but the acid passes through the cathode side diaphragm and moves into the water-containing material in the sample chamber in the adjacent chamber. In this case, it may have various adverse effects. In order to solve the above problem, it is effective to provide a buffer chamber between each sample chamber to block the movement of the generated acid to the next chamber, but with this method, as concentration progresses, alkali is transferred to the sample chamber. However, there was room for improvement as the PH of the water-containing substance sometimes shifted to the alkaline side. With the aim of solving the above problem, the present inventors conducted further intensive studies and found that the pH of the water-containing material in the sample chamber was
We have found a method and apparatus that can maintain almost the original value and dehydrate and concentrate to a high concentration ratio. The present invention is a method for dehydrating a hydrated substance in a sample chamber provided between a cathode and an anode electrode chamber by using the electroosmotic force of a microporous membrane, in which a cation transfer number is small on the anode side of the sample chamber. A cation exchange membrane with a diameter of 0.95 is placed on the cathode side of the sample chamber, even if the cation transfer number is large.
0.95 semipermeable membranes, and the microporous membrane is disposed on the anode side of the semipermeable membrane, and electricity is applied between the two electrodes to form a membrane between the semipermeable membrane and the microporous membrane. This is an electroosmotic dehydration method characterized by dehydration. Further, according to the present invention, a sample chamber is further provided in the space sandwiched between the cathode and anode electrodes, and the anode-side diaphragm 9 and cathode-side diaphragm 7 of the sample chamber 5 each have a cation transference number of at least 0.95. Cation exchange membrane and
A semipermeable membrane having a cation transfer number of at most 0.95 is arranged, a hydrophilic microporous membrane 8 is arranged at least on the anode side of the cathode side diaphragm 7, and a hydrophilic microporous membrane 8 is arranged at least on the anode side of the cathode side diaphragm 7.
An electroosmotic dehydration device is provided in which the microporous membrane 8 and the microporous membrane 8 have most of their surfaces close to each other and are partially spaced apart from each other to provide a space for draining water. FIG. 1 shows an example of a multi-chamber type electroosmotic dewatering device, and FIG. 2 shows an example of a single-chamber type electroosmotic dehydration device. Further, examples of main components are shown in FIGS. 3 and 4. In addition, in FIGS. 1 to 4, 1 is a cathode chamber,
2 is an anode chamber, 3, 4, and 14 are buffer chambers, 6 is a diaphragm in a cathode chamber, 10 is a diaphragm in an anode chamber, 11 is a sample injection port, 12 is a water drain port, 15 is a porous plate, and 16 is a semipermeable membrane. A support frame that supports the diaphragm 7 and the microporous membrane 8 and has a water outlet through which separated water exits the system, 17 is a spacer provided at the water outlet, dynamically supports the diaphragm 7 and the microporous membrane 8, and Water can pass therethrough, and the spacer 17 has a number of holes or grooves communicating from the sample chamber 5 to the outside of the system. In the electroosmotic dehydration apparatus of the present invention, the microporous membrane and the semipermeable membrane are partially separated from each other to form a space 13 for draining water. Space part 13
In the apparatus illustrated in FIGS. 1 to 4, the microporous membrane 8
and the lower part of the cathode side diaphragm 7, but they may be formed in the upper part or the middle part of these films. It is preferable that the microporous membrane and the semipermeable membrane are in contact with each other in a portion other than the water drainage space (most part of the membrane surface) or are in contact with each other through a liquid (water or an aqueous solution). If the space 13 for water drainage is provided at the bottom of both membranes, if the distance between the membranes is so large that the liquid cannot be retained due to surface tension, the liquid between the semipermeable membrane and the microporous membrane will drain into the space. This causes the water to flow downward, cutting off electricity and making dehydration impossible. Therefore, when the water drainage space 13 is provided at the bottom of the membrane, the distance between the membranes should be within the limit where the liquid is retained by surface tension. When the space is provided at the top of the membrane, it is not as constrained as when it is provided at the bottom, but the present invention utilizes the electroosmotic force of the microporous membrane to draw in water and extract the water blocked by the semipermeable membrane. In essence, it is preferable that the distance between the microporous membrane and the semipermeable membrane be relatively small. The method and apparatus of the present invention allow highly efficient electroosmotic dehydration not only of conventionally known gels or pastes, but also of aqueous solutions, colloids, or dispersions, which have been difficult to perform in the past. It has the characteristic of being able to dehydrate to a high concentration ratio while maintaining the value of . Furthermore, since the method and apparatus of the present invention can be carried out under any conditions from room temperature to heated conditions, the feature is that concentrated water-containing substances can be extracted continuously or semi-continuously in an aqueous solution or solid form as needed. There is. Furthermore, the present invention is characterized in that it is possible to dehydrate a hydrated material having a wide range of viscosities within a range in which useful components in the hydrated material are difficult to pass through the microporous membrane during energization. The dehydration method and dehydration apparatus of the present invention are characterized in that various water-containing substances are efficiently dehydrated out of the system mainly by the difference in electroosmotic force between the microporous membrane and the semipermeable membrane. The present invention will be explained in more detail. First, in the method and apparatus of the present invention, under practical current density (2 A/dm ² - 0.2 A/dm ² ) conditions, a cation exchange membrane with a cation transfer number of at least 0.95 is used as the anode side diaphragm. , the desired high-efficiency dehydration (extremely good power efficiency and dehydration speed) is achieved. Below this value, the movement of water into the sample chamber (diluting water-containing substances) due to the electroosmotic properties of the membrane cannot be ignored, resulting in a decrease in efficiency. In addition, by using a semipermeable membrane with a cation transfer number of at most 0.95 as the cathode side diaphragm, the occurrence of water decomposition is significantly suppressed under practical current density conditions, and the PH of the water-containing material in the sample chamber is returned to almost its original value. It becomes possible to hold the When the cation transfer number exceeds this value, the cathode side Since the salt concentration in the water existing between the diaphragm and the microporous membrane is extremely low, when electricity is applied, the water is placed in an extremely large electric field, which causes water decomposition and causes acid and alkali to form. Occur. By using a semipermeable membrane with a cation transfer number of at most 0.95, anions are replenished into the water at a ratio of 0.05 and salts are replenished by diffusion movement, so the generation of acids and alkalis is significantly suppressed. Changes in the PH of the target hydrated substance are significantly reduced. Further, in the present invention, it is preferable that the microporous membrane has a hydrophilic group and is inherently hydrophilic.
Even those that do not have hydrophilic properties can be used by making them hydrophilic with alcohol or a surfactant (so that they become wet immediately when impregnated with water). Microporous membranes that do not get wet when impregnated with water not only cause a lot of power loss due to voltage drop, but also cause water decomposition to occur significantly due to the large electric field applied between the microporous membranes.
Causes a change in PH. The hydrophilic microporous membrane used in the present invention is an inorganic or organic microporous membrane, in which the material itself has hydrophilic properties, as well as surfactant treatment,
It means a microporous membrane made hydrophilic by chemical treatment or various other methods, and the material and manufacturing method are not particularly limited. The thickness, porosity, average pore diameter, and pore diameter distribution of the microporous membrane are appropriately selected from those with a large amount of electroosmosis depending on the type and physical properties of the object to be dehydrated. mm, porosity 20-90%,
A microporous membrane with an average pore diameter of 10〓 to 10μ and a small (uniform) pore size distribution is suitable for achieving the object of the present invention. In addition, in the present invention, the electroosmotic amount of the microporous membrane is at least 360 c.c./F in order to perform more efficient dehydration from gels and pastes than in conventional methods. A microporous membrane with a large amount of water is preferred. In addition, the cation exchange membrane and semipermeable membrane used in the present invention mean that ions permeate through the membrane, and water that has permeated through the microporous membrane can be removed from the anode chamber or buffer chamber (between the sample chambers and between the electrode chamber and the sample chamber). Since it is necessary to make it as difficult as possible for water to pass through (provided), it is desirable that the amount of electroosmosis be small. In addition to ion-exchange membranes, the diaphragm that satisfies these requirements may be a hydrophilic semipermeable homogeneous membrane with a smaller electroosmotic amount than a microporous membrane, such as a typical hydrophilic neutral membrane. Examples include cellophane, polyvinyl alcohol, and cellulose acetate. In addition, the cation exchange membrane used in the present invention is not particularly limited within the scope of the purpose, but examples include a fluororesin exchange membrane having a sulfone group, a styrene-divinylbenzene resin exchange membrane having a sulfone group, etc. In addition to exchange membranes, JP-A-58-17122 and JP-A-58-
Vinyl chloride resin proposed in No. 117225 etc. or
Cation exchange membranes containing sulfone groups obtained from resin compositions containing vinyl chloride resins, cation exchange membranes with sulfone groups introduced into the ethylene copolymer film proposed in Japanese Patent Publication No. 52-29988, A composite ion exchange membrane reinforced with a microporous membrane proposed in Japanese Patent Application Laid-Open No. 57-212232 and Japanese Patent Application No. 58-177057 is suitable. In the present invention, the amount of electroosmosis of the semipermeable membrane constituting the cathode side diaphragm is selected to be smaller than the amount of electroosmosis of the microporous membrane, thereby preventing water from entering the electrode chamber or the buffer chamber. It is desirable that the cation transfer number be as small as possible, and the cation transfer number should be at most 0.95.
It is preferable to select a membrane with a small electrical resistance and electroosmotic amount from among the above membranes. Next, a description will be given of a water-containing material as an object to be dehydrated according to the present invention. The object to be dehydrated is first an aqueous polymer solution containing organic substances used as stabilizers and thickeners,
Colloids, pastes, dispersions or gels may be mentioned. Such organic substances include katsupa,
Seaweed extracts such as lambda or iota type carrageenan, furcelan, alginate, agar, vegetable proteins such as soybean protein and wheat protein, vegetable polysaccharides such as starch, vegetable lipids such as soybean lecithin, locust bean gum, guar gum , seed mucilages such as tamarind gum and quince seed, resin-like mucilages such as gum arabic, gum tragacanth, and gum karaya, plant mucilages such as pectin and arabinogalactan, and mucilage produced by microorganisms such as xanthan gum, pullulan, dextran, and curdlan. , animal proteins such as gelatin, casein, and albumin, animal fats such as egg yolk lecithin,
Starch derivatives such as starch phosphate and carboxymethyl starch, hydroxyethyl cellulose,
In addition to cellulose derivatives such as carboxymethyl cellulose, methyl cellulose, and ethyl cellulose, fine-grain crystallized cellulose, alginic acid derivatives such as alginate propialene glycol ester, and furthermore, polyvinyl alcohol, polyvinyl pyrrolidone, polyacrylic acid, and various other synthetic polymers are used. Can be mentioned. Examples of inorganic substances include metal oxides that have many -OH groups on the surface and become hydrous gels or pastes by absorbing water, such as silicic acid, silicates, aluminum hydroxide, cement, and tortoise; Examples include metal hydroxides. Among these, it goes without saying that the present invention is suitable for dehydrating water-containing materials that cause decomposition, contamination, deterioration of quality, etc. due to pH changes. Hereinafter, the present invention will be further explained in detail in Experimental Examples and Examples. Further, the cation transfer number, viscosity, electroosmotic amount, electrical resistance, and average pore diameter of the microporous membrane used in the present invention were measured by the following methods. Cation transport number Membrane potential was measured according to a conventional method using potassium chloride as an electrolyte, the concentration on both sides of the sample was 0.2M/0.1M, and the liquid temperature was kept at 25℃, and calculated from the Nernst equation. It is a value. Viscosity (centipoise) This is the value measured using a B-type viscometer at a temperature of 25°C. Electroosmotic amount (cc/F) Based on the usual method for measuring electroosmotic amount, 0.05N sodium chloride aqueous solution (25℃) is used as the measurement liquid, and direct current is applied under constant current density conditions of 55 milliampere/ ^cm2 . The amount of solution (cc) moved by applying an electric current is 1
This is the value converted to the amount of electricity per Faraday. Electrical resistance (Ω・cm ² ) Based on the ordinary method for measuring electrical resistance of membranes,
This is a value measured in a 0.05N sodium chloride aqueous solution. Porosity of microporous membrane (%) Calculated by porosity (%) = pore volume / microporous membrane volume x 100. Average pore diameter (μ) of microporous membrane Calculated by averaging the major and minor axes of 200 pores observed in scanning electron micrographs of the surface of a microporous membrane. Experimental example 1 81 parts by weight of vinyl chloride resin (Nipolitsu MH manufactured by Chitsuso Co., Ltd.), 9 parts by weight of chlorinated polyethylene (Elasrene 303B manufactured by Showa Denko Co., Ltd.) and 92.3 parts by weight.
10 parts by weight of a copolymer of mol% ethylene and 7.7 mol% ethyl acrylate (MI=2) were dry blended at room temperature. Next, 31 parts by weight of dioctyl phthalate and 5.5 parts by weight of an organic tin malate stabilizer (manufactured by Nitto Kasei Co., Ltd.) were added to the vinyl chloride resin.
TVSN2000E4) was added to the above resin mixture, melted and kneaded in a kneader at a temperature of 160°C for 30 minutes,
A predetermined resin composition was obtained. Extrusion mold the above resin composition using an extruder to 80μ
It was made into a thick film. The above film was then treated with 10% free sulfur trioxide.
After sulfonating with fuming sulfuric acid (42℃) containing % by weight, washing with concentrated sulfuric acid, dilute sulfuric acid, and water according to the conventional method, and then replacing the sulfonic acid group with sodium salt, the electrical resistance was 2.4Ω・cm. The cation exchange membrane had ^{a 2-} cation transference number of 0.98 and an electroosmotic capacity of 130 c.c./F. Experimental Example 2 A copolymer of 94.2 mol% ethylene and 5.8 mol% methyl methacrylate was saponified (degree of saponification = 60
mol %) and neutralization (degree of neutralization = 30 mol %) to 80 parts by weight of an ethylene copolymer (MI = 1) having -COOCH ₃ , -COOH and -COONa groups,
20 parts by weight of high-density polyethylene (density = 0.955
g/cm ³ , MI=7) in a kneader at a temperature of 190°C for 30 minutes, and then 43 parts by weight of liquid paraffin (manufactured by Kokusan Kagaku Co., Ltd.) was added to 100 parts by weight of the above resin mixture. and further kneaded for 30 minutes at 190°C. Next, the resin composition was extruded from a die at a temperature of 180° C. using an extruder to obtain a film having a thickness of 40 μm. Then, after immersing the film in 1,1,1-trichloroethane and extruding liquid paraffin,
React with fuming sulfuric acid containing 10% free sulfur trioxide, then wash with concentrated sulfuric acid, diluted sulfuric acid, and water, and then
Hydrolyzed and neutralized with a 31% by weight potassium hydroxide aqueous solution at 60℃, further washed with water, and dried to obtain an electrical resistance of 1.0Ω・cm ² , a cation transference number of 0.90, and an electroosmotic amount.
A cation exchange membrane of 290 c.c./F was prepared. Experimental Example 3 Dioctyl phthalate, anhydrous finely divided silicic acid, and powdered high-density polyethylene (density = 0.950 g/cm ² MI =
1) A hydrophilic microporous polyethylene membrane having a thickness of 200 μm and an average pore diameter of 0.02 μm and a porosity of 55% was created by extrusion molding the resin composition obtained from 1) and extracting dioctyl phthalate using a conventionally known method. . Examples 1 to 4 In the apparatus shown in FIG. 1, the cation exchange membrane of Experimental Example 1 (effective membrane area 25
cm ² ), the cation exchange membrane of Experimental Example 2 was placed as the cathode side diaphragm 7 of each sample chamber 5, the microporous membrane of Experimental Example 3 was placed as each microporous membrane 8, and the electrode liquid was
Add 0.5N sodium sulfate aqueous solution to buffer chambers 3, 4, and 14.
Using a 0.1N aqueous sodium chloride solution as a buffer solution, a 1.7% by weight λ-carrageenan aqueous solution was continuously injected into the sample chamber 5 with a maximum volume of 30 ^cm2 .
Electroosmotic dehydration was performed under constant current density conditions of 0.5 A/dm ² . As shown in Table 1, the results showed that the dehydration rate and power efficiency were excellent, and the pH of the resulting concentrated gel remained neutral. During dehydration, the electrode solutions in the cathode and anode chambers were circulated and neutralized, and the buffer solution was continuously replaced with fresh solution.

[Table] Experimental Examples 5 to 7 Electroosmotic dehydration was carried out in the same manner as in Example 1 except that the current density was changed to 0.9 A/dm ² . As shown in Table 2, the results showed good dehydration efficiency and gel pH.

[Table] Example 8 The cation exchange membrane of the cathode side diaphragm 7 was made of a water-insoluble polyvinyl alcohol film (thickness:
120μ, electrical resistance 106Ω・cm ² , electrical osmosis 90c.c./F)
Electroosmotic dehydration was carried out in the same manner as in Example 7, except that As shown in Table 2, although the dehydration efficiency was somewhat inferior, the PH of the gel remained neutral and was good.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view showing an example of a multi-chamber type electroosmotic dehydration device of the present invention, FIG. 2 is a schematic cross-sectional view showing an example of a single-chamber type electroosmotic dehydration device, The figure is a perspective view showing one example of the main components of the sample chamber 5. 1... Cathode chamber, 2... Anode chamber, 3, 4, 14...
...Buffer chamber, 5...Sample chamber, 6...Cathode chamber diaphragm,
7... Cathode side diaphragm of sample chamber, 8... Microporous membrane, 9
...Sample chamber anode side diaphragm, 10...Anode chamber diaphragm, 11...Sample injection port, 12...Water outlet, 13
...Drainage space, 15...Perforated plate, 16...
Support frame, 17...spacer.

Claims (1)

[Claims] 1. A method for dehydrating a hydrated substance in a sample chamber provided between a cathode and an anode electrode chamber using the electroosmotic force of a microporous membrane, in which cations are transported to the anode side of the sample chamber. A cation exchange membrane with a cation exchange rate of at least 0.95 is placed on the cathode side of the sample chamber, a semipermeable membrane with a cation transfer number of at most 0.95 is placed on the cathode side of the sample chamber, and the microporous membrane is placed on the anode side of the semipermeable membrane. An electroosmotic dehydration method characterized in that water is removed from between the semipermeable membrane and the microporous membrane by applying electricity between the two electrodes. 2. A sample chamber is provided in the space between the cathode and anode electrodes, and a cation exchange membrane with a cation transfer number of at least 0.95 and a cation exchange membrane with a large cation transfer number are used as the anode side diaphragm and cathode side diaphragm of the sample chamber, respectively. 0.95 semipermeable membrane, a hydrophilic microporous membrane is arranged at least on the anode side of the cathode side diaphragm, and most of the surfaces of the cathode side diaphragm and the microporous membrane are close to each other. , an electroosmotic dewatering device characterized in that a space for draining water is provided at a partial distance.