JPH0412169B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a separation membrane having heat resistance and organic solvent resistance. Ultrafiltration is a method for concentrating polymers and colloids dissolved in liquids. Ultrafiltration is a method that uses a semipermeable membrane with micropores with a pore diameter of several tens to hundreds of angstroms to perform liquid-liquid separation using pressure as the driving force. It is used for desalting and concentrating enzymes and proteins, and removing pyrogens from the water column. Due to its energy saving properties and ease of operation, its applications are rapidly expanding. The present invention relates to an ultrafiltration membrane used for ultrafiltration. [Prior Art] Ultrafiltration membranes used for ultrafiltration are generally made of synthetic polymers. For example, acrylonitrile-vinyl chloride copolymer, polyvinyl chloride,
Membranes made of polyvinyl alcohol, polysulfone, polyvinylidene fluoride, and the like are commercially available. Furthermore, acetyl cellulose and regenerated cellulose membranes made from naturally derived polymers are also commercially available. All of these materials are organic substances, and it has been pointed out that they have problems in heat resistance and organic solvent resistance, but a film that overcomes these drawbacks has not yet appeared. [Problems to be solved by the present invention] The present invention solves the above-mentioned drawbacks of conventional ultrafiltration membranes, namely, low heat resistance and low organic solvent resistance by using a new membrane material. be. [Detailed Description of the Invention] The gist of the present invention is to use an aluminum oxide film having excellent organic solvent resistance and heat resistance as a material for the ultrafiltration membrane. As is well known, aluminum oxide is commonly used, although it has problems with PH resistance. It is not easily attacked by organic solvents and has a heat resistance of 1000℃.
Compared to the materials of organic polymer ultrafiltration membranes currently used without deformation, such as polysulfone resin, polyvinyl chloride resin, acrylonitrile-vinyl chloride copolymer, etc.
It can be said that it is an extremely good material. Of course, compared to organic polymers, inorganic materials generally have better heat resistance and organic solvent resistance. However, it has traditionally been difficult to mold films that use inorganic materials, such as metals and ceramics, for ultraviolet rays, and therefore organic polymers that are easy to mold are currently being used. It is. The inventors of the present invention have conducted extensive research into forming ultrafiltration membranes using inorganic materials, and discovered that aluminum oxide, which forms on the metal surface when metal aluminum undergoes electrolysis in an anodizing electrolyte, Noting that micropores with a diameter of about 200 angstroms are formed perpendicular to the plane of the aluminum oxide layer, the inventors attempted to extract the aluminum oxide layer individually and completed the present invention. The method for manufacturing the aluminum oxide ultrafiltration membrane of the present invention will be described below. The porous aluminum oxide film of the present invention is produced by anodizing the raw metal aluminum or aluminum alloy, and removing the unoxidized base metal and the (non-porous) aluminum oxide barrier layer from the anodic oxide. It can be manufactured by two steps: 1. In the present invention, the raw metal aluminum or aluminum alloy includes pure aluminum,
High purity aluminum and aluminum and Si, Fe,
An alloy with metals such as Mn, Mg, Cu, Zn, Cr, Ni, Ti, and Pd can be used. The raw material aluminum or aluminum alloy may be in the form of a plate, a foil, a tube, or a hollow fiber, and depending on the shape of the raw material, a porous film in the form of a flat membrane, a tubular membrane, or a hollow fiber membrane may be formed. can be formed. Making the thickness of the raw material larger than necessary is
This is also undesirable in terms of saving raw materials or facilitating the removal of the remaining metal layer in the second step. Generally, a raw material having a thickness in the range of several thousand angstroms to several angstroms is desirable. It is desirable that the metal aluminum or aluminum alloy used as the raw material be subjected to an appropriate surface treatment to clean, smooth, and purify the surface before anodizing. As the surface treatment method, a known degreasing method, electrolytic polishing method, chemical polishing method, or a combination of these methods can be used. As a method for anodizing metal aluminum or an aluminum alloy, widely known methods can be used. That is, using metal aluminum or an aluminum alloy as a raw material as an anode, electrolysis is performed in an electrolyte solution capable of forming a porous aluminum oxide film. In the present invention, it is necessary to anodize only one side of the raw material by contacting the electrolyte solution with only one side of the raw material if it is flat, or only the outer or inner surface of the raw material if it is tubular. At this time, examples of the cathode material used include platinum, iron, tin, aluminum, carbon, and lead. Type and concentration of electrolyte used,
The temperature, electrolysis voltage, current density, and electrolysis time are extremely important because they determine the pore diameter, porosity, pore shape, thickness, hardness, strength, etc. of the porous aluminum oxide film to be produced. Depending on the type of electrolyte used, some produce a porous film and others produce a non-porous insulating film, and in the present invention, it is necessary to use the former electrolyte. Typical electrolytes include, for example, sulfuric acid, oxalic acid, chromic acid, phosphoric acid, benzenesulfonic acid,
Examples include sulfamic acid. Among these, the most desirable electrolytes include sulfuric acid, oxalic acid, phosphoric acid, and chromic acid. When anodic oxidation is performed in such an electrolyte under appropriate conditions, an aluminum oxide film having a regular porous structure can be formed on the surface of the raw metal. The pores generally grow perpendicular to the surface of the raw metal, forming a non-porous aluminum oxide barrier layer between the porous coating and the raw metal. The pore size can basically be varied from about 100 Å to several hundred Å depending on the type of electrolyte used, so membranes with various pore sizes can be created depending on the type of solution to be separated. I can do it. As electrolytes, sulfuric acid, oxalic acid, chromic acid,
When using phosphoric acid, approximately 120 Å, 170 Å,
It is known that pores with diameters of 240 Å and 330 Å are generated. The degree of immersion in the electrolyte is not particularly limited. The porosity of the resulting porous film and the thickness of the nonporous barrier layer basically depend on the electrolysis voltage.
Can be adjusted. Generally, as the electrolysis voltage increases, the barrier layer thickness and pore spacing increase, and the porosity of the coating decreases. For this reason, the electrolysis voltage can be selected from several volts to about 200V, but in order to obtain a membrane with a high gas permeation rate, it is disadvantageous to use an electrolysis voltage that is higher than necessary. From the above, preferred electrolytic voltages include voltages in the range of several volts to 80 volts. The thickness of the oxide film produced by electrolysis increases in proportion to the current density and electrolysis time. Therefore, by selecting the electrolysis time,
An oxide film of desired thickness can be produced. In the present invention, in order to extract only the porous film from the anodized raw material, unoxidized base metal,
It is necessary to etch away the aluminum oxide barrier layer. It is important that etching is always performed from the surface opposite to the surface on which the film has been formed, and that the film is not exposed to the etching atmosphere during etching. The unoxidized bare metal and barrier layer can also be etched sequentially under the same conditions. but,
Generally, the barrier layer is very thin, several hundred Å thick, so after removing the base metal in advance, under milder conditions,
It is desirable to remove the barrier layer at a controlled etch rate. Examples of methods for removing unoxidized aluminum or aluminum alloy include physical methods such as plasma etching, chemical etching methods using alkali or acid, and electrochemical etching methods. Alkaline etching agents include sodium hydroxide; acidic etching agents include hydrochloric acid, nitric acid,
Examples include hydrofluoric acid, sulfuric acid, chromic acid, and mixtures thereof. In addition, known etching methods such as the bromine-methanol method or the iodo-methanol method can also be used. Examples of the electrolyte used in the electrochemical etching method include hydrochloric acid, sulfuric acid, and sodium hydroxide. Methods for removing the aluminum oxide barrier layer include physical methods such as plasma etching or chemical etching methods. The etching agent may be any substance that dissolves aluminum oxide, but preferred etching agents include sulfuric acid, phosphoric acid, oxalic acid, and chromic acid. When etching an aluminum oxide barrier layer, pressurized water or buffer solution is supplied in advance from the surface of the film to prevent the etching agent from entering the film through the holes penetrated by etching and damaging the film. This is desirable. It is also possible to increase the porosity and pore size of the coating by introducing an etching agent into the pores and partially dissolving the pore walls. In order to assemble a separation membrane module using the porous film produced as described above, it is necessary to hermetically seal the ends of the membrane. In the film of the present invention, by leaving the ends of the raw metal aluminum or aluminum alloy in the raw material state without anodizing or etching, it is possible to easily create a seal in the film. Alternatively, a sealed portion can be created by subjecting only the ends of the porous film to a known sealing treatment such as a pressurized steam method. The membrane obtained by the above method preferably has a thickness of 1 .mu.m to 200 .mu.m, particularly 5 .mu.m to 60 .mu.m, in order to provide a sufficient amount of liquid permeation and to have practical strength. Although the membrane of the present invention has extremely excellent heat resistance, the use temperature is preferably 900°C or lower.
In an atmosphere of 900℃ or higher, the membrane is easily deformed.
Destruction becomes more likely. [Effects of the Invention] As is clear from the above description, the aluminum oxide ultrafiltration membrane according to the present invention has excellent solvent resistance and heat resistance, and also exhibits sharp text performance due to its narrow pore size distribution. [Example] Example 1 An anodic oxide film (film area: 2.01 μm) chemically formed to a thickness of 50 μm at a constant voltage of 20 V in a 20% by weight sulfuric acid bath (0°C)
cm ² ), the back side Al was etched with a (20% HCl + 0.1 MCuCl ₂ ) solution, and the barrier layer was etched with 20 wt % sulfuric acid for use in the experiment. The pore diameter of this membrane was 60.8 Å and the thickness was 65 μm. This membrane was attached to an ultrafilter made of brass and glass, and acetone, methanol, benzene, and ethanol were each passed through the membrane at a pressure difference of 1 Kg/cm ² to observe changes in the permeation flow rate over time. The results are shown in Table 1. It can be seen that the film is not completely attacked by organic solvents.

[Table] Comparative example 1 Commercially available polysulfon ultrafiltration membrane (TS-10,
Example ¹
It was attached to the ultrafilter used in 2010, and acetone, methanol, benzene, and ethanol were passed through it at a pressure of 1 Kg/cm ² to observe changes in membrane permeation flow rate over time. Table 2 shows the results.
Shown below.

[Table] Example 2 The membrane used in Example 1 was subjected to glycerin at 190°C. The equipment used was the same as in Example 1. Table 3 shows the change in membrane permeation flow rate over time.

[Table] Example 3 Pore diameter approximately 160 manufactured in the same manner as Example 1
Polyethylene glycol inhibition experiments were carried out using a 3.5-inch aluminum oxide film. Monodisperse polyethylene glycol at a concentration of 500 ppm or
It was dissolved in distilled water to a concentration of 1000 ppm and used as a sample. The membrane was attached to a stirred ultrafilter and filtered at room temperature with a pressure difference of 2 Kg/cm ² . At this time, the initial membrane permeation flow rate was 2 to 4 x 10 ^-4 cm ³ /cm ² ·sec. The polyethylene glycol concentrations in the blocking solution and permeate were determined using a total organic carbon analyzer, and the rejection rate was determined using the following formula. Rejection rate=(1-polyethylene glycol concentration in permeated liquid/polyethylene glycol concentration in blocking liquid)×100 Table 4 shows the rejection rate of the aluminum oxide film against polyethylene glycol of various molecular weights.

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Claims (1)

[Claims] 1 Porous for ultrafiltration, which is obtained by electrolyzing metal aluminum or aluminum alloy in an anodizing electrolyte to form a porous aluminum oxide film on the metal surface, and removing the portion other than the porous film by etching. aluminum oxide film.