JPH0446978B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a composite membrane of regenerated cellulose. In recent years, membrane separation technology has been attracting attention among substance separation and purification technologies. Polymer membranes are used in a wide range of fields, taking advantage of the characteristics of the membrane separation process: unlike distillation, there is no need for temperature changes during separation, less energy is required for separation, and the process is compact. Examples include dairy farming, fisheries, livestock farming, food processing, pharmaceuticals, chemical industry, textile dyeing processing, steel, machinery, surface treatment, water treatment, and nuclear power industry. Fields in which membrane separation systems may become central in the future include fields that require concentration, purification, and recovery at low temperatures (food and biochemical industries), and fields that require sterility and dust-free operation (pharmaceuticals and medical treatments). (engineering, electronics industry), concentration and recovery of trace amounts of expensive substances (nuclear energy, heavy metals field), special small quantity separation field (medical field), energy-intensive field (distillation substitute), etc. There is an increasing need for composite membranes with high membrane separation properties as membranes used in these fields. The composite membrane used in the present invention refers to a membrane composed of two or more layers in which the average pore diameter changes discontinuously in the thickness direction, and each layer is composed of a polymeric material with the same chemical structure. be done. A feature of the composite membrane is that the thickness of the thin membrane A, which has a molecular separation function, can be reduced to 1 μm or less. Therefore, when separating substances using a membrane, the permeation rate of the membrane increases. In the case of composite membranes, the shape retention of the thin membrane,
A porous support layer B is necessary in order to satisfy the conditions of mechanical strength as a composite membrane and not hindering substance permeation. In conventional composite membranes, two types of membranes with different pore sizes are made independently.
Thereafter, the thin film A is produced by physically gluing the two together, or by coating the porous film that will become the support layer B with a polymer film, or by coating the porous film with a monomer and then polymerizing it. In composite membranes obtained by these methods, the material polymers constituting the A and B portions are different, or when the material polymers are the same, the A and B portions are not integrated.
Therefore, the thin layer A placed on the support layer B may get inside the large hole in the B part and become dented, or because it is simply glued together, it is easily damaged or pinholes are formed. Conventional composite membranes have drawbacks, and no membranes have been produced that can be used industrially except by coating methods. In the coating method, the material polymers for parts A and B are different, and
The material polymer constituting part A invades into the large pores of the part, and considering this invaded part, the thickness (d _A ) of part A is practically 1 μm or more. Further, when the material polymers of the A and B portions are different, when the composite membrane is repeatedly swelled/dryed with a solvent, both the A and B layers are likely to separate, causing damage to the A layer. The present invention provides a composite membrane of regenerated cellulose that eliminates such conventional ^drawbacks . The thin film layer A part is composed of cellulose-2 or crystals containing both cellulose-2 and has an average pore size of 200 Å or less and a thickness (d _A ) of 0.01 μm to 1 μm, and _B ) is a cuprammonium regenerated cellulose composite membrane, characterized in that it is composed of a support layer B portion with a thickness of 50 μm to 1 mm, and both layers are substantially integrated. The greatest feature of the cuprammonium regenerated cellulose composite membrane of the present invention is that the membrane is substantially composed of cellulose molecules, and that the membrane has a thin film layer A portion with a molecular separation function and a support layer B portion. The point is that they are essentially integrated. Because the thin film layer A and the support layer B are integrated, the occurrence of dents, pinholes, tears, etc. in the A layer unlike in conventional laminated composite films is reduced. Compared to composite membranes, it has greater strength and is easier to handle. The second feature of the present invention is that the thickness (d _A ) of the thin film layer A is
It is in the range of 0.01 μm to 1 μm. In a composite film having the above-mentioned first and second characteristics, by showing interference color when white light is applied from the A layer direction, A, B
It can be confirmed that there is a large difference in average pore size between layers and that d _A is less than 1 μm. A layer has an average pore size of 50 Å
10 to ¹¹ pores/ ^cm3 with a diameter of 200 Å or more per unit volume
It is desirable for the presence of at least one of these elements to increase the permeation rate. When _dA becomes 1 μm or less, the rate of substance permeation using the membrane increases significantly. On the other hand, the thickness of layer A is
The frequency of appearance of pinholes of 0.01 μm or less increases, the A layer is likely to be damaged when separation conditions change during membrane separation, and the permselective properties of the membrane are significantly reduced. d _A is preferably 0.05 to 0.5 μm, particularly preferably around 0.1 μm. However, since it is difficult to maintain shape and strength during membrane separation with layer A alone, support layer B is not suitable. The third feature of the present invention is that the thickness d _B of the support layer B is
The layer has circular pores of 50 μm to 1 mm and an average pore diameter D of 0.1 μm or more. The thickness of layer B is 100 times or more than the thickness of layer A, and the in-plane porosity (area ratio of pores to the membrane area) of layer B is 10
~80%, or the number of holes per 1 cm ² in the plane is 1 x 10 ² /D (D is in cm) or more and 5 x
It is desirable that the number is 10 ⁴ /D or less in order to increase the mechanical strength of the membrane and increase the permeation rate of substances. In addition, if urn-shaped pores exist at a volume ratio of 0.1% or more on the B part side of the interface between the A layer and the B layer, an organic solvent or various substances can be dissolved in the organic solvent and retained in the composite membrane. It is possible to do so. Here, the pot-shaped hole is a semi-through hole whose penetrating side is on the B layer surface, and since the hole diameter of the penetrating portion is smaller than that inside the hole, it has an apparent pot-shaped hole shape. The average pore diameter of the part corresponding to the neck of the jar is 500 Å or more, and the abundance ratio of pores with this shape is
If it is 0.1% or more, the composite membrane has a sustained release property, a liquid membrane retention function, and a high mass transfer rate in the liquid membrane. The existence of this pot-shaped hole is confirmed by the following method. First, a composite membrane of known sample weight (W ₁ ) is immersed in a mercury medium in vacuum (10 ^-2 mmHg or less). Next, the mercury medium was pressurized to 300 atmospheres, and then after depressurizing at atmospheric pressure, the weight of the composite membrane (W ₂ )
Measure. The abundance rate of pot-shaped pores with a diameter of 500 Å or more is given by {(W ₂ −W ₁ )d _g /d·W ₁ }×100 (%). Here, d is the density of mercury and d _g is the density of regenerated cellulose (1.5 g/ml). The presence of the pot-shaped pores at the interface between layers A and B means that when the film obtained by the above method is observed with the naked eye from direction B, it appears white, and when observed from direction A, it appears black. This can be confirmed by the fact that the resistance value on each surface of A and B of the composite film is 1KΩ/cm or more. The overflowing liquid flows from the thin film layer A to the support layer B of the composite membrane.
Generally, the method of permeating from B to A is effective in increasing the membrane separation throughput per unit area of the composite membrane. The external shape of the porous membrane includes all shapes such as a flat membrane, a tube shape, and a hollow fiber shape. Note that the average pore diameter of layer B (2 _3b and _4b are pore radii) is twice _3b defined by equation (2) below, and that of layer A is defined as ( _3a and _4a ) in equation (7). It means twice ^1/2 . Since the cuprammonium regenerated cellulose composite membrane of the present invention is substantially composed of cellulose molecules, it has high hydrophilicity and excellent organic solvent resistance. An integrated composite membrane composed only of cellulose molecules has never existed before. When removing water from an organic solvent by pervaporation, a composite membrane composed of cellulose molecules has particularly excellent permselectivity. Conventional regenerated cellulose porous membranes, which are produced by regenerating porous bodies made of cellulose derivatives and their membranes through saponification reactions, etc., are brittle in dry conditions and require extreme care in handling. The present inventors investigated the relationship between tensile strength and the molecular weight of cellulose and found that as the molecular weight increases, the strength of the porous membrane increases and brittleness is required. When the average molecular weight is 5×10 ⁴ or more, the strength of the porous membrane is 2×
10 ⁷ dyn/cm ² or more, which makes handling easier.
Breakage of porous membranes is reduced. Of course, even if the molecular weight increases, the composite membrane of the present invention maintains the good biocompatibility and excellent hydrophilicity that are characteristics of regenerated cellulose, and furthermore, the swelling in organic solvents is reduced. In order to improve the heat resistance and solvent resistance of the composite membrane, the composite membrane is immersed in liquid ammonia, and the crystalline region in the composite membrane is made into a mixture of cellulose-2 crystals or cellulose crystals and cellulose-2 crystals. Preferably, the composite membrane is heat-treated in hot water to convert the crystalline regions into cellulose crystals. Separation targets for which the composite membrane of the present invention can be used include:
Separation and removal of target components in a liquid mixture containing water, such as membranes for artificial kidneys, artificial livers, and artificial pancreas). It can be used in almost all other fields where ultrafiltration membranes can be used,
The strong composite membrane of the present invention, which is hydrophilic and has excellent mechanical properties, is particularly suitable for bio-related fields (medicine, biochemical industry) and food fermentation fields. The composite membrane of the present invention can also be used as a retention membrane for a carrier in a liquid membrane, such as benzoylacetone. The composite membrane of the present invention can be produced, for example, by the following method. 30% by weight cellulose copper ammonia solution
The concentration of acetone vapor atmosphere at 30 °C is the saturated vapor pressure.
% atmosphere on a glass plate with a 500 μm thick applicator at a speed of 0.2 m/min, and left in this atmosphere for 3 minutes to cause microphase separation and leaching of the dilute phase to the membrane surface. Check that the cast film is not mixed with the acetone/water ratio.
It was immersed horizontally in a mixed solution of 33.6% by weight and 0.8% by weight of ammonia/water (at 20°C) for 60 minutes, then immersed in a 2% by weight sulfuric acid aqueous solution at 20°C for 15 minutes, and then washed with water. After that, absorb the moisture with paper20
The film was immersed in acetone (100% by weight) at ℃ for 15 minutes to replace the moisture in the film with acetone, and then sandwiched between paper for 30 minutes.
It can be obtained by air drying at ℃. Prior to Examples, methods for measuring various physical property values used in the detailed description of the invention are shown below. Average molecular weight of regenerated cellulose: Calculate the average molecular weight (viscosity average molecular weight) Mv by substituting the intrinsic viscosity number [η] (ml/g) measured in cupric ammonia solution (20°C) into equation (1). . Mv=[η]×3.2×10 ³ (1) Average pore radius _3b , _4b , number of pores in support layer B part
Nb, and in-plane porosity Preb: If the number of pores with a pore radius of r to r+dr per ^cm2 of porous membrane is expressed as N(r)dr (N(r) is related to the pore radius distribution), the average The pore radii _3b , _4b , the number of pores per 1 cm ² Nb, and the in-plane porosity Pred are expressed by formula (2),
It is given by equations (3), (4), and (5). _3b ＝∫ ^∞ ／ _p r ³ N(r)dr／∫ ^∞ ／ _p r ² N(r)dr (2) _4b ＝∫ ^∞ ／ _p r ⁴ N(r)dr／∫ ^∞ ／ _p r ³ N( r)dr (3) b=∫ ^∞ _p N(r)dr (2/cm ² ) (4) Preb=π∫ ^∞ _p r ² N(r)dr×100 (%) (5) For scanning electron microscope used a JEOL JSM-U3 model to take electron micrographs of the front and back surfaces. The pore size distribution function N(r) is calculated from the photograph by a known method and substituted into equations (2) and (3) in the text. That is, a scanning electron micrograph of the area where the pore size distribution is to be determined is enlarged to an appropriate size (for example, 20 cm x 20 cm), printed, and 20 test lines (straight lines) are drawn at equal intervals on the resulting photograph. Each straight line crosses a number of holes. Measure the length of the straight line that exists within the hole when it crosses the hole, and find this frequency distribution function. Using this frequency distribution function, N(r) is determined, for example, by the method of stereology (for example, Norio Suwa, Quantitative Morphology, Iwanami Shoten). The average hole radius _3b and _4b are calculated using equations (2) and (3) using N(r), and the number of holes Nb is calculated using equation (4) using N(r).
In the formula, the in-plane porosity Preb is calculated by formula (5) using N(r). Thickness _dA , _dB : The film was embedded in acrylic resin, an ultra-thin section of its cross section was prepared, and this was observed using a Hitachi HU-11B transmission electron microscope, and the thin film layer A and the support were observed. Measure the thickness of body layer B (d _A and b _B (cm), respectively). Porosity Prp: A planar porous membrane is cut into a circular shape of 47 mmφ, and the porous membrane is dried in vacuum to reduce the moisture content to 0.5% or less. The thickness of the porous membrane after drying is d (cm), the weight is W
(g), the porosity Prp (%) is given by equation (6). Prp=(1-W/17.34×1.5×d)×100...(6) Average pore radius of thin film layer A part ( _3a・_4a ) ^1/2 : The film with a diameter of 47 mm was placed in the Millipore filtering equipment as layer A. Attach with the side up. 1cm when ultrapure water is injected into the filtration device and pressurized to a pressure difference (△P) of 0.35 atm.
Substitute the overspeed J (ml/sec.cm ² ) into equation (7) to calculate the average hole radius ( _3a・_4a ) ^1/2 of part A. ( _3a・_4a ) ^1/2 = [3d _A J/[{17.34 × ((d _A + d _B )Prp−1.2・d _B・Preb)/d _A } {0.35−(6.67J・d _B / _4b・_3b・Prp)}〕〕 ^1/2
...(7) Here, _{3b and 4b} are the average pore radius (cm) of support layer B (calculated from equations (2) and (3)), and Prp is the porosity of the composite membrane (calculated from equation (6)). ) (%), Preb is support layer B
The in-plane porosity (calculated from equation (5)) (%), d _A and d _B are the thickness (cm) of the thin film layer A part and the support layer B part, respectively. Fixation of cellulose and -2 crystals: Using an X-ray generator (Ru-200PL) manufactured by Rigaku Corporation and a goniometer (SG-9R), a scintillation counter for the counter tube, and a pulse height analyzer for the counting section, 30KV, Operate the X-ray generator at 80mA,
The X-ray diffraction intensity is measured using Cu-Kα rays (wavelength λ = 1.5418 Å) made monochromatic with a Nickel filter. In the case of determining the crystal structure, X-rays are incident perpendicularly to the film surface, and in the case of hollow fibers, the X-rays are incident perpendicularly to the fiber axis. Scanning speed 10/min, charting speed 10mm/min, time constant 1 second, divergence slit 1/2°, receiving slit 0.3mm, scattering slit 1/2°, diffraction angle 2θ is ~4°. Measure the X-ray diffraction intensity within a 35° range. Cellulose crystal is 2θ=12゜｜(101)
Reflection from surface}, 20.2゜ {Reflection from (10T) surface},
It is characterized by three types of diffraction: 21° {reflection from (002) plane}. Furthermore, cellulose-2 crystals are characterized by two types of diffraction: 2θ = 12° {reflection from (101) plane} and 20° {reflection from 10T) plane}. Example 1 Cellulose linter (average molecular weight 2.33×10 ⁵ )
4 in a copper ammonia solution prepared by a known method.
After dissolving at a concentration of % by weight, the solution was cast onto a glass plate at a speed of 0.2 m/min with a 500 μm thick applicator in an acetone vapor atmosphere at 30°C with a concentration of 70% of the saturated vapor pressure. . 8 under the said atmosphere
After standing for a minute, it was confirmed that microphase separation had occurred and that the dilute phase had not leached to the membrane surface.The resulting cast film had an acetone/water ratio of 33.6% and an ammonia/water ratio of Immerse horizontally in a 0.8% by weight mixed solution (20℃) for 60 minutes, then
The film was immersed in a 2 wt% sulfuric acid aqueous solution at 20°C for 15 minutes, then washed with water, and then the moisture was absorbed with paper. It was sandwiched and air-dried at 30°C. Table 1 shows various physical property values of the obtained porous membrane. Figure 1 is a scanning electron micrograph of the surface of the thin film layer A of the porous membrane, Figure 2 is a scanning electron microscope picture of the back side of the support layer B, and Figure 3 is a scanning electron micrograph of the surface of the thin film layer A of the porous membrane. FIG. 4 is a schematic diagram of a vertical cross section of the porous membrane of the present invention, showing B at the boundary between thin film layer A and support layer B.
Indicates the presence of a pot-shaped hole on the side. Comparative example 1 Cellulose linter (average molecular weight 2.33×10 ⁵ )
4 in a copper ammonia solution prepared by a known method.
After dissolving at a concentration of % by weight, the solution was placed on a glass plate with a 500 μm thick applicator in an acetone vapor atmosphere at 30°C with a concentration of 80% of the saturated vapor pressure.
Casting was carried out at a speed of 0.2 m/min. The cast film was left in the above atmosphere for 8 minutes, and it was confirmed that microphase separation had occurred and that the dilute phase had not leached onto the membrane surface.The resulting cast film had an acetone/water ratio of 33.6% by weight.
It was immersed horizontally in a mixed solution with an ammonia/water ratio of 0.8% by weight (20°C) for 120 minutes, then immersed in a 2% sulfuric acid aqueous solution at 20°C for 15 minutes, washed with water, and then drained. It was blotted with paper, immersed in acetone (100% by weight) at 20°C for 15 minutes, the water in the film was replaced with acetone, and the film was sandwiched between paper and air-dried at 30°C. Table 2 shows various physical property values of the obtained porous membrane.
Concentration of copper ions using a liquid membrane was carried out using the porous membrane of this comparative example and the composite membrane mentioned in the above-mentioned example. L1×65N in DDispersol for porous membranes and composite membranes
After sufficiently impregnating the solution, the surface is wiped with paper, and the composite membrane is made with the support layer B on the inside, and a commercially available tetrafluoroethylene porous membrane (manufactured by Sumitomo Electric Industries, Ltd.) is bonded together. A liquid film was prepared by gluing together two of the above porous ethylene tetrafluoride membranes, with the surface of the porous membrane in the comparative example facing inside. Figure 5 shows a copper ion concentration model device using the composite membrane of the present invention, in which 1 is an electrode for copper ions, 2
indicates that a PH meter is attached, 3 indicates that a composite membrane of the present invention or a porous membrane of a comparative example, and 4 indicates that a porous ethylene tetrafluoride membrane is attached. The liquid film is placed between A and B of the apparatus shown in FIG. At this time, the first half of the tetrafluoroethylene porous membrane is installed on the B side. A
A copper ion aqueous solution (copper ion concentration 200ppm) with a pH of 7 to 8 is placed in the side cell, and a pH of 1 to 2 is placed in the B side cell.
Filled with 0.1-3N sulfuric acid aqueous solution. Both aqueous phases are
Stirred at 180 rpm. The copper ion concentration of the aqueous phase on the B side was measured using a copper ion electrode with a HORIBA ion meter. A graph plotting the copper concentration on the B side versus time is shown in FIG. According to this, the performance of the liquid membrane containing the carrier decreased as time increased in the porous membrane of the comparative example, but when the composite membrane mentioned in the example was used, the performance was only slightly lower. Does not decrease. This is because in the case of a composite membrane, the carrier is retained because there is a thin layer A with a small pore size at both ends of the membrane, whereas in a porous membrane, the pore size is several times larger than that of layer A, so the carrier cannot be retained for a long enough time. This is due to the fact that it flows out.

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【table】 [Brief explanation of the drawing]

FIG. 1 is a scanning electron micrograph of the surface of thin film A of the composite film of the present invention. Figure 2 is a scanning electron micrograph of the back side of the support layer B. Figure 3 is an electron micrograph of the surface (front side) of the remaining support layer after the ultra-thin film was physically removed. FIG. 4 is a vertical cross-sectional membrane diagram of the composite membrane of the present invention. Figure 5 shows a copper ion concentration model device using the composite membrane of the present invention. 1: Electrode for copper ions, 2: PH meter, 3: Composite membrane of the present invention or porous membrane of comparative example, 4: Indicates that a 4-fluorinated ethylene porous membrane is attached. FIG. 6 shows the results of an experiment conducted using a composite membrane of the present invention and a porous membrane of a comparative example.

Claims (1)

[Scope of Claims] 1. The average molecular weight of cellulose molecules is 5 x 10 ⁴ or more, the crystalline region is substantially composed of cellulose, cellulose-2, or crystals containing a mixture of both, the average pore size is 200 Å or less, and the cellulose is thick. It is composed of a thin film layer A portion having a diameter (d _A ) of 0.01 μm to 1 μm and a support layer B portion having an average pore diameter of 0.1 μm or more and a thickness (d _B ) of 50 μm to 1 mm, and both layers are substantially A copper ammonia method regenerated cellulose composite membrane, which is characterized by being integrated. 2. The copper ammonia according to claim 1, characterized in that at the boundary between the thin film layer A part and the support layer B part, 0.1% or more by volume of pot-shaped pores are present on the B part side. Method regenerated cellulose composite membrane.