JPS618108A - Separation membrane manufacturing method - Google Patents

Abstract

PURPOSE:To obtain a gas separation membrane excellent in permselectivity at a high permeation speed, by using a doctor knife of which the center line roughness is 0.05mum or less. CONSTITUTION:A mixture consisting of polyvinyltriorganosilane and organopolysiloxane is used as a high-molecular membrane material. As polyvinylsilane, one with intrinsic viscosity of 1.5dl/g or more and a degree of dispersion of 2 or less is used and, as polysiloxane, one with a b.p. of 200 deg.C or more and a number average MW of 1,000 or more is used. The mixing ratio of polyvinylsilane and polysiloxane is pref. 1:0.05-1. A membrane forming solution having this membrane material dissolved therein in an amount of 0.1-50wt% is formed into a membrane with a thickness of 500mum or more by using a doctor knife of which the center line average roughness is 0.05 or less. Further, it is necessary to use a cast plate with a contact angle of 40-70 deg..

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing a separation membrane, and particularly to an improvement in the method for manufacturing a separation membrane that simultaneously has good permeation rate and separation performance.

The separation membrane obtained by the method of the present invention is effective in selectively separating substance mixtures, especially gas mixtures, so the gas separation membrane will be described below, but the use of the separation membrane according to the present invention is not limited thereto.

[Conventional technology]

In recent years, continuous methods using synthetic polymer membranes have attracted attention as a means of enriching or separating specific gases from gas mixtures, and are being actively researched for practical use. For example, production of oxygen-enriched air for combustion, medical use, wastewater treatment, fermentation, etc. by separating and concentrating oxygen or nitrogen from the air, separation and recovery of helium from natural gas, coke gas, etc. Examples include separation of hydrogen from etc.

However, conventional membranes have five drawbacks, such as requiring a large membrane area due to the low gas permeation rate, and requiring a separation device.

Therefore, while various methods have been implemented to increase the effective membrane area per device volume, there has been a desire for essential membrane improvements that significantly increase the permeation rate while maintaining high selectivity. .

The gas permeation rate R (cc/sub2·sec·1ynar) is expressed as follows. Here, P is the permeability coefficient amount (cc/sec), S is the membrane area (, i), and ΔP is the pressure difference between the primary and secondary sides of the membrane. Therefore, the gas permeation rate R is the pressure difference across the membrane △Py! If l is constant, it depends on the gas permeation coefficient P and the membrane thickness.The permeation coefficient is uniquely determined by the type of gas and the polymer membrane material used, so the pressure difference across the membrane The maximum permeation rate is obtained by using the minimum film thickness as long as it can withstand the

Among the conventional gas separation membrane materials, Japanese Patent Publication No. 47-51715
Although the polyvinyltriorganosilane described in No. 52-21021 had good gas separation performance, it had an insufficient permeability coefficient. A mixture of polyvinyltriorganosilane and polysiloxane was developed as a material to improve the drawback of such a small gas permeability, as described in Japanese Patent Application Laid-Open No. 54-56.
This was proposed in Publication No. 985.

When this mixture was used as a material for a gas separation membrane, it had improved gas separation performance on the high permeation rate side compared to a polyvinyl triorgano 7 run membrane. However, if an attempt was made to further increase the permeation rate, the gas separation performance tended to drop rapidly and significantly.

These difficulties are not limited to gas separation, but are common to separation of liquids and other mixtures, and need to be improved.

The present inventors have solved the problems of the conventional technology by forming a membrane using a solution of a polymeric material filtered through a microfilter with a specific average pore size. Methods for manufacturing separation membranes that have high performance and high permeation rates have already been proposed, but it has been found that these proposals still have some insufficiencies.

That is, to manufacture the proposed separation membrane, a solution of a polymeric material passed through a microfilter having a specific average pore size is cast onto a smooth surface, leveled with a doctor knife, and then After evaporation for a time, immerse in a coagulation bath,
Forming a separation membrane, especially an asymmetric membrane. At this time, select a membrane forming machine and suitable membrane forming conditions such as temperature and time, and add a solution of the polymeric material to a membrane with a maximum pore size of about 6 μm. Hereinafter, even if the solution uses a polymer with a number average molecular weight of 1000 or more, the permeation rate will increase even if the solution uses a polymer with a number average molecular weight of 1000 or more, which is preferably filtered through a microfilter with a diameter of 4μ or less to remove foreign substances such as floating dust or insoluble polymers in the solution. The selective separation property decreases as the temperature decreases. This decrease in separability is due to
It occurs rapidly and significantly as the permeation rate increases, that is, as the thickness of the dense layer of the asymmetric membrane decreases.

[Problem that the invention seeks to solve]

Nowadays, the fact that separation properties are lost when the thickness of the dense layer is small is an obstacle to the practical application of separation membrane technology.

The present invention has been made to solve the above problems, and its purpose is to provide a method for producing a separation membrane that has a high permeation rate of a specific substance from a mixture and has good separation properties. be.

[Means for solving problems]

To summarize the present invention, the present invention relates to a method for manufacturing a separation membrane, in which a doctor knife with a center line average roughness of 0.05 μm or less is used when forming a membrane using a solution of a polymer membrane material. Characterized by its use.

Hereinafter, the present invention will be explained in detail by taking as an example a method for manufacturing a gas separation membrane using a mixture of polyvinyltriorganosilane and organopolysiloxane as the polymer membrane material.
The invention is not limited to this mixture. That is, it goes without saying that the present invention is also applicable to membrane formation using conventionally known polymer membrane materials such as celluloses such as heptalulose acetate and ethyl cellulose, polysulfone, and polyphenylene oxide. The specific polyvinyltriorganosilane used in the present invention has the formula (1)% formula% (wherein R1 represents a hydrogen atom, an alkyl group, a cycloalkyl group, an aryl group, or an aralkyl group, and R2 and R3 are an alkyl group, Represents a cycloalkyl group, aryl group or aralkyl group.

Bl, Bt, and R3 may be the same or different from each other). The viscosity is i, 5 dA/P or more, preferably 1.5 to 4.5 dA/? And it is preferable that the degree of dispersion described below is 2.0 or less. Here, the intrinsic viscosity of polyvinyltriorganosilane is 1. s d
If it is less than t/y and the degree of dispersion exceeds 2.0, not only the mechanical strength of the resulting gas separation membrane will be low, but also the separation performance in the high permeation rate region will be extremely low, making it impractical.

The polyvinyl triorganosilanes mentioned above are generally obtained by polymerizing one or more vinyl) IJ organosilanes using a suitable catalyst. Specific examples of vinyltriorganosilane include vinyltrimethylsilane, vinyltriethyl7rane, vinyltripropylsilane, vinyltributylsilane, vinyldimethylethylsilane, vinyldimethylethylsilane, vinyltricyclohexylsilane, vinyldimethylcyclohexylsilane, vinyl Dimethylphenylsilane, vinyldimethylbenzylsilane and vinyldimethylphenylsilane are mentioned.

In addition, the polyvinyltriorganosilane in the present invention also includes a polymer compound containing structural units other than the structural unit of formula (υ) in a proportion of up to 25% by weight. It may be a mixture.

Next, the organopolysiloxane used in the present invention is basically a compound consisting of an 8l-0-3l bond skeleton, and has one of the following general formulas (2), (3L (4) and (5)). or more as a repeating unit, and mixtures thereof.

B; R8 (wherein R4, R11 and R6 are an alkyl group, an alkenyl group,
Cycloalkyl group, cycloalkenyl group, aryl group,
Indicates a group in which some or all of the hydrogen atoms of these groups are substituted with a halogen atom, a hydrogen atom, a halogen atom, an amine group, an amide group, an alkoxy group, etc., and may be the same or different from each other. ). Further, the organopolyoxane used in the present invention may be a mixture of one or more organopolyoxanes.

The organopolysiloxane used in the present invention includes a wide range of compounds from low molecular weight compounds to high molecular weight compounds, but as a membrane material, it is not preferable to use one with a low boiling point, and the boiling point should be at least 200°C or higher. preferable. More specifically, those having a number average molecular weight of 1000 or more are preferred.

Specific examples of organopolysiloxane include JP-A-54-
All compounds described in JP 56985 can be mentioned.

The mixing ratio of polyvinyltriorganosilane and organopolysiloxane is 0.05 to 1 parts by weight of organopolysiloxane to 1 part by weight of polyvinyl triol,
o parts by weight, preferably o, i
The effect of polysiloxane can be expected as the mixing ratio of organopolysiloxane to polyvinyltriorganosilane selected from 0.6 parts by weight, particularly preferably 0.15 to 0.4 parts by weight increases. As a result, the strength of the membrane decreases, and defects are likely to occur in the membrane, resulting in a decrease in separation performance. Conversely, as the mixing ratio of organopolysiloxane decreases, the permeation rate at which the separation performance begins to deteriorate decreases, resulting in a membrane that is brittle and has low elongation.

The gas separation membrane of the present invention uses a mixture of the above-mentioned specific polyvinyltriorganosilane and organopolysiloxane as the membrane material, but organic substances, inorganic substances, etc. It may also contain a third component. Furthermore, a nonwoven fabric made of synthetic fibers such as polyamide or polyester or natural fibers may be contained as a reinforcing material.

The solvent for dissolving the above membrane material is selected as described below when manufacturing an asymmetric membrane, and when manufacturing a homogeneous membrane or composite membrane, 7 chlorohexane, benzene, toluene,
selected from xylene aliphatic and aromatic hydrocarbons, and chlorogenated hydrocarbons such as dichloromethane, dichloroethane, chloroform, chlorobenzene, dichlorobenzene. The membrane material concentration in the solution is 0.1-50% by weight, preferably 1-10% by weight.

It is necessary to filter the membrane-forming solution of the above-mentioned membrane material through a microfilter with a maximum pore size of 6 μm or less, preferably 4 μm or less to remove foreign substances such as floating dust or insoluble polymers in the solution. For example, if the filtration treatment is not performed during the production of the asymmetric membrane described below, the selective separation performance will decrease as the permeation rate increases. The material of the specific microfilter is not limited as long as it is inert to the solvent and polymer membrane material forming the membrane forming solution and maintains its performance and function as a filter during the filtration process. and organic materials.

The membrane-forming solution thus prepared is cast onto a smooth cast plate, smoothed with a doctor knife, evaporated for a predetermined period of time, and then immersed in a coagulation bath to form a separation membrane, especially an asymmetric membrane. .

The doctor knife used here is made of metal or glass, and during film formation, the film forming solution is made smooth and uniform by moving or by moving the cast that cast the solution. The roughness of the doctor knife and its separation performance were thought to be unrelated. Surprisingly, however, if the roughness of the doctor knife was made sufficiently small, it was possible to prevent the performance of the asymmetric membrane from deteriorating. In the case of a doctor knife having a normal roughness, the selective separation property decreases as the permeation rate increases.

On the other hand, for asymmetric membranes, the thickness of the porous layer is large, especially 500 μm.
The advantage of making the film larger than m is that the film can be formed in one step using the same material, but in order to do so, smoothness is required.
It is necessary to use a cast plate with a specific adhesive strength, that is, a contact angle of 40 to 70 degrees.

If the film is smooth but the adhesive strength is not within the above specified range, the film will be smooth when cast, but when immersed in the coagulation liquid,
Immediately, wrinkles and unevenness occur on the entire surface or part of the surface. Or, if there are rough irregularities on the surface of the cast plate, the film will exhibit a smooth surface even in the coagulation solution, but during immersion and after drying,
The membrane cannot be easily peeled off from the cast plate.

The membrane obtained by the above method may be a single layer consisting only of a dense layer with selective separation of gases, but it may be a single layer consisting of only a dense layer with selective separation of gas and a selective separation of a dense layer with selective separation. In an asymmetric membrane composed of both layers and a porous layer (not shown), it is relatively easy to form an extremely thin dense layer with no defects (
Therefore, it is preferable in that it is possible to obtain a product that satisfies high permeation rate and separation performance at the same time. The gas separation membrane of the present invention is characterized in that defective portions are extremely unlikely to occur even when the thickness of the dense layer is reduced, and therefore a high permeation rate can be obtained while maintaining high separation performance. Here, the term "dense layer" means a layer that is dense and non-porous and exhibits substantially the same selective permeability to gas or vapor as the layer's constituent material (mainly composed of the above-mentioned mixture); The layer is formed from the same constituent material as the dense layer, has open pores and a spongy structure through which gas can freely pass, and has completely selective permeation due to the gas or vapor simply moving along the pores. It means an inert layer that does not exhibit any properties. Considering the permeation rate, the thickness of the dense layer is preferably 0.01 to 1 μm, but in the present invention, even within this range, gas selectivity hardly decreases and a strong and stable dense layer is formed. I can see that you are doing it. On the other hand, the thickness of the porous layer is preferably 10 μm or more, particularly 100 to 1000 μm, considering the mechanical strength of the membrane and ease of handling, but it may be reinforced with another third component or
If other porous membranes are used in combination as supports for the membranes of the invention, thicknesses of less than 10 μm can also be achieved.

The asymmetric membrane consisting of a dense layer and a porous layer as described above can be manufactured, for example, by the following method. That is, (a) two types of solvents that have a boiling point difference of at least 30°C and are good solvents for the polymer, or two types of solvents and a more volatile solvent of the two types of solvents; (Hereinafter referred to as "heavy solvent") IJ organosilane (organopolysiloxane and polyvinyl) in a three-component mixed solvent consisting of one type of solvent that has a higher boiling point and is a poor solvent for the polymer. Of the two types of solvents in which a mixed and dissolved solution is poured onto the support, the more nonvolatile solvent is hereinafter referred to as the "heavy solvent". ), (b) Mainly to remove part or all of the heavy solventC)
It is produced by treating the produced film with a coagulating liquid (poor solvent) and (d) drying the film.

Heavy solvents and heavy solvents are suitably selected from aliphatic and aromatic hydrocarbons such as cyclohexane, benzene, toluene and xylene, and halogenated hydrocarbons such as dichloromethane, dichloroethane, tetrachloroethylene, chloroborum, chlorobenzene and hiscyclobenzene.

Poor solvents include water, methanol, ethanol, primary, secondary
and 6-butanol. Specific examples of combinations of six-component mixtures consisting of a heavy solvent, a heavy solvent, and a poor solvent include toluene-dichloromethane-isobutanol, benzene-dichloromethane-isobutanol, monochlorobenzene-chloroform-isophtanol, and toluene-chloroform-isobutanol. Examples include isobutanol, toluene, dichloromethane, and secondary butanol. Here, in order to prepare a solution in which organopolysiloxane and polyvinyltriorganosilane are dissolved in a three-component mixture, the order in which the respective substances and solvents are added is not particularly limited.

In the next step of removing the heavy solvent, the proportion of the heavy solvent removed has a significant effect on the thickness of the dense layer formed. That is, the smaller the rate of heavy solvent removal, the thinner the heavy layer will be obtained. Although it varies depending on the evaporation conditions including evaporation time and temperature, the concrete removal rate of the heavy solvent is preferably 10 to 50%, but it may be outside this range.In particular, in the present invention, polyvinyl trichloride having a specific intrinsic viscosity is By using organosilane, gas separation performance may be exhibited even at a removal rate of 10% or less. Since the gas permeation rate through the membrane depends on the thickness of the dense layer, the step of removing this heavy solvent is important in controlling the gas permeation rate. In other words, in order to obtain a membrane with a high gas permeation rate, it is necessary to reduce the amount of heavy solvent removed and to make the thickness of the dense layer as small as possible (3. However, on the other hand, if the dense layer is made even thinner, eventually This is undesirable because it causes defective parts (defects here mean the state of the membrane that gives the same permeation rate to different gases and loses the ability to separate gases from each other).Therefore, such defects are not desirable. It is desirable to control the amount of light solvent removed to such an extent that it does not occur.

The actual evaporation temperature is preferably 15-25°C, more preferably 17-22°C. At higher temperatures, evaporation will be faster, making it difficult to form a uniform dense layer, and resulting in lower separation performance. On the other hand, if the temperature is lower than 15°C, the evaporation time becomes long, the productivity is low, and the formation of a dense layer is insufficient, resulting in a decrease in performance.

The coagulation liquid serves the purpose of gelling the polymer solution, or completing gel formation if it has been started by evaporation of the light solvent. Therefore, a solvent that is miscible with the above-mentioned light solvent, heavy solvent, and poor solvent is selected as the coagulation liquid, and this gelation treatment is continued until as much of the solvent as possible is eluted from the coagulation film. Of course, this process can be carried out continuously or intermittently.

Specific examples of the coagulating liquid include methanol, ethanol, methanol-ethanol mixture, water-methanol, water-dioxane mixture, and the like. The immersion time is not particularly limited, as long as it is sufficient for most of the solvent constituting the polymer solution to be eluted. Generally, 0 at room temperature
．． A soaking time of 1 to 1 hour is sufficient.

Drying of the coagulated film can be carried out at ambient temperature or higher, but it can also be heat-treated at temperatures below 200°C, preferably from 100 to 180°C, if necessary.

〔Example〕

Hereinafter, the present invention will be explained in detail with reference to Examples, but the present invention is not limited to the specific substances, methods, etc. shown in these Examples.

Note that the degree of dispersion is the ratio (MY/MN) between the weight average molecular weight (My) and the number average molecular weight (MN), and was determined by gel permeation chromatography (hereinafter abbreviated as GPC). When the degree of dispersion is large, the molecular weight distribution curve is broad, and as the degree of dispersion approaches 1, the distribution becomes sharper and approaches a monodisperse polymer.

The GPC measurement conditions were as follows: Detection equipment: R1-8 model manufactured by Toyo Ichida, Column: TSK-05000'H.

4000H, 5000H, 2000H, solvent: toluene, flow rate = 1-/min, temperature: 25°C, pressure chemical (calibrated using monodisperse polystyrene made by American manufacturer), and all values were converted to polystyrene.

In addition, the gas permeation rate of the obtained membrane (hereinafter simply indicated by R)
The measurement method is to fix the membrane of the present invention in a membrane device, apply a specified gas to one side of the membrane at 25°C, and measure the gas that permeates and flows out from the other side of the membrane over a fixed period of time using a tOkll/cm' gauge. The amount was measured using a gas burette.

Example 1 Vinyltrimethylsilane was polymerized using tn-bunarlithium as a catalyst, and the intrinsic viscosity in cyclohexane at 25°C was t7.
Polyvinyltrimethylsilane with a dispersity of 8 at/l and a dispersity of 15 was obtained.

Next, the above polymer 1. Of, KE103RT'V0.152 manufactured by Shin-Etsu Chemical Co., Ltd. was processed as organopolysiloxane, and then toluene 5. Of, chloroform 5.8?
After adding '11 and dissolving it, 5.21 of inbutanol was added to make a homogeneous solution. Next, Millipore filter-D
After filtering the solution with AWP (pore size 065 ± 0.03 μm), this solution was cast onto a ferro plate, and a doctor knife was used with a distance of 500 am between the ferro plate and the ferro plate.
The film was formed by running for 7 minutes.

The doctor knife used for film formation was made of polished steel with hard chrome plating and further polished to achieve smoothness.

When the smoothness of the doctor knife was measured using a surface roughness meter [5P-3FK model manufactured by Koita Research Institute], Jl: 5-B
Center line average roughness (Ra) based on O601 is 0.02
~0.04 fin.

After film formation, it was left in the air at 25°C. After 5 minutes, the membrane was immersed together with the ferroplate in a methanol bath at 18°C. After 10 minutes, the membrane was removed from the bath, air dried, and the gas permeation rate was measured. The thickness of the membrane was 205 μm. The measurement results are shown in Table 1 below along with other examples.

Comparative Example 1 The doctor knife used for film formation was made of steel with dome coating, and its center line average roughness Ra
) was 0.07 to 0.10 μm, but the same operation as in Example 1 was performed. The measurement results are shown in Table 1 below.

Example 2 Intrinsic viscosity in cyclohexane at 25°C is 1.57 dt/P
and poly(vinyltrimethylsilane) with a dispersity of 1.9.
X, Ot, organoborisiloxanthosite KE103RTV (manufactured by Shin-Etsu Chemical Co., Ltd.) 0.45 f nitoluene 15 and chlorophor AI 7.4 rv were added and dissolved, and then inbutanol 9.6 f was added to form a homogeneous solution. Next, a film was formed using this homogeneous solution in exactly the same manner as in Example 1, and the gas permeation performance of the obtained film was measured. The results are shown in Table 1 below.
Shown below.

Example 3 Intrinsic viscosity in cyclohexane at 25°C is 1.80 clt/
Using poly(vinyl)IJ methylsilane) with a dispersion degree of 1.6, the distance between the ferro plate and the doctor knife is
A film was formed by performing the same operations as in Example 1, except that the temperature was changed from 0.0 μm to 1600 μm, the evaporation time was changed from 25° C.-5 minutes to 20° C.-9 minutes, and the sample was left in a fume hood.

The obtained film had a smooth surface, a normal appearance, and a thickness of 52 mm.
It was 0 μm. Further, the gas permeation rate of this membrane was good as shown in Table 1 below.

The contact angle of the ferro plate, which is the cast plate used, was measured using a wetting index standard solution (s 4 dyn / crn) and found to be 56 to 57 degrees at 23° C. and 50° RH.

Further, the center line average roughness (Ra) was 0.01 μm.

Example 4 The same operation as in Example 3 was carried out, except that a hard chrome-plated aluminum plate (manufactured by Kasei Naoetsu Co., Ltd., "Allook") was used instead of the ferroplate as a cast plate for film formation.

The obtained film had a smooth surface, a thickness of 507 μm, a gas permeation rate as shown in Table 1 below, a contact angle of 52 to 54 degrees, and a center line average roughness (Ra) of α01 μm.

Table 1 Example 5 Using poly(vinyltrimethylsilane) with an intrinsic viscosity of 16 dat/f and a dispersity of 14 in cyclohexane at 25°C, a homogeneous solution having the same composition ratio as in Example 1 was obtained, and a Millipore filter-RAwP was obtained. (hole diameter t2±0.3 μtn), after passing f, the distance between the ferro plate and the doctor knife was adjusted to 1000
The same operation as in Example 1 was performed except that μ was constantly adjusted.

A film having an area of 0.4 m2 and a thickness of 284 μm with a smooth surface and good appearance was obtained. A part of this was attached to a module with an outer edge α of 15 m2, placed in air at 31° C., and sucked with a vacuum pump to obtain the following oxygen-enriched air that had permeated through the membrane. That is, when the pressure ratio on both sides of the membrane was 0.27, air with an oxygen concentration of 31 cm as measured by an oxygen concentration meter was obtained. At this time R0
2=1, I X 10-3cm"7cm" seconds・cm
Hf and Ro2/RH2 were 2.4.

〔Effect of the invention〕

The membrane obtained by the method of the present invention has excellent selective separation, especially at a high gas permeation rate, and also has practical mechanical strength and ease of handling, so it can separate more of a gas from a mixed gas. It can be used in many fields for the purpose of separating and concentrating by ratio. Fields where such membranes can be used are, for example, recovery of helium from natural gas, concentration of hydrogen from gas streams of hydrogenation reactions, concentration of oxygen in air for combustion,
It is used for medical purposes, wastewater treatment, etc., and contains oxygen, crabmeat,
Hydrogen, carbon dioxide, -carbon, helium, alkone,
It is suitable for separating these gases from gas mixtures containing methane and other gases.

Claims (1)

[Scope of Claims] 1. A method for producing a separation membrane, which comprises using a doctor knife with a center line average roughness of 0.05 μm or less when forming a membrane using a solution of a polymer membrane material. 2. The method for producing a separation membrane according to claim 1, wherein the separation membrane is an asymmetric membrane composed of a dense layer that is gas-selective and a porous layer that is not gas-selective. 3. The polymer membrane material is polyvinyltriorganosilane 1
Claim 1, which is a mixture of parts by weight and organopolysiloxane from 0.05 to 1 part by weight.
A method for producing a separation membrane according to item 1 or 2. 4. Any one of claims 1 to 3, wherein the polyvinyltriorganosilane has an intrinsic viscosity of 1.50 dl/g or more in cyclohexane at 25°C and a dispersity of 2.0 or less. A method for producing the separation membrane described above. 5. In manufacturing an asymmetric separation membrane with a membrane thickness of 500 μm or more, a solution of a polymer membrane material is cast onto a smooth cast plate with a contact angle of 40 to 70 degrees. 4. A method for producing a separation membrane according to any one of Item 4.