JP2009183814A - Separation membrane and manufacturing method thereof - Google Patents

Abstract

Disclosed is a gas and liquid separation membrane having a high permeation rate or a high separation factor in gas permeation and liquid permeation compared to a separation membrane comprising a carbon membrane obtained by carbonizing a synthetic resin.
SOLUTION: After applying a wooden tar to a porous support, for example, by immersing the inorganic porous support in a wooden tar, drying is performed at an appropriate temperature, and the solvent is removed to form a precursor film. The carbon tar membrane on the porous support thus obtained is carbonized at 400 ° C. to 1000 ° C. in a non-oxidizing atmosphere, so that the thickness of the carbon membrane is 0.05 μm to 5 mm, the pore size is 2 nm or less, and the pore size distribution A sharp separation membrane can be obtained.
[Selection figure] None

Description

  The present invention relates to a separation membrane for separating various mixtures of gases or liquids.

  Conventionally, separation of a fluid such as a gas mixture or a liquid mixture has been performed in various industrial scenes for the purpose of enrichment or purification of a specific component.

  As these separation methods, a cryogenic separation method is used for gas separation, and a distillation means is generally used for liquid.

  However, since these methods require a large amount of energy, a so-called membrane separation method using a membrane with low energy consumption has been proposed and has already been partially put into practical use. The significance of membrane separation methods is increasing in the future due to the recent increase in energy costs.

  On the other hand, membrane separation methods have long been used to separate solids from liquids or gases, and include microfiltration, ultrafiltration, reverse osmosis filtration, etc. to separate fine solids such as fungi and metal ions. In general, a porous membrane of micron order or submicron order is used as a filtration membrane.

  In addition, attempts have been made to separate gas mixtures and liquid mixtures with membranes, and gas separation membranes and liquid separation membranes have been developed, such as gas permeation, liquid dialysis, vapor permeation, and pervaporation separation (pervaporation). Has been proposed and already put into practical use. Membranes used for these are composed of nano-sized pores, and are also called non-porous membranes in order to distinguish them from the solid filtration membranes. Various polymers such as cellulose acetate, silicon rubber, polysulfone, and polyimide are known as materials for such separation membranes. With the recent development of polymer technology, separation membranes with high permeation selectivity have been obtained and put to practical use in fields such as hydrogen separation, nitrogen separation, and carbon dioxide separation. There is a reciprocal relationship between the speed) and the separation factor, and a membrane with a large permeation coefficient has a small separation factor, so an upper limit is pointed out in the separation performance of the polymer membrane. Furthermore, there are problems in heat resistance and solvent resistance. For example, when the mixed gas to be separated contains vapor of an organic solvent such as toluene or xylene, there is a drawback that the film is deteriorated and deteriorated.

Therefore, as a new material design to obtain a highly selective and highly permeable separation membrane with excellent heat resistance and solvent resistance, research on molecular sieve membranes of inorganic materials has been advanced, and there are nanometer-sized pores. Research on porous membranes is active. For example, the gas permeability of a silica membrane formed by a CVD method at a high temperature has been reported to be a large value of several thousands of H ₂ / N ₂ separability. Crystalline hydrous aluminosilicate zeolite has been put to practical use in pervaporation separation as a molecular sieve membrane material having pores approximately the same size as the permeation molecular diameter. On the other hand, carbon films prepared through thermal decomposition and carbonization by heat treatment at a temperature of several hundred degrees or more with a polymer as a precursor also have pores close to the gas molecular diameter, and are likely to be molecular sieve carbon films. The As an example of such a carbon film, for example, in Patent Document 1 and Patent Document 2, a carbon film obtained by carbonizing an acrylic hollow system at a high temperature is proposed. In Patent Document 3 and Patent Document 4, an aromatic polyimide hollow system is proposed. Carbon films have been proposed. Patent Document 5 proposes a carbon film formed by carbonizing a polyphenol resin on a ceramic surface. Further, Non-Patent Document 1 also refers to a carbon film obtained by carbonizing lignocresol (ligroin hydrolyzate) together with various organic polymer films and zeolite films.

  However, since these conventional inorganic films do not have sufficient control of the microstructure of the carbon material, the permeation rate and the selective permeability cannot be said to be sufficient. In order to obtain a pinhole-free film, a precursor is repeatedly used. It is necessary to apply and bake, and the current situation is that the strength is not satisfactory. How the uniform pore size can be imparted to the membrane with good reproducibility greatly affects the membrane performance and the practicality of the membrane.

Further, in the case of a zeolite membrane or a silica-based membrane, pinholes are particularly likely to occur, and there is a problem in controlling pores.
JP 60-179102 A Japanese Patent Laid-Open No. 1-222118 JP-A-4-11933 Japanese Patent Laid-Open No. 5-22036 JP-A-10-52629 “Chemical Engineering” Vol. 71, No. 12 (2007), pages 825-828

  The present inventors diligently studied to solve the above-mentioned problems of existing separation membranes, and completed the present invention.

  The present invention relates to a membrane having selective permeability to various fluids such as gas permeation, liquid permeation, vapor permeation, gas-gas separation, liquid-liquid separation, and pervaporation (in the present application, claims and specification). Is simply called "separation membrane").

  That is, the present invention is (1) a separation membrane in which a carbon membrane derived from wood tar that has been heat-treated at 400 ° C. to 1000 ° C., preferably 500 ° C. to 700 ° C., is adhered to the surface of the inorganic porous support.

  Further (2) A preferred embodiment of the present invention is that the carbon film layer has a thickness of 0.05 μm to 5 mm, preferably 0.1 μm to 1 mm, and more preferably 1 μm to 500 μm.

  Further, (3) the carbon film has a large number of pores having an average pore diameter of 2 nm or less, preferably 1 nm or less. Such pores are mainly determined by the heat treatment conditions of wood tar, which is a precursor of the carbon film, and can be obtained by heat treatment between 400 ° C. and 1000 ° C.

  (4) Although the separation membrane of the present invention can itself be used as a molecular sieve, it can usually be used for gas separation, liquid separation, pervaporation and the like.

  (5) The separation membrane of the present invention can be obtained by applying wood tar to the surface of the inorganic porous support, followed by heat treatment at 400 ° C. to 1000 ° C. in a non-oxidizing atmosphere.

  The separation membrane of the present invention has a pore size of 2 nm or less and is a porous material having a sharp pore size distribution, so it is useful as a molecular sieve. Only a specific component from various mixed gases having different molecular sizes can be selected at a high permeation rate. It can be used as a separation membrane for separation. For example, it can be effectively used for practically useful separation processes such as nitrogen / oxygen, methane / hydrogen, carbon dioxide / methane, hydrogen / methane, alcohol / water. Furthermore, according to the method for producing a carbon membrane based on the present invention, wood tar which has been conventionally discarded as a by-product of the charcoal production process can be used as a starting material for producing the separation membrane.

  Further, according to the production method based on the present invention, it is possible to carbonize at a relatively low temperature to obtain a membrane having high separation performance only by a single carbon membrane formation step. Compared with the conventional method, it can be carried out with a simple apparatus and simple operation.

  The greatest feature of the present invention is that wood tar is used as a precursor, which is heat-treated at a temperature of 400 ° C. to 1000 ° C. to be carbonized to form a carbon film.

  Wood tar is obtained when wood is carbonized. That is, when the liquid to be distilled is allowed to stand by dry distillation of wood, such as during the production of charcoal, it is divided into three layers. A small amount of essential oil and oily components float in the upper layer, and a water-soluble component (wood vinegar) is separated in the middle layer, and a wooden tar that is a complex and viscous high-boiling component is separated in the lower layer. For example, in the case of wood tar from hardwood, an example of its composition is 2% acetic acid, 0.65% methanol, 17.75% water, 5% light oil (specific gravity 0.97), heavy oil (specific gravity 1.043). ) 10% and soft pitch 64.60%. A 200-220 degreeC fraction (specific gravity 1.03-1.09) of heavy oil is called creosote oil, and has guaiacol and creosote as a main component, and is used as a raw material for wood preservatives and guaiacol.

  At present, however, they are pushed by products such as petroleum, are hardly produced, are discarded or incinerated as industrial waste, and cause environmental pollution.

  The present invention can be produced by using such wood tar as a carbon membrane precursor, applying it to the surface of the inorganic porous body, and heat-treating it in a non-oxidizing atmosphere at a temperature range of 400 ° C to 1000 ° C.

  Examples of the method for coating the surface of the inorganic porous body include a method in which the porous body is immersed in a solution obtained by dissolving wood tar in an organic solvent or the wood tar itself. The wood tar or the solution thereof is thinly and uniformly applied by a spray gun or the like. The coating method may be selected as appropriate depending on the concentration of the wood tar, the coating method employed, and the target film thickness.

  The thinner the concentration of the wood tar solution, the lower the viscosity of the solution and the better it penetrates into the pores of the porous support. The support surface in the present invention includes the surface in the pores of the support.

  In the present invention, the solvent for dissolving wood tar is not particularly limited as long as it dissolves uniformly, such as methanol, acetone, dimethylformamide, and tetrahydrofuran.

  As the material of the inorganic porous material, for example, alumina, siliceous, or a composition comprising silica or alumina and other components such as mullite and cordierite, porous sintered metal, porous glass, etc. are preferably used. Can do. In addition, other oxides such as zirconia and magnesia, carbides such as silicon carbide and silicon nitride, ceramics such as nitride, gypsum, cement, and the like, or a mixture thereof can be used.

  The porosity of the porous body is usually about 30 to 80%, preferably 35 to 70%, and most preferably 40 to 60%. When the porosity is too small, the permeability of a fluid such as gas is lowered, which is not preferable. When the porosity is too large, the strength of the support is decreased, which is not preferable. The pore diameter of the porous body such as ceramic is usually 10 to 10,000 nm, preferably 100 to 10,000 nm.

  Further, as the porous body, for example, a composite porous support in which the pore diameter in the vicinity of the surface is reduced by a method of impregnating silica sol on the surface of a porous body such as alumina can be suitably used.

  In the present invention, after applying the wooden tar to the porous support, such as by immersing the inorganic porous support in the wooden tar, the precursor film is formed by drying at an appropriate temperature and removing the solvent. . The wood tar film on the porous support thus obtained is carbonized at 400 ° C. to 1000 ° C. in a non-oxidizing atmosphere to form a carbon film on the surface of the porous support. When the carbonization temperature is higher than 1000 ° C., the pores of the carbon film are reduced by heat shrinkage, and the permeability is lowered, which is not preferable. On the other hand, when the temperature is lower than 400 ° C., carbonization is not sufficient, separation performance is low, and heat resistance and chemical resistance are low, which is not preferable. Most preferably, it is the temperature range of 500-700 degreeC.

  In addition, the non-oxidizing atmosphere at this time is a reduced pressure or an inert gas, for example, an atmosphere of nitrogen, argon, helium, etc., and a weak oxidizing gas such as a small amount of carbon dioxide or water vapor or a very small amount of oxygen. It may be included.

  The rate of temperature rise until reaching the maximum processing temperature in the carbonization step is not particularly limited. In addition, the atmosphere during carbonization, the heating rate, the maximum temperature, the retention time at the maximum temperature, etc. are usually determined in consideration of the type of porous support, the pore structure, the pore structure of the target carbon membrane, etc. The optimum conditions are selected by trial work.

  The thickness of the carbon film of the present invention is usually 0.05 μm to 5 mm, preferably 0.1 μm to 500 μm, and the pore diameter of the carbon film is preferably 2 nm or less, particularly preferably 1 nm or less, depending on the target gas molecular diameter. The optimum pore diameter may be selected and determined.

  For example, the molecular diameter of hydrogen is 0.289 nm, carbon dioxide is 0.330 nm, and methane is 0.380 nm. In the separation of these mixtures, the molecular diameter is taken into consideration in the range of about 0.3 to 0.5 nm. When the optimum pore diameter is selected, separation can be performed with high efficiency.

  The carbon film used in the present invention is not particularly limited as long as the porous film is used as a support, and the carbon film formed thereon can exhibit practically sufficient strength, and the thickness and shape of the support are not particularly limited. The shape of the support determines the shape of the separation membrane of the present invention formed thereon, and may be appropriately selected on a flat plate or a cylinder according to the purpose.

  That is, the shape of the separation membrane of the present invention is not particularly limited, and a module structure may be used in order to obtain a practical configuration. As the module shape, for example, a tube type, a flat plate type, a spiral type that can withstand high pressure, a pleated type, and the like are suitable.

  In the separation membrane of the present invention, the carbon membrane layer determines its performance, that is, the permeation coefficient and permeation speed. In the present invention, it is essential that the carbon film layer is obtained by carbonizing wood tar as a precursor and carbonizing it by heat treatment at 400 ° C to 1000 ° C. Using this precursor-derived carbon film, in addition to the benefits of effectively using wood tar close to industrial waste, compared to the use of various synthetic resins and lignin hydrolysates that have been proposed in the past, An excellent effect is obtained. The reason for this is not clear, but the comparison between the examples and comparative examples described later, particularly the comparative examples as shown in the following Table 1 for Example 3 and Comparative Examples 1 and 3 when manufactured under substantially the same conditions. In that case, the ideal separation factor is poor or the gas permeation rate is poor. That is, in the case of the wood tar of the present invention, it is possible to provide a well-balanced intermediate separation membrane.

以下に実施例を挙げて、本発明を具体的に説明する。なお、本発明に用いた気体透過性能の計算式と測定法をまとめて示すと次の通りである。
下記式（１）・（２）理想分離係数Ｒ_１／Ｒ_２
分離膜のガス透過性については、通常、下記の数式１、２で定義される透過係数Ｐ或いは、透過速度Ｒが指標として用いられる。透過係数Ｐ或いは透過速度Ｒの大小により、当該分子ふるい炭素膜の各種ガスの透過性を表す事ができる。本発明では混合ガスの分離性能の指標として理想分離係数Ｒ_１／Ｒ_２を定義した。
（１）透過係数 Ｐ＝ＱＬ／（ｐ_１−ｐ_２）Ａｔ
（２）透過速度 Ｒ＝Ｐ／Ｌ＝Ｑ／（ｐ_１−ｐ_２）Ａｔ
Ｑ：ガス透過量［ｃｍ^３］（０℃、１気圧）
ｐ_１：高圧側ガス圧［ｃｍＨｇ］
ｐ_２：低圧側ガス圧［ｃｍＨｇ］
Ａ：膜面積［ｃｍ^２］
Ｌ：膜厚［ｃｍ］
ｔ：時間［ｓｅｃ］

ガスの透過速度の測定法
本発明の分離膜のガス透過速度測定は、図１に示すガス透過能測定装置により測定した。透過セルに膜をＯリングで固定し、１００℃で脱気処理を行った後、測定温度にて上流側に測定気体を所定圧力導入し、減圧した管状膜の内側に透過した気体による圧力上昇速度を圧力トランスデューサーで測定した。透過速度Ｒ［ｃｍ^３（ＳＴＰ）／ｃｍ^２ ｓ ｃｍＨｇ］は１秒あたりｐ［Ｔｏｒｒ］下流側の圧力が増加したとすると次式によって算出できる。

The present invention will be specifically described below with reference to examples. In addition, it is as follows when the calculation formula and measurement method of gas permeation performance which were used for this invention are shown collectively.
The following formulas (1) and (2) ideal separation factor R ₁ / R ₂
As for the gas permeability of the separation membrane, the permeation coefficient P or permeation rate R defined by the following formulas 1 and 2 is usually used as an index. The permeability of various gases of the molecular sieving carbon film can be expressed by the permeation coefficient P or the permeation speed R. In the present invention, the ideal separation factor R ₁ / R ₂ is defined as an index of the separation performance of the mixed gas.
(1) Transmission coefficient P = QL / (p ₁ −p ₂ ) At
(2) Transmission speed R = P / L = Q / (p ₁ −p ₂ ) At
Q: Gas permeation amount [cm ³ ] (0 ° C., 1 atm)
p ₁ : High-pressure side gas pressure [cmHg]
p ₂ : low-pressure side gas pressure [cmHg]
A: Membrane area [cm ² ]
L: Film thickness [cm]
t: Time [sec]

Gas permeation rate measurement method The gas permeation rate of the separation membrane of the present invention was measured by the gas permeability measuring apparatus shown in FIG. After the membrane is fixed to the permeation cell with an O-ring and degassed at 100 ° C, the measurement gas is introduced at a predetermined pressure upstream at the measurement temperature, and the pressure rises due to the permeated gas inside the decompressed tubular membrane. The speed was measured with a pressure transducer. The permeation rate R [cm ³ (STP) / cm ² s cmHg] can be calculated by the following equation assuming that the pressure on the downstream side of p [Torr] per second increases.

ここでＶは下流側体積［ｃｍ^３］、Ｔは下流側の温度［Ｋ］、Ａは有効膜面積、ΔＰは上流側と下流側の圧力差［ｃｍＨｇ］である。純ガスの透過測定を行った。気体成分１、２の透過速度比Ｒ_１／Ｒ_２より、理想分離係数を算出した。

Here, V is the downstream volume [cm ³ ], T is the downstream temperature [K], A is the effective membrane area, and ΔP is the pressure difference [cmHg] between the upstream side and the downstream side. Pure gas permeation was measured. The ideal separation factor was calculated from the transmission rate ratio R ₁ / R _{2 of the} gas components 1 and 2.

  In this experiment, wood tar derived from hardwood was used as a starting material. From alder, charcoal as a carbon raw material and agricultural vinegar are produced, and a large amount of wood tar is generated as a by-product.

  3 L of THF (tetrahydrofuran) was added to 1 kg of wood tar and stirred well. A brown precipitate (80 g) was separated by suction filtration of the THF solution of wood tar using filter paper to remove insoluble matters. The filtrate was sent to a rotary evaporator and a low-boiling solution such as THF and moisture was collected using a water pump and subsequently a vacuum pump to concentrate the tar. As a result, 450 g of black viscous wood tar was obtained. The composition of tar was: C: 66.9 wt% H: 6.9 wt% N: 4.8 wt%.

  Next, this Hannochital was dissolved in THF to prepare a coating solution of 67 wt% (THF) solution, and a tubular porous alumina support (outer diameter 2.1 mm, inner diameter shown in FIGS. 2 (a) and 2 (b)). 1.8 mm, average pore diameter 0.15 μm, porosity 46%) was prepared as a support. 2A is a tubular support, A is a hollow portion, B is alumina, and an SEM photograph of the shape is shown in FIG. 2B. The substrate was dipped in the coating solution and then pulled up at a speed of 1 cm / min. After drying (70 ° C., 6 hours) and vacuum drying (100 ° C., 20 hours), a high-frequency induction heating apparatus [manufactured by Sekisui Electronics Co., Ltd., MU-1700D] was used for firing in an inert atmosphere. Firing conditions were as follows: atmosphere: nitrogen flow (flow rate 200 ml / min), heating rate: 500 ° C./min, firing temperature 400 ° C., and retention time at maximum temperature: 30 minutes. The number of coatings was 1, and a carbon film was produced.

  The gas permeation measurement of pure gas was performed by the vacuum method. The measurement temperature was 35 ° C., and the differential pressure between the upstream side and the downstream side was 1 atm.

  Table 2 shows the gas permeation speed and the permeation speed ratio after gas permeation.

  In Example 1, the gas permeation rate and the permeation rate ratio measured using a film produced by changing the firing temperature to 500 ° C. are shown in Table 2.

  Table 2 shows the gas permeation rate and the permeation rate ratio measured using the film produced in Example 1 with the firing temperature changed to 600 ° C. A cross-sectional SEM photograph of this film is shown in FIG. From this figure, it can be seen that a 200 nm thin film can be formed on the porous support.

In Example 1, the gas permeation rate and the permeation rate ratio measured using the film produced by changing the firing temperature to 700 ° C. are shown in Table 2.
(Comparative Example 1)

A granular phenol resin (manufactured by Air Water: Bell Pearl S895) was dissolved in THF to prepare a 40 wt% THF solution. A porous alumina tube (outer diameter 2.1 mm, inner diameter 1.8 mm, average pore diameter 0.15 μm, porosity 46%) was prepared as a support. The substrate was dipped in the coating solution and then pulled up at a speed of 1 cm / min. After drying (70 ° C., 6 hours) and vacuum drying (100 ° C., 20 hours), a high-frequency induction heating apparatus [manufactured by Sekisui Electronics Co., Ltd., MU-1700D] was used for firing in an inert atmosphere. The firing conditions were as follows: atmosphere: nitrogen (closed system), temperature rising rate: 500 ° C./min, firing temperature: 600 ° C., holding time at maximum temperature: 30 minutes. The number of coatings was one, a carbon film was prepared, and the gas permeation rate was measured.
(Comparative Example 2)

In Comparative Example 1, the gas permeation rate and the permeation rate ratio measured using a film produced with the number of coatings twice are shown in Table 2. A cross-sectional SEM photograph of this film is shown in FIG. From this figure, it can be seen that the film is 8 microns thick and is 40 times thicker than Example 3.
(Comparative Example 3)

  Lignocresol resin, which is a lignin derivative derived from coniferous cypress, was dissolved in THF to prepare a 35 wt% (THF) coating solution. A porous alumina tube (outer diameter 2.1 mm, inner diameter 1.8 mm, average pore diameter 0.15 μm, porosity 46%) was immersed in the coating solution as a support, and then pulled up at a speed of 1 cm / min. After drying (70 ° C., 6 hours) and vacuum drying (100 ° C., 20 hours), firing was performed under the same firing conditions as in Comparative Example 1. When the gas permeation measurement was performed, there was a pinhole in the membrane and there was no separation performance. Therefore, the second coating, drying, vacuum drying, and firing processes were carried out to produce a lignocresol twice-coated carbon membrane. Table 2 shows the gas permeation measurement results of the produced membrane.

These are the figures which show the outline of the gas-permeation measuring apparatus using the separation membrane of this invention. (A) is a figure which shows 1 type of the alumina porous support body in the separation membrane of this invention, (b) is the SEM photograph. These are SEM photographs showing a cross section of the separation membrane of the present invention. These are SEM photographs of a separation membrane cross section when a phenol resin is used as a comparative example. These are the SEM photographs of the cross section of the separation membrane when lignocresol is used as a comparative example.

Claims (5)

  A separation membrane in which a carbon membrane derived from wood tar that has been heat-treated at 400 ° C. to 1000 ° C. is adhered to the surface of the inorganic porous support.   The separation membrane according to claim 1, wherein the carbon membrane has a thickness of 0.05 μm to 5 mm.   The separation membrane according to claim 1 or 2, wherein the carbon membrane is a membrane having many pores having a diameter of 2 nm or less.   The separation membrane according to any one of claims 1 to 3, which is used for any one of gas separation, pervaporation separation, and liquid separation.   After applying wood tar to the inorganic porous support, heat treatment is performed at 400 ° C. to 1000 ° C. in a non-oxidizing atmosphere, and the heat-treated wood tar-derived carbon film adheres to the surface of the inorganic porous support A method for producing a separation membrane.

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