JP2745768B2 - Asymmetric separation membrane and pervaporation separation method - Google Patents

Description

The present invention relates to a specific aromatic polyimide obtained from an aromatic tetracarboxylic acid component containing diphenylsulfonetetracarboxylic acids as a main component and an aromatic diamine compound. Asymmetric separation membrane (flat membrane, hollow fiber membrane, etc., having an extremely thin dense layer and a relatively thick porous layer integrally)
It is related to.

Further, according to the present invention, a mixed solution of a plurality of organic compounds is brought into direct contact with the asymmetric separation membrane made of the aromatic polyimide, and at least one organic compound in the mixed solution flows through the asymmetric separation membrane. A pervaporation separation method of an organic compound mixture (pervaporation method), in which the organic compound selectively permeated and permeated through the asymmetric separation membrane is separated and recovered as vapor.
Related to

[Description of Prior Art]

Conventionally, a distillation method has been known as a method of separating an organic compound mixed solution into components. However, in the distillation method, it has been extremely difficult to separate an azeotropic mixture, a near-boiling mixture, and an organic compound which is liable to undergo a chemical change by heat.

In order to solve these problems, a method of separating using a separation membrane has been studied. In the method of concentrating and separating an organic substance aqueous solution using a separation membrane, for the concentration of some low-concentration organic substance aqueous solutions, a specific liquid component is selected by the difference in osmotic pressure by bringing the organic substance aqueous solution into contact with the separation membrane. Reverse osmosis, which allows the permeation to occur, has been used. However, since the reverse osmosis method needs to apply a pressure higher than the osmotic pressure of the separated solution, it cannot be applied to a high-concentration aqueous solution of an organic substance having a high osmotic pressure. is there.

Recently, a pervaporation method (pervaporation method) has been used as a method for separating an organic compound mixture different from the conventional separation method.
A new separation method using a separation membrane is attracting attention.
In this pervaporation method, an organic compound mixed solution to be separated is supplied in a liquid state to one side (supply side) of a selectively permeable separation membrane, and brought into direct contact with the supply side of the separation membrane.
The other side (permeate side) of the separation membrane is set in a vacuum or reduced pressure state. As a result, substances selectively permeating from the supply side to the permeate side of the separation membrane are taken out in gaseous form, and the organic compound mixture is concentrated. And a method of separating each organic compound.

Many proposals have been made for the aforementioned pervaporation method.

For example, a benzene-cyclohexane mixed solution, or
The separation of a benzene-hexane mixed solution is described in
JP-A-52-111888 exemplifies a separation method using an ionomer polymer membrane, and JP-A-59-30441 exemplifies a separation method using a polyamide membrane.

However, in the known separation method of an organic compound mixture, the separation membrane used in the pervaporation method has a low permeation rate or selectively permeates at least one organic compound in the organic compound mixture. The problem is that it has only selective separation such that it cannot be sufficiently, or the separation membrane used in the known pervaporation method has heat resistance, or
Solvent resistance was not sufficient, and it was extremely difficult to carry out separation of various organic compound liquid mixtures by pervaporation for an industrially long time.

[Problems to be solved]

An object of the present invention is to provide a novel aromatic polyimide asymmetric separation membrane which can be suitably used in the above-mentioned pervaporation method, and an organic compound mixed solution using the asymmetric separation membrane. In a pervaporation method, at least one organic compound can be efficiently and selectively separated from an organic compound mixed solution by a pervaporation method without disadvantages of a known pervaporation method. It is an object of the present invention to provide a pervaporation separation method that can be carried out for a period of time.

[Means for solving the problem]

The first invention has a general formula [However, in the general formula (I), A is a divalent aromatic residue obtained by removing an amino group from an aromatic diamine.] formula [However, in the general formula (II), B is a divalent aromatic residue obtained by removing an amino group from an aromatic diamine], which is an asymmetric separation formed of an aromatic polyimide. About the membrane.

Further, the second invention is characterized in that an organic compound mixture is brought into direct contact with one surface of the heat-resistant asymmetric separation membrane, and at least one organic compound in the organic compound mixture is mixed with the asymmetric separation membrane. The present invention relates to a method for pervaporation / separation of an organic compound mixed liquid, characterized in that an organic compound permeated through the asymmetric separation membrane is separated as vapor by selectively permeating and permeating the inside.

Hereinafter, each requirement of the present invention will be described in more detail.

The aromatic polyimide used for forming the asymmetric separation membrane of the present invention has a general formula Containing at least 40 mol%, particularly 45 to 100 mol%, of an aromatic tetracarboxylic dianhydride or a derivative thereof (the tetracarboxylic acid, a lower alcohol ester of the acid, etc.), and the remainder is biphenyl An aromatic tetracarboxylic acid component which is a tetracarboxylic acid, and an aromatic diamine compound, particularly an aromatic diamine having at least two benzene rings (preferably at least 60 mol%, especially at least 80 mol%) It is a high molecular weight aromatic polyimide which is obtained by substantially equimolar polymerization and imidation of an aromatic diamine component and is soluble in a phenolic organic solvent or the like.

In the present invention, the soluble aromatic polyimide used for producing the asymmetric separation membrane preferably has a repeating unit represented by the above general formula (I) in an amount of 50 to 100 mol%, and in particular, The repeating unit represented by the formula (I) is
It is more preferably from 70 to 100 mol%, particularly from 80 to 100 mol%, in that the film forming property and spinnability of the asymmetric separation membrane are good.

The aromatic polyimide, for example, an aromatic tetracarboxylic acid component, an aromatic diamine component, uniformly dissolved in a phenolic organic solvent, the solution is about 150 to 2
Heating to a high temperature of 50 ° C., or reacting at a low temperature of about 10 to 100 ° C. in the presence of an imidizing agent, and polymerizing and imidizing both components in the solution. Can be.

Examples of the aromatic tetracarboxylic dianhydride represented by the general formula (III) include 2,3,3 ', 4'-diphenylsulfonetetracarboxylic dianhydride and 3,3', 4,4'-diphenyl Sulfonetetracarboxylic dianhydride and the like can be mentioned.

As the biphenyltetracarboxylic acids, 2,3,
3 ', 4'- or 3,3', 4,4'-biphenyltetracarboxylic acid or an acid dianhydride thereof, or a salt or lower alcohol ester of the acid.

The aromatic tetracarboxylic acid component includes pyromellitic acid or an acid dianhydride thereof, together with an aromatic tetracarboxylic dianhydride or a derivative thereof represented by the general formula (III) and biphenyltetracarboxylic acids. 2-bis (3,4-dicarboxyphenyl) propane or its acid dianhydride, bis (3,4-dicarboxyphenyl) methane or its acid dianhydride, 3,3 ', 4,4'-benzophenonetetra Carboxylic acid or its acid dianhydride, or 3,3 ', 4,
If 4'-diphenyl ether tetracarboxylic acid or its acid dianhydride is used in a small proportion (a proportion of 20 mol% or less, especially 10 mol% or less based on the total aromatic tetracarboxylic acid component), it may be used in combination. Good.

Examples of the aromatic diamine compound having two or more benzene rings include diaminodiphenyl ethers such as 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, and 3,3'-diamino ether;
A "benzene ring" such as diaminobiphenyls such as dianisidine, o-tolidine, m-tolidine, diaminodiphenylthioethers, diaminodiphenylsulfones, diaminodibenzothiophenes, diaminothioxanthenes, and diaminodiphenylalkanes (methane or propane); Aromatic diamine compounds having two benzene rings "such as di (aminophenoxy) benzenes, di (aminophenyl) benzenes, etc .; di [(aminophenoxy)
Examples include "aromatic diamines having four benzene rings" such as phenyl] alkanes, di [(aminophenoxy) phenyl] sulfones, and di (aminophenoxy) biphenyls.

The aromatic diamine component may contain a small amount of phenylenediamine such as m-phenylenediamine and p-phenylenediamine (preferably at most 15 mol%, particularly preferably at most 10 mol%), Also
Diaminobenzoic acid such as 3,5-diaminobenzoic acid and 2,6-diaminobenzoic acid, or alkylbenzenediamines in a small proportion (preferably 30 mol% or less, particularly 20 mol% or less)
Mol% or less).

The asymmetric separation membrane comprising an aromatic polyimide used in the present invention is obtained by casting a thin film (flat membrane or hollow fiber) of the solution using a phenol-based solvent solution of the aromatic polyimide by a casting method or an extrusion method. Then, the thin film is brought into contact with a relatively low-temperature coagulating liquid to solidify the thin film to form a flat membrane-like or hollow fiber-like asymmetric separation membrane. For example, it can be produced by a conventionally known film forming method as described in JP-A-56-21602 and JP-A-56-157435.

In the above-mentioned method for producing an asymmetric separation membrane, the asymmetric separation membrane produced by a wet membrane formation method may be a suitable organic solvent (for example, lower alcohols such as methanol, ethanol, propanol and butanol, and n-hexane). , N
-Washed with an aliphatic or alicyclic hydrocarbon solvent such as heptane, octane, cyclohexane, etc.), further dried sufficiently, and further, under an atmosphere of a gas such as nitrogen or air, at about 150 to 400 ° C, especially It is appropriate to perform a heat treatment or an aging treatment at a temperature of 180 to 350 ° C. for about 1 second to 20 hours. When the heat treatment is sufficiently performed at a high temperature of 250 ° C. or higher, the aromatic polyimide forming the asymmetric separation membrane is partially thermally crosslinked, and particularly becomes insoluble or swells in a solvent. It is preferable because it disappears and chemical resistance and durability are improved.

The asymmetric separation membrane used in the present invention has a thickness of about 0.00
1-5μm homogeneous layer (dense layer) and thickness about 10-2000μ
m having a porous layer continuously and integrally with a porous layer,
A hollow fiber separation membrane or the like may be used.

The asymmetric separation membrane of the present invention supplies a mixed gas of a gas such as hydrogen, helium, carbon monoxide, carbon dioxide, and methane to one surface of the membrane to selectively obtain at least one gas from the permeation side. It is possible to perform gas separation of a mixed gas.For example, the asymmetric separation membrane of the present invention can be used to separate pure gas under measurement conditions of a measurement temperature of 25 ° C., and a measurement pressure of 1 to ² kg / cm ^2. When the gas permeation performance was measured using the helium gas, the permeation speed (PHe) of the helium gas was about 0.1 to 10 × 10 ⁻⁴ cm ³ (STP) / cm ² · sec · cmHg,
The separation performance [the ratio of the permeation rate of helium gas to the permeation rate of sulfur hexafluoride gas (PHe / PSF ₆ )] indicates gas separation performance of about 3 to 20.

The asymmetric separation membrane of the present invention has a permeation amount Q of an organic compound which selectively permeates when a pervaporation separation is performed using an organic compound mixed solution, and the permeation amount Q of the selectively permeating organic compound is about 0.1 kg / m ^2. about
It is about 0.2 to 5 kg / m ² · Hr, and the separation performance (separation coefficient α to be described later) between the permeated organic compound and the non-permeated organic compound is 5 or more, particularly 10 to 10,000, and further 15 to 900.
It is preferably about 0.

The pervaporation separation method of the present invention comprises the steps of: (a) supplying an organic compound mixed solution to a separation membrane module having a built-in asymmetric separation membrane (flat membrane, hollow fiber) made of the aromatic polyimide described above; Contacting the organic compound mixture directly with the supply side of the asymmetric separation membrane in the separation membrane module, and (b) supplying the carrier gas (sweep gas) to the permeate side of the asymmetric separation membrane if necessary. While flowing, or in a decompressed state by connecting to a decompression pump or the like installed outside the separation membrane module, from the supplied organic compound mixed solution, through the asymmetric separation membrane, at least one kind of organic (C) finally, separating the compound from the non-permeate side (supply side) of the asymmetric separation membrane to the outside of the separation membrane module. The solution of the concentrated remaining organic compound which did not permeate is taken out and recovered, and at the same time, the permeation of the organic compound selectively permeating the separation membrane from the permeation side of the asymmetric separation membrane to the outside of the separation membrane module. The vapor (permeate) is taken out, and if necessary, the permeate vapor (permeate) is cooled, condensed and recovered.

In the separation method of the present invention, the organic compound mixed solution supplied to the separation membrane module is about 0 to 120 ° C, particularly preferably 2 to 120 ° C.
It is preferable that the temperature is about 0 to 100 ° C.

In the separation method of the present invention, the pressure applied to the separation method is generally set such that the pressure on the permeation side of the separation membrane is lower than the pressure on the supply side, and the pressure on the supply side is atmospheric pressure to 60 kg / cm ² , preferably It is preferable that the pressure be from atmospheric pressure to 30 kg / cm ² .

The permeation side of the asymmetric separation membrane in the separation membrane module, when performing the pervaporation separation of the organic compound mixed solution, a sweep gas is flowed, or may be in a reduced pressure state,
The reduced pressure state only needs to be lower than the atmospheric pressure,
Particularly preferably about 200 Torr or less, more preferably 100
It is preferable that the pressure is reduced to not more than Torr.

As the organic compound mixture to which the method of permeating and vaporizing the organic compound mixture in the present invention can be applied, there are various combinations of organic compounds.For example, since each organic compound has an azeotropic point, ordinary distillation is performed. This is particularly effective in the case of a mixture of organic compounds which cannot be separated by the method or a mixture of organic compounds which are very difficult to separate by distillation because the boiling points of the organic compounds are close to each other.

Further, all of the organic compound mixed solutions may be uniformly dissolved in each other, or a part of them may be separated and suspended in excess of the solubility. However, the mixed liquid containing the organic compound needs to be liquid under the conditions of temperature and pressure when performing pervaporation separation in the mixed state.

Examples of a mixture of organic compounds having an azeotropic point include benzene / cyclohexane, benzene / normal hexane, methanol / acetone, benzene / methanol, acetone / chloroform (trichloromethane), ethanol / cyclohexane, butanol / cyclohexane, and chloroform / A mixed solution such as normal hexane, ethanol / benzene, ethanol / toluene, and a mixed solution of xylene isomers can be used.

Further, as an organic compound mixed solution having a boiling point difference of about 20 ° C. or less, particularly 10 ° C. or less and having boiling points close to each other,
Examples include ethylbenzene / styrene, parachloroethylbenzene / parachlorostyrene, toluene / methylcyclohexane, butadiene / butenes, butadiene / butanes, and normal butene-1 / isobutene.

The above-mentioned organic compound mixture can be applied not only to the above-mentioned two-component mixture but also to a three-component or more multi-component mixture.

In the pervaporation separation method of the present invention, the composition ratio of the organic compound mixture is not particularly limited, and an arbitrary ratio of the organic compound mixture can be separated or concentrated.

The structure, type, and the like of the separation membrane module are not particularly limited. For example, although not particularly limited, a plate-and-frame module, a spiral module, a hollow fiber membrane module, and the like can be used. Is preferred.

〔Example〕

Hereinafter, examples of the asymmetric separation membrane of the present invention and a pervaporation separation method using the separation membrane will be shown, and the present invention will be described in more detail.

In the examples, the permeation rate Q and the separation coefficient α were determined by cooling and condensing the vaporized components that passed through the membrane, weighing the collected components, adding an internal standard solution to the condensed liquid,
The weight ratio of the organic compounds X and Y was measured by D-gas chromatography, and calculated by the following formula.

In the examples, abbreviations of the compounds used for the aromatic tetracarboxylic acid component and the aromatic diamine component are shown below.

(Aromatic tetracarboxylic acid component)

s-BPDA; 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride DSDA; 3,3', 4,4'-diphenylsulfonetetracarboxylic dianhydride (aromatic diamine compound) DADE; 4 4,4'-Diaminodiphenyl ether DADM; 4,4'-Diaminodiphenylmethane TSN; 2,8-Dimethyl-3,7-diaminodibenzothiophene-5,5-dioxide, 2,6-Dimethyl-3,7-diaminodibenzo Mixture of isomers of thiophene-5,5-dioxide, 4,6-dimethyl-3,7-diaminodibenzothiophene-5,5-dioxide BAPB; 4,4′-di (4-aminophenoxy) biphenyl DABA; 3,5-Diaminobenzoic acid Examples 1 to 6 Using substantially equimolar amounts of an acid component and a diamine component having a charge ratio (composition mol%) shown in Table 1, in an organic polar solvent of paraclophenol, At the polymerization temperature and polymerization time shown in Table 1, the polymerization and Was produced aromatic polyimide solution was imidization.

Table 1 shows the polymer concentration and solution viscosity (rotational viscosity at 100 ° C .; poise) of each aromatic polyimide solution produced as described above.

Using the aromatic polyimide solution obtained as described above, a coagulating solution (ethanol, 0
C), and a wet film formation method at a hollow fiber take-up speed of 10 m / min., Followed by washing with an alcohol and an aliphatic hydrocarbon (n-hexane), drying, and heating at a heat treatment temperature shown in Table 1. Heat treatment was performed for 60 minutes to produce an asymmetric hollow fiber separation membrane made of an aromatic polyimide having the shape (inner diameter and thickness of the hollow fiber) shown in Table 1 respectively.

Examples 7 to 12 Four asymmetric hollow fiber separation membranes each having a length of 7.5 cm produced in Examples 1 to 6 were bundled together to form a yarn bundle, and one end of each of the yarn bundles was epoxy resin. The hollow fiber bundle element is formed in a container having an inlet for supplying the organic compound mixed solution, a non-permeate outlet, and a permeate outlet, respectively. Thus, separation membrane modules were manufactured.

An organic compound mixed solution having the composition and temperature shown in Table 2 is supplied to the separation membrane module, and the inside of the hollow fiber of the hollow fiber element in the separation membrane module is subjected to pervaporation under a reduced pressure of 3 Torr or less, The permeate vapor was cooled and collected.

Table 2 shows the permeation rate Q and the separation coefficient α of each organic compound in the pervaporation.

Example 13 A process in which the asymmetric hollow fiber separation membrane produced in Example 5 was immersed in a treatment solvent composed of a mixture of ethanol and cyclohexane (weight ratio is 1: 1) at 130 ° C. for 20 hours. went. After drying the asymmetric hollow fiber separation membrane subjected to the above treatment at 30 ° C. for 20 hours, in the same manner as in Example 5,
Separation membrane modules were manufactured, and the separation performance of the separation membrane modules in an organic compound mixed solution shown in Table 2 was measured.

 Table 2 shows the results.

Examples 14 to 19 Using the asymmetric hollow fiber separation membranes obtained in Examples 1 to 6, gas separation membrane modules were produced in the same manner as in Example 7.

Helium gum or sulfur hexafluoride gas of 1 to ² kg / cm ² is supplied to each of the gas separation membrane modules manufactured as described above at 25 ° C., and gas permeation of each gas separation membrane module is performed. The speed was measured respectively. Table 3 shows the results.

(Operation and effect of the present invention) The asymmetric separation membrane of the present invention is an asymmetric separation membrane composed of a soluble aromatic polyimide obtained from a specific aromatic tetracarboxylic acid component and an aromatic diamine component,
It can be used for general gas concentration and gas separation, and the pervaporation separation method of the present invention is a separation method related to a pervaporation method using a novel asymmetric separation membrane made of aromatic polyimide. Method, which can be used for separating and concentrating a mixture of various organic compounds, and
It can be used for a wide range of concentrations of organic compound mixtures, and has sufficient heat resistance, solvent resistance and durability, and has a specific polyimide asymmetric membrane with high separation performance. Since it is used, stable separation by pervaporation can be performed for a long time.

Claims (2)

(57) [Claims] (1) General formula [However, in the general formula (I), A is a divalent aromatic residue obtained by removing an amino group from an aromatic diamine.] formula [However, in the general formula (II), B is a divalent aromatic residue obtained by removing an amino group from an aromatic diamine], which is an asymmetric separation formed of an aromatic polyimide. film. 2. The one side of the asymmetric separation membrane according to claim 1,
The organic compound mixture was brought into direct contact, and at least one organic compound in the organic compound mixture was selectively permeated and permeated through the asymmetric separation membrane, thereby permeating the asymmetric separation membrane. A pervaporation separation method for an organic compound mixture, comprising separating an organic compound as vapor.