JP2649707B2 - Pervaporation of organic compound mixture - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a heat-resistant asymmetric separation comprising a specific soluble aromatic polyimide and a mixture of organic compounds such as an organic solvent solution in which the organic compounds are dissolved. Directly contacted with the membrane, at least one organic compound in the organic compound mixture was selectively permeated and permeated through the asymmetric separation membrane, thereby selectively permeating the asymmetric separation membrane. The present invention relates to a pervaporation separation method (pervaporation method) of an organic compound mixed solution for separating and recovering the organic compound as a vapor.

[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 organic compound mixture separation method, the separation membrane used in the pervaporation method has a low permeation rate or selectively allows at least one organic compound in the organic compound mixture to permeate. The problem of having only selective separation properties that cannot be sufficiently achieved, 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 method for pervaporation of an organic compound liquid mixture using an asymmetric separation membrane without the disadvantages of known pervaporation methods and efficiently and selectively separating at least one organic compound from the organic compound liquid mixture. Another object of the present invention is to provide a pervaporation separation method which can be separated by a pervaporation method and can be carried out industrially for a long time.

[Means for solving the problem]

The present invention relates to an aromatic tetracarboxylic acid component containing 70% by mole or more of biphenyltetracarboxylic acids and an aromatic diamino compound having one aromatic ring in a content of 15% by mole.
A soluble fragrance obtained from an aromatic diamine component, which is an aromatic diamine compound having a higher proportion and a content of not more than 50% mol and the balance being an aromatic diamine compound having 2 to 3 benzene rings. One side of a heat-resistant asymmetric separation membrane composed of an aromatic polyimide is brought into direct contact with an organic compound mixture, and at least one organic compound in the organic compound mixture selectively penetrates into the asymmetric separation membrane. The present invention relates to a method for pervaporation and separation of an organic compound mixed liquid, wherein the organic compound having passed through the asymmetric separation membrane is separated as vapor by being permeated.

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

The soluble aromatic polyimide forming the asymmetric separation membrane used in the pervaporation separation method of the present invention comprises: (A) biphenyltetracarboxylic acids, preferably 70 mol% or more, based on the total aromatic tetracarboxylic acid component, preferably Is 80
(B) (a) the content of the aromatic diamine compound having one aromatic ring with respect to the total aromatic diamine component; It is contained in a proportion of more than 15 mol% and a proportion of 50 mol% or less, preferably in a proportion of 16 to 40 mol%, and (b) the remaining benzene It is a high molecular weight aromatic polyimide obtained by polymerization and imidation from an aromatic diamine component, which is an aromatic diamine compound having two or three rings, and soluble in a phenolic organic solvent and the like.

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 to polymerize and imidize both components in the solution Can be.

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.

As the aromatic tetracarboxylic acids, in particular, 3,3 ',
4,4'-biphenyltetracarboxylic dianhydride is preferred for producing an aromatic polyimide.

In the present invention, examples of the aromatic diamine compound having one aromatic ring include diaminobenzoic acids such as 2,4-diaminobenzoic acid, 3,5-diaminobenzoic acid, and 3,6-diaminobenzoic acid; -Diaminobenzoic acids such as lower alcohol ester of diaminobenzoic acid, such as methyl diaminobenzoate and methyl 3,5-diaminobenzoate, 2,6-
Diaminopyridines such as diaminopyridine, 3,5-diaminopyridine, 2-methyl-P-phenylenediamine, 4-methyl-m-phenylenediamine, 2,5-dimethyl-p-phenylenediamine, 2,5-diethyl- p-
Lower alkyl (1 to 5 carbon atoms) phenylenediamines such as phenylenediamine and 4,6-dimethyl-m-phenylenediamine; lower alkoxy such as 2-methoxy-p-phenylenediamine and 4-methoxy-m-phenylenediamine Examples include phenylenediamines.

The aromatic tetracarboxylic acid component is, together with biphenyltetracarboxylic acids, pyromellitic acid or its acid dianhydride, 2,2-bis (3,4-dicarboxyphenyl) propane or its acid dianhydride, bis ( 3,4-dicarboxyphenyl) methane or its acid dianhydride, 3,3 ', 4,4'-benzophenonetetracarboxylic acid or its acid dianhydride, or 3,3'4,4'-diphenyl ether tetra The carboxylic acid or its dianhydride may be used in a small proportion.

In the method for producing an aromatic polyimide, when the content ratio of biphenyltetracarboxylic acids in the tetracarboxylic acid component is too small, the obtained aromatic polyimide has low solubility in a phenolic organic solvent. In addition, it is not preferable because an asymmetric separation membrane having a stable quality cannot be manufactured, or the obtained asymmetric separation membrane has poor separation performance in a pervaporation method.

In the method for producing the aromatic polyimide, together with diaminobenzoic acids, the `` aromatic diamine compound having 2 to 3 benzene rings '' used includes 4,4′-diaminodiphenyl ether, 3,4′-diaminodiphenyl ether and the like. Diaminodiphenyl ethers, 4,4'-
Diaminodiphenylalkanes (methane or propane) such as diaminodiphenylmethane, 3,4'-diaminodiphenylmethane, 2,2-bis (4-aminophenyl) propane, and diaminodiphenylthioethers, diaminodiphenylsulfones, and diaminodibenzothiophene Diamine compounds having two benzene rings, such as diamines, diaminothioxanthenes, diaminobiphenyls, or aromatic compounds having three benzene rings, such as bis (aminophenoxy) benzenes and bis (aminophenyl) benzenes Diamine compounds can be mentioned.

Note that the aromatic diamine component is referred to as “one aromatic ring
If the aromatic diamine compound having too much `` is contained, the aromatic polyimide obtained from such a diamine component and an acid component may have low solubility in an organic polar solvent, It is not suitable because a stable asymmetric separation membrane cannot be produced or the obtained asymmetric separation membrane has insufficient separation performance in the pervaporation method.

The above-mentioned asymmetric separation membrane made of the aromatic polyimide used in the present invention uses a phenol-based solvent solution of the aromatic polyimide to form a thin film (flat membrane,
Aerial thread) by casting, extrusion, etc.
Then, the thin film can be manufactured by a wet film forming method in which the thin film is brought into contact with a relatively low-temperature coagulating liquid to solidify the thin film to form a flat membrane-shaped or hollow fiber-shaped asymmetric separation membrane. 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 production of the asymmetric separation membrane, the asymmetric separation membrane produced by the 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
-Washing with an aliphatic or alicyclic hydrocarbon solvent such as heptane, octane, cyclohexane, etc.) and further drying sufficiently, and further under a gaseous atmosphere such as nitrogen, air, etc., at about 150-350 ° C., especially It is appropriate to perform heat treatment at a temperature of 180 to 330 ° C. for about 0.1 to 5 hours.

The asymmetric separation membrane used in the present invention has a permeation rate Q of an organic compound that selectively permeates when a pervaporation separation is performed using an organic compound mixed solution, and the permeation rate Q of the selectively permeating organic compound is about 0.1 kg / m ² .Hr or more. , In particular, about 0.2 to 5 kg / m ² · Hr, and the separation performance (separation coefficient α) of the permeated organic compound and the non-permeated organic compound is 5 or more, especially 10 to 6000. Is preferred.

The pervaporation separation method of the present invention comprises the steps of: (a) supplying an organic compound mixed solution to a separation membrane module in which the above-described asymmetric separation membrane (flat membrane, hollow fiber) made of aromatic polyimide is incorporated; 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 residual organic compound that did not permeate was taken out and collected, and at the same time, the organic compound selectively permeated through the separation membrane from the permeate side of the asymmetric separation membrane to the outside of the separation membrane module. The permeate vapor (permeate) is taken out, and if necessary, the permeate vapor (permeate) is cooled, condensed and recovered.

In the present invention, the organic compound mixed solution supplied to the separation membrane module is about 0 to 120 ° C, particularly preferably 20 to 100 ° C.
Preferably, the temperature is of the order of magnitude.

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 permeation vaporization separation of the organic compound mixed solution, a sweep gas is flowed, or may be in a reduced pressure state,
The depressurized state may be a pressure lower than the atmospheric pressure, and it is particularly preferably reduced to about 200 Torr or less, more preferably 100 Torr or less.

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 / Examples thereof include normal hexane, ethanol / benzene, ethanol / toluene, and a mixed solution of xylene isomers.

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, the present invention will be described in more detail with reference to Examples and Comparative Examples relating to the pervaporation separation method of the present invention.

In Examples and Comparative Examples, the permeation rate Q and the separation coefficient α were determined by cooling and condensing the vaporized components that had passed through the membrane, collecting the weight, measuring the weight, adding an internal standard solution to the condensate, and measuring the TCD. -The weight ratio of the organic compounds X and Y was measured by gas chromatography, and calculated by the following formula.

In Reference Examples, the 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 (aromatic diamine compound) DABA: 3,5-diaminobenzoic acid DAP; 2,6-diaminopyridine MPP; 2,5- Dimethyl-p-phenylenediamine MMP; 4,6-dimethyl-m-phenylenediamine DADE; 4,4'-diaminodiphenylether DADM; 4,4'-diaminodiphenylmethane TSN; 2,8-dimethyl-3,7-diaminodibenzo Thiophene-5,5-dioxide, 4,6-dimethyl-3,7-diaminodibenzothiophene-5,5-dioxide, 2,6-dimethyl-3,7-diaminodibenzothiophene-5,5-dioxide Mixtures of the isomers of Reference Examples 1 to 7 Using substantially equimolar amounts of an acid component and a diamine component having the charge ratios (composition mol%) shown in Table 1, in an organic polar solvent of paraclophenol, see Table 1 At the polymerization temperature and polymerization time shown in Was produced aromatic polyimide solution was de reduction.

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, once through the outside air from the hollow fiber spinning nozzle,
Coagulation liquid having the composition shown in Table 1 (aqueous ethanol solution at 0 ° C)
After extruding the hollow fiber-like body of the polyimide solution, and performing a semi-dry wet film forming method in which the hollow fiber is spun at a take-up speed of 10 m / min, the hollow fiber is washed with alcohol and an aliphatic hydrocarbon, and dried. Then, it was treated at the heat treatment temperature shown in Table 1 for 30 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.

Examples 1 to 9 A bundle of four asymmetric hollow fiber separation membranes having a length of 7.5 cm manufactured in each reference example was formed into a bundle, and one end of the bundle was sealed with an epoxy resin. A hollow fiber bundle element is formed, and the hollow fiber bundle element is installed in a container having an inlet for supplying an organic compound mixed solution, a non-permeate outlet, and a permeate outlet. Was 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 10 The asymmetric hollow fiber separation membrane produced in Reference Example 4 was subjected to a treatment of immersion in a treatment solvent composed of a mixture of benzene and cyclohexane (weight ratio 1: 1) at 150 ° C. for 20 hours.

Each asymmetric hollow fiber separation membrane subjected to the above treatment
After drying for 20 hours, a separation membrane module was manufactured in the same manner as in Example 1, and the separation performance of the separation membrane module with an organic compound mixed solution shown in Table 2 was measured.

 Table 2 shows the results.

Comparative Reference Example 1 60 mmol of pyromellitic dianhydride, 60 mmol of 4,4'-diaminodiphenyl ether, and 200 g of N-methylpyrrolidone were placed in a three-neck separable flask, and nitrogen gas was passed therethrough, followed by stirring. A polymerization reaction was carried out at 20 ° C. for 10 hours to generate a polyamic acid.Further, 200 g of N-methylpyrrolidone, 27 g of pyridine and 35 g of acetic anhydride were added to the reaction solution, and the temperature was gradually raised to 80 ° C. with vigorous stirring. The mixture was heated and maintained at 80 ° C. for 1 hour to imidize the polymer and precipitate polyimide. Further, ethanol was added to the reaction solution to completely precipitate the polymer, which was separated by filtration, finally washed with ethanol, and further dried under reduced pressure to obtain a polyimide powder.

This polyimide powder was treated with p-chlorophenol, N-
Methyl-2-pyrrolidone or N, N-dimethylacetamide, respectively, the mixture was heated,
Tried to dissolve the polyimide powder in the above solvent,
Substantially no solution of the polyimide could be prepared.

Therefore, an asymmetric separation membrane could not be produced from the aromatic polyimide obtained by using the above pyromellitic dianhydride.

Comparative Reference Examples 2 to 5, 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride and paraphenylenediamine (Comparative Reference Example 2), 2,5-
Dimethyl-paraphenylenediamine (Comparative Reference Example 3),
An organic polar solvent of paraclophenol was prepared in the same manner as in Example 1 by using equimolar amounts of 2,6-diaminopyridine (Comparative Reference Example 4) and 3,5-diaminobenzoic acid (Comparative Reference Example 5). In the middle, polymerization was conducted at a polymerization temperature of 180 ° C. for 6 hours, but aromatic polyimides were precipitated. These aromatic polyimide powders did not substantially dissolve in any of the organic solvents, and a uniform polymer solution could not be prepared.

Comparative Example 1 Aromatic polyimide (General Electric,
10 parts by weight (Ultem), 40 parts by weight of N-methyl-2-pyrrolidone, and 50 parts by weight of tetrahydrofuran were put into a separable flask and stirred to prepare a uniform polymer solution.

The polymer solution was cast on a smooth glass plate with a doctor knife to a thickness of 0.2 mm.
After immersion for a time, an asymmetric separation membrane was formed. Finally, the asymmetric separation membrane was peeled off from the glass plate and dried at 30 ° C. to produce an asymmetric separation membrane.

The above asymmetric separation membrane was subjected to a pervaporation method to separate an organic compound mixture containing equivalent amounts of chloroform and n-hexane.

The asymmetric separation membrane swelled with the organic compound mixture, and stable separation performance could not be measured.

(Operation and effect of the present invention)

Since the separation method of the present invention is a separation method related to pervaporation using an asymmetric separation membrane made of a specific aromatic polyimide, it can be used for separating and concentrating a mixture of various organic compounds, and , Can be used for a wide range of organic compound mixtures, and has sufficient heat resistance,
It has water resistance, solvent resistance and durability, and furthermore,
Since a specific polyimide asymmetric membrane having high separation performance is used, separation by a stable pervaporation method can be performed for a long time.

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-58-5344 (JP, A) JP-A-60-150806 (JP, A) JP-A-61-19813 (JP, A) JP-A-62 38207 (JP, A)

Claims (1)

(57) [Claims] (1) 70% by mole of biphenyltetracarboxylic acid
The aromatic tetracarboxylic acid component contained above and the aromatic diamine compound having one aromatic ring have a content of 15%.
It was obtained from an aromatic diamine component which is an aromatic diamine compound which is an aromatic diamine compound having a content of more than 50 mol% and a content of not more than 50 mol%, and the remainder having 2-3 benzene rings. On one side of a heat-resistant asymmetric separation membrane made of soluble aromatic polyimide, an organic compound mixture is brought into direct contact, and at least one organic compound in the organic compound mixture selectively passes through the asymmetric separation membrane. Permeation and separation of an organic compound mixed solution, wherein the organic compound permeated through the asymmetric separation membrane is separated as vapor by being permeated and permeated into the mixture.