JP2782769B2 - Pervaporation separation method of organic matter aqueous solution - Google Patents

Description

The present invention relates to an aromatic diamine mainly containing a tetracarboxylic acid component mainly containing biphenyltetracarboxylic acids and di [(aminophenoxy) phenyl] propanes Using an asymmetric separation membrane (for example, a flat membrane or a hollow fiber membrane) formed of a soluble aromatic polyimide obtained from the components, an organic aqueous solution is brought into direct contact with the asymmetric separation membrane. The present invention relates to a separation method in which organic matter is concentrated or separated by removing water from an organic aqueous solution by a pervaporation separation method (pervaporation method) for selectively pervaporating water.

[Description of Prior Art]

BACKGROUND ART Conventionally, a distillation method is known as a method of separating an aqueous solution of an organic substance into an organic substance and moisture. However, in the distillation method,
It has been extremely difficult to separate an azeotropic mixture or a near-boiling mixture or 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.

On the other hand, as a separation method not affected by osmotic pressure, a pervaporation separation method (pervaporation method) is attracting attention as a separation method using a new separation membrane. In this pervaporation separation method, an aqueous solution of an organic substance to be separated is supplied in a liquid state to one side (supply side) of a selectively permeable separation membrane, and the separated aqueous solution is brought into direct contact with the supply side of the separation membrane. The other side (permeation side) of the membrane is in a vacuum or reduced pressure state,
As a result, a method is used in which a substance (such as water) that selectively permeates from the supply side to the permeation side of the separation membrane is taken out in a gaseous state, and the organic substance aqueous solution is concentrated or the organic substance is separated from water and the like.

On the other hand, since aromatic polyimide is extremely excellent in heat resistance, chemical resistance, and the like as compared with a polyamide film, a cellulose film, and a cellulose acetate film, it has recently been receiving attention as a material for a separation membrane. Asymmetric separation membranes have also been proposed for water separation of vapors of organic aqueous solutions. However, the conventionally known aromatic polyimide film, under high temperature, when it is in contact with an aqueous solution of an organic substance or water for a long time, due to the hydrolysis action of the aromatic polyimide, the polymer starts to deteriorate, and the deterioration gradually progresses. Therefore, the permeation performance and mechanical strength of the asymmetric separation membrane may be remarkably reduced, and there is a problem in durability, and the membrane separation method of an aqueous organic substance solution has not always been sufficiently satisfactory. In addition, when a known aromatic polyimide membrane is used for the pervaporation separation method of an organic aqueous solution,
There is also a problem that the permeation speed of water and the like and the selective separation performance of organic matter and water are not always satisfactory.

[Problems to be solved]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for pervaporation and separation of an aqueous solution of an organic substance using an asymmetric separation membrane made of aromatic polyimide. It is an object of the present invention to provide a "pervaporation / separation method using an aromatic polyimide membrane" which can be separated by a method and can carry out the pervaporation / separation method industrially for a long period of time.

[Means for solving the problem]

The present invention relates to a pervaporation separation method in which an aqueous solution of an organic substance is brought into contact with an asymmetric separation membrane made of a heat-resistant polymer to selectively permeate and vaporize mainly water from the aqueous solution of an organic substance, wherein the heat-resistant polymer is generally Formula I Containing 60 to 100 mol% of a repeating unit represented by
The remaining repeating unit is a soluble aromatic polyimide which is a repeating unit formed from a biphenyltetracarboxylic acid and an aromatic diamine component which is another aromatic diamine compound having 2 to 5 benzene rings. The present invention relates to a method for pervaporation and separation of an aqueous organic substance solution.

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

The asymmetric separation membrane used in the pervaporation separation method of the present invention is generally formed from a soluble aromatic polyimide mainly having the general formula I described above, and is an extremely thin homogeneous layer directly related to the selective separation performance. (Preferably a homogeneous layer having a thickness of about 0.001 to 5 μm) and a relatively thick porous porous layer supporting the homogeneous layer (preferably a porous layer having a thickness of about 10 to 2000 μm). Having an ability to selectively permeate water in an organic aqueous solution, for example, an asymmetric separation membrane in the form of a flat membrane, a hollow fiber, etc. (A separation membrane having a neutral microporous state).

The soluble aromatic polyimide forming the asymmetric separation membrane has a repeating unit represented by the above general formula I,
It contains 60 mol% or more, preferably 65 to 95 mol%, particularly 70 to 90 mol%, and the remainder of the repeating unit has 2 to 5, especially 2 to 4 biphenyltetracarboxylic acids and benzene rings. It is a “high-molecular-weight aromatic polyimide soluble in a phenolic organic solvent or the like” which is a repeating unit formed from an aromatic diamine component which is an aromatic diamine compound.

The aromatic polyimide includes, for example, an “aromatic tetracarboxylic acid component” containing 60% by mole or more, preferably 80% by mole or more of biphenyltetracarboxylic acids and 60% by weight of di [(aminophenoxy) phenyl] propane.
The "aromatic diamine component" containing at least 80 mol%, preferably at least 80 mol%, is added to a phenolic organic solvent in an approximately equimolar amount, and the solution is uniformly dissolved while adding about 150 to 2 mol%.
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 biphenyltetracarboxylic acids, in particular, 2,3,3 ', 4'- or 3,3', 4,4'-biphenyltetracarboxylic dianhydride is useful for producing a soluble aromatic polyimide. Is preferred.

As the tetracarboxylic acid component, for example, pyromellitic acid, 3,3 ′, 4,4′-biphenyl ether tetracarboxylic acid, 3,3 ′, 4,4′-benzophenone tetra carboxylic acid,
2,2-bis (3,4-dicarboxyphenyl) propane, bis (3,4-dicarboxyphenyl) methane, or an acid anhydride thereof in a small proportion (particularly preferably 20 mol% or less, more preferably May be used in combination at a ratio of 10 mol% or less).

In the method for producing each of the above-mentioned aromatic polyimides, if the content ratio of biphenyltetocarboxylic acids in the tetracarboxylic acid component is too small, the resulting aromatic polyimide has low solubility in a phenolic organic solvent. It is not preferable because an asymmetric separation membrane having stable quality cannot be produced, or the obtained asymmetric separation membrane has poor separation performance in a pervaporation method.

Di [(aminophenoxy) phenyl] propane used as a main component of the aromatic diamine component for forming the repeating unit represented by the general formula I is represented by the general formula II Is an aromatic diamine compound represented by, for example, 2,2
-Bis [4- (4-aminophenoxy) phenyl] propane, 2,2-bis [4- (3-aminophenoxy) phenyl] propane, 2,2-bis [3- (4-aminophenoxy) phenyl] propane And 2,2-bis [(aminophenoxy) phenyl] propane such as 2,2-bis [3- (3-aminophenoxy) phenyl] propane.

In the aromatic polyimide forming the asymmetric separation membrane of the present invention, the repeating unit represented by the aforementioned general formula I
It contains 60 mol% or more, and the remainder is a repeating unit formed from a biphenyltetracarboxylic acid and an aromatic diamine component which is another aromatic diamine compound having 2 to 5 benzene rings.

Examples of the other aromatic diamine compound having 2 to 5 benzene rings include: (a) an aromatic diamine compound having two benzene rings 4,
Diaminodiphenyl ethers such as 4'-diaminodiphenylether, 3,4'-diaminodiphenylether, 3,3'-diaminodiphenylether, 4,4'-diaminodiphenylmethane, 3,4'-diaminodiphenylmethane, 3,3'-diaminodiphenylmethane Such as diaminodiphenylmethanes, diaminodiphenylpropanes,
diaminobiphenyls such as o-dianisidine, o-thyridine, m-tolidine, diaminodiphenylthioethers, diaminodiphenylsulfones, diaminodiphenylenesulfones, diaminodibenzothiophenes, diaminothioxanthenes, etc. Aromatic diamine compounds having three 1,4-bis (3-aminophenoxy) benzene, 1,4-bis (4-aminophenoxy) benzene, 1,3-bis (3
Aromatic diamine compounds having three benzene rings, such as bis (aminophenoxy) benzenes such as -aminophenoxy) benzene and 1,3-bis (4-aminophenoxy) benzene; Aromatic diamine compounds having bis [4- (4-aminophenoxy) phenyl] ether, bis [4- (3-aminophenoxy) phenyl] ether, bis [3- (4-aminophenoxy) phenyl] ether, bis [ Bis [(aminophenoxy) phenyl] ethers such as 3- (3-aminophenoxy) phenyl] ether, 4,4'-bis (4-aminophenoxy) biphenyl, 4,4'-bis (3-aminophenoxy) 4,4-di (aminophenoxy) biphenyls such as biphenyl, di [(aminophenoxy) phenyl] meta Kind, and the like.

Note that the aromatic diamine component contains a small proportion (a content of 10 mol% or less) of “aromatic diamine compound having one benzene ring” such as phenylenediamines and diaminobenzoic acids. Is also good.

Each asymmetric separation membrane made of the above-mentioned aromatic polyimide used in the present invention uses a phenol-based solvent solution of the aromatic polyimide, and a thin film (flat membrane, hollow fiber) of the solution is cast by a casting method. , Formed by an extrusion method, etc., and then produced 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 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, JP-A-56-157435 and the like.

In the above-mentioned method for producing an asymmetric separation membrane, the non-compatible separation membrane produced by the wet membrane formation method may be a suitable organic solvent (for example, a lower alcohol having 1 to 6 carbon atoms and a lower alcohol having 1 to 8 carbon atoms). After washing with a lower aliphatic or alicyclic hydrocarbon solvent, etc.) and further drying sufficiently, further, under an atmosphere of a gas such as nitrogen or air, about 150 to 420 ° C., particularly 180 to 400 ° C.
It is appropriate to perform a heat treatment at a temperature of about 0.1 to 5 hours.

The asymmetric separation membrane used in the present invention has a permeation rate Q of water selectively permeating when pervaporation separation is performed using an aqueous solution of an organic substance (the organic substance concentration is 50% by weight).
Is about 0.2 kg / m ² · Hr or more, particularly about 0.4 to 5.0 kg / m ² · Hr, and has a separation performance of permeated water and non-permeated organic matter (separation coefficient α = water Is preferably 20 or more, particularly about 25 to 200.

The pervaporation separation method of the present invention comprises the steps of: (a) supplying an aqueous organic substance solution to a separation membrane module having a built-in asymmetric separation membrane (flat membrane, hollow fiber) made of the above-mentioned aromatic polyimide; Bringing the aqueous solution into direct contact with the supply side of the asymmetric separation membrane in the separation membrane module; (b) flowing the carrier gas (isop gas) on the permeate side of the asymmetric separation membrane, if necessary, or It is connected to a decompression pump or the like installed outside the separation-side module to be in a decompressed state, and from the supplied organic substance aqueous solution, selectively permeates and permeates moisture through the asymmetric separation membrane, and (C) Finally, from the non-permeate side (supply side) of the asymmetric separation membrane to the outside of the separation membrane module, the concentrated liquid which did not permeate the separation membrane is concentrated. The remaining organic matter aqueous solution is taken out and collected, and at the same time, a permeated vapor (permeate) mainly composed of water selectively permeating the separation membrane is sent from the permeation side of the asymmetric separation membrane to the outside of the separation membrane module. It is removed, and if necessary, the permeated vapor (permeate) is cooled, condensed and recovered.

In the present invention, the organic substance aqueous solution supplied to the separation membrane module is preferably at a temperature of about 25 to 120 ° C, particularly preferably about 50 to 100 ° C.

In the pervaporation separation method of the present invention, the pressure applied to the separation method is generally set such that the pressure on the permeate 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 / c.
m ² , preferably about atmospheric pressure to 30 kg / cm ² .

On the permeate side of the asymmetric separation membrane in the separation membrane module, when performing pervaporation and separation of the organic substance aqueous solution, a sweep gas may be flown or may be in a reduced pressure state. It is preferable that the pressure be lower, and it is particularly preferable that the pressure be reduced to about 200 Torr or less, more preferably 100 Torr or less.

As the organic substance aqueous solution to which the method for pervaporation and separation of an organic substance aqueous solution according to the present invention can be applied, aqueous solutions of various organic substances can be used. For example, examples of the organic substance include methanol, ethanol, and n.
-Propanol, isopropanol, n-butanol,
Aliphatic alcohols such as sec-butanol, tert-butanol and ethylene glycol, alicyclic alcohols such as cyclohexanol, aromatic alcohols such as benzyl alcohol, organic carboxylic acids such as formic acid, acetic acid, propionic acid and butyric acid, butyl acetate and acetic acid Ethyl, organic carboxylic acid esters such as malonic acid methyl ester, acetone, ketones such as methyl ethyl ketone, tetrahydrofuran,
Examples thereof include cyclic ethers such as dioxane, nitriles such as acetonitrile and acrylonitrile, and aldehydes such as formaldehyde and acetaldehyde, and a mixture of two or more thereof.

In the pervaporation separation method of the present invention, the concentration of the organic substance aqueous solution is not particularly limited, and the organic substance aqueous solution containing an organic substance at an arbitrary ratio can be separated or concentrated.

The structure, type, and the like of the separation membrane module are not particularly limited, but are not particularly limited, and include, for example, a plate and frame module, a spiral module, a hollow fiber membrane module, and the like. Is preferred.

〔Example〕

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

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 thereof, and dehydrating n- as an internal standard solution in the condensate. Propanol was added, and the weight ratio of water to organic matter was measured by TCD-gas chromatography, and calculated by the following formula.

Permeation speed Q = permeation amount per unit time (kg / Hr) / membrane area of asymmetric separation membrane (m ² ) Separation coefficient α = weight ratio of water and organic matter in feed solution / water and organic matter in permeate In the Reference Examples, abbreviations of the respective compounds used in the aromatic tetracarboxylic acid component and the aromatic diamine component are shown below.

BPDA; 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride BAPP; 2,2-bis [4- (4-aminophenoxy) phenyl] propane 4,4'-DADE;4,4'- Diaminodiphenyl ether DM; 4,4'-diaminodiphenylmethane TSN; o-tolidinesulfone DABA; 3,5-diaminobenzoic acid Reference Example 1 [Preparation of aromatic polyimide solution] 3,3 ', 4,4'-biphenyltetracarbon Acid dianhydride 1
An equimolar amount of a tetracarboxylic acid component composed of 00 mol% and a diamine component composed of 100 mol% of 2,2-bis [4- (4-aminophenoxy) phenyl] propane (BAPP), parachlorophenol (PCP) Medium, 14 at 180 ° C
PC of high molecular weight aromatic polyimide obtained by polymerization for a long time
A P solution (concentration: 17% by weight) was prepared.

(Spinning of hollow fiber membrane made of aromatic polyimide)

The above aromatic polyimide solution is supplied to a spinning apparatus equipped with a hollow fiber spinning nozzle, and asymmetric hollow fiber separation is performed by a wet film forming method using a coagulation liquid (temperature: 5 ° C, ethanol-water coagulation liquid). A membrane was formed and heat-treated at the heat treatment temperature shown in Table 1 to produce a hollow fiber separation membrane made of aromatic polyimide.

The hollow fiber membrane has an outer diameter of 620 μm and an inner diameter of 370 μm.
It was a continuous long hollow fiber having a thickness of 125 μm (having a thickness of 125 μm).

Table 1 shows the tensile strength (kg / fiber) and elongation (%) of the hollow fiber membrane, and the retention (%) of the tensile strength and elongation after immersion in a 150 ° C. hot ethanol aqueous solution for 20 hours. Shown in

Reference Examples 2 to 7 PCP solutions of aromatic polyimides having the concentrations and rotational viscosities shown in Table 1 in the same manner as in Reference Example 1 except that the diamine component having the type and composition shown in Table 1 was used. Were prepared respectively, and the obtained aromatic polyimide solution was used and subjected to the heat treatment at the heat treatment temperature shown in Table 1 by the same wet film forming method as in Reference Example 1, to the same extent as in Reference Example 1. Hollow fiber membranes comprising an asymmetric separation membrane made of an aromatic polyimide having an outer diameter, an inner diameter, and a wall thickness were respectively manufactured.

Table 1 shows the tensile strength and elongation of each of the hollow fiber membranes and the retention of the tensile strength and elongation after immersion in a hot ethanol aqueous solution at 150 ° C. for 20 hours.

Examples 1 to 3 and Comparative Examples 1 to 6 The asymmetric hollow fiber separation membranes produced in each of the reference examples were heat-treated at the heat treatment temperatures shown in Table 1, and then bundled into four to form a yarn bundle. One end of the bundle is sealed with an epoxy resin to form a hollow fiber bundle element, and the hollow fiber is inserted into a container having an inlet for supplying an aqueous solution of an organic substance, an outlet for a non-permeate, and an outlet for a permeate. A separation membrane module was manufactured with the yarn bundle element provided inside.

An 80% by weight aqueous ethanol solution is supplied to the separation membrane module at 90 ° C., and the inside of the hollow fiber of the hollow fiber element in the separation membrane module is permeated and vaporized under a reduced pressure of 3 meters or less to cool the permeate vapor. And recovered.

Table 2 shows the permeation rate Q and the separation coefficient α between water and organic substances in the pervaporation.

Example 4 and Comparative Examples 7 and 8 The asymmetric hollow fiber separation membrane made of aromatic polyimide obtained in Reference Example 2, Reference Example 4 and Reference Example 6 was treated with water at 150 ° C.
Alternatively, it was immersed in a 60% by weight aqueous ethanol solution for 20 hours.

The asymmetric hollow fiber separation membrane made of aromatic polyimide heat-treated as described above was dried at 60 ° C. under reduced pressure, and a hollow fiber bundle element and a separation membrane module were produced in the same manner as in Example 1. , 80% by weight of an aqueous ethanol solution was supplied at 90 ° C., and the permeation rate Q in pervaporation and the separation coefficient α between water and organic substances are shown in Table 3.

[Operation and effect of the present invention] The pervaporation separation method of the present invention is a separation method related to a pervaporation method using an asymmetric separation membrane made of a specific aromatic polyimide, so that separation and concentration of aqueous solutions of various organic substances are performed. It can be used for aqueous solutions of organic substances having a wide range of concentrations, and has sufficient heat resistance, water resistance, solvent resistance, and durability, and further has high water permeability. Since a specific polyimide asymmetric membrane is used, stable separation by pervaporation can be performed for a long time.

Continuation of the front page (56) References JP-A-63-264121 (JP, A) JP-A-63-166415 (JP, A) JP-A-63-93326 (JP, A) JP-A-60-255112 (JP, A) , A) (58) Field surveyed (Int. Cl. ⁶ , DB name) B01D 61/36 B01D 71/64

Claims (1)

(57) [Claims] 1. A pervaporation separation method in which an organic aqueous solution is brought into contact with an asymmetric separation membrane made of a heat-resistant polymer to selectively permeate and vaporize water mainly from the organic aqueous solution, wherein the heat-resistant polymer is General formula I Containing 60 to 100 mol% of a repeating unit represented by
The remaining repeating unit is a soluble aromatic polyimide which is a repeating unit formed from a biphenyltetracarboxylic acid and an aromatic diamine component which is another aromatic diamine compound having 2 to 5 benzene rings. And vapor permeation separation method of organic matter aqueous solution.