WO1999047247A1

WO1999047247A1 - Solvent-resistant pan (polyacrylonitrile) membrane

Info

Publication number: WO1999047247A1
Application number: PCT/DE1999/000633
Authority: WO
Inventors: Michael Zierke; Heinz Buschatz; Gerda Peters
Original assignee: Gkss-Forschungszentrum Geesthacht Gmbh
Priority date: 1998-03-19
Filing date: 1999-03-10
Publication date: 1999-09-23
Also published as: DE19811998C1

Abstract

The invention relates to a solvent-resistant PAN membrane, especially for ultra- and nanofiltration. Said membrane has a base consisting of polyacrylonitrile (PAN) and a comonomer copolymerised with the same and is formed in water by phase inversion, using a membrane formation process which is known per se. The inventive membrane is obtained by using a comonomer with at least one reactive group which, when reacted with itself or with a cross-linking agent, can cause the membrane to cross-link, and by carrying out the cross-linking reaction during and/or after the formation of the membrane. As a result of the cross-linking, the inventive membrane is resistant to solvents. It can also be produced using existing technological procedures and equipment.

Description

Solvent stabilizer PAN membrane

Description

The invention relates to a 1 eyelid stable 1 PAN membrane, in particular for ultrafiltration and nanofiltration, based on polyacrylonitrile 1 (PAN) and a comonomer copolymerized therewith, the PAN membrane being formed by membrane formation known per se Phase inversion was formed in water, and a method for producing such a PAN membrane.

Depending on the solvent used, different membrane-forming polymer materials are currently used to process a wide variety of organic solvents and solvents with the aid of ultra- and nanofiltration, for example the separation of ingredients. It is therefore necessary to use either special membranes made of material that is resistant only in one solvent or in a few solvents 2 or expensive inorganic membranes to use. In addition, for certain solvents, for example DMF, DMAc, DMSO and NMP, there are still no suitable solvent-stable pore membranes which can be used to a satisfactory extent on an industrial scale.

So far, it has been necessary to use a special polymer material for the membranes or inorganic membranes for the respective separation problem. This makes the manufacture of such membranes and the separation processes equipped with them significantly more expensive.

The previously known 1 eyelet resistant membranes have the disadvantage that the production conditions of the polymers for such membranes are significantly more complicated and expensive than that of the simple acrylic nitri-1 copolymers. This also applies to the formation of such membranes. In some cases, for example, such membranes can only be formed using concentrated sulfuric acid or expensive special solvents.

It is an object of the present invention to provide a universally usable pore membrane based on the membrane material which is already very solvent-resistant, inexpensive to produce and easy to form (polyacryl nitri 1) and a process for producing such a polyacryl nitride membrane (PAN membrane) ) order t 1.

This task is solved by teaching the claims.

The 1 ösemi ttel stable 1 PAN membrane according to the invention is added in the same way or in a conventional manner 3 a membrane is formed using phase inversion in water or in aqueous solution. In order to achieve a largely universal solvent stabilization of the PAN pore membrane according to the invention, which is used in particular for ultrafiltration and nanofiltration, at least one comonomer with a functional group is used together with the acrylic nitrite monomer copolymer si ert and so introduced into the PAN polymer. Reactive groups are used which are capable of causing the membrane to crosslink by reaction with themselves or with a crosslinking agent, this crosslinking reaction being carried out or taking place during and / or and in particular after the membrane has been formed. These functional groups, which are thus crosslinkable and in particular postcrosslinkable, are preferably epoxy, alkoxysilyl and acid amide groups which are introduced with the aid of the comonomer.

A reactive group which causes crosslinking by reaction with itself is understood to be one which can form a bond with another identical group on the PAN copolymer. This includes, for example, the epoxy group. The acid-catalyzed reaction of this epoxy group with water forms a hydroxyl group, which in turn can react with a remaining epoxy group to form an ether bridge.

The following may preferably be mentioned as comonomers which can be used here:

I) methacrylic acid glycidyl ester

II) Methacrylic acid [3- (trimethoxysilyl) propyl ester] or tri ethoxyvinyl si 1 4 III) acrylic acid amid or methacrylic acid amid.

In the case of comonomers I) and II), these can be introduced into the PAN polymer by solution copolymerization of acrylonitrile. In the case of comonomer III), use is advantageously made of the suspension copolymerization.

The reactive groups introduced into the PAN polymer in this way permit chemical crosslinking of the polymer, which takes place during conventional membrane formation or after the conventional membrane formation, this membrane formation taking place by phase inversion in water.

The comonomer preferably makes up 3 to 49 mol%, in particular 5 to 35 mol%, of the PAN copolymer. If a range of 3 to 49 mol% or 5 to 35 mol% is mentioned here, then all intermediate values in between are included and disclosed, for example 3, 4, 5,... 11, 12, 13 ... 18, 19, 20 ... 28, 29, 30, ... 38, 39, 40, ... 45, 46 and 47.

Crosslinking agents which are preferably used are those which have at least two functional groups and are therefore bi-functional 1. The functional groups of the crosslinking agent can then react with corresponding functional groups on the PAN copolymer to form a bond. This creates a kind of bridge or network. Of course, it is also possible to use crosslinking agents with three, four (or more) such groups. 5

The chemical crosslinking of the polymer, in particular, can be carried out in various ways, for example as follows:

1. Cross-linking by reactions of epoxy groups with amino groups

PAN copolymers with 3 to 49 mol% of methacrylic acid glycidyl ester were produced. The respective PAN copolymer was mixed in the form of a DMF solution (17 to 25% solids) with a crosslinking agent. DMAc, DMSO and NMP can also be used as solvents. Various amines served as crosslinking agents, the molar ratio of epoxy group to amino group being approximately 1: 1. The DMF solution was drawn out into a cast film; The corresponding membrane was formed by a subsequent phase inversion in water. The crosslinking takes place through the generally base-catalyzed reaction of an epoxy group with an amino group, with a reactive hydroxyl group also being formed in addition to an amine bond. For successful crosslinking to be as complete as possible, in addition to the epoxy groups, amino groups must be present at least in an equimolar ratio.

It is irrelevant for the production of the membrane according to the invention how and when part of the epoxy groups of the PAN copoly er is functionalized with amino groups, since this step relates to the well-known conventional epoxy chemistry. The following amine compounds 1.) to 10.) were used in the course of the tests carried out:

1.) hexamethyl endiamine, 2.) diethyl entri amine, 6

3.) Tri ethyl entetrami n,

4.) Tetraethyl enpentami n,

5.) 2,4,6-triamino-l, 3,5-triazine,

6.) 1, 3-phenylendiamine,

7.) 1, 4-phenyl endi amine,

8.) 3, 5-Di ami nobenzoic acid,

9.) 2, 6-diamino-4-phenyl-1,3,5-triazi and

10.) 2, 6-Di a inopyridi n.

The amination of one part of the epoxy groups of the PAN copolymer could be carried out as follows:

Part of the PAN copolymer with a significant excess (2 to 4-fold) of the amines mentioned was separately in homogeneous solution (2 to 10% solid, solvent: DMF, DMAc, DMSO or NMP) at 60 to 80 ° C. implemented for a period of 30 to 120 min or at 20 to 25 ° C for a period of 16 to 24 h. This was followed by working up the functionalized polymer (filtering off gel parts, possibly concentrating, precipitating, washing and drying).

The amine-functionalized part of the PAN copolymer was then combined with the epoxy group-bearing PAN copolymer in a solution (solvent: DMF, DMAc, DMSO or NMP) (molar ratio epoxy: amino groups 1: 1), formed into membranes (phase inversion in water) and when annealed in water (60 to 95 ° C, 10 to 30 min) cross-linked to 1 solvent-stable PAN membrane. This was followed by drying at 70 to 90 ° C for a period of 15 to 13 minutes in the drying cabinet.

The advantage of this variant is that the polymeric amine-functionalized crosslinker in the 7

Phase inversion in water can also not be dragged into the precipitation bath by the solvent DMF. Furthermore, the viscosity of the polymer solution is not reduced by the addition of the crosslinking agent, as is the case when the amine compounds 1.) to 4.) are added.

Adequate crosslinking was also possible by adding the water-soluble amine compounds 1) to 4), 6) and 7) (0.1 to 0.5 n, based on the total volume) and by adding Ammonia (10 to 25% solution, based on the total volume) can be achieved in the tempering bath (in water, 60 ° C to 95 ° C, 30 to 90 min). Cross-linking with the above-mentioned aqueous solutions at 20 to 25 ° C (room temperature) for 16 to 24 h in a separate cross-linking bath was also successful, followed by tempering in water (70 to 95 ° C, 10 to 20 min). Following both variants (i.e. crosslinking in the heat treatment bath or crosslinking in the crosslinking bath), the membrane is washed with water in order to remove the adhering unreacted amines or ammonia. The mixture was then dried in a drying cabinet at 70 to 90 ° C. for 15 to 30 minutes.

The most effective and economical method was to mix in the amine compounds mentioned, namely:

- preferably water-insoluble amines 8.) to 10.) in an approximately equimolar ratio of epoxy: amino group = 1: 1, 8th

water-soluble amines 1.) to 4.) and 6.) and 7.) in an at least approximately molar ratio of epoxy: amino groups = 1: 1.5 in order to compensate for the amine discharge into the water,

- In the case of the amine 5.) due to the poor solubility in DMF, dispersing in an at least equimolar ratio of epoxy: amino groups 1: 1

into the polymer casting solution. It was then formed by phase inversion in water and the membrane was annealed in water at 60 to 95 ° C. for a period of 10 to 30 min. This was followed by drying in a drying cabinet at 70 to 90 ° C. for 15 to 30 minutes.

The standing and processing times from the time of adding the crosslinking agent to the polymer solution were

- the A inen 1.) to 4.) at room temperature (20 - 25 ° C)

1 h, at 10 ° C 2 h,

- the amine 5.) at 10 ° C for 45 min, and

- the amines 6.) to 10.) at room temperature (20 - 25 ° C)

2 h, at 10 ° C for 3 h.

It is also possible to add the water-soluble amines and ammonia to the precipitation bath (at 20 - 25 ° C for 16 to 24 h). With this procedure, however, the continuous production can be impaired. In addition, the amounts of amines and ammonia required for this are considerable, and the corresponding waste disposal also affects the conventional one 9

Process so that the crosslinking is preferably subsequent.

2. Cross-linking by reactions of epoxy with hydroxyl groups

PAN copolymers containing methacrylic acid glycidyl esters (3 to 49 mol%) were drawn out into a cast film in the form of a DMF solution (17 to 25% solids; also possible in DMAc, DMSO and NMP as solvents) formed into membranes by subsequent phase inversion in water. Through an acid-catalyzed reaction of the epoxy groups with water to form hydroxyl groups, which in turn reacted with the remaining epoxy groups to form ether bridges, crosslinking with the following additives in the heat treatment bath (water, 60 ° C. to 95 ° C.; 30 to 120 min ) performed:

- acidic, with additions of HCL or H ^ SO «(0.1 to 1.0 n based on the total water volume of the tempering bath)

- acidic, with additions to HCL or H SO. (0.1 to 1.0 n) and glycerol (5 to 15% by volume), the concentration information of which relates in each case to the total water volume of the tempering bath.

In both cases, drying was carried out at 60 to 80 ° C. for 20 to 60 minutes. When using H ^ SO. was still a washing or Neutralization process and subsequent drying for 20 min at 80 ° C followed.

3. Crosslinking by a condensation reaction of Si 1 anol groups 1 0

PAN copolymers with 5 to 35 mol% of methacrylic acid [3- (trimethoxyl silyl) propyl ester or 2 to 7 mol% of triethoxyvinyl silane were prepared in the usual way. The respective PAN copolymer obtained was extracted into a cast film in the form of a DMF solution (10 to 22% solids; also possible in DMAc, DMSO and NMP as a solvent) and by subsequent phase inversion in water or an aqueous solution of 0.1 up to 1.0 n HC1 or 0.1 to 1.0 H ₂ S0 _{4 formed} into a membrane. The saponification of the ethoxysilyl groups to Si 1 anol groups was most advantageously carried out in the tempering bath with an aqueous solution of 0.1 n to 1.0 n HCl or 0.1 to 1.0 n H ₂ S0 ₄ at 60 to 80 ° C. for 20 to 60 min. The saponifications could also be carried out using an aqueous solution of 0.1 to 1.0 N HCl or 0.1 to 1.0 N H ₂ S0. at 20 to 25 ° C (room temperature) for 16 to 24 h either in the precipitation bath or in a separate saponification bath. In any case, drying and an associated thermal condensation reaction of the Si 1 anol groups (60 to 80 ° C., 20 to 60 min) were required. When using H ^ SO, a washing or neutralization process with subsequent drying was added.

4. Cross-linking by reactions of epoxy with acid amide groups

PAN copolymers with 5 to 35 mol% of acrylamide or 5 to 35 mol were used. -% methacrylic aid produced. The respective PAN copolymer obtained was drawn out in the form of a DMF solution (5 to 14% solids, also possible in DMAc, DMSO and NMP as solvent) with a crosslinking agent to give a cast film and formed into a membrane by a subsequent phase inversion in water. The crosslinking agent was 11 following: Bi-sphenol -A / F-diglycidyl ether, M <700 g / mol, molar ratio of acid amide group: Bi-sphenol -A / F-diglycidyl ether = 2: 1. The crosslinking was carried out in an annealing bath with an aqueous solution of 0.1 n to 1.0 n NaOH or 0.1 n to 1.0 n K0H at 60 to 90 ° C. for a period of 15 to 30 min. A neutralization or washing process was then carried out with 0.1 N to 0.5 N aqueous HCl and drying at 60 to 90 ° C. for 10 to 60 min.

The standing and processing times from the time of adding the crosslinking agent were not subject to any restrictions (casting solution examined at 20 to 25 ° C. for up to 8 days). Attempts to cross-link the polymer solution formed by phase inversion in water to form a membrane (polymer and crosslinker in demethyl for amid) at 70 to 90 ° C in pure water (without the addition of alkali such as NaOH) also failed after 4 hours.

5. Crosslinking by reaction of aldehyde groups with acid amide groups

PAN copolymers with 5 to 35 mol% of acrylamide and 5 to 35 mol% of methacryl amide were produced. The corresponding PAN copolymer was drawn out in the form of a DMF solution (5 to 14% solids) with a maximum of 5% by volume (based on the total solution) of a 50% aqueous glutardialdehyde solution as a crosslinking agent to give a cast film. The membrane was formed by subsequent phase inversion in water. For crosslinking, the oven was annealed at 60 to 90 ° C. for 20 to 60 min. It was then washed and dried again at 60 to 90 ° C. for 15 to 30 min. 1 2

The pore size of the membranes according to the invention was set as follows:

The pore size setting was carried out analogously to the conventional forming process by varying the molar masses of the copolymer used, the solids content of the casting solution, the temperature of the precipitation bath, the temperature and duration of the te and the drying temperature and duration. The following two examples illustrate the possibilities for setting the pore size:

a) membranes made of poly (acrylic nitri 1 -co-glycidyl methacrylate) (15.4 mol% glycidyl methacrylate in the polymer) solution of 25% by weight polymer in DMF (at 50 ° C.), Filter, add 0.169 g of crosslinker (triethylene tetramine) to 1 g of polymer, degassing, pulling out the cast film, phase inversion in water, tempering at 70 ° C. for 20 min.

b) Membranes made of poly (acrylic ni tri 1 -co-acrylic amid) (15.0 mol% acrylic id in the polymer)

Solution of 5% by mass of polymer in DMF (at 80 ° C.), filtering, addition of 0.95 g of crosslinking agent (bisphenol -F / F-di-glycidyl ether, M <700 g / mol) to 1 g of polymer Room temperature, degassing, pulling out the cast film, phase inversion in water, tempering at 70 ° C for 30 min in 0.1 N aqueous NaOH, neutralizing in 0.5% aqueous HC1 at 22 ° C for 15 min or washing and drying at 80 ° C in a drying cabinet for 15 min. 1 3

According to the invention, pore membranes are thus provided on the basis of membrane-forming polyacrylnitri copolymers which are chemically crosslinked, the crosslinking being able to take place during the membrane formation by phase inversion in water and / or afterwards.

The subject matter is also a process for the production of a stable PAN membrane according to the teaching of the claims and the use of this PAN membrane for ultra and nanofiltration.

The method according to the invention enables inexpensive production of such a 1-layer, stable 1-PAN pore membrane while maintaining the previously used technological process (formation, tempering in water, drying) and the equipment already available for this. In the case of poly (acrylic ni tri 1 - co-acrylic amide) it is also possible to use the already known industrial suspension polymerisation method for producing the pure polyacryl ni tri 1 s largely unchanged.

14

Membrane no. 1 2

Membrane production Bandgießmaschine Bandgi eßmaschi ne carrier material Histar TH 100 Histar TH 100 drawing speed 2.0 m / min. , 0 m / min. Pouring gap over fleece 150 μm 150 μm air temperature 22 ° C 22 ° C precipitation bath / temperature water / 22 ° C water / 4 ° C

Aftertreatment I *) membrane untempered - membrane untempered and dried and dried at 22 ° C. net at 22 ° C.

Membrane test I

Membrane thickness (µm) 223; 214; 225 208; 216; 205 Test cell 1 e Mi 11 ipore Mi 11 i pore test pressure (MPa) 0.3 0.3 J _w O / h. ) 1273.4 225.7

Aftertreatment II *) Membrane tempered Membrane tempered pert at 70 ° C and at 70 ° C and dried when dried at 22 ° C 22 ° C

Membrane test II

Membrane thickness (μm) 213 - 216 209 test cell 1 e Mi 11 ipore Mi 11 i pore test pressure (MPa) 0.3 0.3 J _w O / hi) 152.7 78.3

^Retention Dextran T250 ^(%) 0 11.9

^J V, dextran T250 ^{(1 / hm J} 32.0 17.9

With individual pieces of the membranes formed under different conditions (membrane numbers 1-4), a different aftertreatment was carried out in some cases. 15

Membrane no. 3 4

Membrane production Bandgießmaschi ne Bandgi eßmaschi ne carrier material al Histar TH 100 Histar TH 100 drawing speed 2.0 m / min. 2.0 m / min. Pouring gap over fleece 200 μm 300 μm air temperature 22 ° C 22 ° C precipitation bath / temperature water / 22 ° C water / 22 ° C

Aftertreatment I membrane annealed membrane annealed at 70 ° C and at 70 ° C and dried at 80 ° C dries at 80 "C.

Membrane test I

Membrane thickness (μm) 159 - 163 167 - 173 test cell 1 e Mi 11 i pore Mi 11 i pore test pressure (MPa) 0.3 0.3 J _w 0 / hι /) 745.0 378.0

Aftertreatment II Membrane tempered Membrane tempered at 70 ° C, at 70 ° C and dried when dried at 80 ° C at 80 ° C and 2h at and after 19h in DMF at 150 ° C after 22 ° C

Membrane test II

Membrane thickness (μm) 161 - 165 168 - 174 test cell 1 e Mi 11 ipore M i 11 ipo re test pressure (MPa) 0.3 0.3 J _w d / hι /) 169.0 246.0

Aftertreatment III membrane tempered membrane tempered at 70 ° C, at 70 ° C and dried when dried at 80 ° C and 80 ° C for 4 hours and after 60 hours in DMF at 150 ° C after 22 ° C

Membrane test III

Membrane thickness (μm) 160 - 164 166 - 171 test cell 1 e Mi 11 i pore Mi 11 i pore test pressure (MPa) 0.3 0.3 * _W (1 / hι /) 132.0 179.3

Claims

16 patent claims

1. solvent stabilized PAN membrane, in particular for ultra and nanofiltration, based on polyacrylonitrile (PAN) and a comonomer copolymerized therewith, the PAN membrane being known by per se membrane formation by phase inversion Water was formed, obtainable by using a comonomer which has at least one reactive group which can bring about crosslinking of the membrane by reaction with itself or with a crosslinking agent, and the crosslinking reaction is carried out during and / or after the membrane formation.

2. PAN membrane according to claim 1, obtainable by using a comonomer which has an epoxy, alkoxysilyl or acid amide group as the reactive group. 17 * _

3. PAN membrane according to claim 2, obtainable in that the comonomer used is methacrylic acid glycidyl ester, methacrylic acid 3 - (trimethoxysilyl) propyl ester, tri ethoxyvi nyl silane, acrylic acid amide or methacrylic acid amide.

4. PAN membrane according to one of the preceding claims, obtainable in that the comonomer makes up 3 to 49 mol%, in particular 5 to 35 mol%, of the PAN copolymer.

5. PAN membrane according to one of the preceding claims, obtainable by using a crosslinking agent having at least two functional groups.

6. PAN membrane according to claim 5, obtainable in that as crosslinking agent hexamethyl endi amine, diethyl entriamine, triethyl entetramine, tetraethyl enpentamine, 2,4,6-triamino-1, 3, 5-tri azi n, 1, 3-phenylendiamine, 1,4-phenylenediamine, 3, 5-diamine nobenzoic acid, 2,6-diamine no-4-phenyl -1.3.5-triazine and 2, 6-Di ami nopyri di n can be used.

7. A process for the production of a 1 ösemi ttel stable 1 PAN membrane, in particular for ultra and nanofiltration, based on polyacrylic nitrite, wherein in each case known per se, acrylonitrile is copolymerized with the comonomer and the membrane by membrane formation by means of phase inversion in water, characterized in that a comonomer is used which has at least one reactive group which can bring about crosslinking of the membrane by reaction with itself or with a crosslinking agent, and the crosslinking reaction during and / or after the Membrane formation is carried out. 18th

8. The method according to claim 7, characterized in that the measures described in claims 2 to 6 are carried out.

9. Use of the PAN membrane according to one of claims 1 to 6 for ultra and nanofiltration.