SOLVENT-RESISTANT POLYMERIC NANOFILTRATION MEMBRANE, PREPARATION METHOD AND USE THEREOF

Abstract

The invention a solvent-resistant polymeric nanofiltration membrane and preparation method thereof. The method includes subjecting a diamine monomer and a dianhydride monomer to cyclization imidization in a first polar organic solvent at 160 to 230° C., to form a polyimide, wherein the diamine monomer includes a diamine monomer with a carboxyl group and a diamine monomer without a carboxyl group; dissolving the polyimide in a second polar organic solvent, to form a membrane-forming solution; performing phase inversion to obtain an intermediate membrane; treating the intermediate membrane with an organic solution of a metal salt, so that the metal ion is coordinated and cross-linked with the carboxyl group in the polyimide, to obtain a solvent-resistant polymeric nanofiltration membrane, wherein the metal salt is a divalent and/or a multi-valent metal salt. The invention also discloses use of the solvent-resistant polymeric nanofiltration membrane in the separation and/or purification of a compound.

Claims

1. A method for preparing a solvent-resistant polymeric nanofiltration membrane, comprising steps of: (1) reacting a diamine monomer with a dianhydride monomer in the presence of a catalyst in a first polar organic solvent at 160-230° C., to form a polyimide; wherein the diamine monomer comprises at least one diamine monomer with a carboxyl group and at least one diamine monomer without a carboxyl group; the structural formula of the polyimide comprises a first repeating unit and a second repeating unit, the first repeating unit comprising at least one polymeric segment of the dianhydride monomer and the diamine monomer with a carboxyl group, the second repeating unit comprising at least one polymeric segment of the dianhydride monomer and the diamine monomer without a carboxyl group; and wherein the boiling point of the first polar organic solvent is higher than 160° C.; (2) dissolving the polyimide in a second polar organic solvent, to form a membrane-forming solution with a concentration of 10 wt % to 40 wt %; then, performing phase inversion after the membrane-forming solution is formed into a membrane, to obtain an intermediate membrane; (3) treating the intermediate membrane with an organic solution of a metal salt, so that the metal ion is coordinated and cross-linked with the carboxyl group in the polyimide, to obtain the solvent-resistant polymeric nanofiltration membrane after the cross-linking is completed, wherein the metal salt is selected from divalent and/or multi-valent metal salts.

2. The method according to claim 1, wherein in step (1), the diamine monomer with a carboxyl group is selected from at least one monomer with a structural formula of NH.sub.2—R″—NH.sub.2, in which R″ in each monomer is selected from the following structural formulas: ##STR00017##

3. The method according to claim 1, wherein in step (1), the diamine monomer without a carboxyl group is selected from at least one monomer with a structural formula of NH.sub.2—R′—NH.sub.2, in which R′ in each monomer is selected from the following structural formulas: ##STR00018## ##STR00019##

4. The method according to claim 1, wherein in step (1), the dianhydride monomer is selected from at least one monomer with a structural formula of ##STR00020## in which R in each monomer is selected from the following structural formulas: ##STR00021##

5. The method according to claim 1, wherein in step (1), the molar ratio of the dianhydride monomer, diamine monomer with a carboxyl group and diamine monomer without a carboxyl group is 10:0.1-9.9:0.1-9.9.

6. The method according to claim 1, wherein in step (2), a method of preparing a flat membrane or a method of preparing a hollow fiber membrane is used to form the membrane-forming solution into a membrane.

7. The method according to claim 1, wherein in step (3), the divalent metal salt is selected from the group consisting of a copper salt, a nickel salt, a zinc salt, a cobalt salt, a magnesium salt, a calcium salt and any combination thereof, and the multi-valent metal salt is selected from the group consisting of an iron salt, a lanthanum salt, an aluminum salt and any combination thereof.

8. A solvent-resistant polymeric nanofiltration membrane prepared by the method of claim 1, comprising a plurality of polyimide polymeric segments, wherein the polyimide polymeric segments comprise the first repeating unit and the second repeating unit, and the ratio of polymerization degrees of the first repeating unit and the second repeating unit is 1-100:1-100; and the carboxyl groups in the different polyimide polymeric segments are coordinated and cross-linked with metal ions.

9. The solvent-resistant polymeric nanofiltration membrane according to claim 8, wherein in each polyimide polymeric segment, the number of the first repeating unit is 10-1000 and the number of the second repeating unit is 10-1000.

10. Use of the solvent-resistant polymeric nanofiltration membrane of claim 8 in the separation and/or purification of a compound in an organic solution.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0066] FIG. 1 is a schematic diagram of the ion cross-linking effect of a solvent-resistant polymeric nanofiltration membrane in a specific embodiment of the present invention;

[0067] FIG. 2 is a schematic diagram of a synthetic route of a polyimide copolymer containing carboxyl groups in an embodiment of the present invention;

[0068] FIG. 3 is a principle diagram of the ion cross-linking effect of a solvent-resistant polymeric nanofiltration membrane in an embodiment of the present invention;

[0069] FIG. 4 is a photo showing that a solvent-resistant polymeric nanofiltration membrane in Example 4 of the present invention is stably present in various organic solvents;

[0070] FIG. 5 is a comparison of mechanical strength between a solvent-resistant polymeric nanofiltration membrane in Example 4 of the present invention and an uncross-linked polyimide membrane;

[0071] FIG. 6 is a scanning electron micrograph of a cross-section of a solvent-resistant polymeric nanofiltration membrane in Example 4 of the present invention;

[0072] FIG. 7 is a comparison of compaction resistance between a solvent-resistant polymeric nanofiltration membrane in Example 4 of the present invention and an uncross-linked polyimide membrane; and

[0073] FIG. 8 is a graph showing changes in the flux of a solvent-resistant polymeric nanofiltration membrane in Example 4 of the present invention over time.

MEANING OF SYMBOLS IN THE DRAWINGS

[0074] M.sup.n+ in FIG. 1 represents a divalent or multi-valent metal ion.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0075] A detailed description of the present invention will be further given below in detail with reference to embodiments. The following embodiments are merely used for illustrating the present invention, and not intended to limit the scope of the present invention.

[0076] The materials involved in the examples are: DURENE represents 2,3,5,6-tetramethyl-1,4-phenylenediamine; DABA represents 3,5-diaminobenzoic acid; 6FDA represents 4,4′-(hexafluoroisopropylene) diphthalic anhydride; Toluene; Ethanol; DMF represents N,N′-dimethylformamide; Acetone; Methanol; Acetonitrile.

[0077] A preferred embodiment is described below, and the present invention is not limited thereto.

EMBODIMENT

[0078] DURENE and DABA (a total amount of 1 mol) are added to 300 mL of an m-cresol solution at room temperature, 44.4 g of 6FDA is added in portions, stirring is performed for 24 h until a uniform solution is formed, and then 50 mL of anhydrous toluene is added. The system is gradually heated to 200° C. for 6 h. The temperature is lowered, and the product solution is poured into methanol with constant stirring. The obtained product is vacuum dried at 120° C. for 12 h to obtain a polyimide material.

[0079] The chemical formula and synthetic route of the polyimide copolymer containing carboxyl groups (PI—COOH) in the formed polyimide material are shown in FIG. 2, where m is an integer greater than or equal to 1, and n is an integer greater than or equal to 1, and n/m=10˜1000:1000˜10.

[0080] The polyimide material is dissolved in a mixed solvent of N,N-dimethylformamide and 1,4-dioxane (10:1 to 1:1), stirred overnight, and left for 24 h to remove bubbles to obtain a 10-40 wt % membrane-forming solution.

[0081] Preparation of a flat membrane material: the height of a doctor blade is adjusted to 100-500 μm, the humidity is controlled at 30-40%, the membrane-forming solution is poured on a glass plate for casting; it is allowed to stand in the air for 10-100 s, the glass plate is transferred to a water bath, phase inversion treatment is carried out for 0.5-2 h; a membrane formed after phase inversion treatment is transferred to a fresh water bath for 24 h, the residual solvent is washed off to ensure the completion of phase inversion; the intermediate membrane is stored in methanol.

[0082] Preparation of a hollow fiber membrane material: the membrane-forming solution is filtered through a screen, a filtrate is transferred to a membrane-forming solution tank, and the filtrate is degassed at a temperature of 15-50° C.; the degassed filtrate is subjected to spinning treatment through a concentric hole spinneret with a central hole, where a core liquid fluid is extruded through the central hole of the spinneret, and the degassed filtrate is extruded through an annular gap, forming a hollow fiber membrane.

[0083] A 0.05-0.5 mol/L methanol solution of copper nitrate is prepared, and the intermediate membrane is immersed in the methanol solution of copper nitrate for cross-linking for 24 h at a temperature of 20-50° C. The formed membrane is removed, washed with methanol, and stored in methanol.

[0084] The molecular weight cut-off of the solvent-resistant polymeric nanofiltration membrane is 850 Da; and the membrane flux is 10-50 Lm.sup.−2 h.sup.−1 bar.sup.−1 at an operating pressure of 1 MPa. It can be applied in the fields of separation and purification of dye molecules, drug molecules and natural products, and recovery of organic solvents.

[0085] The technical solutions of the present invention will be further explained below in conjunction with several examples.

Example 1

[0086] DURENE (0.09 mol, 14.8 g) and DABA (0.01 mol, 1.5 g) were added to 300 mL of an m-cresol solution at room temperature, 44.4 g (0.1 mol) of 6FDA was added in portions, stirring was performed for 24 h until a uniform solution was formed, and then 50 mL of anhydrous toluene and a catalyst quinoline were added to the mixture. The system was gradually heated to 200° C. and held for 6 h. The temperature was lowered, and the product solution was poured into methanol with constant stirring. The obtained product was vacuum dried at 120° C. for 12 h to obtain a polyimide material PI—COOH.sub.10 with a degree of polymerization (m+n) of above 300 and m:n=9:1.

[0087] The polyimide material was dissolved in a mixed solvent of N,N-dimethylformamide and 1,4-dioxane (3:1), stirred overnight, and left for 24 h to remove bubbles to obtain a 22 wt % membrane-forming solution.

[0088] Preparation of a flat membrane material: the height of a doctor blade was adjusted to 300 the humidity was controlled at 30-40%, the membrane-forming solution was poured on a glass plate for casting; it was allowed to stand in the air for 10 s, and the glass plate was transferred to a water bath. After 1 h, a membrane formed after phase inversion treatment was transferred to a fresh water bath for 24 h, the residual solvent was washed off to ensure the completion of phase inversion; the intermediate membrane was stored in methanol.

[0089] Preparation of a hollow fiber membrane material: the membrane-forming solution was filtered through a screen, a filtrate was transferred to a membrane-forming solution tank, and the filtrate was degassed at a temperature of 35° C.; the degassed filtrate was subjected to spinning treatment through a concentric hole spinneret with a central hole, where a core liquid fluid was extruded through the central hole of the spinneret, and the degassed filtrate was extruded through an annular gap, forming a hollow fiber membrane. During the preparation process, the humidity was controlled at 30-40% and the temperature at 20-25° C.

[0090] A 0.1 mol/L methanol solution of copper nitrate was prepared, and the intermediate membrane was immersed in the methanol solution of copper nitrate for cross-linking for 24 h at a temperature of 40° C. The formed membrane was removed, washed with methanol, and stored in methanol.

Example 2

[0091] The synthesis method of the polyimide material was the same as in Example 1, except that the amount of DURENE was 0.08 mol (13.1 g) and the amount of DABA was 0.02 mol (3.0 g) to obtain a polyimide material PI—COOH.sub.20 with a degree of polymerization (m+n) of above 300 and m:n=4:1.

[0092] The preparation method of the solvent-resistant polymeric nanofiltration membrane was the same as in Example 1.

Example 3

[0093] The synthesis method of the polyimide material was the same as in Example 1, except that the amount of DURENE was 0.07 mol (1.5 g) and the amount of DABA was 0.03 mol (4.6 g) to obtain a polyimide material PI—COOH.sub.30 with a degree of polymerization (m+n) of above 300 and m:n=7:3.

[0094] The preparation method of the solvent-resistant polymeric nanofiltration membrane was the same as in Example 1.

Example 4

[0095] The synthesis method of the polyimide material was the same as in Example 1, except that the amount of DURENE was 0.06 mol (9.8 g) and the amount of DABA was 0.04 mol (6.1 g) to obtain a polyimide material PI—COOH.sub.40 with a degree of polymerization (m+n) of above 300 and m:n=3:2.

[0096] The solvent-resistant polymeric nanofiltration membrane was a flat membrane, and the preparation method thereof was the same as in Example 1.

[0097] The prepared solvent-resistant polymeric nanofiltration membrane is stably present in various organic solvents. As shown in FIG. 4, in various polar organic solvents, the polymeric nanofiltration membrane of the present invention has stable morphology without obvious swelling and morphological changes, indicating that its solvent resistance is better. The organic solvents in FIG. 4 are Toluene, Ethanol, DMF, Acetone, Methanol, and Acetonitrile from left to right.

[0098] For comparison, a polyimide material PI—COOH.sub.40 was prepared according to the above-mentioned method of this example, and was finished as a flat membrane, that is, it was not subjected to cross-linking in a methanol solution of copper nitrate. FIG. 5 is the comparison results of tensile strength between the solvent-resistant polymeric nanofiltration membrane (PI—COOH.sub.40—Cu.sup.2+) prepared in this example and the polyimide membrane (PI—COOH.sub.40) not cross-linked in a methanol solution of copper nitrate. It can be seen from the figure that the solvent-resistant polymeric nanofiltration membrane prepared in this example has a higher breaking strength of about 28 MPa and a tensile modulus of 595.04 MPa, and the uncross-linked polyimide membrane has a breaking strength of about 12 MPa, and a tensile modulus of 278.37 MPa.

[0099] FIG. 6 is a scanning electron micrograph of the polymeric nanofiltration membrane prepared in this example. It can be seen from the figure that the surface of the membrane has a complete dense layer structure, a good supporting layer of finger holes is retained inside the membrane, and the overall structure of the membrane is not deformed.

[0100] FIG. 7 is the comparison of compaction resistance between the solvent-resistant polymeric nanofiltration membrane (PI—COOH.sub.40—Cu.sup.2+) in this example and the polyimide membrane (PI—COOH.sub.40) not cross-linked in a methanol solution of copper nitrate. It can be seen from the figure that the flux of the uncross-linked membrane decreases sharply with time, while the cross-linked solvent-resistant polymeric nanofiltration membrane maintains a stable flux level, and after 8 h operation, it still maintains above 80% of the original flux, indicating that the membrane has better compaction resistance.

[0101] FIG. 8 shows the change of the flux of the polymeric nanofiltration membrane prepared in this example over time. It can be seen from the figure that during the continuous operation of up to one week, the membrane flux does not change significantly, and its ratio to the initial flux fluctuates between 99-110%, and the retention rate of the target molecule remains above 99%.

[0102] In addition, the nanofiltration membranes of Examples 2-4 were used to separate Coomassie Brilliant Blue in methanol, and the specific steps were as follows:

[0103] A methanol solution of Coomassie Brilliant Blue was filtered at 1 MPa, and the results showed that the nanofiltration membranes of Examples 2-4 had a retention rate of 95-99% for Coomassie Brilliant Blue, and the flux was 15-30 Lm.sup.−2 h.sup.−1 bar.sup.−1.

Example 5

[0104] The synthesis method of the polyimide material was the same as in Example 1, except that the amount of DURENE was 0.05 mol (8.2 g) and the amount of DABA was 0.05 mol (7.6 g) to obtain a polyimide material PI—COOH.sub.50 with a degree of polymerization (m+n) of above 300 and m:n=1:1.

[0105] The preparation method of the solvent-resistant polymeric nanofiltration membrane was the same as in Example 1.

Example 6

[0106] This example serves as a comparative example. The synthesis method of the polyimide material was the same as that of Example 1, except that in this example, only a diamine monomer with a carboxyl group, DABA (15.2 g) was added to obtain a polyimide material PI—COOH.sub.100.

[0107] The preparation method of the solvent-resistant polymeric nanofiltration membrane was the same as in Example 1.

[0108] The polymeric nanofiltration membrane prepared in this example was used to filter a methanol solution of Coomassie Brilliant Blue at 1 MPa. The results show that the retention rate of Coomassie Brilliant Blue is 98-99%, and the flux is 2-5 Lm.sup.−2 h.sup.−1 bar.sup.−1.

Example 7

[0109] The synthesis method of the polyimide material was exactly the same as in Example 4.

[0110] The preparation method of the solvent-resistant polymeric nanofiltration membrane was the same as in Example 1, except that the salt solution used was replaced with 0.1 mol/L copper sulfate.

Example 8

[0111] The synthesis method of the polyimide material was exactly the same as in Example 4.

[0112] The preparation method of the solvent-resistant polymeric nanofiltration membrane was the same as in Example 1, except that the salt solution used was replaced with 0.1 mol/L lanthanum chloride. The polymeric nanofiltration membrane prepared in this example was used to filter a methanol solution of Coomassie Brilliant Blue at 1 MPa. The results show that the retention rate of Coomassie Brilliant Blue is 95-99%, and the flux is 15-25 Lm.sup.−2 h.sup.−1 bar.sup.−1.

Example 9

[0113] The synthesis method of the polyimide material was the same as in Example 1, except that DURENE was replaced with 4,4′-diaminobenzophenone in an amount of 0.06 mol (12.7 g), and the amount of DABA was 0.04 mol (6.1 g), to obtain a polyimide material PI′—COOH.sub.40 having a structural formula below:

##STR00014##

[0114] in which m:n=3:2.

[0115] The preparation method of the solvent-resistant polymeric nanofiltration membrane was the same as in Example 1.

[0116] The polymeric nanofiltration membrane prepared in this example was used to filter a methanol solution of Coomassie Brilliant Blue at 1 MPa. The results show that the retention rate of Coomassie Brilliant Blue is 95-99%, and the flux is 15-20 Lm.sup.−2 h.sup.−1 bar.sup.−1.

Example 10

[0117] The synthesis method of the polyimide material was the same as in Example 1, except that DURENE was replaced with 5(6)-amino-1-(4-aminophenyl)-1,3,3-trimethylindan in an amount of 0.06 mol (16.9 g), the amount of DABA was 0.04 mol (6.1 g), and 6FDA was replaced with 3,3′,4,4′-benzophenonetetracarboxylic dianhydride in an amount of 32.2 g, to obtain a polyimide material PI″—COOH.sub.40 having a structural formula below:

##STR00015##

[0118] in which m:n=3:2.

[0119] The preparation method of the solvent-resistant polymeric nanofiltration membrane was the same as in Example 1.

[0120] The polymeric nanofiltration membrane prepared in this example was used to filter a methanol solution of Coomassie Brilliant Blue at 1 MPa. The results show that the retention rate of Coomassie Brilliant Blue is 97-99%, and the flux is 15-20 Lm.sup.−2 h.sup.−1 bar.sup.−1.

Example 11

[0121] The synthesis method of the polyimide material was the same as in Example 1, except that DURENE was replaced with 4,4′-diaminodiphenylmethane in an amount of 0.06 mol (11.9 g), and the amount of DABA was 0.04 mol (6.1 g), and 6FDA was replaced with 3,3′,4,4′-benzophenone tetracarboxylic dianhydride in an amount of 32.2 g, to obtain a polyimide material PI″—COOH.sub.40 having a structural formula below:

##STR00016##

[0122] in which m:n=3:2.

[0123] The preparation method of the solvent-resistant polymeric nanofiltration membrane was the same as in Example 1.

[0124] The polymeric nanofiltration membrane prepared in this example was used to filter a methanol solution of Coomassie Brilliant Blue at 1 MPa. The results show that the retention rate of Coomassie Brilliant Blue is 98-99%, and the flux is 10-15 Lm.sup.−2 h.sup.−1 bar.sup.−1.

[0125] The following descriptions will be made regarding other implementations and changes of the present invention:

[0126] 1. The above examples use DURENE or 4,4′-diaminobenzophenone or 5(6)-amino-1-(4-aminophenyl)-1,3,3-trimethylindan or 4,4′-diaminodiphenylmethane as a common diamine monomer, DABA as a diamine monomer with a carboxyl group, m-cresol as a strong polar solvent with a high boiling point, 6FDA or 3,3′,4,4′-benzophenone tetracarboxylic dianhydride as an aromatic acid dianhydride monomer, a mixed solvent of N,N-dimethylformamide and 1,4-dioxane as an organic solvent, water as a component of a phase inversion bath, and copper nitrate, copper sulfate, and lanthanum chloride as metal salts. The present invention is not limited thereto, and various other materials may be combined to prepare different kinds of polyimide materials, and different kinds of metal salts may be used to form different kinds of solvent-resistant polymeric nanofiltration membranes.

[0127] 2. The reaction temperature and humidity conditions, reaction time, and specific parameters used in the above examples can all be adjusted according to actual needs. This embodiment does not apply limitations upon these details.

[0128] The description above merely gives the preferred embodiment of the present invention, and is not intended to limit the present invention. It should be noted that several modifications and variations can be made by those of ordinary skill in the art without departing from the technical principles of the invention, and these modifications and variations should be considered within the scope of the present invention.