A polyamide ultrafiltration membrane with a small pore size and a preparation method thereof

Abstract

The present invention relates to the technical field of ultrafiltration membranes, and particularly relates to a small-aperture polyamide ultrafiltration membrane and a preparation method thereof. The membrane is prepared by this method. The method includes putting an ultrafiltration base membrane into an aqueous solution, after the first soaking treatment, and then carrying out the first vertical placement treatment; the aqueous solution includes polyamine; putting the ultrafiltration base membrane after the first vertical placement treatment into an oil-phase solution, after the second soaking treatment, and then carrying out the second vertical placement treatment; the oil-phase solution includes polyacyl chloride; after the ultrafiltration base membrane after the second vertical placement treatment is dried, it is then placed in an amino crosslinking agent solution for the third soaking treatment to obtain a small-aperture polyamide ultrafiltration membrane. The present invention can not only solve the problem of low permeation flux existing in the existing ultrafiltration membranes, but also solve the problem that polyamide nanofiltration membranes cannot meet the effective separation of dyes and salts.

Description

Technical Field

[0001] The present invention relates to the technical field of ultrafiltration membranes, and particularly to a small-aperture polyamide ultrafiltration membrane and a preparation method thereof. Background Art

[0002] In recent years, the wastewater treatment problems in various industries have received continuous attention and emphasis. Separating and recovering substances in wastewater not only alleviates environmental pollution problems but also enables the recycled resources to be reused. In the printing and dyeing industry, printing and dyeing wastewater contains a large amount of organic matter, dyes, heavy metal ions, etc. Common treatment methods include adsorption, coagulation, chemical oxidation, electrolysis, biological methods, and membrane separation. Among them, as a separation technology, membrane separation can be preferably applied to the printing and dyeing industry due to its low energy consumption, small floor area, simple operation, environmental protection, and high efficiency.

[0003] The ultrafiltration membrane prepared by the phase inversion method is simple to manufacture and relatively low in cost. Some small-aperture ultrafiltration membranes can also separate dyes and salts in printing and dyeing wastewater well, but their permeation flux is low, which greatly limits their application in the printing and dyeing industry. In addition, the retention molecular weight of common polyamide nanofiltration membranes is 150 - 300 Da, and they have a high retention rate for both dyes (dyes can generally be divided into cationic, neutral, and anionic types, with molecular weights in the range of 300 - 1000 Da) and salts, and cannot meet the requirement of effective separation of dyes and salts.

[0004] In summary, it is necessary to develop a small-aperture polyamide ultrafiltration membrane and a preparation method thereof. On the one hand, it is used to solve the problem of low permeation flux of existing ultrafiltration membranes, and on the other hand, it is used to solve the problem that polyamide nanofiltration membranes cannot meet the requirement of effective separation of dyes and salts. Summary of the Invention

[0005] The object of the present invention is to provide a small-aperture polyamide ultrafiltration membrane and a preparation method thereof. The specific technical solutions are as follows:

[0006] In the first aspect, the present invention provides a preparation method of a small-aperture polyamide ultrafiltration membrane, including:

[0007] Step S1: Put the ultrafiltration base membrane into an aqueous solution, after the first soaking treatment, and then perform the first vertical placement treatment; the aqueous solution includes polyamine;

[0008] Step S2: Put the ultrafiltration base membrane after the first vertical placement treatment into an oil-phase solution, after the second soaking treatment, and then perform the second vertical placement treatment; the oil-phase solution includes polyacyl chloride;

[0009] Step S3: After drying the ultrafiltration base membrane after the second vertical placement treatment, immerse it in an amino crosslinking agent solution for the third time to obtain a polyamide ultrafiltration membrane with small pore size; the amino crosslinking agent used in the amino crosslinking agent solution contains chloromethyl; the mass concentration of the amino crosslinking agent used in the amino crosslinking agent solution is 2%-4%.

[0010] Optionally, the amino crosslinking agent includes at least one of 2,5-bis(chloromethyl)-p-xylene, bis(chloromethyl) sulfide, 9,10-bis(chloromethyl) anthracene, and 2,4-bis(chloromethyl) trimethylbenzene.

[0011] Optionally, the polyamine includes at least one of triamterene, 1,4,10-trioxa-7,13-diazacyclopentadecane, 1,4,8,12-tetraazacyclopentadecane, and 1,7,11,17-tetraoxa-2,6,12,16-tetraazacycloicosane; the mass concentration of the polyamine in the aqueous solution is 0.4%-1.0%.

[0012] Optionally, the aqueous solution further includes an acid solution regulator and a base solution regulator; the acid solution regulator includes at least one of acrylic acid, camphorsulfonic acid, and citric acid; the base solution regulator includes at least one of sodium hydroxide and potassium hydroxide; the acid solution regulator and the base solution regulator are used in combination to adjust the pH value of the aqueous solution to 10.5-11.5.

[0013] Optionally, the polyacyl chloride includes at least one of isophthaloyl chloride, terephthaloyl chloride, and 1,3,5-benzenetricarbonyl chloride; the mass concentration of the polyacyl chloride in the oil phase solution is 0.08%-0.15%.

[0014] Optionally, the oil phase solution further includes an organic solvent; the organic solvent includes at least one of cyclohexane, n-hexane, petroleum ether, and m-xylene.

[0015] Optionally, the ultrafiltration base membrane includes polyethersulfone, polysulfone, polyacrylonitrile, or polyvinylidene fluoride.

[0016] Optionally, the soaking time for both the first soaking treatment and the second soaking treatment is 10-30 s; the placement time for both the first vertical placement treatment and the second vertical placement treatment is 2-5 min.

[0017] Optionally, the treatment temperature for the drying treatment is 50-80 °C, and the treatment time is 2-10 min; the soaking time for the third soaking treatment is 1-3 min.

[0018] In a second aspect, the present invention provides a polyamide ultrafiltration membrane with a small pore size, which is prepared by using the preparation method of the polyamide ultrafiltration membrane with a small pore size described above.

[0019] Applying the technical solution of the present invention has at least the following beneficial effects:

[0020] (1) The preparation method of a polyamide ultrafiltration membrane with a small pore size provided by the present invention can not only solve the problem of low permeation flux existing in the existing ultrafiltration membranes, but also solve the problem that the polyamide nanofiltration membrane cannot effectively separate dyes and salts. Specifically, the polyamide ultrafiltration membrane prepared by the present invention contains unreacted amino groups of polyamine, which increases the hydrophilicity of the polyamide ultrafiltration membrane, thereby improving the permeation flux of the membrane. After the polyamine and polyacyl chloride are interfacially polymerized to form a polyamide membrane by the preparation method adopted by the present invention, the polyamide membrane is subjected to a third immersion treatment with an amino crosslinking agent solution. Among them, the C-Cl bond in the chloromethyl group of the amino crosslinking agent connects some unreacted amino groups to form a network structure with smaller spatial pores. At the same time, a specific mass concentration of the amino crosslinking agent is used to regulate the pore size and molecular weight cut-off of the membrane sheet, so as to simply and efficiently prepare a polyamide ultrafiltration membrane with a small pore size. This polyamide ultrafiltration membrane with a small pore size can retain most of the dyes while still maintaining a low desalination rate, realizing the effective separation of dyes and salts. If the mass concentration of the amino crosslinking agent is too high, although it can accelerate the reaction rate, it will cause an increase in the crosslinking degree of the membrane sheet, a reduction in the pore size and molecular weight cut-off, and it is impossible to effectively separate the relatively small molecules of dyes and salts; if the mass concentration of the amino crosslinking agent is too low, it will cause insufficient crosslinking degree of the membrane sheet, an increase in the pore size and molecular weight cut-off, and it is impossible to effectively separate dyes and salts.

[0021] (2) The immersion time adopted for the third immersion treatment in the present invention is 1-3 minutes. If the immersion time is too long, it will cause an increase in the crosslinking degree of the membrane sheet, a further reduction in the pore size and molecular weight cut-off, and it is impossible to effectively separate the relatively small molecules of dyes and salts; if the immersion time is too short, it will cause an increase in the crosslinking degree of the membrane sheet, a further increase in the pore size and molecular weight cut-off, and it is impossible to effectively separate dyes and salts. Detailed implementation mode

[0022] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art belong to the scope of protection of the present invention.

[0023] Example 1:

[0024] A preparation method of a polyamide ultrafiltration membrane with a small pore size, comprising:

[0025] Step S1: First, fix the ultrafiltration base membrane on an iron plate, then place it in an aqueous solution. After the first soaking treatment, then perform the first vertical placement treatment; the aqueous solution includes polyamine, and the polyamine is specifically triamterene; in the aqueous solution, the mass concentration of the polyamine is 0.4% - 1.0%, specifically 0.5% is selected; the aqueous solution also includes an acid solution regulator and a base solution regulator; the acid solution regulator is acrylic acid; the base solution regulator is sodium hydroxide; the acid solution regulator and the base solution regulator are used to jointly adjust the pH value of the aqueous solution to 10.5 - 11.5, and the pH value is specifically 11;

[0026] Step S2: Place the ultrafiltration base membrane after the first vertical placement treatment in an oil phase solution. After the second soaking treatment, then perform the second vertical placement treatment; the oil phase solution includes polyacyl chloride; the polyacyl chloride is isophthaloyl chloride; in the oil phase solution, the mass concentration of the polyacyl chloride is 0.08% - 0.15%, specifically 0.10% is selected; the oil phase solution also includes an organic solvent; the organic solvent is cyclohexane;

[0027] Step S3: After drying the ultrafiltration base membrane after the second vertical placement treatment, then place it in an amino crosslinking agent solution for the third soaking treatment to obtain a small - pore polyamide ultrafiltration membrane; the amino crosslinking agent used in the amino crosslinking agent solution contains chloromethyl, specifically bis(chloromethyl) sulfide; the mass concentration of the amino crosslinking agent used in the amino crosslinking agent solution is 3%.

[0028] The ultrafiltration base membrane is polysulfone.

[0029] The soaking time for both the first soaking treatment and the second soaking treatment is 20 s; the placement time for both the first vertical placement treatment and the second vertical placement treatment is 2 min.

[0030] The treatment temperature for the drying treatment is 70 °C, and the treatment time is 2 min; the soaking time for the third soaking treatment is 1 min.

[0031] First, rinse the small - pore polyamide ultrafiltration membrane prepared in Example 1 with pure water, and then immerse it in pure water for storage for later use.

[0032] Example 2:

[0033] The difference from Example 1 is that the polyamine is 1,4,8,12 - tetraazacyclopentadecane.

[0034] Example 3:

[0035] Different from Example 1, the amino crosslinking agent used in the amino crosslinking agent solution is bis(chloromethyl) sulfide with a mass concentration of 2% and 2,5-bis(chloromethyl)-p-xylene with a mass concentration of 1%.

[0036] Example 4:

[0037] Different from Example 1, the amino crosslinking agent used in the amino crosslinking agent solution is 2,4-bis(chloromethyl) trimethylbenzene with a mass concentration of 2% and 2,5-bis(chloromethyl)-p-xylene with a mass concentration of 2%.

[0038] Comparative Example 1:

[0039] Different from Example 1, the mass concentration of the amino crosslinking agent used in the amino crosslinking agent solution is 1%.

[0040] Comparative Example 2:

[0041] Different from Example 1, the mass concentration of the amino crosslinking agent used in the amino crosslinking agent solution is 5%.

[0042] Comparative Example 3:

[0043] Different from Example 2, the mass concentration of the amino crosslinking agent used in the amino crosslinking agent solution is 1%.

[0044] Comparative Example 4:

[0045] Different from Example 2, the mass concentration of the amino crosslinking agent used in the amino crosslinking agent solution is 5%.

[0046] The small-aperture polyamide ultrafiltration membranes prepared in Examples 1-4 and Comparative Examples 1-4 were respectively subjected to pure water flux experiments, sodium sulfate rejection experiments, sodium chloride rejection experiments, and PEG retention molecular weight experiments; the small-aperture polyamide ultrafiltration membranes prepared in Example 1 and Comparative Examples 1-2 were respectively subjected to methylene blue dye rejection experiments; the small-aperture polyamide ultrafiltration membranes prepared in Example 2 and Comparative Examples 3-4 were respectively subjected to crystal violet dye rejection experiments; the small-aperture polyamide ultrafiltration membranes prepared in Examples 3-4 were respectively subjected to methylene blue dye rejection experiments. The experimental results are shown in Table 1.

[0047] The method for the pure water flux experiment is as follows: Take 4 small-aperture polyamide ultrafiltration membrane sheets and place them on the ultrafiltration membrane sheet test bench in turn. The test liquid is pure water. Under a pressure of 70 psi, in a cross-flow filtration mode, after stable operation for 30 minutes, use a graduated cylinder to collect the filtered pure water and read the volume of pure water within 8 minutes. After conversion, take the average value of the 4 membrane sheets as the pure water flux of the membrane sheet.

[0048] The experimental method for sodium sulfate rejection rate is as follows: Take 4 small-aperture polyamide ultrafiltration membrane sheets and place them on the ultrafiltration membrane sheet test bench in sequence. The test solution is a sodium sulfate solution with a concentration of 2000 ppm. Under a pressure of 70 psi, adopt the cross-flow filtration method. After stable operation for 30 minutes, collect 15 ml of the test solution, and use a conductivity meter to measure the concentration of the produced water and the raw water. After calculation, take the average value of the 4 membrane sheets as the sodium sulfate rejection rate of this membrane sheet.

[0049] The experimental method for sodium chloride rejection rate is as follows: Take 4 small-aperture polyamide ultrafiltration membrane sheets and place them on the ultrafiltration membrane sheet test bench in sequence. The test solution is a sodium chloride solution with a concentration of 2000 ppm. Under a pressure of 70 psi, adopt the cross-flow filtration method. After stable operation for 30 minutes, collect 15 ml of the test solution, and use a conductivity meter to measure the concentration of the produced water and the raw water. After calculation, take the average value of the 4 membrane sheets as the sodium chloride rejection rate of this membrane sheet.

[0050] The experimental method for PEG retention molecular weight is as follows: Take 4 small-aperture polyamide ultrafiltration membrane sheets and place them on the ultrafiltration membrane sheet test bench in sequence. The test solutions are PEG (200, 300, 400, 600, 800, 1000) solutions with a concentration of 1000 ppm and different molecular weights. Under a pressure of 70 psi, adopt the cross-flow filtration method. After stable operation for 30 minutes, collect 20 ml of the test solution, and use a Toc total organic carbon tester (model: Shimadzu TOC-L CPH / CPN total organic carbon tester) to measure the concentration of the produced water and the raw water. After calculation, take the average value of the 4 membrane sheets as the rejection rate of this membrane sheet for each PEG, and plot it as a rejection curve. When the rejection rate is 90%, simulate and calculate the corresponding retention molecular weight of this membrane sheet.

[0051] The experimental method for methylene blue rejection rate is as follows: Take 4 small-aperture polyamide ultrafiltration membrane sheets and place them on the ultrafiltration membrane sheet test bench in sequence. The test solution is a methylene blue solution with a concentration of 50 ppm. Under a pressure of 70 psi, adopt the cross-flow filtration method. After stable operation for 30 minutes, collect 20 ml of the test solution, and use spectrophotometry to measure the concentration of the produced water and the raw water. After calculation, take the average value of the 4 membrane sheets as the methylene blue dye rejection rate of this membrane sheet.

[0052] The experimental method for crystal violet rejection rate is as follows: Take 4 small-aperture polyamide ultrafiltration membrane sheets and place them on the ultrafiltration membrane sheet test bench in sequence. The test solution is a crystal violet solution with a concentration of 50 ppm. Under a pressure of 70 psi, adopt the cross-flow filtration method. After stable operation for 30 minutes, collect 20 ml of the test solution, and use spectrophotometry to measure the concentration of the produced water and the raw water. After calculation, take the average value of the 4 membrane sheets as the crystal violet dye rejection rate of this membrane sheet.

[0053] Table 1 Experimental results of small-aperture polyamide ultrafiltration membrane

[0054]

[0055] As can be seen from Table 1:

[0056] The small-aperture polyamide ultrafiltration membranes prepared in Examples 1-4 can achieve effective separation of dyes and salts while retaining most of the dyes and still maintaining a low desalination rate. In addition, the small-aperture polyamide ultrafiltration membranes prepared in Examples 1-4 have a higher pure water flux compared to existing ultrafiltration membranes.

[0057] As can be seen from Examples 3-4, appropriately increasing the mass concentration of the amino crosslinking agent helps to increase the crosslinking degree of the membrane sheet, achieve an appropriate pore size and cut-off molecular weight, and thus achieve effective separation of dyes and salts.

[0058] As can be seen from Example 1 and Comparative Example 2, and from Example 2 and Comparative Example 4, if the mass concentration of the amino crosslinking agent is too high, it will cause an increase in the crosslinking degree of the membrane sheet and a decrease in the cut-off molecular weight, that is, the pore size decreases, and effective separation between relatively small-molecule dyes and salts cannot be achieved, showing an increase in the salt rejection rate.

[0059] As can be seen from Example 1 and Comparative Example 1, and from Example 2 and Comparative Example 3, if the mass concentration of the amino crosslinking agent is too low, it will cause insufficient crosslinking degree of the membrane sheet and an increase in the cut-off molecular weight, that is, the pore size increases, and effective separation between dyes and salts cannot be achieved.

[0060] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, various changes and modifications can be made to the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a small-pore polyamide ultrafiltration membrane, characterized in that: include: Step S1, placing the ultrafiltration base membrane in an aqueous solution, performing a first soaking treatment, and then performing a first vertical placement treatment; The aqueous phase solution includes a polyamine; Step S2, placing the ultrafiltration base membrane after the first vertical placement treatment into an oil phase solution, performing a second immersion treatment, and then performing a second vertical placement treatment; the oil phase solution includes polyacyl chloride; Step S3, drying the ultrafiltration base membrane after the second vertical placement treatment, and then placing it in an amino cross-linking agent solution for a third soaking treatment to obtain a small-pore polyamide ultrafiltration membrane; the amino cross-linking agent used in the amino cross-linking agent solution contains chloromethyl; the mass concentration of the amino cross-linking agent used in the amino cross-linking agent solution is 2%-4%; The amino crosslinking agent includes at least one of 2,5-bis(chloromethyl)-p-xylene, bis(chloromethyl) sulfide, 9,10-di(chloromethyl)anthracene, and 2,4-bis(chloromethyl)trimethylbenzene; The polyamine includes at least one of triamterene, 1,4,10-trioxa-7,13-diaza-cyclopentadecane, 1,4,8,12-tetraazacyclopentadecane, and 1,7,11,17-tetraoxa-2,6,12,16-tetraazacycloeicosane; and the mass concentration of the polyamine in the aqueous phase solution is 0.4%-1.0%.

2. The method for preparing a small-pore polyamide ultrafiltration membrane according to claim 1, characterized in that: The aqueous phase solution also includes an acid regulator and an alkali regulator; the acid regulator includes at least one of acrylic acid, camphorsulfonic acid and citric acid; the alkali regulator includes at least one of sodium hydroxide and potassium hydroxide; the acid regulator and the alkali regulator are used to adjust the pH value of the aqueous phase solution to 10.5-11.5 in combination.

3. The method for preparing a small-pore polyamide ultrafiltration membrane according to claim 1, characterized in that: The polyacid chloride comprises at least one of isophthaloyl chloride, terephthaloyl chloride and 1,3,5-benzenetricarboxylic acid chloride; and the mass concentration of the polyacid chloride in the oil phase solution is 0.08%-0.15%.

4. The method for preparing a small-pore polyamide ultrafiltration membrane according to claim 1, characterized in that: The oil phase solution also includes an organic solvent; the organic solvent includes at least one of cyclohexane, n-hexane, petroleum ether and m-xylene.

5. The method for preparing a small-pore polyamide ultrafiltration membrane according to claim 1, characterized in that: The ultrafiltration base membrane includes polyethersulfone, polysulfone, polyacrylonitrile or polyvinylidene fluoride.

6. The method for preparing a small-pore polyamide ultrafiltration membrane according to claim 1, characterized in that: The soaking time used in the first soaking treatment and the second soaking treatment is 10-30 seconds; the placement time used in the first vertical placement treatment and the second vertical placement treatment is 2-5 minutes.

7. The method for preparing a small-pore polyamide ultrafiltration membrane according to claim 1, characterized in that: The drying treatment uses a treatment temperature of 50-80° C. and a treatment time of 2-10 minutes; the third soaking treatment uses an soaking time of 1-3 minutes.

8. A small pore size polyamide ultrafiltration membrane, characterized in that: The membrane is prepared by the method for preparing a small-pore polyamide ultrafiltration membrane as described in any one of claims 1 to 7.

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