Small-aperture polyamide ultrafiltration membrane and preparation method thereof

Abstract

The invention relates to the technical field of ultrafiltration membranes, in particular to a small-aperture polyamide ultrafiltration membrane and a preparation method thereof. The membrane is prepared by the method. The method comprises the following steps: putting an ultrafiltration base membrane into a water phase solution, carrying out first soaking treatment, and then carrying out first vertical placement treatment; the water phase solution comprises polyamine; putting the ultrafiltration base membrane subjected to the first vertical placement treatment into an oil phase solution, carrying out second soaking treatment, and then carrying out second vertical placement treatment; the oil phase solution comprises multi-element acyl chloride; and drying the ultrafiltration base membrane subjected to the second vertical placement treatment, and soaking the dried ultrafiltration base membrane in an amino crosslinking agent solution for the third time to obtain the small-aperture polyamide ultrafiltration membrane. The problem that an existing ultrafiltration membrane is low in permeation flux can be solved, and the problem that a polyamide nanofiltration membrane cannot effectively separate dye and salt can also be solved.

Description

Technical Field

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

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

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

[0004] In summary, it is necessary to develop a small-pore polyamide ultrafiltration membrane and a preparation method thereof, which can be used to solve the problem of low permeation flux of existing ultrafiltration membranes on the one hand, and to solve the problem that polyamide nanofiltration membranes cannot effectively separate dyes and salts on the other hand. Summary of the invention

[0005] The present invention aims to provide a small pore size polyamide ultrafiltration membrane and a preparation method thereof. The specific technical scheme is as follows:

[0006] In a first aspect, the present invention provides a method for preparing a small-pore polyamide ultrafiltration membrane, comprising:

[0007] Step S1, placing the ultrafiltration base membrane in an aqueous solution, performing a first immersion treatment, and then performing a first vertical placement treatment; the aqueous solution includes a polyamine;

[0008] 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;

[0009] 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 immersion 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%.

[0010] Optionally, the amino cross-linking 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.

[0011] Optionally, 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%.

[0012] Optionally, 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 in combination to adjust the pH value of the aqueous phase solution to 10.5-11.5.

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

[0014] Optionally, 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.

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

[0016] Optionally, 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.

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

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

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

[0020] (1) The present invention provides a method for preparing a small-pore polyamide ultrafiltration membrane. The prepared polyamide ultrafiltration membrane can not only solve the problem of low permeation flux in existing ultrafiltration membranes, but also solve the problem that polyamide nanofiltration membranes cannot effectively separate dyes and salts. Specifically, the polyamide ultrafiltration membrane prepared by the present invention contains unreacted amino groups of polyamines, which increases the hydrophilicity of the polyamide ultrafiltration membrane and thus improves the permeation flux of the membrane. The preparation method adopted by the present invention is to use an amino crosslinking agent solution to soak the polyamide membrane for the third time after the polyamine and polyacyl chloride are interfacially polymerized to form a polyamide membrane, wherein the C-Cl bond in the chloromethyl group of the amino crosslinking agent connects part of the unreacted amino groups to form a mesh structure with smaller spatial holes, and at the same time, a specific mass concentration of amino crosslinking agent is used to adjust the pore size and molecular weight cutoff of the membrane, thereby simply and efficiently preparing a small-pore polyamide ultrafiltration membrane, which can retain most of the dyes while still maintaining a low desalination rate, and effectively separate dyes and salts. If the mass concentration of the amino cross-linking agent is too high, although the reaction rate can be accelerated, it will lead to an increase in the cross-linking degree of the membrane, a decrease in the pore size and the molecular weight cut-off, and it will not be possible to effectively separate relatively small molecule dyes and salts; if the mass concentration of the amino cross-linking agent is too low, it will lead to insufficient cross-linking of the membrane, a larger pore size and the molecular weight cut-off, and it will not be possible to effectively separate dyes and salts.

[0021] (2) The soaking time used for the third soaking treatment in the present invention is 1-3 minutes. If the soaking time is too long, the cross-linking degree of the membrane will increase, and the pore size and the molecular weight cutoff will further decrease, and it will be impossible to achieve effective separation between relatively small molecular dyes and salts; if the soaking time is too short, the cross-linking degree of the membrane will increase, and the pore size and the molecular weight cutoff will further increase, and it will be impossible to achieve effective separation between dyes and salts. DETAILED DESCRIPTION

[0022] The technical solutions in the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention belong to the scope of protection of the present invention.

[0023] Embodiment 1:

[0024] A method for preparing a small-pore polyamide ultrafiltration membrane comprises:

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

[0026] 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; the polyacyl chloride is isophthaloyl chloride; the mass concentration of the polyacyl chloride in the oil phase solution is 0.08%-0.15%, specifically 0.10%; the oil phase solution also includes an organic solvent; the organic solvent is cyclohexane;

[0027] 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 immersion treatment to obtain a small-pore polyamide ultrafiltration membrane; the amino cross-linking agent used in the amino cross-linking agent solution contains chloromethyl, specifically bis(chloromethyl) sulfide; the mass concentration of the amino cross-linking agent used in the amino cross-linking agent solution is 3%.

[0028] The ultrafiltration base membrane is polysulfone.

[0029] The soaking time used in the first soaking treatment and the second soaking treatment is 20 seconds; the placement time used in the first vertical placement treatment and the second vertical placement treatment is 2 minutes.

[0030] The treatment temperature used in the drying treatment is 70° C., and the treatment time used is 2 minutes; the soaking time used in the third soaking treatment is 1 minute.

[0031] The small-pore polyamide ultrafiltration membrane prepared in Example 1 was first rinsed with pure water, and then immersed in pure water for storage.

[0032] Embodiment 2:

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

[0034] Embodiment 3:

[0035] Different from Example 1, the amino cross-linking agent used in the amino cross-linking 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] Embodiment 4:

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

[0038] Comparative Example 1:

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

[0040] Comparative Example 2:

[0041] The difference from Example 1 is that the mass concentration of the amino cross-linking agent used in the amino cross-linking agent solution is 5%.

[0042] Comparative Example 3:

[0043] The difference from Example 2 is that the mass concentration of the amino cross-linking agent used in the amino cross-linking agent solution is 1%.

[0044] Comparative Example 4:

[0045] The difference from Example 2 is that the mass concentration of the amino cross-linking agent used in the amino cross-linking agent solution is 5%.

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

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

[0048] The experimental method for sodium sulfate retention rate is as follows: take 4 small-pore polyamide ultrafiltration membrane sheets and place them on the ultrafiltration membrane test bench in turn. The test liquid is a 2000ppm sodium sulfate solution. Under a pressure of 70psi, cross-flow filtration is adopted. After stable operation for 30 minutes, 15ml of the test liquid is collected and the produced water concentration and the raw water concentration are tested with a conductivity meter. After calculation, the average value of the 4 membrane sheets is taken as the sodium sulfate retention rate of the membrane sheet.

[0049] The experimental method for sodium chloride retention rate is as follows: take 4 small-pore polyamide ultrafiltration membrane sheets and place them on the ultrafiltration membrane test bench in turn. The test liquid is a 2000ppm sodium chloride solution. Under a pressure of 70psi, cross-flow filtration is adopted. After stable operation for 30 minutes, 15ml of the test liquid is collected and the produced water concentration and the raw water concentration are tested with a conductivity meter. After calculation, the average value of the 4 membrane sheets is taken as the sodium chloride retention rate of the membrane sheet.

[0050] The experimental method of PEG molecular weight cutoff is as follows: take 4 small-pore polyamide ultrafiltration membranes and place them on the ultrafiltration membrane test bench in turn. The test liquid is a 1000ppm concentration of different molecular weight PEG (200, 300, 400, 600, 800, 1000) solution. Under a pressure of 70psi, cross-flow filtration is adopted. After stable operation for 30 minutes, 20ml of the test liquid is taken and the concentration of produced water and raw water is tested with a Toc total organic carbon tester (model: Shimadzu TOC-L CPH / CPN total organic carbon tester). After calculation, the average value of the 4 membranes is taken as the retention rate of the membrane for each PEG, and it is plotted into a retention curve. When the retention rate is 90%, the molecular weight cutoff corresponding to the membrane is simulated and calculated.

[0051] The experimental method for the methylene blue retention rate is as follows: take 4 small-pore polyamide ultrafiltration membrane sheets and place them on the ultrafiltration membrane sheet test bench in turn. The test liquid is a 50ppm concentration of methylene blue solution. Under a pressure of 70psi, cross-flow filtration is adopted. After stable operation for 30 minutes, 20ml of the test liquid is collected and the produced water concentration and the raw water concentration are tested by spectrophotometry. After calculation, the average value of the 4 membrane sheets is taken as the methylene blue dye retention rate of the membrane sheet.

[0052] The experimental method for crystal violet retention rate is as follows: take 4 small-pore polyamide ultrafiltration membrane sheets and place them on the ultrafiltration membrane test bench in turn. The test liquid is a 50ppm concentration of crystal violet solution. Under a pressure of 70psi, cross-flow filtration is adopted. After stable operation for 30 minutes, 20ml of the test liquid is collected and the produced water concentration and the raw water concentration are tested by spectrophotometry. After calculation, the average value of the 4 membrane sheets is taken as the crystal violet dye retention rate of the membrane sheet.

[0053] Table 1 Experimental results of small pore size polyamide ultrafiltration membrane

[0054]

[0055] From Table 1, we know that:

[0056] The small-pore polyamide ultrafiltration membrane prepared by Examples 1-4 can retain most of the dyes while maintaining a low desalination rate, thereby effectively separating the dyes and salts. In addition, the small-pore polyamide ultrafiltration membrane prepared by Examples 1-4 has a higher pure water flux than the existing ultrafiltration membrane.

[0057] It is known from Examples 3-4 that appropriately increasing the mass concentration of the amino cross-linking agent is helpful to increase the cross-linking degree of the membrane, achieve a suitable pore size and molecular weight cut-off, and thus achieve effective separation of dyes and salts.

[0058] It is known from Example 1 and Comparative Example 2 and from Example 2 and Comparative Example 4 that if the mass concentration of the amino cross-linking agent is too high, the degree of cross-linking of the membrane will increase and the molecular weight cutoff will decrease, that is, the pore size will decrease, and effective separation of relatively small molecular dyes and salts cannot be achieved, resulting in an increased retention rate for salts.

[0059] It is known from Example 1 and Comparative Example 1 as well as from Example 2 and Comparative Example 3 that if the mass concentration of the amino crosslinking agent is too low, the crosslinking degree of the membrane will be insufficient, the molecular weight cutoff will increase, that is, the pore size will increase, and effective separation of dyes and salts cannot be achieved.

[0060] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in 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 immersion 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%.

2. The method for preparing a small-pore polyamide ultrafiltration membrane according to claim 1, characterized in that: The amino cross-linking 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.

3. The method for preparing a small-pore polyamide ultrafiltration membrane according to claim 1, characterized in that: 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%.

4. 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.

5. 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%.

6. 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.

7. 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.

8. 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.

9. 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.

10. 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 9.

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