A method for preparing a polyamide reverse osmosis membrane

Abstract

The application provides a preparation method of a polyamide reverse osmosis membrane, comprising the following steps: (1) immersing a non-woven fabric supported ultrafiltration membrane into an aqueous phase solution, and removing the excess aqueous phase solution on the surface of the ultrafiltration membrane after taking out; (2) immersing the ultrafiltration membrane obtained in the step (1) into an oil phase solution to perform interfacial polymerization, and then removing the excess oil phase solution on the surface of the ultrafiltration membrane; (3) coating an alcohol solution containing dansyl on the surface of the membrane obtained in the step (2), performing heat treatment, cleaning with hot water after the reaction is completed, and obtaining the reverse osmosis membrane. The amino group in dansyl reacts with acyl chloride and is grafted in the polyamide network. The tertiary amine in dansyl accepts protons in an acidic solution and shows hydrophilicity, which improves the hydration water content of the polyamide and the stability of the polyamide structure. The naphthalene group in dansyl occurs hydrophobic aggregation in an alkaline solution, which reduces the size and polarity of the polyamide hole, so that the polyamide reverse osmosis membrane with acid and alkali resistance and high boron removal is prepared.

Description

Technical Field

[0001] This invention belongs to the field of reverse osmosis technology, specifically relating to a method for preparing an acid and alkali resistant high-boronization polyamide reverse osmosis membrane. Background Technology

[0002] Reverse osmosis is a water treatment technology that uses physical separation methods. Polyamide reverse osmosis composite membranes can effectively retain ions in water while allowing water to pass through, and they are widely used in brackish water desalination, greywater reuse, and seawater desalination.

[0003] Boron exists in water mainly in the form of boric acid molecules. Its molecular size is extremely small, so conventional reverse osmosis membranes have a poor boron retention effect. The main reasons for the low boron removal rate of reverse osmosis membranes are: (1) In acidic and neutral aqueous solutions, boric acid mainly exists in the form of uncharged boric acid molecules, which renders the charge repulsion mechanism of the reverse osmosis membrane ineffective; (2) The molecular radius of boric acid is smaller than that of most aggregated pores and some mesh pores.

[0004] (3) Boric acid is transported in the membrane in a way that is very similar to that of water (H2O).

[0005] Currently, industrial water treatment mainly improves boron removal rates through multi-stage reverse osmosis, combined use of reverse osmosis and adsorption resins, and enhanced pretreatment methods, but these methods increase costs. The core of reverse osmosis technology is a high-performance reverse osmosis membrane; therefore, preparing a reverse osmosis membrane with high boron removal performance can improve boron removal efficiency from the source.

[0006] There are two main methods to improve the boron removal rate of reverse osmosis membranes: (1) reduce the chemical polarity of the polyamide in the reverse osmosis membrane and reduce the hydrogen bonding force between the polyamide and boric acid molecules; (2) reduce the pore size of the reverse osmosis membrane and improve the physical sieving effect.

[0007] Shultz et al. improved the boron removal rate by swelling polyamide with alcohol and then embedding hydrophobic aliphatic amines into the membrane pores, thereby reducing polarity and shrinking the pore size. Zhang and Raval et al. synthesized sulfonated diamine to replace m-phenylenediamine and used sulfonic acid groups to fill the membrane pores, thus improving the boron removal rate. Patent CN100379488C used a mixed aqueous solution of monoamine and polyamine as the aqueous phase, reacted it with aliphatic acyl chloride, and then treated it with sodium hypochlorite to prepare a high boron removal reverse osmosis membrane.

[0008] Although some technical solutions for preparing polyamide reverse osmosis membranes with high boron removal rates have been developed in the existing technology, membrane fouling exists during the operation of reverse osmosis membranes. Strong acid and strong alkaline solutions are commonly used for cleaning membrane fouling. After cleaning with acid and alkaline solutions, the boron removal rate of polyamide reverse osmosis membranes usually decreases. Therefore, the existing technical solutions are not mature enough or still have room for further improvement. Summary of the Invention

[0009] The purpose of this invention is to address the shortcomings of existing technologies by providing a method for preparing a polyamide reverse osmosis membrane with high acid and alkali resistance and high boron removal rate. The method involves coating a nascent polyamide network surface with an alcohol solution of dansylamine, followed by heat treatment and hot water washing after the reaction is complete to obtain the reverse osmosis membrane.

[0010] The present invention adopts the following technical solution:

[0011] A method for preparing a polyamide reverse osmosis membrane, comprising the following steps:

[0012] (1) Immerse the non-woven fabric-supported ultrafiltration membrane in an aqueous solution, and remove it to remove excess aqueous solution from the surface of the ultrafiltration membrane.

[0013] (2) Immerse the ultrafiltration membrane obtained in step (1) into an oil phase solution for interfacial polymerization, and then remove the excess oil phase solution from the surface of the ultrafiltration membrane;

[0014] (3) The membrane surface obtained in step (2) is coated with an alcohol solution containing dansylamine, heat-treated, and then washed with hot water to obtain a reverse osmosis membrane.

[0015] Preferably, the aqueous solution comprises an aqueous monomer and water, wherein the aqueous monomer is selected from one or more of m-phenylenediamine, p-phenylenediamine, o-phenylenediamine, and hexamethylenediamine;

[0016] Preferably, the concentration of the aqueous monomer in the aqueous solution is 2-6 wt%.

[0017] Preferably, the oil phase solution comprises aromatic polyacrylamide chlorides and organic solvents;

[0018] Preferably, the aromatic polyacryl chloride is trimesoyl chloride, terephthaloyl chloride, or isophthaloyl chloride, and preferably, the concentration of the aromatic polyacryl chloride in the oil phase solution is 0.1-0.3 wt%.

[0019] Preferably, the organic solvent is at least one selected from n-hexane, cyclohexane, n-heptane, and Isopar L isoalkanes.

[0020] Preferably, in step (2), the reaction time of the ultrafiltration membrane in the oil phase solution is 10-120 s.

[0021] Preferably, in step (3), the alcohol is at least one of isopropanol, benzyl alcohol, cyclohexanol, butanol, methanol, ethanol, and propanol.

[0022] Preferably, the dansylamine concentration in the alcoholic solution is 0.01-1 wt%.

[0023] Preferably, in step (3), the heat treatment temperature is 40-70℃ and the time is 0.5-3min.

[0024] Preferably, in step (3), the hot water cleaning temperature is 60-90℃ and the time is 1-10min.

[0025] In the preparation method of this invention, an ultrafiltration membrane is formed into a nascent polyamide through an aqueous phase and an oil phase. Danshensulfonamide is coated on the surface of the nascent polyamide network. The amino groups contained in danshensulfonamide react with the acyl chlorides in the polyamide network, attaching to the polyamide network. The smaller the intermolecular gaps in the polyamide separation functional layer, the higher the solute removal rate of the composite semipermeable membrane. However, on the other hand, if the intermolecular gaps are too small, the chemical resistance decreases. This is because polyamide has ionic functional groups such as amine or carboxyl groups. Therefore, under the interaction between charged sites generated by contact with chemicals such as acids or alkalis, its higher-order structure becomes unstable. The tertiary amine contained in danshensulfonamide can accept protons in acidic solutions. After accepting protons, the amine becomes hydrophilic, increasing the hydration content of the polyamide, increasing the porosity of the polyamide network, and improving the stability of the higher-order structure of the polyamide in acid. Meanwhile, tansulphamide undergoes hydrophobic aggregation of naphthalene groups and tansulphamide chains in alkaline solutions, reducing the pore size and polarity of the polyamide network. Therefore, by utilizing the pH response exhibited by tansulphamide during acid and alkali cleaning, a pH-responsive switch can be formed in the polyamide network to prepare an acid and alkali resistant high boron removal reverse osmosis membrane.

[0026] Compared with the prior art, the advantages of the present invention are as follows:

[0027] By coating the surface of nascent polyamide with an alcohol solution containing dansylsulfonamide (N-(5-aminopentyl)-5-dimethylaminonaphthalene-1-sulfonamide) and then heat-treating it, dansylsulfonamide with pH responsiveness is introduced into the polyamide network. After acid and alkali washing, this separation functional layer still has a high deboronization rate.

[0028] The preparation method of the present invention is simple and easy to implement, and is suitable for industrial production. Detailed Implementation

[0029] The following specific embodiments are further illustrations of the technical solutions provided by the present invention, but should not be construed as limiting the present invention.

[0030] Membrane performance testing:

[0031] 1. Evaluation of water flux, desalination rate, and boron removal rate:

[0032] Water flux (F) is defined as the volume of water passing through a unit membrane area per unit time under a given operating pressure, expressed in L / m². 2 / h.

[0033] Desalination rate (R) is defined as: under certain operating conditions, the salt concentration (C) of the feed solution... f ) and the salt concentration in the permeate (C pThe difference is then divided by the concentration of the feed solution salt.

[0034] Boron removal rate (Rb) is defined as the difference between the boron concentration in the feed solution and the boron concentration in the permeate under certain operating conditions, divided by the boron concentration in the feed solution (characterized by ICP method).

[0035] The operating conditions used for the performance determination of the polyamide reverse osmosis composite membrane in this invention are as follows: the feed liquid is a sodium chloride aqueous solution with a concentration of 32,000 ppm and a boron content of 5 ppm, the operating pressure is 5.5 MPa, the operating temperature is 25°C, and the pH of the aqueous solution is 8.

[0036] 2. Membrane acid and alkali resistance test:

[0037] The prepared polyamide reverse osmosis membrane was immersed in sodium hydroxide at 25℃ and pH=13 for 16 hours, then rinsed with pure water, and then immersed in hydrochloric acid at 25℃ and pH=1 for 4 hours. After rinsing with pure water, the membrane separation performance was tested.

[0038] 3. Raw material source: Dansulfanilamide (Aladdin)

[0039] Examples 1-3

[0040] (1) Preparation of aqueous solution: After mixing m-phenylenediamine and water evenly, an aqueous solution is obtained; the concentration of m-phenylenediamine in the aqueous solution is shown in Table 1.

[0041] (2) Preparation of oil phase solution: Dissolve pyromellitic chloride in n-heptane and stir until homogeneous to obtain oil phase solution. The concentration of pyromellitic chloride in oil phase solution is 0.14 wt%.

[0042] (3) Interface polymerization and post-treatment: The nonwoven fabric-supported polysulfone membrane is directly immersed in the aqueous solution prepared in step (1) for 30s. After taking it out, it is squeezed with a rubber roller to remove the excess aqueous solution on the surface of the polysulfone membrane. Then it is immersed in the oil solution prepared in step (2) and reacted at room temperature for 30s. After the reaction is completed, the excess oil solution on the surface is removed with an air knife to form nascent polyamide. Then, a 200ppm dansylamine benzyl alcohol solution is coated on the surface of the nascent polyamide. Then it is placed in a 45℃ oven for 2min and then washed with 90℃ hot water for 3min to obtain a reverse osmosis membrane.

[0043] Comparative Example 1

[0044] Referring to Example 2, the preparation method differs from that in Example 2 in that: in step (3), after the reaction is complete, a benzyl alcohol solution without dansulphamide is coated.

[0045] The separation performance of the polyamide reverse osmosis membranes prepared according to Examples 1-3 and Comparative Example 1 was tested, and the test results are shown in Table 1.

[0046] Table 1

[0047]

[0048] Example 4

[0049] Referring to Example 1, the main difference between this example and Example 1 is that the concentration of pyromellitic methyl chloride in the oil phase is 0.26 wt%, and the mass concentration of dansyl sulfamethoxam in step (3) is 0.5 wt%.

[0050] Example 5

[0051] Referring to Example 1, the preparation method differs from that in Example 1 in that: in step (3), the mass concentration of dansulphamide is 500 ppm and the solvent is isopropanol.

[0052] Example 6

[0053] Referring to Example 1, the preparation method differs from that in Example 1 in that: in step (3), the oven temperature is 65°C and the reaction time is 1 min.

[0054] Comparative Example 2

[0055] Referring to Example 6, the preparation method differs from that in Example 6 in that the oil phase solution obtained in step (2) is directly placed into the oven, without the coating process in step (3).

[0056] The separation performance of the polyamide reverse osmosis membranes prepared according to Examples 4-6 and Comparative Example 2 was tested, and the test results are shown in Table 2.

[0057] Table 2

[0058]

Claims

1. A method for preparing a polyamide reverse osmosis membrane, characterized in that, Includes the following steps: (1) Immerse the non-woven fabric-supported ultrafiltration membrane in an aqueous solution, and remove it to remove excess aqueous solution from the surface of the ultrafiltration membrane; (2) Immerse the ultrafiltration membrane obtained in step (1) into the oil phase solution for interfacial polymerization, and then remove the excess oil phase solution from the surface of the ultrafiltration membrane; (3) The membrane surface obtained in step (2) is coated with an alcohol solution containing dansulphamide, heat-treated, and then washed with hot water to obtain a reverse osmosis membrane.

2. The preparation method according to claim 1, characterized in that, The aqueous solution comprises an aqueous monomer and water, wherein the aqueous monomer is selected from one or more of m-phenylenediamine, p-phenylenediamine, o-phenylenediamine, and hexamethylenediamine.

3. The preparation method according to claim 1, characterized in that, The concentration of the aqueous monomer in the aqueous solution is 2-6 wt%.

4. The preparation method according to claim 1, characterized in that, The oil phase solution comprises aromatic polyacrylamide chlorides and organic solvents.

5. The preparation method according to claim 4, characterized in that, The aromatic polyacryl chloride is pyromellitic trimethylolpropionate chloride, terephthaloyl chloride, or isophthaloyl chloride.

6. The preparation method according to claim 4, characterized in that, The concentration of aromatic polyacrylamide chlorides in the oil phase solution is 0.1-0.3 wt%.

7. The preparation method according to claim 4, characterized in that, The organic solvent is at least one of n-hexane, cyclohexane, n-heptane, and IsoparL isoalkanes.

8. The preparation method according to claim 1, characterized in that, In step (2), the reaction time of the ultrafiltration membrane in the oil phase solution is 10-120 s.

9. The preparation method according to claim 1, characterized in that, In step (3), the alcohol is at least one of isopropanol, benzyl alcohol, cyclohexanol, butanol, methanol, ethanol, and propanol.

10. The preparation method according to claim 1, characterized in that, The alcoholic solution of dansulamine has a mass concentration of 0.01-1 wt%.

11. The preparation method according to claim 1, characterized in that, In step (3), the heat treatment temperature is 40-70℃ and the time is 0.5-3min.

12. The preparation method according to claim 1, characterized in that, In step (3), the hot water cleaning temperature is 60-90℃ and the time is 1-10min.

Images