Monovalent and divalent ion separation membrane and preparation method thereof

Abstract

The invention discloses a monovalent and divalent ion separation membrane and a preparation method thereof, the separation membrane comprises a support layer and an interfacial polymerization layer formed on the surface of the support layer, the interfacial polymerization layer is formed by polymerizing a water-phase monomer and an oil-phase monomer, the water-phase monomer comprises piperazine and piperazine dicarboxylic acid, and the oil-phase monomer comprises a substance containing an acyl chloride group. According to the monovalent and divalent ion separation membrane and the preparation method thereof, piperazine with carboxyl is applied to preparation of the separation membrane, a plurality of carboxyl groups are introduced, the surface of the obtained membrane carries a large number of negative charges, the repulsive force on divalent ions is large, and the monovalent and divalent ions are separated by using the membrane; and the selectivity coefficient for monovalent ions and divalent ions can reach 19.83.

Description

Technical Field

[0001] The invention relates to the technical field of separation membranes, in particular to a monovalent and divalent ion separation membrane and a preparation method thereof. Background Art

[0002] Membrane separation technology is an emerging separation technology. Due to its advantages such as operability at room temperature, low energy consumption and less pollution, it is widely used in industrial wastewater treatment, municipal sewage treatment, organic pollutant removal, heavy metal ion removal and other fields.

[0003] Nanofiltration membrane is a new type of pressure-driven separation membrane, and its function is between reverse osmosis membrane and ultrafiltration membrane. Compared with other membrane technologies, nanofiltration membrane operates at a lower operating pressure, allowing certain low molecular weight solutes and low-valent ions to pass through, while intercepting substances with larger molecular weights, such as divalent ions and small organic molecules. Common separation membranes generally include an interfacial polymerization layer and a support layer, and the interfacial polymerization layer is used to achieve the separation effect. Interfacial polymerization is a process involving monomer polymerization reactions. Its basic principle is to dissolve two highly reactive monomers in two immiscible solvents respectively, and an irreversible condensation reaction occurs at the interface of the two liquid phases, thereby forming a dense polymer structure. This method is widely used in the preparation of nanofiltration membranes or reverse osmosis membrane materials with microporous structures. When preparing charged nanofiltration membranes, the interfacial polymerization method usually uses ionic monomers as the reaction skeleton to directly synthesize polymeric membranes.

[0004] Interfacial polymerization is an effective method for preparing separation membranes. In this process, the monomers used in interfacial polymerization will basically determine the micropore size and micropore structure of the polymer structure. These micropore structures and micropore sizes will further affect the separation performance and anti-pollution performance of the separation membrane. In recent years, the industry's performance requirements for separation membranes have gradually increased. Not only do they need to have a large flux, strong anti-pollution ability and stability, but they also need to have high selectivity for monovalent and divalent ions. The separation membranes currently on the market cannot meet these requirements at the same time. In order to meet the high requirements of the existing technology for separation membranes, it is necessary to develop a separation membrane with a high divalent ion salt rejection rate, good anti-pollution performance, and long-term stability. Summary of the invention

[0005] The purpose of the present invention is to provide a monovalent and divalent ion separation membrane and a preparation method thereof, so as to solve the problems of poor separation effect of the above separation membrane for monovalent and divalent ions, poor anti-pollution performance and poor long-term stability.

[0006] To achieve the above-mentioned purpose, the first aspect of the present invention provides a divalent ion separation membrane, comprising a support layer and an interfacial polymerization layer formed on the surface of the support layer, wherein the interfacial polymerization layer is formed by polymerization of water phase monomers and oil phase monomers, wherein the water phase monomers include piperazine and piperazine dicarboxylic acid, and the oil phase monomers include substances containing acyl chloride groups.

[0007] Preferably, the material of the support layer is one or more of polyethersulfone, polysulfone and polyvinylidene fluoride.

[0008] Preferably, the mass ratio of piperazine to piperazine dicarboxylic acid is 0-3:1-3.

[0009] Preferably, the oil phase monomer is one or more of trimesoyl chloride, isophthaloyl chloride, phthaloyl chloride and terephthaloyl chloride.

[0010] The second aspect of the present invention provides a method for preparing a monovalent and divalent ion separation membrane, comprising the following steps:

[0011] (1) dissolving an aqueous phase monomer and a surfactant in water to form an aqueous phase solution;

[0012] (2) dissolving the oil phase monomer in an organic solvent to form an oil phase solution;

[0013] (3) The support layer is fixed on the coating device, and then the aqueous solution is poured on the support layer. After standing, the excess aqueous solution is removed. Then, the oil phase solution is poured on the support layer. After continuing to stand, the excess oil phase solution is removed, and then drying is performed to obtain a monovalent and divalent ion separation membrane.

[0014] Preferably, in step (1), the mass concentration of the aqueous phase monomer in the aqueous phase solution is 1-5%, the surfactant is sodium dodecyl sulfate, and the concentration of the surfactant added to the aqueous phase solution is 350-450 mg / L.

[0015] Preferably, in step (2), the organic solvent is one or more of n-hexane, cyclohexane, isoparaffin and n-heptane; and the mass concentration of the oil phase monomer in the oil phase solution is 0.1-0.5%.

[0016] Preferably, in step (3), after the aqueous phase solution is poured onto the support layer, it is allowed to stand at room temperature for 3 to 8 minutes, and after the oil phase solution is poured onto the support layer, it is allowed to stand at room temperature for 5 to 10 minutes.

[0017] Preferably, in step (3), the drying temperature is 50 to 80° C. and the drying time is 10 to 30 minutes.

[0018] Therefore, the present invention adopts a monovalent and divalent ion separation membrane of the above structure and a preparation method thereof, which has the following beneficial effects:

[0019] (1) The present invention applies carboxyl-containing piperazine to the preparation of separation membranes, introduces a large number of carboxyl groups, and obtains a membrane surface with a large amount of negative charge, which has a strong repulsive force on divalent ions. It is used to separate monovalent and divalent ions, and the selectivity coefficient for monovalent ions and divalent ions can reach 19.83.

[0020] (2) The present invention can achieve the separation of ions or molecules of different sizes by adjusting the membrane preparation parameters and then adjusting the cross-linking degree of the separation membrane, with high reliability.

[0021] (3) The membrane prepared by the present invention is tested using a cross-flow filtration device. The separation performance is improved while the water flux is correspondingly improved, thereby reducing energy consumption. The total contamination rate Rt of the optimal separation membrane is 4.62%, the flux recovery rate FRR after water washing is 99.07%, the reversible contamination rate Rr is 3.7%, and the irreversible contamination rate is 0.92%. Therefore, the separation membrane of the present invention can effectively resist contamination and can be used for a long time.

[0022] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The effect of changing the proportion of water phase monomers on the separation membrane rejection rate and the separation coefficient of monovalent and divalent salts;

[0024] Figure 2 The effect of changing the aqueous phase monomer concentration on the separation membrane rejection rate and the separation coefficient of monovalent and divalent salts;

[0025] Figure 3 It is the effect of changing the oil phase monomer concentration on the separation membrane retention rate and the separation coefficient of monovalent and divalent salts. DETAILED DESCRIPTION

[0026] The present invention will be further described below. It should be noted that this embodiment is based on the technical solution and provides a detailed implementation method and a specific operation process, but the present invention is not limited to this embodiment.

[0027] Example 1

[0028] A method for preparing a monovalent and divalent ion separation membrane comprises the following steps:

[0029] (1) dissolving 2 g of piperazine dicarboxylic acid in water to form a piperazine dicarboxylic acid solution with a mass concentration of 2%, adding 40 mg of sodium dodecyl sulfate to a 400 mg / L solution to the piperazine dicarboxylic acid solution under stirring at room temperature, and continuing to stir evenly to obtain an aqueous phase solution;

[0030] (2) dissolving trimesoyl chloride in n-hexane to form an oil phase solution with a mass concentration of 0.4%;

[0031] (3) The support layer (base membrane) is fixed on the coating device, and then the aqueous solution is poured on the support layer. After standing at room temperature of 25°C for 5 minutes, the excess aqueous solution is blown away with a hair dryer, and then the oily solution is poured on the support layer. After standing at room temperature of 25°C for 15 minutes, the excess oily solution is washed with n-hexane to remove the excess oily solution, and then placed in an oven at 60°C for drying for 15 minutes to obtain a monovalent and divalent ion separation membrane.

[0032] The base membrane is a polyethersulfone membrane (ultrafiltration membrane), specification model: MQ PES-50000, manufacturer: Synder.

[0033] Example 2

[0034] The difference between this embodiment and embodiment 1 is that the types of water phase monomers are different. In this embodiment, the water phase monomer is a mixture of piperazine and piperazine dicarboxylic acid, wherein the mass ratio of piperazine to piperazine dicarboxylic acid is 1:3. At the same time, the oil phase solution is poured onto the support layer and allowed to stand for 3 minutes. The other steps are exactly the same as those in embodiment 1.

[0035] Example 3

[0036] The difference between this embodiment and embodiment 2 is that the mass ratio of the water phase monomers is different. The water phase monomers in this embodiment also include piperazine and piperazine dicarboxylic acid, and the mass ratio of piperazine to piperazine dicarboxylic acid is 1:1. The other steps are exactly the same as those in embodiment 2.

[0037] Example 4

[0038] The difference between this embodiment and embodiment 2 is that the mass ratio of the water phase monomers is different. The water phase monomers in this embodiment also include piperazine and piperazine dicarboxylic acid, and the mass ratio of piperazine to piperazine dicarboxylic acid is 3:1. The other steps are exactly the same as those in embodiment 2.

[0039] Example 5

[0040] The difference between this embodiment and embodiment 2 is that the type of the aqueous phase monomer is different. In this embodiment, the aqueous phase monomer is piperazine, and the other steps are exactly the same as those in embodiment 2.

[0041] Example 6

[0042] The difference between this embodiment and embodiment 4 is that the mass concentration of the water phase monomer is different. The mass concentration of the water phase monomer in this embodiment is 1%. The other steps are exactly the same as those in embodiment 4.

[0043] Example 7

[0044] The difference between this embodiment and embodiment 4 is that the mass concentration of the water phase monomer is different. The mass concentration of the water phase monomer in this embodiment is 3%. The other steps are exactly the same as those in embodiment 4.

[0045] Example 8

[0046] The difference between this embodiment and embodiment 4 is that the mass concentration of the water phase monomer is different. The mass concentration of the water phase monomer in this embodiment is 4%. The other steps are exactly the same as those in embodiment 4.

[0047] Example 9

[0048] The difference between this embodiment and embodiment 4 is that the mass concentration of the water phase monomer is different. The mass concentration of the water phase monomer in this embodiment is 5%. The other steps are exactly the same as those in embodiment 4.

[0049] Example 10

[0050] The difference between this embodiment and embodiment 4 is that the mass concentration of the oil phase monomer is different. The mass concentration of the oil phase monomer in this embodiment is 0.1%. The other steps are exactly the same as those in embodiment 4.

[0051] Embodiment 11

[0052] The difference between this embodiment and embodiment 4 is that the mass concentration of the oil phase monomer is different. The mass concentration of the oil phase monomer in this embodiment is 0.2%. The other steps are exactly the same as those in embodiment 4.

[0053] Example 12

[0054] The difference between this embodiment and embodiment 4 is that the mass concentration of the oil phase monomer is different. The mass concentration of the oil phase monomer in this embodiment is 0.3%. The other steps are exactly the same as those in embodiment 4.

[0055] Embodiment 13

[0056] The difference between this embodiment and embodiment 4 is that the mass concentration of the oil phase monomer is different. The mass concentration of the oil phase monomer in this embodiment is 0.5%. The other steps are exactly the same as those in embodiment 4.

[0057] Comparative Example 1

[0058] The difference between this embodiment and embodiment 4 is that the base membrane is not subjected to the preparation of the interfacial polymerization layer, and the base membrane is directly used as a separation membrane to separate monovalent and divalent ions.

[0059] Test example

[0060] (1) Membrane flux detection method

[0061] The laboratory cross-flow filtration device was used to test the membrane flux to water and salt, and the retention rate of different salts. The test system consisted of feed liquid, high-pressure infusion pump, pressure gauge, membrane component filter, pipeline, flow detector and other components. The effective membrane area was 16cm 2, the test pressure is 3 bar, and the test temperature is room temperature (25°C). The calculation formula of membrane flux is J = V / (A·Δt·P), where J is the water flux of the membrane (L / m 2 ·h -1 bar -1 ), V is the volume of organic solvent permeating the membrane (L), A is the effective membrane area (m 2 ), Δt is the working time (h), and P is the operating pressure (bar).

[0062] The specific process of testing the retention rate is as follows: install the membrane sample to be tested in the test membrane pool of the cross-flow filtration device. The effective test area of ​​the test membrane pool is 16cm 2 , using the prepared inorganic salt solution as the feed solution, the inorganic salt solution includes sodium sulfate and sodium chloride, the concentration of sodium sulfate and sodium chloride are both 2000ppm, setting the system pressure to 3bar, collecting the permeate, and measuring its concentration. Calculate its retention rate according to the retention rate calculation formula.

[0063] The calculation formula of interception rate is R = (1-C p / C f )×100%, where C f is the concentration of the raw material solution (g / L), C p is the concentration of the permeate (g / L). The separation coefficient formula for two salts is S = (100-R NaCl ) / (100-R Na2SO4 ).

[0064] (2) Evaluation of antifouling performance

[0065] The fouling process of the separation membrane was evaluated at 25°C and 0.4 MPa pressure using a bovine serum albumin solution (BSA solution) with a concentration of 0.1 g / L as a representative fouling source. The antifouling performance of each separation membrane was evaluated on multiple samples. The following are the specific details of the operation: First, the membrane was pre-pressurized for 1 hour to achieve a constant water flux, and its initial pure water flux was measured as J w1 The membrane was then exposed to the pollutant solution and the pure water flux was measured every 10 min and recorded as J p After the fouling was completed, the membrane was washed with deionized water three times for 20 minutes each time to remove the organic matter that had been adsorbed and deposited on the membrane surface, and finally the pure water flux of the cleaned membrane was tested again and identified as J w2 . Used to evaluate the total fouling rate of the separation membrane (R t ), flux recovery rate after water cleaning (FRR), reversible contamination rate (R r ) and irreversible contamination rate (R ir ), specifically using the following formula to derive:

[0066]

[0067]

[0068]

[0069] Rir=R t -R r

[0070] The test results of the separation membrane are shown in Tables 1 and 2 and the attached Figure 1 to Figure 3 .

[0071] Table 1 Separation membrane water flux and separation performance test results

[0072]

[0073]

[0074] Table 2 Separation membrane antifouling performance test results

[0075]

[0076] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A monovalent and divalent ion separation membrane, comprising a support layer and an interfacial polymerization layer formed on the surface of the support layer, characterized in that: The interfacial polymer layer is formed by polymerization of water phase monomers and oil phase monomers, wherein the water phase monomers include piperazine and piperazine dicarboxylic acid, and the oil phase monomers include substances containing acyl chloride groups.

2. The monovalent and divalent ion separation membrane according to claim 1, characterized in that: The material of the support layer is one or more of polyethersulfone, polysulfone and polyvinylidene fluoride.

3. The monovalent and divalent ion separation membrane according to claim 1, characterized in that: The mass ratio of piperazine to piperazine dicarboxylic acid is 0-3:1-3.

4. The monovalent and divalent ion separation membrane according to claim 1, characterized in that: The oil phase monomer is one or more of trimesoyl chloride, isophthaloyl chloride, phthaloyl chloride and terephthaloyl chloride.

5. The method for preparing a monovalent and divalent ion separation membrane according to any one of claims 1 to 4, characterized in that: The following steps are involved: (1) dissolving an aqueous phase monomer and a surfactant in water to form an aqueous phase solution; (2) dissolving the oil phase monomer in an organic solvent to form an oil phase solution; (3) The support layer is fixed on the coating device, and then the aqueous solution is poured on the support layer. After standing, the excess aqueous solution is removed. Then, the oil phase solution is poured on the support layer. After continuing to stand, the excess oil phase solution is removed, and then drying is performed to obtain a monovalent and divalent ion separation membrane.

6. The method for preparing a monovalent and divalent ion separation membrane according to claim 5, characterized in that: In step (1), the mass concentration of the aqueous phase monomer in the aqueous phase solution is 1-5%, the surfactant is sodium dodecyl sulfate, and the concentration of the surfactant added to the aqueous phase solution is 350-450 mg / L.

7. The method for preparing a monovalent and divalent ion separation membrane according to claim 5, characterized in that: In step (2), the organic solvent is one or more of n-hexane, cyclohexane, isoparaffin and n-heptane; and the mass concentration of the oil phase monomer in the oil phase solution is 0.1-0.5%.

8. The method for preparing a monovalent and divalent ion separation membrane according to claim 5, characterized in that: In step (3), after the aqueous phase solution is poured onto the support layer, it is allowed to stand at room temperature for 3 to 8 minutes, and after the oil phase solution is poured onto the support layer, it is allowed to stand at room temperature for 5 to 10 minutes.

9. The method for preparing a monovalent and divalent ion separation membrane according to claim 5, characterized in that: In step (3), the drying temperature is 50 to 80° C. and the drying time is 10 to 30 minutes.

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