Preparation method of nanobubble-regulated ceramic-based polyamide nanofiltration membrane

Abstract

The invention discloses a preparation method of a nanobubble-regulated ceramic-based polyamide nanofiltration membrane, which comprises the following steps: (1) carrying out ultrasonic cleaning and strong alkali activation on a ceramic membrane, and loading a silane coupling agent to obtain a silane grafted ceramic membrane; (2) reacting the silane grafted ceramic membrane with an aqueous solution containing piperazine, sodium borohydride, lauryl sodium sulfate and a polyamine catalyst at room temperature, and then removing the unreacted aqueous solution; (3) reacting the material obtained in the step (2) with an n-hexane solution of trimesoyl chloride at room temperature, and then removing the unreacted n-hexane solution; and (4) carrying out air drying and heat treatment on the material obtained in the step (3). Sodium borohydride and lauryl sodium sulfate are synchronously introduced into a water phase, nanoscale hydrogen bubbles are generated and stabilized in situ in the interfacial polymerization process, rich nanoscale protruding structures are formed on the surface of a polyamide selection layer, the effective permeation area of the membrane is greatly increased, and therefore the pure water flux is remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of membrane separation technology, specifically relating to a method for preparing a ceramic-based polyamide nanofiltration membrane with nanobubble regulation. Background Technology

[0002] Nanofiltration (NF) is a medium between ultrafiltration and reverse osmosis. It can effectively separate substances with molecular weights of 200–1000 Da. It has advantages such as low operating pressure, low energy consumption, and environmental friendliness. It has been widely used in seawater desalination pretreatment, pharmaceutical concentration, antibiotic separation, dye desalination, and lubricating oil solvent recovery.

[0003] Currently, the most commercially successful nanofiltration membranes are mostly thin-layer composite membranes (TFCs), with a typical structure consisting of an ultrathin polyamide selective layer formed by the interfacial polymerization of piperazine (PIP) and trimesoyl chloride (TMC) on a porous support layer. Traditional support layers mainly use organic ultrafiltration membranes such as polysulfone and polyethersulfone, with pore sizes typically ranging from 10 to 50 nm. While these organic supports are low-cost and have good film-forming properties, the significant difference in thermal expansion coefficients between the support layer and the polyamide active layer under conditions of high temperature, organic solvents, strong acids and alkalis, or long-term operation can easily lead to interfacial delamination, rapid decline in selectivity, and a substantial reduction in lifespan. Furthermore, the organic support layer itself has low porosity and insufficient hydrophilicity, further limiting the permeation flux of the composite membrane.

[0004] In recent years, inorganic ceramic membranes such as alumina, titanium dioxide, and zirconium oxide have been considered ideal supports for next-generation composite nanofiltration membranes due to their excellent mechanical strength, high-temperature resistance, resistance to organic solvents, and chemical corrosion resistance. However, when interfacial polymerization is performed directly on the ceramic membrane surface, the bonding force between the polyamide layer and the ceramic surface is weak, and the polymerization reaction is extremely fast, easily forming an overly dense, smooth selective layer, resulting in a significantly lower flux compared to organic-supported composite membranes. Furthermore, conventional interfacial polymerization lacks effective control over the microstructure of the polyamide layer, making it difficult to significantly increase water flux while maintaining high retention capacity. Summary of the Invention

[0005] The purpose of this invention is to overcome the defects of the prior art and provide a method for preparing a ceramic-based polyamide nanofiltration membrane with nanobubble control.

[0006] The technical solution of the present invention is as follows:

[0007] A method for preparing a ceramic-based polyamide nanofiltration membrane with nanobubble regulation includes the following steps:

[0008] (1) After ultrasonic cleaning and strong alkali activation, the ceramic membrane is loaded with silane coupling agent to obtain silane-grafted ceramic membrane;

[0009] (2) The silane-grafted ceramic membrane obtained in step (1) is reacted with an aqueous solution containing piperazine, sodium borohydride, sodium dodecyl sulfate and polyamine catalyst at room temperature, and then the unreacted aqueous solution is removed.

[0010] (3) After reacting the material obtained in step (2) with a hexane solution of trimesoyl chloride at room temperature, the unreacted hexane solution is removed.

[0011] (4) The material obtained in step (3) is air-dried and heat-treated to obtain the ceramic-based polyamide nanofiltration membrane with nanobubble control.

[0012] In a preferred embodiment of the present invention, the ceramic membrane is made of alumina, titanium dioxide, or zirconium oxide.

[0013] In a preferred embodiment of the present invention, the strong base in the strong base solution is sodium hydroxide or potassium hydroxide, with a concentration of 1-10 mol / L and an activation time of 10-24 h.

[0014] In a preferred embodiment of the present invention, the silane coupling agent is 3-aminopropyltriethoxysilane, diethyltrimethoxysilane, or diethyltrimethoxysilane.

[0015] In a preferred embodiment of the present invention, the aqueous solution in step (2) contains: piperazine at a concentration of 0.05-0.5 wt%, sodium borohydride at a concentration of 0.1-0.5 wt%, sodium dodecyl sulfate at a concentration of 0.1-0.5 wt%, and polyamine catalyst at a concentration of 0.1-0.2 wt%.

[0016] More preferably, the polyamine catalyst is diethylamine or triethylamine.

[0017] More preferably, in the aqueous solution of step (2): the concentration of piperazine is 0.1 wt%, the concentration of sodium borohydride is 0.1 wt%, the concentration of sodium dodecyl sulfate is 0.3 wt%, and the concentration of diethylamine is 0.1 wt%.

[0018] In a preferred embodiment of the present invention, the concentration of trimesoamide in the hexane solution of step (3) is 0.05-0.3 wt%.

[0019] In a preferred embodiment of the present invention, the reaction time in step (2) is 1-10 min, and the reaction time in step (3) is 1-10 min.

[0020] More preferably, the temperature of the heat treatment in step (4) is 50-80 ℃.

[0021] The beneficial effects of this invention are:

[0022] 1. This invention introduces sodium borohydride and sodium dodecyl sulfate simultaneously into the aqueous phase, generating and stabilizing nanoscale hydrogen bubbles in situ during interfacial polymerization. This results in a rich array of nanoscale protrusions on the surface of the polyamide selective layer, significantly increasing the effective permeation area of ​​the membrane and thus dramatically improving the pure water flux.

[0023] 2. In this invention, sodium dodecyl sulfate is directionally adsorbed at the water / n-hexane interface to form a stable monolayer, which effectively slows down the diffusion rate of piperazine into the oil phase, making the polymerization reaction more uniform and controllable. The resulting polyamide layer has a narrow pore size distribution and fewer defects, and while significantly increasing the throughput, it still maintains an extremely high rejection rate for divalent salts.

[0024] 3. This invention employs a strong alkali activation and grafting method with an aminosilane coupling agent to introduce a large number of active amino and hydroxyl groups onto the ceramic surface. This not only enhances the chemical bonding strength between the polyamide layer and the ceramic support, but also provides more reaction sites for interfacial polymerization, thereby improving the adhesion strength of the selective layer and its long-term operational stability.

[0025] 4. The entire preparation process of this invention is completed at room temperature. The process is simple, the conditions are mild, no special equipment is required, and it is easy to scale up industrially.

[0026] 5. The ceramic-based polyamide nanofiltration membrane prepared by this invention has high stability and high selectivity, making it particularly suitable for separation and purification processes in high-temperature, high-concentration organic solvents or highly corrosive systems. Its service life is significantly better than that of traditional organic support composite nanofiltration membranes. Attached Figure Description

[0027] Figure 1 This is an electron microscope image of the ceramic-based polyamide nanofiltration membrane prepared in Comparative Example 2 of the present invention.

[0028] Figure 2 This is an electron microscope image of the ceramic-based polyamide nanofiltration membrane prepared in Example 2 of the present invention. Detailed Implementation

[0029] The technical solution of the present invention will be further explained and described below through specific embodiments.

[0030] Comparative Example 1 (Traditional Organic Support Polyamide Nanofiltration Membrane)

[0031] (1) Immerse the polyethersulfone (PES) ultrafiltration membrane base with a molecular weight cutoff of 10,000 Da in an aqueous solution containing 0.1 wt% piperazine and 0.1 wt% diethylamine, react at room temperature for 10 min, and then remove it and blow off the residual liquid on the surface with an air gun.

[0032] (2) The material obtained in step (1) is immersed in a hexane solution containing 0.2 wt% trimesoyl chloride (TMC), reacted at room temperature for 10 min, removed, rinsed with hexane and dried with an air gun;

[0033] (3) After the polyamide obtained in step (2) is placed in a cool place to air dry naturally, it is placed in a 50 ℃ oven for heat treatment for 15 min and cooled with the oven to obtain a polyamide composite nanofiltration membrane.

[0034] Performance testing: At room temperature and an operating pressure of 0.69 MPa, the pure water flux is 45 L·m³. -2 ·h -1 The rejection rate for 2000 mg / L sodium sulfate solution was 97%.

[0035] Comparative Example 2 (ceramic support + silane modification, but without sodium borohydride and SDS in the aqueous phase)

[0036] 1. Ceramic membrane pretreatment

[0037] Titanium oxide ceramic membrane tubes with an average pore size of 50 nm were cut to a length of approximately 50 cm, ultrasonically cleaned for 2 h, immersed in 1 mol / L potassium hydroxide solution for 10 h, dried at 100 ℃ for 24 h, cooled, and then immersed in an ethanol solution of 0.1 wt% 3-aminopropyltriethoxysilane (KH-550) for 12 h at room temperature. The membrane was then rinsed with ethanol and deionized water sequentially, dried at 150 ℃ for 12 h, and cooled in the furnace to obtain a silane-grafted ceramic membrane.

[0038] 2. Preparation of composite membranes

[0039] (1) The above silane-grafted ceramic membrane was immersed in an aqueous solution containing 0.1 wt% piperazine and 0.1 wt% diethylamine, reacted at room temperature for 10 min, and then removed and the surface residual liquid was dried with an air gun.

[0040] (2) The material obtained in step (1) is immersed in a hexane solution containing 0.2 wt% TMC, reacted at room temperature for 10 min, removed, rinsed with hexane and dried with an air gun;

[0041] (3) After the material obtained in step (2) is naturally air-dried in a cool place, it is heat-treated at 50 ℃ for 15 min and then cooled in the furnace to obtain the desired product. Figure 1 The ceramic-based polyamide nanofiltration membrane shown for comparison has a membrane thickness of 169 nm.

[0042] Performance testing: At room temperature and 0.69 MPa, the pure water flux is 75 L·m. -2 ·h -1 The rejection rate for 2000 mg / L sodium sulfate solution was 95%.

[0043] Comparative Example 3 (ceramics + silane + sodium borohydride, but without SDS)

[0044] Step 1 is the same as Comparative Example 2.

[0045] In step 2, the aqueous solution was changed to contain 0.1 wt% piperazine, 0.1 wt% sodium borohydride and 0.1 wt% diethylamine, with the rest being the same as in comparative example 2.

[0046] Performance testing: At room temperature and 0.69 MPa, the pure water flux is 105 L·m⁻². -2 ·h -1 The rejection rate for 2000 mg / L magnesium sulfate solution was 94.5%.

[0047] Comparative Example 4 (ceramics + silane + SDS, but without sodium borohydride)

[0048] Step 1 is the same as Comparative Example 2.

[0049] In step 2, the aqueous solution was changed to contain 0.1 wt% piperazine, 0.1 wt% sodium dodecyl sulfate (SDS) and 0.1 wt% diethylamine, with the rest being the same as comparative example 2.

[0050] Performance testing: At room temperature and 0.69 MPa, the pure water flux is 92 L·m. -2 ·h -1 The rejection rate for 2000 mg / L magnesium sulfate solution was 96.5%.

[0051] Example 1 (Ceramic + Silane + Sodium Borohydride + Small Amount of SDS)

[0052] Step 1 is the same as Comparative Example 2.

[0053] In step 2, the solute composition in the aqueous solution is: 0.1 wt% piperazine, 0.1 wt% sodium borohydride, 0.1 wt% SDS and 0.1 wt% diethylamine, with the remainder being the same as in Comparative Example 2, to obtain a ceramic-based polyamide nanofiltration membrane.

[0054] Performance testing: At room temperature and 0.69 MPa, the pure water flux is 124 L·m. -2 ·h -1 The rejection rate for 2000 mg / L magnesium sulfate solution was 97.6%.

[0055] Example 2 (Ceramic + Silane + Sodium Borohydride + Appropriate Amount of SDS, the optimal mode of the present invention)

[0056] Step 1 is the same as Comparative Example 2.

[0057] In step 2, the solute composition in the aqueous solution was: 0.1 wt% piperazine, 0.1 wt% sodium borohydride, 0.3 wt% SDS, and 0.1 wt% diethylamine, with the remainder being the same as in Comparative Example 2, to obtain the following... Figure 2 The ceramic-based polyamide nanofiltration membrane shown has a membrane thickness of 67.1 nm, and the polyamide selective layer has a rich array of nanoscale protrusions on its surface. The dense surface of the membrane can significantly increase the effective permeation area of ​​the membrane, thereby significantly improving the pure water flux.

[0058] Performance testing: At room temperature and 0.69 MPa, the pure water flux is 150 L·m. -2 ·h -1 The rejection rate for 2000 mg / L magnesium sulfate solution was 98.2%.

[0059] Example 3 (Ceramic + Silane + Sodium Borohydride + Large Amount of SDS)

[0060] Step 1 is the same as Comparative Example 2.

[0061] In step 2, the solute composition in the aqueous solution is: 0.1 wt% piperazine, 0.1 wt% sodium borohydride, 0.5 wt% SDS, 0.1 wt% diethylamine, and the rest is the same as in comparative example 2, to obtain a ceramic-based polyamide nanofiltration membrane.

[0062] Performance testing: At room temperature and 0.69 MPa, the pure water flux is 133 L·m. -2 ·h -1 The rejection rate for 2000 mg / L magnesium sulfate solution was 98.0%.

[0063] The following list compares the embodiments with the comparative examples:

[0064] Table 1

[0065] project Composition of aqueous solution (wt%) Does the ceramic membrane undergo strong alkali activation and silane modification? <![CDATA[Pure water flux (L·m -2 ·h -1 )]]> <![CDATA[Interception rate of 2000 mg / L MgSO4 (%)]]> <![CDATA[Interception rate of 2000 mg / L Na2SO4 (%)]]> Remark Comparative Example 1 0.1% piperazine + 0.1% diethylamine (no sodium borohydride, no SDS) none 45 — 97 Traditional organic support Comparative Example 2 0.1% piperazine + 0.1% diethylamine (no sodium borohydride, no SDS) have 75 — 95 Silane modification only Comparative Example 3 0.1% piperazine + 0.1% sodium borohydride + 0.1% diethylamine (SDS-free) have 105 94.5 — There are bubbles but no foam stabilizer. Comparative Example 4 0.1% piperazine + 0.1% SDS + 0.1% diethylamine (sodium borohydride-free) have 92 96.5 — It contains foam stabilizer but no bubbles. Example 1 0.1% piperazine + 0.1% sodium borohydride + 0.1% SDS + 0.1% diethylamine have 124 97.6 — Bubbles + a small amount of foam stabilizer Example 2 0.1% piperazine + 0.1% sodium borohydride + 0.3% SDS + 0.1% diethylamine have 150 98.2 — Bubbles + appropriate amount of foam stabilizer Example 3 0.1% piperazine + 0.1% sodium borohydride + 0.5% SDS + 0.1% diethylamine have 133 98 — Bubbles + Excessive Foam Stabilizer

[0066] The above description is merely a preferred embodiment of the present invention, and therefore should not be construed as limiting the scope of the present invention. All equivalent changes and modifications made in accordance with the scope of the patent and the contents of the specification should still fall within the scope of the present invention.

Claims

1. A method for preparing a ceramic-based polyamide nanofiltration membrane with nanobubble regulation, characterized in that: Includes the following steps: (1) After ultrasonic cleaning and strong alkali activation, the ceramic membrane is loaded with silane coupling agent to obtain silane-grafted ceramic membrane; (2) The silane-grafted ceramic membrane obtained in step (1) is reacted with an aqueous solution containing piperazine, sodium borohydride, sodium dodecyl sulfate and polyamine catalyst at room temperature, and then the unreacted aqueous solution is removed. (3) After reacting the material obtained in step (2) with a hexane solution of trimesoyl chloride at room temperature, the unreacted hexane solution is removed. (4) The material obtained in step (3) is air-dried and heat-treated to obtain the ceramic-based polyamide nanofiltration membrane with nanobubble control.

2. The preparation method according to claim 1, characterized in that: The ceramic membrane is made of alumina, titanium dioxide, or zirconium oxide.

3. The preparation method according to claim 1, characterized in that: The strong base in the strong alkaline solution is sodium hydroxide or potassium hydroxide, with a concentration of 1-10 mol / L and an activation time of 10-24 h.

4. The preparation method according to claim 1, characterized in that: The silane coupling agent is 3-aminopropyltriethoxysilane, diethyltrimethoxysilane, or diethyltrimethoxysilane.

5. The preparation method according to claim 1, characterized in that: In the aqueous solution of step (2): the concentration of piperazine is 0.05-0.5 wt%, the concentration of sodium borohydride is 0.1-0.5 wt%, the concentration of sodium dodecyl sulfate is 0.1-0.5 wt%, and the concentration of polyamine catalyst is 0.1-0.2 wt%.

6. The preparation method according to claim 5, characterized in that: The polyamine catalyst is diethylamine or triethylamine.

7. The preparation method according to claim 6, characterized in that: In the aqueous solution of step (2): the concentration of piperazine is 0.1 wt%, the concentration of sodium borohydride is 0.1 wt%, the concentration of sodium dodecyl sulfate is 0.3 wt%, and the concentration of diethylamine is 0.1 wt%.

8. The preparation method according to claim 1, characterized in that: The concentration of trimesoamide in the hexane solution in step (3) is 0.05-0.3 wt%.

9. The preparation method according to any one of claims 1 to 8, characterized in that: The reaction time in step (2) is 1-10 min, and the reaction time in step (3) is 1-10 min.

10. The preparation method according to claim 9, characterized in that: The heat treatment temperature in step (4) is 50-80 ℃.

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