Low-temperature auxiliary preparation method of ceramic-based polyamide nanofiltration membrane

Abstract

The invention discloses a low-temperature auxiliary preparation method of a 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 obtained in the step (1) with an aqueous solution containing piperazine 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 and triethyl phosphate at room temperature, then removing the unreacted n-hexane solution, and pre-cooling the n-hexane solution at 20 DEG C for 12 hours for use; and (4) carrying out air drying and heat treatment on the material obtained in the step (3). According to the method, the oil phase is pre-cooled at low temperature, and the specific oil phase active buffer agent is introduced, so that the reaction activity of the acyl chloride monomer is effectively reduced, the interfacial polymerization process is changed from instantaneous explosion to controllable progressive, and the thickness uniformity and compactness of a separation layer are remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of membrane separation technology, specifically relating to a low-temperature assisted preparation method for ceramic-based polyamide nanofiltration membranes. Background Technology

[0002] Nanofiltration is an emerging pressure-driven membrane separation technology that lies between ultrafiltration and reverse osmosis. Its separation layer typically has a pore size of 1-2 nm, which can effectively retain organic matter and divalent / polyvalent ions with a molecular weight of 200-1000 Da. It has important application value in fields such as seawater desalination pretreatment, heavy metal wastewater treatment, dye / antibiotic desalination and concentration, and lithium extraction from salt lakes.

[0003] Polyamide composite nanofiltration membranes are typically prepared using interfacial polymerization, where aqueous amine monomers and oil-phase acyl chloride monomers undergo a rapid polycondensation reaction on the surface of a porous support layer to form an ultrathin, dense separation layer. This method is simple and fast, but it presents the following technical challenges:

[0004] (1) The interfacial polymerization reaction rate is extremely fast (completed in seconds), and monomer diffusion and reaction are difficult to match precisely, which easily forms a separation layer with uneven thickness or many defects, resulting in a significant trade-off effect in the flux-retention rate of the membrane.

[0005] (2) Traditional organic support layers (such as polysulfone and polyethersulfone) have poor acid and alkali resistance, high temperature resistance and pollution resistance. Under harsh working conditions, the support layer is prone to swelling or degradation.

[0006] (3) Although inorganic ceramic membranes have excellent chemical stability, thermal stability and mechanical strength, their strong hydrophilicity leads to excessive diffusion of oil phase monomers during interfacial polymerization. The bonding force between the polyamide functional layer and the ceramic matrix is ​​weak, which can easily lead to problems such as poor adhesion or excessively thick separation layer. It is difficult to achieve both high throughput and high retention rate.

[0007] To overcome the above problems, the industry has tried to control the interfacial polymerization process by adding acid scavengers, adjusting monomer concentration, and introducing intermediate layers. However, existing methods still make it difficult to achieve precise control over the thickness and structure of the separation layer on ceramic substrates. Summary of the Invention

[0008] The purpose of this invention is to overcome the defects of the prior art and provide a low-temperature assisted preparation method for ceramic-based polyamide nanofiltration membranes.

[0009] The technical solution of the present invention is as follows:

[0010] A low-temperature assisted preparation method for a ceramic-based polyamide nanofiltration membrane includes the following steps:

[0011] (1) After ultrasonic cleaning and strong alkali activation, the ceramic membrane is loaded with silane coupling agent to obtain silane-grafted ceramic membrane;

[0012] (2) The silane-grafted ceramic membrane obtained in step (1) is reacted with an aqueous solution containing piperazine and polyamine catalyst at room temperature, and then the unreacted aqueous solution is removed.

[0013] (3) The material obtained in step (2) is reacted with a hexane solution of pyromellitic methyl chloride and triethyl phosphate at room temperature, and then the unreacted hexane solution is removed. The hexane solution is pre-cooled at −20 °C for 12 h before use.

[0014] (4) The material obtained in step (3) is air-dried and heat-treated to obtain the ion-controlled ceramic-based polyamide nanofiltration membrane.

[0015] In a preferred embodiment of the present invention, the ceramic membrane is made of alumina, titanium dioxide, or zirconium oxide.

[0016] 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.

[0017] In a preferred embodiment of the present invention, the silane coupling agent is 3-aminopropyltriethoxysilane, diethyltrimethoxysilane, or diethyltrimethoxysilane.

[0018] More preferably, in the aqueous solution of step (2): the concentration of piperazine is 0.05-0.5 wt%, and the concentration of polyamine catalyst is 0.1-0.3 wt%.

[0019] More preferably, the polyamine catalyst is diethylamine or triethylamine.

[0020] 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%.

[0021] More preferably, the concentration of triethyl phosphate in the hexane solution in step (3) is 0.01-0.05 wt%.

[0022] 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.

[0023] More preferably, the temperature of the heat treatment in step (4) is 50-80 ℃.

[0024] The beneficial effects of this invention are:

[0025] 1. This invention effectively reduces the reactivity of acyl chloride monomers by pre-cooling the oil phase at low temperature and introducing a specific oil phase active buffer, transforming the interfacial polymerization process from "instantaneous burst" to "controllable gradual" and significantly improving the uniformity and density of the separation layer thickness.

[0026] 2. The present invention pregrafts silane coupling agent onto the surface of ceramic membrane to construct chemical bridging bonds, which greatly improves the bonding strength between the polyamide functional layer and the inorganic matrix and avoids the peeling phenomenon commonly seen in traditional composite ceramic nanofiltration membranes.

[0027] 3. This invention uses inorganic ceramics as a support, which endows the composite membrane with excellent acid and alkali resistance, high temperature resistance, oxidation resistance and anti-fouling properties, and significantly extends the stable life of the membrane during use.

[0028] 4. The preparation process of this invention is simple and the conditions are mild. It can be directly implemented on existing ceramic membrane tube production lines and has good prospects for industrial scale-up.

[0029] 5. The ceramic-based polyamide nanofiltration membrane prepared by the present invention achieves a significant synergistic improvement in pure water flux and divalent salt rejection rate, breaking through the trade-off limitation of traditional polyamide nanofiltration membranes on ceramic substrates. Attached Figure Description

[0030] Figure 1 This is an electron microscope image of the ceramic-based polyamide nanofiltration membrane prepared in Comparative Example 3 of the present invention.

[0031] 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

[0032] The technical solution of the present invention will be further explained and described below through specific embodiments.

[0033] Comparative Example 1 (Traditional Organic Support Polyamide Nanofiltration Membrane)

[0034] (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.

[0035] (2) The material obtained in step (1) is immersed in a 0.2 wt% hexane solution of trimesoyl chloride (TMC), reacted at room temperature for 1 min, and then removed, rinsed with hexane and dried with an air gun.

[0036] (3) After the material obtained in step (2) is placed in a cool place to air dry naturally, it is transferred to a 50 ℃ oven for heat treatment for 15 min and cooled with the oven to obtain a polyamide composite nanofiltration membrane.

[0037] Performance test (room temperature, 0.69 MPa): Pure water flux 45 L·m -2 ·h -1 The rejection rate for 2 g / L sodium sulfate solution was 97%.

[0038] Comparative Example 2 (organic base film, oil phase only at low temperature, no buffer)

[0039] The process is basically the same as Comparative Example 1, except that the n-hexane solution in step (2) is used after being pre-cooled at −20 °C for 12 h.

[0040] Performance test (room temperature, 0.69 MPa): Pure water flux 70 L·m -2 ·h -1 The rejection rate for 2 g / L sodium sulfate solution was 92%.

[0041] Comparative Example 3 (Ceramic-based film + silane modification, room temperature interfacial polymerization, no low temperature and no buffer)

[0042] 1. Ceramic membrane pretreatment

[0043] A tubular titanium dioxide ceramic membrane with an average pore size of 50 nm was cut to a length of approximately 50 cm, ultrasonically cleaned for 2 h, immersed in a 1 mol / L potassium hydroxide solution for 10 h, and dried at 100 ℃ for 24 h. After cooling, it was immersed in an ethanol solution of 0.1 wt% 3-aminopropyltriethoxysilane (KH-550) and reacted at room temperature for 12 h. It 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.

[0044] 2. Preparation of composite membranes

[0045] (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.

[0046] (2) Immerse the material obtained in step (1) in a 0.2 wt% hexane solution of trimesoyl chloride (TMC), react at room temperature for 1 min, remove it, rinse with hexane and dry with an air gun;

[0047] (3) After the material obtained in step (2) is air-dried at room temperature, it is placed in a 50 ℃ oven for heat treatment for 15 min, and then cooled with the oven to obtain the product shown in the figure. Figure 1 The ceramic-based polyamide nanofiltration membrane shown for comparison has a membrane thickness of 199 nm.

[0048] Performance test (room temperature, 0.69 MPa): Pure water flux 75 L·m -2 ·h-1 The rejection rate for 2 g / L sodium sulfate solution is 95%.

[0049] Comparative Example 4 (Ceramic substrate film + silane modification, room temperature interfacial polymerization, no low temperature and no buffer)

[0050] Step 1 is the same as Comparative Example 3, and Step 2 is basically the same as Comparative Example 3, except that the n-hexane solution in Step (2) also contains 0.03 wt% triethyl phosphate.

[0051] Performance test (room temperature, 0.69 MPa): Pure water flux 112 L·m -2 ·h -1 The rejection rate for 2 g / L sodium sulfate solution was 95.6%.

[0052] Comparative Example 5 (Ceramic substrate film + silane modification, low temperature oil phase only, no triethyl phosphate)

[0053] Step 1 is the same as Comparative Example 3, and Step 2 is basically the same as Comparative Example 3, except that the n-hexane solution in Step (2) is used after being pre-cooled at −20℃ for 12 h.

[0054] Performance test (room temperature, 0.69 MPa): Pure water flux 125 L·m -2 ·h -1 The rejection rate for 2 g / L sodium sulfate solution was 94.5%.

[0055] Example 1

[0056] Step 1 is the same as Comparative Example 3, and Step 2 is basically the same as Comparative Example 3, except that the n-hexane solution contains 0.2 wt% TMC and 0.01 wt% triethyl phosphate, and the n-hexane solution is used after being pre-cooled at −20 ℃ for 12 h.

[0057] Performance test (room temperature, 0.69 MPa): Pure water flux 132 L·m -2 ·h -1 The rejection rate for 2 g / L sodium sulfate solution was 98%.

[0058] Example 2

[0059] Step 1 is the same as Comparative Example 3, and Step 2 is basically the same as Comparative Example 3, except that: the n-hexane solution contains 0.2 wt% TMC and 0.03 wt% triethyl phosphate, and the n-hexane solution is pre-cooled at −20 ℃ for 12 h before use. The prepared film layer is as follows: Figure 2 The thickness is 65.8 nm, and the film surface is more uniform and dense.

[0060] Performance test (room temperature, 0.69 MPa): Pure water flux 155 L·m-2 ·h -1 The rejection rate for 2 g / L sodium sulfate solution is 99%.

[0061] Example 3

[0062] Step 1 is the same as Comparative Example 3, and Step 2 is basically the same as Comparative Example 3, except that the n-hexane solution contains 0.2 wt% TMC and 0.05 wt% triethyl phosphate, and the n-hexane solution is used after being pre-cooled at −20 ℃ for 12 h.

[0063] Performance test (room temperature, 0.69 MPa): Pure water flux 144 L·m -2 ·h -1 The rejection rate for 2 g / L sodium sulfate solution was 97.5%.

[0064] The following list compares the embodiments with the comparative examples:

[0065] Table 1

[0066] project Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Example 1 Example 2 Example 3 support PES organic base film PES organic base film <![CDATA[50 nm TiO2 ceramic membrane]]> <![CDATA[50 nm TiO2 ceramic membrane]]> <![CDATA[50 nm TiO2 ceramic membrane]]> <![CDATA[50 nm TiO2 ceramic membrane]]> <![CDATA[50 nm TiO2 ceramic membrane]]> <![CDATA[50 nm TiO2 ceramic membrane]]> Silane coupling agent modification none none have have have have have have Aqueous phase composition 0.1% piperazine + 0.1% diethylamine Tongzuo Tongzuo Tongzuo Tongzuo Tongzuo Tongzuo Tongzuo TMC concentration 0.20% 0.20% 0.20% 0.20% 0.20% 0.20% 0.20% 0.20% Triethyl phosphate (buffer) none none none 0.03% none 0.01% 0.03% 0.05% Is the oil phase pre-cooled at −20℃ for 12 h? no yes no no yes yes yes yes Does it simultaneously possess "low temperature + buffer" properties? no no no no no yes yes yes <![CDATA[Pure water flux (L·m -2 ·h -1 )]]> 45 70 75 112 125 132 155 144 Sodium sulfate retention rate (%) 97 92 95 95.6 94.5 98 99 97.5

[0067] 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 low temperature assisted preparation of ceramic based polyamide nanofiltration membranes, 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 and polyamine catalyst at room temperature, and then the unreacted aqueous solution is removed. (3) The material obtained in step (2) is reacted with a hexane solution of pyromellitic methyl chloride and triethyl phosphate at room temperature, and then the unreacted hexane solution is removed. The hexane solution is pre-cooled at −20 °C for 12 h before use. (4) The material obtained in step (3) is air-dried and heat-treated to obtain the ion-controlled ceramic-based polyamide nanofiltration membrane.

2. The cryogenic-assisted production method of claim 1, wherein: The ceramic membrane is made of alumina, titanium dioxide, or zirconium oxide.

3. The cryogenic-assisted production method of claim 1, wherein: 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 cryogenic-assisted production method of claim 1, wherein: The silane coupling agent is 3-aminopropyltriethoxysilane, diethyltrimethoxysilane, or diethyltrimethoxysilane.

5. The cryogenic-assisted production method of claim 4, wherein: In the aqueous solution of step (2), the concentration of piperazine is 0.05-0.5 wt%, and the concentration of polyamine catalyst is 0.1-0.3 wt%.

6. The cryogenic-assisted production method of claim 5, wherein: The polyamine catalyst is diethylamine or triethylamine.

7. The cryogenic-assisted production method of claim 1, wherein: The concentration of trimesoamide in the hexane solution in step (3) is 0.05-0.3 wt%.

8. The low-temperature assisted preparation method as described in claim 7, characterized in that: The concentration of triethyl phosphate in the hexane solution in step (3) is 0.01-0.05 wt%.

9. The low-temperature assisted 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 low-temperature assisted preparation method as described in claim 9, characterized in that: The heat treatment temperature in step (4) is 50-80 ℃.

Images