Preparation method and application of in-situ secondary interfacial polymerization hydrophilic modified ultra-thin composite membrane

Abstract

The present invention provides a preparation method and application of an in-situ secondary interfacial polymerization hydrophilically modified ultra-thin composite membrane, which belongs to the field of membrane preparation and separation technology, and includes the following preparation steps: using a polyacrylonitrile ultrafiltration membrane as a porous supporting base membrane, performing an in-situ amination treatment on the surface of the porous supporting base membrane, then immersing the aminated supporting base membrane in a polyacyl chloride organic phase solution to carry out a primary interfacial polymerization reaction, and then immersing the membrane in an aqueous phase solution containing a hydrophilic material to carry out a secondary interfacial polymerization reaction. After heat treatment, a hydrophilically modified ultra-thin composite membrane is obtained. The preparation process of the present invention is simple and highly controllable. The prepared composite membrane is applied to the dehydration process of a pervaporation alcohol-water system, exhibits high separation selectivity while maintaining a high permeation flux, and the composite membrane has good long-term operational stability at high temperatures.

Description

Technical Field

[0001] The present invention mainly relates to the field of membrane separation technology, and in particular to a method for preparing an in-situ secondary interfacial polymerization hydrophilic modified ultra-thin composite membrane. Background Art

[0002] Fuel ethanol is a highly efficient, environmentally friendly, clean energy source produced through biofermentation using biomass as raw material. Due to its high octane rating and heat of vaporization, and its compatibility with gasoline, it has become an effective alternative to fossil fuels. Currently, fuel ethanol is primarily produced through fermentation of second-generation feedstocks (cereals, potatoes, and sugars), followed by conventional distillation to produce a 95% ethanol solution. However, the purity of ethanol used as fuel must not be less than 99.5% by weight. Because the water produced during the production process easily forms an azeotrope with ethanol, separation and purification are crucial to further improve the purity of the ethanol product.

[0003] The energy consumption of fuel ethanol purification accounts for approximately 60-80% of the entire production process. Among the numerous separation technologies, pervaporation membrane separation offers advantages such as low energy consumption, pollution-free operation, high separation efficiency, ease of operation, and easy integration with other technologies. It is commonly used for the separation of liquid mixtures, particularly for separating azeotropes / near-boiling mixtures, isomers, and heat-sensitive substances. Currently, methods for preparing pervaporation membranes primarily include phase inversion, interfacial polymerization, and surface coating. Interfacial polymerization, a common method for preparing commercial composite membranes, has garnered widespread attention due to its ease of operation, stable film-forming properties, and ease of industrial production.

[0004] Currently, separation membranes prepared by interfacial polymerization are commonly used in ultrafiltration and nanofiltration processes. However, their application in separating liquid mixtures with strong coupling effects and small molecular size differences is relatively limited. This is due to the following reasons: First, the polyamide separation layer prepared by traditional interfacial polymerization lacks density, which can form defects during the interfacial polymerization reaction, resulting in poor separation performance; second, the separation layer's intrinsic chemical structure is not sufficiently hydrophilic, resulting in poor adsorption selectivity for water molecules; and third, the interfacial compatibility between the separation layer and the support layer is poor. Under high-temperature continuous operation conditions, the separation layer easily swells, resulting in poor stability. Although secondary interfacial polymerization has been reported to enhance the density of the separation layer and the hydrophilicity of the membrane surface (Desalination, 2019, 469, 114090; AIChE Journal, 2021, e17144; Separation and Purification Technology, 2021, 257, 117927), the amine monomer used in the first interfacial polymerization only physically acts on the support layer, without considering the interfacial compatibility between the support layer and the separation layer. In addition, the uneven distribution of amine monomer concentration on the support layer surface will cause the structure of the separation layer to be inhomogeneous. Therefore, it is necessary to develop a simple and easy interfacial polymerization modification method to obtain pervaporation membranes with high separation performance and high stability. Summary of the Invention

[0005] In response to the above problems, the present invention provides a method for preparing a hydrophilic ultra-thin composite membrane by in-situ secondary interfacial polymerization. The interfacial compatibility between the support layer and the separation layer can be effectively improved by in-situ functional modification of the porous support base membrane and in-situ primary interfacial polymerization. On this basis, secondary interfacial polymerization is performed on the surface of the separation layer to improve the density of the surface of the separation layer and the diffusion selectivity of the molecules. The introduction of hydrophilic materials in the secondary interfacial polymerization can improve the adsorption selectivity of the membrane surface for water molecules, thereby enhancing the separation performance of the membrane. The composite membrane prepared by the method of the present invention exhibits high separation selectivity and stability in the process of pervaporation alcohol dehydration while maintaining high permeation flux, and the preparation method is simple, controllable and easy to implement.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] A method for preparing an in-situ secondary interfacial polymerization hydrophilic modified ultra-thin composite membrane comprises the following steps:

[0008] A hydrophilic polymer polyacrylonitrile ultrafiltration membrane is used as a porous support base membrane, and the surface of the porous support base membrane is subjected to in-situ amination treatment. The aminated porous support base membrane is then immersed in a polyacyl chloride organic phase solution for a primary interfacial polymerization reaction. The membrane is then immersed in an aqueous phase solution containing a hydrophilic material for a secondary interfacial polymerization reaction. After heat treatment, a hydrophilically modified ultrathin composite membrane is obtained.

[0009] The nitrile groups on the surface of the polyacrylonitrile ultrafiltration membrane can be functionalized with amino groups. Compared with the prior art in which the amine monomer only physically acts on the support layer during interfacial polymerization, the present invention realizes in-situ interfacial polymerization by in-situ amination of the polyacrylonitrile ultrafiltration membrane, constructs a covalent bond between the support layer and the separation layer, and strengthens the interfacial interaction between the support layer and the separation layer. The introduction of hydrophilic materials in the secondary interfacial polymerization is beneficial to improving the density of the separation layer surface and has a good promoting effect on the selective transmission of water molecules.

[0010] Further:

[0011] Step 1: placing the porous support base membrane polyacrylonitrile ultrafiltration membrane in an alkaline solution of a certain temperature and a certain concentration for heat treatment, and repeatedly washing with deionized water until the pH is neutral to obtain a hydrolyzed porous support base membrane;

[0012] Step 2: placing the hydrolyzed porous support base membrane obtained in step 1 in an amine solution of a certain temperature and a certain concentration for heat treatment, and repeatedly washing with deionized water until the pH is neutral to obtain an aminated porous support base membrane;

[0013] Step 3: Immerse the aminated porous support base membrane obtained in step 2 in a polyacyl chloride organic phase solution to perform an interfacial polymerization reaction to obtain a composite membrane;

[0014] Step 4: Immerse the composite membrane obtained in step 3 in an aqueous solution containing a hydrophilic material to perform a secondary interfacial polymerization reaction, wherein the concentration of the hydrophilic material in the aqueous solution is 0.1 to 10.0 wt %;

[0015] Step 5: placing the composite film obtained in step 4 at a certain temperature for heat treatment to obtain the ultra-thin composite film.

[0016] Furthermore, the alkaline solution is one of sodium hydroxide and potassium hydroxide aqueous solutions, with a concentration of 1.0 to 3.0 M, a treatment temperature of 30 to 100° C., and a heat treatment time of 0.5 to 3 h;

[0017] Furthermore, the amine solution is one of ethylenediamine, m-phenylenediamine, and diethylenetriamine aqueous solutions, with a concentration of 1.0 to 3.0 M, a treatment temperature of 30 to 100° C., and a heat treatment time of 1 to 5 hours;

[0018] Furthermore, the concentration of the polyacyl chloride in the organic phase solution is 0.01-10.0 wt %, the polyacyl chloride is one of trimesoyl chloride, terephthaloyl chloride, and isophthaloyl chloride, the soaking time is 1-10 min, the natural drying time is 5-20 min, and the organic phase solvent is one of n-hexane and n-heptane.

[0019] Furthermore, the hydrophilic material described in step 4 is an amino-containing hydrophilic material, preferably an amino-containing zwitterionic material, and its preparation method is: 0.06 mol of 1,3-propane sultone is dissolved in 65 mL of acetonitrile, 0.045 mol of N-aminoethylpiperazine is added to the above solution, reacted at room temperature for 6 hours, the collected precipitate is washed with acetone, and the product is collected again and dissolved in water and precipitated in acetone, solvent exchange is performed in acetone, and finally vacuum drying is obtained to obtain the product.

[0020] Furthermore, in step 4, the soaking time is 1 to 10 minutes, and the natural drying time is 5 to 20 minutes.

[0021] Furthermore, the heat treatment process is to place the composite film in an oven at 40 to 80° C. for a heat treatment time of 5 to 30 minutes.

[0022] The ultra-thin composite membrane prepared by the invention is used in the dehydration process of the pervaporation alcohol-water system.

[0023] Specifically, the performance of the composite membrane was evaluated at a temperature of 76°C and a raw material solution of 90 wt% ethanol-water solution. The permeation flux was 4000-5000 g / (m 2 h), the separation factor is 1000~4000.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The present invention establishes a covalent interaction between the support layer and the separation layer by subjecting the porous support base membrane to in-situ amino group treatment and in-situ interfacial polymerization, thereby strengthening the interfacial compatibility between the support layer and the separation layer and improving the stability of the membrane during use. A secondary interfacial polymerization process introduces a hydrophilic material, optimizing the membrane structure and effectively improving the hydrophilicity of the membrane surface, which is beneficial for enhancing the membrane's separation selectivity. The preparation method provided by the present invention is simple and highly controllable. The prepared composite membrane is applied to the pervaporation of an ethanol-water system, exhibiting high permeation flux and high selectivity for water molecules. The composite membrane also exhibits good long-term operational stability under high-temperature conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a scanning electron microscope image of the composite membrane surface of Example 2;

[0027] Figure 2 This is a scanning electron microscope image of a cross section of the composite membrane of Example 2;

[0028] Figure 3 This is a scanning electron microscope image of the composite membrane surface of the comparative example;

[0029] Figure 4 is a scanning electron microscope image of a cross section of a composite membrane of a comparative example;

[0030] Figure 5 This is a diagram of the long-term operation stability of the composite membrane of Example 2. DETAILED DESCRIPTION

[0031] The detailed process of the present invention is described below with reference to the accompanying drawings and specific embodiments, but the following embodiments are by no means intended to limit the present invention in any way.

[0032] The preparation process of the amino-containing zwitterionic material described in the following examples is as follows: 0.06 mol of 1,3-propane sultone is dissolved in 65 mL of acetonitrile, 0.045 mol of N-aminoethylpiperazine is added to the above solution, and the reaction is carried out at room temperature for 6 hours. The collected precipitate is washed with acetone, and the product is collected again and dissolved in water and precipitated in acetone. Solvent exchange is carried out in acetone, and finally vacuum drying is obtained to obtain the product.

[0033] Example 1

[0034] An in-situ secondary interfacial polymerization hydrophilic modified ultra-thin composite membrane is prepared, and the preparation steps are as follows:

[0035] Step 1: placing the porous support base membrane polyacrylonitrile ultrafiltration membrane in a 1.5M sodium hydroxide aqueous solution at a temperature of 55° C. for 1 hour, repeatedly washing with deionized water until the pH is neutral, and drying to obtain a hydrolyzed porous support base membrane;

[0036] Step 2: heat-treating the hydrolyzed porous support base membrane obtained in step 1 in a 1.0 M diethylenetriamine aqueous solution at 50° C. for 3 h, and repeatedly washing with deionized water until the pH is neutral to obtain an aminated porous support base membrane;

[0037] Step 3: Soak the aminated porous support base membrane obtained in step 2 in a 0.1 wt% organic phase solution of trimesoyl chloride for 3 minutes to perform an interfacial polymerization reaction, and then naturally dry for 10 minutes to obtain a composite membrane;

[0038] Step 4: Soak the composite membrane obtained in step 3 in an aqueous solution containing an amino zwitterionic material at a concentration of 0.1 wt% for 3 minutes to perform a secondary interfacial polymerization reaction, and then dry naturally;

[0039] Step 5: Place the composite film in a 60° C. oven for heat treatment for 15 minutes, then wash with methanol and air-dry for later use, thereby obtaining an ultra-thin composite film, which is recorded as Film 1.

[0040] Membrane 1 was used for pervaporation of ethanol-water solution system. When the temperature was 76℃ and the water content in the raw liquid was 10wt%, the permeation flux of the membrane was 4545g / (m 2 h), the separation factor is 3035.

[0041] Example 2

[0042] An in-situ secondary interfacial polymerization hydrophilic modified ultrathin composite membrane was prepared. The preparation steps were basically the same as those in Example 1, except that in step 4, the amino zwitterionic material was changed from 0.1 wt % to 0.2 wt %, to obtain an ultrathin composite membrane, which was recorded as Membrane 2.

[0043] Membrane 2 was used for pervaporation of ethanol-water system. When the temperature was 76℃ and the water content in the raw liquid was 10wt%, the permeation flux of the membrane was 4380g / (m 2 h), the separation factor is 3870. Figure 1 and Figure 2 The surface and cross-sectional scanning electron microscopy images of membrane 2 are shown respectively.

[0044] Example 3

[0045] An in-situ secondary interfacial polymerization hydrophilic modified ultrathin composite membrane was prepared. The preparation steps were basically the same as those in Example 1, except that in step 4, the concentration of the amino-containing zwitterionic material was changed from 0.1 wt % to 0.5 wt %, resulting in an ultrathin composite membrane, designated as Membrane 3.

[0046] Membrane 3 was used for pervaporation of ethanol-water system. When the temperature was 76℃ and the water content in the raw liquid was 10wt%, the permeation flux of the membrane was 4353g / (m 2 h), the separation factor is 3190.

[0047] Example 4

[0048] An in-situ secondary interfacial polymerization hydrophilic modified ultrathin composite membrane was prepared. The preparation steps were basically the same as those in Example 1, except that in step 4, the concentration of the amino-containing zwitterionic material was changed from 0.1 wt % to 1.0 wt %, to obtain an ultrathin composite membrane, which was recorded as Membrane 4.

[0049] Membrane 4 was used for pervaporation of ethanol-water system. When the temperature was 76℃ and the water content in the raw liquid was 10wt%, the permeation flux of the membrane was 4422g / (m 2 h), the separation factor is 3101.

[0050] Example 5

[0051] An in-situ secondary interfacial polymerization hydrophilic modified ultrathin composite membrane was prepared. The preparation steps were basically the same as those in Example 1, except that in step 4, the concentration of the amino-containing zwitterionic material was changed from 0.1 wt % to 2.0 wt %, to obtain an ultrathin composite membrane, which was recorded as Membrane 5.

[0052] Membrane 5 was used for pervaporation of ethanol-water system. When the temperature was 76℃ and the water content in the raw liquid was 10wt%, the permeation flux of the membrane was 4313g / (m2 h), the separation factor is 2834.

[0053] Example 6

[0054] An in-situ secondary interfacial polymerization hydrophilic modified ultrathin composite membrane was prepared. The preparation steps were basically the same as those in Example 1, except that in step 4, the concentration of the amino-containing zwitterionic material was changed from 0.1 wt % to 3.0 wt %, to obtain an ultrathin composite membrane, which was recorded as Membrane 6.

[0055] Membrane 6 was used for pervaporation of ethanol-water system. When the temperature was 76℃ and the water content in the raw liquid was 10wt%, the permeation flux of the membrane was 4296g / (m 2 h), the separation factor is 2001.

[0056] Comparative Example

[0057] An in-situ one-step interfacial polymerization ultra-thin composite film is prepared, and the preparation steps are as follows:

[0058] Step 1: placing the porous support base membrane polyacrylonitrile ultrafiltration membrane in a 1.5M sodium hydroxide aqueous solution at a temperature of 55° C. for 1 hour, repeatedly washing with deionized water until the pH is neutral, and drying to obtain a hydrolyzed porous support base membrane;

[0059] Step 2: heat-treating the hydrolyzed porous support base membrane obtained in step 1 in a 1.0 M diethylenetriamine aqueous solution at 50° C. for 3 h, and repeatedly washing with deionized water until the pH is neutral to obtain an aminated porous support base membrane;

[0060] Step 3: Soak the aminated porous support base membrane obtained in step 2 in a 0.1 wt% organic phase solution of trimesoyl chloride for 3 minutes to perform an interfacial polymerization reaction, and then naturally dry for 10 minutes to obtain a composite membrane;

[0061] Step 4: Place the composite membrane in a 60° C. oven for heat treatment for 15 minutes, then wash with methanol and air-dry for later use, which is recorded as the reference membrane. Figure 3 and Figure 4 The surface and cross-sectional scanning electron microscopy images of the comparison membrane are respectively.

[0062] The comparative membrane prepared in this example was used for pervaporation of an ethanol-water solution system. When the temperature was 76°C and the water content in the raw liquid was 10 wt%, the membrane permeation flux was 4462 g / (m 2 h), the separation factor is 1633.

[0063] The permeation flux and separation factor of the composite membranes obtained in Examples 1-6 and Comparative Example 1 are shown in Table 1.

[0064] Table 1 Permeation flux and separation factor of membranes 1-6 of the present invention and comparative membrane 1

[0065] <![CDATA[Permeation flux (g / (m 2 h))]]> Separation factor Membrane 1 4545 3035 Membrane 2 4380 3870 Membrane 3 4353 3190 Membrane 4 4422 3101 Membrane 5 4313 2834 Membrane 6 4296 2001 contrast film 4462 1633

[0066] The present invention adopts an in-situ interfacial polymerization method to regulate the physical structure and chemical properties of the composite membrane by adjusting the content of the hydrophilic material, thereby affecting the mass transfer behavior of water molecules. As can be seen from Table 1, the composite membrane hydrophilically modified by in-situ interfacial polymerization has a higher separation factor than the composite membrane that has not been hydrophilically modified, and can maintain a higher permeation flux. This is because: the in-situ amination treatment of the porous supporting base membrane and the primary interfacial polymerization reaction construct a covalent bond between the supporting layer and the separation layer, strengthen the interfacial interaction between the two, and ensure the stability of the membrane structure; the secondary interfacial polymerization process introduces amino-containing zwitterionic materials, which improves the density of the separation layer while improving the hydrophilicity of the membrane surface. The rich ionized hydrophilic groups can break the strong coupling between water molecules and alcohol molecules, promote the rapid penetration of water molecules and inhibit the transmission of alcohol molecules. Figure 5 It can be seen that the composite membrane prepared in Example 2 of the present invention maintained a relatively stable separation performance after 180 hours of continuous operation, indicating that the composite membrane has good long-term operational stability. It should be noted that in the interfacial polymerization of the prior art, amine monomers are only physically adsorbed on the membrane surface, while the present invention, through in-situ amino functionalization of the porous support base membrane, establishes a strong chemical interaction between the separation layer and the support layer, which is beneficial to the stability of the membrane structure and separation performance during application.

[0067] Although the present invention has been described above in conjunction with the accompanying drawings, the present invention is not limited to the above-mentioned specific embodiments. The above-mentioned specific embodiments are merely illustrative and not restrictive. Under the guidance of the present invention, ordinary technicians in this field can make many variations without departing from the purpose of the present invention, and these are all protected by the present invention.

Claims

1. A method for preparing an in-situ secondary interfacial polymerization hydrophilic modified ultra-thin composite membrane, characterized in that: The preparation steps are as follows: Step 1: placing a porous support base membrane polyacrylonitrile ultrafiltration membrane in a 1.5 M sodium hydroxide aqueous solution at a temperature of 55°C for 1 hour, repeatedly washing with deionized water until the pH is neutral, and drying to obtain a hydrolyzed porous support base membrane; Step 2: heat-treating the hydrolyzed porous support base membrane obtained in step 1 in a 1.0 M diethylenetriamine aqueous solution at 50° C. for 3 h, and repeatedly washing with deionized water until the pH is neutral to obtain an aminated porous support base membrane; Step 3: Soak the aminated porous support base membrane obtained in step 2 in a 0.1 wt% organic phase solution of trimesoyl chloride for 3 min to perform an interfacial polymerization reaction, and then naturally dry for 10 min to obtain a composite membrane; Step 4: Soak the composite membrane obtained in step 3 in an aqueous solution containing an amino zwitterionic material at a concentration of 0.2 wt% for 3 min to perform a secondary interfacial polymerization reaction, and then dry naturally; Step 5: heat-treating the composite film in a 60°C oven for 15 minutes, then washing it with methanol and drying it for later use, thereby obtaining an ultra-thin composite film; The preparation process of the amino-containing zwitterionic material is as follows: 0.06 mol of 1,3-propane sultone is dissolved in 65 mL of acetonitrile, 0.045 mol of N-aminoethylpiperazine is added to the above solution, and the reaction is carried out at room temperature for 6 hours. The collected precipitate is washed with acetone, and the product is dissolved in water and precipitated in acetone after being collected again. Solvent exchange is carried out in acetone, and finally, vacuum drying is performed to obtain the product.

2. A pervaporation alcohol-water system dehydration process, characterized in that: An ultra-thin composite film prepared by the method of claim 1.

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