Cellulose / pvdf electrospun oil-water separation membrane and preparation method thereof

Abstract

The application belongs to the field of separation and specifically relates to a cellulose / PVDF electrostatic spinning oil-water separation membrane and a preparation method thereof. The preparation method comprises the following steps: S1: preparing cellulose stearate; S2: mixing cellulose stearate obtained in step S1 and polyvinylidene fluoride (PVDF) prepared into solutions respectively to obtain a spinning solution; and S3: defoaming the spinning solution obtained in step S2 and then electrostatic spinning to obtain a cellulose stearate / polyvinylidene fluoride (PVDF) hydrophobic oleophilic oil-water separation membrane. The mixed electrostatic spinning nanofiber membrane has better mechanical properties, and due to the addition of modified cellulose, the nanofiber membrane has greater separation flux, higher separation efficiency and greater porosity.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of separation, and particularly relates to a cellulose / PVDF electrospun oil-water separation membrane and a preparation method thereof. BACKGROUND

[0002] Traditional oil-water separation methods such as metal mesh-based filter materials and fabric-based filter materials cannot effectively remove small oil droplets and emulsified oil. In comparison, membrane separation technology has been widely concerned due to its characteristics of high efficiency, adjustable pore size, high flux and no secondary pollution.

[0003] Electrospinning is one of the most direct and simple methods for film preparation. Various polymer solutions can be driven by electrostatic action to be sprayed into micro-nano fibers. In addition, electrospun nanofiber membranes are not easily contaminated and have excellent modification ability, so they can be well applied in oil-water separation.

[0004] Polyvinylidene fluoride (PVDF) is widely concerned as an electrospinning material due to its high thermal stability, hydrophobicity, chemical resistance and mechanical strength. In recent years, PVDF membrane materials have been widely used in microfiltration and ultrafiltration due to their good biocompatibility and chemical corrosion resistance. However, pure PVDF membranes have problems such as poor antifouling performance and low flux in practical application in oil-water separation.

[0005] Cellulose is a rich, biodegradable, non-toxic and low-cost biopolymer, which has shown great application potential in the production of electrospun membrane materials in recent years. At the same time, cellulose is used as a reinforcing agent in electrospinning, which can significantly improve the mechanical properties of various polymer materials. When it is used for oil-water separation, it can also improve the oil / water separation flux of the composite material, and still has certain advantages compared with other composite materials. SUMMARY

[0006] The purpose of the present application is to overcome the shortcomings in the prior art and provide a cellulose / PVDF electrospun oil-water separation membrane and a preparation method thereof.

[0007] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0008] A preparation method of a cellulose / PVDF electrospun oil-water separation membrane, comprising the following steps: S1: preparing cellulose stearate; S2: mixing cellulose stearate obtained in step S1 and polyvinylidene fluoride (PVDF) prepared into solutions respectively to obtain a spinning solution; S3: defoaming the spinning solution obtained in step S2 and then electrospinning to obtain a cellulose stearate / polyvinylidene fluoride (PVDF) hydrophobic and oleophilic oil-water separation membrane.

[0009] The mass ratio of cellulose stearyl ester to PVDF in step S2 is 1:9-3:7.

[0010] The mass ratio of cellulose stearyl ester to PVDF in step S2 is 1:9-2:8.

[0011] The mass ratio of cellulose stearyl ester to PVDF in step S2 is 2:8.

[0012] The cellulose stearyl ester in step S1 is prepared in the following manner: S1-1: adding absolutely dry dissolving pulp into DMAC, adding anhydrous lithium chloride at 70-90 DEG C, and stirring overnight to obtain a dissolving pulp solution; S1-2: adding the dissolving pulp solution and stearyl chloride into a catalyst, and reacting at 60-90 DEG C for 6-8 h, the catalyst being triethylamine, and the molar ratio of dissolving pulp to catalyst being 1:3; then precipitating and drying the product to obtain cellulose stearyl ester; the molar ratio of dissolving pulp to stearyl chloride being 1:3-1:4.

[0013] Preferably, the mass concentration of the dissolving pulp solution in S1 is 2%.

[0014] Preferably, the product is precipitated and washed with a mixed solution of methanol and water in a ratio of 3:1, and is dried in a vacuum drying oven at 25 DEG C for 24 h.

[0015] Step S3 comprises the following steps: defoaming the spinning solution, and electrospinning in an environment with a temperature of 15-25 DEG C and a relative humidity of 35%-45%, and then drying in a vacuum drying oven at room temperature to obtain a cellulose stearyl ester / polyvinylidene fluoride hydrophobic and oleophilic oil-water separation membrane.

[0016] The mass concentration of the solution in the spinning solution is 12%, and the solvent is a mixed solution of DMF and acetone in a volume ratio of 4:1.

[0017] The application also comprises a cellulose / PVDF electrospun oil-water separation membrane prepared by the preparation method.

[0018] Compared with the prior art, the application has the following beneficial effects:

[0019] In the application, cellulose is modified with stearyl chloride under homogeneous conditions to obtain cellulose stearyl ester (CES) with superhydrophobicity, the cellulose stearyl ester is mixed with PVDF to prepare a spinning solution, and a hydrophobic and oleophilic electrospun nanofiber membrane is prepared. The electrospun nanofiber membrane is applied to the separation of trace water in a water-in-oil emulsion. Compared with a general electrospun PVDF nanofiber membrane, the mixed electrospun nanofiber membrane has better mechanical properties, and due to the addition of modified cellulose, the nanofiber membrane has a larger separation flux, a higher separation efficiency, and a larger porosity. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 A photograph of a cellulose stearate / PVDF nanofiber membrane prepared for Example 2; and showing different properties for oil and water

[0021] Figure 2 A SEM photograph of a cellulose stearate / PVDF nanofiber membrane prepared for Example 2 (diameter is 300-800).

[0022] Figure 3 A graph of the contact angle of a cellulose stearate / PVDF nanofiber membrane for oil and water in Examples 1-7.

[0023] Figure 4 A graph of the tensile strength of a cellulose stearate / PVDF nanofiber membrane in Examples 1-7. DETAILED DESCRIPTION

[0024] In order for those skilled in the art to better understand the technical solutions of the present application, the present application will be further described in detail below in combination with the drawings and the best embodiment.

[0025] Example 1: A preparation method of a cellulose stearate / PVDF electrospun oil-water separation membrane, comprising the following steps: (1) 2 g of absolutely dry dissolving pulp (from Shandong Sun Paper) is added into 100 ml of DMAC, 9 g of anhydrous lithium chloride is added at 80°C, and after 3 h of heat preservation, it is stirred overnight to obtain a dissolving pulp solution. (2) In a room temperature environment, 20 g of the dissolving pulp solution obtained in step (1) is taken, 0.95 mL of triethylamine (the molar ratio of dissolving pulp to catalyst triethylamine is 1:3) is added, and then 2.38 ml of stearoyl chloride (the molar ratio of dissolving pulp to stearoyl chloride is 1:3) is added dropwise with a syringe. The system temperature is raised to 60°C, and the reaction is continued for 6 hours. After the reaction is completed, it is washed with methanol / water three times, centrifuged, and the final product is vacuum dried at 30°C for 24 hours. (3) 0.15 g of the product obtained in step (2) is added into DMF, and ultrasonic is used to completely dissolve it. (4) 1.35 g of PVDF powder is added into a mixed solution of DMF and acetone, and stirred at 80°C for 3 h. (5) The solutions obtained in steps (3) and (4) are mixed, the solution concentration is 12%, the total DMF:acetone in the solution is 4:1, and stirring is carried out at 80°C for 2 h. After the stirring is completed, it is ultrasonically degassed at room temperature for 1 h to obtain a uniform transparent spinning solution. (6) The spinning solution obtained in step (5) is electrospun at a voltage of 15 KV, a spinning distance of 15 cm, a pushing speed of 0.5 ml / h, and a rotation speed of 200 r / min. Then the obtained nanofiber membrane is placed into a 50°C vacuum drying oven for drying for 2 h. The obtained nanofiber membrane has a fiber diameter of 500-800 nm, a tensile strength of 23.5 MPa, a water-in-oil emulsion flux of 155 L·m -2 ·h -1 , and a separation efficiency of 94.1%.

[0026] Example 2: The difference between Example 2 and Example 1 is only in the preparation method of cellulose stearyl ester; in step (2), the temperature is increased to 90°C, and the reaction is continued for 6 hours. The obtained nanofiber membrane has a fiber diameter of 500-800 nm, a tensile strength of 22.7 MPa, a water-in-oil emulsion flux of 167 L-m -2 ·h -1 , and a separation efficiency of 94.9%. The results show that, compared with Example 1, in the preparation process of cellulose stearyl ester, increasing the temperature to 90°C slightly improves the hydrophobic and lipophilic properties of cellulose stearyl ester, and the effect of blending with PVDF for spinning on the obtained nanofiber membrane is not obvious. Figure 1 Example 2: The difference between Example 2 and Example 1 is only in the preparation method of cellulose stearyl ester; in step (2), the temperature is increased to 90°C, and the reaction is continued for 6 hours. The obtained nanofiber membrane has a fiber diameter of 500-800 nm, a tensile strength of 22.7 MPa, a water-in-oil emulsion flux of 167 L-m Figure 2 Example 2: The difference between Example 2 and Example 1 is only in the preparation method of cellulose stearyl ester; in step (2), the temperature is increased to 90°C, and the reaction is continued for 6 hours. The obtained nanofiber membrane has a fiber diameter of 500-800 nm, a tensile strength of 22.7 MPa, a water-in-oil emulsion flux of 167 L-m

[0027] Example 3: The difference between Example 3 and Example 1 is only in the preparation method of cellulose stearyl ester; in step (2), 3.17 ml of stearyl chloride is added (the molar ratio of dissolved pulp to stearyl chloride is 1:4), and the rest of the reaction conditions remain unchanged. The obtained nanofiber membrane has a diameter of 500-800 nm, a tensile strength of 22.5 MPa, a water-in-oil emulsion flux of 159 L-m -2 ·h -1 , and a separation efficiency of 94.7%. The results show that, compared with Example 1, in the preparation process of cellulose stearyl ester, increasing the ratio of stearyl chloride to cellulose slightly improves the hydrophobic and lipophilic properties of cellulose stearyl ester, and the effect of blending with PVDF for spinning on the obtained nanofiber membrane is not obvious.

[0028] Example 4: The difference between Example 4 and Example 1 is only in the preparation method of cellulose stearyl ester; in step (2), the reaction time is increased to 8 hours, and the rest of the reaction conditions remain unchanged. The obtained nanofiber membrane has a diameter of 500-800 nm, a tensile strength of 23.1 MPa, a water-in-oil emulsion flux of 163 L-m -2 ·h -1 , and a separation efficiency of 94.2%. The results show that, compared with Example 1, in the preparation process of cellulose stearyl ester, increasing the reaction time slightly reduces the hydrophobic and lipophilic properties of cellulose stearyl ester, and the effect of blending with PVDF for spinning on the obtained nanofiber membrane is not obvious.

[0029] Example 5: The difference between Example 5 and Example 1 is only that the mass ratio of cellulose stearyl ester to PVDF is different, specifically, the amount of cellulose stearyl ester added in step (3) is 0.3 g, and the amount of PVDF added in step (4) is 1.2 g. The fiber diameter of the obtained nanofiber membrane is 400-700 nm, the tensile strength is 25.3 MPa, the water-in-oil emulsion flux is 485 L·m -2 ·h -1 , and the separation efficiency is 96.5%. Compared with Example 1, the results show that, in the process of blending spinning, as the amount of cellulose ester increases, when the ratio of cellulose ester to PVDF reaches 2:8, the tensile strength of the obtained nanofiber membrane increases, the flux of water-in-oil emulsion increases significantly, and the separation efficiency increases.

[0030] Example 6: The difference between Example 6 and Example 1 is only that the mass ratio of cellulose stearyl ester to PVDF is different, specifically, the amount of cellulose stearyl ester added in step (3) is 0.45 g, and the amount of PVDF added in step (4) is 1.05 g. The fiber diameter of the obtained nanofiber membrane is 300-600 nm, the tensile strength is 2.4 MPa, the water-in-oil emulsion flux is 1390 L·m -2 ·h -1 , and the separation efficiency is 90.7%. The results show that, compared with Example 1, in the process of blending spinning, when the ratio of cellulose ester to PVDF reaches 3:7, due to the increase of the proportion of cellulose ester, the low strength of cellulose dominates the composite material, so the tensile strength decreases significantly, and after multiple cycles, the separation efficiency decreases continuously due to the rupture of the composite material.

[0031] Example 7: The difference between Example 7 and Example 1 is that only PVDF is used as the spinning raw material, specifically the following steps are adopted: (1) 1.5 g of PVDF powder is added to a mixed solution of DMF and acetone with a ratio of 4:1, the concentration of PVDF is 12%, and stirring is carried out at 60°C for 3h. (2) Ultrasonic debubbling at room temperature for 1h to obtain a uniform transparent spinning solution. (3) Electrospinning of the spinning solution obtained in step (2) at a voltage of 15KV, a spinning distance of 15cm, a pushing speed of 0.5ml / h, and a rotation speed of 200r / min, and then the obtained nanofiber membrane is placed in a 50°C vacuum drying oven for drying for 2h. The fiber diameter of the obtained nanofiber membrane is 500-600 nm, the tensile strength is 12.6 MPa, the water-in-oil emulsion flux is 109 L·m -2 ·h -1 , and the separation efficiency is 92.6%. The results show that pure PVDF has lower separation flux, smaller tensile strength, and lower separation efficiency, which has a significant disadvantage compared with Examples 1-5.

[0032] The cellulose stearate / PVDF electrospinning nanofiber membrane prepared by the application has adjustable fiber structure and superhydrophobic property, and the contact angle obtained under the condition of example 1 is 138°, the contact angle obtained under the condition of example 2 is 142°, the contact angle obtained under the condition of example 3 is 143°, the contact angle obtained under the condition of example 4 is 139°, the contact angle obtained under the condition of example 5 is 151°, the contact angle obtained under the condition of example 6 is 132°, and the contact angle obtained under the condition of example 7 is 133°. Figure 3 The figure is the contact angle of the cellulose stearate / PVDF nanofiber membrane in examples 1-7 to oil and water. Figure 4 The figure is the tensile strength of the cellulose stearate / PVDF nanofiber membrane in examples 1-7.

[0033] It should be noted that examples 1-7 all use chloroform water-in-oil emulsion for exemplary description, and it has been verified that, for example, toluene water-in-oil emulsion, chloroform water-in-oil emulsion, kerosene water-in-oil emulsion, and soybean oil water-in-oil emulsion can also achieve good implementation effect. In the oil-water separation process, especially for water-in-oil emulsion, the separation efficiency can reach 96.5%, and the particle size of water in oil after separation in examples 1, 2, 3, and 4 is within 30 nm, the particle size of water in oil after separation in example 5 is within 20 nm, and the particle size of water in oil after separation in examples 6 and 7 is within 50 nm. In practical application, the modified cellulose is non-toxic and biodegradable, and is more green and environmentally friendly compared with traditional oil-water separation membranes.

[0034] The application modifies cellulose with stearoyl chloride under homogeneous conditions to obtain cellulose stearate with superhydrophobic property, mixes the cellulose stearate with PVDF to prepare a hydrophobic and oleophilic electrospinning nanofiber membrane. And it is applied to the separation of trace water in water-in-oil emulsion. Compared with general electrospinning PVDF nanofiber membrane, the mixed electrospinning nanofiber membrane has better mechanical properties, and due to the addition of modified cellulose, the nanofiber membrane has larger separation flux, higher separation efficiency and larger porosity.

[0035] The above only describes the preferred embodiments of the application, and it should be noted that those skilled in the art can make several improvements and refinements without departing from the principles of the application, and these improvements and refinements should also be considered as the protection scope of the application.

Claims

1. A method for preparing a cellulose / PVDF electrospun oil-water separation membrane, characterized in that, The method comprises the following steps: S1, preparing cellulose stearyl ester; S2, mixing cellulose stearyl ester and polyvinylidene fluoride prepared into solutions respectively to obtain a spinning solution; S3, defoaming the spinning solution obtained in step S2 and electrospinning to obtain a cellulose stearyl ester / polyvinylidene fluoride hydrophobic and oleophilic oil-water separation membrane; and the mass ratio of cellulose stearyl ester to PVDF in step S2 is 2:

8.

2. The method for preparing the cellulose / PVDF electrospun oil-water separation membrane according to claim 1, characterized in that, In step S1, the cellulose stearyl ester is prepared in the following manner: S1-1, adding absolutely dry dissolving pulp into DMAC, adding anhydrous lithium chloride at 70-90 DEG C, and stirring overnight to obtain a dissolving pulp solution; S1-2, adding the dissolving pulp solution and stearyl chloride into a catalyst and reacting at 60-90 DEG C for 6-8 hours, the catalyst is triethylamine, and the molar ratio of the dissolving pulp to the catalyst is 1:3; then drying the product to obtain cellulose stearyl ester; and the molar ratio of the dissolving pulp to stearyl chloride is 1:3-1:

4.

3. The method of claim 2, wherein the cellulose / PVDF electrospun oil-water separation membrane is prepared by electrospinning a cellulose / PVDF solution onto a collector. The mass concentration of the dissolving pulp solution in step S1 is 2%.

4. The method for preparing the cellulose / PVDF electrospun oil-water separation membrane according to claim 2, characterized in that, The product is washed with a mixed solution of methanol and water in a volume ratio of 3:1, and then is placed in a vacuum drying oven at 25 DEG C for 24 hours.

5. The method for preparing the cellulose / PVDF electrospun oil-water separation membrane according to claim 1, characterized in that, Step S3 comprises the following steps: defoaming the spinning solution, electrospinning at 15-25 DEG C and in an environment with a relative humidity of 35-45%, and then drying in a vacuum drying oven at room temperature to obtain a cellulose stearyl ester / polyvinylidene fluoride hydrophobic and oleophilic oil-water separation membrane.

6. The method of claim 5, wherein the cellulose / PVDF electrospun oil-water separation membrane is prepared by electrospinning a cellulose / PVDF solution onto a collector. The mass concentration of the solution in the spinning solution is 12%, and the solvent is a mixed solution of DMF and acetone in a volume ratio of 4:

1.

7. A cellulose / PVDF electrospinning oil-water separation membrane prepared by the method according to any one of claims 1-6.

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