Lignin-based flexible carbon nanofiber membrane as well as preparation method and application thereof

Abstract

The invention discloses a lignin-based flexible carbon nanofiber membrane as well as a preparation method and application thereof, and relates to the field of biomass derived carbon materials. The preparation method comprises the following steps: adding enzymatic hydrolysis lignin and a high polymer into an N, N-dimethylformamide solution, dissolving to obtain a spinning solution, and spinning the spinning solution into a polymer nanofiber membrane through an electrostatic spinning method; the polymer nanofiber membrane is firstly subjected to pre-oxidation treatment in air, and the nanofiber membrane subjected to the pre-oxidation treatment is subjected to carbonization treatment in a nitrogen atmosphere. According to the lignin-based flexible carbon nanofiber membrane disclosed by the invention, the pore structure of the carbon nanofiber membrane is regulated and controlled by selecting parameters such as raw material selection, pre-oxidation heating rate, carbonization temperature and the like, so that the flexibility is achieved, and the use of traditional chemical materials is reduced by adding lignin; moreover, the lignin-based flexible carbon nanofiber membrane is changed from hydrophobicity to super-hydrophilicity, and the limitation of application of the carbon nanofiber membrane in the field of oil-in-water separation is broken through.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of biomass-derived carbon materials, and particularly relates to a lignin-based flexible carbon nanofiber membrane, a preparation method and application thereof. BACKGROUND

[0002] Currently, with the acceleration of industrialization and the expansion of human activities, a large amount of oil-containing wastewater thus generated poses a serious threat to the earth's ecology and water resources. Therefore, it is urgent to implement efficient oil-water separation technology to reduce environmental pollution caused by oil-containing wastewater and promote resource recycling. Common oil-water separation technologies include mechanical skimming, centrifugal separation, chemical flocculation and membrane separation technology, among which membrane separation technology is considered as one of the most promising technologies in the field of emulsified oil-containing wastewater separation due to its high separation efficiency, simple operation, wide application range and no secondary pollution. In recent years, researchers have found that carbon nanofiber membranes have broad application prospects in extreme environment separation due to their good thermal stability, chemical corrosion resistance and low degradation. Sun et al. (Carbon 182 (2021) 11-22) prepared a polyacrylonitrile-based carbon nanofiber membrane by electrospinning and fluorination treatment, which can effectively separate oil-containing wastewater under harsh conditions. However, the existing carbon nanofiber membranes have poor flexibility and are prone to brittle failure, which limits their further application. SUMMARY

[0003] In order to overcome the shortcomings and deficiencies of the prior art, the primary purpose of the present application is to provide a lignin-based flexible carbon nanofiber membrane, a preparation method and application thereof.

[0004] The purpose of the present application is achieved by the following scheme: In a first aspect, the present application provides a preparation method of a lignin-based flexible carbon nanofiber membrane, comprising the following steps: adding enzymatic lignin and high polymer into a N,N-dimethylformamide solution to obtain a spinning solution after dissolution, and spinning the spinning solution into a polymer nanofiber membrane by electrospinning method; and pre-oxidizing the polymer nanofiber membrane in air first, and then carbonizing the nanofiber membrane in a nitrogen atmosphere.

[0005] As a preferred scheme of the present application, the high polymer is polyacrylonitrile and / or polylactic acid, and the weight ratio of the high polymer to the enzymatic lignin is 0.8-1.2. By adding a suitable proportion of high polymer, the spinning solution has good film-forming performance.

[0006] As a preferred scheme of the present application, the weight ratio of the polyacrylonitrile to the enzymatic lignin is 1-2, and the weight ratio of the polylactic acid to the enzymatic lignin is 0-1. Polyacrylonitrile and polylactic acid balance the strength and flexibility of the membrane together.

[0007] As a more preferred embodiment of the present invention, the weight ratio of polylactic acid to enzymatically hydrolyzed lignin is 0.4 to 0.6. At this ratio, polylactic acid can form pores of suitable size in carbon fibers, significantly improving the flexibility of the membrane.

[0008] As a preferred embodiment of the present invention, the temperature during the dissolution process is 50 ℃~70 ℃ to ensure that the enzymatic hydrolysis of lignin and polymers can be fully dissolved.

[0009] As a preferred embodiment of the present invention, the electrospinning method includes placing the spinning solution in a syringe and performing electrospinning under the conditions of 25 kV voltage, 1.8 mL / h feed rate, 25℃ ambient temperature and 45% relative humidity to prepare a uniform and continuous polymer nanofiber membrane.

[0010] As a preferred embodiment of the present invention, the pre-oxidation treatment includes gradually heating the polymer nanofiber membrane in air to 220-300°C at a pre-oxidation heating rate of 0.25-3°C / min and maintaining it for 1.5-2.5 h. More preferably, the pre-oxidation heating rate is 0.5°C / min, under which the carbon nanofiber membrane exhibits optimal flexibility.

[0011] As a preferred embodiment of the present invention, the carbonization treatment temperature is 600~1000 ℃. Within this temperature range, the fiber is fully carbonized to form a stable carbon structure while retaining its flexible properties, thereby improving its separation performance for oil-in-water wastewater.

[0012] Secondly, the present invention also proposes a lignin-based flexible carbon nanofiber membrane, which is prepared by the above-described method.

[0013] Thirdly, the present invention also proposes an application of the lignin-based flexible carbon nanofiber membrane prepared by the above preparation method in an oil-water separation tool.

[0014] Compared with the prior art, the present invention has the following advantages and beneficial effects: 1. Polylactic acid (PLA) was added to the electrospinning raw material. PLA decomposes at high temperature to produce gas, thereby creating pores in carbon nanofibers. By controlling the PLA content, pre-oxidation heating rate, carbonization temperature, and other conditions, the pore structure of lignin-based carbon nanofibers was controlled. The conditions for the stable preparation of flexible carbon nanofiber membranes were successfully explored, providing a way for the large-scale stable preparation of carbon nanofiber membranes.

[0015] 2. Lignin contains a large number of hydrophilic groups, such as carboxyl and hydroxyl groups, some of which are retained during high-temperature carbonization. This allows lignin-based flexible carbon nanofiber membranes to transform from hydrophobic to superhydrophilic, breaking through the limitations of their application in separating oil-in-water wastewater.

[0016] 3. Using industrial lignin, which is abundant, inexpensive, and has a high carbon yield, as a raw material, the use of petrochemical raw materials is reduced while ensuring the performance of carbon nanofiber membranes. Attached Figure Description

[0017] Figure 1 These are the experimental results showing the effect of different polymer ratios on the mechanical properties of carbon nanofiber membranes; Figure 2 These are the experimental results showing the effect of different pre-oxidation temperatures on the mechanical properties of carbon nanofiber membranes; Figure 3 These are the experimental results showing the effect of different carbonization temperatures on the mechanical properties of carbon nanofiber membranes; Figure 4 These are the experimental results showing the effect of different carbonization temperatures on the separation performance of carbon nanofiber membranes. Detailed Implementation

[0018] To further illustrate the technical means and effects adopted by the present invention to achieve its intended purpose, the specific implementation methods, structures, features, and effects of the present invention will be described in detail below with reference to the accompanying drawings and preferred embodiments. All materials involved in the following embodiments are commercially available.

[0019] Example 1 1.0 g of enzymatically hydrolyzed lignin and 2.0 g of polyacrylonitrile were added to 23.0 g of N,N-dimethylformamide solution and completely dissolved at 60 °C. The solution was then transferred to a syringe and fed at a rate of 1.8 ml per hour under conditions of approximately 25 °C, approximately 45% relative humidity, and 25 kV to peel the polymer nanofiber membrane off the silicone paper. The membrane was then dried overnight. The appropriately cut polymer nanofiber membrane was placed in a muffle furnace and heated to 250 °C at a heating rate of 1.00 °C / min and held for 2 h for pre-oxidation treatment. Subsequently, it was placed in a tube furnace and carbonized at a carbonization temperature of 800 °C to obtain a lignin-based carbon nanofiber membrane.

[0020] Example 2 1.0 g of enzymatically hydrolyzed lignin, 1.8 g of polyacrylonitrile, and 0.2 g of polylactic acid were added to 23 g of N,N-dimethylformamide solution. After complete dissolution at 60 °C, the solution was transferred to a syringe and fed at a rate of 1.8 ml per hour under conditions of approximately 25 °C, approximately 45% relative humidity, and 25 kV to peel the polymer nanofiber membrane off the silicone paper. The membrane was then dried overnight. The appropriately cut polymer nanofiber membrane was placed in a muffle furnace and heated to 250 °C at a heating rate of 1.00 °C / min and held for 2 hours for pre-oxidation treatment. Subsequently, it was placed in a tube furnace and carbonized at a carbonization temperature of 800 °C to obtain a lignin-based carbon nanofiber membrane.

[0021] Example 3 1.0 g of enzymatically hydrolyzed lignin, 1.6 g of polyacrylonitrile, and 0.4 g of polylactic acid were added to 23.0 g of N,N-dimethylformamide solution. After complete dissolution at 60 °C, the solution was transferred to a syringe and fed at a rate of 1.8 ml per hour under conditions of approximately 25 °C, approximately 45% relative humidity, and 25 kV to peel the polymer nanofiber membrane off the silicone paper and allow it to dry overnight. The appropriately cut polymer nanofiber membrane was placed in a muffle furnace and heated to 250 °C at a heating rate of 1.00 °C / min and held for 2 h for pre-oxidation treatment. Then, it was placed in a tube furnace and carbonized at a carbonization temperature of 800 °C to obtain a lignin-based carbon nanofiber membrane.

[0022] Example 4 1.0 g of enzymatically hydrolyzed lignin, 1.4 g of polyacrylonitrile, and 0.6 g of polylactic acid were added to 23.0 g of N,N-dimethylformamide solution. After complete dissolution at 60 °C, the solution was transferred to a syringe and fed at a rate of 1.8 ml per hour under conditions of approximately 25 °C, approximately 45% relative humidity, and 25 kV to peel the polymer nanofiber membrane off the silicone paper and allow it to dry overnight. The appropriately cut polymer nanofiber membrane was placed in a muffle furnace and heated to 250 °C at a heating rate of 1.00 °C / min and held for 2 h for pre-oxidation treatment. Then, it was placed in a tube furnace and carbonized at a carbonization temperature of 800 °C to obtain a lignin-based carbon nanofiber membrane.

[0023] Example 5 1.0 g of enzymatically hydrolyzed lignin, 1.0 g of polyacrylonitrile, and 1.0 g of polylactic acid were added to 23.0 g of N,N-dimethylformamide solution. After complete dissolution at 60 °C, the solution was transferred to a syringe and fed at a rate of 1.8 ml per hour under conditions of approximately 25 °C, approximately 45% relative humidity, and 25 kV to peel the polymer nanofiber membrane off the silicone paper. The membrane was then dried overnight. The appropriately cut polymer nanofiber membrane was placed in a muffle furnace and heated to 250 °C at a heating rate of 1.00 °C / min and held for 2 h for pre-oxidation treatment. Subsequently, it was placed in a tube furnace and carbonized at a carbonization temperature of 800 °C to obtain a lignin-based carbon nanofiber membrane.

[0024] The effect of different polymer ratios on the mechanical properties of carbon nanofiber membranes, such as Figure 1 As shown. Figure 1Part (a) shows the relationship between strain and stress in carbon nanofiber membranes (CNFM) with different polylactic acid (PLA) contents. The curves in the figure correspond to the carbon nanofiber membranes in Examples 1 to 5, with polyacrylonitrile / polylactic acid ratios of 2.0 g / 0.2 g, 1.6 g / 0.4 g, 1.4 g / 0.6 g, and 1.0 g / 1.0 g, respectively. Figure 1 Part (b) statistically analyzed the Young's modulus of CNFM in Examples 1 to 5 based on the data in (a). The figure shows that CNFM with added polylactic acid has a lower elastic modulus and greater flexibility than that without added polylactic acid. This is because the polylactic acid added to the spinning solution decomposes at high temperatures to generate gas, thus creating pores in the carbon nanofibers. By adjusting parameters such as the content of added polylactic acid, pre-oxidation, and temperature, the pore structure in the carbon nanofibers can be controlled. Suitable pores can disperse and deflect stress, alleviating stress concentration and thus improving flexibility.

[0025] Under the conditions of a pre-oxidation rate of 1.00 ℃ / min and a carbonization temperature of 1000 ℃, the elastic modulus of the carbon nanofiber membrane first decreases and then increases with the increase of the polylactic acid ratio, indicating that its flexibility first increases and then decreases. When the ratio of polyacrylonitrile / polylactic acid is 1.4 g / 0.6 g, the flexibility of the carbon nanofiber membrane reaches the optimal value, and the elastic modulus is 168.86 MPa.

[0026] Example 6 1.0 g of enzymatically hydrolyzed lignin, 1.4 g of polyacrylonitrile, and 0.6 g of polylactic acid were added to 23.0 g of N,N-dimethylformamide solution. After complete dissolution at 60 °C, the solution was transferred to a syringe and fed at a rate of 1.8 ml per hour under conditions of approximately 25 °C, approximately 45% relative humidity, and 25 kV to peel the polymer nanofiber membrane off the silicone paper. The membrane was then dried overnight. The appropriately cut polymer nanofiber membrane was placed in a muffle furnace and heated to 250 °C at a heating rate of 0.25 °C / min and held for 2 h for pre-oxidation treatment. Subsequently, it was placed in a tube furnace and carbonized at a carbonization temperature of 800 °C to obtain a lignin-based carbon nanofiber membrane.

[0027] Example 7 1.0 g of enzymatically hydrolyzed lignin, 1.4 g of polyacrylonitrile, and 0.6 g of polylactic acid were added to 23.0 g of N,N-dimethylformamide solution. After complete dissolution at 60 °C, the solution was transferred to a syringe and fed at a rate of 1.8 ml per hour under conditions of approximately 25 °C, approximately 45% relative humidity, and 25 kV to peel the polymer nanofiber membrane off the silicone paper. The membrane was then dried overnight. The appropriately cut polymer nanofiber membrane was placed in a muffle furnace and heated to 250 °C at a heating rate of 0.50 °C / min and held for 2 h for pre-oxidation treatment. Subsequently, it was placed in a tube furnace and carbonized at a carbonization temperature of 800 °C to obtain a lignin-based carbon nanofiber membrane.

[0028] Example 8 1.0 g of enzymatically hydrolyzed lignin, 1.4 g of polyacrylonitrile, and 0.6 g of polylactic acid were added to 23.0 g of N,N-dimethylformamide solution. After complete dissolution at 60 °C, the solution was transferred to a syringe and fed at a rate of 1.8 ml per hour under conditions of approximately 25 °C, approximately 45% relative humidity, and 25 kV to peel the polymer nanofiber membrane off the silicone paper. The membrane was then dried overnight. The appropriately cut polymer nanofiber membrane was placed in a muffle furnace and heated to 250 °C at a heating rate of 2.00 °C / min and held for 2 h for pre-oxidation treatment. Subsequently, it was placed in a tube furnace and carbonized at a carbonization temperature of 800 °C to obtain a lignin-based carbon nanofiber membrane.

[0029] Example 9 1.0 g of enzymatically hydrolyzed lignin, 1.4 g of polyacrylonitrile, and 0.6 g of polylactic acid were added to 23 g of N,N-dimethylformamide solution. After complete dissolution at 60 °C, the solution was transferred to a syringe and fed at a rate of 1.8 ml per hour under conditions of approximately 25 °C, approximately 45% relative humidity, and 25 kV to peel the polymer nanofiber membrane off the silicone paper and allow it to dry overnight. The appropriately cut polymer nanofiber membrane was placed in a muffle furnace and heated to 250 °C at a heating rate of 3.00 °C / min and held for 2 h for pre-oxidation treatment. Then, it was placed in a tube furnace and carbonized at a carbonization temperature of 800 °C to obtain a lignin-based carbon nanofiber membrane.

[0030] The effect of different pre-oxidation temperature heating rates on the mechanical properties of carbon nanofiber membranes, such as Figure 2 As shown. Figure 2 Part (a) shows the relationship between strain and stress for carbon nanofiber membranes with different pre-oxidation heating rates. The curves in the figure correspond to the carbon nanofiber membranes in Examples 4, 6 to 9, respectively, with the pre-oxidation heating rate ranging from 0.25 to 3 °C / min. Figure 2Part (b) statistically analyzed the Young's modulus of the carbon nanofiber membranes in Examples 4, 6 to 9 based on the data in (a). The figure shows that, under the conditions of a polyacrylonitrile / polylactic acid ratio of 1.4 g / 0.6 g and a carbonization temperature of 1000 °C, the flexibility of the carbon nanofiber membrane first increased and then decreased with increasing pre-oxidation heating rate. The flexibility reached its optimal value at a pre-oxidation heating rate of 0.50 °C / min, at which point the modulus was 136.94 MPa.

[0031] Example 10 1.0 g of enzymatically hydrolyzed lignin, 1.4 g of polyacrylonitrile, and 0.6 g of polylactic acid were added to 23.0 g of N,N-dimethylformamide solution. After complete dissolution at 60 °C, the solution was transferred to a syringe and fed at a rate of 1.8 ml per hour under conditions of approximately 25 °C, approximately 45% relative humidity, and 25 kV to peel the polymer nanofiber membrane off the silicone paper. The membrane was then dried overnight. The appropriately cut polymer nanofiber membrane was placed in a muffle furnace and heated to 250 °C at a heating rate of 0.50 °C / min and held for 2 h for pre-oxidation treatment. Subsequently, it was placed in a tube furnace and carbonized at a carbonization temperature of 600 °C to obtain a lignin-based carbon nanofiber membrane.

[0032] Example 11 1.0 g of enzymatically hydrolyzed lignin, 1.4 g of polyacrylonitrile, and 0.6 g of polylactic acid were added to 23.0 g of N,N-dimethylformamide solution. After complete dissolution at 60 °C, the solution was transferred to a syringe and fed at a rate of 1.8 ml per hour under conditions of approximately 25 °C, approximately 45% relative humidity, and 25 kV to peel the polymer nanofiber membrane off the silicone paper. The membrane was then dried overnight. The appropriately cut polymer nanofiber membrane was placed in a muffle furnace and heated to 250 °C at a heating rate of 0.50 °C / min and held for 2 h for pre-oxidation treatment. Subsequently, it was placed in a tube furnace and carbonized at a carbonization temperature of 700 °C to obtain a lignin-based carbon nanofiber membrane.

[0033] Example 12 1.0 g of enzymatically hydrolyzed lignin, 1.4 g of polyacrylonitrile, and 0.6 g of polylactic acid were added to 23.0 g of N,N-dimethylformamide solution. After complete dissolution at 60 °C, the solution was transferred to a syringe and fed at a rate of 1.8 ml per hour under conditions of approximately 25 °C, approximately 45% relative humidity, and 25 kV to peel the polymer nanofiber membrane off the silicone paper and allow it to dry overnight. The appropriately cut polymer nanofiber membrane was placed in a muffle furnace and heated to 250 °C at a heating rate of 0.50 °C / min and held for 2 h for pre-oxidation treatment. Then, it was placed in a tube furnace and carbonized at a carbonization temperature of 900 °C to obtain a lignin-based carbon nanofiber membrane.

[0034] Example 13 1.0 g of enzymatically hydrolyzed lignin, 1.4 g of polyacrylonitrile, and 0.6 g of polylactic acid were added to 23.0 g of N,N-dimethylformamide solution. After complete dissolution at 60 °C, the solution was transferred to a syringe and fed at a rate of 1.8 ml per hour under conditions of approximately 25 °C, approximately 45% relative humidity, and 25 kV to peel the polymer nanofiber membrane off the silicone paper and allow it to dry overnight. A suitable polymer nanofiber membrane was then placed in a muffle furnace and heated to 250 °C at a heating rate of 0.50 °C / min and held for 2 h for pre-oxidation treatment. Subsequently, it was placed in a tube furnace and carbonized at a carbonization temperature of 1000 °C to obtain a lignin-based carbon nanofiber membrane.

[0035] The effect of different carbonization temperatures on the mechanical properties of carbon nanofiber membranes, such as Figure 3 As shown. Figure 3 Part (a) shows the relationship between strain and stress for carbon nanofiber membranes at different carbonization temperatures. The curves in the figure correspond to the carbon nanofiber membranes in Examples 10, 11, 7, 12, and 13, respectively, with carbonization temperatures ranging from 600 to 1000 °C. Figure 3 Part (b) statistically analyzes the Young's modulus of the carbon nanofiber membranes in each embodiment based on the data in (a). The figure shows that, under the conditions of a polyacrylonitrile / polylactic acid ratio of 1.4 g / 0.6 g and a pre-oxidation heating rate of 0.50 ℃ / min, the flexibility of the carbon nanofiber membrane first increases and then decreases with increasing carbonization temperature, reaching its optimal value at a carbonization temperature of 700 ℃, at which point the modulus is 124.61 MPa.

[0036] Simulated oily wastewater without surfactants was obtained by magnetically stirring a certain proportion of oil-water mixture for 40 minutes. A certain amount of emulsifier and soybean oil were dissolved in water, and then the mixture was emulsified by ultrasonic treatment for 20 minutes to obtain simulated emulsified oily wastewater. The carbon nanofiber membranes from Examples 10, 11, 7, 12, and 13 were placed in a glass separation device under gravity to separate the oil-in-water emulsion. The oil-water ratio in the surfactant-free simulated oily wastewater was 1 / 9, and the oil phase was vegetable oil. The emulsifier was sodium dodecyl sulfonate. The effect of different carbonization temperatures on the separation performance of the carbon nanofiber membrane is as follows. Figure 4 As shown. Figure 4 Part (a) shows the separation flux and efficiency of carbon nanofiber membranes for non-emulsified oily wastewater. Figure 4Part (b) shows the separation flux and efficiency of carbon nanofiber membranes for emulsified oily wastewater. The figure shows that the separation flux of the carbon nanofiber membrane for simulated oily wastewater decreases with increasing carbonization temperature, while the separation efficiency remains stable.

[0037] Within the scope of this study, the optimal conditions for lignin-based carbon nanofiber membranes used for oil-water separation were a polyacrylonitrile / polylactic acid ratio of 1.4 g / 0.6 g, a pre-oxidation heating rate of 0.50 °C / min, and a carbonization temperature of 600 °C. Under these conditions, the modulus was 137.54 MPa, and the separation flux for non-emulsified oily wastewater was 367.56 L*m. -2 *h -1 The separation efficiency was 99.2%, and the separation flux for emulsified oily wastewater was 234.15 L*m. -2 *h -1 The separation efficiency was 97.6%. Considering both mechanical and separation properties, these conditions were the optimal preparation conditions.

[0038] The lignin-based flexible carbon nanofiber membrane of this invention achieves sufficient flexibility by controlling the pore structure of the carbon nanofiber membrane through the selection of parameters such as raw material selection, pre-oxidation heating rate, and carbonization temperature. The addition of lignin reduces the use of traditional chemical materials. Furthermore, lignin contains a large number of hydrophilic groups, such as carboxyl and hydroxyl groups, some of which are retained during the high-temperature carbonization process, making the lignin-based flexible carbon nanofiber membrane transform from hydrophobic to superhydrophilic, thus breaking through the limitations of carbon nanofiber membranes in the field of oil-in-water separation.

[0039] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a lignin-based flexible carbon nanofiber membrane, characterized in that, Includes the following steps: Enzymatically hydrolyzed lignin and polymers are added to an N,N-dimethylformamide solution and dissolved to obtain a spinning solution. The spinning solution is then spun into a polymer nanofiber membrane by electrospinning. The polymer nanofiber membrane is pre-oxidized in air and then carbonized in a nitrogen atmosphere.

2. The method for preparing lignin-based flexible carbon nanofiber membranes as described in claim 1, characterized in that: The polymer is polyacrylonitrile and / or polylactic acid, and the mass ratio of the polymer to the enzymatically hydrolyzed lignin is 0.5 to 1.

5.

3. The method for preparing lignin-based flexible carbon nanofiber membranes as described in claim 2, characterized in that: The weight ratio of polyacrylonitrile to enzymatically hydrolyzed lignin is 1-2, and the weight ratio of polylactic acid to enzymatically hydrolyzed lignin is 0-1.

4. The method for preparing the lignin-based flexible carbon nanofiber membrane as described in claim 3, characterized in that, The weight ratio of polylactic acid to enzymatically hydrolyzed lignin is 0.4 to 0.

6.

5. The method for preparing lignin-based flexible carbon nanofiber membranes as described in claim 1, characterized in that, The temperature during the dissolution process is 50 ℃~70 ℃.

6. The method for preparing a lignin-based flexible carbon nanofiber membrane as described in claim 1, characterized in that, The electrospinning method includes placing the spinning solution in a syringe and performing electrospinning under conditions of 25 kV voltage, 1.8 mL / h feed rate, 25 ℃ ambient temperature and 45% relative humidity.

7. The method for preparing a lignin-based flexible carbon nanofiber membrane as described in claim 1, characterized in that, The pre-oxidation treatment includes gradually heating the polymer nanofiber membrane in air to 220-300 °C at a pre-oxidation heating rate of 0.25-3 °C / min and maintaining it for 1.5-2.5 h.

8. The method for preparing a lignin-based flexible carbon nanofiber membrane as described in claim 1, characterized in that, The carbonization process is carried out at a temperature of 600~1000 ℃.

9. A lignin-based flexible carbon nanofiber membrane, characterized in that, It is prepared by the preparation method according to any one of claims 1-8.

10. The application of a lignin-based flexible carbon nanofiber membrane prepared by the preparation method according to any one of claims 1-8 in an oil-water separation tool.

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