Preparation method of cellulose-based composite expanded graphite aerogel oil-water separation material

Abstract

The invention provides a preparation method of a cellulose-based composite expanded graphite aerogel oil-water separation material, and particularly relates to a method for forming natural expanded graphite into blocky composite aerogel by taking cellulose as a supporting framework and PVA as a binder, which is applied to the technical fields of two oil-water separation, namely adsorption separation and continuous separation. The method comprises the three steps of raw material mixing, freeze drying and modifying agent modification, the preparation process is simple, and the cost is low. The composite aerogel material disclosed by the invention has high adsorption capacity on oil / organic solvents, the highest adsorption capacity reaches 44.2 g / g, oil-water separation can be realized through an adsorption effect, and reutilization is realized in a simple extrusion mode. The prepared composite aerogel material can be used for oil / water continuous separation under the action of gravity, and the separation flux reaches 13115 L / m < 2 >. H; and oil / water continuous separation can be carried out through a peristaltic pump, and the transmission rate can reach up to 108.5 L / h.g.

Description

Technical Field

[0001] The invention belongs to the technical field of oil-water separation, and relates to a method for preparing a green, environmentally friendly, simple and efficient cellulose-based aerogel oil-water separation material. Background Art

[0002] With the acceleration of global industrialization, the problem of oil and water pollution is becoming increasingly serious, especially in the oil extraction, transportation, food processing, chemical industry and other industries, the generation and leakage of oil and water mixtures occur frequently. Oil pollution not only pollutes water bodies, but also endangers the survival of aquatic organisms and destroys the balance of the ecosystem. Traditional oil-water separation technology has many limitations in terms of processing efficiency, cost and sustainability. There is an urgent need to develop efficient, environmentally friendly and reusable oil-water separation materials. .

[0003] In the current research field of oil-water separation, the continuous development and innovation of oil-water separation technology has become an important research direction. Cellulose aerogel not only has the advantages of light weight and high porosity, but also has strong lipophilicity and hydrophobicity, which makes it perform well in the separation of various oil-water mixtures and become one of the key materials for solving environmental pollution and resource recovery problems. At the same time, as a functional carbon material, expanded graphite also has great potential for oil-water separation in theory due to its loose and porous structural characteristics. Expanded graphite has shown great application prospects in adsorbing oil pollution and improving the efficiency of oil-water separation. Its high surface area and good pore structure enable it to effectively adsorb oil substances and achieve better separation effects. However, expanded graphite still faces some challenges in practical applications, especially when it exists in granular form, it is difficult to achieve efficient recovery and reuse. This limitation greatly restricts the widespread application of expanded graphite as an oil-water separation material. At present, there are still some challenges to be solved in the process of preparing aerogel materials. For example, the cost of raw materials is high, the preparation process is cumbersome and complicated, and some chemical reagents are often required in the manufacturing process, which may cause a certain degree of environmental pollution. Therefore, it is of great scientific significance and practical application value to use a green, simple and efficient method to prepare cellulose-based composite expanded graphite oil-water separation materials. Summary of the invention

[0004] The present invention discloses a method for preparing a green, simple and efficient cellulose-based aerogel oil-water separation material. Nanocellulose is low-cost, widely available, and green. Natural expanded graphite has a multi-level, rich pore structure and a huge pore volume. PVA can act as an "adhesive" to achieve the connection between nanocellulose and expanded graphite, thereby obtaining a lightweight and porous aerogel. In order to solve the problem that aerogel has poor mechanical properties and is difficult to reuse, glutaraldehyde is added as a cross-linking agent to obtain a reusable oil-water separation material. These materials can adsorb and separate light oil or heavy oil, and continuously separate oil / water mixtures. The recovery of oil and the reuse of oil-water separation materials can be achieved by extrusion.

[0005] The present invention is carried out according to the following steps:

[0006] A hydrophobic and oleophilic aerogel material, characterized by being composed of natural expanded graphite, PVA and nanocellulose;

[0007] Nanocellulose acts as a skeleton material, and PVA acts as a "binder" to shape expanded graphite into a lightweight and porous aerogel;

[0008] Glutaraldehyde is used as a cross-linking agent to cross-link nanocellulose, PVA and expanded graphite to improve their mechanical properties, thereby achieving the reuse of aerogels;

[0009] (1) preparing a solution of cellulose nanofibers, PVA powder, and expanded graphite particles with water as the solvent, and then uniformly mixing the three to obtain a mixed solution A, wherein two portions of the mixed solution are prepared; in the mixed solution A, the mass ratio of cellulose nanofibers to water is (0.4-0.8):100, the mass ratio of PVA to water is 0.3-1.8:100, and the mass ratio of expanded graphite to water is (0.6-1.8):100;

[0010] (2) injecting a portion of the mixed solution A obtained in step 1 into a mold and freezing it in a refrigerator;

[0011] (3) adjusting the pH of another mixed solution A in step 1 to acidic with hydrochloric acid, adding glutaraldehyde solution thereto and mixing evenly to obtain a mixed solution B, which is then injected into a mold and frozen in a refrigerator; the mass ratio of the water in the mixed solution A after the pH is adjusted to the mass ratio of the added glutaraldehyde is (3.85-4.85):(0.005-0.03);

[0012] (4) freeze-drying the frozen samples obtained in step 2 and step 3 to obtain aerogel A and aerogel B, respectively;

[0013] (5) Soaking the aerogel A in step 4 in a PDMS solution for 10 seconds to 2 hours, and then curing it in an oven at a curing temperature of 80 to 100° C. for a curing time of 2 to 8 hours to obtain a PDMS hydrophobically modified aerogel C; n-hexane is used as a solvent in the PDMS solution;

[0014] Alternatively, the aerogel B in step 4 is modified with methyltrimethoxysilane by chemical vapor deposition, and an aerogel B and a glass bottle containing methyltrimethoxysilane are placed in a closed dryer, and the dryer is placed in an oven. The hydrophobic modification is completed by setting the time and temperature of the oven to obtain an aerogel D hydrophobically modified with methyltrimethoxysilane; the mass ratio of aerogel B to methyltrimethoxysilane is 1: (10-20), the oven temperature is 70-90° C., and the reaction time is 1-3 h.

[0015] The method for preparing the cellulose-based composite expanded graphite aerogel described in step 2 is characterized in that the freezing temperature of the refrigerator is -36 to -12°C, and the freezing time is 12 to 24 hours;

[0016] The method for preparing the cellulose-based composite expanded graphite aerogel described in step 3 is characterized in that: the pH of the mixed solution A is adjusted to 2 with 2M hydrochloric acid;

[0017] The method for preparing the cellulose-based composite expanded graphite aerogel described in step 4 is characterized in that: the freeze-drying device is a freeze dryer, and the freeze-drying time is 48 hours;

[0018] The method for preparing the cellulose-based composite expanded graphite aerogel described in step 5 is characterized in that: the mass ratio of PDMS to n-hexane is (1:50) to 150, the aerogel A is soaked in the PDMS solution, and the mass ratio of the aerogel A to the PDMS solution is 1:(100 to 1000);

[0019] The method for preparing the composite expanded graphite aerogel based on cellulose is characterized in that: the cellulose nanofibers are (C6H 10 O5) 500～1500 . Compared with the prior art, the technical advantages of the present invention are as follows:

[0020] The invention prepares a simple, efficient, high-porosity and reusable aerogel oil-water separation material. The equipment used in the invention is simple, no complicated equipment is required, the production process is simple, batch production is possible, and the preparation cycle is short.

[0021] The aerogel prepared by the present invention is a composite expanded graphite aerogel based on cellulose, which can achieve oil-water separation by filtering and separation. Aerogel C can separate / recover heavy oil in an oil-water mixture by gravity. The heavy oil (chloroform) has a high permeation flux and a high separation rate, but water permeates after a period of time. Aerogel C can separate / recover floating oil on the water surface by a peristaltic pump, with a high transmission rate, high separation efficiency, and can be used continuously.

[0022] The cellulose-based composite expanded graphite aerogel prepared by the present invention can achieve oil-water separation by absorption separation. The aerogel D prepared by the present invention has a high oil absorption capacity and a high adsorption capacity for different oil substances and organic solvents. The aerogel D has good reusability, and can be extruded to extrude the adsorbate to achieve oil or organic solvent recovery and reusability of the aerogel. After multiple adsorption-desorption cycles, the mass loss rate of the aerogel is low.

[0023] The aerogel prepared by the invention is a composite expanded graphite aerogel based on cellulose and can separate oil-water mixture or water-in-oil emulsion. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 SEM images of expanded graphite (a), cellulose nanofibers (CNF) (b), aerogel A without glutaraldehyde (c), aerogel B containing glutaraldehyde (d), aerogel C hydrophobically modified with PDMS (e), and aerogel D hydrophobically modified with methyltrimethoxysilane (f).

[0025] Figure 2 FTIR spectra of cellulose nanofibers (CNF), aerogel A, aerogel B, aerogel C, and aerogel D.

[0026] Figure 3 .Permeation flux, separation efficiency and water retention time of aerogel C in oil-water gravity separation.

[0027] Figure 4 . Flow rate and separation efficiency of aerogel C for n-hexane on water surface in continuous separation.

[0028] Figure 5 .Adsorption capacity of aerogel D for different oils and organic solvents.

[0029] Figure 6 . Cyclic adsorption capacity of aerogel D. DETAILED DESCRIPTION

[0030] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0031] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0032] Example 1

[0033] 1.6 g of cellulose nanofibers (CNF, (C6H 10 O5) 1000 ) was dispersed in 98.4g water to prepare a 1.6wt% CNF suspension, 5g PVA was dissolved in 95mL water, stirred at 95°C for 2h to prepare a 5wt% PVA solution, and 1g expanded graphite was dispersed in 100g water. Take the above three solutions to prepare a mixed solution of 10g and mix them evenly. The mass ratio of cellulose nanofibers to water was 0.8:100, the mass ratio of PVA to water was 0.6:100, and the mass ratio of expanded graphite to water was 1.2:100. After transferring it to a mold, it was frozen at -36°C for 12h, and then placed in a freeze dryer for freeze drying for 48h. After demolding, aerogel was obtained. 1g PDMS was dissolved in 100g of n-hexane and stirred evenly to obtain a PDMS diluent. The aerogel was then soaked in the PDMS diluent for 10s and cured in an oven at 100°C for 2h to obtain a PDMS-modified aerogel.

[0034] Example 2

[0035] 1.6 g of cellulose nanofibers (CNF, (C6H 10 O5) 1000 ) was dispersed in 98.4g water to prepare a 1.6wt% CNF suspension, 5g PVA was dissolved in 95mL water, stirred at 95°C for 2h to prepare a 5wt% PVA solution, and 1g expanded graphite was dispersed in 100g water. Take the above three solutions to prepare a mixed solution of 10g and mix them evenly. The mass ratio of cellulose nanofibers to water was 0.6:100, the mass ratio of PVA to water was 0.6:100, and the mass ratio of expanded graphite to water was 1.2:100. After being transferred to a mold, it was frozen at -36°C for 12h, and then placed in a freeze dryer for freeze drying for 48h. After demolding, an aerogel was obtained. 1g PDMS was dissolved in 100g of n-hexane and stirred evenly to obtain a PDMS diluent. The aerogel was then soaked in the PDMS diluent for 10s and cured in an oven at 100°C for 2h to obtain a PDMS-modified aerogel.

[0036] Example 3

[0037] 1.6 g of cellulose nanofibers (CNF, (C6H 10 O5) 1000) was dispersed in 98.4g water to prepare a 1.6wt% CNF suspension, 5g PVA was dissolved in 95mL water, stirred at 95°C for 2h to prepare a 5wt% PVA solution, and 1g expanded graphite was dispersed in 100g water. Take the above three solutions to prepare a mixed solution of 10g and mix them evenly, the mass ratio of cellulose nanofibers to water is 0.8:100, the mass ratio of PVA to water is 0.6:100, the mass ratio of expanded graphite to water is 1.2:100, 2M HCl solution is added dropwise to adjust the pH to 2, and then 0.1g of glutaraldehyde aqueous solution (25wt%) is added and mixed evenly, transferred to a mold and frozen at -36°C for 12h, and then placed in a freeze dryer for freeze drying for 48h, and aerogel B is obtained after demolding. Aerogel B and 2 mL of methyltrimethoxysilane were placed in a desiccator, and the desiccator was placed in an oven. The oven was sealed at 80° C. for 3 h to obtain aerogel modified with methyltrimethoxysilane.

[0038] Example 4

[0039] 1.6 g of cellulose nanofibers (CNF, (C6H 10 O5) 1000 ) was dispersed in 98.4g water to prepare a 1.6wt% CNF suspension, 5g PVA was dissolved in 95mL water, stirred at 95°C for 2h to prepare a 5wt% PVA solution, and 1g expanded graphite was dispersed in 100g water. Take the above three solutions to prepare a mixed solution of 10g and mix them evenly, the mass ratio of cellulose nanofibers to water is 0.6:100, the mass ratio of PVA to water is 0.6:100, the mass ratio of expanded graphite to water is 1.2:100, 2M HCl solution is added dropwise to adjust the pH to 2, and then 0.1g glutaraldehyde aqueous solution (25wt%) is added and mixed evenly, transferred to a mold and frozen at -36°C for 12h, and then placed in a freeze dryer for freeze drying for 48h, and aerogel is obtained after demolding. The aerogel and a glass bottle containing 2 mL of methyltrimethoxysilane were placed in a desiccator, and the desiccator was placed in an oven and sealed at an oven temperature of 80° C. for 2 h to obtain an aerogel modified with methyltrimethoxysilane.

[0040] Figure 1 Scanning electron microscopy is the observed surface morphology, (a) is the microscopic morphology of expanded graphite particles, (b) is nanocellulose, (c) is aerogel A, (d) is aerogel C, (e) is aerogel B, and (f) is aerogel D. It can be observed that expanded graphite is a worm-like particle, CNF is composed of mutually entangled fiber bundles, and aerogels AD are all three-dimensional structures with complete structures and abundant pores. Figure 2 is the adsorption capacity of aerogel D for different oils and organic solvents. Figure 3is the adsorption capacity of aerogel D after 10 cycles of extrusion adsorption. Figure 2 FTIR reflectance spectra of nanocellulose, aerogel A, aerogel B, aerogel C, and aerogel D. (a) is CNF, (b) is aerogel B, (c) is aerogel D, (d) is aerogel A, and (e) is aerogel C. It can be seen that the -OH peak intensity of (b) is lower than that of (a), indicating that acetal bridges may be formed. (b) 2940cm -1 and 2910cm -1 There are two absorption peaks at 1130 cm-1, which are the double absorption peaks of CH stretching vibration of aldehyde compounds. The COC stretching peak of alicyclic ether is at 1130 cm-1. -1 The peak intensity increased significantly after adding GA. The results show that CNF successfully cross-linked with GA and PVA, and the hydroxyl and aldehyde groups were cross-linked and dehydrated to form ether bonds. (c) Compared with (b), the peak intensity at 1260 and 799 cm -1 New diffraction peaks appeared at 1260 and 799 cm, which are attributed to the characteristic vibrations of asymmetric stretching of Si-O-Si and C-Si. The results show that MTMS reacted with the composite aerogel and successfully formed polysiloxane on the surface of the aerogel. Similarly, compared with (e) and (d), the peaks at 1260 and 799 cm -1 A new diffraction peak appeared at , proving that PDMS was successfully modified on the aerogel surface. Figure 3 The permeation flux, separation efficiency and water retention time of aerogel C in oil-water gravity separation show that aerogel C can separate oil from oil-water mixture by gravity separation, and the permeation flux of heavy oil is 13115L / m 2 h. Figure 4 The flow rate and separation efficiency of aerogel C for n-hexane on the water surface in continuous separation show that aerogel C can be used in a continuous separation device. By driving a peristaltic pump, aerogel C can be used to separate n-hexane on the water surface, with a transmission rate of up to 108.5 L / h·g. Figure 5 is the adsorption capacity of aerogel D for different oils and organic solvents, including actual waste oils (i.e., chloroform, 44.12 g / g; soybean oil, 16.94 g / g; and real waste machine oil, 18.38 g / g). Figure 6 Aerogel D has a cyclic adsorption capacity, and the waste oil can be recycled by extrusion.

Claims

1. A method for preparing a composite expanded graphite aerogel oil-water separation material based on cellulose, characterized in that The following steps are included: Step 1: preparing a solution of cellulose nanofibers, PVA powder, and expanded graphite particles with water as the solvent, and then uniformly mixing the three to obtain a mixed solution A, wherein two portions of the mixed solution are prepared; in the mixed solution A, the mass ratio of cellulose nanofibers to water is (0.4-0.8):100, the mass ratio of PVA to water is 0.3-1.8:100, and the mass ratio of expanded graphite to water is (0.6-1.8):100; Step 2: injecting a portion of the mixed solution A obtained in step 1 into a mold and freezing it in a refrigerator; Step 3: adjusting the pH of another mixed solution A in step 1 to acidic with hydrochloric acid, adding glutaraldehyde solution thereto and mixing evenly to obtain a mixed solution B, which is then injected into a mold and frozen in a refrigerator; the mass ratio of the water in the mixed solution A after the pH is adjusted to the mass ratio of the added glutaraldehyde is (3.85-4.85):(0.005-0.03); Step 4: freeze-drying the frozen samples obtained in step 2 and step 3 to obtain aerogel A and aerogel B, respectively; Step 5: Soak the aerogel A in step 4 in the PDMS solution for 10 seconds to 2 hours, and then place it in an oven for curing at a curing temperature of 80 to 100° C. for a curing time of 2 to 8 hours to obtain a PDMS hydrophobically modified aerogel C; n-hexane is used as a solvent in the PDMS solution; Alternatively, the aerogel B in step 4 is modified with methyltrimethoxysilane by chemical vapor deposition, and an aerogel B and a glass bottle containing methyltrimethoxysilane are placed in a closed dryer, and the dryer is placed in an oven. The hydrophobic modification is completed by setting the time and temperature of the oven to obtain an aerogel D hydrophobically modified with methyltrimethoxysilane; the mass ratio of aerogel B to methyltrimethoxysilane is 1: (10-20), the oven temperature is 70-90° C., and the reaction time is 1-3 h.

2. The method according to claim 1, characterized in that: In step 2, the freezing temperature of the refrigerator is -36 to -12°C, and the freezing time is 12 to 24 hours.

3. The method according to claim 1, characterized in that: In step 3, the pH of the mixed solution A is adjusted to 2 with 2M hydrochloric acid.

4. The method according to claim 1, characterized in that: In step 4, the freeze drying device is a freeze dryer, and the freeze drying time is 48 hours.

5. The method according to claim 1, characterized in that: In step 5, the mass ratio of PDMS to n-hexane is (1:50) to 150, aerogel A is soaked in the PDMS solution, and the mass ratio of aerogel A to the PDMS solution is 1:(100 to 1000).

6. The method according to claim 1, characterized in that: Cellulose nanofibers are made of (C6H 10 O5) 500～1500 .

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