A one-way sodium alginate-cellulose fiber aerogel and a preparation method thereof

Abstract

This invention relates to a unidirectional sodium alginate-cellulose fiber aerogel and its preparation method. The invention employs directional freezing technology, where a blended sodium alginate and cellulose dispersion is oriented with an MXene and carbon nanotube dispersion through directional freezing. The sodium alginate and cellulose fibers crystallize from bottom to top due to the low-temperature heat conduction of liquid nitrogen. After crystallization, the resulting aerogel precursor is freeze-dried under low-temperature vacuum conditions, resulting in a large number of microporous structures on the macroscopic fiber surface. Through ionic crosslinking and siloxane grafting modification, a structurally stable, superhydrophobic MXene / carbon nanotube / sodium alginate / cellulose fiber aerogel is obtained. Rapid heating under sunlight reduces the viscosity of crude oil, shortens the adsorption time after crude oil leakage, and has a wide applicable time range, strong practicality, and does not cause environmental pollution.

Description

Technical Field

[0001] This invention relates to the field of aerogel preparation technology, specifically to a unidirectional sodium alginate-cellulose fiber aerogel and its preparation method. Background Technology

[0002] Viscous crude oil is a type of crude oil that is difficult to obtain and recover due to its high viscosity. Leaks of viscous crude oil cause significant environmental pollution and waste of non-renewable resources. Several methods exist for reducing the viscosity of viscous crude oil. One method is heating. Heating viscous crude oil can reduce its viscosity by decreasing the intermolecular forces between hydrocarbon molecules. This method is effective but requires a large amount of energy. Another method for reducing the viscosity of heavy oil is adding chemicals. Chemicals such as surfactants and polymers are added to heavy oil to reduce its viscosity. Adding chemicals is effective but can be expensive. In conclusion, heavy oil has high viscosity and adhesion, making it difficult to pump and transport, and it can potentially pollute the environment. Current methods for reducing the viscosity of viscous crude oil and strategies for recovering it are effective in some aspects, but they can be expensive and may also damage the environment. Further research is needed to develop more economical and effective methods for reducing the viscosity of heavy oil.

[0003] To address the issue of excessive energy consumption in heating crude oil to reduce viscosity, porous materials have seen rapid development in recent years. Porous materials possess large porosity and specific surface area, exhibiting significant potential for adsorbing pollutants such as oil, wastewater, and dyes. The fundamental approach involves controlled synthesis of porous materials with stable internal structures. Compared to porous materials like sponges and felts, aerogels have a larger internal space and specific surface area for the same volume, which also leads to poorer reusability.

[0004] Furthermore, most porous materials do not address new issues such as the amount of superviscous crude oil they can adsorb, or the adsorption rate under different conditions. For example, Chinese Patent No. CN202011304397.0, published on November 19, 2020, entitled "A Hydrophobic Lignin / Cellulose Aerogel Oil-Water Separation Material and Its Preparation Method and Application," has an oil absorption capacity of only 10-25 g / g and does not mention its adsorption capacity and speed for ultra-viscous crude oil. Chinese Patent No. CN202111543939.9, published on December 16, 2021, entitled "A Preparation Method and Application of a Biocompatible Composite Aerogel for High-Efficiency Oil-Water Separation," uses humic acid, which is difficult and costly to obtain and cannot be obtained in large quantities from nature. Chinese Patent No. CN202011326672.3, published on November 24, 2020, entitled "An Epoxy Rosin Modified Cellulose Aerogel Oil Absorbing Material and Its Preparation Method," uses epoxy rosin as a modifier. Its yield is low and the process is complex, making large-scale production difficult, and it cannot adsorb high-viscosity crude oil.

[0005] The adsorption rate and manufacturing difficulty of aerogels for crude oil are not only important indicators for crude oil recovery, but also determine the quality and efficiency of subsequent production and processing of aerogels. Therefore, aerogels with large crude oil adsorption capacity, fast adsorption rate, readily available materials, and strong stability are usually required. Thus, it is necessary to blend MXene and carbon nanotubes with polymer solutions and use directional freezing to obtain an aerogel that meets the requirements. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and to provide a unidirectional sodium alginate-cellulose fiber aerogel and its preparation method.

[0007] The technical solution of the present invention to solve the above-mentioned technical problems is as follows:

[0008] A method for preparing a unidirectional sodium alginate-cellulose fiber aerogel includes the following steps:

[0009] Step 1: Dissolve sodium alginate in deionized water and stir to obtain sodium alginate solution. Then add cellulose fibers to the solution, heat and stir to obtain a uniform suspension.

[0010] Step 2: Add carbon nanotubes and MXene to the suspension from the previous step and disperse them to obtain a mixed solution;

[0011] Step 3: Pour the mixed solution into a mold, and use the low temperature conduction of liquid nitrogen at the bottom to directionally freeze the mixed solution in the mold to obtain the aerogel precursor;

[0012] Step 4: The aerogel precursor is vacuum-frozen in a low-temperature freeze dryer at -45 to -55°C for 40-50 hours to obtain aerogel. The aerogel is then soaked in calcium chloride solution for cross-linking to obtain cross-linked aerogel.

[0013] Step 5: The cross-linked aerogel is treated with siloxane by vapor deposition to obtain a hydrophobic unidirectional MXene / carbon nanotube / sodium alginate / cellulose aerogel.

[0014] Furthermore, in the suspension of step 1, the content of sodium alginate is 1.3-1.5 wt%, and the content of cellulose fiber is 0.5-0.7 wt%.

[0015] Furthermore, in step 2, the content of carbon nanotubes in the mixed solution is 0.5-0.7 wt%, and the content of MXene is 0.2-0.4 wt%.

[0016] Furthermore, step 3 specifically involves:

[0017] The mixed solution is poured into a cylindrical polytetrafluoroethylene mold, and the bottom of the mold is placed on the upper surface of a solid copper column, which is immersed in liquid nitrogen, which is located in a liquid nitrogen container.

[0018] Furthermore, in step 4, the aerogel is cross-linked by soaking in calcium chloride ethanol solution for 12 hours.

[0019] Furthermore, in step 5, the cross-linked aerogel is reacted with an ethanol solution of 1H,1H,2H,2H-perfluorodecyltriethoxysilane for 6 hours via gas-phase precipitation.

[0020] The method for preparing unidirectional sodium alginate-cellulose fiber aerogel is as described above.

[0021] The beneficial effects of this invention are as follows: This invention uses a bottom-up directional freezing method to prepare an aerogel with a directional internal channel structure. The channels are surrounded by numerous micropores, resulting in a large specific surface area and high porosity. The fiber surface is loaded with a large number of uniform carbon nanotubes and MXene as a photothermal network, which is beneficial for improving photothermal conversion efficiency. It can be used to adsorb and rapidly reduce the viscosity of crude oil. While utilizing solar energy to reduce the viscosity of viscous crude oil, it achieves rapid adsorption of crude oil while separating heavy metal ions and avoiding channel blockage, thus exhibiting good adsorption capacity and rate. Furthermore, the raw materials are readily available, biodegradable after use, reducing secondary pollution. The entire preparation process is simple, providing a strategy for green and pollution-free crude oil recovery and wastewater treatment, and has good application potential. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the preparation method of the aerogel of the present invention;

[0023] The components labeled in the diagram are: 1. PTFE mold; 2. Mixed solution; 3. Copper column; 4. Freeze dryer; 5. Vacuum oven;

[0024] Figure 2 These are scanning electron microscope schematic diagrams and water contact angles of the aerogels of the present invention. Figure 1 shows the contact angle between the surface of the unidirectional MXene / carbon nanotube / sodium alginate / cellulose aerogel and water. Figure 2 shows the contact angle between the surface of the non-unidirectional MXene / carbon nanotube / sodium alginate / cellulose aerogel and water. Figure 3 shows the contact angle between the surface of the unidirectional carbon nanotube / sodium alginate / cellulose aerogel and water. Figure 4 shows the cross-section of the unidirectional MXene / carbon nanotube / sodium alginate / cellulose aerogel. Figure 5 shows the cross-section of the non-unidirectional MXene / carbon nanotube / sodium alginate / cellulose aerogel. Figure 6 shows the cross-section of the unidirectional carbon nanotube / sodium alginate / cellulose aerogel.

[0025] Figure 3 It is the oil absorption capacity of unidirectional MXene / carbon nanotube / sodium alginate / cellulose aerogel for different types of oil;

[0026] Figure 4 It is the viscosity-temperature curve of viscous crude oil;

[0027] Figure 5 The adsorption rates of unidirectional MXene / carbon nanotube / sodium alginate / cellulose aerogel on viscous crude oil at different time intervals are shown. Detailed Implementation

[0028] The principles and features of the present invention are described below. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0029] like Figure 1 As shown, a unidirectional sodium alginate-cellulose fiber aerogel and its preparation method are disclosed. The preparation method is as follows:

[0030] Step 1: Dissolve sodium alginate in deionized water and stir to obtain a clear sodium alginate solution. Then add cellulose fibers to the solution and heat and stir until a uniform suspension is obtained.

[0031] Step 2: Carbon nanotubes and MXene are added to the suspension and then uniformly dispersed by ultrasonic and cell disruption treatments to obtain mixed solution 2.

[0032] Step 3: Directional freezing or cryogenic casting of mixed solution 2 to obtain the aerogel precursor.

[0033] Step 4: After freezing the precursor suspension, freeze-dry the aerogel precursor to prepare the aerogel. Then, immerse it in a CaCl2 ethanol aqueous solution for crosslinking.

[0034] Step 5: The cross-linked aerogel is treated with siloxane by vapor deposition to obtain a hydrophobic aerogel.

[0035] Specifically, in step 1 above, sodium alginate is dissolved in deionized water and stirred for 2 hours to obtain a transparent sodium alginate solution (2.5 wt%). Then, cellulose fibers are added to the solution at a weight ratio of 7:3, and the mixture is heated and stirred at 70°C for 2 hours until a uniform suspension is obtained.

[0036] Specifically, in step 2 above, 0.3g of carbon nanotubes and 0.15g of MXene are added to 50mL of suspension and then subjected to ultrasonic treatment and cell disruption for 30min respectively to ensure uniform dispersion in the suspension.

[0037] Specifically, in step 3 above, the aerogel precursor is obtained by directional freezing or cryogenic casting. For the directional freezing method, the MCSC suspension is poured into a cylindrical polytetrafluoroethylene mold 1 (15×30mm), with a copper pillar 3 (15×5mm; 20×35mm) at the bottom of the mold. The copper pillar is kept at a constant temperature using liquid nitrogen to obtain a unidirectional MXene / carbon nanotube / sodium alginate / cellulose aerogel precursor. For the cryogenic casting method, the MCSC suspension is poured into a cylindrical polytetrafluoroethylene mold and placed in a -80°C freezer for 24 hours to obtain a non-unidirectional MXene / carbon nanotube / sodium alginate / cellulose aerogel precursor for comparison.

[0038] Specifically, in step 4 above, after freezing the precursor suspension, the MXene / carbon nanotube / sodium alginate / cellulose aerogel precursor was vacuum freeze-dried in a -50℃ freeze dryer 4 for 48 hours to prepare the aerogel. To prevent structural collapse, the aerogel was immersed in a 2% CaCl2 ethanol-water (8:2) solution for 12 hours for ionic crosslinking. After crosslinking, the aerogel was rinsed multiple times with ethanol and then freeze-dried again to obtain the crosslinked aerogel.

[0039] Specifically, in step five, the unidirectional cross-linked aerogel is treated with siloxanes via thermochemical vapor deposition (CVD) to obtain a hydrophobic aerogel. To achieve this, 0.1 g of siloxanes, such as 1H,1H,2H,2H-perfluorodecyltriethoxysilane or methyltrimethoxysilane, is dissolved in a 10 mL ethanol glass bottle containing the aerogel and placed in a vacuum desiccator. The desiccator is sealed, and the mixture is heated at 60°C for 12 hours in an auxiliary vacuum oven 5 to obtain a hydrophobic unidirectional MXene / carbon nanotube / sodium alginate / cellulose aerogel.

[0040] Example 1:

[0041] A method for preparing a unidirectional sodium alginate-cellulose fiber aerogel, wherein the preparation method comprises:

[0042] Step 1: Dissolve sodium alginate in deionized water and stir to obtain a clear sodium alginate solution. Then add cellulose fibers to the solution and heat and stir until a uniform suspension is obtained.

[0043] Step 2: The carbon nanotubes are added to the suspension and then uniformly dispersed by ultrasonic treatment and cell disruption.

[0044] Step 3: Obtain the aerogel precursor by directional freezing.

[0045] Step 4: After freezing the precursor suspension, the aerogel precursor is freeze-dried to prepare the aerogel. It is then crosslinked by immersion in a CaCl2 ethanol aqueous solution.

[0046] Step 5: The cross-linked aerogel was treated with siloxane by thermochemical vapor deposition (CVD) to obtain a hydrophobic aerogel. To achieve this, 0.1 g of siloxane was dissolved in a 10 mL ethanol glass bottle containing the aerogel and placed in a vacuum desiccator. The desiccator was sealed and heated at 60 °C for 12 hours in a vacuum-assisted oven to obtain a hydrophobic unidirectional carbon nanotube / sodium alginate / cellulose aerogel.

[0047] Example 2:

[0048] A method for preparing a unidirectional sodium alginate-cellulose fiber aerogel, wherein the preparation method comprises:

[0049] Step 1: Dissolve sodium alginate in deionized water and stir to obtain a clear sodium alginate solution. Then add cellulose fibers to the solution and heat and stir until a uniform suspension is obtained.

[0050] Step 2: MXene is added to the suspension and then uniformly dispersed by ultrasonic and cell disruption processes.

[0051] Step 3: Obtain the aerogel precursor by directional freezing.

[0052] Step 4: After freezing the precursor suspension, the aerogel precursor is freeze-dried to prepare the aerogel. It is then crosslinked by immersion in a CaCl2 ethanol aqueous solution.

[0053] Step 5: The cross-linked aerogel was treated with siloxane by thermochemical vapor deposition (CVD) to obtain a hydrophobic aerogel. To achieve this, 0.1 g of siloxane was dissolved in a 10 mL ethanol glass bottle containing the aerogel and placed in a vacuum desiccator. The desiccator was sealed and heated at 60 °C for 12 hours in a vacuum-assisted oven to obtain a hydrophobic uniaxial MXene / sodium alginate / cellulose aerogel.

[0054] Example 3:

[0055] A method for preparing a unidirectional sodium alginate-cellulose fiber aerogel, wherein the preparation method comprises:

[0056] Step 1: Dissolve sodium alginate in deionized water and stir to obtain a clear sodium alginate solution. Then add cellulose fibers to the solution and heat and stir until a uniform suspension is obtained.

[0057] Step 2: MXene and carbon nanotubes are added to the suspension and then uniformly dispersed by ultrasonic and cell disruption treatments, respectively.

[0058] Step 3: Obtain the aerogel precursor by directional freezing.

[0059] Step 4: After freezing the precursor suspension, the aerogel precursor is freeze-dried to prepare the aerogel. It is then crosslinked by immersion in a CaCl2 ethanol aqueous solution.

[0060] Step 5: The cross-linked aerogel was treated with siloxane by thermochemical vapor deposition (CVD) to obtain a hydrophobic aerogel. To achieve this, 0.1 g of siloxane was dissolved in a 10 mL ethanol glass bottle containing the aerogel and placed in a vacuum desiccator. The desiccator was sealed and heated at 60 °C for 12 hours in a vacuum-assisted oven to obtain a hydrophobic unidirectional MXene / carbon nanotube / sodium alginate / cellulose aerogel.

[0061] Example 4:

[0062] A method for preparing a unidirectional sodium alginate-cellulose fiber aerogel, wherein the preparation method comprises:

[0063] Step 1: Dissolve sodium alginate in deionized water and stir to obtain a clear sodium alginate solution. Then add cellulose fibers to the solution and heat and stir until a uniform suspension is obtained.

[0064] Step 2: MXene and carbon nanotubes are added to the suspension and then uniformly dispersed by ultrasonic and cell disruption treatments, respectively.

[0065] Step 3: Obtain the aerogel precursor by cryogenic casting.

[0066] Step 4: After freezing the precursor suspension, the aerogel precursor is freeze-dried to prepare the aerogel. It is then crosslinked by immersion in a CaCl2 ethanol aqueous solution.

[0067] Step 5: The cross-linked aerogel was treated with siloxane by thermochemical vapor deposition (CVD) to obtain a hydrophobic aerogel. To achieve this, 0.1 g of siloxane was dissolved in a 10 mL ethanol glass bottle containing the aerogel and placed in a vacuum desiccator. The desiccator was sealed and heated at 60 °C for 12 hours in a vacuum-assisted oven to obtain a hydrophobic non-unidirectional MXene / carbon nanotube / sodium alginate / cellulose aerogel.

[0068] like Figure 2 As shown, Figures (a), (b), and (c) are the surfaces of unidirectional MXene / carbon nanotube / sodium alginate / cellulose aerogel, non-unidirectional MXene / carbon nanotube / sodium alginate / cellulose aerogel, and unidirectional carbon nanotube / sodium alginate / cellulose aerogel, respectively, exhibiting a porous structure. Figures (d), (e), and (f) are cross-sections of unidirectional MXene / carbon nanotube / sodium alginate / cellulose aerogel, non-unidirectional MXene / carbon nanotube / sodium alginate / cellulose aerogel, and unidirectional carbon nanotube / sodium alginate / cellulose aerogel, respectively, showing an oriented structure in the aerogels after directional freezing.

[0069] like Figure 3 As shown, the relationship between the adsorption capacity of unidirectional MXene / carbon nanotube / sodium alginate / cellulose aerogel for oils and organic solvents and the density of the adsorbate is shown, indicating that the greater the density of the adsorbate, the stronger the adsorption capacity.

[0070] like Figure 4 As shown in the graph, the viscosity of the viscous crude oil used in this invention is related to temperature. As temperature increases, the crude oil viscosity decreases, and at room temperature, the viscosity reaches 10. 6 Order of magnitude;

[0071] like Figure 5 As shown, the adsorption rate of unidirectional MXene / carbon nanotube / sodium alginate / cellulose aerogel on viscous crude oil at different time periods was observed. At 12:00 PM, when sunlight intensity was highest, the adsorption rate reached a maximum exceeding 0.2 g / cm³. -3 s -1 .

[0072] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a unidirectional sodium alginate-cellulose fiber aerogel, characterized in that, Includes the following steps: Step 1: Dissolve sodium alginate in deionized water and stir to obtain sodium alginate solution. Then add cellulose fibers to the solution, heat and stir to obtain a uniform suspension. Step 2: Add carbon nanotubes and MXene to the suspension from the previous step and disperse them to obtain a mixed solution; Step 3: Pour the mixed solution into a mold, and use the low temperature conduction of liquid nitrogen at the bottom to directionally freeze the mixed solution in the mold to obtain the aerogel precursor; Step 4: The aerogel precursor is vacuum-frozen in a low-temperature freeze dryer at -45 to -55°C for 40-50 hours to obtain aerogel. The aerogel is then soaked in calcium chloride solution for cross-linking to obtain cross-linked aerogel. Step 5: The cross-linked aerogel is treated with siloxane by vapor deposition to obtain a hydrophobic unidirectional MXene / carbon nanotube / sodium alginate / cellulose aerogel.

2. The method for preparing unidirectional sodium alginate-cellulose fiber aerogel according to claim 1, characterized in that, In the suspension of step 1, the content of sodium alginate is 1.3-1.5 wt%, and the content of cellulose fiber is 0.5-0.7 wt%.

3. The method for preparing unidirectional sodium alginate-cellulose fiber aerogel according to claim 1, characterized in that, In step 2, the content of carbon nanotubes in the mixed solution is 0.5-0.7 wt%, and the content of MXene is 0.2-0.4 wt%.

4. The method for preparing unidirectional sodium alginate-cellulose fiber aerogel according to claim 1, characterized in that, Step 3 specifically involves: The mixed solution is poured into a cylindrical polytetrafluoroethylene mold, and the bottom of the mold is placed on the upper surface of a solid copper column, which is immersed in liquid nitrogen, which is located in a liquid nitrogen container.

5. The method for preparing unidirectional sodium alginate-cellulose fiber aerogel according to claim 1, characterized in that, In step 4, the aerogel is cross-linked by soaking in calcium chloride ethanol solution for 12 hours.

6. The method for preparing unidirectional sodium alginate-cellulose fiber aerogel according to claim 1, characterized in that, In step 5, the cross-linked aerogel is reacted with an ethanol solution of 1H,1H,2H,2H-perfluorodecyltriethoxysilane for 6 hours by gas-phase precipitation.

7. A unidirectional sodium alginate-cellulose fiber aerogel, characterized in that, Prepared by the method described in any one of claims 1-6.

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