Preparation method of high-stability cellulose nanofluid membrane, product and application thereof

Abstract

The application discloses a preparation method of a high-stability cellulose nanofluid film, and a product and application thereof, and belongs to the field of energy conversion and material science. The method comprises the following steps: adding modified cellulose into an ionic liquid to prepare a solution by heating; dropping and coating the solution onto the surface of a porous polymer film, and preparing a gel film by heating and vacuum treatment; and obtaining the nanofluid film after water soaking and drying of the gel film. The nanofluid film adopts an embedded structure, the cellulose layer is a small-pore structure, the porous polymer film is a large-pore structure, and the nanofluid film has etching and three-dimensional network channel structures. The preparation process is simple and the conditions are mild, the prepared film has excellent ion rapid selective transmission performance, acid-base stability and long-term operation stability, can efficiently convert salinity gradient energy into electric energy, and has a good application prospect in the field of salt-difference osmotic energy utilization.

Description

Technical Field

[0001] This invention relates to the field of energy conversion and materials science, specifically to a method for preparing a highly stable cellulose nanofluid membrane, its products, and applications. Background Technology

[0002] The growing global energy security and environmental pollution problems have driven an urgent demand for green, sustainable, and clean energy. Among numerous renewable energy technologies, salinity gradient osmosis energy, as a renewable energy source with abundant reserves that has not yet been extensively developed, has become one of the current research hotspots due to its potential energy conversion efficiency and broad application prospects. Salinity gradient osmosis energy technology relies on the salinity difference between seawater and freshwater, achieving energy conversion and storage through ion-selective membranes. In recent years, researchers have focused on exploring different membrane materials to achieve this energy conversion process, especially developing high-performance ion-selective nanofluid membranes, which has become key to achieving efficient osmosis energy conversion.

[0003] Existing salinity gradient osmosis membrane materials mostly face some inherent problems, mainly including: 1. Many traditional membrane materials exhibit poor ion selectivity under high salinity or high pressure environments, making it difficult to achieve precise ion sieving at high flux levels. 2. During salinity gradient osmosis, membrane materials are often susceptible to concentration polarization, leading to a significant decrease in osmotic pressure gradient, thus affecting power density and efficiency. 3. Existing membrane materials may experience delamination, shedding, or performance degradation during long-term use, especially under strong acid, strong alkali, or high temperature conditions, where membrane stability is a pressing issue that needs to be addressed.

[0004] To address these challenges, composite membrane materials with heterogeneous structures have emerged. Composite membranes combine the advantages of different membrane materials, maintaining high ion flux while improving ion selectivity, concentration polarization resistance, and chemical stability. Against this backdrop, loading polymer nanofluids onto the membrane surface using vacuum-assisted filtration to form composite membranes has become a cutting-edge technological approach.

[0005] Polycarbonate membranes, cellulose acetate membranes, and polyvinylidene chloride membranes have become ideal substrate materials for composite membrane preparation due to their respective structural characteristics. However, existing composite membranes still need further optimization in terms of interfacial bonding strength, stability, and energy conversion efficiency. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a method for preparing a highly stable cellulose nanofluid membrane, as well as its products and applications. The nanofluid membrane has a typical etched and three-dimensional network channel structure, exhibits rapid and selective transport of solution ions and high stability, and can effectively convert marine salinity gradient energy into electrical energy.

[0007] This invention is implemented as follows: A method for preparing a highly stable cellulose nanofluid membrane, characterized in that: (1) Add modified cellulose to a cellulose solvent and heat to prepare a modified cellulose solution; (2) The modified cellulose solution is drop-coated onto the surface of a porous polymer film and subjected to heating and vacuum treatment to prepare a cellulose-polymer gel film; (3) The cellulose-polymer gel membrane was soaked in water multiple times (until the conductivity did not change significantly) and dried at room temperature to obtain a highly stable cellulose nanofluid membrane.

[0008] Further, the modified cellulose fiber in step (1) is one of sulfonated cellulose, carboxylated cellulose, and phosphorylated cellulose; the cellulose solvent is an ionic liquid.

[0009] Furthermore, the ionic liquid is one of 1-allyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium chloride, 1-vinyl-3-alkylimidazolium chloride, and 1-allyl-3-alkylimidazolium chloride.

[0010] Further, the modified cellulose in step (1) has a mass fraction of 1% to 5% relative to the cellulose solvent.

[0011] Further, the porous polymer film in step (2) is one of polycarbonate film, cellulose acetate filter film, and polyvinylidene chloride filter film, and the pore size of the film is 30~400 nm.

[0012] Furthermore, the vacuum time in step (2) is 1~5 min, the vacuum degree is -0.1 MPa, and the temperature is 80℃.

[0013] Furthermore, the product is prepared by one of the methods described above for preparing a highly stable cellulose nanofluid membrane.

[0014] Furthermore, an application of a highly stable cellulose nanofluid membrane prepared by the method is provided, wherein the highly stable cellulose nanofluid membrane is used to convert salinity gradient energy into electrical energy.

[0015] The present invention has the following advantages: (1) Enhance membrane stability: Cellulose nanofluid material is loaded onto the membrane surface by vacuum filtration, while negatively charged modified cellulose is embedded in the large pores of the porous polymer membrane to form a firmly bonded composite membrane structure, which effectively avoids the interfacial delamination and shedding problems of traditional heterogeneous membranes and ensures the structural and functional stability of the membrane during long-term use.

[0016] (2) Excellent acid and alkali stability: The composite membrane has good acid and alkali resistance and can work stably for a long time in a strong acid environment of pH=3 and a strong alkali environment of pH=11. It has strong resistance to chemical degradation and is suitable for harsh working conditions.

[0017] (3) High efficiency of ion sieving and flux control: Precisely control the loading of nanofluids, improve the ion selectivity and flux of the membrane, significantly improve the salt gradient permeation energy conversion efficiency, and the maximum power density can reach 8.06 W / m².

[0018] (4) Long-term stable operation: In actual application scenarios simulating river water and seawater, the membrane's operational stability exceeds 90 days, the single membrane's continuous working time exceeds 80,000 seconds, and the performance degradation is slow.

[0019] (5) The preparation process has obvious advantages: the vacuum filtration method is adopted, the process is simple and the conditions are mild, the materials used are low cost and sustainable, it is easy to scale up production, and the application prospects are broad. Attached Figure Description

[0020] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0021] Figure 1 SEM cross-sectional images of a blank commercial polycarbonate membrane (left) and a partially sulfonated cellulose nanofluid membrane with embedded cellulose prepared in Example 3 (right).

[0022] Figure 2 The bar chart shows the 30-day stability distribution of the cellulose nanofluid membrane prepared in Example 3 of this invention under strong acid (pH=3) and strong alkali (pH=11) environments. Figure 3 The bar chart shows the stability distribution of the cellulose nanofluid membrane prepared in Example 3 of the present invention during a 90-day ultra-long operation in a simulated river water and seawater salinity gradient system. Figure 4 This is a comparison chart of the maximum power density of Example 3, Comparative Example 1 (sulfonated cellulose membrane), and Comparative Example 2 (polycarbonate membrane) of the present invention. Detailed Implementation

[0023] The present invention is conceived as follows: Polycarbonate membranes, as core-porous membranes prepared by track etching, possess uniform pore size and regular pore shape. Furthermore, the surface chemical properties of the membrane are tunable, making it an ideal mechanical support substrate for constructing high-performance composite nanofluid membranes. Through vacuum filtration and heating, polymer nanofluid materials such as sulfonated cellulose, carboxylated cellulose, and phosphorylated cellulose dissolved in ionic liquids are directly loaded onto the surface of the polycarbonate membrane. The modified cellulose mixture solution is embedded into the interior of the polycarbonate membrane, forming a tightly bonded composite membrane structure within the membrane. This composite membrane has the following advantages: 1. The polymer nanofluid materials and the porous polycarbonate membrane form a strong interfacial bond, avoiding the delamination and detachment problems of traditional heterogeneous membranes. Especially under strong acid and strong alkali environments, the composite membrane exhibits excellent acid and alkali stability, enabling long-term use in harsh environments. 2. Through heating and vacuum-assisted filtration, the nanofluid materials and the porous structure of the membrane form a mechanically interlocked structure, enhancing the membrane's durability and time stability. Even during long-term use, the structure and function of the composite membrane remain unchanged, preventing material aging or performance degradation. Furthermore, cellulose acetate and polyvinylidene chloride (PVDC) membranes with three-dimensional network structures are also widely used in the preparation of composite membranes. The three-dimensional network structure of cellulose acetate membranes effectively enhances the mechanical strength and stability of the membrane, while PVDC membranes provide strong chemical stability and high-temperature resistance. During vacuum filtration, polymer nanofluids can be uniformly loaded onto the membrane surface and undergo strong physical / chemical interactions with the membrane surface, ensuring the structural and functional integrity of the composite membrane during long-term use.

[0024] Compared to other complex membrane fabrication processes, vacuum filtration offers advantages such as simple procedures and mild conditions, and it can utilize low-cost, sustainable polymer materials, demonstrating promising application prospects. This technical approach successfully addresses the shortcomings of traditional membrane materials in terms of acid-base stability and time stability, providing a highly promising solution for developing high-performance, highly stable salinity gradient permeation energy conversion membranes.

[0025] The following will be combined with the appendix Figure 1-3 The technical solution of the present invention will be clearly and completely described in detail with specific embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products. Example 1

[0026] Purchased sulfonated cellulose (carboxymethyl-2-sulfonic acid aldehyde cellulose) was added to an ionic liquid (1-butyl-3-methylimidazolium chloride) and heated to prepare a 1% cellulose solution. The cellulose solution was then dropped onto a PC membrane with a pore size of approximately 30 nm and a thickness of approximately 10 μm. Under a vacuum of -0.1 MPa, the membrane was simultaneously heated to 80 °C and evacuated for 1 minute before immersion in deionized water to form a wet gel membrane. After drying, a cellulose nanofluid membrane with a thickness of approximately 10 μm was obtained.

[0027] Using sodium chloride electrolytes with concentrations of 0.5 M and 10 mM, the cellulose nanofluid membrane achieved an output power density of 6.5 W / m². The single membrane maintained a performance retention rate of over 93% after 80,000 s in both 0.5 M and 10 mM sodium chloride electrolytes, with no significant degradation inflection point. In simulated seawater and river water systems, the membrane remained stable for 90 days, maintaining a performance retention rate of over 96% with no significant degradation inflection point. Acid-base stability was maintained for 30 days, with a performance retention rate of over 93% and no significant degradation inflection point. Example 2

[0028] Purchased carboxymethyl cellulose was added to an ionic liquid (1-vinyl-3-alkylimidazolium chloride) and heated to prepare a 2% cellulose solution. The mixed solution was then dropped onto a PC membrane with a pore size of approximately 50 nm and a thickness of approximately 10 μm. Under a vacuum of -0.1 MPa, the membrane was simultaneously heated to 80°C and evacuated for 2 minutes before immersion in deionized water to form a wet gel membrane. After drying, a cellulose nanofluid membrane with a thickness of approximately 10 μm was obtained.

[0029] Using sodium chloride electrolytes with concentrations of 0.5 M and 10 mM, the cellulose nanofluid membrane output power density was 7.7 W / m2. The single membrane maintained a performance retention rate of over 93% after 80,000 s in both 0.5 M and 10 mM sodium chloride electrolytes, with no obvious degradation inflection point. In a simulated seawater-river water system, the membrane remained stable for 90 days, maintaining a performance retention rate of over 96%, with no obvious degradation inflection point. The membrane also maintained acid-base stability for 30 days, maintaining a performance retention rate of over 93%, with no obvious degradation inflection point. Example 3

[0030] Purchased sulfonated cellulose (carboxymethyl-2-sulfonic acid aldehyde cellulose) was added to an ionic liquid (chlorinated-1-allyl-3-methylimidazolium chloride) and heated to prepare a 3% cellulose solution. The cellulose solution was then dropped onto a PC membrane with a pore size of approximately 100 nm and a thickness of approximately 10 μm. Under a vacuum of -0.1 MPa, the membrane was simultaneously heated to 80°C and evacuated for 3 minutes before immersion in deionized water to form a wet gel membrane. After drying, a cellulose nanofluid membrane with a thickness of approximately 10 μm was obtained.

[0031] Using sodium chloride electrolytes with concentrations of 0.5 M and 10 mM, the cellulose nanofluid membrane achieved an output power density of 8.06 W / m². The single membrane maintained stability of over 93% after 80,000 s in both 0.5 M and 10 mM sodium chloride electrolytes, with no significant degradation inflection point. In simulated seawater and river water systems, the membrane remained stable for 90 days, maintaining a performance retention rate of over 96% without a significant degradation inflection point. Acid-base stability was maintained for 30 days, with a performance retention rate of over 93% and no significant degradation inflection point.

[0032] Figure 1 SEM cross-sectional images of a blank commercial polycarbonate membrane (left) and a partially sulfonated cellulose nanofluid membrane with embedded cellulose prepared in Example 3 (right).

[0033] Figure 2 The bar chart shows the 30-day stability distribution of the cellulose nanofluid membrane prepared in Example 3 under strong acid (left) and strong alkali (right) environments. As can be seen from the figure, the cellulose nanofluid membrane maintained a performance rate of over 93% after 30 days under two extreme acid and alkali environments, proving the excellent chemical degradation resistance of the membrane material of the present invention and solving the problem of easy failure of traditional membranes under harsh acid and alkali conditions.

[0034] Figure 3 The bar chart shows the stability distribution of the cellulose nanofluid membrane prepared in Example 3 during a 90-day ultra-long operation in a simulated river-seawater salinity gradient system. As can be seen from the figure, the power density retention rate of the cellulose nanofluid membrane is stable at over 96% within 90 days in the simulated actual application scenario (river-seawater salinity gradient system), and there is no obvious attenuation inflection point. It can be seen that the cellulose nanofluid membrane prepared in this invention has the technical advantage of "lasting up to 90 days while still having a high power density", which meets the long-term use requirements of actual salinity gradient power generation scenarios. Example 4

[0035] Purchased phosphorylated cellulose (cellulose monophosphate) was added to an ionic liquid (1-allyl-3-alkylimidazolium chloride) and heated to prepare a 4% cellulose solution. The cellulose solution was then dropped onto a PVDF membrane with a pore size of approximately 200 nm and a thickness of approximately 10 μm. Under a vacuum of -0.1 MPa, the membrane was simultaneously heated to 80°C and evacuated for 4 minutes before being immersed in deionized water to form a wet gel membrane. After drying, a cellulose nanofluid membrane with a thickness of approximately 10 μm was obtained.

[0036] Using sodium chloride electrolytes with concentrations of 0.5 M and 10 mM, the cellulose nanofluid membrane output power density was 7 W / m². The single membrane maintained a performance retention rate of over 93% after 80,000 s in both 0.5 M and 10 mM sodium chloride electrolytes, with no obvious degradation inflection point. In a simulated seawater-river water system, the membrane remained stable for 90 days, maintaining a performance retention rate of over 96%, with no obvious degradation inflection point. The membrane also exhibited acid-base stability for 30 days, maintaining a performance retention rate of over 93%, with no obvious degradation inflection point. Example 5

[0037] Purchased sulfonated cellulose (carboxymethyl-2-sulfonic acid aldehyde cellulose) was added to an ionic liquid (1-allyl-3-methylimidazolium chloride) and heated to prepare a 5% cellulose solution. The cellulose solution was then dropped onto a CA membrane with a pore size of approximately 400 nm and a thickness of approximately 10 μm. Under a vacuum of -0.1 MPa, the membrane was simultaneously heated to 80 °C and evacuated for 5 minutes before immersion in deionized water to form a wet gel membrane. After drying, a cellulose nanofluid membrane with a thickness of approximately 10 μm was obtained.

[0038] Using sodium chloride electrolytes with concentrations of 0.5 M and 10 mM, the cellulose nanofluid membrane achieved an output power density of 6.5 W / m². The single membrane maintained a performance retention rate of over 93% after 80,000 s in both 0.5 M and 10 mM sodium chloride electrolytes, with no significant degradation inflection point. In simulated seawater and river water systems, the membrane remained stable for 90 days, maintaining a performance retention rate of over 96% with no significant degradation inflection point. Acid-base stability was maintained for 30 days, with a performance retention rate of over 93% and no significant degradation inflection point.

[0039] Compare with Example 1: Purchased sulfonated cellulose fibers (carboxymethyl-2-sulfonic acid aldehyde cellulose) were added to an ionic liquid (chlorinated-1-allyl-3-methylimidazolium chloride) and heated to prepare a cellulose solution. The cellulose solution was then coated onto a glass plate and immersed in deionized water for 24 hours to form a wet gel membrane. After drying, a sulfonated cellulose membrane with a thickness of 1 mm was obtained.

[0040] Using sodium chloride electrolytes with concentrations of 0.5 M and 10 mM, the output power density of the sulfonated cellulose membrane was only 3.6 W / m2. At 8000 s, the output power density was 20% of the initial value. At 10 days, the output power density was 20% of the initial value. At 5 days, the output power density was 10% of the initial value. Furthermore, cracks appeared in the membranes when only the stable days were considered.

[0041] Compare with Example 2: Commercially available polycarbonate membranes with a thickness of approximately 10 μm, using sodium chloride electrolytes at concentrations of 0.5 M and 10 mM, exhibit an output power density of only 2.3 W / m². At 1000 s, the single-membrane output power density is 30% of the initial value; at 30 days, the output power density is 40% of the initial value; and at 15 days, the acid-base stability is also 40% of the initial value. Compare with Example 3: The purchased sulfonated cellulose fiber (carboxymethyl-2-sulfonic acid aldehyde fiber) is dropped onto a CA membrane with a pore size of 400 nm and a thickness of about 10 μm. After vacuuming for 5 minutes at a vacuum degree of -0.1 MPa and drying, the sulfonated cellulose fiber-polymer nanofluid membrane can be prepared.

[0042] Using sodium chloride electrolytes with concentrations of 0.5 M and 10 mM, the output power density of the cellulose nanofluid membrane was only 2.5 W / m2. After 1000 s, the output power density of the single membrane was 20% of the initial value. After 5 days, the output power density was 40% of the initial value. After 5 days, the output power density was also 40% of the initial value.

[0043] Figure 4 This is a comparison of the maximum power density of Example 3, Comparative Example 1 (sulfonated cellulose membrane), and Comparative Example 2 (polycarbonate membrane). As shown in the figure, the maximum power density of the membrane in Example 3 reaches 8.06 W / m², significantly higher than the 3.6 W / m² of Comparative Example 1 and the 2.3 W / m² of Comparative Example 2. Although the polycarbonate membrane has a cylindrical and regular internal transport structure, its pore walls are inert, resulting in a very thin electrical double layer. While the sulfonated cellulose membrane possesses strong negative charges from its sulfonate groups, its dense three-dimensional structure leads to a tortuous ion transport path and low ionic conductivity. The nanofluid membrane prepared in this invention creates a composite structure that combines rigidity and flexibility, exhibiting both high ionic conductivity and high ion selectivity.

[0044] As can be seen from the comparison between the above embodiments and the control examples, the cellulose nanofluid membrane prepared by the method of the present invention is significantly superior to existing membrane materials in terms of power density, continuous stability, stability over days and acid-base stability, which fully demonstrates the technical advantages of the present invention.

[0045] While specific embodiments of the present invention have been described above, those skilled in the art should understand that the specific embodiments described are merely illustrative and not intended to limit the scope of the invention. Equivalent modifications and variations made by those skilled in the art in accordance with the spirit of the invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a highly stable cellulose nanofluid membrane, characterized in that: (1) Add modified cellulose to a cellulose solvent and heat to prepare a modified cellulose solution; (2) The modified cellulose solution is drop-coated onto the surface of a porous polymer film and subjected to heating and vacuum treatment to prepare a cellulose-polymer gel film; (3) The cellulose-polymer gel membrane is soaked in water and dried at room temperature to obtain a highly stable cellulose nanofluid membrane.

2. The method according to claim 1, characterized in that: The modified cellulose fiber in step (1) is one of sulfonated cellulose, carboxylated cellulose, and phosphorylated cellulose; the cellulose solvent is an ionic liquid.

3. The method according to claim 2, characterized in that: The ionic liquid is one of 1-allyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium chloride, 1-vinyl-3-alkylimidazolium chloride, and 1-allyl-3-alkylimidazolium chloride.

4. The method according to claim 1, characterized in that: The modified cellulose in step (1) has a mass fraction of 1% to 5% relative to the cellulose solvent.

5. The method according to claim 1, characterized in that: The porous polymer membrane in step (2) is one of polycarbonate membrane, cellulose acetate filter membrane, or polyvinylidene chloride filter membrane, and the pore size of the membrane is 30~400 nm.

6. The method according to claim 1, characterized in that: The vacuum time in step (2) is 1~5 min, the vacuum degree is -0.1 MPa, and the temperature is 80℃.

7. A product prepared by a method for preparing a highly stable cellulose nanofluid membrane according to any one of claims 1-6.

8. An application of a highly stable cellulose nanofluid membrane prepared according to any one of claims 1-6, characterized in that: The highly stable cellulose nanofluid membrane is used to convert salinity gradient energy into electrical energy.

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