Response surface methodological optimization-based method for dissolving regenerated cellulose by using eutectic solvent and application of response surface methodological optimization-based method

Abstract

The invention provides a method for dissolving regenerated cellulose by a deep eutectic solvent based on response surface method optimization and application of the method, the method adopts a microwave-assisted green deep eutectic solvent system, key parameters such as dissolution temperature, time, material-liquid ratio and the like are optimized through a response surface method system, a cellulose-containing material and the deep eutectic solvent are mixed, and the regenerated cellulose is dissolved in the deep eutectic solvent. Heating and stirring in a microwave reactor to obtain a cellulose solution; and adding water to regenerate the cellulose, and filtering to obtain regenerated cellulose. The method disclosed by the invention is mild in dissolving condition, low in energy consumption, green and efficient, and has good dissolving capacity for high-polymerization-degree raw cotton fibers. The problems that an existing cellulose treatment means is low in efficiency and high in energy consumption are solved. Meanwhile, a good delignification effect is achieved on lignin-containing materials, and cellulose regeneration can be achieved by adding water into a cellulose solution. The regenerated cellulose prepared by the method can be used for preparing regenerated cellulose aerogel materials or regenerated cellulose membranes for air filtration and oil-water separation.

Description

Technical Field

[0001] This invention relates to the field of renewable biological resource utilization technology, specifically to a method for dissolving regenerated cellulose in a eutectic solvent optimized by response surface methodology and its application. Background Technology

[0002] Cellulose, as one of the most abundant biomass materials in nature, has shown great potential in the production of various green and environmentally friendly materials due to its biodegradable and renewable natural properties. Cotton is a typical cellulose material, with a cellulose content of over 94%. The first challenge encountered in the development and utilization of cotton is the difficulty in dissolving cotton fibers, which is determined by the complex microstructure of cotton. Cotton has a multi-layered structure; its cross-section, from the outside to the inside, mainly consists of a primary layer, a secondary layer, and an inner lumen. The cellulose macromolecules within it are formed by β-D-glucopyranosyl units linked together to form a linear polycyclic structure. These cellulose units aggregate to form the basic protofibril structure, and the cellulose molecular chains are tightly bound together by strong hydrogen bonds, thus exhibiting an extremely high degree of polymerization. Typically, the outer surface of raw cotton fibers is also covered with a layer of wax and pectin, which also significantly hinders its dissolution.

[0003] Response Surface Methodology (RSM) is a statistical experimental method for optimizing processes. It determines the optimal combination of factor levels by quantitatively analyzing the relationship between experimental indicators and factors, and can effectively guide experimental design and process optimization. In the dissolution of cellulose materials, RSM can be used to comprehensively consider reaction conditions, thereby obtaining the optimal dissolution process parameters and dissolving cellulose efficiently and quickly. Microwave heating is a heating method that achieves heating through the interaction between microwaves and matter. It can directly convert microwave energy into heat energy, with high energy utilization and short heating time. Using microwave heating to dissolve cellulose can effectively shorten the reaction time and improve solubility. Among various solvents for cellulose, deep eutectic solvents (DES) have outstanding characteristics, including simple preparation, low cost, and mild dissolution conditions. However, existing technologies still have certain limitations in the following aspects: (1) combining DES with efficient microwave heating technology for the study of cellulose dissolution; (2) using RSM system to optimize the process parameters of microwave-assisted DES dissolution of raw cotton fibers; (3) the potential of DES to achieve synergistic dissolution of cellulose and delignification. These gaps have limited the progress in developing efficient, low-consumption, and green dissolving processes suitable for recalcitrant raw cotton fibers.

[0004] This invention employs a metal-salt eutectic solvent composed of aluminum chloride, zinc chloride, and water (Green Chemistry, 2022, 24, 885-897). This eutectic solvent has been shown to dissolve various types of cellulose, but its application in dissolving highly polymerized raw cotton fibers and lignin-containing materials has not yet been reported. Meanwhile, microwaves, as a highly efficient and low-energy heating method, can penetrate deep into materials, achieving uniform and rapid reactions. However, current research on using microwaves as a heat source for the utilization of biomass resources is limited, which also suggests the technical and economic feasibility of efficiently and with low energy consumption in processing cellulose materials.

[0005] Invention content optimization

[0006] The purpose of this invention is to provide a method for dissolving regenerated cellulose in a eutectic solvent optimized by response surface methodology (RSM) and its application. This method employs a microwave-assisted green eutectic solvent (DES) system. Key parameters such as dissolution temperature, time, and feed-to-liquid ratio are optimized using RSM. Cellulose-containing materials are mixed with the eutectic solvent and heated and stirred in a microwave reactor to obtain a cellulose solution. Water is then added to regenerate the cellulose, and the solution is filtered to obtain regenerated cellulose. The method described in this invention offers mild dissolution conditions, low energy consumption, and is green and efficient, exhibiting excellent dissolution capabilities for high-polymerization-degree virgin cotton fibers. It solves the problems of low efficiency and high energy consumption in existing cellulose treatment methods. Simultaneously, it demonstrates good delignination effects on lignin-containing materials, and cellulose regeneration is achieved simply by adding water to the cellulose solution. The regenerated cellulose prepared by this method can be used to prepare regenerated cellulose aerogel materials or regenerated cellulose membranes for air filtration and oil-water separation.

[0007] The method for dissolving regenerated cellulose in a eutectic solvent optimized by response surface methodology according to the present invention is carried out according to the following steps:

[0008] a. Mix aluminum chloride, zinc chloride and water in a molar ratio of 0.1:0.9:4 and stir at room temperature until a homogeneous and transparent solution is obtained to obtain a eutectic solvent;

[0009] b. Mix the cellulose-containing material with the eutectic solvent obtained in step a at a mass ratio of 0.1-20:100, place the mixture in a microwave reactor and heat and stir at a temperature of 30-90℃ for 5 min-2 h to dissolve the cellulose and obtain a cellulose solution; the cellulose-containing material is raw cotton fiber or degreased cotton fiber with a degree of polymerization of 6000-11000, microcrystalline cellulose or cellulose powder with a degree of polymerization of 15-375, wood fiber, paper fiber, reed stalks or waste cotton fabric;

[0010] c. Add water to the cellulose solution obtained in step b to regenerate the cellulose, and then filter to obtain regenerated cellulose.

[0011] The regenerated cellulose obtained by the method is used in the preparation of regenerated cellulose membranes for oil-water separation and air filtration.

[0012] The regenerated cellulose obtained by the method is used in the preparation of regenerated cellulose aerogels for air filtration.

[0013] The present invention involves pouring the obtained regenerated cellulose solution into a casting mold, immersing the mold in water for regeneration, thereby obtaining a regenerated cellulose membrane, which can be used in the fields of air filtration and oil-water separation.

[0014] The obtained regenerated cellulose is dispersed in acidic water with a pH of 3-5 at a mass ratio of 1:10-30, and the suspension of regenerated cellulose is then freeze-dried to obtain regenerated cellulose aerogel, which can be used in the field of air filtration.

[0015] This invention discloses a method for dissolving regenerated cellulose in a eutectic solvent optimized using response surface methodology. By optimizing three factors—dissolution temperature, dissolution time, and feed-to-liquid ratio—through response surface methodology (central composite design), the conditions for maximizing cellulose dissolution are determined, providing a basis for the high-value utilization of cellulose through dissolution and regeneration. This significantly improves dissolution efficiency, especially for highly polymerized virgin cotton fibers. The process combines the advantages of low solvent cost, simple preparation, and environmental friendliness, and exhibits a synergistic delignification effect on lignin-containing raw materials. After dissolution, nanocellulose materials can be obtained through simple water regeneration and filtration, suitable for the efficient and low-energy preparation of cellulose aerogels, functional films, and other products. This invention achieves green, efficient, and controllable optimization of the entire process of cellulose dissolution, regeneration, and derivative material preparation.

[0016] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0017] The method provided by this invention can dissolve high-polymerization-degree raw cotton fibers that are difficult to process by conventional means.

[0018] This invention uses response surface design to dissolve cellulose-containing materials, optimizing the dissolution process parameters to make the dissolution process efficient and energy-saving.

[0019] This invention uses a green and environmentally friendly eutectic solvent to dissolve cellulose materials, which is less harmful to the environment and human health and the solvent can be recycled.

[0020] This invention uses a highly efficient and low-energy microwave heating method to promote the reaction. The process is simple, low in energy consumption, and highly efficient.

[0021] The method provided by this invention can dissolve various cellulose materials.

[0022] The method provided by this invention can remove lignin from lignin-containing materials.

[0023] The method provided by this invention enables the processing of cellulose-containing raw materials to be used in the production of products such as cellulose aerogels and cellulose membranes.

[0024] The method provided by this invention involves rotary evaporation to concentrate and recover the aqueous solution containing aluminum chloride and zinc chloride obtained after cellulose regeneration and filtration, and then adding water according to the original ratio to re-prepare a reusable eutectic solvent. Attached Figure Description

[0025] Figure 1 This is a schematic diagram illustrating the process of dissolving cellulose-containing materials according to the present invention;

[0026] Figure 2 Infrared spectra of the materials in Examples 1-10;

[0027] Figure 3 Images of the samples before and after the reaction in Examples 1-10;

[0028] Figure 4 The three-dimensional distribution diagram and contour plot (X3 = 1.3) of the response Y = f(X1, X2) when raw cotton fibers are dissolved.

[0029] Figure 5 The three-dimensional distribution diagram and contour map (X2=65) of the response Y=f(X1,X3) when raw cotton fibers are dissolved;

[0030] Figure 6 The three-dimensional distribution diagram and contour map (X1=75) of the response Y=f(X2,X3) when raw cotton fibers are dissolved;

[0031] Figure 7 Image of the prepared cellulose aerogel sample;

[0032] Figure 8 This is a photograph of the prepared cellulose membrane sample. Detailed Implementation

[0033] The raw materials and reagents used in the following examples are all commercially available products, or can be prepared by known methods.

[0034] Example 1

[0035] a. Mix aluminum chloride, zinc chloride and water in a molar ratio of 0.1:0.9:4 and stir at room temperature until a homogeneous and transparent solution is obtained to obtain a eutectic solvent;

[0036] b. Mix raw cotton fibers with a degree of polymerization of 6000 at a mass ratio of 1:100 with the eutectic solvent obtained in step a, place the mixture in a microwave reactor and heat and stir at 70°C for 2 hours to dissolve the cellulose and obtain a cellulose solution.

[0037] c. Add water to the cellulose solution obtained in step b to regenerate the cellulose, and then filter to obtain regenerated cellulose.

[0038] The solubility of the raw cotton fiber is approximately 75%, where solubility = 1 - mass of undissolved fiber / total mass of added fiber. The cellulose can be regenerated by adding water to the dissolved mixture, and the regenerated cellulose is obtained after filtration. This embodiment is one of the experiments on the surface response of raw cotton fiber dissolution.

[0039] Example 2

[0040] a. Mix aluminum chloride, zinc chloride and water in a molar ratio of 0.1:0.9:4 and stir at room temperature until a homogeneous and transparent solution is obtained to obtain a eutectic solvent;

[0041] b. Mix raw cotton fibers with a degree of polymerization of 11000 at a mass ratio of 2:100 with the eutectic solvent obtained in step a, place the mixture in a microwave reactor and heat and stir at 80°C for 1.5 hours to dissolve the cellulose and obtain a cellulose solution.

[0042] c. Add water to the cellulose solution obtained in step b to regenerate the cellulose, and then filter to obtain regenerated cellulose.

[0043] The solubility of the raw cotton fiber is approximately 97%, where solubility = 1 - mass of undissolved fiber / total mass of added fiber. The cellulose can be regenerated by adding water to the dissolved mixture, and the regenerated cellulose is obtained after filtration. The parameters in this embodiment are the results of the optimization of the raw cotton fiber dissolution response surface experiment.

[0044] Example 3

[0045] a. Mix aluminum chloride, zinc chloride and water in a molar ratio of 0.1:0.9:4 and stir at room temperature until a homogeneous and transparent solution is obtained to obtain a eutectic solvent;

[0046] b. Mix microcrystalline cellulose with a degree of polymerization of 15 at a mass ratio of 10:100 with the eutectic solvent obtained in step a, place the mixture in a microwave reactor and heat and stir at 40°C for 30 hours to dissolve the cellulose and obtain a cellulose solution.

[0047] c. Add water to the cellulose solution obtained in step b to regenerate the cellulose, and then filter to obtain regenerated cellulose.

[0048] The solubility of the microcrystalline cellulose is approximately 10%, where solubility = mass of added cellulose / (mass of solvent + mass of cellulose). The dissolved mixture can be regenerated by adding water, and the regenerated cellulose is obtained after filtration. This embodiment is one of the microcrystalline cellulose dissolution response surface experiments.

[0049] Example 4

[0050] a. Mix aluminum chloride, zinc chloride and water in a molar ratio of 0.1:0.9:4 and stir at room temperature until a homogeneous and transparent solution is obtained to obtain a eutectic solvent;

[0051] b. Mix microcrystalline cellulose with a degree of polymerization of 375 at a mass ratio of 20:100 with the eutectic solvent obtained in step a, place the mixture in a microwave reactor and heat and stir at 50°C for 40 minutes to dissolve the cellulose and obtain a cellulose solution.

[0052] c. Add water to the cellulose solution obtained in step b to regenerate the cellulose, and then filter to obtain regenerated cellulose.

[0053] The microcrystalline cellulose has a solubility of 20%, where solubility = mass of added cellulose / (mass of solvent + mass of cellulose). The dissolved mixture can be regenerated by adding water, and the regenerated cellulose is obtained after filtration. This embodiment is one of the microcrystalline cellulose dissolution response surface experiments.

[0054] Example 5

[0055] a. Mix aluminum chloride, zinc chloride and water in a molar ratio of 0.1:0.9:4 and stir at room temperature until a homogeneous and transparent solution is obtained to obtain a eutectic solvent;

[0056] b. Mix the degreased cotton fibers with the eutectic solvent obtained in step a at a mass ratio of 5:100, place the mixture in a microwave reactor and heat and stir at 70°C for 70 minutes to dissolve the cellulose and obtain a cellulose solution.

[0057] c. Add water to the cellulose solution obtained in step b to regenerate the cellulose, and then filter to obtain regenerated cellulose.

[0058] The dissolution rate of the degreased cotton fibers is 5%, where the dissolution rate = mass of added cellulose / (mass of solvent + mass of cellulose). The dissolved mixture can be regenerated by adding water, and the regenerated cellulose is obtained after filtration. This embodiment is one of the surface methodology experiments for the dissolution response of degreased cotton.

[0059] Example 6

[0060] a. Mix aluminum chloride, zinc chloride and water in a molar ratio of 0.1:0.9:4 and stir at room temperature until a homogeneous and transparent solution is obtained to obtain a eutectic solvent;

[0061] b. Mix the cellulose powder with the eutectic solvent obtained in step a at a mass ratio of 15:100, place the mixture in a microwave reactor and heat and stir at 50°C for 50 minutes to dissolve the cellulose and obtain a cellulose solution.

[0062] c. Add water to the cellulose solution obtained in step b to regenerate the cellulose, and then filter to obtain regenerated cellulose.

[0063] The cellulose powder has a solubility of 15%, where solubility = mass of added cellulose / (mass of solvent + mass of cellulose). The dissolved mixture can be regenerated by adding water, and the regenerated cellulose is obtained after filtration. This embodiment is one of the surface methodology experiments for the solubility response of cellulose powder.

[0064] Example 7

[0065] a. Mix aluminum chloride, zinc chloride and water in a molar ratio of 0.1:0.9:4 and stir at room temperature until a homogeneous and transparent solution is obtained to obtain a eutectic solvent;

[0066] b. Mix the wood fiber with the eutectic solvent obtained in step a at a mass ratio of 3:100, place the mixture in a microwave reactor and heat and stir at 30°C for 2 hours to dissolve the cellulose and obtain a cellulose solution.

[0067] c. Add water to the cellulose solution obtained in step b to regenerate the cellulose, and then filter to obtain regenerated cellulose.

[0068] Since wood fibers contain only a portion of cellulose, a partially dissolved suspension can be obtained after dissolving for 40 minutes. Simultaneously, the lignin in the wood fibers is released, turning the solution reddish-brown. The solubility of the wood fibers is 1%, where solubility = (1 - undissolved mass / total mass). Adding water to the dissolved mixture regenerates the cellulose, and filtration yields regenerated cellulose. This embodiment is one of the experiments on the surface methodology of wood fiber dissolution response.

[0069] Example 8

[0070] a. Mix aluminum chloride, zinc chloride and water in a molar ratio of 0.1:0.9:4 and stir at room temperature until a homogeneous and transparent solution is obtained to obtain a eutectic solvent;

[0071] b. Mix the paper fibers with the eutectic solvent obtained in step a at a mass ratio of 5:100, place the mixture in a microwave reactor and heat and stir at 90°C for 5 minutes to dissolve the cellulose and obtain a cellulose solution.

[0072] c. Add water to the cellulose solution obtained in step b to regenerate the cellulose, and then filter to obtain regenerated cellulose.

[0073] The solubility of the paper fiber is 5%, where solubility = mass of added cellulose / (mass of solvent + mass of cellulose). The dissolved mixture can be regenerated by adding water, and the regenerated cellulose is obtained after filtration. This embodiment is one of the experiments on the surface response of paper fiber dissolution.

[0074] Example 9

[0075] a. Mix aluminum chloride, zinc chloride and water in a molar ratio of 0.1:0.9:4 and stir at room temperature until a homogeneous and transparent solution is obtained to obtain a eutectic solvent;

[0076] b. Mix the reed stalks with the eutectic solvent obtained in step a at a mass ratio of 5:100, place the mixture in a microwave reactor and heat and stir at 70°C for 1 hour to dissolve the cellulose and obtain a cellulose solution.

[0077] c. Add water to the cellulose solution obtained in step b to regenerate the cellulose, and then filter to obtain regenerated cellulose.

[0078] Since reed stalks contain only a portion of cellulose, a partially dissolved suspension can be obtained after dissolving for 50 minutes. Simultaneously, the lignin in the reed stalks is released, giving the solution a reddish-brown color. The solubility of the reed stalks is 2%, where solubility = (1 - undissolved mass / total mass). Adding water to the dissolved mixture regenerates the cellulose, and filtration yields regenerated cellulose. This embodiment is one of the reed stalk dissolution response surface experiments.

[0079] Example 10

[0080] a. Mix aluminum chloride, zinc chloride and water in a molar ratio of 0.1:0.9:4 and stir at room temperature until a homogeneous and transparent solution is obtained to obtain a eutectic solvent;

[0081] b. Mix waste cotton fabric (disposable face towel) with the eutectic solvent obtained in step a at a mass ratio of 2.5:100, place it in a microwave reactor and heat and stir at 80°C for 1.5 hours to dissolve the cellulose and obtain a cellulose solution.

[0082] c. Add water to the cellulose solution obtained in step b to regenerate the cellulose, and then filter to obtain regenerated cellulose.

[0083] The paper fiber has a solubility rate of 2.5%, where solubility rate = mass of added cellulose / (mass of solvent + mass of cellulose). The dissolved mixture can be regenerated by adding water, and the resulting solution is filtered to obtain regenerated cellulose. This embodiment is one of the experiments on the dissolution response surface methodology of waste cotton fabrics.

[0084] Depend on Figure 2It can be seen that raw cotton fiber, degreased cotton fiber, microcrystalline cellulose, cellulose powder and disposable face towels exhibit similar cellulose chemical structures, with cellulose as the main component, while wood fiber, paper fiber and reed stalks contain lignin and other components.

[0085] Depend on Figure 3 It can be seen that materials mainly composed of cellulose become homogeneous solutions after dissolution, while materials containing lignin turn reddish-brown due to the release of lignin.

[0086] Depend on Figure 4-6 The response surface plot can visually show the effects of dissolution temperature, dissolution time and material concentration on the solubility of raw cotton fibers.

[0087] Example 11

[0088] The regenerated cellulose obtained in Example 2 was dispersed in acidic water with a pH of 3 at a mass ratio of 1:20. The suspension of regenerated cellulose was then freeze-dried to obtain a regenerated cellulose aerogel. This aerogel is effective against PM2.5. 0.3 Its filtration efficiency is 99.82%.

[0089] Example 12

[0090] The cellulose solution obtained in Example 4 was poured into a casting mold, and the mold was placed in water for regeneration to obtain a regenerated cellulose membrane. The cellulose membrane had a separation efficiency of 97.88% for diesel water-in-oil emulsion.

[0091] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principle of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A method for dissolving regenerated cellulose in a eutectic solvent optimized based on response surface methodology, characterized in that, Follow these steps: a. Mix aluminum chloride, zinc chloride and water in a molar ratio of 0.1:0.9:4 and stir at room temperature until a homogeneous and transparent solution is obtained to obtain a eutectic solvent; b. Mix the cellulose-containing material with the eutectic solvent obtained in step a at a mass ratio of 0.1-20:100, place the mixture in a microwave reactor and heat and stir at a temperature of 30-90℃ for 5 min-2 h to dissolve the cellulose and obtain a cellulose solution; the cellulose-containing material is raw cotton fiber or degreased cotton fiber with a degree of polymerization of 6000-11000, microcrystalline cellulose or cellulose powder with a degree of polymerization of 15-375, wood fiber, paper fiber, reed stalks or waste cotton fabric; c. Add water to the cellulose solution obtained in step b to regenerate the cellulose, and then filter to obtain regenerated cellulose.

2. The use of regenerated cellulose obtained by the method of claim 1 in the preparation of regenerated cellulose membranes for oil-water separation and air filtration.

3. Use of regenerated cellulose obtained by the method of claim 1 in the preparation of regenerated cellulose aerogels for air filtration.

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