Method for efficiently preparing sodium carboxymethyl cellulose by mechanical force

Abstract

The invention belongs to the field of preparation of carboxymethyl cellulose, and relates to a method for efficiently preparing sodium carboxymethyl cellulose by mechanical force. According to the invention, high-substitution-degree sodium carboxymethyl cellulose is prepared from modified cellulose, and the problems of serious environmental pollution, resource waste, tedious process and the like in the preparation process of sodium carboxymethyl cellulose in the current market are solved. Agricultural wastes are adopted as raw materials, useful materials are produced by utilizing the wastes, the purpose of environmental friendliness can be achieved, the raw materials are wide in source, cheap and easy to obtain, the substitution degree can be greatly increased by adding a small amount of etherifying agent and a small amount of water solvent for reaction, and a high-efficiency and high-substitution-degree product is prepared. According to the invention, biomass is used as a reaction raw material, is renewable and degradable, and accords with the green chemistry concept.

Description

Technical Field

[0001] The invention belongs to the field of carboxymethyl cellulose preparation and relates to a method for efficiently preparing sodium carboxymethyl cellulose by mechanical force. Technical Background

[0002] Cellulose is the most abundant renewable polymer in the world today. It usually comes from biomass raw materials such as wood and plants. Biomass is a resource-rich and renewable material with many advantages such as non-toxic, cheap, green and pollution-free, and biodegradable. It can be used sustainably through the natural carbon cycle to achieve the goal of carbon neutrality. It is an important material resource to support the sustainable development of mankind in the future. Natural cellulose is the most widely distributed and most abundant polysaccharide in nature. It has a very rich source and has a supramolecular semi-crystalline structure, that is, it forms a system of interlaced crystalline and amorphous regions. It is insoluble in water and organic solvents, which makes its research and application have certain limitations. Therefore, cellulose needs to be modified.

[0003] At present, the modification technology of cellulose mainly focuses on etherification and esterification, among which carboxymethylation reaction is one of the etherification technologies. Sodium carboxymethyl cellulose obtained by carboxymethylation modification is a water-soluble cellulose ether with good chemical and physical properties. Its aqueous solution has the functions of thickening, film-forming, bonding, moisture retention, colloid protection, emulsification and suspension adsorption. It can be widely used in the fields of petroleum, food, medicine, textile, papermaking and water treatment. It can be used as a biomass raw material to replace other resources such as fossils. It can not only reduce the pollution to the environment during the preparation process and avoid a series of safety hazards in the production and application process, but also as a renewable resource, it has the advantages of wide source of raw materials, cheap and easy to obtain, and environmentally friendly. It is one of the most important cellulose ethers.

[0004] Since sodium carboxymethyl cellulose was invented in 1918, there are two traditional industrial production methods for sodium carboxymethyl cellulose, namely the aqueous medium process and the solvent process. The aqueous medium process is an early process for producing sodium carboxymethyl cellulose. It is a method in which alkaline cellulose and an etherifying agent are reacted in the presence of free alkali and water. During the reaction, there is no organic solvent such as alcohol in the system as a reaction medium. The main process flow is: first, the pulp is put into an impregnation press, and then the raw material is impregnated with sodium hydroxide solution for a certain period of time, and then the excess alkali solution is removed, and the pressed alkaline cellulose is crushed by a pulverizer, and added to a jacketed kneader, and then a certain amount of chloroacetic acid is added for etherification reaction. After the etherification reaction is completed, the mixture is placed in a drum and kept at a constant temperature for aging until the reaction is completed. The crude product obtained after drying and crushing needs to be washed with 70% methanol or ethanol aqueous solution after ripening, and acid is added to neutralize the excess alkali to obtain a product with higher purity [Yan Ruixuan. Water-soluble polymers [M]. Beijing: Chemical Industry Press, 2003, 460-461.]. This method has complicated processes, low reaction efficiency, poor product uniformity, and low degree of substitution. The solvent process is also called the organic solvent process (solvent process). It is a process method for carboxymethylation reaction using organic solvent as the reaction medium. The process flow of the solvent method is similar to that of the water medium method, except that the former is carried out in an organic solvent. During the solvent method reaction, heat and mass transfer are rapid and uniform, the main reaction is faster, and the side reactions are reduced, which improves the utilization rate of the etherifying agent, the stability and uniformity of the reaction, and also greatly improves the degree of substitution and substitution uniformity of the product, expanding the scope of application of the product. However, in the actual production process, it is necessary to optimize the pulp, reaction medium type and dosage, so as to improve the uniformity of the reaction and the utilization rate of the etherifying agent [Yang Zhili, Su Maoyao, Gao Guang. Fundamentals and Applications of Vinyl Ether [M]. Guangzhou: South China University of Technology Press, 1990, 62-66, 202-203, 208-209.]. At the same time, the solvent method uses expensive organic solvents as the medium, which accounts for a large proportion of the cost, and uses a large amount of organic solvents. In terms of safe production, a series of measures must be taken to ensure the smooth progress of production. Summary of the invention

[0005] In view of the problems of large environmental pollution, waste of resources, low production efficiency, etc. in the preparation process of sodium carboxymethyl cellulose in the current market, the present invention provides a method for efficiently preparing sodium carboxymethyl cellulose by using mechanical force.

[0006] The technical solution of the present invention:

[0007] A method for efficiently preparing sodium carboxymethyl cellulose by mechanical force, the steps are as follows:

[0008] Step 1: Add cellulose to sodium hydroxide alkaline solution and stir evenly;

[0009] Step 2: After aging the obtained alkali cellulose, add it into an internal mixer together with the etherifying agent, and stir and mix them evenly;

[0010] Step 3: Raise the temperature to the reaction temperature and react in an internal mixer. After the reaction is completed, crush the obtained product, wash it repeatedly with a 95% ethanol-water solution for several times until the chloride ions are washed out, and filter and dry to obtain the final product.

[0011] The cellulose is one or a mixture of two or more of agricultural wastes such as cotton linters, wheat straws, reeds, and bagasse.

[0012] The mass concentration of the alkalized sodium hydroxide lye is 10%-30%;

[0013] The etherifying agent is chloroacetic acid, and the molar ratio of cellulose to chloroacetic acid is 1:0.5-1:1.5;

[0014] The aging time of the cellulose is 10h-20h, and the aging temperature is 20°C-30°C;

[0015] The reaction temperature in step 3 is 70°C-110°C;

[0016] The reaction time in step 3 is 1 h-3 h.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] (1) The degree of substitution of the product can be greatly improved without adding other solvents. The cellulose particles will be broken and refined by mechanical force, the internal structure will be destroyed, the hydrogen bonds between the molecules will be opened, and the activity of the cellulose molecules will be continuously improved. In addition, the etherification rate of the etherification agent is increased by mechanical force, thereby improving the reaction efficiency.

[0019] (2) The prepared sodium carboxymethyl cellulose has a high degree of substitution and good water solubility, and can be widely used in industries such as petroleum, food, medicine, textile and papermaking. The preparation process is green and pollution-free, and has the advantages of a wide source of raw materials and being environmentally friendly.

[0020] (3) Using agricultural waste as raw materials to prepare high-degree-of-substitution sodium carboxymethyl cellulose and using waste to produce useful materials not only solves the pollution problem of abandoned crops, but also turns waste into treasure and achieves effective utilization. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is the infrared spectra of raw material cellulose, product sodium carboxymethyl cellulose and commercial sodium carboxymethyl cellulose.

[0022] Figure 2 This is the XRD spectrum of the raw material cellulose and the product sodium carboxymethyl cellulose. DETAILED DESCRIPTION

[0023] The specific implementation of the present invention is further described below in conjunction with the accompanying drawings and technical solutions.

[0024] Embodiment 1:

[0025] Take 16.2g of cellulose (cotton linters) and a 20% sodium hydroxide alkaline solution in a beaker, mix and stir for 24h, and after alkalization and stirring, age at 25℃ for 15h. Add the obtained alkali cellulose and the etherifying agent chloroacetic acid in a molar ratio of 1:1 into an internal mixer, mix and stir at 30℃ for 1h, increase the temperature to 90℃, and react for 2h. After the reaction, crush the obtained crude product, wash it repeatedly with 95% ethanol-water solution several times until the chloride ions are washed clean, and filter and dry to obtain the final product.

[0026] This example is the optimal reaction conditions for preparing sodium carboxymethyl cellulose, and the degree of substitution of the obtained product is 0.87. Figure 1 The infrared spectra of cellulose, product sodium carboxymethyl cellulose and commercial sodium carboxymethyl cellulose are shown in Figure 1. According to the Fourier transform infrared spectrum, at 3721 cm -1 ~3017cm -1 The absorption peak at 3003cm -1 ~2790cm -1 The absorption peak is due to the -CH stretching vibration of the methylene group; at 1605cm -1 The absorption peak is the stretching vibration peak of COC, which proves that it is carboxymethylated, 1430cm -1 、1360cm -1 The absorption peak is due to -CH deformation vibration; 1044cm -1 ~1144cm -1 The broad absorption peak also belongs to the COC absorption peak. Comparing the infrared spectra of the product, cellulose and commercial sodium carboxymethyl cellulose, the absorption peak at 1605 cm -1 The absorption peak at the position proves the existence of carbonyl group, which further proves the occurrence of carboxymethylation reaction, namely the formation of sodium carboxymethyl cellulose. Figure 2 The XRD spectrum of the raw material cellulose and the product sodium carboxymethyl cellulose.

[0027] According to the results of X-ray powder diffraction test, it is found that: by comparing the original cellulose and the cellulose after reaction, it can be seen that the diffraction peak characteristics of the original crystal structure gradually weakened, forming a diffuse diffraction characteristic. The polycrystalline particles present an amorphous structure, indicating that the hydrogen bonds between cellulose molecules are opened, most of the crystalline and microcrystalline regions are destroyed, and the corresponding amorphous regions increase. This is because under the action of mechanical forces such as shear, collision, and impact, the hydrogen bonds between cellulose molecules are broken, the cellulose particles are continuously refined, the particle size is continuously reduced, the crystalline structure and microcrystalline region inside the cellulose particles are crushed by mechanical forces, and the long straight-chain starch mixed in the microcrystalline and crystalline regions is released, the disorder of molecular arrangement is enhanced, the activated hydroxyl groups on the molecular chain are increased, and the etherification agent can fully contact the inside of the cellulose particles. The etherification reaction can be carried out in both the inner and outer regions of the particles, and the reaction is very thorough.

[0028] Embodiment 2:

[0029] Take 16.2g of cellulose (wheat straw) and a 10% sodium hydroxide alkaline solution in a beaker, mix and stir for 24h, and after alkalization and stirring, age at 20℃ for 10h. Add the obtained alkali cellulose and the etherifying agent chloroacetic acid in a molar ratio of 1:0.5 into an internal mixer, mix and stir for 1h at 30℃, increase the temperature to 70℃, and react for 1h. After the reaction, crush the obtained crude product, wash it repeatedly with 95% ethanol-water solution several times until the chloride ions are washed clean, filter and dry to obtain the final product, and the degree of substitution of the obtained product is 0.72.

[0030] Embodiment 3:

[0031] Take 16.2g of cellulose (bagasse) and a 30% sodium hydroxide alkaline solution in a beaker, mix and stir for 24h, and after alkalization and stirring, age at 30℃ for 20h. Add the obtained alkali cellulose and etherifying agent chloroacetic acid in a molar ratio of 1:1.5 into an internal mixer, mix and stir at 30℃ for 1h, increase the temperature to 110℃, and react for 3h. After the reaction, crush the obtained crude product, wash it repeatedly with 95% ethanol-water solution several times until the chloride ions are washed clean, filter and dry to obtain the final product, and the obtained product has a degree of substitution of 0.76.

[0032] In summary, the present invention discloses a method for efficiently preparing sodium carboxymethyl cellulose by mechanical force. The method uses abundant and renewable biomass materials as raw materials, utilizes mechanochemistry, and reacts with chloroacetic acid to prepare sodium carboxymethyl cellulose with a high degree of substitution. The prepared product has a high degree of substitution, and the degree of substitution can reach more than 0.8. The reaction efficiency reaches more than 80%, which has the advantages of high reaction efficiency and simple preparation method, and conforms to the concept of green chemistry.

Claims

1. A method for efficiently preparing sodium carboxymethyl cellulose by mechanical force, characterized in that: Here are the steps: Step 1: Add cellulose to sodium hydroxide alkaline solution and stir evenly; Step 2: After aging the obtained alkali cellulose, add it into an internal mixer together with the etherifying agent, and stir and mix them evenly; Step 3: Raise the temperature to the reaction temperature and react in an internal mixer. After the reaction is completed, crush the obtained product, wash it repeatedly with a 95% ethanol-water solution for several times until the chloride ions are washed out, and filter and dry to obtain the final product.

2. The method for efficiently preparing sodium carboxymethyl cellulose by mechanical force according to claim 1, characterized in that: The cellulose is one or a mixture of two or more of cotton linters, wheat straw, reeds and bagasse.

3. The method for efficiently preparing sodium carboxymethyl cellulose by mechanical force according to claim 1 or 2, characterized in that: The mass concentration of the alkalized sodium hydroxide lye is 10%-30%.

4. The method for efficiently preparing sodium carboxymethyl cellulose by mechanical force according to claim 1 or 2, characterized in that: The etherifying agent is chloroacetic acid, and the molar ratio of cellulose to chloroacetic acid is 1:0.5-1:1.

5.

5. The method for efficiently preparing sodium carboxymethyl cellulose by mechanical force according to claim 1 or 2, characterized in that: The aging time of the cellulose is 10h-20h, and the aging temperature is 20℃-30℃.

6. The method for efficiently preparing sodium carboxymethyl cellulose by mechanical force according to claim 1 or 2, characterized in that: The reaction temperature in step 3 is 70°C-110°C.

7. The method for efficiently preparing sodium carboxymethyl cellulose by mechanical force according to claim 1 or 2, characterized in that: The reaction time in step 3 is 1 h-3 h.

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