Method for rapidly preparing carboxymethyl cellulose from corn straw

Abstract

The invention discloses a method for rapidly preparing carboxymethyl cellulose from corn straw, and belongs to the technical field of plant straw comprehensive utilization and green separation engineering. According to the method, the ionic liquid is used as an extraction solvent, and microwave-assisted treatment is combined in a corn straw cellulose component separation stage, so that the corn straw cellulose component can be rapidly extracted and separated; ultrasonic-assisted treatment is combined in the cellulose alkalization and etherification stages, and carboxymethyl cellulose can be efficiently prepared through the alkalization, etherification and other reaction processes of cellulose. Compared with a single technology, the strategy of coupling the three technologies can obtain carboxymethyl cellulose with higher yield and higher substitution degree. Compared with a traditional hydrothermal method or an enzymolysis method which is high in energy consumption and long in time consumption, the method has the advantages that the whole process is easy to operate, the separation speed is high, performance is stable, and the method is environmentally friendly (the ionic liquid can be recycled) and the like, and has important significance on effective separation and comprehensive utilization of corn straw components.

Description

Technical Field

[0001] The invention belongs to the technical field of comprehensive utilization and separation and extraction of plant straws, and particularly relates to a method for quickly preparing carboxymethyl cellulose from corn straws. Background Art

[0002] Cellulose and its derivatives, as multifunctional materials, have great potential application value in the fields of medicine, environmental protection, chemical industry, electronic technology, etc. Crop straw is one of the currently untapped cellulose-rich biomass resources. Among them, corn straw, as one of the important crops, has abundant reserves in my country. Effectively extracting cellulose components from corn straw and then preparing other high-value chemicals, such as carboxymethyl cellulose, is of great significance for realizing the recycling of agricultural waste and creating economic value. However, existing plant straw cellulose extraction technologies and modification methods, such as chemical and physical methods, often have problems such as low extraction efficiency and serious environmental pollution.

[0003] Ionic liquids have good solubility in cellulose, are difficult to volatilize, are non-toxic and pollution-free, have high thermal stability and thermal conductivity, and are green solvents for cellulose extraction. Microwave and ultrasonic methods are fast, energy-saving, and efficient, and have received extensive attention in the extraction process of ingredients such as Chinese herbal medicine, food, and industrial raw materials, as well as in the preparation process of various chemicals. They can effectively reduce the amount of solvent used in the system and reduce environmental pollution, and are a green extraction and preparation technology.

[0004] Carboxymethyl cellulose is an etherified cellulose widely used in the construction, food, pharmaceutical and other industries. Currently, due to the strong hydrogen bonding between cellulose molecules, it is difficult for small molecular compounds to react directly with them, resulting in problems such as uneven substitution and low degree of substitution in the prepared carboxymethyl cellulose, and the preparation process is complicated and time-consuming.

[0005] Therefore, it is of great practical significance to develop an efficient and green technical route to extract cellulose from corn straw and convert it into high-value cellulose. Summary of the invention

[0006] In view of the deficiencies of the prior art, the present invention provides a method for rapidly preparing carboxymethyl cellulose from corn stalks. The present invention uses ionic liquid as a green extraction solvent and combines microwave and ultrasonic processing technology to achieve green, rapid and efficient separation of cellulose from corn stalks and preparation of carboxymethyl cellulose. Coupling the three technologies of ultrasound, microwave and ionic liquid to extract cellulose from corn stalks and rapidly prepare carboxymethyl cellulose has a high application value. Coupling multiple technologies in the extraction, separation and chemical conversion processes simplifies the process flow and achieves the purpose of improving quality and efficiency.

[0007] To achieve the above object, the technical solution adopted by the present invention is:

[0008] The first aspect of the present invention is to provide a method for rapidly preparing carboxymethyl cellulose from corn stalks, wherein the method uses ionic liquid as an extraction solvent, combines microwave-assisted treatment in the corn stalk cellulose component separation stage, and combines ultrasonic-assisted treatment in the cellulose alkalization and etherification stages.

[0009] Furthermore, the preparation method comprises the following steps:

[0010] S1. Wash and dry the corn stalks, and then crush them into powder for later use; wash and dry the corn stalks, and then crush them into powder to increase the specific surface area and improve the extraction efficiency;

[0011] S2. The corn stalk powder obtained in step S1 is extracted by heating in a microwave reactor using an ionic liquid as a solvent; then cooled, an alkali solution is added for reaction, the solid and liquid are separated, the filter residue is washed to neutrality, and dried to constant weight, and the obtained solid is corn stalk cellulose;

[0012] S3. Take the corn straw cellulose obtained in step S2, add 5-15% sodium hydroxide ethanol solution and mix, and perform alkalization reaction under the assistance of ultrasound;

[0013] S4. After the alkalization reaction is completed, 40-60% chloroacetic acid ethanol solution is added to the system, and an etherification reaction is carried out with the assistance of ultrasound;

[0014] S5. After the etherification reaction is completed, the pH of the system is adjusted to 4-6, followed by solid-liquid separation, solid phase washing and drying to obtain carboxymethyl cellulose.

[0015] In some embodiments of the present invention, in step S2, the ionic liquid is an alkyl imidazole salt; preferably, the alkyl imidazole salt is selected from one or a combination of 1-ethyl-3-methyl imidazole acetate, 1-allyl-3-methyl imidazole bromide and 1-butyl-3-methyl imidazole bromide. 1-ethyl-3-methyl imidazole acetate and 1-allyl-3-methyl imidazole bromide are preferred.

[0016] In some embodiments of the present invention, the alkali solution is a 10-30% sodium hydroxide solution.

[0017] In some embodiments of the present invention, in step S2, the mass ratio of the ionic liquid to the corn straw powder is 5:1-20:1.

[0018] In some embodiments of the present invention, in step S2, the microwave power is 300-800 W, and the microwave extraction time is 10-30 minutes.

[0019] In some embodiments of the present invention, in step S3, the volume mass ratio of the alkaline solution to the cellulose is 5:1 to 15:1.

[0020] In some preferred embodiments, in step S3, the volume mass ratio of the alkaline solution to the cellulose is 10:1.

[0021] In some embodiments of the present invention, in step S3, the ultrasonic power is 120-360W, and the ultrasonic alkalization reaction time is 10-30 minutes.

[0022] In some embodiments of the present invention, in step S4, the volume mass ratio of the chloroacetic acid ethanol solution to the cellulose is 1:1-4:1.

[0023] In some preferred embodiments, in step S4, the volume mass ratio of the chloroacetic acid ethanol solution to the cellulose is 2:1.

[0024] In some embodiments of the present invention, in step S5, the ultrasonic power is 120-360 W, and the ultrasonic etherification reaction time is 10-30 minutes.

[0025] In one embodiment, step S2, taking a certain amount of corn stalk powder, using ionic liquid as solvent, heating and extracting in a microwave reactor; then cooling to room temperature, adding 20% ​​sodium hydroxide solution, stirring for 1 hour, and then standing, filtering, washing the filter residue with water until the filtrate is neutral, and then drying to constant weight to obtain corn stalk cellulose;

[0026] In one embodiment, in step S3, 10% sodium hydroxide ethanol solution is used to perform an alkalization reaction under the assistance of ultrasound;

[0027] In one embodiment, in step S4, 50% chloroacetic acid ethanol solution is used to carry out etherification reaction under the assistance of ultrasound;

[0028] In some embodiments, after solid-liquid separation, the obtained solid is washed three times with ethanol and then dried to constant weight to obtain carboxymethyl cellulose.

[0029] The second aspect of the present invention is to provide carboxymethyl cellulose prepared based on the method described above.

[0030] The present invention has the following beneficial effects:

[0031] (1) The present invention effectively couples microwave technology, ultrasonic technology and ionic liquid technology. The whole process has the characteristics of fast reaction speed, simplicity and easy operation. In addition, the ionic liquid solvent used can be recycled, which is green and environmentally friendly. It provides a new method for efficient separation and high-value conversion of plant straw components.

[0032] (2) The carboxymethyl cellulose produced by the present invention is extracted from corn stalks, and is a natural product that is non-toxic and harmless. At the same time, carboxymethyl cellulose with a higher yield and a higher degree of substitution can be obtained.

[0033] The technical solution of the present invention can prepare carboxymethyl cellulose quickly and efficiently. Starting from corn stalks, the carboxymethyl cellulose yield can reach 41% (based on corn stalks) when the cellulose extraction, cellulose alkalization and etherification steps only take 30 minutes, and the degree of substitution can reach 0.84. The degree of substitution meets the relevant requirements of the Chinese national standard GB / T1904-2005 "Sodium Carboxymethyl Cellulose for Industrial Use".

[0034] (3) The coupling strategy of the present invention can use microwaves to form a cavitation effect locally in the reaction system, enhance the wetting and swelling of corn straw components by ionic liquids, increase the effective contact area between ionic liquids and corn straws, promote the rapid entry of ionic liquids into the molecular gaps, and accelerate the dissolution of cellulose. In addition, combined with ultrasonic treatment, weak interactions such as hydrogen bonds within cellulose molecules can be effectively broken, and interchain molecular stacking can be weakened, thereby increasing the porosity and accessibility of cellulose, releasing more hydroxyl active sites, and further promoting the alkalization and etherification reaction processes. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The accompanying drawings are used to provide a further understanding of the present application and constitute a part of the specification. Together with the embodiments of the present application, they are used to explain the present application and do not constitute a limitation of the present application. In the accompanying drawings:

[0036] Figure 1 Example 1 SEM image of cellulose;

[0037] Figure 2 Example 1 Scanning electron microscope (SEM) image of carboxymethyl cellulose. DETAILED DESCRIPTION

[0038] In order to make the above-mentioned purpose, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below in conjunction with the specification examples. Unless otherwise specified, the reagents and raw materials used in the examples can be purchased from the market. The examples in the present invention are only for explaining the present invention, but are not limited to the present invention in any way. Any changes or replacements made based on the present invention belong to the protection scope of the present invention.

[0039] Example 1

[0040] This embodiment is used for a method for quickly preparing carboxymethyl cellulose from corn stalks as follows:

[0041] (1) Add 10 g of crushed corn stalk powder into a reactor, add 200 g of 1-ethyl-3-methylimidazolium acetate, and heat and stir in a microwave reactor at 800 W for 30 min;

[0042] (2) After cooling to room temperature, 100 mL of 20% sodium hydroxide solution was added, stirred for 1 hour, and then allowed to stand. The mixture was filtered, and the residue was washed with water until the filtrate was neutral. The residue was then dried to constant weight to obtain 3.1 g of cellulose solid. The SEM image of the cellulose solid was shown in FIG. Figure 1 ;

[0043] (3) adding 31 mL of 10% sodium hydroxide ethanol solution (the volume mass ratio of the alkaline solution to the cellulose is 10:1) to the above cellulose solid, and ultrasonically treating the cellulose solid for 30 min at a frequency of 40 kHz and a power of 120 W while maintaining the water temperature at 30° C. for alkalinization reaction;

[0044] (4) adding 6.2 mL of 50% chloroacetic acid ethanol solution (the volume mass ratio of chloroacetic acid ethanol solution to cellulose is 2:1) to the alkalized system, and maintaining the water temperature at 30°C for 30 min in an ultrasonic cleaner with a frequency of 40 kHz and a power of 120 W to carry out etherification reaction;

[0045] (5) After the etherification reaction is completed, the system is neutralized with an acid solution to a pH of 4-6, followed by solid-liquid separation. The resulting solid is washed three times with ethanol and dried to a constant weight to obtain carboxymethyl cellulose. The SEM image of the solid is shown in FIG. Figure 2 , the substitution degree is shown in Table 1.

[0046] Example 2

[0047] The implementation method is: the same steps as Example 1, but in step 1, 1-allyl-3-methylimidazolium bromide is used as the ionic liquid solvent. The final yield and degree of substitution of the obtained carboxymethyl cellulose are shown in Table 1.

[0048] Example 3

[0049] The implementation method is: the same steps as Example 1, but in step 1, 1-butyl-3-methylimidazolium bromide is used as the ionic liquid solvent. The final yield and degree of substitution of the obtained carboxymethyl cellulose are shown in Table 1.

[0050] Example 4

[0051] The implementation method is: the same steps as in Example 1, but in steps 3 and 4, an ultrasonic power of 180 W is used for treatment. The final yield and degree of substitution of the obtained carboxymethyl cellulose are shown in Table 1.

[0052] Example 5

[0053] The implementation method is: the same steps as in Example 1, but using 240 W of ultrasonic power for treatment in steps 3 and 4. The final yield and degree of substitution of the obtained carboxymethyl cellulose are shown in Table 1.

[0054] Example 6

[0055] The implementation method is: the same steps as in Example 1, but using 300 W of ultrasonic power for treatment in steps 3 and 4. The final yield and degree of substitution of the obtained carboxymethyl cellulose are shown in Table 1.

[0056] Example 7

[0057] The implementation method is: the same steps as in Example 1, but using 360 W of ultrasonic power for treatment in steps 3 and 4. The final yield and degree of substitution of the obtained carboxymethyl cellulose are shown in Table 1.

[0058] Comparative Example 1: Water as solvent

[0059] The implementation method is: the same steps as Example 1, but deionized water is used as the solvent instead of the ionic liquid. The final yield and degree of substitution of the obtained carboxymethyl cellulose are shown in Table 1.

[0060] Comparative Example 2 without microwave treatment

[0061] The implementation method is: the same steps as Example 1, but the traditional heating at 180° C. is used instead of the microwave treatment. The final yield and degree of substitution of the obtained carboxymethyl cellulose are shown in Table 1.

[0062] Comparative Example 3 without ultrasonic treatment

[0063] The implementation method is: the same steps as in Example 1, but magnetic stirring is used instead of ultrasonic treatment. The final yield and degree of substitution of carboxymethyl cellulose are shown in Table 1.

[0064] Comparative Example 4: No Ultrasonic Treatment in the Etherification Stage

[0065] The implementation method is: the same steps as Example 1, but magnetic stirring is used instead of ultrasonic treatment in the etherification reaction stage. The final yield and degree of substitution of carboxymethyl cellulose are shown in Table 1.

[0066] Example 1: SEM images of cellulose separated from corn stalks and carboxymethyl cellulose obtained by further conversion. Figure 1 and Figure 2 As shown. Figure 1As shown in the figure, the cellulose surface has a large number of wrinkles and a relatively tight structure. In comparison, the surface of carboxymethyl cellulose becomes more fluffy and rough as a whole, and some flaky curls appear. The changes in morphology also explain, to a certain extent, the successful transformation of cellulose to carboxymethyl cellulose under ultrasonic treatment. The cavitation effect under ultrasonic treatment will form a local high temperature and high pressure environment, so that weak interactions such as hydrogen bonds between cellulose molecules are effectively broken, and the stacking of cellulose molecules will become looser, which will lead to deformation and fragmentation of the surface, thereby increasing the porosity of cellulose and improving accessibility, further promoting the alkalization and etherification reaction process.

[0067] Table 1 Comparison of carboxymethyl cellulose yield and degree of substitution of Examples 1-7 and Comparative Examples 1-4

[0068] serial number Solvents Microwave power Ultrasonic power Carboxymethyl cellulose production Degree of substitution DS Example 1 1-Ethyl-3-methylimidazolium acetate 800W 120W 3.4g 0.67 Example 2 1-Allyl-3-methylimidazolium bromide 800W 120W 3.1g 0.64 Example 3 1-Butyl-3-methylimidazolium bromide 800W 120W 1.8g 0.68 Example 4 1-Ethyl-3-methylimidazolium acetate 800W 180W 3.5g 0.71 Example 5 1-Ethyl-3-methylimidazolium acetate 800W 240W 3.7g 0.79 Example 6 1-Ethyl-3-methylimidazolium acetate 800W 300W 4.0g 0.82 Example 7 1-Ethyl-3-methylimidazolium acetate 800W 360W 4.1g 0.84 Comparative Example 1 Deionized water 800W 120W 0.4g 0.54 Comparative Example 2 1-Ethyl-3-methylimidazolium acetate 0W 120W 1.4g 0.46 Comparative Example 3 1-Ethyl-3-methylimidazolium acetate 800W 0W 3.0g 0.28 Comparative Example 4 1-Ethyl-3-methylimidazolium acetate 800W 120W 3.2g 0.49

[0069] As can be known from the data of Table 1, the final carboxymethyl cellulose output obtained by using different ionic liquids can be found that 1-ethyl-3-methylimidazolium acetate and 1-allyl-3-methylimidazolium bromide have the effect that is obviously better than 1-butyl-3-methylimidazolium bromide, and the reason is mainly along with the growth of alkyl chain in alkyl imidazolium salt ionic liquid, the electron supply capacity of alkyl chain increases gradually, which will cause the electron deficiency degree of imidazolium salt cation to weaken gradually, which is unfavorable for the oxygen atom on the imidazolium salt cation attacking cellulose hydroxyl, and the corresponding ionic liquid is made to reduce the dissolving power of cellulose (seeing embodiment 1-3). Although 1-allyl-3-methylimidazolium bromide has a longer alkyl chain than 1-ethyl-3-methylimidazolium acetate, due to the presence of polar double bonds in the allyl group, the electron supply capacity of alkyl chain can be weakened, therefore, when using 1-allyl-3-methylimidazolium bromide as ionic liquid, it shows the effect that is relatively close to 1-ethyl-3-methylimidazolium acetate.

[0070] When deionized water is used instead of ionic liquid as solvent, only a small amount of carboxymethyl cellulose can be obtained under the same conditions (see Comparative Example 1), which proves that ionic liquid can efficiently extract carboxymethyl cellulose from corn stalks. Using deionized water as the extraction solvent, the degree of substitution of the finally obtained carboxymethyl cellulose also decreases slightly. This may be because ionic liquids can better dissolve cellulose, help break the hydrogen bonds in the cellulose molecules, and release more hydroxyl sites for alkalization and etherification processes.

[0071] As can be seen from the data of the embodiments and comparative examples, in the case of not applying microwave or ultrasonic treatment, the degree of substitution of the obtained carboxymethyl cellulose is relatively low. This is due to the presence of a large amount of hydrogen bonds between cellulose molecules and close accumulation, which hinders the hydroxyl and sodium hydroxide reaction in the cellulose molecules during the alkalization reaction, and then hinders the etherification process of subsequent chloroacetic acid and cellulose (see comparative examples 2 and 3). In addition, it can be found by embodiment 1 and comparative example 4 that it is further proved that whether to add ultrasonic treatment during the etherification reaction will also affect the final degree of substitution, which may be due to the local high temperature and molecular rapid vibration produced by ultrasonic treatment can accelerate the substitution reaction of chloroacetic acid and alkalized cellulose, and finally improve reaction efficiency. In comparison, coupling microwave, ultrasonic wave and ionic liquid three technologies, finally can efficiently obtain relatively high yield and high degree of substitution of carboxymethyl cellulose, and its degree of substitution meets the relevant requirements of Chinese national standard GB / T1904-2005 "Sodium Carboxymethyl Cellulose for Industry".

[0072] The present invention uses ionic liquid as an extraction solvent, combines microwave-assisted treatment in the corn straw cellulose component separation stage, can realize rapid extraction and separation of corn straw cellulose components; combines ultrasonic-assisted treatment in the cellulose alkalization and etherification stage, and can efficiently prepare carboxymethyl cellulose through the cellulose alkalization, etherification and other reaction processes. The whole process is simple to operate, fast in separation speed, stable in performance, and green and environmentally friendly, which is of great significance for realizing the effective separation and comprehensive utilization of corn straw components.

[0073] The above are only several embodiments of the present invention and are not intended to limit the present invention in any form. Although the present invention is disclosed as above in the form of a preferred embodiment, it is not intended to limit the present invention. Any technician familiar with the profession, without departing from the scope of the technical solution of the present invention, using the above disclosed technical content to make slight changes or modifications are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A method for rapidly preparing carboxymethyl cellulose from corn stalks, characterized in that: Using ionic liquid as extraction solvent, combining microwave-assisted treatment in the stage of corn straw cellulose component separation, and combining ultrasonic-assisted treatment in the stage of cellulose alkalization and etherification, mainly includes the following steps: S1. Wash and dry the corn stalks, and crush them into powder for later use; S2. The corn stalk powder obtained in step S1 is extracted by heating in a microwave reactor using an ionic liquid as a solvent; then cooled, an alkali solution is added for reaction, the solid and liquid are separated, the filter residue is washed to neutrality, and dried to constant weight, and the obtained solid is corn stalk cellulose; S3. Take the corn straw cellulose obtained in step S2, add 5-15% sodium hydroxide ethanol solution and mix, and perform alkalization reaction under the assistance of ultrasound; S4. After the alkalization reaction is completed, 40-60% chloroacetic acid ethanol solution is added to the system, and an etherification reaction is carried out with the assistance of ultrasound; S5. After the etherification reaction is completed, the pH of the system is adjusted to 4-6, followed by solid-liquid separation, solid phase washing and drying to obtain carboxymethyl cellulose.

2. The method for rapidly preparing carboxymethyl cellulose from corn stalks according to claim 1, characterized in that: In step S2, the ionic liquid is an alkyl imidazole salt; And / or, the alkali solution is 10-30% sodium hydroxide solution.

3. The method for rapidly preparing carboxymethyl cellulose from corn stalks according to claim 2, characterized in that: The alkyl imidazole salt is selected from one or a combination of 1-ethyl-3-methylimidazolium acetate, 1-allyl-3-methylimidazolium bromide and 1-butyl-3-methylimidazolium bromide.

4. The method for rapidly preparing carboxymethyl cellulose from corn stalks according to claim 1, characterized in that: In step S2, the mass ratio of the ionic liquid to the corn straw powder is 5:1-20:

1.

5. The method for rapidly preparing carboxymethyl cellulose from corn stalks according to claim 1, characterized in that: The microwave power is 300-800W, and the microwave extraction time is 10-30 minutes.

6. The method for rapidly preparing carboxymethyl cellulose from corn stalks according to claim 1, characterized in that: In step S3, the volume mass ratio of the alkaline solution to the cellulose is 5:1 to 15:

1.

7. The method for rapidly preparing carboxymethyl cellulose from corn stalks according to claim 1, characterized in that: In step S3, the ultrasonic power is 120-360W, and the ultrasonic alkalization reaction time is 10-30 minutes.

8. The method for rapidly preparing carboxymethyl cellulose from corn stalks according to claim 1, characterized in that: In step S4, the volume mass ratio of the chloroacetic acid ethanol solution to the cellulose is 1:1 to 4:

1.

9. The method for rapidly preparing carboxymethyl cellulose from corn stalks according to claim 1, characterized in that: In step S5, the ultrasonic power is 120-360W, and the ultrasonic etherification reaction time is 10-30 minutes.

10. Carboxymethyl cellulose prepared by the method according to any one of claims 1 to 9.

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