A method for rapidly preparing carboxymethyl cellulose from corn stalks

Abstract

The application discloses a method for rapidly preparing carboxymethyl cellulose from corn stalks, and belongs to the technical field of comprehensive utilization of plant stalks and green separation engineering. In the method, ionic liquid is used as an extraction solvent, and microwave-assisted treatment is combined in the stage of separating the cellulose components of corn stalks, so that the cellulose components of corn stalks can be rapidly extracted and separated. In the stage of alkali treatment and etherification of the cellulose, ultrasonic-assisted treatment is combined, and carboxymethyl cellulose can be efficiently prepared through the reaction processes such as alkali treatment and etherification of the cellulose. The strategy of coupling three kinds of technologies can obtain carboxymethyl cellulose with a higher yield and a higher degree of substitution than that obtained by using a single technology. Compared with the traditional hydrothermal method or enzymatic method with high energy consumption and long time consumption, the whole process is simple in operation, fast in separation speed, stable in performance, green in environment protection (the ionic liquid can be recycled), and the like, and therefore, the method has important significance for realizing effective separation and comprehensive utilization of corn stalk components.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of plant straw comprehensive utilization and separation and extraction, and particularly relates to a method for rapidly preparing carboxymethyl cellulose from corn straw. BACKGROUND

[0002] Cellulose and its derivative products have great potential application value in the fields of medicine, environmental protection, chemical industry, electronic technology, etc. as multifunctional materials. Crop straw is one of the currently underdeveloped biomass resources rich in cellulose. Among them, corn straw, as one of the important crops, is abundant in China. Realizing effective extraction of cellulose components from corn straw and further preparing other high-value chemicals, such as carboxymethyl cellulose, has important significance for realizing the renewable utilization of agricultural waste and creating economic value. However, the existing plant straw cellulose extraction technology and modification method, such as chemical method and physical method, often has problems such as low extraction efficiency and serious environmental pollution.

[0003] Ionic liquids have good solubility for cellulose, are difficult to volatilize, non-toxic and non-polluting, have high thermal stability and thermal conductivity, and are green solvents for cellulose extraction. Microwave method and ultrasonic method are widely concerned in the extraction process of Chinese herbal medicine, food, industrial raw materials and the preparation process of various chemicals due to their characteristics of rapidness, energy saving and high efficiency, which can effectively reduce the solvent consumption and environmental pollution, and is a green extraction and preparation technology.

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

[0005] Therefore, it has important practical significance to develop an efficient and green technical route to realize the extraction of cellulose from corn straw and high-value conversion. SUMMARY

[0006] The present application provides a method for rapidly preparing carboxymethyl cellulose from corn straw, aiming at the deficiencies of the prior art. The present application uses ionic liquid as a green extraction solvent, and combines microwave and ultrasonic treatment technology, aiming to realize green, rapid and efficient separation of cellulose from corn straw and preparation of carboxymethyl cellulose. Coupling ultrasonic, microwave and ionic liquid technologies for extraction of cellulose from corn straw and rapid preparation of carboxymethyl cellulose has high application value. Coupling multiple technologies in the extraction and separation and chemical conversion process can simplify the process flow and achieve the purpose of improving quality and efficiency.

[0007] To achieve the above object, the technical scheme adopted by the present application is:

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

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

[0010] S1. After washing and drying the corn stalks, the corn stalks are crushed into powder for use; the washed corn stalks are dried and then crushed into powder to increase the specific surface area and improve the extraction efficiency;

[0011] S2. The corn stalk powder prepared in step S1 is taken, ionic liquid is used as the solvent, and heating extraction is performed in a microwave reactor; then, after adding alkali solution and reacting, solid-liquid separation is performed, the filter residue is washed until neutral, and drying is performed until the weight is constant; the obtained solid is corn stalk cellulose;

[0012] S3. The corn stalk cellulose prepared in step S2 is taken, 5-15% sodium hydroxide ethanol solution is added, and alkali treatment is performed under ultrasonic assistance;

[0013] S4. After the alkali treatment is completed, 40-60% chloroacetic acid ethanol solution is added to the system, and etherification is performed under ultrasonic assistance;

[0014] S5. After the etherification is completed, the system is adjusted to a pH of 4-6, and then solid-liquid separation is performed; after washing and drying the solid phase, carboxymethyl cellulose can be obtained.

[0015] In some embodiments of the present application, 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. Preferably, 1-ethyl-3-methyl imidazole acetate and 1-allyl-3-methyl imidazole bromide are used.

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

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

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

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

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

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

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

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

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

[0025] In one embodiment, in step S2, a certain amount of corn straw powder is heated for extraction in a microwave reactor using an ionic liquid as a solvent; then cooled to room temperature, 20% sodium hydroxide solution is added and stirred for 1 hour, then left to stand, filtered, washed with water until the filtrate is neutral, and then dried to constant weight to obtain corn straw cellulose;

[0026] In one embodiment, in step S3, 10% sodium hydroxide ethanol solution is used to perform an alkalinization reaction under the assistance of ultrasonic waves.

[0027] In one embodiment, in step S4, 50% chloroacetic acid ethanol solution is used to perform an etherification reaction under the assistance of ultrasonic waves.

[0028] In some embodiments, after solid-liquid separation, the obtained solid is washed with ethanol for 3 times, and then dried to constant weight to obtain carboxymethyl cellulose.

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

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

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

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

[0033] The technical scheme of the present application can quickly and efficiently prepare carboxymethyl cellulose. Starting from corn stalks, the yield of carboxymethyl cellulose can reach 41% (based on corn stalks) and the degree of substitution can reach 0.84 in the case of only 30 minutes required for cellulose extraction, cellulose alkalization, and etherification. The degree of substitution meets the relevant requirements of the Chinese national standard GB / T 1904-2005 "Sodium Carboxymethyl Cellulose for Industrial Use".

[0034] (3) The coupling strategy described in the present application can utilize microwave to form a cavitation effect locally in the reaction system, enhance the infiltration and swelling of ionic liquid on the components of corn stalks, increase the effective contact area of ionic liquid and corn stalks, promote the rapid entry of ionic liquid into the intermolecular space, and accelerate the dissolution of cellulose. In addition, combined with ultrasonic treatment, the weak interactions such as hydrogen bonds in cellulose molecules can be effectively broken, the interchain molecular accumulation is weakened, the porosity of cellulose is increased, the accessibility is improved, more active hydroxyl sites are released, and the alkalization and etherification reaction processes are further promoted. BRIEF DESCRIPTION OF DRAWINGS

[0035] The accompanying drawings are included to provide a further understanding of the present application, and constitute a part of the specification, which together with the embodiments of the present application, serve to explain the present application, and do not constitute a limitation on the present application, in which:

[0036] Figure 1 Example 1: Scanning electron microscope (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 purposes, features and advantages of the present application more obvious and easy to understand, the specific embodiments of the present application will be described in detail below. Unless otherwise stated, the reagents and raw materials used in the examples can be purchased from the market. The examples in the present application are only for explaining the present application, but do not limit the present application in any way, and any transformation or replacement based on the present application also belongs to the protection scope of the present application.

[0039] Example 1

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

[0041] (1) 10 g of pulverized corn straw powder was added to a reactor, 200 g of 1-ethyl-3-methylimidazole acetate was added, and stirring treatment was performed 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, stirring was performed for 1 h, and then standing was performed. Filtration was performed, the filter residue was washed with water until the filtrate was neutral, and then drying was performed until the constant weight was obtained. Cellulose solid 3.1 g was obtained, and the scanning electron microscope (SEM) image thereof is shown in Figure 1 ;

[0043] (3) 31 mL of 10% sodium hydroxide ethanol solution (the volume-mass ratio of the alkali solution to cellulose was 10:1) was added to the above cellulose solid, and alkali treatment was performed in an ultrasonic cleaner at a frequency of 40 KHz and a power of 120 W for 30 min while maintaining the water temperature at 30°C.

[0044] (4) 6.2 mL of 50% chloroacetic acid ethanol solution (the volume-mass ratio of the chloroacetic acid ethanol solution to cellulose was 2:1) was added to the system after the completion of the alkali treatment, and etherification was performed in the ultrasonic cleaner at a frequency of 40 KHz and a power of 120 W for 30 min while maintaining the water temperature at 30°C.

[0045] (5) After the completion of the etherification reaction, the system was neutralized to pH 4-6 with an acid solution, and then solid-liquid separation was performed. The obtained solid was washed with ethanol for 3 times, and then drying was performed until the constant weight was obtained. Carboxymethyl cellulose was obtained, and the scanning electron microscope (SEM) image thereof is shown in Figure 2 , and the degree of substitution is shown in Table 1.

[0046] Example 2

[0047] The implementation method was the same as that in Example 1, but 1-allyl-3-methylimidazole bromide was used as the ionic liquid solvent in step 1. The yield and the degree of substitution of the finally obtained carboxymethyl cellulose are shown in Table 1.

[0048] Example 3

[0049] The implementation method was the same as that in Example 1, but 1-butyl-3-methylimidazole bromide was used as the ionic liquid solvent in step 1. The yield and the degree of substitution of the finally obtained carboxymethyl cellulose are shown in Table 1.

[0050] Example 4

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

[0052] Example 5

[0053] The method was carried out in the same way as Example 1, but in steps 3 and 4 the treatment was carried out using an ultrasonic power of 240 W. The final carboxymethyl cellulose yield and degree of substitution are shown in Table 1.

[0054] Example 6

[0055] The method was carried out in the same way as Example 1, but in steps 3 and 4 the treatment was carried out using an ultrasonic power of 300 W. The final carboxymethyl cellulose yield and degree of substitution are shown in Table 1.

[0056] Example 7

[0057] The method was carried out in the same way as Example 1, but in steps 3 and 4 the treatment was carried out using an ultrasonic power of 360 W. The final carboxymethyl cellulose yield and degree of substitution are shown in Table 1.

[0058] Comparative Example 1 with water as solvent

[0059] The method was carried out in the same way as Example 1, but instead of the ionic liquid, deionized water was used as solvent. The final carboxymethyl cellulose yield and degree of substitution are shown in Table 1.

[0060] Comparative Example 2 without microwave treatment

[0061] The method was carried out in the same way as Example 1, but instead of the microwave treatment, conventional heating at 180°C was used. The final carboxymethyl cellulose yield and degree of substitution are shown in Table 1.

[0062] Comparative Example 3 without ultrasonic treatment

[0063] The method was carried out in the same way as Example 1, but instead of the ultrasonic treatment, magnetic stirring was used. The final carboxymethyl cellulose yield and degree of substitution are shown in Table 1.

[0064] Comparative Example 4 without ultrasonic treatment in the etherification stage

[0065] The method was carried out in the same way as Example 1, but in the etherification stage, instead of the ultrasonic treatment, magnetic stirring was used. The final carboxymethyl cellulose yield and degree of substitution are shown in Table 1.

[0066] The scanning electron microscope (SEM) images of the cellulose isolated from corn stalks and the carboxymethyl cellulose obtained by further conversion in Example 1 are shown in Figures Figure 1 and Figure 2 As can be seen in the SEM images Figure 1As shown, the cellulose surface has a large number of wrinkles, and the structure is relatively tight. In contrast, the carboxymethyl cellulose surface becomes more fluffy and rough as a whole, and some sheet-like curls appear. The change in morphology also to some extent explains the successful conversion of cellulose to carboxymethyl cellulose under ultrasonic treatment. The cavitation under ultrasonic treatment can form a local high-temperature and high-pressure environment, so that the weak interactions such as hydrogen bonds between cellulose molecules are effectively broken, and the accumulation between cellulose molecules becomes more loose, which will lead to the deformation and fragmentation of the surface, thereby increasing the porosity of cellulose and improving the accessibility, further promoting the progress of the alkalization and etherification reaction process.

[0067] Table 1 Carboxymethyl cellulose yield and degree of substitution data of examples 1-7 and comparative examples 1-4

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

[0069] From the data in Table 1, it can be found that the yield of carboxymethyl cellulose obtained by using different ionic liquids can be found that 1-ethyl-3-methyl imidazole acetate and 1-allyl-3-methyl imidazole bromide have obvious effect better than 1-butyl-3-methyl imidazole bromide, the reason is mainly that with the increase of alkyl chain in alkyl imidazole salt ionic liquid, the electron-donating ability of alkyl chain gradually increases, which will lead to the gradual weakening of the electron-deficient degree of imidazole salt cation, which is not conducive to the attack of imidazole salt cation on the oxygen atom of cellulose hydroxyl, so that the solubility of the corresponding ionic liquid to cellulose decreases (see examples 1-3). Although 1-allyl-3-methyl imidazole bromide has a longer alkyl chain than 1-ethyl-3-methyl imidazole acetate, but because of the existence of polar double bond in allyl, the electron-donating ability of alkyl chain can be weakened, therefore, when using 1-allyl-3-methyl imidazole bromide as ionic liquid, it shows a relatively close effect with 1-ethyl-3-methyl imidazole acetate.

[0070] When using deionized water instead of ionic liquid as a 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 straw. When using deionized water as an extraction solvent, the degree of substitution of the final carboxymethyl cellulose also decreases slightly. This may be because ionic liquids can better dissolve cellulose, help to break the hydrogen bonds within the cellulose molecules, and release more hydroxyl sites for the alkalization and etherification process.

[0071] From the data of the examples and comparative examples, it can be seen that without the application of microwave or ultrasonic treatment, the prepared carboxymethyl cellulose has a low degree of substitution. This is because the cellulose molecules are tightly packed due to the presence of a large number of hydrogen bonds, which hinders the reaction of the hydroxyl groups in the cellulose molecules with sodium hydroxide during the alkalization reaction, and further hinders the etherification process of chloroacetic acid with cellulose (see Comparative Examples 2 and 3). In addition, as can be seen from Example 1 and Comparative Example 4, it is further proved that whether ultrasonic treatment is added during the etherification reaction also affects the final degree of substitution, which may be due to the fact that the local high temperature and rapid molecular vibration generated by ultrasonic treatment can accelerate the substitution reaction of chloroacetic acid with alkalized cellulose, thereby improving the reaction efficiency. Compared with the coupling of microwave, ultrasonic and ionic liquid technologies, relatively high yield and high degree of substitution of carboxymethyl cellulose can be obtained with high efficiency, and the degree of substitution meets the requirements of the relevant requirements of Chinese national standard GB / T 1904-2005 "Sodium Carboxymethyl Cellulose for Industrial Use".

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

[0073] The above is only a few embodiments of the present application, and does not limit the present application in any form. Although the present application is disclosed as above with preferred embodiments, it is not intended to limit the present application. Any skilled person in the art can make some changes or modifications to the above disclosed technical content without departing from the scope of the technical solution of the present application, which are equivalent to equivalent embodiments and belong to 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 the extraction solvent, microwave-assisted treatment is combined in the separation stage of corn straw cellulose components, and ultrasonic-assisted treatment is combined in the cellulose alkalization and etherification stages. The main steps include: S1. Wash and dry the corn stalks, then crush them into powder for later use; S2. The corn straw powder obtained in step S1 is extracted by heating in a microwave reactor using an ionic liquid as a solvent; the mixture is cooled, an alkali solution is added to react, the solid-liquid separation is performed, the residue is washed to neutrality, and dried to a constant weight. The resulting solid is corn straw cellulose; S3. The corn straw cellulose obtained in step S2 was mixed with 5-15% sodium hydroxide ethanol solution and subjected to alkalization reaction with the assistance of ultrasound; S4. After the alkalization reaction is completed, a 40-60% chloroacetic acid ethanol solution is added to the system, and an ultrasonic-assisted etherification reaction is performed; S5. After the etherification reaction is completed, the pH of the system is adjusted to 4-6, followed by solid-liquid separation, washing the solid phase and drying to obtain carboxymethyl cellulose; In step S2, the ionic liquid is an alkyl imidazolium salt; the alkyl imidazolium 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.

2. The method for rapidly preparing carboxymethyl cellulose from corn stalks according to claim 1, wherein: The alkali solution is 10-30% sodium hydroxide solution.

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

1.

4. The method for rapidly preparing carboxymethyl cellulose from corn straw according to claim 1, wherein: The microwave power was 300-800 W, and the microwave extraction time was 10-30 min.

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

1.

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

7. The method for rapidly preparing carboxymethyl cellulose from corn straw according to claim 1, wherein: In step S4, the volume mass ratio of the chloroacetic acid ethanol solution to the cellulose is 1:1 to 4:

1.

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

9. Carboxymethyl cellulose prepared by the method according to any one of claims 1 to 8.

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