Method for preparing chitosan based on choline chloride-fructose system and application thereof

Abstract

The invention discloses a method for preparing chitosan based on a choline chloride-fructose system, and the method comprises the following steps: mixing choline chloride and fructose according to a certain molar ratio to prepare the choline chloride-fructose system, then carrying out acetyl removal treatment on chitin in the choline chloride-fructose system, and further preparing the chitosan. When the chitosan is prepared by the method, the deacetylation reaction can be carried out only by combining NaOH with the final mass concentration of 30-35%, the deacetylation degree of the prepared chitosan is greater than 80%, and the molecular weight is not obviously different from that of the chitosan prepared by the traditional method.

Description

Technical Field

[0001] The present invention relates to the technical field of biomass conversion. Specifically, it relates to a method for preparing chitosan based on a choline chloride-fructose system and its application. Background Art

[0002] Currently, the utilization of biomass mainly focuses on lignocellulosic materials such as cellulose and lignin. The research on cellulose and xylose biomass is relatively extensive, while the research on the conversion of chitin biomass lags behind.

[0003] Chitin is formed by the condensation of β-(1,4)-2-acetamido-2-deoxy-D-glucose through β-1,4 glycosidic bonds. It is a natural polymer compound widely present in crustaceans such as shrimps and crabs, as well as in lower organisms such as fungi and algae cells. It is the second largest biological resource in nature after cellulose in terms of production. And chitin itself contains nitrogen and may be the only abundant renewable resource of nitrogen-containing chemical substances and materials. However, the vast majority of chitin biomass is dumped in landfills or the ocean.

[0004] Chitosan is the most important derivative of chitin, which is the product obtained by removing the acetyl group from chitin after treatment with concentrated alkali. When the deacetylation degree of chitin is higher than 55%, it can be called chitosan. The higher the deacetylation degree of chitosan, the more amino groups and the fewer acetyl groups in the chitosan molecule. This characteristic has an important impact on the chemical properties, biological activities, and application performances of chitosan. Chitosan with a high deacetylation degree has stronger solubility, higher reaction activity, stronger antibacterial property, and better compatibility with human tissues than chitosan with a low deacetylation degree. It is more suitable for hemostasis and wound healing in the medical field, and has a more significant antibacterial effect when used as a preservative. And the higher the molecular weight of chitosan, the stronger the mechanical properties, higher viscosity, and slower degradation rate, with stronger stability, but the solubility and permeability may decrease.

[0005] Compared with chitin, chitosan has a large number of amino groups in its molecular structure, which are easy to carry out various chemical reactions, thus greatly improving the reaction activity. However, due to the highly dense structure of chitin, it is not only insoluble in water but also difficult to undergo chemical reactions. When producing chitosan from chitin, a deacetylation reaction needs to be carried out with high-concentration NaOH (usually combined with NaOH with a mass concentration ≥50%) at high temperature, which not only causes environmental pollution but also reduces the molecular weight of chitosan.

[0006] Therefore, there is a need for a new method for preparing chitosan at present, which can obtain chitosan from chitin while combining a lower concentration of NaOH. Summary of the Invention

[0007] The object of the present invention is to overcome the above deficiencies of the prior art and provide a method for preparing chitosan based on a choline chloride - fructose system and its application.

[0008] The first object of the present invention is to provide a method for preparing chitosan based on a choline chloride - fructose system.

[0009] The second object of the present invention is to provide the chitosan prepared by the above method.

[0010] The third object of the present invention is to provide the application of the above method in the treatment of chitin.

[0011] In order to achieve the above object, the present invention is realized through the following solutions:

[0012] A method for preparing chitosan based on a choline chloride - fructose system, comprising the following steps:

[0013] S1. Mix choline chloride and fructose in a molar ratio of 1 - 2:1 - 2, and obtain a choline chloride - fructose system after sufficient reaction;

[0014] S2. Add chitin accounting for 0.5% - 1% of the mass of the choline chloride - fructose system to the choline chloride - fructose system obtained in step S1 and dissolve it fully to obtain a mixed system;

[0015] S3. Add NaOH with a final mass concentration of 30% - 35% to the mixed system obtained in step S2, then place it in an environment of 95 - 100 °C for sufficient reaction, and collect the reaction solution;

[0016] S4. After mixing the reaction solution obtained in step S3 with water, perform solid - liquid separation to collect the precipitate and dry it to obtain chitosan.

[0017] Preferably, in step S1, choline chloride and fructose are mixed in a molar ratio of 1:1.

[0018] Preferably, the sufficient reaction in step S1 is: reacting at 70 - 80 °C for 1 - 3 h.

[0019] More preferably, react at 80 °C for 1 h.

[0020] Preferably, in step S2, add chitin accounting for 0.78% of the mass of the choline chloride - fructose system.

[0021] Preferably, the sufficient dissolution in step S2 is: reacting at 80 °C for 10 h.

[0022] Preferably, in step S3, add NaOH with a final mass concentration of 30% to the mixed system obtained in step S2.

[0023] Preferably, in step S3, it is fully reacted in an environment of 95 °C.

[0024] More preferably, the full reaction is carried out for 14 - 20 h.

[0025] Even more preferably, the full reaction is carried out for 20 h.

[0026] Preferably, step S4 is specifically as follows: The reaction solution obtained in step S3 is mixed with deionized water with a volume three times that of the reaction solution, and solid-liquid separation is carried out to obtain a supernatant and a precipitate. The precipitate is dried to obtain chitosan.

[0027] More preferably, the supernatant is mixed with deionized water with a volume three times that of the supernatant and solid-liquid separation is carried out until the liquid after solid-liquid separation is neutral. The precipitates obtained by solid-liquid separation are combined and dried to obtain chitosan.

[0028] In the present invention, a choline chloride-fructose system is prepared by mixing choline chloride and fructose according to a certain molar ratio, and chitosan is prepared by deacetylating chitin in the choline chloride-fructose system. When preparing chitosan by this method, only NaOH with a final mass concentration of 30% - 35% needs to be combined to carry out the deacetylation reaction, and the degree of deacetylation of the prepared chitosan is greater than 80%, and the molecular weight is not significantly different from that of the traditional method.

[0029] Therefore, the present invention also claims chitosan prepared by any of the above-mentioned methods.

[0030] The present invention also claims the application of any of the above-mentioned methods in treating chitin.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] The present invention provides a method for preparing chitosan based on a choline chloride-fructose system. The method prepares a choline chloride-fructose system by mixing choline chloride and fructose according to a certain molar ratio, and then deacetylates chitin in the choline chloride-fructose system to prepare chitosan. When preparing chitosan by this method, only NaOH with a final mass concentration of 30% - 35% needs to be combined to carry out the deacetylation reaction, and the degree of deacetylation of the prepared chitosan is greater than 80%, and the molecular weight is not significantly different from that of the traditional method. Specific Embodiments

[0033] The following further elaborates on the present invention in detail with reference to specific embodiments. The embodiments are only used to explain the present invention and are not used to limit the scope of the present invention. The test methods used in the following embodiments are all conventional methods unless otherwise specified; the materials, reagents, etc. used are reagents and materials that can be obtained from commercial channels unless otherwise specified.

[0034] The chitin used in the embodiments of the present invention was all purchased from Hefei Bomei Biotechnology Co., Ltd., China, with a CAS number of 1398-61-4.

[0035] Example 1

[0036] A method for preparing chitosan based on a choline chloride - fructose system, comprising the following steps:

[0037] S1. Mix choline chloride and fructose in a molar ratio of 1:1, place them at 80 °C for reaction for 1 h to obtain a choline chloride - fructose system (a homogeneous and transparent solution);

[0038] S2. Add chitin accounting for 0.78% of the mass of the choline chloride - fructose system obtained in step S1 to the choline chloride - fructose system, place it at 80 °C and stir for 10 h until completely dissolved to obtain a mixed system;

[0039] S3. Add a NaOH solution (with a mass concentration of 70%) equal in mass to the choline chloride - fructose system obtained in step S1 to the mixed system obtained in step S2, so that the final concentration of NaOH is 35%, then place it at 95 °C for reaction for 14 h, and collect the reaction solution;

[0040] S4. Add 3 times the volume of deionized water to the reaction solution obtained in step S3, centrifuge to obtain a supernatant and a precipitate. Mix the supernatant with 3 times the volume of deionized water again and centrifuge until the centrifuged liquid is neutral. Combine the precipitates and dry them at 105 °C to obtain chitosan 1.

[0041] Example 2

[0042] The difference between Example 2 and Example 1 is that in step S3, a NaOH solution (with a mass concentration of 60%) equal in mass to the choline chloride - fructose system obtained in step S1 is added, so that the final concentration of NaOH is 30%, then place it at 95 °C for reaction for 20 h, and the remaining treatments are exactly the same to obtain chitosan 2.

[0043] Example 3

[0044] The difference between Example 3 and Example 1 is that in step S3, a NaOH solution (with a mass concentration of 60%) equal in mass to the choline chloride - fructose system obtained in step S1 is added, so that the final concentration of NaOH is 30%, then place it at 95 °C for reaction for 16 h, and the remaining treatments are exactly the same to obtain chitosan 3.

[0045] Example 4

[0046] Example 4 is different from Example 1 in that: in step S3, a NaOH solution (mass concentration of 60%) with the same mass as the choline chloride - fructose system obtained in step S1 is added to make the final concentration of NaOH 30%, and the rest of the treatment is exactly the same, obtaining chitosan 4.

[0047] Example 5

[0048] Example 5 is different from Example 1 in that: in step S3, a NaOH solution (mass concentration of 60%) with the same mass as the choline chloride - fructose system obtained in step S1 is added to make the final concentration of NaOH 30%, and then it is placed in a reaction at 100 °C for 14 h, and the rest of the treatment is exactly the same, obtaining chitosan 5.

[0049] Comparative Example 1

[0050] Comparative Example 1 is different from Example 1 in that: in step S3, a NaOH solution (mass concentration of 30%) with the same mass as the choline chloride - fructose system obtained in step S1 is added to make the final concentration of NaOH 15%, and then it is placed in a reaction at 95 °C for 14 h, and the rest of the treatment is exactly the same, obtaining chitosan 6.

[0051] Comparative Example 2

[0052] Comparative Example 2 is different from Example 1 in that: in step S3, a NaOH solution (mass concentration of 40%) with the same mass as the choline chloride - fructose system obtained in step S1 is added to make the final concentration of NaOH 20%, and then it is placed in a reaction at 95 °C for 14 h, and the rest of the treatment is exactly the same, obtaining chitosan 7.

[0053] Comparative Example 3

[0054] Comparative Example 3 is different from Example 1 in that: in step S3, a NaOH solution (mass concentration of 50%) with the same mass as the choline chloride - fructose system obtained in step S1 is added to make the final concentration of NaOH 25%, and then it is placed in a reaction at 95 °C for 14 h, and the rest of the treatment is exactly the same, obtaining chitosan 8.

[0055] Comparative Example 4

[0056] Comparative Example 4 is different from Example 1 in that: in step S3, a NaOH solution (mass concentration of 60%) with the same mass as the choline chloride - fructose system obtained in step S1 is added to make the final concentration of NaOH 30%, and then it is placed in a reaction at 75 °C for 14 h, and the rest of the treatment is exactly the same, obtaining chitosan 9.

[0057] Comparative Example 5

[0058] The difference between Comparative Example 5 and Example 1 is as follows: In step S3, a NaOH solution (mass concentration: 60%) with the same mass as the choline chloride - fructose system obtained in step S1 was added to make the final concentration of NaOH 30%, and then it was placed in a reaction at 80°C for 14 h. The remaining treatments were exactly the same, and chitosan 10 was obtained.

[0059] Comparative Example 6

[0060] The difference between Comparative Example 6 and Example 1 is as follows: In step S3, a NaOH solution (mass concentration: 60%) with the same mass as the choline chloride - fructose system obtained in step S1 was added to make the final concentration of NaOH 30%, and then it was placed in a reaction at 85°C for 14 h. The remaining treatments were exactly the same, and chitosan 11 was obtained.

[0061] Comparative Example 7

[0062] The difference between Comparative Example 7 and Example 1 is as follows: In step S3, a NaOH solution (mass concentration: 60%) with the same mass as the choline chloride - fructose system obtained in step S1 was added to make the final concentration of NaOH 30%, and then it was placed in a reaction at 90°C for 14 h. The remaining treatments were exactly the same, and chitosan 12 was obtained.

[0063] Comparative Example 8

[0064] The difference between Comparative Example 8 and Example 1 is as follows: In step S3, a NaOH solution (mass concentration: 60%) with the same mass as the choline chloride - fructose system obtained in step S1 was added to make the final concentration of NaOH 30%, and then it was placed in a reaction at 95°C for 4 h. The remaining treatments were exactly the same, and chitosan 13 was obtained.

[0065] Comparative Example 9

[0066] The difference between Comparative Example 9 and Example 1 is as follows: In step S3, a NaOH solution (mass concentration: 60%) with the same mass as the choline chloride - fructose system obtained in step S1 was added to make the final concentration of NaOH 30%, and then it was placed in a reaction at 95°C for 8 h. The remaining treatments were exactly the same, and chitosan 14 was obtained.

[0067] Comparative Example 10

[0068] The difference between Comparative Example 10 and Example 1 is as follows: In step S3, a NaOH solution (mass concentration: 60%) with the same mass as the choline chloride - fructose system obtained in step S1 was added to make the final concentration of NaOH 30%, and then it was placed in a reaction at 95°C for 12 h. The remaining treatments were exactly the same, and chitosan 15 was obtained.

[0069] Comparative Example 11

[0070] A method for preparing chitosan, specifically: adding 0.78 g of chitin into 100 g of an aqueous NaOH solution (mass concentration of 50%), reacting at 100 °C for 22 h, separating the solid and liquid to collect the precipitate and drying it, thus obtaining 16 of chitosan.

[0071] Test Example 1

[0072] I. Experimental method

[0073] 1. Determination of the degree of deacetylation of chitosan

[0074] The degree of deacetylation of chitosan was determined by potentiometric titration, specifically as follows: Weigh 0.2 g of chitosan 1 prepared in Example 1, add it into 20 mL of HCl standard solution (0.1 mol / L), and after magnetic stirring for 2 h, obtain a sample solution; put the pH electrode into the sample solution, gradually titrate with 0.1 mo / L of NaOH standard solution, measure the pH value during the titration process and the consumed volume of the NaOH standard solution, draw the first derivative curve, and determine 2 inflection points in the first derivative curve. Then calculate the volume difference (△v / mL) of the NaOH standard solution consumed between the 2 inflection points, and calculate the degree of deacetylation T of chitosan 1 according to Formula I;

[0075] Formula I: T = Δ V × c NaOH × 10 -3 × 16 * 100%;

[0076] m × 0.0994

[0077] T is the degree of deacetylation; △v is the volume difference of the NaOH standard solution consumed between the inflection points, mL; c NaOH is the concentration of the NaOH standard solution, mol / L; m is the mass of chitosan 1, g.

[0078] Replace chitosan 1 with chitosan 2 to chitosan 16 in turn, and calculate the degrees of deacetylation of chitosan 2 to chitosan 16 according to the above method respectively.

[0079] 2. Determination of the molecular weight of chitosan

[0080] Add 10 mg of chitosan 1 prepared in Example 1 into 50 mL of a lithium chloride / dimethylacetamide (5%, w / w, where lithium chloride and dimethylacetamide are mixed according to a mass ratio of 1:19) solution, place it at 80 °C and continuously stir until chitosan 1 is completely dissolved to obtain a mixed solution. Then measure the viscosity η of the mixed solution at 30 °C using an Ubbelohde viscometer, and calculate the molecular weight of chitosan 1 according to Formula II.

[0081] Formula II: η = K * M w a ;

[0082] η is the viscosity, which is obtained by measurement with an Ubbelohde viscometer; K = 7.6×10 -6 L / g; M w is the molecular weight of chitosan; a = 0.95.

[0083] Chitosan 1 was successively replaced with chitosan 2 to chitosan 16, and the molecular weights of chitosan 2 to chitosan 16 were calculated respectively according to the above method.

[0084] II. Experimental Results

[0085] The test results of the degree of deacetylation and molecular weight of chitosan 1 to chitosan 16 are shown in Table 1.

[0086] Table 1 Test Results of the Degree of Deacetylation and Molecular Weight

[0087] Sample Chitosan 1 Chitosan 2 Chitosan 3 Chitosan 4 Chitosan 5 Chitosan 6 Chitosan 7 Chitosan 8 Degree of deacetylation 86.64％ 90.49％ 84.21％ 83.94％ 86.60％ 23.63％ 32.10％ 55.70％ Molecular weight <![CDATA[7.30×10 5 > <![CDATA[7.27×10 5 > <![CDATA[7.38×10 5 > <![CDATA[7.38×10 5 > <![CDATA[7.35×10 5 > <![CDATA[7.61×10 5 > <![CDATA[7.51×10 5 > <![CDATA[7.43×10 5 > Sample Chitosan 9 Chitosan 10 Chitosan 11 Chitosan 12 Chitosan 13 Chitosan 14 Chitosan 15 Chitosan 16 Degree of deacetylation 39.99％ 55.91％ 59.98％ 68.42％ 59.96％ 62.67％ 67.63％ 82.87％ Molecular weight <![CDATA[1.11×10 6 > <![CDATA[1.10×10 6 > <![CDATA[7.61×10 5 > <![CDATA[7.47×10 5 > <![CDATA[9.10×10 5 > <![CDATA[8.53×10 5 > <![CDATA[7.87×10 5 > <![CDATA[7.44×10 5 >

[0088] The results show that: only by the methods shown in Examples 1 to 5 can chitosan be prepared from chitin, and the degree of deacetylation of the prepared chitosan all reaches more than 80%, and at the same time has an excellent molecular weight (molecular weight > 7×10 5 ); although the degree of deacetylation of the chitosan prepared by the method shown in chitosan 16 also reaches more than 80%, the mass concentration of NaOH combined in the preparation process is higher than 50%, which will cause environmental pollution in the preparation process.

[0089] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present invention rather than limit the protection scope of the present invention. For those of ordinary skill in the art, other different forms of changes or modifications can be made on the basis of the above description and ideas. It is not necessary and impossible to list all the implementation manners here. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the claims of the present invention.

Claims

1. A method for preparing chitosan based on a choline chloride - fructose system, characterized in that, It includes the following steps: S1. Mix choline chloride and fructose in a molar ratio of 1-2:1-2, and obtain a choline chloride-fructose system after sufficient reaction; S2. Add chitin accounting for 0.5%-1% of the mass of the choline chloride-fructose system to the choline chloride-fructose system obtained in step S1 and dissolve it sufficiently to obtain a mixed system; S3. Add NaOH with a final mass concentration of 30%-35% to the mixed system obtained in step S2, then place it in an environment of 95-100 °C for sufficient reaction, and collect the reaction solution; S4. After mixing the reaction solution obtained in step S3 with water, perform solid-liquid separation to collect the precipitate and dry it to obtain chitosan.

2. The method according to claim 1, wherein In step S1, choline chloride and fructose are mixed in a molar ratio of 1:

1.

3. The method according to claim 1, wherein The sufficient reaction in step S1 is: place it at 70-80 °C for reaction for 1-3 h.

4. The method according to claim 1, characterized in that In step S2, chitin accounting for 0.78% of the mass of the choline chloride-fructose system is added.

5. The method according to claim 1, wherein In step S3, NaOH with a final mass concentration of 30% is added to the mixed system obtained in step S2.

6. The method according to claim 1, wherein In step S3, it is placed in an environment of 95 °C for sufficient reaction.

7. The method according to claim 6, characterized in that, The sufficient reaction is to react for 14-20 h.

8. The method according to claim 7, wherein The sufficient reaction is to react for 20 h.

9. Chitosan prepared by the method according to any one of claims 1-8.

10. Use of the method according to any one of claims 1-8 in treating chitin.