Method for adsorbing reducing sugar alkaline degradation pigment by using chitosan gelatin composite gel

Abstract

The invention discloses a method for adsorbing a reducing sugar alkaline degradation pigment by using chitosan gelatin composite gel, which comprises the following steps: preparing the reducing sugar alkaline degradation pigment and preparing into an aqueous solution, and adding the chitosan gelatin composite gel for adsorption, sequentially soaking the adsorbed chitosan gelatin composite gel in a sodium hydroxide solution and a hydrochloric acid solution, washing with deionized water, freeze-drying, and reusing; the chitosan gelatin composite gel is prepared by taking chitosan and gelatin as raw materials, preparing hydrogel through a chemical crosslinking enhanced'solution-gel 'one-step method, and freeze-drying. The chitosan gelatin composite gel prepared by the invention is green and environment-friendly in raw material, low in price, simple to prepare, good in adsorption effect and recyclable, can economically and efficiently realize the adsorption of the reducing sugar alkaline degradation pigment, and has relatively high application prospect and market value.

Description

Technical Field

[0001] The present invention relates to an adsorption and separation method for reducing sugar alkaline degradation pigments, and more particularly to a method for using a chitosan-gelatin composite gel to adsorb reducing sugar alkaline degradation pigments. Background Art

[0002] In the production process of refined sugar, the carbonation method is an efficient method for clarifying raw sugar redissolved syrup. Calcium carbonate generated by lime milk and carbon dioxide can effectively remove substances such as caramel pigments, melanoidins, and phenolic pigments in the syrup, and the obtained sugar has high quality, but it will increase the pH value of the redissolved syrup. In an alkaline environment, not only is it difficult to remove the reducing sugar alkaline degradation pigments in the syrup, but they will even continue to be generated. Research has found that the reducing sugar alkaline degradation pigments contribute approximately 50% to the color of the syrup and are the main colored substances in the redissolved syrup. Therefore, it is necessary to take targeted adsorption and decolorization steps in the subsequent production process.

[0003] Currently, the sugar industry mainly uses ion exchange resins and activated carbon as adsorbents to remove reducing sugar alkaline degradation pigments. Ion exchange resins have good adsorption performance and recyclability, but the commonly used acrylic resins and styrene resins in industry are both toxic to a certain extent, and their monomers, acrylic acid and styrene, are both carcinogens. Activated carbon is divided into granular activated carbon and powdered activated carbon. The decolorization process of granular activated carbon is similar to that of ion exchange resins, but due to the low operating flow rate of activated carbon, the syrup needs to stay in the decolorization system for a long time. Powdered activated carbon is not renewable, and the operating working environment is generally poor.

[0004] In recent years, many scholars have conducted extensive research on the problem of syrup decolorization. The Chinese invention patent with the application number 202010457300.8 uses grafted quaternized magnetic chitosan microspheres to adsorb reducing sugar alkaline degradation pigments, but the preparation method is relatively complex, and it requires the use of relatively expensive iron oxide nanoparticles and toxic petroleum ether, methanol, etc. In the study on the synthesis of rosin-based anion exchange resin and its removal of typical pigments in sugar juice, rosin-based anion exchange resin RAER is used to adsorb hexose alkaline degradation pigments, and in the study of Removal of high-molecular-weight hexose alkaline degradation products by rosin-based anion adsorbent: Kinetics, thermodynamics, and mechanisms, methyl methacrylate tertiary amine type rosin-based adsorbent MTARAR is used to adsorb reducing sugar alkaline degradation pigments. The adsorption rates of both are relatively high, both reaching more than 80%, but the adsorption capacities are relatively low (2.02 mg / g and 6.50 mg / g respectively), and the practical application value is relatively low.

[0005] Therefore, it is necessary to develop an adsorbent that is green and environmentally friendly, inexpensive, easy to prepare, has good adsorption performance, and can be recycled to adsorb the alkaline degradation pigments of reducing sugars. Summary of the Invention

[0006] Aiming at the deficiencies in the existing technology, the purpose of the present invention is to provide a method for using chitosan-gelatin composite gel to adsorb the alkaline degradation pigments of reducing sugars. The chemical structure of the alkaline degradation pigments of reducing sugars contains a large number of carboxyl groups and generally carries a negative charge in syrup. Therefore, the cationic basic polysaccharide chitosan with amino groups is selected to prepare the adsorbent, and the macromolecular hydrophilic colloid gelatin is selected as the starting material for constructing the adsorbent network to make up for the problem of insufficient mechanical strength of the chitosan material.

[0007] The present invention provides a preparation method of chitosan-gelatin composite gel, which includes the following steps:

[0008] S1. Under the conditions of water bath stirring, dissolve chitosan in 2% acetic acid solution to obtain a chitosan solution, and dissolve gelatin in deionized water to obtain a gelatin solution; ultrasonically disperse the chitosan solution to remove bubbles;

[0009] The mass percentage of the chitosan solution is 0-1.5%;

[0010] The mass percentage of the gelatin solution is 10%;

[0011] S2. Mix the chitosan solution and the gelatin solution prepared in S1 according to a mass ratio of 1:1, and magnetically stir until a uniform mixture is formed to obtain a chitosan-gelatin mixed solution;

[0012] S3. Dropwise add 50% glutaraldehyde aqueous solution to the chitosan-gelatin mixed solution prepared in S2 under stirring conditions; the dropping amount of the 50% glutaraldehyde aqueous solution in S3 is 0.5% of the mass of the chitosan-gelatin mixed solution;

[0013] S4. Quickly pour the chitosan-gelatin mixed solution added with 50% glutaraldehyde aqueous solution prepared in S3 into a mold and age at room temperature to obtain a chitosan-gelatin hydrogel;

[0014] Freeze the chitosan-gelatin hydrogel until it is completely frozen, and freeze-dry it to obtain a chitosan-gelatin composite gel.

[0015] Preferably, the water bath stirring conditions in S1 are 50°C and 100 rpm.

[0016] Preferably, the aging time in S4 is 24 h, and the freezing temperature is -20°C.

[0017] The present invention also provides a chitosan-gelatin composite gel prepared by the above preparation method.

[0018] Preferably, both the adsorption rate and adsorption capacity of the chitosan-gelatin composite gel for the reductant-alkali-degraded pigment increase with the increase in the chitosan content.

[0019] The present invention also provides a method for adsorbing the reductant-alkali-degraded pigment by using the above-mentioned chitosan-gelatin composite gel, which includes the following steps:

[0020] S1) Preparation of the pigment aqueous solution: Prepare the reductant-alkali-degraded pigment and configure it into a pigment aqueous solution;

[0021] S2) Adsorption: Use the chitosan-gelatin composite gel to adsorb the reductant-alkali-degraded pigment in the pigment aqueous solution prepared in S1) to obtain the solution after adsorption by the chitosan-gelatin composite gel.

[0022] Preferably, the concentration of the pigment aqueous solution in S1) is 90-210 mg / L.

[0023] Preferably, S1) is specifically:

[0024] Adjust the pH of a 10 g / L glucose solution to 10.5 with 75 g / L calcium oxide, react at 90 °C for 8 h while maintaining the pH at 10.5, and after the reaction, adjust the pH to neutral with 6 mol / L HCl solution; filter with a 0.45 μm filter membrane, dialyze with a dialysis bag having a molecular weight cut-off of 8-14 kDa for 48 h, and obtain the reductant-alkali-degraded pigment powder by vacuum freeze-drying; prepare a reductant-alkali-degraded pigment solution using this powder.

[0025] Preferably, S2) is specifically:

[0026] The addition amount of the chitosan-gelatin composite gel is 5 mg, the volume of the reductant-alkali-degraded pigment solution is 10 mL, place it in a water bath constant temperature oscillator, the rotation speed is 130 rpm, the adsorption temperature is 60 °C, the adsorption time is 6-12 h, and after filtering with a 0.45 μm filter membrane, the solution after adsorption by the chitosan-gelatin composite gel is obtained.

[0027] Preferably, it further includes S3) Reuse of the adsorbent, specifically:

[0028] Desorb the adsorbed chitosan-gelatin composite gel in S2) with 0.1 mol / L sodium hydroxide solution at room temperature for 12 h, then soak it in 0.1 mol / L hydrochloric acid solution for 10 min, wash it thoroughly with deionized water and then freeze-dry it, and repeatedly use it for S2).

[0029] The beneficial effects of the present invention are:

[0030] 1. The present invention uses degradable and renewable chitosan and gelatin as raw materials, and synthesizes chitosan-gelatin hydrogel by a one-step "solution-gel" method enhanced by chemical cross-linking, and prepares chitosan-gelatin composite gel by freeze-drying. The raw materials are green and environmentally friendly and relatively low in price, the preparation method is simple, and the obtained composite gel has a rich pore structure.

[0031] 2. The present invention uses the prepared chitosan-gelatin composite gel to adsorb and reduce the alkaline degradation pigment of reducing sugar. The adsorption rate is 89.59%, the highest adsorption capacity is 285.33 mg / g, and the adsorption rate can still reach more than 60% after being reused 5 times, and the structure remains intact. The composite gel has good adsorption effect, can be recycled, is simple to operate, and effectively adsorbs the alkaline degradation pigment of reducing sugar economically and efficiently, and has good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The drawings are used to provide a further understanding of the present invention, and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention, and do not constitute a limitation to the present invention. In the drawings:

[0033] Figure 1 It is the adsorption rate and adsorption capacity diagram of gels with different chitosan contents prepared in Examples 1-4.

[0034] Figure 2 It is the adsorption effect diagram of the chitosan-gelatin composite gel prepared in Example 4.

[0035] Figure 3 It is the scanning electron microscope micrograph of the chitosan-gelatin composite gel prepared in Example 4.

[0036] Figure 4 It is the Fourier transform infrared spectroscopy diagram of the chitosan-gelatin composite gel prepared in Example 4 and the raw materials.

[0037] Figure 5 It is the fitting curve diagram of the adsorption kinetic model of the chitosan-gelatin composite gel prepared in Example 4.

[0038] Figure 6 It is the fitting curve diagram of the adsorption isotherm model of the chitosan-gelatin composite gel prepared in Example 4.

[0039] Figure 7 It is the repeated use performance effect diagram of the chitosan-gelatin composite gel adsorbing the alkaline degradation pigment of reducing sugar in Example 6. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0040] The preferred embodiments of the present invention will be described below in conjunction with the accompanying drawings. It should be understood that the following examples are given only for the purpose of illustration and are not intended to limit the scope of the present invention. Those skilled in the art can make various modifications and substitutions to the present invention without departing from the spirit and purpose of the present invention.

[0041] The present invention provides a method for preparing a chitosan-gelatin composite gel, comprising the following steps:

[0042] (1) At 50 °C in a water bath with 100 rpm, chitosan is dissolved in a 2% acetic acid solution to obtain a chitosan solution. The chitosan solution is ultrasonically dispersed for 15 min to remove bubbles, and the mass percentage of the chitosan solution is 0-1.5%; gelatin is dissolved in deionized water to obtain a gelatin solution, and the mass percentage of the gelatin solution is 10%.

[0043] (2) The chitosan solution and the gelatin solution are mixed in a mass ratio of 1:1, and magnetically stirred until a uniform mixture is formed. Under stirring conditions, a 50% aqueous glutaraldehyde solution is added dropwise; the addition amount of the 50% aqueous glutaraldehyde solution is 0.5% of the mass of the chitosan-gelatin mixed solution.

[0044] (3) The chitosan-gelatin mixed solution added with the 50% aqueous glutaraldehyde solution prepared in step (2) is quickly poured into a mold and aged at room temperature for 24 h to obtain a chitosan-gelatin hydrogel. Then, the chitosan-gelatin hydrogel is placed in a -20 °C refrigerator and frozen until completely frozen, and then prepared into a chitosan-gelatin composite gel through freeze-drying treatment.

[0045] The present invention also discloses a method for adsorbing and reducing sugar alkaline-degraded pigments using a chitosan-gelatin composite gel. By preparing a reducing sugar alkaline-degraded pigment and configuring it into an aqueous solution, adding the chitosan-gelatin composite gel for adsorption, the adsorbed chitosan-gelatin composite gel is successively soaked in a sodium hydroxide solution and a hydrochloric acid solution and then washed with deionized water, and can be reused after freeze-drying; the chitosan-gelatin composite gel is made of chitosan and gelatin as raw materials, and is made into a hydrogel by a "solution-gel" one-step method enhanced by chemical cross-linking, and then made after freeze-drying. Specifically:

[0046] (a) Preparation of the pigment solution: The pH of a 10 g / L glucose solution is adjusted to 10.5 with 75 g / L calcium oxide, reacted at 90 °C for 8 h while maintaining the pH at about 10.5, and after the reaction, the pH is adjusted to neutral with a 6 mol / L HCl solution. Filtered using a 0.45 μm filter membrane and dialyzed for 48 h with a dialysis bag with a cut-off molecular weight of 8-14 kDa, and obtained a reducing sugar alkaline-degraded pigment powder through vacuum freeze-drying. Using this powder to prepare a reducing sugar alkaline-degraded pigment solution with a concentration of 90-210 mg / L.

[0047] (b) Adsorption: The chitosan-gelatin composite gel was used to adsorb the pigment degraded by reducing sugar under alkaline conditions. The addition amount of the chitosan-gelatin composite gel was 5 mg, the volume of the reducing sugar alkaline degraded pigment solution was 10 mL, and it was placed in a water bath constant temperature oscillator with a rotation speed of 130 rpm, an adsorption temperature of 60 °C, and an adsorption time of 6 - 12 h. After filtering with a 0.45 μm filter membrane, the adsorbed solution was obtained.

[0048] (c) Reuse of adsorbent: The used chitosan-gelatin composite gel in step (b) was desorbed with 0.1 mol / L sodium hydroxide solution at room temperature for 12 h, then soaked in 0.1 mol / L hydrochloric acid solution for 10 min, washed thoroughly with deionized water and freeze-dried, and repeatedly used in step (b).

[0049] Example 1:

[0050] Synthesis of gelatin gel: 1.5 g of gelatin was dissolved in deionized water in a 50 °C water bath at 100 rpm to obtain a 15 g gelatin solution. A 2% acetic acid solution and the gelatin solution were mixed at a mass ratio of 1:1, magnetically stirred until a homogeneous mixture was formed, and 0.15 g of 50% glutaraldehyde aqueous solution was added dropwise under stirring conditions. It was quickly poured into a mold and aged at room temperature for 24 h to prepare a gelatin hydrogel. Then, the gelatin hydrogel was placed in a -20 °C refrigerator and frozen until completely frozen, and then freeze-dried to obtain a gelatin gel with a chitosan content of 0.

[0051] Preparation of pigment solution: The pH of a 10 g / L glucose solution was adjusted to 10.5 with 75 g / L calcium oxide, reacted at 90 °C for 8 h while maintaining the pH at about 10.5, and after the reaction, the pH was adjusted to neutral with 6 mol / L HCl solution. It was filtered with a 0.45 μm filter membrane, dialyzed with a dialysis bag with a molecular weight cut-off of 8 - 14 kDa for 48 h, and the reduced sugar alkaline degraded pigment powder was obtained by vacuum freeze-drying. A 90 mg / L reduced sugar alkaline degraded pigment solution was prepared using this powder.

[0052] Adsorption: The above-prepared gelatin gel was used to adsorb the reduced sugar alkaline degraded pigment. The addition amount of the gelatin gel was 5 mg, the volume of the reduced sugar alkaline degraded pigment solution was 10 mL, and it was placed in a water bath constant temperature oscillator and adsorbed at 130 rpm and 60 °C for 6 h. After filtering with a 0.45 μm filter membrane, the adsorbed solution was obtained.

[0053] The adsorption rate of the synthesized gelatin gel for the reduced sugar alkaline degraded pigment was 51.94%, and the adsorption capacity was 92.61 mg / g.

[0054] Example 2

[0055] Synthesis of chitosan - gelatin composite gel: At 50 °C in a water bath with a speed of 100 rpm, 0.075 g of chitosan was dissolved in 2% acetic acid solution to obtain 15 g of chitosan solution, and ultrasonic dispersion was carried out for 15 min to remove air bubbles; 1.5 g of gelatin was dissolved in deionized water to obtain 15 g of gelatin solution. The chitosan solution and the gelatin solution were mixed in a mass ratio of 1:1, and magnetic stirring was carried out until a uniform mixture was formed. Under stirring conditions, 0.15 g of 50% glutaraldehyde aqueous solution was added dropwise. It was quickly poured into a mold and aged at room temperature for 24 h to obtain chitosan - gelatin hydrogel. Then, the chitosan - gelatin hydrogel was placed in a - 20 °C refrigerator and frozen until completely frozen, and then obtained chitosan - gelatin composite gel through freeze - drying treatment, and its chitosan content was 0.25%.

[0056] The preparation and adsorption of the pigment solution were carried out as in Example 1.

[0057] The adsorption rate of the synthesized chitosan - gelatin composite gel for the reducing sugar - alkaline - degraded pigment was 67.92%, and the adsorption capacity was 120.20 mg / g.

[0058] Example 3

[0059] Synthesis of chitosan - gelatin composite gel: At 50 °C in a water bath with a speed of 100 rpm, 0.15 g of chitosan was dissolved in 2% acetic acid solution to obtain 15 g of chitosan solution, and ultrasonic dispersion was carried out for 15 min to remove air bubbles; 1.5 g of gelatin was dissolved in deionized water to obtain 15 g of gelatin solution. The chitosan solution and the gelatin solution were mixed in a mass ratio of 1:1, and magnetic stirring was carried out until a uniform mixture was formed. Under stirring conditions, 0.15 g of 50% glutaraldehyde aqueous solution was added dropwise. It was quickly poured into a mold and aged at room temperature for 24 h to obtain chitosan - gelatin hydrogel. Then, the chitosan - gelatin hydrogel was placed in a - 20 °C refrigerator and frozen until completely frozen, and then obtained chitosan - gelatin composite gel through freeze - drying treatment, and its chitosan content was 0.5%.

[0060] The preparation and adsorption of the pigment solution were carried out as in Example 1.

[0061] The adsorption rate of the synthesized chitosan - gelatin composite gel for the reducing sugar - alkaline - degraded pigment was 70.69%, and the adsorption capacity was 128.27 mg / g.

[0062] Example 4

[0063] Synthesis of chitosan - gelatin composite gel: Dissolve 0.225 g of chitosan in 2% acetic acid solution to obtain 15 g of chitosan solution, and ultrasonically disperse it for 15 min to remove bubbles; dissolve 1.5 g of gelatin in deionized water to obtain 15 g of gelatin solution. Mix the chitosan solution and the gelatin solution according to a mass ratio of 1:1, and magnetically stir until a uniform mixture is formed. Under stirring conditions, add 0.15 g of 50% glutaraldehyde aqueous solution dropwise. Quickly pour it into a mold and age it at room temperature for 24 h to obtain chitosan - gelatin hydrogel. Then, place the chitosan - gelatin hydrogel in a - 20 °C refrigerator and freeze it until completely frozen, and obtain the chitosan - gelatin composite gel through freeze - drying treatment, with the chitosan content being 0.75%.

[0064] The preparation and adsorption of the pigment solution are as in Example 1.

[0065] The adsorption rate of the synthesized chitosan - gelatin composite gel for the reductant - alkaline - degraded pigment is 89.59%, and the adsorption capacity is 161.26 mg / g.

[0066] Figure 1 It is a graph of the adsorption rate and adsorption capacity of gels with different chitosan contents prepared in Examples 1 - 4. From Figure 1 it can be seen that both the adsorption rate and adsorption capacity of the adsorbent for the reductant - alkaline - degraded pigment increase with the increase of chitosan content. This is because chitosan contains abundant - NH 2 groups, which are protonated in the solution to produce - NH 3 + , and can effectively adsorb the reductant - alkaline - degraded pigment containing - COOH.

[0067] Figure 2 It is the adsorption effect diagram of the chitosan - gelatin composite gel prepared in Example 4. a is the 90 mg / L reductant - alkaline - degraded pigment solution before adsorption, and b is the solution after adsorption obtained in Example 4. It can be clearly seen that the color of the solution after adsorption becomes significantly lighter than that before adsorption.

[0068] Figure 3 It is the scanning electron microscope micrograph of the chitosan - gelatin composite gel prepared in Example 4. Observing the scanning electron microscope photograph at a magnification of 50 times, the chitosan - gelatin composite gel presents a honeycomb - like porous structure, and the pore shapes are irregular and the sizes are different. This is because during the freeze - drying process, the free water molecules in the hydrogel cross - linked structure freeze and then sublimate, resulting in a porous structure with different sizes in the adsorbent.

[0069] Figure 4 It is the Fourier transform infrared spectroscopy diagram of the chitosan - gelatin composite gel prepared in Example 4 and its raw materials. Both chitosan and gelatin can chemically cross - link with glutaraldehyde to enhance the gel strength. From Figure 4 it can be seen that after chitosan cross - links with glutaraldehyde, at 1649 cm -1The absorption peak intensity at the position increases significantly, which represents the stretching vibration of C=N in the Schiff base formed by the reaction between the two, indicating that the reaction between chitosan and glutaraldehyde belongs to the Schiff base reaction. 2 The -CHO reaction with glutaraldehyde forms a new covalent bond, resulting in 3427 cm -1 The amide A band at the position of the chitosan is blue-shifted. In addition, the -COOH of gelatin also reacts with the -NH 2 and -OH interaction, resulting in a decrease in the chitosan-gelatin composite gel size of 1547 cm-1 compared to chitosan + glutaraldehyde. -1 NH bending vibration at 1080cm -1 The CO stretching vibrations at all locations are reduced.

[0070] Figure 5 This is a fitting curve of the chitosan gelatin composite gel adsorption kinetic model prepared in Example 4. The experiment was carried out at 60°C, the initial concentration of reducing sugar alkaline degradation pigment was 90 mg / L, the volume was 10 mL, the chitosan gelatin composite gel dosage was 5 mg, and the reaction time was 12 h. The pseudo-first-order and pseudo-second-order kinetic models were used for fitting, and the corresponding equations were as follows:

[0071]

[0072]

[0073] Table 1 Parameters of the adsorption kinetic model of chitosan-gelatin composite gel adsorbing reducing sugars and alkaline-degradable pigments

[0074]

[0075] Depend on Figure 5 As shown in Table 1, the adsorption process conforms to the pseudo-second-order kinetic model (R 2 =0.9988), indicating that chemical adsorption plays a dominant role in the adsorption process.

[0076] Figure 6 This is a fitting curve of the chitosan gelatin composite gel adsorption isotherm model prepared in Example 4. The experiment was carried out at 60°C, the initial concentration range of the reducing sugar alkaline degradation pigment was 30-210 mg / L, the volume was 10 mL, the chitosan gelatin composite gel dosage was 5 mg, and the reaction time was 6 hours. The Langmuir, Freundlich, and Sips adsorption isotherm models were used for fitting, and the corresponding equations were as follows:

[0077]

[0078]

[0079]

[0080] Table 2 Adsorption Isotherm Model Parameters of Chitosan-Gelatin Composite Gel for Adsorbing Reducing Sugar Alkaline Degraded Pigment

[0081]

[0082] From Figure 6 and Table 2, it can be seen that the adsorption process conforms to the Sips model (R 2 = 0.9890). This model combines the characteristics of the Freundlich and Langmuir models. It is similar to the Freundlich model at low concentrations, occurring in the heterogeneous layer; it is similar to the Langmuir model at high concentrations, representing monolayer adsorption. In addition, the Langmuir model (R 2 = 0.9782) and the Freundlich model (R 2 = 0.9712) were also used to fit the adsorption isotherm data, among which the Langmuir model had a better fitting effect, indicating that the adsorption process may mainly be monolayer adsorption. The specificity factor m of the Sips model is 0.59779, deviating from 1, indicating that the surface heterogeneity cannot be ignored. In summary, this adsorption process is mainly monolayer adsorption and there is a certain degree of heterogeneous adsorption.

[0083] Example 5

[0084] The synthesis of chitosan-gelatin composite gel was the same as in Example 4.

[0085] Preparation of pigment solution: Adjust the pH of 10 g / L glucose solution to 10.5 with 75 g / L calcium oxide, react at 90 °C for 8 h while maintaining the pH at about 10.5. After the reaction, adjust the pH to neutral with 6 mol / L HCl solution. Filter with a 0.45 μm filter membrane, dialyze with a dialysis bag with a molecular weight cut-off of 8 - 14 kDa for 48 h, and obtain the reducing sugar alkaline degraded pigment powder by vacuum freeze-drying. Use this powder to prepare a reducing sugar alkaline degraded pigment solution with a concentration of 210 mg / L.

[0086] Adsorption: Use the above chitosan-gelatin composite gel to adsorb the reducing sugar alkaline degraded pigment. The addition amount of chitosan-gelatin composite gel is 5 mg, and the volume of the reducing sugar alkaline degraded pigment solution is 10 mL. Place it in a water bath constant temperature oscillator and adsorb at 130 rpm and 60 °C for 12 h. After filtering with a 0.45 μm filter membrane, the adsorbed solution is obtained.

[0087] The adsorption rate of the synthesized chitosan-gelatin composite gel for the reducing sugar alkaline degraded pigment is 68.22%, and the adsorption capacity is 285.33 mg / g.

[0088] Example 6

[0089] The chitosan-gelatin composite gel after adsorption in Example 4 was desorbed with 0.1 mol / L sodium hydroxide solution at room temperature for 12 h, then soaked in 0.1 mol / L hydrochloric acid solution for 10 min, washed thoroughly with deionized water and freeze-dried, and repeatedly used for the adsorption step.

[0090] Figure 7 It is the performance effect diagram of the repeated use of the chitosan-gelatin composite gel for adsorbing reducing sugar alkaline degradation pigment in Example 6. After 5 cycles of use, the structure of the composite gel remained intact and no significant change in its shape was observed. From Figure 7 it can be seen that the adsorption rate of the chitosan-gelatin composite gel for reducing sugar alkaline degradation pigment was 89.59% during the first adsorption, and the adsorption rate of the reducing sugar alkaline degradation pigment could still reach 61.23% after 5 repeated uses, which was about 68% of the first use, indicating that the chitosan-gelatin composite gel had good reusability.

[0091] The content not described in detail in this specification belongs to the prior art well-known to those skilled in the art.

[0092] Finally, it should be noted that the above are only preferred examples of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a chitosan-gelatin composite gel, characterized in that: The following steps are involved: S1. Under stirring conditions in a water bath, dissolving chitosan in a 2% acetic acid solution to obtain a chitosan solution, dissolving gelatin in deionized water to obtain a gelatin solution; and ultrasonically dispersing the chitosan solution to remove bubbles; The mass percentage of the chitosan solution is 0 to 1.5%; The mass percentage of the gelatin solution is 10%; S2. The chitosan solution and gelatin solution prepared in S1 were mixed in a mass ratio of 1:1, and magnetically stirred until a uniform mixture was formed to obtain a chitosan-gelatin mixed solution; S3. Add 50% glutaraldehyde aqueous solution to the chitosan-gelatin mixed solution obtained in S2 under stirring; the amount of 50% glutaraldehyde aqueous solution added in S3 is 0.5% by mass of the chitosan-gelatin mixed solution; S4. The chitosan gelatin mixed solution obtained in S3 and added with 50% glutaraldehyde aqueous solution was quickly poured into the mold and aged at room temperature to obtain a chitosan gelatin hydrogel; The chitosan gelatin hydrogel is frozen until completely frozen, and freeze-dried to obtain a chitosan gelatin composite gel.

2. The method for preparing the chitosan-gelatin composite gel according to claim 1, characterized in that: The stirring conditions of the water bath in S1 are 50° C. and 100 rpm.

3. The method for preparing the chitosan-gelatin composite gel according to claim 1, characterized in that: The aging time in S4 is 24 hours, and the freezing temperature is -20°C.

4. A chitosan-gelatin composite gel prepared by the preparation method according to any one of claims 1 to 4.

5. The chitosan-gelatin composite gel according to claim 4, characterized in that: The adsorption rate and adsorption amount of the chitosan-gelatin composite gel on reducing sugar alkaline degradation pigments are increased with the increase of chitosan content.

6. A method for alkaline degradation of pigments by adsorbing reducing sugars using the chitosan-gelatin composite gel of claim 4, characterized in that: The following steps are involved: S1) Preparation of pigment aqueous solution: preparing reducing sugar alkaline degradation pigment and preparing pigment aqueous solution; S2) adsorption: using the chitosan gelatin composite gel to adsorb the reducing sugar in the pigment aqueous solution obtained in S1) to alkalinely degrade the pigment to obtain a chitosan gelatin composite gel adsorbed solution.

7. The method for alkaline degradation of pigments by adsorbing reducing sugars using chitosan-gelatin composite gel according to claim 6, characterized in that: The concentration of the pigment aqueous solution in S1) is 90-210 mg / L.

8. The method for alkaline degradation of pigments by adsorbing reducing sugars using chitosan-gelatin composite gel according to claim 6, characterized in that: The S2) is specifically: The chitosan-gelatin composite gel is added in an amount of 5 mg, and the volume of the reducing sugar alkaline degradation pigment solution is 10 mL. The solution is placed in a water bath constant temperature oscillator at a rotation speed of 130 rpm, an adsorption temperature of 60° C., and an adsorption time of 6 to 12 h. The chitosan-gelatin composite gel adsorption solution is obtained after filtration with a 0.45 μm filter membrane.

9. The method for alkaline degradation of pigments by adsorbing reducing sugars using chitosan-gelatin composite gel according to claim 6, characterized in that: It also includes S3) adsorbent reuse, specifically: The chitosan-gelatin composite gel after adsorption in S2) was desorbed at room temperature for 12 h using 0.1 mol / L sodium hydroxide solution, then soaked in 0.1 mol / L hydrochloric acid solution for 10 min, washed thoroughly with deionized water and freeze-dried, and repeatedly used in S2).

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