CN114736993A - Method for decoloring sugar juice - Google Patents

Abstract

The invention discloses a method for decolorizing sugar juice. The quaternary ammonium functionalized chitosan mixed with quaternized ammonium MOF composite aerogel is uniformly mixed with the sugar juice to absorb the sugar juice pigment. The quaternary ammonium functionalized chitosan mixed with quaternized ammonium MOF composite aerogel uses chitosan and MOF (UIO-66-NH ₂ ) as raw materials, and 50% glutaraldehyde as a cross-linking agent. It is made by doping quaternary ammonium MOF by cross-linking method, and then the amino groups on the chitosan molecular chain are grafted with quaternary ammonium groups. The invention uses chitosan as a raw material to prepare a decolorizing agent for chitosan-based aerogel sugar, and the addition of quaternized MOF solves the problem of easy collapse of the aerogel pore structure after quaternization of chitosan, and makes the chitosan-based The decolorizing agent for aerogel sugar has a rich pore structure, which is coupled with the green sugar production process of the membrane method, and solves the technical problem that the membrane separation technology cannot retain the small molecular pigments in the sugar juice, which leads to the high color value of the finished white sugar, and realizes sugar production. The whole process is green.

Description

A kind of decolorization method of sugar juice

technical field

The invention belongs to the technical field of sugar production, in particular to a method for decolorizing sugar juice.

Background technique

Sugar is a necessities of life. In the production of refined white sugar (high-end sugar products), decolorization of sugar juice is the most critical process. At present, sugar juice decolorization resins are mainly strong base macroporous anion exchange resins synthesized from styrene and divinylbenzene as the matrix. Both styrene and divinylbenzene are derived from petroleum, their raw materials are non-renewable, and they are listed as 2B carcinogens by the International Agency for Research on Cancer. Obviously, the use of such resins for sugar purification will become a hidden danger to sugar safety. Therefore, the development of green, non-toxic and regenerable chitosan-based decolorants with good performance has important research and industrial application significance.

Chitosan, as a natural degradable polymer polysaccharide, belongs to cationic alkaline polysaccharide, and its content is second only to cellulose in nature. Chitosan is cheap and easy to obtain, non-toxic and harmless, and has good biocompatibility. Chitosan-based materials have been widely used in water treatment, polyphenol adsorption, heavy metal adsorption and other fields. The amino and hydroxyl reactive groups in the chitosan molecule can easily introduce targeted functional groups, thereby effectively adsorbing sugar juice pigments. Metal-organic frameworks (MOF, UIO-66-NH ₂ ) contain a large number of amino groups, which are easily protonated in aqueous solution with a strong positive charge. On this basis, the introduction of targeting functional groups (quaternary ammonium groups) further enhances the positive charge content. It is prone to classical interaction with negatively charged pigment molecules in sugar juice. Aerogels have attracted much attention due to their low density, large porosity, and high specific surface area; they have been widely used in electrochemistry, tissue engineering, drug delivery, catalyst carriers, and other fields. In recent years, aerogels have attracted much attention due to their high adsorption capacity and ultrafast adsorption rate. Therefore, chitosan-based aerogels have great potential for removing sugar juice pigments. The introduced target functional group (quaternary ammonium salt) is easily ionized to form electropositive quaternary ammonium salt ions, which can effectively adsorb electronegative pigments.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a decolorization method for sugar juice, which solves the green sugar-making process of the membrane method, adopts the membrane separation technology to filter the sugar juice, and cannot retain the small molecular pigments in the sugar juice, resulting in the partial color value of the finished white sugar. high technical issues.

To achieve the above object, the present invention has adopted the following technical solutions:

A method for decolorizing sugar juice, the sugar juice is mixed with quaternary ammonium functionalized chitosan mixed with quaternary ammonium MOF composite aerogel, fully stirred and then filtered and separated to obtain decolorized sugar juice.

The preparation of the quaternary ammonium functionalized chitosan mixed with quaternized ammonium MOF composite aerogel comprises the following steps:

(1) Swelling chitosan: chitosan, sodium hydroxide aqueous solution with a concentration of 30% to 50% and analytically pure isopropanol solution in a mass ratio of 1.0 to 1.5:2 to 5:12 to 20 Mix the ratio evenly, heat the water bath to 40℃～60℃, stir for 200min～300min;

(2) Introducing quaternary ammonium groups into chitosan chains by nucleophilic substitution reaction: adding 60% (3-chloro-2-hydroxypropyl)trimethylammonium chloride dropwise to the mixture of step (1), The mass ratio of the mixture of trimethylammonium chloride and step (1) is 0.1～1.0:1, the temperature is increased to 60°C～80°C, and stirred for 6～8h;

(3) Adjust the pH of the reaction mixture in step (2) with a 5%-15% dilute HCl solution to keep the pH neutral;

(4) The reaction product was collected by filtration: the mixture in step (3) was washed with methanol and ethanol in turn, and the wet quaternary ammonium functionalized chitosan product was dried under vacuum at 70°C to 90°C for 24 hours. Quaternary ammonium functionalized chitosan;

(5) The MOF and isopropanol solution are uniformly mixed according to the mass ratio of MOF to analytically pure isopropanol solution in a ratio of 1.0～1.5:12～20, heated to 60 ℃～80 ℃ in a water bath, and 60% (3 - Chloro-2-hydroxypropyl)trimethylammonium chloride was added dropwise to the mixture of MOF and isopropanol, (3-chloro-2-hydroxypropyl)trimethylammonium chloride with MOF and isopropanol The mass ratio of the mixture is 0.1-1.0:1, and the pH is kept neutral with 30%-50% aqueous sodium hydroxide solution, and stirred for 6-8h;

(6) The reaction product is collected by filtration: the reaction product of step (5) is washed with ethanol and distilled water for several times in turn, and the wet quaternized product is the dry quaternary ammonium product obtained after drying under vacuum conditions at 40°C to 60°C for 24 hours. Ammonized MOF;

(7) Mix quaternary ammonium functionalized chitosan, chitosan and quaternized MOF powder uniformly in a mass ratio of 7.0～9.0:0.5～2.0:0.5～2.0 until the mass is quaternary ammonium functionalized chitosan , chitosan and quaternized MOF powder mixture mass 4% ~ 5% glacial acetic acid, ultrasonic for 1h;

(8) stirring continuously, adding a 50% glutaraldehyde solution whose mass is 0.01 to 0.05 times the mass of the mixture in step (7) as a cross-linking agent into the mixture in step (7);

(1) Pour the mixed solution in step (8) into the mold, and then rapidly freeze with liquid nitrogen after aging for 120 to 150 minutes. The frozen sample is placed in a freeze dryer for freeze-drying for more than 48 hours to obtain quaternary ammonium functionalized chitosan mixed with quaternary ammonium Ammonized MOF composite aerogel.

The MOF is UIO-66- _NH2 .

The sugar juice and the quaternary ammonium functionalized chitosan mixed with the quaternized ammonium MOF composite aerogel are mixed in a mass ratio of 50:1 to 500:1.

The sugar juice is the sugar juice filtered by a ceramic membrane.

The pore size of the ceramic membrane is 5-50 nm.

The stirring time is 1-2h.

Compared with the prior art, the present invention has the beneficial effects:

(1) Chitosan is the product of natural polysaccharide chitin that removes part of the acetyl group, and has the advantages of good biodegradability, green and non-toxicity, etc. The present invention is based on the structural characteristics of pigments in sugar juice, directional modification of chitosan, introduction of quaternary Ammonium salt ions are used to prepare sugar with decolorizing agent to adsorb and remove pigments in sugar juice, which not only retains the superior clarification and impurity removal advantages of membrane separation technology in sugar juice treatment, but also overcomes the inability of membrane filtration to remove small molecular pigments in sugar juice, resulting in finished sugar color. The defect of high value, compared with the existing sulfite method sugar production, realizes the greening of the whole process of sugar production.

(2) MOF (UIO-66-NH ₂ ) has a rich porous structure, and it has a strong positive charge after grafting with quaternary ammonium group, which is beneficial to the uptake of juice pigments (most of which have negative charges). The hydrophilicity of modified chitosan increased after the introduction of quaternary ammonium salts, resulting in the collapse of the cellular pore structure during the further formation of chitosan-based aerogels. Therefore, doping quaternized MOF into quaternary ammonium-modified chitosan aerogels can not only improve the problem of pore structure collapse, but also enrich the pore structure of aerogels, making quaternary ammonium functionalized chitosan aerogels. The adsorption effect of the doped quaternized MOF composite aerogel was improved.

(3) In the prior art, the styrene (divinylbenzene) type anion exchange resin also has a certain adsorption and removal effect on the pigments in the juice. However, both styrene and divinylbenzene have been listed as 2B carcinogens by the World Health Organization International Agency for Research on Cancer, which are extremely harmful to human body. Moreover, both styrene and divinylbenzene are derived from petroleum, and the raw materials are non-renewable and difficult to degrade, causing serious environmental pollution. The method does not use styrene (divinylbenzene) type anion exchange resin, is non-toxic and environmentally friendly.

(4) In the present invention, the quaternary ammonium functionalized chitosan mixed with quaternized ammonium MOF composite aerogel has a richer network structure and more cations than the existing amorphous adsorbent, which makes the adsorbent easy to use. It is fully contacted with the pigments in the juice (most of them are negatively charged) and undergoes an electrostatic interaction reaction to achieve decolorization.

(5) Existing adsorbents (such as activated carbon, etc.) are usually amorphous adsorbents, and when the adsorption reaction ends, regeneration is difficult and energy consumption is high. The adsorbent of the present invention can elute the pigment from the adsorbent through an ion exchange reaction, which greatly saves economic costs and is beneficial to sustainable development.

Description of drawings

Figure 1 shows the decolorization effect of quaternary ammonium functionalized chitosan mixed with quaternized ammonium MOF composite aerogel on membrane filtrate juice.

Detailed ways

The present invention will be described below with reference to the embodiments. Unless otherwise stated, the reagents used in this example are obtained from commercially available, chitosan, 80%-95% deacetylation degree, Sinopharm Holding Co., Ltd.; sodium hydroxide and hydrochloric acid, all of analytical grade, Tianjin Kemeiou Chemical Reagent Co., Ltd.; (3-chloro-2-hydroxypropyl)trimethylammonium chloride, 60% (w/w), analytical grade, Aladdin Reagent (Shanghai) Co., Ltd.; pentanediol Aldehyde, 25% (v/v), analytical grade, Da Mao Chemical Reagent Co., Ltd.; Isopropanol, analytical grade, Da Mao Chemical Reagent Co., Ltd.; Chemical reagents required for the preparation of MOF (UIO-66-NH ₂ ): chlorine Zirconium, 98% pure, Shanghai Maclean Biochemical Technology Co., Ltd.; Aminoterephthalic acid, 98% pure, Shanghai Maclean Biochemical Technology Co., Ltd.; N,N-Dimethylformamide, 99% pure, Sinopharm Holding Co., Ltd. Co., Ltd.; Glacial acetic acid, analytical grade, Sinopharm Holding Co., Ltd.

Example 1

This example is an application example of using the method of the present invention to decolorize sugar juice. The preparation of quaternary ammonium functionalized chitosan mixed with quaternized ammonium MOF composite aerogel is carried out as follows:

(1) Swelling chitosan: Mix chitosan, 30% sodium hydroxide aqueous solution and analytically pure isopropanol solution in a mass ratio of 1.0:2:12, and heat to 40°C in a water bath , the mixture was stirred for 200 min;

(2) Introducing quaternary ammonium groups into chitosan chains by nucleophilic substitution reaction: adding 60% (3-chloro-2-hydroxypropyl)trimethylammonium chloride dropwise to the mixture of step (1), The mass ratio of trimethylammonium chloride and the mixture of step (1) is 0.1:1, the temperature is increased to 60 ° C, and stirred for 6h;

(3) adjusting the pH of the reaction mixture in step (2) with a 5% dilute HCl solution to keep the pH neutral;

(4) The reaction product was collected by filtration: the reaction product of the mixture in step (3) was washed several times with methanol and ethanol in turn, and the wet quaternary ammonium functionalized chitosan product was dried under vacuum at 70°C for 24 hours. The quaternary ammonium functionalized chitosan;

(5) Mix MOF (UIO-66-NH ₂ ) and analytically pure isopropanol solution in a mass ratio of 1.0:12, heat to 60° C. in a water bath, add 60% (3-chloro-2- Hydroxypropyl) trimethyl ammonium chloride was added dropwise to the mixture of MOF and isopropanol, and the mass ratio of (3-chloro-2-hydroxypropyl) trimethyl ammonium chloride to the mixture of MOF and isopropanol was 0.1 : 1, and keep the pH neutral with 30% aqueous sodium hydroxide solution, and stir for 6h;

(6) The reaction product was collected by filtration: the reaction product of step (5) was washed several times with ethanol and distilled water in turn, and the wet quaternized product was the dry quaternized MOF obtained after drying under vacuum conditions of 40° C. for 24 h. ;

(7) The quaternary ammonium functionalized chitosan, chitosan and quaternized MOFene powder are uniformly mixed in a mass ratio of 7.0:0.5:0.5 to the mass of quaternary ammonium functionalized chitosan, chitosan and In 4% glacial acetic acid by mass of the quaternized MOF powder mixture, sonicated for 1 h;

(8) stirring continuously, adding a 50% glutaraldehyde solution whose mass is 0.01 times the mass of the mixture in step (7) to the mixture in step (7) as a cross-linking agent;

(9) Pour the mixed solution in step (8) into the mold, and after aging for 120 minutes, it is rapidly frozen with liquid nitrogen, and the frozen sample is placed in a freeze dryer for freeze-drying for more than 48 hours to obtain quaternary ammonium functionalized chitosan mixed with quaternary ammonium MOF composite aerogel.

In the preparation method of quaternized ammonium functionalized chitosan mixed with quaternized MOF composite aerogel, the deacetylation degree of chitosan described in step (1) is not less than 80%, and steps (1) and (2) The stirring is carried out in a constant temperature magnetic stirrer.

Decolorization of the juice is carried out as follows:

(1) The sugar juice filtered through a ceramic membrane with a pore size of 5 nm and the quaternary ammonium functionalized chitosan mixed with quaternized MOF composite aerogel are fully mixed in a sugar juice box in a ratio of 50:1 by mass. uniform, react for 1h;

(2) filter and separate the quaternary ammonium functionalized chitosan-doped quaternary ammonium MOF composite aerogel after adsorbing the pigment from the sugar juice to obtain a decolorized clear juice;

(3) after the decolorized clear juice is evaporated and concentrated and boiled and crystallized, white granulated sugar is obtained;

(4) The quaternary ammonium functionalized chitosan mixed with quaternary ammonium MOF composite aerogel after adsorbing the pigment was soaked in 0.1 mol/L sodium hydroxide solution for 2 h and saturated saline for 12 h, and then soaked with distilled water. Wash until neutral and recycle.

In Example 1, there was no significant difference in the sucrose content of sugar juice before and after adsorption treatment with quaternary ammonium functionalized chitosan mixed with quaternized MOF composite aerogel, indicating that the chitosan-based adsorbent would not adsorb sugar juice It can be seen from Figure 1 that after the sugar juice is treated with chitosan adsorbent, its color value can be greatly reduced to meet the needs of national first-class white sugar production.

Example 2

This example is another application example of decolorizing sugar juice using the method of the present invention. The preparation of quaternary ammonium functionalized chitosan mixed with quaternized ammonium MOF composite aerogel is carried out as follows:

(1) Swelling chitosan: Mix chitosan, sodium hydroxide aqueous solution with a concentration of 40% and analytically pure isopropanol solution in a mass ratio of 1.2:3:16, and heat to 50°C in a water bath. , the mixture was stirred for 250 min;

(2) Introducing quaternary ammonium groups into chitosan chains by nucleophilic substitution reaction: add 60% (3-chloro-2-hydroxypropyl) trimethylammonium chloride dropwise to the mixture in step (1), three The mass ratio of methylammonium chloride and the mixture in step (1) is 0.5:1, the temperature is increased to 70°C, and stirred for 7h;

(3) adjust the pH of the reaction mixture in step (2) with 10% dilute HCl solution, and keep the pH as neutral;

(4) The reaction product was collected by filtration: the mixture in step (3) was washed several times with methanol and ethanol in turn, and the wet quaternary ammonium functionalized chitosan product was dried under vacuum at 80° C. for 24 h. Ammonium functionalized chitosan;

(5) Mix MOF (UIO-66-NH ₂ ) and analytically pure isopropanol solution in a mass ratio of 1.2:17, heat to 70° C. in a water bath, add 60% (3-chloro-2- Hydroxypropyl) trimethyl ammonium chloride is added dropwise to the mixture of MOF and isopropanol, and the mass ratio of (3-chloro-2-hydroxypropyl) trimethyl ammonium chloride to the mixture of MOF and isopropanol is 0.6:1, and keep the pH neutral with 40% aqueous sodium hydroxide solution, and stir for 7h;

(6) The reaction product was collected by filtration: the reaction product in step (5) was washed several times with ethanol and distilled water in turn, and the wet quaternized product was the dry quaternized MOF obtained after drying under vacuum conditions at 50° C. for 24 h. ;

(7) The quaternary ammonium functionalized chitosan, chitosan and quaternized MOFene powder are uniformly mixed in a mass ratio of 8.0:1.5:1.5 to the mass of quaternary ammonium functionalized chitosan, chitosan and 4.5% glacial acetic acid by mass of quaternized MOF powder mixture, ultrasonic for 1h;

(8) stirring continuously, adding a 50% glutaraldehyde solution whose mass is 0.02 times the mass of the mixture in step (7) as a cross-linking agent to the mixture in step (7);

(9) Pour the mixed solution in step (8) into the mold, and after aging for 135 minutes, it is rapidly frozen with liquid nitrogen, and the frozen sample is placed in a freeze-drying machine for freeze-drying for more than 48 hours to obtain quaternary ammonium-functionalized chitosan mixed with quaternary ammonium. MOF composite aerogel.

In the preparation method of quaternized ammonium functionalized chitosan mixed with quaternized MOF composite aerogel, the deacetylation degree of chitosan described in step (1) is not less than 80%, and steps (1) and (2) The stirring is carried out in a constant temperature magnetic stirrer.

Decolorization of the juice is carried out as follows:

(1) The sugar juice filtered through a ceramic membrane with a pore size of 50 nm and the quaternary ammonium functionalized chitosan mixed with quaternized MOF composite aerogel are fully mixed in a sugar juice box in a ratio of 500:1 by mass. uniform, react for 2h;

(2) filter and separate the quaternary ammonium functionalized chitosan-doped quaternary ammonium MOF composite aerogel after adsorbing the pigment from the sugar juice to obtain a decolorized clear juice;

(3) after the decolorized clear juice is evaporated and concentrated and boiled and crystallized, white granulated sugar is obtained;

(4) The quaternary ammonium functionalized chitosan mixed with quaternary ammonium MOF composite aerogel after adsorbing the pigment was soaked in 0.1 mol/L sodium hydroxide solution for 2 h and saturated saline for 12 h, and then soaked with distilled water. Wash until neutral and recycle.

In Example 2, there was no significant difference in the sucrose content of sugar juice before and after the adsorption treatment of quaternary ammonium functionalized chitosan mixed with quaternized MOF composite aerogel, indicating that the chitosan-based adsorbent would not adsorb sugar juice It can be seen from Figure 1 that after the sugar juice is treated with chitosan adsorbent, its color value can be greatly reduced to meet the needs of national first-class white sugar production.

Example 3

This embodiment is another application embodiment of decolorizing sugar juice by adopting the method of the present invention. The preparation of quaternary ammonium functionalized chitosan mixed with quaternized ammonium MOF composite aerogel is carried out as follows:

(1) Swelling chitosan: Mix chitosan, 50% sodium hydroxide aqueous solution and analytically pure isopropanol solution in a mass ratio of 1.5:5:20, and heat to 60°C in a water bath , the mixture was stirred for 300 min;

(2) Introducing quaternary ammonium groups into chitosan chains by nucleophilic substitution reaction: add 60% (3-chloro-2-hydroxypropyl) trimethylammonium chloride dropwise to the mixture in step (1), three The mass ratio of methylammonium chloride to the mixture in step (1) is 1.0:1.0, the temperature is increased to 80°C, and stirred for 8h;

(3) adjusting the pH of the reaction mixture in step (2) with a 15% dilute HCl solution to keep the pH neutral;

(4) The reaction product was collected by filtration: the mixture in step (3) was washed several times with methanol and ethanol in turn, and the wet quaternary ammonium functionalized chitosan product was dried under vacuum at 90 ° C for 24 h. Ammonium functionalized chitosan;

(5) Mix MOF (UIO-66-NH ₂ ) and analytically pure isopropanol solution in a mass ratio of 1.5:20, heat to 80° C. in a water bath, add 60% (3-chloro-2- Hydroxypropyl) trimethyl ammonium chloride was added dropwise to the mixture of MOF and isopropanol, and the mass ratio of (3-chloro-2-hydroxypropyl) trimethyl ammonium chloride to the mixture of MOF and isopropanol was 1.0 : 1.0, and use 30%-50% sodium hydroxide aqueous solution to keep the pH neutral, and stir for 8h;

(6) The reaction product was collected by filtration: the reaction product of step (5) was washed several times with ethanol and distilled water in turn, and the wet quaternized product was the dry quaternized MOF obtained after drying under vacuum conditions of 60° C. for 24 h. ;

(7) The quaternary ammonium functionalized chitosan, chitosan and quaternized MOFene powder are uniformly mixed in a mass ratio of 9.0:2.0:2.0 to the mass of quaternary ammonium functionalized chitosan, chitosan and 5% glacial acetic acid by mass of the quaternized MOF powder mixture, sonicated for 1 h;

(8) stirring continuously, adding a 50% glutaraldehyde solution whose mass is 0.05 times the mass of the mixture in step (7) to the mixture in step (7) as a cross-linking agent;

(9) Pour the mixed solution of step (8) into the mold, and after aging for 150 minutes, quickly freeze with liquid nitrogen, and place the frozen sample in a freeze-drying machine for freeze-drying for more than 48 hours to obtain quaternary ammonium-functionalized chitosan mixed with quaternary ammonium. MOF composite aerogel.

In the preparation method of quaternized ammonium functionalized chitosan mixed with quaternized MOF composite aerogel, the deacetylation degree of chitosan described in step (1) is not less than 80%, and steps (1) and (2) The stirring is carried out in a constant temperature magnetic stirrer.

Decolorization of the juice is carried out as follows:

(1) The sugar juice and quaternary ammonium functionalized chitosan mixed with quaternary ammonium MOF composite aerogel after filtration through a ceramic membrane with a pore size of 50nm are fully mixed in a sugar juice box in a ratio of 300:1 by mass. , the reaction is 1h;

(2) filter and separate the quaternary ammonium functionalized chitosan-doped quaternary ammonium MOF composite aerogel after adsorbing the pigment from the sugar juice to obtain a decolorized clear juice;

(3) after the decolorized clear juice is evaporated and concentrated and boiled and crystallized, white granulated sugar is obtained;

(4) The quaternary ammonium functionalized chitosan mixed with quaternary ammonium MOF composite aerogel after adsorbing the pigment was soaked in 0.1 mol/L sodium hydroxide solution for 2 h and saturated saline for 12 h, and then soaked with distilled water. Wash until neutral and recycle.

In Example 3, there was no significant difference in the sucrose content of sugar juice before and after adsorption treatment with quaternary ammonium functionalized chitosan mixed with quaternized MOF composite aerogel, indicating that the chitosan-based adsorbent would not adsorb sugar juice It can be seen from Figure 1 that after the sugar juice is treated with chitosan adsorbent, its color value can be greatly reduced to meet the needs of national first-class white sugar production.

It should be noted that in the above examples, the isopropanol solution adopts an analytically pure concentration, and the purpose is to swell chitosan, which does not mean that it can only be implemented when the isopropanol is analytically pure.

Claims (7)

1. a decolorization method of sugar juice, is characterized in that, sugar juice is mixed with quaternary ammonium functionalized chitosan mixed with quaternized MOF composite aerogel, after fully stirring, carry out filtration separation, obtain decolorized sugar juice. 2. the decolorization method of sugar juice according to claim 1 is characterized in that, the preparation of described quaternary ammonium functionalized chitosan mixed with quaternized ammonium MOF composite aerogel comprises the following steps: (1) Swelling chitosan: chitosan, sodium hydroxide aqueous solution with a concentration of 30% to 50% and analytically pure isopropanol solution are 1.0-1.5:2-5:12-20 by mass ratio Mix the ratio evenly, heat the water bath to 40℃～60℃, and stir for 200min～300min; (2) Introducing quaternary ammonium groups into chitosan chains by nucleophilic substitution reaction: adding 60% (3-chloro-2-hydroxypropyl)trimethylammonium chloride dropwise to the mixture of step (1), The mass ratio of the mixture of trimethylammonium chloride and step (1) is 0.1～1.0:1, the temperature is increased to 60°C～80°C, and stirred for 6～8h; (3) adjusting the pH of the reaction mixture in step (2) with a 5%-15% dilute HCl solution to keep the pH neutral; (4) The reaction product was collected by filtration: the mixture in step (3) was washed with methanol and ethanol in turn, and the wet quaternary ammonium functionalized chitosan product was dried under vacuum at 70°C to 90°C for 24 hours. Quaternary ammonium functionalized chitosan; (5) The MOF and isopropanol solution are uniformly mixed according to the mass ratio of MOF to analytically pure isopropanol solution in a ratio of 1.0～1.5:12～20, heated to 60 ℃～80 ℃ in a water bath, and 60% (3 - Chloro-2-hydroxypropyl)trimethylammonium chloride was added dropwise to the mixture of MOF and isopropanol, (3-chloro-2-hydroxypropyl)trimethylammonium chloride with MOF and isopropanol The mass ratio of the mixture is 0.1-1.0:1, and the pH is kept neutral with 30%-50% aqueous sodium hydroxide solution, and stirred for 6-8h; (6) The reaction product is collected by filtration: the reaction product of step (5) is washed with ethanol and distilled water for several times in turn, and the wet quaternized product is the dry quaternary ammonium product obtained after drying under vacuum conditions at 40°C to 60°C for 24 hours. Ammonized MOF; (7) Mix quaternary ammonium functionalized chitosan, chitosan and quaternized MOF powder uniformly in a mass ratio of 7.0～9.0:0.5～2.0:0.5～2.0 until the mass is quaternary ammonium functionalized chitosan , chitosan and quaternized MOF powder mixture mass 4% ~ 5% glacial acetic acid, ultrasonic for 1h; (8) stirring continuously, adding a 50% glutaraldehyde solution whose mass is 0.01 to 0.05 times the mass of the mixture in step (7) as a cross-linking agent into the mixture in step (7); (9) Pour the mixed solution in step (8) into the mold, and then rapidly freeze with liquid nitrogen after aging for 120 to 150 minutes, and place the frozen sample in a freeze-drying machine for more than 48 hours to obtain quaternary ammonium-functionalized chitosan mixed with quaternary ammonium Ammonized MOF composite aerogel. 3. The method for decolorizing sugar juice according to claim 2, wherein the MOF is UIO-66-NH ₂ . 4. the decolorization method of sugar juice according to claim 1 is characterized in that, described sugar juice and quaternary ammonium functionalized chitosan mixed with quaternized MOF composite aerogel are 50:1～500 by mass ratio :1 for mixing. 5. the decolorization method of sugar juice according to claim 1, is characterized in that, described sugar juice is the sugar juice after ceramic membrane filtration. 6 . The method for decolorizing sugar juice according to claim 5 , wherein the pore size of the ceramic membrane is 5-50 nm. 7 . 7. The decolorization method of sugar juice according to claim 1, is characterized in that, the time of described stirring is 1～2h.

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