CN114736993A - Method for decoloring sugar juice - Google Patents
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- CN114736993A CN114736993A CN202210385081.6A CN202210385081A CN114736993A CN 114736993 A CN114736993 A CN 114736993A CN 202210385081 A CN202210385081 A CN 202210385081A CN 114736993 A CN114736993 A CN 114736993A
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Abstract
The invention discloses a sugar juice decoloring method, which is characterized in that quaternary ammonium functionalized chitosan doped quaternary ammonium fluoride (MOF) composite aerogel is uniformly mixed with sugar juice to adsorb sugar juice pigment. The quaternary ammonium functionalized chitosan doped quaternary ammonium metal-organic framework (MOF) composite aerogel is prepared by mixing chitosan and Metal Organic Framework (MOF) (UIO-66-NH)2) The chitosan quaternary ammonium salt is prepared by taking 50% of glutaraldehyde as a cross-linking agent and doping quaternized MOF through a cross-linking method, and then, amino groups on a chitosan molecular chain are grafted with quaternary ammonium groups. According to the invention, chitosan is used as a raw material to prepare the decolorizing agent for chitosan-based aerogel sugar, the problem that the pore structure of the aerogel is easy to collapse after the chitosan is quaternized is solved by adding quaternized MOF, so that the decolorizing agent for chitosan-based aerogel sugar has rich pore diameter structure and is coupled with a membrane method green sugar making process, the technical problem that the color value of finished white granulated sugar is higher due to the fact that small molecular pigments in sugar juice cannot be intercepted by the membrane separation technology is solved, and the whole sugar making process is greened.
Description
Technical Field
The invention belongs to the technical field of sugar manufacturing engineering, and particularly relates to a method for decoloring sugar juice.
Background
Sugar is a daily necessity, and in the production of refined white granulated sugar (high-end sugar product), the decolorization of sugar juice is the most critical process. At present, the sugar juice decolorizing resin is a strong base type macroporous anion exchange resin mainly synthesized by taking styrene and divinylbenzene as matrixes. Styrene and divinylbenzene are both derived from petroleum, their raw materials are not renewable, and they are classified as class 2B carcinogens by the international agency for research on cancer. Obviously, the resin is used for purifying the sugar, which becomes a potential safety hazard of the sugar. Therefore, the development of the chitosan-based decolorant which is green, nontoxic and good in performance and can be regenerated has important research and industrial application significance.
Chitosan as a natural degradable high molecular polysaccharide belongs to cationic basic polysaccharide, and has a content second to cellulose in nature. The chitosan is cheap and easy to obtain, non-toxic and harmless, and good in biocompatibility, and the chitosan-based material is widely applied to the fields of water treatment, polyphenol adsorption, heavy metal adsorption and the like. The amino and hydroxyl reactive groups in the chitosan molecule are easy to introduce targeting functional groups, thereby effectively adsorbing the sugar juice pigment. Metal organic frameworks (MOF, UIO-66-NH)2) Contains a large amount of amino groups, is easy to protonate in aqueous solution and has strong positive charges, and on the basis, a targeting functional group (quaternary ammonium group) is introduced to further enhance the content of the positive charges, so that the sugar juice is easy to have classical interaction with pigment molecules with negative charges. The aerogel attracts much attention because of its low density, large porosity, high specific surface area and other characteristics; in electrochemistry ofThe method is widely applied to the fields of tissue engineering, drug delivery, catalyst carriers and the like. In recent years, aerogels have received attention because of their high adsorption capacity and ultra-fast adsorption rate. Therefore, chitosan-based aerogels have great potential in depigmenting sugar juices. The introduced target functional group (quaternary ammonium salt) is easy to ionize to form an electronegative quaternary ammonium salt ion, and can effectively adsorb electronegative pigments.
Disclosure of Invention
The invention aims to provide a method for decoloring sugar juice, which solves the technical problem that the color value of finished white granulated sugar is higher due to the fact that small molecular pigments in the sugar juice cannot be intercepted by filtering the sugar juice by adopting a membrane separation technology in a membrane-process green sugar making process.
In order to achieve the purpose, the invention adopts the following technical scheme:
a method for decoloring sugar juice comprises the steps of mixing the sugar juice with quaternary ammonium functionalized chitosan doped quaternary ammonium fluoride organic framework (MOF) composite aerogel, fully stirring, and filtering and separating to obtain the decolored sugar juice.
The preparation method of the quaternary ammonium functionalized chitosan doped quaternary ammonium MOF composite aerogel comprises the following steps:
(1) swelling chitosan: uniformly mixing chitosan, a sodium hydroxide aqueous solution with the concentration of 30-50% and an analytically pure isopropanol solution according to the mass ratio of 1.0-1.5: 2-5: 12-20, heating to 40-60 ℃ in a water bath, and stirring for 200-300 min;
(2) introduction of quaternary ammonium groups into chitosan chains by nucleophilic substitution reactions: dropwise adding 60% of (3-chloro-2-hydroxypropyl) trimethyl ammonium chloride into the mixture in the step (1), wherein the mass ratio of trimethyl ammonium chloride to the mixture in the step (1) is 0.1-1.0: 1, the temperature is increased to 60-80 ℃, and stirring is carried out for 6-8 h;
(3) adjusting the pH value of the reaction mixture in the step (2) by using a 5-15% diluted HCl solution, and keeping the pH value neutral;
(4) and (3) filtering and collecting a reaction product: washing the mixture obtained in the step (3) with methanol and ethanol in sequence, and drying the wet quaternary ammonium functionalized chitosan product for 24 hours under the vacuum condition of 70-90 ℃ to obtain dry quaternary ammonium functionalized chitosan;
(5) uniformly mixing an MOF solution and an isopropanol solution according to the mass ratio of the MOF to the analytically pure isopropanol solution of 1.0-1.5: 12-20, heating in a water bath to 60-80 ℃, dropwise adding 60% of (3-chloro-2-hydroxypropyl) trimethyl ammonium chloride into the mixture of the MOF and the isopropanol, keeping the pH value of the mixture of the (3-chloro-2-hydroxypropyl) trimethyl ammonium chloride and the MOF to be neutral with a 30-50% sodium hydroxide aqueous solution, and stirring for 6-8 hours;
(6) and (3) filtering and collecting a reaction product: washing the reaction product in the step (5) with ethanol and distilled water for several times in sequence, and drying the wet quaternized product for 24 hours under the vacuum condition of 40-60 ℃ to obtain dry quaternized MOF;
(7) uniformly mixing quaternary ammonium functionalized chitosan, chitosan and quaternized MOF powder according to the mass ratio of 7.0-9.0: 0.5-2.0 into glacial acetic acid with the mass being 4% -5% of the mass of the mixture of the quaternary ammonium functionalized chitosan, the chitosan and the quaternized MOF powder, and performing ultrasonic treatment for 1 h;
(8) continuously stirring, and adding 50% glutaraldehyde solution with the mass 0.01-0.05 times of the mass of the mixture in the step (7) into the mixture in the step (7) as a cross-linking agent;
(1) and (3) pouring the mixed solution obtained in the step (8) into a mould, aging for 120-150 min, then rapidly freezing with liquid nitrogen, and freeze-drying the frozen sample in a freeze dryer for more than 48h to obtain the quaternary ammonium functionalized chitosan doped quaternary ammonium hydroxide (MOF) composite aerogel.
The MOF is UIO-66-NH2。
The sugar juice and the quaternary ammonium functionalized chitosan doped quaternary ammonium fluoride organic framework (MOF) composite aerogel are mixed according to the mass ratio of 50: 1-500: 1.
The sugar juice is obtained by filtering with ceramic membrane.
The aperture of the ceramic membrane is 5-50 nm.
The stirring time is 1-2 h.
Compared with the prior art, the invention has the following beneficial effects:
(1) the chitosan is a product of natural polysaccharide chitin with partial acetyl removed, and has the advantages of good biodegradability, greenness, nontoxicity and the like.
(2)MOF(UIO-66-NH2) The polysaccharide has rich porous structure, and strong positive charges are carried after quaternary ammonium groups are grafted, so that the sugar juice pigment (most of which have negative charges) can be absorbed. The modified chitosan has increased hydrophilicity after introduction of the quaternary ammonium salt, resulting in collapse of the cellular pore structure during further formation of the chitosan-based aerogel. Therefore, the quaternary ammonium MOF is doped into the quaternary ammonium modified chitosan aerogel, so that the problem of pore structure collapse can be improved, the pore structure of the aerogel can be enriched, and the adsorption effect of the quaternary ammonium functionalized chitosan doped quaternary ammonium MOF composite aerogel is improved.
(3) In the prior art, styrene (divinylbenzene) type anion exchange resins also have a certain adsorption removal effect on pigments in sugar juice. However, both styrene and divinylbenzene have been classified as 2B carcinogens by the world health organization international cancer research institution and are extremely harmful to human bodies. And the styrene and the divinylbenzene are both from petroleum, so that the raw materials can not be regenerated and are difficult to degrade, and the environmental pollution is serious. The method does not use styrene (divinyl benzene) type anion exchange resin, and is nontoxic and environment-friendly.
(4) Compared with the existing amorphous adsorbent, the quaternary ammonium functionalized chitosan doped quaternary ammonium fluoride (MOF) composite aerogel is richer in network structure and more in introduced cations, so that the adsorbent is easy to fully contact with pigments (mostly with negative charges) in sugar juice and generate electrostatic interaction reaction to realize decolorization.
(5) The existing adsorbent (such as activated carbon and the like) is usually an amorphous adsorbent, and after the adsorption reaction is finished, the regeneration is difficult and the energy consumption is high. The adsorbent can elute the pigment from the adsorbent through ion exchange reaction, thereby greatly saving economic cost and being beneficial to sustainable development.
Drawings
FIG. 1 shows the decolorization effect of a quaternary ammonium functionalized chitosan doped quaternized MOF composite aerogel on membrane filtrate.
Detailed Description
The present invention will now be described with reference to examples. Unless otherwise stated, the reagents used in this example were obtained from the commercial source, chitosan, 80% -95% degree of deacetylation, national drug control, GmbH; sodium hydroxide and hydrochloric acid, both of which are analytically pure, Tianjin, Kemiou chemical reagent, Inc.; (3-chloro-2-hydroxypropyl) trimethylammonium chloride, 60% (w/w), analytically pure, avastin reagent (Shanghai) Co., Ltd; glutaraldehyde, 25% (v/v), analytical grade, maocene chemical reagents ltd; isopropanol, analytically pure, maocene chemical reagents ltd; MOF (UIO-66-NH)2) Preparing the required chemical reagents: zirconium chloride, 98% pure, shanghai mclin biochemical technologies ltd; amino terephthalic acid, 98% pure, Shanghai Michelin Biochemical technology, Inc.; n, N-dimethylformamide, 99% pure, national drug stockings ltd; glacial acetic acid, analytically pure, national medicine stock control, ltd.
Example 1
This example is an example of the application of the method of the present invention to the decolorization of sugar juice. The preparation method of the quaternary ammonium functionalized chitosan doped quaternized MOF composite aerogel comprises the following steps:
(1) swelling chitosan: uniformly mixing chitosan, 30% sodium hydroxide aqueous solution and analytically pure isopropanol solution according to the mass ratio of 1.0:2:12, heating to 40 ℃ in a water bath, and stirring the mixture for 200 min;
(2) introduction of quaternary ammonium groups into chitosan chains by nucleophilic substitution reactions: dropwise adding 60% of (3-chloro-2-hydroxypropyl) trimethyl ammonium chloride into the mixture obtained in the step (1), wherein the mass ratio of trimethyl ammonium chloride to the mixture obtained in the step (1) is 0.1:1, raising the temperature to 60 ℃, and stirring for 6 hours;
(3) adjusting the pH of the reaction mixture in the step (2) by using a 5% diluted HCl solution, and keeping the pH neutral;
(4) and (3) filtering and collecting a reaction product: washing the reaction product of the mixture obtained in the step (3) with methanol and ethanol for several times in sequence, and drying the wet quaternary ammonium functionalized chitosan product for 24 hours at 70 ℃ under a vacuum condition to obtain dry quaternary ammonium functionalized chitosan;
(5) reacting MOF (UIO-66-NH)2) Uniformly mixing analytically pure isopropanol solution according to the mass ratio of 1.0:12, heating in a water bath to 60 ℃, dropwise adding 60% of (3-chloro-2-hydroxypropyl) trimethyl ammonium chloride into the mixture of the MOF and the isopropanol, wherein the mass ratio of the (3-chloro-2-hydroxypropyl) trimethyl ammonium chloride to the mixture of the MOF and the isopropanol is 0.1:1, keeping the pH neutral by using 30% sodium hydroxide aqueous solution, and stirring for 6 hours;
(6) and (3) filtering and collecting a reaction product: washing the reaction product obtained in the step (5) with ethanol and distilled water for several times in sequence, and drying the wet quaternized product under vacuum condition of 40 ℃ for 24 hours to obtain dry quaternized MOF;
(7) uniformly mixing quaternary ammonium functionalized chitosan, chitosan and quaternized MOF alkene powder according to the mass ratio of 7.0:0.5:0.5 into glacial acetic acid with the mass being 4% of the mass of the mixture of the quaternary ammonium functionalized chitosan, the chitosan and the quaternized MOF alkene powder, and performing ultrasonic treatment for 1 h;
(8) continuously stirring, and adding 50% glutaraldehyde solution with the mass 0.01 times that of the mixture in the step (7) into the mixture in the step (7) as a cross-linking agent;
(9) and (3) pouring the mixed solution obtained in the step (8) into a mould, aging for 120min, then rapidly freezing by using liquid nitrogen, and freeze-drying the frozen sample in a freeze dryer for more than 48h to obtain the quaternary ammonium functionalized chitosan doped quaternary ammonium hydroxide (MOF) composite aerogel.
In the preparation method of the quaternary ammonium functionalized chitosan doped quaternary ammonium Metal Organic Framework (MOF) composite aerogel, the deacetylation degree of the chitosan in the step (1) is not lower than 80%, and the stirring in the steps (1) and (2) is carried out in a constant-temperature magnetic stirrer.
The decolouration of the sugar juice was carried out as follows:
(1) fully and uniformly mixing sugar juice filtered by a ceramic membrane with the aperture of 5nm and quaternary ammonium functional chitosan doped quaternary ammonium Metal Organic Framework (MOF) composite aerogel according to the mass ratio of 50:1 in a sugar juice box, and reacting for 1 h;
(2) filtering and separating the quaternary ammonium functionalized chitosan doped quaternary ammonium MOF composite aerogel after adsorbing the pigment from the sugar juice to obtain decolorized clear juice;
(3) evaporating, concentrating, boiling and crystallizing the decolored clear juice to obtain white granulated sugar;
(4) soaking the quaternary ammonium functional chitosan doped quaternary ammonium MOF composite aerogel after adsorbing the pigment for 2 hours by adopting 0.1mol/L sodium hydroxide solution and soaking for 12 hours by adopting saturated salt solution, washing the mixture to be neutral by using distilled water, and recycling.
In example 1, before and after the sugar juice is subjected to adsorption treatment by the quaternary ammonium functionalized chitosan doped quaternized MOF composite aerogel, the sucrose content in the sugar juice has no significant difference, which indicates that the chitosan-based adsorbent cannot adsorb sucrose molecules in the sugar juice; as can be seen from figure 1, the color value of the sugar juice can be greatly reduced after the sugar juice is treated by the chitosan adsorbent, so as to meet the requirement of national first-grade white granulated sugar production.
Example 2
This example is another example of the use of the process of the present invention for the decolorization of sugar juice. The preparation method of the quaternary ammonium functionalized chitosan doped quaternary ammonium MOF composite aerogel comprises the following steps:
(1) swelling chitosan: uniformly mixing chitosan, a 40% sodium hydroxide aqueous solution and an analytically pure isopropanol solution according to the mass ratio of 1.2:3:16, heating to 50 ℃ in a water bath, and stirring the mixture for 250 min;
(2) introduction of quaternary ammonium groups into chitosan chains by nucleophilic substitution reactions: dropwise adding 60% of (3-chloro-2-hydroxypropyl) trimethyl ammonium chloride into the mixture in the step (1), wherein the mass ratio of trimethyl ammonium chloride to the mixture in the step (1) is 0.5:1, the temperature is increased to 70 ℃, and stirring is carried out for 7 hours;
(3) adjusting the pH of the reaction mixture in the step (2) by using a 10% diluted HCl solution, and keeping the pH neutral;
(4) and (3) filtering and collecting a reaction product: washing the mixture obtained in the step (3) with methanol and ethanol for several times in sequence, and drying the wet quaternary ammonium functionalized chitosan product for 24 hours at 80 ℃ under a vacuum condition to obtain dry quaternary ammonium functionalized chitosan;
(5) reacting MOF (UIO-66-NH)2) And an analytically pure isopropanol solution are uniformly mixed according to the mass ratio of 1.2:17, heated to 70 ℃ in a water bath, 60 percent of (3-chloro-2-hydroxypropyl) trimethyl ammonium chloride is dripped into the mixture of the MOF and the isopropanol, the mass ratio of the (3-chloro-2-hydroxypropyl) trimethyl ammonium chloride to the mixture of the MOF and the isopropanol is 0.6:1, the pH is kept neutral by 40 percent of sodium hydroxide aqueous solution, and the mixture is stirred for 7 hours;
(6) and (3) filtering and collecting a reaction product: washing the reaction product obtained in the step (5) with ethanol and distilled water for several times in sequence, and drying the wet quaternized product for 24 hours at 50 ℃ under a vacuum condition to obtain dried quaternized MOF;
(7) uniformly mixing quaternary ammonium functionalized chitosan, chitosan and quaternized MOF alkene powder according to the mass ratio of 8.0:1.5:1.5 into glacial acetic acid with the mass being 4.5% of the mass of the mixture of the quaternary ammonium functionalized chitosan, the chitosan and the quaternized MOF alkene powder, and carrying out ultrasonic treatment for 1 h;
(8) continuously stirring, and adding 50% glutaraldehyde solution with the mass being 0.02 time of that of the mixture in the step (7) into the mixture in the step (7) as a cross-linking agent;
(9) and (3) pouring the mixed solution obtained in the step (8) into a mould, aging for 135min, then rapidly freezing by using liquid nitrogen, and freeze-drying the frozen sample in a freeze dryer for more than 48h to obtain the quaternary ammonium functionalized chitosan doped quaternary ammonium hydroxide (MOF) composite aerogel.
In the preparation method of the quaternary ammonium functionalized chitosan doped quaternary ammonium Metal Organic Framework (MOF) composite aerogel, the deacetylation degree of the chitosan in the step (1) is not lower than 80%, and the stirring in the steps (1) and (2) is carried out in a constant-temperature magnetic stirrer.
The decolouration of the sugar juice was carried out as follows:
(1) fully and uniformly mixing sugar juice filtered by a ceramic membrane with the aperture of 50nm and quaternary ammonium functional chitosan doped quaternary ammonium Metal Organic Framework (MOF) composite aerogel according to the mass ratio of 500:1 in a sugar juice box, and reacting for 2 hours;
(2) filtering and separating the quaternary ammonium functionalized chitosan doped quaternary ammonium MOF composite aerogel after adsorbing the pigment from the sugar juice to obtain decolorized clear juice;
(3) evaporating, concentrating, boiling and crystallizing the decolored clear juice to obtain white granulated sugar;
(4) soaking the quaternary ammonium functionalized chitosan doped quaternary ammonium hydroxide (MOF) composite aerogel after adsorbing the pigment for 2 hours by adopting 0.1mol/L sodium hydroxide solution and soaking the quaternary ammonium functionalized chitosan doped quaternary ammonium hydroxide composite aerogel for 12 hours by adopting saturated salt solution, washing the quaternary ammonium functionalized chitosan doped quaternary ammonium hydroxide composite aerogel to be neutral by using distilled water, and recycling the quaternary ammonium functionalized chitosan doped quaternary ammonium hydroxide composite aerogel.
In example 2, before and after the sugar juice is subjected to adsorption treatment by the quaternary ammonium functionalized chitosan doped quaternized MOF composite aerogel, the sucrose content in the sugar juice has no significant difference, which indicates that the chitosan-based adsorbent cannot adsorb sucrose molecules in the sugar juice; as can be seen from figure 1, the color value of the sugar juice can be greatly reduced after the sugar juice is treated by the chitosan adsorbent, so as to meet the requirement of national first-grade white granulated sugar production.
Example 3
This example is a further example of the use of the process of the invention for the decolorization of sugar juice. The preparation method of the quaternary ammonium functionalized chitosan doped quaternary ammonium MOF composite aerogel comprises the following steps:
(1) swelling chitosan: uniformly mixing chitosan, a 50% sodium hydroxide aqueous solution and an analytically pure isopropanol solution according to the mass ratio of 1.5:5:20, heating to 60 ℃ in a water bath, and stirring the mixture for 300 min;
(2) introduction of quaternary ammonium groups into chitosan chains by nucleophilic substitution reactions: dropwise adding 60% of (3-chloro-2-hydroxypropyl) trimethyl ammonium chloride into the mixture in the step (1), wherein the mass ratio of trimethyl ammonium chloride to the mixture in the step (1) is 1.0:1.0, raising the temperature to 80 ℃, and stirring for 8 hours;
(3) adjusting the pH of the reaction mixture in the step (2) by using a 15% diluted HCl solution, and keeping the pH neutral;
(4) and (3) filtering and collecting a reaction product: washing the mixture obtained in the step (3) with methanol and ethanol for several times in sequence, and drying the wet quaternary ammonium functionalized chitosan product for 24 hours at 90 ℃ under a vacuum condition to obtain dry quaternary ammonium functionalized chitosan;
(5) reacting MOF (UIO-66-NH)2) Uniformly mixing analytically pure isopropanol solution according to the mass ratio of 1.5:20, heating in a water bath to 80 ℃, dropwise adding 60% of (3-chloro-2-hydroxypropyl) trimethyl ammonium chloride into the mixture of the MOF and the isopropanol, keeping the pH value of the mixture of the (3-chloro-2-hydroxypropyl) trimethyl ammonium chloride and the mixture of the MOF and the isopropanol at 1.0:1.0, using 30-50% of sodium hydroxide aqueous solution to keep the pH value neutral, and stirring for 8 hours;
(6) and (3) filtering and collecting a reaction product: washing the reaction product obtained in the step (5) with ethanol and distilled water for several times in sequence, and drying the wet quaternized product under a vacuum condition of 60 ℃ for 24 hours to obtain dried quaternized MOF;
(7) uniformly mixing quaternary ammonium functionalized chitosan, chitosan and quaternized MOF alkene powder according to the mass ratio of 9.0:2.0:2.0 into glacial acetic acid with the mass being 5% of the mass of the mixture of the quaternary ammonium functionalized chitosan, the chitosan and the quaternized MOF alkene powder, and performing ultrasonic treatment for 1 h;
(8) continuously stirring, and adding 50% glutaraldehyde solution with the mass 0.05 times that of the mixture in the step (7) into the mixture in the step (7) as a cross-linking agent;
(9) and (3) pouring the mixed solution obtained in the step (8) into a mould, aging for 150min, then rapidly freezing by using liquid nitrogen, and freeze-drying the frozen sample in a freeze dryer for more than 48h to obtain the quaternary ammonium functionalized chitosan doped quaternary ammonium hydroxide (MOF) composite aerogel.
In the preparation method of the quaternary ammonium functionalized chitosan doped quaternary ammonium Metal Organic Framework (MOF) composite aerogel, the deacetylation degree of the chitosan in the step (1) is not lower than 80%, and the stirring in the steps (1) and (2) is carried out in a constant-temperature magnetic stirrer.
The decolouration of the sugar juice was carried out as follows:
(1) fully and uniformly mixing sugar juice filtered by a ceramic membrane with the aperture of 50nm and quaternary ammonium functional chitosan doped quaternary ammonium fluoride (MOF) composite aerogel in a sugar juice box according to the mass ratio of 300:1, and reacting for 1 h;
(2) filtering and separating the quaternary ammonium functionalized chitosan doped quaternary ammonium MOF composite aerogel after adsorbing the pigment from the sugar juice to obtain decolorized clear juice;
(3) evaporating, concentrating, boiling and crystallizing the decolored clear juice to obtain white granulated sugar;
(4) soaking the quaternary ammonium functionalized chitosan doped quaternary ammonium hydroxide (MOF) composite aerogel after adsorbing the pigment for 2 hours by adopting 0.1mol/L sodium hydroxide solution and soaking the quaternary ammonium functionalized chitosan doped quaternary ammonium hydroxide composite aerogel for 12 hours by adopting saturated salt solution, washing the quaternary ammonium functionalized chitosan doped quaternary ammonium hydroxide composite aerogel to be neutral by using distilled water, and recycling the quaternary ammonium functionalized chitosan doped quaternary ammonium hydroxide composite aerogel.
In example 3, before and after the sugar juice is subjected to adsorption treatment by the quaternary ammonium functionalized chitosan doped quaternized MOF composite aerogel, the sucrose content in the sugar juice has no significant difference, which indicates that the chitosan-based adsorbent cannot adsorb sucrose molecules in the sugar juice; as can be seen from figure 1, the color value of the sugar juice can be greatly reduced after the sugar juice is treated by the chitosan adsorbent, so as to meet the requirement of national first-grade white granulated sugar production.
It should be noted that the isopropanol solution used in the above examples was of analytically pure concentration, which is intended to swell the chitosan and is not meant to be implemented only when the isopropanol is analytically pure.
Claims (7)
1. A sugar juice decoloring method is characterized in that sugar juice and quaternary ammonium functionalized chitosan doped quaternary ammonium hydroxide (MOF) composite aerogel are mixed, fully stirred and then filtered and separated to obtain decolored sugar juice.
2. The sugar juice decoloring method according to claim 1, wherein the preparation of the quaternary ammonium functionalized chitosan doped quaternized MOF composite aerogel comprises the following steps:
(1) swelling chitosan: uniformly mixing chitosan, a sodium hydroxide aqueous solution with the concentration of 30-50% and an analytically pure isopropanol solution according to the mass ratio of 1.0-1.5: 2-5: 12-20, heating to 40-60 ℃ in a water bath, and stirring for 200-300 min;
(2) introduction of quaternary ammonium groups into chitosan chains by nucleophilic substitution reactions: dripping 60% of (3-chloro-2-hydroxypropyl) trimethyl ammonium chloride into the mixture in the step (1), wherein the mass ratio of trimethyl ammonium chloride to the mixture in the step (1) is 0.1-1.0: 1, the temperature is increased to 60-80 ℃, and stirring is carried out for 6-8 hours;
(3) adjusting the pH value of the reaction mixture in the step (2) by using a 5-15% diluted HCl solution, and keeping the pH value neutral;
(4) and (3) filtering and collecting a reaction product: washing the mixture obtained in the step (3) with methanol and ethanol in sequence, and drying the wet quaternary ammonium functionalized chitosan product for 24 hours under the vacuum condition of 70-90 ℃ to obtain dry quaternary ammonium functionalized chitosan;
(5) uniformly mixing an MOF solution and an isopropanol solution according to the mass ratio of the MOF to the analytically pure isopropanol solution of 1.0-1.5: 12-20, heating in a water bath to 60-80 ℃, dropwise adding 60% of (3-chloro-2-hydroxypropyl) trimethyl ammonium chloride into the mixture of the MOF and the isopropanol, keeping the pH value of the mixture of the (3-chloro-2-hydroxypropyl) trimethyl ammonium chloride and the MOF to be neutral with a 30-50% sodium hydroxide aqueous solution, and stirring for 6-8 hours;
(6) and (3) filtering and collecting a reaction product: washing the reaction product in the step (5) with ethanol and distilled water for several times in sequence, and drying the wet quaternized product for 24 hours under the vacuum condition of 40-60 ℃ to obtain dry quaternized MOF;
(7) uniformly mixing quaternary ammonium functionalized chitosan, chitosan and quaternized MOF powder according to the mass ratio of 7.0-9.0: 0.5-2.0 into glacial acetic acid with the mass being 4% -5% of the mass of the mixture of the quaternary ammonium functionalized chitosan, the chitosan and the quaternized MOF powder, and performing ultrasonic treatment for 1 h;
(8) continuously stirring, and adding 50% glutaraldehyde solution with the mass 0.01-0.05 time of that of the mixture in the step (7) into the mixture in the step (7) as a cross-linking agent;
(9) and (3) pouring the mixed solution obtained in the step (8) into a mould, aging for 120-150 min, then rapidly freezing with liquid nitrogen, and freeze-drying the frozen sample in a freeze dryer for more than 48h to obtain the quaternary ammonium functionalized chitosan doped quaternary ammonium hydroxide (MOF) composite aerogel.
3. A process for the decolorization of sugar juice according to claim 2 wherein said MOF is UIO-66-NH2。
4. The sugar juice decoloring method according to claim 1, wherein the sugar juice and the quaternary ammonium functionalized chitosan doped quaternary ammonium MOF composite aerogel are mixed according to a mass ratio of 50: 1-500: 1.
5. A process for the decolorization of sugar juice according to claim 1, wherein said sugar juice is filtered by ceramic membranes.
6. A method for decolouring sugar juice according to claim 5, wherein said ceramic membrane has a pore size of 5-50 nm.
7. The method for decoloring sugar juice according to claim 1, wherein the stirring time is 1 to 2 hours.
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