Method for efficiently preparing oxidized starch
By preparing a supported TEMPO catalyst, the problems of recycling and environmental impact in the preparation of oxidized starch under the TEMPO catalytic system were solved, the yield and catalytic efficiency of oxidized starch were improved, and efficient preparation of oxidized starch was achieved.
Patent Information
- Application Number
- CN202511645771.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-11
- Publication Date
- 2026-02-10
AI Technical Summary
The preparation of oxidized starch under the TEMPO catalytic system in the existing technology has the problem of being difficult to recycle, and the use of oxidant will have a negative impact on the environment. At the same time, the yield and catalytic efficiency of oxidized starch are not good.
A supported TEMPO catalyst was prepared by using polyethylene glycol-encapsulated magnetic particles, calcium adsorption, acyl chloride, composite loading, and other methods. The process involved controlling crystal growth and surface hydroxylation through polyethylene glycol encapsulation of the magnetic particles, adsorbing calcium ions to form a calcium layer on the particle surface, introducing acyl chloride groups through acyl chloride, and bonding the composite oxidized starch with a 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxy radical. During loading, sodium bromide was used to fix the catalyst onto the magnetic particle surface. During the oxidation reaction, a calcium hydroxide layer was formed under alkaline conditions, thus fixing the composite oxidized starch and sodium bromide and improving catalytic efficiency.
This method achieves efficient preparation of oxidized starch, improves the yield of oxidized starch, solves the problem of the difficulty in recycling TEMPO, enhances catalytic efficiency, maintains high levels of carboxyl content and yield in oxidized starch, and retains good performance even after five applications.
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Abstract
Description
Technical Field
[0001] This invention relates to the field of oxidized starch preparation technology, and specifically to a method for efficiently preparing oxidized starch. Background Technology
[0002] Starch is a natural, renewable, and biodegradable carbohydrate formed by plants through photosynthesis. It is abundant and inexpensive. However, native starch has drawbacks such as insolubility in water, poor shear resistance, poor water resistance, and poor melt flowability, thus limiting its further application. The hydroxyl groups in starch provide active groups that facilitate grafting reactions, allowing for the improvement of starch properties through modification techniques such as oxidation, esterification, and etherification. Starch is now widely used in papermaking, textiles, pharmaceuticals, and construction.
[0003] Oxidation, an important method for starch modification, involves oxidizing the hydroxyl groups at the C-2, C-3, and C-6 positions of starch molecules into carbonyl and carboxyl groups. Simultaneously, it breaks some glycosidic bonds in the starch molecule, causing a certain degree of molecular degradation. Oxidation can improve the whiteness of starch, lower its gelatinization temperature, increase its transparency, enhance its adhesiveness, reduce its paste viscosity, and improve its film-forming properties. During starch oxidation, the reaction mainly occurs in the non-crystalline regions of the starch granules. The degree of oxidation depends primarily on the crystallinity and degree of polymerization of the starch. The size and shape of the starch granules affect the adhesion of the oxidized starch. The type of oxidant and the oxidation conditions also influence the performance of the oxidized starch to some extent. Commonly used oxidants include hydrogen peroxide, sodium hypochlorite, ozone, chlorine dioxide, potassium permanganate, periodate, and dichromate.
[0004] However, as mentioned in the research on the preparation and application of starch oxidation under the TEMPO catalytic system (Cao Jingjing, Master's Thesis, Nanjing Forestry University, June 2010), degradation problems exist during starch oxidation. The main reasons for degradation are as follows: First, when hydrogen peroxide is used as an oxidant, in an alkaline medium, hydrogen peroxide readily releases reactive oxygen species, which oxidize the primary alcohol groups in starch molecules into aldehyde groups, and further oxidize the aldehyde groups into carboxyl groups. At the same time, some glycosidic bonds are broken and degraded, resulting in oxidized starch with a lower degree of polymerization. However, under acidic conditions, when hydrogen peroxide is used as an oxidant, oxidized starch with a lower degree of oxidation will be obtained.
[0005] Second, if the amount of oxidant is too large, the degree of starch oxidation will increase, the starch granular structure will be destroyed, and the amount of starch oxidized and degraded into small molecules will increase. Third, when sodium hypochlorite is used as an oxidant, under strongly alkaline conditions, starch produces negatively charged sodium starch, the amount of which increases with increasing pH. Simultaneously, sodium hypochlorite primarily dissociates into hypochlorite ions, which also carry a negative charge; the repulsive effect between these ions affects the oxidation reaction. Since the oxidant is mainly hypochlorite ions, whose oxidizing power is weaker than that of hypochlorous acid molecules, the rate of the oxidation reaction is slowed down. Furthermore, the increased alkalinity of the reaction medium intensifies the alkaline degradation of starch, leading to a decrease in the yield of oxidized starch.
[0006] To address the aforementioned issues, this paper, "Preparation and Application Research of Starch Oxidation under TEMPO Catalysis System," by Cao Jingjing, published in her Master's Thesis at Nanjing Forestry University in June 2010, further disclosed that the use of a TEMPO co-oxidation system and control of the pH value of the oxidation reaction can reduce starch degradation and increase the yield of oxidized starch.
[0007] However, the following problems exist when preparing oxidized starch using a TEMPO co-oxidation system and controlling the pH value of the oxidation reaction: First, as mentioned in the paper "Preparation of Polyamide-Modified TEMPO and Its Catalytic Oxidation Performance" by Liang Huazhe, a master's thesis published in May 2020 at Hebei University of Science and Technology, TEMPO has the problem of being difficult to recycle.
[0008] Secondly, as discussed in the research on the preparation and application of oxidized starch under TEMPO catalysis (Cao Jingjing, Master's Thesis, Nanjing Forestry University, June 2010), the TEMPO / NaClO / NaBr system in the TEMPO co-oxidation system has a high oxidation yield and is a commonly used method. NaBr can enhance the selectivity of polyol monohydroxyl groups through halogen radical transfer. However, as discussed in the ultrasound-assisted TEMPO catalytic preparation of oxidized starch and its structural and property analysis (Li Xinrui, Master's Thesis, Bohai University, June 2019), the presence of NaBr in waste streams is redundant due to environmental and toxicological issues, meaning that the use of NaBr would have a negative impact on the environment. However, the absence of NaBr would lead to a decrease in the selectivity of the oxidation reaction, further accelerating the degradation of starch.
[0009] To address the aforementioned issues, the most common solution currently is to support TEMPO to prepare supported catalysts. For example, the paper "Preparation and Catalytic Oxidation Performance of Polyamidoamine-Supported TEMPO" by Liang Huazhe, a master's thesis from Hebei University of Science and Technology, published in May 2020, indicates that supported catalysts prepared from inorganic and non-water-soluble organic supports exhibit poor catalytic oxidation effects on polysaccharides when TEMPO is supported. This paper used the magnetic macromolecular catalyst MNPS-Gn PAMAM-T as a catalyst; however, as disclosed in that paper, the macromolecular catalyst suffers from steric hindrance during catalysis, affecting its catalytic efficiency. Summary of the Invention
[0010] To address the shortcomings of existing technologies, this invention provides a method for efficiently preparing oxidized starch, which can achieve efficient preparation of oxidized starch, improve the yield of prepared oxidized starch, and solve the problem of the difficulty in recycling TEMPO in the preparation process.
[0011] To solve the above technical problems, the technical solution adopted by the present invention is as follows: A method for efficiently preparing oxidized starch includes: preparing polyethylene glycol-encapsulated magnetic particles, adsorbing calcium, acyl chloride, compounding, loading, and oxidizing.
[0012] To prepare polyethylene glycol-coated magnetic particles, ferrocene and anhydrous ethanol are mixed and stirred at room temperature for 30-60 min. Sodium acetate and polyethylene glycol 4000 are added, and stirring is continued for another 30-60 min. The mixture is then subjected to a hydrothermal reaction at 200-220℃ for 12-13 h. After cooling to room temperature, the mixture is centrifuged, the precipitate is collected, washed with deionized water and anhydrous ethanol, and dried to obtain polyethylene glycol-coated magnetic particles. In the preparation of polyethylene glycol-coated magnetic particles, the ratio of ferrocene, anhydrous ethanol, sodium acetate, and polyethylene glycol 4000 is 3.72g:1000-1100mL:58-60g:58-62g.
[0013] The calcium adsorption process involves mixing polyethylene glycol-coated magnetic particles, calcium chloride, and anhydrous ethanol, stirring at room temperature for 60-90 minutes, centrifuging, and collecting the precipitate as the magnetic particles after calcium adsorption. In the adsorbed calcium, the ratio of polyethylene glycol-coated magnetic particles, calcium chloride, and anhydrous ethanol is 100g:20-25g:1800-2000mL.
[0014] The acyl chloride process involves mixing oxidized starch and pyridine, stirring under nitrogen protection for 30-40 minutes, adding thionyl chloride and anhydrous N,N-dimethylformamide, stirring and refluxing at 70-75°C for 20-24 hours, filtering, taking the filter cake, washing with deionized water, and drying to obtain acyl chloride oxidized starch. In the acyl chloride process, the ratio of oxidized starch, pyridine, thionyl chloride, and anhydrous N,N-dimethylformamide is 30-32 g: 500-550 mL: 95-105 mL: 1-1.1 mL. The oxidized starch contains 9% carboxyl groups by mass.
[0015] The composite process involves mixing acyl chloride oxidized starch and anhydrous tetrahydrofuran, stirring under nitrogen protection for 30-40 minutes, adding 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxy radical and triethylamine, stirring and refluxing at 60-65°C for 24-26 hours, cooling to room temperature, filtering, taking the filter cake, washing with chloroform, and drying to obtain the composite oxidized starch. In the composite, the ratio of acyl chloride oxidized starch, anhydrous tetrahydrofuran, 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxy radical, and triethylamine is 10-10.5g:200-250mL:1-1.1g:5-5.5mL.
[0016] The loading process involves mixing composite oxidized starch and deionized water, stirring at 80-85℃ for 15-20 minutes, cooling to room temperature, adding the magnetic particles after calcium adsorption, stirring for 3-4 hours, adding sodium bromide, stirring for 1-2 hours, centrifuging, taking the precipitate, washing with deionized water, and drying to obtain the loaded TEMPO. In the loading, the ratio of composite oxidized starch, deionized water, magnetic particles after calcium adsorption, and sodium bromide is 9.8-10g:2000-2200mL:100g:10-12g.
[0017] The oxidation reaction involves mixing corn starch and deionized water, stirring at 80-90℃ for 15-20 min, cooling to room temperature, then adding loaded TEMPO at 0-5℃, and simultaneously adding sodium hypochlorite aqueous solution while maintaining the pH at 9.5-9.7. After the addition is complete, stirring continues for 30-40 min to recover the loaded TEMPO. Then, hydrochloric acid aqueous solution is added dropwise to adjust the pH to neutral, resulting in a reaction solution. All reaction solutions are then added to an ethanol aqueous solution, allowed to stand for 2-2.5 h, filtered, and the filter cake is dried and ground to obtain oxidized starch. In the oxidation reaction, the ratio of corn starch, deionized water, supported TEMPO, and sodium hypochlorite aqueous solution is 44-46g: 1000-1100mL: 2.3-2.5g: 380-400mL. The sodium hypochlorite aqueous solution contains 8% available chlorine by mass. The molar concentration of the sodium hydroxide aqueous solution is 0.5 mol / L; The molar concentration of the hydrochloric acid aqueous solution is 6 mol / L; The mass concentration of the ethanol aqueous solution is 95%; The sodium hypochlorite aqueous solution was added over a period of 50-60 minutes. The pH is controlled to neutral by adding hydrochloric acid solution dropwise over a period of 20-30 minutes. When adding all the reaction mixture to the ethanol aqueous solution, the addition time should be 20-30 minutes. The volume of the ethanol-water solution used is 2-2.2 times the volume of the reaction mixture.
[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The efficient method for preparing oxidized starch of the present invention uses loaded TEMPO in the preparation. In the preparation of loaded TEMPO, the following steps are taken in sequence: preparing polyethylene glycol-coated magnetic particles, calcium adsorption, acyl chloride, composite, and loading. Among them, the preparation of polyethylene glycol-coated magnetic particles is to add polyethylene glycol 4000 when preparing magnetic iron oxide particles. Polyethylene glycol 4000 can control the crystal growth rate and crystal morphology of magnetic iron oxide particles. At the same time, polyethylene glycol 4000 can coat the surface of magnetic iron oxide particles and enrich the hydroxyl groups of magnetic iron oxide particles to obtain polyethylene glycol-coated magnetic particles. Calcium adsorption is achieved by utilizing the interaction between calcium ions and hydroxyl groups to adsorb calcium ions onto the surface of magnetic particles. A layer of calcium ions is formed. Acyl chloride is introduced onto the oxidized starch by reacting thionyl chloride with the carboxyl groups of the oxidized starch, resulting in acyl chloride oxidized starch. Composite starch is formed by reacting the acyl chloride groups on the surface of the oxidized starch with the hydroxyl groups of the 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxy radical, thus bonding the oxidized starch to the 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxy radical. Loading is achieved by using the interaction between the hydroxyl groups of the oxidized starch, calcium ions, and polyethylene glycol to fix the composite oxidized starch onto the surface of magnetic particles. Sodium bromide is then added, and its adsorption force from the composite oxidized starch is used to fix the sodium bromide onto the magnetic particle surface, resulting in loaded TEMPO. During the oxidation reaction, because it occurs in an alkaline environment, some calcium ions combine with hydroxide ions to form calcium hydroxide, thus forming a rough surface layer of calcium hydroxide adsorbed on the loaded TEMPO. This further helps to fix the composite oxidized starch and sodium bromide, thereby avoiding the environmental impact of bromide ions. Meanwhile, due to the bonding between oxidized starch and 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxy radical, oxidized starch exhibits good compatibility with corn starch and can form intermolecular forces with corn starch. This further reduces the contact resistance between corn starch and the catalyst, thereby improving the catalytic efficiency of the catalyst. Additionally, calcium hydroxide provides reaction sites. Furthermore, the presence of calcium ions helps prevent the loss of the composite oxidized starch and sodium bromide.
[0019] (2) This invention enables efficient preparation of oxidized starch, improves the yield of the prepared oxidized starch, and solves the problem of the difficulty in recycling TEMPO during the preparation process. The oxidized starch prepared by this invention has a carboxyl content of 9.14-9.38% and a yield of 91.20-92.16%; after applying the loaded TEMPO used in this invention for the 5th time, the oxidized starch prepared has a carboxyl content of 9.05-9.18% and a yield of 91.13-92.10%. Detailed Implementation
[0020] To provide a clearer understanding of the technical features, objectives, and effects of the present invention, specific embodiments of the present invention are now described.
[0021] When testing and calculating the mass content of carboxyl groups in oxidized starch in the examples and comparative examples, the method disclosed in the study on the oxidation of corn starch using the TEMPO / NaBr / NaClO system was used. (Song Lili, Nie Zhaoguang, Li Teng, Zhang Xiaodong, Hu Yanfang. Journal of Qingdao University (Engineering and Technology Edition). December 2013).
[0022] When testing and calculating the yield of oxidized starch in the examples and comparative examples, the method disclosed in "Ultrasonic-Assisted TEMPO Catalysis for the Preparation of Oxidized Starch and Analysis of its Structure and Properties" by Li Xinrui, Master's Thesis, Bohai University, June 2019 was used.
[0023] Example 1 A method for efficiently preparing oxidized starch, specifically: 1. Preparation of polyethylene glycol-coated magnetic particles: 3.72 g of ferrocene and 1000 mL of anhydrous ethanol were added to a reaction vessel. The stirring speed of the reaction vessel was adjusted to 100 rpm and stirred at room temperature for 30 min. 58 g of sodium acetate and 58 g of polyethylene glycol 4000 were added, and stirring was continued for 30 min. The mixture was then transferred to a hydrothermal reactor. After sealing the hydrothermal reactor, it was placed in an oven and the temperature of the oven was adjusted to 200℃. The mixture was allowed to stand for 12 h and then cooled to room temperature. The mixture was then placed in a centrifuge and the centrifugation speed was adjusted to 3000 rpm. The mixture was centrifuged for 10 min. The precipitate was collected and washed three times each with deionized water and anhydrous ethanol, and then dried to obtain polyethylene glycol-coated magnetic particles.
[0024] 2. Calcium adsorption: Add 100g of polyethylene glycol-coated magnetic particles, 20g of calcium chloride, and 1800mL of anhydrous ethanol to a reaction vessel. Adjust the stirring speed of the reaction vessel to 100rpm and stir at room temperature for 60min. Transfer the mixture to a centrifuge and adjust the centrifugation speed to 3000rpm. Centrifuge for 10min and collect the precipitate as the magnetic particles after calcium adsorption.
[0025] 3. Acyl chloride: 30g of oxidized starch and 500mL of pyridine were added to a reactor equipped with a reflux device. Nitrogen gas was continuously introduced into the reactor. The stirring speed of the reactor was adjusted to 100rpm and stirred for 30min. 95mL of thionyl chloride and 1mL of anhydrous N,N-dimethylformamide were added. The temperature of the reactor was adjusted to 70℃. The stirring speed was kept constant and the mixture was stirred and refluxed for 20h. The mixture was filtered, and the filter cake was washed three times with deionized water and dried to obtain acyl chloride oxidized starch. The oxidized starch contains 9% carboxyl groups by mass.
[0026] 4. Compounding: 10g of acyl chloride oxidized starch and 200mL of anhydrous tetrahydrofuran were added to a reactor equipped with a reflux device. Nitrogen gas was continuously introduced into the reactor. The stirring speed of the reactor was adjusted to 100rpm and stirred for 30min. 1g of 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxygen radical (4-OH-TEMPO) and 5mL of triethylamine were added. The temperature of the reactor was adjusted to 60℃, and the stirring speed was kept constant. The mixture was stirred and refluxed for 24h. After cooling to room temperature, the mixture was filtered, and the filter cake was washed three times with chloroform and dried to obtain the compound oxidized starch.
[0027] 5. Loading: Add 9.8g of composite oxidized starch and 2000mL of deionized water to the reactor. Adjust the temperature of the reactor to 80℃ and the stirring speed to 100rpm. Stir for 15min and cool to room temperature. Add 100g of magnetic particles after calcium adsorption and stir for 3h. Add 10g of sodium bromide and stir for 1h. Add to a centrifuge and adjust the centrifugation speed to 3000rpm. Centrifuge for 10min. Take the precipitate, wash it three times with deionized water, and dry it to obtain loaded TEMPO.
[0028] 6. Oxidation reaction: Add 44g of corn starch and 1000mL of deionized water to a reaction vessel. Adjust the temperature of the reaction vessel to 80℃ and the stirring speed to 100rpm. Stir for 15min and cool to room temperature. Transfer the reaction vessel to an ice-water bath and adjust the temperature of the reaction vessel to 1℃. Keep the stirring speed constant. Add 2.3g of loaded TEMPO and add 380mL of sodium hypochlorite aqueous solution dropwise over a time of 50min. During the dropwise addition, add sodium hydroxide aqueous solution dropwise to maintain the pH at 9.5. After the dropwise addition is complete, continue stirring for 30min. Recover the loaded TEMPO with a magnet, wash with deionized water, dry, and reuse. Then, add hydrochloric acid aqueous solution dropwise to the reaction vessel to adjust the pH to neutral over a time of 20min. After the dropwise addition is complete, obtain the reaction solution. Slowly add all the reaction solution to an ethanol aqueous solution with a volume twice that of the reaction solution over a time of 20min. After the addition is complete, let stand for 2h, filter, collect the filter cake, dry, and grind to obtain oxidized starch. The sodium hypochlorite aqueous solution contains 8% available chlorine by mass. The molar concentration of the sodium hydroxide aqueous solution is 0.5 mol / L; The molar concentration of the hydrochloric acid aqueous solution is 6 mol / L; The mass concentration of the ethanol aqueous solution is 95%.
[0029] Example 2 A method for efficiently preparing oxidized starch, specifically: 1. Preparation of polyethylene glycol-coated magnetic particles: 3.72 g of ferrocene and 1050 mL of anhydrous ethanol were added to a reaction vessel. The stirring speed of the reaction vessel was adjusted to 200 rpm, and the mixture was stirred at room temperature for 40 min. 59 g of sodium acetate and 60 g of polyethylene glycol 4000 were added, and the mixture was stirred for another 40 min. The mixture was then transferred to a hydrothermal reactor, sealed, and placed in an oven. The temperature of the oven was adjusted to 210 °C, and the mixture was allowed to stand for 12.5 h. After cooling to room temperature, the mixture was placed in a centrifuge, and the centrifuge speed was adjusted to 3500 rpm. The mixture was centrifuged for 12 min. The precipitate was collected and washed three times each with deionized water and anhydrous ethanol, and then dried to obtain polyethylene glycol-coated magnetic particles.
[0030] 2. Calcium adsorption: Add 100g of polyethylene glycol-coated magnetic particles, 22g of calcium chloride, and 1900mL of anhydrous ethanol to a reaction vessel. Adjust the stirring speed of the reaction vessel to 200rpm and stir at room temperature for 60-90min. Transfer the mixture to a centrifuge and adjust the centrifugation speed to 3500rpm. Centrifuge for 12min and collect the precipitate as the magnetic particles after calcium adsorption.
[0031] 3. Acyl chloride: 31g of oxidized starch and 520mL of pyridine were added to a reactor equipped with a reflux device. Nitrogen gas was continuously introduced into the reactor. The stirring speed of the reactor was adjusted to 200rpm and stirred for 35min. 100mL of thionyl chloride and 1.1mL of anhydrous N,N-dimethylformamide were added. The temperature of the reactor was adjusted to 75℃. The stirring speed was kept constant and the mixture was stirred and refluxed for 22h. The mixture was filtered, and the filter cake was washed 4 times with deionized water and dried to obtain acyl chloride oxidized starch. The oxidized starch contains 9% carboxyl groups by mass.
[0032] 4. Compounding: 10.2g of acyl chloride oxidized starch and 220mL of anhydrous tetrahydrofuran were added to a reactor equipped with a reflux device. Nitrogen gas was continuously introduced into the reactor. The stirring speed of the reactor was adjusted to 200rpm and stirred for 35min. 1g of 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxy radical (4-OH-TEMPO) and 5.2mL of triethylamine were added. The temperature of the reactor was adjusted to 62℃, and the stirring speed was kept constant. The mixture was stirred and refluxed for 25h. After cooling to room temperature, the mixture was filtered, and the filter cake was washed 4 times with chloroform and dried to obtain the compound oxidized starch.
[0033] 5. Loading: Add 9.9g of composite oxidized starch and 2100mL of deionized water to the reactor. Adjust the temperature of the reactor to 82℃ and the stirring speed to 200rpm. Stir for 18min and cool to room temperature. Add 100g of magnetic particles after calcium adsorption and stir for 3.5h. Add 11g of sodium bromide and stir for 1.5h. Add to a centrifuge and centrifuge at 3500rpm for 12min. Take the precipitate, wash it 4 times with deionized water, and dry it to obtain loaded TEMPO.
[0034] 6. Oxidation reaction: Add 45g corn starch and 1050mL deionized water to a reaction vessel. Adjust the temperature of the reaction vessel to 85℃ and the stirring speed to 200rpm. Stir for 17min and cool to room temperature. Transfer the reaction vessel to an ice-water bath and adjust the temperature of the reaction vessel to 3℃. Keep the stirring speed constant. Add 2.4g loaded TEMPO and add 390mL sodium hypochlorite aqueous solution dropwise over a time of 55min. During the dropwise addition, add sodium hydroxide aqueous solution dropwise to maintain the pH at 9.6. After the dropwise addition is complete, continue stirring for 35min. Recover the loaded TEMPO with a magnet, wash with deionized water, dry, and reuse. Then, add hydrochloric acid aqueous solution dropwise to the reaction vessel to adjust the pH to neutral over a time of 25min. After the dropwise addition is complete, obtain the reaction solution. Slowly add all the reaction solution to 2.1 times the volume of the reaction solution in an ethanol aqueous solution over a time of 25min. After the addition is complete, let stand for 2.5h, filter, collect the filter cake, dry, and grind to obtain oxidized starch. The sodium hypochlorite aqueous solution contains 8% available chlorine by mass. The molar concentration of the sodium hydroxide aqueous solution is 0.5 mol / L; The molar concentration of the hydrochloric acid aqueous solution is 6 mol / L; The mass concentration of the ethanol aqueous solution is 95%.
[0035] Example 3 A method for efficiently preparing oxidized starch, specifically: 1. Preparation of polyethylene glycol-coated magnetic particles: 3.72 g of ferrocene and 1100 mL of anhydrous ethanol were added to a reaction vessel. The stirring speed of the reaction vessel was adjusted to 300 rpm, and the mixture was stirred at room temperature for 60 min. 60 g of sodium acetate and 62 g of polyethylene glycol 4000 were added, and the mixture was stirred for another 60 min. The mixture was then transferred to a hydrothermal reactor, sealed, and placed in an oven. The oven temperature was adjusted to 220 °C, and the mixture was allowed to stand for 13 h. After cooling to room temperature, the mixture was placed in a centrifuge, and the centrifuge speed was adjusted to 4000 rpm. The mixture was centrifuged for 15 min. The precipitate was collected and washed four times each with deionized water and anhydrous ethanol, and then dried to obtain polyethylene glycol-coated magnetic particles.
[0036] 2. Calcium adsorption: Add 100g of polyethylene glycol-coated magnetic particles, 25g of calcium chloride, and 2000mL of anhydrous ethanol to a reaction vessel. Adjust the stirring speed of the reaction vessel to 300rpm and stir at room temperature for 90min. Transfer the mixture to a centrifuge and adjust the centrifugation speed to 4000rpm. Centrifuge for 15min and collect the precipitate as the magnetic particles after calcium adsorption.
[0037] 3. Acyl chloride: 32g of oxidized starch and 550mL of pyridine were added to a reactor equipped with a reflux device. Nitrogen gas was continuously introduced into the reactor. The stirring speed of the reactor was adjusted to 300rpm and stirred for 40min. 105mL of thionyl chloride and 1.1mL of anhydrous N,N-dimethylformamide were added. The temperature of the reactor was adjusted to 75℃. The stirring speed was kept constant and the mixture was stirred and refluxed for 24h. The mixture was filtered, and the filter cake was washed 5 times with deionized water and dried to obtain acyl chloride oxidized starch. The oxidized starch contains 9% carboxyl groups by mass.
[0038] 4. Compounding: 10.5g of acyl chloride oxidized starch and 250mL of anhydrous tetrahydrofuran were added to a reactor equipped with a reflux device. Nitrogen gas was continuously introduced into the reactor. The stirring speed of the reactor was adjusted to 300rpm and stirred for 40min. 1.1g of 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxygen radical (4-OH-TEMPO) and 5.5mL of triethylamine were added. The temperature of the reactor was adjusted to 65℃, and the stirring speed was kept constant. The mixture was stirred and refluxed for 26h. After cooling to room temperature, the mixture was filtered, and the filter cake was washed 5 times with chloroform and dried to obtain the compound oxidized starch.
[0039] 5. Loading: Add 10g of composite oxidized starch and 2200mL of deionized water to the reactor. Adjust the temperature of the reactor to 85℃ and the stirring speed to 300rpm. Stir for 20min. Cool to room temperature. Add 100g of magnetic particles after calcium adsorption and stir for 4h. Add 12g of sodium bromide and stir for 2h. Add to a centrifuge and adjust the centrifugation speed to 4000rpm. Centrifuge for 15min. Take the precipitate, wash it 5 times with deionized water, and dry it to obtain loaded TEMPO.
[0040] 6. Oxidation reaction: Add 46g corn starch and 1100mL deionized water to a reaction vessel. Adjust the temperature of the reaction vessel to 90℃ and the stirring speed to 300rpm. Stir for 20min and cool to room temperature. Transfer the reaction vessel to an ice-water bath and adjust the temperature of the reaction vessel to 5℃. Keep the stirring speed constant. Add 2.5g loaded TEMPO and add 400mL sodium hypochlorite aqueous solution dropwise over a time of 60min. During the dropwise addition, add sodium hydroxide aqueous solution dropwise to maintain the pH at 9.7. After the dropwise addition is complete, continue stirring for 40min. Recover the loaded TEMPO with a magnet, wash with deionized water, dry, and reuse. Then, add hydrochloric acid aqueous solution dropwise to the reaction vessel to adjust the pH to neutral over a time of 30min. After the dropwise addition is complete, obtain the reaction solution. Slowly add all the reaction solution to 2.2 times the volume of the reaction solution in an ethanol aqueous solution over a time of 30min. After the addition is complete, let stand for 2.5h, filter, collect the filter cake, dry, and grind to obtain oxidized starch. The sodium hypochlorite aqueous solution contains 8% available chlorine by mass. The molar concentration of the sodium hydroxide aqueous solution is 0.5 mol / L; The molar concentration of the hydrochloric acid aqueous solution is 6 mol / L; The mass concentration of the ethanol aqueous solution is 95%.
[0041] Comparative Example 1 Based on the efficient method for preparing oxidized starch in Example 1, the second step of calcium adsorption is omitted, and the polyethylene glycol-coated magnetic particles prepared in the first step of preparing polyethylene glycol-coated magnetic particles are directly used in the fourth step of the composite process.
[0042] Comparative Example 2 Based on the efficient method for preparing oxidized starch in Example 1, the third step of acyl chloride and the fourth step of compounding are omitted, and 0.89 g of 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxy radical is used to replace the addition of compound oxidized starch in the fifth step of loading.
[0043] Test Example 1 The mass content and yield of carboxyl groups in the oxidized starch prepared in Examples 1-3 and Comparative Examples 1-2 were statistically analyzed, and the results are as follows:
[0044] The results above show that, compared with Example 1, the oxidized starch prepared in Comparative Examples 1-2 has the problems of low carboxyl content and low yield.
[0045] Test Example 2 Following the preparation methods of loaded TEMPO in Examples 1-3 and Comparative Examples 1-2, loaded TEMPO was prepared. Then, oxidized starch was prepared according to the oxidation reaction steps in Examples 1-3 and Comparative Examples 1-2, respectively. The loaded TEMPO was then recovered, processed, and reused. On the fifth reuse, the mass content of carboxyl groups and the yield of the prepared oxidized starch were statistically analyzed. The statistical results are as follows:
[0046] The results above show that, compared with Example 1, the oxidized starch prepared by applying the loaded TEMPO prepared in Comparative Examples 1-2 has a serious problem of reduced carboxyl content and yield.
Claims
1. A method for efficiently preparing oxidized starch, characterized in that, include: Preparation of polyethylene glycol-encapsulated magnetic particles, adsorption of calcium, acyl chloride, composite, loading, and oxidation reactions; To prepare polyethylene glycol-coated magnetic particles, ferrocene and anhydrous ethanol are mixed and stirred at room temperature. Sodium acetate and polyethylene glycol 4000 are added and stirred. The mixture is then subjected to a hydrothermal reaction at 200-220°C for 12-13 hours. After cooling to room temperature, the mixture is centrifuged, the precipitate is collected, washed, and dried to obtain polyethylene glycol-coated magnetic particles. The adsorbed calcium is obtained by mixing polyethylene glycol-coated magnetic particles, calcium chloride, and anhydrous ethanol, stirring at room temperature, centrifuging, and taking the precipitate as the magnetic particles after calcium adsorption. The acyl chloride process involves mixing oxidized starch and pyridine, stirring under nitrogen protection, adding thionyl chloride and anhydrous N,N-dimethylformamide, stirring and refluxing at 70-75°C, filtering, taking the filter cake, washing, and drying to obtain acyl-chlorinated oxidized starch. The composite process involves mixing acyl chloride oxidized starch and anhydrous tetrahydrofuran, stirring under nitrogen protection, adding 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxy free radical and triethylamine, stirring and refluxing at 60-65°C, cooling to room temperature, filtering, taking the filter cake, washing, and drying to obtain the composite oxidized starch. The loading process involves mixing composite oxidized starch and deionized water, stirring at 80-85°C, cooling to room temperature, adding the magnetic particles that have adsorbed calcium, stirring, adding sodium bromide, stirring again, centrifuging, collecting the precipitate, washing, and drying to obtain the loaded TEMPO.
2. The method for efficiently preparing oxidized starch according to claim 1, characterized in that, In the preparation of polyethylene glycol-coated magnetic particles, the ratio of ferrocene, anhydrous ethanol, sodium acetate, and polyethylene glycol 4000 is 3.72g:1000-1100mL:58-60g:58-62g.
3. The method for efficiently preparing oxidized starch according to claim 1, characterized in that, In the adsorbed calcium, the ratio of polyethylene glycol-coated magnetic particles, calcium chloride, and anhydrous ethanol is 100g:20-25g:1800-2000mL.
4. The method for efficiently preparing oxidized starch according to claim 1, characterized in that, In the acyl chloride process, the ratio of oxidized starch, pyridine, thionyl chloride, and anhydrous N,N-dimethylformamide is 30-32 g: 500-550 mL: 95-105 mL: 1-1.1 mL. The oxidized starch contains 9% carboxyl groups by mass.
5. The method for efficiently preparing oxidized starch according to claim 1, characterized in that, In the composite, the ratio of acyl chloride oxidized starch, anhydrous tetrahydrofuran, 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxy radical, and triethylamine is 10-10.5g:200-250mL:1-1.1g:5-5.5mL.
6. The method for efficiently preparing oxidized starch according to claim 1, characterized in that, In the loading, the ratio of composite oxidized starch, deionized water, magnetic particles after calcium adsorption, and sodium bromide is 9.8-10g:2000-2200mL:100g:10-12g.
7. The method for efficiently preparing oxidized starch according to claim 1, characterized in that, The oxidation reaction involves mixing corn starch and deionized water, stirring at 80-90°C, cooling to room temperature, adding loaded TEMPO at 0-5°C, and then adding sodium hypochlorite aqueous solution dropwise while maintaining the pH at 9.5-9.
7. After the addition is complete, stirring continues for 30-40 minutes to recover the loaded TEMPO. The pH is then adjusted to neutral, and the reaction solution is obtained after the addition is complete. All the reaction solution is added to an ethanol aqueous solution, allowed to stand, filtered, and the filter cake is collected, dried, and ground to obtain oxidized starch.
8. The method for efficiently preparing oxidized starch according to claim 7, characterized in that, In the oxidation reaction, the ratio of corn starch, deionized water, supported TEMPO, and sodium hypochlorite aqueous solution is 44-46g:1000-1100mL:2.3-2.5g:380-400mL.
9. The method for efficiently preparing oxidized starch according to claim 7, characterized in that, In the oxidation reaction, the available chlorine content in the sodium hypochlorite aqueous solution is 8% by mass. The molar concentration of the sodium hydroxide aqueous solution is 0.5 mol / L; The molar concentration of the hydrochloric acid aqueous solution is 6 mol / L; The mass concentration of the ethanol aqueous solution is 95%; The sodium hypochlorite aqueous solution was added over a period of 50-60 minutes. The pH is controlled to neutral by adding hydrochloric acid solution dropwise over a period of 20-30 minutes. When adding all the reaction mixture to the ethanol aqueous solution, the addition time should be 20-30 minutes. The volume of the ethanol-water solution used is 2-2.2 times the volume of the reaction mixture.