Synthesis method of chloride-free hydroxypropyl starch ether

Abstract

The invention discloses a synthesis method of chloride-free hydroxypropyl starch ether, and belongs to the technical field of chemical synthesis and application. Comprising the following steps: mixing sodium hydroxide, organic alcohol and a catalyst, and adding potato starch for alkalization; adding propylene oxide for reaction, and after the reaction is finished, carrying out reduced pressure distillation on the reaction product to obtain a hydroxypropyl starch ether crude product; the catalyst is a barium-doped molybdenum disulfide loaded carbon nanotube catalyst, and is prepared by the following steps: taking thiourea and ammonium molybdate tetrahydrate as precursors, doping and modifying by barium metal ions, loading on a carbon nanotube carrier, and synthesizing by a hydrothermal method. Molybdenum disulfide loaded aluminum oxide doped Ba is used as the catalyst, so that the conversion rate of reactants is effectively increased, the content of residual epoxypropane is reduced, side reactions are inhibited, the selectivity of the product is improved, meanwhile, the catalyst has excellent stability and can be repeatedly used in industrial production, and the cost is remarkably reduced.

Description

Technical Field

[0001] This invention belongs to the field of chemical synthesis and application technology, specifically relating to a method for synthesizing chlorine-free hydroxypropyl starch ether. Background Technology

[0002] In the synthesis of starch ethers, hydroxyl etherifying agents are one of the core raw materials determining product performance. Taking hydroxypropyl starch ether as an example, it is a derivative produced by the etherification reaction of natural starch with an etherifying agent (such as propylene oxide) under alkaline conditions. It belongs to the nonionic starch ether category and is widely used in the construction, food, and pharmaceutical industries. In building materials, hydroxypropyl starch ether, as a functional additive, can significantly improve the material's adhesion and water retention properties. The reaction characteristics of the etherifying agent directly affect the degree of substitution of functional groups on the starch molecule, thus determining the solubility, stability, and other functional properties of the final product.

[0003] However, existing hydroxyl etherifying agents still suffer from numerous technical drawbacks in industrial applications. For example, traditional etherifying agents such as propylene oxide have limited reactivity, resulting in low etherification efficiency and prolonged production cycles. Their reaction selectivity is also low, making them prone to side reactions, which not only reduce yield but also introduce impurities, affecting product purity and application stability. Furthermore, existing processes generally rely heavily on solvents as reaction media, increasing raw material and energy costs, as well as the burden of solvent recovery and environmental remediation. These factors collectively drive up the overall production cost of starch ethers, hindering their competitiveness in the mass market. Summary of the Invention

[0004] To overcome the aforementioned technical problems in the existing technology, this invention provides a method for synthesizing chlorine-free hydroxypropyl starch ether. This invention uses a barium-doped molybdenum disulfide-supported carbon nanotube composite material as a catalyst, which significantly improves the reaction rate, effectively reduces the content of residual propylene oxide, and suppresses side reactions, thereby improving the selectivity and purity of the product. Furthermore, this catalyst exhibits excellent stability and can be repeatedly used in industrial production, significantly reducing production costs.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] In one aspect, this invention provides a method for synthesizing chlorine-free hydroxypropyl starch ether, comprising the following steps:

[0007] (1) Add sodium hydroxide and organic alcohol to the reaction vessel, stir and mix evenly at 30~40℃, then add catalyst and continue stirring;

[0008] (2) Add potato starch to the reaction vessel while stirring continuously, keep the temperature at 40~50℃, continue stirring, and alkalize for 0.5~1 hours;

[0009] (3) Add propylene oxide to the reaction vessel and stir the reaction at 40~50℃ for 6~10 hours. After the reaction is completed, the reaction product is subjected to vacuum distillation to obtain crude hydroxypropyl starch ether.

[0010] The catalyst is a barium-doped molybdenum disulfide supported carbon nanotube catalyst, which is prepared by a method including the following steps: using thiourea and ammonium molybdate tetrahydrate as precursors, after modification by barium metal ion doping, they are loaded onto a carbon nanotube support and synthesized by a hydrothermal method to obtain the catalyst.

[0011] As a further aspect of the present invention: in step (1), the organic alcohol is selected from at least one of ethanol, propanol, isopropanol or butanol;

[0012] And / or, in step (1), the mass ratio of sodium hydroxide to organic alcohol is 1.5 to 4:15.

[0013] As a further embodiment of the present invention: in step (2), the mass ratio of sodium hydroxide to potato starch is 1:10~17;

[0014] And / or, in step (2), the mass ratio of the catalyst to potato starch is 10~15:1000.

[0015] As a further aspect of the present invention: in step (3), the mass ratio of propylene oxide to potato starch is 1:20~30.

[0016] As a further aspect of the present invention, the method for preparing the catalyst specifically includes the following steps:

[0017] S1. Dissolve anhydrous barium sulfate in distilled water, add ethylenediaminetetraacetic acid, polyvinylpyrrolidone K-300, hydrazine hydrate and ammonia, stir and react in a 60℃ water bath for 2-3 hours, then add alumina, react for 2-3 hours, and then wash and dry to obtain barium-doped carbon nanotube composite material.

[0018] S2. Thiourea and ammonium molybdate tetrahydrate are dissolved in distilled water, added to the barium-doped carbon nanotube composite material, ultrasonically dispersed, and then transferred to a reaction vessel. The mixture is subjected to hydrothermal reaction at 170-200℃ for 36-48 hours. After cooling to room temperature, the mixture is washed and dried to obtain the barium-doped molybdenum disulfide supported carbon nanotube catalyst.

[0019] As a further embodiment of the present invention: in step S1, the mass ratio of anhydrous barium sulfate to aluminum oxide is 2~3:5;

[0020] And / or, in step S1, the mass ratio of ethylenediaminetetraacetic acid, polyvinylpyrrolidone K-300, hydrazine hydrate and ammonia is 1:0.6~0.75:40~50:50~55;

[0021] And / or, in step S1, the mass ratio of anhydrous barium sulfate to ethylenediaminetetraacetic acid is 4~5:1;

[0022] And / or, in step S1, the solvent used for washing is distilled water and anhydrous ethanol;

[0023] And / or, in step S1, the drying is carried out at 60~80°C. o Perform C for 8-10 hours.

[0024] As a further embodiment of the present invention: in step S2, the mass ratio of the thiourea, ammonium molybdate tetrahydrate and barium-doped carbon nanotube composite material is 1:0.4~0.7:0.3~0.4;

[0025] And / or, in step S2, the ultrasound duration is 5-10 minutes;

[0026] And / or, in step S2, the solvent used for washing is distilled water and anhydrous ethanol;

[0027] And / or, in step S2, the drying is carried out at 60~80°C. o Perform C for 8-10 hours.

[0028] As a further aspect of the present invention: after step (3), the method further includes:

[0029] The crude hydroxypropyl starch ether was purified by extraction with ethanol or acetone and crystallization to obtain the chlorine-free hydroxypropyl starch ether.

[0030] The beneficial effects of this invention are as follows:

[0031] (1) This invention significantly improves the efficiency of etherification reaction by optimizing reaction conditions and using barium-doped molybdenum disulfide supported carbon nanotubes as catalysts, specifically by shortening the reaction time and increasing the reaction yield. Simultaneously, this method exhibits excellent selectivity, effectively suppressing side reactions and thus improving the purity of the target product, hydroxypropyl starch ether.

[0032] (2) The hydroxypropyl starch ether product obtained by the method of the present invention has higher hydroxypropyl content, viscosity and solution transparency, while its ash content is significantly reduced. In addition, the preparation method is simple, has low production cost, is environmentally friendly, and is very suitable for industrial production. Detailed Implementation

[0033] The present invention is further illustrated below by way of examples, but these examples do not limit the invention to the scope of the embodiments described. Experimental methods in the following examples, unless otherwise specified, were performed according to conventional methods and conditions, or as selected in the product instructions. Furthermore, all reagents and raw materials used in this invention are commercially available.

[0034] Example 1

[0035] A method for synthesizing chlorine-free hydroxypropyl starch ether specifically includes the following steps:

[0036] (1) Dissolve 2g of anhydrous barium sulfate in 50g of distilled water and stir well. Add 0.48g of ethylenediaminetetraacetic acid, 0.32g of polyvinylpyrrolidone K-300, 20.4g of hydrazine hydrate and 25.1g of ammonia water to the above solution and stir at 60°C. o The reaction mixture was stirred in a water bath at C for 2 hours. Then, 5 g of alumina was added to the reacted solution and the reaction was continued for another 2 hours. The reacted solution was then removed and washed 8 times each with distilled water and anhydrous ethanol. The washed sample was then dried in a vacuum drying oven at 70°C for 9 hours to obtain the barium-doped carbon nanotube composite material Ba@CNTs.

[0037] (2) Dissolve 1.3g thiourea and 0.6g ammonium molybdate tetrahydrate in 50g distilled water, add the prepared 0.5g Ba@CNTs to the solution, sonicate in an ultrasonic cleaner for 5min, stir until completely dissolved, transfer to a reaction vessel, and dry in an oven at 170°C. o Heating at C for 36 hours, cooling to room temperature and removing, washing 8 times with triple-distilled water and anhydrous ethanol by centrifugation, and drying in a vacuum drying oven at 60°C for 8 hours, yielded a barium-doped molybdenum disulfide supported carbon nanotube catalyst.

[0038] (3) Mixing reaction: Add 6g of sodium hydroxide and 45g of ethanol to the reaction vessel and stir and mix evenly at 30°C. Then add 1g of barium-doped molybdenum disulfide supported carbon nanotube catalyst and continue stirring. Add 85g of potato starch to the reaction vessel while stirring continuously. Keep the temperature at 40°C and continue stirring to alkalize for 1 hour. Add 4g of propylene oxide to the reaction vessel and keep the temperature at 40°C. Stir and react for 6 hours.

[0039] (4) Separation and purification: After the reaction is completed, the reaction product is subjected to vacuum distillation to remove unreacted raw materials and low-boiling-point impurities to obtain crude hydroxypropyl starch ether. The crude hydroxypropyl starch ether is then further purified by acetone extraction and crystallization to obtain a high-purity hydroxypropyl starch ether product.

[0040] Example 2

[0041] A method for synthesizing chlorine-free hydroxypropyl starch ether specifically includes the following steps:

[0042] (1) Dissolve 2g of anhydrous barium sulfate in 50g of distilled water and stir until homogeneous. Add 0.48g of ethylenediaminetetraacetic acid, 0.32g of polyvinylpyrrolidone K-300, 20.4g of hydrazine hydrate and 25.1g of ammonia to the above solution and stir at 60°C. o The reaction mixture was stirred in a water bath at temperature C for 2 hours. Then, 5 g of alumina was added to the resulting solution and the reaction was continued for 3 hours. The resulting solution was then removed and washed 8 times each with distilled water and anhydrous ethanol. The washed sample was then placed in a vacuum drying oven at 70°C. o After drying at C for 9 hours, barium-doped carbon nanotube composite material Ba@CNTs was obtained.

[0043] (2) Dissolve 1.3g thiourea and 0.6g ammonium molybdate tetrahydrate in 50g distilled water, add the prepared 0.5g Ba@CNTs to the solution, sonicate in an ultrasonic cleaner for 10min, stir until completely dissolved, transfer to a reaction vessel, and dry in an oven at 190°C. o Heat at 40°C for 48 hours, cool to room temperature, remove, wash 8 times with triple-distilled water and anhydrous ethanol by centrifugation, and place in a vacuum drying oven at 70°C. o Drying at C for 8 hours yields a barium-doped molybdenum disulfide supported carbon nanotube catalyst.

[0044] (3) Mixing reaction: Add 6g of sodium hydroxide and 45g of propanol to the reaction vessel and stir and mix evenly at 35°C. Then add 1g of barium-doped molybdenum disulfide supported carbon nanotube catalyst and continue stirring. Add 85g of potato starch to the reaction vessel while stirring continuously. Keep the temperature at 40°C and continue stirring to alkalize for 1 hour. Add 4g of propylene oxide to the reaction vessel and keep the temperature at 40°C. Stir and react for 6 hours.

[0045] (4) Separation and purification: After the reaction is completed, the reaction product is subjected to vacuum distillation to remove unreacted raw materials and low-boiling-point impurities to obtain crude hydroxypropyl starch ether. The crude hydroxypropyl starch ether is then further purified by ethanol extraction, crystallization and other methods to obtain high-purity hydroxypropyl starch ether product.

[0046] Example 3

[0047] A method for synthesizing chlorine-free hydroxypropyl starch ether specifically includes the following steps:

[0048] (1) Dissolve 2g of anhydrous barium sulfate in 50g of distilled water and stir well. Add 0.48g of ethylenediaminetetraacetic acid, 0.32g of polyvinylpyrrolidone K-300, 20.4g of hydrazine hydrate and 25.1g of ammonia water to the above solution and stir at 60°C. o The reaction mixture was stirred in a water bath at temperature C for 2 hours. Then, 5 g of alumina was added to the resulting solution and the reaction was continued for 3 hours. The resulting solution was then removed and washed 8 times each with distilled water and anhydrous ethanol. The washed sample was then placed in a vacuum drying oven at 70°C. oAfter drying at C for 9 hours, barium-doped carbon nanotube composite material Ba@CNTs was obtained.

[0049] (2) Dissolve 1.3g thiourea and 0.6g ammonium molybdate tetrahydrate in 50g distilled water, add the prepared 0.5g Ba@CNTs to the solution, sonicate in an ultrasonic cleaner for 10min, stir until completely dissolved, transfer to a reaction vessel, and dry in an oven at 180°C. o Heat at 42°C for 42 hours, cool to room temperature, remove, wash 8 times with triple-distilled water and anhydrous ethanol by centrifugation, and place in a vacuum drying oven at 80°C. o Drying at C for 10 h yields a barium-doped molybdenum disulfide supported carbon nanotube catalyst.

[0050] (3) Mixing reaction: Add 6g of sodium hydroxide and 45g of isopropanol to the reaction vessel and stir and mix evenly at 40°C. Then add 1g of barium-doped molybdenum disulfide supported carbon nanotube catalyst and continue stirring. Add 85g of potato starch to the reaction vessel while stirring continuously. Keep the temperature at 40°C and continue stirring to alkalize for 1 hour. Add 4g of propylene oxide to the reaction vessel and keep the temperature at 40°C. Stir and react for 6 hours.

[0051] (4) Separation and purification: After the reaction is completed, the reaction product is subjected to vacuum distillation to remove unreacted raw materials and low-boiling-point impurities to obtain crude hydroxypropyl starch ether. The crude hydroxypropyl starch ether is then further purified by ethanol extraction, crystallization and other methods to obtain high-purity hydroxypropyl starch ether product.

[0052] Comparative Example 1

[0053] Add 300 mL of deionized water to a stirred reactor, turn on the stirrer, and slowly add 85 g of potato starch. Stir for 20-30 minutes until the starch is completely dispersed. Let stand for 10 minutes, then add 10% NaOH solution dropwise while stirring to alkalize for 1 hour. Raise the temperature of the starch slurry to 35°C, and slowly add propylene oxide dropwise while maintaining the temperature at 35°C. Stir the reaction for 6 hours, then slowly add acid. After demulsification and sedimentation, wash repeatedly to remove residual alkali and salt.

[0054] Comparative Example 2

[0055] The only difference from Example 1 is that steps (1) and (2) are omitted, and no catalyst is added in step (3).

[0056] Comparative Example 3

[0057] The only difference from Example 1 is that in step (1), the mass ratio of alumina is 2.5g and the mass ratio of anhydrous barium sulfate to alumina is 4:5.

[0058] Comparative Example 4

[0059] The only difference from Example 1 is that in step (2), the mass of ammonium molybdate tetrahydrate is 1.2g and the mass of barium-doped carbon nanotube composite material is 0.2g. At this time, the mass ratio of thiourea, ammonium molybdate tetrahydrate and barium-doped carbon nanotube composite material is 1:0.9:0.15.

[0060] Comparative Example 5

[0061] The only difference from Example 1 is that in step (2), the hydrothermal reaction temperature is 160°C and the reaction time is 30 hours.

[0062] Comparative Example 6

[0063] The only difference from Example 1 is that in step (3), the mass of sodium hydroxide is 11g.

[0064] Effect Example

[0065] The performance of samples from Examples 1-3 and Comparative Examples 1-6 was tested using the following methods or standards:

[0066] I. Light transmittance (2% aqueous solution), tested according to GB / T34263-2017;

[0067] II. Viscosity (5% aqueous solution, test temperature 20℃) shall be tested in accordance with GB / T22427.7-2023;

[0068] III. Hydroxypropyl content shall be tested in accordance with GB / T40998-2021;

[0069] IV. Moisture content (oven drying method) shall be tested in accordance with GB / T12087-2008;

[0070] V. Ash content (carbonized by heating in a platinum crucible, dried by calcination in a muffle furnace, and weighed) shall be tested in accordance with GB / T 22427.1-2008;

[0071] VI. Propylene oxide shall conform to GB / T16080-2009;

[0072] 7. pH shall be determined by potentiometric method.

[0073] The samples from Examples 1-3 and Comparative Examples 1-6 were tested, and the results are shown in Table 1.

[0074] Table 1

[0075] name Hydroxypropyl content / % Moisture / % Ash content / % Transmittance (2% aqueous solution) / % Viscosity (5% aqueous solution at 20℃) / mPa·s pH value Residual propylene oxide (ppm) Example 1 28.5 8.3 13.2 14 14000 10.5 50.37 Example 2 31.2 7.8 12.1 16 14500 10.7 67.25 Example 3 33.9 7.3 11.8 17 14500 10.6 34.54 Comparative Example 1 21.8 8.6 13.6 11 12800 10.3 200.89 Comparative Example 2 24.36 8.9 13.9 12 13900 10.4 123.78 Comparative Example 3 25.31 8.8 13.6 11 13700 10.5 98.65 Comparative Example 4 25.45 8.5 13.4 12 14100 10.6 93.23 Comparative Example 5 25.67 8.6 13.8 11 14000 10.6 89.67 Comparative Example 6 25.61 8.3 13.4 13 13900 10.5 88.23

[0076] As shown in Table 1, the hydroxypropyl starch ethers prepared in Examples 1-3 of this invention exhibit superior performance in terms of hydroxypropyl content, transmittance, and viscosity. Among them, Example 3 achieves the best performance in key indicators such as hydroxypropyl content, moisture and ash content, transmittance, and workability. Furthermore, its catalyst exhibits only a 1.21% mass loss after more than 360 hours of use, demonstrating excellent stability, making it the best example in terms of overall performance.

[0077] Finally, it should be noted that in this invention, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus.

[0078] Although this disclosure has been described above through specific embodiments, it should be understood that those skilled in the art can devise various modifications, improvements, or equivalents to this disclosure within the spirit and scope of the appended solutions. Such modifications, improvements, or equivalents should also be considered to be included within the scope of protection claimed in this disclosure.

Claims

1. A method for synthesizing chlorine-free hydroxypropyl starch ether, characterized in that, Includes the following steps: (1) Add sodium hydroxide and organic alcohol to the reaction vessel, stir and mix evenly at 30~40℃, then add catalyst and continue stirring; (2) Add potato starch to the reaction vessel while stirring continuously, keep the temperature at 40~50℃, continue stirring, and alkalize for 0.5~1 hours; (3) Add propylene oxide to the reaction vessel and stir the reaction at 40~50℃ for 6~10 hours. After the reaction is completed, the reaction product is subjected to vacuum distillation to obtain crude hydroxypropyl starch ether. The catalyst is a barium-doped molybdenum disulfide supported carbon nanotube catalyst, which is prepared by a method including the following steps: using thiourea and ammonium molybdate tetrahydrate as precursors, after modification by barium metal ion doping, they are loaded onto a carbon nanotube support and synthesized by a hydrothermal method to obtain the catalyst.

2. The method for synthesizing chlorine-free hydroxypropyl starch ether according to claim 1, characterized in that, In step (1), the organic alcohol is selected from at least one of ethanol, propanol, isopropanol or butanol; And / or, in step (1), the mass ratio of sodium hydroxide to organic alcohol is 1.5 to 4:

15.

3. The method for synthesizing chlorine-free hydroxypropyl starch ether according to claim 1, characterized in that, In step (2), the mass ratio of sodium hydroxide to potato starch is 1:10~17; And / or, in step (2), the mass ratio of the catalyst to potato starch is 10~15:1000.

4. The method for synthesizing chlorine-free hydroxypropyl starch ether according to claim 1, characterized in that, In step (3), the mass ratio of propylene oxide to potato starch is 1:20~30.

5. The method for synthesizing chlorine-free hydroxypropyl starch ether according to claim 1, characterized in that, The preparation method of the catalyst specifically includes the following steps: S1. Dissolve anhydrous barium sulfate in distilled water, add ethylenediaminetetraacetic acid, polyvinylpyrrolidone K-300, hydrazine hydrate and ammonia, stir and react in a 60℃ water bath for 2-3 hours, then add alumina, react for 2-3 hours, and then wash and dry to obtain barium-doped carbon nanotube composite material. S2. Thiourea and ammonium molybdate tetrahydrate are dissolved in distilled water, added to the barium-doped carbon nanotube composite material, ultrasonically dispersed, and then transferred to a reaction vessel. The mixture is subjected to hydrothermal reaction at 170-200℃ for 36-48 hours. After cooling to room temperature, the mixture is washed and dried to obtain the barium-doped molybdenum disulfide supported carbon nanotube catalyst.

6. The method for synthesizing chlorine-free hydroxypropyl starch ether according to claim 5, characterized in that, In step S1, the mass ratio of anhydrous barium sulfate to aluminum oxide is 2~3:5; And / or, in step S1, the mass ratio of ethylenediaminetetraacetic acid, polyvinylpyrrolidone K-300, hydrazine hydrate and ammonia is 1:0.6~0.75:40~50:50~55; And / or, in step S1, the mass ratio of anhydrous barium sulfate to ethylenediaminetetraacetic acid is 4~5:1; And / or, in step S1, the solvent used for washing is distilled water and anhydrous ethanol; And / or, in step S1, the drying is carried out at 60~80°C. o Perform C for 8-10 hours.

7. The method for synthesizing chlorine-free hydroxypropyl starch ether according to claim 5, characterized in that, In step S2, the mass ratio of the thiourea, ammonium molybdate tetrahydrate, and barium-doped carbon nanotube composite material is 1:0.4~0.7:0.3~0.4; And / or, in step S2, the ultrasound duration is 5-10 minutes; And / or, in step S2, the solvent used for washing is distilled water and anhydrous ethanol; And / or, in step S2, the drying is carried out at 60~80°C. o Perform C for 8-10 hours.

8. The method for synthesizing chlorine-free hydroxypropyl starch ether according to claim 1, characterized in that, After step (3), the method further includes: The crude hydroxypropyl starch ether was purified by extraction with ethanol or acetone and crystallization to obtain the chlorine-free hydroxypropyl starch ether.