Modified activated carbon and its preparation method and application
By introducing polyhydroxy functional groups on the surface of activated carbon and adsorbing triglycerides, the problem that conventional activated carbon is difficult to remove trace dioxins in natural vitamin E is solved, and a highly efficient dioxin adsorption effect is achieved.
Patent Information
- Application Number
- CN202510918780.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2025-07-04
- Publication Date
- 2025-09-30
- Estimated Expiration
- 2045-07-04
AI Technical Summary
Conventional activated carbon is difficult to effectively remove trace dioxins from natural vitamin E.
Through the initial modification and re-modification steps, polyhydroxy functional groups are introduced on the surface of activated carbon, and triglycerides (such as hydrogenated cocoyl glyceride and tripalmitin glyceride) are adsorbed to enhance the adsorption capacity of dioxins.
The adsorption efficiency of activated carbon on dioxins was significantly improved, reducing its relative content to below 2ppb.
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Abstract
Description
Technical Field
[0001] The present application relates to the field of modified adsorption materials, and specifically to a modified activated carbon and its preparation method and application. Background Art
[0002] Vitamin E (VE) is a major antioxidant, soluble in organic solvents like ethanol but insoluble in water. Natural vitamin E is typically isolated and extracted from deodorized distillate (DD oil). Due to the diverse raw material composition, trace amounts of contaminants remain, particularly dioxins. Dioxins are not a single substance, but rather two broad categories of organic compounds with similar structures and properties, encompassing numerous congeners or isomers. Dioxins encompass 210 compounds. These substances are extremely stable, have high melting points, are extremely insoluble in water, and readily accumulate in organisms, posing a serious threat to humans.
[0003] Activated carbon is a common adsorption material that has a good adsorption effect on dioxins. However, dioxins are present in very small amounts in natural vitamin E, making their removal difficult. Summary of the Invention
[0004] To address the difficulty of conventional activated carbon in removing trace dioxins from natural vitamin E, this application provides a modified activated carbon, its preparation method, and its application. Through primary and secondary modification steps, the modified activated carbon introduces a large number of hydroxyl groups onto its surface, and a certain amount of triglycerides (hydrogenated cocoyl glyceride and tripalmitin) are adsorbed on the surface of the activated carbon. Through the coordinated action of hydroxyl groups and triglycerides, the modified activated carbon can effectively adsorb trace dioxins from natural vitamin E.
[0005] In a first aspect, the present application provides a method for preparing modified activated carbon, which adopts the following technical solution:
[0006] A method for preparing modified activated carbon comprises the following steps:
[0007] Primary modification: Add activated carbon to sodium hydroxide solution, heat to 160-190℃ for hydrothermal reaction, then wash and dry to obtain primary modified activated carbon;
[0008] Re-modification: heating the triglyceride until it melts, then immersing the primary modified activated carbon into the triglyceride and stirring, and then centrifuging to obtain the modified activated carbon;
[0009] The triglyceride includes at least one of hydrogenated cocoyl glyceride and tripalmitin glyceride.
[0010] By employing this technical solution, the activated carbon surface was successfully modified through a hydrothermal reaction with sodium hydroxide solution, introducing polyhydroxyl functional groups. These hydroxyl functional groups not only increase the polarity of the activated carbon surface but also provide binding sites for subsequent triglyceride adsorption. Hydrogen bonds are formed between the polyhydroxyl groups on the primary modified activated carbon and the ester groups of triglycerides. This interaction enables triglycerides to be firmly adsorbed on the activated carbon surface. Triglycerides are highly effective in adsorbing lipophilic pollutants such as dioxins.
[0011] Because hydrogenated cocoyl glyceride and tripalmitin are triglycerides formed from long-chain fatty acids, compared to triglycerides formed from short-chain fatty acids, the primary modified activated carbon still has a large number of residual hydroxyl groups. These hydroxyl groups can interact with dioxin molecules, further enhancing the activated carbon's adsorption capacity for dioxins. At the same time, the presence of triglycerides also promotes the diffusion and adsorption of dioxins on the activated carbon surface.
[0012] Through the initial modification and re-modification steps, the functional groups and structure of the activated carbon surface are optimized in this application, so that it can fully adsorb triglycerides (hydrogenated coconut oil glyceride and tripalmitin glyceride) while leaving more hydroxyl groups, significantly improving the adsorption efficiency of pollutants such as dioxins.
[0013] Preferably, in the initial modification step, the concentration of the sodium hydroxide solution is 2.5-3.5 mol / L.
[0014] If the concentration of the sodium hydroxide solution is too low, the surface modification effect on the activated carbon may be insufficient. Specifically, low-concentration sodium hydroxide solutions may not effectively introduce a sufficient number of hydroxyl functional groups onto the activated carbon surface, thereby affecting the subsequent adsorption of triglycerides and dioxin removal.
[0015] High-concentration sodium hydroxide solutions are highly corrosive and may damage the pore structure of activated carbon, leading to a decrease in its specific surface area and adsorption performance. Specifically, high-concentration alkali solutions may partially destroy the pore structure of the activated carbon surface, causing internal pores to collapse and become interconnected, thereby reducing its adsorption capacity.
[0016] Preferably, in the initial modification step, the ratio between the mass of the activated carbon and the volume of the sodium hydroxide solution is 1 g: (8-10) mL.
[0017] If the ratio is too low, meaning the volume of the sodium hydroxide solution is too small, the contact area between the activated carbon and the solution will be reduced. This can lead to uneven surface modification of the activated carbon, with some areas failing to fully react with the sodium hydroxide, thus affecting the overall modification effect. If the ratio is too high, meaning the volume of the sodium hydroxide solution is excessive, resources will be wasted. Excessive sodium hydroxide solution not only increases the cost of raw materials but also increases the complexity and energy consumption of subsequent processing (such as washing and drying).
[0018] Preferably, in the initial modification step, the reaction time of the hydrothermal reaction is 6-8 hours.
[0019] If the hydrothermal reaction time is too short, the activated carbon may not react fully with the sodium hydroxide solution, resulting in incomplete functionalization of the activated carbon surface. This will directly affect the subsequent adsorption of triglycerides and dioxin removal. Excessively long hydrothermal reaction times may lead to an over-crowding of functional groups on the activated carbon surface, which in turn reduces its adsorption performance. Furthermore, excessive functionalization may also cause structural damage to the activated carbon, such as pore collapse.
[0020] Preferably, in the re-modification step, the centrifugal speed is 1000-2000 rpm.
[0021] When using the above technical solution, if the centrifugal speed is too low, the activated carbon adsorbed with triglycerides may not be effectively separated from the triglycerides. This will cause a large amount of triglycerides to remain in the pores of the activated carbon, reducing its adsorption efficiency and use effect.
[0022] Excessively high centrifugal rates may cause some triglycerides to fall off the surface of the activated carbon and be centrifuged out along with excess triglycerides. This not only reduces the utilization rate of triglycerides, but may also affect the modified effect of the activated carbon.
[0023] In a second aspect, the present application provides a modified activated carbon, which adopts the following technical solution:
[0024] A modified activated carbon is prepared by the above-mentioned modified activated carbon preparation method.
[0025] In a third aspect, the present application provides an application of modified activated carbon, which adopts the following technical solution:
[0026] An application of modified activated carbon is the application of the modified activated carbon in adsorbing dioxins.
[0027] Preferably, the application of the modified activated carbon comprises the following steps: dissolving crude VE in ethanol, adding modified activated carbon, heating and stirring, and then filtering and drying to obtain fine VE, wherein the heating temperature is 40-70°C.
[0028] By employing the above technical solution, ethanol, as an organic solvent, exhibits excellent solubility for crude VE. After the initial and secondary modification steps, the surface of the modified activated carbon is enriched with polyhydroxyl functional groups and adsorbed with triglycerides (including hydrogenated cocoyl glyceride and tripalmitin). These triglycerides have low solubility in ethanol, allowing them to remain stable on the modified activated carbon and not be easily dissolved by ethanol. Due to the low solubility of triglycerides in ethanol, their presence on the modified activated carbon has little impact on its adsorption of dioxins.
[0029] Because the melting point of hydrogenated coco-glyceride is 30-34°C and that of tripalmitin is 66°C, limiting the heating temperature to 40-70°C ensures that the hydrogenated coco-glyceride or tripalmitin on the modified activated carbon is in a molten or nearly molten state during use, providing better adsorption of dioxins in crude VE, thereby ensuring the modified activated carbon's adsorption effect on dioxins.
[0030] In summary, this application has the following beneficial effects:
[0031] Through the initial modification and re-modification steps, the functional groups and structure of the activated carbon surface are optimized in this application, so that it can fully adsorb triglycerides (hydrogenated coconut oil glyceride and tripalmitin glyceride) while leaving more hydroxyl groups, significantly improving the adsorption efficiency of pollutants such as dioxins. DETAILED DESCRIPTION
[0032] The raw materials in this application include the following parts:
[0033] Activated carbon: A commercially available product with CAS number 64365-11-3 is used. The average particle size of the activated carbon can be between 20 and 150 μm. This application only uses activated carbon with an average particle size of 40 μm as an example;
[0034] Hydrogenated cocoglyceryl: a commercially available product with CAS number 91744-42-2;
[0035] Tripalmitin: a commercial product with CAS number 555-44-2 was used;
[0036] The present application is further described in detail below with reference to the following examples and comparative examples.
[0037] Example 1
[0038] A method for preparing modified activated carbon comprises the following steps:
[0039] Primary modification: 100 g of activated carbon (average particle size of 40 μm) was washed and dried, then added to 1000 mL of 3 mol / L sodium hydroxide solution in a polytetrafluoroethylene tank. The polytetrafluoroethylene tank was then placed in a stainless steel autoclave and heated to 170 ° C for hydrothermal reaction for 7 h. The activated carbon was then washed with deionized water until neutral and vacuum dried to obtain the primary modified activated carbon.
[0040] Re-modification: Heat 400 g of hydrogenated cocoyl glyceride until melted, immerse the primary modified activated carbon into the melted hydrogenated cocoyl glyceride and stir. After 1 hour, centrifuge the primary modified activated carbon immersed in hydrogenated cocoyl glyceride for 5 minutes at a centrifugal speed of 1500 rpm to obtain modified activated carbon.
[0041] An application of modified activated carbon comprises the following steps: dissolving 200 g of crude VE (the dioxin content is 2132 ppb relative to the crude VE content) in 800 mL of ethanol, adding 10 g of modified activated carbon, heating and stirring at a rate of 300 rpm for 1 hour at a heating temperature of 40°C, filtering out the modified activated carbon, and vacuum drying to obtain fine VE.
[0042] Example 2
[0043] Example 2 Based on the preparation method of Example 1, 400g of hydrogenated cocoglyceryl was replaced with 400g of tripalmitin, and the heating temperature during the application was changed to 70°C.
[0044] Comparative Examples 1-4
[0045] Comparative Example 1: Based on the preparation method of Example 1, the activated carbon was directly immersed in 400 g of hydrogenated cocoglyceride without initial modification, and the other conditions remained unchanged.
[0046] Comparative Example 2: Based on the application of Example 1, 10 g of primary modified activated carbon was added to the crude VE solution, and the other conditions remained unchanged.
[0047] Comparative Example 3 Based on the preparation method of Example 1, 400g of hydrogenated cocoglyceryl was replaced with 400g of triacetin, and the other conditions remained unchanged.
[0048] Comparative Example 4 Based on the preparation method of Example 1, 400g of hydrogenated cocoglyceryl was replaced with 400g of tributyrin, and the other conditions remained unchanged.
[0049] Performance testing
[0050] The following performance tests were performed on Examples 1-2 and Comparative Examples 1-4. The test results are shown in Table 1.
[0051] The content of dioxins in fine VE relative to fine VE was determined according to HJ 77.1-2008 "Determination of dioxins in water by isotope dilution high-resolution gas chromatography-high-resolution mass spectrometry".
[0052] Table 1 Performance test table of Examples 1-2 and Comparative Examples 1-4
[0053]
[0054] Referring to Table 1, by comparing Examples 1-2 and Comparative Examples 1-4, it can be seen that the modified activated carbon prepared through the primary modification and secondary modification steps can fully adsorb dioxins in crude VE, reducing its relative content to below 2 ppb.
[0055] Compared to Example 1 and Comparative Example 1, the hydrothermal reaction with sodium hydroxide solution successfully modified the activated carbon surface, introducing polyhydroxyl functional groups. These hydroxyl functional groups not only increased the polarity of the activated carbon surface but also provided binding sites for subsequent adsorption of hydrogenated cocoyl glycerol, allowing the activated carbon to adsorb more hydrogenated cocoyl glycerol, thereby adsorbing lipophilic pollutants such as dioxins. Furthermore, the hydroxyl groups themselves can interact with dioxin molecules, further enhancing the activated carbon's adsorption capacity for dioxins.
[0056] Compared with Example 1 and Comparative Example 2, it can be seen that the primary modified activated carbon with polyhydroxyl groups can only adsorb part of the dioxins, indicating that the adsorption capacity of hydroxyl groups is not as good as that of hydrogenated cocoglyceryl.
[0057] Compared with Example 1 and Comparative Examples 3-4, it can be seen that since triacetin and tributyrin are easily soluble in ethanol, when the modified activated carbon of Comparative Examples 3-4 is placed in an ethanol solution of crude VE, the hydroxyl groups on the modified activated carbon compete with ethanol for triacetin and tributyrin, causing some triacetin and tributyrin to dissolve in the ethanol solution, thereby reducing the adsorption effect of the modified activated carbon on dioxins.
[0058] In comparison, Example 1 performs better than Example 2, possibly because when the temperature is too high, the molecular thermal motion intensifies, which may cause the pore structure of the activated carbon to reduce its ability to capture pollutants. Therefore, Example 1 is preferred.
[0059] Examples 3-4
[0060] In Example 3-4, based on the preparation method of Example 1, the reaction temperature of the hydrothermal reaction was adjusted. The specific adjustments are shown in Table 2.
[0061] Comparative Examples 5-6
[0062] Comparative Examples 5-6 Based on the preparation method of Example 1, the reaction temperature of the hydrothermal reaction was adjusted. The specific adjustments are shown in Table 2.
[0063] The relative content of dioxins in the fine VE of Examples 3-4 and Comparative Examples 5-6 was subjected to the above performance test. The test results are shown in Table 2.
[0064] Table 2 Reaction temperature and performance test table of hydrothermal reaction of Example 1, Examples 3-4 and Comparative Examples 5-6
[0065]
[0066] As shown in Table 2, a comparison of Example 1, Examples 3-4, and Comparative Examples 5-6 reveals that as the hydrothermal reaction temperature increases, the relative dioxin content in the refined VE decreases and then increases. Maintaining the hydrothermal reaction temperature between 160°C and 190°C allows for more effective modification of the activated carbon. This is likely due to the fact that increasing the hydrothermal reaction temperature gradually increases the amount of hydroxyl groups on the activated carbon surface, improving its adsorption performance. However, exceeding a certain reaction temperature range can disrupt the activated carbon's pore structure, such as causing pore collapse or penetration, thereby reducing its specific surface area and adsorption performance.
[0067] Examples 5-8
[0068] In Examples 5-8, based on the preparation method of Example 1, the concentration of the sodium hydroxide solution was adjusted, and the specific adjustments are shown in Table 3.
[0069] The relative content of dioxins in the fine VE of Examples 5-8 was tested for performance, and the test results are shown in Table 3.
[0070] Table 3 Concentration and performance test table of sodium hydroxide solution of Example 1 and Examples 5-8
[0071]
[0072] As shown in Table 3, a comparison of Example 1 and Examples 5-8 reveals that as the concentration of the sodium hydroxide solution increases, the relative dioxin content in the refined VE decreases and then increases. This is likely due to the gradual introduction of hydroxyl groups onto the activated carbon surface as the sodium hydroxide solution concentration increases, improving the activated carbon's adsorption performance. When the reaction temperature exceeds a certain range, the activated carbon's pore structure may be damaged, such as pore collapse or penetration, thereby reducing its specific surface area and adsorption performance.
[0073] Examples 9-12
[0074] In Examples 9-12, based on the preparation method of Example 1, the amount of sodium hydroxide solution added was adjusted, and the specific adjustments are shown in Table 4.
[0075] The relative content of dioxins in the fine VE of Examples 9-12 was subjected to the above performance test, and the test results are shown in Table 4.
[0076] Table 4 Addition amount of sodium hydroxide solution of embodiment 1 and embodiment 9-12 and performance test table
[0077]
[0078] Referring to Table 4, by comparing Example 1 with Examples 9-12, it can be seen that as the amount of sodium hydroxide solution added continues to increase, the relative content of dioxins in the fine VE shows a trend of gradually increasing and then tending to a stable state. This may be because as the concentration of the sodium hydroxide solution continues to increase, the surface modification of the activated carbon gradually becomes uniform, thereby improving the adsorption performance of the activated carbon.
[0079] Examples 13-16
[0080] In Examples 13-16, based on the preparation method of Example 1, the time of the hydrothermal reaction was adjusted. The specific adjustments are shown in Table 5.
[0081] The relative content of dioxins in the fine VE of Examples 13-16 was subjected to the above performance test, and the test results are shown in Table 5.
[0082] Table 5 Hydrothermal reaction time and performance test table of Example 1 and Examples 13-16
[0083]
[0084] As shown in Table 5, a comparison of Example 1 and Examples 13-16 reveals that the relative dioxin content in the refined VE decreases and then increases with increasing hydrothermal reaction time. This is likely due to the fact that increasing hydrothermal reaction time gradually increases the amount of hydroxyl groups on the activated carbon surface, improving the adsorption performance of the activated carbon. When the reaction temperature exceeds a certain range, the functional groups on the activated carbon surface may become overly dense, which in turn may damage the pore structure of the activated carbon, such as causing pore collapse or penetration, thereby reducing its specific surface area and adsorption performance.
[0085] Examples 17-20
[0086] In Examples 17-20, based on the preparation method of Example 1, the centrifugal rate was adjusted. The specific adjustments are shown in Table 6.
[0087] The relative content of dioxins in the fine VE of Examples 17-20 was subjected to the above performance test, and the test results are shown in Table 6.
[0088] Table 6 Centrifugal rate and performance test table of Example 1 and Examples 17-20
[0089]
[0090] Referring to Table 6, a comparison of Example 1 and Examples 17-20 shows that as the centrifugal rate continues to rise, the relative content of dioxins in the fine VE shows a trend of first decreasing and then increasing. This may be because as the centrifugal rate continues to rise, excess hydrogenated cocoyl glyceride is thrown off as much as possible, making it difficult to block the pores of the activated carbon and improve the adsorption performance of the activated carbon. When the centrifugal rate exceeds a certain range, some hydrogenated cocoyl glyceride may fall off the surface of the activated carbon and be centrifuged out along with the excess hydrogenated cocoyl glyceride. This not only reduces the utilization rate of hydrogenated cocoyl glyceride, but also may affect the modification effect of the activated carbon.
[0091] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.
Claims
1. A method for preparing modified activated carbon for adsorbing dioxins, characterized in that: The following steps are involved: Primary modification: Add activated carbon to a sodium hydroxide solution with a concentration of 2.5-3.5 mol / L, heat to 160-190°C for hydrothermal reaction for 6-8 hours, then wash and dry to obtain primary modified activated carbon; The ratio between the mass of the activated carbon and the volume of the sodium hydroxide solution is 1 g: (8-10) mL; Re-modification: heating the triglyceride until it melts, then immersing the primary modified activated carbon into the triglyceride and stirring, and then centrifuging to obtain the modified activated carbon; The triglyceride comprises at least one of hydrogenated coconut oil glyceride and tripalmitin glyceride; In the re-modification step, the centrifugal speed is 1000-2000 rpm.
2. A modified activated carbon, characterized in that: The modified activated carbon is prepared by the preparation method of claim 1.
3. The use of modified activated carbon in adsorbing dioxins according to claim 2, characterized in that: The following steps are involved: The crude VE is dissolved in ethanol, modified activated carbon is added, heated and stirred, and then filtered and dried to obtain fine VE, wherein the heating temperature is 40-70°C.