Specific adsorbent for terramycin impurity C and its preparation method

Abstract

This invention relates to the field of materials technology, and more particularly to a specific adsorbent for oxytetracycline impurity C and its preparation method. The specific adsorbent for oxytetracycline impurity C is prepared by covalently grafting a silane coupling agent onto chemically modified biochar, wherein the particle size of the chemically modified biochar is 0.125~0.18 mm. The specific adsorbent for oxytetracycline impurity C prepared by this invention achieves the effect of a solid adsorbent by covalently bridging aminosilane onto biochar. Subsequent filtration can achieve the separation of oxytetracycline from the solid adsorbent. Compared with using free phenylhydrazine, this not only significantly simplifies the process and makes it suitable for industrial application, but also reduces the possibility of free phenylhydrazine contaminating the finished product.

Description

Technical Field

[0001] This invention relates to the field of materials technology, and in particular to a specific adsorbent for oxytetracycline impurity C and its preparation method. Background Technology

[0002] 2-Acetyl-2-deamidooxytetracycline (oxytetracycline impurity C) is a commensal impurity produced during the fermentation of oxytetracycline, accounting for approximately 2%. As early as 1982, oxytetracycline impurity C was chemically identified, and its biological activity was determined using 33 microorganisms. It was found that oxytetracycline impurity C has an extremely similar spectral pattern to oxytetracycline, but its antibacterial activity is very low; furthermore, the parent ring structure of oxytetracycline impurity C is the same as that of oxytetracycline, and their molecular formulas are very similar. Therefore, for a long time, there has been no effective method to separate oxytetracycline impurity C from oxytetracycline, thus purifying oxytetracycline. Under acidic conditions, oxytetracycline undergoes a dehydration reaction to form dehydrated oxytetracycline. Further degradation of the dehydrated oxytetracycline forms a mixture of stereoisomers of α- and β-oxytetracycline. Under acidic conditions, the oxytetracycline is then oxidized to remove the dimethyl group and aromatized to form terrinolide. Under more intense conditions, terrinolide forms a deamide derivative. The content of the deamide derivative in the finished oxytetracycline product must be less than 2.0%. Therefore, shortening the downstream processing time can significantly reduce the formation of the deamide derivative, ensuring that the content of 2-acetyl-2-deamide oxytetracycline does not exceed 2%. CN 118878436 B discloses a preparation method for reducing the content of impurity C in oxytetracycline. This method involves adding phenylhydrazine to induce a hydrazone reaction, causing impurity C to react with phenylhydrazine to form a soluble hydrazone compound. Subsequent pulping, filtration, and recrystallization operations then separate the impurity C. However, this method has a poor yield, and the pulping process after the reaction adds an extra step, which is not conducive to industrial production. Furthermore, free phenylhydrazine may remain in the raw material, further increasing the risk of contamination in the finished product and the cost of removal. CN116621724 A discloses a method for extracting oxytetracycline to reduce the content of the impurity 2-acetyl-2-deamidoxycycline. In the initial acidification stage of extraction, a strong reducing agent, ferrous sulfate, is added. The introduced ferrous and ferric ions can inhibit the oxidation reaction after the Cope elimination reaction, inhibiting the formation of oxyphenolide, thereby reducing the formation of the impurity 2-acetyl-2-deamidoxycycline, lowering the content of 2-acetyl-2-deamidoxycycline, and improving the purity of oxytetracycline. However, this method requires operation during fermentation, cannot perform secondary treatment of the impurities in the finished oxytetracycline base, and the amount of reagent added depends on the calculation of multiple process indicators, which is cumbersome. The final content of the oxytetracycline impurity C is still higher than 0.5%.

[0003] In recent years, biomass-derived carbonaceous materials have attracted widespread attention due to their low cost, simple preparation, and abundant biomass resources. Firstly, activated carbon possesses excellent chemical and physical properties. Its inherent thermal stability and rich surface structure are significant advantages as catalyst supports. The abundant pores and high specific surface area on its surface facilitate further modification and the immobilization and dispersion of metallic active components. Secondly, to adapt to different modification needs or the immobilization requirements of different metallic active components, the pore structure and pore volume of the carbon surface can be adjusted by changing the preparation conditions. Simple chemical modifications to the activated carbon support surface, such as oxidation or ammoniation, not only can the desired functional groups be added, but these treatments also improve the hydrophilicity of the carbon surface, enhancing its interaction with modified functional groups and improving the dispersibility of these groups. Due to its excellent structural characteristics, activated carbon materials have already been applied in halogenation, redox, and hydrodehydrogenation reactions.

[0004] Currently, the main method for preparing activated carbon carriers is pyrolysis (i.e., high-temperature carbonization). The surface structure of the carbon carrier product can be adjusted by changing the reaction conditions of carbonization and activation. Activation methods can be divided into physical activation, which uses steam and carbon dioxide, and chemical activation, which uses chemical reagents such as zinc chloride, potassium hydroxide, and phosphoric acid. Chemical activation is often used to prepare activated carbon carriers because of its rich pore structure and strong ability. There are many sources for preparing activated carbon carriers, such as coconut shells, sugarcane bagasse, wood, and bamboo.

[0005] Based on the above, this invention proposes a specific adsorbent for oxytetracycline impurity C and its preparation method. Summary of the Invention

[0006] The purpose of this invention is to provide a specific adsorbent for oxytetracycline impurity C and its preparation method.

[0007] To achieve the above objectives, the present invention provides a specific adsorbent for oxytetracycline impurity C, which is prepared by covalently grafting a silane coupling agent onto chemically modified biochar, wherein the chemically modified biochar has a particle size of 0.125~0.18 mm.

[0008] Preferably, the chemical modification method includes one of acidification modification, alkalization modification, acetylation modification, and oxidation modification.

[0009] Preferably, the oxidative modification includes one of potassium permanganate oxidative modification, hydrogen peroxide oxidative modification, and nitric acid oxidative modification.

[0010] Preferably, the silane coupling agent is an aminosilane coupling agent.

[0011] Preferably, the aminosilane coupling agent includes one of monoaminosilane, diaminosilane, triaminosilane, and secondary aminosilane.

[0012] Preferably, the monoaminosilane includes one of 3-aminopropylmethyldimethoxysilane, 3-aminopropylmethyldiethoxysilane, 3-aminopropyltrimethoxysilane, and 3-aminopropyltriethoxysilane.

[0013] Preferably, the diaminosilane includes one of N-2-aminoethyl-3-aminopropylmethyldiethoxysilane, N-2-aminoethyl-3-aminopropylmethyldimethoxysilane, N-2-aminoethyl-3-aminopropyltriethoxysilane, and N-2-aminoethyl-3-aminopropyltrimethoxysilane.

[0014] Preferably, the method for preparing the specific adsorbent comprises the following steps: (1) After cleaning and drying, chestnut shells are crushed and passed through 80 and 120 mesh sieves in sequence. The intermediate sieve of 80-120 mesh is selected. The chestnut shells and deionized water are mixed according to the material-liquid ratio of 1g:20-25ml. After stirring evenly, the mixture is sealed and the pressure is adjusted to 1.5-2.0Mpa. The temperature is raised to 180-200℃ at a rate of 20-25℃ / min and reacted for 10-12h. After the reaction is completed, the reaction system is cooled to below 80℃ within 30±5min. Then it is naturally cooled to room temperature. The reaction solid is taken out, washed with deionized water in sequence, vacuum filtered, dried at 60±5℃ to constant weight, crushed and passed through 80 and 120 mesh sieves in sequence. The intermediate sieve of 80-120 mesh is selected to obtain biohydrothermal carbon. (2) Take the biohydrothermal carbon obtained in step (1), mix the biohydrothermal carbon with nitric acid with a concentration of 3-5 mol / L at a material-liquid ratio of 1g:30-35ml, reflux and heat in a water bath at 75-80℃ for 2.5-3h, cool and wash with deionized water until neutral, vacuum filter, dry at 60±5℃ to constant weight to obtain oxidized biohydrothermal carbon; (3) Take the oxidized biohydrothermal carbon obtained in step (2) and crush it into granules. Take the oxidized biohydrothermal carbon, silane coupling agent and toluene in the ratio of 1g:1~1.5ml:25~30ml respectively and mix them evenly. Adjust the pH to 4.0~5.0 with acetic acid. Stir and reflux at 110±2℃ for 12±0.5h under nitrogen protection. After the reaction is complete, filter it and wash it with dichloromethane and anhydrous ethanol 2~3 times. Then place it in a Soxhlet extractor and extract it with ethanol for 24±0.5h. Dry it at 60±5℃ to constant weight. Then crush it and pass it through 120 mesh. Keep the part on the sieve to obtain the product.

[0015] The present invention also provides a method for preparing high-purity oxytetracycline, the method comprising the following steps: (1) Measure crude oxytetracycline and specific adsorbent at a mass ratio of 10:0.5~1 and add them to an alcohol-water solution with a volume concentration of 95%. The total amount of crude oxytetracycline and specific adsorbent to the alcohol-water solution is 1g:5~6ml. Then add acetone accounting for 0.5%~0.75% of the total solvent volume and add acetic acid to adjust the pH to 4~6. React at a temperature of 40~55℃ for 1.5~2h and maintain stirring at 250~300 r / min during the reaction. (2) After the reaction is completed, filter with a 200-mesh filter cloth to remove the reaction solvent. Then add an alcohol aqueous solution with a volume concentration of 95% with the same volume as the alcohol aqueous solution used in step (1), adjust the pH to 2 with hydrochloric acid, stir for 0.5~1h, filter with a 200-mesh filter cloth, adjust the pH of the filtrate to 5 with ammonia water, filter to obtain oxytetracycline crystals, dry the oxytetracycline crystals under vacuum at 50±5℃ to obtain high-purity oxytetracycline.

[0016] Preferably, the crude oxytetracycline contains ≥1% oxytetracycline impurity C and ≥95% oxytetracycline alkaloids.

[0017] Preferably, the alcohol-water solution in step (1) is an aqueous ethanol solution.

[0018] Preferably, the alcohol-water solution in step (2) is an aqueous methanol solution.

[0019] Compared with the prior art, the present invention has the following beneficial effects: 1. The specific adsorbent for oxytetracycline impurity C prepared by the present invention achieves the effect of a solid adsorbent by covalently bridging aminosilane to biochar. The oxytetracycline can be separated from the solid adsorbent by subsequent filtration. Compared with the use of free phenylhydrazine, the process is not only greatly simplified and suitable for industrialization, but also reduces the possibility of free phenylhydrazine contaminating the finished product.

[0020] 2. The specific adsorbent for oxytetracycline impurity C prepared in this invention is a solid adsorbent. Its reaction mechanism is a Schiff base reaction, in which it specifically reacts with oxytetracycline impurity C. Compared with free phenylhydrazine, which diffuses freely in solution and may weakly react with the carbonyl group on the oxytetracycline base core, the solid adsorbent of this invention reacts only at the solid-liquid interface. Moreover, the solubility of oxytetracycline impurity C is higher than that of oxytetracycline base, making it easier for the solid adsorbent to capture oxytetracycline impurity C in the liquid phase, thus greatly improving selectivity.

[0021] 3. The specific adsorbent for oxytetracycline impurity C prepared by this invention can be eluted, regenerated, and reused, reducing reagent costs and hazardous waste, and is more in line with the trend of green pharmaceuticals and green chemistry. Detailed Implementation Example

[0022] (1) After cleaning and drying, chestnut shells are crushed and passed through 80 and 120 mesh sieves in sequence. The intermediate sieve of 80-120 mesh is selected. The chestnut shells and deionized water are mixed according to the material-liquid ratio of 1g: 25ml. After stirring evenly, the mixture is sealed and the pressure is adjusted to 2.0Mpa. The temperature is raised to 200℃ at a rate of 25℃ / min and reacted for 10h. After the reaction is completed, the reaction system is cooled to below 80℃ within 30±5min. Then it is naturally cooled to room temperature. The reaction solid is taken out, washed with deionized water in sequence, vacuum filtered, dried at 60±5℃ to constant weight, crushed and passed through 80 and 120 mesh sieves in sequence. The intermediate sieve of 80-120 mesh is selected to obtain biohydrothermal carbon. (2) Take the biohydrothermal carbon obtained in step (1), mix the biohydrothermal carbon with nitric acid with a concentration of 3mol / L according to the material-liquid ratio of 1g: 35ml, reflux and heat in a water bath at 80℃ for 2.5h, cool and wash with deionized water until neutral, vacuum filter, dry at 60±5℃ to constant weight to obtain oxidized biohydrothermal carbon. (3) Take the oxidized biohydrothermal carbon obtained in step (2) and crush it into granules. Take the oxidized biohydrothermal carbon, silane coupling agent and toluene in the ratio of 1g: 1.5ml: 30ml respectively and mix them evenly. Adjust the pH to 5.0 with acetic acid. Stir and reflux at 110±2℃ for 12h under nitrogen protection. After the reaction is complete, filter it and wash it with dichloromethane and anhydrous ethanol 2~3 times. Then place it in a Soxhlet extractor and extract it with ethanol for 24h. Dry it at 60±5℃ to constant weight. Then crush it and pass it through 120 mesh. Keep the part on the sieve to obtain the product. (4) Measure crude oxytetracycline and specific adsorbent at a mass ratio of 10:1 and add them to an alcohol-water solution with a volume concentration of 95%. The total amount of crude oxytetracycline and specific adsorbent to the alcohol-water solution is 1g:6ml. Then add acetone accounting for 0.75% of the total solvent volume and add acetic acid to adjust the pH to 6. React at 55℃ for 1.5h and maintain stirring at 300 r / min during the reaction. (5) After the reaction is completed, filter with a 200-mesh filter cloth to remove the reaction solvent. Then add an alcohol aqueous solution with a volume concentration of 95% with the same volume as the alcohol aqueous solution used in step (4), adjust the pH to 2 with hydrochloric acid, stir for 1 hour, filter with a 200-mesh filter cloth, adjust the pH of the filtrate to 5 with ammonia water, filter to obtain oxytetracycline crystals, dry the oxytetracycline crystals under vacuum at 50±5℃ to obtain high-purity oxytetracycline. Example

[0023] (1) After cleaning and drying, chestnut shells are crushed and passed through 80 and 120 mesh sieves in sequence. The intermediate sieve of 80-120 mesh is selected. The chestnut shells and deionized water are mixed according to the material-liquid ratio of 1g:20ml. After stirring evenly, the mixture is sealed and the pressure is adjusted to 1.5Mpa. The temperature is raised to 180℃ at a rate of 20℃ / min and reacted for 12h. After the reaction is completed, the reaction system is cooled to below 80℃ within 30±5min. Then it is naturally cooled to room temperature. The reaction solid is taken out, washed with deionized water in sequence, vacuum filtered, dried at 60±5℃ to constant weight, crushed and passed through 80 and 120 mesh sieves in sequence. The intermediate sieve of 80-120 mesh is selected to obtain biohydrothermal carbon. (2) Take the biohydrothermal carbon obtained in step (1), mix the biohydrothermal carbon with nitric acid with a concentration of 5 mol / L according to the material-liquid ratio of 1g:30ml, reflux and heat in a water bath at 75℃ for 3h, cool and wash with deionized water until neutral, vacuum filter, dry at 60±5℃ to constant weight to obtain oxidized biohydrothermal carbon. (3) Take the oxidized biohydrothermal carbon obtained in step (2) and crush it into granules. Take the oxidized biohydrothermal carbon, silane coupling agent and toluene in the ratio of 1g: 1.5ml: 25ml respectively and mix them evenly. Adjust the pH to 4.0 with acetic acid. Stir and reflux at 110±2℃ for 12h under nitrogen protection. After the reaction is complete, filter it and wash it with dichloromethane and anhydrous ethanol 2~3 times. Then place it in a Soxhlet extractor and extract it with ethanol for 24h. Dry it at 60±5℃ to constant weight. Then crush it and pass it through 120 mesh. Keep the part on the sieve to obtain the product. (4) Measure the crude oxytetracycline and the specific adsorbent at a mass ratio of 10:1 and add them to an alcohol-water solution with a volume concentration of 95%. The total amount of crude oxytetracycline and the specific adsorbent to the alcohol-water solution is 1g:5ml. Then add acetone accounting for 0.5% of the total solvent volume and add acetic acid to adjust the pH to 4. React at 40℃ for 2h and maintain stirring at 250r / min during the reaction. (5) After the reaction is completed, filter with a 200-mesh filter cloth to remove the reaction solvent. Then add an alcohol-water solution with a volume concentration of 95% with the same volume as the alcohol-water solution used in step (4), adjust the pH to 2 with hydrochloric acid, stir for 0.5 h, filter with a 200-mesh filter cloth, adjust the pH of the filtrate to 5 with ammonia water, filter to obtain oxytetracycline crystals, dry the oxytetracycline crystals under vacuum at 50±5℃ to obtain high-purity oxytetracycline. Example

[0024] (1) After cleaning and drying, chestnut shells are crushed and passed through 80 and 120 mesh sieves in sequence. The intermediate sieve of 80-120 mesh is selected. The chestnut shells and deionized water are mixed according to the material-liquid ratio of 1g: 25ml. After stirring evenly, the mixture is sealed and the pressure is adjusted to 2.0Mpa. The temperature is raised to 200℃ at a rate of 25℃ / min and reacted for 12h. After the reaction is completed, the reaction system is cooled to below 80℃ within 30±5min. Then it is naturally cooled to room temperature. The reaction solid is taken out, washed with deionized water in sequence, vacuum filtered, dried at 60±5℃ to constant weight, crushed and passed through 80 and 120 mesh sieves in sequence. The intermediate sieve of 80-120 mesh is selected to obtain biohydrothermal carbon. (2) Take the biohydrothermal carbon obtained in step (1), mix the biohydrothermal carbon with nitric acid with a concentration of 5 mol / L according to the material-liquid ratio of 1 g: 35 ml, reflux and heat in a water bath at 80 ℃ for 3 h, cool and wash with deionized water until neutral, vacuum filter, dry at 60±5 ℃ to constant weight to obtain oxidized biohydrothermal carbon. (3) Take the oxidized biohydrothermal carbon obtained in step (2) and crush it into granules. Take the oxidized biohydrothermal carbon, silane coupling agent and toluene in the ratio of 1g:1ml:25ml respectively and mix them evenly. Adjust the pH to 5.0 with acetic acid. Stir and reflux at 110±2℃ for 12h under nitrogen protection. After the reaction is complete, filter it and wash it with dichloromethane and anhydrous ethanol 2~3 times. Then place it in a Soxhlet extractor and extract it with ethanol for 24h. Dry it at 60±5℃ to constant weight. Then crush it and pass it through 120 mesh. Keep the part on the sieve to obtain the product. (4) Take crude oxytetracycline and specific adsorbent at a mass ratio of 10:0.5 and add them to an alcohol-water solution with a volume concentration of 95%. The total amount of crude oxytetracycline and specific adsorbent to the alcohol-water solution is 1g:6ml. Then add acetone accounting for 0.5% to 0.75% of the total solvent volume and add acetic acid to adjust the pH to 5. React at 55℃ for 2 hours and maintain stirring at 300 r / min during the reaction. (5) After the reaction is completed, filter with a 200-mesh filter cloth to remove the reaction solvent. Then add an alcohol aqueous solution with a volume concentration of 95% with the same volume as the alcohol aqueous solution used in step (4), adjust the pH to 2 with hydrochloric acid, stir for 1 hour, filter with a 200-mesh filter cloth, adjust the pH of the filtrate to 5 with ammonia water, filter to obtain oxytetracycline crystals, dry the oxytetracycline crystals under vacuum at 50±5℃ to obtain high-purity oxytetracycline. Example

[0025] Unlike Example 3, 3-aminopropyltriethoxysilane was used as the silane coupling agent. The other preparation steps were the same as in Example 3.

[0026] Unlike Example 3, N-2-aminoethyl-3-aminopropyltriethoxysilane (bisaminosilane) was used as the silane coupling agent. The other preparation steps were the same as in Example 3.

[0027] Unlike Example 3, N-2-aminoethyl-3-aminopropyltriethoxysilane (bisaminosilane) was used as the silane coupling agent. The other preparation steps were the same as in Example 3.

[0028] Unlike Example 3, step (4) uses a 75% (v / v) aqueous ethanol solution instead of the aqueous ethanol solution. The other preparation steps are the same as in Example 3.

[0029] Unlike Example 3, in step (4), the total amount of crude oxytetracycline and specific adsorbent is in a ratio of 1g to 15ml to the alcohol-water solution.

[0030] Unlike Example 3, acetone was not added in step (4).

[0031] The specific dosage and results are shown in Table 1 and Table 2.

[0032] Table 1

[0033] Table 2

[0034] Table 2 shows that Examples 2 and 4 exhibit the best purification effects, indicating that modification with ethoxysilane is slightly superior to modification with methoxysilane. Comparative Examples 1 and 2 both used diamine silane coupling agents, but their Schiff base reaction efficiency with oxytetracycline impurity C was much lower than in Examples 1-4, resulting in a slightly weaker impurity removal effect after purification compared to activated carbon adsorbents modified with monoamine silane coupling agents. In Comparative Example 3, replacing the 95% ethanol aqueous solution with a 75% volume concentration ethanol aqueous solution in step (4) increases the solubility of free oxytetracycline base in the reaction system, leading to loss during subsequent filtration and a decrease in yield. Furthermore, the increased water content in the system reduces the efficiency of the Schiff base reaction between oxytetracycline impurity C and aminosilane, resulting in a poorer impurity removal effect. In Comparative Example 4, the increased solvent volume increases the solubility of free oxytetracycline base to a certain extent, subsequently causing a decrease in yield.

[0035] The foregoing description of specific exemplary embodiments of the invention is for illustrative and explanatory purposes. These descriptions are not intended to limit the invention to the precise forms disclosed, and it will be apparent that many changes and variations can be made in accordance with the foregoing teachings. The exemplary embodiments were chosen and described in order to explain the specific principles of the invention and its practical application, thereby enabling those skilled in the art to implement and utilize various different exemplary embodiments of the invention, as well as various different choices and variations. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A specific adsorbent for oxytetracycline impurity C, characterized in that, The specific adsorbent is prepared by covalently grafting a silane coupling agent onto chemically modified biochar, wherein the particle size of the chemically modified biochar is 0.125~0.18 mm.

2. The specific adsorbent according to claim 1, characterized in that, The chemical modification method includes one of the following: acidification modification, alkalization modification, acetylation modification, and oxidation modification.

3. The specific adsorbent according to claim 2, characterized in that, The oxidation modification includes one of the following: potassium permanganate oxidation modification, hydrogen peroxide oxidation modification, and nitric acid oxidation modification.

4. The specific adsorbent according to claim 1, characterized in that, The silane coupling agent is an aminosilane coupling agent.

5. The specific adsorbent according to claim 4, characterized in that, The aminosilane coupling agent includes one of monoaminosilane, diaminosilane, triaminosilane, and secondary aminosilane.

6. The specific adsorbent according to claim 5, characterized in that, The monoaminosilane includes one of 3-aminopropylmethyldimethoxysilane, 3-aminopropylmethyldiethoxysilane, 3-aminopropyltrimethoxysilane, and 3-aminopropyltriethoxysilane.

7. The specific adsorbent according to claim 5, characterized in that, The diaminosilane includes one of N-2-aminoethyl-3-aminopropylmethyldiethoxysilane, N-2-aminoethyl-3-aminopropylmethyldimethoxysilane, N-2-aminoethyl-3-aminopropyltriethoxysilane, and N-2-aminoethyl-3-aminopropyltrimethoxysilane.

8. A method for preparing a specific adsorbent according to any one of claims 1 to 7, characterized in that, The preparation method includes the following steps: (1) After cleaning and drying, chestnut shells are crushed and passed through 80 and 120 mesh sieves in sequence. The intermediate sieve of 80-120 mesh is selected. The chestnut shells and deionized water are mixed according to the material-liquid ratio of 1g:20-25ml. After stirring evenly, the mixture is sealed and the pressure is adjusted to 1.5-2.0Mpa. The temperature is raised to 180-200℃ at a rate of 20-25℃ / min and reacted for 10-12h. After the reaction is completed, the reaction system is cooled to below 80℃ within 30±5min. Then it is naturally cooled to room temperature. The reaction solid is taken out, washed with deionized water in sequence, vacuum filtered, dried at 60±5℃ to constant weight, crushed and passed through 80 and 120 mesh sieves in sequence. The intermediate sieve of 80-120 mesh is selected to obtain biohydrothermal carbon. (2) Take the biohydrothermal carbon obtained in step (1), mix the biohydrothermal carbon with nitric acid with a concentration of 3-5 mol / L at a material-liquid ratio of 1g:30-35ml, reflux and heat in a water bath at 75-80℃ for 2.5-3h, cool and wash with deionized water until neutral, vacuum filter, dry at 60±5℃ to constant weight to obtain oxidized biohydrothermal carbon; (3) Take the oxidized biohydrothermal carbon obtained in step (2) and crush it into granules. Take the oxidized biohydrothermal carbon, silane coupling agent and toluene in the ratio of 1g:1~1.5ml:25~30ml respectively and mix them evenly. Adjust the pH to 4.0~5.0 with acetic acid. Stir and reflux at 110±2℃ for 12±0.5h under nitrogen protection. After the reaction is complete, filter it and wash it with dichloromethane and anhydrous ethanol 2~3 times. Then place it in a Soxhlet extractor and extract it with ethanol for 24±0.5h. Dry it at 60±5℃ to constant weight. Then crush it and pass it through 120 mesh. Keep the part on the sieve to obtain the product.

9. A method for preparing high-purity oxytetracycline, characterized in that, The method includes the following steps: (1) Measure crude oxytetracycline and specific adsorbent at a mass ratio of 10:0.5~1 and add them to an alcohol-water solution with a volume concentration of 95%. The total amount of crude oxytetracycline and specific adsorbent to the alcohol-water solution is 1g:5~6ml. Then add acetone accounting for 0.5%~0.75% of the total solvent volume and add acetic acid to adjust the pH to 4~6. React at a temperature of 40~55℃ for 1.5~2h and maintain stirring at 250~300 r / min during the reaction. (2) After the reaction is completed, filter with a 200-mesh filter cloth to remove the reaction solvent. Then add an alcohol aqueous solution with a volume concentration of 95% with the same volume as the alcohol aqueous solution used in step (1), adjust the pH to 2 with hydrochloric acid, stir for 0.5~1h, filter with a 200-mesh filter cloth, adjust the pH of the filtrate to 5 with ammonia water, filter to obtain oxytetracycline crystals, dry the oxytetracycline crystals under vacuum at 50±5℃ to obtain high-purity oxytetracycline. The specific adsorbent is any one of the specific adsorbents described in claims 1 to 7.

10. The method according to claim 9, characterized in that, The alcohol-water solution in step (1) is an ethanol-water solution, and the alcohol-water solution in step (2) is a methanol-water solution.

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