A method for extracting high-purity caffeine from tea leaves
By combining imprinted polymer membranes with low-temperature crystallization, high-purity caffeine can be extracted from tea leaves, solving the problems of complex operation and the use of toxic solvents in existing technologies, and achieving efficient and safe caffeine extraction and purification.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- XINYANG NORMAL UNIVERSITY
- Filing Date
- 2026-04-14
- Publication Date
- 2026-06-30
AI Technical Summary
Existing technologies for extracting caffeine from tea leaves suffer from problems such as cumbersome operating procedures, the need to use toxic solvents, and difficulty in effectively removing impurities.
A method combining imprinted polymer membranes with alkaline low-temperature crystallization was adopted to extract high-purity caffeine from tea leaves by preparing imprinted polymer membranes with caffeine recognition sites and combining them with low-temperature crystallization. This method avoids the use of toxic solvents and achieves highly selective extraction and purification through multiple hydrogen bonding interactions.
It achieves highly selective extraction and purification of caffeine, simplifies the operation process, reduces energy consumption, reduces organic solvent residue, meets food safety requirements, and is suitable for industrial production.
Abstract
Description
Technical Field
[0001] This invention relates to the field of caffeine extraction technology, specifically a method for extracting high-purity caffeine from tea leaves. Background Technology
[0002] Caffeine, also known as caffeine, has the chemical name 1,3,7-trimethyl-3,7-dihydro-1H-purine-2,6-dione hydrate, with the chemical formula C8H10H2O. 10 N4O2, with a relative molecular weight of 194.2, is readily soluble in water, ether, chloroform, and dichloromethane. It is a colorless, bitter-tasting white crystalline powder. As a xanthine alkaloid compound, caffeine has the effect of dispelling drowsiness and restoring energy, and is therefore considered a central nervous system stimulant.
[0003] Currently, synthetically produced caffeine inevitably contains harmful impurities, while tea contains approximately 3-5% caffeine. Therefore, extracting pure natural caffeine from tea is necessary. However, most separation and purification methods used in actual production rely on toxic solvents such as dichloromethane or trichloromethane. Chinese patent CN201510858158.7 discloses a method for extracting caffeine from tea by combining membrane separation technology with column chromatography to separate caffeine from other components such as tea polysaccharides, tea polyphenols, and theanine, followed by crystallization purification to obtain high-purity caffeine. However, this process is cumbersome, making it essential to provide a novel method for extracting high-purity caffeine from tea leaves. Summary of the Invention
[0004] The purpose of this invention is to provide a method for extracting high-purity caffeine from tea leaves, so as to solve the problems mentioned in the background art.
[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a method for extracting high-purity caffeine from tea leaves, comprising the following steps:
[0006] Furthermore, in step 1, the alcohol solution is an aqueous solution of methanol or ethanol.
[0007] Furthermore, in step 1, the amount of alcohol solution added is 10~30mL / g based on the weight of fresh tea leaves.
[0008] Furthermore, in step 1, the extraction temperature is 50~80℃, the extraction time is 60~90min, and the extraction is performed 3~5 times.
[0009] Furthermore, in step 2, the method for preparing the imprinted polymer film includes the following steps:
[0010] Caffeine, acrylic acid, tannic acid functional monomers, and N,N'-methylenebisacrylamide were added to an ethanol-water solution and ultrasonically dispersed for 30 min. Then, the initiator azobisisobutyronitrile was added to obtain a reaction mixture. Under nitrogen atmosphere, a nylon microporous filter membrane was placed on a glass slide, and the reaction mixture was dropped onto the membrane surface. After the membrane was wetted, another glass slide was placed on top of it. After removing air bubbles, the membrane was transferred to a nitrogen atmosphere and polymerized at 60-70℃ for 20-24 h. After cooling, the glass slide was removed, and the molecularly imprinted polymer was eluted with a mixture of methanol and acetic acid to obtain an imprinted polymer membrane.
[0011] Further, the preparation method of the tannic acid functional monomer is as follows: tannic acid is dispersed in N,N-dimethylformamide, then triethylamine is added, and after stirring evenly, acryloyl chloride is added dropwise while stirring in an ice-water bath at 0~4℃; after the acryloyl chloride is completely added, the reaction is carried out at 25~30℃ for 24h. After the reaction is completed, N,N-dimethylformamide is removed under reduced pressure, the product is dispersed in deionized water, centrifuged and washed with anhydrous ethanol, and then vacuum dried at 80~90°C for 24h.
[0012] Furthermore, tannic acid and acryloyl chloride react in a mass ratio of (12~15):(8~9).
[0013] Furthermore, the molar ratio of caffeine, acrylic acid, tannic acid functional monomer, and N,N'-methylenebisacrylamide is 1:5:5:2.
[0014] Further, in step 2, the eluent is obtained by mixing methanol and acetic acid in a volume ratio of 9:1.
[0015] Compared with the prior art, the beneficial effects achieved by the present invention are as follows: The present invention provides a method for extracting high-purity caffeine from tea leaves. The core of the method lies in the innovative design and preparation of an imprinted polymer membrane material that recognizes caffeine molecular sites, and its combination with an alkaline low-temperature crystallization process, thereby achieving highly selective extraction and purification of caffeine from natural tea leaves.
[0016] In this invention, during the imprinting process, acryloyl chloride is first acylated with tannic acid to prepare a functional monomer containing a polyphenol structure. This functional monomer is then combined with acrylic acid as a bifunctional monomer system and polymerized using molecular imprinting technology to form an imprinted polymer with specific recognition vacancy sites. The polyphenolic hydroxyl groups and aromatic rings abundant in the tannic acid molecule can form multiple hydrogen bonds with the target molecule caffeine, while acrylic acid provides additional carboxyl hydrogen bond sites, further enhancing the anchoring ability for caffeine molecules, thus constructing a multiple recognition mechanism. This synergistic effect significantly improves the imprinted polymer's specific recognition ability and adsorption capacity for caffeine, effectively eliminating interference from complex components such as tea polyphenols, amino acids, and pigments in the mixture system, achieving one-step targeted enrichment of caffeine from the extract, and greatly simplifying the multiple extraction and purification steps required in traditional separation processes.
[0017] In terms of separation and purification processes, this invention employs a strategy combining selective enrichment with molecularly imprinted membranes and alkaline low-temperature crystallization. Specifically, the caffeine-enriched extract is adjusted to pH 9 with calcium hydroxide and then crystallized at low temperature, avoiding the problem of residual impurities that are difficult to remove in traditional methods. This method uses methanol or ethanol-water solutions as extraction solvents, completely avoiding the use of toxic organic solvents such as chloroform and dichloromethane, fundamentally eliminating the potential threat to food safety posed by organic solvent residues, and meeting the safety requirements of modern green food processing. Furthermore, the membrane separation process is carried out at room temperature, requiring no heating, and the energy consumption is significantly lower than that of traditional distillation and concentration processes. The eluent can be recycled after simple treatment, effectively reducing the consumption of chemical reagents and the emission of waste, embodying the concept of clean production.
[0018] The process parameters of each step in this invention are precisely controllable, and the membrane filtration operation is easy to implement for continuous and automated production, making it suitable for industrial-scale scaling. Simultaneously, it boasts high raw material utilization, simple operation, and good repeatability, demonstrating promising prospects for industrial application and economic benefits. This invention, through the organic combination of material innovation and process optimization, establishes a new environmentally friendly, highly efficient, energy-saving, and selective technique for the extraction and purification of natural caffeine, providing important technical reference for the green separation of natural products. Detailed Implementation
[0019] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0020] Materials and sources used in this invention: The nylon microporous filter membrane is from Zhejiang Tailin Biotechnology Co., Ltd., with a pore size of 0.45μm; the fresh tea leaves are fresh spring tea leaves of black tea; the remaining materials are all commercially available conventional products.
[0021] Example 1: A method for extracting high-purity caffeine from tea leaves, comprising the following steps:
[0022] Step 1: Take fresh tea leaves, freeze and crush them, and pass them through a 40-mesh sieve to obtain tea powder; add the tea powder to an alcohol solution for extraction, combine the extracts and concentrate under reduced pressure until there is no alcohol odor, cool to 20°C to obtain concentrated extract; the alcohol solution is an aqueous solution of ethanol; the amount of alcohol solution added is 10 mL / g based on the weight of fresh tea leaves, the extraction temperature is 50°C, the extraction time is 60 min, and the extraction is performed 3 times;
[0023] Step 2: Pass the concentrated extract through the imprinted polymer membrane at a rate of 1 mL / min to obtain a caffeine-enriched solution. Concentrate the caffeine-enriched solution to a density of 1.1 g / cm³. 3 Then, the pH is adjusted to 9 with a saturated calcium hydroxide aqueous solution, and the mixture is frozen to 4°C for crystallization. The crystals are then removed and washed with water to obtain high-purity caffeine. The method for preparing the imprinted polymer film includes the following steps:
[0024] S1: 12g of tannic acid was dispersed in N,N-dimethylformamide, and then 27mL of triethylamine was added. After stirring evenly, 8g of acryloyl chloride was added dropwise in an ice-water bath at 0°C. After the acryloyl chloride was added, the reaction was carried out at 25°C for 24h. After the reaction was completed, N,N-dimethylformamide was removed under reduced pressure. The product was dispersed in deionized water, centrifuged, and washed with anhydrous ethanol. It was then vacuum dried at 80°C for 24h to obtain the tannic acid functional monomer.
[0025] S2: Add 0.1 mmol caffeine, 0.5 mmol acrylic acid, 0.5 mmol tannic acid functional monomer, and 2 mmol N,N'-methylenebisacrylamide to an ethanol aqueous solution. After ultrasonic dispersion for 30 min, add the initiator azobisisobutyronitrile to obtain a reaction mixture solution. Place a nylon microporous filter membrane on a glass slide under nitrogen atmosphere, drop the reaction mixture solution onto the membrane surface, wet the membrane, cover it with another glass slide, remove air bubbles, and transfer it to a nitrogen atmosphere. Polymerize at 60℃ for 20 h. After cooling, remove the glass slide, mix methanol and acetic acid in a volume ratio of 9:1 to prepare an eluent. Elute the molecularly imprinted polymer to obtain an imprinted polymer membrane.
[0026] Example 2: A method for extracting high-purity caffeine from tea leaves, comprising the following steps:
[0027] Step 1: Take fresh tea leaves, freeze and crush them, and pass them through a 50-mesh sieve to obtain tea powder; add the tea powder to an alcohol solution for extraction, combine the extracts and concentrate under reduced pressure until there is no alcohol odor, cool to 25°C to obtain concentrated extract; the alcohol solution is an aqueous solution of methanol or ethanol; the amount of alcohol solution added is 20 mL / g based on the weight of fresh tea leaves, the extraction temperature is 60°C, the extraction time is 75 min, and the extraction is performed 4 times;
[0028] Step 2: Pass the concentrated extract through the imprinted polymer membrane at a rate of 1.2 mL / min to obtain a caffeine-enriched solution. Concentrate the caffeine-enriched solution to a density of 1.15 g / cm³. 3 Then, the pH is adjusted to 9 with a saturated calcium hydroxide aqueous solution, and the mixture is frozen to 4°C for crystallization. The crystals are then removed and washed with water to obtain high-purity caffeine. The method for preparing the imprinted polymer film includes the following steps:
[0029] S1: 13g of tannic acid was dispersed in N,N-dimethylformamide, and then 27mL of triethylamine was added. After stirring evenly, 8.5g of acryloyl chloride was added dropwise in an ice-water bath at 2℃. After the acryloyl chloride was added, the reaction was carried out at 28℃ for 24h. After the reaction was completed, N,N-dimethylformamide was removed under reduced pressure. The product was dispersed in deionized water, centrifuged, washed with anhydrous ethanol, and vacuum dried at 85°C for 24h to obtain the tannic acid functional monomer.
[0030] S2: Add 0.1 mmol caffeine, 0.5 mmol acrylic acid, 0.5 mmol tannic acid functional monomer, and 2 mmol N,N'-methylenebisacrylamide to an ethanol aqueous solution. After ultrasonic dispersion for 30 min, add the initiator azobisisobutyronitrile to obtain a reaction mixture solution. Place a nylon microporous filter membrane on a glass slide under nitrogen atmosphere, drop the reaction mixture solution onto the membrane surface, wet the membrane, cover it with another glass slide, remove air bubbles, and transfer it to a nitrogen atmosphere. Polymerize at 65℃ for 22 h. After cooling, remove the glass slide, mix methanol and acetic acid in a volume ratio of 9:1 to prepare an eluent. Elute the molecularly imprinted polymer to obtain an imprinted polymer membrane.
[0031] Example 3: A method for extracting high-purity caffeine from tea leaves, comprising the following steps:
[0032] Step 1: Take fresh tea leaves, freeze and crush them, and pass them through a 60-mesh sieve to obtain tea powder; add the tea powder to an alcohol solution for extraction, combine the extracts and concentrate under reduced pressure until there is no alcohol odor, cool to 30°C to obtain concentrated extract; the alcohol solution is an aqueous solution of methanol or ethanol; the amount of alcohol solution added is 30 mL / g based on the weight of fresh tea leaves, the extraction temperature is 80°C, the extraction time is 90 min, and the extraction is performed 5 times;
[0033] Step 2: Pass the concentrated extract through the imprinted polymer membrane at a rate of 1.5 mL / min to obtain a caffeine-enriched solution. Concentrate the caffeine-enriched solution to a density of 1.2 g / cm³. 3 Then, the pH is adjusted to 9 with a saturated calcium hydroxide aqueous solution, and the mixture is frozen to 4°C for crystallization. The crystals are then removed and washed with water to obtain high-purity caffeine. The method for preparing the imprinted polymer film includes the following steps:
[0034] S1: 15g of tannic acid was dispersed in N,N-dimethylformamide, and then 27mL of triethylamine was added. After stirring evenly, 9g of acryloyl chloride was added dropwise in an ice-water bath at 4°C. After the acryloyl chloride was added, the reaction was carried out at 30°C for 24h. After the reaction was completed, N,N-dimethylformamide was removed under reduced pressure. The product was dispersed in deionized water, centrifuged, and washed with anhydrous ethanol. It was then dried under vacuum at 90°C for 24h to obtain the tannic acid functional monomer.
[0035] S2: Add 0.1 mmol caffeine, 0.5 mmol acrylic acid, 0.5 mmol tannic acid functional monomer, and 2 mmol N,N'-methylenebisacrylamide to an ethanol aqueous solution. After ultrasonic dispersion for 30 min, add the initiator azobisisobutyronitrile to obtain a reaction mixture solution. Place a nylon microporous filter membrane on a glass slide under nitrogen atmosphere, drop the reaction mixture solution onto the membrane surface, wet the membrane, cover it with another glass slide, remove air bubbles, and transfer it to a nitrogen atmosphere. Polymerize at 70℃ for 24 h. After cooling, remove the glass slide, mix methanol and acetic acid in a volume ratio of 9:1 to prepare an eluent. Elute the molecularly imprinted polymer to obtain an imprinted polymer membrane.
[0036] Comparative Example 1: Extracting caffeine from tea leaves using existing technology (the technology disclosed in CN201510858158.7).
[0037] Step 1: Take fresh tea leaves, freeze and crush them, and pass them through a 40-mesh sieve to obtain tea powder; add the tea powder to an alcohol solution for extraction, combine the extracts and concentrate under reduced pressure until there is no alcohol odor, cool to 20°C to obtain concentrated extract; the alcohol solution is an aqueous solution of ethanol; the amount of alcohol solution added is 10 mL / g based on the weight of fresh tea leaves, the extraction temperature is 50°C, the extraction time is 60 min, and the extraction is performed 3 times;
[0038] Step 2: Filter the concentrated extract obtained in Step 1 using an ultrafiltration membrane with a flow rate of 30 kDa. Take the filtrate and concentrate it using MVR until the weight is 1 / 7 of the filtrate weight. Then, use XAD7 macroporous adsorption resin to elute with the first eluent to remove caffeine, followed by the second eluent to obtain an eluent containing tea polyphenols. Concentrate the eluent containing tea polyphenols until there is no alcohol odor, and dry it to obtain tea polyphenols. Concentrate the eluent containing caffeine until there is no alcohol odor, extract with ethyl acetate, take the organic phase, and remove the solvent by rotary evaporation to obtain crude caffeine product.
[0039] Step 3: Dissolve the crude caffeine product obtained in Step 2 in hot water at 79℃, allow the water to evaporate naturally until the concentration of crude caffeine product is 0.179g / ml, then adjust the pH to 9 with saturated calcium hydroxide aqueous solution, and then freeze at 3℃ for crystallization;
[0040] Step 4: After the crystallization process in Step 3 is completed, remove the crystals, dissolve them in 80°C hot water, add 1% activated carbon by mass of the crystals for decolorization, filter, and obtain the filtrate.
[0041] Step 5: Concentrate the filtrate obtained in Step 4 to a density of 1.11 g / cm³. 3 Then, the pH was adjusted to 9 with a saturated calcium hydroxide aqueous solution, and the mixture was frozen to 3°C for secondary crystallization. The crystals were then removed and washed with water to obtain high-purity caffeine. The volume of the washing water was one times the volume of the crystals.
[0042] The decolorization process involves stirring at 79°C for 29 minutes at a stirring speed of 80 rpm. MVR concentration is achieved using MVR equipment manufactured by Jiangyin Weijie Pharmaceutical Equipment Co., Ltd. Secondary crystallization in step 5 is performed using stirring at a speed of 15 rpm.
[0043] Comparative Example 2: A nylon microporous filter membrane was used instead of the imprinted polymer membrane, and the other parameters were the same as in Example 2.
[0044] Step 1: Take fresh tea leaves, freeze and crush them, and pass them through a 50-mesh sieve to obtain tea powder; add the tea powder to an alcohol solution for extraction, combine the extracts and concentrate under reduced pressure until there is no alcohol odor, cool to 25°C to obtain concentrated extract; the alcohol solution is an aqueous solution of methanol or ethanol; the amount of alcohol solution added is 20 mL / g based on the weight of fresh tea leaves, the extraction temperature is 60°C, the extraction time is 75 min, and the extraction is performed 4 times;
[0045] Step 2: Pass the concentrated extract through a nylon microporous membrane at a rate of 1.2 mL / min to obtain a caffeine-enriched solution. Concentrate the caffeine-enriched solution to a density of 1.15 g / cm³. 3Then, the pH was adjusted to 9 with a saturated calcium hydroxide aqueous solution, and the mixture was frozen to 4°C for crystallization. The crystals were then removed and washed with water to obtain caffeine.
[0046] Comparative Example 3: Imprinted polymer films were prepared without using tannic acid functional monomers, and the remaining parameters were the same as in Example 3.
[0047] Step 1: Take fresh tea leaves, freeze and crush them, and pass them through a 60-mesh sieve to obtain tea powder; add the tea powder to an alcohol solution for extraction, combine the extracts and concentrate under reduced pressure until there is no alcohol odor, cool to 30°C to obtain concentrated extract; the alcohol solution is an aqueous solution of methanol or ethanol; the amount of alcohol solution added is 30 mL / g based on the weight of fresh tea leaves, the extraction temperature is 80°C, the extraction time is 90 min, and the extraction is performed 5 times;
[0048] Step 2: Pass the concentrated extract through the imprinted polymer membrane at a rate of 1.5 mL / min to obtain a caffeine-enriched solution. Concentrate the caffeine-enriched solution to a density of 1.2 g / cm³. 3 Then, the pH is adjusted to 9 with a saturated calcium hydroxide aqueous solution, and the mixture is frozen to 4°C for crystallization. The crystals are then removed and washed with water to obtain high-purity caffeine. The method for preparing the imprinted polymer film includes the following steps:
[0049] 0.1 mmol of caffeine, 1 mmol of acrylic acid, and 2 mmol of N,N'-methylenebisacrylamide were added to an ethanol-water solution and ultrasonically dispersed for 30 min. Then, the initiator azobisisobutyronitrile was added to obtain a reaction mixture. Under nitrogen atmosphere, a nylon microporous membrane was placed on a glass slide, and the reaction mixture was dropped onto the membrane surface. After the membrane was wetted, another glass slide was placed on top of it. After removing air bubbles, the membrane was transferred to a nitrogen atmosphere and polymerized at 70 °C for 24 h. After cooling, the glass slide was removed, and methanol and acetic acid were mixed at a volume ratio of 9:1 to prepare an eluent. The molecularly imprinted polymer was eluted to obtain an imprinted polymer membrane.
[0050] Experiment: The purity and yield of caffeine prepared in Examples 1-3 and Comparative Examples 1-3 were analyzed and tested, and the results are shown in Table 1.
[0051] Table 1.
[0052] project purity yield Example 1 99.25% 91.8% Example 2 99.21% 92.1% Example 3 99.18% 91.7% Comparative Example 1 99.23% 85.7% Comparative Example 2 74.43% 52.4% Comparative Example 3 90.65% 80.3%
[0053] Conclusion: The caffeine obtained in Examples 1-3 achieved a purity of over 99% and a yield of over 90%. Comparative Example 1, following the method described in the prior art (CN201510858158.7), involved filtering tea extract using an ultrafiltration membrane, concentrating the filtrate, and adsorbing it with a macroporous adsorption resin. After elution and crystallization, high-purity caffeine was obtained. Compared to Comparative Example 1, Example 1, using the method of this invention, yielded caffeine with comparable purity and a higher yield, indicating that the imprinted polymer membrane prepared in this invention has a superior enrichment effect on caffeine compared to traditional macromolecular resin adsorption. In Comparative Example 2, a conventional nylon microporous membrane was used to enrich caffeine. Compared to Example 2, the nylon microporous membrane had poor selective permeability, resulting in a high impurity content in the product and poor product purity and yield. In Comparative Example 3, the imprinted polymer membrane used only acrylic acid as a functional monomer, while Example 3 used both tannic acid and acrylic acid as bifunctional monomers, achieving highly efficient enrichment of caffeine molecules. In summary, this invention has the advantages of being safe, non-toxic, efficient, and low-cost. The purity of the caffeine prepared is comparable to that of existing technologies, while the yield is slightly higher.
[0054] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.
Claims
1. A method for extracting high-purity caffeine from tea leaves, comprising the following steps: Step 1: Take fresh tea leaves, freeze and crush them, and pass them through a 40-60 mesh sieve to obtain tea powder; add the tea powder to an alcohol solution for extraction 3-5 times, combine the extracts and concentrate under reduced pressure until there is no alcohol taste, cool to 20-30℃ to obtain concentrated extract; Step 2: The concentrated extract solution is passed through the imprinted polymer membrane at a rate of 1 to 1.5 mL / min to obtain a caffeine-enriched solution, and the caffeine-enriched solution is concentrated to a density of 1.1 to 1.2 g / cm 3 After adjusting the pH to 9 with saturated aqueous calcium hydroxide solution, crystallization is performed by freezing at 4°C, and the crystals are removed and washed with water to obtain high-purity caffeine.
2. The method for extracting high-purity caffeine from tea leaves according to claim 1, characterized in that: In step 1, the alcohol solution is an aqueous solution of methanol or ethanol.
3. The method for extracting high-purity caffeine from tea leaves according to claim 1, characterized in that: In step 1, the amount of alcohol solution added is 10~30mL / g based on the weight of fresh tea leaves.
4. The method for extracting high-purity caffeine from tea leaves according to claim 1, characterized in that: In step 1, the extraction temperature is 50~80℃ and the extraction time is 60~90min.
5. The method for extracting high-purity caffeine from tea leaves according to claim 1, characterized in that: Step 2, the preparation method of the imprinted polymer membrane includes the following steps: adding caffeine, acrylic acid, tannic acid functional monomer, and N,N'-methylenebisacrylamide to an ethanol aqueous solution, ultrasonically dispersing for 30 min, and then adding the initiator azobisisobutyronitrile to obtain a reaction mixture solution; placing a nylon microporous filter membrane on a glass slide under a nitrogen atmosphere, dropping the reaction mixture solution onto the membrane surface, wetting the membrane, covering it with another glass slide, removing air bubbles, and transferring it to a nitrogen atmosphere, polymerizing at 60~70℃ for 20~24 h, cooling down, removing the glass slide, and eluting the molecularly imprinted polymer with a mixed solution of methanol and acetic acid as the eluent to obtain the imprinted polymer membrane.
6. The method for extracting high-purity caffeine from tea leaves according to claim 5, characterized in that: The preparation method of tannic acid functional monomer is as follows: tannic acid is dispersed in N,N-dimethylformamide, then triethylamine is added, and after stirring evenly, acryloyl chloride is added dropwise while stirring in an ice-water bath at 0~4℃; after the acryloyl chloride is added, the reaction is carried out at 25~30℃ for 24h. After the reaction is completed, N,N-dimethylformamide is removed under reduced pressure, the product is dispersed in deionized water, centrifuged and washed with anhydrous ethanol, and then vacuum dried at 80~90°C for 24h.
7. The method for extracting high-purity caffeine from tea leaves according to claim 6, characterized in that: Tannic acid and acryloyl chloride react in a mass ratio of (12~15):(8~9).
8. The method for extracting high-purity caffeine from tea leaves according to claim 5, characterized in that: The molar ratio of caffeine, acrylic acid, tannic acid functional monomer, and N,N'-methylenebisacrylamide is 1:5:5:
2.
9. The method for extracting high-purity caffeine from tea leaves according to claim 1, characterized in that: In step 2, the eluent is obtained by mixing methanol and acetic acid in a volume ratio of 9:
1.
10. High-purity caffeine prepared by any one of claims 1 to 9.