Purification method of eugenol

Abstract

The invention relates to the technical field of separation and purification, in particular to a purification method of eugenol, which comprises the following steps: (a) dissolving crude eugenol in an ethanol aqueous solution to prepare a solution with eugenol mass concentration of 20-30%; (b) adding a composite protective agent into the solution, uniformly stirring and standing to obtain a mixed solution, the composite protective agent comprising modified chitosan, sodium ascorbate and nano-silica; (c) carrying out reduced pressure evaporation on the mixed solution, and recovering the solvent to obtain a concentrated solution; (d) adding the concentrated solution into a glycine aqueous solution with the mass concentration of 1-2%, uniformly stirring and standing; and (e) carrying out segmented temperature control rectification on the concentrated solution treated in the step (d), and collecting a target fraction to obtain the high-purity eugenol. By introducing a novel protective agent system and a staged temperature control rectification technology, the occurrence rate of thermal decomposition and oxidation reaction is remarkably reduced, and the product purity and the production efficiency are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of separation and purification, and in particular to a method for purifying eugenol. Background Art

[0002] Eugenol, as an important chemical raw material and spice, is widely used in the fields of food, medicine, cosmetics, etc. However, its purification process has always been a key factor restricting product quality and production efficiency. Existing eugenol purification methods have significant deficiencies in thermal stability and antioxidant properties. Especially under high temperature or long-term operation conditions, thermal decomposition and oxidation reactions are prone to occur, resulting in a decrease in product purity, darkening of color, and even the production of by-products, which seriously affect the quality of the final product. CN108383695B proposes a method for synthesizing crude eugenol under alkaline conditions using guaiacol and allyl chloride as raw materials, and improving the anti-discoloration performance by adding an antioxidant during the distillation process. However, although this technical solution delays the oxidation process to a certain extent, it fails to fundamentally solve the problem of reduced purity of eugenol caused by thermal decomposition during the high-temperature distillation process. In addition, the introduction of antioxidants not only increases the complexity of subsequent processing, but may also have a potential impact on the safety of the product. CN104628542B discloses a method for preparing high-purity eugenol using clove leaf oil as raw material through vacuum distillation, chemical treatment, and complexing metal ions. However, this method has high requirements for temperature control during vacuum distillation. If the temperature is too high, it may still cause thermal decomposition of eugenol; if the temperature is too low, the process time will be extended, reducing production efficiency. In addition, the removal of metal ions by this method depends on the complexing effect of EDTA-2Na, but the selectivity and efficiency of the complexing process may be limited, and it is difficult to completely avoid the impact of metal ions on product stability.

[0003] The above problems indicate that the existing eugenol purification methods still have certain shortcomings in terms of thermal decomposition inhibition, antioxidant performance improvement and process efficiency optimization. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide an efficient, stable and environmentally friendly eugenol purification method in view of the shortcomings of the existing eugenol purification method in terms of thermal decomposition inhibition, antioxidant performance improvement and process efficiency optimization. By introducing a new protective agent system and staged temperature-controlled distillation technology, the incidence of thermal decomposition and oxidation reactions is significantly reduced, and the product purity and production efficiency are improved.

[0005] The technical solution adopted by the present invention to solve its technical problem is:

[0006] A method for purifying eugenol comprises the following steps:

[0007] (a) dissolving crude eugenol in an ethanol aqueous solution to prepare a solution having a eugenol concentration of 20% to 30%;

[0008] (b) adding a composite protective agent to the solution, stirring evenly and then standing for 1 hour to obtain a mixed solution, wherein the composite protective agent comprises modified chitosan, sodium ascorbate and nano-silica;

[0009] (c) evaporating the mixed solution under reduced pressure, controlling the vacuum degree to -0.08 MPa and the temperature to 45°C to 55°C, recovering the solvent and obtaining a concentrated solution;

[0010] (d) adding the concentrated solution to a 1% to 2% aqueous solution of glycine, stirring evenly, and then allowing to stand for 30 minutes;

[0011] (e) subjecting the concentrated solution treated in (d) to segmented temperature-controlled distillation, collecting target fractions, and obtaining high-purity eugenol.

[0012] This protocol establishes the key process for eugenol purification: first, dissolution through ethanol and aqueous solution, synergistically interacting with a composite protective agent, forms a stable molecular protective layer, effectively inhibiting thermal decomposition and oxidation reactions. Subsequently, the pH value of the system is adjusted using aqueous glycine solution to further enhance antioxidant properties. Finally, efficient separation is achieved through staged temperature-controlled distillation, avoiding quality degradation caused by high temperatures or prolonged operation. This protocol combines molecular protection with staged temperature control to form a complete green purification process chain.

[0013] Preferably, the amount of the composite protective agent added in step (b) is as follows: 0.5-0.8 g of modified chitosan, 0.3-0.5 g of sodium ascorbate, and 0.2-0.4 g of nano-silica per 100 mL of solution.

[0014] The problem of thermal decomposition is overcome through the synergistic effect of composite protective agents: modified chitosan adsorbs free radicals, sodium ascorbate removes oxidative active substances, and nano-silica disperses heat, which significantly improves thermal stability and reduces the generation of by-products.

[0015] Preferably, the modified chitosan is carboxymethylated chitosan with a substitution degree of ≥80%, and the nano-silica is a hydrophilic nano-material with a particle size of ≤50 nm.

[0016] Carboxymethylated chitosan and hydrophilic nano-silica pretreatment ensure the dispersibility and stability of the protective agent in the system, and significantly enhance the thermal decomposition inhibition effect without using traditional antioxidants.

[0017] Preferably, the reduced pressure evaporation in step (c) is carried out using a rotary evaporator at a rotation speed of 60 to 80 rpm.

[0018] Rotary evaporation replaces traditional static evaporation, which not only improves evaporation efficiency but also avoids component degradation caused by local overheating.

[0019] Preferably, the staged temperature-controlled distillation in step (e) is carried out in two stages: the first stage: temperature 50°C to 60°C, pressure -0.06 MPa; the second stage: temperature 70°C to 80°C, pressure -0.04 MPa.

[0020] By matching the volatility characteristics of eugenol through segmented temperature-controlled distillation, dynamic temperature control technology improves thermal energy utilization and product purity compared to traditional constant temperature distillation.

[0021] Preferably, the amount of the glycine aqueous solution in step (d) is 1.5 to 2.0 mL per 100 mL of concentrated solution.

[0022] That is, 1.5 to 2.0 mL of glycine aqueous solution needs to be added to every 100 mL of concentrated solution. Glycine can adjust the pH value of the system to weak alkalinity, inhibit the oxidation reaction, and promote the precipitation and separation of impurities.

[0023] Preferably, before the distillation in step (e), a β-cyclodextrin solution with a mass concentration of 0.5% to 1% is added to the concentrated solution in an amount of 1.0 mL / 100 mL of concentrated solution.

[0024] That is, for every 100 mL of concentrated solution, 1.0 mL of 0.5% to 1% β-cyclodextrin solution needs to be added. β-cyclodextrin can include eugenol molecules, reduce the probability of their contact with oxygen, and further enhance the antioxidant performance.

[0025] Preferably, after the reduced pressure evaporation in step (c), the concentrated solution is placed in a 4° C. environment and cooled for 1 hour.

[0026] Low-temperature cooling is used to promote the precipitation of impurities while preventing structural changes in eugenol molecules due to temperature fluctuations, thereby ensuring product purity and stability.

[0027] In step (a) of this scheme, crude eugenol is dissolved in an ethanol-water solution to prepare a solution with a mass concentration of 20% to 30%. The key to this step is to select the appropriate solvent ratio and dissolution conditions. The mass concentration range of the ethanol-water solution has been verified by a large number of experiments. It was found that when the ratio of ethanol to water is between 7:3 and 8:2, the crude eugenol can be effectively dissolved and its chemical stability can be maintained. The dissolution process should be carried out at room temperature and stirred at 300 rpm for 30 minutes using a magnetic stirrer to ensure that the eugenol is fully dispersed and to avoid precipitation caused by excessive local concentration.

[0028] Next, in step (b), a composite protective agent is added to the above solution, stirred evenly, and allowed to stand for 1 hour. The composite protective agent is composed of modified chitosan, sodium ascorbate, and nano-silica, and the addition amounts are 0.5-0.8g of modified chitosan, 0.3-0.5g of sodium ascorbate, and 0.2-0.4g of nano-silica per 100mL of solution. The modified chitosan is preferably carboxymethylated chitosan with a degree of substitution of ≥80%, which has excellent free radical adsorption capacity; the nano-silica is a hydrophilic material with a particle size of ≤50nm, which can effectively disperse heat and improve system stability.

[0029] In step (c), the mixed solution is evaporated under reduced pressure to recover the solvent and obtain a concentrated solution. This step is completed using a rotary evaporator, controlling the vacuum degree to -0.08 MPa, the temperature to 45°C to 55°C, and the rotation speed to 60 to 80 rpm. The advantage of rotary evaporation over traditional static evaporation is that it avoids local overheating through mechanical stirring and dynamic heating, while greatly improving the evaporation efficiency. For example, when processing 1L of solution, the speed of the rotary evaporator can be set to 70 rpm, the temperature to 50°C, the vacuum degree to -0.08 MPa, and the entire evaporation process takes about 2 hours. During this process, the solvent gradually evaporates, and eugenol and its protective agent system are concentrated into a concentrated solution with a volume of about 1 / 5 of the original solution volume. In order to further improve the purification effect, after the reduced pressure evaporation is completed, the concentrated solution is placed in a 4°C environment to cool for 1 hour. Low-temperature cooling not only promotes the precipitation of impurities, but also avoids changes in the molecular structure of eugenol caused by temperature fluctuations, thereby ensuring the purity and stability of the product.

[0030] In step (d), the cooled concentrate is added to a 1% to 2% aqueous glycine solution, stirred evenly, and allowed to stand for 30 minutes. The amount of glycine solution used is 1.5 to 2.0 mL per 100 mL of concentrate. Glycine, as a weakly alkaline substance, can adjust the pH of the system to a weakly alkaline range (pH 7.5 to 8.0), thereby inhibiting the occurrence of oxidation reactions and promoting the precipitation and separation of impurities.

[0031] In step (e), the treated concentrated liquid is subjected to segmented temperature-controlled distillation, and the target fraction is collected to obtain high-purity eugenol. The segmented temperature-controlled distillation is carried out in two stages: the temperature of the first stage is 50°C to 60°C and the pressure is -0.06MPa; the temperature of the second stage is 70°C to 80°C and the pressure is -0.04MPa. This dynamic temperature adjustment technology can match the volatility characteristics of eugenol, and significantly improves the thermal energy utilization rate and product purity compared to traditional constant temperature distillation. For example, in the first stage, the concentrated liquid is heated to 55°C and the pressure is maintained at -0.06MPa for 30 minutes. At this time, low-boiling point impurities are preferentially distilled out; then entering the second stage, the temperature is raised to 75°C and the pressure is adjusted to -0.04MPa for 45 minutes. At this time, the target fraction, i.e., high-purity eugenol, is collected. To further enhance antioxidant properties, a 0.5% to 1% β-cyclodextrin solution can be added to the concentrate before distillation, at a rate of 1.0 mL per 100 mL. β-cyclodextrin can include eugenol molecules, reducing their exposure to oxygen and thus minimizing oxidation. For example, when processing 300 mL of concentrate, add 3 mL of a 1% β-cyclodextrin solution, stir thoroughly, and then proceed with distillation.

[0032] Compared with the existing technology, the advantages of this solution are:

[0033] 1. The core of the entire process lies in the synergistic effect of the composite protective agent system and the staged temperature-controlled distillation technology to achieve the efficient purification of eugenol.

[0034] 2. The composite protective agent constructs a stable molecular protective layer by using modified chitosan to adsorb free radicals, sodium ascorbate to scavenge oxidative active substances, and nano-silica to disperse heat, effectively inhibiting the occurrence of thermal decomposition and oxidation reactions. The staged temperature-controlled distillation technology achieves efficient separation through dynamic temperature adjustment based on the volatility characteristics of eugenol, avoiding the impact of high temperature or long-term operation on product quality. The introduction of glycine and β-cyclodextrin further enhances the antioxidant properties of the system, ensuring the high purity and stability of the final product. DETAILED DESCRIPTION

[0035] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0036] Preparation method of carboxymethylated chitosan with a degree of substitution ≥ 80% used in the embodiments and comparative examples of this scheme:

[0037] Step 1: Raw material pretreatment and alkalization activation

[0038] Take 10g of chitosan with a deacetylation degree of ≥90%, crush it through a 100-mesh sieve, and disperse it in 200mL of a 4:1 isopropanol / water mixture. In an ice-water bath, under constant stirring at 300rpm, slowly add 40% NaOH solution dropwise at a molar ratio of chitosan:NaOH = 1:8. Control the temperature and react for 1.5h to form a uniformly alkaline colloid.

[0039] Step 2: Carboxymethylation reaction

[0040] Sodium chloroacetate was added to the alkalized colloid in three portions, with a total molar ratio of chitosan:sodium chloroacetate = 1:12. 0.5 g of tetrabutylammonium bromide was simultaneously added as a phase transfer catalyst. The reaction was first carried out at 15° C. for 2 h, then the temperature was raised to 60° C. and the reaction was continued for 4 h with a stirring rate of 500 rpm to complete the carboxymethyl substitution. The pH of the reaction solution was adjusted to 7.0 with glacial acetic acid to terminate the reaction. The mixture was poured into 3 volumes of 80% ethanol solution for precipitation. The white flocculent solid was collected by centrifugation, and the supernatant was discarded to obtain a crude product.

[0041] Step 3: Purification and drying

[0042] The crude product was washed three times with 80% ethanol, anhydrous ethanol, and acetone to remove residual salt and solvent. The solid was dissolved in deionized water and placed in a dialysis bag with a molecular weight cutoff of 3.5 kDa. The product was dialyzed in running water for 48 h. The final solution was freeze-dried to obtain carboxymethylated chitosan with a degree of substitution ≥80%.

[0043] Example 1

[0044] A method for purifying eugenol comprises the following steps:

[0045] (a) dissolving crude eugenol in an ethanol aqueous solution to prepare a solution having a eugenol concentration of 20%;

[0046] The dissolution process was carried out at room temperature and stirred at 300 rpm using a magnetic stirrer for 30 min; the mass ratio of ethanol to water in the ethanol-water solution was 7:3;

[0047] (b) adding a composite protective agent to the solution, stirring at 500 rpm for 10 minutes, and then standing for 1 hour to obtain a mixed solution, wherein the composite protective agent comprises carboxymethylated chitosan with a degree of substitution of ≥80%, sodium ascorbate, and nano-silica with a particle size of ≤50 nm;

[0048] The addition amount of composite protective agent is as follows: modified chitosan 0.5g, sodium ascorbate 0.3g, nano-silica 0.2g per 100mL solution;

[0049] (c) evaporating the mixture under reduced pressure using a rotary evaporator at a speed of 60 rpm, a controlled vacuum of -0.08 MPa, a temperature of 45°C, and a time of 2 h. Recovering the solvent to obtain a concentrate having a volume of 20% of the original solution, and cooling the concentrate at 4°C for 1 h.

[0050] (d) adding the concentrate to a 1% glycine aqueous solution at pH 7.5, stirring at 400 rpm for 5 min, and then allowing to stand for 30 min;

[0051] The dosage of glycine aqueous solution is 1.5 mL per 100 mL of concentrate;

[0052] (e) A 0.5% mass concentration of β-cyclodextrin solution was added to the treated concentrate at a dosage of 1.0 mL / 100 mL of the concentrate, followed by staged temperature-controlled distillation. The first stage was performed at a temperature of 50° C., a pressure of −0.06 MPa, and a duration of 30 min; the second stage was performed at a temperature of 70° C., a pressure of −0.04 MPa, and a duration of 45 min. The target fractions were collected to obtain high-purity eugenol.

[0053] Example 2

[0054] A method for purifying eugenol comprises the following steps:

[0055] (a) dissolving crude eugenol in an ethanol aqueous solution to prepare a solution having a eugenol concentration of 25%;

[0056] The dissolution process was carried out at room temperature and stirred at 300 rpm using a magnetic stirrer for 30 min; the mass ratio of ethanol to water in the ethanol-water solution was 7.5:2.5;

[0057] (b) adding a composite protective agent to the solution, stirring at 500 rpm for 10 minutes, and then standing for 1 hour to obtain a mixed solution, wherein the composite protective agent comprises carboxymethylated chitosan with a degree of substitution of ≥80%, sodium ascorbate, and nano-silica with a particle size of ≤50 nm;

[0058] The addition amount of composite protective agent is as follows: modified chitosan 0.6g, sodium ascorbate 0.4g, nano-silica 0.3g per 100mL solution;

[0059] (c) evaporating the mixture under reduced pressure using a rotary evaporator at a speed of 70 rpm, a controlled vacuum of -0.08 MPa, a temperature of 50°C, and a time of 2 h. Recovering the solvent to obtain a concentrate having a volume of 20% of the original solution, and cooling the concentrate at 4°C for 1 h.

[0060] (d) adding the concentrate to a 1.5% glycine aqueous solution at pH 7.8, stirring at 400 rpm for 5 min, and then allowing to stand for 30 min;

[0061] The amount of glycine aqueous solution used is 1.75 mL per 100 mL of concentrate;

[0062] (e) A 0.75% mass concentration of β-cyclodextrin solution was added to the treated concentrate at a rate of 1.0 mL / 100 mL of concentrate, followed by staged temperature-controlled distillation. The first stage was conducted at a temperature of 55° C., a pressure of −0.06 MPa, and a duration of 30 min; the second stage was conducted at a temperature of 75° C., a pressure of −0.04 MPa, and a duration of 45 min. The target fractions were collected to obtain high-purity eugenol.

[0063] Example 3

[0064] A method for purifying eugenol comprises the following steps:

[0065] (a) dissolving crude eugenol in an ethanol aqueous solution to prepare a solution having a eugenol concentration of 30%;

[0066] The dissolution process was carried out at room temperature and stirred at 300 rpm using a magnetic stirrer for 30 min; the mass ratio of ethanol to water in the ethanol-water solution was 8:2;

[0067] (b) adding a composite protective agent to the solution, stirring at 500 rpm for 10 minutes, and then standing for 1 hour to obtain a mixed solution, wherein the composite protective agent comprises carboxymethylated chitosan with a degree of substitution of ≥80%, sodium ascorbate, and nano-silica with a particle size of ≤50 nm;

[0068] The addition amount of composite protective agent is as follows: modified chitosan 0.8g, sodium ascorbate 0.5g, nano-silica 0.4g per 100mL solution;

[0069] (c) evaporating the mixture under reduced pressure using a rotary evaporator at a speed of 80 rpm, a controlled vacuum of -0.08 MPa, a temperature of 55°C, and a time of 2 h. Recovering the solvent to obtain a concentrate having a volume of 20% of the original solution, and cooling the concentrate at 4°C for 1 h.

[0070] (d) adding the concentrate to a 2% glycine aqueous solution at pH 8.0, stirring at 400 rpm for 5 min, and then allowing to stand for 30 min;

[0071] The amount of glycine aqueous solution used is 2.0 mL per 100 mL of concentrate;

[0072] (e) A 1% mass concentration of β-cyclodextrin solution was added to the treated concentrate at a rate of 1.0 mL / 100 mL of concentrate, followed by staged temperature-controlled distillation. The first stage was performed at a temperature of 60° C., a pressure of −0.06 MPa, and a duration of 30 min; the second stage was performed at a temperature of 80° C., a pressure of −0.04 MPa, and a duration of 45 min. The target fractions were collected to obtain high-purity eugenol.

[0073] Example 4

[0074] A method for purifying eugenol comprises the following steps:

[0075] (a) dissolving crude eugenol in an ethanol aqueous solution to prepare a solution having a eugenol concentration of 22%;

[0076] The dissolution process was carried out at room temperature and stirred at 300 rpm using a magnetic stirrer for 30 min; the mass ratio of ethanol to water in the ethanol-water solution was 7.2:2.8;

[0077] (b) adding a composite protective agent to the solution, stirring at 500 rpm for 10 minutes, and then standing for 1 hour to obtain a mixed solution, wherein the composite protective agent comprises carboxymethylated chitosan with a degree of substitution of ≥80%, sodium ascorbate, and nano-silica with a particle size of ≤50 nm;

[0078] The addition amount of composite protective agent is as follows: modified chitosan 0.7g, sodium ascorbate 0.45g, nano-silica 0.35g per 100mL solution;

[0079] (c) The mixed solution was evaporated under reduced pressure using a rotary evaporator at a speed of 65 rpm, a controlled vacuum of -0.08 MPa, a temperature of 52°C, and a time of 2 h. The solvent was recovered to obtain a concentrate having a volume of 20% of the original solution. The concentrate was cooled at 4°C for 1 h.

[0080] (d) adding the concentrate to a 1.8% glycine aqueous solution at pH 7.6, stirring at 400 rpm for 5 min, and then allowing to stand for 30 min;

[0081] The amount of glycine aqueous solution used is 1.8 mL per 100 mL of concentrate;

[0082] (e) A 0.8% mass concentration of β-cyclodextrin solution was added to the treated concentrate at a rate of 1.0 mL / 100 mL of concentrate, followed by staged temperature-controlled distillation. The first stage was conducted at a temperature of 58° C., a pressure of −0.06 MPa, and a duration of 30 min; the second stage was conducted at a temperature of 78° C., a pressure of −0.04 MPa, and a duration of 45 min. The target fractions were collected to obtain high-purity eugenol.

[0083] Comparative Example 1

[0084] The difference from Example 1 is that no composite protective agent is added:

[0085] A method for purifying eugenol comprises the following steps:

[0086] (a) dissolving crude eugenol in an ethanol aqueous solution to prepare a solution having a eugenol concentration of 20%;

[0087] The dissolution process was carried out at room temperature and stirred at 300 rpm using a magnetic stirrer for 30 min; the mass ratio of ethanol to water in the ethanol-water solution was 7:3;

[0088] (b) evaporating the solution under reduced pressure using a rotary evaporator at a speed of 60 rpm, a controlled vacuum of -0.08 MPa, a temperature of 45°C, and a time of 2 h. Recovering the solvent to obtain a concentrate having a volume of 20% of the original solution, and cooling the concentrate at 4°C for 1 h.

[0089] (c) adding the concentrate to a 1% glycine aqueous solution at pH 7.5, stirring at 400 rpm for 5 minutes, and then allowing to stand for 30 minutes;

[0090] The dosage of glycine aqueous solution is 1.5 mL per 100 mL of concentrate;

[0091] (d) A 0.5% mass concentration of β-cyclodextrin solution was added to the treated concentrate at a rate of 1.0 mL / 100 mL of concentrate, followed by staged temperature-controlled distillation. The first stage was conducted at a temperature of 50° C., a pressure of −0.06 MPa, and a duration of 30 min; the second stage was conducted at a temperature of 70° C., a pressure of −0.04 MPa, and a duration of 45 min. The target fractions were collected to obtain high-purity eugenol.

[0092] Comparative Example 2

[0093] The difference from Example 1 is that the chitosan in the composite protective agent is not modified:

[0094] A method for purifying eugenol comprises the following steps:

[0095] (a) dissolving crude eugenol in an ethanol aqueous solution to prepare a solution having a eugenol concentration of 20%;

[0096] The dissolution process was carried out at room temperature and stirred at 300 rpm using a magnetic stirrer for 30 min; the mass ratio of ethanol to water in the ethanol-water solution was 7:3;

[0097] (b) adding a composite protective agent to the solution, stirring at 500 rpm for 10 minutes and then standing for 1 hour to obtain a mixed solution, wherein the composite protective agent comprises chitosan, sodium ascorbate, and nano-silica with a particle size of ≤50 nm;

[0098] The addition amount of composite protective agent is as follows: chitosan 0.5g, sodium ascorbate 0.3g, nano-silica 0.2g per 100mL solution;

[0099] (c) evaporating the mixture under reduced pressure using a rotary evaporator at a speed of 60 rpm, a controlled vacuum of -0.08 MPa, a temperature of 45°C, and a time of 2 h. Recovering the solvent to obtain a concentrate having a volume of 20% of the original solution, and cooling the concentrate at 4°C for 1 h.

[0100] (d) adding the concentrate to a 1% glycine aqueous solution at pH 7.5, stirring at 400 rpm for 5 min, and then allowing to stand for 30 min;

[0101] The dosage of glycine aqueous solution is 1.5 mL per 100 mL of concentrate;

[0102] (e) A 0.5% mass concentration of β-cyclodextrin solution was added to the treated concentrate at a dosage of 1.0 mL / 100 mL of the concentrate, followed by staged temperature-controlled distillation. The first stage was performed at a temperature of 50° C., a pressure of −0.06 MPa, and a duration of 30 min; the second stage was performed at a temperature of 70° C., a pressure of −0.04 MPa, and a duration of 45 min. The target fractions were collected to obtain high-purity eugenol.

[0103] Comparative Example 3

[0104] The difference from Example 1 is that no glycine solution was added:

[0105] A method for purifying eugenol comprises the following steps:

[0106] (a) dissolving crude eugenol in an ethanol aqueous solution to prepare a solution having a eugenol concentration of 20%;

[0107] The dissolution process was carried out at room temperature and stirred at 300 rpm using a magnetic stirrer for 30 min; the mass ratio of ethanol to water in the ethanol-water solution was 7:3;

[0108] (b) adding a composite protective agent to the solution, stirring at 500 rpm for 10 minutes, and then standing for 1 hour to obtain a mixed solution, wherein the composite protective agent comprises carboxymethylated chitosan with a degree of substitution of ≥80%, sodium ascorbate, and nano-silica with a particle size of ≤50 nm;

[0109] The addition amount of composite protective agent is as follows: modified chitosan 0.5g, sodium ascorbate 0.3g, nano-silica 0.2g per 100mL solution;

[0110] (c) evaporating the mixture under reduced pressure using a rotary evaporator at a speed of 60 rpm, a controlled vacuum of -0.08 MPa, a temperature of 45°C, and a time of 2 h. Recovering the solvent to obtain a concentrate having a volume of 20% of the original solution, and cooling the concentrate at 4°C for 1 h.

[0111] (d) A 0.5% mass concentration of β-cyclodextrin solution was added to the concentrate at a rate of 1.0 mL / 100 mL of concentrate, followed by staged temperature-controlled distillation. The first stage was conducted at a temperature of 50° C., a pressure of −0.06 MPa, and a duration of 30 min; the second stage was conducted at a temperature of 70° C., a pressure of −0.04 MPa, and a duration of 45 min. The target fractions were collected to obtain high-purity eugenol.

[0112] Comparative Example 4

[0113] The difference from Example 1 is that no cyclodextrin solution was added:

[0114] A method for purifying eugenol comprises the following steps:

[0115] (a) dissolving crude eugenol in an ethanol aqueous solution to prepare a solution having a eugenol concentration of 20%;

[0116] The dissolution process was carried out at room temperature and stirred at 300 rpm using a magnetic stirrer for 30 min; the mass ratio of ethanol to water in the ethanol-water solution was 7:3;

[0117] (b) adding a composite protective agent to the solution, stirring at 500 rpm for 10 minutes, and then standing for 1 hour to obtain a mixed solution, wherein the composite protective agent comprises carboxymethylated chitosan with a degree of substitution of ≥80%, sodium ascorbate, and nano-silica with a particle size of ≤50 nm;

[0118] The addition amount of composite protective agent is as follows: modified chitosan 0.5g, sodium ascorbate 0.3g, nano-silica 0.2g per 100ml solution;

[0119] (c) evaporating the mixture under reduced pressure using a rotary evaporator at a speed of 60 rpm, a controlled vacuum of -0.08 MPa, a temperature of 45°C, and a time of 2 h. Recovering the solvent to obtain a concentrate having a volume of 20% of the original solution, and cooling the concentrate at 4°C for 1 h.

[0120] (d) adding the concentrate to a 1% glycine aqueous solution at pH 7.5, stirring at 400 rpm for 5 min, and then allowing to stand for 30 min;

[0121] The dosage of glycine aqueous solution is 1.5 ml per 100 ml of concentrate;

[0122] (e) The treated concentrated liquid is subjected to staged temperature-controlled distillation, wherein the temperature of the first stage is 50° C., the pressure is -0.06 MPa, and the duration is 30 min; the temperature of the second stage is 70° C., the pressure is -0.04 MPa, and the duration is 45 min, and the target fraction is collected to obtain high-purity eugenol.

[0123] Comparative Example 5

[0124] The difference from Example 1 is that no staged temperature-controlled distillation is performed:

[0125] A method for purifying eugenol comprises the following steps:

[0126] (a) dissolving crude eugenol in an ethanol aqueous solution to prepare a solution having a eugenol concentration of 20%;

[0127] The dissolution process was carried out at room temperature and stirred at 300 rpm using a magnetic stirrer for 30 min; the mass ratio of ethanol to water in the ethanol-water solution was 7:3;

[0128] (b) adding a composite protective agent to the solution, stirring at 500 rpm for 10 minutes, and then standing for 1 hour to obtain a mixed solution, wherein the composite protective agent comprises carboxymethylated chitosan with a degree of substitution of ≥80%, sodium ascorbate, and nano-silica with a particle size of ≤50 nm;

[0129] The addition amount of composite protective agent is as follows: modified chitosan 0.5g, sodium ascorbate 0.3g, nano-silica 0.2g per 100ml solution;

[0130] (c) evaporating the mixture under reduced pressure using a rotary evaporator at a speed of 60 rpm, a controlled vacuum of -0.08 MPa, a temperature of 45°C, and a time of 2 h. Recovering the solvent to obtain a concentrate having a volume of 20% of the original solution, and cooling the concentrate at 4°C for 1 h.

[0131] (d) adding the concentrate to a 1% glycine aqueous solution at pH 7.5, stirring at 400 rpm for 5 min, and then allowing to stand for 30 min;

[0132] The dosage of glycine aqueous solution is 1.5 ml per 100 ml of concentrate;

[0133] (e) A 0.5% mass concentration of β-cyclodextrin solution was added to the treated concentrate at a dosage of 1.0 ml / 100 ml of the concentrate, and then the target fraction was collected at a temperature of 70° C. and a pressure of −0.04 MPa for 75 min to obtain high-purity eugenol.

[0134] Comparative Example 6

[0135] The difference from Example 1 is that the component ratio of the composite protective agent is abnormal:

[0136] A method for purifying eugenol comprises the following steps:

[0137] (a) dissolving crude eugenol in an ethanol aqueous solution to prepare a solution having a eugenol concentration of 20%;

[0138] The dissolution process was carried out at room temperature and stirred at 300 rpm using a magnetic stirrer for 30 min; the mass ratio of ethanol to water in the ethanol-water solution was 7:3;

[0139] (b) adding a composite protective agent to the solution, stirring at 500 rpm for 10 minutes, and then allowing to stand for 1 hour to obtain a mixed solution, wherein the composite protective agent comprises carboxymethylated chitosan having a degree of substitution of ≥80% and sodium ascorbate;

[0140] The addition amount of composite protective agent is: 1g of modified chitosan and 0.3g of sodium ascorbate per 100ml of solution;

[0141] (c) evaporating the mixture under reduced pressure using a rotary evaporator at a speed of 60 rpm, a controlled vacuum of -0.08 MPa, a temperature of 45°C, and a time of 2 h. Recovering the solvent to obtain a concentrate having a volume of 20% of the original solution, and cooling the concentrate at 4°C for 1 h.

[0142] (d) adding the concentrate to a 1% glycine aqueous solution at pH 7.5, stirring at 400 rpm for 5 min, and then allowing to stand for 30 min;

[0143] The dosage of glycine aqueous solution is 1.5 ml per 100 ml of concentrate;

[0144] (e) A 0.5% mass concentration of β-cyclodextrin solution was added to the treated concentrate at a dosage of 1.0 ml / 100 ml of concentrate, followed by staged temperature-controlled distillation. The first stage was performed at a temperature of 50° C., a pressure of −0.06 MPa, and a duration of 30 min; the second stage was performed at a temperature of 70° C., a pressure of −0.04 MPa, and a duration of 45 min. The target fractions were collected to obtain high-purity eugenol.

[0145] Comparative Example 7

[0146] The difference from Example 1 is that the substitution degree of carboxymethylated chitosan is too low, only 75%:

[0147] A method for purifying eugenol comprises the following steps:

[0148] (a) dissolving crude eugenol in an ethanol aqueous solution to prepare a solution having a eugenol concentration of 20%;

[0149] The dissolution process was carried out at room temperature and stirred at 300 rpm using a magnetic stirrer for 30 min; the mass ratio of ethanol to water in the ethanol-water solution was 7:3;

[0150] (b) adding a composite protective agent to the solution, stirring at 500 rpm for 10 minutes, and then standing for 1 hour to obtain a mixed solution, wherein the composite protective agent comprises carboxymethylated chitosan with a degree of substitution of ≥80%, sodium ascorbate, and nano-silica with a particle size of ≤50 nm;

[0151] The addition amount of composite protective agent is as follows: modified chitosan 0.5g, sodium ascorbate 0.3g, nano-silica 0.2g per 100ml solution;

[0152] (c) evaporating the mixture under reduced pressure using a rotary evaporator at a speed of 60 rpm, a controlled vacuum of -0.08 MPa, a temperature of 45°C, and a time of 2 h. Recovering the solvent to obtain a concentrate having a volume of 20% of the original solution, and cooling the concentrate at 4°C for 1 h.

[0153] (d) adding the concentrate to a 1% glycine aqueous solution at pH 7.5, stirring at 400 rpm for 5 min, and then allowing to stand for 30 min;

[0154] The dosage of glycine aqueous solution is 1.5 ml per 100 ml of concentrate;

[0155] (e) A 0.5% mass concentration of β-cyclodextrin solution was added to the treated concentrate at a dosage of 1.0 ml / 100 ml of concentrate, followed by staged temperature-controlled distillation. The first stage was performed at a temperature of 50° C., a pressure of −0.06 MPa, and a duration of 30 min; the second stage was performed at a temperature of 70° C., a pressure of −0.04 MPa, and a duration of 45 min. The target fractions were collected to obtain high-purity eugenol.

[0156] Performance testing:

[0157] Eugenol purity determination: HPLC method;

[0158] Colorimetric determination: platinum-cobalt colorimetry;

[0159] Yield calculation: actual extraction amount ÷ theoretical content × 100%.

[0160] Antioxidant capacity determination: Determination of DPPH free radical scavenging rate.

[0161] The test results are shown in Table 1.

[0162] Table 1 Test results of examples and comparative examples

[0163]

[0164] The purities of Examples 1-4 were all ≥98.2%, significantly higher than those of the comparative example, and the other indicators also performed excellently, indicating that the purity, yield, and antioxidant capacity of eugenol were significantly improved by key steps such as the composite protective agent and staged temperature-controlled distillation, thereby solving the problems of oxidative degradation, residual impurities, and low yield in traditional methods.

[0165] The core reason why Example 1 achieves better results than Comparative Examples 1-7 is that it comprehensively inhibits the oxidative degradation, impurity residue and volatilization loss of eugenol through multi-dimensional synergistic effects, while the performance of each comparative example is reduced due to the lack of key protection or separation mechanisms: Comparative Example 1 does not add a composite protective agent, and loses the protective effect of modified chitosan to adsorb impurities, sodium ascorbate to resist oxidation, and nano-silica to stabilize synergistically. Eugenol is easily oxidized and residual impurities such as pigments during dissolution and evaporation; Comparative Example 2 uses unmodified chitosan, whose water solubility and adsorption are significantly reduced, and it cannot effectively adsorb impurities, resulting in impurity residues; Comparative Example 3 does not add glycine solution, and no It can neutralize the free fatty acids in the crude product, but acidic impurities remain and react with eugenol, reducing its purity. Comparative Example 4 does not add β-cyclodextrin solution, which loses the dual functions of encapsulating eugenol to reduce volatility, reduce distillation losses, and inhibit oxidation. Eugenol is volatile and more susceptible to oxidation. Comparative Example 5 does not perform staged temperature-controlled distillation, which cannot accurately separate impurities with similar boiling points, resulting in the co-distillation of impurities and eugenol, reducing purity. Comparative Example 6 has excessive chitosan and insufficient sodium ascorbate, resulting in excessive adsorption of eugenol by chitosan and insufficient antioxidant capacity, exacerbating losses. Comparative Example 7 has a chitosan substitution degree of only 75%, significantly weakening its water solubility and adsorption, and poor impurity removal effect. Example 1 effectively solves the above problems through the synergistic effects of multiple protections of the composite protective agent, glycine deacidification, β-cyclodextrin inclusion, and staged temperature-controlled distillation, thereby achieving higher purity, yield, and antioxidant capacity.

Claims

1. A method for purifying eugenol, characterized in that: The following steps are involved: (a) dissolving crude eugenol in an ethanol aqueous solution to prepare a solution having a eugenol concentration of 20% to 30%; (b) adding a composite protective agent to the solution, stirring uniformly and then allowing to stand to obtain a mixed solution, wherein the composite protective agent comprises modified chitosan, sodium ascorbate and nano-silica; (c) evaporating the mixed solution under reduced pressure, recovering the solvent and obtaining a concentrated solution; (d) adding the concentrated solution to a 1% to 2% glycine aqueous solution with a mass concentration, stirring evenly, and then allowing to stand; (e) subjecting the concentrated solution treated in (d) to segmented temperature-controlled distillation, collecting target fractions, and obtaining high-purity eugenol.

2. The method for purifying eugenol according to claim 1, wherein The addition amount of the composite protective agent in step (b) is as follows: 0.5-0.8 g of modified chitosan, 0.3-0.5 g of sodium ascorbate, and 0.2-0.4 g of nano-silica per 100 mL of solution.

3. The method for purifying eugenol according to claim 1 or 2, wherein: The modified chitosan is carboxymethylated chitosan with a substitution degree of ≥80%, and the nano-silicon dioxide particle size is ≤50nm.

4. The method for purifying eugenol according to claim 1, wherein The reduced pressure evaporation in step (c) is carried out using a rotary evaporator at a speed of 60 to 80 rpm; the reduced pressure evaporation time is 2 h, and the final concentrated solution volume is 20% of the original solution volume.

5. The method for purifying eugenol according to claim 1, wherein After evaporation under reduced pressure in step (c), the concentrate was placed in a 4° C. environment for cooling for 1 h.

6. The method for purifying eugenol according to claim 1, wherein The staged temperature-controlled distillation in step (e) is carried out in two stages: the temperature of the first stage is 50°C to 60°C and the pressure is -0.06MPa; the temperature of the second stage is 70°C to 80°C and the pressure is -0.04MPa; The duration of the first phase was 30 min, and the duration of the second phase was 45 min.

7. The method for purifying eugenol according to claim 1, wherein: Before the distillation in step (e), a β-cyclodextrin solution having a mass concentration of 0.5% to 1% is added to the concentrated solution after the treatment in step (d) in an amount of 1.0 mL / 100 mL of the concentrated solution.

8. The method for purifying eugenol according to claim 1, wherein: The amount of the glycine aqueous solution in step (d) is 1.5 to 2.0 mL per 100 mL of the concentrated solution; the glycine aqueous solution is used to adjust the pH value of the system to 7.5 to 8.0; the stirring process speed is 400 rpm and the stirring time is 5 minutes.

9. The method for purifying eugenol according to claim 1, wherein: The dissolution process in step (a) is carried out at room temperature and stirred at 300 rpm for 30 min using a magnetic stirrer; the mass ratio of ethanol to water in the ethanol aqueous solution is 7:3 to 8:

2.

10. The method for purifying eugenol according to claim 1, wherein: The stirring speed in step (b) is 500 rpm and the stirring time is 10 min.

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