Preparation method and application of hydrogenation catalyst

Abstract

The invention discloses preparation of a hydrogenation catalyst and a method for improving fragrance of tetrahydrogeraniol. By changing the water content in the catalyst, influencing the generation of the key product tetrahydrocitral, doping orange fragrance and effectively improving the fragrance problem, the process can effectively improve the additional value, consume the citral product in the industrial chain and effectively reduce the emission of three wastes.

Description

Technical Field

[0001] This invention relates to the field of hydrogenation, specifically to the preparation of a hydrogenation catalyst and a method for improving the aroma of tetrahydrogeraniol. Background Technology

[0002] Tetrahydrogeraniol, chemically known as 3,7-dimethyloctane-1-ol, is a colorless to pale yellow viscous liquid with a soft, long-lasting, and sweet rose and lily floral scent, accompanied by a slight fruity and woody undertone. Tetrahydrogeraniol is an extremely important and commonly used raw material in everyday fragrances, its application primarily driven by the pursuit of high-quality and stable aromas. It is widely used in high-end perfumes, skincare products, shower gels, shampoos, and conditioners. It is also frequently used as a main ingredient or harmonizing agent in floral fragrances such as rose, lily, lily of the valley, and magnolia, providing a rich and lingering floral base to the formula. Furthermore, it can be used as an organic synthesis intermediate in the synthesis of other more complex fragrance or pharmaceutical molecules.

[0003] Patent document CN 1210240C describes the direct catalytic hydrogenation of a mixture of products synthesized from linalool, citronellol, citronellol, or geraniol / nerol, along with distillation residues. Appropriate hydrogenation catalysts and process conditions, such as using metallic catalysts like copper, silver, or gold, are employed. This method achieves high conversion and selectivity in the preparation of tetrahydrogeraniol, extends catalyst life, reduces production costs, and improves yield and separation efficiency. However, this patent only mentions the preparation method of tetrahydrogeraniol and does not describe its characteristic rose and fruity aroma, nor does it address how to enhance its aroma quality.

[0004] Patent document CN 113996346B discloses a method for preparing a novel catalyst for the hydrogenation of citral to tetrahydrogeraniol. The catalyst comprises three parts: a matrix, a ligand, and an auxiliary agent. The matrix is ​​a porphyrin compound containing a central metal, the ligand is a phosphine ligand compound containing a specific functional group, and the auxiliary agent is an iron, nickel, aluminum, or chromium compound. The catalyst described in this invention is suitable for catalyzing the hydrogenation reaction of substances with multiple degrees of unsaturation, and has the advantages of high catalytic efficiency, minimal loss of active components, and stable activity. Although this method achieves high conversion and selectivity, it does not address the aroma issue of the prepared tetrahydrogeraniol.

[0005] Methods for preparing tetrahydrogeraniol by hydrogenating unsaturated precursors such as citral, citronellol, citronellol, or nerol / geraniol have been documented for a long time. As early as 1912, Ipatjew (Chem. Ber., 45, 1912, 3222) reported the hydrogenation of citral on a palladium catalyst. In 1981, Savoia, Tagliavini, Trombini, and Umani-Ronchi (J. Org. Chem., 1981, 46, 5344-5348) documented their research on the hydrogenation of citral on a potassium-graphite supported metal catalyst, in which a Ni / graphite catalyst yielded 95% tetrahydrogeraniol. In 1993, the hydrogenation of citronellol on a Pd / C catalyst yielded tetrahydrogeraniol in a 93% yield. In addition, in 1995, Iyer and Varghese (J. Chem. Soc. Chem. Commun., 1995, 465-466) reported the hydrogenation of 3,7-dimethyloctanal using the homogeneous catalyst NiCl2(PPh3)2 with a yield of 57%. However, the literature reports on the preparation of tetrahydrogeraniol showed low selectivity and did not mention the odor problem of the prepared product.

[0006] Citral contains isolated C=C double bonds, C=O bonds, and C=C double bonds conjugated with the carbonyl group, making the hydrogenation products quite complex, largely depending on the catalyst and hydrogenation conditions. Tetrahydrogeraniol is primarily prepared via selective catalytic hydrogenation. Geraniol or nerol, being cis-trans isomers, are the most direct starting materials; citronellol is an even cheaper starting material, but its hydrogenation process is more complex, requiring hydrogenation or protection / deprotection steps.

[0007] Aroma is one of the most important physical properties of fragrance raw materials, and how to adjust the aroma of the product is a key focus of current research. During the hydrogenation of citral, the numerous and complex double bonds in the molecule lead to complex impurities in the product, resulting in decreased selectivity for tetrahydrogeraniol. Therefore, developing a hydrogenation process with high yield, selectivity, and stable, long catalyst life by adjusting the physical properties of the catalyst and precisely controlling the key components in the hydrogenation product is currently necessary. Tetrahydrogeraniol prepared in this way also has better commercial value and prospects. Summary of the Invention

[0008] The purpose of this invention is to provide a hydrogenation catalyst. Using the catalyst of this invention, citral is directly catalytically hydrogenated to tetrahydrogeraniol with high selectivity, producing a sweet rose and lily aroma. Furthermore, by altering the water content of the catalyst, the formation of the key component tetrahydrocitral can be influenced, thus regulating the off-flavor of orange and effectively improving the aroma of tetrahydrogeraniol. This process can effectively increase added value, consume citral byproducts in the industrial chain, and effectively reduce the emission of waste gas, wastewater, and solid waste.

[0009] To effectively achieve the above-mentioned invention, the present invention uses the following technical solution:

[0010] In a first aspect, the present invention provides a hydrogenation catalyst.

[0011] A hydrogenation catalyst comprising: active components Pd and Ru, and supports Al2O3 and H2O; wherein, based on the weight of the catalyst (the sum of the masses of Pd, Ru, Al2O3, and H2O), the content of active component Pd in ​​the catalyst is 5-20 wt%, preferably 10-20 wt%, the content of Ru is 0.1-5 wt%, preferably 1-4 wt%, and the water content is 5-20 wt%, preferably 7-18 wt%.

[0012] The present invention also provides a method for preparing the hydrogenation catalyst, comprising the following steps:

[0013] 1) Preparation of Ru-Pd bimetallic nanoparticles, the active ingredient;

[0014] Place the aqueous solution containing ruthenium and palladium sources in a container, add the reducing agent, set the heating temperature and stirring speed, and ensure that all substances are completely dissolved and mixed.

[0015] 2) Preparation of catalyst precursor Pd-Ru / Al2O3 by hydrothermal method;

[0016] Transfer the solution from step 1) to a polytetrafluoroethylene reactor, add Al2O3, seal the reactor and place it in a forced-air drying oven, set the reaction temperature and time, and then carry out a hydrothermal reaction. After the reaction is completed, centrifuge to remove the supernatant and collect the catalyst precursor at the bottom of the centrifuge tube.

[0017] 3) Preparation of Pd-Ru / Al2O3 catalysts with different water contents;

[0018] The catalyst precursor was dried to obtain catalysts with different water contents.

[0019] In the preparation method, the ruthenium source in step 1) is selected from ammonium ruthenium chlororuthenate, ruthenium nitrate, and ruthenium chloride, and the palladium source is selected from ammonium chloropalladiumate, palladium nitrate, and palladium chloride;

[0020] The reducing agent is selected from urea, sodium citrate and glucose, and the amount of reducing agent used is 10-50 wt%, based on the total mass of ruthenium and palladium.

[0021] In step 1), the heating temperature is 60-80℃ and the stirring speed is 600-800rpm.

[0022] In step 2), the reaction temperature is 100-120℃ and the time is 6-10h.

[0023] In step 3), the catalyst precursor is dried: in specific embodiments, a refrigerator, a regular drying oven, and a vacuum drying oven can be used for drying.

[0024] In another aspect, the present invention provides the application of the catalyst in the hydrogenation of citral to prepare tetrahydrogeraniol.

[0025] A method for preparing tetrahydrogeraniol includes: hydrogenating citral feedstock in the presence of a catalyst as described above.

[0026] In the method, the citral raw material contains 80-98 wt% geranialdehyde, preferably 85-95%, with the remainder mainly being neraldehyde.

[0027] In the method, the amount of catalyst added is 0.5-3 wt% of the reaction raw materials.

[0028] In the method described, the reaction temperature is 40-100℃ and the pressure is 1-4MPa.

[0029] In one specific embodiment, the specific reaction steps are as follows: citral is added to the reaction vessel, a catalyst is added, and the mixture is replaced multiple times with nitrogen and hydrogen. Then, the temperature of the reaction vessel is set to 40-100℃, and hydrogen is pressurized to 1-4MPa to carry out the reaction.

[0030] In this invention, the catalyst has different water contents. After hydrogenation, citral yields tetrahydrogeraniol products with different purities. The higher the water content, the more it promotes the formation of the key component tetrahydrogeraniol. The orange aroma will be mixed into the tetrahydrogeraniol product, thereby improving the overall product aroma. According to the test, the catalyst has a water content of 12.4%, and the product aroma is optimal when the tetrahydrogeraniol content is 2.5%.

[0031] An aroma-enhancing tetrahydrogeraniol is prepared by the above method, wherein it preferably contains 1-6 wt% tetrahydrocitral.

[0032] Compared with existing technical solutions, the advantages of this invention are as follows:

[0033] 1. The catalyst of the present invention has a bimetallic structure and is supported by Al2O3, which effectively improves the surface pore structure of the catalyst itself, increases its surface area, promotes the adsorption of hydrogen bonds by the catalyst, and effectively reduces citral to produce tetrahydrogeraniol.

[0034] 2. The catalyst of this invention has high activity and can be stably used for at least 20 batches. The conversion rate of the reaction can reach over 99%, the selectivity of tetrahydrogeraniol is over 90%, and the selectivity of tetrahydrocitral is less than 10%.

[0035] 3. The tetrahydrogeraniol prepared by this invention has a sweet rose aroma. By controlling the water content of the catalyst, the aroma regulating component tetrahydrocitral can be generated, which increases the orange aroma effect and enhances the top note effect and aroma residence time of tetrahydrogeraniol, effectively improving the aroma of the product. Detailed Implementation

[0036] To facilitate understanding of the present invention, the following description, in conjunction with embodiments, will further illustrate the invention. It should be understood that the following embodiments are merely for a better understanding of the invention and do not imply that the invention is limited to these embodiments.

[0037] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The term "and / or" may be used herein to include any and all combinations of one or more of the associated listed items.

[0038] Raw material source:

[0039] Ammonium ruthenium chloride: 99.9 wt%, Aladdin Reagent Co., Ltd.

[0040] Ruthenium nitrate: 99.9 wt%, Thermo Fisher Scientific (China) Co., Ltd.

[0041] Ruthenium chloride: 99.9 wt%, Aladdin Reagent Co., Ltd.

[0042] Ammonium chloropalladium: 99.9 wt%, Aladdin Reagent Co., Ltd.

[0043] Palladium nitrate: 99.9 wt%, Thermo Fisher Scientific (China) Co., Ltd.

[0044] Palladium chloride: 99.9 wt%, Aladdin Reagent Co., Ltd.

[0045] Urea: 99.5 wt%, Aladdin Reagent Co., Ltd.

[0046] Glucose: 98wt%, Aladdin Reagent Co., Ltd.

[0047] Sodium citrate: 99wt%, Aladdin Reagent Co., Ltd.

[0048] Citral: Geraniol content is 90wt%, Wanhua Chemical Group Co., Ltd.

[0049] Test method:

[0050] Gas chromatograph: Agilent 7890, column: Wax, injection port temperature: 300℃; split ratio: 50:1; carrier gas flow rate: 52.8 mL / min; temperature program: hold at 150℃ for 10 min, increase to 260℃ at a rate of 10℃ / min, hold for 5 min; detector temperature: 280℃.

[0051] Catalyst water content analysis: thermogravimetric analyzer, instrument heating rate 5-20℃ / min, initial temperature 20℃, target temperature 800-1000℃, gas atmosphere: N2.

[0052] Aroma Evaluation Method: Sensory evaluation panel (five members, at least 80% agreement for reliable aroma results). Core testing items include: 1. Aroma Identification and Description: Identifying the overall aroma characteristics of the sample and accurately describing them using professional terminology (fruit, floral, green, woody, etc.). 2. Aroma Intensity Assessment: Evaluating the strength or intensity of the sample's aroma. 3. Off-Odor / Defect Detection: Identifying and assessing the presence of any unexpected or unpleasant odors in the product. 4. Aroma Persistence / Stability Testing: Assessing how the aroma changes over time during the product's lifecycle or under specific storage conditions.

[0053] Example 1

[0054] 1) Place an aqueous solution containing 1.17g of ammonium chlororuthenate and 5.62g of ammonium chloropalladate in a flask, add 0.96g of urea, set the oil bath temperature to 80℃, the magnetic stirring speed to 800rpm, and the reaction time to 6h.

[0055] 2) Transfer the solution prepared in 1) to a 50 mL polytetrafluoroethylene reactor, add 7.62 g Al2O3, seal the reactor and place it in a forced-air drying oven, set the reaction temperature to 100 °C and the reaction time to 10 h, centrifuge after the reaction, remove the supernatant and collect the catalyst precursor at the bottom of the centrifuge tube.

[0056] 3) Place the catalyst precursor in a vacuum drying oven and dry it at 60°C for 12 hours. Analyze the water content of the treated catalyst.

[0057] Preparation of aroma-enhancing tetrahydrogeraniol:

[0058] Weigh 150g of citral raw material and place it in the reactor. Add 3.36g of the prepared hydrogenation catalyst and pressurize it to 4MPa with nitrogen. Hold the pressure for 2 hours. Then release the pressure inside the reactor and replace it with nitrogen and hydrogen three times. Turn on the built-in stirrer in the reactor and set the speed to 1200rpm. Heat it to 80℃, open the hydrogen valve, and control the gas flow meter speed to 100mL / min. The reaction pressure is 4MPa.

[0059] a. Results testing and fragrance evaluation:

[0060] When the instantaneous flow rate of the gas flow meter drops to 0, the hydrogenation reaction ends. Then, a sample is taken for analysis and sent to a fragrance evaluator for aroma evaluation.

[0061] The catalyst prepared in Example 1 was used in more than 20 batches to observe its stability and reaction effect.

[0062] Example 2

[0063] 1) Place an aqueous solution containing 1.17g of ammonium chlororuthenate and 5.62g of ammonium chloropalladate in a flask, add 0.92g of glucose, set the oil bath temperature to 80℃, the magnetic stirrer speed to 800rpm, and the reaction time to 6h.

[0064] 2) Transfer the solution prepared in 1) to a 50 mL polytetrafluoroethylene reactor, add 7.62 g Al2O3, seal the reactor and place it in a forced-air drying oven, set the reaction temperature to 100 °C and the reaction time to 10 h, centrifuge after the reaction, remove the supernatant and collect the catalyst precursor at the bottom of the centrifuge tube.

[0065] 3) Place the catalyst precursor in a vacuum drying oven and dry it at 80°C for 12 hours. Then send the treated catalyst to the testing center to analyze its water content.

[0066] Preparation of aroma-enhancing tetrahydrogeraniol:

[0067] Weigh 150g of citral raw material and place it in the reactor. Add 3.36g of the prepared hydrogenation catalyst and pressurize it to 4MPa with nitrogen. Hold the pressure for 2 hours. Then release the pressure inside the reactor and replace it with nitrogen and hydrogen three times. Turn on the built-in stirrer in the reactor and set the speed to 1200rpm. Heat it to 80℃, open the hydrogen valve, and control the gas flow meter speed to 100mL / min. The reaction pressure is 4MPa.

[0068] a. Results testing and fragrance evaluation:

[0069] When the instantaneous flow rate of the gas flow meter drops to 0, the hydrogenation reaction ends. Then, a sample is taken for analysis and sent to a fragrance evaluator for aroma evaluation.

[0070] Example 3

[0071] 1) Place an aqueous solution containing 0.92g of ammonium chlororuthenate and 4.39g of ammonium chloropalladium in a flask, add 0.79g of sodium citrate, set the oil bath temperature to 80℃, the magnetic stirrer speed to 800rpm, and the reaction time to 6h.

[0072] 2) Preparation of catalyst precursor Pd-Ru / Al2O3 by hydrothermal method;

[0073] Transfer the solution prepared in step 1) to a 50 mL polytetrafluoroethylene reactor, add 8.17 g Al2O3, seal the reactor and place it in a forced-air drying oven, set the reaction temperature to 100 °C and the reaction time to 10 h, centrifuge after the reaction, remove the supernatant and collect the catalyst precursor at the bottom of the centrifuge tube.

[0074] 3) Dry the catalyst precursor sample and place it in a regular drying oven at 100°C for 24 hours. Send the treated catalyst to the testing center to analyze the water content.

[0075] Preparation of aroma-enhancing tetrahydrogeraniol:

[0076] Weigh 150g of citral raw material, add 3.36g of the prepared hydrogenation catalyst, place it in the reactor, pressurize it to 4MPa with nitrogen, maintain the pressure for 2h, then release the pressure inside the reactor, replace it three times with nitrogen and hydrogen respectively, turn on the built-in stirrer of the reactor, set the speed to 1200rpm, raise the temperature to 80℃, open the hydrogen valve, control the gas flow meter speed to 100mL / min, and the reaction pressure to 4MPa.

[0077] a. Results testing and fragrance evaluation:

[0078] When the instantaneous flow rate of the gas flow meter drops to 0, the hydrogenation reaction ends. Then, a sample is taken for analysis and sent to a fragrance evaluator for aroma evaluation.

[0079] Example 4

[0080] 1) Place an aqueous solution containing 0.92g of ammonium chlororuthenate and 3.95g of ammonium chloropalladate in a flask, add 0.69g of urea, set the oil bath temperature to 80℃, the stirring speed to 800rpm, and the reaction time to 6h.

[0081] 2) Transfer the solution prepared in 1) to a 50 mL polytetrafluoroethylene reactor, add 8.29 g Al2O3, seal the reactor and place it in a forced-air drying oven, set the reaction temperature to 100 °C and the reaction time to 10 h, centrifuge after the reaction, remove the supernatant and collect the catalyst precursor at the bottom of the centrifuge tube.

[0082] 3) The catalyst precursor sample was dried and placed in a regular drying oven at 120°C for 24 hours. The treated catalyst was then sent to the testing center to analyze its water content.

[0083] Preparation of aroma-enhancing tetrahydrogeraniol:

[0084] Weigh 150g of citral raw material, add 3.36g of the prepared hydrogenation catalyst, place it in the reactor, pressurize it to 4MPa with nitrogen, maintain the pressure for 2h, then release the pressure inside the reactor, replace it three times with nitrogen and hydrogen respectively, turn on the built-in stirrer of the reactor, set the speed to 1200rpm, raise the temperature to 80℃, open the hydrogen valve, control the gas flow meter speed to 100mL / min, and the reaction pressure to 4MPa.

[0085] a. Results testing and fragrance evaluation:

[0086] When the instantaneous flow rate of the gas flow meter drops to 0, the hydrogenation reaction ends. Samples are then taken for analysis and sent to a fragrance evaluator for aroma evaluation.

[0087] Example 5

[0088] 1) Place an aqueous solution containing 0.52g of ruthenium nitrate and 5.62g of palladium nitrate in a flask, add 0.86g of urea, set the oil bath temperature to 80℃, the magnetic stirrer speed to 800rpm, and the reaction time to 6h.

[0089] 2) Transfer the solution prepared in 1) to a 50 mL polytetrafluoroethylene reactor, add 8.56 g Al2O3, seal the reactor and place it in a forced-air drying oven, set the reaction temperature to 100 °C and the reaction time to 10 h, centrifuge after the reaction, remove the supernatant and collect the catalyst precursor at the bottom of the centrifuge tube.

[0090] 3) Dry the catalyst precursor sample, place it in a refrigerator, and dry it at 4°C for 24 hours. Then send the treated catalyst to the testing center to analyze the water content.

[0091] Preparation of aroma-enhancing tetrahydrogeraniol:

[0092] Weigh 150g of citral raw material, add 3.36g of the prepared hydrogenation catalyst, place it in the reactor, pressurize it to 4MPa with nitrogen, maintain the pressure for 2h, then release the pressure inside the reactor, replace it three times with nitrogen and hydrogen respectively, turn on the built-in stirrer of the reactor, set the speed to 1200rpm, raise the temperature to 80℃, open the hydrogen valve, control the gas flow meter speed to 100mL / min, and the reaction pressure to 4MPa.

[0093] a. Results testing and fragrance evaluation:

[0094] When the instantaneous flow rate of the gas flow meter drops to 0, the hydrogenation reaction ends. Then, a sample is taken for analysis and sent to a fragrance evaluator for aroma evaluation.

[0095] Comparative Example 1

[0096] 1) Place an aqueous solution containing 0.52g of ruthenium nitrate and 5.62g of palladium nitrate in a flask, add 0.86g of urea, set the oil bath temperature to 80℃, the magnetic stirrer speed to 800rpm, and the reaction time to 6h.

[0097] 2) Transfer the solution prepared in 1) to a 50 mL polytetrafluoroethylene reactor, add 8.56 g Al2O3, seal the reactor and place it in a forced-air drying oven, set the reaction temperature to 100 °C and the reaction time to 10 h, and then carry out a hydrothermal reaction. After the reaction is completed, centrifuge, remove the supernatant, and collect the catalyst precursor at the bottom of the centrifuge tube.

[0098] 3) The catalyst precursor sample was dried and placed in a vacuum drying oven at 80°C for 24 hours. The treated catalyst was then sent to the testing center to analyze its water content.

[0099] Preparation of aroma-enhancing tetrahydrogeraniol:

[0100] Weigh 150g of citral raw material, add 3.36g of the prepared hydrogenation catalyst, place it in the reactor, pressurize it to 4MPa with nitrogen, maintain the pressure for 2h, then release the pressure inside the reactor, replace it three times with nitrogen and hydrogen respectively, turn on the built-in stirrer of the reactor, set the speed to 1200rpm, raise the temperature to 80℃, open the hydrogen valve, control the gas flow meter speed to 100mL / min, and the reaction pressure to 4MPa.

[0101] a. Results testing and fragrance evaluation:

[0102] When the instantaneous flow rate of the gas flow meter drops to 0, the hydrogenation reaction ends. Then, a sample is taken for analysis and sent to a fragrance evaluator for aroma evaluation.

[0103] Table 1 Comparative results of the examples

[0104]

[0105] Table 2 Performance Evaluation of Example 1

[0106] Number of times to apply Reaction conversion rate / % Tetrahydrogeraniol selectivity / % Tetrahydrocitral selectivity / % 1 99.9 97.3 2.5 2 99.9 97.2 2.6 3 99.9 97.4 2.1 4 99.9 98.1 1.6 5 99.9 98.2 1.6 10 99.9 97.9 1.9 15 99.9 97.8 1.9 20 99.9 98.1 1.7

Claims

1. A hydrogenation catalyst, comprising: Active components: Pd and Ru; Supports: Al2O3 and H2O; The active component Pd has a content of 5-20 wt%, preferably 10-20 wt%, and Ru has a content of 0.1-5 wt%, preferably 1-4 wt%, based on the weight of the catalyst. The water content is 5-20 wt%, preferably 7-18 wt%.

2. The method for preparing the hydrogenation catalyst according to claim 1, comprising: 1) Place the aqueous solution containing ruthenium and palladium sources in a container, add the reducing agent, set the heating temperature and stirring speed, and ensure that all substances are completely dissolved and mixed; 2) Transfer the solution from 1) to a polytetrafluoroethylene reactor, add Al2O3, seal the reactor and place it in a forced-air drying oven for hydrothermal reaction. After the reaction is completed, centrifuge to remove the supernatant and collect the catalyst precursor at the bottom of the centrifuge tube. 3) The catalyst precursor was dried to obtain catalysts with different water contents.

3. The preparation method according to claim 2, wherein, Step 1) The ruthenium source is selected from ammonium ruthenium chlororuthenate, ruthenium nitrate and ruthenium chloride, and the palladium source is selected from ammonium chloropalladiumate, palladium nitrate and palladium chloride; The reducing agent is selected from urea, sodium citrate and glucose, and the amount of reducing agent is 10-50 wt%, based on the total mass of ruthenium and palladium; The heating temperature is 60-80℃, and the stirring speed is 600-800rpm.

4. The preparation method according to claim 2, wherein, In step 2), the reaction temperature is 100-120℃ and the time is 6-10h.

5. A method for preparing tetrahydrogeraniol, comprising: The citral feedstock undergoes a hydrogenation reaction under the action of the hydrogenation catalyst described in claim 1.

6. The method according to claim 2, wherein, The citral raw material contains 80-98 wt% geranialdehyde.

7. The method according to claim 5 or 6, wherein, The amount of catalyst added is 0.5-3 wt% of the reactants.

8. The method according to claim 5 or 6, wherein, The reaction temperature is 40-100℃ and the pressure is 1-4MPa.

9. An aroma-enhancing tetrahydrogeraniol, prepared by the method of claim 5, wherein, It contains 1-6 wt% tetrahydrocitral.

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