A process for the preparation of a catalyst and geranial

Abstract

The application discloses a catalyst and a preparation method of geranial. The catalyst comprises a clay carrier, a composite nanometal active center and an additive, a supergravity rotating packed bed is used to realize a supergravity environment, the catalyst of the composite nanometal is prepared, an isomerization reaction is carried out under the condition of nitrogen, and the isomerization reaction of citral is catalyzed to convert the citral into geranial; the content of the geranial is high, and a side reaction of polymerization of the isomerization reaction of citral is obviously reduced.

Description

Technical Field

[0001] This invention relates to the fields of catalysts and nutritional chemicals, and more specifically to the preparation of geranialdehyde. Background of the Invention

[0002] Citral is an important synthetic fragrance and also a raw material or intermediate for the preparation of various valuable materials and active ingredients. Normally, citral can be isolated from natural products or prepared through chemical synthesis, and it exists in a mixed form of nerol and geranialdehyde. In the fragrance industry and fine chemical synthesis, a single component is usually required as a raw material. Because nerol and geranialdehyde can easily interconvert, obtaining a single component is very difficult, making efficient methods for preparing geranialdehyde a key research direction.

[0003] Patent WO2014096063A discloses a method using biphenyl 4,4'-dithiol as a catalyst and the residue after citral separation as raw material to obtain a mixture of neraldehyde and geranialdehyde in a 1:1 molar ratio via catalysis, followed by further isomer separation. However, this method requires repeated heating of the raw material, leading to an increase in the content of heavy components and waste of raw materials.

[0004] Patent CN106256816B discloses a method using chiral nitrogen-containing binatidine phosphite as a catalyst to catalyze an excess of an isomer of a raw material, resulting in a product with a geranialdehyde to neraldehyde ratio close to 1:1. The catalyst used in this invention is complex to synthesize and requires an additional reactor, leading to high production costs.

[0005] Patent CN101687751B discloses a method for preparing pure or enriched nerol by distilling a mixture of nerol and geranialdehyde. This method uses a partitioned column to reduce equipment investment and distillation energy consumption. However, after separating nerol or geranialdehyde from citral by distillation, the remaining material is difficult to reuse, reducing the utilization rate of citral and causing a significant increase in cost.

[0006] Patent CN112898118A discloses a method for preparing trans-1,3-dichloropropene. This method uses a catalyst and light conditions to convert cis-1,3-dichloropropene into trans-1,3-dichloropropene, but the conversion rate is low. Finally, cis-1,3-dichloropropene and trans-1,3-dichloropropene need to be separated by distillation, which is difficult to separate, complicated to operate, and has high production costs.

[0007] Therefore, it is necessary to find more efficient and low-cost methods to convert nerol to geranialdehyde, so as to obtain a single isomer from citral efficiently and at low cost. Summary of the Invention

[0008] To address the above technical problems, this invention relates to a method for preparing a catalyst for the conversion of citral to geranialdehyde. The catalyst is used to catalyze the conversion of citral to geranialdehyde, exhibiting a high geranialdehyde content and significantly reducing the side reaction of polymerization during the isomerization of citral.

[0009] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows:

[0010] A method for preparing a catalyst for the preparation of geranialdehyde from citral includes the following steps:

[0011] S1: Load the metal active component and tellurium salt onto the carrier, then add the nonionic surfactant and mix thoroughly;

[0012] S2: The product from step S1 is added to a high-gravity rotating packed bed for treatment, and then a reducing agent is added to react and obtain crude catalyst.

[0013] S3: Wash the crude catalyst with methanol and water, dry it, and calcine it.

[0014] In S1 of this invention, the support is one or more of kaolin, montmorillonite, and illite, preferably kaolin. Kaolin has good fluidity and is easy to uniformly load with metal active sites when preparing heterogeneous catalysts.

[0015] In S1 of this invention, the tellurium salt is one or more of tellurium dioxide, di-tert-butyl tellurium, and tellurium tetrachloride, preferably tellurium tetrachloride. Taking tellurium tetrachloride as an example, during the isomerization reaction, tellurium tetrachloride can decompose to generate TeH· free radicals. The generated TeH· free radicals can also react with R· free radicals (R· represents) generated during the polymerization of citral, effectively preventing the recurrence of side reactions in the polymerization of citral. The reaction equation is: R· + TeH· = TeH + S, thereby improving the selectivity of the isomerization reaction and ensuring that the reaction yield and product purity are within the specified range.

[0016] In S1 of the present invention, the metal active component includes a main metal active component and a helper metal active component.

[0017] In S1 of the present invention, the main metal active component is a gold compound, preferably one or more of tetrachloroauric acid, dichloro(2-pyridinecarboxylic acid) gold, and chloro(trimethylphosphine) gold, with tetrachloroauric acid being the most preferred.

[0018] In S1 of the present invention, the auxiliary metal active component is one or more of a compound of platinum, manganese, and cesium; the platinum compound is selected from one or more of platinum chloride, potassium chloroplatinate, platinum acetylacetonate, and platinum tetraamminenitrate, preferably platinum chloride; the manganese compound is selected from at least one of manganese nitrate, manganese chloride, manganese acetate, manganese sulfate, and manganese acetylacetonate, preferably manganese chloride; the cesium compound is selected from one or more of cesium carbonate, cesium phosphate, and cesium sulfate, preferably cesium sulfate.

[0019] The addition of metal-based active components can modulate the valence band structure on the surface of gold nanoparticles, improve the dispersibility of gold, and thus enhance catalytic selectivity and conversion rate. Platinum has high catalytic activity and can improve the catalytic performance of gold particles; cesium can prevent the aggregation of metal active centers and improve the dispersibility of gold particles; manganese can improve the stability and lifetime of the catalyst. The synergistic effect of these four metals enhances the activity and stability of the catalyst.

[0020] In S1 of this invention, the nonionic surfactant is one or more of fatty alcohol polyoxyethylene ether, polyoxyethylene alkyl ether, and polyoxyethylene alkylamine, preferably fatty alcohol polyoxyethylene ether. Suitable examples include, but are not limited to, fatty alcohol polyoxyethylene ethers with Mw of 315, 480, and 590. Nonionic surfactants have strong chelating and dispersing properties, which are beneficial for the dispersion of gold particles and improve catalytic performance.

[0021] In the catalyst preparation method of the present invention, the mass fractions of each raw material are as follows: 70-80 parts of support, 10-20 parts of metal active component, 1-5 parts of nonionic surfactant, 5-10 parts of tellurium salt, and 1-5 parts of reducing agent. Among the metal active components, the content of the main metal active component is 30-50%, and the content of the auxiliary metal active component is 50-70%.

[0022] In S2 of the present invention, the reducing agent is one or more of hydrazine hydrate, sodium borohydride, and citric acid, preferably citric acid.

[0023] In S2 of the present invention, the hypergravity level of the hypergravity rotating filling bed is 150-220; the temperature is 80-120℃, preferably 80-100℃.

[0024] As a preferred embodiment, in step S1, tetrachloroauric acid, platinum chloride, manganese chloride, cesium sulfate, and tellurium tetrachloride are mixed with water to obtain a mixed solution. Kaolin is then impregnated into the mixed solution under water bath conditions. After mixing, a nonionic surfactant, fatty alcohol polyoxyethylene ether, is added and mixed evenly.

[0025] Preferably, the water bath temperature in S1 of the present invention is 30-50℃, more preferably 30-40℃.

[0026] As a preferred embodiment, in step S2, the reaction temperature is set to 80-120℃, preferably 80-100℃, and the hypergravity level is 150-220. The impregnated mixed solution is added to the hypergravity rotating packed bed through the feed inlet, with a residence time of 10-20 minutes. Then, the reducing agent citric acid is added, with a residence time of 10-20 minutes, to prepare the crude catalyst.

[0027] As a preferred embodiment, in step S3, the crude catalyst is filtered with methanol and ultrapure water, then vacuum dried and calcined to obtain a composite nano-metal catalyst. The gold ions are 2-10 nanometers in size. Nano-gold particles possess size-dependent high electron density and dielectric properties; this invention optimizes the size to control the catalytic effect. Gold particles smaller than 2 nm are insulators, significantly reducing the catalytic effect; therefore, 2-10 nm gold particles are preferred, exhibiting selective isomerization catalysis.

[0028] In the present invention, the drying temperature in S3 is 100-150℃, preferably 100-120℃, and the drying time is 2-4h.

[0029] In S3 of the present invention, the calcination temperature is 400-600℃, preferably 500-560℃; the time is 2-12h, preferably 4-8h.

[0030] A method for preparing geranialdehyde from citral includes the following steps: preparing geranialdehyde by isomerization of citral in the presence of the catalyst described in this invention.

[0031] In the isomerization reaction described in this invention, the amount of catalyst used is 0.5%-5% of the mass of citral, preferably 1%-2%.

[0032] As a preferred embodiment, the isomerization reaction is carried out in the presence of an inert gas, such as nitrogen; preferably, the absolute pressure of the nitrogen is 0.1-5 MPa, and more preferably 0.1-2 MPa.

[0033] The isomerization reaction temperature described in this invention is 30-110℃, and the reaction time is 2h-10h. Preferably, the isomerization reaction temperature is 50-80℃, and the reaction time is 5h-8h.

[0034] This invention utilizes a composite nano-metal catalyst to convert materials with a near 1:1 ratio of nerol and geranialdehyde into geranialdehyde during the isomerization process of citral, thereby achieving the production of geranialdehyde from citral and improving the utilization rate and yield of citral.

[0035] The technical solution provided by this invention has the following beneficial effects: it effectively prevents the recurrence of side reactions in the polymerization of citral, improves the selectivity of isomerization reactions, and ensures reaction yield and product purity. Detailed Implementation

[0036] To better understand the technical solution of the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0037] Analytical Instruments

[0038] The size of gold particles was observed using a transmission electron microscope (Hitachi, H9500).

[0039] Gas chromatograph: Agilent 7890, column DB-5 (for determining the ratio of nerol to geraniol), injection port temperature: 300℃; split ratio: 50:1; carrier gas flow rate: 52.8 ml / min; temperature program: hold at 85℃ for 20 min, increase to 180℃ at a rate of 10℃ / min, hold for 40 min; detector temperature: 280℃.

[0040] Information on the main raw material sources used in the embodiments of this invention; unless otherwise specified, all other raw materials are common commercially available materials:

[0041] Tetrachloroauric acid: 99 wt%, Aladdin Reagent Co., Ltd.;

[0042] Kaolin: 1000 mesh (Shanghai Maclean Biochemical Technology Co., Ltd.)

[0043] Tellurium tetrachloride: 99.9 wt%, Aladdin Reagent Co., Ltd.

[0044] Fatty alcohol polyoxyethylene ether: Aladdin Reagent Co., Ltd.;

[0045] Citric acid: 99.5 wt%, Aladdin Reagent Co., Ltd.;

[0046] Manganese chloride: 99.9 wt%, Aladdin Reagent Co., Ltd.;

[0047] Cobalt chloride: 99.9 wt%, Aladdin Reagent Co., Ltd.;

[0048] Cesium sulfate: 99.9 wt%, Bailingwei Technology Co., Ltd.

[0049] Methanol: 99.9 wt%, Aladdin Reagent Co., Ltd.

[0050] Citral: purity ≥98%, Hubei Julongtang Pharmaceutical Chemical Co., Ltd., wherein neraldehyde: geranialdehyde (mass ratio) is 1:1;

[0051] Example 1

[0052] In a 35℃ constant temperature water bath, 4g tetrachloroauric acid, 2g platinum chloride, 2g manganese chloride, and 2g cesium chloride were added to ultrapure water and stirred until clear. Then, 76g kaolin and 5g tellurium tetrachloride were added to the solution and stirred evenly. Next, 2g fatty alcohol polyoxyethylene ether (Mw315, Aladdin) was added and stirred until evenly mixed. The reaction temperature of the rotating packed bed under hypergravity was set to 90℃, and the hypergravity level was set to 180. The evenly mixed solution was added to the rotating packed bed through the inlet, and the residence time was 15min. Then, 2g citric acid was added through the inlet, and the residence time was 15min. The crude catalyst was then obtained.

[0053] After removal, the product was cooled and filtered, washed with 1000 ml of ultrapure water and 1000 ml of methanol, and dried in a vacuum drying oven at 100°C for 2 hours. The dried product was then placed in a muffle furnace and calcined at 500°C for 6 hours to obtain the composite nano-metal catalyst. The size of the gold particles was observed to be 6 nanometers using a transmission electron microscope.

[0054] In a 500ml reactor, add 100g of citral and 1g of the above-prepared catalyst. Purge with nitrogen to adjust the reaction pressure to 0.5MPa (reaction pressure, gauge pressure). Start stirring and heat the reaction system to 50℃. Keep the nitrogen pressure in the reactor constant during the isomerization reaction. After 5 hours of reaction, take a sample for gas phase analysis. The results are shown in Table 1.

[0055] Example 2

[0056] In a 35℃ constant temperature water bath, 4.5g tetrachloroauric acid, 5g platinum chloride, 3.5g manganese chloride, and 2g cesium chloride were added to ultrapure water and stirred until clear. Then, 80g kaolin and 6g tellurium tetrachloride were added to the solution and stirred evenly. Next, 2g fatty alcohol polyoxyethylene ether (Mw315, Aladdin) was added and stirred evenly. The reaction temperature of the rotating packed bed under hypergravity was set to 90℃, and the hypergravity level was set to 200. The evenly mixed solution was added to the rotating packed bed through the inlet and the residence time was 10min. Then, 2g citric acid was added through the inlet and the residence time was 15min. The crude catalyst was then obtained.

[0057] After removal, the product was cooled and filtered, washed with 1000 ml of ultrapure water and 1000 ml of methanol, and dried in a vacuum drying oven at 110 °C for 4 h. The dried product was then placed in a muffle furnace and calcined at 530 °C for 4 h to obtain the composite nano-metal catalyst. The size of the gold particles was observed to be 10 nanometers using a transmission electron microscope.

[0058] In a 500ml reactor, add 100g of citral and 1.5g of the above-prepared catalyst. Purge with nitrogen to adjust the reaction pressure to 1MPa (reaction pressure, gauge pressure). Start stirring and heat the reaction system to 80℃. Keep the nitrogen pressure in the reactor constant during the isomerization reaction. After 6 hours of reaction, take a sample for gas phase analysis. The results are shown in Table 1.

[0059] Example 3

[0060] In a 30℃ constant temperature water bath, 8g of tetrachloroauric acid, 5g of platinum chloride, 4g of manganese chloride, and 3g of cesium chloride were added to ultrapure water and stirred until clear. Then, 70g of kaolin and 5g of tellurium tetrachloride were added to the solution and stirred evenly. Next, 3g of fatty alcohol polyoxyethylene ether (Mw315, Aladdin) was added and stirred until evenly mixed. The reaction temperature of the rotating packed bed under hypergravity was set to 80℃, and the hypergravity level was set to 220. The evenly mixed solution was added to the rotating packed bed through the inlet, and the residence time was 10min. Then, 1g of citric acid was added through the inlet, and the residence time was 15min. The crude catalyst was then obtained.

[0061] After removal, the product was cooled and filtered, washed with 1000 ml of ultrapure water and 1000 ml of methanol, and dried in a vacuum drying oven at 100°C for 3 hours. The dried product was then placed in a muffle furnace and calcined at 520°C for 4 hours to obtain the composite nano-metal catalyst. The size of the gold particles was observed to be 5 nanometers using a transmission electron microscope.

[0062] In a 500ml reactor, add 100g of citral and 1g of the above-prepared catalyst. Purge with nitrogen to adjust the reaction pressure to 0.5MPa (reaction pressure, gauge pressure). Start stirring and heat the reaction system to 50℃. Keep the nitrogen pressure in the reactor constant during the isomerization reaction. After 5 hours of reaction, take a sample for gas phase analysis. The results are shown in Table 1.

[0063] Example 4

[0064] In a 30℃ constant temperature water bath, 4g tetrachloroauric acid, 5g platinum chloride, 2g manganese chloride, and 2g cesium chloride were added to ultrapure water and stirred until clear. Then, 74g kaolin and 10g tellurium tetrachloride were added to the solution and stirred evenly. Next, 5g fatty alcohol polyoxyethylene ether (Mw315, Aladdin) was added and stirred until evenly mixed. The reaction temperature of the rotating packed bed under hypergravity was set to 100℃, and the hypergravity level was set to 150. The evenly mixed solution was added to the rotating packed bed through the inlet, and the residence time was 20min. Then, 1g citric acid was added through the inlet, and the residence time was 15min. The crude catalyst was then obtained.

[0065] After removal, the product was cooled and filtered, washed with 1000 ml of ultrapure water and 1000 ml of methanol, and dried in a vacuum drying oven at 120°C for 2 hours. The dried product was then placed in a muffle furnace and calcined at 560°C for 8 hours to obtain the composite nano-metal catalyst. The size of the gold particles was observed to be 2 nanometers using a transmission electron microscope.

[0066] In a 500ml reactor, add 100g of citral and 2g of the above-prepared catalyst. Purge with nitrogen to adjust the reaction pressure to 2MPa (reaction pressure, gauge pressure). Start stirring and heat the reaction system to 60℃. Keep the nitrogen pressure in the reactor constant during the isomerization reaction. After 8 hours of reaction, take a sample for gas phase analysis. The results are shown in Table 1.

[0067] Example 5

[0068] In a 30℃ constant temperature water bath, 8.5g tetrachloroauric acid, 5g platinum chloride, 3g manganese chloride, and 2g cesium chloride were added to ultrapure water and stirred until clear. Then, 72g kaolin and 5g tellurium tetrachloride were added to the solution and stirred evenly. Then, 1g fatty alcohol polyoxyethylene ether (Mw315, Aladdin) was added and stirred evenly. The reaction temperature of the rotating packed bed under hypergravity was set to 90℃ and the hypergravity level was set to 200. The evenly mixed solution was added to the rotating packed bed through the inlet and the residence time was 15min. Then, 5g citric acid was added through the inlet and the residence time was 20min. The crude catalyst was then obtained.

[0069] After removal, the product was cooled and filtered, washed with 1000 ml of ultrapure water and 1000 ml of methanol, and dried in a vacuum drying oven at 100 °C for 3 h. The dried product was then placed in a muffle furnace and calcined at 550 °C for 4 h to obtain the composite nano-metal catalyst. The size of the gold particles was observed to be 6 nm using a transmission electron microscope.

[0070] In a 500ml reactor, add 100g of citral and 1g of the above-prepared catalyst. Purge with nitrogen to adjust the reaction pressure to 0.1MPa (reaction pressure, gauge pressure). Start stirring and heat the reaction system to 50℃. Keep the nitrogen pressure in the reactor constant during the isomerization reaction. After 5 hours of reaction, take a sample for gas phase analysis. The results are shown in Table 1.

[0071] Comparative Example 1

[0072] Except for the absence of tellurium tetrachloride, the process was the same as in Example 3. The gold particles were observed to be 5 nanometers in size using a transmission electron microscope.

[0073] Comparative Example 2

[0074] Except for adding the uniformly mixed solution into the rotating packed bed through the inlet, with a residence time of 30 minutes, and then adding 1 g of citric acid through the inlet, with a residence time of 30 minutes, the rest is the same as in Example 3. The gold particle size was observed to be 1 nanometer using a transmission electron microscope.

[0075] Comparative Example 3

[0076] Except for adding the uniformly mixed solution into the rotating packed bed through the inlet, with a residence time of 5 minutes, and then adding 1 g of citric acid through the inlet, with a residence time of 5 minutes, the rest was the same as in Example 3. The gold particle size was observed to be 16 nanometers using a transmission electron microscope.

[0077] Comparative Example 4

[0078] Except for the use of 10g tetrachloroauric acid and the omission of platinum chloride, manganese chloride, and cesium chloride, the process was the same as in Example 3. The gold particles were observed to be 5 nanometers in size using a transmission electron microscope.

[0079] Comparative Example 5

[0080] Except for the use of 8g tetrachloroauric acid and 12g platinum chloride, and the omission of manganese chloride and cesium chloride, the process was the same as in Example 3. The gold particles were observed to be 5 nanometers in size using a transmission electron microscope.

[0081] Comparative Example 6

[0082] Except for the use of 8g tetrachloroauric acid and 12g manganese chloride, and the omission of platinum chloride and cesium chloride, the process was the same as in Example 3. The gold particles were observed to be 5 nanometers in size using a transmission electron microscope.

[0083] Comparative Example 7

[0084] Except for the use of 8g tetrachloroauric acid and 12g cesium chloride, and the omission of platinum chloride and manganese chloride, the process was the same as in Example 3. The gold particles were observed to be 5 nanometers in size using a transmission electron microscope.

[0085] Comparative Example 8

[0086] Except for the use of 8g tetrachloroauric acid, 7g platinum chloride, and 5g manganese chloride, and the omission of cesium chloride, the process was the same as in Example 3. The gold particles were observed to be 5 nanometers in size using a transmission electron microscope.

[0087] Comparative Example 9

[0088] Except for the use of 8g tetrachloroauric acid, 7g platinum chloride, and 5g cesium chloride, and the omission of manganese chloride, the process was the same as in Example 3. The gold particles were observed to be 5 nanometers in size using a transmission electron microscope.

[0089] Comparative Example 10

[0090] Except for the use of 8g tetrachloroauric acid, 7g manganese chloride, and 5g cesium chloride, and the omission of platinum chloride, the process was the same as in Example 3. The gold particles were observed to be 5 nanometers in size using a transmission electron microscope.

[0091] Table 1 shows the reaction results of the examples and comparative examples.

[0092] Table 1. Response results of the examples and comparative examples.

[0093]

[0094]

Claims

1. A method for preparing a catalyst for the preparation of geranialdehyde from citral, comprising the following steps: S1: The metal active component and tellurium salt are loaded onto a support, and then a nonionic surfactant is added and mixed evenly; the metal active component includes a main metal active component and a co-metal active component; the main metal active component is a gold compound; the co-metal active component is one or more compounds of platinum, manganese, and cesium; S2: The product from step S1 is added to a high-gravity rotating packed bed for treatment, and then a reducing agent is added to react and obtain crude catalyst. S3: The crude catalyst was washed with methanol and water, dried, and calcined; the gold particles in the resulting catalyst were 2-10 nanometers in size.

2. The method according to claim 1, characterized in that, The carrier is one or more of kaolin, montmorillonite, and illite.

3. The method according to claim 1, characterized in that, The tellurium salt is one or more of tellurium dioxide, di-tert-butyl tellurium, and tellurium tetrachloride.

4. The method according to claim 1, characterized in that, The main metal active component is selected from one or more of tetrachloroauric acid, dichloro(2-pyridinecarboxylic acid) gold, and chloro(trimethylphosphine) gold; the auxiliary metal active component is selected from one or more of platinum chloride, potassium chloroplatinate, platinum acetylacetonate, platinum tetraamminenitrate, manganese nitrate, manganese chloride, manganese acetate, manganese sulfate, manganese acetylacetonate, cesium carbonate, cesium phosphate, and cesium sulfate.

5. The method according to claim 1, characterized in that, The mass fractions of each raw material are as follows: 70-80 parts carrier, 10-20 parts metal active component, 1-5 parts nonionic surfactant, 5-10 parts tellurium salt, and 1-5 parts reducing agent. Among the metal active components, the content of the main metal active component is 30-50%, and the content of the auxiliary metal active component is 50-70%.

6. The method according to claim 1, characterized in that, The reducing agent is one or more of hydrazine hydrate, sodium borohydride, and citric acid.

7. The method according to claim 1, characterized in that, The hypergravity level of the hypergravity rotating filling bed is 150-220°C; the temperature is 80-120°C.

8. The method according to claim 1, characterized in that, Includes the following steps: S1: Mix tetrachloroauric acid, platinum chloride, manganese chloride, cesium sulfate and tellurium tetrachloride with water to obtain a mixed solution. Impregnate kaolin into the mixed solution under water bath conditions. After mixing, add nonionic surfactant fatty alcohol polyoxyethylene ether and mix evenly. S2: Set the reaction temperature to 80-120℃ and the hypergravity level to 150-220. Add the impregnated mixed solution into the hypergravity rotating packed bed through the feed inlet. The residence time is 10-20 min. Then add the reducing agent citric acid. The residence time is 10-20 min. The crude catalyst is then prepared. S3: The crude catalyst was filtered with methanol and ultrapure water, then dried under vacuum and calcined to obtain a composite nano-metal catalyst, in which the gold particles were 2-10 nanometers in size.

9. A method for preparing geranialdehyde from citral, comprising the following steps: Geranialdehyde is prepared by isomerization reaction in the presence of a catalyst prepared by the method according to any one of claims 1-8.

10. The method according to claim 9, characterized in that, The catalyst dosage is 0.5%-5% of the mass of citral.

11. The method according to claim 9, characterized in that, The amount of catalyst used is 1%-2% of the mass of citral.

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