Preparation method of convallaria majalis pyrane

Abstract

The invention provides a preparation method of convallaria majalis pyrane, which comprises the following specific steps: carrying out isomerization reaction on a raw material containing 4, 4-dimethyl-2-isobutyl-1, 3-dioxane (formula i) under the catalytic action of a loaded WO3 / HY molecular sieve to prepare the convallaria majalis pyrane (formula ii). The preparation method disclosed by the invention has the advantages of simple process, mild reaction conditions, high yield, no three wastes and the like.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of preparation of lily pyran, and particularly relates to a preparation method of lily pyran. BACKGROUND

[0002] Lily pyran (Formula II) is a fragrance material with lily and lily fragrance, and has soft, fresh and elegant fragrance, and is widely used in daily chemical fragrances. With the discovery of the sensitization and reproductive toxicity of lily aldehyde, the EU has banned its application in the field of cosmetics. Lily pyran is safe and can be used as a substitute for lily aldehyde, and has great potential in the future application market.

[0003]

[0004] At present, the main method for synthesizing lily pyran in industry is to prepare it by one-step method of isopentanal and isopentenyl alcohol under acidic conditions, such as patents CN105175372B, CN102428077B and CN105164110B. The above-mentioned acid catalytic system will produce a certain amount of 4,4-dimethyl-2-isobutyl-1,3-dioxane (Formula I) as a by-product. In order to avoid the influence of trace amount of 4,4-dimethyl-2-isobutyl-1,3-dioxane on the aroma quality of lily pyran, 4,4-dimethyl-2-isobutyl-1,3-dioxane is often removed by distillation separation in industry, which may cause a part of lily pyran to be lost in the process, and there is a corresponding report in patent CN103003258B.

[0005]

[0006] In order to fully utilize the value of 4,4-dimethyl-2-isobutyl-1,3-dioxane, CN106170483B reports a method for preparing lily pyran by using 4,4-dimethyl-2-isobutyl-1,3-dioxane as raw material and strong acid or acid ion exchange resin as catalyst. The catalyst is easy to obtain and the process is simple, but the yield is less than 50%, the utilization rate of 4,4-dimethyl-2-isobutyl-1,3-dioxane is not high, and part of it generates small molecule substances affecting the aroma of lily pyran; CN113831311B mentions a method for preparing lily pyran from 4,4-dimethyl-2-isobutyl-1,3-dioxane under the catalysis of inorganic acid. The yield of this method can reach 85%, but the process produces high-salinity wastewater which is difficult to handle, and brings certain pressure to environmental protection;

[0007] CN114315777B mentions a method for preparing lily pyran by hydrating waste containing 4,4-dimethyl-2-isobutyl-1,3-dioxane and dehydration by-products under the catalysis of supported catalyst praseodymium oxide-alumina supported molybdenum oxide and / or tungsten oxide catalyst. The total yield of lily pyran in this synthesis method is as high as 98%, but the catalyst preparation process is complex and costly, and a large amount of wastewater is difficult to avoid.

[0008] In view of the above, there is still an urgent need to develop a green and low-cost synthetic method for preparing lily pyran from 4,4-dimethyl-2-isobutyl-1,3-dioxane with high efficiency, to improve the utilization value of 4,4-dimethyl-2-isobutyl-1,3-dioxane, and to reduce the production cost of lily pyran. SUMMARY

[0009] The purpose of the present application is to provide a method for preparing lily pyran, which uses 4,4-dimethyl-2-isobutyl-1,3-dioxane as raw material, fully improves the utilization value of by-products in the production of lily pyran, enhances the cost advantage of lily pyran fragrance raw materials, and basically produces no waste water in the preparation process.

[0010] In order to achieve the above invention purposes, the technical solutions provided by the present application are as follows:

[0011] A method for preparing lily pyran, characterized in that 4,4-dimethyl-2-isobutyl-1,3-dioxane (formula I) is used as raw material, and isomerization reaction occurs under heating in the presence of a supported WO3 / HY molecular sieve catalyst to obtain lily pyran (formula II).

[0012]

[0013] In one specific embodiment, a method for preparing lily pyran, comprising 4,4-dimethyl-2-isobutyl-1,3-dioxane (formula I) as raw material, isomerization reaction occurs under heating in the presence of a supported WO3 / HY molecular sieve catalyst, and after the catalyst is filtered, a reaction solution containing lily pyran (formula II) is obtained.

[0014] In one specific embodiment, the preparation process of the supported WO3 / HY molecular sieve catalyst is as follows:

[0015] (1) Dissolve ammonium tungstate in water to prepare a tungsten-containing solution, take a certain amount of HY molecular sieve and immerse it in the tungsten-containing solution, and then place it in an ultrasonic bath for treatment and stand still;

[0016] (2) Take the immersed sample in step (1) and place it in an oven for drying, then transfer it to a muffle furnace for high-temperature calcination in an air atmosphere, and the supported WO3 / HY molecular sieve catalyst is obtained.

[0017] In one specific embodiment, in the above step (1), the mass concentration of ammonium tungstate in the tungsten-containing solution is 1-10 wt%, for example, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, etc., and preferably 2-5 wt%.

[0018] In one specific embodiment, in the step (1) above, the HY molecular sieve has a silica-to-alumina molar ratio (Si02 / Al203) of 4.0-5.0, such as 4.0, 4.2, 4.5, 4.8, 5.0, etc.; and the amount of the ammonium tungstate solution is 10-30 wt% of the mass of the ammonium tungstate solution, such as 11 wt%, 12 wt%, 15 wt%, 18 wt%, 19 wt%, 20 wt%, 22 wt%, 25 wt%, 28 wt%, 30 wt%, etc., preferably 15-20%.

[0019] In one specific embodiment, in the step (2) above, the drying temperature is 100-150°C, such as 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, etc., preferably 120-140°C; the drying time is 3-12 h, such as 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h, etc., preferably 4-8 h; the calcination temperature is 450-600°C, such as 450°C, 480°C, 500°C, 520°C, 550°C, 580°C, 600°C, etc., preferably 500-550°C; and the calcination time is 3-15 h, such as 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h, 13 h, 14 h, 15 h, etc., preferably 5-10 h.

[0020] In one specific embodiment, the raw material containing 4,4-dimethyl-2-isobutyl-1,3-dioxane has a mass content of 4,4-dimethyl-2-isobutyl-1,3-dioxane of 5-100 wt%, such as 5 wt%, 10 wt%, 20 wt%, 30 wt%, 40 wt%, 50 wt%, 60 wt%, 70 wt%, 80 wt%, 90 wt%, 100 wt%, etc. When the mass content of 4,4-dimethyl-2-isobutyl-1,3-dioxane in the raw material containing 4,4-dimethyl-2-isobutyl-1,3-dioxane is less than 100%, the balance can be a solvent, such as one or more of toluene, xylene, and cyclohexane.

[0021] In one specific embodiment, the amount of the WO3 / HY molecular sieve catalyst is 0.1-5 wt% of the amount of the raw material (calculated as 4,4-dimethyl-2-isobutyl-1,3-dioxane), such as 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, 5 wt%, etc., preferably 0.5-1.5 wt%.

[0022] In one specific embodiment, the isomerization reaction is controlled to have a reaction temperature of 50-160℃, such as 50℃, 60℃, 70℃, 80℃, 90℃, 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, 160℃, etc., preferably 110-140℃; and a reaction time of 3-20h, such as 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 13h, 15h, 18h, 19h, 20h, etc., preferably 6-10h.

[0023] In the present application, the isomerization reaction solvent can be selected from one or more of toluene, xylene, and cyclohexane, or no solvent can be added, preferably no solvent is added.

[0024] Compared with the prior art, the present application has the following positive effects:

[0025] The preparation method of the present application uses 4,4-dimethyl-2-isobutyl-1,3-dioxane as a raw material, effectively recovers the by-product in the production process of lily pyran, and has mild reaction conditions and a selectivity as high as 95%, and the recovery process basically does not produce wastewater.

[0026] The preparation method of the present application uses the supported WO3 / HY molecular sieve catalyst prepared by the impregnation method, which has the advantages of simple preparation process and low catalyst cost. DETAILED DESCRIPTION

[0027] The following examples are not intended to limit the scope of the present application, and modifications or equivalent replacements to the present application, without departing from the spirit and scope of the present application, should be covered in the protection scope of the claims of the present application.

[0028] The raw materials used in the examples are all conventional raw materials in the art, and the purity specifications used are analytical pure or industrial pure;

[0029] I. In the following examples, the raw material source information is as follows:

[0030] The HY molecular sieve (molar ratio of silicon to aluminum is 150 / 200), ammonium tungstate, toluene, xylene, and cyclohexane are all analytical grade purity, and are purchased from Shanghai Aldrich Biochemical Technology Co., Ltd.

[0031] The macroporous sulfonic acid type ion exchange resin MF-11-28 is from Shandong Maofa Chemical Industry.

[0032] The method for preparing 4,4-dimethyl-2-isobutyl-1,3-dioxane is known to those skilled in the art. The raw material containing 4,4-dimethyl-2-isobutyl-1,3-dioxane can be prepared from isopentyl glycol and isovaleraldehyde under acidic conditions, or can be produced from the waste liquid of the separation process in the lily pyran production process, for example, reference is made to the preparation in Example 2 of CN106170483B.

[0033]

[0034] Secondly, the following test methods are used in the examples of the present application:

[0035] 4,4-dimethyl-2-isobutyl-1,3-dioxane, lily pyran and other components in the reaction solution are quantitatively analyzed by GC-7890 chromatograph, and the chromatographic conditions are as follows: initial temperature 50°C, holding for 5 min, programmed temperature rising to 280°C at a rate of 10°C / min, then holding for 5 min; gasification chamber temperature 300°C, detection chamber temperature 300°C; FID detection; injection volume 0.2 μL; chromatographic column Agilent HP-5 type.

[0036] Example 1

[0037] 5 g of ammonium tungstate is added to 95 g of deionized water, and stirred until dissolved. 15 g of HY molecular sieve (molar ratio of SiO2 / Al2O3 is 4.0) is added to the above ammonium tungstate solution, and soaked and placed for 12 h. The above soaked sample is taken out and transferred to an oven, and kept at 120°C for 6 h. Then the dried sample is placed in a muffle furnace, and the calcination temperature is set to 500°C, and the process is kept in air flow. After keeping for 5 h, the sample is taken out and cooled to room temperature, to obtain a WO3 / HY molecular sieve catalyst, which is named as catalyst A.

[0038] The macroporous sulfonic acid type ion exchange resin is stirred with isopentyl alcohol and isovaleraldehyde at 50°C for 2 h, and then the reaction solution is rectified and separated to obtain 4,4-dimethyl-2-isobutyl-1,3-dioxane raw material with a purity of 99%. 100 g of the above raw material is taken, 1 g of catalyst A is added, and the temperature is controlled at 110°C, and kept for 10 h. After the reaction is completed, the mixture is cooled to room temperature, and the catalyst in the mixture is filtered out to obtain a clear and transparent reaction solution.

[0039] The GC analysis of the composition of the reaction solution shows that the content of 4,4-dimethyl-2-isobutyl-1,3-dioxane is 2.47 wt%, and the content of lily pyran is 90.0%. The conversion rate of 4,4-dimethyl-2-isobutyl-1,3-dioxane is calculated to be 97.5%, and the selectivity of lily pyran is 93.2%.

[0040] Example 2

[0041] The 2 g of ammonium tungstate was added to 98 g of deionized water and stirred until dissolved. 20 g of HY zeolite (SiO2 / Al2O3 molar ratio of 5.0) was added to the ammonium tungstate solution and soaked overnight. The soaked sample was removed and transferred to an oven and heated at 140°C for 4 h. The dried sample was then placed in a muffle furnace and heated at 550°C with air flowing through the furnace. After 10 h, the sample was removed and allowed to cool to room temperature to produce a WO3 / HY zeolite catalyst, which was designated as Catalyst B.

[0042] A waste liquid from the production of lily of the valley lactone, which contains 4,4-dimethyl-2-isobutyl-1,3-dioxane at a content of 21.5%, lily of the valley lactone at a content of 42.6%, isoamyl alcohol at a content of 1.4%, and total lily of the valley lactone dehydration byproducts at a content of 32.1%, and the rest of the components being lily of the valley lactone isomers. 100 g of the waste liquid was added to 0.3 g of Catalyst B, and heated at 125°C for 8 h. After the reaction was completed, the mixture was allowed to cool to room temperature, and the catalyst was filtered out to obtain a clear and transparent reaction liquid.

[0043] The reaction liquid was analyzed by GC, and the components were 4,4-dimethyl-2-isobutyl-1,3-dioxane at a content of 0.6%, lily of the valley lactone at a content of 62.5%, isoamyl alcohol at a content of 1.5%, and total lily of the valley lactone dehydration byproducts at a content of 32.3%, and the rest of the components being lily of the valley lactone isomers. The conversion rate of 4,4-dimethyl-2-isobutyl-1,3-dioxane was calculated to be 97.2%, and the selectivity of lily of the valley lactone was calculated to be 95.2%.

[0044] Example 3

[0045] The 1 g of ammonium tungstate was added to 99 g of deionized water and stirred until dissolved. 10 g of HY zeolite (SiO2 / Al2O3 molar ratio of 4.5) was added to the ammonium tungstate solution and soaked overnight. The soaked sample was removed and transferred to an oven and heated at 100°C for 12 h. The dried sample was then placed in a muffle furnace and heated at 450°C with air flowing through the furnace. After 15 h, the sample was removed and allowed to cool to room temperature to produce a WO3 / HY zeolite catalyst, which was designated as Catalyst C.

[0046] A waste liquid from the production of lily of the valley lactone, which contains 4,4-dimethyl-2-isobutyl-1,3-dioxane at a content of 5.0%, lily of the valley lactone at a content of 62.4%, isoamyl alcohol at a content of 0.4%, and total lily of the valley lactone dehydration byproducts at a content of 31.0%, and the rest of the components being lily of the valley lactone isomers. 100 g of the waste liquid was added to 0.25 g of Catalyst C, and heated at 160°C for 3 h. After the reaction was completed, the mixture was allowed to cool to room temperature, and the catalyst was filtered out to obtain a clear and transparent reaction liquid.

[0047] The reaction solution was analyzed by GC, and the composition was 4,4-dimethyl-2-isobutyl-1,3-dioxane 0.24%, lily pyran 66.7%, isoamyl alcohol 0.6%, total lily pyran dehydration by-products 31.8%, and the rest was lily pyran isomers. The conversion of 4,4-dimethyl-2-isobutyl-1,3-dioxane was calculated to be 95.2%, and the selectivity of lily pyran was 90.3%.

[0048] Example 4

[0049] 10 g of ammonium tungstate was added to 90 g of deionized water, and stirred until dissolved. 30 g of HY molecular sieve (molar ratio of SiO2 / Al2O3 was 4.2) was added to the above ammonium tungstate solution, and soaked overnight. The above soaked sample was removed and transferred to an oven, and incubated at 150°C for 3 h. Then the dried sample was placed in a muffle furnace, and the calcination temperature was set to 600°C with air flow. After incubation for 3 h, the sample was removed and cooled to room temperature to obtain a WO3 / HY molecular sieve catalyst, which was named catalyst D.

[0050] A waste liquid from the production of lily pyran, which had a composition of 4,4-dimethyl-2-isobutyl-1,3-dioxane 52.1%, lily pyran 4.6%, isoamyl alcohol 0.1%, total lily pyran dehydration by-products 41.3%, and the rest was lily pyran isomers. 100 g of the above waste liquid was added to 0.26 g of catalyst D, and incubated at 140°C for 6 h. After the reaction was completed, the mixture was cooled to room temperature, and the catalyst was filtered out to obtain a clear and transparent reaction solution.

[0051] The reaction solution was analyzed by GC, and the composition was 4,4-dimethyl-2-isobutyl-1,3-dioxane 1.12%, lily pyran 51.1%, isoamyl alcohol 0.1%, total lily pyran dehydration by-products 41.9%, and the rest was lily pyran isomers. The conversion of 4,4-dimethyl-2-isobutyl-1,3-dioxane was calculated to be 97.9%, and the selectivity of lily pyran was 91.2%.

[0052] Example 5

[0053] To 97.2 g of deionized water, 2.8 g of ammonium tungstate was added and stirred until dissolved. To the above ammonium tungstate solution, 18 g of HY zeolite (SiO2 / Al2O3 molar ratio of 4.8) was added and soaked overnight. The soaked sample was removed and transferred to an oven and kept at 130 °C for 8 h. The oven-dried sample was then placed in a muffle furnace and the temperature was set to 520 °C with air flowing through the furnace. After 6 h, the sample was removed and allowed to cool to room temperature to produce a WO3 / HY zeolite catalyst, which was designated as Catalyst E.

[0054] A waste liquid from the production of lily of the valley lactone, which contains 21.5% of 4,4-dimethyl-2-isobutyl-1,3-dioxane, 42.6% of lily of the valley lactone, 1.4% of prenyl alcohol, and 32.1% of total lily of the valley lactone dehydration by-products, and the rest of the components are lily of the valley lactone isomers. To 100 g of the above waste liquid, 0.26 g of Catalyst E was added and the temperature was controlled at 130 °C for 9 h. After the reaction was completed, the mixture was allowed to cool to room temperature and the catalyst was filtered out to obtain a clear and transparent reaction liquid.

[0055] The reaction liquid was analyzed by GC and the components were 4,4-dimethyl-2-isobutyl-1,3-dioxane 0.43%, lily of the valley lactone 62.9%, prenyl alcohol 1.5%, total lily of the valley lactone dehydration by-products 42.9%, and the rest of the components are lily of the valley lactone isomers. The conversion of 4,4-dimethyl-2-isobutyl-1,3-dioxane was calculated to be 98.0% and the selectivity of lily of the valley lactone was 96.3%.

[0056] Example 6

[0057] To 93 g of deionized water, 7 g of ammonium tungstate was added and stirred until dissolved. To the above ammonium tungstate solution, 25 g of HY zeolite (SiO2 / Al2O3 molar ratio of 4.0) was added and soaked overnight. The soaked sample was removed and transferred to an oven and kept at 120 °C for 6 h. The oven-dried sample was then placed in a muffle furnace and the temperature was set to 500 °C with air flowing through the furnace. After 5 h, the sample was removed and allowed to cool to room temperature to produce a WO3 / HY zeolite catalyst, which was designated as Catalyst F.

[0058] The 4,4-dimethyl-2-isobutyl-1,3-dioxane raw material with a purity of 99% was obtained by stirring isopentyldiol and isovaleraldehyde with a macroporous sulfonic acid type ion exchange resin at 50 °C for 2 h, and then distilling and separating the reaction liquid. To 100 g of the above raw material, 3 g of Catalyst F was added and the temperature was controlled at 110 °C for 10 h. After the reaction was completed, the mixture was allowed to cool to room temperature and the catalyst was filtered out to obtain a clear and transparent reaction liquid.

[0059] The GC analysis of the reaction liquid composition shows that the content of 4,4-dimethyl-2-isobutyl-1,3-dioxane is 1.59 wt%, the content of lily pyran is 89.2%, the conversion rate of 4,4-dimethyl-2-isobutyl-1,3-dioxane is 98.4%, and the selectivity of lily pyran is 91.6%.

[0060] Example 7

[0061] The tungsten acid ammonium was added to 98.5 g of deionized water and stirred until dissolved. 13 g of HY molecular sieve (molar ratio of SiO2 / Al2O3 was 4.0) was added to the tungsten acid ammonium solution and soaked overnight. The soaked sample was removed and transferred to an oven, and kept at 120°C for 6 h. Then the dried sample was placed in a muffle furnace, and the temperature was set to 500°C. The sample was kept at this temperature for 5 h, and then removed and allowed to cool to room temperature to obtain a WO3 / HY molecular sieve catalyst, which was named catalyst G.

[0062] The isopentyl glycol and isovaleraldehyde were stirred with the macroporous sulfonic acid type ion exchange resin at 50°C for 2 h, and then the reaction liquid was separated by distillation to obtain 4,4-dimethyl-2-isobutyl-1,3-dioxane raw material with a purity of 99%. 100 g of the raw material was added to 0.2 g of catalyst G, and the temperature was controlled at 110°C for 10 h. After the reaction was completed, the mixture was allowed to cool to room temperature, and the catalyst was filtered out to obtain a clear and transparent reaction liquid.

[0063] The GC analysis of the reaction liquid composition shows that the content of 4,4-dimethyl-2-isobutyl-1,3-dioxane is 4.31 wt%, the content of lily pyran is 87.1%, the conversion rate of 4,4-dimethyl-2-isobutyl-1,3-dioxane is 95.6%, and the selectivity of lily pyran is 92.0%.

[0064] Comparative Example 1

[0065] The HY molecular sieve in Example 1 was replaced with HX molecular sieve, and the molar ratio of SiO2 / Al2O3 was unchanged. The preparation of the catalyst and the reaction conditions were unchanged.

[0066] The GC analysis of the reaction liquid composition shows that the content of 4,4-dimethyl-2-isobutyl-1,3-dioxane is 23.39 wt%, the content of lily pyran is 41.70%, the conversion rate of 4,4-dimethyl-2-isobutyl-1,3-dioxane is 76.4%, and the selectivity of lily pyran is 55.2%.

[0067] The above merely describes the preferred embodiments of the present application, and it should be noted that, for those skilled in the art, several improvements and supplements can be made without departing from the method of the present application, and these improvements and supplements should also be considered as the protection scope of the present application.

Claims

1. A process for the preparation of convallapyran, characterized in that, The raw material containing 4,4-dimethyl-2-isobutyl-1,3-dioxane (formula I) is subjected to isomerization reaction under heating in the presence of a supported WO3 / HY molecular sieve catalyst to prepare lily of the valley pyran (formula II).

2. The production method according to claim 1, characterized by, The preparation process of the supported WO3 / HY molecular sieve catalyst is as follows: (1) Dissolve ammonium tungstate in water to prepare a tungsten-containing solution, and immerse a certain amount of HY molecular sieve in the tungsten-containing solution, and then place it in an ultrasonic cleaner for ultrasonic treatment and then stand still; (2) Take the immersed sample in step (1) and place it in an oven for drying, and then transfer it to a muffle furnace for high-temperature calcination in an air atmosphere to obtain the supported WO3 / HY molecular sieve catalyst.

3. The production method according to claim 2, characterized by, In step (1), the mass concentration of ammonium tungstate in the tungsten-containing solution is 1-10 wt%, preferably 2-5 wt%.

4. The production method according to claim 2 or 3, characterized by, In step (1), the HY molecular sieve has a silicon-aluminum ratio (molar ratio of SiO2 / Al2O3) of 4.0-5.0, and the amount of the HY molecular sieve is 10-30 wt% of the mass of the ammonium tungstate solution, preferably 15-20 wt%.

5. The preparation method according to claim 2, characterized in that, In step (2), the drying temperature is 100-150°C, preferably 120-140°C, and the drying time is 3-12 h, preferably 4-8 h.

6. The production method according to claim 2 or 5, characterized by, In step (2), the calcination temperature is 450-600°C, preferably 500-550°C, and the calcination time is 3-15 h, preferably 5-10 h.

7. The method of any one of claims 1-6, wherein, The mass content of 4,4-dimethyl-2-isobutyl-1,3-dioxane in the raw material containing 4,4-dimethyl-2-isobutyl-1,3-dioxane is 5-100 wt%.

8. The method of any one of claims 1-7, wherein, The amount of the supported WO3 / HY molecular sieve catalyst is 0.1-5 wt% of the amount of the raw material based on 4,4-dimethyl-2-isobutyl-1,3-dioxane, preferably 0.5-1.5 wt%.

9. The method of any one of claims 1-8, wherein, The reaction temperature of the isomerization reaction is controlled to be 50-160°C, preferably 110-140°C, and the reaction time is 3-20 h, preferably 6-10 h.

10. The method of any one of claims 1-9, wherein, The isomerization reaction is carried out with or without a solvent, preferably without a solvent. Preferably, the solvent includes one or more of toluene, xylene, and cyclohexane.

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