Method for preparing menthol

Abstract

The present invention relates to a method for preparing menthol, the method comprising a step of preparing menthol by a reduction reaction of thymol in the presence of an ammonia-treated metal-supported catalyst and hydrogen. The method for preparing menthol according to an aspect can satisfy both an excellent reaction rate and menthol selectivity.

Description

Method for producing menthol

[0001] The present disclosure relates to a method for producing menthol from thymol.

[0002] Menthol (2-Isopropyl-5-methylcyclohexanol) is a useful material in various industries, including medicine, cosmetics, and food. Menthol is a compound with three chiral centers, and there are four isomers: D / L-menthol, D / L-isomenthol, D / L-neomenthol, and D / L-neoisomentol. The material widely used in industry is D / L-menthol (hereinafter referred to as menthol).

[0003] Currently, the hydrogenation of thymol (2-isopropyl-5-methylphenol), which is easy to commercialize, is mainly used as a method for producing menthol in the industry. However, since the hydrogenation of thymol produces a complex mixture of the four isomers mentioned above and a hydrocarbon byproduct, menthane, improving the selectivity for menthol is still an issue that needs to be solved. Various studies have been conducted to improve the selectivity of menthol, but there are limitations such as the need for a multi-step process or the use of methods that slow down the reaction rate, which leads to excessively long process times and low conversion rates. In addition, even when methods to increase the activity of the hydrogenation reaction were applied, excessive byproducts were produced or the selectivity for the target product, menthol, was lowered or maintained.

[0004] Therefore, a new technology is needed that can simultaneously satisfy the selectivity for menthol, reaction speed, and by-product formation inhibition effect.

[0005] One aspect of the present invention relates to a method for producing menthol that can satisfy both excellent reaction speed and excellent menthol selectivity.

[0006] One aspect of the present invention provides a method for producing menthol, comprising the step of producing menthol by reducing thymol in the presence of an ammonia-treated metal-supported catalyst and hydrogen.

[0007] The above metal-supported catalyst may be a nickel-supported catalyst comprising one or more active metals selected from nickel and nickel oxide.

[0008] The above metal-supported catalyst may include a silica support.

[0009] The above ammonia treatment may be performed with ammonia gas at a temperature of 300°C or less.

[0010] The above reduction reaction may be performed under solvent-free conditions.

[0011] The above reduction reaction may be performed under conditions of 1 to 100 bar of hydrogen and a temperature of 150 to 200°C.

[0012] The above reduction reaction may be performed for 0.5 to 5 hours.

[0013] The amount of the metal-supported catalyst used may be 0.01 to 10 wt% based on the total amount of menthol produced.

[0014] The conversion rate of the above Timol can be over 95%.

[0015] The yield of the menthol isomer mixture can be greater than 95%.

[0016] The above menthol isomer mixture may include menthol, isomenthol, neomenthol, and neoisomenthol.

[0017] The selectivity of menthol over the mixture of menthol isomers can be greater than 50%.

[0018] A method for producing menthol according to one embodiment can satisfy all of the following: excellent reaction speed, menthol selectivity, and suppression of by-product formation even under solvent-free conditions. Specifically, the method for producing menthol according to one embodiment can achieve an excellent reaction speed even at low temperatures and with a low catalyst usage, while effectively suppressing the formation of by-products (hydrocarbons) generated during the reduction of thymol, and can improve the selectivity of menthol over menthol isomers.

[0019] In addition, the process can be further simplified by using a small amount of catalyst under solvent-free conditions according to one aspect, and productivity can be significantly improved because menthol can be produced in a high yield even under mild reaction conditions.

[0020] The terminology used herein is intended solely to describe specific embodiments and is not intended to limit the present invention.

[0021] As used herein, the singular forms may be intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0022] Throughout this specification, the terms "comprises," "includes," "contains," or "has" a component, unless specifically stated to the contrary, do not exclude other components, but rather may include other components, and do not exclude additional unrecited elements, materials, or processes.

[0023] The numerical ranges used herein include the lower and upper limits and all values ​​within that range, increments logically derived from the shape and width of the defined range, all doubly defined values, and all possible combinations of the upper and lower limits of numerical ranges defined in different shapes. Unless otherwise specified herein, values ​​outside the defined range that may arise due to experimental error or rounding of values ​​are also included in the defined numerical range.

[0024] Unless otherwise specified herein, “about” may be considered a value within 30%, 25%, 20%, 15%, 10% or 5% of the stated value.

[0025] Below, the present disclosure will be described in detail. However, this is merely exemplary and the present disclosure is not limited to the specific embodiments described as examples.

[0026] The hydrogenation of thymol (2-isopropyl-5-methylphenol) to produce menthol is a widely used method in industry. However, thymol hydrogenation has the limitation of low selectivity for menthol because it produces a complex mixture of menthol isomers and hydrocarbon byproducts. Therefore, various studies have been conducted to improve the selectivity of menthol. However, these methods required multi-step processes or used methods that slowed down the reaction rate, which resulted in excessively long process times and low conversion rates, making commercialization difficult. Furthermore, even when methods to increase the activity of the hydrogenation reaction were applied, there were limitations such as excessive production of byproducts.

[0027] Accordingly, the present invention provides a method for producing menthol that can satisfy both excellent menthol selectivity and by-product production inhibition effects while securing an excellent reaction speed.

[0028] A method for producing menthol according to one aspect may include a step of producing menthol by reducing thymol in the presence of an ammonia-treated metal-supported catalyst and hydrogen.

[0029] Specifically, a method for producing menthol according to one embodiment may include (a) a step of treating a metal-supported catalyst with ammonia; (b) a step of hydrogenating (reducing) thymol with the ammonia-treated metal-supported catalyst in the presence of hydrogen to obtain menthol.

[0030] The above ammonia treatment may be treatment of an aqueous ammonia solution (NH4OH), vapor of an aqueous ammonia solution, or ammonia gas (NH3).

[0031] The temperature at which the ammonia treatment is performed is not particularly limited, but may be, for example, performed at 300°C or less, or 10 to 300°C, or 10 to 200°C, or 10 to 100°C, or 20 to 100°C, or 20 to 80°C.

[0032] The metal-supported catalyst according to one embodiment may be one in which an active metal is supported on a support to form a complex, and the active metal may be, for example, one or more selected from ruthenium, iron, nickel, cobalt, platinum, palladium, vanadium, copper, chromium, tungsten, molybdenum, iridium, rhodium, zirconium, cobalt, zinc, calcium, and oxides thereof. Specifically, the metal-supported catalyst according to one embodiment may be a nickel-supported catalyst including one or more active metals selected from nickel (Ni) and nickel oxide (NiO).

[0033] The support may be, for example, one or more selected from silica, alumina, magnesium chloride, calcium chloride, bauxite, zeolite, magnesium oxide, zirconium oxide, titanium oxide, boron trioxide, calcium oxide, zinc oxide, barium oxide, and thorium oxide, and may be specifically silica. Specifically, the metal-supported catalyst according to one embodiment may be a nickel-silica-supported catalyst in which an active metal including nickel, nickel oxide, or a combination thereof is supported on a silica support to form a complex.

[0034] For example, the metal-supported catalyst may contain 5 to 50 parts by weight, or 5 to 40 parts by weight, or 10 to 40 parts by weight of the support relative to 100 parts by weight of the active metal. Specifically, when the metal-supported catalyst according to one embodiment is a nickel-silica-supported catalyst in which an active metal including nickel and nickel oxide is supported on a silica support to form a complex, the catalyst may contain 50 to 70 wt% of nickel, 10 to 30 wt% of nickel oxide, and 10 to 30 wt% of silica relative to the total weight of the catalyst, and specifically, it may contain 50 to 60 wt% of nickel, 15 to 25 wt% of nickel oxide, or 15 to 25 wt% of silica.

[0035] The metal-supported catalyst according to one embodiment may further include one or more promoters, and when the metal-supported catalyst further includes a promoter, the promoter may be included in an amount of 0.1 to 3.0 parts by weight based on 100 parts by weight of the active metal, and the catalytic activity may be further improved.

[0036] In addition, the method for producing menthol according to one aspect is characterized in that it is performed under solvent-free conditions.

[0037] That is, the method for producing menthol according to one embodiment can satisfy all of the following: excellent reaction speed, menthol selectivity, and suppression of by-product formation even under solvent-free conditions. Specifically, the method for producing menthol according to one embodiment can achieve an excellent reaction speed even at low temperatures and with a low amount of catalyst, achieve a thymol conversion rate close to 100% in a short time, effectively suppress by-product formation, and achieve high menthol selectivity for menthol isomers.

[0038] For example, the reduction reaction according to one aspect may be performed under conditions of 1 to 100 bar of hydrogen and a temperature of 100 to 200°C, or 1 to 50 bar of hydrogen and a temperature of 150 to 200°C, or 1 to 30 bar of hydrogen and a temperature of 160 to 190°C.

[0039] For example, the amount of the metal-supported catalyst may be 0.01 to 20 wt%, or 0.01 to 15 wt%, or 0.01 to 10 wt%, or 0.1 to 10 wt%, or 1 to 10 wt%, or 2 to 10 wt% based on the total weight of the menthol isomer mixture produced.

[0040] For example, the reduction reaction according to one aspect may be performed for 0.5 to 5 hours, or 0.5 to 3 hours, or 0.1 to 2 hours under the conditions described above.

[0041] For example, in a method for manufacturing menthol according to one aspect, the conversion rate of thymol ((amount of thymol input - amount of thymol remaining after completion of reaction) / amount of thymol input x 100) may be 90% or more, or 95% or more, or 98% or more, specifically 100%.

[0042] For example, in a method for producing menthol according to one embodiment, the yield of the menthol isomer mixture may be 80% or more, or 85% or more, 90% or more, or 95% or more, and the upper limit may be 99% or less, or 98% or less.

[0043] The above menthol isomer mixture may include menthol, isomenthol, neomenthol, and neoisomenthol.

[0044] For example, in a method for producing menthol according to one embodiment, the selectivity of menthol with respect to a mixture of menthol isomers ((amount of menthol produced / amount of menthol isomer mixture produced) x 100) may be 30% or more, or 40% or more, or 50% or more, and in this case, the upper limit may be 95% or less, or 90% or less, or 80% or less.

[0045] Hereinafter, the above-described implementation examples will be described in more detail through examples. However, the following examples are for illustrative purposes only and do not limit the scope of the rights.

[0046] [Manufacturing Example] Manufacturing of a Metal-Supported Catalyst

[0047] 300m 2 / g of porous silica powder with a surface area of ​​100g, a pore size of 21nm, and an average particle size of 7㎛, 40g of nickel sulfate (LiSO4), 491g of copper sulfate (CuSO4), and 2,000ml of distilled water were placed in a precipitation vessel and stirred while heating to 80℃. After reaching 80℃, 1,500mL of a solution containing 262g of sodium carbonate (Na2CO3) was injected within 1 hour using a syringe pump. After precipitation was complete, the pH of the slurry was 7.6, and it was washed and filtered with about 30L of distilled water, and then dried in a drying oven at 100℃ for more than 12 hours. After being divided into small portions, it was calcined at a temperature of 350℃ in an air atmosphere. After being divided again, it was activated by reduction at a temperature of 350℃ in a hydrogen atmosphere. The activated catalyst was passivated using a nitrogen mixture containing 1% oxygen to prepare a nickel-silica supported catalyst.

[0048] [Example 1]

[0049] Preparation of ammonia-treated metal-supported catalysts

[0050] The nickel-silica supported catalyst obtained in the above Preparation Example 1 was placed in a reactor, and the inside of the reactor was purged with nitrogen gas at a rate of 7.5 ml / min per g of catalyst. Thereafter, the reaction was treated with ammonia (NH3) gas diluted to 10% in helium (He) at a rate of 5 ml / min per g of catalyst for 30 minutes while maintaining the temperature at 20°C, and then nitrogen gas purging was performed again to obtain an ammonia-treated nickel-silica supported catalyst. All processes were carried out under atmospheric pressure conditions.

[0051] Manufacturing of menthol

[0052] An autoclave was charged with 300 g of thymol and heated to below 60 ℃. When the thymol melted, 4.5 g of the ammonia-treated nickel-silica supported catalyst obtained above was added and sealed. After sequentially purging with nitrogen and hydrogen, the reactor was heated to 160 ℃ by stirring at 1600 rpm with a gas-induced hollow stirrer while filling with hydrogen up to 2 bar. When the internal temperature of the reactor reached 160 ℃, hydrogen was added up to 10 bar, heated to 170 ℃, and the reaction was carried out while maintaining the temperature and pressure. Samples were collected at each reaction time and analyzed for the content of residual thymol, generated intermediate (menthone), menthol isomer, and hydrocarbon byproduct (menthane) through gas chromatography (column: CP-ChiraSil-DEX CB (CP7502)). The results are shown in Table 1 below.

[0053] [Example 2]

[0054] The same procedure as Example 1 was followed, except that the amount of catalyst used was changed to 18 g and the reaction temperature was changed to 180°C.

[0055] [Example 3]

[0056] The same procedure as Example 2 was followed, except that the reaction temperature was changed to 190°C.

[0057] [Comparative Example 1]

[0058] The same procedure as Example 1 was followed, except that the nickel-silica supported catalyst obtained in Preparation Example 1 was used instead of the ammonia-treated nickel-silica supported catalyst.

[0059] Comparative Example 1 Example 1 Example 2 Example 3 Reaction time (h) 2323130.51 Thymol (wt%) 0.20.20.20.00.00.00.00.0 Menthone (wt%)4.54.43.62.32.72.53.83.6Menthol isomer mixture(wt%)Menthol26.528.727.632.943.154.144.654.7Neomenthol13.614.415.416.320.925.422.126.2Isomenthol49.045.544.042.829.615.625.713.3Neoisomenthol2.31.49.15.63.62.33.72.1Hydrocarbon byproduct(wt%)3.95.40.10.10.10.10.10.10.1

[0060] Referring to Table 1 above, it can be seen that all of the manufacturing methods according to the examples have excellent reaction rates and simultaneously satisfy the suppression of hydrocarbon by-product production and menthol selectivity. On the other hand, the manufacturing method of the comparative example was performed at the same reaction temperature as Example 1, but thymol was not completely converted within 3 hours, hydrocarbon by-products increased significantly over time, and menthol selectivity was also significantly reduced compared to the examples.

[0061] As described above, the present invention has been described by limited embodiments, but these are provided only to help a more general understanding of the present invention, and the present invention is not limited to the above embodiments, and those skilled in the art to which the present invention pertains can make various modifications and variations based on this description.

[0062] Therefore, the idea of ​​the present invention should not be limited to the described embodiments, and all things that are equivalent or equivalent to the following claims as well as the claims are considered to fall within the scope of the idea of ​​the present invention.

Claims

1. A method for producing menthol, comprising the step of producing menthol by reducing thymol in the presence of an ammonia-treated metal-supported catalyst and hydrogen.

2. In paragraph 1, A method for producing menthol, wherein the metal-supported catalyst is a nickel-supported catalyst comprising at least one active metal selected from nickel and nickel oxide.

3. In paragraph 2, A method for producing menthol, wherein the metal-supported catalyst comprises a silica support.

4. In paragraph 1, A method for producing menthol, wherein the above ammonia treatment is performed with ammonia gas under temperature conditions of 300°C or less.

5. In paragraph 1, A method for producing menthol, wherein the above reduction reaction is performed under solvent-free conditions.

6. In paragraph 1, A method for producing menthol, wherein the above reduction reaction is performed under conditions of 1 to 100 bar of hydrogen and a temperature of 150 to 200°C.

7. In paragraph 1, A method for producing menthol, wherein the above reduction reaction is performed for 0.5 to 5 hours.

8. In paragraph 1, A method for producing menthol, wherein the amount of the metal-supported catalyst used is 0.01 to 10 wt% based on the total amount of menthol produced.

9. In paragraph 1, A method for producing menthol, wherein the conversion rate of the above thymol is 95% or higher.

10. In paragraph 9, A method for producing menthol, wherein the yield of the mixture of menthol isomers is 95% or more.

11. In paragraph 10, A method for producing menthol, wherein the above menthol isomer mixture includes menthol, isomenthol, neomenthol, and neoisomenthol.

12. In paragraph 11, A method for producing menthol, wherein the selectivity of menthol with respect to a mixture of menthol isomers is at least 50%.