Method for preparing menthol

Abstract

The present invention relates to a method for preparing menthol, which allows menthol to be prepared from thymol with a fast reaction rate and high conversion, while suppressing the formation of hydrocarbon by-products, which are impurities that cannot be reused.

Description

Method for producing menthol

[0001] Cross-citation with related application(s)

[0002] This application claims the benefit of priority to Korean Patent Application No. 10-2024-0120733, filed September 5, 2024, the entire contents of which are incorporated herein by reference.

[0003] The present invention relates to a method for producing menthol from thymol.

[0004]

[0005] 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).

[0006] The industrial production of menthol primarily involves the hydrogenation of thymol (2-isopropyl-5-methylphenol). The hydrogenation of thymol yields the four menthol isomers described above, along with the byproducts menthone, isomenthone, and hydrocarbons.

[0007] Among these, menthone and isomenthone are intermediates of the reaction and can be reused as raw materials after separation, but hydrocarbon by-products cannot be reused. Therefore, in order to increase efficiency and economic feasibility in the mass production process of menthol, it is necessary to suppress the production of the hydrocarbon by-products.

[0008]

[0009] Accordingly, the present invention aims to provide a method for producing menthol that can secure a high conversion rate of thymol into menthol while suppressing the production of hydrocarbon byproducts, which are impurities that cannot be reused.

[0010]

[0011] According to one embodiment of the present invention, a method for producing menthol is provided, which comprises a step of hydrogenating thymol in the presence of a solvent and a metal-supported catalyst, wherein the solvent includes a non-polar solvent and a polar solvent, and the content of the polar solvent in the solvent is 1 wt% to 6 wt%.

[0012] In one embodiment, the polar solvent may have a dielectric constant of 15 or greater at a temperature of 20° C. and a pressure of 0.1 MPa.

[0013] In one embodiment, the nonpolar solvent may have a dielectric constant of less than 5 at a temperature of 20° C. and a pressure of 0.1 MPa.

[0014] In one embodiment, the polar solvent may be at least one selected from the group consisting of water, methanol, ethanol, n-propanol, and isopropanol.

[0015] In one embodiment, the nonpolar solvent may be at least one selected from the group consisting of n-pentane, n-hexane, cyclopentane, cyclohexane, chloroform, methylcyclohexane, and isopropylcyclohexane.

[0016] In one embodiment, the metal-supported catalyst may include, as an active ingredient, at least one selected from the group consisting of nickel, nickel oxide, palladium, ruthenium, rhodium, osmium, iridium, and platinum.

[0017] In one embodiment, the metal-supported catalyst may comprise a silica carrier.

[0018] In one embodiment, the metal-supported catalyst may be treated with ammonia at a temperature of 300°C or less.

[0019] In one embodiment, the metal-supported catalyst may be used in an amount of 0.2 to 15 parts by weight based on 100 parts by weight of thymol.

[0020] In one embodiment, the step of hydrogenating the thymol can be performed at a hydrogen pressure of 2 to 100 bar and a temperature of 120 to 220° C.

[0021]

[0022] The method for producing menthol of the present invention can improve the efficiency and economy of the process because it has excellent reaction speed and conversion rate while significantly reducing the generation of hydrocarbon byproducts, which are non-reusable impurities.

[0023]

[0024] The terminology used herein is for the purpose of describing exemplary embodiments only and is not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly indicates otherwise. In this specification, it should be understood that the terms "comprise," "include," or "have" indicate the presence of a feature, step, component, or combination thereof, but do not preclude the possibility of the presence or addition of one or more other features, steps, components, or combinations thereof.

[0025]

[0026] The present invention is susceptible to various modifications and takes various forms. Specific embodiments are illustrated and described in detail below. However, this is not intended to limit the present invention to specific disclosed forms, but rather to encompass all modifications, equivalents, and alternatives falling within the spirit and technical scope of the present invention.

[0027]

[0028] Hereinafter, the present invention will be described in detail.

[0029]

[0030] The present invention provides a method for producing menthol, comprising a step of hydrogenating thymol in the presence of a solvent and a metal-supported catalyst, wherein the solvent includes a non-polar solvent and a polar solvent, and the content of the polar solvent in the solvent is 1 wt% to 6 wt%.

[0031]

[0032] The present inventors have conducted repeated research on a method for suppressing the production of hydrocarbon byproducts during the hydrogenation reaction of thymol, and as a result, they have confirmed that the above purpose can be achieved by using a nonpolar solvent with a predetermined amount of a polar solvent added thereto, thereby completing the present invention.

[0033]

[0034] The above polar solvent may have a dielectric constant of 15 or more at a temperature of 20°C and a pressure of 0.1 MPa.

[0035]

[0036] Specifically, the polar solvent may be at least one selected from the group consisting of water, methanol, ethanol, n-propanol, and isopropanol. In one embodiment, the polar solvent may be water and / or ethanol.

[0037]

[0038] The above non-polar solvent may have a dielectric constant of less than 5 at a temperature of 20°C and a pressure of 0.1 MPa.

[0039]

[0040] In one embodiment, the nonpolar solvent may be at least one selected from the group consisting of n-pentane, n-hexane, cyclopentane, cyclohexane, chloroform, methylcyclohexane, and isopropylcyclohexane.

[0041]

[0042] In one embodiment, water and / or ethanol may be used as the polar solvent, and cyclohexane may be used as the non-polar solvent.

[0043]

[0044] In order to secure the above-described effect of reducing the production of hydrocarbon by-products, the polar solvent is included in an amount of 1 wt% or more in the solvent, preferably 1.3 wt% or more, or 2.6 wt% or more, and 6 wt% or less, or 5 wt% or less, or 4 wt% or less.

[0045]

[0046] As such, by including a small amount of polar solvent in the solvent during the reaction, the production of hydrocarbon byproducts can be effectively suppressed. However, if the polar solvent content exceeds 6 wt%, the reaction rate may significantly decrease, resulting in reduced productivity. Therefore, it is preferable to maintain the above range.

[0047]

[0048] Meanwhile, the amount of solvent used in the hydrogenation reaction step of thymol is not particularly limited, but may be used in an amount of, for example, 70 parts by weight or more, or 80 parts by weight or more, or 90 parts by weight or more, or 100 parts by weight or more, but 200 parts by weight or less, or 190 parts by weight or less, or 180 parts by weight or less, or 170 parts by weight or less, relative to 100 parts by weight of thymol.

[0049]

[0050] The metal-supported catalyst has an active component supported on a carrier, and the active component may be, for example, at least one selected from the group consisting of nickel, nickel oxide, palladium, ruthenium, rhodium, osmium, iridium, and platinum. In one embodiment, the active component of the metal-supported catalyst may be at least one selected from the group consisting of nickel, nickel oxide, palladium, and ruthenium, or may be nickel and / or nickel oxide.

[0051]

[0052] The carrier is not particularly limited, and 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 can be used as the carrier.

[0053]

[0054] In one embodiment, the metal-supported catalyst may be 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.

[0055]

[0056] Specifically, the nickel-silica supported catalyst may comprise 50 to 70 wt% of nickel, 10 to 30 wt% of nickel oxide, and 10 to 30 wt% of silica based on the total weight of the catalyst. Alternatively, the nickel-silica supported catalyst may comprise 50 to 60 wt% of nickel, 15 to 25 wt% of nickel oxide, or 15 to 25 wt% of silica based on the total weight of the catalyst.

[0057]

[0058] 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.

[0059]

[0060] Meanwhile, the metal-supported catalyst may be treated with ammonia at a temperature of 300°C or lower. Here, 'ammonia treatment' means contacting the metal-supported catalyst with an aqueous ammonia solution (NH4OH), vapor of an aqueous ammonia solution, or ammonia gas (NH3).

[0061]

[0062] The temperature at which the ammonia treatment is performed may be, for example, 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.

[0063]

[0064] The above metal-supported catalyst can be used in an amount of 0.2 parts by weight or more, or 0.5 parts by weight or more, and 15 parts by weight or less, or 13 parts by weight or less, or 10 parts by weight or less, based on 100 parts by weight of thymol.

[0065]

[0066] The step of hydrogenating the above thymol can be accomplished by stirring a mixture of a solvent, a metal-supported catalyst, and thymol under a hydrogen atmosphere and bringing thymol into contact with hydrogen gas.

[0067]

[0068] This hydrogenation step of thymol can be carried out at a hydrogen pressure of 2 bar or more, or 10 bar or more, but not more than 100 bar, or not more than 90 bar, and at a temperature of 120°C or more, or 150°C or more, but not more than 220°C, or not more than 200°C. Under these conditions, the hydrogenation reaction can be carried out for 0.1 hour or more, or 0.5 hour or more, or 1 hour or more, but not more than 5 hours, or not more than 3 hours, or not more than 2 hours.

[0069]

[0070] In one embodiment, the hydrogenation reaction may be performed in a stirred tank reactor equipped with a gas-induced hollow stirrer. The use of such a reactor is preferred as it can further improve reaction efficiency.

[0071]

[0072] The amount of the menthol isomer mixture in the product obtained after the hydrogenation reaction, i.e., the total amount of menthol, isomenthol, neomenthol, and neoisomenthol, may be 90 wt% or more, 93 wt% or more, or 96 wt% or more.

[0073]

[0074] The amount of hydrocarbon byproducts among the products obtained after the hydrogenation reaction may be 2 wt% or less, or 1.8 wt% or less, 1.5 wt% or less, or 1.0 wt% or less.

[0075]

[0076] Hereinafter, preferred examples are presented to help understand the present invention, but the following examples are only illustrative of the present invention, and it is obvious to those skilled in the art that various changes and modifications are possible within the scope and technical idea of ​​the present invention, and it is also natural that such changes and modifications fall within the scope of the appended patent claims.

[0077]

[0078] [Example]

[0079] Manufacturing example: Manufacturing of metal-supported catalyst

[0080] 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 (NiSO4), 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 (55 wt% Ni, 25 wt% NiO, 20 wt% SiO2, measured by X-ray diffraction and inductively coupled plasma methods). All of the above processes were carried out under atmospheric pressure.

[0081]

[0082] Examples 1 to 4 and Comparative Examples 1 to 3: Preparation of menthol

[0083] A nonpolar solvent (cyclohexane) and a polar solvent (distilled water or ethanol) were added to the autoclave, then thymol and the catalyst prepared in the above manufacturing example were added, and the autoclave was closed. The types and amounts of the nonpolar solvent and polar solvent used in each example and comparative example, as well as the amounts of thymol and the catalyst used, are as shown in Table 1 below.

[0084] After sequentially purging nitrogen and hydrogen gases, the mixture was heated to 160°C while stirring at 1600 rpm using a gas-induced hollow stirrer while filling the mixture with hydrogen gas at 2 bar. After increasing the hydrogen gas pressure to 70 bar, the mixture was heated to the reaction temperature (170°C) and the reaction was carried out while maintaining the temperature and pressure.

[0085] After 3 hours, the reaction was completed, cooled, and purged with nitrogen gas. The contents of thymol, menthone and isomenthone, a mixture of menthol isomers, and hydrocarbon byproducts (expressed as weight %, wt%) in the product were analyzed using gas chromatography, and the results are shown in Table 1 below. The GC analysis system and column used are as follows.

[0086] GC system: Shimadzu GC-2010 FID

[0087] Column: CP-ChiraSil-DEXCB (CP7502)

[0088]

[0089]

[0090]

[0091] Referring to Table 1 above, it can be confirmed that Examples 1 to 4, in which the hydrogenation reaction was performed under conditions in which the polar solvent was included in an amount of 1 to 6 wt%, had a high yield of menthol and produced less hydrocarbon byproducts.

[0092] On the other hand, Comparative Example 1, which used only nonpolar solvents, had a high menthol yield but produced a large amount of non-reusable hydrocarbon byproducts, and Comparative Example 3, which used only polar solvents, had a slow reaction rate and significantly reduced the amount of menthol produced. On the other hand, when the amount of polar solvent among the solvents exceeded 6 wt%, the production of hydrocarbon byproducts was reduced, but the reaction rate was significantly reduced, which was disadvantageous in the process, as confirmed from the results of Comparative Example 2.

Claims

A method for producing menthol, comprising the step of hydrogenating thymol in the presence of a solvent and a metal-supported catalyst, The above solvent includes a non-polar solvent and a polar solvent, The content of polar solvent among the above solvents is 1 wt% to 6 wt%, Method for producing menthol. In the first paragraph, The above polar solvent has a dielectric constant of 15 or more at a temperature of 20°C and a pressure of 0.1 MPa. Method for producing menthol. In claim 1 or 2, The above non-polar solvent has a dielectric constant of less than 5 at a temperature of 20°C and a pressure of 0.1 MPa. Method for producing menthol. In any one of the first to third paragraphs, The above polar solvent is at least one selected from the group consisting of water, methanol, ethanol, n-propanol, and isopropanol. Method for producing menthol. In any one of the first to fourth paragraphs, The above nonpolar solvent is at least one selected from the group consisting of n-pentane, n-hexane, cyclopentane, cyclohexane, chloroform, methylcyclohexane, and isopropylcyclohexane. Method for producing menthol. In any one of the first to fifth paragraphs, The above metal-supported catalyst comprises at least one selected from the group consisting of nickel, nickel oxide, palladium, ruthenium, rhodium, osmium, iridium, and platinum as an active ingredient. Method for producing menthol. In any one of claims 1 to 6, The above metal-supported catalyst comprises a silica carrier, Method for producing menthol. In any one of the first to seventh paragraphs, The above metal-supported catalyst is treated with ammonia at a temperature of 300°C or less. Method for producing menthol. In any one of claims 1 to 8, The above metal-supported catalyst is used in an amount of 0.2 to 15 parts by weight based on 100 parts by weight of thymol. Method for producing menthol. In any one of claims 1 to 9, The step of hydrogenating the above thymol is performed at a hydrogen pressure of 2 to 100 bar and a temperature of 120 to 220°C. Method for producing menthol.

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