Method for preparing methyl 6-hydroxyhexanoate from methyl tetrahydrofuran acetate

Abstract

The invention discloses a method for preparing methyl 6-hydroxyhexanoate by using methyl tetrahydrofuran acetate, which comprises the following steps of: reacting methyl tetrahydrofuran acetate serving as a raw material in a proper solvent in a reducing gas atmosphere under the action of a catalyst by using a fixed bed at a certain air speed, reaction temperature, pressure and hydrogen-ester ratio, distilling out the solvent, and separating the methyl 6-hydroxyhexanoate from the methyl tetrahydrofuran acetate to obtain the methyl 6-hydroxyhexanoate. The product of methyl 6-hydroxyhexanoate can be obtained. According to the method, fixed bed equipment is used, and the methyl 6-hydroxyhexanoate is prepared from the renewable resource tetrahydrofuran methyl acetate under the conditions of mild reaction conditions and no pollution in the reaction process. According to the method, efficient utilization of the catalyst is guaranteed, continuous flow reaction can be carried out, operation is easy and convenient, waste materials are not generated in the reaction process, pollution to the environment is avoided, efficient conversion of tetrahydrofuran methyl acetate is achieved, the generated 6-hydroxyhexanoic acid methyl ester can be used as a monomer of a polymer, and the method is suitable for industrial production. The application range of the tetrahydrofuran methyl acetate is expanded, and the demand of preparing the 6-hydroxyhexanoic acid methyl ester on petrochemical resources is relieved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of chemical synthesis, and particularly relates to a method for preparing 6-hydroxyhexanoic acid methyl ester by using methyl tetrahydrofurfuryl acetate. BACKGROUND

[0002] 6-hydroxyhexanoic acid methyl ester is an important organic intermediate, which has both hydroxyl and ester functional groups. The ester group can be hydrolyzed to generate 6-hydroxyhexanoic acid, which can be used as an intermediate for organic synthesis, medicine, etc., or can be ammonolysed to obtain an amide derivative, which is used for preparing polyamide materials or as a drug carrier. The hydroxyl group can be oxidized, esterified or generated into a halogenated product, which is an important raw material for synthesizing perfumes, and can be used in biodegradable plastics, surfactants, etc., and has multiple application functions. 6-hydroxyhexanoic acid methyl ester itself can also undergo intramolecular cyclization to generate caprolactone, which is an aliphatic lactone with important application value.

[0003] At present, the main way for industrial synthesis of 6-hydroxyhexanoic acid methyl ester is the methanol ring-opening method of ε-caprolactone. The mechanism of this method is that methanol is subjected to ester exchange with ε-caprolactone through acid or base catalysis. This method needs to control the concentration of acid and base, so that the operation is more complex. In addition, the price of ε-caprolactone raw material fluctuates, and a large amount of raw material demand will increase the cost. The use of acid and base catalysts also makes it necessary to perform neutralization and water washing treatment in the later stage, which will also produce wastewater and cause great harm to the environment. The present application ensures the efficient use of the catalyst, can perform continuous flow reaction and is simple to operate. In addition, no waste is generated in the reaction process, which will not pollute the environment. The present application realizes the efficient conversion of methyl tetrahydrofurfuryl acetate, and the generated 6-hydroxyhexanoic acid methyl ester can be used as a monomer for polymers, which expands the application range of methyl tetrahydrofurfuryl acetate and relieves the demand for petrochemical resources for preparing 6-hydroxyhexanoic acid methyl ester. SUMMARY

[0004] The present application aims to overcome the defects of the prior art and provide a method for preparing 6-hydroxyhexanoic acid methyl ester by using methyl tetrahydrofurfuryl acetate, which relieves the demand for petrochemical resources for preparing 6-hydroxyhexanoic acid methyl ester.

[0005] The specific content is that methyl tetrahydrofurfuryl acetate is used as a raw material, and is subjected to reaction in a suitable solvent (with a certain mass fraction), a reducing gas atmosphere and under the action of a catalyst by using a fixed bed at a certain space velocity, reaction temperature, pressure and hydrogen-ester ratio, and then the solvent is distilled to obtain 6-hydroxyhexanoic acid methyl ester product. The reaction equation is as follows: The solvent is cyclohexane; and the reducing gas is hydrogen.

[0006] In order to achieve the above object, the present application is implemented by the following scheme: A method for preparing 6-hydroxyhexanoic acid methyl ester by using tetrahydrofuran ethyl acetate, the process is as follows: (1) Fixed bed catalyst, reduction of activated catalyst, configuration of mass fraction of 70~80% of tetrahydrofuran ethyl acetate cyclohexane solution; (2) then access to fixed bed, step (1) solution and hydrogen in space velocity (1 hour of feed and catalyst mass ratio) 0.15~0.25 h -1 , reaction temperature 110~130℃, pressure 3~5 MPa under the same into the fixed bed to start the reaction, after the reaction, distillation of solvent, can get 6-hydroxyhexanoic acid methyl ester product.

[0007] The catalyst is obtained by the following process: S1, the metal salt solution and carrier precursor solution are mixed and stirred uniformly; S2, under the condition of water bath heating and stirring, dropwise adding precipitator, stirring 1~3 hours, then standing for 6~9 hours; S3, after filtration, using deionized water repeatedly, then drying; S4, the obtained solid is calcined to obtain the catalyst; Among them, the metal salt is two or more of platinum salt (chloroplatinic acid), palladium salt (palladium chloride, palladium nitrate), rhodium salt (rhodium chloride, rhodium nitrate), iridium salt (chloroiridic acid, iridium chloride, iridium acetate, sodium chloroiridate hexahydrate), ruthenium salt (ruthenium chloride, potassium ruthenate, ruthenium nitrate, ruthenium sulfate), cobalt salt (cobalt nitrate), copper salt (copper nitrate, copper chloride), nickel salt (nickel nitrate, nickel chloride), tungsten salt (ammonium metatungstate) and molybdenum salt (ammonium heptamolybdate), the mass ratio of metal elements in the metal salt in the catalyst is 5%-40%; the carrier is at least one of alumina, zirconia, silica, titania, ceria, magnesia, the carrier precursor is at least one of aluminum salt (such as aluminum nitrate, aluminum chloride), zirconium salt (such as zirconium nitrate), silica precursor (such as one of tetraethyl silicate, tetrapropyl silicate, tetramethyl silicate, sodium silicate and silica dispersion), titanium salt (such as titanium nitrate, titanium chloride), cerium salt (cerium nitrate, cerium chloride) and magnesium salt (such as magnesium nitrate, magnesium chloride, magnesium sulfate), the precipitator is one of ammonia, sodium hydroxide solution, potassium hydroxide solution, sodium carbonate solution and potassium carbonate solution.

[0008] The concentration of metal salt is 0.001mol / L~0.5 mol / L, preferably the concentration of metal salt is 0.007mol / L~0.4mol / L; the carrier precursor concentration is 0.1 mol / L ~1 mol / L, preferably 0.2 mol / L~0.8mol / L.

[0009] The concentration of the sodium hydroxide solution, the potassium hydroxide solution, the sodium carbonate solution and the potassium carbonate solution is 0.1 mol / L~1 mol / L, preferably 0.1 mol / L~0.2 mol / L.

[0010] The catalyst of the present application has multiple functional characteristics, mainly embodied in: 1. directional ring-opening of the tetrahydrofuran ring (1,5 cleavage of carbon-oxygen bond), 2. hydrogenation ability after ring-opening.

[0011] Further, the water bath heating temperature in step S2 is 50~70℃, preferably 60℃.

[0012] Further, after adding the precipitant in step S2, the pH value of the reaction solution is 6~10 to ensure complete precipitation.

[0013] Further, the calcination temperature in step S4 is 350~500℃, the calcination atmosphere is air atmosphere, and the calcination time is 3~5 hours.

[0014] Further, in step (1), the reduced activated catalyst refers to being reduced in a mixed gas of hydrogen and nitrogen at 300~400℃ for 5~7 hours, and the volume ratio of hydrogen to nitrogen is 1:(4~6); preferably, the volume ratio of hydrogen to nitrogen is 1:5, the reduction temperature is 350℃, and the reduction time is 6 hours.

[0015] Further, in step (2), the hydrogen ester ratio (molar ratio of hydrogen to methyl tetrahydrofuran acetate) is (30~40):1, preferably 35:1.

[0016] Specifically, the cyclohexane solution of methyl tetrahydrofuran acetate in step (1) is preferably 75%.

[0017] The principle of preparing 6-hydroxyhexanoic acid methyl ester in the present application is as follows: methyl tetrahydrofuran acetate is adsorbed to the active site of the catalyst in a directional manner, and ring-opening hydrogenation is performed to obtain the target product.

[0018] Compared with the prior art, the present application has the following beneficial effects: 1) Using renewable resource methyl tetrahydrofuran acetate to prepare 6-hydroxyhexanoic acid methyl ester, which alleviates the demand for petrochemical resources in the preparation of 6-hydroxyhexanoic acid methyl ester.

[0019] 2) The present application uses a fixed bed device to produce 6-hydroxyhexanoic acid methyl ester, which has a simple process flow, easy operation, high safety of production process and no pollution to the environment. DETAILED DESCRIPTION

[0020] The technical solutions of the present application are further described in detail below, but the protection scope of the present application is not limited thereto.

[0021] The present application utilizes 6-hydroxyhexanoic acid methyl ester produced by a fixed bed process under the action of a catalyst to be prepared by the following method: 1) A fixed bed is filled with a certain amount of catalyst, the catalyst is reduced and activated according to catalyst reduction conditions, and a 75% mass fraction of methyl tetrahydrofuran acetate-cyclohexane solution is configured; 2) Subsequently, the fixed bed is connected, the above-mentioned solution and hydrogen gas (hydrogen ester ratio 35:1) are introduced into the fixed bed to start the reaction under the conditions of space velocity 0.2 h -1 , reaction temperature 120℃, pressure 4 MPa, and 6-hydroxyhexanoic acid methyl ester reaction liquid is obtained after the reaction.

[0022] The present application is further described in detail in combination with specific examples. In the following examples, if not otherwise specified, the raw materials used are ordinary commercially available products or can be prepared by using conventional techniques in the art.

[0023] Example 1 A method for preparing 6-hydroxyhexanoic acid methyl ester by using methyl tetrahydrofuran acetate, the process is as follows: Preparation of composite catalyst 15%Ni / 5%Mo / alumina: 0.15 mol / L nickel nitrate solution, 0.007 mol / L ammonium heptamolybdate solution and 0.8 mol / L aluminum nitrate solution are mixed uniformly, and stirred for 3h. Then ammonia water (commercial AR grade ammonia water) is slowly added dropwise under the condition of 60℃ constant temperature water bath and stirring until the solution pH=8.0-8.5. After standing for 6h, filtration and washing with deionized water, natural drying, and calcination at 400℃ in air for 3h, the composite catalyst is obtained, wherein the nickel accounts for 15% of the mass of the catalyst, and the molybdenum accounts for 5% of the mass of the catalyst.

[0024] A fixed bed is filled with a certain amount of catalyst, and the catalyst is reduced and activated in a mixed gas of hydrogen and nitrogen (volume ratio 1:5) at 350℃ for 6h, and a 75% mass fraction of methyl tetrahydrofuran acetate cyclohexane solution is configured; subsequently, the fixed bed is connected, the above-mentioned solution and hydrogen gas (hydrogen ester ratio 35:1) are introduced into the fixed bed to start the reaction under the conditions of space velocity 0.2 h -1 , reaction temperature 120℃, pressure 4 MPa, and 6-hydroxyhexanoic acid methyl ester reaction liquid is obtained after the reaction.

[0025] According to the determination of the chemical content of the reaction liquid by gas chromatograph, the conversion rate of methyl tetrahydrofuran acetate and the molar selectivity of 6-hydroxyhexanoic acid methyl ester product are obtained according to the content of 6-hydroxyhexanoic acid methyl ester and material balance.

[0026] The sample was tested, and the conversion rate of tetrahydrofuran methyl acetate was 98.6%, and the molar selectivity of 6-hydroxyhexanoic acid methyl ester product was 96.9%. The solvent was distilled at a pressure of-0.09 MPa and a temperature of 40-55°C using a circulating water vacuum pump, and 6-hydroxyhexanoic acid methyl ester product was obtained.

[0027] Example 2 A method for preparing 6-hydroxyhexanoic acid methyl ester from tetrahydrofuran methyl acetate, the process is as follows: Preparation of composite catalyst 30% Ni / 10% Pt / zirconia: Mix 0.3 mol / L nickel nitrate solution, 0.1 mol / L chloroplatinic acid solution and 0.6 mol / L zirconium nitrate solution uniformly, and stir for 1 h. Then slowly add sodium hydroxide solution (0.1 mol / L-0.2 mol / L) dropwise under the condition of constant temperature water bath at 60°C and stirring, until the solution pH=8.0-9.0. After standing for 6 h, filter and wash with deionized water, dry naturally, and calcine at 500°C in air for 5 h to obtain the composite catalyst, in which the nickel accounts for 30% of the mass of the catalyst and the platinum accounts for 10% of the mass of the catalyst.

[0028] A certain amount of catalyst was packed in a fixed bed, and the catalyst was reduced and activated at 350°C for 6 h in a mixed gas of hydrogen and nitrogen (volume ratio 1:5). A 75% mass fraction tetrahydrofuran methyl acetate cyclohexane solution was prepared; then the solution was connected to the fixed bed, and the above solution and hydrogen (hydrogen to ester ratio 35:1) were introduced into the fixed bed at a space velocity of 0.2 h -1 , a reaction temperature of 120°C and a pressure of 4 MPa to start the reaction. The 6-hydroxyhexanoic acid methyl ester reaction liquid obtained after the reaction flowed into the fixed bed storage tank.

[0029] According to the determination of the chemical content of the reaction liquid by gas chromatograph, the conversion rate of tetrahydrofuran methyl acetate and the molar selectivity of 6-hydroxyhexanoic acid methyl ester product were calculated according to the content of 6-hydroxyhexanoic acid methyl ester and material balance.

[0030] The sample was tested, and the conversion rate of tetrahydrofuran methyl acetate was 98.2%, and the molar selectivity of 6-hydroxyhexanoic acid methyl ester product was 96.3%.

[0031] The solvent was distilled at a pressure of-0.09 MPa and a temperature of 40-55°C using a circulating water vacuum pump, and 6-hydroxyhexanoic acid methyl ester product was obtained.

[0032] Example 3 A method for preparing 6-hydroxyhexanoic acid methyl ester from tetrahydrofuran methyl acetate, the process is as follows: Preparation of composite catalyst 6% Cu / 40% Ru / titanium oxide: 0.06 mol / L copper nitrate solution, 0.4 mol / L ruthenium chloride solution and 0.54 mol / L titanium nitrate solution were mixed uniformly and stirred for 3 h. Then, under the condition of constant temperature water bath at 60°C and stirring, sodium carbonate solution (0.1 mol / L ~ 0.2 mol / L) was slowly added dropwise until the pH of the solution was 7.0-7.5. After aging for 8 h, the solution was filtered, washed with deionized water, naturally dried and calcined at 450°C in air for 3 h to obtain the composite catalyst, in which the copper accounted for 6% of the mass of the catalyst and the ruthenium accounted for 40% of the mass of the catalyst.

[0033] A certain amount of catalyst was loaded in a fixed bed, reduced and activated at 350°C for 6 h in a mixed gas of hydrogen and nitrogen (volume ratio 1:5) and a 75% mass fraction of methyl tetrahydrofuran acetate-cyclohexane solution was prepared; then the above solution and hydrogen (hydrogen-ester ratio 35:1) were introduced into the fixed bed to start the reaction at a space velocity of 0.2 h -1 , a reaction temperature of 120°C and a pressure of 4 MPa. The reaction liquid obtained after the reaction flowed into the fixed bed storage tank.

[0034] According to the determination of the chemical content of the reaction liquid by gas chromatograph, the conversion rate of methyl tetrahydrofuran acetate and the molar selectivity of 6-hydroxyhexanoic acid methyl ester product were calculated according to the content of 6-hydroxyhexanoic acid methyl ester.

[0035] The sample was tested, and the conversion rate of methyl tetrahydrofuran acetate was 99.0% and the molar selectivity of 6-hydroxyhexanoic acid methyl ester product was 97.2%.

[0036] The solvent was distilled at a pressure of -0.09 MPa and a temperature of 40-55°C using a circulating water vacuum pump to obtain the 6-hydroxyhexanoic acid methyl ester product.

[0037] Example 4 A method for preparing 6-hydroxyhexanoic acid methyl ester from methyl tetrahydrofuran acetate, the process is as follows: Preparation of composite catalyst 15% Co / 15% Mo / alumina: 0.15 mol / L cobalt nitrate solution, 0.02 mol / L ammonium heptamolybdate solution and 0.7 mol / L aluminum nitrate solution were mixed uniformly and stirred for 1 h. Then, under the condition of constant temperature water bath at 60°C and stirring, sodium carbonate solution (0.1 mol / L ~ 0.2 mol / L) was slowly added dropwise until the pH of the solution was 7.0-9.0. After aging for 6 h, the solution was filtered, washed with deionized water, naturally dried and calcined at 400°C in air for 5 h to obtain the composite catalyst, in which the cobalt accounted for 15% of the mass of the catalyst and the molybdenum accounted for 15% of the mass of the catalyst.

[0038] A fixed bed is filled with a certain amount of catalyst, which is reduced and activated at 350°C for 6h in a mixed gas of hydrogen and nitrogen (volume ratio 1:5), and a 75% mass fraction of methyl tetrahydrofuran acetate cyclohexane solution is configured; then the above solution and hydrogen gas (hydrogen ester ratio 35:1) are connected to the fixed bed at a space velocity of 0.2 h -1 , and the reaction is started at a reaction temperature of 120°C and a pressure of 4 MPa. After the reaction, the obtained 6-hydroxyhexanoic acid methyl ester reaction liquid flows into the fixed bed storage tank.

[0039] According to the determination of the chemical content of the reaction liquid by gas chromatograph, the conversion rate of methyl tetrahydrofuran acetate and the molar selectivity of 6-hydroxyhexanoic acid methyl ester product are calculated according to the content of 6-hydroxyhexanoic acid methyl ester.

[0040] The sample is tested, and the conversion rate of methyl tetrahydrofuran acetate is 98.1%, and the molar selectivity of 6-hydroxyhexanoic acid methyl ester product is 97.5%.

[0041] The solvent is distilled at a pressure of -0.09 MPa and a temperature of 40-55°C using a circulating water vacuum pump, and the 6-hydroxyhexanoic acid methyl ester product is obtained.

[0042] Example 5 A method for preparing 6-hydroxyhexanoic acid methyl ester from methyl tetrahydrofuran acetate, the process is as follows: Preparation of composite catalyst 20% Ni / 10% W / ceria+zirconia: Mix 0.2 mol / L nickel nitrate solution, 0.008 mol / L ammonium metatungstate solution, 0.35 mol / L cerium nitrate solution and 0.35 mol / L zirconium nitrate solution uniformly, and stir for 3h. Then slowly add potassium hydroxide solution (0.1 mol / L-0.2 mol / L) under the condition of constant temperature water bath at 60°C and stirring, until the pH of the solution is 9.0-10.0. After standing for 9h, filter and wash with deionized water, dry naturally, and calcine at 500°C in air for 5h to obtain the composite catalyst, wherein the nickel accounts for 20% of the mass of the catalyst, the tungsten accounts for 10% of the mass of the catalyst, the ceria accounts for 35% of the mass of the catalyst, and the zirconia accounts for 35% of the mass of the catalyst.

[0043] A fixed bed is filled with a certain amount of catalyst, which is reduced and activated at 350°C for 6h in a mixed gas of hydrogen and nitrogen (volume ratio 1:5), and a 75% mass fraction of methyl tetrahydrofuran acetate cyclohexane solution is configured; then the above solution and hydrogen gas (hydrogen ester ratio 35:1) are connected to the fixed bed at a space velocity of 0.2 h -1 , and the reaction is started at a reaction temperature of 120°C and a pressure of 4 MPa. After the reaction, the obtained 6-hydroxyhexanoic acid methyl ester reaction liquid flows into the fixed bed storage tank.

[0044] According to the determination of the chemical content of the reaction liquid by the gas chromatograph, the conversion rate of methyl tetrahydrofuran acetate and the molar selectivity of the methyl 6-hydroxyhexanoate product are obtained according to the content of methyl 6-hydroxyhexanoate and the material balance.

[0045] The sample is tested, and the conversion rate of methyl tetrahydrofuran acetate is 98.7%, and the molar selectivity of the methyl 6-hydroxyhexanoate product is 96.5%.

[0046] The solvent is distilled at a pressure of -0.09 MPa and a temperature of 40-55°C using a circulating water vacuum pump, and the methyl 6-hydroxyhexanoate product is obtained.

[0047] Example 6 A method for preparing methyl 6-hydroxyhexanoate from methyl tetrahydrofuran acetate, the process is as follows: Preparation of composite catalyst 15% Ni / 5% Mo / zirconium oxide + aluminum oxide: uniformly mix 0.15 mol / L nickel nitrate solution, 0.007 mol / L ammonium heptamolybdate solution, 0.2 mol / L zirconium nitrate solution and 0.6 mol / L aluminum nitrate solution, and stir for 1 h. Then slowly add ammonia water (commercial AR grade ammonia water) dropwise under the condition of constant temperature water bath at 60°C and stirring until the solution pH=8.0-9.0. After standing for 6 h, filter and wash with deionized water, dry naturally, and calcine at 500°C in air for 5 h to obtain the composite catalyst, wherein the nickel accounts for 15% of the mass of the catalyst, the molybdenum accounts for 5% of the mass of the catalyst, the zirconium oxide accounts for 20% of the mass of the catalyst, and the aluminum oxide accounts for 60% of the mass of the catalyst.

[0048] A certain amount of catalyst is loaded into a fixed bed, and the catalyst is reduced and activated at 350°C for 6 h in a mixed gas of hydrogen and nitrogen (volume ratio 1:5). A cyclohexane solution of methyl tetrahydrofuran acetate with a mass fraction of 75% is prepared; then the solution is connected to the fixed bed, and the above-mentioned solution and hydrogen gas (hydrogen to ester ratio 35:1) are introduced into the fixed bed at a space velocity of 0.2 h -1 , a reaction temperature of 120°C and a pressure of 4 MPa to start the reaction. The reaction liquid after the reaction is flowed into the fixed bed storage tank to obtain the methyl 6-hydroxyhexanoate reaction liquid.

[0049] According to the determination of the chemical content of the reaction liquid by the gas chromatograph, the conversion rate of methyl tetrahydrofuran acetate and the molar selectivity of the methyl 6-hydroxyhexanoate product are obtained according to the content of methyl 6-hydroxyhexanoate and the material balance.

[0050] The sample is tested, and the conversion rate of methyl tetrahydrofuran acetate is 98.8%, and the molar selectivity of the methyl 6-hydroxyhexanoate product is 97.3%.

[0051] The solvent is distilled at 40-55℃ under the pressure of -0.09 MPa by using a circulating water vacuum pump, and 6-hydroxyhexanoic acid methyl ester product is obtained.

[0052] Although the preferred embodiments of the present application have been shown and described, it is to be understood that the described embodiments are only part of the embodiments of the present application, and all other embodiments obtained by those skilled in the art based on the embodiments of the present application without creative labor are within the scope of protection of the present application.

Claims

1. A method for preparing methyl 6-hydroxyhexanoate using methyl tetrahydrofuranacetate, characterized in that, The process is as follows: (1) The catalyst is packed in a fixed bed, the catalyst is reduced and activated, and a cyclohexane solution of methyl tetrahydrofuran acetate with a mass fraction of 70-80% is prepared. (2) Subsequently, the solution from step (1) was connected to a fixed bed, and hydrogen gas was mixed with the solution at a space velocity of 0.15~0.25 h⁻¹. -1 The reaction mixture is introduced into a fixed bed at a reaction temperature of 110~130℃ and a pressure of 3~5 MPa to start the reaction. After the reaction is completed, the solvent is distilled off to obtain methyl 6-hydroxyhexanoate.

2. The method for preparing methyl 6-hydroxyhexanoate using methyl tetrahydrofuranacetate as described in claim 1, characterized in that, The catalyst is obtained through the following process: S1. Mix the metal salt solution and the carrier precursor solution thoroughly. S2. Under water bath heating and stirring conditions, add precipitant dropwise, stir for 1-3 hours, and then let stand for 6-9 hours to age. S3. After filtration, wash repeatedly with deionized water and then dry. S4. The obtained solid is calcined to obtain a catalyst; The metal salt is two or more of the following: platinum salt, palladium salt, rhodium salt, iridium salt, ruthenium salt, cobalt salt, copper salt, nickel salt, tungsten salt, and molybdenum salt. The mass percentage of the metal element in the metal salt in the catalyst is 5% to 40%. The support is at least one of the following: alumina, zirconium oxide, silicon dioxide, titanium oxide, cerium oxide, and magnesium oxide. The precipitant is one of the following: ammonia water, sodium hydroxide solution, potassium hydroxide solution, sodium carbonate solution, and potassium carbonate solution.

3. The method for preparing methyl 6-hydroxyhexanoate using methyl tetrahydrofuranacetate as described in claim 2, characterized in that, The water bath heating temperature in step S2 is 50~70℃; the concentrations of sodium hydroxide solution, potassium hydroxide solution, sodium carbonate solution and potassium carbonate solution are all 0.1 mol / L~1 mol / L.

4. The method for preparing methyl 6-hydroxyhexanoate using methyl tetrahydrofuranacetate as described in claim 2, characterized in that, After adding the precipitant in step S2, the pH of the reaction solution is adjusted to 6-10.

5. The method for preparing methyl 6-hydroxyhexanoate using methyl tetrahydrofuranacetate as described in claim 1, characterized in that, The roasting temperature in step S4 is 350~500℃, the roasting atmosphere is air, and the roasting time is 3~5 hours.

6. The method for preparing methyl 6-hydroxyhexanoate using methyl tetrahydrofuranacetate as described in claim 1, characterized in that, In step (1), the reduction activation catalyst refers to the reduction at 300~400℃ for 5~7 h in a mixed gas of hydrogen and nitrogen, with a volume ratio of hydrogen to nitrogen of 1:(4~6).

7. The method for preparing methyl 6-hydroxyhexanoate from methyl tetrahydrofuranacetate as described in claim 1, characterized in that, In step (2), the hydrogen-to-ester ratio is (30~40):

1.

8. The method for preparing methyl 6-hydroxyhexanoate using methyl tetrahydrofuranacetate as described in claim 2, characterized in that, The carrier precursor is at least one of aluminum salt, zirconium salt, silica precursor, titanium salt, cerium salt and magnesium salt, with the concentration of metal salt being 0.001 mol / L to 0.5 mol / L and the concentration of carrier precursor being 0.1 mol / L to 1 mol / L.

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