A Co / Al 2 O 3 Application of catalyst in preparing γ-valerolactone and preparation method of γ-valerolactone

Abstract

The present invention provides an application of a Co / Al2O3 catalyst in the preparation of γ-valerolactone and a preparation method of γ-valerolactone, belonging to the technical field of organic synthesis. The present invention provides an application of a Co / Al2O3 catalyst in the in-situ hydrogenation of levulinate to prepare γ-valerolactone. Using a low-concentration alcohol-water phase as an in-situ hydrogen source not only further reduces the reaction cost, but also for the first time realizes a higher yield of γ-valerolactone with the Co / Al2O3 catalyst. The Co / Al2O3 catalyst not only has good alcohol-water phase reforming hydrogen production activity, but also excellent levulinate hydrogenation activity, and can utilize the active hydrogen in-situ generated by alcohol reforming to achieve high-yield preparation of γ-valerolactone without the aid of an external hydrogen source.

Description

Technical Field

[0001] The present invention relates to the technical field of organic preparation, and particularly relates to the application of a Co / Al 2 O 3 catalyst in the preparation of γ-valerolactone and a preparation method of γ-valerolactone. Background Art

[0002] The development and utilization of green and renewable biomass resources are considered to be effective means to reduce the dependence on fossil fuels, mitigate climate change and reduce environmental pollution. High-value-added chemicals such as sugar alcohols, furans, organic acids and their derivatives can be prepared from biomass raw materials such as lignocellulose, and these chemicals can be further converted into a variety of liquid fuels. γ-Valerolactone is one of the most representative substances among these high-value-added chemicals. Due to the advantages of good stability, low toxicity and easy storage, γ-valerolactone is an ideal precursor for the synthesis of various fine chemicals. It can also be used as a liquid fuel, fuel additive, food additive and green organic solvent, and is widely used in the fields of petrochemical industry, medicine, food industry, etc. At present, the main raw material for the preparation of γ-valerolactone is levulinic acid, but it is still challenging to produce levulinic acid on a large scale and with high efficiency, and the corrosiveness of levulinic acid increases the production cost, so levulinic acid is not an ideal raw material for synthesis. The hydrogenation of levulinate can also prepare γ-valerolactone, which has the advantages of no acidity, easy separation and high-efficiency preparation from biomass derivatives. The research results show that levulinates with shorter alkyl chains are more likely to synthesize γ-valerolactone, and their activation ability ranking is: methyl levulinate > ethyl levulinate > butyl levulinate.

[0003] The safe storage and transportation of hydrogen are important factors restricting the large-scale application of the hydrogenation of levulinic acid and its esters to prepare γ-valerolactone. In addition, directly using hydrogen as a hydrogen source for the preparation of γ-valerolactone usually requires relatively high reaction pressures and temperatures, making the safety issues during the reaction equally non-negligible. To solve the above problems, developing a more suitable hydrogen source has become an important topic. Currently, some researchers have used various alcohols as hydrogen sources to achieve the preparation of γ-valerolactone through the catalytic transfer hydrogenation reaction of levulinate. Xing Tang et al. (Chemsuschem, 2015, 8, 1601 - 1607) used methanol as a hydrogen donor and achieved a conversion rate of 97.4% of methyl levulinate and a selectivity of 87.6% for γ-valerolactone under the condition of 240 °C; Xuejuan Cao et al. (Journal of Chemical Technology & Biotechnology, 2019, 94, 167 - 177; Xuejuan Cao et al., Chinese Journal of Catalysis, 2019, 40, 192 - 203) used Cu-Mg oxide and CuO x -CaCO 3 as catalysts and also achieved the hydrogenation of methyl levulinate in methanol solvent to prepare γ-valerolactone. The Cu-Mg oxide catalyst achieved a γ-valerolactone yield of 90.6% under the condition of 220 °C for 4 hours, and the CuO x -CaCO 3 catalyst achieved a γ-valerolactone yield of 95.6% under the conditions of 240 °C and a reaction time of 3 hours. Although these previous works have made significant progress, a large amount of organic solvents were used as hydrogen donors in the reaction, which will undoubtedly increase costs and cause environmental pollution, and there is still room for further improvement in the yield of γ-valerolactone. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide an application of a Co / Al 2 O 3 catalyst in the preparation of γ-valerolactone and a method for preparing γ-valerolactone. The present invention uses the active hydrogen generated by the aqueous-phase reforming of alcohol to in-situ hydrogenate levulinate to obtain γ-valerolactone with high yield.

[0005] To achieve the above invention purpose, the present invention provides the following technical solutions:

[0006] The present invention provides an application of a Co / Al 2 O 3The invention discloses an application of the catalyst in preparing gamma-valerolactone by in-situ hydrogenation of levulinic acid ester. The preparation is carried out in an alcohol-water phase environment. The alcohol in the alcohol-water phase environment includes methanol and / or ethanol.

[0007] The present invention also provides a method for preparing γ-valerolactone by in-situ hydrogenation of levulinic acid ester, comprising the following steps:

[0008] Levulinate, alcohol aqueous solution and Co / Al 2 O 3 The catalysts are mixed to carry out in-situ hydrogenation reaction to obtain the gamma-valerolactone, and the alcohol in the alcohol aqueous solution includes methanol and / or ethanol.

[0009] Preferably, the mass concentration of the alcohol aqueous solution is 5-30%.

[0010] Preferably, the Co / Al 2 O 3 The mass of the catalyst is 5 to 50% of the mass of the levulinic ester.

[0011] Preferably, the temperature of the in-situ hydrogenation reaction is 180-280° C., the initial pressure is 1-6 MPa, and the time is 0.5-8 h.

[0012] Preferably, the Co / Al 2 O 3 The catalyst comprises a metal Co element and an amorphous aluminum oxide coated on the surface of the metal Co element.

[0013] Preferably, the Co / Al 2 O 3 The specific surface area of ​​the catalyst is 50 to 120 m 2 / g, and the average pore size is 10-30nm.

[0014] Preferably, the Co / Al 2 O 3 The average particle size of the metal Co single substance in the catalyst is 15-40nm, and the mass content of the metal Co single substance is 40%-85%.

[0015] Preferably, the Co / Al 2 O 3 The catalyst is prepared by a process comprising the following steps:

[0016] mixing a soluble cobalt salt, a soluble aluminum salt and water to obtain a mixed solution;

[0017] Providing NaOH solution;

[0018] Provide Na 2 CO 3 Solution;

[0019] Add the mixture and the NaOH solution dropwise to the Na 2 CO 3 solution, and maintain the pH value at 10 ± 0.5 during the dropping process. After the dropping is completed, aging and drying are carried out in sequence to obtain a CoAl layered double hydroxide precursor;

[0020] Reduce the CoAl layered double hydroxide precursor in an H 2 -Ar mixed gas to obtain the Co / Al 2 O 3 catalyst.

[0021] Preferably, the molar ratio of cobalt to aluminum in the CoAl layered double hydroxide precursor is 1:2 to 10:1.

[0022] The present invention provides an application of a Co / Al 2 O 3 catalyst in the in-situ hydrogenation of levulinate to prepare γ-valerolactone. The preparation is carried out in an alcohol-water phase environment, and the alcohol in the alcohol-water phase environment includes methanol and / or ethanol.

[0023] The present invention couples the liquid-phase reforming of alcohol and water to produce hydrogen and the hydrogenation reaction of levulinate, realizing the in-situ high-efficiency preparation of γ-valerolactone in an environment without external hydrogen, avoiding the use of external hydrogen sources, significantly improving the safety and reliability of the reaction, and reducing the overall cost. The present invention uses an aqueous solution of alcohol as a hydrogen donor and a reaction medium, and the mass concentration of alcohol in the solution is low (5 - 30 wt%), and the alcohol used is methanol or ethanol, further reducing the cost. Moreover, the Co / Al 2 O 3 catalyst used in the present invention is cheap and easily available, and has good economy. The active center of the catalyst is metallic Co, which can not only efficiently catalyze the liquid-phase reforming of alcohol and water to produce hydrogen, but also simultaneously catalyze the hydrogenation cyclization of levulinate to obtain γ-valerolactone in high yield. Aluminum oxide is the site for adsorbing and activating levulinate.

[0024] The data of the examples show that the conversion rate of methyl levulinate can reach 97.4%, the yield of γ-valerolactone is 96.5%, and there is no over-hydrogenation product generated. At the same time, the catalyst has good reusability and a simple separation process from the reaction solution, and has great potential for industrial application.

[0025] The present invention also provides a preparation method of the Co / Al 2 O 3 catalyst described in the above technical solution. The prepared Co / Al 2 O 3 catalyst has high activity. Description of the Drawings

[0026] Figure 1 TEM images of the Co / Al 2 O 3 catalyst used in Example 1 at low magnification;

[0027] Figure 2 TEM images of the Co / Al 2 O 3 catalyst used in Example 1 at high magnification;

[0028] Figure 3 GC chromatogram of γ-valerolactone prepared in Example 1. Detailed implementation mode

[0029] The present invention provides an application of a Co / Al 2 O 3 catalyst in the in-situ hydrogenation of levulinate to prepare γ-valerolactone, wherein the preparation is carried out in an alcohol-water phase environment, and the alcohol in the alcohol-water phase environment includes methanol and / or ethanol.

[0030] In the present invention, the levulinate preferably includes one or more of methyl levulinate, ethyl levulinate, propyl levulinate, and butyl levulinate.

[0031] The present invention also provides a method for preparing γ-valerolactone by in-situ hydrogenation of levulinate, comprising the following steps:

[0032] Mixing levulinate, an aqueous alcohol solution, and a Co / Al 2 O 3 catalyst for in-situ hydrogenation reaction to obtain the γ-valerolactone, and the alcohol in the aqueous alcohol solution includes methanol and / or ethanol.

[0033] In the present invention, unless otherwise specified, the raw materials used are all commercially available products in the art.

[0034] In the present invention, the levulinate preferably includes one or more of methyl levulinate, ethyl levulinate, propyl levulinate, and butyl levulinate.

[0035] In the present invention, the mass concentration of the aqueous alcohol solution is preferably 5-30%, more preferably 8-26%, and most preferably 15%.

[0036] In the present invention, the mass of the Co / Al 2 O 3 catalyst is preferably 5-50% of the mass of levulinate, more preferably 15-20%.

[0037] In the present invention, the temperature of the in-situ hydrogenation reaction is preferably 180-280°C, more preferably 220-230°C, the initial pressure is preferably 1-6 MPa, more preferably 2-3 MPa, and the time is preferably 0.5-8 h, more preferably 2-4 h.

[0038] In the present invention, the Co / Al 2 O 3 The catalyst preferably includes a metal Co element and an amorphous aluminum oxide coated on the surface of the metal Co element.

[0039] In the present invention, the Co / Al 2 O 3 The specific surface area of ​​the catalyst is preferably 50 to 120 m 2 / g, and the average pore diameter is preferably 10 to 30 nm.

[0040] In the present invention, the Co / Al 2 O 3 The average particle size of the metal Co element in the catalyst is preferably 15 to 40 nm, and the mass content of the metal Co element is preferably 40% to 85%.

[0041] In the present invention, the Co / Al 2 O 3 The catalyst is preferably prepared by a process comprising the steps of:

[0042] mixing a soluble cobalt salt, a soluble aluminum salt and water to obtain a mixed solution;

[0043] Providing NaOH solution;

[0044] Provides Na 2 CO 3 Solution;

[0045] The mixed solution and NaOH solution are added dropwise to the Na 2 CO 3 In the solution, the pH value is maintained at 10±0.5 during the dropping process, and after the dropping is completed, aging and drying are performed in sequence to obtain a CoAl layered double hydroxide precursor;

[0046] The CoAl layered double hydroxide precursor is heated in H 2 -Ar mixed gas reduction to obtain the Co / Al 2 O 3 catalyst.

[0047] The invention mixes soluble cobalt salt, soluble aluminum salt and water to obtain a mixed solution.

[0048] In the present invention, the soluble cobalt salt is preferably cobalt chloride, cobalt nitrate, cobalt acetate or cobalt sulfate, and the soluble aluminum salt is preferably aluminum chloride, aluminum nitrate or aluminum sulfate.

[0049] The present invention provides a NaOH solution.

[0050] Preferably, in the present invention, NaOH is weighed and dissolved in water to prepare the NaOH solution.

[0051] In the present invention, the concentration of the NaOH solution is preferably 0.1 - 3 mol / L.

[0052] The present invention provides Na 2 CO 3 solution.

[0053] In the present invention, the 2 CO 3 in the solution and Al 3 2- in the mixed solution preferably have a molar ratio of 0.5 - 4. 3+ In the present invention, the molar ratio of CO

[0054] Preferably, in the present invention, Na 2 CO 3 is weighed and dissolved in water to form the Na 2 CO 3 solution.

[0055] After obtaining the mixed solution, the NaOH solution and the Na 2 CO 3 solution, in the present invention, the mixed solution and the NaOH solution are dropped into the Na 2 CO 3 solution, and the pH value is maintained at 10 ± 0.5 during the dropping process. After the dropping is completed, aging and drying are carried out in sequence to obtain a CoAl layered double hydroxide precursor.

[0056] In the present invention, the molar ratio of cobalt to aluminum in the CoAl layered double hydroxide precursor is preferably 1:2 - 10:1, more preferably 2:1 - 6:1.

[0057] In the present invention, the temperature of the aging is preferably 80 °C, and the time is preferably 18 h.

[0058] After the aging is completed, preferably, the present invention further includes washing the obtained solid with distilled water.

[0059] In the present invention, the temperature of the drying is preferably 80 °C, and the time is preferably 12 h.

[0060] After obtaining the CoAl layered double hydroxide precursor, in the present invention, the CoAl layered double hydroxide precursor is treated in H2 Reduce in an Ar mixed gas to obtain the Co / Al 2 O 3 catalyst.

[0061] In the present invention, the H 2 volume fraction of H in the -Ar mixed gas is preferably 10%. 2 In the present invention, the reduction temperature is preferably 400 - 1000 °C, more preferably 500 - 800 °C, most preferably 700 °C, and the time is preferably 2 - 8 h, more preferably 3 - 5 h.

[0062] After the reduction is completed, the present invention preferably further includes natural cooling to room temperature.

[0063] To further illustrate the present invention, the application of the Co / Al

[0064] catalyst provided by the present invention in the preparation of γ-valerolactone and the preparation method of γ-valerolactone will be described in detail below, but they should not be construed as limiting the protection scope of the present invention. 2 O 3 catalyst in the preparation of γ-valerolactone and the preparation method of γ-valerolactone will be described in detail below, but they should not be construed as limiting the protection scope of the present invention.

[0065] Example 1

[0066] Dissolve 12.125 g of cobalt nitrate and 3.125 g of aluminum nitrate in 100 mL of distilled water to prepare solution A; weigh 0.25 mol of sodium hydroxide and dissolve it in 250 mL of distilled water to prepare solution B; then dissolve 1.767 g of sodium carbonate in 200 mL of distilled water to prepare solution C. Dropwise add solution A and B into solution C, and keep the solution pH = 10 ± 0.5 during the dropping process. After the dropping is completed, age the obtained precipitate for 18 hours, then wash it several times with distilled water, and after centrifugation, dry the obtained sample in an oven at 80 °C overnight to obtain the CoAl layered double hydroxide precursor. Calcinate and reduce the above precursor in a 10 vol% H 2 / Ar mixed gas at 700 °C for 3 h to obtain the Co / Al 2 O 3 catalyst (TEM images at different magnification factors are as Figures 1-2 shown).

[0067] Introduce 0.3 g of methyl levulinate, 15 g of methanol aqueous solution (methanol mass concentration 15%) and 0.05 g of the above Co / Al with a molar ratio of 5 and a reduction temperature of 700 °C into a 30 mL high-pressure reactor, and charge 2 MPa of N 2 O 3 catalyst, and charge 2 MPa of N 2, then heat up to 220 °C, hold for 2 h, cool down to room temperature, separate the catalyst from the reaction solution with a magnet, and quantitatively analyze the products using a gas chromatograph and a liquid chromatograph (as Figure 2 shown). The test results show that the conversion rate of methyl levulinate is 93.3%, and the yield of γ-valerolactone is 90.9%. The catalyst is relatively stable. After 4 cycles of stability tests, the conversion rate of methyl levulinate is 92.4%, and the yield of γ-valerolactone is 87.8%, indicating that the catalyst can be reused repeatedly.

[0068] Example 2

[0069] Introduce 0.3 g of methyl levulinate, 15 g of an ethanol aqueous solution (ethanol mass concentration 15%) and 0.05 g of the Co / Al 2 O 3 catalyst in Example 1 into a 30 mL high-pressure reactor, and flush in 2 MPa of N 2 , then heat up to 220 °C, hold for 2 h, cool down to room temperature, separate the catalyst from the reaction solution with a magnet, and quantitatively analyze the products using a gas chromatograph and a liquid chromatograph. The conversion rate of methyl levulinate is 97.2%, and the yield of γ-valerolactone is 88.4%.

[0070] Example 3

[0071] Introduce 0.3 g of methyl levulinate, 15 g of a methanol aqueous solution (methanol mass concentration 26%) and 0.05 g of the Co / Al 2 O 3 catalyst in Example 1 into a 30 mL high-pressure reactor, and flush in 2 MPa of N 2 , then heat up to 220 °C, hold for 2 h, cool down to room temperature, separate the catalyst from the reaction solution with a magnet, and quantitatively analyze the products using a gas chromatograph and a liquid chromatograph. The conversion rate of methyl levulinate is 86.2%, and the yield of γ-valerolactone is 80.2%.

[0072] Example 4

[0073] Introduce 0.3 g of methyl levulinate, 15 g of a methanol aqueous solution (methanol mass concentration 8%) and 0.05 g of the Co / Al 2 O 3 catalyst in Example 1 into a 30 mL high-pressure reactor, and flush in 2 MPa of N 2 , then heat up to 220 °C, hold for 2 h, cool down to room temperature, separate the catalyst from the reaction solution with a magnet, and quantitatively analyze the products using a gas chromatograph and a liquid chromatograph. The conversion rate of methyl levulinate is 97.4%, and the yield of γ-valerolactone is 96.5%.

[0074] Example 5

[0075] Into a 30 mL autoclave, 0.3 g of methyl levulinate, 15 g of methanol aqueous solution (methanol concentration 26%) and 0.05 g of the Co / Al prepared in Example 1 were introduced. 2 O 3 Catalyst, and flushed with 2MPaN 2 Then the temperature was raised to 220°C, maintained for 4 hours, cooled to room temperature, the catalyst was separated from the reaction liquid by a magnet, and the product was quantitatively analyzed in a gas chromatograph and a liquid chromatograph. The conversion rate of methyl levulinate was 93.3%, and the yield of γ-valerolactone was 90%.

[0076] Example 6

[0077] Into a 30 mL autoclave, 0.335 g of ethyl levulinate, 15 g of methanol aqueous solution (methanol concentration 15%) and 0.05 g of the Co / Al prepared in Example 1 were introduced. 2 O 3 Catalyst, and flushed with 2MPaN 2 Then the temperature was raised to 220°C, maintained for 2 hours, cooled to room temperature, the catalyst was separated from the reaction liquid by a magnet, and the product was quantitatively analyzed in a gas chromatograph and a liquid chromatograph. The conversion rate of ethyl levulinate was 93.6%, and the yield of γ-valerolactone was 76.1%.

[0078] Example 7

[0079] Into a 30 mL autoclave, 0.335 g of ethyl levulinate, 15 g of ethanol aqueous solution (ethanol concentration 15%) and 0.05 g of the Co / Al prepared in Example 1 were introduced. 2 O 3 Catalyst, and flushed with 2MPaN 2 Then the temperature was raised to 220°C, maintained for 2 hours, cooled to room temperature, the catalyst was separated from the reaction liquid by a magnet, and the product was quantitatively analyzed in a gas chromatograph and a liquid chromatograph. The conversion rate of ethyl levulinate was 92.2%, and the yield of γ-valerolactone was 72.9%.

[0080] Example 8

[0081] Dissolve 11.64 g of cobalt nitrate and 3.75 g of aluminum nitrate in 100 mL of distilled water to prepare solution A; weigh 0.25 mol of sodium hydroxide and dissolve it in 250 mL of distilled water to prepare solution B; then dissolve 2.12 g of sodium carbonate in 200 mL of distilled water to prepare solution C. Dropwise add solutions A and B into solution C, and maintain the solution pH = 10 ± 0.5 during the dropping process. After dropping, age the obtained precipitate for 18 hours, then wash it several times with distilled water, and after centrifugation, dry the obtained sample in an oven at 80 °C overnight to obtain the CoAl layered double hydroxide precursor. Calcinate and reduce the above precursor in a 10 vol% H 2 / Ar mixed gas at 700 °C for 3 h to obtain the Co / Al 2 O 3 catalyst of this example.

[0082] Introduce 0.3 g of methyl levulinate, 15 g of methanol aqueous solution (methanol mass concentration 15%) and 0.05 g of Co / Al with a Co / Al molar ratio of 4 and a reduction temperature of 700 °C into a 30 mL high-pressure reactor 2 O 3 catalyst, and charge 2 MPa of N 2 , then raise the temperature to 220 °C, hold for 2 h, cool to room temperature, separate the catalyst from the reaction solution with a magnet, and conduct quantitative analysis of the products in a gas chromatograph and a liquid chromatograph. The conversion rate of methyl levulinate is 94.2%, and the yield of γ-valerolactone is 88.1%. This catalyst is very stable. After 4 cycles of stability tests, the conversion rate of methyl levulinate is 93%, and the yield of γ-valerolactone is 92.2%, indicating that the catalyst can be used repeatedly for many times.

[0083] Example 9

[0084] Introduce 0.3 g of methyl levulinate, 15 g of ethanol aqueous solution (ethanol mass concentration 15%) and 0.05 g of Co / Al 2 O 3 catalyst in Example 8 into a 30 mL high-pressure reactor, and charge 2 MPa of N 2 , then raise the temperature to 220 °C, hold for 2 h, cool to room temperature, separate the catalyst from the reaction solution with a magnet, and conduct quantitative analysis of the products in a gas chromatograph and a liquid chromatograph. The conversion rate of methyl levulinate is 95.2%, and the yield of γ-valerolactone is 88.7%.

[0085] Example 10

[0086] Introduce 0.3 g of methyl levulinate, 15 g of ethanol aqueous solution (ethanol mass concentration 26%) and 0.05 g of Co / Al 2 O3 a catalyst, and introduce 2 MPa of N 2 , then raise the temperature to 220 °C, hold for 2 h, cool to room temperature, separate the catalyst from the reaction solution with a magnet, and conduct quantitative analysis of the products in a gas chromatograph and a liquid chromatograph. The conversion rate of methyl levulinate is 88.9%, and the yield of γ-valerolactone is 82.4%.

[0087] Example 11

[0088] Introduce 0.3 g of methyl levulinate, 15 g of an aqueous methanol solution (methanol mass concentration 26%) and 0.05 g of the Co / Al in Example 8 into a 30 mL high-pressure reactor 2 O 3 a catalyst, and introduce 2 MPa of N 2 , then raise the temperature to 220 °C, hold for 2 h, cool to room temperature, separate the catalyst from the reaction solution with a magnet, and conduct quantitative analysis of the products in a gas chromatograph and a liquid chromatograph. The conversion rate of methyl levulinate is 85.4%, and the yield of γ-valerolactone is 79.4%.

[0089] Example 12

[0090] Introduce 0.3 g of methyl levulinate, 15 g of an aqueous methanol solution (methanol mass concentration 26%) and 0.15 g of the Co / Al in Example 8 into a 30 mL high-pressure reactor 2 O 3 a catalyst, and introduce 2 MPa of N 2 , then raise the temperature to 220 °C, hold for 2 h, cool to room temperature, separate the catalyst from the reaction solution with a magnet, and conduct quantitative analysis of the products in a gas chromatograph and a liquid chromatograph. The conversion rate of methyl levulinate is 97.7%, and the yield of γ-valerolactone is 95%.

[0091] Example 13

[0092] Introduce 0.3 g of methyl levulinate, 15 g of an aqueous methanol solution (methanol mass concentration 15%) and 0.05 g of the Co / Al in Example 8 into a 30 mL high-pressure reactor 2 O 3 a catalyst, and introduce 2 MPa of N 2 , then raise the temperature to 230 °C, hold for 2 h, cool to room temperature, separate the catalyst from the reaction solution with a magnet, and conduct quantitative analysis of the products in a gas chromatograph and a liquid chromatograph. The conversion rate of methyl levulinate is 97.2%, and the yield of γ-valerolactone is 86.1%.

[0093] Example 14

[0094] Introduce 0.3 g of methyl levulinate, 15 g of aqueous methanol solution (methanol mass concentration 26%) and 0.05 g of Co / Al in Example 8 into a 30 mL high-pressure reactor 2 O 3 catalyst, and charge 2 MPa of N 2 , then heat up to 220 °C, hold for 4 h, cool down to room temperature, separate the catalyst from the reaction solution with a magnet, and conduct quantitative analysis of the products in a gas chromatograph and a liquid chromatograph. The conversion rate of methyl levulinate is 95.3%, and the yield of γ-valerolactone is 90.6%.

[0095] Example 15

[0096] Introduce 0.3 g of methyl levulinate, 15 g of aqueous methanol solution (methanol mass concentration 26%) and 0.05 g of CoAl catalyst in Example 8 into a 30 mL high-pressure reactor, and charge 3 MPa of N 2 , then heat up to 220 °C, hold for 4 h, cool down to room temperature, separate the catalyst from the reaction solution with a magnet, and conduct quantitative analysis of the products in a gas chromatograph and a liquid chromatograph. The conversion rate of methyl levulinate is 94%, and the yield of γ-valerolactone is 92.8%.

[0097] Example 16

[0098] Set the reduction temperature of the precursor in Example 8 to 800 °C to obtain the Co / Al 2 O 3 catalyst in this example. Introduce 0.3 g of methyl levulinate, 15 g of aqueous methanol solution (methanol mass concentration 26%) and 0.05 g of Co / Al 2 O 3 catalyst in this example, and charge 2 MPa of N 2 , then heat up to 220 °C, hold for 2 h, cool down to room temperature, separate the catalyst from the reaction solution with a magnet, and conduct quantitative analysis of the products in a gas chromatograph and a liquid chromatograph. The conversion rate of methyl levulinate is 82.5%, and the yield of γ-valerolactone is 81.6%.

[0099] Example 17

[0100] Dissolve 12.47g of cobalt nitrate and 2.67g of aluminum nitrate in 100mL of distilled water to prepare solution A; weigh 0.25mol of sodium hydroxide and dissolve it in 250mL of distilled water to prepare solution B; then dissolve 1.51g of sodium carbonate in 200mL of distilled water to prepare solution C. Add solutions A and B dropwise to solution C, and keep the solution pH = 10±0.5 during the addition process. After the addition is completed, the resulting precipitate is aged for 18 hours, then washed with distilled water several times, and after centrifugation, the resulting sample is dried in an oven at 80°C overnight to obtain a CoAl layered double hydroxide precursor. The above precursor is heated at 700°C with 10vol% H 2 / Ar mixed gas for 3h to obtain the Co / Al 2 O 3 catalyst.

[0101] Into a 30 mL autoclave, 0.3 g of methyl levulinate, 15 g of methanol aqueous solution (methanol mass concentration 26%) and 0.05 g of Co / Al with a Co / Al molar ratio of 6 and a reduction temperature of 700 °C were introduced. 2 O 3 Catalyst, and flushed with 2MPaN 2 Then the temperature was raised to 220°C, maintained for 4 hours, cooled to room temperature, the catalyst was separated from the reaction liquid by a magnet, and the product was analyzed by gas chromatograph and liquid chromatograph. The conversion rate of methyl levulinate was 90.8%, and the yield of γ-valerolactone was 83.5%.

[0102] Embodiment 18

[0103] Dissolve 10.91g of cobalt nitrate and 4.69g of aluminum nitrate in 100mL of distilled water to prepare solution A; weigh 0.25mol of sodium hydroxide and dissolve it in 250mL of distilled water to prepare solution B; then dissolve 2.65g of sodium carbonate in 200mL of distilled water to prepare solution C. Add solutions A and B dropwise to solution C, and keep the solution pH = 10±0.5 during the addition process. After the addition is completed, the resulting precipitate is aged for 18 hours, then washed several times with distilled water, and after centrifugation, the resulting sample is dried in an oven at 80°C overnight to obtain a CoAl layered double hydroxide precursor. The above precursor is heated at 700°C with 10vol% H 2 / Ar mixed gas for 3h to obtain the Co / Al 2 O 3 catalyst.

[0104] Into a 30 mL autoclave, 0.3 g of methyl levulinate, 15 g of methanol aqueous solution (methanol mass concentration 26%) and 0.05 g of Co / Al with a Co / Al molar ratio of 3 and a reduction temperature of 700 °C were introduced. 2O 3 The catalyst was added, and 2 MPa of N 2 was introduced. Then the temperature was raised to 220 °C and maintained for 4 h. After cooling to room temperature, the catalyst was separated from the reaction solution using a magnet, and the products were analyzed using a gas chromatograph analyzer and a liquid chromatograph analyzer. The conversion rate of methyl levulinate was 92.1%, and the yield of γ-valerolactone was 81.7%.

[0105] Comparative Example 1

[0106] 2.47 g of cobalt nitrate was dissolved in 1 g of water, and 500 mg of commercially available γ-Al 2 O 3 (Aladdin reagent) was added. The mixture was stirred vigorously at 60 °C until the solution was completely evaporated, and then maintained at 60 °C in a vacuum oven for 10 h. The obtained sample was first dried at 120 °C for 10 h in a muffle furnace, and then calcined at 400 °C for 5 h. The catalyst obtained by the above impregnation method was reduced with a 10 vol% H 2 / Ar mixed gas at 700 °C for 3 h to obtain a supported Co / Al 2 O 3 catalyst with a cobalt content similar to that of the catalyst in Example 11.

[0107] In a high-pressure reactor, 0.3 g of methyl levulinate, 15 g of an aqueous methanol solution (methanol mass concentration 26%), and 0.05 g of the above Co / Al 2 O 3 catalyst were introduced, and 2 MPa of N 2 was introduced. Then the temperature was raised to 220 °C and maintained for 2 h. After cooling to room temperature, the catalyst was separated from the reaction solution by centrifugation, and the products were analyzed using a gas chromatograph analyzer and a liquid chromatograph analyzer. The conversion rate of methyl levulinate was 79.7%, the yield of γ-valerolactone was 29.1%, and the selectivity was only 36.5%.

[0108] As can be seen from Example 11 and Comparative Example 1, compared with the supported Co / Al 2 O 3 catalyst, the Co / Al 2 O 3 catalyst derived from CoAl layered double hydroxide has more excellent reaction performance, and the conversion rate of in-situ hydrogenation of methyl levulinate and the yield of γ-valerolactone are significantly improved, achieving the goal of highly selectively preparing γ-valerolactone without the aid of an external hydrogen source.

[0109] Comparative Example 2

[0110] In a high-pressure reactor, 0.3 g of methyl levulinate, 15 g of pure methanol, and 0.05 g of the Co / Al 2 O 3 catalyst in Example 1 were introduced, and 2 MPa of N2 , then the temperature was raised to 220 °C and maintained for 2 h, and then cooled to room temperature. The catalyst was separated from the reaction solution by centrifugation, and the products were analyzed by gas chromatography analyzer and liquid chromatography analyzer. The conversion rate of methyl levulinate was 28.2%, and the yield of γ-valerolactone was only 0.5%.

[0111] It can be seen from Example 1 and Comparative Example 2 that when pure methanol was used as the solvent, the efficiency of in-situ hydrogenation of methyl levulinate was very low, indicating that water is an indispensable reaction solvent. In the Co / Al 2 O 3 Under the action of the catalyst, methanol and water undergo a reforming reaction to generate in-situ hydrogen, which then reacts with methyl levulinate to finally produce γ-valerolactone.

[0112] The above are only the preferred embodiments of the present invention and do not impose any formal limitations on the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing γ-valerolactone by in-situ hydrogenation of levulinate, characterized in that, it comprises the following steps: Mix levulinate, an aqueous alcohol solution and a Co / Al 2 O 3 catalyst to carry out an in-situ hydrogenation reaction to obtain the γ-valerolactone, wherein the alcohol in the aqueous alcohol solution is selected from methanol and / or ethanol, and the mass concentration of the aqueous alcohol solution is 5-30%; The Co / Al 2 O 3 catalyst is prepared by a method comprising the following steps: Mix a soluble cobalt salt, a soluble aluminum salt and water to obtain a mixed solution; Provide an NaOH solution; Provide Na 2 CO 3 solution; Add the mixture solution and the NaOH solution dropwise to the Na 2 CO 3 solution. During the dropping process, maintain the pH value at 10 ± 0.

5. After the dropping is complete, carry out aging and drying in sequence to obtain a CoAl layered double hydroxide precursor; Reduce the CoAl layered double hydroxide precursor in an H 2 -Ar mixed gas to obtain the Co / Al 2 O 3 catalyst; The Co / Al 2 O 3 The mass content of metallic Co in the catalyst is 40% to 85%.

2. The method according to claim 1, characterized in that, The Co / Al 2 O 3 mass of the catalyst is 5-50% of the mass of the levulinate ester.

3. The method according to claim 1, characterized in that, the temperature of the in-situ hydrogenation reaction is 180-280 °C, the initial pressure is 1-6 MPa, and the time is 0.5-8 h.

4. The method according to claim 1, characterized in that, The Co / Al 2 O 3 catalyst includes metallic Co element and amorphous aluminum oxide coated on the surface of the metallic Co element.

5. The method according to claim 1 or 4, characterized in that, The Co / Al 2 O 3 catalyst has a specific surface area of 50 to 120 m 2 / g and an average pore diameter of 10 to 30 nm.

6. The method according to claim 1 or 4, characterized in that, The Co / Al 2 O 3 The average particle size of metallic Co in the catalyst is 15 to 40 nm.

7. The method according to claim 1, characterized in that, the molar ratio of cobalt to aluminum in the CoAl layered double hydroxide precursor is 1:2 to 10:1.

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