A preparation method for obtaining γ-valerolactone by solvent-free hydrogenation of levulinic acid

Abstract

The present invention discloses a preparation method for obtaining γ-valerolactone by solvent-free hydrogenation of levulinic acid. Using levulinic acid as a raw material, a heteropolyacid-modified composite metal oxide catalyst is added under solvent-free conditions, and γ-valerolactone is obtained through a heating and pressurization reaction. By adding the heteropolyacid-modified composite metal oxide catalyst, the present invention relies on the synergistic effect between non-precious metals and the introduction of heteropolyacid to obtain strong acid characteristics, and γ-valerolactone can be prepared under solvent-free conditions. Compared with traditional metal oxide catalysts, it has high activity and good stability, can significantly accelerate the hydrogenation reaction rate of levulinic acid under mild conditions, and improve the yield of γ-valerolactone.

Description

Technical Field

[0001] The present invention relates to a method for preparing γ-valerolactone, and more particularly to a method for preparing γ-valerolactone by solvent-free hydrogenation of levulinic acid. Background Art

[0002] Levulinic acid is an important biomass-based platform compound, which can be prepared by hydrolysis of biomass raw materials such as plant cellulose and agricultural waste under the action of an acidic catalyst. Levulinic acid can be hydrogenated to synthesize a series of high-value-added chemicals, such as γ-valerolactone, 1,5-pentanediol, and methyl-tetrahydrofuran. Among them, γ-valerolactone is considered to be the most promising biomass-based platform compound. At present, there are two main methods for preparing γ-valerolactone by hydrogenation of levulinic acid: direct hydrogenation and transfer hydrogenation using hydrogen donors such as isopropanol and formic acid. However, both of these methods require the use of solvents such as water, isopropanol, 1,4-dioxane, and tetrahydrofuran to participate in the reaction. Homogeneous or heterogeneous catalysts are usually used in the hydrogenation catalytic reaction of levulinic acid. The structure of homogeneous catalysts is complex, and it is difficult to separate the catalyst when the solvent is present; heterogeneous catalysts such as palladium-carbon and ruthenium-carbon or noble metal catalysts have high costs. Hengst et al. (Hengst K, Schubert M, Carvalho H W P, et al. Synthesis of γ-valerolactone by hydrogenation of levulinic acid over supported nickel catalysts[J]. Applied Catalysis A: General, 2015, 502: 18-26.) reported that Ni / γ-Al 2 O 3 catalyst was used to react for 6 h at 150 °C and 1.0 MPa H 2 pressure to prepare γ-valerolactone from levulinic acid using different solvents. The researchers found that the yield of γ-valerolactone in aqueous solution was only 2%, while in alcohol solvents, only isopropanol had a slightly higher yield, but it was only 34%. The reason was attributed to the fact that alcohol would react with levulinic acid to form levulinic acid esters, and the esterification and hydrogenation formed a competition, resulting in a decrease in its yield.

[0003] Therefore, in recent years, the hydrogenation of levulinic acid using non-noble metal catalysts has attracted much attention. Since the hydrogen activation performance of non-noble metals is lower than that of noble metals, a single non-noble metal catalyst cannot achieve good hydrogenation results. Therefore, dual (multi)-metal catalysts have been gradually applied to the hydrogenation reaction of biomass, and excellent effects comparable to noble metal catalysts can be achieved by relying on the synergistic effect between non-noble metals. However, when using non-noble metal catalysts for hydrogenation reactions, usually a very high reaction temperature is required. Mohan et al. (Mohan V, Venkateshwarlu V, Pramod CV, et al. Vapour phase hydrocyclisation of levulinic acid to γ-valerolactone over supported Ni catalysts[J]. Catal Sci Technol, 2014, 4, 1253-1259.) used the conventional wet impregnation method to prepare a Ni catalyst with a Ni content of 30% using alumina, silica, zinc oxide, zirconia, titanium dioxide, and magnesium oxide as supports. At 250 °C and 1.0 MPa H 2 pressure, γ-valerolactone was obtained after continuous reaction for 25 h. However, long-term continuous reaction and high reaction temperature may cause C-C bond breakage, and long-term high-temperature reaction will also cause the metal active components in the non-noble metal catalyst to agglomerate and form carbon on the catalyst surface, affecting the activity of the catalyst and thus reducing the selectivity of the product. Summary of the Invention

[0004] Object of the Invention: The object of the present invention is to provide a preparation method for obtaining γ-valerolactone by solvent-free hydrogenation of levulinic acid, which simplifies the product separation process and improves the reaction efficiency.

[0005] Technical Solution: A preparation method for obtaining γ-valerolactone by solvent-free hydrogenation of levulinic acid according to the present invention specifically comprises: using levulinic acid as a raw material, adding a catalyst under solvent-free conditions, and heating and pressurizing the reaction to obtain γ-valerolactone. The catalyst is a heteropolyacid-modified composite metal oxide catalyst.

[0006] Preferably, the heteropolyacid is one or more of phosphotungstic acid, silicotungstic acid, phosphomolybdic acid, or silicomolybdic acid.

[0007] Preferably, the addition amount of the catalyst is 0.5% to 5% of the mass of levulinic acid.

[0008] Preferably, the reaction temperature is 140 to 200 °C, the hydrogen pressure of the reaction is 1.0 to 5.0 MPa, and the reaction time is 1 to 10 h.

[0009] Preferably, the composite metal oxide is one or more of copper-nickel-aluminum composite oxide, copper-zinc-aluminum composite oxide, or copper-magnesium-aluminum composite oxide.

[0010] Preferably, the heteropolyacid-modified composite metal oxide catalyst is prepared by the following steps:

[0011] (1) Take one of nickel nitrate, zinc nitrate, or magnesium nitrate, and mix it with copper nitrate and aluminum nitrate in a molar ratio of 12:1 to 3:1 to 5, dissolve it in water and mix well to obtain solution A; dissolve sodium hydroxide in water and mix well to obtain solution B;

[0012] (2) Mix solutions A and B and drop them into a reaction vessel, adjust the pH value to form a coprecipitation mixture, age at 60 - 80 °C for 18 - 24 h, then filter, wash, dry, and calcine in sequence to obtain the composite metal oxide;

[0013] (3) Add the obtained composite metal oxide and heteropolyacid into water, stir until well mixed; let it stand at 80 - 110 °C for 6 - 12 h, then filter, wash, dry, and calcine in sequence to obtain the precursor of the heteropolyacid-modified composite metal oxide catalyst;

[0014] (4) Carry out a reduction reaction on the precursor of the heteropolyacid-modified composite metal oxide catalyst with hydrogen to obtain the heteropolyacid-modified composite metal oxide catalyst.

[0015] Preferably, in step (2), the pH value is 9 - 11, the drying temperature is 60 - 120 °C, and the drying time is 2 - 8 h. The calcination temperature is 400 - 600 °C, and the calcination time is 2 - 6 h.

[0016] Preferably, in step (3), the mass of the heteropolyacid added is 0% - 30% of the mass of the composite metal oxide.

[0017] Preferably, in step (3), the drying temperature is 60 - 120 °C, and the drying time is 2 - 8 h; the calcination temperature is 200 - 400 °C, and the calcination time is 2 - 6 h.

[0018] Preferably, in step (4), the temperature of the reduction reaction is 200 - 400 °C, and the time of the reduction reaction is 1 - 5 h.

[0019] Principle of the invention: The present invention conducts heteropolyacid modification on the composite metal oxide catalyst. The metal oxide catalyst has Lewis acid active sites, and the heteropolyacid, as a strong acid, modifies the metal oxide catalyst so that it can simultaneously have Lewis acid and acid active sites. The hydrogenation reaction of levulinic acid mainly relies on the acidic active sites (Lewis acid and It is carried out with an acid. When the acidity on the catalyst surface is insufficient, the intermediate product 4-hydroxyvaleric acid will be formed. Therefore, compared with the metal oxide catalyst with only Lewis acid active sites, the composite metal oxide catalyst modified by heteropolyacid can, to a certain extent, strongly promote the cyclization and dehydration of the intermediate product 4-hydroxyvaleric acid to form the target product γ-valerolactone, improve the product selectivity, and at the same time, relying on the synergistic effect between non-precious metals, can significantly accelerate the hydrogenation reaction rate of levulinic acid under mild conditions and improve the product yield. Applying the heteropolyacid-modified composite metal oxide catalyst to the solvent-free hydrogenation of levulinic acid to γ-valerolactone can efficiently obtain γ-valerolactone. Among them, the hydrogenation product γ-valerolactone of levulinic acid itself can also be regarded as an excellent solvent to promote the reaction, and the solvent-free system also simplifies the product separation process.

[0020] Beneficial effects: Compared with the prior art, the present invention has the following remarkable advantages: (1) The preparation method of the present invention can reduce production costs, simplify the product separation process, and improve the reaction efficiency, and has industrial application prospects; (2) The heteropolyacid-modified composite metal oxide catalyst prepared by the present invention relies on the synergistic effect between non-precious metals and the introduction of heteropolyacid to obtain strong acid characteristics. Compared with the traditional metal oxide catalyst, it can significantly increase the reaction rate of the solvent-free hydrogenation of levulinic acid to γ-valerolactone under mild reaction conditions, maintain high selectivity while increasing the yield of γ-valerolactone, with the highest selectivity reaching 99.6%, and the atomic utilization rate approaching 100%. Specific embodiments

[0021] The technical solution of the present invention will be further described below.

[0022] Example 1

[0023] A preparation method for obtaining γ-valerolactone by the solvent-free hydrogenation of levulinic acid specifically includes the following steps:

[0024] First, prepare a heteropolyacid-modified composite metal oxide catalyst:

[0025] (1) Mix 1.21 g of Cu(NO 3 ) 2 ·3H 2 O, 5.82 g of Ni(NO 3 ) 2 ·6H 2 O, 3.13 g of Al(NO 3 ) 3 ·9H 2 O and 50 ml of deionized water evenly, and stir well to obtain solution A; mix 3.20 g of NaOH and 50 ml of deionized water evenly, and stir well to obtain solution B;

[0026] (2) At a constant temperature of 65 °C, solutions A and B were simultaneously dropped into a four-necked flask, and the pH value of the solution was controlled to be about 11 to obtain a coprecipitation mixture. After the coprecipitation mixture was aged at a constant temperature of 65 °C for 24 h, it was filtered, washed with deionized water until neutral, then dried at 60 °C for 6 h and calcined at 500 °C for 6 h to obtain a CuNiAl composite metal oxide, denoted as CuNiAl-LDH;

[0027] (3) The CuNiAl composite metal oxide obtained in step (2) and 0.10 g of silicotungstic acid were added to deionized water and stirred until evenly mixed. It was left standing at 110 °C for 6 h, filtered, and washed. The washed material was dried at 60 °C for 4 h and calcined at 300 °C for 4 h. A heteropolyacid-modified composite metal oxide catalyst precursor with a silicotungstic acid loading of 5% was obtained, denoted as CuNiAl-5SiW;

[0028] (4) The precursor CuNiAl-5SiW was placed in a tubular furnace at 300 °C and reduced with hydrogen for 2 h to obtain a CuNiAl-5SiW catalyst;

[0029] Secondly, 2.50 g of levulinic acid and 0.05 g of the CuNiAl-5SiW catalyst were added to the autoclave; they were mixed evenly, the autoclave was sealed, and the air in the autoclave was replaced 3 times with N 2 and then the nitrogen in the autoclave was replaced 3 times with H 2 After that, 3 MPa of H 2 was charged, the reaction temperature was set at 180 °C, the stirring speed was 300 r / min, the reaction time was 2 h, and the hydrogenation reaction was carried out under solvent-free conditions;

[0030] Finally, after the reaction was completed, the temperature of the autoclave was quickly cooled to room temperature, the gas in the autoclave was vented, the reaction kettle was opened, and the liquid product was taken out after filtering the catalyst; the obtained liquid product was qualitatively analyzed by gas chromatography-mass spectrometry and quantitatively analyzed by gas chromatography.

[0031] According to the definitions of the conversion rate of levulinic acid, the yield of γ-valerolactone, and the product selectivity:

[0032] Conversion rate of levulinic acid = (amount of levulinic acid added before reaction - amount of levulinic acid remaining after reaction) / amount of levulinic acid added before reaction × 100%;

[0033] Yield of γ-valerolactone = amount of γ-valerolactone actually produced / amount of γ-valerolactone theoretically produced;

[0034] Product selectivity of γ-valerolactone = yield of γ-valerolactone / conversion rate of levulinic acid;

[0035] The conversion rate of levulinic acid in Example 1 was 96.9%, the yield of γ-valerolactone was 95.9%, and the selectivity of γ-valerolactone was 99.0%.

[0036] Example 2

[0037] Compared with Example 1, Example 2 changed the initial hydrogen pressure at the start of the hydrogenation reaction performance test:

[0038] The preparation method of the catalyst was the same as that in Example 1. CuNiAl-5SiW was placed in a tubular furnace at 300 °C and reduced with hydrogen for 2 h. Then, the hydrogenation reaction performance test of the catalyst was carried out in a micro high-pressure reactor. 2.50 g of levulinic acid and 0.05 g of CuNiAl-5SiW catalyst were added to a 0.1 L autoclave. After mixing evenly, the autoclave was sealed, and the air in the autoclave was replaced with N 2 three times, and then the nitrogen in the autoclave was replaced with H 2 three times. After that, 2 MPa of H 2 was charged, the reaction temperature was set at 180 °C, the stirring speed was 300 r / min, the reaction time was 2 h, and the hydrogenation reaction was carried out under solvent-free conditions.

[0039] After the reaction, the temperature of the autoclave was quickly cooled to room temperature, the gas in the autoclave was vented, the autoclave was opened, and the catalyst was filtered and the liquid product was taken out. The obtained liquid product was qualitatively analyzed by gas chromatography-mass spectrometry and quantitatively analyzed by gas chromatography. The conversion rate of levulinic acid was 77.9%, the yield of γ-valerolactone was 76.2%, and the selectivity of γ-valerolactone was 97.8%.

[0040] Within a certain range, the influence of the initial hydrogen pressure at the start of the reaction on the hydrogenation reaction of levulinic acid was positively correlated. The higher the initial hydrogen pressure, the higher the conversion rate of levulinic acid and the yield of γ-valerolactone would be.

[0041] Example 3

[0042] Compared with Example 2, Example 3 changed the ratio of levulinic acid to the heteropolyacid-modified composite metal oxide catalyst and the reaction time in the hydrogenation reaction performance test:

[0043] The preparation method of the catalyst was the same as that in Example 1. CuNiAl-5SiW was placed in a tubular furnace at 300 °C and reduced with hydrogen for 2 h. Then, the hydrogenation reaction performance test of the catalyst was carried out in a micro high-pressure reactor. 2.50 g of levulinic acid and 0.10 g of CuNiAl-5SiW catalyst were added to a 0.1 L autoclave. After mixing evenly, the autoclave was sealed, and the air in the autoclave was replaced with N 2 three times, and then the nitrogen in the autoclave was replaced with H 2 three times. After that, 2 MPa of H 2, the reaction temperature was set at 180 °C, the stirring speed was 300 r / min, the reaction time was 6 h, and the hydrogenation reaction was carried out under solvent-free conditions.

[0044] After the reaction was completed, the temperature of the autoclave was rapidly cooled to room temperature, the gas in the autoclave was vented, the reaction kettle was opened, and the liquid product was taken out after filtering the catalyst. The obtained liquid product was qualitatively analyzed by gas chromatography-mass spectrometry and quantitatively analyzed by gas chromatography. The conversion rate of levulinic acid was 87.2%, the yield of γ-valerolactone was 86.4%, and the selectivity of γ-valerolactone was 99.1%.

[0045] When the initial hydrogen pressure of the reaction was the same, increasing the ratio of the raw material levulinic acid to the catalyst and prolonging the reaction time would, to a certain extent, increase the conversion rate of levulinic acid and the yield of γ-valerolactone.

[0046] Example 4

[0047] Compared with Example 1, in Example 4, 0.10 g of silicotungstic acid added in Step 3 of the catalyst preparation method was changed to 0.20 g of silicotungstic acid. A heteropolyacid-modified composite metal oxide catalyst precursor was obtained, and the loading amount of silicotungstic acid was 10%, denoted as CuNiAl-10SiW.

[0048] Change the reaction temperature in the hydrogenation reaction performance test: Place CuNiAl-10SiW in a 300 °C tubular furnace, pass hydrogen for reduction for 2 h, and then carry out the hydrogenation reaction performance test of the catalyst in a micro-autoclave. Add 2.50 g of levulinic acid and 0.05 g of CuNiAl-10SiW catalyst to a 0.1 L autoclave. Mix well, seal the autoclave, and use N 2 to displace the air in the autoclave 3 times, and then use H 2 to displace the nitrogen in the autoclave 3 times, and then fill it with 3 MPa of H 2 , set the reaction temperature at 160 °C, the stirring speed at 300 r / min, the reaction time at 2 h, and carry out the hydrogenation reaction under solvent-free conditions.

[0049] After the reaction was completed, the temperature of the autoclave was rapidly cooled to room temperature, the gas in the autoclave was vented, the reaction kettle was opened, and the liquid product was taken out after filtering the catalyst. The obtained liquid product was qualitatively analyzed by gas chromatography-mass spectrometry and quantitatively analyzed by gas chromatography. The conversion rate of levulinic acid was 85.0%, the yield of γ-valerolactone was 84.6%, and the selectivity of γ-valerolactone was 99.5%.

[0050] Appropriately increasing the loading amount of silicotungstic acid but decreasing the reaction temperature, the reaction effect was lower than that of Example 1, indicating that only increasing the loading amount of a small amount of silicotungstic acid could not improve the hydrogenation reaction performance when the temperature was significantly reduced.

[0051] Example 5

[0052] Compared with Example 1, in Example 5, Ni(NO 3 ) 2 ·6H 2 O in Step 1 of the catalyst preparation method was replaced with Zn(NO 3 ) 2 ·6H 2 O, and in Step 3, adding 0.10 g of silicotungstic acid was changed to adding 0.60 g of phosphotungstic acid. A heteropolyacid-modified composite metal oxide catalyst precursor was obtained, and the loading amount of phosphotungstic acid was 30%, denoted as CuZnAl-30PW.

[0053] The ratio of levulinic acid to the heteropolyacid-modified composite metal oxide catalyst, reaction temperature, initial hydrogen pressure, and reaction time in the hydrogenation reaction performance test were changed: CuZnAl-30PW was placed in a 300 °C tubular furnace and reduced with hydrogen for 2 h, and then the hydrogenation reaction performance test of the catalyst was carried out in a micro high-pressure reactor. 4.00 g of levulinic acid and 0.02 g of the CuZnAl-30PW catalyst were added to a 0.1 L autoclave. After mixing evenly, the autoclave was sealed, and the air in the autoclave was replaced with N 2 three times, and then the nitrogen in the autoclave was replaced with H 2 three times, and then 4 MPa of H 2 was charged. The reaction temperature was set at 140 °C, the stirring speed was 300 r / min, and the reaction time was 10 h. The hydrogenation reaction was carried out under solvent-free conditions.

[0054] After the reaction was completed, the temperature of the autoclave was quickly cooled to room temperature, the gas in the autoclave was vented, the autoclave was opened, and the liquid product was taken out after filtering the catalyst. The obtained liquid product was qualitatively analyzed by gas chromatography-mass spectrometry and quantitatively analyzed by a gas chromatograph. The conversion rate of levulinic acid was 100%, the yield of γ-valerolactone was 99.6%, and the selectivity of γ-valerolactone was 99.6%.

[0055] The reaction temperature was lowered, the ratio of the raw material levulinic acid to the catalyst was lowered, but the hydrogen pressure and reaction time were increased. Example 5 investigated the hydrogenation performance of the catalyst under extreme reaction conditions. It shows that when the reaction time is extended to a certain time, the hydrogenation reaction of levulinic acid can be unaffected by low temperature and low-dose catalyst, and levulinic acid can also be completely converted, and the selectivity of γ-valerolactone can still be stabilized above 99%.

[0056] Example 6

[0057] Compared with Example 1, in Example 6, Ni(NO 3 ) 2 ·6H 2 O in Step 1 of the catalyst preparation method was replaced with Mg(NO 3 ) 2 ·6H2 O. Place the CuMgAl composite metal oxide obtained in Step 2 of the catalyst preparation method, namely CuMgAl-LDH, directly in a tubular furnace at 300 °C and introduce hydrogen for reduction for 2 h.

[0058] Change the reaction temperature in the hydrogenation reaction performance test: The reduced CuMgAl catalyst is used for the hydrogenation reaction performance test of the catalyst in a micro high-pressure reactor. Add 2.50 g of levulinic acid and 0.05 g of CuMgAl catalyst to a 0.1 L high-pressure reactor. Mix evenly, seal the reactor, and use N 2 to displace the air in the reactor 3 times, and then use H 2 to displace the nitrogen in the reactor 3 times, and then fill it with 3 MPa of H 2 . Set the reaction temperature to 200 °C, the stirring speed to 300 r / min, and the reaction time to 2 h, and carry out the hydrogenation reaction under solvent-free conditions.

[0059] After the reaction is completed, quickly cool the temperature of the high-pressure reactor to room temperature, vent the gas in the reactor, open the reactor, filter the catalyst, and take out the liquid product. The obtained liquid product is qualitatively analyzed by gas chromatography-mass spectrometry and quantitatively analyzed by gas chromatography. The conversion rate of levulinic acid is 73.5%, the yield of γ-valerolactone is 72.7%, and the selectivity of γ-valerolactone is 98.9%.

[0060] There will be certain differences in the hydrogenation effects of different metals. For the non-precious metal magnesium, the hydrogenation effect of metal nickel is better. Therefore, in Example 6, the reaction temperature was increased, but the hydrogenation effect was not as good as that in Example 1. And by comparing Example 6 with Comparative Example 4, it can also better illustrate that after only increasing the temperature, the hydrogenation effect of metal magnesium is not as good as that of metal nickel.

[0061] Comparative Example 1

[0062] The catalyst preparation method is the same as that in Example 1, except that the solvent-free condition in the reaction performance test is changed to using water as the solvent.

[0063] Place CuNiAl-5SiW in a tubular furnace at 300 °C and introduce hydrogen for reduction for 2 h. Then, carry out the hydrogenation reaction performance test of the catalyst in a micro high-pressure reactor. Add 2.50 g of levulinic acid, 10.00 g of water, and 0.05 g of CuNiAl-5SiW catalyst to a 0.1 L high-pressure reactor. Mix evenly, seal the reactor, and use N 2 to displace the air in the reactor 3 times, and then use H 2 to displace the nitrogen in the reactor 3 times, and then fill it with 3 MPa of H 2 . Set the reaction temperature to 180 °C, the stirring speed to 300 r / min, and the reaction time to 2 h, and carry out the hydrogenation reaction under aqueous phase conditions.

[0064] After the reaction was completed, the temperature of the autoclave was rapidly cooled to room temperature, the gas in the autoclave was vented, the autoclave was opened, and the catalyst was filtered before the liquid product was taken out. The obtained liquid product was qualitatively analyzed by gas chromatography-mass spectrometry and quantitatively analyzed by gas chromatography. The conversion rate of levulinic acid was 21.6%, the yield of γ-valerolactone was 21.6%, and the selectivity of γ-valerolactone was 100%.

[0065] When the water content in levulinic acid increased to a certain extent (the aqueous solution of levulinic acid was very dilute), a large amount of liquid phase water existed in the reaction system, which affected the thickness of the liquid film on the catalyst surface, blocked the hydrogenation reaction rate, and thus reduced the conversion rate of levulinic acid and the yield of γ-valerolactone.

[0066] Comparative Example 2

[0067] The preparation method of the catalyst was the same as that in Example 1, except that the solvent-free condition in the reaction performance test was changed to using 1,4-dioxane as the solvent.

[0068] CuNiAl-5SiW was placed in a tubular furnace at 300 °C and reduced with hydrogen for 2 h, and then the hydrogenation reaction performance of the catalyst was tested in a micro-autoclave. 2.50 g of levulinic acid, 10.00 g of 1,4-dioxane and 0.05 g of CuNiAl-5SiW catalyst were added to a 0.1 L autoclave. After mixing evenly, the autoclave was sealed, and the air in the autoclave was replaced with N 2 three times, and then the nitrogen in the autoclave was replaced with H 2 three times, and then H 2 with a pressure of 3 MPa was charged. The reaction temperature was set at 180 °C, the stirring speed was 300 r / min, and the reaction time was 2 h. The hydrogenation reaction was carried out under the condition of an organic phase.

[0069] After the reaction was completed, the temperature of the autoclave was rapidly cooled to room temperature, the gas in the autoclave was vented, the autoclave was opened, and the catalyst was filtered before the liquid product was taken out. The obtained liquid product was qualitatively analyzed by gas chromatography-mass spectrometry and quantitatively analyzed by gas chromatography. The conversion rate of levulinic acid was 64.3%, the yield of γ-valerolactone was 64.3%, and the selectivity of γ-valerolactone was 100%.

[0070] The influence of the initial hydrogen pressure on the hydrogenation reaction of levulinic acid was mainly reflected in the solubility of hydrogen in the solution. The more hydrogen the solution could dissolve, the more beneficial it was to the reaction. In the same solvent, the higher the hydrogen pressure, the higher the hydrogen concentration dissolved in the solution, and the better the reaction effect; at the same initial hydrogen pressure, the solubility of hydrogen in levulinic acid was higher than that in 1,4-dioxane. Therefore, compared with Example 1, the hydrogenation effect of Comparative Example 2 was worse.

[0071] Comparative Example 3

[0072] The preparation method of the catalyst is the same as that of Example 1, except that the solvent-free condition in the reaction performance test is changed to using isopropanol as the solvent.

[0073] Place CuNiAl-5SiW in a tubular furnace at 300 °C. After introducing hydrogen and reducing for 2 h, conduct the hydrogenation reaction performance test of the catalyst in a micro high-pressure reactor. Add 2.50 g of levulinic acid, 10.00 g of isopropanol, and 0.05 g of CuNiAl-5SiW catalyst into a 0.1 L autoclave. Mix evenly, seal the autoclave, and use N 2 to displace the air in the autoclave 3 times, and then use H 2 to displace the nitrogen in the autoclave 3 times. Then, charge 3 MPa of H 2 , set the reaction temperature to 180 °C, the stirring speed to 300 r / min, and the reaction time to 2 h, and conduct the hydrogenation reaction under the condition of the organic phase.

[0074] After the reaction is completed, quickly cool the temperature of the autoclave to room temperature, vent the gas in the autoclave, open the autoclave, filter the catalyst, and then take out the liquid product. The obtained liquid product is qualitatively analyzed by gas chromatography-mass spectrometry and quantitatively analyzed by gas chromatography. The conversion rate of levulinic acid is 100%, the yield of γ-valerolactone is 80.4%, and the selectivity of γ-valerolactone is 80.4%.

[0075] In the hydrogenation reaction of levulinic acid, if an alcohol substance is used as the solvent, levulinic acid will undergo an esterification reaction with the alcohol. The decrease in selectivity in Comparative Example 3 is caused by the formation of the by-product isopropyl levulinate.

[0076] Comparative Example 4

[0077] The preparation method of the catalyst is the same as that of Example 1, except that the CuNiAl composite metal oxide obtained in step 2, namely CuNiAl-LDH, is directly placed in a tubular furnace at 300 °C and reduced with hydrogen for 2 h.

[0078] The reduced CuNiAl catalyst is used to conduct the hydrogenation reaction performance test of the catalyst in a micro high-pressure reactor. Add 2.50 g of levulinic acid and 0.05 g of CuNiAl catalyst into a 0.1 L autoclave. Mix evenly, seal the autoclave, and use N 2 to displace the air in the autoclave 3 times, and then use H 2 to displace the nitrogen in the autoclave 3 times. Then, charge 3 MPa of H 2 , set the reaction temperature to 180 °C, the stirring speed to 300 r / min, and the reaction time to 2 h, and conduct the hydrogenation reaction under the solvent-free condition.

[0079] After the reaction was completed, the temperature of the autoclave was rapidly cooled to room temperature, the gas in the autoclave was vented, the reaction kettle was opened, and the liquid product was taken out after filtering the catalyst. The obtained liquid product was qualitatively analyzed by gas chromatography-mass spectrometry and quantitatively analyzed by gas chromatography. The conversion rate of levulinic acid was 80.1%, the yield of γ-valerolactone was 79.4%, and the selectivity of γ-valerolactone was 99.1%.

[0080] Table 1. Conversion rate, yield and selectivity of raw materials in the preparation method of γ-valerolactone of the present invention

[0081] Conversion rate of levulinic acid Yield of γ-valerolactone Selectivity of γ-valerolactone Example 1 96.9％ 95.9％ 99.0％ Example 2 77.9％ 76.2％ 97.8％ Example 3 87.2％ 86.4％ 99.1％ Example 4 85.0％ 84.6％ 99.5％ Example 5 100％ 99.6％ 99.6％ Example 6 73.5％ 72.7％ 98.9％ Comparative Example 1 21.6％ 21.6％ 100％ Comparative Example 2 64.3％ 64.3％ 100％ Comparative Example 3 100％ 80.4％ 80.4％ Comparative Example 4 80.1％ 79.4％ 99.1％

[0082] As shown in Table 1, the highest conversion rate of levulinic acid in Examples 1-6 can reach 100%, the highest yield of γ-valerolactone can reach 99.6%, the selectivity of the product can reach 99.6%, and the atom utilization rate is close to 100%; although the selectivity of the products in Comparative Examples 1 and 2 is high, the raw material conversion rate and product yield are much lower than those in Example 1; the yield and selectivity of Comparative Example 3 are inferior to those in Example 1; compared with Example 1, in Comparative Example 4, the nickel-containing metal catalyst was not modified. The reason why the conversion rate of levulinic acid and the yield of γ-valerolactone are relatively high is that the hydrogenation of the nickel-containing metal catalyst itself has a strong catalytic effect. Combined with better process conditions, higher conversion rate and yield will be obtained in the reaction. However, compared with the preparation method of the heteropolyacid-modified composite metal oxide catalyst used in Example 1, there is still a certain gap in the conversion rate of levulinic acid and the yield of γ-valerolactone.

Claims

1. A preparation method of γ-valerolactone obtained by solvent-free hydrogenation of levulinic acid, characterized in that, the preparation method comprises the following steps: (1) Mix 1.21 g of Cu(NO 3 ) 2 •3H 2 O, 5.82 g of Ni(NO 3 ) 2 •6H 2 O, 3.13 g of Al(NO 3 ) 3 •9H 2 O and 50 ml of deionized water evenly, and stir well to obtain solution A; mix 3.20 g of NaOH and 50 ml of deionized water evenly, and stir well to obtain solution B; (2) At a constant temperature of 65 °C, solutions A and B are simultaneously dropped into a four-necked flask, and the pH value of the solution is controlled to be about 11 to obtain a coprecipitation mixture; after the coprecipitation mixture is aged at 65 °C for 24 h, it is filtered, washed with deionized water until neutral, then dried at 60 °C for 6 h and calcined at 500 °C for 6 h to obtain a CuNiAl composite metal oxide, denoted as CuNiAl-LDH; (3) The CuNiAl composite metal oxide obtained in step 2 and 0.10 g of silicotungstic acid are added to deionized water and stirred until evenly mixed; left standing at 110 °C for 6 h, filtered and washed; the washed material is dried at 60 °C for 4 h and calcined at 300 °C for 4 h; a heteropolyacid-modified composite metal oxide catalyst precursor is obtained, and the loading amount of silicotungstic acid is 5%, denoted as CuNiAl-5SiW; (4) Place the precursor CuNiAl-5SiW in a tube furnace at 300 °C and introduce hydrogen for reduction for 2 h to obtain the CuNiAl-5SiW catalyst; add 2.50 g of levulinic acid and 0.05 g of the CuNiAl-5SiW catalyst into the autoclave; mix evenly, seal the autoclave, and use N 2 to displace the air in the autoclave three times, and then use H 2 to displace the nitrogen in the autoclave three times. After that, charge 3 MPa of H 2 , set the reaction temperature at 180 °C, the stirring speed at 300 r / min, and the reaction time at 2 h, and carry out the hydrogenation reaction under solvent-free conditions.

2. A preparation method of γ-valerolactone obtained by solvent-free hydrogenation of levulinic acid, characterized in that, the preparation method comprises the following steps: (1) Mix 1.21 g of Cu(NO 3 ) 2 •3H 2 O, 5.82 g of Zn(NO 3 ) 2 •6H 2 O, 3.13 g of Al(NO 3 ) 3 •9H 2 O and 50 ml of deionized water evenly, and stir well to obtain solution A; mix 3.20 g of NaOH and 50 ml of deionized water evenly, and stir well to obtain solution B; (2) At a constant temperature of 65 °C, solutions A and B are simultaneously dropped into a four-necked flask, and the pH value of the solution is controlled to be about 11 to obtain a coprecipitation mixture; after the coprecipitation mixture is aged at 65 °C for 24 h, it is filtered, washed with deionized water until neutral, then dried at 60 °C for 6 h and calcined at 500 °C for 6 h to obtain a CuZnAl composite metal oxide, denoted as CuZnAl-LDH; (3) The CuZnAl composite metal oxide obtained in step 2 and 0.60 g of phosphotungstic acid are added to deionized water and stirred until evenly mixed; left standing at 110 °C for 6 h, filtered and washed; the washed material is dried at 60 °C for 4 h and calcined at 300 °C for 4 h; a heteropolyacid-modified composite metal oxide catalyst precursor is obtained, and the loading amount of phosphotungstic acid is 30%, denoted as CuZnAl-30PW; (4) The precursor CuZnAl-30PW was placed in a tubular furnace at 300 °C and reduced with hydrogen for 2 h to obtain the CuZnAl-30PW catalyst; 4.00 g of levulinic acid and 0.02 g of the CuZnAl-30PW catalyst were added to a 0.1 L autoclave, mixed evenly, sealed, and the air in the autoclave was replaced with N 2 three times, and then the nitrogen in the autoclave was replaced with H 2 three times. After that, 4 MPa of H 2 was charged, the reaction temperature was set at 140 °C, the stirring speed was 300 r / min, and the reaction time was 10 h. The hydrogenation reaction was carried out under solvent-free conditions.

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