Cerium-based catalyst for preparing DL menthol as well as preparation method and application of cerium-based catalyst

Abstract

The invention belongs to the technical field of DL menthol preparation, and particularly relates to a cerium-based catalyst for preparing DL menthol and a preparation method and application of the cerium-based catalyst, the cerium-based catalyst is a cerium oxide catalyst or a cerium oxide catalyst doped with other metal oxides, and metal elements contained in the other metal oxides comprise one or two of Sm, Y, Pr, Nb and La; the preparation method comprises the following steps: preparing a cerium oxide catalyst through a precipitation method or preparing a cerium oxide catalyst doped with other metal oxides through a coprecipitation method; the catalyst is used for catalyzing a thymol hydrogenation reaction to prepare DL menthol. Compared with the prior art, the prepared cerium-based catalyst is used for catalyzing thymol hydrogenation, the conversion rate of thymol can reach 99%, the selectivity of generated DL menthol can reach 57.37%, the preparation steps are simple, and the prepared catalyst is high in activity and good in stability in the use process.

Description

Technical Field

[0001] The invention belongs to the technical field of DL menthol preparation, and particularly relates to a cerium-based catalyst for preparing DL menthol, and a preparation method and application thereof. Background Art

[0002] DL menthol is mainly used to synthesize L menthol, which is mainly used in the fields of medicine, food additives and spices. Due to the rapid growth of the global economy, the demand for menthol is also increasing. At present, the annual global consumption is about 40,000 tons, which occupies an important position in the spice industry. Natural menthol is extracted from plants, and the output is greatly affected by the season, planting area, etc., resulting in a very large price fluctuation. The output of naturally extracted menthol can no longer meet the growing industrial needs. Synthetic menthol has a stable output and a relatively cheap price, so chemically synthesized menthol is becoming more and more important.

[0003] The main method for chemically synthesizing menthol is the racemic menthol splitting synthesis method. Although the method for synthesizing racemic menthol is relatively simple, it will produce an equal amount of D-menthol as L-menthol. Now it is usually adopted to convert D-menthol into racemic menthol first, and then continue to split to obtain L-menthol, and repeat this process until all of it is converted into L-menthol. Among them, the most common way to synthesize racemic menthol is by hydrogenation of thymol, but from the current technical means, it is impossible to control the reaction to only produce racemic menthol, and a large part of it produces three other pairs of isomers. Thymol is hydrogenated to obtain eight menthol isomers, including DL neo-menthol (bp: 211.7℃), DL neo-iso-menthol (bp: 214.6℃), DL menthol (bp: 216.5℃) and DL iso-menthol (bp: 218.6℃), and their structural formulas are as follows:

[0004]

[0005] There are several reports on the hydrogenation of thymol to synthesize DL-menthol and three other isomers:

[0006] DE2314813A1 describes the hydrogenation of thymol at 170-220°C and 20 MPa using a Co / Mn catalyst fixed bed. The examples of the patent are carried out at 160-210°C and a pressure of more than 20 MPa, and a mixture of 8 menthol isomers is produced, wherein the DL menthol content is 56.5-59% and the content of other isomers is 10.6-10.8%. There are 4-5% light components in the mixture, and these light components are by-products that cannot be recycled.

[0007] Patent WO2016 / 184328A1 uses a metal composite catalyst with an elemental composition of 70-85% nickel, 8-10% aluminum, 5-10% vanadium, and 2-10% cobalt. The reaction is carried out at 180°C and 6MPa pressure for 7 to 11.5 hours. The content of DL menthol in the product is 50.2 to 64.5%, the content of other isomers is 10.6 to 10.8%, and there is 0.2 to 6.1% of light components. The preparation process of this catalyst is complicated, and the content of light components and isomers obtained by catalysis is high.

[0008] Patent CN111871428A describes a composite metal catalyst of rhodium, nickel and zinc. However, the catalyst has high cost and a complicated preparation process. The reaction conditions are 80-100°C and 4.0-5.0MPa. The conversion rate of thymol is 99.9%, the selectivity of DL menthol is 65-70%, the selectivity of DL isomenthol is 6-8%, and less than 1% of impurities are produced.

[0009] In the method of synthesizing menthol by hydrogenation of thymol, increasing the content of DL-menthol is a key factor in obtaining L-menthol in high yield. However, the catalysts currently used for the hydrogenation of thymol generally use precious metals, and the reaction product still has problems such as excessively high impurity content. Summary of the invention

[0010] The purpose of the present invention is to provide a cerium-based catalyst for preparing DL-menthol and a preparation method and application thereof in order to solve at least one of the above problems, so as to solve the problem of high cost of preparing thymol hydrogenation reaction catalyst in the prior art, realize the preparation of DL-menthol by thymol hydrogenation reaction catalyzed by cerium-based catalyst, and improve the conversion rate of thymol and the selectivity of DL-menthol of cerium-based catalyst.

[0011] The catalyst of the present invention uses transition metals instead of precious metals to reduce the preparation cost, and can greatly reduce the content of impurities in the reaction product while ensuring high activity. In addition, the catalyst has excellent stability and can still maintain high activity after multiple cycles of use.

[0012] The purpose of the present invention is achieved through the following technical solutions:

[0013] One of the technical solutions of the present invention is to provide a cerium-based catalyst for preparing DL menthol, wherein the cerium-based catalyst is a cerium oxide catalyst or a cerium oxide catalyst doped with other metal oxides, and the metal elements contained in the other metal oxides include any one of Sm, Y, Pr, Nb and La.

[0014] Furthermore, the doping amount of the metal oxide in the cerium-based catalyst is 5 to 50%.

[0015] Furthermore, the specific surface area of ​​the cerium-based catalyst is 50 to 150 m 2 / g, pore volume is 0.2~1.0cm 3 / g, and the average pore size is 5 to 20 nm.

[0016] The second technical solution of the present invention is to provide a method for preparing the cerium-based catalyst for preparing DL menthol as described above, the preparation method comprising preparing the cerium oxide catalyst by precipitation method or preparing the cerium oxide catalyst doped with other metal oxides by co-precipitation method.

[0017] Furthermore, the specific steps of preparing cerium oxide by precipitation method include: adding Ce salt into alkaline solution, and obtaining the cerium oxide catalyst through precipitation, aging, filtering, washing, drying, calcining and other steps.

[0018] Furthermore, the specific steps of preparing the cerium oxide catalyst doped with other metal oxides by the co-precipitation method include: mixing the salt solution of the metal element and the Ce salt solution and adding them to an alkaline solution, and obtaining the cerium oxide catalyst doped with other metal oxides through precipitation, aging, filtration, washing, drying, calcination and other steps.

[0019] Furthermore, the salt solution of the metal element is a salt solution of samarium nitrate, yttrium nitrate, praseodymium nitrate, neodymium nitrate or lanthanum nitrate.

[0020] Furthermore, the precipitation temperature is 20-60°C, preferably 20°C.

[0021] Furthermore, the aging time is 2 to 4 hours, preferably 2 hours.

[0022] Furthermore, the drying temperature is 110-120° C., and the drying time is 10-12 hours, preferably drying at 110° C. for 12 hours.

[0023] Furthermore, the calcination temperature is 400-500° C., and the calcination time is 4-6 hours, preferably calcination at 400° C. for 4 hours in an air atmosphere.

[0024] Furthermore, the specific steps of preparing cerium oxide by precipitation method include: adding Ce salt to alkaline solution, stirring evenly for 1 hour, aging for 2 hours, washing and filtering to remove impurities to obtain a precipitate, drying at 110°C for 12 hours, and then calcining at 400°C in an air atmosphere for 4 hours to obtain the cerium oxide catalyst.

[0025] Furthermore, the specific steps of preparing the cerium oxide catalyst doped with other metal oxides by co-precipitation method include: mixing a salt solution of samarium nitrate, yttrium nitrate, praseodymium nitrate, neodymium nitrate or lanthanum nitrate and a Ce salt solution, then adding the mixed salt solution to an alkaline solution, stirring evenly for 1 hour, aging for 2 hours, washing and filtering to remove impurities to obtain a precipitate, drying at 110°C for 12 hours, and then calcining at 400°C in an air atmosphere for 4 hours to obtain the cerium-based catalyst.

[0026] Thymol is a key intermediate in the synthesis of menthol. The last step of its synthesis is to carry out a hydrogenation catalytic reaction of thymol under high temperature and high pressure conditions to obtain the target menthol. In this step reaction, the inventors found that cerium oxide or a cerium-based catalyst doped with cerium oxide can be used to catalyze the hydrogenation reaction of thymol under high temperature and high pressure.

[0027] The third technical solution of the present invention is to provide an application of the cerium-based catalyst for preparing DL menthol as described above in catalyzing the hydrogenation reaction of thymol to prepare DL menthol.

[0028] Furthermore, the reaction temperature of the hydrogenation reaction is 160-200° C., and the time is 5-7 hours.

[0029] Furthermore, the thymol hydrogenation reaction is carried out in an autoclave reactor, and the gas pressure during the reaction is 6 MPa.

[0030] Furthermore, the mass ratio of the cerium-based catalyst to the reactants added in the thymol hydrogenation reaction is 1:50.

[0031] On the basis of being in accordance with the common sense in the art, the above-mentioned preferred conditions can be arbitrarily combined to obtain the preferred embodiments of the present invention.

[0032] Compared with the prior art, the present invention has the following advantages:

[0033] 1. The cerium-based catalyst prepared by the present invention is used for catalyzing the hydrogenation of thymol to obtain various isomers mainly composed of DL-menthol. The thymol conversion rate can reach 99%, and the selectivity of generating DL-menthol can reach 57.37%. The selectivity of generating DL-isomenthol is low, and the proportion of DL-isomenthol in the product is 10.9-12.68%. The impurity content is extremely low, and the impurity content does not exceed 0.6% of the total product. The reaction time is short and the reaction conditions are simple.

[0034] 2. The preparation steps of the cerium-based catalyst of the present invention are simple, the conditions are easy to achieve, and the prepared catalyst has high stability, good stability during the use of the catalyst, and excellent cycle stability. It is not deactivated after five cycles of reaction, and is a relatively ideal catalyst for thymol hydrogenation reaction.

[0035] 3. The present invention adopts a cerium-based catalyst to replace a noble metal catalyst for catalytic hydrogenation reaction, which reduces the preparation cost of the catalyst, has high production efficiency, is suitable for the continuous production of menthol, and has a simple preparation process that is also conducive to industrial production, which is in line with the future development direction of green and continuous fine chemical industry.

[0036] 4. The present invention has simple steps, less operations and is easy to implement. DETAILED DESCRIPTION

[0037] The present invention is described in detail below in conjunction with specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0038] Unless otherwise specified, the experimental reagents and raw materials used in the present invention are commercially available.

[0039] The experimental methods without specific conditions in the following implementations are all selected according to conventional methods and conditions, or according to the product instructions. Unless otherwise specified, the experimental instruments used in the present invention are all conventional experimental instruments in the laboratory.

[0040] Example 1

[0041] 0.1M cerium acetate and 0.15M sodium carbonate were dissolved in 150ml distilled water respectively; sodium carbonate solution was added to cerium acetate solution, stirred and precipitated evenly at 20°C for 1 hour and aged for 2 hours, washed and filtered to remove impurities to obtain a precipitate, dried at 110°C for 12 hours, and then calcined at 400°C in air atmosphere for 4 hours to obtain a catalyst. The catalyst performance evaluation results are shown in Table 1, the reaction temperature is 200°C, and the reaction pressure is 6Mpa.

[0042] Example 2

[0043] 0.1M cerium nitrate and 0.15M sodium carbonate were dissolved in 150ml of distilled water respectively; the cerium nitrate solution was added to the sodium carbonate solution, stirred and uniformly precipitated at 20°C for 1 hour and aged for 2 hours, washed and filtered to remove impurities to obtain a precipitate, dried at 110°C for 12 hours, and then calcined at 400°C in an air atmosphere for 4 hours to obtain a catalyst. The catalyst performance evaluation results are shown in Table 1, the reaction temperature is 200°C, and the reaction pressure is 6Mpa.

[0044] Example 3

[0045] 0.1M cerium nitrate and 0.15M sodium carbonate were dissolved in 150ml distilled water respectively; sodium carbonate solution was added to cerium nitrate solution, stirred and precipitated evenly at 20°C for 1 hour and aged for 2 hours, washed and filtered to remove impurities to obtain a precipitate, dried at 110°C for 12 hours, and then calcined at 400°C in air atmosphere for 4 hours to obtain a catalyst. The catalyst performance evaluation results are shown in Table 1, the reaction temperature is 200°C, and the reaction pressure is 6Mpa.

[0046] Example 4

[0047] Sm-doped cerium oxide is used as a catalyst, wherein the Sm doping amount is 20%. Catalyst preparation method: 0.02M samarium nitrate and 0.08M cerium nitrate are dissolved in 100mL deionized water, and 0.15M sodium carbonate is dissolved in 150mL deionized water; the sodium carbonate solution is poured into the mixed salt solution, stirred and precipitated evenly at 20°C for 1 hour and aged for 2 hours, washed and filtered to remove impurities to obtain a precipitate, dried at 110°C for 12 hours, and then calcined at 400°C in an air atmosphere for 4 hours to obtain a catalyst. The reaction temperature is 200°C and the reaction pressure is 6Mpa.

[0048] Example 5

[0049] Nb-doped cerium oxide is used as a catalyst, wherein the Nb doping amount is 20%. Catalyst preparation method: 0.02M neodymium nitrate and 0.08M cerium nitrate are dissolved in 100mL deionized water, and 0.15M sodium carbonate is dissolved in 150mL deionized water; the sodium carbonate solution is poured into the mixed salt solution, stirred and precipitated evenly at 20°C for 1 hour and aged for 2 hours, washed and filtered to remove impurities to obtain a precipitate, dried at 110°C for 12 hours, and then calcined at 400°C in an air atmosphere for 4 hours to obtain a catalyst. The reaction temperature is 200°C and the reaction pressure is 6Mpa.

[0050] Example 6

[0051] Y-doped cerium oxide is used as a catalyst, wherein the Y doping amount is 20%. Catalyst preparation method: 0.02M yttrium nitrate and 0.08M cerium nitrate are dissolved in 100mL deionized water, and 0.15M sodium carbonate is dissolved in 150mL deionized water; the sodium carbonate solution is poured into the mixed salt solution, stirred and precipitated evenly at 20°C for 1 hour and aged for 2 hours, washed and filtered to remove impurities to obtain a precipitate, dried at 110°C for 12 hours, and then calcined at 400°C in an air atmosphere for 4 hours to obtain a catalyst. The reaction temperature is 200°C and the reaction pressure is 6Mpa.

[0052] Example 7

[0053] Pr-doped cerium oxide is used as a catalyst, wherein the Pr doping amount is 20%. Catalyst preparation method: 0.02M praseodymium nitrate and 0.08M cerium nitrate are dissolved in 100mL deionized water, and 0.15M sodium carbonate is dissolved in 150mL deionized water; the sodium carbonate solution is poured into the mixed salt solution, stirred and precipitated evenly at 20°C for 1 hour and aged for 2 hours, washed and filtered to remove impurities to obtain a precipitate, dried at 110°C for 12 hours, and then calcined at 400°C in an air atmosphere for 4 hours to obtain a catalyst. The reaction temperature is 200°C and the reaction pressure is 6Mpa.

[0054] Example 8

[0055] La-doped cerium oxide is used as a catalyst, wherein the La doping amount is 20%. Catalyst preparation method: 0.02M lanthanum nitrate and 0.08M cerium nitrate are dissolved in 100mL deionized water, and 0.15M sodium carbonate is dissolved in 150mL deionized water; the sodium carbonate solution is poured into the mixed salt solution, stirred and precipitated evenly at 20°C for 1 hour and aged for 2 hours, washed and filtered to remove impurities to obtain a precipitate, dried at 110°C for 12 hours, and then calcined at 400°C in an air atmosphere for 4 hours to obtain a catalyst. The reaction temperature is 200°C and the reaction pressure is 6Mpa.

[0056] The catalyst formulations of the above Examples 1-8 are shown in Table 1:

[0057] Table 1 Catalyst formulations for Examples 1-8

[0058] Ce salt Metal Salts Metal doping amount Example 1 0.1M cerium acetate - 0％ Example 2 0.1M Cerium Nitrate - 0％ Example 3 0.1M Cerium Nitrate - 0％ Example 4 0.08M Cerium Nitrate 0.02M Samarium Nitrate 20％ Example 5 0.08M Cerium Nitrate 0.02M neodymium nitrate 20％ Example 6 0.08M Cerium Nitrate 0.02M Yttrium nitrate 20％ Example 7 0.08M Cerium Nitrate 0.02M Praseodymium Nitrate 20％ Example 8 0.08M Cerium Nitrate 0.02M Lanthanum Nitrate 20％

[0059] Test Case

[0060] The performance of a commercially available hydrogenation catalyst in the above Examples 1-8 and Comparative Example 1 was tested, and the specific parameters are as follows:

[0061] In a 250 ml autoclave, add 0.8 g of catalyst and 40.0 g of thymol, fix the reactor with a reinforcement ring, and replace the air with nitrogen three times; introduce hydrogen, start stirring and heat, and control the internal pressure at 6.0 MPa. After the temperature in the autoclave reaches the set temperature of 200°C, set the reaction for 6 hours, separate and filter the reaction liquid through a chromatography column to obtain various isomer products mainly composed of DL menthol and the catalyst, use a gas chromatograph to quantitatively analyze the liquid product, and calculate the conversion rate and selectivity. The recovered catalyst can be used for the next batch of reactions.

[0062] The product compositions of the cerium-based catalysts of Examples 1-8 and a commercially available hydrogenation catalyst of Comparative Example 1 for the hydrogenation reaction of thymol are shown in Table 2:

[0063] Table 2 Product composition of thymol hydrogenation reaction catalyzed by the cerium-based catalyst of Examples 1-8

[0064] Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 Comparative Example 1 Impurities(%) 0.53 0.38 0.03 0.05 0.12 0.06 0.08 0.02 4.72 Menthone(%) 0.48 0.4 0.46 0.44 0.45 0.06 0.51 0.08 1.1 DL neomenthol (%) 34.46 32.79 31.97 28.98 30.54 30.12 29.52 30.92 33.08 DL-Menthol (%) 48.13 51.99 52.25 57.37 55.49 56.18 56.76 54.79 31.35 DL neoisomenthol (%) 2.75 2.68 2.61 2.26 2.43 2.08 2.25 2.58 4.83 DL-isomenthol (%) 12.15 11.76 12.68 10.9 10.97 11.5 10.88 11.61 14.37 Thymol(%) 1.5 -- -- -- -- -- -- -- 10.55

[0065] As can be seen from Table 2, the cerium-based catalyst prepared by the present invention has excellent performance in catalyzing thymol to prepare DL menthol. The test results show that under the catalysis of the catalyst, the conversion rate of thymol can reach 99%, and the selectivity of generating DL menthol can reach 57.37%; the selectivity of generating DL isomenthol is low, and the proportion of DL isomenthol in the product is 10.9-12.68%, the impurity content is extremely low, and the impurity content does not exceed 0.6% of the total product, and the catalyst has high stability and is not deactivated after five cycles of reaction.

[0066] Example 4 in the above embodiments uses Sm-doped cerium oxide as a catalyst, wherein the Sm doping amount is 20%. The prepared cerium-based catalyst doped with 20% Sm has excellent thymol hydrogenation catalytic performance. Under the catalytic action of the cerium-based catalyst doped with 20% Sm, the thymol conversion rate can reach 99%, the selectivity for generating DL menthol is 57.37%, the selectivity for generating DL isomenthol is as low as 10.9%, and the impurity content is 0.05% of the total product.

[0067] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A cerium-based catalyst for preparing DL menthol, characterized in that: The cerium-based catalyst is a cerium oxide catalyst or a cerium oxide catalyst doped with other metal oxides, the metal elements contained in the other metal oxides include one or two of Sm, Y, Pr, Nb and La, and the catalyst is used to catalyze the hydrogenation reaction of thymol to prepare DL menthol.

2. A cerium-based catalyst for preparing DL menthol according to claim 1, characterized in that: The doping amount of the metal element in the cerium-based catalyst is 5-50%.

3. A cerium-based catalyst for preparing DL menthol according to claim 1, characterized in that: The specific surface area of ​​the cerium-based catalyst is 50 to 150 m 2 / g, pore volume is 0.2~1.0cm 3 / g, and the average pore size is 5 to 20 nm.

4. A method for preparing a cerium-based catalyst for preparing DL menthol as claimed in claim 1, characterized in that: The preparation method comprises preparing the cerium oxide catalyst by a precipitation method or preparing the cerium oxide catalyst doped with other metal oxides by a co-precipitation method.

5. The method for preparing a cerium-based catalyst for preparing DL menthol according to claim 4, characterized in that: The specific steps of preparing cerium oxide by precipitation method include: adding Ce salt into alkaline solution, and obtaining the cerium oxide catalyst through precipitation, aging, filtering, washing, drying, calcining and other steps.

6. The method for preparing a cerium-based catalyst for preparing DL menthol according to claim 4, characterized in that: The specific steps of preparing the cerium oxide catalyst doped with other metal oxides by the co-precipitation method include: mixing the salt solution of the metal element and the Ce salt solution and adding them to an alkaline solution, and obtaining the cerium oxide catalyst doped with other metal oxides through steps such as precipitation, aging, filtering, washing, drying, and calcining.

7. The method for preparing a cerium-based catalyst for preparing DL menthol according to claim 5 or 6, characterized in that: The aging time is 2 to 4 hours.

8. The method for preparing a cerium-based catalyst for preparing DL menthol according to claim 5 or 6, characterized in that: The drying temperature is 110-120° C., and the time is 10-12 hours. The calcination temperature is 400-500° C., and the time is 4-6 hours.

9. Use of the cerium-based catalyst for preparing DL menthol as claimed in claim 1 in catalyzing the hydrogenation reaction of thymol to prepare DL menthol.

10. The use of a cerium-based catalyst for preparing DL menthol according to claim 9, characterized in that: The reaction temperature of the hydrogenation reaction is 160-200° C. and the reaction time is 5-7 hours.

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