Dehydrogenation catalyst and preparation method thereof, and application of dehydrogenation catalyst in preparation of carvacrol by dehydrogenation of carvone

Abstract

The invention belongs to the technical field of organic synthesis, and particularly discloses a dehydrogenation catalyst, a preparation method of the dehydrogenation catalyst and application of the dehydrogenation catalyst to preparation of carvacrol through dehydrogenation of carvone, the dehydrogenation catalyst provided by the invention is Pd / Ni-coated CeOx-gamma-Al2O3, and by mass fraction, Pd accounts for 2.5%, Ni accounts for 2.5%, x accounts for 2, CeOx accounts for 20%, and gamma-Al2O3 accounts for 75%. The preparation method of the catalyst comprises the following steps: (1) preparing the CeOx-gamma-Al2O3 composite carrier through a coprecipitation method; and (2) carrying out equivalent-volume impregnation and H2 reduction in a tubular furnace to prepare the Pd / Ni-coated CeOx-gamma-Al2O3 finished product catalyst. The Pd / Ni-coated CeOx-gamma-Al2O3 catalyst prepared by the preparation method disclosed by the invention is used for preparing carvacrol by dehydroaromatization of carvone; wherein the carvone is a by-product generated in the production process of preparing carvacrol by dehydrogenation of dihydrocarvone, the method realizes full utilization of the by-product, saves energy and reduces emission, solves the environmental protection problem in production, and creates new social benefits and economic benefits at the same time. And the catalyst can be efficiently and repeatedly used for a long time, and is relatively low in use cost.

Description

Technical Field

[0001] The invention belongs to the technical field of organic synthesis and relates to the preparation of a catalyst for a dehydrogenation reaction, in particular to a dehydrogenation catalyst and a preparation method thereof and application in the dehydrogenation of carvacrol from carvimentone. Background Art

[0002] Carvacrol is a colorless to pale yellow viscous liquid. It possesses strong antibacterial properties, inhibiting the growth of microorganisms such as mites and insects. Currently, as a green, low-toxic food additive and broad-spectrum antiseptic, it is commonly used in toothpaste, mouthwash, cosmetics, and food preservation. Natural carvacrol is primarily found in various plants of the Lamiaceae family, such as thyme and oregano.

[0003] Currently, there are several methods for the synthesis of carvacrol:

[0004] The first method uses o-cresol as the raw material and a strong Lewis acid such as aluminum chloride or ferric chloride as a catalyst to produce carvacrol through a Friedel-Crafts alkylation reaction with isopropanol or 2-chloropropane. This method, already proposed in patent CN1488615, produces a large amount of metal salts, which pollute the environment and are difficult to produce and apply on a large scale.

[0005] The second method uses carvone as a raw material and aromatizes carvacrol in the presence of a strong acid or metal catalyst. For example, in patent CN101475448A, PEG is used as an adjuvant to promote the intramolecular rearrangement of carvone to produce carvacrol through acid catalysis. However, carvone, as a raw material, is often more expensive than carvacrol, making production costs difficult to justify.

[0006] The third method involves sulfonating p-isopropyltoluene with sulfuric acid to produce p-isopropyltoluene-2-sulfonic acid, which is then alkali-melted to obtain carvacrol. This method uses large amounts of acid and alkali, places high demands on the corrosion resistance of production equipment, and produces large amounts of wastewater, posing a significant environmental burden.

[0007] Technicians have noticed that carvacrol and carvone have similar chemical structures. Theoretically, carvacrol can be obtained by dehydrogenation aromatization of carvone. However, this reaction has not been reported so far. Summary of the Invention

[0008] In view of the shortcomings of the prior art, the present invention aims to provide a dehydrogenation catalyst, using the self-made dehydrogenation catalyst Pd / Ni@CeO xγ-Al₂O₃ is used to dehydrogenate carvimentone to produce carvacrol, resulting in a carvacrol content exceeding 99%. This invention converts low-value carvimentone into high-value carvacrol through a simple dehydrogenation process, recycling these byproducts while also reducing overall production costs, generating greater economic benefits, and minimizing environmental pollution.

[0009] The present invention is achieved through the following technical solutions:

[0010] A dehydrogenation catalyst, the catalyst is Pd / Ni@CeO x -γ-Al2O3, by mass fraction, Pd accounts for 2.5%, Ni accounts for 2.5%, x is 2, CeO x It accounts for 20% and γ-Al2O3 accounts for 75%.

[0011] A further improvement of the present invention is:

[0012] A method for preparing a dehydrogenation catalyst comprises the following steps:

[0013] (1) A CeOx-γ-Al2O3 composite support is prepared by a co-precipitation method: aluminum salt and cerium salt are weighed according to the molar ratio required for the support, cerium salt and half of the aluminum salt are mixed to prepare an aqueous solution, and the mixture is stirred to obtain an acidic aluminum-cerium salt mixed aqueous solution; after the other half of the aluminum salt is prepared into an aqueous solution, an alkaline precipitant is added dropwise under stirring to adjust the pH to neutral, and the acidic aluminum-cerium salt mixed aqueous solution is added dropwise while stirring. After the addition is completed, an alkaline precipitant is continued to be added dropwise, and the pH is adjusted to 9-10. After continued stirring, the mixture is allowed to stand for aging, filtered, and washed to obtain a support precursor; the support precursor is dried, crushed, spheroidized, sieved, calcined at high temperature, and naturally cooled to obtain CeOx-γ-Al2O3 composite support. x -γ-Al2O3 composite support;

[0014] (2) Pd / Ni@CeO was prepared by equal volume impregnation and H2 reduction in a tube furnace. x -γ-Al2O3 finished catalyst: prepare a mixed aqueous solution of palladium salt and nickel salt, immerse an equal volume of the composite carrier powder obtained in step (1) in the mixed aqueous solution of palladium salt and nickel salt, immerse for a period of time, and remove water by rotary evaporation to obtain a catalyst precursor; dry the catalyst precursor and place it in a tube furnace, reduce it in an atmosphere of H2 / N2 mixed gas, and cool it naturally to obtain Pd / Ni@CeO x -γ-Al2O3 finished catalyst.

[0015] Furthermore, the aluminum salt is one or a mixture of two or more of aluminum sulfate, aluminum nitrate or aluminum chloride;

[0016] And / or, the cerium salt is one or a mixture of two or more of cerium sulfate, cerium nitrate or cerium chloride;

[0017] And / or, the nickel salt is one or a mixture of two or more of nickel sulfate, nickel nitrate or nickel chloride;

[0018] And / or, the palladium salt is one or a mixture of two or more of palladium nitrate, palladium chloride or sodium chloropalladate;

[0019] And / or, the alkaline additive is one or a mixture of two or more of sodium hydroxide, potassium hydroxide, sodium carbonate or potassium carbonate.

[0020] Furthermore, the molar ratio of the aluminum salt, the cerium salt, the palladium salt, and the nickel salt is 1:0.079:0.016:0.029.

[0021] Furthermore, the temperature rise program of the high temperature calcination in step (1) is 2°C / min to 450°C, and the high temperature calcination time is 4-6h;

[0022] And / or, in step (2), the temperature raising program of the reduction is 1.5°C / min to 400°C, and the reduction time is 4-6h.

[0023] A further improvement of the present invention is:

[0024] A dehydrogenation catalyst is used in the dehydrogenation of carvacrol to prepare carvacrol, comprising the following steps: x -γ-Al2O3 is used as a dehydrogenation catalyst, an alkaline auxiliary agent is added, and heating is carried out in a nitrogen atmosphere to cause carvacrol to undergo a dehydrogenation aromatization reaction of carvacrol.

[0025] The chemical equation is as follows:

[0026]

[0027] Parsley menthol, chemical name is 2-methyl-5-(1-methylethyl)cyclohexanone, CAS: 59471-80-6.

[0028] Furthermore, the carvone in the present invention is selected from the by-product of dehydrogenation of dihydrocarvone to carvacrol.

[0029] Furthermore, the method is characterized in that the amount of the dehydrogenation catalyst is between 0.5% and 2% of the carvone, and the amount of the alkaline auxiliary agent is between 0.01% and 1%, both of which are expressed in mass percentages.

[0030] Furthermore, the dehydrogenation aromatization reaction temperature is 180-220 ° C, and the time is 8-30 hours.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] The catalyst provided by the present invention has the characteristics of moderate reaction activity, safety and stability, and simple and easy reproducible production. The addition of nickel element can achieve higher dehydrogenation catalytic activity with a lower precious metal content. The carrier modified by cerium oxide can reduce the loaded particle size of the main active ingredient, effectively improve the activity and service life of the catalyst, and can also enhance the stability of the elemental nickel catalyst at room temperature.

[0033] The present invention adopts the prepared Pd / Ni@CeO x Using γ-Al₂O₃ as a dehydrogenation catalyst, an alkaline additive, and heating in a nitrogen atmosphere, carvone undergoes a dehydrogenation aromatization reaction to produce carvacrol. This effectively utilizes the byproducts of the dihydrocarvone-to-carvacrol production line, enabling the production of low-value-added products, improving material utilization, increasing economic benefits, and reducing environmental pollution. The use of the alkaline additive effectively promotes the dehydrogenation of carbonyl alicyclic compounds and allows for multiple recycling. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is the C NMR spectrum of the menthol isolated in Example 3;

[0035] Figure 2 This is the H NMR spectrum of the carvimentone separated in Example 3. DETAILED DESCRIPTION

[0036] The present invention will be described in detail below with reference to specific embodiments.

[0037] A specific embodiment of the present invention provides a dehydrogenation catalyst Pd / Ni@CeO x -The preparation process of γ-Al2O3, specifically:

[0038] Example 1: Pd / Ni@CeO x -Preparation of γ-Al2O3 catalyst

[0039] Weigh 27.59kg of Al(NO3)3·9H2O and 5.05kg of Ce(NO3)3·6H2O into a 200L PVC plastic bucket, add 150L of deionized water, and mechanically stir to mix. Weigh 27.59kg of Al(NO3)3·9H2O into a 1t reactor, add 100L of deionized water, and mechanically stir to mix. Slowly add 10% NH3·H2O to adjust the pH to neutral. At this time, begin pumping the acidic cerium aluminum salt mixed aqueous solution into the reaction system until addition is complete. Heat to 50°C and stir for 2 hours. Continue to add ammonia water dropwise and adjust the pH to 9-10. Continue stirring for 6 hours. Let it stand naturally for 24 hours of aging. Filter through a plate and frame filter and repeatedly wash with deionized water until the filtrate is neutral to obtain the carrier precursor.

[0040] The precursor was spread evenly, placed in a forced air drying oven at 110°C for 24 hours, dried, crushed, and ball-milled to pass through a 200-mesh sieve. The powder was placed in a muffle furnace and heated at 2.0°C / min to 450°C, calcined at high temperature for 5 hours, and cooled naturally to obtain a CeOx-γ-Al2O3 composite support.

[0041] Weigh 1.25kg Ni(NO3)2·6H2O and 0.63kg Pd(NO3)2·2H2O to prepare 9L of palladium-nickel mixed aqueous solution. After stirring overnight, slowly pour it into the powder, soak it in equal volumes for 12 hours, and then air dry it at 110℃ for 24 hours to remove moisture. The dried catalyst precursor is placed in a tube furnace and heated to 400℃ at 1.5℃ / min under 15% H2 / N2 mixed gas. Reduce it for 5 hours and cool it naturally to obtain the finished product Pd / Ni@CeO x -γ-Al2O3 catalyst 9.37kg.

[0042] Example 2: Pd / Ni@CeO x -Preparation of γ-Al2O3 catalyst

[0043] Weigh 137.92g of Al(NO3)3·9H2O and 25.25g of Ce(NO3)3·6H2O into a 1L beaker, add 500mL of deionized water, sonicate to dissolve, and mix evenly with magnetic stirring. Weigh 137.92g of Al(NO3)3·9H2O into a 5L beaker, add 300mL of deionized water, sonicate, and prepare a solution separately. Mechanically stir evenly at room temperature, and add 10% NH3·H2O to adjust the pH to 6.5. Start adding the acidic cerium aluminum salt mixed aqueous solution dropwise with a peristaltic pump until the addition is complete. Heat to 50°C, stir for 1h, continue to add ammonia water, and adjust the pH to 9. Continue stirring for 4h. Let it stand naturally for aging for 24h, filter, and repeatedly wash with distilled water until the filtrate is neutral to obtain a carrier precursor.

[0044] The precursor was placed in a forced air drying oven at 110°C for 24 hours, dried, crushed, and ground through a 200-mesh sieve. The powder was placed in a muffle furnace and heated at 2.0°C / min to 450°C. High-temperature calcination was performed for 5 hours, followed by natural cooling to obtain a CeOx-γ-Al2O3 composite support. The composite support was crushed, and the saturated water absorption per unit mass was measured multiple times and averaged to approximately 90% of the support's weight. 45 mL of a palladium-nickel mixed salt solution was prepared by weighing 6.2 g of Ni(NO3)2·6H2O and 3.13 g of Pd(NO3)2·2H2O. This solution was slowly poured into the support, and the mixture was impregnated with equal volumes for 12 hours. The water was then removed by rotary evaporation. The catalyst precursor was dried in an oven at 110°C for 24 hours.

[0045] The dried catalyst precursor was placed in a tube furnace, heated to 400°C at 1.5°C / min under a 10% H2 / N2 mixed gas, reduced for 4 hours, and cooled naturally to obtain 47.6g of finished catalyst.

[0046] The specific embodiment of the present invention provides the prepared Pd / Ni@CeO x -γ-Al2O3 catalyst is used to catalyze the dehydrogenation of carvacrol to produce carvacrol, wherein carvacrol is a by-product of the dehydrogenation of dihydrocarvone to produce carvacrol. The process of obtaining carvacrol is shown in Example 3.

[0047] Example 3: Obtaining carvone

[0048] Researchers studying the dehydrogenation of dihydrocarvone to carvacrol discovered that the reaction is an equilibrium reaction, with simultaneous hydrogenation occurring. The hydrogenation product is carvacrol. Carvacrol was isolated from the foot oil of the dihydrocarvone dehydrogenation reaction and its structure was verified by nuclear magnetic resonance. Dehydrogenation of carvacrol to carvacrol requires higher energy levels, which the catalyst described in CN107365247 cannot meet. Therefore, a more active dehydrogenation catalyst is needed.

[0049]

[0050] Example 4: Preparation of carvacrol by dehydrogenation of carvacrol

[0051] 1000 mL of carvacrol was placed in a 2 L stainless steel reactor, and 5 g of the catalyst prepared in Example 1 was added. The mixture was stirred vigorously, purged with nitrogen, and heated to 180°C. Samples were taken every 2 hours and analyzed for composition changes by gas chromatography. The reaction mixture was allowed to react for approximately 8 hours, reaching equilibrium. The reaction mixture was cooled to below 80°C, filtered while hot, and the catalyst recovered. The mixture was then subjected to low vacuum distillation to remove light components. High vacuum distillation was then performed to obtain 478 g of finished carvacrol containing greater than 99% carvacrol.

[0052] The reactor was negatively pressurized and the catalyst in the filter was pushed back into the reactor with 1.0 kg of material. Stir vigorously, introduce nitrogen, and raise the temperature to 180°C. Samples were taken every 2 hours and analyzed for changes in composition by gas chromatography. The reaction lasted about 8 hours and equilibrium was reached. The reaction mixture was cooled to below 80°C, filtered while hot, and the catalyst was recovered. The above operation was repeated up to 25 times, but the reaction temperature needed to be raised to 210°C and the reaction time increased to 14 hours, but the product yield did not change.

[0053] Example 5: Preparation of carvacrol by dehydrogenation of carvacrol

[0054] 50 kg of the material was put into a 100 L stainless steel reactor, and 250 g of Pd / Ni@CeO prepared according to the method of Example 1 was added. x The reaction mixture was heated to 180°C with a γ-Al2O3 catalyst, stirred vigorously, and nitrogen was introduced (nitrogen removes hydrogen produced by the reaction). Samples were taken every three hours and analyzed for composition changes by gas chromatography. The reaction mixture was allowed to react for 10 hours to reach equilibrium. The reaction mixture was cooled to below 80°C, filtered while hot, and the catalyst recovered. The mixture was then subjected to low vacuum distillation to remove light components. High vacuum distillation was then performed to obtain 23.7 kg of finished carvacrol with a content greater than 99%.

[0055] The reactor was negatively pressurized, and the catalyst in the filter was returned to the reactor with the treated material. Stir vigorously, introduce nitrogen, and raise the temperature to 190°C. Samples were taken every 3 hours and analyzed for composition changes by gas chromatography. The reaction reached equilibrium after approximately 12 hours. The reaction mixture was cooled to below 80°C, filtered while hot, and the catalyst recovered. This cycle was repeated up to 30 times, at which point the reaction temperature needed to be raised to 210°C. The product yield remained unchanged, but the reaction time increased to 18 hours.

[0056] Example 6: Dehydrogenation of carvacrol to carvacrol

[0057] 1.0 t of material was put into a 3 t reactor, and 5.5 kg of Pd / Ni@CeO prepared according to the method of Example 1 was added. x The mixture was stirred evenly, nitrogen was introduced, and the temperature was raised to 180°C. Samples were taken every four hours and analyzed for composition changes by gas chromatography. The reaction mixture was allowed to react for 20 hours to reach equilibrium. The reaction mixture was cooled to below 80°C, filtered while hot, and the catalyst recovered. The mixture was then subjected to low vacuum distillation to remove light components. The mixture was then distilled under high vacuum to obtain 491 kg of finished carvacrol with a content greater than 99%.

[0058] Repeat the feeding process and cycle the above operations. The same batch of catalyst can react up to 30 times. At this time, the reaction temperature needs to be raised to 220°C, but the product yield does not change at all, only the reaction time is increased to 30h.

[0059] The above embodiments are intended only to illustrate the technical concepts and features of the present invention. Their purpose is to enable those skilled in the art to understand the contents of the present invention and implement them accordingly. They are not intended to limit the scope of protection of the present invention. Any equivalent changes or modifications made in accordance with the spirit of the present invention are intended to be covered by the scope of protection of the present invention.

Claims

1. A dehydrogenation catalyst, characterized in that The catalyst is Pd / Ni@CeO x -γ-Al2O3, by mass fraction, Pd accounts for 2.5%, Ni accounts for 2.5%, x is 2, CeO x It accounts for 20% and γ-Al2O3 accounts for 75%.

2. The method for preparing a dehydrogenation catalyst according to claim 1, wherein: The following steps are involved: (1) A CeOx-γ-Al2O3 composite support is prepared by a co-precipitation method: aluminum salt and cerium salt are weighed according to the molar ratio required for the support, cerium salt and half of the aluminum salt are mixed to prepare an aqueous solution, and the mixture is stirred to obtain an acidic aluminum-cerium salt mixed aqueous solution; after the other half of the aluminum salt is prepared into an aqueous solution, an alkaline precipitant is added dropwise under stirring to adjust the pH to neutral, and the acidic aluminum-cerium salt mixed aqueous solution is added dropwise while stirring. After the addition is completed, an alkaline precipitant is continued to be added dropwise, and the pH is adjusted to 9-10. After continued stirring, the mixture is allowed to stand for aging, filtered, and washed to obtain a support precursor; the support precursor is dried, crushed, spheroidized, sieved, calcined at high temperature, and naturally cooled to obtain CeOx-γ-Al2O3 composite support. x -γ-Al2O3 composite support; (2) Pd / Ni@CeO was prepared by equal volume impregnation and H2 reduction in a tube furnace. x -γ-Al2O3 finished catalyst: prepare a mixed aqueous solution of palladium salt and nickel salt, immerse an equal volume of the composite carrier powder obtained in step (1) in the mixed aqueous solution of palladium salt and nickel salt, immerse for a period of time, and remove water by rotary evaporation to obtain a catalyst precursor; dry the catalyst precursor and place it in a tube furnace, reduce it in an atmosphere of H2 / N2 mixed gas, and cool it naturally to obtain Pd / Ni@CeO x -γ-Al2O3 finished catalyst.

3. The method for preparing a dehydrogenation catalyst according to claim 2, wherein: The aluminum salt is one or a mixture of two or more of aluminum sulfate, aluminum nitrate or aluminum chloride; And / or, the cerium salt is one or a mixture of two or more of cerium sulfate, cerium nitrate or cerium chloride; And / or, the nickel salt is one or a mixture of two or more of nickel sulfate, nickel nitrate or nickel chloride; And / or, the palladium salt is one or a mixture of two or more of palladium nitrate, palladium chloride or sodium chloropalladate; And / or, the alkaline additive is one or a mixture of two or more of sodium hydroxide, potassium hydroxide, sodium carbonate or potassium carbonate.

4. The method for preparing a dehydrogenation catalyst according to claim 2, wherein: The molar ratio of the aluminum salt, the cerium salt, the palladium salt, and the nickel salt is 100:8:1.6:

3.

5. The method for preparing a dehydrogenation catalyst according to claim 2, wherein: The high temperature calcination in step (1) is performed at a temperature of 2°C / min up to 450°C, and the high temperature calcination time is 4-6 hours; And / or, in step (2), the temperature raising program of the reduction is 1.5°C / min to 400°C, and the reduction time is 4-6h.

6. Use of a dehydrogenation catalyst according to claim 1 in the dehydrogenation of carvacrol to produce carvacrol, characterized in that: The following steps are involved: Pd / Ni@CeO x -γ-Al2O3 is used as a dehydrogenation catalyst, an alkaline auxiliary agent is added, and heating is carried out in a nitrogen atmosphere to cause carvacrol to undergo a dehydrogenation aromatization reaction of carvacrol.

7. Use of a dehydrogenation catalyst according to claim 6 in the dehydrogenation of carvacrol to produce carvacrol, characterized in that: The carvone is a by-product in the dehydrogenation of dihydrocarvone to carvacrol.

8. Use of a dehydrogenation catalyst according to claim 6 in the dehydrogenation of carvacrol to produce carvacrol, characterized in that: The carvone, dehydrogenation catalyst and alkaline auxiliary agent are characterized in that the feeding amount of the dehydrogenation catalyst is between 0.5% and 2% of the carvone, and the feeding amount of the alkaline auxiliary agent is between 0.01% and 1%, all of which are expressed in mass percentages.

9. Use of a dehydrogenation catalyst according to claim 6 in the dehydrogenation of carvacrol to produce carvacrol, characterized in that: The temperature of the dehydrogenation aromatization reaction is 180-220° C., and the time is 8-30 hours.

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