Preparation method and application of supported catalyst for synthesizing high-purity carvacrol

Abstract

This invention provides a method for preparing a supported catalyst for synthesizing high-purity carvacrol and its application, belonging to the field of carvacrol synthesis reaction technology. The o-cresol alkylation catalyst prepared by this method mainly uses modified zinc aluminate as the catalytic component, which has active centers suitable for o-cresol alkylation. The addition of alumina support can distribute the active centers and prevent the aggregation of active sites, thereby preventing the formation of heavy components and coke, maintaining a high conversion rate of o-cresol and selectivity of carvacrol, and maintaining the stability of catalyst activity. It has the advantages of simple preparation method and good stability. The average conversion rate of o-cresol is above 55%, and the selectivity of carvacrol is above 93%. It has high selectivity, few by-products, low reaction temperature, significantly reduced energy consumption, and less waste, making it suitable for industrial application. Moreover, the purity of the obtained carvacrol is above 99.5%.

Description

Technical Field

[0001] The invention belongs to the technical field of carvacrol synthesis reaction, and particularly relates to a preparation method and application of a catalyst for synthesizing high-purity carvacrol. Background Art

[0002] Carvacrol is a volatile, light yellow, transparent, oily liquid with a rich aroma. It has antibacterial and antioxidant properties, can stimulate appetite, and promote absorption, making it a promising candidate for development. Carvacrol is primarily used in the formulation of flavors such as dill, clove, mint, and vanilla, and is found in toothpaste, tooth powder, oral products, talcum powder, soap, and other daily industrial products.

[0003] The current methods for extracting or synthesizing carvacrol are as follows: (1) isolating carvacrol from oregano oil or thyme oil by making phenol salts with alkali solution. (2) sulfonating p-cymene to the corresponding p-cymene-2-sulfonic acid, and then converting it by alkali fusion treatment. (3) dehydrogenating menthol in the presence of copper or nickel catalysts. (4) preparing carvacrol by Friedel-Crafts alkylation of o-cresol with isopropanol or 2-chloropropane. (5) preparing carvacrol by isomerization catalysis of carvone in the presence of organic or inorganic acid catalysts. (6) synthesizing carvacrol in a one-step process using carveol as a raw material and Lewis acid as a catalyst. (7) synthesizing epoxy limonene, carvacrol, and carvone from limonene, and finally synthesizing carvacrol from carvone in the final step. (8) preparing carvacrol using o-cresol and isopropanol / propylene as raw materials using a composite catalyst.

[0004] Numerous studies have been conducted on the synthesis of carvacrol, but currently the industry primarily uses methods extracted from natural plants. Existing synthesis methods have the following main problems: (1) severe pollution in the synthesis process; (2) raw materials are difficult to obtain and are expensive; (3) conversion efficiency is poor and there are many by-products. Among these, the process using o-cresol as a raw material has become a research focus due to its environmental friendliness, simplicity, and high conversion efficiency. Examples of such processes include CN112920022B and CN113896617B. The key to this process lies in the conversion rate and selectivity of the catalyst, as well as the control of reaction temperature and pressure.

[0005] Catalysts for the alkylation of o-cresol can generally be divided into two categories: molecular sieve catalysts and oxide catalysts. Domestic reports, such as the modified Al2O3 / CuAl2O4 composite porous catalyst prepared in CN113896617B, the Ce and Al co-doped porous nano-ZrO2 active catalyst prepared in CN113304743B, and the modified catalysts combining molecular sieves and binders prepared in CN116253618A, have demonstrated relatively good activity and target selectivity. However, literature and patent reports on carvacrol catalysts and synthesis processes have high reaction temperatures and pressures, limited research on service life and regeneration performance, and most have not yet achieved industrial application. Summary of the Invention

[0006] In order to solve the above technical problems, the present invention provides a preparation method of a supported catalyst for synthesizing high-purity carvacrol and its application, with mild reaction temperature and pressure, and a matching carvacrol synthesis method is developed, which is suitable for industrial production, with an o-cresol conversion rate of more than 50%, a carvacrol selectivity of more than 90%, mild reaction conditions, and few by-products.

[0007] To achieve the above objectives, this solution first provides a method for preparing a supported catalyst for synthesizing high-purity carvacrol, comprising the following steps:

[0008] S1. Dissolve soluble aluminum salt and soluble zinc salt in deionized water, then add Al2O3 particles and stir evenly;

[0009] S2. Slowly add aqueous ammonia to the system obtained in S1 until the pH value reaches 8-9; continue stirring for 1-2 hours after the addition of aqueous ammonia; filter and wash the resulting precipitate until the pH reaches neutral, and filter to separate the solid;

[0010] S3, washing the solid obtained in S2, adding distilled water to prepare a suspension, stirring at high temperature and filtering to obtain solid particles, drying at 100-140°C for 12-20h, and finally calcining at high temperature for 6-8h to obtain a supported catalyst;

[0011] The supported catalyst comprises zinc aluminate and Al2O3, wherein the Al2O3 serves as a carrier to support the zinc aluminate.

[0012] Preferably, in step S1, the soluble aluminum salt is aluminum nitrate nonahydrate, the soluble zinc salt is zinc nitrate hexahydrate; and the Al2O3 is γ-alumina.

[0013] Preferably, the mass ratio of the soluble aluminum salt, the soluble zinc salt and the Al2O3 particles is 1:1-2:1.5-2.5, and the mass of the distilled water added to form the suspension is 5-10 times that of the aluminum salt.

[0014] Preferably, the concentration of the ammonia water in step S2 is 15-25%.

[0015] Preferably, in step S3, the amount of distilled water added is 10-20 times the amount of solid, the high-temperature stirring temperature is 160-190°C, the high-temperature stirring time is 3-5h, and the high-temperature calcination temperature is 400-500°C.

[0016] Based on a general inventive concept, the present invention also provides an application of a supported catalyst for synthesizing high-purity carvacrol in synthesizing high-purity carvacrol.

[0017] Preferably, the application method is: loading the supported catalyst into a fixed bed reactor, flowing o-cresol and propylene into the reactor in parallel, obtaining crude carvacrol after the reaction, and subjecting the crude carvacrol to reduced pressure distillation to obtain a high-purity carvacrol product.

[0018] Preferably, the molar ratio of o-cresol to propylene is 1:1.5-2, the reaction temperature is 150° C.-180° C., the reaction pressure is 0.05-0.15 MPa, and the reaction space velocity is 0.3-1 h -1 .

[0019] Preferably, the vacuum degree of the distillation is controlled at 95-99 KPa, and the distillation temperature is 110-140°C.

[0020] The catalytic mechanism of the supported catalyst in this scheme is as follows:

[0021] The catalyst prepared in this scheme is a supported catalyst, zinc aluminate is an effective active component and active center, and Al2O3 serves as a carrier structure to support and disperse the active component. It is used for the catalyst o-cresol propylene alkylation reaction and has a good catalytic effect.

[0022] The supported catalyst of this scheme mainly has zinc aluminate as its active component, which plays a major role in the catalytic reaction and has active centers suitable for the alkylation of o-cresol. Al2O3, as a catalyst carrier, can fix and disperse the active components, prevent the active components from coking and agglomerating, thereby preventing the formation of heavy components and coke-like products, and maintaining a high conversion rate of o-cresol and selectivity of carvacrol.

[0023] The active component zinc aluminate is prepared by a co-precipitation method, and the loading process is completed during the co-precipitation. Overall, it is a loaded catalyst, and the preparation process is also a loaded preparation process. The structure of the catalyst is characterized by the catalyst active component zinc aluminate being evenly distributed on the surface and pore surface of the carrier alumina. Zinc aluminate and alumina each maintain their own microstructure. At the microscopic level, zinc aluminate and alumina exist separately.

[0024] Due to the particularity of the active components, the catalyst of this scheme can be prepared by co-precipitation with ammonia water, and the calcination temperature during preparation is lower than that of existing catalysts. In particular, the reaction temperature during the catalytic reaction is significantly lower than that of existing catalysts, which can greatly save preparation costs and improve catalytic efficiency.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] (1) The supported modified zinc aluminate / alumina catalyst prepared by the present invention has the advantages of simple preparation method and good stability. The average conversion rate of o-cresol is more than 55%, the selectivity of carvacrol is more than 93%, the selectivity is high, the by-products are small, and the life is long.

[0027] (2) The calcination temperature of the supported catalyst prepared by this scheme is lower than that of the existing technology, and the reaction temperature involved in the reaction is significantly lower than that of the existing technology, which greatly saves the reaction cost and improves the reaction efficiency.

[0028] (3) This scheme provides the preparation process parameters of carvacrol. The reaction temperature is low, the energy consumption is significantly reduced, and there are few wastes, wastes, and wastes. It is suitable for industrial applications. The crude reaction product is purified and the purity of the obtained carvacrol is above 99.5%. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0030] Figure 1 This is a simplified diagram of the preparation process of the supported catalyst in Example 1;

[0031] Figure 2 This is the XRD pattern of the supported catalyst in Example 1;

[0032] Figure 3 This is the distribution diagram of the reaction products of the supported catalyst in Experimental Example 1;

[0033] Figure 4 This is a performance test chart of the long-term supported catalyst in Experimental Example 1. DETAILED DESCRIPTION

[0034] In order to make the technical problems, technical solutions and advantages to be solved by the present invention clearer, a detailed description will be given below with reference to the accompanying drawings and specific embodiments.

[0035] The following examples are provided to illustrate the present invention but are not intended to limit the scope of the present invention. Without departing from the spirit and substance of the present invention, modifications or substitutions made to the methods, steps or conditions of the present invention are within the scope of the present invention.

[0036] Unless otherwise specified, the technical means used in the examples are conventional means well known to those skilled in the art; unless otherwise specified, the reagents used in the examples are commercially available.

[0037] Example 1: Preparation of a supported catalyst for synthesizing high-purity carvacrol.

[0038] S1. Dissolve 100 g of Al(NO3)3·9H2O and 200 g of Zn(NO3)2·6H2O in 1000 mL of deionized water until completely dissolved. Then add 250 g of γ-alumina and stir evenly.

[0039] S2. Slowly add 20% ammonia water to the above system and stop adding when the pH reaches 8; continue stirring for 2 hours after the addition of ammonia water; filter and wash the resulting precipitate until the pH reaches neutral, and filter to separate the solid;

[0040] S3. Add 1000 g of distilled water to the washed solid to form a suspension, stir at 170° C. for 5 h, and filter the obtained solid particles; then dry at 120° C. for 18 h, and finally calcine at 450° C. for 8 h to obtain a catalyst.

[0041] The catalyst preparation process is shown in the following diagram: Figure 1 The XRD pattern of the obtained catalyst is shown in Figure 2 As shown, according to the spectrum analysis, the XRD spectrum of the catalyst prepared by the present invention has obvious characteristic peaks of spinel of zinc and aluminum oxides, indicating that the active centers of the catalyst loaded by precipitation are distributed more evenly on the carrier.

[0042] Example 2: Preparation of a supported catalyst for synthesizing high-purity carvacrol.

[0043] S1. Dissolve 100 g of Al(NO3)3·9H2O and 150 g of Zn(NO3)2·6H2O in 1000 mL of deionized water until completely dissolved. Then add 200 g of γ-alumina and stir evenly.

[0044] S2. Slowly add 20% ammonia water to the above mixture, and stop adding when the pH value reaches 8; continue stirring for 1 hour after the addition of ammonia water; filter and wash the resulting precipitate until the pH reaches neutral, and filter to separate the solid;

[0045] S3. Add 800 g of distilled water to the washed solid to form a suspension, stir at 180° C. for 3 h, and filter the obtained solid particles; then dry at 110° C. for 12 h, and finally calcine at 400° C. for 6 h to obtain a catalyst.

[0046] Example 3: Preparation of a supported catalyst for synthesizing high-purity carvacrol.

[0047] S1. Dissolve 100 g of Al(NO3)3·9H2O and 180 g of Zn(NO3)2·6H2O in 1000 mL of deionized water until completely dissolved. Then add 220 g of γ-alumina and stir evenly.

[0048] S2. Slowly add 25% ammonia water to the above mixture, and stop adding when the pH value reaches 8; continue stirring for 1.5 hours after the addition of ammonia water; filter and wash the resulting precipitate until the pH reaches neutral, and filter and separate the solid;

[0049] S3. Add 900 g of distilled water to the washed solid to form a suspension, stir at 190° C. for 4 h, and filter the obtained solid particles; then dry at 130° C. for 15 h, and finally calcine at 500° C. for 7 h to obtain a catalyst.

[0050] Example 4: Preparation of a supported catalyst for synthesizing high-purity carvacrol.

[0051] S1. Dissolve 100 g of Al(NO3)3·9H2O and 190 g of Zn(NO3)2·6H2O in 1000 mL of deionized water until completely dissolved. Then add 150 g of γ-alumina and stir evenly.

[0052] S2. Slowly add 25% ammonia water to the above mixture, and stop adding when the pH value reaches 8; continue stirring for 1.5 hours after the addition of ammonia water; filter and wash the resulting precipitate until the pH reaches neutral, and filter and separate the solid;

[0053] S3. Add 500 g of distilled water to the washed solid to form a suspension, stir at 190° C. for 3 h, and filter the obtained solid particles; then dry at 100° C. for 12 h, and finally calcine at 450° C. for 7 h to obtain a catalyst.

[0054] Example 5: Preparation of a supported catalyst for synthesizing high-purity carvacrol.

[0055] S1. Dissolve 100 g of Al(NO3)3·9H2O and 100 g of Zn(NO3)2·6H2O in 1000 mL of deionized water until completely dissolved. Then add 200 g of γ-alumina and stir evenly.

[0056] S2. Slowly add 20% ammonia water to the above mixture, and stop adding when the pH value reaches 8; continue stirring for 1 hour after the addition of ammonia water; filter and wash the resulting precipitate until the pH reaches neutral, and filter to separate the solid;

[0057] S3. Add 800 g of distilled water to the washed solid to form a suspension, stir at 180° C. for 3 h, and filter the obtained solid particles; then dry at 100° C. for 18 h, and finally calcine at 500° C. for 7 h to obtain a catalyst.

[0058] Comparative Example 1

[0059] (1) Preparation of modified Al2O3 / CuAl2O4 composite porous catalyst: 0.4 mol aluminum nitrate, 0.1 mol copper nitrate and 0.8 mol anhydrous citric acid were added to distilled water, and then 0.2 mol hexadecyltrimethylammonium bromide was added, poured into a reactor and stirred to fully dissolve, heated at 120°C, and evaporated by heating until the solution viscosity reached 113 mPas, and the solution was calcined at 650°C in an air atmosphere for 2 hours to obtain an Al2O3 / CuAl2O4 composite porous catalyst; the Al2O3 / CuAl2O4 composite porous catalyst was immersed in 0.4 mol / L ammonium sulfate solution at a soaking temperature of 65°C for 1.5 hours, dried in an oven at 100°C for 2 hours, and finally placed in a muffle furnace and calcined at 420°C to obtain a modified Al2O3 / CuAl2O4 composite porous catalyst.

[0060] (2) Preparation of carvacrol: 0.1 mol of modified Al2O3 / CuAl2O4 composite porous catalyst was loaded into the constant temperature section of the reactor and heated to 240°C. 108.14 g of o-cresol was added to the reactor and propylene was introduced at the same time. The molar ratio of o-cresol to propylene was 1:4. The reaction pressure was 0.4 MPa. The reaction liquid was collected after the reaction was completed.

[0061] Comparative Example 2: Preparation of an unsupported catalyst.

[0062] Without adding γ-alumina, the remaining steps were the same as those in Example 1.

[0063] Experimental Example 1: The effects of the catalysts prepared in Examples 1-5 and Comparative Examples 1-2 on the products in the catalytic reaction were investigated.

[0064] The catalyst prepared in Examples 1-5 was loaded into a fixed bed reactor, and o-cresol and propylene were flowed into the reactor in parallel, with a molar ratio of o-cresol to propylene of 1:1.5-2, and a reaction temperature of 150°C. The effect of high temperature on the catalytic reaction was investigated at 220°C using the catalyst prepared in Example 1, with a reaction pressure of 0.15 MPa and a reaction space velocity of 0.3 -1 h-1 , and the reaction product was refined, the vacuum degree of distillation was controlled at 99KPa, the reactor temperature was 140℃, the reaction and refining results are shown in Table 1, the distribution diagram of the supported catalyst reaction product of Example 1 is shown in Figure 3 As shown, the long-term performance test of Example 1 is as follows Figure 4 As shown:

[0065]

[0066] As can be seen from Table 1 and Examples 1-5, the catalyst prepared in this scheme has an average conversion rate of phenol of more than 55%, an o-cresol selectivity of more than 93%, and few by-products.

[0067] Figure 3 The reaction product distribution corresponding to the o-cresol alkylation catalyst prepared in Example 1 is as high as 53.9% in carvacrol content and low in by-product content.

[0068] Figure 4 The catalyst prepared in Example 1 of the present invention was stably operated for 200 h in a single pass without decreasing its activity. Although the activity of the catalyst was high at 220 ° C, it was easily coked at high temperatures. After the catalyst was operated for 150 h, its activity began to decline, and the selectivity of the target product was poor. After the catalyst in Comparative Example 1 was operated for 100 h, its activity began to decline. This is because, in this reaction system, the zinc-aluminum active component is better than the copper-aluminum active component, and the active component can inhibit coking and deactivation. In addition, the introduction of the carrier is also conducive to the dispersion of the active component and can also inhibit coking. After running for 72 h, the activity of Comparative Example 2 began to decline. This is because the catalyst of the present invention is a supported catalyst, and the carrier contributes to the uniform distribution of the active component. The XRD pattern shows an obvious spinel crystal form, and the carrier between the active centers has a good inhibitory effect on coking and sintering of the active center at high temperature. Comparative Example 1 is prepared by coprecipitation of all active components, and the active component is continuously distributed. The initial catalyst activity is high, but over time, the material easily forms coke at the active site, and the continuous active center is easily sintered, resulting in instability of the catalyst activity and a decrease in life. The actual operation data also proves this point.

[0069] Compared with Comparative Example 2, Example 1 has a phenol conversion rate increased by about 15%, a selectivity increased by nearly 5%, and a catalyst life and stability improved, indicating that the support has a significant effect on the stability of the catalyst. The catalytic support can fix and disperse the active components, prevent the active components from coking and agglomerating, thereby preventing the formation of heavy components and coke-like products, and maintaining a high conversion rate of o-cresol and selectivity of carvacrol.

[0070] Comparing the results of the reaction of the catalyst of Example 1 at 150°C and 220°C, it can be seen that increasing the reaction temperature is beneficial to improving the conversion rate of the reaction, but the selectivity of the catalyst decreases significantly. This is because as the temperature increases, the material undergoes cracking and over-alkylation, resulting in an increase in by-products; the optimal reaction temperature of the catalyst in this scheme is 150-180°C, and a low reaction temperature can effectively save costs.

[0071] The above description is only a preferred embodiment of the present invention, and the scope of protection of the present invention is not limited to the above embodiment. For those skilled in the art, improvements and modifications obtained without departing from the technical concept of the present invention should also be considered as the scope of protection of the present invention.

Claims

1. Application of a supported catalyst in the synthesis of high-purity carvacrol, characterized in that: The preparation method of the supported catalyst comprises the following steps: S1. Dissolve soluble aluminum salt and soluble zinc salt in deionized water, add Al2O3 particles, and stir evenly; S2. Slowly add aqueous ammonia to the system obtained in S1 until the pH value reaches 8-9; continue stirring for 1-2 hours after the addition of aqueous ammonia; filter and wash the obtained precipitate until the pH value reaches neutral, and filter and separate the solid; S3, washing the solid obtained in S2, adding distilled water to prepare a suspension, filtering to obtain solid particles after high temperature stirring, drying at 100-140°C for 12-20h, and finally high temperature roasting for 6-8h to obtain a supported catalyst; The mass ratio of the soluble aluminum salt, the soluble zinc salt and the Al2O3 particles is 1:1-2:1.5-2.5, and the mass of the distilled water added to form the suspension is 5-10 times that of the aluminum salt; In the step S3, the amount of distilled water added is 10-20 times of the solid, the high temperature stirring temperature is 160-190°C, the high temperature stirring time is 3-5h, and the high temperature roasting temperature is 400-500°C; The supported catalyst comprises zinc aluminate and Al2O3, wherein the Al2O3 is used as a carrier to support the zinc aluminate.

2. The use according to claim 1, characterized in that: In the step S1, the soluble aluminum salt is aluminum nitrate nonahydrate, the soluble zinc salt is zinc nitrate hexahydrate; and the Al2O3 is γ-alumina.

3. The use according to claim 1, characterized in that: The concentration of the aqueous ammonia in step S2 is 15-25%.

4. The use according to claim 1, characterized in that: The application method comprises: loading a supported catalyst into a fixed bed reactor, flowing o-cresol and propylene into the reactor in parallel, obtaining a crude carvacrol product after the reaction is completed, and subjecting the crude carvacrol product to reduced pressure distillation to obtain a high-purity carvacrol product.

5. The use according to claim 4, characterized in that: The molar ratio of o-cresol to propylene is 1:1.5-2, the reaction temperature is 150°C-180°C, the reaction pressure is 0.05-0.15 MPa, and the reaction space velocity is 0.3 -1 h -1 .

6. The use according to claim 4, characterized in that: The vacuum degree of the distillation is controlled at 95-99 KPa, and the distillation temperature is 110-140°C.

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