Isopropanolamine cyclization dehydrogenation synthesis 2,5-dimethyl pyrazine catalyst, preparation method and application

Abstract

The present application relates to the technical field of catalyst, in particular to a kind of isopropanolamine cyclization dehydrogenation synthesis 2,5-dimethylpyrazine catalyst, the preparation method of the catalyst and the application of the catalyst in isopropanolamine cyclization dehydrogenation synthesis 2,5-dimethylpyrazine reaction.The catalyst is composed of nitrogen-doped carbon-based carrier and metal elements copper element, zinc element, manganese element, potassium element on the carrier;The particle size of nitrogen-doped carbon-based carrier is 40-1000 mesh, the specific surface area is 500m 2 / g-2000m 2 / g, the average pore size is 1-30nm, nitrogen element in nitrogen-doped carbon-based carrier is directly doped into carbon skeleton or connected with carbon material by N-C bond, wherein the content of nitrogen element is 0.5wt%-10wt%.The specific surface area of the catalyst is large, its structure and chemical properties can be unchanged for a long time in catalytic reaction, which significantly improves the catalytic activity and stability of the catalyst.

Description

Technical Field

[0001] This invention relates to the field of catalyst technology, and more specifically, to a catalyst for the cyclization and dehydrogenation of isopropanolamine to synthesize 2,5-dimethylpyrazine, a method for preparing the catalyst, and the application of the catalyst in the cyclization and dehydrogenation of isopropanolamine to synthesize 2,5-dimethylpyrazine. Background Technology

[0002] 2,5-Dimethylpyrazine is a colorless or pale yellow transparent liquid with a boiling point of 155°C and a flash point of 64°C. It is soluble in water and organic solvents such as ethanol and ether. It has nutty and chocolate aromas and is a permitted flavoring agent according to my country's GB-2760-86 standard. It is commonly used in the formulation of flavorings for baked goods, coffee, meat, and nuts. Furthermore, 2,5-Dimethylpyrazine can be oxidized to 5-methylpyrazine-2-carboxylic acid, which is an intermediate in the synthesis of novel drugs such as glipizide, acipimox, and methyl 5-methylpyrazine-2-carboxylic acid.

[0003] Liquid-phase synthesis is one of the main methods for synthesizing 2,5-dimethylpyrazine, and there are several main synthetic routes: (1) synthesis from ketones containing active methylene groups. This route is complicated, has low yield, and is not suitable for large-scale industrial production; (2) synthesis from acrolein cyclization. This route uses highly toxic raw materials, and explosions are likely to occur during the reaction, posing a high safety risk; (3) synthesis from α-halomethyl ketones. This reaction requires high temperature and high pressure conditions, and has high equipment requirements; (4) synthesis by condensation of 1,2-propanediamine and 1,2-propanedione. This route easily generates 2,6-dimethylpyrazine, which will lead to a decrease in the yield of the target product, 2,5-dimethylpyrazine. In summary, liquid-phase synthesis of 2,5-dimethylpyrazine faces many challenges and is not suitable for large-scale production. There are two main routes for the gas-phase synthesis of 2,5-dimethylpyrazine: (1) cyclization reaction of 1,2-propanediamine and 1,2-propanediol. This process route is relatively short, but the selectivity of 2,5-dimethylpyrazine is poor, resulting in low yield and difficulty in separation; (2) gas-solid catalytic synthesis using isopropanolamine as raw material. However, the catalyst has a significant impact on the results.

[0004] Invention patent CN1513846A discloses a method for preparing a gas-solid phase contact catalytic catalyst for the synthesis of 2,5-dimethylpyrazine, using a Zn-Cu-Cr-Al composite condensation catalyst. This catalyst achieves a maximum yield of 86.25%, but the reaction temperature is high (380℃-420℃), resulting in significant energy consumption and increased production costs, hindering industrial application. Invention patent CN106582672B discloses a method for synthesizing a 2,5-dimethylpyrazine catalyst, comprising a SiO2 support and Cr, Cu, and Zn active components supported on the SiO2 support. This catalyst is environmentally unfriendly due to the use of the heavy metal chromium, limiting its large-scale application. Invention patent CN103949266A discloses a method for synthesizing a 2,5-dimethylpyrazine catalyst using isopropanolamine as a raw material, employing a copper, zinc, and chromium / silver mixed oxide catalyst. This catalyst achieves a maximum yield of 86.2%, but the production cost of the silver catalyst is high, and it also faces the environmental problem of using the heavy metal chromium. Summary of the Invention

[0005] To address the shortcomings of existing industrial synthesis methods for 2,5-dimethylpyrazine, this application provides a catalyst, preparation method, and application for the cyclization and dehydrogenation of isopropanolamine to synthesize 2,5-dimethylpyrazine.

[0006] The primary objective of this invention is to provide a catalyst for the cyclization and dehydrogenation synthesis of 2,5-dimethylpyrazine from isopropanolamine. The catalyst comprises a nitrogen-doped carbon-based support and supporting metal elements of copper, zinc, manganese, and potassium. The nitrogen-doped carbon-based support has a particle size of 40-1000 mesh and a specific surface area of ​​500 m². 2 / g-2000m 2 / g, with an average pore size of 1nm-30nm, nitrogen elements are directly doped into the carbon framework or connected to the carbon material by NC bonds in the nitrogen-doped carbon-based support, and the nitrogen content is 0.5wt%-10wt%.

[0007] A second objective of this invention is to provide a method for preparing the catalyst for the cyclization and dehydrogenation synthesis of 2,5-dimethylpyrazine from isopropanolamine, comprising:

[0008] S1. The carbon-based support is treated with nitric acid solution, filtered and washed until neutral, and then dried under vacuum to obtain a carbon-based support with oxygen-containing functional groups.

[0009] S2. Mix the carbon-based support with oxygen-containing functional groups with a nitrogen source and dry it to obtain a nitrogen-doped carbon-based precursor.

[0010] S3. Grind the nitrogen-doped carbon-based precursor and calcine it in a nitrogen atmosphere to obtain a nitrogen-doped carbon-based support;

[0011] S4. Mix manganese salt, potassium salt, copper salt and zinc salt evenly, dissolve and stir evenly to obtain a mixed salt solution. Impregnate the nitrogen-doped carbon-based support in the mixed salt solution to obtain a precursor solution.

[0012] S5. The precursor solution is aged, dried, and calcined in a nitrogen atmosphere to obtain the 2,5-dimethylpyrazine catalyst.

[0013] In some embodiments, step S1 satisfies at least one of the following: (1) the carbon-based support is selected from one or more of activated carbon, carbon fiber, and mesoporous carbon; (2) in the operation of treating the carbon-based support with nitric acid solution, the treatment temperature is 60℃-100℃ and the treatment time is 6h-10h, preferably the treatment temperature is 70℃-90℃ and the treatment time is preferably 7h-9h; (3) the vacuum drying treatment time is 10h-15h.

[0014] In some embodiments, step S2 satisfies at least one of the following: (1) the nitrogen source is selected from one or more of melamine, dicyandiamide, and urea, preferably dicyandiamide; (2) in the mixing operation, the mixing time is 3h-7h, preferably 4h-6h; (3) in the drying operation, the drying temperature is 100℃-140℃ and the drying time is 10h-15h, preferably 110℃-130℃ and preferably 11h-13h.

[0015] In some embodiments, step S3 satisfies at least one of the following: (1) In the calcination operation, the initial temperature is 30°C, the temperature is increased to 600°C-1000°C at a heating rate of 1°C / min-10°C / min and held for 2h-6h, preferably at a heating rate of 3°C / min-6°C / min to 700°C-900°C and held for 3h-5h; (2) The flow rate of the nitrogen atmosphere is 10mL / min-100mL / min, preferably 20mL / min-50mL / min.

[0016] In some embodiments, step S4 satisfies at least one of the following: (1) the manganese salt is selected from one or more of manganese acetate tetrahydrate, manganese nitrate tetrahydrate (II), manganese nitrate hexahydrate (II), and manganese chloride, preferably manganese nitrate tetrahydrate and / or manganese acetate tetrahydrate; (2) the potassium salt is selected from one or more of potassium acetate, potassium nitrate, and potassium chloride, preferably potassium nitrate and / or potassium chloride; (3) the copper salt is selected from one or more of copper acetate monohydrate, anhydrous copper acetate, copper nitrate trihydrate, and anhydrous copper chloride (II), preferably copper nitrate trihydrate and / or anhydrous copper chloride (II). (4) The zinc salt is selected from one or more of zinc acetate, zinc nitrate hexahydrate, and zinc chloride, preferably zinc nitrate hexahydrate and / or zinc chloride; (5) The loading of the active components on the nitrogen-doped carbon-based support is based on the mass percentage of the nitrogen-doped carbon-based support, and the mass fraction of manganese in the catalyst is 1wt%-15wt%, the mass fraction of copper is 5wt%-30wt%, the mass fraction of zinc is 5wt%-20wt%, and the mass fraction of potassium is 1wt%-15wt%.

[0017] In some embodiments, step S5 satisfies at least one of the following: (1) In the aging operation, the aging time is 10h-24h, preferably 12h-20h; (2) In the drying operation, the drying temperature is 60℃-120℃ and the drying time is 10h-24h, preferably 80℃-110℃ and preferably 15h-18h; (3) In the calcination operation, the initial temperature is 30℃, the temperature is increased to 350℃-650℃ at a heating rate of 1℃ / min-10℃ / min and held for 3h-8h, preferably 400℃-600℃ at a heating rate of 3℃ / min-6℃ / min and held for 4h-6h; (4) The atmosphere flow rate of the nitrogen atmosphere is 10mL / min-100mL / min, preferably 20mL / min-50mL / min.

[0018] A third objective of this invention is to provide a method for synthesizing 2,5-dimethylpyrazine by cyclization and dehydrogenation of isopropanolamine, wherein the catalyst used is prepared by the above-described method.

[0019] In some embodiments, the catalyst is packed into a fixed-bed reaction tube, N2 is continuously introduced and the temperature is raised to the reaction temperature, and isopropanolamine is introduced into the reaction tube, where isopropanolamine undergoes a cyclization and dehydrogenation reaction to give 2,5-dimethylpyrazine.

[0020] In some embodiments, at least one of the following is satisfied: (1) the N2 atmosphere flow rate is 5 mL / g cat / min-20mL / g cat / min, with a preferred atmosphere flow rate of 8 mL / gcat / min; (2) The reaction temperature is 200℃-320℃, preferably 250℃; (3) The feed rate of isopropanolamine is 1g / g cat / h-3g / g cat The preferred feed rate is 1.5 g / g / h. cat / h; (4) The amount of catalyst used is 0.33g / g-1g / g based on the mass of isopropanolamine.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] (1) This invention relates to a catalyst for the cyclization dehydrogenation synthesis of 2,5-dimethylpyrazine by isopropanolamine. The catalyst is prepared by nitrogen-doped carbon-based support. The resulting catalyst has a large specific surface area. The incorporation of electron-rich nitrogen can increase the π electron density of the carbon-based support, promote the exposure of active sites in the reactants, and maintain its structure and chemical properties unchanged for a long time during the catalytic reaction, thus significantly improving the catalytic activity and stability of the catalyst.

[0023] (2) This invention relates to a method for preparing a catalyst for the cyclization dehydrogenation synthesis of 2,5-dimethylpyrazine using isopropanolamine. The preparation method uses a nitrogen-doped carbon-based support and metal elements copper, zinc, manganese and potassium supported on the nitrogen-doped carbon-based support as active components. The preparation method is inexpensive and the catalyst obtained has high activity, high stability, few side reactions and low energy consumption. Based on the above characteristics, the catalyst obtained by this preparation method is suitable for large-scale industrial production of 2,5-dimethylpyrazine.

[0024] (3) This invention relates to a method for synthesizing 2,5-dimethylpyrazine by cyclization and dehydrogenation of isopropanolamine. For the first time, 2,5-dimethylpyrazine is synthesized by hydrogen-free reduction. Compared with existing methods for synthesizing 2,5-dimethylpyrazine, the method provided in this application consumes less energy, saves costs, has a yield of 2,5-dimethylpyrazine >70%, and the synthesized 2,5-dimethylpyrazine generally has high purity. Furthermore, it can operate stably for 120 hours under the reaction conditions. Attached Figure Description

[0025] Figure 1 This is a catalyst stability test curve for Example 2 of this application;

[0026] Figure 2 This is a catalyst stability test curve for Example 4 of this application;

[0027] Figure 3 This is a catalyst stability test curve for Example 7 of this application. Detailed Implementation

[0028] The present invention will be further described below with reference to specific embodiments. These embodiments are only used to more clearly illustrate the technical solutions of the present invention and should not be construed as limiting the scope of protection of the present invention. Anything not described in detail in the present invention patent application is considered to be common knowledge in the art.

[0029] Example 1

[0030] This embodiment provides a catalyst for the cyclization and dehydrogenation synthesis of 2,5-dimethylpyrazine from isopropanolamine. The catalyst comprises a nitrogen-doped mesoporous carbon support and metal elements supported on the nitrogen-doped mesoporous carbon support. The loading of the active components on the nitrogen-doped mesoporous carbon support is based on the mass percentage of the nitrogen-doped mesoporous carbon support. The catalyst contains 1 wt% manganese, 1 wt% potassium, 5 wt% copper, and 5 wt% zinc.

[0031] The specific preparation method of this catalyst is as follows:

[0032] S1. Take 2g of mesoporous carbon, treat the mesoporous carbon with 100mL of 5mol / L nitric acid solution at 60℃ for 6h, then filter and wash with deionized water until neutral, and vacuum dry for 10h to obtain mesoporous carbon with oxygen-containing functional groups.

[0033] S2. The treated mesoporous carbon with oxygen-containing functional groups and 2g of melamine were stirred in 100mL of deionized water at room temperature for 3h, and then dried in a 100℃ forced-air drying oven for 10h to obtain nitrogen-doped mesoporous carbon precursor.

[0034] S3. After grinding the nitrogen-doped mesoporous carbon precursor, place it in a tube furnace and raise the temperature to 600℃ at a rate of 1℃ / min under a nitrogen atmosphere of 10mL / min. Hold the temperature for 2h and then let it cool naturally to room temperature to obtain the nitrogen-doped mesoporous carbon support.

[0035] S4. Weigh out 0.0457g of Mn(NO3)2·4H2O, 0.0259g of KNO3, 0.1901g of Cu(NO3)2·3H2O and 0.2275g of Zn(NO3)2·6H2O respectively, mix them evenly, dissolve them in 100mL of deionized water, stir evenly to obtain a mixed salt solution, and impregnate 1g of nitrogen-doped mesoporous carbon support in the mixed salt solution to obtain a precursor solution;

[0036] S5. The precursor solution obtained in step S4 is aged for 12 hours, then placed in a forced-air drying oven and dried at 60°C for 12 hours. After that, it is placed in a tube furnace and heated to 350°C at a rate of 1°C / min under a nitrogen atmosphere of 10 mL / min and held for 3 hours. It is then naturally cooled to room temperature to obtain the catalyst.

[0037] Example 2

[0038] This embodiment provides a catalyst for the cyclization and dehydrogenation synthesis of 2,5-dimethylpyrazine from isopropanolamine. The catalyst and preparation method are basically the same as those in Example 1, except that the carbon-based support is an equal amount of activated carbon.

[0039] Example 3

[0040] This embodiment provides a catalyst for the cyclization and dehydrogenation synthesis of 2,5-dimethylpyrazine from isopropanolamine. The catalyst and preparation method are basically the same as those in Example 1, except that the carbon-based support is an equal amount of carbon fiber.

[0041] Example 4

[0042] This embodiment provides a catalyst for the cyclization and dehydrogenation synthesis of 2,5-dimethylpyrazine from isopropanolamine. The catalyst comprises a nitrogen-doped activated carbon support and metal elements supported on the nitrogen-doped activated carbon support. The loading of active components on the nitrogen-doped activated carbon support is based on the mass percentage of the nitrogen-doped activated carbon support. The catalyst contains 5 wt% manganese, 5 wt% potassium, 15 wt% copper, and 10 wt% zinc.

[0043] The specific preparation method of this catalyst is as follows:

[0044] S1. Take 2g of activated carbon, take 100mL of 5mol / L nitric acid solution and treat the activated carbon at 80℃ for 8h. Then filter and wash with deionized water until neutral, and vacuum dry for 12h to obtain activated carbon with oxygen-containing functional groups.

[0045] S2. The treated activated carbon with oxygen-containing functional groups and 2g of dicyandiamide were stirred in 100mL of deionized water at room temperature for 5h, and then dried in a 120℃ forced-air drying oven for 12h to obtain nitrogen-doped activated carbon precursor.

[0046] S3. After grinding the nitrogen-doped activated carbon precursor, place it in a tube furnace and raise the temperature to 800°C at a rate of 5°C / min under a nitrogen atmosphere of 20 mL / min. Hold the temperature for 4 hours and then allow it to cool naturally to room temperature to obtain the nitrogen-doped activated carbon support.

[0047] S4. Weigh out 0.2284g of Mn(NO3)2·4H2O, 0.129g of KNO3, 0.5703g of Cu(NO3)2·3H2O and 0.455g of Zn(NO3)2·6H2O respectively, mix them evenly, dissolve them in 100mL of deionized water, stir evenly to obtain a mixed salt solution, and impregnate 1g of nitrogen-doped activated carbon support in the mixed salt solution to obtain a precursor solution.

[0048] S5. The precursor solution obtained in step S4 is aged for 15 hours, then placed in a forced-air drying oven and dried at 80°C for 15 hours. After that, it is placed in a tube furnace and heated to 450°C at a rate of 5°C / min under a nitrogen atmosphere of 50 mL / min and held for 5 hours. It is then naturally cooled to room temperature to obtain the catalyst.

[0049] Example 5

[0050] This embodiment provides a catalyst for the cyclization and dehydrogenation synthesis of 2,5-dimethylpyrazine from isopropanolamine. The catalyst and preparation method are basically the same as those in Example 4, except that the carbon-based support is an equal amount of mesoporous carbon.

[0051] Example 6

[0052] This embodiment provides a catalyst for the cyclization and dehydrogenation synthesis of 2,5-dimethylpyrazine from isopropanolamine. The catalyst and preparation method are basically the same as those in Example 4, except that the carbon-based support is an equal amount of carbon fiber.

[0053] Example 7

[0054] This embodiment provides a catalyst for the cyclization and dehydrogenation synthesis of 2,5-dimethylpyrazine from isopropanolamine. The catalyst comprises a nitrogen-doped carbon fiber support and metal elements supported on the nitrogen-doped carbon fiber support. The loading of the active components on the nitrogen-doped carbon fiber support is based on the mass percentage of the nitrogen-doped carbon fiber support. The catalyst contains 5 wt% manganese, 15 wt% potassium, 30 wt% copper, and 5 wt% zinc.

[0055] The specific preparation method of this catalyst is as follows:

[0056] S1. Take 2g of carbon fiber, take 100mL of 5mol / L nitric acid solution and treat the activated carbon at 100℃ for 10h. Then filter and wash with deionized water until neutral, and vacuum dry for 15h to obtain carbon fiber with oxygen-containing functional groups.

[0057] S2. The treated carbon fibers with oxygen-containing functional groups were stirred with 2g of urea in 100mL of deionized water at room temperature for 7h, and then dried in a forced-air drying oven at 140℃ for 14h to obtain nitrogen-doped carbon fiber precursor.

[0058] S3. After grinding the nitrogen-doped carbon fiber precursor, it was placed in a tube furnace and heated to 1000℃ at a heating rate of 10℃ / min under a nitrogen atmosphere of 30mL / min and held for 6h. Finally, it was naturally cooled to room temperature to obtain the nitrogen-doped carbon fiber carrier.

[0059] S4. Weigh out 0.2284g of Mn(NO3)2·4H2O, 0.3879g of KNO3, 1.1406g of Cu(NO3)2·3H2O and 0.2275g of Zn(NO3)2·6H2O respectively, mix them evenly, dissolve them in 100mL of deionized water, stir evenly to obtain a mixed salt solution, and impregnate 1g of nitrogen-doped carbon fiber support in the mixed salt solution to obtain a precursor solution;

[0060] S5. The precursor solution obtained in step S4 is aged for 24 hours, then placed in a forced-air drying oven and dried at 120°C for 24 hours. After that, it is placed in a tube furnace and heated to 650°C at a rate of 10°C / min under a nitrogen atmosphere of 100 mL / min and held at that temperature for 8 hours. It is then naturally cooled to room temperature to obtain the catalyst.

[0061] Example 8

[0062] This embodiment provides a catalyst for the cyclization and dehydrogenation synthesis of 2,5-dimethylpyrazine from isopropanolamine. The catalyst and preparation method are basically the same as those in Example 7, except that the carbon-based support is an equal amount of activated carbon.

[0063] Example 9

[0064] This embodiment provides a catalyst for the cyclization and dehydrogenation synthesis of 2,5-dimethylpyrazine from isopropanolamine. The catalyst comprises a nitrogen-doped mesoporous carbon support and metal elements supported on the nitrogen-doped mesoporous carbon support. The loading of the active components on the nitrogen-doped mesoporous carbon support is based on the mass percentage of the nitrogen-doped mesoporous carbon support. The catalyst contains 15 wt% manganese, 5 wt% potassium, 10 wt% copper, and 20 wt% zinc.

[0065] The specific preparation method of this catalyst is as follows:

[0066] S1. Take 2g of mesoporous carbon, take 100mL of 5mol / L nitric acid solution and treat the activated carbon at 100℃ for 10h. Then filter and wash with deionized water until neutral, and vacuum dry for 15h to obtain mesoporous carbon with oxygen-containing functional groups.

[0067] S2. The treated mesoporous carbon with oxygen-containing functional groups was stirred with 2g of urea in 100mL of deionized water at room temperature for 7h, and then dried in a 140℃ forced-air drying oven for 14h to obtain nitrogen-doped mesoporous carbon precursor.

[0068] S3. After grinding the nitrogen-doped mesoporous carbon precursor, place it in a tube furnace and raise the temperature to 1000℃ at a rate of 10℃ / min under a nitrogen atmosphere of 100mL / min and hold for 6h. Finally, allow it to cool naturally to room temperature to obtain the nitrogen-doped mesoporous carbon support.

[0069] S4. Weigh out 0.6853g of Mn(NO3)2·4H2O, 0.1293g of KNO3, 0.3802g of Cu(NO3)2·3H2O and 0.91g of Zn(NO3)2·6H2O respectively, mix them evenly, dissolve them in 100mL of deionized water, stir evenly to obtain a mixed salt solution, and impregnate 1g of nitrogen-doped mesoporous carbon support in the mixed salt solution to obtain a precursor solution;

[0070] S5. The precursor solution obtained in step S4 is aged for 12 hours, then placed in a forced-air drying oven and dried at 100°C for 12 hours. After that, it is placed in a tube furnace and heated to 500°C at a rate of 3°C / min under a nitrogen atmosphere of 30 mL / min and held for 6 hours. It is then naturally cooled to room temperature to obtain the catalyst.

[0071] Example 10

[0072] This embodiment provides a catalyst for the cyclization and dehydrogenation synthesis of 2,5-dimethylpyrazine from isopropanolamine. The catalyst and preparation method are basically the same as those in Example 9, except that the carbon-based support is an equal amount of carbon fiber.

[0073] Example 11

[0074] This embodiment provides a catalyst for the cyclization and dehydrogenation synthesis of 2,5-dimethylpyrazine from isopropanolamine. The catalyst and preparation method are basically the same as those in Example 9, except that the carbon-based support is an equal amount of activated carbon.

[0075] Experimental Example 1

[0076] To verify the stability of the catalysts in each example, the catalysts prepared in Examples 2, 4, and 7 were selected for stability testing, and the results are as follows: Figures 1 to 3 As shown.

[0077] Figure 1 The results showed that after the catalyst prepared in Example 2 was continuously reacted for 120 h at a reaction temperature of 250 °C, a feed rate of isopropanolamine of 1.2 g / h, and a N2 flow rate of 10 mL / min, the catalyst activity decreased by about 30.5% to 69.5%; the yield of 2,5-dimethylpyrazine decreased by about 25.3% to 35.2%.

[0078] Figure 2 The results showed that after the catalyst prepared in Example 4 was continuously reacted for 120 h at a reaction temperature of 280 °C, a feed rate of isopropanolamine of 1.5 g / h, and a N2 flow rate of 8 mL / min, the catalyst activity decreased by about 5.65% to 94.35%; the yield of 2,5-dimethylpyrazine decreased by about 17.2% to 57.3%.

[0079] Figure 3 The results showed that after the catalyst prepared in Example 7 was continuously reacted for 120 h at a reaction temperature of 320 °C, a feed rate of isopropanolamine of 3 g / h, and a N2 flow rate of 20 mL / min, the catalyst activity decreased by about 19.6% to 80.4%; the yield of 2,5-dimethylpyrazine decreased by about 21.2% to 44.7%.

[0080] Experimental Example 2

[0081] To verify the catalyst activity in each example, 1g of the catalyst prepared in the above examples was used in the reaction of isopropanolamine cyclization and dehydrogenation to synthesize 2,5-dimethylpyrazine. The yield and purity of the product 2,5-dimethylpyrazine were detected by Fuli GC9790Plus gas chromatograph and STI501 isocratic high performance liquid chromatograph to determine the catalyst activity.

[0082] This application employs a continuous gas-solid phase contact catalytic reaction to synthesize 2,5-dimethylpyrazine, with the following reaction formula:

[0083]

[0084] The specific method is as follows: The catalyst is loaded into a fixed-bed reaction tube, N2 is continuously introduced and the temperature is raised to the reaction temperature, isopropanolamine is introduced into the reaction tube, and isopropanolamine undergoes a cyclization and dehydrogenation reaction to yield 2,5-dimethylpyrazine. The specific reaction conditions include the following five:

[0085] (1) 1g of catalyst was packed into a fixed bed reaction tube and N2 was introduced at a flow rate of 20mL / min. When the reactor temperature was raised to 200℃, the raw material isopropanolamine was fed into the reactor at a rate of 1g / h and N2 was continuously introduced at a flow rate of 5mL / min to make isopropanolamine undergo cyclization dehydrogenation reaction to obtain 2,5-dimethylpyrazine.

[0086] (2) 1g of catalyst was packed into a fixed bed reaction tube and N2 was introduced at a flow rate of 20mL / min. When the reactor temperature was raised to 280℃, the raw material isopropanolamine was fed into the reactor at a rate of 1.5g / h and N2 was continuously introduced at a flow rate of 8mL / min to make isopropanolamine undergo cyclization dehydrogenation reaction to obtain 2,5-dimethylpyrazine.

[0087] (3) 1g of catalyst was packed into a fixed bed reaction tube and N2 was introduced at a flow rate of 20mL / min. When the reactor temperature was raised to 320℃, the raw material isopropanolamine was fed into the reactor at a rate of 3g / h and N2 was continuously introduced at a flow rate of 20mL / min to make isopropanolamine undergo cyclization dehydrogenation reaction to obtain 2,5-dimethylpyrazine.

[0088] (4) 1g of catalyst was packed into a fixed bed reaction tube and N2 was introduced at a flow rate of 20mL / min. When the reactor temperature was raised to 300℃, the raw material isopropanolamine was fed into the reactor at a rate of 2g / h and N2 was continuously introduced at a flow rate of 15mL / min to make isopropanolamine undergo cyclization dehydrogenation reaction to obtain 2,5-dimethylpyrazine.

[0089] (5) 1g of catalyst was packed into a fixed bed reaction tube and N2 was introduced at a flow rate of 20mL / min. When the reactor temperature reached 250℃, the raw material isopropanolamine was fed into the reactor at a rate of 1.2g / h and N2 was continuously introduced at a flow rate of 10mL / min to make isopropanolamine undergo cyclization dehydrogenation reaction to obtain 2,5-dimethylpyrazine.

[0090] The catalysts prepared in Examples 1-11 were applied to the synthesis of 2,5-dimethylpyrazine under five different conditions to obtain the product 2,5-dimethylpyrazine. The yield and purity of 2,5-dimethylpyrazine were determined, and the results are shown in Table 1.

[0091] Table 1. Yield and purity of product 2,5-dimethylpyrazine

[0092] Example 1 Yield 40.8%, purity 90.2% Example 2 Yield: 60.5%; Purity: 92% Example 3 Yield: 55.7%; Purity: 70.3% Example 4 Yield 74.5%, purity 99.5% Example 5 Yield: 59.2%; Purity: 90.3% Example 6 Yield: 40.6%; Purity: 86.9% Example 7 Yield: 65.9%; Purity: 95.1% Example 8 Yield 66.2%, purity 80% Example 9 Yield 70.5%, purity 96.5% Example 10 Yield: 35.6%; Purity: 91.2% Example 11 Yield: 50.4%; Purity: 88.4%

[0093] The catalytic test results of the above catalyst on the cyclization and dehydrogenation of isopropanolamine to synthesize 2,5-dimethylpyrazine show that the catalyst prepared with appropriate loading and calcination temperature possesses excellent catalytic activity and stability. Compared with other existing methods for synthesizing 2,5-dimethylpyrazine, this invention is the first to synthesize 2,5-dimethylpyrazine using a hydrogen-free reduction method, which consumes less energy, saves costs, and generally produces 2,5-dimethylpyrazine with high purity.

[0094] Based on the preferred embodiments of the present invention described above, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. The application of a catalyst in the cyclization and dehydrogenation of isopropanolamine to synthesize 2,5-dimethylpyrazine, characterized in that, The catalyst is composed of a nitrogen-doped carbon-based support and supporting metallic elements copper, zinc, manganese, and potassium; the nitrogen-doped carbon-based support has a particle size of 40-1000 mesh and a specific surface area of ​​500 m². 2 / g-2000m 2 / g, with an average pore size of 1nm-30nm, wherein nitrogen is directly doped into the carbon framework or connected to the carbon material via NC bonds, and the nitrogen content is 0.5wt%-10wt%; The method for preparing the catalyst includes: S1. The carbon-based support is treated with nitric acid solution, filtered and washed until neutral, and then dried under vacuum to obtain a carbon-based support with oxygen-containing functional groups. S2. The carbon-based support with oxygen-containing functional groups is mixed with a nitrogen source and dried to obtain a nitrogen-doped carbon-based precursor; S3. Grind the nitrogen-doped carbon-based precursor and calcine it in a nitrogen atmosphere to obtain a nitrogen-doped carbon-based support; S4. Mix manganese salt, potassium salt, copper salt and zinc salt evenly, dissolve and stir evenly to obtain a mixed salt solution, and immerse the nitrogen-doped carbon-based support in the mixed salt solution to obtain a precursor solution; S5. The precursor solution is aged, dried, and calcined in a nitrogen atmosphere to obtain the catalyst.

2. The application according to claim 1, characterized in that, The catalyst was packed into a fixed-bed reaction tube, N2 was continuously introduced and the temperature was raised to the reaction temperature, and isopropanolamine was introduced into the reaction tube. The isopropanolamine underwent a cyclization and dehydrogenation reaction to obtain 2,5-dimethylpyrazine.

3. The application according to claim 2, characterized in that, At least one of the following must be met: (1) The flow rate of the N2 atmosphere is 5 mL / g cat / min-20mL / g cat / min; (2) The reaction temperature is 200℃-320℃; (3) The feed rate of the isopropanolamine is 1 g / g cat / h-3g / g cat / h; (4) The amount of the catalyst used is 0.33 g / g to 1 g / g based on the mass of isopropanolamine.

4. The application according to claim 3, characterized in that, The flow rate of the N2 atmosphere was 8 mL / g. cat / min.

5. The application according to claim 3, characterized in that, The reaction temperature is 250°C.

6. The application according to claim 3, characterized in that, The feed rate of the isopropanolamine is 1.5 g / g. cat / h.

7. The application according to claim 1, characterized in that, Step S1 must satisfy at least one of the following: (1) The carbon-based support is selected from one or more of activated carbon, carbon fiber, and mesoporous carbon; (2) In the operation of treating with nitric acid solution, the treatment temperature is 60℃-100℃ and the treatment time is 6h-10h; (3) The vacuum drying process takes 10-15 hours.

8. The application according to claim 7, characterized in that, In the operation of treating the carbon-based support with nitric acid solution, the treatment temperature is 70℃-90℃ and the treatment time is 7h-9h.

9. The application according to claim 1, characterized in that, Step S2 must satisfy at least one of the following: (1) The nitrogen source is selected from one or more of melamine, dicyandiamide, and urea; (2) In the mixing operation, the mixing time is 3h-7h; (3) In the drying operation, the drying temperature is 100℃-140℃ and the drying time is 10h-15h.

10. The application according to claim 9, characterized in that, The nitrogen source is dicyandiamide.

11. The application according to claim 9, characterized in that, The mixing time in the mixing operation is 4-6 hours.

12. The application according to claim 9, characterized in that, In the drying operation described in step S2, the drying temperature is 110℃-130℃ and the drying time is 11h-13h.

13. The application according to claim 1, characterized in that, Step S3 must satisfy at least one of the following: (1) In the calcination operation, the initial temperature is 30℃, and the temperature is increased to 600℃-1000℃ at a heating rate of 1℃ / min-10℃ / min and held for 2h-6h; (2) The flow rate of the nitrogen atmosphere is 10 mL / min-100 mL / min.

14. The application according to claim 13, characterized in that, In the calcination operation described in step S3, the temperature is increased to 700℃-900℃ at a heating rate of 3℃ / min-6℃ / min and held for 3h-5h.

15. The application according to claim 13, characterized in that, The flow rate of the nitrogen atmosphere in step S3 is 20 mL / min to 50 mL / min.

16. The application according to claim 1, characterized in that, Step S4 must satisfy at least one of the following: (1) The manganese salt is selected from one or more of manganese acetate tetrahydrate, manganese nitrate tetrahydrate (II), manganese nitrate hexahydrate (II), and manganese chloride; (2) The potassium salt is selected from one or more of potassium acetate, potassium nitrate, and potassium chloride; (3) The copper salt is selected from one or more of copper acetate monohydrate, anhydrous copper acetate, copper nitrate trihydrate, and anhydrous copper chloride (II); (4) The zinc salt is selected from one or more of zinc acetate, zinc nitrate hexahydrate, and zinc chloride; (5) The loading of active components on the nitrogen-doped carbon-based support is expressed as the mass percentage of the nitrogen-doped carbon-based support. The mass fraction of manganese in the catalyst is 1wt%-15wt%, the mass fraction of copper is 5wt%-30wt%, the mass fraction of zinc is 5wt%-20wt%, and the mass fraction of potassium is 1wt%-15wt%.

17. The application according to claim 16, characterized in that, The manganese salt is manganese nitrate (II) tetrahydrate and / or manganese acetate tetrahydrate.

18. The application according to claim 16, characterized in that, The potassium salt is potassium nitrate and / or potassium chloride.

19. The application according to claim 16, characterized in that, The copper salt is copper nitrate trihydrate and / or anhydrous copper chloride (II).

20. The application according to claim 16, characterized in that, The zinc salt is zinc nitrate hexahydrate and / or zinc chloride.

21. The application according to claim 1, characterized in that, Step S5 must satisfy at least one of the following: (1) In the aging process, the aging time is 10h-24h; (2) In the drying operation, the drying temperature is 60℃-120℃ and the drying time is 10h-24h; (3) In the calcination operation, the initial temperature is 30℃, and the temperature is increased to 350℃-650℃ at a heating rate of 1℃ / min-10℃ / min and held for 3h-8h; (4) The flow rate of the nitrogen atmosphere is 10 mL / min-100 mL / min.

22. The application according to claim 21, characterized in that, In the aging process, the aging time is 12h-20h.

23. The application according to claim 21, characterized in that, In the drying operation described in step S5, the drying temperature is 80℃-110℃ and the drying time is 15h-18h.

24. The application according to claim 21, characterized in that, In the calcination operation described in step S5, the temperature is increased to 400℃-600℃ at a heating rate of 3℃ / min-6℃ / min and held for 4h-6h.

25. The application according to claim 21, characterized in that, The flow rate of the nitrogen atmosphere in step S5 is 20 mL / min to 50 mL / min.

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