Method for preparing 2-cyanopyridine by fixed bed sectional temperature control

Abstract

The invention discloses a method for preparing 2-cyanopyridine through fixed bed sectional temperature control, and belongs to the field of chemical engineering. The invention discloses a method for preparing 2-cyanopyridine by sectional temperature control of a fixed bed, which is characterized in that the reaction is controlled in a catalytic bed at multiple sections of different temperatures, the bed temperature is controlled, and side reactions are reduced, so that the yield of the prepared 2-cyanopyridine is more than or equal to 90%, the conversion rate of 2-methylpyridine is more than 99.9%, and the reaction selectivity is more than 90%.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for preparing 2-cyanopyridine by fixed bed segmented temperature control, belonging to the field of chemical industry. BACKGROUND

[0002] 2-cyanopyridine is an important organic compound with the chemical formula C6H4N2 and a molecular weight of 104.11. It appears as white to light yellow crystals at low temperatures and is insoluble in water but has good solubility in organic solvents. 2-cyanopyridine has weak basicity and can act as a Lewis base in reactions. It has good thermal stability and can be used at high temperatures. In addition, 2-cyanopyridine has low solubility in water but good solubility in organic solvents. 2-cyanopyridine has wide applications in various fields: as an intermediate product in the pharmaceutical and dye industries for the production of various organic compounds. It is used in analytical chemistry and coordination chemistry as a complexing agent for metal ions in basic chemical research. It also has wide applications in organic synthesis, especially in the production of pyridine-based pharmaceutical molecules.

[0003] The existing technology for catalytic synthesis of 2-cyanopyridine still has problems such as uneven distribution of bed layer fractions and high content of by-products. For example, patent CN101602720A uses 2-methylpyridine and ammonia as raw materials to generate 2-cyanopyridine through ammonia oxidation reaction in a fixed bed reactor with high-activity catalyst. However, this method for synthesizing 2-cyanopyridine causes the ammonia oxidation reaction to concentrate at the front end of the catalyst, resulting in uneven temperature distribution and possible bed temperature rise during the reaction process, which increases the by-product reaction of pyridine, affects the yield of the finished product, and may cause problems such as catalyst coking due to temperature runaway.

[0004] Patent CN110804014A uses 2-pyridinecarboxamide as raw material to react with oxygen-containing gas and ammonia at 350-400℃ to generate 2-cyanopyridine. The conversion rate of 2-pyridinecarboxamide obtained by this method is >98% and the product yield is >86%. This method mainly obtains 2-cyanopyridine by dehydration of 2-pyridinecarboxamide. However, during the dehydration process, other sensitive sites on the pyridine ring may undergo side reactions (such as oxidation, ring opening, or halogenation), leading to an increase in impurities. At the same time, the amide group may not be completely converted to cyanide, and the residual raw material needs to be separated through complex purification steps, which also reduces the overall yield.

[0005] However, the existing technology for catalytic synthesis of 2-cyanopyridine all uses a single-layer fixed bed method to improve the overall yield, and there is no technology for segmented temperature control for the preparation of 2-cyanopyridine by ammonia oxidation.

[0006] Therefore, how to improve the problems of low production efficiency, high byproduct content and high production cost caused by traditional catalytic method has important research significance. SUMMARY

[0007] The application provides a method for preparing 2-cyanopyridine by fixed bed segmented temperature control, which controls the reaction in the catalytic bed at different temperatures in multiple stages, reduces the occurrence of side reactions by controlling the bed temperature, and improves the yield of finished products.

[0008] The first object of the application is to provide a method for preparing 2-cyanopyridine based on fixed bed segmented temperature control, comprising the steps of: (1) Preparation of catalyst: mix TiO2 with 2.0-5.0 g / L ammonium metavanadate solution, stir, filter, dry, calcine, cool, repeat stirring, filtering, drying, calcining and cooling 5-6 times to obtain a catalyst with V2O5 active component accounting for 9-11%, add K2O with a final concentration of 0.3-0.7% (w / w) to the catalyst, and finally obtain a vanadium-based modified 2-cyanopyridine catalyst; (2) Catalytic reaction: fill the catalyst into the bed layer of a fixed bed reactor containing three layers of fixed bed, the bed layers are named bed layer 1, bed layer 2 and bed layer 3 from top to bottom; mix 2-methylpyridine, ammonia and air after preheating, and pass into the fixed bed reactor at a flow rate of 10-30 g / h for reaction, collect the reaction liquid from the outlet after 1-3 h of continuous feeding to obtain 2-cyanopyridine; Wherein, the reaction temperature in bed layer 1 is 280-300℃; Wherein, the reaction temperature in bed layer 2 is 335-350℃; Wherein, the reaction temperature in bed layer 3 is 370-385℃.

[0009] In one embodiment, the addition ratio of TiO2 to 2.0-5.0 g / L ammonium metavanadate solution in step (1) is 130-230 g: 700-1000 mL.

[0010] In one embodiment, the preheating temperature in step (2) is 180-220℃.

[0011] In one embodiment, in step (2), the volume ratio of the three layers of fixed bed from top to bottom is 80-100: 55-68: 73-100.

[0012] In one embodiment, in step (2), the molar ratio of 2-methylpyridine: ammonia: air is 1-10: 45-55: 300-360.

[0013] In an embodiment, the doping in step (1) is adding a KNO3 solution containing 1-4 g of KNO3 to the catalyst under stirring, sealing and drying at 90-110℃ for 1-3 h after the liquid is completely absorbed, and calcining at 400-500℃ for 5-7 h.

[0014] A second object of the present application is to provide a method for simultaneously improving the catalytic efficiency of 2-cyanopyridine, comprising the steps of: (1) Preparation of the catalyst: mixing TiO2 with 2.0-5.0 g / L of ammonium metavanadate solution, stirring, filtering, drying, calcining, and cooling, and repeating the stirring, filtering, drying, calcining, and cooling for 5-6 times to obtain a catalyst with a V2O5 active component content of 9-11%, adding K2O to the catalyst to a final concentration of 0.3-0.7% (w / w), and finally obtaining a vanadium-based modified 2-cyanopyridine catalyst; (2) Catalytic reaction: filling the catalyst into the bed layers of a fixed bed reactor containing three fixed bed layers, with the bed layers being named bed layer 1, bed layer 2, and bed layer 3 from top to bottom; preheating 2-methylpyridine, ammonia, and air to 180-220℃, mixing, and passing into the fixed bed reactor at a flow rate of 10-30 g / h for reaction, collecting the reaction liquid from the outlet after 1-3 h of continuous feeding to obtain 2-cyanopyridine, wherein the reaction temperature in bed layer 1 is 280-300℃; wherein the reaction temperature in bed layer 2 is 335-350℃; wherein the reaction temperature in bed layer 3 is 370-385℃.

[0015] In an embodiment, the addition ratio of TiO2 to 2.0-5.0 g / L of ammonium metavanadate solution in step (1) is 130-230 g: 700-1000 mL.

[0016] In an embodiment, the volume ratio of the catalyst filled in the three fixed bed layers from top to bottom in step (2) is 80-100: 55-68: 73-100.

[0017] In an embodiment, the molar ratio of 2-methylpyridine: ammonia: air in step (2) is 1-10: 45-55: 300-360.

[0018] A third object of the present application is to provide the use of the above-mentioned method in the preparation of 2-cyanopyridine.

[0019] Advantages The segmented temperature control technology can realize precise temperature gradient control, optimize the temperature of each reaction stage through segmented temperature control, improve the reaction selectivity, reduce the generation of by-products, and enhance the active metal adsorption efficiency, thereby improving the product yield (≥90%). Meanwhile, local overheating can be inhibited, the temperature is prevented from rising sharply due to strong exothermic reaction, the catalyst life is prolonged, and high conversion rate (>99.9%) is maintained. DETAILED DESCRIPTION

[0020] The application will be further described in conjunction with specific examples. These examples are only used to illustrate the application and are not used to limit the scope of the application. Unless specific conditions are indicated in the following examples, the experimental methods are generally in accordance with the conventional conditions in the art. Unless otherwise defined, all professional and scientific terms used herein have the same meaning as familiar to those skilled in the art.

[0021] Source of raw materials: The TiO2 carrier was purchased from Suzhou Hongfeng Titanium Industry Co., Ltd.; Ammonium metavanadate was purchased from Jinan Jiayang Chemical Co., Ltd.; The determination methods and experimental methods involved in the following examples are as follows: 1. Determination of 2-cyanopyridine yield High performance liquid chromatography (HPLC) method was used, and the chromatographic conditions were selected as follows: C18 column, 2-cyanopyridine as internal standard, and determination of 2-cyanopyridine aqueous solution content; The calculation formula of the absorption rate is as follows:

[0022] In the formula: γ: 2-cyanopyridine yield; m1: mass of aqueous solution; wt 1%: 2-cyanopyridine mass content; M1: molecular weight of 2-methylpyridine; M2: molecular weight of 2-cyanopyridine; m2: feed amount.

[0023] 2. Determination of 2-methylpyridine conversion rate High performance liquid chromatography (HPLC) method was used, and 2-methylpyridine was used as an internal standard to determine the content of 2-methylpyridine aqueous solution.

[0024] The calculation formula of the 2-methylpyridine conversion rate is as follows:

[0025] In the formula: α: 2-methylpyridine conversion rate; m1: mass of aqueous solution; wt 2%: 2-methylpyridine mass content; m2: feed amount.

[0026] 3. Determination of 2-cyanopyridine reaction selectivity The reaction selectivity of the present application refers to the ability of catalyzing the oxidation of ammonia to generate 2-cyanopyridine, reducing the generation of by-products pyridine and 2-pyridinecarboxamide.

[0027] The calculation formula of 2-cyanopyridine reaction selectivity is as follows: 2-cyanopyridine reaction selectivity = 2-cyanopyridine yield / 2-methylpyridine conversion rate x 100%; 4. Determination of the content of by-product 2-pyridinecarboxamide The content of 2-pyridinecarboxamide aqueous solution is determined by high performance liquid chromatography (HPLC) method with 2-pyridinecarboxamide as an internal standard.

[0028] 5. Determination of the content of by-product pyridine The content of pyridine aqueous solution is determined by high performance liquid chromatography (HPLC) method with pyridine as an internal standard.

[0029] Examples 1-6 1. Preparation of vanadium modified 2-cyanopyridine catalyst Put 150 g TiO2 carrier into 1000 mL of 3.8 g / L ammonium metavanadate solution, stir at 450 rpm for 30 min, then filter to obtain a filter product; after drying, the filter product is placed in a muffle furnace and calcined at 450℃ for 14 h, then cooled, and the process of stirring, filtering, drying, calcining and cooling is repeated 5 times to obtain a catalyst with V2O5 active component accounting for 10% of the mass of the catalyst. Add KNO3 solution (containing 1.5 g KNO3) to the catalyst and stir, seal and place in an oven at 100℃ for 2 h after the liquid is completely absorbed, then calcine at 450℃ for 6 h to decompose the K2O precursor KNO3 and interact with the carrier, thereby finally preparing a vanadium modified high-activity 2-cyanopyridine catalyst.

[0030] 2. Catalytic synthesis of 2-cyanopyridine The prepared vanadium modified 2-cyanopyridine catalyst is filled into a fixed bed reactor containing three fixed beds, which are named bed layer 1, bed layer 2 and bed layer 3 from top to bottom; the filling amount of bed layer 1 is 800 mL, the amount of bed layer 2 is 550 mL, and the filling amount of bed layer 3 is 730 mL. Mix 2-methylpyridine, ammonia and air in a molar ratio of 1:45:300 after preheating to 210℃, pass 2-methylpyridine into the fixed bed reactor at a flow rate of 18 g / h, control the temperature of bed layer 1 to be 280℃, control the temperature of bed layer 2 to be 335℃, and control the temperature of bed layer 3 to be 370℃, and after 2 h of reaction, collect the reaction liquid for subsequent detection.

[0031] Examples 2-6 differ from Example 1 in that the parameters are different, and the specific differences are shown in Table 1, and the rest are the same as Example 1.

[0032] Table 1. Preparation parameters and test results of Examples 1-6

[0033] Comparative Example 1: only a single temperature is used On the basis of Example 6, the temperatures of the bed layers 1-3 are kept the same, and the rest of the steps are kept the same, and the specific temperatures and test results are shown in Table 2.

[0034] Table 2. Preparation parameters and test results of Comparative Example 1

[0035] Comparative Example 2: reduce the temperature of bed layer 1 On the basis of Example 6, the temperature control of bed layer 1 is changed to 275℃, and the rest of the steps are kept the same.

[0036] Comparative Example 3: increase the temperature of bed layer 2 On the basis of Example 6, the temperature control of bed layer 2 is changed to 360℃, and the rest of the steps are kept the same.

[0037] Comparative Example 4: reduce the temperature of bed layer 3 On the basis of Example 6, the temperature control of bed layer 3 is changed to 365℃, and the rest of the steps are kept the same.

[0038] The yield of 2-cyanopyridine, the conversion rate of 2-methylpyridine, the reaction selectivity, the content of 2-pyridinecarboxamide, and the content of pyridine of Comparative Examples 1-3 are tested, and the results are shown in Table 3. It can be seen that after changing the bed layer parameters, the yield of 2-cyanopyridine, the conversion rate of 2-methylpyridine, and the reaction selectivity of the prepared product are all significantly reduced, which are much lower than Examples 1-6.

[0039] Table 3. Test results of Comparative Examples 2-3

[0040] Although the present application has been disclosed with reference to the preferred embodiments above, it is not intended to limit the present application, and anyone skilled in the art can make various modifications and modifications without departing from the spirit and scope of the present application, therefore the protection scope of the present application should be defined by the claims.

Claims

1. A method for preparing 2-cyanopyridine based on fixed-bed segmented temperature control, characterized in that, Including the following steps: (1) Preparation of catalyst: TiO2 is mixed with 2.0~5.0 g / L ammonium metavanadate solution, stirred, filtered, dried, calcined and cooled. The stirring, filtering, drying, calcining and cooling are repeated 5~6 times until a catalyst with V2O5 active component ratio of 9~11% is obtained. K2O is doped into the catalyst with a final concentration of 0.3~0.7% (w / w) to finally obtain vanadium-modified 2-cyanopyridine catalyst; (2) Catalytic reaction: The catalyst is packed into the bed of a fixed bed reactor containing three fixed beds, which are bed 1, bed 2 and bed 3 from top to bottom; 2-methylpyridine, ammonia and air are preheated and mixed, and then fed into the fixed bed reactor at a flow rate of 10~30 g / h for reaction. After continuous feeding for 1~3 h, the reaction liquid at the outlet is collected to obtain 2-cyanopyridine; The reaction temperature in bed 1 is 280~300℃; The reaction temperature in bed 2 is 335~350℃; The reaction temperature in bed 3 is 370~385℃.

2. The method according to claim 1, characterized in that, In step (1), the addition ratio of TiO2 to 2.0~5.0 g / L ammonium metavanadate solution is 130~230 g: 700~1000 mL.

3. The method according to claim 1, characterized in that, The preheating temperature in step (2) is 180~220℃.

4. The method according to claim 1, characterized in that, In step (2), the volume ratio of catalysts packed in the three fixed beds from top to bottom is 80~100:55~68:73~100.

5. The method according to claim 1, characterized in that, In step (2), the molar ratio of 2-methylpyridine:ammonia:air is 1~10:45~55:300~360.

6. A method for simultaneously improving the catalytic efficiency of 2-cyanopyridine, characterized in that, Including the following steps: (1) Preparation of catalyst: TiO2 is mixed with 2.0~5.0 g / L ammonium metavanadate solution, stirred, filtered, dried, calcined and cooled. The stirring, filtering, drying, calcining and cooling are repeated 5~6 times until a catalyst with V2O5 active component ratio of 9~11% is obtained. K2O with a final concentration of 0.3~0.7% (w / w) is added to the catalyst to finally obtain vanadium-modified 2-cyanopyridine catalyst; (2) Catalytic reaction: The catalyst is packed into the bed of a fixed bed reactor containing three fixed beds, which are named bed 1, bed 2 and bed 3 from top to bottom; 2-methylpyridine, ammonia and air are preheated to 180~220℃ and mixed, and then fed into the fixed bed reactor at a flow rate of 10~30 g / h. After continuous feeding for 1~3 h, the reaction liquid at the outlet is collected to obtain 2-cyanopyridine; The reaction temperature in bed 1 is 280~300℃; The reaction temperature in bed 2 is 335~350℃; The reaction temperature in bed 3 is 370~385℃.

7. The method according to claim 6, characterized in that, In step (1), the addition ratio of TiO2 to 2.0~5.0 g / L ammonium metavanadate solution is 130~230 g: 700~1000 mL.

8. The method according to claim 6, characterized in that, In step (2), the volume ratio of catalysts packed in the three fixed beds from top to bottom is 80~100:55~68:73~100.

9. The method according to claim 6, characterized in that, In step (2), the molar ratio of 2-methylpyridine:ammonia:air is 1~10:45~55:300~360.

10. The use of the method according to any one of claims 1 to 9 in the preparation of 2-cyanopyridine.

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