A supercritical fluid extraction process for 2-cyanopyridines

Abstract

The application provides a supercritical extraction process of 2-cyanopyridine, and the specific process steps comprise ammonia oxidation of 2-methylpyridine, supercritical extraction, and separation and purification. The extraction process can effectively solve the problems of general separation efficiency, poor product quality, and low yield in the current mainstream 2-cyanopyridine preparation process. The extraction process of the application avoids the use of sulfuric acid, and the production process is more environmentally friendly. The hydrolysis of 2-cyanopyridine is inhibited, the product yield is improved, the yield of 2-cyanopyridine reaches 88%, only a small amount of solvent material is left in the supercritical extraction extract, and the product quality is higher. The supercritical extraction achieves the purpose of extraction by changing the pressure and temperature, and the process is simple and the extraction speed is fast.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of chemical synthesis, in particular to a supercritical extraction process of 2-cyanopyridine. BACKGROUND

[0002] 2-cyanopyridine is an important pharmaceutical and pesticide intermediate, commonly used as an intermediate of herbicide, with the characteristics of low toxicity, less residue in soil and plants, and short residue period. 2-cyanopyridine can also be used for the synthesis of chromium picolinate, which has been basically applied to the breeding industry, and has achieved ideal application effect and economic benefit. At present, there are mainly two production methods of 2-cyanopyridine, introducing cyanide at the 2nd position of pyridine and synthesizing from 2-methylpyridine. ① Introducing cyanide at the 2nd position of pyridine: halogen, especially bromine or fluorine, substitution in polar solvents such as dimethyl sulfoxide or dimethyl formamide. In these cyanation routes, many use heavy metal reagents containing copper or nickel, which produce toxic waste liquid, and use polar reagents that are difficult to recover. Moreover, the method involving the formation of pyridine N-oxide or N-alkyl pyridine includes multiple steps, and the product yield is low. In terms of scale-up to industrial scale, these shortcomings are particularly important. ② Ammonia oxidation of 2-methylpyridine: 2-cyanopyridine is vaporized and mixed with ammonia and air in the presence of a catalyst, and then absorbed and extracted to obtain 2-cyanopyridine product. In this process, sulfuric acid is used for neutralization, and benzene is used for extraction. The extractant is easy to remain in the extract, and there are also environmental problems.

[0003] Chinese patent CN101602720A discloses a synthesis method of 2-cyanopyridine, which is obtained by vaporizing 2-methylpyridine and mixing it with ammonia and air in the presence of a catalyst, and then absorbing and extracting to obtain 2-cyanopyridine product. The conversion rate of 2-methylpyridine is about 97%, and the yield of 2-cyanopyridine is about 84%. The conversion rate and yield are not high. Chinese patent CN104356061A discloses a high-efficiency absorption method of 2-cyanopyridine, which is as follows: in the process of preparing 2-cyanopyridine by ammonia oxidation of 2-methylpyridine, high-pressure fine water mist is used as an absorbent to cool and absorb the mixed gas obtained after ammonia oxidation and preliminary cooling, and the temperature of the mixed gas is 200-230℃. The particle size of the high-pressure fine water mist is not more than 100um (preferably less than 50um). This method uses high-pressure fine water mist with a particle size of not more than 100um to rapidly cool and absorb the mixed gas generated in the production of 2-methylpyridine, inhibits the hydrolysis of the product 2-cyanopyridine, and improves the absorption efficiency. However, the water used in the high-pressure fine water mist is pure water, which is used once and not directly recycled, resulting in a large amount of waste water.

[0004] Chinese patent CN110804014A discloses a process for synthesizing 2-cyanopyridine by a continuous method, comprising the following steps: (1) ammonia oxidation of 2-picolinamide: heating the reactor containing the catalyst to 350-400 DEG C, and introducing oxygen-containing gas, ammonia and 2-picolinamide into the reactor, wherein the molar ratio of the oxygen-containing gas, ammonia and 2-picolinamide is 100:10-20:1-2, and the generated reaction gas enters the next process; (2) condensing the reaction gas of step (1), and separating the condensate in a layering kettle, controlling the residence time of 2-cyanopyridine in the layering kettle to be 2-30 minutes, and continuously pumping the 2-cyanopyridine in the lower layer into a rectification kettle to obtain 2-cyanopyridine product by rectification. The reaction gas is directly condensed, and the separation effect is poor, resulting in low yield.

[0005] The existing process still has the following problems: 1) poor separation effect of water absorption extraction; 2) solvent residues in the extract; 3) high sulfuric acid consumption, and serious environmental protection problems. SUMMARY

[0006] In view of the above problems, the present application provides a supercritical extraction process for 2-cyanopyridine, which solves the problems of general separation efficiency, poor product quality and low yield in the current mainstream 2-cyanopyridine preparation process.

[0007] The present application provides a supercritical extraction process for 2-cyanopyridine, and the specific process steps include:

[0008] S1: ammonia oxidation of 2-methylpyridine: adding a catalyst into a reactor, heating to 350-400 DEG C, and then introducing oxygen-containing gas, ammonia and 2-methylpyridine to obtain a reaction liquid;

[0009] S2: supercritical extraction: introducing the reaction liquid into an extraction tower and adding an extraction solvent to carry out an extraction reaction to obtain an extraction liquid;

[0010] S3: separating and purifying the extraction liquid to obtain the 2-cyanopyridine.

[0011] Preferably, the catalyst is an ammonia oxidation catalyst.

[0012] Further preferably, the ammonia oxidation catalyst is a mixture of one or more of vanadium, aluminum, titanium, silicon, molybdenum and phosphorus containing compounds.

[0013] Further preferably, the ammonia oxidation catalyst is a combination of one or more of vanadium pentoxide and titanium dioxide.

[0014] Preferably, the feeding temperature when introducing the oxygen-containing gas, ammonia and 2-methylpyridine in step S1 is 220-250 DEG C.

[0015] Preferably, the order of feeding in step S1 is: first, the oxygen-containing gas; second, the ammonia; and last, the 2-methylpyridine.

[0016] In order to effectively improve the conversion rate and yield, preferably, the molar ratio of the oxygen-containing gas, the ammonia and the 2-methylpyridine in step S1 is 130:10-20:1-2.

[0017] When the molar ratio of the oxygen-containing gas, the ammonia and the 2-methylpyridine is controlled to be 130:10-20:1-2, the conversion rate is the highest and the post-processing is simple, which effectively controls the cost. The inventor found in experiments that when too little ammonia is used, the yield is reduced; however, if too much ammonia is used, ammonia recovery processing is required after the extraction process is completed, which is complex and costly.

[0018] Preferably, the oxygen-containing gas in step S1 is air.

[0019] Preferably, after the oxygen-containing gas, the ammonia and the 2-methylpyridine are fed in step S1, the reaction gas generated is condensed to obtain a reaction liquid.

[0020] Preferably, in step S2, the temperature in the extraction tower is 350-420°C and the pressure is 9-11 MPa.

[0021] Preferably, in step S2, the extraction solvent is supercritical state benzene.

[0022] When supercritical state benzene is used as the extraction solvent and the temperature in the extraction tower is controlled to be 350-420°C and the pressure is controlled to be 9-11 MPa, selective extraction of the reaction liquid can be achieved, the content of benzene in the reaction product is effectively reduced, and the conversion rate of the raw material and the yield of 2-cyanopyridine are improved. The inventor analyzed that this may be because, under the specific conditions of temperature and pressure, 2-methylpyridine has the best solubility in the extraction agent and has good stability and is not prone to decomposition and other problems. The inventor found in experiments that if the temperature used is too low, the amount of benzene used needs to be increased, which will cause product residues in the extraction liquid and a low yield. However, if the extraction temperature is too high, the yield of the product will be reduced and the extraction liquid will contain more impurities such as pyridine and 2-picolinamide, which may be due to the decomposition of the product caused by the high temperature, which reduces the yield.

[0023] Further preferably, in step S2, the supercritical state benzene is sprayed from a high-pressure nozzle at the bottom of the extraction tower; and the reaction liquid enters the tower from the top of the extraction tower.

[0024] Preferably, the feeding flow rate of the reaction liquid is 5-20 kg / h.

[0025] Preferably, the feeding flow rate of the supercritical state benzene is 40-70 kg / h.

[0026] Further preferably, in the step S2, the residence time of the reaction liquid in the extraction tower is 10-60 min.

[0027] Further preferably, in the step S2, the residence time of the reaction liquid in the extraction tower is 10-40 min.

[0028] Preferably, the separation and purification in the step S3 comprises continuous evaporation and rectification processes.

[0029] Preferably, the supercritical extraction process of 2-cyanopyridine comprises the following steps:

[0030] S1: Ammonia oxidation of 2-methylpyridine: adding catalyst into a reactor, heating to 350-400℃, then sequentially feeding in oxygen-containing gas, ammonia and 2-methylpyridine in a molar ratio of 130:10-20:1-2, controlling the feeding temperature to be 220-250℃, to obtain reaction gas; cooling the reaction gas to obtain reaction liquid;

[0031] S2: Supercritical extraction: feeding the reaction liquid into an extraction tower, and adding supercritical benzene to carry out extraction reaction to obtain extraction liquid, the temperature in the extraction tower being 350-420℃, and the pressure being 9-11 MPa;

[0032] S3: Separating and purifying the extraction liquid by continuous evaporation and rectification processes to obtain the 2-cyanopyridine.

[0033] Compared with the prior art, the present application has the following beneficial effects:

[0034] The present application provides a supercritical extraction process of 2-cyanopyridine, which uses supercritical benzene to extract and absorb the reaction liquid, and carries out selective extraction according to the influence of pressure and temperature on the solubility of benzene; the condensed liquid is separated in a separation kettle, the organic phase is continuously pumped into a rectification kettle, and 2-cyanopyridine is obtained by rectification. The process eliminates the use of sulfuric acid, is more environmentally friendly, inhibits the hydrolysis of 2-cyanopyridine, improves the yield of the product, and the yield of 2-cyanopyridine reaches 88%; only a small amount of solvent remains in the supercritical extraction extract, and the product quality is higher; the supercritical extraction achieves the purpose of extraction by changing the pressure and temperature, and the process is simple and fast. DETAILED DESCRIPTION

[0035] The present application will be further described in detail below with reference to specific examples. It should be understood that the specific examples described herein are merely used to explain the present application, and are not used to limit the present application. It should be noted that the examples in the present application and the features in the examples can be combined with each other without conflict.

[0036] EXAMPLE

[0037] Example 1

[0038] The present example provides a supercritical extraction process of 2-cyanopyridine, the specific steps including:

[0039] S1: Ammoxidation of 2-methylpyridine: the reactor containing titanium dioxide catalyst is heated to 360℃, air, ammonia, 2-methylpyridine are introduced for reaction, the feed temperature is controlled at 220-230℃; the molar ratio of air, ammonia and 2-methylpyridine is 130:20:1, the reaction gas after ammoxidation is cooled to about 40℃ by heat exchanger and cooler, and the reaction liquid is obtained;

[0040] S2: Supercritical extraction: the cooled reaction liquid is transported to the extraction tower, wherein the reaction liquid feed flow is 10.4kg / h. In the extraction tower, the supercritical state benzene with a temperature of 380℃, a pressure of 9.5Mpa and a flow of 41.6kg / h is sprayed from the nozzle, and the residence time is 20min;

[0041] S3: The extraction liquid is punched into the evaporation tank to recover benzene, and then sent to the 2-cyanopyridine fractionation system to obtain the finished product; the rectification process adopts continuous rectification, and the qualified product is collected from the top of the tower.

[0042] Example 2:

[0043] S1: Ammoxidation of 2-methylpyridine: the reactor containing titanium dioxide catalyst is heated to 360℃, air, ammonia, 2-methylpyridine are introduced for reaction, the feed temperature is controlled at 220-230℃; the molar ratio of air, ammonia and 2-methylpyridine is 130:20:1, the reaction gas after ammoxidation is cooled to about 40℃ by heat exchanger and cooler, and the reaction liquid is obtained;

[0044] S2: Supercritical extraction: the cooled reaction liquid is transported to the extraction tower 1, wherein the reaction liquid feed flow is 10.4kg / h. In the extraction tower, the supercritical state benzene with a temperature of 400℃, a pressure of 10Mpa and a flow of 41.6kg / h is sprayed from the nozzle, and the residence time is 40min;

[0045] S3: The extraction liquid is punched into the evaporation tank to recover benzene, and then sent to the 2-cyanopyridine fractionation system to obtain the finished product; the rectification process adopts continuous rectification, and the qualified product is collected from the top of the tower.

[0046] Example 3

[0047] S1: Ammoxidation of 2-methylpyridine: the reactor containing the titanium dioxide catalyst was heated to 360°C, and air, ammonia, and 2-methylpyridine were introduced into the reactor for reaction, with the feed temperature controlled at 220-230°C; the molar ratio of the air, ammonia, and 2-methylpyridine was 130:20:1, and the reaction gas after ammoxidation was cooled to about 40°C by a heat exchanger and a cooler, to obtain a reaction liquid;

[0048] S2: Supercritical extraction: the cooled reaction liquid was delivered to an extraction tower, with the reaction liquid feed flow rate being 10.4 kg / h. In the extraction tower, benzene in a supercritical state at a temperature of 380°C, a pressure of 9 MPa, and a flow rate of 41.6 kg / h was sprayed from a nozzle, with a residence time of 20 min;

[0049] S3: The extraction liquid was introduced into an evaporation tank to recover benzene, and then was sent to a 2-cyanopyridine fractionation system to obtain a finished product; the fractionation process was performed in a continuous distillation mode, and the qualified product was collected from the top of the tower.

[0050] Comparative Example 1

[0051] This example provides a supercritical extraction process for 2-cyanopyridine, which specifically includes the following steps:

[0052] S1: Ammoxidation of 2-methylpyridine: the reactor containing the titanium dioxide catalyst was heated to 360°C, and air, ammonia, and 2-methylpyridine were introduced into the reactor for reaction, with the feed temperature controlled at 220-230°C; the molar ratio of the air, ammonia, and 2-methylpyridine was 130:20:1, and the reaction gas after ammoxidation was cooled to about 40°C by a heat exchanger and a cooler, to obtain a reaction liquid;

[0053] S2: Supercritical extraction: the cooled reaction liquid was delivered to an extraction tower, with the reaction liquid feed flow rate being 10.4 kg / h. In the extraction tower, benzene in a supercritical state at a temperature of 300°C, a pressure of 12 MPa, and a flow rate of 41.6 kg / h was sprayed from a nozzle, with a residence time of 50 min;

[0054] S3: The extraction liquid was introduced into an evaporation tank to recover benzene, and then was sent to a 2-cyanopyridine fractionation system to obtain a finished product; the fractionation process was performed in a continuous distillation mode, and the qualified product was collected from the top of the tower.

[0055] Comparative Example 2

[0056] This example provides a supercritical extraction process for 2-cyanopyridine, which specifically includes the following steps:

[0057] S1: Ammonia oxidation of 2-methylpyridine: The reactor containing the titanium dioxide catalyst was heated to 360°C, and air, ammonia, and 2-methylpyridine were fed into the reactor, with the feed temperature controlled at 220-230°C. The molar ratio of the air, ammonia, and 2-methylpyridine was 130:20:1. The reaction gas after ammonia oxidation was cooled to about 40°C by a heat exchanger and a cooler, and a reaction liquid was obtained.

[0058] S2: Supercritical extraction: The cooled reaction liquid was fed into an extraction tower, with a feed flow rate of 10.4 kg / h. In the extraction tower, supercritical benzene at a temperature of 450°C, a pressure of 8 MPa, and a flow rate of 41.6 kg / h was sprayed from a nozzle, and the residence time was 20 min.

[0059] S3: The extraction liquid was fed into an evaporation tower to recover benzene, and then was fed into a 2-cyanopyridine fractionation system to obtain the finished product. The fractionation system used continuous fractionation, and the qualified product was collected from the top of the tower.

[0060] Performance test

[0061] 1. Benzene content test: A gas chromatograph was used to test the benzene content.

[0062] 2. Raw material conversion rate: A liquid chromatograph was used to obtain the 2-methylpyridine content, and the conversion rate was calculated.

[0063] 3. 2-cyanopyridine yield: The mass of the finished product / theoretical amount of the finished product.

[0064] The collected samples of Examples 1-3 and Comparative Examples 1-2 were tested according to the above test methods, and the test results are shown in Table 1.

[0065] Table 1

[0066] Example Benzene content / ppm Feed conversion / % 2-cyanopyridine yield / % Example 1 < 10 ppm 99.6 88.5 Example 2 < 10 ppm 99.5 88.4 Example 3 < 10 ppm 99.6 87.7 Comparative Example 1 < 10 ppm 99.5 85.3 Comparative Example 2 < 10 ppm 99.5 86.5

Claims

1. A supercritical fluid extraction process for 2-cyanopyridines, characterized in that, The specific process steps include: S1: Ammonia oxidation of 2-methylpyridine: the catalyst is added to the reactor, heated to 350-400℃, and then oxygen-containing gas, ammonia, and 2-methylpyridine are introduced to obtain a reaction liquid; S2: Supercritical extraction: the reaction liquid is introduced into an extraction tower and an extraction solvent is added to perform an extraction reaction to obtain an extraction liquid; S3: The extraction liquid is separated and purified to obtain the 2-cyanopyridine; In the step S1, the feed temperature when the oxygen-containing gas, ammonia, and 2-methylpyridine are introduced is 220-250℃; in the step S1, the molar ratio of the oxygen-containing gas, ammonia, and 2-methylpyridine is 130:10-20:1-2; in the step S2, the temperature in the extraction tower is 350-420℃, and the pressure is 9-11 MPa; in the step S2, the extraction solvent is supercritical state benzene.

2. A supercritical fluid extraction process for 2-cyanopyridine according to claim 1, wherein The catalyst is an ammonia oxidation type catalyst.

3. A supercritical fluid extraction process for 2-cyanopyridine according to claim 2, wherein The ammonia oxidation type catalyst is a mixture of one or more of vanadium, aluminum, titanium, silicon, molybdenum, and phosphorus-containing compounds.

4. The supercritical fluid extraction process of claim 1, wherein the 2-cyanopyridine is 2-cyanopyridine-4-carboxylic acid. In the step S1, the oxygen-containing gas is air.

5. The supercritical fluid extraction process of claim 1, wherein the 2-cyanopyridine is 2-cyanopyridine-4-carboxylic acid. In the step S2, the residence time of the reaction liquid in the extraction tower is 10-60 min.

6. A supercritical fluid extraction process for 2-cyanopyridine according to claim 1, wherein In the step S3, the separation and purification includes continuous evaporation and rectification processes.