A purification method for imidazole cyclization solution

Abstract

This invention relates to a method for purifying imidazole cyclized liquid, comprising the following steps: adding an alkali and montmorillonite to an imidazole cyclized liquid to obtain a mixture; heating the mixture under vacuum to remove water, obtaining an imidazole concentrate; distilling the imidazole concentrate to collect the crude imidazole distillate; and crystallizing, centrifuging, and drying the crude imidazole distillate to obtain imidazole. This invention utilizes the addition of an alkali to effectively release free imidazole, promoting its dissolution, facilitating distillation, and increasing the imidazole distillation yield. Montmorillonite, used in the purification and distillation process of imidazole, effectively reduces the viscosity of the residue, facilitating heat and mass transfer and promoting complete distillation of imidazole. This invention can obtain a high-content imidazole concentrate at a lower distillation temperature, which, after further processing, yields high-purity imidazole. The method of this invention has the advantages of simple process, low cost, environmental friendliness, and high yield.

Description

Technical Field

[0001] This invention belongs to the field of chemical synthesis, and specifically relates to a method for purifying imidazole cyclized liquid. Background Technology

[0002] Imidazole, with the chemical formula C3H4N2, is a five-membered heterocyclic organic compound containing two nitrogen atoms. It has a wide range of applications, such as being used as an epoxy resin curing agent to improve the mechanical properties of products, including bending, stretching, and compression; as a rust inhibitor for copper in printed circuit boards and integrated circuits; and as a pharmaceutical raw material or intermediate to participate in various chemical reactions and manufacture antifungal drugs or antibiotics.

[0003] The main synthetic processes of imidazole include (1) cyclization of o-phenylenediamine with formic acid to generate benzimidazole, followed by cyclization with hydrogen peroxide to obtain 4,5-dihydroxyimidazole, and finally decarboxylation to obtain imidazole; (2) cyclization reaction of glyoxal and formaldehyde under the action of ammonia or ammonium salt; after the imidazole synthesis reaction (cyclization reaction) is completed, the purification is currently mainly carried out by distilling water and distilling imidazole.

[0004] Taking the preparation of imidazole from glyoxal, formaldehyde, and ammonia as an example, in actual production, ammonia is injected into a cyclization reactor in a certain proportion. After the ammonia in the cyclization reactor is heated to 45°C, a mixed aldehyde (formaldehyde and glyoxal) is added dropwise to the cyclization reactor to carry out the cyclization reaction, resulting in a cyclized liquid containing imidazole. However, the cyclization reaction between the mixed aldehyde and ammonia produces side reactions, generating a certain amount of hexamethylenetetramine (urotropine) and 2,2'-biimidazole. These side reactions not only increase production costs, but also produce a large amount of black viscous polymer during the distillation of imidazole. This polymer has high viscosity and poor thermal conductivity, requiring increased distillation temperature to ensure purification, increasing energy consumption and reducing safety and stability. Furthermore, this black viscous polymer can dissolve some imidazole, resulting in a large amount of imidazole residue in the purifying residue, causing a decrease in yield. Summary of the Invention

[0005] The purpose of this invention is to overcome the above-mentioned technical deficiencies and provide a method for purifying imidazole cyclized liquid, thereby solving the technical problems of high energy consumption and low yield in the purification of imidazole in the prior art.

[0006] To achieve the above-mentioned technical objectives, the technical solution provided by this invention is as follows:

[0007] In a first aspect, the present invention provides a method for purifying an imidazole cyclized solution, comprising the following steps: S1, adding alkali and montmorillonite to the imidazole cyclized solution to obtain a mixture; S2, heating the mixture under vacuum to remove water, obtaining an imidazole concentrate; S3, distilling the imidazole concentrate to collect the crude imidazole distillate; S4, crystallizing, centrifuging and drying the crude imidazole distillate to obtain imidazole.

[0008] Compared with the prior art, the beneficial effects of the present invention include:

[0009] This invention involves adding alkali and montmorillonite to an imidazole cyclization solution. The addition of the alkali effectively releases free imidazole, promoting its dissolution, facilitating distillation, and increasing the distillation yield. Montmorillonite, a natural inorganic mineral material with good stability and weather resistance, is used in the purification and distillation process of imidazole. Its dispersing and suspending properties effectively reduce the viscosity of the residue, facilitating heat and mass transfer and promoting complete distillation of imidazole. This invention can obtain a high-content imidazole concentrate at a lower distillation temperature, which can then be further processed to obtain high-purity imidazole. The method of this invention has the advantages of simple process, low cost, environmental friendliness, and high yield. Detailed Implementation

[0010] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0011] In the main synthesis process of imidazole, ammonia water is added to a cyclization reactor in a certain proportion. After the ammonia water in the cyclization reactor is heated to 45°C, a mixed aldehyde consisting of formaldehyde and glyoxal is added dropwise to the cyclization reactor to carry out the cyclization reaction, obtaining a cyclized solution containing imidazole product. The main reaction is as follows:

[0012]

[0013] There are also certain side reactions, producing hexamethylenetetramine ((CH2)6N4 hexamethylenetetramine) or 2,2'-biimidazole:

[0014] (1)

[0015] (2)

[0016] In existing technologies, during the purification of imidazole through distillation, these byproducts tend to increase the viscosity of the residue in the distillation vessel, leading to poor heat transfer and frequent necessitation of higher distillation temperatures. This results in a sharp decline in production safety and stability, and also leaves a large amount of imidazole residue in the distillation residue, significantly increasing production costs. Therefore, this invention is proposed.

[0017] In a first aspect, the present invention provides a method for purifying an imidazole cyclized solution, comprising the following steps:

[0018] S1, add alkali and montmorillonite to the imidazole cyclization solution to obtain a mixture;

[0019] S2, Under vacuum conditions, the mixture is heated to remove water, resulting in an imidazole concentrate;

[0020] S3, distill the imidazole concentrate and collect the crude imidazole distillate;

[0021] S4, the crude distillate of imidazole is crystallized, centrifuged and dried to obtain imidazole.

[0022] Preferably, in step S1, the imidazole mass concentration in the imidazole cyclization solution is 16-22%; the mass ratio of the imidazole cyclization solution to the alkali and montmorillonite is (1700-1900):(30-50):(50-100), specifically including but not limited to 1700:30:50, 1700:40:50, 1700:50:50, 1700:40:80, 1700:40:100, 1800:50:50, 1800:40:60, 1800:50:70, 1900:30:50, 1900:40:60 or 1900:50:100, etc.

[0023] Preferably, in step S1, the alkali includes sodium hydroxide solution, caustic soda flakes, or quicklime. Specifically, the mass concentration of the sodium hydroxide solution can be 32%; the alkali actually added to the imidazole cyclization solution is calculated based on the effective component, such as the sodium hydroxide solution being calculated based on the NaOH it contains.

[0024] Preferably, in step S2, the vacuum condition is a vacuum degree ≥ -0.08 MPa.

[0025] Preferably, in step S2, the conditions for heating to remove water include: a temperature of 95–100°C and a time of 2–4 hours. Specifically, the temperature includes, but is not limited to, 95°C, 96°C, 97°C, 98°C, 99°C, or 100°C; the time includes, but is not limited to, 2 hours, 2.5 hours, 3 hours, 3.5 hours, or 4 hours.

[0026] Preferably, in step S3, the distillation conditions include: a vacuum degree ≥ -0.095 MPa; an internal temperature at the top of the vessel of 160–190°C; and a time of 10–12 hours. It is understood that throughout the entire heating, dehydration, and distillation process, the total liquid level of the material is controlled to not exceed 2 / 3 of the total volume of the distillation vessel. Specifically, the internal temperature at the top of the vessel includes, but is not limited to, 160°C, 165°C, 170°C, 175°C, 180°C, or 190°C; and the time includes, but is not limited to, 10 hours, 10.5 hours, 11 hours, 11.5 hours, or 12 hours.

[0027] In a further preferred embodiment, distillation is carried out in a jacketed distillation vessel, with heat transfer oil as the heating medium within the jacket; the heating oil temperature is 250–260°C. It is understood that this invention primarily controls the internal temperature of the vessel top, while the external heating source for the distillation vessel can be selected and adjusted according to actual conditions.

[0028] Preferably, in step S4, crystallization specifically includes: mixing the crude imidazole distillate with water at a mass ratio of 100:(5-10) uniformly, and cooling to 20-30°C at a cooling rate of 1-3°C / min for crystallization. Specifically, the mass ratio of the crude imidazole distillate to water includes, but is not limited to, 100:5, 100:6, 100:7, 100:8, 100:9, or 100:10; the cooling rate includes, but is not limited to, 1°C / min, 1.5°C / min, 2°C / min, 2.5°C / min, or 3°C / min; and the crystallization temperature includes, but is not limited to, 20°C, 22°C, 24°C, 25°C, 26°C, 28°C, or 30°C.

[0029] In this invention, the cooling rate during crystallization must not be too fast, otherwise the crystallization speed will slow down or even be inhibited, affecting production efficiency.

[0030] Preferably, in step S4, centrifugation separates wet imidazole and a primary mother liquor; the primary mother liquor is returned to step S1 and combined with the imidazole cyclization solution.

[0031] Preferably, in step S4, the drying conditions include: a drying temperature of 50-55°C, a vacuum degree of -0.095 MPa, drying until the moisture content is <0.3%, to obtain the imidazole product, which is then weighed and packaged as needed.

[0032] The main mechanism of action and advantages of this invention are as follows:

[0033] (1) In this invention, alkali and montmorillonite are added to the imidazole cyclization solution. Imidazole itself has a certain alkalinity. By adding alkali substances, the free imidazole can be released well, promoting the dissolution of imidazole and facilitating its distillation into the finished product tank, thereby improving the distillation yield of imidazole. Montmorillonite is a natural inorganic mineral material with good stability and weather resistance. Its dispersion and suspension properties are used in the purification and distillation process of imidazole, which can effectively reduce the viscosity of the residue, facilitate heat and mass transfer, and promote the full distillation of imidazole.

[0034] (2) The method of the present invention can purify the imidazole cyclized liquid with a mass concentration of 16-22% obtained from the imidazole synthesis reaction to obtain a crude distillate with high imidazole content, and then obtain a high-purity imidazole product through crystallization, centrifugation and drying. This method has the advantages of simple process, low cost and green environmental protection.

[0035] The present invention will be further described in detail below through specific embodiments. The source of the imidazole cyclization solution is as follows: a mixed aldehyde is obtained by mixing 37 wt% formaldehyde aqueous solution and 40 wt% glyoxal aqueous solution, wherein the concentration of glyoxal in the mixed aldehyde is 26.5%; 17 wt% ammonia water is heated to 45°C, and the mixed aldehyde is added dropwise to the ammonia water to carry out a cyclization reaction, thereby obtaining a cyclization solution containing imidazole product.

[0036] Example 1

[0037] A method for purifying an imidazole cyclized solution includes the following steps:

[0038] S1. Pump 1800 kg of 18% imidazole cyclized solution into a distillation vessel, add 100 kg of 32% liquid alkali and 50 kg of montmorillonite.

[0039] S2. After feeding is completed, start the vacuum unit. When the vacuum degree in the distillation kettle reaches -0.085MPa, open the heat transfer oil valve of the distillation kettle and the circulating water valve of the condenser to heat and remove water. During heating and water removal, control the liquid temperature in the distillation kettle to 98℃ and continue operating for 2 hours to obtain imidazole concentrate.

[0040] S3. Continue heating the distillation kettle with heat transfer oil. When the kettle top temperature reaches 110℃, switch the receiving valve to the crude distillate receiving tank and simultaneously switch the condenser circulating water to hot water circulation. Distill the imidazole concentrate. During normal receiving, control the vacuum degree to be greater than -0.095MPa and the distillation kettle top temperature to 180℃. After continuously receiving for 10 hours, when the residue discharge from the kettle is slow and almost non-existent, close the heat transfer oil inlet and outlet valves to stop distillation, obtaining the imidazole crude distillate.

[0041] S4, the crude distillate of imidazole and water are mixed evenly at a mass ratio of 100:5, and the temperature is reduced to 30℃ at a cooling rate of 1℃ / min for crystallization; then the wet imidazole and the primary mother liquor are obtained by centrifugation; the wet imidazole is dried at 50℃ and a vacuum degree of -0.095Mpa until the moisture content is less than 0.3% to obtain imidazole.

[0042] Example 2

[0043] A method for purifying an imidazole cyclized solution includes the following steps:

[0044] S1. Pump 1800 kg of 22% imidazole cyclized solution into a distillation vessel, add 150 kg of 32% liquid alkali and 100 kg of montmorillonite.

[0045] S2. After feeding is completed, start the vacuum unit. When the vacuum degree in the distillation kettle reaches -0.085MPa, open the heat transfer oil valve of the distillation kettle and the circulating water valve of the condenser to heat and remove water. During heating and water removal, control the liquid temperature in the distillation kettle to 98℃ and continue operating for 4 hours to obtain imidazole concentrate.

[0046] S3. Continue heating the distillation kettle with heat transfer oil. When the kettle top temperature reaches 110℃, switch the receiving valve to the crude distillate receiving tank, and simultaneously switch the condenser circulating water to hot water circulation. Distill the imidazole concentrate. During normal receiving, control the vacuum degree to be greater than -0.095MPa and the distillation kettle top temperature to 170℃. After continuously receiving for 12 hours, the imidazole crude distillate is obtained.

[0047] S4, the crude distillate of imidazole and water are mixed evenly at a mass ratio of 100:8, and the mixture is cooled to 25℃ at a cooling rate of 2℃ / min for crystallization; then the mixture is separated by centrifugation to obtain wet imidazole and primary mother liquor; the wet imidazole is dried at 52℃ and a vacuum degree of -0.095Mpa until the moisture content is less than 0.3% to obtain imidazole.

[0048] Example 3

[0049] A method for purifying an imidazole cyclized solution includes the following steps:

[0050] S1. Pump 1800 kg of 20% imidazole cyclized solution into a distillation vessel, add 125 kg of 32% liquid alkali and 80 kg of montmorillonite.

[0051] S2. After feeding is completed, start the vacuum unit. When the vacuum degree in the distillation vessel reaches -0.085MPa, open the heat transfer oil valve of the distillation vessel and the circulating water valve of the condenser to heat and remove water. During heating and water removal, control the liquid temperature in the distillation vessel to 100℃ and continue operating for 3 hours to obtain imidazole concentrate.

[0052] S3. Continue heating the distillation kettle with heat transfer oil. When the kettle top temperature reaches 110℃, switch the receiving valve to the crude distillate receiving tank and simultaneously switch the condenser circulating water to hot water circulation. Distill the imidazole concentrate. During normal receiving, control the vacuum degree to be greater than -0.095MPa and the distillation kettle top temperature to 190℃. After continuously receiving for 11 hours, the imidazole crude distillate is obtained.

[0053] S4, the crude distillate of imidazole and water are mixed evenly at a mass ratio of 100:10, and the mixture is cooled to 20℃ at a cooling rate of 3℃ / min for crystallization; then the mixture is separated by centrifugation to obtain wet imidazole and primary mother liquor; the wet imidazole is dried at 55℃ and a vacuum degree of -0.095Mpa until the moisture content is less than 0.3% to obtain imidazole.

[0054] Example 4

[0055] Compared with Example 3, the only difference is that the mother liquor obtained in step S4 is returned to step S1 and combined with the imidazole cyclization solution, while the other steps and conditions are the same as in Example 3.

[0056] Comparative Example 1

[0057] Compared with Example 3, the only difference is that in step S1, liquid alkali is not added, while the other steps and conditions are the same as in Example 3.

[0058] Comparative Example 2

[0059] Compared with Example 3, the only difference is that in step S1, the amount of 32% liquid alkali added is 170 kg, and the other steps and conditions are the same as in Example 3.

[0060] Comparative Example 3

[0061] Compared with Example 3, the only difference is that montmorillonite is not added in step S1, while the other steps and conditions are the same as in Example 1.

[0062] Comparative Example 4

[0063] Compared with Example 3, the only difference is that in step S1, the amount of montmorillonite added is 120 kg, and the other steps and conditions are the same as in Example 3.

[0064] Comparative Example 5

[0065] Compared with Example 3, the only difference is that in step S1, neither liquid alkali nor montmorillonite is added, while the other steps and conditions are the same as in Example 3.

[0066] Comparative Example 6

[0067] Compared with Example 3, the only difference is that in step S1, montmorillonite is replaced with activated carbon, and the other steps and conditions are the same as in Example 3.

[0068] The imidazole cyclized liquid, crude imidazole distillate, and imidazole product used in the examples and comparative examples were analyzed for component content by loss on drying and liquid chromatography. The total impurity content in the imidazole cyclized liquid was the total content of hexamethylenetetramine and 2,2'-biimidazole. The results are shown in Table 1 below.

[0069] Table 1. Test results of raw material and product composition content in each embodiment and comparative example.

[0070]

[0071] As shown in Table 1, after the imidazole cyclized solution is purified by the method of the present invention, a high concentration of imidazole concentrate can be obtained at a lower distillation temperature; after further processing such as crystallization and centrifugation, imidazole with high purity and high imidazole yield can be obtained.

[0072] A comparison of Examples 3 and 4 shows that recycling the mother liquor obtained from centrifugation promotes the imidazole yield.

[0073] As can be seen from the comparison between Example 3 and Comparative Examples 1-2, in Comparative Example 1, the addition of montmorillonite without the addition of liquid alkali resulted in a high impurity content and a significant decrease in the imidazole yield. In Comparative Example 2, the excessive addition of liquid alkali slightly improved the purity of imidazole, but the yield decreased slightly, and the excessive addition of liquid alkali led to an increase in cost.

[0074] A comparison of Example 3 and Comparative Examples 3-4 shows that in Comparative Example 3, without the addition of montmorillonite, both the purity and yield of imidazole decreased. In Comparative Example 4, after further increasing the amount of montmorillonite compared to Example 3, the effect was basically the same, but the large amount of raw materials resulted in high costs.

[0075] As can be seen from the comparison of Example 3, Comparative Example 1, Comparative Example 3 and Comparative Example 5, the present invention achieves a synergistic effect by adding an appropriate amount of liquid alkali and montmorillonite, which is beneficial to obtaining imidazole with high purity and high yield.

[0076] As can be seen from Example 3 and Comparative Example 6, the purification effect deteriorated and the imidazole yield decreased after montmorillonite replacement, indicating that not all substances can be used for imidazole purification.

[0077] In summary, this invention can concentrate low-concentration imidazole (16-22%) to obtain a high-content imidazole concentrate, which can then be further processed to obtain imidazole with high purity and yield. The method of this invention has the advantages of simple process, low cost, environmental friendliness, and high yield.

[0078] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for purifying an imidazole cyclized solution, characterized in that, Includes the following steps: S1, add alkali and montmorillonite to the imidazole cyclization solution to obtain a mixed solution; the alkali is sodium hydroxide solution; the imidazole cyclization solution is a cyclization solution containing imidazole product obtained by the cyclization reaction. S2, Under vacuum conditions, the mixture is heated to remove water, resulting in an imidazole concentrate; S3, the imidazole concentrate is distilled to collect the crude imidazole distillate; S4, the crude distillate of imidazole is subjected to crystallization, centrifugation and drying to obtain imidazole; In step S4, the crystallization specifically includes: mixing the crude distillate of imidazole with water at a mass ratio of 100:(5-10) and cooling it down to 20-30°C at a cooling rate of 1-3°C / min to crystallize.

2. The purification method for the imidazole cyclization solution according to claim 1, characterized in that, In step S1, the imidazole mass concentration in the imidazole cyclization solution is 16-22%; the mass ratio of the imidazole cyclization solution to the alkali and montmorillonite is (1700-1900):(30-50):(50-100).

3. The purification method for the imidazole cyclization solution according to claim 1, characterized in that, In step S2, the vacuum condition is a vacuum degree ≥ -0.08 MPa.

4. The purification method for the imidazole cyclization solution according to claim 1, characterized in that, In step S2, the conditions for heating and dehydration include: a temperature of 95–100°C and a time of 2–4 hours.

5. The purification method for the imidazole cyclization solution according to claim 1, characterized in that, In step S3, the distillation conditions include: vacuum degree ≥ -0.095MPa, internal temperature at the top of the vessel 160~190℃, and time 10~12h.

6. The purification method for the imidazole cyclization solution according to claim 5, characterized in that, The distillation is carried out in a jacketed distillation vessel, where the heating medium is heat transfer oil.

7. The purification method for the imidazole cyclization solution according to claim 1, characterized in that, In step S4, the centrifugation separation yields wet imidazole and a primary mother liquor; the primary mother liquor is returned to step S1 and combined with the imidazole cyclization solution.

8. The purification method for the imidazole cyclization solution according to claim 1, characterized in that, In step S4, the drying conditions include: a drying temperature of 50-55°C, a vacuum degree of -0.095 MPa, and drying to a moisture content of <0.3%.

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