Permanent violet nitration production method

Abstract

The invention discloses a permanent violet nitration production method, which relates to the technical field of chemical substance preparation, and comprises the following steps: uniformly dissolving N-ethyl carbazole in an inert organic solvent to prepare a component A, and injecting the component A into a nitration kettle; taking nitric acid as a component B, and connecting the component B into a reaction liquid pipe of the nitration kettle through a pipeline; mixing the component B with the reaction liquid from the nitration kettle, dispersing the mixture into fine particles through a high-speed dispersion pump, and feeding the fine particles into a tubular reactor; cooling the mixed material through an outer jacket of the tubular reactor, returning the cooled mixed material to the nitration kettle to realize circulation, and continuing stirring reaction; and recovering the material, cooling, standing for layering, discarding upper-layer waste acid, and cooling, crystallizing and filtering a lower-layer solvent layer to obtain a nitration product.

Description

Technical Field

[0001] The invention relates to the technical field of chemical substance preparation, in particular to permanent purple nitration, and specifically to a production method of permanent purple nitration. Background Art

[0002] Permanent Violet is an important organic pigment with excellent performance. Its production is mature in China. The key step in the production process is the synthesis of the intermediate 3-nitro-N-ethylcarbazole, which is mainly achieved through the nitration reaction of N-ethylcarbazole. N-ethylcarbazole is a substance that is easily nitrated. Studies have shown that when the nitric acid concentration is too low and the reaction temperature is too low, the nitration reaction is slow and can easily lead to incomplete reaction. However, when the nitric acid concentration is too high and the reaction temperature is too high, the nitration reaction is accelerated but can easily lead to polynitration, resulting in an increase in by-products. In the domestic Permanent Violet production industry, the nitration reaction generally adopts the traditional batch production process of kettle type.

[0003] This production process has a series of significant technical problems and defects: 1. The reaction starts slowly and takes a long time. During the production process, it takes 6 to 8 hours to add nitric acid, and it takes another 10 to 12 hours to stir after the addition is complete. It often takes 24 hours to complete a batch of materials. 2. The reaction is incomplete, with high raw material consumption, numerous side reactions, and low yield of the main product. Limited by mass transfer efficiency and reaction kinetics, even after a long reaction time, unreacted raw materials (more than 2% N-ethylcarbazole) still remain in the final system, and the amount of nitrate generated is relatively high (about 15%). The final product 3-nitro-N-ethylcarbazole that can be obtained after separation has a yield of only 82-83%, which limits the overall economic benefits of permanent purple production. 3. There are many problems such as low equipment utilization. In addition, due to the large amount of materials in the nitration kettle, if the reaction fails to start, the nitric acid added will accumulate to a certain amount, causing an instantaneous violent reaction, thus posing safety risks such as heat exothermic runaway and material rushing. 4. The traditional post-treatment method does not fully extract the product dissolved in the nitration mother liquor, which restricts the further improvement of the total yield. Summary of the Invention

[0004] The invention provides a nitration production method for permanent violet in order to solve a series of problems in the current batch production of 3-nitro-N-ethylcarbazole using a kettle, such as slow reaction start-up, many side reactions and low yield of the main product.

[0005] The present invention is realized by the following technology: The present invention provides a permanent purple nitration production method, comprising the following steps: a. Dissolution of N-ethylcarbazole N-ethylcarbazole is uniformly dissolved in an inert organic solvent, wherein the inert organic solvent is any one of 1,2-dichloroethane, acetic acid, chlorobenzene, and dichlorobenzene, and the mass volume ratio of the solute to the solvent is 1:2.0-4.0. The dissolution temperature is controlled by an outer jacket of the dissolving kettle, and the dissolution temperature is 25-30°C. The dissolution process is carried out in the dissolving kettle under constant stirring to obtain component A, i.e., N-ethylcarbazole dissolved in the inert organic solvent, and the component is injected into the nitrating kettle; b. Pretreatment with nitric acid Nitric acid with a concentration of 36-45% is used as component B. Component B is connected to the reaction liquid pipe of the nitration kettle through a pipeline. The molar ratio of component A to component B is controlled to be 1:1.5-1.7. By controlling the ratio of raw materials, the occurrence of the side reaction polynitration (generating 3,6-dinitro-N-ethylcarbazole) is reduced. c. Nitration reaction Component B is mixed with the reaction liquid from the nitration kettle, dispersed into fine particles by a high-speed dispersion pump, and enters the tubular reactor. At this time, the nitric acid of component B is mixed with the solution of component A, and a nitration reaction occurs to produce a mixed material; d. Temperature controlled reaction in a tubular reactor The mixed material entering the tubular reactor in step c is cooled by the outer jacket of the tubular reactor to control the temperature to 25-75° C. The residence time of the mixed material in the tubular reactor is 100-200 seconds. The tubular reactor can better achieve timely removal of reaction heat to prevent partial overheating and polynitration, so that 80% of the reaction is completed in the tubular reactor, effectively improving safety; e. Mixed materials The cooled mixture is returned to the nitration kettle, and the temperature in the nitration kettle is 25-30°C to realize circulation. The stirring reaction is continued in the nitration reactor for 3 hours until the nitration endpoint is qualified. f. Product reception The material is recovered in the nitration kettle and cooled. Specifically, the cooling includes first naturally cooling to 30° C. under slow stirring, then introducing ice water into the outer jacket of the nitration kettle, and cooling in an ice bath until the temperature inside the nitration kettle is lower than 15° C., standing and stratifying, discarding the upper layer of waste acid, and cooling the lower solvent layer to crystallize and filter to obtain the nitration product 3-nitro-N-ethylcarbazole.

[0006] Furthermore, the above method is implemented by a nitration system, which includes a dissolving kettle, a dissolving kettle outer jacket is provided outside the dissolving kettle, a carbazole feeding pipe and a solvent feeding pipe are provided on the top of the dissolving kettle for fully mixing to obtain component A, a bottom discharge port of the dissolving kettle is connected to the nitrating kettle through a pipeline, a propeller stirrer is provided inside the nitrating kettle, a guide tube groove is provided on the inner wall of the nitrating kettle for fully stirring in the nitrating kettle, the outer wall of the nitrating kettle is wrapped with a nitrating kettle jacket, a bottom discharge port of the nitrating kettle is connected to a reaction liquid pipe, the reaction liquid pipe is connected to a nitric acid feeding pipe, a high-speed dispersion pump is provided at the rear end of the nitric acid feeding pipe, an interface for the nitric acid feeding pipe to be connected to the reaction liquid pipe and the high-speed dispersion pump are both installed near the inlet of the tubular reactor, and the high-speed dispersion pump is used to enhance mass transfer, thereby changing the reaction in the prior art that can only be carried out by contact between the two-phase interface into a reaction of the entire dispersed system, greatly increasing the contact opportunity of the two phases and greatly accelerating the reaction speed, the reaction liquid pipe is connected to the tubular reactor, and the top outlet of the tubular reactor is connected to the top of the nitrating kettle.

[0007] Compared with the prior art, the present invention has the following beneficial effects: This invention discloses a method for producing permanent purple nitration. A newly added high-speed dispersing pump disperses nitric acid into fine, even mist-like particles, significantly increasing the chance of contact between the two-phase interface and the raw material liquid, enhancing heat and mass transfer, effectively reducing polynitration side reactions, and significantly improving reaction selectivity. A tubular reactor is added behind the high-speed dispersing pump, allowing the majority of the reaction to be completed within the tubular reactor. The nitric acid concentration, molar ratio, and reaction temperature are determined based on the principle of preventing polynitration, ensuring a more complete reaction and reducing raw material residue. Unreacted N-ethylcarbazole is reduced to below 0.2%, and the amount of polynitrations generated is reduced to below 12%, increasing the yield to 88%. This process completes the reaction in just three hours, significantly shortening reaction time and improving equipment utilization. Furthermore, the tubular reactor removes reaction heat, shifting the reaction from the autoclave to the outside, significantly improving production safety. Furthermore, this method improves reaction yield and reduces raw material costs, achieving multiple optimizations in efficiency, cost, and safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 Schematic diagram of the nitrification system principle of the present invention.

[0009] 1-dissolving kettle; 2-nitrification kettle; 3-high-speed dispersion pump; 4-tubular reactor; 5-carbazole feed pipe; 6-solvent feed pipe; 7-reaction liquid pipe; 8-nitric acid feed pipe. DETAILED DESCRIPTION

[0010] Specific embodiments of the present invention will be described below with reference to the accompanying drawings. Example 1

[0011] A permanent purple nitration production method, such as Figure 1 As shown, the following steps are included: a. Dissolution of N-ethylcarbazole N-ethylcarbazole is uniformly dissolved in an inert organic solvent, wherein the inert organic solvent is any one of 1,2-dichloroethane, acetic acid, chlorobenzene, and dichlorobenzene, and the mass volume ratio of the solute to the solvent is 1:2.0-4.0. The dissolution temperature is controlled by an outer jacket of the dissolving kettle, and the dissolution temperature is 25-30°C. The dissolution process is carried out in the dissolving kettle 1 under constant stirring to obtain component A, i.e., N-ethylcarbazole dissolved in the inert organic solvent, and injected into the nitrating kettle 2; b. Pretreatment with nitric acid Nitric acid with a concentration of 36-45% is used as component B, and component B is connected to the reaction liquid pipe 7 of the nitration reactor 2 through a pipeline, and the molar ratio of component A to component B is controlled to be 1:1.5-1.7; c. Nitration reaction Component B is mixed with the reaction solution from the nitration reactor 2, dispersed into fine particles by a high-speed dispersion pump 3, and then enters the tubular reactor 4. At this time, the nitric acid of component B is mixed with the solution of component A, and a nitration reaction occurs to produce a mixed material; d. Temperature controlled reaction in a tubular reactor The mixed material entering the tubular reactor 4 in step c is cooled by the outer jacket of the tubular reactor, and the temperature is controlled to be 25-75° C. The residence time of the mixed material in the tubular reactor 4 is 100 s-200 s; e. Mixed materials The cooled mixture is returned to the nitration reactor 2, where the temperature is kept at 25-30°C, to achieve circulation. The mixture is stirred and reacted for 3 hours in the nitration reactor. f. Product reception The material is recovered in the nitration kettle 2 and cooled. Specifically, the cooling includes first naturally cooling to 30° C. under slow stirring, then passing ice water into the outer jacket of the nitration kettle, and cooling in an ice bath until the temperature in the nitration kettle 2 is lower than 15° C., standing and stratifying, discarding the upper layer of waste acid, and cooling the lower solvent layer to crystallize and filter to obtain the nitration product 3-nitro-N-ethylcarbazole.

[0012] The yield of the nitration product 3-nitro-N-ethylcarbazole was measured to be 88%. Comparative Example 1

[0013] A permanent purple nitration production method comprises the following steps: Except for not using the high-speed dispersion pump, the rest is exactly the same as Example 1, and the measured yield is 83.0%. Comparative Example 2

[0014] A permanent purple nitration production method comprises the following steps: Except for controlling the molar ratio of component A to component B in step b to be 1:1.7-2.0, the rest is exactly the same as in Example 1, and the measured yield is 82.5%.

[0015] By comparing the examples with comparative example 1, it can be seen that in example 1, nitric acid is dispersed into fine particles to increase the contact area between the two phases, while in comparative example 1, the yield drops to 83.0% after the high-speed dispersion pump is eliminated. It can be concluded that the use of a high-speed dispersion pump to enhance mass transfer is the core factor in improving the yield.

[0016] By comparing the embodiment with comparative example 2, it can be seen that in comparative example 2, the increase in the molar ratio to 1.7-2.0 results in a 5.5% decrease in yield, i.e., 88% vs. 82.5%. It can be verified that a molar ratio greater than 1.7 will induce polynitration side reactions, and the optimal molar ratio range is 1:1.5-1.7.

[0017] Comparing Example 1 with Comparative Examples 1 and 2, the yield of Example 1 can verify that there is a synergistic effect between high-speed dispersion, tubular reaction, and precise molar ratio.

[0018] The scope of protection claimed by the present invention is not limited to the above specific embodiments. For those skilled in the art, the present invention may have various variations and modifications. Any modifications, improvements and equivalent substitutions made within the concept and principle of the present invention should be included in the scope of protection of the present invention.

Claims

1. A permanent purple nitration production method, characterized in that: The following steps are involved: a. Dissolution of N-ethylcarbazole N-ethylcarbazole is uniformly dissolved in an inert organic solvent, the dissolution process being carried out in a dissolving kettle (1) under constant stirring to obtain component A, which is then injected into a nitrifying kettle (2); b. Pretreatment with nitric acid Nitric acid with a concentration of 36-45% is used as component B, and component B is connected to the reaction liquid pipe (7) of the nitrification reactor (2) through a pipeline, and the molar ratio of component A to component B is controlled to be 1:1.5-1.7; c. Nitration reaction The component B is mixed with the reaction solution from the nitration kettle (2), dispersed into fine particles by a high-speed dispersion pump (3), and enters the tubular reactor (4). At this time, the nitric acid of the component B is mixed with the solution of the component A, and a nitration reaction occurs to obtain a mixed material; d. Temperature controlled reaction in a tubular reactor The mixed material entering the tubular reactor (4) in step c is cooled by the outer jacket of the tubular reactor, and the temperature is controlled to be 25-75° C. The residence time of the mixed material in the tubular reactor (4) is 100 s-200 s; e. Mixed materials The cooled mixture is returned to the nitration kettle (2) to achieve circulation, and the stirring reaction is continued in the nitration kettle (2) for 3 hours; f. Product reception The material is recovered in the nitration kettle (2), cooled, allowed to stand for stratification, and the upper layer of waste acid is discarded. The lower solvent layer is cooled, crystallized, and filtered to obtain the nitration product 3-nitro-N-ethylcarbazole.

2. a permanent purple nitration production method according to claim 1, characterized in that: The method is implemented through a nitration system, which comprises a dissolving kettle (1), wherein a carbazole feed pipe (5) and a solvent feed pipe (6) are provided on the top of the dissolving kettle (1), a bottom discharge port of the dissolving kettle (1) is connected to a nitration kettle (2) via a pipeline, an outer wall of the nitration kettle (2) is wrapped with a nitration kettle jacket, a bottom discharge port of the nitration kettle (2) is connected to a reaction liquid pipe (7), the reaction liquid pipe (7) is connected to a nitric acid feed pipe (8), a high-speed dispersion pump (3) is provided at the rear end of the nitric acid feed pipe (8), the reaction liquid pipe (7) is connected to a tubular reactor (4), and a top outlet of the tubular reactor (4) is connected to the top of the nitration kettle (2).

3. a permanent purple nitration production method according to claim 1, characterized in that: The nitrification kettle (2) is provided with a propeller stirrer, and the inner wall of the nitrification kettle (2) is provided with a guide tube groove.

4. a permanent purple nitration production method according to claim 1, characterized in that: In step a, the inert organic solvent is any one of 1,2-dichloroethane, acetic acid, chlorobenzene, and dichlorobenzene, the mass volume ratio of the solute to the solvent is 1:2.0~4.0, and the dissolution temperature is 25~30°C.

5. a permanent purple nitration production method according to claim 2, characterized in that: In step e, the temperature in the nitrification kettle (2) is 25-30°C.

6. a permanent purple nitration production method according to claim 2, characterized in that: In step f, the cooling comprises naturally cooling to 30°C under slow stirring, then introducing ice water into the outer jacket of the nitrification kettle, and cooling in an ice bath until the temperature inside the nitrification kettle (2) is lower than 15°C.

Images