Preparation method of high-purity N-N-dimethylaniline
By using copper-zinc-aluminum catalyst for methylation reaction, combined with the process of reduced pressure distillation and falling film crystallization, the problems of catalyst stability and product purity in N,N-dimethylaniline production were solved, and efficient preparation and economic improvement of high-purity products were achieved.
Patent Information
- Application Number
- CN202311374472.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2023-10-23
- Publication Date
- 2025-04-25
AI Technical Summary
The existing N,N-dimethylaniline production process has problems such as poor catalyst stability, many impurities in the product, low product purity and high separation cost.
The methylation reaction was carried out using a copper-zinc-aluminum catalyst, combined with a multi-step process of decompression distillation and falling membrane crystallization, and a high-purity N,N-dimethylaniline product was separated.
It improves the selectivity and purity of N,N-dimethylaniline, reduces equipment investment and operation energy consumption, and solves the problems of catalyst stability and product purity in traditional processes.
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Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of organic chemical industry, and in particular relates to a production method of high-purity NN-dimethylaniline. Background Art
[0002] NN-dimethylaniline (DMA) is mainly used to produce methane dyes, and can also be used as a raw material for the production of solvents, explosives, and medicines. The main consumption areas of DMA are dyes and spices. Due to the good sales of varieties such as basic yellow and basic purple in recent years, DMA consumption has increased. In the spice industry, DMA is mainly used to produce vanillin. As a broad-spectrum spice, vanillin is one of the most widely used spices, and the application of DMA in the spice industry is on the rise. In the pharmaceutical industry, DMA is mainly used as an intermediate for products such as SSM.
[0003] The traditional liquid phase process for the production of N,N-dimethylaniline is carried out in a reactor using sulfuric acid as a catalyst. Although the technology is mature and the product yield is high, the corrosion to the equipment is serious and does not conform to the current concept of green chemical industry. The improvement of the traditional process mainly includes catalyst research and raw material selection. Foreign researchers have tried Raney nickel, Pd / C, liquid homogeneous catalysts, etc., but none of them achieved a high yield. Replacing the N-methylation reagent with alcohols and more active aldehydes and ketones did not solve the problem of low product yield.
[0004] The new gas phase method was first developed by the Indian National Laboratory using a modified alumina catalyst, which achieved continuous low-pressure gas phase production. However, the catalyst stability of this process was poor, and liquid additives needed to be continuously provided to reduce the catalyst. There were also many impurities in the product, and subsequent research processes were improved. BASF modified the alumina catalyst by phosphoric acid impregnation. The modified catalyst had a good effect in the preparation of N,N-dimethylaniline, but the yield was found to be low in the production research of N-methylaniline. Some foreign researchers used co-precipitated self-made molecular sieve catalysts to achieve good yields in the research of N,N-dimethylaniline, but they were limited to laboratory research data and were not enlarged, and the stability of the catalyst needed to be studied.
[0005] Traditionally, N,N-dimethylaniline is separated from products by distillation. However, since the boiling point of its impurities is not much different from that of the product, the product purity is low, or the number of plates in the distillation tower is high, the separation cost is high, and the economic efficiency is poor. At the same time, trace amounts of aniline in the product will affect its color. Summary of the invention
[0006] In view of the problems existing in the prior art, the present invention is proposed to provide a method for preparing high-purity NN-dimethylaniline, wherein the entire reaction process comprises an organic combination of multiple unit operations such as methylation reaction, vacuum distillation, and crystallization, forming a complete set of process technology.
[0007] The main technical scheme of the present invention is a method for preparing high-purity NN-dimethylaniline: methanol and aniline or N-methylaniline are used as raw materials, and a methylation reaction is carried out in the presence of a catalyst; the materials after the reaction are first subjected to reduced pressure distillation to remove methanol and aniline, and then N-methylaniline, aniline and methanol are separated by a falling film crystallization method, and the obtained crystals are NN-dimethylaniline products.
[0008] A typical preparation method of the present invention uses methanol and aniline or N-methylaniline as raw materials, adopts a fixed bed reaction process equipped with a copper-zinc-aluminum catalyst, and is heated at 230-270°C, a pressure of 2.0-2.5 MPa, and a liquid space velocity of 0.3-0.6 h -1 , the molar ratio of methanol to aniline (or N-methylaniline) is 3~7:1, and the circulating gas space velocity is 500~2000h -1 The reaction is carried out under process conditions; the materials after the reaction are first distilled under reduced pressure to remove methanol and aniline, and then N-methylaniline, aniline and methanol are separated by falling film crystallization, and the obtained crystals are NN-dimethylaniline products.
[0009] Furthermore, the copper-zinc-aluminum catalyst used in the present invention has a mass composition of 20-35% copper oxide, 40-60% zinc oxide, 20-35% aluminum oxide, and 0-1% additives. The specific surface area of the copper-based hydrogenation catalyst is 40-80 m 2 / g. Compared with the traditional solid acid catalyst, it can reduce the amount of N-methylaniline produced, facilitate the subsequent product separation, and improve the purity of NN-dimethylaniline product.
[0010] The falling film crystallization in the product separation process of the present invention is operated according to the following process: firstly, the temperature of the crystallizer is controlled at -5-0 DEG C, the material is slowly flowed along the surface of the crystallizer, NN-dimethylaniline is gradually crystallized from top to bottom on the surface of the crystallizer, when the crystallization reaches the lower end of the crystallizer, the material is stopped, and after stagnation for 10-15 minutes, the temperature of the crystallizer is gradually raised to 1.5-2.5 DEG C, and the crystal part is slowly dissolved and dripped; when the crystallizer no longer drips liquid, the temperature is raised to 3-5 DEG C for a second time, the crystal is dissolved and dripped, and then the NN-dimethylaniline product is collected.
[0011] The invention uses methanol and aniline or methanol and N-methylaniline as raw materials: when methanol and aniline are used as raw materials, the molar ratio is 5-7:1; when methanol and N-methylaniline are used as raw materials, the molar ratio is 3-5:1.
[0012] The circulating gas of the present invention is nitrogen or hydrogen, preferably hydrogen.
[0013] The invention has the advantages that the selectivity of N,N-dimethylaniline is improved by using a copper-zinc-aluminum catalyst modified by an auxiliary agent, the generation amount of N-methylaniline which is difficult to separate is reduced, and the vacuum distillation and crystallization coupling process are combined to reduce equipment investment and operating energy consumption compared with the traditional distillation method. Implementation
[0014] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the embodiments of the specification.
[0015] Example 1 Preparation of Catalyst The specific preparation method of the catalyst of the present invention comprises the following steps:
[0016] (1) Prepare an aqueous solution A of a precipitant of either sodium bicarbonate or sodium carbonate with a mass fraction of 13%, and heat to 62°C with stirring; (2) preparing a mixed aqueous solution B containing 10% to 15% copper nitrate and zinc nitrate by mass; (3) Add pseudo-boehmite to the stirred solution A, stir for 30 to 40 minutes, control the temperature at 60 to 70°C during the stirring process, and obtain a mixed suspension C; (4) Add solution B dropwise to suspension C over a period of 15 to 30 minutes, with the temperature controlled at 60 to 70°C. When the reaction is complete, the endpoint pH is controlled to be 8.1. (5) washing and filtering to obtain a filter cake, and drying; (6) Granulation; (7) Spray the additive solution onto the particles, dry them, and then calcine them at 360°C for 3-4 hours; (8) The catalyst is obtained by tableting.
[0017] The amounts of copper nitrate, zinc nitrate, pseudo-boehmite and auxiliary agents cerium nitrate and manganese nitrate in sodium bicarbonate or sodium carbonate are adjusted to obtain catalysts with different physical properties. The specific catalysts are shown in Table 1: Table 1 Physicochemical properties of catalysts
[0018] Example 2 Production of N,N-dimethylaniline The activity of the catalyst sample prepared in Example 1 was evaluated in a fixed bed reactor with a specification of ￠32×2 mm. The activity was evaluated under the conditions in Table 2. The reaction results are shown in Appendix 3.
[0019] Table 2 Reaction process conditions
[0020] The process conditions of the specific embodiment are shown in Table 3.
[0021] Table 3 Example process conditions and results
[0022] From the data in the examples, it can be seen that the use of methanol and N-methylaniline as raw materials is conducive to the formation of N,N-dimethylaniline, and high temperature and high alcohol-amine ratio are conducive to the formation of N,N-dimethylaniline, but side reactions will occur when the temperature is too high. The catalyst N,N-dimethylaniline selectivity of the conditional auxiliary agent is relatively high.
[0023] Example 3 Separation and purification of N,N-dimethylaniline
[0024] The crude product obtained in Implementation 2 is subjected to vacuum distillation and falling film crystallization to obtain NN-dimethylaniline product. The specific operation process and control indicators are as follows: The reacted material is first subjected to reduced pressure distillation to remove methanol and aniline, and then subjected to falling film crystallization. The temperature of the crystallizer is first controlled at -5 to 0°C, and the material is slowly made to flow along the surface of the crystallizer, and NN-dimethylaniline is gradually crystallized from top to bottom on the surface of the crystallizer. When the crystallization reaches the lower end of the crystallizer, the material is stopped from being added, and after stagnation for 10 to 15 minutes, the temperature of the crystallizer is gradually raised to 1.5 to 2.5°C, and the crystal part slowly dissolves and drips; when the crystallizer no longer drips liquid, the temperature is raised to 3 to 5°C for a second time, and the crystal is dissolved and dripped, and then the NN-dimethylaniline product is collected.
[0025] The purity of NN-dimethylaniline is tested by gas chromatography (national standard GB / T 26603-2011).
[0026] Table 4 Conditions and results of separation and purification of N,N-dimethylaniline in Example
[0027] It can be seen from the data in the table that the purity of NN-dimethylaniline obtained by the separation and purification method of coupling reduced pressure distillation and crystallization can reach 99.8%, which is higher than the requirement of 99.5% purity of NN-dimethylaniline in GB / T 26603-2011, and the operating conditions are simple.
Claims
1. A method for preparing high-purity NN-dimethylaniline, characterized in that: Methanol and aniline or N-methylaniline are used as raw materials, and a methylation reaction is carried out in the presence of a catalyst; the materials after the reaction are first subjected to reduced pressure distillation to remove methanol and aniline, and then N-methylaniline, aniline and methanol are separated by a falling film crystallization method, and the obtained crystals are NN-dimethylaniline products.
2. The method for preparing high-purity NN-dimethylaniline according to claim 1, characterized in that: Methanol and aniline or N-methylaniline are used as raw materials, and a fixed bed reaction process equipped with a copper-zinc-aluminum catalyst is used at 230-270°C, a pressure of 2.0-2.5 MPa, and a liquid space velocity of 0.3-0.6 h -1 , the molar ratio of methanol to aniline or N-methylaniline is 3-7: 1, and the circulating gas space velocity is 500-2000h -1 The reaction is carried out under process conditions; the materials after the reaction are first distilled under reduced pressure to remove methanol and aniline, and then N-methylaniline, aniline and methanol are separated by falling film crystallization, and the obtained crystals are NN-dimethylaniline products.
3. The method for preparing high-purity NN-dimethylaniline according to claim 2, characterized in that The mass composition of the copper-zinc-aluminum catalyst is 20-35% copper oxide, 40-60% zinc oxide, 20-35% aluminum oxide, and 0-1% additive. The specific surface area of the copper-zinc-aluminum catalyst is 40-80m 2 / g.
4. The method for preparing high-purity NN-dimethylaniline as claimed in claim 3, characterized in that The auxiliary agent of the copper-zinc-aluminum catalyst is one of manganese or cerium, which is added in the form of nitrate.
5. A method for preparing high-purity NN-dimethylaniline as claimed in claim 1 or 2, characterized in that The falling film crystallization process is as follows: firstly, the temperature of the crystallizer is controlled at -5 to 0°C, the material is slowly flowed along the surface of the crystallizer, and NN-dimethylaniline is gradually crystallized from top to bottom on the surface of the crystallizer; when the crystallization reaches the lower end of the crystallizer, the material is stopped, and after stagnation for 10 to 15 minutes, the temperature of the crystallizer is gradually raised to 1.5 to 2.5°C, and the crystal part is slowly dissolved and dripped; when the crystallizer no longer drips liquid, the temperature is raised to 3 to 5°C for a second time, and the crystal is dissolved and dripped, and then the NN-dimethylaniline product is collected.
6. A method for preparing high-purity NN-dimethylaniline as claimed in claim 1 or 2, characterized in that The molar ratio of methanol to aniline is 5~7:
1.
7. A method for preparing high-purity NN-dimethylaniline as claimed in claim 1 or 2, characterized in that When methanol and N-methylaniline are used as raw materials, the molar ratio is 3~5:
1.
8. The method for preparing high-purity NN-dimethylaniline according to claim 2, wherein The circulating gas is nitrogen or hydrogen.
9. The method for preparing high-purity NN-dimethylaniline according to claim 2 or 8, wherein the circulating gas is hydrogen.