CN1807401A

CN1807401A - Process for synthesizing dimethylacetamide by ethyl acetate and dimethylamine

Info

Publication number: CN1807401A
Application number: CN 200510022446
Authority: CN
Inventors: 张晓阳; 胡志彪; 刘婷; 黄宏; 李倩; 刘京林
Original assignee: Southwest Research and Desigin Institute of Chemical Industry
Current assignee: Southwest Research and Desigin Institute of Chemical Industry
Priority date: 2005-12-29
Filing date: 2005-12-29
Publication date: 2006-07-26
Anticipated expiration: 2025-12-29
Also published as: CN100420668C

Abstract

The related preparation method for DMAC comprises: using ethyl acetate and dimethylamine by mole ratio as 1: 0. 8~2 as material and at least one of tungsten trioxide, molybdenum trioxide and sodium metavanadate as catalyst to compose the product on condition of 0. 8~2. 5MPa and 80~190Deg. This invention has 92% conversion of ethyl acetate as high material utilization and product purity more than 99. 5%.

Description

Process for synthesizing dimethyl acetamide from ethyl acetate and dimethylamine

The technical field is as follows:

the invention relates to a process synthesis method of an important chemical product, namely dimethylacetamide, in particular to a process method for preparing N, N-dimethylacetamide by utilizing a liquid-phase reaction of ethyl acetate and dimethylamine.

Background art:

n, N-dimethylacetamide (abbreviated as DMAC) is a colorless transparent liquid, has low toxicity, can dissolve various inorganic compounds, and is miscible with water, alcohols, ethers, esters, and aromatic compounds. Has good stability under the condition of no water, acid or alkali. Is an excellent polar solvent for synthesizing natural resin, is used for synthesizing polyimide, polysulfonamide and other high molecular compounds, is also used for film forming and spinning of synthetic resin, crystallization purification of synthetic drugs and aromatic dicarboxylic acid (such as terephthalic acid) and the like, and has wide application in the synthetic materials, petroleum processing and petrochemical industry departments. Can also be used as a catalyst in certain organic reactions, and has high thermal stability, hydrolytic stability, and small corrosivity and toxicity compared with homologous dimethylformamide.

The current international DMAC production methods mainly comprise an acetic anhydride method, an acetyl method and an acetic acid method, wherein the acetic acid method comprises a high-pressure condensation method and a catalytic condensation method, and the two methods arethe current international main methods for producing DMAC.

The industrialized production method is that acetic acid and dimethylamine are subjected to gas phase reaction, a dehydration type solid catalyst is used, the reaction is continuous at normal pressure, the reaction temperature is 260-280 ℃, and the product yield is high. However, the cost for producing the N, N-dimethylacetamide by the route is high due to the increase of investment caused by acetic acid corrosion; the acetic acid and dimethylamine liquid phase intermittent reaction process is carried out under the conditions of high temperature and high pressure, and molybdenum trioxide is introduced into an industrialized device to serve as a catalyst, so that the reaction condition is reduced, the reaction speed is improved, and the yield of DMAC is improved. In addition, the carbonylation reaction of DMAC and trimethylamine synthesized by the reaction of acetic acid, ammonia and methanol and CO is also researched, but no industrial report exists at present. In US Pat.3342862, methyl acetate and methanol with different proportions are reacted with dimethylamine, water and dioxane are respectively used as solvents, and the yield of N, N-dimethylacetamide is close to 90% under the conditions of normal pressure and-6-30 ℃; in Ger Offen.2437702, an azeotrope of methyl acetate and methanol is mentioned to react with dimethylamine, and sodium methoxide is used as a catalyst, so that 45% of N, N-dimethylacetamide is obtained in a reaction product; in US Pat.4258200, a 20% azeotrope of methanol-methyl acetate is reacted with excess dimethylamine, using cobalt acetate tetrahydrate as the catalyst, to give a higher reaction product at 55psi and 160 ° F.

The invention content is as follows:

in order to overcome the defects of the prior art, the invention provides a production process for preparing high-purity N, N-dimethylacetamide by using a liquid-phase reaction of ethyl acetate and dimethylamine.

In order to achieve the aim, the invention uses renewable resource ethanol as a raw material of ethyl acetate, and the chemical reaction equation is as follows:

the overall reaction equation is:

the whole process route is environment-friendly and has high resource utilization rate. Ethanol can be prepared by fermenting crops, and the byproduct hydrogen is clean energy. The invention is technically characterized in that ethyl acetate and dimethylamine are used as raw materials, and N, N-dimethylacetamide is prepared by liquid phase reaction under the action of a catalyst, and the process is characterized by comprising a catalytic reaction technology and a continuous rectification technology:

(a) the catalytic reaction process comprises the following steps: adding ethyl acetate, dimethylamine and a catalyst into a kettle-type reactor according to a certain proportion, heating, pressurizing, stirring and reacting, cooling and separating the reaction liquid to remove the catalyst;

(b) and (3) continuous rectification process: and continuously rectifying the reaction product to separate dimethylamine, ethyl acetate and ethanol, and rectifying the crude distillation product to obtain the product N, N-dimethylacetamide. Excess dimethylamine, ethyl acetate and part of the ethanol were recycled in the system.

The special catalyst used in the reaction system is at least one of tungsten trioxide, molybdenum trioxide and sodium metavanadate, and the catalyst is a powder. The reaction is carried out in a high-pressure reaction kettle which is provided with a stirrer and an electric heating device. Adding ethyl acetate, dimethylamine and catalyst into a reaction kettle according to a certain proportion, heating the reaction kettle, and pressurizing the system by adopting excessive dimethylamine or self-boosting the system or pressurizing the system by using nitrogen to ensure that the system reaches the required pressure condition.

The invention has the technical effects that: compared with the traditional acetic acid method for synthesizing DMAC, the process reduces the corrosion of acetic acid and the reaction temperature; the catalyst selected by the process has high conversion rate and high selectivity, high yield and good stability, and can be recycled; the product is easy to separate, the purity of the dimethylacetamide can reach more than 99.5 percent, and the method has the advantages of high utilization rate of raw materials, low production cost, reasonable process and higher industrial application value.

Drawings

The attached drawing is a schematic and diagrammatic production process flow of the embodiment of the invention.

The specific implementation mode is as follows:

the present invention will be described in detail below by way of examples with reference to the accompanying drawings.

The letter numbers in the figures denote: A. b, C represents three important reaction units: a reaction kettle, a rectifying tower I and a rectifying tower II; the reaction raw materials are D (ethyl acetate), E (dimethylamine), F (catalyst)and I (ethanol);

the substance recycled in the reaction is H (dimethylamine, ethyl acetate, ethanol); g is the crude product in the reaction; the final product of the reaction is J (N, N-dimethylacetamide); other reaction devices comprise an L (vacuum system), a P (pressure gauge) and a T (thermometer); the reaction process comprises M (vacuum condensate) and N (kettle liquid containing acetic acid); in the reaction, W represents that cooling water enters, and Q represents that the cooling water exits; r represents steam in, and S represents steam out.

Example 1:

adding ethyl acetate (720g), dimethylamine (420g) and molybdenum trioxide catalyst (3.6g) and tungsten trioxide catalyst (3g) into A (a kettle type reactor), heating to 142 ℃, naturally raising the pressure to 2.0Mpa, stirring for reaction for 24 hours, cooling and separating reaction liquid to remove the catalyst, continuously rectifying reaction products, namely separating dimethylamine, ethyl acetate and ethanol through B (a rectifying tower I) and C (a rectifying tower II), and rectifying crude distillation products to obtain the product N, N-dimethylacetamide. Excess dimethylamine, ethyl acetate and part of the ethanol were recycled in the system. The conversion rate of ethyl acetate is 92.6 percent, and the selectivity of N, N-dimethylacetamide is more than or equal to 99 percent.

Example 2:

adding ethyl acetate (720g), dimethylamine (420g) and molybdenum trioxide catalyst (8g) into A (a kettle reactor), heating to 172 ℃, pressurizing to 2.5Mpa, stirring for reaction for 20 hours, cooling and separating the reaction liquid to remove the catalyst, continuously rectifying the reaction product, namely separating dimethylamine, ethyl acetate and ethanol through B (a rectifying tower I) and C (a rectifying tower II), and rectifying the crude distillation product to obtain the product N, N-dimethylacetamide. Excess dimethylamine, ethyl acetate and part of the ethanol were recycled in the system. The conversion rate of ethyl acetate is 92.4 percent, and the selectivity of N, N-dimethylacetamide is more than or equal to 99 percent.

Example 3:

adding ethyl acetate (720g), dimethylamine (420g), a tungsten trioxide catalyst (3g), a molybdenum trioxide catalyst (3g) and a sodium metavanadate catalyst (3g) into the reactor A, heating to 165 ℃, pressurizing to 2.2Mpa, stirring for reaction for 20 hours, cooling and separating the reaction liquid to remove the catalyst, continuously rectifying the reaction product, namely separating dimethylamine, ethyl acetate and ethanol through a rectifying tower B (I) and a rectifying tower C (II), and rectifying the crude distillation product to obtain the product N, N-dimethylacetamide. Excess dimethylamine, ethyl acetate and part of the ethanol were recycled in the system. The conversion rate of ethyl acetate is 92.8 percent, and the selectivity of N, N-dimethylacetamide is more than or equal to 99.2 percent.

Example 4:

adding ethyl acetate (720g), dimethylamine (380g) and molybdenum trioxide catalyst (8g) into A (a kettle reactor), heating to 172 ℃, pressurizing to 2.5Mpa, stirring for reaction for 24 hours, cooling and separating the reaction liquid to remove the catalyst, continuously rectifying the reaction product, namely separating dimethylamine, ethyl acetate and ethanol through B (a rectifying tower I) and C (a rectifying tower II), and rectifying the crude distillation product to obtain the product N, N-dimethylacetamide. Excess dimethylamine, ethyl acetate and part of the ethanol were recycled in the system. The conversion rate of ethyl acetate is 92.1 percent, and the selectivity of N, N-dimethylacetamide is more than or equal to 99 percent.

Example 5:

the reaction product containing 7.18% dimethylamine, 30.29% ethanol, 5.19% ethyl acetate, 57.22% N, N-dimethyl acetamide and 0.12% acetic acid is rectified in a glass tower with diameter of 40mm, the height of glass spring packing is 1500mm, the top of the tower is arranged below the condenser, a side draw is arranged 500mm above the tower, the bottom of the tower is heated by an electric heating jacket, the feeding is carried out 500mm below the tower, and the continuous operation is carried out.

The tower I is a normal pressure rectification tower, excessive dimethylamine and a small amount of unreacted ethyl acetate are extracted from the tower top, and ethanol is extracted from the tower.

The tower II is vacuum rectification, a small amount of ethanol is extracted from the tower top, the purity of the N, N-dimethylacetamide obtained in the tower is more than 99.5%, and the once-through recovery rate of the product can reach more than 94%. The kettle liquid containing acetic acid in the tower kettle returns to the reaction kettle.

Claims

1. A process for preparing N, N-dimethyl acetamide is characterized in that ethyl acetate and dimethylamine are used as raw materials, and N, N-dimethyl acetamide is prepared by liquid phase reaction under the action of a catalyst, and the process is characterized by comprising a catalytic reaction technology and a continuous rectification technology:

(b) and (3) continuous rectificationprocess: and continuously rectifying the reaction product to separate dimethylamine, ethyl acetate and ethanol, and rectifying the crude distillation product to obtain the product N, N-dimethylacetamide. Excess dimethylamine, ethyl acetate and part of the ethanol were recycled in the system.

2. The method according to claim 1, wherein at least one of tungsten trioxide, molybdenum trioxide and sodium metavanadate is used as the catalyst for the synthesis.

3. The method of claim 1, wherein the process catalyst is used in the following ratio: the ratio of ethyl acetate to the catalyst (wt) is 1: 0.005-0.1.

4. According to the requirement of claim 3, the proper proportion of the catalyst used in the process is as follows: the ratio of ethyl acetate to the catalyst (wt) is 1: 0.01-0.02.

5. The process of claim 1, wherein the molar ratio of ethyl acetate to dimethylamine in the process is 1: 0.8-2.

6. According to the claim 5, the process has a suitable ratio of ethyl acetate to dimethylamine (mol) of 1: 1.2-1.5.

7. The process according to claim 1, wherein the reaction temperature is 80 to 190 ℃.

8. According to the claim 7, the process is more suitable for the reaction temperature of 140-180 ℃.

9. The process according to claim 1, wherein the reaction pressure is 0.8 to 2.5 MPa.

10. The process ofclaim 1, wherein the dimethylamine has a purity of 99% or more.