Refining device and method for nitrogen-containing solvent precursor and application

Abstract

The invention discloses a refining device and method for a nitrogen-containing solvent precursor and application. The refining method comprises the following steps: by taking an acetamide-containing intermediate product of acetonitrile prepared by ammoniation and dehydration of methyl acetate through a two-step method as a separation raw material, obtaining an acetamide main product, an acetonitrile byproduct and a recycled unreacted raw material through the steps of raw material recovery, azeotropic breaking refining and three-waste separation, and dissolving trace impurity noncondensable gas through self-produced wastewater, and pollution gas is prevented from being discharged. The refining method provided by the invention is environment-friendly and suitable for industrial large-scale continuous operation.

Description

Technical Field

[0001] The present application relates to a refining device and method for a nitrogen-containing solvent precursor and application thereof, and belongs to the technical field of chemical engineering. Background Art

[0002] Acetonitrile is a colorless, transparent, sweet-tasting liquid compound. It is an important fine chemical raw material and is widely used in the synthesis of pharmaceutical and pesticide chemical intermediates. It is also an organic solvent with good performance. At present, there are only two mature acetonitrile synthesis routes: the acrylonitrile byproduct method and the acetic acid ammoniation dehydration method. The acetonitrile production of the former is severely restricted by the acrylonitrile production capacity, and the raw materials of the latter are highly corrosive. At the same time, the profit margin is sharply compressed due to the influence of the raw material price. The new acetonitrile preparation routes are basically in the laboratory research stage and have not been explored for industrialization. Therefore, there is a need for continuous research.

[0003] The two-step ammoniation and dehydration process of methyl acetate is a low-cost, high-purity method for preparing acetonitrile. The difficulty in industrialization of this method lies in the separation and purification process of preparing acetamide by ammoniation of methyl acetate in the first step. Summary of the invention

[0004] According to one aspect of the present application, a method for refining a nitrogen-containing solvent precursor is provided, comprising the following steps:

[0005] a) passing the ammoniation product into a light-removing tower for fractional condensation to obtain a mixture I containing dimethyl ether at the top of the tower, ammonia gas at the side line, and an intermediate product I at the bottom of the tower;

[0006] b) passing the intermediate product I into a methanol column, azeotropically separating I, obtaining a mixture II containing methyl acetate and methanol at the top of the column, and obtaining an intermediate product II at the bottom of the column;

[0007] c) passing the intermediate product II and water into an acetonitrile column to azeotropically separate II to obtain acetonitrile and a mixture III containing acetamide and water;

[0008] d) passing the mixture III into a product tower for separation, obtaining water at the top of the tower and acetamide at the bottom of the tower;

[0009] The molar composition of the amination product is:

[0010] Methyl acetate 3.5~7.5%,

[0011] Ammonia 70~85%,

[0012] Acetonitrile 0.3~2.5%,

[0013] Acetamide 0.4-8.5%;

[0014] Methanol 2.5~7.5%,

[0015] Dimethyl ether 0.001~0.05%,

[0016] Water 0.5~3.5%.

[0017] As a specific refining process, the aminated product is first sent to the light removal tower 1 for condensation, and the dimethyl ether impurity is separated at the top of the tower and a small amount of ammonia is entrained, and sent to the absorption tank 5, where it is mixed with wastewater for absorption and discharged. The light removal tower 1 extracts ammonia from the side line and uses it as a circulating raw material, and the material obtained at the bottom of the tower is sent to the methanol tower 2. The methanol tower 2 breaks part of the azeotropic system through pressure design, separates the mixture of unreacted methyl acetate and methanol at the top of the tower, and sends it to the esterification unit to produce reaction raw materials. The light removal material obtained at the bottom of the tower is sent to the acetonitrile tower 3. The acetonitrile tower 3 breaks the remaining azeotropic system through pressure design, and injects part of the circulating wastewater at the bottom of the tower to avoid acetamide crystallization, obtains acetonitrile byproduct at the top of the tower, and obtains heavy components containing water and acetyl at the bottom of the tower. The bottom material of the acetonitrile tower 3 is separated in the product tower 4 to obtain wastewater and acetamide, and the wastewater is sent to the absorption tank 5 and the bottom of the acetonitrile tower 3 respectively.

[0018] Optionally, in step a), the mixture I is introduced into an absorption tank and mixed with water.

[0019] Optionally, in step b), the mixture II is introduced into an esterification unit for esterification reaction.

[0020] Optionally, in step d), the water obtained from the top of the tower is respectively introduced into the acetonitrile tower and the absorption tank.

[0021] Optionally, in step a), the reflux ratio of the lightness removal tower is 200 to 1000, the number of theoretical plates is 10 to 80, the top temperature is -20 to 60°C, and the operating pressure is 200 to 900 kPaA.

[0022] Optionally, in step b), the reflux ratio of the methanol tower is 0.1-10, the number of theoretical plates is 10-80, the tower top temperature is 60-150° C., and the operating pressure is 300-800 kPaA.

[0023] Optionally, in step c), the reflux ratio of the acetonitrile tower is 0.1 to 60, the number of theoretical plates is 10 to 80, the top pressure is -60 to 20° C., and the operating pressure is 0 to 20 kPaA.

[0024] Optionally, in step d), the reflux ratio of the product tower is 0.01 to 20, the number of theoretical plates is 10 to 80, the tower top temperature is 10 to 60° C., and the operating pressure is 0 to 200 kPaA.

[0025] According to another aspect of the present application, a refining device for a nitrogen-containing solvent precursor is provided, comprising a light removal tower, a methanol tower, an acetonitrile tower, a product tower, and an absorption tank.

[0026] The top outlet of the light-removal tower is connected to the absorption tank, the ammonia outlet of the light-removal tower is connected to the reaction unit, and the bottom outlet of the light-removal tower is connected to the feed port of the methanol tower;

[0027] The top outlet of the methanol tower is connected to the esterification unit, and the bottom outlet of the methanol tower is connected to the feed inlet of the acetonitrile tower;

[0028] The top outlet of the acetonitrile tower is connected to the acetonitrile collection unit, and the bottom outlet of the acetonitrile tower is connected to the feed inlet of the product tower;

[0029] The bottom outlet of the product tower is connected to the acetamide collection unit, and the water vapor outlet of the product tower is connected to the absorption tank and the acetonitrile tower respectively.

[0030] Optionally, the absorption tank is a gas-liquid mixer.

[0031] Optionally, the gas-liquid mixer comprises a two-phase mixing pipe with a gas phase inlet inserted into an insulated container or an internal injection nozzle below the liquid surface.

[0032] According to another aspect of the present application, a method for refining and separating acetamide, a precursor of acetonitrile produced by ammoniation of methyl acetate, is provided, wherein the above-mentioned refining device is selected and the above-mentioned refining method is adopted for refining and separation.

[0033] The beneficial effects of this application include:

[0034] The refining method provided in the present application obtains the main product of acetamide, the by-product of acetonitrile and the unreacted raw materials for recycling after the steps of raw material recovery, azeotropic refining and three waste separation, and dissolves the trace impurities and non-condensable gases by self-produced wastewater, thereby avoiding the discharge of polluting gases. The process is continuous and can be used for the separation and refining of acetamide, the precursor of acetonitrile produced by ammoniation of methyl acetate, which is environmentally friendly and suitable for large-scale continuous operation in industrialization. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a schematic diagram of a method for separating a liquid-phase ammonia-containing mixed product according to Example 1 of the present application; 1. light removal tower, 2. methanol tower, 3. acetonitrile tower, 4. product tower, 5. absorption tank. DETAILED DESCRIPTION

[0036] The present application is described in detail below with reference to embodiments, but the present application is not limited to these embodiments.

[0037] According to one embodiment of the present application, a separation raw material having a molar composition of an amination product of 3.5-7.5% methyl acetate, 70-85% ammonia, 0.3-2.5% acetonitrile, 0.4-8.5% acetamide, 2.5-7.5% methanol, 0.5-3.5% water, and 0.001-0.05% dimethyl ether is refined and separated.

[0038] Figure 1 This is a schematic diagram of a method for separating a liquid phase ammonia-containing mixed product of the present application, the method comprising the following steps:

[0039] 1) The separated raw materials are first sent to the light removal tower 1, where the dimethyl ether impurity is separated at the top of the tower and a small amount of ammonia is entrained, and then sent to the absorption tank 5 to be mixed with the wastewater in the tank for absorption and then discharged; the light removal tower 1 produces ammonia from the side line and uses it as a circulating raw material; the material obtained at the bottom of the light removal tower 1 is sent to the methanol tower 2;

[0040] 2) The methanol tower 2 separates the unreacted methyl acetate and methanol mixture at the top of the tower, and sends it to the esterification unit to produce reaction raw materials. The light-removed material obtained at the bottom of the tower is sent to the acetonitrile tower 3;

[0041] 3) The acetonitrile tower 3 is designed to break the remaining azeotropic system by pressure, and a portion of the circulating wastewater is injected near the bottom of the tower to avoid acetamide crystallization, and acetonitrile byproduct is obtained at the top of the tower, and heavy components containing water and acetyl are obtained at the bottom of the tower;

[0042] 4) The bottom material of the acetonitrile tower 3 is separated in the product tower 4 to obtain waste water and acetamide product, and the waste water is sent to the absorption tank 5 and the acetonitrile tower 3 respectively.

[0043] Example 1

[0044] The separation raw material (molar composition is 5.44% methyl acetate, 82.46% ammonia, 1.10% acetonitrile, 4.40% acetamide, 5.49% methanol, 1.11% water, and 0.0049% dimethyl ether) is first sent to a lightness removal tower 1. The top pressure of the lightness removal tower 1 is 600 kPaA, the top temperature is 3°C, 30 theoretical plates are provided, and the reflux ratio is 600. Waste gas with a molar content of 28.19% of dimethyl ether is separated at the top of the separation tower 1 and sent to an absorption tank 5, where it is adiabatically mixed with waste water and absorbed before being discharged. Ammonia gas with a molar concentration of 99.4% is extracted on the 14th theoretical plate and can be used as a circulating raw material. The material obtained at the bottom of the light removal tower 1 is sent to the methanol tower 2. The top pressure of the methanol tower 2 is 665kPaA, the top temperature is 114°C, 40 theoretical plates are set, and the reflux ratio is 7. A mixture of methanol and methyl acetate is separated at the top of the methanol tower 2 and sent to the esterification device for synthesis. The light removal material obtained at the bottom of the tower is sent to the acetonitrile tower 3. The top pressure of the acetonitrile tower 3 is 1kPaA, the top temperature is -20°C, 50 theoretical plates are set, the reflux ratio is 30, and waste water is injected into the bottom of the tower. The acetonitrile by-product is obtained at the top of the acetonitrile tower 3, and the heavy components containing water and acetyl are obtained at the bottom of the tower. The material at the bottom of the tower is sent to the product tower 4. The top pressure of the product tower 4 is 10kPaA, the top temperature is 46°C, 30 theoretical plates are set, and the reflux ratio is 1. The material is separated in the product tower 4 to obtain waste water and the target product acetamide with a molar concentration of 99.82%. The waste water is divided into two streams and sent to the absorption tank 5 and the bottom of the acetonitrile tower 3 respectively.

[0045] The above are only a few embodiments of the present application and do not constitute any form of limitation to the present application. Although the present application is disclosed as above with preferred embodiments, it is not intended to limit the present application. Any technician familiar with the profession, without departing from the scope of the technical solution of the present application, using the technical content disclosed above to make slight changes or modifications are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A method for purifying a nitrogen-containing solvent precursor, characterized in that: The following steps are involved: a) passing the ammoniation product into a light-removing tower for fractional condensation to obtain a mixture I containing dimethyl ether at the top of the tower, ammonia gas at the side line, and an intermediate product I at the bottom of the tower; b) passing the intermediate product I into a methanol column, azeotropically separating I, obtaining a mixture II containing methyl acetate and methanol at the top of the column, and obtaining an intermediate product II at the bottom of the column; c) passing the intermediate product II and water into an acetonitrile column to azeotropically separate II to obtain acetonitrile and a mixture III containing acetamide and water; d) passing the mixture III into a product tower for separation, obtaining water at the top of the tower and acetamide at the bottom of the tower; The molar composition of the amination product is: Methyl acetate 3.5~7.5%, Ammonia 70-85%, Acetonitrile 0.3~2.5%, Acetamide 0.4-8.5%; Methanol 2.5~7.5%, Dimethyl ether 0.001~0.05%, Water 0.5~3.5%.

2. The refining method according to claim 1, characterized in that In step a), the mixture I is introduced into an absorption tank and mixed with water; Preferably, in step b), the mixture II is introduced into an esterification unit for esterification reaction; Preferably, in step d), the water obtained from the top of the tower is respectively introduced into the acetonitrile tower and the absorption tank.

3. The purification method according to claim 1, characterized in that: In step a), the reflux ratio of the lightness removal tower is 200-1000, the number of theoretical plates is 10-80, the tower top temperature is -20-60°C, and the operating pressure is 200-900 kPaA.

4. The refining method according to claim 1, characterized in that: In step b), the reflux ratio of the methanol tower is 0.1-10, the number of theoretical plates is 10-80, the tower top temperature is 60-150° C., and the operating pressure is 300-800 kPaA.

5. The purification method according to claim 1, characterized in that: In step c), the reflux ratio of the acetonitrile tower is 0.1 to 60, the number of theoretical plates is 10 to 80, the set pressure is -60 to 20° C., and the operating pressure is 0 to 20 kPaA.

6. The purification method according to claim 1, characterized in that: In step d), the reflux ratio of the product tower is 0.01-20, the number of theoretical plates is 10-80, the tower top temperature is 10-60° C., and the operating pressure is 0-200 kPaA.

7. A purification device for a nitrogen-containing solvent precursor, characterized in that: Including light removal tower, methanol tower, acetonitrile tower, product tower, absorption tank, The top outlet of the light-removal tower is connected to the absorption tank, the ammonia outlet of the light-removal tower is connected to the reaction unit, and the bottom outlet of the light-removal tower is connected to the feed port of the methanol tower; The top outlet of the methanol tower is connected to the esterification unit, and the bottom outlet of the methanol tower is connected to the feed inlet of the acetonitrile tower; The top outlet of the acetonitrile tower is connected to the acetonitrile collection unit, and the bottom outlet of the acetonitrile tower is connected to the feed inlet of the product tower; The bottom outlet of the product tower is connected to the acetamide collection unit, and the water vapor outlet of the product tower is connected to the absorption tank and the acetonitrile tower respectively.

8. The refining device according to claim 7, characterized in that: The absorption tank is a gas-liquid mixer.

9. The refining device according to claim 8, characterized in that: The gas-liquid mixer comprises a two-phase mixing pipeline with a gas phase inlet inserted into an insulated container or an internal injection nozzle below the liquid surface.

10. A method for refining and separating acetamide, a precursor of acetonitrile produced by ammoniation of methyl acetate, characterized in that: The refining and separation method is selected from the refining method described in any one of claims 1 to 6; the device for the refining and separation method is selected from the refining device described in any one of claims 7 to 9.

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