Method for separating acetonitrile-methanol-ethyl acetate azeotropic system through extraction and pressure swing distillation

Abstract

The invention discloses a method for separating an acetonitrile-methanol-ethyl acetate azeotropic system through three-tower extraction pressure swing distillation, which is characterized in that an acetonitrile-methanol-ethyl acetate azeotropic mixed solution is separated through three-tower operation of an extraction distillation tower T1, an extraction pressurized distillation tower T2 and a solvent recovery pressurized distillation tower T3, the purity of the separated acetonitrile is greater than 99.9%, the yield is greater than 99.9%, and the purity of the separated acetonitrile is greater than 99.9%. The purity of methanol is greater than 99.9%, the yield of methanol is greater than 99.9%, the purity of ethyl acetate is greater than 99.9%, and the yield of ethyl acetate is greater than 99.9%. And the used entrainer chlorobenzene is less in dosage, relatively strong in thermal stability, easy to recycle, relatively low in toxicity and environment-friendly. According to the process, the purity and yield of acetonitrile, methanol and ethyl acetate are improved, and the equipment cost is reduced.

Description

[Technical field]

[0001] The invention belongs to the field of chemical separation and purification, and specifically relates to a method for separating an acetonitrile-methanol-ethyl acetate azeotropic system by pressure swing extraction and distillation. [Background technology]

[0002] As a highly polar solvent, acetonitrile is widely used in synthetic drugs, pesticides, synthetic fibers, spices and other chemicals, such as intermediates such as vitamin B1, ethambutol, and ethoxime. In organic synthesis, it can be used as a reaction medium to participate in halogenation, alkylation and cross-coupling reactions. Methanol is a basic chemical raw material, mainly used to produce compounds such as formaldehyde, acetic acid, and methyl tert-butyl ether (MTBE). It can be used as a hydrogen source for fuel cells and a conversion medium for biodiesel, and plays an important role in the fields of coatings, plastics and synthetic fibers. Ethyl acetate is the preferred solvent for coatings, inks, and adhesives due to its low toxicity and good solubility. It is also used for drug extraction and purification in the pharmaceutical industry and as a natural flavor ingredient in the food industry.

[0003] Acetonitrile, methanol, ethyl acetate mixture will form three binary azeotropic mixtures, acetonitrile-methanol azeotropic point 63.66 ℃, acetonitrile-ethyl acetate azeotropic point 75.78 ℃, methanol-ethyl acetate azeotropic point 62.25 ℃ under 1atm. However, ordinary distillation process cannot achieve effective separation, so it is necessary to adopt a special distillation method. Since acetonitrile-methanol azeotrope, acetonitrile-ethyl acetate azeotrope and methanol-ethyl acetate azeotrope are all pressure-sensitive substances, the present invention adopts a process of coupling pressure swing distillation and extractive distillation. Not only the effective separation of the azeotropic system is achieved, but also the cost and gas emission are relatively small, achieving economic and environmental benefits.

[0004] patent

[0005] The present invention uses an extractive pressure swing distillation method, uses chlorobenzene as an entrainer, and utilizes the characteristics of the entrainer and pressure change to respectively affect the relative volatility and azeotropic composition of the azeotropic system, thereby realizing efficient separation and recovery of the acetonitrile-methanol-ethyl acetate azeotropic mixture and reducing process energy consumption. The method can make the purity of acetonitrile, methanol, and ethyl acetate reach more than 99.9%, the purity of the entrainer chlorobenzene reach more than 99.99%, and the high-purity entrainer can be recycled and reused, reducing process energy consumption and cost. The entrainer chlorobenzene used is used in a small amount, and its high thermal stability and chemical inertness make it difficult to decompose in high-temperature operation, avoiding product contamination, and at the same time, it is easy to be recycled and reused through simple distillation. [Summary of the invention]

[0006] [Technical issues to be solved]

[0007] The purpose of the present invention is to provide a method for separating an azeotropic system of acetonitrile-methanol-ethyl acetate by extractive pressure swing distillation. The coupling influence mechanism of entrainer and pressure on the separation of the azeotropic system of acetonitrile-methanol-ethyl acetate is utilized to make the product purity of acetonitrile, methanol and ethyl acetate after treatment greater than 99.90%. At the same time, the process energy consumption is greatly reduced.

[0008] [Technical solution]

[0009] The method for separating acetonitrile-methanol-ethyl acetate ternary azeotrope by three-tower extractive pressure swing distillation of the present invention is based on the pressure sensitivity characteristics of the azeotropic composition, takes chlorobenzene as an extractant, and adopts a three-tower distillation method of extractive pressure distillation tower T1, extractive pressure distillation tower T2 and solvent recovery distillation tower T3 to achieve high-purity separation of acetonitrile, methanol and ethyl acetate. The method solves the problems of complex process and difficult separation in the current technology and improves the purity of the product.

[0010] The device of the present invention for realizing the method of extractive pressure swing distillation separation of acetonitrile-methanol-ethyl acetate azeotropic system mainly comprises the following parts:

[0011] Extraction pressure distillation tower T1, extraction pressure distillation tower T2, solvent recovery distillation tower T3, condenser C1, condenser C2, condenser C3, cooler C4, reboiler B1, reboiler B2, reboiler B3, centrifugal pump P1, centrifugal pump P2, centrifugal pump P3;

[0012] The method for separating the azeotropic system of acetonitrile-methanol-ethyl acetate by heat-integrated extraction pressure swing distillation using the above device comprises the following steps:

[0013] (1) The acetonitrile-methanol-ethyl acetate raw material mixture and the extractant chlorobenzene enter the extractive pressure distillation tower T1 from different positions. After effective contact and separation, the gas phase at the top of the extractive pressure distillation tower T1 is condensed by the condenser C1, and a part of it is refluxed to the extractive distillation tower T1, and a part of it is extracted as a high-purity product methanol. A part of the acetonitrile-ethyl acetate-extractant mixture in the bottom of the extractive pressure distillation tower T1 enters the reboiler B1 for heating and then refluxes to the bottom of the tower, and the other part is sent to the extractant pressure distillation tower T2 by the centrifugal pump P1;

[0014] (2) After the acetonitrile-ethyl acetate-extractant mixture enters the extractive pressure distillation tower T2, a high-purity acetonitrile product is obtained at the top of the tower, and part of it is refluxed to the extractive distillation tower T2. A part of the liquid phase ethyl acetate-extractant mixture in the bottom of the extractive pressure distillation tower T2 enters the reboiler B1 for heating and then refluxes to the bottom of the tower, and the other part is sent to the extractive pressure distillation tower T3 by the centrifugal pump P2;

[0015] (3) After the ethyl acetate-extractant mixture enters the solvent recovery distillation tower T3, a high-purity ethyl acetate product is obtained at the top of the tower, and part of it is refluxed to the solvent recovery distillation tower T3; the high-purity extractant chlorobenzene is extracted from the bottom stream of the solvent recovery distillation tower T3, and enters the cooler C4 through the centrifugal pump P3, and after cooling, the extractant is supplemented through the mixer and then refluxed to the extractive pressure distillation tower T1;

[0016] The operating pressure of the extractive pressure distillation tower T1 is 1.5 atm, the number of tower plates is 72, the feeding position of the acetonitrile-methanol-ethyl acetate mixture is the 56th plate, the feeding position of the extractant chlorobenzene is the 25th plate, the tower top temperature is 75°C, and the tower bottom temperature is 120°C;

[0017] The operating pressure of the extractive pressure distillation tower T2 is 3.8 atm, the number of plates is 150, the feed position of the mixture is the 78th plate, the feed position of the extractant chlorobenzene is the 25th plate, the top temperature is 130°C, and the bottom temperature is 186°C;

[0018] The operating pressure of solvent recovery distillation tower T3 is 5 atm, the number of plates is 60, the feed position is 30 plates, the top temperature is 135 °C, and the bottom temperature is 207 °C;

[0019] After separation by the method, the purity of acetonitrile is greater than 99.9%, and the yield is greater than 99.9%, the purity of methanol is greater than 99.9%, and the yield is greater than 99.9%, and the purity of ethyl acetate is greater than 99.9%, and the yield is greater than 99.9%.

[0020] [Beneficial Effects]

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) The invention adopts three-tower extractive pressure swing distillation to separate the acetonitrile-methanol-ethyl acetate ternary azeotropic system, which greatly reduces the equipment investment cost, equipment operation energy consumption and operating cost.

[0023] (2) The purity of acetonitrile, methanol and ethyl acetate separated by the extractive pressure swing distillation method is improved, and the economic benefits are improved.

[0024] (3) The amount of extractant used is small, the extractant used is easy to recover, has good chemical and thermal stability, and is green and pollution-free.

Brief Description of the Drawings

[0025] The accompanying drawing is a schematic diagram of a method for separating an azeotropic system of acetonitrile-methanol-ethyl acetate by heat-integrated extraction and pressure swing distillation.

[0026] In the figure, T1-extractive pressure distillation tower, T2-extractive pressure distillation tower, T3-solvent recovery distillation tower, C1-condenser, C2-condenser, C3-condenser, C4-cooler, B1-reboiler, B2-reboiler, B3-reboiler, P1-centrifugal pump, P2-centrifugal pump, P3-centrifugal pump. [Specific implementation method]

[0027] The following is further described in conjunction with the accompanying drawings, which does not limit the scope of the present invention.

[0028] Embodiment 1:

[0029] The feed flow rate is 4932kg / h, the feed contains 24.9% acetonitrile, 28.5% methanol, and 46.6% ethyl acetate (mass fraction). The number of theoretical plates of the extractive pressure distillation tower T1 is 63, and the pressure is 3atm. The acetonitrile-methanol-ethyl acetate mixture enters from the 53rd plate of the extractive distillation tower T1, and the extractant chlorobenzene enters from the 22nd plate of the extractive distillation tower T1, and the flow rate is 10130kg / h. Methanol with a purity greater than 99.9% is obtained at the top of the extractive distillation tower T1, the yield is greater than 99.9%, and the temperature is 95°C; the bottom flow acetonitrile / ethyl acetate / extractant mixture enters from the 74th plate of the extractive pressure distillation tower T2, and the temperature is 141°C. The number of theoretical plates of the extractive pressure distillation tower T2 is 139, and the pressure is 36atm. Acetonitrile with a purity greater than 99.9% and a yield greater than 99.9% is obtained at the top of the extractive pressure distillation tower T2, and the temperature is 151°C; the ethyl acetate / extractant mixture at the bottom of the tower enters the 26th plate of the extractive pressure distillation tower T3, and the temperature is 206°C. The number of theoretical plates of the solvent recovery distillation tower T3 is 42, and the pressure is 9atm. Ethyl acetate with a purity greater than 99.9% and a yield greater than 99.9% is obtained at the top of the solvent recovery distillation tower T3. Chlorobenzene, an extractant with a purity greater than 99.99%, is obtained at the bottom of the tower, and the yield is greater than 99.9% and the temperature is 229°C. The extractant at the bottom of the tower is cooled to 25°C by cooler C4 and supplemented with a small amount of extractant through a mixer, and refluxed to the extractive pressure distillation tower T1.

[0030] Embodiment 2:

[0031] The feed flow rate is 5156kg / h, the feed contains 23.8% acetonitrile, 24.8% methanol, and 51.4% ethyl acetate (mass fraction). The number of theoretical plates of the extractive pressure distillation tower T1 is 72, and the pressure is 1.5atm. The acetonitrile-methanol-ethyl acetate mixture enters from the 56th plate of the extractive distillation tower T1, and the extractant chlorobenzene enters from the 25th plate of the extractive distillation tower T1, with a flow rate of 12944kg / h. Methanol with a purity greater than 99.9% is obtained at the top of the extractive distillation tower T1, with a yield greater than 99.9% and a temperature of 75°C; the bottom stream acetonitrile / ethyl acetate / extractant mixture enters from the 78th plate of the extractive pressure distillation tower T2, with a temperature of 120°C. The number of theoretical plates of the extractive pressure distillation tower T2 is 150, and the pressure is 3.8atm. Acetonitrile with a purity greater than 99.9% and a yield greater than 99.9% is obtained at the top of the extractive pressure distillation tower T2, and the temperature is 130°C; the ethyl acetate / extractant mixture at the bottom of the tower enters the 30th plate of the extractive pressure distillation tower T3, and the temperature is 186°C. The number of theoretical plates of the solvent recovery distillation tower T3 is 60, and the pressure is 5atm. Ethyl acetate with a purity greater than 99.9% and a yield greater than 99.9% is obtained at the top of the solvent recovery distillation tower T3. Chlorobenzene, an extractant with a purity greater than 99.99%, is obtained at the bottom of the tower, and the yield is greater than 99.9% and the temperature is 207°C. The extractant at the bottom of the tower is cooled to 25°C by cooler C4 and supplemented with a small amount of extractant through a mixer, and refluxed to the extractive pressure distillation tower T1.

Claims

1. A method for separating an acetonitrile-methanol-ethyl acetate azeotropic system by three-tower extractive pressure swing distillation, characterized in that The device for implementing the method mainly includes the following parts: (1) The acetonitrile-methanol-ethyl acetate raw material mixed liquid is fed to the extractive pressure distillation tower T1. After the top vapor is condensed by the condenser, part of it is refluxed into the extractive pressure distillation tower T1, and part of the stream flows out of the extractive pressure distillation tower T1 to obtain the methanol product D1. The bottom liquid stream is heated by the reboiler and then enters the extractive pressure distillation tower T2 through the pressure pump P1. (2) After the top vapor of the extractive pressure distillation tower T2 is condensed by the condenser, part of it is refluxed into the extractive pressure distillation tower T2, and part of the flow stream flows out of the extractive pressure distillation tower T2 to obtain acetonitrile product D2. The liquid phase flow stream at the bottom of the tower flows into the solvent recovery tower T3 through the pressure pump P2. (3) The top vapor of the solvent recovery tower T3 is condensed in the condenser and partially refluxed into the solvent recovery tower T3, and partially flows out of the solvent recovery tower T3 to obtain the ethyl acetate product D3. The bottom liquid stream carries the entrainer chlorobenzene product W3 through the pressure reducing valve P3 and the heat exchanger C4 and then circulates into the extractive pressure distillation tower T1 and the extractive pressure distillation tower T2.

2. The method for separating the acetonitrile-methanol-ethyl acetate azeotropic system by three-tower extraction and pressure swing according to claim 1, characterized in that: The molar purity of the acetonitrile product is greater than 99.9%, and the yield is greater than 99.9%; the molar purity of the methanol product is greater than 99.9%, and the yield is greater than 99.9%; the molar purity of the ethyl acetate product is greater than 99.9%; the molar purity of the entrainer chlorobenzene is greater than 99.99%, and the yield is greater than 99.99%.

3. A method for separating acetonitrile-methanol-ethyl acetate azeotropic system by three-tower extractive pressure swing distillation according to claim 1, characterized in that: The molar purity of acetonitrile, methanol and ethyl acetate in the feed composition is 30%, 40% and 30% respectively.

4. The method for separating the azeotropic system of acetonitrile-methanol-ethyl acetate by three-tower extractive pressure swing distillation according to claim 1, characterized in that: The operating pressure of the extractive pressure distillation tower T1 is 1.5 atm, and the reflux ratio is 3; The operating pressure of the extractive pressure distillation tower T2 is 3.8 atm, and the reflux ratio is 4.5; the operating pressure of the solvent recovery tower T3 is 5 atm, and the reflux ratio is 4; the plate pressure drop of the three towers is 0.0068 atm.

5. The method for separating the azeotropic system of acetonitrile-methanol-ethyl acetate by three-tower extractive pressure swing distillation according to claim 1, characterized in that: The top temperature of the extractive pressure distillation tower T1 is 75.21°C, and the bottom temperature is 120.22°C; the top temperature of the extractive pressure distillation tower T2 is 130.92°C, and the bottom temperature is 186.85°C; the top temperature of the solvent recovery tower T3 is 135.94°C, and the bottom temperature is 207.61°C.

6. The method for separating the azeotropic system of acetonitrile-methanol-ethyl acetate by three-tower extractive pressure swing distillation according to claim 1, characterized in that: The theoretical number of plates of the extractive pressure distillation tower T1 is 72 plates, and the feed positions of the entrainer and the acetonitrile-methanol-ethyl acetate mixture are 25 plates and 56 plates, respectively; the theoretical number of plates of the extractive pressure distillation tower T2 is 150 plates, and the feed positions of the entrainer and the mixture are 25 plates and 78 plates, respectively; the theoretical number of plates of the solvent recovery tower T3 is 60 plates, and the feed position is 30 plates.

Images