阅读说明：本技术 一种高纯乙腈的精制方法和精制装置 (Refining method and refining device for high-purity acetonitrile ) 是由 周怡 张莹 于 2020-06-02 设计创作，主要内容包括：一种高纯乙腈的精制方法和精制装置,属于有机化工试剂精制领域。高纯乙腈的精制方法包括先将粗乙腈进行脱氰初步除杂,得到乙腈及其共沸物；将乙腈及其共沸物冷凝后,依次加入乙二胺和甲醛,进行化学除杂反应,将化学除杂后的混合物依次进行减压除杂、提纯,得到高纯乙腈。其装置包括脱氰塔、化学除杂反应器、减压精馏除杂塔、加压精馏成品塔和成品接收罐；该方法利用乙二胺提供碱性条件,使氢氰酸、丙烯腈等发生聚合及相互交联反应生成高沸聚合物；然后加入的甲醛与乙二胺形成醛-胺混合液,与剩余的氢氰酸发生反应,生成高沸化合物-乙二胺四乙腈,易于分离,不产生新的杂质,其产生的有机废气和废水均可进行焚烧处理,环境友好,绿色经济。(A refining method and a refining device of high-purity acetonitrile, belonging to the field of organic chemical reagent refining. The refining method of the high-purity acetonitrile comprises the steps of firstly, decyanating crude acetonitrile and primarily removing impurities to obtain acetonitrile and an azeotrope thereof; condensing acetonitrile and azeotrope thereof, sequentially adding ethylenediamine and formaldehyde, carrying out chemical impurity removal reaction, and sequentially carrying out reduced pressure impurity removal and purification on the mixture subjected to chemical impurity removal to obtain high-purity acetonitrile. The device comprises a decyanation tower, a chemical impurity removal reactor, a vacuum rectification impurity removal tower, a pressurized rectification finished product tower and a finished product receiving tank; the method utilizes ethylenediamine to provide alkaline conditions, so that hydrocyanic acid, acrylonitrile and the like are polymerized and cross-linked with each other to generate a high-boiling polymer; then the added formaldehyde and the ethylenediamine form aldehyde-amine mixed solution, and the aldehyde-amine mixed solution reacts with the rest hydrocyanic acid to generate a high-boiling compound, namely ethylene diamine tetraacetic nitrile, which is easy to separate and does not generate new impurities, and organic waste gas and waste water generated by the high-boiling compound can be incinerated, so that the method is environment-friendly and green and economical.)

1. A method for refining high-purity acetonitrile is used for continuously recovering the high-purity acetonitrile from industrial waste crude acetonitrile, and is characterized by comprising the following steps:

the method comprises the following steps:

carrying out decyanation and preliminary impurity removal on the crude acetonitrile to obtain acetonitrile and an azeotrope thereof;

step two:

condensing acetonitrile and an azeotrope thereof, adding ethylenediamine and formaldehyde, and carrying out chemical impurity removal reaction to obtain a mixture after chemical impurity removal; wherein the addition amount of the ethylenediamine is 0.1-0.3 wt% of the addition amount of the crude acetonitrile, and the addition amount of the formaldehyde is 0.2-0.4 wt% of the addition amount of the crude acetonitrile;

step three:

removing impurities from the mixture after chemical impurity removal to obtain impurity-removed acetonitrile;

step four:

purifying the acetonitrile subjected to impurity removal, and removing water, light impurities and heavy impurities to obtain the high-purity acetonitrile with the acetonitrile mass percentage content of more than or equal to 99.5%.

2. The method for refining high-purity acetonitrile according to claim 1, wherein in the first step, light substances and heavy impurities are also obtained in the decyanation process; condensing and refluxing the light substances, burning the uncondensed light substances and discharging heavy impurities.

3. The method for refining high-purity acetonitrile according to claim 1, wherein in the first step, the decyanation process comprises the following process parameters: the pressure at the bottom of the decyanation tower is 0.01-0.1 MPa, the temperature is 100-115 ℃, the side-draw temperature of a stripping section is 80-100 ℃, and the temperature at the top of the decyanation tower is 60-80 ℃.

4. The method for refining high-purity acetonitrile according to claim 1, wherein in the second step, ethylenediamine and formaldehyde are sequentially added, ethylenediamine is added for reaction, and formaldehyde is added after 2-15 hours.

5. The method for refining high-purity acetonitrile according to claim 1, wherein in the second step, the process parameters of the chemical impurity removal reaction are as follows: under normal pressure, the reaction temperature is 40-80 ℃, the pH value is 7-13, and the reaction time is 5-20 h.

6. The method for purifying high-purity acetonitrile according to claim 1, wherein in the second step, the mass concentration of hydrocyanic acid in the obtained mixture after chemical impurity removal is not more than 100 ppm.

7. The method for refining high-purity acetonitrile according to claim 1, wherein in the third step, the process parameters of the secondary impurity removal are as follows: the pressure is controlled to be 150-190 mmHg, the temperature at the top of the tower is 25-45 ℃, and the temperature at the bottom of the tower is 70-90 ℃.

8. The method for refining high-purity acetonitrile according to claim 1, wherein in the fourth step, the process parameters of the purification are as follows: the pressure at the top of the tower is 0.05-0.15 MPa, the temperature at the top of the tower is 85-95 ℃, the temperature at the bottom of the tower is 95-110 ℃, and the discharging temperature is 100-110 ℃.

9. The method for purifying high-purity acetonitrile according to any one of claims 1 to 8, wherein the high-purity acetonitrile contains not less than 99.5% by mass of acetonitrile and not more than 50ppm by mass of water.

10. The method for refining the high-purity acetonitrile according to any one of claims 1 to 8, wherein the device for refining the high-purity acetonitrile adopted by the method comprises a decyanation tower, a chemical impurity removal reactor, a reduced pressure distillation impurity removal tower, a pressurized distillation finished product tower and a finished product receiving tank;

the device comprises a decyanation tower, a chemical impurity removal reactor, a pressure-reduction rectification impurity removal tower, a finished product pressurization rectification tower, a finished product receiving tank, a first heat exchanger, a second heat exchanger, a third heat exchanger, a fourth heat exchanger, a fifth heat exchanger, a sixth heat exchanger, a fifth heat exchanger, a sixth.

Technical Field

The invention belongs to the technical field of organic chemical reagent refining, and particularly relates to a refining method and a refining device for high-purity acetonitrile.

Background

Acetonitrile is also called methyl cyanide, is an organic chemical raw material with wide application, has certain toxicity, can be dissolved with water and alcohol without limit, and is widely used as an extracting agent, a synthetic raw material and a mobile phase solvent of chromatography. Acetonitrile can be subjected to typical nitrile reactions, can prepare a plurality of typical nitrogen-containing compounds, and is an important organic intermediate.

At present, most of chromatographic-grade acetonitrile is obtained by purifying and refining crude acetonitrile which is a byproduct generated in the process of preparing acrylonitrile by propylene ammoxidation. Wherein, contain more impurity in the crude acetonitrile, the majority is water, and organic impurity mainly includes: hydrocyanic acid, acrylonitrile, oxazole, water, acrylic acid, propionitrile, butyronitrile, acetone, and the like.

CN105439903A discloses a method for preparing chromatographic grade acetonitrile by removing impurities through adsorption of graphite oxide and rectifying. In CN106890478A, under the protection of high-purity nitrogen, the impurities in acetonitrile are removed by using a specially treated adsorbent. The adsorbents used in the adsorption method are selective adsorbents, and have poor adsorption effect on part of organic impurities, so that the impurity removal effect is influenced.

In CN1328994A, acetonitrile is continuously recovered by using a combination of traditional processes of chemical treatment, decompression and pressurized azeotropic distillation to remove impurities such as water, hydrocyanic acid, acrylonitrile and the like in the acetonitrile. However, most of the chemical treatment processes in the process all use the alkaline condition provided by sodium hydroxide lye to react and consume hydrocyanic acid and acrylonitrile contained in the crude acetonitrile, a large amount of salt-containing wastewater is generated in the process, the salt-containing wastewater cannot be directly incinerated, and the treatment difficulty and cost of three wastes are increased.

Disclosure of Invention

In view of the problems of the prior art, the present invention provides a method and an apparatus for purifying high-purity acetonitrile, which remove impurities azeotropic with acetonitrile, such as hydrocyanic acid and acrylonitrile, in acetonitrile by using a method of ethylenediamine and formaldehyde. Compared with the traditional process in which a sodium hydroxide solution is directly adopted or the sodium hydroxide solution and formaldehyde are combined, the use of the organic alkali ethylenediamine and formaldehyde avoids the generation of salt-containing wastewater, and the generated organic wastewater can be directly subjected to incineration treatment, so that the process is more green and environment-friendly. In addition, compared to other organic bases, for example: the use of the ethylenediamine does not introduce additional organic impurities, and the ethylenediamine firstly provides an alkali environment to react the impurities acrylonitrile and hydrocyanic acid in the crude acetonitrile to generate succinonitrile high-boiling products, while unreacted hydrocyanic acid is completely reacted to generate high-boiling products such as ethylenediamine diacetonitrile, ethylenediamine tetraacetic nitrile and the like through the reaction of the ethylenediamine, formaldehyde and the hydrocyanic acid. Moreover, the method can not only greatly reduce the content of acrylonitrile in the azeotrope, but also control the content of hydrocyanic acid within 100ppm in the step of the reactor, thereby improving the efficiency and safety of the subsequent purification steps.

The reaction equation for acrylonitrile and hydrocyanic acid under alkaline conditions is as follows:

the reaction equation for ethylenediamine, formaldehyde and hydrocyanic acid is as follows:

H₂NCH₂CH₂NH₂+4HCHO+4HCN→(NC-CH₂)₂N-CH₂-N(CH₂CN)₂+4H₂O

the purpose of the invention is realized by the following technical scheme:

the invention relates to a method for refining high-purity acetonitrile, which is used for continuously recovering the high-purity acetonitrile from industrial waste crude acetonitrile and comprises the following steps:

the method comprises the following steps: carrying out decyanation and preliminary impurity removal on the crude acetonitrile to obtain acetonitrile and an azeotrope thereof;

step two: condensing acetonitrile and an azeotrope thereof, adding ethylenediamine and formaldehyde, and carrying out chemical impurity removal reaction to obtain a mixture after chemical impurity removal; wherein the addition amount of the ethylenediamine is 0.1-0.3 wt% of the addition amount of the crude acetonitrile, and the addition amount of the formaldehyde is 0.2-0.4 wt% of the addition amount of the crude acetonitrile;

step three: removing impurities from the mixture after chemical impurity removal to obtain impurity-removed acetonitrile;

step four: purifying the acetonitrile subjected to impurity removal, and removing water, light impurities and heavy impurities to obtain the high-purity acetonitrile with the acetonitrile mass percentage content of more than or equal to 99.5%.

In the first step, light substances and heavy impurities are also obtained in the decyanation process; condensing and refluxing the light substances, burning the uncondensed light substances and discharging heavy impurities.

In the first step, the decyanation process comprises the following process parameters: the pressure at the bottom of the decyanation tower is 0.01-0.1 MPa, the temperature is 100-115 ℃, the side-draw temperature of a stripping section is 80-100 ℃, and the temperature at the top of the decyanation tower is 60-80 ℃.

In the first step, the heavy impurities removed in the decyanation process are water, propionitrile and butyronitrile.

The light substances are hydrocyanic acid, acrylonitrile and acetone.

In the second step, preferably, ethylenediamine and formaldehyde are sequentially added, ethylenediamine is added for reaction, and formaldehyde is added after 2-15 hours.

In the second step, the technological parameters of the chemical impurity removal reaction are as follows: under normal pressure, the reaction temperature is 40-80 ℃, the pH value is 7-13, and the reaction time is 5-20 h.

In the above technical solution, preferably, ethylenediamine is added into the reactor to provide an alkaline condition, so that organic impurities such as hydrocyanic acid, acrylonitrile and the like which are azeotropic with acetonitrile undergo polymerization and mutual crosslinking reaction under the alkaline condition to generate a high-boiling polymer; and then adding formaldehyde into the reactor to ensure that formaldehyde and ethylenediamine in the reactor form aldehyde-amine mixed liquid to react with the rest hydrocyanic acid in the reactor to firstly generate ethylenediamine diacetonitrile, wherein the ethylenediamine diacetonitrile can continuously react with the hydrocyanic acid to generate ethylenediamine tetraacetonitrile due to the existence of a large amount of hydrocyanic acid in the reactor, so that the hydrocyanic acid, acrylonitrile and other impurities in the reactor are consumed, a high-boiling product which is not azeotropic with acetonitrile is generated, and acetonitrile purification is carried out.

In the above technical scheme, preferably, the mass concentration of hydrocyanic acid in the mixture after chemical impurity removal is less than or equal to 100 ppm.

And in the third step, after secondary impurity removal, obtaining heavy impurities and water which are subjected to secondary impurity removal and discharging the heavy impurities and the water for incineration.

In the third step, the process parameters of secondary impurity removal are as follows: the pressure is controlled to be 150-190 mmHg, the temperature at the top of the tower is 25-45 ℃, and the temperature at the bottom of the tower is 70-90 ℃.

In the fourth step, the process parameters of the purification are as follows: the pressure at the top of the tower is 0.05-0.15 MPa, the temperature at the top of the tower is 85-95 ℃, the temperature at the bottom of the tower is 95-110 ℃, and the discharging temperature is 100-110 ℃.

In the fourth step, in the high-purity acetonitrile, the mass percentage content of the acetonitrile is more than or equal to 99.5 percent, and the mass concentration content of water is less than or equal to 50 ppm.

In order to realize the refining method of the high-purity acetonitrile, the invention also provides a refining device of the high-purity acetonitrile, which comprises a decyanation tower, a chemical impurity removal reactor, a vacuum rectification impurity removal tower, a pressurized rectification finished product tower and a finished product receiving tank;

wherein, connect azeotropic condenser at decyanation tower ejection of compact layer through the pipeline, azeotropic condenser and chemical edulcoration reactor are connected, and chemical edulcoration reactor and decompression rectification edulcoration tower are connected, and decompression rectification edulcoration tower is connected through first heat exchanger and pressurization rectification finished product tower, and pressurization rectification finished product tower passes through the second heat exchanger and is connected with finished product receiving tank.

Furthermore, a reflux branch of a third heat exchanger is arranged at the top of the decyanation tower.

Furthermore, a reflux branch of a fourth heat exchanger is arranged at the bottom of the decyanation tower.

Furthermore, a pump is arranged on a pipeline connecting the chemical impurity removal reactor and the vacuum rectification impurity removal tower, and a reflux branch which flows back to the chemical impurity removal reactor is arranged.

Furthermore, the tower bottom of the vacuum distillation impurity removing tower is provided with a reflux branch of a fifth heat exchanger, and the tower top of the vacuum distillation impurity removing tower is provided with a reflux branch of a sixth heat exchanger.

Furthermore, a reflux branch of a seventh heat exchanger is arranged at the top of the pressurized rectification finished product tower and is connected with a feed inlet of the decyanation tower through a branch pipeline.

Furthermore, a reflux branch of an eighth heat exchanger is arranged at the bottom of the pressurized rectification finished product tower, and a reflux branch of a pressurized rectification finished product tower of a ninth heat exchanger is arranged between pipelines of the pressurized rectification finished product tower and the second heat exchanger.

The invention relates to a refining method and a refining device of high-purity acetonitrile, in particular to a novel chemical impurity removal method, which takes chemical waste crude acetonitrile as a raw material, adopts a device which combines a decyanation tower, a chemical impurity removal reactor, a reduced pressure rectification impurity removal tower and a pressurized rectification finished product tower, and sequentially adds ethylenediamine and formaldehyde into the chemical impurity removal reactor to replace the traditional method of adding caustic alkali for chemical impurity removal. Because of the alkali environment provided by the ethylenediamine added in advance, hydrocyanic acid, acrylonitrile and other organic impurities which are azeotropic with acetonitrile react to generate polymerization and mutual crosslinking, and the succinonitrile high-boiling-point substance is formed. And adding formaldehyde to form an aldehyde-amine mixed solution from formaldehyde and ethylenediamine, removing hydrocyanic acid azeotropic impurities in acetonitrile by using ethylenediamine and formaldehyde, wherein the ethylenediamine and formaldehyde can react with hydrocyanic acid to generate a high-boiling compound, namely ethylenediamine tetraacetic nitrile, so that the ethylenediamine and the formaldehyde are easy to separate, new impurities are not generated, the concentration of hydrocyanic acid in acetonitrile is less than 100ppm, and subsequent purification is facilitated.

Drawings

FIG. 1 is a process flow diagram of a refining method of high-purity acetonitrile according to the present invention.

FIG. 2 is a schematic structural view of a purification apparatus for high-purity acetonitrile according to example 2 of the present invention.

FIG. 3 is a schematic structural view of a purification apparatus for high-purity acetonitrile according to example 3 of the present invention.

In the above figures, a is crude acetonitrile, b is noncondensable light component material flow at the top of a decyanation tower, c is side material flow at a stripping section of the decyanation tower, d is ethylenediamine and formaldehyde, e is upper layer material flow of a chemical impurity removal reactor, f is noncondensable light component material flow at the top of a vacuum distillation impurity removal tower, g is noncondensable light component material flow at the top of a pressurized distillation finished product tower, h is upper side material flow at the stripping section of the pressurized distillation finished product tower, i is high-purity acetonitrile, k is bottom material flow of a decyanation tower, m is bottom material flow of the vacuum distillation impurity removal tower, and n is bottom material flow of the pressurized distillation finished product tower.

The device comprises a decyanation tower 1, a chemical impurity removal reactor 2, a vacuum rectification impurity removal tower 3, a pressurized rectification finished product tower 4, a finished product receiving tank 5, an azeotropic condenser 6, a first heat exchanger 7, a second heat exchanger 8, a third heat exchanger 9, a fourth heat exchanger 10, a fifth heat exchanger 11, a sixth heat exchanger 12, a seventh heat exchanger 13, an eighth heat exchanger 14 and a ninth heat exchanger 15.

Detailed Description

The invention is further illustrated by the following examples:

in the following examples, the raw material crude acetonitrile comprises the following components in percentage by mass: 10-60% of acetonitrile, 0.01-0.3% of acrylonitrile, 0.5-2% of propionitrile, 0.5-1% of acetone, 40-90% of water and 18000-25000 ppm of HCN, wherein the total mass percentage of all the components is 100%.

The process flow of the purification method of high purity acetonitrile will be described with reference to FIG. 1.

Crude acetonitrile a enters from the middle part of a decyanation tower 1, light substances such as hydrocyanic acid, acrylonitrile and the like are removed from the top of the decyanation tower, and after being cooled by a third heat exchanger 9 at the top of the decyanation tower, the crude acetonitrile a is totally refluxed by a reflux pump of the decyanation tower, a liquid phase extraction opening is added at the upper part of the crude acetonitrile a, oxazole materials with higher concentration are extracted, and uncondensed gas and tower top discharge liquid (uncondensed light component material flow b at the top of the decyanation tower) are both sent to an incinerator for treatment; a stripping section side stream c (containing acetonitrile with the mass percentage of 70-80%) of the decyanation tower is extracted from a stripping section side stream gas phase of the decyanation tower 1 and is fed to a chemical impurity removal reactor 2 for chemical treatment after being condensed by an azeotropic condenser 6; part of the water and the recombinant product (decyanation tower bottom material flow k) are discharged from the decyanation tower kettle. The water-containing acetonitrile (side stream c of stripping section of decyanation tower) without most of light components is fed into a chemical impurity removal reactor 2, and ethylenediamine and formaldehyde d are sequentially added for chemical treatment, so that the water-containing acetonitrile reacts with hydrocyanic acid and acrylonitrile to form stable and easily separated components such as ethylenediamine tetraacetonitrile and succinonitrile. The method comprises the following steps of (1) feeding water-containing acetonitrile (upper layer material flow e of a chemical impurity removal reactor) subjected to chemical treatment to remove free hydrocyanic acid and acrylonitrile into a vacuum rectification impurity removal tower 3 for vacuum rectification, removing heavy component impurities (bottom material flow m of the vacuum rectification impurity removal tower) from a tower kettle of the vacuum rectification impurity removal tower 3, feeding acetonitrile (containing acetonitrile with mass percentage concentration of 80-95%) subjected to removal of most of water from the tower top of the vacuum rectification impurity removal tower 3 into a pressure rectification finished product tower 4 for pressure rectification through a first heat exchanger 7; meanwhile, the light component material flow f which is not condensed at the top of the vacuum distillation impurity removing tower flows back to the vacuum distillation impurity removing tower 3 through a sixth heat exchanger 12. And (3) refluxing light components at the top of the pressurized rectification finished product tower 4 (noncondensable light component stream g at the top of the pressurized rectification finished product tower) to the pressurized rectification finished product tower 4 through a seventh heat exchanger 13, extracting high-purity acetonitrile i (side stream h at the upper part of the stripping section of the pressurized rectification finished product tower) from the side stream of the stripping section of the pressurized rectification finished product tower 4 through a second heat exchanger 8, cooling the high-purity acetonitrile i, conveying the high-purity acetonitrile i to a finished product receiving tank 5 (the acetonitrile content is more than or equal to 99.5 percent and the water content is less than 50ppm), exchanging heat of a pressurized rectification finished product tower bottom stream n at the bottom of the pressurized rectification finished product tower 4 through an eighth heat exchanger 14.

Comparative example 1

By adopting the process shown in figure 1, crude acetonitrile raw material containing impurities such as acetonitrile, acrylonitrile, water, propionitrile and the like enters from the middle part of a decyanation tower 1, the feeding temperature is 40 ℃, light components in the crude acetonitrile are discharged from the top of the tower, and the temperature of the top of the tower is 70 ℃; discharging heavy components from the bottom of the tower, wherein the pressure of the bottom of the tower is 0.02MPa, and the temperature of the bottom of the tower is 100 ℃; extracting the acetonitrile-water azeotrope from the stripping section of the decyanation tower in a gas phase mode, wherein the discharging temperature is 90 ℃; the material is sent to a chemical impurity removal reactor after being condensed, alkali (sodium hydroxide or diethylamine and triethylamine) is added into the chemical impurity removal reactor, the temperature of the reactor is controlled to be 40 ℃, the pH value is 11, the reaction time is 10 hours, the hydrocyanic acid content in an azeotrope after the reaction is 4500ppm, and when the diethylamine or triethylamine is added, new impurities are generated while the hydrocyanic acid is consumed, the difficulty of subsequent rectification is increased, and the yield of the finished product acetonitrile is reduced; and (2) sending the azeotrope in the chemical impurity removal reactor to an impurity removal tower, performing reduced pressure rectification under a vacuum condition, wherein the discharged gas at the top of the tower is semi-dry acetonitrile, the temperature at the top of the impurity removal tower is 40 ℃, the gas is sent to a finished product tower for pressure rectification after being condensed, the top pressure of the finished product tower is 0.1MPa, the temperature is 85 ℃, the temperature at the bottom of the tower is 95 ℃, and high-purity acetonitrile is led out to a finished product tank (the acetonitrile content is 99.5%) from a stripping section.