A method for continuous pressure swing separation and purification of methacrylic acid

Abstract

The present application relates to a kind of continuous pressure separation purification method of methacrylic acid, to provide a kind of vacuum rectification tower-atmospheric rectification tower combination of pressure rectification, methacrylic acid and water azeotrope as circulating stream, effectively reduce the polymerization of methacrylic acid, obtain high-purity methacrylic acid, reduce the loss of methacrylic acid purification separation iteration, its technical scheme is: methacrylic acid aqueous solution is passed into mixer and is mixed thoroughly;Mixed solution is passed into vacuum rectification tower, and high-purity methacrylic acid product is obtained at the bottom of vacuum rectification tower, and the azeotrope of methacrylic acid and water collected at the top is pumped into atmospheric rectification tower by pipeline;Waste water is discharged from the top of atmospheric rectification tower, and the concentrated methacrylic acid azeotrope obtained at the top flows to mixer and mixes with fresh methacrylic acid aqueous solution, and steps (1) and (2) are repeated;Belong to chemical rectification separation field.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of chemical rectification separation, in particular to a method for continuously separating and purifying methacrylic acid by continuous pressure swing rectification. BACKGROUND

[0002] Molecular formula of methacrylic acid is C4HO2, English abbreviation is MAA, its relative molecular mass is 86.09, it is colorless liquid at normal temperature, it is colorless crystal when temperature is below 15℃, it has irritating odor, it is soluble in hot water, and it can form azeotrope with water. Methacrylic acid can be used for making coating, adhesive, resin and the like. Methacrylic acid is also a chemical raw material with many uses, and it is often used for producing polyol ester.

[0003] A large amount of water is generated in the process of producing polyol ester by direct esterification method using methacrylic acid as raw material. Methacrylic acid and water can form azeotrope, and the molar content of methacrylic acid in the azeotrope composition of methacrylic acid and water under normal pressure is 0.034. In addition, methacrylic acid is a heat-sensitive material, and it is easy to polymerize at high temperature, thus bringing difficulty to the separation of methacrylic acid and water. The energy consumption required for separating the azeotrope of methacrylic acid and water by azeotropic rectification is high, so the industrial separation of methacrylic acid aqueous solution is generally carried out by extractive rectification, that is, methacrylic acid is introduced from the bottom of the extractive rectification column, the extractant is introduced from the upper part of the extractive rectification column, the methacrylic acid aqueous solution and the extractant are countercurrently contacted, then the extractive phase enters the extractant recovery column, the methacrylic acid product is obtained at the bottom of the column, and the overhead stream returns to the extractive column.

[0004] At present, many patents have proposed extractive separation methods for separating methacrylic acid. Chinese patent application CN1850771A discloses an extractive method for methacrylic acid aqueous solution, which comprises adding an additive to the methacrylic acid aqueous solution, and then contacting the solution with an extractant to separate methacrylic acid and water. Chinese patent CN1810758A discloses a method for extracting methacrylic acid aqueous solution by using a mixed solution of ester and hydrocarbon. Chinese patent CN1249739A discloses an extractive method for methacrylic acid aqueous solution, which comprises contacting the methacrylic acid aqueous solution with an extractant to make the extractive and conversion into methacrylic acid. However, the extractive separation process has the disadvantages of partial mutual solubility of the extractive phase and the raffinate phase, and generation of emulsified and flocculated substances at the extractive interface. Compared with the extractive method, the pressure swing method for separating methacrylic acid aqueous solution can obtain high-purity methacrylic acid and greatly improve the thermodynamic effect of the process. SUMMARY

[0005] In view of the above problems, the present application uses two rectification columns with different operating pressures to separate methacrylic acid and water from the idea that the azeotrope composition of the azeotrope is sensitive to pressure.

[0006] To achieve the above object, the present application is realized by the following technical solutions.

[0007] A method for continuously separating and purifying methacrylic acid, which comprises the following steps in sequence:

[0008] (1) mixing: passing the aqueous methacrylic acid solution into a mixer for thorough mixing;

[0009] (2) vacuum rectification: passing the mixed solution into a vacuum rectification column, wherein the operating pressure of the vacuum rectification column is 5-50 KPa, the theoretical plate number is 10, the reflux ratio is 3, the feed position is the 8th plate, and high-purity methacrylic acid product is obtained at the bottom of the vacuum rectification column, and the azeotrope of methacrylic acid and water collected at the top is pumped into a normal-pressure rectification column through a pipeline;

[0010] (3) normal-pressure rectification: pumping the azeotrope at the top of the vacuum rectification column into a normal-pressure rectification column, wherein the operating pressure is 101.325 KPa, the theoretical plate number is 10, the feed position is the 8th plate, the reflux ratio is 3, waste water is discharged from the top of the normal-pressure rectification column, and the concentrated azeotrope of methacrylic acid obtained at the top is flowed to the mixer through a pipeline to mix with fresh aqueous methacrylic acid solution, and steps (1) and (2) are repeated.

[0011] Further, in the above method for continuously separating and purifying methacrylic acid, the difference between the operating pressures of the vacuum rectification column and the normal-pressure rectification column is 50-100 KPa.

[0012] Further, in the above method for continuously separating and purifying methacrylic acid, the polymerization inhibitor is one or more of hydroquinone, p-tert-butyl hydroquinone, tetramethoxyphenol, and DNPC.

[0013] Further, in the above method for continuously separating and purifying methacrylic acid, the total pressure drop of the vacuum rectification column is 2 KPa.

[0014] Further, in the above method for continuously separating and purifying methacrylic acid, the mass ratio of methacrylic acid in the aqueous methacrylic acid solution is 10%-90%.

[0015] Compared with the prior art, the method for separating methacrylic acid and water provided by the present application has the following advantages:

[0016] The technical scheme provided by the present application utilizes the fact that acrylic acid is a heat-sensitive substance and is extremely easy to polymerize at high temperature, and uses pressure swing distillation combining a vacuum distillation column and an atmospheric distillation column, uses the azeotrope of methacrylic acid and water as a circulating stream, effectively reduces the polymerization of methacrylic acid, and obtains high-purity and high-quality methacrylic acid, thereby reducing the loss of methacrylic acid. In addition, the present application does not need to add other substances, thereby reducing the energy consumption in the separation process and greatly improving the thermodynamic effect of the process. DETAILED DESCRIPTION

[0017] The present application will be further described in conjunction with specific examples, but does not constitute any limitation to the present application, and any limited modification made by anyone within the scope of protection of the claims of the present application is still within the scope of protection of the claims of the present application.

[0018] Example 1

[0019] The method for continuously separating and purifying methacrylic acid provided by the present application sequentially comprises the following steps:

[0020] A methacrylic acid solution to be separated with a mass flow of 100 Kg / hr is introduced into a mixer, wherein the mass fraction of methacrylic acid is 0.7 and the mass fraction of water is 0.3. After mixing, the raw material liquid is pumped into a vacuum distillation column, 7 g of hydroquinone is added at the bottom of the vacuum distillation column as a polymerization inhibitor to prevent the polymerization of methacrylic acid, the operating pressure of the vacuum distillation column is 45 KPa, the theoretical tray number is 10, the reflux ratio is 3, the feeding position is the 8th tray, and the total column pressure drop is 2 KPa. High-purity methacrylic acid product is obtained at the bottom of the vacuum distillation column, and the azeotrope of methacrylic acid and water collected at the top is pumped into an atmospheric distillation column through a pipeline; the operating pressure of the atmospheric distillation column is 101.325 KPa, the theoretical tray number is 10, the reflux ratio is 3, the feeding position is the 8th tray, and the total column pressure drop is 2 KPa. Waste water is discharged from the top of the atmospheric distillation column, and the concentrated methacrylic acid azeotrope obtained at the top is flowed to the mixer through a pipeline to be mixed with fresh methacrylic acid aqueous solution. The separation results of the whole process are shown in Table 1.

[0021] Table 1: Results of pressure swing distillation separation streams

[0022]

[0023] Example 2

[0024] The method for continuously separating and purifying methacrylic acid provided by the present application sequentially comprises the following steps:

[0025] The methacrylic acid solution to be separated with a mass flow of 100 Kg / hr is introduced into the mixer, wherein the mass fraction of methacrylic acid is 0.7 and the mass fraction of water is 0.3. The raw material liquid is pumped into the vacuum rectifying column after mixing. 7 g of hydroquinone is added at the bottom of the vacuum rectifying column as a polymerization inhibitor to prevent the polymerization of methacrylic acid. The operating pressure of the vacuum rectifying column is 40 KPa, the theoretical plate number is 10, the reflux ratio is 3, the feeding position is the 8th plate, and the total column pressure drop is 2 KPa. High-purity methacrylic acid product is obtained at the bottom of the vacuum rectifying column. The methacrylic acid and water azeotrope at the top is pumped into the atmospheric rectifying column through a pipeline. The operating pressure of the atmospheric rectifying column is 101.325 KPa, the theoretical plate number is 10, the reflux ratio is 3, the feeding position is the 8th plate, and the total column pressure drop is 2 KPa. Waste water is discharged from the top of the atmospheric rectifying column. The concentrated methacrylic acid azeotrope obtained at the top is flowed to the mixer through a pipeline to mix with fresh methacrylic acid aqueous solution. The separation results of the whole process are shown in Table 2.

[0026] Table 2: Results of pressure swing rectification separation streams

[0027]

[0028] Example 3

[0029] The present application provides a continuous pressure swing separation method for purifying methacrylic acid, which comprises the following steps in sequence:

[0030] The methacrylic acid solution to be separated with a mass flow of 100 Kg / hr is introduced into the mixer, wherein the mass fraction of methacrylic acid is 0.7 and the mass fraction of water is 0.3. The raw material liquid is pumped into the vacuum rectifying column after mixing. 7 g of hydroquinone is added at the bottom of the vacuum rectifying column as a polymerization inhibitor to prevent the polymerization of methacrylic acid. The operating pressure of the vacuum rectifying column is 40 KPa, the theoretical plate number is 10, the reflux ratio is 3, the feeding position is the 8th plate, and the total column pressure drop is 2 KPa. High-purity methacrylic acid product is obtained at the bottom of the vacuum rectifying column. The methacrylic acid and water azeotrope at the top is pumped into the atmospheric rectifying column through a pipeline. The operating pressure of the atmospheric rectifying column is 101.325 KPa, the theoretical plate number is 10, the reflux ratio is 3, the feeding position is the 8th plate, and the total column pressure drop is 2 KPa. Waste water is discharged from the top of the atmospheric rectifying column. The concentrated methacrylic acid azeotrope obtained at the top is flowed to the mixer through a pipeline to mix with fresh methacrylic acid aqueous solution. The separation results of the whole process are shown in Table 2.

[0031] Table 3: Results of pressure swing rectification separation streams

[0032]

[0033] Example 4

[0034] The application provides a method for continuously separating and purifying methacrylic acid, which comprises the following steps in sequence:

[0035] The methacrylic acid solution to be separated with a mass flow of 100 Kg / hr is introduced into a mixer, wherein the mass fraction of the methacrylic acid is 0.8 and the mass fraction of water is 0.2. The raw material liquid is pumped into a vacuum rectifying tower after mixing, 8 g of hydroquinone is added at the bottom of the vacuum rectifying tower as a polymerization inhibitor to prevent the methacrylic acid from polymerizing, the operation pressure of the vacuum rectifying tower is 25 KPa, the theoretical plate number is 10, the reflux ratio is 3, the feeding position is the 8th plate, and the total tower pressure drop is 2 KPa. High-purity methacrylic acid products are obtained at the bottom of the vacuum rectifying tower, the methacrylic acid and water azeotrope at the top is pumped into an atmospheric rectifying tower through a pipeline, the operation pressure of the atmospheric rectifying tower is 101.325 KPa, the theoretical plate number is 10, the reflux ratio is 3, the feeding position is the 8th plate, and the total tower pressure drop is 2 KPa. Waste water is discharged from the top of the atmospheric rectifying tower, and the concentrated methacrylic acid azeotrope obtained at the top is flowed to the mixer through a pipeline to be mixed with fresh methacrylic acid aqueous solution. The separation results of the whole process are shown in Table 4.

[0036] Table 4: Separation results of the variable pressure rectification

[0037]

[0038] Example 5

[0039] The application provides a method for continuously separating and purifying methacrylic acid, which comprises the following steps in sequence:

[0040] The methacrylic acid solution to be separated with a mass flow of 100 Kg / hr is introduced into a mixer, wherein the mass fraction of the methacrylic acid is 0.7 and the mass fraction of water is 0.3. The raw material liquid is pumped into a vacuum rectifying tower after mixing, 7 g of hydroquinone is added at the bottom of the vacuum rectifying tower as a polymerization inhibitor to prevent the methacrylic acid from polymerizing, the operation pressure of the vacuum rectifying tower is 20 KPa, the theoretical plate number is 10, the reflux ratio is 3, the feeding position is the 8th plate, and the total tower pressure drop is 2 KPa. High-purity methacrylic acid products are obtained at the bottom of the vacuum rectifying tower, the methacrylic acid and water azeotrope at the top is pumped into an atmospheric rectifying tower through a pipeline, the operation pressure of the atmospheric rectifying tower is 101.325 KPa, the theoretical plate number is 10, the reflux ratio is 3, the feeding position is the 8th plate, and the total tower pressure drop is 2 KPa. Waste water is discharged from the top of the atmospheric rectifying tower, and the concentrated methacrylic acid azeotrope obtained at the top is flowed to the mixer through a pipeline to be mixed with fresh methacrylic acid aqueous solution. The separation results of the whole process are shown in Table 5.

[0041] Table 5: Separation results of the variable pressure rectification

[0042]

[0043] Example 6

[0044] The application provides a method for continuously separating and purifying methacrylic acid, which comprises the following steps in sequence:

[0045] The methacrylic acid solution to be separated with a mass flow of 100 Kg / hr is introduced into a mixer, wherein the mass fraction of methacrylic acid is 0.8 and the mass fraction of water is 0.2. After mixing, the raw material liquid is pumped into a vacuum rectifying tower, 8 g of hydroquinone is added at the bottom of the vacuum rectifying tower as a polymerization inhibitor to prevent the polymerization of methacrylic acid, the operation pressure of the vacuum rectifying tower is 45 KPa, the theoretical plate number is 10, the reflux ratio is 3, the feeding position is the 8th plate, and the total pressure drop of the tower is 2 KPa. High-purity methacrylic acid product is obtained at the bottom of the vacuum rectifying tower, and the methacrylic acid and water azeotrope at the top of the tower is pumped into an atmospheric rectifying tower through a pipeline, the operation pressure of the atmospheric rectifying tower is 101.325 KPa, the theoretical plate number is 10, the reflux ratio is 3, the feeding position is the 8th plate, and the total pressure drop of the tower is 2 KPa. Waste water is discharged from the top of the atmospheric rectifying tower, and the concentrated methacrylic acid azeotrope obtained at the top is flowed to the mixer through a pipeline to mix with fresh methacrylic acid aqueous solution. The separation results of the whole process are shown in Table 6.

[0046] Table 6: Separation results of the pressure swing rectification

[0047]

[0048] Example 7

[0049] The application provides a method for continuously separating and purifying methacrylic acid, which comprises the following steps in sequence:

[0050] The methacrylic acid solution to be separated with a mass flow of 100 Kg / hr is introduced into a mixer, wherein the mass fraction of methacrylic acid is 0.8 and the mass fraction of water is 0.2. After mixing, the raw material liquid is pumped into a vacuum rectifying tower, 8 g of hydroquinone is added at the bottom of the vacuum rectifying tower as a polymerization inhibitor to prevent the polymerization of methacrylic acid, the operation pressure of the vacuum rectifying tower is 45 KPa, the theoretical plate number is 10, the reflux ratio is 3, the feeding position is the 8th plate, and the total pressure drop of the tower is 2 KPa. High-purity methacrylic acid product is obtained at the bottom of the vacuum rectifying tower, and the methacrylic acid and water azeotrope at the top of the tower is pumped into an atmospheric rectifying tower through a pipeline, the operation pressure of the atmospheric rectifying tower is 101.325 KPa, the theoretical plate number is 10, the reflux ratio is 3, the feeding position is the 8th plate, and the total pressure drop of the tower is 2 KPa. Waste water is discharged from the top of the atmospheric rectifying tower, and the concentrated methacrylic acid azeotrope obtained at the top is flowed to the mixer through a pipeline to mix with fresh methacrylic acid aqueous solution. The separation results of the whole process are shown in Table 6.

[0051] Table 7: Separation results of the pressure swing rectification

[0052]

[0053] Example 8

[0054] The application provides a method for continuously separating and purifying methacrylic acid, which sequentially comprises the following steps:

[0055] The methacrylic acid solution to be separated with a mass flow of 100 Kg / hr is introduced into a mixer, wherein the mass fraction of methacrylic acid is 0.8 and the mass fraction of water is 0.2. After mixing, the raw material liquid is pumped into a vacuum rectification column, 8 g of hydroquinone is added at the bottom of the vacuum rectification column as a polymerization inhibitor to prevent the polymerization of methacrylic acid, the operating pressure of the vacuum rectification column is 25 KPa, the theoretical plate number is 10, the reflux ratio is 3, the feed position is the 8th plate, and the total column pressure drop is 2 KPa. High-purity methacrylic acid product is obtained at the bottom of the vacuum rectification column, and the methacrylic acid and water azeotrope at the top is pumped into an atmospheric rectification column through a pipeline, the operating pressure of the atmospheric rectification column is 101.325 KPa, the theoretical plate number is 10, the reflux ratio is 3, the feed position is the 8th plate, and the total column pressure drop is 2 KPa. Waste water is discharged from the top of the atmospheric rectification column, and the concentrated methacrylic acid azeotrope obtained at the top is flowed to the mixer through a pipeline to mix with fresh methacrylic acid aqueous solution. The separation results of the whole process are shown in Table 8.

[0056] Table 8: Results of pressure swing rectification separation streams

[0057]

[0058] As can be seen from the above example results, the separation method provided by the application can better separate methacrylic acid and reduce the loss of methacrylic acid. From the conclusions of Examples 1, 2, 3, 4 and 5, the greater the pressure difference between the two columns, the easier the separation of methacrylic acid and water, and the higher the purity of the obtained methacrylic acid. From Examples 1 and 6, Examples 2 and 7, and Examples 4 and 8, it can be concluded that under the same operating pressure, the higher the content of methacrylic acid in the methacrylic acid aqueous solution to be separated, the better the separation effect.

Claims

1. A method for the purification of methacrylic acid by continuous pressure swing separation, characterized in that, The method comprises the following steps in sequence: (1) mixing: passing the aqueous solution of methacrylic acid into a mixer for mixing; (2) vacuum rectification: passing the mixed solution into a vacuum rectification tower, adding a polymerization inhibitor at the bottom of the tower, and obtaining high-purity methacrylic acid product at the bottom of the vacuum rectification tower under the operation pressure of 5-50 KPa, the theoretical plate number of 10, the reflux ratio of 3, and the feeding position of the 8th plate; the azeotrope of methacrylic acid and water collected at the top of the tower is pumped into a normal-pressure rectification tower through a pipeline; (3) normal-pressure rectification: pumping the azeotrope at the top of the vacuum rectification tower into the normal-pressure rectification tower under the operation pressure of 101.325 KPa, the theoretical plate number of 10, the feeding position of the 8th plate, and the reflux ratio of 3; the waste water is discharged from the top of the normal-pressure rectification tower, and the concentrated methacrylic acid azeotrope obtained at the top of the tower is flowed into the mixer through a pipeline to mix with the fresh aqueous solution of methacrylic acid, and the steps (1) and (2) are repeated; wherein: the mass ratio of methacrylic acid in the aqueous solution of methacrylic acid is 70%-90%. The operation pressure difference between the vacuum rectification tower and the normal-pressure rectification tower is 50-100 KPa.

2. A process for continuous pressure swing separation and purification of methacrylic acid according to claim 1, characterized in that: The polymerization inhibitor is one or more of hydroquinone, p-tert-butyl hydroquinone, tetramethoxyphenol, and DNPC.

3. The method of claim 1, wherein the method is a continuous process. The total pressure drop of the vacuum rectification tower is 2 KPa.

4. The method of claim 1, wherein the method is a continuous pressure swing separation method for purifying methacrylic acid. ​

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