Method for preparing low-moisture and high-purity methyl acetate

Abstract

The invention provides a method for preparing methyl acetate with low moisture (less than or equal to 100ppm) and high purity (more than or equal to 99.5%). The method comprises the following steps: extracting a mixed solution of methanol and methyl acetate with saline water (potassium acetate) to obtain high-purity methyl acetate with high moisture content, then adding cyclopentene for azeotropic dehydration, and carrying out rectification, heavy component removal and decoloration to obtain low-moisture and high-purity methyl acetate.

Description

Technical Field

[0001] The invention relates to the technical field of methyl acetate preparation, and in particular to a method for preparing low-moisture and high-purity methyl acetate. Background Art

[0002] Methanol and methyl acetate are both important chemical products. In the industrial production of polyvinyl alcohol, the problem of separating methyl acetate-methanol mixture is often encountered. Since the above two compounds can form low-boiling azeotropes, they cannot be separated by conventional distillation methods. The commonly used method in industry is extractive distillation (Zhang Donghao, Simulation and Optimization of Extractive Distillation Process of Methyl Acetate-Methanol, Dissertation of Hebei University of Technology, 2003) or salt-adding extractive distillation (Zhao Linxiu et al., Extractive distillation separation of methyl acetate-methanol binary azeotropes, Petrochemicals, February 2005, Volume 34, Issue 2). Extractive distillation is to separate by adding another high-boiling substance (generally referred to as extractive distillation solvent) or adding a salt at the same time, utilizing the different interaction forces between it and each component to be separated to change the relative volatility between the light and heavy key components to achieve separation.

[0003] The separation of methyl acetate and methanol is usually achieved by extractive distillation with water as the extractant, but the extractive distillation process with water as the extractant has the disadvantages of low product purity, large amount of extractant when the methanol concentration is high, and high energy consumption. Therefore, 8-10% salt (potassium acetate) is generally added to water as an extractant to increase the relative volatility difference between the two and reduce energy consumption. The above method can obtain methyl acetate with a purity of more than 99%, but the water content is as high as about 3%, which does not meet market requirements. Summary of the invention

[0004] In view of this, the object of the present invention is to provide a method for preparing low-moisture, high-purity methyl acetate to solve one or more of the above-mentioned prior art problems.

[0005] To achieve the above object, the present invention provides a method for manufacturing a quick-finished resin lens, comprising:

[0006] A. Passing a mixed solution of methanol and methyl acetate into a first distillation tower for distillation, wherein the content of methyl acetate is 78-80%, the content of methanol is 20-22%, and high-water content and high-purity methyl acetate is separated from the top of the tower, wherein the water content of the high-water content and high-purity methyl acetate is greater than 3% and the purity is greater than 99%;

[0007] B. Send the top material of step A to a second distillation tower, add cyclopentene to the top reflux tank for dehydration, and obtain low-moisture methyl acetate at the bottom of the tower, wherein the moisture content of the low-moisture methyl acetate is ≤100ppm;

[0008] C. Sending the bottom material of step B into a third distillation tower for deweighting and decolorization treatment, and obtaining the low-moisture, high-purity methyl acetate at the top of the tower, wherein the low-moisture, high-purity methyl acetate has a moisture content of ≤100ppm and a purity of >99.5%.

[0009] In some embodiments, the distillation conditions of the first distillation tower are: the extractant is 8-10% brine, the number of theoretical plates of the distillation tower is 60-80, the top pressure is 0.2-0.5 MPa, the top temperature is 50-80°C, the bottom temperature is 80-120°C, the reflux ratio is 2-15, and the solvent ratio is 1-8.

[0010] In some embodiments, the distillation conditions of the second distillation tower are: theoretical plate number of 50-70, top temperature of 40-65°C, bottom temperature of 60-80°C, operating pressure of 0.05-0.1 MPa, upstream reflux ratio of 3-8, and downstream reflux / feed of 2-10.

[0011] In some embodiments, the distillation conditions of the third distillation tower are: theoretical plate number of 20 to 30, top temperature of 40 to 60°C, bottom temperature of 50 to 70°C, operating pressure of -0.09 to -0.04 MPa, and reflux ratio of 1 to 3.

[0012] In some embodiments, the cyclopentene content in the reflux tank of the second distillation tower in step B is 60-80%.

[0013] Compared with the prior art, the beneficial effects of the present invention are:

[0014] The methyl acetate produced by the invention has a purity of ≥99.5% and a water content of ≤100 ppm, thereby solving the problem that the methyl acetate with a purity of more than 99% obtained in the prior art has a water content of up to about 3%.

[0015] The first innovation of the present invention is to find a substance with a lower boiling point than methyl acetate and can azeotrope with water. Cyclopentene has a boiling point of 44°C, which is lower than methyl acetate and can azeotrope with water. The cyclopentene at the second reflux port below the distillation tower and the material at the feed port are exchanged for gas and liquid, and the water is azeotropically brought to the top of the tower.

[0016] The second innovation of the present invention is that the cyclopentene content in the reflux tank of the second distillation tower is maintained at 60-80% to ensure the dehydration effect. At the same time, the reflux tank should be regularly operated to separate water to extract the water brought up by the azeotropic reaction to ensure the dehydration effect of methyl acetate.

[0017] The third innovation of the present invention is that the third distillation tower adopts negative pressure distillation, which reduces energy consumption on the one hand and more importantly ensures that methyl acetate has no olefin odor. Even if there is a trace amount of cyclopentene at the bottom of the second distillation tower, it will be pumped into the tail gas treatment system under the vacuum condition of the third distillation tower, and will not affect the quality of methyl acetate. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is the liquid chromatogram of methyl acetate prepared in Example 1. DETAILED DESCRIPTION

[0019] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0020] like Figure 1 As shown:

[0021] Embodiment 1:

[0022] S1. Simple distillation of the mixture of methyl acetate and methanol to obtain a solution that meets their azeotropic composition (methyl acetate 78-80%, methanol 20-22%);

[0023] S2, sending the above solution into a first distillation tower with a theoretical plate number of 60 to 80 for extractive distillation, the tower top temperature is 55 to 70 ° C, the tower bottom temperature is 90 to 110 ° C, the reflux ratio is 2 to 5, the solvent ratio is preferably 2 to 4, and the operating pressure of the tower is 0.2 to 0.5 MPa;

[0024] S3. The purity of the material obtained from the top of the tower is above 99%, and the water content is theoretically around 3%;

[0025] S4, sending the top material of step S2 into a second distillation tower with a theoretical plate number of 50 to 70, the tower has two reflux ports, one is a normal top reflux, and the other is 10 to 15 plates below the feed port, and the two ports are refluxed simultaneously;

[0026] S5. In step S4, the tower top temperature is 50-60°C, the tower bottom temperature is 70-80°C, the tower operating pressure is 0.05-0.1MPa, the upper reflux ratio is 3-6, and the lower reflux / feed ratio is preferably 2-5;

[0027] S6, the cyclopentene to be added to the reflux tank at the top of the tower to azeotropically separate the water, and the cyclopentene content in the reflux tank is maintained at 60-80% to ensure the dehydration effect. If the cyclopentene content does not meet the standard, it can be replaced regularly. At this time, water, cyclopentene, and a small amount of methyl acetate are produced from the top of the tower, and high-purity, low-water methyl acetate is produced from the bottom of the tower;

[0028] S7, the bottom liquid of step S6 is sent to a third distillation tower with a theoretical plate number of 20 to 30 for decolorization and deweighting treatment, the operating pressure of the tower is controlled to be -0.09 to -0.05MPa, the tower top temperature is 40 to 50°C, the tower bottom temperature is 50 to 60°C, the reflux ratio is 1 to 2, and low-water, high-purity methyl acetate can be obtained at the tower top. Its liquid chromatogram is as follows Figure 1 As shown, the purity is greater than 99.9%.

[0029] Sampling test:

[0030] 1. Methyl acetate-methanol extraction process

[0031] 1) The extraction tower ① used has a diameter of DN1000, a theoretical number of plates of about 72, a feed position at the 30th plate, an extractant brine feed position at the 57th plate, heat is provided by 0.9MPa steam, and material transport is controlled by a pump.

[0032] 2) Tower ① is fed with feed according to the set feed amount, and the operating pressure, temperature and reflux are operated according to the calculated set conditions. The material at the top of the tower is analyzed by chromatography, and the results are as follows:

[0033]

[0034]

[0035] It can be seen from the above table that the water content of the high-moisture, high-purity methyl acetate is greater than 3% and the purity is greater than 99%.

[0036] 2. Methyl acetate dehydration process

[0037] 1) The diameter of the tower ② used is DN800, the theoretical number of plates is about 70, the feed position is at the 45th plate, the second reflux is at the 33rd plate, the heat is provided by 0.9MPa steam, and the material transportation is controlled by a pump.

[0038] 2) Tower ② is fed with feed according to the set feed amount, and the operating pressure, temperature and reflux are operated according to the calculated set conditions. The material at the top of the tower is analyzed by chromatography, and the results are as follows:

[0039] Two-way reflux / feed Methyl acetate Methanol Cyclopentene Heavy components Moisture / w% Sample 1 1.5 99.67 - 0.02 0.31 0.053 Sample 2 2 99.91 - 0.04 0.05 0.011 Sample 3 3 99.95 - - 0.05 0.0085 Sample 4 4 99.94 - - 0.06 0.0093 Sample 5 5 99.98 - 0.01 0.01 0.0070 Sample 6 6 99.85 - 0.11 0.04 0.0075 Sample 7 8 98.56 - 1.35 0.09 0.0072

[0040] As can be seen from the above table, the moisture content of the low-moisture vinegar methyl acetate is ≤100ppm.

[0041] 3. Remove the heavy substances and distill to obtain the target product methyl acetate

[0042] 1) The theoretical number of plates of the tower ③ used is about 21, the feed position is at the 12th plate position, the heat is provided by 0.9MPa steam, the material transportation is controlled by a pump, and the negative pressure environment is provided by a vacuum pump.

[0043] 2) Tower ③ is fed with feed according to the set feed amount, and the operating pressure, temperature and reflux are operated according to the calculated set conditions. The material at the top of the tower is analyzed by chromatography, and the results are as follows:

[0044]

[0045]

[0046] From the table above, we can see that low moisture, high purity methyl acetate moisture ≤ 100ppm, purity > 99.5%

[0047] In summary, the methyl acetate produced by the present invention has a purity of ≥99.5% and a water content of ≤100 ppm, which solves the problem that the prior art obtains methyl acetate with a purity of more than 99% but a water content of up to about 3%.

[0048] Finally, it should be noted that: technicians in this industry should understand that the present invention is not limited to the above-mentioned implementation cases. The above-mentioned embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which shall fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A method for preparing low-moisture, high-purity methyl acetate, characterized in that: include: A. Passing a mixed solution of methanol and methyl acetate into a first distillation tower for distillation, wherein the content of methyl acetate is 78-80%, the content of methanol is 20-22%, and high-water content and high-purity methyl acetate is separated from the top of the tower, wherein the water content of the high-water content and high-purity methyl acetate is greater than 3% and the purity is greater than 99%; B. Send the top material of step A to a second distillation tower, add cyclopentene to the top reflux tank for dehydration, and obtain low-moisture methyl acetate at the bottom of the tower, wherein the moisture content of the low-moisture methyl acetate is ≤100ppm; C. Sending the bottom material of step B into a third distillation tower for deweighting and decolorization treatment, and obtaining the low-moisture, high-purity methyl acetate at the top of the tower, wherein the low-moisture, high-purity methyl acetate has a moisture content of ≤100ppm and a purity of >99.5%.

2. The method according to claim 1, characterized in that The distillation conditions of the first distillation tower are as follows: the extractant is 8-10% brine, the theoretical plate number of the distillation tower is 60-80, the top pressure is 0.2-0.5 MPa, the top temperature is 50-80°C, the bottom temperature is 80-120°C, the reflux ratio is 2-15, and the solvent ratio is 1-8.

3. The method according to claim 1, characterized in that The distillation conditions of the second distillation tower are as follows: theoretical plate number of 50-70, tower top temperature of 40-65°C, tower bottom temperature of 60-80°C, operating pressure of 0.05-0.1MPa, upstream reflux ratio of 3-8, and downstream reflux / feed of 2-10.

4. The method according to claim 1, characterized in that The distillation conditions of the third distillation tower are: theoretical plate number of 20 to 30, tower top temperature of 40 to 60° C., tower bottom temperature of 50 to 70° C., operating pressure of -0.09 to -0.04 MPa, and reflux ratio of 1 to 3.

5. The method according to claim 1, characterized in that: The cyclopentene content in the reflux tank of the second distillation tower in step B is 60-80%.

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