Preparation method of high-purity propylene glycol methyl ether acetate

Abstract

The invention relates to the technical field of high-purity chemicals, and provides a preparation method of high-purity propylene glycol methyl ether acetate. The method comprises the following steps: mixing propylene glycol monomethyl ether, acetic acid and a catalyst to carry out a first-stage reaction, mixing the obtained first reaction liquid with alkali metal to carry out a second-stage reaction, and rectifying the obtained second reaction liquid to obtain the high-purity propylene glycol methyl ether acetate. The alkali metal is added into the reaction liquid obtained in the first-stage reaction, so that the acidity of the product can be reduced, and the key problem that the acidity is relatively high in an esterification synthesis route of propylene glycol methyl ether acetate is solved; unreacted propylene glycol monomethyl ether can be converted into propylene glycol monomethyl ether alkali metal salt with a relatively high boiling point, and the separation difficulty of impurities and a target product can be reduced in subsequent rectification; in addition, hydrolysis of the generated propylene glycol methyl ether alkali metal salt can further promote esterification reaction. The method provided by the invention is simple in required rectification device, high in product purity, low in water content and wide in prospect.

Description

Technical Field

[0001] This invention relates to the field of electronic chemicals technology, and in particular to a method for preparing high-purity propylene glycol methyl ether acetate. Background Technology

[0002] With the rapid growth of the global electronics industry, the market demand for electronic chemicals, as core materials, is constantly increasing. High-purity propylene glycol methyl ether acetate has a very wide solubility and is a low-toxicity, high-performance industrial solvent with wide applications in the field of electronic components, such as in the manufacturing processes of liquid crystal displays and semiconductors.

[0003] Due to the specific requirements in the electronic component industry, high-purity propylene glycol methyl ether acetate requires extremely low levels of moisture and acidic impurities. Due to operational and production cost considerations, esterification synthesis is typically employed, using propylene glycol methyl ether (PM) and acetic acid as raw materials to produce propylene glycol methyl ether acetate. However, this method generates a large amount of water, and the acidic raw materials and catalysts used result in high system acidity, requiring significant investment in post-processing. Currently, propylene glycol methyl ether acetate is typically purified by distillation. Distillation separates components in a mixture based on their different volatility. However, industrially, multiple distillation columns are often connected in series for purification, which is not only energy-intensive and costly but also complex. Simple distillation, on the other hand, is insufficient to effectively obtain high-purity products.

[0004] Chinese patent CN107098810A discloses a method for purifying high-purity propylene glycol methyl ether acetate. The method involves removing light components from the product through distillation using a main column with an attached side column. Simultaneously, a dehydration column is used, and toluene is employed as an entrainer. Distillation is carried out under normal pressure, and the product has an acidity content of <80ppm. However, this method has complex post-processing, and the entrainer toluene used is highly toxic and easily pollutes the environment.

[0005] Chinese patent CN101693661A discloses a method for producing propylene glycol methyl ether acetate. In this method, after the reaction is complete, the product and unreacted materials are first distilled off and then passed through an acid trap to recover the acidic catalyst. The gaseous material then enters a reactive distillation column. An azeotropic agent is added to the upper part of the column to remove water through azeotropic reaction. In the reaction section of the column, under the action of a layered solid acid catalyst, the remaining acetic acid in the material is reacted completely. This patent produces a product with an acidity of 0.0085%. However, this method requires an acid trap and a layered solid catalyst installed below the feed inlet of the distillation column, making the equipment complex and costly.

[0006] Chinese patent CN114702385A discloses a method and apparatus for producing electronic-grade propylene glycol methyl ether acetate. The apparatus includes a precision distillation column, a microfilter, an anion and cation remover, a dehydration processor, and a nanofilter. The precision distillation column includes a string of partitioned columns for precision distillation, which consists of a partitioned column with an upper partition and a partitioned column with an intermediate partition connected in series. In this patent, a precision distillation column is used to remove organic impurities and a small amount of water from industrial-grade propylene glycol methyl ether acetate, and then a dehydration processor is used to remove most of the water. The process has strong continuity, but the use of two distillation columns for separation and purification results in high energy consumption and cost.

[0007] In summary, current methods for preparing high-purity propylene glycol methyl ether acetate all suffer from problems such as complex operation, high energy consumption, and environmental pollution. Developing efficient, environmentally friendly, and economical separation and purification technologies for high-purity propylene glycol methyl ether acetate is of great significance for improving the quality of electronic products and promoting the sustainable development of the industry. Summary of the Invention

[0008] In view of this, the present invention provides a method for preparing high-purity propylene glycol methyl ether acetate. The preparation method provided by the present invention is simple to operate, low in cost, environmentally friendly, and has high removal efficiency for moisture and light component impurities. The resulting high-purity propylene glycol methyl ether acetate has a purity >99.90%, a moisture content <90 mg / L, and a pH value of 7 ± 0.1.

[0009] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0010] A method for preparing high-purity propylene glycol methyl ether acetate includes the following steps:

[0011] Propylene glycol methyl ether, acetic acid and catalyst are mixed to carry out the first stage reaction to obtain the first reaction solution;

[0012] The first-stage reaction solution is mixed with an alkali metal to carry out the second-stage reaction, resulting in a second reaction solution.

[0013] The second reaction solution was distilled to obtain high-purity propylene glycol methyl ether acetate.

[0014] Preferably, the molar ratio of propylene glycol methyl ether to acetic acid is 1 to 10:1.

[0015] Preferably, the catalyst includes one or more of the following: solid acid catalyst resin T-62MP, amberlyst15 catalyst resin, perfluorosulfonic acid resin HNF-5W, and nkc-9 catalyst resin.

[0016] Preferably, the molar ratio of propylene glycol methyl ether to catalyst is 15 to 50:1.

[0017] Preferably, the temperature of the first stage reaction is 60–100°C and the time is 1–4 hours.

[0018] Preferably, the alkali metal includes one or more of sodium, potassium, and lithium; the molar amount of the alkali metal is 1 to 5% of the molar amount of propylene glycol methyl ether.

[0019] Preferably, the temperature of the second-stage reaction is 80–100°C, and the reaction time is 0.5–4 h.

[0020] Preferably, the operating conditions for distillation include: feed temperature of 80–120°C, reboiler temperature of 100–140°C, top reflux ratio of 1–3, middle reflux ratio of 5–10, and pressure of 10–150 kPa; the top product of distillation includes water, propylene glycol methyl ether, and acetic acid, and the middle product includes high-purity propylene glycol methyl ether acetate.

[0021] Preferably, the apparatus used in the preparation method includes a reaction vessel 1;

[0022] Feed pump 2 is connected to the discharge port of reactor 1;

[0023] And a distillation column 3 connected to the outlet of the feed pump 2.

[0024] Preferably, the high-purity propylene glycol methyl ether acetate has a purity >99.90%, a moisture content <90mg / L, a propylene glycol methyl ether content ≤200ppm, a single metal content <10ng / L, and a pH value of 7±0.1.

[0025] This invention provides a method for preparing high-purity propylene glycol methyl ether acetate, comprising the following steps: mixing propylene glycol methyl ether (PM), acetic acid, and a catalyst for a first-stage reaction to obtain a first reaction solution; mixing the first reaction solution with an alkali metal for a second-stage reaction to obtain a second reaction solution; and distilling the second reaction solution to obtain high-purity propylene glycol methyl ether acetate. This invention first esterifies propylene glycol methyl ether and acetic acid, then adds an alkali metal to the reaction solution. The alkali metal reacts with water in the system to generate sodium hydroxide, thereby neutralizing acidic substances in the product and reducing its acidity, solving the key problem of high acidity in the esterification synthesis route of propylene glycol methyl ether acetate. Furthermore, the alkali metal can also react with propylene glycol methyl ether in the system to generate a high-boiling-point propylene glycol methyl ether alkali metal salt, which reduces the difficulty of separating impurities and the target product in subsequent distillation. In addition, the hydrolysis of the propylene glycol methyl ether alkali metal salt promotes the reversible esterification reaction, improving the raw material conversion rate and product yield with high purity. In summary, the method provided by this invention requires a simple distillation apparatus, produces a product with high purity and low water content, and eliminates the need for toxic reagents such as toluene. High-purity propylene glycol methyl ether acetate with extremely low water content can be obtained through a single simple distillation. Example results show that the high-purity propylene glycol methyl ether acetate prepared by this invention has a purity >99.90%, a water content <90 mg / L, a propylene glycol methyl ether content ≤200 ppm, a single metal content <10 ng / L, and a pH value of 7 ± 0.1. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the apparatus used in the preparation method of the present invention; wherein: 1-reaction vessel, 2-feed pump, 3-distillation column. Detailed Implementation

[0027] This invention provides a method for preparing high-purity propylene glycol methyl ether acetate, comprising the following steps:

[0028] Propylene glycol methyl ether, acetic acid and catalyst are mixed to carry out the first stage reaction to obtain the first reaction solution;

[0029] The first reaction solution is mixed with an alkali metal to carry out a second-stage reaction, resulting in a second reaction solution.

[0030] The second reaction solution was distilled to obtain high-purity propylene glycol methyl ether acetate.

[0031] This invention involves mixing propylene glycol methyl ether, acetic acid, and a catalyst to conduct a first-stage reaction, yielding a first reaction solution. In this invention, the preferred molar ratio of propylene glycol methyl ether to acetic acid is 1–10:1, more preferably 1–5:1, and even more preferably 1:1; both propylene glycol methyl ether and acetic acid are preferably industrial grade; the catalyst preferably includes one or more of the following: solid acid catalyst resin T-62MP, amberlyst15 catalyst resin, perfluorosulfonic acid resin HNF-5W, and nkc-9 catalyst resin; the preferred molar ratio of propylene glycol methyl ether to the catalyst is 15–50:1, more preferably 15:1, 25:1, 40:1, or 50:1.

[0032] In this invention, the temperature of the first-stage reaction is preferably 60-100°C, more preferably 60-80°C, and the reaction time is preferably 1-4 hours, more preferably 2-3 hours. The first-stage reaction is specifically an esterification reaction of propylene glycol methyl ether and acetic acid. The main components of the resulting first reaction solution include propylene glycol methyl ether acetate, water, and unreacted propylene glycol methyl ether and acetic acid. In a specific embodiment of this invention, the water content of the first reaction solution is 150-200 mg / L.

[0033] After obtaining the first reaction solution, the present invention mixes the first reaction solution with an alkali metal to carry out a second-stage reaction to obtain a second reaction solution. In the present invention, the alkali metal preferably includes one or more of sodium, potassium, and lithium, more preferably sodium; the molar amount of the alkali metal is preferably 1 to 5% of the molar amount of propylene glycol methyl ether, more preferably 2 to 3%.

[0034] In this invention, the preferred temperature for the second-stage reaction is 80–100°C, more preferably 85–95°C, and the preferred reaction time is 0.5–4 h, more preferably 1–3 h. In this invention, the alkali metal exhibits high reactivity with the hydroxyl groups in the propylene glycol methyl ether structure. The specific reactions occurring in the second-stage reaction include: the reaction of the alkali metal and propylene glycol methyl ether to generate a propylene glycol methyl ether alkali metal salt; the hydrolysis of the propylene glycol methyl ether alkali metal salt and its promotion of the continued esterification reaction of acetic acid and propylene glycol methyl ether in the system; and the neutralization reaction between sodium hydroxide and hydrogen ions. Taking sodium alkali metal as an example, the reactions occurring in the second stage are as follows:

[0035] 2PM + 2Na = 2PMNa + H2↑;

[0036] PMNa + H2O = NaOH + PM;

[0037]

[0038] NaOH + H+ + =H2O + Na + .

[0039] The present invention adds an alkali metal to the first reaction solution, which can remove acid and at the same time convert propylene glycol methyl ether into a high-boiling-point propylene glycol methyl ether alkali metal salt, which is then removed by distillation as a heavy component, thus reducing the difficulty of separating impurities and target products.

[0040] In this invention, the main components of the second reaction solution include propylene glycol methyl ether acetate, propylene glycol methyl ether alkali metal salt, a very small amount of unreacted propylene glycol methyl ether and acetic acid, and a very small amount of water; in a specific embodiment of this invention, the water content in the second reaction solution is ≤90 mg / L. In a specific embodiment of this invention, after the second stage reaction is completed, it is preferable to raise the temperature of the second reaction solution to the feed temperature for distillation, and then allow it to enter the distillation column for distillation.

[0041] After obtaining the second reaction solution, the present invention performs distillation on the second reaction solution to obtain high-purity propylene glycol methyl ether acetate. In the present invention, the distillation is preferably single-tower distillation; the preferred operating conditions for distillation include: feed temperature preferably 80-120℃, more preferably 90-110℃, bottom temperature preferably 100-140℃, more preferably 120-130℃, top reflux ratio preferably 1-3, more preferably 2-3, middle reflux ratio preferably 5-10, more preferably 6-8, and pressure preferably 10-150 kPa, more preferably 50-100 kPa; the top product of the distillation includes water, propylene glycol methyl ether, and acetic acid, the middle product includes high-purity propylene glycol methyl ether acetate, and the bottom residue is propylene glycol methyl ether alkali metal salt; in a specific embodiment of the present invention, the top fraction is preferably reused as raw material.

[0042] In this invention, the apparatus used in the preparation method preferably includes a reaction vessel 1;

[0043] Feed pump 2 is connected to the discharge port of reactor 1;

[0044] And a distillation column 3 connected to the outlet of the feed pump 2.

[0045] In this invention, the structural schematic diagram of the device is as follows: Figure 1 As shown below. (Combined with...) Figure 1 The specific process of this invention is as follows: First, propylene glycol methyl ether and acetic acid are added to reactor 1 for the first stage reaction. Then, the reactor is heated and alkali metal is added for the second stage reaction. After the second stage reaction is completed, the temperature of reactor 1 is raised to the feed temperature of distillation column 3, and the resulting second reaction liquid is pumped into distillation column 3 via feed pump 2 for distillation. Water, propylene glycol methyl ether, and acetic acid are collected at the top of the column, and high-purity propylene glycol methyl ether acetate is collected from the column. The reaction of propylene glycol methyl ether and acetic acid in reactor 1 is a continuous reaction, and after the reaction is completed, it can be directly purified by distillation in distillation column 3.

[0046] In this invention, the moisture and organic purity of propylene glycol methyl ether acetate products are tested using a moisture analyzer and a gas chromatograph, and the results are compared with the SEMI high-purity propylene glycol methyl ether acetate standard to determine the product purity level. High-purity propylene glycol methyl ether acetate has a purity >99.90%, a moisture content <90 mg / L, a propylene glycol methyl ether content ≤200 ppm, a single metal content <10 ng / L, and a pH value of 7 ± 0.1.

[0047] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0048] The apparatus used in the embodiments is as follows Figure 1 As shown, the raw materials, propylene glycol methyl ether and acetic acid, are both industrial grade, and the catalyst is Amberlyst 15.

[0049] Example 1

[0050] Propylene glycol methyl ether (PM), acetic acid, and catalyst were added to reactor 1, with 5.4 mol of propylene glycol methyl ether used. The molar ratio of propylene glycol methyl ether to acetic acid was 1:1, and the molar ratio of propylene glycol methyl ether to catalyst was 15:1. The reaction was carried out at 60°C for 4 hours, and the conversion rate of PM was found to be 40%. Then, reactor 1 was heated to 80°C, and sodium metal was added, with the amount of sodium metal being 2% of the molar amount of propylene glycol methyl ether. After reacting for 2 hours, the temperature of reactor 1 was raised to 100°C, and the reaction solution was pumped into distillation column 3 for distillation. The distillation operating conditions were: column bottom temperature of 110°C, top reflux ratio of 1, middle reflux ratio of 5, and distillation pressure of 100 kPa. Propylene glycol methyl ether, acetic acid, and water were collected from the top of the column, high-purity propylene glycol methyl ether acetate was collected from the middle of the column, and the remaining residue was sodium propylene glycol methyl ether. The water content and purity of the obtained product were detected by a moisture analyzer and a gas chromatograph. The results showed that the PM content of the obtained high-purity propylene glycol methyl ether acetate was as low as 150 ppm, the water content was as low as 82 mg / L, the pH value was 7±0.1, and the purity of the main product propylene glycol methyl ether acetate was 99.9580%.

[0051] Example 2

[0052] Propylene glycol methyl ether (PM), acetic acid, and catalyst were added to reactor 1, with 5 mol of propylene glycol methyl ether used. The molar ratio of propylene glycol methyl ether to acetic acid was 1:1, and the molar ratio of propylene glycol methyl ether to catalyst was 40:1. The reaction was carried out at 80°C for 3 hours, and the conversion rate of PM was measured to be 45%. Then, reactor 1 was heated to 90°C, and sodium metal was added, with the amount of sodium metal being 1% of the molar amount of propylene glycol methyl ether. After reacting for 3 hours, the temperature of reactor 1 was raised to 110°C, and the reaction solution was pumped into distillation column 3 for distillation. The distillation operating conditions were: column bottom temperature of 130°C, top reflux ratio of 3, middle reflux ratio of 8, and distillation pressure of 140 kPa. Propylene glycol methyl ether, acetic acid, and water were collected from the top of the column, high-purity propylene glycol methyl ether acetate was collected from the middle of the column, and the remaining residue was sodium propylene glycol methyl ether. The water content and purity of the obtained product were detected by a moisture analyzer and a gas chromatograph. The results showed that the PM content of the obtained high-purity propylene glycol methyl ether acetate was as low as 200 ppm, the water content was as low as 85 mg / L, the pH value was 7±0.1, the single metal content was <10 ng / L, and the purity of the main product propylene glycol methyl ether acetate was 99.9450%.

[0053] Example 3

[0054] Propylene glycol methyl ether (PM), acetic acid, and catalyst were added to reactor 1, with 4 mol of propylene glycol methyl ether used. The molar ratio of propylene glycol methyl ether to acetic acid was 1:1, and the molar ratio of propylene glycol methyl ether to catalyst was 50:1. The reaction was carried out at 100°C for 1 hour, and the conversion rate of PM was found to be 50%. Then, reactor 1 was heated to 90°C, and sodium metal was added, with the amount of sodium metal being 3% of the molar amount of propylene glycol methyl ether. After reacting for 1 hour, the temperature of reactor 1 was raised to 120°C, and the reaction solution was pumped into distillation column 3 for distillation. The distillation operating conditions were: column bottom temperature of 140°C, top reflux ratio of 3, middle reflux ratio of 10, and distillation pressure of 60 kPa. Propylene glycol methyl ether, acetic acid, and water were collected from the top of the column, high-purity propylene glycol methyl ether acetate was collected from the middle of the column, and the remaining residue was sodium propylene glycol methyl ether. The water content and purity of the obtained product were detected by a moisture analyzer and a gas chromatograph. The results showed that the PM content of the obtained high-purity propylene glycol methyl ether acetate was as low as 120 ppm, the water content was as low as 75 mg / L, the acidity was 7 ± 0.1, the single metal content was < 10 ng / L, and the purity of the main product, propylene glycol methyl ether acetate, was 99.9600%.

[0055] Example 4

[0056] Propylene glycol methyl ether (PM), acetic acid, and catalyst were added to reactor 1, with 6 mol of propylene glycol methyl ether used. The molar ratio of propylene glycol methyl ether to acetic acid was 1:1, and the molar ratio of propylene glycol methyl ether to catalyst was 25:1. The reaction was carried out at 70°C for 3 hours, and the conversion rate of PM was measured to be 42%. Then, reactor 1 was heated to 80°C, and sodium metal was added, with the amount of sodium metal being 5% of the molar amount of propylene glycol methyl ether. After reacting for 0.5 hours, the temperature of reactor 1 was raised to 90°C, and the reaction solution was then pumped into distillation column 3 for distillation. The distillation operating conditions were: column bottom temperature of 100°C, top reflux ratio of 2, middle reflux ratio of 6, and distillation pressure of 90 kPa. Propylene glycol methyl ether, acetic acid, and water were collected from the top of the column, high-purity propylene glycol methyl ether acetate was collected from the middle of the column, and the remaining residue was sodium propylene glycol methyl ether. The water content and purity of the obtained product were detected by a moisture analyzer and a gas chromatograph. The results showed that the PM content of the obtained high-purity propylene glycol methyl ether acetate was as low as 100 ppm, the water content was as low as 70 mg / L, the pH value was 7±0.1, the single metal content was <10 ng / L, and the purity of the main product propylene glycol methyl ether acetate was 99.9630%.

[0057] Example 5

[0058] Other conditions were the same as in Example 1, except that sodium was replaced with potassium. Testing revealed that the obtained high-purity propylene glycol methyl ether acetate had a PM content as low as 130 ppm, a moisture content as low as 78 mg / L, an acidity of 7 ± 0.1, a single metal content of <10 ng / L, and a purity of 99.9670% for the main product, propylene glycol methyl ether acetate.

[0059] Example 6

[0060] Other conditions were the same as in Example 1, except that sodium metal was replaced with lithium metal. Testing revealed that the obtained high-purity propylene glycol methyl ether acetate had a PM content as low as 195 ppm, a moisture content as low as 89 mg / L, a pH value of 7 ± 0.1, a single metal content of <10 ng / L, and a purity of 99.9370% for the main product, propylene glycol methyl ether acetate.

[0061] Comparative Example 1

[0062] Other conditions were the same as in Example 1, except that metallic sodium was omitted. Testing revealed that the obtained high-purity propylene glycol methyl ether acetate contained 1070 mg / L of PM, 385 ppm of moisture, and a pH of 7 ± 0.5. The purity of the main product, propylene glycol methyl ether acetate, was 99.8380%.

[0063] Comparative Example 2

[0064] Other conditions were the same as in Example 1, except that sodium was replaced with calcium. Testing revealed that the obtained high-purity propylene glycol methyl ether acetate contained 1100 mg / L of PM, 260 ppm of moisture, and a pH of 7 ± 0.5. The purity of the main product, propylene glycol methyl ether acetate, was 99.8500%.

[0065] In summary, the present invention provides a method for preparing high-purity propylene glycol methyl ether acetate. By adding an alkali metal to the reaction solution, the alkali metal reacts with water in the system to generate sodium hydroxide, thereby neutralizing acidic substances in the product and reducing its acidity. This solves the key problem of high acidity in the esterification synthesis route of propylene glycol methyl ether acetate. Furthermore, the alkali metal can also react with propylene glycol methyl ether in the system to generate a high-boiling-point propylene glycol methyl ether alkali metal salt, which reduces the difficulty of separating impurities and the target product in subsequent distillation. In addition, the hydrolysis of the propylene glycol methyl ether alkali metal salt promotes the reversible esterification reaction, improving the raw material conversion rate and product yield. The method provided by the present invention requires a simple distillation apparatus, produces a high-purity product with low water content, eliminates the need for toxic reagents such as toluene, and yields high-purity propylene glycol methyl ether acetate with extremely low water content through only one simple distillation.

[0066] The above are merely preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing high-purity propylene glycol methyl ether acetate, characterized in that, Includes the following steps: Propylene glycol methyl ether, acetic acid and catalyst are mixed to carry out the first stage reaction to obtain the first reaction solution; The first-stage reaction solution is mixed with an alkali metal to carry out a second-stage reaction, resulting in a second reaction solution. The second reaction solution was distilled to obtain the high-purity propylene glycol methyl ether acetate.

2. The preparation method according to claim 1, characterized in that, The molar ratio of propylene glycol methyl ether to acetic acid is 1 to 10:

1.

3. The preparation method according to claim 1, characterized in that, The catalyst includes one or more of the following: solid acid catalyst resin T-62MP, amberlyst15 catalyst resin, perfluorosulfonic acid resin HNF-5W, and nkc-9 catalyst resin.

4. The preparation method according to claim 1 or 3, characterized in that, The molar ratio of propylene glycol methyl ether to catalyst is 15–50:

1.

5. The preparation method according to claim 1, characterized in that, The temperature of the first stage reaction is 60–100℃, and the time is 1–4 hours.

6. The preparation method according to claim 1, characterized in that, The alkali metal includes one or more of sodium, potassium, and lithium; the molar amount of the alkali metal is 1 to 5% of the molar amount of the propylene glycol methyl ether.

7. The preparation method according to claim 1, characterized in that, The temperature of the second stage reaction is 80–100℃, and the reaction time is 0.5–4 hours.

8. The preparation method according to claim 1, characterized in that, The operating conditions for the distillation include: feed temperature of 80–120°C, reboiler temperature of 100–140°C, top reflux ratio of 1–3, middle reflux ratio of 5–10, and pressure of 10–150 kPa; the top product of the distillation includes water, propylene glycol methyl ether, and acetic acid, and the middle product includes high-purity propylene glycol methyl ether acetate.

9. The preparation method according to claim 1 or 8, characterized in that, The apparatus used in the preparation method includes a reaction vessel (1); A feed pump (2) connected to the outlet of the reactor (1); And a distillation column (3) connected to the outlet of the feed pump (2).

10. The preparation method according to claim 1, characterized in that, The high-purity propylene glycol methyl ether acetate has a purity >99.90%, a moisture content <90mg / L, a propylene glycol methyl ether content ≤200ppm, a single metal content <10ng / L, and a pH value of 7±0.1.

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