High-purity propylene glycol monomethyl ether and preparation method thereof

Abstract

The invention relates to a preparation method of propylene glycol monomethyl ether, in particular to high-purity propylene glycol monomethyl ether and a preparation method thereof. The method comprises the following steps: (1) carrying out first reaction on epoxypropane and methanol to obtain a first reaction material; (2) carrying out second reaction on the first reaction material and a ketene compound to obtain a second reaction material; and (3) carrying out rectification treatment on the second reaction material. According to the method disclosed by the invention, the yield and the purity of the propylene glycol monomethyl ether product are remarkably and effectively improved.

Description

Technical Field

[0001] The present invention relates to a preparation method of propylene glycol methyl ether, and particularly to a high-purity propylene glycol methyl ether and a preparation method thereof. Background Art

[0002] Due to its special structure: containing both a lipophilic ether bond and a hydrophilic hydroxyl group, propylene glycol methyl ether has extremely strong solubility and is known as the "universal solvent". Compared with other alcohol ethers, propylene glycol methyl ether has low toxicity and high safety, and is widely used in industries such as coatings, paints, printing and dyeing, and electronic chemicals; propylene glycol methyl ether is also an extremely important chemical intermediate and can be further synthesized into aldehyde acetals, nitrile derivatives, polyethers, carboxylic acid ester derivatives, etc.

[0003] There are many synthesis methods for propylene glycol methyl ether, including the Williamson synthesis method, the acetaldehyde condensation method, the alkoxypropylene oxide method, and the propylene oxide method. Among them, the propylene oxide method, which directly adds propylene oxide and methanol, has high atom utilization rate and is simple, safe and convenient to operate, and is the current industrial production method of propylene glycol methyl ether.

[0004] In the reaction of propylene oxide and methanol, in addition to generating propylene glycol methyl ether, isomer 2-methoxy-1-propanol will also be generated. The toxicity of this isomer is significantly higher than that of propylene glycol methyl ether. To reduce the content of 2-methoxy-1-propanol, the original acid catalyst has been abandoned in industry, and sodium alkoxide has been used as the catalyst in the reaction process. However, about 5% of 2-methoxy-1-propanol will still be inevitably generated in this process, increasing the subsequent separation difficulty and significantly increasing the separation cost. Summary of the Invention

[0005] The purpose of the present invention is to overcome the problem of a large amount of isomer 2-methoxy-1-propanol existing in propylene glycol methyl ether in the prior art, and to provide a high-purity propylene glycol methyl ether and a preparation method thereof. The purity of the ether substance obtained by this method is greater than 99.99%, and the content of alcohol isomers of this ether in the system is less than 0.1 ppm.

[0006] To achieve the above purpose, the first aspect of the present invention provides a preparation method of high-purity propylene glycol methyl ether, which includes the following steps: (1) propylene oxide and methanol undergo a first reaction to obtain a first reaction material; (2) the first reaction material and an ethenone-based compound undergo a second reaction to obtain a second reaction material; (3) the second reaction material is subjected to rectification treatment.

[0007] The second aspect of the present invention provides a high-purity propylene glycol methyl ether obtained by the method described in the first aspect.

[0008] Through the above technical solutions, the present invention has the following beneficial effects:

[0009] The method of the present invention significantly improves the yield and purity of propylene glycol methyl ether products. Detailed implementation manners

[0010] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0011] The present invention provides a method for preparing high-purity propylene glycol methyl ether, and the method comprises the following steps:

[0012] (1) Propylene oxide reacts with methanol to obtain a first reaction material; (2) The first reaction material reacts with a ketene-based compound to obtain a second reaction material; (3) The second reaction material is subjected to rectification treatment.

[0013] The method of the present invention significantly improves the yield and purity of propylene glycol methyl ether products.

[0014] According to a preferred embodiment of the present invention, the ketene-based compound includes substituted and / or unsubstituted ketene, preferably the substituent is selected from halogen and / or C1-3 alkyl, and further preferably the ketene-based compound is ketene and / or dimethyl ketene, and more preferably the ketene-based compound is dimethyl ketene.

[0015] In the present invention, the conditions of the first reaction can be selected by conventional techniques in the art. According to a preferred embodiment of the present invention, the conditions of the first reaction include: the temperature is 100-160 °C, the pressure is 3-5 MPa, the reaction is usually carried out in the presence of a sodium alkoxide catalyst, and there is no special limitation on the amounts of the reactants and the catalyst in the first reaction system, as long as the reaction can be completed. For example, methanol and propylene oxide react at a mass ratio of 4:1 in the presence of a 3 wt% sodium alkoxide.

[0016] According to a preferred embodiment of the present invention, the second reaction is carried out without adding a catalyst. The prior art usually needs to be carried out in the presence of a catalyst, generally in the presence of an acidic catalyst, and the acidic catalyst is selected from at least one of concentrated sulfuric acid, p-toluenesulfonic acid, heteropolyacid, acidic ionic liquid and solid acid. Compared with the prior art using a catalyst, the present invention does not use a catalyst and has the advantage of not introducing external impurities.

[0017] According to a preferred embodiment of the present invention, the conditions for the second reaction include: temperature of -20 - 50°C, preferably -10 - 40°C; and / or pressure of 0 - 5 MPa, preferably 0 - 3 MPa. The reaction time is determined according to the reaction temperature and pressure, for example, it can be 0.01 - 0.5 h, preferably 0.01 - 0.2 h.

[0018] According to a preferred embodiment of the present invention, the conditions for the rectification treatment include: the bottom temperature of the tower is 120 - 150°C; the pressure is 50 - 150 kPa; the reflux ratio is 0.2 - 10, preferably 0.2 - 5; collect the fraction with the top temperature of the tower being 110 - 125°C.

[0019] According to a preferred embodiment of the present invention, the mass content of 2 - methoxy - 1 - propanol in the second reaction material is 3 - 10 wt%.

[0020] According to a preferred embodiment of the present invention, in the second reaction, the molar ratio of the added amount of the ketene - based compound to the molar amount of 2 - methoxy - 1 - propanol in the first reaction material is 1 - 2, preferably 1.2 - 2.

[0021] The present invention provides high - purity propylene glycol methyl ether obtained by the described method.

[0022] According to a preferred embodiment of the present invention, the purity of propylene glycol methyl ether in the high - purity propylene glycol methyl ether is not less than 99.99%, and the content of 2 - methoxy - 1 - propanol is less than 0.1 ppm.

[0023] The present invention will be described in detail below through examples.

[0024] In the following examples, the product purity and impurity content were measured by gas chromatography analysis; unless otherwise specified, the raw materials were commercially available products.

[0025] Example 1

[0026] (1) React methanol and propylene oxide (mass ratio of 4:1) under the condition of using 3 wt% sodium alkoxide as a catalyst, the reaction temperature is 120°C, the pressure is 4 MPa, the residence time of this process is 4 h, and a crude product solution A of propylene glycol methyl ether is obtained. The product is analyzed by gas chromatography, and the content of 2 - methoxy - 1 - propanol in the obtained product is 4.33 wt%;

[0027] (2) React ketene with the crude product of propylene glycol methyl ether in step (1) (the molar ratio of the ketene feed to the molar amount of 2-methoxy-1-propanol in the crude product is 1.5) at a temperature of -10 °C and a pressure of 1 MPa for 0.1 h to obtain a crude product solution B of propylene glycol methyl ether. Analyze the product by gas chromatography, and the content of 2-methoxy-1-propanol in the obtained product is 0.026 ppm;

[0028] (3) Distill the crude product solution B of propylene glycol methyl ether obtained in step (2). The temperature of the bottom of the distillation column is 130 °C, the column pressure is 80 kPa, the temperature at the top of the column is 113 °C, and the reflux ratio is 1. Analyze the product by gas chromatography, and the content of 2-methoxy-1-propanol in the obtained product is 0.020 ppm, and the product purity is 99.99%.

[0029] Example 2

[0030] (1) The same as step (1) in Example 1;

[0031] (2) React ketene with the crude product of propylene glycol methyl ether in step (1) (the molar ratio of the ketene feed to the molar amount of 2-methoxy-1-propanol in the crude product is 1.3) at a temperature of 20 °C and a pressure of 0.5 MPa for 0.2 h to obtain a crude product solution B of propylene glycol methyl ether. Analyze the product by gas chromatography, and the content of 2-methoxy-1-propanol in the obtained product is 0.038 ppm;

[0032] (3) Distill the crude product solution B of propylene glycol methyl ether obtained in step (2). The temperature of the bottom of the distillation column is 130 °C, the column pressure is 80 kPa, the temperature at the top of the column is 113 °C, and the reflux ratio is 1. Analyze the product by gas chromatography, and the content of 2-methoxy-1-propanol in the obtained product is 0.021 ppm, and the product purity is 99.99%.

[0033] Example 3

[0034] (1) The same as step (1) in Example 1;

[0035] (2) React dimethyl ketene with the crude product of propylene glycol methyl ether in step (1) (the molar ratio of the ketene feed to the molar amount of 2-methoxy-1-propanol in the crude product is 1.5) at a temperature of 40 °C and a pressure of 3 MPa for 0.05 h to obtain a crude product solution B of propylene glycol methyl ether. Analyze the product by gas chromatography, and the content of 2-methoxy-1-propanol in the obtained product is 0.015 ppm;

[0036] (3) The crude product solution B of propylene glycol methyl ether obtained in step (2) is subjected to rectification. The temperature of the rectification column kettle is 130 °C, the column pressure is 80 kPa, the temperature at the top of the column is 113 °C, and the reflux ratio is 1. The product is analyzed by gas chromatography. The content of 2-methoxy-1-propanol in the obtained product is 0.012 ppm, and the product purity is 99.99%.

[0037] Example 4

[0038] All conditions are the same as in Example 1, except that: in step (2), the molar ratio of the feed amount of ketene to the molar amount of 2-methoxy-1-propanol in the crude product is 1.

[0039] Collect the fraction drawn at the top temperature of the column and analyze it by gas chromatography. The content of 2-methoxy-1-propanol in the product is 0.051 ppm, and the product purity is 99.99%.

[0040] Example 6

[0041] Same as Example 1, except that: in step (2), the reaction conditions are: temperature is 50 °C, pressure is 5 MPa, and reaction duration is 0.01 h.

[0042] Collect the fraction drawn at the top temperature of the column and analyze it by gas chromatography. The content of 2-methoxy-1-propanol in the product is 0.028 ppm, and the product purity is 99.99%.

[0043] Comparative Example 1

[0044] All are the same as in Example 1, except that: the crude product solution A of propylene glycol methyl ether obtained in step (1) is directly subjected to rectification. The temperature of the rectification column kettle is 130 °C, the column pressure is 80 kPa, the temperature at the top of the column is 113 °C, and the reflux ratio is 1. The product is analyzed by gas chromatography. The content of 2-methoxy-1-propanol in the obtained product is 133 ppm, and the product purity is 99.52%.

[0045] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A method for preparing high-purity propylene glycol methyl ether, characterized in that, the method comprises the following steps: (1) Propylene oxide reacts with methanol in a first reaction to obtain a first reaction material; (2) The first reaction material reacts with a ketene-based compound in a second reaction to obtain a second reaction material; (3) The second reaction material is subjected to rectification treatment.

2. The method according to claim 1, wherein, the ketene-based compound includes substituted and / or unsubstituted ketene, preferably the substituent is selected from halogen and / or C1-3 alkyl, and further preferably the ketene-based compound is ketene and / or dimethyl ketene, and more preferably the ketene-based compound is dimethyl ketene.

3. The method according to claim 1 or 2, wherein, the conditions of the first reaction include: the temperature is 100-160 °C, and the pressure is 3-5 MPa.

4. The method according to any one of claims 1-3, wherein, the second reaction is carried out without adding a catalyst.

5. The method according to any one of claims 1-4, wherein, the conditions of the second reaction include: the temperature is -20-50 °C, preferably -10-40 °C; and / or the pressure is 0-5 MPa, preferably 0-3 MPa.

6. The method according to any one of claims 1-5, wherein, the conditions of the rectification treatment include: the bottom temperature of the tower is 120-150 °C; the pressure is 50-150 kPa; the reflux ratio is 0.2-10, preferably 0.2-5; and the fraction with a top temperature of 110-125 °C is collected.

7. The method according to any one of claims 1-6, wherein, the mass content of 2-methoxy-1-propanol in the second reaction material is 3-10 wt%.

8. The method according to any one of claims 1-7, wherein, in the second reaction, the molar ratio of the added amount of the ketene-based compound to the molar amount of 2-methoxy-1-propanol in the first reaction material is 1-2.

9. High-purity propylene glycol methyl ether obtained by the method according to any one of claims 1-8.

10. The method according to claim 9, wherein, the purity of propylene glycol methyl ether in the high-purity propylene glycol methyl ether is not less than 99.99%, and the content of 2-methoxy-1-propanol is lower than 0.1 ppm.