A purification method of propylene glycol monomethyl ether

Abstract

The present invention provides a method for purifying propylene glycol monomethyl ether, which relates to the technical field of separation and purification. By utilizing the hydrogen bond interaction between the ester compound and propylene glycol monomethyl ether and the hydrophobicity of the extractant itself, the selective extraction of propylene glycol monomethyl ether is realized, and then rectification is carried out, so that high-purity propylene glycol monomethyl ether can be obtained, and the recovery rate of propylene glycol monomethyl ether is high. As shown by the test results of the examples, the purity of the propylene glycol monomethyl ether obtained by the purification method provided by the present invention is as high as 99.9%, and the recovery rate is as high as 99.4%. The ester compound has relatively low toxicity and strong chemical stability. Compared with the traditional azeotropic distillation process, the energy consumption level of the purification method provided by the present invention is reduced by 70%, achieving the goal of significantly reducing energy consumption. Moreover, the purification method provided by the present invention has mild operating conditions, is simple to operate, energy-saving and consumption-reducing, and has strong operation flexibility.

Description

Technical Field

[0001] The invention relates to the technical field of separation and purification, and in particular to a method for purifying propylene glycol monomethyl ether. Background Art

[0002] Propylene glycol monomethyl ether contains two chemical functional groups with strong solubility—hydroxyl and ether bonds. It has good solubility for polar or non-polar substances. It is a general solvent with excellent performance. It is also a very important intermediate compound. It is widely used in coatings, printing, electronic chemicals, textiles and other industries, and has high economic value. However, propylene glycol monomethyl ether and water can form azeotropes, which causes the purity of propylene glycol methyl ether to be insufficient, affecting its application. For example, propylene glycol monomethyl ether can react with acetic acid through esterification reaction to form propylene glycol methyl ether acetate. The presence of azeotropes of propylene glycol monomethyl ether and water makes separation complicated, resulting in the loss of propylene glycol monomethyl ether in the product flow, thereby affecting the conversion rate and product purity.

[0003] At present, azeotropic distillation is the main method for separating the azeotrope of propylene glycol monomethyl ether and water in industry. Since benzene azeotropes with water but not with propylene glycol monomethyl ether, and benzene and water are easy to separate, benzene is usually selected as the azeotrope for separating water and propylene glycol monomethyl ether. However, the contradiction between the higher water content in the feed liquid and the extremely low water content (only 8.9wt%) in the benzene-water azeotrope requires a large amount of benzene to be consumed when the azeotropic distillation technology is used to remove the water through benzene, which not only significantly increases the energy consumption. In addition, the characteristic of water being discharged from the top of the tower leads to a significant increase in the heat load of the reboiler at the bottom of the tower, further increasing the energy consumption burden. Moreover, due to the high toxicity of benzene, it has an adverse effect on the environment.

[0004] At present, the separation and recovery technology of propylene glycol monomethyl ether faces many challenges, such as low recovery efficiency, low product purity, high economic cost, huge energy consumption and serious environmental pollution. Therefore, it is urgent to develop a new method for separation and recovery of propylene glycol monomethyl ether that is both efficient and economical and has little environmental impact. Summary of the invention

[0005] In view of this, the object of the present invention is to provide a method for purifying propylene glycol monomethyl ether. The propylene glycol monomethyl ether purified by the purification method provided by the present invention has high purity and high recovery rate, and the purification method provided by the present invention has low energy consumption, is green and environmentally friendly, and has low cost.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a method for purifying propylene glycol monomethyl ether, comprising the following steps:

[0008] The aqueous solution of propylene glycol monomethyl ether is subjected to multi-stage countercurrent extraction with an extractant to obtain an organic phase; the extractant includes an ester compound, and the ester compound includes one or more of ethyl methyl succinate, 2-methylbutyl acetate, amyl acetate, ethyl phenylacetate, dimethyl phthalate, diethyl phthalate, tributyl phosphate, dibutyl oxalate, ethylene glycol monobutyl ether acetate, isobutyl isobutyrate, and butyl propionate;

[0009] The organic phase is rectified to obtain propylene glycol monomethyl ether.

[0010] Preferably, the multi-stage countercurrent extraction is carried out in an extraction column. The theoretical number of plates of the extraction column is 4 to 12; the aqueous solution of propylene glycol monomethyl ether is fed into the first plate of the extraction column, and the extractant is fed into the last plate of the extraction column;

[0011] The pressure of the multi-stage countercurrent extraction is atmospheric pressure.

[0012] Preferably, the flow rate ratio of the aqueous solution of propylene glycol monomethyl ether to the extractant is 1:0.35 to 5.

[0013] Preferably, the rectification is carried out in a rectification column; the rectification includes: conveying the organic phase to a first rectification column for first rectification to obtain overhead gas and a first bottom liquid respectively; conveying the first bottom liquid to a second rectification column for second rectification to obtain propylene glycol monomethyl ether and a second bottom liquid respectively;

[0014] The pressure of the rectification is atmospheric pressure.

[0015] Preferably, the theoretical number of plates of the first rectification column is 5 to 15, and the first rectification column is connected with a heat exchanger.

[0016] Preferably, the overhead gas is condensed into a liquid phase by the heat exchanger and then subjected to multi-stage countercurrent extraction again.

[0017] Preferably, the temperature of the heat exchanger is 20 to 40 °C.

[0018] Preferably, the theoretical number of plates of the second rectification column is 6 to 20, and the first bottom liquid is fed into the 3rd to 10th plates.

[0019] Preferably, the reflux ratio of the second rectification is 0.2 to 5.

[0020] Preferably, the second bottom liquid is subjected to extractant recovery to obtain a recovered extractant, and the recovered extractant is used for the multi-stage countercurrent extraction step.

[0021] The present invention utilizes the hydrogen bonding between ester compounds and propylene glycol monomethyl ether, as well as the hydrophobicity of the extractant itself, to achieve the selective extraction of propylene glycol monomethyl ether, and then perform rectification, enabling the obtaining of high-purity propylene glycol monomethyl ether with a high recovery rate. As shown by the test results of the examples, for the purification method provided by the present invention, the purity of propylene glycol monomethyl ether is as high as 99.9%, and the recovery rate is as high as 99.4%. The obtained propylene glycol monomethyl ether can meet the quality standards of "HG / T 3939-2007 Propylene Glycol Methyl Ether for Industrial Use".

[0022] Ester compounds have relatively low toxicity, pose little harm to the human body and the environment, and have relatively low volatility. During use, the emissions of VOCs are less, and the pollution to the atmospheric environment is small, meeting the requirements of environmental protection and safety.

[0023] Compared with the traditional azeotropic distillation process, the energy consumption level of the purification method provided by the present invention is reduced by 70%, achieving the goal of significantly reducing energy consumption. The purification method provided by the present invention has mild operating conditions, simple operation, energy conservation and consumption reduction, low cost, strong operation flexibility, and is suitable for industrial production.

[0024] The purification method provided by the present invention can flexibly adjust the operating parameters of the extraction column and the rectification column according to different production requirements and material characteristics, such as the feed ratio of the extractant to the aqueous solution of propylene glycol monomethyl ether, the reflux ratio, and the heat exchanger temperature, which can further improve the purification effect of propylene glycol monomethyl ether. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is the process flow diagram for the purification of propylene glycol monomethyl ether in the present invention;

[0026] Figure 2 is the process flow diagram for the purification of propylene glycol monomethyl ether in Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0027] The present invention provides a method for purifying propylene glycol monomethyl ether, comprising the following steps:

[0028] Performing multi-stage countercurrent extraction on an aqueous solution of propylene glycol monomethyl ether with an extractant to obtain an organic phase; the extractant includes ester compounds, and the ester compounds include one or more of ethyl methyl succinate, 2-methylbutyl acetate, amyl acetate, ethyl phenylacetate, dimethyl phthalate, diethyl phthalate, tributyl phosphate, dibutyl oxalate, ethylene glycol monobutyl ether acetate, isobutyl isobutyrate, and butyl propionate;

[0029] Rectifying the organic phase to obtain propylene glycol monomethyl ether.

[0030] Unless otherwise specified, the materials and equipment used in the present invention are commercially available products in the art.

[0031] The present invention uses an extractant to perform multi-stage countercurrent extraction on an aqueous solution of propylene glycol monomethyl ether to obtain an organic phase.

[0032] In the present invention, the extractant includes an ester compound, and the ester compound includes one or more of ethyl methyl succinate, 2-methylbutyl acetate, amyl acetate, ethyl phenylacetate, dimethyl phthalate, diethyl phthalate, tributyl phosphate, dibutyl oxalate, ethylene glycol monobutyl ether acetate, isobutyl isobutyrate, and butyl propionate. In a specific embodiment, it can be a single ester compound or a mixture of ester compounds; the mixture of ester compounds preferably includes a mixture of dibutyl oxalate and ethyl methyl succinate, a mixture of dibutyl oxalate and 2-methylbutyl acetate, a mixture of dibutyl oxalate and amyl acetate, a mixture of dibutyl oxalate and ethyl phenylacetate, a mixture of dibutyl oxalate and dimethyl phthalate, a mixture of dibutyl oxalate and diethyl phthalate, a mixture of dibutyl oxalate and tributyl phosphate, a mixture of dibutyl oxalate and butyl propionate, a mixture of dibutyl oxalate and isobutyl isobutyrate, a mixture of dibutyl oxalate and ethylene glycol monobutyl ether acetate, a mixture of dibutyl oxalate, isobutyl isobutyrate, and ethylene glycol monobutyl ether acetate, or a mixture of dibutyl oxalate, butyl propionate, and ethylene glycol monobutyl ether acetate.

[0033] In the present invention, the mass fraction of dibutyl oxalate in the mixture of dibutyl oxalate and ethyl methyl succinate is preferably 40-90%, and in a specific embodiment, it can be 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, or 90%.

[0034] In the present invention, the mass fraction of dibutyl oxalate in the mixture of dibutyl oxalate and 2-methylbutyl acetate is preferably 40-90%, and in a specific embodiment, it can be 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, or 90%.

[0035] In the present invention, the mass fraction of dibutyl oxalate in the mixture of dibutyl oxalate and amyl acetate is preferably 40-90%, and in a specific embodiment, it can be 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, or 90%.

[0036] In the present invention, the mass fraction of dibutyl oxalate in the mixture of dibutyl oxalate and ethyl phenylacetate is preferably 40-90%, and in a specific embodiment, it can be 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, or 90%.

[0037] In the present invention, the mass fraction of dibutyl oxalate in the mixture of dibutyl oxalate and dimethyl phthalate is preferably 40 - 90%, and in specific embodiments, it can be 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85% or 90%.

[0038] In the present invention, the mass fraction of dibutyl oxalate in the mixture of dibutyl oxalate and diethyl phthalate is preferably 40 - 90%, and in specific embodiments, it can be 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85% or 90%.

[0039] In the present invention, the mass fraction of dibutyl oxalate in the mixture of dibutyl oxalate and tributyl phosphate is preferably 40 - 90%, and in specific embodiments, it can be 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85% or 90%.

[0040] In the present invention, the mass fraction of dibutyl oxalate in the mixture of dibutyl oxalate and butyl propionate is preferably 40 - 90%, and in specific embodiments, it can be 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85% or 90%.

[0041] In the present invention, the mass fraction of dibutyl oxalate in the mixture of dibutyl oxalate and isobutyl isobutyrate is preferably 40 - 90%, and in specific embodiments, it can be 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85% or 90%.

[0042] In the present invention, the mass fraction of dibutyl oxalate in the mixture of dibutyl oxalate and ethylene glycol monobutyl ether acetate is preferably 40 - 90%, and in specific embodiments, it can be 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85% or 90%.

[0043] In the present invention, the mass fraction of dibutyl oxalate in the mixture of dibutyl oxalate, butyl propionate and ethylene glycol monobutyl ether acetate is preferably 40 - 80%, and in specific embodiments, it can be 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75% or 80%; the mass fraction of ethylene glycol monobutyl ether acetate in the mixture of dibutyl oxalate, butyl propionate and ethylene glycol monobutyl ether acetate is preferably 10 - 50%, and in specific embodiments, it can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45% or 50%.

[0044] In the present invention, the mass fraction of dibutyl oxalate in the mixture of dibutyl oxalate, isobutyl isobutyrate and ethylene glycol monobutyl ether acetate is preferably 40 - 80%, and in specific embodiments, it can be 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75% or 80%; the mass fraction of ethylene glycol monobutyl ether acetate in the mixture of dibutyl oxalate, isobutyl isobutyrate and ethylene glycol monobutyl ether acetate is preferably 10 - 50%, and in specific embodiments, it can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45% or 50%.

[0045] In the present invention, the multi-stage countercurrent extraction is preferably carried out in an extraction column (EC). The multi-stage countercurrent extraction preferably includes: using an extractant to perform multi-stage countercurrent extraction on an aqueous solution of propylene glycol monomethyl ether in the extraction column to obtain an organic phase. In the present invention, the organic phase is withdrawn from the top of the column.

[0046] In the present invention, the number of theoretical plates of the extraction column is preferably 4 - 12, and in specific embodiments, it can be 4, 5, 6, 7, 8, 9, 10, 11 or 12. In the present invention, the aqueous solution of propylene glycol monomethyl ether is preferably fed from the first plate (top of the column) of the extraction column, and the extractant is preferably fed from the last plate (bottom of the column) of the extraction column.

[0047] In the present invention, the mass content of propylene glycol monomethyl ether in the aqueous solution of propylene glycol monomethyl ether is preferably 1 - 70%, and in specific embodiments, it can be 1%, 5%, 10%, 15%, 20%, 22%, 25%, 30%, 35%, 36%, 40%, 45%, 45.8%, 50%, 52.9%, 55%, 55.6%, 58.4%, 60%, 62.8%, 65% or 70%.

[0048] In the present invention, the flow rate ratio of the aqueous solution of propylene glycol monomethyl ether to the extractant is preferably 1:0.35 - 5, and in specific embodiments, it can be 1:0.35, 1:0.5, 1:0.75, 1:1, 1:1.25, 1:1.5, 1:1.7, 1:2, 1:2.2, 1:2.5, 1:2.9, 1:3, 1:3.1, 1:3.5, 1:4, 1:4.5 or 1:5.

[0049] In the present invention, the temperature of the multi-stage countercurrent extraction is preferably 20 to 40 °C, and in specific embodiments, it can be 20 °C, 21 °C, 22 °C, 23 °C, 24 °C, 25 °C, 26 °C, 27 °C, 28 °C, 29 °C, 30 °C, 31 °C, 32 °C, 33 °C, 34 °C, 35 °C, 36 °C, 37 °C, 38 °C, 39 °C or 40 °C; the pressure of the multi-stage countercurrent extraction is preferably atmospheric pressure. In the present invention, during the multi-stage countercurrent extraction process, water is taken out from the bottom of the extraction column (i.e., the bottom of the column).

[0050] After obtaining the organic phase, the present invention rectifies the organic phase to obtain propylene glycol monomethyl ether.

[0051] In the present invention, the rectification is preferably carried out in a rectification column, and the rectification column preferably includes a first rectification column (DC1) and a second rectification column (DC2); the pressure of the rectification is preferably atmospheric pressure; the rectification preferably includes first rectification and second rectification carried out in sequence. The first rectification is preferably carried out in the first rectification column, and the second rectification is preferably carried out in the second rectification column. Specifically, the organic phase is transported to the first rectification column for the first rectification to obtain overhead gas and a first bottom liquid respectively; the first bottom liquid is transported to the second rectification column for the second rectification to obtain propylene glycol monomethyl ether and a second bottom liquid respectively.

[0052] In the present invention, the number of theoretical plates of the first rectification column is preferably 5 to 15, and in specific embodiments, it can be 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 or 15; the organic phase is preferably fed from the first plate. In the present invention, the first rectification column is preferably connected with a heat exchanger; the temperature of the heat exchanger is preferably 20 to 40 °C, and in specific embodiments, it can be 20 °C, 21 °C, 22 °C, 23 °C, 24 °C, 25 °C, 26 °C, 27 °C, 28 °C, 29 °C, 30 °C, 31 °C, 32 °C, 33 °C, 34 °C, 35 °C, 36 °C, 37 °C, 38 °C, 39 °C or 40 °C.

[0053] In the present invention, the overhead gas is preferably condensed into a liquid phase by the heat exchanger and then subjected to multi-stage countercurrent extraction again (i.e., the liquid phase is condensed into a liquid phase by the heat exchanger and then transported to the extraction column).

[0054] In the present invention, the number of theoretical plates of the second rectification column is preferably 6 to 20, and in specific embodiments, it can be 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20. In the present invention, the first bottom liquid is preferably fed from the 3rd to 10th plates, and in specific embodiments, the first bottom liquid can be fed from the 3rd, 4th, 5th, 6th, 7th, 8th, 9th or 10th plates.

[0055] In the present invention, the reflux ratio of the second distillation is preferably 0.2-5, and in specific embodiments can be 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 2.5, 3, 3.5, 4, 4.5 or 5.

[0056] In the present invention, the second bottom liquid is preferably subjected to extractant recovery to obtain a recovered extractant, and the recovered extractant is used in the multi-stage countercurrent extraction step (ie, the recovered extractant is transported to the extraction tower).

[0057] The purification method provided by the present invention can flexibly adjust the operating parameters of the extraction tower and the distillation tower according to different production requirements and material properties, such as the feed ratio of the extractant to the propylene glycol monomethyl ether aqueous solution, the reflux ratio, and the heat exchanger temperature, thereby further improving the purification effect of propylene glycol monomethyl ether.

[0058] In order to further illustrate the present invention, the purification method of propylene glycol monomethyl ether provided by the present invention is described in detail below in conjunction with examples, but they should not be construed as limiting the scope of protection of the present invention. Example

[0059] Water and propylene glycol monomethyl ether were mixed uniformly at a mass ratio of 2:2.5 to obtain a propylene glycol monomethyl ether aqueous solution. Propylene glycol monomethyl ether aqueous solution and ethyl methyl succinate were heated and stirred at 20°C and 500r / min for 2.5h at a mass ratio of 1:1, and then allowed to stand at 25°C for 2.5h. After the two phases were completely separated, samples were taken, and the substances in the two phases were analyzed by gas chromatography, and the selectivity of propylene glycol monomethyl ether was calculated to be 9.05 and the distribution coefficient was 0.7. Example

[0060] Water and propylene glycol monomethyl ether were mixed uniformly at a mass ratio of 2:2.5 to obtain a propylene glycol monomethyl ether aqueous solution. Propylene glycol monomethyl ether aqueous solution and 2-methylbutyl acetate were heated and stirred at 20°C and 500r / min for 2.5h at a mass ratio of 1:1, and then allowed to stand at 25°C for 2.5h. After the two phases were completely separated, samples were taken, and the substances in the two phases were analyzed by gas chromatography, and the selectivity of propylene glycol monomethyl ether was calculated to be 9.85 and the distribution coefficient was 0.76. Example

[0061] Mix water and propylene glycol monomethyl ether evenly at a mass ratio of 2:2.5 to obtain an aqueous solution of propylene glycol monomethyl ether. According to a mass ratio of 1:1, heat and stir the aqueous solution of propylene glycol monomethyl ether and amyl acetate at 20 °C and 500 r / min for 2.5 h, then let it stand at 25 °C for 2.5 h. After the two phases are completely separated, take samples and analyze each substance in the two phases by gas chromatography. The calculated selectivity of propylene glycol monomethyl ether is 10.15, and the distribution coefficient is 0.76. Example

[0062] Mix water and propylene glycol monomethyl ether evenly at a mass ratio of 2:2.5 to obtain an aqueous solution of propylene glycol monomethyl ether. According to a mass ratio of 1:1, heat and stir the aqueous solution of propylene glycol monomethyl ether and ethyl phenylacetate at 20 °C and 500 r / min for 2.5 h, then let it stand at 25 °C for 2.5 h. After the two phases are completely separated, take samples and analyze each substance in the two phases by gas chromatography. The calculated selectivity of propylene glycol monomethyl ether is 10.49, and the distribution coefficient is 0.72. Example

[0063] Mix water and propylene glycol monomethyl ether evenly at a mass ratio of 2:2.5 to obtain an aqueous solution of propylene glycol monomethyl ether. According to a mass ratio of 1:1, heat and stir the aqueous solution of propylene glycol monomethyl ether and dimethyl phthalate at 20 °C and 500 r / min for 2.5 h, then let it stand at 25 °C for 2.5 h. After the two phases are completely separated, take samples and analyze each substance in the two phases by gas chromatography. The calculated selectivity of propylene glycol monomethyl ether is 9.58, and the distribution coefficient is 0.74. Example

[0064] Mix water and propylene glycol monomethyl ether evenly at a mass ratio of 2:2.5 to obtain an aqueous solution of propylene glycol monomethyl ether. According to a mass ratio of 1:1, heat and stir the aqueous solution of propylene glycol monomethyl ether and diethyl phthalate at 20 °C and 500 r / min for 2.5 h, then let it stand at 25 °C for 2.5 h. After the two phases are completely separated, take samples and analyze each substance in the two phases by gas chromatography. The calculated selectivity of propylene glycol monomethyl ether is 8.56, and the distribution coefficient is 0.85. Example

[0065] Mix water and propylene glycol monomethyl ether evenly at a mass ratio of 2:2.5 to obtain an aqueous solution of propylene glycol monomethyl ether. According to a mass ratio of 1:1, heat and stir the aqueous solution of propylene glycol monomethyl ether and tributyl phosphate at 20 °C and 500 r / min for 2.5 h, then let it stand at 25 °C for 2.5 h. After the two phases are completely separated, take samples and analyze each substance in the two phases by gas chromatography. The calculated selectivity of propylene glycol monomethyl ether is 1.34, and the distribution coefficient is 1.58. Example

[0066] Mix water and propylene glycol monomethyl ether evenly at a mass ratio of 2:2.5 to obtain an aqueous solution of propylene glycol monomethyl ether. According to a mass ratio of 1:1, heat and stir the aqueous solution of propylene glycol monomethyl ether and ethylene glycol monobutyl ether acetate at 20°C and 500 r / min for 2.5 h, then let it stand at 20°C for 2.5 h. After the two phases are completely separated, take samples and analyze each substance in the two phases by gas chromatography. The calculated selectivity of propylene glycol monomethyl ether is 3.94 and the distribution coefficient is 0.6. Example

[0067] Mix water and propylene glycol monomethyl ether evenly at a mass ratio of 2:2.5 to obtain an aqueous solution of propylene glycol monomethyl ether. According to a mass ratio of 1:1, heat and stir the aqueous solution of propylene glycol monomethyl ether and ethylene glycol monobutyl ether acetate at 30°C and 500 r / min for 2.5 h, then let it stand at 30°C for 2.5 h. After the two phases are completely separated, take samples and analyze each substance in the two phases by gas chromatography. The calculated selectivity of propylene glycol monomethyl ether is 3.67 and the distribution coefficient is 0.54. Example

[0068] Mix water and propylene glycol monomethyl ether evenly at a mass ratio of 2:2.5 to obtain an aqueous solution of propylene glycol monomethyl ether. According to a mass ratio of 1:1, heat and stir the aqueous solution of propylene glycol monomethyl ether and isobutyl isobutyrate at 20°C and 500 r / min for 2.5 h, then let it stand at 20°C for 2.5 h. After the two phases are completely separated, take samples and analyze each substance in the two phases by gas chromatography. The calculated selectivity of propylene glycol monomethyl ether is 6.93 and the distribution coefficient is 0.38. Example

[0069] Mix water and propylene glycol monomethyl ether evenly at a mass ratio of 2:2.5 to obtain an aqueous solution of propylene glycol monomethyl ether. According to a mass ratio of 1:1, heat and stir the aqueous solution of propylene glycol monomethyl ether and isobutyl isobutyrate at 30°C and 500 r / min for 2.5 h, then let it stand at 30°C for 2.5 h. After the two phases are completely separated, take samples and analyze each substance in the two phases by gas chromatography. The calculated selectivity of propylene glycol monomethyl ether is 6.08 and the distribution coefficient is 0.36. Example

[0070] Mix water and propylene glycol monomethyl ether evenly at a mass ratio of 2:2.5 to obtain an aqueous solution of propylene glycol monomethyl ether. At a mass ratio of 1:1, heat and stir the aqueous solution of propylene glycol monomethyl ether and butyl propionate at 20 °C and 500 r / min for 2.5 h, then let it stand at 20 °C for 2.5 h. After the two phases are completely separated, take samples and analyze each substance in the two phases by gas chromatography. The calculated selectivity of propylene glycol monomethyl ether is 19.67 and the distribution coefficient is 0.48. Example

[0071] Mix water and propylene glycol monomethyl ether evenly at a mass ratio of 2:2.5 to obtain an aqueous solution of propylene glycol monomethyl ether. At a mass ratio of 1:1, heat and stir the aqueous solution of propylene glycol monomethyl ether and butyl propionate at 30 °C and 500 r / min for 2.5 h, then let it stand at 30 °C for 2.5 h. After the two phases are completely separated, take samples and analyze each substance in the two phases by gas chromatography. The calculated selectivity of propylene glycol monomethyl ether is 17.03 and the distribution coefficient is 0.47. Example

[0072] Mix water and propylene glycol monomethyl ether evenly at a mass ratio of 2:2.5 to obtain an aqueous solution of propylene glycol monomethyl ether. At a mass ratio of 1:1, heat and stir the aqueous solution of propylene glycol monomethyl ether and dibutyl oxalate at 20 °C and 500 r / min for 2.5 h, then let it stand at 20 °C for 2.5 h. After the two phases are completely separated, take samples and analyze each substance in the two phases by gas chromatography. The calculated selectivity of propylene glycol monomethyl ether is 57.75 and the distribution coefficient is 0.3. Example

[0073] Mix water and propylene glycol monomethyl ether evenly at a mass ratio of 2:2.5 to obtain an aqueous solution of propylene glycol monomethyl ether. At a mass ratio of 1:1, heat and stir the aqueous solution of propylene glycol monomethyl ether and dibutyl oxalate at 30 °C and 500 r / min for 2.5 h, then let it stand at 30 °C for 2.5 h. After the two phases are completely separated, take samples and analyze each substance in the two phases by gas chromatography. The calculated selectivity of propylene glycol monomethyl ether is 55.13 and the distribution coefficient is 0.28.

[0074] By comparing Examples 1 to 15, it can be seen that ethyl methyl succinate, 2-methylbutyl acetate, amyl acetate, ethyl phenylacetate, dimethyl phthalate, diethyl phthalate, tributyl phosphate, dibutyl oxalate, ethylene glycol monobutyl ether acetate, isobutyl isobutyrate, and butyl propionate all have the extraction ability for propylene glycol monomethyl ether. The extraction effects are as follows: dibutyl oxalate > butyl propionate > ethyl phenylacetate > amyl acetate > 2-methylbutyl acetate > dimethyl phthalate > ethyl methyl succinate > diethyl phthalate > isobutyl isobutyrate > ethylene glycol monobutyl ether acetate > tributyl phosphate. Example

[0075] Mix water and propylene glycol monomethyl ether evenly according to a mass ratio of 2:0.5625 to obtain an aqueous solution of propylene glycol monomethyl ether. Mix the aqueous solution of propylene glycol monomethyl ether and dibutyl oxalate at a mass ratio of 2.5625:2, heat and stir at 30 °C and 500 r / min for 2.5 h, then let it stand at 30 °C for 2.5 h. After the two phases are completely separated, take samples and analyze the substances in the two phases by gas chromatography. The selectivity of propylene glycol monomethyl ether is calculated to be 26.58, and the distribution coefficient is 0.17. Example

[0076] Mix water and propylene glycol monomethyl ether evenly according to a mass ratio of 2:1.125 to obtain an aqueous solution of propylene glycol monomethyl ether. Mix the aqueous solution of propylene glycol monomethyl ether and dibutyl oxalate at a mass ratio of 3.125:2, heat and stir at 30 °C and 500 r / min for 2.5 h, then let it stand at 30 °C for 2.5 h. After the two phases are completely separated, take samples and analyze the substances in the two phases by gas chromatography. The selectivity of propylene glycol monomethyl ether is calculated to be 18.65, and the distribution coefficient is 0.21. Example

[0077] Mix water and propylene glycol monomethyl ether evenly according to a mass ratio of 2:1.6875 to obtain an aqueous solution of propylene glycol monomethyl ether. Mix the aqueous solution of propylene glycol monomethyl ether and dibutyl oxalate at a mass ratio of 3.6875:2, heat and stir at 30 °C and 500 r / min for 2.5 h, then let it stand at 30 °C for 2.5 h. After the two phases are completely separated, take samples and analyze the substances in the two phases by gas chromatography. The selectivity of propylene glycol monomethyl ether is calculated to be 15.49, and the distribution coefficient is 0.25. Example

[0078] Mix water and propylene glycol monomethyl ether evenly according to a mass ratio of 2:2.25 to obtain an aqueous solution of propylene glycol monomethyl ether. Mix the aqueous solution of propylene glycol monomethyl ether and dibutyl oxalate according to a mass ratio of 4.25:2, heat and stir at 30 °C and 500 r / min for 2.5 h, then let it stand at 30 °C for 2.5 h. After the two phases are completely separated, take samples and analyze the substances in the two phases by gas chromatography. The calculated selectivity of propylene glycol monomethyl ether is 12.49, and the distribution coefficient is 0.28. Example

[0079] Mix water and propylene glycol monomethyl ether evenly according to a mass ratio of 2:2.8125 to obtain an aqueous solution of propylene glycol monomethyl ether. Mix the aqueous solution of propylene glycol monomethyl ether and dibutyl oxalate according to a mass ratio of 4.8125:2, heat and stir at 30 °C and 500 r / min for 2.5 h, then let it stand at 30 °C for 2.5 h. After the two phases are completely separated, take samples and analyze the substances in the two phases by gas chromatography. The calculated selectivity of propylene glycol monomethyl ether is 10.06, and the distribution coefficient is 0.32. Example

[0080] Mix water and propylene glycol monomethyl ether evenly according to a mass ratio of 2:3.375 to obtain an aqueous solution of propylene glycol monomethyl ether. Mix the aqueous solution of propylene glycol monomethyl ether and dibutyl oxalate according to a mass ratio of 5.375:2, heat and stir at 30 °C and 500 r / min for 2.5 h, then let it stand at 30 °C for 2.5 h. After the two phases are completely separated, take samples and analyze the substances in the two phases by gas chromatography. The calculated selectivity of propylene glycol monomethyl ether is 8.32, and the distribution coefficient is 0.4.

[0081] By comparing Examples 16 - 21, it can be seen that dibutyl oxalate has a good extraction effect on propylene glycol monomethyl ether in propylene glycol monomethyl ether solutions with different concentrations, and there is a large operating space. Example

[0082] Aqueous solution of propylene glycol monomethyl ether: propylene glycol monomethyl ether 55.56 wt%, water 44.44 wt%.

[0083] Adopt Figure 1The flow chart shown purifies propylene glycol monomethyl ether, and the specific steps are as follows: The number of theoretical plates in the extraction column is 8. The aqueous solution of propylene glycol monomethyl ether is fed from the first plate, and dibutyl oxalate (the flow rate of dibutyl oxalate is 2.9 times that of the aqueous solution of propylene glycol monomethyl ether) is fed from the eighth plate. The operating pressure of the extraction column is atmospheric pressure. Water is withdrawn from the bottom of the column, and propylene glycol monomethyl ether enters the organic phase. The organic phase is withdrawn from the top of the extraction column and introduced into the first distillation column (without a condenser connected). The number of theoretical plates in the first distillation column is 9, and it is fed from the first plate. The operating pressure of the first distillation column is atmospheric pressure. The temperature of the heat exchanger connected to the top of the column is 30°C. The overhead gas is condensed to obtain a liquid phase, and the liquid phase and the aqueous solution of propylene glycol monomethyl ether are fed into the extraction column again for extraction. The first bottom liquid is withdrawn from the bottom of the first distillation column and sent to the second distillation column. The number of theoretical plates in the second distillation column is 9, and it is fed from the fifth plate. The operating pressure of the second distillation column is atmospheric pressure, and the reflux ratio is 0.29. The second bottom liquid is subjected to solvent recovery, and the recovered extractant obtained is sent to the extraction column. The propylene glycol monomethyl ether product is withdrawn from the top (the content of propylene glycol monomethyl ether is 99.9 wt%, and the recovery rate is 99.4%). Example

[0084] Purify propylene glycol monomethyl ether according to the method of Example 22, and the difference from Example 22 is only that: the flow rate of dibutyl oxalate is 2.2 times that of the aqueous solution of propylene glycol monomethyl ether; the content of propylene glycol monomethyl ether in the propylene glycol monomethyl ether product is 93.3 wt%, and the recovery rate is 92.8%. Example

[0085] Purify propylene glycol monomethyl ether according to the method of Example 22, and the difference from Example 22 is only that: the number of theoretical plates in the extraction column is 5; dibutyl oxalate is fed from the fifth plate; the content of propylene glycol monomethyl ether in the propylene glycol monomethyl ether product is 97.3 wt%, and the recovery rate is 96.8%. Example

[0086] Purify propylene glycol monomethyl ether according to the method of Example 22, and the difference from Example 22 is only that: the number of theoretical plates in the extraction column is 5; dibutyl oxalate is fed from the fifth plate; the number of theoretical plates in the second distillation column is 7, and it is fed from the fourth plate; the content of propylene glycol monomethyl ether in the propylene glycol monomethyl ether product is 97.3 wt%, and the recovery rate is 96.7%. Example

[0087] Purify propylene glycol monomethyl ether according to the method of Example 22, and the difference from Example 22 is only that: the number of theoretical plates in the extraction column is 5; dibutyl oxalate is fed from the fifth plate; the number of theoretical plates in the first distillation column is 7; the temperature of the heat exchanger connected to the top of the first distillation column is 25°C; the number of theoretical plates in the second distillation column is 7, and it is fed from the fourth plate; the reflux ratio is 0.3; the content of propylene glycol monomethyl ether in the propylene glycol monomethyl ether product is 97.2 wt%, and the recovery rate is 96.7%. Example

[0088] Purify propylene glycol monomethyl ether according to the method of Example 22, with the difference from Example 22 being only that: the aqueous solution of propylene glycol monomethyl ether: 70 wt% of propylene glycol monomethyl ether and 30 wt% of water. The number of theoretical plates in the extraction column is 8. The aqueous solution of propylene glycol monomethyl ether is fed from the first plate, and dibutyl oxalate (the flow rate of dibutyl oxalate is 1.7 times that of the aqueous solution of propylene glycol monomethyl ether) is fed from the eighth plate. The operating pressure of the extraction column is atmospheric pressure. Water is withdrawn from the bottom of the column, and propylene glycol monomethyl ether enters the organic phase and is withdrawn from the top of the column; the content of propylene glycol monomethyl ether in the propylene glycol monomethyl ether product is 94.3 wt%, and the recovery rate is 94.3%. Example

[0089] Purify propylene glycol monomethyl ether according to the method of Example 22, with the difference from Example 22 being only that: the aqueous solution of propylene glycol monomethyl ether: 70 wt% of propylene glycol monomethyl ether and 30 wt% of water. The number of theoretical plates in the extraction column is 15. The aqueous solution of propylene glycol monomethyl ether is fed from the first plate, and dibutyl oxalate (the flow rate of dibutyl oxalate is 3.1 times that of the aqueous solution of propylene glycol monomethyl ether) is fed from the 15th plate. The operating pressure of the extraction column is atmospheric pressure. Water is withdrawn from the bottom of the column, and propylene glycol monomethyl ether enters the organic phase and is withdrawn from the top of the column; the content of propylene glycol monomethyl ether in the propylene glycol monomethyl ether product is 98.9 wt%, and the recovery rate is 98.9%. Example

[0090] Purify propylene glycol monomethyl ether according to the method of Example 22, with the difference from Example 22 being only that: the extractant is a mixture of dibutyl oxalate and butyl propionate (70 wt% of dibutyl oxalate and 30 wt% of butyl propionate), and the flow rate of the extractant is 3 times that of the aqueous solution of propylene glycol monomethyl ether; the number of theoretical plates in the extraction column is 12, and the extractant is fed from the 12th plate; the number of theoretical plates in the first distillation column is 15; the number of theoretical plates in the second distillation column is 20, and it is fed from the 10th plate; the reflux ratio is 5; the content of propylene glycol monomethyl ether in the propylene glycol monomethyl ether product is 82.6 wt%, and the recovery rate is 80.7%. Example

[0091] Purify propylene glycol monomethyl ether according to the method of Example 22, with the difference from Example 22 being only that: the extractant is a mixture of dibutyl oxalate and isobutyl isobutyrate (70 wt% of dibutyl oxalate and 30 wt% of isobutyl isobutyrate), and the flow rate of the extractant is 3 times that of the aqueous solution of propylene glycol monomethyl ether; the number of theoretical plates in the extraction column is 9, and the extractant is fed from the 9th plate; the number of theoretical plates in the first distillation column is 15; the number of theoretical plates in the second distillation column is 20, and it is fed from the 10th plate; the reflux ratio is 5; the content of propylene glycol monomethyl ether in the propylene glycol monomethyl ether product is 92.6 wt%, and the recovery rate is 94.3%. Example

[0092] Purify propylene glycol monomethyl ether according to the method of Example 22, the difference from Example 22 is only that: the extractant is a mixture of dibutyl oxalate and ethylene glycol monobutyl ether acetate (70 wt% dibutyl oxalate, 30 wt% ethylene glycol monobutyl ether acetate), and the flow rate of the extractant is 3 times that of the aqueous solution of propylene glycol monomethyl ether; the number of theoretical plates in the extraction column is 12, and the extractant is fed from the 12th plate; the number of theoretical plates in the first distillation column is 15; the number of theoretical plates in the second distillation column is 20, and it is fed from the 10th plate; the reflux ratio is 5; the content of propylene glycol monomethyl ether in the propylene glycol monomethyl ether product is 97.6 wt%, and the recovery rate is 96.8%. Example

[0093] Purify propylene glycol monomethyl ether according to the method of Example 22, the difference from Example 22 is only that: the extractant is a mixture of dibutyl oxalate and ethylene glycol monobutyl ether acetate (50 wt% dibutyl oxalate, 50 wt% ethylene glycol monobutyl ether acetate), and the flow rate of the extractant is 3 times that of the aqueous solution of propylene glycol monomethyl ether; the number of theoretical plates in the extraction column is 12, and the extractant is fed from the 12th plate; the number of theoretical plates in the first distillation column is 15; the number of theoretical plates in the second distillation column is 20, and it is fed from the 10th plate; the reflux ratio is 5; the content of propylene glycol monomethyl ether in the propylene glycol monomethyl ether product is 96.8 wt%, and the recovery rate is 96.9%. Example

[0094] Purify propylene glycol monomethyl ether according to the method of Example 22, the difference from Example 22 is only that: the extractant is a mixture of dibutyl oxalate, butyl propionate and ethylene glycol monobutyl ether acetate (50 wt% dibutyl oxalate, 20 wt% butyl propionate, 30 wt% ethylene glycol monobutyl ether acetate), and the flow rate of the extractant is 3 times that of the aqueous solution of propylene glycol monomethyl ether; the number of theoretical plates in the extraction column is 12, and the extractant is fed from the 12th plate; the number of theoretical plates in the first distillation column is 15; the number of theoretical plates in the second distillation column is 20, and it is fed from the 10th plate; the reflux ratio is 5; the content of propylene glycol monomethyl ether in the propylene glycol monomethyl ether product is 81.4 wt%, and the recovery rate is 80.4%. Example

[0095] Purify propylene glycol monomethyl ether according to the method of Example 22, the difference from Example 22 is only that: the extractant is a mixture of dibutyl oxalate, isobutyl isobutyrate and ethylene glycol monobutyl ether acetate (50 wt% dibutyl oxalate, 20 wt% isobutyl isobutyrate, 30 wt% ethylene glycol monobutyl ether acetate), and the flow rate of the extractant is 3 times that of the aqueous solution of propylene glycol monomethyl ether; the number of theoretical plates in the extraction column is 9, and the extractant is fed from the 9th plate; the number of theoretical plates in the first distillation column is 15; the number of theoretical plates in the second distillation column is 20, and it is fed from the 10th plate; the reflux ratio is 5; the content of propylene glycol monomethyl ether in the propylene glycol monomethyl ether product is 93.7 wt%, and the recovery rate is 93.8%.

[0096] Comparative Example 1

[0097] Using Figure 2 The shown flow chart, with benzene as the azeotropic agent, uses a plate column azeotropic distillation column to separate water and propylene glycol monomethyl ether. The composition of the propylene glycol monomethyl ether aqueous solution is 55.56 wt% propylene glycol monomethyl ether and 44.44 wt% water. A plate column azeotropic distillation column is used, with 21 theoretical plates, at atmospheric pressure. The propylene glycol monomethyl ether aqueous solution is fed into the 12th plate, and benzene (the flow rate of benzene is 4.6 times that of the propylene glycol monomethyl ether aqueous solution) is fed into the 3rd plate. The azeotropic vapor formed by benzene and water is condensed by a condenser at the top of the azeotropic distillation column, and the formed material is transported to a phase separator for phase separation. The separated aqueous phase is discharged, and the organic phase is returned to the azeotropic distillation column for reuse. The propylene glycol monomethyl ether mixture is taken out from the bottom of the column, and the content of propylene glycol monomethyl ether is 99.9 wt%. When treating the same mass of propylene glycol monomethyl ether aqueous solution, the total energy consumption of the process in this comparative example is 3.3 times that of the extraction process total energy consumption in Example 22 of the present invention.

[0098] When treating the same mass of propylene glycol monomethyl ether aqueous solution, the mass of benzene used in azeotropy in Comparative Example 1 is more than the mass of the extractant used in extraction in the present invention. At the same time, the purity of the products obtained by azeotropic distillation and extraction is not much different, but the energy consumption of the extraction process is greatly reduced. Therefore, the purification method provided by the present invention is better.

[0099] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A purification method of propylene glycol monomethyl ether, characterized in that, It includes the following steps: Performing multi-stage countercurrent extraction on the aqueous solution of propylene glycol monomethyl ether with an extractant to obtain an organic phase; the extractant includes an ester compound, and the ester compound is dibutyl oxalate or a mixture of ester compounds; the mixture of ester compounds is a mixture of dibutyl oxalate and ethyl methyl succinate, a mixture of dibutyl oxalate and 2-methylbutyl acetate, a mixture of dibutyl oxalate and amyl acetate, a mixture of dibutyl oxalate and ethyl phenylacetate, a mixture of dibutyl oxalate and dimethyl phthalate, a mixture of dibutyl oxalate and diethyl phthalate, a mixture of dibutyl oxalate and butyl propionate, a mixture of dibutyl oxalate and isobutyl isobutyrate, a mixture of dibutyl oxalate and ethylene glycol monobutyl ether acetate, a mixture of dibutyl oxalate, isobutyl isobutyrate and ethylene glycol monobutyl ether acetate, or a mixture of dibutyl oxalate, butyl propionate and ethylene glycol monobutyl ether acetate; Rectifying the organic phase to obtain propylene glycol monomethyl ether.

2. The purification method according to claim 1, wherein The multi-stage countercurrent extraction is carried out in an extraction column, and the number of theoretical plates of the extraction column is 4 to 12; the aqueous solution of propylene glycol monomethyl ether is fed into the first plate of the extraction column, and the extractant is fed into the last plate of the extraction column; The pressure of the multi-stage countercurrent extraction is atmospheric pressure.

3. The purification method according to claim 1 or 2, characterized in that, The flow rate ratio of the aqueous solution of propylene glycol monomethyl ether to the extractant is 1:0.35 to 5.

4. The purification method according to claim 1, characterized in that, The rectification is carried out in a rectification column; the rectification includes: conveying the organic phase to a first rectification column for first rectification to obtain overhead gas and a first bottom liquid respectively; conveying the first bottom liquid to a second rectification column for second rectification to obtain propylene glycol monomethyl ether and a second bottom liquid respectively; The pressure of the rectification is atmospheric pressure.

5. The purification method according to claim 4, characterized in that, The number of theoretical plates of the first rectification column is 5 to 15, and the first rectification column is connected with a heat exchanger.

6. The purification method according to claim 4, characterized in that, The overhead gas is condensed into a liquid phase by the heat exchanger and then undergoes multi-stage countercurrent extraction again.

7. The purification method according to claim 5 or 6, characterized in that, The temperature of the heat exchanger is 20 to 40 °C.

8. The purification method according to claim 4, characterized in that The number of theoretical plates of the second rectification column is 6 to 20, and the first bottom liquid is fed into the 3rd to 10th plates.

9. The purification method according to claim 4 or 8, characterized in that, The reflux ratio of the second rectification is 0.2 to 5.

10. The purification method according to claim 4, wherein The second bottom liquid is subjected to extractant recovery to obtain a recovered extractant, and the recovered extractant is used for the multi-stage countercurrent extraction step.

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