Purification method of propylene glycol monomethyl ether

Abstract

The invention provides a purification method of propylene glycol monomethyl ether, and relates to the technical field of separation and purification. According to the method, the propylene glycol monomethyl ether is selectively extracted by utilizing the hydrogen-bond interaction between the ester compound and the propylene glycol monomethyl ether and the hydrophobicity of the extracting agent, then rectification is performed, the high-purity propylene glycol monomethyl ether can be obtained, and the recovery rate of the propylene glycol monomethyl ether is high. The test result of the embodiment shows that the purity of the propylene glycol monomethyl ether obtained by the purification method provided by the invention is as high as 99.9%, and the recovery rate is as high as 99.4%. The ester compound is relatively low in toxicity and high in chemical stability. Compared with the traditional azeotropic distillation process, the purification method provided by the invention has the advantages that the energy consumption level is reduced by 70%, and the goal of greatly reducing the energy consumption is achieved. Moreover, the purification method provided by the invention is mild in operation condition, simple to operate, energy-saving, consumption-reducing and high in 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: The present invention provides a method for purifying propylene glycol monomethyl ether, comprising the following steps: The propylene glycol monomethyl ether aqueous solution is subjected to multi-stage countercurrent extraction using an extractant to obtain an organic phase; the extractant comprises an ester compound, and the ester compound comprises one or more of ethyl methyl succinate, 2-methylbutyl acetate, amyl acetate, ethyl phenylacetate, dimethyl phthalate, diethyl phthalate, tributyl phosphate, dibutyl oxalate, ethylene glycol butyl ether acetate, isobutyl isobutyrate and butyl propionate; The organic phase is distilled to obtain propylene glycol monomethyl ether.

[0007] Preferably, the multi-stage countercurrent extraction is carried out in an extraction tower, the multi-stage countercurrent extraction is carried out in an extraction tower, the theoretical number of plates of the extraction tower is 4 to 12; the propylene glycol monomethyl ether aqueous solution is fed from the first plate of the extraction tower, and the extractant is fed from the last plate of the extraction tower; The pressure of the multi-stage countercurrent extraction is normal pressure.

[0008] Preferably, the flow ratio of the propylene glycol monomethyl ether aqueous solution to the extractant is 1:0.35-5.

[0009] Preferably, the distillation is carried out in a distillation tower; the distillation comprises: conveying the organic phase to a first distillation tower for a first distillation to obtain a tower top gas and a first tower bottom liquid respectively; conveying the first tower bottom liquid to a second distillation tower for a second distillation to obtain propylene glycol monomethyl ether and a second tower bottom liquid respectively; The distillation pressure is normal pressure.

[0010] Preferably, the number of theoretical plates of the first distillation tower is 5 to 15, and the first distillation tower is connected to a heat exchanger.

[0011] Preferably, the tower top gas is condensed into a liquid phase through a heat exchanger and then subjected to multi-stage countercurrent extraction again.

[0012] Preferably, the temperature of the heat exchanger is 20-40°C.

[0013] Preferably, the second distillation tower has 6 to 20 theoretical plates, and the first tower bottom liquid is fed from the 3rd to 10th plates.

[0014] Preferably, the reflux ratio of the second distillation is 0.2-5.

[0015] Preferably, the second bottom liquid is subjected to extractant recovery to obtain a recovered extractant, and the recovered extractant is used in the multi-stage countercurrent extraction step.

[0016] The present invention utilizes the hydrogen bonding effect between the ester compound and propylene glycol monomethyl ether and the hydrophobicity of the extractant itself to achieve the selective extraction of propylene glycol monomethyl ether, and then performs rectification to obtain high-purity propylene glycol monomethyl ether, and the recovery rate of propylene glycol monomethyl ether is high. As shown in the test results of the embodiment, the purification method provided by the present invention has a purity of propylene glycol monomethyl ether of up to 99.9% and a recovery rate of up to 99.4%, and the obtained propylene glycol monomethyl ether can meet the quality standard of "HG / T 3939-2007 Industrial Propylene Glycol Methyl Ether".

[0017] Ester compounds have relatively low toxicity, little harm to humans and the environment, and low volatility. During use, they emit less VOCs and cause less pollution to the atmospheric environment, meeting environmental protection and safety requirements.

[0018] Compared with the traditional azeotropic distillation process, the purification method provided by the present invention reduces energy consumption 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 saving and consumption reduction, low cost, strong operating flexibility, and is suitable for industrial production.

[0019] 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The figure is a process flow chart of the purification of propylene glycol monomethyl ether in the present invention; Figure 2 This is a flow chart of the purification process of propylene glycol monomethyl ether in Comparative Example 1. DETAILED DESCRIPTION

[0021] The present invention provides a method for purifying propylene glycol monomethyl ether, comprising the following steps: The propylene glycol monomethyl ether aqueous solution is subjected to multi-stage countercurrent extraction using an extractant to obtain an organic phase; the extractant comprises an ester compound, and the ester compound comprises one or more of ethyl methyl succinate, 2-methylbutyl acetate, amyl acetate, ethyl phenylacetate, dimethyl phthalate, diethyl phthalate, tributyl phosphate, dibutyl oxalate, ethylene glycol butyl ether acetate, isobutyl isobutyrate and butyl propionate; The organic phase is distilled to obtain propylene glycol monomethyl ether.

[0022] Unless otherwise specified, the materials and equipment used in the present invention are all commercially available products in the art.

[0023] The invention uses an extractant to perform multi-stage countercurrent extraction on a propylene glycol monomethyl ether aqueous solution to obtain an organic phase.

[0024] 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 butyl 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 ester compound mixture preferably includes a mixture of dibutyl oxalate and ethyl methyl succinate, a mixture of dibutyl oxalate and 2-methylbutyl acetate. esters, 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 butyl glycol acetate, a mixture of dibutyl oxalate, isobutyl isobutyrate and butyl glycol acetate, or a mixture of dibutyl oxalate, butyl propionate and butyl glycol acetate.

[0025] 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 specific embodiments may be 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85% or 90%.

[0026] 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 can be 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85% or 90%.

[0027] 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 specific embodiments may be 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85% or 90%.

[0028] 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 specific embodiments may be 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85% or 90%.

[0029] 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 may be 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85% or 90%.

[0030] 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 a specific embodiment can be 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85% or 90%.

[0031] 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 may be 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85% or 90%.

[0032] 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 a specific embodiment can be 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85% or 90%.

[0033] 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 may 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 ethylene glycol butyl ether acetate is preferably 40-90%, and in a specific embodiment 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, butyl propionate and ethylene glycol butyl ether acetate is preferably 40-80%, and in a specific embodiment it can be 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75% or 80%; the mass fraction of ethylene glycol butyl ether acetate in the mixture of dibutyl oxalate, butyl propionate and ethylene glycol butyl ether acetate is preferably 10-50%, and in a specific embodiment it can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45% or 50%.

[0036] In the present invention, the mass fraction of dibutyl oxalate in the mixture of dibutyl oxalate, isobutyl isobutyrate and ethylene glycol butyl ether acetate is preferably 40-80%, and in a specific embodiment it can be 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75% or 80%; the mass fraction of ethylene glycol butyl ether acetate in the mixture of dibutyl oxalate, isobutyl isobutyrate and ethylene glycol butyl ether acetate is preferably 10-50%, and in a specific embodiment it can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45% or 50%.

[0037] In the present invention, the multi-stage countercurrent extraction is preferably carried out in an extraction tower (EC), and the multi-stage countercurrent extraction preferably comprises: using an extractant to carry out multi-stage countercurrent extraction of a propylene glycol monomethyl ether aqueous solution in an extraction tower to obtain an organic phase. In the present invention, the organic phase is extracted from the top of the tower.

[0038] In the present invention, the number of theoretical plates of the extraction tower is preferably 4 to 12, and in a specific embodiment, it can be 4, 5, 6, 7, 8, 9, 10, 11 or 12. In the present invention, the propylene glycol monomethyl ether aqueous solution is preferably fed from the first plate (tower top) of the extraction tower, and the extractant is preferably fed from the last plate (tower bottom) of the extraction tower.

[0039] In the present invention, the mass content of propylene glycol monomethyl ether in the propylene glycol monomethyl ether aqueous solution is preferably 1-70%, and in a specific embodiment 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%.

[0040] In the present invention, the flow ratio of the propylene glycol monomethyl ether aqueous solution and the extractant is preferably 1:0.35-5, and in a specific embodiment 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.

[0041] In the present invention, the temperature of the multi-stage countercurrent extraction is preferably 20-40°C, and in a specific embodiment, 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 produced from the bottom of the extraction tower (i.e., the bottom of the tower).

[0042] After obtaining the organic phase, the present invention performs rectification on the organic phase to obtain propylene glycol monomethyl ether.

[0043] In the present invention, the distillation is preferably carried out in a distillation tower, and the distillation tower preferably includes a first distillation tower (DC1) and a second distillation tower (DC2); the pressure of the distillation is preferably atmospheric pressure; the distillation preferably includes sequentially carrying out a first distillation and a second distillation, and the first distillation is preferably carried out in the first distillation tower, and the second distillation is preferably carried out in the second distillation tower. Specifically, the organic phase is transported to the first distillation tower for a first distillation to obtain a top gas and a first bottom liquid, respectively; the first bottom liquid is transported to the second distillation tower for a second distillation to obtain propylene glycol monomethyl ether and a second bottom liquid, respectively.

[0044] In the present invention, the number of theoretical plates of the first distillation tower is preferably 5 to 15, and in a specific embodiment, 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 distillation tower is preferably connected to a heat exchanger; the temperature of the heat exchanger is preferably 20 to 40°C, and in a specific embodiment, 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.

[0045] In the present invention, the tower top gas is preferably condensed into a liquid phase through a heat exchanger and then subjected to multi-stage countercurrent extraction again (ie, the liquid phase is condensed into a liquid phase through a heat exchanger and then transported to the extraction tower).

[0046] In the present invention, the number of theoretical plates of the second distillation tower is preferably 6 to 20, and in a specific embodiment, it can be 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 8, 19 or 20. In the present invention, the first bottom liquid is preferably fed from the 3rd to 10th plates, and in a specific embodiment, the first bottom liquid can be fed from the 3rd, 4th, 5th, 6th, 7th, 8th, 9th or 10th plates.

[0047] 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.

[0048] 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).

[0049] 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.

[0050] 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.

[0051] Example 1 Water and ethyl methyl succinate 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.

[0052] Example 2 Water and 2-methylbutyl acetate 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. The selectivity of propylene glycol monomethyl ether was calculated to be 9.85 and the distribution coefficient was 0.76.

[0053] Example 3 Water and amyl acetate were mixed evenly at a mass ratio of 2:2.5 to obtain a propylene glycol monomethyl ether aqueous solution. Propylene glycol monomethyl ether aqueous solution and amyl 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 10.15 and the distribution coefficient was 0.76.

[0054] Example 4 Water and ethyl phenylacetate were mixed evenly 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 phenylacetate 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 10.49 and the distribution coefficient was 0.72.

[0055] Example 5 Water and dimethyl phthalate were mixed evenly at a mass ratio of 2:2.5 to obtain a propylene glycol monomethyl ether aqueous solution. Propylene glycol monomethyl ether aqueous solution and dimethyl phthalate 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. The selectivity of propylene glycol monomethyl ether was calculated to be 9.58 and the distribution coefficient was 0.74.

[0056] Example 6 Water and diethyl phthalate were mixed evenly at a mass ratio of 2:2.5 to obtain a propylene glycol monomethyl ether aqueous solution. Propylene glycol monomethyl ether aqueous solution and diethyl phthalate 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. The selectivity of propylene glycol monomethyl ether was calculated to be 8.56 and the distribution coefficient was 0.85.

[0057] Example 7 Water and tributyl phosphate were mixed evenly at a mass ratio of 2:2.5 to obtain a propylene glycol monomethyl ether aqueous solution. Propylene glycol monomethyl ether aqueous solution and tributyl phosphate 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. The selectivity of propylene glycol monomethyl ether was calculated to be 1.34 and the distribution coefficient was 1.58.

[0058] Example 8 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 ethylene glycol butyl ether 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 20°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 3.94 and the distribution coefficient was 0.6.

[0059] Example 9 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 ethylene glycol butyl ether acetate were heated and stirred at 30°C and 500r / min for 2.5h at a mass ratio of 1:1, and then allowed to stand at 30°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. The selectivity of propylene glycol monomethyl ether was calculated to be 3.67 and the distribution coefficient was 0.54.

[0060] Example 10 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 isobutyl isobutyrate 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 20°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. The selectivity of propylene glycol monomethyl ether was calculated to be 6.93 and the distribution coefficient was 0.38.

[0061] Embodiment 11 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 isobutyl isobutyrate were heated and stirred at 30°C and 500r / min for 2.5h at a mass ratio of 1:1, and then allowed to stand at 30°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. The selectivity of propylene glycol monomethyl ether was calculated to be 6.08, and the distribution coefficient was 0.36.

[0062] Example 12 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 butyl propionate 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 20°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. The selectivity of propylene glycol monomethyl ether was calculated to be 19.67 and the distribution coefficient was 0.48.

[0063] Embodiment 13 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 butyl propionate were heated and stirred at 30°C and 500r / min for 2.5h at a mass ratio of 1:1, and then allowed to stand at 30°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. The selectivity of propylene glycol monomethyl ether was calculated to be 17.03 and the distribution coefficient was 0.47.

[0064] Embodiment 14 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 dibutyl oxalate 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 20°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. The selectivity of propylene glycol monomethyl ether was calculated to be 57.75, and the distribution coefficient was 0.3.

[0065] Embodiment 15 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 dibutyl oxalate were heated and stirred at 30°C and 500r / min for 2.5h at a mass ratio of 1:1, and then allowed to stand at 30°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. The selectivity of propylene glycol monomethyl ether was calculated to be 55.13 and the distribution coefficient was 0.28.

[0066] 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 butyl ether acetate, isobutyl isobutyrate and butyl propionate all have the ability to extract propylene glycol monomethyl ether, and the extraction effect is: dibutyl oxalate>butyl propionate>ethyl phenylacetate>amyl acetate>2-methylbutyl acetate>dimethyl phthalate>ethyl methyl succinate>diethyl phthalate>isobutyl isobutyrate>ethylene glycol butyl ether acetate>tributyl phosphate.

[0067] Example 16 Water and propylene glycol monomethyl ether were mixed uniformly at a mass ratio of 2:0.5625 to obtain a propylene glycol monomethyl ether aqueous solution. The propylene glycol monomethyl ether aqueous solution and dibutyl oxalate were heated and stirred at 30°C and 500r / min for 2.5h at a mass ratio of 2.5625:2, and then allowed to stand at 30°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 26.58 and the distribution coefficient was 0.17.

[0068] Embodiment 17 Water and propylene glycol monomethyl ether were mixed uniformly at a mass ratio of 2:1.125 to obtain a propylene glycol monomethyl ether aqueous solution. The propylene glycol monomethyl ether aqueous solution and dibutyl oxalate were heated and stirred at 30°C and 500r / min for 2.5h at a mass ratio of 3.125:2, and then allowed to stand at 30°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 18.65 and the distribution coefficient was 0.21.

[0069] Embodiment 18 Water and propylene glycol monomethyl ether were mixed uniformly at a mass ratio of 2:1.6875 to obtain a propylene glycol monomethyl ether aqueous solution. The propylene glycol monomethyl ether aqueous solution and dibutyl oxalate were heated and stirred at 30°C and 500r / min for 2.5h at a mass ratio of 3.6875:2, and then allowed to stand at 30°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. The selectivity of propylene glycol monomethyl ether was calculated to be 15.49, and the distribution coefficient was 0.25.

[0070] Embodiment 19 Water and propylene glycol monomethyl ether were mixed uniformly at a mass ratio of 2:2.25 to obtain a propylene glycol monomethyl ether aqueous solution. The propylene glycol monomethyl ether aqueous solution and dibutyl oxalate were heated and stirred at 30°C and 500r / min for 2.5h at a mass ratio of 4.25:2, and then allowed to stand at 30°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 12.49 and the distribution coefficient was 0.28.

[0071] Embodiment 20 Water and propylene glycol monomethyl ether were mixed uniformly at a mass ratio of 2:2.8125 to obtain a propylene glycol monomethyl ether aqueous solution. The propylene glycol monomethyl ether aqueous solution and dibutyl oxalate were heated and stirred at 30°C and 500r / min for 2.5h at a mass ratio of 4.8125:2, and then allowed to stand at 30°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. The selectivity of propylene glycol monomethyl ether was calculated to be 10.06 and the distribution coefficient was 0.32.

[0072] Embodiment 21 Water and propylene glycol monomethyl ether were mixed uniformly at a mass ratio of 2:3.375 to obtain a propylene glycol monomethyl ether aqueous solution. The propylene glycol monomethyl ether aqueous solution and dibutyl oxalate were heated and stirred at 30°C and 500r / min for 2.5h at a mass ratio of 5.375:2, and then allowed to stand at 30°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 8.32 and the distribution coefficient was 0.4.

[0073] By comparing Examples 16 to 21, it can be seen that dibutyl oxalate has a good extraction effect on propylene glycol monomethyl ether solutions of different concentrations, and the operating space is large.

[0074] Embodiment 22 Propylene glycol monomethyl ether aqueous solution: 55.56wt% propylene glycol monomethyl ether, 44.44wt% water.

[0075] use Figure 1The flow chart shown is for purifying propylene glycol monomethyl ether, and the specific steps are as follows: the extraction tower has 8 theoretical plates, the propylene glycol monomethyl ether aqueous solution is fed from the 1st plate, dibutyl oxalate (the flow rate of dibutyl oxalate is 2.9 times the flow rate of the propylene glycol monomethyl ether aqueous solution) is fed from the 8th plate, the operating pressure of the extraction tower is normal pressure, water is extracted from the bottom of the tower, propylene glycol monomethyl ether enters the organic phase, the organic phase is extracted from the top of the extraction tower and introduced into the first distillation tower (without connecting the condenser), the first distillation tower has 9 theoretical plates, and is fed from the 1st plate, the operating pressure of the first distillation tower is normal pressure, the temperature of the heat exchanger connected to the top of the tower is 30°C, the top gas is condensed to obtain the liquid phase, and the liquid phase and the propylene glycol monomethyl ether aqueous solution enter the extraction tower together for extraction again. The first bottom liquid of the first distillation tower is produced and transported to the second distillation tower. The second distillation tower has 9 theoretical plates, and feed is taken from 5 plates. The operating pressure of the second distillation tower is normal pressure, and the reflux ratio is 0.29. The solvent is recovered from the second bottom liquid, and the recovered extractant is transported to the extraction tower. Propylene glycol monomethyl ether product is produced from the top of the tower (the content of propylene glycol monomethyl ether is 99.9wt%, and the recovery rate is 99.4%).

[0076] Embodiment 23 Propylene glycol monomethyl ether was purified according to the method of Example 22, the only difference from Example 22 being that the flow rate of dibutyl oxalate was 2.2 times the flow rate of the propylene glycol monomethyl ether aqueous solution; the content of propylene glycol monomethyl ether in the propylene glycol monomethyl ether product was 93.3 wt %, and the recovery rate was 92.8%.

[0077] Embodiment 24 Propylene glycol monomethyl ether was purified according to the method of Example 22, the only difference from Example 22 being that the theoretical number of plates of the extraction tower was 5; dibutyl oxalate was fed from the 5th plate; the content of propylene glycol monomethyl ether in the propylene glycol monomethyl ether product was 97.3 wt %, and the recovery rate was 96.8%.

[0078] Embodiment 25 Propylene glycol monomethyl ether was purified according to the method of Example 22, the only difference from Example 22 being that: the number of theoretical plates of the extraction tower was 5; dibutyl oxalate was fed from the 5th plate; the number of theoretical plates of the second distillation tower was 7, and it was fed from the 4th plate; the content of propylene glycol monomethyl ether in the propylene glycol monomethyl ether product was 97.3 wt%, and the recovery rate was 96.7%.

[0079] Embodiment 26 Propylene glycol monomethyl ether was purified according to the method of Example 22, the only difference from Example 22 being that: the extraction tower had 5 theoretical plates; dibutyl oxalate was fed from the 5th plate; the first distillation tower had 7 theoretical plates; the temperature of the heat exchanger connected to the top of the first distillation tower was 25°C; the second distillation tower had 7 theoretical plates, and was fed from 4 plates; the reflux ratio was 0.3; the propylene glycol monomethyl ether content in the propylene glycol monomethyl ether product was 97.2wt%, and the recovery rate was 96.7%.

[0080] Embodiment 27 Propylene glycol monomethyl ether was purified according to the method of Example 22, and the only difference from Example 22 was: propylene glycol monomethyl ether aqueous solution: propylene glycol monomethyl ether 70wt%, water 30wt%. The extraction tower had 8 theoretical plates, the propylene glycol monomethyl ether aqueous solution was fed from the first plate, dibutyl oxalate (the flow rate of dibutyl oxalate was 1.7 times the flow rate of the propylene glycol monomethyl ether aqueous solution) was fed from the eighth plate, the operating pressure of the extraction tower was normal pressure, water was extracted from the bottom of the tower, and propylene glycol monomethyl ether entered the organic phase and was extracted from the top of the tower; the propylene glycol monomethyl ether content in the propylene glycol monomethyl ether product was 94.3wt%, and the recovery rate was 94.3%.

[0081] Embodiment 28 Propylene glycol monomethyl ether was purified according to the method of Example 22, and the only difference from Example 22 was: Propylene glycol monomethyl ether aqueous solution: 70wt% propylene glycol monomethyl ether, 30wt% water. The number of theoretical plates of the extraction tower was 15, the propylene glycol monomethyl ether aqueous solution was fed from the first plate, and dibutyl oxalate (the flow rate of dibutyl oxalate was 3.1 times the flow rate of the propylene glycol monomethyl ether aqueous solution) was fed from the 15th plate. The operating pressure of the extraction tower was normal pressure, water was produced from the bottom of the tower, and propylene glycol monomethyl ether entered the organic phase and was produced from the top of the tower; the propylene glycol monomethyl ether content in the propylene glycol monomethyl ether product was 98.9wt%, and the recovery rate was 98.9%.

[0082] Embodiment 29 Propylene glycol monomethyl ether was purified according to the method of Example 22, which differs from Example 22 only in that: the extractant was a mixture of dibutyl oxalate and butyl propionate (70wt% of dibutyl oxalate and 30wt% of butyl propionate), the flow rate of the extractant was 3 times the flow rate of the propylene glycol monomethyl ether aqueous solution; the extraction tower had 12 theoretical plates, and the extractant was fed from the 12th plate; the first distillation tower had 15 theoretical plates; the second distillation tower had 20 theoretical plates, and was fed from 10 plates; the reflux ratio was 5; the propylene glycol monomethyl ether content in the propylene glycol monomethyl ether product was 82.6wt%, and the recovery rate was 80.7%.

[0083] Embodiment 30 Propylene glycol monomethyl ether was purified according to the method of Example 22, which differs from Example 22 only in that: the extractant was a mixture of dibutyl oxalate and isobutyl isobutyrate (70wt% of dibutyl oxalate and 30wt% of isobutyl isobutyrate), the flow rate of the extractant was 3 times the flow rate of the propylene glycol monomethyl ether aqueous solution; the extraction tower had 9 theoretical plates, and the extractant was fed from the 9th plate; the first distillation tower had 15 theoretical plates; the second distillation tower had 20 theoretical plates, and was fed from the 10th plate; the reflux ratio was 5; the propylene glycol monomethyl ether content in the propylene glycol monomethyl ether product was 92.6wt%, and the recovery rate was 94.3%.

[0084] Embodiment 31 Propylene glycol monomethyl ether was purified according to the method of Example 22, which differed from Example 22 only in that: the extractant was a mixture of dibutyl oxalate and ethylene glycol butyl ether acetate (70wt% of dibutyl oxalate and 30wt% of ethylene glycol butyl ether acetate), the flow rate of the extractant was 3 times the flow rate of the propylene glycol monomethyl ether aqueous solution; the extraction tower had 12 theoretical plates, and the extractant was fed from the 12th plate; the first distillation tower had 15 theoretical plates; the second distillation tower had 20 theoretical plates, and was fed from 10 plates; the reflux ratio was 5; the propylene glycol monomethyl ether content in the propylene glycol monomethyl ether product was 97.6wt%, and the recovery rate was 96.8%.

[0085] Embodiment 32 Propylene glycol monomethyl ether was purified according to the method of Example 22, which differed from Example 22 only in that: the extractant was a mixture of dibutyl oxalate and ethylene glycol butyl ether acetate (50wt% of dibutyl oxalate and 50wt% of ethylene glycol butyl ether acetate), the flow rate of the extractant was 3 times the flow rate of the propylene glycol monomethyl ether aqueous solution; the extraction tower had 12 theoretical plates, and the extractant was fed from the 12th plate; the first distillation tower had 15 theoretical plates; the second distillation tower had 20 theoretical plates, and was fed from 10 plates; the reflux ratio was 5; the propylene glycol monomethyl ether content in the propylene glycol monomethyl ether product was 96.8wt%, and the recovery rate was 96.9%.

[0086] Embodiment 33 Propylene glycol monomethyl ether was purified according to the method of Example 22, which differs from Example 22 only in that: the extractant was a mixture of dibutyl oxalate, butyl propionate and ethylene glycol butyl ether acetate (50wt% of dibutyl oxalate, 20wt% of butyl propionate and 30wt% of ethylene glycol butyl ether acetate), the flow rate of the extractant was 3 times the flow rate of the propylene glycol monomethyl ether aqueous solution; the extraction tower had 12 theoretical plates, and the extractant was fed from the 12th plate; the first distillation tower had 15 theoretical plates; the second distillation tower had 20 theoretical plates, and was fed from 10 plates; the reflux ratio was 5; the propylene glycol monomethyl ether content in the propylene glycol monomethyl ether product was 81.4wt%, and the recovery rate was 80.4%.

[0087] Embodiment 34 Propylene glycol monomethyl ether was purified according to the method of Example 22, which differs from Example 22 only in that: the extractant was a mixture of dibutyl oxalate, isobutyl isobutyrate and ethylene glycol butyl ether acetate (50wt% of dibutyl oxalate, 20wt% of isobutyl isobutyrate and 30wt% of ethylene glycol butyl ether acetate), and the flow rate of the extractant was 3 times the flow rate of the propylene glycol monomethyl ether aqueous solution; the extraction tower had 9 theoretical plates, and the extractant was fed from the 9th plate; the first distillation tower had 15 theoretical plates; the second distillation tower had 20 theoretical plates, and was fed from the 10th plate; the reflux ratio was 5; the propylene glycol monomethyl ether content in the propylene glycol monomethyl ether product was 93.7wt%, and the recovery rate was 93.8%.

[0088] Comparative Example 1 use Figure 2 The flow chart shown uses benzene as an azeotropic agent and uses a plate tower azeotropic distillation tower to separate water and propylene glycol monomethyl ether. The propylene glycol monomethyl ether aqueous solution is composed of 55.56wt% propylene glycol monomethyl ether and 44.44wt% water. A plate tower azeotropic distillation tower is used, the theoretical number of plates is 21, the pressure is normal pressure, the propylene glycol monomethyl ether aqueous solution is fed on the 12th plate, and benzene (the flow rate of benzene is 4.6 times the flow rate of the propylene glycol monomethyl ether aqueous solution) is fed on the 3rd plate. After the azeotropic vapor formed by benzene and water is condensed by the condenser at the top of the azeotropic distillation tower, the formed material is transported to the phase separator for phase separation, the aqueous phase after phase separation is discharged, and the organic phase returns to the azeotropic distillation tower for reuse. The propylene glycol monomethyl ether mixture is extracted from the bottom of the tower, wherein the propylene glycol monomethyl ether content is 99.9wt%. When treating the same mass of propylene glycol monomethyl ether aqueous solution, the total energy consumption of the process of this comparative example is 3.3 times the total energy consumption of the extraction process of Example 22 of the present invention.

[0089] When treating the same mass of propylene glycol monomethyl ether aqueous solution, the mass of benzene used for azeotropy in Comparative Example 1 is greater than the mass of the extractant used for 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.

[0090] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for purifying propylene glycol monomethyl ether, characterized in that: The following steps are involved: The propylene glycol monomethyl ether aqueous solution is subjected to multi-stage countercurrent extraction using an extractant to obtain an organic phase; the extractant comprises an ester compound, and the ester compound comprises one or more of ethyl methyl succinate, 2-methylbutyl acetate, amyl acetate, ethyl phenylacetate, dimethyl phthalate, diethyl phthalate, tributyl phosphate, dibutyl oxalate, ethylene glycol butyl ether acetate, isobutyl isobutyrate and butyl propionate; The organic phase is distilled to obtain propylene glycol monomethyl ether.

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

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

4. The purification method according to claim 1, characterized in that The distillation is carried out in a distillation tower; the distillation comprises: conveying the organic phase to a first distillation tower for a first distillation to obtain a tower top gas and a first tower bottom liquid respectively; conveying the first tower bottom liquid to a second distillation tower for a second distillation to obtain propylene glycol monomethyl ether and a second tower bottom liquid respectively; The distillation pressure is normal pressure.

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

6. The purification method according to claim 4, characterized in that: The tower top gas is condensed into a liquid phase through a heat exchanger and then subjected to 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 20-40°C.

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

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

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

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