A method for separating and purifying 1,3-propylene glycol

Abstract

The present invention provides a method for separating and purifying 1,3-propylene glycol, including 1) inputting the first material and the extractant into an extractive distillation tower respectively, extracting the second material from the top of the extractive distillation tower and the third material from the bottom of the tower;Wherein, the first material includes 1,3-propylene glycol, 3-hydroxymethyltetrahydropyran and 1,3-dioxane-2-ethanol, and is prepared by dealcoholization, dehydration, heavy removal and light removal of the material obtained by acrolein hydration method;The extractant includes one or more of diethylene glycol, triethylene glycol, 1,5-pentanediol, 1,4-butanediol, sulfolane and glycerol;2) the third material is extracted from the top of the tower after rectification by a refining tower, 1,3-propylene glycol product. The present invention effectively separates the difficult-to-separate impurities with a boiling point close to that in 1,3-propylene glycol by the mode of extractive distillation, obtains high-purity 1,3-propylene glycol product, and improves the separation efficiency and yield of 1,3-propylene glycol;The process of the present invention is simple, highly operable, and reduces separation cost.

Description

Technical Field

[0001] The present invention relates to the technical field of chemical industry, in particular to a method for separating and purifying crude 1,3-propylene glycol obtained by an acrolein process. Background Art

[0002] 1,3-Propanediol (1,3-Propanediol) is an important chemical raw material used in the synthesis of plasticizers, detergents, preservatives, and emulsifiers, as well as in the food, cosmetics, and pharmaceutical industries. Its primary application is as a monomer in the synthesis of the novel polyester material poly(trimethylene terephthalate) (PTT) with purified terephthalic acid (PTA). PTT boasts easy processability, good resilience, and stain resistance, as well as being easily dyeable and wear-resistant. It has significant applications in carpets, engineering plastics, and clothing fabrics. The physical and mechanical properties of PTT fibers surpass those of polyethylene terephthalate (PET) and polybutylene terephthalate (PBT), earning it the nickname "the king of polyesters." Consequently, the preparation and purification of 1,3-propanediol, a key raw material for PTT synthesis, has become a hot topic in international synthetic fiber development.

[0003] The main industrial methods for producing 1,3-propylene glycol include ethylene oxide carbonylation, bioengineering, and acrolein hydration. Acrolein hydration has a high yield, high safety factor, and low equipment requirements, making it a competitive production method. The acrolein hydration process for producing 1,3-propylene glycol mainly includes the following two steps:

[0004] (1) Acrolein is hydrated to produce allyl alcohol, and the reaction equation is CH2=CHCHO+H2O→CH2=CHCH2OH;

[0005] (2) Propylene alcohol reacts with hydrogen to produce 1,3-propylene glycol. The reaction equation is CH2=CHCH2OH+H2→CH2OHCH2CH2OH.

[0006] Although the hydration of acrolein to produce 1,3-propylene glycol has high selectivity and conversion rate, the hydration reaction in this process inevitably produces aldehyde impurities, mainly including acetaldehyde, acrolein, 4-heterooxyheptanedial, 3,4-dihydro-2H-pyran-2-carboxaldehyde, 5,6-dihydro-2H-pyran-3-carboxaldehyde, etc. Among them, 5,6-dihydro-2H-pyran-3-carboxaldehyde will produce 3-hydroxymethyltetrahydropyran during the hydrogenation process. In addition, 1,3-dioxane-2-ethanol will be produced during the hydrogenation reaction. The impurities 3-hydroxymethyltetrahydropyran and 1,3-dioxane-2-ethanol have very close boiling points to the product 1,3-propylene glycol, making them difficult to separate by distillation. The presence of these difficult-to-separate impurities will affect the quality of 1,3-propylene glycol and further affect the quality of PTT.

[0007] In the prior art, chemical reactions are often used to remove difficult-to-separate impurities from materials produced using chemical processes (acrolein hydration or ethylene oxide carbonylation). Patent CN112979420A discloses a method for purifying 1,3-propylene glycol. This method reacts aldehydes in the raw material under specific pH conditions to form macromolecular substances, avoiding the formation of aldehydes with a boiling point close to that of 1,3-propylene glycol, which is difficult to separate. A resin adsorption step is also incorporated to effectively reduce the content of the acetal impurity 3-hydroxymethyltetrahydropyran in the raw material and remove trace organic aldehydes. CN1708467A discloses a method for removing impurities formed during the preparation of 1,3-propylene glycol. This method uses acidic zeolites, acidic cation exchange resins, or soluble acids to treat materials containing small amounts of aldehyde groups, primarily removing hydroxyethyldioxane (MW 132) cyclic acetals, thereby removing acetal impurities. However, this method may cause direct condensation of PDO itself to form di-PDO or tri-PDO. The above chemical treatment methods for treating the difficult-to-separate impurities in the material prepared by acrolein hydration, although achieving effective removal of acetal impurities, increase the reaction and separation process, increase the difficulty of operation, increase the separation cost, and may also cause side reactions and reduce product yield. Summary of the Invention

[0008] In response to the deficiencies in the prior art, the present invention discloses a method for separating and purifying 1,3-propylene glycol by extractive distillation. This method does not require the introduction of new chemical reactions, can efficiently separate and remove difficult-to-separate impurities in materials prepared by acrolein hydration, thereby improving product purity and yield and reducing separation difficulty and cost.

[0009] In order to achieve the above technical objectives, the present invention proposes a method for separating and purifying 1,3-propylene glycol, comprising the following steps:

[0010] (1) A first material and an extractant are respectively fed into an extractive distillation tower, and a second material is extracted from the top of the extractive distillation tower and a third material is extracted from the bottom of the tower; wherein the first material comprises 1,3-propylene glycol, 3-hydroxymethyltetrahydropyran and 1,3-dioxane-2-ethanol, and is obtained by dealcoholization, dehydration, heavy removal and light removal of materials obtained by acrolein hydration method; the extractant comprises one or more of diethylene glycol, triethylene glycol, 1,5-pentanediol, 1,4-butanediol, sulfolane and glycerol;

[0011] (2) After the third material is distilled in a refining tower, 1,3-propylene glycol product is extracted from the top of the tower.

[0012] The target product of the present invention, 1,3-propylene glycol, has a boiling point of 210-211°C, while the difficult-to-separate impurities 3-hydroxymethyltetrahydropyran and 1,3-dioxane-2-ethanol contained in the first material have boiling points of approximately 210-214°C. It is not difficult to see that due to the close boiling points of the target product and the difficult-to-separate impurities, the target product and the difficult-to-separate impurities are almost impossible to separate by conventional distillation. To simplify the process and avoid the need to separate and purify the material produced by the acrolein hydration method by adding chemical reactions, the research and development team of the present invention conducted a large number of exploratory experiments on the method of separating the difficult-to-separate impurities in the crude 1,3-propylene glycol material to be separated and purified by distillation.

[0013] The research and development team conducted distillation separation experiments on 1,3-propylene glycol (PD) and either 3-hydroxymethyltetrahydropyran (3-Hydroxymethyltetrahydropyran) or 1,3-dioxane-2-ethanol. For systems with varying mass ratios of target product and difficult-to-separate impurities, the team unexpectedly discovered azeotropy between the impurities and the target product, with the 1,3-PD mass fraction of the azeotrope reaching 65%-85% or 70%-95%. Furthermore, the team discovered that the boiling points of the azeotropic system and the target product were close, further exacerbating target product losses. The target product loss rate during the entire distillation separation process reached 39%-77%. This exploratory experiment is illustrated in the pilot examples of the present invention.

[0014] Based on this unexpected discovery, the research and development team of the present invention speculated that directly using distillation to separate and purify 1,3-propylene glycol (the first material) would not only be more difficult, but more importantly, would inevitably result in a significant loss of the target product 1,3-propylene glycol (the azeotrope has a high 1,3-propylene glycol content). To reduce the difficulty of distillation separation and improve the yield of the target product, the research and development team further explored refining the distillation process conditions, organically combining different distillation steps, and experimenting with distillation separation methods that incorporate a third component as an extractant.

[0015] Based on a large number of experimental trials, the R&D team found that by adding a polar organic solvent extractant similar to 1,3-propylene glycol to the first material and combining extractive distillation with fine distillation, the target product and difficult-to-separate impurities can be efficiently separated. This can also effectively reduce the loss of the target product, increase the yield, and obtain a high-purity 1,3-propylene glycol product.

[0016] In the above technical solution, the first material contains 1,3-propylene glycol and the difficult-to-separate impurities 3-hydroxymethyltetrahydropyran and 1,3-dioxane-2-ethanol. The water content in the first material is less than 1%, and both light and heavy impurities have been removed. The second material is a mixture of 1,3-propylene glycol and difficult-to-separate impurities. The 1,3-propylene glycol content in this mixture is lower than the azeotropic 1,3-propylene glycol content in the pilot test. Excluding this second material in the technical solution of the present invention effectively reduces the loss of the target product while ensuring a high-purity product.

[0017] Based on the above technical solution, the research and development team of the present invention explored and optimized the type and amount of the extractant used. Optionally, the extractant includes one or more of diethylene glycol, triethylene glycol, 1,5-pentanediol, 1,4-butanediol, sulfolane, and glycerol. Further, when the extractant includes any two of diethylene glycol, triethylene glycol, 1,5-pentanediol, 1,4-butanediol, sulfolane, and glycerol, the mass ratio of the two components is 1-10.

[0018] Based on the above technical solution, the research and development team of the present invention optimized the feed mass ratio of the first material to the extractant. Optionally, the feed mass ratio of the first material to the extractant is 1:(0.5-20), and can further be 1:(0.5-5).

[0019] Based on the above technical solution, the present invention optimizes the parameters and process conditions of the extraction column. Optionally, the extractive distillation column has 30 to 60 theoretical plates, the first material is fed from the 25th to 40th plate from the top, the extractant is fed from the 10th to 35th plate from the top, and the reflux ratio is 0.5 to 10. Optionally, the operating pressure of the extractive distillation column is 1 to 200 kPa, the top temperature is 30 to 120°C, and the bottom temperature is 100 to 180°C.

[0020] Based on the above technical solution, the present invention optimizes the technical feature of recycling the extractant. Optionally, a fourth material is extracted from the bottom of the refining tower, and the fourth material is returned to the extractive distillation tower as the extractant.

[0021] Based on the above technical solution, the present invention optimizes the parameters and process conditions of the refining tower. Optionally, the refining tower has 20 to 60 theoretical plates, the third material is fed from the 15th to 35th plate from the top, and the reflux ratio is 0.5 to 10. Optionally, the refining tower has an operating pressure of 1 to 500 kPa, a tower top temperature of 30 to 120°C, and a bottom operating temperature of 100 to 180°C.

[0022] It should be noted that the present invention does not limit the structure and specifications of the extraction tower and the refining tower. Those skilled in the art can select extraction towers and refining towers with appropriate structures and specifications based on the technical solutions of the present invention, and the technical solutions thus formed are all within the scope of protection of the present invention.

[0023] Beneficial effects: Compared with the prior art, the present invention uses extractive distillation to effectively separate difficult-to-separate impurities with a boiling point close to that of crude 1,3-propylene glycol prepared by acrolein hydration, thereby obtaining a high-purity 1,3-propylene glycol product and improving the separation efficiency and yield of 1,3-propylene glycol. The process flow of the present invention is simple, the operability is strong, and the separation cost is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0025] Figure 1 The process flow chart of the method for separating and purifying 1,3-propylene glycol of the present invention is shown.

[0026] The above drawings include the following reference numerals:

[0027] 1- Extraction distillation tower, 2- Refining tower. DETAILED DESCRIPTION

[0028] To facilitate understanding of the present invention, the present invention will be described in more detail below, with preferred embodiments of the present invention provided. However, it should be understood that these embodiments are merely for the purpose of further explanation and are not to be construed as limiting the present invention in any form, i.e., they are not intended to limit the scope of protection of the present invention.

[0029] It should be noted that, unless otherwise defined, the technical terms used in the following embodiments have the same meanings as commonly understood by those skilled in the art to which the present invention pertains. Relational terms such as "first," "second," "primary," "secondary," and the like in this embodiment are used solely to distinguish one component from another having the same name, and do not necessarily require or imply any actual relationship or order between these components. Features defined as "first," "second," "primary," "secondary," and the like may explicitly or implicitly include one or more of such features.

[0030] It should be noted that the specific steps for obtaining the first material used in the following embodiments are: separating the 3-hydroxypropanal obtained by the hydration of acrolein, hydrogenating it to obtain a preliminary product of 1,3-propylene glycol, and subjecting the preliminary product of 1,3-propylene glycol to dealcoholization, dehydration, heavy removal, and light removal to obtain the first material. The water content in the first material is less than 1%, and light and heavy impurities have been excluded, but it contains difficult-to-separate impurities (mainly tetrahydropyran-3-methanol and 1,3-dioxane-2-ethanol) whose boiling points form an azeotrope with 1,3-propylene glycol generated during the hydration, carbonylation, and hydrogenation reactions; the mass proportion of difficult-to-separate impurities is 3%-10%, and it is difficult to obtain a high-purity 1,3-propylene glycol product by simple distillation separation.

[0031] Small test embodiment

[0032] In this small-scale experiment, distillation separation experiments of 1,3-propylene glycol, 3-hydroxymethyltetrahydropyran, and 1,3-dioxane-2-ethanol were carried out respectively. Specifically:

[0033] In a pilot experiment for the distillation separation of 1,3-propylene glycol and 3-hydroxymethyltetrahydropyran, the R&D team constructed separation and purification systems containing 1,3-propylene glycol and 3-hydroxymethyltetrahydropyran in varying mass ratios in a batch glass distillation apparatus, performing distillation at pressures between 1 and 200 Pa. The ratios of 3-hydroxymethyltetrahydropyran to 1,3-propylene glycol in these systems were 1:20, 1:50, and 1:80, respectively.

[0034] During the experiment, the following findings were observed: 1) When the tower top temperature rose to 45-75°C, Fraction A containing 3-hydroxymethyltetrahydropyran was first distilled and separated. This fraction is a mixture of 1,3-propylene glycol and 3-hydroxymethyltetrahydropyran. Composition analysis of Fraction A revealed that the mass proportion of 1,3-propylene glycol in Fraction A obtained with different mass ratios of the separation and purification system was stable, ranging from 65% to 85%, confirming the formation of an azeotrope of 1,3-propylene glycol and 3-hydroxymethyltetrahydropyran. 2) Furthermore, as Fraction A was continuously withdrawn, the 1,3-propylene glycol content in the overhead product rapidly increased as the tower top temperature continued to rise. This suggests that the boiling point of the azeotrope is very close to that of 1,3-propylene glycol. 3) When the temperature rose to 60-85°C, pure 1,3-propylene glycol was distilled and separated from the system. During the entire distillation process, the loss rates of 1,3-propylene glycol in the systems to be separated and purified with different mass ratios reached 77%, 51%, and 43%, respectively.

[0035] In a pilot experiment for the distillation separation of 1,3-propylene glycol and 1,3-dioxane-2-ethanol, the R&D team constructed separation and purification systems containing different mass ratios of 1,3-propylene glycol and 1,3-dioxane-2-ethanol in a batch glass distillation apparatus and performed distillation at pressures of 1-200 Pa. The ratios of 3-hydroxymethyltetrahydropyran to 1,3-propylene glycol in these separation and purification systems were 1:30, 1:60, and 1:100, respectively.

[0036] During the experiment, the following findings were observed: 1) When the temperature rose to 48-76°C, Fraction B containing 1,3-dioxane-2-ethanol was first distilled out. This fraction is a mixture of 1,3-propylene glycol and 1,3-dioxane-2-ethanol. Composition analysis of Fraction B revealed that the 1,3-propylene glycol content in Fraction B obtained with different mass ratios of the separation and purification system ranged from 70% to 95%, and remained stable, confirming the formation of an azeotrope of 1,3-propylene glycol and 1,3-dioxane-2-ethanol. 2) Furthermore, as Fraction B was continuously withdrawn, the 1,3-propylene glycol content in the overhead product rapidly increased as the tower top temperature continued to rise. This suggests that the boiling point of the azeotrope is very close to that of 1,3-propylene glycol. 3) When the temperature rose to 60-85°C, pure 1,3-propylene glycol was distilled out of the system. During the entire distillation process, the loss rates of 1,3-propylene glycol in the systems to be separated and purified with different mass ratios reached 62%, 47%, and 39%, respectively.

[0037] Example 1

[0038] A method for separating and purifying 1,3-propylene glycol is disclosed. The method is used for separating and purifying a crude 1,3-propylene glycol material to be separated and purified obtained by acrolein hydration, and diethylene glycol is used as an extractant.

[0039] Step (1): If Figure 1 As shown, a first material and an extractant are respectively fed into an extractive distillation column 1, and a second material is withdrawn from the top and a third material is withdrawn from the bottom of the extractive distillation column 1. The operating conditions of the extractive distillation column 1 are: 60 theoretical plates, the first material is fed at the 30th plate from the top, the extractant is fed at the 5th plate from the top, and the reflux ratio is 5; the top pressure is 10 Pa, the top temperature is 73.9°C, and the bottom temperature is 131.4°C. A second material comprising difficult-to-separate impurities and 1,3-propylene glycol is withdrawn from the top, and a third material comprising 1,3-propylene glycol and the extractant is withdrawn from the bottom.

[0040] Step (2): After the third material is distilled in refining tower 2, a 1,3-propylene glycol product is extracted from the top of the tower. The operating conditions of refining tower 2 are: 55 theoretical plates, 20 feed positions; a top pressure of 2 Pa, a top temperature of 79.4°C, and a bottom temperature of 123.1°C. Pure 1,3-propylene glycol product with a purity of 99.97% is extracted from the top of the tower. A fourth material containing 1,3-propylene glycol and an extractant is extracted from the bottom of refining tower 2 and returned to the top of extractive distillation tower 1 as the extractant. The flow rate and composition of each stream are shown in Table 1.

[0041] Table 1

[0042]

[0043] Example 2

[0044] A method for separating and purifying 1,3-propylene glycol is disclosed. The method is used for separating and purifying a crude 1,3-propylene glycol material to be separated and purified obtained by acrolein hydration, and the extractant is 1,5-pentanediol.

[0045] Step (1): If Figure 1 As shown, a first material and an extractant are respectively fed into extractive distillation column 1, and a second material is withdrawn from the top and a third material is withdrawn from the bottom of extractive distillation column 1. The operating conditions of extractive distillation column 1 are as follows: 60 theoretical plates, the first material is fed at the 35th plate from the top, the extractant is fed at the 5th plate from the top, a reflux ratio of 5, a top pressure of 5 Pa, a top temperature of 72.2°C, and a bottom temperature of 117.7°C. A second material comprising difficult-to-separate impurities and 1,3-propylene glycol is withdrawn from the top, and a third material comprising 1,3-propylene glycol and the extractant is withdrawn from the bottom.

[0046] Step (2): After the third material is distilled in refining tower 2, a 1,3-propylene glycol product is extracted from the top of the tower. The operating conditions of refining tower 2 are: 55 theoretical plates, 20 feed positions; top pressure of 3 Pa, top temperature of 81.4°C, and bottom temperature of 127.9°C. Pure 1,3-propylene glycol product with a purity of 99.93% is extracted from the top of the tower. A fourth material containing 1,3-propylene glycol and an extractant is extracted from the bottom of refining tower 2 and returned to the top of extractive distillation tower 1 as the extractant. The flow rate and composition of each stream are shown in Table 2.

[0047] Table 2

[0048]

[0049] Example 3

[0050] A method for separating and purifying 1,3-propylene glycol is disclosed. The method is used for separating and purifying a crude 1,3-propylene glycol material to be separated and purified obtained by acrolein hydration method. The extractant is a mixed extractant of diethylene glycol and triethylene glycol, and the mass ratio of the mixed extractant diethylene glycol to triethylene glycol is 4:1.

[0051] Step (1): If Figure 1 As shown, a first material and an extractant are respectively fed into extractive distillation column 1, and a second material is withdrawn from the top and a third material is withdrawn from the bottom of extractive distillation column 1. The operating conditions of extractive distillation column 1 are as follows: 55 theoretical plates, the first material is fed at the 30th plate from the top, and the extractant is fed at the 5th plate from the top; a reflux ratio of 5; a top pressure of 3 Pa, a top temperature of 71.3°C, and a bottom temperature of 129.8°C; a second material comprising difficult-to-separate impurities and 1,3-propylene glycol is withdrawn from the top, and a third material comprising 1,3-propylene glycol and the extractant is withdrawn from the bottom.

[0052] Step (2): After the third material is distilled in refining tower 2, a 1,3-propylene glycol product is extracted from the top of the tower. The operating conditions of refining tower 2 are: 50 theoretical plates, 18 feed positions; a top pressure of 2 Pa, a top temperature of 78.9°C, and a bottom temperature of 124.5°C. A pure 1,3-propylene glycol product with a purity of 99.98% is extracted from the top of the tower. A fourth material containing 1,3-propylene glycol and an extractant is extracted from the bottom of refining tower 2 and returned to the top of extractive distillation tower 1 as the extractant. The flow rate and composition of each stream are shown in Table 3.

[0053] Table 3

[0054]

[0055] The second material extracted from the top of the extractive distillation tower 1 in Examples 1-3 contains impurities that are difficult to separate and a portion of 1,3-propylene glycol. The second material will be discharged from the boundary area.

[0056] Comparative Example

[0057] In this comparative example, direct distillation was used to separate impurities from the first material. Specifically, the first material was fed into a distillation tower operating under the following conditions: 60 theoretical plates, the first material feed position was the 30th plate from the top, the extractant feed position was the 5th plate from the top, a reflux ratio of 5, a top pressure of 9 Pa, a top temperature of 73.6°C, and a bottom temperature of 127.7°C. A fifth material containing difficult-to-separate impurities and 1,3-propylene glycol was withdrawn from the top of the distillation tower, while a pure 1,3-propylene glycol product with a purity of 99.91% was withdrawn from the bottom of the tower. The 1,3-propylene glycol loss rate was 39.38%. The flow rates and compositions of each stream are shown in Table 4.

[0058] Table 4

[0059]

[0060] It can be confirmed from Examples 1-3 and the comparative example that the present invention can efficiently separate the target product from the difficult-to-separate impurities by adding an extractant and separating and purifying the first material by extractive distillation, thereby improving the efficiency of separation and purification. In the pilot experiment, the separation loss rate of 1,3-propylene glycol was as high as 39%-77%. In comparison, the loss rate of 1,3-propylene glycol in the comparative example was 39.38%, and the separation loss rate of 1,3-propylene glycol in Examples 1-3 of the present invention was 12%-14%. Therefore, the technical solution of the present invention can improve the yield while ensuring high purity of the 1,3-propylene glycol product, thereby reducing product loss and reducing separation costs. The technical solution of the present invention has a simple process flow, a high purification and separation yield, and is suitable for large-scale industrial production.

[0061] It should be noted that the above content is a further detailed description of the present invention in conjunction with specific implementation methods, and the specific implementation of the present invention cannot be considered to be limited to these descriptions; the dimensional data of this embodiment does not necessarily limit the technical solution, but only illustrates one specific working condition. For those skilled in the art of the present invention, simple improvements and modifications can be made without departing from the concept of the present invention, and all of these should be considered to fall within the scope of protection of the present invention.

Claims

1. A method for separating and purifying 1,3-propylene glycol, characterized in that: The following steps are involved: (1) The first material and the extractant are respectively fed into an extractive distillation tower, and the second material is extracted from the top of the extractive distillation tower and the third material is extracted from the bottom of the tower; wherein the first material comprises 1,3-propylene glycol, 3-hydroxymethyltetrahydropyran and 1,3-dioxane-2-ethanol, and is obtained by dealcoholization, dehydration, heavy removal and light removal of the material obtained by acrolein hydration method; the extractant is selected from one or more of diethylene glycol, triethylene glycol, 1,5-pentanediol, 1,4-butanediol, sulfolane and glycerol; (2) After the third material is distilled in a refining tower, 1,3-propylene glycol product is extracted from the top of the tower.

2. The method for separating and purifying 1,3-propylene glycol according to claim 1, wherein The extractant is selected from any two components of diethylene glycol, triethylene glycol, 1,5-pentanediol, 1,4-butanediol, sulfolane, and glycerol.

3. The method for separating and purifying 1,3-propylene glycol according to claim 2, wherein: The mass ratio of any two components in the extractant is 1-10.

4. The method for separating and purifying 1,3-propylene glycol according to claim 1, wherein The feed mass ratio of the first material to the extractant is 1:(0.5-20).

5. The method for separating and purifying 1,3-propylene glycol according to claim 4, wherein: The feed mass ratio of the first material to the extractant is 1:(0.5-5).

6. The method for separating and purifying 1,3-propylene glycol according to claim 1, characterized in that: The number of theoretical plates of the extractive distillation tower is 30 to 60 theoretical plates, the feeding position of the first material is the 25th to 40th plate from the top, the feeding position of the extractant is the 10th to 35th plate from the top, and the reflux ratio is 0.5 to 10.

7. The method for separating and purifying 1,3-propylene glycol according to claim 1, characterized in that: The operating pressure of the extractive distillation tower is 1-200 kPa, the tower top temperature is 30-120° C., and the tower bottom temperature is 100-180° C.

8. The method for separating and purifying 1,3-propylene glycol according to claim 1, wherein A fourth material is taken out from the bottom of the refining tower, and the fourth material is returned to the extractive distillation tower as an extractant.

9. The method for separating and purifying 1,3-propylene glycol according to claim 1, characterized in that: The number of theoretical plates of the refining tower is 20 to 60 theoretical plates, the feeding position of the third material is the 15th to 35th plate from the top, and the reflux ratio is 0.5 to 10.

10. The method for separating and purifying 1,3-propylene glycol according to claim 1, characterized in that: The operating pressure of the refining tower is 1-500 kPa, the tower top temperature is 30-120° C., and the tower bottom operating temperature is 100-180° C.

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