A method for recovering glycolic acid from polyglycolic acid and its application

Abstract

The present invention discloses a method for recovering glycolic acid from polyglycolic acid and its application. The method comprises the following steps: step A, mixing polyglycolic acid, an organic solvent and water; step B, subjecting the product of step A to liquid-liquid separation to obtain an aqueous phase and an organic solvent phase. The method for recovering glycolic acid from polyglycolic acid provided by the present invention adopts a method of simultaneously hydrolyzing and extracting polyglycolic acid, water and an organic solvent, and adding an organic solvent during the hydrolysis process so that the glycolic acid obtained by hydrolysis enters the aqueous phase, and the colored impurities and unhydrolyzed oligomers generated during the hydrolysis process are dissolved in the organic solvent oil phase, thereby enabling the glycolic acid to be quickly separated, promoting the progress of the hydrolysis process, making the hydrolysis process more thorough, and the obtained glycolic acid has a low impurity content and a high purity, and the obtained glycolic acid can directly meet the recycling needs.

Description

Technical Field

[0001] The present invention relates to a method for recovering glycolic acid from polyglycolic acid and application thereof. Background Art

[0002] Glycolic acid is an aliphatic hydroxycarboxylic acid with the simplest molecular chain. As an important organic synthesis intermediate, it is used in chemical cleaning, welding, sterilization, and polymer materials. Polyglycolic acid, formed from glycolic acid monomers, exhibits excellent biodegradability and is widely used in the medical industry, for example, as surgical sutures.

[0003] However, due to the relatively active nature of glycolic acid, it is highly susceptible to side reactions such as oxidation and carbonization at polymerization temperatures, resulting in severe yellowing of the resulting polyglycolic acid. Existing processes for synthesizing polyglycolic acid are unable to directly polymerize glycolic acid. Furthermore, the polyglycolic acid obtained by direct polymerization of glycolic acid has a low molecular weight and cannot meet practical application requirements. Conventionally, glycolic acid is dimerized to produce glycolide, which is then used as a monomer in ring-opening polymerization to effectively address the aforementioned yellowing and low molecular weight issues.

[0004] Generally speaking, the process of preparing glycolide using glycolic acid requires three steps: prepolymerization, depolymerization and purification.

[0005] CN111087381A relates to a method for refining glycolide, which mainly solves the problem of high acid value of glycolide crystals obtained by refining treatment. By adopting a method for refining glycolide, including stirring and mixing crude glycolide with a solvent in a stirring form combined with a stirring paddle and a stirring blade, and then crystallizing, the problem is effectively solved and the method can be used in the industrial production of glycolide.

[0006] CN100999516A relates to a method for purifying glycolide. This method removes glycolide oligomers, glycolic acid, water, and other impurities from crude glycolide, thereby producing high-yield, high-purity glycolide. The technical solution involves mixing a glycolide mixture containing glycolide oligomers, glycolic acid, and water with an organic solvent. This removes glycolic acid and water from the crude glycolide, prevents glycolide hydrolysis, and produces high-purity glycolide in high yield.

[0007] Both of the aforementioned technical solutions involve washing the crude glycolide produced by depolymerization with an alcohol / ester solvent to remove glycolic acid monomer, linear oligomers, and colored impurities. Furthermore, to improve raw material utilization, the glycolic acid oligomers in the washing solution must be recycled. Therefore, efficient and stable recovery of glycolic acid monomer from glycolic acid oligomers remains a pressing challenge. Summary of the Invention

[0008] To address the aforementioned issues with the existing technology, the present invention provides a method for recovering glycolic acid from polyglycolic acid and its application. In this method, polyglycolic acid, an organic solvent, and water are simultaneously mixed and reacted, allowing the colored impurities and unhydrolyzed oligomers produced during the hydrolysis process to be dissolved in the organic solvent. Furthermore, the glycolic acid in the aqueous phase obtained through liquid-liquid separation can be directly reused.

[0009] A first aspect of the present invention provides a method for recovering glycolic acid from polyglycolic acid, the method comprising the following steps:

[0010] Step A, mixing polyglycolic acid, an organic solvent and water;

[0011] Step B: The product of step A is subjected to liquid-liquid separation to obtain an aqueous phase and an organic solvent phase.

[0012] The present invention provides a method for recovering glycolic acid from polyglycolic acid. Polyglycolic acid, an organic solvent, and water are directly mixed to allow hydrolysis and extraction of the polyglycolic acid to proceed simultaneously. The glycolic acid obtained by hydrolysis enters the aqueous phase, and impurities and some unhydrolyzed oligomers generated during the hydrolysis process dissolve in the organic solvent phase, thereby promoting the hydrolysis process. In addition, the glycolic acid obtained in the aqueous phase can directly meet the recycling requirements.

[0013] According to some embodiments of the method of the present invention, the organic solvent is selected from aliphatic alcohols above C4, aliphatic polyols above C4, aliphatic alcohols above C6, aliphatic polyols above C6 and aliphatic ketones.

[0014] According to some embodiments of the method of the present invention, at room temperature, the solubility of the organic solvent in water is less than 3 g / 100 mL.

[0015] According to a preferred embodiment of the method of the present invention, at room temperature, the solubility of the organic solvent in water is less than 0.1 g / 100 mL.

[0016] According to some embodiments of the method of the present invention, the organic solvent is selected from at least one of n-butanol, n-hexanol, n-octanol, n-hexanoic acid and methyl isobutyl ketone.

[0017] According to some embodiments of the method of the present invention, the polyglycolic acid is selected from at least one low molecular weight polyglycolic acid.

[0018] According to some embodiments of the method of the present invention, the number average molecular weight of the low molecular weight polyglycolic acid is 400-2000.

[0019] According to some embodiments of the method of the present invention, based on the total weight of the polyglycolic acid, the weight content of hexamers and above in the low molecular weight polyglycolic acid is greater than 50%.

[0020] According to a preferred embodiment of the method of the present invention, based on the total weight of the polyglycolic acid, the weight content of hexamers and above in the low molecular weight polyglycolic acid is greater than 70%.

[0021] According to some embodiments of the method of the present invention, the polyglycolic acid contains colored impurities.

[0022] According to some embodiments of the method of the present invention, preferably, the weight content of the colored impurities is ≤10% based on the total weight of the polyglycolic acid.

[0023] According to some embodiments of the method of the present invention, the weight ratio of the polyglycolic acid, the organic solvent and water is 1:0.01-3:0.1-10.

[0024] According to a preferred embodiment of the method of the present invention, the weight ratio of the polyglycolic acid, the organic solvent and water is 1:0.1 to 1:0.3-5.

[0025] According to some embodiments of the method of the present invention, the conditions of the mixing process of the polyglycolic acid, organic solvent and water include: a temperature of 70°C to 150°C and a time of 0.1h to 10h. For example, in different embodiments of the present invention, the temperature of the mixing process can be 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, and any values ​​and any combination ranges therebetween. The time of the mixing process can be 0.1h, 0.5h, 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, and any values ​​and any combination ranges therebetween.

[0026] According to a preferred embodiment of the method of the present invention, the temperature during the mixing of the polyglycolic acid, the organic solvent and the water is 80°C to 140°C.

[0027] According to some embodiments of the method of the present invention, in step B, the temperature of the liquid-liquid separation process is ≤50°C.

[0028] According to a preferred embodiment of the method of the present invention, in step B, the temperature of the liquid-liquid separation process is ≤40°C.

[0029] According to some embodiments of the method of the present invention, step B further comprises: concentrating the aqueous phase.

[0030] According to a preferred embodiment of the method of the present invention, the weight content of water in the aqueous phase after the concentration treatment is ≤50%.

[0031] A second aspect of the present invention provides an application of the above-mentioned method for recovering glycolic acid from polyglycolic acid in glycolic acid production, preferably in glycolide production, but not limited thereto.

[0032] Beneficial effects of the present invention:

[0033] The method for recovering glycolic acid from polyglycolic acid provided by the present invention uses polyglycolic acid, water and an organic solvent to simultaneously perform hydrolysis and extraction. The organic solvent is added during the hydrolysis process, so that the glycolic acid obtained by hydrolysis enters the aqueous phase, and the colored impurities and unhydrolyzed oligomers generated during the hydrolysis process are dissolved in the organic solvent oil phase, thereby enabling the glycolic acid to be quickly separated, promoting the progress of the hydrolysis process, making the hydrolysis process more thorough, and the obtained glycolic acid has a low impurity content and high purity, and the obtained glycolic acid can directly meet the recycling needs. DETAILED DESCRIPTION

[0034] In order to make the present invention easier to understand, the present invention will be described in detail below with reference to embodiments. These embodiments are only for illustrative purposes and do not limit the scope of application of the present invention.

[0035] The test method of the present invention and the equipment used in the test are as follows:

[0036] (1) The high performance liquid chromatograph was a 2695 model purchased from Waters. The operating conditions for the high performance liquid chromatography analysis of the oil phase and the aqueous phase were as follows: the mobile phase was a 0.5% phosphoric acid aqueous solution and acetonitrile in a ratio of 95:5, the chromatographic column was a C18 column, and the detector was an ultraviolet detector with a detection wavelength of 210 nm.

[0037] (2) The rotary evaporator was a Heizbad Hei-VAP model purchased from Heidolph.

[0038] (3) The absorbance value was measured using a spectrophotometer. The spectrophotometer model was Shanghai Yidian L5S.

[0039] The reagents used in the following examples and comparative examples can all be obtained commercially.

[0040] [Example 1]

[0041] The raw material composition in this embodiment is shown in Table 1 below:

[0042] Table 1

[0043]

[0044] 30 g of the raw materials listed in Table 1, 60 g of water, and 30 g of n-octanol were placed in a 250 mL stainless steel reactor. The reactor was sealed and nitrogen was introduced into the reactor three times to displace the air inside the reactor, followed by a further flush of nitrogen at 0.5 MPa. The stainless steel reactor was heated to 130°C for a hydrolysis reaction for 3 hours.

[0045] After the reaction is complete, the reaction system is stirred until it cools to 50°C, then the reaction solution is transferred to a separatory funnel and allowed to stand for separation. After separation, impurities such as colored substances in the reaction system are concentrated in the upper oil phase (i.e., n-octanol), while the glycolic acid produced by hydrolysis is concentrated in the lower aqueous phase.

[0046] The oil phase and the aqueous phase were analyzed by HPLC (high performance liquid chromatography), and the compositions of the oil phase and the aqueous phase were shown in Table 2.

[0047] The aqueous phase product was diluted to a monomer content of 5.00% by weight based on the monomer content. The absorbance of the product was measured at 390 nm and the value was 0.01735.

[0048] The aqueous phase was separated and concentrated in a rotary evaporator under vacuum until the glycolic acid content in the aqueous phase reached 65%, and then the rotary evaporator was turned off to obtain a recovered glycolic acid aqueous solution.

[0049] Table 2

[0050]

[0051] [Example 2]

[0052] The process was the same as in Example 1, except that n-butanol was used instead of n-octanol. The oil phase and aqueous phase finally separated were analyzed by HPLC, and the compositions of the oil phase and aqueous phase were shown in Table 3.

[0053] The aqueous phase product was diluted to a monomer content of 5.00% by weight based on the monomer content. The absorbance of the product was measured at 390 nm and the value was 0.01801.

[0054] Table 3

[0055]

[0056] [Example 3]

[0057] The process was the same as in Example 1, except that n-hexanol was used instead of n-octanol. The oil phase and aqueous phase finally separated were analyzed by HPLC, and the compositions of the oil phase and aqueous phase were shown in Table 4.

[0058] The aqueous phase product was diluted to a monomer content of 5.00% by weight based on the monomer content. The absorbance of the product was measured at 390 nm and the value was 0.01769.

[0059] Table 4

[0060]

[0061] [Example 4]

[0062] The process was the same as in Example 1, except that n-octanol was replaced with n-hexanoic acid. The oil phase and aqueous phase finally separated were analyzed by HPLC, and the compositions of the oil phase and aqueous phase were shown in Table 5.

[0063] The aqueous phase product was diluted to a monomer content of 5.00% by weight based on the monomer content. The absorbance of the product was measured at 390 nm and the value was 0.01881.

[0064] Table 5

[0065]

[0066] [Example 5]

[0067] The process was the same as in Example 1, except that methyl isobutyl ketone was used instead of n-octanol. The oil phase and aqueous phase finally separated were analyzed by HPLC, and the compositions of the oil phase and aqueous phase were shown in Table 6.

[0068] The aqueous phase product was diluted to a monomer content of 5.00% by weight based on the monomer content. The absorbance of the product was measured at 390 nm and the value was 0.01806.

[0069] Table 6

[0070]

[0071] [Example 6]

[0072] The process was the same as in Example 1, except that 30 g of the raw materials shown in Table 1, 9 g of water, and 30 g of n-octanol were added to a 250 mL stainless steel reactor. The resulting separated oil and aqueous phases were analyzed by HPLC, and the compositions of the oil and aqueous phases are shown in Table 7.

[0073] The aqueous phase product was diluted to a monomer content of 5.00% by weight based on the monomer content. The absorbance of the product was measured at 390 nm and the value was 0.03235.

[0074] Table 7

[0075]

[0076] [Example 7]

[0077] The process was the same as in Example 1, except that 30 g of the raw materials shown in Table 1, 30 g of water, and 30 g of n-octanol were added to a 250 mL stainless steel reactor. The resulting separated oil and aqueous phases were analyzed by HPLC, and the compositions of the oil and aqueous phases were shown in Table 8.

[0078] The aqueous phase product was diluted to a monomer content of 5.00% by weight based on the monomer content. The absorbance of the product was measured at 390 nm and the value was 0.02661.

[0079] Table 8

[0080]

[0081] [Example 8]

[0082] The process was the same as in Example 1, except that 30 g of the raw materials shown in Table 1, 90 g of water, and 30 g of n-octanol were added to a 250 mL stainless steel reactor. The resulting separated oil and aqueous phases were analyzed by HPLC, and the compositions of the oil and aqueous phases are shown in Table 9.

[0083] The aqueous phase product was diluted to a monomer content of 5.00% by weight based on the monomer content. The absorbance of the product was measured at 390 nm and the value was 0.01704.

[0084] Table 9

[0085]

[0086]

[0087] [Example 9]

[0088] The process was the same as in Example 1, except that 30 g of the raw materials shown in Table 1, 150 g of water, and 30 g of n-octanol were added to a 250 mL stainless steel reactor. The resulting separated oil and aqueous phases were analyzed by HPLC, and the compositions of the oil and aqueous phases are shown in Table 10.

[0089] The aqueous phase product was diluted to a monomer content of 5.00% by weight based on the monomer content. The absorbance of the product was measured at 390 nm and the value was 0.01700.

[0090] Table 10

[0091]

[0092] [Example 10]

[0093] The process was the same as in Example 1, except that 30 g of the raw materials shown in Table 1, 30 g of water, and 3 g of n-octanol were added to a 250 mL stainless steel reactor. The resulting separated oil and aqueous phases were analyzed by HPLC, yielding the compositions of the oil and aqueous phases shown in Table 11.

[0094] The aqueous phase product was diluted to a monomer content of 5.00% by weight based on the monomer content. The absorbance of the product was measured at 390 nm and the value was 0.01933.

[0095] Table 11

[0096]

[0097] [Example 11]

[0098] The process was the same as in Example 1, except that 30 g of the raw materials shown in Table 1, 30 g of water, and 15 g of n-octanol were added to a 250 mL stainless steel reactor. The resulting separated oil and aqueous phases were analyzed by HPLC, and the compositions of the oil and aqueous phases are shown in Table 12.

[0099] The aqueous phase product was diluted to a monomer content of 5.00% by weight based on the monomer content. The absorbance of the product was measured at 390 nm and the value was 0.01910.

[0100] Table 12

[0101]

[0102] [Example 12]

[0103] The process is the same as that of Example 1, except that the raw material composition in this example is shown in Table 15 below:

[0104] Table 13

[0105]

[0106] The operation process of this example is the same as that of Example 1. The oil phase and water phase finally separated are analyzed by HPLC, and the compositions of the oil phase and water phase are shown in Table 14.

[0107] The aqueous phase product was diluted to a monomer content of 5.00% by weight based on the monomer content. The absorbance of the product was measured at 390 nm and the value was 0.01666.

[0108] Table 14

[0109]

[0110] [Comparative Example 1]

[0111] 40 g of the raw materials listed in Table 1 and 80 g of water were placed in a 250 mL stainless steel reactor. The reactor was sealed and nitrogen was introduced into the reactor to displace the air within the reactor. Nitrogen was then flushed into the reactor at 0.5 MPa. The stainless steel reactor was heated to 130°C for a hydrolysis reaction for 3 h.

[0112] After the reaction, the reaction system was stirred until the reaction system was cooled to 50° C. After the reaction, no stratification occurred in the reaction liquid. The reaction liquid was analyzed by HPLC, and its composition was shown in Table 15.

[0113] The product was diluted to a monomer content of 5.00% by weight based on the monomer content. The absorbance of the product was measured at 390 nm and the value was 0.33582.

[0114] Table 15

[0115]

[0116] [Comparative Example 2]

[0117] Take 60 g of the product after the reaction of Comparative Example 1, add 20 g of n-octanol, stir at room temperature for 30 minutes, and then separate the layers. The separated oil phase and aqueous phase are analyzed by HPLC respectively. The compositions of the oil phase and aqueous phase are shown in Table 16.

[0118] The aqueous phase product was diluted to a monomer content of 5.00% by weight based on the monomer content. The absorbance of the product was measured at 390 nm and the value was 0.03557.

[0119] Table 16

[0120]

[0121] As can be seen from the above examples and comparative examples, the method for recovering glycolic acid from low molecular weight polyglycolic acid provided by the present invention, by using low molecular weight polyglycolic acid, water, and an organic solvent for simultaneous hydrolysis and extraction, can allow the glycolic acid obtained by hydrolysis to enter the aqueous phase, and the colored impurities and unhydrolyzed oligomers generated during the hydrolysis process are dissolved in the organic solvent oil phase, so that the glycolic acid can be quickly separated, thereby promoting the progress of the hydrolysis process, making the hydrolysis process more thorough, and the obtained glycolic acid has a low impurity content and high purity.

[0122] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, under the technical enlightenment provided by the present invention, as common knowledge in the art, other equivalent variations and improvements can be made, which should also be considered as the scope of protection of the present invention.

Claims

1. A method for recovering glycolic acid from polyglycolic acid, the method comprising the following steps: Step A, mixing polyglycolic acid, an organic solvent and water; Step B: The product of step A is subjected to liquid-liquid separation to obtain an aqueous phase and an organic solvent phase. Step B also includes: Concentrating the aqueous phase to obtain a recovered glycolic acid aqueous solution; The organic solvent is selected from at least one of n-hexanol and n-octanol, The weight ratio of the polyglycolic acid, organic solvent and water is 1:0.1 to 1:0.3 to 5. The polyglycolic acid is selected from at least one low molecular weight polyglycolic acid, and the weight content of hexamers and above in the low molecular weight polyglycolic acid is greater than 50% based on the total weight of the polyglycolic acid, and the hexamers and above are composed of octamers, decamers, undecamers and dodecamers.

2. The method according to claim 1, characterized in that Based on the total weight of the polyglycolic acid, the weight content of hexamers and above in the low molecular weight polyglycolic acid is greater than 70%.

3. The method according to any one of claims 1 to 2, characterized in that The polyglycolic acid contains colored impurities.

4. The method according to claim 3, characterized in that The weight content of the colored impurities is ≤10% based on the total weight of the polyglycolic acid.

5. The method according to any one of claims 1 to 2, characterized in that In step A, the conditions of the mixing process of the polyglycolic acid, organic solvent and water include: temperature of 70° C. to 150° C., time of 0.1 h to 10 h; and / or, In step B, the temperature of the liquid-liquid separation process is ≤50°C.

6. The method according to claim 5, characterized in that In step A, the temperature during the mixing process of the polyglycolic acid, the organic solvent and the water is 80° C. to 140° C.; and / or, In step B, the temperature of the liquid-liquid separation process is ≤40°C.

7. The method according to any one of claims 1 to 2, characterized in that The weight content of water in the aqueous phase after the concentration treatment after step B is ≤50%.

8. Use of the method for recovering glycolic acid from polyglycolic acid according to any one of claims 1 to 7 in the production of glycolic acid.

9. The use according to claim 8, characterized in that The application is application in glycolide production.

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