A method for purifying and recovering glycolic acid, anode product of PET electrocatalytic reforming

Abstract

The present invention discloses a method for purifying and recovering glycolic acid, an anode product of PET electrocatalytic reforming. The purification and recovery method is mainly based on the compound distribution of the anolyte and combines the vacuum distillation characteristics, solubility characteristics, and acidification characteristics of various compounds to achieve separation and purification of the main product glycolic acid and preparation of high-purity glycolic acid crystals. At the same time, it realizes the recycling and utilization of by-products, further improving the economic value of the electrocatalytic reforming PET technical route. Specifically, the purification and recovery method of the present invention achieves a glycolic acid recovery rate of ≥95%, a glycolic acid purity of ≥99%, and a purity of other by-products of ≥95%.

Description

Technical Field

[0001] The present invention relates to the field of electrochemical catalysis, and more specifically, to a method for purifying and recovering glycolic acid, an anode product of PET electrocatalytic reforming. Background Art

[0002] Using a palladium-based catalyst as the anode catalyst, waste plastic PET can be converted into high-value-added chemicals - glycolate and hydrogen through electrocatalytic reforming technology, where glycolate is produced at the anode and hydrogen is produced at the cathode. Hydrogen is a gas at room temperature and pressure, so it can be separated from the cathode electrolyte by simple collection and storage. However, after the electrolysis is completed at the anode, the anolyte contains not only the main product sodium glycolate (note: sodium hydroxide solution is used as the alkaline environment solution), but also unreacted sodium hydroxide, unelectrolyzed ethylene glycol, by-product sodium carbonate, by-product sodium oxalate, by-product sodium formate, by-product sodium acetate, and sodium terephthalate and sodium isophthalate remaining after the PET hydrolysis reaction. For this system, there is currently no corresponding process that can effectively achieve the separation and purification of glycolic acid. Therefore, not only is the purity of the main product glycolic acid low, but it also causes waste of by-product resources. Therefore, it is necessary to explore a complete set of process flows to achieve the separation and purification of glycolic acid, and ultimately to achieve the preparation of high-purity glycolic acid crystals. At the same time, the by-products can be recycled and utilized, thereby improving the economic value of the electrocatalytic reforming PET technology route. Summary of the Invention

[0003] In view of the above background, the main purpose of the present invention is to provide a method for purifying and recovering glycolic acid, the anode product of PET electrocatalytic reforming, which can not only purify and prepare high-purity glycolic acid crystals, but also recycle the by-products.

[0004] In order to achieve the above object, the present invention adopts the following technical solutions:

[0005] In a first aspect, the present invention provides a method for purifying and recovering glycolic acid, an anode product of PET electrocatalytic reforming, wherein the anode catalyst used in the PET electrocatalytic reforming is a palladium-based catalyst and the electrolyte used is an alkaline electrolyte, comprising the following steps:

[0006] (1) performing vacuum rotary evaporation on the anolyte after the electrocatalytic reforming of PET to remove water and obtain a solid powder;

[0007] (2) washing the solid powder with an organic solvent, performing solid-liquid separation, collecting the resulting solid, and recovering an alkaline liquid containing ethylene glycol; wherein the solid contains glycolate;

[0008] (3) washing the solid obtained in step (2) with water, retaining the washing liquid, and recovering the solid oxalate;

[0009] (4) acidifying the water washing liquid obtained in step (3), separating the solid, retaining the liquid, and recovering the solid terephthalic acid and isophthalic acid;

[0010] (5) vacuum rotary evaporation of the liquid obtained in step (4), retaining the obtained solid, and recovering the formic acid and acetic acid aqueous solution;

[0011] (6) dissolving the solid obtained in step (5) with an organic solvent, extracting and filtering to achieve solid-liquid separation, retaining the liquid, and recovering the solid metal salt compound; wherein the liquid contains glycolic acid;

[0012] (7) The liquid obtained in step (6) is subjected to vacuum rotary evaporation to precipitate glycolic acid crystals, and the remaining liquid is recycled.

[0013] It should be noted that PET electrocatalytic reforming involves an electrochemical reaction in which an alkaline hydrolyzate of PET or its products undergoes an electrochemical reaction in the presence of a catalyst. This electrochemical reaction can be a two-electrode or three-electrode system. In the two-electrode system, the active material at the anode is the anode catalyst; in the three-electrode system, the active material at the working electrode is equivalent to the aforementioned anode catalyst. Furthermore, the palladium-based catalyst refers to a catalyst whose primary active ingredient is metallic palladium, and the primary anode product is glycolic acid.

[0014] Preferably, in step (1), the vacuum rotary evaporation is carried out under the following conditions: a temperature of 40° C. to 80° C. and a pressure of 5 kPa to 50 kPa. The solid powder obtained in this step contains glycolate.

[0015] Preferably, in step (2), the organic solvent is one of acetone, methanol, ethanol and acetonitrile, or a mixture of more thereof. The alkali in the alkaline liquid containing ethylene glycol obtained in this step is derived from an alkaline electrolyte, and the alkaline liquid can be directly used for electrolysis again after readjusting the concentration. In addition, the types of solvents defined in the present invention can better dissolve the target substance. In a specific example of the present invention, N,N-dimethylformamide is used as a solvent, and the recovered liquid contains more glycolate, which ultimately results in a decrease in the recovery rate of the main product glycolic acid.

[0016] More preferably, the molar ratio of the organic solvent to the glycolate is 2 to 20:1.

[0017] Preferably, in step (3), the molar ratio of water to glycolate is 5 to 20:1. The water wash solution obtained in this step contains glycolate. Furthermore, the amount of water used in this step, within the scope of the present invention, can better dissolve the main product, glycolate. If the amount is too large or too small, the recovery rate or purity of glycolic acid will be reduced to a certain extent.

[0018] Preferably, in step (4), the acid solution used in the acidification treatment is one of dilute sulfuric acid, dilute hydrochloric acid and dilute nitric acid, or a mixture of more than one of the above, wherein the liquid obtained in this step contains glycolic acid.

[0019] In addition, the process sequence of the present invention is more conducive to the purification of glycolic acid. In a specific example of the present invention, step (4) is performed in advance, which requires a large amount of acid solution to neutralize the hydroxide in the alkaline electrolyte. In another specific example of the present invention, the acidification operation of step (4) is delayed, resulting in that glycolic acid cannot be precipitated in the form of crystals.

[0020] Preferably, the molar ratio of hydrogen ions in the acid solution to the glycolate is 0.3 to 3:1.

[0021] Preferably, in step (5), the reduced-pressure rotary evaporation conditions are: a temperature of 30°C to 80°C and a pressure of 3kPa to 30kPa. The solid obtained in this step contains glycolic acid. Furthermore, the present invention has found that a rotary evaporation temperature within the present invention range can better precipitate glycolic acid crystals. If the temperature is too high, the recovery rate of glycolic acid will be reduced.

[0022] Preferably, in step (6), the organic solvent is one of ethyl acetate, acetone, methanol, ethanol, and acetonitrile, or a mixture of multiple thereof. The solvent types specified in the present invention can better dissolve the target compound. In a specific example, using dichloromethane as a solvent resulted in a reduced recovery rate of glycolic acid.

[0023] Preferably, the molar ratio of the organic solvent to the glycolic acid is 1 to 20:1.

[0024] Preferably, in step (7), the vacuum rotary evaporation conditions are: temperature of 30°C to 70°C and pressure of 3kPa to 30kPa. The vacuum rotary evaporation conditions defined in the present invention are more conducive to the crystallization of glycolic acid.

[0025] In addition, it is understood that since 100% of glycolic acid cannot be crystallized during the recrystallization process, the remaining liquid (crystallization mother liquor) of this step still contains glycolic acid. Therefore, it is necessary to repeat the crystallization of the liquid to improve the recovery rate; preferably, the cycle is 3 to 10 times.

[0026] Preferably, the glycolate is sodium glycolate; the oxalate is sodium oxalate; and the solid metal salt compound is a sodium salt. The type of alkaline electrolyte used in PET electrocatalytic reforming determines the type of metal element in the glycolate, oxalate, and solid metal salt compound. Choosing sodium hydroxide solution as the alkaline electrolyte can reduce the economic cost of PET electrocatalytic reforming, so the various salts are preferably sodium salts.

[0027] Preferably, after step (4), the method further comprises the step of separating terephthalic acid and isophthalic acid by utilizing solubility differences; wherein the purity of the obtained terephthalic acid is ≥95%, and the purity of the isophthalic acid is ≥97%.

[0028] After step (5), the method further comprises the step of separating formic acid and acetic acid by vacuum rotary evaporation, wherein the purity of the obtained formic acid is ≥96%, and the purity of the obtained acetic acid is ≥95%.

[0029] Preferably, the purity of the glycolic acid crystals is ≥99%, and the recovery rate of the glycolic acid crystals is ≥95%; and the purity of the oxalate salt is ≥98%.

[0030] In addition, unless otherwise specified, any range described herein includes the endpoints and any values ​​between the endpoints, as well as any subranges formed by the endpoints or any values ​​between the endpoints. The preparation methods herein are all conventional methods unless otherwise specified, and the raw materials used are all commercially available or prepared according to prior art unless otherwise specified. The percentages are all mass percentages unless otherwise specified, and the solutions are all aqueous solutions unless otherwise specified.

[0031] The beneficial effects of the present invention are as follows:

[0032] The purification and recovery method provided by the present invention removes all anode products in sequence by coordinating the overall operation sequence and regulating the operating conditions of each step. At the same time, it basically ensures that the purity of the product obtained in each step meets the general usage standard. The product can be directly put into use or production without further purification, further improving the economic value of the electrocatalytic reforming PET technology route.

[0033] The purification and recovery method provided by the present invention can separate and purify glycolic acid, the main product of the anolyte from the electrocatalytic reforming of PET, specifically to achieve a glycolic acid recovery rate of ≥95% and a glycolic acid purity of ≥99%. At the same time, other compounds in the anolyte can be recycled and reused. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0035] Figure 1 The process flow chart of the purification and recovery method of the present invention is shown.

[0036] Figure 2The NMR spectrum of the solid powder obtained in step (1) of Example 1 is shown; wherein (a) is the NMR spectrum of the solid powder 1 H spectrum; (b) NMR of solid powder 13 C spectrum.

[0037] Figure 3 The solid powder obtained in step (2) of Example 1 is shown 1 H NMR spectrum.

[0038] Figure 4 The liquid obtained in step (2) of Example 1 is shown 1 H NMR spectrum.

[0039] Figure 5 The NMR spectrum of the liquid obtained in step (3) of Example 1 is shown; wherein (a) is the NMR spectrum of the liquid 1 H spectrum; (b) is the NMR of the liquid 13 C spectrum.

[0040] Figure 6 The solid obtained in step (3) of Example 1 is shown. 13 C NMR spectrum.

[0041] Figure 7 The liquid obtained in step (4) of Example 1 is shown 1 H NMR spectrum.

[0042] Figure 8 The solid obtained in step (4) of Example 1 is shown 1 H NMR spectrum.

[0043] Figure 9 The solid obtained in step (4) of Example 1 is shown after separation. 1 H NMR spectrum; (a) is the NMR spectrum of terephthalic acid 1 H spectrum; (b) is the NMR of isophthalic acid 1 H spectrum.

[0044] Figure 10 The solid powder obtained in step (5) of Example 1 is shown 1 H NMR spectrum.

[0045] Figure 11 The liquid obtained in step (5) of Example 1 is shown 1 H NMR spectrum.

[0046] Figure 12 The liquid obtained in step (5) of Example 1 is shown after separation. 1 H NMR spectrum; (a) is the NMR spectrum of formic acid 1 H spectrum; (b) NMR of acetic acid1 H spectrum.

[0047] Figure 13 The liquid obtained in step (6) of Example 1 is shown 1 H NMR spectrum.

[0048] Figure 14 The XRD spectrum of the solid obtained in step (6) of Example 1 is shown.

[0049] Figure 15 The solid obtained in step (7) of Example 1 is shown. 1 H NMR spectrum.

[0050] Figure 16 The acetic acid crystals obtained in Experimental Example 1 are shown. 1 H NMR spectrum.

[0051] Figure 17 The acetic acid crystals obtained in Experimental Example 2 are shown. 13 C NMR spectrum.

[0052] Figure 18 The acetic acid crystals obtained in Experimental Example 3 are shown. 1 H NMR spectrum.

[0053] Figure 19 The acetic acid crystals obtained in Experimental Example 4 are shown. 1 H NMR spectrum. DETAILED DESCRIPTION

[0054] Due to the complex composition of the anode product after PET electrocatalytic reforming, in addition to the difficulty in ensuring the purity of the target product glycolic acid, other anode products are basically unrecoverable. Even if a small portion can be recovered, it needs further purification before it can be put into use again. In order to solve these problems, the present invention conducts a series of explorations on the purification process, operation flow and process conditions of the anode product, and cites the following experimental examples and preferred embodiments to describe the implementation scheme of the present invention. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention and are not intended to limit the patent requirements of the present invention.

[0055] There is no particular limitation on the purity of all raw materials in the present invention, and analytical purity is preferably adopted in the present invention.

[0056] All raw materials of the present invention, their sources and abbreviations are conventional sources and abbreviations in the field, and are clear and unambiguous in the field of their relevant uses. Those skilled in the art can purchase them from commercial sources or prepare them by conventional methods based on the abbreviations and corresponding uses.

[0057] The anolyte involved in the following experimental examples and embodiments is prepared by electrocatalytic PET using the method in the invention patent application number 202210527916.7, which preferably uses sodium hydroxide solution as the alkaline electrolyte.

[0058] In the present invention, the calculation formula of glycolic acid crystal recovery rate is: recovery rate = mass 析出的乙醇酸晶体 / quality 阳极电解液中的乙醇酸质量 ×100%.

[0059] Exploration Experiment Example 1

[0060] Purification and recovery of the anode product of PET electrocatalytic reforming includes the following steps:

[0061] (1) Use a certain amount of dilute hydrochloric acid solution (the amount of substance 盐酸 : amount of substance 乙醇酸钠 =0.5~1.5:1) acidifying the anolyte to obtain a suspension system, which is then filtered to achieve solid separation.

[0062] (2) The liquid obtained in step (1) is subjected to reduced pressure rotary evaporation (the rotary evaporation temperature is controlled at 40-50° C. and the pressure is controlled at 5 kPa-10 kPa) to rotary evaporate all low-boiling point compounds to obtain solid powder, thereby achieving solid-liquid separation.

[0063] (3) Mix a certain amount of ethyl acetate / acetone (v:v=1:1) with an organic solvent (amount of substance 有机溶剂 : amount of substance 乙醇酸 =2-5:1) stirring and ultrasonicating the solid obtained in step (2), and then filtering to achieve solid-liquid separation.

[0064] (4) The liquid obtained in step (3) is subjected to reduced pressure rotary evaporation (the rotary evaporation temperature is controlled at 40-50°C and the pressure is controlled at 5kPa-10kPa) to precipitate glycolic acid crystals, which are then filtered to achieve solid-liquid separation. 1 H NMR spectrum see Figure 16 As shown, it can be seen that the glycolic acid crystals obtained in this example contain a large amount of ethylene glycol impurities.

[0065] Exploration Experiment Example 2

[0066] Purification and recovery of the anode product of PET electrocatalytic reforming includes the following steps:

[0067] (1) The anolyte after the electrolysis reaction is subjected to reduced pressure rotary evaporation (the rotary evaporation temperature is controlled at 50° C. to 60° C., and the pressure is controlled at 10 kPa to 20 kPa) to evaporate all the water and obtain a solid powder.

[0068] (2) Mix an organic solvent (amount of substance) with a certain amount of ethanol / acetonitrile (v:v=1:1)有机溶剂 : amount of substance 乙醇酸钠 =5-10:1) the solid powder obtained in step (1) is stirred and ultrasonicated, and then filtered to achieve solid-liquid separation.

[0069] (3) Use a certain amount of dilute hydrochloric acid solution (the amount of substance 盐酸 : amount of substance 乙醇酸钠 =0.5~1.5:1) dissolving the solid obtained in step (2) to obtain a suspension system, and then filtering to separate the solid.

[0070] (4) The liquid obtained in step (3) is subjected to reduced pressure rotary evaporation (the rotary evaporation temperature is controlled at 40-50° C. and the pressure is controlled at 5 kPa-10 kPa) to rotary evaporate all low-boiling point compounds to obtain solid powder, thereby achieving solid-liquid separation.

[0071] (5) Mix a certain amount of ethyl acetate / acetone (v:v=1:1) with an organic solvent (the amount of substance 有机溶剂 : amount of substance 乙醇酸 =2-5:1) stirring and ultrasonicating the solid obtained in step (4), and then filtering to achieve solid-liquid separation.

[0072] (6) The liquid obtained in step (5) is subjected to reduced pressure rotary evaporation (the rotary evaporation temperature is controlled at 40-50°C and the pressure is controlled at 5kPa-10kPa) to precipitate glycolic acid crystals, which are then filtered to achieve solid-liquid separation. 1 H NMR spectrum see Figure 17 As shown, it can be seen that the glycolic acid crystals obtained in this example contain more oxalic acid.

[0073] Exploration Experiment Example 3

[0074] Purification and recovery of the anode product of PET electrocatalytic reforming includes the following steps:

[0075] (1) The anolyte after the electrolysis reaction is subjected to reduced pressure rotary evaporation (the rotary evaporation temperature is controlled at 50° C. to 60° C., and the pressure is controlled at 10 kPa to 20 kPa) to evaporate all the water and obtain a solid powder.

[0076] (2) Mix an organic solvent (amount of substance) with a certain amount of ethanol / acetonitrile (v:v=1:1) 有机溶剂 : amount of substance 乙醇酸钠 =5-10:1) the solid powder obtained in step (1) is stirred and ultrasonicated, and then filtered to achieve solid-liquid separation.

[0077] (3) Use appropriate amount of water (amount of substance 水 : amount of substance 乙醇酸钠=1-3:1) dissolving the mixed solid obtained in step (2) to obtain a suspension system, and then filtering to achieve solid-liquid separation.

[0078] (4) The liquid obtained in step (3) is subjected to reduced pressure rotary evaporation (the rotary evaporation temperature is controlled at 40-50° C. and the pressure is controlled at 5 kPa-10 kPa) to rotary evaporate all low-boiling point compounds to obtain solid powder, thereby achieving solid-liquid separation.

[0079] (5) Mix a certain amount of ethyl acetate / acetone (v:v=1:1) with an organic solvent (the amount of substance 有机溶剂 : amount of substance 乙醇酸 =2-5:1) stirring and ultrasonicating the solid obtained in step (4), and then filtering to achieve solid-liquid separation.

[0080] (6) The liquid obtained in step (5) was subjected to reduced pressure rotary evaporation (the rotary evaporation temperature was controlled at 40-50°C and the pressure was controlled at 5kPa-10kPa) to precipitate glycolic acid crystals, which were then filtered to achieve solid-liquid separation. The 1H NMR spectrum of the glycolic acid crystals is shown in FIG. Figure 18 As shown, it can be seen that the glycolic acid crystals obtained in this example contain more formic acid, isophthalic acid and terephthalic acid.

[0081] Exploration Experiment Example 4

[0082] Purification and recovery of the anode product of PET electrocatalytic reforming includes the following steps:

[0083] (1) The anolyte after the electrolysis reaction is subjected to reduced pressure rotary evaporation (the rotary evaporation temperature is controlled at 50° C. to 60° C., and the pressure is controlled at 10 kPa to 20 kPa) to evaporate all the water and obtain a solid powder.

[0084] (2) Mix an organic solvent (amount of substance) with a certain amount of ethanol / acetonitrile (v:v=1:1) 有机溶剂 : amount of substance 乙醇酸钠 =5-10:1) the solid powder obtained in step (1) is stirred and ultrasonicated, and then filtered to achieve solid-liquid separation.

[0085] (3) Use appropriate amount of water (amount of substance 水 : amount of substance 乙醇酸钠 =1-3:1) dissolving the mixed solid obtained in step (2) to obtain a suspension system, and then filtering to achieve solid-liquid separation.

[0086] (4) Use a certain amount of dilute hydrochloric acid solution (the amount of substance 盐酸 : amount of substance 乙醇酸钠 =0.5~1.5:1) the liquid obtained in step (3) is acidified to obtain a suspension system, which is then filtered to separate the solid.

[0087] (5) Mix a certain amount of ethyl acetate / acetone (v:v=1:1) with an organic solvent (the amount of substance 有机溶剂 : amount of substance 乙醇酸 =2~5:1) extracting the liquid obtained in step (4) to achieve solid-liquid separation.

[0088] (6) The liquid obtained in step (5) is subjected to reduced pressure rotary evaporation (the rotary evaporation temperature is controlled at 40-50°C and the pressure is controlled at 5kPa-10kPa) to precipitate glycolic acid crystals, which are then filtered to achieve solid-liquid separation. 1 H NMR spectrum see Figure 19 As shown, it can be seen that the glycolic acid crystals obtained in this example contain more formic acid and acetic acid impurities.

[0089] Summary: After investigation, it was found that the purification process, process operation flow and process conditions of the anode product will affect the recovery rate and purity of the main product glycolic acid and by-products. After analysis and summary, the optimal process flow and operating conditions were combined, and the following examples are provided.

[0090] Example

[0091] A method for purifying and recovering the anode product of PET electrocatalytic reforming, comprising the following steps (see the operation flow) Figure 1 shown):

[0092] (1) The anolyte after the electrolysis reaction is subjected to reduced pressure rotary evaporation (the rotary evaporation temperature is controlled at 50°C to 60°C and the pressure is controlled at 10kPa to 20kPa) to remove all the water and obtain a solid powder. The nuclear magnetic resonance spectrum of this solid powder is shown in FIG. Figure 2 As shown, it can be seen that the solid powder mainly includes sodium glycolate, unreacted sodium hydroxide, unelectrolyzed ethylene glycol, as well as by-products such as sodium carbonate, sodium oxalate, sodium formate, sodium acetate, sodium terephthalate and sodium isophthalate.

[0093] (2) Mix an organic solvent (amount of substance) with a certain amount of ethanol / acetonitrile (v:v=1:1) 有机溶剂 : amount of substance 乙醇酸钠 =5~10:1) the solid powder obtained in step (1) is stirred and ultrasonicated, and then filtered to achieve solid-liquid separation. The solid powder obtained in this step is 1 H NMR spectrum see Figure 3 As shown, the solid powder includes: main product sodium glycolate, by-product sodium carbonate, by-product sodium oxalate, by-product sodium formate, by-product sodium acetate, sodium terephthalate, sodium isophthalate. The recovered liquid contains sodium hydroxide and ethylene glycol, which 1 H NMR spectrum see Figure 4 As shown, this liquid can be recovered and recycled.

[0094] (3) Use appropriate amount of water (amount of substance 水 : amount of substance 乙醇酸钠 =6~10:1) dissolving the mixed solid obtained in step (2) to obtain a suspension system, and then filtering to achieve solid-liquid separation. The NMR spectrum of the obtained liquid is shown in Figure 5 , it can be seen that the liquid contains: main product sodium glycolate, by-product sodium carbonate, by-product sodium formate, by-product sodium acetate, sodium terephthalate, sodium isophthalate. The NMR spectrum of the obtained solid is shown in Figure 6 It can be seen that the solid obtained in this step is mainly sodium oxalate with a purity of ≥98%. This step can remove the by-product sodium oxalate, and the sodium oxalate can be recovered as a by-product.

[0095] (4) Use a certain amount of dilute hydrochloric acid (amount of substance 盐酸 : amount of substance 乙醇酸钠 =0.5~1.5:1) acidify the liquid obtained in step (3) to obtain a suspension system, and then filter to separate the solids. The obtained liquid 1 H NMR spectrum see Figure 7 As shown, the liquid includes: main product glycolic acid, by-product formic acid, by-product acetic acid, and sodium chloride. 1 H NMR spectrum see Figure 8 As shown, the solid contains terephthalic acid and isophthalic acid, with the contents of the two products being 9% and 91% respectively. Furthermore, by utilizing the difference in solubility of the salt solutions of the two compounds, the two can be separated by dissolving and filtering to obtain terephthalic acid with a purity of ≥95% and isophthalic acid with a purity of ≥97%, respectively. Figure 9 The above steps can convert the by-product sodium carbonate into the corresponding sodium chloride and simultaneously remove terephthalic acid and isophthalic acid, which can be recovered as by-products.

[0096] (5) The liquid obtained in step (4) is subjected to reduced pressure rotary evaporation (the rotary evaporation temperature is controlled at 40-50°C and the pressure is controlled at 5kPa-10kPa), and all low-boiling point compounds are rotary evaporated to obtain solid powder, thereby achieving solid-liquid separation. 1 H NMR spectrum see Figure 10 As shown, the solid contains glycolic acid and sodium chloride. 1 H NMR spectrum see Figure 11 As shown, the aqueous solution includes formic acid and acetic acid, and the corresponding contents of the two products are 92% and 8%, respectively. Furthermore, by utilizing the difference in the vacuum distillation characteristics of the two compounds, the two can be separated by vacuum rotary evaporation to obtain formic acid with a purity of ≥96% and acetic acid with a purity of ≥95%, respectively. Figure 12The above steps can remove the by-products formic acid and acetic acid, and the formic acid and acetic acid aqueous solutions can be recovered as by-products.

[0097] (6) Mix an organic solvent (amount of substance) with a certain amount of ethyl acetate / acetone (v:v=1:1) 有机溶剂 : amount of substance 乙醇酸 =2~5:1) the solid obtained in step (5) is stirred and ultrasonicated, and then filtered to achieve solid-liquid separation, and the liquid 1 H NMR spectrum see Figure 13 As shown in the figure, the liquid product includes glycolic acid and a small amount of ethylene glycol that has not been removed. The XRD spectrum of the solid powder is shown in Figure 14 As shown in the figure, the solid powder only includes sodium chloride. This step can remove sodium chloride and the sodium chloride can be recovered as a by-product.

[0098] (7) The liquid obtained in step (6) is subjected to reduced pressure rotary evaporation (the rotary evaporation temperature is controlled at 40-50°C and the pressure is controlled at 5kPa-10kPa) to precipitate glycolic acid crystals, which are then filtered to achieve solid-liquid separation. The liquid is the crystallization mother liquor, and the crystallization mother liquor is circulated and reduced pressure rotary evaporation is performed 5 times to obtain solid 1 H NMR spectrum see Figure 15 As shown, the solid is glycolic acid crystals with a purity of ≥99% and a recovery rate of ≥95%.

[0099] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not limitations on the implementation methods of the present invention. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the implementation methods here. All obvious changes or modifications derived from the technical solution of the present invention are still within the scope of protection of the present invention.

Claims

1. A method for purifying and recovering glycolic acid, an anode product of PET electrocatalytic reforming, wherein the anode catalyst used in the PET electrocatalytic reforming is a palladium-based catalyst and the electrolyte used is an alkaline electrolyte, characterized in that: The following steps are involved: (1) The anolyte after PET electrocatalytic reforming is subjected to vacuum rotary evaporation to remove water to obtain a solid powder; (2) washing the solid powder with an organic solvent, performing solid-liquid separation, collecting the obtained solid, and recovering an alkaline liquid containing ethylene glycol; wherein the solid contains glycolate; wherein the organic solvent is a mixture of ethanol and acetonitrile, the volume ratio of ethanol to acetonitrile is 1:1, and the molar ratio of the organic solvent to the glycolate is 5 to 10:1; (3) washing the solid obtained in step (2) with water, retaining the water washing solution, and recovering the solid oxalate; wherein the molar ratio of the water to the glycolate is 6 to 10:1; (4) The water washing liquid obtained in step (3) is subjected to acidification treatment, solid separation, liquid retention, and solid terephthalic acid and isophthalic acid are recovered; (5) vacuum rotary evaporation of the liquid obtained in step (4), retaining the obtained solid, and recovering the formic acid and acetic acid aqueous solutions; (6) extracting the solid obtained in step (5) with an organic solvent and filtering it to achieve solid-liquid separation, retaining the liquid, and recovering the solid metal salt compound; wherein the liquid contains glycolic acid; wherein the organic solvent is a mixture of ethyl acetate / acetone, the volume ratio of ethyl acetate to acetone is 1:1, and the molar ratio of the organic solvent to the glycolate is 2 to 5:1; (7) The liquid obtained in step (6) is subjected to vacuum rotary evaporation to precipitate glycolic acid crystals, and the remaining liquid is recycled.

2. The purification and recovery method according to claim 1, wherein: In step (1), the conditions for the reduced pressure rotary evaporation are: temperature of 40°C to 80°C, and pressure of 5 kPa to 50 kPa.

3. The purification and recovery method according to claim 1, wherein: In step (4), the acid solution used in the acidification treatment is one of dilute sulfuric acid, dilute hydrochloric acid and dilute nitric acid, or a mixture of multiple types.

4. The purification and recovery method according to claim 3, wherein: The molar ratio of hydrogen ions in the acid solution to the glycolate is 0.3 to 3:

1.

5. The purification and recovery method according to claim 1, wherein: In step (5), the conditions for the reduced pressure rotary evaporation are: temperature of 30°C to 80°C, and pressure of 3 kPa to 30 kPa.

6. The purification and recovery method according to claim 1, wherein: In step (7), the conditions for the reduced pressure rotary evaporation are: temperature of 30°C to 70°C, and pressure of 3 kPa to 30 kPa.

7. The purification and recovery method according to claim 1, wherein: After step (4), the method further includes separating terephthalic acid and isophthalic acid by utilizing solubility differences; wherein the purity of the obtained terephthalic acid is ≥95%, and the purity of the obtained isophthalic acid is ≥97%; After step (5), the method further includes separating formic acid and acetic acid by vacuum rotary evaporation, wherein the purity of the formic acid is ≥96%, and the purity of the acetic acid is ≥95%.

8. The purification and recovery method according to claim 1, wherein: The purity of the glycolic acid crystals is ≥99%, and the recovery rate is ≥95%; the purity of the oxalate is ≥98%.

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