A preparation method of polyethylene glycol dicarboxylic acid

Abstract

The invention discloses a method for preparing polyethylene glycol dicarboxylic acid, comprising the following steps: polyethylene glycol is dissolved in deionized water, palladium / platinum / carbon composite catalyst, hydrogen peroxide are added, liquid caustic soda is added to adjust pH to 9-11, and the temperature is reacted under the condition of 40-95 ° C, so that polyethylene glycol is converted into polyethylene glycol dicarboxylate, and the polyethylene glycol dicarboxylic acid is obtained through post-treatment; the palladium / platinum / carbon composite catalyst is made of the following mass percentage components: 2-5% palladium chloride, 1-4% platinum chloride, 0.2-0.6% bismuth chloride, 0.3-0.6% cobalt nitrate, 90-96.5% activated carbon. The method for preparing polyethylene glycol dicarboxylic acid provided by the invention has simple process, fast reaction rate, high yield, easy control of production process, high product purity, stable quality, green production process, fast reaction speed, low energy consumption, and more economical production process.

Description

Technical Field

[0001] The invention belongs to the technical field of fine chemical preparation, and in particular relates to a method for preparing polyethylene glycol dicarboxylic acid. Background Art

[0002] The reports on the use of polyethylene glycol dicarboxylic acid in the connection of biological proteins and polypeptide compounds and metal recovery are as follows: Patent application with publication number CN100497437C discloses a preparation method of polyethylene glycol carboxylic acid and its use; Patent application with publication number CN112626344A discloses a method for recovering Li and Co in lithium battery positive electrode materials using polyethylene glycol dicarboxylic acid.

[0003] At present, the synthesis methods of polyethylene glycol dicarboxylic acid are divided into two categories: the first category is to introduce a carboxyl group on the hydroxyl group of polyethylene glycol through chemical reaction, and the second category is to convert the hydroxyl group of polyethylene glycol into carboxyl group. The first category of methods mostly uses the method of halogenated acetic acid substitution. The patent application with publication number TW474912B discloses a method for preparing low molecular weight polyethylene glycol-carboxylic acid, which adopts ethyl bromoacetate to connect PEG and then obtain it through hydrolysis. The second category of methods directly converts polyethylene glycol into polyethylene glycol carboxylic acid, that is, oxidizes the terminal hydroxyl group of PEG into carboxylic acid. The most commonly used methods are as follows: (1) PEG carboxylic acid is prepared by nitric acid oxidation or potassium permanganate oxidation, but the ether bond of PEG is easily broken during the reaction. Therefore, the molecular weight distribution of the obtained PEG carboxylic acid is relatively wide, which is not conducive to subsequent applications. (2) Using mild oxidant MnO2 to first oxidize PEG into aldehyde, and then oxidize PEG aldehyde into PEG carboxylic acid under the action of hydrogen peroxide. The conditions of this method are mild, but the yield is low (such as JP5096516, EP0206448). (3) In recent years, direct oxidation preparation using relatively mild oxidants has been disclosed. For example, patent application with publication number CN100497437C discloses a method for preparing polyethylene glycol carboxylic acid and its use. Ammonia nitrogen free radicals and bromide are used as catalysts and hypochlorite is used as an oxidant to oxidize polyethylene glycol carboxylic acid at room temperature and normal pressure, but a large amount of chloride-containing salts are produced.

[0004] In view of this, it is necessary to develop a preparation method of polyethylene glycol dicarboxylic acid with simple operation, mild conditions, environmental friendliness and high conversion rate. Summary of the invention

[0005] The purpose of the present invention is to provide a method for preparing polyethylene glycol dicarboxylic acid with simple operation, mild conditions, environmental friendliness and high conversion rate.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] The first aspect of the present invention provides a method for preparing polyethylene glycol dicarboxylic acid, comprising the following steps:

[0008] Dissolve polyethylene glycol in deionized water, add palladium / platinum / carbon composite catalyst and hydrogen peroxide, the mass ratio of polyethylene glycol, palladium / platinum / carbon composite catalyst and hydrogen peroxide is 1:(0.001-0.05):(0.01-2.0), add liquid caustic soda to adjust the pH to 9-11, react at a temperature of 40-95° C., so that the polyethylene glycol is converted into polyethylene glycol dicarboxylate, and obtain the polyethylene glycol dicarboxylic acid through post-treatment;

[0009] The palladium / platinum / carbon composite catalyst is made of the following components in percentage by mass: 2-5% of palladium chloride, 1-4% of platinum chloride, 0.2-0.6% of bismuth chloride, 0.3-0.6% of cobalt nitrate, and 90-96.5% of activated carbon.

[0010] The palladium / platinum / carbon composite catalyst is made of the following components in percentage by mass: 3% palladium chloride, 2% platinum chloride, 0.5% bismuth chloride, 0.5% cobalt nitrate and 94% activated carbon.

[0011] The preparation method of the palladium / platinum / carbon composite catalyst comprises the following steps:

[0012] Palladium chloride, platinum chloride, bismuth chloride and cobalt nitrate are dissolved in a hydrochloric acid solution with a concentration of 0.15-0.35 mol / L, the mass ratio of palladium chloride to hydrochloric acid is 1:(2-4), the mixed solution is slowly dripped into deionized water containing pretreated activated carbon, the mass ratio of palladium chloride to pretreated activated carbon is 1:(20-50), the mass concentration of pretreated activated carbon dispersed in deionized water is 4%-15%, and the mixture is stirred evenly. After the dripping is completed, stirring is continued for 4-6 hours, the pH value is adjusted to 11-13 with a NaOH solution, and formaldehyde with a mass fraction of 5% is slowly dripped, and the formaldehyde is 0.5-3.5 times the mass of palladium chloride. At the same time, the system is slowly heated to 60-75°C, reacted at a constant temperature for 2-3 hours, cooled to room temperature, filtered, the filtered solid is washed with deionized water, nitrogen is blown in and sealed for storage, and the palladium / platinum / carbon composite catalyst is obtained.

[0013] The mass concentration of the polyethylene glycol dissolved in deionized water is 5% to 40%.

[0014] The base is selected from sodium hydroxide or potassium hydroxide.

[0015] The mass concentration of the liquid caustic soda is 5-50%.

[0016] The molecular weight of the polyethylene glycol is 200-50000.

[0017] The mesh number of the activated carbon is 80-100 mesh, preferably 85 mesh.

[0018] The pretreatment steps of the pretreated activated carbon are as follows:

[0019] Add activated carbon to hydrochloric acid solution, the mass ratio of activated carbon to hydrochloric acid solution is 1: (5-50), heat at 40-80°C for 1-8h, filter, wash with distilled water, add NaOH solution to activated carbon, the mass ratio of activated carbon to NaOH solution is 1: (5-50), heat at 40-80°C for 1-8h, filter, wash with distilled water, dry, then place the filtered activated carbon in distilled water, boil for 1-5h, filter, wash the filter cake until there is no chloride ion, and dry at 100-110°C for 1-12h to obtain pretreated activated carbon.

[0020] The concentration of the hydrochloric acid solution is 0.1-0.5 mol / L, preferably 0.15-0.30 mol / L.

[0021] The concentration of the NaOH solution is 0.2-2 mol / L.

[0022] The steps of obtaining the polyethylene glycol dicarboxylic acid through post-treatment are as follows:

[0023] The filtrate and the filter cake are obtained by filtration. The filtrate is a polyethylene glycol dicarboxylate solution, and the filter cake is a palladium / platinum / carbon composite catalyst. The filter cake is washed with deionized water for 3 to 5 times and recycled. A portion of water is evaporated from the filtrate, an acid is added, heated to 70 to 90° C. for reaction for 1 to 4 hours, carbon dioxide is introduced, the upper layer is separated after standing, and polyethylene glycol dicarboxylic acid is obtained after dehydration and drying.

[0024] The acid is selected from at least one of sulfuric acid, hydrochloric acid or phosphoric acid.

[0025] The acid is an acid solution with a mass fraction of 15-55%, and the amount of the acid solution added is 0.1 to 2 times the mass of the polyethylene glycol.

[0026] The amount of carbon dioxide introduced is 10%-30% of the theoretical mass of polyethylene glycol dicarboxylic acid and is measured by a gas flow meter.

[0027] The molecular formula of the polyethylene glycol dicarboxylic acid is HOOCCH2-O(CH2CH2O)n-CH2COOH, where n=4-1780.

[0028] Due to the adoption of the above technical solution, the present invention has the following advantages and beneficial effects:

[0029] The preparation method of polyethylene glycol dicarboxylic acid provided by the invention has the advantages of simple process, fast reaction rate, high yield, easy control of production process, high product purity, stable quality, green and environmentally friendly production process, fast reaction speed, low energy consumption and more economical production process.

[0030] The preparation method of polyethylene glycol dicarboxylic acid provided by the present invention uses hydrogen peroxide and a series of polyethylene glycols as raw materials, and in the presence of a catalyst, the series of polyethylene glycols and hydrogen peroxide undergo an oxidation reaction to generate polyethylene glycol dicarboxylic acid, and the reaction is carried out in an alkaline system to generate polyethylene glycol dicarboxylate, which is easy to dissolve in an aqueous solution, and the reaction is relatively complete with few by-products. The product is acidified and concentrated with acid and carbon dioxide to remove inorganic salts in the system, and the method is relatively environmentally friendly.

[0031] The preparation method of polyethylene glycol dicarboxylic acid provided by the invention adopts one-time feeding in the presence of a noble metal catalyst, has a simple process, and adopts hydrogen peroxide, so that the materials are well mixed, the reaction speed is fast, and the energy consumption is low; the catalyst can be recycled, and the three wastes are less; the noble metal is loaded on activated carbon, and the recycling of the catalyst can be achieved through filtration, the process is safe, no gas is used, the equipment requirements in the whole process are low, and the process safety is good.

[0032] The preparation method of polyethylene glycol dicarboxylic acid provided by the present invention is simple to operate, mild in conditions, environmentally friendly and has a high conversion rate. The polyethylene glycol dicarboxylic acid has both an ether bond and a carboxylic acid bond, has a certain adsorption effect on metal ions, can be used for mineral ion enrichment, recovery of lithium electrons in the new energy field, and can be used as a linker for proteins and polypeptides in the biological field. DETAILED DESCRIPTION

[0033] In order to explain the present invention more clearly, the present invention is further described below in conjunction with preferred embodiments. It should be understood by those skilled in the art that the following specific description is illustrative rather than restrictive, and should not be used to limit the scope of protection of the present invention.

[0034] The reagents and materials used in the embodiments of the present invention are as follows:

[0035] Polyethylene glycol PEG400, PEG750, PEG1000, PEG5000 and PEG10000 (molecular weights of 400, 750, 1000, 5000 and 10000, respectively) were all from Liaoning Aoke Chemical Co., Ltd., industrial grade; precious metal palladium chloride and platinum chloride were from Guiyan Platinum Co., Ltd.; bismuth chloride and cobalt nitrate were purchased from Sinopharm Group; activated carbon was purchased from Guangdong Hanyan Activated Carbon Co., Ltd.

[0036] Example 1

[0037] Preparation of catalyst:

[0038] The pretreatment steps of the activated carbon carrier are as follows: 20 g of 85 mesh activated carbon is added to 250 mL of 0.25 mol / L hydrochloric acid solution, heated at 75°C for 2 h, filtered, and washed with distilled water; the precipitate is filtered out, the activated carbon is placed in a flask, 250 mL of 0.5 mol / L NaOH solution is added, the mixture is heated at 75°C for 3 h, filtered, washed with distilled water, and dried; then the filtered activated carbon is placed in 300 mL of distilled water, boiled for 2 h, filtered, and the filter cake is washed until there is no chloride ion, dried at 105°C for 4 h, and stored in a dryer for use to obtain 19.8 g of pretreated activated carbon.

[0039] Preparation of palladium / platinum / carbon composite catalyst:

[0040] 0.6 g of palladium chloride, 0.4 g of platinum chloride, 0.1 g of bismuth chloride and 0.1 g of cobalt nitrate were dissolved in 50 mL of 1 mol / L hydrochloric acid solution, and the mixed solution was slowly dripped into 380 mL of deionized water containing 19 g of the above-mentioned pretreated activated carbon, and stirred evenly. After dripping, stirring was continued for 4.5 h, and the pH was adjusted to 12.1 with a 1 mol / L NaOH solution. 10 mL of formaldehyde with a mass fraction of 5% was slowly dripped, and the system was slowly heated to 70°C, reacted at a constant temperature for 2.5 h, cooled to room temperature, filtered, washed with deionized water to remove the solid, filled with nitrogen, sealed and stored for use, to obtain 20 g of palladium / platinum / carbon composite catalyst.

[0041] The basic performance test data of the palladium / platinum / carbon composite catalyst are shown in Table 1:

[0042] Table 1

[0043]

[0044] Example 2

[0045] In a 1L three-necked flask, 50g PEG400 is dissolved in 150g deionized water, 0.5g palladium / platinum / carbon composite catalyst, 45g hydrogen peroxide (27.5%) are added, liquid caustic soda (concentration is 32% sodium hydroxide) is added to adjust pH to 10.8, reflux is loaded, stirring is turned on, heated to 80 ℃ and reacted for 4 hours, filtrated to obtain filtrate and filter cake, the filtrate is a polyethylene glycol dicarboxylate solution, the filter cake is a palladium / platinum / carbon composite catalyst, the filter cake is washed three times with deionized water, and is placed in 0.5N sodium hydroxide solution and preserved. 70g water is steamed off the filtrate, 10g 50% sulfuric acid is added, heated to 80 ℃ and reacted for 2 hours, 3g carbon dioxide is introduced, the upper layer is separated after standing, and 47.6g polyethylene glycol dicarboxylic acid is obtained after dehydration and drying, with a yield of 89.0%. The acid number of polyethylene glycol dicarboxylic acid is 268mgKOH / g.

[0046] In a 250mL three-necked flask, 10g PEG400 is dissolved in 50g deionized water, 0.1g of palladium / platinum / carbon composite catalyst recovered, 10g of hydrogen peroxide (27.5%) are added, liquid caustic soda (concentration is 32% sodium hydroxide) is added to adjust pH to 10.9, reflux is installed, stirring is turned on, heated to 85 ℃ and reacted for 4 hours, filtrate and filter cake are obtained by filtration, the filtrate is a polyethylene glycol dicarboxylate solution, the filter cake is a palladium / platinum / carbon composite catalyst, the filter cake is washed three times with deionized water, and is placed in a 0.5N sodium hydroxide solution and preserved. 20g water is steamed off the filtrate, 2g of 50% sulfuric acid is added, heated to 80 ℃ and reacted for 2 hours, 1g of carbon dioxide is introduced, the upper layer is separated after standing, and 7.3g polyethylene glycol dicarboxylic acid is obtained after the upper layer is dehydrated and dried, with a yield of 70.2%. The acid number of polyethylene glycol dicarboxylic acid is 262mgKOH / g.

[0047] The catalyst can be reused more than 25 times.

[0048] Example 3

[0049] In a 1L three-necked flask, 50g PEG750 is dissolved in 160g deionized water, 0.3g palladium / platinum / carbon composite catalyst, 26g hydrogen peroxide (27.5%) are added, liquid caustic soda (concentration is 32% sodium hydroxide) is added to adjust pH to 10.6, reflux is installed, stirring is turned on, heated to 75 ℃ and reacted for 4 hours, filtrated to obtain filtrate and filter cake, the filtrate is polyethylene glycol dicarboxylate solution, the filter cake is palladium / platinum / carbon composite catalyst, the filter cake is washed three times with deionized water, and is placed in 0.5N sodium hydroxide solution and preserved. 85g water is steamed off the filtrate, 9g 50% sulfuric acid is added, heated to 80 ℃ and reacted for 2 hours, 2.5g carbon dioxide is introduced, the upper layer is separated after standing, and 46g polyethylene glycol dicarboxylic acid is obtained after the upper layer is dehydrated and dried, with a yield of 88.7%. The acid number of polyethylene glycol dicarboxylic acid is 142mgKOH / g.

[0050] Example 4

[0051] In a 1L three-necked flask, 50g PEG1000 was dissolved in 180g deionized water, 0.3g palladium / platinum / carbon composite catalyst, 23g hydrogen peroxide (27.5%), and liquid caustic soda (sodium hydroxide with a concentration of 32%) was added to adjust the pH to 10.6, reflux was installed, stirring was turned on, heated to 80°C for 4 hours, and filtered to obtain a filtrate and a filter cake. The filtrate was a polyethylene glycol dicarboxylate solution, and the filter cake was a palladium / platinum / carbon composite catalyst. The filter cake was washed three times with deionized water and placed in a 0.5N sodium hydroxide solution for storage. 85g of water was evaporated from the filtrate, 9g of 50% sulfuric acid was added, heated to 80°C for 2 hours, 2.5g of carbon dioxide was introduced, and the upper layer was separated after standing. After the upper layer was dehydrated and dried, 46.3g of polyethylene glycol dicarboxylic acid was obtained, with a yield of 90.1%. The acid value of polyethylene glycol dicarboxylic acid was 110mgKOH / g. FT-IR: 1725cm -1 Wave number, C=O stretching vibration peak, 3460cm -1 Wave number, OH absorption peak; 1080cm -1 Wave number, COC asymmetric stretching vibration peak.

[0052] Example 5

[0053] In a 1L three-necked flask, 50g PEG5000 is dissolved in 200g deionized water, 0.2g palladium / platinum / carbon composite catalyst, 6g hydrogen peroxide (27.5%) are added, liquid caustic soda (potassium hydroxide with a concentration of 20%) is added to adjust the pH to 10.5, reflux is installed, stirring is turned on, heated to 85°C for 4 hours, filtrated to obtain a filtrate and a filter cake, the filtrate is a polyethylene glycol dicarboxylate solution, the filter cake is a palladium / platinum / carbon composite catalyst, the filter cake is washed three times with deionized water, and is placed in a 0.5N sodium hydroxide solution for preservation. 70g water is steamed off the filtrate, 9.5g 50% sulfuric acid is added, heated to 80°C for 2 hours, 5g carbon dioxide is introduced, the upper layer is separated after standing, and 44g polyethylene glycol dicarboxylic acid is obtained after the upper layer is dehydrated and dried, with a yield of 87.5%. The acid number of polyethylene glycol dicarboxylic acid is 21mgKOH / g.

[0054] Example 6

[0055] In a 1L three-necked flask, 50g PEG10000 was dissolved in 250g deionized water, 0.1g palladium / platinum / carbon composite catalyst, 3g hydrogen peroxide (27.5%) were added, liquid caustic soda (potassium hydroxide with a concentration of 20%) was added to adjust the pH to 10.8, reflux was installed, stirring was turned on, heated to 90°C for 4 hours, filtrated to obtain a filtrate and a filter cake, the filtrate was a polyethylene glycol dicarboxylate solution, the filter cake was a palladium / platinum / carbon composite catalyst, the filter cake was washed three times with deionized water, and placed in a 0.5N sodium hydroxide solution for preservation. 70g water was removed from the filtrate, 10g 50% sulfuric acid was added, heated to 80°C for 2 hours, 7.5g carbon dioxide was introduced, the upper layer was separated after standing, and 45.8g polyethylene glycol dicarboxylic acid was obtained after the upper layer was dehydrated and dried, with a yield of 91.3%. The acid number of the polyethylene glycol dicarboxylic acid was 10mgKOH / g.

[0056] Application Example 1

[0057] Polyethylene glycol dicarboxylic acid is used to recover metal elements:

[0058] Polyethylene glycol dicarboxylic acid is used to recover metals from lithium batteries. The positive electrode materials recovered from lithium batteries are crushed and samples are taken for determination of the content of Li, Co, Mn and Ni elements therein using the ICP method.

[0059] 2g of positive electrode material powder recovered from lithium batteries, 20g of polyethylene glycol 750 dicarboxylic acid, and 1g of water were mixed, stirred, heated to 95°C, reacted for 1 hour, and the solid powder was filtered out to obtain 15g of liquid. The content of Li, Co, Mn, and Ni elements was determined, and the calculated recovery rates were 88%, 82%, 85%, and 91%, respectively.

[0060] The above is only a preferred embodiment of the present invention, and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment, it is not used to limit the present invention. Any technician familiar with this patent can make some changes or modify the technical contents suggested above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the scope of the solution of the present invention.

Claims

1. A method for preparing polyethylene glycol dicarboxylic acid, characterized in that: The following steps are involved: Dissolve polyethylene glycol in deionized water, add palladium / platinum / carbon composite catalyst and hydrogen peroxide, the mass ratio of polyethylene glycol, palladium / platinum / carbon composite catalyst and hydrogen peroxide is 1:(0.001-0.05):(0.01-2.0), add liquid caustic soda to adjust the pH to 9-11, react at a temperature of 40-95° C., so that the polyethylene glycol is converted into polyethylene glycol dicarboxylate, and obtain the polyethylene glycol dicarboxylic acid through post-treatment; The palladium / platinum / carbon composite catalyst is made of the following components in percentage by mass: 2-5% palladium chloride, 1-4% platinum chloride, 0.2-0.6% bismuth chloride, 0.3-0.6% cobalt nitrate, and 90-96.5% activated carbon; The preparation method of the palladium / platinum / carbon composite catalyst comprises the following steps: Palladium chloride, platinum chloride, bismuth chloride and cobalt nitrate are dissolved in a hydrochloric acid solution with a concentration of 0.15-0.35 mol / L, the mass ratio of palladium chloride to hydrochloric acid is 1:(2-4), the mixed solution is slowly dripped into deionized water containing pretreated activated carbon, the mass ratio of palladium chloride to pretreated activated carbon is 1:(20-50), the mass concentration of pretreated activated carbon dispersed in deionized water is 4%-15%, and the mixture is stirred evenly. After the dripping is completed, stirring is continued for 4-6 hours, the pH value is adjusted to 11-13 with a NaOH solution, and formaldehyde with a mass fraction of 5% is slowly dripped, and the formaldehyde is 0.5-3.5 times the mass of palladium chloride. At the same time, the system is slowly heated to 60-75°C, reacted at a constant temperature for 2-3 hours, cooled to room temperature, filtered, the filtered solid is washed with deionized water, nitrogen is blown in and sealed for storage, and the palladium / platinum / carbon composite catalyst is obtained.

2. The method for preparing polyethylene glycol dicarboxylic acid according to claim 1, characterized in that: The palladium / platinum / carbon composite catalyst is made of the following components in percentage by mass: 3% palladium chloride, 2% platinum chloride, 0.5% bismuth chloride, 0.5% cobalt nitrate and 94% activated carbon.

3. The method for preparing polyethylene glycol dicarboxylic acid according to claim 1, characterized in that: The mass concentration of the polyethylene glycol dissolved in deionized water is 5% to 40%; The base is selected from sodium hydroxide or potassium hydroxide; The molecular weight of the polyethylene glycol is 200-50000.

4. The method for preparing polyethylene glycol dicarboxylic acid according to claim 1, characterized in that: The pretreatment steps of the pretreated activated carbon are as follows: Add activated carbon to hydrochloric acid solution, the mass ratio of activated carbon to hydrochloric acid solution is 1: (5-50), heat at 40-80°C for 1-8h, filter, wash with distilled water, add NaOH solution to activated carbon, the mass ratio of activated carbon to NaOH solution is 1: (5-50), heat at 40-80°C for 1-8h, filter, wash with distilled water, dry, then place the filtered activated carbon in distilled water, boil for 1-5h, filter, wash the filter cake until there is no chloride ion, and dry at 100-110°C for 1-12h to obtain pretreated activated carbon.

5. The method for preparing polyethylene glycol dicarboxylic acid according to claim 4, characterized in that: The concentration of the hydrochloric acid solution is 0.1-0.5 mol / L; The concentration of the NaOH solution is 0.2-2 mol / L.

6. The method for preparing polyethylene glycol dicarboxylic acid according to claim 1, characterized in that: The steps of obtaining the polyethylene glycol dicarboxylic acid through post-treatment are as follows: The filtrate and the filter cake are obtained by filtration. The filtrate is a polyethylene glycol dicarboxylate solution, and the filter cake is a palladium / platinum / carbon composite catalyst. The filter cake is washed with deionized water for 3 to 5 times and recycled. A portion of water is evaporated from the filtrate, an acid is added, heated to 70 to 90° C. for reaction for 1 to 4 hours, carbon dioxide is introduced, the upper layer is separated after standing, and polyethylene glycol dicarboxylic acid is obtained after dehydration and drying.

7. The method for preparing polyethylene glycol dicarboxylic acid according to claim 6, characterized in that: The acid is selected from at least one of sulfuric acid, hydrochloric acid or phosphoric acid.

8. The method for preparing polyethylene glycol dicarboxylic acid according to claim 6, characterized in that: The acid is an acid solution with a mass fraction of 15-55%, and the amount of the acid solution added is 0.1 to 2 times the mass of the polyethylene glycol.

9. The method for preparing polyethylene glycol dicarboxylic acid according to claim 1, characterized in that: The molecular formula of the polyethylene glycol dicarboxylic acid is HOOCCH2-O(CH2CH2O)n-CH2COOH, where n=4-1780.

Images