Method for preparing electronic-grade tetramethylammonium bicarbonate

Abstract

The invention discloses a method for preparing electronic grade tetramethyl ammonium bicarbonate. The method comprises the following steps: respectively pumping dimethyl carbonate and trimethylamine as raw materials and methanol as a solvent into a modified ion exchange resin tower for demetalization, mixing in a mixing kettle, and then entering a tandem reaction kettle; reaction materials are fed from the bottom of the previous stage, discharged from the upper part of the reactor and fed into the next stage of reactor, and are catalyzed and dehydrated in the last stage of reactor to further remove metal ions; feeding into a flash tank after passing through a multi-stage reaction kettle, separating excessive methanol and dimethyl carbonate, and refluxing to the mixing kettle; materials at the bottom of the flash tank enter a hydrolysis rectifying tower, methanol at the top partially flows back, and the product tetramethyl ammonium bicarbonate is obtained at the bottom of the rectifying tower. The reaction is stable, the reaction is driven by pressure difference, the number of moving equipment is minimum, continuous operation and automatic control are achieved, meanwhile, metal ion control in the raw material and synthesis process is achieved, and the quality of the electronic-grade tetramethylammonium bicarbonate is improved.

Description

Technical Field

[0001] The present invention relates to the field of wet electronic chemical synthesis, and particularly to a preparation method for an electronic-grade developer solution. Background Art

[0002] Tetramethylammonium bicarbonate (TMAC) is a raw material for preparing tetramethylammonium hydroxide (TMAH) by electrolysis. Among them, TMAH is the strongest organic base and is easily decomposed into methanol and trimethylamine after heating. Since TMAH has strong alkalinity and does not leave any substances after heating and decomposition, especially does not leave conductive ionic substances, it is widely used as a developer in the manufacturing processes of liquid crystal displays, LEDs, and semiconductor chips. The current mainstream process technology for producing TMAH is to first prepare TMAC from trimethylamine (TMA) and dimethyl carbonate (DMC), and then electrolytically produce TMAH.

[0003] For the preparation of electronic-grade TMAC, it is necessary to control metal ions at the raw material end and the synthesis end. For the removal of metal ions at the raw material end, rectification is often used to enrich metal ions in the bottom of the column and remove them. However, this method can only control metal ions at about 1 ppb, which is far from meeting the requirements for electronic-grade products of G4 and above grades. Using ion exchange resins can control metal ions at lower contents. For example, CN101314573A uses ion exchange resins to treat TMAC solutions. Due to the strong alkalinity of TMAC, this patent can only control metal ions at the ppm level.

[0004] To control metal ion pollution at the synthesis end, in addition to the requirement that the treatment of equipment materials be met, it is also necessary to minimize the investment in moving equipment to reduce the frequent scouring of the equipment wall by materials and thus introduce metal impurities. At the same time, at the synthesis end, achieving stable and continuous production of the device is the key to producing stable and qualified batches. In terms of the design of the reactor, CN101992055A proposes to use a series of reactors in series, making the reaction process stable, easy to control, enabling continuous production and automated control, and facilitating large-scale production. However, this invention uses a stirred reactor and a transfer pump, and the introduction of moving equipment is not conducive to the control of metal ions in electronic-grade products.

[0005] The existing technology still fails to break through the G4 grade and needs to be systematically and comprehensively optimized from aspects such as raw material treatment and process control. Summary of the Invention

[0006] The present invention aims to overcome the above technical problems, and provides a method for preparing electronic-grade tetramethylammonium bicarbonate. This method overcomes the deficiencies of previous production processes, with lower metal ion content in raw materials, fewer dynamic equipment introduced. Moreover, we found that the methylation reaction process is a liquid-phase reaction, and reducing the gas phase space can effectively increase the reaction rate, thereby reducing the residence time of the materials, reducing the precipitation of metal ions from the materials and saving the floor space of the equipment. This method is more stable and easier to control, enabling continuous operation and automatic control. At the same time, it realizes the control of metal ions in raw materials and the synthesis process, improving the quality of electronic-grade TMAC.

[0007] In terms of raw material treatment, the metal material of the distillation column is used under high-temperature conditions, inevitably introducing metal impurities, and it is difficult to control metal ions at a higher level. In terms of process control, reducing the introduction of dynamic equipment can greatly reduce the pollution caused by problems such as sealing and erosion. Moreover, the present invention improves the reaction rate through physical means, reducing the residence time, that is, reducing the contact between the materials and the materials, and further improving the quality control of wet electronic chemicals.

[0008] To achieve the above object, the present invention adopts the following technical solutions:

[0009] A method for preparing electronic-grade tetramethylammonium bicarbonate, comprising the following steps:

[0010] (1) Using a modified ion exchange resin column for the raw materials to reduce the metal ions in the raw materials;

[0011] (2) The product of step (1) enters a series of multi-kettles. The reaction materials are fed from the bottom and overflow from the top. The last kettle of the series of multi-kettles uses a modified resin catalyst.

[0012] (3) Using flash evaporation to recover the excessive dimethyl carbonate and methanol from the product of step (2);

[0013] (4) Using a hydrolysis distillation column to separate the product tetramethylammonium bicarbonate and the by-product methanol from the product of step (3).

[0014] In step (1) of the present invention, the raw materials are pressurized by a pump, and then the materials enter the subsequent units under the drive of pressure. There is no additional dynamic equipment from the resin column to the product tank.

[0015] In step (1) of the present invention, the metal ions include K, Na, Ca, Mg, Al, Fe, Mn, Zn. The content of each metal ion in the raw material methanol is 10-20 ppb, the content of each metal in dimethyl carbonate is 1-10 ppb, and the content of each metal ion in trimethylamine is 1-5 ppb. After being treated by the ion exchange resin, the content of each metal ion in the raw materials is less than 1 ppb.

[0016] In step (2) of the present invention, the series-connected multi-reactors are 2 to 5 reactors connected in series.

[0017] In step (2) of the present invention, the erosion of the fluid on the vessel wall is reduced to reduce the introduction of metal ions, and the gas phase space is reduced during the operation, which is beneficial to the progress of the liquid phase reaction and reduces the equipment investment and floor area.

[0018] In step (2) of the present invention, the last reactor is treated with a modified water-absorbing resin, which can catalyze the complete progress of the reaction and can remove moisture to further reduce the metal ion content.

[0019] Preferably, the raw material pump in step (1) pressurizes the raw materials to 0.5 to 3 MPa.

[0020] In the present invention, the molar ratio of trimethylamine: dimethyl carbonate: methanol in the raw materials in step (1) is 1:0.7:2 to 1:1.5:8.

[0021] In step (1) of the present invention, the preparation method of the modified ion exchange resin includes the following steps:

[0022] (a) Cleaning the resin with 5 to 10 BV of ultrapure water;

[0023] (b) Cleaning with 2 to 5 BV of 2 wt% to 10 wt% HCl, and then cleaning with ultrapure water until the pH is 5 to 7;

[0024] (c) Cleaning with electronic grade tetramethylammonium bicarbonate (2 to 5 BV, 2% to 10%), and then cleaning with ultrapure water until the pH is 7 to 9;

[0025] (d) Cleaning with a chelating agent (0.2 wt% to 5 wt%, 1 to 10 BV), and then cleaning with ultrapure water until neutral.

[0026] Preferably, the resin used in step (a) includes gel resins such as Mitsubishi UBK16, chelating resins such as Purolite MTS9300, polishing resins such as DuPont HPR650H, and the treatment temperature of the ion resin is 20 to 80 °C, and the treatment flow rate is 1 to 20 BV.

[0027] The combined chelating agent is selected from one or more of ammonium citrate, glycolic acid, and organic polyphosphonic acids (hydroxyethylidene diphosphonic acid (HEDP), aminotrimethyl phosphonic acid (ATMP), and ethylenediaminetetramethyl phosphonic acid (EDTMP)).

[0028] The surface grafting of the modified ion exchange resin of the present invention is selected from one or several of carboxyl groups, carboxylamino groups, phosphonic acid groups, etc.

[0029] Preferably, the series of multiple reactors in step (2) are 2-5 reactors, the reaction temperature is 80-150 °C, the reaction pressure is 0.3-3 MPa, the residence time is 2-8 h, and the full-pot overflow method is adopted. The liquid loading in the reactor is 60-95% of the reactor volume, and the position of the top material is in the liquid phase region.

[0030] In step (2) of the present invention, the preparation method of the modified resin catalyst includes the following steps:

[0031] (a’) Using the water-absorbing resin as a carrier, cleaning it thoroughly with ultrapure water;

[0032] (b’) Adding an electronic-grade tetramethylammonium bicarbonate solution (2 wt% - 20 wt%) and soaking and grafting (at 40 - 80 °C, for 3 - 8 h) to graft tetramethylammonium ions on the surface;

[0033] (c’) Filtering, cleaning, and drying.

[0034] In step (a’) of the present invention, the water-absorbing resin is selected from one or more of Dongying Qimai New Materials, CA-90, CA-100T, and CA-10.

[0035] Preferably, the flash pressure in step (3) is 0.1 - 2 MPa, and the flash temperature is 60 - 130 °C.

[0036] Preferably, the bottom temperature of the distillation column in step (4) is 60 - 90 °C, the top temperature is 4 - 20 °C, and the operating pressure is 10 - 500 hPa.

[0037] This modified resin catalyst catalyzes the reaction process through the amine groups on the surface, increases the final conversion rate of the reaction to >99%, reduces the downstream separation load, and improves the product purity.

[0038] The reaction of the present invention is stable, driven by the pressure difference, with the least moving equipment, realizes continuous operation and automatic control, and at the same time realizes the control of metal ions in the raw materials and the synthesis process, improving the quality of electronic-grade TMAC. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 Schematic flow diagram of preparing electronic-grade tetramethylammonium bicarbonate by three reactors in series in the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0040] The following are specific examples to further illustrate the technical solutions of the present invention.

[0041] In the present invention, unless otherwise specified, the raw materials and equipment used can be purchased from the market or are commonly used in the art.

[0042] The methods in the examples are all conventional methods in the art unless otherwise specified.

[0043] Example 1

[0044] (1) Before raw material treatment, the raw materials are pressurized to 2 MPa using a pump. The molar ratio of trimethylamine: dimethyl carbonate: methanol is 1:1.1:4. Subsequently, the material enters the subsequent unit under pressure drive.

[0045] (2) Preparation of modified ion exchange resin:

[0046] (a) Wash the UBK16 resin (10 g) with 5 BV of ultrapure water.

[0047] (b) Wash with 2 BV of 2 wt% HCl, and then wash with ultrapure water until the pH is 5 - 7.

[0048] (c) Wash with electronic grade tetramethylammonium bicarbonate (2 BV, 2%), and then wash with ultrapure water until the pH is 7 - 9.

[0049] (d) Soak with ammonium citrate (5 wt%, 50 mL) and glycolic acid (5 wt%, 50 mL) at room temperature for 5 h, and then wash with ultrapure water until neutral.

[0050] Subsequently, the modified ion exchange resin column is used to treat metal ions in the raw materials. The operating temperature is 60 °C, and the treatment capacity is 12 BV / h.

[0051] (3) Preparation of modified resin catalyst:

[0052] (a’) Use the water-absorbing resin CA-90 as the carrier and wash it clean with ultrapure water.

[0053] (b’) Add an electronic grade tetramethylammonium bicarbonate solution (2 wt%) and soak for grafting (40 °C, 3 h) to graft tetramethylammonium ions on the surface.

[0054] (c’) Filter, wash, and dry.

[0055] The reaction kettle is a series connection of three kettles. The last kettle uses a PFA lining and adds the resin catalyst. The reaction material is fed at the bottom and overflows at the top. The liquid loading is 90%. The reaction temperature is 130 °C, the reaction pressure is 2.2 MPa, and the residence time is 6 h.

[0056] (4) After the reaction, the flash evaporation temperature is 110 °C, and the flash evaporation pressure is 1.8 MPa.

[0057] (5) Use a hydrolysis distillation column to separate the product tetramethylammonium bicarbonate and the by-product methanol. The bottom temperature of the column is 75 °C, the top temperature of the column is 10 °C, and the operating pressure is 30 hPa.

[0058] Example 2

[0059] (1) Before the raw material treatment, the raw materials are pressurized to 0.5 MPa by a pump. The molar ratio of trimethylamine: dimethyl carbonate: methanol is 1:0.7:2. Subsequently, the materials enter the subsequent unit under pressure drive;

[0060] (2) Preparation of modified ion exchange resin:

[0061] (a) Wash the MTS9300 resin (10 g) with 10 BV of ultrapure water;

[0062] (b) Wash with 5 BV of 10 wt% HCl, and then wash with ultrapure water until the pH is 5 - 7;

[0063] (c) Wash with electronic grade tetramethylammonium bicarbonate (5 BV, 10%), and then wash with ultrapure water until the pH is 7 - 9;

[0064] (d) Immerse in HEDP (5 wt%, 100 mL) at room temperature for 6 h, and then wash with ultrapure water until neutral;

[0065] Subsequently, use the modified ion exchange resin to treat the metal ions in the raw materials. The operating temperature is 20 °C and the treatment volume is 20 BV / h;

[0066] (3) Preparation of modified resin catalyst:

[0067] (a’) Use the water-absorbing resin CA-100T as the carrier and wash it clean with ultrapure water;

[0068] (b’) Add an electronic grade tetramethylammonium bicarbonate solution (20 wt%) and soak for grafting (80 °C, 8 h) to graft tetramethylammonium ions on the surface;

[0069] (c’) Filter, wash, and dry.

[0070] The reaction kettle is a series connection of three kettles. The last kettle uses a PFA liner and adds the resin catalyst. The reaction materials are fed from the bottom and overflow from the top. The liquid loading is 60%. The reaction temperature is 80 °C, the reaction pressure is 0.3 MPa, and the residence time is 8 h.

[0071] (4) After the reaction, the flash evaporation temperature is 60 °C and the flash evaporation pressure is 0.1 MPa.

[0072] (5) Use a hydrolysis distillation column to separate the product tetramethylammonium bicarbonate and the by-product methanol. The bottom temperature of the column is 60 °C, the top temperature of the column is 4 °C, and the operating pressure is 10 hPa.

[0073] Example 3

[0074] (1) Before raw material treatment, the raw materials are pressurized to 3 MPa using a pump. The molar ratio of trimethylamine: dimethyl carbonate: methanol is 1:1.5:8. Subsequently, the materials enter the subsequent unit under pressure drive;

[0075] (2) Preparation of modified ion exchange resin:

[0076] (a) Wash the HPR650H resin (10 g) with 8 BV of ultrapure water;

[0077] (b) Wash with 3 BV of 5 wt% HCl, and then wash with ultrapure water until the pH is 5 - 7;

[0078] (c) Wash with electronic grade tetramethylammonium bicarbonate (3 BV, 5%), and then wash with ultrapure water until the pH is 7 - 9;

[0079] (d) Soak with ATMP (3 wt%, 50 mL) at room temperature for 8 h, and then wash with ultrapure water until neutral;

[0080] Subsequently, use the modified ion exchange resin to treat metal ions in the raw materials. The operating temperature is 80 °C and the treatment volume is 1 BV / h;

[0081] (3) Preparation of modified resin catalyst:

[0082] (a’) Use the water-absorbing resin CA-10 as the carrier and wash it clean with ultrapure water;

[0083] (b’) Add an electronic grade tetramethylammonium bicarbonate solution (10 wt%) and soak for grafting (60 °C, 6 h) to graft tetramethylammonium ions on the surface;

[0084] (c’) Filter, wash, and dry.

[0085] The reaction kettle is a series connection of three kettles. The last kettle uses a PFA liner and adds the resin catalyst. The reaction materials are fed at the bottom and overflow at the top. The liquid filling volume is 95%. The reaction temperature is 150 °C, the reaction pressure is 3 MPa, and the residence time is 2 h.

[0086] (4) After the reaction, the flash evaporation temperature is 130 °C and the flash evaporation pressure is 2 MPa.

[0087] (5) Use a hydrolysis distillation column to separate the product tetramethylammonium bicarbonate and the by-product methanol. The bottom temperature of the column is 90 °C, the top temperature of the column is 20 °C, and the operating pressure is 500 hPa.

[0088] Example 4

[0089] (1) Before raw material treatment, the raw materials are pressurized to 1.5 MPa using a pump. The molar ratio of trimethylamine: dimethyl carbonate: methanol is 1:1.3:6. Subsequently, the materials enter the subsequent unit under pressure drive;

[0090] (2) Preparation of modified ion exchange resin:

[0091] (a) Wash the MTS9300 resin (10 g) with 3 BV of ultrapure water;

[0092] (b) Wash with 4 BV of 6 wt% HCl, and then wash with ultrapure water until the pH is 5 - 7;

[0093] (c) Wash with electronic grade tetramethylammonium bicarbonate (3 BV, 7%), and then wash with ultrapure water until the pH is 7 - 9;

[0094] (d) Soak with EDTMP (1 wt%, 20 mL) at room temperature for 4 h, and then wash with ultrapure water until neutral;

[0095] Subsequently, use the modified ion exchange resin to treat the metal ions in the raw material, the operating temperature is 40 °C, and the treatment capacity is 10 BV / h;

[0096] (3) Preparation of modified resin catalyst:

[0097] (a’) Use the water-absorbing resin CA-90 as the carrier and wash it clean with ultrapure water;

[0098] (b’) Add an electronic grade tetramethylammonium bicarbonate solution (15 wt%) and soak for grafting (70 °C, 5 h) to graft tetramethylammonium ions on the surface;

[0099] (c’) Filter, wash, and dry.

[0100] The reaction kettle is a series connection of three kettles. The last kettle uses a PFA lining and adds the resin catalyst. The reaction material is fed from the bottom and overflows from the top. The liquid loading is 80%. The reaction temperature is 110 °C, the reaction pressure is 1.8 MPa, and the residence time is 4 h.

[0101] (4) The flash evaporation temperature after the reaction is 90 °C, and the flash evaporation pressure is 0.6 MPa.

[0102] (5) Use a hydrolysis distillation column to separate the product tetramethylammonium bicarbonate and the by-product methanol. The bottom temperature of the column is 80 °C, the top temperature of the column is 10 °C, and the operating pressure is 200 hPa.

[0103] Example 5

[0104] (1) Before the raw material treatment, use a pump to pressurize the raw material to 3 MPa. The molar ratio of trimethylamine: dimethyl carbonate: methanol is 1:0.9:3. Subsequently, the material enters the subsequent unit under pressure drive;

[0105] (2) Preparation of modified ion exchange resin:

[0106] (a) Wash the UBK16 resin (10 g) with ultrapure water at 6 BV.

[0107] (b) Wash with 4 BV of 8 wt% HCl, and then wash with ultrapure water until the pH is 5 - 7.

[0108] (c) Wash with electronic grade tetramethylammonium bicarbonate (4 BV, 3%), and then wash with ultrapure water until the pH is 7 - 9.

[0109] (d) Soak with EDTMP (0.5 wt%, 20 mL) at room temperature for 6 h, and then wash with ultrapure water until neutral.

[0110] Subsequently, use the modified ion exchange resin to remove metal ions in the treated raw materials. The operating temperature is 50 °C, and the treatment capacity is 6 BV / h.

[0111] (3) Prepare the modified resin catalyst:

[0112] (a’) Use the water-absorbing resin CA-10 as the carrier and wash it clean with ultrapure water.

[0113] (b’) Add an electronic grade tetramethylammonium bicarbonate solution (5 wt%) and soak for grafting (60 °C, 6 h) to graft tetramethylammonium ions on the surface.

[0114] (c’) Filter, wash, and dry.

[0115] The reactor is a series of three reactors. The last reactor uses a PFA liner and adds the resin catalyst. The reaction material is fed at the bottom and discharged overflow at the top. The liquid loading is 70%. The reaction temperature is 140 °C, the reaction pressure is 2.5 MPa, and the residence time is 5 h.

[0116] (4) The flash temperature after the reaction is 120 °C, and the flash pressure is 1.9 MPa.

[0117] (5) Use a hydrolysis distillation column to separate the product tetramethylammonium bicarbonate and the by-product methanol. The bottom temperature of the column is 85 °C, the top temperature of the column is 15 °C, and the operating pressure is 400 hPa.

[0118] Comparative Example 1

[0119] Compared with Example 1, in step (1), each raw material (methanol, trimethylamine, dimethyl carbonate) is treated with a distillation column (see the following table for the operating conditions of the distillation column) instead of the modified ion exchange resin, and then pumped into the subsequent reaction unit. The reaction conditions and the operating conditions of the subsequent unit are the same as those in Example 1.

[0120] Table 1 Operating conditions for the rectification and purification of raw materials

[0121]

[0122]

[0123] Comparative Example 2

[0124] Compared with Example 1, no catalyst is used in the last reactor of the series of reactors, and other reaction conditions and separation unit operating conditions are the same as those in Example 1.

[0125] Comparative Example 3

[0126] Compared with Example 1, the resin in Step 2 is not modified, and other reaction conditions and separation unit operating conditions are the same as those in Example 1.

[0127] Comparative Example 4

[0128] Compared with Example 1, the resin in Step 3 is not modified, and other reaction conditions and separation unit operating conditions are the same as those in Example 1.

[0129] Comparative Example 4

[0130] Compared with Example 1, 1 reactor is used, and other reaction conditions and separation unit operating conditions are the same as those in Example 1.

[0131] Comparative Example 5

[0132] Compared with Example 1, 6 reactors in series are used, and other reaction conditions and separation unit operating conditions are the same as those in Example 1.

[0133] Comparative Example 6

[0134] Compared with Example 1, 7 reactors in series are used, and other reaction conditions and separation unit operating conditions are the same as those in Example 1.

[0135] Table 2 shows the metal element contents (ppb) of raw material methanol treated with modified ion exchange resin. The measurement of metal elements is carried out in a Class 5 clean working environment specified in GB 50073-2013, and the determination is carried out by the method specified in GB / T 37403-2019.

[0136] Table 2

[0137]

[0138]

[0139] Table 3 shows the metal element contents (ppb) of raw material DMC treated with modified ion exchange resin.

[0140] Table 3

[0141]

[0142] Table 4 shows the metal element contents (ppb) of raw material trimethylamine treated with modified ion exchange resin.

[0143] Table 4

[0144]

[0145] Table 5 shows the comparison of the results between the examples and the comparative examples.

[0146] Table 5 Comparison of the results between the examples and the comparative examples

[0147]

Claims

1. A method for preparing electronic-grade tetramethylammonium hydrogencarbonate, comprising the following steps: (1) Using a modified ion exchange resin column to reduce metal ions in the raw materials; (2) The product of step (1) enters a series of multi-reactors. The reaction materials are fed at the bottom and overflow and discharge at the top. The last reactor in the series of multi-reactors uses a modified resin catalyst; (3) Using flash evaporation to recover excess dimethyl carbonate and methanol from the product of step (2); (4) Using a hydrolysis distillation column to separate the product tetramethylammonium hydrogencarbonate and by-product methanol from the product of step (3).

2. The method according to claim 1, characterized in that, The metal ions in step (1) include K, Na, Ca, Mg, Al, Fe, Mn, Zn. The content of each metal ion in the raw material methanol is 10-20 ppb, the content of each metal in dimethyl carbonate is 1-10 ppb, and the content of each metal ion in trimethylamine is 1-5 ppb. After treatment with the modified ion exchange resin, the content of each metal ion in the raw material is less than 1 ppb.

3. The method according to claim 1, characterized in that, In step (2), the series of multi-reactors are 2-5 reactors in series.

4. The method according to claim 1, wherein The molar ratio of trimethylamine:dimethyl carbonate:methanol in the raw materials in step (1) is 1:0.7:2 to 1:1.5:

8.

5. The method according to claim 1, characterized in that, In step (1), the preparation method of the modified ion exchange resin includes the following steps: (a) Cleaning the resin with 5-10 BV of ultrapure water; (b) Cleaning with 2-5 BV of 2 wt%-10 wt% HCl, and then cleaning with ultrapure water until the pH is 5-7; (c) Cleaning with 2-5 BV of 2 wt%-10 wt% electronic-grade tetramethylammonium hydrogencarbonate, and then cleaning with ultrapure water until the pH is 7-9; (d) Cleaning with 1-10 BV of 0.2 wt%-5 wt% chelating agent, and then cleaning with ultrapure water until neutral.

6. The method according to claim 5, wherein The resin used in step (a) includes one or more of gel resin, chelating resin, and polishing resin; preferably one or more of UBK16, MTS9300, and HPR650H.

7. The method according to claim 5, characterized in that The chelating agent is selected from one or more of ammonium citrate, glycolic acid, hydroxyethylidene diphosphonic acid, aminotrimethyl phosphinic acid, and ethylenediamine tetramethyl phosphinic acid.

8. The method according to claim 1, characterized in that, In step (2), the series of multi-reactors are 2-5 reactors, the reaction temperature is 80-150 °C, the reaction pressure is 0.3-3 MPa, and the residence time is 2-8 h.

9. The method according to claim 1, wherein In step (2), the preparation method of the modified resin catalyst includes the following steps: (a’) Cleaning the water-absorbing resin with ultrapure water; (b’) Adding an electronic-grade tetramethylammonium hydrogencarbonate solution to soak and graft; (c’) Filtering, cleaning, and drying.

10. The method according to claim 7, characterized in that, In step (a’), the water-absorbing resin is selected from one or more of CA-90, CA-100T, and CA-10.

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