A regeneration method for ion exchange resin used in caprolactam refining

Abstract

The present invention discloses a regeneration method for ion exchange resins used in caprolactam refining, which comprises the following steps: First, after draining the caprolactam aqueous solution in the resin, the resin is washed with demineralized water solution, and at the same time, the resin bed layer is broken with demineralized water; Then, a neutral or acidic desorbing solution is introduced into the anion resin tower to desorb organic impurities, and a neutral or alkaline desorbing solution is introduced into the cation resin tower to desorb organic impurities, and then the resin is washed clean with demineralized water; Subsequently, acid-base regeneration is carried out. The anion exchange resin is regenerated with an alkali regenerant, and the cation exchange resin is regenerated with an acid regenerant. Finally, the resin is washed clean with demineralized water. The present invention provides a regeneration method for ion exchange resins combining salt solution desorption and acid-base regeneration, which reduces the resource consumption of acids and alkalis and lowers the cost; at the same time, nitric acid is not used in the acid regenerant, avoiding the generation of nitrate nitrogen in wastewater. The present invention has the characteristics of low production cost and environmental friendliness.

Description

Technical Field

[0001] The present invention relates to the field of ion exchange resin regeneration, and particularly to a regeneration method for ion exchange resin used in caprolactam refining. Background Art

[0002] Ion exchange resins are widely used in the production processes of chemical industry, biochemistry, and pharmaceutical products to extract and refine compounds. The recyclable regeneration of ion exchange resins is one of the main advantages for their wide use in industrial production.

[0003] For the ion exchange resins used in caprolactam refining, a three-column series connection mode is adopted, which are a first anion exchanger, a cation exchanger, and a second anion exchanger in sequence. During operation, not only can inorganic ions in the caprolactam aqueous solution be removed by ion exchange, but also a small amount of organic impurities in the caprolactam aqueous solution can be intercepted by adsorption. Therefore, the requirements for ion exchange resins in caprolactam refining are very high, and the regeneration of the resins used in caprolactam refining is more complex and cumbersome than the regeneration process of ordinary water treatment resins.

[0004] Traditional caprolactam production enterprises adopt a two-step method for regeneration: the anion exchange resin is first desorbed with dilute nitric acid and then regenerated with dilute caustic soda solution, and the cation exchange resin is first desorbed with dilute caustic soda solution and then regenerated with dilute nitric acid solution. Most of the caprolactam impurities are polar and hydrophilic organic substances, with many power supply groups in the molecular structure, and are easily adsorbed by the positively charged anion resin matrix in the anion resin. On the contrary, passing a negatively charged salt solution into the resin can desorb the organic impurities into the salt solution and be washed out of the system by demineralized water. In addition, during the salt formation process, due to the reduction of ionic radius, the organic impurities adsorbed by the anion and cation resins are desorbed during the shrinkage process.

[0005] CN201210255163.5 discloses a regeneration method for ion exchange resin used in caprolactam aqueous solution refining. This invention adopts a combination of methanol regeneration and traditional acid-base regeneration, reducing the usage amount of nitric acid and caustic soda. To a certain extent, this invention reduces the usage amount of the regenerant, but nitric acid is used in the regeneration process, and the regenerated wastewater still contains a large amount of nitrate nitrogen, with the nitrate nitrogen content in the wastewater as high as 0.5%, making the wastewater treatment difficult. In addition, a large amount of steam is consumed for the purification of the organic desorbent, and the cost is relatively high.

[0006] CN201510572906.5 discloses a method for regenerating an ion exchange resin, which is characterized by comprising the following steps: 1) Backwashing: introducing a dilute regeneration solution from the bottom of the ion exchange resin column to backwash the ion exchange resin therein. After soaking for 25 - 35 minutes, the dilute regeneration solution in the column is converted into a concentrated regeneration solution, and the obtained concentrated regeneration solution is discharged to a concentrated liquid collection tank by compressed air. The inlet flow rate of the dilute regeneration solution is 2 - 4 BV / h, and the dosage of the dilute regeneration solution is 1 times the bed volume; 2) Forward washing: introducing 10% dilute sulfuric acid from the top of the ion exchange resin column, with an inlet flow rate of 1 - 2 BV / h. The dosage of the 10% dilute sulfuric acid is 1 times the bed volume. The dilute sulfuric acid is converted into a dilute regeneration solution in the column and discharged to a dilute liquid collection tank, and the residual liquid is drained to complete the regeneration of the ion exchange resin. This regeneration method divides the regeneration solution into a concentrated solution and a dilute solution, which can effectively save the dosage of the regeneration solution and effectively reduce the regeneration cost.

[0007] CN201310043411.4 discloses a method for regenerating a deactivated strong acid cation exchange resin, which is realized through the following steps: (1) Alkaline washing: soaking the waste resin with a strong alkali solution with a mass concentration of 5 - 30%, and stirring to make the resin fully contact with the alkali solution; (2) Acid washing: soaking the resin several times with an inorganic acid or organic sulfonic acid with a mass concentration of 10 - 20% to replace the alkali metal ions in the sulfonate on the resin with hydrogen ions; (3) Water washing: rinsing the resin with deionized water and filtering to dry the water; (4) Drying: putting the wet resin into an organic solvent with an azeotropic property with water, heating for azeotropic distillation until its moisture content is reduced to the dryness required for it to be used as a catalyst. The present invention has thorough drying, effectively restores the activity of the old resin, reduces the environmental pollution caused by waste resin, improves the resin utilization rate, and reduces the production cost.

[0008] Liu Bin, et al., Reactions and Applications of Pendant Double Bonds in Highly Crosslinked Styrene - Divinylbenzene Copolymers, Ion Exchange and Adsorption, Vol. 18, No. 1, 2002, introduces the existence, reactions, and related applications of pendant double bonds in highly crosslinked macroporous styrene - divinylbenzene (St(DVB)) copolymers. The existing research results show that using the functional group reactions of pendant double bonds is an important way to modify St(DVB) copolymers.

[0009] Liu Shuai, et al., Preparation, Modification and Application of Polydivinylbenzene Microspheres Containing Pendant Double Bonds, Polymer Chemistry and Physics, Nankai University, 2010. First, using divinylbenzene (DVB) as a monomer and azobisisobutyronitrile as an initiator, and using a good solvent toluene, an inert solvent n - heptane, and a toluene - n - heptane mixed solvent as porogens respectively, a polydivinylbenzene resin containing pendant double bonds was synthesized by suspension polymerization.

[0010] In the prior art, there are many methods for regenerating ion exchange resins, but they are all for ion exchange resins used in ordinary water treatment. After the ion exchange resin adsorbed caprolactam, a lot of organic impurities are adsorbed in it, and the methods of the prior art are not applicable to the regeneration of ion exchange resins for caprolactam refining. And the existing regeneration process of caprolactam ion exchange resin has many steps, the desorption process consumes a large amount of acid and alkali, the cost is high, and a large amount of nitrogen-containing wastewater is generated. The wastewater treatment volume is large and it is not environmentally friendly. Based on the deficiencies of the prior art, the present invention provides a regeneration method combining salt solution desorption and acid-base regeneration. The acid regenerant does not use nitric acid, which greatly reduces the regeneration cost, and at the same time avoids the generation of nitrate nitrogen in the wastewater. The present invention has the characteristics of low production cost and environmental friendliness. Summary of the Invention

[0011] The present invention provides a regeneration method for ion exchange resins for caprolactam refining. The present invention provides an ion exchange resin regeneration method combining salt solution desorption and acid-base regeneration, which reduces the resource consumption of acid and alkali and reduces the cost; at the same time, the acid regenerant does not use nitric acid to avoid the generation of nitrate nitrogen in the wastewater. The present invention has the characteristics of low production cost and environmental friendliness.

[0012] A regeneration method for ion exchange resins for caprolactam refining, characterized by comprising the following steps:

[0013] Step 1, first drain the caprolactam aqueous solution in the resin, then wash the resin with demineralized water solution, and at the same time break the resin bed layer with demineralized water.

[0014] Step 2, then pass a neutral or acidic desorbing solution into the anion resin tower to desorb organic impurities, with a flow rate of 20-25m 3 / h, and the elution time is 3.5-4.5h. Pass a neutral or alkaline desorbing solution into the cation resin tower to desorb organic impurities, with a flow rate of 20-25m 3 / h, and the elution time is 3.5-4.5h. Then wash the resin clean with demineralized water.

[0015] Step 3, hydrosilylation reaction of pendant double bonds:

[0016] Since the ion exchange resin is a copolymer of styrene and divinylbenzene, the pendant double bonds on the divinylbenzene can participate in the hydrosilylation reaction, and its technical solution is:

[0017] According to mass parts, 20-30 parts of ion exchange resin, 3-8 parts of methylvinylcyclosiloxane, 0.5-2.8 parts of N-vinylcaprolactam, 0.31-0.73 parts of chloroplatinic acid, 100-145 parts of dichloroethane are controlled at 60-70 °C and reacted for 2-5h. After completion, filter and wash with water to obtain the described caprolactam-based ion exchange resin.

[0018] Step 4, then perform acid-base regeneration. The anion exchange resin is regenerated with an alkaline regenerant, and the cation exchange resin is regenerated with an acid regenerant. The flow rate of the regenerant is 20 - 25 m 3 / h, the regeneration time is 4 - 6 hours, and finally the resin is cleaned with demineralized water.

[0019] The pendant double bonds of the ion exchange resin undergo a hydrosilylation reaction with methyl vinyl cyclosiloxane and N-vinylcaprolactam to obtain a caprolactam-based ion exchange resin. The partial reaction mechanism is shown as:

[0020]

[0021]

[0022] Preferably, the neutral or acidic analytical solution described in Step 2 is one of a single-charge strong acid-strong base salt solution, a strong acid-weak base salt solution, and a mixed solution of salt and strong acid.

[0023] Preferably, the single-charge strong acid-strong base salt solution is a composition of one or more of sodium chloride solution and potassium chloride solution; the strong acid-weak base salt solution is ammonium chloride solution; the mixed solution of salt and strong acid is one of a mixed solution of sodium chloride and hydrochloric acid and a mixed solution of potassium chloride and hydrochloric acid.

[0024] Preferably, in the neutral analytical solution, the mass concentration of the single-charge strong acid-strong base salt or strong acid-weak base salt solution is 3 - 8%; in the acidic analytical solution, the mass concentration of the salt is 3 - 8%, and the mass concentration of the acid is 0.5 - 1.5%.

[0025] Preferably, the neutral or alkaline analytical solution described in Step 2 is one of a single-charge strong acid-strong base salt solution, a strong base-weak acid salt solution, and a mixed solution of salt and strong base.

[0026] Preferably, the single-charge strong acid-strong base salt solution is a composition of one or more of sodium chloride and potassium chloride solutions; the strong base-weak acid salt solution is a composition of one or more of sodium carbonate and potassium carbonate solutions; the mixed solution of salt and strong base is one of a mixed solution of sodium chloride and sodium hydroxide and a mixed solution of potassium chloride and potassium hydroxide.

[0027] Preferably, the mass concentration of the single-charge strong acid-strong base salt is 3 - 8%; the mass concentration of the strong base-weak acid salt is 3 - 8%; in the mixed solution of salt and strong base, the mass concentration of the salt is 3 - 8%, and the mass concentration of the base is 0.5 - 1.5%.

[0028] Preferably, the alkaline regenerant described in Step 3 is a composition of one or more of sodium hydroxide aqueous solution and potassium hydroxide aqueous solution, and the mass concentration of the aqueous solution is 3 - 10%.

[0029] Preferably, the acid regenerant described in Step 3 is a composition of one or more of hydrochloric acid aqueous solution, sulfuric acid aqueous solution, and hydrobromic acid aqueous solution, and the mass concentration of the aqueous solution is 2-10%.

[0030] Some reaction mechanism equations during the regeneration of the ion exchange resin are shown as follows:

[0031]

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0033] 1. The present invention provides a regeneration method combining salt solution desorption and acid-base regeneration. The acid regenerant does not use nitric acid, which greatly reduces the regeneration cost. At the same time, it avoids the generation of nitrate nitrogen in wastewater. The present invention has the characteristics of low production cost and environmental friendliness. Description of the Drawings

[0034] Figure 1 It is the Fourier infrared spectrogram of the cation exchange resin regenerated in Example 1:

[0035] There are stretching absorption peaks of the benzene ring skeleton near 1607 / 1504 / 1451 / 1377 cm-1, and stretching absorption peaks of carbon and hydrogen near 2946 cm-1, indicating that the ion exchange resin participated in the reaction; there is an asymmetric stretching absorption peak of the silicon-oxygen bond near 1070 cm-1 and a symmetric stretching absorption peak of the silicon-oxygen bond near 914 cm-1, indicating that methyl vinyl cyclosiloxane participated in the reaction; there is a stretching absorption peak of the carbonyl group of the amide near 1682 cm-1 and a stretching absorption peak of the carbon-nitrogen single bond near 1320 cm-1, indicating that N-vinylcaprolactam participated in the reaction. Specific Embodiments

[0036] The raw materials used in the following examples are all commercially available products. The examples are further descriptions of the present invention, rather than limiting the scope of the present invention;

[0037] The methods for testing each performance are as follows:

[0038] 1. Test of the regeneration degree of cation exchange resin: Take 2 g of the regenerated cation exchange resin, wash it with demineralized water, and then pass it through 200 ml of sodium chloride solution with a concentration of 1 mol / L under dynamic conditions. Collect the effluent, determine the content of hydrogen ions in it by titration method, and calculate the group capacity of the cation exchange resin; Take 2 g of the regenerated cation exchange resin, pass 300 ml of hydrochloric acid solution with a concentration of 1 mol / L through it, then wash it with demineralized water until neutral, and then pass it through 200 ml of sodium chloride solution with a concentration of 1 mol / L under dynamic conditions. Collect the effluent, determine the content of hydrogen ions in it, and calculate the total exchange capacity of the cation exchange resin; The regeneration degree is the group capacity divided by the total exchange capacity.

[0039] 2. Test of the regeneration degree of anion exchange resin: Take 2 g of the regenerated anion exchange resin, wash it with demineralized water, and then pass it through 200 ml of hydrochloric acid solution with a concentration of 0.1 mol / L under dynamic conditions. Collect the effluent, determine the content of hydrogen ions in it by titration method, and calculate the group content of the ion exchange resin; Take 2 g of the regenerated anion exchange resin, pass it through 500 ml of sodium hydroxide solution with a concentration of 1 mol / L, then wash it with demineralized water until neutral, then add 2 g of resin particles to 150 ml of hydrochloric acid solution with a concentration of 0.1 mol / L, soak for 2 h, then filter to obtain the filtrate, determine the content of hydrogen ions by titration method, and calculate the total exchange capacity of the anion exchange resin; The regeneration degree is the group capacity divided by the total exchange capacity.

[0040] Example 1

[0041] The regeneration of the deactivated caprolactam ion exchange resin is carried out as follows:

[0042] Step 1: First, drain the caprolactam aqueous solution in the resin, then wash the resin with demineralized water solution, and at the same time break the resin bed layer with demineralized water.

[0043] Step 2: Then pass a sodium chloride solution with a concentration of 3% through the anion resin tower to desorb organic impurities at a flow rate of 20 m 3 / h, and the elution time is 3.5 h. Pass a sodium chloride solution with a concentration of 3% through the cation resin tower to desorb organic impurities at a flow rate of 20 m 3 / h, and the elution time is 3.5 h. Then wash the resin clean with demineralized water.

[0044] Step 3, hydrosilylation reaction of pendant double bonds:

[0045] Add 20 kg of ion exchange resin, 3 kg of methyl vinyl cyclosiloxane, 0.5 kg of N-vinyl caprolactam, 0.31 kg of chloroplatinic acid, and 100 kg of dichloroethane. Control the temperature at 60 °C and react for 2 h. After completion, filter and wash with water to obtain the described caprolactam-based ion exchange resin.

[0046] Step 4: Subsequently, perform acid-base regeneration. The cation exchange resin is regenerated with a 2% aqueous hydrochloric acid solution, and the anion exchange resin is regenerated with a 3% aqueous NaOH solution. The regeneration agent flow rate is 20 m 3 / h, and the regeneration time is 4 hours. Finally, wash with demineralized water until neutral.

[0047] The regeneration degree of the obtained regenerated resin is 95.2%.

[0048] Example 2

[0049] The regeneration of the deactivated caprolactam ion exchange resin is carried out as follows:

[0050] Step 1: First, drain the caprolactam aqueous solution in the resin, then wash the resin with demineralized water solution, and at the same time, crush the resin bed with demineralized water.

[0051] Step 2: Then, pass a 4% potassium chloride solution into the anion resin tower to desorb organic impurities at a flow rate of 22 m 3 / h, and the elution time is 4.0 h. Pass a 5% potassium chloride solution into the cation resin tower to desorb organic impurities at a flow rate of 22 m 3 / h, and the elution time is 3.8 h. Then wash the resin clean with demineralized water.

[0052] Step 3, hydrosilylation reaction of pendant double bonds:

[0053] Add 23 kg of ion exchange resin, 4 kg of methyl vinyl cyclosiloxane, 0.7 kg of N-vinyl caprolactam, 0.42 kg of chloroplatinic acid, and 110 kg of dichloroethane. Control the temperature at 62 °C and react for 3 h. After completion, filter and wash with water to obtain the described caprolactam-based ion exchange resin.

[0054] Step 4: Subsequently, perform acid-base regeneration. The cation exchange resin is regenerated with a 4% aqueous hydrochloric acid solution, and the anion exchange resin is regenerated with a 4.5% aqueous NaOH solution. The regeneration agent flow rate is 22 m 3 / h, and the regeneration time is 5 hours. Finally, wash with demineralized water until neutral.

[0055] The regeneration degree of the obtained regenerated resin is 96.5%.

[0056] Example 3

[0057] The regeneration of the deactivated caprolactam ion exchange resin is carried out as follows:

[0058] Step 1: First, drain the caprolactam aqueous solution in the resin, then wash the resin with deionized water solution, and at the same time, break the resin bed with deionized water;

[0059] Step 2: Then, pass a mixed solution of sodium chloride and hydrochloric acid with a sodium chloride concentration of 5.5% and a hydrochloric acid concentration of 0.5% into the anion resin tower to desorb organic impurities, with a flow rate of 24 m 3 / h and an elution time of 4.0 h. Pass a sodium carbonate solution with a concentration of 6% into the cation resin tower to desorb organic impurities, with a flow rate of 23 m 3 / h and an elution time of 4.2 h. Then, wash the resin clean with deionized water;

[0060] Step 3, hydrosilylation reaction of pendant double bonds:

[0061] Add 27 kg of ion exchange resin and 6 kg of dichloroethane, control the temperature at 67 °C, react for 4 h, and after completion, filter and wash with water to obtain the described caprolactam-based ion exchange resin.

[0062] Step 4: Subsequently, perform acid-base regeneration. The cation exchange resin is regenerated with a 6% hydrochloric acid aqueous solution, and the anion exchange resin is regenerated with a mixed aqueous solution of 6% sodium hydroxide and potassium hydroxide. The flow rate of the regenerant is 24 m 3 / h, and the regeneration time is 5 hours. Finally, wash with deionized water until neutral.

[0063] The regeneration degree of the obtained regenerated resin is 97.3%.

[0064] Example 4

[0065] The regeneration of the deactivated caprolactam ion exchange resin is carried out as follows:

[0066] Step 1: First, drain the caprolactam aqueous solution in the resin, then wash the resin with deionized water solution, and at the same time, break the resin bed with deionized water;

[0067] Step 2: Then, pass a mixed solution of potassium chloride and hydrochloric acid with a potassium chloride concentration of 8% and a hydrochloric acid concentration of 1.5% into the anion resin tower to desorb organic impurities, with a flow rate of 25 m 3 / h and an elution time of 4.5 h. Pass a potassium carbonate solution with a concentration of 8% into the cation resin tower to desorb organic impurities, with a flow rate of 25 m 3 / h and an elution time of 4.5 h. Then, wash the resin clean with deionized water;

[0068] Step 3, hydrosilylation reaction of pendant double bonds:

[0069] Add 30 kg of ion exchange resin, 8 kg of methyl vinyl cyclosiloxane, 2.8 kg of N-vinyl caprolactam, 0.73 kg of chloroplatinic acid, and 145 kg of dichloroethane. Control the temperature at 70 °C and react for 5 h. After completion, filter and wash with water to obtain the described caprolactam-based ion exchange resin.

[0070] Step 4: Subsequently, perform acid-base regeneration. The cation exchange resin is regenerated with a 10% aqueous hydrochloric acid solution, and the anion exchange resin is regenerated with a 10% aqueous NaOH solution. The regeneration agent flow rate is 25 m 3 / h, and the regeneration time is 6 hours. Finally, wash with demineralized water until neutral.

[0071] The regeneration degree of the obtained regenerated resin is 98.5%.

[0072] Comparative Example 1

[0073] Compared with Example 1, Step 2 is omitted, and the rest is the same as in Example 1. The regeneration degree of the obtained regenerated resin is 81.2%.

[0074] Comparative Example 2

[0075] Compared with Example 1, Step 1 is omitted, and the rest is the same as in Example 1. The regeneration degree of the obtained regenerated resin is 82.4%.

[0076] Comparative Example 3

[0077] Compared with Example 1, Step 3 is omitted, and the rest is the same as in Example 1. The regeneration degree of the obtained regenerated resin is 87.5%.

[0078] Comparative Example 4

[0079] Compared with Example 1, the amount of N-vinyl caprolactam added in Step 3 is 0 kg, and the rest is the same as in Example 1. The regeneration degree of the obtained regenerated resin is 89.7%.

Claims

1. A regeneration method for an ion exchange resin used in caprolactam refining, characterized in that, It includes the following steps: Step 1: First, drain the caprolactam aqueous solution in the resin, then wash the resin with deionized water solution, and at the same time break the resin bed with deionized water. Step 2: Then, a neutral or acidic desorbing solution is introduced into the anion resin column to desorb organic impurities at a flow rate of 20 - 25 m 3 / h, and the elution time is 3.5 - 4.5 h. A neutral or alkaline desorbing solution is introduced into the cation resin column to desorb organic impurities at a flow rate of 20 - 25 m 3 / h, and the elution time is 3.5 - 4.5 h. Then, the resin is cleaned with demineralized water until it is clean; Step 3: Hydrosilylation reaction of pendant double bonds Since the ion exchange resin is a copolymer of styrene and divinylbenzene, the pendant double bonds on the divinylbenzene can participate in the hydrosilylation reaction. The technical solution is as follows: By mass, 20 - 30 parts of ion exchange resin, 3 - 8 parts of methylvinylcyclosiloxane, 0.5 - 2.8 parts of N-vinylcaprolactam, 0.31 - 0.73 parts of chloroplatinic acid, and 100 - 145 parts of dichloroethane are used. The temperature is controlled at 60 - 70 °C, and the reaction is carried out for 2 - 5 h. After completion, filtration and washing with water are carried out to obtain caprolactam-based ion exchange resin. Step 4: Subsequently, acid-base regeneration is carried out. The anion exchange resin is regenerated with an alkaline regenerant, and the cation exchange resin is regenerated with an acid regenerant. The flow rate of the regenerant is 20 - 25 m3 / h, and the regeneration time is 4 - 6 hours. Finally, the resin is washed clean with deionized water.

2. The method according to claim 1, characterized in that, The neutral or acidic analytical solution described in Step 2 is one of a single-charge strong acid-strong base salt solution, a strong acid-weak base salt solution, and a mixed solution of salt and strong acid.

3. The method according to claim 2, wherein The single-charge strong acid-strong base salt solution is a composition of one or more of sodium chloride solution and potassium chloride solution; the strong acid-weak base salt solution is ammonium chloride solution; the mixed solution of salt and strong acid is one of the mixed solutions of sodium chloride and hydrochloric acid, and potassium chloride and hydrochloric acid.

4. The method according to claim 2, wherein In the neutral analytical solution, the mass concentration of the single-charge strong acid-strong base salt or strong acid-weak base salt solution is 3 - 8%; in the acidic analytical solution, the mass concentration of the salt is 3 - 8%, and the mass concentration of the acid is 0.5 - 1.5%.

5. The method according to claim 1, wherein The neutral or alkaline analytical solution described in Step 2 is one of a single-charge strong acid-strong base salt solution, a strong base-weak acid salt solution, and a mixed solution of salt and strong base.

6. The method according to claim 5, characterized in that The single-charge strong acid-strong base salt solution is a composition of one or more of sodium chloride and potassium chloride solutions; the strong base-weak acid salt solution is a composition of one or more of sodium carbonate and potassium carbonate solutions; the mixed solution of salt and strong base is one of the mixed solutions of sodium chloride and sodium hydroxide, and potassium chloride and potassium hydroxide.

7. The method according to claim 5, wherein The mass concentration of the single-charge strong acid-strong base salt is 3 - 8%; the mass concentration of the strong base-weak acid salt is 3 - 8%; in the mixed solution of salt and strong base, the mass concentration of the salt is 3 - 8%, and the mass concentration of the base is 0.5 - 1.5%.

8. The method according to claim 1, wherein The alkaline regenerant described in Step 4 is a composition of one or more of sodium hydroxide aqueous solution and potassium hydroxide aqueous solution, and the mass concentration of the aqueous solution is 3 - 10%.

9. The method according to claim 1, characterized in that, The acid regenerant described in Step 4 is a composition of one or more of hydrochloric acid aqueous solution, sulfuric acid aqueous solution, and hydrobromic acid aqueous solution, and the mass concentration of the aqueous solution is 2 - 10%.

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