Chelating resin and method for its preparation

Abstract

The application belongs to the field of polymer synthesis and particularly relates to a preparation method of a chelating resin. The method comprises the following steps: 1) pretreating a carrier; 2) uniformly mixing the pretreated carrier, an amine compound and an amide compound in proportion to prepare an activated carrier; 3) uniformly mixing the activated carrier, a quaternary ammonium salt and an ionic liquid in proportion to prepare a precursor; and 4) uniformly mixing the precursor, a lipid heterocyclic compound and a cationic surfactant in proportion to prepare the chelating resin. The method is more green and efficient, all high-risk reagents such as toxic diazonium salt and carcinogenic chloromethyl ether commonly used in traditional processes are abandoned, the whole reaction process is carried out under mild temperature and pressure conditions, controllability is high, and the chelating treatment capacity for metal ions is high.

Description

Technical Field

[0001] This invention belongs to the field of polymer synthesis, specifically relating to a method for preparing a chelating resin. Background Technology

[0002] Chelating resins are a class of polymeric materials capable of forming stable coordination structures with metal ions. They possess advantages such as high selectivity, large adsorption capacity, and reusability, and are widely used in hydrometallurgy, wastewater treatment, and precious metal recovery. Currently, common methods for synthesizing chelating resins mainly include direct polymerization of functional monomers and surface functionalization modification of carriers. However, these methods generally suffer from problems such as cumbersome synthesis steps, low functional group loading rates, use of toxic reagents, and difficulty in industrialization.

[0003] In recent years, research on chelating resins targeting specific metal ions has made some progress. For example, Sai Bingchan synthesized tetramethylammonium chloride (TMAC) chelating resin using polystyrene as a backbone through nitration, ammoniation, diazotization, and coupling steps. Its saturated adsorption capacity for silver ions reached 89.30 mg / g, but the synthetic route was long, the diazotization step was dangerous, and the yield was unstable. Ying Yongwen used commercially available CH-93 chelating resin to study the adsorption of calcium and magnesium ions in rubidium salt solutions. Although the adsorption effect was good, the resin was purchased externally, limiting its synthetic methods and the ability to customize functional groups, and the selective mechanism for different metal ions remained unclear.

[0004] Therefore, developing a chelating resin preparation method with a simple synthetic route, tunable functional groups, synergistic and efficient catalyst system, environmental friendliness, and ease of industrialization has significant scientific research value and application prospects. Summary of the Invention

[0005] This invention addresses the technical challenges in the preparation of traditional chelating resins, such as low functional group loading, complex synthesis process, unfriendly environment, and poor reusability, by providing a method for preparing chelating resins.

[0006] The main objective of this invention is: I. To construct a multi-level catalyst system with a clear progressive relationship to achieve high loading and uniform distribution of functional groups; II. A chelating resin synthesis process suitable for continuous production is provided to avoid the use of high-risk reagents and improve production safety; Third, a chelating resin with high selectivity and high adsorption capacity for various metal ions such as silver, calcium, and magnesium was prepared, and it also has good reusability.

[0007] To achieve the above objectives, the present invention adopts the following technical solution.

[0008] A method for preparing a chelating resin, The method includes: 1) Pre-treat the carrier; 2) The pretreated support, amine compound, and amide compound are mixed evenly in a certain proportion to prepare the activated support; 3) The activated support, quaternary ammonium salt, and ionic liquid are mixed evenly in a certain proportion to prepare the precursor; 4) Mix the precursor, alicyclic compound and cationic surfactant in a certain proportion to form a chelating resin.

[0009] As a preferred option Step 1) The carrier is polystyrene microspheres with a particle size of 200-300 μm; Step 1) The pretreatment uses a sulfuric acid solution with a mass concentration of 65-75% and a mass ratio of 6-10 times that of polystyrene microspheres, and is treated at a temperature of 65-75 ℃ for 2.5-3.5 h.

[0010] As a preferred option Step 2) The amine compound is ethylenediamine; Step 2) The amide compound is N,N-dimethylformamide.

[0011] As a preferred option Step 2) The pretreatment carrier, amine compound and amide compound are mixed evenly at a mass ratio of 1:(3-5):(0.3-0.5).

[0012] As a preferred option Step 2) The preparation of the activated support is carried out under a nitrogen atmosphere and at a temperature of 55-65 °C for 5-7 h.

[0013] As a preferred option Step 3) The quaternary ammonium salt is 3-chloro-2-hydroxypropyltrimethylammonium chloride; Step 3) The ionic liquid is 1-butyl-3-methylimidazolium hexafluorophosphate; Step 3) The activated carrier, quaternary ammonium salt and ionic liquid are mixed evenly at a mass ratio of 1:(0.8~1.2):0.4.

[0014] As a preferred option Step 3) The precursor preparation is carried out in a 75% ethanol aqueous solution at a temperature of 45-55 °C for 4-6 h.

[0015] As a preferred option Step 4) The alicyclic compound is epichlorohydrin; Step 4) The cationic surfactant is benzyltriethylammonium chloride; Step 4) The precursor, alicyclic compound and cationic surfactant are mixed evenly at a mass ratio of 1:(0.15-0.25):(0.25-0.35).

[0016] As a preferred option Step 4) The prepared chelating resin is reacted at a temperature of 75-85 ℃ and a stirring speed of 250-350 rpm for 3-4 h.

[0017] A chelating resin.

[0018] This invention addresses the problems commonly found in existing chelating resin synthesis technologies, such as lengthy preparation routes, single catalytic systems, low functional group loading efficiency, and insufficient cycle stability. It provides a preparation method based on a three-stage catalytic chain reaction procedure of sulfonation-amineation-quaternization. This system utilizes three functionally complementary catalysts that sequentially intervene and synergistically achieve efficient grafting, directional chemical coupling, and final network structure stabilization of functional monomers on the polymer support. This significantly improves the resin's adsorption capacity, selectivity, and mechanical durability for target metal ions, while greatly enhancing the industrial feasibility and environmental friendliness of the process.

[0019] The core of this invention lies in constructing a multi-stage catalytic chain reaction system with strict temporal sequence and functional progression. This system is not a simple superposition of catalysts, but rather, through precise reaction path design, each catalytic step is interconnected, forming an irreversible or uninterrupted "reaction chain".

[0020] The core innovation of this system lies in decoupling the complex resin functionalization process into three clearly defined and functionally specific catalytic modules. The first-stage catalysis uses N,N-dimethylformamide (DMF) as the reaction medium and dehydrating agent. Utilizing its strong polarity and weakly alkaline environment, it promotes the condensation reaction between ethylenediamine and the sulfonic acid groups (-SO3H) on the sulfonated support, forming a stable sulfonamide bond (-SO2-NH-). Simultaneously, the terminal amino group of ethylenediamine remains a free amino group (-NH2). This step not only achieves high loading and uniform distribution of amino groups on the support surface, forming a robust amination intermediate, but the resulting alkaline microenvironment also creates suitable chemical conditions for subsequent reactions. The secondary catalysis employs 1-butyl-3-methylimidazolium hexafluorophosphate, an ionic liquid possessing both green solvent and high-efficiency catalyst properties. This catalyst utilizes its unique ionic microenvironment and solubility to precisely promote the nucleophilic substitution reaction between 3-chloro-2-hydroxypropyltrimethylammonium chloride and a free amino group on the amination intermediate. The active chlorine atom in the 3-chloro-2-hydroxypropyltrimethylammonium chloride molecule is attacked by the amino group, generating a quaternary ammonium cation group (-N). +Functionalized segments of (CH3)3 and hydroxyl (-OH) groups are introduced covalently to introduce the target chelating groups. Tertiary catalysis uses benzyltriethylammonium chloride as a phase transfer catalyst. Its core role is to catalyze ring-opening addition and condensation reactions between the epichlorohydrin crosslinking agent and the remaining amino or hydroxyl groups on the resin backbone, constructing a robust three-dimensional crosslinked network and preventing the loss of functional groups during recycling. This design ensures that the catalytic products at each step of the process—from support activation to amine grafting to functional group coupling to structural reinforcement—provide the necessary active sites and optimal chemical microenvironment for the next reaction, achieving precise programmed control of the reaction pathway.

[0021] The key to this three-stage catalytic system in this invention lies in its inherent strong synergistic effect and strict sequence dependence. Any deviation from the predetermined sequence or substitution of catalytic components will lead to a significant deterioration in product performance. Its irreplaceability stems from the deep coupling of the reaction mechanisms at each step: the sulfonamide bond and terminal free amino group formed by the primary catalysis are the only precursors for the secondary nucleophilic substitution reaction; the charged functional groups and specific spatial structures constructed by the secondary catalysis create the necessary molecular conformation and reaction driving force for the tertiary crosslinking reaction. Specifically, each catalytic reaction creates the necessary chemical prerequisites and exclusive reaction environment for the next step.

[0022] As mentioned earlier, primary catalysis, through its strong polarity and weak basicity, activates the support surface while simultaneously promoting a condensation reaction between ethylenediamine and the sulfonic acid groups (-SO3H) on the support surface, forming a sulfonamide bond (-SO2-NH-) and retaining the terminal primary amine group (-NH2). These amine groups (free amine groups) are not only active sites for subsequent reactions, but this process also transforms the strongly acidic sulfonic acid groups into weakly acidic sulfonamide groups and introduces a basic free amino group, constructing an amphoteric active interface (retaining both weakly acidic sites and introducing basic sites), providing a suitable chemical microenvironment for secondary nucleophilic substitution reactions. If this step is skipped, the support surface lacks sufficient and uniformly distributed nucleophilic sites, and the surface is strongly acidic, directly leading to extremely low efficiency or even failure of secondary nucleophilic substitution reactions.

[0023] Secondary catalysis utilizes the unique bifunctional properties of ionic liquids. The cationic portion pre-assembles with the amination support through ion-dipole interactions, increasing the local concentration of the active quaternary ammonium salt monomer (i.e., 3-chloro-2-hydroxypropyltrimethylammonium chloride) and activating the C-Cl bond in the 3-chloro-2-hydroxypropyltrimethylammonium chloride molecule through the weak coordination ability of its anion, promoting efficient nucleophilic substitution with the amino group. This step successfully introduces positively charged quaternary ammonium salt groups. These positively charged centers not only endow the resin with ion exchange capacity, but more importantly, the specific steric hindrance and hydrophilic microregions they form are crucial for the uniform diffusion and effective contact of the subsequent epoxy crosslinking agent with the reaction sites. If this step is pre-positioned or replaced, the support surface will lack the correct charge distribution and spatial conformation, leading to uneven distribution of the crosslinking agent and the formation of dense, non-porous, ineffective crosslinking.

[0024] Tertiary catalysis, as a phase-transfer catalyst, relies entirely on the microstructure established in the first two steps to achieve its function. It requires catalyzing intramolecular or intermolecular ring-opening addition and condensation polymerization of epoxy groups between functionalized segments formed in the first two steps, which contain specific spacer arms (such as -SO2-NH-CH2-CH2-NH-CH2-CH(OH)-CH2-). If the preceding functionalization is incomplete or uneven, the crosslinking reaction will fail to form a uniform and stable three-dimensional network, and may instead produce defective structures with localized over-crosslinking or under-crosslinking, severely affecting the mechanical strength and cycling stability of the resin.

[0025] From the perspective of material structure evolution, the catalyst system process of this invention is a strictly linear process of microstructure transformation from "skeleton construction" to "functional modification" and then to "network reinforcement." Each step permanently alters the chemical and physical structure of the support and sets a unique reaction pathway for the next step. Sulfonamide conversion transforms sulfonic acid cation exchange sites into reactive nucleophilic interfaces; quaternary ammonium salt coupling assembles functional "tentacles" with specific ion selectivity on these interfaces; and the final crosslinking reinforces these "tentacles" at their bases, preventing them from detaching or swelling during repeated adsorption-desorption processes. The absence or disorder of any step will lead to a fundamental loss of the target structure. For example, performing crosslinking first will block the pores and active sites of the support (sulfonic acid groups are encapsulated), preventing subsequent sulfonamide and quaternization reactions from reaching the interior of the material, allowing them to occur only on the surface, resulting in extremely low functional group loading and easy loss.

[0026] The beneficial effects of this invention are as follows: This invention pursues high performance while adhering to green chemistry principles. It completely eliminates high-risk reagents commonly used in traditional processes, such as highly toxic diazonium salts and carcinogenic chloromethyl ethers. Although this method uses concentrated sulfuric acid for sulfonation, it avoids the carcinogenic reagents found in traditional chloromethylation routes. Furthermore, the ionic liquid, a core catalytic component, can be easily recycled and reused, reducing costs and environmental pollution. The entire reaction process is carried out under mild temperature and pressure conditions, with clearly defined and highly controllable parameters for each step. The reaction system exhibits good fluidity and is perfectly compatible with continuous production equipment such as tubular reactors or series-connected batch reactors. It also demonstrates strong chelation capabilities for metal ions. Detailed Implementation

[0027] The present invention will be further described clearly and in detail below with reference to specific embodiments. Those skilled in the art will be able to implement the present invention based on these descriptions. Furthermore, the embodiments of the present invention described below are generally only some, not all, of the embodiments of the present invention. Therefore, all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0028] Unless otherwise specified, all raw materials used in the embodiments of the present invention are commercially available or obtainable by those skilled in the art; unless otherwise specified, all methods used in the embodiments of the present invention are methods mastered by those skilled in the art.

[0029] Example 1 A method for preparing a chelating resin, The method includes: 1) Polystyrene microspheres with a particle size of 200 μm were pretreated by using a sulfuric acid solution with a mass concentration of 65% and a mass ratio of 6 times that of the polystyrene microspheres, and treated at a temperature of 65 °C for 3.5 h. 2) The pretreated support, ethylenediamine and N,N-dimethylformamide were mixed evenly at a mass ratio of 1:3:0.3 and reacted at 55 °C for 7 h under a nitrogen atmosphere to prepare the activated support; 3) The activated support, 3-chloro-2-hydroxypropyltrimethylammonium chloride and 1-butyl-3-methylimidazolium hexafluorophosphate were mixed evenly at a mass ratio of 1:0.8:0.4 to prepare the reaction material. 20 mL of 75% (volume concentration) ethanol aqueous solution was used for each gram of reaction material. The reaction material was added to the ethanol aqueous solution and mixed. The mixture was then reacted at 45 °C for 6 h to prepare the precursor. 4) The precursor, epichlorohydrin and benzyltriethylammonium chloride were mixed evenly at a mass ratio of 1:0.15:0.3 and reacted at 75 ℃ and 250 rpm for 4 h to prepare a chelating resin (labeled as R-1).

[0030] The material R-1 prepared in Example 1 was subjected to performance testing, and the specific characterization results are as follows.

[0031] Performance testing methods: The loading of amine and quaternary ammonium salt groups was determined by elemental analysis and ion chromatography; the degree of resin crosslinking was calculated by the swelling method; for Ag... + The saturated adsorption capacity was determined by ICP-OES after static adsorption for 6 h in HAc-NaAc buffer at pH 3.5; for Ca... 2+ The saturated adsorption capacity was determined after static adsorption in rubidium chloride solution at 70 °C for 70 min; the stability for repeated use was evaluated by the capacity retention rate after 5 cycles of adsorption-0.5 mol / L HNO3 desorption.

[0032] Analyzing the characterization results above, this embodiment uses relatively mild conditions to verify the feasibility of the three-stage catalytic chain reaction route. Specifically, under sufficient primary catalysis (DMF), a stable amination intermediate (amine loading 2.91 mmol / g) forms on the support surface, containing terminal free amino groups that can serve as subsequent reaction sites, laying the necessary active site foundation for subsequent reactions. Secondary catalysis (ionic liquid) successfully introduces quaternary ammonium salt functional groups (loading 2.01 mmol / g) onto this amine base layer, but the relatively mild reaction temperature may limit further improvement in coupling efficiency. Tertiary catalysis (phase transfer catalyst) constructs a moderately cross-linked network (cross-linking degree 82.4%) on the functionalized framework, enabling the resin to initially possess a stable three-dimensional structure, thereby achieving effective adsorption of silver and calcium ions and good cycling stability. This result demonstrates the effectiveness of the strictly sequential linear reaction pathway from "sulfonamide amine grafting" to "quaternary ammonium salt functional coupling" and then to "epoxy cross-linked network reinforcement," providing a benchmark for performance optimization.

[0033] Example 2 A method for preparing a chelating resin, The method includes: 1) Polystyrene microspheres with a particle size of 250 μm were pretreated by using a sulfuric acid solution with a mass ratio of 8 times that of the polystyrene microspheres and a mass concentration of 70% at a temperature of 70 °C for 3.0 h. 2) The pretreated support, ethylenediamine and N,N-dimethylformamide were mixed evenly at a mass ratio of 1:4.0:0.4 and reacted at 60 °C under a nitrogen atmosphere for 6 h to prepare the activated support; 3) The activated support, 3-chloro-2-hydroxypropyltrimethylammonium chloride and 1-butyl-3-methylimidazolium hexafluorophosphate were mixed evenly at a mass ratio of 1:1.0:0.4 to form the reaction material. 20 mL of 75% (volume concentration) ethanol aqueous solution was taken for each gram of reaction material. The reaction material was added to the ethanol aqueous solution and mixed. The mixture was reacted at 50 °C for 5 h to prepare the precursor. 4) The precursor, epichlorohydrin and benzyltriethylammonium chloride were mixed evenly at a mass ratio of 1:0.20:0.3 and reacted at 80 ℃ and 300 rpm for 3.5 h to prepare a chelating resin (labeled as R-2).

[0034] The performance of material R-2 prepared in Example 2 was tested, and the specific characterization results are as follows.

[0035] Performance testing methods: The loading of amine and quaternary ammonium salt groups was determined by elemental analysis and ion chromatography; the degree of resin crosslinking was calculated by the swelling method; for Ag... + The saturated adsorption capacity was determined by ICP-OES after static adsorption for 6 h in HAc-NaAc buffer at pH 3.5; for Ca... 2+ The saturated adsorption capacity was determined after static adsorption in rubidium chloride solution at 70 °C for 70 min; the stability for repeated use was evaluated by the capacity retention rate after 5 cycles of adsorption-0.5 mol / L HNO3 desorption.

[0036] Analyzing the above characterization results, this embodiment employs balanced optimization conditions to fully demonstrate the strong synergistic effect of the three-stage catalytic chain reaction system. Under these conditions, the first-stage catalysis creates a high-density and uniformly distributed amine-based active layer, providing an ideal precursor for subsequent steps. The unique microenvironment of the ionic liquid in the second-stage catalysis is efficiently utilized, achieving precise and high-loading coupling of the quaternary ammonium salt on the amine substrate, successfully constructing dense functional "tentacles." Based on this, the third-stage catalysis constructs a uniform and stable three-dimensional cross-linked network between structurally regular functionalized segments. This perfect progression from "skeleton construction" to "functional modification" and then to "network reinforcement" results in resin R-2 exhibiting the highest adsorption capacity and optimal mechanical durability, strongly validating the optimal synergistic state of the catalytic system described in this invention under sequential dependence.

[0037] Example 3 A method for preparing a chelating resin, The method includes: 1) Polystyrene microspheres with a particle size of 300 μm were pretreated by using a sulfuric acid solution with a mass concentration of 75% and a mass ratio of 10 times that of the polystyrene microspheres, and treated at a temperature of 75 °C for 2.5 h. 2) The pretreated support, ethylenediamine and N,N-dimethylformamide were mixed evenly at a mass ratio of 1:5:0.5 and reacted at 65 °C for 5 h under a nitrogen atmosphere to prepare the activated support; 3) The activated support, 3-chloro-2-hydroxypropyltrimethylammonium chloride and 1-butyl-3-methylimidazolium hexafluorophosphate were mixed evenly at a mass ratio of 1:1.2:0.4 to form the reaction mixture. 20 mL of 75% (volume concentration) ethanol aqueous solution was used for each gram of reaction mixture. The reaction mixture was added to the ethanol aqueous solution and mixed. The mixture was then reacted at 55 °C for 4 h to prepare the precursor. 4) The precursor, epichlorohydrin and benzyltriethylammonium chloride were mixed evenly at a mass ratio of 1:0.25:0.3 and reacted at 85 ℃ and 350 rpm for 3 h to prepare a chelating resin (marked as R-3).

[0038] The performance of material R-3 prepared in Example 3 was tested, and the specific characterization results are as follows.

[0039] Performance testing methods: The loading of amine and quaternary ammonium salt groups was determined by elemental analysis and ion chromatography; the degree of resin crosslinking was calculated by the swelling method; for Ag... + The saturated adsorption capacity was determined by ICP-OES after static adsorption for 6 h in HAc-NaAc buffer at pH 3.5; for Ca... 2+ The saturated adsorption capacity was determined after static adsorption in rubidium chloride solution at 70 °C for 70 min; the stability for repeated use was evaluated by the capacity retention rate after 5 cycles of adsorption-0.5 mol / L HNO3 desorption.

[0040] Analyzing the above characterization results, this embodiment employs enhanced conditions with a high feed ratio to verify the performance boundaries of the catalytic chain reaction under a rich feed environment. While a higher feed ratio of functional monomers (especially ethylenediamine and 3-chloro-2-hydroxypropyltrimethylammonium chloride) theoretically benefits the increase in loading, the dynamic balance between increased reaction temperature (from 55 °C to 65 °C) and shortened reaction time (from 6 h to 4 h) resulted in the actual loading not reaching the theoretical optimum. Specifically, high temperature may promote partial hydrolysis of sulfonamide bonds or increase side reactions of 3-chloro-2-hydroxypropyltrimethylammonium chloride, while the shortened reaction time limits the kinetic equilibrium. Nevertheless, the highly cross-linked network (85.2%) constructed by the tertiary catalysis effectively stabilized the functional groups, allowing resin R-3 to achieve its absolute adsorption capacity (93.2 mg / g Ag). + The performance reached the highest level, even slightly better than Example 2, but the cycle stability (91.5%) was significantly lower than that of Example 2, indicating that excessive crosslinking may reduce the regeneration flexibility of the resin. This fully demonstrates that the catalytic chain reaction pathway of the present invention is sensitive to parameter windows, and a balance must be sought between loading efficiency and structural stability.

[0041] Comparative Example 1 Based on Example 2, this example only modifies the process sequence; the total amount of other materials and actual operating parameters are the same as in Example 2. The specific settings are as follows: The performance testing method for the comparative product is completely consistent with that of Example 1. Partial performance characterization was performed, and the characterization results are shown in the table below.

[0042] Analysis of the characterization results shows that this comparative example, by changing the catalytic sequence and prioritizing the network crosslinking step, directly resulted in the premature "blocking" of the support pores and surface sulfonic acid groups by the crosslinking network. This prevented the subsequent primary catalytic sulfonamide grafting reaction from effectively proceeding into the support interior, instead occurring only on the severely hindered surface, leading to a sharp decrease in the loading of sulfonamide bonds and free amino groups. Since the amination intermediate formed by the primary catalysis is the only precursor for the secondary catalytic nucleophilic substitution reaction of 3-chloro-2-hydroxypropyltrimethylammonium chloride, its severe deficiency directly caused a catastrophic decrease in the efficiency of introducing quaternary ammonium salt functional groups. Although the degree of crosslinking itself was high, this crosslinking network was built on a "blank" skeleton lacking functional groups, forming an ineffective mechanical structure. Therefore, the final resin's reaction with Ag... +The adsorption capacity dropped sharply by 74.7%, and due to the weak anchoring of the functional groups, the adsorption capacity retention rate deteriorated significantly after only 3 cycles. This result strongly demonstrates, as a negative example, the strict dependence and irreversibility of the reaction sequence of "primary sulfonamideation → secondary quaternization → tertiary crosslinking reinforcement" established in this invention. Any deviation from this sequence will lead to a fundamental loss of the target functional structure and a complete deterioration of performance.

[0043] Comparative Example 2 Based on Example 2, this example omits the primary catalytic (amine grafting) step and attempts to perform a one-step mixing reaction of ethylenediamine and 3-chloro-2-hydroxypropyltrimethylammonium chloride with a pretreated support in the presence of a secondary catalyst (ionic liquid), followed by tertiary crosslinking. The total amount of other materials and actual operating parameters are the same as in the corresponding steps of Example 2. Specific settings are as follows: The performance testing method for the comparative product was exactly the same as that for Example 2, and the content of free amine groups in the resin was additionally measured to evaluate the change in reaction pathway. The characterization results are shown in the table below.

[0044] Analysis of the characterization results shows that this comparative example directly disrupts the starting point of the tertiary catalytic chain reaction by omitting the pre-catalytic step specifically involved in sulfonamideation. Without DMF-mediated dehydration condensation, ethylenediamine cannot efficiently condense with the sulfonic acid groups (-SO3H) on the support surface to form sulfonamide bonds (-SO2-NH-) and retain the terminal free amino groups. This results in a significant decrease in the total amino group content in the final resin, with the vast majority existing as physically adsorbed or weakly interacting free amino groups (measured at 0.95 mmol / g free amino groups, far higher than the 0.12 mmol / g in Example 2, indicating a lack of covalent anchoring). This loose and unstable amino group distribution leads to extremely low efficiency in the subsequent nucleophilic substitution reaction of 3-chloro-2-hydroxypropyltrimethylammonium chloride with amino groups under ionic liquid catalysis, with the quaternary ammonium salt group loading only 33.5% of that in Example 2. Despite subsequent crosslinking, the functionalized precursor structure itself suffers from a severe defect—a lack of covalently anchored, high-density sulfonamide active sites—leading to a significant deterioration in both the final resin's adsorption capacity (a 60.5% decrease) and cycling stability (71.2% retention after 3 cycles). This result directly demonstrates that the primary sulfonamide step is the unique and indispensable starting point for constructing all subsequent functional structures, and the resulting covalent sulfonamide bonds are the chemical basis for the efficient and directional progression of the entire chain reaction. Omitting this step prevents subsequent catalytic steps from achieving high loading and stabilization of functional groups.

[0045] Comparative Example 3 Based on Example 2, this example replaces each stage of the core catalyst with a catalyst that has similar function but different structure. Only one catalyst is replaced in each experiment group, while the other two catalysts, all process steps, reaction conditions, and material dosages remain consistent with Example 2. The specific settings are as follows: The performance testing method for the comparative product is completely consistent with that of Example 1. Partial performance characterization was performed, and the characterization results are shown in the table below.

[0046] Analysis of the above characterization results shows that, under the premise of maintaining the three-stage catalytic chain reaction sequence, replacing each stage of the catalyst in this comparative example resulted in varying degrees of decline in the final resin performance. This directly proves that the catalysts selected in this invention have unique structural functions and cannot be easily replaced.

[0047] D3-1 uses dimethyl sulfoxide (DMSO) instead of N,N-dimethylformamide (DMF). Although DMSO is also a strongly polar aprotic solvent, its basicity is weaker than that of DMF, resulting in insufficient activation ability on the support surface and insufficient promotion of the condensation reaction between ethylenediamine and sulfonic acid groups. This leads to a decrease in the loading of amine groups and has a chain reaction effect on the loading of subsequent functional groups and the final adsorption performance.

[0048] D3-2 replaces the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate with the conventional quaternary ammonium salt tetrabutylammonium bromide. The former only has a cationic moiety and completely loses the unique ionic microenvironment of ionic liquids, which has the dual function of "solvent-catalyst". It cannot effectively promote the nucleophilic substitution reaction between 3-chloro-2-hydroxypropyltrimethylammonium chloride and amino groups, resulting in a significant decrease in the loading of quaternary ammonium salt groups, which becomes a performance bottleneck.

[0049] D3-3 replaces benzyltriethylammonium chloride with long-chain hexadecyltrimethylammonium bromide. The steric hindrance effect of the long-chain alkyl group may affect its effective mass transfer as a phase transfer catalyst between the resin phase and the aqueous phase (or interface), resulting in a decrease in the catalytic efficiency of the epichlorohydrin ring-opening crosslinking reaction and a significantly insufficient degree of resin crosslinking, thereby significantly affecting the mechanical stability and recycling performance of the resin.

[0050] The comparative results of this series of studies comprehensively demonstrate that the three-stage catalytic chain system of this invention is a highly optimized whole. The specific function of each catalyst stage is essential for constructing the final high-performance resin, and its role cannot be completely replaced by other substances of the same class.

[0051] Comparative Example 4 Based on Example 2, two sets of control experiments were designed to simulate scenarios where it is used solely as a solvent or solely as a catalyst, respectively, and compared with its effect as a dual-function "solvent-catalyst" in Example 2. The sequence of process steps, material dosages, and reaction conditions for all experiments, except for the secondary catalytic system, were strictly consistent with those of Example 2. Specific settings are as follows: The performance testing method for the comparative product is completely consistent with that of Example 1. Partial performance characterization was performed, and the characterization results are shown in the table below.

[0052] Analysis of the above characterization results clearly demonstrates the indispensability of the integrated "solvent-catalyst" design in the second-order catalytic step by deconstructing the dual function of the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate.

[0053] D4-1 uses the good solvent NMP but lacks specific catalytic function, resulting in extremely low efficiency of the nucleophilic substitution reaction between 3-chloro-2-hydroxypropyltrimethylammonium chloride and the amino group, with the quaternary ammonium salt loading plummeting to 31.2% as in Example 2. This demonstrates that physical dissolution alone cannot drive the efficient conduction of this nucleophilic substitution directional coupling reaction, and the unique catalytic activity of ionic liquids is its core function.

[0054] Although D4-2 attempted to replace the solvent and anionic catalytic function of 1-butyl-3-methylimidazolium hexafluorophosphate with ethanol and NaBF4, respectively, the quaternary ammonium salt group loading was still much lower than in Example 2, and the resin crosslinking degree decreased. This indicates that the specific ionic microenvironment created by ionic liquids and the synergistic effect of their anions and cations cannot be simulated by simple separation and conventional solvents and inorganic salts. This unique microenvironment plays a crucial role in promoting reactant pre-assembly, stabilizing the transition state, and maintaining the resin's swelling state during the reaction to facilitate mass transfer and subsequent crosslinking.

[0055] A comprehensive analysis of this example demonstrates that the results of Comparative Example 4 strongly confirm that the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate used in the secondary catalysis is not a typical solvent or catalyst. Its integrated "solvent-catalyst" dual-function is one of the key factors enabling the tertiary catalytic chain system of this invention to achieve high quaternary ammonium salt loading and thus obtain excellent adsorption performance. Any attempt to disassemble or replace its function will result in a significant loss of performance, thus proving the irreplaceable nature of this component in the overall technical solution of this invention.

Claims

1. A method for preparing a chelating resin, characterized in that, The method includes: 1) Pre-treat the carrier; 2) The pretreated support, amine compound, and amide compound are mixed evenly in a certain proportion to prepare the activated support; 3) The activated support, quaternary ammonium salt, and ionic liquid are mixed evenly in a certain proportion to prepare the precursor; 4) Mix the precursor, alicyclic compound and cationic surfactant in a certain proportion to form a chelating resin.

2. The method for preparing a chelating resin according to claim 1, characterized in that, Step 1) The carrier is polystyrene microspheres with a particle size of 200-300 μm; Step 1) The pretreatment uses a sulfuric acid solution with a mass concentration of 65-75% and a mass ratio of 6-10 times that of polystyrene microspheres, and is treated at a temperature of 65-75 ℃ for 2.5-3.5 h.

3. The method for preparing a chelating resin according to claim 1, characterized in that, Step 2) The amine compound is ethylenediamine; Step 2) The amide compound is N,N-dimethylformamide.

4. A method for preparing a chelating resin according to claim 1 or 3, characterized in that, Step 2) The pretreatment carrier, amine compound and amide compound are mixed evenly at a mass ratio of 1:(3-5):(0.3-0.5).

5. The method for preparing a chelating resin according to claim 1, characterized in that, Step 2) The preparation of the activated support is carried out under a nitrogen atmosphere and at a temperature of 55-65 °C for 5-7 h.

6. The method for preparing a chelating resin according to claim 1, characterized in that, Step 3) The quaternary ammonium salt is 3-chloro-2-hydroxypropyltrimethylammonium chloride; Step 3) The ionic liquid is 1-butyl-3-methylimidazolium hexafluorophosphate; Step 3) The activated carrier, quaternary ammonium salt and ionic liquid are mixed evenly at a mass ratio of 1:(0.8~1.2):0.

4.

7. A method for preparing a chelating resin according to claim 1 or 6, characterized in that, Step 3) The precursor preparation is carried out in a 75% ethanol aqueous solution at a temperature of 45-55 °C for 4-6 h.

8. The method for preparing a chelating resin according to claim 1, characterized in that, Step 4) The alicyclic compound is epichlorohydrin; Step 4) The cationic surfactant is benzyltriethylammonium chloride; Step 4) The precursor, alicyclic compound and cationic surfactant are mixed evenly at a mass ratio of 1:(0.15-0.25):(0.25-0.35).

9. A method for preparing a chelating resin according to claim 1 or 8, characterized in that, Step 4) The prepared chelating resin is reacted at a temperature of 75-85 ℃ and a stirring speed of 250-350 rpm for 3-4 h.

10. A chelating resin prepared by any one of claims 1 to 9.

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