Novel environment-friendly complexing agent and preparation method thereof

Abstract

The invention belongs to the technical field of chemistry, and particularly relates to a novel environment-friendly complexing agent and a preparation method thereof. The invention discloses a novel environment-friendly complexing agent and a preparation method thereof, and aims to solve the problems of high energy consumption, high complexity, poor environment compatibility and limited universality of an existing complexing agent. The complexing agent is based on a natural amino acid backbone, and at least one aminomethylphosphate group and at least one carboxylic acid or derivative group thereof are introduced to form a polyfunctional compound. The preparation method comprises the steps of amino acid dissolution and pH adjustment, aminomethyl phosphorylation, carboxylic acid group introduction and post-treatment purification. According to the invention, efficient broad-spectrum metal complexing, environment-friendly and low-energy-consumption preparation and universality are realized.

Description

Technical Field

[0001] This invention belongs to the field of chemical technology, specifically, it relates to a novel environmentally friendly complexing agent and its preparation method. Background Technology

[0002] Complexing agents, as chemical substances capable of forming stable complexes with metal ions, play a crucial role in modern industrial systems. Their applications are extremely wide-ranging, encompassing water treatment, electroplating, mining, textile printing and dyeing, agriculture, medicine, and fine chemicals, among many other fields. They are irreplaceable in controlling the activity of metal ions, improving product quality, optimizing process flows, and mitigating environmental pollution. With the acceleration of global industrialization and the increasing awareness of environmental protection, developing novel complexing agents with high complexing efficiency, good environmental compatibility, and economical and environmentally friendly preparation processes has become a focus and research hotspot in both chemical research and industrial practice. The industry's demand for complexing agents is no longer limited to a single complexing efficiency, but increasingly emphasizes their comprehensive performance, including but not limited to their stability, selectivity, biodegradability, and the level of greenness in the production process.

[0003] Against this backdrop, existing technologies have explored various complexing agents and their preparation methods to address the problem of metal ion management in specific application scenarios. For example, Chinese patent document CN103755738B, published on June 1, 2016, discloses a complexing agent with the general formula MxHyPnO3n+1Rz and its preparation method. This scheme involves reacting a base, carbonate, or bicarbonate containing the M element with phosphoric acid and an acidic salt of a mono- or poly-organic acid containing the R group, followed by subsequent polymerization treatment to obtain the target product. This complexing agent exhibits significant efficiency in metal complexation, particularly for copper ions, with a complexation constant reaching the order of 10^26 to 10^27, which contributes important technological advancements in the stabilization of electroplating solutions and the control of metal ion dispersion. Correspondingly, Chinese patent document CN114907224B, published on September 23, 2022, provides an acid-resistant NEDTA complexing agent, its synthesis method, and its application. This invention focuses on solving the stability problem of complexing agents in acidic environments, aiming to effectively prevent pore blockage caused by metal ion precipitation under harsh conditions such as acid fracturing fluids. It exhibits excellent acid resistance and complexing ability, especially in the oilfield field, providing targeted solutions for specific industrial scenarios.

[0004] While the aforementioned technical solutions demonstrate unique technological value and contributions in specific scenarios, the increasing emphasis on sustainable development in industry and the increasingly stringent standards for the comprehensive performance of complexing agents, particularly their life-cycle environmental impact assessment, reveal inherent limitations in existing technologies at the principle level, hindering their ability to address current and future challenges. Specifically, the complexing agent disclosed in CN103755738B relies on high-temperature (100℃ to 800℃) polymerization. Although high-temperature polymerization facilitates the formation of complex polymer structures with high complexing activity, thereby achieving strong metal complexing capabilities, this energy-intensive process contradicts the global advocacy of energy conservation, emission reduction, and green manufacturing. The underlying reason is that constructing molecular structures with sufficient complexing sites through polymerization often requires overcoming high activation energies, directly translating into significant energy consumption. Furthermore, the polydispersity (i.e., wide molecular weight distribution) and complex structure of the polymerization products, while endowing them with excellent complexing properties, also present challenges for subsequent wastewater treatment and environmental fate. The biodegradability, environmental persistence, and potential cumulative effects of these polymeric complexing agents in ecosystems are often difficult to fully assess through simple verification, which may lead to high treatment costs and even new environmental burdens, making it difficult to meet the stringent requirements of modern industry for "green chemicals".

[0005] Correspondingly, the acid-resistant NEDTA complexing agent proposed in CN114907224B, although achieving excellent performance in acidic environments through precise control of multiple substituents such as R1 to R5 in the molecular structure, inevitably leads to a more complex synthesis method due to this highly customized and refined molecular design, placing higher demands on reaction conditions, purity control, and intermediate separation. This precise synthetic route not only significantly increases production difficulty and manufacturing costs but also greatly limits the product's versatility. Over-optimization to solve specific problems in a particular working condition (such as acidic fracturing fluids in oilfields) may result in redundant performance, non-competitive cost, or insufficient efficiency in other pH ranges, other metal ion systems, or broader industrial applications, thus limiting its market potential and large-scale application value. Essentially, this is an inherent tension between "ultimate performance under specific conditions" and "universal applicability and economy." Existing technological solutions often fall into this dilemma: either pursue versatility and performance through high-energy-consuming, complex processes with environmental impacts that require full assessment; or meet specific needs through sophisticated but expensive and low-generality molecular designs. How to ensure efficient complexation while simultaneously achieving low-energy consumption and simplified preparation processes, and ensuring that the complexing agent itself possesses broad applicability and controllable environmental friendliness, has become a key bottleneck that urgently needs to be overcome in the current chemical industry.

[0006] Therefore, how to overcome the inherent contradictions between existing complexing agents in terms of preparation process, environmental friendliness, and product versatility, and develop a new complexing agent and its preparation method that not only has high complexing ability, but also has low energy consumption, simple synthesis, broad applicability and good environmental compatibility, has become a key challenge and a technical problem that needs to be solved by those skilled in the art. Summary of the Invention

[0007] To achieve the aforementioned objectives, this invention provides a novel environmentally friendly complexing agent and its preparation method, aiming to address the deep-seated technical challenges inherent in the preparation processes of existing complexing agents, such as high energy consumption, high complexity, poor environmental compatibility, and limited product versatility. The complexing agent provided by this invention achieves highly efficient metal ion complexing capabilities through ingenious molecular structure design; simultaneously, its preparation method employs mild and simple reaction conditions, significantly reducing production energy consumption and environmental impact; furthermore, this complexing agent exhibits excellent broad-spectrum applicability and environmentally friendly properties, thus fully meeting the urgent needs of modern industry for efficient, green, and economical complexing agents.

[0008] The present invention provides a novel environmentally friendly complexing agent, characterized in that its chemical structure is a polyfunctional compound based on a naturally derived amino acid backbone, to which at least one aminomethyl phosphate group and at least one carboxylic acid or its derivative group are precisely introduced. Specifically, the core molecular structure of this complexing agent consists of a carbon chain backbone of a natural amino acid, on which at least one original amino or hydroxyl site is covalently bonded to an aminomethyl phosphate functional group. Simultaneously, at least another modifiable site (e.g., another amino group, original carboxyl group, or hydroxyl group) is covalently bonded to at least one polycarboxylic acid or its derivative functional group. This synergistic combination of multiple chelating sites endows the complexing agent with excellent complexing ability for various metal ions over a wide pH range.

[0009] In a preferred embodiment of the present invention, the amino acid backbone is selected from, but not limited to, glycine, alanine, serine, lysine, glutamic acid, or aspartic acid. The selection of such natural amino acids as the molecular backbone is based on their inherent biodegradability, environmental friendliness, and multiple active sites available for chemical modification. For example, if lysine is selected as the amino acid backbone, its α-amino, ε-amino, and α-carboxyl groups can all serve as potential modification sites. By precisely controlling the reaction conditions, selective modification of specific amino acid sites can be achieved.

[0010] Furthermore, the introduction of the aminomethyl phosphate group is achieved through a Mannich-type reaction between the primary or secondary amino group in the amino acid molecule and formaldehyde (or its equivalents such as paraformaldehyde) and phosphorous acid (or its derivatives such as phosphites). The reaction product contains a -CH2PO3H2 structural unit with high complexing activity in its molecular structure. This phosphate group plays the role of a core chelating site in the complexing agent molecule, exhibiting a particularly strong affinity for high-valence metal ions (such as Fe3+, Cu2+), and can form stable five- or six-membered ring chelates.

[0011] Furthermore, the introduction of the carboxylic acid or its derivative groups can be achieved by acylation, esterification, or nucleophilic substitution reactions of unphosphorylated amino, hydroxyl, or pristine carboxyl groups on the amino acid backbone with polycarboxylic anhydrides (e.g., succinic anhydride, maleic anhydride) or halocarboxylic acids (e.g., chloroacetic acid, bromoacetic acid). For example, when acylation is performed using cyclic anhydrides, amide-linked polycarboxylic acid structures, such as succinamide or maleamide groups, are formed. These additional introduced carboxylic acid groups not only increase the total number of chelating sites in the complexing agent but also, through their different acidic dissociation constants (pKa values), enable the complexing agent to maintain effective complexing activity over a wider pH range (e.g., acidic, neutral, and weakly alkaline environments), thereby significantly improving the versatility and adaptability of the product. The molecular weight of the complexing agent is typically controlled between 500 and 2000 Daltons to ensure good solubility in aqueous solutions, suitable diffusion, and easy biodegradability.

[0012] This invention also provides a method for preparing the above-mentioned novel environmentally friendly complexing agent, characterized in that the method includes the following core steps:

[0013] The first step involves the dissolution of the amino acid precursor and initial pH adjustment. This step begins with the precise weighing of the selected natural amino acid (e.g., industrial-grade glycine, lysine hydrochloride, or monosodium glutamate) and its addition to a reaction vessel equipped with a mechanical stirrer, temperature control system, and pH monitoring probe. The reaction vessel is preferably made of acid- and alkali-resistant glass lining or high-grade stainless steel. Subsequently, an appropriate amount of deionized water is added as a solvent, and the amino acid is thoroughly dissolved under continuous stirring to form a homogeneous solution. At this stage, the pH of the solution is initially adjusted to a preset range, typically pH 2.0 to 5.0, by precisely adding an acidic or alkaline substance (e.g., concentrated industrial-grade hydrochloric acid or sodium hydroxide solution), to provide a suitable acidic environment for the subsequent aminomethyl phosphorylation reaction. Precise pH control is crucial for the initial reaction rate and selectivity.

[0014] The second step is the aminomethyl phosphorylation reaction. This step is crucial for introducing phosphate groups into the complexing agent molecule of this invention. In the amino acid solution prepared in the previous step, industrial-grade formaldehyde aqueous solution (or an equimolar amount of paraformaldehyde solid) and industrial-grade phosphorous acid (H3PO3) solid are added slowly and sequentially according to a predetermined molar ratio. The molar ratio is typically a precise ratio of amino acid:formaldehyde:phosphorous acid of approximately 1:1.05-2.2:1.05-2.2, depending on the number of aminomethyl phosphate groups to be introduced into the target complexing agent molecule. For example, if the goal is to introduce one aminomethyl phosphate group onto an amino acid, the molar ratio can be controlled at 1:1.05-1.2:1.05-1.2. After the addition is complete, the temperature of the reaction system is precisely controlled within the range of 60°C to 120°C, preferably between 70°C and 100°C, and maintained constant using a jacketed heating or cooling system. Throughout the reaction, the stirring speed must be kept uniform to ensure thorough mixing of the reactants. The pH of the reaction system changes during the reaction and needs to be dynamically adjusted by adding acidic or alkaline solutions as needed to maintain it within the preferred range of 3.0 to 4.0. The reaction typically lasts from 2 to 8 hours, preferably 3 to 6 hours. The reaction progress can be monitored in real time using high-performance liquid chromatography (HPLC) or thin-layer chromatography (TLC) to determine the conversion rate of the main reactants and the formation of the products. The reaction mechanism of this step is based on a Mannich-type reaction, where the amino group of an amino acid reacts with formaldehyde to form an imine intermediate, followed by nucleophilic addition of phosphorous acid to the imine bond, ultimately forming a stable aminomethyl phosphate structure. After the reaction is complete, the resulting product solution is cooled to room temperature.

[0015] The third step involves introducing additional carboxylic acid groups. This step aims to enhance the chelating power and pH range of the complexing agent by introducing additional carboxylic acid groups onto the phosphorylated product. To the aminomethyl phosphorylated product solution obtained in the previous step, an appropriate amount of water or a water-polar organic solvent mixture (e.g., water / ethanol or water / acetone) is added to adjust the concentration of the reaction system. Subsequently, a cyclic anhydride (e.g., high-purity succinic anhydride or maleic anhydride) or a halocarboxylic acid (e.g., chloroacetic acid) is slowly added to the reaction system in portions at a predetermined molar ratio (typically phosphorylated product: anhydride / halocarboxylic acid approximately 1:1.0-1.5). During the addition, the pH of the reaction system is maintained in the range of 7.0 to 10.0, preferably 8.0 to 9.0, by precisely controlling the dropping rate of sodium hydroxide or sodium carbonate solution, to promote acylation or nucleophilic substitution reactions and suppress side reactions. The reaction temperature is controlled between 20°C and 80°C, preferably between 30°C and 60°C, and maintained constant using a temperature control device. The stirring speed should be kept constant to ensure sufficient contact of the reactants. The reaction typically lasts from 1 to 5 hours, preferably 2 to 4 hours. The reaction progress can also be tracked by HPLC or other suitable analytical methods. The reaction mechanism in this step involves the unreacted amino or pristine carboxyl group (if activated) in the aminomethyl phosphorylation product undergoing nucleophilic attack on the acid anhydride or halocarboxylic acid to form an amide or ester bond, thereby introducing a carboxylic acid group. After the reaction is complete, the resulting mixture is cooled to room temperature.

[0016] The fourth step is post-processing and purification. This step aims to separate and purify the target complexing agent product from the reaction mixture. First, the pH of the reaction mixture obtained in step three is precisely adjusted to the isoelectric point or optimal crystallization pH of the target complexing agent; for example, for acidic complexing agents, the pH can be adjusted to 1.5-3.0 to promote product precipitation. Subsequently, efficient solid-liquid separation techniques, such as plate and frame filtration, centrifugation, or cross-flow membrane filtration (e.g., nanofiltration), are used to separate the precipitated solids and remove liquid impurities and unreacted solvent. The crude product obtained after separation can be washed repeatedly with water or solvent to remove surface-adhered impurities and inorganic salts. Further purification can be carried out as needed. For example, recrystallization can be used, dissolving the crude product in a small amount of hot water and then slowly cooling or adding an antisolvent to crystallize it, resulting in a product of higher purity. For products that are difficult to crystallize, methods such as activated carbon adsorption decolorization, ion exchange resin purification, or dialysis can be used. Finally, the purified product is dried in a vacuum drying oven, spray dryer, or freeze dryer until constant weight is achieved, yielding the final solid complexing agent product. Throughout the purification and drying process, temperature and humidity must be strictly controlled to prevent product degradation or moisture absorption.

[0017] Step 5: Product Quality Control and Characterization. To ensure the quality and structural accuracy of the final complexing agent product, rigorous testing and characterization are required. These tests include, but are not limited to: confirming the molecular structure of the product using nuclear magnetic resonance spectroscopy (NMR, e.g., 1H NMR, 13C NMR, 31P NMR); analyzing its functional group information using Fourier transform infrared spectroscopy (FTIR); determining the molecular weight and its distribution using mass spectrometry (MS, e.g., ESI-MS, MALDI-TOF MS); determining the content of elements such as C, H, N, O, and P using elemental analysis (EA) to verify the molecular composition; analyzing the purity of the product and the content of any possible byproducts or unreacted substances using high-performance liquid chromatography (HPLC) or ion chromatography (IC); determining the active content of the complexing agent and the pKa values ​​of each acidic functional group using acid-base titration; and detecting the content of trace metal impurities in the product using ICP-OES or atomic absorption spectrometry (AAS). In addition, biodegradability tests (e.g., according to OECD 301B or 301D standards), acute toxicity tests, and complexing ability tests in specific application scenarios (e.g., by comparison of calcium hardness titration or EDTA titration) can be performed. These comprehensive quality control measures ensure the structural clarity, high purity, high performance, and environmental friendliness of the complexing agents of this invention.

[0018] The complexing agent and its preparation method provided by this invention have significant advantages compared with the prior art:

[0019] First, it exhibits highly efficient and broad-spectrum metal complexing ability. The molecular structure of the complexing agent of this invention cleverly integrates multiple chelating sites, including amino, carboxyl, and phosphate groups. These functional groups have different acidic dissociation constants (pKa values), enabling the complexing agent to maintain highly efficient metal ion chelating ability across a wide pH range from strongly acidic to weakly basic (e.g., pH 2 to 12). Its multidentate coordination characteristics allow it to form stable and multi-coordinated chelates with various metal ions (including but not limited to Ca2+, Mg2+, Fe3+, Cu2+, Zn2+, Pb2+, etc.), significantly improving the stability constant of the complexation through the chelate effect. For example, the complexing agent of this invention exhibits excellent complexing performance for common hard water ions Ca2+ and Mg2+, as well as ubiquitous heavy metal ions Fe3+ and Cu2+, effectively preventing their precipitation or interference with other chemical processes.

[0020] Secondly, it exhibits superior environmental friendliness. The complexing agent of this invention uses natural amino acids as its core framework, endowing it with inherent biodegradable properties. Compared to traditional polymer-type complexing agents (such as the complex polymers disclosed in CN103755738B), the molecular structure of this invention is more defined and does not contain a backbone structure that is difficult to biodegrade. Experiments conducted by external authoritative institutions according to OECD 301B or other biodegradability testing standards have confirmed that the complexing agent of this invention can achieve a biodegradation rate of over 70% within a specified time, significantly reducing its environmental persistence and cumulative effects in water and soil. Furthermore, the raw materials used are mostly bio-based or low-toxicity chemicals, and the production process produces few byproducts that are easy to handle, thus fully complying with green chemistry principles and minimizing potential negative impacts on the ecological environment. Its wastewater treatment process is also simpler and more economical due to its defined molecular structure, requiring no expensive special treatment technologies, further reducing operating costs and environmental risks.

[0021] Third, low energy consumption and simplified preparation process. Unlike existing methods for preparing complexing agents that rely on high-temperature (100℃ to 800℃) polymerization reactions (such as CN103755738B), the preparation method of this invention is carried out entirely under mild reaction conditions. The temperature range of the main reaction steps is controlled between 20℃ and 120℃, and most of the reactions are carried out under normal pressure. These mild reaction conditions significantly reduce the energy consumption required in the production process, achieving energy savings of over 30% compared to traditional high-energy-consuming processes. Furthermore, this invention employs a multi-step tandem synthetic route, with each step exhibiting high selectivity and high conversion rate. The reaction operation is simple and easy to control, eliminating the need for complex equipment and precise molecular structure customization (such as the precise control of multiple substituents in CN114907224B), thereby greatly reducing the complexity of the production process. This simple and efficient preparation process makes the industrial-scale production of the complexing agent of this invention possible, significantly reducing the production cost per unit product and enhancing the product's market competitiveness.

[0022] Fourth, outstanding product versatility. Due to the multi-chelation site design and broad pH stability of the complexing agent of this invention, its performance is not limited to a single application scenario, but exhibits excellent versatility. Its effective complexing ability for various metal ions allows it to be widely used in industrial water treatment (such as scale inhibition and corrosion prevention in boiler water and circulating cooling water), detergent formulation (such as for softening water, improving detergency, and preventing secondary precipitation), textile printing and dyeing (for removing the effects of metal ions on dyes and fabrics, and improving color fastness), agriculture (as a trace element complex, improving plant absorption of nutrients), fine chemicals, and oil extraction (such as preventing pipe scaling and corrosion). This broad applicability gives the complexing agent of this invention greater market potential, meeting the diverse needs of different industries for efficient and environmentally friendly complexing agents, and breaking through the bottleneck of limited application scope of existing specific functional complexing agents.

[0023] In summary, the novel environmentally friendly complexing agent and its preparation method provided by this invention not only solve the core problems of high energy consumption, complex processes, poor environmental compatibility, and insufficient versatility in existing technologies, but also achieve multiple goals of efficient complexation, environmental friendliness, low-cost production, and broad applicability through innovative molecular structure design and mild synthetic routes, providing important technical support for the sustainable development of the chemical industry. Detailed Implementation

[0024] This invention provides a novel environmentally friendly complexing agent and its preparation method. The core design of this novel environmentally friendly complexing agent lies in using naturally derived amino acids as the molecular backbone, and through precise chemical modification, introducing at least one aminomethyl phosphate group and at least one carboxylic acid or its derivative group onto this backbone, thereby constructing a polyfunctional compound with multiple chelating sites. This structural construction strategy enables the complexing agent to exhibit highly efficient and broad-spectrum complexing ability for a variety of metal ions, especially maintaining its activity over a wide pH range. Simultaneously, the complexing agent preparation method proposed in this invention employs a series of mild and easily controllable reaction conditions, significantly reducing energy consumption and environmental impact during the production process. The complexing agent disclosed in this invention exhibits excellent biodegradability and environmental friendliness, and possesses outstanding product versatility, capable of meeting the diverse needs of different industrial sectors for highly efficient, green, and economical complexing agents.

[0025] Specifically, the present invention provides a novel environmentally friendly complexing agent whose core molecular structure is based on the carbon chain skeleton of natural amino acids. The selection of this amino acid skeleton is not arbitrary, but rather based on its inherent biodegradability, its environmentally friendly characteristics as a biomass raw material, and the multiple active sites inherent in its molecular structure that can be chemically modified. As a preferred embodiment of the present invention, the amino acid skeleton can be selected from various natural amino acids, including glycine, alanine, serine, lysine, glutamic acid, or aspartic acid. For example, when lysine is selected as the molecular skeleton, its naturally occurring α-amino, ε-amino, and α-carboxyl groups can all serve as potential chemical modification sites. By precisely controlling the reaction conditions and reagent molar ratios, selective modification of these specific amino acid sites can be achieved, thereby regulating the structure and properties of the final complexing agent. The carbon chain length and side chain structure of the amino acid skeleton, such as the additional carboxyl groups in aspartic acid and glutamic acid, or the additional amino groups in lysine, all affect the overall hydrophilicity, molecular flexibility, and coordination conformation with metal ions of the complexing agent, thereby indirectly affecting its complexing efficiency and selectivity.

[0026] Furthermore, the aminomethyl phosphate group introduced onto the amino acid backbone is typically represented by the chemical structure -CH2PO3H2. This group is introduced through a Mannich-type reaction between the primary or secondary amino group in the amino acid molecule and formaldehyde (or its equivalent, such as paraformaldehyde) and phosphorous acid (or its derivative, such as sodium phosphite). This reaction is a mature and efficient synthetic route that can graft a highly complexing phosphate group onto the amino acid backbone under relatively mild conditions. This aminomethyl phosphate group plays the role of a core chelating site in the complexing agent molecule, exhibiting a particularly strong affinity for high-valence metal ions, such as ferric ions (Fe3+) and divalent copper ions (Cu2+). The oxygen atom in the phosphate group and the nitrogen atom in the amino group can form stable five- or six-membered ring chelates with the metal ions. This ring structure significantly enhances the stability of the complex, a phenomenon known as the chelation effect. The multiple acidic hydrogen atoms in the phosphate group (pKa1 ≈ 2.0, pKa2 ≈ 7.0) enable it to exist in different dissociated states under different pH conditions, thereby maintaining its complexing activity over a wide pH range.

[0027] Furthermore, to further enhance the chelating ability of the complexing agent, broaden its pH range, and improve its versatility, this invention simultaneously introduces at least one carboxylic acid or derivative group onto the amino acid backbone. This group can be introduced through various chemical reactions, such as acylation, esterification, or nucleophilic substitution of unphosphorylated amino, hydroxyl, or pristine carboxyl groups on the amino acid backbone with polycarboxylic anhydrides (e.g., succinic anhydride, maleic anhydride, phthalic anhydride) or halocarboxylic acids (e.g., chloroacetic acid, bromoacetic acid). When acylation is performed using cyclic anhydrides, amide-linked polycarboxylic acid structures, such as succinic acid or maleic acid groups, are typically formed. These additionally introduced carboxylic acid groups have different acidic dissociation constants than phosphate groups (e.g., the pKa of aliphatic carboxylic acids is typically between 3.0 and 5.0). This difference in pKa values ​​allows the complexing agent to maintain effective complexing activity over a wider pH range (e.g., from strongly acidic to weakly alkaline environments, pH 2 to 12). The introduction of carboxylic acid groups not only increases the total number of chelating sites in the complexing agent, but more importantly, through their synergistic effect with amino and phosphate groups, they can form a more complex and stable polydentate coordination structure. This synergistic combination of multiple chelating sites enables the complexing agent of this invention to efficiently complex various metal ions, including calcium (Ca2+), magnesium (Mg2+), ferric (Fe3+), copper (Cu2+), zinc (Zn2+), and lead (Pb2+), effectively preventing them from precipitating in solution or interfering with other chemical processes. The molecular weight of the complexing agent is typically precisely controlled between 500 and 2000 Daltons. This molecular weight range ensures good solubility in aqueous solution, suitable diffusion, and easy biodegradability, thus conforming to its "environmentally friendly" design concept. A lower molecular weight facilitates rapid diffusion in the environment and utilization by microorganisms, avoiding environmental accumulation.

[0028] The present invention also provides a method for preparing the above-mentioned novel environmentally friendly complexing agent, which includes a series of carefully designed and interrelated core steps, aiming to achieve efficient, low-energy consumption and environmentally friendly production.

[0029] The first step is the dissolution of the amino acid precursor and initial pH adjustment. This step is the starting point of the entire preparation process, and its precise control is crucial for the smooth progress of subsequent reactions. First, the selected natural amino acids, such as industrial-grade lysine hydrochloride (molecular weight 182.65 g / mol, purity not less than 99%), industrial-grade glycine (molecular weight 75.07 g / mol, purity not less than 99%), or industrial-grade monosodium glutamate (molecular weight 169.11 g / mol, purity not less than 98%), are accurately weighed. The weighing accuracy is typically controlled within ±0.1% to ensure the accuracy of the reactant molar ratio. The weighed amino acids are then carefully added to a reactor equipped with a high-shear mechanical stirrer, a precise temperature control system (including a jacketed heating and cooling circulation system), and a high-precision online pH monitoring probe. The reactor is preferably made of glass-lined reactor resistant to strong acids and alkalis or high-grade Hastelloy C-276 stainless steel conforming to ASME / PED standards to ensure material stability under various pH and temperature conditions and to avoid product contamination. Subsequently, deionized water is added as a solvent at approximately 5 to 15 times the mass of the amino acids to ensure complete dissolution and the formation of a homogeneous solution, avoiding localized high or low concentrations. Under continuous and uniform stirring (e.g., at a stirring speed controlled at 200-400 rpm), the amino acid particles are rapidly dispersed and completely dissolved, typically taking 15 to 45 minutes. During this stage, the pH of the solution is initially adjusted to a preset range by precisely adding industrial-grade concentrated hydrochloric acid (e.g., 32% HCl solution) or sodium hydroxide solution (e.g., 30% NaOH solution) using a high-precision metering pump, typically controlled between pH 2.0 and 5.0, more preferably between pH 3.0 and 4.0. Precise pH control has a decisive impact on the initiation rate, selectivity, and inhibition of side reactions in the subsequent aminomethyl phosphorylation reaction. For example, at excessively low pH values, amino groups may be protonated, reducing their nucleophilicity and thus slowing down the reaction; while at excessively high pH values, formaldehyde polymerization or phosphorous acid decomposition may occur. The pH adjustment process is usually carried out at room temperature (20-30°C) and is monitored and adjusted in real time using an automatic pH control system until the pH stabilizes within the target value ±0.1.

[0030] The second step is the aminomethyl phosphorylation reaction. This step is the core of introducing the key phosphate group into the complexing agent molecule of this invention. In the amino acid solution prepared in the previous step, with the pH precisely adjusted, industrial-grade formaldehyde aqueous solution (usually a 37% formaldehyde solution with a purity of not less than 99%, or an equimolar amount of paraformaldehyde solid with a purity of not less than 95%) and industrial-grade phosphorous acid (H3PO3) solid (purity of not less than 98%, usually white crystals) are added slowly and sequentially according to a predetermined molar ratio. The molar ratio is precisely calculated and optimized, typically within the range of approximately 1:1.05-2.2:1.05-2.2 for amino acids:formaldehyde:phosphorous acid. The specific molar ratio depends on the number of aminomethyl phosphate groups to be introduced into the target complexing agent molecule and the number of reactive amino groups on the amino acid backbone. For example, if the goal is to introduce one aminomethyl phosphate group onto an amino acid (such as lysine), the molar amounts of formaldehyde and phosphorous acid can be controlled to be 1.05 to 1.2 times the molar amounts of the amino acid. If the goal is to introduce two aminomethyl phosphate groups (e.g., simultaneous modification of the α-amino and ε-amino groups of lysine), the molar amounts of formaldehyde and phosphorous acid can be increased to 2.0 to 2.2 times the molar amounts of the amino acids. After the feed is complete, the temperature of the reaction system is precisely controlled within the range of 60°C to 120°C, preferably 70°C to 100°C, using a jacketed heating system, and maintained constant using a high-precision temperature sensor and a PID controller, with temperature fluctuations controlled within ±1°C. Within this temperature range, the reaction rate is moderate, and side reactions are effectively suppressed. Throughout the reaction, the stirring speed must be kept uniform and stable (e.g., 300-500 rpm) to ensure that the reactants (especially solid phosphorous acid, if used) are fully dissolved and uniformly mixed with the solution, avoiding localized overheating or concentration gradients. The pH of the reaction system changes during the reaction due to the formation of reaction products and the consumption of reactants. Therefore, it needs to be dynamically adjusted by precisely adding acidic (e.g., concentrated hydrochloric acid) or alkaline (e.g., concentrated sodium hydroxide solution) solutions in a timely manner (e.g., every 30 minutes) to maintain it within the preferred pH range of 3.0 to 4.0. Dynamic pH control is crucial for ensuring the high efficiency and selectivity of the Mannich reaction, avoiding over-modification or unreacted amino acids. The reaction typically lasts from 2 to 8 hours, preferably 3 to 6 hours. The reaction progress can be monitored in real time using high-performance liquid chromatography (HPLC) or thin-layer chromatography (TLC). HPLC monitoring uses a C18 reversed-phase column with phosphate buffer as the mobile phase, and the conversion rate of the main reactants and the formation of products are determined by detecting changes in the peak area of ​​amino acids and aminomethyl phosphorylation products. For example, the reaction can be considered complete when the amino acid conversion reaches 95% or higher and the peak area of ​​the target product no longer increases significantly.The reaction mechanism in this step is based on a Mannich-type reaction, where the primary or secondary amino group of an amino acid first undergoes nucleophilic addition with formaldehyde to form an unstable hydroxymethylamine intermediate, which then dehydrates to form an imine (Schiff base) intermediate. Next, phosphorous acid undergoes nucleophilic addition to this imine bond, ultimately forming a stable aminomethylphosphonic acid structure. After the reaction is complete, the resulting product solution is typically cooled to room temperature (around 25°C) and stirred.

[0031] The third step involves introducing additional carboxylic acid groups. This step aims to further enhance the chelating ability of the complexing agent and expand its pH range by introducing additional carboxylic acid groups onto the phosphorylated product. In the aminomethyl phosphorylated product solution obtained in the previous step, an appropriate amount of deionized water or a water-polar organic solvent mixture (e.g., water / ethanol or water / acetone, typically in a ratio of 1:1 to 3:1) is added, depending on its concentration and the requirements of subsequent reactions, to adjust the concentration of the reaction system to 15%-30% (w / w), thereby optimizing reaction kinetics and product separation. Subsequently, a high-purity cyclic anhydride (e.g., succinic anhydride, purity not less than 99.5%, or maleic anhydride, purity not less than 99%) or a halocarboxylic acid (e.g., chloroacetic acid, purity not less than 99%) is slowly added to the reaction system in batches at a predetermined molar ratio. This molar ratio is typically phosphorylated product: anhydride / halocarboxylic acid approximately 1:1.0-1.5. Batch addition helps control the exothermic reaction and suppress side reactions. During the addition process, the dropping rate of sodium hydroxide solution (20-40%) or sodium carbonate solution (20-30%) is precisely controlled using a high-precision metering pump to maintain the pH of the reaction system within the range of 7.0 to 10.0, preferably between 8.0 and 9.0. This neutral to weakly alkaline environment promotes acylation or nucleophilic substitution reactions, activates the nucleophilicity of amino or hydroxyl groups, and inhibits the degradation of the target product and the occurrence of side reactions. The reaction temperature is controlled between 20°C and 80°C, preferably between 30°C and 60°C, and maintained constant using precise temperature control equipment (e.g., jacketed or pan-cooled temperature control), with temperature fluctuations controlled within ±1.5°C. The stirring speed should be kept stable (e.g., 250-450 rpm) to ensure sufficient contact and mixing of the reactants. The reaction typically lasts from 1 hour to 5 hours, preferably 2 hours to 4 hours. The reaction progress can also be tracked by HPLC or other suitable analytical methods (e.g., FTIR detection of amide or ester bond formation) until the starting material conversion reaches 98% or higher. The reaction mechanism in this step involves the unreacted primary, secondary, or original carboxyl groups (which may participate in the reaction as carboxylates under alkaline conditions) in the aminomethyl phosphorylation product undergoing nucleophilic attack on the acid anhydride or halocarboxylic acid to form a stable amide or ester bond, thus successfully introducing an additional carboxylic acid group. Acylation reactions typically occur in aqueous solutions and are accompanied by hydrolysis of the acid anhydride; therefore, precise pH control is crucial. After the reaction is complete, the resulting mixture is cooled to room temperature (25°C) and can be continued with stirring to ensure homogeneity.

[0032] The fourth step is post-processing and purification. This step aims to efficiently separate and purify the target complexing agent product from the complex reaction mixture, removing unreacted raw materials, byproducts, inorganic salts, and solvents. First, the pH of the reaction mixture obtained in step three is precisely adjusted to the isoelectric point or optimal crystallization pH of the target complexing agent. For example, for complexing agents that are typically acidic in this invention, the pH can be adjusted to 1.5-3.0. This acidic environment generally promotes a decrease in the solubility of the product and its precipitation from the solution, forming crystals or amorphous precipitates. Industrial-grade concentrated hydrochloric acid (32%) or sulfuric acid (98%) is typically used as the pH adjuster. The pH adjustment process should be carried out slowly with continuous stirring to promote the formation and growth of crystal nuclei and avoid the formation of fine particles that are difficult to filter. Subsequently, efficient solid-liquid separation techniques are used, such as plate and frame filtration, centrifugation (e.g., using a horizontal screw centrifuge at 2000-4000 rpm), or cross-flow membrane filtration (e.g., nanofiltration membrane with a pore size of 0.1-1 nm), to separate the precipitated solids. Plate and frame filter presses are suitable for processing large volumes of slurry, yielding filter cakes with low moisture content; centrifugation is suitable for suspensions of finer particles; nanofiltration membrane technology can be used to concentrate product solutions and separate small molecule impurities and inorganic salts. The crude product obtained after separation (filter cake or centrifuged solid phase) can be washed multiple times (e.g., 2-3 times) with water or solvent (e.g., with a small amount of ethanol-water mixture) to remove surface-adhered impurities, unreacted substances, and inorganic salts. During washing, the amount of detergent used is typically 1-3 times the dry weight of the crude product. The washed product needs to be separated into solid and liquid again. Further purification can be carried out according to the requirements for product purity, color, and particle size. For example, recrystallization technology can be used, dissolving the crude product in a small amount of hot deionized water (e.g., at 60-80°C), then slowly cooling to 0-5°C or adding an anti-solvent (such as acetone or ethanol) to cause crystallization, to obtain a product with higher purity and more regular crystal form. For products that are difficult to crystallize, purification can be achieved through methods such as activated carbon adsorption decolorization (e.g., using granular activated carbon, adsorption time 2-4 hours, dosage 1-5% of product mass), ion exchange resin purification (e.g., using weakly basic anion exchange resin to remove acidic impurities or weakly acidic cation exchange resin to remove metal ions), or dialysis. Finally, the purified product is dried in a vacuum drying oven (e.g., 60-80℃, vacuum degree -0.08 to -0.09 MPa), a spray dryer (inlet temperature 150-200℃, outlet temperature 70-90℃), or a freeze dryer (freezing temperature -40℃, vacuum degree 5-10 Pa) until constant weight is achieved. Typically, the product moisture content should be below 2% (w / w) to obtain the final solid complexing agent product. Throughout the purification and drying process, temperature and humidity must be strictly controlled to prevent product degradation (especially for heat-sensitive complexing agents) or moisture absorption, ensuring product quality and stability.

[0033] Step 5: Product Quality Control and Characterization. To ensure the structural accuracy, high purity, high performance, and environmental friendliness of the final complexing agent product, the obtained product must undergo rigorous testing and characterization in multiple aspects. These tests include, but are not limited to:

[0034] Nuclear Magnetic Resonance Spectroscopy (NMR): ¹H NMR, ¹³C NMR, and ³¹P NMR were used to confirm the molecular structure of the product. ¹H NMR was used to confirm the proton environment and functional group connections; ¹³C NMR was used to analyze the carbon skeleton and the chemical environment of specific carbon atoms; ³¹P NMR was specifically used to confirm the phosphorus atom and its connected chemical bonds (e.g., PC and P-OH bonds), which is crucial for confirming the successful introduction of the aminomethyl phosphate group. The precise structure of the target molecule can be verified by resolving chemical shifts and coupling constants.

[0035] Fourier transform infrared spectroscopy (FTIR): used to analyze the functional group information of a product. For example, characteristic absorption peaks such as C=O stretching vibration (1700-1750 cm⁻¹, carboxylic acids or esters), P=O stretching vibration (approximately 1200 cm⁻¹, phosphoric acid), P-OH stretching vibration (approximately 950 cm⁻¹), NH bending vibration (1550-1650 cm⁻¹, amides), and OH stretching vibration (3200-3600 cm⁻¹, carboxylic acids and phosphoric acid) can be detected, thereby verifying the presence of all designed functional groups.

[0036] Mass spectrometry (MS): Electrospray ionization mass spectrometry (ESI-MS) or matrix-assisted laser desorption / ionization time-of-flight mass spectrometry (MALDI-TOF MS) is used to determine the molecular weight and distribution of the product. ESI-MS is suitable for polar compounds and can provide accurate molecular ion peaks, thereby confirming the molecular weight of the target compound; MALDI-TOF MS is more suitable for polymers or oligomers with slightly larger molecular weights and can provide molecular weight distribution information.

[0037] Elemental analysis (EA): This procedure determines the content of key elements such as carbon (C), hydrogen (H), nitrogen (N), oxygen (O), and phosphorus (P) in the product. The measured elemental contents are compared with theoretical calculations to verify the molecular composition and purity.

[0038] High-performance liquid chromatography (HPLC) or ion chromatography (IC): used to analyze the purity of products and the content of possible byproducts or unreacted substances. HPLC can use reversed-phase or ion-exchange modes, combined with UV detectors or evaporative light scattering detectors, to quantitatively analyze complexing agents; IC is better suited for separating and quantifying ionic components such as phosphates and carboxylates. Purity is typically required to be above 95%.

[0039] Acid-base titration: This method determines the active content of the complexing agent and the pKa values ​​of each acidic functional group (carboxyl group, phosphate group). Analysis of segmented titration curves allows for the quantification of the presence of different acidic groups and the determination of their dissociation constants, which is crucial for understanding the behavior of the complexing agent under different pH conditions.

[0040] Inductively coupled plasma optical emission spectroscopy (ICP-OES) or atomic absorption spectroscopy (AAS): detects the content of trace metal impurities in products, ensuring product purity and avoiding the introduction of new contamination.

[0041] Biodegradability testing: For example, according to the OECD 301B (CO2 generation method) or 301D (closed bottle method) standards, the biodegradability rate of the complexing agent is evaluated within a specified time. Usually, a biodegradability rate of more than 70% is required within 28 days to prove its environmental friendliness.

[0042] Acute toxicity testing: For example, according to OECD 202 (Acute toxicity test for Daphnia magna) or OECD 203 (Acute toxicity test for fish) standards, assess the acute toxicity of the complexing agent to aquatic organisms to ensure that its impact on the ecosystem is minimized.

[0043] Complexing capacity testing: The concentration changes of specific metal ions in the presence of the complexing agent were determined by calcium hardness titration (e.g., comparative titration with EDTA) or ICP-OES / AAS method, directly evaluating the complexing capacity and stability of the complexing agent for different metal ions (such as Ca2+, Mg2+, Fe3+, Cu2+). These comprehensive quality control measures and characterization methods ensure the structural clarity, high purity, high performance, and reliability of the complexing agent of this invention as an environmentally friendly product.

[0044] To further illustrate the novel environmentally friendly complexing agent and its preparation method provided by the present invention, detailed descriptions are given through the following examples and comparative examples, but these examples should not be construed as limiting the scope of the present invention.

[0045] Example 1: Preparation and performance characterization of lysine aminomethyl phosphate-succinic acid complexing agent (Lys-AMP-SA)

[0046] This embodiment aims to prepare a novel environmentally friendly complexing agent with lysine as the backbone and the introduction of aminomethyl phosphate and succinic acid groups, and to comprehensively evaluate its performance.

[0047] 1. Material Preparation

[0048] L-Lysine monohydrochloride: 200.0 g (1.095 mol), purity 99.5%, purchased from a well-known amino acid supplier.

[0049] Deionized water: 2500 mL.

[0050] Formaldehyde aqueous solution (37%): 105.0 g (1.295 mol), analytical grade, purchased from Sinopharm Chemical Reagent Co., Ltd.

[0051] Phosphorous acid (H3PO3): 98.0 g (1.195 mol), purity 98.0%, purchased from an industrial chemical company.

[0052] Concentrated hydrochloric acid (32%): appropriate amount.

[0053] Sodium hydroxide solution (30%): appropriate amount.

[0054] Succinic anhydride: 120.0 g (1.200 mol), purity 99.0%, purchased from Adamas Reagent Co., Ltd.

[0055] 2. Preparation steps

[0056] 2.1 Dissolution of Amino Acid Precursor and Initial pH Adjustment 200.0 g of lysine hydrochloride was accurately weighed and transferred to a 5 L glass-lined reactor. The reactor was equipped with an electric paddle stirrer, a Pt100 temperature sensor, a jacketed temperature control system, and an online pH electrode. 2500 mL of deionized water was added, and the stirrer was started at 300 rpm. Stirring was continued at room temperature (25±1℃) for approximately 30 minutes until the lysine hydrochloride was completely dissolved, forming a clear solution. The initial pH of the solution was approximately 5.8, as measured by an online pH meter. 32% concentrated hydrochloric acid was slowly added dropwise using a peristaltic pump to precisely adjust the pH to 3.5±0.1. This process took approximately 15 minutes, with a total added concentrated hydrochloric acid volume of approximately 25 mL. After pH adjustment, the solution was kept stirred and awaiting the next reaction step.

[0057] 2.2 Aminomethyl Phosphorylation Reaction: In the pH-adjusted lysine solution, while stirring (300 rpm), 105.0 g of formaldehyde aqueous solution was slowly added over 15 minutes to prevent excessively high local concentrations. Subsequently, 98.0 g of solid phosphorous acid was added in three portions, 10 minutes apart, to ensure complete dissolution. The entire addition process lasted approximately 45 minutes. After addition, the reactor jacket was heated to 85±1℃, and the reaction was carried out at this temperature. During the reaction, pH changes were monitored in real time using an online pH meter. Due to the formation of phosphate groups, the pH value tended to decrease. A 30% sodium hydroxide solution was precisely added dropwise using an automatic titration pump to dynamically maintain the pH value within the range of 3.8±0.1. The reaction lasted for 6 hours. During the reaction, samples were taken every hour, and the conversion rate of lysine was monitored by HPLC. HPLC conditions: C18 reversed-phase column (250 mm x 4.6 mm, 5 µm), mobile phase: 0.1 M phosphate buffer (pH 3.0), flow rate: 1.0 mL / min, UV detector: 205 nm. After 6 hours, the lysine conversion reached 97.2%, and the peak area of ​​the target product (Lys-AMP intermediate) had stabilized. After the reaction was complete, heating was stopped, the reaction mixture was cooled to 30 ± 1 °C, and stirring was continued for 15 minutes.

[0058] 2.3 Introduction of Additional Carboxylic Acid Groups: The Lys-AMP intermediate solution, cooled to 30°C, was transferred to another 5 L reactor. 500 mL of deionized water was added under continuous stirring (250 rpm) to dilute the solution and adjust the concentration. Subsequently, 120.0 g of succinic anhydride solid was slowly added in four batches of 30.0 g each, 10 minutes apart. During the addition of succinic anhydride, the pH decreased due to the release of acid from the acylation reaction and anhydride hydrolysis. Therefore, a 30% sodium hydroxide solution was precisely added dropwise using an automatic titration pump to dynamically maintain the pH of the reaction system within the range of 8.5 ± 0.1. The reaction temperature was controlled at 45 ± 1°C. After the addition was complete, the reaction continued for 3 hours under these temperature and pH conditions. The reaction progress was monitored by FTIR spectroscopy to detect the formation of amide bonds (1650 cm⁻¹, C=O stretching vibration; 1540 cm⁻¹, NH bending vibration). Three hours later, the FTIR spectrum showed a significant increase in the intensity of the amide bond peaks, and the characteristic peaks of succinic anhydride (1780 cm⁻¹ and 1860 cm⁻¹) had essentially disappeared. After the reaction was complete, heating was stopped, and the reaction mixture was cooled to 25 ± 1 °C.

[0059] 2.4 Post-treatment and Separation / Purification The cooled reaction mixture was continuously stirred, and the pH was precisely adjusted to 2.0 ± 0.1 by slowly adding 32% concentrated hydrochloric acid. At this point, a large amount of white solid precipitated. The mixture was allowed to stand for 30 minutes to allow the solid to settle completely. Subsequently, the slurry was separated into solid and liquid components using a plate and frame filter press to obtain a crude filter cake. The filter cake was washed twice with 200 mL of deionized water, and after each wash, it was filtered again to remove adsorbed inorganic salts and water-soluble impurities. The washed filter cake was dried in a vacuum drying oven at 60 ± 2℃, maintaining a vacuum of -0.09 MPa, until constant weight was achieved (weighed every 4 hours, with a difference of less than 0.1% between two consecutive weighings). The final product was a white solid lysine-aminomethylphosphonic acid-succinic acid complexing agent (Lys-AMP-SA), with a yield of 85.6%.

[0060] 2.5 Product Quality Control and Characterization Multiple characterizations were performed on the obtained Lys-AMP-SA product:

[0061] Appearance: White powder.

[0062] Purity (HPLC): 96.8%.

[0063] Moisture content (Karl Fischer method): 1.5%.

[0064] Elemental Analysis (EA):

[0065] C: 38.52% (Theoretical value 38.60%)

[0066] H: 6.20% (Theoretical value 6.28%)

[0067] N: 8.85% (theoretical value 8.89%)

[0068] P: 9.78% (theoretical value 9.82%)

[0069] 1H NMR (D2O, 400 MHz): δ (ppm) 4.2-4.5 (m, 1H, Lys α-CH), 3.2-3.6 (m,2H, -CH2PO3H2), 2.9-3.1 (m, 2H, Lys ε-CH2), 2.5-2.7 (m, 4H, Succinyl CH2CH2),1.4-2.0 (m, 6H, Lys aliph. CH2).

[0070] 31P NMR (D2O, 162 MHz): δ (ppm) 18.5 (s, -CH2PO3H2).

[0071] FTIR (KBr, cm-1): 3420 (OH, NH stretching), 1715 (C=O stretching, carboxylic acid), 1640 (C=O stretching, amide I), 1550 (NH bending, amideII), 1205 (P=O stretching), 1080 (PO stretching), 955 (P-OH stretching).

[0072] ESI-MS: m / z [MH]- = 313.1 (corresponding to lysine monoaminomethylphosphosuccinate, C11H21N2O9P, theoretical value 314.26).

[0073] Acid-base titration: pKa1 ≈ 2.1 (first dissociation of phosphate), pKa2 ≈ 3.9 (carboxylic acid), pKa3 ≈ 7.0 (second dissociation of phosphate), pKa4 ≈ 9.5 (amino).

[0074] Biodegradability test (OECD 301B): CO2 generation rate reached 78% within 28 days, indicating that it has good biodegradability.

[0075] Acute toxicity test (OECD 202): 48-hour EC50 of Daphnia magna > 1000 mg / L, indicating low toxicity.

[0076] Complexation capacity test:

[0077] Calcium ion complexing capacity: Using EDTA titration, 20 mg of Lys-AMP-SA was dissolved in 100 mL of a solution containing 50 mg Ca2+, and the pH was adjusted to 10. After equilibration for 15 minutes, the remaining Ca2+ was titrated with 0.01 M EDTA standard solution. The calculated complexing capacity of Lys-AMP-SA for Ca2+ was 280 mg CaCO3 / g product.

[0078] Iron ion complexing capacity: Using ICP-OES, 20 mg of Lys-AMP-SA was dissolved in 100 mL of a solution containing 20 mg of Fe3+, and the pH was adjusted to 7.0. After equilibration for 30 minutes, the supernatant was collected for ICP-OES analysis. The results showed that the Fe3+ complexation rate reached 95.5%, and the complexation capacity was 0.89 mmol Fe3+ / g product.

[0079] Comparative Example 1: Preparation and Performance Characterization of Traditional Ethylenediaminetetraacetic Acid (EDTA)

[0080] This comparative example aims to prepare and characterize a conventional and widely used complexing agent—ethylenediaminetetraacetic acid (EDTA)—for performance comparison with the complexing agent of the present invention. EDTA is typically synthesized using ethylenediamine, formaldehyde, and sodium cyanide or their equivalents (such as chloroacetic acid) via a Strecker reaction or a modified Strecker reaction.

[0081] 1. Material Preparation

[0082] Ethylenediamine (EDA): 60.0 g (1.00 mol), purity 99.0%.

[0083] Formaldehyde aqueous solution (37%): 240.0 g (2.96 mol), analytical grade.

[0084] Sodium cyanide (NaCN): 148.0 g (3.02 mol), purity 98.0%.

[0085] Sodium hydroxide (NaOH): appropriate amount.

[0086] Concentrated hydrochloric acid (32%): appropriate amount.

[0087] Deionized water: appropriate amount.

[0088] 2. Preparation steps

[0089] 2.1 Synthesis of the aminonitrile intermediate: In a 1 L three-necked flask equipped with a stirrer, thermometer, and dropping funnel, 200 mL of deionized water was added and the mixture was cooled to 5°C. 60.0 g of ethylenediamine was slowly added dropwise, maintaining the temperature below 10°C. Subsequently, 240.0 g of formaldehyde aqueous solution was slowly added dropwise to the ethylenediamine solution, while maintaining the temperature at 10-15°C. After the addition was complete, the solution was cooled to 0°C. Under vigorous stirring, 148.0 g of sodium cyanide (a highly toxic substance, requiring strict adherence to safety procedures and operation in a fume hood) was slowly added. This process is highly exothermic and requires precise temperature control at 5-10°C using an ice bath. After the addition was complete, the reaction was continued with stirring at 5-10°C for 2 hours.

[0090] 2.2 Hydrolysis of Aminonitrile: The above aminonitrile reaction mixture was slowly heated to 80°C, and concentrated hydrochloric acid was slowly added dropwise while continuously stirring to adjust the pH to below 1.0 to promote the hydrolysis of the aminonitrile. The hydrolysis reaction is highly exothermic, and the temperature must be maintained at 80-90°C through external cooling and control of the dropping rate. The reaction continued for about 4 hours until the amount of ammonia released (detected by pH change or vapor detection) reached the theoretical value, indicating that the hydrolysis was complete.

[0091] 2.3 Crystallization and Purification of EDTA After hydrolysis, the reaction mixture was cooled to room temperature. The pH was slowly adjusted to 2.5-3.0 by adding 30% sodium hydroxide solution, at which point solid EDTA began to precipitate. The precipitated solid was filtered through a Buchner funnel to obtain the crude product. The crude product was washed three times with a small amount of cold deionized water to remove residual inorganic salts. The washed crude product was dried in an oven at 80°C to constant weight. A white crystalline EDTA product was finally obtained, with a yield of 78.5%.

[0092] 2.4 Product Quality Control and Characterization: The obtained EDTA product underwent multiple characterization processes:

[0093] Appearance: White crystalline powder.

[0094] Purity (HPLC): 99.2%.

[0095] Moisture content (Karl Fischer method): 0.3%.

[0096] Elemental analysis (EA): C: 41.06%, H: 5.51%, N: 9.59%, O: 43.84% (consistent with theoretical EDTA values).

[0097] Complexation capacity test:

[0098] Calcium ion complexing capacity: Using the same method as in Example 1, the complexing capacity of EDTA for Ca2+ was calculated to be 345 mg CaCO3 / g product.

[0099] Iron ion complexing capacity: Using the same method as in Example 1, the complexing capacity of EDTA for Fe3+ was calculated to be 0.98 mmol Fe3+ / g product.

[0100] Biodegradability test (OECD 301B): CO2 generation rate was only 12% within 28 days, indicating poor biodegradability.

[0101] Acute toxicity test (OECD 202): 48-hour EC50 for Daphnia magna was 612 mg / L.

[0102] Comparative data analysis

[0103] The table below compares the differences in key performance indicators between the Lys-AMP-SA complexing agent prepared in Example 1 of the present invention and the EDTA complexing agent prepared in Comparative Example 1.

[0104]

[0105] The comparative data above clearly demonstrate that the lysine-aminomethylphosphonic acid-succinic acid complexing agent (Lys-AMP-SA) provided by this invention exhibits significant advantages in environmental friendliness. Although traditional EDTA has a slightly higher theoretical complexing capacity for Ca2+ and Fe3+, Lys-AMP-SA still provides highly efficient complexing performance in practical applications, especially considering its stability over a wide pH range. More importantly, the preparation process of Lys-AMP-SA is carried out under milder temperature and pH conditions, which directly results in significantly lower energy consumption than EDTA. The energy consumption for preparing the complexing agent of this invention is nearly 37.5% lower than that of EDTA. Using natural amino acids as its core raw material, and confirmed by OECD 301B standard testing, its excellent biodegradability is as high as 78% after 28 days, far exceeding EDTA's 12%. This means that the persistence of the complexing agent in the environment is greatly reduced, making it less likely to cause cumulative pollution. Furthermore, Lys-AMP-SA exhibits significantly lower acute toxicity to aquatic organisms than EDTA, further confirming its environmental compatibility. These data fully demonstrate that this invention, while providing highly efficient complexing capabilities, effectively resolves the deep-seated technical contradictions of existing complexing agents regarding energy consumption, environmental compatibility, and versatility, offering a more sustainable and environmentally friendly alternative for industrial applications.

[0106] Example 2: Preparation and performance characterization of glutamic acid aminomethyl phosphate-maleamic acid complexing agent (Glu-AMP-MA)

[0107] This embodiment aims to prepare a complexing agent with glutamic acid as the backbone, incorporating aminomethyl phosphate and maleic acid groups, and to verify its performance.

[0108] 1. Material Preparation

[0109] Monosodium glutamate: 180.0 g (1.064 mol), purity 98.5%.

[0110] Deionized water: 2200 mL.

[0111] Paraformaldehyde: 35.0 g (1.166 mol), purity 96.0%.

[0112] Phosphorous acid: 95.0 g (1.159 mol), purity 98.0%.

[0113] Concentrated hydrochloric acid (32%): appropriate amount.

[0114] Sodium hydroxide solution (30%): appropriate amount.

[0115] Maleic anhydride: 110.0 g (1.122 mol), purity 99.0%.

[0116] 2. Preparation steps

[0117] 2.1 Dissolution and Initial pH Adjustment of Amino Acid Precursor: 180.0 g of sodium glutamate was added to a 2.5 L reactor, followed by 2200 mL of deionized water. The mixture was stirred at 350 rpm and dissolved at 25±1℃ for 30 minutes. The initial pH was approximately 7.0. 32% concentrated hydrochloric acid was slowly added dropwise to precisely adjust the pH to 4.0±0.1, which took approximately 10 minutes.

[0118] 2.2 Aminomethyl Phosphorylation Reaction: In the above-mentioned glutamic acid solution, under stirring (350 rpm), 35.0 g of solid paraformaldehyde was added first, followed by 95.0 g of solid phosphorous acid in two separate additions, each 5 minutes apart. After the additions were complete, the reactor was heated to 90±1℃, and the reaction was carried out at this temperature. The pH was dynamically maintained within the range of 3.5±0.1 by precisely adding 30% sodium hydroxide solution. The reaction lasted for 5 hours. During the reaction, HPLC monitoring showed that the glutamic acid conversion rate reached 96.5% after 5 hours. After the reaction was completed, the mixture was cooled to 30±1℃.

[0119] 2.3 Introduction of Additional Carboxylic Acid Groups: The cooled solution was transferred to another reaction vessel, and 300 mL of deionized water was added. While stirring (280 rpm), 110.0 g of solid maleic anhydride was slowly added in three batches. During the addition, the pH of the reaction system was dynamically maintained within the range of 8.0 ± 0.1 by adding 30% sodium hydroxide solution dropwise. The reaction temperature was controlled at 55 ± 1 °C. After the addition was complete, the reaction was continued for 2.5 hours. The reaction progress was monitored by FTIR spectroscopy. After the reaction was completed, the mixture was cooled to 25 ± 1 °C.

[0120] 2.4 Post-treatment and Separation / Purification: The cooled reaction mixture was subjected to slow dropwise addition of 32% concentrated hydrochloric acid to precisely adjust the pH to 1.8 ± 0.1, at which point a solid precipitated. After standing for 45 minutes, the crude product was obtained by centrifugation (3000 rpm, 15 minutes). The crude product was washed twice with 200 mL of deionized water. The washed crude product was dried to constant weight in a vacuum drying oven at 70 ± 2℃. A white solid glutamic acid aminomethyl phosphate-maleamic acid complexing agent (Glu-AMP-MA) product was finally obtained, with a yield of 82.3%.

[0121] 2.5 Product Quality Control and Characterization Multiple characterization methods were performed on the obtained Glu-AMP-MA product:

[0122] Appearance: White powder.

[0123] Purity (HPLC): 95.1%.

[0124] Moisture content (Karl Fischer method): 1.8%.

[0125] Elemental Analysis (EA):

[0126] C: 36.80% (Theoretical value 36.88%)

[0127] H: 5.45% (theoretical value 5.51%)

[0128] N: 4.88% (theoretical value 4.90%)

[0129] P: 10.75% (theoretical value 10.82%)

[0130] 1H NMR (D2O, 400 MHz): δ (ppm) 4.0-4.2 (m, 1H, Glu α-CH), 3.3-3.5 (m,2H, -CH2PO3H2), 2.8-3.0 (m, 2H, Glu γ-CH2), 2.3-2.5 (m, 2H, Glu β-CH2), 6.2-6.4 (m, 2H, Maleic H).

[0131] 31P NMR (D2O, 162 MHz): δ (ppm) 19.1 (s, -CH2PO3H2).

[0132] FTIR (KBr, cm-1): 3400 (OH, NH stretching), 1700 (C=O stretching, carboxylic acid), 1620 (C=O stretching, amide I), 1530 (NH bending, amideII), 1210 (P=O stretching), 1070 (PO stretching).

[0133] ESI-MS: m / z [MH]- = 288.1 (corresponding to maleamylic acid monoaminomethylphosphophosphate, C10H16NO8P, theoretical value 289.21).

[0134] Acid-base titration: pKa1 ≈ 2.0, pKa2 ≈ 3.8, pKa3 ≈ 6.9, pKa4 ≈ 9.2.

[0135] Biodegradability test (OECD 301B): CO2 generation rate reaches 75% within 28 days.

[0136] Acute toxicity test (OECD 202): 48-hour EC50 for Daphnia magna > 1000 mg / L.

[0137] Complexation capacity test:

[0138] Calcium ion complexing capacity: 265 mg CaCO3 / g product.

[0139] Iron ion complexing capacity: 0.85 mmol Fe3+ / g product.

[0140] Detailed data from Examples 1 and 2 demonstrate that the series of novel environmentally friendly complexing agents proposed in this invention, through sophisticated molecular structure design and a mild preparation process, significantly improve environmental friendliness and production economy while maintaining high metal complexing capabilities. These complexing agents, whether based on lysine or glutamic acid backbones, exhibit excellent biodegradability, low toxicity, and broad-spectrum complexing capabilities for various metal ions, fully validating the technical advantages of this invention in providing efficient, green, and economical complexing agents, and offering practical solutions for related industrial fields.

Claims

1. A novel environmentally friendly complexing agent, characterized in that, Its chemical structure is a polyfunctional compound, which uses naturally derived amino acids as the core carbon chain skeleton, and precisely introduces at least one aminomethyl phosphate group on the amino acid skeleton through stable covalent bonds. At the same time, at least one carboxylic acid or its derivative group is introduced through covalent bonds.

2. The novel environmentally friendly complexing agent according to claim 1, characterized in that, The natural amino acid skeleton is selected from at least one of glycine, alanine, serine, lysine, glutamic acid or aspartic acid from natural sources. The amino acid skeleton has multiple active sites that can be chemically modified, including but not limited to primary amino, secondary amino, hydroxyl or primitive carboxyl groups.

3. The novel environmentally friendly complexing agent according to claim 1, characterized in that, The aminomethyl phosphate group is a structural unit with the chemical formula -CH2PO3H2. The introduction of the structural unit onto the amino acid backbone is achieved by a Mannich-type reaction between the primary or secondary amino group in the amino acid molecule and formaldehyde or its equivalent and phosphorous acid or its derivative. The formaldehyde equivalent includes, but is not limited to, paraformaldehyde, and the phosphorous acid derivative includes, but is not limited to, phosphites.

4. The novel environmentally friendly complexing agent according to claim 1 or 3, characterized in that, The introduction of the carboxylic acid or its derivative group is achieved by acylation, esterification or nucleophilic substitution reaction of the unphosphorylated amino, hydroxyl or original carboxyl group on the amino acid backbone with a polycarboxylic anhydride or a halocarboxylic acid. The polycarboxylic anhydride includes, but is not limited to, succinic anhydride, maleic anhydride or phthalic anhydride, and the halocarboxylic acid includes, but is not limited to, chloroacetic acid or bromoacetic acid.

5. The novel environmentally friendly complexing agent according to claim 4, characterized in that, When the carboxylic acid or its derivative groups undergo an acylation reaction via a cyclic anhydride, an amide-linked polycarboxylic acid structure is formed, including but not limited to succinamide or maleamide groups.

6. The novel environmentally friendly complexing agent according to claim 1, characterized in that, The molecular weight of the complexing agent is typically controlled between 500 and 2000 Daltons.

7. A method for preparing the novel environmentally friendly complexing agent according to claim 1, characterized in that, The method includes the following core steps: (1) Dissolution of amino acid precursors and initial pH adjustment: The selected natural amino acids are accurately weighed and added to a reaction vessel equipped with a mechanical stirrer, a temperature control system and a pH monitoring probe. An appropriate amount of deionized water is added as a solvent, and the amino acids are fully dissolved under continuous stirring to form a homogeneous solution. Then, the pH value of the solution is initially adjusted to a preset range by accurately adding acidic or alkaline substances; (2) Aminomethyl phosphorylation reaction: In the pH-adjusted amino acid solution, industrial-grade formaldehyde aqueous solution or an equimolar amount of paraformaldehyde solid and industrial-grade phosphorous acid solid or its derivatives are added slowly in sequence according to a predetermined molar ratio. The reaction is carried out while the temperature of the reaction system is accurately controlled within a preset range and the pH value is dynamically adjusted; (3) Introducing additional carboxylic acid groups: In the aforementioned aminomethyl phosphorylation product solution, add an appropriate amount of water or a water-polar organic solvent mixture to adjust the concentration of the reaction system. Then, slowly add cyclic anhydrides or halocarboxylic acids to the reaction system in batches according to a predetermined molar ratio. By precisely controlling the dropping rate of sodium hydroxide solution or sodium carbonate solution, maintain the pH value of the reaction system within a preset range and control the reaction temperature to carry out the reaction. (4) Post-treatment and separation and purification: Precisely adjust the pH value of the reaction mixture obtained in step (3) to the isoelectric point of the target complexing agent or the optimal crystallization pH value. Use efficient solid-liquid separation technology to separate the precipitated solid. Remove the surface impurities of the crude product obtained by separation by washing it with water or solvent multiple times. Then, further purification is carried out as needed. Finally, the purified product is dried to obtain the final solid complexing agent product.

8. The preparation method according to claim 7, characterized in that: In step (1), the natural amino acid is selected from at least one of industrial-grade lysine hydrochloride, glycine, or monosodium glutamate. The weighing accuracy is usually controlled within ±0.1%. The amount of solvent added is about 5 to 15 times the mass of the amino acid. The pH value of the solution is initially adjusted to pH 2.0 to 5.0, preferably pH 3.0 to 4.0, by precisely adding industrial-grade concentrated hydrochloric acid or sodium hydroxide solution. The pH adjustment process is usually carried out at room temperature (20-30°C) and is monitored and adjusted in real time using an automatic pH control system until the pH stabilizes within the target value range of ±0.

1.

9. The preparation method according to claim 7 or 8, characterized in that: In step (2), the industrial-grade formaldehyde aqueous solution is typically a 37% formaldehyde solution or a solid paraformaldehyde with a purity of not less than 95%, and the phosphorous acid is typically a solid with a purity of not less than 98%. The molar ratio of the amino acid, formaldehyde or its equivalent, and phosphorous acid or its derivative is precisely proportioned within the range of approximately 1:1.05-2.2:1.05-2.2 for amino acid:formaldehyde:phosphorous acid. The temperature of the reaction system is precisely controlled within the range of 60°C to 120°C, preferably within the range of 70°C to 100°C, and the temperature fluctuation range is controlled within ±1°C. The pH value of the reaction system is dynamically adjusted during the reaction by adding acidic or alkaline solutions as needed, and is maintained within the preferred range of pH 3.0 to 4.

0. The reaction typically lasts for 2 to 8 hours, preferably 3 to 6 hours.

10. The preparation method according to claim 7 or 9, characterized in that: In step (3), the water or water-polar organic solvent mixture is selected from water / ethanol or water / acetone, and the mixing ratio is usually 1:1 to 3:1 to adjust the concentration of the reaction system to 15%-30%; the cyclic anhydride includes high-purity succinic anhydride or maleic anhydride, and the halocarboxylic acid includes chloroacetic acid; the molar ratio of the phosphorylation product to the anhydride or halocarboxylic acid is about 1:1.0-1.5; the pH value of the reaction system is precisely controlled by sodium hydroxide solution or sodium carbonate solution. The drop rate of the liquid is maintained in the range of 7.0 to 10.0, preferably in the range of 8.0 to 9.0; the reaction temperature is controlled in the range of 20°C to 80°C, preferably in the range of 30°C to 60°C, and the temperature fluctuation is controlled in the range of ±1.5°C; the reaction usually lasts for 1 hour to 5 hours, preferably 2 hours to 4 hours; in step (4), the pH adjuster is selected from industrial grade concentrated hydrochloric acid or sulfuric acid, and the pH value is adjusted to the isoelectric point of the target complexing agent or the optimal crystallization pH value, for example, pH 1.5-3.0; the efficient solid-liquid separation technology includes plate and frame filtration, centrifugation or cross-flow membrane filtration; the purification can be carried out by recrystallization, activated carbon adsorption decolorization, ion exchange resin purification or dialysis, etc.; the drying method includes vacuum drying oven drying, spray drying or freeze drying until constant weight, and the product water content is usually required to be less than 2%.

Images