Compound heavy metal chelating agent, its preparation method and application

Abstract

The application relates to the technical field of mercury removal, in particular to a compound heavy metal chelating agent and a preparation method and application thereof. The preparation method of the compound heavy metal chelating agent comprises the following steps: mixing N-dithiocarboxyl-amino phenyl formic acid, cyclohexyl-3,5-diene-1,2-dicarboxylic acid solution, propionic acid solution and sodium hydroxide solution, stirring until completely dissolved, and then completing evaporation crystallization after standing, and separating and purifying the precipitated chelating agent. The compound reagent formed by mixing N-dithiocarboxyl-amino phenyl formic acid, cyclohexyl-3,5-diene-1,2-dicarboxylic acid, propionic acid and proper sodium hydroxide has better chelating absorption effect on heavy metal Hg in natural gas wastewater, and the formed chelate is very stable and is not easy to decompose.

Description

Technical Field

[0001] This invention relates to the field of mercury removal technology, and in particular to compound heavy metal chelating agents, their preparation methods, and applications. Background Technology

[0002] The treatment of high levels of residual heavy metals (Hg) in wastewater from natural gas processing has always been a key focus and challenge in environmental treatment. Mercury pollutes the environment in many ways, including its volatility, mobility, and bioaccumulation, posing a significant threat to human survival and development. Currently, the sulfur-impregnated activated carbon method is used to treat high-mercury feedstock gas and wastewater from natural gas processing. However, this method suffers from problems such as difficulty in determining the appropriate dosage of reagents, challenges in flocculation and sedimentation, and high levels of residual mercury, failing to achieve true mercury removal. Furthermore, over time, Hg, being a heavy metal, typically precipitates from the adsorbent as divalent ions, leading to severe environmental pollution.

[0003] While there are examples of using chelation technology to address the large-scale enrichment of Hg metal in wastewater, research and analysis show that commercially available heavy metal chelating agents such as DTC, TMT, and PEI can only temporarily solve the problem of Hg purification. Due to the molecular instability of these products, Hg ions gradually dissociate from them through chemical adsorption. The amount of Hg released increases with the increase of the gradient concentration in the reaction system, so the reliability of existing technologies is very low.

[0004] Therefore, there is an urgent need for a heavy metal chelating agent that has a strong chelating effect, produces stable chelates that do not leach harmful Hg metals in the reverse direction, and is itself environmentally friendly. Summary of the Invention

[0005] To address the aforementioned problems in the prior art, this invention provides a compound heavy metal chelating agent, its preparation method, and its application.

[0006] Based on this, the present invention has the following technical solution:

[0007] In a first aspect, the present invention provides a method for preparing a compound heavy metal chelating agent, comprising: mixing N-dithiocarboxy-aminophenylcarboxylic acid, cyclohexyl-3,5-diene-1,2-dicarboxylic acid solution, propionic acid solution and sodium hydroxide solution, stirring until completely dissolved and allowed to stand to complete evaporation and crystallization, and separating and purifying the precipitated chelating agent.

[0008] According to the present invention, a method for preparing a compound heavy metal chelating agent is provided, wherein the mass ratio of N-dithiocarboxy-aminophenylcarboxylic acid, cyclohexyl-3,5-diene-1,2-dicarboxylic acid and propionic acid is (4-5):2:1.

[0009] According to the preparation method of a compound heavy metal chelating agent provided by the present invention, the mixing temperature is 50~60 degrees Celsius.

[0010] According to a method for preparing a compound heavy metal chelating agent provided by the present invention, in the cyclohexyl-3,5-diene-1,2-dicarboxylic acid solution, the mass ratio of cyclohexyl-3,5-diene-1,2-dicarboxylic acid powder to water is 1:(8~9.5).

[0011] According to a method for preparing a compound heavy metal chelating agent provided by the present invention, the concentration of the propionic acid solution is 20-25 wt%.

[0012] According to a method for preparing a compound heavy metal chelating agent provided by the present invention, the concentration of the sodium hydroxide solution is 70-80 wt%.

[0013] According to a method for preparing a compound heavy metal chelating agent provided by the present invention, the method for preparing N-dithiocarboxy-aminophenylcarboxylic acid includes: dissolving aminophenylcarboxylic acid in water at 50-60 degrees Celsius, then cooling the solution to 25-30 degrees Celsius, and then adding carbon disulfide dropwise to the cooled aminophenylcarboxylic acid solution to carry out the reaction. After the reaction is completed, N-dithiocarboxy-aminophenylcarboxylic acid is obtained.

[0014] Secondly, the present invention provides a compound heavy metal chelating agent, which is prepared by the above-mentioned method for preparing compound heavy metal chelating agents.

[0015] Thirdly, the present invention provides the application of the above-mentioned compound heavy metal chelating agent in mercury removal.

[0016] According to the application of the compound heavy metal chelating agent provided by the present invention in mercury removal, the dosage of the compound heavy metal chelating agent in mercury-containing wastewater is 5-15 g / L, and the concentration of mercury ions in the mercury-containing wastewater is 50-150 mg / L.

[0017] The compound heavy metal chelating agent, its preparation method, and its application provided by this invention, formed by mixing N-dithiocarboxy-aminophenylcarboxylic acid, cyclohexyl-3,5-diene-1,2-dicarboxylic acid, propionic acid, and an appropriate amount of sodium hydroxide, has a better chelation and absorption effect on heavy metal Hg in natural gas wastewater. Moreover, the chelate formed is very stable and not easily decomposed. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0019] Figure 1 This is the carbon NMR spectrum of the compound metal chelating agent in Example 1 of the present invention.

[0020] Figure 2 This is the hydrogen nuclear magnetic resonance spectrum of the compound metal chelating agent in Example 1 of the present invention.

[0021] Figure 3 This is a schematic diagram of the stable spatial structure of the compound metal chelating agent in Example 1 provided by the present invention. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0023] In a first aspect, the present invention provides a method for preparing a compound heavy metal chelating agent, comprising: mixing N-dithiocarboxy-aminophenylcarboxylic acid, cyclohexyl-3,5-diene-1,2-dicarboxylic acid solution, propionic acid solution and sodium hydroxide solution, stirring until completely dissolved and allowed to stand to complete evaporation and crystallization, and separating and purifying the precipitated chelating agent.

[0024] In this invention, the structural formulas of N-dithiocarboxy-aminophenylcarboxylic acid, cyclohexyl-3,5-diene-1,2-dicarboxylic acid solution, and propionic acid are shown below:

[0025] .

[0026] This invention discovers that the N, -COO-, and -CSS- groups contained in N-dithiocarboxy-aminophenylcarboxylic acid, cyclohexyl-3,5-diene-1,2-dicarboxylic acid, and propionic acid can all react with heavy metal ions (Hg). 2+A highly stable coordination structure system is formed. Specifically, not only do the effective electron pairs provided by these molecules coordinate with mercury ions, but the sodium salt formed by the three molecules also forms large-area clusters between mercury ions in aqueous solution. This near-cage-like clustering effect between molecules, under the polydentate coordination state between molecules and mercury ions, further reduces the intermolecular distance, and mercury ions are adsorbed in a "multifaceted" manner. Thus, through strong electrostatic interactions and electronic effects, the coordination chelation effect strengthens the binding of mercury ions. These synergistic effects induced by strong inductive and electrostatic forces ensure that heavy metal mercury ions are in a stable chemical state in the chelating agent. Through energy optimization calculations using the applicable force basis set: B3LYP / 6-311G+, it can be seen that during the solvation reaction, the dissolution free energy of the mercury-containing chelate compound in the system is at a very low value, taking the value of -3.72 kcal / mol. In chelation systems, stable cluster structures prevent contact space with strong oxidants, acidic small molecules in the environment, and other impurities. Therefore, the chelates formed have significant antioxidant and acid corrosion resistance. Furthermore, the multidentate ligand structural units enhance molecular stability. The chelates do not change with environmental changes and almost never allow heavy metal mercury to form a reverse shedding state.

[0027] According to a preferred embodiment of the present invention, the mass ratio of N-dithiocarboxy-aminophenylcarboxylic acid, cyclohexyl-3,5-diene-1,2-dicarboxylic acid and propionic acid is (4-5):2:1.

[0028] According to a preferred embodiment of the present invention, the mixing temperature is 50-60 degrees Celsius.

[0029] According to a preferred embodiment of the present invention, in the cyclohexyl-3,5-diene-1,2-dicarboxylic acid solution, the mass ratio of cyclohexyl-3,5-diene-1,2-dicarboxylic acid powder to water is 1:(8~9.5).

[0030] According to a preferred embodiment of the present invention, the concentration of the propionic acid solution is 20-25 wt%.

[0031] According to a preferred embodiment of the present invention, the concentration of the sodium hydroxide solution is 70-80 wt%.

[0032] According to a preferred embodiment of the present invention, the preparation method of N-dithiocarboxy-aminophenylcarboxylic acid includes: dissolving aminophenylcarboxylic acid in water at 50-60 degrees Celsius, then cooling the solution to 25-30 degrees Celsius, and then adding carbon disulfide dropwise to the cooled aminophenylcarboxylic acid solution to carry out the reaction. After the reaction is completed, N-dithiocarboxy-aminophenylcarboxylic acid is obtained.

[0033] According to a preferred embodiment of the present invention, the preparation method of the compound heavy metal chelating agent includes the following steps:

[0034] Aminophenylcarboxylic acid powder was added to the reactor and dissolved in distilled water. The temperature was raised to 50-60°C using an electric heater, then cooled to 25-30°C. Dithiocarboxyl groups were introduced using the branching effect of CS2. This step mainly involved adding CS2 solvent dropwise to the cooled aminophenylcarboxylic acid solution, controlling the reaction rate, with a total reaction time of 25-35 minutes. After the reaction was complete, the reaction temperature was raised to 50-60°C and maintained at a low temperature. 20-25 wt% propionic acid solution and 70-80 wt% NaOH alkaline solution were added to the reactor. After thorough stirring, cyclohexyl-3,5-diene-1,2-dicarboxylic acid powder was mixed with distilled water at a ratio of 1:8-9.5 (mass ratio) to form a solution. Once the temperature returned to 30°C, the solution was added to the reactor as before. After thorough mixing, the liquid phase was cooled for 30-35 minutes before crystallization.

[0035] As a preferred option, the ratio of N-dithiocarboxy-aminophenylcarboxylic acid: cyclohexyl-3,5-diene-1,2-dicarboxylic acid: propionic acid = (4-5): 2: 1 (mass ratio) is the most effective in forming a mercury removal chelating agent.

[0036] Secondly, the present invention provides a compound heavy metal chelating agent, which is prepared by the above-mentioned method for preparing compound heavy metal chelating agents.

[0037] Thirdly, the present invention provides the application of the above-mentioned compound heavy metal chelating agent in mercury removal.

[0038] According to a preferred embodiment of the present invention, the dosage of the compound heavy metal chelating agent in mercury-containing wastewater is 5-15 g / L, and the concentration of mercury ions in the mercury-containing wastewater is 50-150 mg / L.

[0039] To further illustrate the technical solution of the present invention, the present invention provides the following specific embodiments and comparative examples.

[0040] Unless otherwise specified, all raw materials used in the examples and comparative examples are commercially available conventional raw materials, and the technical means used are conventional means well known to those skilled in the art.

[0041] Example 1

[0042] This embodiment provides a compound metal chelating agent, the preparation method of which includes the following steps:

[0043] Aminophenylcarboxylic acid powder was added to a reactor and dissolved in distilled water. The solution was heated to 50-60°C using an electric heater, then cooled to 25-30°C. Dithiocarboxyl groups were introduced using the branching effect of CS2. This step mainly involved adding CS2 solvent dropwise to the cooled aminophenylcarboxylic acid solution, controlling the reaction rate, with a total reaction time of 25-35 minutes. After the reaction was complete, the reaction temperature was raised to 50-60°C and maintained at a low temperature. 20-25 wt% propionic acid solution and 70-80 wt% NaOH alkaline solution were added to the reactor. After thorough stirring, cyclohexyl-3,5-diene-1,2-dicarboxylic acid powder was mixed with distilled water at a ratio of 1:8-9.5 (mass ratio) to form a solution. Once the temperature returned to 30°C, the solution was added to the reactor as before. After thorough mixing, the liquid phase was cooled for 30-35 minutes before crystallization, completing the preparation of the complex metal chelating agent.

[0044] The carbon NMR spectrum of the compound metal chelating agent is shown below. Figure 1 The proton NMR spectrum of the compound metal chelating agent is shown in [reference needed]. Figure 2 .

[0045] Using quantum chemical calculation software, the basis set, also employing density functional theory (B3LYP / 6-311G+), yields a total molecular potential energy of 106.5585 kcal / mol. However, after forming a stable cluster structure with propionic acid and cyclohexyl-3,5-diene-1,2-dicarboxylic acid, as... Figure 3 As shown, its total molecular potential energy is 1.2638 kcal / mol. It can be seen that the potential energy decreases sharply during the process of development from a monolayer to a multi-molecular cluster, indicating that the system will become more stable after contact with mercury ions.

[0046] Comparative Example 1

[0047] This comparative example provides a commercially available chelating agent, EDTA-2Na, supplied by Shandong Wantong Chemical Co., Ltd.

[0048] Comparative Example 2

[0049] This comparative example provides a commercially available chelating agent, PEI, supplied by Shandong Wantong Chemical Co., Ltd.

[0050] Comparative Example 3

[0051] This comparative example provides a commercially available chelating agent, DTC-1, provided by Shanghai Puyi Environmental Protection Technology Co., Ltd.

[0052] Comparative Example 4

[0053] This comparative example provides a commercially available chelating agent, DTC-2, provided by Shanghai Puyi Environmental Protection Technology Co., Ltd.

[0054] Test case

[0055] The compound metal chelating agent prepared in the above embodiments and the commercially available chelating agent provided in the comparative example were respectively subjected to heavy metal chelation experiments.

[0056] Heavy metal selection: 100 ml of natural gas treatment wastewater containing mercury ions, with a concentration of 100 mg / L. Heavy metal concentration detection and analysis were performed using liquid chromatography-ion chromatography.

[0057] The chelation experiment was conducted as follows: 1 gram of chelating agent (the compound metal chelating agent prepared in the examples and the commercially available chelating agents EDTA-2Na, PEI, DTC-1, and DTC-2 provided in Comparative Examples 1-4) was added to each heavy metal pollutant. After stirring and allowing the chelation reaction to proceed for 25 minutes, the concentration of residual free heavy metal ions in the solution was measured. Each group of experiments was repeated 5 times, and the average value was taken. The results are shown in Table 1.

[0058] Table 1. Chelating Effects of Various Chelating Agents on Heavy Metals

[0059]

[0060] For the next 30 days, the concentration of residual free heavy metal ions in the solutions of the treatment groups in Table 1 was tested once a day at a fixed time. For 30 consecutive days, the change in the concentration of free heavy metals in each group of solutions was less than 0.001 mg / L, which proves that the heavy metal chelates formed by the chelating agent provided by the present invention have extremely high stability.

[0061] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a compound heavy metal chelating agent, characterized in that, include: N-dithiocarboxy-aminophenylcarboxylic acid, cyclohexyl-3,5-diene-1,2-dicarboxylic acid solution, propionic acid solution and sodium hydroxide solution were mixed, stirred until completely dissolved and allowed to stand to complete evaporation and crystallization, and the precipitated chelating agent was separated and purified. The preparation method of N-dithiocarboxy-aminophenylcarboxylic acid includes: dissolving aminophenylcarboxylic acid in water at 50~60 degrees Celsius, then cooling it to 25~30 degrees Celsius, and then adding carbon disulfide dropwise to the cooled aminophenylcarboxylic acid solution to carry out the reaction. After the reaction is completed, N-dithiocarboxy-aminophenylcarboxylic acid is obtained. The mass ratio of N-dithiocarboxy-aminophenylcarboxylic acid, cyclohexyl-3,5-diene-1,2-dicarboxylic acid and propionic acid is (4-5):2:

1.

2. The preparation method of the compound heavy metal chelating agent according to claim 1, characterized in that, The mixing temperature is 50-60 degrees Celsius.

3. The method for preparing the compound heavy metal chelating agent according to claim 1 or 2, characterized in that, In the cyclohexyl-3,5-diene-1,2-dicarboxylic acid solution, the mass ratio of cyclohexyl-3,5-diene-1,2-dicarboxylic acid powder to water is 1:(8~9.5).

4. The method for preparing the compound heavy metal chelating agent according to claim 1 or 2, characterized in that, The concentration of the propionic acid solution is 20 wt% to 25 wt%.

5. The method for preparing the compound heavy metal chelating agent according to claim 1 or 2, characterized in that, The concentration of the sodium hydroxide solution is 70 wt% to 80 wt%.

6. A compound heavy metal chelating agent, characterized in that, It is prepared by the method of any one of claims 1 to 5 for preparing a compound heavy metal chelating agent.

7. The application of the compound heavy metal chelating agent according to claim 6 in mercury removal.

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