Compound heavy metal chelating agent as well as preparation method and application thereof

Abstract

The invention 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-dithio carboxyl-amino phenyl formic acid, a cyclohexyl-3, 5-diene-1, 2-dicarboxylic acid solution, a propionic acid solution and a sodium hydroxide solution, stirring until complete dissolution and standing, then completing evaporative crystallization, and separating and purifying the separated chelating agent. The N-dithio carboxyl-amino phenyl formic acid, the cyclohexyl-3, 5-diene-1, 2-dicarboxylic acid, the propionic acid and a proper amount of sodium hydroxide are mixed to form a compound reagent, the chelating absorption effect on the heavy metal Hg in the natural gas wastewater is better, and the formed chelate is very stable and not easy to decompose.

Description

Technical Field

[0001] The invention relates to the technical field of mercury removal, and in particular to a composite heavy metal chelating agent and a preparation method and application thereof. Background Art

[0002] The treatment of high levels of heavy metal Hg in wastewater during the natural gas processing process has always been a key and difficult point in environmental treatment. Mercury pollutes the environment in many ways, including its volatility, mobility, and bioaccumulation, which have a huge impact on human survival and development. At present, the sulfur-impregnated activated carbon method is used to treat high-mercury raw gas and wastewater in natural gas processing, but there are problems such as difficulty in determining the dosage of reagents, difficulty in flocculation and sedimentation, and large amounts of mercury residues, which make it impossible to achieve true mercury removal. Moreover, as time goes by, Hg belongs to the category of heavy metals and usually precipitates from the adsorbent in the form of divalent ions, causing serious environmental pollution.

[0003] Although there are examples of solving the problem of large-scale enrichment of Hg metal in wastewater through chelation technology, research and analysis show that the heavy metal chelating agents such as DTC, TMT, PEI, etc. that already exist on the market for chelating heavy metal Hg can only temporarily solve the problem of heavy metal Hg purification. Due to the instability of the above products at the molecular level, Hg ions will gradually dissociate through chemical adsorption. The amount of Hg precipitated increases with the increase of the gradient concentration of the reaction system, so the reliability of the existing technology is very low.

[0004] Therefore, there is an urgent need for a heavy metal chelating agent that has a strong heavy metal chelating effect, a stable chelate, will not reversely leach harmful Hg metal, and is environmentally friendly. Summary of the invention

[0005] In order to solve the above problems in the prior art, the present invention provides a composite heavy metal chelating agent and a preparation method and application thereof.

[0006] Based on this, the present invention has the following technical solutions: In a first aspect, the present invention provides a method for preparing a composite heavy metal chelating agent, comprising: mixing N-dithiocarboxyl-aminophenylcarboxylic acid, cyclohexyl-3,5-diene-1,2-dicarboxylic acid solution, propionic acid solution and sodium hydroxide solution, stirring until completely dissolved and standing to complete evaporation and crystallization, and separating and purifying the precipitated chelating agent.

[0007] According to a method for preparing a composite heavy metal chelating agent provided by the present invention, the mass ratio of N-dithiocarboxyl-aminophenylcarboxylic acid, cyclohexyl-3,5-diene-1,2-dicarboxylic acid and propionic acid is (4-5):2:1.

[0008] According to the method for preparing a composite heavy metal chelating agent provided by the present invention, the mixing temperature is 50-60 degrees Celsius.

[0009] According to a method for preparing a composite 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).

[0010] According to the method for preparing a composite heavy metal chelating agent provided by the present invention, the concentration of the propionic acid solution is 20-25wt%.

[0011] According to the method for preparing a composite heavy metal chelating agent provided by the present invention, the concentration of the sodium hydroxide solution is 70-80wt%.

[0012] According to a preparation method of a composite heavy metal chelating agent provided by the present invention, the preparation method of N-dithiocarboxyl-aminobenzoic acid comprises: dissolving aminobenzoic acid in water at 50-60 degrees Celsius, cooling to 25-30 degrees Celsius, and then adding carbon disulfide dropwise to the aminobenzoic acid cooling solution for reaction, and obtaining N-dithiocarboxyl-aminobenzoic acid after the reaction is completed.

[0013] In a second aspect, the present invention provides a composite heavy metal chelating agent, which is prepared by the above-mentioned preparation method of the composite heavy metal chelating agent.

[0014] In a third aspect, the present invention provides the use of the above-mentioned composite heavy metal chelating agent in mercury removal.

[0015] According to the use of the composite heavy metal chelating agent in mercury removal provided by the present invention, the dosage of the composite 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.

[0016] The composite heavy metal chelating agent provided by the present invention, as well as its preparation method and application, is a composite reagent formed by mixing N-dithiocarboxyl-aminophenylcarboxylic acid, cyclohexyl-3,5-diene-1,2-dicarboxylic acid, propionic acid and an appropriate amount of sodium hydroxide, which has a better chelating and absorbing effect on heavy metal Hg in natural gas wastewater, and the formed chelate is very stable and not easy to decompose. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0018] Figure 1 It is the carbon nuclear magnetic resonance spectrum of the composite metal chelator in Example 1 provided by the present invention.

[0019] Figure 2 This is the hydrogen nuclear magnetic resonance spectrum of the composite metal chelator in Example 1 provided by the present invention.

[0020] Figure 3 It is a schematic diagram of the stable spatial structure of the complex metal chelator in Example 1 provided by the present invention. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the drawings of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0022] In a first aspect, the present invention provides a method for preparing a composite heavy metal chelating agent, comprising: mixing N-dithiocarboxyl-aminophenylcarboxylic acid, cyclohexyl-3,5-diene-1,2-dicarboxylic acid solution, propionic acid solution and sodium hydroxide solution, stirring until completely dissolved and standing to complete evaporation and crystallization, and separating and purifying the precipitated chelating agent.

[0023] In the present invention, the structural formulas of N-dithiocarboxyl-aminophenylcarboxylic acid, cyclohexyl-3,5-diene-1,2-dicarboxylic acid solution and propionic acid are as follows: .

[0024] The present invention found that the N, -COO-, -CSS- and other groups contained in N-dithiocarboxyl-aminophenylcarboxylic acid, cyclohexyl-3,5-diene-1,2-dicarboxylic acid and propionic acid can react with heavy metal ions Hg 2+A very stable coordination structure system is formed. Specifically, not only the effective electron pairs provided by these molecules can coordinate with mercury ions, but also the sodium salt formed by the three molecules can form a large-area cluster structure between mercury ions in aqueous solution, and the near-cage cluster effect between molecules. Under the multi-dentate coordination state between molecules and mercury ions, the molecular distance will be gradually reduced, and mercury ions will also be "multifaceted" adsorbed, thus strengthening the binding of mercury ions by coordination chelation through strong electrostatic and electronic effects. These synergistic effects caused by strong inductive force and electrostatic force can make heavy metal mercury ions present a stable chemical state in the chelating agent. Through energy optimization calculation, using the force basis set applicable to the basis set: B3LYP / 6-311G+ calculation, it can be known that during the solvation reaction, the solubility free energy of the mercury ion chelate compound in the system is at a very low value state, with a value of -3.72 kcal / mol. In the chelating system, the stable cluster structure will avoid contact with strong oxidants, acidic small molecules in the environment and other impurities, so the formed chelate has obvious antioxidant and anti-acid corrosion effects, and the multi-dentate ligand structural elements will also enhance the stability of the molecule. The chelate will not change with the changes in the environment, and heavy metal mercury will hardly form a reverse analysis state.

[0025] According to a preferred embodiment provided by the present invention, the mass ratio of N-dithiocarboxyl-aminophenylcarboxylic acid, cyclohexyl-3,5-diene-1,2-dicarboxylic acid and propionic acid is (4-5):2:1.

[0026] According to a preferred embodiment provided by the present invention, the mixing temperature is 50-60 degrees Celsius.

[0027] According to a preferred embodiment 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).

[0028] According to a preferred embodiment provided by the present invention, the concentration of the propionic acid solution is 20-25wt%.

[0029] According to a preferred embodiment provided by the present invention, the concentration of the sodium hydroxide solution is 70-80wt%.

[0030] According to a preferred embodiment provided by the present invention, a method for preparing N-dithiocarboxyl-aminobenzoic acid comprises: dissolving aminobenzoic acid in water at 50-60 degrees Celsius, cooling the solution to 25-30 degrees Celsius, and then adding carbon disulfide dropwise to the aminobenzoic acid cooling solution for reaction, and obtaining N-dithiocarboxyl-aminobenzoic acid after the reaction is completed.

[0031] According to a preferred embodiment provided by the present invention, the preparation method of the composite heavy metal chelating agent comprises the following steps: Add aminophenylcarboxylic acid powder to the reactor, dissolve it with distilled water, heat it to 50-60 degrees Celsius through an electric heater, cool it to 25-30 degrees Celsius, and introduce dithiocarboxyl groups by the branching effect of CS2. The main steps are: add CS2 solvent dropwise to the aminophenylcarboxylic acid cooling solution to control the reaction rate. The total reaction time is 25-35 minutes. After the reaction is completed, raise the reaction temperature to 50-60 degrees Celsius, keep it in a slightly hot state, add 20-25wt% propionic acid solution and 70-80wt% NaOH alkaline solution to the reactor, stir it thoroughly, mix cyclohexyl-3,5-diene-1,2-dicarboxylic acid powder with distilled water in a ratio of 1:8-9.5 (mass ratio) to form a solution, wait for the temperature to return to 30 degrees Celsius, add it to the previous reactor, stir it thoroughly, cool the liquid phase for 30-35 minutes, and then perform crystallization.

[0032] Preferably, the mercury removal chelating agent formed by N-dithiocarboxyl-aminophenylcarboxylic acid: cyclohexyl-3,5-diene-1,2-dicarboxylic acid: propionic acid = (4-5): 2: 1 (mass ratio) has the best effect.

[0033] In a second aspect, the present invention provides a composite heavy metal chelating agent, which is prepared by the above-mentioned preparation method of the composite heavy metal chelating agent.

[0034] In a third aspect, the present invention provides the use of the above-mentioned composite heavy metal chelating agent in mercury removal.

[0035] According to a preferred embodiment provided by the present invention, the dosage of the composite heavy metal chelating agent in the mercury-containing wastewater is 5-15 g / L, and the concentration of mercury ions in the mercury-containing wastewater is 50-150 mg / L.

[0036] In order to further illustrate the technical solution of the present invention, the present invention provides the following specific embodiments and comparative examples.

[0037] Unless otherwise specified, the various 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.

[0038] Example 1 This embodiment provides a composite metal chelator, and its preparation method comprises the following steps: The aminobenzoic acid powder is added to the reactor, dissolved with distilled water, and heated to 50-60 degrees Celsius by an electric heater, and then cooled to 25-30 degrees Celsius, and the dithiocarboxyl group is introduced by the branching effect of CS2. The step mainly includes: using CS2 solvent to add dropwise to the aminobenzoic acid cooling solution to control the reaction rate, and the total reaction time is: 25-35 minutes. After the reaction is completed, the reaction temperature is raised to 50-60 degrees Celsius, and 20-25wt% propionic acid solution and 70-80wt% NaOH alkaline solution are added to the reactor under a slightly hot state. After sufficient stirring, the cyclohexyl-3,5-diene-1,2-dicarboxylic acid powder and distilled water are mixed in a ratio of 1:8-9.5 (mass ratio) to form a solution, and after the temperature is restored to 30 degrees Celsius, it is added to the previous reactor, and after sufficient stirring and mixing, the liquid phase is cooled for 30-35 minutes and then the crystallization operation is performed to complete the preparation of the composite metal chelator.

[0039] The carbon NMR spectrum of the composite metal chelator is shown in Figure 1 , the H NMR spectrum of the complex metal chelator is shown in Figure 2 .

[0040] After the quantum chemical calculation software, the basis set also uses the density functional B3LYP / 6-311G+ to obtain the total potential energy of the molecule as 106.5585 kcal / mol. However, after forming a cluster stable structure with propionic acid and cyclohexyl-3,5-diene-1,2-dicarboxylic acid, Figure 3 As shown, the total molecular potential energy is 1.2638 kcal / mol. It can be seen that in the process of developing from a monolayer to a multi-molecular cluster, the potential energy decreases sharply, indicating that after contacting with mercury ions again, the system will be more stable.

[0041] Comparative Example 1 This comparative example provides a commercially available chelating agent EDTA-2Na, which is provided by Shandong Wangtong Chemical Co., Ltd.

[0042] Comparative Example 2 This comparative example provides a commercially available chelating agent PEI, which is provided by Shandong Wangtong Chemical Co., Ltd.

[0043] Comparative Example 3 This comparative example provides a commercially available chelating agent DTC-1, which is provided by Shanghai Puyi Environmental Protection Technology Co., Ltd.

[0044] Comparative Example 4 This comparative example provides a commercially available chelating agent DTC-2, which is provided by Shanghai Puyi Environmental Protection Technology Co., Ltd.

[0045] Test example The composite metal chelating agent prepared in the above examples and the commercially available chelating agent provided in the comparative example were respectively subjected to heavy metal chelation experiments.

[0046] Heavy metal selection: 100 ml of natural gas treatment wastewater containing mercury ions at a concentration of 100 mg / L. Heavy metal concentration detection and analysis was performed using liquid ion chromatography.

[0047] The chelation test method is as follows: 1 gram of chelating agent (composite metal chelating agent prepared in the example and commercially available chelating agents EDTA-2Na, PEI, DTC-1, and DTC-2 provided in comparative examples 1 to 4) is added to each heavy metal pollutant, stirred for chelation reaction for 25 minutes, and then the residual free heavy metal ion concentration of the solution is detected. Each group of experiments is repeated 5 times and the average value is taken. The results are shown in Table 1.

[0048] Table 1 The chelating effect of each chelating agent on heavy metals

[0049] In the following 30 days, the residual free heavy metal ion concentration in the solution of the treatment group in Table 1 was tested once a day at a fixed time. For 30 consecutive days, the change value of the free heavy metal concentration in each group of solutions was less than 0.001 mg / L, proving that the heavy metal chelate formed by the chelating agent provided by the present invention is extremely stable.

[0050] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a composite heavy metal chelating agent, characterized in that: include: N-dithiocarboxyl-aminophenylcarboxylic acid, cyclohexyl-3,5-diene-1,2-dicarboxylic acid solution, propionic acid solution and sodium hydroxide solution are mixed, stirred until completely dissolved and allowed to stand for evaporation and crystallization, and the precipitated chelating agent is separated and purified.

2. The method for preparing a composite heavy metal chelating agent according to claim 1, characterized in that: The mass ratio of N-dithiocarboxyl-aminophenylcarboxylic acid, cyclohexyl-3,5-diene-1,2-dicarboxylic acid and propionic acid is (4-5):2:

1.

3. The method for preparing a composite heavy metal chelating agent according to claim 1 or 2, characterized in that: The mixing temperature is 50-60 degrees Celsius.

4. The method for preparing a composite heavy metal chelating agent according to any one of claims 1 to 3, 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).

5. The method for preparing a composite heavy metal chelating agent according to any one of claims 1 to 4, characterized in that: The concentration of the propionic acid solution is 20-25 wt %.

6. The method for preparing a composite heavy metal chelating agent according to any one of claims 1 to 5, characterized in that: The concentration of the sodium hydroxide solution is 70-80 wt %.

7. The method for preparing a composite heavy metal chelating agent according to any one of claims 1 to 6, characterized in that: The preparation method of N-dithiocarboxyl-aminobenzoic acid comprises: dissolving aminobenzoic acid in water at 50-60 degrees Celsius, cooling down to 25-30 degrees Celsius, and then adding carbon disulfide dropwise into the aminobenzoic acid cooling solution to react, and obtaining N-dithiocarboxyl-aminobenzoic acid after the reaction is completed.

8. A composite heavy metal chelating agent, characterized in that: The compound heavy metal chelating agent is prepared by the preparation method of the compound heavy metal chelating agent according to any one of claims 1 to 7.

9. Use of the composite heavy metal chelating agent prepared by the preparation method according to any one of claims 1 to 7 or the composite heavy metal chelating agent according to claim 8 in mercury removal.

10. The use of the composite heavy metal chelating agent in mercury removal according to claim 9, characterized in that: The dosage of the composite heavy metal chelating agent in the mercury-containing wastewater is 5-15 g / L, and the concentration of mercury ions in the mercury-containing wastewater is 50-150 mg / L.

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