A method for preparing a thiazole-modified polyethyleneimine and a method for selectively recovering palladium from wastewater

Abstract

The application discloses a preparation method of thiazole modified polyethylene imine and a method for selectively recovering palladium in wastewater, and the thiazole modified polyethylene imine can specifically chelate with Pd (II). In a harsh water environment with pH less than or equal to 1 or total concentration of cations and anions greater than or equal to 0.2 mol / L, the thiazole modified polyethylene imine can self-assemble to form a three-dimensional network structure, so that high selective capture of Pd (II) can be realized in a complex wastewater system containing competitive organic matters and other various metal ions. The thiazole modified polyethylene imine effectively overcomes the problem that the existing polymer material (polyethylene imine) has weak combination capacity with metal ions, and breaks through the technical limitation that traditional water-soluble polymers are only suitable for ultrafiltration process.

Description

Technical Field

[0001] This invention relates to a method for preparing thiazole-modified polyethyleneimine, and also to a method for selectively recovering palladium from wastewater using the thiazole-modified polyethyleneimine obtained by the above method. Background Technology

[0002] Polyethylene imine (PEI), as a polyelectrolyte, can bind with various metal ions in water, thus enabling the removal of heavy metals from wastewater through membrane filtration or the addition of surfactants. pH adjustment can then facilitate metal recovery and the reuse of PEI. However, PEI has limitations in its application, particularly its high dependence on the pH of the treated water. In acidic environments (pH < 3), the protonation level of PEI increases significantly, leading to a decrease in its complexation sites with metal cations. Consequently, it exhibits poor performance in removing metal cations and other pollutants from acidic water. Achieving a metal removal rate of over 95% in raw water with lower pH levels necessitates an unlimited increase in the dosage of PEI.

[0003] Furthermore, current methods for removing palladium ions from industrial wastewater using complexation adsorption typically utilize water-soluble polymers to form stable complexes with palladium ions. However, in actual solid-liquid separation processes, the capture effect of these water-soluble polymer materials on metal ions is limited to the nanoscale, meaning removal is achieved through polymer-enhanced ultrafiltration (PEUF). This results in extremely small polymer-metal complexes that cannot be effectively retained by conventional microfiltration membranes. Therefore, separating the concentrated complex solution from the palladium-removed wastewater requires ultrafiltration systems with even smaller pore sizes and lower molecular weight cutoffs. This directly leads to high equipment investment and high operating energy consumption, becoming a key bottleneck restricting the large-scale application of this technology. Summary of the Invention

[0004] Purpose of the invention: The purpose of this invention is to provide a method for preparing thiazole-modified polyethyleneimine that exhibits good binding selectivity for specific metal ions (Pd(II)) in complex water samples with low pH and high salinity; another purpose of this invention is to provide a method for selectively recovering palladium from wastewater using the thiazole-modified polyethyleneimine prepared by the above method.

[0005] Technical solution: The preparation method of thiazole-modified polyethyleneimine according to the present invention includes the following steps:

[0006] (1) Mix the hydrochloride compound containing the thiazole group with NaOH, neutralize the hydrochloric acid, and then add an aqueous solution of PEI; after the reaction, add NaOH to the mixed solution again to neutralize the acid generated in the reaction;

[0007] (2) Under stirring, the mixture from step (1) is heated in a water bath. After a precipitate is formed, sulfuric acid is added to it. The solution is then heated in a water bath under stirring until no more precipitate is formed in the solution, thus obtaining thiazole-modified polyethyleneimine.

[0008] (3) The mixture from step (2) is placed into a dialysis bag for purification to obtain Thz-PEI aqueous solution.

[0009] In step (1), the hydrochloride compound containing a thiazole group includes 4-chloromethylthiazole hydrochloride, 2-chloromethylthiazole hydrochloride, 2-(bromomethyl)thiazole hydrobromide, 4-(bromomethyl)thiazole hydrobromide, 2-chloro-5-chloromethylthiazole, 4-chloromethyl-2-methylthiazole hydrochloride, 2-bromo-5-bromomethylthiazole, or 4-(bromomethyl)-2-methylthiazole hydrobromide. The PEI (polyethyleneimine) has a branched chain structure with a molecular weight of 70 kDa or higher. The initial molar amount of NaOH added is determined by the amount of hydrochloric acid in the hydrochloride compound containing the thiazole group, with a molar ratio of hydrochloric acid to NaOH of 1:1; the molar ratio of the hydrochloride containing the thiazole group to PEI (based on monomers) is also 1:1. The subsequent addition of NaOH is consistent with the molar amount of PEI added.

[0010] In step (2), the water bath heating temperature is 60~70℃ and the heating time is 0.5~1h; continue to heat the solution in the water bath for no less than 4h with stirring.

[0011] In step (3), the permeable molecular weight of the dialysis bag is 7 kDa, and the dialysis time is not less than 12 hours.

[0012] The method for selectively recovering palladium from wastewater using thiazole-modified polyethyleneimine prepared by the above method is as follows: Thz-PEI is added to palladium-containing industrial wastewater at a molar ratio of Thz-PEI to Pd(II) of not less than 2:1. After sufficient reaction, the solution is concentrated by microfiltration to obtain a concentrated solution enriched with Thz-PEI-Pd(II) complex and wastewater after palladium removal. The concentrated solution is then placed in an electrolytic cell for electrolysis to obtain decomplexed Thz-PEI and Pd.

[0013] During the application process, it is necessary to first measure the concentration of Pd(II) in the wastewater. When the Thz-PEI:Pd molar ratio is less than 2:1, Pd(II) cannot be completely complexed. When the Thz-PEI:Pd molar ratio is greater than 2:1, excessive Thz-PEI will combine with other metal ions, resulting in a decrease in the selectivity of Pd(II). It will also cause excess Thz-PEI to act as a dispersant, causing the original large particles to redisperse and dissolve, resulting in a decrease in the removal rate.

[0014] In hydrochloride compounds containing thiazole groups, the carbon atom (electrophilic center) bonded to the halogen atom is easily attacked by electron-rich amino groups (nucleophiles) in high-temperature and polar solutions, forming NC covalent bonds (SN2 reaction), thereby grafting the thiazole group onto the PEI backbone. The introduction of this group makes Thz-PEI more selective for Pd(II), achieving specific and efficient chelation with Pd(II) under strong acid (pH≤1) and high salinity (total concentration of anions and cations ≥0.2mol / L). Furthermore, under the condition of a Thz-PEI:Pd(II) molar ratio of 2:1, combined with tangential flow microfiltration, the removal rate of Pd(II) in wastewater can reach 96.3%. Finally, Pd(II) is recovered through electrolysis of the concentrate, with a Pd metal recovery rate of over 70%.

[0015] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) The Thz-PEI material used in the present invention can achieve specific chelation of Pd(II) in complex water environments with strong acidity (such as pH≤1), high salinity and multiple coexisting metal ions, effectively overcoming the problem that the binding capacity of traditional polyethyleneimine (PEI) to metal ions decreases significantly under low pH and high salinity conditions; (2) Based on the specific structure of Thz-PEI and its specific molar ratio with Pd(II), the present invention constructs a separation system suitable for low energy consumption and high throughput microfiltration processes, which can achieve specific chelation of Pd(II) in complex water environments with strong acidity and high salinity. In wastewater, Thz-PEI can efficiently bind with Pd(II), and due to the "charge shielding" effect caused by high ionic strength, it significantly compresses the double layer of the Thz-PEI-Pd(II) complex, reduces the intermolecular repulsion, and promotes the aggregation of the complex to form large-sized particles, which can then be efficiently retained by the microfiltration membrane; the removal rate of Pd(II) by this method can reach more than 95%, and it has both high selectivity and high removal efficiency; (3) The method of this invention can not only meet the high-efficiency treatment requirements of industrial palladium-containing wastewater and realize the high-selectivity separation and recovery of Pd(II), but also has the characteristics of simple process, low energy consumption, and easy scalability. The captured palladium element can be further recycled and reused, with a recovery rate of more than 70%, which has important application value in resource recovery and environmental protection. Attached Figure Description

[0016] Figure 1 The Fourier transform infrared spectra of Thz-PEI and PEI in Example 1 are shown.

[0017] Figure 2 Turbidity of solutions under different pH conditions when Thz-PEI:Pd(II)=2:1;

[0018] Figure 3The turbidity of solutions at different Thz-PEI:Pd(II) molar ratios under pH 1 and 0.1 mol / L NaCl and Na2SO4 conditions;

[0019] Figure 4 The results of Pd(II) removal by microfiltration under different polymer materials (Thz-PEI and PEI) at pH=1;

[0020] Figure 5 The results of Pd(II) removal by dialysis under different pH and polymer materials (Thz-PEI and PEI) conditions;

[0021] Figure 6 The results of Pd(II) removal by Thz-PEI under different concentrations of small molecule organic ligands and salinity conditions;

[0022] Figure 7 The results of Pd(II) removal by Thz-PEI under coexisting ion concentration conditions are shown. Detailed Implementation

[0023] Example 1

[0024] The preparation method of thiazole-modified polyethyleneimine of the present invention specifically includes the following steps:

[0025] (1) Weigh 4.2987 g of 4-chloromethylthiazolium hydrochloride and add it to a 50 mL centrifuge tube; add 2.5 mL of 10 mol / L NaOH solution to the centrifuge tube to neutralize the hydrochloric acid in the 4-chloromethylthiazolium hydrochloride;

[0026] (2) Add 2.15g of PEI aqueous solution to the centrifuge tube. The mass concentration of PEI in the PEI aqueous solution is 50%, and the molar ratio of 4-chloromethylthiazolium hydrochloride to PEI (based on monomer) is 1:1. After the reaction, add 2.5mL of 10mol / L NaOH solution to the centrifuge tube again to neutralize the hydrochloric acid generated in the reaction.

[0027] (3) Place the mixture in a 70°C water bath and stir. After 1 hour, a brown precipitate will form in the solution and the rotor will not be able to rotate. At this time, add 4 mL of 5 mol / L H2SO4 solution and shake the centrifuge tube quickly to allow the rotor to continue rotating.

[0028] (4) Heat and stir the solution at 70°C for 4 hours until there is no more precipitate in the solution. Then dilute with water to the mark to obtain a uniform brownish-red solution, i.e., 50 mL of Thz-PEI aqueous solution with a concentration of 0.5 mol / L.

[0029] The reaction equation for the above reaction is:

[0030] .

[0031] pass Figure 2 It can be seen that the FTIR spectrum of PEI shows typical characteristic peaks, including the NH stretching vibration peaks of primary and secondary amines located at 3300~3500 cm⁻¹. -1 The NH bending vibration peak is at 1595 cm⁻¹ -1 The peak of CN tensile vibration is around 1050 cm⁻¹. -1 In contrast, the FTIR spectrum of Thz-PEI, in addition to the characteristic peaks of PEI mentioned above, also shows a peak at 1512 cm⁻¹. -1 1408cm -1 Deformation vibration peaks of the thiazole ring plane were observed, suggesting that the thiazole group of the small molecule has been successfully grafted onto the PEI backbone.

[0032] Example 2

[0033] Based on the Thz-PEI prepared in Example 1, highly selective removal of Pd(II) from palladium-containing wastewater was achieved: In fourteen groups of palladium-containing wastewater, the initial Pd(II) concentration was 0.2 mM, and the pH of the wastewater was adjusted to 1-4. The Thz-PEI aqueous solution from Example 1 was added to each of the fourteen groups of palladium-containing wastewater at a Thz-PEI to Pd(II) molar ratio of 2:1. After stirring for 5 seconds, the turbidity was measured, and the results are as follows: Figure 2 As shown. Turbidity detection mainly reflects the concentration of suspended particles with a diameter greater than 0.1 μm. A significant increase in turbidity indicates the formation of particulate matter that can be effectively retained by microfiltration. When the solution pH is <1.5, its turbidity remains stable above 20 NTU. This is due to the bridging effect between the metal and polymer, which forms a three-dimensional network structure. At this point, microfiltration can be used to concentrate the solution and obtain a concentrated solution.

[0034] Example 3

[0035] The Thz-PEI prepared in Example 1 was used for the highly selective removal of Pd(II) from palladium-containing wastewater. The initial Pd(II) concentration in the palladium-containing wastewater was 0.2 mmol / L. Three experimental groups were set up. In one group, the pH was adjusted to 1. In the other two groups, 0.1 mol / L NaCl and Na2SO4 (pH=3) were added, respectively. Thz-PEI was then added, and the turbidity was measured after stirring for 5 seconds at different molar ratios. The results are as follows: Figure 3 As shown, under pH=1 conditions, the turbidity reaches its highest point at a molar ratio of 2; the turbidity of the groups with added NaCl and Na2SO4 continues to increase.

[0036] Thz-PEI material exhibits excellent Pd(II) removal performance in strongly acidic environments (pH=1), achieving a removal rate of 96.3% at the optimal molar ratio. Under high salinity conditions, the "charge shielding" effect compresses the electric double layer of the complex, reducing electrostatic repulsion and promoting the formation of large aggregates, significantly improving the removal efficiency (e.g., at pH=3 and 4 times the dosage, the removal rates in NaCl and Na2SO4 systems are as high as 97.7% and 98.7%, respectively). However, it should be noted that due to the presence of protonated amine and thiazole groups in its structure, excessive addition introduces a high density of positive charges, leading to enhanced electrostatic repulsion between the complexes. This, in turn, inhibits the formation of the three-dimensional network structure, causing a decrease in the removal rate (to 84.4% at 4 times the dosage). These removal rate results are consistent with changes in turbidity. Therefore, Thz-PEI has a highly efficient removal capability for Pd(II) in strongly acidic and high-salt environments.

[0037] Example 4

[0038] The Thz-PEI method prepared in Example 1 was used for highly selective removal of Pd(II) from palladium-containing wastewater: The initial Pd(II) concentration in the palladium-containing wastewater was 0.2 mmol / L. The pH was adjusted to 1, and two parallel experiments were conducted. The specific steps are as follows:

[0039] (1) Add Thz-PEI aqueous solution of different concentrations to five portions of palladium-containing wastewater in the first parallel experiment, so that the molar ratio of Thz-PEI to Pd(II) is 0, 1, 2, 3 and 4 respectively, and stir for 5s to allow it to react fully; add PEI aqueous solution of different concentrations to another five portions of palladium-containing wastewater in the second parallel experiment (pH is 1), so that the molar ratio of PEI to Pd(II) is 0, 1, 2, 3 and 4 respectively, and stir for 5s to allow it to react fully.

[0040] (2) The fully reacted solution was concentrated and filtered through microfiltration to obtain a concentrated Pd(II) solution and Pd(II)-removed wastewater. The Pd(II) concentration in the microfiltration effluent was measured to determine the removal rate. When the molar ratio of Thz-PEI to Pd(II) was 2:1, the removal rate reached 96.3%. As the concentration of Thz-PEI increased, the Pd(II) removal rate decreased to 84.4%. However, the Pd(II) removal rate was less than 15% at any dosage of PEI. Figure 4 As shown.

[0041] Take 300 mL of the filtered concentrated Pd(II) solution (containing Thz-PEI-Pd(II) complex) obtained above and place it in an electrolytic cell for electrolysis. The cathode and anode electrodes are titanium electrodes and IrO2-Ta2O5 coated titanium plates, respectively, with an electrode area of ​​20 cm². 2With the current controlled at a constant 0.04A and the electrolysis time at 3 hours, the Pd(II) recovery rate was over 70%. Furthermore, the resulting electrolyte could still effectively trap Pd(II) as a polymer, and after two cycles, the Pd(II) removal rate of Thz-PEI remained above 90%.

[0042] Example 5

[0043] The Thz-PEI method prepared in Example 1 was used for highly selective removal of Pd(II) from palladium-containing wastewater: The initial Pd(II) concentration in the palladium-containing wastewater was 0.2 mmol / L, and the volume was 100 mL. Two dialysis experiments were conducted. In one experiment, two beakers (with initial pH values ​​of 1 and 3 for the palladium-containing wastewater) were placed in dialysis bags containing PEI solution, with a PEI to Pd(II) molar ratio of 4. In the other experiment, two beakers (with initial pH values ​​of 1 and 3 for the palladium-containing wastewater) were placed in dialysis bags containing Thz-PEI solution, with a Thz-PEI to Pd(II) molar ratio of 2. Dialysis was performed for 48 h, and the Pd(II) concentration in the solution outside the bags was then measured to determine the removal rate. At pH values ​​of 1 and 3, the removal rates using PEI were only 28.7% and 43.4%, respectively, while the removal rates of the Thz-PEI group reached 88.2% and 94.9%. Figure 5 As shown.

[0044] Example 6

[0045] The process of Example 6 is basically the same as that of Example 4. In the palladium-containing wastewater, the initial Pd(II) concentration was 0.2 mmol / L. The pH was adjusted to 1, and three parallel experiments were set up. In the first parallel experiment, 1 mmol / L and 2 mmol / L EDTA were added to two beakers, respectively. In the second parallel experiment, 1 mmol / L and 2 mmol / L citric acid were added to two beakers, respectively. In the third parallel experiment, 1 mmol / L and 2 mmol / L NaCl were added to two beakers, respectively. Thz-PEI was added to all beakers to a concentration of 0.4 mmol / L. The mixture was stirred for 5 seconds to allow for complete reaction. The fully reacted solution was concentrated and filtered through microfiltration. The microfiltration effluent was tested to determine the Pd(II) removal rate. It was found that the Pd(II) removal rate was not affected by small molecule organic matter or salt ions. Under conditions of 10 times the concentration of EDTA, citric acid, and NaCl, the removal rates were 95.3%, 95.5%, and 96.0%, respectively. The results are as follows: Figure 6 As shown.

[0046] Example 7

[0047] The process in Example 7 was basically the same as in Example 4, except that the wastewater contained nine heavy metal ions: Mg(II), Ca(II), Fe(III), Cr(III), Cu(II), Zn(II), Ni(II), Pb(II), and Pd(II), all with a concentration of 0.2 mmol / L. Two parallel experiments were conducted: one group was treated with Thz-PEI at a concentration of 0.4 mmol / L, while the other group was treated without the polymer. The removal rate of each metal ion was determined by testing the microfiltration effluent. The removal rate of Pd(II) was 93.8%, while the removal rates of the other heavy metal ions were all less than 10%. Figure 7 As shown.

Claims

1. A method for preparing thiazole-modified polyethyleneimine, characterized in that, Includes the following steps: (1) Mix the hydrochloride compound containing the thiazole group with NaOH, neutralize the hydrochloric acid, and then add an aqueous solution of PEI; after the reaction, add NaOH to the mixed solution again to neutralize the acid generated in the reaction; (2) Under stirring, the mixture from step (1) is heated in a water bath. After a precipitate is formed, sulfuric acid is added to it. The solution is then heated in a water bath under stirring until no more precipitate is formed in the solution, thus obtaining thiazole-modified polyethyleneimine. (3) The mixture from step (2) is placed into a dialysis bag for purification to obtain Thz-PEI aqueous solution.

2. The method for preparing thiazole-modified polyethyleneimine according to claim 1, characterized in that: In step (1), the hydrochloride compound containing a thiazole group includes 4-chloromethylthiazole hydrochloride, 2-chloromethylthiazole hydrochloride, 2-(bromomethyl)thiazole hydrobromide, 4-(bromomethyl)thiazole hydrobromide, 2-chloro-5-chloromethylthiazole, 4-chloromethyl-2-methylthiazole hydrochloride, 2-bromo-5-bromomethylthiazole, or 4-(bromomethyl)-2-methylthiazole hydrobromide.

3. The method for preparing thiazole-modified polyethyleneimine according to claim 1, characterized in that: In step (1), the PEI is a branched chain structure with a molecular weight of not less than 70 kDa.

4. The method for preparing thiazole-modified polyethyleneimine according to claim 1, characterized in that: In step (1), the molar amount of NaOH added for the first time is determined by the amount of hydrochloric acid in the hydrochloride compound containing the thiazole group, and the molar ratio of hydrochloric acid to NaOH is 1:

1.

5. The method for preparing thiazole-modified polyethyleneimine according to claim 1, characterized in that: In step (1), based on the ethyleneimine monomer in polyethyleneimine, the molar ratio of the hydrochloride containing the thiazole group to PEI is 1:1; the amount of NaOH added again is the same as the molar amount of PEI added.

6. The method for preparing thiazole-modified polyethyleneimine according to claim 1, characterized in that: In step (2), the water bath heating temperature is 60~70℃ and the heating time is 0.5~1h; continue to heat the solution in the water bath for no less than 4h with stirring.

7. The method for preparing thiazole-modified polyethyleneimine according to claim 1, characterized in that: In step (3), the permeable molecular weight of the dialysis bag is 7 kDa, and the dialysis time is not less than 12 hours.

8. The method for preparing thiazole-modified polyethyleneimine according to claim 1, characterized in that: In step (3), the molecular weight of the thiazole-modified polyethyleneimine is not less than 250 kDa.

9. A method for selectively recovering palladium from wastewater using the thiazole-modified polyethyleneimine prepared according to claim 1, characterized in that... Specifically, Thz-PEI is added to palladium-containing industrial wastewater at a molar ratio of Thz-PEI to Pd(II) of not less than 2:

1. After the reaction is complete, the solution is concentrated by microfiltration to obtain a concentrated solution enriched with Thz-PEI-Pd(II) complex and the wastewater after palladium removal. The concentrated solution is then placed in an electrolytic cell for electrolysis to obtain decomplexed Thz-PEI and Pd.

10. The method according to claim 9, characterized in that: During electrolysis, the current density is 0.002~0.0025 A / cm². 2 .

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