Pyridine-modified polyethyleneimine and method for high selective removal of cu(ii) from industrial wastewater based on the above material

Abstract

The application discloses pyridine modified polyethylene imine and a method for removing Cu(II) in industrial wastewater with high selectivity based on the material, and the method comprises the following steps: (1) adding PPEI with a Cu(II) molar ratio of 4:1 into copper-containing industrial wastewater and stirring, and PPEI selectively chelates Cu(II) in the wastewater; (2) filtering the solution after sufficient reaction through an electric ultrafiltration device to obtain a concentrated solution rich in chelates and wastewater after copper removal. The pyridine modified polyethylene imine (PPEI) can chelate with Cu(II) in low-pH water, thereby overcoming the problem that existing polyelectrolyte materials have poor binding force with metal ions in low-pH water; the method can realize high-selectivity removal of Cu(II) in industrial wastewater or complex water bodies containing copper in low-pH water through polyelectrolyte materials with specific structures and specific molar ratios of polyelectrolyte materials and Cu(II), and the removal rate can be more than 95%; the membrane is electrified in the ultrafiltration process, which can increase the anti-pollution ability of the membrane, and the membrane flux decline rate is nearly 0.5 times of that without electrification.

Description

Technical Field

[0001] This invention relates to a pyridine-modified polyethyleneimine, and also to a method for highly selectively removing Cu(II) from industrial wastewater based on the above-mentioned modified material. Background Technology

[0002] Traditional technologies for treating heavy metal wastewater and recovering copper include chemical precipitation, oxidation-reduction, ion exchange, adsorption, and electrochemical methods. While each method has its own advantages, they also have limitations. Chemical precipitation offers advantages such as rapid flocculation, low cost, ease of operation, and a certain degree of selectivity; however, Cu(II) removal is extremely sensitive to pH changes. High removal rates (over 90%) can be achieved when the pH is between 8.5 and 9.5; however, when the pH exceeds this range, the Cu(II) removal rate drops significantly, falling below 80%. Oxidation-reduction methods consume large amounts of reagents, cannot recover the catalyst, and are expensive to adjust the pH; Cu(II) removal efficiency typically does not exceed 60%. Ion exchange offers high removal efficiency and good selectivity, with removal rates exceeding 95%. However, it is costly, the resin is easily contaminated by heavy metal ions, and regeneration is difficult. While adsorption methods have low investment and operating costs, require no reagents, and produce no secondary pollution, their regeneration efficiency is low, typically not exceeding 70%, making heavy metal recycling difficult. Electrochemical methods offer high removal efficiency and stable treatment results, with removal rates exceeding 90%, but for low-concentration electrolyte solutions, they suffer from high energy consumption and rapid anode material depletion.

[0003] PEI (polyethyleneimine), as a polyelectrolyte material, can bind with various metal ions in water, thereby removing heavy metals from wastewater in conjunction with membrane filtration or the addition of surfactants. With pH adjustment, metal recovery and reuse of PEI can be achieved. However, the selectivity of PEI in binding with metal ions is poor, and the ability of PEI to bind with metal ions is weak in water with low pH (acidic). Summary of the Invention

[0004] Objective of the invention: The present invention aims to provide a pyridine-modified polyethyleneimine that can chelate with Cu(II) in water with low pH; another objective of the present invention is to provide a method for highly selective removal of Cu(II) from industrial wastewater based on the above-mentioned modified material, which can achieve specific and efficient removal of Cu(II) from industrial wastewater at any pH.

[0005] Technical solution: The pyridine-modified polyethyleneimine of this invention has the following structural formula:

[0006]

[0007] Among them, pyridine-modified polyethyleneimine has a molecular weight of 218,000 or higher, which makes it easier for ultrafiltration membranes to retain it.

[0008] The above-mentioned pyridine-modified polyethyleneimine was prepared by the following method, the specific steps of which are as follows:

[0009] (1) First, mix 2-chloromethylpyridine hydrochloride or 4-chloromethylpyridine hydrochloride with NaOH, and after the reaction, add PEI aqueous solution to it;

[0010] (2) NaOH was then added again to the mixed solution to neutralize the hydrochloric acid produced in the reaction;

[0011] (3) The mixture from step (2) is heated in a water bath and stirred, and a precipitate is formed;

[0012] (4) Add sulfuric acid solution to it. The precipitate dissolves slowly under acidic conditions. Heat the solution in a water bath and stir for 4 hours until there is no more precipitate in the solution to obtain PPEI aqueous solution.

[0013] In step (1), the PEI (polyethyleneimine) has a branched chain structure and a molecular weight of 70,000 or higher.

[0014] In step (1), the molar ratio of 2-chloromethylpyridine hydrochloride or 4-chloromethylpyridine hydrochloride to NaOH is 1:1; the molar ratio of 2-chloromethylpyridine hydrochloride or 4-chloromethylpyridine hydrochloride to PEI (based on monomer) is 1:1.

[0015] In step (2), the amount of NaOH added is the same as that added in step (1).

[0016] In step (3), the water bath heating temperature is 60-70℃ and the heating time is 1h.

[0017] The method for highly selectively removing Cu(II) from industrial wastewater using pyridine-modified polyethyleneimine, as described above, includes the following steps:

[0018] (1) PPEI was added to copper-containing industrial wastewater at a molar ratio of PPEI to Cu(II) of 4:1 and stirred. PPEI selectively chelates Cu(II) in the wastewater.

[0019] (2) The fully reacted solution is filtered through an electro-filtering device to obtain a concentrated solution enriched with chelates and wastewater after copper removal;

[0020] (3) The concentrated solution filtered in step (2) is placed in an electrolytic cell for electrolysis to recover copper and PPEI solution. The recovered PPEI solution can be recycled.

[0021] The method of this invention requires first measuring the concentration of Cu(II) in the wastewater for different industrial wastewaters, and then adding PPEI according to the molar ratio of PPEI to Cu(II) of 4:1 based on the amount of Cu(II) to achieve efficient chelation.

[0022] In step (2), the electro-optic ultrafiltration device includes a membrane tank; the membrane tank is provided with an inlet electrode plate, an outlet electrode plate, and an ultrafiltration membrane attached to the outlet electrode plate; the inlet electrode plate and the outlet electrode plate are arranged opposite to each other and are respectively connected to an external power source through wires; the inlet electrode plate and the outlet electrode plate are fixed in the membrane tank by a sealing device, and the space between the inlet electrode plate and the outlet electrode plate is enclosed by the sealing device to form a filtration area; the inlet electrode plate and the outlet electrode plate are both metal electrode plates, and the electrode plates are provided with through holes for water to pass through; the solution after reaction is pumped into the membrane tank by a pump, and after flowing through the filtration area, the macromolecules that have not passed through the ultrafiltration membrane flow out of the membrane tank through the concentrate outlet on one side of the inlet electrode plate, and the substances that have passed through the ultrafiltration membrane flow out of the membrane tank from the outlet outlet on one side of the outlet electrode plate.

[0023] The outlet electrode plate and the inlet electrode plate are connected to the positive and negative terminals of the power supply, respectively. The operating pressure of the ultrafiltration system is 0.15–0.20 MPa.

[0024] In step (3), the electrode spacing in the electrolytic cell is 8 cm, the electrolytic current is 0.2 A, and the current density is 44.44 A·m. -2 .

[0025] PPEI is made by introducing pyridine groups into polyethyleneimine (PEI) molecules. The introduction of these groups makes PPEI more selective for Cu(II), enabling it to chelate Cu(II) efficiently at lower pH levels. Under the condition of a PPEI:Cu(II) molar ratio of 4:1, combined with the use of an electrostatic ultrafiltration device, the removal rate of Cu(II) in wastewater can reach 95%. Finally, Cu(II) is recovered and PPEI is reused through the electrolysis of the concentrate.

[0026] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) The pyridine-modified polyethyleneimine (PPEI) of the present invention can chelate with Cu(II) in water with low pH, thereby overcoming the problem of poor binding force between existing polyelectrolyte materials and metal ions in water with low pH; (2) The method of the present invention achieves high selective removal of Cu(II) in industrial wastewater or complex water bodies containing copper in water with low pH by using polyelectrolyte materials with specific structures and specific molar ratios; the removal rate can reach more than 95%; the ultrafiltration process of the present invention can increase the membrane's antifouling ability by charging the membrane, and the membrane flux decrease rate is nearly 0.5 times that without charging; the method of the present invention can achieve low-cost treatment of industrial wastewater, which can remove Cu(II) from the wastewater and meet the wastewater discharge standards; and can also achieve selective capture and recovery of Cu(II). Attached Figure Description

[0027] Figure 1 The reaction equation for the preparation of pyridine-modified polyethyleneimine in Example 1;

[0028] Figure 2 The reaction equation for the preparation of pyridine-modified polyethyleneimine in Example 2;

[0029] Figure 3 Fourier transform infrared spectra of PPEI and PEI in Example 1;

[0030] Figure 4 The results of Cu(II) removal by different pH values ​​and different polyelectrolyte materials (PPEI and PEI) are shown.

[0031] Figure 5 This is a schematic diagram of the structure of an electro-optical ultrafiltration device.

[0032] Figure 6 This is a schematic diagram of the membrane tank in an electro-filtration device;

[0033] Figure 7 The results show the decrease in membrane flux over time under different power conditions. Detailed Implementation

[0034] Example 1

[0035] like Figure 1 As shown, the preparation method of pyridine-modified polyethyleneimine of the present invention specifically includes the following steps:

[0036] (1) Weigh 4.101g of 2-chloromethylpyridine hydrochloride and add it to a 50mL centrifuge tube; add an equivalent amount (relative to 2-chloromethylpyridine hydrochloride) of NaOH to the centrifuge tube to neutralize the hydrochloric acid in 2-chloromethylpyridine hydrochloride, that is, add 2.5mL of 10mol / L NaOH solution;

[0037] (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 2-chloromethylpyridine 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.

[0038] (3) Place the mixture in a 70°C water bath and stir. After 1 hour, a red precipitate will form in the solution and the rotor will not be able to rotate. At this time, add 2 mL of 5 mol / L H2SO4 solution and shake the centrifuge tube quickly so that the rotor can continue to rotate.

[0039] (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-yellow solution, i.e., 50 mL of PPEI aqueous solution with a concentration of 0.5 mol / L.

[0040] Figure 3 The Fourier transform infrared (FTIR) spectra of branched PEI and PPEI products are presented. The FTIR spectrum of PEI exhibits typical characteristic peaks, namely the NH stretching vibrations of the primary and secondary amines at approximately 3300-3500 cm⁻¹. -1 The bending length of NH is approximately 1600-1650 cm. -1 The CN length is approximately 1050cm. -1 In contrast, the infrared absorption spectrum of PPEI shows that -C=C- at 1472 cm⁻¹ -1 and -C=N- at 1570cm -1 Additional tensile vibration absorption peaks were observed at 1435 and 999 cm⁻¹, respectively. -1 The deformation absorption peaks of the ring plane of the 2-substituted pyridine group appeared at all positions, and these characteristic peaks confirmed that the 2-methylpyridine group had been successfully grafted onto the main chain of PEI.

[0041] Example 2

[0042] like Figure 2 As shown, the preparation method of pyridine-modified polyethyleneimine of the present invention specifically includes the following steps:

[0043] (1) Weigh 4.101g of 4-chloromethylpyridine hydrochloride (amount n = 0.025mol) and add it to a 50mL centrifuge tube; add an equivalent amount (relative to 4-chloromethylpyridine hydrochloride) of NaOH to the centrifuge tube to neutralize the hydrochloric acid in the 4-chloromethylpyridine hydrochloride, that is, add 2.5mL of 10mol / L NaOH solution;

[0044] (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-chloromethylpyridine 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.

[0045] (3) Place the mixture in a 70°C water bath and stir. After 1 hour, a red precipitate will form in the solution and the rotor will not be able to rotate. At this time, add 2 mL of 5 mol / L H2SO4 solution and shake the centrifuge tube quickly so that the rotor can continue to rotate.

[0046] (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-yellow solution, i.e., 50 mL of PPEI aqueous solution with a concentration of 0.5 mol / L.

[0047] Example 3

[0048] The method for highly selective removal of Cu(II) from copper-containing wastewater using pyridine-modified polyethyleneimine prepared in Example 1, wherein the initial Cu(II) concentration in the copper-containing wastewater is 1 mM and the pH of the copper-containing wastewater is 3, is as follows:

[0049] (1) Add 16 mL of the PPEI aqueous solution prepared in Example 1 to 2000 mL of copper-containing wastewater at a PPEI to Cu(II) molar ratio of 4:1 and stir. PPEI selectively chelates Cu(II) in the wastewater.

[0050] (2) Stir for 10 seconds, and filter the fully reacted solution through an electric ultrafiltration device. The electrode voltage is constant at 0.2V, and the ultrafiltration pressure is maintained at 0.15-0.20Mpa. After filtration for 8 hours, a concentrated solution with a concentration of 5 times and a Cu(II) removal rate of more than 95% can be obtained. The Cu(II) concentration in the effluent is below 0.05mM.

[0051] (3) The concentrated solution filtered in step (2) is placed in an electrolytic cell for electrolysis. The anode and cathode electrodes are graphite sheets and copper sheets, respectively. The effective size of the electrode plates is 9×5cm, the electrode spacing is 8cm, the current during the electrolysis process is constant at 0.2A, and the copper recovery rates after 1h, 5h and 8h of electrolysis are 20.3%, 0.666% and 84.0%, respectively. The PPEI solution after electrolysis can be recycled.

[0052] Figure 5 This is a schematic diagram of the structure of an electro-optical ultrafiltration device. The electro-optical ultrafiltration device of this invention is a tangential flow filtration system, which... Figures 5-6 It is known that the electro-assisted ultrafiltration device includes an inlet, an outlet, and a concentrate outlet; the electro-assisted ultrafiltration device also includes a membrane tank; the membrane tank is equipped with an inlet electrode plate, an outlet electrode plate, and an ultrafiltration membrane attached to the outlet electrode plate; the inlet electrode plate and the outlet electrode plate are arranged opposite to each other and are respectively connected to an external power source through wires; the inlet electrode plate and the outlet electrode plate are fixed in the membrane tank by a sealing device, and the space between the inlet electrode plate and the outlet electrode plate is enclosed by the sealing device to form a filtration area; both the inlet electrode plate and the outlet electrode plate are metal electrode plates, and the electrode plates are provided with through holes for water to pass through; the solution after the reaction is pumped into the membrane tank by a pump, and after flowing through the filtration area, the macromolecules that have not passed through the ultrafiltration membrane flow out of the membrane tank through the concentrate outlet on the side of the inlet electrode plate, and the substances that have passed through the ultrafiltration membrane flow out of the membrane tank from the outlet outlet on the side of the outlet electrode plate.

[0053] The electro-optic ultrafiltration process is as follows: the feed is pumped into the membrane tank and provided with the pressure required for ultrafiltration (0.15~0.20 MPa). The concentrate outlet flows out of the membrane tank from one side of the inlet electrode plate. The filtrate passes through the ultrafiltration membrane to obtain copper-removed water. The electro-optic ultrafiltration device also includes a pump set, which consists of a peristaltic pump and a constant pressure regulating valve. The membrane tank includes two coplanar electrode plates (circular electrode plates), which are made of titanium plated with platinum. The electrode plates have through holes for water to pass through. The diameter of each electrode plate is d = 10 cm, and the spacing is 5 mm. The ultrafiltration membrane is a polyethersulfone ultrafiltration membrane with an effective filtration size of diameter d = 10 cm. The ultrafiltration membrane is in contact with the outlet electrode plate. The two coplanar electrode plates are connected to the power supply through wires. The outlet electrode plate and the inlet electrode plate are connected to the positive and negative terminals of the power supply, respectively. The power supply is a DC power supply.

[0054] Figure 7The graph illustrates the variation in membrane flux under different power sources. 0.2V indicates that the effluent and influent electrode plates are connected to the positive and negative terminals of a power source, respectively, with a constant 0.2V voltage provided. 0V indicates no power supply. -0.2V indicates that the effluent and influent electrode plates are connected to the negative and positive terminals of a power source, respectively, with a constant 0.2V voltage provided. The results show that under 0.2V conditions, the decrease in membrane flux is 0.42 times that under no power supply and 0.30 times that under -0.2V conditions, respectively. This indicates that under 0.2V conditions, the ultrafiltration membrane exhibits better antifouling performance and can treat more wastewater in the same filtration time.

[0055] Example 4

[0056] The process of Example 4 is basically the same as that of Example 3, except that the initial pH of the copper-containing wastewater is 1; the concentration of Cu(II) in the filtrate is below 0.08 mM; and the copper recovery rate is 82.0% after 8 hours of electrolysis.

[0057] Comparative Example 1

[0058] The process of Comparative Example 1 is basically the same as that of Example 3, except that in step (1), PEI is added to the copper-containing wastewater at a molar ratio of 4:1 to Cu(II); after filtration, the concentration of Cu(II) in the copper-removed wastewater is 46%.

[0059] Comparative Example 2

[0060] The process of Comparative Example 2 is basically the same as that of Example 4, except that in step (1), PEI is added to the copper-containing wastewater at a molar ratio of 4:1 to Cu(II); after filtration, the concentration of Cu(II) in the copper-removed wastewater is 28%.

[0061] Under two different pH conditions, with an initial Cu(II) concentration of 1 mM, PEI and PPEI solutions with different proportions of Cu(II) were added to the solution. The complexation with Cu(II) was completed within 10 seconds under stirring. The Cu(II) concentration in the effluent was detected by ultrafiltration, and the removal rate results are as follows: Figure 4 .pass Figure 4 It can be seen that when the molar ratio of PPEI to Cu(II) is 4:1, the removal rate of copper by PPEI reaches more than 92%.

Claims

1. A method for highly selective removal of Cu(II) from industrial wastewater based on pyridine-modified polyethyleneimine, characterized in that, Includes the following steps: (1) PPEI was added to copper-containing industrial wastewater at a molar ratio of PPEI to Cu(II) of 4:1 and stirred. PPEI selectively chelates Cu(II) in the wastewater. The pH of the copper-containing wastewater is 3. (2) Stir for 10 seconds, and filter the fully reacted solution through an electro-filtration device to obtain a concentrated solution enriched with chelates and wastewater after copper removal. (3) The concentrated solution filtered in step (2) is placed in an electrolytic cell for electrolysis to recover copper and PPEI solution. The recovered PPEI solution can be recycled. In step (1), the structural formula of the PPEI is: The PPEI has a molecular weight of 218,000 or higher.

2. The method according to claim 1, characterized in that: The PPEI was prepared using the following method, with the specific steps as follows: (1.1) First, mix 2-chloromethylpyridine hydrochloride or 4-chloromethylpyridine hydrochloride with NaOH, and after the reaction, add PEI aqueous solution to it; (1.2) NaOH was then added to the mixed solution again to neutralize the hydrochloric acid produced in the reaction; (1.3) The mixture from step (1.2) is heated in a water bath and stirred, and a precipitate is formed; (1.4) Add sulfuric acid solution to it. The precipitate dissolves slowly under acidic conditions. Heat the solution in a water bath and stir until there is no more precipitate in the solution to obtain PPEI aqueous solution.

3. The method according to claim 2, characterized in that: In step (1.1), the PEI is a branched chain structure with a molecular weight of 70,000 or higher.

4. The method according to claim 2, characterized in that: In step (1.1), the molar amounts of 2-chloromethylpyridine hydrochloride or 4-chloromethylpyridine hydrochloride and NaOH are the same; on a monomer basis, the molar amounts of 2-chloromethylpyridine hydrochloride or 4-chloromethylpyridine hydrochloride and PEI are the same.

5. The method according to claim 2, characterized in that: In step (1.2), the amount of NaOH added again is the same as that added in step (1.1).

6. The method according to claim 2, characterized in that: In step (1.3), the water bath heating temperature is 60-70℃ and the heating time is not less than 1 hour.

7. The method according to claim 1, characterized in that: In step (2), the electro-filtration device includes a membrane tank; the membrane tank is provided with an inlet electrode plate, an outlet electrode plate, and an ultrafiltration membrane attached to the outlet electrode plate; the inlet electrode plate and the outlet electrode plate are arranged opposite to each other and are respectively connected to an external power source through wires; the inlet electrode plate and the outlet electrode plate are fixed in the membrane tank by a sealing device, and the space between the inlet electrode plate and the outlet electrode plate is enclosed by the sealing device to form a filtration area; the inlet electrode plate and the outlet electrode plate are provided with through holes for water to pass through; the solution after reaction is pumped into the membrane tank by a pump, and after flowing through the filtration area, the macromolecules that have not passed through the ultrafiltration membrane flow out of the membrane tank through the concentrate outlet on the side of the inlet electrode plate, and the substances that have passed through the ultrafiltration membrane flow out of the membrane tank from the outlet outlet on the side of the outlet electrode plate.

8. The method according to claim 7, characterized in that: The outlet electrode plate and the inlet electrode plate are connected to the positive and negative terminals of the power supply, respectively. The working pressure of the ultrafiltration is 0.15 to 0.20 MPa.

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