A method for preparing a proton-buffered polymeric adsorbent for removing hexavalent chromium

Abstract

The application relates to a preparation method of a proton buffer polymer adsorbent for removing hexavalent chromium, and relates to a preparation method of a hexavalent chromium adsorbent. The application aims to solve the technical problem that the existing nitrogen-containing polymer adsorbent has poor adsorption effect on hexavalent chromium anions under alkaline conditions. In the process of synthesizing the polyamine adsorbent, acrylic small-molecule compounds are introduced, the double bonds in the molecules of the acrylic small-molecule compounds can be opened under the action of active free radicals and form carbon positive free radicals, the carbon positive free radicals can collide with amine monomer free radicals with opened double bonds, and the acrylic-amine polymer is successfully crosslinked and polymerized under the action of a crosslinking agent. Experimental results prove that the proton buffer adsorbent provided by the application can efficiently remove Cr(VI) under wide pH conditions (pH=1-10), and the removal rate under alkaline conditions is kept above 79.5%.

Description

Technical Field

[0001] The invention relates to a method for preparing a hexavalent chromium adsorbent. Background Art

[0002] Hexavalent chromium is a highly toxic carcinogen. Severe hexavalent chromium pollution in water bodies can endanger human life and health. Adsorption technology has many advantages in water treatment, such as high efficiency, wide applicability, simple operation, resource recycling, and environmental friendliness. It is an important water treatment method. Polymers are compounds with large relative molecular mass composed of many structurally identical, simple chemical structures repeatedly connected by covalent bonds. Polymer adsorbents have great potential for water treatment applications due to their wide range of functional group selection, adjustable structural design, simple synthesis methods, high chemical stability, and high mechanical strength. There is a strong coordination or electrostatic interaction between nitrogen and chromium. By selecting small molecular monomers with nitrogen functional groups (pyridine, amine, pyrrole, etc.) and the appropriate polymerization reaction type, nitrogen-containing polymers can be obtained for the selective removal of Cr(VI) from water bodies. However, the removal of Cr(VI) by nitrogen-containing adsorbents mainly relies on the strong electrostatic interaction between the protonated N functional groups and Cr(VI), which results in the adsorption of Cr(VI) by nitrogen-containing adsorbents being highly dependent on the environmental pH. The highest adsorption capacity is usually obtained at a lower pH, and the adsorption capacity will drop significantly under alkaline conditions. Summary of the Invention

[0003] The present invention aims to solve the technical problem that the existing nitrogen-containing polymer adsorbent has poor adsorption effect on hexavalent chromium anions under alkaline conditions, and provides a preparation method of a proton buffering polymer adsorbent for removing hexavalent chromium.

[0004] The preparation method of the proton buffering polymer adsorbent for removing hexavalent chromium of the present invention is carried out according to the following steps:

[0005] 1. Add amino monomer, acrylic monomer, crosslinker, initiator and organic solvent to a stoppered glass bottle, then tighten the cap and ultrasonicate at room temperature for 20-30 minutes to completely dissolve the solids and mix them evenly.

[0006] The amino monomer is 4-vinylbenzylamine or 4-vinylaniline (containing a small molecule compound capable of providing electrostatic interaction sites);

[0007] The acrylic acid monomer is acrylic acid, itaconic acid or 2-(trifluoromethyl) acrylic acid (containing a small molecule compound that can provide a proton buffer site);

[0008] The molar ratio of the amino monomer to the acrylic monomer is (1-9):(9-1);

[0009] 2. Take out the glass bottle containing the mixed reaction solution in step 1, open the bottle cap, seal the bottle mouth with plastic wrap, pass the air inlet tube through the plastic wrap and insert it below the liquid surface, continuously introduce nitrogen into the glass bottle for 5 minutes to 10 minutes to expel air, remove the air inlet tube and quickly tighten the bottle cap, and place the glass bottle in a constant temperature box to cause polymerization reaction to obtain a polymer solid;

[0010] The polymerization temperature is 60°C to 90°C and the time is 24h to 25h;

[0011] 3. The polymer solid obtained in step 2 is washed with methanol and deionized water for multiple times to remove small molecular oligomers and impurities, and then dried, ground and sieved in sequence to obtain an acrylic acid-amine polymer adsorbent.

[0012] The key point of the present invention is to introduce a Brønsted acid monomer during the synthesis of a polyamine adsorbent, which serves to provide proton buffering sites for the polymer adsorbent. The Brønsted acid monomer is a small molecule acrylic acid compound containing a small molecule compound capable of providing proton buffering sites. The double bond within the molecule can be opened under the initiation of active free radicals to form a carbon positive free radical, which can collide with the amino monomer free radical whose double bond has also been opened, and successfully cross-link and polymerize under the action of a cross-linking agent to prepare an acrylic acid-amine polymer; the proton carried by the carboxyl group (-COOH) within the molecule can be released when the ambient pH is higher than its acidity coefficient, forming a proton buffering site (-COO - ). The present invention utilizes organic conjugate acid-base to react -COOH / -COO - The ability to store and release protons imparts proton buffering functionality to amino-based adsorbents. Experimental results demonstrate that the introduction of acrylic monomers effectively reduces the alkalinity of the polymer and significantly improves its Cr(VI) removal efficiency under alkaline conditions. The proton buffering adsorbent provided by the present invention efficiently removes Cr(VI) over a wide range of pH conditions (pH = 1-10), maintaining a removal rate exceeding 79.5% under alkaline conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 A synthetic route for preparing the proton-buffered polymer of the present invention;

[0014] Figure 2 The equilibrium pH value of the product obtained in the above test when stably dispersed in deionized water;

[0015] Figure 3 The adsorption effect of Be-AP prepared in experiment 18, Be4Ac1 prepared in experiment 1, and Be4Tf1 prepared in experiment 10 on Cr(VI) under alkaline conditions;

[0016] Figure 4The adsorption effect of Be-AP prepared in experiment 18, Be4Tf1 prepared in experiment 10, Be1Tf1 prepared in experiment 12, Be1Tf4 prepared in experiment 13 and Tf prepared in experiment 14 on Cr(VI) under different pH conditions is shown;

[0017] Figure 5 This is a data graph showing the effect of the initial pH value of the solution on the removal of Cr(VI) and Cr(total) by Be4Tf1 prepared in Experiment 10 and Be4Ac1 prepared in Experiment 1. DETAILED DESCRIPTION

[0018] Specific embodiment 1: This embodiment is a preparation method of a proton buffered polymer adsorbent for removing hexavalent chromium, which is specifically carried out according to the following steps:

[0019] 1. Add amino monomer, acrylic monomer, crosslinker, initiator and organic solvent to a stoppered glass bottle, then tighten the cap and ultrasonicate at room temperature for 20-30 minutes to completely dissolve the solids and mix them evenly.

[0020] The amino monomer is 4-vinylbenzylamine or 4-vinylaniline;

[0021] The acrylic acid monomer is acrylic acid, itaconic acid or 2-(trifluoromethyl) acrylic acid;

[0022] The molar ratio of the amino monomer to the acrylic monomer is (1-9):(9-1);

[0023] 2. Take out the glass bottle containing the mixed reaction solution in step 1, open the bottle cap, seal the bottle mouth with plastic wrap, pass the air inlet tube through the plastic wrap and insert it below the liquid surface, continuously introduce nitrogen into the glass bottle for 5 minutes to 10 minutes to expel air, remove the air inlet tube and quickly tighten the bottle cap, and place the glass bottle in a constant temperature box to cause polymerization reaction to obtain a polymer solid;

[0024] The polymerization temperature is 60°C to 90°C and the time is 24h to 25h;

[0025] 3. The polymer solid obtained in step 2 is washed with methanol and deionized water for multiple times to remove small molecular oligomers and impurities, and then dried, ground and sieved in sequence to obtain an acrylic acid-amine polymer adsorbent.

[0026] Specific embodiment 2: This embodiment differs from specific embodiment 1 in that the crosslinking agent in step 1 is an oil-soluble crosslinking agent, specifically ethylene glycol dimethacrylate or trimethylolpropane trimethacrylate. Other aspects are the same as specific embodiment 1.

[0027] Specific embodiment 3: This embodiment differs from specific embodiments 1 or 2 in that the initiator in step 1 is an azo free radical initiator and / or a peroxide free radical initiator, specifically one or a mixture of azobisisobutyronitrile, azobisisoheptanenitrile, and benzoyl peroxide. Other aspects are the same as specific embodiments 1 or 2.

[0028] Specific embodiment 4: This embodiment differs from any one of specific embodiments 1 to 3 in that the organic solvent in step 1 is toluene, tetrahydrofuran, dimethyl sulfoxide, N,N-dimethylformamide, acetonitrile, dichloroethane, chloroform, cyclohexanol, 2-methoxyethanol, isopropanol, ethanol, or methanol. Otherwise, this embodiment is the same as any one of specific embodiments 1 to 3.

[0029] Specific embodiment 5: This embodiment differs from specific embodiment 4 in that the ratio of the sum of the amount of the amino monomer and the acrylic monomer to the amount of the crosslinking agent in step 1 is 5:1. Other aspects are the same as specific embodiment 4.

[0030] Specific embodiment 6: This embodiment differs from specific embodiment 5 in that the volume ratio of the sum of the amounts of the amino monomer and acrylic monomer described in step 1 to the organic solvent is (1 mmol to 2 mmol): (2 mL to 4 mL). Other aspects are the same as specific embodiment 5.

[0031] Specific embodiment 7: This embodiment differs from specific embodiment 6 in that the mass ratio of the crosslinking agent to the initiator in step 1 is (1 mmol to 2 mmol): (80 mg to 120 mg). Other aspects are the same as specific embodiment 6.

[0032] Specific embodiment eight: This embodiment differs from specific embodiment seven in that in step three, the polymer solid obtained in step two is washed 1 to 5 times with methanol and deionized water to remove small molecule oligomers and impurities. Other aspects are the same as specific embodiment seven.

[0033] Specific embodiment 9: This embodiment differs from specific embodiment 8 in that the drying temperature in step 3 is 60° C. to 120° C. The rest is the same as specific embodiment 8.

[0034] The present invention is verified by the following test:

[0035] Experiment 1: This experiment is a method for preparing a proton-buffered polymer adsorbent for removing hexavalent chromium, which is specifically carried out in the following steps:

[0036] 1. Add amino monomer, acrylic monomer, crosslinker (trimethylolpropane trimethacrylate, 1 mmol), initiator (azobisisobutyronitrile, 100 mg) and organic solvent (10 mL of methanol) to a stoppered glass bottle, then tighten the cap and sonicate at room temperature for 30 min to completely dissolve the solids and mix evenly;

[0037] The amino monomer is 4-vinylbenzylamine, 4 mmol;

[0038] The acrylic acid monomer is acrylic acid, 1 mmol;

[0039] 2. Take out the glass bottle containing the mixed reaction solution in step 1, open the bottle cap, seal the bottle mouth with plastic wrap, pass the air inlet tube through the plastic wrap and insert it below the liquid surface, continuously introduce nitrogen gas into the glass bottle for 5 minutes to expel the air, remove the air inlet tube and quickly tighten the bottle cap, and place the glass bottle in a constant temperature box to allow polymerization reaction to occur to obtain a polymer solid, named Be4Ac1;

[0040] The polymerization temperature was 70°C and the reaction time was 24 h;

[0041] 3. The polymer solid obtained in step 2 was washed twice with methanol and deionized water respectively to remove small molecular oligomers and impurities, and then dried, ground and sieved in sequence to obtain an acrylic acid-amine polymer adsorbent named Be4Ac1; the drying temperature was 100°C.

[0042] Experiment 2: This experiment differs from Experiment 1 in that the amino monomer in Step 1 is 4-vinylbenzylamine (2.5 mmol), the acrylic monomer is acrylic acid (2.5 mmol), and the final product in Step 3 is named Be1Ac1. All other conditions are the same as Experiment 1.

[0043] Experiment 3: This experiment differs from Experiment 1 in that the amino monomer in Step 1 is 1 mmol of 4-vinylbenzylamine; the acrylic monomer is 4 mmol of acrylic acid; and the final product in Step 3 is named Be1Ac4. All other conditions are the same as Experiment 1.

[0044] Experiment 4: This experiment is a comparative experiment. The difference from Experiment 1 is that no amino monomer is added in step 1, the acrylic acid monomer is 0.345 mL of acrylic acid, and the final product of step 3 is pure acrylic acid polymer (Ac). Other aspects are the same as Experiment 1.

[0045] Experiment 5: This experiment differs from Experiment 1 in that the acrylic acid monomer in Step 1 is itaconic acid (1 mmol) and the final product in Step 3 is named Be4It1. Other modifications are the same as Experiment 1.

[0046] Experiment 6: This experiment differs from Experiment 5 in that the amino monomer in Step 1 is 4-vinylbenzylamine (3 mmol), the acrylic acid monomer is itaconic acid (2 mmol), and the final product in Step 3 is named Be3It2. All other conditions are the same as Experiment 5.

[0047] Experiment 7: This experiment differs from Experiment 5 in that the amino monomer in step 1 is 4-vinylbenzylamine (2.5 mmol), the acrylic acid monomer is itaconic acid (2.5 mmol), and the final product in step 3 is named Be1It1. All other conditions are the same as Experiment 5.

[0048] Experiment 8: This experiment differs from Experiment 5 in that the amino monomer in step 1 is 4-vinylbenzylamine, 1 mmol; the acrylic acid monomer is itaconic acid, 4 mmol; and the final product in step 3 is named Be1It4. All other conditions are the same as Experiment 5.

[0049] Experiment 9: This experiment is a comparative experiment. The differences from Experiment 5 are as follows: in step 1, no amino monomer is added, the acrylic monomer is 0.6505 g of itaconic acid, and the final product of step 3 is pure itaconic acid polymer (It). Other conditions are the same as Experiment 5.

[0050] Experiment 10: This experiment differs from Experiment 1 in that the acrylic monomer in Step 1 is 1 mmol of 2-(trifluoromethyl)acrylic acid, and the order of addition must be methanol first, followed by 4-vinylbenzylamine, to prevent fuming (i.e., the formation of the ammonium salt followed by the amidation reaction). The final product in Step 3 is named Be4Tf1. All other conditions are the same as in Experiment 1.

[0051] Experiment 11: This experiment differs from Experiment 10 in that the amino monomer in Step 1 is 4-vinylbenzylamine (3 mmol); the acrylic monomer is 2-(trifluoromethyl)acrylic acid (2 mmol); and the final product in Step 3 is named Be3Tf2. All other conditions are the same as Experiment 10.

[0052] Experiment 12: This experiment differs from Experiment 10 in that the amino monomer in Step 1 is 4-vinylbenzylamine (2.5 mmol); the acrylic monomer is 2-(trifluoromethyl)acrylic acid (2.5 mmol); and the final product in Step 3 is named Be1Tf1. All other conditions are the same as Experiment 10.

[0053] Experiment 13: This experiment differs from Experiment 10 in that the amino monomer in Step 1 is 1 mmol of 4-vinylbenzylamine; the acrylic monomer is 4 mmol of 2-(trifluoromethyl)acrylic acid; and the final product in Step 3 is named Be1Tf4. All other conditions are the same as Experiment 10.

[0054] Experiment 14: This experiment was a comparative experiment. The differences from Experiment 10 were as follows: no amino monomer was added in Step 1, and the acrylic monomer was 0.7003 g of 2-(trifluoromethyl)acrylic acid; the final product of Step 3 was a 2-(trifluoromethyl)acrylic acid polymer (Tf). All other conditions were the same as Experiment 10.

[0055] Experiment 15: This experiment differs from Experiment 1 in that the amino monomer in Step 1 is 4.5 mmol of 4-vinylaniline; the acrylic monomer in Step 1 is 0.5 mmol of 2-(trifluoromethyl)acrylic acid; and the final product in Step 3 is named Ph9Tf1. All other conditions are the same as Experiment 1.

[0056] Experiment 16: This experiment differed from Experiment 15 in that the amino monomer in Step 1 was 4 mmol of 4-vinylaniline; the acrylic monomer was 1 mmol of 2-(trifluoromethyl)acrylic acid; and the final product in Step 3 was named Ph4Tf1. All other conditions were the same as Experiment 15.

[0057] Experiment 17: This experiment differs from Experiment 15 in that the amino monomer in Step 1 is 4-vinylaniline (3.5 mmol); the acrylic monomer is 2-(trifluoromethyl)acrylic acid (1.5 mmol); and the final product in Step 3 is named Ph7Tf3. All other conditions are the same as Experiment 15.

[0058] Experiment 18: This experiment is a comparative experiment. The differences from Experiment 1 are as follows: no acrylic acid monomer is added in Step 1, the amino monomer is 4-vinylbenzylamine (5 mmol), and the final product of Step 3 is a benzylamine polymer (Be-AP). All other conditions are the same as Experiment 1.

[0059] Experiment 19: This experiment is a comparative experiment. The differences from Experiment 1 are as follows: no acrylic acid monomer is added in Step 1, the amino monomer is 4-vinylaniline (5 mmol), and the final product of Step 3 is an aniline polymer (Ph-AP). Other conditions are the same as Experiment 1.

[0060] Experiment 20: This experiment is a comparative experiment. The differences from Experiment 1 are as follows: no acrylic monomer and amino monomer are added in Step 1; the final product of Step 3 is CP. All other aspects are the same as Experiment 1.

[0061] Figure 1 This is the synthetic route for preparing the proton-buffered polymer of the present invention. The light green part is the amino monomer and the pink part is the acrylic monomer.

[0062] Figure 2 The pH value of the product obtained in the above test when stably dispersed in deionized water is balanced. Figure 2The results show that the introduction of acrylic acid monomers effectively reduces the alkalinity of polyamine materials and buffers the pH change of the aqueous environment caused by amino groups. The ability of different types of acrylic acid to reduce the alkalinity of polymers is closely related to the pK a Positively correlated, pK a The smaller the value, the stronger the buffering capacity, that is, the ability to buffer the pH changes caused by amino groups is as follows: Tf>It>Ac.

[0063] Figure 3 Figure 1 shows the adsorption effect of Be-AP prepared in experiment 18, Be4Ac1 prepared in experiment 1, and Be4Tf1 prepared in experiment 10 on Cr(VI) under alkaline conditions. The initial Cr(VI) concentration was 45±1 mg·L -1 ; Figure 4 Figure 1 shows the adsorption effect of Be-AP prepared in experiment 18, Be4Tf1 prepared in experiment 10, Be1Tf1 prepared in experiment 12, Be1Tf4 prepared in experiment 13, and Tf prepared in experiment 14 on Cr(VI) under different pH conditions. The initial Cr(VI) concentration was 50±2 mg·L -1 . Figure 3 and Figure 4 It was verified that the introduction of acrylic acid monomers significantly increased the adsorption capacity of Cr(VI) by polyamine materials under alkaline conditions.

[0064] Figure 5 Figure 2 shows the effect of the initial pH value of the solution on the removal of Cr(VI) (Figure a) and Cr(total) (Figure b) by Be4Tf1 prepared in Experiment 10 and Be4Ac1 prepared in Experiment 1. The initial Cr(VI) concentration was 45±3 mg·L -1 . Figure 5 It shows that Be4Tf1 prepared in experiment 10 can efficiently remove Cr(VI) under a wide range of pH conditions (pH=1~10), and the removal rate remains above 79.5% under alkaline conditions.

Claims

1. A method for preparing a proton-buffered polymer adsorbent for removing hexavalent chromium, characterized in that The preparation method of the proton buffered polymer adsorbent for removing hexavalent chromium is carried out according to the following steps:

1. Add amino monomer, acrylic monomer, crosslinker, initiator and organic solvent to a stoppered glass bottle, then tighten the cap and ultrasonicate at room temperature for 20-30 minutes to completely dissolve the solids and mix them evenly. The amino monomer is 4-vinylbenzylamine or 4-vinylaniline; The acrylic acid monomer is acrylic acid, itaconic acid or 2-(trifluoromethyl) acrylic acid; The molar ratio of the amino monomer to the acrylic monomer is (1-9):(9-1); 2. Take out the glass bottle containing the mixed reaction solution in step 1, open the bottle cap, seal the bottle mouth with plastic wrap, pass the air inlet tube through the plastic wrap and insert it below the liquid surface, continuously introduce nitrogen into the glass bottle for 5 minutes to 10 minutes to expel air, remove the air inlet tube and quickly tighten the bottle cap, and place the glass bottle in a constant temperature box to cause polymerization reaction to obtain a polymer solid; The polymerization temperature is 60°C to 90°C and the time is 24h to 25h; 3. The polymer solid obtained in step 2 is washed with methanol and deionized water for multiple times to remove small molecular oligomers and impurities, and then dried, ground and sieved in sequence to obtain an acrylic acid-amine polymer adsorbent.

2. The method for preparing a proton-buffered polymer adsorbent for removing hexavalent chromium according to claim 1, characterized in that The cross-linking agent in step 1 is an oil-soluble cross-linking agent, specifically ethylene glycol dimethacrylate or trimethylolpropane trimethacrylate.

3. The method for preparing a proton-buffered polymer adsorbent for removing hexavalent chromium according to claim 1, characterized in that The initiator described in step 1 is an azo free radical initiator and / or a peroxide free radical initiator, specifically one or a mixture of azobisisobutyronitrile, azobisisoheptanenitrile and benzoyl peroxide.

4. The method for preparing a proton buffering polymer adsorbent for removing hexavalent chromium according to claim 1, characterized in that The organic solvent described in step 1 is toluene, tetrahydrofuran, dimethyl sulfoxide, N,N-dimethylformamide, acetonitrile, dichloroethane, chloroform, cyclohexanol, 2-methoxyethanol, isopropanol, ethanol or methanol.

5. The method for preparing a proton-buffered polymer adsorbent for removing hexavalent chromium according to claim 1, characterized in that The ratio of the sum of the amounts of the amino monomer and the acrylic monomer to the amount of the cross-linking agent in step 1 is 5:

1.

6. The method for preparing a proton-buffered polymer adsorbent for removing hexavalent chromium according to claim 1, characterized in that The volume ratio of the sum of the amounts of the amino monomer and the acrylic monomer described in step 1 to the organic solvent is (1 mmol to 2 mmol): (2 mL to 4 mL).

7. The method for preparing a proton-buffered polymer adsorbent for removing hexavalent chromium according to claim 1, characterized in that The ratio of the amount of the cross-linking agent described in step 1 to the mass of the initiator is (1 mmol to 2 mmol): (80 mg to 120 mg).

8. The method for preparing a proton buffering polymer adsorbent for removing hexavalent chromium according to claim 1, characterized in that In step three, the polymer solid obtained in step two is washed with methanol and deionized water for 1 to 5 times to remove small molecular oligomers and impurities.

9. The method for preparing a proton buffering polymer adsorbent for removing hexavalent chromium according to claim 1, characterized in that The drying temperature in step 3 is 60°C to 120°C.

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