Preparation method of modified membrane material and application thereof in water treatment

Abstract

The present application relates to the technical field of adsorption membrane, and discloses a preparation method of modified membrane material and application thereof in water treatment, wherein polyacrylonitrile fiber membrane is added into a benzophenone-containing acetone solution, and after soaking, the fiber membrane is irradiated under a UV lamp for activation, then is added into a polymer monomer solution, and after soaking, the fiber membrane is irradiated under a UV lamp for polymerization reaction, thereby obtaining the modified membrane material.The present application grafts three-dimensional network structure polyacrylic acid cross-linked polymer gel on the surface of the polyacrylonitrile fiber membrane, which is beneficial to improve the water absorption rate of the fiber membrane.Meanwhile, the polyacrylic acid cross-linked polymer gel contains a large number of carboxyl, primary amino and dithio carbamate groups, and has strong chelation adsorption capacity and removal rate for metal ions such as lead and cadmium.The present application can be used as ultrafiltration membrane, permeation membrane and filtration membrane materials, and has good practical application in metal-containing wastewater treatment.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of adsorption membrane technology, in particular to a preparation method of modified membrane material and application thereof in water treatment. BACKGROUND

[0002] Polyacrylonitrile fiber membrane has good acid and alkali resistance, heat resistance, mechanical strength and dimensional stability, and its preparation method is simple, cheap and easy to obtain, and it can be made into ultrafiltration membrane, permeation membrane, separation membrane and other products, and has wide application in wastewater treatment and material separation. The traditional polyacrylonitrile fiber membrane has poor hydrophilicity, low water absorption rate, and low adsorption performance for lead, cadmium and other metal ions, which limits its practical application in metal-containing wastewater treatment.

[0003] At present, the modification methods of polyacrylonitrile fiber membrane mainly include graft modification, hydrolysis modification and coating modification. The Chinese patent with publication number CN110975651B discloses a multifunctional high-efficiency sewage treatment membrane and a preparation method thereof. Polyaniline nanoparticles are in-situ polymerized and grown on the polyacrylonitrile fiber skeleton, and then polyacrylic acid and polyethyleneimine are sequentially modified on the membrane surface by chemical grafting method. The prepared sewage treatment membrane has good water absorption and adsorption performance. However, the membrane material does not exhibit good adsorption performance and removal rate for lead, cadmium and other metal ions. SUMMARY

[0004] The present application solves the problem of poor hydrophilicity and poor adsorption performance for metal ions of polyacrylonitrile fiber membrane material.

[0005] The technical scheme of the present application is a preparation method of modified membrane material:

[0006] (1) adding N,N'-bis(2-hydroxyethyl)ethylenediamine (CAS registration number 4439-20-7), N-Boc-bromoethylamine (CAS registration number 39684-80-5) and triethylamine in a molar ratio of 1:(2-2.4):(4-6) into N,N-dimethylformamide, stirring at 0-5℃ for 18-24h to carry out substitution reaction, reducing pressure distillation, silica gel column chromatography separation, eluting with petroleum ether and ethyl acetate solution to obtain an intermediate. The preparation reaction formula is:

[0007]

[0008] (2) adding the bis-amino cross-linking monomer intermediate, acryloyl chloride and triethylamine into dichloromethane at a molar ratio of 1: (2-2.6): (2-2.2) at 0-5℃, stirring at 20-25℃ for acyl chloride esterification reaction for 8-10h, adding trifluoroacetic acid into the filtrate after filtration, stirring at 20-30℃ for 4-6h to remove the boc protective group, then adding sodium bicarbonate solution, stirring and standing to separate layers, removing the water phase, collecting dichloromethane organic phase, distilling under reduced pressure, and separating by silica gel column chromatography, eluting with petroleum ether and ethyl acetate solution to obtain the bis-amino cross-linking monomer. The preparation reaction formula is as follows:

[0009]

[0010] (3) adding acrylic acid and bis-amino cross-linking monomer into deionized water to obtain a polymerization monomer solution.

[0011] (4) adding the polyacrylonitrile fiber membrane into the acetone solution containing benzophenone, soaking, and irradiating the fiber membrane under the ultraviolet lamp for activation, washing with acetone and drying, then adding into the polymerization monomer solution, soaking, taking out the fiber membrane, and irradiating under the ultraviolet lamp for polymerization reaction, washing with acetone, and extracting the fiber membrane in a Soxhlet extractor with xylene, drying the fiber membrane after extraction to obtain the modified membrane material.

[0012] Preferably, the concentration of the acrylic acid in the polymerization monomer solution in (3) is 1.5-6 mol / L.

[0013] Preferably, the concentration of the bis-amino cross-linking monomer in (3) is 0.03-0.1 mol / L.

[0014] Preferably, the concentration of benzophenone in the acetone solution in (4) is 0.05-0.18 mol / L.

[0015] Preferably, the power of the ultraviolet lamp in (4) is 200-400W; the time for irradiation activation is 20-30min; and the time for polymerization reaction is 30-50min.

[0016] Preferably, the modified membrane material further comprises a dithio-carbamate modified membrane material. The preparation method is as follows: adding the modified membrane material into a 10-18% sodium hydroxide aqueous solution, adding carbon disulfide ethanol solution, controlling the mass ratio of the modified membrane material and carbon disulfide to be 100: (8-30), stirring at 30-45℃ for 6-10h, filtering, washing with deionized water and ethanol, and drying to obtain the dithio-carbamate modified membrane material.

[0017] Preferably, the modified membrane material is applied to water treatment.

[0018] Beneficial technical effects: the present application reacts N,N'-bis(2-hydroxyethyl)ethylenediamine, N-Boc-bromoethylamine, acryloyl chloride, etc., to obtain a bis-amino crosslinking monomer containing two primary amino groups and two alkenyl groups, then grafts the polyacrylonitrile fiber membrane with acrylic acid as a grafting monomer under ultraviolet irradiation, to cause crosslinking polymerization reaction, thereby introducing a polyacrylic acid crosslinked polymer gel containing a large amount of primary amino groups on the surface of the polyacrylonitrile fiber membrane, and the crosslinked polymer gel has a three-dimensional network structure, and hydrophilic primary amino groups and carboxyl groups, which are beneficial to improve the water absorption rate of the fiber membrane.

[0019] The grafted polyacrylic acid crosslinked polymer gel on the surface of the polyacrylonitrile fiber membrane of the present application contains a large amount of carboxyl groups and primary amino groups, has a very strong chelating adsorption capacity for metal ions such as lead and cadmium, and the three-dimensional network structure of the crosslinked polymer gel contains more adsorption sites, so that the fiber membrane exhibits very high adsorption performance and metal ion removal rate.

[0020] The primary amino groups of the grafted polyacrylic acid crosslinked polymer gel of the polyacrylonitrile fiber membrane of the present application are further reacted with carbon disulfide to generate a large amount of dithiocarbamate salt groups with stronger chelating performance, further improving the adsorption performance of the polyacrylonitrile fiber membrane for metal ions such as lead and cadmium, and exhibiting higher removal rate. The prepared modified polyacrylonitrile fiber membrane material can be used as ultrafiltration membrane, permeation membrane, filtration membrane and other materials, and has good practical application in metal-containing wastewater treatment. DETAILED DESCRIPTION

[0021] The present application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present application more thorough and comprehensive.

[0022] Example 1:

[0023] (1) 30 mmol of N,N'-bis(2-hydroxyethyl)ethylenediamine, 60 mmol of N-Boc-bromoethylamine, and 120 mmol of triethylamine were added to 120 mL of N,N-dimethylformamide, and stirred at 0°C for 24 h, then distilled under reduced pressure, separated by silica gel column chromatography, and eluted with petroleum ether and ethyl acetate solution to obtain an intermediate.

[0024] (2) 50 mmol of the diamino crosslinking monomer intermediate, 100 mmol of acryloyl chloride, 100 mmol of triethylamine were added to 250 mL of dichloromethane at 0°C, the reaction was stirred at 25°C for 8 h, distilled under reduced pressure until the solution volume was about 120 mL, 80 mL of trifluoroacetic acid was added to the filtrate after filtration, the reaction was stirred at 20°C for 6 h, sodium bicarbonate solution was added, stirred and then separated into layers, the water phase was removed, the dichloromethane organic phase was collected, distilled under reduced pressure, and separated by silica gel column chromatography, eluted with petroleum ether and ethyl acetate solution to obtain the diamino crosslinking monomer.

[0025] (3) 1.5 mol of acrylic acid, 0.03 mol of the diamino crosslinking monomer were added to 1 L of water to obtain a polymerization monomer solution; the polyacrylonitrile fiber membrane was soaked in a 0.05 mol / L benzophenone acetone solution for 2 h, the fiber membrane was taken out, activated under a 300 W ultraviolet lamp for 20 min, washed with acetone and dried, then soaked in the polymerization monomer solution for 2 h, the fiber membrane was taken out and subjected to polymerization reaction under the ultraviolet lamp for 30 min, washed with acetone, and then extracted with xylene in a Soxhlet extractor, after extraction, the fiber membrane was dried to obtain a modified membrane material.

[0026] Example 2:

[0027] (1) 30 mmol of N,N'-bis(2-hydroxyethyl)ethylenediamine, 72 mmol of N-Boc-bromoethylamine, and 180 mmol of triethylamine were added to 150 mL of N,N-dimethylformamide, the reaction was stirred at 5°C for 18 h, distilled under reduced pressure, and separated by silica gel column chromatography, eluted with petroleum ether and ethyl acetate solution to obtain the intermediate.

[0028] (2) 50 mmol of the diamino crosslinking monomer intermediate, 130 mmol of acryloyl chloride, and 110 mmol of triethylamine were added to 250 mL of dichloromethane at 5°C, the reaction was stirred at 20°C for 10 h, distilled under reduced pressure until the solution volume was about 120 mL, 70 mL of trifluoroacetic acid was added to the filtrate after filtration, the reaction was stirred at 30°C for 4 h, sodium bicarbonate solution was added, stirred and then separated into layers, the water phase was removed, the dichloromethane organic phase was collected, distilled under reduced pressure, and separated by silica gel column chromatography, eluted with petroleum ether and ethyl acetate solution to obtain the diamino crosslinking monomer.

[0029] (3) To 1 L of water, 4 mol of acrylic acid and 0.08 mol of diamino crosslinking monomer were added to obtain a polymerization monomer solution; the polyacrylonitrile fiber membrane was immersed in a 0.13 mol / L benzophenone acetone solution for 3 h, the fiber membrane was taken out, and was irradiated under a 200 W ultraviolet lamp for activation for 30 min, and was washed with acetone and dried, and then was immersed in the polymerization monomer solution for 3 h, the fiber membrane was taken out, and was irradiated under the ultraviolet lamp for polymerization for 50 min, and was washed with acetone, and was extracted with xylene in a Soxhlet extractor, and after extraction, the fiber membrane was dried to obtain a modified membrane material.

[0030] Example 3:

[0031] (1) To 1 L of water, 6 mol of acrylic acid and 0.1 mol of diamino crosslinking monomer (prepared in Example 1) were added to obtain a polymerization monomer solution; the polyacrylonitrile fiber membrane was immersed in a 0.18 mol / L benzophenone acetone solution for 3 h, the fiber membrane was taken out, and was irradiated under a 400 W ultraviolet lamp for activation for 20 min, and was washed with acetone and dried, and then was immersed in the polymerization monomer solution for 3 h, the fiber membrane was taken out, and was irradiated under the ultraviolet lamp for polymerization for 50 min, and was washed with acetone, and was extracted with xylene in a Soxhlet extractor, and after extraction, the fiber membrane was dried to obtain a modified membrane material.

[0032] Comparative Example 1:

[0033] (1) To 1 L of water, 1.5 mol of acrylic acid was added to obtain a polymerization monomer solution; the polyacrylonitrile fiber membrane was immersed in a 0.05 mol / L benzophenone acetone solution for 2 h, the fiber membrane was taken out, and was irradiated under a 300 W ultraviolet lamp for activation for 20 min, and was washed with acetone and dried, and then was immersed in the polymerization monomer solution for 2 h, the fiber membrane was taken out, and was irradiated under the ultraviolet lamp for polymerization for 30 min, and was washed with acetone, and was extracted with xylene in a Soxhlet extractor, and after extraction, the fiber membrane was dried to obtain a modified membrane material.

[0034] Comparative Example 2:

[0035] (1) To 1 L of water, 1.5 mol of acrylic acid and 0.03 mol of N,N'-methylenebisacrylamide as a crosslinking monomer were added to obtain a polymerization monomer solution; the polyacrylonitrile fiber membrane was immersed in a 0.05 mol / L benzophenone acetone solution for 2 h, the fiber membrane was taken out, and was irradiated under a 300 W ultraviolet lamp for activation for 20 min, and was washed with acetone and dried, and then was immersed in the polymerization monomer solution for 2 h, the fiber membrane was taken out, and was irradiated under the ultraviolet lamp for polymerization for 30 min, and was washed with acetone, and was extracted with xylene in a Soxhlet extractor, and after extraction, the fiber membrane was dried to obtain a modified membrane material.

[0036] Comparative Example 3:

[0037] (1) To 1 L of water, 1.5 mol of acrylic acid and 0.03 mol of N-(3- aminopropyl) methacrylamide hydrochloride (CAS No. 72607-53-5) were added to obtain a polymerization monomer solution; a polyacrylonitrile fiber membrane was immersed in a 0.05 mol / L benzophenone acetone solution for 2 h, the fiber membrane was taken out, activated under a 300 W ultraviolet lamp for 20 min, and then dried after acetone washing; the fiber membrane was then immersed in the polymerization monomer solution for 2 h, and the polymerization reaction was carried out under the ultraviolet lamp for 30 min; after acetone washing, the fiber membrane was extracted with xylene in a Soxhlet extractor, and then dried to obtain a modified membrane material containing an amino group.

[0038] Example 4: 2 g of the modified membrane material (prepared in Example 2) was added to 600 mL of a 10% by mass sodium hydroxide aqueous solution, 10 mL of an ethanol solution containing 0.16 g of carbon disulfide was added, and the reaction was stirred at 35°C for 6 h; after filtration, the product was washed with deionized water and ethanol, and dried to obtain a dithio carbamate modified membrane material.

[0039] Example 5: 2 g of the modified membrane material (prepared in Example 2) was added to 600 mL of a 15% by mass sodium hydroxide aqueous solution, 20 mL of an ethanol solution containing 0.4 g of carbon disulfide was added, and the reaction was stirred at 45°C for 6 h; after filtration, the product was washed with deionized water and ethanol, and dried to obtain a dithio carbamate modified membrane material.

[0040] Example 6: 2 g of the modified membrane material (prepared in Example 2) was added to 600 mL of an 18% by mass sodium hydroxide aqueous solution, 30 mL of an ethanol solution containing 0.6 g of carbon disulfide was added, and the reaction was stirred at 30°C for 10 h; after filtration, the product was washed with deionized water and ethanol, and dried to obtain a dithio carbamate modified membrane material.

[0041] Comparative Example 4:

[0042] (1) 2 g of the modified membrane material (prepared in Comparative Example 3) was added to 600 mL of a 10% by mass sodium hydroxide aqueous solution, 10 mL of an ethanol solution containing 0.16 g of carbon disulfide was added, and the reaction was stirred at 35°C for 6 h; after filtration, the product was washed with deionized water and ethanol, and dried to obtain a dithio carbamate modified membrane material.

[0043] The membrane material was made into a 10 cm x 10 cm sample, weighed, and then immersed in deionized water for 12 h; the membrane material was taken out, the surface water was absorbed with filter paper, and weighed to calculate the water absorption rate. The water absorption rate = (the mass after water absorption - the mass before water absorption) ÷ the mass before water absorption x 100%.

[0044] Table 1 Water absorption rate test of membrane material

[0045]

[0046]

[0047] Take 100 mg of membrane material and add to 500 mL of Pb 2+ standard solution (mass concentration of 50 mg / L), stir and adsorb for 1.5 h at room temperature, determine the concentration of Pb 2+ in the solution by atomic absorption spectrophotometry, and calculate the removal rate. Removal rate = (concentration before adsorption - concentration after adsorption) ÷ concentration before adsorption × 100%.

[0048] Take 150 mg of membrane material and add to 500 mL of Cd 2+ standard solution (mass concentration of 50 mg / L), stir and adsorb for 1.5 h at room temperature, determine the concentration of Cd 2+ in the solution by atomic absorption spectrophotometry, and calculate the removal rate. Removal rate = (concentration before adsorption - concentration after adsorption) ÷ concentration before adsorption × 100%.

[0049] Table 2 Metal ion removal rate test

[0050] Pb 2+ Removal rate (%)]] Cd 2+ Removal rate (%)]] Example 1 68.2 60.1 Example 2 81.4 75.4 Example 3 83.6 78.8 Comparative Example 1 35.0 29.5 Comparative Example 2 59.4 51.9 Comparative Example 3 38.2 33.0 Example 4 89.7 84.3 Example 5 97.5 95.5 Example 6 99.8 99.1 Comparative Example 4 43.7 38.8

[0051] After testing, Examples 1-3 use acrylic acid as a grafting monomer, and a diamino crosslinking monomer (containing two primary amino groups -NH2) to perform a crosslinking polymerization reaction on the surface of the polyacrylonitrile fiber membrane, introducing a polyacrylic acid crosslinked polymer gel containing a large number of primary amino groups on the surface of the polyacrylonitrile fiber membrane. The crosslinked polymer gel has a three-dimensional network structure, as well as hydrophilic primary amino groups and carboxyl groups, which are beneficial to improving the water absorption rate of the fiber membrane. At the same time, the large number of carboxyl groups and primary amino groups have a strong chelation and adsorption capacity for metal ions such as lead and cadmium. The three-dimensional network structure of the crosslinked polymer gel contains more adsorption sites, so that the fiber membrane exhibits high adsorption performance and metal ion removal rate. Examples 4-6 use the large number of primary amino groups of the polyacrylic acid crosslinked polymer gel to react with carbon disulfide to generate a large number of dithiocarbamate salt groups with stronger chelation performance which further improves the adsorption performance of the polyacrylonitrile fiber membrane for metal ions such as lead and cadmium, and has a higher removal rate.

[0052] Compared with Example 1, the graft polymerization of acrylic acid on the polyacrylonitrile fiber membrane is carried out in Comparative Example 1 without adding a crosslinking agent, and linear polyacrylic acid molecular chains are grafted on the surface of the fiber membrane without forming a three-dimensional network structure of crosslinked polymer gel and without containing hydrophilic amino groups, resulting in a low water absorption rate of the fiber membrane and a poor chelating adsorption capacity and a low removal rate of metal ions such as lead and cadmium.

[0053] Compared with Comparative Example 1, the graft crosslinking polymerization of acrylic acid on the polyacrylonitrile fiber membrane is carried out in Comparative Example 2 with conventional N,N'-methylenebisacrylamide as a crosslinking monomer, and polyacrylic acid crosslinked polymer gel is introduced on the surface of the polyacrylonitrile fiber membrane, the water absorption rate is obviously improved, and the removal rate of metal ions such as lead and cadmium is also higher, but N,N'-methylenebisacrylamide does not contain primary amino groups, resulting in a lower water absorption rate of the fiber membrane and a lower removal rate of metal ions such as lead and cadmium than in Example 1.

[0054] The graft polymerization of acrylic acid and N-(3-aminopropyl) methacrylamide hydrochloride (containing only one alkenyl group) on the polyacrylonitrile fiber membrane is carried out in Comparative Example 3, and no crosslinking reaction occurs, linear polyacrylic acid molecular chains containing amino groups are generated, and no three-dimensional network structure of crosslinked polymer gel is formed, resulting in a low water absorption rate of the fiber membrane and a low removal rate of metal ions such as lead and cadmium. However, the removal rate of metal ions such as lead and cadmium is slightly higher than that of Comparative Example 1 after the introduction of amino groups.

[0055] The amino groups of the linear polyacrylic acid molecular chains grafted on the modified membrane material of Comparative Example 3 are reacted with carbon disulfide in Comparative Example 4 to generate dithiocarbamate groups with stronger chelating properties, further improving the removal rate of metal ions such as lead and cadmium from the fiber membrane. However, N-(3-aminopropyl) methacrylamide hydrochloride contains only one amino group, and the generated dithiocarbamate groups are also less, resulting in no significant improvement in the removal rate.

[0056] The above examples only express several embodiments of the present application, facilitate the specific and detailed understanding of the technical solutions of the present application, but cannot be understood as a limitation on the protection scope of the invention patent. It should be noted that for ordinary skilled persons in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are within the protection scope of the present application.

Claims

1. A method for preparing a modified membrane material, characterized in that: The preparation method is: (1) adding acrylic acid and diamino cross-linking monomer to deionized water to obtain a polymerization monomer solution; (2) adding a polyacrylonitrile fiber membrane to an acetone solution containing benzophenone, irradiating the fiber membrane under an ultraviolet lamp to activate it after soaking, washing and drying it, and then adding it to a polymerization monomer solution. After soaking, taking out the fiber membrane, irradiating it under an ultraviolet lamp to carry out polymerization reaction, washing and placing the fiber membrane in a Soxhlet extractor for extraction and drying to obtain a modified membrane material; The structural formula of the diamino cross-linking monomer is ； The preparation method of the diamino cross-linking monomer is as follows: (1) Add N,N'-bis(2-hydroxyethyl)ethylenediamine, N-Boc-bromoethylamine, and triethylamine in a molar ratio of 1:(2-2.4):(4-6) to N,N-dimethylformamide, stir and react at 0-5°C for 18-24 hours, evaporate under reduced pressure, and separate by silica gel column chromatography to obtain an intermediate; (2) Adding a diamino crosslinking monomer intermediate, acryloyl chloride, and triethylamine in a molar ratio of 1:(2-2.6):(2-2.2) to dichloromethane at 0-5°C, stirring and reacting at 20-25°C for 8-10 hours, filtering, adding trifluoroacetic acid to the filtrate, stirring and reacting at 20-30°C for 4-6 hours, adding sodium bicarbonate solution, stirring, and then standing to separate, removing the aqueous phase, collecting the dichloromethane organic phase, distilling under reduced pressure, and separating by silica gel column chromatography to obtain a diamino crosslinking monomer.

2. The method for preparing a modified membrane material according to claim 1, wherein: The concentration of acrylic acid in the polymerization monomer solution in (1) is 1.5-6 mol / L.

3. The method for preparing a modified membrane material according to claim 1, wherein: The concentration of the diamino cross-linking monomer in (1) is 0.03-0.1 mol / L.

4. The method for preparing a modified membrane material according to claim 1, wherein: The concentration of benzophenone in the acetone solution in (2) is 0.05-0.18 mol / L.

5. The method for preparing a modified membrane material according to claim 1, wherein: The power of the ultraviolet lamp in (2) is 200-400W; the irradiation activation time is 20-30min; and the polymerization reaction time is 30-50min.

6. The method for preparing a modified membrane material according to any one of claims 1 to 5, characterized in that: The modified membrane material also includes a dithiocarbamate-modified membrane material; the preparation method of the dithiocarbamate-modified membrane material is: adding the modified membrane material to a sodium hydroxide aqueous solution with a mass fraction of 10-18%, adding an ethanol solution of carbon disulfide, stirring and reacting at 30-45°C for 6-10 hours, filtering, washing, and drying to obtain the dithiocarbamate-modified membrane material.

7. The method for preparing a modified membrane material according to claim 6, wherein: The mass ratio of the modified membrane material to carbon disulfide is 100:(8-30).

8. Use of the modified membrane material obtained by the preparation method according to any one of claims 1 to 7 in water treatment.

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