CN114534525B

CN114534525B - Amination modified anti-pollution porous membrane and preparation method thereof

Info

Publication number: CN114534525B
Application number: CN202111663434.6A
Authority: CN
Inventors: 王军; 汤超; 孟圆圆; 唐妮; 杜延华; 李玲; 陈鲁昌; 张镇
Original assignee: Shandong Huaxia Shenzhou New Material Co Ltd
Current assignee: Shandong Huaxia Shenzhou New Material Co Ltd
Priority date: 2021-12-31
Filing date: 2021-12-31
Publication date: 2023-05-23
Anticipated expiration: 2041-12-31
Also published as: CN114534525A

Abstract

The invention belongs to the technical field of membrane separation, and particularly relates to an amination modified anti-pollution porous membrane and a preparation method thereof. Dissolving a polymer, a hydrophilic diamine monomer compound and polyethylene glycol in dimethylacetamide, and stirring at 60-80 ℃ until the mixture is uniform, thus forming uniform casting solution; pouring the casting film liquid at the room temperature of 25 ℃ on one end of a clean glass plate, scraping the casting film liquid to the other end at a constant speed by using a coating scraper, and forming a nascent film on the glass plate or pouring the casting film liquid into a spinning machine to extrude the nascent film; the nascent membrane is pre-evaporated in air for 5-30s and then is quickly placed in a coagulating bath at 20-30 ℃ for phase inversion and solidified into an asymmetric ultrafiltration membrane. The method has the advantages of simple operation, mild condition, good pollution resistance, high mechanical strength and good separation performance, and can be used in the fields of wastewater treatment and the like.

Description

Amination modified anti-pollution porous membrane and preparation method thereof

Technical Field

The invention belongs to the technical field of membrane separation, and particularly relates to an amination modified anti-pollution porous membrane and a preparation method thereof.

Background

At present, common polymers of the water treatment membrane are polyvinylidene fluoride, polyvinyl chloride, polysulfone, polyether sulfone, cellulose acetate, polyethylene, polypropylene and the like, and the common problems at present are that the pollution resistance of the surface of the membrane material needs to be further improved, the surface is not easy to carry out chemical grafting modification, and the polyvinylidene fluoride has good thermal stability, chemical stability and mechanical strength, so that the polyvinylidene fluoride is widely applied to the water treatment membrane. In recent years, as the application of membrane separation technology expands, membrane fouling has also become a concern. The introduction of hydrophilic groups on the membrane surface is an effective strategy for improving the antifouling capacity of the membrane. The surface charge modification of the membrane is the modification with negative charges, but there is also a great market demand for high pollution resistance in the field of ultrafiltration membranes with positive charges.

Surface modification is a common method for preparing a positively charged film. The surface of the membrane is introduced with positive charge groups, so that the hydrophilicity can be improved, the anti-pollutant performance of the membrane is obviously improved, and the electrostatic repulsion force between the membrane and pollutants is realized. As a film-forming material having excellent overall properties, PVDF has been widely used and studied in the film field. However, polyvinylidene fluoride (PVDF) as a film-forming material has the problems of low alkali resistance, low probability of generating active sites during hydrophilization modification by a grafting method, and the like. And polyvinylidene fluoride-chlorotrifluoroethylene (PVDF-CTFE) is used as a film-forming material, and the copolymer introduces a reactive C-Cl active site on the basis of retaining excellent performances such as thermal stability and chemical stability of PVDF, and is easy to graft and modify.

At present, researchers at home and abroad do much work on the modification of polyvinylidene fluoride-chlorotrifluoroethylene, and the related patents mainly include:

patent CN 110066415A discloses a preparation method of a porous membrane with a functionalized surface, which uses vinylidene fluoride-chlorotrifluoroethylene copolymer as a base membrane, and uses chlorine groups in the molecular structure of the copolymer to react with amine compounds to prepare the porous membrane with positively charged surface. However, in the method, the base film formed by PVDF-CTFE is taken as a grafting point, so that the amino group is not easy to be introduced into the molecular chain of the polymer, and the grafting is difficult.

Patent CN 111659267A discloses a preparation method of a pollution-resistant modified porous membrane, which makes a C-Cl bond in a polymer molecular chain and a small-molecule monoamine hydrophilic compound undergo a reaction of removing HCl to prepare a surface-modified negatively charged or electrically neutral pollution-resistant high-blood-compatibility polymer porous membrane, but the small-molecule monoamine compound is easy to run off in the use process, and the stability of a membrane product is affected.

Patent CN108579474B discloses a negatively charged fluoropolymer based composite membrane enhanced based on interlayer covalent interactions. The support layer and the functional layer in the composite membrane are combined under the action of C-O and/or C-N covalent bonds, the composite membrane is a negatively charged microfiltration membrane or an ultrafiltration membrane, and the surface of the composite membrane contains carboxyl and/or sulfonic groups. The composite membrane has the characteristics of high flux, good flux stability, excellent interception and pollution resistance, stable combination between layers in the membrane and the like. Due to the electronegativity of the membrane itself, the composite membrane has better selectivity and pollution resistance to certain charged pollutants. But the grafting process tends to plug the membrane pores.

In a word, the modification research of polyvinylidene fluoride-chlorotrifluoroethylene is mainly carried out by copolymerization with other functional monomers or blending with other substances, and the aims of the modification research are mainly to improve hydrophilicity and surface charge, solve the problems of easy pollution caused by PVDF and the like.

Disclosure of Invention

Aiming at the defects of the prior art, the invention aims to provide an aminated modified anti-pollution porous membrane, which is prepared by grafting a modified polymer in an aminated mode, has good anti-pollution property, high mechanical strength and good separation performance, and can be used in the fields of wastewater treatment and the like; the invention also provides a preparation method, which is simple to operate and mild in condition.

The invention adopts an amination mode to modify the polymer, and amine radicals in amine compound molecules directly generate in-situ substitution reaction at C-Cl active sites in alkaline environment to generate free Cl ^- The process does not involve bond formation or bond breaking, and the required activation energy is low, so the reaction is aproticMore readily occurs in polar solvents. The PVDF-CTFE undergoes elimination reaction at the C-Cl active site to remove HCl and form C=C double bond, and the amine compound carries amine radical to attack the C=C double bond so that the double bond is opened to further undergo addition reaction. The reaction selects diamine monomer with hydrophilic polar groups such as hydroxyl, carboxyl and the like as graft copolymer, and carries out graft copolymerization with PVDF-CTFE in casting solution, thus completing graft copolymerization modification by a one-step method, and being simple and easy to implement.

The invention uses the mode of graft copolymerization of the amide with hydrophilic polar groups to modify polyvinylidene fluoride-chlorotrifluoroethylene, improves the hydrophilicity and membrane surface charge of the polyvinylidene fluoride-chlorotrifluoroethylene, reduces pollutant adsorption and improves the pollution resistance by adding hydrophilic amino compounds.

The invention is realized by the following technical scheme:

according to the preparation method of the aminated modified anti-pollution porous membrane, a non-solvent induced phase separation method is adopted, and hydrophilic diamine monomer compounds are introduced into a polymer membrane material body to prepare the ultrafiltration membrane.

Wherein the hydrophilic diamine monomer compound contains a benzene ring structure, the benzene ring contains a hydrophilic group, and the hydrophilic group is one of hydroxyl, carboxyl, sulfonic group or sulfhydryl.

Preferably, the preparation method of the aminated modified anti-pollution porous membrane comprises the following steps:

1) Dissolving the polymer, hydrophilic diamine monomer compound and polyethylene glycol after vacuum drying in dimethylacetamide, and stirring at a constant temperature of 60-80 ℃ until the mixture is uniform, thus forming uniform casting solution;

pouring the casting solution at one end of a clean and nondestructive glass plate at room temperature, scraping the casting solution to the other end at a constant speed by adopting a coating scraper, and forming a nascent film on the glass plate; or pouring the casting solution into a spinning machine to extrude into a nascent film; pre-evaporating the nascent membrane in air, and then placing the nascent membrane in a coagulating bath for phase inversion;

3) Solidifying to obtain an asymmetric ultrafiltration membrane, and transferring to deionized water for soaking for 24 h.

Preferably, the polymer is one or more than two of polyvinyl chloride, poly (chlorotrifluoroethylene), copolymer of polyvinylidene fluoride and vinyl chloride or copolymer of polyvinylidene fluoride and chlorotrifluoroethylene.

In the present invention, the hydrophilic diamine monomer compound is preferably one or a mixture of two or more of 3, 3-dihydroxybenzidine, 3, 4-diaminobiphenyl sulfone, 3, 5-diaminobenzoic acid and 2-aminophenol.

In the casting film liquid, the preferable mass percentage of the polymer is 16-20%, the mass percentage of the polyethylene glycol is 3-5%, the mass percentage of the hydrophilic diamine monomer compound is 1-5%, and the mass percentage of the dimethylacetamide is 70-80%.

Scraping the casting film liquid to the other end at a constant speed by adopting a coating scraper, wherein the thickness of a nascent film formed on the glass plate is 150-250 mu m, and the scraping speed is 55-65mm/s, preferably 60mm/s; or pouring the casting solution into a spinning machine to extrude into a nascent film at an extrusion rate of 5-10ml/min, preferably 6ml/min. The flat membrane is prepared by a coating scraper, and the hollow fiber membrane is prepared by a spinning machine.

The ultrafiltration membrane prepared by the invention is a flat membrane or a hollow fiber membrane.

The aminated modified anti-pollution porous membrane is prepared by the preparation method.

Compared with the prior art, the invention has the following beneficial effects:

1. the invention uses diamine compound grafted modified polymer containing hydrophilic polar groups to prepare the water treatment ultrafiltration membrane, which enhances the chargeability of the membrane surface, improves the hydrophilicity of the membrane surface, improves the membrane pore structure, and improves the separation performance, mechanical performance and anti-pollution performance of the membrane.

2. The preparation method of the invention has simple operation and mild condition

Drawings

FIG. 1-1 is a graph of contact angle shown for a sample prepared in example 1;

FIGS. 1-2 are graphs showing contact angles of samples prepared in comparative example 1;

FIG. 2 is a graph of contact angle shown for a sample prepared in example 2;

FIG. 3 is a graph of contact angle shown for a sample prepared in example 3;

FIG. 4 is a graph of contact angle shown for a sample prepared in example 4;

fig. 5 is a graph of contact angle shown for a sample prepared in example 5.

Detailed Description

The invention is further illustrated by the following examples, which are intended to be illustrative only and not limiting in any way.

Example 1

1) 48.0g of dimethylacetamide, 9.6g of polyvinylidene fluoride-chlorotrifluoroethylene, 1.8g of polyethylene glycol and 0.6g of 3, 3-dihydroxybenzidine are stirred at a constant temperature of 80 ℃ until being uniformly mixed to form uniform casting solution;

2) Pouring the casting solution at room temperature of 25 ℃ to one end of a clean and nondestructive glass plate, scraping the casting solution to the other end of the glass plate at a constant speed of 60mm/s by using a 200 mu m thick coating scraper, and forming a nascent film on the glass plate. Pre-evaporating the nascent membrane in air for 10s, rapidly placing the nascent membrane in a coagulating bath at 25 ℃ to carry out phase inversion in deionized water, and solidifying the nascent membrane into the asymmetric ultrafiltration membrane. Then transferring the mixture into deionized water for soaking for 24 hours for standby. The obtained membrane had a water contact angle of 67.8 °, and the ultrafiltration membrane was subjected to performance test, and the results are shown in table 1.

Comparative example 1

1) 48.6g of dimethylacetamide, 9.6g of polyvinylidene fluoride-chlorotrifluoroethylene and 1.8g of polyethylene glycol are stirred at a constant temperature of 80 ℃ until being uniformly mixed to form uniform casting solution;

2) Pouring the casting solution at room temperature of 25 ℃ to one end of a clean and nondestructive glass plate, scraping the casting solution to the other end of the glass plate at a constant speed of 60mm/s by using a 200 mu m thick coating scraper, and forming a nascent film on the glass plate. Pre-evaporating the nascent membrane in air for 10s, rapidly placing the nascent membrane in a coagulating bath at 25 ℃ to carry out phase inversion in deionized water, and solidifying the nascent membrane into the asymmetric ultrafiltration membrane. Then transferring the mixture into deionized water for soaking for 24 hours for standby. The resulting membrane had a water contact angle of 105.3 °, and the ultrafiltration membrane was subjected to performance test, and the results are shown in table 1.

Example 2

1) 45g of dimethylacetamide, 10.8g of polytrifluoroethylene, 2.4g of polyethylene glycol and 1.8g of 3, 5-diaminobenzoic acid are stirred at a constant temperature of 70 ℃ until the materials are uniformly mixed to form a uniform casting solution.

2) Pouring the casting solution into a spinning machine at room temperature of 25 ℃ to extrude into a nascent film at an extrusion rate of 6ml/min. Pre-evaporating the nascent membrane in air for 5s, rapidly placing the nascent membrane in a coagulating bath at 25 ℃ to carry out phase inversion in deionized water, and solidifying the nascent membrane into the asymmetric ultrafiltration membrane. Then transferring the mixture into deionized water at 25 ℃ for soaking for 24 hours for standby. The resulting membrane had a water contact angle of 51.5 °, and the ultrafiltration membrane was subjected to performance test, and the results are shown in table 1.

Example 3

1) 42g of dimethylacetamide, 12g of polyvinyl chloride, 3g of polyethylene glycol and 3g of 3, 4-diaminobiphenyl sulfone are stirred at a constant temperature of 60 ℃ until the materials are uniformly mixed to form uniform casting solution.

2) Pouring the casting solution at room temperature of 25 ℃ to one end of a clean and nondestructive glass plate, scraping the casting solution to the other end of the glass plate at a constant speed of 60mm/s by using a 200 mu m thick coating scraper, and forming a nascent film on the glass plate. And (3) pre-evaporating the nascent membrane in air for 20 seconds, rapidly placing the nascent membrane in a coagulating bath at 20 ℃ to carry out phase inversion in deionized water, and solidifying the nascent membrane into the asymmetric ultrafiltration membrane. Then transferring the mixture into deionized water for soaking for 24 hours for standby. The resulting membrane had a water contact angle of 53.2 °, and the ultrafiltration membrane was subjected to performance test, and the results are shown in table 1.

Example 4

1) 47.4g of dimethylacetamide, 9.6g of polyvinylidene fluoride-chloroethylene, 1.8g of polyethylene glycol and 1.2g of 2, 4-aminophenol are stirred at a constant temperature of 70 ℃ until the materials are uniformly mixed to form a uniform casting solution;

2) Pouring the casting solution at room temperature of 25 ℃ to one end of a clean and nondestructive glass plate, scraping the casting solution to the other end of the glass plate at a constant speed of 60mm/s by using a 200 mu m thick coating scraper, and forming a nascent film on the glass plate. Pre-evaporating the nascent membrane in air for 30s, rapidly placing the nascent membrane in a coagulating bath at 30 ℃ to be deionized water for phase inversion, and solidifying the nascent membrane into the asymmetric ultrafiltration membrane. Then transferring the mixture into deionized water for soaking for 24 hours for standby. The resulting membrane had a water contact angle of 52.2 °, and the ultrafiltration membrane was subjected to performance test, and the results are shown in table 1.

Example 5

2) Pouring the casting solution at room temperature of 25 ℃ to one end of a clean and nondestructive glass plate, scraping the casting solution to the other end of the glass plate at a constant speed of 60mm/s by using a 200 mu m thick coating scraper, and forming a nascent film on the glass plate. Pre-evaporating the nascent membrane in air for 5s, rapidly placing the nascent membrane in a coagulating bath at 25 ℃ to carry out phase inversion in deionized water, and solidifying the nascent membrane into the asymmetric ultrafiltration membrane. Then transferring the mixture into deionized water at 25 ℃ for soaking for 24 hours for standby. The resulting membrane had a water contact angle of 71.2 °, and the ultrafiltration membrane was subjected to performance test, and the results are shown in table 1.

To demonstrate the performance effect of ultrafiltration membranes, the hydrophilicity of the membrane surface was evaluated using the water contact angle, the lower the contact angle, the better the hydrophilicity. The anti-pollution performance of the membrane is evaluated by adopting the flux recovery rate, and the higher the flux recovery rate is, the better the anti-pollution performance is. The mechanical property of the film is evaluated by adopting the tensile strength and the elongation at break, and the harder the tensile strength is, the harder the material is broken in the deformation process; the larger the elongation at break, the better the material is adapted to deformation, and the better mechanical properties indicate that the film has a longer service life. The test method is as follows:

the contact angle of the film was characterized in this experiment by means of a contact angle tester (DSA 30S) using water as the probe liquid. After the sample is cleaned and dried in vacuum, the sample is fixed on a glass slide by using double-sided adhesive tape and placed on an instrument table, 3 mu l of deionized water is dripped on the surface of the membrane, the pattern of the water drop on the surface of the membrane is captured by a camera and stored, and the contact angle value is automatically obtained by equipment. Each film sample was tested 5 times and averaged.

The tensile property and the elongation at break of the film are tested by a high-low temperature press (GT-7001-HC 6), and the specific steps of the test are as follows: the film obtained from which the water was completely removed was cut into 1cm×15cm strips, and the strips were placed on an instrument for tensile mechanical property test at a tensile speed of 10mm/min.

The flux recovery rate is tested by cutting an ultrafiltration membrane into discs with proper size or filling membrane wires with proper length into a filter, filling a material liquid tank and the filter with deionized water, and prepressing for 30min under the operating pressure of 0.2MPa until the water flux is stable. After the pre-pressing process is finished, the material liquid tank and the filter are filled with deionized water again, the mass of the permeate liquid is recorded under the operating pressure of 0.1MPa, the water flux is calculated, the stable flux A1 is obtained after 30min to be measured, and the measurement is stopped. After the initial flux measurement is finished, the material liquid tank is filled with BSA solution, the filter is filled with BSA solution, the quality of the permeate is recorded under the operating pressure of 0.1MPa, the permeate flux is calculated, and the stable flux is obtained after 30min to be measured. After the BSA solution flux measurement is finished, the filter is replaced by deionized water, and the surface of the membrane is subjected to hydraulic cleaning for 30min. After the hydraulic cleaning is finished, pouring the cleaning liquid, filling the buffer tank and the filter with deionized water again, recording the mass of the permeate liquid under the operating pressure, calculating the water flux, obtaining the stable flux A2 after 30min to be measured, and finishing the measurement. Flux recovery frr=a2/a1×100%.

See table 1 for specific results.

Table 1 film test data

Numbering device	Water contact angle (°)	Flux recovery (%)	Tensile Strength (MPa)	Elongation at breakRate (%)
					Example 1	67.8	82.5	4.3	28.5
Comparative example 1	105.3	46.9	2.9	11.3
					Example 2	51.5	89.8	4.1	22.9
Example 3	53.2	86.5	4.3	27.2
					Example 4	52.2	87.3	4.9	26.9
Example 5	71.2	77.2	4.8	27.6

The content of the embodiments of the present invention, which is not described in the prior art, is not described in detail.

The foregoing is merely a preferred embodiment of the present invention, and it should be noted that it will be apparent to those skilled in the art that variations and modifications can be made without departing from the scope of the invention.

Claims

1. A preparation method of an aminated modified anti-pollution porous membrane is characterized by comprising the following steps of: the method comprises the following steps:

2) Pouring the casting solution at one end of a clean and nondestructive glass plate at room temperature, scraping the casting solution to the other end at a constant speed by adopting a coating scraper, and forming a nascent film on the glass plate; or pouring the casting solution into a spinning machine to extrude into a nascent film; pre-evaporating the nascent membrane in air, and then placing the nascent membrane in a coagulating bath for phase inversion;

3) Solidifying into an asymmetric ultrafiltration membrane, and transferring into deionized water for soaking for standby;

the hydrophilic diamine monomer compound is one or more than two of 3, 3-dihydroxybenzidine, 3, 5-diaminobenzoic acid or 2, 4-diaminophenol;

wherein:

the polymer is one or more than two of polyvinyl chloride, poly (chlorotrifluoroethylene), copolymer of polyvinylidene fluoride and vinyl chloride or copolymer of polyvinylidene fluoride and chlorotrifluoroethylene;

in the casting film liquid, the mass percentage of the polymer is 16-20%, the mass percentage of the polyethylene glycol is 3-5%, the mass percentage of the hydrophilic diamine monomer compound is 1-5%, and the mass percentage of the dimethylacetamide is 70-80%.

2. The method for producing an aminated modified antipollution porous film according to claim 1, characterized in that: scraping the casting film liquid to the other end at a constant speed by adopting a coating scraper, wherein the thickness of a nascent film formed on the glass plate is 150-250 mu m; or pouring the casting film liquid into a spinning machine to extrude into the nascent film at an extrusion rate of 5-10 ml/min.

3. The method for producing an aminated modified antipollution porous film according to claim 1, characterized in that: the pre-evaporation time of the nascent membrane in the air is 5-30s, and the coagulating bath temperature is 20-30 ℃.

4. The method for producing an aminated modified antipollution porous film according to claim 1, characterized in that: the ultrafiltration membrane is a flat membrane or a hollow fiber membrane.

5. An aminated modified anti-fouling porous membrane, characterized in that: a method according to any one of claims 1 to 4.