CN102000511A - Method for preparing positive charge hollow fiber nanofiltration membrane through surface UV irradiation grafting - Google Patents

Abstract

The invention provides a method for preparing a positively charged hollow fiber nanofiltration membrane by surface ultraviolet irradiation grafting. The preparation method is: take the polymer hollow fiber ultrafiltration membrane as the base membrane, in the presence of the cross-linking agent N, N methylenebisacrylamide, initiate by high-energy ultraviolet light irradiation, and the surface of the polymer ultrafiltration membrane Grafting vinyl monomers with quaternary ammonium groups, such as trimethylallyl ammonium chloride (TMAAC) or dimethyldiallyl ammonium chloride (DMDAAC), prepared a good rejection rate Positively charged hollow fiber nanofiltration membrane. The positively charged hollow fiber nanofiltration membrane has an excellent retention effect on high-priced heavy metal ions. The invention has the advantages of simple operation, short reaction time, relatively stable membrane performance, and good interception effect can still be maintained after long-term operation. The prepared nanofiltration membrane has a rejection rate of 48.6%-94.21% for CaCl ₂ with a concentration of 0.3g/L under the pressure of 0.2MPa.

Description

A method for preparing positively charged hollow fiber nanofiltration membranes by surface ultraviolet irradiation grafting

Technical field:

The invention belongs to the field of membrane material modification, and in particular relates to a method for preparing a hollow fiber nanofiltration membrane by surface irradiation grafting. The present invention selects functional monomers with special properties, grafts the functional monomers to the basement membrane surface through surface irradiation grafting, reduces the pore size of the membrane surface, and prepares a hollow fiber nanofiltration membrane with a positive charge on the membrane surface .

Background technique:

Nanofiltration membrane is a new type of separation membrane developed recently. Nanofiltration membrane technology is widely used in water treatment, pharmaceutical, biochemical, and food industries. But at present, the domestic nanofiltration membrane market is almost occupied by foreign nanofiltration membrane products. Commercial nanofiltration membranes are mainly obtained through interfacial polymerization. Although the resulting membranes have excellent separation performance, the manufacturing process is complicated, the product quality is not easy to control, and the equipment investment and production costs are high. At present, domestic reports on nanofiltration membranes are mostly negatively charged nanofiltration membranes, and there are few reports on positively charged nanofiltration membranes, especially positively charged hollow fiber nanofiltration membranes. Lu Xueren et al. used amine and epoxy polycondensate as the charged material, polyvinylidene fluoride (PVDF) and polysulfoneamide (PSA) membrane as the base membrane, and prepared a positively charged nanofiltration membrane by dip coating. Under the condition of 0.6 MPa, the rejection rate of the membrane to Na ₂ SO ₄ is greater than 50%, and the water flux is 10-15 mL·cm ^-2 ·h ^-1 . Du Runhong from Tianjin Polytechnic University used polysulfone microporous membrane as the supporting membrane, polydimethylaminoethyl methacrylate as the active layer material, and p-dichlorobenzyl/n-heptane as the crosslinking agent, and prepared the method of interfacial polymerization. PDMAEMA/PSF composite nanofiltration membrane, the removal rate of the membrane is about 90% for MgSO ₄ , the removal rate for NaCl is 78%, and the water flux is about 7.5-23.7L/m ² h. Cao Xuzhi et al prepared a positively charged nanofiltration membrane by grafting hydrophilic monomers on the surface of a phenolphthalein-based polyaryletherketone microporous flat membrane with UV irradiation, and the rejection rates for high-valent cations and low-valent cations were 95% and 65%.

Although the positively charged nanofiltration membrane prepared by interfacial polymerization has a good interception effect, the conditions for interfacial polymerization are strict, and the reaction conditions are not easy to control, and the functional layer formed on the surface of the membrane by the polymerization method, with the membrane for a long time The operation of the function layer will appear unstable. In the reported nanofiltration membranes prepared by surface grafting, the base membranes used are all flat membranes as supporting membranes. The method of preparing hollow fiber positively charged nanofiltration membranes by ultraviolet irradiation grafting has not been reported in China. The method of membrane surface modification can not only improve the performance of the membrane surface, but also realize the preparation of smaller pore membranes. The UV surface irradiation modification method has low equipment cost, simple and convenient operation, and is especially suitable for modifying photosensitive polymers, such as polysulfone and polyethersulfone polymers.

Based on the current research status, we proposed to use the hollow fiber ultrafiltration membrane with more effective filtration area as the supporting membrane, and adopt the ultraviolet irradiation grafting method, which is easy to operate in the reaction process and has less damage to the material body performance, to graft on the surface of the membrane. Preparation of positively charged hollow fiber nanofiltration membranes.

Invention content:

The purpose of the present invention is to propose a preparation method of a positively charged hollow fiber nanofiltration membrane with simple operation and stable performance.

Concrete steps of the present invention are as follows:

1) Repeatedly rinsing the polysulfone hollow fiber ultrafiltration membrane with ultrapure water to remove impurities remaining on the surface of the basement membrane;

2) Prepare a trimethylallyl ammonium chloride (TMAAC) or dimethyl diallyl ammonium chloride (DMDAAC) monomer aqueous solution with a mass percentage concentration of 1%-20%, wherein the mass percentage concentration 0.1%-5% N, N methylenebisacrylamide as a crosslinking agent;

3) Soak the base film in the monomer and cross-linking agent aqueous solution prepared in step 2 for 6-12 hours. Under the protective atmosphere of sufficient nitrogen, select a high-energy ultraviolet lamp with a power of 300W-1000W for radiation grafting. The distance of the irradiation source is 5cm-50cm, and the irradiation time is 0.5min-35min.

4) After the grafting reaction is completed, the membrane is repeatedly washed with reverse osmosis water to remove unreacted residual monomers and homopolymers on the surface of the membrane to obtain a positively charged hollow fiber nanofiltration membrane.

The method of the positively charged hollow fiber nanofiltration membrane proposed by the present invention adopts the surface irradiation grafting method, and starts from the ultrafiltration membrane to make the nanofiltration membrane. The preparation feature is that the surface pore size of the ultrafiltration membrane can be changed through surface grafting, and at the same time, the surface of the grafted membrane is positively charged. After the modification of the membrane, the functional layer is firmly grafted to the surface of the membrane in the form of chemical bonds, so that the interception performance of the membrane can be kept stable for a long time, and it has excellent interception performance for high-valent metal cations.

The irradiation grafting method used in the present invention is mainly high-energy ultraviolet lamp irradiation. Due to the stable physical and chemical properties of the base membrane used, the equipment cost of the ultraviolet irradiation device is low, the area is small, and it is easy to operate. The grafting reaction only occurs on the surface of the base membrane, which has little damage to the performance of the material itself, and the effective surface area of the hollow fiber membrane is large. , the method of ultraviolet grafting is suitable for the present invention.

The monomers used in the present invention are quaternary ammonium salt monomers with high activity and special groups. Most of these monomers have ethyl group double bonds in their structure, and the effect of surface grafting is achieved through free radical polymerization. . During the preparation process, since both the monomer and the cross-linking agent are water-soluble, water is generally used as the solvent, the mass concentration of the monomer is generally 1%-20%, and the concentration of the cross-linking agent is generally 0.1%-5%.

According to the present invention, the irradiation light source is a high-pressure ultraviolet lamp, the base power is between 500w-1000w, and the irradiation distance is 1cm-30cm. During irradiation grafting, charged films with different properties can be prepared by adjusting the irradiation distance and irradiation time. Considering the actual industrial operation process, irradiation grafting at room temperature is generally adopted.

In the present invention, the test of nanofiltration performance is carried out in a self-made membrane performance tester, and the operating pressure is carried out at 0.2Mpa-0.6Mpa. The 0.3g/L CaCl ₂ solution was selected as the original solution, and the interception performance of the nanofiltration membrane was characterized by testing the concentration of the original solution and the filtrate, and the operating temperature was selected as room temperature 20°C.

Detailed ways

The specific embodiments of the present invention are introduced below, but the present invention is not limited by the embodiments.

Example 1:

1) Repeatedly rinsing a polysulfone hollow fiber ultrafiltration membrane with a molecular weight cut-off of 20,000 with ultrapure water to remove impurities remaining on the surface of the basement membrane;

2) Prepare an aqueous solution of trimethylallyl ammonium chloride (TMAAC) monomer with a mass percentage concentration of 6%, which contains 0.6% N, N methylenebisacrylamide as a cross-linking agent;

3) Soak the base film in the monomer and cross-linking agent aqueous solution prepared in step 2 for 6 hours. Under the protective atmosphere of sufficient nitrogen, select a high-energy ultraviolet lamp with a power of 300W-1000W for radiation grafting, and the film is separated from the ultraviolet lamp. The distance between the tubes is 30 cm, and the irradiation time is 5 min.

4) After the grafting reaction is completed, the membrane is repeatedly washed with reverse osmosis water to remove unreacted residual monomers and homopolymers on the surface of the membrane to obtain a positively charged hollow fiber nanofiltration membrane (PSf-g-TMAAC).

PSf-g-TMAAC charged membrane hollow fiber membrane has a pure water flux of 11.64L/m ² h at a pressure of 0.2MPa, and a water flux of 10.78L/m to a CaCl ₂ solution with a concentration of 0.3g/L ² h, the rejection rate was 48.6%.

Example 2:

1) Repeatedly rinsing a polysulfone hollow fiber ultrafiltration membrane with a molecular weight cut-off of 20,000 with ultrapure water to remove impurities remaining on the surface of the basement membrane;

2) Prepare an aqueous solution of 8% dimethyl diallyl ammonium chloride (DMDAAC) monomer in which the mass percentage concentration is 0.6% N, N methylenebisacrylamide as a cross-linking agent;

3) Soak the base film in the monomer and cross-linking agent aqueous solution prepared in step 2 for 6 hours. Under the protective atmosphere of sufficient nitrogen, select a high-energy ultraviolet lamp with a power of 300W-1000W for radiation grafting, and the film is separated from the ultraviolet lamp. The distance between the tubes is 25 cm and the irradiation time is 10 min.

4) After the grafting reaction is completed, the membrane is repeatedly washed with reverse osmosis water to remove unreacted residual monomers and homopolymers on the surface of the membrane to obtain a positively charged hollow fiber nanofiltration membrane (PSf-g-DMDAAC).

PSf-g-DMDAAC charged membrane hollow fiber membrane has a pure water flux of 7.97L/m ² h at a pressure of 0.2MPa, and a water flux of 7.63L/m ² h for a CaCl ₂ solution with a concentration of 0.3g/L , The rejection rate is 79.35%.

Example 3:

1) Repeatedly rinsing a polysulfone hollow fiber ultrafiltration membrane with a molecular weight cut-off of 20,000 with ultrapure water to remove impurities remaining on the surface of the basement membrane;

2) Prepare a 10% dimethyl diallyl ammonium chloride (DMDAAC) monomer aqueous solution, which contains 0.6% N, N methylenebisacrylamide as the cross joint agent;

3) Soak the base film in the monomer and cross-linking agent aqueous solution prepared in step 2 for 6 hours. Under the protective atmosphere of sufficient nitrogen, select a high-energy ultraviolet lamp with a power of 300W-1000W for radiation grafting, and the film is separated from the ultraviolet lamp. The distance of the tubes is 20cm, and the irradiation time is 20min.

4) After the grafting reaction is completed, the membrane is repeatedly washed with reverse osmosis water to remove unreacted residual monomers and homopolymers on the surface of the membrane to obtain a positively charged hollow fiber nanofiltration membrane (PSf-g-DMDAAC).

PSf-g-DMDAAC charged membrane hollow fiber membrane has a pure water flux of 2.98L/m ² h at a pressure of 0.2MPa, and a water flux of 2.47L/m ² h for a CaCl ₂ solution with a concentration of 0.3g/L , The rejection rate is 83.25%.

Example 4:

1) Repeatedly rinsing a polysulfone hollow fiber ultrafiltration membrane with a molecular weight cut-off of 20,000 with ultrapure water to remove impurities remaining on the surface of the basement membrane;

2) Prepare an aqueous solution of dimethyl diallyl ammonium chloride (DMDAAC) monomer with a mass percentage concentration of 8%, which contains 0.8% N, N methylenebisacrylamide as the cross joint agent;

3) Soak the base film in the monomer and cross-linking agent aqueous solution prepared in step 2 for 6 hours. Under the protective atmosphere of sufficient nitrogen, select a high-energy ultraviolet lamp with a power of 300W-1000W for radiation grafting, and the film is separated from the ultraviolet lamp. The distance of the tubes is 20cm, and the irradiation time is 20min.

4) After the grafting reaction is completed, the membrane is repeatedly washed with reverse osmosis water to remove unreacted residual monomers and homopolymers on the surface of the membrane to obtain a positively charged hollow fiber nanofiltration membrane (PSf-g-DMDAAC).

PSf-g-DMDAAC charged membrane hollow fiber membrane has a pure water flux of 1.57L/m ² h at a pressure of 0.2MPa, and a water flux of 1.36L/m ² h for a CaCl ₂ solution with a concentration of 0.3g/L , The rejection rate is 94.21%.

Claims (4)

1. A method for preparing a positively charged hollow fiber nanofiltration membrane by surface ultraviolet irradiation grafting, the main steps of its synthesis are as follows: 1) Repeatedly rinsing the polysulfone hollow fiber ultrafiltration membrane with ultrapure water to remove impurities remaining on the surface of the basement membrane; 2) preparing an aqueous monomer solution with a concentration of 1%-20% by mass, which contains N,N methylenebisacrylamide with a concentration of 0.1%-5% by mass as a crosslinking agent; 3) Soak the base film in the monomer and cross-linking agent aqueous solution prepared in step 2) for 6-12 hours. Under the protective atmosphere of sufficient nitrogen, select a high-energy ultraviolet lamp with a power of 300W-1000W for radiation grafting. The distance from the ultraviolet lamp is 5cm-50cm, and the irradiation time is 0.5min-35min. 4) After the grafting reaction is completed, the membrane is repeatedly washed with reverse osmosis water to remove unreacted residual monomers and homopolymers on the surface of the membrane to obtain a positively charged hollow fiber nanofiltration membrane. 2. according to the described preparation method of claim 1, it is characterized in that the cationic monomer that adopts is the hydrophilic vinylic monomer that has quaternary ammonium group, as trimethyl allyl ammonium chloride (TMAAC) Or dimethyldiallylammonium chloride (DMDAAC). 3. According to the requirement of claim 1, it is characterized in that only water is used as the solvent to prepare the monomer solution, the mass percentage concentration of the monomer is 1%-10%, and the mass percentage concentration of the crosslinking agent is 0.1%-5%. . 4. according to the requirement of claims 1, it is characterized in that, the molecular weight cut-off of polymer base film used is generally less than 50000, and the nanofiltration membrane of preparation, under 0.2MPa pressure, is the CaCl of 0.3g/L to concentration ₂ cut-off rate It is 48.6%-94.21%.