CN108854593B - Preparation method of high-flux and high-rejection-rate dual-excellent PVDF flat membrane - Google Patents
Preparation method of high-flux and high-rejection-rate dual-excellent PVDF flat membrane Download PDFInfo
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- CN108854593B CN108854593B CN201810610044.4A CN201810610044A CN108854593B CN 108854593 B CN108854593 B CN 108854593B CN 201810610044 A CN201810610044 A CN 201810610044A CN 108854593 B CN108854593 B CN 108854593B
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
- B01D71/06—Organic material
- B01D71/30—Polyalkenyl halides
- B01D71/32—Polyalkenyl halides containing fluorine atoms
- B01D71/34—Polyvinylidene fluoride
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
- B01D67/0002—Organic membrane manufacture
- B01D67/0009—Organic membrane manufacture by phase separation, sol-gel transition, evaporation or solvent quenching
- B01D67/0011—Casting solutions therefor
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
- B01D69/02—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor characterised by their properties
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
- B01D69/06—Flat membranes
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2325/00—Details relating to properties of membranes
- B01D2325/04—Characteristic thickness
Abstract
The invention belongs to the technical field of membrane separation, and particularly relates to a preparation method of a fluorocarbon special surfactant blending modified PVDF membrane with high flux and high rejection rate. A preparation method of a high-flux and high-rejection rate dual-excellent PVDF flat membrane comprises the steps of mixing a pore-foaming agent, a non-ionic fluorocarbon special surfactant, a main membrane material and an organic solvent, heating in a water bath and stirring for 6-10 hours, wherein the mass of the pore-foaming agent, the non-ionic fluorocarbon special surfactant, the main membrane material and the organic solvent respectively accounts for 1% -3%, 1% -7%, 12% -20% and 70% -86% of the total mass; pouring the casting solution after ultrasonic-vacuum-standing defoaming on a glass plate or non-woven fabric according to a Z shape, scraping the casting solution into a film with the thickness of 30-200 mu m, standing the film in the air for 15-30 s, and performing coagulation bath by using emulsified oil/water mixed solution as a non-solvent phase to prepare a membrane, namely the double-excellent PVDF flat membrane with high flux and high rejection rate.
Description
Technical Field
The invention belongs to the technical field of membrane separation, and particularly relates to a preparation method of a fluorocarbon special surfactant blending modified PVDF membrane with high flux and high rejection rate.
Background
Membrane technology is widely used in many fields, and advances and developments in the related industries have been promoted. Film modification has been a fundamental method and research direction for solving film contamination and improving film performance, and can be broadly divided into surface modification and blend modification according to the modification method, and blend modification is preferred for stability and reliability. For a long time, modification research of membranes has always had some problems, which seriously hampered the development of membrane science and limited the popularization of membrane technology. Among them, the improvement of both flux and rejection of the modified membrane has been the subject of the art. The blending modification of the membrane mainly blends some nano particles with hydroxyl or carboxyl groups on the surface, high polymers, some small molecular organic matters and the like. These materials present problems in the blending stage as well as in the phase inversion stage of the casting solution. Wherein, the blending of the nano particles has obvious particle agglomeration phenomenon, so that the pore size distribution of the formed film is not uniform and the interception effect is poor. Most of high polymers and organic micromolecules belong to substances with strong water solubility, and the high polymers and the organic micromolecules are easy to run off along with the exchange of a solvent phase and a non-solvent phase in the phase inversion process of the blend membrane, so that hydrophilic groups on the surface of the membrane are not well retained, the aperture of the blend membrane is increased, and the retention effect is reduced. Therefore, in the field of blended membrane modification research, the difficulty of simultaneously improving the membrane flux and the rejection rate still exists.
Surface ofThe active agent is a chemical substance which can change the interfacial characteristics between aqueous liquid and non-aqueous liquid by adding a small amount of the active agent, so that the interfacial state of a solution system is obviously changed. At present, some researches for solving the problems existing in the modification of the blend membrane by utilizing the basic properties of the surfactant are carried out, related researches are mainly focused on common surfactants, and the problem solving effect of the common surfactants is not outstanding due to the strong water-solubility characteristics of the common surfactants. For example, Chinese patent CN102294180A utilizes common surfactant sodium dodecyl sulfate to blend and prepare nano TiO2The modified PVDF ultrafiltration membrane is used for solving the agglomeration problem of nano particles. For example, Chinese patent CN102921317A uses a common surfactant-organic solvent-water ternary system to prepare a polysulfone ultrafiltration membrane, although the rejection rate of the polysulfone ultrafiltration membrane on ovalbumin reaches 98.9%, the flux of the polysulfone ultrafiltration membrane is only 73L/m2H, low efficiency in practical application.
Disclosure of Invention
The invention aims to solve the problem of the prior art and provides a method for preparing a double-excellent PVDF flat membrane with high flux and high rejection rate by utilizing the basic properties of a non-ionic fluorocarbon special surfactant and exerting the double functions of assisting pore forming and balancing thermodynamic and kinetic stability in a membrane preparation process.
The technical scheme adopted by the invention is as follows: a preparation method of a high-flux and high-rejection dual-excellent PVDF flat membrane comprises the following steps:
step one, preparing a membrane casting solution, mixing a pore-foaming agent, a non-ionic fluorocarbon special surfactant, a main membrane material and an organic solvent, and heating and stirring in a water bath for 6-10 hours, wherein the mass of the pore-foaming agent, the mass of the non-ionic fluorocarbon special surfactant, the mass of the main membrane material and the mass of the organic solvent respectively account for 1% -3%, 1% -7%, 12% -20% and 70% -86% of the total mass;
and step two, preparing a membrane, namely pouring the casting solution after ultrasonic-vacuum-standing defoaming on a glass plate or non-woven fabric according to a Z shape, scraping the film into a film with the thickness of 30-200 mu m, standing the film in the air for 15-30 s, and performing coagulation bath by using emulsified oil/water mixed solution as a non-solvent phase to prepare the membrane, namely the double-excellent PVDF flat membrane with high flux and high rejection rate.
As a preferred mode: the non-ionic fluorocarbon special surfactant is a fluorocarbon surfactant with a hydrophilic end oxygen-containing group less than or equal to 2, and the oxygen-containing group is one or two of an ether group and a hydroxyl group.
As a preferred mode: the pore-forming agent is lithium chloride (LiCl).
As a preferred mode: the main film material is polyvinylidene fluoride (PVDF) with the intrinsic viscosity of 1.60-2.10 dl/g and the appearance of white powder or particles.
As a preferred mode: mixing the pore-foaming agent, the non-ionic fluorocarbon special surfactant, the main membrane material and the organic solvent in the first step means that the pore-foaming agent, the non-ionic fluorocarbon special surfactant and the main membrane material are sequentially added into the organic solvent, and before the latter substance is added, the former substance is ensured to be uniformly mixed and completely dissolved.
As a preferred mode: in the step one, the water bath is heated and stirred for 6-10 h, firstly the water bath is heated and stirred for 2-3h at 70-80 ℃, then the water bath is heated and stirred for 3-5h at 40-50 ℃, and finally the water bath is heated and stirred for 1-2h at 70-80 ℃.
As a preferred mode: and the ultrasonic-vacuum-standing defoaming process of the membrane casting solution in the second step comprises the steps of ultrasonic defoaming for 1 hour at room temperature, then vacuum defoaming for 30 minutes, and finally standing and defoaming for 6 hours in the air.
As a preferred mode: and in the second step, the volume ratio of the emulsified oil to the water is 1:9 to 3: 7.
as a preferred mode: the organic solvent is N, N-dimethylacetamide.
The invention provides a preparation method of a fluorocarbon special surfactant blending modified PVDF (polyvinylidene fluoride) membrane with double excellent characteristics based on the special properties of a non-ionic fluorocarbon surfactant and the unique effect of the non-ionic fluorocarbon surfactant in a liquid phase conversion process of a casting membrane, namely, the dynamic stability of the fluorocarbon special surfactant is changed while the thermodynamic stability is influenced, so that the blending membrane has excellent performances of high flux and high rejection rate. The PVDF flat membrane prepared by the invention can obviously improve the water treatment efficiency and is suitable for various water treatment processes/technologies such as algae removal, bacteria interception, reclaimed water reuse and the like. In consideration of all aspects, the PVDF flat membrane modified by the non-ionic fluorocarbon surfactant has good practical application effect and application prospect.
The fluorocarbon special surfactant is a surfactant containing a nonmetallic element F. The difference of the molecular structure of the surfactant from the common surfactant and the unique property of fluorine element enable the surfactant to have the characteristics which other surfactants do not have. Chinese patent CN101837251A utilizes amphiphilic nonionic fluorocarbon surfactant, and adopts a surface embedding process to make the surfactant (hydrophilic group) remain on the surface layer of the membrane, so as to endow the polyvinylidene fluoride porous membrane with hydrophilic performance. However, the modification mode of physical adsorption can cause a great amount of surfactant on the surface layer of the modified membrane to run away after a period of time, and the use value of the membrane is difficult to maintain; and the surfactant exists in the surface layer of the film only for a short time, does not participate in the preparation process of the matrix film, and does not influence the structure and the performance of the matrix film. Our research has found that the addition of certain fluorocarbon surfactants during the blending phase inversion process of the film-making process improves the pore structure of the film, and the surfactants do not constitute film components after coagulation bath and cleaning treatment. On one hand, as a non-solvent phase component, the addition of the surfactant is beneficial to the instantaneous phase separation of the membrane to form a mature finger-shaped pore structure, thereby being beneficial to the promotion of membrane flux; on the other hand, because H atoms on a hydrocarbon chain at the hydrophobic end of the fluorocarbon surfactant are partially or completely substituted by F atoms, the fluorocarbon surfactant has the characteristics of unique hydrophobicity and oleophobicity, under a coagulation bath system of the emulsified oil/water mixed solution (the volume of oil and water is 1: 9-3: 7), the hydrophilic end of the surfactant firstly drives molecules to the contact interface of the oil-water mixed solution and the membrane, and the hydrophobic end generates reverse repulsion to the double-hydrophobic effect of the emulsified oil/water mixed solution. Since the hydrophilic-lipophilic balance (HLB) of the nonionic fluorocarbon surfactant is just between the hydrophilic-lipophilic critical point, the lipophobicity is relatively weaker than the hydrophobicity. Earlier researches show that the volume of the oil-water mixed liquid coagulating bath is controlled to be 1: 9-3: 7, so that the exchange rate of a solvent and a non-solvent can be greatly reduced, the surface layer of the blending membrane has a tendency of delayed phase separation, the surface layer structure of the blending membrane is slightly compact, and the guarantee of the membrane retention rate is facilitated.
In addition, the invention controls the temperature by a three-section program (the first section is 70-80 degrees for 2h, the middle section is 40-50 degrees for 3h, and the last section is 70-80 degrees for 1 h)
The homogenization time of the casting solution blended with the surfactant can be shortened from 12 hours to 6 hours; the ultrasonic (1 h), vacuum (30 min) and standing (6 h) deaeration can shorten the casting solution from 24-48h of independent standing to 7-8 h. The two improvements aiming at the processing technology of the main casting solution have important values for reducing the film-making cost and improving the film-making efficiency.
Detailed Description
Example 1
1.0 gLithium chloride (LiCl),Sequentially dissolving 0.5 g of non-ionic fluorocarbon special surfactant (FS-30) and 8.0 g of polyvinylidene fluoride in 40.5 g N, N-dimethylacetamide, and stirring for 6 hours by using a programmed temperature-controlled water bath for heating (the first section is 70-80 degrees for 2 hours, the middle section is 40-50 degrees for 3 hours, and the last section is 70-80 degrees for 1 hour) to prepare a uniform casting solution; then ultrasonic (40 kHZ) defoaming for 1h at room temperature (18-22 ℃), vacuum (negative pressure 0.08 Mpa) defoaming for 30min, and standing and defoaming for 6 h. Casting the casting solution on a clean glass plate at room temperature, and scraping a filter membrane with the thickness of 150 mu m by using an adjustable scraper; drying in air for 30 s; coagulating bath is carried out at 20 ℃ by using emulsified oil/water mixed solution (oil-water volume ratio is 2: 8) as a non-solvent phase; washing and soaking for 24 h by pure water to prepare the FSS/PVDF flat membrane.
Example 2
1.0 gLithium chloride (LiCl), 1Sequentially dissolving 5 g of non-ionic fluorocarbon special surfactant (FS-30) and 8.0 g of polyvinylidene fluoride in 39.5 g N, N-dimethylacetamide, heating in a programmed temperature-controlled water bath (70-80 degrees for 2 hours at the first section, 40-50 degrees for 3 hours at the middle section and 70-80 degrees for 1 hour at the last section), and stirring for 6 hours to prepare a uniform casting solution; then ultrasonic (40 kHZ) defoaming for 1h at room temperature (18-22 ℃), vacuum (negative pressure 0.08 Mpa) defoaming for 30min, and standing and defoaming for 6 h. Casting the casting solution on a clean glass plate at room temperature, and scraping a filter membrane with the thickness of 150 mu m by using an adjustable scraper; drying in air for 30 s; at 20 deg.C, emulsified oil/water mixed solution (oil-water volume ratio of 2: 8) is used as non-emulsified oil/water mixed solutionCarrying out a coagulation bath on the solvent phase; washing and soaking for 24 h by pure water to prepare the FSS/PVDF flat membrane.
Example 3
1.0 gLithium chloride (LiCl), 2Sequentially dissolving 5 g of non-ionic fluorocarbon special surfactant (FS-30) and 8.0 g of polyvinylidene fluoride in 38.5 g N, N-dimethylacetamide, heating in a programmed temperature-controlled water bath (70-80 degrees for 2 hours at the first section, 40-50 degrees for 3 hours at the middle section and 70-80 degrees for 1 hour at the last section), and stirring for 6 hours to prepare a uniform casting solution; then ultrasonic (40 kHZ) defoaming for 1h at room temperature (18-22 ℃), vacuum (negative pressure 0.08 Mpa) defoaming for 30min, and standing and defoaming for 6 h. Casting the casting solution on a clean glass plate at room temperature, and scraping a filter membrane with the thickness of 150 mu m by using an adjustable scraper; drying in air for 30 s; coagulating bath is carried out at 20 ℃ by using emulsified oil/water mixed solution (oil-water volume ratio is 2: 8) as a non-solvent phase; washing and soaking for 24 h by pure water to prepare the FSS/PVDF flat membrane.
Example 4
1.0 gLithium chloride (LiCl), 3Sequentially dissolving 5 g of non-ionic fluorocarbon special surfactant (FS-30) and 8.0 g of polyvinylidene fluoride in 37.5 g N, N-dimethylacetamide, heating in a programmed temperature-controlled water bath (70-80 degrees for 2 hours at the first section, 40-50 degrees for 3 hours at the middle section and 70-80 degrees for 1 hour at the last section), and stirring for 6 hours to prepare a uniform casting solution; then ultrasonic (40 kHZ) defoaming for 1h at room temperature (18-22 ℃), vacuum (negative pressure 0.08 Mpa) defoaming for 30min, and standing and defoaming for 6 h. Casting the casting solution on a clean glass plate at room temperature, and scraping a filter membrane with the thickness of 150 mu m by using an adjustable scraper; drying in air for 30 s; coagulating bath is carried out at 20 ℃ by using emulsified oil/water mixed solution (oil-water volume ratio is 2: 8) as a non-solvent phase; washing and soaking for 24 h by pure water to prepare the FSS/PVDF flat membrane.
Example 5 (comparative example)
1.0 gLithium chloride (LiCl)And 8.0 g of polyvinylidene fluoride are sequentially dissolved in 41.0 g N and N-dimethylacetamide, stirred for 6 hours in a 70 ℃ water bath condition to prepare uniform casting solution, and then the uniform casting solution is kept stand and defoamed for 24 hours at room temperature. Casting the casting solution on a clean glass plate at room temperature, and scraping a filter membrane with the thickness of 150 mu m by using an adjustable scraper; drying in air for 30 s; at 20 deg.CCoagulating and bathing in pure water; soaking the PVDF flat membrane in pure water for 24 hours to prepare the PVDF flat membrane.
TABLE 1 PVDF Flat Membrane Performance comparison
The invention realizes the control of the membrane aperture and porosity by utilizing the influence of the fluorocarbon surfactant on the thermodynamic and kinetic stability of the casting solution in the phase conversion process of the blended membrane. The blend membrane has the advantages of high flux and high retention rate, thereby having important value and wide prospect in the practical application of the membrane.
Claims (8)
1. A preparation method of a double-excellent PVDF flat membrane with high flux and high rejection rate is characterized by comprising the following steps: the method comprises the following steps:
step one, preparing a membrane casting solution, mixing a pore-foaming agent, a non-ionic fluorocarbon special surfactant, a main membrane material and an organic solvent, heating in a water bath and stirring for 6-10 hours, wherein the mass of the pore-foaming agent, the non-ionic fluorocarbon special surfactant, the main membrane material and the organic solvent respectively accounts for 1% -3%, 1% -7%, 12% -20% and 70% -86% of the total mass, the main membrane material is polyvinylidene fluoride (PVDF) with the intrinsic viscosity of 1.60-2.10 dl/g and the appearance of white powder or granular PVDF;
and step two, preparing a membrane, namely pouring the casting solution after ultrasonic-vacuum-standing defoaming on a glass plate or non-woven fabric according to a Z shape, scraping the film into a film with the thickness of 30-200 mu m, standing the film in the air for 15-30 s, and performing coagulation bath by using emulsified oil/water mixed solution as a non-solvent phase to prepare the membrane, namely the double-excellent PVDF flat membrane with high flux and high rejection rate.
2. The preparation method of the high-flux and high-rejection dual-excellent PVDF flat membrane as claimed in claim 1, wherein: the non-ionic fluorocarbon special surfactant is a fluorocarbon surfactant with a hydrophilic end oxygen-containing group less than or equal to 2, and the oxygen-containing group is one or two of an ether group and a hydroxyl group.
3. The preparation method of the high-flux and high-rejection dual-excellent PVDF flat membrane as claimed in claim 1, wherein: the pore-forming agent is lithium chloride LiCl.
4. The preparation method of the high-flux and high-rejection dual-excellent PVDF flat membrane as claimed in claim 1, wherein: mixing the pore-foaming agent, the non-ionic fluorocarbon special surfactant, the main membrane material and the organic solvent in the first step means that the pore-foaming agent, the non-ionic fluorocarbon special surfactant and the main membrane material are sequentially added into the organic solvent, and before the latter substance is added, the former substance is ensured to be uniformly mixed and completely dissolved.
5. The preparation method of the high-flux and high-rejection dual-excellent PVDF flat membrane as claimed in claim 1, wherein: in the step one, the water bath is heated and stirred for 6-10 h, firstly the water bath is heated and stirred for 2-3h at 70-80 ℃, then the water bath is heated and stirred for 3-5h at 40-50 ℃, and finally the water bath is heated and stirred for 1-2h at 70-80 ℃.
6. The preparation method of the high-flux and high-rejection dual-excellent PVDF flat membrane as claimed in claim 1, wherein: and the ultrasonic-vacuum-standing defoaming process of the membrane casting solution in the second step comprises the steps of ultrasonic defoaming for 1 hour at room temperature, then vacuum defoaming for 30 minutes, and finally standing and defoaming for 6 hours in the air.
7. The preparation method of the high-flux and high-rejection dual-excellent PVDF flat membrane as claimed in claim 1, wherein: and in the second step, the volume ratio of the emulsified oil to the water is 1:9 to 3: 7.
8. the preparation method of the high-flux and high-rejection dual-excellent PVDF flat membrane as claimed in claim 1, wherein: the organic solvent is N, N-dimethylacetamide.
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| CN101837251B (en) * | 2010-04-07 | 2012-05-23 | 南京工业大学 | Method for hydrophilic modification on polyvinylidene fluoride porous film surface by amphipathic molecule |
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