CN103223300A - Hollow fiber type composite nano-filtration membrane and preparation method thereof - Google Patents

Abstract

The invention relates to a hollow fiber type composite nano-filtration membrane and a preparation method thereof. The hollow fiber type composite nano-filtration membrane comprises a hollow fiber microporous base membrane adopted as a supporting layer, a polysulfone transition layer, and a polyamide composite layer, wherein the polysulfone transition layer is positioned inside membrane holes of the hollow fiber microporous base membrane, and the polyamide composite layer is positioned inside membrane holes of the polysulfone transition layer. The preparation method comprises: adopting a thermally induced phase separation method to obtain an asymmetric microporous base membrane, adopting an impregnation phase transformation method to obtain the polysulfone transition layer in the micro holes, and adopting pressure control and an interface condensation polymerization reaction to obtain the polyamide composite layer. The hollow fiber type composite nano-filtration membrane provides a sodium chloride salt solution entrapment rate of more than 90%, a divalent salt ion entrapment rate of more than 95%, and a pollutant entrapment rate of more than 99% under 0.2-0.8 MPa, such that the hollow fiber type composite nano-filtration membrane has characteristics of high strength, washing resistance, large flux and the like, wherein the pollutants have a molecular weight of 300-200,000 Daltons.

Description

A kind of hollow fiber type composite nanofiltration membrane and preparation method thereof

technical field

The invention relates to a hollow fiber type composite nanofiltration membrane capable of treating suspended pollutants and a preparation method thereof. the

Background technique

The research and development of hollow fiber reverse osmosis membrane is expected to lead the future of membrane technology. At present, commercial RO membranes are all composite roll membranes, which are easy to pollute and difficult to clean, which puts forward high requirements on the influent water quality of RO membranes, so hollow fiber ultra/microfiltration (UF/MF) membranes have to be used as RO membranes. Pretreatment, the so-called dual-membrane (UF/MF-RO) water treatment integrated process, severely restricts the further reduction of membrane water treatment costs. Improving the anti-fouling performance of the membrane can relax the requirements of the influent water quality: this is the key to the integration of the double membrane method (UF/MF-RO) into the ultra/microfiltration influent to directly obtain the RO product water standard. the

Compared with the composite roll-type membrane, the composite hollow fiber membrane can achieve improved anti-pollution and washing resistance, high compressive strength and high tensile strength of the membrane, and the hollow fiber membrane can be made very thin. The hollow fiber membrane has a high packing density, and the effective filtration area of the NF membrane within the same unit volume is larger. The hollow fiber membrane can greatly increase the effective membrane area per unit volume, and the self-supporting membrane structure makes backwashing possible, effectively improving the anti-pollution ability of the membrane. However, in the currently reported patents, the influent water quality of the hollow fiber membrane requires that the suspended solids turbidity SDI<3, which is strictly limited by the requirements for the influent water quality of reverse osmosis, so the pretreatment of RO influent water is still necessary. the

Many works have reported pollution-resistant hollow fiber nanofiltration membranes, which can be divided into two categories according to the position of the separation layer: the internal pressure hollow fiber membrane with the separation layer located on the inner surface of the hollow fiber membrane and the one with the separation layer located on the outer surface of the hollow fiber membrane. External pressure hollow fiber membrane. During internal pressure operation, the separation layer is less subject to flow erosion and has higher pressure resistance, so it was first reported. The Japanese patent (JP022842) prepared hollow fiber nanofiltration membranes of external pressure type and internal pressure type. Due to the limitation of membrane material strength and operating conditions, the internal pressure type structure is tended to be used in the patent application, but when the internal pressure type hollow fiber membrane is used, its structural advantages over the roll type membrane cannot be brought into play , limiting its application. the

US Patent (US5,784,079) reported an external pressure type hollow fiber membrane. In order to improve the stability of the membrane under higher operating pressure, the outer diameter of the base membrane used is smaller, so the mechanical stability of the membrane is poor, and the hollow fiber membrane is prone to breakage during operation. In addition, due to the use of a fiber structure with a smaller outer diameter, the pretreatment requirements of the membrane module on the influent are more stringent, which is not convenient for engineering applications. the

Currently known is an anti-pollution hollow fiber membrane (application number: 200810059988.3), which consists of a three-layer structure. Using polyolefin hollow fiber microporous base membrane as support layer, polyvinyl alcohol crosslinked structure as transition layer and polyamide as composite layer, an external pressure hollow fiber nanofiltration membrane was obtained. The composite layer with nanofiltration separation performance is located on the outer surface of the hollow fiber membrane. During the operation and cleaning process, the surface of the hollow fiber membrane is easy to rub against each other, and the surface coating of the hollow fiber membrane is easily damaged. Tricarboyl chloride is a two-phase reaction monomer, and the obtained polyamide composite layer has a loose structure and is easy to fall off, which will seriously affect the separation performance of the membrane. the

In addition, in this patent, the polyvinyl alcohol cross-linked structure is filled into the pores of the hollow fiber membrane. Due to the crystallinity of polyvinyl alcohol and the tightness of the cross-linked structure, the mass transfer resistance of water molecules inside the membrane is increased, which is not conducive to pure Increased water flux. In this patent, piperazine is used as a water phase monomer to prepare a composite layer, and its structure only has a retention performance of about 90% for divalent ions, while the retention rate for monovalent sodium chloride salt ions is about 20%. the

To sum up, when the composite layer is located on the inner surface of the hollow fiber base membrane, the internal pressure operation cannot exert its advantages over the rolled membrane; when the composite layer is located on the outer surface of the hollow fiber base membrane, the external pressure flushing operation will destroy the composite layer. layer structure. It is necessary to develop a hollow fiber composite nanofiltration membrane in which the composite layer is located inside the membrane pores of the hollow fiber base membrane, so as to make full use of the hollow fiber composite nanofiltration membrane to periodically air wash and backwash to reduce membrane pollution. The structure protection of the fiber microporous base membrane effectively broadens the treatment concentration range of the hollow fiber membrane influent. the

Contents of the invention

The purpose of the present invention is to solve the problem that the washout resistance of the existing external pressure hollow fiber nanofiltration membrane is relatively poor, and propose a preparation method for preparing the washout external pressure hollow fiber nanofiltration membrane and the preparation method thereof. The hollow fiber nanofiltration membrane can be fed into the microfiltration membrane to prepare a hollow fiber nanofiltration membrane with erosion resistance, large flux and high strength. the

Technical scheme of the present invention is as follows:

A hollow fiber type composite nanofiltration membrane is characterized in that: the hollow fiber type composite nanofiltration membrane is composed of a hollow fiber microporous base membrane as a support layer, a polysulfone transition layer and a polyamide composite layer, the polysulfone type The transition layer is located inside the membrane pores of the hollow fiber membrane microporous base membrane, and the polyamide composite layer is located inside the membrane pores of the polysulfone transition layer. the

The hollow fiber microporous base membrane of the present invention is a hollow fiber microporous membrane with an outer diameter of 0.6 to 1.8 mm, an inner diameter of 0.3 to 1.2 mm, and a ratio of the outer diameter to the inner diameter of 1.5 to 2; the alcohol bubble point is 0.2 to 0.4 MPa, the tensile strength is at least 7MPa, and the compressive strength is at least 2MPa. the

The thickness L2 of the polysulfone transition layer according to the present invention accounts for 5-25% of the thickness L1 of the support layer; the thickness L3 of the polyamide composite layer accounts for 1-10% of the thickness L2 of the polysulfone transition layer; 150nm, the pore diameter D2 of the polysulfone transition layer is 30-70nm, and the pore diameter of the polyamide composite layer is 0.5-2nm. the

The polysulfone transition layer described in the present invention is polysulfone, polyethersulfone, polyether sulfone ketone, sulfonated polysulfone, sulfonated polyether sulfone or sulfonated polyether ether ketone; the polyamide composite layer is Semi-aromatic polyamide or fully aromatic polyamide formed by interfacial polymerization of aliphatic polyamine or aromatic polyamine and aromatic polyacyl chloride. the

A kind of preparation method of hollow fiber type composite nanofiltration membrane provided by the invention is characterized in that described method is carried out according to the following steps:

1) First, the polysulfone casting membrane solution with a concentration between 2 and 20wt% is impregnated in the membrane pores of the hollow fiber microporous base membrane by impregnation method. The impregnation method includes: the hollow fiber microporous base membrane is immersed in the casting membrane solution for 0.5-10 minutes, or make the hollow fiber microporous basement membrane pass through the casting solution storage tank for 0.5-10 minutes, or rotate the hollow fiber microporous basement membrane on the surface of the casting solution;

2) Immerse the hollow fiber membrane obtained in step 1) in the coagulation bath for 10-120 minutes;

3) After the hollow fiber membrane is taken out from the coagulation bath, it is packaged into a membrane device to obtain a modified hollow fiber membrane filled with a polysulfone transition layer in the membrane pores of the hollow fiber microporous base membrane;

4) Flow the polyamine aqueous phase solution with a concentration of 0.2-5wt% on the inner surface of the modified hollow fiber membrane, so that the pressure difference between the inner and outer surface of the modified hollow fiber membrane is 0.01-0.3MPa, and the pressure is maintained for 1-10min;

5) Purge the argon gas on the outer surface of the modified hollow fiber membrane for 0.5-10 minutes or circulate the organic solvent for 5-30 minutes, then flow the polyacyl chloride oil phase solution with a concentration of 0.05-2wt% on the outer surface of the modified hollow fiber membrane for 1-10 minutes, react;

6) Circulate the organic solvent on the outer surface of the modified hollow fiber membrane to clean the outer surface of the modified hollow fiber base membrane;

7) The membrane device is placed in an oven, heat-treated at 40-90°C for 5-30 minutes, heated to promote the further reaction of amine and acid chloride, and remove the solvent of the reactant to obtain a hollow fiber composite nanofiltration membrane. the

In the above preparation method, the solute of the casting solution used in step 1) is polysulfone, polyethersulfone, polyethersulfone ketone, sulfonated polysulfone, sulfonated polyethersulfone or sulfonated polyether ether Ketone; the solvent of casting solution is N, N-dimethylformamide, N, N-dimethylacetamide, ethyl acetate, propyl acetate, N-methylpyrrolidone, dimethyl sulfoxide, chloroform, One or more of carbon tetrachloride, dichloromethane and dichloroethane are mixed, and the concentration of the casting solution is between 2 and 10wt%; the coagulation bath described in step 2) is water, ethanol, isophthalic acid One or more mixtures of propanol, isobutanol, dimethyl sulfoxide and acetonitrile. The casting solution contains a hydrophilic additive or a pore-forming additive, and the hydrophilic additive is ethanol, isopropanol, n-butanol, tert-amyl alcohol, 2-octanol or diethylene glycol, and the mass of the hydrophilic additive is 100%. The porogenic additive is polyethylene glycol or polyvinylpyrrolidone with a molecular weight of 300,000 to 900,000 daltons, and the porogenic additive mass percentage is between 0.1 and 10 wt%. In the step 4), the pressure difference between the inner and outer surfaces of the modified hollow fiber membrane is between 0.05-0.2MPa; the concentration of the polyamine aqueous phase solution is 0.5-2wt%; the polyamine is an aliphatic polyhydric Amines or aromatic polyamines, the aliphatic polyamines are piperazine and derivatives thereof; the aromatic polyamines are aromatic polyamines or derivatives of sulfonic acid groups, carboxylic acid groups, sulfonates or carboxylates . The concentration of the polyacyl chloride in the oil phase solution in step 5) is 0.05-0.6wt%, the polyacyl chloride is trimesoyl chloride, isophthaloyl chloride or terephthaloyl chloride, and the solvent of the oil phase solution It is n-hexane or cyclohexane; the organic solvent used is cyclohexane or n-hexane; the time for purging argon on the outer surface of the modified hollow fiber membrane is 2-5 minutes; the time for circulating the organic solvent is 15-30 minutes; the reaction time 5 to 10 minutes. In step 7), after the reaction is carried out, the film post-treatment temperature is 50-70° C., and the post-treatment time is 10-20 min. the

Compared with the prior art, the present invention has the following advantages and prominent effects: at 0.2-0.8 MPa, the retention rate of sodium chloride salt solution is >90%; the retention rate of divalent salt ions is >95%; The interception performance of pollutants with a molecular weight between 300 and 200,000 Daltons is >99%. The hollow fiber nanofiltration membrane has the characteristics of high strength, erosion resistance and large flux. the

Description of drawings

Figure 1 is a schematic cross-sectional view of a hollow fiber composite nanofiltration membrane. the

FIG. 2 is a top view of FIG. 1 . the

Figure 3 is the stress-strain diagram of the hollow fiber base membrane before and after modification. the

Figure 4 shows the nanofiltration performance of the hollow fiber composite nanofiltration membrane during long-term stable operation. the

Figure 5 shows the washing resistance and anti-pollution performance of commercial flat nanofiltration membrane NF-90 and hollow fiber composite nanofiltration membrane. the

Figure 6 is the relationship between the pure water flux of the hollow fiber composite nanofiltration membrane and the retention performance of sodium sulfate. the

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings and embodiments. the

Specifically, a hollow fiber composite nanofiltration membrane provided by the present invention is composed of a hollow fiber microporous base membrane support layer 1, a polysulfone transition layer 2 positioned inside the membrane pores of the hollow fiber microporous base membrane and a A hollow fiber composite nanofiltration membrane composed of a polyamide composite layer 3 inside the membrane pores of the polysulfone transition layer (as shown in Figures 1 and 2). the

According to the present invention, the hollow fiber microporous base membrane should have suitable inner and outer diameters. The outer diameter is 0.6-1.8 mm, the inner diameter is 0.3-1.2 mm, and the ratio of the outer diameter to the inner diameter is 1.5-2. the

According to the present invention, the alcohol bubble point of the hollow fiber microporous base membrane should be greater than 0.2MPa. If the alcohol bubble point of the base membrane is less than 0.2 MPa, the composite layer of the obtained hollow fiber composite nanofiltration membrane is easily damaged by the pressure applied during nanofiltration during use, which affects its interception performance of salt ions. the

At the same time, the tensile strength of the base film used should be greater than 7MPa, and the compressive strength should be at least 2MPa. If the tensile strength and compressive strength of the base membrane used are low, the hollow fiber membrane is likely to break due to frequent air and water flushing during the use of the nanofiltration membrane, resulting in a decrease in system efficiency. the

Hollow fiber microporous base membranes usually use highly hydrophobic polyolefin polymers, such as vinylidene fluoride and polypropylene, whose surface energies are 25mN/m and 30mN/m respectively, and the polyamide composite layer is due to the amide bond and incomplete reaction. The effect of carboxyl and amine functional groups belongs to hydrophilic polymers with surface energy. If it is reacted and compounded directly on the surface of polyolefin, due to the influence of surface energy, it is difficult for the nanofiltration composite layer to be uniformly coated on the surface of the base membrane, and the combination of the nanofiltration composite layer and the base membrane is poor, making it easy to separate the prepared two layers. stripping, seriously destroying the retention properties. the

In addition, the pore diameter of the hollow fiber microporous base membrane is 100-150 nm, but the pore diameter of the base membrane required for the preparation of the polyamide composite membrane is usually 30-70 nm. If the composite nanofiltration membrane is directly prepared by using a polyolefin microporous base membrane with a larger pore size, the polyamide composite layer of the composite nanofiltration membrane will be easily damaged during use at an operating pressure above 0.3 MPa, which will greatly reduce the separation performance. the

Therefore, in order to make full use of the mechanical strength of polyolefin membranes to prepare nanofiltration membranes with high strength and high dirt-holding capacity, it is necessary to modify the hollow fiber microporous substrate before preparing a composite layer on the surface of polyolefin-based membranes by interfacial polymerization. Membrane, so that a transition layer is formed in the membrane pores of the basement membrane. the

The transition layer is made of polysulfone, polyethersulfone, polynaphthalene polyether sulfone ketone, sulfonated polysulfone, sulfonated polyether sulfone or sulfonated polyetheretherketone, and aliphatic polyamine or aromatic polyamine and A polyamide composite layer is prepared from a semi-aromatic polyamide or a fully aromatic polyamide formed by interfacial polymerization of aromatic polyacyl chlorides. After phase inversion, polysulfones are composited inside the polyolefin-based pores, and then the polyamide composite layer is embedded in the membrane structure by interfacial polymerization. It is characterized in that: the thickness L2 of the polysulfone transition layer accounts for 5-25% of the thickness L1 of the support layer; the thickness L3 of the polyamide composite layer accounts for 1-10% of the thickness L2 of the polysulfone transition layer; the pore diameter D1 of the support layer is 100-150nm , The pore diameter D2 of the polysulfone transition layer is 30-70nm, and the pore diameter of the polyamide composite layer is 0.5-2nm. the

The preparation method of hollow fiber type composite nanofiltration membrane provided by the invention, the method is carried out in the following steps:

1) First, the polysulfone casting membrane solution with a concentration of 2 to 20wt% is immersed in the membrane pores of the hollow fiber microporous base membrane by the impregnation method. The impregnation method includes: immersing the hollow fiber microporous base membrane in the casting membrane solution for 0.5-10 minutes, or make the hollow fiber microporous basement membrane pass through the casting solution storage tank for 0.5-10 minutes, or rotate the hollow fiber microporous basement membrane on the surface of the casting solution;

2) Immerse the hollow fiber membrane obtained in step 1) in the coagulation bath for 10-120 minutes;

3) After the hollow fiber membrane is taken out from the coagulation bath, it is packaged into a membrane device to obtain a modified hollow fiber membrane filled with a polysulfone transition layer in the membrane pores of the hollow fiber microporous base membrane;

4) Flow a polyamine aqueous phase solution with a concentration of 0.2-5wt% on the inner surface of the modified hollow fiber membrane, so that the pressure difference between the inner and outer surface of the modified hollow fiber membrane is between 0.01-0.3 MPa, and the pressure is maintained for 1-10 minutes;

5) Purge the argon gas on the outer surface of the modified hollow fiber membrane for 0.5-10 minutes or circulate the organic solvent for 5-30 minutes, and then flow the polyacyl chloride oil phase solution with a concentration of 0.05-2wt% on the outer surface of the modified hollow fiber membrane for 1-10 minutes, react;

6) Circulate the organic solvent on the outer surface of the modified hollow fiber membrane to clean the outer surface of the modified hollow fiber base membrane;

7) The membrane device is placed in an oven, heat-treated at 40-90°C for 5-30 minutes, heated to promote the further reaction of amine and acid chloride, and remove the solvent of the reactant to obtain a hollow fiber composite nanofiltration membrane. the

Among the present invention, polysulfone transition layer is prepared by the following scheme:

1) First, the polysulfone casting membrane solution with a concentration between 2 and 20wt% is impregnated in the membrane pores of the hollow fiber microporous base membrane by impregnation method. The impregnation method includes: the hollow fiber microporous base membrane is immersed in the casting membrane solution for 0.5-10 minutes, or make the hollow fiber microporous basement membrane pass through the casting solution storage tank for 0.5-10 minutes, or rotate the hollow fiber microporous basement membrane on the surface of the casting solution;

2) Immerse the hollow fiber membrane obtained in step 1) in the coagulation bath for 10-120 minutes;

3) After the hollow fiber membrane is taken out from the coagulation bath, it is packaged into a membrane device to obtain a modified hollow fiber membrane filled with a polysulfone transition layer in the membrane pores of the hollow fiber microporous base membrane;

The solute of the casting solution used in step 1) is polysulfone, polyethersulfone, polyether sulfone ketone, sulfonated polysulfone, sulfonated polyethersulfone or sulfonated polyether ether ketone; the solvent of the casting solution N, N-dimethylformamide, N, N-dimethylacetamide, ethyl acetate, propyl acetate, N-methylpyrrolidone, dimethyl sulfoxide, chloroform, carbon tetrachloride, dichloro One or more of methane and dichloroethane are mixed, and the concentration of the casting solution is between 2 and 10wt%; the coagulation bath in the step 2) is water, ethanol, isopropanol, isobutanol , dimethyl sulfoxide and acetonitrile or a combination of several. the

The casting solution contains hydrophilic additives or pore-causing additives, and the hydrophilic additives are ethanol, isopropanol, n-butanol, tert-amyl alcohol, 2-octanol or diethylene glycol, and the mass percentage of the hydrophilic additives is at 10-50wt%; the porogenic additive is polyethylene glycol or polyvinylpyrrolidone with a molecular weight of 300,000-900,000 daltons, and the porogenic additive mass percentage is between 0.1-10wt%. the

Polyamide composite layer is prepared by the following scheme among the present invention:

1) Flow a polyamine aqueous phase solution with a concentration of 0.2-5wt% on the inner surface of the modified hollow fiber membrane, so that the pressure difference between the inner and outer surface of the modified hollow fiber membrane is between 0.01-0.3 MPa, and the pressure is maintained for 1-10 minutes;

2) Purge the argon gas on the outer surface of the modified hollow fiber membrane for 0.5-10 minutes or circulate the organic solvent for 5-30 minutes, then flow the polyacyl chloride oil phase solution with a concentration of 0.05-2wt% on the outer surface of the modified hollow fiber membrane for 1-10 minutes, react;

3) Circulate the organic solvent on the outer surface of the modified hollow fiber membrane to clean the outer surface of the modified hollow fiber base membrane;

4) The membrane device is placed in an oven, heat-treated at 40-90°C for 5-30 minutes, heated to promote the further reaction of amine and acid chloride, and remove the solvent of the reactant to obtain a hollow fiber composite nanofiltration membrane. the

In step 1), the pressure applied to the aqueous polyamine solution is 0.05-0.2MPa; the concentration of the aqueous polyamine solution is 0.5-2wt%; the polyamine is an aliphatic polyamine or an aromatic polyamine, and the aliphatic polyamine is The polyamines are piperazine and its derivatives. the

Aromatic polyamines are derivatives of aromatic polyamines or their sulfonic acid groups, carboxylic acid groups, sulfonates, and carboxylates; the concentration of polyacyl chlorides in the oil phase solution is 0.05 to 0.6wt%; The acyl chloride is trimesoyl chloride, isophthaloyl chloride or terephthaloyl chloride; the solvent of the oil phase solution is an organic solvent that is not compatible with the water phase and has a certain solubility for the use of polyamines, such as n-hexane or cyclohexane ; The organic solvent used in step 2) is the same as that used in the oil phase solution; the argon purging time is 2-5 minutes; the organic solvent circulation time is 15-30 minutes; the reaction time is 5-10 minutes. In step 7), after the reaction is carried out, the film post-treatment temperature is 50-70° C., and the post-treatment time is 10-20 min. the

The hollow fiber nanofiltration membrane obtained by the above reaction has a rejection rate of more than 95% for magnesium sulfate (2000ppm, 0.4MPa), and a rejection rate of more than 99% for suspended pollutants (SDI=5), while the representative chlorination rate for monovalent salts is greater than 95%. The retention rate of sodium (2000ppm, 0.4MPa) is greater than 90%. The water flux of the obtained nanofiltration membrane is greater than 61L·m-2·h-1·MPa-1, preferably greater than 102L·m ^-2 ·h ^-1 ·MPa ^-1 . The higher the water flux of the nanofiltration membrane, the nanofiltration membrane can operate at a lower operating pressure under the same water production requirement, which reduces the pollution of the hollow fiber membrane at a higher pressure and the hollow fiber membrane damage. The prepared hollow fiber membranes usually operate at a relatively low pressure of 0.1-0.8 MPa.

Therefore, since the hollow fiber nanofiltration membrane of the present invention has high mechanical strength and separation and permeation performance at the same time, it can be operated for a long time while maintaining a high separation and permeation level, has low requirements for pretreatment of influent water, and can hold pollutants Suspended solid pollutants (SDI=5). the

The casting solution used to prepare the polysulfone transition layer contains hydrophilic additives or pore-forming additives, and the mass percentage of the hydrophilic additives is between 10 and 50 wt%, preferably, the added content is between 10 and 30 wt%. The mass percentage of the pore additive is between 0.1 and 10 wt%, preferably between 0.1 and 5 wt%. the

The polyamine used for preparing the polyamide composite layer is aliphatic polyamine or aromatic polyamine, and the aliphatic polyamine is piperazine and its derivatives. Aromatic polyamines are derivatives of aromatic polyamines or their sulfonic acid groups, carboxylic acid groups, sulfonates, and carboxylates, such as o-phenylenediamine, m-phenylenediamine, p-phenylenediamine, 2,4- Diaminobenzoic acid, 3,5-diaminobenzoic acid, 2,4-diaminobenzoic acid triethylamine salt, 3,5-diaminobenzoic acid triethylamine salt, 2,4-diaminobenzenesulfonic acid, 3,5-diaminobenzenesulfonic acid, 2,4-diaminobenzenesulfonic acid triethylamine salt, 3,5-diaminobenzenesulfonic acid triethylamine salt, etc. the

The polyacyl chloride used for preparing the polyamide composite layer is trimesoyl chloride, isophthaloyl chloride or terephthaloyl chloride, etc., preferably trimesoyl chloride. the

Figure 3 shows the tensile strength of the modified hollow fiber base membrane tested by the AGS-J model tensile instrument, and a 5 cm modified hollow fiber base membrane was taken as a sample strip, and different components of the modified hollow fiber base membrane were obtained at a tensile rate of 10 cm/min. Stress-strain diagram of the fibrous basement membrane. the

As shown in Figure 3, the mechanical strength of the original PVDF hollow fiber microporous base membrane is 11.65MPa, and the mechanical strength of the hollow fiber base membrane modified by the PES/NMP solution polysulfone solution with a concentration of 2, 5, and 10w/v% increases to 11.66, 13.07, 15.68MPa, which proves that the modified hollow fiber base membrane has more excellent mechanical properties. the

Fig. 4 is the hollow fiber type composite nanofiltration membrane obtained by the method described in the patent, and its nanofiltration performance during long-term stable operation is tested. In a 40-hour test cycle, the water flux of the nanofiltration membrane and the rejection rate to 2000ppm magnesium sulfate Basically stable. the

Figure 5 shows the washing resistance and anti-pollution performance of the hollow fiber composite nanofiltration membrane characterized by using the commercial flat nanofiltration membrane NF-90 as a control. At 25°C and an operating pressure of 0.4MPa, 2.5 cycle tests were performed, and both membrane devices were subjected to nanofiltration experiments at a cross-flow operation of 1L/min. The solution uses bovine serum albumin (BSA) as the model molecule, and the buffer is adjusted to pH=4.7±0.1 (pH=pIBSA). First, use 2000ppm MgSO ₄ aqueous solution as the feed liquid to test the water flux; then use 2000ppm MgSO ₄ and 100ppm BSA mixed aqueous solution as the feed liquid to test the water flux of the two membranes; finally, use deionized water to Flush at a flow rate of 5 L/min. After the above 2.5 cycles of operation, the ratio of the obtained water flux data to the initial water flux value represents the attenuation of the water flux in the presence of pollutants.

The technical solution of the present invention will be further specifically described below through several specific examples. the

Example 1

A polyolefin hollow fiber membrane with an outer diameter of 1.2mm and an inner diameter of 0.8mm was prepared by thermally induced phase separation as the base membrane. The alcohol bubble point is 0.24-0.25MPa, the tensile strength is 9.5MPa, and the operating pressure is 1150.6L at 0.01MPa. The flux of pure water in m ^-2 ·h ^-1 and the elongation at break is 150%.

Prepare a nitrogen-methylpyrrolidone (NMP) solution of polysulfone polymers, prepare 25mL casting solution with a concentration of 2w/v%, stir at room temperature for 24 hours to fully dissolve, and then vacuum oven at 0.09MPa for 30min to defoam. Cast the casting solution on a clean glass plate, rotate the hollow fiber membrane on the edge of the casting solution on the glass plate, so that the micropores of the membrane are soaked in the solution, and the membrane is immersed in deionized water for 1 hour to fully exchange the solvent, take it out, and dry it at room temperature Use after drying. the

Prepare a polydiamine solution containing 2w/v% and an oil phase solution containing 0.1w/v%. Four 10cm-long membrane filaments coated with a transition layer were made into a membrane device, and the aqueous phase solution was passed through the membrane filaments inside the membrane filaments for 1 min under a pressure of 0.05 MPa. Then, the shell of the membrane device was purged with argon for 2 min, and the surface of the membrane filament was dried. The interfacial polymerization reaction occurs when the oil phase solution flows through the membrane device. After 10 minutes, n-hexane flows through the shell layer of the membrane device for 1 minute to elute the unreacted polyamide small molecules and reactive monomers on the surface of the membrane filament. The membrane was placed in an oven at 60°C for heat treatment for 20 minutes. the

After preparing the hollow fiber composite nanofiltration membrane, compact it under 0.4MPa pressure for 1 hour, and then intercept 2000ppm of MgSO4 solution under 0.4MPa pressure. After connecting the filtrate for 1 hour, take 0.5mL and dilute 100 times to make the magnesium ions in the solution Reach the order of magnitude of 1-10ppm, use the standard curve of magnesium ions in ICP 1-10ppm to calculate the concentration of magnesium ions, and the magnesium sulfate rejection rate of the hollow fiber composite nanofiltration membrane is 1-filtrate concentration/raw material concentration. The obtained hollow fiber composite nanofiltration membrane was tested, and the results are shown in Table 4. the

Example 2:

The same base film as in Example 1 was used. the

Prepare a polysulfone polymer dimethyl sulfoxide (DMSO) film casting solution with a concentration of 10w/v%, stir at room temperature for 24 hours to fully dissolve, and then vacuum oven at 0.09MPa for 30min to defoam. The membrane filaments were immersed in the casting solution for 5 minutes, so that the pores of the membrane filaments were infiltrated with the solution, and the membrane filaments were immersed in deionized water for 2 hours to fully exchange the solvent, then taken out, and dried at room temperature before use. the

Prepare a polyvalent diamine solution containing 2w/v%, and a polyacyl chloride oil phase solution containing 0.1w/v%. Four 10cm-long membrane filaments coated with a transition layer were made into a membrane device, and the aqueous phase solution was passed through the membrane filaments inside the membrane filaments for 5 minutes under a pressure of 0.2 MPa. Then the membrane device was purged with argon for 5 min to dry the surface of the membrane filament. The oil phase solution flows through the shell of the membrane device for 10 minutes to undergo interfacial polymerization, and n-hexane flows through the shell of the membrane device for 3 minutes to elute unreacted polyamide small molecules and reactive monomers on the surface of the membrane filaments. The membrane was placed in an oven at 60°C for heat treatment for 20 minutes. the

After preparing the hollow fiber composite nanofiltration membrane, compact it under 0.4MPa pressure for 1 hour, and then intercept _2000ppm of MgSO solution under 0.4MPa pressure. After connecting the filtrate for 1 hour, take 0.5mL and dilute 100 times to make the magnesium in the solution The ions reach the order of 1-10ppm, and the magnesium ion concentration is calculated using the standard curve of 1-10ppm magnesium ions in ICP. The magnesium sulfate rejection rate of the hollow fiber composite nanofiltration membrane is 1-filtrate concentration/raw material concentration.

The obtained hollow fiber composite nanofiltration membrane was tested, and the results are shown in Table 4. the

Example 3

Compared with Example 1, except that the immersion time of the membrane filaments in the casting solution was changed, other reaction conditions were the same. The relationship between the obtained nanofiltration membrane pure water flux and the 2000ppm rejection rate is shown in Table 1. Impregnation of PES into the micropores improves the support of the membrane pores to the composite layer and increases the rejection rate; when the immersion time is too long, the NMP solvent will destroy the membrane pore structure of the PVDF hollow fiber microporous base membrane, and the pore size of the support layer is too large However, the structure of the composite layer cannot be supported, and the interception performance is destroyed. the

Table 1 Effect of membrane silk immersion time on nanofiltration membrane performance

Example 4

The same base film as in Example 1 was used. Prepare a dimethyl sulfoxide (DMSO) film casting solution with a concentration of 10w/v% polysulfone polymer, dissolve a certain amount of different additives in the solution (as shown in Table 2), stir at room temperature for 24 hours to fully dissolve and vacuum Oven 0.09MPa degassing 30min. The membrane filaments were immersed in the casting solution for 5 minutes, so that the pores of the membrane filaments were infiltrated with the solution, and the membrane filaments were immersed in deionized water for 10 minutes to undergo solvent exchange and then taken out. the

Prepare an oil phase solution containing 2w/v% polyvalent diamine and 0.1w/v% polyacyl chloride. Four 10cm-long membrane filaments coated with a transition layer were made into a membrane device, and the aqueous phase solution was passed through the membrane filament inside the membrane filament for 5 minutes under a pressure of 0.1 MPa. Then the membrane device was purged with argon for 5 min to dry the surface of the membrane filament. The membrane shell is filled with the oil phase solution for 10 minutes to undergo interfacial polymerization, and n-hexane flows through the membrane shell for 3 minutes to elute the unreacted polyamide small molecules and reactive monomers on the membrane surface. The membrane was placed in an oven at 60°C for heat treatment for 20 minutes. the

The relationship between the obtained nanofiltration membrane pure water flux and the 2000ppm rejection rate is shown in the table. It can be seen from Table 2 that the water flux of Comparative Example 2 is higher, which is related to the change of the hydrophilicity and pore structure of the transition layer by the additive; and the change of the rejection rate is related to the pore size. the

Table 2 Effect of transition layer additives on nanofiltration performance

^a The relative molecular weight is 300,000 Daltons

^b The relative molecular weight is 900,000 Daltons

Example 5

Use the same base membrane as in Example 1; prepare a dimethylsulfoxide (DMSO) casting solution with a polysulfone polymer concentration of 10w/v% and a PVP-K30 content of 0.1wt%, and stir at room temperature for 24 hours to fully dissolve Vacuum oven 0.09MPa defoaming 30min. The membrane filaments were immersed in the casting solution for 5 minutes, so that the pores of the membrane filaments were infiltrated with the solution, and the membrane filaments were immersed in a water/ethanol coagulation bath with a volume ratio of 90:10 for solvent exchange for 10 minutes and then taken out. the

Prepare an oil phase solution containing 2w/v% polyvalent diamine and 0.1w/v% polyacyl chloride. Four 10cm-long membrane filaments coated with a transition layer were made into a membrane device, and the aqueous phase solution was passed through the membrane filament inside the membrane filament for 5 minutes under a pressure of 0.1 MPa. Subsequently, the membrane device was purged with argon for 4 min to dry the surface of the membrane filament. The shell of the membrane device is filled with the oil phase solution for 5 minutes to undergo interfacial polymerization, and n-hexane flows through the shell of the membrane device for 3 minutes to elute the unreacted polyamide small molecules and reactive monomers on the surface of the membrane filaments. The membrane was placed in an oven at 60°C for heat treatment for 20 minutes. the

After the hollow fiber composite nanofiltration membrane was prepared, it was compacted under a pressure of 0.4MPa for 1 hour, and then the retention rate and pure water flux of 2000ppm sodium sulfate solution under a pressure of 0.2-0.8MPa are shown in Figure 6. the

Example 6

The same base film as in Example 1, and the same transition layer preparation method as in Example 2. the

Prepare a solution containing 4w/v% piperazine and a solution containing 0.2w/v% polyacyl chloride. Make 4 membrane filaments coated with a transition layer with a length of 10 cm into a membrane device, make the aqueous phase solution flow through the membrane filament inside the membrane filament for 5 minutes under a pressure of 0.2 MPa, and flow the organic solvent through the shell of the membrane device for 15 minutes, and then Continue to circulate the oil phase reaction solution for 10 minutes to generate interfacial polymerization reaction, and then circulate the aforementioned organic solvent membrane shell for 5 minutes to clean. The membrane was placed in an oven at 50°C for heat treatment for 20 minutes. the

After the hollow fiber composite nanofiltration membrane was prepared, it was compacted under a pressure of 0.4 MPa for 1 hour. The results are shown in Table 4. the

Example 7

Using the same base film as in Example 1, and the same transition layer preparation method as in Example 2. the

Preparation contains 0.4w/v% m-phenylenediamine and 0.1w/v% piperazine as an aqueous phase reaction solution, and 0.05w/v% polyacyl chloride is an oil phase solution. Four modified hollow fiber base membranes with a length of 10 cm were made into a membrane device, and the water phase solution was circulated to the inner surface of the modified hollow fiber base membrane for 5 minutes at a pressure of 0.2 MPa. The organic solvent was circulated through the shell of the membrane device for 30 minutes, and then the oil phase reaction solution was continued to flow for 10 minutes to cause interfacial polymerization reaction, and then the shell of the membrane device was circulated for 5 minutes to clean the aforementioned organic solvent. The shell layer of n-hexane flowing through the membrane device was eluted for 3 minutes to elute unreacted polyamide small molecules and reactive monomers on the outer surface of the modified hollow fiber base membrane. The membrane was placed in an oven at 60°C for heat treatment for 20 minutes. the

After the hollow fiber composite nanofiltration membrane was prepared, it was compacted under a pressure of 0.4 MPa for 1 hour. The results are shown in Table 4. the

Example 8

Using the same base film as in Example 1, and the same transition layer preparation method as in Example 2. the

Prepare a polyvalent diamine solution containing 2w/v%, and a polyacyl chloride oil phase solution containing 0.6w/v%. Four modified hollow fiber base membranes with a length of 10 cm and a transition layer have been formed to make a membrane device, and the water phase solution is passed through the inner surface of the modified hollow fiber base membrane at a pressure of 0.2 MPa for 5 minutes, and then the membrane is purged with argon. The outer surface of the modified hollow fiber base membrane is rinsed by passing through the shell of the membrane device for 5 minutes, the oil phase solution flowing through the shell of the membrane device for 5 minutes, and the interfacial polymerization reaction occurs. The membrane was placed in an oven at 70°C for heat treatment for 10 minutes. The obtained hollow fiber composite nanofiltration membrane was tested, and the results are shown in Table 4. the

Example 9

Using the same base film as in Example 1, and the same transition layer preparation method as in Example 2. the

Prepare a m-phenylenediamine solution containing 2w/v%, and a cyclohexane solution containing 0.2w/v% polyacyl chloride as an oil phase solution. Four modified hollow fiber base membranes with a length of 10 cm were made into a membrane device, and the water phase solution was flowed to the inner surface of the modified hollow fiber base membrane at a pressure of 0.1 MPa for 1 min, and then the shell of the membrane device was purged with argon for 5 min , the oil phase solution flows through the shell of the membrane device for 10 minutes to undergo interfacial polymerization, and the cyclohexane flows through the shell of the membrane device for 3 minutes to elute unreacted polyamide small molecules and reactive monomers on the outer surface of the modified hollow fiber base membrane. The membrane was placed in an oven at 50°C for heat treatment for 20 minutes. The obtained hollow fiber composite nanofiltration membrane was tested, and the results are shown in Table 4. the

Example 10

Using the same base film as in Example 1, and the same transition layer preparation method as in Example 2. the

Prepare 2w/v% m-phenylenediamine solution and 0.05w/v% polyacyl chloride oil phase solution. Four modified hollow fiber base membranes with a length of 10 cm were made into a membrane device, and the water phase solution was flowed to the inner surface of the modified hollow fiber base membrane at a pressure of 0.2 MPa for 1 min, and then the shell of the membrane device was purged with argon for 5 min , the oil phase solution flows through the shell of the membrane device for 10 minutes to generate interfacial polymerization, and n-hexane flows through the shell of the membrane device for 3 minutes to clean the outer surface of the modified hollow fiber base membrane. The membrane was placed in an oven at 70°C for heat treatment for 20 minutes. The obtained hollow fiber composite nanofiltration membrane was tested, and the lower pure water flux was related to the formation of a denser polyamide layer at this temperature, as shown in Table 4. the

Summary of performance results of hollow fiber type composite nanofiltration membranes in each embodiment of table 4

^a Polyvinylidene fluoride hollow fiber microporous base membrane

^b Polysulfone modified hollow fiber base membrane.

Claims (10)

1. A hollow fiber type composite nanofiltration membrane, characterized in that: the hollow fiber type composite nanofiltration membrane is composed of a hollow fiber microporous base membrane as a support layer (1), a polysulfone transition layer (2) and a polysulfone transition layer The polyamide composite layer (3), the polysulfone transition layer is located inside the membrane pores of the hollow fiber membrane microporous base membrane, and the polyamide composite layer is located inside the membrane pores of the polysulfone transition layer. 2. The hollow fiber composite nanofiltration membrane according to claim 1, characterized in that: the hollow fiber microporous base membrane is a hollow fiber microporous membrane with an outer diameter of 0.6 to 1.8 mm and an inner diameter of 0.3 to 1.2 mm. mm, the ratio of outer diameter to inner diameter is 1.5~2; the alcohol bubble point is 0.2~0.4MPa, the tensile strength is at least 7MPa, and the compressive strength is at least 2MPa. 3. The hollow fiber type composite nanofiltration membrane according to claim 1, characterized in that: the polysulfone transition layer thickness L2 accounts for 5% to 25% of the support layer thickness L1; the polyamide composite layer thickness L3 accounts for 5% to 25% of the polysulfone transition layer thickness L3. The thickness of the transition layer is 1-10% of L2; the pore diameter D1 of the support layer is 100-150nm, the pore diameter D2 of the polysulfone transition layer is 30-70nm, and the pore diameter of the polyamide composite layer is 0.5-2nm. 4. The hollow fiber type composite nanofiltration membrane according to claim 1, characterized in that: the polysulfone transition layer is polysulfone, polyethersulfone, polynaphthalene polyethersulfone ketone, sulfonated polysulfone, sulfonated Polyethersulfone or sulfonated polyetheretherketone; the polyamide composite layer is semi-aromatic or fully aromatic polyamide formed by interfacial polymerization of aliphatic polyamine or aromatic polyamine and aromatic polyacyl chloride. 5. the preparation method of a kind of hollow fiber type composite nanofiltration membrane as described in claim 1～4 any one claim, it is characterized in that described method is carried out according to the following steps: 1) First, the polysulfone casting membrane solution with a concentration between 2 and 20wt% is impregnated in the membrane pores of the hollow fiber microporous base membrane by impregnation method. The impregnation method includes: the hollow fiber microporous base membrane is immersed in the casting membrane solution 0.5 to 10 minutes, or make the hollow fiber microporous basement membrane pass through the casting solution storage tank for 0.5 to 10 minutes, or rotate the hollow fiber microporous basement membrane on the surface of the casting solution; 2) Immerse the hollow fiber membrane obtained in step 1) in the coagulation bath for 10-120 minutes; 3) After the hollow fiber membrane is taken out from the coagulation bath, it is packaged into a membrane device to obtain a modified hollow fiber membrane filled with a polysulfone transition layer in the membrane pores of the hollow fiber microporous base membrane; 4) Flow a polyamine aqueous phase solution with a concentration of 0.2-5wt% on the inner surface of the modified hollow fiber membrane, so that the pressure difference between the inner and outer surface of the modified hollow fiber membrane is between 0.01-0.3 MPa, and the pressure is maintained for 1-10 minutes; 5) Purge the argon gas on the outer surface of the modified hollow fiber membrane for 0.5-10 minutes or circulate the organic solvent for 5-30 minutes, and then flow the polyacyl chloride oil phase solution with a concentration of 0.05-2wt% on the outer surface of the modified hollow fiber membrane for 1-10 minutes, react; 6) Circulating an organic solvent on the outer surface of the modified hollow fiber membrane to clean the outer surface of the modified hollow fiber base membrane; 7) The membrane device is placed in an oven, heat-treated at 40-90°C for 5-30 minutes, heated to promote the further reaction of amine and acid chloride, and remove the solvent of the reactant to obtain a hollow fiber composite nanofiltration membrane. 6. The preparation method of hollow fiber composite nanofiltration membrane as claimed in claim 5, characterized in that: the solute of the casting solution used in step 1) is polysulfone, polyethersulfone, polynaphthalene polyethersulfone ketone , sulfonated polysulfone, sulfonated polyethersulfone or sulfonated polyether ether ketone; the solvent of the casting solution is N, N-dimethylformamide, N, N-dimethylacetamide, ethyl acetate, acetic acid One or more of propyl ester, N-methylpyrrolidone, dimethyl sulfoxide, chloroform, carbon tetrachloride, dichloromethane and dichloroethane are mixed, and the concentration of the casting solution is between 2 and 10wt%. Between; the coagulation bath described in step 2) is one or more mixtures of water, ethanol, isopropanol, isobutanol, dimethyl sulfoxide and acetonitrile. 7. The preparation method of hollow fiber type composite nanofiltration membrane as claimed in claim 6, characterized in that: the casting solution described in step 1) contains a hydrophilic additive or a pore-forming additive, and the hydrophilic additive is ethanol, iso Propanol, n-butanol, tert-amyl alcohol, 2-octanol or diethylene glycol, the mass percentage of the hydrophilic additive is between 10 and 50 wt%; the pore-forming additive has a molecular weight of 300,000 to 900,000 Daltons polyethylene glycol or polyvinylpyrrolidone, and the mass percentage content of the pore-forming additive is between 0.1 and 10 wt%. 8. The preparation method of hollow fiber composite nanofiltration membrane according to claim 5, characterized in that: in the step 4), the pressure difference between the inner and outer surface of the modified hollow fiber membrane is between 0.01-0.3MPa between; the concentration of polyamine aqueous phase solution is 0.5～2wt%; described polyamine is aliphatic polyamine or aromatic polyamine, and aliphatic polyamine is piperazine and derivative thereof; described aromatic polyamine is Aromatic polyamine or its sulfonic acid group, carboxylic acid group, sulfonate or carboxylate derivatives. 9. The preparation method of hollow fiber type composite nanofiltration membrane as claimed in claim 5, characterized in that: the concentration of polyacyl chloride in the oil phase solution in step 5) is 0.05～0.6wt%, and the concentration of polyacyl chloride is homogeneous Tricarboyl chloride, isophthaloyl chloride or terephthaloyl chloride, the solvent of the oil phase solution is n-hexane or cyclohexane; the organic solvent used is the same as that used in the oil phase solution; in the modified hollow fiber membrane The outer surface is purged with argon for 2-5 minutes; the organic solvent is circulated for 15-30 minutes; and the reaction time is 5-10 minutes. 10. The preparation method of the hollow fiber composite nanofiltration membrane according to claim 5, characterized in that: in the step 7), after the reaction is carried out, the membrane post-treatment temperature is 50-70°C, and the post-treatment time is In 10-20 minutes.

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