CN111389238A - Composite nanofiltration membrane based on modified polyolefin microporous substrate and preparation method thereof - Google Patents

Abstract

The invention provides a composite nanofiltration membrane for modifying a polyolefin microporous substrate. The composite nanofiltration membrane comprises: the composite nanofiltration membrane comprises a polyolefin microporous membrane, a modification layer and an interface polymerization layer, wherein the polyolefin microporous membrane is positioned at the innermost layer of the composite nanofiltration membrane, the modification layer is arranged on the polyolefin microporous membrane, and the interface polymerization layer is positioned on the outer surface of the composite nanofiltration membrane. The method comprises the following steps: preparing a homogeneous dilute solution with a certain concentration by using resin, a pore-forming agent and a solvent, and dropwise adding a non-solvent into the homogeneous dilute solution to form gel to form a modifying solution; and modifying the polyolefin microporous substrate by using a modifying solution in a dipping coating mode, and carrying out interfacial polymerization on the modified polyolefin microporous substrate to obtain the composite nanofiltration membrane. The modified polyolefin microporous membrane substrate of the composite nanofiltration membrane is beneficial to interfacial polymerization reaction in the aspects of pore diameter, pores and hydrophilicity and hydrophobicity, and has good desalting and water flux, good tolerance and long-term stability.

Description

Composite nanofiltration membrane based on modified polyolefin microporous substrate and preparation method thereof

Technical Field

The invention relates to the technical field of composite membranes, in particular to a composite nanofiltration membrane based on a modified polyolefin microporous substrate and a preparation method thereof.

Background

In the beginning of the 20 th century, membrane technology became a new separation technology. The demand in the production process of water treatment and water purification industry is increasingly urgent. Nanofiltration membranes are a novel membrane separation technology between ultrafiltration and reverse osmosis, and are gradually and widely applied to various fields due to the advantages of low operating pressure, high water flux, high rejection rate, retention of small molecular organic matters and low-price inorganic salts beneficial to the body and the like.

The composite membrane is a very important nanofiltration separation membrane, and has become the nanofiltration membrane with the highest commercialization degree due to the stable structure and the operation performance. The structure of the composite membrane is divided into a porous supporting layer at the lower layer and an ultrathin selective cortex layer at the upper layer. It is believed that the lower support layer provides mechanical strength to the composite membrane, while the upper selective skin layer determines the separation performance of the composite membrane. At present, the composite nanofiltration membrane is mostly prepared by an interfacial polymerization method.

The polyolefin microporous membrane has developed aperture and porosity, the polyolefin material has good tolerance to organic solvents, and the swelling phenomenon is basically avoided at the temperature of the nanofiltration process. Meanwhile, compared with the conventional nanofiltration substrate, the thickness and the cost of the polyolefin microporous membrane substrate are greatly reduced, the unit filling amount of elements can be effectively improved, the water yield is further improved, and the low cost is realized.

In recent years, researches and patents taking polyolefin microporous membranes as substrates appear at home and abroad, and composite nanofiltration membranes with still-available performance are prepared. The related documents and patents mostly focus on the problem that the surface of the traditional polyolefin microporous membrane is poor in hydrophilicity and is subjected to hydrophilic modification, so that the problem that the water phase is difficult to uniformly disperse on the surface in the interfacial polymerization process is solved. But the tolerance properties and long-term stability of the composite membranes are unknown. Numerous studies have demonstrated that the pore size, porosity and hydrophobicity of the substrate have a significant impact on the permeability and stability of the composite membrane. The research and patents for improving the comprehensive application performance by using the polyolefin microporous membrane as the substrate are not reported yet. By coating the nano spherical gel resin on the surface of the polyolefin microporous membrane substrate, the specific surface area of the composite nanofiltration membrane can be effectively increased, and further the flux is greatly improved. Meanwhile, the comprehensive performances such as separation performance, tolerance performance, long-term stability and the like of the composite nanofiltration membrane are improved by controlling the aperture, the porosity and the hydrophilicity and the hydrophobicity of the modified polyolefin microporous membrane substrate.

Related documents and patents in the prior art mostly focus on poor hydrophilicity of the surface of the traditional polyolefin microporous membrane, and the problem that the water phase is difficult to uniformly disperse on the surface in the interfacial polymerization process is solved by performing hydrophilic modification. But the tolerance properties and long-term stability of the composite membranes are unknown. A large number of researches prove that the pore diameter, the porosity and the hydrophobicity of the substrate have important influence on the permeability and the stability of the composite membrane, and no scheme for improving the comprehensive application performance of the polyolefin microporous membrane substrate by designing the reasonable pore diameter, the porosity and the hydrophobicity of the substrate exists in the prior art.

Disclosure of Invention

The embodiment of the invention provides a composite nanofiltration membrane based on a polyolefin microporous substrate modified by a substrate and a preparation method thereof, which aim to overcome the problems in the prior art.

A composite nanofiltration membrane based on a modified polyolefin microporous substrate, comprising: the composite nanofiltration membrane comprises a polyolefin microporous membrane, a modification layer and an interface polymerization layer, wherein the polyolefin microporous membrane is positioned at the innermost layer of the composite nanofiltration membrane, the modification layer is arranged on the polyolefin microporous membrane, and the interface polymerization layer is positioned on the outer surface of the composite nanofiltration membrane.

Preferably, the thickness of the polyolefin microporous membrane is between 10 and 30 mu m, and the thickness of the modification layer is between 30 and 500 nm.

A preparation method of a composite nanofiltration membrane based on a modified polyolefin microporous substrate is characterized by comprising the following steps:

step 1, preparing a homogeneous dilute solution with a certain concentration by using a resin with a certain concentration and a certain molecular weight, gradually dropwise adding a non-solvent into the homogeneous dilute solution until the gel becomes a relatively uniform emulsion, and taking the emulsion as a modifying solution;

step 2, modifying the polyolefin microporous substrate by using the modifying solution in a dipping coating mode to obtain a modified polyolefin microporous substrate with certain aperture, porosity and hydrophilicity;

and 3, carrying out interfacial polymerization on the modified polyolefin microporous substrate to obtain the composite nanofiltration membrane with separation performance and tolerance performance.

Preferably, the resin is polyvinylidene fluoride, polysulfone, polyethersulfone, polyetheretherketone, sulfonated polysulfone or sulfonated polyethersulfone, and the resin content is 1-3%.

Preferably, when the resin adopts sulfonated polysulfone or sulfonated polyether sulfone, the sulfonation degree is 15-100%.

Preferably, the pore-forming agent adopts small molecular ketones, small molecular alcohols, polyethylene glycols with different molecular weights or polyvinylpyrrolidone with different molecular weights, and the content is 1-3%.

Preferably, the solvent is at least one of dimethylformamide, dimethylacetamide, dimethyl sulfoxide and ethylene glycol monomethyl ether.

Preferably, the non-solvent is at least one of water and glycol and glycerol alcohol.

Preferably, the step 2 specifically includes:

the temperature of the modifying liquid is controlled at 20-50 ℃, the modifying liquid is treated by adopting a dipping coating mode, the dipping time is 2-5min, and the modification running speed of the substrate is 2-5m/min, so that the modified polyolefin microporous substrate with certain aperture, porosity and hydrophilicity is obtained.

According to the technical scheme provided by the embodiment of the invention, the modified polyolefin microporous membrane substrate of the composite nanofiltration membrane provided by the embodiment of the invention is beneficial to interfacial polymerization reaction in the aspects of pore diameter, pores and hydrophilicity and hydrophobicity; the thickness of the polymeric layer on the interface of the composite nanofiltration membrane is uniform and stable, has no obvious defects, and has good desalination and water flux, good tolerance and long-term stability.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without inventive labor.

Fig. 1 is a structural diagram of a composite nanofiltration membrane based on a modified polyolefin microporous substrate according to an embodiment of the present invention;

fig. 2 is a process flow diagram of a method for preparing a composite nanofiltration membrane based on a modified polyolefin microporous substrate according to an embodiment of the present invention;

FIG. 3 is a schematic view of the surface of a polyolefin microporous membrane according to an embodiment of the present invention;

FIG. 4 is a schematic view of the surface of two modified polyolefin microporous membranes provided by an embodiment of the present invention;

fig. 5 is an SEM schematic view of a surface of a composite nanofiltration membrane according to an embodiment of the present invention.

Detailed Description

For the convenience of understanding the embodiments of the present invention, the following description will be further explained by taking several specific embodiments as examples in conjunction with the drawings, and the embodiments are not to be construed as limiting the embodiments of the present invention.

The embodiment of the invention provides a modified polyolefin microporous substrate-based composite nanofiltration membrane and a preparation method thereof.

The structure of the composite nanofiltration membrane based on the modified polyolefin microporous substrate is shown in fig. 1, and comprises a polyolefin microporous membrane, a modification layer and an interface polymerization layer, wherein the polyolefin microporous membrane is positioned at the innermost layer of the composite nanofiltration membrane, the modification layer is arranged on the polyolefin microporous membrane of the substrate, and the interface polymerization layer is positioned on the outer surface of the composite nanofiltration membrane.

The composite membrane is not limited to a nanofiltration membrane, and can be expanded to other composite membrane material preparation methods such as reverse osmosis and the like.

The thickness of the polyolefin microporous membrane is between 10 and 30 mu m, and the thickness of the modification layer is between 30 and 500 nm.

The following will describe the embodiments of the present invention by taking the base material as a polyolefin microporous membrane as an example. Fig. 2 is a process flow diagram of a method for preparing a composite nanofiltration membrane based on a modified polyolefin microporous substrate according to an embodiment of the present invention; the method comprises the following steps:

step 10, preparing a modification liquid:

the homogeneous diluted solution with certain concentration is prepared with sulfonated polysulfone or sulfonated polyether sulfone and other resin in certain concentration and certain molecular weight, pore forming agent and solvent. And (3) gradually dropwise adding a non-solvent into the dilute solution until the gel becomes a relatively uniform emulsion, wherein the emulsion is the prepared modification solution.

Step 20, modified polyolefin microporous substrate:

and (3) modifying the polyolefin microporous substrate by using the prepared modifying solution in a dipping and coating mode to obtain the polyolefin microporous substrate with proper pore diameter and porosity and certain hydrophilicity. The surface of a microporous substrate of polyolefin provided by the embodiment of the invention after different modifications is shown in FIG. 1.

The special polyolefin microporous substrate modification device is a water-phase tank device similar to the existing interfacial polymerization composite membrane.

Step 30, preparation of the composite nanofiltration membrane:

and (3) carrying out interfacial polymerization on the modified polyolefin microporous substrate by adopting a traditional interfacial polymerization mode to obtain the composite nanofiltration membrane with good separation performance and tolerance performance.

In the preparation method (1) of the composite nanofiltration membrane, the modification liquid system is prepared by mixing the following components:

the resin can be polyvinylidene fluoride, polysulfone, polyethersulfone, polyether ether ketone, sulfonated polysulfone or sulfonated polyethersulfone, etc., and the resin content is 1-3%. When sulfonated polysulfone or sulfonated polyether sulfone is adopted, the sulfonation degree is 15-100%;

the pore-forming agent can be small molecular ketones, small molecular alcohols, polyethylene glycols with different molecular weights, polyvinylpyrrolidone with different molecular weights and the like, and the content is 1-3%.

The balance is solvent, and the solvent can adopt at least one of dimethylformamide, dimethylacetamide, dimethyl sulfoxide, ethylene glycol monomethyl ether and the like.

The non-solvent may be at least one of water, alcohols, etc.

The preparation method of the modified polyolefin microporous substrate composite nanofiltration membrane (2) comprises the following steps:

the temperature of the modifying liquid is controlled at 20-50 ℃;

performing dip coating treatment in a dipping tank for 2-5 min;

the running speed of substrate modification is 2-5 m/min.

The first embodiment is as follows:

the resin, additives and solvent were formulated into homogeneous dilute solutions of a certain concentration using 25% sulfonated polysulfone at 1 wt.% of different molecular weights with different degrees of sulfonation as the resin, 1 wt.% polyvinylpyrrolidone (k30) as the additive, and the balance ethylene glycol monomethyl ether as the solvent. Pure water is taken as a gelling agent (i.e. a non-solvent), and the dilute solution and the pure water are prepared into relatively uniform emulsion according to the proportion of 2:1, wherein the emulsion is the modification solution. And (3) adopting a dipping coating tank to modify the polyolefin microporous substrate, wherein the dipping time is 1-5min, and the running speed is 2-5 m/min. And (3) carrying out interface polymerization on the modified polyolefin microporous substrate by the traditional process to obtain the prepared composite nanofiltration membrane based on the modified polyolefin microporous substrate.

Preparing an aqueous solution of piperazine with the concentration of 1 g/L, and preparing a ParG solution of trimesoyl chloride with the concentration of 1 g/L.

The basic properties of the composite nanofiltration membrane obtained in this example are shown in table 1 below.

TABLE 1 basic Properties of composite nanofiltration membranes

Detailed description of the preferred embodiments	Sulfonated polysulfone molecular weight/Da	Water flux (L MH)	Magnesium sulfate rejection (%)
				F-1	40000	50	97.5
F-2	10000	70	97.2
				F-3	200000	60	92.0

Remarking: the test was carried out using 2000ppm magnesium sulfate, 70psi

Example two:

fig. 3 is a schematic view of a modified substrate of polyolefin micropores according to an embodiment of the present invention, and fig. 4 is a schematic view of another modified substrate of polyolefin micropores according to an embodiment of the present invention.

The method comprises the steps of changing the sulfonation degree of sulfonated polysulfone on the basis of implementation, using 1 wt.% sulfonated polysulfone with 10 ten thousand molecular weight as resin, using 1 wt.% polyvinylpyrrolidone (k30) as an additive, using 98 wt.% ethylene glycol monomethyl ether as a solvent, preparing the resin, a pore-forming agent and the solvent into a homogeneous dilute solution with a certain concentration, using pure water as a gelling agent, and preparing the dilute solution and the pure water into a relatively uniform emulsion which is a modification solution according to a ratio of 2:1, using an immersion coating tank to modify the polyolefin microporous substrate, wherein the immersion time is 1-5min, the operation speed is 2-5m/min, performing traditional process interfacial polymerization on the modified polyolefin microporous substrate, and using an aqueous solution of piperazine with the concentration of 1 g/L and a ParG solution of trimesoyl chloride with the concentration of 1 g/L.

The basic properties of the composite nanofiltration membrane obtained in this example are shown in table 2 below.

TABLE 2 basic Properties of composite nanofiltration membranes

Detailed description of the preferred embodiments	Sulfonation degree/% of sulfonated polysulfone	Water flux (L MH)	Magnesium sulfate rejection (%)
				F-4	15	60	97.1
F-2	25	70	97.8
				F-5	40	80	97.4

Remarking: the test was carried out using 2000ppm magnesium sulfate, 70psi

Example three:

adding strong solvent N-Dimethylformamide (DMF) on the basis of the second implementation, adopting 1 wt.% of sulfonated polysulfone with a sulfonation degree of 25% and a molecular weight of 10 ten thousand as resin, adopting 1 wt.% of polyvinylpyrrolidone (k30) as an additive, and adopting the balance of ethylene glycol monomethyl ether and DMF as solvent, preparing the resin, a pore-forming agent and the solvent into a homogeneous dilute solution with a certain concentration, adopting pure water as a gelling agent, preparing a relatively uniform emulsion which is a modification solution from the dilute solution and the pure water according to a ratio of 2:1, adopting an immersion coating tank to modify a polyolefin microporous substrate, wherein the immersion time is 1-5min, the operating speed is 2-5m/min, carrying out interface polymerization on the modified polyolefin microporous substrate by using the traditional process, and preparing an aqueous solution of piperazine with a concentration of 1 g/L, and preparing a ParG solution of trimesoyl chloride with a concentration of 1 g/L.

The basic properties, the tolerance properties, and the long-term stability of the composite nanofiltration membrane obtained in this example are shown in tables 3, 4, and 5 below.

TABLE 3 basic Properties of composite nanofiltration membranes

Detailed description of the preferred embodiments	Concentration of DMF addition/%)	Water flux (L MH)	Magnesium sulfate rejection (%)
				F-2	0	70	97.8
F-6	5	75	99.2
				F-7	10	60	96.4
F-8	20	52	96.2

Remarking: the test was carried out using 2000ppm magnesium sulfate, 70psi

TABLE 4 tolerance of composite nanofiltration membranes

Remarking: after soaking in sodium hydroxide solution with pH 13 for certain time, the membrane performance is tested.

TABLE 5 Long-term stability of composite nanofiltration membranes

Remarking: long run with 2000ppm magnesium sulfate, 70psi, 30% recovery, acid base wash with pH 2 and pH 12 every 5 d.

Fig. 5 is an SEM schematic view of a surface of a composite nanofiltration membrane according to an embodiment of the present invention.

Those of ordinary skill in the art will understand that: the figures are merely schematic representations of one embodiment, and the blocks or flow diagrams in the figures are not necessarily required to practice the present invention.

Those of ordinary skill in the art will understand that: modules in the devices in the embodiments may be distributed in the devices in the embodiments according to the description of the embodiments, or may be located in one or more devices different from the embodiments with corresponding changes. The modules of the above embodiments may be combined into one module, or further split into multiple sub-modules.

In summary, the embodiment of the invention provides a composite nanofiltration membrane based on a modified polyolefin microporous substrate and a preparation method thereof, wherein the modified polyolefin microporous substrate is beneficial to interfacial polymerization reaction in the aspects of aperture, pore space and hydrophilicity and hydrophobicity; the composite nanofiltration membrane interfacial polymerization layer has uniform and stable thickness and no obvious defects, and has good desalination and water flux, good tolerance and long-term stability.

According to the embodiment of the invention, the nano spherical gel resin is impregnated and coated on the surface of the substrate of the polyolefin microporous membrane, so that the specific surface area of the composite nanofiltration membrane can be effectively increased, and the flux is greatly improved. Meanwhile, the comprehensive performances such as separation performance, tolerance performance, long-term stability and the like of the composite nanofiltration membrane are improved by controlling the aperture, the porosity and the hydrophilicity and the hydrophobicity of the modified polyolefin microporous membrane substrate.

The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims (9)

1. A composite nanofiltration membrane based on a modified polyolefin microporous substrate, which is characterized by comprising: the composite nanofiltration membrane comprises a polyolefin microporous membrane, a modification layer and an interface polymerization layer, wherein the polyolefin microporous membrane is positioned at the innermost layer of the composite nanofiltration membrane, the modification layer is arranged on the polyolefin microporous membrane, and the interface polymerization layer is positioned on the outer surface of the composite nanofiltration membrane.

2. The microporous polyolefin membrane of claim 1, wherein the microporous polyolefin membrane has a thickness of 10-30 μm and a modifying layer thickness of 30-500 nm.

3. The preparation method of the composite nanofiltration membrane based on the modified polyolefin microporous substrate of claim 1 or 2, which is characterized by comprising the following steps:

step 1, preparing a homogeneous dilute solution with a certain concentration by using a resin with a certain concentration and a certain molecular weight, gradually dropwise adding a non-solvent into the homogeneous dilute solution until the gel becomes a relatively uniform emulsion, and taking the emulsion as a modifying solution;

step 2, modifying the polyolefin microporous substrate by using the modifying solution in a dipping coating mode to obtain a modified polyolefin microporous substrate with certain aperture, porosity and hydrophilicity;

and 3, carrying out interfacial polymerization on the modified polyolefin microporous substrate to obtain the composite nanofiltration membrane with separation performance and tolerance performance.

4. The method according to claim 3, wherein the resin is polyvinylidene fluoride, polysulfone, polyethersulfone, polyetheretherketone, sulfonated polysulfone or sulfonated polyethersulfone, and the resin content is 1-3%.

5. The method according to claim 4, wherein when the resin is sulfonated polysulfone or sulfonated polyether sulfone, the sulfonation degree is 15-100%.

6. The method of claim 3, wherein the pore-forming agent is selected from small molecular ketones, small molecular alcohols, polyethylene glycols of different molecular weights, or polyvinylpyrrolidones of different molecular weights, and the content of the pore-forming agent is 1-3%.

7. The method according to claim 3, wherein the solvent is at least one of dimethylformamide, dimethylacetamide, dimethylsulfoxide, and ethylene glycol monomethyl ether.

8. The method of claim 3, wherein the non-solvent is at least one of water and glycol, glycerol alcohol.

9. The method according to claim 3, wherein the step 2 specifically comprises:

the temperature of the modifying liquid is controlled at 20-50 ℃, the modifying liquid is treated by adopting a dipping coating mode, the dipping time is 2-5min, and the modification running speed of the substrate is 2-5m/min, so that the modified polyolefin microporous substrate with certain aperture, porosity and hydrophilicity is obtained.

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