CN113117539A - Reverse osmosis membrane based on modified polyolefin substrate and preparation method thereof - Google Patents
Reverse osmosis membrane based on modified polyolefin substrate and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a reverse osmosis membrane based on a modified polyolefin substrate and a preparation method thereof, wherein the reverse osmosis membrane comprises the following components in parts by weight: (1) blending high-density polyethylene, crosslinked polyvinylpyrrolidone, an antioxidant and a diluent to form a homogeneous blend, extruding and casting to obtain a solid thick sheet; (2) stretching the solid slab into a strip-shaped film; (3) then extracting, heat setting and rolling to obtain a modified polyethylene microporous membrane; (4) dissolving polysulfone in N, N-dimethylformamide to obtain a membrane casting solution; (5) coating the membrane casting solution on the surface of a modified polyethylene microporous membrane, and soaking the modified polyethylene microporous membrane in water to form a membrane through phase inversion to obtain a polysulfone base membrane; (6) mixing m-phenylenediamine, sodium camphorsulfonate and water to obtain a water phase liquid; soaking polysulfone-based membrane in the solution, separating and removing the liquid on the surface of the membrane; (7) dissolving trimesoyl chloride in an organic solvent to prepare an oil phase liquid; and (3) polymerizing the polysulfone-based membrane in an oil-phase liquid-phase interface, separating and removing the liquid on the surface of the membrane, drying, and washing with water to obtain the reverse osmosis membrane based on the modified polyolefin substrate.
Description
Technical Field
The invention relates to the technical field of water treatment membranes, in particular to a reverse osmosis membrane based on a modified polyolefin substrate and a preparation method thereof.
Background
The polyamide reverse osmosis membrane has the advantages of high separation efficiency, wide pH application range, energy conservation, environmental protection and the like, and is more and more widely applied to the fields of seawater desalination, industrial sewage treatment, pure water preparation and the like. The conventional reverse osmosis membrane comprises a three-layer structure, i.e., a PET non-woven fabric support layer, a polysulfone porous layer, and a polyamide desalting layer. At present, only a few countries have the capacity of producing PET non-woven fabrics for reverse osmosis membranes, the price of the non-woven fabrics is higher, and meanwhile, the raw material polysulfone particles of the polysulfone porous layer are monopolized by foreign chemical companies for a long time, so the cost of the raw material for producing the reverse osmosis membranes is difficult to reduce. In addition, because the PET non-woven fabric is limited by factors such as strength, smoothness and the like, the thickness of the PET non-woven fabric is generally 80-100 micrometers, low-viscosity casting solution is seriously infiltrated on the surface of the non-woven fabric, a certain thickness is also required to be ensured, and the thickness of polysulfone is generally 30-50 micrometers, so that the polysulfone cannot be further reduced. For membrane elements rolled with reverse osmosis membranes, the thickness of the membrane severely limits the effective rolling area of the element. At present, reducing the cost of raw materials and increasing the rolling area of elements are one of effective ways for improving the competitiveness of reverse osmosis membrane products.
With the development of battery technology, the technology for preparing polyolefin membranes has also advanced dramatically, and generally, polyolefin membranes are prepared by adopting a stretching technology, have the thickness of 10-40 microns, the average pore diameter of 20-60 microns, and have the characteristics of thin thickness, high strength and the like, can meet the requirements of reverse osmosis base membranes on strength, and if thinner reverse osmosis membranes can be prepared by replacing PET non-woven fabrics, the manufacturing cost of membranes can be effectively reduced, and meanwhile, the rolling area of elements is increased.
However, the traditional polyolefin microporous membrane has poor surface hydrophilicity, the water phase in the interfacial polymerization process cannot be uniformly dispersed, and the polyamide desalting layer which is uniform and has no defects is difficult to successfully prepare on the surface. Therefore, the related documents and patents in the prior art, such as CN106975371A, CN111389238A and CN109453674A, are mostly focused on solving the problem of the defect of preparing the desalting layer by performing hydrophilization modification on the surface of the conventional polyolefin microporous membrane. However, these modification methods, such as surface grafting and plasma treatment, can destroy the surface morphology of the substrate, cause phenomena such as pore blocking and membrane structure collapse, and thus affect the membrane performance, and also affect the pressure resistance and long-term stability of the reverse osmosis membrane. In addition, because the polyolefin itself has strong non-polarity, the characteristics of the material itself cannot be changed only through surface hydrophilic modification, and the adhesive property of the glue and the polyolefin substrate is poor in the process of rolling the element by using commercial polyurethane glue, which may affect the long-term use stability of the membrane element, but no report exists for the glue adhesive strength research of a reverse osmosis membrane or a nanofiltration membrane prepared by using a polyolefin microporous membrane as a substrate at present.
Disclosure of Invention
The invention aims to provide a preparation method of a reverse osmosis membrane with simple process and low cost, and the reverse osmosis membrane prepared by the method has higher water flux and salt rejection rate, excellent pressure resistance and long-term stability.
The invention is realized by the following technical scheme:
a preparation method of a reverse osmosis membrane based on a modified polyolefin substrate comprises the following steps:
firstly, preparing a modified polyethylene microporous membrane:
(1) melting and blending high-density polyethylene, crosslinked polyvinylpyrrolidone, an antioxidant and a diluent to form a homogeneous blend, extruding the homogeneous blend, and casting to obtain a solid thick sheet;
(2) stretching the solid thick sheet to form a strip-shaped film;
(3) extracting, heat setting and rolling the strip-shaped film in sequence to obtain the modified polyethylene microporous film;
secondly, preparing a polysulfone-based membrane:
(1) dissolving polysulfone in N, N-dimethylformamide to prepare a membrane casting solution;
(2) coating the casting solution on the surface of the modified polyethylene microporous membrane, and then soaking the modified polyethylene microporous membrane in water to form a membrane through phase inversion to obtain the polysulfone base membrane;
thirdly, preparing a reverse osmosis membrane:
(1) mixing m-phenylenediamine, sodium camphorsulfonate and water to prepare aqueous phase liquid; then, the polysulfone basal membrane is placed in the aqueous phase liquid for dipping treatment, and then the liquid on the surface of the polysulfone basal membrane is separated and removed;
(2) dissolving trimesoyl chloride in an organic solvent to prepare an oil phase liquid; and then placing the polysulfone based membrane in the oil phase liquid again for interfacial polymerization, separating and removing the liquid on the surface of the membrane, drying, and washing with water to obtain the reverse osmosis membrane based on the modified polyolefin substrate.
Further, the preparation of the modified polyethylene microporous membrane comprises the following steps: (1) melting and blending high-density polyethylene, crosslinked polyvinylpyrrolidone, an antioxidant and a diluent at the temperature of 150-190 ℃ to form a homogeneous blend, extruding the homogeneous blend by adopting a screw extrusion process, and casting to obtain a solid thick sheet; wherein the high density polyethylene comprises 15 to 30 wt% of the homogeneous blend; the crosslinked polyvinylpyrrolidone comprises 5-15 wt% of the homogeneous blend; the antioxidant accounts for 0.5-5 wt% of the homogeneous blend; the diluent accounts for 50-79% of the mass fraction of the homogeneous blend; the rotating speed of screw extrusion is 50-100 rpm; the high density polyethylene has an average molecular weight of 2.0X 105-1.0×106The density is 0.940-0.976g/cm3。
Further, the antioxidant is selected from at least one of dodecyl phosphite triester, dioctadecyl pentaerythritol diphosphite, dilauryl thiodipropionate or dibutyl hydroxy toluene; the diluent is at least one selected from paraffin oil, mineral oil, soybean oil, diphenyl ether, xylene or toluene. Preferably, the antioxidant is dodecyl phosphite triester; preferably, the diluent is paraffin oil.
Further, the preparation of the modified polyethylene microporous membrane comprises the following steps: (2) longitudinally stretching and transversely stretching the solid thick sheet to form a strip-shaped film; the temperature of the longitudinal stretching is 100-115 ℃, and the magnification of the longitudinal stretching is 3-9 times; the temperature of transverse stretching is 105-120 ℃, and the magnification of transverse stretching is 6-12 times.
Further, the preparation of the modified polyethylene microporous membrane comprises the following steps: (3) the extracting agent adopted in the extraction is at least one of dichloromethane, ethanol, diethyl ether or acetone, and the temperature during the extraction is 20-25 ℃; the heat setting temperature is 100-125 ℃, and the heat setting time is 20-50 minutes. The thickness of the modified polyethylene microporous membrane is 12-25 μm, the average pore diameter is 0.05-2 μm, the contact angle is 75-90 degrees, and the pure water flux is 1000-5000 LMH/bar.
Further, step two, preparation of polysulfone-based membrane: (1) the concentration of the polysulfone in the membrane casting solution is 15-22 wt%. The concentration of the polysulfone is preferably 18 to 20 wt.%.
Further, step two, preparation of polysulfone-based membrane: (2) the coating thickness of the casting solution is 20-100 μm; the temperature of the phase inversion is 20-60 ℃, and the time of the phase inversion is 10-90 seconds. Preferably, the coating thickness of the casting solution on the surface of the modified polyethylene microporous membrane is 25-50 μm; the temperature of the phase inversion is preferably 25 to 40 ℃ and the phase inversion time is preferably 20 to 50 seconds.
Further, step three, preparation of a reverse osmosis membrane: (1) the concentration of the m-phenylenediamine in the aqueous phase liquid is 1-4 wt%; the concentration of the sodium camphorsulfonate in the aqueous phase liquid is 1 to 4 weight percent; the time of the dipping treatment is 0.5-5 minutes. Preferably, the concentration of the m-phenylenediamine in the aqueous phase liquid is 1.5 to 2.5 wt%; the concentration of the sodium camphorsulfonate in the aqueous phase liquid is preferably 2 to 3 wt%; the time of the impregnation treatment is preferably 1 to 3 minutes.
Further, step three, preparation of a reverse osmosis membrane: (2) the concentration of trimesoyl chloride in the oil phase liquid is 0.05 to 0.5 weight percent; the organic solvent is at least one of n-hexane, cyclohexane, ethylcyclohexane, n-heptane or isoparaffin solvent; the time of the interfacial polymerization reaction is 10-60 seconds; the drying temperature is 30-90 ℃, and the drying time is 1-8 minutes. Preferably, the concentration of the trimesoyl chloride is 0.1-0.2 wt%; the organic solvent is preferably ethyl cyclohexane; preferably, the interfacial polymerization reaction time is 30 to 50 seconds; the drying temperature is preferably 40-60 ℃, and the drying time is preferably 2-4 minutes.
The preparation method of the invention carries out bulk modification on the polyethylene microporous membrane by adding the water-insoluble crosslinked polyvinylpyrrolidone, the preparation process is simple and easy to implement, and the prepared reverse osmosis membrane has higher water flux and desalination rate and can obviously improve the bonding strength with polyurethane glue. In addition, due to the existence of the polysulfone layer on the surface of the modified polyethylene substrate, the prepared reverse osmosis membrane has excellent pressure resistance and long-term stability, the comprehensive performance of the reverse osmosis membrane is close to that of a commercial reverse osmosis membrane, and the use requirement in the industrial field is completely met.
A reverse osmosis membrane based on a modified polyolefin substrate is prepared by adopting the preparation method. Specifically, the reverse osmosis membrane prepared based on the preparation method comprises a modified polyolefin substrate, a polysulfone porous layer and a polyamide desalting layer; the modified polyolefin substrate is a polyethylene microporous membrane modified by blending extrusion; the polysulfone porous layer is prepared by dissolving polysulfone in N, N-dimethylformamide and then coating the solution on the surface of a modified polyethylene microporous membrane through immersion phase conversion; the polyamide desalting layer is prepared by immersing a polysulfone porous layer impregnated with m-phenylenediamine and sodium camphorsulfonate into a trimesoyl chloride oil phase solution and performing interfacial polymerization reaction. Specifically, the polysulfone-based membrane is formed by a modified polyethylene microporous membrane and a polysulfone porous layer loaded on the microporous membrane; the reverse osmosis membrane is formed by a polysulfone-based membrane and a polyamide desalting layer supported thereon.
The invention has the beneficial effects that:
(1) the preparation method of the invention carries out bulk modification on the polyethylene microporous membrane by adding the water-insoluble crosslinked polyvinylpyrrolidone, has simple and easy preparation process, not only can improve the hydrophilic performance of the membrane surface and provide larger water permeation flux, but also is beneficial to the permeation of polyurethane glue in the polyethylene base material and obviously improves the bonding strength.
(2) Compared with PET non-woven fabrics, the modified polyethylene microporous membrane has smaller surface aperture, the infiltration degree of the membrane casting solution on the surface is low, the thickness of the coated polysulfone can be effectively reduced, the raw material cost is saved, and the thickness of the obtained polysulfone base membrane is reduced.
(3) Compared with a reverse osmosis membrane directly prepared on the surface of a polyolefin microporous membrane, the reverse osmosis membrane prepared by interfacial polymerization of the polysulfone base membrane obtained by the method has excellent pressure resistance and long-term stability, has comprehensive performance closer to that of the current commercial reverse osmosis membrane, and completely meets the use requirements in the industrial field.
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 creative efforts.
FIG. 1 is a scanning electron micrograph of the surface of a modified polyethylene microporous membrane prepared in example 1 of the present invention;
FIG. 2 is a scanning electron micrograph of the surface of a polysulfone-based film prepared in example 1 of the present invention;
FIG. 3 is a scanning electron micrograph of the surface of a reverse osmosis membrane prepared in example 1 of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the invention, its application, or uses. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Example 1
A preparation method of a reverse osmosis membrane based on a modified polyolefin substrate comprises the following steps:
firstly, preparing a modified polyethylene microporous membrane:
(1) mixing high density polyethylene (molecular weight 4.0 × 10)5Density of 0.960g/cm3) Melting and blending the crosslinked polyvinylpyrrolidone, the antioxidant (dodecyl phosphate triester) and the diluent (paraffin oil) at 175 ℃ to form a homogeneous blend, then extruding the homogeneous blend at the speed of 80rpm by a double-screw extruder, and forming a solid slab by a sheet casting process; 25 wt% of high-density polyethylene, 10 wt% of cross-linked polyvinylpyrrolidone, 1 wt% of antioxidant (dodecyl tri-phosphite), and 64 wt% of diluent (paraffin oil) in the homogeneous blend;
(2) longitudinally stretching the obtained solid thick sheet, and then transversely stretching to form a strip-shaped film; the temperature of longitudinal stretching is 100 ℃, and the magnification of longitudinal stretching is 6 times; the temperature of the transverse stretching is 110 ℃, and the magnification of the transverse stretching is 10 times;
(3) placing the obtained banded film in dichloromethane for extraction at 25 ℃, performing heat setting at 110 ℃ for 25 minutes after extraction, and finally rolling to obtain the modified polyethylene microporous film;
secondly, preparing a polysulfone-based membrane:
(1) dissolving polysulfone in N, N-dimethylformamide to prepare a membrane casting solution; and the polysulfone in the membrane casting solution accounts for 18 wt%;
(2) coating the membrane casting solution on the surface of the modified polyethylene microporous membrane, and then soaking the membrane casting solution into water at 25 ℃ for 30 seconds to form a membrane through phase inversion, so as to obtain the polysulfone base membrane; the coating thickness of the casting solution is 45 micrometers;
thirdly, preparing a reverse osmosis membrane:
(1) mixing m-phenylenediamine, sodium camphorsulfonate and water to prepare the aqueous phase liquid; then, putting the polysulfone basal membrane into the aqueous phase liquid for immersion treatment for 2 minutes, then pouring the aqueous phase liquid and removing the liquid remained on the surface of the polysulfone basal membrane; the metaphenylene diamine accounts for 2.5 wt% and the sodium camphorsulfonate accounts for 3.0 wt% in the aqueous phase liquid;
(2) dissolving trimesoyl chloride in ethylcyclohexane to prepare the oil phase liquid (the trimesoyl chloride in the oil phase liquid accounts for 0.15 wt%); and then placing the polysulfone base membrane in the oil phase liquid again for 30 seconds of interfacial polymerization reaction, pouring the oil phase liquid after the reaction and removing residual liquid on the surface of the membrane, then drying in a 50 ℃ oven for 3 minutes, and finally taking out the membrane and washing with water to obtain the reverse osmosis membrane based on the modified polyolefin substrate.
Examples 2 to 8
Examples 2 to 8 are different from example 1 in the addition amounts of the high density polyethylene, the crosslinked polyvinylpyrrolidone, the antioxidant and the diluent, and the draw ratio of the solid slab and the coating thickness of the casting solution are different from example 1, and the rest are the same as example 1, specifically referring to table 1.
Example 9
A preparation method of a reverse osmosis membrane based on a modified polyolefin substrate comprises the following steps:
firstly, preparing a modified polyethylene microporous membrane:
(1) mixing high density polyethylene (molecular weight 2.0 × 10)5Density of 0.940g/cm3) Melting and blending the cross-linked polyvinylpyrrolidone, the antioxidant (dioctadecyl pentaerythritol diphosphite) and the diluent (diphenyl ether) at 190 ℃ to form a homogeneous blend, then extruding the homogeneous blend by a double-screw extruder at the speed of 100rpm, and forming a solid slab by a sheet casting process; 25 wt% of high-density polyethylene, 10 wt% of cross-linked polyvinylpyrrolidone, 1 wt% of antioxidant (dioctadecyl pentaerythritol diphosphite) and 64 wt% of diluent (diphenyl ether) in the homogeneous blend;
(2) longitudinally stretching the obtained solid thick sheet, and then transversely stretching to form a strip-shaped film; the temperature of longitudinal stretching is 105 ℃, and the magnification of longitudinal stretching is 6 times; the temperature of the transverse stretching is 120 ℃, and the magnification of the transverse stretching is 10 times;
(3) extracting the obtained banded film in ethanol at 20 ℃, performing heat setting for 50 minutes at 100 ℃ after extraction, and finally rolling to obtain the modified polyethylene microporous film;
secondly, preparing a polysulfone-based membrane:
(1) dissolving polysulfone in N, N-dimethylformamide to prepare a membrane casting solution; and the polysulfone in the membrane casting solution accounts for 18 wt%;
(2) coating the membrane casting solution on the surface of the modified polyethylene microporous membrane, and then soaking the membrane casting solution into water at 40 ℃ for 90 seconds to form a membrane through phase inversion, so as to obtain the polysulfone base membrane; the coating thickness of the casting solution is 45 micrometers;
thirdly, preparing a reverse osmosis membrane:
(1) mixing m-phenylenediamine, sodium camphorsulfonate and water to prepare the aqueous phase liquid; then, putting the polysulfone basal membrane into the aqueous phase liquid for dipping treatment for 1 minute, then pouring the aqueous phase liquid and removing the liquid remained on the surface of the polysulfone basal membrane; the metaphenylene diamine accounts for 1.5 wt% and the sodium camphorsulfonate accounts for 2.5 wt% in the aqueous phase liquid;
(2) dissolving trimesoyl chloride in n-hexane to prepare the oil phase liquid (the trimesoyl chloride in the oil phase liquid accounts for 0.1 wt%); and then placing the polysulfone base membrane in the oil phase liquid again for 50 seconds of interfacial polymerization reaction, pouring the oil phase liquid after the reaction and removing residual liquid on the surface of the membrane, then drying in an oven at 30 ℃ for 8 minutes, and finally taking out the membrane and washing with water to obtain the reverse osmosis membrane based on the modified polyolefin substrate.
Example 10
A preparation method of a reverse osmosis membrane based on a modified polyolefin substrate comprises the following steps:
firstly, preparing a modified polyethylene microporous membrane:
(1) mixing high density polyethylene (molecular weight 1.0 × 10)6Density of 0.976g/cm3) Melting and blending the crosslinked polyvinylpyrrolidone, the antioxidant (dibutyl hydroxy toluene) and the diluent (toluene) at 150 ℃ to form a homogeneous blend, extruding the homogeneous blend by a double-screw extruder at the speed of 50rpm, and forming a solid slab by a sheet casting process; said homogeneous blending25 wt% of high-density polyethylene, 10 wt% of cross-linked polyvinylpyrrolidone, 1 wt% of antioxidant (dibutyl hydroxy toluene) and 64 wt% of diluent (toluene);
(2) longitudinally stretching the obtained solid thick sheet, and then transversely stretching to form a strip-shaped film; the temperature of longitudinal stretching is 115 ℃, and the magnification of longitudinal stretching is 6 times; the temperature of the transverse stretching is 105 ℃, and the magnification of the transverse stretching is 10 times;
(3) placing the obtained banded film in acetone for extraction at 25 ℃, performing heat setting for 40 minutes at 125 ℃ after extraction, and finally rolling to obtain the modified polyethylene microporous film;
secondly, preparing a polysulfone-based membrane:
(1) dissolving polysulfone in N, N-dimethylformamide to prepare a membrane casting solution; and the polysulfone in the membrane casting solution accounts for 18 wt%;
(2) coating the membrane casting solution on the surface of the modified polyethylene microporous membrane, and then soaking the membrane casting solution into water at 55 ℃ for 50 seconds to form a membrane through phase inversion, so as to obtain the polysulfone base membrane; the coating thickness of the casting solution is 45 micrometers;
thirdly, preparing a reverse osmosis membrane:
(1) mixing m-phenylenediamine, sodium camphorsulfonate and water to prepare the aqueous phase liquid; then, the polysulfone basal membrane is placed in the aqueous phase liquid for dipping treatment for 3 minutes, and then the aqueous phase liquid is poured out and the residual liquid on the surface of the polysulfone basal membrane is removed; the metaphenylene diamine accounts for 2.0 wt% and the sodium camphorsulfonate accounts for 2.0 wt% in the aqueous phase liquid;
(2) dissolving trimesoyl chloride in n-heptane to prepare the oil phase liquid (the trimesoyl chloride in the oil phase liquid accounts for 0.2 wt%); and then placing the polysulfone base membrane in the oil phase liquid again for 60 seconds of interfacial polymerization reaction, pouring the oil phase liquid after the reaction and removing residual liquid on the surface of the membrane, then drying in a 60 ℃ oven for 2 minutes, and finally taking out the membrane and washing with water to obtain the reverse osmosis membrane based on the modified polyolefin substrate.
The above examples 9 to 10 and example 1 are the same as example 1 in terms of the addition amounts of the high-density polyethylene, the crosslinked polyvinylpyrrolidone, the antioxidant and the diluent, the draw ratio of the solid slab and the coating thickness of the casting solution, and the differences are that there are differences in the selection of the molecular weight and the density of the high-density polyethylene, there are differences in the selection of the kind of the antioxidant and the diluent, and there are also differences in the temperature of melt blending, the speed of twin-screw extrusion, the drawing temperature, the temperature and time of heat setting, the temperature and time of phase inversion water, the immersion treatment time of the aqueous phase liquid, the concentrations of m-phenylenediamine and sodium camphorsulfonate in the aqueous phase liquid, the concentration of trimesoyl chloride in the oil phase liquid, the interfacial polymerization reaction time of the oil phase liquid, and the final drying temperature and time.
Comparative example 1
Comparative example 1 is different from example 1 in that crosslinked polyvinylpyrrolidone is not added during the preparation of the polyethylene microporous membrane of comparative example 1, and the other preparation conditions are the same as those of example 1, specifically referring to table 1.
Comparative example 2
The difference between the comparative example 2 and the example 1 is that the preparation process of the polysulfone-based membrane is not performed in the preparation process of the reverse osmosis membrane of the comparative example 2, i.e. the casting solution is not coated on the modified polyethylene microporous membrane, i.e. the prepared modified polyethylene microporous membrane is directly placed in the aqueous phase liquid and the oil phase liquid to be respectively subjected to the immersion treatment and the interfacial polymerization, except for the above differences, the preparation conditions of the comparative example 2 and the example 1 are the same, and the specific reference is made to table 1.
Comparative examples 3 to 6
Examples 3-6 differ from comparative example 2 in that the amounts of high density polyethylene, crosslinked polyvinylpyrrolidone, antioxidant, diluent added and the draw ratio of the solid slab are different from those of comparative example 2, and the rest are the same as in comparative example 2, see table 1.
Table 1 shows the amounts of the components added and the stretch ratios and the coating thicknesses of the casting solutions in examples 1 to 10 and comparative examples 1 to 6:
test example 1
The reverse osmosis membranes prepared in the above examples 1 to 10 and comparative examples 1 to 6 were tested for thickness, performance and adhesive strength, and the test results are shown in table 2; in addition, in order to compare the performance and the bonding strength of the prepared reverse osmosis membrane, an ULP (ultra low pressure) reverse osmosis membrane of the Kyotto company is selected for testing, and the test results are shown in Table 2.
Specifically, the performance evaluation method adopted by the reverse osmosis membrane is as follows:
(1) evaluation of separation Performance: the separation performance of the prepared reverse osmosis membrane is evaluated and is characterized by two characteristic parameters, namely the water flux and the salt rejection rate of the membrane;
water flux (LMH) is defined as: the volume of water per unit time that permeates the active membrane area under certain operating pressure conditions.
Salt rejection calculation formula: r ═ 1-Cp/Cf) X 100%, wherein R represents the rejection rate, CfAnd CpThe concentrations of the salts (ppm) in the permeate and in the feed, respectively.
The test conditions of the separation performance of the membrane are as follows: the feed solution was 1500ppm aqueous sodium chloride, the feed temperature was 25 ℃ and the test pressure was 150 psi.
(2) Evaluation of pressure resistance: the specific steps of the pressure resistance test of the membrane are as follows:
s1, taking the prepared reverse osmosis membrane, and testing the salt rejection rate R of the reverse osmosis membrane according to a normal test method0；
S2, increasing the test pressure to 400psi, reducing the test pressure to the normal test pressure after operating for 2 hours under high pressure, and testing the salt rejection R after stably operating for 0.5 hour1；
S3, calculating the difference value delta R of the desalination rate before and after the membrane pressure resistance0–R1。
(3) Thickness of the membrane: the thickness of the membrane was measured using a Mitutoyo 215-151-10 thickness gauge, Japan.
(4) Glue bonding strength: dripping the prepared polyurethane adhesive on the edge of the prepared membrane, folding to form a membrane bag, standing at room temperature for 12h, and testing at 22 deg.C and 30 deg.C with a tensile testerTearing the film bag at a stretching speed of 0mm/min along a 180-degree direction, wherein the strength of the torn film bag is the bonding strength P between the film and the glue0(N/mm)。
Table 2 shows the results of the tests of examples 1 to 10 and comparative examples 1 to 6 and ULP ultra low pressure reverse osmosis membranes of Timton:
as can be seen from the test results in table 2, compared with comparative example 1, the properties of the polyolefin substrate can be significantly changed by introducing crosslinked polyvinylpyrrolidone into the preparation of the microporous polyethylene membrane, and the prepared reverse osmosis membrane has higher water flux and salt rejection rate, and can significantly improve the adhesive strength with polyurethane glue. In addition, due to the existence of the polysulfone layer on the surface of the modified polyethylene substrate, the prepared reverse osmosis membrane has better pressure resistance, and the comprehensive performance is close to that of a commercial reverse osmosis membrane. Although the reverse osmosis membranes prepared in comparative examples 2 to 6 had good water flux and adhesive strength of glue, the salt rejection rate was low and the pressure resistance was poor, and thus the use requirements in the industrial field could not be satisfied.
Test example 2
The modified polyethylene microporous membrane, polysulfone-based membrane and reverse osmosis membrane prepared in example 1 were observed by Scanning Electron Microscopy (SEM), and the results are shown in fig. 1, 2 and 3, respectively, from which it can be seen that the surface of the prepared reverse osmosis membrane had a typical leaf-like structure.
The above examples of the invention and the sources of the raw materials used in the comparative examples are given in table 3 below:
table 3 shows the sources of the main raw materials used in the present invention
The above-mentioned preferred embodiments of the present invention are provided for illustration only and not for the purpose of limiting the invention. Obvious variations or modifications of the present invention are within the scope of the present invention.
Claims (10)
1. A method for preparing a reverse osmosis membrane based on a modified polyolefin substrate, comprising the steps of:
firstly, preparing a modified polyethylene microporous membrane:
(1) melting and blending high-density polyethylene, crosslinked polyvinylpyrrolidone, an antioxidant and a diluent to form a homogeneous blend, extruding the homogeneous blend, and casting to obtain a solid thick sheet;
(2) stretching the solid thick sheet to form a strip-shaped film;
(3) extracting, heat setting and rolling the strip-shaped film in sequence to obtain the modified polyethylene microporous film;
secondly, preparing a polysulfone-based membrane:
(1) dissolving polysulfone in N, N-dimethylformamide to prepare a membrane casting solution;
(2) coating the casting solution on the surface of the modified polyethylene microporous membrane, and then soaking the modified polyethylene microporous membrane in water to form a membrane through phase inversion to obtain the polysulfone base membrane;
thirdly, preparing a reverse osmosis membrane:
(1) mixing m-phenylenediamine, sodium camphorsulfonate and water to prepare aqueous phase liquid; then, the polysulfone basal membrane is placed in the aqueous phase liquid for dipping treatment, and then the liquid on the surface of the polysulfone basal membrane is separated and removed;
(2) dissolving trimesoyl chloride in an organic solvent to prepare an oil phase liquid; and then placing the polysulfone based membrane in the oil phase liquid again for interfacial polymerization, separating and removing the liquid on the surface of the membrane, drying, and washing with water to obtain the reverse osmosis membrane based on the modified polyolefin substrate.
2. The preparation method of the reverse osmosis membrane based on the modified polyolefin substrate according to claim 1, characterized by comprising the following steps: (1) melting and blending high-density polyethylene, crosslinked polyvinylpyrrolidone, an antioxidant and a diluent at the temperature of 150-190 ℃ to form a homogeneous blend, extruding the homogeneous blend by adopting a screw extrusion process, and casting to obtain a solid thick sheet; wherein the high density polyethylene comprises 15 to 30 wt% of the homogeneous blend; the crosslinked polyvinylpyrrolidone comprises 5-15 wt% of the homogeneous blend; the antioxidant accounts for 0.5-5 wt% of the homogeneous blend; the diluent accounts for 50-79% of the mass fraction of the homogeneous blend; the rotating speed of the screw for extrusion is 50-100 rpm; the high density polyethylene has an average molecular weight of 2.0X 105-1.0×106The density is 0.940-0.976g/cm3。
3. A method of preparing a reverse osmosis membrane based on a modified polyolefin substrate according to claim 2, wherein the antioxidant is selected from at least one of dodecyl phosphite, dioctadecyl pentaerythritol diphosphite, dilauryl thiodipropionate or dibutyl hydroxytoluene; the diluent is at least one selected from paraffin oil, mineral oil, soybean oil, diphenyl ether, xylene or toluene.
4. The preparation method of the reverse osmosis membrane based on the modified polyolefin substrate according to claim 1, characterized by comprising the following steps: (2) longitudinally stretching and transversely stretching the solid thick sheet to form a strip-shaped film; the temperature of the longitudinal stretching is 100-115 ℃, and the magnification of the longitudinal stretching is 3-9 times; the temperature of transverse stretching is 105-120 ℃, and the magnification of transverse stretching is 6-12 times.
5. The preparation method of the reverse osmosis membrane based on the modified polyolefin substrate according to claim 1, characterized by comprising the following steps: (3) the extracting agent adopted in the extraction is at least one of dichloromethane, ethanol, diethyl ether or acetone, and the temperature during the extraction is 20-25 ℃; the heat setting temperature is 100-125 ℃, and the heat setting time is 20-50 minutes.
6. The method for preparing a reverse osmosis membrane based on a modified polyolefin substrate according to claim 1, characterized in that the preparation of polysulfone based membrane in the second step: (1) the concentration of the polysulfone in the membrane casting solution is 15-22 wt%.
7. The method for preparing a reverse osmosis membrane based on a modified polyolefin substrate according to claim 1, characterized in that the preparation of polysulfone based membrane in the second step: (2) the coating thickness of the casting solution is 20-100 μm; the temperature of the phase inversion is 20-60 ℃, and the time of the phase inversion is 10-90 seconds.
8. The preparation method of the reverse osmosis membrane based on the modified polyolefin substrate as claimed in claim 1, characterized in that the preparation of the reverse osmosis membrane in the third step: (1) the concentration of the m-phenylenediamine in the aqueous phase liquid is 1-4 wt%; the concentration of the sodium camphorsulfonate in the aqueous phase liquid is 1 to 4 weight percent; the time of the dipping treatment is 0.5-5 minutes.
9. The preparation method of the reverse osmosis membrane based on the modified polyolefin substrate as claimed in claim 1, characterized in that the preparation of the reverse osmosis membrane in the third step: (2) the concentration of trimesoyl chloride in the oil phase liquid is 0.05 to 0.5 weight percent; the organic solvent is at least one of n-hexane, cyclohexane, ethylcyclohexane, n-heptane or isoparaffin solvent; the time of the interfacial polymerization reaction is 10-60 seconds; the drying temperature is 30-90 ℃, and the drying time is 1-8 minutes.
10. A reverse osmosis membrane based on a modified polyolefin substrate, characterized in that it has been obtained by the process according to any one of claims 1 to 9.
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