WO2019165840A1

WO2019165840A1 - Forward osmosis membrane, and preparation method therefor

Info

Publication number: WO2019165840A1
Application number: PCT/CN2018/124702
Authority: WO
Inventors: 刘长坤; 王琳
Original assignee: 深圳大学
Priority date: 2018-02-27
Filing date: 2018-12-28
Publication date: 2019-09-06
Also published as: CN108479395A; CN108479395B

Abstract

A forward osmosis membrane, and a preparation method therefor. A sacrificial layer is used, in combination with a casting method, for preparing a bottom macroporous polysulfone supporting layer; then an ultraviolet grafting method is used for grafting a hydrophilic PSMP polymer onto the bottom and pore internal walls of the supporting layer; and finally, an interfacial polymerization method is used for preparing an active skin layer on the top of the polysulfone supporting layer so as to obtain a forward osmosis membrane. According to the method, ultraviolet grafting of a hydrophilic PSMP polymer is used for implementing hydrophilic modification on the bottom and pore internal walls of a macroporous polysulfone supporting layer, so that the stability of an active skin layer is maintained, and the permeability performance of a forward osmosis membrane is further improved.

Description

Positive osmosis membrane and preparation method thereof

Technical field

The invention relates to the field of forward osmosis technology, in particular to a forward osmosis membrane and a preparation method thereof.

Background technique

At present, people have adopted various water treatment methods such as seawater desalination and wastewater recovery in order to obtain sufficient fresh water supply, but at the cost of consuming a large amount of energy, thus reducing the gap between the actual energy consumption and the thermodynamic minimum separation energy of the solution. It is a hot spot of research. Among them, forward osmosis is an emerging desalination and separation technology, which uses the difference in osmotic pressure at both ends of the semipermeable membrane to achieve spontaneous separation of the solution. In recent years, positive infiltration has been used in many fields, such as: seawater desalination, sewage treatment, and concentrated landfill leachate. In the field of water treatment, compared with traditional technologies such as microfiltration, ultrafiltration, nanofiltration, reverse osmosis and other membrane processes, the forward osmosis process has the advantages of low energy consumption, low pollution tendency and easy cleaning. However, forward osmosis still faces many problems, among which concentration polarization is one of the main problems affecting the positive osmosis performance. Concentration polarization phenomenon is ubiquitous in the membrane separation process, because the semipermeable membrane has a retention effect, the raw material liquid The portion that fails to pass through the semipermeable membrane accumulates on the surface of the membrane or the accumulation of the solute inside the membrane due to the non-uniform structure of the membrane significantly reduces the osmotic pressure, thereby reducing the performance of forward osmosis.

The forward osmosis membrane is composed of an active skin layer and a porous support layer. In recent years, a large amount of research has been devoted to improving the structure and properties of the support layer of the membrane to reduce the concentration polarization phenomenon to improve the performance of the forward osmosis membrane. For example, a support layer having a finger structure can be obtained by changing the solvent of the casting solution, the composition and concentration of the polymer, or a hydrophilic support material can be obtained by adding a hydrophilic substance. Since the hydrophilic support layer pore wall surface can be effectively wetted by the solution, the mass transfer is promoted to reduce the concentration polarization. However, in the hydrophilic modification of the support layer, there are also the following problems: (1) the hydrophilic support has reduced mechanical stability and is easy to swell in water; (2) affects the interfacial polymerization reaction or changes the active cortex. nature.

Therefore, the prior art has yet to be improved and developed.

Summary of the invention

In view of the above-mentioned deficiencies of the prior art, the object of the present invention is to provide a forward osmosis membrane and a preparation method thereof, which aim to solve the problem that the hydrophilicity of the support layer which is hydrophilically modified by the existing support layer is reduced, and the mechanical stability is reduced. Swelling in water affects interfacial polymerization or alters the properties of the active skin.

The technical solution of the present invention is as follows:

A method for preparing a forward osmosis membrane, comprising:

Step A, separately configuring a polysulfone solution and a polyetherimide solution, and respectively stirring the polysulfone solution and the polyetherimide solution at 60-80 ° C for 6-7 hours;

Step B, the polyetherimide solution is scraped into a polyetherimide film on a glass plate, and then the polysulfone solution is scraped on the polyetherimide film to form a polysulfone film;

Step C, tearing off the polyetherimide film to obtain a polysulfone support layer, and the side close to the polyetherimide film is used as the bottom of the polysulfone support layer;

Step D: The polysulfone support layer is immersed in a methanol solution of benzophenone for 1.5-2.5 hours, and the polysulfone support layer is taken out and placed in an SMP solution, and the bottom of the polysulfone support layer faces the ultraviolet lamp. Grafting a PSMP polymer on the bottom of the polysulfone support layer and the inner wall of the pore under irradiation of a UV lamp;

Step E: separately dissolving the aqueous solution of m-phenylenediamine and the solution of trimellitic acid chloride in n-hexane, and immersing the top of the polysulfone support layer obtained in step D in the aqueous solution of m-phenylenediamine for 3-10 minutes; and then obtaining the obtained polysulfone support layer. The top was immersed in a solution of trimesoyl chloride in hexane for 1-3 minutes. An active skin layer was prepared on top of the polysulfone support layer.

In the method for preparing a forward osmosis membrane, in the step A, the polysulfone solution is obtained by disposing N,N-dimethylacetamide, polyethylene glycol 400 and polysulfone.

In the method for preparing a forward osmosis membrane, in the step A, the polyetherimide solution is obtained by disposing N-methylpyrrolidone and a polyetherimide.

The method for preparing a forward osmosis membrane, wherein the step D comprises a step of: immersing the polysulfone membrane in a methanol solution for 1.5-2.5 hours.

The method for preparing a forward osmosis membrane, wherein in the step D, the concentration of the benzophenone in the methanol solution of benzophenone is 0.1-0.2 mol/L.

The method for preparing a forward osmosis membrane, wherein in the step D, the ultraviolet lamp is irradiated for 20-40 minutes.

The method for preparing a forward osmosis membrane, wherein in the step D, the ultraviolet lamp is irradiated for 30 minutes. a forward osmosis membrane comprising a polysulfone support layer and an active skin layer compounded on top of the polysulfone support layer, a bottom of the polysulfone support layer and a pore inner wall grafted with a PSMP polymer; the forward osmosis membrane It is prepared by the method described in the present invention.

The forward osmosis membrane, wherein the polysulfone support layer has a pore diameter of 25 to 35 nm.

The forward osmosis membrane, wherein the polysulfone support layer has a thickness of 80 to 120 μm, and the active skin layer has a thickness of 5 to 15 nm.

Advantageous Effects: The present invention combines the method of preparing a bottom macroporous support layer by sacrificial layer joint casting for the first time and the method of ultraviolet radiation grafting hydrophilic PSMP polymer modification to comprehensively improve the positive permeability of the membrane. The method for grafting hydrophilic PSMP polymer by ultraviolet irradiation only hydrophilically modifies the bottom of the porous support layer and the inner wall of the pore, thereby maintaining the stability of the active skin layer and further improving the positive The water permeability of the permeable membrane. The operation steps of the invention are simple and easy, the effect is stable and obvious, the water permeability is good, and the separation selectivity of the positive permeation is greatly improved.

DRAWINGS

1 is an SEM image of a forward osmosis membrane of a non-grafted PSMP and a forward osmosis membrane to which a PSMP has been grafted in the examples.

Detailed ways

The present invention provides a forward osmosis membrane and a preparation method thereof, and the present invention will be further described in detail below in order to clarify and clarify the objects, technical solutions and effects of the present invention. It is understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

The invention discloses a preparation method of a forward osmosis membrane, which comprises:

Step D: The polysulfone support layer is immersed in a methanol solution of benzophenone for 1.5-2.5 hours, and the polysulfone support layer is taken out and placed in an SMP monomer solution, and the bottom of the polysulfone support layer faces the ultraviolet lamp. Grafting a PSMP polymer on the bottom of the polysulfone support layer and the inner wall of the pore under irradiation of a UV lamp;

The hydrophilic modification of the conventional forward osmosis membrane is a method of increasing the content of the hydrophilic group in the polymer or blending with the hydrophilic polymer, and these methods make the top and bottom of the support layer hydrophilic. Sex, which has a certain effect on the performance of the active cortex, and the retention of salt is reduced. However, by the method of the present invention, a macroporous support layer having a hydrophilic top portion at the top can be prepared, so that a stable active skin layer can be prepared on the top of the support layer, thereby improving the water permeability of the forward osmosis membrane without affecting the salt retention. the amount. The invention grafts the hydrophilic polymer to the bottom of the porous support layer and the inner wall of the pore by the method of ultraviolet grafting. Compared with the traditional method of grafting the surface polymer, the method of ultraviolet grafting is simple, and the grafting time is short. The operation is simple and the grafting result is stable and controllable.

The invention adopts a sacrificial layer joint casting method to prepare a polysulfone support layer with a large bottom hole, and the sacrificial layer joint casting method specifically includes the steps A-C:

The step A specifically includes first configuring two polymer solutions. The polysulfone solution is prepared from N,N-dimethylacetamide (DMAc), polyethylene glycol 400 (PEG400) and polysulfone (PSf); the polyetherimide solution is composed of N-methylpyrrolidone (NMP). And polyetherimide (PEI) configuration. The two solutions were separately stirred in a water bath at 60 ° C - 80 ° C for 6-7 hours until the polymer was completely dissolved.

The step B specifically comprises: first pouring the PEI solution on a dry and flat glass plate, scraping the PEI solution with a 100 μm scraper to form a PEI film; and then pouring the PSf solution onto the PEI film and scraping with a 300 μm scraper. A PSf film was produced.

The step C specifically comprises: placing the glass plate in pure water for 1-2 minutes, with the purpose of utilizing phase inversion, so that the high molecular polymer is rapidly precipitated at the interface to form a very thin dense layer, and is formed under the dense layer. The porous layer forms a film structure with an outer dense interior. The PEI film was peeled off to obtain a PSf support layer, and the side close to the PEI film was used as the bottom of the PSf support layer.

The present invention employs a method of ultraviolet grafting to graft a hydrophilic PSMP polymer to the bottom of the PSf support layer and the inner wall of the pore. Compared with the conventional method for grafting a surface polymer, the method of the ultraviolet grafting method of the invention has the advantages of simple steps, short grafting time, simple operation, and stable and controllable grafting results. And the macroporous PSf support layer which is hydrophilic at the top hydrophobic bottom can be prepared by the method of ultraviolet grafting of the invention, so that a stable active skin layer is prepared on the top of the PSf support layer, so that the positive skin layer is improved without affecting the salt retention. The water flux of the permeable membrane. The method of ultraviolet grafting is step D:

The step D specifically includes: immersing the polysulfone support layer in a methanol solution for 1.5-2.5 hours (for example, two hours), so that impurities on the surface of the polysulfone support layer are removed. Then, the polysulfone support layer was taken out from the methanol solution and immersed in a methanol solution of 0.1-0.2 mol/L benzophenone (BP) (as a photoinitiator to activate the surface of the polysulfone support layer) for 1.5-2.5 hours ( Such as two hours). Finally, the polysulfone support layer was taken out from the methanol solution of benzophenone and placed in a concentration of 100-200 mL of SMP monomer solution (wherein the solvent is volume ratio V methanol: V water = 4:1, concentration of SMP monomer). 0.025-0.15g/mL, such as 0.05g/mL, 0.1g/mL or 0.15g/mL), placed in a UV light box for 20-40 minutes (such as 30 minutes) grafted PSMP polymer, polysulfone support The bottom of the layer faces upwards, and a piece of quartz glass is placed at the top to reduce the evaporation of the monomer solvent to change the monomer concentration and reduce the test error.

The present invention prepares a polyamide active skin layer on a polysulfone support layer by an interfacial polymerization method, and the interfacial polymerization method is the step E:

Step E specifically includes: disposing 25 mL of a 3 wt% aqueous solution of m-phenylenediamine (MPD) and 25 mL of a 0.15% by weight solution of trimesoyl chloride (TMC) in n-hexane. Place the polysulfone support layer obtained in step D on a jig, drop the MPD aqueous solution on top of the polysulfone support layer with a dropper until it is completely covered, keep it for 3-10 minutes, remove the excess MPD aqueous solution; then The TMC n-hexane solution was dropped onto the top of the polysulfone support layer using a dropper until it was completely covered for 1-3 minutes, and the excess TMC n-hexane solution was removed. An active skin layer is prepared by interfacial polymerization on top of the polysulfone support layer.

The invention firstly adopts a sacrificial layer combined casting method to prepare a polysulfone support layer with a large pore at the bottom, and then grafts a hydrophilic PSMP polymer to the bottom of the PSf support layer and the inner wall of the pore by ultraviolet grafting, and finally adopts interfacial polymerization. The method comprises preparing an active skin layer on top of a polysulfone support layer to obtain a forward osmosis membrane. After the positive osmosis membrane is prepared by the present invention, the forward osmosis membrane is subjected to a forward osmosis desalination test.

Forward osmosis desalination test: The permeation performance of the forward osmosis membrane and the separation selectivity to NaCl were measured by a forward osmosis apparatus. The raw material liquid is pure water, and the extract liquid is a 0.5-4 M NaCl solution. Conductivity meter is used to measure the change of conductivity of the raw material liquid for a certain period of time. According to the curve of conductivity and NaCl concentration, the salt permeation amount is calculated for a certain period of time, and the volume change of the draw solution is measured to determine the forward osmosis membrane. Water flux.

The hydrophilic modification of the conventional forward osmosis membrane is a method of increasing the content of the hydrophilic group in the polymer or blending with the hydrophilic polymer, and the present invention is to polymerize the hydrophilic PSMP by ultraviolet irradiation. The method of the material only hydrophilically modifies the bottom of the porous support layer and the inner wall of the pore, thereby maintaining the stability of the active skin layer and further improving the water permeability of the forward osmosis membrane. The invention combines the method of preparing the bottom macroporous support layer by the joint casting of the sacrificial layer for the first time and the method of modifying the hydrophilic PSMP polymer by the ultraviolet irradiation grafting to comprehensively improve the positive permeability of the membrane. The operation steps of the invention are simple and easy, the effect is stable and obvious, the water permeability is good, and the separation selectivity of the positive permeation is greatly improved.

The present invention also provides a forward osmosis membrane comprising a polysulfone support layer and an active skin layer compounded on top of the polysulfone support layer, wherein the bottom of the polysulfone support layer and the inner wall of the pore are grafted with a PSMP polymer; The forward osmosis membrane is prepared by the method described in the present invention. The polysulfone support layer has an effective pore size of about 25-35 nanometers (e.g., 30 nanometers). The polysulfone support layer has a thickness of about 80-120 microns (e.g., 100 microns) and the active skin layer has a thickness of about 5-15 nanometers (e.g., 10 nanometers).

The invention will now be described in detail by way of examples.

The preparation method of the positive osmosis membrane of this embodiment comprises the following steps:

1. Prepare the PSf support layer with large holes at the bottom by sacrificial layer joint casting method:

First, configure two polymer solutions, polysulfone solution: dissolve 18g polysulfone (PSf) material in 74g N, N-dimethylacetamide (DMAC) solution, add 15g polyethylene glycol (PEG400); polyether amide Imine solution: 17 g of polyetherimide (PEI) was dissolved in N-methylpyrrolidone (NMP). Then, the two solutions were respectively placed in a 65 ° C water bath and stirred for 7 hours, and the stirring speed was 380 r/min.

PEI solution was first poured on a dry and flat glass plate, the PEI solution was scraped off with a 100 μm scraper, and the PSf solution was poured onto the PEI and scraped with a 300 μm scraper. Finally, the glass plate was placed in pure water for 1 minute, and torn. The PEI layer is removed from the PEI layer, and the side close to the PEI layer is used as the bottom of the PSf support layer. The resulting PSf support layer was stored in deionized water.

2. Grafting PSMP polymer with UV light:

The PSf support layer was immersed in a methanol solution for two hours to remove surface impurities. The PSf support layer was then immersed in a 0.13 mol/L benzophenone (BP) solution in methanol (photoinitiator) for two hours. Finally, the treated PSf support layer was taken out and placed in a 100 mL 0.05 g/mL SMP monomer solution, and placed in a UV light box for half an hour to graft the PSMP polymer. The bottom of the PSf support layer was directed toward the UV lamp, and a piece was placed at the top. Quartz glass flakes reduce the solvent volatilization in the monomer solution to change the monomer concentration and reduce the test error.

3. Preparation of active cortex by interfacial polymerization:

25 mL of a 2 wt% aqueous solution of m-phenylenediamine (MPD) and 25 mL of a 0.1 wt% solution of trimesoyl chloride (TMC) in n-hexane were placed. Place the PSf support layer on the fixture, drop the MPD aqueous solution on the upper surface of the polysulfone support layer with a dropper until it is completely covered, keep it for 5 minutes, remove the excess MPD aqueous solution; then use the dropper to bring the TMC to the right The alkane solution was dropped onto the upper surface of the PSf support layer until it was completely covered and held for 2 minutes to remove excess TMC n-hexane solution. The active skin layer is prepared and the forward osmosis membrane is stored in deionized water.

4. Positive osmosis desalination test:

The permeation performance of the forward osmosis membrane and the separation selectivity to NaCl were measured by a forward osmosis apparatus. The raw material liquid was pure water, and the extract liquid was 0.5 M, 1 M, 1.5 M, 2 M, 4 M NaCl solution, respectively. The water flux and reverse salt flux of the forward osmosis membrane in the two modes of AL-FS (the cortex facing the raw material liquid) and AL-DS (the cortex facing the draw liquid) were measured. The reverse salt flux is the conductivity change of the raw material liquid measured by a conductivity meter for a certain period of time, and the salt permeation amount is calculated according to the curve of the conductivity and the NaCl concentration. The water flux is determined by measuring the volume change of the draw liquid during this period of time to determine the water flux of the forward osmosis membrane. When 0.5M NaCl is in the draw AL-DS mode, the water flux can be as high as 24L/m ² ·h, while the reverse salt flux is only about 0.5g, showing excellent separation selectivity.

5. Structural characterization of the forward osmosis membrane:

As shown in Fig. 1, Fig. 1a is a positive osmosis membrane skin layer of ungrafted PSMP, Fig. 1d is a cross-sectional structure of a positive osmosis membrane which is not grafted with PSMP near the cortex; Fig. 1b is a positive osmosis membrane skin layer to which PSMP has been grafted, Figure 1e is a cross-sectional structure of a positive osmosis membrane grafted with PSMP adjacent to the skin layer. It can be seen from the figure that the ungrafted forward osmosis membrane skin layer is relatively rough, the cortex of the grafted PSMP forward osmosis membrane is relatively smoother and smoother, and the more stable skin layer contributes to the retention of NaCl.

In summary, the present invention provides a forward osmosis membrane and a preparation method thereof. The hydrophilic modification of a conventional forward osmosis membrane is by increasing the content of a hydrophilic group in the polymer or co-synthesizing with a hydrophilic polymer. a method of mixing, and the method of grafting a hydrophilic PSMP polymer by ultraviolet irradiation only hydrophilically modifies the bottom of the porous support layer and the inner wall of the pore, thereby maintaining the stability of the active skin layer. Further improved the water permeability of the forward osmosis membrane. The invention combines the method of preparing the bottom macroporous support layer by the joint casting of the sacrificial layer for the first time and the method of modifying the hydrophilic PSMP polymer by the ultraviolet irradiation grafting to comprehensively improve the positive permeability of the membrane. The operation steps of the invention are simple and easy, the effect is stable and obvious, the water permeability is good, and the separation selectivity of the forward osmosis is greatly improved.

It is to be understood that the application of the present invention is not limited to the above-described examples, and those skilled in the art can make modifications and changes in accordance with the above description, all of which are within the scope of the appended claims.

Claims

A method for preparing a forward osmosis membrane, comprising:

Step A, separately configuring a polysulfone solution and a polyetherimide solution, and respectively stirring the polysulfone solution and the polyetherimide solution at 60-80 ° C for 6-7 hours;

Step B, the polyetherimide solution is scraped into a polyetherimide film on a glass plate, and then the polysulfone solution is scraped on the polyetherimide film to form a polysulfone film;

Step C, tearing off the polyetherimide film to obtain a polysulfone support layer, and the side close to the polyetherimide film is used as the bottom of the polysulfone support layer;

Step D: The polysulfone support layer is immersed in a methanol solution of benzophenone for 1.5-2.5 hours, and the polysulfone support layer is taken out and placed in an SMP solution, and the bottom of the polysulfone support layer faces the ultraviolet lamp. Grafting a PSMP polymer on the bottom of the polysulfone support layer and the inner wall of the pore under irradiation of a UV lamp;

Step E: separately dissolving the aqueous solution of m-phenylenediamine and the solution of trimellitic acid chloride in n-hexane, and immersing the top of the polysulfone support layer obtained in step D in the aqueous solution of m-phenylenediamine for 3-10 minutes; and then obtaining the obtained polysulfone support layer. The top was immersed in a solution of trimesoyl chloride in hexane for 1-3 minutes to prepare an active skin layer on top of the polysulfone support layer.
The method for preparing a forward osmosis membrane according to claim 1, wherein in the step A, the polysulfone solution is configured by N,N-dimethylacetamide, polyethylene glycol 400 and polysulfone. .
The method for preparing a forward osmosis membrane according to claim 1, wherein in the step A, the polyetherimide solution is obtained by disposing N-methylpyrrolidone and a polyetherimide.
The method for preparing a forward osmosis membrane according to claim 1, wherein the step D comprises the step of: immersing the polysulfone membrane in a methanol solution for 1.5 to 2.5 hours.
The method for preparing a forward osmosis membrane according to claim 1, wherein in the step D, the concentration of the benzophenone in the methanol solution of benzophenone is 0.1-0.2 mol/L. .
The method for preparing a forward osmosis membrane according to claim 1, wherein in the step D, the ultraviolet lamp is irradiated for a time of 20-40 minutes.
The method of preparing a forward osmosis membrane according to claim 6, wherein in the step D, the ultraviolet lamp is irradiated for 30 minutes.
A forward osmosis membrane comprising a polysulfone support layer and an active skin layer compounded on top of the polysulfone support layer, wherein a bottom portion of the polysulfone support layer and an inner wall of the pore are grafted with a PSMP polymer; A permeable membrane is prepared by the method of any of claims 1-7.
The forward osmosis membrane according to claim 8, wherein the polysulfone support layer has a pore diameter of 25 to 35 nm.
The forward osmosis membrane according to claim 8, wherein the polysulfone support layer has a thickness of 80 to 120 μm and the active skin layer has a thickness of 5 to 15 nm.