Method for preparing ultrafiltration membrane by spraying block copolymer micelles and ultrafiltration membrane

Abstract

The application relates to a method for preparing an ultrafiltration membrane by spraying block copolymer spherical micelles, which comprises the following steps: placing block copolymers in a selective solvent, preparing at least two block copolymer spherical micelle solutions with different particle sizes by different heating induction methods; spraying the at least two block copolymer spherical micelle solutions with different particle sizes on the surface of a macroporous base film in the order of block copolymer spherical micelle particle sizes from large to small; obtaining a composite membrane composed of a plurality of micelle solutions with different particle sizes; and naturally drying the composite membrane in air to form a film. The application also provides an ultrafiltration membrane, which comprises a base layer, a support layer and a separation layer, the support layer and the separation layer are formed by layer-by-layer spraying and gradient deposition of at least two block copolymer spherical micelle solutions with different particle sizes, and the layer-by-layer spraying is performed in the order of block copolymer spherical micelle particle sizes from large to small. The method is simple, the obtained composite membrane has an asymmetric structure, and the pore size and separation performance can be adjusted.

Description

Technical Field

[0001] This invention relates to a method for preparing a composite ultrafiltration membrane, and more particularly to a method for preparing an ultrafiltration membrane by spraying block copolymer spherical micelles. Background Technology

[0002] Membrane separation is a technology that uses membrane materials as a medium to achieve efficient separation of substances through the principle of selective permeability. Compared with other separation technologies, membrane separation has outstanding advantages in terms of high efficiency and energy saving. Depending on the size of the substances to be separated, membrane separation is divided into different application areas such as microfiltration, ultrafiltration, nanofiltration, reverse osmosis, and gas separation. Microfiltration and ultrafiltration are the earliest developed membrane separation technologies, and their applications are widespread, thus possessing a huge market. Generally, the pore size ranges of microfiltration membranes and ultrafiltration membranes are considered to be ~0.1-10 μm and ~2-100 nm, respectively, but there are no strict boundaries between their pore size ranges, and both are mainly prepared through wet phase inversion methods; therefore, they are often referred to together as "ultra-microfiltration membranes." Microfiltration and ultrafiltration membranes have advantages such as relatively large pore size, low operating pressure drop (<0.5 MPa), no phase change in the separation process, and low energy consumption, and have been widely used in water treatment processes such as wastewater treatment, reclaimed water reuse, and tap water production.

[0003] Although widely used, the further development of ultrafiltration membranes faces several bottlenecks, hindering their application and expansion. Ultrafiltration membranes are primarily prepared through a phase inversion process involving polymer solutions in water. This is a macroscopic phase separation process, with phase separation occurring randomly and disordered. The formation of the polymer-depleted phase is the pore-forming process, highly susceptible to minute kinetic disturbances, resulting in temporal and spatial dispersion of the membrane pores. The transformation of the polymer-depleted phase into pores occurs simultaneously with phase separation, making it difficult to control the pore microstructure. This results in a wide pore size distribution in the separated membrane, causing flux and selectivity to be mutually constrained and unable to be improved simultaneously. Furthermore, this process requires large amounts of organic solvents and generates difficult-to-treat wastewater. Therefore, the phase inversion manufacturing process of ultrafiltration membranes presents significant safety, environmental, and pollution risks.

[0004] Therefore, it is of great significance to invent a simple, efficient, and adjustable membrane pore size preparation method. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a simple and efficient method for preparing ultrafiltration membranes based on block copolymer micelles.

[0006] The above-mentioned objective of this invention is achieved through the following technical solution:

[0007] Firstly, a method for preparing an ultrafiltration membrane by spraying block copolymer spherical micelles is provided. This method uses block copolymer spherical nanomicelles as casting units, and sequentially sprays block copolymer micelles of different sizes onto the surface of a macroporous membrane to form a separation layer with a gradient structure, thereby preparing the ultrafiltration membrane. The specific steps are as follows:

[0008] a) Block copolymers were placed in a selective solvent and at least two different block copolymer spherical micelle solutions with different particle sizes were prepared by different heating induction methods;

[0009] b) On the surface of the macroporous membrane, at least two block copolymer spherical micelle solutions with different particle sizes obtained in a) are sequentially sprayed in layers according to the order of the block copolymer spherical micelle particle size from large to small; a composite membrane composed of micelle solutions with multiple particle sizes is obtained.

[0010] c) Allow the composite film formed by spraying in b) to air dry naturally.

[0011] In a preferred embodiment of the present invention, a) the block copolymer is composed of block A and block B, wherein block A is polysulfone and block B is polyethylene glycol; and block A accounts for 30%-50% of the total volume percentage of the block copolymer.

[0012] In a preferred embodiment of the present invention, in the block copolymer spherical micelle solutions with at least two different particle sizes obtained in a), the particle size of the block copolymer spherical micelles is all in the range of 30-600 nm; preferably all in the range of 30-300 nm; more preferably all in the range of 30-250 nm.

[0013] In a more preferred embodiment, the block copolymer spherical micelle solution with at least two different particle sizes obtained in a) includes two block copolymer spherical micelle solutions with an average particle size of 200-250 nm and an average particle size of 30-100 nm; in a further preferred embodiment, the block copolymer spherical micelle solution with at least two different particle sizes obtained in a) includes two block copolymer spherical micelle solutions with an average particle size of 250 nm and an average particle size of 30-80 nm.

[0014] In a preferred embodiment of the present invention, the selective solvent in step a) is acetic acid or ethanol; more preferably, the block copolymer is added to the acetic acid or ethanol to form a solution with a mass percentage concentration of 0.1%-3%.

[0015] In the scheme described in this invention, the macroporous base membrane in step b) is any membrane material that does not react with the selective solvent described in a); preferably, the macroporous base membrane is a polyethersulfone membrane.

[0016] In the scheme described in this invention, during the spraying process in step b), it is preferable to control the amount of the block copolymer spherical micelle solution used in each spray layer to be 0.16-0.28 mL / cm. 2 Base membrane.

[0017] In a more preferred embodiment, the spraying described in b) is performed using a spraying device, and more preferably, the spraying pressure of the spraying device is controlled at 1 bar, the spraying height at 62 mm, and the spraying moving speed at 100 mm / min. -1 .

[0018] Secondly, the present invention also provides an ultrafiltration membrane, comprising a base layer, a support layer and a separation layer, wherein the support layer and the separation layer are formed by layered spraying and stepwise deposition of at least two block copolymer spherical micelle solutions with different particle sizes, wherein the layered spraying is performed in descending order of the particle size of the block copolymer spherical micelles.

[0019] In a preferred embodiment of the present invention, the block copolymer contained in the at least two different particle size block copolymer spherical micelle solution is composed of block A and block B, wherein block A is polysulfone and block B is polyethylene glycol; and block A accounts for 30%-50% of the total volume percentage of the block copolymer.

[0020] In a preferred embodiment of the present invention, the block copolymer spherical micelle solutions with at least two different particle sizes have a particle size of 30-600 nm; preferably 30-300 nm; and more preferably 30-250 nm.

[0021] In a more preferred embodiment, the at least two block copolymer spherical micelle solutions with different particle sizes include two block copolymer spherical micelle solutions with an average particle size of 200-250 nm and an average particle size of 30-100 nm; in a further preferred embodiment, the at least two block copolymer spherical micelle solutions with different particle sizes include two block copolymer spherical micelle solutions with an average particle size of 250 nm and an average particle size of 30-80 nm; or include three block copolymer spherical micelle solutions with an average particle size of 250 nm, an average particle size of 70-80 nm, and an average particle size of 25-35 nm.

[0022] In a preferred embodiment of the present invention, the mass percentage concentration of the at least two block copolymer spherical micelle solutions with different particle sizes is 0.1%-3%.

[0023] In the solution described in this invention, the base layer is any polyethersulfone film.

[0024] In summary, the present invention provides a process for preparing an ultrafiltration membrane: at least two types of block copolymer micelles are sprayed onto the surface of a base membrane to form a structure in which large-particle micelles are placed below as a support layer and small-particle micelles are placed above as a single-layer, double-layer, or multi-layer gradient micelle separation layer, and the ultrafiltration membrane is obtained by natural drying.

[0025] Compared with the prior art, the beneficial effects of the present invention are mainly reflected in the following aspects:

[0026] (1) A new approach to preparing block copolymer micelle composite films using a spraying method is proposed. The method is simple and easy to operate.

[0027] (2) By using micelles of different particle sizes to deposit in a stepwise manner, the structure of the micelle support layer and the separation layer can be controlled to obtain a gradient pore structure, which is beneficial to overcome the trade-off effect of membrane flux retention.

[0028] (3) The effective pore size of the prepared ultrafiltration membrane separation layer can be controlled by changing the particle size of the micelles, and the minimum molecular weight cutoff can be as low as 1493 Da. Attached Figure Description

[0029] Figure 1 The images shown are scanning electron microscope (SEM) images of the block copolymer micelle composite film sprayed in Example 1; where (a) is a surface SEM image and (b) is a cross-sectional SEM image.

[0030] Figure 2 The graphs show the pure water flux and the retention data of bovine serum albumin (BSA) and 50nm silica spheres for the ultrafiltration membranes prepared by spraying different volumes of micelles in Example 2. 5+4 is a membrane prepared by adding 5mL of micelles with an average particle size of 250nm and 4mL of micelles with an average particle size of 75nm. The same applies to 5+5, 5+6 and 5+7.

[0031] Figure 3 The graph shows the pure water flux and the retention data of bovine serum albumin (BSA) and lysozyme of the ultrafiltration membrane prepared by spraying different volumes of micelles in Example 3. 3+3 is a membrane prepared by spraying 3 mL of micelles with an average particle size of 250 nm and 3 mL of micelles with an average particle size of 30 nm. The same applies to 3+2 and 3+1.

[0032] Figure 4 The graph shows the molecular weight cutoff curves of ultrafiltration membranes prepared by spraying micelles of different volumes in Example 3. 3+3 is a membrane prepared by adding 3 mL of micelles with an average particle size of 250 nm and 3 mL of micelles with an average particle size of 30 nm. The same applies to 3+2 and 3+1. Detailed Implementation

[0033] The present invention will be further described below with reference to specific embodiments, but the given embodiments do not constitute a limitation on the scope of the claims of the present invention.

[0034] Example 1

[0035] An ultrafiltration membrane with a bilayer micelle structure containing a support layer and a single-layer separation layer was prepared by spraying block copolymer spherical micelles, comprising the following steps:

[0036] a) Polysulfone-polyethylene glycol was added to acetic acid at a mass fraction of 0.1%, and the solution was heated at 180°C for 12 hours to obtain a block copolymer spherical micelle solution with an average particle size of 250 nm.

[0037] b) Polysulfone-polyethylene glycol was added to ethanol at a mass fraction of 0.1%, and the solution was heated at 180°C for 12 hours to obtain a block copolymer spherical micelle solution with an average particle size of 30 nm.

[0038] c) Take a piece of polyethersulfone (PES) membrane (membrane area 25 cm²). 2 Place it under the sprayer and fix it in place;

[0039] d) Measure 5 mL of a spherical micelle solution of polysulfone-polyethylene glycol block copolymer with a particle size of 250 nm, and spray it onto the surface of a polyethersulfone-based film. Control the spraying pressure of the sprayer to be 1 bar, the spraying height to be 62 mm, and the spraying speed to be 100 mm / min. -1 This forms the first micelle layer;

[0040] e) Measure 3 mL of a spherical micelle solution of polysulfone-polyethylene glycol block copolymer with a particle size of 30 nm, and spray it onto the surface of a polyethersulfone-based film. Control the spraying pressure of the sprayer to be 1 bar, the spraying height to be 62 mm, and the spraying moving speed to be 100 mm / min. -1 This forms a second micelle layer;

[0041] f) The ultrafiltration membrane prepared by spraying is placed in the air and dried naturally to obtain a three-layer ultrafiltration membrane with PES as the base layer, large-particle micelles as the support layer, and small-particle micelles as the separation layer.

[0042] Depend on Figure 1 As can be seen, the block copolymer micelle composite membrane prepared in Example 1 has a smooth surface, uniform micelle distribution, and clearly visible double-layer micelles in cross-section. The thickness of the small micelle layer, which determines the separation performance, is 202 nm.

[0043] Example 2

[0044] An ultrafiltration membrane with a bilayer micelle structure containing a support layer and a single-layer separation layer was prepared by spraying block copolymer spherical micelles, comprising the following steps:

[0045] a) Polysulfone-polyethylene glycol was added to acetic acid at a mass fraction of 0.1%, and the solution was heated at 180°C for 12 hours to obtain a block copolymer micelle solution with an average particle size of 250 nm.

[0046] b) Polysulfone-polyethylene glycol was added to acetic acid at a mass fraction of 0.1%, and the solution was heated at 180°C for 6 hours to obtain a block copolymer micelle solution with an average particle size of 75 nm.

[0047] c) Take a piece of polyethersulfone (PES) membrane (membrane area 25 cm²). 2 Place it under the sprayer and fix it in place;

[0048] d) Measure 5 mL of a block copolymer micelle solution of polysulfone-polyethylene glycol with a particle size of 250 nm and spray it onto the surface of a polyethersulfone-based film to form the first micelle layer;

[0049] e) Take 4 mL, 5 mL, 6 mL, and 7 mL of a block copolymer micelle solution of polysulfone-polyethylene glycol with a particle size of 75 nm, respectively, and spray it onto the surface of the polyethersulfone-based film to form a second micelle layer.

[0050] f) The ultrafiltration membrane prepared by spraying is placed in the air to dry naturally, and a three-layer ultrafiltration membrane with PES as the base layer, large-particle micelles as the support layer and small-particle micelles as the separation layer is obtained.

[0051] Depend on Figure 2 It can be seen that, in the block copolymer micelle composite membrane prepared in Example 2, as the amount of the second layer of micelles sprayed increased from 4 mL to 7 mL, the water flux of the ultrafiltration membrane gradually decreased from 87 L·m⁻¹ to 69 L·m⁻¹. -2 ·h -1 ·bar -1 The retention of BSA increased from 4.5% to 9.8%, and the retention of SiO2 was about 50%. This is because as the amount of micelles sprayed increases, the thickness of the separation layer increases, which increases the mass transfer resistance of the membrane, resulting in a decrease in water flux and an increase in retention.

[0052] Example 3

[0053] An ultrafiltration membrane with a bilayer micelle structure containing a support layer and a single-layer separation layer was prepared by spraying block copolymer spherical micelles, comprising the following steps:

[0054] a) Polysulfone-polyethylene glycol was added to acetic acid at a mass fraction of 0.1%, and the solution was heated at 180°C for 12 hours to obtain a block copolymer micelle solution with an average particle size of 250 nm.

[0055] b) Polysulfone-polyethylene glycol was added to ethanol at a mass fraction of 0.1%, and the solution was heated at 180°C for 12 hours to obtain a block copolymer micelle solution with an average particle size of 30 nm.

[0056] c) Take a piece of polyethersulfone (PES) membrane (membrane area 25 cm²). 2 Place it under the sprayer and fix it in place;

[0057] d) Measure 3 mL of a block copolymer micelle solution of polysulfone-polyethylene glycol with a particle size of 250 nm and spray it onto the surface of a polyethersulfone-based film to form the first micelle layer;

[0058] e) Take 3 mL, 2 mL, and 1 mL of polysulfone-polyethylene glycol block copolymer micelle solutions with a particle size of 30 nm respectively, and spray them onto the surface of the polyethersulfone-based film to form a second micelle layer.

[0059] f) The ultrafiltration membrane prepared by spraying is placed in the air to dry naturally, and a three-layer ultrafiltration membrane with PES as the base layer, large-particle micelles as the support layer and small-particle micelles as the separation layer is obtained.

[0060] Depend on Figure 3 It can be seen that, for the block copolymer micelle composite membrane prepared in Example 3, when the amount of the second micelle coating is 3 mL, 2 mL, and 1 mL, the water flux of the ultrafiltration membrane is 15, 17, and 170 L·m, respectively. -2 ·h -1 ·bar -1 The retention rates of BSA were 98%, 96%, and 11%, respectively, and the retention rates of lysozyme were 98%, 97%, and 13%, respectively.

[0061] Depend on Figure 4 It can be seen that the ultrafiltration membrane prepared in Example 3 has the smallest molecular weight cutoff of 1493 Da when the micelle layer is constructed by 3 mL of 250 nm + 3 mL of 30 nm micelles.

[0062] Example 4

[0063] The preparation of a three-layer micelle structure containing a support layer and a bilayer separation layer by spraying block copolymer spherical micelles includes the following steps:

[0064] a) Polysulfone-polyethylene glycol was added to acetic acid at a mass fraction of 0.1%, and the solution was heated at 180°C for 12 hours to obtain a block copolymer micelle solution with an average particle size of 250 nm.

[0065] b) Polysulfone-polyethylene glycol was added to acetic acid at a mass fraction of 0.1%, and the solution was heated at 180°C for 6 hours to obtain a block copolymer micelle solution with an average particle size of 75 nm.

[0066] c) Polysulfone-polyethylene glycol was added to ethanol at a mass fraction of 0.1%, and the solution was heated at 180°C for 12 hours to obtain a block copolymer micelle solution with an average particle size of 30 nm.

[0067] d) Take a piece of polyethersulfone (PES) film (film area 25cm2) and fix it under the sprayer;

[0068] e) Measure 3 mL of a block copolymer micelle solution of polysulfone-polyethylene glycol with a particle size of 250 nm and spray it onto the surface of a polyethersulfone-based film to form the first micelle layer.

[0069] f) Measure 2 mL of a block copolymer micelle solution of polysulfone-polyethylene glycol with a particle size of 75 nm and spray it onto the surface of a polyethersulfone-based film to form a second micelle layer.

[0070] g) Measure 1 mL of a block copolymer micelle solution of polysulfone-polyethylene glycol with a particle size of 30 nm and spray it onto the surface of a polyethersulfone-based film to form a third micelle layer.

[0071] h) The ultrafiltration membrane prepared by spraying is placed in the air and dried naturally to obtain a multilayer micelle ultrafiltration membrane with PES as the base layer, 250nm large-particle micelles as the support layer, and 75nm+30nm small-particle micelles as the double separation layer.

Claims

1. A method for preparing an ultrafiltration membrane by spraying block copolymer spherical micelles, characterized in that, Includes the following steps: a) Block copolymers are placed in selective solvents and at least two different block copolymer spherical micelle solutions with different particle sizes are prepared by different heating induction methods; the block copolymers are composed of block A and block B, wherein block A is polysulfone and block B is polyethylene glycol; b) On the surface of the macroporous membrane, at least two block copolymer spherical micelle solutions with different particle sizes obtained in a) are sequentially sprayed in layers according to the order of block copolymer spherical micelle particle size from large to small. Composite membranes composed of micelle solutions with various particle sizes were obtained; c) Allow the composite film formed by spraying in b) to air dry naturally.

2. The method as described in claim 1, characterized in that: a) Block A accounts for 30%-50% of the total volume percentage of the block copolymer.

3. The method as described in claim 1, characterized in that: a) In the obtained block copolymer spherical micelle solutions with at least two different particle sizes, the particle size of the block copolymer spherical micelles is in the range of 30-600 nm.

4. The method as described in claim 1, characterized in that: a) In the obtained block copolymer spherical micelle solutions with at least two different particle sizes, the particle size of the block copolymer spherical micelles is 30-250 nm.

5. The method as described in claim 1, characterized in that: a) The obtained block copolymer spherical micelle solutions with at least two different particle sizes include two block copolymer spherical micelle solutions with an average particle size of 200-250 nm and an average particle size of 30-100 nm.

6. The method as described in claim 1, characterized in that: a) The obtained block copolymer spherical micelle solutions with at least two different particle sizes include two block copolymer spherical micelle solutions with an average particle size of 250 nm and an average particle size of 30-80 nm.

7. The method as described in claim 1, characterized in that: The selective solvent mentioned in a) is acetic acid or ethanol.

8. The method as described in claim 7, characterized in that: The block copolymer is added to the acetic acid or ethanol to form a solution with a mass percentage concentration of 0.1%-3%.

9. The method as described in claim 1, characterized in that: The macroporous membrane described in b) is any membrane material that does not react with the selective solvent described in a).

10. The method as described in claim 1, characterized in that: The macroporous membrane described in b) is a polyethersulfone membrane.

11. The method as described in claim 1, characterized in that: In the spraying process described in b), the amount of the block copolymer spherical micelle solution in each spray layer is controlled to be 0.16-0.28 mL / cm. 2 .

12. The method as described in claim 1, characterized in that: b) The spraying is performed using a spraying device, and the spraying pressure of the spraying device is controlled at 1 bar, the spraying height at 62 mm, and the spraying moving speed at 100 mm / min. -1 .

13. An ultrafiltration membrane, comprising a base layer, a support layer, and a separation layer, characterized in that: The support layer and the separation layer are formed by layering and stepwise deposition of block copolymer spherical micelle solutions of at least two different particle sizes, wherein the layering is carried out in descending order of the particle size of the block copolymer spherical micelles.

14. The ultrafiltration membrane as described in claim 13, characterized in that: The block copolymer contained in the at least two different particle size block copolymer spherical micelle solution is composed of block A and block B, wherein block A is polysulfone and block B is polyethylene glycol; and block A accounts for 30%-50% of the total volume percentage of the block copolymer.

15. The ultrafiltration membrane as described in claim 13, characterized in that: In the block copolymer spherical micelle solutions with at least two different particle sizes, the particle size of the block copolymer spherical micelles is 30-600 nm.

16. The ultrafiltration membrane as described in claim 13, characterized in that: In the block copolymer spherical micelle solutions with at least two different particle sizes, the particle size of the block copolymer spherical micelles is 30-250 nm.

17. The ultrafiltration membrane as described in claim 13, characterized in that: The block copolymer spherical micelle solution with at least two different particle sizes includes two block copolymer spherical micelle solutions with an average particle size of 200-250 nm and an average particle size of 30-100 nm.

18. The ultrafiltration membrane as described in claim 13, characterized in that: The block copolymer spherical micelle solution with at least two different particle sizes includes two block copolymer spherical micelle solutions with an average particle size of 250 nm and an average particle size of 30-80 nm.

19. The ultrafiltration membrane as described in claim 13, characterized in that: The mass percentage concentration of the at least two block copolymer spherical micelle solutions with different particle sizes is 0.1%-3%.

20. The ultrafiltration membrane as described in claim 13, characterized in that: The base layer is a polyethersulfone film.

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