An alternating composite membrane and a preparation method and application thereof

Abstract

This invention provides an alternating composite membrane composed of a polymer-nanofiber intercalation layer and a porous support layer. The invention also provides a method for preparing the alternating composite membrane and its applications. The preparation method of this invention is simple and controllable, uses readily available raw materials, operates under mild conditions, and has wide applicability.

Description

Technical Field

[0001] This invention relates to the field of membrane separation technology, specifically to an alternating composite membrane, its preparation method, and its application. Background Technology

[0002] Propylene oxide is a high-end chemical raw material that the country strongly encourages its development. During the direct oxidation process of propylene oxide, byproducts such as methanol and propylene glycol monomethyl ether (PME) are produced. During purification, methanol and other substances in the wastewater are easily removed and recovered. However, PME forms an azeotrope with water, and conventional distillation methods (such as azeotropic distillation and extractive distillation) suffer from long process flows and high energy consumption. Furthermore, PME is an excellent solvent widely used in coatings, printing and dyeing, and chemical industries. Therefore, designing and developing a novel and efficient technology for the recovery of PME has significant socio-economic benefits. Membrane separation for organic solvent dehydration is a new energy-saving and environmentally friendly technology with advantages such as high efficiency, convenient operation, and easy process control, making it one of the most promising emerging technologies of the 21st century.

[0003] In membrane separation, composite membranes are commonly used in industrial applications. During their preparation, a separation layer is typically constructed on a support layer (base membrane) using methods such as coating with a polymer or monomer solution. However, due to the nature of the process, composite membranes often exhibit porosity and leakage, leading to defects in the membrane layer. To overcome this difficulty, an intermediate layer is generally introduced to pretreat the support layer, optimizing the surface structure of the macroporous support layer and preventing porosity and leakage during polymer solution coating, thereby obtaining a thin and uniform polymer separation layer.

[0004] Furthermore, various separation systems in liquid environments place more stringent requirements on the stability of composite membranes. This is mainly because during the separation process, polymer materials adsorb specific solvent molecules, resulting in swelling, which increases the free volume between polymer chain segments and leads to a decrease in selectivity. Summary of the Invention

[0005] In view of the above-mentioned prior art, the present invention proposes an alternating composite membrane, its preparation method and application. It adopts a multi-alternating spin-coating strategy and synergistically uses one-dimensional nanomaterials to obtain a highly stable thin-layer composite membrane for dehydration of propylene glycol monomethyl ether mixed solution. Moreover, the preparation method is simple and controllable, the raw materials are readily available, the conditions are mild, and it has wide applicability.

[0006] The present invention provides an alternating composite membrane, which is composed of a polymer-nanofiber intercalation layer and a porous support layer.

[0007] The present invention also provides a method for preparing the alternating composite membrane, comprising the following steps: depositing a nanofiber layer on a porous support layer by vacuum filtration to obtain a base film; and repeatedly spin-coating a polymer solution and a crosslinking agent / curing agent solution onto the base film to obtain an alternating composite membrane.

[0008] Preferably, it includes the following steps:

[0009] S1. Preparation of nanofiber solution: Mix metal salt solution and ethanolamine solution evenly, and let stand at room temperature to obtain nanofiber solution;

[0010] S2. Deposition of nanofiber layer: The porous support layer is placed in a vacuum filtration device, the nanofiber solution is poured in and filtered, and a nanofiber layer is deposited on the porous support layer to obtain a base film. After filtration, the base film is taken out and placed at room temperature to dry. After drying, the base film is fixed on a spin coater with tape for later use.

[0011] S3. Preparation of crosslinking agent / curing agent solution: Dissolve the crosslinking agent and curing agent in a solvent, stir evenly, and let stand to obtain the crosslinking agent / curing agent solution;

[0012] S4. Preparation of polymer solution: Dissolve the polymer in an organic solvent, stir until homogeneous, and let stand to obtain a polymer solution;

[0013] S5. Coating the polymer layer: Continue stirring the crosslinking agent / curing agent solution and the polymer solution at room temperature. Using a spin coater, select an appropriate rotation speed and spin coat a certain amount of polymer solution and crosslinking agent / curing agent solution alternately onto the surface of the nanofiber layer multiple times. Allow the mixture to stand at room temperature for crosslinking and then dry to obtain an alternating composite film.

[0014] Preferably, in S1, the concentration of the metal salt solution is 4-6 mM / L, the concentration of the ethanolamine solution is 1.2-1.6 mM / L, the volume ratio of the metal salt solution to the ethanolamine solution is 1:1, and the metal salt solution is a copper nitrate solution.

[0015] Preferably, in step S2, the deposition rate of the nanofiber solution is 0.4–0.8 ml / cm³. 2 The porous support layer is a polyacrylonitrile support layer.

[0016] Preferably, in S3, the crosslinking agent is tetraethyl orthosilicate (TEOS), and the content of the crosslinking agent is 1 wt%; the curing agent is dibutyltin dilaurate (DBTDL), and the content of the curing agent is 0.1 wt%.

[0017] Preferably, in S4, the polymer is polydimethylsiloxane (PDMS), and the concentration of the polymer solution is 5-20 wt%.

[0018] Preferably, in step S5, the alternating spin coating is performed 2 to 8 times, and the total coating amount of the polymer solution is 5 to 20 mg / cm³. 2 The static crosslinking time is 20-30 hours.

[0019] The present invention further provides the application of the alternating composite membrane in the dehydration of organic solvents.

[0020] Preferably, the organic solvent is a propylene glycol monomethyl ether mixture, the feed content of the propylene glycol monomethyl ether mixture is 0.5-5 wt%, and the feed temperature is 10-60°C.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] 1. This invention develops an alternating polymer-nanofiber composite membrane for separation applications. During its preparation, nanofibers are deposited and stacked on the surface of a macroporous membrane as an intermediate layer using a vacuum filtration method. This effectively alleviates pore permeation and facilitates the formation of a thin and uniform polymer separation layer. Simultaneously, by alternately depositing monomer solutions on top of the nanofiber layers, an intercalation structure is formed. The synergistic effect between the polymer and fiber layers endows the membrane with high structural stability.

[0023] 2. The preparation process of the present invention is simple and controllable, the raw materials are readily available, the conditions are mild, and it has wide applicability.

[0024] 3. The composite membrane prepared by this invention is used in the dehydration process of propylene glycol monomethyl ether byproduct of propylene oxide. It has the great advantages of high efficiency and energy saving, does not introduce a third component, avoids pollution to the environment or products, and has high product quality. Attached Figure Description

[0025] Figure 1 This is a SEM image of the polyacrylonitrile support layer in Embodiment 1 of the present invention.

[0026] Figure 2 This is a SEM image of the copper hydroxide nanowire layer in Example 1 of the present invention.

[0027] Figure 3 This is a surface SEM image of the alternating polymer-nanofiber composite membrane obtained in Example 1 of the present invention.

[0028] Figure 4 This is a flowchart of the apparatus for testing the pervaporation separation performance in the experimental examples of this invention. Detailed Implementation

[0029] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below with reference to specific illustrations.

[0030] Example 1

[0031] A method for preparing an alternating composite membrane includes the following steps:

[0032] S1. Preparation of copper hydroxide nanowire solution: Add 100 ml of 4 mM / L copper nitrate solution and 100 ml of 1.6 mM / L ethanolamine solution to a container, mix well, and let stand at room temperature to obtain copper hydroxide nanowire solution.

[0033] S2. Deposition of copper hydroxide nanowire layer: A polyacrylonitrile support layer (pore size approximately 25 nm, SEM image shown) is then deposited. Figure 1 (As shown) Place it in a vacuum filtration apparatus, with a deposition rate of 0.4 ml / cm³. 2 The copper hydroxide nanowire solution was poured in and filtered to deposit a copper hydroxide nanowire layer on a polyacrylonitrile support layer, resulting in a base film. After filtration, the base film was removed and air-dried at room temperature. After drying, the base film was fixed onto a spin-coating plate with adhesive tape for later use. The SEM image of the obtained copper hydroxide nanowire layer is shown below. Figure 2 As shown.

[0034] S3. Preparation of crosslinking agent / curing agent solution: Dissolve the crosslinking agent and curing agent in a solvent, stir evenly, and let stand to obtain the crosslinking agent / curing agent solution; the crosslinking agent and curing agent are tetraethyl orthosilicate and dibutyltin dilaurate, respectively, with contents of 1wt% and 0.1wt% respectively;

[0035] S4. Preparation of polymer solution: Dissolve the polymer in n-heptane, stir evenly and let stand to obtain a polymer solution with a concentration of 10wt%.

[0036] S5. Coating the polymer layer: The crosslinking agent / curing agent solution and the polymer solution are stirred separately at room temperature. Using a spin coater (KW-4A), a suitable rotation speed is selected, and a certain amount of polymer solution and crosslinking agent / curing agent solution are alternately spin-coated onto the surface of the copper hydroxide nanowire layer multiple times. The number of alternating spin-coating cycles is 4, and the total coating amount of polydimethylsiloxane solution is 10 mg / cm³. 2 The polymer was allowed to crosslink at room temperature for 20 hours, then dried in a vacuum oven to obtain an alternating polymer-nanofiber composite membrane. The surface SEM image of this alternating polymer-nanofiber composite membrane is shown below. Figure 3 As shown.

[0037] contrast Figure 1 and Figure 2 The SEM images show a significant reduction in membrane pore size, indicating that the substrate surface is covered by a layer of copper hydroxide nanowires. Figure 3As can be seen, the copper hydroxide nanowire layer is completely covered, and the surface of the coated polymer layer is smooth and without defects.

[0038] Example 2

[0039] A method for preparing an alternating composite membrane differs from Example 1 in that the amount of copper hydroxide nanowire solution added in step 2 is changed from 0.4 ml / cm². 2 Replace with 0.8ml / cm 2 Alternating polymer-nanofiber composite membranes were obtained.

[0040] Example 3

[0041] A method for preparing an alternating composite membrane differs from Example 1 in that the total coating amount of the polydimethylsiloxane solution in step 5 is reduced from 10 mg / cm³. 2 Replace with 20mg / cm 2 Alternating polymer-nanofiber composite membranes were obtained.

[0042] Example 4

[0043] A method for preparing an alternating composite membrane differs from Example 1 in that the number of alternating spin coating cycles in step 5 is changed from 4 to 8, and the standing crosslinking time is changed from 20h to 30h, resulting in an alternating polymer-nanofiber composite membrane.

[0044] Example 5

[0045] An alternating composite membrane preparation method differs from Example 1 in that the concentration of copper nitrate solution in step 1 is replaced from 4 mM / L to 6 mM / L, and the concentration of ethanolamine solution is replaced from 1.6 mM / L to 1.2 mM / L, to obtain an alternating polymer-nanofiber composite membrane.

[0046] Comparative Example 1

[0047] Preparation of polymer composite film: The polymer was dissolved in n-heptane to obtain a 10 wt% polymer solution. Tetraethyl orthosilicate and dibutyltin dilaurate were added, with a mass ratio of polymer to tetraethyl orthosilicate and dibutyltin dilaurate of 1:0.1:0.01. After stirring and mixing evenly, the mixture was allowed to stand for crosslinking to obtain a polydimethylsiloxane solution. The coating amount of the polydimethylsiloxane solution was 20 mg / cm². 2 The crosslinking time was 30 hours. The above polydimethylsiloxane solution was spin-coated onto the surface of the polyacrylonitrile support layer fixed on the spin coating sheet using a spin coater (KW-4A). The spin coating speed was (6s-200rpm, 40s-3000rpm). The mixture was then dried in a vacuum drying oven to obtain a polymer composite film.

[0048] Comparative Example 2

[0049] Preparation of polymer-nanofiber composite membrane: The polyacrylonitrile support layer was placed in a vacuum filtration apparatus, and the deposition rate was 0.8 ml / cm³. 2 The copper hydroxide nanowire solution obtained in step 1 of Example 1 was poured into the membrane and filtered. A copper hydroxide nanowire layer was deposited on the polyacrylonitrile support layer. After filtration, the membrane was removed and dried at room temperature, then fixed to a spin-coated sheet with tape for later use. The polymer was dissolved in n-heptane to obtain a 10 wt% polymer solution. Tetraethyl orthosilicate and dibutyltin dilaurate were added, with a mass ratio of polymer to tetraethyl orthosilicate and dibutyltin dilaurate of 1:0.1:0.01. After stirring and mixing evenly, the mixture was allowed to stand for crosslinking to obtain a polydimethylsiloxane solution. The coating amount of the polydimethylsiloxane solution was 20 mg / cm². 2 The crosslinking time was 30 h. The above polydimethylsiloxane solution was spin-coated onto the surface of the copper hydroxide nanowire layer using a spin coater (KW-4A) at a speed of (6 s-200 rpm, 40 s-3000 rpm). The mixture was then dried in a vacuum drying oven to obtain a polymer-nanofiber composite film.

[0050] Test case

[0051] The separation performance of propylene glycol monomethyl ether / water mixed solutions was tested using the alternating polymer-nanofiber composite membranes prepared in Examples 1-5, the polymer composite membrane prepared in Comparative Example 1, and the polymer-nanofiber composite membrane prepared in Comparative Example 2, respectively. Pervaporation separation performance was tested using a membrane separation device; the specific apparatus flow is as follows. Figure 4 As shown in the table below, the test results of each composite membrane were obtained at 40℃ with a propylene glycol monomethyl ether / water mass ratio of 1:99 in the feed solution:

[0052]

[0053] Among them, after 30 minutes of testing, the composite membrane of Comparative Example 1 was destroyed (membrane collapse); after 60 hours of testing, the composite membrane of Example 1 was destroyed; and after 120 hours of testing, the composite membranes of Examples 2-5 and Comparative Example 2 remained intact. As can be seen from the table above, the preparation process of the alternating polymer / nanofiber composite membrane of this invention is simple and controllable, the raw materials are readily available, the conditions are mild, and the stability is significantly improved compared to composite membranes prepared by directly coating polymers onto macroporous base membranes and nanofiber layers.

[0054] The above are merely embodiments of the present invention and do not limit the patent scope of the present invention. Any equivalent structures made using the contents of the present invention specification and drawings, whether directly or indirectly applied to other related technical fields, are similarly within the patent protection scope of the present invention.

Claims

1. A method for producing an alternating composite film, characterized by, It comprises the following steps: S1, preparing a nanofiber solution: uniformly mixing a metal salt solution and an ethanolamine solution, and standing at room temperature to obtain a nanofiber solution; S2, depositing a nanofiber layer: placing a porous support layer into a vacuum filtration device, pouring the nanofiber solution into the device for filtration, and depositing a nanofiber layer on the porous support layer to obtain a base film; after the filtration is completed, the base film is taken out and dried at room temperature; after drying, the base film is fixed on a spin-coating piece for use; S3, preparing a crosslinking agent / curing agent solution: dissolving a crosslinking agent and a curing agent in a solvent, uniformly stirring, and standing to obtain a crosslinking agent / curing agent solution; S4, preparing a polymer solution: dissolving a polymer in an organic solvent, uniformly stirring, and standing to obtain a polymer solution; S5, coating a polymer layer: continuously stirring the crosslinking agent / curing agent solution and the polymer solution at room temperature, using a spin coater, selecting a suitable rotation speed, and alternately spin-coating a certain amount of the polymer solution and the crosslinking agent / curing agent solution on the surface of the nanofiber layer multiple times, and standing for crosslinking at room temperature to obtain an alternating composite film, which is composed of a polymer-nanofiber interpenetrating layer and a porous support layer.

2. The production method according to claim 1, wherein In S1, the concentration of the metal salt solution is 4-6 mM / L, the concentration of the ethanolamine solution is 1.2-1.6 mM / L, the volume ratio of the metal salt solution to the ethanolamine solution is 1:1, and the metal salt solution is a copper nitrate solution.

3. The production method according to claim 1 or 2, characterized by, In S2, the deposition amount of the nanofiber solution is 0.4-0.8 ml / cm 2 , and the porous support layer is a polyacrylonitrile support layer.

4. The production method according to claim 1 or 2, wherein In S3, the crosslinking agent is tetraethyl orthosilicate, and the content of the crosslinking agent is 1 wt%; the curing agent is dibutyltin dilaurate, and the content of the curing agent is 0.1 wt%.

5. The production method according to claim 1 or 2, wherein In S4, the polymer is polydimethylsiloxane, and the concentration of the polymer solution is 5-20 wt%.

6. The production method according to claim 1 or 2, wherein In S5, the number of times of the alternate spin coating is 2-8 times, and the total coating amount of the polymer solution is 5-20 mg / cm 2 , and the time of the static cross-linking is 20-30 h.

7. The use of the alternating composite film prepared by the preparation method of any one of claims 1-6 in organic solvent dehydration.

8. Use according to claim 7, wherein the compound is ###0002### The organic solvent is a propylene glycol monomethyl ether mixed solution, the feed content of the propylene glycol monomethyl ether mixed solution is 0.5-5wt%, the feed temperature is 10-60 o C.

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