A fluoride-modified pervaporation membrane and a preparation method and application thereof

Abstract

The application relates to a fluoride-modified pervaporation membrane and a preparation method and application thereof, and belongs to the field of membrane separation technology. The fluoride-modified pervaporation membrane comprises a support layer and a selection layer; the selection layer is a fluoride-modified aminated polydimethylsiloxane membrane, the fluoride-modified aminated polydimethylsiloxane membrane takes a siloxane bond as a main chain, and fluoride is connected with amine groups on side chains of the polydimethylsiloxane membrane through an amide bond. The prepared fluoride-modified pervaporation membrane has high separation performance on ethanol, the separation factor of the fluoride-modified pervaporation membrane can reach 5.66-8.14, the permeation flux is 727-8528 g.m ‑2 ·h ‑1 .

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of membrane separation technology, more specifically, relates to a fluoride-modified pervaporation membrane and a preparation method and application thereof, in particular to a fluoride-modified polydimethylsiloxane pervaporation membrane with high permeation flux and separation factor. BACKGROUND

[0002] Clean and renewable bioethanol produced by biomass fermentation has great prospects for solving the existing energy crisis. However, the recovery of bioethanol from fermentation broth still faces great challenges due to the relatively low recovery rate. Membrane-based pervaporation technology, as an advanced separation technology, has the potential to efficiently recover bioethanol from fermentation broth. The core part of the pervaporation technology is the membrane with high permeability and selective transport properties. Therefore, designing a membrane with high separation efficiency is the key to achieving efficient recovery of bioethanol.

[0003] Currently, polydimethylsiloxane (PDMS) has been widely studied as a membrane material for alcohol and water separation. However, traditional PDMS membranes have low separation factors and extremely poor flux, making them unsuitable for industrial applications. In order to improve the permeability of PDMS membranes, researchers have explored different crosslinking agents, changing PDMS side groups, adding ZIFs particles, etc. to improve permeation flux and separation factor. However, due to trade-off effects, defects, etc., the application of these membrane materials still has challenges. Therefore, there is an urgent need to develop a membrane material that is easy to prepare, increases flux, and improves separation factor.

[0004] Patent No. CN202011199011 discloses a method of using siloxane containing fluorine groups to crosslink with PDMS to form a selective layer, the fluorine groups are selected from at least one of -F, -CF3, -C2H4CF3, etc. The chain segment of PDMS is at least one of The membrane mainly uses the hydrophobicity of the -F group to further improve the separation performance. The separation factor of the prepared membrane material is between 7-12, and the permeation flux is between 300-800 g·m -2 ·h -1 .

[0005] Currently, the separation factor of PDMS membrane material used for alcohol and water separation is generally between 6-7, and the permeation flux is between 1000 g·m -2 ·h -1 The flux and separation factor are low. Therefore, it is necessary to further explore effective methods to improve the separation factor and flux. SUMMARY

[0006] The present application solves the technical problem of low permeation flux and molecular factor of the pervaporation membrane in the prior art, and provides a fluoride-modified pervaporation membrane, wherein the selective layer is a fluoride-modified aminated polydimethylsiloxane membrane, the fluoride-modified aminated polydimethylsiloxane membrane has a siloxane bond as a main chain, and the fluoride is connected to the amine group on the side chain of the polydimethylsiloxane membrane through an amide bond.

[0007] According to a first aspect of the present application, a fluoride-modified aminated polydimethylsiloxane pervaporation membrane is provided, which comprises a support layer and a selective layer; the selective layer is a fluoride-modified aminated polydimethylsiloxane membrane, the fluoride-modified aminated polydimethylsiloxane membrane has a siloxane bond as a main chain, and the fluoride is connected to the uncrosslinked amine group on the side chain of the aminated polydimethylsiloxane through an amide bond.

[0008] Preferably, the fluoride has a structural formula of X-CO-R, wherein R is a fluorinated alkyl chain or a cyclic group, and X is a halogen.

[0009] Preferably, the X is Cl or Br.

[0010] Preferably, the support layer is a microfiltration membrane.

[0011] Preferably, the microfiltration membrane is a polyvinylidene fluoride membrane.

[0012] According to another aspect of the present application, a preparation method of any one of the fluoride-modified aminated polydimethylsiloxane pervaporation membranes is provided, which comprises the following steps:

[0013] (1) a casting solution, which is a crosslinking solution of an aminated polydimethylsiloxane solution and a crosslinking agent hexamethylene diisocyanate solution, is coated on a base membrane as a support layer;

[0014] (2) after film formation, a fluoride solution is added for modification, the fluoride is connected to the amine group on the side chain of the polydimethylsiloxane membrane through an amide bond, and thus the fluoride-modified polydimethylsiloxane pervaporation membrane is obtained.

[0015] Preferably, the fluoride has a structural formula of X-CO-R, wherein R is a fluorinated alkyl chain or a cyclic group, and X is a halogen.

[0016] Preferably, the modification time is less than or equal to 60 seconds.

[0017] Preferably, the preparation method of the base membrane comprises the following steps:

[0018] (1) polyvinylidene fluoride, triethyl phosphate, polyvinylpyrrolidone and N-methyl pyrrolidone are mixed to obtain a homogeneous casting solution;

[0019] (2) the casting solution obtained in step (1) is coated on a substrate, then soaked in a water coagulation bath, after removing the remaining triethyl phosphate, polyvinylpyrrolidone and N-methyl pyrrolidone, the substrate is freeze-dried to obtain the base film.

[0020] According to another aspect of the present application, the application of the fluoride-modified aminated polydimethylsiloxane pervaporation membrane according to any one of the above aspects is used for separating alcohol from a mixture of alcohol and water.

[0021] Preferably, the separation temperature is 25-60℃.

[0022] Overall, compared with the prior art, the above technical solutions conceived by the present application mainly have the following technical advantages:

[0023] (1) The fluoride-modified polydimethylsiloxane membrane preparation method provided by the present application uses a new type of aminated polydimethylsiloxane (MAPDMS) and hexamethylene diisocyanate (HDI) as a crosslinking agent to form a film, and a fluorine-containing pervaporation membrane material is designed by modifying the amine groups on the surface of the film and in the film which do not participate in crosslinking. The fluorine-containing pervaporation membrane prepared by the present application helps to destroy the ethanol-water cluster structure and improve the separation performance of the membrane for ethanol aqueous solution, because of the strong hydrogen bond interaction between the introduced fluorine and water. When the fluoride-modified MAPDMS pervaporation membrane of the present application separates an ethanol aqueous solution with a concentration of 5wt.% at a temperature of 25-80℃, the separation factor can reach 5.66-8.14, and the permeation flux is 727-8528 g·m -2 ·h -1 .

[0024] (2) For pervaporation technology, the separation of small molecules can be explained by the dissolution and diffusion mechanism, and the dissolution process is mainly related to the affinity between the surface groups of the membrane and the substances to be separated. Based on the above principle, the present application introduces fluorine into the surface and interior of the separation membrane, not only to improve the separation performance and flux of the membrane for ethanol aqueous solution by using its strong hydrophobicity, but more importantly, to break the hydrogen bonds between ethanol and water by using the stronger hydrogen bond interaction between the fluorine-containing groups and water, thereby destroying the cluster structure and achieving the improvement of the separation factor of the membrane for organic aqueous solution such as ethanol aqueous solution.

[0025] (3) Compared with the traditional PDMS membrane, the fluorine-containing pervaporation membrane prepared by the application has strong hydrophobicity and more free body, which helps to improve the separation factor and permeation flux. The traditional PDMS membrane is prepared by using hydroxyl group as the end group of polydimethylsiloxane (PDMS) as the main film forming body, which is crosslinked with the crosslinking agent tetraethyl orthosilicate (TEOS) under the action of the catalyst dibutyltin dilaurate (DBTL). The essence of the above crosslinking process is the high molecular polymerization reaction between the hydroxyl group in PDMS and the ester group in TEOS. In the application, hexamethylene diisocyanate (HDI) is used as the crosslinking agent, and no catalyst is needed for crosslinking compared with TEOS. The surface of the polydimethylsiloxane membrane formed after crosslinking is modified by fluoride, and the fluoride is selected from X-CO-R, R is a fluorinated alkyl long chain or cyclic group, and X is halogen.

[0026] (4) The main chain of the fluorine-containing pervaporation membrane prepared by the application is still a hydrophobic Si-O-Si main chain, so that the prepared membrane still has strong stability and flexibility. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 is a schematic diagram of the traditional polydimethylsiloxane film forming mechanism.

[0028] Figure 2 is a schematic diagram of the structure mechanism of the fluorine-containing pervaporation membrane of the application.

[0029] Figure 3 is a schematic diagram of the preparation process mechanism of the fluorine-containing pervaporation membrane of the application.

[0030] Figure 4 is the FT-IR characterization of the MAPDMS-HDI-F15 membrane, which proves that F15 successfully modifies the MAPDMS-HDI membrane.

[0031] Figure 5 is the thermogravimetric analysis diagram of MAPDMS-HDI-F15-x(s), which proves that the degradation amount is different under different F15 modification times.

[0032] Figure 6 is the benchmark diagram of MAPDMS-HDI-F15-x(s), which shows that the membrane prepared by the application has better performance compared with other preparation methods. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical scheme and advantages of the application clearer, the application will be further described in detail below in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the application and do not limit the application. In addition, the technical features involved in each embodiment of the application described below can be combined with each other as long as they do not conflict with each other.

[0034] The present application discloses a fluoride-modified polydimethylsiloxane pervaporation membrane, which comprises a support layer and a selective layer, wherein the support layer is a microfiltration membrane, and the selective layer is a fluoride-modified aminated polydimethylsiloxane membrane; the fluoride-modified aminated polydimethylsiloxane membrane takes a siloxane bond as a main chain, fluorides are on side chains, and the fluorides are connected to amine groups on the side chains of the polydimethylsiloxane membrane through amide bonds.

[0035] In some embodiments, the fluorides are selected from X-CO-R, R is a fluorinated alkyl long chain or a cyclic group, and X is Cl or Br halogen.

[0036] In some embodiments, the aminated polydimethylsiloxane (MAPDMS) is The modified structure is

[0037]

[0038] In some embodiments, the microfiltration membrane is a polyvinylidene fluoride membrane (PVDF).

[0039] The fluoride-modified polydimethylsiloxane membrane in the present application has a separation factor of 5.66-8.14 and a permeation flux of 727-8528 g·m-2·h-1 when separating an ethanol aqueous solution with a concentration of 5 wt.% at 25-80 ℃. -2 ·h -1 .

[0040] The present application discloses a preparation method of a fluoride-modified polydimethylsiloxane membrane, which comprises the following steps:

[0041] (1) Preparing a casting solution: crosslinking an aminated polydimethylsiloxane solution with a hexamethylene diisocyanate (HDI) solution, and stopping further crosslinking of the HDI when the crosslinking concentration reaches about 34 m·Pa·s;

[0042] (2) Preparing a polydimethylsiloxane membrane: coating the casting solution on a base film as a support layer, and placing the base film in an atmospheric environment to react at a film-forming temperature of 40-60 ℃ for 12 h to form a film;

[0043] (3) Preparing a fluoride-modified polydimethylsiloxane membrane: evenly spreading the polydimethylsiloxane membrane in a plate frame, and performing surface modification with different concentrations of fluoride solutions or for different times.

[0044] In some embodiments, the solvent used for preparing the fluoride-modified polydimethylsiloxane membrane is n-hexane.

[0045] In some embodiments, the casting solution of step (1) is prepared by mixing polydimethylsiloxane and solvent in a mass ratio of 1:10, and crosslinking agent and solvent in a mass ratio of 1:100.

[0046] In some embodiments, the base membrane is polyvinylidene fluoride (PVDF), and the method for preparing the base membrane comprises the following steps:

[0047] (1) PVDF casting solution preparation: PVDF, triethyl phosphate (TEP), polyvinylpyrrolidone (PVP, Mn = 24000 g / mol) and N-methylpyrrolidone (NMP) were mixed in a flask and stirred at 80°C for 24 h to obtain a homogeneous casting solution; the casting solution was left at room temperature for 48 h to remove air bubbles;

[0048] (2) PVDF base membrane preparation: the casting solution was coated onto a polyester non-woven fabric using a 150 μιη thick doctor blade, and the coated PVDF base membrane was immediately immersed in a room temperature water coagulation bath, with the deionized water changed every 6 h, and the immersion time being 48 h to completely remove TEP, PVP and NMP from the PVDF base membrane; finally, the PVDF base membrane was freeze-dried.

[0049] In some embodiments, the casting solution is prepared by mixing PVDF, TEP, PVP and NMP in a mass ratio of 18:30:6:46.

[0050] In some embodiments, the PVDF powder in the present application is dried at 80°C under vacuum for 12 hours before use. PVDF casting solution is prepared using PVDF (18 wt.%), PVP (6 wt.%), TEP (30 wt.%) and NMP (46 wt.%). After removing air bubbles, the casting solution is coated onto a polyester non-woven fabric using a 200 μιη doctor blade, and then transferred to a water bath for non-solvent induced phase separation (NIPS). To further remove NMP, PVP and TEP from the membrane, the PVDF deionized water is changed in time, and the immersion time is more than 12 hours, and finally the PVDF support membrane is obtained by freeze-drying.

[0051] Example 1

[0052] Under rapid stirring, a solution of HDI (1 wt.%) in n-hexane was slowly added to a solution of MAPDMS (10 wt.%). The pouring solution of 2.4 mL HDI solution reached a suitable viscosity (34.2 m·Pa·s). A 100 μιη blade was used to pour onto the PVDF base membrane. Subsequently, the membrane was placed in a graphene heating plate at 40°C for drying and further crosslinking reaction to form a MAPDMS-HDI membrane, whose crosslinking mechanism is completely different from that of the traditional crosslinking agent tetraethyl orthosilicate (TEOS) and polydimethylsiloxane (PDMS), as shown in Figure 1 and Figure 2 respectively.Figure 3 is a schematic diagram of the preparation process mechanism of the fluorine-containing pervaporation membrane of embodiment 1.

[0053] Application test

[0054] The MAPDMS-HDI membrane was immersed in a 10wt.% perfluorooctanoyl chloride (F15) solution for 0s, 15s, 30s, 45s and 60s, respectively, to form F15-x membranes, and the specific modification process is as shown in Figure 2 It was found by FTIR( Figure 4 ) that the absorption peak of the carbonyl group (C=O) after F15 modification was red-shifted, and the absorption peak of the C-F bond appeared after the modification of the MAPDMS-HDI membrane, indicating that the MAPDMS-HDI membrane was successfully modified. It was found by thermogravimetric graph( Figure 5 ) that as the F15 grafting time increased, the degradation amount of the membrane at about 200℃ gradually increased, which was due to the thermal decomposition of the amide bond in the membrane, and after the degradation equilibrium (after 700℃), the final remaining amount increased, indicating that F15 was successfully introduced. The pervaporation performance data are shown in Table 1 and Table 2. Table 1 is the separation performance of different modification times, and Table 2 is the separation performance at different temperatures. By observing Table 1, it was found that as the modification time increased, the permeation flux first increased and then decreased, and the separation factor gradually increased. By observing Table 2, it was found that as the temperature increased, the permeation flux gradually increased, and the separation factor first increased and then decreased.

[0055] The separation performance of the F15 modified membrane material was best at a time of 45s and a test temperature of 60℃, with a permeation flux of 4584.07g·m -2 ·h -1 and a separation factor of 8.14, as shown in Figure 6 .

[0056] Table 1

[0057]

[0058] Table 2

[0059]

[0060] Those skilled in the art will readily understand that the above description is only the preferred embodiment of the present application and is not intended to limit the present application, and any modifications, equivalent replacements and improvements made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A fluoride-modified aminosilicone pervaporation membrane, characterized in that, The fluoride-modified aminosilicone pervaporation membrane comprises a support layer and a selection layer; the selection layer is a fluoride-modified aminosilicone membrane, the fluoride-modified aminosilicone membrane takes a siloxane bond as a main chain, and the fluoride is connected to an uncrosslinked amine group on a side chain of the aminosilicone through an amide bond.

2. The fluoride-modified aminosiloxane pervaporation membrane of claim 1, wherein, The fluoride has a structural formula of X-CO-R, wherein R is a fluorinated alkyl chain or a cyclic group, and X is a halogen.

3. The fluoride-modified aminosiloxane pervaporation membrane of claim 2, wherein, The X is Cl or Br.

4. The fluoride-modified aminosiloxane pervaporation membrane according to any one of claims 1 to 3, wherein, The support layer is a microfiltration membrane. The microfiltration membrane is a polyvinylidene fluoride membrane.

5. Process for the preparation of a fluorinated amine-based polydimethylsiloxane pervaporation membrane according to any one of claims 1 to 4, characterized in that, The method comprises the following steps: (1) coating a casting solution, which is a crosslinking solution of an aminosilicone solution and a crosslinking agent hexamethylene diisocyanate solution, on a base film as the support layer; (2) after film formation, adding a fluoride solution for modification, and connecting the fluoride to the amine group on the side chain of the polysilicone membrane through an amide bond, to obtain the fluoride-modified polysilicone pervaporation membrane.

6. The production method according to claim 5, wherein The fluoride has a structural formula of X-CO-R, wherein R is a fluorinated alkyl chain or a cyclic group, and X is a halogen.

7. The production method according to claim 5 or 6, characterized by, The modification time is less than or equal to 60 seconds.

8. The production method according to claim 5 or 6, wherein The preparation method of the base film comprises the following steps: (1) uniformly mixing polyvinylidene fluoride, triethyl phosphate, polyvinylpyrrolidone and N-methylpyrrolidone to obtain a homogeneous casting solution; (2) coating the casting solution obtained in step (1) on a substrate, then soaking in a water coagulation bath, removing the remaining triethyl phosphate, polyvinylpyrrolidone and N-methylpyrrolidone, and then freeze-drying to obtain the base film.

9. Use of a fluoride-modified aminosiloxane polydimethylsiloxane pervaporation membrane according to any one of claims 1 to 4, characterized in that, Application for separating alcohol from a mixture of alcohol and water.

10. Use according to claim 9, wherein The separation temperature is 25-60 DEG C.

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