Fluoride-modified metal ion cross-linked pervaporation membranes, preparation and use thereof

Abstract

This invention relates to a fluoride-modified metal ion crosslinked pervaporation membrane, its preparation, and its application, belonging to the field of membrane separation. The pervaporation membrane of this invention uses a fluoride-modified metal ion crosslinked amino-modified polydimethylsiloxane membrane as its selective layer. The transition metal ions are crosslinked with the amino groups on the side chains of the polydimethylsiloxane membrane via coordination bonds. The fluoride modification involves the fluoride being linked to the uncrosslinked amino groups on the side chains of the amino-modified polydimethylsiloxane membrane via amide bonds. The fluoride-modified pervaporation membrane prepared by this invention exhibits high separation performance for organic alcohols. Specifically, when the MAPDMS pervaporation membrane crosslinked with cobalt and copper ions separates a 5 wt.% ethanol aqueous solution at 60°C, the modified separation factor and permeate flux are preferably 13.17 and 11.77, respectively, with a flux of 3907.73 g·m³. ‑2 ·h ‑1 and 4090.95 g·m ‑2 ·h ‑1 .

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of membrane separation, more particularly, relates to a fluoride-modified metal ion cross-linked pervaporation membrane, preparation and application, especially to a fluoride-modified metal ion cross-linked 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 an organicophilic membrane material for ethanol recovery. However, traditional PDMS membranes have low separation factor and extremely poor flux, which are not suitable for industrial applications. In order to improve the permeability of PDMS membranes, researchers have explored different cross-linking agents, changing the PDMS side groups, adding ZIFs particles, etc. to improve the permeation flux and separation factor. However, due to the trade-off effect, 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 CN112246111A discloses a method for preparing a metal-organic framework (MOF) membrane. First, a PDMS / PSf membrane is immersed in an aqueous PVA solution or an aqueous PVA solution containing metal ions for a first immersion and drying. The resulting PDMS / PSf membrane with a PVA layer is then immersed in an aqueous metal salt solution for a second immersion and drying. Finally, the resulting PDMS / PSf membrane with a metal ion-modified PVA layer is immersed in an aqueous ligand solution for a third immersion to allow the ligands to bind with the metal ions. After drying, washing, and further drying, the final MOF membrane is obtained. This entire preparation process is carried out in aqueous solution, making it environmentally friendly. The resulting MOF membrane has a dense surface, a thickness of 80-350 nm, and exhibits excellent CO2 permeability and CO2 / N2 selectivity. Patent CN110508166A discloses a method for grafting a silane coupling agent containing active epoxy functional groups onto the surface of a polydimethylsiloxane (PDMS) composite membrane, followed by ring-opening of the epoxy groups under alkaline conditions to covalently bind a multidentate chelating agent onto the membrane. The multidentate chelating property of the chelating agent chelates metal ions onto the surface of the PDMS composite membrane, thus preparing a metal ion-modified PDMS composite membrane. The pervaporation desulfurization membrane prepared by this method is simple to prepare, and its mechanical properties, thermal stability, and swelling properties are significantly improved, resulting in a significant improvement in the membrane's desulfurization performance.

[0005] Currently, the most commonly used PDMS membranes for preferential alcohol permeation typically have a separation factor between 6 and 7, and a permeation flux of 1000 g·m³. -2 ·h -1 The flux and separation factor are low. Therefore, further exploration is needed to find effective methods to improve the separation factor and flux. Summary of the Invention

[0006] This invention solves the technical problem of low permeation flux and molecular factor in existing pervaporation membranes by providing a fluoride-modified metal ion crosslinked pervaporation membrane. The pervaporation membrane of this invention comprises a support layer and a selective layer; the selective layer is a fluoride-modified metal ion crosslinked amino-modified polydimethylsiloxane membrane. The metal ion crosslinked amino-modified polydimethylsiloxane membrane is obtained by coordinating metal ions with amino groups on the side chains of polydimethylsiloxane. The fluoride modification involves connecting the fluoride with the uncrosslinked amino groups on the side chains of the amino-modified polydimethylsiloxane membrane via amide bonds. The pervaporation membrane provided by this invention exhibits high permeation flux and selectivity.

[0007] According to a first aspect of the invention, a fluoride-modified metal ion crosslinked pervaporation membrane is provided, the pervaporation membrane comprising a support layer and a selective layer; the selective layer is a fluoride-modified metal ion crosslinked aminodimethylsiloxane membrane, the metal ion crosslinked aminodimethylsiloxane membrane being obtained by crosslinking metal ions with amino groups on the side chains of polydimethylsiloxane via coordination bonds, and the fluoride modification being that the fluoride is connected to the uncrosslinked amino groups on the side chains of the aminodimethylsiloxane membrane via amide bonds.

[0008] Preferably, the metal ion is a transition metal ion.

[0009] Preferably, the transition metal ion is a cobalt ion, copper ion, zinc ion, iron ion, chromium ion, or cadmium ion.

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

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

[0012] Preferably, the fluoride has the structural formula X-CO-R, where R is a fluorinated alkyl long chain or cyclic group, and X is a halogen.

[0013] According to another aspect of the present invention, a method for preparing any one of the fluoride-modified metal ion crosslinked pervaporation membranes is provided, comprising the following steps:

[0014] (1) Crosslinking an amino-modified polydimethylsiloxane solution with a transition metal ion solution to obtain a casting solution;

[0015] (2) The casting solution obtained in step (1) is scraped onto the base membrane as a support layer. After the membrane is formed, a fluoride solution is added for modification. The fluoride is connected to the uncrosslinked amine groups on the side chain of the amino-modified polydimethylsiloxane membrane through amide bonds, thus obtaining the fluoride-modified metal ion crosslinked pervaporation membrane.

[0016] Preferably, the transition metal ion is a cobalt ion, copper ion, zinc ion, iron ion, chromium ion, or cadmium ion;

[0017] Preferably, the fluoride has the structural formula X-CO-R, where R is a fluorinated alkyl long chain or cyclic group, and X is a halogen.

[0018] Preferably, in step (2), the modification time is less than or equal to 45 seconds.

[0019] Preferably, the method for preparing the base film includes the following steps:

[0020] (1) After mixing polyvinylidene fluoride, triethyl phosphate, polyvinylpyrrolidone and N-methylpyrrolidone, a homogeneous casting solution is obtained.

[0021] (2) The casting solution obtained in step (1) is scraped onto the substrate, then immersed in a water coagulation bath to remove the remaining triethyl phosphate, polyvinylpyrrolidone and N-methylpyrrolidone, and then freeze-dried to obtain the base film.

[0022] According to another aspect of the invention, the application of the fluoride-modified metal ion crosslinked pervaporation membrane described in any one of the claims is provided for the separation of alcohol from a mixture of alcohol and water.

[0023] In summary, compared with the prior art, the above-described technical solutions conceived by this invention mainly possess the following technical advantages:

[0024] (1) The method for preparing metal-crosslinked polydimethylsiloxane membranes provided by this invention uses novel amination-modified polydimethylsiloxane (MAPDMS) and metal ions as crosslinking agents to form the membrane, and designs a pervaporation membrane material with higher flexibility than covalent bonds. The metal-crosslinked membrane prepared by this invention, due to the strong hydrogen bonding between the introduced fluorine and water, helps to disrupt the cluster structure of organic solvents and water such as ethanol-water, thereby improving the membrane's separation performance for ethanol-water solutions.

[0025] (2) For pervaporation technology, the separation of small molecules can be explained by the dissolution-diffusion mechanism. The dissolution process mainly includes adsorption on the upper surface of the membrane, diffusion within the membrane, and desorption on the lower surface of the membrane. Compared with covalent bonds, metal ion coordination bonds have greater flexibility between molecules and a faster diffusion rate, thus resulting in a larger permeation flux.

[0026] (3) Traditional PDMS membranes use polydimethylsiloxane (PDMS) with hydroxyl-terminated groups as the main film-forming component, which is cross-linked with tetraethyl orthosilicate (TEOS) under the action of the catalyst dibutyltin dilaurate (DBTL). The essence of the above cross-linking process is a polymer polymerization reaction between the hydroxyl groups in PDMS and the ester groups in TEOS. In contrast, the present invention uses metal ions as the cross-linking agent, which does not require a catalyst compared to TEOS cross-linking, and is inexpensive and readily available. Compared with traditional PMDS membranes, the fluorinated pervaporation membrane prepared by the present invention has strong hydrophobicity and higher flexibility, which helps to improve the separation factor and permeate flux.

[0027] (4) When the MAPDMS pervaporation membrane of the present invention, which is crosslinked with cobalt ions and copper ions, separates 5 wt.% ethanol aqueous solution at a temperature of 60°C, the separation factors are 7.26 and 5.38, respectively, and the permeation flux is 2127.83 g·m⁻¹. -2 ·h -1 and 3576.95 g·m -2 ·h -1The best pervaporation membrane modified with perfluorooctanoyl chloride (F15) had a separation factor of 13.17 and a permeation flux of 11.77, and a permeation flux of 3907.73 g·m³. -2 ·h -1 and 4090.95 g·m -2 ·h -1 .

[0028] (5) The main chain of the fluorine-containing pervaporation membrane prepared by the present invention is still a hydrophobic Si-O-Si main chain, which makes the membrane still have strong stability and flexibility. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the structural mechanism of cross-linking of metal ions with amino-modified polydimethylsiloxane to form a film.

[0030] Figure 2 This is a schematic diagram illustrating the preparation of the fluoride-modified metal ion crosslinked amino-modified polydimethylsiloxane membrane of the present invention.

[0031] Figure 3 XPS characterization of the MAPDMS-Co(II) membrane demonstrates that Co(II) ions successfully crosslink the MAPDMS polymer.

[0032] Figure 4 The thermogravimetric analysis (TGA) diagrams of MAPDMS polymer, MAPDMS-Cu(II) membrane, and MAPDMS-Co(II) membrane demonstrate that the metal ions are successfully cross-linked with MAPDMS, and that the cross-linking strength varies among different metal ions.

[0033] Figure 5 The FT-IR characterization of the MAPDMS-Co(II)-F15 membrane proves that F15 successfully modified the MAPDMS-Co(II) membrane.

[0034] Figure 6 XPS characterization of the MAPDMS-Cu(II) membrane demonstrates that Cu(II) ions successfully crosslink the MAPDMS polymer.

[0035] Figure 7 The FT-IR characterization of the MAPDMS-Cu(II)-F15 membrane proves that F15 successfully modified the MAPDMS-Cu(II) membrane.

[0036] Figure 8 This is a schematic diagram of the film-forming mechanism of traditional polydimethylsiloxane. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0038] The present invention provides a fluoride-modified metal ion crosslinked pervaporation membrane, comprising a support layer and a selective layer. The separation layer is a fluoride-modified metal ion crosslinked aminodimethylsiloxane membrane. The fluoride is selected from X-CO-R, where R is a fluorinated alkyl long-chain or cyclic group, and X is a Cl or Br halogen. The aminodimethylsiloxane (MAPDMS) has the following structural formula:

[0039] The fluoride-modified metal ion crosslinked amino-modified polydimethylsiloxane membrane has a silicon-oxygen bond as its main chain. The membrane is crosslinked with the amino groups on the side chains of polydimethylsiloxane via coordination bonds between metal ions and each other. The specific reaction process is as follows: Figure 1 As shown, Figure 8 This is a schematic diagram of the film-forming mechanism of traditional polydimethylsiloxane.

[0040] In this invention, the fluoride is linked to the amine group on the side chain of the polydimethylsiloxane membrane via an amide bond. Figure 2 This is a schematic diagram illustrating the preparation of the fluoride-modified metal ion crosslinked amino-dimethylsiloxane membrane of the present invention.

[0041] Furthermore, the microfiltration membrane is a polyvinylidene fluoride (PVDF) membrane.

[0042] In some embodiments, the transition metal ions are cobalt ions, copper ions, zinc ions, iron ions, chromium ions, cadmium ions, etc.

[0043] In this invention, the chemically modified metal crosslinked pervaporation membrane is a selective layer, and its preparation method includes the following steps:

[0044] (1) Preparation of casting solution: crosslinking polydimethylsiloxane solution with transition metal ion solution;

[0045] (2) Preparation of metal ion crosslinking membrane: The casting solution is scraped onto the base membrane and placed in an atmospheric environment. After reacting at a film-forming temperature of 40-60℃ for 12 hours, the membrane can be formed.

[0046] (3) Preparation of pervaporation membrane: The polydimethylsiloxane membrane is spread flat on the plate frame and surface modified by using fluoride solutions of different concentrations or for different times.

[0047] In some embodiments, the base film is polyvinylidene fluoride (PVDF), and its preparation method includes the following steps:

[0048] (1) Preparation of PVDF casting solution: 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;

[0049] (2) Preparation of PVDF base film: The casting solution was coated onto the polyester nonwoven fabric with a 150μm thick doctor blade. The coated PVDF base film was immediately immersed in a room temperature water coagulation bath. The deionized water was changed every 6 hours and the film was soaked for 48 hours to completely remove TEP, PVP and NMP from the PVDF base film. Finally, the PVDF base film was freeze-dried.

[0050] In this invention, the solvent used to prepare the selective layer of the metal crosslinked pervaporation membrane is tetrahydrofuran.

[0051] In this invention, the casting solution of the fluoride-modified metal crosslinked pervaporation membrane is formulated as follows: the mass ratio of polydimethylsiloxane to solvent is 1:10, and the molar ratio of crosslinking agent to amino group content in MAPDMS is 1:2.

[0052] In this invention, the crosslinking agent is a transition metal ion.

[0053] In this invention, the polydimethylsiloxane is MAPDMS.

[0054] In this invention, the PVDF casting solution is formulated as follows: the mass ratio of PVDF:TEP:PVP:NMP is 18:30:6:46.

[0055] In this invention, the film-forming temperature of the selective layer is preferably 40-60℃.

[0056] Example 1

[0057] PVDF powder was dried under vacuum at 80°C for 12 hours before use. A PVDF casting solution was prepared using PVDF (18 wt.%), PVP (6 wt.%), TEP (30 wt.%), and NMP (46 wt.%). After removing air bubbles, the casting solution was coated onto a polyester nonwoven fabric using a 200 μm doctor blade, and then transferred to a water bath for solvent-inducing phase separation (NIPS). To further remove NMP, PVP, and TEP from the membrane, the PVDF was promptly replaced with deionized water and soaked for at least 12 hours. Finally, the PVDF supported membrane was obtained by freeze-drying.

[0058] Under rapid stirring, 0.03 mM / g Co2+ A tetrahydrofuran solution was slowly added to a MAPDMS (10 wt.%) solution to achieve a suitable viscosity. The solution was then coated onto a PVDF substrate using a 100 μm blade. Subsequently, the membrane was placed on a graphene heating plate at 40 °C for drying and further crosslinking to form a MAPDMS-Co(II) membrane. XPS characterization revealed that… Figure 3 Cobalt ions successfully coordinated with N atoms; furthermore, TGA characterization showed that... Figure 4 The comparison between the MAPDMS-Co(II) membrane and MAPDMS further demonstrates that cobalt ions are successfully crosslinked with MAPDMS.

[0059] MAPDMS-Co(II) membranes were immersed in a 10 wt.% perfluorooctanoyl chloride (F15) solution for 0 s, 15 s, 30 s, 45 s, and 60 s, respectively, to form MAPDMS-Co(II)-F15-x membranes. FTIR characterization revealed that... Figure 5 The sample was successfully modified with F15 at different modification times. Its specific performance values ​​were obtained through pervaporation performance testing, and the data are shown in Table 1. With increasing modification time, the flux gradually increased, while the separation factor showed a trend of first increasing and then decreasing. The optimal performance was achieved at a modification time of 45 s, with a performance of 3609.27 g·m³. -2 ·h -1 , 10.49.

[0060] Table 1

[0061]

[0062] Example 2

[0063] The PVDF base film is as described above.

[0064] Under rapid stirring, 0.03 mM / g Cu 2+ A tetrahydrofuran solution was slowly added to a MAPDMS (10 wt.%) solution to achieve a suitable viscosity. The solution was then coated onto a PVDF substrate using a 100 μm blade. Subsequently, the membrane was placed on a graphene heating plate at 40 °C for drying and further crosslinking to form a MAPDMS-Co(II) membrane. XPS characterization revealed… Figure 6 Copper ions successfully coordinated with N atoms; furthermore, TGA characterization showed that... Figure 4 The comparison between the MAPDMS-Cu(II) membrane and MAPDMS further demonstrates that copper ions successfully crosslink with MAPDMS.

[0065] MAPDMS-Co(II) membranes were immersed in a 10 wt.% perfluorooctanoyl chloride (F15) solution for 0 s, 15 s, 30 s, 45 s, and 60 s, respectively, to form MAPDMS-Cu(II)-F15-y membranes. FTIR characterization revealed... Figure 7 The sample was successfully modified with F15 at different modification times. Its specific performance values ​​were obtained through pervaporation performance testing, and the data are shown in Table 2. With increasing modification time, the flux gradually decreased, then increased sharply; the separation factor showed a trend of first increasing and then decreasing. The optimal performance was achieved at a modification time of 30 s, with a performance of 2754.29 g·m³. -2 ·h -1 , 9.85.

[0066] Table 2

[0067]

[0068] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A fluoride-modified metal ion crosslinked pervaporation membrane, characterized in that, The pervaporation membrane includes a support layer and a selective layer; the selective layer is a fluoride-modified metal ion crosslinked amino-modified polydimethylsiloxane membrane, which is obtained by crosslinking metal ions with amino groups on the side chains of polydimethylsiloxane via coordination bonds, and the fluoride modification is achieved by connecting fluoride with uncrosslinked amino groups on the side chains of the amino-modified polydimethylsiloxane membrane via amide bonds.

2. The fluoride-modified metal ion crosslinked pervaporation membrane as described in claim 1, characterized in that, The metal ions are transition metal ions.

3. The fluoride-modified metal ion crosslinked pervaporation membrane as described in claim 2, characterized in that, The transition metal ions are cobalt ions, copper ions, zinc ions, iron ions, chromium ions, or cadmium ions.

4. The fluoride-modified metal ion crosslinked pervaporation membrane as described in claim 1, characterized in that, The support layer is a microfiltration membrane.

5. The fluoride-modified metal ion crosslinked pervaporation membrane as described in claim 4, characterized in that, The microfiltration membrane is a polyvinylidene fluoride membrane.

6. The fluoride-modified metal ion crosslinked pervaporation membrane as described in claim 1, characterized in that, The fluoride has the structural formula X-CO-R, where R is a fluorinated alkyl long chain or cyclic group, and X is a halogen.

7. The method for preparing a fluoride-modified metal ion crosslinked pervaporation membrane according to any one of claims 1-6, characterized in that, Includes the following steps: (1) Crosslinking an amino-modified polydimethylsiloxane solution with a transition metal ion solution to obtain a casting solution; (2) The casting solution obtained in step (1) is scraped onto the base membrane as a support layer. After the membrane is formed, a fluoride solution is added for modification. The fluoride is connected to the uncrosslinked amine groups on the side chain of the amino-modified polydimethylsiloxane membrane through amide bonds, thus obtaining the fluoride-modified metal ion crosslinked pervaporation membrane.

8. The preparation method according to claim 7, characterized in that, The transition metal ions are cobalt ions, copper ions, zinc ions, iron ions, chromium ions, or cadmium ions.

9. The preparation method according to claim 8, characterized in that, The fluoride has the structural formula X-CO-R, where R is a fluorinated alkyl long chain or cyclic group, and X is a halogen.

10. The preparation method according to claim 7 or 8, characterized in that, In step (2), the modification time is less than or equal to 45 seconds.

11. The preparation method according to claim 7 or 8, characterized in that, The method for preparing the base film includes the following steps: (1) After mixing polyvinylidene fluoride, triethyl phosphate, polyvinylpyrrolidone and N-methylpyrrolidone, a homogeneous casting solution is obtained. (2) The casting solution obtained in step (1) is scraped onto the substrate, then immersed in a water coagulation bath to remove the remaining triethyl phosphate, polyvinylpyrrolidone and N-methylpyrrolidone, and then freeze-dried to obtain the base film.

12. The application of the fluoride-modified metal ion crosslinked pervaporation membrane as described in any one of claims 1-6, characterized in that, Applications for separating alcohols from mixtures of alcohols and water.

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