A solvent-resistant high-flux polyimide / polyethyleneimine@titanium dioxide nanohybrid ultrafiltration membrane and a preparation method thereof

Abstract

The application provides a solvent-resistant high-flux polyimide / polyethyleneimine@titanium dioxide nanohybrid ultrafiltration membrane and a preparation method thereof. First, a titanium dioxide precursor Ti-BALDH is dissolved in N-methyl pyrrolidone together with polyimide to prepare a film casting solution, and then the film casting solution is scraped on a non-woven fabric to prepare a solvent-resistant nanohybrid polyimide membrane by a non-solvent induced phase inversion-interface crosslinking-in-situ biomimetic mineralization coupling method. The chemical crosslinking of polyethyleneimine and polyimide significantly improves the solvent resistance of the membrane; meanwhile, the catalytic effect of polyethyleneimine enables the Ti-BALDH precursor to be in-situ mineralized into nanometer titanium dioxide in the membrane, which greatly improves the solvent flux of the membrane without sacrificing the molecular weight cut-off. The synchronous coupling of the non-solvent induced phase inversion, chemical crosslinking and in-situ biomimetic mineralization processes also improves the preparation efficiency of the membrane.

Description

Technical Field

[0001] This invention relates to a solvent-resistant, high-flux polyimide / polyethyleneimide@titanium dioxide nanohybrid ultrafiltration membrane (PI / PEI@TiO2) and its preparation method. Background Technology

[0002] Organic solvents are widely used in chemical, pharmaceutical, and food industries, with large quantities and diverse types. Traditional separation methods such as distillation, extraction, and adsorption are used for the purification of organic systems and the recovery of organic solvents, but these methods are energy-intensive, time-consuming, and have low recovery rates. Compared with traditional separation methods, membrane separation technology is energy-saving, efficient, easy to operate, and easy to integrate, and has broad application prospects in the separation of organic solvent systems.

[0003] Ultrafiltration (UF) is a widely used pressure-driven membrane separation technology aimed at separating large molecules from small molecules. UF membranes typically operate at pressures of 0–0.2 MPa, have pore sizes between 2–50 nm, and molecular weight cutoffs (MWCO) between 2000 and 500,000. Existing commercially available UF membranes exhibit good stability and separation performance in aqueous systems, but they are prone to swelling or dissolution in many organic solvents, leading to membrane performance degradation and limiting their application. In recent years, the enormous application potential of membrane technology in the separation of products and solvent recovery in organic solvent systems has been recognized, such as the emerging solvent-resistant nanofiltration (SRNF) technology. The ultrafiltration membrane, as the supporting substrate, is crucial to the performance stability of the SRNF membrane, requiring it to possess excellent solvent resistance. Furthermore, similar to the use of UF membranes as pretreatment in membrane-based water treatment, membrane-based treatment of organic solvent systems often also requires UF membranes with good solvent resistance for subsequent SRNF pretreatment. Therefore, the development of solvent-resistant ultrafiltration membranes is of great significance for the application of membrane separation technology in the separation of organic solution systems.

[0004] However, research on solvent-resistant ultrafiltration membranes is scarce to date. Cao Yiming et al. reported that using photoactive polyethylene glycol diacrylate (PEGDA) as the monomer and ethanol as the solvent, membranes were formed under ultraviolet light irradiation in the presence of a photosensitizer. The prepared membranes exhibited a BSA rejection rate of 20–60% and a pure water flux of 100–310 L / (m²). 2The prepared membrane is insoluble in common organic solvents such as methanol and ethanol [J.Membr.Sci.,2008,318(1 / 2):227-232]. In recent years, there has been a lot of research on the preparation of SRNF membranes. Most of the supporting membranes used are made of polyimide (PI) through a solvent-inducible phase inversion method. Due to the excellent thermodynamic properties, low-temperature resistance and stable chemical properties of PI, the ultrafiltration membranes prepared from it have good resistance to solvents such as alcohols, ketones and esters. However, they are difficult to maintain stability in polar aprotic solvents such as dimethylformamide (DMF), methylpyrrolidone (NMP) and dimethyl sulfoxide (DMSO), and the solvent flux is low. Studies have reported that crosslinking modification [Prog. Polym. Sci., 2013, 38(6): 874-896] and surface modification [J. Membr. Sci., 2003, 213(1): 159-180] can improve the stability of PI membranes in polar aprotic solvents, but this will sacrifice solvent flux to some extent. Therefore, Wang et al. [Sep. Purif. Technol., 2019, 227(15): 115687] introduced carbonized ZIF-8 nanoparticles into polyimide membranes through physical blending, which simultaneously increased the specific surface area, pore size and total porosity of the membrane, thereby improving the flux of the membrane to solvents such as ethanol. However, the nanoparticles have poor compatibility with the PI bulk polymer, which leads to the aggregation of nanoparticles in the membrane and thus reduces the separation performance. Subsequently, Si et al. [Sep. Purif. Technol., 2020, 241(15): 116545] added aminated MCM-41 nanoparticles to the PI membrane. Because the nanoparticles form chemical bonds with the polyimide, reducing aggregation, the solvent flux of the membrane is increased without affecting the retention rate. However, the PI membrane modified with nano-hybrid technology still has difficulty tolerating polar aprotic solvents such as DMF, NMP, and DMSO. Therefore, this invention proposes a novel membrane fabrication method to prepare a solvent-resistant, high-flux nano-hybrid ultrafiltration membrane. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a method for preparing a polyimide / polyethyleneimide@TiO2 nanohybrid ultrafiltration membrane (PEI / PI@TiO2) that has both a wide solvent tolerance range and high solvent flux. The method for preparing the solvent-resistant, high-flux PEI / PI@TiO2 ultrafiltration membrane involves first coating a uniformly mixed Ti-BALDH and polyimide casting solution onto the surface of a nonwoven fabric to form a liquid film. Then, the film is placed in a coagulation bath containing polyethyleneimine to simultaneously undergo solvent-inducing phase transformation, crosslinking of polyethyleneimine and polyimide, and in-situ biomimetic mineralization of Ti-BALDH catalyzed by polyethyleneimine. Because polyethyleneimine can chemically crosslink with polyimide, the membrane exhibits excellent stability in strongly polar aprotic solvents such as DMF, NMP, and DMSO, as well as conventional polar solvents such as alcohols and ketones, and nonpolar solvents such as n-hexane. Simultaneously, due to the biomimetic mineralization effect of polyethyleneimine on Ti-BALDH, nano-titanium dioxide particles are generated in situ within the membrane. Compared to conventional methods of introducing nanoparticles through physical blending to modify the membrane, this approach overcomes nanoparticle aggregation within the membrane and improves the compatibility between the nanoparticles and the polymer bulk. By adjusting the Ti-BALDH content, the membrane porosity can be controlled, thereby improving the solvent flux without affecting the membrane's molecular rejection rate.

[0006] This invention proposes a simple, solvent-free, phase transformation-interfacial chemical crosslinking-in-situ biomimetic mineralization coupling method to prepare a solvent-resistant, high-throughput polyimide / polyethyleneimide@TiO2 nanohybrid ultrafiltration membrane (PEI / PI@TiO2).

[0007] A solvent-resistant, high-flux polyimide / polyethyleneimide@TiO2 nanocomposite ultrafiltration membrane was prepared by the following method:

[0008] (1) Add 8-13 parts by weight of polyimide and 50 parts by weight of N-methylpyrrolidone (NMP) to a container and stir to form a homogeneous solution;

[0009] (2) Add 1 to 5 parts by mass of a mixed solution of di(2-hydroxypropionic acid) diammonium dihydrogen phosphate titanium (Ti-BALDH) containing 40 to 60 wt% (most preferably 50 wt%) NMP to the homogeneous solution in step (1), stir and let stand to remove bubbles to obtain a casting solution.

[0010] (3) The casting solution from step (2) is scraped onto a nonwoven fabric and quickly placed in a coagulation bath aqueous solution containing 15-35 parts by mass of polyethyleneimine. Solvent-induced phase transformation, crosslinking of polyethyleneimine and polyimide, and in-situ biomimetic mineralization of Ti-BALDH catalyzed by polyethyleneimine are carried out simultaneously for 1-8 hours. Afterward, the residual crosslinking agent on the membrane surface is rinsed off with deionized water and then stored in ethanol to remove the residual solvent in the membrane. Finally, a solvent-resistant polyimide / polyimide@titanium dioxide nano-hybrid ultrafiltration membrane is obtained.

[0011] Furthermore, in step (1), a homogeneous solution is formed after stirring at 30-60°C for 6-10 hours.

[0012] Further, in step (2), the method for preparing the solvent-resistant nano-hybrid polyimide film is as follows: after evaporating and removing water from 2 parts by mass of a Ti-BALDH solution containing 50wt% water, 1 part by mass of NMP is added to it to obtain a Ti-BALDH mixed solution containing 50wt% NMP.

[0013] Preferably, in step (2), the weight percentages of polyimide, NMP, and Ti-BALDH, calculated at 100% by weight, are as follows:

[0014] 16 wt% polyimide;

[0015] Ti-BALDH 0~6.5wt%;

[0016] NMP margin.

[0017] Preferably, in step (2), after stirring at 30–60°C for 12–24 hours, the mixture is allowed to stand for 12–24 hours to remove bubbles. More preferably, after stirring at 50°C for 24 hours, the mixture is allowed to stand for 12 hours to remove bubbles.

[0018] Preferably, in step (3), the ultrafiltration membrane is soaked in the coagulation bath for 1 to 8 hours, and more preferably 3 hours.

[0019] Preferably, in step (3), the concentration of polyethyleneimine is 1.5 to 3.5 wt%, more preferably 2.5 wt%.

[0020] Preferably, in step (3), the molar molecular weight of polyethyleneimine is 300 to 70,000, and more preferably 300.

[0021] Preferably, in step (3), the polyethyleneimine is configured as branched polyethyleneimine or / and linear polyethyleneimine.

[0022] Preferably, in step (3), the thickness of the film coating solution on the nonwoven fabric is 150 to 250 micrometers, and more preferably 200 micrometers.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] This invention introduces PEI and TiO2 nanoparticles into a PI ultrafiltration membrane simultaneously using a simple non-solvent-induced phase transformation-interfacial chemical crosslinking-in-situ biomimetic mineralization coupling method. Because polyethyleneimine can chemically crosslink with polyimide, the membrane exhibits excellent stability in strongly polar aprotic solvents such as DMF, NMP, and DMSO, conventional polar solvents such as alcohols and ketones, and non-polar solvents such as n-hexane. Simultaneously, due to the biomimetic mineralization effect of polyethyleneimine on Ti-BALDH, nano-titanium dioxide particles are generated in-situ within the membrane and are uniformly distributed. Compared to conventional methods of introducing nanoparticles to modify the membrane through physical blending, this method overcomes nanoparticle aggregation within the membrane and improves the compatibility between the nanoparticles and the polymer bulk. Furthermore, by adjusting the Ti-BALDH content to regulate the membrane porosity, the solvent flux of the membrane can be improved without affecting the molecular rejection rate. Attached Figure Description

[0025] Figure 1 The Fourier attenuated total reflectance infrared (ATR-FTIR) spectra of the uncrosslinked polyimide ultrafiltration membrane (PI), the crosslinked but unmineralized polyimide / polyethyleneimide ultrafiltration membrane (PI / PEI), and the crosslinked polyimide / polyethyleneimide@TiO2 nanohybrid ultrafiltration membrane (PI / PEI@TiO2) with a precursor content of 3.1 wt% are described in this invention.

[0026] Figure 2 The images show X-ray photoelectron spectroscopy (XPS) spectra of the uncrosslinked polyimide ultrafiltration membrane (PI), the crosslinked but unmineralized polyimide / polyethyleneimide ultrafiltration membrane (PI / PEI), and the crosslinked polyimide / polyethyleneimide@TiO2 nanohybrid ultrafiltration membrane (PI / PEI@TiO2) with a precursor content of 3.1 wt%.

[0027] Figure 3 The images show the cross-linked and uncross-linked membranes before and after immersion in DMF for 5 days. These membranes are uncross-linked polyimide ultrafiltration membranes (PI), cross-linked but unmineralized polyimide / polyethyleneimide ultrafiltration membranes (PI / PEI), and cross-linked polyimide / polyethyleneimide@TiO2 nanohybrid ultrafiltration membranes (PI / PEI@TiO2) with a precursor content of 3.1 wt%.

[0028] Figure 4The images show a comparison of the surface morphology of the uncrosslinked polyimide ultrafiltration membrane (PI), the crosslinked but unmineralized polyimide / polyethyleneimide ultrafiltration membrane (PI / PEI), and the crosslinked polyimide / polyethyleneimide@TiO2 nanohybrid ultrafiltration membrane (PI / PEI@TiO2) with a precursor content of 3.1 wt% before and after immersion in DMF for 5 days. Detailed Implementation

[0029] The following detailed description, in conjunction with specific embodiments, further clarifies the invention. However, the scope and content of this patent are not limited to the following embodiments. Any variations or implementations that do not depart from the scope and content of this invention should be included within the technical scope of this invention.

[0030] Example 1:

[0031] ① Preparation of casting solution

[0032] First, 10g of PI ( 5218) was dissolved in 50.4 mL of NMP and stirred at 50 °C for 8 hours. Then, 0.74 g of a Ti-BALDH mixed solution containing 50 wt% NMP was added dropwise to the solution under vigorous stirring and stirred at 50 °C for 24 hours. The solution was then allowed to stand overnight for 12 hours to obtain a homogeneous casting solution without bubbles.

[0033] ② Non-solvent-induced phase transformation

[0034] The casting solution was uniformly poured onto the nonwoven fabric S53, and then scraped into a uniform liquid film using a 200-micron doctor blade. The nonwoven fabric coated with the liquid film was then immersed in 1 kg of an aqueous solution containing 2.5 wt% polyethyleneimine (300 molecular weight) for a solvent-inducible phase transformation for 3 hours to obtain a solvent-resistant high-flux polyimide / polyethyleneimine@TiO2 nanohybrid ultrafiltration membrane (PI / PEI@TiO2). The membrane performance data are listed in Table 1.

[0035] Example 2:

[0036] The Ti-BALDH concentration in step 1 was changed from 1.8 wt% to 3.1 wt%, and other operations were the same as in Example 1. The performance data of the prepared PI / PEI@TiO2 film are listed in Table 1.

[0037] Example 3:

[0038] The Ti-BALDH concentration in step 1 was changed from 1.8 wt% to 6.5 wt%, and other operations were the same as in Example 1. The performance data of the prepared PI / PEI@TiO2 film are listed in Table 1.

[0039] Example 4:

[0040] The Ti-BALDH concentration in step 1 was changed from 1.8 wt% to 0 wt%, and other operations were the same as in Example 1. The performance data of the prepared PI / PEI membrane are listed in Table 1.

[0041] Comparative Example 1:

[0042] The Ti-BALDH concentration in step 1 was changed from 3.1 wt% to 0 wt%, and the coagulation bath was changed from an aqueous solution of 2.5 wt% polyethyleneimine to pure water. Other operations were the same as in Example 1. The performance data of the prepared PI membrane are listed in Table 1.

[0043] like Figure 1 The Fourier attenuated total reflectance infrared (ATR-FTIR) spectra of polyimide / polyethyleneimide@titanium dioxide nanohybrid ultrafiltration membrane (PI / PEI@TiO2-5), cross-linked polyimide ultrafiltration membrane (PI / PEI) without precursor, and uncross-linked polyimide ultrafiltration membrane (PI) with a precursor content of 3.1 wt% and a theoretical TiO2 conversion rate of 5% are shown.

[0044] like Figure 2 The image shows X-ray photoelectron spectroscopy (XPS) spectra of a polyimide / polyethyleneimide@titanium dioxide nanohybrid ultrafiltration membrane (PI / PEI@TiO2-5) with a precursor content of 3.1 wt% and a theoretical TiO2 conversion rate of 5%, and a cross-linked polyimide ultrafiltration membrane (PI / PEI) without precursor.

[0045] like Figure 3 The figure shows the changes of polyimide / polyethyleneimide@titanium dioxide nanohybrid ultrafiltration membrane (PI / PEI@TiO2-5), cross-linked polyimide ultrafiltration membrane (PI / PEI) without precursor, and uncross-linked polyimide ultrafiltration membrane (PI) before and after immersion in DMF for 5 days, with a precursor content of 3.1 wt% and a theoretical TiO2 conversion rate of 5%.

[0046] like Figure 4 The images show SEM images of polyimide / polyethyleneimide@titanium dioxide nanohybrid ultrafiltration membrane (PI / PEI@TiO2-5), cross-linked polyimide ultrafiltration membrane (PI / PEI) without precursor, and uncross-linked polyimide ultrafiltration membrane (PI) before and after immersion in DMF for 5 days, with a precursor content of 3.1 wt% and a theoretical TiO2 conversion rate of 5%.

[0047] Table 1 Comparison of the separation performance of ultrafiltration membranes prepared in Examples 1-4 and Comparative Example 1

[0048] Example 1 59.4 94.3 Example 2 65.4 95.3 Example 3 58.4 85.0 Example 4 50.7 95.0 Comparative Example 1 none none

[0049] Note: "None" means the membrane is completely dissolved in the solvent.

[0050] Solvent flux performance was tested using three membranes prepared in Examples 2 and 4, and Comparative Example 1. The solvents used were pure water, ethanol, n-hexane, NMP, DMSO, and DMAc, respectively, and the test conditions were 25°C and 0.2 MPa. The test results are shown in Table 2.

[0051] Table 2 Comparison of solvent flux in Examples 2 and 4 and Comparative Example 1

[0052] ethanol 977 755.6 1580.0 pure water 713.7 419.5 1077.2 n-Hexane 6.5 5.1 14.7 NMP 48.5 39.4 none DMSO 48.5 43.1 none DMAc 74.9 45.2 none

[0053] Note: "None" means the membrane is completely dissolved in the solvent.

[0054] Solvent resistance tests were conducted using three membranes prepared in Examples 2 and 4, and Comparative Example 1. The membranes prepared in Examples 2 and 4, and Comparative Example 1, were immersed in DMF for 5 days. Then, the flux of the membranes to pure DMF solvent and their retention capacity for 70,000 molecular weight polyethylene glycol in water were tested at 25°C and 0.2 MPa. The test results are shown in Table 3.

[0055] Table 3 shows the changes in DMF flux and PEG-7W rejection rate of the membranes prepared in Examples 2 and 4 and Comparative Example 1 after immersion in DMF solvent for 5 days.

[0056]

[0057]

[0058] Note: "None" means the membrane is completely dissolved in the solvent.

[0059] Based on the above results, the polyimide / polyethyleneimide@titanium dioxide nanohybrid ultrafiltration membrane (PI / PEI@TiO2) prepared in this invention exhibits significantly improved solvent resistance compared to traditional polyimide ultrafiltration membranes (PI). Furthermore, compared to polyimide / polyethyleneimide ultrafiltration membranes that only undergo crosslinking (PI / PEI), its DMF flux is significantly increased while maintaining a stable molecular rejection rate. This confirms that the chemical crosslinking of polyethyleneimine can significantly improve the stability of conventional polyimide ultrafiltration membranes in organic solvents, and the introduction of TiO2 through in-situ biomimetic mineralization can further enhance the membrane's solvent flux without affecting its molecular rejection rate.

Claims

1. A method for preparing a solvent-resistant, high-flux polyimide / polyethyleneimide@titanium dioxide nanohybrid ultrafiltration membrane, characterized in that, Includes the following steps: (1) Add 8-13 parts by weight of polyimide and 50 parts by weight of N-methylpyrrolidone (NMP) to a container and stir to form a homogeneous solution; (2) Add 1 to 5 parts by mass of a di(2-hydroxypropionic acid) diammonium dihydrogen phosphate titanium solution containing 40 to 60 wt% N-methylpyrrolidone to the homogeneous solution in step (1), stir and let stand to remove bubbles to obtain casting solution; (3) The casting solution from step (2) is scraped onto a nonwoven fabric and placed in a coagulation bath aqueous solution containing 1000 parts by mass of polyethyleneimine. Solvent-induced phase transformation, crosslinking of polyethyleneimine and polyimide, and in-situ biomimetic mineralization of Ti-BALDH catalyzed by polyethyleneimine are carried out simultaneously for 1 to 8 hours. Afterward, the residual crosslinking agent on the membrane surface is rinsed off with deionized water and then stored in ethanol to remove the residual solvent in the membrane. Finally, a solvent-resistant polyimide / polyimide@titanium dioxide nano-hybrid ultrafiltration membrane is obtained.

2. The method for preparing a solvent-resistant, high-flux polyimide / polyethyleneimide@titanium dioxide nanohybrid ultrafiltration membrane as described in claim 1, characterized in that: In step (1), a homogeneous solution is formed after stirring at 30-60°C for 6-10 hours.

3. The method for preparing a solvent-resistant, high-flux polyimide / polyethyleneimide@titanium dioxide nanohybrid ultrafiltration membrane as described in claim 1, characterized in that: In step (2), the preparation of the diammonium di(2-hydroxypropionic acid) dihydrogen phosphate titanium solution containing 40-60 wt% N-methylpyrrolidone includes: evaporating and removing water from an aqueous Ti-BALDH solution, and then adding N-methylpyrrolidone to it to obtain the diammonium di(2-hydroxypropionic acid) dihydrogen phosphate titanium solution containing 40-60 wt% N-methylpyrrolidone.

4. The method for preparing a solvent-resistant, high-flux polyimide / polyethyleneimide@titanium dioxide nanohybrid ultrafiltration membrane as described in claim 1, characterized in that: In step (2), after stirring at 30-60°C for 12-24 hours, let stand for 12-24 hours to remove bubbles.

5. The method for preparing a solvent-resistant, high-flux polyimide / polyethyleneimide@titanium dioxide nanohybrid ultrafiltration membrane as described in claim 1, characterized in that: In step (3), the concentration of polyethyleneimine in the coagulation bath aqueous solution containing polyethyleneimine is 1.5 to 3.5 wt%.

6. The method for preparing a solvent-resistant, high-flux polyimide / polyethyleneimide@titanium dioxide nanohybrid ultrafiltration membrane as described in claim 1, characterized in that: In step (3), the molar molecular weight of polyethyleneimine is 300 to 70,000.

7. The method for preparing a solvent-resistant, high-flux polyimide / polyethyleneimide@titanium dioxide nanohybrid ultrafiltration membrane as described in claim 1, characterized in that: In step (3), the configuration of polyethyleneimine is branched polyethyleneimine or / and linear polyethyleneimine.

8. The method for preparing a solvent-resistant, high-flux polyimide / polyethyleneimide@titanium dioxide nanohybrid ultrafiltration membrane as described in claim 1, characterized in that: In step (3), the thickness of the film coated on the nonwoven fabric by the casting solution is 150 to 250 micrometers.

9. A solvent-resistant, high-flux polyimide / polyethyleneimide@titanium dioxide nanohybrid ultrafiltration membrane prepared by the preparation method according to any one of claims 1 to 8.

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