A biphenylamine-based compound organic solvent nanofiltration composite membrane and a preparation method thereof

Abstract

The application discloses a diphenylamine-based organic solvent composite nanofiltration membrane and a preparation method thereof, and belongs to the technical field of separation membranes. The diphenylamine-based organic solvent composite nanofiltration membrane is prepared by the following steps: taking polyacrylonitrile or polyimide ultrafiltration membrane as a base film, removing a surface pore preserving agent, immersing in an aqueous solution containing a 2,2'-diphenylamine-based compound, then immersing in an organic solution containing a polybasic acid chloride to perform an interfacial polymerization reaction, and finally performing a heat crosslinking post-treatment to obtain the composite nanofiltration membrane. The prepared composite nanofiltration membrane has an about 8 times flux increase compared with a traditional polyamide membrane due to the introduction of the rigid twistable monomer diphenylamine-based compound, and the selectivity of the prepared composite nanofiltration membrane to organic small molecule dyes is not obviously reduced. Meanwhile, the prepared composite nanofiltration membrane has high stability in tests of various polar solvents, and therefore has high economic value in separation of organic solvent systems in the industry.

Description

Technical Field

[0001] This invention relates to the field of membrane separation technology, and in particular to a benzidine-based compound organic solvent nanofiltration composite membrane and its preparation method. Background Technology

[0002] In recent years, membrane separation technology has become a promising water treatment technology due to its energy efficiency, environmental friendliness, and ease of commercialization. Organic solvent nanofiltration is an emerging membrane separation technology with significant advantages over traditional separation processes. It can be used for the efficient separation of small organic molecules with molecular weights ranging from 200 to 1000 g / mol in organic solvent systems, and has found wide application in petrochemicals, fine chemicals, pharmaceuticals, and vegetable oil extraction. Currently, organic solvent nanofiltration membranes are mainly prepared using phase inversion and interfacial polymerization methods. However, these membrane materials generally suffer from poor stability and low upper limits of permeate selectivity, which limit the application of organic solvent nanofiltration in industrial development. Therefore, developing high-performance solvent-resistant nanofiltration membranes is crucial for the development and application of organic solvent nanofiltration technology.

[0003] The structure of the membrane determines the membrane performance, and the monomer molecular structure is an important factor affecting the microporous structure and separation performance of TFC OSN membranes. Existing studies have shown that the introduction of monomers with inherent 3D microporous structure and rigid torsion structure can greatly improve the microporosity of the separation layer, so as to prepare TFC OSN membranes with high permeability and high selectivity. For example, Jiang et al. (Nature, 2022, 609(7925):58-64.) synthesized amino-functionalized macrocycles by functionalizing the primary hydroxyl groups on the upper edge of cyclodextrin and 4-sulfonyl compound [4] aryl sodium salt to highly active amino groups. Due to the enhanced arrangement of the functionalized macrocyclic molecules, macrocyclic cavities are arranged in ultrathin nanofilms to form sub-nanometer channels, providing faster solvent transport and molecular sieves corresponding to the cavity size, which have higher solvent selectivity than thicker nanofilms. JIMENEZ-SOLOMON MF (Nature Materials, 2016, 15: 760-7.) et al. used twisted monomers for interfacial polymerization, which can achieve enhanced microporosity and higher interconnectivity of molecular network voids rationalized by molecular simulation, and the membranes prepared with nanofilms made with non-twisted planar monomers have solvent permeability up to two orders of magnitude higher.

[0004] Currently, the development and application of commercially available organic solvent nanofiltration membranes have stagnated due to their low performance, necessitating the search for more cost-effective organic solvent nanofiltration membrane materials. To address these issues, a solution is proposed below. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing a nanofiltration membrane with high permeability selectivity for organic solvents, in order to solve the problems of poor stability and low upper limit of permeability selectivity of the aforementioned organic solvent nanofiltration membranes.

[0006] To achieve the above-mentioned objectives, this invention provides a method for preparing a benzidine-based organic solvent composite nanofiltration membrane, comprising the following steps:

[0007] (1) Soak the base membrane in deionized water for 4-5 hours, and change the water every hour to fully remove the pore-retaining agent on the membrane surface. The base membrane is a polyacrylonitrile or polyimide ultrafiltration membrane.

[0008] (2) Remove the soaked base film and drain the surface water. Then soak it in an aqueous solution of 2,2'-benzidine compound at 25°C for 1-2 minutes. The aqueous solution of 2,2'-benzidine compound also contains an alkaline additive. After soaking, remove the base film and remove the water droplets remaining on the surface of the base film for later use.

[0009] (3) At 25°C, the base membrane treated in step (2) is immersed in an organic solution and reacted for 15s-5min. Then it is taken out and the organic phase solution on the surface of the membrane is removed with an organic solvent. The organic phase solution contains polyacrylamide chloride.

[0010] (4) The composite nanofiltration membrane after the reaction in step (3) is placed in an oven at 40-70℃ and heated for 2-15 minutes to perform thermal crosslinking, thereby obtaining a benzidine-based organic solvent composite nanofiltration membrane.

[0011] Preferably, the structure of the 2,2'-benzidine compound of the present invention is as follows:

[0012]

[0013] Preferably, the alkali auxiliary agent in step (2) is at least one of sodium hydroxide, potassium hydroxide, and triethylamine. More preferably, the concentration of the alkali auxiliary agent in step (2) is 0.1%-2wt%.

[0014] Preferably, the aqueous solution in step (2) further includes a surfactant, wherein the surfactant is dodecyltrimethylammonium chloride. More preferably, the concentration of the surfactant in the aqueous solution in step (2) is 0.02 wt%.

[0015] Preferably, the polyacrylamide chloride is one or a mixture of several of pyromellitic chloride, isophthaloyl chloride, and terephthaloyl chloride.

[0016] Preferably, the organic solution in step (3) is prepared by dissolving polyacrylamide chloride in an organic solvent, wherein the organic solvent is at least one of n-hexane, isoalkanes or toluene.

[0017] The present invention has the following beneficial effects:

[0018] The interfacial polymerization membrane-forming method selected in this invention is simple, the experimental conditions are mild, and the membrane-forming process is relatively short. The rigid and torsion-like properties of the 2,2'-benzidine compound endow the polymer film with high microporosity, while the relatively large molecular structure slows down the diffusion rate towards the organic phase, which helps to form a thin, well-ordered separation layer. The 2,2'-benzidine compound forms a special "4+3" crosslinking structure with trimesoyl chloride, giving the membrane high thermal stability and long-term stability with solvents of different polarities. The combination of rigidity and flexibility of the 2,2'-benzidine compound results in a composite nanofiltration membrane that significantly improves organic solvent permeability compared to traditional polyamide membranes, while maintaining a high rejection rate for small molecule dyes.

[0019] The composite nanofiltration membrane prepared by this invention has a high permeation flux (>15 LMH / bar) to organic solvents such as acetone and methanol, and can effectively retain dye molecules such as methyl orange, acid blue, orange-yellow G, rhodamine B, acid red 27, and brilliant blue R. It can be fully applied to chemical processes such as active drug separation, crude oil extraction, and catalyst recovery in organic solvent systems. Attached Figure Description

[0020] Figure 1 This is an electron microscope image of the surface of the polyacrylonitrile-based film in Example 1 of the present invention;

[0021] Figure 2 These are electron microscope images of the surface of the composite nanofiltration membrane prepared in Example 1 of this invention;

[0022] Figure 3 This is an electron microscope image of the surface of the composite nanofiltration membrane prepared in Example 5 of this invention;

[0023] Figure 4 This is a graph showing the separation performance of the composite nanofiltration membrane prepared in Example 1 of this invention for various dyes;

[0024] Figure 5 This is a graph showing the permeation performance of the composite nanofiltration membrane prepared in Example 1 of this invention to various solvents;

[0025] Figure 6 This is a graph showing the long-term stability of the composite nanofiltration membrane prepared in Example 1 of this invention against various solvents.

[0026] Figure 7 This is a graph showing the separation performance of the composite nanofiltration membrane prepared in Example 5 of this invention against various dyes;

[0027] Figure 8 This is a graph showing the permeation performance of the composite nanofiltration membrane prepared in Example 5 of this invention to various solvents.

[0028] Figure 9 This is a thermal stability diagram of the composite nanofiltration membrane prepared in Example 1 of the present invention. Detailed Implementation

[0029] The technical solution of the present invention will be further defined below with reference to specific embodiments, but the scope of protection is not limited to the description.

[0030] The technical solution of the present invention will be further defined below with reference to specific embodiments, but the scope of protection is not limited to the description.

[0031] In the following examples, the separation performance test conditions used were as follows: after pre-pressurizing for 2 hours at 0.6 MPa and 25°C, the pressure was adjusted to 0.5 MPa. The rejection rate of the prepared composite nanofiltration membrane to 50 ppm dye methanol solution and the permeation flux of various solvents were tested. The flux unit is LMH / bar (liters / square meter / hour / bar).

[0032] Example 1

[0033] A method for preparing a benzidine-based organic solvent composite nanofiltration membrane, comprising the following steps:

[0034] (1) Soak the polyacrylonitrile ultrafiltration membrane in pure water for 4 hours to remove the pore-retaining agent on the membrane surface;

[0035] (2) Take out the above polyacrylonitrile ultrafiltration membrane, wipe the water droplets remaining on the surface of the ultrafiltration membrane with lint-free paper, and soak it in an aqueous solution of 1.0 wt% 6,6'-dihydroxy-2,2'-benzidine and 4 eq. sodium hydroxide at 25°C for 2 min. Take out the ultrafiltration membrane and remove the water droplets remaining on the membrane surface with a rubber roller for later use.

[0036] (3) At 25°C, the polyacrylonitrile ultrafiltration membrane treated in step (2) was immersed in a solution of isoparaffinic hydrocarbons with a concentration of 0.1 wt% and reacted for 30 s.

[0037] (4) Place the filter membrane after the reaction in step (3) in an oven at 65°C and heat for 5 minutes to obtain a benzidine-based organic solvent composite nanofiltration membrane.

[0038] The prepared composite nanofiltration membrane was used to separate 4-p-nitroaniline (AR), Sudan Orange G (SOG), methyl orange (MO), orange yellow G (OG), rhodamine B (RDB), acid red 27 (AR27), and brilliant blue R (BBR). The experimental results are as follows: Figure 4 As shown, the retention capacity gradually increases with the increase of dye molecular weight; the molecular weight cutoff of the above organic solvent nanofiltration membrane is approximately 306 g / mol.

[0039] The prepared composite nanofiltration membrane was tested for permeation performance with various solvents, and the results are as follows: Figure 5 As shown, the composite nanofiltration membrane of this invention has a permeation flux of 15.08 LMH / bar for methanol and 30.63 LMH / bar for acetone. Furthermore, the permeability of the composite nanofiltration membrane to various solvents is directly proportional to the reciprocal of the viscosity of the corresponding solution.

[0040] The prepared composite nanofiltration membrane was sequentially filtered through methanol, tetrahydrofuran, ethanol, toluene, water, and methanol, and its flux performance changes were tested, as shown in the attached figure. Figure 6 As shown, the permeability of the composite nanofiltration membrane to various solvents did not change significantly over a certain period of time. Furthermore, after alternating tests with the aforementioned solvents, the permeability of the prepared composite nanofiltration membrane to methanol was restored to its original state.

[0041] Example 2

[0042] A method for preparing a benzidine-based organic solvent composite nanofiltration membrane, comprising the following steps:

[0043] (1) Soak the polyacrylonitrile ultrafiltration membrane in pure water for 4 hours to remove the pore-retaining agent on the membrane surface;

[0044] (2) Take out the above polyacrylonitrile ultrafiltration membrane, wipe the water droplets remaining on the surface of the ultrafiltration membrane with lint-free paper, and soak it in an aqueous solution of 1.0 wt% 6,6'-dihydroxy-2,2'-benzidine and 4 eq. sodium hydroxide at 25°C for 2 min. Take out the ultrafiltration membrane and remove the water droplets remaining on the membrane surface with a rubber roller for later use.

[0045] (3) At 25°C, the polyacrylonitrile ultrafiltration membrane treated in step (2) was immersed in a solution of isoparaffinic hydrocarbons with a concentration of 0.1 wt% of pyromellitic chloride and reacted for 1 min.

[0046] (4) Place the filter membrane after the reaction in step (3) in an oven at 65°C and heat for 5 minutes to obtain a benzidine-based organic solvent composite nanofiltration membrane.

[0047] The separation performance test of the prepared composite nanofiltration membrane showed that the methanol flux was 12.41 LMH / bar and the rejection rate of methyl orange (MW 327 Da) was 93.01%.

[0048] Example 3

[0049] A method for preparing a benzidine-based organic solvent composite nanofiltration membrane, comprising the following steps:

[0050] (1) Soak the polyacrylonitrile ultrafiltration membrane in pure water for 4 hours to remove the pore-retaining agent on the membrane surface;

[0051] (2) Take out the above polyacrylonitrile ultrafiltration membrane, wipe the water droplets remaining on the surface of the ultrafiltration membrane with lint-free paper, and soak it in an aqueous solution of 1.0 wt% 6,6'-dihydroxy-2,2'-benzidine and 4 eq. sodium hydroxide at 25°C for 2 min. Take out the ultrafiltration membrane and remove the water droplets remaining on the membrane surface with a rubber roller for later use.

[0052] (3) At 25°C, the polyacrylonitrile ultrafiltration membrane treated in step (2) was immersed in a solution of isoparaffinic hydrocarbons with a concentration of 0.1 wt% and reacted for 2 min.

[0053] (4) Place the filter membrane after the reaction in step (3) in an oven at 65°C and heat for 5 minutes to obtain a benzidine-based organic solvent composite nanofiltration membrane.

[0054] The separation performance test of the prepared composite nanofiltration membrane showed that the methanol flux was 10.69 LMH / bar and the rejection rate of methyl orange (MW 327 Da) was 94.04%.

[0055] Example 4

[0056] A method for preparing a benzidine-based organic solvent composite nanofiltration membrane, comprising the following steps:

[0057] (1) Soak the polyacrylonitrile ultrafiltration membrane in pure water for 4 hours to remove the pore-retaining agent on the membrane surface;

[0058] (2) Take out the above polyacrylonitrile ultrafiltration membrane, wipe the water droplets remaining on the surface of the ultrafiltration membrane with lint-free paper, and soak it in an aqueous solution of 1.0 wt% 6,6'-dihydroxy-2,2'-benzidine and 4 eq. sodium hydroxide at 25°C for 2 min. Take out the ultrafiltration membrane and remove the water droplets remaining on the membrane surface with a rubber roller for later use.

[0059] (3) At 25°C, the polyacrylonitrile ultrafiltration membrane treated in step (2) was immersed in a solution of isoparaffinic hydrocarbons with a concentration of 0.1 wt% of pyromellitic chloride and reacted for 5 min.

[0060] (4) Place the filter membrane after the reaction in step (3) in an oven at 65°C and heat for 5 minutes to obtain a benzidine-based organic solvent composite nanofiltration membrane.

[0061] The separation performance test of the prepared composite nanofiltration membrane showed that the methanol flux was 10.50 LMH / bar and the rejection rate of methyl orange (MW 327 Da) was 93.47%.

[0062] Example 5

[0063] A method for preparing a benzidine-based organic solvent composite nanofiltration membrane, comprising the following steps:

[0064] (1) Soak the polyacrylonitrile ultrafiltration membrane in pure water for 4 hours to remove the pore-retaining agent in the membrane;

[0065] (2) Take out the above polyacrylonitrile ultrafiltration membrane and immerse it in an aqueous solution of 1.0 wt% 6,6'-diamino-2,2'-benzidine and 0.06% sodium dodecyl sulfonate (SDS) at 25°C. After 2 minutes, take out the membrane and remove the water droplets remaining on the membrane surface with a rubber roller for later use.

[0066] (3) At 25°C, the polyacrylonitrile ultrafiltration membrane treated in step (2) was immersed in a 0.1 wt% isoalkane solution of terephthaloyl chloride and reacted for 1 min.

[0067] (4) The nanofiltration membrane after the reaction in step (3) is placed in an oven at 65°C and heated for 5 minutes to obtain a benzidine-based organic solvent composite nanofiltration membrane.

[0068] The prepared composite nanofiltration membrane was used to separate 4-p-nitroaniline (AR), Sudan Orange G (SOG), methyl orange (MO), orange yellow G (OG), rhodamine B (RDB), acid red 27 (AR27), and brilliant blue R (BBR). The experimental results are as follows: Figure 7 As shown, the retention capacity gradually increases with the increase of dye molecular weight; the molecular weight cutoff of the above organic solvent nanofiltration membrane is approximately 283 g / mol.

[0069] The separation performance tests of the prepared composite nanofiltration membrane showed that the flux for methanol was 15.68 LMH / bar and the flux for acetone was 40.08 LMH / bar. Furthermore, the permeability of the composite nanofiltration membrane to various solvents was as follows: Figure 8 As shown.

[0070] Comparative Example 1

[0071] A method for preparing a composite nanofiltration membrane is as follows:

[0072] (1) Soak the polyacrylonitrile ultrafiltration membrane in pure water for 4 hours to remove the pore-retaining agent in the membrane;

[0073] (2) Take out the above polyacrylonitrile ultrafiltration membrane, immerse it in an aqueous solution with a concentration of 1.0 wt% m-phenylenediamine and a concentration of 2 wt% triethylamine at 25°C, take out the membrane after 2 min, and remove the water droplets remaining on the membrane surface with a rubber roller for later use.

[0074] (3) At 25°C, the polyacrylonitrile ultrafiltration membrane treated in step (2) was immersed in a solution of isoparaffinic hydrocarbons with a concentration of 0.1 wt% and reacted for 30 s.

[0075] (4) Place the composite membrane after the reaction in step (3) in an oven at 65°C and heat for 5 minutes to obtain a m-phenylenediamine-based organic solvent composite nanofiltration membrane.

[0076] The separation performance test of the prepared composite nanofiltration membrane showed that the methanol flux was 2.60 LMH / bar and the rejection rate of methyl orange (MW327 Da) was 97.5%.

[0077] Comparative Example 2

[0078] A method for preparing a benzidine-based organic solvent composite nanofiltration membrane, following the method of Example 5, wherein no phase transfer catalyst is added to the aqueous solution in step (2), and the specific steps are as follows:

[0079] (1) Soak the polyacrylonitrile ultrafiltration membrane in pure water for 4 hours to remove the pore-retaining agent in the membrane;

[0080] (2) Take out the above polyacrylonitrile ultrafiltration membrane, immerse it in 6,6'-diamino-2,2'-benzidine at 25°C for 2 minutes, remove the membrane, and remove the water droplets remaining on the membrane surface with a rubber roller for later use;

[0081] (3) At 25°C, the polyacrylonitrile ultrafiltration membrane treated in step (2) was immersed in a 0.1 wt% isoalkane solution of terephthaloyl chloride and reacted for 1 min.

[0082] (4) The nanofiltration membrane after the reaction in step (3) is placed in an oven at 65°C and heated for 5 minutes to obtain a benzidine-based organic solvent composite nanofiltration membrane.

[0083] Separation performance tests on the prepared composite nanofiltration membrane showed that the methanol flux was 20.04 LMH / bar and the rejection rate for methyl orange (MW327 Da) was 88%.

[0084] A comparison of Example 1 and Comparative Example 1 shows that, under the same conditions, when 6,6'-dihydroxy-2,2'-benzidine was used instead of the traditional aqueous monomer m-phenylenediamine to prepare the composite nanofiltration membrane, its methanol flux increased by nearly 8 times, while its retention of organic molecules did not decrease significantly. The retention rate of methyl orange (MW327 Da) decreased from 97.5% to 92.69%. This fully demonstrates the significant performance advantages of our designed benzyl molecule as an interfacial polymerization monomer for membrane fabrication.

[0085] Finally, it should be noted that the above examples are merely some specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments and other modifications are possible. Any modifications, equivalent substitutions, or improvements made by those skilled in the art based on the disclosure of this invention should be considered within the scope of protection of this invention.

Claims

1. A method for preparing a benzidine-based organic solvent composite nanofiltration membrane, characterized in that, Includes the following steps: (1) Soak the base membrane in deionized water for 4-5 hours, and change the water every hour to fully remove the pore-retaining agent on the membrane surface. The base membrane is a polyacrylonitrile or polyimide ultrafiltration membrane. (2) Remove the soaked base film and drain the surface water. Then soak it in an aqueous solution of 2,2'-benzidine compound at 25°C for 1-2 min. The aqueous solution of 2,2'-benzidine compound also contains an alkaline additive. After soaking, remove the base film and remove the water droplets remaining on the surface of the base film for later use. (3) At 25°C, the base membrane treated in step (2) is immersed in an organic solution and reacted for 15 s-5 min. Then it is taken out and the organic phase solution on the surface of the membrane is removed with an organic solvent. The organic phase solution contains polyacrylamide chloride. (4) The composite nanofiltration membrane after the reaction in step (3) is placed in an oven at 40-70℃ and heated for 2-15 min to perform thermal crosslinking, thereby obtaining a benzidine-based organic solvent composite nanofiltration membrane; The structure of the 2,2'-benzidine compound is shown in formula (1): 。 2. The method for preparing the benzidine-based organic solvent composite nanofiltration membrane as described in claim 1, characterized in that, The pore-retaining agent is one or a mixture of glycerol and polyethylene glycol.

3. The method for preparing the benzidine-based organic solvent composite nanofiltration membrane as described in claim 1, characterized in that, The concentration of the aqueous solution of the 2,2'-benzidine compound is 0.1 wt%-2 wt%, and the pH of the aqueous solution in step (2) is 9-12.

4. The method for preparing the benzidine-based organic solvent composite nanofiltration membrane as described in claim 1, characterized in that, The alkali additive mentioned in step (2) is at least one of sodium hydroxide, potassium hydroxide, and triethylamine.

5. The method for preparing the benzidine-based organic solvent composite nanofiltration membrane as described in claim 1, characterized in that, The concentration of the alkali additive in step (2) is 0.6%-2wt%.

6. The method for preparing the benzidine-based organic solvent composite nanofiltration membrane as described in claim 1, characterized in that, The aqueous solution in step (2) also includes a surfactant, which is one or more of sodium dodecyl sulfonate, dodecyl trimethylammonium chloride, and Tween 20.

7. The method for preparing the benzidine-based organic solvent composite nanofiltration membrane as described in claim 1, characterized in that, The polyacryl chloride in step (3) is one or a mixture of several of pyromellitic chloride, isophthaloyl chloride, and terephthaloyl chloride; the concentration of the polyacryl chloride is 0.05 wt%-0.15 wt%.

8. The method for preparing the benzidine-based organic solvent composite nanofiltration membrane as described in claim 1, characterized in that, The organic solution in step (3) is prepared by dissolving polyacrylamide chloride in an organic solvent, wherein the organic solvent is at least one of n-hexane, isoalkanes or toluene.

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