Organic solvent composite nanofiltration membrane as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of nanofiltration membrane separation, and particularly relates to an organic solvent composite nanofiltration membrane as well as a preparation method and application thereof. A cross-linked polyimide ultrafiltration membrane is used as a base membrane, and a polyesteramide separation layer is obtained by polycondensation of a polyacyl chloride monomer and a polyamine monomer on the cross-linked polyimide base membrane. The preparation method comprises the following steps: soaking a naturally aired polyimide ultrafiltration base membrane in a water phase solution containing polyamine, airing, soaking in an organic phase solution containing polyacyl chloride, carrying out interfacial polymerization reaction, and carrying out thermal crosslinking post-treatment on the prepared membrane to obtain the thin-film composite nanofiltration membrane. And hydrophobic trifluoromethyl and hydrophilic phenolic hydroxyl are introduced by utilizing a functional group effect to prepare the thin-film composite nanofiltration membrane with a Janus pore channel structure. The membrane composite nanofiltration membrane can simultaneously improve the permeation flux of polar and non-polar solvents, obviously improves the flux of the non-polar solvent, can maintain low molecular weight cut-off, and has high economic value for separation of an organic solvent system in industry.

Description

Technical Field

[0001] The invention belongs to the technical field of nanofiltration membrane separation, and specifically relates to an organic solvent composite nanofiltration membrane and a preparation method and application thereof. Background Art

[0002] Compared with traditional separation technology, membrane separation technology has the advantages of high separation efficiency, low energy consumption, and no secondary pollution. Organic solvent nanofiltration, as a new type of membrane separation technology, can be used for the efficient separation of small organic molecules with a molecular weight of 200 to 1000 g / mol in an organic solvent system. Therefore, it has been widely used in the fields of petrochemicals, fine chemicals, pharmaceutical intermediates, and vegetable oil extraction. At present, organic solvent nanofiltration membranes are commonly prepared by phase inversion method and interfacial polymerization method. However, these membrane materials will encounter some problems in the actual application process, such as poor stability and low permeability selectivity, which to a certain extent limits their application in industrial development. Therefore, the development of high-performance solvent-resistant organic nanofiltration membranes has become crucial.

[0003] In actual industrial production, highly permeable and selective organic-resistant nanofiltration membranes can efficiently treat large amounts of organic waste liquid. However, traditional polyamide membrane materials, due to the presence of polar functional groups such as amide bonds and carboxyl groups in their polymer networks, exhibit high permeation flux for polar solvents and low permeation flux for non-polar solvents. In order to improve the permeation flux of the membrane to non-polar solvents, two strategies are usually adopted, one is to construct Janus channels, and the other is to introduce hydrophobic functional groups. For example: Liu (Adv. Mater. 2018, 30, 1705933) et al. used β-CD, which has an amphiphilic structure, as an aqueous phase monomer and prepared a polyamide membrane with trimesoyl chloride through interfacial polymerization. This not only improves the permeation flux of the membrane to non-polar solvents, but also has a higher permeation flux to polar solvents. Li (Chem. Sci., 2020, 11, 4263-4271) et al. introduced hydrophobic methylene groups into the polymer network and utilized the action of functional groups to prepare a molecular sieve membrane with a Janus pore structure, which can simultaneously meet the requirements of high permeation flux for both polar and non-polar solvents.

[0004] At present, the stability and permeation separation performance of commercialized organic nanofiltration membranes are relatively low, especially for non-polar organic reagents, which cannot meet the needs of actual application scenarios. The development of organic nanofiltration membranes with stable performance and high separation accuracy is of great significance to promoting the application and development of organic nanofiltration technology. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide an organic nanofiltration membrane with high organic solvent flux and low molecular weight cut-off, so as to solve the problem of mutual restriction between permeability and selectivity of existing organic nanofiltration membranes in organic solvent recovery.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0007] The present invention provides an organic solvent composite nanofiltration membrane, comprising a porous ultrafiltration support base membrane and a polyamide separation layer constructed on the porous ultrafiltration support base membrane;

[0008] The polyamide separation layer is obtained by polycondensation of polyacyl chloride monomers and polyamine monomers on the porous ultrafiltration support base membrane; the polyamide separation layer is obtained by polycondensation of polyacyl chloride monomers and polyamine monomers on the porous ultrafiltration support base membrane; the polyamine monomer is selected from 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane, 2,2-bis(4-hydroxy-3-aminophenyl)propane, bis(3-amino-4-hydroxyphenyl)methanone or 4,4'-oxybis(2-aminophenol); the specific structural formula is as follows Figure 4 shown.

[0009] The polyamine monomer is selected from the group consisting of: maintaining the main structure of biphenylaminophenol, and changing the functional groups on the main chain, such as trifluoromethyl, methyl, ketocarbonyl, and ether bond.

[0010] The thin film composite nanofiltration membrane has improved permeability to organic solvents.

[0011] Preferably, the porous ultrafiltration support base membrane is preferably constructed on a non-woven fabric substrate.

[0012] Preferably, the porous ultrafiltration supporting base membrane is selected from polyethersulfone ultrafiltration membrane, polyacrylonitrile ultrafiltration membrane, polysulfone ultrafiltration membrane, sulfonated polysulfone ultrafiltration membrane, vinylidene chloride ultrafiltration membrane or polyimide ultrafiltration membrane; the pore size of the porous ultrafiltration supporting base membrane is 5-100 nm.

[0013] Furthermore, the porous ultrafiltration supporting base membrane is selected from polyimide ultrafiltration membrane.

[0014] Preferably, the polyacyl chloride monomer is selected from one or more of trimesoyl chloride, terephthaloyl chloride, isophthaloyl chloride and adipoyl chloride.

[0015] The present invention also provides a method for preparing the organic solvent composite nanofiltration membrane, comprising the following steps:

[0016] S11: mixing a polyamine monomer and an aqueous solution containing an alkali auxiliary agent to obtain an aqueous phase solution; at the same time, mixing a polyacyl chloride monomer and a hydrocarbon solvent to obtain an organic phase solution;

[0017] S12: Under the conditions of room temperature (25±5°C) and humidity of 50-60%, apply the aqueous solution to the porous ultrafiltration support base membrane and then drain it, then apply the organic solution to perform interfacial polymerization to form a polyamide separation layer; the interfacial polymerization reaction temperature needs to be controlled at 25-30°C. Within a certain temperature range, an increase in temperature can intensify the movement of monomer molecules, accelerate the monomer reaction rate, and promote the formation of a thinner membrane, but if the reaction temperature is too high, it will lead to excessive crosslinking, thereby reducing the flux of the membrane.

[0018] S13: thermally cross-linking the porous ultrafiltration support base membrane containing the polyamide separation layer at 60-80° C. for 10-60 min to obtain the organic solvent composite nanofiltration membrane.

[0019] The present invention adds an alkali auxiliary agent to an aqueous solution containing polyamine monomers, and allows the aqueous solution and an organic solution containing polyacyl chloride monomers to sequentially infiltrate a porous ultrafiltration support base membrane; the polyamine monomers in the aqueous solution can be well dissolved in the aqueous solution in the presence of the alkali auxiliary agent; and the addition of the alkali auxiliary agent can also activate the organic phase acyl chloride, thereby increasing the reaction activity and reaction degree of interfacial polymerization, thereby preparing a dense and defect-free organic nanofiltration membrane.

[0020] Preferably, in step S11, the polyamine monomer and the aqueous solution containing the alkali auxiliary agent are mixed by heating at 40-80° C. for 0.5-5 min, so that the polyamine monomer is better dissolved in water to form a homogeneous aqueous solution.

[0021] Preferably, the concentration of the polyamine monomer in the aqueous solution is 0.1-10 g / L.

[0022] Furthermore, the concentration of the polyamine monomer in the aqueous solution is more preferably 0.4-3 g / L, such as 0.4 g / L, 0.5 g / L, 1 g / L, 1.5 g / L, 2 g / L, including but not limited to the concentrations listed above.

[0023] Preferably, the alkali auxiliary agent is selected from one or more of sodium hydroxide, potassium hydroxide, triethylamine and calcium hydroxide, and the mass concentration of the alkali auxiliary agent in the aqueous phase solution is 0.6-2wt%.

[0024] Further, the alkali auxiliary agent in the aqueous phase solution is sodium hydroxide and triethylamine, wherein the mass of the alkali auxiliary agent sodium hydroxide added in the aqueous phase is 10-300 mg, and the volume of triethylamine is 20-1000 μL. Too much or too low content of the alkali auxiliary agent in the aqueous phase solution will affect the performance of the organic nanofiltration membrane. Therefore, under the premise of ensuring that the organic nanofiltration membrane has a lower molecular weight cutoff, the permeation flux of the organic nanofiltration membrane to the solvent is improved, and the amount of the alkali auxiliary agent needs to be determined at a suitable value, for example, the amount of the alkali auxiliary agent sodium hydroxide is regulated to 100 mg, and the amount of triethylamine is adjusted to 275 μL.

[0025] Preferably, in step S12, the methods of applying the aqueous phase solution and the organic phase solution are both selected from coating, casting, spraying or dipping.

[0026] Furthermore, in step S12, the methods of applying the aqueous solution and the organic solution are both selected from casting.

[0027] Preferably, the hydrocarbon solvent is selected from one or more of n-hexane, cyclohexane and benzene.

[0028] Preferably, the concentration of the polyacyl chloride monomer in the organic phase solution is 0.5-10 g / L.

[0029] Furthermore, the concentration of the polyacyl chloride monomer in the organic phase solution is more preferably 1-5 g / L, such as 1.5 g / L, 2 g / L, 3 g / L, 4 g / L, including but not limited to the concentrations listed above.

[0030] Preferably, the aqueous phase solution is applied to the porous ultrafiltration supporting base membrane for 10-180 seconds, and the organic phase solution is applied to the porous ultrafiltration supporting base membrane for 80-140 seconds.

[0031] Furthermore, the aqueous solution is applied to the porous ultrafiltration support base membrane for 80-120 seconds.

[0032] Preferably, in step S12, after the aqueous phase solution fully infiltrates the surface of the porous ultrafiltration support base membrane and there is no obvious visible water stain on the surface of the porous ultrafiltration support base membrane, an organic phase solution containing polyacyl chloride monomers is applied to the membrane surface to make the membrane surface fully infiltrated with the polyacyl chloride monomer organic phase solution, and the polyamine monomer and the polyacyl chloride monomer complete the interfacial polymerization reaction at the interface between the two phases.

[0033] Specifically, the method for preparing the thin film composite nanofiltration membrane comprises the following steps:

[0034] (1) uniformly mixing a polyamine monomer, an alkali auxiliary agent and an aqueous solution to obtain an aqueous phase solution; uniformly mixing a polyacyl chloride monomer and a hydrocarbon solvent to obtain an organic phase solution;

[0035] (2) The porous ultrafiltration support base membrane is completely immersed in the aqueous solution. After the immersion is completed, the porous ultrafiltration support base membrane is taken out and the aqueous solution on the membrane surface is drained. Subsequently, the porous ultrafiltration support base membrane is completely immersed in the organic solution to perform an interfacial polymerization reaction, and a polyesteramide separation layer is formed on the surface of the porous ultrafiltration support base membrane. After the interfacial polymerization reaction is completed, the membrane is taken out and the organic solution on the membrane surface is drained. Finally, the prepared organic nanofiltration membrane is placed in a 60°C oven for thermal crosslinking for 10 minutes to obtain the organic nanofiltration membrane.

[0036] The present invention also provides the application of the above-mentioned organic solvent composite nanofiltration membrane in the separation and recovery of organic solvents, which is mainly used to improve the permeation flux of the membrane to polar and non-polar solvents; the polar solvent is one or more of methanol, ethanol, acetone, NN-dimethylformamide and acetonitrile, and the non-polar solvent is one or more of n-hexane, toluene, cyclohexane and n-heptane.

[0037] Furthermore, the organic nanofiltration membrane can be used in the fields of pretreatment of printing and dyeing wastewater, separation of mixed dyes or recovery and treatment of industrial organic waste liquid.

[0038] The present invention utilizes the functional group effect to prepare an organic nanofiltration membrane having high permeation flux and low molecular weight cutoff for polar and non-polar solvents. Compared with the traditional planar diamine monomer, the water phase monomer designed with functional groups contains both the hydrophobic functional group trifluoromethyl and the hydrophilic functional group hydroxyl. The organic nanofiltration membrane having a Janus pore structure is prepared by reacting with the organic phase monomer trimesoyl chloride by an interfacial polymerization method. The polymer network constructed by utilizing the functional group effect has both the polar group amide bond and carboxyl group in the traditional polyamide network and the large volume hydrophobic functional group trifluoromethyl. Due to the introduction of the hydrophobic functional group trifluoromethyl and the hydrophilic functional group hydroxyl, specific hydrophobic regions and hydrophilic regions can be formed inside the polymer. Thus, a structure similar to the Janus pore is formed to improve the permeation flux of the membrane to polar and non-polar solvents. In addition, the dual active functional groups of hydroxyl and amino can also form a double cross-linked network with the acyl chloride, thereby providing excellent solvent resistance and separation performance for the organic nanofiltration membrane.

[0039] CN117282277A discloses a hollow fiber desalination membrane and its preparation method. The present invention mainly studies organic nanofiltration membranes, and the background is also for organic nanofiltration systems. CN117282277A is a water-salt system. The research focus and research objects of different systems are very different. The requirements for separation membranes for different systems are also different. It is impossible to make a unified standard to compare the advantages and disadvantages of the work. Secondly, the types of separation membranes of the two are also different. The present invention mainly studies thin film composite membranes, and CN117282277A studies hollow fiber membranes. Different types of membranes correspond to different processes and production requirements, so they are essentially different from the present invention.

[0040] The technical solution of the present invention has the following advantages over the prior art:

[0041] 1. The present invention introduces an alkali auxiliary agent to polymerize polyamine monomers and polyacyl chloride monomers on the surface of a porous ultrafiltration support base membrane to obtain a polyesteramide separation layer with adjustable pore size within a certain range, so that the prepared organic nanofiltration membrane has the excellent properties of high permeability flux and low molecular weight cutoff; and the present invention can adjust the separation performance of the thin film composite nanofiltration membrane for dyes of different molecular weights by changing the content of the alkali auxiliary agent in the aqueous phase solution.

[0042] 2. The present invention also provides a method for designing the monomer structure of the above-mentioned high-performance organic nanofiltration membrane, which realizes the regulation of the polymer structure by utilizing the functional group effect. The introduction of an aqueous phase monomer having a hydrophobic functional group trifluoromethyl and a hydrophilic functional group hydroxyl, utilizes the functional functional groups to construct a polymer network having a Janus-like pore structure. In addition, the introduction of hydroxyl groups to the aqueous phase monomers, on the one hand, is conducive to the dissolution of the fluorinated biphenyl structure monomer in the presence of an alkali auxiliary agent, and on the other hand, the presence of the dual active functional groups can construct a dual cross-linked network, which not only improves the solvent resistance of the organic nanofiltration membrane but also improves the separation selectivity. The above-mentioned high-performance organic nanofiltration membrane is prepared by the functional group effect, which not only makes the raw materials easy to obtain, but also the performance of the prepared organic nanofiltration membrane is controllable, can meet the needs of different application scenarios, and has the potential for industrialization.

[0043] 3. The retention rate of the above high-performance organic nanofiltration membrane for dye molecules with a molecular weight higher than 300Da at a concentration of 20mmol / L is greater than 90%, and the flux for polar solvents such as methanol is as high as 16.6L m -2 h -1 bar -1 ; The flux of non-polar solvent n-hexane is up to 8.5 L m -2 h -1 bar -1 Toluene flux up to 3.1 L m -2 h -1 bar -1 The above-mentioned organic nanofiltration membrane with excellent permeability and separation performance has a wide range of application scenarios in printing and dyeing wastewater, mixed dye separation, industrial organic waste liquid treatment, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 This is an evaluation diagram of the wettability of the thin film composite nanofiltration membrane surface prepared in Example 1 to different organic solvents;

[0045] Figure 2 The graph of carbon dioxide gas adsorption by the thin film composite nanofiltration membrane prepared by the aqueous phase monomers described in Example 1 and Comparative Example 2;

[0046] Figure 3 The pore size distribution diagram of the thin film composite nanofiltration membrane prepared from the aqueous phase monomers described in Example 1 and Comparative Example 2;

[0047] Figure 4 This is a structural diagram of the aqueous phase monomers described in Examples 1 to 4 and Comparative Examples 1 and 2. DETAILED DESCRIPTION

[0048] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0049] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

[0050] Example 1

[0051] This embodiment relates to the preparation of a thin film composite nanofiltration membrane, which is prepared by a porous ultrafiltration support base membrane and a polyamide separation layer constructed on the porous ultrafiltration support base membrane, and the polyamide separation layer is prepared by interfacial polymerization reaction of 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (bisAPAF, a polyamine monomer) and trimesoyl chloride (TMC, a polyacyl chloride monomer) under the control of an alkali auxiliary (100 mg of sodium hydroxide and 275 μL of triethylamine). The specific preparation process is as follows:

[0052] (1) Preparation of aqueous phase solution and organic phase solution: Under the conditions of temperature of 25° C. and relative humidity of 60%, bisAPAF was mixed with sodium hydroxide and triethylamine and uniformly dissolved in a pure water solution to prepare an aqueous phase solution with a concentration of 0.5 g / L; TMC was dissolved in n-hexane solution to prepare an organic phase solution with a concentration of 1.5 g / L.

[0053] (2) Preparation of polyamide separation layer: At room temperature, the cross-linked polyimide ultrafiltration bottom membrane was soaked with the aqueous solution prepared above for 120 seconds, and then the solution on the membrane surface was drained until there was no obvious water stain, and then the membrane surface was soaked with the organic solution prepared above for 120 seconds to form a polyamide separation layer on the membrane surface, and then the membrane was soaked in n-hexane for 30 seconds to wash away the unreacted trimesoyl chloride monomer on the membrane surface. Finally, the membrane was transferred to an oven, heat treated at 60°C for 10 minutes, and then soaked in anhydrous methanol and stored in a refrigerator.

[0054] Figure 1The graph shows the contact angle of the thin film composite nanofiltration membrane prepared in this example for different organic solvents. It can be seen from the graph that the organic nanofiltration membrane prepared after functional group design exhibits excellent hydrophobicity and lipophilicity. The performance of the thin film composite nanofiltration membrane prepared under the experimental conditions is: Methanol flux: 16.6Lm -2 h -1 bar -1 , Toluene flux: 3.1Lm -2 h - 1 bar -1 , n-hexane flux: 8.5Lm -2 h -1 bar -1 , Coomassie Brilliant Blue retention rate: 99.2%, Congo Red retention rate: 99.1%, Acid Fuchsin retention rate: 98.4%, Rhodamine B retention rate: 97.5%, Methyl Orange retention rate: 88%.

[0055] Example 2

[0056] This embodiment relates to the preparation of a thin film composite nanofiltration membrane, and the only difference from the embodiment 1 is the selection of the aqueous phase monomer for preparing the thin film composite membrane. In this embodiment, 2,2-bis(4-hydroxy-3-aminophenyl)propane is selected as the aqueous phase monomer, and the rest is the same as the embodiment 1. The performance of the thin film composite nanofiltration membrane prepared under the experimental conditions is: Methanol flux: 13.6L m -2 h -1 bar -1 , Toluene flux: 2.3Lm -2 h -1 bar -1 , n-hexane flux: 2.2Lm -2 h -1 bar -1 , Coomassie Brilliant Blue retention rate: 99.3%, Congo Red retention rate: 98.9%, Acid Fuchsin retention rate: 98.7%, Rhodamine B retention rate: 96.2%, Methyl Orange retention rate: 81.3%.

[0057] Example 3

[0058] This embodiment relates to the preparation of a thin film composite nanofiltration membrane, and the only difference from the embodiment 1 is the selection of the aqueous phase monomer for preparing the thin film composite membrane. In this embodiment, bis(3-amino-4-hydroxyphenyl)methanone is selected as the aqueous phase monomer, and the rest is the same as the embodiment 1. The performance of the thin film composite nanofiltration membrane prepared under the experimental conditions is: methanol flux: 14.3Lm -2 h -1 bar -1 , Toluene flux: 0.7Lm -2 h -1bar -1 , n-hexane flux: 1.1Lm -2 h -1 bar -1 , Coomassie Brilliant Blue retention rate: 99.5%, Congo Red retention rate: 99.2%, Acid Fuchsin retention rate: 98.9%, Rhodamine B retention rate: 96.5%, Methyl Orange retention rate: 83.6%.

[0059] Example 4

[0060] This embodiment relates to the preparation of a thin film composite nanofiltration membrane, and the only difference from the embodiment 1 is the selection of the aqueous phase monomer for preparing the thin film composite membrane. In this embodiment, 4,4'-oxybis(2-aminophenol) is selected as the aqueous phase monomer, and the rest is the same as the embodiment 1. The performance of the thin film composite nanofiltration membrane prepared under the experimental conditions is: Methanol flux: 14.7Lm -2 h -1 bar -1 , Toluene flux: 0.8Lm -2 h -1 bar -1 , n-hexane flux: 1.3Lm -2 h -1 bar -1 , Coomassie Brilliant Blue retention rate: 99.3%, Congo Red retention rate: 99.1%, Acid Fuchsin retention rate: 98.6%, Rhodamine B retention rate: 95.9%, Methyl Orange retention rate: 83.3%.

[0061] Example 5

[0062] This example relates to the preparation of a thin film composite nanofiltration membrane. The only difference from Example 1 is that no alkali auxiliary agent sodium hydroxide is added, and the rest is the same as Example 1. The performance of the thin film composite nanofiltration membrane prepared under the experimental conditions is: methanol flux: 18.4Lm -2 h -1 bar -1 , Toluene flux: 4.1Lm -2 h -1 bar -1 , n-hexane flux: 8.7Lm -2 h -1 bar -1 , Coomassie Brilliant Blue retention rate: 99.1%, Congo Red retention rate: 98.5%, Acid Fuchsin retention rate: 95.7%, Rhodamine B retention rate: 91%, Methyl Orange retention rate: 73%.

[0063] Example 6

[0064] This example relates to the preparation of a thin film composite nanofiltration membrane. The only difference from Example 1 is that no alkali auxiliary agent triethylamine is added, and the rest is the same as Example 1. The performance of the thin film composite nanofiltration membrane prepared under the experimental conditions is: methanol flux: 8.3L m -2 h -1 bar -1 , Toluene flux: 1.9Lm -2 h -1 bar -1 , n-hexane flux: 1.7Lm -2 h -1 bar -1 , Coomassie Brilliant Blue retention rate: 99.7%, Congo Red retention rate: 99.5%, Acid Fuchsin retention rate: 99.3%, Rhodamine B retention rate: 99.1%, Methyl Orange retention rate: 95%.

[0065] Example 7

[0066] This example relates to the preparation of a thin film composite nanofiltration membrane, and the only difference from Example 1 is the concentration of bisAPAF in the aqueous solution. The concentration of bisAPAF in the aqueous solution in this example is 2 g / L, and the rest is the same as in Example 1. The performance of the thin film composite nanofiltration membrane prepared under the experimental conditions is: methanol flux: 8.3 L m -2 h -1 bar -1 , Toluene flux: 1.2Lm -2 h -1 bar -1 , hexane flux: 3.7 L m -2 h -1 bar -1 , Coomassie Brilliant Blue retention rate: 99.6%, Congo Red retention rate: 99.5%, Acid Fuchsin retention rate: 99.2%, Rhodamine B retention rate: 98.7%, Methyl Orange retention rate: 90%.

[0067] Example 8

[0068] This example relates to the preparation of a thin film composite nanofiltration membrane, and the only difference from Example 1 is the reaction time of interfacial polymerization. The reaction time of interfacial polymerization in this example is 140 s, and the rest is the same as in Example 1. The performance of the thin film composite nanofiltration membrane prepared under the experimental conditions is: methanol flux: 10.7 L m -2 h -1 bar -1 , Toluene flux: 1.9Lm -2 h -1 bar -1 , n-hexane flux: 5.2Lm -2 h -1bar -1 , Coomassie Brilliant Blue retention rate: 99.4%, Congo Red retention rate: 99.3%, Acid Fuchsin retention rate: 99.1%, Rhodamine B retention rate: 98.5%, Methyl Orange retention rate: 89%.

[0069] Example 9

[0070] This example relates to the preparation of a thin film composite nanofiltration membrane. The only difference from Example 1 is the amount of alkali additive added. In this example, the amount of sodium hydroxide added to the alkali additive is 50 mg, and the rest is the same as Example 1. The performance of the thin film composite nanofiltration membrane prepared under the experimental conditions is: Methanol flux: 17.8 Lm -2 h -1 bar -1 , Toluene flux: 3.7Lm -2 h - 1 bar -1 , n-hexane flux: 8.7Lm -2 h -1 bar -1 , Coomassie Brilliant Blue retention rate: 99.3%, Congo Red retention rate: 99.2%, Acid Fuchsin retention rate: 99%, Rhodamine B retention rate: 98.5%, Methyl Orange retention rate: 83%.

[0071] Comparative Example 1

[0072] This comparative example involves the preparation of a thin film composite nanofiltration membrane, and the only difference from Example 1 is the selection of the aqueous phase monomer for preparing the thin film composite membrane. In this example, 3,3'-dihydroxybenzidine without a hydrophobic functional group trifluoromethyl is selected as the aqueous phase monomer, and the rest is the same as Example 1. The performance of the thin film composite nanofiltration membrane prepared under the experimental conditions is: methanol flux: 11L m -2 h -1 bar -1 , toluene flux: 0.3 L m -2 h -1 bar -1 , hexane flux: 0.4 L m -2 h - 1 bar -1 , Coomassie Brilliant Blue retention rate: 99.3%, Congo Red retention rate: 99.2%, Acid Fuchsin retention rate: 99%, Rhodamine B retention rate: 97.9%, Methyl Orange retention rate: 91.7%.

[0073] Comparative Example 2

[0074] This comparative example involves the preparation of a thin film composite nanofiltration membrane, and the only difference from Example 1 is the selection of the aqueous phase monomer for preparing the thin film composite membrane. In this example, planar m-phenylenediamine is selected as the aqueous phase monomer, and the rest is the same as Example 1. The performance of the thin film composite nanofiltration membrane prepared under the experimental conditions is: methanol flux: 4.1 L m -2 h -1 bar-1, toluene flux: 0.1Lm -2 h -1 bar -1 , hexane flux: 0.1 L m -2 h -1 bar -1 , Coomassie Brilliant Blue retention rate: 99.7%, Congo Red retention rate: 99.5%, Acid Fuchsin retention rate: 98.7%, Rhodamine B retention rate: 97.9%, Methyl Orange retention rate: 95%.

[0075] Effect evaluation 1 Effect of the introduction of functional groups on the permeation separation performance of thin film composite nanofiltration membrane

[0076] The present invention takes Example 1 and Comparative Example 1 as examples to study the effect of the introduction of a hydrophobic functional group trifluoromethyl on the permeation separation performance of a thin film composite nanofiltration membrane.

[0077] Figure 2 The polyamine monomers in the aqueous solution are 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane and planar structured meta-phenylenediamine with the hydrophobic functional group trifluoromethyl introduced. The adsorption curve of carbon dioxide gas under the same test conditions shows that the thin film composite nanofiltration membrane with the introduction of large-volume hydrophobic trifluoromethyl has a higher specific surface area.

[0078] Figure 3 The pore size distribution diagram of the thin film composite nanofiltration membrane prepared under the conditions of Example 1 and Comparative Example 2 shows that the thin film composite nanofiltration membrane prepared in Example 1 has larger and more abundant micropores than the thin film composite nanofiltration membrane prepared in Example 3. This is because the introduction of large-volume trifluoromethyl groups can effectively inhibit the close stacking of molecular chains, resulting in a larger free volume in the polymer network. On the other hand, the presence of dual active functional groups in the 4+3 system can form a dual cross-linked network, thereby increasing the porosity of the polymer network.

[0079] Effect evaluation 2 Study on solvent flux and retention rate of nanofiltration membrane

[0080] The solvent flux and the retention rate of dyes with different molecular weights of the thin film composite nanofiltration membranes prepared in the above examples and comparative examples were tested. The specific operation was as follows: at a temperature of 25° C. and an operating pressure of 5 bar,

[0081] (1) Testing the permeation flux of organic solvents;

[0082] (2) Test the retention rate of 20 ppm CBB dye;

[0083] (3) Test the retention rate of 20 ppm CR dye;

[0084] (4) Test the retention rate of 20ppm ACF dye;

[0085] (5) Testing the retention rate of 20 ppm RhB dye;

[0086] (6) Test the retention rate of 20 ppm MO dye.

[0087] The separation performance of the thin film composite nanofiltration membrane was evaluated using a cross-flow filtration device. The effective test membrane area was 3.14 cm 2 , the test pressure is 5 bar. Before the test, the membrane is pre-pressurized until the test solvent flux reaches a stable level.

[0088] Organic solvent permeation flux test: The organic solvent permeation flux (Permeance, L m-1) of the membrane was calculated by formula 1. 2 h- 1 bar- 1 ):

[0089] P=Δm / ρSPΔt (1)

[0090] Where Δm (Kg) is the mass of solvent permeate collected within Δt (s) (cross-flow time); ρ is the density of the permeate solvent in Kg / m 3 ; S is the effective filtration area of ​​the separation membrane, in m 2 ; ΔP is the transmembrane pressure, the unit is bar.

[0091] Solute separation test: Prepare 20ppm dye solutions of different molecular weights as feed solutions. Measure the absorbance of the feed solution and filtrate using a UV-visible spectrophotometer and calculate the retention rate (R). The calculation formula (2) is:

[0092]

[0093] Among them, C p and C f represent the concentration of solute in the permeate and feed solution (mg mL -1 ).

[0094] It can be seen from Example 1 and Comparative Examples 1 and 2 that the introduction of the hydrophobic functional group trifluoromethyl can improve the membrane's permeation flux to organic solvents, especially the permeation flux to non-polar solvents. This is because the introduction of the hydrophobic functional group trifluoromethyl and the hydrophilic functional group hydroxyl can construct a Janus pore structure in the polymer network to improve the membrane's permeation flux to polar and non-polar solvents.

[0095] It can be seen from Examples 1 and 7 that increasing the content of polyamine monomers in the aqueous solution to a certain extent has little effect on the dye retention rate but will reduce the flux of the membrane to the solvent. This is because the increase in the content of polyamine monomers will increase the reaction activity of the monomers and improve the degree of cross-linking, making the prepared membrane denser.

[0096] It can be seen from Examples 1 and 8 that extending the interfacial polymerization reaction time to a certain extent can further improve the retention rate of the thin film composite membrane, but it will reduce the membrane's permeation flux to the solvent. This is because as the interfacial polymerization reaction time increases, the thickness of the separation layer increases.

[0097] It can be seen from Examples 1 and 9 that increasing the amount of alkali additive added to the aqueous solution can increase the dye retention rate of the membrane, but will reduce the permeation flux of the membrane to the solvent. This is because increasing the amount of alkali additive in the aqueous solution to a certain extent is beneficial to the conversion of hydroxyl groups into sodium phenol salts, increasing the reaction activity of the monomer and improving the degree of crosslinking.

[0098] It can be seen from Example 1, Example 5 and Example 6 that the addition of the alkali auxiliary sodium hydroxide can further improve the retention rate of the membrane, because the addition of sodium hydroxide can promote the conversion of hydroxyl groups into sodium phenolate, increase the monomer reactivity and improve the crosslinking degree, and prepare a denser thin film composite nanofiltration membrane. The addition of the alkali auxiliary triethylamine can increase the permeation flux of the membrane to the organic solvent, because the addition of triethylamine can activate the acyl chloride and promote the reaction.

[0099] It can be seen from Examples 2 to 4 and Comparative Examples 1 and 2 that the introduction of different active functional groups on the main chain of the aqueous phase monomer will affect the separation performance of the organic solvent composite nanofiltration membrane. This is because the electron-withdrawing ability of different active functional groups on the main chain will affect the reaction activity of the amino and hydroxyl groups on the side chain, thereby affecting the separation performance of the organic solvent composite nanofiltration membrane.

[0100] In summary, the present invention can prepare a polyesteramide separation layer with a Janus pore structure by introducing a hydrophobic functional group trifluoromethyl and a hydrophilic functional group hydroxyl into the reaction system of preparing a polyamide separation layer from a polyamine monomer and a polyacyl chloride monomer, thereby obtaining a thin film composite nanofiltration membrane with high flux and low molecular weight cutoff for polar and non-polar solvents, which can be used for solvent recovery of organic waste liquid; in addition, the pore size of the thin film composite nanofiltration membrane can be adjusted by changing the amount of alkali additive added in the aqueous phase solution.

[0101] Obviously, the above embodiments are merely examples for clear explanation and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the protection scope of the invention.

Claims

1. An organic solvent composite nanofiltration membrane, characterized in that: It includes a porous ultrafiltration support base membrane and a polyamide separation layer constructed on the porous ultrafiltration support base membrane; The polyamide separation layer is obtained by polycondensation of polyacyl chloride monomers and polyamine monomers on the porous ultrafiltration support base membrane; the polyamine monomers are selected from 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane, 2,2-bis(4-hydroxy-3-aminophenyl)propane, bis(3-amino-4-hydroxyphenyl)ketone or 4,4'-oxybis(2-aminophenol).

2. The organic solvent composite nanofiltration membrane according to claim 1, characterized in that: The porous ultrafiltration supporting base membrane is selected from polyethersulfone ultrafiltration membrane, polyacrylonitrile ultrafiltration membrane, polysulfone ultrafiltration membrane, sulfonated polysulfone ultrafiltration membrane, vinylidene chloride ultrafiltration membrane or polyimide ultrafiltration membrane; the pore size of the porous ultrafiltration supporting base membrane is 5-100nm.

3. The organic solvent composite nanofiltration membrane according to claim 1, characterized in that: The polyacyl chloride monomer is selected from one or more of trimesoyl chloride, terephthaloyl chloride, isophthaloyl chloride and adipoyl chloride.

4. A method for preparing the organic solvent composite nanofiltration membrane according to any one of claims 1 to 3, characterized in that: The steps include: S11: mixing a polyamine monomer and an aqueous solution containing an alkali auxiliary agent to obtain an aqueous phase solution; at the same time, mixing a polyacyl chloride monomer and a hydrocarbon solvent to obtain an organic phase solution; S12: applying the aqueous phase solution to the porous ultrafiltration support base membrane at room temperature and a humidity of 50-60% and then draining it, and then applying the organic phase solution to perform an interfacial polymerization reaction to form a polyamide separation layer; S13: thermally cross-linking the porous ultrafiltration support base membrane containing the polyamide separation layer at 60-80° C. for 10-60 min to obtain the organic solvent composite nanofiltration membrane.

5. The preparation method according to claim 4, characterized in that: The concentration of the polyamine monomer in the aqueous phase solution is 0.1-10 g / L.

6. The preparation method according to claim 4, characterized in that: The alkali auxiliary agent is selected from one or more of sodium hydroxide, potassium hydroxide, triethylamine, and calcium hydroxide, and the mass concentration of the alkali auxiliary agent in the aqueous phase solution is 0.6-2wt%.

7. The preparation method according to claim 4, characterized in that: In the step S12, the methods of applying the aqueous solution and the organic solution are selected from coating, casting, spraying or dipping.

8. The preparation method according to claim 4, characterized in that: The hydrocarbon solvent is selected from one or more of n-hexane, cyclohexane and benzene.

9. The preparation method according to claim 4, characterized in that: The concentration of the polyacyl chloride monomer in the organic phase solution is 0.5-10 g / L.

10. Use of the organic solvent composite nanofiltration membrane according to any one of claims 1 to 3 in separation and recovery of organic solvents.

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