Preparation method and application of high-temperature-resistant and acid-resistant polysulfide urea composite nanofiltration membrane

Abstract

The application discloses a preparation method of a high-temperature-resistant and acid-resistant polysulfide urea composite nanofiltration membrane and application thereof, and belongs to the technical field of membrane materials. The method uses a porous base film as a support layer, sequentially contacts an aqueous solution containing a polyamine compound and an amino inorganic filler with an oil phase solution containing a diisothiocyanate compound, generates a polymerization reaction at an interface to form a polysulfide urea separation layer, and obtains the high-temperature-resistant and acid-resistant polysulfide urea composite nanofiltration membrane after heat treatment. The obtained nanofiltration membrane has high water flux, excellent separation selectivity, and good high-temperature resistance, strong acid resistance and long-term operation stability, and can be applied to the separation of inorganic salt, organic acid, dye, antibiotic, divalent anion salt, organic acid, dye, antibiotic, heavy metal ion and rare earth metal complex and the like in a high-temperature and strong-acid system, and to the fields of hydrometallurgy, pickling waste liquid treatment and resource recovery and the like.

Description

Technical Field

[0001] This invention belongs to the field of membrane material technology, specifically relating to a method for preparing a high-temperature and acid-resistant polythiourea composite nanofiltration membrane and its application. Background Technology

[0002] Nanofiltration, a pressure-driven membrane separation technology situated between ultrafiltration and reverse osmosis, combines high water flux with excellent separation selectivity, and has been widely applied in fields such as advanced drinking water purification, industrial wastewater treatment, resource recovery, food and pharmaceutical separation and concentration, and chemical product refining. In recent years, with the rapid development of industries such as new energy, hydrometallurgy, and resource recycling, the separation requirements for complex industrial liquids such as high-temperature and strong acid solutions have placed higher demands on nanofiltration membranes.

[0003] Currently, most commercially available nanofiltration membranes are polyamide thin-layer composite structures, with their separation layers typically formed by interfacial polymerization of polyamines and polyacrylamide chlorides. Polyamide nanofiltration membranes have advantages such as mature manufacturing processes and excellent separation performance. However, their separation layers contain a large number of amide bonds, which are prone to acid-catalyzed hydrolysis under strong acid conditions. This leads to changes in the surface charge properties of the membrane, gradual destruction of the polyamide crosslinking network, and consequently, problems such as decreased rejection rate, abnormally increased water flux, and even separation layer failure.

[0004] As operating temperatures rise, the thermal motion of polymer chain segments intensifies, and the cross-linked structure is prone to relaxation or even partial chain segment degradation. This causes irreversible swelling of the separation layer, increasing membrane pore size and reducing separation performance. Therefore, most commercially available polyamide nanofiltration membranes operate below 45 °C, making it difficult to meet the long-term stable separation requirements of high-temperature industrial processes.

[0005] In some industrial processes, high-temperature and strong-acid environments often coexist. For example, in processes such as lithium extraction from geothermal brine, separation of acid leaching solutions in hydrometallurgical processes, treatment of metal pickling waste, and high-temperature chemical cleaning, separation membranes need to operate in high-temperature acidic media for extended periods. High temperatures promote acid diffusion into the polymer and increase the chemical reaction rate, while acid catalysis further accelerates the degradation of polymer segments. The synergistic effect of these two factors significantly accelerates membrane aging, leading to a substantial reduction in membrane lifespan. Therefore, developing nanofiltration membranes that possess both high-temperature and strong-acid resistance has significant engineering application value.

[0006] Patent document CN121003900A discloses a polythiourea composite nanofiltration membrane, its preparation method and application. The polythiourea separation layer is constructed by interfacial polymerization of polyamines and polyisothiocyanate compounds and applied to the field of water treatment, which improves the structural stability of the composite nanofiltration membrane in a strong acid environment and improves the acid resistance of the composite nanofiltration membrane.

[0007] Patent document CN112717712A discloses an acid-resistant nanofiltration membrane and its preparation method. By using an aqueous phase system containing sulfonamide monomers to perform interfacial polymerization with an oil phase monomer, and combining multiple interfacial polymerization processes to construct a polysulfonamide separation layer, the structural stability and inorganic salt separation performance of the nanofiltration membrane under acidic conditions are improved.

[0008] The aforementioned existing technologies have studied acid-resistant nanofiltration membranes, mainly focusing on improving the chemical stability of the membrane by constructing an acid-resistant polymer separation layer. However, research on issues such as the relaxation of cross-linked structures caused by enhanced thermal motion of polymer segments under high temperatures, and the promotion of acid hydrolysis of the separation layer at high temperatures, remains lacking. Therefore, developing a nanofiltration membrane that can balance acid resistance and high-temperature resistance is of great significance. Summary of the Invention

[0009] This invention provides a method for preparing a high-temperature and acid-resistant polythiourea composite nanofiltration membrane. The method involves an interfacial polymerization reaction between a polyamine compound and an aminated inorganic filler with a diisothiocyanate compound on the surface of a porous membrane, thereby constructing an organic-inorganic polythiourea separation layer in situ. The resulting nanofiltration membrane possesses a stable polythiourea crosslinked network structure, which significantly improves the membrane material's high-temperature and acid resistance, as well as its long-term operational stability, while also exhibiting excellent nanofiltration separation performance and high water flux.

[0010] The specific technical solution adopted is as follows: A method for preparing a high-temperature and acid-resistant polythiourea composite nanofiltration membrane includes the following steps: (1) The aqueous solution containing polyamine compounds and aminated inorganic fillers is brought into full contact with the porous base membrane to ensure that the solution uniformly wets the porous base membrane; (2) After removing excess aqueous solution from the surface of the porous base membrane, it is then contacted with an oil solution containing diisothiocyanate compound to undergo interfacial polymerization reaction and form an organic-inorganic polythiourea separation layer. (3) After the interfacial polymerization is completed, the membrane is subjected to heat treatment to cure and crosslink, thereby obtaining a high-temperature and acid-resistant polythiourea composite nanofiltration membrane. In the aqueous solution, the concentration of polyamine compounds is 0.05~20 g / L, and the concentration of aminated inorganic filler is 0.01~2 g / L; The concentration of the oil phase solution is 0.025~10 g / L.

[0011] The polyamine compounds contain multiple amino functional groups and can undergo rapid interfacial polymerization with diisothiocyanates. The sulfur atoms in the thiourea bonds have a large electron cloud polarization ability, which can form strong intermolecular hydrogen bonding. The high bond stability is also beneficial to improving the chemical stability of the polymer network in acidic media.

[0012] The surface of the aminated inorganic filler contains active amino groups, which can react with diisothiocyanate compounds. The inorganic nanofiller is embedded in the polythiourea network through organic-inorganic synergistic crosslinking nodes, which restricts the thermal movement of chain segments and improves the structural stability of the separation layer. As a result, the obtained nanofiltration membrane has excellent high temperature resistance, strong acid resistance and long-term operational stability.

[0013] Preferably, the polyamine compound is at least one of triaminoguanidine, melamine, 3,3′,4,4′-tetraaminobiphenyl, diethylenetriamine, tetraethylenepentamine, and polyethyleneimine. Aromatic polyamines can further improve the rigidity of the separation layer, which is beneficial to improving the high-temperature resistance of the membrane. Aliphatic polyamines have high reactivity, which can improve the interfacial polymerization efficiency and facilitate the formation of a dense and continuous polythiourea separation layer.

[0014] Preferably, the concentration of polyamine compounds in the aqueous solution is 0.5~5 g / L.

[0015] Preferably, the preparation steps of the aminated inorganic filler include: mixing inorganic nanoparticles with a solvent, dispersing them by ultrasound to form a uniform suspension; then adding an aminated modifier and deionized water, stirring at 60-80 °C for 6-12 h; after the reaction is completed, centrifuging, washing, and drying are performed to obtain an aminated inorganic filler with amino functional groups on its surface.

[0016] Preferably, the aminated modifier is 3-aminopropyltriethoxysilane (APTES).

[0017] Preferably, the aminated inorganic filler is at least one of aminated silica, aminated zirconium oxide, aminated alumina, aminated hexagonal boron nitride, aminated halloysite nanotubes, and aminated montmorillonite.

[0018] The aforementioned inorganic filler possesses high structural rigidity and good thermal stability. After surface amination, active amino groups capable of reacting with diisothiocyanate groups are introduced onto its surface. During interfacial polymerization, these surface amino groups can participate in the formation of the polythiourea network, enabling the inorganic filler not only to be dispersed as a physical filling phase in the separation layer but also to act as organic-inorganic interface connecting nodes embedded in the polythiourea network. Simultaneously, the rigid structure of the inorganic filler can spatially constrain the surrounding polymer chains, suppressing excessive movement of polymer chains and pore expansion under high-temperature conditions, thus improving the structural stability of the separation layer under high-temperature and strong acid conditions.

[0019] Preferably, the concentration of the aminated inorganic filler in the aqueous solution is 0.05~0.5 g / L. A suitable addition amount is beneficial for improving the dispersibility of the filler.

[0020] Preferably, the average particle size of the aminated inorganic filler is 5~100 nm.

[0021] More preferably, the average particle size of the aminated inorganic filler is 10-30 nm. A suitable nanoparticle size is beneficial for improving the dispersibility of the filler and the organic-inorganic interface contact area.

[0022] Preferably, the amino density on the surface of the amination-treated inorganic filler is 0.2~5 mmol / g.

[0023] More preferably, the amino density on the surface of the amination-treated inorganic filler is 0.5~3 mmol / g. Excessive amino density can easily cause particle agglomeration and excessively rapid local reactions, while insufficient amino density will reduce the interfacial contact area and the degree of effective cross-linking, both of which are detrimental to the formation of a uniform and dense separation layer.

[0024] The porous base membrane includes polyethersulfone ultrafiltration membrane, polysulfone ultrafiltration membrane, polyimide ultrafiltration membrane, polyacrylonitrile ultrafiltration membrane, polybenzimidazole ultrafiltration membrane or polyisophthalamide ultrafiltration membrane.

[0025] In step (2), the oil phase solvent is at least one of n-hexane, n-heptane, cyclohexane, isoparaffin, toluene, or ethyl acetate.

[0026] Preferably, the diisothiocyanate compound is at least one selected from p-phenylene diisothiocyanate, toluene-2,4-diisothiocyanate, 1,3-phenylene diisothiocyanate, 1,2-phenylene diisothiocyanate, hexamethylene diisothiocyanate, naphthalene diisothiocyanate, and binaphthalene diisothiocyanate.

[0027] Preferably, the concentration of diisothiocyanate compound in the oil phase solution is 0.5~2 g / L. A suitable concentration ensures sufficient reaction between diisothiocyanate and the amino groups on the surface of polyamines and aminated inorganic fillers, promoting the formation of a continuous and dense polythiourea network. Too low a concentration may lead to insufficient polymerization and crosslinking, while too high a concentration may result in excessively rapid interfacial reactions, an excessively thick separation layer, or an uneven structure.

[0028] Preferably, the weight ratio of the polyamine compound to the diisothiocyanate compound is 1:5 to 10:1. By adjusting the relative ratio of the two reactive monomers, the interfacial mass transfer and polymerization reaction rate can be coordinated, the degree of crosslinking of the polythiourea network and the density of the separation layer can be controlled, thereby taking into account the membrane's permeability, separation selectivity and high-temperature acid resistance.

[0029] In step (3), after the interfacial polymerization is completed, heat treatment is performed to further improve the crosslinking degree and stability of the polythiourea separation layer, thereby improving the high temperature and acid resistance of the membrane and its long-term operational stability.

[0030] Preferably, the heat treatment temperature is 40~120℃ and the heat treatment time is 1~90 min.

[0031] The present invention also provides a high-temperature and acid-resistant polythiourea nanofiltration membrane prepared by the above method. The nanofiltration membrane includes a porous base membrane and a polythiourea separation layer. The polythiourea separation layer is formed by interfacial polymerization of diisothiocyanate with polyamine and aminated inorganic filler, and contains repeating thiourea bond (-NH-C(=S)-NH-) structure. The high temperature is a temperature higher than 45°C, and the strong acid is a pH value less than 3.

[0032] This invention also provides the application of the high-temperature and acid-resistant polythiourea nanofiltration membrane, which can be applied to nanofiltration separation processes in high-temperature strong acid systems and is suitable for the efficient separation and recovery of substances such as divalent anionic salts, organic acids, dyes, antibiotics, heavy metal ions and rare earth metal complexes.

[0033] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention uses surface-aminated inorganic fillers to participate in the interfacial polymerization reaction of polythiourea. The active amino groups on the surface of the filler can react chemically with diisothiocyanate, so that the inorganic nanofiller is uniformly embedded in the polythiourea separation layer as an organic-inorganic synergistic crosslinking node, which improves the overall crosslinking degree of the separation layer and helps to balance high water flux and excellent retention performance.

[0034] (2) The present invention uses diisothiocyanate and polyamine compounds to construct a polythiourea separation layer. The thiourea bond has high chemical stability. At the same time, the organic-inorganic synergistic crosslinking network further inhibits the erosion of the polymer network by the acidic medium, thereby improving the structural stability and separation performance of the nanofiltration membrane in a high temperature and strong acid environment.

[0035] (3) The present invention can realize the construction of organic-inorganic synergistic crosslinked polythiourea separation layer by using conventional interfacial polymerization process. The preparation process is simple and has good repeatability. The obtained nanofiltration membrane has high water flux, excellent selectivity and good high temperature resistance and strong acid resistance. It can be applied to hydrometallurgy, geothermal brine lithium extraction, pickling waste liquid treatment, resource recovery and other high temperature acid media separation fields. Attached Figure Description

[0036] Figure 1 This is a scanning electron microscope image of the surface of a polyethersulfone ultrafiltration membrane.

[0037] Figure 2 This is a scanning electron microscope image of the surface of the polythiourea nanofiltration membrane prepared in Example 1.

[0038] Figure 3 This is a scanning electron microscope image of the surface of the polythiourea nanofiltration membrane prepared in Comparative Example 1. Detailed Implementation

[0039] The specific embodiments of the present invention will be described in detail below with reference to the examples and accompanying drawings. It should be noted that the embodiments are merely illustrative and intended to aid in understanding the present invention, and do not limit the scope of protection of the present invention. Any modifications, additions, or substitutions made by those skilled in the art based on the embodiments of the present invention without inventive effort should be considered within the scope of protection of the present invention.

[0040] Unless otherwise specified, all reagents and raw materials used are commercially available analytical grade, and the operating conditions are generally standard.

[0041] Preparation of Aminated Inorganic Fillers The aminated inorganic filler used in this invention can be prepared by surface amination modification of corresponding commercial inorganic fillers. In this specific embodiment, 3-aminopropyltriethoxysilane (APTES) is used as the amination modifier.

[0042] Inorganic nanoparticles were mixed with a solvent and ultrasonically dispersed to form a uniform suspension. Then, an amination modifier and deionized water were added, and the mixture was stirred at 60–80 °C for 6–12 h. After the reaction was completed, the mixture was centrifuged, washed, and dried to obtain an amination-modified inorganic filler with amino functional groups on its surface.

[0043] Example 1 Polyethyleneimine (PEI, molecular weight 70,000) was dissolved in deionized water to prepare an aqueous monomer solution with a concentration of 1.0 g / L. 0.10 g / L of aminated silica nanoparticles (average particle size 15 nm, surface amino density 1.0 mmol / g) were added and ultrasonically dispersed to obtain the aqueous solution for later use. Terephthalic diisothiocyanate was dissolved in n-hexane to prepare an oil phase solution with a concentration of 1.0 g / L. A polyethersulfone ultrafiltration membrane was completely immersed in the aqueous solution for 1 min, removed, and excess liquid was removed using a rubber roller. It was then immediately immersed in the oil phase solution for interfacial polymerization for 1 min. Subsequently, it was heat-treated at 80 °C for 5 min to obtain a polythiourea organic-inorganic composite nanofiltration membrane.

[0044] Among them, the surface morphology of polyethersulfone ultrafiltration membrane is as follows Figure 1 As shown, numerous nanoscale pores are dispersed on the surface of the polyethersulfone ultrafiltration membrane. The surface morphology of the finally prepared polythiourea organic-inorganic composite nanofiltration membrane is as follows. Figure 2 As shown, aminated silica is uniformly distributed on the surface, confirming the successful preparation of the inorganic-organic polythiourea nanofiltration membrane.

[0045] Example 2 This embodiment is the same as that in Embodiment 1, except that the aminated inorganic filler is 0.10 g / L aminated hexagonal boron nitride nanoparticles (average particle size of 20 nm and surface amino density of 1.0 mmol / g).

[0046] Example 3 This embodiment is the same as that in Embodiment 1, except that the aminated inorganic filler is 0.10 g / L aminated halloysite nanotubes (average particle size of 18 nm and surface amino density of 1.0 mmol / g).

[0047] Example 4 This embodiment is the same as that in Embodiment 1, except that the aminated inorganic filler is 0.10 g / L aminated montmorillonite (average particle size of 25 nm and surface amino density of 1.0 mmol / g).

[0048] Example 5 This embodiment is the same as Example 1, except that the aqueous monomer is 2.0 g / L triaminoguanidine.

[0049] Example 6 This embodiment is the same as Example 1, except that the aqueous monomer is 2.0 g / L melamine.

[0050] Example 7 This embodiment is the same as Example 1, except that the aqueous phase monomer is 2.0 g / L 3,3′,4,4′-tetraaminobiphenyl, and 0.10 g / L aminated hexagonal boron nitride is added at the same time, while the oil phase monomer is still 1.0 g / L terephthalocyanate.

[0051] Example 8 This embodiment is the same as Example 1, except that the oil phase monomer is 0.5 g / L of 1,2-phenyl diisothiocyanate.

[0052] Example 9 This embodiment is the same as Example 1, except that the aqueous phase monomer is 1 g / L of 3,3′,4,4′-tetraaminobiphenyl and the oil phase monomer is 1 g / L of 1,2-phenyl diisothiocyanate.

[0053] Example 10 This embodiment is basically the same as Example 1, except that the concentration of polyethyleneimine in the aqueous phase is adjusted from 1.0 g / L to 2.0 g / L, while the other preparation conditions remain unchanged.

[0054] Example 11 This embodiment is basically the same as Example 1, except that the concentration of aminated silica nanoparticles is adjusted from 0.10 g / L to 0.30 g / L, while the other preparation conditions remain unchanged.

[0055] Example 12 This embodiment is basically the same as Example 1, except that the concentration of p-phenylenediisothiocyanate in the oil phase is adjusted from 1.0 g / L to 1.5 g / L, while the other preparation conditions remain unchanged.

[0056] Example 13 This embodiment is basically the same as Example 1, except that the concentration of polyethyleneimine in the aqueous phase is 2.0 g / L and the concentration of terephthalic diisothiocyanate in the oil phase is 1.0 g / L; when the amounts of the two phase solutions are the same, the weight ratio of polyethyleneimine to terephthalic diisothiocyanate is 2:1, and the other preparation conditions remain unchanged.

[0057] Example 14 This embodiment is basically the same as Example 1, except that it uses aminated silica nanoparticles with an average particle size of 20 nm, the amount of aminated silica added is 0.10 g / L, the surface amino density is the same as in Example 1, and the other preparation conditions remain unchanged.

[0058] Example 15 This embodiment is basically the same as Example 1, except that it uses aminated silica nanoparticles with a surface amino density of 1.5 mmol / g, the amount of the particles added is 0.10 g / L, the average particle size is the same as in Example 1, and the other preparation conditions remain unchanged.

[0059] Example 16 Similar to Example 1, except that the amount of aminated silica added was adjusted to 0.03 g / L, its average particle size remained 15 nm, the surface amino density was 1.0 mmol / g, and the other conditions remained unchanged.

[0060] Example 17 Similar to Example 1, except that aminated silica nanoparticles with an average particle size of 80 nm were used, with an addition amount of 0.10 g / L and a surface amino density of 1.0 mmol / g, while the other conditions remained the same.

[0061] Example 18 Similar to Example 1, except that aminated silica nanoparticles with a surface amino density of 0.30 mmol / g and an average particle size of 15 nm were used, and the addition amount was 0.10 g / L, while the other conditions remained the same.

[0062] Comparative Example 1 This comparative example is the same as Example 1, except that no aminated inorganic filler was added to the aqueous phase. Instead, only polyethyleneimine and terephthalic diisothiocyanate were used for interfacial polymerization to obtain a polythiourea nanofiltration membrane.

[0063] The surface morphology of the obtained polythiourea film is as follows: Figure 3 As shown, the membrane surface is smooth and defect-free, compared to the morphology of the polyethersulfone ultrafiltration membrane used as the substrate. Figure 1 This demonstrates the successful preparation of the polythiourea separation layer.

[0064] Comparative Example 2 This comparative example is the same as Example 1, except that unmodified silica is used instead of aminated silica, while the other conditions remain unchanged.

[0065] Comparative Example 3 This comparative example is the same as Example 1, except that the oil phase monomer is replaced by terephthalic diisothiocyanate with trimesoyl pyromellitic acid chloride, while the other conditions remain the same, to prepare a polyamide nanofiltration membrane.

[0066] Comparative Example 4 This comparative example is the same as Example 1, except that the amount of aminated silica added is increased to 2.0 g / L, while the other conditions remain the same.

[0067] Comparative Example 5 This comparative example is basically the same as Example 1, except that the concentration of polyethyleneimine in the aqueous phase is reduced to 0.01 g / L, while the other preparation conditions remain unchanged.

[0068] Comparative Example 6 This comparative example is basically the same as Example 1, except that the concentration of aminated silica is increased to 2.5 g / L, while the other conditions remain unchanged.

[0069] Comparative Example 7 This comparative example is basically the same as Example 1, except that the concentration of terephthalic diisothiocyanate in the oil phase is increased to 12 g / L, while the other conditions remain unchanged.

[0070] Comparative Example 8 This comparative example is basically the same as Example 1, except that the amount of polyamine compound and diisothiocyanate compound added is adjusted so that the weight ratio of the two is 1:50.

[0071] Comparative Example 9 This comparative example is basically the same as Example 1, except that aminated silica with an average particle size of 150 nm is used as an inorganic filler; the filler addition amount and surface amino density remain unchanged, and the other preparation conditions are the same as in Example 1.

[0072] Comparative Example 10 This comparative example is basically the same as Example 1, except that aminated silica nanoparticles with a surface amino density of 0.10 mmol / g are used; the average particle size and amount of filler remain unchanged, and the other preparation conditions are the same as in Example 1.

[0073] Performance Analysis: (1) Nanofiltration performance of high temperature and acid resistant polythiourea composite nanofiltration membrane In this invention, water flux and salt rejection rate are used as key indicators for evaluating the performance of composite nanofiltration membranes. Water flux is defined as the volume of filtrate passing through a unit membrane area per unit time under unit operating pressure, and the specific calculation formula is as follows:

[0074] in, F (L) m -2 h -1 bar -1 () represents water flux. V (L) represents the volume of filtrate. A (m) 2 () indicates the filter area. t (h) represents the filtering time. P (bar) indicates the test pressure; The salt rejection rate is calculated using the following formula:

[0075] in, R (%) indicates the retention rate. C p (g / L) and C f (g / L) represents the solute concentration of the filtrate and the feed solution, respectively.

[0076] The high-temperature and acid-resistant separation performance of the nanofiltration membranes prepared in the examples and comparative examples was evaluated through high-temperature cross-flow filtration experiments. Magnesium sulfate aqueous solutions with a concentration of 1.0 g / L were prepared and, under the same operating pressure and cross-flow conditions, were first run at 25 °C and pH=7 until the membrane separation performance stabilized. The feed temperature was then raised to 85 °C using a circulating heating device. Water permeability and magnesium sulfate rejection rate were recorded. Subsequently, a magnesium sulfate aqueous solution with pH=0 was used as the feed solution, and the feed temperature was raised from 25 °C to 85 °C using a circulating heating device. After the temperature and membrane separation performance stabilized, water permeability and magnesium sulfate rejection rate were measured again to evaluate the separation stability of different nanofiltration membranes under high-temperature and strong acid conditions. The test results are shown in Tables 1 and 2.

[0077] Table 1. Test results of water flux and magnesium sulfate rejection rate of the separation membrane in Examples 1-18 and Comparative Examples 1-10 at pH=7.

[0078] Table 2. Test results of water flux and magnesium sulfate rejection rate of the separation membrane in Examples 1-18 and Comparative Examples 1-10 at pH=0.

[0079] The results in Tables 1 and 2 show that the polythiourea composite nanofiltration membranes prepared in Examples 1-15 of this invention maintain high magnesium sulfate rejection performance under both neutral and strong acid conditions, and exhibit good high-temperature stability. For the pH=7 system, the magnesium sulfate rejection rate of the membranes in the examples was 94.5%–99.7% at 25 °C, and remained at 94.5%–99.4% after the temperature was increased to 85 °C. Although the water flux increased significantly with increasing temperature, the rejection rate changed little, indicating that the increase in temperature mainly promoted water molecule transport and did not cause significant irreversible relaxation of the separation layer or expansion of the pore structure.

[0080] The high-temperature and acid resistance of nanofiltration membranes should be evaluated by a combination of water flux, rejection rate, and the degree to which the rejection rate is maintained. Under conditions of 1.0 g / L magnesium sulfate, pH=0, and 85 °C, when the water flux is not less than 20 L... m -2 h -1 bar -1 When the magnesium sulfate rejection rate is not less than 93.0%, and the decrease in rejection rate relative to 25 °C does not exceed 2.0 percentage points, the membrane can be considered to have achieved the effect of high temperature and acid resistance technology; when the water flux is not less than 25 L m -2 h -1 bar -1When the rejection rate is not less than 98.5% and the rejection rate decreases by no more than 1.0 percentage point, the membrane can be considered to have excellent high temperature and acid resistance.

[0081] In Examples 10-15, the water flux under the above conditions was 25.8-30.9 L. m -2 h -1 bar -1 The retention rates were 98.7%–99.2%, with a decrease of only 0.4–0.6 percentage points, all meeting the excellent performance standards. This indicates that the optimized monomer and aminated inorganic filler parameters can effectively balance membrane permeability, selectivity, and structural stability. In particular, Examples 11, 14, and 15 maintained a magnesium sulfate retention rate of over 99% at 85 °C, indicating that appropriate aminated inorganic filler addition amount, particle size, and surface amino density are beneficial for enhancing the interfacial bonding and chain segment confinement effect between the filler and the polythiourea network, thereby improving the thermal stability of the separation layer.

[0082] Examples 16-18 further demonstrate that, although the amount of amination-modified inorganic filler, average particle size, or surface amino density are still within the broad range defined by this invention, when they deviate from the preferred range, the resulting nanofiltration membrane can still meet the requirements for high-temperature and acid resistance. However, its separation performance and structural stability under high-temperature and strong acid conditions are slightly lower than those of the preferred examples. This indicates that there is a synergistic optimization range for the above parameters, and the preferred range is more conducive to constructing a uniform and stable organic-inorganic polythiourea crosslinked network, thereby obtaining better overall separation performance.

[0083] In contrast, Comparative Examples 1–10 all showed varying degrees of decrease in retention rate after heating, indicating that the lack of amination of inorganic fillers, unaminated fillers, and deviations of monomer or filler parameters from suitable ranges all weaken the structural integrity of the separation layer.

[0084] This difference is even more pronounced under the more stringent pH=0 conditions. Examples 1–18 showed a magnesium sulfate rejection rate of 94.7%–99.6% at 25 °C, which remained at 93.1%–99.2% after being heated to 85 °C. Examples 10–15 generally maintained a rejection rate above 98.7%, indicating that the optimized organic-inorganic polythiourea network can effectively resist the synergistic effects of strong acid and high temperature.

[0085] In particular, Examples 11, 14 and 15 achieved retention rates of 99.1%, 99.1% and 99.2% at 85 °C and pH=0, respectively, further demonstrating that suitable filler concentration, particle size and surface amino density can promote the formation of uniform and stable organic-inorganic connection nodes, improve network crosslinking integrity and inhibit chain segment movement at high temperatures.

[0086] In contrast, the performance of the comparative samples significantly declined under strong acid and high temperature conditions. The retention rates of the samples without aminated fillers, using unaminated silica, and the traditional polyamide system dropped to 50.3%, 60.1%, and 25.2%, respectively. Even the membranes with excessive filler, excessively large particle size, or excessively low surface amino density only maintained a retention rate of 63.5%–78.3%. This indicates that the chemical participation of aminated inorganic fillers and the reasonable control of their parameters are the key to obtaining excellent high temperature and strong acid resistance.

[0087] (2) Comparison of nanofiltration performance of sodium sulfate and sodium chloride aqueous solutions The separation performance of the nanofiltration membranes prepared in Examples 1-18 and Comparative Examples 1-10 for different inorganic salts was evaluated by cross-flow filtration experiments. Sodium sulfate and sodium chloride aqueous solutions with a concentration of 1.0 g / L were used as feed solutions, and filtration tests were conducted at 25 °C under the same operating pressure and cross-flow conditions. After the water permeability of the membranes stabilized, the feed solution and permeate were collected, and their salt concentrations were measured. The water permeability and salt rejection rate were calculated to evaluate the selective separation performance of the obtained nanofiltration membranes for salt ions of different valence states. The test results are shown in Table 3.

[0088] Table 3. Nanofiltration performance of nanofiltration membranes in Examples 1-18 and Comparative Examples 1-10 for sodium sulfate and sodium chloride aqueous solutions.

[0089] As shown in Table 3, the nanofiltration membranes prepared in Examples 1-18 of this invention exhibit significantly different separation performances for sulfate and sodium chloride. For sodium sulfate solution, the water flux of the membranes in each example ranges from 8.3 to 12.6 L. m -2 h -1 bar -1 The retention rates remained between 96.1% and 99.7%, indicating that the obtained separation layer has a good dense structure and a high divalent anion retention capacity.

[0090] In contrast, for sodium chloride solutions, the water flux of the membranes in each embodiment was slightly increased, ranging from 9.2 to 14.2 L. m -2 h -1 bar -1The rejection rate was only 23.2%–42.5%, significantly lower than that of sodium sulfate. Table 1 shows that the membranes in the examples maintained high rejection rates for both magnesium sulfate and sodium sulfate, indicating that the nanofiltration membranes prepared in this invention have excellent separation performance for salts containing divalent anions, while exhibiting a low rejection rate for sodium chloride. This further proves that the membrane's separation behavior conforms to the typical synergistic mechanism of charge sieving and size sieving in nanofiltration membranes.

[0091] The temperature response and cycling stability of the nanofiltration membrane prepared in Example 1 under strong acid conditions were evaluated through a high-temperature cross-flow filtration experiment. A magnesium sulfate aqueous solution with a concentration of 1.0 g / L and pH=0 was used as the feed solution. Under the same operating pressure and cross-flow conditions, filtration was first performed at 25 °C. Subsequently, the feed solution temperature was sequentially increased to 40 °C, 55 °C, 70 °C, and 85 °C using a circulating heating device, and then sequentially decreased to 70 °C, 55 °C, 40 °C, and 25 °C. After one heating and cooling cycle, the above heating and cooling process was repeated. After the feed solution temperature and membrane separation performance stabilized at each set temperature, the water permeability and magnesium sulfate rejection rate were measured to evaluate the temperature cycling stability and reversibility of the separation performance of the nanofiltration membrane under high-temperature strong acid conditions. The test results are shown in Table 4.

[0092] Table 4. Water flux and magnesium sulfate (1.0 g / L, pH=0) rejection rate of nanofiltration membrane in Example 1 at different temperatures.

[0093] As shown in Table 4, the nanofiltration membrane prepared in Example 1 exhibited excellent separation stability within a temperature range of 25–85 °C. As the operating temperature gradually increased from 25 °C to 85 °C, the membrane's water flux increased from 10.3 L / L. m -2 h -1 bar -1 Increased to 30.2 L m -2 h -1 bar -1 The flux increased with increasing temperature; while the magnesium sulfate rejection rate remained consistently between 98.4% and 99.3%, with only slight fluctuations, indicating that the membrane could maintain highly stable separation selectivity under high-temperature and strong acid conditions. Through heating and cooling cycle tests, the water flux and rejection rate were basically consistent, demonstrating that the nanofiltration membrane of this invention still exhibits good temperature cycling stability under strong acid conditions.

[0094] (3) Long-term stability of high temperature and acid resistant nanofiltration membrane The present invention also evaluated the long-term stability of the nanofiltration membrane with high temperature and acid resistance. The nanofiltration performance of the product nanofiltration membrane in Example 1 was tested over time in magnesium sulfate solution (1.0 g / L, pH=0, 70 °C). The results are shown in Table 5.

[0095] Table 5. Long-term nanofiltration stability of the nanofiltration membrane in Example 1 for magnesium sulfate solution.

[0096] As shown in Table 5, the nanofiltration membrane prepared in Example 1 exhibited excellent long-term stability during 65 days of continuous operation. Throughout the test period, the water flux remained consistently between 25.0 and 25.7 L. m -2 h -1 bar -1 The flux remained relatively stable, with only minor fluctuations. The magnesium sulfate rejection rate remained consistently between 98.0% and 98.3%, showing almost no downward trend. During the test, typical characteristics of membrane structure instability, such as a continuous increase in water flux and a continuous decrease in rejection rate, were not observed, indicating that the cross-linked network on the membrane surface and inside remained intact, and no obvious defects or pore size expansion occurred in the separation layer. These results demonstrate that the nanofiltration membrane of this invention can maintain both high flux and stable selectivity under prolonged high-temperature and strong acid operation.

[0097] The embodiments described above provide a detailed explanation of the technical solutions of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, additions, or similar substitutions made within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a high-temperature and acid-resistant polythiourea composite nanofiltration membrane, comprising: (1) The aqueous solution containing polyamine compounds and aminated inorganic fillers is brought into full contact with the porous base membrane to ensure that the solution uniformly wets the porous base membrane; (2) After removing excess aqueous solution from the surface of the porous base membrane, it is then contacted with an oil solution containing diisothiocyanate compound to undergo interfacial polymerization reaction and form an organic-inorganic polythiourea separation layer. (3) After the interfacial polymerization is completed, the membrane is subjected to heat treatment to cure and crosslink, thereby obtaining a high-temperature and acid-resistant polythiourea composite nanofiltration membrane. In the aqueous solution, the concentration of polyamine compounds is 0.05~20 g / L, and the concentration of aminated inorganic filler is 0.01~2 g / L; The concentration of the oil phase solution is 0.025~10 g / L.

2. The method for preparing the high-temperature resistant and acid-resistant polythiourea composite nanofiltration membrane according to claim 1, characterized in that, The weight ratio of the polyamine compound to the diisothiocyanate compound is 1:5 to 10:

1.

3. The method for preparing the high-temperature resistant and acid-resistant polythiourea composite nanofiltration membrane according to claim 1, characterized in that, The polyamine compound is at least one of triaminoguanidine, melamine, 3,3′,4,4′-tetraaminobiphenyl, diethylenetriamine, tetraethylenepentamine, and polyethyleneimine; The aminated inorganic filler is at least one of aminated silica, aminated zirconium oxide, aminated alumina, aminated hexagonal boron nitride, aminated halloysite nanotubes, and aminated montmorillonite. The diisothiocyanate compound is at least one selected from p-phenylene diisothiocyanate, toluene-2,4-diisothiocyanate, 1,3-phenylene diisothiocyanate, 1,2-phenylene diisothiocyanate, hexamethylene diisothiocyanate, naphthalene diisothiocyanate, and binaphthalene diisothiocyanate.

4. The method for preparing the high-temperature resistant and acid-resistant polythiourea composite nanofiltration membrane according to claim 1, characterized in that, In the aqueous solution, the concentration of polyamine compounds is 0.5~5 g / L.

5. The method for preparing the high-temperature and acid-resistant polythiourea composite nanofiltration membrane according to claim 1, characterized in that, In the aqueous solution, the concentration of the aminated inorganic filler is 0.05~0.5 g / L.

6. The method for preparing the high-temperature resistant and acid-resistant polythiourea composite nanofiltration membrane according to claim 1 or 5, characterized in that, The average particle size of the aminated inorganic filler is 5~100 nm, preferably 10~30 nm.

7. The method for preparing the high-temperature resistant and acid-resistant polythiourea composite nanofiltration membrane according to claim 1 or 5, characterized in that, The amino density on the surface of the amination-modified inorganic filler is 0.2~5 mmol / g, preferably 0.5~3 mmol / g.

8. The method for preparing the high-temperature resistant and acid-resistant polythiourea composite nanofiltration membrane according to claim 1, characterized in that, The concentration of the oil phase solution is 0.5~2 g / L.

9. The high-temperature resistant and acid-resistant polythiourea composite nanofiltration membrane prepared by the method according to any one of claims 1-8, wherein the high temperature is a temperature higher than 45°C, and the strong acid is a pH value less than 3.

10. The application of the high-temperature and acid-resistant polythiourea composite nanofiltration membrane according to claim 9 in the nanofiltration separation process of divalent anionic salts, organic acids, dyes, antibiotics, heavy metal ions and rare earth metal complexes.

Images