A high-temperature resistant nanofiltration membrane and its preparation method

Abstract

The present invention relates to the technical field of nanofiltration membranes, and particularly relates to a high-temperature resistant nanofiltration membrane and a preparation method thereof. The nanofiltration membrane is prepared by this method. The method includes preparing a nano-layer; coating a CHO-SiO2 nano-particle solution with a required mass concentration on the surface of a porous support layer to form a base membrane containing the nano-layer; preparing a high-temperature resistant nanofiltration membrane; immersing the base membrane in an aqueous solution, taking out the base membrane after the first immersion treatment and air-drying the water droplets on its surface; secondly, immersing the base membrane in an oil-phase solution, taking out the base membrane after the second immersion treatment and performing a drying treatment to obtain a high-temperature resistant nanofiltration membrane; the aqueous solution includes polyamine, an acid absorbent, inorganic salts and a first organic solvent; the polyamine is a bis-benzene N-heterocyclic derivative; the oil-phase solution includes polyacyl chloride. The present invention can solve the problem that the directly introduced nano-particles are liable to fall off after film formation in the prior art.

Description

Technical Field

[0001] The present invention relates to the technical field of nanofiltration membranes, and particularly to a high-temperature resistant nanofiltration membrane and a preparation method thereof. Background Art

[0002] In recent years, the demand for water purification at high temperatures (such as thermal desalination) has sparked great interest in high-temperature resistant nanofiltration membranes. Due to their inherent chemical structure and chemical properties, traditional nanofiltration membranes are generally limited to use at 50 °C. Currently, some methods for preparing high-temperature resistant nanofiltration membranes involve introducing nanoparticles into the polysulfone layer and the polyamide layer, and the high-temperature resistance of the nanofiltration membrane is improved by the high-temperature resistance of the nanoparticles. However, there are poor compatibility between the nanoparticles and the aqueous monomers, and the nanoparticles are prone to falling off after film formation, which restricts their large-scale application.

[0003] In summary, there is a need to provide a high-temperature resistant nanofiltration membrane and a preparation method thereof to solve the problem that the nanoparticles are prone to falling off after film formation in the prior art. Summary of the Invention

[0004] The object of the present invention is to provide a high-temperature resistant nanofiltration membrane and a preparation method thereof, and the specific technical solutions are as follows:

[0005] In a first aspect, the present invention provides a preparation method of a high-temperature resistant nanofiltration membrane, including:

[0006] Step S1, preparing a nano-layer;

[0007] Coating a CHO-SiO2 nanoparticle solution with a required mass concentration on the surface of a porous support layer to form a base membrane containing a nano-layer;

[0008] Step S2, preparing a high-temperature resistant nanofiltration membrane;

[0009] First, immerse the base membrane in an aqueous solution, take out the base membrane after the first immersion treatment and air-dry the water droplets on its surface; secondly, immerse the base membrane in an oil-phase solution, take out the base membrane after the second immersion treatment and perform a drying treatment to obtain a high-temperature resistant nanofiltration membrane;

[0010] The aqueous solution includes polyamine, an acid absorbent, inorganic salts, and a first organic solvent; the polyamine is a dibenzo N-heterocyclic derivative;

[0011] The oil-phase solution includes polyacyl chloride.

[0012] Optionally, the dibenzo N - heterocyclic derivatives include at least one of 10H - phenothiazine - 2,8 - diamine, 10H - phenothiazine - 2,8 - diamine - 5,5 - dioxide, 10H - phenoxazine - 2,8 - diamine, 10H - phenoxazine - 2,7 - diamine - 10 - methyl, and 3,6 - diamino - 9 - acridone;

[0013] The mass concentration of the dibenzo N - heterocyclic derivatives in the aqueous solution is 0.5% - 1%.

[0014] Optionally, the inorganic salts include at least one of anhydrous potassium chloride, anhydrous potassium carbonate, and anhydrous calcium chloride;

[0015] The mass concentration of the inorganic salts in the aqueous solution is 0.2% - 0.5%.

[0016] Optionally, the acid absorbent includes at least one of sodium hydroxide, sodium carbonate, and sodium bicarbonate;

[0017] The mass concentration of the acid absorbent in the aqueous solution is 0.2% - 0.5%;

[0018] The aqueous solution further includes a surfactant; the surfactant includes at least one of ammonium dodecyl sulfate, sodium dodecylbenzenesulfonate, cetyltrimethylammonium bromide, and benzalkonium chloride;

[0019] The mass concentration of the surfactant in the aqueous solution is 0.05% - 0.1%.

[0020] Optionally, the first organic solvent includes at least one of N,N′ - dimethylacetamide, N,N′ - dimethylformamide, dimethyl sulfoxide, and tetrahydrofuran;

[0021] The volume ratio of water to the first organic solvent used in the aqueous solution is 1:1 - 4:1.

[0022] Optionally, the oil - phase solution further includes a second organic solvent; the second organic solvent includes at least one of n - hexane, cyclohexane, n - heptane, and Isopar G;

[0023] The polyacyl chloride includes at least one of trimesoyl chloride, terephthaloyl chloride, phthaloyl chloride, and 1,2,4,5 - benzenetetracarbonyl chloride;

[0024] The mass concentration of the polyacyl chloride in the oil - phase solution is 0.1% - 0.3%.

[0025] Optionally, the soaking time for both the first soaking treatment and the second soaking treatment is 30 - 120 s;

[0026] The drying process adopts a drying temperature of 50-80° C. and a drying time of 1-5 min.

[0027] Optionally, the method for preparing the high temperature resistant nanofiltration membrane further includes a non-woven fabric base layer; the non-woven fabric base layer is arranged on a side of the porous support layer away from the nanolayer; and the porous support layer is a hydrophilic porous support layer.

[0028] Optionally, the mass concentration of the CHO-SiO2 nanoparticle solution is 0.1%-1%;

[0029] The coating time used in the coating is 60-300s.

[0030] In a second aspect, the present invention provides a high temperature resistant nanofiltration membrane, which is prepared by using the method for preparing the high temperature resistant nanofiltration membrane.

[0031] The application of the technical solution of the present invention has at least the following beneficial effects:

[0032] (1) The present invention provides a method for preparing a high temperature resistant nanofiltration membrane, which can solve the problem of easy falling off after film formation when nanoparticles are directly introduced in the prior art. Specifically, the present invention firstly uses aldehyde-rich silica CHO-SiO2 nanoparticles to be coated on the surface of a porous support layer to form a base membrane containing a nanolayer; secondly, the nitrogen atom on the secondary amine of a dibenzo-N heterocyclic derivative is used as a nucleophilic agent to attack the carbon atom on the carbonyl group in the aldehyde-rich silica CHO-SiO2 nanoparticle to form an intermediate product, and the intermediate product undergoes a Stork enamine synthesis reaction to generate an enamine after dehydration by an inorganic salt, which strengthens the bonding effect between the nanolayer and the polyamide layer and solves the problem of easy falling off after film formation when nanoparticles are directly introduced; at the same time, on the basis that the nanolayer itself has high temperature resistance, the polyamide layer formed on the nanolayer has a higher breaking energy due to the strong rigidity and large steric effect of the dibenzo structure, thereby effectively improving the stability of the nanofiltration membrane at high temperatures. In addition, the electron-withdrawing heteroatoms on the middle ring of the dibenzo N-heterocyclic derivatives can reduce the electron cloud density of the amino group connected to the benzene ring, making the amino group more susceptible to attack by the partially positively charged acyl group, thereby promoting the amidation interfacial polymerization reaction between the amino group on the benzene ring and the acyl chloride, and improving the cross-linking degree of the polyamide layer. The increased cross-linking degree helps the polyamide to form a denser multilayer network structure, thereby improving its structural deformation resistance under high temperature conditions and achieving high temperature resistance. An acid absorbent is used to neutralize the hydrogen ions produced in the interfacial polymerization reaction, promote the interfacial polymerization reaction, and maintain the stability of the pH of the system. Furthermore, the multilayer network structure formed by cross-linking can effectively penetrate into the porous support layer, ensuring the stability of the overall structure of the high temperature resistant nanofiltration membrane.

[0033] (2) The high-temperature resistant nanofiltration membrane prepared by the present invention has high-temperature resistance performance, can be effectively applied to intercept high-valence anion salts in saline feed liquid under high-temperature environment, and has good application prospects in the treatment of high-temperature feed liquid. Detailed implementation manners

[0034] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art shall fall within the protection scope of the present invention.

[0035] Example 1:

[0036] A preparation method of a high-temperature resistant nanofiltration membrane, comprising:

[0037] Step S1, preparing a nano-layer;

[0038] Coat a CHO-SiO2 nanoparticle solution with a required mass concentration on the surface of a porous support layer to form a base membrane containing a nano-layer;

[0039] The preparation method of the porous support layer is as follows:

[0040] Weigh 200 g of polysulfone and 20 g of PEG-600, disperse them in 780 g of N,N′-dimethylformamide, stir at 70 °C until completely dissolved, then perform vacuum degassing to obtain a polymer solution. Coat the polymer solution on a non-woven fabric with a scraper, and then cure it in a coagulation bath to form a polysulfone support layer, that is, a porous support layer, and store it in a freezer at 5 °C for later use;

[0041] Step S2, preparing a high-temperature resistant nanofiltration membrane;

[0042] First, immerse the base membrane in an aqueous solution, take out the base membrane after the first immersion treatment and air-dry the water droplets on its surface; secondly, immerse the base membrane in an oil-phase solution, take out the base membrane after the second immersion treatment and place it in an oven for drying treatment to obtain a high-temperature resistant nanofiltration membrane;

[0043] The aqueous solution includes polyamine, acid absorbent, inorganic salt and a first organic solvent; the polyamine is a dibenzo N-heterocyclic derivative, specifically 10H-phenothiazine-2,8-diamine;

[0044] The oil-phase solution includes polyacyl chloride, and the polyacyl chloride is specifically trimesoyl chloride.

[0045] The mass concentration of the dibenzo N-heterocyclic derivative in the aqueous solution is 0.5%-1%, specifically taking 0.8%.

[0046] The inorganic salt is anhydrous potassium chloride to prevent the introduction of other impurities into the inorganic salt;

[0047] The mass concentration of the inorganic salt in the aqueous solution is 0.2%-0.5%, specifically 0.5%.

[0048] The acid absorbent is sodium hydroxide;

[0049] The mass concentration of the acid absorbent in the aqueous solution is 0.2%-0.5%, specifically 0.3%;

[0050] The aqueous solution further includes a surfactant; the surfactant is ammonium dodecyl sulfate;

[0051] The mass concentration of the surfactant in the aqueous solution is 0.05%-0.1%, specifically 0.05%.

[0052] The first organic solvent is dimethyl sulfoxide; the first organic solvent is water-soluble and is used to dissolve the dibenzo-N-heterocyclic derivatives.

[0053] The volume ratio of water to the first organic solvent used in the aqueous solution is 4:1.

[0054] The oil phase solution further includes a second organic solvent; the second organic solvent is n-hexane;

[0055] The mass concentration of the polyacyl chloride in the oil phase solution is 0.1%-0.3%, specifically 0.1%.

[0056] The soaking time for both the first soaking treatment and the second soaking treatment is 60 s;

[0057] The drying temperature for the drying treatment is 70 °C and the drying time is 5 min.

[0058] The mass concentration of the CHO-SiO2 nanoparticle solution (the solute is CHO-SiO2 nanoparticles, obtained by purchase) is 0.1%-1%, specifically 0.5%;

[0059] The coating time for the coating is 120 s.

[0060] Example 2:

[0061] The difference from Example 1 is that the dibenzo-N-heterocyclic derivative is 10H-phenothiazine-2,8-diamine-5,5-dioxide.

[0062] Example 3:

[0063] The difference from Example 1 is that the dibenzo-N-heterocyclic derivative is 10H-phenoxazine-2,8-diamine.

[0064] Example 4:

[0065] Different from Example 1, the dibenzo-N-heterocyclic derivative is 10H-phenoxazine-2,7-diamine-10-methyl.

[0066] Example 5:

[0067] Different from Example 1, the dibenzo-N-heterocyclic derivative is 3,6-diamino-9-acridone.

[0068] Example 6:

[0069] Different from Example 1, the mass concentration of the dibenzo-N-heterocyclic derivative in the aqueous solution is 0.5%; the mass concentration of the CHO-SiO2 nanoparticle solution is 0.1%.

[0070] Example 7:

[0071] Different from Example 1, the mass concentration of the dibenzo-N-heterocyclic derivative in the aqueous solution is 1%; the mass concentration of the CHO-SiO2 nanoparticle solution is 1%.

[0072] Comparative Example 1:

[0073] Different from Example 1, the polyamine is piperazine.

[0074] Comparative Example 2:

[0075] Different from Example 1, the preparation of the nano-layer is cancelled.

[0076] Comparative Example 3:

[0077] Different from Example 1, the polyamine is dapsone.

[0078] Comparative Example 4:

[0079] Different from Example 1, the polyamine is 2,8-dibenzothiophene diamine.

[0080] Comparative Example 5:

[0081] Different from Example 1, the polyamine is 2,8-dibenzothiophene diamine-5,5-dioxide.

[0082] Comparative Example 6:

[0083] Different from Example 1, the mass concentration of the dibenzo-N-heterocyclic derivative in the aqueous solution is 0.3%.

[0084] Comparative Example 7:

[0085] Different from Example 1, the mass concentration of the dibenzo N-heterocyclic derivative in the aqueous solution is 1.2%.

[0086] Comparative Example 8:

[0087] Different from Example 1, the mass concentration of the CHO-SiO2 nanoparticle solution is 0.05%.

[0088] Comparative Example 9:

[0089] Different from Example 1, the mass concentration of the CHO-SiO2 nanoparticle solution is 0.15%.

[0090] Samples were taken from the high-temperature resistant nanofiltration membranes prepared in Examples 1-7 and Comparative Examples 1-9 respectively to complete the normal temperature test and the high-temperature resistance test. The test results are shown in Table 1. The experimental method is as follows:

[0091] Three membrane sheets were tested for each sample. The test results of the normal temperature test and the high-temperature resistance test were both averaged. Specifically, each membrane sheet was tested on a cross-flow membrane sheet detection platform. First, the normal temperature test was carried out, that is, tested according to Test Condition ①, and then the high-temperature resistance test was carried out, that is, tested according to Test Condition ②. Among them, Test Condition ① is: 2000 ppm of MgSO4 aqueous solution, operating pressure 100 psi, test temperature 25 °C, and pH value 6.8; Test Condition ② is: 2000 ppm of MgSO4 aqueous solution, operating pressure 100 psi, test temperature 80 °C, and pH value 6.8.

[0092] Table 1 High-temperature resistance test results

[0093]

[0094]

[0095] As can be seen from the data in Table 1:

[0096] Compared with Comparative Examples 1-9, the membrane sheets prepared in Examples 1-7 of the present invention have appropriate water flux and significant high-temperature resistance effect.

[0097] In Comparative Example 1, the traditional piperazine aqueous amine monomer was used. The membrane sheet prepared by it has a high rejection rate for divalent anions at normal temperature; however, due to the boat conformation of the piperazine monomer being prone to bond breakage at high temperature, the rejection rate drops sharply. However, in Example 1, using the dibenzo N-heterocyclic derivative as the aqueous monomer has a significant effect on improving the high-temperature resistance performance of the nanofiltration membrane.

[0098] In Comparative Example 2, the membrane sheet prepared without using the nano-layer has a significantly decreased rejection rate at high temperature, while in Example 1, using the nano-layer has a significant effect on improving the high-temperature resistance performance of the nanofiltration membrane.

[0099] Compared with the non-N-heterocyclic bisaniline derivatives used in Comparative Examples 3-5, the dibenzo-N-heterocyclic derivatives used in Examples 1-5 of the present invention have a significant effect on improving the high-temperature resistance of the nanofiltration membrane. Specifically, the nitrogen atom on the secondary amine of the dibenzo-N-heterocyclic derivative is used as a nucleophile, which can attack the carbon atom on the carbonyl group in the aldehyde-rich silica CHO-SiO2 nanoparticles to form an intermediate product. The intermediate product undergoes a dehydration reaction with an inorganic salt to carry out a Stork enamine synthesis reaction to generate an enamine, which strengthens the binding effect between the nano-layer and the polyamide layer; at the same time, on the basis that the nano-layer itself has high-temperature resistance, the polyamide layer formed on the nano-layer has a higher bond-breaking energy due to the strong rigidity and large steric hindrance effect of the dibenzo structure, so the stability of the nanofiltration membrane at high temperatures can be effectively improved. In addition, the electron-withdrawing heteroatom on the middle ring of the dibenzo-N-heterocyclic derivative can reduce the electron cloud density of the amino group connected to the benzene ring, making the amino group more susceptible to attack by the acyl group with partial positive charge, thereby promoting the amidation interfacial polymerization reaction between the amino group on the benzene ring and the acyl chloride, improving the crosslinking degree of the polyamide layer, and the increase in the crosslinking degree helps the polyamide to form a denser multi-layer network structure, thereby improving its anti-deformation ability under high-temperature conditions and achieving high-temperature resistance.

[0100] Compared with Comparative Examples 6-9, the use of appropriate amounts of CHO-SiO2 nanoparticles and dibenzo-N-heterocyclic derivatives in Examples 1 and 6-7 of the present invention has a significant effect on improving the high-temperature resistance of the nanofiltration membrane. Using too low an amount of the dibenzo-N-heterocyclic derivative in Comparative Example 6 and too low an amount of the CHO-SiO2 nanoparticles in Comparative Example 8 will both result in a significant decrease in the high-temperature resistance of the prepared membrane sheets; using too high an amount of the dibenzo-N-heterocyclic derivative in Comparative Example 7 and too high an amount of the CHO-SiO2 nanoparticles in Comparative Example 9 does not significantly improve the high-temperature resistance of the nanofiltration membrane, but instead increases the production cost.

[0101] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a high temperature resistant nanofiltration membrane, characterized in that: include: Step S1, preparing a nanolayer; coating a CHO-SiO2 nanoparticle solution of a desired mass concentration on the surface of the porous support layer to form a base film containing a nanolayer; Step S2, preparing a high temperature resistant nanofiltration membrane; First, the base membrane is immersed in an aqueous solution, and after the first immersion treatment is completed, the base membrane is taken out and the water droplets on the surface are air-dried; secondly, the base membrane is immersed in an oil solution, and after the second immersion treatment is completed, the base membrane is taken out and dried to obtain a high temperature resistant nanofiltration membrane; The aqueous phase solution comprises a polyamine, an acid absorbent, an inorganic salt and a first organic solvent; the polyamine is a dibenzo-N heterocyclic derivative; The oil phase solution includes polyacid chloride.

2. The method for preparing a high temperature resistant nanofiltration membrane according to claim 1, characterized in that: The bisbenzoheterocyclic derivatives include at least one of 10H-phenothiazine-2,8-diamine, 10H-phenothiazine-2,8-diamine-5,5-dioxide, 10H-phenoxazine-2,8-diamine, 10H-phenoxazine-2,7-diamine-10-methyl and 3,6-diamino-9-acridone; The mass concentration of the bisbenzoheterocyclic derivative in the aqueous solution is 0.5%-1%.

3. The method for preparing a high temperature resistant nanofiltration membrane according to claim 1, characterized in that: The inorganic salt includes at least one of anhydrous potassium chloride, anhydrous potassium carbonate and anhydrous calcium chloride; The mass concentration of the inorganic salt in the aqueous phase solution is 0.2%-0.5%.

4. The method for preparing a high temperature resistant nanofiltration membrane according to claim 1, characterized in that: The acid absorbent comprises at least one of sodium hydroxide, sodium carbonate and sodium bicarbonate; The mass concentration of the acid absorbent in the aqueous solution is 0.2%-0.5%; The aqueous phase solution further comprises a surfactant; the surfactant comprises at least one of dodecyl ammonium sulfate, sodium dodecylbenzene sulfonate, hexadecyl trimethyl ammonium bromide and benzalkonium chloride; The mass concentration of the surfactant in the aqueous phase solution is 0.05%-0.1%.

5. The method for preparing a high temperature resistant nanofiltration membrane according to claim 1, characterized in that: The first organic solvent includes at least one of N,N′-dimethylacetamide, N,N′-dimethylformamide, dimethyl sulfoxide and tetrahydrofuran; The volume ratio of water to the first organic solvent used in the aqueous phase solution is 1:1-4:

1.

6. The method for preparing a high temperature resistant nanofiltration membrane according to claim 1, characterized in that: The oil phase solution further comprises a second organic solvent; the second organic solvent comprises at least one of n-hexane, cyclohexane, n-heptane and Isopar G; The polyacid chloride comprises at least one of trimesoyl chloride, terephthaloyl chloride, phthaloyl chloride and 1,2,4,5-benzene tetracarboxylic acid chloride; The mass concentration of the polyacid chloride in the oil phase solution is 0.1%-0.3%.

7. The method for preparing a high temperature resistant nanofiltration membrane according to claim 1, characterized in that: The soaking time used in the first soaking treatment and the second soaking treatment is 30-120s; The drying process adopts a drying temperature of 50-80° C. and a drying time of 1-5 min.

8. The method for preparing a high temperature resistant nanofiltration membrane according to claim 1, characterized in that: It also includes a non-woven fabric base layer; the non-woven fabric base layer is arranged on the side of the porous support layer away from the nano layer; the porous support layer is a hydrophilic porous support layer.

9. The method for preparing a high temperature resistant nanofiltration membrane according to any one of claims 1 to 8, characterized in that: The mass concentration of the CHO-SiO2 nanoparticle solution is 0.1%-1%; The coating time used in the coating is 60-300s.

10. A high temperature resistant nanofiltration membrane, characterized in that: The high temperature resistant nanofiltration membrane is prepared by the preparation method of claim 9.

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