Anti-pollution reverse osmosis membrane and preparation method thereof

Abstract

The invention relates to the technical field of reverse osmosis membranes, in particular to an anti-pollution reverse osmosis membrane and a preparation method thereof. The anti-pollution reverse osmosis membrane is prepared by the preparation method. The preparation method comprises the following steps: reversibly protecting part of amino groups in a polyamine substance by adopting an amino protection compound to prepare specific polyamine; preparing a nascent state polyamide membrane; and removing the protected amino compound by using a deamination reagent to expose the protected amino, thereby obtaining the anti-pollution reverse osmosis membrane. The reverse osmosis membrane prepared by the preparation method disclosed by the invention has relatively good anti-pollution performance and high water flux and desalination rate performance.

Description

Technical Field

[0001] The invention relates to the technical field of reverse osmosis membranes, and in particular to an anti-pollution reverse osmosis membrane and a preparation method thereof. Background Art

[0002] At present, reverse osmosis membrane separation technology occupies an advantageous position in wastewater treatment. The anti-pollution performance of reverse osmosis membrane in the application process directly affects its separation performance. The research and development of anti-pollution reverse osmosis membrane materials will be an important direction for the development of membrane technology.

[0003] The surface desalination layer of the existing reverse osmosis membrane is mostly a polyamide structure prepared by diamine and tribasic acid chloride. This structure has an excess of acid chloride groups, which are easily hydrolyzed to form carboxylic acid groups, making the surface of the reverse osmosis membrane electronegative; during its application, it is easy to electrostatically adsorb positively charged pollutants, thereby causing reverse osmosis membrane surface contamination, resulting in reverse osmosis membrane water flux attenuation and reduced separation performance. However, most of the anti-pollution reverse osmosis membrane products currently available on the market also have the problem of not being resistant to contamination by positively charged pollutants.

[0004] In summary, it is necessary to develop an anti-pollution reverse osmosis membrane and a preparation method thereof to solve the problem that existing anti-pollution reverse osmosis membrane products are not resistant to contamination by positively charged pollutants. Summary of the invention

[0005] The object of the present invention is to provide an anti-pollution reverse osmosis membrane and a preparation method thereof. The specific technical scheme is as follows:

[0006] In a first aspect, the present invention provides a method for preparing an anti-fouling reverse osmosis membrane, comprising:

[0007] Step S1: Preparation of specific polyamine

[0008] Dissolving a polyamine substance and a protected amino compound in a first solvent to prepare a first solution; adding an acid absorbent to the first solution, and after a first reaction, obtaining a specific polyamine in which some amino groups in the polyamine substance are reversibly protected;

[0009] The polyamine material includes at least three amino groups;

[0010] The protected amino compound includes any one of benzyl chloroformate, 2-trimethylsilylethoxycarbonyl chloride, fluorenylmethoxycarbonyl chloride, p-toluenesulfonyl chloride, triphenylmethane chloride, 4-methoxybenzyl bromide and benzyl bromide;

[0011] Step S2: preparing nascent polyamide membrane

[0012] Adding water to the specific polyamine prepared in step S1 to prepare an aqueous solution, and performing interfacial polymerization reaction with an oil solution containing polyacyl chloride to prepare a nascent polyamide membrane;

[0013] Step S3: Preparation of anti-pollution reverse osmosis membrane

[0014] Adding a deaminating agent to a second solvent to prepare a second solution; adding the nascent polyamide membrane obtained in step S2 to the second solution, and after a second reaction, removing the protective amino compound so that the protected amino group is exposed, thereby obtaining an anti-pollution reverse osmosis membrane;

[0015] The deamination agent includes any one of hydrogen bromide, piperidine, tetrabutylammonium fluoride, tetraethylammonium fluoride, hydrazine, ammonia and cerium ammonium nitrate.

[0016] Optionally, in step S1, the first solvent includes any one of chloroform, glacial acetic acid, dioxane, methanol and acetonitrile;

[0017] The mass concentration of the protected amino compound in the first solution is 1%-10%;

[0018] The mass concentration of the polyamine substance in the first solution is 80%-95%;

[0019] Optionally, in step S1, the reaction temperature used in the first reaction is 50-80°C and the reaction time is 2-12h.

[0020] Optionally, in step S1, the polyamine substance includes at least one of benzene-1,2,3-triamine, benzene-1,2,4-triamine, benzene-1,3,5-triamine, 2,4,6-triaminotoluene, diethylenetriamine and triethylenetetramine.

[0021] Optionally, in step S1, the acid absorbent includes any one of sodium carbonate, sodium bicarbonate, potassium carbonate, triethylamine and sodium hydroxide.

[0022] Optionally, in step S2, the mass concentration of the specific polyamine in the aqueous solution is 1%-10%;

[0023] The mass concentration of the polyacid chloride in the oil phase solution is 0.05%-0.5%.

[0024] Optionally, in step S2, the polyacyl chloride includes at least one of isophthaloyl chloride, terephthaloyl chloride, phthaloyl chloride, benzene-1,3,5-tricarboxylic acid chloride, benzene-1,2,4,5-tetracarboxylic acid chloride and benzene-1,2,4-tricarboxylic acid chloride;

[0025] The solvent used in the oil phase solution includes an organic solvent, which includes any one of N-methylpyrrolidone, n-hexane, cyclohexane and Isopar G.

[0026] Optionally, in step S3, the second solvent includes any one of glacial acetic acid, N,N-dimethylformamide solution, tetrahydrofuran, methanol, ethanol, phenol, dichloromethane and acetonitrile;

[0027] The mass concentration of the deamination agent in the second solution is 2%-20%.

[0028] Optionally, in step S3, the reaction temperature used in the second reaction is 40-50° C., and the reaction time is 1-10 h.

[0029] In a second aspect, the present invention provides an anti-pollution reverse osmosis membrane, which is prepared by using the method for preparing the anti-pollution reverse osmosis membrane.

[0030] The application of the technical solution of the present invention has at least the following beneficial effects:

[0031] The present invention provides an anti-pollution reverse osmosis membrane and a preparation method thereof. The surface polyamide structure layer of the prepared anti-pollution reverse osmosis membrane presents an electrical neutrality effect, is difficult to electrostatically adsorb positively charged pollutants, has good anti-pollution performance, and solves the problem that existing anti-pollution reverse osmosis membrane products are not resistant to pollution by positively charged pollutants; at the same time, the anti-pollution reverse osmosis membrane prepared by the present invention also has high water flux and desalination rate performance.

[0032] Specifically, in terms of reaction mechanism:

[0033] The present invention adopts step S1 to obtain a specific polyamine in which part of the amino groups in the polyamine substance are reversibly protected, adopts step S2 to form a polyamide structural layer, and adopts step S3 to remove the protected amino compound so that the protected amino group is exposed to obtain an anti-pollution reverse osmosis membrane. The present invention uses steps S1-S3 in combination to ensure that there are abundant amino groups in the polyamide structural layer, and the amino groups are protonated in an aqueous solution to form positively charged ammonium groups, which can neutralize the electronegative carboxyl groups formed by the hydrolysis of the excess acyl chloride groups, so that the charge of the polyamide structural layer presents an effect of electrical neutrality, is difficult to electrostatically adsorb positively charged pollutants, has good anti-pollution performance, and greatly improves the operation stability and service life of the reverse osmosis membrane; at the same time, because the amino groups exist in the polyamide structural layer and are not easily washed away, the stability of the desalination layer is ensured, a high desalination rate is maintained, and the prepared reverse osmosis membrane has long-term anti-pollution performance; due to the presence of a large number of hydrophilic amino groups, the hydrophilicity of the surface of the reverse osmosis membrane is also improved, thereby improving the water flux performance of the reverse osmosis membrane.

[0034] The reaction principle of the present invention adopting step S1 to reversibly protect part of the amino groups in the polyamine substance by means of the protective amino compound is as follows: the carbonyl carbon in the protective amino compound attacks the amino group in the polyamine to form a carbon-nitrogen bond, and simultaneously generates a byproduct of hydrogen halide, and an acid absorbent is used to absorb the hydrogen halide, thereby promoting the protective amino compound to reversibly protect part of the amino groups in the polyamine substance;

[0035] The present invention adopts step S3 to remove the protected amino compound with the help of a deaminating agent so that the protected amino group is exposed. The reaction principle is as follows: for benzyl chloroformate, p-toluenesulfonyl chloride or triphenylmethane in the protected amino compound, the deaminating agent used in the present invention is a hydrogen halide, such as hydrogen bromide, which can provide H + , through H + Attack the carbon-nitrogen bond formed by reversibly protecting some amino groups in the polyamine substance, so that the carbon-nitrogen bond is hydrolyzed to expose the protected amino group;

[0036] For the 2-trimethylsilylethoxycarbonyl chloride in the protected amino compound, the deamination reagent used in the present invention is tetrabutylammonium fluoride or tetraethylammonium fluoride, which can generate fluoride ions. The fluoride ions attack the carbon-nitrogen bonds formed by the reversible protection of some amino groups in the polyamine substance, so that the carbon-nitrogen bonds are hydrolyzed to expose the protected amino groups.

[0037] For the protected fluorenylmethoxycarbonyl chloride in the amino compound, the deamination reagent used in the present invention is piperidine, hydrazine or ammonia, which can provide mild alkaline conditions to promote the hydrolysis of the carbon-nitrogen bonds formed by the reversible protection of some amino groups in the polyamine substance to expose the protected amino groups.

[0038] For 4-methoxybenzyl bromide or benzyl bromide in the protected amino compound, the deamination reagent used in the present invention is cerium ammonium nitrate, which, as an oxidant, can oxidatively break the carbon-nitrogen bond formed by reversibly protecting some amino groups in the polyamine substance, exposing the protected amino groups. DETAILED DESCRIPTION

[0039] The technical solutions in the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention belong to the scope of protection of the present invention.

[0040] Embodiment 1:

[0041] A method for preparing an anti-pollution reverse osmosis membrane, comprising:

[0042] Step S1: Preparation of specific polyamine

[0043] A polyamine substance (specifically benzene-1,3,5-triamine) and a protected amino compound (specifically benzyl chloroformate) are dissolved in a first solvent (specifically chloroform) to prepare a first solution; an acid absorbent (specifically triethylamine) and water (water is used to dissolve and disperse the acid absorbent, promote the acid absorbent to absorb the acid of one of the products in the first reaction, and promote the generation of specific polyamines) are added to the first solution; after the first reaction, purification (conventional drying process, removal of the first solvent and water) is performed to obtain a specific polyamine in which one amino group in the polyamine substance is reversibly protected;

[0044] Step S2: preparing nascent polyamide membrane

[0045] Adding water to the specific polyamine prepared in step S1 to prepare an aqueous phase solution, and performing interfacial polymerization reaction with an oil phase solution containing a polyacid chloride (specifically benzene-1,3,5-tricarboxylic acid chloride) to prepare a nascent polyamide membrane;

[0046] Step S3: Preparation of anti-pollution reverse osmosis membrane

[0047] A deamination agent (specifically hydrogen bromide) is added to a second solvent (specifically glacial acetic acid) to prepare a second solution; the nascent polyamide membrane obtained in step S2 is added to the second solution, and after a second reaction, the protective amino compound is removed so that the protected amino group is exposed, and after washing with pure water, an anti-pollution reverse osmosis membrane is obtained;

[0048] The mass concentration of the protected amino compound in the first solution is 3%;

[0049] The mass concentration of the polyamine substance in the first solution is 95%;

[0050] In step S1, the reaction temperature used in the first reaction is 50° C. and the reaction time is 6 h.

[0051] In step S2, the mass concentration of the specific polyamine in the aqueous solution is 6%;

[0052] The mass concentration of the polyacid chloride in the oil phase solution is 0.2%.

[0053] The solvent used in the oil phase solution includes an organic solvent, specifically n-hexane.

[0054] The mass concentration of the deamination reagent in the second solution is 5%.

[0055] In step S3, the reaction temperature used in the second reaction is 50° C. and the reaction time is 5 h.

[0056] Embodiment 2:

[0057] Different from Example 1, in step S1, the protected amino compound is fluorenylmethoxycarbonyl chloride; the first solvent is tetrahydrofuran; the acid absorbent is sodium bicarbonate; the mass concentration of the protected amino compound in the first solution is 4%; the mass concentration of the polyamine substance in the first solution is 90%; the reaction temperature adopted in the first reaction is 50°C and the reaction time is 5h.

[0058] In step S2, the mass concentration of the specific polyamine in the aqueous solution is 5%;

[0059] The mass concentration of the polyacid chloride (specifically benzene-1,2,4,5-tetracarboxylic acid chloride) in the oil phase solution is 0.15%.

[0060] In step S3, the mass concentration of the deamination reagent (specifically piperidine) in the second solution is 20%; and the second solvent is N,N-dimethylformamide solution.

[0061] In step S3, the reaction temperature used in the second reaction is 50° C. and the reaction time is 4 h.

[0062] Embodiment 3:

[0063] Different from Example 1, in step S1, the polyamine substance is 2,4,6-triaminotoluene, the protected amino compound is 4-methoxybenzyl bromide; the first solvent is acetonitrile; the acid absorbent is potassium carbonate; the mass concentration of the protected amino compound in the first solution is 6%; the mass concentration of the polyamine substance in the first solution is 88%; the reaction temperature adopted in the first reaction is 60°C, and the reaction time is 8h.

[0064] In step S2, the mass concentration of the specific polyamine in the aqueous solution is 4.5%;

[0065] The mass concentration of the polyacid chloride (specifically benzene-1,2,4-tricarboxylic acid chloride) in the oil phase solution is 0.3%.

[0066] In step S3, the mass concentration of the deamination reagent (specifically ammonium cerium nitrate) in the second solution is 8%; and the second solvent is methanol.

[0067] In step S3, the reaction temperature used in the second reaction is 40° C. and the reaction time is 6 h.

[0068] Comparative Example 1:

[0069] Different from Example 1, the use of protective amino compounds and deaminating agents is eliminated (i.e., step S3 is eliminated), and the polyamine substance in step S1 is directly used to prepare an aqueous solution, and an interfacial polymerization reaction is carried out with an oil phase solution containing polyacyl chlorides to prepare a nascent polyamide membrane.

[0070] Comparative Example 2:

[0071] The difference from the first embodiment is that step S3 is cancelled.

[0072] The reverse osmosis membranes prepared in Examples 1-3 and Comparative Examples 1-2 were tested for desalination rate, water flux performance and anti-pollution performance. The specific test process is as follows:

[0073] 1) Salt rejection rate test:

[0074] The above reverse osmosis membrane was tested for desalination rate of 2000 mg / L NaCl aqueous solution under the operating conditions of 25°C and 1.55 MPa;

[0075] The salt rejection rate is the most commonly used index to evaluate the separation performance of reverse osmosis membranes, which is represented by R0 and is expressed as formula (I):

[0076]

[0077] In expression (I), C0 represents the inlet water conductivity, μs / cm; C f Indicates the conductivity of produced water, μs / cm.

[0078] 2) Water flux performance test:

[0079] The reverse osmosis membrane was tested for water flux of 2000 mg / L NaCl aqueous solution at 25°C and 1.55 MPa operating pressure. The water flux (F) was calculated according to formula (a):

[0080]

[0081] In formula (a):

[0082] F——water flux, in liters per square meter per hour [L / (m 2 h)];

[0083] V——The volume of permeate collected in time t, in liters (L);

[0084] A——Effective membrane area, in square meters (m 2 );

[0085] t is the time taken to collect V volume of permeate, in hours (h).

[0086] 3) Anti-pollution performance test:

[0087] A CTAB (cetyltrimethylammonium bromide) solution with a concentration of 20 ppm of positively charged pollutants was prepared, and the pH was adjusted to 7.0 using 1 mol / L HCl or 1 mol / L NaOH. After the reverse osmosis membrane was run in the CTAB solution for 1 hour, the membrane surface was rinsed with pure water. Then, the desalination rate of the reverse osmosis membrane was tested according to 1) the desalination rate; and the water flux of the reverse osmosis membrane was tested according to 2) the water flux performance.

[0088] The water flux attenuation rate is the most commonly used indicator for evaluating the anti-fouling performance of reverse osmosis membranes, represented by R, and its expression (b) is as follows:

[0089]

[0090] In formula (b):

[0091] R——water flux attenuation rate, %;

[0092] F0——initial water flux, in liters per square meter per hour [L / (m 2 h)];

[0093] F f ——Water flux after pollution, in liters per square meter per hour [L / (m 2 ·h)].

[0094] The test results of 1)-2) above are shown in Table 1.

[0095] Table 1 Changes in water flux performance of the reverse osmosis membranes prepared by Examples 1-3 and Comparative Examples 1-2 before and after contamination

[0096]

[0097] It can be seen from the data in Table 1 that compared with Comparative Examples 1-2, the combination of protected amino compounds and deaminating agents in Examples 1-3 of the present invention can enable the prepared reverse osmosis membrane to maintain high water flux and desalination rate performance, and can also greatly reduce the flux attenuation rate after the anti-pollution performance test, showing excellent anti-pollution performance.

[0098] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing an anti-pollution reverse osmosis membrane, characterized in that: include: Step S1: Preparation of specific polyamine Dissolving the polyamine substance and the protected amino compound in a first solvent to prepare a first solution; An acid absorbent is added to the first solution, and after a first reaction, a specific polyamine in which some amino groups in the polyamine substance are reversibly protected is obtained; The polyamine material includes at least three amino groups; The protected amino compound includes any one of benzyl chloroformate, 2-trimethylsilylethoxycarbonyl chloride, fluorenylmethoxycarbonyl chloride, p-toluenesulfonyl chloride, triphenylmethane chloride, 4-methoxybenzyl bromide and benzyl bromide; Step S2: preparing nascent polyamide membrane Adding water to the specific polyamine prepared in step S1 to prepare an aqueous solution, and performing interfacial polymerization reaction with an oil solution containing polyacyl chloride to prepare a nascent polyamide membrane; Step S3: Preparation of anti-pollution reverse osmosis membrane Adding a deaminating agent to a second solvent to prepare a second solution; adding the nascent polyamide membrane obtained in step S2 to the second solution, and after a second reaction, removing the protective amino compound so that the protected amino group is exposed, thereby obtaining an anti-pollution reverse osmosis membrane; The deamination agent includes any one of hydrogen bromide, piperidine, tetrabutylammonium fluoride, tetraethylammonium fluoride, hydrazine, ammonia and cerium ammonium nitrate.

2. The method for preparing an anti-pollution reverse osmosis membrane according to claim 1, characterized in that: In step S1, the first solvent includes any one of chloroform, glacial acetic acid, dioxane, methanol and acetonitrile; The mass concentration of the protected amino compound in the first solution is 1%-10%; The mass concentration of the polyamine substance in the first solution is 80%-95%; 3. The method for preparing an anti-pollution reverse osmosis membrane according to claim 1, characterized in that: In step S1, the reaction temperature used in the first reaction is 50-80°C and the reaction time is 2-12h.

4. The method for preparing an anti-pollution reverse osmosis membrane according to claim 1, characterized in that: In step S1, the polyamine substance includes at least one of benzene-1,2,3-triamine, benzene-1,2,4-triamine, benzene-1,3,5-triamine, 2,4,6-triaminotoluene, diethylenetriamine and triethylenetetramine.

5. The method for preparing an anti-pollution reverse osmosis membrane according to claim 1, characterized in that: In step S1, the acid absorbent includes any one of sodium carbonate, sodium bicarbonate, potassium carbonate, triethylamine and sodium hydroxide.

6. The method for preparing an anti-pollution reverse osmosis membrane according to claim 1, characterized in that: In step S2, the mass concentration of the specific polyamine in the aqueous solution is 1%-10%; The mass concentration of the polyacid chloride in the oil phase solution is 0.05%-0.5%.

7. The method for preparing an anti-pollution reverse osmosis membrane according to claim 1, characterized in that: In step S2, the polyacyl chloride includes at least one of isophthaloyl chloride, terephthaloyl chloride, phthaloyl chloride, benzene-1,3,5-tricarboxylic acid chloride, benzene-1,2,4,5-tetracarboxylic acid chloride and benzene-1,2,4-tricarboxylic acid chloride; The solvent used in the oil phase solution includes an organic solvent, which includes any one of N-methylpyrrolidone, n-hexane, cyclohexane and Isopar G.

8. The method for preparing an anti-pollution reverse osmosis membrane according to claim 1, characterized in that: In step S3, the second solvent includes any one of glacial acetic acid, N,N-dimethylformamide solution, tetrahydrofuran, methanol, ethanol, phenol, dichloromethane and acetonitrile; The mass concentration of the deamination agent in the second solution is 2%-20%.

9. The method for preparing an anti-pollution reverse osmosis membrane according to claim 1, characterized in that: In step S3, the reaction temperature used in the second reaction is 40-50° C. and the reaction time is 1-10 h.

10. An anti-pollution reverse osmosis membrane, characterized in that: The anti-pollution reverse osmosis membrane is prepared by the method for preparing the anti-pollution reverse osmosis membrane according to any one of claims 1 to 9.

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