Desalination nanofiltration membrane as well as preparation method and application thereof

Abstract

The invention discloses a desalting nanofiltration membrane as well as a preparation method and application thereof. The preparation method of the desalting nanofiltration membrane comprises the step of compounding a polyaminopiperazine selective separation layer on the surface of a base membrane to obtain the desalting nanofiltration membrane. The molecular weight cut-off of the desalting nanofiltration membrane provided by the invention can be as low as 150Da, the cut-off rate of the desalting nanofiltration membrane to small molecular organic matters such as xylose and glucose is greater than 90%, and the cut-off rate of sodium chloride is less than 30%, namely, the desalting nanofiltration membrane shows relatively high small molecular organic matter-salt selectivity.

Description

Technical Field

[0001] The invention belongs to the technical field of nanofiltration membranes, and in particular relates to a desalination nanofiltration membrane and a preparation method and application thereof. Background Art

[0002] The core feature of NF membrane (nanofiltration membrane) lies in its unique separation characteristics, and its performance is related to the pore size and is affected by the surface charge. The molecular weight cutoff (MWCO) of nanofiltration membrane is between reverse osmosis membrane and ultrafiltration membrane (200-1000Da). The retention rate of divalent salts is usually higher than 90%, while the retention rate of monovalent salts is slightly lower. In recent years, nanofiltration membranes have been increasingly used in the deep treatment and reuse of sewage, deep purification of drinking water, and desalination of organic matter (such as desalination of antibiotics or dyes). Whether it is deep treatment of drinking water or desalination of organic matter, it is expected that the nanofiltration membrane has a lower molecular weight cutoff (the molecular weight corresponding to neutral organic matter when the retention rate is 90%) and a lower salt retention rate. In other words, it is necessary to retain small molecular organic matter and ensure that salt can pass through. At present, commercial nanofiltration membranes are mainly fully aromatic and semi-aromatic polyamide thin-layer composite membranes prepared by interfacial polymerization. Since polyamide nanofiltration membranes were originally designed for desalination, their salt retention rate is high, but the selectivity of organic matter-salt is not outstanding. That is to say, the retention rate of small molecule organic matter is high while the retention rate of salt is also high. Summary of the invention

[0003] In order to solve the above technical problems, one of the objectives of the present invention is to provide a method for preparing a desalination nanofiltration membrane, wherein the nanofiltration membrane prepared by the method can intercept small molecular organic matter while allowing salt ions to pass through.

[0004] In order to achieve the above object, the technical scheme of the present invention is as follows: a method for preparing a desalination nanofiltration membrane, wherein a polyaminopiperazine selective separation layer is compounded on the surface of a base membrane to obtain a desalination nanofiltration membrane.

[0005] The specific operation of compounding the polyaminopiperazine selective separation layer on the surface of the basement membrane in the above technical solution is as follows:

[0006] Step 1: soaking the base film in an aqueous solution containing aminopiperazine and a bifunctional additive until saturated;

[0007] Step 2: Take out the base film soaked in step 1 and remove the liquid stains remaining on its surface;

[0008] Step 3: The surface of the base membrane treated in step 2 is contacted with an oil phase solution of polyacid chloride and reacted to form a polyaminopiperazine selective separation layer on the surface of the base membrane due to the interfacial reaction, and then treated in a low-temperature water bath to obtain a desalting nanofiltration membrane.

[0009] The base membrane in the above technical solution is a porous microfiltration membrane or an ultrafiltration membrane.

[0010] The base membrane in the above technical solution is a polysulfone membrane or a polyethersulfone membrane.

[0011] Step 1 in the above technical solution must meet at least one of the following conditions:

[0012] A1: The aminopiperazine may be N-aminoethylpiperazine or N-methylpiperazine;

[0013] B1: the additive is one of taurine, homotaurine, aminobenzenesulfonic acid, 3-aminopropylene glycol, diethanolamine and diglycolamine;

[0014] C1: The concentration of aminopiperazine in the aqueous phase solution is 0.05-0.2wt%;

[0015] D1: The concentration of the additive in the aqueous solution is 0.01-0.1wt%;

[0016] E1: The temperature of the aqueous solution is 0-10°C;

[0017] F1: The base film is immersed in the aqueous solution for 1-30 minutes.

[0018] Step 3 in the above technical solution must meet at least one of the following conditions:

[0019] A2: The polyacyl chloride is one of trimesoyl chloride, terephthaloyl chloride, trimesoyl chloride and terephthaloyl chloride;

[0020] B2: The solvent in the oil phase solution is an alkane solvent or an alkane mixed solvent;

[0021] C2: The concentration of polyacid chloride in the oil phase solution is 0.05-0.5 w / v%;

[0022] D2: The temperature of the oil phase solution is between -5°C and 5°C;

[0023] E2: The contact time between the base film and the oil phase solution is 1-60s;

[0024] F2: The treatment temperature of the low temperature water bath is 0-5°C.

[0025] The alkane solvent in the above technical solution is n-hexane or n-heptane.

[0026] The base membrane in the above technical solution comprises a base membrane body layer and a non-woven fabric support layer which are composited with each other, and the polyaminopiperazine selective separation layer is composited on the side of the base membrane body layer away from the non-woven fabric support layer.

[0027] The second object of the present invention is to provide a desalination nanofiltration membrane prepared by the above preparation method.

[0028] The third object of the present invention is to provide an application of the above-mentioned desalination nanofiltration membrane in the desalination treatment of small molecule organic matter.

[0029] The beneficial effect of the present invention is that the molecular weight cutoff of the desalination nanofiltration membrane provided by the present invention can be as low as 150Da, the retention rate of small molecule organic matter such as xylose and glucose is greater than 90%, and the retention rate of sodium chloride is less than 30%, that is, it shows a higher small molecule organic matter-salt selectivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 are the NaCL and xylose rejection rates and water flux of polyaminopiperazine nanofiltration membrane at different taurine contents;

[0031] Figure 2 The NaCL and xylose rejection rates and water flux of polyaminopiperazine nanofiltration membranes at different 3-aminopropanediol contents;

[0032] Figure 3 are the NaCL and xylose rejection rates and water flux of polyaminopiperazine nanofiltration membrane at different diethanolamine contents; DETAILED DESCRIPTION

[0033] The principles and features of the present invention are described below in conjunction with embodiments. The examples are only used to explain the present invention and are not used to limit the scope of the present invention. The advantages and features of the present invention will be more clearly described according to the following description and claims.

[0034] The present invention provides a method for preparing a desalination nanofiltration membrane, wherein a polyaminopiperazine selective separation layer is compounded on the surface of a base membrane to obtain a desalination nanofiltration membrane. The base membrane comprises a base membrane body layer and a non-woven fabric support layer (which belongs to the prior art and is not described here in detail), and the polyaminopiperazine selective separation layer is compounded on the side of the base membrane body layer away from the non-woven fabric support layer.

[0035] The specific operation of compounding the polyaminopiperazine selective separation layer on the surface of the basement membrane in the above technical solution is as follows:

[0036] Step 1: soaking the base film in an aqueous solution containing aminopiperazine and a bifunctional additive until saturated;

[0037] Step 2: Take out the base film soaked in step 1 and remove the liquid stains remaining on its surface;

[0038] Step 3: The surface of the base membrane treated in step 2 is contacted with an oil phase solution of polyacid chloride and reacted to form a polyaminopiperazine selective separation layer on the surface of the base membrane due to the interfacial reaction, and then treated in a low-temperature water bath to obtain a desalting nanofiltration membrane.

[0039] Wherein, polyaminopiperazine is a polymer of monomer aminopiperazine.

[0040] In the above technical solution, the base membrane is classified into a porous microfiltration membrane or an ultrafiltration membrane based on function, and the base membrane is classified into a polysulfone membrane based on material.

[0041] Step 1 in the above technical solution must meet at least one of the following conditions:

[0042] A1: The aminopiperazine may be N-aminoethylpiperazine or N-methylpiperazine;

[0043] B1: the additive is one of taurine, homotaurine, aminobenzenesulfonic acid, 3-aminopropylene glycol, diethanolamine and diglycolamine;

[0044] C1: the concentration of aminopiperazine in the aqueous solution is 0.05-0.2wt% (can be any value among 0.05wt%, 0.06wt%, 0.07wt%, 0.08wt%, 0.09wt%, 0.1wt%, 0.11wt%, 0.12wt%, 0.13wt%, 0.14wt%, 0.15wt%, 0.16wt%, 0.17wt%, 0.18wt%, 0.19wt% and 0.2wt% or the range corresponding to any two values);

[0045] D1: The concentration of the additive in the aqueous solution is 0.01-0.1wt% (can be any value among 0.01wt%, 0.02wt%, 0.03wt%, 0.04wt%, 0.05wt%, 0.06wt%, 0.07wt%, 0.08wt%, 0.09wt% and 0.1wt% or the range corresponding to any two values);

[0046] E1: The temperature of the aqueous solution is 0-10°C (can be any value among 0°C, 1°C, 2°C, 3°C, 4°C, 5°C, 6°C, 7°C, 8°C, 9°C and 10°C or a range corresponding to any two values);

[0047] F1: The time for which the base film is immersed in the aqueous solution is 1-30 min (it can be any value among 1 min, 2 min, 3 min, 4 min, 5 min, 6 min, 7 min, 8 min, 9 min, 10 min, 11 min, 12 min, 13 min, 14 min, 15 min, 16 min, 17 min, 18 min, 19 min, 20 min, 21 min, 22 min, 23 min, 24 min, 25 min, 26 min, 27 min, 28 min, 29 min and 30 min, or the corresponding range between any two values).

[0048] Step 3 in the above technical solution must meet at least one of the following conditions:

[0049] A2: The polyacyl chloride is one of trimesoyl chloride, terephthaloyl chloride, trimesoyl chloride and terephthaloyl chloride;

[0050] B2: The solvent in the oil phase solution is an alkane solvent (n-hexane, n-heptane or Isopar G, etc.);

[0051] C2: the concentration of the polyacyl chloride in the oil phase solution is 0.05-0.5 w / v% (can be any value among 0.05 w / v%, 0.1 w / v%, 0.15 w / v%, 0.2 w / v%, 0.25 w / v%, 0.3 w / v%, 0.35 w / v%, 0.4 w / v%, 0.45 w / v% and 0.5 w / v% or the range corresponding to any two values);

[0052] D2: The temperature of the oil phase solution is between -5°C and 5°C (can be any value among -5°C, -4°C, -3°C, -2°C, -1°C, 0°C, 1°C, 2°C, 3°C, 4°C and 5°C or a range corresponding to any two values);

[0053] E2: The contact time between the base film and the oil phase solution is 1-60 s (can be any value among 1 s, 5 s, 10 s, 15 s, 20 s, 25 s, 30 s, 35 s, 40 s, 45 s, 50 s, 55 s and 60 s, or a range corresponding to any two values);

[0054] F2: The treatment temperature of the low-temperature water bath is 0-5°C (it can be any value among 0°C, 1°C, 2°C, 3°C, 4°C and 5°C or a corresponding range between any two values).

[0055] Example introduction:

[0056] Preparation of base film: Use NN dimethylacetamide as solvent, add polysulfone and polyvinyl pyrrolidone to prepare a membrane liquid with a concentration of 15wt% polysulfone and 3wt% polyvinyl pyrrolidone, and stir it at room temperature until it is completely dissolved and there are no bubbles; use a 250μm thick scraper to evenly coat the membrane liquid on the PET non-woven fabric, and then quickly immerse it in deionized water to form it, and let it stand for 12 hours to obtain the base film.

[0057] Example 1

[0058] Step 1: prepare five portions of 0.07 wt% N-aminoethylpiperazine aqueous solutions, and then add taurine to obtain aqueous phase solutions, wherein the concentrations of taurine in the five portions of aqueous phase solutions are 0, 0.01 wt%, 0.03 wt%, 0.07 wt% and 0.1 wt%, respectively. After the taurine is completely dissolved, place the solution in a refrigerator and cool it to 4°C;

[0059] Step 2: dissolve trimesoyl chloride in n-hexane to prepare an oil phase solution with a concentration of 0.2 w / v%. After the solution is completely dissolved, place the solution in a refrigerator and cool it to 4°C;

[0060] Step 3: Take five base membranes, which correspond to five aqueous solutions one by one. Soak each base membrane in the corresponding aqueous solution, take it out after 10 minutes, blow off the residual solution on the surface of the base membrane with an air gun, and then contact the side of the base membrane away from the PET non-woven fabric with the oil phase solution to produce an interfacial polymerization reaction. The contact time is 15 seconds, and then soak it in 4°C deionized water to obtain a desalting nanofiltration membrane.

[0061] The five prepared desalination nanofiltration membranes were tested for performance. The test indicators were mainly the retention rate of xylose and NaCl, and the membrane flux. The test temperature was 25°C and the operating pressure was 4 bar. The specific results are as follows: Figure 1 shown.

[0062] Example 2

[0063] Same as Example 1, except that: in step 1, four aqueous phase solutions are prepared, and the additive of the aqueous phase solution is 3-aminopropanediol, and the four concentrations are 0, 0.01wt%, 0.07wt% and 0.1wt%), and after both are completely dissolved, the solution is placed in a refrigerator and cooled to 4°C; the measured results are as follows Figure 2 shown.

[0064] Example 3

[0065] Same as Example 2, except that the additive of the aqueous phase solution in step 1 is diethanolamine; the measured results are as follows Figure 3 shown.

[0066] The aminopiperazine monomer contains primary amine and piperazine groups, has high reaction activity and fast film-forming rate. The polyaminopiperazine selective separation layer in the present invention is formed by low-concentration aminopiperazine aqueous solution and acyl chloride oil phase solution through low-temperature, ultra-short-time interfacial polymerization reaction, and low-temperature post-treatment. The addition of bifunctional group additives in the aqueous phase further changes the pore size and charge properties of the membrane. The prepared desalination nanofiltration membrane has high organic / salt selectivity (especially suitable for desalination of small molecule organic matter).

[0067] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a desalination nanofiltration membrane, characterized in that: A desalination nanofiltration membrane is obtained by compounding a polyaminopiperazine selective separation layer on the surface of the base membrane.

2. The method for preparing a desalination nanofiltration membrane according to claim 1, characterized in that: The specific operation of compounding the polyaminopiperazine selective separation layer on the surface of the basement membrane is as follows: Step 1: soaking the base film in an aqueous solution containing aminopiperazine and a bifunctional additive until saturated; Step 2: Take out the base film soaked in step 1 and remove the liquid stains remaining on its surface; Step 3: The surface of the base membrane treated in step 2 is contacted with an oil phase solution of polyacid chloride and reacted to form a polyaminopiperazine selective separation layer on the surface of the base membrane due to the interfacial reaction, and then treated in a low-temperature water bath to obtain a desalting nanofiltration membrane.

3. The method for preparing a desalination nanofiltration membrane according to claim 2, characterized in that: The base membrane is a porous microfiltration membrane or an ultrafiltration membrane.

4. The method for preparing a desalination nanofiltration membrane according to claim 2, characterized in that: The base membrane is a polysulfone membrane or a polyethersulfone membrane.

5. The method for preparing a desalination nanofiltration membrane according to claim 2, characterized in that: Step 1 must meet at least one of the following conditions: A1: The aminopiperazine may be N-aminoethylpiperazine or N-methylpiperazine; B1: the additive is one of taurine, homotaurine, aminobenzenesulfonic acid, 3-aminopropylene glycol, diethanolamine and diglycolamine; C1: The concentration of aminopiperazine in the aqueous phase solution is 0.05-0.2wt%; D1: The concentration of the additive in the aqueous solution is 0.01-0.1wt%; E1: The temperature of the aqueous solution is 0-10°C; F1: The base film is immersed in the aqueous solution for 1-30 minutes.

6. The method for preparing a desalination nanofiltration membrane according to claim 2, characterized in that: Step 3 must meet at least one of the following conditions: A2: The polyacyl chloride is one of trimesoyl chloride, terephthaloyl chloride, trimesoyl chloride and terephthaloyl chloride; B2: The solvent in the oil phase solution is an alkane solvent or an alkane mixed solvent; C2: The concentration of polyacid chloride in the oil phase solution is 0.05-0.5 w / v%; D2: The temperature of the oil phase solution is between -5°C and 5°C; E2: The contact time between the base film and the oil phase solution is 1-60s; F2: The treatment temperature of the low temperature water bath is 0-5°C.

7. The method for preparing a desalination nanofiltration membrane according to claim 6, characterized in that: The alkane solvent is n-hexane, n-heptane or Isopa G.

8. The method for preparing a desalination nanofiltration membrane according to claim 1, characterized in that: The base membrane comprises a base membrane main body layer and a non-woven fabric support layer which are compounded with each other, and the polyaminopiperazine selective separation layer is compounded on the side of the base membrane main body layer away from the non-woven fabric support layer.

9. A desalination nanofiltration membrane, characterized in that: The method is prepared according to any one of claims 1 to 8.

10. Use of the desalination nanofiltration membrane according to claim 9, characterized in that: Used in the desalination of small molecule organic matter.

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