A polybenzoxazine anion exchange membrane and a preparation method thereof

Abstract

The application discloses a kind of polybenzoxazine anion exchange membrane and preparation method thereof, belong to ion exchange membrane technical field. Bis-primary amine monomer, m-cresol and polyoxymethylene are dissolved in organic solvent to obtain benzoxazine monomer with oxazine ring at both ends, which is dissolved in organic solvent to form uniform casting solution, and then coated on the substrate. The polybenzoxazine base film is obtained by polymerization through temperature program. Finally, the base film is soaked in halogenated alkane solution for quaternary ammonium reaction to obtain polybenzoxazine anion exchange membrane. The preparation method of the anion exchange membrane provided by the application has the advantages of low cost of raw materials, mild preparation conditions and the like, thereby the film preparation cost can be greatly reduced. At the same time, the prepared membrane shows better performance than commercial AMV membrane in the field of electrodialysis desalination, and has broad application prospect in the field of seawater desalination.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of ion exchange membranes, and particularly relates to a preparation method of a polybenzoxazine anion exchange membrane for electrodialysis desalination. BACKGROUND

[0002] An ion exchange membrane is a polymer membrane containing ion groups and having selective permeation ability for ions in a solution. It has a wide range of applications in the fields of seawater desalination and salt solution concentration. An anion exchange membrane is an ion exchange membrane having positively charged ion exchange groups and capable of selectively conducting anions through ion exchange.

[0003] Polybenzoxazine is a new type of high-performance thermosetting resin, which has many advantages. First, the precursor can be synthesized simply and efficiently through Mannich reaction, and the reactants for synthesizing the precursor are low in cost. Second, polybenzoxazine not only has the characteristics of high strength, high modulus and high temperature resistance, but also has a low expansion coefficient and low water absorption. However, polybenzoxazine is less used in the field of ion exchange membranes, and there is almost no polybenzoxazine ion exchange membrane used in the field of electrodialysis. Therefore, the development of polybenzoxazine ion exchange membranes for electrodialysis has a broad development prospect.

[0004] CN202011286293.6 discloses a benzoxazine resin containing quaternary ammonium groups and a preparation method and application thereof. The main chain type benzoxazine containing quaternary ammonium groups is prepared through Mannich reaction and quaternization reaction. Then, the polybenzoxazine film containing quaternary ammonium groups is obtained through thermal curing. The main chain type benzoxazine resin containing quaternary ammonium groups is designed and synthesized, which not only can simply and efficiently introduce quaternary ammonium groups into the benzoxazine resin, but also can obtain the cross-linked polybenzoxazine film by using the resin as a precursor. CN202011076012.4 discloses a benzoxazine resin containing zwitterionic groups and a preparation method and application thereof. The benzoxazine resin containing side chain tertiary amine groups is synthesized through Mannich reaction, and then reacts with a quaternization reagent to prepare the benzoxazine resin containing zwitterionic groups. The zwitterionic groups are introduced through quaternization reaction of the low steric hindrance side chain tertiary amine groups, which simply and efficiently prepares the benzoxazine resin with a betaine functionalization degree close to 100%, and prepares the cross-linked polybenzoxazine film containing betaine groups by using the resin as a precursor.

[0005] However, the polybenzoxazine ion exchange membrane prepared by the prior art represented by the above method has a main chain containing a large number of rigid aromatic ring structures, which reduces the toughness and strength of the membrane, and limits its large-scale application. SUMMARY

[0006] The application aims to provide a polybenzoxazine anion exchange membrane and a preparation method thereof, raw materials are low in cost, preparation conditions are mild, and film preparation cost is greatly reduced.

[0007] To achieve the above-mentioned purpose, the application adopts the following technical solutions:

[0008] A preparation method of a polybenzoxazine anion exchange membrane for electrodialysis desalination, specific steps are as follows: a double primary amine monomer, m-cresol and polyformaldehyde are dissolved in an organic solvent A according to a proportion to form a precursor reaction solution with a concentration of 2wt%-40wt%, a Mannich reaction is performed to obtain a benzoxazine precursor, the benzoxazine precursor is dissolved in an organic solvent B to obtain a casting solution with a concentration of 2-20%, then the casting solution is coated on a glass plate to be solidified into a film to obtain a polybenzoxazine base film, and finally the base film is soaked in a halogenated alkane solution to perform a quaternary ammonium reaction to obtain the polybenzoxazine anion exchange membrane.

[0009] The double primary amine monomer is selected from ethylenediamine, hexanediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine and pentaethylenehexamine.

[0010] The molar ratio of the double primary amine monomer, m-cresol and polyformaldehyde is 1:2:4.

[0011] The organic solvent A is one of 1,4-dioxane solution, N-methylpyrrolidone (NMP), dimethyl sulfoxide, toluene and chloroform.

[0012] The Mannich reaction temperature is 60-130 DEG C, and the time is 4-12h.

[0013] The organic solvent B is one of 1,4-dioxane solution, N-methylpyrrolidone, dimethyl sulfoxide, toluene and chloroform.

[0014] The temperature for the precursor thermal polymerization and solidification into a film is preferably 120-200 DEG C, and the preferred time is 0.5-24h.

[0015] The halogenated alkane solution is selected from one of methyl iodide, bromoethane, bromobutane, dibromoethane and the like, and the solvent is preferably methanol, ethanol, diethyl ether or 1,4-dioxane.

[0016] The concentration of the halogenated alkane solution is 2wt%-100wt%, and the temperature is 25-80 DEG C.

[0017] The quaternary ammonium reaction time is preferably 6-48h.

[0018] The application has the following beneficial effects:

[0019] (1) The polybenzoxazine anion exchange membrane of the application uses reactants which are not only low in cost, but also simple to prepare, greatly reducing the cost of membrane preparation.

[0020] (2) The polybenzoxazine ion exchange membrane prepared by the application has a more flexible fatty amine as the amine monomer, making the polybenzoxazine main chain structure more flexible, and the reduced branched structure greatly enhances the mechanical strength of the membrane, with a maximum tensile strength of 98 MPa.

[0021] (3) The secondary amine structure and tertiary amine structure in different primary amine monomers provide more modification sites for halogenated alkane solution, greatly improving the IEC of the polybenzoxazine membrane, with a maximum of 2.8 mmol·g -1 The three-dimensional cross-linked structure of the polybenzoxazine material makes the membrane more dense, and the water content is greatly reduced, compared with the commercial membrane, the water content is reduced by 30%, the IEC is increased by 20%, the resistance is reduced by 300%, and the ion transference number is increased from 0.95 of the commercial membrane to 0.98. Under the same electrodialysis desalination conditions, the desalination rate of the polybenzoxazine anion exchange membrane can reach 91.8%, which is much higher than the 79.6% of the commercial membrane. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 The nuclear magnetic resonance spectrum of the benzoxazine precursor in Example 1.

[0023] Figure 2 The full-scan XPS spectrum of the polybenzoxazine-based membrane and the polybenzoxazine anion exchange membrane in Example 1.

[0024] Figure 3 The high-resolution scanning XPS spectrum of the N1s region of the polybenzoxazine-based membrane and the polybenzoxazine anion exchange membrane in Example 1. DETAILED DESCRIPTION

[0025] In order to make the content of the application more convenient to understand, the technical solutions of the application will be further described below in combination with specific embodiments, but the application is not limited to this.

[0026] The chemical reagents used in the examples of the application are commercially available.

[0027] Example 1

[0028] The ethylenediamine, m-cresol, and paraformaldehyde were dissolved in 1,4-dioxane to prepare a solution with a concentration of 2wt% according to the molar ratio of 1:2:4 of ethylenediamine, m-cresol, and formaldehyde contained in paraformaldehyde, and heated to 60°C for 4h to obtain the precursor with a yield of 35%. The precursor was dissolved in NMP to prepare a casting solution with a concentration of 8wt%, and thermally polymerized to obtain the base film, and then soaked in a 40°C, 20wt% iodomethane solution for 24h. The ion exchange capacity (IEC) was measured to be 1.48mmol·g -1 , the water content was 10.65%, the tensile strength was 36.75MPa, the membrane surface resistance was 1.47Ω·cm 2 , and the transport number was 0.951.

[0029] The polybenzoxazine anion exchange membrane prepared in Example 1 was used for electrodialysis experiments at 25°C. 200ml of 0.1M NaCl solution was added to the concentrated and diluted chambers, and the circulating flow rate was 30ml·min -1 . The operating current was constant at 0.11A. The NaCl removal rate of the obtained membrane was 82.35%, the current efficiency was 85.44%, and the membrane stack energy consumption was 5.65kWh·kg -1 , which was greatly improved compared with the commercial membrane (manufactured by Asahi Glass Company, Japan, with a NaCl removal rate of 79.44%, a current efficiency of 89.95%, and a membrane stack energy consumption of 3.15kWh·kg -1 .

[0030] Example 2

[0031] The polybenzoxazine anion exchange membrane was prepared by a method similar to that of Example 1, except that the concentration was changed to 30wt%, and the precursor yield was 80%. Then it was soaked in a 30°C, 20wt% iodomethane solution for 24h, and the IEC was measured to be 1.34mmol·g -1 , the water content was 10.07%, the tensile strength was 35.71MPa, the membrane surface resistance was 1.65Ω·cm 2 , the transport number was 0.942, the desalination rate was 81.52%, the energy consumption was 6.63kWh·kg -1 , and the current efficiency was 85.65%.

[0032] Example 3

[0033] The polybenzoxazine anion exchange membrane was prepared by a method similar to that of Example 1, except that the concentration was changed to 30wt% and the reaction temperature was adjusted to 90°C, and the precursor yield was 85%. Then it was soaked in a 35°C, 20wt% iodomethane solution for 24h, and the IEC was measured to be 1.41mmol·g -1, water content is 10.65%, tensile strength is 36.16MPa, film surface resistance is 1.58Ω·cm 2 , migration number is 0.948, desalination rate is 82.21%, energy consumption is 6.41kWh·kg -1 , current efficiency is 85.74%.

[0034] Example 4

[0035] The polybenzoxazine anion exchange membrane is prepared by the similar method of Example 1, only the concentration is changed to 30wt%, the reaction temperature is adjusted to 90℃, and the reaction time is adjusted to 8h, and the precursor yield is 95%. Then soak in 45℃, 20wt% iodomethane solution for 24h, the IEC is 1.51mmol·g -1 , water content is 11.12%, tensile strength is 38.56MPa, film surface resistance is 1.42Ω·cm 2 , migration number is 0.951, desalination rate is 83.96%, energy consumption is 4.67kWh·kg -1 , current efficiency is 85.96%.

[0036] Comprehensive Examples 1-4, under the conditions of reactant mass fraction of 30%, temperature of 90℃, and time of 8h, the preparation requirements are met, and further increasing the temperature and prolonging the time have little effect on the yield.

[0037] Example 5

[0038] Diethylenetriamine, m-cresol and polyformaldehyde are dissolved in 1,4-dioxane to prepare a solution with a concentration of 30wt% according to a molar ratio of 1:2:4, heated to 90℃ for 8h to obtain a precursor. The precursor is dissolved in NMP to prepare a casting solution with a concentration of 8wt%, and a base film is obtained by thermal polymerization. Then soak in 40℃, 20wt% iodomethane ethanol solution for 24h, the IEC is 1.69mmol·g -1 , water content is 10.22%, tensile strength is 45.37MPa, film surface resistance is 1.31Ω·cm 2 , migration number is 0.956, desalination rate is 84.67%, energy consumption is 3.67kWh·kg -1 , current efficiency is 86.68%.

[0039] Example 6

[0040] The polybenzoxazine anion exchange membrane is prepared by the similar method of Example 1, only the di-primary amine monomer is changed to triethylenetetramine, and the prepared anion exchange membrane, the IEC is 1.78mmol·g -1, water content is 10.95%, tensile strength is 58.62 MPa, membrane surface resistance is 1.24 Ω·cm 2 , migration number is 0.967, desalination rate is 86.73%, energy consumption is 3.67 kWh·kg -1 , current efficiency is 87.67%.

[0041] Example 7

[0042] The polybenzoxazine anion exchange membrane is prepared by the similar method of Example 1, only the double primary amine monomer is changed to tetraethylene pentaamine, the prepared anion exchange membrane, the IEC is 1.96 mmol·g -1 , water content is 11.86%, tensile strength is 60.27 MPa, membrane surface resistance is 0.95 Ω·cm 2 , migration number is 0.971, desalination rate is 88.62%, energy consumption is 2.67 kWh·kg -1 , current efficiency is 89.19%.

[0043] Example 8

[0044] The polybenzoxazine anion exchange membrane is prepared by the similar method of Example 1, only the double primary amine monomer is changed to pentaethylene hexamine, the prepared anion exchange membrane, the IEC is 2.23 mmol·g -1 , water content is 11.98%, tensile strength is 64.35 MPa, membrane surface resistance is 0.87 Ω·cm 2 , migration number is 0.961, desalination rate is 89.67%, energy consumption is 2.48 kWh·kg -1 , current efficiency is 89.69%.

[0045] It is not difficult to find from Examples 5-8 that by increasing the length of the main chain, the mechanical strength of the membrane can be effectively increased, and by increasing the modification site in the double primary amine monomer, the modification site of the membrane can be increased, thereby increasing the degree of quaternization of the membrane and increasing the IEC.

[0046] Example 9

[0047] The polybenzoxazine anion exchange membrane is prepared by the similar method of Example 8, only the modification temperature is changed to 20℃, the iodomethane solution concentration is changed to 2wt%, and the modification time is changed to 48h, the prepared anion exchange membrane, the IEC is 1.34 mmol·g -1 , water content is 7.36%, tensile strength is 32.27 MPa, membrane surface resistance is 2.07 Ω·cm 2 , migration number is 0.941, desalination rate is 81.69%, energy consumption is 6.27 kWh·kg -1 , current efficiency is 82.65%.

[0048] Example 10

[0049] A polybenzoxazine anion exchange membrane was prepared by the similar method of Example 8, only the modification temperature was changed to 60℃, the concentration of methyl iodide solution was changed to 50wt%, and the modification time was changed to 24h. The obtained anion exchange membrane was measured to have an IEC of 2.68mmol·g -1 , a water content of 19.95%, a tensile strength of 78.27MPa, a membrane surface resistance of 0.63Ω·cm 2 , a transfer number of 0.983, a desalination rate of 91.68%, an energy consumption of 2.31kWh·kg -1 , and a current efficiency of 93.19%.

[0050] Example 11

[0051] A polybenzoxazine anion exchange membrane was prepared by the similar method of Example 8, only the modification temperature was changed to 80℃, the concentration of methyl iodide solution was changed to 100wt%, and the modification time was changed to 48h. The obtained polybenzoxazine anion exchange membrane was measured to have an IEC of 2.83mmol·g -1 , a water content of 21.05%, a tensile strength of 86.95MPa, a membrane surface resistance of 0.56Ω·cm 2 , a transfer number of 0.991, a desalination rate of 92.08%, an energy consumption of 2.18kWh·kg -1 , and a current efficiency of 94.37%.

[0052] Example 12

[0053] A polybenzoxazine anion exchange membrane was prepared by the similar method of Example 8, only the modification temperature was changed to 60℃, the modification solution was changed to a 50wt% bromoethane ethanol solution, and the modification time was changed to 48h. The obtained polybenzoxazine anion exchange membrane was measured to have an IEC of 2.34mmol·g -1 , a water content of 12.56%, a tensile strength of 76.45MPa, a membrane surface resistance of 0.68Ω·cm 2 , a transfer number of 0.976, a desalination rate of 90.28%, an energy consumption of 2.39kWh·kg -1 , and a current efficiency of 91.98%.

[0054] Example 13

[0055] A polybenzoxazine anion exchange membrane was prepared by the similar method of Example 8, only the modification temperature was changed to 60℃, the modification solution was changed to a 50wt% bromoethane 1,4-dioxane solution, and the modification time was changed to 48h. The obtained polybenzoxazine anion exchange membrane was measured to have an IEC of 2.39mmol·g -1, the water content is 12.87%, the tensile strength is 77.37 MPa, and the membrane surface resistance is 0.71 Omega-cm 2 , the migration number is 0.972, the desalination rate is 90.57%, and the energy consumption is 2.34 kWh-kg -1 , the current efficiency is 91.87%.

[0056] Example 14

[0057] The polybenzoxazine anion exchange membrane is prepared by the similar method of Example 8, only the modification temperature is changed to 60 DEG C, the modification solution is changed to a 1,4-dioxane solution with a concentration of 45 wt% of bromoethane, and the modification time is changed to 48 h, and the IEC of the obtained polybenzoxazine anion exchange membrane is 2.28 mmol-g -1 , the water content is 11.67%, the tensile strength is 65.25 MPa, and the membrane surface resistance is 0.82 Omega-cm 2 , the migration number is 0.969, the desalination rate is 88.98%, and the energy consumption is 2.73 kWh-kg -1 , the current efficiency is 88.43%.

[0058] Example 15

[0059] The polybenzoxazine anion exchange membrane is prepared by the similar method of Example 8, only the modification temperature is changed to 60 DEG C, the modification solution is changed to a 1,4-dioxane solution with a concentration of 45 wt% of bromoethane, and the modification time is changed to 48 h, and the IEC of the obtained polybenzoxazine anion exchange membrane is 2.28 mmol-g -1 , the water content is 19.18%, the tensile strength is 75.25 MPa, and the membrane surface resistance is 0.63 Omega-cm 2 , the migration number is 0.981, the desalination rate is 91.85%, and the energy consumption is 2.28 kWh-kg -1 , the current efficiency is 97.86%.

[0060] The above example results show that the best reaction temperature of the benzoxazine precursor prepared by the application is 90 DEG C, and the time is 8 h, and it is not difficult to find from the comparison of the polybenzoxazine anion exchange membranes prepared by different diamine monomers that the flexible structure of the polybenzoxazine main chain has a greater influence on the mechanical strength of the whole membrane, and the polybenzoxazine-based membrane synthesized by the amine with multiple modification sites has a higher IEC, and exhibits better performance in the electrodialysis desalination. At present, the polybenzoxazine ion exchange membrane is less researched, and there is almost no research in the field of electrodialysis desalination, so it has a broad development prospect.

[0061] The above only describes the preferred embodiments of the application, and any changes and modifications made within the scope of the application should be included in the scope of the application.

Claims

1. A method for preparing a polybenzoxazine anion exchange membrane, characterized by: The diamine monomer, m-cresol and paraformaldehyde are dissolved in an organic solvent to form a precursor solution with a concentration of 2-40 wt%, and then a Mannich reaction is carried out to obtain a benzoxazine precursor; the benzoxazine precursor is dissolved in an organic solvent to obtain a casting solution with a concentration of 2-20 wt%, and then a film is coated on a glass plate, and solidification is carried out to form a film, thereby obtaining a polybenzoxazine base film; the base film is soaked in a halogenated alkane solution to carry out a quaternary ammonium reaction, thereby obtaining the polybenzoxazine anion exchange film. The diamine monomer is one of ethylenediamine, hexanediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine and pentaethylenehexamine. The molar ratio of the diamine monomer, m-cresol and paraformaldehyde is 1:2:

4. The Mannich reaction is carried out at a temperature of 60-130°C for 4-12 h.

2. The method of claim 1, wherein: The organic solvent is one of 1,4-dioxane solution, N-methylpyrrolidone, dimethyl sulfoxide, toluene and chloroform.

3. The method of claim 1, wherein: The temperature for solidification to form a film is 120-200°C, and the time is 0.5-24 h.

4. The method of claim 1, wherein: The concentration of the halogenated alkane solution is 2-50 wt%, the solute is one of iodomethane, bromoethane, bromobutane and dibromoethane, and the solvent is one of methanol, ethanol, diethyl ether and 1,4-dioxane.

5. The method of claim 1, wherein: The temperature for the quaternary ammonium reaction is 25-80°C, and the time is 6-48 h.

6. A polybenzoxazine anion exchange film prepared by the method of any one of claims 1-5.

7. Application of the polybenzoxazine anion exchange film prepared by the method of any one of claims 1-5 in electrodialysis desalination.

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