High-pressure reverse osmosis membrane based on ε-caprolactam and precise construction of polyamide network and preparation method thereof

Abstract

The present invention discloses a high-pressure reverse osmosis membrane based on ε-caprolactam to accurately construct a polyamide network and a preparation method thereof. The preparation method of the high-pressure reverse osmosis membrane based on ε-caprolactam to accurately construct a polyamide network comprises the following steps: step 1, preparing an aqueous phase solution, and using the aqueous phase solution to completely infiltrate an ultrafiltration membrane; step 2, preparing an organic phase solution and then performing an interfacial polymerization reaction; step 3, drying and heat setting treatment; step 4, soaking the ultrafiltration membrane after drying and heat treatment in step 3 in an aqueous solution, and then rinsing the membrane surface with deionized water to obtain the high-pressure reverse osmosis membrane based on ε-caprolactam to accurately construct a polyamide network. The present invention innovatively proposes a method for preparing a high-performance high-pressure reverse osmosis membrane of "main chain linking-conformation adjustment-cavity construction". While maintaining an extremely high desalination capacity (≥99.70%, up to 99.78%), the permeate flux is greatly improved (up to 60L·m ‑2 ·h ‑1 ).

Description

Technical Field

[0001] The present invention relates to the technical field of reverse osmosis membranes, and in particular to a high-pressure reverse osmosis membrane having a polyamide network precisely constructed based on ε-caprolactam and a preparation method thereof. Background Art

[0002] Reverse osmosis technology is generally divided into three types: low, medium and high pressure, according to the operating pressure range required for its operation. The corresponding reverse osmosis membrane characteristics of each type are different. Among them, high-pressure reverse osmosis membrane technology is particularly suitable for various wastewater treatment and resource recovery fields with extremely high salt or hardness. In the research and application of high-pressure reverse osmosis membrane technology, how to improve the permeation flux of the membrane while ensuring efficient desalination performance, and achieve better separation effect and higher energy utilization has always been a core issue of concern in the industry and an important direction for technology research and development.

[0003] At present, the mainstream high-pressure reverse osmosis membrane desalination layer is formed by interfacial polymerization (IP) reaction of metaphenylenediamine (MPD) and trimesoyl chloride (TMC) monomers on the surface of polysulfone ultrafiltration membrane to form a dense all-aromatic polyamide layer. In this process, a fully cross-linked and linearly cross-linked polyamide network is formed between MPD and TMC. These networks are folded and compressed through interchain interactions, and the interface is unstable due to the violent exothermic reaction of the IP process. Based on thermodynamic and kinetic drive, an APA layer with a nano-wrinkled structure and irregular sub-nano channels is finally formed. There is an inherent trade-off between permeability and selectivity, resulting in the permeation flux of SWRO membranes that can meet the requirements of seawater desalination under high-salt and high-pressure conditions (32000 ppm NaCl, 5.5MPa) is usually low. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing a high-pressure reverse osmosis membrane with a precisely constructed polyamide network based on ε-caprolactam in order to solve the problem of low permeation flux of existing reverse osmosis membranes under high-salt and high-pressure conditions in the prior art.

[0005] Another object of the present invention is to provide a high-pressure reverse osmosis membrane prepared based on the preparation method.

[0006] The technical solution adopted to achieve the purpose of the present invention is:

[0007] A method for preparing a high-pressure reverse osmosis membrane based on the precise construction of a polyamide network using ε-caprolactam, comprising the following steps:

[0008] Step 1, preparing an aqueous solution containing ε-caprolactam, m-phenylenediamine, camphorsulfonic acid and triethylamine, and using the aqueous solution to completely infiltrate an ultrafiltration membrane;

[0009] Step 2, preparing an organic phase solution containing benzyl chloride, and contacting the surface of the ultrafiltration membrane completely soaked with the aqueous phase solution obtained in step 1 with the organic phase solution to carry out an interfacial polymerization reaction;

[0010] Step 3, drying and heat-setting the ultrafiltration membrane obtained after the interfacial polymerization reaction in step 2;

[0011] Step 4, immersing the ultrafiltration membrane after drying and heat treatment in step 3 in an aqueous solution, and then washing the membrane surface with deionized water to obtain the high-pressure reverse osmosis membrane with a polyamide network precisely constructed based on ε-caprolactam.

[0012] In the above technical solution, the aqueous phase solution in step 1 includes 3.5-6wt% of m-phenylenediamine, 0.01-5wt% of ε-caprolactam, 3.6-6.5wt% of camphorsulfonic acid and 2.1-4wt% of triethylamine.

[0013] In the above technical solution, the aqueous solution in step 1 completely infiltrates the ultrafiltration membrane by the following method: the aqueous solution is evenly covered on the surface of the polysulfone ultrafiltration membrane, and allowed to stand for 30-60 seconds to ensure that the polysulfone base membrane is fully infiltrated, and then the excess solution remaining on the membrane surface is removed and the surface of the ultrafiltration membrane is dried.

[0014] In the above technical solution, the mass fraction of benzene trimesoyl chloride in the organic phase solution in step 2 is 0.2-0.45wt%.

[0015] In the above technical solution, the organic solvent of the organic phase solution in step 2 is one or more of n-hexane, cyclohexane, toluene, Isopar G, Isopar H, Isopar L, and Isopar M.

[0016] In the above technical solution, the heat setting temperature in step 3 is 100-120° C., and the heat setting time is 240-360 seconds.

[0017] In the above technical solution, the pH of the aqueous solution in step 4 is 2-12, and the number of times the deionized water is used to rinse the membrane surface is 3-10 times.

[0018] Another aspect of the present invention provides a high-pressure reverse osmosis membrane having a polyamide network precisely constructed based on ε-caprolactam, which is prepared by the preparation method.

[0019] In the above technical solution, the NaCl rejection rate of the high-pressure reverse osmosis membrane is greater than 99.5%; the permeation flux of the high-pressure reverse osmosis membrane is greater than 49L·m -2 ·h -1 .

[0020] Another aspect of the present invention provides an application of the high-pressure reverse osmosis membrane having a precisely constructed polyamide network based on ε-caprolactam in seawater desalination, wastewater treatment or resource recovery.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. The present invention innovatively proposes a method for preparing high-performance high-pressure reverse osmosis membranes by "main chain linking-conformation adjustment-cavity construction". ε-caprolactam (CPL) with good solubility and unique non-planar, cyclic structure is used as a small molecule regulator. During the IP process, CPL is introduced into the aqueous solution to react with the acyl chloride group of TMC to undergo a nucleophilic substitution reaction and be connected to the MPD-TMC polyamide chain; CPL weakens the folding of the polyamide chain in the form of a molecular space barrier, thereby increasing the sub-angstrom spacing between benzene ring molecules, thereby designing and regulating the internal microstructure and nano-surface morphology of APA; subsequently, due to the unique properties of CPL-TMC, during the soaking process, the CPL molecules gradually detach, and after detachment, a smaller carboxylic acid group remains on the polyamide chain, that is, additional molecular-scale voids are created inside the polyamide structure. The preparation method of the present invention can optimize the polyamide network structure, promote chain extension, and induce the formation of an overall stable polyamide network with optimized chain spacing and additional molecular-level voids, and the change to the physicochemical structure of the original membrane is minimal. The present invention uses CPL as a small molecule regulator of the "main chain linking-conformation adjustment-cavity construction" strategy to prepare a series of high-pressure reverse osmosis membranes, which can significantly increase the permeation flux (up to 60L·m -2 ·h -1 ), showing the great potential and application value of the present invention in various wastewater treatment and resource recovery fields with extremely high salinity or hardness, such as seawater desalination, deep purification of industrial high-salt wastewater, and effective concentration and separation of high-concentration salt or high-value component wastewater.

[0023] 2. The preparation method of the present invention is simple and easy to industrialize. CPL participates in the interfacial polymerization reaction in the form of an aqueous phase additive. Compared with other chemical modification or post-treatment methods, the present invention does not require the addition of complex production steps or additional equipment investment, thereby greatly simplifying the production process, lowering the implementation threshold, and being more conducive to large-scale production and application.

[0024] 3. The high-pressure reverse osmosis membrane of the present invention is cost-effective and has excellent control effect. First, CPL itself has a low cost, which provides economic advantages for the production process. Secondly, although the addition ratio of CPL is only in a relatively small range of 0-5wt%, its effect on improving the performance of the high-pressure reverse osmosis membrane is very prominent, and the performance of the membrane is greatly enhanced while maintaining low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a scanning electron microscope image of the high-pressure reverse osmosis membrane of Example 1.

[0026] Figure 2 is the surface AFM image of the high-pressure reverse osmosis membrane, where: Figure 2 a is the high pressure reverse osmosis membrane of Comparative Example 1, Figure 2 b is the high pressure reverse osmosis membrane of Example 1, Figure 2 c is the high pressure reverse osmosis membrane of Example 2, Figure 2 d is the high pressure reverse osmosis membrane of Example 3, Figure 2 e is the high pressure reverse osmosis membrane of Example 4, Figure 2 f is the high pressure reverse osmosis membrane of Example 5.

[0027] Figure 3 Infrared spectrum of high pressure reverse osmosis membrane, where: Figure 3 a is the prepared high pressure reverse osmosis membrane immersed in deionized water, Figure 3 b: Do not rinse or soak after taking out from the oven. DETAILED DESCRIPTION

[0028] The present invention is further described in detail below in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0029] Embodiment 1:

[0030] A high-pressure reverse osmosis membrane with a precisely constructed polyamide network based on ε-caprolactam is prepared by the following method:

[0031] Step 1, remove the polysulfone ultrafiltration membrane from the deionized water, fix it on the acrylic frame, drain the water droplets on the membrane surface, and use nitrogen to remove the water droplets on the non-woven fabric side of the bottom. Then, spread the aqueous solution containing ε-caprolactam (CPL), m-phenylenediamine, camphorsulfonic acid and triethylamine evenly on the surface of the polysulfone ultrafiltration membrane, and remove the droplets on the membrane surface with nitrogen after 45 seconds. Among them, the weight percentage of ε-caprolactam is 0.1wt%, the weight percentage of m-phenylenediamine is 4.7wt%, the weight percentage of camphorsulfonic acid is 4.1wt%, and the weight percentage of triethylamine is 2.3wt%;

[0032] Step 2, placing an organic phase solution containing trimesoyl chloride on the surface of the membrane obtained in step 1, reacting for 46 seconds and then draining. The weight percentage of trimesoyl chloride is 0.29wt%;

[0033] Step 3, placing the film obtained in step 2 into an oven and curing it at 115° C. for 275 seconds.

[0034] Step 4, soaking the membrane cured in step 3 in an aqueous solution with a pH of 5.5 for 18 minutes, dissociating the N-acyl substituted caprolactam and obtaining a carboxyl functional group on the polyamide chain, and finally rinsing with deionized water for 5 times to thoroughly remove any unreacted residues and impurities on the membrane surface to obtain the high-pressure reverse osmosis membrane.

[0035] Embodiment 2:

[0036] A high-pressure reverse osmosis membrane with a precisely constructed polyamide network based on ε-caprolactam, which is different from Example 1 in that: in step 1, the weight percentage of CPL is 0.3wt%, and the other conditions remain unchanged.

[0037] Embodiment 3:

[0038] A high-pressure reverse osmosis membrane with a precisely constructed polyamide network based on ε-caprolactam, which is different from Example 1 in that: in step 1, the weight percentage of CPL is 0.5wt%, and the other conditions remain unchanged.

[0039] Embodiment 4:

[0040] A high-pressure reverse osmosis membrane with a precisely constructed polyamide network based on ε-caprolactam, which is different from Example 1 in that: in step 1, the weight percentage of CPL is 0.7wt%, and the other conditions remain unchanged.

[0041] Embodiment 5:

[0042] A high-pressure reverse osmosis membrane with a precisely constructed polyamide network based on ε-caprolactam, which is different from Example 1 in that: in step 1, the weight percentage of CPL is 1wt%, and the other conditions remain unchanged.

[0043] Embodiment 6:

[0044] A high-pressure reverse osmosis membrane with a precisely constructed polyamide network based on ε-caprolactam, which is different from Example 1 in that: in step 1, the weight percentage of CPL is 1.5wt%, and the other conditions remain unchanged.

[0045] Comparative Example 1

[0046] A high-pressure reverse osmosis membrane is different from Example 1 in that: in step 1, CPL is not added to the aqueous phase solution, and other conditions remain unchanged.

[0047] Embodiment 7:

[0048] In the present invention, a cross-flow filtration evaluation system was used to test the membrane performance of the high-pressure reverse osmosis membranes prepared in Examples 1 to 6 and Comparative Example 1. The prepared membrane samples were first placed in 7 parallel filtration units with an effective area of ​​29.2 cm 2 , the flow channel height is 1mm. First, pre-pressurize for 30min at 5.5MPa and 25±1℃, and then collect the produced water at a filtration pressure of 5.5MPa and a cross-flow rate of 6LPM. The water flux is calculated by the following formula (1):

[0049] (1)

[0050] In the formula, is the water flux, S is the effective membrane area, At a certain time The amount of permeate collected in the

[0051] The retention rate of the reverse osmosis membrane is determined using a NaCl solution with a concentration of 32000ppm as the raw water. An appropriate amount of NaOH solution is added to adjust the pH of the raw water to 7.0±0.5. Both the raw water and the produced water need to be sampled for concentration determination. The retention rate of the solute is calculated by the following formula (2):

[0052] (2)

[0053] In the formula, and are the solute concentrations of the permeate and feed solutions, respectively.

[0054] Table 1 Separation performance of high pressure reverse osmosis membrane

[0055]

[0056] As shown in Table 1, when the CPL content is maintained at 1% or below (Examples 1 to 5), the retention efficiency of NaCl reaches or exceeds 99.7%, among which Example 1 has the best desalination performance, with a retention rate of up to 99.78%. This excellent performance is particularly suitable for treating wastewater with extremely high salinity and water hardness, seawater desalination, and other scenarios, and shows great potential in the application of recovering high-value resources. At the same time, the permeability of the membrane has been significantly enhanced, with a maximum permeation flux of 60L·m -2 ·h -1Compared with the membrane without CPL (Comparative Example 1), the permeation flux increased by 32.50%, which has excellent performance beyond most commercial membranes. When the CPL content increased to 1.5% (Example 6), although the rejection rate of monoion NaCl was slightly reduced to 99.59%, it still had a desalination rate comparable to that of commercial membranes.

[0057] In order to further explain the above effects, the high-pressure reverse osmosis membranes prepared in Examples 1 to 6 and Comparative Example 1 were characterized and analyzed. Figure 1 The scanning electron microscope image of the high-pressure reverse osmosis membrane prepared by the present invention is shown. It can be seen that the surface is composed of a large range of uniform small vesicle-like structures, interspersed with a small number of small leaf-like structures, showing typical polyamide structural characteristics. As shown in Table 2, after CPL is added to the aqueous solution, the surface and water-oil interfacial tension can be weakened, and MPD is more likely to break through the constraints of solution tension and diffuse, which helps to accelerate the IP reaction rate and thus change the membrane surface morphology. Figure 2 The atomic force images and roughness data shown in the figure confirm this conclusion, showing that as the CPL concentration gradient increases, the "ridge-like" morphology of the film surface becomes more obvious and grows, and the corresponding surface roughness also shows an increasing trend. Figure 3 It is revealed that CPL can not only react with acyl chloride groups and connect to the main chain of polyamide, causing the expansion of the distance between benzene rings to the sub-angstrom scale (Table 3), but also involves the instability of CPL-TMC, causing CPL to dissociate during water immersion, thereby leaving additional molecular-level gaps in the polyamide layer. Therefore, the present invention proposes to cleverly use CPL as a small molecule regulator of the "main chain linking-conformation adjustment-cavity construction" strategy, which on the one hand regulates the internal microstructure, and on the other hand regulates the macroscopic morphology and creates additional molecular-level gaps. The synergistic effect of these factors has enabled the high-pressure reverse osmosis membrane to significantly increase the permeation flux while maintaining an extremely high rejection rate.

[0058] Table 2 Surface / interfacial tension data of aqueous solution and water-oil two-phase solution

[0059]

[0060] Table 3 Benzene ring spacing parameters obtained by fitting WAXS scattering curves

[0061]

[0062] The above is only a preferred embodiment of the present invention. It should be pointed out that, for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a high-pressure reverse osmosis membrane based on ε-caprolactam to accurately construct a polyamide network, characterized in that: The following steps are involved: Step 1, preparing an aqueous solution containing ε-caprolactam, m-phenylenediamine, camphorsulfonic acid and triethylamine, and using the aqueous solution to completely infiltrate an ultrafiltration membrane; Step 2, preparing an organic phase solution containing benzyl chloride, and contacting the surface of the ultrafiltration membrane completely soaked with the aqueous phase solution obtained in step 1 with the organic phase solution to carry out an interfacial polymerization reaction; Step 3, drying and heat-setting the ultrafiltration membrane obtained after the interfacial polymerization reaction in step 2; Step 4, immersing the ultrafiltration membrane after drying and heat treatment in step 3 in an aqueous solution, and then washing the membrane surface with deionized water to obtain the high-pressure reverse osmosis membrane with a polyamide network precisely constructed based on ε-caprolactam, The aqueous solution in step 1 comprises 3.5-6 wt% of m-phenylenediamine, 0.01-5 wt% of ε-caprolactam, 3.6-6.5 wt% of camphorsulfonic acid and 2.1-4 wt% of triethylamine. The pH of the aqueous solution in step 4 is 2-12. During the soaking treatment, ε-caprolactam gradually detaches, and after detachment, a smaller carboxylic acid group remains on the polyacryl chain. The mass fraction of benzene trimesoyl chloride in the organic phase solution in step 2 is 0.2-0.45wt%.

2. The method for preparing a high-pressure reverse osmosis membrane based on the precise construction of a polyamide network using ε-caprolactam according to claim 1, characterized in that: In step 1, the aqueous solution completely infiltrates the ultrafiltration membrane by the following method: the aqueous solution is evenly covered on the surface of the polysulfone ultrafiltration membrane, and allowed to stand for 30-60 seconds to ensure that the polysulfone base membrane is fully infiltrated, and then the excess solution remaining on the membrane surface is removed and the surface of the ultrafiltration membrane is dried.

3. The method for preparing a high-pressure reverse osmosis membrane based on the precise construction of a polyamide network using ε-caprolactam according to claim 1, characterized in that: The organic solvent of the organic phase solution in step 2 is one or more of n-hexane, cyclohexane, toluene, Isopar G, Isopar H, Isopar L, and Isopar M.

4. The method for preparing a high-pressure reverse osmosis membrane based on the precise construction of a polyamide network using ε-caprolactam according to claim 1, characterized in that: The heat setting temperature in step 3 is 100-120° C., and the heat setting time is 240-360 seconds.

5. The method for preparing a high-pressure reverse osmosis membrane based on the precise construction of a polyamide network using ε-caprolactam according to claim 1, characterized in that: The deionized water is used to rinse the membrane surface 3 to 10 times.

6. A high-pressure reverse osmosis membrane based on ε-caprolactam precisely constructed polyamide network, characterized in that: It is prepared by the preparation method according to any one of claims 1 to 5.

7. The high-pressure reverse osmosis membrane with a precisely constructed polyamide network based on ε-caprolactam according to claim 6, characterized in that: The NaCl rejection rate of the high-pressure reverse osmosis membrane is greater than 99.5%; the permeation flux of the high-pressure reverse osmosis membrane is greater than 49L·m -2 ·h -1 .

8. Use of a high-pressure reverse osmosis membrane having a precisely constructed polyamide network based on ε-caprolactam as claimed in any one of claims 6 to 7 in seawater desalination, wastewater treatment or resource recovery.

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