A household reverse osmosis composite membrane and a preparation method thereof

Abstract

This invention provides a household reverse osmosis composite membrane and its preparation method. The preparation method includes preparing a hybrid hydrogel layer, preparing a hybrid aerogel layer, and preparing a polyamide functional layer to obtain the household reverse osmosis composite membrane. This household reverse osmosis composite membrane is prepared using this method. This invention can prepare a household reverse osmosis composite membrane with high water flux and desalination rate, and also has antibacterial properties and can improve the taste of purified water.

Description

Technical Field

[0001] This invention relates to the field of reverse osmosis membrane technology, specifically to a household reverse osmosis composite membrane and its preparation method. Background Technology

[0002] Reverse osmosis technology, as one of the most important water treatment technologies, has wide applications not only in industrial fields (such as water reuse in the steel / coal chemical industry), ultrapure water preparation in the electronics industry, and seawater desalination, but also in household water purifiers.

[0003] A typical household reverse osmosis water purifier consists of five filter stages: PP cotton, granular activated carbon, compressed activated carbon, reverse osmosis membrane filter, and post-activated carbon. The reverse osmosis membrane filter is the core component, while the PP cotton, granular activated carbon, and compressed activated carbon primarily filter coarse particulate impurities from tap water, adsorb residual chlorine, odor, color, and some organic matter, thus protecting the reverse osmosis membrane filter. The post-activated carbon, mainly composed of fruit shell activated carbon, is used to improve the taste of drinking water.

[0004] The current development trend of household water purifiers is mainly focused on small size and high flow rate. The mainstream technology aims to achieve the same filtration effect while reducing the number or size of filter elements. For example, patent CN215712121U assembles PP filter media, pre-carbon rod filter media, reverse osmosis filter element, and post-filter media into a single composite filter element; patent CN208684569U combines the reverse osmosis filter element and post-filter element within a single filter element assembly, thereby reducing the number of filter elements and the volume of the reverse osmosis water purifier. These technologies primarily optimize space through filter element combination design, thus reducing the size of the water purifier. However, regarding high flow rate, the optimized combination of filter elements does not increase the flow rate; it is mainly achieved by increasing the area of ​​the reverse osmosis membrane, which in turn increases the volume.

[0005] Therefore, from the perspective of preparing reverse osmosis membrane materials, it is of great significance to provide a small-volume, high-flux household reverse osmosis composite membrane for household water purifiers and its preparation method. Summary of the Invention

[0006] The purpose of this invention is to provide a household reverse osmosis composite membrane and its preparation method, the specific technical solution of which is as follows:

[0007] In a first aspect, the present invention provides a method for preparing a household reverse osmosis composite membrane, comprising:

[0008] Step S1: Preparation of hybrid hydrogel layer

[0009] The chitosan acetate solution and β-cyclodextrin aqueous solution of the required mass concentration are stirred and mixed; the crosslinking agent of the required mass concentration is added; the fruit shell activated carbon particles of the required mass are added, and after stirring and mixing, the mixture is placed in a water bath at 55-65℃ for 1-3 hours to obtain a hybrid hydrogel layer; the crosslinking agent is glutaraldehyde.

[0010] Step S2: Preparation of hybrid aerogel layer

[0011] The hybrid hydrogel layer prepared in step S1 is immersed in pure water and washed until neutral; the washed hybrid hydrogel layer is pre-frozen for 12-48 hours; the pre-frozen hybrid hydrogel layer is freeze-dried for 24-48 hours to obtain a hybrid aerogel layer.

[0012] Step S3: Prepare the polyamide functional layer

[0013] The hybrid aerogel layer is immersed in an aqueous amine solution for 30-90 seconds; the hybrid aerogel layer is then immersed in an acyl chloride solution in an organic phase, and after reacting for 15-30 seconds, it is removed to obtain a polyamide functional layer, i.e., a composite layer, that grows on the hybrid aerogel layer; the composite layer is then dried to obtain a household reverse osmosis composite membrane.

[0014] Optionally, in step S1, the mass concentration of the chitosan acetate solution is 1 wt%-5 wt%; and the mass concentration of the β-cyclodextrin aqueous solution is 5 wt%-10 wt%.

[0015] Optionally, in step S1, the mass concentration of the crosslinking agent is 0.5-1.5 wt%.

[0016] Optionally, in step S1, the mass ratio of chitosan acetate solution, β-cyclodextrin aqueous solution, crosslinking agent, and coconut shell activated carbon particles is 50:50:1:5.

[0017] Optionally, in step S1, the activated carbon granules may include activated carbon made from coconut shells or walnut shells.

[0018] Optionally, in step S1, the size of the fruit shell activated carbon particles is 0.5-2 mm.

[0019] Optionally, in step S1, the chitosan acetate solution is prepared by dissolving chitosan in an acetic acid solution.

[0020] Optionally, in step S3, the concentration of the amine solution is 2.8 wt%-3.6 wt%, which includes at least one of m-phenylenediamine solution, o-phenylenediamine solution and p-phenylenediamine solution.

[0021] Optionally, in step S3, the concentration of the acyl chloride solution is 0.08wt%-0.12wt%, which includes at least one of trimesoyl chloride solution, isophthaloyl chloride solution and terephthaloyl chloride solution.

[0022] In a second aspect, the present invention provides a household reverse osmosis composite membrane, which is prepared using the method for preparing the household reverse osmosis composite membrane.

[0023] The application of the technical solution of the present invention has at least the following beneficial effects:

[0024] (1) Compared with traditional polyamide reverse osmosis composite membranes (the structure of traditional polyamide reverse osmosis composite membranes includes nonwoven fabric, polysulfone, and a polyamide layer), this invention adopts a method for preparing household reverse osmosis composite membranes. In step S1, glutaraldehyde is used as a crosslinking agent. On the one hand, the aldehyde group of glutaraldehyde undergoes an aldol condensation reaction with the hydroxyl group of β-cyclodextrin; on the other hand, the aldehyde group of glutaraldehyde undergoes a Schiff base reaction with the amino group of chitosan. Finally, after treatment in step S2, a three-dimensional porous network structure of a crosslinked system is formed. The three-dimensional porous network structure is used as the base membrane for the interfacial polymerization reaction in step S3 to generate a polyamide functional layer. Since the β-cyclodextrin and chitosan in the aerogel layer contain a large number of hydroxyl and amino groups, respectively, they have good hydrophilicity, which is more conducive to the adsorption of aqueous amine solution. At the same time, there is a hydrogen bond between the amine in the aqueous phase and the hydroxyl and amino groups on the aerogel, which reduces the diffusion rate of amine to the organic phase during interfacial polymerization, resulting in a relatively thinner polyamide functional layer. On the one hand, because the resulting polyamide functional layer is thinner and the polysulfone layer is reduced compared to traditional polyamide reverse osmosis membranes, the water mass transfer resistance during separation will be significantly lower. On the other hand, the three-dimensional porous network structure is more conducive to water transport in the water channels. Therefore, compared to traditional polyamide reverse osmosis composite membranes, the water flux will be greatly improved.

[0025] (2) Traditional nonwoven fabrics are mainly composed of polyester fibers, and antimony-containing catalysts are used in the preparation process. Therefore, there is often a risk of antimony exceeding the standard in the evaluation of drinking water hygiene and safety indicators. The hybrid aerogel layer in this invention, on the one hand, uses mostly natural polymer materials with good biocompatibility, and no metal compound catalysts are used in the preparation process; on the other hand, the positive charge in chitosan molecules interacts with the negative charge in the microbial cell membrane, inhibiting bacterial metabolism and ultimately leading to bacterial death. Therefore, the hybrid aerogel layer in this invention has a certain antibacterial effect, which helps to solve the risk of bacterial growth in the post-activated carbon of current reverse osmosis water purifiers. Therefore, the household reverse osmosis composite membrane made based on the hybrid aerogel layer in this invention is safer for drinking water than traditional polyamide reverse osmosis composite membranes.

[0026] (3) In step S1 of this invention, the activated carbon particles from the fruit shell are introduced into the aerogel layer chemically cross-linked with chitosan and β-cyclodextrin through a blending method. The activated carbon particles from the fruit shell are firmly encapsulated in a three-dimensional porous network structure, avoiding the risk of leakage. After water passes through the polyamide functional layer, it then passes through the activated carbon from the fruit shell, thereby further improving the taste and directly reducing the amount of post-activated carbon used in the water purifier, which is beneficial for reducing design space and cost.

[0027] In addition to the objectives, features, and advantages described above, the present invention has other objectives, features, and advantages. The invention will now be described in further detail with reference to the figures. Attached Figure Description

[0028] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0029] Figure 1 This is a schematic diagram of the structure of a household reverse osmosis composite membrane in Embodiment 1 of the present invention;

[0030] Among them, 1. Hybrid aerogel layer, 1.1. Fruit shell activated carbon particles, 2. Polyamide functional layer. Detailed Implementation

[0031] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention are within the scope of protection of the present invention.

[0032] Example 1:

[0033] See Figure 1 A method for preparing a household reverse osmosis composite membrane, comprising:

[0034] Step S1: Preparation of hybrid hydrogel layer

[0035] Chitosan acetate solution and β-cyclodextrin aqueous solution of the required mass concentration were stirred and mixed; crosslinking agent of the required mass concentration was added; 1.1g of fruit shell activated carbon particles of the required mass were added, and after stirring and mixing, the mixture was placed in a 60℃ water bath for 2 hours to obtain a hybrid hydrogel layer; the crosslinking agent was glutaraldehyde.

[0036] Step S2: Preparation of hybrid aerogel layer 1

[0037] The hybrid hydrogel layer prepared in step S1 was immersed in pure water and washed until neutral; the washed hybrid hydrogel layer was placed in an ultra-low temperature freezer and pre-frozen at -65℃ to -80℃ for 24 hours; the pre-frozen hybrid hydrogel layer was placed in a freeze dryer and freeze-dried for 24 hours at a temperature of -80℃ to obtain hybrid aerogel layer 1.

[0038] Step S3: Prepare polyamide functional layer 2

[0039] The hybrid aerogel layer 1 was immersed in an aqueous amine solution for 1 min; the hybrid aerogel layer 1 was then immersed in an acyl chloride solution in an organic phase and reacted for 15 s before being removed to obtain a polyamide functional layer 2, i.e., a composite layer, which was grown on the hybrid aerogel layer 1; the composite layer was then dried to obtain a household reverse osmosis composite membrane.

[0040] In step S1, the chitosan acetate solution has a mass concentration of 3 wt%; the β-cyclodextrin aqueous solution has a mass concentration of 8 wt%; and the crosslinking agent has a mass concentration of 1 wt%.

[0041] In step S1, the mass ratio of chitosan acetate solution, β-cyclodextrin aqueous solution, crosslinking agent and coconut shell activated carbon particles 1.1 is 50:50:1:5.

[0042] In step S1, the activated carbon granules 1.1 (commercially available products) include activated carbon made from coconut shells.

[0043] In step S1, the size of the fruit shell activated carbon particles 1.1 is 0.5-2mm, and their function is to further adsorb impurities and odors, thereby improving the taste.

[0044] In step S1, the chitosan acetate solution is prepared by dissolving chitosan in an acetic acid solution (the mass fraction of the acetic acid solution is 2 wt%).

[0045] In step S3, the amine solution is a m-phenylenediamine solution, wherein the mass concentration of m-phenylenediamine is 3 wt%.

[0046] In step S3, the acyl chloride solution is a trimesoyl chloride solution, wherein the mass concentration of trimesoyl chloride is 0.1 wt%, and the solution used is n-hexane.

[0047] Example 2:

[0048] Unlike Example 1, the β-cyclodextrin aqueous solution has a mass concentration of 5 wt%.

[0049] Example 3:

[0050] Unlike Example 1, the β-cyclodextrin aqueous solution has a mass concentration of 10 wt%.

[0051] Example 4:

[0052] Unlike Example 1, the chitosan acetate solution has a mass concentration of 1 wt%.

[0053] Example 5:

[0054] Unlike Example 1, the chitosan acetate solution has a mass concentration of 5 wt%.

[0055] Comparative Example 1:

[0056] Unlike Example 1, the β-cyclodextrin aqueous solution has a mass concentration of 12 wt%.

[0057] Comparative Example 2:

[0058] Unlike Example 1, the β-cyclodextrin aqueous solution has a mass concentration of 4 wt%.

[0059] Comparative Example 3:

[0060] Unlike Example 1, the chitosan acetate solution has a mass concentration of 0.5 wt%.

[0061] Comparative Example 4:

[0062] Unlike Example 1, the chitosan acetate solution has a mass concentration of 5.5 wt%.

[0063] Comparative Example 5:

[0064] Unlike Example 1, the crosslinking agent is epichlorohydrin.

[0065] Comparative Example 6:

[0066] A household reverse osmosis composite membrane was prepared using a conventional preparation method. The specific preparation method is as follows:

[0067] Step 1: Prepare a polysulfone solution with a mass concentration of 18wt%, filter to remove undissolved impurities, degas and then uniformly coat the polysulfone solution onto a commercial nonwoven fabric. Then place the aerogel layer coated with the polysulfone solution in a 15℃ pure water coagulation bath to undergo phase inversion to form an ultrafiltration layer.

[0068] Step 2: Pour an aqueous solution (specifically, a 3 wt% m-phenylenediamine aqueous solution) onto the surface of the ultrafiltration layer in Step 1. After 1 minute, remove excess water droplets from the surface and then pour in an organic solution (specifically, a 0.1 wt% trimesoyl chloride n-hexane organic solvent). After reacting for 15 seconds, place the membrane in a 60°C oven and dry for 1 minute to obtain a household reverse osmosis composite membrane.

[0069] Diaphragm performance testing:

[0070] According to the test conditions for household membranes in GB / T 32373-2015, the household reverse osmosis composite membranes prepared in Examples 1-5 and Comparative Examples 1-6 (eight membranes of each type were selected for testing) were placed on a cross-flow membrane test platform. The tests were conducted under the following conditions: operating pressure 0.41±0.02MPa, sodium chloride aqueous solution concentration in feed water 250±5mg / L, test temperature 25±0.5℃, surface flow rate ≥0.45m / s, and pH 7-8. The water flux (J) and desalination rate (R) of the polyamide reverse osmosis membrane were calculated according to formulas a and b, respectively. The test results are shown in Table 1.

[0071] Calculation formula a:

[0072] Water flux (J) refers to the volume (V) of water passing through a unit membrane area (S) per unit time (t) under certain operating conditions. The unit of water flux (J) is L·m. -2 ·h -1 V is the permeate volume (in L); S is the effective surface area of ​​the polyamide reverse osmosis membrane (in m²). 2 ); t is the permeation time (in hours).

[0073] Calculation formula b:

[0074] Where R represents the solute removal rate of the reverse osmosis membrane, i.e., the desalination rate (%), and C p C f These represent the total dissolved solids content of the test solution and the total dissolved solids content of the permeate, respectively, in milligrams per liter (mg / L).

[0075] The household reverse osmosis composite membranes prepared in Examples 1-5 and Comparative Examples 1-6 were subjected to hygiene and safety (antimony content) immersion tests:

[0076] Take 500cm 2 The reverse osmosis composite membrane was immersed in 1L of pure water and left to soak at room temperature for 24 hours. The antimony content in the soaking water and the original pure water was tested, and the increase in antimony was calculated. The test results are shown in Table 2.

[0077] The household reverse osmosis composite membranes prepared in Examples 1-5 and Comparative Examples 1-6 were subjected to antibacterial tests:

[0078] Antimicrobial performance was tested using Staphylococcus aureus as the test microorganism. Antimicrobial performance was tested according to GB / T20944.3 on the commercial nonwoven fabric in Comparative Example 6, and the hybrid aerogels in Examples 1-5. The antimicrobial rate was calculated as follows: (Viable bacterial concentration of the blank control group after contact with colonies and incubation for 18 hours - Viable bacterial concentration of the nonwoven fabric or aerogel after contact with colonies and incubation for 18 hours) / Viable bacterial concentration of the blank control group after contact with colonies and incubation for 18 hours × 100%. The blank control group refers to the nonwoven fabric sample without any antimicrobial agent. The test results are shown in Table 3.

[0079] Table 1 shows the performance test results of the reverse osmosis composite membranes prepared in Comparative Examples 1-6 and Examples 1-5 of this invention.

[0080]

[0081]

[0082] As shown in Table 1, compared with Comparative Examples 1-6, the present invention, by using appropriate amounts of chitosan acetate solution, β-cyclodextrin aqueous solution and glutaraldehyde in Examples 1-5, can prepare household reverse osmosis composite membranes with higher water flux and desalination rate.

[0083] In Comparative Examples 1 and 4, while using excessively high amounts of β-cyclodextrin aqueous solution and chitosan acetate solution could produce household reverse osmosis composite membranes with high desalination rates, the water flux decreased. This indicates that using excessively high amounts of β-cyclodextrin aqueous solution and chitosan acetate solution increases the total solids content, reduces the pore size of the prepared aerogel layer, and relatively decreases the porosity, thus leading to a decrease in water flux.

[0084] In Comparative Examples 2 and 3, although household reverse osmosis composite membranes with high water flux could be prepared using excessively low amounts of β-cyclodextrin aqueous solution and chitosan acetate solution, the desalination rate decreased. This indicates that using excessively low amounts of β-cyclodextrin aqueous solution and chitosan acetate solution leads to a decrease in total solids content, resulting in a relatively larger pore size of the prepared hybrid aerogel. During pressure operation, the polyamide layer may collapse or peel off, leading to damage and thus a decrease in desalination rate.

[0085] In Comparative Example 5, the desalination rate of the household reverse osmosis composite membrane prepared using epichlorohydrin as a crosslinking agent decreased. This indicates that the aerogel layer formed by using epichlorohydrin has a relatively large pore size, and the polyamide functional layer formed on its surface is prone to collapse defects during pressure operation, resulting in a sharp decrease in the desalination rate.

[0086] In Comparative Example 6, the household reverse osmosis composite membrane prepared using conventional methods exhibited a low water flux. This indicates that the use of a polysulfone layer during water separation tends to increase water mass transfer resistance and reduce water flux; simultaneously, the thicker polyamide layer formed on the polysulfone layer also tends to increase water mass transfer resistance and reduce water flux.

[0087] Table 2 shows the immersion results of the reverse osmosis composite membranes prepared in Comparative Examples 1-6 and Examples 1-5 of this invention.

[0088] Experimental Case Increase in antimony (μg / L) Comparative Example 6 0.42 Comparative Example 5 Not detected Comparative Example 4 Not detected Comparative Example 3 Not detected Comparative Example 2 Not detected Comparative Example 1 Not detected Example 1 Not detected Example 2 Not detected Example 3 Not detected Example 4 Not detected Example 5 Not detected

[0089] Antimony content is a crucial testing indicator for water purifier manufacturers. Table 2 shows that in Comparative Example 6, the antimony increase in the reverse osmosis composite membrane prepared using traditional commercial nonwoven fabric was 0.42 μg / L (the hygiene standard is ≤0.5 μg / L). While this meets hygiene requirements, there is still a risk of exceeding the standard when using a larger membrane area to form a high-flow-rate reverse osmosis filter cartridge. This is mainly because antimony-containing compounds are used as catalysts in the preparation of nonwoven fabric. In contrast, the reverse osmosis composite membranes prepared in Examples 1-5 of this invention using appropriate amounts of chitosan acetate solution, β-cyclodextrin aqueous solution, and glutaraldehyde did not show any detectable antimony, thus better meeting the needs of household water purifiers.

[0090] Table 3 shows the antibacterial properties of the reverse osmosis composite membranes prepared in Comparative Examples 1-6 and Examples 1-5 of this invention.

[0091]

[0092]

[0093] As shown in Table 3, the commercially available nonwoven fabric used in the household reverse osmosis composite membrane prepared in Comparative Example 6 showed virtually no antibacterial activity against Staphylococcus aureus. In contrast, the household reverse osmosis composite membranes prepared in Examples 1-5 of this invention all exhibited an antibacterial activity against Staphylococcus aureus exceeding 87% due to the use of a hybrid aerogel layer. This is primarily because the hybrid aerogel layer contains chitosan. Chitosan inhibits cell wall formation in cells undergoing division or newly formed cells, and disrupts the cell membrane at the site of division, causing cell membrane rupture, cytoplasmic leakage, and ultimately cell death. Simultaneously, for mature cells, chitosan, through its positively charged protonated amino groups, interacts with the Staphylococcus aureus cell wall, inhibiting cell metabolism and ultimately leading to cell death.

[0094] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a household reverse osmosis composite membrane, characterized in that, include: Step S1: Preparation of hybrid hydrogel layer A chitosan acetate solution and a β-cyclodextrin aqueous solution of the desired mass concentration are stirred and mixed. A crosslinking agent of the desired mass concentration is added. Activated carbon granules from fruit shells of the desired mass are added. After stirring and mixing, the mixture is placed in a water bath at 55-65℃ and reacted for 1-3 hours to obtain a hybrid hydrogel layer. The crosslinking agent is glutaraldehyde. The mass concentration of the chitosan acetate solution is 1wt%-5wt%; the mass concentration of the β-cyclodextrin aqueous solution is 5wt%-10wt%; and the mass concentration of the crosslinking agent is 0.5-1.5wt%. Step S2: Preparation of hybrid aerogel layer The hybrid hydrogel layer prepared in step S1 is immersed in pure water and washed until neutral; the washed hybrid hydrogel layer is pre-frozen for 12-48 hours; the pre-frozen hybrid hydrogel layer is freeze-dried for 24-48 hours to obtain a hybrid aerogel layer. Step S3: Prepare the polyamide functional layer The hybrid aerogel layer is immersed in an aqueous amine solution for 30-90 seconds; the hybrid aerogel layer is then immersed in an acyl chloride solution in an organic phase, and after reacting for 15-30 seconds, it is removed to obtain a polyamide functional layer, i.e., a composite layer, that grows on the hybrid aerogel layer; the composite layer is then dried to obtain a household reverse osmosis composite membrane.

2. The method for preparing the household reverse osmosis composite membrane according to claim 1, characterized in that, In step S1, the mass ratio of chitosan acetate solution, β-cyclodextrin aqueous solution, crosslinking agent and coconut shell activated carbon particles is 50:50:1:

5.

3. The method for preparing the household reverse osmosis composite membrane according to claim 1, characterized in that, In step S1, the activated carbon granules from the fruit shells include activated carbon made from coconut shells or walnut shells.

4. The method for preparing a household reverse osmosis composite membrane according to claim 1, characterized in that, In step S1, the size of the fruit shell activated carbon particles is 0.5-2 mm.

5. The method for preparing a household reverse osmosis composite membrane according to claim 1, characterized in that, In step S1, the chitosan acetate solution is prepared by dissolving chitosan in an acetic acid solution.

6. The method for preparing a household reverse osmosis composite membrane according to claim 1, characterized in that, In step S3, the concentration of the amine solution is 2.8wt%-3.6wt%, and it includes at least one of m-phenylenediamine solution, o-phenylenediamine solution and p-phenylenediamine solution.

7. The method for preparing a household reverse osmosis composite membrane according to claim 1, characterized in that, In step S3, the concentration of the acyl chloride solution is 0.08wt%-0.12wt%, and it includes at least one of trimesoyl chloride solution, isophthaloyl chloride solution, and terephthaloyl chloride solution.

8. A household reverse osmosis composite membrane, characterized in that, The membrane was prepared using the method described in any one of claims 1-7 for preparing a household reverse osmosis composite membrane.

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