Loose nanofiltration membrane for dye / salt mixed wastewater treatment and preparation method and application thereof

Abstract

This invention discloses a loose nanofiltration membrane for treating dye / salt mixed wastewater, its preparation method, and its application, belonging to the field of water treatment membrane technology. This invention uses diphosgene or triphosgene as a linear crosslinking agent to prepare a high-performance loose nanofiltration membrane by crosslinking some inexpensive biopolymers with three-dimensional dendritic structures. This linear crosslinking method and the three-dimensional dendritic structure of the polymer help reduce the density of the nanofiltration membrane and improve the permeability of inorganic salts, thereby achieving efficient separation of dyes and salts. The reduction in density also contributes to the improvement of nanofiltration membrane permeability. Furthermore, these biomolecules are rich in hydroxyl and amino groups, which endow the membrane material with good hydrophilicity, which is beneficial to improving the water permeability of the nanofiltration membrane. The preparation process of this invention is simple, the raw materials are readily available and low in cost, and the resulting loose nanofiltration membrane has a good effect on the separation of dye / salt mixed wastewater. This preparation method has promising prospects for large-scale application.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of water treatment membranes, and particularly relates to a loose nanofiltration membrane for treating dye / salt mixed wastewater and a preparation method and application thereof. BACKGROUND

[0002] The information disclosed in this Background section is for the purpose of generally presenting the context of the application. The information disclosed in this Background section is not to be necessarily taken as an acknowledgement or any form of suggestion that this information forms part of the prior art already known to a person skilled in the art.

[0003] The printing and dyeing process in the printing and dyeing industry consumes a large amount of water and also produces a large amount of printing and dyeing wastewater composed of dyes (Congo red, acid fuchsin, etc.) and inorganic salts (sodium chloride, sodium sulfate, etc.). Direct discharge of the wastewater will have a serious adverse impact on human health and the ecological environment, so it is necessary to pretreat the wastewater before discharge. Compared with traditional printing and dyeing wastewater treatment methods (oxidation method, adsorption method, etc.), nanofiltration technology has the advantages of high treatment efficiency, low cost, and small energy consumption. A loose nanofiltration membrane can separate and recover dyes and salts in the wastewater, realize resource recycling and reduce resource waste, and at the same time purify the water quality. The loose nanofiltration membrane can selectively permeate inorganic salts while retaining dyes, thereby realizing efficient separation of dyes and salts, purifying the printing and dyeing wastewater, and recycling resources with reuse value in the wastewater, which has a broad application prospect in the treatment of printing and dyeing wastewater and is of great significance for saving resources and reducing carbon emissions. Therefore, exploring and developing a high-performance loose nanofiltration membrane for application in the treatment of printing and dyeing wastewater to improve the treatment efficiency has attracted widespread interest in the nanofiltration membrane industry and the printing and dyeing industry.

[0004] However, current commercial nanofiltration membranes are mainly based on polyamide materials, and the structure is relatively dense (MWCO < 500 Da). Such nanofiltration membranes are usually obtained by interfacial polymerization of organic amines and trimesoyl chloride. Since the crosslinking process is two-dimensional crosslinking, the structure of the nanofiltration membrane prepared using this crosslinking agent will be too dense to effectively separate salts and dyes, and it is mainly used for separating divalent and multivalent salt ions in aqueous solutions. The research on loose nanofiltration membranes for the purpose of dye and salt separation is still in its infancy, and there are problems such as high raw material cost, complex preparation process, and separation effect that still cannot meet the actual application requirements. These problems restrict the widespread application of loose nanofiltration membranes in the treatment of printing and dyeing wastewater, and it is urgent to develop a nanofiltration membrane preparation method with low cost, high permeability, and high separation selectivity. SUMMARY

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a loose nanofiltration membrane for treating dye / salt mixed wastewater, its preparation method, and its application. The present invention uses hydrophilic polymers with three-dimensional dendritic structures, which are green and inexpensive in nature, as raw materials. By selecting a suitable crosslinking agent, and through crosslinking between the active functional groups of the polymer, a loose nanofiltration membrane with high separation selectivity and high permeability is obtained, thereby improving membrane preparation efficiency, saving preparation time, reducing raw material costs, and optimizing the preparation process.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] A first aspect of the present invention provides a method for preparing a loose nanofiltration membrane for treating dye / salt mixed wastewater, comprising the following steps:

[0008] (1) Immerse the surface of the ultrafiltration membrane in an aqueous solution containing a hydrophilic polymer compound with a three-dimensional structure, let it stand for 3-30 minutes, then remove the ultrafiltration membrane and rinse the surface with water;

[0009] (2) Let the sample obtained in step (1) stand at room temperature for 5-20 minutes to remove the liquid residue on the membrane surface;

[0010] (3) Immerse the sample surface obtained in step (2) in a hydrophobic organic solvent containing a crosslinking agent to carry out a crosslinking reaction. After the reaction lasts for 0.5-10 minutes, rinse the sample surface with the hydrophobic organic solvent.

[0011] (4) The sample obtained in step (3) is thermally crosslinked at 45℃-80℃ for 5-20 minutes, and then soaked in water for storage to obtain the sample.

[0012] The crosslinking agent is at least one of bisphosgene (chemical name: trichloromethyl chloroformate, chemical formula: C2Cl4O2) and triphosgene (chemical name: bis(trichloromethyl) carbonate, chemical formula: C3Cl6O3).

[0013] This invention uses naturally occurring, inexpensive hydrophilic polymers with a three-dimensional dendritic structure as raw materials. By selecting appropriate crosslinking agents and then crosslinking between the active functional groups of the polymers, a loose nanofiltration membrane with high separation selectivity and high permeability for dye / salt wastewater is obtained, thereby improving membrane preparation efficiency, saving preparation time, reducing raw material costs, and optimizing the preparation process.

[0014] In some embodiments of the present invention, the hydrophilic polymer compound with a three-dimensional structure is at least one selected from alkaline lignin, ammonium lignin, quaternized lignin, tannic acid, and chitosan (chitosan molecular weight is 30kDa-50kDa). These polymer compounds have abundant amino or hydroxyl groups, which can impart good hydrophobicity to the membrane material, thus improving the water permeability of the porous nanofiltration membrane.

[0015] In some embodiments of the present invention, the ultrafiltration membrane is a polysulfone ultrafiltration membrane, a polyethersulfone ultrafiltration membrane, or a polyacrylonitrile ultrafiltration membrane with a molecular weight cutoff of 50 kDa-200 kDa. Ultrafiltration membranes are generally prepared by phase inversion methods and mostly have an asymmetric structure composed of a dense surface layer and a loose sublayer. The present invention involves linear crosslinking of a hydrophilic polymer material with a three-dimensional dendritic structure on a dense surface layer.

[0016] In some embodiments of the present invention, the mass percentage concentration of the aqueous solution containing the hydrophilic polymer compound with a three-dimensional structure is 0.5-5 wt%.

[0017] In some embodiments of the present invention, in step (1), the rinsing time is 30-180 seconds.

[0018] In some embodiments of the present invention, the crosslinking agent has a mass percentage concentration of 0.03-1 wt% in a hydrophobic organic solvent.

[0019] This invention achieves high permeability of loose nanofiltration membranes to inorganic salts and excellent retention of organic dyes by using specific concentrations of aqueous solutions containing hydrophilic polymers with three-dimensional structures and crosslinking agents. This avoids the problem of membrane flux reduction caused by increased membrane thickness and density due to excessively high solution concentration, while also avoiding defects in loose nanofiltration membranes caused by excessively low solution concentration, which makes it difficult to effectively retain target components.

[0020] In some embodiments of the present invention, the hydrophobic organic solvent is at least one selected from n-hexane, cyclohexane, n-heptane, isoheptane, n-octane, isooctane, and Isopar G.

[0021] In some embodiments of the present invention, in step (3), the rinsing time is 10-30 seconds.

[0022] In a second aspect, the present invention provides a loose nanofiltration membrane for treating dye / salt wastewater, which is prepared by the above-described preparation method.

[0023] The loose nanofiltration membrane provided by this invention is obtained by crosslinking some inexpensive, three-dimensional dendritic bio-hydrophilic polymers with diphosgene or triphosgene as linear crosslinking agents. This reduces the density of the nanofiltration membrane and increases the permeability of inorganic salts, thereby achieving efficient separation of dyes and salts. The loose nanofiltration membrane of this invention exhibits excellent selectivity and permeability for dye / salt separation. Therefore, a third aspect of this invention provides the application of the above-mentioned loose nanofiltration membrane in the treatment of dye / salt mixed wastewater.

[0024] In some embodiments of the present invention, the salt comprises sodium chloride and the dye comprises Congo red.

[0025] The beneficial effects of this invention are as follows:

[0026] This invention discloses a method for preparing a loose nanofiltration membrane for treating dye / salt mixed wastewater. The method uses diphosgene or triphosgene as a linear crosslinking agent to crosslink inexpensive biopolymers with three-dimensional dendritic structures, thereby preparing a high-performance loose nanofiltration membrane. This linear crosslinking method and the three-dimensional dendritic structure of the polymers help reduce the density of the nanofiltration membrane and improve the permeability of inorganic salts, thus achieving efficient separation of dyes and salts. The reduced density also contributes to improved permeability of the nanofiltration membrane. Furthermore, these biomolecules are rich in hydroxyl and amino groups, which endow the membrane material with good hydrophilicity, further enhancing the water permeability of the nanofiltration membrane.

[0027] The method for preparing a loose nanofiltration membrane for treating dye / salt mixed wastewater disclosed in this invention has low raw material costs, which significantly reduces the preparation cost of the loose nanofiltration membrane. The preparation process does not require special equipment and is easy to promote and scale up.

[0028] The loose nanofiltration membrane disclosed in this invention for treating dye / salt mixed wastewater exhibits excellent selectivity and permeability for the separation of dyes and salts. Specifically, the nanofiltration membrane prepared from quaternized lignin achieves a selectivity of 59.3 for Congo red / NaCl mixed wastewater, with a pure water permeability of 40 L / m³. 2 h bar.

[0029] In summary, the preparation process of this invention is simple, the raw materials are readily available and the cost is low, and the resulting loose nanofiltration membrane has a good effect on the separation of dye / salt mixed wastewater. This preparation method has the prospect of large-scale application. Detailed Implementation

[0030] The present invention aims to provide a method for preparing a high-performance porous nanofiltration membrane.

[0031] As introduced in the background section, the technical challenge of preparing high-performance loose nanofiltration membranes for treating dye / salt mixed wastewater lies in addressing the current issues with the preparation and separation performance of loose nanofiltration membranes. Furthermore, natural polymers such as lignin, tannic acid, and chitosan possess abundant reserves and low costs, along with rich hydrophilic amino and hydroxyl functional groups and three-dimensional dendritic structures. Developing these inexpensive raw materials into novel loose nanofiltration membrane materials, and simultaneously improving the selectivity and permeability of the nanofiltration membrane for dye / salt separation by optimizing its separation layer structure, is a key breakthrough in improving the separation performance of loose nanofiltration membranes. Therefore, this invention proposes a method for preparing a loose nanofiltration membrane for dye / salt wastewater treatment, the loose nanofiltration membrane prepared by this method, and its application in the field of dye / salt wastewater treatment.

[0032] A method for preparing a loose nanofiltration membrane for treating dye / salt mixed wastewater includes the following steps:

[0033] Prepare 0.5-5 wt% aqueous solutions containing a three-dimensional hydrophilic polymer and 0.03-1 wt% hydrophobic organic solutions containing a crosslinking agent. First, immerse the surface of the ultrafiltration membrane in the aqueous solution containing the three-dimensional hydrophilic polymer and let it stand for 3-30 minutes. Then, remove the ultrafiltration membrane and rinse its surface with water. Next, place the ultrafiltration membrane at room temperature (15℃-35℃) and let it stand for 5-20 minutes to remove any residual liquid. Then, immerse the surface of the ultrafiltration membrane in the hydrophobic organic solvent containing the crosslinking agent for a crosslinking reaction. After the reaction lasts for 0.5-10 minutes, rinse the membrane surface with the aforementioned hydrophobic organic solvent. Finally, place the obtained sample in an oven at 45℃-80℃ for thermal crosslinking for 5-20 minutes, then remove it and store it in water.

[0034] The crosslinking agent is at least one of diphosgene and triphosgene.

[0035] Preferably, the ultrafiltration membrane is a polysulfone ultrafiltration membrane, a polyethersulfone ultrafiltration membrane, or a polyacrylonitrile ultrafiltration membrane.

[0036] Preferably, the hydrophilic polymer compound with a three-dimensional structure is at least one of lignin, ammonified lignin, quaternized lignin, tannic acid, and chitosan (chitosan has a molecular weight of 30kDa-50kDa).

[0037] This invention provides a method for preparing a loose nanofiltration membrane for treating dye / salt mixed wastewater. This method involves structurally cross-linking a biopolymer rich in amino and hydroxyl groups using a cross-linking agent to form a cross-linked biopolymer separation layer on the surface of the ultrafiltration membrane, thereby obtaining a loose nanofiltration membrane with good selectivity and permeability for dye / salt separation. This invention features a simple preparation process, high operability, easily controllable process conditions, and ease of large-scale production.

[0038] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0039] Example 1

[0040] A method for preparing a loose nanofiltration membrane for treating dye / salt mixed wastewater includes the following steps:

[0041] Prepare 2 wt% quaternized lignin aqueous solution and 0.1 wt% triphosgene-hexane solution respectively; then immerse the surface of the polysulfone ultrafiltration membrane in the above quaternized lignin aqueous solution, let it stand for 5 minutes, then take out the polysulfone ultrafiltration membrane and rinse the surface with water for 60 seconds; then place the ultrafiltration membrane at room temperature (15℃) and let it stand for 10 minutes to remove the residual liquid on the surface; then immerse the surface of the ultrafiltration membrane in the triphosgene-containing hexane solution to carry out the crosslinking reaction, and after the reaction lasts for 2 minutes, rinse the membrane surface with hexane for 30 seconds; then place the obtained sample in a 60℃ oven for thermal crosslinking for 5 minutes, then take it out and soak it in water for storage.

[0042] Example 2

[0043] A method for preparing a loose nanofiltration membrane for treating dye / salt mixed wastewater includes the following steps:

[0044] Prepare 0.5 wt% alkaline lignin aqueous solution and 0.03 wt% diphosgene-heptane solution, respectively. Then, immerse the surface of the polyethersulfone ultrafiltration membrane in the above alkaline lignin aqueous solution, let it stand for 3 minutes, and then take out the ultrafiltration membrane and rinse the surface with water for 30 seconds. Then, place the polyethersulfone ultrafiltration membrane at room temperature (35°C) and let it stand for 5 minutes to remove the residual liquid on the surface. Then, immerse the surface of the ultrafiltration membrane in the diphosgene-heptane solution to carry out the crosslinking reaction. After the reaction lasts for 0.5 minutes, rinse the membrane surface with n-heptane for 10 seconds. Then, place the obtained sample in a 45°C oven for thermal crosslinking for 20 minutes, and then take it out and soak it in water for storage.

[0045] Example 3

[0046] A method for preparing a loose nanofiltration membrane for treating dye / salt mixed wastewater includes the following steps:

[0047] Prepare 5 wt% ammoniated lignin aqueous solution and 0.1 wt% triphosgene-n-octane solution respectively. Then, immerse the surface of the polyacrylonitrile ultrafiltration membrane in the above ammoniated lignin aqueous solution and let it stand for 30 minutes. After that, take out the ultrafiltration membrane and rinse the surface with water for 180 seconds. Then, place the polyacrylonitrile ultrafiltration membrane at room temperature (25°C) and let it stand for 20 minutes to remove the residual liquid on the surface. Then, immerse the surface of the ultrafiltration membrane in a triphosgene-containing n-octane solution to carry out the crosslinking reaction. After the reaction lasts for 10 minutes, rinse the membrane surface with n-octane for 30 seconds. Then, place the obtained sample in an 80°C oven for thermal crosslinking for 5 minutes, and then take it out and soak it in water for storage.

[0048] Example 4

[0049] A method for preparing a loose nanofiltration membrane for treating dye / salt mixed wastewater includes the following steps:

[0050] Prepare 2.5 wt% tannic acid aqueous solution and 1 wt% triphosgene isoheptane solution respectively; then immerse the surface of the polyacrylonitrile ultrafiltration membrane in the above tannic acid aqueous solution, let it stand for 15 minutes, then take out the ultrafiltration membrane and rinse the surface with water for 90 seconds; then place the polyacrylonitrile ultrafiltration membrane at room temperature (20℃) and let it stand for 10 minutes to remove the residual liquid on the surface; then immerse the surface of the ultrafiltration membrane in the triphosgene isoheptane solution to carry out the crosslinking reaction, and after the reaction lasts for 5 minutes, rinse the membrane surface with isoheptane for 15 seconds; then place the obtained sample in a 60℃ oven for thermal crosslinking for 10 minutes, then take it out and soak it in water for storage.

[0051] Example 5

[0052] A method for preparing a loose nanofiltration membrane for treating dye / salt mixed wastewater includes the following steps:

[0053] Prepare 2.5 wt% chitosan (molecular weight 30 kDa) aqueous solution and 1 wt% diphosgene cyclohexane solution respectively. Then, immerse the surface of the polysulfone ultrafiltration membrane in the above chitosan aqueous solution and let it stand for 15 minutes. After that, take out the ultrafiltration membrane and rinse the surface with water for 90 seconds. Then place the polysulfone ultrafiltration membrane at room temperature (20°C) and let it stand for 10 minutes to remove the residual liquid on the surface. Then, immerse the surface of the ultrafiltration membrane in the diphosgene cyclohexane solution to carry out the crosslinking reaction. After the reaction lasts for 5 minutes, rinse the membrane surface with cyclohexane for 15 seconds. Then, put the obtained sample into a 60°C oven for thermal crosslinking for 10 minutes, and then take it out and soak it in water for storage.

[0054] Comparative Example 1

[0055] A method for preparing a nanofiltration membrane includes the following steps:

[0056] Prepare 2 wt% aqueous solution of quaternized lignin and 0.1 wt% hexane solution of trimesoyl chloride. Immerse the surface of the polysulfone ultrafiltration membrane in the above aqueous solution of quaternized lignin and let it stand for 5 minutes. Then remove the polysulfone ultrafiltration membrane and rinse the surface with water for 60 seconds. Place the ultrafiltration membrane at room temperature (15°C) and let it stand for 10 minutes to remove the residual liquid on the surface. Then immerse the surface of the ultrafiltration membrane in hexane solution containing triphosgene for crosslinking reaction. After the reaction lasts for 2 minutes, rinse the membrane surface with hexane for 30 seconds. Place the obtained sample in a 60°C oven for thermal crosslinking for 5 minutes, then remove it and soak it in water for storage.

[0057] The separation performance of the loose nanofiltration membrane prepared in the above embodiments for the dye / salt mixture was tested in the following manner:

[0058] Cross-flow filtration was employed, using a dye / salt mixture of 1 g / L sodium chloride and 200 mg / L Congo red as the test solution. The separation performance of the resulting loose nanofiltration membrane was tested at 0.5 MPa. The test solution temperature was 25°C. After pre-pressurization at 0.5 MPa for 30 minutes, permeate was collected for 15 minutes. The desalination rate (Rb) of the nanofiltration membrane was calculated based on the conductivity values ​​of the permeate and influent. NaCl The dye removal rate (R0) of the nanofiltration membrane was calculated based on the absorbance values ​​of the permeate and influent water. 刚果红 The nanofiltration membrane selectivity (S) is calculated based on the desalination rate and dye removal rate. Under the same conditions, the test solution is changed to deionized water, and the permeability (F) of the nanofiltration membrane is calculated based on the volume of the permeate. The average value of three consecutive tests is taken as the final result.

[0059] Desalination rate R NaCl The calculation formula is as follows:

[0060]

[0061] Where C1 represents the conductivity of the test liquid and C2 represents the conductivity of the product water;

[0062] Dye removal rate R 刚果红 The calculation formula is as follows:

[0063]

[0064] Where A1 represents the absorbance of the test solution and A2 represents the absorbance of the product water;

[0065] The formula for calculating selectivity S is as follows:

[0066]

[0067] The formula for calculating permeability F is as follows:

[0068]

[0069] Where V represents the volume of permeate collected, A is the effective membrane area, t is the permeate collection time, and ΔP is the transmembrane pressure.

[0070] Table 1 shows the separation performance of the loose nanofiltration membranes prepared under the above conditions.

[0071]

[0072]

[0073] As shown in Table 1, the nanofiltration membrane prepared using the loose nanofiltration membrane preparation method proposed in this invention exhibits excellent retention performance for dye molecules and good permeability to inorganic salts, demonstrating excellent dye / salt selectivity. Furthermore, pure water permeation tests demonstrate that the membrane material prepared in this invention has excellent permeability. In contrast, comparative examples reveal that the nanofiltration membrane prepared using pyromellitic trichloroethylene chloride (PTH) has poor permeability to inorganic salts due to its excessively strong crosslinking properties. Moreover, due to its overly dense membrane structure, its permeability is significantly lower than that of nanofiltration membranes prepared using diphosgene or triphosgene as crosslinking agents.

[0074] 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 loose nanofiltration membrane for dye / salt mixed wastewater treatment, characterized by, The method comprises the following steps: (1) immersing the surface of the ultrafiltration membrane in a water solution containing a hydrophilic polymer compound with three-dimensional structure, and taking out the ultrafiltration membrane after standing for 3-30 minutes and rinsing the surface with water; (2) standing the sample obtained in step (1) at room temperature for 5-20 minutes to remove the residual liquid on the surface; (3) immersing the sample obtained in step (2) in a hydrophobic organic solvent containing a crosslinking agent to perform crosslinking reaction, and rinsing the surface of the sample with the hydrophobic organic solvent after the reaction lasts for 0.5-10 minutes; (4) heat crosslinking the sample obtained in step (3) at 45-80°C for 5-20 minutes, and then soaking in water for storage, thereby obtaining the product; The crosslinking agent is at least one of diphosgene and triphosgene. The hydrophilic polymer compound with three-dimensional structure is at least one of alkaline lignin, ammoniated lignin, quaternized lignin, tannic acid and chitosan.

2. The method for preparing a loose nanofiltration membrane for dye / salt mixed wastewater treatment according to claim 1, characterized by, The ultrafiltration membrane is a polysulfone ultrafiltration membrane, a polyethersulfone ultrafiltration membrane or a polyacrylonitrile ultrafiltration membrane.

3. The method for preparing a loose nanofiltration membrane for dye / salt mixed wastewater treatment according to claim 1, characterized by, The mass percentage concentration of the water solution containing the hydrophilic polymer compound with three-dimensional structure is 0.5-5 wt%.

4. The method for preparing a loose nanofiltration membrane for dye / salt mixed wastewater treatment according to claim 1, characterized by, In step (1), the rinsing time is 30-180 seconds.

5. The method for preparing a loose nanofiltration membrane for dye / salt mixed wastewater treatment according to claim 1, wherein the polyamide is prepared by the reaction of 1,3-benzenediamine with trimesoyl chloride. The mass percentage concentration of the crosslinking agent in the hydrophobic organic solvent is 0.03-1 wt%.

6. The method for preparing a loose nanofiltration membrane for dye / salt mixed wastewater treatment according to claim 1, wherein the polyamide is prepared by the reaction of 1,3-benzenediamine with trimesoyl chloride. The hydrophobic organic solvent is at least one of n-hexane, cyclohexane, n-heptane, isoheptane, n-octane, iso-octane and Isopar G.

7. The method for preparing a loose nanofiltration membrane for dye / salt mixed wastewater treatment according to claim 1, wherein the polyamide compound is represented by the following formula 1. In step (3), the rinsing time is 10-30 seconds.

8. A loose nanofiltration membrane for dye / salt mixed wastewater treatment, characterized by, The method is prepared by using the method for preparing a loose nanofiltration membrane for dye / salt mixed wastewater treatment according to any one of claims 1-7.

9. The use of the loose nanofiltration membrane for salt dye wastewater treatment according to claim 8 in the treatment of dye / salt mixed wastewater.

10. Use according to claim 9, wherein The salt comprises sodium chloride, and the dye comprises Congo red.

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