Preparation method and application of loose nanofiltration membrane based on in-situ self-polymerization of furfuryl alcohol

Abstract

The application discloses a preparation method and application of a loose nanofiltration membrane based on in-situ self-polymerization of furfuryl alcohol, relates to the technical field of printing and dyeing wastewater treatment, and is characterized in that the loose nanofiltration membrane based on in-situ self-polymerization of furfuryl alcohol is made of the following components in proportion by weight: a surfactant sodium dodecyl sulfate (SDS), a porogen polyethylene glycol-10000 (PEG-10000), a wetting agent isopropyl alcohol (IPA), a solvent ultrapure water, a prepolymer furfuryl alcohol (FA) and a catalyst concentrated sulfuric acid. The preparation method of the loose nanofiltration membrane based on in-situ self-polymerization of furfuryl alcohol comprises the following steps: step one, mixing of component solutions; step two, preparation of a prepolymer solution; step three, immersion and adsorption of the prepolymer; and step four, heating and polymerization. The preparation method and application of the loose nanofiltration membrane based on in-situ self-polymerization of furfuryl alcohol can be used for selective separation of organic salts and inorganic dyes in wastewater, improves water quality, realizes recycling of waste resources, and promotes the development of green membrane separation technology.

Description

Technical Field

[0001] This invention relates to the field of dyeing and printing wastewater treatment technology, specifically to a method for preparing and applying a loose nanofiltration membrane based on furfuryl alcohol in situ self-polymerization. Background Technology

[0002] Under the multiple pressures of global population growth and environmental pollution, water scarcity has become a major bottleneck restricting socio-economic development. Dyes are widely used in the textile, cosmetics, and printing industries, and the wastewater generated during their production and application has become a significant contributor to industrial pollution. It must be emphasized that dye-based pollutants often possess significant toxicity, carcinogenicity, and potential mutagenicity, posing a serious threat to environmental safety and human health. Furthermore, large amounts of inorganic salts (approximately 6 wt% NaCl and 5.6 wt% Na₂SO₄) are frequently added as auxiliary or promoting components during the dyeing process. The discharge of these high-salt dyeing and printing wastewaters into the environment will cause permanent negative impacts on ecosystems, severely hindering sustainable environmental development. Separating and reusing organic dyes and inorganic salts from dyeing and printing wastewater can not only solve the pollution problem but, more importantly, achieve sustainable resource utilization. Traditional processes such as chemical oxidation, physical adsorption, and biodegradation have achieved good results in treating high-salt dyeing and printing wastewater, but they are difficult to effectively remove harmful substances such as color and COD (chemical oxygen demand), and are often accompanied by high costs and energy consumption, easily causing secondary pollution. To more effectively recover and recycle dyes and salts while addressing pollution issues, it is necessary to modify and upgrade treatment processes. Developing high-salt dyeing and printing wastewater treatment technologies that align with sustainable development principles, achieving efficient and precise salt / dye separation and resource reuse, is a current challenge.

[0003] In recent years, nanofiltration technology, as an emerging and cost-effective technology for separating small molecules, organic matter, and multivalent ions, has shown broad application prospects in wastewater treatment and water purification. Nanofiltration separation technology possesses natural advantages such as environmental friendliness, energy efficiency, and high separation efficiency, and has proven to be a practical and competitive option for treating high-salinity textile industrial wastewater. The Donner effect and particle size distribution are the main mechanisms by which nanofiltration membranes achieve wastewater separation and purification. Unfortunately, commercially available polyamide nanofiltration membranes typically have a dense selective layer, resulting in high retention rates of inorganic salts (>30%) and low dye / salt selectivity when treating high-salinity wastewater, making it difficult to effectively separate organic matter and inorganic salts, severely hindering the potential recovery of valuable solutes. Furthermore, severe trade-offs cause membrane failure when treating complex wastewaters, thus limiting their effectiveness in treating dye wastewater. Therefore, developing nanofiltration membrane materials with high flux and ideal selectivity is key to promoting technological innovation in textile dyeing and printing wastewater treatment.

[0004] Loose nanofiltration technology provides a reliable platform for the separation and reuse of high-salinity organic wastewater. The term "loose nanofiltration" first appeared in literature in 2001, where "loose" simply referred to its porous morphology. Subsequent research has focused primarily on its selective separation of organic dyes and inorganic salts. Separating molecules or ions with different properties requires membranes with precise and tunable pore structures. The concept of loose nanofiltration lies precisely in creating a new process that selectively transfers water molecules and small molecule solutes while blocking large molecules or ions. In fact, compared to dense polyamide and other traditional nanofiltration membranes, the relatively loose nanofiltration active layer accelerates salt permeation and water flux. Simultaneously, in loose nanofiltration systems, the "sieving effect" and "Donnan effect" have a significant repulsive effect on dyes, making the separation of salts and dyes easier. Furthermore, the loose microstructure gives the membrane higher permeation flux and better antifouling capabilities, making it more adaptable and efficient in treating complex wastewater. Regarding industrial application prospects, improving membrane permeability and selectivity remains key to reducing investment and operating costs.

[0005] Furfuryl alcohol (FA) is a renewable biomass material extracted from sugarcane bagasse, corn cobs, rice husks, and wood. Due to its environmental friendliness, abundant resources, good thermal stability, and good chemical inertness, furfuryl alcohol-based biomaterials are increasingly being applied in various environmental engineering projects. The furfuryl alcohol molecule contains a furan ring and a reactive hydroxymethyl functional group, and under acidic or alkaline conditions, it can self-condense to form polyfurfuryl alcohol (PFA) with a three-dimensional network structure. Previous studies have shown that carbon molecular sieve membranes prepared with furfuryl alcohol exhibit great potential in gas separation due to their excellent stability, selectivity, and heat resistance. As a green material with abundant chemical activity and good film-forming properties, furfuryl alcohol provides a framework for constructing inexpensive, high-efficiency, and highly stable loose active layers. Therefore, we propose a method for preparing and applying a loose nanofiltration membrane based on in-situ self-polymerization of furfuryl alcohol. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the existing defects and provide a preparation method and application of furfuryl alcohol-based in-situ self-polymerized loose nanofiltration membrane. This method can selectively separate organic salts and inorganic dyes in wastewater, improve water quality while reducing the environmental burden, promote the development of green membrane separation technology, and effectively solve the problems in the background technology.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a loose nanofiltration membrane based on furfuryl alcohol in situ self-polymerization, which is made of the following components in the indicated weight ratios: 0.75wt% sodium dodecyl sulfate, 2.0wt% polyethylene glycol-10000, 20.0wt% isopropanol, 72.25wt%-74.75wt% ultrapure water, 0.5-3.0wt% furfuryl alcohol, and 2.0wt% concentrated sulfuric acid.

[0008] Preferably, it is made from the following components in parts by weight: 0.75 wt% sodium dodecyl sulfate, 2.0 wt% polyethylene glycol-10000, 20.0 wt% isopropanol, 74.75 wt% ultrapure water, 0.5 wt% furfuryl alcohol and 2.0 wt% concentrated sulfuric acid.

[0009] Preferably, it is made from the following components in parts by weight: 0.75 wt% sodium dodecyl sulfate, 2.0 wt% polyethylene glycol-10000, 20.0 wt% isopropanol, 74.25 wt% ultrapure water, 1.0 wt% furfuryl alcohol and 2.0 wt% concentrated sulfuric acid.

[0010] Preferably, it is made from the following components in parts by weight: 0.75 wt% sodium dodecyl sulfate, 2.0 wt% polyethylene glycol-10000, 20.0 wt% isopropanol, 73.75 wt% ultrapure water, 1.5 wt% furfuryl alcohol and 2.0 wt% concentrated sulfuric acid.

[0011] Preferably, it is made from the following components in parts by weight: 0.75 wt% sodium dodecyl sulfate, 2.0 wt% polyethylene glycol-10000, 20.0 wt% isopropanol, 73.25 wt% ultrapure water, 2.0 wt% furfuryl alcohol and 2.0 wt% concentrated sulfuric acid.

[0012] Preferably, it is made from the following components in parts by weight: 0.75 wt% sodium dodecyl sulfate, 2.0 wt% polyethylene glycol-10000, 20.0 wt% isopropanol, 72.75 wt% ultrapure water, 2.5 wt% furfuryl alcohol and 2.0 wt% concentrated sulfuric acid.

[0013] Preferably, it is made from the following components in parts by weight: 0.75 wt% sodium dodecyl sulfate, 2.0 wt% polyethylene glycol-10000, 20.0 wt% isopropanol, 72.25 wt% ultrapure water, 3.0 wt% furfuryl alcohol and 2.0 wt% concentrated sulfuric acid.

[0014] A method for preparing a loose nanofiltration membrane based on furfuryl alcohol in situ self-polymerization includes the following steps:

[0015] Step 1: Weigh out sodium dodecyl sulfate, polyethylene glycol-10000, polyethylene glycol and water and add them to a reagent bottle. Use an ultrasonic disperser to completely dissolve each component to obtain a homogeneous solution.

[0016] Step 2: Add 0.5-3.0 wt% furfuryl alcohol to the solution described in Step 1, shake thoroughly to mix evenly, then add 2.0 wt% concentrated sulfuric acid as a catalyst, shake thoroughly again, and the resulting light brown mixed solution is the furfuryl alcohol prepolymerization solution.

[0017] Step 3: Fix the active layer of the PES ultrafiltration membrane upward in a specially made polytetrafluoroethylene frame, pour in the prepolymer solution described in Step 2, soak for 5 minutes, pour it out, and use a clean paper towel to absorb the excess prepolymer solution on the membrane surface.

[0018] Step 4: Transfer the PES substrate soaked in the prepolymerization solution in Step 3 to an oven at 130°C for in-situ self-polymerization for 15 minutes. Based on the mass percentage of furfuryl alcohol in the prepolymerization solution, name the prepared membrane PES / PFA-x (x = 0.5-3.0).

[0019] An application based on furfuryl alcohol in-situ self-polymerized loose nanofiltration membrane: selective separation and resource utilization of organic salts and inorganic dyes in high-salt dyeing and printing wastewater based on furfuryl alcohol in-situ self-polymerized loose nanofiltration membrane.

[0020] Compared with existing technologies, the preparation method and application of furfuryl alcohol-based in-situ self-polymerized loose nanofiltration membranes have the following advantages:

[0021] 1. A polyfurfuryl alcohol loose nanofiltration membrane was constructed on a PES ultrafiltration membrane by sulfuric acid-catalyzed polymerization reaction between furfuryl alcohol molecules, so as to efficiently and selectively separate salts and dyes in dyeing and printing wastewater;

[0022] 2. Polyfurfuryl alcohol loose nanofiltration membrane can remove the color of dyes in printing and dyeing wastewater, making the effluent clearer, and effectively reduce chemical oxygen demand and biochemical oxygen demand to improve water quality;

[0023] 3. Filtration and separation of dyeing and printing wastewater using polyfurfuryl alcohol loose nanofiltration membrane can effectively reduce the discharge of harmful substances in the wastewater, thereby alleviating the environmental burden. Compared with traditional filtration methods, it can also improve the selectivity of the membrane for pollutants and reduce energy consumption, thus realizing resource recycling.

[0024] 4. By changing the concentration of furfuryl alcohol, the pore size and thickness of the polyfurfuryl alcohol active layer can be adjusted to ensure the feasibility and potential of polyfurfuryl alcohol loose nanofiltration membrane in the resource utilization of high-salt dyeing and printing wastewater, so as to promote the development of green membrane separation technology. Attached Figure Description

[0025] Figure 1 This is a schematic diagram illustrating the preparation of the polyfurfuryl alcohol loose nanofiltration membrane in Examples 1-6;

[0026] Figure 2 These are actual macroscopic optical photographs of the furfuryl alcohol prepolymer mixture prepared in Examples 1-6 and the PES / PFA film obtained therefrom;

[0027] Figure 3 The images show the surface SEM images, cross-sectional SEM images, AFM phase diagrams, and roughness of the PES base films used in Examples 1-6.

[0028] Figure 4 The images show the surface SEM image, cross-sectional SEM image, AFM phase diagram, and roughness of the PES / PFA-1.0 loose nanofiltration membrane obtained in Example 2.

[0029] Figure 5 The images show the surface SEM image, cross-sectional SEM image, AFM phase diagram, and roughness of the PES / PFA-2.0 loose nanofiltration membrane obtained in Example 4.

[0030] Figure 6 The images show the surface SEM image, cross-sectional SEM image, AFM phase diagram, and roughness of the PES / PFA-3.0 loose nanofiltration membrane obtained in Example 6.

[0031] Figure 7 This is a schematic diagram of the selective separation of salt / dye by the PES / PFA loose nanofiltration membranes obtained in Examples 1-6;

[0032] Figure 8 The results show the retention stability of the PES / PFA-2.0 loose nanofiltration membrane obtained in Example 4 for Congo red and methylene blue dyes. Detailed Implementation

[0033] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0034] Example 1: A loose nanofiltration membrane based on furfuryl alcohol in situ self-polymerization, made from the following components in parts by weight: 0.75wt% sodium dodecyl sulfate, 2.0wt% polyethylene glycol-10000, 20.0wt% isopropanol, 74.75wt% ultrapure water, 0.5wt% furfuryl alcohol and 2.0wt% concentrated sulfuric acid.

[0035] A method for preparing a loose nanofiltration membrane based on furfuryl alcohol in situ self-polymerization includes the following steps:

[0036] Step 1: Weigh out sodium dodecyl sulfate, polyethylene glycol-10000, polyethylene glycol and water and add them to a reagent bottle. Use an ultrasonic disperser to completely dissolve each component to obtain a homogeneous solution.

[0037] Step 2: Add 0.5 wt% furfuryl alcohol to the solution described in Step 1, shake thoroughly to mix evenly, then add 2.0 wt% concentrated sulfuric acid as a catalyst, shake thoroughly again, and the resulting light brown mixed solution is the furfuryl alcohol prepolymerization solution.

[0038] Step 3: Fix the active layer of the PES ultrafiltration membrane upward in a specially made polytetrafluoroethylene frame, pour in the prepolymer solution described in Step 2, soak for 5 minutes, pour it out, and use a clean paper towel to absorb the excess prepolymer solution on the membrane surface.

[0039] Step 4: Transfer the PES substrate soaked in the prepolymerization solution in Step 3 to an oven at 130°C for in-situ self-polymerization for 15 minutes. After self-polymerization, thoroughly clean the target membrane with ultrapure water to remove residual prepolymerization solution. Based on the mass percentage of furfuryl alcohol in the prepolymerization solution, name the prepared membrane PES / PFA-0.5.

[0040] Example 2: A loose nanofiltration membrane based on furfuryl alcohol in situ self-polymerization, made from the following components in parts by weight: 0.75wt% sodium dodecyl sulfate, 2.0wt% polyethylene glycol-10000, 20.0wt% isopropanol, 74.25wt% ultrapure water, 1.0wt% furfuryl alcohol and 2.0wt% concentrated sulfuric acid.

[0041] A method for preparing a loose nanofiltration membrane based on furfuryl alcohol in situ self-polymerization includes the following steps:

[0042] Step 1: Weigh out sodium dodecyl sulfate, polyethylene glycol-10000, polyethylene glycol and water and add them to a reagent bottle. Use an ultrasonic disperser to completely dissolve each component to obtain a homogeneous solution.

[0043] Step 2: Add 1.0 wt% furfuryl alcohol to the solution described in Step 1, shake thoroughly to mix evenly, then add 2.0 wt% concentrated sulfuric acid as a catalyst, shake thoroughly again, and the resulting light brown mixed solution is the furfuryl alcohol prepolymerization solution.

[0044] Step 3: Fix the active layer of the PES ultrafiltration membrane upward in a specially made polytetrafluoroethylene frame, pour in the prepolymer solution described in Step 2, soak for 5 minutes, pour it out, and use a clean paper towel to absorb the excess prepolymer solution on the membrane surface.

[0045] Step 4: Transfer the PES substrate soaked in the prepolymerization solution in Step 3 to an oven at 130°C for in-situ self-polymerization for 15 minutes. After self-polymerization, thoroughly clean the target membrane with ultrapure water to remove residual prepolymerization solution. Based on the mass percentage of furfuryl alcohol in the prepolymerization solution, name the prepared membrane PES / PFA-1.0.

[0046] Example 3: A loose nanofiltration membrane based on furfuryl alcohol in situ self-polymerization, made from the following components in parts by weight: 0.75wt% sodium dodecyl sulfate, 2.0wt% polyethylene glycol-10000, 20.0wt% isopropanol, 73.75wt% ultrapure water, 1.5wt% furfuryl alcohol and 2.0wt% concentrated sulfuric acid.

[0047] A method for preparing a loose nanofiltration membrane based on furfuryl alcohol in situ self-polymerization includes the following steps:

[0048] Step 1: Weigh out sodium dodecyl sulfate, polyethylene glycol-10000, polyethylene glycol and water and add them to a reagent bottle. Use an ultrasonic disperser to completely dissolve each component to obtain a homogeneous solution.

[0049] Step 2: Add 1.5 wt% furfuryl alcohol to the solution described in Step 1, shake thoroughly to mix evenly, then add 2.0 wt% concentrated sulfuric acid as a catalyst, shake thoroughly again, and the resulting light brown mixed solution is the furfuryl alcohol prepolymerization solution.

[0050] Step 3: Fix the active layer of the PES ultrafiltration membrane upward in a specially made polytetrafluoroethylene frame, pour in the prepolymer solution described in Step 2, soak for 5 minutes, pour it out, and use a clean paper towel to absorb the excess prepolymer solution on the membrane surface.

[0051] Step 4: Transfer the PES substrate soaked in the prepolymerization solution in Step 3 to an oven at 130°C for in-situ self-polymerization for 15 minutes. After self-polymerization, thoroughly clean the target membrane with ultrapure water to remove residual prepolymerization solution. Based on the mass percentage of furfuryl alcohol in the prepolymerization solution, name the prepared membrane PES / PFA-1.5.

[0052] Example 4: A loose nanofiltration membrane based on furfuryl alcohol in situ self-polymerization, made from the following components in parts by weight: 0.75 wt% sodium dodecyl sulfate, 2.0 wt% polyethylene glycol-10000, 20.0 wt% isopropanol, 73.25 wt% ultrapure water, 2.0 wt% furfuryl alcohol and 2.0 wt% concentrated sulfuric acid.

[0053] A method for preparing a loose nanofiltration membrane based on furfuryl alcohol in situ self-polymerization includes the following steps:

[0054] Step 1: Weigh out sodium dodecyl sulfate, polyethylene glycol-10000, polyethylene glycol and water and add them to a reagent bottle. Use an ultrasonic disperser to completely dissolve each component to obtain a homogeneous solution.

[0055] Step 2: Add 2 wt% furfuryl alcohol to the solution described in Step 1, shake thoroughly to mix evenly, then add 2.0 wt% concentrated sulfuric acid as a catalyst, shake thoroughly again, and the resulting light brown mixed solution is the furfuryl alcohol prepolymerization solution.

[0056] Step 3: Fix the active layer of the PES ultrafiltration membrane upward in a specially made polytetrafluoroethylene frame, pour in the prepolymer solution described in Step 2, soak for 5 minutes, pour it out, and use a clean paper towel to absorb the excess prepolymer solution on the membrane surface.

[0057] Step 4: Transfer the PES substrate soaked in the prepolymerization solution in Step 3 to an oven at 130°C for in-situ self-polymerization for 15 minutes. After self-polymerization, thoroughly clean the target membrane with ultrapure water to remove residual prepolymerization solution. Based on the mass percentage of furfuryl alcohol in the prepolymerization solution, name the prepared membrane PES / PFA-2.0.

[0058] Example 5: A loose nanofiltration membrane based on furfuryl alcohol in situ self-polymerization, made from the following components in parts by weight: 0.75 wt% sodium dodecyl sulfate, 2.0 wt% polyethylene glycol-10000, 20.0 wt% isopropanol, 72.75 wt% ultrapure water, 2.5 wt% furfuryl alcohol and 2.0 wt% concentrated sulfuric acid.

[0059] A method for preparing a loose nanofiltration membrane based on furfuryl alcohol in situ self-polymerization includes the following steps:

[0060] Step 1: Weigh out sodium dodecyl sulfate, polyethylene glycol-10000, polyethylene glycol and water and add them to a reagent bottle. Use an ultrasonic disperser to completely dissolve each component to obtain a homogeneous solution.

[0061] Step 2: Add 2.5 wt% furfuryl alcohol to the solution described in Step 1, shake thoroughly to mix evenly, then add 2.0 wt% concentrated sulfuric acid as a catalyst, shake thoroughly again, and the resulting light brown mixed solution is the furfuryl alcohol prepolymerization solution.

[0062] Step 3: Fix the active layer of the PES ultrafiltration membrane upward in a specially made polytetrafluoroethylene frame, pour in the prepolymer solution described in Step 2, soak for 5 minutes, pour it out, and use a clean paper towel to absorb the excess prepolymer solution on the membrane surface.

[0063] Step 4: Transfer the PES substrate soaked in the prepolymerization solution in Step 3 to an oven at 130°C for in-situ self-polymerization for 15 minutes. After self-polymerization, thoroughly clean the target membrane with ultrapure water to remove residual prepolymerization solution. Based on the mass percentage of furfuryl alcohol in the prepolymerization solution, name the prepared membrane PES / PFA-2.5.

[0064] Example 6: A loose nanofiltration membrane based on furfuryl alcohol in situ self-polymerization, made from the following components in parts by weight: 0.75 wt% sodium dodecyl sulfate, 2.0 wt% polyethylene glycol-10000, 20.0 wt% isopropanol, 72.25 wt% ultrapure water, 3.0 wt% furfuryl alcohol and 2.0 wt% concentrated sulfuric acid.

[0065] A method for preparing a loose nanofiltration membrane based on furfuryl alcohol in situ self-polymerization includes the following steps:

[0066] Step 1: Weigh out sodium dodecyl sulfate, polyethylene glycol-10000, polyethylene glycol and water and add them to a reagent bottle. Use an ultrasonic disperser to completely dissolve each component to obtain a homogeneous solution.

[0067] Step 2: Add 3.0 wt% furfuryl alcohol to the solution described in Step 1, shake thoroughly to mix evenly, then add 2.0 wt% concentrated sulfuric acid as a catalyst, shake thoroughly again, and the resulting light brown mixed solution is the furfuryl alcohol prepolymerization solution.

[0068] Step 3: Fix the active layer of the PES ultrafiltration membrane upward in a specially made polytetrafluoroethylene frame, pour in the prepolymer solution described in Step 2, soak for 5 minutes, pour it out, and use a clean paper towel to absorb the excess prepolymer solution on the membrane surface.

[0069] Step 4: Transfer the PES substrate soaked in the prepolymerization solution in Step 3 to an oven at 130°C for in-situ self-polymerization for 15 minutes. After self-polymerization, thoroughly clean the target membrane with ultrapure water to remove residual prepolymerization solution. Based on the mass percentage of furfuryl alcohol in the prepolymerization solution, name the prepared membrane PES / PFA-3.0.

[0070] Macroscopic optical photographs of polyfurfuryl alcohol membranes obtained by in-situ polymerization of different concentrations of furfuryl alcohol on the bottom of a PES ultrafiltration membrane in Examples 1-6 are shown below. Figure 2 As shown in the figure, under the catalysis of acid, the color of the prepolymer solution gradually deepened with the increase of furfuryl alcohol concentration, and the brown color of the resulting polyfurfuryl alcohol film also gradually deepened. These results demonstrate that the reaction of high-concentration furfuryl alcohol on the substrate is more intense and complete, indicating to some extent that the formed PFA layer is more dense. The morphology characterization (SEM+AFM) of the base film and the polyfurfuryl alcohol films prepared in Examples 2, 4, and 6 are shown in the figure. Figure 3 , Figure 4 , Figure 5 and Figure 6 As shown, from Figure 3 As can be seen, the PES substrate surface is smooth and the pores are uniform (roughness Ra is about 4.45 nm). After the polyfurfuryl alcohol layer is grown in situ under acid catalysis, the surface morphology of the bottom of the PES ultrafiltration membrane changes significantly. The polyfurfuryl alcohol membranes prepared in Examples 2, 4 and 6 exhibit horizontally dispersed nanoscale nodular structures on the PES surface, similar to the entangled network of a sponge, proving that the polyfurfuryl alcohol active layer was successfully generated. In addition, as the furfuryl alcohol content increases, the nodular structure gradually becomes larger, but the roughness decreases slightly.

[0071] The pore size of the polyfurfuryl alcohol nanofiltration membranes prepared in Examples 2, 4, and 6 was analyzed, and the results are shown in Table 1. The data in Table 1 show that as the concentration of furfuryl alcohol increases, the molecular weight cutoff and average pore size of the prepared polyfurfuryl alcohol nanofiltration membrane decrease, but overall remain within the pore size range of nanofiltration membranes. The pore size and molecular weight cutoff results tested in Examples 2, 4, and 6 indicate that the pore size cutoff of the membrane can be optimized by controlling the concentration of the target precursor furfuryl alcohol.

[0072] Table 1

[0073] Group Average pore size (nm) Molecular weight cutoff (Da) Example 2 0.452 1967.35 Example 4 0.347 1681.82 Example 6 0.201 1293.80

[0074] Applications of furfuryl alcohol-based in-situ self-polymerized loose nanofiltration membranes in the selective separation and resource utilization of organic salts and inorganic dyes in high-salt dyeing and printing wastewater:

[0075] Application Example 1: Pure Water Flux Test

[0076] The polyfurfuryl alcohol nanofiltration membranes (PES / PFA-X) and the base membrane prepared in Examples 1-6 above were used to conduct pure water flux tests. The operating steps are as follows:

[0077] (1) Cut the prepared polyfurfuryl alcohol nanofiltration membrane into membrane sheets of appropriate size and place them in the filtration equipment;

[0078] (2) The pure water flux of the polyfurfuryl alcohol nanofiltration membrane was determined at a test pressure of 2.0 bar;

[0079] (3) The pure water flux of the PES base membrane and the PES / PFA membrane prepared in Examples 1-6 was collected by an online acquisition system to obtain the test results.

[0080] The experimental results are shown in Table 1:

[0081] Table 1

[0082]

[0083] The flux of the PES ultrafiltration membrane is 668.98 L / m³. -2 h -1 bar -1 In Examples 1-6, the membrane flux generally decreased with increasing concentration of furfuryl alcohol in situ self-polymerization on the surface. When the furfuryl alcohol concentration increased from 0.5 wt% to 3.0 wt%, the water flux increased from 156.02 L / m³. -2 h -1 bar -1 Attenuation to 65.36 L m -2 h -1 bar -1As the concentration of furfuryl alcohol increases, the intermolecular reactions between furfuryl alcohol molecules become more complete and intense, resulting in a denser polyfurfuryl alcohol network. Increased membrane thickness and decreased pore size significantly increase the membrane's mass transfer resistance, leading to reduced water permeability.

[0084] Application Example 2: Single Salt or Dye Retention Test

[0085] The polyfurfuryl alcohol nanofiltration membranes prepared in Examples 1-6 above were used for single salt or dye rejection tests, and the operating steps are as follows:

[0086] (1) Cut the prepared polyfurfuryl alcohol nanofiltration membrane into membrane sheets of appropriate size and place them in the filtration equipment;

[0087] (2) The retention capacity of polyfurfuryl alcohol nanofiltration membrane for several single dyes or salts was determined at a pressure of 2.0 bar.

[0088] (3) Multiple experiments were conducted to test the stability of the membrane.

[0089] The organic dyes used in step (2) of Application Example 2 are Acid Orange, Acid Violet, Congo Red and Methylene Blue (all at a concentration of 200 ppm), and the inorganic salts are Sodium Sulfate, Magnesium Sulfate, Sodium Chloride and Magnesium Chloride (all at a concentration of 2000 ppm).

[0090] The experimental results are shown in Table 2:

[0091] Table 2

[0092]

[0093] The retention performance of the polyfurfuryl alcohol (PFA) membranes prepared in Examples 1-6 was studied using single dye solutions (Acid Orange, Acid Violet, Congo Red, and Methylene Blue) and single salt solutions (Sodium Chloride, Magnesium Chloride, Sodium Sulfate, and Magnesium Sulfate), respectively. Table 2 shows the retention rates of the FPA nanofiltration membranes for single dyes or salt solutions. The results show that when the FPA concentration increases from 0.5 wt% to 3.0 wt%, the removal rate of single dyes by the membrane is significantly improved, approaching complete removal. Particle size sieving and the Donan effect determine the membrane's retention performance. Higher FPA concentrations result in a thicker selective layer, higher cross-linking degree, and smaller pores, leading to a higher dye retention rate while reducing permeability. Furthermore, the increased electronegativity due to increased FPA concentration also contributes to improved dye removal rates. The retention results for single salts showed that when the furfuryl alcohol concentration increased from 0.5 wt% to 3.0 wt%, the retention rate of all membranes for single salts was less than 21%, indicating that the prepared series of polyfurfuryl alcohol membranes have a significantly loose structure, which has significant advantages for the desalination and resource recovery of high-salinity wastewater. The retention performance trends of Examples 1-6 for single dyes or salts are as follows:

[0094] Application Example 2-1: At a pressure of 2.0 bar, the polyfurfuryl alcohol (PFA) membrane prepared in Examples 1-6 was used to test the retention of 200 ppm of Acid Orange. The results showed that when the FPA concentration changed from 0.5 wt% → 1.0 wt% → 1.5 wt% → 2.0 wt% → 2.5 wt% → 3.0 wt%, the retention trend of the prepared FPA membrane for Acid Orange was: 69.55% → 89.06% → 91.46% → 94.70% → 96.93% → 98.05%.

[0095] Application Example 2-2: At a pressure of 2.0 bar, the polyfurfuryl alcohol membrane prepared in Examples 1-6 was used to test the retention of 200 ppm of Acid Violet. The results showed that when the furfuryl alcohol concentration changed from 0.5 wt% → 1.0 wt% → 1.5 wt% → 2.0 wt% → 2.5 wt% → 3.0 wt%, the retention trend of the prepared polyfurfuryl alcohol membrane for Acid Violet was: 70.22% → 81.22% → 83.54% → 87.15% → 91.55% → 95.38%.

[0096] Application Examples 2-3: Retention tests were conducted on 200 ppm of Congo red using the polyfurfuryl alcohol (PFOA) membranes prepared in Examples 1-6 at a pressure of 2.0 bar. The results showed that when the PFOA concentration changed from 0.5 wt% → 1.0 wt% → 1.5 wt% → 2.0 wt% → 2.5 wt% → 3.0 wt%, the retention trend of the prepared PFOA membrane for Congo red was: 90.86% → 97.60% → 98.07% → 99.33% → 99.13% → 99.49%.

[0097] Application Examples 2-4: Retention tests were conducted on 200 ppm of methylene blue using the polyfurfuryl alcohol (PFOA) membranes prepared in Examples 1-6 at a pressure of 2.0 bar. The results showed that as the PFOA concentration changed from 0.5 wt% → 1.0 wt% → 1.5 wt% → 2.0 wt% → 2.5 wt% → 3.0 wt%, the retention trend of the prepared PFOA membrane for methylene blue was: 83.14% → 95.72% → 96.00% → 97.58% → 97.87% → 98.93%.

[0098] Application Examples 2-5: The polyfurfuryl alcohol (PFA) membranes prepared in Examples 1-6 were used to test the retention of 2000 ppm sodium sulfate at a pressure of 2.0 bar. The results showed that when the FPA concentration changed from 0.5 wt% → 1.0 wt% → 1.5 wt% → 2.0 wt% → 2.5 wt% → 3.0 wt%, the retention trend of the prepared PPA membranes for sodium sulfate was: 6.06% → 8.86% → 12.25% → 13.72% → 16.18% → 20.38%.

[0099] Application Examples 2-6: The polyfurfuryl alcohol (PFA) membranes prepared in Examples 1-6 were used to test the retention of 2000 ppm magnesium sulfate at a pressure of 2.0 bar. The results showed that when the FPA concentration changed from 0.5 wt% → 1.0 wt% → 1.5 wt% → 2.0 wt% → 2.5 wt% → 3.0 wt%, the retention trend of the prepared PPA membrane for magnesium sulfate was: 3.21% → 3.58% → 3.87% → 4.47% → 8.90% → 15.11%.

[0100] Application Examples 2-7: The polyfurfuryl alcohol (PFA) membranes prepared in Examples 1-6 were used to test the retention of 2000 ppm sodium chloride at a pressure of 2.0 bar. The results showed that when the FPA concentration changed from 0.5 wt% → 1.0 wt% → 1.5 wt% → 2.0 wt% → 2.5 wt% → 3.0 wt%, the retention trend of the prepared PPA membrane for sodium chloride was: 2.47% → 3.02% → 3.39% → 3.58% → 7.04% → 7.07%.

[0101] Application Examples 2-8: Retention tests were conducted on 2000 ppm magnesium chloride using the polyfurfuryl alcohol (PFOA) membranes prepared in Examples 1-6 at a pressure of 2.0 bar. The results showed that as the PFOA concentration changed from 0.5 wt% → 1.0 wt% → 1.5 wt% → 2.0 wt% → 2.5 wt% → 3.0 wt%, the retention trend of the prepared PFOA membrane for magnesium chloride was: 1.73% → 1.79% → 2.78% → 2.47% → 4.28% → 6.937%.

[0102] Application Example 3: Selective Separation Test of Salt-Dye Composite System:

[0103] The PES / PFA nanofiltration membranes prepared in Examples 1-6 above were used to perform separation tests on the salt-dye composite system. The operation steps are as follows:

[0104] (1) Cut the prepared polyfurfuryl alcohol nanofiltration membrane into membrane sheets of appropriate size and place them in the filtration equipment;

[0105] (2) Prepare a salt-dye mixed solution (specifically, 200 ppm dye solution + 2000 ppm salt solution);

[0106] (3) The separation capability of polyfurfuryl alcohol nanofiltration membrane for dye-salt mixture was determined at a pressure of 2.0 bar;

[0107] (4) Conduct multiple experiments to test the stability of the membrane.

[0108] The organic dyes used in step (2) of Application Example 3 are one of Acid Orange, Congo Red and Methylene Blue; the inorganic salts are one of Sodium Sulfate and Sodium Chloride.

[0109] The experimental results are shown in Table 3:

[0110] Table 3

[0111]

[0112] The results of Application Example 3 show that when the series of polyfurfuryl alcohol (PFOA) membranes prepared in Examples 1-6 were used for filtration and separation of salt-dye mixtures, both monovalent and divalent ions could pass through the membranes well, while the dyes in the mixtures exhibited high retention. With increasing concentrations of added PFOA, the membrane's selectivity for separating salt and dye gradually increased. When the added PFOA was greater than 2.0 wt%, a high overall separation effect was achieved. Besides pore size sieving, the negative charge on the PFOA surface played a crucial role in selective separation. The trends in selective separation of the salt-dye composite system in Examples 1-6 are as follows:

[0113] Application Example 3-1: The polyfurfuryl alcohol (PFA) membrane prepared in Examples 1-6 was used to retain an acid orange / sodium sulfate mixture at a pressure of 2.0 bar. The results showed that as the FPA concentration changed from 0.5 wt% → 1.0 wt% → 1.5 wt% → 2.0 wt% → 2.5 wt% → 3.0 wt%, the selectivity factor of the prepared PPA membrane for the acid orange / sodium sulfate mixture changed as follows: 3.21 → 8.94 → 10.41 → 17.36 → 30.55 → 64.54.

[0114] Application Example 3-2: The acid orange-sodium chloride mixture was retained using the polyfurfuryl alcohol (PFOA) membrane prepared in Examples 1-6 at a pressure of 2.0 bar. The results showed that when the PFOA concentration changed from 0.5 wt% → 1.0 wt% → 1.5 wt% → 2.0 wt% → 2.5 wt% → 3.0 wt%, the selectivity factor of the prepared PFOA membrane for the acid orange-sodium chloride mixture changed as follows: 3.09 → 8.40 → 10.41 → 15.56 → 27.56 → 55.20.

[0115] Application Example 3-3: The polyfurfuryl alcohol (PFA) membrane prepared in Examples 1-6 was used to retain a Congo red-sodium sulfate mixture at a pressure of 2.0 bar. The results showed that as the FPA concentration changed from 0.5 wt% → 1.0 wt% → 1.5 wt% → 2.0 wt% → 2.5 wt% → 3.0 wt%, the selectivity factor of the prepared PPA membrane for the Congo red-sodium sulfate mixture changed as follows: 10.07 → 36.80 → 70.69 → 107.62 → 126.07 → 160.06.

[0116] Application Examples 3-4: The polyfurfuryl alcohol (PFA) membranes prepared in Examples 1-6 were used to retain the Congo red-sodium chloride mixture at a pressure of 2.0 bar. The results showed that when the FPA concentration changed from 0.5 wt% → 1.0 wt% → 1.5 wt% → 2.0 wt% → 2.5 wt% → 3.0 wt%, the selectivity factor of the FPA membrane for the Congo red-sodium chloride mixture changed as follows: 10.84 → 46.27 → 102.25 → 135.33 → 157.61 → 197.74.

[0117] Application Examples 3-5: The polyfurfuryl alcohol (PFA) membranes prepared in Examples 1-6 were used to retain a methylene blue-sodium sulfate mixture at a pressure of 2.0 bar. The results showed that when the FPA concentration changed from 0.5 wt% → 1.0 wt% → 1.5 wt% → 2.0 wt% → 2.5 wt% → 3.0 wt%, the selectivity factor of the prepared PPA membrane for the methylene blue-sodium sulfate mixture changed as follows: 5.11 → 21.44 → 23.23 → 42.95 → 63.08 → 80.92.

[0118] Application Examples 3-6: The polyfurfuryl alcohol (PFA) membranes prepared in Examples 1-6 were used to retain a methylene blue-sodium chloride mixture at a pressure of 2.0 bar. The results showed that as the FPA concentration changed from 0.5 wt% → 1.0 wt% → 1.5 wt% → 2.0 wt% → 2.5 wt% → 3.0 wt%, the selectivity factor of the prepared FPA membrane for the methylene blue-sodium chloride mixture changed as follows: 5.31 → 22.84 → 29.48 → 55.52 → 79.61 → 92.98.

[0119] Based on the selective separation performance and characteristics of the polyfurfuryl alcohol membrane for the salt-dye mixture system demonstrated in Application Example 3, a corresponding selective separation schematic diagram was drawn, see [link to diagram]. Figure 7 .

[0120] Application Example 4: Stability Test of the Best Implementation Example

[0121] The long-term stability of the optimal polyfurfuryl alcohol loose nanofiltration membrane (Example 4) was tested at a pressure of 2.0 bar.

[0122] In Application Example 4, the stability test results of the polyfurfuryl alcohol nanofiltration membrane prepared with 2.0 wt% furfuryl alcohol are shown in the figure. Figure 8Stability filtration tests were conducted using 200 ppm of methylene blue and Congo red as contaminants, respectively. After 12 hours of dye filtration, the pure water flux of the membrane prepared in Example 4 decreased slightly, while the fluxes of methylene blue and Congo red decreased by 10.71% and 5.69%, respectively. During this process, the membrane rejection rates of the dyes remained generally stable (approximately 98% and 99%, respectively). Overall, due to the membrane's loose structure and strong electronegativity, it exhibits excellent dye suppression. In long-term operation, both flux and rejection rates remained within acceptable fluctuation ranges.

[0123] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for preparing a loose nanofiltration membrane based on furfuryl alcohol in situ self-polymerization, characterized in that, Includes the following steps: Step 1: Mix 0.75wt% sodium dodecyl sulfate, 2.0wt% polyethylene glycol-10000, 20.0wt% isopropanol and 72.25wt%-74.75wt% ultrapure water, and use an ultrasonic disperser to completely dissolve each component to obtain a homogeneous solution; Step 2: Add 0.5-3.0 wt% furfuryl alcohol to the solution from Step 1, shake to mix, then add 2.0 wt% concentrated sulfuric acid as a catalyst, and shake again to obtain a furfuryl alcohol prepolymerization solution; Step 3: Fix the active layer of the PES ultrafiltration membrane upward in the polytetrafluoroethylene frame, pour in the prepolymer solution and soak for 5 minutes, then pour it out and remove the excess solution from the surface. Step 4: Heat the soaked PES substrate in a 130℃ oven for 15 minutes to perform in-situ self-polymerization. After self-polymerization, wash with ultrapure water to obtain a loose nanofiltration membrane named PES / PFA-x, where x = 0.5-3.

0.

2. The method for preparing a loose nanofiltration membrane based on furfuryl alcohol in situ self-polymerization according to claim 1, characterized in that: The amount of furfuryl alcohol added in step two is 2.0 wt%.

3. The method for preparing a loose nanofiltration membrane based on furfuryl alcohol in situ self-polymerization according to claim 1, characterized in that: The amount of furfuryl alcohol added in step two is 0.5 wt%.

4. The method for preparing a loose nanofiltration membrane based on furfuryl alcohol in situ self-polymerization according to claim 1, characterized in that: The amount of furfuryl alcohol added in step two is 1.0 wt%.

5. The method for preparing a loose nanofiltration membrane based on furfuryl alcohol in situ self-polymerization according to claim 1, characterized in that: The amount of furfuryl alcohol added in step two is 1.5 wt%.

6. The method for preparing a loose nanofiltration membrane based on furfuryl alcohol in situ self-polymerization according to claim 1, characterized in that: The amount of furfuryl alcohol added in step two is 2.5 wt%.

7. The method for preparing a loose nanofiltration membrane based on furfuryl alcohol in situ self-polymerization according to claim 1, characterized in that: The amount of furfuryl alcohol added in step two is 3.0 wt%.

8. The method for preparing a loose nanofiltration membrane based on furfuryl alcohol in situ self-polymerization according to claim 1, characterized in that: In step four, after the self-polymerization is completed, the target membrane is thoroughly cleaned with ultrapure water to remove any residual prepolymerization solution.

9. A loose nanofiltration membrane prepared by any one of claims 1-8 for the selective separation and resource utilization of organic salts and inorganic dyes in high-salt dyeing and printing wastewater.

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