Method for preparing electrospinning filter membrane using sludge and electrospinning filter membrane

Abstract

The present invention discloses a method for enhancing the efficiency of filtering particulate matter in the air by strengthening electrospinning membranes using sludge extract. The present invention uses nylon as the main spinning component, and incorporates sludge extract in the electrospinning process. The rich functional groups contained in the sludge extract can enhance the fiber's capture of polar particulate matter, which is a new type of high-value utilization of solid waste "sludge". Using sludge extract to manufacture mask filter membranes can not only meet the demand for masks, but also treat a large amount of accumulated residual sludge solid waste as a resource, and has the advantage of low production cost; at the same time, the fusion of nylon and sludge extract reduces the use of existing plastics and reduces the accumulation of global plastic waste. Therefore, compared with traditional filter membranes, the product of the present invention has high efficiency and low resistance, is made from solid waste, has low cost and achieves "waste treatment with waste", and is more easily degradable than ordinary plastic bags.

Description

Technical Field

[0001] The present invention relates to the field of electrostatic spinning filter membranes, and in particular to a method for preparing electrostatic spinning filter membranes by using sludge. Background Art

[0002] At present, air particulate matter has become one of the most deadly air pollutants affecting public health. It can damage the respiratory and cardiovascular systems and cause diseases such as asthma and bronchitis. Therefore, from the perspective of public environmental health, how to effectively remove particulate matter is an important and critical task. In recent years, research has mainly focused on fine particulate matter (PM 2.5 ) control.

[0003] Traditional particle filtration methods rely on air filtration devices to intercept indoor particulate matter, while also relying on filter membrane materials such as masks to capture outdoor particles. However, existing methods fail to meet filtration requirements. To achieve efficient filtration, the number or power of air filtration devices must be increased, which leads to increased operating costs. Alternatively, increasing the thickness of the filter membrane material to increase filtration efficiency can increase the pressure drop during filtration, resulting in increased air resistance and thicker materials.

[0004] Electrospinning is a technology that enables the simple manufacture of nanofibers for efficient particulate matter (PM) filtration with low pressure drop. Polymers are spun into fibrous membranes under the influence of a high-voltage electric field, enabling efficient air filtration. This technology features fine fibers (diameter: 50-1000nm) and a tunable pore structure. Currently, various polymers, such as PAN, PI, and nylon, have been used to produce electrospun fibers. Nylon, in particular, has gained increasing attention for its high mechanical strength, durability, and non-toxicity.

[0005] The material used for meltblown cloth in traditional masks is polypropylene, which has the disadvantage of being non-degradable. The masks discarded each year are equivalent to 4,680 to 6,240 tons of plastic waste, causing huge pressure on waste disposal.

[0006] The filtration mechanism includes passive capture (screening, inertial collision, interception, diffusion) and active capture (chemical and electrostatic effects).

[0007] Traditional electrospun filter membranes, made from a single polymer, rely primarily on passive capture for filtration. Their dense fibers provide good filtration for larger particles. However, submicron particles (100nm to 1.0μm) (which have a larger surface area and a higher content of potentially toxic hydrocarbons) are difficult to effectively filter through simple physical interception due to their small size. This allows them to easily enter indoor environments, directly impacting human health.

[0008] Sludge is the residual material discharged from municipal sewage treatment plants and is the solid sediment produced during the sewage treatment process. As a solid waste, sludge contains a large amount of recyclable proteins, lipids, and polysaccharides. These substances are rich in functional groups and active sites, but are often simply forgotten and discarded, resulting in a significant waste of resources. Summary of the Invention

[0009] The purpose of the present invention is to address the deficiencies in the prior art and to provide a method for preparing an electrospun filter membrane using sludge and an electrospun filter membrane that enhances the air purification efficiency of the filter membrane.

[0010] To solve the above technical problems, the technical method adopted by the present invention is as follows: The present invention discloses a method for preparing an electrospinning filter membrane using sludge, comprising the following steps:

[0011] S1. Place the freeze-dried sludge in a NaCl solution and add Na2CO3 to accelerate the reaction rate while ensuring a final Na2CO3 concentration of 0.5%;

[0012] S2. The sludge extract was obtained by centrifugation, and the supernatant was filtered through a membrane, purified by dialysis, concentrated, and freeze-dried;

[0013] S3. The sludge extract was added to formic acid and a cross-linking agent was added. After the three were fully dissolved, a sludge extract solution was prepared. After that, nylon was added to the system to prepare a nylon-sludge extract solution.

[0014] S4. The nylon / sludge extract electrospinning solution is transferred to a syringe via a syringe pump. A high potential is applied to the needle tip. Under the action of the electric field, the mixed solution is ejected to form a "jet" and stretched into nanofibers.

[0015] S5. Wrap the copper mesh around a drum-shaped collector to collect the nanofibers to obtain an electrospun filter membrane.

[0016] Furthermore, in step S1, the mass ratio of freeze-dried sludge to NaCl solution is 25:1, the extraction is performed at 80°C, and Na2CO3 is added to accelerate the reaction rate.

[0017] Furthermore, in step S2, the centrifuge speed is 4000 rpm, and the centrifugation time is 20 min; the supernatant is filtered using a 0.45 μm filter membrane.

[0018] Furthermore, in step S2, the supernatant is filtered through a filter membrane and then dialyzed for 24 hours to obtain a sludge extract solution; the sludge extract solution is concentrated at 50°C for 4 hours, and the obtained sludge extract is freeze-dried at -50°C for 48 hours.

[0019] Furthermore, in step S3, the mass ratio of the sludge extract to formic acid is 3:100, and the overall configuration is a 3 wt% sludge extract solution;

[0020] The mass ratio of nylon to formic acid was 1:5, and a 20 wt% nylon-3 wt% sludge extract solution was prepared.

[0021] Furthermore, in step S3, the cross-linking agent is isophorone diisocyanate, and the mass ratio of isophorone diisocyanate to formic acid is 1:20, so as to promote the cross-linking of macromolecules in the sludge extract and accelerate the dissolution of the sludge extract.

[0022] Furthermore, the flow rate of the injection pump is 0.1 ml / h, and the syringe is 10 ml.

[0023] Furthermore, a high potential of 20 kV was applied to the needle tip, the distance between the collector and the needle tip was 21 cm, and the pore size of the copper mesh used was 0.125 mm.

[0024] The present invention also discloses an electrospinning filter membrane prepared using sludge, which is prepared by any of the above methods for preparing an electrospinning filter membrane using sludge.

[0025] Beneficial effects:

[0026] 1. The primary drawback of current air filtration membranes is their low removal efficiency for submicron particles (100nm to 1.0μm). These particles, due to their larger surface area and potential for contact with air pollutants and bacteria, can enter indoor environments, impacting human health and indoor air quality. This drawback stems from the fact that traditional fibers can only remove large particles through direct interception, Brownian motion, and inertial collisions. However, submicron particles, due to their small diameter, require strong electrostatic forces for effective removal. The limited number of polar groups and active sites on the fibers renders them ineffective against submicron particles.

[0027] However, the addition of sludge extract significantly altered the number of polar groups and active sites on the fibers. Before the addition of sludge extract, the optimal filtration efficiency of the nylon fiber membrane for 0.3μm and 0.5μm filters was only 85.68% and 89.64% respectively. However, after the addition of sludge extract, the filtration efficiency of both filters increased, and this efficiency increased with increasing sludge concentration, reaching 94.74% and 95.12% at a sludge concentration of 3wt%. The contact angle of the fiber also increased from 131.7° to 27.9°, enhancing the membrane's hydrophilicity.

[0028] The addition of sludge extract strengthens the oxygen-containing and hydrophilic functional groups on the fiber, such as -COOH, COH, -NH2, etc. These functional groups will rub against the submicron particles during the filtration process, thereby generating charge-enhanced electrostatic effects and improving filtration efficiency.

[0029] In addition, the addition of sludge extract also strengthens the polymerization of the solution to a certain extent, increasing the diameter of the filter membrane fiber from the original 118.66nm to 200.59nm, which strengthens the direct interception and inertial collision effect. Compared with pure nylon fiber filter membrane, it has a better effect on PM 2.5 The filtration efficiency of the above particles has been further improved.

[0030] 2. The present invention uses nylon as the main spinning component and incorporates sludge extract during the electrospinning process. The rich functional groups contained in the sludge extract can enhance the fiber's capture of polar particles, which is a new high-value utilization of solid waste "sludge".

[0031] Using sludge extract to manufacture mask filters not only meets the demand for masks during the pandemic, but also recycles the large amount of accumulated residual sludge solid waste, and has the advantage of low production costs. Furthermore, by fusing nylon with sludge extract, the use of existing plastics can be reduced, thus reducing the accumulation of global plastic waste. Therefore, compared with traditional filter membranes, the product of the present invention has high efficiency and low resistance. It is made from solid waste, is low-cost, achieves "waste treatment with waste", and is biodegradable.

[0032] 3. The existing natural organic synthetic fiber filter membrane has the disadvantages of weak mechanical properties, low viscosity and inability to effectively form a membrane. The cross-linking agent and durable nylon are combined to ensure the stability of the sludge extract electrospun filter membrane. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a schematic diagram of the overall process of the method for preparing an electrospinning filter membrane using sludge in the present invention;

[0034] Figure 2 This is a state diagram of the electrospinning filter membrane before and after filtration in the present invention. DETAILED DESCRIPTION

[0035] The present invention will be described in further detail below with reference to the accompanying drawings and specific implementation methods.

[0036] Combine Figure 1 The present invention discloses a method for preparing an electrospinning filter membrane using sludge, comprising the following steps:

[0037] S1. Place freeze-dried sludge in a NaCl solution at a mass ratio of 25:1. Extraction was performed at 80°C. Na2CO3 was added to accelerate the reaction rate while ensuring a final concentration of 0.5% Na2CO3.

[0038] S2. Centrifuge the mixture at 4000 rpm for 20 min; filter the supernatant through a 0.45 μm filter membrane; remove the supernatant, filter the supernatant through the filter membrane, and dialyze for 24 h to obtain a sludge extract solution; concentrate the sludge extract solution at 50°C for 4 h, and freeze-dry the obtained sludge extract at -50°C for 48 h to obtain a sludge extract;

[0039] S3. The sludge extract was added to formic acid and a cross-linking agent was added, the mass ratio of the sludge extract to formic acid was 3:100; the cross-linking agent was isophorone diisocyanate, the mass ratio of which to formic acid was 1:20 to promote cross-linking of macromolecules in the sludge extract and accelerate the dissolution of the sludge extract; after the three were fully dissolved, the overall configuration was a 3wt% sludge extract solution;

[0040] Then, nylon was added to the system in a mass ratio of nylon to formic acid of 1:5, to prepare a 20wt% nylon-3wt% sludge extract solution;

[0041] S4. Transfer the nylon / sludge extract electrospinning solution to a syringe via a syringe pump with a flow rate of 0.1 ml / h and a syringe of 10 ml; apply a high potential of 20 kV to the needle tip, and set the distance between the collector and the needle tip to 21 cm. The copper mesh used is 0.125 mm thick; under the action of the electric field force, the mixed solution will be ejected to form a "jet" and stretched into nanofibers; S5. Wrap the copper mesh around a drum-shaped collector to collect the nanofibers to obtain an electrospinning filter membrane.

[0042] The electrospun filter membrane obtained by this method is subjected to a filter membrane efficiency test, comprising the following steps:

[0043] Step 1: Burning incense produces PM 2.5 The airflow fan was provided with a stable speed by a voltage controller. An electrospun nanofiber filter with a cross-sectional area of 6 cm × 6 cm was inserted in the middle of the setup.

[0044] Step 2: A manometer is used to measure the pressure drop. Two particle monitors are used to measure the PM mass concentration on both sides of the filter within one minute.

[0045] Step 3: Calculate the particle filtration efficiency using the following formula:

[0046]

[0047] Where P1 is the particle concentration before filtration (mg / m 3 ), P2 is the particle concentration after filtration. (mg / m 3 )

[0048] Step 4: In order to measure the relationship between filtration efficiency and pressure drop, a single indicator is used to determine the filtration properties of the membrane. The quality factor QF is introduced to measure it. The formula is:

[0049]

[0050] Where p is the filtration pressure drop (Pa) and η is the filtration efficiency (%).

[0051] Combine Figure 2 , you can clearly see the particles attached to the fiber filter membrane. When the sludge extract is added, the number of polar groups and active sites on the fiber is improved. Before the addition of sludge extract, the best filtration efficiency of the existing nylon fiber filter membrane for 0.3μm and 0.5μm was only 85.68% and 89.64%. After the addition of sludge extract, the filtration efficiency of the two increased and increased with the increase of sludge concentration. When the sludge concentration was 3wt%, the filtration efficiency reached 94.74% and 95.12%, and the contact angle of the fiber also changed from 131.7° to 27.9°, which improved the hydrophilicity of the filter membrane.

[0052] The addition of sludge extract strengthens the oxygen-containing and hydrophilic functional groups on the fiber, such as -COOH, COH, and -NH2. These functional groups will rub against each other with submicron particles during the filtration process, thereby generating charge-enhanced electrostatic effects, thereby improving filtration efficiency. In addition, the addition of sludge extract also strengthens the polymerization of the solution to a certain extent, increasing the diameter of the filter membrane fiber from the original 118.66nm to 200.59nm, which strengthens the direct interception and inertial collision effects. Compared with pure nylon fiber filter membrane, it has a better effect on PM2.5. 2.5 The filtration efficiency of the above particles has been further improved.

[0053] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the foregoing embodiments. The foregoing embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and modifications are intended to fall within the scope of the present invention. The scope of protection claimed in the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing an electrospinning filter membrane using sludge, characterized in that: The following steps are involved: Step S1. Place the freeze-dried sludge in a NaCl solution and add Na2CO3 to accelerate the reaction rate while ensuring that the final concentration of Na2CO3 is 0.5%; Step S2. The sludge extract is obtained by centrifuging the sludge and collecting the supernatant. The supernatant is filtered through a membrane, purified by dialysis, concentrated, and freeze-dried. Step S3. adding the sludge extract to formic acid and a cross-linking agent, and after the three are fully dissolved, preparing a sludge extract solution, and then adding nylon to the system to prepare a nylon-sludge extract solution; Step S4. The nylon / sludge extract electrospinning solution is transferred to a syringe. A high potential is applied to the needle tip. Under the action of the electric field, the mixed solution is ejected to form a "jet" and stretched into nanofibers. Step S5: Wrapping the copper mesh on a drum-shaped collector to collect the nanofibers to obtain an electrospun filter membrane.

2. The method for preparing an electrospinning filter membrane using sludge according to claim 1, characterized in that: In step S1, the mass ratio of freeze-dried sludge to NaCl solution is 25:1, extraction is performed at 80°C, and Na2CO3 is added to accelerate the reaction rate.

3. The method for preparing an electrospinning filter membrane using sludge according to claim 1, wherein: In step S2, the centrifuge speed is 4000 rpm, and the centrifugation time is 20 min; the supernatant is filtered using a 0.45 μm filter membrane.

4. The method for preparing an electrospinning filter membrane using sludge according to claim 1, wherein: In step S2, the supernatant is filtered through a filter membrane and then dialyzed for 24 hours to obtain a sludge extract solution; the sludge extract solution is concentrated at 50°C for 4 hours, and the obtained sludge extract is freeze-dried at -50°C for 48 hours.

5. The method for preparing an electrospinning filter membrane using sludge according to claim 1, wherein: In step S3, the mass ratio of the sludge extract to formic acid is 3:100, and the overall configuration is a 3 wt% sludge extract solution; The mass ratio of nylon to formic acid was 1:5, and a 20 wt% nylon-3 wt% sludge extract solution was prepared.

6. The method for preparing an electrospinning filter membrane using sludge according to claim 1, characterized in that: In step S3, the cross-linking agent is isophorone diisocyanate, and the mass ratio of isophorone diisocyanate to formic acid is 1:20, so as to promote the cross-linking of macromolecules in the sludge extract and accelerate the dissolution of the sludge extract.

7. The method for preparing an electrospinning filter membrane using sludge according to claim 1, wherein: The syringe is 10 ml and the injection flow rate is 0.1 ml / h.

8. The method for preparing an electrospinning filter membrane using sludge according to claim 1, wherein: A high potential of 20 kV was applied to the needle tip, the distance between the collector and the needle tip was 21 cm, and the pore size of the copper mesh used was 0.125 mm.

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