Secondary membrane for retarding membrane pollution of separation membrane as well as forming method and application of secondary membrane

Abstract

The invention provides a secondary membrane for retarding membrane pollution of a separation membrane as well as a forming method and application of the secondary membrane. The secondary membrane comprises a bridging stacking layer loaded on the surface of the separation membrane; and the porosity of the bridging stacking layer is 30-70%. The secondary membrane is formed by bridging and stacking particles on the surface of the separation membrane, so that direct blockage of fine particle pollution to membrane holes of the separation membrane can be effectively reduced, the service life of the separation membrane is prolonged, and the overall efficiency of a membrane separation system is improved; the problems of difficult effective control of membrane pollution, rapid reduction of separation membrane performance, high operation cost and the like in the prior art are solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of membrane separation, and particularly relates to a secondary membrane for mitigating membrane fouling of a separation membrane, a method for forming the same, and an application thereof. Background Art

[0002] As an efficient separation means, membrane separation technology has been widely applied in the fields of water treatment, food processing, pharmaceutical manufacturing, and industrial wastewater reuse. However, in practical applications, membrane fouling is one of the main obstacles restricting its wide application and long-term stable operation. Membrane fouling generally includes particulate fouling, organic fouling, biological fouling, and inorganic scaling. These fouling forms will significantly reduce the membrane permeation flux, separation efficiency, and service life, and increase the operation and maintenance costs.

[0003] Among various forms of membrane fouling, particulate fouling is a relatively common and difficult-to-fully-avoid problem. Pollutant particles accumulate on the membrane surface, and the formed fouling layer will increase the resistance of the membrane, resulting in a decrease in flux and an increase in energy consumption. In addition, particulate fouling often occurs concomitantly with other fouling forms. For example, the accumulation of particles may become a carrier for microbial growth, further exacerbating biological fouling. Therefore, how to effectively alleviate particulate fouling and control the occurrence of other fouling is a hot and difficult point in the current research on membrane separation technology.

[0004] To solve the membrane fouling problem, various countermeasures have been developed currently, such as membrane material modification, pretreatment process optimization, cleaning method improvement, and operation parameter adjustment. Although these methods have alleviated fouling to a certain extent, most of them have limitations, such as high cost, short-lasting effect, or complex operation. In addition, traditional methods usually focus on reducing the formation of fouling, but fail to effectively utilize the potential of the particulate fouling layer itself.

[0005] In recent years, researchers have gradually paid attention to the controllability of the fouling layer and its potential positive effect on membrane performance under certain conditions. For example, by reasonably controlling the particle accumulation process on the membrane surface, it is possible to form a "secondary membrane", which can protect the membrane surface, reduce direct fouling, and optimize the filtration effect under specific conditions. However, the current research on the regulation of particle accumulation behavior is still in its initial stage, and no mature engineering application method has been formed.

[0006] Therefore, developing an efficient method for forming a stable secondary membrane through particle bridging accumulation to mitigate membrane fouling has important theoretical significance and practical application value. This method can not only significantly reduce the direct blockage of membrane pores by fine particles, but also further improve the overall performance of the membrane separation system through the selective separation characteristics of the secondary membrane, thus providing a new solution for the development of membrane separation technology. Summary of the Invention

[0007] Aiming at the deficiencies of the existing technologies, the purpose of the present invention is to provide a secondary membrane for mitigating membrane fouling of a separation membrane, a formation method thereof, and an application thereof. The present invention forms a secondary membrane on the surface of the separation membrane by using bridging particles, which can effectively reduce the direct blockage of the membrane pores of the separation membrane by fine particle fouling, improve the service life of the separation membrane and the overall efficiency of the membrane separation system, and solve the problems in the existing technologies such as difficult effective control of membrane fouling, rapid decline in the performance of the separation membrane, and high operating costs.

[0008] To achieve the purpose of this invention, the following technical solutions are adopted:

[0009] In the first aspect, the present invention provides a secondary membrane for mitigating membrane fouling of a separation membrane, and the secondary membrane includes a bridging accumulation layer loaded on the surface of the separation membrane;

[0010] The porosity of the bridging accumulation layer is 30-70%, for example, it can be 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65% or 70%, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0011] In the present invention, the secondary membrane has a primary filtration function, can intercept pollution particles or colloidal substances, prevent fine particles from blocking the pores of the separation membrane, and increase the filtration operation time of the separation membrane; in addition, the secondary membrane can also reduce the fouling of other types to the separation membrane to a certain extent, such as organic fouling, biological fouling, etc.

[0012] In addition, the porosity of the bridging accumulation layer of the present invention is 30-70%. If the porosity is too low, it will cause a significant increase in the osmotic pressure during the membrane separation process, thereby affecting the operation efficiency of the reactor; if the porosity is too high, it will cause a decrease in the mechanical strength of the secondary membrane, making it difficult to form a stable structure, and may allow pollution particles to penetrate the secondary membrane and directly contact the separation membrane, reducing the filtration effect.

[0013] As a preferred technical solution of the present invention, the separation membrane includes any one of a hollow fiber membrane, a flat membrane or a tubular membrane.

[0014] Preferably, the material of the separation membrane includes any one of a metal membrane, a ceramic membrane, a composite membrane or an organic polymer membrane.

[0015] Preferably, the metal membrane includes a titanium metal microporous membrane or a stainless steel membrane.

[0016] Preferably, the ceramic membrane includes an alumina membrane or a zirconia membrane.

[0017] Preferably, the organic polymer membrane includes, for example, a polyvinylidene fluoride membrane or a polytetrafluoroethylene membrane.

[0018] Preferably, the composite membrane includes a metal-ceramic composite membrane or an organic-inorganic composite membrane.

[0019] In a second aspect, the present invention provides a method for forming a secondary membrane for mitigating membrane fouling of a separation membrane as provided in the first aspect, and the forming method includes the following steps:

[0020] (1) Mix water and bridging particles, and obtain a mixed solution after stirring;

[0021] (2) Perform membrane separation treatment on the mixed solution obtained in step (1) using a separation membrane to obtain the secondary membrane.

[0022] In the present invention, by performing membrane separation treatment on a mixed solution containing bridging particles using a separation membrane, and optimizing hydrodynamic parameters such as the flow rate, operating pressure, and shear force of the liquid during the membrane separation treatment, increasing the membrane osmotic pressure, and reducing the stirring speed to weaken the shear force received on the membrane surface, bridging particles are induced to form a secondary membrane on the surface of the separation membrane, thereby achieving an extension of the service life of the separation membrane.

[0023] As a preferred technical solution of the present invention, the bridging particles in step (1) include organic particles and / or inorganic particles.

[0024] Preferably, the bridging particles in step (1) include any one or a combination of at least two of ceramic particles, silica gel particles, or polyvinylidene fluoride microspheres. Typical but non-limiting combinations include: a combination of ceramic particles and silica gel particles, a combination of ceramic particles and polyvinylidene fluoride microspheres, a combination of silica gel particles and polyvinylidene fluoride microspheres, or a combination of ceramic particles, silica gel particles, and polyvinylidene fluoride microspheres.

[0025] It should be noted that the bridging particles of the present invention are non-toxic and have good chemical stability, meeting the requirements of the use environment and conforming to the requirements of green chemistry.

[0026] Preferably, the particle size of the bridging particles in step (1) is ≥10 μm. For example, it can be 10 μm, 12 μm, 14 μm, 16 μm, 18 μm, 20 μm, 22 μm, 24 μm, or 26 μm, etc., but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0027] It should be noted that in order to prevent the particle size of the bridging particles from being too small, resulting in too low porosity or unstable accumulation of the secondary membrane, it is necessary to limit the particle size of the bridging particles to ≥10 μm.

[0028] Preferably, when the pore size of the separation membrane ≥ 5 μm, the particle size of the bridging particles in step (1) is 2 to 5 times the pore size of the separation membrane. For example, it can be 2 times, 2.5 times, 3 times, 3.5 times, 4 times, 4.5 times or 5 times, etc., but not limited to the listed values. Other values within the numerical range that are not listed are equally applicable.

[0029] More specifically, the selection of the particle size of the bridging particles in the present invention is crucial for forming an effective packing structure. If the particle size of the bridging particles is too small, the porosity of the secondary membrane will be relatively low, which may lead to a significant increase in the osmotic pressure, thus affecting the operation efficiency of the reactor. If the particle size of the bridging particles is too large, the packing structure may be too loose to effectively intercept fine pollutants, resulting in a reduction in the membrane fouling control effect. In short, selecting bridging particles with an appropriate particle size range can not only form a stable secondary membrane on the membrane surface but also avoid blocking the membrane pores, ensuring the effective permeability of the separation membrane and the efficient operation of the system.

[0030] As a preferred technical solution of the present invention, the content of the bridging particles in the mixed solution in step (1) is 0.01 to 1 wt%, for example, it can be 0.01 wt%, 0.05 wt%, 0.1 wt%, 0.2 wt%, 0.5 wt% or 1 wt%, etc., but not limited to the listed values. Other values within the numerical range that are not listed are equally applicable.

[0031] In the present invention, when the content of the bridging particles in the mixed solution is too low, it will lead to uneven or insufficient formation of the secondary membrane, making it difficult to effectively cover the surface of the separation membrane and reducing the interception ability of fine pollution particles, thus increasing the risk of membrane pore blockage. On the contrary, when the content of the bridging particles is too high, it will lead to a significant increase in the viscosity of the mixed solution, affecting the fluidity of the liquid during the membrane separation process, possibly causing the secondary membrane to be too thick or the packing to be unstable, while increasing the operation energy consumption and the equipment cleaning frequency, and reducing the overall efficiency of the system.

[0032] As a preferred technical solution of the present invention, the temperature of the stirring in step (1) is 20 to 50 °C, for example, it can be 20 °C, 25 °C, 30 °C, 35 °C, 40 °C, 45 °C or 50 °C, but not limited to the listed values. Other values within the numerical range that are not listed are equally applicable.

[0033] Preferably, the time of the stirring in step (1) is 2 to 30 min, for example, it can be 2 min, 5 min, 10 min, 15 min, 20 min, 25 min or 30 min, but not limited to the listed values. Other values within the numerical range that are not listed are equally applicable.

[0034] Preferably, the rotation speed of the stirring in step (1) is 50 - 600 r / min. For example, it can be 50 r / min, 100 r / min, 200 r / min, 300 r / min, 400 r / min, 500 r / min or 600 r / min. However, it is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0035] As a preferred technical solution of the present invention, the flow rate of the mixed solution in the membrane separation in step (2) is 0.1 - 5 m / s. For example, it can be 0.1 m / s, 1 m / s, 2 m / s, 3 m / s, 4 m / s or 5 m / s. However, it is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0036] Preferably, the ambient pressure of the membrane separation in step (2) is 0.1 - 5 MPa. For example, it can be 0.1 MPa, 1 MPa, 2 MPa, 3 MPa, 4 MPa or 5 MPa. However, it is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0037] In the present invention, by adjusting hydrodynamic parameters such as the flow rate of the liquid, the operating pressure, and the shear force, the membrane osmotic pressure is increased, and the stirring speed is reduced to weaken the shear force on the membrane surface, inducing the bridging particles to form a secondary membrane on the surface of the separation membrane. During the membrane separation process, by adjusting the flow rate and the ambient pressure, the conditions required for membrane separation are achieved. Finally, after the bridging accumulation layer is stable (the thickness of the accumulation layer no longer changes), a secondary membrane with a certain porosity and a three-dimensional stable structure is formed;

[0038] More specifically, when the flow rate of the mixed solution during the membrane separation process is too fast, it will cause the accumulation layer formed by the bridging particles on the surface of the separation membrane to be unstable, and phenomena such as particle redispersion or the washing away of the accumulation layer may occur, thereby reducing the effectiveness and filtration ability of the secondary membrane; conversely, when the flow rate of the mixed solution is too slow, it will cause the accumulation process of the particles on the membrane surface to be too slow, making it difficult to form a uniform secondary membrane, and at the same time, it may increase the risk of particle aggregation and pore blockage, thereby affecting the permeation flux and filtration efficiency;

[0039] When the ambient pressure during the membrane separation process is too large, it will cause the compaction degree of the bridging accumulation layer to be too high, thereby reducing the porosity of the accumulation layer, increasing the permeation resistance, and may cause the particles to embed in the pores of the separation membrane, resulting in irreversible blockage; conversely, when the ambient pressure during the membrane separation process is too small, it will cause the bridging particles to be difficult to stably accumulate on the membrane surface, the formed secondary membrane structure is loose, the filtration performance is insufficient, and it cannot effectively intercept the contaminated particles, thereby reducing the separation efficiency and the protective effect of the membrane.

[0040] As a preferred technical solution of the present invention, the end point of the membrane separation in step (2) is that the thickness of the secondary membrane is constant.

[0041] In a third aspect, the present invention provides an application of a secondary membrane for slowing down membrane fouling of a separation membrane as provided in the first aspect, and the secondary membrane is used for membrane separation.

[0042] As a preferred technical solution of the present invention, the ambient pressure in the membrane separation is 0.1 to 5 MPa. For example, it can be 0.1 MPa, 1 MPa, 2 MPa, 3 MPa, 4 MPa or 5 MPa, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0043] It should be noted that during the operation of the separation membrane loaded with the secondary membrane of the present invention, the stability of the particle accumulation layer can be maintained by periodically adjusting the fluid conditions, controlling the particle concentration or performing on-line cleaning, so as to ensure the long-term efficient operation of the filtration process;

[0044] In addition, during the operation of the secondary membrane of the present invention, when the secondary membrane reaches a specific fouling threshold, it is manifested as a continuous increase in the osmotic pressure. The bridging particles can be removed by external backwashing and the secondary membrane can be re-constructed, so as to achieve the sustainable operation of the system;

[0045] Among them, the washing pressure in the external backwashing process should be strictly controlled within the maximum pressure range that the filtration membrane can withstand, so as to prevent the separation membrane from being damaged or deformed due to excessive pressure; preferably, the washing pressure can be set according to the membrane material and structural characteristics, for example, it is 80% to 90% of its maximum pressure-bearing value, so as to protect the integrity and long-term use performance of the membrane while ensuring the cleaning effect.

[0046] The secondary membrane of the present invention can be applied to a variety of membrane separation processes, including but not limited to: chemical separation, water treatment, food processing, pharmaceutical industry, etc.;

[0047] Preferably, the chemical separation includes: the real-time separation of the catalyst and the reaction solution in a continuous reaction; the water treatment includes any one of municipal sewage treatment, drinking water purification or industrial wastewater reuse; the food processing includes dairy product concentration or fruit juice clarification; the pharmaceutical industry includes: drug purification or fermentation broth filtration.

[0048] The numerical range described in the present invention not only includes the above-listed point values, but also includes any point values between the above numerical ranges that are not listed. Due to space limitations and for the sake of brevity, the present invention does not exhaustively list the specific point values included in the range.

[0049] Compared with the prior art, the present invention has the following beneficial effects:

[0050] (1) The secondary membrane provided by the present invention has a multi-stage filtration function, which can intercept pollution particles or colloidal substances, prevent fine particles from blocking the pores of the separation membrane, thereby optimizing the membrane separation effect, increasing the removal rate of pollutants, effectively alleviating the direct pollution on the surface of the separation membrane, and significantly extending the service life of the separation membrane;

[0051] (3) The method for forming the secondary membrane for mitigating membrane fouling of the separation membrane provided by the present invention is simple, and the application method is simple, with high engineering feasibility and economic benefits;

[0052] (4) The secondary membrane for mitigating membrane fouling of the separation membrane provided by the present invention can be seamlessly connected with the existing membrane separation technology and has wide applicability. Description of the Drawings

[0053] Figure 1 It is a comparison diagram of the membrane fluxes of the separation membrane loaded with the secondary membrane for mitigating membrane fouling of the separation membrane provided in Example 1 of the present invention and the separation membrane provided in Comparative Example 1. Detailed Embodiments

[0054] The technical solutions of the present invention will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be construed as specific limitations on the present invention.

[0055] In one specific embodiment, the present invention provides a secondary membrane for mitigating membrane fouling of the separation membrane. The secondary membrane includes a bridging accumulation layer loaded on the surface of the separation membrane; the porosity of the bridging accumulation layer is 30-70%.

[0056] In another specific embodiment, the present invention provides a method for forming the above-mentioned secondary membrane for mitigating membrane fouling of the separation membrane. The forming method includes the following steps:

[0057] (1) Mix water and bridging particles, and stir for 2-30 minutes at 20-50 °C and a stirring speed of 50-600 r / min to obtain a mixed solution;

[0058] Among them, the particle size of the bridging particles ≥ 10 μm; when the pore size of the separation membrane ≥ 5 μm, the particle size of the bridging particles is 2-5 times the pore size of the separation membrane; the content of the bridging particles in the mixed solution is 0.01-1 wt%;

[0059] (2) Perform membrane separation treatment on the mixed solution obtained in step (1) using the separation membrane until the thickness of the secondary membrane is constant to obtain the secondary membrane;

[0060] Among them, the flow rate of the mixed solution in the membrane separation is 0.1-5 m / s, and the ambient pressure is 0.1-5 MPa.

[0061] In another specific embodiment, the secondary membrane for reducing membrane fouling of the separation membrane is used for membrane separation; the environmental pressure of the membrane separation is 0.1 to 5 MPa.

[0062] Example 1

[0063] This example provides a secondary membrane for reducing membrane fouling of the separation membrane. The secondary membrane includes a bridging accumulation layer loaded on the surface of the separation membrane;

[0064] The porosity of the bridging accumulation layer is 50%.

[0065] The separation membrane is a tubular membrane, and the material of the separation membrane is a titanium metal microporous membrane with a pore size of 20 μm.

[0066] The formation method of the secondary membrane for reducing membrane fouling of the separation membrane includes the following steps:

[0067] (1) Mix water and bridging particles, and stir for 15 min at 30 °C and a stirring speed of 200 r / min to obtain a mixed solution;

[0068] Among them, the average particle size of the bridging particles is 50 μm; the content of the bridging particles in the mixed solution is 0.05 wt%; the bridging particles are silica particles;

[0069] (2) Perform membrane separation treatment on the mixed solution obtained in step (1) using the separation membrane until the thickness of the secondary membrane is constant to obtain the secondary membrane;

[0070] Among them, the flow rate of the mixed solution in the membrane separation is 1.5 m / s, and the environmental pressure is 0.3 MPa.

[0071] During the operation of membrane separation using the secondary membrane provided in this example, a short-term backwash is performed every 48 h through an online cleaning system to remove the fouled secondary membrane, and a new secondary membrane is re-constructed on the surface of the separation membrane.

[0072] The secondary membrane in this example is used for the real-time separation of the catalyst and the reaction solution in a continuous reaction.

[0073] Example 2

[0074] This example provides a secondary membrane for reducing membrane fouling of the separation membrane. The secondary membrane includes a bridging accumulation layer loaded on the surface of the separation membrane;

[0075] The porosity of the bridging accumulation layer is 30%.

[0076] The separation membrane is a hollow fiber membrane, the material is polyethylene (PE), and the pore size is 0.5 μm.

[0077] The method for forming the secondary membrane for mitigating membrane fouling of the separation membrane comprises the following steps:

[0078] (1) Mix water and bridging particles, and stir for 20 min under the conditions of 20°C and a stirring speed of 100 r / min to obtain a mixed solution;

[0079] Among them, the average particle size of the bridging particles is 10 μm; the content of the bridging particles in the mixed solution is 0.1 wt%; the bridging particles are ceramic particles;

[0080] (2) Perform membrane separation treatment on the mixed solution obtained in step (1) using the separation membrane until the thickness of the secondary membrane is constant to obtain the secondary membrane;

[0081] Among them, the flow rate of the mixed solution in the membrane separation is 2 m / s, and the ambient pressure is 0.25 MPa.

[0082] The secondary membrane provided in this example is used to treat municipal sewage; after the separation membrane loaded with the secondary membrane operates for 96 h, the decline rate of the membrane flux of the separation membrane is controlled within 15%, and the operation efficiency is increased by more than 25% compared with only using the separation membrane for treatment.

[0083] Example 3

[0084] This example provides a secondary membrane for mitigating membrane fouling of the separation membrane, and the secondary membrane comprises a bridging accumulation layer loaded on the surface of the separation membrane;

[0085] The porosity of the bridging accumulation layer is 30%.

[0086] The separation membrane is a flat membrane, the material is polyethersulfone (PES), and the pore size is 0.2 μm.

[0087] The method for forming the secondary membrane for mitigating membrane fouling of the separation membrane comprises the following steps:

[0088] (1) Mix water and bridging particles, and stir for 10 min under the conditions of 40°C and a stirring speed of 500 r / min to obtain a mixed solution;

[0089] Among them, the average particle size of the bridging particles is 10 μm; the content of the bridging particles in the mixed solution is 0.3 wt%;

[0090] (2) Perform membrane separation treatment on the mixed solution obtained in step (1) using the separation membrane until the thickness of the secondary membrane is constant to obtain the secondary membrane;

[0091] Among them, the flow rate of the mixed solution in the membrane separation is 1 m / s, and the ambient pressure is 0.15 MPa.

[0092] The secondary membrane in this embodiment is used for juice clarification. The separation membrane loaded with the secondary membrane operates for 72 hours, the pollution rate of the juice filtration system is reduced by 40%, the cleaning interval of the juice filtration device is extended from the traditional 12 hours to 36 hours, and the transparency of the filtered juice is increased by 15%.

[0093] Example 4

[0094] This embodiment provides a secondary membrane for reducing membrane fouling of a separation membrane. The secondary membrane includes a bridging accumulation layer loaded on the surface of the separation membrane;

[0095] The porosity of the bridging accumulation layer is 50%.

[0096] The difference between the formation method of the secondary membrane for reducing membrane fouling of the separation membrane and that of Example 1 is only that:

[0097] In this embodiment, the content of bridging particles in the mixed solution described in step (1) is adjusted to 0.2 wt%.

[0098] Example 5

[0099] This embodiment provides a secondary membrane for reducing membrane fouling of a separation membrane. The secondary membrane includes a bridging accumulation layer loaded on the surface of the separation membrane;

[0100] The porosity of the bridging accumulation layer is 50%.

[0101] The difference between the formation method of the secondary membrane for reducing membrane fouling of the separation membrane and that of Example 1 is only that:

[0102] In this embodiment, the content of bridging particles in the mixed solution described in step (1) is adjusted to 1.2 wt%.

[0103] Example 6

[0104] This embodiment provides a secondary membrane for reducing membrane fouling of a separation membrane. The secondary membrane includes a bridging accumulation layer loaded on the surface of the separation membrane;

[0105] The porosity of the bridging accumulation layer is 30%.

[0106] The difference between the formation method of the secondary membrane for reducing membrane fouling of the separation membrane and that of Example 1 is only that:

[0107] In this embodiment, the average particle size of the bridging particles described in step (1) is adjusted to 30 μm.

[0108] Example 7

[0109] This embodiment provides a secondary membrane for reducing membrane fouling of a separation membrane. The secondary membrane includes a bridging accumulation layer loaded on the surface of the separation membrane;

[0110] The porosity of the bridging accumulation layer is 70%.

[0111] The method for forming the secondary membrane for mitigating membrane fouling of the separation membrane is different from that of Example 1 only in that:

[0112] In this embodiment, the average particle size of the bridging particles described in step (1) is adjusted to 150 μm.

[0113] Example 8

[0114] This embodiment provides a secondary membrane for mitigating membrane fouling of the separation membrane, and the secondary membrane includes a bridging accumulation layer loaded on the surface of the separation membrane;

[0115] The porosity of the bridging accumulation layer is 60%.

[0116] The method for forming the secondary membrane for mitigating membrane fouling of the separation membrane is different from that of Example 1 only in that:

[0117] In this embodiment, the flow rate of the mixed solution in the membrane separation described in step (2) is adjusted to 5 m / s.

[0118] Example 9

[0119] This embodiment provides a secondary membrane for mitigating membrane fouling of the separation membrane, and the secondary membrane includes a bridging accumulation layer loaded on the surface of the separation membrane;

[0120] The porosity of the bridging accumulation layer is 70%.

[0121] The method for forming the secondary membrane for mitigating membrane fouling of the separation membrane is different from that of Example 1 only in that:

[0122] In this embodiment, the flow rate of the mixed solution in the membrane separation described in step (2) is adjusted to 7 m / s.

[0123] Example 10

[0124] This embodiment provides a secondary membrane for mitigating membrane fouling of the separation membrane, and the secondary membrane includes a bridging accumulation layer loaded on the surface of the separation membrane;

[0125] The porosity of the bridging accumulation layer is 35%.

[0126] The method for forming the secondary membrane for mitigating membrane fouling of the separation membrane is different from that of Example 1 only in that:

[0127] In this embodiment, the environmental pressure in the membrane separation described in step (2) is adjusted to 1.5 Mpa.

[0128] Example 11

[0129] This embodiment provides a secondary membrane for mitigating membrane fouling of a separation membrane. The secondary membrane includes a bridging accumulation layer loaded on the surface of the separation membrane;

[0130] The porosity of the bridging accumulation layer is 30%.

[0131] The difference between the formation method of the secondary membrane for mitigating membrane fouling of the separation membrane and that of Example 1 is only that:

[0132] In this embodiment, the ambient pressure in the membrane separation described in step (2) is adjusted to 6 MPa.

[0133] Comparative Example 1

[0134] This comparative example provides a separation membrane. The separation membrane is a tubular membrane, the material is a titanium metal microporous membrane, and the pore diameter is 20 μm.

[0135] Performance detection:

[0136] The membrane flux of the separation membrane loaded with the secondary membranes provided in the above Examples 1, 4 - 11 and Comparative Example 1 was detected, and the time when the membrane flux of the separation membrane decreased to the initial flux is shown in Table 1.

[0137] Table 1

[0138]

[0139]

[0140] Based on the data in Table 1 and Examples 2 - 3, the following points can be known:

[0141] (1) Through comprehensive analysis of Examples 1 - 3, it can be seen that the secondary membrane provided by the present invention can be applied to various fields, and can extend the service life of the separation membrane;

[0142] (2) Through comprehensive analysis of Example 1 and Examples 4 - 5, it can be seen that when the content of bridging particles in the mixed solution is on the high side, it will cause the secondary membrane to be too thick, the permeation resistance to increase significantly, thereby reducing the flux efficiency of the separation membrane. At the same time, it may cause the instability of the secondary membrane structure, increasing the risk of particle shedding or blockage, and ultimately affecting the overall performance of the separation process;

[0143] (3) Through comprehensive analysis of Example 1 and Examples 6 - 7, it can be seen that when the particle size of the bridging particles is on the low side, the porosity of the secondary membrane will be too low, the permeation resistance will increase, the liquid flow will be blocked, and the system flux efficiency will be reduced; on the contrary, when the particle size of the bridging particles is on the high side, the structure of the secondary membrane will be too loose, the filtration accuracy will decrease, and it will be difficult to effectively intercept fine fouling particles, ultimately reducing the separation effect;

[0144] (4) By comprehensively analyzing Examples 1 and 8-9, it can be seen that when forming the secondary membrane, when the flow rate of the mixed solution in the membrane separation is on the high side, it will cause the bridging particles to be unable to effectively accumulate on the surface of the separation membrane, resulting in an unstable or washed-away secondary membrane structure, thereby affecting the filtration effect and the durability of the secondary membrane; however, a stronger flow rate will make it difficult for the particles to accumulate, but instead enhance the scouring effect of the mixed solution on the particles, helping to reduce the risk of particle aggregation or large particle deposition;

[0145] (5) By comprehensively analyzing Examples 1 and 10-11, it can be seen that when forming the secondary membrane, when the environmental pressure in the membrane separation is on the high side (such as in Example 10), the accumulation layer is compacted to form a stable secondary membrane structure, and at the same time, the increase in pressure will improve the bonding strength and filtration stability of the secondary membrane; however, too high a pressure will cause the secondary membrane to be over-compacted, with a significant reduction in porosity, thereby increasing the permeation resistance and affecting the flux efficiency. At the same time, it may cause the bridging particles to embed in the membrane pores, resulting in membrane blockage or damage, ultimately reducing the service performance and lifespan of the separation membrane;

[0146] (6) By comprehensively analyzing Example 1 and Comparative Example 1, it can be seen that compared with a single separation membrane, the secondary membrane provided by the present invention can greatly improve the running time of the separation membrane and enhance the processing capacity;

[0147] The control chart of the membrane flux change over time of the separation membrane loaded with the secondary membrane provided in Example 1 and the single separation membrane provided in Comparative Example 1 is as Figure 1 shown.

[0148] In summary, by forming a secondary membrane on the surface of the separation membrane, the present invention can effectively reduce the direct blockage of the membrane pores by fine particle pollution, and at the same time make full use of the filtration characteristics of the secondary membrane to improve the overall efficiency and operation stability of the membrane separation system; it solves the problems of difficult effective control of membrane pollution, decline in the performance of the separation membrane, and high operation costs in the prior art.

[0149] The applicant declares that the above description is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A secondary membrane for mitigating membrane fouling of a separation membrane, characterized in that: The secondary membrane includes a bridging stacking layer supported on the surface of the separation membrane; The porosity of the bridge stacking layer is 30-70%.

2. The secondary membrane for mitigating membrane fouling of a separation membrane according to claim 1, characterized in that: The separation membrane includes any one of a hollow fiber membrane, a flat membrane or a tubular membrane.

3. A method for forming a secondary membrane for alleviating membrane fouling of a separation membrane as claimed in claim 1 or 2, characterized in that: The forming method comprises the following steps: (1) mixing water and bridging particles, and stirring to obtain a mixed solution; (2) Using a separation membrane to perform membrane separation treatment on the mixed solution obtained in step (1) to obtain the secondary membrane.

4. The forming method according to claim 3, characterized in that: The bridging particles in step (1) include organic particles and / or inorganic particles; Preferably, the bridging particles in step (1) include any one of ceramic particles, silica gel particles or polyvinylidene fluoride microspheres, or a combination of at least two thereof; Preferably, the particle size of the bridging particles in step (1) is ≥10 μm; Preferably, when the pore size of the separation membrane is ≥5 μm, the particle size of the bridging particles in step (1) is 2 to 5 times the pore size of the separation membrane.

5. The forming method according to claim 3 or 4, characterized in that: The content of the bridging particles in the mixed solution of step (1) is 0.01 to 1 wt %.

6. The forming method according to any one of claims 3 to 5, characterized in that: The stirring time in step (1) is 2 to 30 minutes; Preferably, the stirring speed in step (1) is 50 to 600 r / min.

7. The forming method according to any one of claims 3 to 6, characterized in that: The flow rate of the mixed solution in the membrane separation in step (2) is 0.1 to 5 m / s; Preferably, the environmental pressure of the membrane separation in step (2) is 0.1-5 MPa.

8. The forming method according to any one of claims 3 to 7, characterized in that: The end point of the membrane separation in step (2) is: the thickness of the secondary membrane is constant.

9. An application of a secondary membrane for mitigating membrane fouling of a separation membrane as claimed in claim 1 or 2, characterized in that: The secondary membrane for alleviating separation membrane fouling is used for membrane separation.

10. The use according to claim 9, characterized in that: The ambient pressure during the membrane separation is 0.1-5 MPa.

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