CN117258547A

CN117258547A - Folding nanofiltration membrane filter device and preparation method thereof

Info

Publication number: CN117258547A
Application number: CN202311540057.6A
Authority: CN
Inventors: 贾建东; 王祉健
Original assignee: Hangzhou Cobetter Filtration Equipment Co Ltd
Current assignee: Hangzhou Cobetter Filtration Equipment Co Ltd
Priority date: 2023-08-28
Filing date: 2023-11-20
Publication date: 2023-12-22
Anticipated expiration: 2043-11-20
Also published as: CN117258547B

Abstract

The application relates to the technical field of filter devices, in particular to a folding nanofiltration membrane filter device and a preparation method thereof, wherein the folding nanofiltration membrane filter comprises a filter layer, the filter layer at least comprises a filter membrane, the filter membrane is pleated and is wound into a cylinder shape in an end-to-end connection way, and end covers are welded at two ends of the filter layer, and the method comprises the following steps: s1, pleating a filter layer; s2, performing heat setting on the pleated filter layer; s3, cutting the heat-set filter layer, encircling the heat-set filter layer into a cylinder, and sealing edges at the end-to-end connection positions to obtain a cylinder filter layer; s4, end covers are welded at two ends of the cylindrical filter layer; in the above process, the filter layer is wetted with the pore size holding agent having a boiling point not lower than the lower one of the welding temperature of the end cap and the edge sealing temperature of the filter layer. In the application, the phenomenon of collapse of the membrane holes in the packaging process is reduced by wetting the nanofiltration membrane, so that the prepared filter has better flux.

Description

Folding nanofiltration membrane filter device and preparation method thereof

Technical Field

The application relates to the technical field of filter devices, in particular to a folding nanofiltration membrane filter device and a preparation method thereof.

Background

In the biomedical field, filtration is an important process. Wherein, the nanofiltration membrane is a filtration membrane with nanometer micropores, and can be used for purifying and removing viruses in the field of biological medicine.

In the actual production process, in order to improve the filtering effect of the nanofiltration membrane, the strength, the filtering area and the liquid flowing effect of the nanofiltration membrane are increased, and the nanofiltration membrane can be folded to form a folding filter element. The folding filter element generally comprises the steps of pleating, shaping, edge sealing, end cover welding and the like in the processing process.

In the prior art, a lot of proposals are made on how a general filter membrane is prepared into a folding filter element, for example, specific construction methods and parameter selection of steps such as pleating, end cover welding and the like are disclosed in US5006235A, US4521309A, but when the processing method is applied to the processing process of the nanofiltration membrane, the surface membrane holes of the nanofiltration membrane are collapsed, so that the flux of the nanofiltration membrane is reduced, and the filtration performance is deteriorated.

Disclosure of Invention

Based on the technical problems, the application provides a folding nanofiltration membrane filter device and a preparation method thereof, which can reduce the problem of collapse of membrane holes of nanofiltration membranes in the preparation process, so that the folding filter element filter device prepared by the nanofiltration membranes can have better flux.

Firstly, the application provides a preparation method of a folding nanofiltration membrane filter device, wherein the folding nanofiltration membrane filter device comprises a filter layer, the filter layer at least comprises a filter membrane, the filter membrane is pleated and is connected end to end and surrounds to form a cylinder, and end covers are welded at two ends of the filter layer, and the preparation method specifically comprises the following steps:

s1, pleating a filter layer;

s2, performing heat setting on the pleated filter layer;

s3, cutting the heat-set filter layer, encircling the heat-set filter layer into a cylinder, and sealing edges at the connection part of the tail parts to obtain a cylinder filter layer;

s4, end covers are welded at two ends of the cylindrical filter layer;

during the processing of the folded filter element, which comprises four steps of pleating, heat setting, encircling and welding, particularly during the steps of steps S2, S3 and S4, the filter layer is generally required to be wetted by an aperture maintaining agent, and the boiling point of the aperture maintaining agent is not lower than the welding temperature of the end cover and the edge sealing temperature of the filter layer;

the filter element is stored in a preservation solution after being prepared.

In the process of processing a filter device, end covers are usually required to be welded at two ends of a folded and edge-sealed filter layer, in the process, the filter layer is required to be soaked or partially soaked by a pore size maintaining agent, otherwise, after the processing is finished, filter pores on the filter layer collapse or deform, and the filtering effect of the filter layer is further adversely affected.

After the pore size maintaining agent is added, the pore size maintaining agent can wet or partially wet micropores on the filter membrane in the construction process, and the micropores in the filter membrane in a micron-sized or nano-sized state can be maintained in a shaped state through the surface tension of the pore size maintaining agent, so that the flux and the filtering effect of the prepared filter device are improved. Meanwhile, in the processing process, the inner wall of the micropore is in a wet or partially wet state, so that the influence of gas expansion or external stress on the micropore is small, and the membrane hole is not easy to collapse under the influence of the two factors, so that the prepared filter has better flux.

In the above technical scheme, the effect of pore size maintenance can be achieved by wetting the filter layer in advance. Meanwhile, the boiling point of the pore size maintaining agent should not be lower than the temperature required by the welding or edge sealing process, so that wetting liquid cannot excessively volatilize or boil in a system in the construction process, small bubbles cannot be generated, and huge volume change occurs, so that the pore size is expanded or the pore type is deformed, and the filtration interception effect is deteriorated.

After the preparation, in the process of storage, the filter membrane is required to be stored by a preservation solution because the filter membrane is not generally placed at a higher temperature in the process of storage of the filter device, a system such as water, ethanol and the like can be used as the preservation solution, and meanwhile, alkali or other antibacterial agents (such as benzalkonium chloride) can be added to improve the antibacterial performance.

In summary, in the above technical solution, the flux of the filter can be improved by wetting the wetting layer with the pore size maintaining agent, and the collapse of the membrane pores can be reduced, thereby achieving a good membrane pore protection effect.

Preferably, the total moisture content of the filter membrane is 10 to 70% before step S1, and the moisture content of the filter membrane is 1 to 50% in step S4.

In this application, wetting refers to the percentage of the mass of pore size retention agent adsorbed in the filter compared to the mass of pore size retention agent adsorbed by the filter with sufficient wetting and without dripping.

In this solution, the wettability of the filter membrane is continuously reduced during the processing, because the filter membrane and the moisture-retaining layer are pressed against each other during the pleating in step S1, and thus the pore size-maintaining agent is somewhat lost, for example, remains on the surface of the pleating knife or is extruded to flow out.

In step S4, the filter layer needs to be kept within a certain moisture range, wherein too high moisture may lead to insufficient welding and difficult heating, and the pore size maintaining agent may infiltrate into the welded portion during the welding process, resulting in reduced welding strength, reduced sealability, and reduced durability. If the pore size retention agent is small, the pore size retention effect cannot be achieved.

Under the condition of combining the considerations, in the step S1, the higher total wettability of the filter membrane is adopted, so that the influence on the follow-up caused by the loss of the wettability can be reduced, and under the wettability, the heat setting can have better setting effect, and liquid is not easy to run off in a large amount in the pleating process and influence the follow-up construction process. In step S4, the relatively low pore size holding agent content can better achieve the effect of welding, improve the welding strength, and simultaneously, because the welding is located in a local area, the influence on the filter membrane is small, so that the effect of pore size holding can be achieved due to low wettability.

Preferably, in step S1, the following formula is satisfied between the wettability of the filter membrane and the average pore diameters of the inlet surface and the outlet surface of the filter membrane by SEM:

φ=

wherein phi is the wettability of the filter membrane, R1 is the SEM average pore size of the inlet liquid surface of the filter membrane, R2 is the SEM average pore size of the outlet liquid surface, and k is a parameter, and the range of k is 0.045-0.120.

In the above technical solution, the range of the wettability in the step S1 is further defined, the wettability of the filter membrane is related to the SEM average pore size of both sides of the filter membrane, and considering the characteristics of the nanofiltration membrane, the SEM average pore size of the liquid surface is generally fixed and is about 15-40 nm. The pore size of the liquid inlet is generally larger than the SEM average pore size of the liquid outlet. In the formula, the ratio of the average pore diameter of the SEM of the liquid inlet surface to the average pore diameter of the SEM of the liquid outlet surface has a positive correlation with the wetting saturation, on the one hand, the larger the average pore diameter of the SEM of the liquid inlet surface is, the stronger the maintenance capability of the filter membrane on the pore diameter maintaining agent is, the pore diameter maintaining agent is not easy to run off under higher wetting degree, the better pore diameter maintaining effect is realized, meanwhile, the larger pore diameter reduces the specific surface area in the filter membrane, and in consideration that the tension of the pore diameter maintaining agent may not be enough to form a liquid film in the larger pore diameter, more pore diameter maintaining agent is needed to maintain the filter membrane in a better wetting state.

Preferably, the pore size maintaining agent comprises at least a polyol.

In the technical scheme, the polyol is selected, on one hand, the polyol can wet the filter membrane better, has better spreading effect on the surface of the filter membrane, and meanwhile, because the polyol is provided with a plurality of hydroxyl groups, the polyol can form a multi-point crosslinking structure to a certain extent in the filter holes of the filter membrane, so that better aperture preservation effect is achieved. In addition, after the construction is completed, the polyol can be cleaned by flushing with a preservation solution, so that the polyol basically does not remain in the filter holes, and a small amount of residue does not influence the filtering behavior.

Preferably, the contact angle of the pore size maintaining agent on the surface of the filter membrane is 80-200% of water and not more than 80 °.

In the above scheme, the contact angle of the pore size maintaining agent on the surface of the filter membrane is close to or greater than that of water, and as the nanofiltration membrane generally needs to have better affinity for water, the pore size maintaining agent should also have better affinity for the pore size maintaining agent, so that the pore size maintaining agent can maintain a better spreading state in the membrane pores of the filter membrane, and meanwhile, the pore size maintaining agent cannot have too high affinity for the filter membrane, i.e. the contact angle on the filter membrane cannot be too low, otherwise, the pore size maintaining agent is difficult to elute from the filter membrane in the post-treatment process, and has a certain influence on the subsequent filtration.

Preferably, the pore size maintaining agent comprises at least one of ethylene glycol, glycerol, propylene glycol, butylene glycol, and polyethylene glycol. Further preferably, the pore size maintaining agent is glycerol.

The polyol, particularly the mixed system of glycerol and water, is selected, so that the whole film hole maintaining effect is better, the processing performance is better in the processing process, and the prepared filter layer has more excellent filtering effect.

Preferably, in step S2, the filter layer is passed through a heating zone having a higher temperature at the outlet end than at the inlet end during heat setting.

Because the filter membrane is not in a saturated and wet state, the pore size maintaining agent cannot fill the whole filter pore in the filter pore of the filter membrane, generally only partially fills the filter pore, and is easier to fill larger segments in the filter pore. In the technical scheme, during heat setting, the lower temperature is adopted to preheat firstly, after preheating, under the lower temperature, firstly the filter membrane and the screen on the surface of the moisturizing layer are heated firstly, and as the distribution of wetting liquid in the filter membrane is uneven, the filter membrane can be activated by the earlier lower temperature, so that the wetting liquid in the filter membrane can be better spread in the filter holes, and then the temperature is raised to gradually set, so that the wetting liquid can keep the wetting state of the filter membrane better as much as possible in the setting process, and the effects of wetting and aperture maintenance are improved.

Preferably, the heating zone comprises at least in part a gradient set temperature, wherein the temperature gradient is as follows: t=t0+5 to 20 ℃/s·t; wherein T0 is the initial temperature in the whole heating process, and the value range is 40-80 ℃; t is the heat setting temperature when heating for T seconds, and the final temperature is 90-130 ℃.

In the technical scheme, the heat setting is performed in a gradient heating mode, a good setting effect is achieved in the heating process, setting efficiency is guaranteed under the gradient, problems of loss of pore diameter maintaining agent, collapse of membrane materials, hole sinking and the like caused by overlong setting time are reduced, and pleating setting effect is improved.

After the temperature rise is finished, the temperature can be kept at the highest temperature and the shape can be set. Typically the total time is not less than 5s.

Preferably, in the step S4, the welding temperature is 150-250 ℃, and the welding contact time is 2-10S.

In the technical scheme, the welding effect is good, the welding time is short, the temperature is low in the welding process, the pore size maintaining agent can be less dissolved into the welding structure in the welding process, the formed welding structure has better strength, meanwhile, the loss of the pore size maintaining agent is reduced, and the protection effect of the pore size maintaining agent on the filter membrane is improved.

Preferably, the preservation solution is a system containing alkali or alcohol.

In the scheme, the preservation solution can fill the whole membrane package and fully moisten the filter membrane, and alkali or alcohol is added into the preservation solution, so that the wettability of the preservation solution to the membrane package can be improved, and the flux loss of the membrane holes in the membrane package is reduced.

Preferably, the preservation solution contains 0.01 to 0.5M of alkali.

In the above scheme, the preservation solution is pure water or an alkaline solution of water, wherein the alkaline medium can be inorganic alkali or organic alkali, so long as the membrane and other structures in the system can not be damaged, for example, sodium hydroxide and the like can be used, and the addition of the alkali improves the antibacterial property of the preservation solution, so that the prepared membrane package has longer preservation period.

In addition, on the basis of the method, the application also provides a folding nanofiltration membrane filter device prepared based on the method.

In the preparation scheme, the good retention effect on the aperture can be realized through the whole-course wetting scheme of the aperture retention agent, and in the processing process, the aperture retention agent can always maintain the wetting effect on the aperture in the filter membrane, is not easy to overflow and has influence on equipment and subsequent processing effects.

Preferably, the filter membrane is any one of polyvinylidene fluoride, cellulose and polyethersulfone.

The pore size maintaining agent can realize good pore size maintaining effect in the filter membranes made of the three materials, and remarkably improves the flux and the integrity of the prepared filter membrane.

Preferably, the SEM average pore diameter of the liquid outlet surface is 15-25 nm; the SEM average pore diameter of the liquid inlet surface is 200-2000 nm.

Within the above range of SEM average pore size, the pore size retention agent may better remain in the filter pores and wet the inner surface of the filter pores, making the pores less prone to collapse.

Preferably, the filter layer further comprises a moisture retention layer positioned on both sides of the filter membrane.

On the one hand, the filter hole collapse phenomenon caused by volatilization of the pore diameter maintaining agent can be reduced by adding the moisture-preserving layer, and the moisture-preserving layer has strong water absorption performance, so that a wet gas environment can be formed outside the filter membrane, and meanwhile, liquid infiltration and direct dripping on equipment in the filter membrane processing process can be reduced by the moisture-preserving layer, so that the processing difficulty is reduced.

Preferably, the end cap is polypropylene.

A better fusion welding system can be formed between the end cover and the filter membrane, the whole welding structure is strong, and the filter membrane has larger hydrophobicity, so that the pore size maintaining agent is not easy to infiltrate into the welding system, and the system is facilitated to form a firmer welding structure.

In summary, the filter membrane is wetted by the pore size maintaining agent, and then the filter membrane is processed into the folded nanofiltration membrane filter device, and micropores in the filter membrane can not collapse after the filter device is processed, so that a good filtering effect can be maintained.

Drawings

FIG. 1 is a schematic diagram of the overall structure of a folded nanofiltration membrane filter device of the present application;

FIG. 2 is a partial schematic view of the filter layer and the moisturizing layer of the filter device of FIG. 1 after being folded;

FIG. 3 is an SEM image (magnification 20000) of the liquid inlet surface of a filter membrane in example 1 of the present application;

FIG. 4 is an SEM image (magnification of 20000) of the liquid surface of a filter membrane in example 1 of the present application.

In the figure, 1, a filter membrane; 2. a moisture retention layer; 3. a welding area; 4. an end cap.

Detailed Description

The following description of the embodiments of the present invention will be made apparent and fully in view of the accompanying drawings, in which some, but not all embodiments of the invention are shown. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.

In the description of the present invention, it should be noted that the directions or positional relationships indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. are based on the directions or positional relationships shown in the drawings, are merely for convenience of describing the present invention and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a specific orientation, be configured and operated in a specific orientation, and thus should not be construed as limiting the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.

In the description of the present invention, it should be noted that, unless explicitly specified and limited otherwise, the terms "mounted," "connected," and "connected" are to be construed broadly, and may be either fixedly connected, detachably connected, or integrally connected, for example; can be mechanically or electrically connected; can be directly connected or indirectly connected through an intermediate medium, and can be communication between two elements. The specific meaning of the above terms in the present invention will be understood in specific cases by those of ordinary skill in the art.

In the following examples, the SEM average pore size of the liquid inlet or outlet surface of the filter layer, or the SEM average pore size of the cross section, can be measured by computer software (e.g. Matlab, NIS-Elements, etc.) or manually after the morphology of the membrane structure is characterized by using a scanning electron microscope, and calculated accordingly. In actual measurement, the surface of the membrane can be first characterized by an electron microscope to obtain a corresponding SEM image, and since the pores on the surface of the membrane are approximately uniform, a certain area, for example, 1 μm2 (1 μm by 1 μm) or 25 μm2 (5 μm by 5 μm), can be selected, the specific area size is determined according to the actual situation, the pore diameters of all the pores on the area are measured by corresponding computer software or manually, and then calculation is performed to obtain the average pore diameter of the pores on the surface; of course, the person skilled in the art can also obtain the above parameters by other measuring means, which are only used as reference.

The integrity test is carried out by a seed air diffusion flow test, and the specific test method is as follows:

the prepared filter element was wetted with water, the liquid inlet end of the element was connected to compressed air, and a pressure of 0.1mPa was applied to the liquid inlet end, and then the air flow rate was measured at the liquid outlet end to evaluate the integrity. The smaller the air flow, the better the integrity of the filter device is demonstrated.

The method for calculating the wettability of the filter membrane is as follows: the method comprises the steps of fully immersing a filter membrane in an aperture maintaining agent, taking out and suspending until the aperture maintaining agent is not dripped, weighing to obtain the mass of the aperture maintaining agent which can be contained in the filter membrane in a saturated wetting state of the aperture maintaining agent, and calculating the ratio of the mass of the aperture maintaining agent absorbed by the filter membrane to the mass of the aperture maintaining agent in the saturated wetting state, namely the wetting degree.

The flux detection method of the filter membrane comprises the following steps: the test was performed with reference to the method of pure water transmittance test of 5.1 in GB/T32360-2015, wherein the feed liquid was deionized water, the operating pressure was 30psi, the operating temperature was 25℃and the pH of the solution was 7.

The processability was evaluated as follows: since the pore size maintaining agent has a boiling point substantially higher than the construction temperature in the following examples, after the completion of the processing, the filter membrane and the moisturizing layer of a specific area are cut, the mass of the pore size maintaining agent lost in the filter membrane can be obtained by the mass change of the filter membrane during the start and end, the mass change of the moisturizing layer can be weighed to obtain the mass of the pore size maintaining agent absorbed in the moisturizing layer, the difference between the mass of the pore size maintaining agent remaining in the apparatus during the processing, and in the following examples, the processing performance is measured as the loss rate of the pore size maintaining agent by the percentage between the mass of the pore size maintaining agent remaining in the apparatus and the mass of the original pore size maintaining agent in the moisturizing layer.

Embodiment 1, this embodiment relates to a folded nanofiltration membrane filter device, the overall structure of which is shown in fig. 1 and 2, and the overall preparation method thereof includes the following steps;

s1, in the step S1, three layers are combined into a filter layer according to the sequence of the moisturizing layer 2-the filter membrane 1-the moisturizing layer 2, the filter layer is pleated, in this embodiment, the filter membrane 1 is pleated by a pleating knife, a specific method can be referred to as US5006235A, parameters of the filter membrane can be adjusted according to the thickness, the hardness and the like of the filter membrane, and the general shape after pleating is shown in fig. 2.

S2, after pleating, performing heat setting on the filter layer, wherein the heat setting is realized by enabling the pleated filter layer to pass through a heating area, and in the embodiment, the time for the filter layer to pass through the heating area is 8S, and the temperature of the heating area is stable at 130 ℃.

S3, cutting the heat-set filter layer, then winding the filter layer into a cylinder, and welding the end-to-end positions, wherein in the embodiment, an ultrasonic welding method is adopted, the moisture-retaining layer and the filter membrane are welded together during welding, and the width of a welding area 3 is 0.6cm.

And S4, after welding, welding end covers 4 at two ends of the cylindrical filter layer, wherein the end covers 4 are made of polypropylene, and the welding temperature is 170 ℃ and the welding time is 10S.

In the above process, the filter membrane is kept in a state of being wetted by the pore size maintaining agent, wherein the pore size maintaining agent is glycerin, the filter membrane is PES filter membrane, the average pore size of the inlet liquid surface SEM is about 720nm, the average pore size of the outlet liquid surface SEM is 20.4nm, the morphology of the inlet liquid surface and the outlet liquid surface under SEM is shown in fig. 3 and 4 respectively, the contact angle of glycerin on the surface of the filter membrane is 60.4 degrees, and the contact angle of pure water on the surface of the filter membrane is 54.0 degrees.

In step S1, the wettability of the pore size maintaining agent was 55%, and the wettability of the filter membrane was reduced to 32% during the processing to step S3. In step S1, wetting is accomplished by spraying or coating a specific weight of pore size holding agent onto the surface of the filter membrane and standing until the filter membrane absorbs. And compounding the wetted filter membrane with a moisturizing layer.

After the preparation is finished, the filter membrane is fully wetted by the preservation liquid by introducing the preservation liquid into the filter device, then the filter membrane is preserved in a closed environment, and the preservation liquid is periodically replenished, so that the filter membrane is always in a wetted state during preservation. Wherein the preservation solution is 0.05M sodium hydroxide aqueous solution.

As a control, in comparative example 1, compared with example 1, the wetting was performed without adding the pore size maintaining agent in step S1, and after the completion of the heat setting, the pore size maintaining agent was applied to the filter between step S2 and step S3. The moisture degree of the filter membrane in the step S4 is controlled to be 36 percent.

In comparative example 2, the same degree of wetting as in example 1 was used in step S1, and the degree of wetting was reduced to 21% in step S4, as compared with example 1, in which pure water was used as the wetting agent.

Comparative example 3 one piece of the same film package as prepared in example 1 was selected, washed with a preservation solution, and then air-dried and preserved in a natural state.

For example 1 and comparative examples 1 and 2, the integrity of the filter device and the flux of the filter membrane, and the flux after 30 days of storage, as well as the pore size retention agent loss are shown in table 1.

From the above experimental data, it can be seen. In example 1, after wet encapsulation with glycerol, the flux of the membrane was significantly improved compared with the filters without encapsulation, while comparative example 2 had significant loss in membrane flux compared with comparative examples 1 and 1, probably because the membrane was collapsed inside, and the inner wall of the pore was easily softened due to higher temperature during heat setting and welding, and the molecular chains were freely diffused, thus leading to a change in the shape and structure of the pore, and a significant decrease in membrane flux.

In comparative example 2, water was used as the pore size maintaining agent, and the boiling point of pure water was lower than the temperature of the membrane package process (including the heat setting temperature and the welding temperature), so that during the process, water volatilized and even boiled, on the one hand, the protective effect on the membrane pores was lost, and on the other hand, the integrity of the filter device was remarkably lowered due to the rapid volume expansion.

In comparative example 3, since no preservation solution was added during preservation, the phenomenon of collapse of the membrane pores was also generated during long-term storage, and thus the flux loss after 30 days of preservation was significantly greater than that of the product prepared in example 1.

Example 2 the initial wetting degree in step S1 was adjusted on the basis of example 1 and in accordance with Φ=The k value was calculated, where R1 is the membrane inlet SEM average pore size and R2 is the membrane outlet SEM average pore size, and the specific results are shown in table 2.

Example 3 based on example 1, different filters were used, the material of the filters, the average pore size of the inlet SEM and the average pore size of the outlet SEM, and the degree of wetting in step S1 was tested in different experimental groups, and the specific parameters are shown in table 3.

It should be noted that the welding temperature and time required in step S4 are correspondingly different by using different materials, and are also shown in table 4.

It is worth noting that the welding temperature and time can be adjusted according to actual process requirements, the influence on the overall properties is small, the general temperature rise can correspond to the shortening of the construction time, specifically, the welding temperature is 150-250 ℃, and the welding contact time is 2-10 s, so that good welding effect can be achieved.

In table 3, the results of the different experimental groups are shown in table 5.

From a combination of tables 3 and 5, it can be seen that the total wettability of the filter membrane set before step S1 is in the range of 30 to 70% for different materials, with different inlet and outlet pores, with higher flux and lower pore size retention agent loss rate. Further, for Φ=When the formula is calculated to obtain k within the range of 0.045-0.120, the whole has more excellent effect. The above properties have a similar trend in the filters of all three classes of materials.

Example 4 the type of pore size-maintaining agent and the surface tension on the surface of the filter membrane were as shown in Table 6, based on example 3, by changing the pore size-maintaining agent for different filter membranes and measuring the results of the related experiments.

In example 4, the experimental results of each experimental group are shown in table 7.

From the data in the table, it can be seen that, in the three parameters of the integrity of the integrated filter device, the flux of the filter membrane and the loss rate of the pore size maintaining agent, when the surface of the corresponding filter membrane has a contact angle of 80-200% compared with pure water, and the contact angle is not more than 80 degrees, the corresponding pore size maintaining agent has a good effect of maintaining the pore size of the filter membrane. The scheme has certain superiority in the comprehensive effect of the glycerol.

Example 5 the heat-setting process in step S2 was modified on the basis of example 1, and the heat-setting temperature settings for the different experimental groups in example 5 are shown in table 8.

In the above embodiment, the temperature setting may be set as a plurality of heating sections connected to each other, arranged in the advancing direction of the folded filter layer. The running speed of the filter membrane is generally 50 to 100 folds/min.

The experimental measurement was performed in example 5, and the results are shown in table 9.

Comparing the technical scheme with the embodiment 1, it can be seen that the filter membrane formed by using the gradient temperature increase has better integrity and better flux loss compared with the filter membrane formed by adopting the same temperature from end to end in the heat setting process. The temperature gradient is increased to help the pore size maintaining agent to exert the protection effect on the pores in the filter membrane, so that the prepared filter membrane has better flux.

In example 6, the preservation solution was adjusted based on example 1, and the following experimental groups were specifically obtained:

6-1: the preservation solution was replaced with ethanol.

6-2: the preservation solution was replaced with glycerol.

6-3: the preservation solution was replaced with a 20% by mass ethanol aqueous solution.

6-4: the preservation solution was replaced with an aqueous solution of 20% by mass of ethanol and 20% by mass of glycerol.

6-5: the preservation solution is replaced by 0.05M ethanol/water mixed solution of sodium hydroxide, and the mass ratio of the ethanol to the water is 1:4.

6-6: the concentration of sodium hydroxide in the preservation solution was 0.01M.

6-7: the concentration of sodium hydroxide in the preservation solution was 0.1M.

6-8: the concentration of sodium hydroxide in the preservation solution was 0.5M.

The flux of the membrane packs of the different experimental groups in example 6 after 30 days of storage under airtight moisture retention is shown in table 10.

The above experiment results show that the ethanol or glycerol system is adopted to replace the water system, and alkali is optionally added or not added, so that the filter layer has good pore size maintaining effect, and the flux does not obviously decrease after long-term storage. In the system, water, ethanol and glycerin have better performance, and different preservation solutions can be replaced for preservation according to the actual use requirements, such as factors of convenience in preservation solution supplementation, alkali resistance and alcohol resistance of the shell and the like.

The above embodiments are only preferred embodiments of the present invention, and the scope of the present invention is not limited thereto, but any insubstantial changes and substitutions made by those skilled in the art on the basis of the present invention are intended to be within the scope of the present invention as claimed.

Claims

1. The preparation method of the folding nanofiltration membrane filter device comprises a filter layer, wherein the filter layer at least comprises a filter membrane, the filter membrane is pleated and is connected end to end and surrounds to form a cylinder, and end covers are welded at two ends of the filter layer, and the preparation method is characterized by comprising the following steps:

s1, pleating a filter layer;

s2, performing heat setting on the pleated filter layer;

s3, cutting the heat-set filter layer, encircling the heat-set filter layer into a cylinder, and sealing edges at the end-to-end connection positions to obtain a cylinder filter layer;

s4, end covers are welded at two ends of the cylindrical filter layer;

in the process, the filter layer is wetted by the aperture maintaining agent, and the boiling point of the aperture maintaining agent is not lower than the welding temperature of the end cover and the edge sealing temperature of the filter layer;

the filter element is stored in a preservation solution after being prepared.

2. The method for producing a folded nanofiltration membrane filtration device according to claim 1, wherein the total moisture content of the filtration membrane is 10 to 70% before step S1, and the moisture content of the filtration membrane is 1 to 50% in step S4.

3. The method for preparing a folded nanofiltration membrane filter device according to claim 1, wherein in step S1, the wettability of the membrane and the average pore size of the inlet and outlet SEM of the membrane satisfy the following formula:

φ=

4. The method of making a pleated nanofiltration membrane filtration device of claim 1 wherein the pore size retention agent comprises at least a polyol.

5. The method of producing a pleated nanofiltration membrane filtration device according to claim 4, wherein the pore size retainer has a contact angle of 80 to 200% of water on the surface of the filtration membrane, and not more than 80 °.

6. The method of producing a pleated nanofiltration membrane filtration device of claim 5 wherein the pore size retainer comprises at least one of ethylene glycol, glycerol, propylene glycol, butylene glycol, polyethylene glycol.

7. The folded nanofiltration membrane filter device of claim 6, wherein the pore size retention agent is glycerol.

8. The method of producing a pleated nanofiltration membrane filtration device according to claim 1, wherein in step S2, the filtration layer is passed through a heating zone having a higher temperature at the outlet end than at the inlet end during heat setting.

9. The method of making a pleated nanofiltration membrane filter device of claim 8 wherein the heating zone comprises at least in part a gradient set temperature, wherein the temperature gradient is as follows: t=t0+5 to 20 ℃/s·t; wherein T0 is the initial temperature in the whole heating process, and the value range is 40-80 ℃; t is the heat setting temperature when heating for T seconds, and the final temperature is 90-130 ℃.

10. The method for producing a folded nanofiltration membrane filtration device according to claim 1, wherein the welding temperature is 150 to 250 ℃ and the welding contact time is 2 to 10S in step S4.

11. The method for preparing a pleated nanofiltration membrane filter device according to claim 1, wherein the preservation solution is a system comprising a base or an alcohol.

12. The method for producing a pleated nanofiltration membrane filter device according to claim 11, wherein the preservation solution contains 0.01 to 0.5M of alkali.

13. A folded nanofiltration membrane filter device produced by the method of producing a folded nanofiltration membrane filter device as claimed in any one of claims 1 to 12.

14. The folded nanofiltration membrane filter device of claim 13, wherein the filter membrane is any one of polyvinylidene fluoride, cellulose, polyethersulfone.

15. The folded nanofiltration membrane filter device of claim 13, wherein the outlet liquid level has an SEM average pore size of 15-40 nm; the SEM average pore diameter of the liquid inlet surface is 200-2000 nm.

16. The pleated nanofiltration membrane filter device of claim 13, wherein the filter layer further comprises a moisture retention layer on both sides of the filter membrane.

17. The pleated nanofiltration membrane filter device of claim 13, wherein the end cap is polypropylene.