JP6783281B2 - Ultrafiltration membrane manufacturing method, ultrafiltration membrane device, ultrapure water manufacturing device and ultrapure water manufacturing method - Google Patents

Description

The present invention provides a method for producing an ultrafiltration membrane having high particle removal performance (hereinafter, "manufacturing" of the ultrafiltration membrane may be referred to as "preparation") , and the ultrafiltration membrane obtained by this preparation method. Regarding the ultrafiltration membrane device to have. This ultrafiltration membrane device can be used as a filtration device for ultrapure water. By installing this ultrafiltration membrane device at or near the end of the subsystem in the ultrapure water production device, it is possible to provide ultrapure water with a small number of fine particles.

In the semiconductor manufacturing industry, silicon wafers are washed using ultrapure water from which impurities are highly removed. Ultrapure water generally removes some of the suspended substances and organic substances contained in raw water (river water, groundwater, industrial water) in the pretreatment process, and then removes the treated water in the primary pure water system and secondary water. Manufactured by sequential processing in a pure water system (subsystem) and supplied to use points for wafer cleaning. The ultrapure water production apparatus is generally equipped with a filtration membrane apparatus for removing fine particles, bacteria, colloids, polymer compounds and the like from the ultrapure water.

As a filtration membrane device used for removing fine particles and the like from ultrapure water, an ultrafiltration membrane (UF membrane) and a microfiltration membrane (microfiltration membrane) are used. The ultrafiltration membrane is a dense layer on the surface of the membrane that removes fine particles and polymer substances. The filtration performance of the ultrafiltration membrane is defined by the molecular weight cut-off value. This fractionated molecular weight indicates the molecular weight at which an inhibition rate of 90% can be obtained when an index substance having a known molecular weight is filtered. On the other hand, the precision filtration membrane is formed as a porous membrane, and fine particles are removed not only on the surface of the membrane but also inside the membrane (inside the pores of the porous structure), and the filtration performance is about 99%. It is defined by the "rated filtration accuracy" by the particle size of the standard particles of. (Non-Patent Document 1)

Patent Document 1 includes a primary pure water production device and a secondary pure water production device as subsystems, and provides a degassing device for reducing dissolved oxygen in the treated water to stabilize the water quality. An ultrafiltration membrane device is placed at the end of the secondary pure water production device to supply ultrapure water to the point of use, and the remaining ultrapure water used is circulated to the primary pure water production device. Ultrapure water production equipment is disclosed.
The fractional molecular weight of the ultrafiltration membrane used in the ultrapure water production equipment is in the range of several thousand to tens of thousands.

Patent Documents 2 and 3 disclose a method for directly measuring fine particles in ultrapure water, and Patent Document 4 discloses a method for evaluating the particle removal performance of a filter.
On the other hand, regarding the distribution of fine particles contained in ultrapure water, Non-Patent Document 1 describes the relationship between the particle size (for example, diameter) and the number of particles in relation to the number of particles being "1 / (particle size) ³ ". It is stated that there is a report that the number of particles increases as the particle size decreases, such as being distributed exponentially, and further, even if the number concentration of small particles is not measured, for example, it is more than 0.1 μm. It has been proposed to estimate the number concentration of smaller particles by measuring the number concentration of larger particles.

Japanese Unexamined Patent Publication No. 06-31275 Japanese Unexamined Patent Publication No. 09-276672 JP-A-2007-701126 Japanese Unexamined Patent Publication No. 2013-31835

"Clean Technology", Nihon Kogyo Shuppan, May 2003, pp. 70-74

Regarding the distribution of fine particles in ultrapure water, Non-Patent Document 1 suggests that the number of fine particles increases at a large rate as the particle size decreases, and a considerable number of particle sizes are found in ultrapure water. Fine particles smaller than 50 nm (sub-50 nm fine particles) may be contained. On the other hand, a particle counter for measuring sub-50 nm fine particles is also provided, but the reliability in measuring sub-50 nm fine particles in ultrapure water is still in the verification stage. Therefore, at present, there are no detailed reports of experimental values and measured values regarding the distribution of sub-50 nm fine particles contained in ultrapure water. In this way, when there is not enough information about the distribution of sub-50nm fine particles in ultrapure water, when the ultrapure water contains sub-50nm fine particles, the sub-50nm fine particles are reduced to the required standard. The effectiveness of the ultrafiltration membrane and the technical issues in removing sub-50 nm fine particles from ultrapure water by the ultrafiltration membrane have not been focused on so far, and even these points have been examined. I wasn't. That is, sufficient information on what kind of ultrafiltration membrane and what kind of ultrafiltration membrane device is effective for removing sub-50 nm fine particles from ultrapure water has not yet been obtained.

An object of the present invention is a method for preparing an ultrafiltration membrane that can achieve high performance and high reliability of the ultrafiltration membrane by a simple method, and water using the ultrafiltration membrane prepared by such a preparation method. The purpose is to provide a processing method. A further object of the present invention is to provide an ultrafiltration membrane device having an ultrafiltration membrane prepared by such a preparation method, having high performance and high reliability, and capable of suppressing costs. ..

The ultrafiltration membrane device according to the present invention is an ultrafiltration membrane device used in a subsystem of an ultrapure water production device, and is an ultrafiltration membrane device to which spherical fine particles having a size selected from the range of 5 nm to 500 nm are added. have a filtration membrane, the fine particles, gold particles having a size selected from the ultrafiltration membrane of fractionation molecular weight largest component in the pore size distribution of the ultrafiltration membrane based on holes of the hole larger than the diameter, polystyrene It is characterized by being at least one of latex particles and silica particles .
The ultrapure water production apparatus according to the present invention is characterized in that an ion exchange apparatus and the above-mentioned ultrafiltration membrane apparatus are provided after the ion exchange apparatus.
The method for producing an ultrafiltration membrane according to the present invention is to pass preparation water containing fine particles through an ultrafiltration membrane used in a subsystem of an ultrapure water production apparatus to add the fine particles to the ultrafiltration membrane. This is a method for producing an ultrafiltration membrane having improved particle-removing performance, wherein the fine particles have a pore size distribution of the ultrafiltration membrane based on the fractional molecular weight of the ultrafiltration membrane from the range of 5 nm to 500 nm. gold particles having a size selected from the most a significant percentage holes of the hole larger than the diameter, polystyrene latex particles, at least one of the silica particles is selected, the preparation water is to disperse the fine particles in pure water or ultrapure water It is characterized in that it is prepared by.
In the method for producing ultrapure water according to the present invention, the water to be treated is ion-exchanged by an ion exchange device and the ion exchange treatment is performed by the above-mentioned ultrafiltration membrane device provided after the ion exchange device. It is characterized by including a step of filtering the water to be treated.

According to the method for preparing an ultrafiltration membrane and the water treatment method according to the present invention, high performance of the ultrafiltration membrane can be achieved by a simple treatment of adding fine particles to the ultrafiltration membrane. By using an ultrafiltration membrane device having an ultrafiltration membrane prepared by this preparation method, it is possible to provide an ultrafiltration membrane device having high performance, high reliability, and cost reduction. ..

It is a figure which shows typically an example of the apparatus which performs the treatment with the preparation water of the ultrafiltration membrane which concerns on this invention. It is a figure which shows typically an example of the ultrafiltration membrane apparatus in the case of performing the treatment with the preparation water of the ultrafiltration membrane which concerns on this invention in the ultrafiltration membrane apparatus. It is a flow figure for demonstrating one Embodiment of the structure of the ultrapure water apparatus.

The method for preparing an ultrafiltration membrane according to the present invention includes a step of adding fine particles to the membrane surface of the ultrafiltration membrane.

By adding fine particles to the membrane surface of the ultrafiltration membrane and adhering and / or fixing the added fine particles to the membrane surface of the ultrafiltration membrane, it is possible to improve the particle removal performance of the ultrafiltration membrane. it can. The present inventors consider that the improvement of the particle removal performance of this ultrafiltration membrane is due to the following reasons.
The molecular weight cut-off is generally used as an index of the separation performance of the ultrafiltration membrane. The fractionated molecular weight is determined from the molecular weight corresponding to a blocking rate of 90% by permeating a standard substance having a known molecular weight. That is, an ultrafiltration membrane having a molecular weight cut off of 5000 can capture 90% of a substance having a molecular weight of 5000. The pore size of the ultrafiltration membrane is not completely uniform and usually has a variation including the main pore size that defines the molecular weight cut-off. The holes having the main pore diameter occupy the largest proportion in the pore size distribution, but if there are holes larger than the main pore diameter, fine particles of the size to be removed may pass through the holes and cannot be removed. That is, there is a possibility that a substance having a molecular weight larger than the specified fractional molecular weight will not be captured. Therefore, by closing such large pores with fine particles, the integrity of the ultrafiltration membrane can be improved, the particle removal performance can be improved, and the reliability of the ultrafiltration membrane can be improved. Furthermore, when water is passed through the ultrafiltration membrane, the probability that water will pass through larger pores is increased, that is, the ease of water passage of the micro-ultrafiltration membrane is distributed on the membrane surface, and more. It is considered that the flow of water around the large hole is likely to be formed. Therefore, when the preparation water containing the pore-closing fine particles is passed through the ultrafiltration membrane, the probability that the pore-closing fine particles are supplied to the large pores increases, and the large pores can be efficiently closed. It is believed that there is.

As described above, the pore-closing fine particles close some of the many pores of the ultrafiltration membrane to improve integrity (close the large pore diameter in the dense layer on the membrane surface of the ultrafiltration membrane, and the fine particles. It is used for the purpose of improving the particle removal performance (elimination rate) and reducing the number of defective parts that cause leaks.
The type of pore-closing fine particles is not particularly limited, and can be appropriately selected depending on the target ultrafiltration membrane and its intended use. In particular, when applied to an ultrafiltration membrane device installed at or near the end of an ultrapure water system, low elution is required. Therefore, it is preferable to use spherical synthetic particles having a small amount of elution in order to obtain the desired effect by adding as little fine particles as possible. Further, it is preferable that the particles are monodisperse or close to monodisperse (substantially monodisperse) in order to control the preparation conditions such as the addition rate of the pore closing fine particles to the film.
Examples of the pore closing fine particles include gold particles (gold colloid), PSL (polystyrene latex) particles, silica particles and the like.

The size of the pore-closing fine particles can be set according to the molecular weight cut-off of the ultrafiltration membrane and the particle removal performance desired in the filtration process. It is selected from those having a size based on the fractional molecular weight of the ultrafiltration membrane according to the size of the fine particles in the water to be removed, for example, a size larger than the size (pore diameter) of the main pore of the ultrafiltration membrane. Pore closing fine particles having a different size can be selected and used.
Further, the pore-closing fine particles shall be determined by experimentally confirming the particle removal rate (exclusion rate) of the particles to be removed in the water to be treated before and after the addition of the pore-closing fine particles to the ultrafiltration membrane. You can also. Specifically, first, using the fractionated molecular weight of the ultrafiltration membrane as a guide, select an ultrafiltration membrane that can obtain the desired particle removal performance (removal rate of fine particles to be removed from the water to be treated). , The particle removal rate (R1) of the fine particles to be removed by the selected ultrafiltration membrane is determined by passing water to be treated. Next, after adding the pore-closing fine particles to the ultrafiltration membrane, water to be treated is passed to determine the particle removal rate (R2) of the ultrafiltration membrane after the pore-closing fine particles are added. In this way, R1 and R2 are sorted according to the type and size of the pore closing fine particles, and an experiment is performed to select the pore closing fine particles in which R2> R1.

When an ultrafiltration membrane having a molecular weight cut-off of 5000 to 7000 is used, the size of the fine particles for pore closure is in the range of 5 nm to 500 nm, and the exclusion rate is improved in the target fine particle size after the addition of the fine particles for pore closure. You can choose the size to achieve. In this case, the lower limit of the size of the fine particles for closing the pores is preferably 10 nm, and the upper limit of the size of the fine particles for closing the pores is preferably 100 nm, more preferably 50 nm, and even more preferably 30 nm. The size of the fine particles referred to here is an average particle size, and it is preferable to use one having a particle size width (CV) of 15% or less.
By setting the addition rate of the fine particles for pore closure to the ultrafiltration membrane to 10% (area ratio) or less with respect to the membrane area, the particle removal performance is improved and the cake filtration state is not formed. , Preferred for suppressing a significant increase in differential pressure during water flow. The addition rate of the fine particles for closing the pores can be set to a value of 0.01% or more, preferably 0.1% or more, and more preferably 0.5% or more. The addition rate of the pore-closing fine particles to the membrane area is the ratio of the total projected fine particle projected area to the membrane area when it is assumed that the fine particles are a single sphere having a diameter of the fine particles and adhere to the membrane surface as a single layer. ..

The fine particle addition rate can be calculated by the following formula (1) based on the number of fine particles added to the membrane surface of the ultrafiltration membrane.
Fine particle addition rate = [Area occupied by fine particles on the membrane surface obtained from the amount of fine particles added (number)] / [Area of the membrane surface of the ultrafiltration membrane] x 100% ... Equation (1)
The amount of fine particles added (number) can be obtained from the concentration of fine particles in the preparation water x the cumulative amount of water flow in the preparation water (water flow per unit time x time), and the area occupied by the fine particles on the film surface is calculated by the following formula. It can be obtained by (2).
Amount of fine particles added (number) x projected area of each fine particle on the film surface ... Equation (2)
The projected area S of each spherical fine particle is S = π (L / 2) ² (L = diameter of the spherical fine particle).

The preparation water may contain fine particles smaller than the size of the pore closing fine particles. The small particles pass through the ultrafiltration membrane and are discharged. It does not affect the particle removal performance of the ultrafiltration membrane after treatment. However, in order to prevent the fine particles contained in the preparation water from flowing out into the treated water from the ultrafiltration membrane, the small fine particles adhering to the membrane or the secondary side of the ultrafiltration membrane are washed or blown before use. It is preferable to discharge in advance by treatment. On the other hand, even if the preparation water contains fine particles larger than the size for closing the pores, it does not matter because the larger pores can be closed.

To specify the size of the pore closing fine particles, those usually used in the art when handling the fine particles may be used, and if the fine particles are spherical, the diameter thereof can be used.

The preparation water for adding the pore-closing fine particles to the ultrafiltration membrane can be prepared by dispersing the pore-closing fine particles in water. The water for obtaining the water for preparation can be selected according to the grade of the water to be ultrafiltered. For example, if the water to be ultrafiltered is pure water or ultrapure water, it is preferable to use pure water or ultrapure water as the water for obtaining the water for preparation. The concentration of the pore-closing fine particles in the preparation water may be set so that the fine particle addition rate with respect to the target membrane area can be obtained. For example, it can be selected from the range of 10 ² to 10 ¹⁵ pieces / ml, preferably 10 ³ to 10 ¹³ pieces / ml.
The cumulative amount of water flowing to obtain the pore-closing effect on the ultrafiltration membrane of the preparation water containing the pore-closing fine particles may be set so that the desired pore-closing effect can be obtained, and the above-mentioned addition rate is used. It is preferable to set the fine particles for pore closure based on the concentration in the preparation water, the water flow time, the flow velocity, and the like so as to be achieved.

Preparation by adding the pore-closing fine particles to the ultrafiltration membrane should be performed in advance by installing the ultrafiltration membrane in the preparation device and before installing the ultrapure water production device in the ultrafiltration membrane device. Can be done.

FIG. 1 shows an example of a preparation device. The preparation device of FIG. 1 is a supply system for supplying preparation water from the treatment unit 4, the storage tank 2-1 of the preparation water, and the storage tank 2-1 in which the ultrafiltration membrane module 1 is detachably installed. 2-2, has a discharge system 3 that discharges the filtrate from the processing unit 4 to a recovery system (not shown). The supply system 2-2 has a pipe and a valve and a pump arranged in the middle of the pipe. A supply system 2-4 is provided so as to be switchable from the supply system 2-2, and the filling liquid can be supplied from the filling liquid storage tank 2-3 to the ultrafiltration membrane module 1.
In the illustrated example, the ultrafiltration membrane module 1 and the supply system 2-2 are detachably connected to each other via the stopper 1-1, and the discharge system 3 is detachably connected to the outlet system 2 via the stopper 1-2. After the treatment is completed, the ultrafiltration membrane module 1 sealed with the stoppers 1-1 and 1-2 closed and filled with the filler can be taken out from the processing unit 4.

The ultrafiltration membrane module 1 is installed in the processing unit 4, connected to the supply system 2-2 and the discharge system 3, the stoppers 1-1 and 1-2 are opened, and the storage tank 2-1 to the supply system 2-2. Then, the water for preparation is supplied to the primary side 1A of the ultrafiltration membrane module 1. The filtrate from the secondary side 1B is discharged via the discharge system 3. When the desired amount of fine particles added on the primary side membrane surface of the ultrafiltration membrane is obtained, the supply of the preparation water to the primary side of the ultrafiltration membrane is stopped. The supply system 2-2 is switched to the supply system 2-4, and the filling liquid is passed from the storage tank 2-3 to the ultrafiltration membrane module. With the preparation water in the ultrafiltration membrane module 1 replaced with the filler, the stoppers 1-1 and 1-2 are closed and sealed, and the treated ultrafiltration membrane module is used in the subsystem of the ultrapure water production apparatus. It can be used for removing fine particles.

The packing solution is for preventing the membrane from drying, and a chemical solution such as pure water or formalin (formamide aqueous solution) can be used. A chemical solution such as formalin can be used for long-term storage of the treated ultrafiltration membrane module, and the formamide concentration of formalin can be about several thousand ppm. Pure water may be used as the packing liquid, and water may be passed through the ultrafiltration membrane module to perform a cleaning treatment for removing small particles permeated through the secondary side 1B from the ultrafiltration membrane module.

The ultrafiltration membrane module can be a cartridge type having a structure in which the ultrafiltration membrane is housed in a sealable container and can be detachably installed in the ultrafiltration membrane device. This cartridge type ultrafiltration membrane module is treated with preparation water by the preparation device as described above, filled and sealed with the filler, stored, transported, etc., and then the ultrapure water production device is limited. It can be used by installing it in a filtration membrane device. Further, as the membrane module, various membrane modules such as a tubular type, a spiral type, and a monolith type can be used in addition to the hollow fiber type.
The treatment with the preparation water in the apparatus shown in FIG. 1 is a total filtration treatment, but the ultrafiltration membrane module is configured so that the concentrated water can be taken out, and the preparation water is supplied to the ultrafiltration membrane by cross flow. , Filtration conditions for taking out concentrated water may be adopted. The concentrated water for preparation can also be returned to the storage tank for reuse using the circulation system. This point is the same in the treatment in the ultrafiltration membrane device shown in FIG. 2, which will be described later.

The ultrafiltration membrane using the ultrafiltration membrane to which fine particles are added by the preparation method according to the present invention is, for example, at or near the end of a subsystem of an ultrapure water production apparatus as disclosed in Patent Document 1. It can be suitably used for the provided ultrafiltration membrane device.

In the water treatment method of the water to be treated according to the present invention, a preparation step of passing the preparation water containing fine particles through the ultrafiltration membrane to add the fine particles to the ultrafiltration membrane and the preparation step were performed. After that, the step of passing water to be treated through the ultrafiltration membrane is included.
In the above preparation step, the ultrafiltration membrane is attached to the first device for passing the preparation water containing fine particles through the ultrafiltration membrane, and the preparation water is applied to the ultrafiltration membrane attached to the first device. It can be a process of passing water. As the first device, the preparation device shown in FIG. 1 can be used.
In the step of passing the water to be treated through the ultrafiltration membrane, the preparation water was passed through the ultrafiltration membrane attached to the first apparatus in the preparation step, and then the ultrafiltration membrane was attached to the first apparatus. The ultrafiltration membrane is removed from the first device, and the ultrafiltration membrane removed from the first device is attached to a second device for producing ultrapure water from water to be treated, and a second device is used. The step may be a step of passing water to be treated through the ultrafiltration membrane mounted on the apparatus.

As shown in one embodiment of FIG. 2, the preparation by the addition treatment of the pore-closing fine particles to the ultrafiltration membrane is performed in the form in which the preparation device is added in front of the ultrafiltration membrane device of the ultrapure water production device. You can also do it. The illustrated ultrafiltration membrane device is for supplying the ultrafiltration membrane module 1, the water supply system 6 to be treated, the water storage tank 5 to be treated, the water storage tank 2 for preparation, and the treated water to the use point. It has a discharge system 3A and a concentrated water extraction system 3B. Prior to the main operation of processing the water to be treated with the ultrafiltration membrane module 1, the switching bubble is adjusted to connect the ultrafiltration membrane module 1 and the preparation water supply system, and the concentrated water extraction system 3B is closed. In this state, the water for preparation in the storage tank 2 is supplied to the primary side of the ultrafiltration membrane module 1 to pass water through the ultrafiltration membrane. The preparation water that has passed through the ultrafiltration membrane is discharged from a blow (not shown) branched from a discharge system provided on the secondary side of the ultrafiltration membrane device. When the desired addition amount of the fine particles contained in the preparation water is obtained on the membrane surface of the ultrafiltration membrane, the flow of the preparation water is stopped and the preparation process is completed. The water supply system for preparation is switched to the water supply system to be treated, and the water to be treated is introduced into the ultrafiltration membrane module 1 from the storage tank 5 to perform particle removal treatment.
If a predetermined time after switching from the water supply system for preparation to the water supply system to be treated is used for the cleaning process and small fine particles are permeated and exist on the secondary side of the ultrafiltration membrane module 1. , This may be removed by a cleaning treatment and discarded by a separately provided discharge system (not shown). Alternatively, a cleaning water supply system (not shown) for supplying cleaning water, for example, ultrapure water to the primary side of the ultrafiltration membrane module 1 is separately installed, and the water to be treated is supplied from the preparation water supply system. At the time of switching to, cleaning may be performed before switching to the water supply system to be treated.
In the main operation of the ultrafiltration membrane device shown in FIG. 2, the concentrated water extraction system 3B may be used when extracting concentrated water, and the concentrated water extraction system 3B may be closed when performing a total filtration operation.

The ultrafiltration membrane to be prepared is not particularly limited, and can be selected according to the type of water to be treated such as clean water, industrial water, pure water, and ultrapure water, and the purpose of filtration. In particular, it is preferably applied to an ultrafiltration membrane device installed at or near the end of an ultrapure water system. As such ultrafiltration membranes, for example, Asahi Kasei Chemicals (OLT-6036H) and Nitto Denko (NTU-3306-K6R) can be mentioned as ultrafiltration membrane modules for plants. Both are hollow fiber membrane modules made of polysulfone having a molecular weight cut off of 6000.
The ultrafiltration membrane using the ultrafiltration membrane to which fine particles are added by the preparation method according to the present invention is, for example, at or near the end of a subsystem of an ultrapure water production apparatus as disclosed in Patent Document 1. It can be suitably used for the provided ultrafiltration membrane device.

FIG. 3 shows a flow chart of an embodiment of an ultrapure water production apparatus incorporating the ultrafiltration membrane apparatus of the present invention. The apparatus shown in FIG. 3 has a primary pure water system 41 and a secondary pure water system 42 (subsystem) connected to the downstream side thereof.
The secondary pure water system 42 includes an ultraviolet oxidizing device 44 (indicated by UV in the figure), a strongly acidic cation exchange resin, and a strongly basic anion exchange resin on the downstream side of the pure water storage tank 43 for storing the primary pure water. A one-tower non-regenerative ion exchange device 45 (indicated by CP in the figure), a membrane degassing device 46 (indicated by MD in the figure), and an ultrafiltration membrane device 47 (indicated by UF in the figure). , It is installed so that water can flow in this order. As the ultrafiltration membrane device 47, the ultrafiltration membrane device of the present invention is incorporated. The ultrapure water from the ultrafiltration membrane device 47 is supplied to use point 48. In the secondary pure water system 42, continuous circulation operation is performed, and a part of the obtained ultrapure water is sent to the use point 48 and the rest is circulated to the pure water storage tank 43. Between the ultraviolet oxidizing device 44 and the non-regenerative ion exchange device 45 in the subsequent stage, between the non-regenerative ion exchange device 45 and the membrane degassing device 46 in the subsequent stage, the membrane degassing device 46 and the subsequent stage. If necessary, another device may be installed between the ultrafiltration membrane device 47 and the device.

Further, the primary pure water system 41 may be configured to obtain the desired primary pure water. For example, water from which suspended substances, a part of organic substances, etc. have been removed by a pretreatment system is introduced, and the water thereof is introduced. A system can be used to obtain primary pure water by removing most of the ions, nonionic substances, dissolved gas, etc. in water.
The particle removal performance of the ultrafiltration membrane obtained by the preparation method according to the present invention can be confirmed by a particle counter, a direct measurement method disclosed in Patent Documents 2 and 3, or the like, depending on the size of the fine particles.
According to the preparation method of the present invention, high performance and high reliability can be achieved even when an ultrafiltration membrane having a proven track record in conventional filtration is used. In addition, since the preparation process can be performed by a simple method for commercially available ultrafiltration, the cost for installing and replacing the ultrafiltration membrane can be kept low.

According to the preparation method of the present invention, the integrity of the ultrafiltration membrane can be improved and the particle removal rate can be increased by adding fine particles for closing pores to the ultrafiltration membrane. In particular, it is possible to provide an ultrafiltration membrane that is effective in removing sub-50 nm fine particles in ultrapure water.
In the ultrafiltration treatment using ultrapure water containing fine particles as the water to be treated, fine particles having a pore-closing effect in the water to be treated are formed after a certain period of time has elapsed from the start of water flow through the ultrafiltration membrane of the water to be treated. If it is contained, the effect of improving the particle removal performance according to the present invention can be expected. However, the filtration performance does not improve within the time until the large pores are closed, and the type of fine particles in the ultrapure water and the distribution regarding the size and number thereof depend on the type of ultrapure water and its production method. Since it fluctuates and the type of ultrafiltration membrane is also set according to the purpose of filtration, the water flow time until the effect of closing the large pores is obtained differs depending on the water flow treatment. Moreover, the membrane area of the ultrafiltration membrane used industrially is very large, and the water flow time is long when the particle removal performance is not improved.
On the other hand, in the present invention, the improvement of the particle removal performance is obtained with good reproducibility by surely adding the pore-closing fine particles to the ultrafiltration membrane under preset conditions, which is normal. This is significantly different from the ultrafiltration treatment of ultrapure water containing fine particles.

Example 1
A small module in which the hollow fiber membrane of the polysulfone hollow fiber type ultrafiltration membrane module having a fractionated molecular weight of 6000 was set was prepared, and the particle size was specified in ultrapure water from the primary side (outside) of the hollow fiber membrane. The preparation water to which gold particle (gold colloid) reagent (average particle size 10 nm, particle size width (CV) less than 10%) is added and dispersed is passed through, and the fine particle removal rate of the water to be treated is adjusted with respect to the addition rate of gold particles. It was measured. The gold concentration contained in the preparation water was about 1 ppb. Water was passed under all dead-end filtration conditions. The addition rate of gold particles to the film area was calculated by the equations (1) and (2) shown above based on the cumulative water flow at each time point.
The permeate (water permeating the inside of the hollow fiber membrane) from the ultrafiltration membrane was collected, and the gold concentration in the permeate was measured by ICP-MS analysis. The removal rate (exclusion rate) of gold particles in the ultrafiltration membrane was determined from the gold concentrations at the inlet and outlet of the ultrafiltration membrane (see Patent Document 4).
Table 1 shows the relationship between the particle addition rate of gold particles and the particle removal rate of gold particles. As the gold particles were added to the ultrafiltration membrane (the particle addition rate increased), the particle removal rate increased. The ultrafiltration membrane having a molecular weight cut-off of 6000 can sufficiently eliminate particles having a fraction of 10 nm (exclusion rate of 90% or more). That is, the main pore diameter is smaller than 10 nm. However, the slight leakage of gold particles to the secondary side of the ultrafiltration indicates that the ultrafiltration membrane has a pore size distribution and at least has pores through which 10 nm particles can pass (). Imperfections). According to this embodiment, by adding 10 nm particles (gold particles) to the ultrafiltration membrane, the pores through which the 10 nm particles can pass are blocked (the larger the particle addition rate, the more pores are blocked). It was confirmed that the particle removal rate was increased. The gold particle (gold colloid) reagent has a particle size distribution, and even if it is defined as 10 nm, there are particles larger than 10 nm. The large particles can block the pores in the ultrafiltration membrane through which the 10 nm particles can pass. Further, even 10 nm particles may be trapped in the pores through which the 10 nm particles can pass, and the pores through which the 10 nm particles can pass can be closed. As a result, it was confirmed that the particle removal performance (particle removal rate of fine particles) of the ultrafiltration membrane was improved by adding particles to the ultrafiltration membrane. At this time, no obvious decrease in flux was observed.

1 Ultrafiltration membrane module 1
1-1, 1-2 Plug 2-1 Storage tank for preparation water 2-2 Supply system for preparation water 2-3 Storage tank for filling liquid 2-4 Supply system for filling liquid 3 Discharge system 4 Treatment unit

Claims (6)

A ultrafiltration membrane apparatus used in the subsystem of ultrapure water production apparatus, have a ultrafiltration membrane by adding a fine spherical size is selected from a range of 5 nm to 500 nm,
The fine particles are gold particles, polystyrene latex particles, and silica particles having a size selected from the pore diameters or more that occupy the largest proportion in the pore size distribution of the ultrafiltration membrane based on the fractional molecular weight of the ultrafiltration membrane. An ultrafiltration membrane device characterized by being at least one of them . An ultrapure water production apparatus provided with an ion exchange device and an ultrafiltration membrane device according to claim 1 after the ion exchange device. The ultrapure water production apparatus according to claim 2, wherein the ultrafiltration membrane apparatus is installed at the end of a subsystem. Ultrafiltration with enhanced particle removal performance, in which preparation water containing fine particles is passed through the ultrafiltration membrane used in the subsystem of the ultrapure water production equipment to add the fine particles to the ultrafiltration membrane. It is a method of manufacturing a membrane.
The fine particles are gold particles and polystyrene having a size selected from the pore diameters of 5 nm to 500 nm, which occupy the largest proportion in the pore size distribution of the ultrafiltration membrane based on the fractional molecular weight of the ultrafiltration membrane. At least one of latex particles and silica particles is selected,
Method of manufacturing a ultrafiltration membrane with enhanced particle removal performance, wherein the preparation water is those prepared by the fine particles were dispersed in pure water or ultrapure water. The step of ion-exchange processing the water to be treated with an ion exchange device and the filtration treatment of the water to be treated with the ultrafiltration membrane device according to claim 1 provided after the ion exchange device. An ultrapure water production method including a step to be performed. The ultrapure water production method according to claim 5 , wherein the ultrafiltration membrane device is installed at the end of a subsystem.

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