JPS62221489A - Method for making pure water - Google Patents

Abstract

PURPOSE:To easily prepare high quality pure potable water, by treating general tap water with a reverse osmosis membrane and subsequently contacting treated tap water with one surface side of a hydrophobic polymer porous membrane at predetermined temp. as raw water. CONSTITUTION:Raw water with predetermined temp. is introduced into a raw water passage 3 and the steam generated from raw water transmits through a membrane pipe 2 to reach a steam space 10. Said steam is cooled on the surface of a heat transfer pipe 9 to generate transmitted water which in turn flows down along the surface of the heat transfer pipe to be guided to the outside of the apparatus from a transmitted lead-out pipe 13. Tap water is supplied to a reverse osmosis membrane apparatus through an appropriate pipeline before subjected to thermo-pervaporation treatment to mainly remove a carbonic acid component and a surface active substance in said membrane apparatus and heated to predetermined temp. by a heater. By this method, the hydrophilicity of a hydrophobic membrane is held over a long period of time and, a suspended substance and a dissolved substance are perfectly removed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method and apparatus for producing pure water from general tap water, and more specifically, to purify general tap water by treating general tap water by a so-called thermopervaporation method. The present invention relates to a method of producing water that can easily produce high-quality pure water by simply including a step of subjecting general tap water to a reverse osmosis membrane treatment as a pretreatment.

(Prior Art) Various methods for producing pure water using general tap water as raw water have been proposed and put into practical use. As such a method, for example, prefiltration of general tap water as raw water,
A method of ion exchange treatment, distillation, and further filtration is known. Such a method usually results in a conductivity of 1.0.
Pure water of μS/cry or less can be obtained. Depending on the use of pure water, further processing may be added, for example,
When producing pure water for medical purposes, it may be treated with chemicals or sterilized with ultraviolet light.

In the present invention, general tap water usually refers to river water, well water,
Including tap water, industrial water, pharmacopoeia regular water, etc., and generally contains Ca
Cations such as 1M g-, Na% K, anions such as chlorine ions, sulfate ions, bicarbonate ions, organic substances decomposed by living organisms, dissolved gases such as oxygen, carbon dioxide, nitrogen, chlorine, ammonia, etc. Contains dissolved substances, inorganic and organic particles, and suspended substances such as microorganisms as impurities. In addition, in the present invention, pure water generally refers to, for example, water used for preparing standard solutions for analytical instruments, cleaning instruments, culturing microorganisms, etc., water for boilers, water specified by the Japanese Pharmacopoeia, etc. Purified water for syringes, distilled water,
Includes hospital water such as sterile water.

According to the conventionally known method of producing pure water from general tap water, in order to remove various impurities with different properties as described above, basically ion exchange is used to remove inorganic substances. , distillation, membrane separation, etc., as well as filtration to separate microorganisms and fine particles, and in addition to these separation operations, various pre-treatments and post-treatments are added to complete the entire pure water production process. It consists of

However, producing pure water through a large number of steps as described above not only increases production costs, but also makes it difficult to maintain and manage the production equipment. Moreover, such a multi-step method requires storage of the treated water between each step, and there is a risk that microorganisms will grow during storage.

(Objective of the Invention) As a result of intensive research to solve the above-mentioned problems in the production of pure water from general tap water, the present inventors have found that, in particular, dissolved gases and volatile substances contained in general tap water are If this amount is large, it may partially permeate through the separation membrane in thermopervaporation treatment and mix into the permeated water as pure water, reducing its quality. If substances with such properties (hereinafter referred to as surfactants) are included, they will be used during long-term thermopervaporation treatment.
This will reduce the hydrophobicity of the hydrophobic porous membrane used, and some of the general tap water will be mixed into the permeated water, which will also reduce the quality of the pure water obtained. It has been found that if the active substance is removed in advance by reverse osmosis membrane treatment, all other (7) impurities can be removed by thermopervaporation. Thus, the present inventors removed dissolved gases, volatile substances, surfactants, or substances having such properties from general tap water by reverse osmosis membrane treatment as a pretreatment, and then performed thermopervaporation. It has been discovered that pure water having a quality equal to or higher than that of the conventional method described above can be produced very easily and economically by processing with
This led to the present invention.

(Structure of the Invention) A method for producing pure water according to the present invention includes: (a) a first step of treating common water with a reverse osmosis membrane; and (b) the above-mentioned first step. The normal tap water that has passed through the process is brought into contact with one side of a hydrophobic polymer porous membrane that allows water vapor to pass through but does not allow water to pass through as raw water at a predetermined temperature, and water vapor is generated from this raw water, which is then transferred to the above porous membrane. It is characterized by including a second step of permeating through the other side of the membrane, cooling and condensing it to obtain condensed water as pure water.

Volatile components and dissolved gases cannot be sufficiently removed even by the thermopervaporation method described below, and some of them are mixed into the permeated water obtained as pure water by the thermopervaporation method, and some of them dissociate. This causes a decrease in the specific resistance, leading to a decrease in the quality of pure water. In the present invention, volatile components refer to components that generate gas when heated, particularly carbon dioxide gas, hydrogen carbonate ions (HC
O:l-) and carbonic acid (HzCO+) (hereinafter, these may be referred to as carbonic acid components). These are contained in particularly large amounts in common tap water compared to other volatile components, and are usually contained in approximately several tens of ppm. Volatile components other than carbonic acid components and dissociative dissolved gases are, for example,
Ammonia, chlorine, etc., which are normally only contained in very small amounts in general tap water. In addition, carbonate ion (Coal
"-) does not generate carbon dioxide gas even when heated. In this way, when general tap water containing carbonic acid components is treated by the thermopervaporation method, there is no carbon dioxide in the permeated water.
Contains a carbonic acid component at a concentration of 5 ppm or more, and has an electrical conductivity of more than 1 μS/cm.

The carbonic acid component in general tap water is C02 or H, CO+ IC0, - each + co3"-
Heating shifts the equilibrium to the left and generates carbon dioxide, which cannot be removed even by thermopervaporation.

In the method of the present invention, as a first step, the above-mentioned dissolved gas and volatile substances, particularly an ionic carbonate component,
Surfactants are removed by reverse osmosis membrane treatment. Here, the reverse osmosis membrane used is used when saline solution with a concentration of 1% is treated at room temperature under a low pressure of 20 kg/cJ or less in order to remove mainly ionic carbonic acid components and surfactant substances contained in general tap water. , it is preferable to have a membrane performance with a salt removal rate of 50% or more, especially 10 kg/cff
Salt removal rate is 50% when treated at pressures below 1
The above reverse osmosis membranes are suitable. Furthermore, general water supply is
Since it generally contains trace amounts of chlorine, it is preferable that the reverse osmosis membrane used has chlorine resistance.

Reverse osmosis membranes having such performance are already commercially available and can be easily obtained.

The reverse osmosis membrane used in the present invention is not particularly limited in terms of the chemical structure or surface condition of its polymer material; However, even if the removal rate of common salt is low, the ionic carbonate component can be particularly removed at a high removal rate, so it is preferably used. However, in the present invention, a reverse osmosis membrane made of an uncharged polymer can also be used.

In addition, in the present invention, the reverse osmosis membrane treatment of general tap water, which is the first step, may be performed multiple times as necessary. Furthermore, in order to obtain high-quality pure water, deaeration and anion exchange treatment of general tap water may be performed to remove carbonate components (and dissolved gases) before or after reverse osmosis membrane treatment, as necessary. It is advantageous to carry out and/or ultrasound irradiation.

Degassing can be done by any conventionally known degassing method, such as aeration,
Examples include heating deaeration, vacuum deaeration, inert gas blowing, and ultrasonic irradiation.

In particular, when general tap water is treated using the thermopervaporation method, the general tap water is heated.
The method of subsequent thermopervaporation treatment is also thermoeconomically advantageous.

Moreover, ultrasonic irradiation is particularly effective in removing carbonic acid components in rise water. For example, 3 W / 1N of general tap water
By irradiating ultrasonic waves of 0.2 MH2 or more at a CO1 or higher for 5 minutes or more, the general tap water is partially turned into a spray state, and the carbonic acid component is effectively removed.

Anion exchange of common tap water is particularly effective in removing carbonic acid components. Of course, conventionally using ion exchange resin,
It is well known that general tap water is treated, but in the past, ion exchange treatment was used to quickly saturate the ion exchange resin because the purpose was to remove all the ions contained in the rise water. , the amount of general tap water treated by a unit amount of ion exchange resin is extremely small. In particular, in conventional methods, anion exchange resins are rarely used alone in the treatment of general tap water, and in most cases they are used in combination with cation exchange resins.

However, in the method of the present invention, non-volatile ions are substantially completely removed by thermopervaporation treatment as the second step, so in anion exchange treatment, anions, which are volatile components, are removed, especially anions. ,
Since it is sufficient to remove only the carbonate component contained in large amounts in general tap water, a large amount of general tap water can be treated with a unit amount of anion exchange resin. Moreover, it has the advantage of not requiring treatment with a cation exchange resin.

The anion exchange resin is not particularly limited as long as it has a cationic dissociable M group.
An anion exchange resin in which the hydroxyl group is ion-exchanged is preferred. However, in the present invention, in addition to the above-mentioned strong base type, if necessary,
Weakly basic anion exchange resins can also be used.

Next, the thermopervaporation method as the second step in the method of the present invention will be explained.

The thermopervaporation method generally involves heating raw water to generate water vapor, and selectively passing this water vapor through a porous membrane made of a hydrophobic polymer.
This is cooled and condensed to obtain permeated water as pure water.

In order to treat general tap water using such a thermopervaporation method, one of the following methods can be used.

The first method is to bring raw water at a predetermined temperature into contact with one side of a hydrophobic polymer porous membrane that allows water vapor to pass through but does not allow water or solutes to pass through, and the other side of this porous membrane is exposed to water from the membrane surface. Heat transfer walls maintained at a predetermined low temperature are provided at appropriate intervals, and water vapor generated from the raw water and transmitted through the porous membrane is cooled by the heat transfer wall soil and condensed to obtain permeated water. .

The second method involves contacting one side of the hydrophobic polymer porous membrane with raw water at a predetermined temperature as described above, and contacting the other side with a predetermined low-temperature cooling medium, such as pure water for cooling. By doing so, water vapor generated from raw water and passed through the porous membrane is directly cooled and condensed with pure water as a cooling medium, and this is obtained in the cooling medium.

In any of the above methods, the polymer porous membrane is
It must be hydrophobic to water, and must have the property of not allowing microorganisms such as molds and fungi to pass through, as well as water itself, but allowing water vapor to pass through.

Therefore, such hydrophobic polymer porous membranes usually have 0.0
It is preferable that it has micropores of about 5 to 50 μm, preferably about 0.1 to 10 μm, and has a porosity of 50% or more. In addition, although the film thickness is not particularly limited,
Usually, it is about 1 μm to 2 Tsuru, preferably about 50 μm to 1 Tsuru.

Therefore, in the present invention, as such a porous membrane, a porous membrane made of a fluororesin such as polytetrafluoroethylene resin is hydrophobic and has excellent heat resistance. Alternatively, it is particularly preferably used because common tap water can be sterilized at high temperature at the same time during membrane treatment. Also preferably used is a porous membrane obtained by extrusion molding a solution or melt of a fluororesin such as vinylidene fluoride resin or ethylene-tetrafluoroethylene copolymer resin. However, when a porous membrane made of a hydrophilic resin such as polysulfone or cellulose resin is coated with a water-repellent resin such as a fluororesin or silicone resin to provide a hydrophobic porous surface,
These resin films can also be used.

Next, a thermopervaporation device suitable for carrying out the second step in the method of the present invention will be described based on the drawings.

FIGS. 1 and 2 show an example of a thermopervaporation device that can be suitably used in the method of the present invention.

That is, the membrane tube 2 made of the above-mentioned hydrophobic polymer porous membrane is coaxially disposed inside the outer tube 1, and the raw water at a predetermined temperature is placed between the outer tube and the membrane tube. A raw water passage 3 is formed. Therefore, the outer tube preferably has heat retaining properties, and is made of resin, for example. A raw water inlet pipe 4 and a raw water outlet pipe 5 are connected to the raw water passage 3, and the raw water heated to a predetermined temperature by a heater 6 installed in these pipes as necessary is passed through the raw water circuit through the pipes 4 and 5. It is circulated and distributed. Raw water is appropriately replenished into the raw water circuit through a supply pipe 8 equipped with a valve 7, and a portion of the raw water is discharged from the raw water circuit as necessary through a discharge pipe (not shown).

A heat transfer tube 9 is further disposed coaxially inside the membrane tube 2, and is spaced at an appropriate distance from the membrane tube so as to have a vapor diffusion space IO between the tube and the membrane tube. It is preferable for the vapor diffusion space to be narrow from the point of view of water vapor condensation efficiency, but if it is too narrow, it will actually create a flow resistance for permeated water, so it is usually preferably about 0.2 to 511 mm. The heat transfer tube is preferably a thin-walled stainless steel tube that has high heat conductivity and is free from ion extraction. This heat transfer tube includes an inlet pipe 1 for the cooling medium.
1 and an outlet pipe 12 are connected, and a cooling medium such as cooling water is circulated within the heat transfer tube.

Further, connected to the vapor diffusion space is an outlet pipe 13 for permeated water that has permeated through the membrane tube, been cooled by the heat exchanger tube, and condensed.

Note that, if the porous membrane constituting the membrane tube has low strength, it may be supported on an appropriate support (not shown). Such a support only needs to be able to reinforce the porous membrane and allow water vapor to pass therethrough, and for example, a woven or nonwoven fabric made of polyamide or a porous tube made of ceramic is preferably used.

Further, as shown in FIG. 3, the thermopervaporation device includes a plurality of membrane tubes 2 disposed inside an outer tube 1, each membrane tube having a heat transfer tube 9 inside, and an outer tube and each membrane tube. The space between the pipe and the pipe may be configured to be the raw water passage 3.

4 and 5 also show an example of a thermopervaporation device for carrying out the first method, and the same parts as in FIG. 1 are given the same reference numerals. That is, the membrane tube 2 is disposed coaxially within the outer tube l, and the raw water passage 3 is formed between the outer tube and the membrane tube, which is the same as the above-mentioned first point.
The device is the same as the one shown in the figure, but in this device, the membrane tube 2
A spacer 14 is disposed inside and in contact with this, and further,
A heat exchanger tube 9 is disposed inside and in contact with this spacer. That is, since the spacer is cooled by the heat transfer tube, the spacer itself forms a cooled vapor diffusion space and also forms a passage for permeated water. Therefore, the steam generated from the raw water and permeated through the membrane tube is cooled by the spacer and the heat transfer tube, and the spacer is communicated with the condensed permeated water outlet tube 13.

This spacer must be porous so that the steam that has passed through the membrane tube can pass through to the heat transfer tube, and must also have permeability in at least a predetermined direction for water that has been cooled and condensed by the heat transfer wall. Furthermore, it is preferable that the material has excellent thermal conductivity. In the illustrated device, the spacer needs to have liquid permeability at least in the vertical direction so that the generated permeated water can flow down in the vertical direction.

Of course, the spacer may be bonded in advance to the porous membrane, the heat exchanger tube surface, or both.

Examples of the spacer include woven fabrics, non-woven fabrics made of 10 to 1000 meshes of natural or synthetic fibers, such as polyethylene, polyester, polyamide, etc.
Carbon fiber cloth, metal mesh, etc. are preferably used. The thickness of the spacer is not particularly limited, but if it is too thick, it will actually reduce the steam condensation efficiency, so normally,
5 cranes or less, particularly preferably in the range of 0.2 to 3 mm. That is, by using a spacer with a small thickness, the interval between the vapor diffusion spaces can be reduced, and at the same time, the efficiency of condensing water vapor and the acquisition rate of permeated water or pure water can be increased.

An inlet pipe 4 and an outlet pipe 5 for general tap water as raw water or permeated water from the first step are connected to the raw water passage 3, and a heater 6 is provided in this pipe as necessary. It is the same as in the previous device that raw water is replenished into the raw water circuit through a supply pipe 8 equipped with a valve 7. Further, the heat exchanger tube is connected to the inlet tube 11 and the outlet tube 12 for the cooling medium, as described above, and the cooling medium is circulated within the heat exchanger tube.

In the thermopervaporation apparatus shown in FIGS. 1 and 2, raw water at a predetermined temperature is introduced into the raw water passage 3, and water vapor generated from the raw water passes through the membrane tube 2 and reaches the steam space 10. The permeated water is cooled on the surface of the heat exchanger tube 9 to generate permeated water, which flows down the surface of the heat exchanger tube and is led out of the apparatus through the passed water outlet tube 13. Microorganisms in the raw water are prevented from permeating through the membrane tube and remain in the raw water.

According to the thermopervaporation device shown in FIG. 4, water vapor generated from raw water permeates through the membrane tube 2, is cooled by the spacer 14 and the heat transfer tube 9, is condensed, and flows down the spacer to increase the temperature of the permeated water. It is led out of the device through a pipe 13.

FIGS. 6 and 7 show an example of another thermopervaporation device that can be suitably used in the method of the present invention, in which the same parts as in FIG. 1 are given the same reference numerals.

A membrane tube 2 made of a hydrophobic polymer porous membrane as described above is disposed coaxially within the outer tube 1, and a raw water passage 3 is formed between the outer tube and the membrane tube. Raw water at a predetermined temperature is passed through the membrane tube, and pure water is passed through the membrane tube as a cooling medium. That is, raw water and pure water as a cooling medium are brought into contact through the membrane tube. An inlet pipe 4 and an outlet pipe 5 for flowing raw water are connected to the raw water passage 3, and similarly, a membrane pipe 2 is connected to the raw water passage 3.
An inlet pipe 11 and an outlet pipe 12 for circulating a cooling medium are also connected to the pipe.

According to this second thermopervaporation device,
Water vapor generated from raw water and permeated through the membrane tube wall is immediately cooled and condensed in pure water as a cooling medium, and is recovered in pure water as a cooling medium.

In the same way as described above, raw water is replenished from the supply pipe 8 as necessary, heated by the heater 6, and then supplied to the pipes 4 and 5.
The cooling medium is circulated through the cooling medium circuit while being cooled to a predetermined temperature by a cooler 14 provided in the cooling medium circuit as necessary, and a part of the cooling medium is circulated through the obtained permeated water. It is taken out of the apparatus from the take-out pipe 15 together with water.

According to this second thermopervaporation device,
Since raw water at a predetermined temperature and pure water as a cooling medium are brought into direct contact through the membrane tube, the water vapor generated from the raw water is immediately cooled and condensed by the pure water as a cooling medium. Collected in pure water. Therefore, not only is the vapor permeation rate high, but it can also be made smaller than a thermopervaporation device that provides a vapor space between the membrane tube and the heat transfer wall, and the effective membrane area per unit volume is large, making it highly efficient. You can easily obtain pure water.

Although not shown, as a modification of the thermopervaporation device shown in FIG. may be formed to form a raw water passage.

In addition, in the case of any of the above-mentioned thermopervaporation devices, the present invention has been described in detail assuming that raw water is passed through the raw water passage 3 between the outer tube and the membrane tube, and a cooling medium is circulated within the membrane tube. However, it goes without saying that the cooling medium may be passed through the raw water passage, while the raw water may be made to flow through the cooling medium passage.

In addition, when a thermopervaporation device has a spacer between the membrane tube and the heat transfer tube, the spacer itself is also cooled by the low-temperature heat transfer wall, so the vapor that has passed through the membrane is absorbed by the spacer and the heat transfer wall. It is immediately cooled and condensed, and as a result, the condensation rate of the steam increases, making it possible to obtain pure water with high efficiency.

In addition, in all of the illustrated thermopervaporation devices, the raw water passage or the cooling medium passage is formed in an annular shape. , at least one pair are arranged facing each other with or without a vapor diffusion space therebetween;
By enclosing each passage in a suitable container corresponding to the outer tube and connecting a circuit for circulation of raw water or a cooling medium to each passage, a cross section corresponding to each of the above-mentioned thermopervaporation devices can be obtained. It is possible to obtain a thermopervaporation device having a rectangularly extending raw water passage and a cooling medium passage.

Furthermore, by arranging the membrane wall and the heat transfer wall in contact with each other via a spacer, a thermopervaporation device corresponding to FIG. 4 can be obtained.

It will be clear that such thermopervaporation equipment'fl can also be suitably used to carry out the method of the invention.

In the above-described apparatus, in the thermopervaporation treatment in the second step, the heating temperature of the raw water is as follows:
The higher the temperature, the more permeated water can be obtained, and from the viewpoint of deaeration efficiency, boiling temperature is preferable, but if necessary, it is usually
The temperature can be 0°C or higher. Furthermore, the temperature of the cooling water in thermopervaporation is preferably lower, but is usually about 10 to 40°C.

Note that, if necessary, the thermopervaporation device can be configured in multiple stages, and the permeated water from the first device can be further subjected to thermopervaporation treatment.

FIG. 8 shows the configuration of an apparatus for subjecting general tap water to reverse osmosis membrane treatment and then thermopervaporation treatment as a first step according to the present invention.
1 to the reverse osmosis membrane device 22, where, as mentioned above, mainly carbonic acid components and surfactant substances are removed, and then heated to a predetermined temperature by the heater 23, and then heated to a thermopar It is supplied to the vaporization device 24.

General tap water treated with reverse osmosis membrane is transferred to pipe 25 as necessary.
It is returned to the reverse osmosis membrane device again.

(Effects of the Invention) As described above, according to the method of the present invention, in the first step, general tap water is treated with a reverse osmosis membrane to remove volatile components, especially ionic carbonate components and surface-active substances. Therefore, even during long-term thermopervaporation treatment, the hydrophobicity of the hydrophobic membrane used is maintained, and carbonic acid components do not mix with the purified water as permeated water. Dissolved substances such as the aforementioned cations and organic substances, and suspended substances such as fine particles and microorganisms are substantially completely removed. Therefore, according to the method of the present invention, high quality pure water can be easily and economically produced through a few steps.

(Example) Examples of the present invention are listed below.

Example 1 Using the apparatus shown in FIG. 1, pure water was produced using Ibaraki city tap water as general tap water. The properties of this general tap water are as follows.

pJ a 10.7 Akebono/βK
2.08■/βCa
14.2 ■/1M g
3.84 mg/'bicarbonate ion 4
6.4 ■/Il chloride ion 16.9 ■
/1 sulfate ion 18.4 trcr/1
Silica 18,2 Akebono/l total phosphorus
0.05■/l free chlorine 1
．． 0 ppm or less Ammonia nitrogen 0.5
Specific resistance below ppm 180, tj
s/cm particles approximately 100,000 pieces/
For the reverse osmosis membrane treatment as the first step, reverse osmosis membrane NTR7197 (number 1) manufactured by Nitto Electric Industry Co., Ltd.
Using a spiral-shaped module equipped with R7250 (number 2) and a reverse osmosis membrane (number 3) containing a sulfonic acid group as a dissociative group, the operating pressure was 10 kg/csA.
, at a water permeation rate of 131/min. Table 1 shows the performance of the reverse osmosis membrane used and the water quality after treating general tap water with this reverse osmosis membrane. In addition, the performance of reverse osmosis membrane is 1% concentration.
of saline solution at 25°C, 10kg/cn! It is expressed as the salt removal rate when treated with

In addition, the thermopervaporation device uses a flat membrane made of a porous polytetrafluoroethylene membrane lined with a porous polyamide woven fabric and a spacer with a thickness of 0.5 mm.
This is a flat cell device constructed by stacking polyamide meshes of m-2 and arranging cooling water passages equipped with heat transfer walls made of stainless steel plates on the surface of the spacer, and the porous membrane has an average pore diameter of 0. It has micropores of 2 μm, porosity is 80%, and the effective membrane area in the device is 40. It is Oc-.

While cooling water at a temperature of 20°C is supplied to the cooling water passage of this equipment at a rate of 517 minutes, regular tap water heated to 80°C after reverse osmosis membrane treatment is supplied to the raw water passage of the equipment, and the water is purified as pure water. Permeate water was obtained at a rate of about 1.51/min. Table 2 shows the properties of the pure water thus obtained.

Table 2 shows that by performing reverse osmosis membrane treatment before thermopervaporation treatment, the amount of scale adhering to the surface of the porous membrane is significantly reduced, and the contact angle of the porous membrane with water is continuously 200 mm. After driving for hours, the angle was 109°, which was almost the same as before driving. On the other hand, when reverse osmosis membrane treatment was not performed as a pretreatment, the porous membrane was 74° after 200 hours of continuous operation.

Example 2 In Example 1, NTI? manufactured by Nitto Electric Industry Co., Ltd. was used as the reverse osmosis membrane. 7197 (number 4) and NTI? 72
Pure water was produced in the same manner as in Example 1, except that ordinary tap water was subjected to reverse osmosis membrane treatment three times using each of the samples.

Table 3 shows the water quality when ordinary tap water was subjected to reverse osmosis membrane treatment only, and Table 4 shows the water quality of pure water obtained by thermopervaporation treatment following reverse osmosis membrane treatment.

Furthermore, for comparison, Table 4 shows the quality of permeated water obtained by thermopervaporating general tap water as a comparative example.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view showing an example of a thermopervaporation device used in the method of the present invention, FIG. 2 is a sectional view taken along line A-A in FIG. 1, and FIG. 3 is a sectional view showing another device. Figure 4 is a vertical sectional view showing yet another device;
The figures are a sectional view taken along vAB-8 in FIG. 4, FIG. 6 a longitudinal sectional view showing yet another device, and FIG. 7 a sectional view taken along line CC in FIG. 6.

Claims (6)

[Claims] (1) In a method for producing pure water from general tap water, (a
) A first step of treating general tap water with a reverse osmosis membrane, and (b) applying the general tap water that has undergone the first step to one side of a hydrophobic polymer porous membrane that allows water vapor to pass through but not water. A second step of contacting raw water at a predetermined temperature to generate water vapor from the raw water, passing it through the other side of the porous membrane, cooling and condensing it to obtain condensed water as pure water. A method for producing pure water, comprising: (2) The method for producing pure water according to claim 1, wherein in the first step, reverse osmosis membrane treatment is performed at a pressure of 20 kg/cm^2 or less. (3) The reverse osmosis membrane absorbs 2% sodium chloride aqueous solution.
The method for producing pure water according to claim 1 or 2, wherein the removal rate of sodium chloride is 50% or more when treated at a pressure of 0 kg/cm^2 or less. (4) The method for producing pure water according to any one of claims 1 to 3, wherein the reverse osmosis membrane has a dissociative group on its surface. (5) The method for producing pure water according to any one of claims 1 to 3, wherein the reverse osmosis membrane is made of an uncharged polymer. (6) The method for producing pure water according to any one of claims 1 to 5, characterized in that the second step is performed after performing reverse osmosis membrane treatment for general tap water multiple times. .