JPH0751505A - Method and apparatus for removal of gal dissolved in aqueous solution - Google Patents

Abstract

PURPOSE:To heighten the removal efficiency without degrading the removal function of a dissolved gas even if an apparatus is used for a long duration by raising the temperature of the aqueous solution to be brought into contact with a hollow yarn membrane at the time when one side of the porous hollow yarn member 2 made of a specified hydrophobic polymer is brought into contact with the aqueous solution and the other side is brought to be under a decreased pressure. CONSTITUTION:When one side of a porous hollow yarn membrane 2 made of a hydrophobic polymer having wettability to water of 90 deg. or bigger wet angle, fine pores with 0.05mum or smaller diameter is brought into contact with an aqueous solution and the other side is brought to be under a decreased pressure, the temperature of the aqueous solution to be brought into contact with the hollow yarn membrane 2 is raised. A dissolved gas removing and steam leading out outlet 6 which communicates with the gaps formed among hollow yarn membranes 2, 2,... is formed at a part of the circumferential face of a container 1 and connected with a water seal type vacuum pump 7. The container 1 is further covered with a temperature keeping cover 8 in order not to lower the gas or water temperature. A leading in inlet 4 to introduce the aqueous solution containing dissolved gas into the container 1 is connected with a water temperature raising apparatus 9.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for removing dissolved gas existing in an aqueous solution, and particularly to a method for removing dissolved oxygen, which is a major factor for corroding water for cleaning semiconductors, soft drink water or boiler piping Method and device for removing volatile organic substances (particularly trihalomethanes such as chloroform and dichlorobromoform and volatile organic halogen substances such as 1,1,1-trichloroethane, trichloroethylene and tetrachloroethylene) dissolved in tap water and well water Regarding

[0002]

2. Description of the Related Art As a conventional method for removing a dissolved gas, a method of decompressing a container containing a solution and a method and an apparatus for removing a dissolved gas by chemical treatment are known.

In such an apparatus, there is a problem that it is difficult to completely remove the dissolved gas and the removal time is long. Therefore, recently, a dissolved gas removing apparatus using a hydrophobic porous membrane has been proposed (special feature: (Kaisho 62-42707).

Further, a method is known in which a dissolved gas is removed by a composite hollow fiber membrane having a three-layer structure in which a homogeneous layer is sandwiched by porous layers from both sides (Japanese Utility Model Laid-Open No. 3-7908, JP-A 3-1).
69303 each gazette).

[0005]

However, in the method using the hollow fiber membrane described above, although the dissolved gas removal performance corresponding to the membrane area is maintained, the membrane resistance formed at the interface between the hollow fiber membrane and the solution is reduced. Because of its large size, even if the gas permeation performance of the hollow fiber membrane is enhanced, the removal efficiency is not improved, and there is a problem that the removal device becomes large.

An object of the present invention is to solve the above-mentioned problems and to provide a method of high removal efficiency and a small-sized removal device, in which the removal performance of dissolved gas does not deteriorate even after long-term use.

[0007]

The gist of the present invention is as follows.

(1) One of the porous hollow fiber membranes made of a hydrophobic polymer having a wetting property of water of 90 ° or more and a pore diameter of the membrane of 0.05 μm or less is contacted with an aqueous solution,
A method for removing dissolved gas in an aqueous solution, which comprises heating the temperature of the aqueous solution in contact with the hollow fiber membrane when depressurizing the other.

(2) The hollow fiber membrane has a three-layer structure in which a homogeneous layer is sandwiched by porous layers from both sides, and the oxygen permeation rate of the material constituting the homogeneous layer is 0.8 × 10 ^-5 (cm). ³ (S
The method according to (1) above, which is a composite hollow fiber membrane having a performance of TP) / cm ² · sec · cmHg) or higher.

(3) A container, a hollow fiber membrane located in the container, a short portion of the hollow fiber membrane are supported, and a space communicating with the hollow portion of the hollow fiber membrane and the outer surface of the hollow fiber membrane are communicated with each other. An inlet and an outlet for flowing an aqueous solution containing a dissolved gas into the space formed by the outer surface of the hollow fiber membrane and the inner wall surface of the container having a partition wall for separating the space, or for reducing the pressure of the space Dissolved gas removal module A in an aqueous solution provided with a depressurization port and an inlet and an outlet for flowing an aqueous solution containing a dissolved gas in the hollow part of the hollow fiber membrane or a degassing port for depressurizing the hollow part. An apparatus for removing dissolved gas in water, characterized in that an apparatus B for heating the aqueous solution is provided in front of the aqueous solution inlet of module A.

(4) The apparatus according to (3) above, characterized in that the reduced pressure state of the space is maintained at the saturated vapor pressure of the aqueous solution introduced into the module A.

(5) The apparatus according to (3) above, wherein the module A is a sheet-shaped product in which a hollow fiber membrane is knitted in a Russell knitting shape or a blind knitting shape.

(6) The filling amount of the hollow fiber membrane to be filled in the module A is set such that the volume ratio of the hollow fiber membrane to the volume of the space surrounded by the adhesive at both ends of the container is in the range of 20 to 50%. The apparatus described in (3) above.

The porous hollow fiber membrane used in the present invention is a polyolefin such as polyethylene, polypropylene or poly-4-methylpentene-1, a fluoropolymer such as tetrafluoroethylene or vinylidene fluoride, polystyrene, polyetheretherketone or polyether. It is composed of a hydrophobic polymer such as a ketone, and in order to prevent water from penetrating into the inside of the pores of the hollow fiber membrane, the wetting property of water on the surface is preferably 90 ° or more as the wetting angle increases. is necessary.

Further, for the purpose of long-term use of the pore diameter of the hollow fiber membrane, the smaller the pore diameter, the higher the surface tension of water and the more difficult it is for water to enter.
The following porous membranes are preferred.

When these hydrophobic porous hollow fiber membranes are used for a long time, water vapor condenses inside the pores of the hydrophobic hollow fiber membrane and the inside of the pores is completely buried with water, and as a result, the water is hollow fiber membrane. There is a risk of leaking from.

The hollow fiber membrane structure has a three-layer structure in which a homogeneous layer is sandwiched from both sides by a porous layer, and the oxygen permeation rate of the material constituting the homogeneous layer is 0.8 × 10 ^-5 (cm ^3).
A composite hollow fiber membrane having a performance of (STP) / cm ² · sec · cmHg) or more is a more preferable hollow fiber membrane in the present invention.

The oxygen transmission rate is 0.8 × 10 ^-5 (cm
^If it is less than ³ (STP) / cm ² · sec · cmHg, the rate at which the gas dissolved in water permeates the homogeneous membrane is slow and the dissolved gas cannot be removed efficiently.

Such a composite hollow fiber membrane is subjected to melt spinning by alternately arranging a polymer forming a homogeneous membrane and a polymer forming a porous membrane by using a multi-cylindrical type spinning nozzle, followed by melt spinning, and then forming a homogeneous membrane. It is produced by a method of stretching under the condition that only the porous membrane is made porous without being made porous.

As the polymer material forming the homogeneous layer,
Starting with silicone rubber polymers with excellent gas permeability, polydimethylsiloxane, silicone rubber polymers such as silicone-polycarbonate copolymers, poly 4-
Polyolefin polymers such as methylpentene-1, low density polyethylene, fluorine-containing polymers such as perfluoroalkyl polymers, cellulosic polymers such as ethyl cellulose, polyphenylene oxide, poly-4-vinylpyridine, urethane polymers, and copolymers of these polymer materials. Various polymers such as coalesced or blended materials can be mentioned.

As the polymer material constituting the porous layer, a polyolefin-based polymer such as polyethylene, polypropylene, poly-3-methylbutene-1, poly-4-methylpentene-1 or the like, a fluorine-based polymer such as polyvinylidene fluoride, polytetrafluoroethylene or the like. Polymer, polystyrene,
Hydrophobic polymers such as polyetheretherketone and polyetherketone may be mentioned.

The combination of the polymer material forming the homogeneous layer and the polymer material forming the porous layer is not particularly limited, and different kinds of polymers may of course be the same kind of polymers.

Since the homogeneous layer has a sandwich structure in which it is physically sandwiched between porous layers, even if the adhesiveness between the two films is poor, no practical adverse effect occurs.

By heating the aqueous solution containing the dissolved gas to be introduced into the porous membrane or the composite hollow fiber membrane, the membrane resistance formed at the boundary between the hollow fiber membrane and water is reduced, and in the water. In the composite hollow fiber membrane, the diffusion constant of the dissolved gas is increased, and the gas permeability coefficient of the homogeneous membrane is increased, so that the degassing efficiency is rapidly increased.

As a method for heating, there are a method of heating an aqueous solution to be introduced into the hollow fiber membrane module by passing it through a generally used heat exchanger, and a method of heating the entire module. I'm not stuck.

However, when the temperature on the gas side in the module is significantly lower than the water temperature, condensed water accumulates in the gas side voids and reduces the film area, so that there is no large temperature difference between the gas side and the water temperature. It is important to.

As a method for preventing the reduction of the membrane area due to the condensing of the bundle of yarns by the condensed water, the hollow fiber membranes are knitted in a Russell knitting or a comb shape, and the filling amount of the hollow fiber membranes is adjusted by an adhesive on both ends of the container. The volume ratio of the hollow fiber membrane in the volume of the enclosed space is 20 to 50% (preferably 25 to 45%).
It is possible to set it within the range of.

When knitting in a Russell knitting or a interlace knitting, the hollow fiber membranes are processed into a sheet with yarns, so that a space can be maintained between the hollow fiber membranes by the thickness of the warp yarns. Therefore, it is preferable to knit the hollow fiber membranes one by one, but several hollow fiber membranes may be knitted together.

The volume ratio of the hollow fiber membranes to the volume of the space surrounded by the adhesive on both ends of the container is 20%.
If it is less than%, the volume becomes large to secure the necessary membrane area, and if it exceeds 50%, condensed water remains between the hollow fiber membranes and the membrane area effective for deaeration decreases.

When the reduced pressure state is set to be equal to or lower than the saturated water vapor pressure of the aqueous solution introduced into the module, the amount of water vapor that permeates the hollow fiber membrane is rapidly increased, and the exhaust amount of the vacuum pump is very large.

Further, at a pressure reduction degree equal to or higher than the saturated water vapor pressure, the degassed gas component remains on the gas side, and only the gas-liquid equilibrium concentration corresponding to the gas partial pressure can be removed.

Therefore, as the degree of pressure reduction, the saturated water vapor pressure of the aqueous solution introduced into the module is optimum. A method of maintaining such a degree of reduced pressure can be easily achieved by using a water-sealed vacuum pump having a high sealing property.

FIG. 1 shows an example of an apparatus suitable for removing a dissolved gas in an aqueous solution of the present invention, in which 1 is an airtight and watertight container, and a large number of hollow fibers are inside the container. The membrane 2 is arranged at a predetermined interval so that both ends thereof are supported and fixed by the potting agent 3.

At both ends of the container 1, a hollow fiber membrane 2 supported and fixed by the potting agent and an inlet port 4 and an outlet port 5 for an aqueous solution containing a dissolved gas, which communicate with the voids formed between the inner walls of the container 1, respectively. Is provided.

By the potting agent, the voids formed between the large number of hollow fiber membranes 2, 2, 2, ..., And the inlet 4 and outlet 5 of the aqueous solution containing the dissolved gas.
A partition wall 3 for blocking the above is formed.

Further, a part of the peripheral surface of the container 1 is formed with a dissolved gas and water vapor port 6 which communicates with the void formed between the hollow fiber membranes 2, 2, 2, ... The dissolved and dissolved gas and water vapor port 6 is connected to a water-sealed vacuum pump 7.

Further, the container 1 is covered with a heat insulating cover 8 so as not to lower the gas temperature or the water temperature. The inlet port 4 for introducing the aqueous solution containing the dissolved gas into the container 1 is connected to a water temperature heating device 9 so that the aqueous solution containing the dissolved gas can be introduced into the module by setting a predetermined water temperature.

The present inventors have conducted a study using a method and a device for removing dissolved gas in an aqueous solution, and as a result, surprisingly found that the dissolved gas can be removed with extremely high efficiency by raising the water temperature. It is a thing. The water temperature is 20 to 80 ° C., preferably 25 to 60 ° C., more preferably 30 to 50 ° C. from the viewpoint of efficiency and energy cost.

[0039]

With such a structure, according to the method and apparatus of the present invention, the aqueous solution containing the dissolved gas flows through the hollow portion (or outer surface) of the hollow fiber after being heated and, at the same time, the outer surface (or hollow surface) of the hollow fiber membrane. The dissolved gas becomes a gas because it is decompressed, and the gas permeates the hollow fiber membrane efficiently and is discharged to the outside. In addition, the amount of water vapor exhausted is small, and the device can be implemented by a small water-sealed vacuum pump. Therefore, by using the method and apparatus of the present invention, it is possible to remove dissolved gas in a very small space.

[0040]

The present invention will be described in detail with reference to the following examples.

The "dissolved gas removal rate" was calculated from the following equation for each component. Dissolved gas x removal rate (%) = {1- (C _xi −C _xo ) /
C _x } C _xi ; concentration of dissolved gas x contained in water entering the device C _xo ; concentration of dissolved gas x contained in water exiting the device

The "oxygen gas permeation rate of the hollow fiber membrane" was measured by gas chromatography.

Reference Example 1 High density polyethylene (Hizex 2200J manufactured by Mitsui Petrochemical Co., Ltd.) as a polymer material to be supplied to the inner layer and the outer layer of a hollow fiber manufacturing nozzle having three discharge ports arranged concentrically Segmented polyurethane (Therme
dics Inc. Made by Tecoflex EG80A)
, Discharge temperature 165 ° C, winding speed 180 m / m
It was spun in.

The hollow fiber undrawn yarn thus obtained was annealed at 100 ° C. for 1 hour. Then, the annealed yarn is stretched by 80% at room temperature, and subsequently subjected to hot stretching in a heating furnace heated to 105 ° C. until the thermal stretch ratio reaches 130%,
A composite hollow fiber membrane was obtained.

The obtained composite hollow fiber membrane has a three-layer structure of a porous layer, a homogeneous layer and a porous layer in order from the innermost layer as shown in FIG. 2, the inner diameter is 200 μm, and the thickness is 25 μm from the innermost layer.
m, 1 μm, and 25 μm concentric circles.

As a result of observing the surface of the porous layer of the composite hollow fiber membrane with a scanning electron microscope, the width was 0.06 to 0.09 μm.
A slit-like hole having a length of 0.1 to 0.5 μm was formed. The oxygen permeation rate of this hollow fiber membrane is 1.2 × 10.
^{It was −5} (cm ³ (STP) / cm ² · sec · cmHg).

Reference Example 2 High density polyethylene (Hizex 220 manufactured by Mitsui Petrochemical Industry Co., Ltd.) was used as a polymer material to be supplied to a hollow fiber manufacturing nozzle having concentrically arranged discharge ports.
0J), discharge temperature 155 ° C, winding speed 150
It was spun at m / min.

The obtained hollow fiber undrawn yarn was annealed at 110 ° C. for 1 hour. Then, the annealed yarn was stretched by 150% at room temperature, and subsequently, was thermally stretched in a heating furnace heated to 115 ° C. until the thermal stretch ratio reached 200% to obtain a hollow fiber membrane.

The hollow fiber membrane obtained had an inner diameter of 200 μm,
It was a concentric circle having a thickness of 60 μm. As a result of observing the surface of the porous layer of the hollow fiber membrane with a scanning electron microscope, a width of 0.0
Slit-shaped holes having a diameter of 4 to 0.08 μm and a length of 0.1 to 0.2 μm were formed. The oxygen permeation rate of this hollow fiber membrane was 1.0 × 10 ^-2 (cm ³ (STP) / cm ² · sec.
-CmHg).

Example 1 Using the apparatus shown in FIG. 1, the removal rate of oxygen dissolved in water was measured. The dissolved gas is represented by oxygen gas, and water containing 6 ppm of oxygen gas is introduced at a water temperature of 25 ° C. and 35 ° C. and a flow rate of 0.64 l / min. The hollow fiber membranes obtained from Reference Examples 1 and 2 were prepared at a pressure reduction level of not less than the pressure, and the Russell knitted sheet shown in FIG. 3 was prepared at a filling rate of 40%. .

As a result of the evaluation, the results of the dissolved oxygen concentration at the outlet of the apparatus and the degassing efficiency of the apparatus are shown in Table 1. Reference examples 1 and 2
No matter which hollow fiber membrane is used, the dissolved oxygen concentration at the outlet of the apparatus is lowered and the degassing efficiency is increased by raising the water temperature.

[0052]

According to the present invention, the dissolved gas in the aqueous solution can be efficiently removed by slightly heating the aqueous solution containing the dissolved gas. Further, by setting the degree of pressure reduction to saturated water vapor pressure, it is possible to provide a compact device that can be operated by a vacuum pump with a small displacement.

[0053]

[Table 1]

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of an apparatus for removing dissolved gas from an aqueous solution of the present invention.

FIG. 2 is a schematic diagram showing an example of a composite hollow fiber membrane having a three-layer structure of a porous layer, a homogeneous layer, and a porous layer.

FIG. 3 is a schematic view showing an example of Russell knitting of a hollow fiber membrane.

FIG. 4 is a schematic view showing an example of Russell knitting of a hollow fiber membrane.

FIG. 5 is a schematic view showing an example in which a hollow fiber membrane is knitted in a comb shape.

[Explanation of symbols]

 1 Container 2 Hollow Fiber Membrane 3 Adhesive Part 4 Water Inlet 5 Water Outlet 6 Gas Outlet 7 Vacuum Pump 8 Insulation Cover 9 Heating Device

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display area C02F 1/20 A

Claims (6)

[Claims] 1. A porous hollow fiber membrane made of a hydrophobic polymer having a wetting property of water having a wetting angle of 90 ° or more and a pore size of the membrane of 0.05 μm or less is in contact with one of the aqueous solutions and the other is depressurized. At this time, the method for removing dissolved gas in an aqueous solution, which comprises heating the temperature of the aqueous solution in contact with the hollow fiber membrane. 2. The hollow fiber membrane has a three-layer structure in which a homogeneous layer is sandwiched by porous layers from both sides thereof, and the oxygen gas permeation rate of the material constituting the homogeneous layer is 0.8 × 10 ⁻⁵ (cm 2). ³ (S
The method according to claim 1, which is a composite hollow fiber membrane having a performance of TP) / cm ² · sec · cmHg) or higher. 3. A container and a hollow fiber membrane located inside the container,
The outer surface of the hollow fiber membrane has a partition wall that supports the end portion of the hollow fiber membrane with an adhesive and separates a space communicating with the hollow portion of the hollow fiber membrane from a space communicating with the outer surface of the hollow fiber membrane. In order to flow the aqueous solution containing the dissolved gas into the inlet and the outlet for flowing the aqueous solution containing the dissolved gas into the space defined by Module A for removing dissolved gas in an aqueous solution, which is provided with a degassing port for depressurizing the inlet and outlet or the hollow portion of the An apparatus for removing dissolved gas in an aqueous solution, characterized in that B is provided. 4. The apparatus according to claim 3, wherein the reduced pressure state of the space is maintained at the saturated vapor pressure of the aqueous solution introduced into the module A. 5. The device according to claim 3, wherein the module A is a sheet-shaped product in which a hollow fiber membrane is knitted in a Russell knitting shape or a blind knitting shape. 6. The volume ratio of the hollow fiber membranes to be filled in the module A is set within a range of 20 to 50% in the volume of the space surrounded by the adhesive on both ends of the container. The apparatus of claim 3 characterized.