JP2000288306A - Degassing method and degassing apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make highly efficiently performable degassing of even a liquid with a high viscosity by a degassing apparatus with a small size without causing disadvantageous pressure loss by immersing a degassing container having a gas permeation membrane and a gas permeation chamber in a gas-dissolving solution and removing the dissolved gas by permeating the gas through the gas permeation membrane while keeping the degassing container still. SOLUTION: The degassing container 1 is provided with a gas permeation chamber in the inside of a gas permeable membrane, equipped with a gas discharge pipe 13 for decreasing the pressure of the permeation chamber and a vacuum suction pump 14, and housed in a tank 2 as a whole. That is, the degassing container 1 is composed of overlaying two flat membrane 11 while sandwiching a spacer 13 for holding the permeation chamber, sealing the membrane by heat sealing, and connecting the gas discharge pipe 13 to the inside space between the flat membranes 11. The gas-dissolving solution is poured in the tank 2 and while keeping the poured solution still without forcibly moving the solution, the vacuum pump 14 is driven to carry out vacuum suction for the gas permeation chamber of the degassing container 1. In that case, the temperature gradation of the gas is generated in the solution accompanying the progress of the degassing, so that the gas in the solution is moved toward the membranes and discharged.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for degassing a gas-dissolved liquid, and more particularly to a method for removing a gas-dissolved high-viscosity liquid having a viscosity of 5 cP or more, for example, a photoresist liquid.

[0002]

BACKGROUND OF THE INVENTION The use of liquids requires degassing in a wide range of fields. For example, in liquid chromatography, when air is dissolved in a solvent, air bubbles are generated in a pump or a detector, and there is a fear of chemical reaction with a solute. Therefore, degassing is indispensable for analysis accuracy. In automatic clinical chemistry analysis, degassing is indispensable because even a small amount of dissolved oxygen adversely affects the analysis accuracy. Furthermore, in the production of ultrapure water in the electronics industry, degassing is necessary because dissolved oxygen and dissolved carbon dioxide gas shorten the life of the ion exchange resin. Furthermore, in the boiler water, degassing is required because dissolved oxygen promotes corrosion of containers and pipes.

As is well known, the use of a gas permeable membrane for degassing a gas-dissolved liquid is well known (for example, JP-A-60-25514, JP-A-4-145906, and JP-A-2511732). Publication, Patent No. 27748
43, etc.). In these degassing methods, while the gas-dissolved liquid comes into contact with the gas-permeable membrane, the dissolved gas in the contact liquid is taken into the membrane from the surface of the gas-permeable membrane, and the resulting concentration gradient is driven. As a force, the gas diffuses through the polymer chain gap of the membrane and is further discharged through the permeation chamber.

Conventionally, as a membrane device, an immersion type membrane device in which a membrane module is immersed in a liquid tank to be treated is known, but also in this device, the liquid to be treated is forced by a stirrer or a circulation pump. The liquid to be treated is caused to flow along the membrane surface by stirring or circulating.

[0005]

When the above-mentioned membrane degassing method is used for removing dissolved gases in a highly viscous liquid, the pressure loss becomes large. Costs are inevitable. In particular, the viscosity of a photoresist solution used for forming a pattern of a semiconductor or a magnetic head is usually 10 cP or more, and when it is high, the viscosity can reach 100 cP. There is also a concern that the reactivity may decrease, and the degassing method for forcibly driving the gas-dissolved liquid has a serious problem.

[0006] The movement of fluid molecules in a medium is as follows.
This is a result of diffusing the molecular gap of the medium by using the concentration gradient as a driving force, and the difficulty of the diffusion depends on the interaction and affinity between the fluid molecules and the medium molecules. Thus, conventional membrane degassing utilizes the high diffusivity of the film for gas molecules and the high uptake of gas molecules on the film surface, but the movement of gas molecules to the film surface is dependent on the liquid to be treated. It can be said that means for forcibly moving the (medium), that is, means for moving the gas molecules by using the liquid to be treated as a carrier, is employed.

It is an object of the present invention to dissolve dissolved gas molecules to the membrane surface by performing a gas concentration gradient and the diffusivity of a liquid to be treated, unlike the above-mentioned conventional method, to reduce the pressure loss. And it is possible to degas even a highly viscous liquid with a small degasser.

[0008]

The degassing method according to the present invention comprises immersing a gas permeable membrane and a degasser having a gas permeable chamber inside the gas permeable membrane into a gas dissolved liquid, and removing the gas dissolved liquid. This is a configuration characterized in that dissolved gas is removed through a gas permeable membrane while being kept in a non-driving state, and is usually applied to a gas dissolved liquid having a viscosity of 5 cP or more. Further, it is preferable to use a polytetrafluoroethylene membrane having excellent chemical resistance as the gas permeable membrane.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a drawing showing an example of a degassing apparatus according to the present invention. In FIG. 1, reference numeral 1 denotes a degasser, which is provided with a gas permeable chamber inside a gas permeable membrane, and an exhaust pipe 13 and a vacuum pump 14 for depressurizing the permeable chamber, or a gas to be degassed. Another purging means for lowering the partial pressure is provided. Reference numeral 2 denotes a tank containing the degasser 1.

It is preferable to use a degasser 1 having no complicated stock solution passage unlike the conventional hollow fiber membrane module or spiral membrane module, for example, as shown in FIG. As shown in (a) and (b) of FIG. 2 (cross-sectional view of (b) in FIG. 2), two flat membranes 11 are connected via a mesh or net spacer 12 for holding a permeation chamber. A stack obtained by heat-sealing the superposed film with the exhaust pipe 13 drawn out from the inside can be used. FIG.
As shown in (a) and (b) of FIG. 3 (a cross-sectional view of FIG. 3 (a)), two flat membranes 11 are meshed with a mesh or net spacer 12 for holding a transmission chamber. It is also possible to use one in which a frame edge 132 with an exhaust pipe 131 is attached to the superimposed film and the space between the frame edge and the film is sealed with an epoxy resin adhesive or the like.

As the gas permeable membrane, a permeable membrane having a high permeation rate with respect to the gas to be degassed is used, and the oxygen permeation rate is usually 10,000 (cc · 25.4 μm / m ² ···
day) At 23 ° C. or higher is used. For example,
In consideration of chemical resistance, a polytetrafluoroethylene film [17000 (cc · 25.4 μm / m ² · day) a
t23 ° C.] can be used. As the gas permeable membrane, any porous membrane can be used as long as it is hydrophobic with respect to the liquid to be treated and can prevent liquid from passing through the pores.

In order to remove gas from a gas-dissolved liquid using the degassing apparatus according to the present invention, the tank is filled with the gas-dissolved liquid, and the filled liquid is kept stationary without being forcedly driven. The vacuum pump is driven to continue evacuation of the gas permeation chamber of the degasser. In this case, first, the dissolved gas in the liquid in contact with the liquid surface permeates the membrane and is degassed,
Due to the degassing, a gas concentration gradient is generated in the liquid, and the dissolved gas in the liquid is moved toward the membrane surface by the concentration gradient as a driving force, is taken into the membrane from the membrane surface, and permeates from the membrane inner surface. It goes out of the room and is discharged from the exhaust pipe. Therefore, no pressure loss occurs because the gas dissolved liquid does not flow, and there is no fear that the liquid molecules are sheared and deteriorated because no shear force acts on the gas dissolved liquid.

According to the degassing method of the present invention, a photoresist having a high viscosity (5 cP or more) having a large pressure loss due to a flow and removing a dissolved gas of a liquid which may be deteriorated by shearing, for example, having a viscosity of 5 cP or more, It is suitable for removing dissolved gas from a liquid.

[0014]

EXAMPLE An aqueous dispersion of polytetrafluoroethylene powder having a solid content of 60% by weight was applied to a polyimide carrier sheet, and the dispersion medium (water) was dried and removed at 90 DEG C. for 2 minutes. Firing was performed at 360 ° C. for 2 minutes, and then the above-mentioned coating and firing were repeated twice, and peeled from the carrier sheet to obtain a 25 μm thick polytetrafluoroethylene film. This film is 20cm ×
The sheet was cut to 50 cm, and the two cut films were cut into a 100-mesh net of tetrafluoroethylene-perfluoroalkylvinyl ether copolymer (a space for holding a transmission chamber).
2), and the periphery of this superposed film was heat-sealed with the exhaust pipe drawn out from the inside to produce the degasser shown in FIG. The degasser is immersed in a tank containing about 500 milliliters of a photoresist solution having a viscosity of about 10 cP, and the pressure in the permeation chamber of the degasser is reduced to 30 torr to about 1
Degas for hours. As a result, the initial dissolved nitrogen partial pressure was reduced from about 804 mb to about 201 mb, and a recycled photoresist liquid having a dissolved gas removal rate of 75% was obtained.

[0015]

According to the degassing method of the present invention, since the gas-dissolved liquid is degassed by gas permeation from the permeable membrane while being kept substantially stationary without forcibly flowing, the pressure is reduced. There is no loss, the size of the apparatus can be reduced and the power cost can be reduced in combination with the non-use of a pump or the like, and even a high-viscosity photoresist liquid which is liable to be deteriorated by shearing can be safely degassed. In particular, when the flat membrane type degasser shown in FIGS. 2 and 3 is used, the cleaning is easy and the maintenance of the apparatus is advantageous.

[Brief description of the drawings]

FIG. 1 is a view showing degassing according to the present invention.

FIG. 2 is a drawing showing an example of a degasser used in the present invention.

FIG. 3 is a drawing showing another example of a degasser used in the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Degasser 11 Gas permeable membrane 13 Gas exhaust pipe 14 Decompression pump 2 Tank

Claims (4)

[Claims] 1. A gas permeable membrane and a degasser having a gas permeable chamber inside the gas permeable membrane are immersed in the gas dissolved liquid, and the dissolved gas is passed through the gas permeable membrane while keeping the gas dissolved liquid in an undriven state. A degassing method characterized by removing. 2. The degassing method according to claim 1, wherein the viscosity of the gas-dissolved liquid is 5 cP or more. 3. The degassing method according to claim 1, wherein a polytetrafluoroethylene membrane is used as the gas permeable membrane. 4. A degassing method according to claim 1, wherein a gas permeable membrane and a degasser having a gas permeable chamber inside the gas permeable membrane are disposed in a gas-dissolved liquid tank. apparatus.