JPH0341207B2 - - Google Patents

Description

[Detailed description of the invention]

(Technical Field) The present invention relates to a method of applying high frequency waves to a liquid/membrane interface in separating compatible liquid mixtures using a membrane. (Prior Art and its Problems) Generally, it is difficult to separate the components of a liquid mixture that are compatible with each other. The most commonly used industrial separation method is distillation. However, the distillation method cannot be applied unless the system has a large boiling point difference between the components, does not form an azeotrope, and is stable against heat. Furthermore, even when applicable, distillation requires a large amount of thermal energy, and there is a need for a separation method that consumes less energy. A separation method that has the potential to meet this demand is membrane separation. From this point of view, various attempts have been made to membrane separation of liquid mixtures. Among these, the relatively common methods are reverse osmosis and pervaporation. Reverse osmosis is a method that has been put to practical use in desalination of seawater, etc., and uses a semipermeable membrane that is impermeable to salts (ions), which are solutes, and ideally allows only the solvent to pass through. In this method, a pressure higher than the osmotic pressure generated in the solution is applied to the solution side to allow the solvent to permeate and separate the solution. This principle should also be applicable to liquid mixtures, and there have been many attempts to apply reverse osmosis to the separation of liquid mixtures. However, since compatible liquid mixtures often have similar molecular sizes, chemical properties, etc., separation is not always good. Furthermore, the osmotic pressure between the solution and the permeate cannot be ignored, and there is a concentration limit. At normal operating pressures, the limit is about 10-15%, and the application of reverse osmosis to liquid mixtures is currently not useful except in special cases. The pervaporation process consists of a system in which one side of the membrane is in contact with the liquid mixture to be separated and the other side is under reduced pressure or in contact with a carrier gas. In principle, separation of components in this system is performed based on differences in solubility of component liquids in the membrane and differences in diffusion rates within the membrane, so it is thought that there is no limit like reverse osmosis, and separation of liquid mixtures is possible. is seen as promising. However, as can be seen from the separation process described above, in the case of a combination of liquids with similar chemical and physical properties, it is necessary to devise the material and structure of the membrane.
To date, there are almost no examples of practical use of the pervaporation method. A membrane separation method different from these universal methods has recently been announced. Its outline is shown in Figure 1, and it is said that ethanol can be separated from an aqueous ethanol solution using high-frequency vibrations. To explain Figure 1, 1 is the ethanol aqueous solution to be separated, 2 is the potassium carbonate or potassium lactate aqueous solution, 3 is the permeated ethanol, 4 is the porous core Teflon membrane, and 5 is the surface of the Teflon membrane subjected to radicalization treatment. The radicalized Teflon film 6 is a vinylidene fluoride film having conductivity. In FIG. 1, a high frequency current of 100 to 1000 KHz is applied to the radicalized Teflon film 5 through electrodes 7 and 7' to cause microwave vibrations on the surface of the vinylidene fluoride film 6, and the microwave vibration energy is applied to the surface of the vinylidene fluoride film 6. The supply between the ethanol clathrate compound, which has a structure in which water is held in the center of the associated ethanol molecules, and the surrounding water is cut off, and only the ethanol clathrate compound passes through the membranes 4, 5, and 6 into the liquid 2. It is said that the permeated liquid 3 is taken out through the Teflon membrane 10. It is said that permeation can be promoted by applying a DC voltage between electrodes 8 and 9. However, there is no specific description of this method, and Japanese Patent Application Laid-open No. 58-95502 to 95520, which are considered to be related techniques,
There is no description of an embodiment in the publication, and the contents of the structure are unknown. (Structure of the Invention) The present invention provides a method for separating a liquid mixture using a membrane.
The present invention provides a method for easily and efficiently applying high frequency waves to a liquid/film interface. That is, since microwaves have wavelengths on the order of cm to mm, they have the properties of so-called radio waves, and cannot be propagated using ordinary electric wires, nor can an electric field be applied using ordinary electrodes. Therefore, in order to apply this to the membrane/liquid interface, a special waveguide is provided, and the shape of the application space,
The arrangement of the membrane must be devised. The present invention provides a method for performing membrane separation while applying microwaves to a membrane/liquid interface in an application space provided separately from a waveguide. An embodiment of the present invention shown in FIG. 2 will be described below. 21 is a space surrounded by a conductor that serves as a microwave propagation space, 24 is a microwave transmitter, and 23 is a waveguide. The microwave emitted at 24 passes through the antenna 22, travels within the waveguide, and is radiated into the microwave propagation space 21 from the opening 27. A container 25 made of a dielectric material is installed inside the microwave propagation space 21, and a hollow polytetrafluoroethylene porous membrane tube 26 is arranged inside the container. The liquid mixture to be separated is stored in tank 1.
1, the polytetrafluoroethylene porous membrane tube 26 is circulated again to the storage tank 11 by the pump 12. Nitrogen gas used as a carrier gas is introduced into the container 25 through the pipe 13 and, after contacting the outer surface of the polytetrafluoroethylene porous membrane tube 26, is guided to the cold trap 14. The permeate passing through the polytetrafluoroethylene porous membrane tube 26 is carried out of the container 25 and the microwave propagation space 21 together with the carrier gas, and is separated from the carrier gas in the cold trap 14. In the above example, a polytetrafluoroethylene porous membrane tube was used as the membrane, but if the membrane is made of a material with a small dielectric loss tangent in the microwave band, that is, a small loss, it does not need to be polytetrafluoroethylene. Approximately 300×
Materials below 10 ^-4 are suitable as membrane materials. When a non-porous membrane is used, reduced pressure may be used instead of using a carrier gas. Further, the carrier gas is not limited to nitrogen gas as long as it is an inert gas that does not react with the components of the liquid mixture to be separated. In a system with such a configuration, when microwaves are emitted into the microwave propagation space 21 as described above, the container 25 and the membrane 26 are made of dielectric material and therefore hardly absorb the microwaves, but they are absorbed by the liquid mixture. Activates liquid ingredients. Therefore, in this state, due to the difference in activation of the liquid components, a specific component permeates through the membrane at a higher rate than other components, improving the permeation rate and separation efficiency. Because microwaves are attenuated by absorption in the liquid, the absorption is large near the liquid-membrane interface, and the microwaves are attenuated as they move toward the inside. In membrane separation, what is actually effective for separation is the limited range of the liquid/membrane interface, so in the configuration described above, the maximum absorption at the liquid/membrane interface is due to microwave utilization efficiency. It is advantageous in terms of As can be seen from the above explanation, providing a thin liquid/film interface layer on the path of the microwave is more effective in improving the microwave utilization efficiency. This can be done, for example, by bundling a large number of hollow fiber-like membranes with minute diameters, flowing the liquid to be separated into one of the inside or outside of the hollow fibers, and flowing a carrier gas into the other part, or by reducing the pressure. This can be achieved by stacking planar membranes in layers, by flowing a liquid on one side of the membrane and a carrier gas on the other side, or by applying reduced pressure. Examples of these are described below. FIG. 3 shows a conceptual cross-sectional view of the inside of the container 25 shown in FIG. 2 in a plane perpendicular to the direction in which the liquid travels. container 2
5 is filled with a hollow membrane 31 of minute diameter, and the lower half is omitted. In such a configuration, the liquid to be separated is passed inside the hollow membrane, and a carrier gas is passed or a reduced pressure is applied to the outside. Also, the inside and outside may be reversed. FIG. 4 is a cross-sectional view of a bag-shaped membrane 41 with both ends sealed and placed in a rolled-up container 25, in which a carrier gas is flowed or depressurized into the space 42 on one side of the membrane, and the other side is The liquid to be separated flows into the side space 43. In this case as well, the spaces 42 and 43 may be used in reverse. Although not shown in the figure, it is also possible to stack them without forming them into a spiral shape, leaving a space in a planar shape, and alternately providing carrier gas or reduced pressure sections and sections through which liquid flows. Examples of liquid separation using this method will be described below. Example 1 Using an apparatus with the configuration shown in Figure 2, the pore size of the membrane was
Using a polytetrafluoroethylene porous membrane tube of 0.1 μm, membrane thickness 0.5 mm, tube diameter 15 mm, and length 19 cm,
By irradiating 2.45GHz microwave, the liquid to be separated is approximately 4
% ethanol aqueous solution was circulated at a flow rate of 14 ml/min, and nitrogen gas was flowed at a flow rate of 1 ml/min. A glass tube with a length of 30 cm and an inner diameter of 2.2 cm was used as the container. Comparative Example 1 Liquid separation was carried out under the same conditions as in Example 1, except that microwave irradiation was not performed. The results obtained from Example 1 and Comparative Example 1 are summarized in the following table.

[Table] Example 2 Using an apparatus having the configuration shown in FIG. 2, a test was carried out with the container 25 having the configuration shown in FIG. 3. The container used was the same as in Example 1, and was irradiated with microwaves with a frequency of 2.45 GHz to form a membrane with a pore diameter of 10.1 μm, a film thickness of 0.5 mm, and a tube diameter of 1.
28 polytetrafluoroethylene porous membrane tubes with a length of 19 cm and a length of 19 cm are bundled together and irradiated with microwaves at a frequency of 2.45 GHz to circulate an approximately 4% ethanol aqueous solution of the liquid to be separated inside the membrane at a flow rate of 14 ml/min. , nitrogen gas was flowed at a flow rate of 1 ml/min. Comparative Example 2 Liquid separation was carried out under the same conditions as in Example 2, except that microwave irradiation was not performed. The results obtained from Example 2 and Comparative Example 2 are summarized in the following table.

[Table] (Effects of the invention) According to the present invention, there is no need for a complicated membrane structure as in the past, and a microwave transmitter that has already been technically proven is used to efficiently transmit microwaves near the liquid/membrane interface. Since the liquid can be supplied, the efficiency of liquid separation using high frequency can be improved, and the operability can be improved.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing a conventional membrane separation method for liquid mixtures, FIG. 2 is a diagram showing an embodiment of the present invention, and FIG. FIG. 4 is a conceptual cross-sectional view of the surface of the container 25 shown in FIG. 2, in which a bag-shaped membrane with both ends sealed is arranged in a roll. 1... Ethanol aqueous solution, 2... Potassium carbonate or potassium lactate aqueous solution, 3... Permeated ethanol, 4... Porous core Teflon membrane, 5... Radicalized Teflon membrane, 6... Vinylidene fluoride membrane, 7.
7', 8, 9... Electrode, 10... Teflon membrane, 2
DESCRIPTION OF SYMBOLS 1...A space surrounded by a conductor that acts as a microwave propagation space, 22...Antenna, 23...Waveguide, 24...Microwave transmitter, 25...Container made of dielectric material, 26...Polymer Tetrafluoroethylene porous membrane tube, 27...opening, 11...storage tank,
12...Pump, 13...Piping, 14...Cold trap, 31...Hollow membrane with micropores, 41...
...a bag-shaped membrane with both sides sealed, 42...a space on one side of the membrane, 43...a space on the other both sides.

Claims (1)

[Claims] 1. A method for separating liquid components from a liquid mixture using a membrane in the presence of a high-frequency electromagnetic field, in which a dielectric material is disposed in a waveguide path for propagating microwaves emitted from a microwave oscillation source. The inside of the container is partitioned with a polymer membrane, one side of the membrane is brought into contact with the liquid mixture to be separated, and the other side is provided with a membrane for guiding and trapping the components passing through the membrane. A method for membrane separation of liquids characterized by forming a carrier gas or a reduced pressure atmosphere. 2. The liquid membrane separation method according to claim 1, wherein the polymer membrane that partitions the inside of the container in the microwave waveguide path has a structure in which a plurality of fine diameter hollow fiber membranes are bundled.