JPH0341205B2 - - Google Patents

Description

[Detailed description of the invention]

(Technical Field) The present invention relates to a separation device used in a membrane separation method in which compatible liquid mixtures are separated by applying microwaves to the liquid/membrane interface. (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. The actual separation is based on the difference in the solubility of the component liquids in the membrane,
This is done based on differences in diffusion rates within the membrane. In principle, it does not seem to have the same limitations as reverse osmosis, and it appears to be promising for separating liquid mixtures. 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 consider the material and structure of the membrane. There are very few examples. A membrane separation method different from these universal methods has recently been announced. This was only announced in the press and the details are unknown, but it is said that with the configuration shown in Figure 1, 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 radialized 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 the electrodes 7 and 7' to cause microwave vibrations on the surface of the vinylidene fluoride film 6, and the energy of the microwave vibrations causes the particles to bind together. The bond between the ethanol clathrate compound, which has a structure in which water is held in the center of the ethanol molecule, and the surrounding water is broken, and only the ethanol clathrate compound is extracted into the liquid 2 through the membranes 4, 5, and 6. It is said that the permeate is further taken out as a permeate 3 through a 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 the patent publication publication JP-A-58-1989, which is considered to be a related technology, has not been found.
No. 95502 to No. 95520 also contain no description of an embodiment, 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 liquid separation device that can easily and efficiently apply microwaves to a liquid/membrane 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 must be provided, and the shape of the application space and the arrangement of the membranes must be devised. The present invention provides a waveguide, an application space, and a waveguide suitable for applying microwaves to membrane separation.
Provides membrane placement. An embodiment of the present invention shown in FIG. 2 will be described below. 61 is a coaxial cable-like structure, and 62 and 63 are a center conductor and an outer conductor, respectively. When a microwave is applied to this from a microwave transmitter 64, the microwave can propagate within the structure. 65 is a polytetrafluoroethylene porous tube. Polytetrafluoroethylene may not be used as a membrane if it is made of a material with a small dielectric loss tangent in the microwave band, that is, a material with low loss.In particular, a material with a dielectric loss tangent of about 300×10 ^-4 or less is suitable as a membrane material. . In this embodiment, the tubes are arranged coaxially with the center conductor 62 as the center. 66 is a terminal structure for maintaining airtightness. The liquid mixture to be separated is circulated from the storage tank 51 through the inside of the polytetrafluoroethylene porous tube 65 by the pump 52 and back to the storage tank 51. Reference numeral 55 denotes a nitrogen gas cylinder. In this example, the nitrogen gas used as a carrier gas is fed into the coaxial cable-like structure 61 after moisture is removed by the cold trap 54, and is connected to the outer conductor 63 and the polytetrafluoroethylene porous structure. It passes through the space between the body tube 65 and is guided to the cold trap 54. 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. Further, when a porous body is not used as the membrane, reduced pressure may be used instead of using a carrier gas. When microwaves are supplied in a system having such a configuration, the microwaves propagate in the length direction of the structure 61, and the accompanying electric field is in a plane orthogonal to the central conductor surface and the outer conductor surface. For this reason, there is almost no loss due to the membrane placed parallel to the direction of microwave propagation, and the surface current in the plane parallel to the direction of propagation of the liquid to be separated that is in contact with it is almost the same as the wavelength of the microwave. Appears at equal intervals. If the liquid could be considered a perfect conductor, this surface current loss would be extremely small, but in normal liquids, absorption occurs in this area. Microwaves also suffer losses due to dielectric relaxation of the liquid, which is also large at the surface and decreases as it goes deeper. Since absorption occurs in the region near the surface, for the purpose of liquid separation using a membrane, absorption is large near the membrane/liquid interface, but it is not effective for separation deep inside the liquid. absorption is small, and microwave energy can be effectively used for membrane separation. As can be seen from this situation, hollow fibers with a fine diameter are used as membranes, and a large number of them are bundled and arranged parallel to the direction of propagation of the microwave, and separated either inside or outside the hollow fiber. By flowing the liquid to be treated and flowing a carrier gas to other parts, or by reducing the pressure, the number of liquid-film contact interfaces increases, and the efficiency of using microwaves is improved. Examples of liquid separation using this method will be described below. Example 1 The membrane has a pore diameter of 0.1 μm, a membrane thickness of 0.5 mm, a tube diameter of 15 mm,
Using a polytetrafluoroethylene porous membrane tube with a length of 17 cm, irradiation with microwaves at a frequency of 500 MHz circulates an approximately 4% ethanol aqueous solution to be separated at a flow rate of 7 ml/min, and nitrogen gas at a flow rate of 0.5/min. It was washed away. Example 2 Liquid separation was carried out under the same conditions as in Example 1 except that microwaves with a frequency of 5 GHz were used. 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 Examples 1 and 2 and Comparative Example 1 are summarized in the table below.

[Table] Next, other examples will be described. In FIG. 3, 21 is a space surrounded by conductors that acts as a microwave propagation space, 24 is a microwave transmitter,
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 circulated from the storage tank 51 through the polytetrafluoroethylene porous membrane tube 26 by the pump 52 and back to the storage tank 51. Nitrogen gas used as a carrier gas is introduced into the container 25 through the pipe 53 and, after contacting the outer surface of the polytetrafluoroethylene porous membrane tube 26, is guided to the cold trap 54. Polytetrafluoroethylene porous membrane tube 26
The permeate 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 54. 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. Materials with a density of about 300×10 ^-4 or less 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 and the liquid Activate 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 a limited range of the liquid/membrane interface, so with the above configuration, the liquid/membrane interface is effective.
Showing maximum absorption at the membrane interface is advantageous in terms of microwave utilization efficiency. 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. 4 shows a conceptual cross-sectional view of the interior of the container 25 shown in FIG. 3 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. 5 shows a membrane 41 sealed at both ends in a bag-like shape and placed in a container 25 in the form of a roll. 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 flat shape, and alternately providing carrier gas or reduced pressure areas and areas through which liquid flows. An example of liquid separation using this method will be described below. Example 3 Using an apparatus with the configuration shown in Figure 3, 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 2 Liquid separation was carried out under the same conditions as in Example 3, except that microwave irradiation was not performed. The results obtained from Example 3 and Comparative Example 2 are summarized in the following table.

[Table] Example 4 Using an apparatus having the structure shown in FIG. 3, a test was carried out using the container 25 having the structure shown in FIG. The container used was the same as in Example 3, and the membrane had a pore diameter of 0.1 μm, a film thickness of 0.5 mm,
Twenty-eight polytetrafluoroethylene porous membrane tubes with a tube diameter of 1 mm and a length of 19 cm are bundled together and irradiated with microwaves at a frequency of 2.45 GHz to inject an approximately 4% ethanol aqueous solution of the liquid to be separated into the membrane at a flow rate of 14 ml/min. It was circulated and nitrogen gas was passed at a flow rate of 1 ml/min. Comparative Example 3 Liquid separation was carried out under the same conditions as in Example 4, except that microwave irradiation was not performed. The results obtained from Example 4 and Comparative Example 3 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 micro-waves near the liquid/membrane interface. Since waves can be supplied, the efficiency of liquid separation using microwaves can be improved, and the operability can be improved.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram showing a conventional membrane separation method for liquid mixtures, Figure 2 is an explanatory diagram of one embodiment of the present invention, Figure 3 is an explanatory diagram of another embodiment, and Figure 4 is an explanatory diagram of another embodiment.
The figure is a conceptual cross-sectional view of a plane perpendicular to the direction of liquid movement inside the container 25 of FIG. 3, and FIG. 5 shows a bag-shaped membrane with both ends sealed inside the container 25 of FIG. It is a sectional view arranged in a spiral shape. 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, 31... Hollow membrane with a fine diameter, 41... Membrane sealed at both ends to form a bag shape, 42... Space on one side of the membrane, 43... ...Space on the other surface side, 51...Storage tank, 52...Pump, 53
...Piping, 54...Cold trap, 55...
Nitrogen gas cylinder, 61... Coaxial cable-like structure, 62... Center conductor, 63... Outer conductor, 64
... Microwave transmitter, 65 ... Polytetrafluoroethylene porous tube, 66 ... Terminal structure.

Claims (1)

[Claims] 1. A part to which a microwave electromagnetic field is applied, a membrane provided within the electromagnetic field to partition a liquid phase and a gas phase,
A device that includes a part that cools the liquid phase component that permeates through the membrane to the gas phase side, and the part that applies the microwave electromagnetic field has an outer conductor and a center (inner) conductor that are coaxially provided. It consists of
A microwave electromagnetic field is applied between the two conductors, or a microwave-emitting part and a space surrounded by the conductor serve as a propagation space for the emitted microwaves. Characteristic liquid separation equipment.