JPH0341206B2 - - 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 method 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 is thought that there are no limitations like reverse osmosis, and it seems 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 devise the material and structure of the membrane.
To date, there are almost no examples of practical use of pervaporation. 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 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 bond between the ethanol clathrate, which has a structure in which water is held in the center of the associated ethanol molecules, and the surrounding water is broken, and only the ethanol clathrate is taken out 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 95520 also contain no description of embodiments, 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 through 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 membrane must be devised. The present invention provides a method of integrating a waveguide and an application space, arranging a membrane within the waveguide, and performing membrane separation while applying microwaves to the membrane/liquid interface. An embodiment of the present invention shown in FIG. 2 will be described below. 61 is a coaxial cable-like structure, 62, 6
Reference numerals 3 denote a center conductor and an outer conductor, respectively, and when a microwave transmitter 64 applies microwaves to these, the microwaves can propagate within the structure. 65 is a polytetrafluoroethylene porous tube. Polytetrafluoroethylene may not be used as long as the membrane 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. There is. 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 permeate that has passed through the polytetrafluoroethylene porous tube 65 becomes a gas and is carried out of the structure 61 together with the carrier gas, where it is separated from the carrier gas in 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 have losses due to dielectric relaxation of the liquid, but
This is also large on the surface and decreases as you go deeper. Since such absorption occurs in the region near the surface, for the purpose of liquid separation by a membrane, absorption is large near the membrane-liquid interface, but it is not effective for separation deep inside the liquid. absorption is small;
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 fibers. 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 Using an apparatus with the configuration shown in Figure 2, a polytetrafluoroethylene porous tube with a pore diameter of 0.1 μm, a film thickness of 0.5 mm, a tube diameter of 15 mm, and a length of 17 cm was used as the membrane, and a microwave with a frequency of 500 MHz was used. The liquid to be separated, an approximately 4% aqueous ethanol solution, was circulated at a flow rate of 7 ml/min, and nitrogen gas was passed at a flow rate of 0.5/min. 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 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 Examples are summarized in the table below.

[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, and FIG. 2 is an explanatory diagram of an embodiment of the present invention. 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, 5
DESCRIPTION OF SYMBOLS 1...Storage tank, 52...Pump, 55...Nitrogen gas cylinder, 54...Cold trap, 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. In a membrane separation method in which a liquid mixture is separated using a polymer membrane in the presence of a high-frequency electromagnetic field, microwaves generated from a microwave oscillator are transmitted to a coaxial microelectromagnetic wave generator consisting of a central conductor and an outer conductor. The space between the center conductor and the outer conductor is defined by a polymer membrane, one side of which is in contact with the liquid mixture to be separated, and the other side is in contact with an inert carrier gas or an inert carrier gas. is a membrane separation method for liquids, which is characterized by performing separation while contacting with a reduced pressure atmosphere. 2 A hollow structure is used as the polymer membrane, and the hollow polymer membrane is arranged concentrically so that the longitudinal center line of the hollow polymer membrane overlaps the longitudinal axis of the coaxial microwave transmission path. A liquid membrane separation method according to claim 1, characterized in that: 3. The liquid membrane separation method according to claim 1, wherein the polymer membrane is a plurality of fine-diameter hollow fiber membranes.