JP2006130385A - Microwave chemical reactor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a new means of heating, with microwaves, a sample flowing through the central part of a cylindrical cavity resonator or housed in the central part of the resonator to promote the chemical reaction of the sample. <P>SOLUTION: The cavity resonator 1 consists of a metal-made cylindrical side wall 7 and a metal-made end side wall 8 closing electromagnetically both ends of the cylindrical side wall 7 in the axial direction. A tube 2 or a cylindrical container made of an electromagnetic wave transmitting dielectric is arranged coaxially within the cavity resonator, and a sample is housed in the tube or container. Microwaves are combined externally with a combining slot 4 arranged on the cylindrical side wall 7 of the cavity resonator 1 in the axial direction. A microwave electric field which is constant in size along the circumference and changes in the radial direction so as to become practically zero in size at two or three points including the cylindrical side wall is generated within the cavity resonator 1 to heat the sample so as to promote the chemical reaction. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a chemical reaction apparatus that promotes a chemical reaction by irradiating a microwave, and despite using a cavity resonator, an object to be heated (hereinafter referred to as a “sample”) such as a liquid, a gas, or a powder. This is related to a microwave chemical reaction apparatus in which there is almost no need to adjust the resonance frequency with respect to changes in dielectric properties such as the relative dielectric constant and tan δ of the sample accompanying temperature changes, or the necessity is greatly reduced.

Microwaves are widely used as a heat source for industrial heating furnaces including microwave ovens. Microwaves not only heat water contained in substances, but also act on polar dielectric substances to directly and selectively heat them, so that samples can be heated from outside like conventional heating means. Compared to the device that performs this, it has the feature that the sample can be heated efficiently in a short time.
In recent years, when microwaves are radiated on a substance to be subjected to a chemical reaction, a phenomenon that can greatly accelerate the reaction has been found, and the use as a chemical reaction apparatus that performs a chemical reaction in a short time is not limited to a simple heating device. Opening up.
Microwave chemical reaction devices are roughly classified into a matching waveguide type in which a matching load is connected to the terminal, a short-circuited waveguide type in which the terminal is short-circuited, and a cavity resonator type using a cavity resonator.
In general, a chemical reaction is performed by placing a sample in an apparatus of these types. The matching waveguide type requires almost no adjustment, so it is simple in use, but there is a problem that only the microwave power propagating toward the end can be used due to the configuration of the device, and the efficiency is not so high. Have drawbacks. However, even if there is such a problem, it has the ability to accelerate the chemical reaction correspondingly considerably, so that its use is widespread because of its convenience in use. In contrast to this device, the short-circuited waveguide type can use microwaves reflected and returned for reaction, and the phase of the traveling and reflected microwaves is adjusted to be in phase at the sample position. However, it has the disadvantage that the short-circuit position must be adjusted to some extent according to the difference or change in the dielectric properties of the sample. The cavity resonator type is designed to irradiate the sample multiple times with multiple reflections of the microwaves on the cavity wall, which has the advantage of extremely high efficiency, but responds to differences and changes in sample characteristics. It has the disadvantage that it is necessary to adjust the resonance frequency to always tune. Therefore, there is an increasing demand for development of a device having high efficiency characteristics such as a short-circuited waveguide type and a cavity resonator type and a simple matching waveguide type. That is, there is a demand for development of an apparatus that does not require any adjustment or that can be adjusted by a simple method.
Another important requirement for chemical reactions is reaction uniformity. Satisfying this requirement is to irradiate the sample with microwaves of equal strength. In particular,
When a catalyst is used for a chemical reaction, it is desirable to irradiate the catalyst and a sample in the vicinity thereof with a substantially uniform microwave and selectively heat only this portion to an equal temperature. The use of microwaves for chemical reactions has become widespread, but in the future, the demand for uniform irradiation, which is not much considered at present, will increase.
As a technique for greatly increasing the efficiency of chemical reaction using a cavity resonator, for example, an apparatus shown in Patent Document 1 has been proposed. In this method, a microwave propagating in a waveguide is guided to an annular waveguide, and a coaxial cylindrical space is provided inside the annular waveguide, and provided in a partition wall between the waveguide and the cylindrical space. Microwaves radiated from at least three slots in the axial direction are irradiated to a sample disposed in the center of the cylindrical space to cause a chemical reaction. It is described that even if the dielectric property of the sample changes with increasing temperature, microwaves are irradiated from a plurality of slots and automatically tuned so that there is no need for external compensation. However, this method has a complicated apparatus configuration and not only a complicated coupling in terms of electromagnetic waves, but also an electric field is canceled out to zero at the center of the cylindrical space. I can not say.
U.S. Patent No. 6,713,739

  The present invention has been made based on the background and requirements as described above, and an object thereof is to provide a new means for promoting a chemical reaction by microwaves.

  In the invention described in claim 1, in order to solve the above-described problem, a microwave is coupled from a waveguide through a coupling slot into a cylindrical cavity resonator, and strict frequency tuning is not required. In addition, a microwave chemical reaction device for promoting a chemical reaction of a sample disposed in the central portion of the cylindrical cavity is configured.

  The invention described in claim 2 provides a means that allows the microwave chemical reaction device according to claim 1 to perform rough frequency tuning by a simple method.

  The invention described in claim 3 provides means for enabling automatic frequency tuning in the microwave chemical reaction device described in claim 1 or 2.

  In the invention described in claim 1, frequency tuning is not required for the change in the characteristics of the dielectric during heating.

  In the invention described in claim 2, tuning can be secured for a large difference in dielectric characteristics due to a difference in dielectric.

  In the invention described in claim 3, tuning can be ensured by utilizing an electromechanical feedback means with respect to a change in dielectric characteristics.

  An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing the basic structure of the present invention, FIG. 2 is an external view for explaining a coupling method of a cavity and a waveguide, and FIG. 3 is a characteristic diagram for explaining the broadband property obtained by the configuration of the present invention. 4 is an explanatory diagram relating to the Q characteristic of the resonator that reduces the degree of tuning required in cooperation with the configuration of FIG. 3, FIG. 5 is a perspective view showing a means for changing the resonance frequency relatively large, and FIG. 6 is a dielectric. It is a fragmentary sectional view which shows one Example of the method of preventing the leakage of the electromagnetic waves from the part which inserted the stick | rod.

  In FIG. 1, 1 is a cylindrical cavity resonator, which has a cylindrical side wall 7 and end side walls 8 at both ends in the axial direction. A circular tube 2 is arranged concentrically with the cavity and allows a sample to cause a chemical reaction to flow inside. The circular tube 2 is made of a material having a low microwave loss and excellent heat insulating properties, such as quartz, and the microwave heats a sample that passes through the circular tube and flows therein, and its chemical reaction. Promote. The circular tube 2 may be replaced with a cylindrical container such as a test tube that accommodates a sample therein as necessary, as long as the circular tube 2 is disposed substantially coaxially with the cavity. Hereinafter, for the sake of simplicity, the case of a circular pipe will be taken up and described. As shown in FIG. 2, the waveguide 3 is connected to the side wall 7 of the cylindrical cavity resonator from the direction perpendicular to the central axis at the substantially center in the axial direction. The short-circuit plate 5 at the end of the waveguide 3 has a slot-like coupling hole 4 extending in the axial direction of the cavity resonator 1 at the center. The short-circuit plate 3 is partially in common with the side wall of the cavity resonator 1. This coupling hole 4 excites TM020 or TM030 mode electromagnetic waves from the waveguide 3 into the cavity resonator 1. The electric field of this electromagnetic wave does not change along the circumference, is constant in the axial direction, and is distributed so that it is zero in two or three locations including the side wall of the cavity resonator 1 in the radial direction. Yes. The directions of the electric fields inside and outside the zero position are opposite to each other. The axial distribution is constant when nothing is in the cavity, but when a sample that absorbs microwaves is inserted, it tends to become somewhat weaker toward the ends of the shaft. The axial uniformity is worse in the container than in the circular tube.

  FIG. 3 shows the change in the resonant peripheral edge with respect to the relative permittivity when the TM010, TM020, TM030, and TM040 modes are excited. In the figure, for the sake of convenience, the last 0 of the symbol indicating the mode is omitted. The cavity radius is chosen to resonate at approximately 2,300 to 2,600 MHz for TM020, TM030, and TM040 when the dielectric constant is relatively large. That is, in this calculation, the radius of the dielectric is 10 mm, and the cavity radius for these modes is 80, 120, and 180 mm, respectively. The cavity radius for TM010 is 45mm. From the figure, it can be seen that the frequency change of TM010 with respect to the dielectric constant is large, but the change in the resonance peripheral number is small in the mode of TM020 or higher. Note that the higher the mode, the larger the cavity diameter becomes impractical, so it is advisable to choose around TM020, TM030.

  FIG. 4 shows the Q characteristics of the cavity. When nothing is accommodated in the circular tube 2, Q takes a very high value of about 4,000 to 5,000. Thus, when Q takes a high value, the band becomes extremely narrow, and the electric field generated in the cavity suddenly weakens when the frequency slightly deviates from resonance. When Q is a low value of about 10, even if the frequency is shifted from resonance by about 120 MHz, the electric field strength is only reduced to about half. If the sample to be subjected to the chemical reaction absorbs microwaves well, the Q will be low, so there is no need to tune closely.

  When a relatively large microwave absorption solvent such as water or ethylene glycol is used for a sample that causes a chemical reaction, the Q is sufficiently low and the resonance characteristics are broad, depending on the amount of charge. As a result, even if the dielectric characteristics change to some extent as the temperature changes or the chemical reaction proceeds, most of the microwave power can be absorbed non-tuned.

  When a solvent such as ethanol is used for the sample, the dielectric constant is smaller than that of the above-mentioned solvent. For example, when the solvent is switched to ethanol while maintaining a structure that resonates with water, it is considerably out of resonance. In that case, a method as shown in FIG. 5 is adopted. Here, four adjustment rods 6 made of a dielectric are inserted into an end side wall 8 orthogonal to the central axis of the cavity resonator 1 so as to be freely accessible. The four adjusting rods 6 are arranged along the coaxial circumference of the cavity resonator 1 so as to be parallel to the central axis. You may increase the number if necessary. The resonance frequency is lowered due to the effect of the dielectric constant of the adjusting rod 6, so that tuning can be achieved.

  In order to increase the resonance frequency, a metal adjusting rod 6 may be used instead of the dielectric. By selecting an appropriate number, diameter, and material, the resonance frequency can be adjusted for a considerable number of samples. Usually, Q is not so high, and it is not necessary to adjust the resonance frequency strictly. In addition, since this method simply inserts or removes an appropriate number of adjusting rods, the purpose of tuning can be easily achieved. Since the dielectric constant changes as the temperature rises and the reaction progresses, tuning can be secured in a wider range by taking a technique such as removing the tuning in advance so that the degree of the change can be offset.

  In addition, the method of tuning by the comparatively simple method was shown above. However, especially when Q is high or when it is desired to ensure the tuning fairly strictly, the electromagnetic wave generated in the cavity using a coupler. It is sufficient to use a frequency adjusting means that can automatically control the value so as to maximize the value. As a means for changing the resonance frequency of the cavity, a means for changing the insertion amount of the dielectric or metal adjusting rod 6 as described above and a method for inserting a small piece made of a dielectric or metal into the cylindrical surface are used. It can also be used. In the present invention, since the resonance mode is TM020 or TM030, the change in the resonance frequency with respect to the change in the dielectric constant is small. As a result, even in the case of automatic control, the adjustment width is advantageously reduced. When the Q is extremely high, it is necessary to adopt such an automatic resonance mechanism, but in many cases, this is not necessary in a normal chemical reaction apparatus.

  When the adjusting rod 6 is inserted into the end side wall 7 of the cavity resonator 1, electromagnetic waves may leak from the insertion hole. FIG. 6 shows an example of countermeasures against radio wave leakage when the adjustment rod 6 is inserted. In the metal circular tube 9 of FIG. 6, the inner diameter is a value that cuts off the microwave. The length of the metal circular tube 8 is set to such a value that leakage is sufficiently reduced. When the adjusting rod 6 is made of metal, there is a possibility of discharge between the end side wall 8 and the metal rod 6, so that they are completely brought into contact with each other, or a little gap is made. In this case, a coaxial line is formed with the metal circular tube 9, so that the metal circular tube 9 and the metal rod 6 are completely short-circuited at the end.

  When a sample is inserted into the cavity resonator 1, the impedance of the cavity changes and the matching with the waveguide 3 becomes worse. For this problem, a matching device such as a 3-stub tuner is used. Matching also varies with sample differences and property changes. However, if matching is performed with respect to typical conditions, a certain level of requirements can be satisfied without matching each time. If you want to always achieve perfect matching, you may use a matching unit that can automatically match.

  In addition to being able to make a highly efficient chemical reaction device by irradiating a sample flowing in a circular tube disposed in the center of the cavity with a microwave, this invention can generate a uniform electric field in the circumferential direction. Therefore, the chemical reaction can be promoted relatively uniformly, and a wide range of industrial applications are possible.

It is sectional drawing of the chemical reaction apparatus which concerns on embodiment of this invention. 1 is an external view of a chemical reaction device according to an embodiment of the present invention. It is explanatory drawing of the resonance characteristic which concerns on embodiment of this invention. It is explanatory drawing of the resonance characteristic which concerns on embodiment of this invention. 1 is a perspective view of a chemical reaction device according to an embodiment of the present invention. It is a partial sectional view of a chemical reaction device concerning an embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Cavity resonator 2 Circular tube 3 Waveguide 4 Coupling hole 5 Shorting plate 6 Adjustment rod 7 End side wall 8 Metal circular tube

Claims (3)

A cavity resonator composed of a metal cylindrical side wall and a metal end side wall that electromagnetically closes both axial ends of the side wall;
Coaxially disposed in the cavity resonator, and includes a circular tube or a cylindrical container made of an electromagnetic wave transmitting dielectric material that accommodates a sample therein,
The microwave is coupled from the outside by a coupling slot provided along the axial direction on the cylindrical side wall of the cavity resonator,
In the cavity resonator, the size is constant along the circumference, and the size changes so that the size becomes substantially zero in two or three locations including the cylindrical side wall in the radial direction. A microwave chemical reaction device that generates a wave electric field and heats the sample to promote a chemical reaction.   2. The microwave chemical reaction device according to claim 1, wherein a rod-like dielectric or metal piece is inserted into the cavity resonator so as to freely enter and exit, thereby adjusting a resonance frequency of the cavity resonator. .   A coupler is provided on the wall surface of the cavity resonator to extract a part of the electromagnetic field generated in the cavity, and the resonance frequency of the cavity is changed so that the intensity of the electromagnetic field is substantially maximized. The microwave chemical reaction device according to claim 1 or 2, wherein

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