JPH04317737A - Laser beam chemical reaction device - Google Patents

Abstract

PURPOSE:To enhance the photochemical reacting efficiency of laser output by a method wherein three optical systems are arranged in such a manner that the condensing laser beams therefrom coincide at least twice in their condensing position and the three optical systems are disposed in a reactor. CONSTITUTION:The laser beams 1 are CO2 laser beams generated by a laser beam generator and are condensed by a ZnSe-made condensing lens 2 having both its sides coated with a nonreflecting coating material to prevent the loss of the laser beam reflection from its surface. The laser beams 1 are introduced into a reactor 5, converged into a focus, reflected by a spherical mirror 3, converged near the center of an angle reactor 5, and then the laser beams reach a spherical mirror 4. The laser beams repeat multiple reflection between the spherical mirrors 3 and 4 and coincide near the center of the reactor 5 and a reactant material gas 6 is supplied under a predetermined pressure from the side face of the reacter 5 through a throat-shaped gas outlet 8 into the reacter 5. After laser irradiation, the reactant gas, together with the reaction product, is carried out from the reactor 5 from its gas suction opening 9 to separate the reaction product therefrom.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a reaction device for performing photochemical reactions such as isotope separation using a laser beam, and in particular, the present invention relates to a reaction device for performing photochemical reactions such as isotope separation using a laser beam. The present invention relates to a laser photochemical reaction device that is highly reliable and does not cause damage to optical components due to strong laser energy density.

0002

BACKGROUND OF THE INVENTION In recent years, the increase in output power and the diversification of oscillation wavelengths in laser technology have promoted research into the use of lasers for photochemical reactions. The most typical example of the application of lasers to photochemical reactions is isotopic separation and enrichment technology for various elements ranging from hydrogen to uranium. This is by promoting the chemical reaction of only substances containing isotopic elements. Conventionally, various methods and apparatuses have been proposed for such isotope separation/concentration reactions using laser beams. For example, in the method disclosed in FIG. 1 of JP-A No. 60-132,629, a pulsed carbon dioxide laser beam is focused by a long focal length lens and introduced into a reactor, and photochemical reactions are performed near the focal plane. It causes a reaction to occur.

In such photochemical reactions using infrared multiphoton absorption, the reaction efficiency generally increases exponentially as the laser energy density increases up to a certain value, and beyond this point the reaction efficiency saturates. There is a so-called critical fluence. For this purpose, the laser beam is converged by a condensing lens having a focal length such that a critical fluence can be obtained at the condensed position, and the reaction proceeds near the focal point. Therefore, in such a reactor, the laser power is only used effectively in a part of the reactor, and in the region of the reactor below the critical fluence, the laser energy is absorbed without contributing to the reaction. Furthermore, since the remaining energy is dissipated from the output end of the reactor, there is a problem in that only a few to 20% of the laser power actually output from the laser oscillator is effectively used for chemical reactions.

In addition, in the photochemical reaction process using a laser beam, the laser accounts for the highest proportion of both initial cost and running cost, and in order to realize a low-cost laser photochemical reaction process, it is necessary to increase the laser power. Effective utilization technology is an essential requirement. In order to deal with this problem, a series multi-stage light condensing system as shown in FIG. 3 of Japanese Patent Application Laid-Open No. 59-123-517 has been proposed. However, in this method, as the number of condensing stages increases, the utilization rate of laser power increases compared to the above method, but the reactor becomes extremely long and it is difficult to ensure the stability of the optical axis. In addition, there are problems such as a large loss of laser energy that does not contribute to the reaction due to absorption of the raw material before and after the focal point of each stage. Regarding the latter problem, in order to limit the presence of the raw material only in the region where critical fluence is obtained, it is possible to shorten the length of the reactor to match that region. , critical fluence is several J/cm
If it is higher than 2, the light resistance strength of the window material for transmitting the laser beam will be exceeded, and the window material will frequently break, resulting in the problem that a stable and reliable reaction device cannot be realized. Furthermore, as a solution to the former problem, as a system in which the length of the reactor is short and the laser power can be used effectively, multiple reflection as shown in Figure 1 of Japanese Patent Application Laid-Open No. 54-12,290 has been developed. There is an example of a reactor equipped with a pair of mirrors. In this case, multiple reflections of the beam repeat the superposition without focusing, so this method is very effective when the required critical fluence is as low as 1 J/cm2, but it is very effective when the required critical fluence is as low as 1 J/cm2. ~6J
/cm2 is required, it is difficult to realize this over the entire overlap region. Furthermore, since the surface shape of the reflecting mirror becomes complex and the reaction occurs near the reflecting mirror, the reflecting mirror surface is contaminated by the reaction products, and there is also the problem that a stable reaction over a long period of time cannot be realized.

[0005] Also, even higher fluences, such as 10
For cases where J/cm2 is required, Japanese Patent Application Laid-open No. 5
As disclosed in FIG. 1 of Japanese Patent No. 9-42,026, a method of multiple reflection of a laser beam within a reactor has been proposed. In this method, a pair of spherical mirrors for multiple reflection of the laser beam is provided inside the reactor, and multiple focal points are focused at different positions within the reactor. When the absorption coefficient is small, the amount of reaction increases in a manner close to linear with respect to a single light collection by the number of times of light collection. However, the absorption coefficient is 0
．． If it is 1%/cm or more, the laser power loss in the region where the beam is not focused becomes large, and a large increase in the amount of reaction cannot be expected. Furthermore, since a small amount of reaction occurs near the surface of the reflecting mirror, there is a problem that the surface of the reflecting mirror is contaminated by reaction products.

[0006] In order to deal with such a problem of contamination of the reflector, Japanese Patent Application Laid-Open No. 153-126-1983 discloses a system in which a carrier gas is passed only in the vicinity of the reflector in FIG. 1. In this example, a large number of reflecting mirrors are installed, and in order to separate the isotope separation chamber and the carrier gas distribution chamber, a partition plate with passage holes for transmitting laser light is installed. If the laser optical axis fluctuates during operation, there is a problem that stable laser irradiation cannot be achieved.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to
The goal is to realize a low-cost and highly reliable reaction process, and in particular, by effectively utilizing the power of the laser beam, which accounts for the highest price, it is a simple method that can improve the photochemical reaction efficiency with respect to laser output. The object of the present invention is to provide a laser photochemical reaction device.

[0008]

[Means for Solving the Problems] The present invention provides a laser photochemical reaction in which a laser beam is focused and introduced into a reaction region where a raw material exists, and a desired reaction is carried out using the light absorption characteristics of the raw material. In the apparatus, an optical system including a second light reflector for refocusing the laser beam is provided behind the focal position of the first optical system for concentrating the laser beam,
Furthermore, an optical system consisting of a third light reflector is installed at a position facing the second optical system, and the laser beam is multiple-reflected between the second and third optical systems, and the first, second, and The laser beam focused by the third optical system is configured to overlap twice or more at the focused position, and all three types of optical systems are installed in the reaction vessel, and the laser energy density of the raw material to be reacted is such that the photochemical reaction takes place. Laser photochemistry that flows in a direction perpendicular to the laser optical axis so that it exists only in the region where the value above the required critical fluence is obtained, and the region where the laser energy density is below the critical fluence is a space that does not absorb laser light. This is a reaction device that effectively uses most of the laser energy extracted from the laser oscillator for photochemical reactions, and provides a highly reliable device that does not damage optical components due to strong laser energy density. be.

[0009]

[Operation] The present invention will be explained in detail below. First, the principle of the optical system in the laser photochemical reaction device of the present invention will be explained using FIG. In FIG. 2, the arrangement of three types of optical systems and their coordinate systems are shown, and the laser beam 1
The locus of the central optical axis is shown up to the fifth pass. In this figure, as a typical condition, the case where the value of the X coordinate of the focal point of the lens 2 and the value of the X coordinate of the centers of curvature of each of the two spherical mirrors 3 and 4 are all f. That is, the coordinates of the lens principal point position are (0, 0), its focal length is f, and the center coordinates (X1, Y1) of the spherical mirror 3 are (
f, Y1), and its radius of curvature R1 is f,
The center coordinates (X2, Y2) of the spherical mirror 4 are (f, Y2
), and its radius of curvature R2 is f. Note that the focal length of each spherical mirror 3, 4 is 1/ of the radius of curvature R1, R2.
It is given as a value of 2.

First of all, the conditions for the laser beam 101 (incident beam) that has passed through the lens 2 by the two spherical mirrors 3 and 4 to start multiple reflection without loss are as follows.
When the laser beam 102 first reflected by the spherical mirror 3 reaches the spherical mirror 4, the Y coordinate value of the center of the optical axis is smaller than the Y coordinate value (Y=0) when it passes through the lens 2, which is the diameter of the incident beam. It is necessary to deviate by the same amount. Therefore, when the diameter of the incident beam is D, the condition for the Y coordinate value (Y1) of the center of curvature of this spherical mirror 3 is Y1 ≦-
(D/4) is given.

At this time, from the spherical mirror 3 to the spherical mirror 4
The Y-coordinate value (Ycmin) of the optical axis at the focal position of the beam that goes to the first stage is given by 2Y1, and the Y-coordinate value (Yc) of the optical axis at the focal position in subsequent multiple reflections is given by the spherical mirror. By selecting an appropriate value for the Y coordinate value (Y2) of the center of curvature of No. 4, it is possible to appropriately change the Ycmin≦Yc≦0. Here, the conditions for sequentially superimposing the laser beams at the focal position are the Y-coordinate value (Y2) of the optical axis at the focal position in multiple reflections determined by the setting of the Y-coordinate value (Y2) of the center of curvature of the spherical mirror 4 ( It is determined based on the balance between the amount of change in Yc ) and the diameter of the condensed beam, but under general conditions it is given in the following range. -(D/2)≦Y1≦-(D/4)

Next, regarding the setting of the Y coordinate value (Y2) of the center of curvature of the spherical mirror 4, R1 = R2 = X1 = X2 = f = 1,5 using the ray tracing method in geometric optics.
A simulation was performed under the following conditions: 00mm, D=31mm, and Y1=-8mm. The calculation results were displayed so that one laser beam was represented by two trajectories at both outer edges of the beam in order to display the convergence and diffusion status of the laser beam. Note that this calculation is based on geometric optics, and the beam diameter near the focal point is underestimated compared to the actual one.

FIG. 3(a) shows the calculation results when Y2 = 1.25Y1, and the number 1i added to the laser beam in the figure (i is a two-digit number, 01 to 10 in FIG. 3). ) corresponds to the i-th reflection path. Under this condition, Yc
For the value of , the value of 5 points obtained by dividing the interval between 0 and Ycmin into four is taken twice each time, and in the 10th pass, it coincides with the incident optical axis and returns to the incident side via the lens. As an example, if we consider the case where the diameter of the condensed beam is 8 mm under the conditions of Fig. 3(a), Y cm
Since in=-16mm, the value of Yc is 0, -
As a result of taking five values twice each: 4 mm, -8 mm, -12 mm, and -16 mm, an area of 16 mm in the Y direction (-16 mm
Four beam superpositions were obtained over m≦Y≦0 mm), and 4 mm each at both ends (0 mm≦Y≦4 mm, -20
Two beam superpositions are obtained in a total area of 8 mm (mm≦Y≦−16 mm). FIG. 3(b) is an enlarged diagram schematically showing a region where multiple reflections and superpositions occur. Note that this superposition situation assumes that the ratio of Y2 /Y1 is constant and that Y
Although it can be controlled appropriately by changing the value of 1, it is clear that overlapping occurs two or more times.

Next, the reason why multiple reflection of a laser beam and superimposition at the focal position is more advantageous than focusing the laser beam at different positions in multiple stages will be explained. For convenience, the laser beam has a square shape,
Further, it is assumed that there is no absorption of laser energy by the source gas, and that the fluence at the focal position in one pass shown in the above example is 1/4 of the critical fluence. Also, the depth of focus is 300 with the above numerical settings.
mm, the reaction volume under this condition is 8 mm x 16 mm x 300 mm = 3 where 4 times of superposition has occurred.
It becomes 8.4cm3. On the other hand, if you try to obtain critical fluence with one focusing, the diameter of the focused beam is proportional to the focal length, so it becomes necessary to reduce the focal length of the focusing lens to half the value, and the focused beam becomes The shape is 4mm
×4mm, since the depth of focus is proportional to the square of the focal length, 7
It will be 5mm. In order to make this region correspond to the above 10-pass superposition, even if it is made from 10 regions, the total reaction volume is 4 mm x 4 mm x 75 mm x 10 = 12 cm3
The former is more than three times larger than the latter. Furthermore, if the absorption of laser energy by the source gas cannot be ignored, the difference becomes even larger. In the above calculation, the propagation delay of the laser beam was ignored. However, in the numerical example above, the propagation delay at the focal position of the 1st and 10th passes is 90 ns.
ec. This is equivalent to the typical pulse width of a pulsed carbon dioxide laser used for infrared multiphoton excitation, so this degree of propagation delay does not have a large effect on the reaction characteristics.

In the above example, the reaction area was expanded by realizing multiple reflections and superposition near the focal point, but
It is also possible to keep the reaction area constant and reduce the laser power. For general pulsed discharge gas lasers, if the laser output is lowered below its limit value, the lifespan of the laser gas, high voltage switch, electrodes, power supply, etc. will be much longer than the reciprocal of the decrease in output, so consumables costs will be increased. Since the laser running cost including the above is significantly improved, it is effective in improving the reaction efficiency and realizing a low-cost process.

[0016] Next, the rationale for restricting the raw material to be reacted to a region exceeding the required critical fluence and flowing it in a direction perpendicular to the laser optical axis and the method for realizing this will be explained. As explained in the prior art section, in photochemical reactions using infrared multiphoton absorption, when the laser energy density decreases below the critical fluence, the reaction efficiency decreases exponentially. However, the laser energy absorption rate does not depend much on the laser fluence. As an example, in the multiple reflection superposition reaction system of the above numerical example, the length of the reaction region per pass is 30 cm, while the length of the non-reaction region is as much as 270 cm. If the laser energy absorption rate is 0.2%/cm, the energy absorption rate in the reaction area is 5.8%, while the energy absorption rate in the non-reaction area is as high as 41.7%. Due to multiple reflections, the superimposing effect is almost eliminated. Therefore, the non-reactive area needs to be a space that does not absorb laser light. Here, the simplest method is to install a reactor with a length that matches the reaction region length above in a place where multiple reflections and superpositions are obtained, but as mentioned above, if the critical fluence is high, the laser beam This cannot be realized due to the problem of damage to the entrance window material.

Therefore, as a result of intensive studies to solve this problem, we found that when the raw material gas to be reacted is circulated over a length of about 200 mm or less in vacuum, the flow rate is 10 mm/sec.
．． It has been found that by forming a laminar flow using the above-mentioned relatively high-speed flow, it is possible to suppress the diffusion of particles without particularly providing partition walls. Furthermore, it has been found that by forming a laminar flow of a different type of gas maintained at a more positive pressure at both ends of the laminar flow, it is possible to more precisely limit the flow area in the central portion. Here, if a different type of gas is added, this gas will be mixed into the mixture of the reaction product and reacted raw material to be recovered, so in order to prevent the reaction product from reacting with this gas, It is necessary to use an inert gas. Further, formation of a laminar flow of gas can be realized by making the shape of the gas jet port into a throat shape.

As shown in the explanation of multiple reflection superposition above, the shape of the reaction region is approximately a rectangular parallelepiped, and it is longest in the direction of the laser optical axis, and in any direction perpendicular to it, it is shorter than the former. It's quite short. Therefore, in order to prevent the reaction material gas from diffusing, it is necessary to flow the gas in the short side direction, that is, in the direction orthogonal to the laser optical axis. Furthermore, with the above configuration, the raw materials to be reacted do not reach the vicinity of the three types of optical systems installed in the reactor, so there is no problem of contamination of optical components by reaction products.

Although FIGS. 2 and 3 show examples in which the lens 2 is used as the first optical system, this may also be a light reflector such as a spherical mirror or an off-axis parabolic mirror.
Although the second and third optical systems use concave spherical mirrors 3 and 4, respectively, a combination of a collimator convex lens and a plane mirror may be used.

[0020]

EXAMPLES Hereinafter, the laser photochemical reaction apparatus according to the present invention will be specifically explained based on examples. FIG. 1 is a configuration diagram showing an embodiment of the laser photochemical reaction device of the present invention. The trajectory of the laser beam 1 introduced into the reactor 5 is a line centered on the optical axis (1
01 to 105). The laser beam 1 has a square shape (D
= 31 mm) pulsed TEA CO2 laser beam (output 2 J/pulse), and a ZnSe condenser lens 2 (focal length f = 1.
5m). Here, the condenser lens 2 also functions as a window material for blocking the inside of the reactor from the atmosphere. After the laser beam 1 introduced into the reactor 5 is focused, it passes through a spherical mirror 3 (copper, gold coated, R1 = 1.5
m), and after connecting again near the center of the reactor 5, it reaches the spherical mirror 4 (copper, gold coated, R2 = 1.5 m). Thereafter, multiple reflections are repeated between the two spherical mirrors 3 and 4, and superposition is realized near the center of the reactor 5. The raw material gas 6 to be reacted is supplied into the reactor 5 from the side of the reactor 5 through a throat-shaped gas outlet 8 at a pressure adjusted by a pressure regulator (not shown), and after being irradiated with a laser, the gas is The reaction product is taken out from the reactor 5 through the suction port 9, and the reaction product is separated from other substances by a separation/recovery device (not shown). The inert gas 7 is introduced into the reactor 5 through the supply port 8, taken out through the suction port 9, purified, and recycled again.

Using the reaction apparatus shown above, f=R1
=R2 =X1 =X2 =1.5m, Y1 =-8
mm, Y2 = -10 mm, and the focused beam diameter is 8 mm.
We constructed a system in which superposition occurs four times each. Then, set the oscillation line of the carbon dioxide laser to 9P (22) (1045.0
2cm-1) and 70% as the raw material gas 6 to be reacted.
torr of CHClF2 at 20 mm/sec. 75 torr as an inert gas 7.
Laser irradiation was performed while r of Ar was flowing at the same speed, and carbon-13 isotope enrichment was performed. As a result, about 80% of the laser energy was effectively consumed, and 7.5 x 10-8 mol of 13C2F4 was produced as a reaction efficiency per pulse. In addition, for comparison, the reaction efficiency was investigated by performing multistage light focusing 10 times at different points, and the results showed that
A value of ol/pulse was obtained. Therefore, it has been found that the present invention improves the reaction efficiency per unit laser pulse energy by more than three times as compared to the prior art.

[0022]

As explained above, according to the present invention, the power of the laser beam, which accounts for the highest cost in the photochemical reaction process using a laser beam, can be effectively used, and the photochemical reaction efficiency with respect to laser energy can be improved. This makes it possible to improve the performance and reduce various costs of lasers, and also eliminates the problem of damage to optical parts caused by high laser energy density, realizing a low-cost and highly reliable laser photochemical reaction process. It has the advantage of being able to

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a laser photochemical reaction device of the present invention.

FIG. 2 is a schematic diagram for explaining the principle of the optical system that constitutes the multiple reflection superimposition system in the laser photochemical reaction device of the present invention.

[Figure 3] (a) is a graph showing the results of calculating the laser condensation situation in the present invention under typical conditions, and (b) is a schematic enlarged view of the region where multiple reflections and superpositions occur. FIG.

[Explanation of symbols]

1 Laser beams 101 to 110 Multiple reflection laser beam 2 Condensing lens 3 Spherical mirror 4 Spherical mirror 5 Reactor 6 Raw material gas to be reacted 7 Inert gas 8 Gas supply port 9 Gas suction port

Claims (4)

[Claims] [Claim 1] A laser photochemical reaction device that focuses a laser beam and introduces it into a reaction region where a source material is present, and performs a desired reaction using the light absorption characteristics of the source material. An optical system consisting of a second light reflector for refocusing the laser beam is provided behind the focal position of the first optical system for An optical system consisting of a light reflector is installed, and the laser beam is multiple-reflected between the second and third optical systems.
In addition, the laser beams focused by the first, second, and third optical systems overlap each other twice or more at their focusing positions, and all three types of optical systems are installed in the reaction vessel, and the raw materials to be reacted are The laser beam is distributed in a direction perpendicular to the laser optical axis so that it exists only in the area where the laser energy density is higher than the critical fluence required for photochemical reaction, and the laser beam is distributed in the area where the laser energy density is lower than the critical fluence. A laser photochemical reaction device characterized by a non-absorbing space. 2. The laser photochemical reaction device according to claim 1, wherein the space that does not absorb laser light is a vacuum. [Claim 3] Claim 1, wherein the space that does not absorb laser light is an inert gas flow maintained at a more positive pressure than the raw material to be reacted.
The laser photochemical reaction device described. 4. The optical system according to claim 1, wherein the first optical system is a lens, a spherical mirror, or an off-axis parabolic mirror, and the second and third optical systems are a spherical mirror or a combination of a lens and a plane mirror. Laser photochemical reaction device.