JPH0624962B2 - Method for recovering high-purity argon from exhaust gas from a single crystal manufacturing furnace - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for recovering high-purity argon from exhaust gas from a single crystal manufacturing furnace, and more specifically, to a method for recovering a silicon single crystal or the like used as a substrate material for a semiconductor. As described above, the exhaust gas containing argon gas as a main component after being used as an atmospheric gas during the production of a single crystal is collected, and the exhaust gas is purified to be collected as high-purity argon.

[Conventional technology]

Since argon gas has an inert property, it has been widely used in various industrial fields such as a shielding gas for welding and an atmosphere gas for heat treatment of metal. In recent years, along with the remarkable development of the semiconductor industry, there has been a remarkable increase in the production amount of silicon single crystal plates that are the substrates. However, in producing a single crystal such as a silicon single crystal plate, an argon gas, which is an inert gas, is used as an atmospheric gas in order to obtain a high quality single crystal. The high-purity (99.999% by volume) argon gas supplied to the manufacturing furnace during the production of such a single crystal is used with the atmosphere gas in the furnace and then sequentially discharged from the inside of the furnace to the outside of the furnace. This exhaust gas is a gas whose main component is argon, which still contains 99.9% by volume of argon. However, as a result of using it as an atmospheric gas in a furnace, not only dust such as silicon dioxide, silicon oxide, and carbon is mixed and entrained, but also hydrogen, oxygen, carbon monoxide, carbon dioxide, as well as nitrogen, hydrocarbon, It was found that a wide variety of components such as water were mixed in although they were in trace amounts (about 0.1% by volume). Even though the exhaust gas discharged as described above contains 99.9% by volume of argon, it contains the above-mentioned impurity components and is released to the atmosphere without being effectively used. Is the reality. However, high-purity argon is extremely expensive. Therefore, it is economical to recover the exhaust gas containing argon as a main component, which is discharged from the above-mentioned crystal manufacturing furnace, remove impurities to purify it as high-purity argon, and reuse it. It is preferable in terms of effects, and the appearance of such a method is desired.

[Problems to be solved by the invention]

However, the exhaust gas from the single crystal manufacturing furnace contains a large amount of impurities, though in a trace amount, and it is difficult to remove these impurities efficiently, and various methods have been proposed for examination, but The reality is that we have not yet come up with a satisfactory method.

The present invention has been invented in view of the above situation, and contains solid dust such as silicon oxide, silicon dioxide, and carbon containing argon as a main component and containing hydrogen, oxygen, carbon monoxide, hydrocarbon,
Exhaust gas from a single crystal manufacturing furnace containing multi-component impurities such as nitrogen and water is removed, the impurities are removed and purified, and highly pure argon that can be reused efficiently is collected. It is intended.

[Means for solving problems]

To achieve the above object, the present invention contains argon as a main component,
Exhaust gas from a single crystal manufacturing furnace containing dust, oil, carbon monoxide, oxygen, hydrogen, nitrogen, etc. as impurities is first removed of solids such as dust and oil, and then necessary for the reaction of oxygen in the exhaust gas. Excessive stoichiometric amount of hydrogen is added to convert oxygen to water by catalytic reaction, then carbon monoxide and hydrogen are reacted with copper oxide to convert to carbon dioxide and water, and then the conversion is performed through an adsorption column. The water, carbon dioxide and nitrogen impurities are removed to recover high-purity argon, and a part of the high-purity argon is used for regenerating the adsorption column, and then oxygen is added to the high-purity argon to raise the temperature. The present invention relates to a method for recovering high-purity argon from exhaust gas of a single crystal manufacturing furnace, which is used for oxidative regeneration of reduced copper produced by a reaction of carbon monoxide and hydrogen with copper oxide.

[Embodiment] Next, the method of the present invention will be described with reference to the drawings, illustrating a system diagram of an embodiment of the present invention. In the figure, 1 is a single crystal manufacturing furnace,
2 is a gas holder, 3 is a venturi scrubber for removing dust such as silicon monoxide, silicon dioxide and carbon,
Reference numeral 4 is a compressor, 5 is an oil removal cylinder filled with activated carbon for adsorbing and removing oil, 6 is a catalyst cylinder filled with palladium or platinum for removing oxygen, and 7 is for reacting hydrogen and carbon monoxide Therefore, in the reaction cylinder filled with copper oxide, the two cylinders 7a and 7b can be operated such that either the reaction process or the regeneration process is switched and the one cylinder is always in the reaction process and the other cylinder is in the regeneration process. Is equipped.
Reference numeral 8 is a first adsorption column filled with zeolite as an adsorbent for adsorbing and removing carbon dioxide and water. At least two columns 8a and 8b are installed as one set or more, one of which is an adsorption step and the other is in the meantime. The switching operation is performed so that the desorption / regeneration process is performed. Reference numeral 9 is a second adsorption column filled with mordenite type zeolite as an adsorbent for removing nitrogen components. Like the carbon dioxide gas removal column, two columns 9a and 9b are installed as one set or more, and one of them is adsorbed. The process is sequentially switched so that the other process is the desorption / regeneration process. And 10, 11, 12, 13, 14 are heaters, 15, 1
6 is a heat exchanger for cooling, which are refrigerators 15a and 16a, respectively.
Is attached. Reference numeral 17 is a tank for storing the collected high-purity argon.

Next, a method for purifying and recovering exhaust gas from the single crystal production furnace of the present invention by using the above devices will be described. First, high-purity argon used as an atmosphere gas is fed to the single crystal furnace 1 through a pipe 21. During this time, the exhaust gas is discharged from the single crystal manufacturing furnace 1 through the pipe 22. The exhaust gas is accompanied by dusts such as silicon dioxide, silicon monoxide and carbon in the case of producing a single crystal of silicon, and in addition, hydrogen, oxygen, nitrogen, carbon monoxide, carbon dioxide are generated by heating in a furnace. , A gas containing 99.9% of argon containing small amounts of impurities such as hydrocarbons, water and oil, and stored in the gas holder 2. Such exhaust gas is introduced into the Venturi scrubber 3 through the pipe 23, the dusts contained in the exhaust gas are removed, and the exhaust gas is led out through the pipe 24. Then, in order to obtain a pressure necessary for the subsequent processing in the compressor 4, it is pressurized to a gauge pressure of 4 to 5 kg / cm ² and introduced into the oil removing cylinder 5 filled with activated carbon through the pipe 25. Activated carbon especially adsorbs oil and almost completely removes a trace amount of oil. Thus, the gas from which oil and dust are removed is 4 to 5
While maintaining a gauge pressure of kg / cm ² , it is heated to about 120 ° C. by the heater 10 through the pipe 26 and led to the pipe 27.
More hydrogen is added and introduced into the catalyst cylinder 6 through the pipe 29. The catalyst cylinder 6 is filled with a catalyst such as palladium or platinum, and the hydrogen-added processing gas introduced into the cylinder 6 is treated with oxygen at a temperature of about 120 ° C. by the catalyst. The reaction between hydrogen and hydrogen is promoted to generate water and oxygen is removed. In this case, the amount of hydrogen added to the processing gas is an excess amount than the stoichiometric amount necessary for the reaction of this oxygen amount by detecting the oxygen content in the processing gas introduced into the catalyst cylinder 6. By adding it, the oxygen content as an impurity in the processing gas is effectively removed. The processing gas from which the dust, oil and oxygen components have been removed in this way is led out from the catalyst tube 6 to the tube 30 and is further heated by the heater 11 to a temperature of about 320 ° C.
At least two cylinders in one set have valves 32a, 32b, valves 33a,
33b, valves 34a, 34b, and valves 35a, 35b are introduced into any one of reaction tubes 7a, 7b filled with copper oxide used for switching between successive reactions and regeneration. And, for example, when the reaction cylinder 7a is in the reaction process and the reaction cylinder 7b is in the regeneration process (the valves 32a, 33a,
The valves 34a and 35b are opened, and the valves 32b, 33b and 34 are opened.
a, the valve 35a is closed), the heated processing gas at about 320 ° C. is introduced into the reaction column 7a, and hydrogen and carbon monoxide contained in the processing gas are charged in the column 7a at the above temperature. It reacts with existing copper oxide and is converted into water and carbon dioxide.

Thus, the processing gas discharged from the reaction tube 7a through the pipe 36 contains argon, water, carbon dioxide and nitrogen as main components. The processing gas is then fed to the refrigerator 15
It is led to a cooling heat exchanger 15 additionally provided with a, cooled to about 15 ° C., and introduced into the first adsorption tower 8 via a pipe 37. The first
Zeolite is filled as an adsorbent in the graded cylinder 8,
Valves 38a, 38b, valves 39a, 39b, valves 40a, 40
b, valves 41a and 41b, and two cylinders 8a which are used by sequentially switching the adsorption / regeneration steps by these operations.
It is equipped with 8b as a set. And for example the first
If the adsorption cylinder 8a is in the adsorption process and the adsorption cylinder 8b is in the regeneration process (the valve 38a, the valve 39a, the valve 40b, the valve 4).
1b is open, valve 38b, valve 39b, valve 40a, valve 41a are closed), and the processing gas containing argon as a main component and having a temperature of about 15 ° C. is introduced into the adsorption column 8a of the first adsorption column 8, and the column 8a Water and carbon dioxide in the processing gas are adsorbed and removed, and the pipe 4
2 is derived as a processing gas containing argon as a main component and a small amount of nitrogen. This process gas is then fed to the refrigerator 16
It is cooled to about −50 ° C. through the cooling heat exchanger 16 provided with a and introduced into the second adsorption cylinder 9 via the pipe 43. Second
The adsorption cylinder 9 is filled with mordenite type zeolite, and the attached valves 44a, 44b and valves 45a, 45 are attached.
b, the valves 46a, 46b, and the valves 47a, 47b are operated, and the adsorption / regeneration process is sequentially switched to be used. A pair of adsorption cylinders 9a, 9b are used. One adsorption cylinder 9a is in the adsorption step. The other adsorption cylinder 9b is used in the regeneration process (the valve 44a, the valve 45a, the valve 46b and the valve 47b are opened, and the valve 44b, the valve 45b, the valve 46a and the valve 47a are closed). At this time, the processing gas composed of argon containing nitrogen is adsorbed on the adsorption column 9a.
Nitrogen in the processing gas is adsorbed by the mordenite type zeolite introduced into the cylinder 9a and filled in the cylinder 9a. Moreover, since the treatment gas is cooled to about −50 ° C. and introduced, nitrogen is very effectively adsorbed on the mordenite zeolite.

In this way, the nitrogen component is effectively adsorbed and removed, and as a result, an extremely high-purity argon gas is discharged from the pipe 48 and collected. Then, a part of this is branched by a pipe 49 and used for regeneration of a reaction cylinder 7, a first adsorption cylinder 8 and a second adsorption cylinder 9 which will be described later, but most of them are divided by a pipe 50 from the storage tank 1.
It is sent to 7 and stored. Then, it is appropriately led out from the pipe 51, is passed through the filter 52, is fed from the pipe 53 to the pipe 21 for supplying the argon gas to the single crystal furnace 1, and is reused.

On the other hand, a reaction tube 7 and a first adsorption tube 8 which are used by switching the reaction or adsorption / regeneration process as a set of at least two tubes described above.
When regenerating the second adsorption cylinder 9, the high-purity argon gas derived from the adsorption cylinder 9a of the second adsorption cylinder 9 through the pipe 48 is partially branched by the pipe 49 and used through the following steps. .

That is, part of the high-purity argon branched in the tube 49 is
4 to reach the three-way valve 55, and operate the three-way valve 55 so as to flow into the pipe 56. The pipe 56 is heated by the heater 14 to about 70 ° C.
For example, the gas is introduced into the adsorption cylinder 9b in the regeneration process so that the gas flows in the opposite direction (countercurrent) to that in the adsorption process,
The cylinder 9b is led to the flow pipe 58 while raising the temperature of the cylinder 9b held at about -50 ° C in the adsorption step,
During this time, the nitrogen component adsorbed by the adsorbent of the mordenite-type zeolite filled in the adsorption column 9b is desorbed, entrained, and discharged from the pipe 58 to the pipe 62. At this time the tube 58
The blower 59 is connected to and the gas in the adsorption cylinder 9b is sucked, and a part of the gas in the pipe 58 is circulated from the pipe 60 to the pipe 54 to reduce the amount of effective argon gas used for regeneration. And save money.

In this way, while the argon gas at a temperature of about 70 ° C. is being circulated to the adsorption column 9b in the regeneration step, the adsorption column 9b
The nitrogen content adsorbed therein is sequentially discharged, and the temperature thereof is gradually increased until it reaches the temperature of 70 ° C., which is almost the same as the temperature of the supplied argon gas for purging. At this point, most of the nitrogen content adsorbed by the adsorbent in the adsorption column 9b is desorbed. Then after stopping heating and circulation and performing only purging,
By operating the three-way valve 55, the flow of the argon gas is controlled by the pipe 5.
The pipe 61 is switched from 6 to the cooling heat exchanger 16 for circulation. Argon gas is supplied to the heat exchanger 16 at about −5.
Adsorption cylinder 9b after cooling to 0 ° C. and desorption through the pipe 57
To the adsorption operating temperature of about −5.
Cool to 0 ° C. In this way, the second adsorption cylinder 9 is regenerated.

Next, in the regeneration of the first adsorption cylinder 8, the argon gas used for desorption and pre-cooling in the regeneration process of the second adsorption cylinder 9 and led out from the pipe 58 is made to flow into the pipe 62, and the three-way valve 63 is used to first make the pipe 64. To about 250 ℃
It is made to flow into the adsorption cylinder 8b in the regeneration step, for example, through the temperature raising tube 65. Then, the water and carbon dioxide adsorbed by the zeolite adsorbent filled in the cylinder 8b are desorbed, and the water and carbon dioxide are entrained and led out from the pipe 66. At this time, since the argon purge gas introduced into the cylinder 8b is supplied at a temperature of about 250 ° C., water and carbon dioxide can be desorbed extremely efficiently.

When the desorption of water and carbon dioxide in the adsorption cylinder 8b is completed in this way, the three-way valve 63 is operated to supply argon gas to the pipe 6.
Switch to 7 circulation. Then, the argon gas flowing through the pipe 67 is cooled to about 15 ° C. by the cooling heat exchanger 15, introduced into the adsorption cylinder 8b through the pipe 65, cooled the cylinder 8b, and led to the pipe 66. During this period, the zeolite adsorbent filled in the adsorption column 8b is cooled to an operating temperature of about 15 ° C. in the adsorption step in the next step. The argon gas, which is circulated in the adsorption column 8b in the regeneration process of the first adsorption column 8 and discharged to the pipe 66, is nitrogen in the second adsorption column 9 and moisture and dioxide in the first adsorption column 8 as described above. Carbon is desorbed and entrained, but the argon gas is further heated to about 280 ° C. through the heater 12 and reaches the pipe 68 where oxygen is added from the pipe 69 to the reaction cylinder. Used to play 7. That is, for example, as described above, the argon gas heated to about 280 ° C. and added with oxygen is introduced into the reaction tube 7b in the regeneration step, and as a result, the hydrogen gas is filled in the tube 7b and hydrogen is generated in the reaction step of the previous step. The reduced copper formed as a result of acting to react carbon monoxide to generate water and carbon dioxide is converted into copper oxide by the oxygen added at the above temperature. In this way, the argon gas used to regenerate the reaction tube is led out from the pipe 70 and diffused to the outside air.

As described above, the present invention can effectively utilize the expensive argon gas used as the atmosphere gas in the single crystal manufacturing furnace, and further enables such a method to be continuously operated. is there. And if the use of argon gas as the atmosphere gas in the single crystal manufacturing furnace fluctuates,
For example, when the use amount of argon, which is an atmospheric gas, increases, the treated exhaust gas surplus is discharged from the pipe 22 through the valve 71 according to the capacity of the compressor 4 in the system to be treated, and when the use amount decreases, A pipe 72 for supplying a part of the purified argon gas from a pipe 50 for feeding the purified argon gas to the tank 17,
The valve 73 is branched to join the pipe 22 of the processing system to adjust the processing gas to a predetermined amount. In this way, the processing gas of the capacity is always supplied according to the capacity of the compressor 4, so that more stable operation can be maintained.

Next, an experimental example when the above method is used will be described.

Argon discharged from the gas holder 2 is 99.9% by volume,
Dust 150 mg / Nm ³ , oil (H, C) 10 ppm, oxygen 10
ppm, hydrogen 20ppm, carbon monoxide 50ppm, carbon dioxide 10ppm, nitrogen 50ppm, water content (dew point -16 ° C) 150 Nm ³ / hr, pressure 20 mmAq, temperature 25 ° C
Dust is removed by the venturi scrubber 3, and the treated gas is discharged to the pipe 24 at a flow rate of 145 Nm ³ / hr, pressure of -1500 mmAq, and temperature of 25 ° C, and the pressure of 4 kg is compressed by the compressor 4.
The pressure is increased to / cm ² G, the oil content is removed in the oil content removal cylinder 5 at a flow rate of 142 Nm ³ / hr, and then 1
After being heated to 20 ° C., hydrogen was added from the pipe 28, and the hydrogen of the gas composition became 250 ppm and was introduced into the catalyst cylinder 6,
Oxygen and hydrogen in the treated gas react with each other in the cylinder 6 to generate water, and the oxygen is removed.
It becomes 0ppm and is led out to the pipe 30, and then the heater 1
1 was heated to 320 ° C. and introduced at a pressure of 3.8 kg / cm ² G into the reaction tube 7, where hydrogen and carbon monoxide react with copper oxide to be converted into water and carbon dioxide, and argon 99. 9% by volume, hydrogen 0.5 ppm or less, carbon monoxide 1 ppm or less, carbon dioxide 60 ppm, nitrogen 50 ppm, water content (dew point -11
)), Is discharged from the pipe 36, cooled to 15 ° C. by the cooling heat exchanger 15, and introduced into the first adsorption column 8 at a pressure of 3.5 kg / cm ² G from the pipe 37. Moisture and carbon dioxide are adsorbed and removed to obtain 99.99% by volume of argon, 1 ppm or less of carbon dioxide, and water (dew point -60 ° C), which is led to the pipe 42 and cooled to -50 ° C by the heat exchanger 16 for cooling. Then, it is introduced into the second adsorption column 9 through the pipe 43 at a pressure of 3.3 kg / cm ² G, and about 50 ppm of nitrogen contained therein is adsorbed and removed, and 99.999% by volume or more of argon and 0.2 ppm of oxygen are contained. Hydrogen 0.5ppm or less, carbon monoxide 1pp
m or less, carbon dioxide 1ppm or less, nitrogen 0.1ppm or less,
High-purity argon gas with a water content (dew point −75 ° C. or lower) of 14
2 Nm ³ / hr was collected. And part of it 42 Nm ³ / hr
Is used as a regeneration gas by branching with a pipe 49,
m ³ / hr could be stored in the tank 17 and reused for the successive single crystal production furnace 1.

〔The invention's effect〕

As described above, the method of the present invention, as described above, first removes the solid content such as dust and the oil content from the argon gas containing impurities such as dust, oil content, carbon monoxide, oxygen, hydrogen, nitrogen, and then the oxygen in the exhaust gas. Excessive stoichiometric amount of hydrogen is added to the reaction to convert oxygen into water by catalytic reaction, and then carbon monoxide and hydrogen are reacted with copper oxide to convert into carbon dioxide and water. High-purity argon was recovered by removing the converted water, carbon dioxide, and impurity nitrogen through the adsorption column, and a part of the high-purity argon was used for regeneration of the adsorption column, and then oxygen was added to raise it. Since it is used for oxidative regeneration of reduced copper produced by the reaction of carbon monoxide and hydrogen with copper oxide in a warm state, oxygen as an impurity was added in excess of the stoichiometric amount required for the reaction. Removed to a very small amount by hydrogen Moreover, the excess hydrogen is effectively removed with carbon monoxide in a subsequent process, further resulting water and carbon dioxide in these steps, and the nitrogen is removed in the adsorption process.

Further, since the regeneration of the adsorption column and the regeneration of reduced copper into copper oxide are performed in series with a part of the recovered high-purity argon, the regeneration step can be economically performed with a small amount of gas.

Therefore, the steps of recovering high-purity argon and the regeneration process of the apparatus are extremely simplified, the impurities can be removed to a very small amount, and the exhaust gas from the single crystal manufacturing furnace that contains a large amount of a small amount of impurities is expensive. It is possible to purify pure argon gas to an extremely high purity and reuse it.

[Brief description of drawings]

The figure is a system diagram for explaining an embodiment of the method of the present invention. 1 ... Single crystal manufacturing furnace, 2 ... Gas holder, 3 ... Venturi scrubber, 4 ... Compressor, 5 ... Oil removal cylinder,
6 ... Catalyst tube, 7 ... Reaction tube, 8 ... First adsorption tube, 9 ...
... Second adsorption column, 10 to 14 ... Heater, 15,1
6 ... Cooling heat exchanger, 17 ... Tank

Claims (1)

[Claims] 1. Exhaust gas from a single crystal production furnace containing argon as a main component and containing dust, oil, carbon monoxide, oxygen, hydrogen, nitrogen, etc. as impurities, after first removing solids such as dust and oil. , Adding oxygen in excess of the stoichiometric amount necessary for the reaction of oxygen in the exhaust gas to convert oxygen into water by a catalytic reaction, and then reacting carbon monoxide and hydrogen with copper oxide to form carbon dioxide. After converting to water, the converted water, carbon dioxide and impurity nitrogen are removed through an adsorption column to recover high-purity argon, and a part of the high-purity argon is used for regeneration of the adsorption column. , High-purity argon is recovered from the exhaust gas of the single crystal manufacturing furnace, which is used for the oxidation regeneration of the reduced copper generated by the reaction of the above-mentioned carbon monoxide and hydrogen with copper oxide at a temperature rise by adding oxygen. how to.