JP2008013406A - Method for recovering ammonia, method for reutilizing ammonia, ammonia recovery system and ammonia reutilization system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for recovering ammonia where high purity ammonia is recovered from an exhaust gas exhausted from nitride semiconductor fabrication equipment in such a manner that the concentration of impurities is reduced at most to ≤50 ppb, to provide a method for reutilizing ammonia, to provide an ammonia recovery system, and to provide an ammonia reutilization system. <P>SOLUTION: The method for recovering ammonia is provided with: a stage where a reaction product of ammonia and organic metals, and organic metals are removed from an ammonia-containing exhaust gas exhausted from nitride semiconductor fabrication equipment 11, so as to obtain a gaseous mixture; a stage where crude gaseous ammonia is separated from the gaseous mixture; a stage where the crude gaseous ammonia is liquified, so as to obtain liquified crude ammonia; and a stage where the liquified crude ammonia is distilled, thus impurities are removed from the liquified crude ammonia, so as to obtain high purity ammonia. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an ammonia recovery method, an ammonia recycling method, an ammonia recovery device, and an ammonia recycling device, and for example, supplies the nitride semiconductor manufacturing device from exhaust gas discharged from the nitride semiconductor manufacturing device. The present invention relates to an ammonia recovery method, an ammonia reuse method, an ammonia recovery device, and an ammonia reuse device.

  Nitride semiconductors have been used and used in blue LEDs (Light Emitting Diodes), blue LDs (Laser Diodes), and the like, and their production has increased dramatically. When manufacturing a nitride semiconductor, a large amount of ammonia is used as an N (nitrogen) source. As the demand for nitride semiconductors such as LEDs increases, the amount of ammonia used is greatly increased, and in some cases, it may exceed 100 tons per factory per year. Most of the ammonia used in this way is generally discharged as it is after production, is detoxified by an ammonia decomposing apparatus or the like, and is discarded. Thus, in order to detoxify ammonia discharged in large quantities, there is a problem that processing costs are required.

  Therefore, in recent years, it has been proposed to recover ammonia from the exhausted gas. For example, in Japanese Patent Laid-Open No. 4-292413 (Patent Document 1), an unhydrogenated getter alloy is used to remove impurities in order to increase the purity of ammonia gas used in semiconductor manufacturing. A method for purifying ammonia is disclosed.

Further, for example, in Japanese Patent Laid-Open No. 2000-317246 (Patent Document 2), in order to recover ammonia in a short time from a large amount of gas containing high-purity ammonia, a multi-tube adsorber is filled with an ammonia adsorbent. A method and apparatus for recovering ammonia that adsorbs and desorbs ammonia to and from the adsorbent are disclosed.
JP-A-4-292413 JP 2000-317246 A

  Ammonia used in a nitride semiconductor manufacturing apparatus such as an LED is required to have an extremely high purity with an impurity concentration of 50 ppb or less. However, in the above Patent Documents 1 and 2, although certain elements can be removed to a certain low concentration, all of hydrogen, nitrogen, organometallics (MO), fine particles, etc. contained in the exhaust gas are extremely It is difficult to remove to a low concentration. Therefore, there is a problem that it is difficult to achieve a purity that can be used for a nitride semiconductor or the like.

  Further, high-purity ammonia used in the nitride semiconductor manufacturing apparatus is carried into a nitride semiconductor manufacturing factory in a state where, for example, a large container is filled with a liquid with a filling amount of 500 kg to 1000 kg, and nitrided by piping from the large container Supplied to semiconductor manufacturing equipment. High-purity ammonia is often filled and transported in a large container as the amount of use thereof increases, so that there is a problem that the transportation cost in the large container is excessive.

  Therefore, the present invention has been made to solve the above-described problems, and an object of the present invention is to reduce the concentration of impurities to 50 ppb or less from the exhaust gas discharged from the nitride semiconductor manufacturing apparatus. An ammonia recovery method, an ammonia recycling method, an ammonia recovery device, and an ammonia recycling device that recover high-purity ammonia.

  The ammonia recovery method according to the present invention includes a step of obtaining a mixed gas, a step of separating crude ammonia, a step of obtaining liquefied crude ammonia, and a step of obtaining high-purity ammonia. In the step of obtaining the mixed gas, the reaction product of the ammonia and the organic metal and the organic metal are removed from the exhaust gas containing ammonia discharged from the nitride semiconductor manufacturing apparatus to obtain the mixed gas. In the step of separating the crude ammonia, the crude ammonia gas is separated from the mixed gas. In the step of obtaining liquefied crude ammonia, crude ammonia gas is liquefied to obtain liquefied crude ammonia. In the step of obtaining high purity ammonia, the liquefied crude ammonia is distilled to remove impurities from the liquefied crude ammonia to obtain high purity ammonia.

  Preferably, in the ammonia recovery method, the step of obtaining high-purity ammonia includes a step of removing high-boiling impurities having a boiling point higher than that of ammonia in the first distillation column, and a step of removing low boiling point of ammonia in the second distillation column. Removing boiling point impurities.

  In the present specification, “high purity” means a purity having an impurity concentration of 50 ppb or less.

  The method for reusing ammonia of the present invention includes a step of obtaining high-purity ammonia recovered by any one of the above ammonia recovery methods, and a step of supplying to the nitride semiconductor manufacturing apparatus. The step of supplying the nitride semiconductor manufacturing apparatus supplies a high purity ammonia gas obtained by vaporizing high purity ammonia to the nitride semiconductor manufacturing apparatus.

  Preferably, the method for reusing ammonia further includes a step of removing fine particles from the high-purity ammonia with two or more filters after the step of obtaining the high-purity ammonia.

  Preferably, in the above ammonia recycling method, the supplying step is performed by controlling the amount of high purity ammonia gas.

  The ammonia recovery device of the present invention includes a removal device, a separation device, a liquefaction device, and a distillation device. The removal device produces a mixed gas by removing a reaction product of the ammonia and the organic metal and the organic metal from the exhaust gas containing ammonia discharged from the nitride semiconductor manufacturing device. The crude ammonia separator produces crude ammonia gas from the mixed gas. The liquefying device liquefies crude ammonia gas to produce liquefied crude ammonia. The distillation apparatus distills the liquefied crude ammonia to remove impurities from the liquefied crude ammonia to produce high purity ammonia.

  Preferably, in the ammonia recovery apparatus, the distillation apparatus includes a first distillation column for removing high boiling impurities having a boiling point higher than that of ammonia, and a second distillation column for removing low boiling impurities having a boiling point lower than that of ammonia. It is out.

  Preferably, the ammonia recovery device further includes a storage device for storing liquefied crude ammonia.

  The ammonia recycling apparatus of the present invention includes any one of the above ammonia recovery apparatuses and a supply apparatus. The supply device supplies high purity ammonia gas obtained by vaporizing high purity ammonia to the nitride semiconductor manufacturing device.

  The ammonia recycling apparatus preferably further includes two or more filters for removing fine particles from high-purity ammonia.

  In the above ammonia recycling apparatus, the supply device preferably includes a control device for controlling the amount of the high purity ammonia gas.

  According to the ammonia recovery method and the ammonia recovery apparatus of the present invention, high-purity ammonia can be recovered from the exhaust gas discharged from the nitride semiconductor manufacturing apparatus by reducing the impurity concentration to 50 ppb or less. In addition, according to the ammonia recycling method and the ammonia recycling apparatus of the present invention, high purity ammonia recovered by reducing the impurity concentration to 50 ppb or less can be supplied to the nitride semiconductor manufacturing apparatus.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following drawings, the same or corresponding parts are denoted by the same reference numerals, and description thereof will not be repeated.

(Embodiment 1)
FIG. 1 is a diagram for explaining an ammonia recovery apparatus according to Embodiment 1 of the present invention. With reference to FIG. 1, an ammonia recovery apparatus according to Embodiment 1 of the present invention will be described. As shown in FIG. 1, the ammonia recovery device according to the first embodiment includes a removal device 13, a crude ammonia separation device 15, a liquefaction device 17, and a distillation device 18. The removal device 13 produces a mixed gas by removing a reaction product of the ammonia and the organic metal and the organic metal from the exhaust gas containing ammonia discharged from the nitride semiconductor manufacturing device 11. The crude ammonia separation device 15 produces crude ammonia gas from the mixed gas. The liquefying device 17 liquefies crude ammonia gas to produce liquefied crude ammonia. The distillation device 18 distills the liquefied crude ammonia to remove impurities from the liquefied crude ammonia to produce high purity ammonia.

  Specifically, the ammonia recovery device 10 includes a first pressure booster 12, a removal device 13, a second pressure booster 14, a crude ammonia separator 15, a third pressure booster 16, a liquefaction device 17, and a distillation. A device 18, a high-purity ammonia storage device 19, and a crude ammonia storage device are provided.

  Nitride semiconductor manufacturing apparatus 11 in the first embodiment is an apparatus for manufacturing LEDs, for example. The nitride semiconductor device 11 is supplied with, for example, nitrogen, hydrogen, and ammonia.

  The first booster 12 boosts the exhaust gas discharged from the nitride semiconductor manufacturing apparatus 11 and supplies it to the removal device 13.

  The removing device 13 includes a fine particle removing cylinder 13a and an MO removing cylinder 13b. The removal device 13 produces a mixed gas by removing a reaction product of the ammonia and the organic metal and the organic metal from the exhaust gas containing ammonia discharged from the nitride semiconductor manufacturing device 11.

  The fine particle removal cylinder 13a removes the reaction product of ammonia and organometallics from the exhaust gas containing ammonia discharged from the nitride semiconductor manufacturing apparatus 11. The particulate removal cylinder 13a includes, for example, two or more filters.

  The MO removal cylinder 13b removes organometallics from the gas from which the fine particles discharged from the fine particle removal cylinder 13a have been removed. The MO removal cylinder 13b is, for example, an adsorption cylinder filled with an adsorbent. The adsorbent is preferably a catalyst carrying a chemical that fixes activated carbon or organometallics (MO). By filling such an adsorbent or catalyst, it is possible to effectively remove MO and realize a state in which there is almost no in the mixed gas. The height at which the adsorbent is filled is not particularly limited, but is preferably 2 m or less from the viewpoint of reducing pressure loss. Moreover, it is preferable that the MO removal cylinder 13b includes two or more adsorption towers from the viewpoint that continuous operation is possible.

  The second pressure increasing device 14 increases the pressure of the mixed gas discharged from the removing device 13 and supplies it to the crude ammonia separation device 15.

  The crude ammonia separation device 15 produces crude ammonia gas from the mixed gas. The crude ammonia separation device 15 is not particularly limited as long as the crude ammonia gas can be produced from the mixed gas, but preferably includes a pressure swing adsorption device and a vacuum pump. The number of pressure swing adsorption devices is not particularly limited, but 2 to 5 are preferably arranged from the viewpoint of continuously recovering crude ammonia gas. The adsorption cylinder of one pressure swing adsorption device is filled with activated carbon or the like, for example. The pressure swing adsorption device produces crude ammonia gas by adsorbing ammonia in a mixed gas and causing hydrogen and nitrogen to flow out.

  The third booster 16 boosts the crude ammonia gas discharged from the crude ammonia separator 15 and supplies it to the liquefier 17.

  The liquefying device 17 liquefies crude ammonia gas to produce liquefied crude ammonia. The liquefying device 17 includes, for example, a condenser cooler and a storage tank. The crude ammonia gas is cooled and condensed by a condenser to form liquefied crude ammonia, which is stored in a storage tank.

  The distillation device 18 distills the liquefied crude ammonia to remove impurities from the liquefied crude ammonia to produce high purity ammonia. As shown in FIG. 2, the distillation apparatus 18 includes a first distillation column 18a that removes high-boiling impurities having a boiling point higher than that of ammonia, and a second distillation column 18b that removes low-boiling impurities having a boiling point lower than that of ammonia. It is preferable to include. FIG. 2 is a schematic diagram showing the distillation apparatus 18 in Embodiment 1 of the present invention.

  As shown in FIG. 2, the first distillation column 18a includes an upper reflux section 18a1, an intermediate ammonia introduction section 18a2, a lower reflux section 18a3, a lower storage section 18a4, a lower boiling heating section 18a5, and high boiling point impurity removal. An ammonia extraction part 18a6, a middle reflux part 18a7, and a high boiling point impurity-containing ammonia extraction part 18a8 are included. The high boiling point impurity-removed ammonia extraction unit 18a6 takes out the ammonia gas from which the high boiling point impurities have been removed, and sends it to the second distillation column 18b. In the middle reflux section 18a7, part of the liquefied high-purity ammonia is refluxed from the lower storage section 18b4 of the second distillation column 18b.

  The second distillation column 18b includes an upper reflux section 18b1, an intermediate ammonia introduction section 18b2, a lower reflux section 18b3, a lower storage section 18b4, a lower boiling heating section 18b5, a low boiling point impurity-containing ammonia gas extraction section 18b6, Condensing part 18b7, high purity ammonia extraction part 18b8, return part 18b9, and low boiling point impurity containing ammonia gas discharge | release part 18b10 are included. The condensing part 18b7 has a low-boiling-point impurity-containing ammonia gas releasing part 18b10, and discharges ammonia in which the low-boiling-point impurities are condensed at a high concentration at a constant rate. The condensing part 18b7 is connected to an ammonia gas extraction part 18b6 and a return part 18b9 for liquefied ammonia.

  The high purity ammonia storage device 19 stores the high purity ammonia recovered by the distillation device 18. The high purity ammonia storage device 19 includes, for example, a cooler, a liquid level gauge, and a pressure control device. The cooler liquefies high-purity ammonia recovered from the distillation apparatus 18.

  The crude ammonia storage device 20 is a member for liquefying and storing crude ammonia containing a large amount of high-boiling impurities and low-boiling impurities discharged from the distillation device 18, storing them, and filling them into a recovery container. . The crude ammonia storage device 20 includes, for example, a condensing cooler, a storage tank, a tank pressure controller, and a filling unit for a recovery container. The crude ammonia storage device 20 may be an ammonia decomposition device for detoxifying ammonia, for example.

  As described above, according to the ammonia recovery apparatus 10 in the first embodiment of the present invention, the reaction product of ammonia and organometallics from the exhaust gas containing ammonia discharged from the nitride semiconductor manufacturing apparatus 11 and A removal device 13 for producing a mixed gas by removing organic metals, a crude ammonia separation device 15 for producing a crude ammonia gas from the mixed gas, a liquefaction device 17 for producing a liquefied crude ammonia by liquefying the crude ammonia gas, And a distillation apparatus 18 for producing high-purity ammonia by removing impurities from the liquefied crude ammonia by distilling the liquefied crude ammonia. The removal device 13 can remove the reaction product of the ammonia and the organic metal and the organic metal. The distillation apparatus 18 can remove low-boiling impurities such as hydrogen and nitrogen and high-boiling impurities such as moisture. Therefore, the concentration of each impurity contained in the exhaust gas discharged from the nitride semiconductor manufacturing apparatus 11 can be reduced to 50 ppb or less and removed. Therefore, high purity ammonia can be recovered from the exhaust gas discharged from the nitride semiconductor manufacturing apparatus by reducing the impurity concentration to 50 ppb or less.

  Preferably, in the ammonia recovery apparatus 10, the distillation apparatus 18 includes a first distillation column 18 a that removes high-boiling impurities having a boiling point higher than that of ammonia, and a second distillation column that removes low-boiling impurities having a boiling point lower than that of ammonia. 18b. Thereby, the impurities contained in the exhaust gas can be removed to a lower concentration. Therefore, ammonia with higher purity can be recovered.

  The ammonia recovery device 10 preferably further includes a crude ammonia storage device 20 for storing crude ammonia. Thereby, crude ammonia can be discharged from the ammonia recovery device 10.

(Embodiment 2)
With reference to FIG. 3, an ammonia recycling apparatus according to Embodiment 2 will be described. FIG. 3 is a diagram for explaining an ammonia recycling apparatus according to Embodiment 2 of the present invention.

  The ammonia recycling apparatus 30 according to the second embodiment includes the ammonia recovery apparatus 10 according to the first embodiment, and a supply apparatus that supplies the nitride semiconductor manufacturing apparatus 11 with high-purity ammonia gas obtained by vaporizing high-purity ammonia. It has.

  Specifically, the ammonia recycling apparatus 30 includes a first pressure increasing device 12, a removing device 13, a second pressure increasing device 14, a crude ammonia separation device 15, a third pressure increasing device 16, and a liquefying device 17. , A distillation apparatus 18, a high-purity ammonia storage apparatus 19, a particulate removal filter 31, and a control apparatus 32.

  Specifically, the particulate removal filter 31 has two or more filters and removes particulates from high-purity ammonia. Here, the fine particles mean fine particles generated in the high-purity ammonia recovery apparatus 10. The particulate removal filter 31 removes particulates contained in high-purity ammonia extracted from the upper part of the high-purity ammonia storage device 19 in the gas phase, for example.

  The control device 32 controls the amount of high purity ammonia gas. That is, supply control of high-purity ammonia is performed based on a command from the nitride semiconductor manufacturing apparatus 11. The control apparatus 32 consists of a mass flow controller, for example.

  As described above, according to the ammonia recycling apparatus 30 in the second embodiment, the ammonia recovery apparatus 10 in the first embodiment and the high purity ammonia gas obtained by vaporizing high purity ammonia using the nitride semiconductor manufacturing method. And a supply device for supplying to the device 11. Thereby, high-purity ammonia with the impurity concentration reduced to 50 ppb or less can be supplied to the nitride semiconductor manufacturing apparatus 11. Since the cost required for recovering ammonia is lower than the price of high-purity ammonia, the cost can be reduced. Moreover, since the transportation cost for conveying highly pure ammonia from the outside is not required, the cost can be further reduced.

  The ammonia recycling apparatus 30 preferably further includes two or more filters (particulate removal filter 31) for removing particulates from high-purity ammonia. Thereby, even if the fine particles are generated in the ammonia recovery apparatus 10, the fine particles can be easily removed. Therefore, the purity of the high purity ammonia to be reused can be further improved.

  In the ammonia recycling apparatus 30, the supply apparatus preferably includes a control device 32 that controls the amount of high-purity ammonia gas. Thereby, high-purity ammonia in an amount required in the nitride semiconductor manufacturing apparatus 11 can be supplied.

(Embodiment 3)
A method for recovering ammonia in Embodiment 3 will be described with reference to FIGS. 1, 2, and 4. The ammonia recovery method in the third embodiment is performed using the ammonia recovery apparatus 10 in the first embodiment shown in FIGS. FIG. 4 is a flowchart showing an ammonia recovery method according to Embodiment 3 of the present invention and an ammonia recycling method according to Embodiment 4 of the present invention described later.

  As shown in FIG. 4, first, a process for obtaining a mixed gas by removing reaction products and organic metals of ammonia and organic metals from exhaust gas containing ammonia discharged from the nitride semiconductor manufacturing apparatus 11 ( S11) is carried out. The exhaust gas supplied to this step (S11) generally contains 10 to 40% ammonia, 10 to 50% hydrogen, and 10 to 50% nitrogen. In the exhaust gas, reaction products (fine particles) that are a reaction product of ammonia and MO, unreacted MO, and the like are mixed. Further, the exhaust gas is mixed with high-boiling impurities such as moisture and low-boiling impurities such as air (hydrogen, oxygen, nitrogen, carbon monoxide, carbon dioxide, methane, etc.) in the middle of the discharge path.

  In the step of obtaining a mixed gas (S11), first, the first booster 12 is used to boost the exhaust gas and supply it to the particulate removal cylinder 13a. Then, the reaction product of ammonia and MO is removed from the exhaust gas by the fine particle removing cylinder 13a. Then, it is supplied to the MO removal cylinder 13b. Then, the MO removal cylinder 13b removes the MO to obtain a mixed gas. In addition, it is preferable to perform this process (S11) at room temperature.

  In the particulate removal cylinder 13a, it is preferable to measure a differential pressure by disposing a differential pressure gauge before and after each filter. When the prescribed differential pressure is reached, the reaction product can be continuously removed by switching to a filter in which no differential pressure is generated.

  Similarly, in the MO removing cylinder 13b, it is preferable to perform switching operation with two cylinders in order to continuously remove the MO.

In the MO removing cylinder 13b, the space velocity (SV) is preferably 500 Hr ⁻¹ or less. This is because the target MO can be reliably removed by setting it to 500 Hr ⁻¹ or less.

  Next, the process (S12) which isolate | separates crude ammonia gas from mixed gas is implemented. The mixed gas supplied to this step (S12) is made up of ammonia, hydrogen, nitrogen and the like by removing fine particles and MO in step (S11). Using the second booster 14, the mixed gas is boosted and supplied to the crude ammonia separator 15.

  The step (S12) of separating the crude ammonia is performed, for example, by an adsorption device filled with an adsorbent. In the third embodiment, the step (S12) of separating the crude ammonia gas is performed by a pressure swing adsorption device.

  Specifically, for example, one adsorption device (adsorption cylinder) adsorbs ammonia in a mixed gas and causes a gas other than ammonia (hereinafter referred to as off-gas) such as hydrogen and nitrogen to flow out of the adsorption device. Then, the adsorbed ammonia is desorbed under reduced pressure. Thereby, crude ammonia gas can be obtained. Then, the off-gas that has flowed out is fed to equalize the inside of the adsorption cylinder to a predetermined pressure. And it will be in a standby state. In addition, when implementing after the process to desorb | desorb, it is preferable to flow ammonia into another adsorption cylinder and to adsorb ammonia. As a result, the mixed gas can be continuously supplied and the crude ammonia gas can be continuously recovered. In addition, it is preferable to perform this process (S12) at room temperature.

  Next, the process (S13) which liquefies crude ammonia gas and obtains liquefied crude ammonia is carried out. The crude ammonia gas supplied to this step (S13) is composed of high-boiling impurities, low-boiling impurities, ammonia, and the like that could not be removed after part of the hydrogen and nitrogen were removed in step (S12). . Using the third booster 16, the crude ammonia gas is boosted and supplied to the liquefaction device 17.

  In the step of obtaining liquefied crude ammonia (S13), the crude ammonia gas is cooled and liquefied. The liquefied crude crude ammonia is stored in a storage tank.

  Next, a step (S14) of obtaining high-purity ammonia by removing impurities from the liquefied crude ammonia by distilling the liquefied crude ammonia is performed. The liquefied crude ammonia supplied to this step (S14) is composed of high-boiling impurities, low-boiling impurities, ammonia, and the like, similar to the crude ammonia. In the step (S14), the high-boiling impurities and the low-boiling impurities remaining in the liquid crude ammonia recovered from the exhaust gas are separated and purified by distillation operations.

  The step of obtaining high-purity ammonia (S14) is a step of removing high-boiling impurities having a boiling point higher than that of ammonia in the first distillation column 18a, and a removal of low-boiling impurities having a boiling point lower than that of ammonia in the second distillation column 18b. And a process of performing.

  Specifically, liquefied crude ammonia is supplied to the intermediate ammonia introduction part 18a2 of the first distillation column 18a and stored in the lower storage part 18a4. Then, the liquefied crude ammonia stored in the lower boiling heating unit 18a5 is heated and refluxed in the lower reflux unit 18a3 and the upper reflux unit 18a1. Thereby, high boiling impurities such as moisture can be removed from the liquefied crude ammonia. Then, the crude ammonia gas from which the high boiling point impurities have been removed is supplied from the high boiling point impurity removing ammonia extraction part 18a6 to the second distillation column 18b. On the other hand, the liquefied ammonia in which the high boiling point impurities are concentrated is discharged from the high boiling point impurity-containing ammonia extraction portion 18a8.

  Then, the crude ammonia gas from which the high boiling impurities have been removed is supplied to the intermediate ammonia introduction part 18b2 of the second distillation column 18b. Then, the ammonia gas in which the low-boiling-point impurities are concentrated in the condensing unit 18b7 is released via the low-boiling-point impurity-containing ammonia gas extraction unit 18b6, and the condensed liquefied ammonia is returned to the upper reflux unit 18b1 through the return unit 18b9. Supply. Then, the condensed and liquefied ammonia is stored in the lower reservoir 18b4, heated by the lower boiling heating unit 18b5, and continuously led to the condensing unit 18b7 while being refluxed by the lower reflux unit 18b3 and the upper reflux unit 18b1. Thereby, high purity ammonia from which the low boiling point impurities are further removed is stored in the lower storage portion 18b4. On the other hand, while condensing ammonia enriched with low-boiling impurities from the low-boiling impurity-containing ammonia gas releasing portion 18b10, the condensed and liquefied ammonia is supplied to the upper refluxing portion 18b1.

  A part of the high-purity ammonia from which the low-boiling-point impurities thus obtained are removed is supplied to the high-purity ammonia storage device 19 via the high-purity ammonia extraction part 18b8, and the remainder is supplied to the first distillation column 18a. To the upper reflux portion 18a1. Thereby, the remaining high-purity ammonia can be further distilled to further increase the purity.

  The temperature of the lower boiling heating unit 18a5 of the first distillation column 18a is preferably maintained in a temperature range of 30 to 50 ° C. By setting the temperature of the lower boiling heating portion 18a5 to 30 ° C. or higher, the boiling point difference between the high boiling point impurities and the liquefied crude ammonia is increased, and the effect of expelling impurities dissolved by boiling is improved. On the other hand, by setting the temperature of the lower boiling heating unit 18a5 to 50 ° C. or less, the temperature and pressure of the liquefied crude ammonia do not become too high, and the pressure difference from the liquefied crude ammonia supplied from the liquefier 17 does not become small. The required amount of liquefied crude ammonia introduced can be easily obtained.

  The temperature of the lower boiling heating unit 18b4 of the second distillation column 18b is preferably maintained in a temperature range 5 to 10 ° C. lower than the temperature of the lower boiling heating unit 18a5 of the first distillation column 18a. By setting the temperature difference to 5 ° C. or more, it is possible to smoothly introduce ammonia from the high boiling point impurity-removed ammonia extraction portion 18a6 of the first distillation column 18a to the intermediate ammonia introduction portion 18b2 of the second distillation column 18b. On the other hand, by setting the temperature difference to 10 ° C. or less, the liquefied crude ammonia can be smoothly refluxed from the high-purity ammonia extraction part 18b8 of the second distillation column 18b to the upper reflux part 18a1 of the first distillation column 18a. .

  Moreover, it is preferable to maintain the temperature of the condensation part 18b7 of the 2nd distillation column 18b in the temperature range of -5-10 degreeC. By setting the temperature of the condensing unit 18b7 to −5 ° C. or higher, the temperature of the liquefied crude ammonia does not become too low, and it is not necessary to make the heating source of the lower boiling heating unit 18b5 excessive. On the other hand, by setting the temperature of the lower boiling heating unit 18b5 to 10 ° C. or less, it is possible to prevent an increase in the heat exchange area necessary for increasing the condensation efficiency.

Further, in the first distillation column 18a, the flow rate of the liquid crude ammonia from which the high boiling point impurities discharged from the high boiling point impurity removal ammonia extraction unit 18a6 with respect to the flow rate of the liquid crude ammonia supplied to the intermediate ammonia introduction unit 18a2 is: It is preferable to set within the range of 1 to 20%. By setting it to 1% or more, the amount of liquid crude ammonia from which high-boiling impurities flowing to the second distillation column 18b are removed is not reduced, which is economically advantageous. On the other hand, by setting it to 20% or less, the concentration of high-boiling impurities that are concentrated components in the first distillation column 18a does not increase, so that high-purity ammonia having a desired purity can be obtained. The flow rate of the high-purity ammonia discharged from the high-purity ammonia extraction portion 18b8 with respect to the flow rate of the liquid crude ammonia from which the high-boiling impurities are supplied to the intermediate ammonia introduction portion 18b2 of the column 18b is in the range of 1 to 15%. It is preferable to set to. By setting it to 1% or more, the amount of high-purity ammonia discharged from the high-purity ammonia extraction part 18b8 is not reduced, which is economically advantageous. On the other hand, by setting it to 15% or less, the concentration of the low-boiling impurities, which are the concentrated components in the second distillation column 18b, does not increase, so that high-purity ammonia having a desired purity can be obtained.

  The reflux ratio of the first distillation column 18a is preferably 5-15. This is because the high boiling point impurities can be removed to an appropriate level by setting it to 5 or more. On the other hand, by setting it to 15 or less, it is possible to prevent an excessive increase in the amount of energy required to remove high-boiling impurities.

  The reflux ratio of the second distillation column 18b is preferably 5-20. This is because by setting it to 5 or more, low boiling point impurities can be removed to an appropriate level. On the other hand, by setting it to 20 or less, it is possible to prevent an excessive amount of energy required for removing low-boiling impurities.

  By performing the above steps (S11 to S14), the impurity concentration can be reduced to 50 ppb or less, and high-purity ammonia can be obtained.

  Next, a step of storing the obtained high purity ammonia in the high purity ammonia storage device 19 is performed. Specifically, the high-purity ammonia stored in the step (S14) is provided with a liquid level gauge and a pressure control device by passing the high-purity ammonia extracted from the high-purity ammonia extraction part 18b8 of the second distillation column 18b through a cooler. Store in device 19. The high-purity ammonia thus obtained can be supplied to, for example, the nitride semiconductor manufacturing apparatus 11 or used for other purposes.

  In addition, it is preferable to implement the process of storing the high boiling point impurities discharged from the first distillation column 18a and the low boiling point impurities discharged from the second distillation column 18b in the crude ammonia storage device 20. By this step, impurities contained in the liquid crude ammonia can be treated outside the ammonia recovery apparatus 10.

  As described above, according to the ammonia recovery method (S10) in the third embodiment of the present invention, the reaction between ammonia and organometallics from the exhaust gas containing ammonia discharged from the nitride semiconductor manufacturing apparatus 11 A step of removing a product and organometallics to obtain a mixed gas (S11), a step of separating crude ammonia gas from the mixed gas (S12), and a step of liquefying the crude ammonia gas to obtain liquefied crude ammonia (S13). ) And a step (S14) of distilling the liquefied crude ammonia to remove impurities from the liquefied crude ammonia to obtain higher purity ammonia than the exhaust gas. By the step (S11) of obtaining the mixed gas, the reaction product of the ammonia and the organic metal and the organic metal can be removed. By the step of obtaining high purity ammonia (S14), low boiling point impurities such as hydrogen and nitrogen and high boiling point impurities such as moisture can be removed. Therefore, each impurity contained in the exhaust gas discharged from the nitride semiconductor manufacturing apparatus 11 can be removed to a low concentration. Therefore, high purity ammonia can be recovered from the exhaust gas discharged from the nitride semiconductor manufacturing apparatus by reducing the impurity concentration to 50 ppb or less.

  Conventionally, a method of purifying industrial ammonia having an ammonia concentration of about 99.9% and improving the purity has been adopted. However, even if such purification is applied to exhaust gas, the concentration of impurities is However, it could not be reduced to 50 ppb or less. However, according to the method for recovering high-purity ammonia in the present invention, by providing the steps (S11 to S14), high-purity ammonia can be recovered from the exhaust gas having a very high impurity concentration.

  In addition, the step of obtaining a mixed gas (S11) and the step of separating crude ammonia gas (S12) are performed at room temperature, the step of obtaining liquefied crude ammonia (S13) and the step of obtaining high-purity ammonia (S14) are − It can carry out in the temperature range of 5-50 degreeC. Further, the operation for recovering the exhaust gas to the high-purity ammonia can be performed at a pressure of 1 MPaG or less by the low-pressure ammonia recovery device 10 which is an economical structure. Therefore, high purity ammonia can be recovered very easily.

  In the above ammonia recovery method, preferably, the step of obtaining high purity ammonia (S14) includes the step of removing high boiling impurities having a boiling point higher than that of ammonia in the first distillation column 18a, and the step of removing ammonia from the ammonia in the second distillation column 18b. And a step of removing low boiling point impurities having a low boiling point. Thereby, the impurities contained in the exhaust gas can be removed to a lower concentration. Therefore, higher purity ammonia can be recovered.

(Embodiment 4)
With reference to FIG. 4, a method for reusing ammonia in Embodiment 4 of the present invention will be described. The method for reusing ammonia in the fourth embodiment includes a step (S10) of obtaining high purity ammonia by the ammonia recovery method in the third embodiment, and a high purity ammonia gas obtained by vaporizing the high purity ammonia is converted into a nitride semiconductor. And a step (S20) of supplying to the manufacturing apparatus.

  Specifically, as shown in FIG. 4, first, a step (S10) of obtaining high-purity ammonia by an ammonia recovery method is performed. This step (S10) is performed by the ammonia recovery method in the third embodiment.

  Next, a step (S20) of supplying high purity ammonia gas obtained by vaporizing high purity ammonia to the nitride semiconductor manufacturing apparatus 11 is performed. In the supplying step (S20), for example, the following steps (S21, S22) are performed.

  After the step of obtaining high-purity ammonia (S10), a step of removing fine particles from the high-purity ammonia with two or more filters (S21) is performed. Thereby, the microparticles | fine-particles contained in either process of the process (S10) of obtaining highly purified ammonia can be removed. Moreover, it can pass through a filter continuously by making a filter into 2 or more.

  Specifically, in the step of removing fine particles (S21), for example, high-purity ammonia extracted in a gas phase from the upper portion of the high-purity ammonia storage device 19 is passed through the fine particle removal filter 31.

  Next, a step (S22) of supplying high purity ammonia to the nitride semiconductor manufacturing apparatus 11 is performed. The supplying step (S22) is performed by controlling the amount of high purity ammonia gas. Here, the amount means a flow rate required for the nitride semiconductor manufacturing apparatus 11.

  By performing the above steps (S10, S20), high-purity ammonia can be supplied to the nitride semiconductor manufacturing apparatus 11.

  As described above, according to the ammonia recycling method in Embodiment 4 of the present invention, the step (S10) of obtaining high purity ammonia by the ammonia recovery method, and the high purity obtained by vaporizing the high purity ammonia. A step of supplying ammonia gas to the nitride semiconductor manufacturing apparatus 11 (S20). High-purity ammonia obtained by the step (S10) of obtaining high-purity ammonia can be used in the nitride semiconductor manufacturing apparatus 11 because the impurity concentration is reduced to 50 ppb or less. Further, since it is not necessary to transport high-purity ammonia in the nitride semiconductor manufacturing apparatus 11, the transportation cost can be reduced.

  Preferably, the ammonia recycling method further includes a step (S21) of removing fine particles from the high purity ammonia with two or more filters after the step (S10) of obtaining high purity ammonia. Thereby, even if it is a case where microparticles | fine-particles mix in the process (S10) of obtaining highly purified ammonia, the mixed microparticles | fine-particles can be removed. Therefore, high-purity ammonia can be supplied to the nitride semiconductor manufacturing apparatus 11 without reducing the purity of the high-purity ammonia.

  In the above ammonia recycling method, preferably, the supplying step (S22) is performed by controlling the amount of high purity ammonia gas. Thereby, a necessary amount of high-purity ammonia gas can be supplied to the nitride semiconductor manufacturing apparatus 11.

[Example]
EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited to these.

(Example 1)
In Example 1, high-purity ammonia was recovered by the ammonia recovery method in Embodiment 3 using the ammonia recovery apparatus in Embodiment 1. And the assumption exhaust gas prepared as follows was used as exhaust gas of a nitride semiconductor manufacturing apparatus. The ammonia flow rate was adjusted to 10 L / min, and hydrogen at a flow rate of 28.3 L / min and nitrogen at a flow rate of 28.3 L / min were independently mixed with the ammonia after the flow rate control. Then, MO with a flow rate of 135 mL / min and flow rate were controlled independently. As the MO, 0.1 vol% trimethylgallium (TMG) / N ₂ was used. Moisture was added by passing nitrogen through a water storage tank controlled at 7 ° C. for 34 mL / min to entrain the water. The exhaust gas thus prepared (assumed exhaust gas) is about 15 vol% ammonia, about 42.5 vol% hydrogen, about 42.5 vol% nitrogen, and about from the flow control value of each gas. 2 vol. ppm MO (TMG) and about 5 vol. It contained ppm moisture.

  And the process (S11) which removes the reaction product and organic metals of ammonia and organic metals from the exhaust gas containing ammonia discharged | emitted from the nitride semiconductor manufacturing apparatus, and obtained mixed gas was implemented. Specifically, two stainless steel cylinders having an inner diameter of 21.2 mm and a height of 500 mm were used as the MO removal cylinder. Each cylinder was filled with 0.7 liters of columnar activated carbon having a diameter of 1 mm and a length of 2 to 5 mm.

  The exhaust gas was passed through the MO removal cylinder, a part of the mixed gas after the passage was branched, passed through a water bubbler, TMG was trapped in the form of gallium hydroxide, and measured by ICP-OES. As a result, the TMG concentration in the mixed gas was 0.01 vol. It was less than ppm, and it was confirmed that TMG was removed from the mixed gas.

  Further, as a result of the TMG breakthrough test in the MO removal cylinder, it was found that there was an adsorption ability of TMG 0.1 g / activated carbon 1 g. From this result, the TMG adsorption amount per cylinder (inner diameter 10 cm, length 100 cm) was 269 l, the exhaust gas was 1000 SLM, and the unreacted TMG concentration was 2 vol. If it is set to ppm, it will process about 90 days. From this, assuming that the safety factor is 1.5, the switching timing of the two cylinders in the MO removal cylinder is every two months.

Next, the process (S12) which isolate | separates crude ammonia gas from mixed gas was implemented. Specifically, the mixed gas after the step (S11) was pressurized to 0.3 MPa and vented at a flow rate of about 0.7 Nm ³ / hr through the pressure swing type adsorption device. The pressure swing type adsorption device was composed of four adsorption cylinders. The four adsorption cylinders were sequentially switched, the mixed gas was continuously supplied, and the crude ammonia gas was continuously recovered. The purity of the recovered crude ammonia gas was about 99.9 vol% or more, and the balance was hydrogen, nitrogen, and inevitable impurities.

  Next, a step of liquefying crude ammonia gas to obtain liquefied crude ammonia (S13) was performed. In the step (S13), the recovery rate of the crude ammonia gas was measured with a liquid level gauge provided in the storage tank of the liquefaction device, and as a result, it was confirmed that it was 90% or more. Moreover, the water | moisture content in the liquefied crude ammonia extract | collected from the sampling point provided in the exit of the extraction part of the liquefied crude ammonia from the bottom part of a storage tank was 3-5 ppm. The moisture was measured with a cavity ring down cell spectrophotometer (CRDS).

  Next, the process (S14) which removes impurities from liquefied crude ammonia, and obtains high purity ammonia by distilling liquefied crude ammonia was carried out. Specifically, the liquefied crude ammonia was supplied to the first distillation column via the intermediate ammonia introduction part of the first distillation column of the ammonia distillation apparatus. And it heated by the lower boiling heating part temperature-controlled at 45 degreeC with the heater in the lower storage part of the 1st distillation tower, and vaporized liquefied crude ammonia.

  Then, liquefied crude ammonia from which high-boiling impurities were removed in the first distillation column was supplied to the second distillation column. In the second distillation column, the liquefied crude ammonia was liquefied in a condensing and cooling unit whose temperature was controlled at −5 ° C. by a refrigerator, and was flowed down to the lower storage unit and stored. Part of this was vaporized in the lower boiling heating section to further separate low boiling impurities. A part of the ammonia gas containing a large amount of low-boiling impurities was exhausted from the discharge port by a certain amount, and high-purity ammonia from which the low-boiling impurities were removed was stored in the lower reservoir and taken out by a certain amount.

  In addition, the reflux ratio of the 1st distillation column was set to 10, and the reflux ratio of the 2nd distillation column was set to 15, and the process (S14) was implemented.

  And, impurities in high purity ammonia collected from a sampling point provided downstream from the high purity ammonia outlet from the lower reservoir of the second distillation column, CRDS, gas chromatograph with photoionization detector (GC-PID), And GC-FID. The results are shown in Table 1.

  As shown in Table 1, it was confirmed that the water in the high-purity ammonia was removed to an extremely low concentration. It was also confirmed that hydrogen, oxygen, nitrogen, carbon monoxide, carbon dioxide, and methane were also removed to an extremely low concentration. Moreover, it has confirmed that the C2-C8 hydrocarbon which was hardly contained in exhaust gas was hardly contained also in high purity ammonia.

(Example 2)
In Example 2, the same operation as in Example 1 was basically performed, but only the distillation operation in the step (S14) was different. Specifically, the temperature of the condensation cooling part of the second distillation column is set to −5 ° C., 0 ° C., 5 ° C., and 10 ° C., and the temperature of the lower boiling heating part of the first distillation column is set at each temperature. 30 degreeC, 40 degreeC, and 50 degreeC and the temperature of the lower boiling heating part of the 2nd distillation column were changed into 25 degreeC, 35 degreeC, and 45 degreeC, respectively, and high purity ammonia was collect | recovered.

  In addition, the upper pressure of each of the first distillation column and the second distillation column under each temperature condition was set as shown in Table 2 below. This pressure is a value having no practical problem. The “upper part” means a space between the high boiling point impurity-removed ammonia extraction part 18a6 and the upper reflux part 18a1 and a space between the low boiling point impurity-containing ammonia gas extraction part 18b6 and the upper reflux part 18b1 in FIG.

  The impurity concentration was measured in the same manner as in Example 1 for the high purity ammonia recovered from each. As a result, it was found that the same impurity concentration as the result of Example 1 (Table 1) was contained. That is, it was confirmed that even if the temperature and pressure of the distillation apparatus were set within the range where the distillation operation was easy, impurities could be removed from the exhaust gas and very high purity ammonia could be recovered.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is shown not by the above-described embodiment but by the scope of claims, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims.

It is a figure for demonstrating the collection | recovery apparatus of ammonia in Embodiment 1 of this invention. It is a schematic diagram which shows the distillation apparatus in Embodiment 1 of this invention. It is a figure for demonstrating the ammonia reuse apparatus in Embodiment 2 of this invention. It is a flowchart which shows the collection | recovery method of ammonia in Embodiment 3 of this invention, and the reuse method of ammonia in Embodiment 4 of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Ammonia collection | recovery apparatus, 11 Nitride semiconductor manufacturing apparatus, 12 1st pressure | voltage rise apparatus, 13 removal apparatus, 13a Fine particle removal cylinder, 13b MO removal cylinder, 14 2nd pressure | voltage rise apparatus, 15 Crude ammonia separation apparatus, 16 3rd pressure | voltage rise apparatus , 17 Liquefaction device, 18 Distillation device, 18a First distillation device, 18a1, 18b1 Upper reflux part, 18a2, 18b2 Intermediate ammonia introduction part, 18a3, 18b3 Lower reflux part, 18a4, 18b4 Lower storage part, 18a5, 18b5 Lower boiling heating Part, 18a6 high boiling point impurity removal ammonia extraction part, 18a7 middle reflux part, 18a8 high boiling point impurity containing ammonia extraction part, 18b second distillation column, 18b6 low boiling point impurity containing ammonia gas extraction part, 18b7 condensation cooling part, 18b8 high purity ammonia Extraction part, 18b9 return part, 8b10 low boiling impurities containing ammonia gas discharge portion, 19 a high-purity ammonia storage device, 20 crude ammonia storage device, 30 ammonia recycling device 31 particulate removal filter, 32 control device.

Claims (11)

A step of removing a reaction product of ammonia and an organic metal and an organic metal from an exhaust gas containing ammonia discharged from the nitride semiconductor manufacturing apparatus to obtain a mixed gas;
Separating crude ammonia gas from the mixed gas;
Liquefying the crude ammonia gas to obtain liquefied crude ammonia;
And a step of removing impurities from the liquefied crude ammonia to obtain high-purity ammonia by distilling the liquefied crude ammonia. The step of obtaining high-purity ammonia is a step of removing high-boiling impurities having a boiling point higher than that of ammonia in the first distillation column;
The method for recovering ammonia according to claim 1, comprising a step of removing low-boiling impurities having a boiling point lower than that of ammonia in the second distillation column. A step of removing a reaction product of ammonia and an organic metal and an organic metal from an exhaust gas containing ammonia discharged from the nitride semiconductor manufacturing apparatus to obtain a mixed gas;
Separating crude ammonia gas from the mixed gas;
Liquefying the crude ammonia gas to obtain liquefied crude ammonia;
Removing the impurities from the liquefied crude ammonia by distilling the liquefied crude ammonia to obtain high purity ammonia;
A method for recycling ammonia, comprising: supplying a high purity ammonia gas obtained by vaporizing the high purity ammonia to the nitride semiconductor manufacturing apparatus.   The method for reusing ammonia according to claim 3, further comprising a step of removing fine particles from the high-purity ammonia with two or more filters after the step of obtaining the high-purity ammonia.   The method of reusing ammonia according to claim 3 or 4, wherein the supplying step is performed by controlling an amount of the high purity ammonia gas. A removal device for producing a mixed gas by removing a reaction product of ammonia and an organic metal and an organic metal from an exhaust gas containing ammonia discharged from the nitride semiconductor production device;
A crude ammonia separator for producing crude ammonia gas from the mixed gas;
A liquefying apparatus for liquefying the crude ammonia gas to produce liquefied crude ammonia;
An ammonia recovery apparatus comprising: a distillation apparatus for producing high-purity ammonia by removing impurities from the liquefied crude ammonia by distilling the liquefied crude ammonia.   The ammonia according to claim 6, wherein the distillation apparatus includes a first distillation column that removes high-boiling impurities having a boiling point higher than that of ammonia, and a second distillation column that removes low-boiling impurities having a boiling point lower than that of ammonia. Recovery equipment.   The ammonia recovery device according to claim 6 or 7, further comprising a storage device for storing the liquefied crude ammonia. A removal device for producing a mixed gas by removing a reaction product of ammonia and an organic metal and an organic metal from an exhaust gas containing ammonia discharged from the nitride semiconductor production device;
A crude ammonia separator for producing crude ammonia gas from the mixed gas;
A liquefying apparatus for liquefying the crude ammonia gas to produce liquefied crude ammonia;
A distillation apparatus for producing high-purity ammonia by removing impurities from the liquefied crude ammonia by distilling the liquefied crude ammonia;
An ammonia recycling apparatus, comprising: a supply device that supplies the high purity ammonia gas obtained by vaporizing the high purity ammonia to the nitride semiconductor manufacturing device.   The ammonia recycling apparatus according to claim 9, further comprising two or more filters for removing fine particles from the high-purity ammonia.   The ammonia recycling apparatus according to claim 9 or 10, wherein the supply device includes a control device that controls an amount of the high-purity ammonia gas.

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