JP5232686B2 - Gas purification method and purification apparatus - Google Patents

Description

  The present invention relates to a method and apparatus for purifying by removing hydrogen, carbon monoxide, carbon dioxide, oxygen and water contained in a rare gas such as nitrogen gas or argon gas used for semiconductor production.

  In the semiconductor manufacturing process, a large amount of inert gas such as nitrogen gas or argon gas is used. These gases are produced by a cryogenic air separation device, and in the nitrogen gas and argon gas produced by this separation device, hydrogen, carbon monoxide, carbon dioxide, oxygen, water of ppm to ppb level are contained. Etc. are included as impurities.

  However, with the recent high integration of semiconductors, the impurity concentration in the gas used in the semiconductor manufacturing process is desired to be ppb or less, and the gas needs to be further purified. In recent years, with the increase in the size of semiconductor factories, the amount of gas used has increased significantly, and the introduction of large-scale refining equipment has increased. However, due to fierce semiconductor price competition, the cost of refining equipment has been reduced. Is also strongly desired.

As a method for removing and purifying a small amount of impurities in such nitrogen gas or rare gas for semiconductor manufacturing, Japanese Patent No. 2741622 proposes a method of removing impurities by a zirconium getter.
However, this method has a problem that the zirconium getter is expensive and cannot be regenerated, and is not suitable for mass gas purification.

Japanese Patent No. 2602670 discloses a method of removing oxygen and carbon monoxide with a reducing metal, and then removing carbon dioxide and water with an adsorbent such as zeolite.
In this purification method, the reduced metal after adsorption can be regenerated and reused with hydrogen gas. However, the amount of carbon dioxide adsorbed at a partial pressure of ppb level of zeolite is very small. In such a case, the apparatus becomes large, resulting in an increase in cost.

Japanese Patent No. 3462604 discloses a method of removing carbon dioxide with zinc oxide, removing oxygen and carbon monoxide with a nickel catalyst or a copper catalyst, and removing water with synthetic zeolite.
In this purification method, when carbon monoxide and oxygen are adsorbed on a nickel catalyst, a small amount of carbon dioxide is generated by the catalytic action. Therefore, it is necessary to pack a large amount of synthetic zeolite in order to adsorb the generated carbon dioxide again. As a result, there is a disadvantage that the adsorption tower becomes large and the cost is increased.

Japanese Patent Application Laid-Open Nos. 11-518 and 2001-104737 disclose the removal of carbon dioxide by alumina. In both cases, it is described that the amount of carbon dioxide adsorbed on alumina increases by containing alkali metal and earth in alumina.
However, both are intended for removal of carbon dioxide in the air, that is, high concentration carbon dioxide of about 400 ppm, and there is no knowledge of adsorption treatment of low concentration carbon dioxide. Further, in the adsorption treatment of carbon dioxide having a high concentration of about 400 ppm, since zeolite adsorbs more carbon dioxide than alumina, conventionally, zeolite has been mainly used in a purification apparatus.

  In any of the above prior invention methods, in order to purify a large amount of gas, the adsorbent is expensive, the adsorption tower is large, and the production cost is high. For this reason, a method capable of efficiently purifying a large amount of gas is desired.

Japanese Patent No. 2741622 Japanese Patent No. 2602670 Japanese Patent No. 3462604 Japanese Patent Laid-Open No. 11-518 JP 2001-104737 A

  Therefore, the problem in the present invention is that, when purifying by removing hydrogen, carbon monoxide, carbon dioxide, oxygen and water in a large amount of nitrogen gas or rare gas, the purification apparatus can be made compact and expensive. The purpose is to reduce the amount of catalyst used such as a zirconium getter or a nickel catalyst, thereby reducing the purification cost.

To solve this problem,
The invention according to claim 1 is a gas purification method for removing hydrogen, carbon monoxide, carbon dioxide, oxygen and water in a large amount of nitrogen gas or rare gas,
Nitrogen gas or rare gas is contacted with a moisture adsorbent to remove water and the flow of gas is rectified, then contacted with a nickel catalyst to remove hydrogen, carbon monoxide and oxygen, and then contacted with alumina to form carbon dioxide. to remove carbon, and the gas flow and down-flow, the gas flow rate theoretically filler is a method for purifying a gas, characterized in that a higher rate that causes fluidization.

The invention according to claim 2 is the gas purification method according to claim 1, wherein the partial pressure of carbon dioxide in the nitrogen gas or the rare gas is 19 Pa or less.
The invention according to claim 3 is the gas purification method according to claim 1 or 2, wherein the alumina contains 0.1 to 10 wt% of sodium.

The invention according to claim 4 is the gas purification method according to any one of claims 1 to 3, wherein the gas flow rate is set to 31 to 100 cm / second as a superficial velocity.

The invention according to claim 5 is a gas purifier for removing hydrogen, carbon monoxide, carbon dioxide, oxygen and water in a large amount of nitrogen gas or rare gas,
A gas purification apparatus comprising an adsorption tower in which a moisture adsorbent, a nickel catalyst, and alumina are packed in this order from the inflow side to the outflow side of nitrogen gas or rare gas.

In the present invention, “a large amount of nitrogen gas or rare gas” means that the flow rate per hour is in the range of 1000 to 100,000 Nm ³ . “Rectification” means that the fluctuation value of the flow velocity between all positions in a plane orthogonal to the gas flow in the adsorption tower is within ± 1 cm / second.

According to the present invention, since the gas to be purified flows at a high flow rate by downflow, it is not necessary to make the adsorption tower have a large diameter even when a large amount of gas to be purified of 1000 to 100,000 Nm ³ / hour is flowed.
In addition, when the gas flow rate is high, pressure distribution occurs in the upper space of the adsorption tower, gas drift occurs in the adsorption layer, and impurities can not be sufficiently removed in the drift section, so that the adsorbent is used effectively. Although a new problem arises, the moisture adsorbent is charged in the previous stage and rectification is performed by the moisture adsorbent, and the water is removed, so that the nickel catalyst is effectively used and the amount of filling is reduced. This makes it possible to reduce costs.

  Carbon dioxide is removed by alumina. Even if the partial pressure of carbon dioxide in the gas to be refined is 19 Pa or less, that is, even if it is contained in a trace amount in the gas to be refined, it is more efficient than a conventional adsorption tower. Carbon dioxide removal is possible. If sodium is contained in the alumina, carbon dioxide can be removed with a smaller adsorption tower.

Carbon monoxide and oxygen react on nickel catalyst to generate a small amount of carbon dioxide, but the moisture adsorbent has little adsorption capability of low partial pressure carbon dioxide in nitrogen gas due to co-adsorption of carbon dioxide and nitrogen. Therefore, it was necessary to fill a large amount of zeolite in order to adsorb carbon dioxide.
However, it is possible to significantly reduce the amount of the adsorbent by adsorbing this trace amount of carbon dioxide on sodium-containing activated alumina having a large adsorption ability of low partial pressure carbon dioxide in nitrogen gas.

It is a schematic block diagram which shows an example of the gas purification apparatus of this invention. It is the graph which compared the adsorption amount of the low partial pressure carbon dioxide of a zeolite and the alumina of this invention. It is a graph which shows the sodium content contained in the alumina of this invention, and the adsorption amount of a carbon dioxide. It is a graph which shows the superficial velocity of the alumina layer which concerns on this invention, and the pressure loss by Ergun type | formula.

FIG. 1 shows an example of a gas purification apparatus of the present invention.
In FIG. 1, reference numerals 1A and 1B denote adsorption towers. The adsorption tower 1A (1B) has a moisture adsorbent layer 2 filled with a moisture adsorbent from above, a nickel catalyst layer 3 filled with a nickel catalyst, and an alumina layer 4 filled with alumina. The gas to be purified passes through the moisture adsorbent layer 2, the nickel catalyst layer 3, and the alumina layer 4 from above and flows downward (downflow).

When one of the adsorption towers 1A is in the adsorption process, the other adsorption tower 1B is in the regeneration process, and is operated by alternately switching both adsorption towers by opening and closing valves V1, V2, V3,. It is like that.
Further, a heater 5 for heating the regeneration gas is provided, and the heated regeneration gas is configured to flow upward from the bottom of the adsorption tower 1A (1B). As the regeneration gas, a mixed gas of hydrogen and an inert gas and an inert gas are used, and a part of the purified gas is used as the inert gas.

As the moisture adsorbent, activated alumina, silica gel, synthetic zeolite or the like is used.
As the nickel catalyst, a catalyst in which nickel metal is supported on a carrier such as activated alumina, diatomaceous earth, activated carbon or the like is used in an amount of 10 to 90 wt%, subjected to reduction treatment with hydrogen, and in the presence of an inert gas such as nitrogen. It can be reused after heat treatment.
As the alumina, γ-alumina containing 1 to 10 wt% of sodium is used.

The use of alumina has an advantage in carbon dioxide adsorption over zeolite.
The first is that it has higher capacity than zeolite to adsorb low partial pressure carbon dioxide.
FIG. 2 compares the adsorption amounts of low partial pressure carbon dioxide between zeolite and alumina. The carbon dioxide adsorption amount was measured by using a constant capacity gas adsorption amount measuring device while keeping the temperature constant at 25 ° C. and arbitrarily setting the pressure.
FIG. 2 shows that when the partial pressure of carbon dioxide is 19 Pa or less, the carbon dioxide adsorption amount of alumina is larger than the carbon dioxide adsorption amount of zeolite.

  Second, since zeolite generally has a high nitrogen adsorption capacity, it is known that the amount of carbon dioxide adsorbed is reduced particularly when nitrogen gas is purified with zeolite.

Thirdly, by adding sodium to alumina, the amount of carbon dioxide adsorbed by alumina containing sodium is larger than that of alumina not containing sodium.
As shown in FIG. 3, it can be seen that the amount of carbon dioxide adsorption increases when 1-10 wt% sodium is included in alumina. The carbon dioxide adsorption amount was measured using a constant capacity type gas adsorption amount measuring device at a temperature of 25 ° C. and a pressure of 1 Pa.

A large amount of gas to be purified such as nitrogen and argon from the cryogenic air separation apparatus at 1000 to 100,000 Nm ³ / hour is introduced from the pipe 6 through the valve V1 to the upper part of the adsorption tower 1A. This gas to be purified contains hydrogen, carbon monoxide, carbon dioxide, oxygen, and water as impurities in the ppm to ppb level. It is desirable that the carbon dioxide in the gas to be purified has a partial pressure of 19 Pa or less and a small content.
The flow rate of the gas to be purified is 31 to 100 cm / second at the superficial velocity, and if it is less than 31 cm / second, the diameter of the adsorption tower becomes large, resulting in an increase in the size of the apparatus and the cost. The pressure loss of the gas to be purified introduced into the gas becomes too large, and the pressure of the purified gas becomes low.
Furthermore, in the purification apparatus, the purification gas flow in the adsorption tower is generally up-flow. However, if the superficial velocity is 31 cm / second or more, the filler fluidizes and gas purification is sufficiently performed. Absent. Therefore, in the present invention, the flow rate is increased and the purification is performed by downflow.

For example, FIG. 4 shows the superficial velocity when the alumina layer 4 is formed with a packing density of 780 kg / m ³ , a porosity of 0.41, and a thickness of 100 mm using spherical alumina having a diameter of 1.6 mm (ΔP / L). / GB is a graph representing the relationship and can be estimated using the Ergun equation, which is often used for flows through porous media. In the Ergun equation, ΔP is the pressure loss, L is the packed layer thickness, and GB is the packing density.
Since the condition in which the alumina filled in the alumina layer 4 does not flow is (ΔP / L) / GB ≦ 1, the superficial velocity at which alumina does not flow in this example is 31 cm / second or less. Therefore, it is necessary to adopt downflow at 31 cm / second or more.

The gas to be purified first flows into the uppermost moisture adsorbent layer 2, where moisture out of impurities is adsorbed and removed, and at the same time, the gas to be purified is drifted and rectified.
When the gas to be purified flows into the upper part of the adsorption tower 1A at a high flow rate of 31 to 100 cm / sec, a drift of the gas to be purified occurs above the moisture adsorbent layer 2, and the gas flows uniformly into the moisture adsorbent layer 2. In the surface layer of the moisture adsorbent layer 2, a part having a high flow rate and a part having a low flow rate are partially generated, and the flow rate difference may be about 5 cm / second.

This refined gas has a small flow rate difference in the middle of the gas flow between the moisture adsorbent particles in the moisture adsorbent layer 2. That is, the moisture adsorbent layer 2 exhibits a kind of rectification function, and when the gas to be purified flows out of the moisture adsorbent layer 2, the flow rate difference becomes 1 cm / second or less, and a drift is created and rectified. In this state, it flows into the nickel catalyst layer 3 at the next stage.
Since the gas to be purified flows uniformly in the nickel catalyst layer 3, all of the existing nickel catalyst contributes to the removal of hydrogen, oxygen, and carbon monoxide.

  On the other hand, when the gas to be purified flows directly into the nickel catalyst layer 3 in a drift state, the contact between the gas to be purified and the nickel catalyst particles is not performed uniformly. It is necessary to increase the thickness of the catalyst layer 3, and a large amount of expensive nickel catalyst is used, which increases the cost.

Next, the gas to be purified flows into the nickel catalyst layer 3 in a rectified state, where impurities such as hydrogen, oxygen, and carbon monoxide are removed. At the same time, a portion of carbon monoxide and oxygen react to produce a trace amount of carbon dioxide.
Further, the gas to be purified flowing out of the nickel catalyst layer 3 is introduced into the alumina layer 4 where carbon dioxide as impurities and carbon dioxide generated in the nickel catalyst layer 3 are adsorbed and removed.

  The to-be-purified gas flowing out of the alumina layer 4 is a purified gas in which hydrogen, carbon monoxide, carbon dioxide, oxygen and water contained therein are removed, and the concentration of these impurities is reduced to the ppb level or less. The purified gas is led out as a product gas through the valve V7 and the pipe 7.

After introducing the gas to be purified into the adsorption tower 1A for a predetermined time, the valves V1 to V8 are opened and closed, and the gas to be refined is switched to the adsorption tower 1B through the valve V2 and introduced into the adsorption tower 1B. Then, the purified gas from the bottom of the adsorption tower 1B is led out from the valve V8 and the pipe 7 as product gas.
On the other hand, the adsorption tower 1A enters the regeneration step.

In the regeneration, hydrogen supplied from the pipe 8 and purified gas such as nitrogen and argon branched by the pipe 9 are mixed to obtain a mixed gas having a hydrogen concentration of 1 to 5 vol%, and this is sent to the heater 5, and 150 to After heating to 300 ° C., it is introduced into the bottom of the adsorption tower 1A through the tube 10 and the valve V5, and flows upward.
By introducing this heated mixed gas, the carbon dioxide adsorbed on the alumina layer 4 is desorbed, and the oxygen and carbon monoxide adsorbed on the nickel catalyst layer 3 are reduced and desorbed by hydrogen to desorb the moisture adsorbent layer 2. Moisture adsorbed on is desorbed. From the upper part of the adsorption tower 1A, the mixed gas containing the desorbed impurities is discharged out of the system through the valve V3 and the pipe 11 as exhaust gas.
The adsorption tower 1A that has been regenerated in this way waits for the next adsorption step.

  The adsorption tower 1A is again an adsorption process, and the adsorption tower 1B is a regeneration process. The regeneration of the adsorption tower 1B is carried out by introducing a regeneration gas upward from the bottom of the adsorption tower 1B through the pipe 10 and the valve V6, and exhaust gas from the top of the adsorption tower 1B through the valve 4 and the pipe 11 outside the system. It is done by discharging.

Example 1
A 100 mm thick zeolite layer (MS5A), a 100 mm thick nickel catalyst layer (N112), and a 100 mm thick alumina layer were formed from above in a stainless steel cylinder having an inner diameter of 100 mm to form an adsorption tower.
Each layer of this adsorption tower was regenerated under the following conditions.

First, nitrogen containing a hydrogen concentration of 2 vol% was heated to 200 ° C. and allowed to flow at a flow rate of ³ Nm ³ / hour for 3 hours, then nitrogen was heated to 200 ° C. and allowed to flow at a flow rate of ³ Nm ³ / hour for 3 hours, and further cooled.
Thereafter, 1 ppm-hydrogen, 1 ppm-carbon monoxide, 0.5 ppm-carbon dioxide, 1 ppm-oxygen, 2.6 ppm-nitrogen containing moisture is used as the gas to be purified, pressure 100 PaG, temperature 25 ° C., flow rate (superficial velocity) ) It was introduced into the adsorption tower by downflow under the conditions of 53 cm / second and a flow rate of 30 Nm ³ / hour.
Hydrogen was detected as the first breakthrough component when 24 hours passed after the start of introduction.

(Example 2)
Formed in a stainless steel cylinder with an inner diameter of 100 mm is an alumina containing a zeolite layer (MS5A) having a thickness of 100 mm, a nickel catalyst layer (N112) having a thickness of 100 mm, and sodium containing 5.8% by weight of sodium having a thickness of 50 mm. Thus, an adsorption tower was obtained.

After the adsorption tower was regenerated under the same conditions as in Example 1, a gas to be purified having the same composition as in Example 1 was introduced under the same conditions.
Hydrogen was detected as the first breakthrough component when 24 hours passed after the start of introduction.

(Comparative Example 1)
A nickel catalyst layer (N112) having a thickness of 100 mm, a zeolite layer (MS5A) having a thickness of 100 mm, and an alumina layer having a thickness of 100 mm were formed from above in a stainless steel cylinder having an inner diameter of 100 mm to obtain an adsorption tower.
After this adsorption tower was regenerated under the same conditions as in Example 1, a gas to be purified having the same composition as in Example 1 was introduced under the same conditions.
Hydrogen was detected as the first breakthrough component when 18 hours passed after the start of introduction.

(Comparative Example 2)
An adsorption tower was formed by forming a nickel catalyst layer (N112) having a thickness of 50 mm, a zeolite layer (MS5A) having a thickness of 50 mm, and an alumina layer having a thickness of 50 mm in a stainless steel cylinder having an inner diameter of 100 mm.
Each layer of this adsorption tower was regenerated under the following conditions.

First, nitrogen containing a hydrogen concentration of 2 vol% is heated to 200 ° C. and flowed at a flow rate of 1.5 Nm ³ / hour for 3 hours, then nitrogen is heated to 200 ° C. and flowed at a flow rate of 1.5 Nm ³ / hour for 3 hours and further cooled did.
Thereafter, 1 ppm-hydrogen, 1 ppm-carbon monoxide, 0.5 ppm-carbon dioxide, 1 ppm-oxygen, 2.6 ppm-nitrogen containing moisture is used as the gas to be purified, pressure 100 PaG, temperature 25 ° C., flow rate (superficial velocity) ) It was introduced into the adsorption tower by downflow under the conditions of 26.5 cm / second and a flow rate of 15 Nm ³ / hour.
Hydrogen was detected as the first breakthrough component when 23 hours had elapsed after the start of introduction.

(Comparative Example 3)
A zeolite layer (MS5A) having a thickness of 100 mm, a nickel catalyst layer (N112) having a thickness of 100 mm, and an alumina having a thickness of 50 mm were formed from above in a stainless steel cylinder having an inner diameter of 100 mm to obtain an adsorption tower.
After this adsorption tower was regenerated under the same conditions as in Example 1, a gas to be purified having the same composition as in Example 1 was introduced under the same conditions.
Carbon dioxide was detected as the first breakthrough component when 13 hours had passed after the start of introduction.

  From Example 1 and Comparative Example 1, it can be seen that the amount of hydrogen adsorbed on the nickel catalyst layer is increased by forming the zeolite layer on the nickel catalyst layer.

  From Example 1 and Comparative Examples 1-2, when the nickel catalyst layer is the first layer, the hydrogen breakthrough time is long when the flow rate of the gas to be purified is low, but breakthrough occurs when the flow rate is high. Time is shortened and the effect of high flow rate can be confirmed.

  From Example 2 and Comparative Example 3, it can be seen that when alumina containing sodium is used, carbon dioxide is not detected even if the filling amount is greatly reduced.

1A (1B) ... Adsorption tower 1, 2, ... Moisture adsorbent layer, 3 .... Nickel catalyst layer, 4 .... Alumina layer, 5 .... Heater, 6, 7, 8, 9, 10, 11, ... Tube, V1-V8 ... Valve

Claims (5)

A gas purification method for removing hydrogen, carbon monoxide, carbon dioxide, oxygen and water in a large amount of nitrogen gas or rare gas,
Nitrogen gas or rare gas is contacted with a moisture adsorbent to remove water and the flow of gas is rectified, then contacted with a nickel catalyst to remove hydrogen, carbon monoxide and oxygen, and then contacted with alumina to form carbon dioxide. method for purifying a gas, characterized in that removal of carbon, and the gas flow and down-flow, the gas flow rate is theoretically the filler be at least the speed causing fluidization.   The method for purifying a gas according to claim 1, wherein the partial pressure of carbon dioxide in the nitrogen gas or rare gas is 19 Pa or less.   The gas purification method according to claim 1 or 2, wherein the alumina contains 0.1 to 10 wt% of sodium. The gas purification method according to any one of claims 1 to 3 , wherein the gas flow rate is set to 31 to 100 cm / second as a superficial velocity. A gas purifier for removing hydrogen, carbon monoxide, carbon dioxide, oxygen and water in a large amount of nitrogen gas or rare gas,
A gas purification apparatus comprising an adsorption tower in which a moisture adsorbent, a nickel catalyst, and alumina are packed in this order from the inflow side to the outflow side of nitrogen gas or rare gas.

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