JP5133929B2 - Method and apparatus for producing ultra-high purity nitrogen gas - Google Patents

Description

  The present invention relates to a method and an apparatus for producing ultra high purity nitrogen gas from nitrogen gas obtained from an air liquefaction separation apparatus.

  Inert gases such as helium, argon, krypton, xenon or nitrogen are widely used in the electronics industry. Inert gases used in the electronics field include those used in each process of semiconductor manufacturing and those for general use that are used as purge gas or dilution gas between processes. The level of purity that can be achieved varies greatly. In particular, when used in a semiconductor manufacturing process, the requirement for purity is particularly strict, and ultrahigh purity is required in which each impurity concentration is 1 ppb or less.

Gases to be removed as impurities in the gas used in the semiconductor manufacturing process are oxygen, carbon dioxide, carbon monoxide, hydrogen, water, and the like.
One method for removing these impurity gases and obtaining a purified gas is a getter method using a chemical reaction with a highly active getter agent. This method is excellent in that various impurity gases can be removed to 1 ppb or less, but since it cannot be regenerated, it must be replaced when it reaches the end of its life. Applications are limited.

Renewable purification methods include (1) supplementing oxygen, carbon monoxide and hydrogen contained in the gas with a catalyst such as nickel or copper, and then adsorbing and removing moisture and carbon dioxide with an adsorbent such as synthetic zeolite. Method (2) Convert oxygen, carbon monoxide and hydrogen into carbon dioxide by catalytic reaction, then supplement the excess oxygen with nickel catalyst, adsorb and remove carbon dioxide with zinc oxide, and finally water with synthetic zeolite Adsorption and removal method (Japanese Patent Laid-Open No. 2-120212), (3) Carbon dioxide is first adsorbed and removed with an adsorbent mainly composed of zinc oxide with high carbon dioxide adsorption ability, and then nickel or copper is used as an active ingredient There is a method of removing oxygen, carbon monoxide, hydrogen and a small amount of remaining carbon dioxide with a catalyst, and finally adsorbing and removing moisture (JP-A-8137748).

A method for improving the carbon dioxide adsorption capacity of the nickel catalyst has also been intensively studied. (4) A method in which a carbonate such as sodium carbonate is supported on a nickel catalyst (JP 2005-319345), or (5) a nickel compound on activated carbon. In addition, there is a method of carrying an alkali metal compound (Japanese Patent Laid-Open No. 2005-324155).

On the other hand, in the pretreatment of the air liquefaction separation apparatus, zeolite is generally used for the removal of carbon dioxide in the air, but there is also a method of using this by improving the carbon dioxide adsorption amount of activated alumina. Proposed. As a method for improving the carbon dioxide adsorption performance of activated alumina, a method in which activated alumina is impregnated with a basic solution (Japanese Patent Laid-Open No. 11-518) or a method containing 0.001 to 7.25% of an alkali or alkaline earth metal oxide (special feature) Open 2001-104737).

JP-A-2-120212 JP-A-8-173748 JP 2005-319345 A JP 2005-324155 A Japanese Patent Laid-Open No. 11-518 JP 2001-104737 A

  In recent semiconductor factories, due to the expansion of production scale, the need to purify the total amount of nitrogen gas produced by an air separation device is increasing, and the required amount of processing is increasing. On the other hand, since the conventional purification apparatus requires a large amount of expensive adsorbent as described above, the ratio of the agent price occupying the total cost is relatively high particularly in a large apparatus for processing a large flow rate. There is a problem that initial cost is high, and improvement is required.

The method (1) has a problem that the amount of carbon dioxide adsorbed by the nickel catalyst is small, and synthetic zeolite cannot remove carbon dioxide concentration to the required purity.
Therefore, methods (2) and (3) were devised. However, the method (2) requires expensive oxidation catalysts such as Pt and Pd, and there is a problem that it is necessary to always heat to promote the reaction, and there is a problem that initial cost and running cost are high. there were.
In the method (3), since carbon dioxide cannot be sufficiently removed to the required purity with zinc oxide, it was necessary to dispose carbon dioxide by disposing a nickel catalyst after the zinc oxide. Since the amount of carbon dioxide adsorbed by the nickel catalyst is small, a large amount of expensive nickel catalyst is required, and the problem of high initial cost remains.
In the methods (4) and (5), since both are supported on a single substance in the form of an alkali metal compound, there is no concern about contamination due to peeling of the supported alkali metal compound. Since semiconductor factories dislike these alkali metals in particular, a method different from loading was required.

To solve the above problem,
The invention according to claim 1 is a method for producing ultra-high purity nitrogen gas from nitrogen gas obtained by an air liquefaction separation method, and adsorbs oxygen, carbon monoxide, and hydrogen at room temperature with a nickel catalyst. This is a method for producing ultra-high purity nitrogen gas in which carbon dioxide is adsorbed and removed at room temperature using sodium-bonded activated alumina after removal.

  The invention according to claim 2 is an ultra-high purity nitrogen gas production apparatus comprising a nickel catalyst and an adsorption cylinder filled with sodium-bonded activated alumina in the subsequent stage.

According to the method and apparatus of the present invention, the amount of expensive nickel catalyst used can be greatly reduced, and in particular, the initial cost is reduced and ultra-high purity nitrogen gas is produced from nitrogen obtained by the air liquefaction separation method. can do.

It is a figure which shows the result of having measured the breakthrough adsorption amount in 0.1 ppm of four types of sodium bond activated alumina.

Synthetic zeolite is an example of an adsorbent that is generally said to have a large amount of carbon dioxide adsorption. On the other hand, activated alumina used for moisture removal, etc., adsorbs carbon dioxide slightly, but its adsorption amount is not particularly large compared to other adsorbents, so it is generally noted as an adsorbent for carbon dioxide. It never happened.

Nitrogen gas produced by the air liquefaction separation apparatus has a relatively low carbon dioxide concentration of about 100 ppb among the contained impurity components. For example, at a low concentration (partial pressure of 0.1 Pa or less) than the amount of adsorption at a high concentration (partial pressure of several hundred Pa) as required when used in a pretreatment device of an air liquefaction separation device. The amount of adsorption is important. Until now, no substance has been known that effectively adsorbs oxygen dioxide at such extremely low concentrations.

As a result of intensive studies, the inventors have found that activated alumina having sodium bound to its surface specifically adsorbs extremely low concentrations of carbon dioxide at room temperature.

  In the present invention, nitrogen gas produced by an air liquefaction separation method is passed through a nickel catalyst at room temperature, and oxygen, carbon monoxide, and hydrogen are previously adsorbed and removed. At this time, oxygen contained in the nitrogen gas reacts with carbon monoxide, and a part thereof becomes carbon dioxide and flows out downstream. Therefore, it is desirable to install sodium-bound activated alumina on the downstream side. Ultra high purity nitrogen gas is produced by adsorbing and removing carbon dioxide with sodium-bonded activated alumina at room temperature.

Sodium-bound activated alumina can be used repeatedly by regenerating with a regeneration gas of about 200 ° C. (a part of the product high purity nitrogen gas may be used).
An apparatus for producing ultra-high purity nitrogen gas by such a method comprises an adsorption cylinder filled with a nickel catalyst and sodium-bound activated alumina, and this adsorption cylinder is for regenerating sodium-bound activated alumina. It has a heater for heating the regeneration gas.

With such an ultra-high purity nitrogen gas production method and production equipment, it is possible to reduce the concentration of each impurity in the nitrogen gas produced by the air liquefaction separation apparatus to 1 ppb or less, which can be used for semiconductor production processes. Purity nitrogen gas can be obtained.

Example 1
The amount of carbon dioxide adsorbed at 25 ° C. was measured by the constant volume method for four types of sodium-binding activated alumina (sodium content was 1.5%, 6.0%, 8.0%, 10.2%). Table 1 shows the amount of carbon dioxide adsorbed at a pressure of 1 Pa corresponding to a concentration of 1 ppm.
Next, purified nitrogen gas added with 0.1 ppm of carbon dioxide as an impurity was passed through an adsorption cylinder filled with 100 mm of sodium-binding activated alumina and having an inner diameter of 28.4 mm, and the time until breakthrough was measured.
The time until breakthrough was determined by analyzing the outlet gas using API-MS.
The breakthrough adsorption amount was determined for each of the four types of sodium-bound activated alumina having different sodium contents. The results are shown in Table 1 and FIG.

(Comparative Example 1)
Examples of synthetic zeolites were selected from Ca-A zeolite, Ca-X zeolite, two types of commercially available activated alumina, and nickel catalyst, which contain Ca ions and are generally said to have high carbon dioxide adsorption. As in 1, the carbon dioxide adsorption at 25 ° C. was measured by the constant volume method. Table 1 shows the amount of carbon dioxide adsorbed at a pressure of 1 Pa corresponding to a concentration of 1 ppm.
Similarly to Example 1, the amount of breakthrough adsorption was determined using Ca-A type zeolite, Ca-X type zeolite, two types of commercially available activated alumina, and a nickel catalyst. The results are shown in Table 1.

From Table 1, it can be seen that the adsorption amount of carbon dioxide at 1 Pa is extremely low for the breakthrough adsorption amount showing the dynamic performance, although the activated alumina is relatively high. A similar tendency is observed for zeolite, and it is understood that none of them is suitable for adsorption of low concentration carbon dioxide. The cause of this is presumed that the diffusion of gas inside the adsorbent is rate-limiting, that is, the crystal structure (pore structure) has an effect.

On the other hand, the nickel catalyst that has been used for adsorption of carbon dioxide at a low concentration so far is inferior in the adsorption amount at 1 Pa, but has a small decrease in breakthrough adsorption amount at 0.1 ppm, and is at a level that can be put to practical use. As shown in Table 1, the amount of carbon dioxide adsorbed at 1 Pa of sodium-bound activated alumina is increased compared to activated alumina, but the amount of breakthrough adsorption is greatly increased, and the dynamic adsorption characteristics are increased. It turns out that it is improving.

In Table 1, it can be seen that the amount of carbon dioxide adsorption tends to increase as the sodium content increases. However, as shown in FIG. 1, there is an optimum value for the sodium content in terms of dynamic characteristics, and the amount is It turns out that an effect will fall when too much.

(Example 2)
The inlet side of the adsorption cylinder having an inner diameter of 28.4 mm was filled with 200 mm of nickel catalyst, and the subsequent stage was filled with 150 mm of sodium-bound activated alumina. Nitrogen gas added with carbon monoxide 1.0 ppm, hydrogen 1.0 ppm, and carbon dioxide 0.5 ppm as impurities was circulated through this adsorption cylinder at 2.4 Nm3 / h, and the gas at the adsorption cylinder outlet was analyzed. Analysis used API-MS and GC-FID. The first breakthrough was carbon dioxide, and the breakthrough time was about 48 hours.

(Comparative Example 2)
An adsorption cylinder having an inner diameter of 28.4 mm was filled with 350 mm of nickel catalyst. Purified nitrogen gas added with carbon monoxide 1.0 ppm, hydrogen 1.0 ppm, and carbon dioxide 0.5 ppm as impurities was passed through this adsorption cylinder at 2.4 Nm3 / h, and the purified gas at the outlet was analyzed. Analysis was performed using GC-FID (manufactured by Shimadzu Corporation). The first breakthrough was carbon dioxide, and the breakthrough time was approximately 21 hours.

Claims (2)

    A method for producing ultra-high purity nitrogen gas from nitrogen gas obtained by an air liquefaction separation method, wherein the nitrogen gas is adsorbed and removed at room temperature with a nickel catalyst, and then sodium-bonded activated alumina A method for producing ultra-high purity nitrogen gas that uses carbon to adsorb and remove carbon dioxide at room temperature. An ultra-high purity nitrogen gas production apparatus comprising a nickel catalyst and an adsorption cylinder filled with sodium-bonded activated alumina in the subsequent stage.

Images