JPH0616402A - Method for refining nitrous oxide - Google Patents

Abstract

PURPOSE:To obtain a high-purity refined gas by surely removing oxygen contained in nitrous oxide or in a gas contg, nitrous oxide as the impurity without by-producing the impurity such as nitrogen to be generated by the decomposition of nitrous oxide. CONSTITUTION:Nitrous oxide or a gas contg. nitrous oxide diluted with nitrogen, argon, etc., is brought into contact with a catalyst consisting essentially of manganese oxide, especially a lower manganese oxide. Besides, the catalyst is brought into contact with nitrous oxide, as required, prior to refining and pretreated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for purifying nitrous oxide, and more particularly to a method for purifying nitrous oxide capable of removing oxygen contained as an impurity in nitrous oxide to an extremely low concentration. Nitrous oxide is used in semiconductor manufacturing, such as used for forming a silicon oxide film for a surface insulating film in LSI manufacturing, but with the progress of film forming technology, it is required to have very few impurities.

[0002]

2. Description of the Related Art Nitrous oxide used in semiconductor manufacturing is generally marketed as pure nitrous oxide (liquefied gas). In particular, oxygen and water are contained as impurities in these nitrous oxides, of which water can be removed by a dehumidifying agent such as synthetic zeolite. Oxygen concentration in commercially available nitrous oxide is usually 20 ppm
As shown below, high-purity nitrous oxide containing about 5 nines in a cylinder, which has a relatively low oxygen concentration of 0.1 to 1 ppm, is commercially available.

[0003]

However, if the oxygen content is less than 1 ppm, it is not possible to sufficiently meet the demands in the recent semiconductor manufacturing process.
It is strongly desired that the content be less than or equal to ppm, more preferably less than or equal to 0.01 ppm. Further, recently, it has become possible to purify a gas such as silane used together with nitrous oxide at the time of semiconductor manufacturing to high purity, and for example, it becomes possible to obtain oxygen containing 0.01 ppm or less as impurities. (Japanese Patent Laid-Open No. 3-12303, etc.). Therefore, the demand for nitrous oxide, which has an extremely low oxygen content, is increasing. Further, these nitrous oxides may be contaminated by impurities such as air in the process of supplying them to the semiconductor device during the connection of the cylinder or switching of the pipes, so it is desirable to finally remove the impurities immediately before the device. Thus, the demand for high-purity nitrous oxide is increasing year by year,
As a method of removing oxygen contained in nitrous oxide, a method of ventilating an alkaline dithionate aqueous solution is known, but since it is a wet method, the configuration of the apparatus is complicated and disadvantageous in terms of simplicity. Not only is it necessary to remove water again. For this reason, it is desirable to use a deoxygenation catalyst packed in a purification column for purification such as nitrogen and inert gas, but deoxidation catalyst such as reduced nickel almost decomposes nitrous oxide even at room temperature. There is a problem.

[0004]

[Means for Solving the Problems] The present inventors have earnestly studied a purification method capable of efficiently removing oxygen contained in nitrous oxide to an extremely low concentration without decomposing nitrous oxide. As a result, by contacting nitrous oxide with a catalyst containing manganese oxide as a main component, oxygen was added at 0.1 pp.
The present invention has been completed by finding that it can be removed to m or less, and further to 0.01 ppm or less, and that decomposition of nitrous oxide is small. That is, the present invention is a method for purifying nitrous oxide, which comprises contacting crude nitrous oxide with a catalyst containing manganese oxide as a main component to remove oxygen contained in the crude nitrous oxide. . The present invention includes nitrous oxide alone represented by the chemical formula N ₂ O, and nitrous oxide diluted with an inert gas (inert gas base) such as nitrogen and argon (hereinafter collectively referred to as crude nitrous oxide). It is applied to remove oxygen contained in the material.

In the present invention, various manganese oxides can be used, but among them, lower oxides of manganese are generally preferred. The lower oxide has the chemical formula MnO
And manganese monoxide represented by Mn ₂ O ₃ , trimanganese tetraoxide represented by Mn ₃ O ₄ , and mixtures thereof. There are various methods for obtaining these lower oxides, but a typical method is to reduce higher oxides such as manganese dioxide with hydrogen or carbon monoxide. Alternatively, lower oxides having various compositions such as a mixture of two or more kinds of oxides can be obtained. It is also possible to prepare these oxides from manganese salts of corresponding oxidation numbers, for example to obtain manganese monoxide,
There is a method of heating manganese (II) carbonate, manganese (II) hydroxide, manganese (II) oxalate, manganese (II) acetate, etc. in a state where air is cut off. These manganese oxides may be used as they are after molding, or may be crushed to an appropriate size, or may be used in the form of being supported on a catalyst carrier. As a method of supporting manganese oxide on a carrier, for example, a carrier powder such as diatomaceous earth, alumina, silica-alumina, aluminosilicate and calcium silicate is dispersed in an aqueous solution of manganese salt, and alkali is added to the carrier powder to add manganese to the carrier powder. After the components are deposited and then filtered and optionally washed with water, the cake obtained is dried at 120 to 150 ° C. and then 30 times in nitrogen.
The product is calcined at 0 ° C. or higher and the calcined product is crushed, or an inorganic salt such as MnCO ₃ or Mn (OH) ₂ or MnC ₂ O is used.
₄ , there is a method in which an organic salt such as Mn (CH ₃ COO) ₂ is calcined in nitrogen, crushed, mixed with heat resistant cement, and calcined again in nitrogen. These manganese oxides are usually formed into a molded product by extrusion molding, tablet molding, etc., and are used as they are, or if necessary, crushed to an appropriate size. As a molding method, a dry method or a wet method can be used, in which case a small amount of water, a lubricant or the like may be used. When using lower manganese oxide, the handling work must be done in a nitrogen gas atmosphere in a glove box without touching oxygen. Regarding the content of manganese oxide, the lower oxide of manganese is mainly contained, and usually 10 wt% or more, preferably 2
It is 0 wt% or more. Manganese oxide content is 10wt
If it is less than%, the deoxidizing ability is lowered and there is a possibility that oxygen cannot be sufficiently removed.

In the present invention, a molded product containing manganese oxide, particularly a lower oxide, as an active ingredient may be filled in a purifying cylinder, and crude nitrous oxide may be flowed as it is for purification.
In order to prevent the decomposition of nitrous oxide, it is preferable to perform a pretreatment with nitrous oxide prior to the purification. For the pretreatment, nitrous oxide alone or a mixed gas with an inert gas such as argon is usually used to obtain an empty cylinder linear velocity (LV) of 1 to 10 cm / se.
It is carried out by circulating it for 30 minutes to 2 hours. The pretreatment condition is that the temperature is higher than the temperature during the purification of crude nitrous oxide, usually 50 ° C or higher, but if it becomes too high, the reaction with nitrous oxide causes deoxidizing activity as a catalyst. Since it may be impaired, it is preferably carried out in a temperature range higher by 10 to 100 ° C. than the temperature at the time of purification. If pretreatment is not applied, the concentration of nitrogen generated by the decomposition of nitrous oxide may be close to 3 vol% depending on the purification conditions. It is almost certainly prevented. The pretreatment may be performed before the filling into the purification column or after the filling.If the pretreatment is performed after the manganese oxide is filled in the purification column in advance, the crude nitrous oxide of This is convenient because purification can be performed.

Purification of crude nitrous oxide is carried out by passing the crude nitrous oxide through a purification column filled with the above-mentioned catalyst containing manganese oxide as a main component, and the crude nitrous oxide comes into contact with the manganese oxide catalyst. As a result, oxygen contained as impurities is removed without decomposing nitrous oxide. The oxygen concentration in the crude nitrous oxide applied to the present invention is usually 100 ppm or less. When the oxygen concentration is higher than this, the amount of heat generated increases, so heat removal means is required depending on the conditions.

The filling length of the manganese oxide catalyst packed in the purifying cylinder is determined by the amount of crude nitrous oxide supplied, the oxygen concentration, the characteristics of the catalyst used, the oxygen removal conditions, etc., but it is usually 50-1500 mm. is there. Filling length is 50m
If it is shorter than m, the oxygen removal rate may decrease,
If it is longer than 1500 mm, the pressure loss may increase. In addition, the void linear velocity (LV) of crude nitrous oxide during purification varies depending on the oxygen concentration in the nitrous oxide supplied and operating conditions, and cannot be specified unconditionally,
Usually 100 cm / sec or less, preferably 30 cm /
It is less than or equal to sec. The contact temperature between the nitrous oxide and the manganese oxide catalyst is the temperature of the gas supplied to the inlet of the purification column and is usually 50 ° C or lower, preferably 0 to 40 ° C. If the contact temperature is too high, nitrous oxide is decomposed, the deoxidizing ability is reduced, and nitrogen may be generated as an impurity.
The pressure upon contact of the gas normal pressure, reduced pressure, but it is possible either process the pressure is usually 10 Kg / cm ² abs or less, preferably 0.1Kg~5Kg / cm ² abs. If the pressure is too high, nitrous oxide may decompose.

In the present invention, even if a small amount of water is contained in nitrous oxide, there is no particular adverse effect on the deoxidizing ability, and when a carrier is used,
Depending on its type, water is also removed at the same time. Further, if necessary, the oxygen removal step using manganese oxide can be combined with the water removal step using a dehumidifying agent such as synthetic zeolite, which completely removes the water, resulting in an extremely high-purity purified suboxide. Nitrogen can be obtained.

[0010]

【Example】

Example 1 (Preparation of Purification Cylinder) A commercially available manganese oxide catalyst was used.
This is an extruded product of MnO ₂ , which is black. This is crushed and sifted on 8-12 mesh 63
300 ml of inner diameter of 16.4 mm and length of 400 mm in a stainless steel purifying cylinder with a packing length of 300 mm (packing density 1.6 g / m
l). Nitrogen is added to this at a temperature of 300 ° C. and a flow rate of 25.
After purging the system while preheating by flowing at 0 ml / min for 1 hour, carbon monoxide at a normal pressure and a flow rate of 127 ml / min.
(LV = 1 cm / sec) for 3 hours for reduction treatment. Then, it switched to nitrogen and cooled to room temperature.
In addition, as a result of reduction under the same conditions in a quartz tube, the color of the catalyst changed to green, confirming that MnO ₂ was reduced and a lower oxide of manganese was produced. (Purification of Crude Nitrous Oxide) Subsequently, purification was carried out using the above-mentioned stainless steel purification cylinder. 50% nitrous oxide (helium base) containing 0.8 ppm of oxygen as an impurity in the purification column was 1266 ml / min (LV = 10 c
When the oxygen concentration in the outlet gas was measured using a yellow phosphorus luminescence type oxygen analyzer (lower limit concentration of 0.01 ppm), oxygen was not detected and was 0.01 ppm or less. In addition, gas chromatography (detector TC
When the nitrogen concentration in the outlet gas was measured in D), it was 1.3%
Met. 100 minutes after the purification was started, the oxygen concentration in the outlet gas was 0.01 ppm or less, and the nitrogen concentration was 0.55%.

Example 2 (Preparation of Purification Cylinder) A purification cylinder was prepared under the same conditions as in Example 1. Prior to the purification of nitrous oxide, the purification column is heated to 100 ° C., and 50% nitrous oxide (helium base) is heated at normal pressure to 127 ml / min (LV = 1 cm / sec), 30 m.
A pretreatment was performed by flowing in. (Purification of nitrous oxide) In the same manner as in Example 1, 50% nitrous oxide (helium base) containing 0.8 ppm of oxygen as an impurity was added to this purification column at 1266 ml / min (LV =
Flow rate at 10 cm / sec) and the outlet gas was analyzed to find that the oxygen concentration was 0.01 ppm or less and the nitrogen concentration was 230.
It was ppm. 100 minutes after starting the purification, the oxygen concentration in the outlet gas was 0.01 ppm or less and the nitrogen concentration was 170 ppm.

Example 3 (Preparation of Purification Cylinder) A commercially available manganese catalyst similar to that used in Example 1 was charged into a stainless steel purification cylinder, and then hydrogen was added at atmospheric pressure to 2
Flow rate 127 ml / min (LV = 1 cm / se at 00 ° C.)
The reduction treatment was carried out by flowing in c) for 4 hours. Separately from this, it was confirmed that the color of the catalyst changed to grayish brown as a result of reduction under the same conditions in a quartz tube. In addition, the catalyst in the quartz tube was taken out into the air and identified by a powder X-ray diffractometer to confirm that it was a mixture of manganese oxide mainly containing manganese monoxide and dimanganese trioxide. (Purification of nitrous oxide) In the same manner as in Example 1, 50% nitrous oxide (helium base) containing 0.8 ppm of oxygen was passed through this purification column, and the outlet gas was analyzed. As a result, the oxygen concentration was 0.01 ppm or less. The nitrogen concentration was 360 ppm. 100 minutes after the purification was started, the oxygen concentration in the outlet gas was 0.01 ppm or less and the nitrogen concentration was 180 pp.
It was m.

Comparative Example 1 (Preparation of Purification Cylinder) Commercially available nickel catalyst (manufactured by JGC Corporation,
N-111) was used. The composition of this is Ni + NiO
Of Ni, 45 to 47 wt% as Ni, Cr2 to 3
wt%, Cu 2-3 wt%, diatomaceous earth 27-29 wt% and graphite 4-5 wt%, diameter 5 mm, height 4.5.
It is a molded body of mm. This nickel catalyst is 8-10 me
63 ml crushed into sh was packed in the same purification cylinder as used in the example (packing density 1.0 g / ml). Hydrogen is added to this at atmospheric pressure at a temperature of 150 ° C and a flow rate of 595 ml / min.
After performing a reduction treatment at (LV = 3.6 cm / sec) for 3 hours, it was cooled to room temperature. (Purification of Nitrous Oxide) When crude nitrous oxide was circulated in this purification column in the same manner as in Example 1, the purification column generated remarkably heat.
When the outlet gas was analyzed here, the oxygen concentration was 0.01.
Although it was below ppm, nitrous oxide was not detected, only nitrogen was detected, and it was found that most of nitrous oxide was decomposed.

[0014]

Industrial Applicability According to the present invention, it is possible to remove oxygen in nitrous oxide, which has been difficult to remove in the past, to an extremely low concentration of 0.1 ppm or less, further 0.01 ppm or less. At times, it was possible to prevent the inclusion of impurity nitrogen due to the decomposition of nitrous oxide, and it was possible to obtain high-purity nitrous oxide.

Claims (4)

[Claims] 1. A method for purifying nitrous oxide, which comprises contacting crude nitrous oxide with a catalyst containing manganese oxide as a main component to remove oxygen contained in the crude nitrous oxide. 2. Manganese oxide is manganese monoxide (Mn
O), dimanganese trioxide (Mn ₂ O ₃ ), trimanganese tetraoxide (Mn ₃ O ₄ ), or a mixture thereof. 3. The method for purifying nitrous oxide according to claim 1, wherein prior to the purification, the catalyst is pretreated by contacting the catalyst with nitrous oxide at a temperature higher than the temperature during purification. 4. The purification method according to claim 3, wherein the difference between the pretreatment temperature with nitrous oxide and the temperature during purification is 10 to 100 ° C.