JP3359928B2 - Ammonia purification method - Google Patents

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 ammonia, and more particularly to a method for purifying ammonia capable of removing oxygen contained as an impurity in ammonia to an extremely low concentration. Ammonia is used together with silane to form a silicon nitride film in the silicon semiconductor manufacturing process, and is also used in the manufacture of compound semiconductors such as gallium nitride together with triethylgallium. Is required.

[0002]

2. Description of the Related Art In general, ammonia used in the production of semiconductors is commercially available in the form of diluted with hydrogen gas or inert gas in addition to pure ammonia, and usually supplied to semiconductor production equipment in a gaseous state. Is done. Such ammonia contains oxygen, moisture, and the like as impurities, and is usually purified by distillation of the raw material ammonia. In addition, moisture can be removed by a dehumidifier such as synthetic zeolite. The oxygen content in commercially available purified ammonia is usually 10 ppm or less,
In recent years, ammonia in cylinders is commercially available, which has a relatively low oxygen content of 0.5 to 1.0 ppm.

[0003]

However, if the oxygen content is less than 1 ppm, it is not possible to sufficiently cope with the demands in recent semiconductor manufacturing processes.
It is strongly desired that the content be less than or equal to 0.01 ppm, and more preferably less than or equal to 0.01 ppm. In addition, recently, silane and the like used together with ammonia in the production of semiconductors can be purified to high purity. For example, oxygen contained as impurities can be removed to 0.01 ppm or less. For this reason, ammonia having an extremely low oxygen content is being demanded. In addition, these ammonias may be contaminated by impurities such as air during the supply process to the semiconductor device such as when connecting the cylinder or switching the piping, so it is desirable to finally remove the impurities immediately before the device. However, although the demand for high-purity ammonia is increasing year by year, there is a known method for efficiently removing oxygen contained in ammonia and supplying high-purity ammonia-based gas to a semiconductor manufacturing process or the like. Technology is hardly found.

[0004]

The present inventors have SUMMARY OF THE INVENTION may, oxygen contained in the ammonia results to diligent research efficiently removed to an extremely low concentration, the <br/> nickel reduction treatment and ammonia by contact with purification agent mainly, the oxygen concentration 0.1ppm or less, more 0.01p
It has been found that it can be removed down to pm or less, and the present invention has been completed. That is, the present invention provides a process for reducing crude ammonia
And removing oxygen contained in the crude ammonia by contact with a purified agent containing nickel as a main component. The present invention is intended to remove oxygen contained in ammonia alone, hydrogen (based on hydrogen gas) and ammonia diluted with an inert gas (inert gas base) such as nitrogen or argon (hereinafter referred to as crude ammonia). Applied to

[0005] The purifying agent used in the present invention is mainly composed of a nickel compound or a nickel compound which is easily reduced, such as nickel oxide, which has been subjected to a reduction treatment . In addition, chromium, iron,
It may contain a small amount of metal such as cobalt or copper. These nickels may be used alone or may be used in a form supported on a carrier or the like.However, for the purpose of increasing the contact efficiency between the nickel surface and gas, the nickel is usually supported on a carrier or the like. It is preferable to use it in the form. As a method of supporting nickel 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 a nickel salt, and an alkali is added to the carrier powder to add nickel to the carrier powder. The ingredients were precipitated, then filtered and, if necessary, washed with water to give a cake of 1 part.
After drying at 20 to 150 ° C., firing is performed at 300 ° C. or higher, and the fired product is pulverized, or NiCO ₃ , Ni (OH)
₂ , an inorganic salt such as Ni (NO ₃ ) ₂ , NiC ₂ O ₄ , N
After baking and pulverizing an organic salt such as i (CH ₃ COO) ₂ , a heat-resistant cement is mixed with this, followed by baking. These are usually formed into a molded product by extrusion molding, tablet molding, or the like, and are used as they are, or crushed to an appropriate size as needed. As a molding method, a dry method or a wet method can be used, and in that case, a small amount of water, a lubricant, or the like may be used. Further, as a nickel-based catalyst, for example, a steam conversion catalyst, C11-2-03 (Ni
O-cement), C11-2-06 (NiO-refractory), C11-2 (Ni-calcium aluminate),
C11-9 (Ni-alumina); hydrogenation catalyst, C46-
7 (Ni-diatomaceous earth), C46-8 (Ni-silica), C
36 (Ni-Co-Cr-alumina); gasification catalyst, X
C99 (NiO); hydrotransformation catalyst, C20-7 (Ni
-Mo-alumina) [all manufactured by Toyo CCI Co., Ltd.] and a hydrogenation catalyst, N-111 (Ni-diatomaceous earth); a gasification shift catalyst, N-174 (NiO); a gasification catalyst, N-18
There are various types such as 5 (NiO) (both manufactured by JGC Corporation), and those selected from them may be used. In short, it is sufficient if reduced nickel, nickel oxide, and the like are finely dispersed and have a large surface area and a high contact efficiency with gas.

[0006] The specific surface area of the purifying agent is usually BET.
In the range of 10 to 300 m ² / g, preferably 3
It is in the range of 0 to 250 m ² / g. The content of nickel is usually 5 to 95 wt% in terms of metallic nickel.
%, Preferably 20 to 95 wt%. If the content of nickel is less than 5 wt%, the deoxidizing ability is reduced. If the content is more than 95 wt%, sintering may occur during reduction with hydrogen, and the activity may be reduced.
In order to activate the purifying agent , hydrogen reduction is usually performed. Hydrogen reduction can be performed, for example, by passing a mixed gas of hydrogen and nitrogen at a cylinder linear velocity (LV) of about 5 cm / sec at a temperature of about 350 ° C. or less. is necessary.

[0007] Purification of ammonia is usually carried out by passing crude ammonia through a purification cylinder filled with a purifying agent mainly composed of reduced nickel, and the crude ammonia is brought into contact with the purifying agent. Oxygen contained therein as impurities is removed. The oxygen concentration in the crude ammonia applied to the present invention is usually 100 ppm or less. If the oxygen concentration is higher than this, the calorific value increases, so a heat removal means is required depending on the conditions. The filling length of the purifying agent filled in the purifying cylinder is usually 50 to
It is 1500 mm. If the filling length is shorter than 50 mm, the oxygen removal rate may decrease.
If it is longer than mm, the pressure loss may be too large. Cylinder linear velocity (LV) of crude ammonia during refining
Depends on the oxygen concentration in the supplied ammonia and operating conditions, etc., and cannot be specified unconditionally.
cm / sec or less, preferably 30 cm / sec or less. The contact temperature between ammonia and the purifying agent is the temperature of the gas supplied to the inlet of the purifying cylinder, and is 200 ° C. or less, preferably 1 ° C.
The temperature is not higher than 00 ° C., usually at room temperature, and does not particularly require heating or cooling. The pressure at the time of contact with the refining agent is not particularly limited, and the treatment can be carried out at normal pressure, reduced pressure, or increased pressure, but is usually 20 kg / cm ² abs or less, preferably 0.1 to 10 kg / cm ^2. abs. In addition, even if a small amount of water is contained in ammonia, there is no particular adverse effect on the deoxygenation ability, and when a carrier or the like is used as a refining agent , water is also removed depending on the type. You. In the present invention, it is also possible to appropriately combine a water removal step with a dehumidifier such as a synthetic zeolite as needed, in the oxygen removal step with a purifying agent ,
As a result, moisture is completely removed, and extremely high-purity ammonia can be obtained.

[0008]

【Example】

Example 1 (Nickel reduction treatment) A commercially available nickel catalyst (N-111, manufactured by JGC Corporation) was used. Its composition is N
In the form of i + NiO, 45 to 47 wt% as Ni,
Cr 2-3 wt%, Cu 2-3 wt%, diatomaceous earth 27-2
9 wt% and graphite 4-5 wt%, specific surface area 150 m
² / g, a molded body having a diameter of 5 mm and a height of 4.5 mm. 63 ml of this nickel catalyst crushed to 8 to 10 mesh was packed in a stainless steel purification cylinder having an inner diameter of 16.4 mm and a length of 400 mm, and a filling length of 300 mm (filling density:
1.0 g / ml). Hydrogen was added thereto at normal pressure at a temperature of 150 ° C. and a flow rate of 595 ml / min (LV = 3.6 cm).
/ Sec) for 3 hours, and then cooled to room temperature. (Purification of Ammonia) Subsequently, hydrogen-based crude ammonia containing 10 vol% of ammonia and 0.53 ppm of oxygen as an impurity was added to this purification column at room temperature (20 ° C.).
633 ml / min (LV = 5 cm / sec)
As a result of measuring the oxygen concentration in the outlet gas at a flow rate of c) using a yellow phosphorus emission type oxygen analyzer (measurement lower limit concentration: 0.01 ppm), no oxygen was detected and the concentration was 0.01 ppm or less. Also, even after 100 minutes from the start of the gas flow, the oxygen concentration in the outlet gas was 0.01 ppm or less. ,

[0009] Example 2 (Preparation of a nickel catalyst) of water 3L Al (NO _{3) 3} 9
454 g of H ₂ O were dissolved and cooled to 5-10 ° C. in an ice bath. While stirring vigorously, add NaOH, 200g
Was dissolved in 1 L of water and a solution cooled to 5 to 10 ° C. was added dropwise over 2 hours to obtain sodium aluminate. next,
Ni (NO ₃ ) ₂ .6H ₂ O, 101 g, was dissolved in 600 ml of water, and 45 ml of concentrated nitric acid was added thereto.
The solution cooled to ° C. was added to the sodium aluminate solution over 1 hour with vigorous stirring. The resulting precipitate was filtered, and the obtained precipitate was stirred six times in 2 L of water for 15 minutes and washed to make the precipitate neutral. The obtained precipitate was subdivided, dried in an air bath at 105 ° C. for 16 hours, and then pulverized, and sieved to collect 12 to 24 mesh. It contained 29.5 wt% nickel oxide (NiO). (Reduction treatment of nickel) 63 ml of this was packed in the same purification cylinder as used in Example 1 (packing density: 0.77
g / ml) and hydrogen at normal pressure at a temperature of 350 ° C. and a flow rate of 1
After performing reduction treatment by flowing at 65 cc / min (LV = 1 cm / sec) for 16 hours, the mixture was cooled to room temperature. (Purification of ammonia) Subsequently, the purification of ammonia was performed. 10 vol% ammonia (hydrogen base) containing about 0.53 ppm oxygen used in Example 1
At normal temperature (20 ° C), 633 ml / min
(LV = 5 cm / sec) The oxygen concentration in the outlet gas was measured by flowing at a speed of 5 cm / sec. Even after 100 minutes from the start of the purification, the oxygen concentration of the outlet gas was 0.01 ppm or less.

Comparative Example When activated carbon (coconut shell charcoal) was crushed into 8 to 24 meshes and 48 g was placed in Example 1, 300 mm was placed in the same purification cylinder.
(Filling density: 0.57 g / ml), the mixture was heated in a helium stream at 270 to 290 ° C. for an hour, and then cooled to room temperature. About 0.53p which is the same as that used in Example 1
633 ml / min (LV = 5 cm / s) of 10 vol% ammonia (hydrogen base) containing pm oxygen
As a result of measuring the oxygen concentration in the outlet gas by flowing in ec),
It was 0.53 ppm, and the flow was continued for 2 hours in this state, but no change in oxygen concentration was observed.

[0011]

According to the present invention, it is possible to remove oxygen in ammonia which has been conventionally difficult to remove to an extremely low concentration of 0.1 ppm or less, and even to 0.01 ppm or less. It became possible to obtain.

Continuation of the front page (56) References JP-A-4-292413 (JP, A) JP-A-55-124538 (JP, A) JP-A-57-184435 (JP, A) (58) Fields investigated (Int) .Cl. ⁷ , DB name) C01C 1/02 B01J 20/02

Claims (3)

(57) [Claims] 1. A method for purifying ammonia, comprising contacting crude ammonia with a purifying agent mainly composed of reduced nickel to remove oxygen contained in the crude ammonia. 2. The refining agent contains nickel of 5 to 95% by weight in terms of metal and has a specific surface area of 10 to 3 by a BET method.
The method for purifying ammonia according to claim 1, wherein the amount is 00 m ² / g. 3. The contact temperature between ammonia and a purifying agent is 20.
The method for purifying ammonia according to claim 1, wherein the temperature is 0 ° C or lower.