JPH09142833A - Removal of moisture in ammonia and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a process and device for removing moisture in ammonia which can reduce the moisture in ammonia the utmost limit even under conditions of room temperature, increase the space velocity with excellent moisture removal rate (the moisture removal per unit weight of the filler). SOLUTION: Ammonia containing a trace amount of moisture is brought into contact with single BaO or a BaO mixture under substantially room temperature conditions to reduce the moisture in ammonia to <=5ppb (determination limit). A purifier 1 equipped with a column 1a filled with a filler 1d, and filter media 1b, 1c is set to the ammonia line is used as a moisture remover.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for removing water from ammonia containing a trace amount of water to the utmost limit. It also relates to a device therefor.

[0002]

2. Description of the Related Art In the field of using high-purity ammonia, particularly in the semiconductor industry, a large amount of ammonia is consumed as a nitrogen source in order to obtain a light emitting diode of a compound semiconductor or an insulating film using a nitride film. The amount is increasing year by year.

Moisture as an impurity contained in ammonia causes oxygen atoms contained in the water molecules to form an oxide with Si in the plasma reaction process, resulting in a decrease in device yield. Therefore, the water concentration in the ammonia used must be as low as possible.

As a method of removing water in the industrial ammonia production process, there are a method of removing by distillation and an adsorption removing method using molecular sieves. High-purity ammonia is manufactured by each company's method. The shipping inspection value of the ammonia purity is generally 99.999% or more, and the water content of impurities is 2 ppm to 0.5 ppm (500 ppb).
) Is about. That is, up to this degree, purification has been achieved by conventional techniques.

Japanese Unexamined Patent Publication No. 4-292413 discloses Zr.
A getter alloy composed of -V-Fe was used under an inert gas for 30
A method is disclosed in which after activation by heating to a temperature above 0 ° C., it is brought into contact with ammonia at a temperature below 150 ° C. (preferably about 100 ° C.) to reduce the water content in the ammonia to about 20 ppb. The temperature of about 100 ° C. is adopted because this temperature is low enough to prevent decomposition of ammonia and has an activity for removing impurities. In the embodiment of the invention of this publication, the water content in the ammonia is reduced to less than 20 ppb by contacting the getter alloy with ammonia containing 3 ppm of water under the temperature condition of 100 ° C.

[0006]

As is well known, ammonia has a very high affinity with water, and it is not easy to remove a trace amount of water from ammonia. As mentioned above, the water content in the products of each company currently marketed as high-purity ammonia is 2 ppm to 0.5 ppm (500 ppb).
To some extent, it is desired to further reduce the water content by about two digits in order to further improve the performance of the semiconductor.

According to the studies by the present inventors, if a method of adsorbing and removing commercially available high-purity ammonia using a column packed with molecular sieves, which is a common means for removing water, is adopted, the SV (space velocity) is It was found that the water content in ammonia can be removed to a level below the detection limit (5 ppb) in small areas, but from an industrial point of view, there is a practical problem with low SV and the removal of water content per unit weight from the packing material. There is a limit that the amount, that is, the water removal rate is small because ammonia itself co-adsorbs.

In the method using a getter alloy described in JP-A-4-292413, a heating means at about 100 ° C. is always used in order to bring out a chemical reaction ability to dissociate and adsorb H ₂ O into H ⁺ and O ^2-. Since it is necessary, there are restrictions on application to the field. In addition, this method lacks the moisture level required by the semiconductor industry in recent years (for example, 5 ppb or less).

Under such a background, the present invention can reduce the water content in ammonia to the utmost even under room temperature conditions, increase the space velocity, and remove the water content (per unit weight). It is an object of the present invention to provide a method for removing water in ammonia, which has an excellent removal amount of water with respect to the filling material, and an apparatus therefor.

[0010]

The method of removing water in ammonia according to the present invention comprises contacting ammonia containing a trace amount of water with BaO alone or a mixture mainly containing BaO under substantially room temperature conditions. It is characterized by.

The apparatus for removing water in ammonia according to the present invention comprises a purifier equipped with a column filled with BaO alone or a mixture mainly containing BaO and a filter medium, which is installed in the ammonia line. .

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. Needless to say, BaO is barium oxide and CaO is calcium oxide.

Ammonia for which water is to be removed includes
NH ₃ purity is 99.999% or more, water content is 5ppm
About 0.1 ppm (100 ppb), usually 2 ppm to 0.5 ppm
Commercially available high-purity ammonia of about (500 ppb) is preferably used. The water content may be higher than the above range (for example, up to about 10 ppm), but if the water content exceeds the limit, there are many other impurities and it is suitable as high-purity ammonia in the first place. Because there is no, there is a restriction from that aspect. Further, the water content may be lower than the above range, but it is generally difficult to bring such a low water content.

As the packing, (a) BaO alone or
(b) A mixture mainly composed of BaO is used. The latter (b)
In this case, a mixture with CaO is particularly important, and the proportion of BaO in the mixture at this time is preferably 50 mol% or more. The shape of the filler may be any of powder, granules, molded products and the like.

From the viewpoint of the water removal efficiency, as shown in (a) above, B
Most preferably, aO is used alone. In this case, it may be used as a powder, or as a granule or a molded product. When BaO is uniformly mixed with CaO as shown in (b) above, the binder action of CaO facilitates the formation of granules or molded products, and the moisture removal action of CaO is also utilized without waste. Although it is possible to remove water only with CaO, the upper limit of SV is low and the water removal rate is low. Therefore, in order to exert the characteristic ability of the present invention, it is preferable to mix BaO in an amount of 50 mol% or more as described above.

BaO alone or a mixture mainly composed of BaO is used in a state packed in a column. The column size and packing height are often, for example, about 1 to 3 inches in inner diameter and about 20 to 50 mm in packing height.
It does not necessarily have to be within such a range. Especially when dealing with a large flow rate, the range is not limited. In Examples described later, in order to obtain the breakthrough time, a column having a small diameter is intentionally used and the packing height is also made small.

The purifier equipped with the column filled with the packing material and the filter medium is installed at an appropriate position of the ammonia line. The supplied ammonia is often gas, but it may be liquid. After removing water in ammonia according to the present invention, a small-sized purifier having the same structure can be installed in the branch pipe portion downstream thereof for further safety. In addition to the method using a column, a method of charging the above-mentioned packing into a container filled with liquefied ammonia can be adopted depending on the case.

The SV can be set arbitrarily, but it is 1300 hr ^-1.
More than 10,000 hr ^-1, more than 100,000 hr ^-1
Even with the above settings, an excellent moisture removal rate can be obtained in the present invention.

Although the temperature condition is room temperature, it does not mean that some heating or cooling is excluded, and the temperature condition may be substantially room temperature.

According to the present invention, it is possible to remove the water content of ammonia to 5 ppb or less, which is the quantitative limit. In this case, for applications that do not require severe moisture reduction up to that point, as long as it is below the target moisture content,
The flow rate can be increased or the filling amount can be decreased.

<Action> In the present invention, a substance which essentially does not react with ammonia and can absorb only moisture is used, and the moisture is captured as Ba (OH) ₂ . The hydroxide thus produced is solid and the reaction of BaO and H ₂ O to Ba (OH) ₂ is an irreversible reaction. Therefore, water is not re-released in ammonia from which water has been removed, and it is not contaminated by a reaction substance or a by-product.
There is no risk of recontamination of ammonia after removing water.

Thus, according to the present invention, ammonia is added to B
Moisture in ammonia is reduced to the utmost limit only by contacting with aO alone or a mixture mainly composed of BaO (and at room temperature), and its excellent water removing action is maintained even if SV is set high. There is also the advantage of being done.

[0023]

The present invention will be further described with reference to the following examples.

<Apparatus Structure> FIG. 1 is a front view of the purifier (1), and a part thereof is shown in a sectional view. FIG. 2 is a flow chart of a water removing device incorporating the purifier (1) of FIG.

In FIG. 1, (1) is a purifier, which is a column (1
a), pre-filter (1b), main filter (1c), packing (1
d) consists of joints (1e) and (1e).

In FIG. 2, (2) is an ammonia cylinder as an ammonia source, and (3) is an ammonia line. (Four)
Is a moisture analysis line for ammonia, although details are omitted.

<Measurement of Water Content> The water content of ammonia at the outlet of the apparatus was measured by converting water content into acetylene with carbide and detecting the acetylene by GC-MS. The limit of quantification is 5 ppb.

<Removal of Water in Ammonia> Example 1 A column (1a) made of stainless steel (SUS316) was packed with powdered BaO as a packing material (1d), and the purifier (1) shown in FIG. Then, ammonia having a water concentration of 2 ppm was contacted with BaO. The conditions were as follows.・ Ammonia flow rate 60 ml / min ・ Inlet water concentration 2 ppm ・ Column nominal diameter 1/4 inch ・ Packing height 2 mm ・ Packing material, packing amount BaO powder (0.052 g) ・ SV 120,000 hr ^-1・ LV 6.73 cm / sec ・ Temperature room temperature ・ Outlet water concentration 5 ppb or less

Example 2 Example 1 was repeated except that the following conditions were adopted.・ Ammonia flow rate 550 ml / min ・ Inlet water concentration 2 ppm ・ Column nominal diameter 3/8 inch ・ Packing height 6 mm ・ Packing material and packing amount BaO powder (0.481 g) ・ SV 120,000 hr ^-1・ LV 20.2 cm / sec ・ Temperature room temperature ・ Outlet water concentration 5 ppb or less

Example 3 Using a BaO-CaO mixture (BaO: 50 mol% (73.2 wt%), CaO: 50 mol% (26.8 wt%)) granulated into granules as a water removing agent, the following conditions were used. Example 1 was repeated except that it was adopted.・ Ammonia flow rate 60 ml / min ・ Inlet water concentration 1 ppm ・ Column nominal diameter 3/8 inch ・ Packing height 7 mm ・ Packing material, packing amount BaO-CaO mixture (0.266 g) ・ SV 11,300 hr ^-1・ LV 2.20 cm / sec ・ Temperature room temperature ・ Outlet water concentration 5 ppb or less

Comparative Examples 1 to 3 As the water removing agent, CaO particles (Comparative Example 1), Molecular Sieves MS-3A (Comparative Example 2) and Molecular Sieves MS-13X (Comparative Example 3) were used. Example 1 was repeated except that the conditions were adopted.

<Conditions and Results> Table 1 shows the conditions and results of Examples 1 to 3. Table 2 shows the conditions and results of Comparative Examples 1 to 3.

[0033]

[Table 1] Example 1 Example 2 Example 3 Packing type BaO BaO BaO + CaO Packing weight (g) 0.052 0.481 0.266 Column nominal diameter (inch) 1/4 3/8 3/8 Packing height (mm) 2 6 7 NH ₃ flow rate (ml / min) 60 550 60 SV (hr ^-1 ) 120000 120000 11300 LV (cm / sec) 6.73 20.2 2.20 Temperature (℃) Room temperature Room temperature Room temperature Inlet water concentration (ppm) 2 2 1 Outlet water concentration (ppb) ) <5 <5 <5 Breakthrough time (hr) 64 64 535 Moisture removal (mg) 0.370 3.394 1.55 Moisture removal rate (mg / g) 7.12 7.06 5.8

[0034]

[Table 2] Comparative Example 1 Comparative Example 2 Comparative Example 3 Packing type CaO MS-3A MS-13X Packing material weight (g) 0.1593 0.0914 0.0992 Nominal column diameter (inch) 1/4 1/4 1/4 Packing height (mm) 10 10 10 NH ₃ Flow rate (ml / min) 60 60 60 SV (hr ^-1 ) 24300 24300 24300 LV (cm / sec) 6.73 6.73 6.73 Temperature (℃) Room temperature Room temperature Room temperature Inlet water concentration (ppm) 1 1 1 Outlet water concentration (ppb) <5 <5 <5 Breakthrough time (hr) 112 41.5 24.5 Moisture removal (mg) 0.370 3.394 0.0668 Moisture removal rate (mg / g) 2.03 1.29 0.676

<Analysis> As is clear from the comparison between Table 1 and Table 2, the water removal rate was 6 in the example.
It is about 7 mg / g filling or around, whereas it is about 2 mg / g filling or less in Comparative Example, and it can be seen that the water removal rate in the case of Example is remarkably large. Regarding SV, as in Examples 1 and 2, 120,000 hr
^It can be seen that there is no change in the water removal rate even if it is increased to ^-1 .

Example 4 The inside of an autoclave made of stainless steel was purged with purified nitrogen having a water concentration of 1 ppb or less, and then powdered B
After a small amount of aO was charged, liquefied ammonia having a known water content was filled, and after stirring for 30 minutes, the liquid phase portion was introduced into a vaporizer with a siphon tube, and water content was measured. The conditions and results were as follows.・ Ammonia volume (liquid) 300 ml ・ Moisture concentration (gas conversion value) 1 ppm ・ Packing material, filling amount BaO powder (1.0 g) ・ Temperature room temperature ・ Outlet water concentration (gas conversion value) 5 ppb or less

[0037]

EFFECTS OF THE INVENTION According to the present invention, the water content in ammonia is kept to the limit (the quantitative limit of 5 pp even under room temperature conditions).
b) and space velocity (SV) can be increased, and the water removal rate (amount of water removed from the filling material per unit weight) is excellent. In addition, water is not re-released in ammonia, and there is no risk of re-contamination of ammonia after water removal by a reaction material with ammonia and a by-product.

Therefore, a higher-performance semiconductor product can be efficiently produced only by attaching a purifier equipped with a column filled with BaO alone or a mixture mainly containing BaO and a filter medium to the ammonia line.
In addition, if ammonia that has passed through a large-scale refiner compatible with a large flow rate is stored in a clean tank, it is possible to stably supply high-purity ammonia even at a factory-scale flow rate.

[Brief description of the drawings]

FIG. 1 is a front view of a purifier (1), a part of which is shown in a sectional view.

FIG. 2 is a flow chart of a water removal device incorporating the purifier (1) of FIG.

[Explanation of symbols]

(1) ... Purifier, (1a) ... Column, (1b) ... Prefilter, (1
c) ... main filter, (1d) ... filling material, (1e) ... joint part,
(2)… Ammonia source, (3)… Ammonia line, (4)…
Analysis line

Claims (2)

[Claims] 1. A method for removing water from ammonia, which comprises contacting ammonia containing a trace amount of water with BaO alone or a mixture mainly containing BaO under substantially room temperature conditions. 2. A device for removing water in ammonia, comprising a purifier equipped with a column filled with BaO alone or a mixture mainly containing BaO and a filter medium, which is installed in an ammonia line.