KR100577958B1 - Process for refining nitrogen trifluoride gas using alkali earth metal exchanged zeolite 5A - Google Patents

Abstract

The present invention relates to a method for purifying nitrogen trifluoride gas and an adsorbent used therein, wherein the carbon tetrafluoride (I) is ion-exchanged with alkaline earth metal and heated through a column filled with zeolite 5A heated at 150 to 600 ° C. for 30 minutes to 100 hours. Nitrogen trifluoride adsorbent comprising a zeolite 5A and a method for purifying nitrogen trifluoride gas comprising the step of venting nitrogen trifluoride (NF ₃ ) gas containing CF ₄ ) to selectively adsorb only nitrogen trifluoride. It is about.

Nitrogen trifluoride, NF3, carbon tetrafluoride, CF4, zeolite, zeolite 5A, ion exchange

Description

Process for refining nitrogen trifluoride gas using alkali earth metal exchanged zeolite 5A using zeolite 5A ion-exchanged with alkaline earth metal

The present invention relates to a method for purifying nitrogen trifluoride (NF ₃ ) gas, and more particularly, to a method for removing carbon tetrafluoride (CF ₄ ) from nitrogen trifluoride gas.

Nitrogen trifluoride gas is a material used as a dry etching agent for semiconductors, a cleaning gas for CVD devices, and a propellant fuel for rockets. As the semiconductor industry is activated, the demand for nitrogen trifluoride gas has increased rapidly in recent years. In addition, the demand for nitrogen trifluoride gas is growing exponentially in view of the increasing demand for the use of gas without any environmental pollution. Such nitrogen trifluoride gas is required to be of high purity.

Nitrogen trifluoride is a method of directly fluorinating ammonia, using plasma, and so-called molten salt, which electrolytically decomposes NH ₄ · xHF (x: 1.8 to 2.1) based on acidic ammonium fluoride or ammonium fluoride and hydrogen fluoride. It is manufactured by various methods such as a solution or a reaction of ammonia and fluorine.

In the method, most of nitrous oxide (N ₂ O), carbon dioxide (CO _2), carbon tetrafluoride (CF _4), bedding tetroxide (N ₂ F ₂₎ the NF ₃ gas, because impurities are relatively large amount of generation of ultra-high purity, etc. Purification is required to obtain.

Specifically, contained as impurities in the nitrogen trifluoride gas CF ₄ is similar to the boiling point and _{NF 3 (NF 3: -129 ℃} , CF 4: -128 ℃), similar to the molecular size _{(NF 3: 4.5Å, CF 4} : 4.8Å ), It has similar heat of adsorption (Dipole moment: NF ₃ : 0.235D, CF ₄ : 0D) and cannot be removed by common methods such as distillation or bulk adsorption. Therefore, in order to purify NF ₃ gas, a separation method using an adsorbent is mainly used, and a method using an adsorbent such as activated carbon, activated alumina, or synthetic zeolite is known. Among them, the method using an activated carbon or activated alumina in the adsorbent is the frequent replacement or regeneration of the adsorbent is required because the adsorbent is receiving much that the amount of impurities less loss in a high speed adsorption capacity of the adsorbent, whereby NF ₃ gas according Inevitably, the loss of is inevitable in terms of manpower and cost.

On the other hand, as a method for purifying a NF ₃ gas by using a synthetic zeolite, Takashi et NF ₃ by using as an adsorbent a synthetic zeolite having a certain size and a certain moisture content in U.S. Patent No. 5,069,887 No. under constant temperature and flow rate conditions A method of purifying a gas is disclosed, in which case the NF ₃ gas is adsorbed to the zeolite and then desorbed and recovered. This method is disadvantageous in that the process of resorbing the adsorbed NF ₃ is added and the moisture content of the synthetic zeolite must be adjusted to a specific range, and the purified NF ₃ gas purity is less than 93%, so that high purity is required. There is a problem in that it cannot be used directly.

As another purification method using synthetic zeolites, Philip et al. Disclosed a kinetic gas-solid chromatography method in US Pat. No. 5,069,690, wherein the method was hydrothermally treated. Selective separation of NF ₃ gas is achieved by using a zeolite of a certain size and supplying a mixed gas in discrete pulse form to provide a kinetic mechanism in the column. However, in the above method, since the size of the zeolite is controlled by hydrothermal treatment, there is a problem in that the conditions of the treatment are difficult. In addition, the use time of the zeolite used as the adsorbent, that is, the saturation time is short, requires a large amount of gas to be purified. There is a problem that is difficult to apply to the commercialization process.

Therefore, the present inventors have studied a method for purifying NF ₃ by using a synthetic zeolite, and as a result, only an NF ₃ can be selectively adsorbed from the NF ₃ containing CF ₄ by ion-exchanging an alkaline earth metal with an appropriate amount in zeolite 5A. The present invention has been completed and the present invention has been completed.

The present invention relates to a method for purifying NF ₃ using zeolite 5A ion-exchanged with alkaline earth metals and to a nitrogen trifluoride adsorbent composed of zeolite 5A used in the purification method.

If it was used in the purification of NF ₃ for zeolite 5A is a commercial it is both the adsorption of NF ₃ and CF ₄ cursor capability problem. This is because the pore size of zeolite 5A is about 5.0 kPa. To selectively adsorb only NF ₃ , the pore size of the adsorbent must be made smaller than CF ₄ , but larger than NF ₃ .

As described above, there is a method of changing the pore size of the zeolite by ion exchange or impregnation with various metal cations. Thus, the present invention changes the pore size by ion-exchanging zeolite 5A with an appropriate amount of alkaline earth metal at an appropriate temperature. It is characterized by. That is, the pore size of zeolite 5A is changed to selectively adsorb only NF ₃ , and as a result, nitrogen trifluoride gas from which CF ₄ is removed is recovered.

The ion exchange method used in the present invention is widely used when a new metal component is supported on a specific support such as silica, silica-alumina, zeolite and the like. In particular, zeolites have cation exchange properties, and the ion exchange method is mainly used to carry metal ions. The cations of the zeolite can be exchanged with other cations depending on the type of ion to be exchanged or the concentration of the exchange solution. Although cation exchange capacity is used to separate metal ions, it is also a means of controlling acidity of zeolite and introducing metal ions into zeolite. Usually, zeolite A is synthesize | combined using sodium ion as a cation. The effective pore size of type A with cation is sodium ion is about 0.4 nm. Brother). The cations of the zeolite can be exchanged with other cations depending on the type of cation being exchanged or the concentration of the exchange solution. Supporting by the ion exchange method has the advantage that the active material is very uniformly distributed.

In the present invention, in removing carbon tetrafluoride (CF ₄ ) from nitrogen trifluoride, a mixed gas of carbon tetrafluoride and nitrogen trifluoride is introduced into a column packed with zeolites ion-exchanged with alkaline earth metals to vent carbon tetrafluoride as it is and only nitrogen trifluoride. Provided is a method for purifying nitrogen trifluoride by selectively adsorbing and desorption.

The present invention will be described in more detail below.

The zeolite used in the present invention is zeolite 5A. The pore size of zeolite 5A is 5 mm 3. In order to selectively filter out only NF ₃ by artificially reducing the pore size of the zeolite, the zeolite should be ion exchanged with alkaline earth metal.

Examples of the metal ion-exchanged with the zeolite include at least one of beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba). The precursor of the alkaline earth metal for the ion exchange may be a water-soluble metal salt, in particular, nitric acid (NO ₃ ), carbonic acid (CO ₃ ), chloride (Cl), hydroxide (OH) and sulfuric acid (SO ₄ ) of the alkaline earth metal. Salts or hydrates thereof are preferred.

A beryllium precursor is beryllium nitrate trihydrate _{(Be (NO 3) 2 ·} xH 2 O), beryllium chloride (BeCl _2), beryllium sulfate tetrahydrate (BeSO ₄ · 4H ₂ O), etc., and preferably a beryllium chloride ( BeCl ₂ ).

The precursors of magnesium include magnesium nitrate hexahydrate (Mg (NO ₃ ) ₂ · 6H ₂ O), magnesium carbonate hydroxide pentahydrate (MgCO ₃ · Mg (OH) ₂ · 5H ₂ O), magnesium chloride (MgCl ₂ ), Magnesium chloride hexahydrate (MgCl ₂ · 6H ₂ O), magnesium hydroxide (Mg (OH) ₂ ), magnesium sulfate (MgSO ₄ ), magnesium sulfate monohydrate (MgSO ₄ · H ₂ O), magnesium sulfate hepta Hydrate (MgSO ₄ · 7H ₂ O) and the like, and preferably magnesium chloride hexahydrate (MgCl ₂ · 6H ₂ O).

By the calcium precursor is calcium nitrate hydrate _{(Ca (NO 3) 2 ·} xH 2 O), calcium carbonate (CaCO _3), calcium chloride (CaCl _2), calcium chloride dihydrate _{(CaCl 2 · 2H 2 O)} , calcium Chloride hexahydrate (CaCl ₂ · 6H ₂ O), calcium chloride hydrate (CaCl ₂ · xH ₂ O), calcium hydroxide (Ca (OH) ₂ ), calcium sulfate (CaSO ₄ ), calcium sulfate hexahydrate (CaSO ₄ · 6H ₂ O) and preferably calcium chloride hexahydrate (CaCl ₂ · 6H ₂ O).

As the strontium precursor, strontium nitrate _{(Sr (NO 3) 2)} , strontium carbonate (SrCO _3), strontium chloride (SrCl _2), strontium chloride hydrate _{(SrCl 2 · xH 2 O)} , strontium hydroxide (Sr ( is OH) _2), strontium hydroxide octa-hydrate _{(Sr (OH) 2 · 8H} 2 O), strontium sulfate (SrSO _4), and is preferably strontium chloride hydrate (SrCl ₂ · xH ₂ O) and the like.

The precursors of barium include barium nitrate (Ba (NO ₃ ) ₂ ), barium carbonate (BaCO ₃ ), barium chloride (BaCl ₂ ), barium chloride dihydrate (BaCl ₂ · 2H ₂ O), barium hydroxide (Ba (OH) ₂ ), barium hydroxide monohydrate (Ba (OH) ₂ .H ₂ O), barium hydroxide octahydrate (Ba (OH) ₂ .8H ₂ O), barium sulfate (BaSO ₄ ), and the like. And preferably barium chloride dihydrate (BaCl ₂ · 2H ₂ O).

In order to make ion exchange-zeolite by ion-exchanging zeolite, the aqueous solution of the raw material compound containing the metal to be ion-exchanged is prepared at a concentration of 0.01-3M, preferably at a concentration of 0.5-1.5M. If the concentration of the aqueous solution in which the metal to be ion-dissolved is less than 0.01 M, the desired metal ion is not sufficiently ion exchanged to the zeolite, and even if the concentration exceeds 3M, the ion exchange capacity does not increase by the concentration increase of the aqueous solution.

The zeolite is added to the aqueous solution and stirred at a temperature of 35 to 100 ° C., preferably at 50 to 80 ° C., for a time ranging from 0.5 hour to 24 hours, preferably 2 to 12 hours. The stirring speed is 5 to 100 rpm, preferably 10 to 50 rpm. By the above ion exchange, the size of the zeolite pores is adjusted between the NF ₃ and CF ₄ molecular sizes so as to be suitable for the adsorption of NF _3, and ion exchange may be performed two or more times if necessary for the size control.

The amount of alkaline earth metal present in the zeolite as a result of ion exchange is preferably 20 to 95% by weight relative to the total amount of metal in the zeolite. Less than 20% by weight of the amount of the metal to be exchanged into the zeolite too small, the size of the pores do not suitable for absorption only NF ₃ has a problem, and at most less than 95 wt% did not controlled in the pore size desired rather than NF ₃ adsorbed There is a problem that the amount is small.

The zeolite is preferably a spherical form having a particle size of 4 to 100 mesh, more preferably 8 to 40 mesh. In the present invention, the zeolite having such a particle size is ion-exchanged with an alkali metal, and then 30 to 100 hours, preferably 2 to 50 hours, more preferably 4 to 150 ° C to 600 ° C, preferably 200 to 500 ° C. Heated for 20 hours.

By heating the zeolite in the above temperature range, an adsorbent having a sufficiently high adsorption property can be obtained to achieve the object of the present invention. When the heat treatment temperature is lower than 150 ° C., no matter how long the heat treatment is performed for a long time, the adsorption capacity of the zeolite rapidly decreases after the start of operation, and the content of nitrogen trifluoride adsorbed to the zeolite becomes very small. This is thought to be because when heated at a temperature below 150 ° C., the moisture present in the zeolite occupies most of the sites where nitrogen trifluoride is adsorbed, thereby decreasing the adsorption capacity of NF ₃ per unit volume of zeolite. Therefore, in order to remove substantially the water in a zeolite substantially, it heat-processes above the said temperature.

On the other hand, when it heats more than 600 degreeC, the phenomenon that the crystal structure of a zeolite changes or a pore collapses occurs. As a result, the adsorption capacity is greatly impaired and adsorption is not possible, or a problem of saturated adsorption within a short time after gas flow occurs.

The heat treatment of the zeolite is preferably carried out under an inert gas stream of nitrogen, helium, neon, argon, xenon gas, or the like that contains substantially no moisture. Moreover, you may heat-process, sucking these gas under reduced pressure.

In the heat treatment method, a zeolite having a desired particle size distribution may be thinly spread in a drier and heated with an inert gas flowing over the surface of the thin layer. More preferably, the heat treatment and the adsorption tablet of nitrogen trifluoride gas are the same. It is better to do it in a container. That is, a zeolite having a desired particle size distribution is filled into a suitable container or column to form a packed layer, and then heated with aeration of the inert gas in the packed bed, and then cooled without removing the zeolite out of the container, thereby filling the packed layer of the zeolite. The method of venting nitrogen trifluoride gas to is most preferred. At this time, as a material of the column, conventional materials such as stainless steel, copper, nickel, iron, and the like can be used.

The zeolite after the heat treatment is completed is cooled to room temperature (25 ° C.) or lower by being cooled or forced cooled in preparation for the next adsorption treatment. It is desirable to avoid moisture incorporation into the zeolite during cooling.

Purification of the nitrogen trifluoride gas in the present invention is made through the following four steps using a synthetic zeolite that has undergone the pretreatment process as described above.

First, nitrogen trifluoride gas containing carbon tetrafluoride was vented to a column through a pre-treated column filled with zeolite 5A ion-exchanged with alkaline earth metal to adsorb NF ₃ .

At this time, the temperature condition at the time of aeration of the nitrogen trifluoride gas in the column is preferably in the range of -100 to 50 ℃, preferably -50 to 30 ℃. The more preferred one because it is the aeration temperature was a low temperature, the boiling point is -129 ℃ NF _3, because the temperature below the operation is in effect is difficult, carried out at more than -100 ℃ range. When it exceeds 50 degreeC, since unnecessary heat supply is needed at the time of ventilation, it is not good.

On the other hand, the nitrogen trifluoride gas to be purified may be vented using an inert gas as a mixed gas. The mixed gas to be used may be an inert gas to NF ₃ and zeolite. Nitrogen, helium, neon, argon, xenon gas is preferable, and the concentration is preferably 20 to 80 vol%.

When the nitrogen trifluoride gas is aerated, the diameter of the zeolite packed layer is adjusted to 1 to 50 cm, the packed bed height is set to 5 to 200 cm, the flow rate of the nitrogen trifluoride gas is 1 to 25 g / cm 2 · hr, and the pressure is 1 to 10 kgf. It is preferable to adjust to / cm <2>. According to the purification process of the NF ₃ gas of the present invention may adjust the CF ₄ content in the NF ₃ gas to the range of 0~30ppm.

Second, the NF ₃ thus adsorbed is collected through a purge process. In the purge process, it is preferable to flow an inert gas at a mass flow rate of 1 to 100 g / cm 2 · hr, preferably at a mass flow rate of 30 to 60 g / cm 2 · hr. The gas flowing for the collection may be any gas inert to NF ₃ and zeolite, and nitrogen, helium, neon, argon, and xenon gas are preferable. Mass flow rate is defined as the linear velocity of a fluid multiplied by the density of the fluid. In the case of a pipeline having a constant cross-sectional area, the mass velocity is always constant even if the linear velocity changes during heating and cooling during the reaction, which is particularly convenient when handling gases.

The temperature of the purge process is maintained at -30 to 50 ℃, preferably 20 to 30 ℃. If the temperature is too low, the purge time takes too long. If the temperature is too high, impurities chemically bound to the adsorbent may desorb during the purge and come out with NF ₃ .

Third, it goes through a temperature desorption process for reuse of the adsorbent. The temperature desorption process completely removes the impurities remaining in the adsorbent. If the adsorption-purging process is repeated several times without the temperature desorption process, the temperature increase and desorption is necessary.

The rate of temperature increase is carried out in air or inert gas flow at a rate of 0.1-20 占 폚 / min, preferably 1-5 占 폚 / min. The maximum value of the temperature which raises temperature is 500 degreeC, Preferably it is 200 degreeC.

Finally, the first and third steps are repeated when the impurity content is higher than the desired content by examining the impurity content in the NF _{3 which} has been collected.

Hereinafter, one embodiment of the present invention will be described in more detail with reference to the following examples, which are intended for the purpose of description and are not intended to limit the present invention.

[Production Example 1]

Zeolite 5A (manufactured by Aldrich. Inc., US particle size 8-12 mesh, spherical shape) was mixed at room temperature in a 1M solution prepared by dissolving an alkaline earth metal precursor to be ion exchanged in distilled water. After stirring at 80 ° C. for 6 hours, the zeolite 5A was recovered by filtration. After drying for 6 hours at 130 ℃ in the oven, and baked for 12 hours at 500 ℃ to prepare a zeolite 5A ion-exchanged with alkaline earth metal. The amount of alkaline earth metal in the metal in zeolite 5A was measured by an X-ray Fluorescence (XRF) Spectrometer. The results are shown in Table 1.

[Production Example 2]

Except for varying the type, concentration, stirring temperature and / or time of the alkaline earth metal precursor aqueous solution to prepare zeolite 5A having different types and contents of ion exchanged metals, it was treated as in Preparation Example 1 and ion exchanged to alkaline earth metals. Prepared zeolite 5A. The results are shown in Table 1.

Example I

Zeolite 5A ion-exchanged with alkaline earth metals prepared in Preparation Examples 1 and 2 was charged to a column of 10 mm in diameter to 400 mm in height, and then heated at 300 ° C. for 6 hours under atmospheric pressure and an inert gas atmosphere. . The packed bed was then cooled to -20 ° C and a CF4 containing NF ₃ gas (50 vol% of inert gas in the gas, 49.75 vol% of NF _3, 0.25 vol% of CF ₄ ) with an inert gas was passed at a 22.5 weight flow rate (g / cm 2 hr) was vented until NF ₃ and CF ₄ were sufficiently adsorbed (about 3 hours). After this, after cooling to 30 ° C. at a rate of 5 ° C./min, the amount of NF ₃ released while only flowing the inert gas was calculated, and the value was expressed as a volume of NF ₃ per gram of adsorbent (cc). Analysis of NF ₃ gas was performed by gas chromatography. Table 1 shows the results according to the type of zeolite 5A used.

Comparative Example I

For comparison with the present invention, it was carried out in the same manner as in Example I, using an ordinary zeolite 5A (manufactured by Aldrich. Inc., particle size 8-12 mesh, spherical) not ion-exchanged with alkaline earth metals. Table 1 shows.

As a result, zeolite 5A which was not ion-exchanged with alkaline earth metal was adsorbed by both CF ₄ and NF _3, and as a result, separation of NF ₃ was impossible.

[Table 1] Results of Changes in Kinds and Amounts of Ion-Exchanged Alkaline Earth Metals

Example II

The adsorption process was carried out in the same manner as in Example I, except that the packed bed temperature was changed to -50, 0 and 30 ° C. to determine the change in the adsorption amount of CF ₄ and NF ₃ according to the temperature change. The results are shown in Table 2.

[Table 2] Result of temperature change of packed bed during adsorption (Ion exchanged content 50% by weight)

Example III

The same type of inert gas as with NF ₃ during the adsorption process was set to He, N ₂ and Ar, and the concentration of the entire gas was changed to 20 vol%, 40 vol% and 80 vol%. The adsorption amount of CF ₄ and NF ₃ according to the type and concentration of inert gas was examined. The results are shown in Tables 3 and 4.

[Table 3] Result (I) (50% by weight of ion exchanged content) according to the type and concentration of mixed gas

[Table 4] Result of the type and concentration of mixed gas (II) (Ion-exchanged content 50% by weight)

Example IV

In order to purify NF ₃ with ultra high purity, CF ₄ containing NF ₃ obtained in Example I was again vented to an adsorbent layer containing zeolite 5A ion-exchanged with alkaline earth metals. That is, after collecting NF ₃ containing a small amount of CF ₄ without inert gas by passing NF ₃ containing 226 ppm CF ₄ containing inert gas, which was first purified in Example I, through a storage tank containing liquid nitrogen, Zeolite 5A prepared in Preparation Example was packed into a 10 mm internal stainless column with a height of 400 mm, cooled to −20 ° C., and a gas containing 50 vol% of an inert gas and 50 vol% of NF ₃ having a CF ₄ content of 226 ppm was 22.5 weight. It was aerated for about 3 hours until NF ₃ and CF ₄ sufficiently adsorbed at a flow rate (g / cm 2 · hr). This was calculated the amount of adsorption and to 400 ℃ temperature was raised at a rate of 1 ℃ / min removable since it can be seen the removed more than 99.3% the calculation of CF ₄ removal rate relative to the primary before purification CF ₄ content, expressed as a result 5 is shown.

[Table 5] Result of two times of adsorption purification by adsorbent (50% by weight of ion-exchanged content)

The present invention can provide an effective method for purifying nitrogen trifluoride gas by removing the CF ₄ component from the nitrogen trifluoride gas.

Claims (12)

Nitrogen trifluoride (NF ₃ ) gas containing carbon tetrafluoride (CF ₄ ) was vented through a column packed with zeolite 5A ion-exchanged with alkaline earth metals to selectively adsorb only nitrogen trifluoride and vented carbon tetrafluoride, A method for purifying nitrogen trifluoride gas for recovering pure nitrogen trifluoride. The method of purifying nitrogen trifluoride gas according to claim 1, wherein the amount of the ion-exchanged alkaline earth metal is 20 to 95% by weight relative to the total metal in the zeolite. The method for purifying nitrogen trifluoride gas according to claim 1 or 2, wherein the alkaline earth metal is magnesium (Mg). The method for purifying nitrogen trifluoride gas according to claim 1 or 2, wherein the alkaline earth metal is calcium (Ca). The method for purifying nitrogen trifluoride gas according to claim 1 or 2, wherein the alkaline earth metal is strontium (Sr). The method for purifying nitrogen trifluoride gas according to claim 1 or 2, wherein the alkaline earth metal is barium (Ba). The method for purifying nitrogen trifluoride gas according to claim 1 or 2, wherein the temperature at which NF ₃ containing CF ₄ is passed through a packed bed filled with an adsorbent is maintained at -100 to 50 ° C. The method for purifying nitrogen trifluoride gas according to claim 1 or 2, wherein NF ₃ containing CF ₄ is incorporated into the packed bed together with an inert gas, but the amount of inert gas is set to 20 vol% to 80 vol%. . 9. The method of purifying nitrogen trifluoride gas according to claim 8, wherein the inert gas is one of argon, helium and nitrogen. The method for purifying nitrogen trifluoride gas according to claim 1 or 2, wherein the adsorption and recovery of the nitrogen trifluoride (NF ₃ ) gas using zeolite 5A ion-exchanged with alkaline earth metal is repeated two or more times. Nitrogen trifluoride adsorbent, consisting of zeolite 5A ion-exchanged with alkaline earth metals, selectively adsorbing only nitrogen trifluoride from nitrogen trifluoride (NF ₃ ) gas containing carbon tetrafluoride (CF ₄ ) as impurities . 12. The nitrogen trifluoride adsorbent according to claim 11, wherein the amount of the ion exchanged alkaline earth metal is 20 to 95% by weight relative to the total metal in the zeolite.