TWI457285B - Method for driving high purity chlorine - Google Patents

Description

Method for producing high purity chlorine

The present invention relates to a method for producing high purity chlorine. More specifically, the present invention relates to a method for producing high-purity chlorine which suppresses generation of oxygen of impurities after filling liquid chlorine into a cylinder. The high-purity chlorine produced by the above-described production method can be used for dry etching and cleaning of semiconductor elements, optical fibers, liquid crystal display panels, and the like which are used for VLSI.

Generally, when liquid chlorine is transported, it is filled in a cylinder for high-pressure gas. However, after being filled in a cylinder, impurities such as oxygen may be generated in liquid chlorine, and the purity of liquid chlorine generated may be lowered.

A method of removing a non-condensable gas such as oxygen or nitrogen, which is an impurity in liquid chlorine, has been disclosed (for example, see Patent Document 1). Further, a method of purifying impurities adsorbed by zeolite is also known. For example, a method of contacting activated carbon or synthetic zeolite in liquid helium and removing moisture or carbon dioxide of a trace amount of impurities in liquid helium is known, and an increase in removal effect by adsorption at a low temperature has been revealed (for example, refer to the patent literature). 2). Further, a method of removing impurities such as oxygen from chlorine gas, after adsorbing chlorine gas by zeolite or activated carbon, and releasing the adsorbed chlorine gas at a pressure different from that at the time of introduction, thereby improving the purity of chlorine gas has been disclosed (for example, refer to the patent literature) 3 and 4).

However, although the oxygen or the like for removing impurities by such methods has been described, the purity of the liquid chlorine remaining in the cylinder is not disclosed. Further, in Patent Document 1, although the oxygen in the liquid chlorine is removed, it has not been studied or suggested that oxygen is generated after the removal.

Further, in Patent Document 2, although impurities such as water and the like are removed by the zeolite, the related oxygen has not been described, and the impurities are not studied or implied by the subsequent storage. Further, in Patent Document 2, there is a description about the removal of impurities of liquid nitrogen and liquid helium, but liquid chlorine is not described.

[Patent Literature]

[Patent Document 1] JP-A-2002-316804

[Patent Document 2] Japanese Patent Publication No. 03-59385

[Patent Document 3] Japanese Patent Publication No. 04-367504

[Patent Document 4] Japanese Patent Publication No. 05-155603

The present invention has been made in view of the above problems, and an object of the invention is to provide a method for producing high-purity chlorine which can suppress generation of oxygen of impurities after filling liquid chlorine in a cylinder.

The present invention is as follows.

A method for producing high-purity chlorine, characterized in that liquid chlorine is brought into contact with zeolite, and the purified liquid chlorine obtained by the contact is filled in a cylinder tube to suppress generation of oxygen in the cylinder.

2. The method for producing high-purity chlorine according to the above item 1, wherein the liquid chlorine before the contact with the zeolite is obtained by liquefying chlorine gas obtained by the electrolytic brine; (1) thereafter being subjected to rectification to separate non-condensing. a gas, which is then rectified to separate impurities of a high-boiling component, and then contacted with the zeolite and then filled in the cylinder; or, (2) thereafter, contacted with the zeolite to obtain the purified liquid chlorine, and then refined The liquid chlorine is subjected to rectification to separate the non-condensable gas, and thereafter, the impurities of the high boiling component are separated by rectification, and then filled in the cylinder.

3. The method for producing high-purity chlorine according to the above item 1, wherein the concentration of the oxygen contained in the purified liquid chlorine after the contact with the zeolite is from 0.01 to 1.5 vol. ppm.

4. The method for producing high-purity chlorine according to any one of the items 1 to 3, wherein the pore diameter of the zeolite is 0.3 nm or more.

5. The method for producing high-purity chlorine according to any one of the items 1 to 4, wherein, after the contact with the zeolite, the concentration of the oxygen contained in the purified liquid chlorine after 25 days is 0.01 to 1.0 vol. ppm. .

The method for producing high-purity chlorine according to any one of the items 1 to 5, wherein the pore diameter of the zeolite is 0.4 nm or more.

7. The method for producing high-purity chlorine according to any one of the items 3 to 6, wherein the liquid chlorine is not contacted with the zeolite, and after being filled in the cylinder, the liquid chlorine is removed after 25 days and one day later. The ratio (X ₂ ) of the concentration of oxygen contained in the purified liquid chlorine after the purified liquid chlorine is filled in the cylinder, and the ratio (X ₂ ) of the oxygen concentration contained in the purified liquid chlorine after one day is 1.0~2.1, the above X ₂ / X ₁ above is 0.2 to 0.4.

According to the method for producing high-purity chlorine according to the present invention, the liquid chlorine is brought into contact with the zeolite, and the purified liquid chlorine obtained by the contact is filled in the cylinder tube to suppress the generation of oxygen in the cylinder. By purifying by contact with such a zeolite, even if a conventional cylinder is filled with high-purity chlorine, impurities such as oxygen can be suppressed, and liquid chlorine which maintains purity over a long period of time can be produced. Further, since the refining by the contact does not require the intermittent operation of purification by adsorption and release, continuous production can be performed.

Further, the liquid chlorine before the contact with the zeolite is obtained by liquefying the chlorine gas obtained by the electrolyzed brine; (1) the liquid chlorine obtained thereafter is rectified to separate the non-condensable gas, and then is separated by distillation. The impurity of the boiling point component is then contacted with the zeolite, and then the purified liquid chlorine obtained by the contact is filled in the cylinder; or, (2) thereafter, the refined liquid chlorine is obtained by contacting the zeolite, and then the refined liquid chlorine is refined. The non-condensable gas is separated by distillation, and then the impurities of the high-boiling component are separated by rectification, and when it is filled in the cylinder, the effect of suppressing the generation of oxygen in the cylinder can be obtained. Further, in (1), rectification may be carried out before the step of contacting with the zeolite, and the powder of the zeolite which inhibits contact may be rectified to be mixed in the cylinder. Further, in (2), rectification is carried out between the step of contacting with the zeolite and the step of filling the cylinder, and the zeolite to be used is easily exchanged.

Further, when the range of the oxygen concentration contained in the liquid chlorine after the passage of the specific period is limited, the purity of the high-purity chlorine can be maintained for a long period of time in a sufficient period of time during the general storage period of 25 days.

Further, when the effective diameter of the pores of the zeolite is within a specific range, the effect of suppressing the generation of oxygen in the cylinder can be further enhanced, and the purity of the high-purity chlorine can be maintained over a long period of time.

Further, when the ratios X ₁ , X ₂ and X ₂ /X ₁ of the oxygen concentration contained in the liquid chlorine and the purified liquid chlorine are in a specific range, the oxygen generated by the contact of the zeolite with X ₁ and X ₂ over time is obtained. The inhibitory effect is obtained, and the effect of suppressing the presence or absence of oxygen by the contact of the zeolite can be obtained by X ₂ /X ₁ , so that oxygen generation in the cylinder can be obtained in a sufficient period for a general storage period of 25 days. The inhibitory effect and high purity chlorine can maintain purity over a long period of time.

[Formation for implementing the invention]

Hereinafter, a method for producing high-purity chlorine of the present invention will be described in detail.

The method for producing high-purity chlorine according to the present invention is a method for suppressing generation of oxygen after filling a cylinder, characterized in that liquid chlorine is brought into contact with zeolite, and chlorine after contact with the contact is filled in a cylinder, and the cylinder is restrained The production of oxygen inside.

The above-mentioned "liquid chlorine" can be produced by any production method, for example, by electrolyzing salt water to obtain chlorine gas, and then dehydrating the chlorine gas with sulfuric acid, followed by compression and liquefaction.

The above-mentioned "zeolite" is in contact with liquid chlorine, and any of natural or synthetic materials can be used for the purpose of adsorbing a substance which is considered to generate oxygen in liquid chlorine. Further, the shape of the zeolite can be arbitrarily selected, and examples thereof include a pellet form, a bead shape, a plate shape, a rod shape, and a tubular shape.

Further, the zeolite system has a structure in which a large number of pores are formed. The above "effective diameter" of the size of the molecules which can pass through the pores can be arbitrarily selected, and is preferably 0.3 nm or more, and may be a mixture of plural effective diameters. For example, when it is 0.3 nm or more, a synthetic zeolite such as molecular sieve 3A, molecular sieve 4A, molecular sieve 5A, and molecular sieve 13X, and the like may be mentioned. Further, in the case of 0.4 nm or more, for example, molecular sieve 4A, molecular sieve 5A, molecular sieve 13X, and the like may be mentioned. Further, when it is 0.5 nm or more, for example, molecular sieve 5A, molecular sieve 13X, and the like are mentioned. Further, the maximum value of the effective diameter is preferably 10 nm or less.

The above "cylinder" is a container in which liquid chlorine is stored in contact with purified liquid chlorine purified by zeolite. The refined liquid chlorine can be shipped in the state of being filled in a cylinder. Further, the material of the cylinder tube can be arbitrarily selected, and examples thereof include a metal such as iron or steel such as steel or stainless steel. Among them, the iron cylinder is inexpensive and can be widely used, and may be a preferred example.

When the impurities are continuously removed, the liquid can be handled without replacing the liquid in the container containing the zeolite, so that the work efficiency is higher than that of the batch type, and it is preferable. When it is carried out in a continuous manner, the contact conditions of the zeolite with the liquid chlorine can be appropriately selected by conditions such as distillation. When the superficial velocity per unit time (hereinafter, abbreviated as "SV") is defined, it is preferably SV = 0.1 to 50 [1/hour] (preferably 1 to 25 [1/hour]). If the SV is too large, the suppression effect of oxygen generation is small, and if the SV is too small, the removal equipment must be made larger.

The liquid chlorine system can be separated and removed by distillation to remove the above-mentioned "non-condensable gas". This non-condensable gas system is, for example, a lower boiling point impurity than liquid chlorine such as oxygen and nitrogen. Further, the above-mentioned "high-boiling component impurities" can be removed by distillation. The impurities of the high boiling component are impurities having a higher boiling point than the liquid chlorine such as bromine or metal.

Each of the above rectification systems may be carried out before the contact treatment of the zeolite with the liquid chlorine, or may be carried out thereafter.

For example, as illustrated in Fig. 1, the liquid chlorine before the contact with the zeolite liquefies the chlorine gas obtained by the electrolyzed brine, and thereafter, the liquefied material is rectified to separate the non-condensable gas, and then the distillate is further rectified. It is obtained by separating impurities of high boiling components. Further, as shown in FIG. 2, the purified liquid chlorine is contacted with the zeolite, and before being filled in the cylinder, the distillation is carried out to separate the non-condensable gas, and then the distillation product is further rectified to separate the impurities of the high boiling component. Come and get.

The contact treatment between the zeolite and the liquid chlorine is carried out before or after the rectification step, and the effect of suppressing the occurrence of oxygen in the cylinder can also be obtained. Further, when it is carried out before the rectification, even if the powder of the contacted zeolite is discharged, it is preferable that the rectification treatment suppresses the mixing of the powder into the cylinder. Further, it is preferred that the zeolite to be used is easily exchanged after the rectification is carried out before the cylinder is filled.

The oxygen concentration contained in the purified liquid chlorine after 25 days after contact with the zeolite may be, for example, 0.01 to 1.5 vol. ppm (preferably 0.01 to 1.4, more preferably 0.01 to 1.3). Further, for example, it may be 0.01 to 1.0 vol. ppm (preferably 0.01 to 0.9, more preferably 0.01 to 0.8).

The oxygen gas concentration contained in the gas phase portion of the cylinder in which the purified liquid chlorine is filled after 25 days after the contact with the zeolite is higher than the liquid phase portion which is easy to grasp in the liquid phase portion, for example, 1~ 220 vol. ppm (preferably 1 to 180, more preferably 1 to 100).

The ratio of the oxygen concentration Y _{1 (1)} contained in the liquid chlorine after one day to the cylinder, and the oxygen concentration Y _{1 (25)} contained in the liquid chlorine after 25 days after the liquid chlorine is not contacted with the zeolite. (X ₁ =Y ₁₍₂₅₎ /Y ₁₍₁₎ ) For example, 2.3 to 6.0, after filling in the cylinder, the oxygen concentration Y _{2 (1)} contained in the hard liquid chlorine after 1 day, and 25 days later The ratio of the oxygen concentration Y _{2 (25} ) contained in the purified liquid chlorine (X ₂ = Y _{2 (25)} / Y _{2 (1)} ) is 1.0 to 2.1.

Further, X ₂ /X ₁ which is a ratio of the increase in oxygen in the liquid chlorine which is caused by the contact with the zeolite in contact with the zeolite, is 0.2 to 0.4 in the range of the values of X ₁ and X ₂ described above. Further, X ₁ and X ₂ may form values satisfying the above range of X ₂ /X ₁ in the above respective ranges.

If it is within this range, the effect of suppressing the generation of oxygen in the cylinder can be made constant or more, and the purity of the high-purity chlorine can be maintained over a long period of time.

Further, the concentration of oxygen contained in the liquid chlorine is a concentration of oxygen measured in a state in which liquid chlorine forms a full amount of gas at room temperature.

Further, after the liquid chlorine is not contacted with the zeolite and filled in the cylinder, the oxygen concentration Y _{3 (1)} in the gas phase portion of the cylinder after 1 day, and the oxygen concentration Y ₃ in the gas phase portion of the cylinder after 25 days _{(25) )} ratio _{(X 3 = Y 3 (25} ) / Y 3 (1)) , for example, 3.1 to 6.0, after filling the purified liquid chlorine, the oxygen concentration in the gas phase after 1 of the cylinder portion of the Y _{4 (1),} and The ratio of the oxygen concentration Y _{4 (25)} in the gas phase portion of the cylinder after 25 days (X ₄ = Y _{4 (25)} / Y _{4 (1)} ) is 1.0 to 2.1.

Further, X ₄ /X ₃ which is a ratio of the oxygen increase in the gas phase portion of the cylinder which is in contact with the zeolite in contact with the zeolite, and a range which can be obtained within the range of the values of X ₄ and X ₃ can be, for example, It is 0.2~0.7.

If it is within this range, the effect of suppressing the generation of oxygen in the cylinder can be made constant or more, and the purity of the high-purity chlorine can be maintained over a long period of time.

[Examples]

Hereinafter, a method for producing high-purity chlorine of the present invention will be specifically described with reference to Fig. 1 .

(1) Manufacture of liquid chlorine

As shown in Fig. 1, the chlorine gas generated by the electrolysis of salt water is dehydrated with sulfuric acid, and then compressed at 0.7 to 0.8 MPa to obtain crude liquid chlorine. The crude liquid chlorine obtained by this has a liquefaction rate of 80 to 95% and contains 99.8% or more of chlorine. Further, the crude liquid chlorine contains oxygen as an impurity, and thereafter, rectification is carried out to remove oxygen or the like of a low-boiling non-condensable gas. Then, the bromine and the metal component of the impurities of the high-boiling component are removed, and rectification is performed again. Thereby, liquid chlorine containing 0.6 vol. ppm of oxygen (volume concentration of liquid chlorine taken from the liquid phase portion to form a full amount of gas at room temperature) was obtained.

(2) Contact and filling with zeolite

Then, the adsorption column of the above-mentioned production method is contacted with liquid chlorine prepared by the above-described production method in an adsorption column of a type 3A synthetic zeolite (molecular sieve 3A, manufactured by Baline Industries, Ltd.) having an effective diameter of 0.3 nm, and is contacted at SV = 13 [1/hour], for example, 1 refined liquid chlorine. Thereafter, the steel cylinder (capacity 10 liters) was filled to a capacity of 8.5 kg of 60%. Then, it was stored at room temperature, and after 1 day, 13 days, and 25 days, quantitative analysis of oxygen was performed. The analysis was carried out by using a PID as a detector, a 2 m "Unibeads 1S" and a 3 m "molecular sieve 13XS" as a column, and a gas chromatographic analysis using a helium gas as a carrier gas (product name G3900, manufactured by Hitachi, Ltd.). The temperature was carried out at 60 °C. Further, the quantitative analysis of oxygen is shown in Tables 1 and 2 for the liquid chlorine portion (hereinafter referred to as the liquid phase portion) in the cylinder and the gas phase portion in the cylinder.

Further, in the second embodiment, the same production method as in Example 1 was carried out except that a 13X-type synthetic zeolite having a pore diameter of 1.0 nm ("Molecular Sieve 13X", manufactured by Baiya Kogyo Co., Ltd.) was used. Liquid chlorine, which is filled in a steel cylinder. Thereafter, quantitative analysis of oxygen was carried out in the same manner as in Example 1.

Further, in Comparative Example 1, the liquid chlorine raw material was filled in a steel cylinder without contacting the zeolite. In addition, in Comparative Example 2, a cerium oxide gel ("Unibeads 1S", manufactured by JL Science Co., Ltd.) having an average pore diameter of 2.5 nm was used in place of the zeolite, and the same production method as in Example 1 was carried out to obtain purified liquid chlorine. And filled in a steel cylinder. Thereafter, quantitative analysis of oxygen was carried out in the same manner as in Example 1.

(3) Oxygen concentration in the liquid phase after 1 day of cylinder filling

As shown in Table 1, it is understood that in the comparative example 1 in which the oxygen concentration in the liquid phase portion after the filling of the cylinder tube was not contacted with zeolite at 0.7 vol. ppm after 1 day, the example 1 and the method of contacting with the zeolite were carried out. In Example 2, any of them was 0.2 vol. ppm, and the oxygen content at the point of filling the cylinder was less than that of Comparative Example 1.

Further, in Comparative Example 2 in which the cylinder tube was in contact with liquid chlorine, the oxygen concentration in the liquid phase portion was 0.6 vol. ppm, and the effect of suppressing the oxygen content at the time of cylinder filling at the time of comparison with 0.2 vol. ppm in Examples 1 and 2 was small. .

(4) Oxygen concentration in the liquid phase after 25 days of cylinder filling

As shown in Table 1, it can be seen that in the comparative example 1 in which the oxygen concentration in the liquid phase portion after the filling of the cylinder tube was not contacted with the zeolite after 21 days, it was 2.1 vol. ppm. However, Example 1 and the method of contacting with the zeolite were carried out. Example 2 was 1.3 vol. ppm and 0.2 vol. ppm, respectively, and the oxygen content was less than that of Comparative Example 1.

Further, in Example 2, the oxygen concentration ratio X ₂ after the liquid phase portion and after 1 day was 0.2/0.2 = 1.0, and the oxygen concentration did not change slightly during the 24 days.

Further, it was found that Comparative Example 1 which was not in contact with the zeolite increased the oxygen concentration ratio X ₁ after the gas phase portion by 25 days and after 1 day to 2.1/0.7 = 3.0. That is, Example 2 was 1.0/3.0 = 0.3 in the increase inhibition ratio X ₂ /X ₁ of oxygen generated by the contact of the zeolite in the gas phase portion, which was significantly less than that of Comparative Example 1.

(5) Oxygen concentration in the gas phase after 1 day of cylinder filling

As shown in Table 2, it was found that in the comparative example 1 in which the oxygen concentration in the gas phase portion after 1 day was not contacted with the zeolite, it was 92 vol. ppm, but the example 1 in contact with the zeolite was 28 vol. The ppm and Example 2 were 26 vol. ppm, and the oxygen content at the time of filling the cylinder was less than that of Comparative Example 1 as in the liquid phase.

Further, in Comparative Example 2 in which the cylinder tube was in contact with liquid chlorine, the oxygen concentration in the gas phase portion was 81 vol. ppm, and compared with 28 vol. ppm in Example 1 and 26 vol. ppm in Example 2, the oxygen at the point of filling the cylinder tube was obtained. The inhibitory effect of the content is small.

(6) Oxygen concentration in the gas phase after 25 days of cylinder filling

As shown in Table 2, in Comparative Example 1 in which the oxygen concentration in the gas phase portion after 25 days was not filled with the zeolite, it was found to be 330 vol. ppm. However, Examples 1 and Examples in contact with the zeolite were found. 2 was 169 vol. ppm and 26 vol. ppm, respectively, and the oxygen content was less than that of Comparative Example 1 in the same manner as in the liquid phase portion.

Further, after the filling of the first and second comparative examples, the amount of increase in the oxygen concentration in the liquid phase portion was 1.3-0.2 = 1.1 vol. ppm, and 1.6 - 0.6 = 1.0, respectively, after 1 day and 25 days later. Vol.ppm is slightly the same value. However, in the gas phase portion where the finer change was observed, the increase amount of the oxygen concentration in Example 1 was 169-28 = 141 vol. ppm, but in Comparative Example 2, it was found that 245-81 = 161 vol. ppm was large. The effect of suppressing the content of oxygen in Example 1 was larger than that of Comparative Example 2.

Further, in Example 2, the ratio X ₄ of the oxygen concentration after the liquid phase portion and the day after the day was 26/26 = 1.0, and the oxygen concentration did not change slightly during the 24 days.

Further, in Comparative Example 1 in which the zeolite was not in contact with the zeolite, the ratio X ₃ of the oxygen concentration after the liquid phase portion was increased to 330/92 = 3.6. That is, in Example 2, the increase inhibition ratio X ₄ /X ₃ of oxygen generated by the contact of the zeolite in the liquid phase portion was 1.0/3.6 = 0.3, which was significantly less than that of Comparative Example 1 as in the liquid phase portion. .

Further, it is considered that the increase in oxygen in the gas phase portion is released due to the oxygen present in the liquid chlorine.

In the second embodiment, the oxygen concentration in the liquid phase portion and the gas phase portion is maintained to be slightly constant, and the oxygen generation in the cylinder can be suppressed in a sufficient period during the normal storage period of 25 days. The effect is formed to a certain extent or more, and the high purity chlorine is kept in purity for a long period of time.

Further, it can be seen that in Examples 1 and 2, the effective diameter of the pores was small with respect to Comparative Example 2, but the oxygen concentration after one day of filling the cylinder was small. In particular, it is understood that the second embodiment having an effective diameter of 1.0 nm has a large effect of suppressing an increase in oxygen even after a period of 25 days.

This is considered to be a cerium oxide gel having a large pore diameter distribution with respect to Comparative Example 2 as shown in Fig. 3, but Examples 1 and 2 are molecular sieves (zeolites) having a narrow pore diameter distribution.

Further, the present invention is not limited to the ones described in the above embodiments, and various modifications can be made within the scope of the invention depending on the purpose and application. For example, after the rectification in Examples 1 and 2, the liquid chlorine is brought into contact with the zeolite. However, the present invention is not limited thereto, and as shown in Fig. 2, after the crude liquid chlorine is brought into contact with the zeolite, each rectification is carried out. The obtained liquid chlorine is filled in the cylinder. Even if high-purity chlorine is produced in this order, the effect of suppressing the generation of oxygen in the cylinder can be obtained, and the purity of the high-purity chlorine can be maintained for a long period of time.

Figure 1 is a flow chart for explaining the steps of producing high purity chlorine.

Figure 2 is a flow chart illustrating the steps of making other high purity chlorine.

Fig. 3 is a graph for explaining the difference in pore distribution between the molecular sieve and the cerium oxide gel.

Claims (6)

A method for producing high-purity chlorine, which is characterized in that liquid chlorine is brought into contact with zeolite, and the purified liquid chlorine obtained by the contact is filled in a cylinder tube to suppress the generation of oxygen in the cylinder, and a method for producing high-purity chlorine is produced. The liquid chlorine before the contact with the zeolite is obtained by liquefying the chlorine gas obtained by the electrolyzed brine; (1) thereafter, the non-condensable gas is separated by rectification, and then the impurities of the high boiling component are separated by rectification. Thereafter, the zeolite is contacted with the zeolite and then filled in the cylinder; or, (2) thereafter, the refined liquid chlorine is obtained by contacting the zeolite, and then the refined liquid chlorine is rectified to separate the non-condensable gas, and thereafter The impurities of the high-boiling component are separated by rectification, and then filled in the cylinder; the superficial velocity (SV) of the liquid chlorine contacting the zeolite is 0.1 to 25 [1/hour]. The method for producing high-purity chlorine according to the first aspect of the invention, wherein the concentration of the oxygen contained in the purified liquid chlorine after 25 days after contact with the zeolite is 0.01 to 1.5 vol. ppm. A method for producing high-purity chlorine according to claim 1 or 2, wherein the pore diameter of the zeolite is 0.3 nm or more. The method for producing high-purity chlorine according to claim 1 or 2, wherein the concentration of the oxygen contained in the purified liquid chlorine after 25 days after contact with the zeolite is 0.01 to 1.0 vol. ppm. A method for producing high-purity chlorine according to claim 1 or 2, wherein the pore diameter of the zeolite is 0.4 nm or more. The method for producing high-purity chlorine according to claim 1 or 2, wherein the liquid chlorine is not contacted with the zeolite, and after being filled in the cylinder, the oxygen concentration in the liquid chlorine after 25 days and one day later is When the ratio (X ₁ ) is 2.3 to 6.0, and the purified liquid chlorine is filled in the cylinder, the ratio (X ₂ ) of the oxygen concentration contained in the purified liquid chlorine after 25 days and 1 day later is 1.0 to 2.1, X ₂ / X ₁ above is 0.2 to 0.4.