JP5117797B2 - Perfluorocarbon gas purification method and apparatus - Google Patents

Description

  The present invention relates to a purification method and apparatus for perfluorocarbon gas.

Gases commonly referred to as perfluorocarbon (PFC), such as tetrafluoromethane (CF ₄ ), hexafluoroethane (C ₂ F ₆ ), are important materials in semiconductor or liquid crystal production.

However, these gases have a global warming potential of 5,700 for CF ₄ and 11,900 for C ₂ F ₆ , which is much higher than carbon dioxide (CO ₂ ) with a global warming potential of 1. The value is large. For this reason, releasing these gases into the atmosphere as they are after the use of semiconductor or liquid crystal production has a great adverse effect on global warming. On the other hand, in the “Kyoto Protocol” on the reduction of chlorofluorocarbons (effective on February 16, 2005), the reduction rate of these gases in Japan was determined to be 6% compared to 1990 and 1995, respectively. .

  As a result, the voluntary reduction target for the electronics industry was decided to be 10% reduction in the liquid crystal industry to the 2000 level in 2010 and in the IC industry to the 1995 level in 2010. It was.

After these gases are supplied to the semiconductor or liquid crystal manufacturing apparatus and used for the manufacture of the semiconductor or liquid crystal, the concentration is less than 1 vol% (the remainder is almost N ₂ , and the reaction in the semiconductor or liquid crystal manufacturing apparatus causes The generated chemically reactive halogen-based gas is mixed). At present, this exhaust gas is generally detoxified using a detoxifying device of various principles.

However, for example, in an atmospheric pressure plasma apparatus which is a general detoxification processing apparatus, the amount of consumption of CF ₄ is enormous, and for this reason, the load of detoxification processing of the exhaust gas has become excessive. is there.

On the other hand, attempts have been made to recover these exhaust gases. These recovered gases are either destroyed at a waste CFC treatment facility or returned to the production plant of these gases for purification and reuse. Furthermore, the halogen-based gas (for example, HF, SiF _{4 and the} like), oxygen (O ₂ ), and moisture (H ₂ O) as impurities are removed until the concentration is less than 1 volppm, and the collected and concentrated concentration is 80 to 80%. It has begun to supply 95 vol% (the rest is N ₂ ) gas to a reusable semiconductor or liquid crystal manufacturing apparatus.

Various studies have been made on the method of recovery, but gas purification is a major point for practical use. If this point can be overcome, it can be reused in the manufacturing process of semiconductors or liquid crystals, which is expected to make a significant contribution from the perspective of preventing global warming, and will lead to a substantial reduction in the consumption of these gases. Therefore, it can make a significant economic contribution.
JP 2004-284834 A JP 2000-15056 A

From the background described above, perfluorocarbon gas or SF ₆ is increased from a mixed gas of perfluorocarbon gas discharged from a semiconductor or liquid crystal manufacturing process or SF ₆ which is another semiconductor manufacturing gas and N _2. The method of obtaining with purity has been studied.

The aforementioned Patent Document 1, nitrogen (N ₂₎ sulfur hexafluoride SF ₆ from a gas mixture containing (SF ₆₎ high purity in, can be recovered at a high recovery rate, the N ₂ to be discharged purification process and apparatus of SF ₆ that it is possible to realize a state where SF ₆ is hardly contained is disclosed. However, in the above-mentioned Patent Document 1, it is not limited to purifying SF ₆ having a relatively large molecular weight, and it cannot effectively separate and purify perfluorocarbon gases such as CF ₄ and C ₂ F ₆ having a small molecular weight.

The aforementioned patent document 1, the activated carbon is used as the first suction means, the activated carbon, which selectively adsorb SF _6, it is not intended to adsorb N _2. In addition, the purity of SF ₆ purified by the method of Patent Document 1 remains at 99.998%, and a high purity of five nines (99.999%) or more, which is a purity sufficient for reuse, has been achieved. Absent. Furthermore, the above Patent Document 1 does not clearly indicate what kind of activated carbon is used.

In addition, Patent Document 2 describes a method for purifying tetrafluoromethane (CF ₄ ) using zeolite and activated carbon. This is because ethylene is produced when CF ₄ is produced by a conventionally known production method. Since compounds, hydrocarbon compounds, carbon monoxide and / or carbon dioxide are contained as impurities in the CF ₄ production process, these impurities are removed with zeolite, carbonaceous adsorbent, etc., and the purity of CF ₄ Is not intended to be purified in order to reuse the perfluorocarbon gas after use in the semiconductor manufacturing process. Further, for this reason, since the object of adsorption removal from the mixed gas is not N ₂ but the above-described impurity gas, the perfluorocarbon gas is effectively a high-purity perfluorocarbon gas from a raw material gas containing 85% or more. Cannot be purified.

  Thus, in the currently disclosed method relating to the purification of perfluorocarbon gas using adsorption of zeolite, the gas species that can be purified and the composition of the source gas are limited, and after use in the semiconductor or liquid crystal manufacturing process It is thought that few have focused on the removal and purification of impurity components for the purpose of reusing perfluorocarbon gas.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a purification method and apparatus for perfluorocarbon gas that enables reuse of the perfluorocarbon gas after use in a semiconductor or liquid crystal manufacturing process. .

That is, the method for purifying perfluorocarbon gas according to the present invention is the above-mentioned impurity component from a gas to be treated containing nitrogen gas as an impurity component with respect to CF ₄ and C ₂ F ₆ which are perfluorocarbon gases having a molecular weight of 140 or less. nitrogen gas was removed by adsorption on zeolite 4A, you are summarized in that to separate and purify the perfluorocarbon gas.

Further, the purifier for perfluorocarbon gas of the present invention uses the above perfluorocarbon gas from a gas to be treated containing nitrogen gas as an impurity with respect to CF ₄ and C ₂ F ₆ which are perfluorocarbon gases having a molecular weight of 140 or less. It is an apparatus for separation and purification, and is summarized in that an adsorption tower is packed with zeolite 4A for adsorbing and removing the impure nitrogen gas.

The present invention uses a gas containing nitrogen gas as an impure component relative to the perfluorocarbon gas as a treatment target gas of the starting material, and adsorbs the impure nitrogen gas from the treatment target gas onto the zeolite 4A, thereby producing a perfluorocarbon gas. Was separated and purified. By doing so, it was possible to effectively adsorb and remove nitrogen, which is an impurity, and to separate and purify high-purity perfluorocarbon gas of 99.999% or more. Accordingly, for example, perfluorocarbon gas discharged from a semiconductor or liquid crystal manufacturing process can be effectively reused by increasing the purity.
The processing target gas containing nitrogen gas as an impure component with respect to CF ₄ and C ₂ F ₆ which are perfluorocarbon gases having a molecular weight of 140 or less is the adsorbed nitrogen gas on zeolite 4A, and only the perfluorocarbon gas is adsorbed. Can be separated and purified with high accuracy.

An adsorption step for removing nitrogen gas, which is an impure component, is adsorbed on the zeolite 4A, and a desorption step for desorbing the nitrogen gas from the zeolite 4A on which the nitrogen gas is adsorbed under reduced pressure.

  When the concentration of the perfluorocarbon gas is 85 volume% or more and 99 volume% or less, the processing target gas may be used to purify the perfluorocarbon gas after use in a semiconductor or liquid crystal manufacturing process to obtain a large amount of purified gas. Can be reused.

  A plurality of adsorption towers filled with an adsorbent are connected in series to perform adsorption in a plurality of stages, adsorbing nitrogen gas with the zeolite 4A in the adsorption tower arranged on the upstream side, and adsorption tower arranged on the downstream side Then, when using activated carbon and adsorbing nitrogen gas, it can adsorb | suck nitrogen gas very effectively and can obtain perfluorocarbon gas of high purity.

  When the downstream adsorption tower uses both zeolite 4A and activated carbon to adsorb nitrogen gas, the nitrogen gas can be adsorbed very effectively to obtain a high-purity perfluorocarbon gas.

  When the zeolite 4A and activated carbon are layered and packed in the downstream adsorption tower, nitrogen gas can be adsorbed very effectively to obtain a high-purity perfluorocarbon gas.

  When the downstream adsorption tower is filled with zeolite 4A on the upstream side with respect to the gas flow and activated carbon is filled on the downstream side, the nitrogen gas is adsorbed very effectively and a high-purity par A fluorocarbon gas can be obtained.

  When the zeolite 4A and activated carbon are approximately half packed in the adsorption tower on the downstream side, nitrogen gas can be adsorbed very effectively to obtain a high-purity perfluorocarbon gas.

  Next, the best mode for carrying out the present invention will be described.

  In the method for purifying perfluorocarbon gas of the present invention, the perfluorocarbon gas is adsorbed on zeolite 4A from the gas to be treated containing nitrogen gas as an impurity to the perfluorocarbon gas. Separate and purify.

  The gas to be treated is a gas to be treated containing nitrogen gas as an impure component with respect to the perfluorocarbon gas, and the gas having a perfluorocarbon gas concentration of 85 vol% to 99 vol% is converted into nitrogen gas by zeolite 4A. Since it is suitable for separation and purification by adsorption and suitable for reusing the separated and purified perfluorocarbon gas, it can be suitably used.

As the perfluorocarbon gas, those having a molecular weight of 140 or less, specifically CF ₄ and C ₂ F ₆ can be suitably used.

  A plurality of adsorption towers filled with an adsorbent are connected in series to perform adsorption in a plurality of stages, adsorbing nitrogen gas with the zeolite 4A in the adsorption tower arranged on the upstream side, and adsorption tower arranged on the downstream side Then, activated carbon or both zeolite 4A and activated carbon can be used to adsorb nitrogen gas.

  As the activated carbon, molecular sieve carbon or carbon molecular sieve can be preferably used. For example, a uniform mixture of a thermosetting phenol resin powder, a thermosetting resin solution, and a polymer binder is formed into a granular shape. By performing a primary heat treatment at a temperature of 500 to 1100 ° C. in a non-oxidizing atmosphere or a weakly oxidizing atmosphere, and further performing a secondary heat treatment at a temperature of 150 to 1000 ° C. for 30 to 240 minutes in a weakly oxidizing atmosphere. What was obtained can be used conveniently.

  More specifically, as the thermosetting phenol resin powder, spherical primary particles of phenol resin having a particle diameter of 1 to 150 μm or thermosetting phenol resin fine powder composed of the secondary aggregate thereof is used. Preferred spherical primary particles have a particle size in the range of 2 to 80 μm. Moreover, the said thermosetting phenol resin powder used the thing of the magnitude | size which can pass a 100 Tyler mesh sieve at least 50 weight% of the whole. More preferably, at least 90% by weight of the total is sized to pass through a 100 Tyler mesh screen.

Further, as the thermosetting phenol resin powder, those containing a methylol group in a reasonable ratio are used. That is, in the infrared absorption spectrum by the KBr tablet method, the absorption intensity at ₁₆₀₀ cm ⁻¹ (absorption peak attributed to benzene) is the largest absorption intensity in the range of D ₁₆₀₀ , 900 to 1015 cm ⁻¹ (absorption peak attributed to methylol group). When the absorption intensity of D _{900 to 1015} and 890 cm ⁻¹ (absorption peak of isolated hydrogen atom of benzene nucleus) is represented by D ₈₉₀ , those satisfying the following formulas (1) and (2) are used. Here, the value of the ratio of D _{900 to 1015} / D ₁₆₀₀ is preferably in the range of 0.3 to 7.0, and more preferably in the range of 0.4 to 0.5.
D _{900 to 1015} / D ₁₆₀₀ = 0.2 to 9.0 (1)
_{D 890 / D 1600 = 0.09~1.0 ...} (2)

  Furthermore, as the thermosetting phenol resin powder, a thermosetting phenol resin fine powder having a solubility in methanol of 50% by weight or less under reflux can be used.

Here, the methanol solubility is obtained by accurately weighing about 100 g of a sample (the weight of the weight is precisely C), heat-treating in about 500 ml of 100% methanol for 30 minutes under reflux, filtering through a glass filter, The filter residual sample is washed with about 100 ml of methanol on the filter, and then the filter residual sample is dried at a temperature of 100 ° C. for 2 hours (the weight of the precise balance is D). is there.
Methanol solubility (%) = (C−D) / C × 100 (3)

  The methanol solubility defined by the above formula (3) is a property that is manifested when the phenol resin fine powder has a structure in which the crosslinking density is moderately controlled and contains a considerable amount of methylol groups. . That is, when the crosslink density is low and the content of methynol groups is large, the methanol solubility is high. Conversely, when the crosslink density is high and the reactive methylol groups are decreased, the methanol solubility is low. The methanol solubility is preferably 1 to 40% by weight, more preferably 2 to 35% by weight.

  As the thermosetting resin solution, a phenol resin or melamine resin solution can be suitably used.

  Examples of the phenol resin solution include a liquid resol resin or a novolac resin.

  The resol resin is an initial product obtained by reacting phenols with aldehydes in the presence of a basic catalyst, and is usually a self-heat-crosslinking phenol resin rich in methylol groups and having a molecular weight of about 600 or less. Usually, it is often used as a liquid resin using methanol or acetone as a solvent, but initial condensation is performed by reacting 1.5 to 3.5 moles of aldehyde with 1 mole of phenol in the presence of a slight excess of an alkali catalyst. It is also used as a water-soluble resol resin that keeps the product in a stable water-soluble state. As a curing catalyst for accelerating the curing of the resole resin, inorganic acids such as sulfuric acid and hydrochloric acid, or organic acids such as oxalic acid, acetic acid, paratoluenesulfonic acid, maleic acid and malonic acid can be used.

  The novolak resin is used in the presence of an acid catalyst such as oxalic acid, formic acid, hydrochloric acid, etc. in an excess of phenol such that the molar ratio of phenols to aldehydes is, for example, 1 / 0.7 to 1 / 0.9. And obtained by reacting phenol with formalin. It can be supplied as a liquid resin with a solvent such as methanol or acetone. This novolak resin can be cured by adding, for example, hexamethylenetetramine (hexamine) and causing a heat reaction.

  The melamine resin is an initial condensate of melamine-formaldehyde, and can be used as an aqueous solution because it has water solubility. Examples of curing agents for melamine resins include inorganic acids such as hydrochloric acid and sulfuric acid, carboxylic acid esters such as dimethyl oxalate, and hydrochlorides of amines such as ethylamine hydrochloride and triethanolamine hydrochloride. Can do.

  As the polymer binder, polyvinyl alcohol or water-soluble or water-swellable cellulose derivatives can be used.

  As said polyvinyl alcohol, polymerization degree 100-5000. Those having a saponification degree of 70% or more are preferably used. Those partially modified with a carboxyl group or the like are also preferably used.

Moreover, as said cellulose derivative, methylcellulose, carboxymethylcellulose, hydroxypropyl methylcellulose etc. are used suitably, for example. Cellulose derivatives can be used in various viscosities depending on the amount of methoxy group (—OCH ₃ ), hydroxypropoxy group (—OC ₃ H ₃ OH) introduced, the degree of polymerization, and the like.

  The thermosetting phenol resin powder, the thermosetting resin solution, and the polymer binder are 5 to 50 parts by weight of the thermosetting resin solution and 1 polymer binder with respect to 100 parts by weight of the thermosetting phenol resin powder. -30 parts by weight are mixed to obtain a uniform mixture.

  The mixing amount of the thermosetting resin solution per 100 parts by weight of the thermosetting phenol resin fine powder is more preferably 7 to 40 parts by weight, and still more preferably 10 to 30 parts by weight. Further, the mixing amount of the polymer binder is preferably 2 to 20 parts by weight, and more preferably 3 to 15 parts by weight.

  The thermosetting phenol resin powder, the thermosetting resin solution, and the polymer binder can be mixed as they are, or other than these, for example, water can be added and sufficiently mixed in the presence of water. For example, water can be added in a form in which the polymer binder is dissolved in water before the three components are mixed. The amount of water added is preferably 5 to 30% by weight, more preferably 8 to 20% by weight, based on the solid content of the uniform mixture.

  In addition to the above three components, for example, starch, a derivative or a modified product thereof can be added in an amount of 5 to 50 parts by weight, more preferably 10 to 40 parts by weight, per 100 parts by weight of the thermosetting phenol resin fine powder.

  Examples of the above-mentioned compounds such as starch include starch such as potato starch, corn starch, esterified starch such as starch acetate, sulfate starch and phosphate starch, etherified starch such as hydroxyalkyl starch and carboxymethyl starch, distarch phosphate, glycerol A starch derivative such as a cross-linked starch such as distarch, or a modified starch such as an enzyme-modified dextrin can be used.

  These components such as starch suitably act as a pore-forming material, and are considered to be involved in the generation of pores due to thermal decomposition during carbonization in a non-oxidizing atmosphere described later. These components can be used in a state of being dispersed in water as a powder, or in a state of being subjected to a heat treatment such as an alpha treatment with warm water.

  In addition, in the production of the activated carbon, surface activity such as ethylene glycol, polyoxyethylene alkyl ether, polyoxyethylene fatty acid ester, polycarboxylic acid ammonium salt, etc. is used to improve workability without losing its characteristics. A small amount of an agent, a curing agent for a liquid thermosetting resin, a crosslinking agent for polyvinyl alcohol, a plasticizer for extrusion granulation, a fine powder of coconut shell, a fine powder of coal, tar, pitch or other synthetic resins can be added.

  For preparing the homogeneous mixture of the thermosetting phenol resin powder, the thermosetting resin solution, and the polymer binder, the above-described raw materials are mixed by, for example, a ribbon mixer, a V-type mixer, a cone mixer, a kneader, or the like. Can be done.

  For example, in these mixers, starch is added to a predetermined amount of thermosetting phenol resin fine powder, if necessary, and dry mixed, and then dissolved in a predetermined amount of thermosetting resin solution and pre-warm water It can be carried out by adding a polymer binder such as polyvinyl alcohol prepared in this manner and mixing well.

  The homogeneous mixture obtained as described above is then formed into granules. The granulation can be performed, for example, with a single-screw or twin-screw wet granulator, a vertical granulator such as a basket-reuser, or a semi-dry disk pelleter.

  In particular, a granulate granulated by a wet extrusion granulator is preferable because it has a high particle strength and a high ability to separate activated carbon after carbonization. The shape of the granular material is, for example, a columnar shape or a spherical shape. The size of the granule obtained by this granulation is not particularly limited. For example, in the case of a cylinder, the diameter is 0.5 to 5 mm, the length is about 1 to 10 mm, and in the case of a sphere, the diameter is 0.5 to 10 mm. The degree is preferred.

  The granular molded body thus obtained is subjected to primary heat treatment at a temperature of 500 to 1100 ° C. in a non-oxidizing atmosphere or a weakly oxidizing atmosphere.

The non-oxidizing atmosphere can be obtained as an inert gas atmosphere such as H ₂ , Ar, He, N ₂ or the like. The weakly oxidizing atmosphere is an atmosphere containing a small amount of oxidizing gas, for example, an atmosphere in which an inert gas and an oxidizing gas such as a small amount of oxygen, carbon dioxide, carbon monoxide, water vapor, or a mixture thereof are mixed. Can be obtained as The mixing ratio is not particularly limited, but it is preferable to determine the amount of oxidizing gas so that the residual coal rate is 95% or more with respect to the residual coal rate when the heat treatment is performed under the same conditions in a non-oxidizing atmosphere. When the residual carbon ratio is 95% or more, pores suitable for separating and purifying perfluorocarbon gas with high purity are easily formed. The residual carbon ratio indicates the ratio of the weight after the heat treatment to the weight before the heat treatment.

  The primary heat treatment is performed in a temperature range of 500 to 1100 ° C. When the heat treatment temperature is lower than 500 ° C., only activated carbon having a small specific surface area, a sufficient adsorption capacity and low adsorption selectivity can be obtained. On the other hand, when the temperature exceeds 1100 ° C., the pores of the obtained activated carbon contract, eventually reducing the specific surface area and pore volume, and the tendency to obtain only activated carbon having a low adsorption capacity increases.

  As for the heating temperature of the said primary heat processing, 600-1000 degreeC is more preferable, and 650-950 degreeC is still more preferable. Moreover, the temperature increase rate until it reaches the said heating temperature becomes like this. Preferably it is 5-300 degreeC / hr, More preferably, it is 10-180 degreeC / hr, More preferably, it is 15-120 degreeC / hr.

  Next, the granular heat-treated body is further subjected to secondary heat treatment at a temperature of 150 to 1000 ° C. for 30 to 240 minutes in a weakly oxidizing atmosphere.

  As described above, the weak oxidizing atmosphere is an atmosphere containing a small amount of oxidizing gas. For example, an inert gas and a small amount of oxidizing gas such as oxygen, carbon dioxide, carbon monoxide, water vapor, or a mixture thereof can be used. It can be obtained as a mixed atmosphere. The mixing ratio is not particularly limited, but it is preferable to determine the amount of oxidizing gas so that the residual coal rate is 95% or more with respect to the residual coal rate when the heat treatment is performed under the same conditions in a non-oxidizing atmosphere. When the residual carbon ratio is 95% or more, pores suitable for separating and purifying perfluorocarbon gas with high purity are easily formed. The residual carbon ratio indicates the ratio of the weight after the heat treatment to the weight before the heat treatment.

  The secondary heat treatment is performed in a temperature range of 150 to 1000 ° C. If the heat treatment temperature is less than 150 ° C, the pores do not expand sufficiently, and a sufficient adsorption rate and desorption rate of nitrogen gas cannot be obtained. Conversely, if the temperature exceeds 1000 ° C, the pores expand too much. This is because the perfluorocarbon gas to be purified is adsorbed and high-precision separation and purification cannot be performed.

  In the secondary heat treatment, for example, in the case of an atmosphere using a mixed gas of oxygen and nitrogen or the like as a weak oxidizing atmosphere when heating, a range of 150 to 600 ° C. is preferable, and carbon dioxide is included as the weak oxidizing atmosphere. In the case of an atmosphere, a temperature range of 800 to 1000 ° C. is preferable. The rate of temperature rise is not particularly limited, but it is desirable to raise the temperature in an inert gas and to switch to a weak oxidizing atmosphere after raising the temperature to the heating temperature.

  The activated carbon thus obtained has a nitrogen adsorption rate of 0.2% when the adsorption time from the start of adsorption to the total adsorption time until the adsorption equilibrium is reached. 10% or more of the amount. Further, the adsorption rate is preferably such that the amount of adsorption when the adsorption time from the start of adsorption is 0.8% of the total adsorption time is 40% or more of the total amount of adsorption at equilibrium. Further, the adsorption rate is preferably such that the adsorption amount after 1.6% of the total adsorption time from the start of adsorption is 60% or more of the total adsorption amount at equilibrium.

  FIG. 1 is a diagram showing an example of a purifier for perfluorocarbon gas according to the present invention.

  This apparatus is filled with the above-mentioned activated carbon as an adsorbent for adsorbing nitrogen gas, which is an impure component, in the adsorption towers 10A, 10B, 10C, 10D, and contains nitrogen gas as an impure component with respect to perfluorocarbon gas. This is an apparatus for separating and purifying perfluorocarbon gas from gas.

  This apparatus is a pressure swing type purification apparatus including four adsorption towers 10A, 10B, 10C, and 10D. In each of the adsorption towers 10A, 10B, 10C, and 10D, (1) an adsorption step, (2) a first pressure equalizing step, (3) an exhaust step, (4) a desorption step, (5) a purge step, (6) The second pressure equalization step and (7) the pressure return step are repeated. At this time, purified gas can be obtained continuously by shifting the steps between the adsorption towers 10A, 10B, 10C, and 10D.

  Each of the adsorption towers 10A, 10B, 10C, and 10D communicates with the introduction path 12 for introducing the processing target gas, and has introduction valves 1A, 1B, 1C, and 1D that open and close the introduction state of the processing target gas from the introduction path 12. Is provided. Further, the adsorption towers 10A, 10B, 10C, and 10D communicate with the lead-out path 13 that leads out the product gas after the purification process, respectively, and lead-out valves 6A and 6B that open and close the lead-out state of the product gas to the lead-out path 13 , 6C, 6D are provided.

  Each of the adsorption towers 10A, 10B, 10C, and 10D has a vacuum exhaust path 18 for evacuating the inside of each of the adsorption towers 10A, 10B, 10C, and 10D by the vacuum pump 11 and desorbing the nitrogen gas adsorbed by the adsorbent. The vacuum exhaust valves 3A, 3B, 3C, and 3D that open and close the communication state with the vacuum exhaust path 18 are provided.

  The adsorption towers 10A, 10B, 10C, and 10D are communicated with the other adsorption towers 10A, 10B, 10C, and 10D after the evacuation process by the vacuum pump 11 after the adsorption process is completed. Pressure equalizing passages 16A, 16B for performing a pressure equalizing process for recovering the perfluorocarbon gas remaining in the adsorption towers 10A, 10B, 10C, 10D to the other adsorption towers 10A, 10B, 10C, 10D after the vacuum exhaust process. , 16C, 16D are provided. The pressure equalizing passages 16A, 16B, 16C, and 16D are respectively provided with pressure equalizing valves 7A, 7B, 7C, and 7D that open and close the communication state.

  In this example, the tower top part of the first adsorption tower 10A and the tower bottom part of the third adsorption tower 10C are communicated by the pressure equalizing passage 16A and the pressure equalizing valve 7A so that the pressure equalizing process can be performed. Similarly, the tower top of the second adsorption tower 10B and the tower bottom of the fourth adsorption tower 10D are connected to the tower top of the third adsorption tower 10C and the tower bottom of the first adsorption tower 10A by the pressure equalizing passage 16B and the pressure equalizing valve 7B. The pressure equalizing path 16C and the pressure equalizing valve 7C allow the top of the fourth adsorption tower 10D and the tower bottom of the second adsorption tower 10B to communicate with each other via the pressure equalizing path 16D and the pressure equalizing valve 7D.

  Each adsorption tower 10A, 10B, 10C, 10D communicates with a discharge path 17 for discharging the gas remaining in each adsorption tower 10A, 10B, 10C, 10D after the pressure equalization step. Discharge valves 2A, 2B, 2C, and 2D that open and close the communication state are provided.

  Each of the adsorption towers 10A, 10B, 10C, and 10D communicates with a purge path 15 for performing a purge process for introducing product gas from the outlet path 13 to the top of the tower, and a purge valve 4A that opens and closes the communication state with the purge path 15 , 4B, 4C, 4D. Further, each of the adsorption towers 10A, 10B, 10C, and 10D communicates with a return pressure passage 14 for performing a return pressure step for introducing a product gas from the outlet passage 13 to the top of the tower after the pressure equalizing step to return the pressure. The return pressure valves 5A, 5B, 5C, and 5D that open and close the communication state with the passage 14 are provided. A first opening / closing valve 8 is provided in the outlet passage 13, and a second opening / closing valve 9 is provided in the return pressure passage 14.

  Next, (1) adsorption step, (2) first pressure equalization step, (3) exhaust step, (4) desorption step, (5) purge step, (6) second pressure equalization step, (7) return pressure Each step will be described.

  As shown in FIG. 2, in this apparatus, the seven processes described above are executed in eight stages of the first to eighth steps, and the product gas is continuously generated while shifting the processes between the adsorption towers 10A, 10B, 10C, and 10D. Can be obtained.

That is, in the first step, (1) the adsorption process is performed in the first adsorption tower 10A, (6) the second pressure equalization process is performed in the second adsorption tower 10B, and (4) the desorption process is performed in the third adsorption tower 10C. (2) The first pressure equalizing step is performed in the four adsorption tower 10D.
In the second step, the first adsorption tower 10A (1) performs the adsorption process, the second adsorption tower 10B (7) the return pressure process, the third adsorption tower 10C (5) the purge process, and the fourth adsorption tower 10D. (3) The exhaust process is performed.
In the third step, (2) the first pressure equalization step is performed in the first adsorption tower 10A, (1) the adsorption step is performed in the second adsorption tower 10B, and (6) the second pressure equalization step is performed in the third adsorption tower 10C. (4) Desorption step is performed in the fourth adsorption tower 10D.
In the fourth step, the first adsorption tower 10A performs (3) the exhaust process, the second adsorption tower 10B performs the (1) adsorption process, the third adsorption tower 10C performs the (7) return pressure process, and the fourth adsorption tower 10D. (5) A purge process is performed.
In the fifth step, (4) desorption process is performed in the first adsorption tower 10A, (2) first pressure equalization process is performed in the second adsorption tower 10B, and (1) adsorption process is performed in the third adsorption tower 10C. (6) The second pressure equalizing step is performed in the tower 10D.
In the sixth step, (5) purge process is performed in the first adsorption tower 10A, (3) exhaust process is performed in the second adsorption tower 10B, (1) adsorption process is performed in the third adsorption tower 10C, and the fourth adsorption tower 10D. (7) A pressure recovery process is performed.
In the seventh step, (6) the second pressure equalization process is performed in the first adsorption tower 10A, (4) the desorption process is performed in the second adsorption tower 10B, and (2) the first pressure equalization process is performed in the third adsorption tower 10C. (1) The adsorption step is performed in the fourth adsorption tower 10D.
In the eighth step, the first adsorption tower 10A performs (7) the return pressure process, the second adsorption tower 10B performs the (5) purge process, the third adsorption tower 10C performs the (3) exhaust process, and the fourth adsorption tower 10D. (1) The adsorption process is performed.

  The first to eighth steps will be described with reference to FIGS. In the following description, each process is described mainly focusing on the first adsorption tower 10A, and description of similar processes performed in the second to fourth adsorption towers 10B, 10C, and 10D is omitted.

  FIG. 3 shows the first step.

(1) Adsorption process In the first step, (1) the adsorption process is performed in the first adsorption tower 10A. (1) In the adsorption step, the introduction valve 1A, the lead-out valve 6A, and the first on-off valve 8 are opened, and the gas to be treated is introduced into the tower bottom of the first adsorption tower 10A at an adsorption pressure (for example, 0.55 MPaG). In the column maintained at the adsorption pressure, the column is brought into contact with the adsorbent packed in the column. In this (1) adsorption process, nitrogen gas is adsorbed to the adsorbent from the gas to be treated mixed with 80 to 99 vol% of nitrogen gas as an impure component to the perfluorocarbon gas, and the purified product gas is purified. It is taken out from the tower top and led out from the lead-out path 13.

  In this first step, (1) the adsorption step is performed in the first adsorption tower 10A, and at the same time, the second adsorption tower 10B will be described later (6) the second pressure equalizing step will be described later in the third adsorption tower 10C ( 4) The desorption process is performed in the fourth adsorption tower 10D (2) a first pressure equalizing process which will be described later.

  FIG. 4 shows the second step.

  In the second step, (1) the adsorption step is performed in the first adsorption tower 10A following the first step. (1) When the adsorption step is finished, the introduction valve 1A and the outlet valve 6A are closed, and the second step is finished.

  In the second step, (1) the adsorption step is performed in the first adsorption tower 10A, and at the same time, the second adsorption tower 10B will be described later (7) the re-pressure process, and the third adsorption tower 10C will be described later (5) purge. In the fourth adsorption tower 10 </ b> D, the step (3) evacuation step described later is performed.

  FIG. 5 shows the third step.

(2) First pressure equalization step In the third step, in the first adsorption tower 10A, (1) the adsorption step is completed, and (2) the first pressure equalization step is performed. (2) In the first pressure equalization step, the pressure equalization valve 7A is opened, and the top of the first adsorption tower 10A and the bottom of the third adsorption tower 10C are communicated with each other via the pressure equalization path 16A to achieve a pressure equalization state. To do. By this (2) first pressure equalization step, (1) the first adsorption tower 10A in the pressurized state after the adsorption step is completed, and the (5) purge step, which will be described later, is completed to the third adsorption tower 10C in the reduced pressure state. On the other hand, perfluorocarbon gas remaining in the tower is moved and recovered. Through this (2) first pressure equalization step, the pressure in the first adsorption tower 10A falls, for example, from 0.55 MPaG to 0.15 MPaG. (2) When the first pressure equalizing step is finished, the pressure equalizing valve 7A is closed and the third step is finished.

  In the third step, (2) the first pressure equalization process is performed in the first adsorption tower 10A, and at the same time, the above-described (1) adsorption process in the second adsorption tower 10B is described later in the third adsorption tower 10C (6 ) The second pressure equalization step is performed in the fourth adsorption tower 10D (4) desorption step described later.

  FIG. 6 shows the fourth step.

(3) Exhaust process In the fourth step, in the first adsorption tower 10A, (2) the first pressure equalization process ends, and (3) the exhaust process is performed. (3) In the exhaust process, the exhaust valve 2A is opened, and (2) the perfluorocarbon gas is discharged from the first adsorption tower 10A in the pressurized state after the first pressure equalization process is completed, and the pressure in the tower is increased. Return to atmospheric pressure (0 MPaG). (3) The perfluorocarbon gas discharged in the exhaust process can be removed by detoxification with a decontamination device (not shown), for example. (3) When the exhaust process is finished, the exhaust valve 2A is closed and the fourth step is finished.

  In the fourth step, (3) the exhaust process is performed in the first adsorption tower 10A, and at the same time, the above-described (1) adsorption process is performed in the second adsorption tower 10B, and (7) return pressure is described later in the third adsorption tower 10C. In the fourth adsorption tower 10D, a process (5) purge process described later is performed.

  FIG. 7 shows the fifth step.

(4) Desorption process In the fifth step, in the first adsorption tower 10A, (3) the exhaust process is completed, and (4) the desorption process is performed. (4) In the desorption process, the vacuum exhaust valve 3A is opened, the inside of the tower is decompressed by the vacuum pump 11, and the nitrogen gas adsorbed by the adsorbent in the tower is desorbed. (4) The pressure in the tower in the desorption process is set to about -0.095 MPaG, for example.

  In the fifth step, (4) the desorption process is performed in the first adsorption tower 10A, and at the same time, the (2) first pressure equalization process described above in the second adsorption tower 10B is described above (1) in the third adsorption tower 10C (1). ) The adsorption step is performed in the fourth adsorption tower 10D (6) a second pressure equalizing step which will be described later.

  FIG. 8 shows the sixth step.

(5) Purge Step In the sixth step, (4) the desorption step is completed and (5) the purge step is performed in the first adsorption tower 10A. (5) In the purge step, (4) The pressure reduction in the tower is continued with the vacuum exhaust valve 3A being opened following the desorption step, and the purge valve 4A is opened and the product gas flowing through the outlet passage 13 is opened. Is introduced from the top of the first adsorption tower 10A through the purge passage 15 to desorb the nitrogen gas adsorbed by the adsorbent, and at the same time, the first adsorption tower 10A is cleaned. (5) The pressure in the tower in the purge step is maintained at, for example, about −0.095 MPaG, which is the same level as in the (4) desorption step. At this time, the perfluorocarbon gas discharged from the vacuum exhaust path 18 can be removed by detoxification with a non-illustrated detoxification device, for example. (5) When the purge step is finished, the vacuum exhaust valve 3A and the purge valve 4A are closed, and the sixth step is finished.

  In the sixth step, the (5) purge process is performed in the first adsorption tower 10A, and at the same time, the (3) exhaust process is performed in the second adsorption tower 10B, and the (1) adsorption process is performed in the third adsorption tower 10C. However, in the fourth adsorption tower 10D, the later-described (7) return pressure step is performed.

  FIG. 9 shows the seventh step.

(6) Second pressure equalization step In the seventh step, in the first adsorption tower 10A, (5) the purge step is completed, and (6) the second pressure equalization step is performed. (6) In the second pressure equalizing step, the pressure equalizing valve 7C of the third adsorption tower 10C is opened, and the tower top of the third adsorption tower 10C and the tower bottom of the first adsorption tower 10A are communicated via the pressure equalizing path 16C. To equalize the pressure. By this (6) second pressure equalization step, (5) the first adsorption tower 10A in the depressurized state after the purge step is completed, the (1) the third adsorption tower 10C in the pressurized state after the adsorption step is completed The perfluorocarbon gas remaining inside is moved and recovered. Through this (6) second pressure equalization step, the pressure in the first adsorption tower 10A rises, for example, from −0.095 MPaG to 0.15 MPaG. (6) When the second pressure equalizing step is finished, the pressure equalizing valve 7C is closed and the seventh step is finished.

  In the seventh step, (6) the second pressure equalization process is performed in the first adsorption tower 10A, and at the same time, the (4) desorption process described above in the second adsorption tower 10B and the above (2) in the third adsorption tower 10C. In the first pressure equalizing step, the above-described (1) adsorption step is performed in the fourth adsorption tower 10D.

  FIG. 10 shows the eighth step.

(7) Pressure recovery step In the eighth step, in the first adsorption tower 10A, (6) the second pressure equalization step ends, and (7) the pressure recovery step is performed. (7) In the return pressure step, the return pressure valve 5A is opened, the product gas flowing through the outlet passage 13 is supplied from the top of the first adsorption tower 10A through the return pressure path 14, and the pressure in the tower is adjusted to the adsorption pressure (for example, 0.55 MPaG). (7) When the return pressure process is finished, the return pressure valve 5A is closed and the eighth step is finished.

  In the eighth step, the (7) return pressure step described above is performed in the first adsorption tower 10A, and at the same time, the (5) purge step described above is performed in the second adsorption tower 10B, and the above described is described in the third adsorption tower 10C. (3) The exhaust process is the above-described (1) adsorption process in the fourth adsorption tower 10D.

  When the eighth step ends, the process returns to the first step again, and the first to eighth steps are repeated. Thereby, in 1st-4th adsorption tower 10A, 10B, 10C, 10D, respectively, (1) adsorption process, (2) 1st pressure equalization process, (3) exhaust process, (4) desorption process, (5) The purge process, (6) second pressure equalization process, and (7) pressure recovery process are repeated.

  If necessary, the adsorption apparatus using the plurality of (four in this example) adsorption towers 10A to 10D described above in parallel is connected in a plurality of stages to perform the adsorption in a plurality of stages to perform perfluorocarbon. Gas separation and generation can be performed.

  In this case, as described above, the nitrogen gas is adsorbed by the zeolite 4A in the adsorption tower arranged on the upstream side, and the adsorption gas arranged in the downstream side uses the activated carbon or both the zeolite 4A and the activated carbon. Can be adsorbed.

  When the downstream adsorption tower uses both zeolite 4A and activated carbon to adsorb nitrogen gas, the downstream adsorption tower can be packed with zeolite 4A and activated carbon stacked in layers. Further, in this case, the downstream adsorption tower can be filled with zeolite 4A on the upstream side with respect to the gas flow and filled with activated carbon on the downstream side. In this case, the adsorption tower on the downstream side can be filled with approximately half of zeolite 4A and activated carbon.

  Next, examples will be described.

An adsorption test of N ₂ , CF ₄ , and C ₂ F ₆ was performed using the synthetic zeolite (4A). When the adsorption pressure was changed while keeping the adsorption temperature constant, the amount of gas adsorbed per unit weight of the activated carbon was measured to obtain an adsorption isotherm. The results are shown in FIG. As can be seen from this result, the adsorption phenomenon of N ₂ is confirmed, but the adsorption phenomenon of CF ₄ and C ₂ F ₆ is hardly seen.

  Next, activated carbon was produced as follows.

  First, with respect to 100 parts by weight of phenol resin powder (Air Pearl Co., Ltd., Bell Pearl R800), 8 parts by weight of a melamine resin aqueous solution in a solid content, polyvinyl alcohol having a polymerization degree of 1700 and a saponification degree of 99% with warm water is 20% by weight. 20 parts by weight of an aqueous polyvinyl alcohol solution dissolved in an aqueous solution, 2 parts by weight of potato starch, and 0.7 parts by weight of a surfactant (Perex NB-L, manufactured by Kao Corporation) were weighed.

  Next, the melamine resin aqueous solution, polyvinyl alcohol aqueous solution, potato starch and surfactant were mixed for 5 minutes, and the phenol resin powder was added to the mixture and mixed for another 10 minutes.

  Next, this mixed composition was extruded with a biaxial extrusion granulator (Fuji Paudal Co., Ltd., Pelletta Double EXDF-100 type) to obtain 1.3φ × 1-3 mm cylindrical pellets.

  The obtained pellets were sufficiently dried at 115 ° C. under a nitrogen stream for 4 hours, then placed in a rotary kiln having an effective diameter of 750 mmφ × 4250 mm L, and as a primary heat treatment, up to 650 ° C. in a non-oxidizing atmosphere under a nitrogen stream. The temperature was raised and held at that temperature for 3 hours, and then cooled in a furnace under a nitrogen stream to obtain carbonized pellets.

  Further, the obtained carbonized pellets were put into a stationary furnace, and as a secondary heat treatment, the temperature was raised to 300 ° C. in a nitrogen stream, and a weak oxidizing atmosphere in which oxygen was 10% in nitrogen was 1 After holding for a period of time, the furnace was cooled in a nitrogen stream to obtain activated carbon.

  The activated carbon obtained as described above was measured for change with time in the amount of nitrogen gas adsorbed by the volumetric method. BELSORP-HP (manufactured by Nippon Bell Co., Ltd.) was used as a measuring device. The reference volume Vs was 92.95 ml, the dead volume Vd of the activated carbon was 27.3382 ml, and the weight W of the activated carbon was 2.176 g. In addition, the initial set pressure of the apparatus is 4000 Torr (533.288 kPa), that is, the actually introduced initial pressure Pi is 4144.11 Torr (552.501 kPa), the equilibrium is obtained when 2500 seconds have elapsed from the start of measurement, and the equilibrium pressure Pe is 2941. .68 Torr (392.191 kPa), the equilibrium adsorption amount was 17.36 Nml / g. The measurement temperature was 25 ° C.

In this case, the first adsorption amount V ¹ after a predetermined adsorption time has elapsed is obtained by the following equation. Here, P ° is the saturated vapor pressure of nitrogen at the measurement temperature, and T is the absolute temperature.
V ¹ = [{Pi ¹ Vs−Pe ¹ (Vs + Vd)} × 273.15] / P ° WT

Further, the second amount of adsorption V ^2-1 after a predetermined adsorption time has elapsed from the first point of adsorption time is obtained by the following equation.
ΔV ^2-1 = [{(Pi ² Vs + Pe ¹ Vd) −Pe ² (Vs + Vd)} × 273.15] / P ° WT

The second adsorption amount V ² is a value obtained by adding the adsorption increase amount ΔV ^2-1 to the ^first adsorption amount V ¹ .

Then, when the total adsorption time from the start of adsorption to the adsorption equilibrium time is 2500 seconds, the adsorption rate (%) was calculated as the adsorption rate (%) of the adsorption amount at each elapsed time with respect to the total adsorption amount at equilibrium. The results are shown in Table 2 below. Thus, the adsorption rate after 5 seconds was 11.58%, the adsorption rate after 20 seconds was 44.61%, and the adsorption rate after 40 seconds was 68.73%.

  That is, the adsorption rate of nitrogen is such that the adsorption amount when the adsorption rate of nitrogen is 0.2% of the adsorption time from the start of adsorption until the adsorption equilibrium is equal to the total adsorption amount at equilibrium. 10% or more. Further, the adsorption rate is preferably such that the amount of adsorption when the adsorption time from the start of adsorption is 0.8% of the total adsorption time is 40% or more of the total amount of adsorption at equilibrium. It can be seen that the adsorption rate is preferably 60% or more of the total adsorption amount at equilibrium when the adsorption time from the start of adsorption is 1.6% of the total adsorption time.

The activated carbon obtained as described above was used to perform adsorption tests of N ₂ , CF ₄ , and C ₂ F ₆ to obtain adsorption isotherms similar to those described above. The results are shown in FIG. As can be seen from this result, the adsorption phenomenon of N ₂ is confirmed, but the adsorption amount of perfluorocarbon gas is less than 0.1 Nl / kg, and the adsorption phenomenon of CF ₄ and C ₂ F ₆ is hardly seen.

Next, as a comparative example, the same adsorption isotherm was obtained using synthetic zeolite (5A). The results are shown in FIG. 13 and Table 4. As can be seen from this result, since all of these gases shown here are adsorbed in the zeolite 5A, it is difficult to selectively remove N ₂ from these gases by, for example, the pressure swing adsorption method.

Next, in the separation and purification apparatus shown in FIG. 1 using the zeolite 4A, the gas to be treated (CF ₄ + N ₂ ), which is a mixed gas with perfluorocarbon gas containing N ₂ as an impurity, is subjected to pressure swing adsorption. Separation and purification of perfluorocarbon gas was performed.

  Here, the gas to be treated was supplied to the above-described four-column separation / purification apparatus, and the completion of one cycle was regarded as one-stage treatment, and the composition of the purified gas after the first-stage treatment and the second-stage treatment was measured.

In Example 1, both the first stage and the second stage were purified by filling the adsorption tower with zeolite 4A. The operating conditions of the pressure swing type separation and purification apparatus of Example 1 are shown in Table 5 below.

In Example 2, the first-stage adsorption tower is packed with zeolite 4A, and the second-stage adsorption tower is packed with both the activated carbon produced as described above and zeolite 4A for purification. The packed state of the second stage, that is, the downstream adsorption tower is shown in FIG. 14 (A). Zeolite 4A is placed upstream of the gas flow, that is, the lower part of the tower, and activated carbon is placed downstream, that is, the upper part of the tower. Almost half of each layer is stacked and filled. The operating conditions of the pressure swing type separation and purification apparatus of Example 2 are shown in Table 6 below.

In Experimental Example 3, the first stage adsorption tower is packed with zeolite 4A, and the second stage adsorption tower is packed with activated carbon produced as in the above example and purified. The second stage, that is, the packed state of the adsorption tower on the downstream side is as shown in FIG. The operating conditions of the pressure swing type separation and purification apparatus of Experimental Example 3 are shown in Table 7 below.

In Experimental Example 4, the first stage adsorption tower is filled with zeolite 4A, and the second stage adsorption tower is filled with the activated carbon produced as in the above example and purified. The packed state of the adsorption column in the second stage, that is, the downstream side is as shown in FIG. 14A. Zeolite 4A is placed in about one third of the upstream side, that is, the lower part side of the gas, and the downstream side, that is, Activated carbon is laminated and packed in about two thirds of the tower upper side. The operating conditions of the pressure swing type separation and purification apparatus of Experimental Example 4 are shown in Table 8 below.

Under the operating conditions of Examples 1 and 2 and Experimental Examples 3 and 4, the composition of each purified gas was measured after the first stage treatment and after the second stage treatment when CF ₄ + N ₂ was separated and purified as a raw material gas. The results of Examples 1 and 2 are shown in Table 9 below, and the results of Experimental Examples 3 and 4 are shown in Table 10 below.

Above as in, by using a pressure swing adsorption method using the synthetic zeolite 4A, from CF ₄ mixed gas containing N _2, it was possible to purify the CF ₄ in high purity. Therefore, it can be seen that the perfluorocarbon gas discharged from the semiconductor or liquid crystal manufacturing process can be effectively reused by purifying it.

  As described above, in the present embodiment, a gas containing nitrogen gas as an impure component with respect to the perfluorocarbon gas is used as a treatment target gas of the starting material, and the impure nitrogen gas is adsorbed on the zeolite 4A from the treatment target gas. The perfluorocarbon gas was separated and purified. By doing so, it was possible to effectively adsorb and remove nitrogen, which is an impurity, and to separate and purify high-purity perfluorocarbon gas of 99.999% or more. Accordingly, for example, perfluorocarbon gas discharged from a semiconductor or liquid crystal manufacturing process can be effectively reused by increasing the purity.

  When the perfluorocarbon gas has a molecular weight of 140 or less, nitrogen gas, which is an impurity, can be adsorbed on the zeolite 4A, and only the perfluorocarbon gas can be separated and purified with high accuracy.

  When the concentration of the perfluorocarbon gas is 85 volume% or more and 99 volume% or less, the processing target gas may be used to purify the perfluorocarbon gas after use in a semiconductor or liquid crystal manufacturing process to obtain a large amount of purified gas. Can be reused.

  A plurality of adsorption towers filled with an adsorbent are connected in series to perform adsorption in a plurality of stages, adsorbing nitrogen gas with the zeolite 4A in an adsorption tower arranged on the upstream side, and an adsorption tower arranged on the downstream side Then, when both zeolite 4A and activated carbon are used and nitrogen gas is adsorbed, nitrogen gas can be adsorbed very effectively and a high-purity perfluorocarbon gas can be obtained.

  When the zeolite 4A and activated carbon are layered and packed in the downstream adsorption tower, nitrogen gas can be adsorbed very effectively to obtain a high-purity perfluorocarbon gas.

  When the downstream adsorption tower is filled with zeolite 4A on the upstream side with respect to the gas flow and activated carbon is filled on the downstream side, the nitrogen gas is adsorbed very effectively and a high-purity par A fluorocarbon gas can be obtained.

  When the zeolite 4A and activated carbon are approximately half packed in the adsorption tower on the downstream side, nitrogen gas can be adsorbed very effectively to obtain a high-purity perfluorocarbon gas.

  In the present invention, the activated carbon is formed into a granular mixture of a thermosetting phenol resin powder, a thermosetting resin solution, and a polymer binder in a granular form, and is 500 to 500 in a non-oxidizing atmosphere or a weak oxidizing atmosphere. When the primary heat treatment is performed at a temperature of 1100 ° C. and the secondary heat treatment is performed at a temperature of 150 to 1000 ° C. for 30 to 240 minutes in a weakly oxidizing atmosphere, the secondary heat treatment is performed. Pore diameter is considered to be reasonably large, sufficient nitrogen adsorption rate is obtained, and when the gas to be treated is brought into contact with activated carbon, nitrogen is not sufficiently adsorbed and cannot be separated and purified with sufficient purity Or the problem that the desorption of the adsorbed nitrogen is too slow and it takes too much time in the entire process including the regeneration process of the activated carbon is solved. Moreover, adsorption of perfluorocarbon gas can also be prevented. For this reason, perfluorocarbon gas can be separated and purified with high purity efficiently in a short time.

  In the present invention, the activated carbon has an adsorption rate of nitrogen when the initial introduction pressure is 552.501 kPa when the adsorption time from the start of adsorption is 0.2% with respect to the total adsorption time until the adsorption equilibrium time. When the adsorption amount is 10% or more of the total adsorption amount at equilibrium, when the gas to be treated is brought into contact with the activated carbon, nitrogen is not sufficiently adsorbed and cannot be separated and purified with sufficient purity. Or, the problem that the desorption of the adsorbed nitrogen is too slow and it takes too much time in the entire process including the regeneration process of activated carbon can be solved, and the perfluorocarbon gas can be separated and purified with high purity efficiently in a short time. become.

It is a systematic diagram which shows an example of the separation production | generation apparatus of the perfluorocarbon gas of this invention. It is process drawing of the separation production | generation using the said separation production | generation apparatus. It is a figure explaining a 1st step. It is a figure explaining a 2nd step. It is a figure explaining a 3rd step. It is a figure explaining a 4th step. It is a figure explaining a 5th step. It is a figure explaining a 6th step. It is a figure explaining a 7th step. It is a figure explaining an 8th step. It is a figure which shows the adsorption isotherm of zeolite 4A. It is a figure which shows the adsorption isotherm of activated carbon. It is a figure which shows the adsorption isotherm of the zeolite 5A. It is a figure which shows the packing state in the 2nd stage adsorption tower.

Explanation of symbols

1A, 1B, 1C, 1D: Inlet valves 2A, 2B, 2C, 2D: Exhaust valves 3A, 3B, 3C, 3D: Vacuum exhaust valves 4A, 4B, 4C, 4D: Purge valves 5A, 5B, 5C, 5D: Return Pressure valves 6A, 6B, 6C, 6D: Deriving valves 7A, 7B, 7C, 7D: Pressure equalizing valve 8: First on-off valve 9: Second on-off valves 10A, 10B, 10C, 10D: Adsorption tower 11: Vacuum pump 12: Introduction Path 13: Derivation path 14: Pressure return path 15: Purge paths 16A, 16B, 16C, 16D: Pressure equalization path 17: Discharge path 18: Vacuum exhaust path

Claims (11)

From the gas to be treated containing nitrogen gas as an impure component to CF ₄ and C ₂ F ₆ which are perfluorocarbon gases having a molecular weight of 140 or less, the impure component nitrogen gas is removed by adsorbing to zeolite 4A, A method for purifying perfluorocarbon gas, wherein the perfluorocarbon gas is separated and purified.   The perfluorocarbon gas according to claim 1, wherein an adsorption step of removing nitrogen gas, which is an impure component, is adsorbed on the zeolite 4A, and a desorption step of desorbing the nitrogen gas adsorbed on the zeolite 4A under reduced pressure. Purification method. The method for purifying perfluorocarbon gas according to claim 1 or 2, wherein the concentration of the perfluorocarbon gas is 85 vol% or more and 99 vol% or less.   A plurality of adsorption towers filled with an adsorbent are connected in series to perform adsorption in a plurality of stages, adsorbing nitrogen gas with the zeolite 4A in the adsorption tower arranged on the upstream side, and adsorption tower arranged on the downstream side Then, the purification method of the perfluorocarbon gas as described in any one of Claims 1-3 which adsorb | sucks nitrogen gas using activated carbon.   The method for purifying perfluorocarbon gas according to claim 4, wherein the downstream adsorption tower uses both zeolite 4A and activated carbon to adsorb nitrogen gas.   The method for purifying perfluorocarbon gas according to claim 5, wherein the downstream adsorption tower is filled with zeolite 4A and activated carbon laminated in layers.   The method for purifying perfluorocarbon gas according to claim 6, wherein the downstream adsorption tower is filled with zeolite 4A on the upstream side with respect to the gas flow and with activated carbon on the downstream side.   The method for purifying perfluorocarbon gas according to claim 7, wherein the downstream adsorption tower is filled with approximately half of zeolite 4A and activated carbon. An apparatus for separating and purifying the perfluorocarbon gas from a gas to be treated containing nitrogen gas as an impure component with respect to CF ₄ and C ₂ F ₆ which are perfluorocarbon gases having a molecular weight of 140 or less. An apparatus for purifying perfluorocarbon gas, which is filled with zeolite 4A for adsorbing and removing nitrogen gas.   The perfluorocarbon gas according to claim 9, wherein an adsorption step of removing nitrogen gas, which is an impurity component, is adsorbed on the zeolite 4A, and a desorption step of desorbing the nitrogen gas adsorbed on the zeolite 4A under reduced pressure. Purification equipment.   A plurality of adsorption towers filled with an adsorbent are connected in series to perform adsorption in a plurality of stages, adsorbing nitrogen gas with the zeolite 4A in the adsorption tower arranged on the upstream side, and adsorption tower arranged on the downstream side The apparatus for purifying perfluorocarbon gas according to claim 9 or 10, wherein activated carbon is used to adsorb nitrogen gas.

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