JP2004035423A - Method for purifying tetrafluoroethylene and method for purifying hexafluoropropylene - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To efficiently purify tetrafluoroethylene from a gas mixture containing carbon monoxide. <P>SOLUTION: A thermal decomposition product of chlorodifluoromethane is distilled under pressure and then introduced into a gas separation membrane module (module) 9 containing a hollow fiber membrane made of a polyimide. A gas discharged from the module 9 through a gas flow control valve 10 contains a component (tetrafluoroethylene, etc.) other than the carbon monoxide and is returned to a gas holder again. The tetrafluoroethylene in the gas discharged through the gas flow control valve 10 is concentrated by repeating a step from the gas holder 1 to the gas separation membrane module 9. The tetrafluoroethylene discharged through the gas flow control valve 10 is suitably collected from a sampling valve 14. <P>COPYRIGHT: (C)2004,JPO

Description

【００３２】
但し、表中において、
濃度（％）：
ガスクロマトグラフィによる測定濃度
入口濃度：
モジュール９に流入するガス中の濃度
ＴＦＥ回収率（％）：
１００×非透過側ガス流量×ＴＦＥ濃度／（非透過側ガス流量×ＴＦＥ濃度＋透過側ガス流量×ＴＦＥ濃度）
ＣＯ除去率（％）：
１００×透過側ガス流量×ＣＯ濃度／（非透過側ガス流量×ＣＯ濃度＋透過側ガス流量×ＣＯ濃度）
ＴＦＥ入口濃度（％）：
（非透過側ガス流量×ＴＦＥ濃度＋透過側ガス流量×ＴＦＥ濃度）／（非透過側ガス流量＋透過側ガス流量）
ＣＯ入口濃度（％）：
（非透過側ガス流量×ＣＯ濃度＋透過側ガス流量×ＣＯ濃度）／（非透過側ガス流量＋透過側ガス流量）
ＣＯ残留分率（％）：
「Ｙ＝１−（ＣＯ除去率／１００）」とすると、
リサイクルｎ回目の入口ＣＯ残留率（％）＝１００×Ｙ^ｎ、
ＴＦＥロス分率＝１−（ＴＦＥ回収率／１００）であるから、
リサイクルｎ回目のＴＦＥロス率（％）＝１００×（ＴＦＥ入口濃度／ＣＯ入口濃度）×［１−（ＴＦＥ回収率／１００）］×Ｙ^ｎ
リサイクルｎ回目のＴＦＥ回収率（％）＝ＴＦＥ回収率−１００×（ＴＦＥ入口濃度／ＣＯ入口濃度）×（１−ＴＦＥ回収率／１００）×ΣＹ^ｋ　（ここで、ｋ＝１〜ｎ）
ΣＹ^ｋ＝［Ｙ−Ｙ^ｎ＋１］となり、
０＜Ｙ＜１だから、ｎ→∞のとき、ｌｉｍＹ^ｎ＋１＝０となる。
故に、
ｎ→∞のとき、ｌｉｍＹ^ｋ＝Ｙ／（１−Ｙ）＝［１−（ＣＯ除去率／１００）］／（ＣＯ除去率／１００）
である。
【００３３】
すなわち、ｎ→∞のとき、リサイクルｎ回目のＴＦＥ回収率（％）＝ＴＦＥ回収率−１００×（ＴＦＥ入口濃度／ＣＯ入口濃度）×［１−（ＴＦＥ回収率／１００）］×［１−（ＣＯ除去率／１００）］／（ＣＯ除去率／１００）となる。
【００３４】
とくに、表中における実施例４の条件を採用した場合、ポリイミド製中空糸膜を採用しない従来の精製工程に比べ約半分のＣＯ排出量に対して、９０％以上のＴＦＥ回収率が得られることが、発明者らによって確認された。このように、本実施の形態にかかる精製方法を採用することで、製造原価の低減や、環境保全といった観点において極めて高い効果を奏することができる。
【００３５】
とくに、既存設備の大幅な変更を伴うことなく、簡易且つ安価な方法で、既存設備から排出されるテトラフルオロエチレンを効率的に回収し、且つ、一酸化炭素を外部に排出することなく確実に除害設備に送ることができる。
【００３６】
なお、クロロジフルオロメタンの熱分解生成物（ガス）をガスホルダ１に貯蔵する工程に替え、テトラフルオロエチレンの熱分解生成物（ガス）をガスホルダ１に貯蔵し、図１にかかる作業工程と同様の作業工程を実行してもよい。これにより、本実施の形態と同等に、若しくはこれに準じて、ヘキサフルオロプロピレンを主成分とするテトラフルオロエチレンの熱分解生成物から、効率的にヘキサフルオロプロピレンを回収し、且つ、一酸化炭素を外部に排出することなく確実に除害設備に送ることができる。
【００３７】
また、本実施の形態において、モジュール９を通過するガスをプレヒータ６により予熱することとした。このような予熱を行わなくとも、テトラフルオロエチレンやヘキサフルオロプロピレンを一酸化炭素と分離する上で十分な効果を得ることはできるが、３０〜１００℃に予熱を行うことでポリイミド中空糸膜の分離性能を最適化できることが、本発明者らによって確認されている。
【００３８】
また、モジュール９に内蔵される膜構造としては、ポリイミドを主成分とする種々の中空糸膜を適用することができる。
【００３９】
【発明の効果】
以上説明したように、第１の発明によれば、簡易且つ安価な方法により、一酸化炭素を含んだテトラフルオロエチレンのガス混合物からテトラフルオロエチレンを効率的に精製することができる。
第２の発明によれば、簡易且つ安価な方法により、一酸化炭素を含んだヘキサフルオロプロピレンのガス混合物からヘキサフルオロプロピレンを効率的に精製することができる。
【００４０】
【図面の簡単な説明】
【図１】クロロジフルオロメタンの熱分解生成物からテトラフルオロエチレンを精製する方法として、一連の作業工程を実行する上で必要な設備を示す略図。
【符号の説明】
１　　　ガスホルダ
２　　　圧縮機
３　　　液化凝縮器
３ａ　　　非凝縮性ガス抜き口
４　　　加圧蒸留塔
４ａ　　　塔頂ガス抜き口
５　　　プレフィルタ
６　　　プレヒータ
７　　　圧力計
８　　　温度計
９　　　ガス分離膜モジュール
９ａ　　　非透過側出口
９ｂ　　　透過側出口
１０，１１　　　ガス流量制御弁
１２，１３　　　ガス流量計
１４　　　サンプリング弁[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for purifying tetrafluoroethylene from a thermal decomposition product of chlorofluoromethane, or a method of purifying hexafluoropropylene from a thermal decomposition product of tetrafluoroethylene, the method comprising the steps of: The present invention relates to a method for recovering tetrafluoroethylene and the like discharged together with carbon monoxide from a vent or a vent at the top of a pressure distillation column.
[0002]
[Prior art]
Generally, tetrafluoroethylene (hereinafter abbreviated as TFE) is produced by thermally decomposing chlorodifluoromethane (hereinafter abbreviated as R22), and purifying and separating the reaction product by distillation or the like. Hexafluoropropylene (hereinafter abbreviated as HFP) is produced by thermally decomposing TFE and purifying and separating the reaction product by distillation or the like.
[0003]
Since the thermal decomposition of TFE and R22 is performed at a high temperature of 600 to 900 ° C., many by-products are generated, and the recovery of TFE and HFP is deteriorated.
[0004]
Industrially, in order to suppress the generation of this by-product, the yield is improved by a method of mixing a raw material with a diluent such as an inert gas and subjecting it to thermal decomposition. Since the thermal decomposition reaction of R22 is an endothermic reaction, TFE generally dilutes R22 with superheated steam at 800 to 1100 ° C. and performs thermal decomposition. At this time, the water vapor is considered to be almost inert, but a small amount of carbon monoxide (hereinafter abbreviated as CO) is by-produced by the water gas reaction.
[0005]
Since the TFE pyrolysis reaction is an exothermic reaction, in order to generate HFP, an increase in by-products due to the over-decomposition of TFE using CO, a high-boiling by-product, and the like, which are by-produced in the production of TFE as raw materials. In general, TFE is thermally decomposed by externally heating while suppressing the temperature.
[0006]
[Problems to be solved by the invention]
By the way, CO as a by-product or CO contained in a raw material is used to purify a reaction product when a non-condensable gas vent of a liquefied condenser or a gas vent at the top of a pressure distillation column. Is discharged from With the emission of CO, 3 to 7% of the produced TFE and unreacted TFE are emitted to the outside of the system accompanying the CO, which deteriorates the production cost of TFE and HFP, and reduces global warming and the like. Environmental protection, such as depletion of the ozone layer, is also a serious problem.
[0007]
In recent years, TFE and R22 have been described as those that may impair human health or hinder the inhabitation and growth of animals and plants. Designated as a Class 1 Designated Chemical Substance under the Law (PRTR), the 2000 PRTR Pilot Project Report states that TFE emissions are 1,720 tons / year, No. 10.
[0008]
To solve such a problem, various methods have been proposed for recovering TFE. Typical examples thereof include an absorption method using a perhalogenated carbohydrate (Japanese Patent Publication No. 48-10444) and an octafluorocyclobutane (hereinafter abbreviated as C318) conversion method by heating TFE (Japanese Patent Publication No. 62-7175). )It has been known.
[0009]
However, all of these methods have high equipment costs and operating costs, and the production costs of TFE and HFP are relatively high. Therefore, there is a concern that the desire of manufacturers, etc. to voluntarily and proactively engage in environmental conservation will decrease. is there.
[0010]
The present invention has been made in view of such circumstances, and an object thereof is to efficiently purify tetrafluoroethylene from a gas mixture containing carbon monoxide.
Another object of the present invention is to efficiently purify hexafluoropropylene from a gas mixture containing carbon monoxide.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, (1) a first invention is a method for purifying tetrafluoroethylene from a thermal decomposition product of chlorofluoromethane, especially a thermal decomposition product of chlorodifluoromethane, comprising: Liquefaction condensation or pressure distillation of the gas mixture obtained by thermally decomposing the non-condensable component obtained by the liquefaction condensation or the distillation component obtained by the pressure distillation to a polyimide hollow fiber membrane. And separating carbon monoxide from the component containing tetrafluoroethylene.
[0012]
Further, in the above purification method, prior to passing the non-condensable component obtained by the liquefaction condensation or the distillation component obtained by the pressure distillation through the hollow fiber membrane made of polyimide, the non-condensable component or the distillation component is removed. It is preferable to include a step of preheating to 30 to 100 ° C.
[0013]
According to the above configuration, not only can the efficiency of the entire operation step of purifying tetrafluoroethylene from a gas mixture of tetrafluoroethylene containing carbon monoxide be improved through a gas separation step using a hollow fiber membrane made of polyimide, Carbon monoxide as a by-product is also reliably removed.
[0014]
(2) A second invention is a method for purifying hexafluoropropylene from a pyrolysis product of tetrafluoroethylene, wherein a gas mixture obtained by pyrolyzing tetrafluoroethylene is liquefied or condensed or pressurized. A step of distillation, and a non-condensable component obtained by the liquefaction condensation or a distillation component obtained by the pressure distillation is passed through a polyimide hollow fiber membrane to separate a component containing hexafluoropropylene and carbon monoxide. And a step of performing the above.
[0015]
Further, in the above purification method, prior to passing the non-condensable component obtained by the liquefaction condensation or the distillation component obtained by the pressure distillation through the hollow fiber membrane made of polyimide, the non-condensable component or the distillation component is removed. It is preferable to include a step of preheating to 30 to 100 ° C.
[0016]
According to the above configuration, not only can the efficiency of the entire working process of purifying hexafluoropropylene from a gas mixture of hexafluoropropylene containing carbon monoxide be increased through a gas separation process using a hollow fiber membrane made of polyimide, Carbon monoxide as a by-product is also reliably removed.
[0017]
Note that the above configurations can be combined as much as possible. For example, when the thermal decomposition product of chlorofluoromethane contains tetrafluoroethylene and hexafluoropropylene, the gas separated from carbon monoxide by the purification method according to the first invention includes tetrafluoroethylene and hexafluoropropylene. And propylene. The gas mixture obtained by pyrolyzing this may be subjected to the purification method according to the second invention to purify hexafluoropropylene.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the present invention will be described.
[0019]
FIG. 1 is a schematic diagram showing equipment required for performing a series of operation steps as a method for purifying tetrafluoroethylene (TFE) from a thermal decomposition product of chlorodifluoromethane.
[0020]
In this work process, the pyrolysis gas is temporarily stored in a gas holder 1 through an absorption (deoxidation) / adsorption (drying) process, and is pressurized by a compressor 2, and then is pressurized by a well-known liquefied condenser 3 or pressurization. It is sent to the still 4 for purification.
[0021]
The carbon monoxide (CO) accumulated in the upper portion of the liquefied condenser 3 or the pressure distillation column 4 is intermittently, semi-continuously or continuously mixed with the non-condensable gas vent 3a of the liquefied condenser 3 or the heat exchanger. It is discharged to the outside from the top gas vent 4a of the pressure distillation column 4.
[0022]
The discharged CO is removed by a pre-filter 5 and further pre-heated by a pre-heater 6, and then introduced into a gas separation membrane module (hereinafter abbreviated as a module) 9 containing a polyimide hollow fiber membrane. A pressure gauge 7 for monitoring the pressure of the gas introduced into the module 9 and a thermometer 8 for monitoring the temperature of the gas also introduced into the module 9 are provided on the way from the preheater 6 to the module 9. Is provided.
[0023]
The module 9 has an outlet (non-permeate side outlet) 9a for gas (non-permeate gas) discharged without permeating through the internal hollow fiber membrane (not shown) and a gas permeating and discharging through the internal hollow fiber membrane. Outlet (permeate side outlet) 9b for the gas (permeate gas).
[0024]
A gas flow control valve 10 and a gas flow control valve 11 are provided at the non-permeate-side outlet 9a and the permeate-side outlet 9b, respectively, to adjust the residence time of the gas introduced into the module 9 in the module 9. The gas flow meters 12 and 13 are used to monitor the flow rate of gas discharged through the respective gas flow control valves 10 and 11.
[0025]
The gas discharged through the gas flow control valve 10 contains components other than CO (such as TFE) and is returned to the gas holder 1 again. The more the process from the gas holder 1 to the module 9 is repeated, the more the TFE and the like in the gas discharged through the gas flow control valve 10 are concentrated. Gas (such as TFE) discharged through the gas flow control valve 10 is sampled from the sampling valve 14 as appropriate.
[0026]
On the other hand, the gas discharged through the gas flow control valve 11 contains CO concentrated in the module 9. The gas discharged through the gas flow control valve 11 is sent to an abatement equipment (not shown), and is finally discharged into the atmosphere.
[0027]
In addition, a further gas separation membrane module may be installed downstream of the non-permeate side outlet 9a and the permeate side outlet 9b to further enhance the efficiency of the concentration of CO, TFE and the like.
[0028]
(Gas separation membrane module)
In the present embodiment, a commercially available N2 separator (NM-C05A: manufactured by Ube Industries, Ltd.) was used as the gas separation membrane module 9. The relative permeation speed of various gases permeating the polyimide separation membrane used in the module 9 is shown below.
[0029]
(Fast) H ₂ O (1.1 × 10 ⁻⁹ )> H ₂ (1.1 × 10 ⁻⁷ )> He (9 × 10 ⁻⁸ )> CO ₂ (10 ⁻⁸ )> O ₂ (4. 2 × 10 ⁻⁹ )> Ar (1.5 × 10 ⁻⁹ )> CO (1.1 × 10 ⁻⁹ )> N ₂ (6 × 10 ⁻¹⁰ )> Hydrocarbons C ₂ H ₄ (5 × 10 ⁻⁹ ) ⁻¹⁰ ), CH ₄ (4 × 10 ⁻¹⁰ ), C ₂ H ₆ (1.1 × 10 ⁻¹⁰ ) (slow)
However, the numerical value in parentheses means a unit (Nm ³ / m ² · sec · mmHg) as the transmission rate data at 60 ° C. of the A-type membrane (Source: Catalog of polyimide gas separation membrane Ube Industries, Ltd.).
[0030]
Table 1 shows that each of the working examples 1 to 7 in which the setting conditions of the temperature, the pressure, and the flow rate of the gas passing through the module 9 were changed and the above-described working steps were performed, the respective setting conditions, and the TFE collection corresponding to the respective setting conditions. The rate and the CO removal rate are also shown.
[0031]
[Table 1]

[0032]
However, in the table,
concentration(%):
Inlet concentration measured by gas chromatography:
Concentration TFE recovery rate (%) in gas flowing into module 9:
100 × non-permeate gas flow rate × TFE concentration / (non-permeate gas flow rate × TFE concentration + permeate gas flow rate × TFE concentration)
CO removal rate (%):
100 × permeate gas flow rate × CO concentration / (non-permeate gas flow rate × CO concentration + permeate gas flow rate × CO concentration)
TFE inlet concentration (%):
(Non-permeate gas flow rate x TFE concentration + permeate gas flow rate x TFE concentration) / (non-permeate gas flow + permeate gas flow)
CO inlet concentration (%):
(Non-permeate gas flow rate × CO concentration + permeate gas flow rate × CO concentration) / (non-permeate gas flow + permeate gas flow)
CO residual fraction (%):
When “Y = 1− (CO removal rate / 100)”,
N-th inlet CO residual ratio (%) = 100 × Y ⁿ ,
Since TFE loss fraction = 1− (TFE recovery rate / 100),
TFE loss rate (%) at the n-th recycling = 100 × (TFE inlet concentration / CO inlet concentration) × [1- (TFE recovery rate / 100)] × Y ⁿ
TFE recovery rate (%) at the n-th recycling = TFE recovery rate−100 × (TFE inlet concentration / CO inlet concentration) × (1−TFE recovery rate / 100) × ΣY ^k (where k = 1 to n)
ΣY ^k = [Y−Y ^{n + 1} ], and
Since 0 <Y <1, limY ^{n + 1} = 0 when n → ∞.
Therefore,
When n → ∞, limY ^k = Y / (1-Y) = [1- (CO removal rate / 100)] / (CO removal rate / 100)
It is.
[0033]
That is, when n → ∞, the TFE recovery rate (%) at the n-th recycling = TFE recovery rate−100 × (TFE inlet concentration / CO inlet concentration) × [1- (TFE recovery rate / 100)] × [1- (CO removal rate / 100)] / (CO removal rate / 100).
[0034]
In particular, when the conditions of Example 4 in the table are adopted, a TFE recovery rate of 90% or more can be obtained for about half of the CO emission compared to the conventional purification step that does not employ the hollow fiber membrane made of polyimide. Was confirmed by the inventors. As described above, by employing the purification method according to the present embodiment, it is possible to achieve extremely high effects in terms of reduction of manufacturing cost and environmental conservation.
[0035]
In particular, it is possible to efficiently recover tetrafluoroethylene discharged from existing equipment without a significant change in existing equipment, and to reliably recover carbon monoxide without discharging carbon monoxide to the outside. Can be sent to abatement equipment.
[0036]
In addition, instead of the step of storing the pyrolysis product (gas) of chlorodifluoromethane in the gas holder 1, the pyrolysis product (gas) of tetrafluoroethylene is stored in the gas holder 1, and the same as the operation process according to FIG. Work steps may be performed. Thereby, hexafluoropropylene is efficiently recovered from the pyrolysis product of tetrafluoroethylene containing hexafluoropropylene as a main component, and carbon monoxide is equivalent to or similar to this embodiment. Can be reliably sent to the abatement equipment without discharging to the outside.
[0037]
In the present embodiment, the gas passing through the module 9 is preheated by the preheater 6. Even without performing such preheating, a sufficient effect can be obtained in separating tetrafluoroethylene and hexafluoropropylene from carbon monoxide.However, by performing preheating at 30 to 100 ° C., the polyimide hollow fiber membrane can be obtained. It has been confirmed by the present inventors that the separation performance can be optimized.
[0038]
Further, as the membrane structure incorporated in the module 9, various hollow fiber membranes containing polyimide as a main component can be applied.
[0039]
【The invention's effect】
As described above, according to the first invention, tetrafluoroethylene can be efficiently purified from a gas mixture of tetrafluoroethylene containing carbon monoxide by a simple and inexpensive method.
According to the second invention, hexafluoropropylene can be efficiently purified from a gas mixture of hexafluoropropylene containing carbon monoxide by a simple and inexpensive method.
[0040]
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing equipment required for performing a series of operation steps as a method for purifying tetrafluoroethylene from a thermal decomposition product of chlorodifluoromethane.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Gas holder 2 Compressor 3 Liquefied condenser 3a Non-condensable gas vent 4 Pressurized distillation column 4a Top gas vent 5 Prefilter 6 Preheater 7 Pressure gauge 8 Thermometer 9 Gas separation membrane module 9a Non-permeate side outlet 9b Permeation Side outlet 10, 11 Gas flow control valve 12, 13 Gas flow meter 14 Sampling valve

Claims (4)

A method for purifying tetrafluoroethylene from a pyrolysis product of chlorofluoromethane,
Liquefaction condensation or pressure distillation of a gas mixture obtained by pyrolyzing chlorofluoromethane, and
Passing a non-condensable component obtained by the liquefaction condensation or a distillation component obtained by the pressure distillation through a polyimide hollow fiber membrane, and separating a component containing tetrafluoroethylene and carbon monoxide,
And a method for purifying tetrafluoroethylene. Prior to passing the non-condensable component obtained by liquefaction condensation or the distillation component obtained by pressure distillation through a polyimide hollow fiber membrane, the non-condensable component or the distillation component is preheated to 30 to 100 ° C. The method for purifying tetrafluoroethylene according to claim 1, comprising a step. A method for purifying hexafluoropropylene from a pyrolysis product of tetrafluoroethylene,
Liquefaction condensation or pressure distillation of the gas mixture obtained by pyrolysis of tetrafluoroethylene, and
Passing a non-condensable component obtained by the liquefaction condensation or a distillation component obtained by the pressure distillation through a polyimide hollow fiber membrane, and separating a component containing hexafluoropropylene and carbon monoxide,
A method for purifying hexafluoropropylene comprising: Prior to passing the non-condensable component obtained by liquefaction condensation or the distillation component obtained by pressure distillation through a polyimide hollow fiber membrane, the non-condensable component or the distillation component is preheated to 30 to 100 ° C. The method for purifying hexafluoropropylene according to claim 3, comprising a step.

Images