JP4518460B2 - Method for selectively recovering fluorine components from exhaust gas - Google Patents

Description

【００２４】
本発明では、水素を含む化合物として水蒸気を添加して分解することもできる。この場合、排ガス中の硫黄分はＳＯｘ（ＳＯ_２およびＳＯ_３）となる。
【００２５】
本発明において、ＨＦだけを選択的に吸収させる固体吸収剤としては、Ｎａ、Ｌｉ、Ｋ、Ｃａ、Ｍｇ及びＳｉよりなる群から選ばれる１種の炭酸塩、Ｎａ、Ｌｉ、Ｋ、Ｃａ、Ｍｇ及びＳｉよりなる群から選ばれる１種の酸化物、又は炭酸水素ナトリウムなどが挙げられる。好ましくは、炭酸ナトリウム、炭酸水素ナトリウム、炭酸カルシウム、酸化カルシウムである。これらの固体吸収剤は、固体の状態で用いなければならない。水溶液の状態で用いられると、ＨＦと硫黄化合物の両方吸収してしまい、分離することができないからである。
【００２６】
また、固体吸収剤は、粒状であることが好ましい。これは、表面積が大きくなり吸収しやすくなるからである。
【００２７】
本発明においては、フッ素硫黄含有ガスの水素添加による分解により生成したＨＦと、これにともない生成した硫黄化合物の反応性の違いを利用している。固体吸収剤とこれらとの接触反応を、反応性の高いＨＦだけが反応し、硫黄化合物とは反応しない温度で行い、ＨＦだけを選択的に吸収させることにより、ＨＦと硫黄化合物を分離する。したがって、接触反応させる際の温度は、硫黄化合物と固体吸収剤が反応できず、かつＨＦと固体吸収剤とが反応できる温度でなければならない。
【００２８】
フッ素硫黄含有ガスを水素の添加により分解してＨＦとＨ_２Ｓが生成した場合、固体吸収剤に吸収させる温度の好ましい範囲は、２００℃〜８００℃、更に好ましくは２００〜５００℃、特に好ましくは２００〜３００℃である。
【００２９】
図２はＨ_２Ｓ１モル、ＨＦ６モル、Ｎａ_２ＣＯ_３５モルの１気圧での化学平衡組成を示したものである。図２から、炭酸ナトリウムは２００℃〜８００℃の広範囲で、ＨＦと反応しＮａＦとなるが、Ｈ_２Ｓとは殆ど反応せず、Ｈ_２Ｓはガス状が安定であることがわかる。６００℃以下では炭酸ナトリウムとＨ_２Ｓは全く反応せず、また、３００℃〜６００℃で、炭酸ナトリウムはＨＦと良く反応する。したがって、炭酸ナトリウムの場合、接触反応における好ましい温度の範囲は２００℃〜８００℃、更に好ましくは２００℃〜５００℃、特に好ましくは２００℃〜３００℃である。
【００３０】
また、炭酸カルシウム、酸化カルシウムの場合は、２００℃〜６００℃でＨ_２Ｓとは反応せず、ＨＦとは２００℃〜６００℃で良く反応する。カルシウム系の固体吸収剤の場合は、２００℃〜６００℃で接触反応させて吸収させることが好ましく、更に好ましくは、２００℃〜５００℃、特に好ましくは２００℃〜３００℃である。
【００３１】
また、炭酸カルシウムを用い、５００℃でＨＦとＳＯｘを分離することもできた。
【００３２】
このようにして温度条件を管理することにより、ＨＦのみが選択的に固体吸収剤に固定化され、排ガス中からフッ素成分を分離回収することができる。
【００３３】
ＨＦを固体吸収剤に固定化し分離する工程の後に、更に固体吸収剤に固定化されない硫黄化合物を処理する工程を設けることが好ましい。通常行われるような酸性ガスを除去する処理工程と同様に行えばよい。例えば、Ｈ_２Ｓの場合、燃焼させてＳＯｘとした後、以下のように炭酸カルシウム溶液等と反応させれば、石膏（ＣａＳＯ_４）として回収することができ、再資源化できる。
【００３４】
ＳＯ_２＋ＣａＣＯ_３＋１／２Ｏ_２ → ＣａＳＯ_４＋ＣＯ_２
【００３５】
図１に、本発明の分離回収の処理システムの１例のフローを示す。
【００３６】
それぞれ入口１、入口２から入ったＳＦ_６、Ｈ_２は、高温熱分解炉３に導入され、ＳＦ_６は分解されてＨ_２Ｓ、ＨＦが生成する。生成したＨ_２Ｓ、ＨＦは入口７から導入された空気と共に２００℃〜８００℃に調整された固定化反応槽４に導入され、ここでＨＦのみが炭酸ナトリウムや炭酸カルシウム等の固体吸収剤に吸収され、固定化される。また、Ｈ_２Ｓは固定化反応槽４内で燃焼しＳＯｘとなる。以下に示す反応によりフッ化ナトリウムやフッ化カルシウムが生成する。炭酸ナトリウムの場合、９０％以上の純度のフッ化ナトリウムが得られた。
【００３７】
２ＨＦ＋２Ｎａ_２ＣＯ_３ → ２ＮａＦ＋Ｈ_２Ｏ＋２ＣＯ_２＋１／２Ｏ_２
２ＨＦ＋２ＣａＣＯ_３ → ２ＣａＦ_２＋Ｈ_２Ｏ＋ＣＯ_２
これらのフッ化化合物を回収することにより、排ガスからフッ素分のみを、硫黄成分と分離して除去回収することができる。ＮａＦは、さらにまた、以下の反応式に示す炭酸カルシウム溶液との反応によりＣａＦ_２に転換することが好ましく、これにより高純度のＣａＦ_２が得られ、再資源化することができる。
【００３８】
２ＮａＦ＋ＣａＣＯ_３＋Ｈ_２Ｏ → ＣａＦ_２＋２ＮａＯＨ＋ＣＯ_２
【００３９】
固定化反応槽４内で燃焼しなかったＨ_２ＳおよびＳＯｘはともに吸収されず、ガス状のまま固定化反応槽４を出る。これを吸収反応槽５に導き炭酸カルシウム溶液と反応させ、濾過器６で濾過して石膏として回収する。このように、硫黄化合物を処理する工程をもつ方法により、フッ化物、硫黄化合物を別々に分離回収することができ、それぞれの高純度の化合物が得られ、再資源化することができる。
【００４０】
次に、本発明の水を用いたフッ素の選択的回収方法について説明する。
【００４１】
この方法では、前述の固体吸収剤を用いる方法と同様にフッ素硫黄含有ガスを分解するが、硫黄化合物としてＨ_２Ｓを生成させるためにＨ_２を添加して加熱分解する。水を添加すると、ＳＯｘが生成してしまうので用いることはできない。加熱方法は前述の方法と同様に行える。Ｈ_２ガスの量は、フッ素硫黄含有ガス中のフッ素、硫黄がすべてＨＦ、Ｈ_２Ｓになる量を添加して、ＨＦ、Ｈ_２Ｓだけを生成させ、固体吸収剤の代わりに水にＨＦを選択的に吸収させる。従来の排ガスの処理では、分解するために水蒸気または空気を添加しているためＨＦとともにＳＯｘが生成し、ＨＦとともにＳＯｘも水に吸収されるため、これらを分離することはできなかった。
【００４２】
本発明の方法では、ＨＦのみを水に溶解させ分離する。Ｈ_２Ｓの水およびＨＦ水溶液への溶解度が極端に小さいことによりＨＦとＨ_２Ｓを分離できる。
【００４３】
図６に本発明の方法の１例のフローの概略図を示す。ここでは排ガスとしてＳＦ_６を用いている。ＳＦ_６はＨ_２の存在下、黒鉛発熱体を用いた熱分解炉１５で分解される。分解により生成したＨＦ及Ｈ_２Ｓは、水好ましくは脱塩水の入った吸収槽２４に導入される。ＨＦは極めて水に溶解しやすいのに対して、他方、Ｈ_２Ｓは水に極めて溶解しにくいため、Ｈ_２Ｓガスとして分離できる。水に吸収されずに分離されたＨ_２Ｓガスは、燃焼炉２５で燃焼してＳＯｘとした後、一般的な石灰石石膏法を用いて吸収反応槽５で石膏とし、回収できる。この工程は、前述した固体吸収剤を用いる方法で述べたものと同様である。
【００４４】
分離した後のフッ酸水はそのまま再利用するか、固定化材料と反応させて再資源化することができる。
【００４５】
ＨＦを水に吸収させ分離する工程の後に、吸収されないＨ_２Ｓを処理する工程を設けることが好ましい。この工程は、前述した固体吸収剤を用いる方法で述べたものと同様である。
【００４６】
この水を用いた方法は、比較的簡単にＨＦとＨ_２Ｓを分離できるという利点がある。一方、前述の固体吸収剤を用いる方法は、分離条件を固体吸収剤の種類により調整しなければならないが、フッ素化合物の分離・固定化方法を同時にかつ乾式で行うことができ、再資源化を目的としたシステムを簡略化することができるという利点がある。
【００４７】
本発明のいずれの方法でも、排ガス中のＨＦと硫黄化合物を分離して回収することができる。
【００４８】
【実施例】
本発明について以下に実施例を挙げて説明するが、本発明はこれに限定されるものではない。
【００４９】
（実施例１）
図３で用いたＳＦ_６ガスの熱分解炉の後段にアルミナ製セラミックチューブを有する固定化反応炉を設け、ＳＦ_６分解ガスの吸収実験を行った。そのフロー図を図４に、試験条件を表２に示す。
【００５０】
【表２】

【００５１】
図４において、１０、１１、１２はそれぞれ、Ａｒ、ＳＦ_６、Ｈ_２ボンベであり、１５は熱分解炉、４は固定化反応炉である。固定化反応炉は電気炉２０によって加熱される。２１は外筒、２２は目皿、２３は内筒であり、すべて高純度アルミナ製である。内径３０ｍｍのアルミナ製チューブの中に目皿を固定し、その上に固体吸収剤として、炭酸水素ナトリウム（粒度：１．１８〜２．３６ｍｍ）を、１１６ｇ充填した。固定化反応炉の温度は３００℃に設定した。処理ガス成分は、Ａｒ：５００ｍl／ｍｉｎ、ＳＦ_６ ：２０ｍl／ｍｉｎ、Ｈ_２：８０ｍl／ｍｉｎとし、熱分解炉の温度は１１００℃で設定した。ここで、Ａｒは希釈用ガスとして用いている。また、空間速度は３８４ｈ^−１であった。この条件でＳＦ_６は１００％分解することを事前に確認している。固定化反応炉の出口ガス中に含まれるＨＦ、Ｈ_２Ｓガス濃度を１９のサンプリング点で検知管により確認した。図５にその試験結果を示す。また、図５にはＮａＨＣＯ_３がＨＦと反応する時の反応率の推定値（理論値）も示した。
【００５２】
固定化反応炉出口でのＨ_２Ｓガス濃度は、反応開始時から分析精度の範囲でほぼ一定値を示しているのに対して、ＨＦ濃度は全く検出できなかった。したがって、ＨＦガスとＨ_２Ｓの分離を確認した。この反応式を以下の示す。
【００５３】
６ＨＦ＋Ｈ_２Ｓ＋６ＮａＨＣＯ_３→６ＮａＦ＋Ｈ_２Ｓ＋６Ｈ_２Ｏ＋６ＣＯ_２
【００５４】
（実施例２）
図３と同様の装置により、１６の吸収槽に蒸留水を用い、ＳＦ_６の熱分解ガスの処理実験を行った。分解条件は表１の試験番号２と同様である。熱分解炉においてＳＦ_６の分解により生成したＨＦ、Ｈ_２Ｓのうち、ＨＦは全て蒸留水に吸収されることをフッ素のマスバランスから確認した。また、吸収液（ＨＦ濃度が約０．５％のフッ酸水）中のＨ_２Ｓをメチレンブルー吸光光度法により確認したところ検出されず、全く溶解していないことを確認した。したがって、ＳＦ_６がＨ_２とともに熱分解炉で分解することにより生成するＨＦとＨ_２Ｓが水により分離できることを確認した。
【００５５】
【発明の効果】
現在、電気絶縁ガスとして使われ、不純物の混入により再利用できないＳＦ_６ガスは、回収されて水蒸気を用いた湿式燃焼法で処理され生成物は廃棄物として処理されている。しかしながら、本発明により、ＳＦ_６などのフッ素と硫黄を含むガスからフッ素成分を選択的に固体吸収剤に吸収させて取り出すことができ、フッ素成分を硫黄成分と分離して回収できるため、再資源化が可能となるような硫黄成分の混在しない純度の高いフッ素化合物を得ることができる。また、更に、吸収されない硫黄成分のガスの処理工程を設ければ、排ガス中の硫黄成分をフッ化物の混在しない高純度の硫黄化合物として回収することができる。
【００５６】
また、固体吸収剤を用いる方法においては、分離と同時に高純度の再資源化生成物を直接得ることができるという大きなメリットがある。例えば、現状技術では、フロンの分解ガスのＨＦはいったん水に吸収させてフッ酸水とし、その後フッ酸水と炭酸カルシウムを湿式で反応させて蛍石としているが、未反応の炭酸カルシウムが蛍石の中に含まれ、純度もあまり高くない。本発明では、分解ガス中のＨＦガスを直接炭酸カルシウムと反応させることで、硫黄化合物との分離と蛍石の生成が同時にできる。また、得られる蛍石の純度も高くできる。
【００５７】
また、水素ガスを添加して、黒鉛発熱体を用いる本発明の分解方法は、コストがかからず酸素を含まない排ガスを熱分解することができ、本発明の排ガスからフッ素成分を選択的に回収する方法にも優れた方法である。
【００５８】
以上のように、本発明により、排ガスの処理によって得られる物質を再資源化することができ、二次廃棄物の低減と、資源の有効利用を図ることができる。
【図面の簡単な説明】
【図１】 本発明の固体吸収剤を用いて排ガスからフッ素成分を選択的に回収する方法の実施形態の一例を示す概略図である。
【図２】 Ｈ_２Ｓ、ＨＦおよびＮａ_２ＣＯ_３の化学平衡図である。
【図３】 ＳＦ_６ガスの熱分解試験のフローを示す概略図である。
【図４】 実施例１の方法のフローを示す概略図である。
【図５】 実施例１の試験結果を示すグラフである。
【図６】 本発明の水を用いて排ガスからフッ素成分を選択的に回収する方法の実施形態の一例を示す概略図である。
【符号の説明】
１ ＳＦ_６入口
２ Ｈ_２入口
３ 高温熱分解炉
４ 固定化反応槽
５ 吸収反応槽
６ 濾過器
７ 空気入口
１０ Ａｒボンベ
１１ ＳＦ_６ボンベ
１２ Ｈ_２ボンベ
１３ マスフローメーター
１４ 水柱マノメーター
１５ 熱分解炉
１６ 吸収槽
１７ ミスト除去槽
１８ 膜式流量計
１９ サンプリング点
２０ 電気炉
２１ 外筒
２２ 目皿
２３ 内筒
２４ 水の入った吸収槽
２５ 燃焼炉[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method of treating and recycling exhaust gas containing fluorine and sulfur having a high global warming potential, and more specifically, by separating and treating the fluorine component and the sulfur component for subsequent immobilization. The present invention relates to a method for increasing the purity of a fluoride or sulfur-added compound produced by treatment and recycling it.
[0002]
[Prior art]
A typical greenhouse gas containing a sulfur component and a fluorine component is SF ₆ gas. SF ₆ gas has high insulation performance and arc extinguishing performance, and is widely used in high voltage equipment and circuit breakers. Further, it is used as a gas having excellent etching characteristics together with CF ₄ in the semiconductor manufacturing process. However, because it has a large infrared absorption coefficient and a long atmospheric lifetime of 3,200 years, it is one of the highest greenhouse gases with a global warming potential (GWP) of 23,900 (integration period 100 years). In addition, there is a need to reduce emissions, such as being added to regulated gases at the COP3 Kyoto Conference. Therefore, even if the power industry is the largest consumer of SF ₆ gas, electrical insulation equipment manufacturing, testing, maintenance, in such removal, improvement of the recovery rate of SF ₆ gas, such as promotion of recycling, the atmosphere Steady efforts are being made to reduce the amount of SF ₆ gas discharged into the plant. However, those that cannot be recycled due to contamination of impurities must be safely destroyed. At present, SF ₆ gas that cannot be reused is destroyed by diverting a destruction treatment facility for fluorocarbon or the like. In this destructive treatment, combustion is performed with city gas while adding water vapor, and the product after the combustion product gas is treated is mixed with fluoride and sulfur compounds and has low purity and cannot be recycled. It is disposed of as industrial waste.
[0003]
In addition, as a technology at the research and development stage, a method of injecting SF ₆ gas into a TiO ₂ -based catalyst reactor together with air, nitrogen, and water vapor and conducting a decomposition treatment has been studied. The decomposition product gas is neutralized with an aqueous NaOH solution, mist is removed, and then a desiccant is passed through and exhausted. As the treatment results, the destruction efficiency at 99.93% was achieved in the destruction test at 800 ° C. when the SF ₆ gas concentration at the catalyst layer inlet was 0.5% (treatment amount 2.4 g / h). However, this method also absorbs and removes the fluorine compound and the sulfur compound at the same time, so that they cannot be separated and are not aimed at recycling.
[0004]
[Patent Document 1]
International Publication WO00 / 09258
[0005]
[Problems to be solved by the invention]
In the conventional treatment of exhaust gas containing fluorine and sulfur, only a product in which a fluoride and a sulfur compound are mixed can be obtained, and since the purity is low, it cannot be recycled.
[0006]
In the present invention, in the treatment of exhaust gas containing fluorine and sulfur such as SF ₆ , by selectively absorbing and extracting only the fluorine component from the exhaust gas, the fluorine component and the sulfur component can be separated and recycled. An object of the present invention is to provide a method capable of recovering such a high-purity fluorine compound not containing sulfur components, and further a method capable of separately recovering a sulfur compound.
[0007]
[Means for Solving the Problems]
In the present invention, hydrogen or a compound containing hydrogen is added to an exhaust gas containing fluorine and sulfur and thermally decomposed into HF and a sulfur compound in advance at 700 ° C. to 1200 ° C., and then the HF and the sulfur compound are used as a solid absorbent. The contact reaction temperature is 200 ° C. to 800 ° C., and the solid absorbent is one carbonate selected from the group consisting of Na, Li, K, Ca, Mg and Si, Na, Li, K, Ca, Mg. And a method of selectively recovering a fluorine component from exhaust gas , wherein the solid absorbent selectively absorbs only HF as one oxide selected from the group consisting of Si and sodium bicarbonate. It is to provide. In the present invention, a compound containing H ₂ gas or hydrogen is added to an exhaust gas containing fluorine and sulfur and brought into contact with a solid absorbent, the contact reaction temperature is set to 600 ° C to 800 ° C, and the solid absorbent is Na. As a carbonate selected from the group consisting of Li, K, Ca, Mg and Si, as an oxide selected from the group consisting of Na, Li, K, Ca, Mg and Si, or sodium hydrogen carbonate The present invention provides a method for selectively recovering a fluorine component from exhaust gas , wherein the solid absorbent selectively absorbs only HF while pyrolyzing the exhaust gas into HF and a sulfur compound .
[0008]
In the present invention, the exhaust gas is added with H ₂ gas having a mole number or more necessary for all the fluorine atoms and sulfur atoms in the exhaust gas to become HF and H ₂ S, respectively, and the exhaust gas is heated to 700 ° C. HF and H ₂ S are generated by thermal decomposition at 1200 ° C., and these are introduced into water. By utilizing the fact that H ₂ S does not dissolve in hydrofluoric acid water formed by absorbing HF, only HF is obtained. The present invention provides a method for selectively recovering a fluorine component from exhaust gas, characterized in that it is absorbed in water and HF and H ₂ S are separated and recovered.
[0009]
Further, the present invention provides a method including a step of treating a sulfur compound produced together with HF after the HF contact immobilization step or the water dissolution step.
[0010]
Further, the present invention provides a method for decomposing the exhaust gas, characterized in that H ₂ gas is added to an exhaust gas containing no fluorine and sulfur and not containing oxygen, and is brought into contact with a graphite heating element and heated.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
The exhaust gas to which the method of the present invention is applied is one containing fluorine and sulfur in the gas (hereinafter referred to as fluorine-sulfur-containing gas), and in the present invention, these are separately collected. Specifically, a compound containing fluorine and sulfur such as SF ₆ (hereinafter referred to as a fluorine sulfur compound), a fluoride (C, H, F compound) such as Freon and a sulfur compound (SF ₆ , SO ₂ , H ₂ S or the like). Among them, it is very effective for treating SF ₆ gas.
[0012]
In the present invention, the exhaust gas is a fluorine sulfur-containing gas, after previous pyrolysis and compounds HF and sulfur compounds at 700 ° C. to 1200 ° C. was added to a containing hydrogen as hydrogen and water vapor, HF and sulfur compounds Is contacted with the solid absorbent to fix HF, and only the fluorine component is recovered from the exhaust gas. Sulfur compounds are produced together with HF during decomposition. However, by using a specific solid absorbent and controlling the temperature conditions, only HF is selectively absorbed, and HF and sulfur components are separated to obtain a high purity fluorine. It is characterized by taking out as a chemical.
[0013]
The present invention is characterized by separating HF and sulfur compounds produced by decomposing fluorine-sulfur-containing gas, and any method may be used for decomposing fluorine-sulfur-containing gas into HF. . For example, it can be decomposed by a conventional method of burning with steam or other fuel such as city gas.
[0014]
Moreover, it can also decompose | disassemble by adding the compound containing hydrogen, such as hydrogen and water, and heating. For example, by adding hydrogen and bringing it into contact with a graphite heating element, a metal heating element or the like, it is heated and decomposed. Heating by the graphite heating element and the metal heating element can be performed by electric resistance heating, that is, by causing electricity to flow through the graphite and metal. Examples of the metal include copper and stainless steel. The decomposition method using the graphite heating element of the present invention is excellent in that graphite is inexpensive, does not react with HF and H ₂ S, and is hardly corroded or damaged by the corrosive gas of the graphite heating element.
[0015]
When the exhaust gas contains air (oxygen), that is, when the gas obtained by decomposing the exhaust gas contains water vapor, and when water vapor is added as a compound containing hydrogen to thermally decompose, hydrofluoric acid formed by HF dissolving in the water vapor Water is very corrosive, and metal heating elements and graphite heating elements cannot be used. In such a case, a ceramic that can be used even with water vapor is heated and the exhaust gas is decomposed by the heat. What is necessary is just to select a heating method according to a condition.
[0016]
If the fluorine-containing gas does not contain air, adding hydrogen and decomposing it using a graphite or metal heating element eliminates the need for countermeasures against corrosion and makes it easy to control the temperature of the heating element. Therefore, the design of the cracking furnace (electric heating furnace) becomes extremely easy, the equipment cost is not required, and the energy can be reduced.
[0017]
In the decomposition, the amount of hydrogen or a compound containing hydrogen added is preferably not less than the number of moles necessary for all the fluorine atoms of the fluorine-sulfur-containing gas to be HF. Below this number of moles, not all of the fluorine atoms in the fluorine-sulfur-containing gas become HF, so the fluorine component in the exhaust gas cannot be completely fixed to the solid absorbent and recovered . More preferably, a fluorine atom and a sulfur atom of fluorine sulfur-containing gas, respectively all HF, is to decompose by addition of hydrogen over the number of moles required to be H 2 _S. If the number of moles is equal to or greater than this, all fluorine atoms in the fluorine-sulfur-containing gas are converted to HF and all sulfur atoms are converted to H ₂ S by decomposition, so that fluorine and sulfur can be completely separated and recovered. More preferably, the fluorine atom and the sulfur atom are all HF and H ₂ S, respectively, and the number of moles necessary for all the halogens contained in the treatment gas to be hydride is more than that.
[0018]
Decomposition is performed prior to the step of selectively absorbing only HF in the solid absorbent, but even if it is performed at the same time, that is, adding hydrogen gas and a compound containing hydrogen, the solid absorption is performed while decomposing. You may make it absorb in an agent. In this case, the temperature must be maintained at a temperature that selectively absorbs only HF. For example, the solid absorbing agent is sodium carbonate, sodium bicarbonate, if a calcium carbonate or calcium oxide, decomposed easily as 500 ° C. to 800 ° C., and more preferably set to 600 ° C. to 800 ° C.. In this case, since the decomposition is slow, it takes time to completely decompose, and the decomposition rate of the exhaust gas is slow, but in the case where the decomposition process is performed by slowly staying in the packed bed packed with the solid absorbent. no problem.
[0019]
Preferable is a method of performing thermal decomposition with hydrogen in advance of the absorption step.
[0020]
The temperature at which hydrogen is added and decomposed is preferably 700 ° C. to 1200 ° C., more preferably 900 ° C. to 1000 ° C. If it is less than 700 ° C., the decomposition is not sufficiently performed, and if it exceeds 1200 ° C., energy required for the decomposition increases, which is not preferable. Using a graphite heating element and a metal heating element, the decomposition is sufficiently performed at the above temperature.
[0021]
Table 1 shows the results of an experiment in which SF ₆ gas was pyrolyzed using a graphite heating element. The experiment was performed using the apparatus shown in FIG. In FIG. 3, 11 is an SF ₆ cylinder, 12 is a hydrogen cylinder, 13 is a mass flow meter, and 14 is a water column manometer. Reference numeral 15 denotes a pyrolysis furnace, which uses graphite as a heating element. 16 is an absorption tank containing tap water, 17 is a mist removal tank, 18 is a membrane flow meter, and 19 is a sampling point. Using this apparatus, decomposition was carried out by adding 4 times the molar amount of hydrogen gas as the SF ₆ gas. From Table 1, the temperature of the heating element was 1050 ° C. and 1200 ° C., and the decomposition rate was 99.999% or more. HF and H ₂ S are generated according to the following reaction formula.
[0022]
SF ₆ + 4H ₂ → 6HF + H ₂ S
It was confirmed that HF was not detected from the exhaust gas at the sampling point after the cracked gas was absorbed with water, and only H ₂ S was detected. It can be seen that pyrolysis of SF ₆ gas using a graphite heating element is a very good method. Further, since the graphite heating element does not react with HF and H ₂ S gas, there is an advantage that there is almost no corrosion or damage due to the corrosive gas.
[0023]
[Table 1]

[0024]
In the present invention, it is also possible to decompose by adding water vapor as a compound containing hydrogen. In this case, the sulfur content in the exhaust gas becomes SOx (SO ₂ and SO ₃ ).
[0025]
In the present invention, as a solid absorbent that selectively absorbs only HF, one carbonate selected from the group consisting of Na, Li, K, Ca, Mg and Si, Na, Li, K, Ca, Mg And one oxide selected from the group consisting of Si and sodium hydrogen carbonate. Sodium carbonate, sodium hydrogen carbonate, calcium carbonate, and calcium oxide are preferable. These solid absorbents must be used in the solid state. This is because when used in an aqueous solution state, both HF and sulfur compounds are absorbed and cannot be separated.
[0026]
The solid absorbent is preferably granular. This is because the surface area increases and it becomes easy to absorb.
[0027]
In the present invention, the difference in reactivity between HF generated by decomposition of a fluorine-containing sulfur-containing gas by hydrogenation and the sulfur compound generated accordingly is utilized. The contact reaction between the solid absorbent and these is carried out at a temperature at which only highly reactive HF reacts and does not react with the sulfur compound, and only HF is selectively absorbed to separate HF and the sulfur compound. Therefore, the temperature at the time of the contact reaction must be a temperature at which the sulfur compound and the solid absorbent cannot react and the HF and the solid absorbent can react.
[0028]
When HF and H ₂ S are generated by decomposing fluorine-containing gas by adding hydrogen, the preferred range of the temperature absorbed by the solid absorbent is 200 ° C. to 800 ° C., more preferably 200 ° C. to 500 ° C., particularly preferably. Is 200-300 ° C.
[0029]
FIG. 2 shows the chemical equilibrium composition of 1 mole of H ₂ S, 6 moles of HF, and 5 moles of Na ₂ CO ₃ . From Figure 2, a wide range of sodium carbonate 200 ° C. to 800 ° C., although the NaF reacts with HF, hardly react with _{H 2} S, _{H 2} S is seen that the gaseous is stable. Below 600 ° C., sodium carbonate and H ₂ S do not react at all, and sodium carbonate reacts well with HF at 300 ° C. to 600 ° C. Therefore, in the case of sodium carbonate, the preferable temperature range in the catalytic reaction is 200 ° C to 800 ° C, more preferably 200 ° C to 500 ° C, and particularly preferably 200 ° C to 300 ° C.
[0030]
In the case of calcium carbonate and calcium oxide, it does not react with H ₂ S at 200 ° C. to 600 ° C., and reacts well with HF at 200 ° C. to 600 ° C. In the case of a calcium-based solid absorbent, it is preferably absorbed by contact reaction at 200 ° C to 600 ° C, more preferably 200 ° C to 500 ° C, and particularly preferably 200 ° C to 300 ° C.
[0031]
Moreover, it was also possible to separate HF and SOx at 500 ° C. using calcium carbonate.
[0032]
By managing the temperature conditions in this manner, only HF is selectively immobilized on the solid absorbent, and the fluorine component can be separated and recovered from the exhaust gas.
[0033]
After the step of fixing and separating HF in the solid absorbent, it is preferable to further provide a step of treating a sulfur compound that is not immobilized in the solid absorbent. What is necessary is just to carry out similarly to the process process which removes acidic gas which is normally performed. For example, in the case of H ₂ S, after burning to SOx and reacting with a calcium carbonate solution or the like as follows, it can be recovered as gypsum (CaSO ₄ ) and can be recycled.
[0034]
SO ₂ + CaCO ₃ + 1 / 2O ₂ → CaSO ₄ + CO ₂
[0035]
FIG. 1 shows a flow of an example of the separation and recovery processing system of the present invention.
[0036]
SF ₆ and H ₂ entering from the inlet 1 and the inlet 2, respectively, are introduced into the high temperature pyrolysis furnace 3, and the SF ₆ is decomposed to generate H ₂ S and HF. The produced H ₂ S and HF are introduced into the immobilization reaction tank 4 adjusted to 200 ° C. to 800 ° C. together with the air introduced from the inlet 7, where only HF is used as a solid absorbent such as sodium carbonate or calcium carbonate. Absorbed and immobilized. Further, H ₂ S burns in the immobilized reaction tank 4 and becomes SOx. Sodium fluoride and calcium fluoride are produced by the reaction shown below. In the case of sodium carbonate, sodium fluoride having a purity of 90% or more was obtained.
[0037]
2HF + 2Na ₂ CO ₃ → 2NaF + H ₂ O + 2CO ₂ + 1 / 2O ₂
2HF + 2CaCO ₃ → 2CaF ₂ + H ₂ O + CO ₂
By recovering these fluorinated compounds, only the fluorine content from the exhaust gas can be separated and recovered from the sulfur component. Furthermore, NaF is preferably converted to CaF ₂ by a reaction with a calcium carbonate solution shown in the following reaction formula, whereby high-purity CaF ₂ can be obtained and recycled.
[0038]
2NaF + CaCO ₃ + H ₂ O → CaF ₂ + 2NaOH + CO ₂
[0039]
Both H ₂ S and SOx that have not burned in the immobilized reaction tank 4 are not absorbed, and leave the immobilized reaction tank 4 in a gaseous state. This is introduced into the absorption reaction tank 5 to react with the calcium carbonate solution, filtered through a filter 6 and recovered as gypsum. Thus, by the method having the step of treating the sulfur compound, the fluoride and the sulfur compound can be separated and recovered separately, and the respective high-purity compounds can be obtained and recycled.
[0040]
Next, the method for selectively recovering fluorine using the water of the present invention will be described.
[0041]
In this method, the fluorine-sulfur-containing gas is decomposed similarly to the method using the solid absorbent described above, but H ₂ is added and decomposed by heating in order to generate H ₂ S as a sulfur compound. When water is added, SOx is generated and cannot be used. The heating method can be performed in the same manner as described above. The amount of H ₂ gas is fluorine fluorine sulfur-containing gas, sulfur is added in an amount of all _{HF, H 2 S, HF,} H 2 S only to produce, HF in water instead of solid sorbent Is absorbed selectively. In the conventional exhaust gas treatment, since water vapor or air is added for decomposition, SOx is generated together with HF, and SOx is also absorbed by water together with HF, so that they cannot be separated.
[0042]
In the method of the present invention, only HF is dissolved in water and separated. HF and H ₂ S can be separated by the extremely low solubility of H ₂ S in water and HF aqueous solution.
[0043]
FIG. 6 shows a schematic diagram of an example flow of the method of the present invention. Here, SF ₆ is used as the exhaust gas. SF ₆ is decomposed in a pyrolysis furnace 15 using a graphite heating element in the presence of H ₂ . HF and H ₂ S produced by the decomposition are introduced into an absorption tank 24 containing water, preferably demineralized water. HF is very easy to dissolve in water, whereas H ₂ S is very difficult to dissolve in water, so it can be separated as H ₂ S gas. The H ₂ S gas separated without being absorbed by water is burned in the combustion furnace 25 to form SOx, and can then be recovered as gypsum in the absorption reaction tank 5 using a general limestone gypsum method. This step is the same as that described in the method using the solid absorbent described above.
[0044]
The hydrofluoric acid water after separation can be reused as it is, or can be recycled by reacting with the immobilization material.
[0045]
It is preferable to provide a step of treating unabsorbed H ₂ S after the step of absorbing and separating HF in water. This step is the same as that described in the method using the solid absorbent described above.
[0046]
This method using water has an advantage that HF and H ₂ S can be separated relatively easily. Meanwhile, a method of using the above-mentioned solid sorbent is a separation conditions must be adjusted depending on the type of solid sorbent can be carried out separation and immobilization methods fluorine compounds simultaneously and dry, recycled There is an advantage that the intended system can be simplified.
[0047]
In any method of the present invention, HF and sulfur compounds in the exhaust gas can be separated and recovered.
[0048]
【Example】
The present invention will be described below with reference to examples, but the present invention is not limited thereto.
[0049]
Example 1
An SF ₆ gas pyrolysis furnace used in FIG. 3 was followed by an immobilized reactor having an alumina ceramic tube, and an SF ₆ cracked gas absorption experiment was conducted. The flowchart is shown in FIG. 4 and the test conditions are shown in Table 2.
[0050]
[Table 2]

[0051]
In FIG. 4, 10, 11 and 12 are Ar, SF ₆ and H ₂ cylinders, respectively, 15 is a pyrolysis furnace, and 4 is an immobilized reaction furnace. The fixed reaction furnace is heated by the electric furnace 20. 21 is an outer cylinder, 22 is an eye plate, and 23 is an inner cylinder, all made of high-purity alumina. The eye plate was fixed in an alumina tube having an inner diameter of 30 mm, and 116 g of sodium hydrogen carbonate (particle size: 1.18 to 2.36 mm) was filled thereon as a solid absorbent. The temperature of the immobilization reactor was set to 300 ° C. The processing gas components were Ar: 500 ml / min, SF ₆ : 20 ml / min, H ₂ : 80 ml / min, and the temperature of the pyrolysis furnace was set at 1100 ° C. Here, Ar is used as a dilution gas. The space velocity was 384 h ⁻¹ . It has been confirmed in advance that SF ₆ decomposes 100% under these conditions. The concentration of HF and H ₂ S gas contained in the outlet gas of the immobilized reactor was confirmed by a detector tube at 19 sampling points. FIG. 5 shows the test results. FIG. 5 also shows an estimated value (theoretical value) of the reaction rate when NaHCO ₃ reacts with HF.
[0052]
The H ₂ S gas concentration at the exit of the immobilized reactor showed a substantially constant value within the range of analysis accuracy from the start of the reaction, whereas no HF concentration could be detected. Therefore, separation of HF gas and H ₂ S was confirmed. This reaction formula is shown below.
[0053]
6HF + H ₂ S + 6 NaHCO ₃ → 6NaF + H ₂ S + 6H ₂ O + 6CO ₂
[0054]
(Example 2)
Using an apparatus similar to that shown in FIG. 3, a treatment experiment of pyrolysis gas of SF ₆ was performed using distilled water in 16 absorption tanks. The decomposition conditions are the same as in test number 2 in Table 1. It was confirmed from the mass balance of fluorine that HF was absorbed by distilled water among HF and H ₂ S produced by the decomposition of SF _{6 in} the pyrolysis furnace. Further, when H ₂ S in the absorbing solution (HF solution having an HF concentration of about 0.5%) was confirmed by methylene blue absorptiometry, it was not detected and it was confirmed that it was not dissolved at all. Accordingly, it was confirmed that HF and H ₂ S produced by the decomposition of SF ₆ together with H _{2 in a} pyrolysis furnace can be separated by water.
[0055]
【The invention's effect】
At present, SF ₆ gas, which is used as an electric insulating gas and cannot be reused due to the mixing of impurities, is recovered and processed by a wet combustion method using water vapor, and the product is processed as waste. However, since the present invention, a fluorine component from a gas containing fluorine and sulfur such as SF ₆ selectively absorbed onto the solid absorbent can be retrieved, the fluorine component may be recovered by separating the sulfur components, recycling It is possible to obtain a high-purity fluorine compound that does not contain a sulfur component that can be converted into a sulfur compound. Furthermore, if a process for treating the sulfur component gas that is not absorbed is provided, the sulfur component in the exhaust gas can be recovered as a high-purity sulfur compound that does not contain fluoride.
[0056]
In addition, the method using a solid absorbent has a great merit that a high-purity recycled product can be directly obtained simultaneously with the separation. For example, in the state of the art, HF, which is a decomposition gas of chlorofluorocarbon, is once absorbed in water to form hydrofluoric acid water, and then hydrofluoric acid water and calcium carbonate are reacted in a wet manner to form fluorite. It is contained in stone and is not very pure. In the present invention, by reacting the HF gas in the cracked gas directly with calcium carbonate, separation from sulfur compounds and generation of fluorite can be performed simultaneously. In addition, the purity of the obtained fluorite can be increased.
[0057]
In addition, the decomposition method of the present invention using hydrogen gas and using a graphite heating element can thermally decompose exhaust gas that does not include oxygen and does not contain oxygen, and selectively contains fluorine components from the exhaust gas of the present invention. It is also an excellent method for recovery .
[0058]
As described above, according to the present invention, a substance obtained by treating exhaust gas can be recycled, and secondary waste can be reduced and resources can be effectively used.
[Brief description of the drawings]
FIG. 1 is a schematic view showing an example of an embodiment of a method for selectively recovering a fluorine component from exhaust gas using the solid absorbent of the present invention.
FIG. 2 is a chemical equilibrium diagram of H ₂ S, HF and Na ₂ CO ₃ .
FIG. 3 is a schematic diagram showing a flow of a pyrolysis test of SF ₆ gas.
4 is a schematic diagram showing a flow of a method of Example 1. FIG.
5 is a graph showing the test results of Example 1. FIG.
FIG. 6 is a schematic view showing an example of an embodiment of a method for selectively recovering a fluorine component from exhaust gas using water of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 SF ₆ inlet 2 H ₂ inlet 3 High-temperature pyrolysis furnace 4 Immobilization reaction tank 5 Absorption reaction tank 6 Filter 7 Air inlet 10 Ar cylinder 11 SF ₆ cylinder 12 H ₂ cylinder 13 Mass flow meter 14 Water column manometer 15 Pyrolysis furnace 16 Absorption tank 17 Mist removal tank 18 Membrane flow meter 19 Sampling point 20 Electric furnace 21 Outer cylinder 22 Eye plate 23 Inner cylinder 24 Absorption tank 25 containing water Combustion furnace

Claims (10)

A compound containing H ₂ gas or hydrogen is added to an exhaust gas containing fluorine and sulfur and thermally decomposed into HF and a sulfur compound in advance at 700 ° C. to 1200 ° C., and then the HF and the sulfur compound are used as a solid absorbent. The contact reaction temperature is 200 ° C. to 800 ° C., and the solid absorbent is one carbonate selected from the group consisting of Na, Li, K, Ca, Mg and Si, Na, Li, K, Ca, A fluorine component is selectively recovered from the exhaust gas , wherein only one of the HF is selectively absorbed by the solid absorbent as one kind of oxide selected from the group consisting of Mg and Si, or sodium bicarbonate. Method. A compound containing H ₂ gas or hydrogen is added to an exhaust gas containing fluorine and sulfur and brought into contact with a solid absorbent, the contact reaction temperature is set to 600 ° C. to 800 ° C., and the solid absorbent is Na, Li, K, The exhaust gas is treated as HF as one carbonate selected from the group consisting of Ca, Mg and Si, one oxide selected from the group consisting of Na, Li, K, Ca, Mg and Si, or sodium hydrogen carbonate. A method of selectively recovering a fluorine component from exhaust gas , wherein only the HF is selectively absorbed by the solid absorbent while thermally decomposing it into a sulfur compound . The method according to claim 1 or 2 fluorine atoms in the flue gas is carried out in the presence of a compound everything, including moles or more H ₂ gas or hydrogen required for the HF. The method according to claim 1 or 2, wherein the method is carried out in the presence of H ₂ gas having a mole number or more necessary for all the fluorine atoms and sulfur atoms in the exhaust gas to become HF and H ₂ S, respectively. The method according to claim 1 or 2, wherein the solid absorbent is sodium carbonate, sodium hydrogen carbonate, calcium carbonate, or calcium oxide . The method according to claim 1, wherein the solid absorbent is granular . To the exhaust gas containing fluorine and sulfur, H ₂ gas having a mole number or more necessary for all the fluorine atoms and sulfur atoms in the exhaust gas to become HF and H ₂ S, respectively, is added, and the exhaust gas is kept at 700 ° C. to 1200 ° C. HF and H ₂ S are generated by thermal decomposition at 0 ° C., and these are introduced into water. By utilizing the fact that H ₂ S is not dissolved in hydrofluoric acid water formed by absorbing HF, only HF is dissolved in water. A method for selectively recovering a fluorine component from an exhaust gas , wherein HF and H ₂ S are separated and recovered . The method according to claim 1, 2 or 7, wherein the decomposition of the exhaust gas not containing oxygen is performed by adding H ₂ gas and bringing it into contact with a graphite heating element for thermal decomposition . The method according to claim 1, 2 or 7, wherein the exhaust gas is SF ₆ . After the HF contact immobilization step or the water dissolution step, HF is further added.
The method of Claim 1, 2 or 7 including the process of processing the sulfur compound produced | generated together .

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