JP4265940B2 - Method for removing nitrogen compounds - Google Patents
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- JP4265940B2 JP4265940B2 JP2003189187A JP2003189187A JP4265940B2 JP 4265940 B2 JP4265940 B2 JP 4265940B2 JP 2003189187 A JP2003189187 A JP 2003189187A JP 2003189187 A JP2003189187 A JP 2003189187A JP 4265940 B2 JP4265940 B2 JP 4265940B2
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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- Y02C—CAPTURE, STORAGE, SEQUESTRATION OR DISPOSAL OF GREENHOUSE GASES [GHG]
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Description
【０００１】
【発明の属する技術分野】
本発明は、燃焼排ガスなどの排気ガスや窒素フッ化物、窒素酸化フッ化物合成工程での粗製品中に含まれる不要な窒素酸化物、窒素酸化ハロゲン化物、並びにそれらのハロゲン化水素との複合体ガスを高効率に無害化あるいは精製する窒素化合物の除去方法に関する。
【０００２】
【従来の技術および発明が解決しようとする課題】
従来、燃焼排ガスなどに含まれる窒素酸化物などはアンモニア接触還元法（特許文献１）、酸化マンガン−酸化セリウムによる吸着除去法（特許文献２）、光触媒担持組成物にＮＯｘ吸着させ紫外線を照射して分解する方法（特許文献３）、プラズマ分解とオゾン吸収剤とを組み合わせた方法（特許文献４）などが提案されている。しかしアンモニア接触還元法では、支燃性物質中に可燃性物質を混合する危険性があり、触媒充填式では、大量のガスを処理するためには大規模な施設が必要となり、プラズマ式では、大量のガスを分解することは実質的に困難である問題があった。また、本発明で除去対象の一つとしている窒素酸化物とハロゲン化水素の付加体に関しては、有効な除去手段は知られていなかった。さらに、三フッ化窒素などのフッ化物製造工程に於いても、反応器からの大気や水分の混入、あるいは原料中に微量に含まれる酸素や水分の影響から窒素酸化物、窒素酸化ハロゲン化物並びにそれらのハロゲン化水素付加体が生成する場合があった。このような場合、ガスを精製するために精製設備の規模を大型化したり、多段化したりする必要があった。特にハロゲン化水素付加体の場合は、ガス中から選択的に取り除くことは困難であった。さらに、水でこれらの化合物を除去しようとすると、水中に亜硝酸あるいは亜硝酸イオンが検出される。亜硝酸は、式（１）に示したように除去が極めて困難な一酸化窒素の発生要因となるため好ましくない。
３ＨＮＯ2 → ２ＮＯ + ＨＮＯ3 + Ｈ2Ｏ ・・・（１）
【０００３】
以上のことから高効率に、かつ簡便に不要な窒素酸化物、窒素酸化ハロゲン化物、窒素フッ化物、並びにそれらのハロゲン化水素との複合体を取り除くことができ、亜硝酸を硝酸まで酸化し、一酸化窒素などの２次汚染物質の発生を起こさない方法が必要とされていた。
【０００４】
【特許文献１】
特開平９−２１３５９６号公報
【特許文献２】
特開２００２−３７１８３０号公報
【特許文献３】
特開２００３−０６３８５２号公報
【特許文献４】
特開２００１−２５９３６２号公報
【０００５】
【課題を解決するための手段】
本発明者らは、上記の問題点に鑑み鋭意検討の結果、窒素酸化物、窒素酸化ハロゲン化物、及びそれらのハロゲン化水素との複合体ガスを湿式スクラバー溶液として過酸化水素とフッ酸（ＨＦ）、塩酸（ＨＣｌ）、臭化水素酸（ＨＢｒ）、ヨウ化水素酸（ＨＩ）のいずれかであるハロゲン酸との混合水溶液を使用することにより窒素化合物を除去できることを見出し本発明に到達した。
【０００６】
すなわち、本発明は、湿式スクラバーにおいて、ＮＯｘ、ＮＯｘＡｙ、ＨＮＯｘ、ＮＯｘ・ｎＨＡ、ＮＯｘＡｙ・ｎＨＡ、ＨＮＯｘ・ｎＨＡ、またはこれらの混合物を除去するに際し、スクラバー液として過酸化水素とフッ酸（ＨＦ）、塩酸（ＨＣｌ）、臭化水素酸（ＨＢｒ）、ヨウ化水素酸（ＨＩ）のいずれかであるハロゲン酸とを含有した水溶液を使用することを特徴とする窒素化合物の除去方法（ただし、Ａ＝ハロゲン、ｘ≧０．５、ｙ＞０、ｎは、１以上の整数を表す。）を提供するものである。
【０００７】
以下、本発明を詳細に説明する。
窒素酸化物が水スクラバーに導入されると、例えば、ＮＯ2であればスクラバー液中に一部吸収され亜硝酸と硝酸となる。亜硝酸として吸収されると前述のように一酸化窒素のように除去が困難な窒素酸化物の再生成が起こる。また過酸化水素溶液中にこれら窒素酸化物を導入しても、酸化力が弱く亜硝酸の生成は避けがたい。しかし、鋭意検討の結果、過酸化水素溶液にハロゲン酸を混合することにより飛躍的にスクラバー液の酸化力が向上し、亜硝酸を硝酸に変換できることを見出したものである（式（２））。
ＨＮＯ2 +Ｈ2Ｏ2 +ＨＡ ＝ ＨＮＯ3 +Ｈ2Ｏ +ＨＡ ・・・（２）
Ａは、Ｆ，Ｃｌ，Ｂｒ，Ｉである。
【０００８】
この場合、ハロゲン酸は触媒的に働き、そのもの自体は化学的変化を起こさない。なお、酸化ハロゲン化窒素の場合は、水との反応でハロゲン酸と過酸化水素を生成するが、生成率が低く予めスクラバー液の酸化力を上げておかないと十分な除去効果が得られない。本発明において、使用するハロゲン酸とは、フッ酸（ＨＦ）、塩酸（ＨＣｌ）、臭化水素酸（ＨＢｒ）、ヨウ化水素酸（ＨＩ）等が挙げられるが、フッ酸、塩酸が特に好ましい。
【０００９】
本発明において、対象となる窒素酸化物、窒素酸化ハロゲン化物、及びそれらのハロゲン化水素との複合体ガスとは、一般式では、ＮＯｘ、ＮＯｘＡｙ、ＨＮＯｘ、ＮＯｘ・ｎＨＡ、ＮＯｘＡｙ・ｎＨＡ、またはＨＮＯｘ・ｎＨＡ（ただし、Ａ＝ハロゲン、ｘ≧０．５、ｙ＞０、ｎは、１以上の整数を表す。）で表される。ＨＦの付加は、水素結合により連鎖的に会合しておりその最大値は不明である。しかし、ＨＦとの複合体が存在することは古くから知られている（Ｆ．ｓｅｅｌ ａｎｄ Ｗ．Ｂｉｒｎｋｒａｕｔ、Ａｎｇｅｗａｎｄｔｅ Ｃｈｅｍｉｅ ７３， ５３１−２（１９６１）等）。具体的には、ＮＯ2・４ＨＦ、ＮＯ2・８ＨＦ、ＮＯ2・１２ＨＦ、ＮＯＦ・４ＨＦ、ＮＯ2Ｆ・４ＨＦ、ＮＯ2Ｆ・８ＨＦ、ＮＯ2Ｆ・１２ＨＦ等が挙げられる。
【００１０】
本発明において、スクラバー液中の過酸化水素の濃度は、１０ｐｐｍ以上５０容積％以下が好ましく、より好ましくは、１００ｐｐｍ以上１０容積％以下である。１０ｐｐｍ未満では、効果が殆ど認められず、５０容積％を越える濃度では、顕著な効果の向上が認められず好ましくない。ハロゲン酸の濃度は、０．１〜３０容積％の範囲が好ましく、より好ましくは、１〜１０容積％である。０．１容積％以下では、添加の効果が顕著ではなく、３０容積％より多く添加しても効果に顕著な差異が認められない。
【００１１】
また、過酸化水素や酸濃度を維持するためには、ハロゲン酸の種類が、フッ酸の場合ならば窒素酸化物を含むガスにフッ素を添加しても良い。フッ素と水との反応により、式（３）に示すように過酸化水素とフッ酸が生成するため効率が良い。
２Ｈ2Ｏ + Ｆ2(ｇ) = Ｈ2Ｏ2(ｇ) + ２ＨＦ(ｇ) ・・・・（３）
【００１２】
【実施例】
以下、実施例により本発明を詳細に説明するが、本発明はかかる実施例に限定されるものではない。
【００１３】
実施例１、比較例１、２
１００ｍｌメスフラスコを用い、亜硝酸濃度を０．２２ｍｍｏｌに調整し、これを標準液とした。過酸化水素水溶液（比較例１）、過酸化水素とフッ酸水溶液（実施例１）、過酸化水素と水酸化カリウム水溶液（比較例２）の三種類と混合し、溶液中の硝酸、亜硝酸イオン濃度をイオンクロマトグラフで測定した。その結果、表１に示した。表１から分かるように過酸化水素とフッ酸との混合溶液のみ亜硝酸イオンが硝酸イオンに変換されており、その他の溶液では酸化能力が発現されない結果となった。
【００１４】
【表１】
実施例２、比較例３
Ｈｅで１０００ｐｐｍに希釈したＮＯ2ガスを予め真空に減圧した１Ｌ容器に９３ｋＰａまで導入した後、純水、もしくは過酸化水素(０．３２ｍｍｏｌ)とフッ酸(０．１２ｍｍｏｌ)との混合水溶液を１００ＣＣ導入して１時間攪拌した。その後、溶液中の亜硝酸イオンと硝酸イオンの濃度から窒素酸化物の溶液への捕集率を求めた。その結果、純水では、亜硝酸イオンとして３５容積％、硝酸として３５容積％、合計７０容積％の酸化窒素成分が捕集されていた。一方、過酸化水素とフッ酸との混合液には、全て硝酸イオンとして８５容積％の酸化窒素成分が捕集されていた。以上から、過酸化水素とフッ酸の混合液は、不純物を再発生させる亜硝酸を硝酸に酸化すると効果と同時に、液への捕集率を向上させる効果が有ることが解った。
【００１６】
実施例３〜５、比較例４〜６
次に、純水並びに過酸化水素とフッ酸との混合液に、ＮＯ2に替えてＮＯ2・２ＨＦ、ＮＯ2Ｆ・２ＨＦ、ＮＯＦ・２ＨＦを１Ｌ容器に導入して実施例２、比較例３と同様の実験を行った。各々の硝酸イオン、亜硝酸イオンとしての捕集率並びにそれらの合計を表２に示した。この結果から、過酸化水素とフッ酸の混合液にすることで亜硝酸イオンを全て硝酸イオンに変換でき、さらに捕集率も向上させられることが解った。また、フッ酸の代わりに塩酸、シュウ化水素酸、ヨウ化水素酸を混合しても同様の結果が得られた。
【００１７】
【表２】
実施例６〜８、比較例７〜９
内径２．５ｃｍ、長さ１００ｃｍのラシヒリング充填塔を具備したスクラバーに塔下部から、Ｎ2で５０００ｐｐｍに希釈したＮＯ2（実施例６、比較例７）、ＮＯ2Ｆ（実施例７、比較例８）、ＮＯＦ（実施例８、比較例９）を含むガスを流通させ、塔上部から循環水（あいは水溶液）を０．５Ｌ／ｍｉｎの流量で落下循環させた。その結果、スクラバー液に純水を使用した場合には７５％，８６％，７６％であった捕集率が、過酸化水素とフッ酸の混合溶液を用いたところ全てほぼ１００％捕集できた。
【００１９】
【発明の効果】
本発明の方法により、燃焼排ガスなどの排気ガスや窒素フッ化物等の合成工程での粗製品中に含まれる不要な窒素酸化物、窒素酸化ハロゲン化物、及びそれらのハロゲン化水素との複合体ガスを高効率に無害化あるいは精製除去することを可能とした。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust gas such as combustion exhaust gas, nitrogen fluoride, unnecessary nitrogen oxides contained in a crude product in a nitrogen oxyfluoride synthesis process, nitrogen oxide halides , and composites thereof with hydrogen halides. The present invention relates to a method for removing a nitrogen compound that renders a gas harmless or highly efficient.
[0002]
[Background Art and Problems to be Solved by the Invention]
Conventionally, nitrogen oxides contained in combustion exhaust gas, etc. are contacted with ammonia by the catalytic reduction method (Patent Document 1), the adsorption removal method using manganese oxide-cerium oxide (Patent Document 2), and the photocatalyst-supported composition is adsorbed with NOx and irradiated with ultraviolet rays. And a method of decomposing (Patent Document 3), a method of combining plasma decomposition and an ozone absorbent (Patent Document 4), and the like. However, in the ammonia catalytic reduction method, there is a risk of mixing flammable substances in the combustion-supporting substance. In the catalyst filling type, a large-scale facility is required to process a large amount of gas, and in the plasma type, There is a problem that it is substantially difficult to decompose a large amount of gas. Further, no effective removal means has been known for the adduct of nitrogen oxide and hydrogen halide, which is one of the removal targets in the present invention. Furthermore, even in the production process of fluorides such as nitrogen trifluoride, nitrogen oxides, nitrogen oxide halides, and the like can be found due to air and water contamination from the reactor, or the effects of oxygen and moisture contained in trace amounts in the raw materials. In some cases, these hydrogen halide adducts were produced. In such a case, it is necessary to increase the scale of the purification equipment or to increase the number of stages in order to purify the gas. In particular, in the case of a hydrogen halide adduct, it was difficult to selectively remove it from the gas. Furthermore, when these compounds are removed with water, nitrous acid or nitrite ions are detected in the water. Nitrous acid is not preferable because it causes generation of nitric oxide which is extremely difficult to remove as shown in the formula (1).
3HNO 2 → 2NO + HNO 3 + H 2 O (1)
[0003]
From the above, highly efficient and simple removal of unnecessary nitrogen oxides, nitrogen oxide halides, nitrogen fluorides, and their complexes with hydrogen halides, oxidizing nitrous acid to nitric acid, There has been a need for a method that does not generate secondary pollutants such as nitric oxide.
[0004]
[Patent Document 1]
JP-A-9-213596 [Patent Document 2]
JP 2002-371830 A [Patent Document 3]
JP 2003-063852 A [Patent Document 4]
Japanese Patent Laid-Open No. 2001-259362
[Means for Solving the Problems]
As a result of intensive studies in view of the above problems, the present inventors have determined that hydrogen oxide and hydrofluoric acid (HF) are obtained by using a nitrogen oxide, a nitrogen oxide halide , and a complex gas of these hydrogen halides as a wet scrubber solution. ), Hydrochloric acid (HCl), hydrobromic acid (HBr), hydroiodic acid (HI), and the use of a mixed aqueous solution with a halogen acid, the nitrogen compound can be removed, and the present invention has been achieved. .
[0006]
That is, in the present invention, when removing NOx, NOxAy, HNOx, NOx · nHA, NOxAy · nHA, HNOx · nHA , or a mixture thereof in a wet scrubber, hydrogen peroxide and hydrofluoric acid (HF) are used as the scrubber liquid . A method for removing a nitrogen compound, characterized by using an aqueous solution containing a halogen acid that is one of hydrochloric acid (HCl), hydrobromic acid (HBr), and hydroiodic acid (HI) (where A = halogen, x ≧ 0.5, y> 0 , n is to provide a representative.) an integer of 1 or more.
[0007]
Hereinafter, the present invention will be described in detail.
When nitrogen oxides are introduced into the water scrubber, for example, NO 2 is partially absorbed into the scrubber liquid and becomes nitrous acid and nitric acid. When absorbed as nitrous acid, nitrogen oxide such as nitric oxide, which is difficult to remove, is regenerated as described above. Moreover, even if these nitrogen oxides are introduced into a hydrogen peroxide solution, the oxidizing power is weak and it is difficult to avoid the formation of nitrous acid. However, as a result of intensive studies, it has been found that the oxidizing power of the scrubber liquid is dramatically improved by mixing halogen acid with a hydrogen peroxide solution, and nitrous acid can be converted to nitric acid (formula (2)). .
HNO 2 + H 2 O 2 + HA = HNO 3 + H 2 O + HA (2)
A is F, Cl, Br, or I.
[0008]
In this case, the halogen acid acts catalytically and itself does not undergo a chemical change. In the case of nitrogen oxide halide, halogen acid and hydrogen peroxide are produced by reaction with water. However, if the oxidation rate of the scrubber liquid is not increased in advance, a sufficient removal effect cannot be obtained. . In the present invention, the halogen acid used includes hydrofluoric acid (HF), hydrochloric acid (HCl), hydrobromic acid (HBr), hydroiodic acid (HI), etc., and hydrofluoric acid and hydrochloric acid are particularly preferable. .
[0009]
In the present invention, the target nitrogen oxides, nitrogen oxide halides , and complex gases thereof with hydrogen halide are, in the general formula, NOx, NOxAy, HNOx, NOx · nHA, NOxAy · nHA, or HNOx. NHA (where A = halogen, x ≧ 0.5, y> 0, n represents an integer of 1 or more). The addition of HF is linked in a chain by hydrogen bonds, and the maximum value is unknown. However, the existence of a complex with HF has been known for a long time (F. seel and W. Birnkraut, Angewante Chemie 73, 531-2 (1961), etc.). Specifically, NO 2 · 4HF, NO 2 · 8HF, NO 2 · 12HF, NOF · 4HF, NO 2 F · 4HF, NO 2 F · 8HF, NO 2 F · 12HF and the like.
[0010]
In the present invention, the concentration of hydrogen peroxide in the scrubber liquid is preferably 10 ppm or more and 50% by volume or less, and more preferably 100 ppm or more and 10% by volume or less. If the concentration is less than 10 ppm, the effect is hardly recognized, and if the concentration exceeds 50% by volume, a significant improvement in the effect is not recognized. The concentration of the halogen acid is preferably in the range of 0.1 to 30% by volume, more preferably 1 to 10% by volume. Below 0.1% by volume, the effect of addition is not significant, and no significant difference is observed in the effect even if added more than 30% by volume.
[0011]
Further, in order to maintain the hydrogen peroxide or acid concentration, fluorine may be added to a gas containing nitrogen oxides if the type of halogen acid is hydrofluoric acid. Since the reaction between fluorine and water produces hydrogen peroxide and hydrofluoric acid as shown in the formula (3), the efficiency is high.
2H 2 O + F 2 (g) = H 2 O 2 (g) + 2HF (g) (3)
[0012]
【Example】
EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to this Example.
[0013]
Example 1, Comparative Examples 1 and 2
Using a 100 ml volumetric flask, the nitrous acid concentration was adjusted to 0.22 mmol, and this was used as a standard solution. Mix with three types of hydrogen peroxide aqueous solution (Comparative Example 1), hydrogen peroxide and hydrofluoric acid aqueous solution (Example 1), and hydrogen peroxide and potassium hydroxide aqueous solution (Comparative Example 2). The ion concentration was measured with an ion chromatograph. The results are shown in Table 1. As can be seen from Table 1, nitrite ions were converted into nitrate ions only in the mixed solution of hydrogen peroxide and hydrofluoric acid, and the oxidation ability was not expressed in the other solutions.
[0014]
[Table 1]
Example 2 and Comparative Example 3
After introducing NO 2 gas diluted to 1000 ppm with He up to 93 kPa into a 1 L container whose pressure has been reduced to a vacuum in advance, pure water or a mixed aqueous solution of hydrogen peroxide (0.32 mmol) and hydrofluoric acid (0.12 mmol) is added to 100 CC. It was introduced and stirred for 1 hour. Thereafter, the collection rate of nitrogen oxides in the solution was determined from the concentrations of nitrite ions and nitrate ions in the solution. As a result, in pure water, 35% by volume as nitrite ions and 35% by volume as nitric acid, a total of 70% by volume of nitrogen oxide components were collected. On the other hand, in the mixed solution of hydrogen peroxide and hydrofluoric acid, 85% by volume of the nitrogen oxide component was all collected as nitrate ions. From the above, it was found that the mixed liquid of hydrogen peroxide and hydrofluoric acid has the effect of improving the collection rate in the liquid simultaneously with the effect of oxidizing nitrous acid that regenerates impurities into nitric acid.
[0016]
Examples 3-5, Comparative Examples 4-6
Next, pure water and a mixture of hydrogen peroxide and hydrofluoric acid, NO 2 · 2HF instead of NO 2, NO 2 F · 2HF, Example 2 was introduced NOF · 2HF in 1L containers, comparative example The same experiment as 3 was performed. Table 2 shows the collection rate of each nitrate ion and nitrite ion, and their total. From this result, it was found that by using a mixed solution of hydrogen peroxide and hydrofluoric acid, all nitrite ions can be converted to nitrate ions, and the collection rate can be improved. Similar results were obtained by mixing hydrochloric acid, hydrofluoric acid, or hydroiodic acid instead of hydrofluoric acid.
[0017]
[Table 2]
Examples 6-8, Comparative Examples 7-9
NO 2 (Example 6, Comparative Example 7), NO 2 F (Example 7, Comparative Example) diluted to 5000 ppm with N 2 from the bottom of a scrubber equipped with a Raschig ring packed tower having an inner diameter of 2.5 cm and a length of 100 cm. 8) Gas containing NOF (Example 8, Comparative Example 9) was circulated, and circulating water (or an aqueous solution) was dropped and circulated at a flow rate of 0.5 L / min from the top of the tower. As a result, when pure water was used as the scrubber liquid, the collection rates were 75%, 86%, and 76%, and almost 100% could be collected using a mixed solution of hydrogen peroxide and hydrofluoric acid. It was.
[0019]
【The invention's effect】
By the method of the present invention, unnecessary nitrogen oxides, nitrogen oxide halides , and complex gases of these hydrogen halides contained in the crude product in the synthesis process of exhaust gas such as combustion exhaust gas and nitrogen fluoride Can be made harmless or purified and removed with high efficiency.
Claims (1)
ただし、Ａ＝ハロゲン、ｘ≧０．５、ｙ＞０、ｎは、１以上の整数を表す。In a wet scrubber, when removing NOx, NOxAy, HNOx, NOx · nHA, NOxAy · nHA, HNOx · nHA , or a mixture thereof, hydrogen peroxide, hydrofluoric acid (HF), hydrochloric acid (HCl), odor A method for removing a nitrogen compound, comprising using an aqueous solution containing a halogen acid which is either hydrofluoric acid (HBr) or hydroiodic acid (HI) .
However, A = halogen, x ≧ 0.5, y> 0, n represents an integer of 1 or more.
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