JP3901382B2 - NOx gas suppression method using hydrogen peroxide - Google Patents
NOx gas suppression method using hydrogen peroxide Download PDFInfo
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- JP3901382B2 JP3901382B2 JP10167699A JP10167699A JP3901382B2 JP 3901382 B2 JP3901382 B2 JP 3901382B2 JP 10167699 A JP10167699 A JP 10167699A JP 10167699 A JP10167699 A JP 10167699A JP 3901382 B2 JP3901382 B2 JP 3901382B2
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Description
【０００１】
【発明の属する技術分野】
本発明は、過酸化水素を添加することによって、硝酸含有液中で金属を処理する場合におけるＮＯx ガスの発生を抑制する方法に関する。
【０００２】
【従来の技術】
工業分野において硝酸は広く使われているが、その中で硝酸含有液を用いて金属を処理する場合には、しばしば環境および人体に対して悪影響を及ぼすＮＯx ガスが発生する。例えば、硝酸と弗酸との混酸によるステンレス鋼の酸洗処理の場合、処理液中ではステンレス鋼の溶解とともに溶液中に亜硝酸が生じる。亜硝酸は溶液中で種々の反応を経てＮＯやＮＯ2 となり、ＮＯx ガスとして系外へ放出される。ここでＮＯx ガスの処理にスクラバー等を用いる場合、排ガス処理装置の設備コストがかかり、定期的なメンテナンスも必要となる。
【０００３】
これに対して、硝酸含有液に過酸化水素を添加して、ＮＯx ガスを抑制する方法があるが（米国特許第３，９４５，８６５号）、過酸化水素の添加量を適切に調製することが問題となる。過剰な添加は、金属イオンの存在する硝酸、弗酸液中では、自ら分解するだけであり、過酸化水素を無駄に消費させることになるからである。特開昭５５−１３４６９４号公報では、亜硝酸含有液の酸化還元電位に基づいて、過酸化水素の添加を調整する方法が開示されているが、酸化還元電位と亜硝酸濃度との相関が一定せず、過酸化水素の添加量の調整が難しい。
【０００４】
【発明が解決しようとする課題】
本発明の目的は、従来技術における上記したような課題を解決し、硝酸含有液のＮＯx ガスの発生を効果的に抑制させる方法を提供することにある。
【０００５】
【課題を解決するための手段】
本発明者らは、過酸化水素の添加量の調整について鋭意研究を重ねた結果、硝酸含有液を定電位電解した場合、電解電流値と液中の亜硝酸イオン濃度および発生するＮＯx ガス量との間に一定の関係があることを見出し、本発明に到達した。
【０００６】
すなわち、本発明は、過酸化水素の添加によって硝酸含有液からのＮＯx ガスの放出を抑制する方法において、硝酸含有液を一定電位で電解し、電解電流値に基づいて、過酸化水素の添加量を調整することを特徴とするＮＯx ガスの抑制方法に関するものである。
【０００７】
【発明の実施の形態】
本発明は、ステンレス鋼の酸洗処理に用いられる硝酸と弗酸との混酸、および銅、真鍮等の表面処理に用いられる硝酸含有液に好適に用いられる。例えば、ステンレス鋼の酸洗は、バッチまたは連続で処理され、硝酸含有液の温度や金属溶解量も変化するため、ＮＯx 発生量も変化する。従って、必要な過酸化水素の添加量も時間によって変化することになる。
【０００８】
また、本発明は、ＮＯx の吸収溶液として使用される硝酸含有液に過酸化水素を添加することにより、酸化されて硝酸になる場合にも適用できる。例えば、石炭、オイルまたは他の燃料を燃焼して生じるＮＯx ガス、硝酸を用いた有機化合物の硝化・酸化のための設備から生じるＮＯx ガスを吸収・酸化する場合である。
【０００９】
本発明の定電位電解法は、陰極の電位を一定に保ちながら電解する方法であり、具体的には作用極、対極、参照電極を具備したいわゆる３電極式電位制御装置を用い、硝酸、弗酸液を電解し電流値を検出する方法である。作用極および対極の材質は安定で溶解しないことが必要であり、電解液が硝酸、弗酸であることから白金が好ましい。参照電極は特に限定しないが、取り扱いやすさと弗酸液中ではガラスは溶解してしまうことから樹脂製の銀／塩化銀電極で、かつ、電解液の汚染を起こさないダブルジャンクション型が好ましい。
【００１０】
また、２極式電位制御装置を用い、作用極と対極に白金を用い、両極間にかかる電位を一定に保ちながら電解し電流値を検出しても３極式電位制御装置を用いた場合と同様の相関が得られる。第１図は、３極式電位制御装置を用いた場合の装置の概略図、第２図は、２極式電位制御装置を用いた場合の装置の概略図である。
【００１１】
電極の表面積については特に制限はないが、検出電流値に影響するものであるから、求める電流の大きさに応じて決められる。ＮＯx ガスの発生量を一定レベルに制御しようとする場合、得られた電流値に応じて亜硝酸イオンと反応させるための過酸化水素を自動供給するのが好ましく、このような場合には、自動供給装置を制御させるに必要な電解電流値を取り出すことのできる大きさの電極表面が必要となる。電極間距離および電解温度は、安定した電解電流値を検出するために一定であることが好ましい。
【００１２】
第３図は、２極式電位制御装置を用いた場合の酸洗液の電位と電流値との関係を示すグラフである。亜硝酸イオンはイオンクロマトグラフで測定した。この硝酸、弗酸液は一般にステンレス鋼を酸洗する際に用いられる液であり、測定条件は以下のとおりである。
被測定酸洗液：硝酸１０重量％、弗酸４重量％、
電解温度：４０℃（スターラー攪拌状態）、
作用極および対極：白金線（表面積４．７ｃｍ2 ）、
極間距離：４ｃｍ、
液量：４００ｍｌ。
建浴直後の電位−電流値曲線とステンレス鋼（ＳＵＳ４３０）を浸漬した後の電位−電流値曲線を比較すると、常に浸漬後の電流値のほうが大きい。また、電圧が０．２０Ｖから１．２５Ｖの間では、建浴後の電流値が約１０ｍＡで一定している。
【００１３】
第４図は、電解電位０．５Ｖでの電解電流値と、イオンクロマトグラフによる亜硝酸イオン濃度の測定値および硝酸、弗酸液面上部でのＮＯx ガス検知管による測定値との関係を示すグラフである。このことよりＮＯx ガス発生量と電解電流値との間に比例関係があることが明瞭である。そして、この比例関係を利用すれば、一定の電解電流値以下になるように過酸化水素を添加することによって、ＮＯx ガスの発生量を抑制することができる。
【００１４】
本発明においては、電解電流の最大値の設定値は、上限とするＮＯx ガス濃度によって適宜選択される。例えば、ＮＯx ガス濃度を８０ｐｐｍ以下にする場合は、電解電位０．５Ｖでは、第４図より電流値が２０ｍＡになるまで過酸化水素を添加すればよい。この電解電流値の設定に応じてＮＯx ガス発生量を、ある基準値に一定に保つことができる。また、過酸化水素の添加方法は、簡便なオンオフ制御を用いることができる。
【００１５】
【実施例】
以下に本発明を実施例によって詳細に説明するが、本発明は実施例によって制限されるものでない。
【００１６】
実施例１
第２図に示す２電極式電圧制御装置を用いて、硝酸（１０重量％）、弗酸（４重量％）からなる酸洗液（１Ｌ、４０℃）でＳＵＳ４３０（３×５ｃｍ角板）を浸漬処理し溶解した。電解電位を０．５Ｖとし、電解電流値が２０ｍＡを越えると過酸化水素が添加されるように制御した。過酸化水素の添加による電解電流値の挙動は、第５図に示す変化であった。この場合、酸洗液の液面上部のＮＯxガス量は常に約８０ｐｐｍ以下であった。
【００１７】
実施例２
電解電流値が５ｍＡを越えると過酸化水素が添加されるよう制御した以外は、実施例１と同様の処理を行った。この場合、酸洗液の液面上部のＮＯx ガス量は常に約１０ｐｐｍ以下であった。
【００１８】
実施例３
第１図に示す３電極式電圧制御装置（参照電極に銀／塩化銀ダブルジャンクション電極）を用いて、硝酸（１０重量％）、弗酸（４重量％）からなる酸洗液（１Ｌ、４０℃）でＳＵＳ４３０（３×５ｃｍ角板）を浸漬処理し溶解した。電解電位を１．１Ｖ（vsＡｇ／ＡｇＣｌ）とし、電解電流値が２０ｍＡを越えると過酸化水素が添加されるように制御した。この場合、酸洗液の液面上部のＮＯx ガス量は常に約７０ｐｐｍ以下であった。
【００１９】
比較例１
硝酸（１０重量％）、弗酸（４重量％）からなる酸洗液（１Ｌ、４０℃）でＳＵＳ４３０（３×５ｃｍ角板）を浸漬処理し溶解した。この場合、酸洗液の液面上部のＮＯx ガス量はステンレス鋼の処理毎に増加し、最大１０００ｐｐｍに達した。
【００２０】
【発明の効果】
本発明によれば、ＮＯx ガス量に応じた必要最小限の過酸化水素添加量を制御することが可能となる。
【図面の簡単な説明】
【図１】３電極式電圧制御を用いた装置の概略図。
【図２】２電極式電圧制御を用いた装置の概略図。
【図３】２極式電位制御装置を用いた場合の酸洗液の電位と電流値との関係。
【図４】電解電位０．５Ｖ印可時の電解電流値と亜硝酸イオン濃度およびＮＯx ガス発生濃度との関係。
【図５】実施例１の電解電流値の挙動。
【符号の説明】
１：酸洗い浴
２：硝酸含有液
３：過酸化水素供給ポンプ
４：白金電極
５：参照電極
６：３電極式電圧制御装置（ポテンシオスタット）
７：２電極式電圧制御装置
８：供給ポンプ駆動制御信号
９：亜硝酸イオンが存在しない場合の電位−電流値曲線
１０：亜硝酸イオンが０．５５ｇ／Ｌの場合の電位−電流値曲線
１１：電流値とＮＯxガス発生濃度の関係
１２：電流値と亜硝酸イオン濃度の関係[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for suppressing the generation of NOx gas when a metal is treated in a nitric acid-containing liquid by adding hydrogen peroxide.
[0002]
[Prior art]
Although nitric acid is widely used in the industrial field, when a metal is treated using a nitric acid-containing liquid, NOx gas is often generated that adversely affects the environment and the human body. For example, in the case of pickling treatment of stainless steel with a mixed acid of nitric acid and hydrofluoric acid, nitrous acid is generated in the solution as the stainless steel is dissolved in the treatment solution. Nitrous acid undergoes various reactions in the solution to become NO and NO 2 and is released out of the system as NOx gas. Here, when a scrubber or the like is used for the treatment of NOx gas, the equipment cost of the exhaust gas treatment device is required, and regular maintenance is also required.
[0003]
On the other hand, there is a method for suppressing NOx gas by adding hydrogen peroxide to a nitric acid-containing liquid (US Pat. No. 3,945,865). Is a problem. This is because excessive addition merely decomposes itself in nitric acid or hydrofluoric acid solution in which metal ions are present, and wastes hydrogen peroxide. Japanese Patent Application Laid-Open No. 55-134694 discloses a method of adjusting the addition of hydrogen peroxide based on the oxidation-reduction potential of a nitrous acid-containing liquid, but the correlation between the oxidation-reduction potential and the concentration of nitrous acid is constant. It is difficult to adjust the amount of hydrogen peroxide added.
[0004]
[Problems to be solved by the invention]
An object of the present invention is to provide a method for solving the above-described problems in the prior art and effectively suppressing the generation of NOx gas in a nitric acid-containing liquid.
[0005]
[Means for Solving the Problems]
As a result of intensive studies on the adjustment of the amount of hydrogen peroxide added, the present inventors have found that when a nitric acid-containing liquid is electrolyzed at a constant potential, the electrolysis current value, the concentration of nitrite ions in the liquid, and the amount of NOx gas generated The inventors have found that there is a certain relationship between the two and arrived at the present invention.
[0006]
That is, the present invention relates to a method for suppressing the release of NOx gas from a nitric acid-containing liquid by the addition of hydrogen peroxide, wherein the nitric acid-containing liquid is electrolyzed at a constant potential, and the amount of hydrogen peroxide added based on the electrolysis current value. The present invention relates to a method for suppressing NOx gas, characterized by adjusting the above.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
The present invention is preferably used for a mixed acid of nitric acid and hydrofluoric acid used for pickling treatment of stainless steel, and a nitric acid-containing liquid used for surface treatment of copper, brass and the like. For example, pickling of stainless steel is processed batchwise or continuously, and the temperature of the nitric acid-containing liquid and the amount of dissolved metal also change, so the amount of NOx generated also changes. Therefore, the required amount of hydrogen peroxide to be added also varies with time.
[0008]
The present invention can also be applied to the case where the nitric acid-containing liquid used as the NOx absorbing solution is oxidized to nitric acid by adding hydrogen peroxide. For example, NOx gas generated by burning coal, oil or other fuel, or NOx gas generated from a facility for nitrification / oxidation of an organic compound using nitric acid is absorbed and oxidized.
[0009]
The constant-potential electrolysis method of the present invention is a method of performing electrolysis while keeping the cathode potential constant. Specifically, using a so-called three-electrode potential control device having a working electrode, a counter electrode, and a reference electrode, nitric acid, fluorine In this method, an acid solution is electrolyzed to detect a current value. Platinum is preferred because the working electrode and counter electrode materials must be stable and do not dissolve, and the electrolyte is nitric acid or hydrofluoric acid. The reference electrode is not particularly limited, but is preferably a resin-made silver / silver chloride electrode and double junction type that does not cause contamination of the electrolyte because glass is dissolved in hydrofluoric acid solution.
[0010]
In addition, using a bipolar electric potential control device, using platinum as the working electrode and the counter electrode, and using a tripolar electric potential control device even if the current value is detected by electrolysis while keeping the electric potential applied between the two electrodes constant. Similar correlation is obtained. FIG. 1 is a schematic diagram of an apparatus when a three-pole potential control device is used, and FIG. 2 is a schematic diagram of the device when a two-pole potential control device is used.
[0011]
Although there is no restriction | limiting in particular about the surface area of an electrode, Since it affects a detection electric current value, it determines according to the magnitude | size of the electric current calculated | required. When the amount of NOx gas generated is to be controlled to a certain level, it is preferable to automatically supply hydrogen peroxide for reaction with nitrite ions according to the obtained current value. An electrode surface having a size capable of extracting an electrolytic current value necessary for controlling the supply device is required. The distance between the electrodes and the electrolysis temperature are preferably constant in order to detect a stable electrolysis current value.
[0012]
FIG. 3 is a graph showing the relationship between the potential of the pickling solution and the current value when the bipolar potential control device is used. Nitrite ions were measured by ion chromatography. These nitric acid and hydrofluoric acid liquids are generally used when pickling stainless steel, and the measurement conditions are as follows.
Measurement pickling solution:
Electrolysis temperature: 40 ° C. (stirred stirring state)
Working electrode and counter electrode: platinum wire (surface area 4.7 cm 2 ),
Distance between electrodes: 4cm,
Liquid volume: 400 ml.
When the potential-current value curve immediately after the bathing is compared with the potential-current value curve after immersion of stainless steel (SUS430), the current value after immersion is always larger. Further, when the voltage is between 0.20 V and 1.25 V, the current value after the bathing is constant at about 10 mA.
[0013]
FIG. 4 shows the relationship between the electrolysis current value at an electrolysis potential of 0.5 V, the measured value of the nitrite ion concentration by ion chromatography, and the measured value by the NOx gas detector tube above the nitric acid and hydrofluoric acid liquid surfaces. It is a graph. From this, it is clear that there is a proportional relationship between the NOx gas generation amount and the electrolysis current value. If this proportional relationship is utilized, the amount of NOx gas generated can be suppressed by adding hydrogen peroxide so as to be equal to or less than a certain electrolysis current value.
[0014]
In the present invention, the set value of the maximum value of the electrolysis current is appropriately selected according to the NOx gas concentration as the upper limit. For example, when the NOx gas concentration is 80 ppm or less, hydrogen peroxide may be added at an electrolysis potential of 0.5 V until the current value reaches 20 mA from FIG. According to the setting of the electrolytic current value, the NOx gas generation amount can be kept constant at a certain reference value. In addition, as a method for adding hydrogen peroxide, simple on / off control can be used.
[0015]
【Example】
EXAMPLES The present invention will be described in detail below with reference to examples, but the present invention is not limited to the examples.
[0016]
Example 1
Using a two-electrode voltage controller shown in FIG. 2, SUS430 (3 × 5 cm square plate) was washed with a pickling solution (1 L, 40 ° C.) made of nitric acid (10 wt%) and hydrofluoric acid (4 wt%). It was immersed and dissolved. The electrolytic potential was 0.5 V, and control was performed so that hydrogen peroxide was added when the electrolytic current value exceeded 20 mA. The behavior of the electrolysis current value by the addition of hydrogen peroxide was the change shown in FIG. In this case, the amount of NOx gas above the pickling solution was always about 80 ppm or less.
[0017]
Example 2
The same treatment as in Example 1 was performed except that the hydrogen peroxide was controlled to be added when the electrolytic current value exceeded 5 mA. In this case, the amount of NOx gas at the upper surface of the pickling solution was always about 10 ppm or less.
[0018]
Example 3
Using a three-electrode voltage control device (a silver / silver chloride double junction electrode as a reference electrode) shown in FIG. 1, pickling solution (1 L, 40%) composed of nitric acid (10 wt%) and hydrofluoric acid (4 wt%) SUS430 (3 × 5 cm square plate) was subjected to immersion treatment at a temperature of (° C.) and dissolved. The electrolytic potential was 1.1 V (vsAg / AgCl), and control was performed so that hydrogen peroxide was added when the electrolytic current value exceeded 20 mA. In this case, the amount of NOx gas above the pickling solution was always about 70 ppm or less.
[0019]
Comparative Example 1
SUS430 (3 × 5 cm square plate) was immersed and dissolved in a pickling solution (1 L, 40 ° C.) composed of nitric acid (10 wt%) and hydrofluoric acid (4 wt%). In this case, the amount of NOx gas in the upper part of the pickling solution increased with each stainless steel treatment, reaching a maximum of 1000 ppm.
[0020]
【The invention's effect】
According to the present invention, it is possible to control the minimum hydrogen peroxide addition amount according to the NOx gas amount.
[Brief description of the drawings]
FIG. 1 is a schematic view of an apparatus using three-electrode voltage control.
FIG. 2 is a schematic view of an apparatus using two-electrode voltage control.
FIG. 3 shows the relationship between the potential of the pickling solution and the current value when a bipolar electrode potential control device is used.
FIG. 4 shows a relationship between an electrolysis current value when an electrolysis potential of 0.5 V is applied, a nitrite ion concentration, and a NOx gas generation concentration.
5 shows the behavior of the electrolytic current value in Example 1. FIG.
[Explanation of symbols]
1: Pickling bath 2: Nitric acid-containing liquid 3: Hydrogen peroxide supply pump 4: Platinum electrode 5: Reference electrode 6: Three-electrode voltage controller (potentiostat)
7: Two-electrode voltage control device 8: Supply pump drive control signal 9: Potential-
Claims (2)
Priority Applications (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP10167699A JP3901382B2 (en) | 1999-04-08 | 1999-04-08 | NOx gas suppression method using hydrogen peroxide |
| US09/542,847 US6475373B1 (en) | 1999-04-08 | 2000-04-04 | Method of controlling NOx gas emission by hydrogen peroxide |
| DE60003743T DE60003743T2 (en) | 1999-04-08 | 2000-04-06 | Process for controlling NOx gas emissions by hydrogen peroxide |
| EP00107103A EP1043422B1 (en) | 1999-04-08 | 2000-04-06 | Method of controlling NOx gas emission by hydrogen peroxide |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP10167699A JP3901382B2 (en) | 1999-04-08 | 1999-04-08 | NOx gas suppression method using hydrogen peroxide |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JP2000290787A JP2000290787A (en) | 2000-10-17 |
| JP3901382B2 true JP3901382B2 (en) | 2007-04-04 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP10167699A Expired - Lifetime JP3901382B2 (en) | 1999-04-08 | 1999-04-08 | NOx gas suppression method using hydrogen peroxide |
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| Country | Link |
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| JP (1) | JP3901382B2 (en) |
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- 1999-04-08 JP JP10167699A patent/JP3901382B2/en not_active Expired - Lifetime
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| Publication number | Publication date |
|---|---|
| JP2000290787A (en) | 2000-10-17 |
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