JP3924418B2 - Exhaust gas treatment catalyst and exhaust gas treatment method - Google Patents
Exhaust gas treatment catalyst and exhaust gas treatment method Download PDFInfo
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- JP3924418B2 JP3924418B2 JP2000172260A JP2000172260A JP3924418B2 JP 3924418 B2 JP3924418 B2 JP 3924418B2 JP 2000172260 A JP2000172260 A JP 2000172260A JP 2000172260 A JP2000172260 A JP 2000172260A JP 3924418 B2 JP3924418 B2 JP 3924418B2
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- Prior art keywords
- exhaust gas
- gas treatment
- catalyst
- titanium oxide
- treatment catalyst
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- 239000003054 catalyst Substances 0.000 title claims description 83
- 238000000034 method Methods 0.000 title claims description 15
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 claims description 63
- QGZKDVFQNNGYKY-UHFFFAOYSA-N ammonia Natural products N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 claims description 42
- OGIDPMRJRNCKJF-UHFFFAOYSA-N titanium oxide Inorganic materials [Ti]=O OGIDPMRJRNCKJF-UHFFFAOYSA-N 0.000 claims description 36
- 239000013078 crystal Substances 0.000 claims description 25
- 238000000634 powder X-ray diffraction Methods 0.000 claims description 15
- 239000013558 reference substance Substances 0.000 claims description 12
- 102100025490 Slit homolog 1 protein Human genes 0.000 claims description 8
- 101710123186 Slit homolog 1 protein Proteins 0.000 claims description 8
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 claims description 8
- 150000003609 titanium compounds Chemical class 0.000 claims description 8
- 239000007864 aqueous solution Substances 0.000 claims description 7
- LLZRNZOLAXHGLL-UHFFFAOYSA-J titanic acid Chemical compound O[Ti](O)(O)O LLZRNZOLAXHGLL-UHFFFAOYSA-J 0.000 claims description 6
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- 239000004480 active ingredient Substances 0.000 description 3
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Images
Description
【０００１】
【発明の属する技術分野】
本発明は、排ガス処理用触媒および排ガス処理方法に関する。特に、排ガス中のダイオキシン類などの毒性有機ハロゲン化合物を除去する有機ハロゲン化合物除去用触媒、排ガス中の窒素酸化物（ＮＯｘ）を除去するための脱硝触媒、及び排ガス中のアンモニアを分解するためのアンモニア分解触媒として優れた排ガス処理用触媒および排ガス処理方法に関する。
【０００２】
【従来の技術】
産業廃棄物や都市廃棄物を処理する焼却施設から発生する排ガス中にはダイオキシン類、ＰＣＢ、クロロフェノールなどの極微量の毒性有機ハロゲン化合物が含まれており、特にダイオキシン類は微量であってもきわめて有毒であり、人体に重大な影響を及ぼすため、その除去技術が早急に求められている。一般に有機ハロゲン化合物は化学的にきわめて安定であり、特にダイオキシン類においては自然界では半永久的に残存するといわれているほど分解しにくい物質であるのに加え、排ガス中でのその含有量が非常に低いため、これを効率よく除去することは従来の排ガス処理触媒では困難である。これまでにバナジウム酸化物やタングステン酸化物を酸化チタンに担持した触媒や白金をはじめとする貴金属触媒が用いられているが、排ガス条件によっては充分な性能とはいえず、さらなる触媒性能の向上が望まれている。
【０００３】
また、現在実用化されている排ガス中の窒素酸化物除去方法としては、アンモニアまたは尿素などの固体還元剤を用いて排ガス中の窒素酸化物を脱硝触媒上で接触還元し、無害な窒素と水とに分解する選択的触媒還元（ＳＣＲ）法が一般的である。これに用いられる脱硝触媒としては、例えば特開平１０−２３５２０６号公報に記載のチタン−バナジウム系触媒などが知られているが、排ガス条件によっては充分な性能とはいえず、さらなる触媒性能の向上が望まれている。
また、アンモニアを含有する排ガスの浄化においては、Ｐｔ−Ａｌ2Ｏ3触媒などの貴金属触媒や、Ｎｉ、Ｍｎ、Ｃｕ、Ｆｅ等の金属酸化物系触媒が一般的であるが、アンモニア分解活性が高くなると、反応生成物として窒素、水の他にＮＯｘが生成するという問題も残されており、これらの解決が望まれている。
【０００４】
【発明が解決しようとする課題】
本発明の課題は、排ガス中のダイオキシン類などの有機ハロゲン化合物の除去性能、脱硝性能、アンモニア分解性能に優れた触媒、および、この触媒を用いた排ガス処理方法を提供することである。
【０００５】
【課題を解決するための手段】
本発明者らは、酸化チタンを含有する触媒が基本的には有効であることを確認した上で、一般的に有機ハロゲン化合物の除去、脱硝、アンモニア分解において高活性であるとされてきたアナタース構造の割合の高い酸化チタンに代えて、アモルファス構造の割合のより高い酸化チタンを用いることにより、排ガス中の微量の有害物質（有機ハロゲン化合物、窒素酸化物、アンモニア）に対する吸着力および排ガスの触媒に対する接触効率を向上させ、排ガス中に含まれる極微量の有害物質の分解反応を促進するよう触媒設計したものである。
【０００６】
すなわち、本発明にかかる排ガス処理用触媒は、アモルファス相の酸化チタンを含有する有機ハロゲン化合物除去用触媒において、前記酸化チタンが、可溶性チタン化合物水溶液とアンモニア水との中和反応によりチタン水酸化物を調製し３５０℃〜５５０℃で焼成することにより得るものであり、粉末Ｘ線回折の２θ＝２４．７゜〜２５．７゜の間に存在するアナタース結晶を示すピークの強度が、基準物質である５重量％Ｖ２Ｏ５−９５重量％ＴｉＯ２（ミレニアム社製酸化チタンＤＴ−５１）の粉末Ｘ線回折の２θ＝２４．７゜〜２５．７゜の間に存在するアナタース結晶を示すピークの強度の３０％以上、７５％以下であることを特徴とする。
また、下記の条件で測定した粉末Ｘ線回折の２θ＝２４．７゜〜２５．７゜の間に存在するアナタース結晶を示すピークの強度が３８５０カウント／秒以上、１００００カウント／秒以下であることを特徴とする。
【０００７】
機種 Ｒｉｇａｋｕ ＲＥ−３００
Ｘ線源 ＣｕＫα１／５０ｋＶ／３００ｍＡ
カウンタ シンチレーションカウンタ
フィルタ なし
モノクロメータ 湾曲結晶モノクロメータ
発散スリット １゜
散乱スリット １゜
受光スリット ０．３ｍｍ
スキャンスピード ４゜／ｍｉｎ
【０００８】
【発明の実施の形態】
以下、本発明を詳細に説明する。
本発明の触媒はその構成成分としてアモルファス相の酸化チタンを一定量以上含有すること、すなわち、粉末Ｘ線回折の２θ＝２４．７゜〜２５．７゜の間に存在するアナタース結晶を示すピークの強度が、基準物質の粉末Ｘ線回折の２θ＝２４．７゜〜２５．７゜の間に存在するアナタース結晶を示すピークの強度の７５％以下であることを特徴とし、好ましくは５０％以下である。言い換えれば、上記基準物質について下記の条件で測定した粉末Ｘ線回折の２θ＝２４．７゜〜２５．７゜の間に存在するアナタース結晶を示すピークの強度が約１３０２７カウント／秒であるため、本発明の触媒はその７５％の値である約１００００カウント／秒以下であることを特徴とし、好ましくは６５００カウント／秒以下である。
【０００９】
機種 Ｒｉｇａｋｕ ＲＥ−３００
Ｘ線源 ＣｕＫα１／５０ｋＶ／３００ｍＡ
カウンタ シンチレーションカウンタ
フィルタ なし
モノクロメータ 湾曲結晶モノクロメータ
発散スリット １゜
散乱スリット １゜
受光スリット ０．３ｍｍ
スキャンスピード ４゜／ｍｉｎ
酸化チタンのアナタース結晶は粉末Ｘ線回折の２θ＝２４．７゜〜２５．７゜の間にピークを示すが、アモルファス相の酸化チタンは結晶ピークを示さない。したがって、上記ピークの強度が小さければ小さいほど、アナタース型の酸化チタンの割合が少なく、アモルファス相の酸化チタンの割合が多い傾向がある。本発明で用いる基準物質は、５重量％Ｖ2Ｏ5−９５重量％ＴｉＯ2（ミレニアム社製酸化チタンＤＴ−５１）であり、その製法は、後述の実施例に示すとおりである。基準物質中の酸化チタンはアナタース型の割合が非常に高いものである。
【００１０】
本発明の触媒を調製する際に使用するチタン源の種類については特に制限はなく、酸化チタンの他、焼成してチタン酸化物を生成するものであればよい。例えば、四塩化チタン、硫酸チタンなどの無機チタン化合物、及びシュウ酸チタン、テトライソプロピルチタネート等の有機チタン化合物を用いることができるが、可溶性チタン化合物またはチタンアルコキシドを用いることが好ましい。
本発明の触媒は、構成成分として、バナジウム、モリブデン、タングステン、マンガン、コバルト、ニッケル、亜鉛、ジルコニウム、ニオブ、スズ、タンタル、ランタンおよびセリウムよりなる群から選ばれる少なくとも１種類の酸化物を含有することが好ましく、これらの中でも特にバナジウムの酸化物が好ましい。これらの酸化物の含有量は０．１〜５０重量％であることが好ましく、より好ましくは５〜２０重量％である。
【００１１】
これらの金属酸化物を含有する場合にも、それぞれの元素の出発原料について特に制限はない。これらの酸化物の他、焼成後にその酸化物を生じる水酸化物、アンモニウム塩、シュウ酸塩、ハロゲン化物、硫酸塩、硝酸塩などのいずれも使用することができる。
本発明の触媒は、構成成分として、さらにパラジウム、白金、ロジウム、ルテニウム、銀、金およびイリジウムよりなる群から選ばれる少なくとも１種類の金属および／またはその金属酸化物を含有することが好ましく、これらの中でも特に白金が好ましい。これらの金属および／またはその金属酸化物の含有量は０．０１〜５重量％であることが好ましく、より好ましくは０．０５〜０．５重量％である。
【００１２】
本発明の触媒を調製するには、可溶性チタン化合物の中和またはチタンアルコキシドの加水分解によりチタン水酸化物を調製し、これを３５０℃〜５５０℃で、好ましくは４００℃〜５００℃で焼成して酸化チタンを得ることが好ましい。焼成温度が３５０℃未満では、反応中に触媒が熱劣化をおこす可能性が高い。焼成温度が５５０℃を超えると、アナタース型の酸化チタンの割合が多くなる。
具体的には、例えば以下の手順によって調製されることが好ましい。（Ａ）塩化チタン等の可溶性チタン化合物の水溶液を攪拌しながら、これにアンモニアなどの塩基を滴下し、チタンの水酸化物沈殿を得る。最終的にｐＨが６〜９となったところで沈殿が完了したものとする。酸化チタンの結晶核の生成を抑えるため塩基物質を滴下中は水溶液の温度を５０℃以下に保持することが好ましい。沈殿を熟成し、よく洗浄後、上記温度範囲で焼成をおこなう。（Ｂ）蒸留水を攪拌しながら、チタンのアルコキシドを滴下し、チタンの水酸化物沈殿を得る。沈殿を完了させるため、少量のアンモニアを添加する。沈殿をよく洗浄後、上記温度範囲で焼成をおこなう。また、（Ａ）、（Ｂ）のチタンの水酸化物沈殿にケイ素、イットリウム、セリウム、硫黄などの酸化物または塩類を添加したのち焼成することによって、あるいは（Ａ）、（Ｂ）のチタンの水酸化物沈殿時にケイ素、イットリウム、セリウム、硫黄などの酸化物または塩類を同時に共沈させたのち焼成することによって、酸化チタンのアナタース結晶化およびルチル結晶化を抑制し、４００℃以上の焼成温度においても酸化チタンのアモルファス構造を維持させることができる。
【００１３】
酸化チタン（以下、「Ａ成分」という）にバナジウム、モリブデン、タングステン、マンガン、コバルト、ニッケル、亜鉛、ジルコニウム、ニオブ、スズ、タンタル、ランタンおよびセリウムよりなる群から選ばれる少なくとも１種類の酸化物（以下、「Ｂ成分」という）を添加する方法としては、例えばＡ成分の粉体又はスラリーにＢ成分の塩類もしくはその溶液を添加する方法や、また、Ａ成分の成型体にＢ成分の塩類の溶液を含浸担持させる方法などが挙げられる。すなわち本発明の触媒の成型体は、上記Ａ成分とＢ成分又はその塩類とからなる粉体やスラリーなどから成型して用いてもよく、また上記Ａ成分よりなる成型体にＢ成分を担持して用いることもできる。
【００１４】
また、本発明の触媒は、板状、波板状、網状、ハニカム状、円柱状、円筒状などの形状に成型して用いても良いし、アルミナ、シリカ、コーディライト、チタニア、ステンレス金属などよりなる板状、波板状、網状、ハニカム状、円柱状、円筒状などの形状の担体に担持して使用しても良い。
本発明の触媒を用いることにより、排ガス中の微量の有害物質に対する吸着力および排ガスの触媒に対する接触効率が向上するだけでなく、アナタース型酸化チタンやルチル型酸化チタンを用いた場合に比べてバナジウム酸化物などの活性成分含有量を著しく増加させることができる。
【００１５】
本発明の触媒は、各種排ガスの処理に用いられる。排ガスの組成については特に制限はないが、本発明の触媒は、有機ハロゲン化合物除去用触媒、脱硝触媒、アンモニア分解触媒として非常に有用である。
本発明の触媒を有機ハロゲン化合物除去用触媒として用いる場合、本発明の触媒を用いて処理する排ガスの組成については、有機ハロゲン化合物を含むものであれば特に制限はないが、本発明の触媒は特にダイオキシン類やＰＣＢを含む排ガスの処理に好適である。本発明の触媒を用いて有機ハロゲン化合物を除去するには、排ガスを１３０〜３５０℃の温度、好ましくは１５０〜２５０℃の温度で、本発明の触媒と接触させることが望ましい。
【００１６】
本発明の触媒を脱硝触媒として用いる場合、本発明の触媒をアンモニアや尿素などの還元剤の存在下、排ガスと接触させ、排ガス中の窒素酸化物を還元除去する。この際の条件については、特に制限がなく、この種の反応に一般的に用いられている条件で実施することができる。具体的には、排ガスの種類、性状、要求される窒素酸化物の分解率などを考慮して適宜決定すればよいが、温度は、１３０〜５５０℃であることが好ましい。排ガス温度が１３０℃より低いと脱硝効率が低下し、５５０℃を超えると活性成分のシンタリングなどの問題が起こる。
本発明の触媒をアンモニア分解触媒として用いる場合、条件については特に制限がなく、この種の反応に一般的に用いられている条件で実施することができる。排ガス処理温度については１３０〜５５０℃であることが好ましい。１３０℃未満では分解効率が低くなるからであり、５５０℃を超える場合は活性成分のシンタリングおよびＮＯｘの生成がおこるからである。
【００１７】
本発明の触媒を用いた排ガスの処理条件については、排ガスの種類、性状、要求されるダイオキシン類などの有機ハロゲン化合物の分解率などにより異なるので一概に特定できないが、実施に際しては、これらの条件を考慮して適宜決定すればよい。処理対象ガスの本発明の触媒に対する空間速度は、１００〜１０００００Hr-1、好ましくは２００〜５００００Hr-1の範囲にあるのがよい。１００Hr-1未満の場合は、処理装置が大きくなりすぎ非効率であり、１０００００Hr-1を超える場合は、分解効率が低下するためである。
【００１８】
【実施例】
以下に実施例を用いて本発明をさらに詳細に説明するが、本発明はこれら実施例のみに限定されるものではない。
なお、粉末Ｘ線回折は下記条件にて測定した。
機種 Ｒｉｇａｋｕ ＲＥ−３００
Ｘ線源 ＣｕＫα１／５０ｋＶ／３００ｍＡ
カウンタ シンチレーションカウンタ
フィルタ なし
モノクロメータ 湾曲結晶モノクロメータ
発散スリット １゜
散乱スリット １゜
受光スリット ０．３ｍｍ
スキャンスピード ４゜／ｍｉｎ
［調製例（基準物質の合成）］
酸化チタン（ミレニアム社製ＤＴ−５１）２０ｋｇにメタバナジン酸アンモニウム１．４ｋｇ、シュウ酸１．７ｋｇ、モノエタノールアミン０．４ｋｇを水５リットルに溶解させた薬液を加え、均一になるまで充分に混合した。次いで、８０℃で乾燥後、４５０℃で５時間空気雰囲気下で焼成し、Ｖ2Ｏ5：ＴｉＯ2重量比＝５：９５の組成をもつ基準物質を得た。
【００１９】
得られた基準物質の粉末Ｘ線回折スペクトルを図１に示す。２θ＝２４．７゜〜２５．７゜の間に存在するアナタース結晶を示すピークの強度は１３０２７カウント／秒であった。
［実施例１］
酸化チタンを以下に述べる方法で調製した。１０重量％アンモニア水７００リットルに硫酸チタニルの硫酸溶液（ＴｉＯ2として１２５ｇ／リットル、硫酸濃度５５０ｇ／リットル）３４０リットルを撹拌しながら徐々に滴下した。得られたゲルを３時間放置後、濾過水洗し、続いて１００℃で１０時間乾燥した。次いで４００℃で焼成した。アナタース結晶を示すＸ線回折ピークの強度は３８５０カウント／秒であり、基準物質の３０％であった。
【００２０】
次に、上記酸化チタン２０ｋｇにメタバナジン酸アンモニウム１．４ｋｇ、シュウ酸１．７ｋｇ、モノエタノールアミン０．４ｋｇを水５リットルに溶解させた薬液を加え、さらにフェノール樹脂１ｋｇと成形助剤として澱粉を加えて混合しニーダーで混練りした後、押し出し成型機で外形８０ｍｍ角、目開き４．０ｍｍ、肉厚１．０ｍｍ、長さ５００ｍｍのハニカム状に成形した。次いで８０℃で乾燥後、３８０℃で５時間空気雰囲気下で焼成し、触媒（Ａ）を得た。こうして得られた触媒（Ａ）の組成は、Ｖ2Ｏ5：ＴｉＯ2＝５：９５（重量比）であった。アナタース結晶を示すＸ線回折ピークの強度は４６８８カウント／秒であり、基準物質の３６％であった。
【００２１】
触媒（Ａ）の粉末Ｘ線回折スペクトルを図２に示す。
［実施例２］
実施例１に述べた方法と同様の調製法で、Ｖ2Ｏ5：ＴｉＯ2＝３：９７（重量比）の組成をもつ触媒（Ｂ）を調製した。アナタース結晶を示すＸ線回折ピークの強度は４３２６カウント／秒であり、基準物質の３３％であった。
［実施例３］
実施例１に述べた方法と同様の調製法で、Ｖ2Ｏ5：ＴｉＯ2＝１０：９０（重量比）の組成をもつ触媒（Ｃ）を調製した。アナタース結晶を示すＸ線回折ピークの強度は４７９６カウント／秒であり、基準物質の３７％であった。
【００２２】
［実施例４］
実施例１で調製された触媒（Ａ）を、０．０１Ｍ硝酸パラジウム水溶液に含浸した後、１２０℃で乾燥、３５０℃で焼成し、触媒（Ｄ）を得た。酸化パラジウムの担持量は０．０６重量％であった。
［比較例１］
実施例１に述べた方法で調製された酸化チタンをさらに５５０℃で焼成し、アナタース結晶度の高い酸化チタンを得た。アナタース結晶を示すＸ線回折ピークの強度は１０３４３カウント／秒であり、基準物質の７９％であった。このアナタース結晶度の高い酸化チタン２０ｋｇにメタバナジン酸アンモニウム１．４ｋｇ、シュウ酸１．７ｋｇ、モノエタノールアミン０．４ｋｇを水５リットルに溶解させた薬液を加え、さらにフェノール樹脂１ｋｇと成形助剤として澱粉を加えて混合しニーダーで混練りした後、押し出し成型機で外形８０ｍｍ角、目開き４．０ｍｍ、肉厚１．０ｍｍ、長さ５００ｍｍのハニカム状に成形した。次いで８０℃で乾燥後、４５０℃で５時間空気雰囲気下で焼成し、触媒（Ａ′）を得た。こうして得られた触媒（Ａ′）の組成は、Ｖ2Ｏ5：ＴｉＯ2＝５：９５（重量比）であった。アナタース結晶を示すＸ線回折ピークの強度は１１７２６カウント／秒であり、基準物質の９０％であった。
【００２３】
［比較例２］
比較例１に述べた方法と同様の調製法で、Ｖ2Ｏ5：ＴｉＯ2＝３：９７（重量比）の組成をもつ触媒（Ｂ′）を調製した。アナタース結晶を示すＸ線回折ピークの強度は１１６６５カウント／秒であり、基準物質の９０％であった。
［比較例３］
比較例１に述べた方法と同様の調製法で、Ｖ2Ｏ5：ＴｉＯ2＝１０：９０（重量比）の組成をもつ触媒（Ｃ′）を調製した。アナタース結晶を示すＸ線回折ピークの強度は１１７９６カウント／秒であり、基準物質の９１％であった。
【００２４】
［比較例４］
比較例１で調製された触媒（Ａ′）を、０．０１Ｍ硝酸パラジウム水溶液に含浸した後、１２０℃で乾燥、３５０℃で焼成し、触媒（Ｄ′）を得た。酸化パラジウムの担持量は０．０６重量％であった。
［実施例５］
実施例１〜４および比較例１〜４で調製した触媒（Ａ）〜（Ｄ）、（Ａ′）〜（Ｄ′）を用いて有機塩素化合物分解試験を行った。処理対象となる有機塩素化合物としてクロロフェノール（以下、ＣＰと略す）を用い、以下の条件で反応を行った。
【００２５】
結果を表１に示す。ＣＰ分解率すなわちＣＰ除去率は下記式により求めた。
（試験条件）
処理ガス組成
ＣＰ：３０ｐｐｍ，Ｏ2：１０％，Ｈ2Ｏ：１５％，Ｎ2：Balance
ガス温度：１６０℃
空間速度（ＳＶ）：４０００Ｈｒ-1
（式）
ＣＰ分解率（％）＝［（反応器入口ＣＰ濃度）−（反応器出口ＣＰ濃度）］／（反応器入口ＣＰ濃度）×１００
【００２６】
【表１】
表１に見るように、比較例の触媒では、バナジウム酸化物含有量の増加に伴い、有機ハロゲン化合物除去率は増大するものの５％以上では増大がほとんど認められない。一方、実施例のアモルファス酸化チタンを多く含む触媒の場合、バナジウム酸化物含有量の増加に伴い、有機ハロゲン化合物除去率は増大し、１０％においては従来の触媒に比べて遥かに高い有機ハロゲン化合物除去率を示す。
［実施例６］
実施例１および比較例１で調製した触媒（Ａ）、（Ａ′）を用いて以下の条件で脱硝反応を行った。脱硝率を下記式により求めたところ、触媒（Ａ）については９９％であり、触媒（Ａ′）については９４％であった。
【００２８】
（試験条件）
処理ガス組成
ＮＯ：１９０ｐｐｍ，ＮＨ3：１９０ｐｐｍ，Ｏ2：９％，
Ｈ2Ｏ：１７％，：Ｎ2：Balance
ガス温度：２５０℃
空間速度（ＳＶ）：４０００Ｈｒ-1
（式）
脱硝率（％）＝［（反応器入口ＮＯｘ濃度）−（反応器出口ＮＯｘ濃度）］／（反応器入口ＮＯｘ濃度）×１００
［実施例７］
実施例４および比較例４で調製した触媒（Ｄ）、（Ｄ′）を用いて以下の条件でアンモニア分解反応を行った。アンモニア分解率を下記式により求めたところ、触媒（Ｄ）については９８％であり、触媒（Ｄ′）については９３％であった。
【００２９】
（試験条件）
処理ガス組成
ＮＨ3：３０ｐｐｍ，Ｏ2：２％，Ｈ2Ｏ：１０％，：Ｎ2：Balance
ガス温度：３３０℃
空間速度（ＳＶ）：４０００Ｈｒ-1
（式）
アンモニア分解率（％）＝［（反応器入口アンモニア濃度）−（反応器出口アンモニア濃度）］／（反応器入口アンモニア濃度）×１００
【００３０】
【発明の効果】
本発明の触媒は、ダイオキシン類などの毒性有機ハロゲン化合物の分解活性やアンモニア分解活性に優れる。また、脱硝性能にも優れ、窒素酸化物とダイオキシン類などの毒性有機ハロゲン化合物の同時除去触媒として有用である。
【図面の簡単な説明】
【図１】 調製例で調製した基準物質の粉末Ｘ線回折スペクトル
【図２】 実施例１で調製した触媒（Ａ）の粉末Ｘ線回折スペクトル[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a medium you and exhaust gas processing method catalyst for exhaust gas treatment. In particular, an organic halogen compound removing catalyst for removing toxic organic halogen compounds such as dioxins in exhaust gas, a denitration catalyst for removing nitrogen oxides (NOx) in exhaust gas, and an element for decomposing ammonia in exhaust gas. excellent catalytic contact and the exhaust gas processing method for an exhaust gas treatment as an ammonia decomposition catalyst.
[0002]
[Prior art]
Exhaust gas generated from incineration facilities that treat industrial waste and municipal waste contains trace amounts of toxic organic halogen compounds such as dioxins, PCBs, and chlorophenols. Because it is extremely toxic and has a serious effect on the human body, its removal technology is urgently required. In general, organohalogen compounds are chemically very stable. In particular, dioxins are substances that are said to remain semipermanent in nature and are not easily decomposed, and their content in exhaust gas is very low. Therefore, it is difficult to remove this efficiently with a conventional exhaust gas treatment catalyst. So far, catalysts with vanadium oxide or tungsten oxide supported on titanium oxide and noble metal catalysts such as platinum have been used, but depending on the exhaust gas conditions, it is not sufficient performance, and further improvement in catalyst performance can be achieved. It is desired.
[0003]
In addition, as a method for removing nitrogen oxides in exhaust gas currently in practical use, nitrogen oxides in exhaust gas are contact-reduced on a denitration catalyst using a solid reducing agent such as ammonia or urea, and harmless nitrogen and water are removed. A selective catalytic reduction (SCR) method is generally used which decomposes into As a denitration catalyst used for this, for example, a titanium-vanadium catalyst described in JP-A-10-235206 is known, but depending on the exhaust gas conditions, it cannot be said that the performance is sufficient, and further improvement of the catalyst performance. Is desired.
Moreover, in the purification of exhaust gas containing ammonia, noble metal catalysts such as Pt—Al 2 O 3 catalyst and metal oxide catalysts such as Ni, Mn, Cu, and Fe are generally used. When it becomes high, the problem of generating NOx in addition to nitrogen and water remains as a reaction product, and these solutions are desired.
[0004]
[Problems to be solved by the invention]
An object of the present invention is to provide removal performance of organic halogen compounds such as dioxins in the exhaust gas, the denitration performance, ammonia decomposition performance superior catalytic, your and exhaust gas treatment process using the catalyst.
[0005]
[Means for Solving the Problems]
The present inventors have confirmed that a catalyst containing titanium oxide is basically effective, and in general, anatase has been considered to be highly active in the removal of organic halogen compounds, denitration, and ammonia decomposition. By using titanium oxide with a higher proportion of amorphous structure instead of titanium oxide with a higher proportion of structure, adsorption power for trace amounts of harmful substances (organohalogen compounds, nitrogen oxides, ammonia) in exhaust gas and exhaust gas catalyst The catalyst is designed to improve the contact efficiency with respect to the gas and to promote the decomposition reaction of trace amounts of harmful substances contained in the exhaust gas.
[0006]
That is , the exhaust gas treatment catalyst according to the present invention is an organic halogen compound removal catalyst containing amorphous phase titanium oxide , wherein the titanium oxide is a titanium hydroxide by a neutralization reaction between a soluble titanium compound aqueous solution and aqueous ammonia. The intensity of the peak showing anatase crystals existing between 2θ = 24.7 ° and 25.7 ° in the powder X-ray diffraction is obtained by baking at 350 ° C. to 550 ° C. Anatase crystals existing between 2θ = 24.7 ° to 25.7 ° of powder X-ray diffraction of 5 wt% V 2 O 5 -95 wt% TiO 2 (titanium oxide DT-51 manufactured by Millennium) It is characterized by being 30% or more and 75% or less of the intensity of the peak shown.
In addition, the intensity of the peak indicating anatase crystals existing between 2θ = 24.7 ° to 25.7 ° of powder X-ray diffraction measured under the following conditions is 3850 counts / second or more and 10,000 counts / second or less. It is characterized by that.
[0007]
Model Rigaku RE-300
X-ray source CuKα1 / 50kV / 300mA
Counter Scintillation counter filter None Monochromator Curved crystal monochromator Divergence slit 1 ° Scattering slit 1 ° Receiving slit 0.3mm
Scanning speed 4 ° / min
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail.
The catalyst of the present invention contains a certain amount or more of an amorphous phase titanium oxide as a constituent component, that is, a peak showing anatase crystals existing between 2θ = 24.7 ° to 25.7 ° of powder X-ray diffraction. Is less than 75% of the peak intensity of anatase crystals existing between 2θ = 24.7 ° to 25.7 ° of the powder X-ray diffraction of the reference substance, preferably 50% It is as follows. In other words, the intensity of the peak indicating the anatase crystal existing between 2θ = 24.7 ° to 25.7 ° of the powder X-ray diffraction measured for the above-mentioned reference substance under the following conditions is about 13027 counts / second. The catalyst of the present invention is characterized by 75% or less of about 10,000 counts / second, and preferably 6500 counts / second or less.
[0009]
Model Rigaku RE-300
X-ray source CuKα1 / 50kV / 300mA
Counter Scintillation counter filter None Monochromator Curved crystal monochromator Divergence slit 1 ° Scattering slit 1 ° Receiving slit 0.3mm
Scanning speed 4 ° / min
Anatase crystals of titanium oxide show a peak between 2θ = 24.7 ° to 25.7 ° of powder X-ray diffraction, but titanium oxide in an amorphous phase shows no crystal peak. Therefore, the smaller the intensity of the peak, the smaller the proportion of anatase-type titanium oxide and the larger the proportion of titanium oxide in the amorphous phase. The reference substance used in the present invention is 5% by weight V 2 O 5 -95% by weight TiO 2 (Titanium oxide DT-51 manufactured by Millennium), and the production method is as shown in the examples described later. Titanium oxide in the reference material has a very high anatase-type ratio.
[0010]
There is no restriction | limiting in particular about the kind of titanium source used when preparing the catalyst of this invention, What is necessary is just to produce | generate a titanium oxide by baking other than titanium oxide. For example, inorganic titanium compounds such as titanium tetrachloride and titanium sulfate, and organic titanium compounds such as titanium oxalate and tetraisopropyl titanate can be used, but a soluble titanium compound or titanium alkoxide is preferably used.
The catalyst of the present invention contains at least one oxide selected from the group consisting of vanadium, molybdenum, tungsten, manganese, cobalt, nickel, zinc, zirconium, niobium, tin, tantalum, lanthanum and cerium as a constituent component. Of these, vanadium oxide is particularly preferable. The content of these oxides is preferably 0.1 to 50% by weight, more preferably 5 to 20% by weight.
[0011]
Even when these metal oxides are contained, there are no particular restrictions on the starting materials of the respective elements. In addition to these oxides, any of hydroxides, ammonium salts, oxalates, halides, sulfates, nitrates, and the like that generate the oxides after firing can be used.
The catalyst of the present invention preferably contains at least one metal selected from the group consisting of palladium, platinum, rhodium, ruthenium, silver, gold and iridium and / or a metal oxide thereof as a constituent component. Of these, platinum is particularly preferred. The content of these metals and / or metal oxides thereof is preferably 0.01 to 5% by weight, more preferably 0.05 to 0.5% by weight.
[0012]
To prepare the catalyst of the present invention, a titanium hydroxide is prepared by neutralizing a soluble titanium compound or hydrolyzing a titanium alkoxide, and calcining at 350 ° C. to 550 ° C., preferably 400 ° C. to 500 ° C. Thus, it is preferable to obtain titanium oxide. If the calcination temperature is less than 350 ° C., the catalyst is likely to undergo thermal degradation during the reaction. When the firing temperature exceeds 550 ° C., the proportion of anatase-type titanium oxide increases.
Specifically, for example, it is preferably prepared by the following procedure. (A) While stirring an aqueous solution of a soluble titanium compound such as titanium chloride, a base such as ammonia is added dropwise thereto to obtain a hydroxide precipitate of titanium. It is assumed that the precipitation is completed when the pH finally reaches 6-9. In order to suppress generation of crystal nuclei of titanium oxide, it is preferable to keep the temperature of the aqueous solution at 50 ° C. or lower during the dropwise addition of the basic substance. The precipitate is aged, washed well, and then fired in the above temperature range. (B) While stirring distilled water, titanium alkoxide is dropped to obtain titanium hydroxide precipitate. A small amount of ammonia is added to complete the precipitation. After thoroughly washing the precipitate, firing is performed in the above temperature range. Further, by adding an oxide or salt such as silicon, yttrium, cerium, sulfur or the like to the titanium hydroxide precipitate of (A) or (B) and firing, or (T) of titanium of (A) or (B) By simultaneously co-precipitating oxides or salts of silicon, yttrium, cerium, sulfur, etc. during hydroxide precipitation and then firing, the anatase crystallization and rutile crystallization of titanium oxide are suppressed, and the firing temperature is 400 ° C. or higher. In this case, the amorphous structure of titanium oxide can be maintained.
[0013]
At least one oxide selected from the group consisting of vanadium, molybdenum, tungsten, manganese, cobalt, nickel, zinc, zirconium, niobium, tin, tantalum, lanthanum and cerium (hereinafter referred to as “component A”) Hereinafter, as a method of adding "B component", for example, a method of adding a salt of B component or a solution thereof to a powder or slurry of A component, or a method of adding a salt of B component to a molded product of A component Examples include a method of impregnating and supporting a solution. That is, the molded article of the catalyst of the present invention may be used by molding from a powder or slurry comprising the A component and the B component or a salt thereof, and the molded article comprising the A component carries the B component. Can also be used.
[0014]
Further, the catalyst of the present invention may be used after being molded into a plate shape, a corrugated plate shape, a net shape, a honeycomb shape, a columnar shape, a cylindrical shape, alumina, silica, cordierite, titania, stainless steel, etc. It may be used by being supported on a carrier having a plate shape, corrugated plate shape, net shape, honeycomb shape, columnar shape, cylindrical shape or the like.
By using the catalyst of the present invention, not only the adsorption power for a trace amount of harmful substances in the exhaust gas and the contact efficiency of the exhaust gas to the catalyst are improved, but also vanadium as compared with the case where anatase type titanium oxide or rutile type titanium oxide is used. The content of active ingredients such as oxides can be significantly increased.
[0015]
The catalyst of the present invention is used for treating various exhaust gases. The composition of the exhaust gas is not particularly limited, but the catalyst of the present invention is very useful as an organic halogen compound removal catalyst, a denitration catalyst, and an ammonia decomposition catalyst.
When the catalyst of the present invention is used as a catalyst for removing an organic halogen compound, the composition of the exhaust gas treated with the catalyst of the present invention is not particularly limited as long as it contains an organic halogen compound, It is particularly suitable for treating exhaust gas containing dioxins and PCBs. In order to remove the organic halogen compound using the catalyst of the present invention, it is desirable to contact the exhaust gas with the catalyst of the present invention at a temperature of 130 to 350 ° C, preferably 150 to 250 ° C.
[0016]
When the catalyst of the present invention is used as a denitration catalyst, the catalyst of the present invention is brought into contact with exhaust gas in the presence of a reducing agent such as ammonia or urea to reduce and remove nitrogen oxides in the exhaust gas. The conditions at this time are not particularly limited, and can be carried out under conditions generally used for this type of reaction. Specifically, the temperature is preferably 130 to 550 ° C., although it may be appropriately determined in consideration of the type and properties of exhaust gas, the required decomposition rate of nitrogen oxides, and the like. When the exhaust gas temperature is lower than 130 ° C, the denitration efficiency is lowered, and when it exceeds 550 ° C, problems such as sintering of the active ingredient occur.
When the catalyst of the present invention is used as an ammonia decomposition catalyst, the conditions are not particularly limited, and the reaction can be carried out under conditions generally used for this type of reaction. The exhaust gas treatment temperature is preferably 130 to 550 ° C. It is because decomposition efficiency will become low if it is less than 130 degreeC, and since it will sinter an active ingredient and the production | generation of NOx will occur when it exceeds 550 degreeC.
[0017]
The treatment conditions of the exhaust gas using the catalyst of the present invention cannot be specified in general because it differs depending on the type and properties of the exhaust gas, the decomposition rate of the required organic halogen compounds such as dioxins, etc. May be appropriately determined in consideration of the above. Space velocity relative to the catalyst of the present invention to be processed gas, 100~100000Hr -1, preferably, from the 200~50000Hr -1. If it is less than 100 Hr −1 , the processing apparatus becomes too large and inefficient, and if it exceeds 100,000 Hr −1 , the decomposition efficiency is lowered.
[0018]
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples.
Powder X-ray diffraction was measured under the following conditions.
Model Rigaku RE-300
X-ray source CuKα1 / 50kV / 300mA
Counter Scintillation counter filter None Monochromator Curved crystal monochromator Divergence slit 1 ° Scattering slit 1 ° Receiving slit 0.3mm
Scanning speed 4 ° / min
[Preparation Example (Synthesis of Reference Material)]
Add chemical solution prepared by dissolving 1.4 kg of ammonium metavanadate, 1.7 kg of oxalic acid, 0.4 kg of monoethanolamine in 5 liters of water to 20 kg of titanium oxide (DT-51 manufactured by Millennium) and mix well until uniform. did. Next, after drying at 80 ° C., baking was performed at 450 ° C. in an air atmosphere for 5 hours to obtain a reference material having a composition of V 2 O 5 : TiO 2 weight ratio = 5: 95.
[0019]
The powder X-ray diffraction spectrum of the obtained reference material is shown in FIG. The intensity of the peak indicating the anatase crystal existing between 2θ = 24.7 ° and 25.7 ° was 13027 counts / second.
[Example 1]
Titanium oxide was prepared by the method described below. To 700 liters of 10 wt% aqueous ammonia, 340 liters of a sulfuric acid solution of titanyl sulfate (125 g / liter as TiO 2 , sulfuric acid concentration 550 g / liter) was gradually added dropwise with stirring. The obtained gel was allowed to stand for 3 hours, washed with filtered water, and then dried at 100 ° C. for 10 hours. Subsequently, it baked at 400 degreeC. The intensity of the X-ray diffraction peak showing the anatase crystal was 3850 counts / second, which was 30% of the reference substance.
[0020]
Next, a chemical solution in which 1.4 kg of ammonium metavanadate, 1.7 kg of oxalic acid and 0.4 kg of monoethanolamine are dissolved in 5 liters of water is added to 20 kg of the above titanium oxide, and 1 kg of phenol resin and starch as a molding aid are added. In addition, after mixing and kneading with a kneader, it was formed into a honeycomb shape having an external shape of 80 mm square, an opening of 4.0 mm, a wall thickness of 1.0 mm, and a length of 500 mm by an extrusion molding machine. Subsequently, after drying at 80 degreeC, it baked in the air atmosphere at 380 degreeC for 5 hours, and obtained the catalyst (A). The composition of the catalyst (A) thus obtained was V 2 O 5 : TiO 2 = 5: 95 (weight ratio). The intensity of the X-ray diffraction peak showing the anatase crystal was 4688 counts / second, which was 36% of the reference substance.
[0021]
The powder X-ray diffraction spectrum of the catalyst (A) is shown in FIG.
[Example 2]
A catalyst (B) having a composition of V 2 O 5 : TiO 2 = 3: 97 (weight ratio) was prepared by the same preparation method as described in Example 1. The intensity of the X-ray diffraction peak showing the anatase crystal was 4326 counts / second, which was 33% of the reference substance.
[Example 3]
A catalyst (C) having a composition of V 2 O 5 : TiO 2 = 10: 90 (weight ratio) was prepared by the same preparation method as described in Example 1. The intensity of the X-ray diffraction peak showing the anatase crystal was 4796 counts / second, 37% of the reference substance.
[0022]
[Example 4]
The catalyst (A) prepared in Example 1 was impregnated with 0.01M palladium nitrate aqueous solution, dried at 120 ° C., and calcined at 350 ° C. to obtain a catalyst (D). The amount of palladium oxide supported was 0.06% by weight.
[Comparative Example 1]
The titanium oxide prepared by the method described in Example 1 was further baked at 550 ° C. to obtain titanium oxide having a high anatase crystallinity. The intensity of the X-ray diffraction peak showing anatase crystal was 10343 counts / second, which was 79% of the reference substance. A chemical solution in which 1.4 kg of ammonium metavanadate, 1.7 kg of oxalic acid and 0.4 kg of monoethanolamine are dissolved in 5 liters of water is added to 20 kg of titanium oxide having a high anatase crystallinity, and 1 kg of phenol resin and a molding aid are added. Starch was added and mixed and kneaded with a kneader, and then formed into a honeycomb shape having an external shape of 80 mm square, an opening of 4.0 mm, a thickness of 1.0 mm, and a length of 500 mm by an extrusion molding machine. Subsequently, after drying at 80 degreeC, it baked in the air atmosphere at 450 degreeC for 5 hours, and obtained the catalyst (A '). The composition of the catalyst (A ′) thus obtained was V 2 O 5 : TiO 2 = 5: 95 (weight ratio). The intensity of the X-ray diffraction peak showing the anatase crystal was 11726 counts / second, which was 90% of the reference substance.
[0023]
[Comparative Example 2]
A catalyst (B ′) having a composition of V 2 O 5 : TiO 2 = 3: 97 (weight ratio) was prepared by the same preparation method as described in Comparative Example 1. The intensity of the X-ray diffraction peak showing the anatase crystal was 11665 counts / second, which was 90% of the reference substance.
[Comparative Example 3]
A catalyst (C ′) having a composition of V 2 O 5 : TiO 2 = 10: 90 (weight ratio) was prepared by the same preparation method as described in Comparative Example 1. The intensity of the X-ray diffraction peak showing anatase crystal was 11796 counts / second, which was 91% of the reference substance.
[0024]
[Comparative Example 4]
The catalyst (A ′) prepared in Comparative Example 1 was impregnated with 0.01M palladium nitrate aqueous solution, dried at 120 ° C., and calcined at 350 ° C. to obtain a catalyst (D ′). The amount of palladium oxide supported was 0.06% by weight.
[Example 5]
Organochlorine compound decomposition tests were performed using the catalysts (A) to (D) and (A ′) to (D ′) prepared in Examples 1 to 4 and Comparative Examples 1 to 4. Chlorophenol (hereinafter abbreviated as CP) was used as the organic chlorine compound to be treated, and the reaction was carried out under the following conditions.
[0025]
The results are shown in Table 1. The CP decomposition rate, that is, the CP removal rate was obtained by the following formula.
(Test conditions)
Process gas composition CP: 30 ppm, O 2 : 10%, H 2 O: 15%, N 2 : Balance
Gas temperature: 160 ° C
Space velocity (SV): 4000 Hr −1
(formula)
CP decomposition rate (%) = [(reactor inlet CP concentration) − (reactor outlet CP concentration)] / (reactor inlet CP concentration) × 100
[0026]
[Table 1]
As seen in Table 1, with the catalyst of the comparative example, the organic halogen compound removal rate increases with increasing vanadium oxide content, but almost no increase is observed at 5% or more. On the other hand, in the case of the catalyst containing a large amount of amorphous titanium oxide in the examples, the organic halogen compound removal rate increases with an increase in the vanadium oxide content, and at 10%, the organic halogen compound is much higher than the conventional catalyst. Indicates the removal rate.
[Example 6]
Using the catalysts (A) and (A ′) prepared in Example 1 and Comparative Example 1, a denitration reaction was performed under the following conditions. When the denitration rate was determined by the following formula, it was 99% for the catalyst (A) and 94% for the catalyst (A ′).
[0028]
(Test conditions)
Process gas composition NO: 190 ppm, NH 3 : 190 ppm, O 2 : 9%,
H 2 O: 17%,: N 2 : Balance
Gas temperature: 250 ° C
Space velocity (SV): 4000 Hr −1
(formula)
Denitration rate (%) = [(reactor inlet NOx concentration) − (reactor outlet NOx concentration)] / (reactor inlet NOx concentration) × 100
[Example 7]
Using the catalysts (D) and (D ′) prepared in Example 4 and Comparative Example 4, ammonia decomposition reaction was performed under the following conditions. When the ammonia decomposition rate was determined by the following formula, it was 98% for the catalyst (D) and 93% for the catalyst (D ').
[0029]
(Test conditions)
Process gas composition NH 3 : 30 ppm, O 2 : 2%, H 2 O: 10%,: N 2 : Balance
Gas temperature: 330 ° C
Space velocity (SV): 4000 Hr −1
(formula)
Ammonia decomposition rate (%) = [(reactor inlet ammonia concentration) − (reactor outlet ammonia concentration)] / (reactor inlet ammonia concentration) × 100
[0030]
【The invention's effect】
The catalyst of the present invention is excellent in decomposition activity and ammonia decomposition activity of toxic organic halogen compounds such as dioxins. In addition, it has excellent denitration performance and is useful as a catalyst for simultaneous removal of toxic organic halogen compounds such as nitrogen oxides and dioxins.
[Brief description of the drawings]
1 is an X-ray powder diffraction spectrum of a reference material prepared in Preparation Example. FIG. 2 is an X-ray powder diffraction spectrum of catalyst (A) prepared in Example 1.
Claims (5)
機種 Ｒｉｇａｋｕ ＲＥ−３００
Ｘ線源 ＣｕＫα１／５０ｋＶ／３００ｍＡ
カウンタ シンチレーションカウンタ
フィルタ なし
モノクロメータ 湾曲結晶モノクロメータ
発散スリット １゜
散乱スリット １゜
受光スリット ０．３ｍｍ
スキャンスピード ４゜／ｍｉｎIn the exhaust gas treatment catalyst containing amorphous phase titanium oxide, the titanium oxide is obtained by preparing titanium hydroxide by neutralization reaction between a soluble titanium compound aqueous solution and aqueous ammonia and calcining at 350 ° C. to 550 ° C. is intended, the intensity of the peak indicating the anatase crystal existing between 2 [Theta] = 24.7 ° ～25.7 ° of powder X-ray diffraction was measured under the following conditions is 3850 counts / sec or more, 10000 counts / sec An exhaust gas treatment catalyst characterized by the above.
Model Rigaku RE-300
X-ray source CuKα1 / 50kV / 300mA
Counter Scintillation counter Filter None Monochromator Curved crystal monochromator Divergence slit 1 ° Scattering slit 1 ° Receiving slit 0.3mm
Scanning speed 4 ° / min
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2000172260A JP3924418B2 (en) | 1999-08-12 | 2000-06-08 | Exhaust gas treatment catalyst and exhaust gas treatment method |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP22856399 | 1999-08-12 | ||
| JP11-228563 | 1999-08-12 | ||
| JP2000172260A JP3924418B2 (en) | 1999-08-12 | 2000-06-08 | Exhaust gas treatment catalyst and exhaust gas treatment method |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JP2001113169A JP2001113169A (en) | 2001-04-24 |
| JP3924418B2 true JP3924418B2 (en) | 2007-06-06 |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US8288309B2 (en) | 2009-10-01 | 2012-10-16 | Mitsubishi Heavy Industries, Ltd. | Mercury oxidation catalyst and method for producing the same |
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| JP4538198B2 (en) * | 2002-04-18 | 2010-09-08 | 日揮触媒化成株式会社 | Titanium dioxide powder for honeycomb exhaust gas treatment catalyst and honeycomb exhaust gas treatment catalyst using the titanium dioxide powder |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US8288309B2 (en) | 2009-10-01 | 2012-10-16 | Mitsubishi Heavy Industries, Ltd. | Mercury oxidation catalyst and method for producing the same |
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