JP4320702B2 - Exhaust gas purification device - Google Patents
Exhaust gas purification device Download PDFInfo
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- JP4320702B2 JP4320702B2 JP2002326851A JP2002326851A JP4320702B2 JP 4320702 B2 JP4320702 B2 JP 4320702B2 JP 2002326851 A JP2002326851 A JP 2002326851A JP 2002326851 A JP2002326851 A JP 2002326851A JP 4320702 B2 JP4320702 B2 JP 4320702B2
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- Prior art keywords
- exhaust gas
- catalyst
- partition wall
- honeycomb structure
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Images
Landscapes
- Exhaust Gas After Treatment (AREA)
- Processes For Solid Components From Exhaust (AREA)
- Exhaust Gas Treatment By Means Of Catalyst (AREA)
- Catalysts (AREA)
Description
【０００１】
【発明の属する技術分野】
本発明は、触媒作用を利用して排気ガスを浄化するディーゼルエンジンの排気ガス浄化装置に関するものである。
【０００２】
【従来の技術】
ディーゼルエンジンはその燃費効率の高さから、欧州を中心に需要が増大している。しかしながら、ディーゼルエンジンの排気ガス中に含まれている粒子状物質（ＰＭ：Particulate Matter）及び窒素酸化物（ＮＯx）の人体の健康に与える影響が大きいことから、このＰＭ及びＮＯxの低減技術が種々検討されている。
この排気ガス中のＰＭ及びＮＯxを低減する排気ガスの後処理技術の一つとして、ＰＭ浄化のための連続再生式ＤＰＦ（Ｄｉｅｓｅｌ ＰａｔｉｃｕｒａｔｅＦｉｌｔｅｒ）とＮＯｘ浄化装置用の代表的な例としてＳＣＲ（ＳＣＲ：Ｓｅｌｅｃｔｉｖｅ Ｃａｔａｌｙｔｉｃ Ｒｅｄｕｃｔｉｏｎ、選択還元触媒）を組み合わせたシステムが期待されている。このシステムでは、排気系の上流側に連続再生式ＤＰＦを、下流側にＳＣＲが配置されている。連続再生式ＤＰＦでは例えば特許文献１に記載されているように、排気系の上流に、外周壁と外周壁の内側に軸方向に隔壁により仕切られた多数の流通孔を有するハニカム構造体の隔壁表面にＰｔ属金属を担持した酸化触媒、その下流に外周壁と外周壁の内側で軸方向に隔壁により仕切られた多数の流通孔を有し、排気ガスの流入側と流出側の所望の流通孔を目封止した排気微粒子捕集用のＤＰＦを配置し、上流側の酸化触媒で排気ガス中のＮＯ（一酸化窒素）をＮＯ２（二酸化窒素）に変換し、下流のＤＰＦで排気ガス中のＰＭを捕集するとともに、この捕集されたＰＭを前記の酸化触媒で生成したＮＯ２ を用いて酸化させることにより、ＤＰＦ上のＰＭを除去するというものである。
一方、連続再生式ＤＰＦの後段に配置されたＳＣＲに代表されるＮＯｘ浄化装置では、例えば特許文献２に開示されているように、高温の排気ガス中にアンモニア水溶液や尿素水溶液や液体アンモニア等から発生するアンモニアを注入した後に金属触媒と接触させて脱硝し、ＮＯxが浄化される。具体的には図４に示すように、エンジンの排気通路にＳＣＲ触媒２５を設けるとともに、このＳＣＲ触媒２５の上流側にアンモニア等の還元剤タンクから還元剤を排気通路に供給する還元剤供給装置２６を設けて、ＳＣＲ触媒の触媒作用によりこの還元剤供給装置から供給されるアンモニアで排気ガス中のＮＯｘを還元して排気ガスを浄化する。この還元は、４ＮＯ＋４ＮＨ３＋Ｏ２＝４Ｎ２＋６Ｈ２Ｏの反応で行なわれ、ＳＣＲ触媒としては、コージェライト（５ＳｉＯ２・２Ａｌ２Ｏ３・２ＭｇＯ）、酸化アルミニウム（Ａｌ２Ｏ３）、酸化チタン（ＴｉＯ２）等からなり、外周壁と外周壁の内側に軸方向に隔壁により仕切られた多数の流通孔を有するハニカム構造体の隔壁表面に、白金族金属、酸化バナジウム（Ｖ２Ｏ５）、酸化鉄（Ｆｅ２Ｏ３）、酸化銅（ＣｕＯ）、酸化マンガン（Ｍｎ２Ｏ３）、酸化クロム（Ｃｒ２Ｏ３）、酸化モリブデン（ＭｏＯ３）、酸化チタン（ＴｉＯ２）等、酸化タングステン（ＷＯ３）等が塗布され、使用される。
【０００３】
【特許文献１】
特開平１−３１８７１５号公報
【特許文献２】
特開２０００−３０３８２６号公報
【０００４】
【発明が解決しようとする課題】
しかしながら、上記排気ガス後処理技術においては、排気ガス通路に、酸化触媒、ＤＰＦ、及びＳＣＲ触媒の各装置が直列に配置され、いずれの装置も外周壁と外周壁の内側で軸方向に隔壁により仕切られた多数の流通孔を有するハニカム構造体が使用されるため、取り付けスペースが膨大になるという問題があり、小型で高効率の排気ガス浄化装置が求められていた。
本発明の目的は、小型で効率の良い排気ガス浄化装置を得ることにある。
【０００５】
【課題を解決するための手段】
本発明者らは排気ガス浄化装置の小型化を図るために、特にＳＣＲ装置に代表されるＮＯｘ浄化装置の効率を上げ、小型化することを考えた。基本的には排気ガス浄化装置は、排気ガスと触媒との触媒反応を利用していることから、触媒担体の単位体積当たりの表面積を大きくして、触媒担体表面に担持される触媒の量を増加させることにより、排気ガスとの触媒反応を促進すれば、従来よりも小型の装置で同じ浄化効率をえられると考えた。 そこで、本発明者らは従来のＳＣＲ装置に用いられている触媒担体に着目した。従来用いられていた触媒担体は、外周壁と外周壁の内側で軸方向に隔壁により仕切られた多数の流通孔を有し、該流通孔に目封止が施されていないハニカム構造体であった。排気ガスは、前記流通孔に目封止が施されずに開口した多数の流通孔を流入側から流出側にストレートに通過することから、このハニカム構造体の単位体積当たりの表面積は次式で表される。 単位体積当たりの表面積Ｓ＝４×(Ｐ−ｔ)／Ｐ２ (ｍｍ2/ｍｍ3) ここで、Ｐは隔壁のピッチ（ｍｍ）、ｔは隔壁の厚さ（ｍｍ）を示す。 このため、ハニカム構造体の単位体積当たりの表面積を大きくするには、隔壁の厚さを薄く、或いは隔壁のピッチを小さくした、所謂、薄壁、高セル密度のハニカム構造体を用いる必要があった。ところが、例えば、隔壁厚さ０．１ｍｍ以下、隔壁のピッチ１．０ｍｍ以下の薄壁、高セル密度のハニカム構造体を用いると、ハニカム構造体流路方向の開口面積が小さくなることからハニカム構造体の入口の圧力損失が大きくなるため、ハニカム構造体全体の圧力損失が大きくなるといった問題点のあることが判った。また、ディーゼルエンジン用の触媒担体の場合、通常、外径１５０ｍｍ以上の大型ハニカム構造体となることから、壁厚が０．１ｍｍ以下の隔壁では、成形時にハニカム構造体自身の自重により、隔壁が変形しやすく、アイソスタティック強度が低下するという問題点もあり、従来のハニカム構造体の改良によるＳＣＲ触媒装置の小型化には、限界が有ることが判った。 そこで、本発明者らは、さらに検討を重ねた結果、従来のＳＣＲ触媒用担体として使用されていた外周壁と外周壁の内側で軸方向に隔壁により仕切られた多数の流通孔を有するハニカム構造体に対し、排気ガスの流入側と流出側の所望の流通孔に目封止を採用し、排気ガスを隔壁内にも通過させて触媒との接触機会を増加させることにより、ＳＣＲ触媒装置を小型化できることを見出し本発明に想到した。 すなわち、本発明の排気ガス浄化装置は、エンジンの排気通路に、上流側から酸化触媒、ＤＰＦ、ＳＣＲ触媒を設けて構成される排気ガス浄化装置であって、前記ＳＣＲ触媒に用いられる触媒担体は、外周壁と外周壁の内側で軸方向に隔壁により仕切られた多数の流通孔を有し、排気ガスの流入側と流出側の所望の流通孔を目封止することにより、排気ガスを前記隔壁を通過させるハニカム構造体からなる排気ガス浄化用触媒担体であり、前記触媒担体の外径が１５０ｍｍ以上、前記隔壁の気孔率が５０％〜８０％、隔壁中の細孔径が１０μm以上である細孔の総細孔表面積が０．０２ｍ ２ ／ｇ以上、前記目封止の長さが３〜２０ｍｍであり、排気ガスを前記隔壁表面及び隔壁内の細孔を通過させて浄化することを特徴とする。 本発明の排気ガス浄化装置は、エンジンの排気通路に、上流側から酸化触媒、ＤＰＦ、ＳＣＲ触媒を設けて構成される排気ガス浄化装置であって、前記ＳＣＲ触媒に用いられる触媒担体は、外周壁と外周壁の内側に軸方向に隔壁により仕切られた多数の流通孔を有し、排気ガスの流入側と流出側の所望の流通孔を目封止することにより、排気ガスを前記隔壁に通過させるハニカム構造の排気ガス浄化用触媒担体であることから、従来の外周壁と外周壁の内側に軸方向に隔壁により仕切られた多数の流通孔を有するハニカム構造体に比べて単位体積当たりの表面積を大きくできる。これは、従来構造のハニカム構造体では、隔壁表面に形成された細孔を利用し、隔壁表面に触媒物質を担持させ、排気ガスを軸方向に隔壁により仕切られた多数の流通孔内を、排気ガス流入側から流出側にストレートに通過させることにより、隔壁表面に担持された触媒物質の作用により浄化を行っていたことから、排気ガス浄化のために有効な表面積は隔壁の幾何学的表面積により決定されていたが、本発明の排気ガス浄化装置に備えられるハニカム構造の触媒担体は、従来のハニカム構造体の排気ガス浄化作用に加えて、流通孔の所望部位の目封止により排気ガスを隔壁中に形成された細孔をも通過させることができることから、流通孔を構成する隔壁表面に加えて、隔壁内に形成された細孔の表面をも有効に使え、隔壁表面及び隔壁内の細孔表面に端持された触媒物質と排気ガスとの接触機会が増えることになり、従来のハニカム構造体に比べて単位体積当たりの有効表面積を大きくすることが出来る。このため、単位体積当たりに有効に使える触媒量を従来のハニカム構造体に比べて多くすることが出来るため、浄化性能を低下させずに排気ガス浄化用触媒担体の小型化が可能となるのと共に、排気ガス浄化装置全体を小型化することが可能となる。
【０００６】
図１は、本発明に係る排気ガス浄化装置に備えられる、ハニカム構造体からなる排気ガス浄化用触媒担体１１の斜視図であり、図２は、図１の排気ガス浄化装置に備えられる、ハニカム構造体からなる排気ガス浄化用触媒担体１１の模式断面図である。図１及び図２に示すように、本発明の排気ガス浄化装置に備えられる、ハニカム構造体からなる排気ガス浄化用触媒担体は、略円筒状又は略楕円筒状である。外周壁１１ａと、この外周壁１１ａの内周側で隔壁１１ｂにより囲まれた多数の流通孔１１ｃを有する多孔質セラミックハニカム構造体（以下、「多孔質セラミックハニカム構造体」を略して「ハニカム構造体」という）１１での流通孔１１ｃの流入側１１ｄ、流出側１１ｅの両端面において、流通孔１１ｃのいずれか一方が封止されるように交互に目封止材１２ａ、１２ｂで目封止している。
排気ガス浄化装置に備えられる、ハニカム構造体からなる排気ガス浄化用触媒担体１１での排気ガスとの触媒反応は、例示的には、以下の通り行われる。図２で、排気ガスは、例えば、排気ガス浄化用触媒担体１１の流入側１１ｄで開口している流路１１ｃから流入（３０ａで示す）し、出口側は目封止されているため、流入した排気ガスはそのまま流出することはできずに、隔壁１１ｂに形成された細孔（図示せず）を通過した後、隣接した流路１１ｅの流出側から排出（３０ｂで示す）される。勿論、排気ガスは隔壁１１ｂを通過して隣接した流路１１ｅに流出する以外にも、複数の隔壁を通過し、複数の隣接した流路にも流出する。そして、排気ガスは隔壁表面及び隔壁１１ｂに形成された細孔表面に担持された触媒物質により例えばＮＯｘが浄化される。
【０００７】
本発明の排気ガス浄化装置に備えられる、排気ガス浄化用触媒担体の隔壁の気孔率が、５０％〜８０％、隔壁中の細孔径が１０μm以上である細孔の総細孔表面積が０．０２ｍ２／ｇ以上であることが好ましいとしたのは、以下の理由による。
排気ガス浄化用触媒担体の隔壁の気孔率が５０％未満であると、隔壁を排気ガスが通過する際の通気抵抗が大きくなるため、排気ガス浄化用触媒担体の圧力損失が大きくなるからである。一方、気孔率が８０％を超えると、排気ガス浄化用触媒担体の強度が低下し、排気ガス浄化用装置として使用された際の、機械的応力や振動により破損するおそれがあるからである。排気ガス浄化用触媒担体の隔壁の気孔率は、好ましくは、６０〜７５％である。
【０００８】
また、排気ガス浄化用触媒担体の隔壁中の細孔径が１０μｍ以上である細孔の総細孔表面積が０．０２ｍ２／ｇ以上が好ましいとしたのは、排気ガス浄化装置に、例えば、ＳＣＲ触媒物質を担持した際に、触媒物質が細孔を塞いで、圧力損失が上昇するのを防ぐためである。即ち、触媒物質が隔壁中に形成された細孔の表面にコートされる際に、細孔径が１０μｍ以上の細孔であれば、細孔を閉塞して圧力損失の上昇を防ぐことができるからである。そしてこの細孔径が１０μｍ以上である細孔の総細孔表面積が０．０２ｍ２／ｇ以上存在することにより、隔壁中で、細孔径が１０μｍ以上である細孔に３次元的なつながりが得られ、排気ガスの流入側と流出側の所望の流通孔を目封止したハニカム構造の排気ガス浄化用触媒担体を備えた排気ガス浄化装置の圧力損失の上昇を防ぐことができる。細孔径が１０μｍ以上である細孔の総細孔表面積が０．０２ｍ２／ｇ未満であると、ＳＣＲ触媒担持後の排気ガス浄化装置の圧力損失が上昇し、エンジン出力の低下につながることから好ましくない。尚、排気ガス浄化用触媒担体の隔壁中の細孔径が１０μｍ以上である細孔の総細孔表面積は、上記圧力損失の上昇を低減するためには０．０７ｍ２／ｇ以上がより好ましい。ここで気孔率および細孔径が１０μｍ以上である細孔の総細孔表面積は水銀圧入法で測定する。
【０００９】
本発明の排気ガス浄化装置に備えられる、排気ガス浄化用触媒担体の隔壁厚は、０．１〜０．５ｍｍが好ましく、隔壁のピッチは１．３ｍｍ以上が好ましい。隔壁厚が０．１ｍｍ未満では、隔壁の気孔率を５０〜８０％の高い範囲に設定していることから排気ガス浄化用触媒担体の強度が低下し、好ましくない。一方、隔壁厚が０．５ｍｍを超えると、如何に隔壁が高気孔率であっても、排気ガスに対する隔壁の通気抵抗が大きくなるため、排気ガス浄化用触媒担体の圧力損失が大きくなるからである。より好ましい隔壁厚さは、０．２〜０．４ｍｍである。また、隔壁のピッチが１．３ｍｍ未満であると、排気ガス浄化用触媒担体の貫通孔入口の開口面積が小さくなることから、排気ガス浄化用触媒担体入口の圧力損失が大きくなるためである。
本発明の排気ガス浄化装置において、排気ガス浄化用触媒担体の目封止材１２ａ、１２ｂの流路方向の長さは３〜２０ｍｍが好ましい。目封止材の長さが３ｍｍ未満では、排気ガス浄化装置として使用中の機械的振動や熱衝撃応力により目封止材が脱落し、目封止の役目を果たさなくなることから好ましくなく、目封止材の長さが２０ｍｍを越える場合は、排気ガスを通過させる隔壁の長さが短くなり、単位体積当たりの有効表面積が小さくなるため、排気ガスの浄化性能が低下するからである。
【００１０】
上記、排気ガス浄化用触媒担体の隔壁を構成する材料としては、本発明が主にディーゼルエンジンの排気ガスを浄化するために使用されるため、耐熱性に優れた材料を使用することが好ましく、コージェライト、アルミナ、ムライト、窒化珪素、炭化珪素及びＬＡＳからなる群から選ばれた少なくとも１種を主結晶とするセラミック材料を用いることが好ましい。中でも、コージェライトを主結晶とするハニカム構造体は、安価で耐熱性、耐食性に優れ、また低熱膨張であることから最も好ましい。
【００１１】
次に、本発明の排気ガス浄化装置において、前記排気ガス浄化用触媒担体に使用される外周壁と外周壁の内側に軸方向に隔壁により仕切られた多数の流通孔を有するセラミックハニカム構造体を製造する方法の一例について説明する。まずセラミックス原料粉末に有機バインダー、潤滑剤等の成形助剤、および造孔材を添加、混合後、所定量の水を注入して、混合、混練を行い可塑性を有する坏土を調整する。その後、この坏土を公知のハニカム構造体用金型を用いて押出成形することにより、外周壁と外周壁の内側で軸方向に隔壁により囲まれた、断面が角形状の流通孔を有するハニカム構造の成形体を得、その後所定の長さで、切断、乾燥、焼成を行い外周壁と外周壁の内側で隔壁により仕切られた多数の流通孔を有するセラミックハニカム構造体を得る。尚、この際、気孔率５０〜８０％が、細孔径が１０μｍ以上である細孔の総細孔表面積０．０２ｍ２／ｇが得られるよう、造孔材の選択、及び添加量を調整する。具体的には、造孔材として、平均粒径が１０μｍ以上で粒径の揃ったものを選択し、セラミック原料粉末１００質量部に対して１０質量部以上添加すれば、細孔径が１０μｍ以上である細孔の総細孔表面積を０．０２ｍ２／ｇ以上とすることができる。
尚、焼成後のハニカム構造を有するセラミック焼成体の外周壁と、その周縁部を除去加工した上で、除去加工された外周面にセラミック骨材と無機バインダ、有機バインダ等からなるコーティング材を塗布、乾燥、硬化させて外周壁を形成し、外周壁と外周壁の内側に隔壁により仕切られた多数の貫通孔を有するセラミックハニカム構造体とする方法を採用しても良い。
【００１２】
次に、本発明の排気ガス浄化装置に使用される、外周壁と外周壁の内側で軸方向に隔壁により仕切られた多数の流通孔を有するハニカム構造体を目封止する方法の一例について図３を用いて説明する。図３は、ハニカム構造体１０に目封止材を導入している状況を示す模式断面図である。まずハニカム構造体１０の端面１０ｆに図３に示すようにマスキングフィルム１４、１５を配置した後、ハニカム構造体の流通孔に対して交互に穿孔部１６、１７を形成する。また、セラミックスラリー１３を調整し、容器１８に収納しておく。次いで、上記のように作成したセラミックスラリー１３に、ハニカム構造体１０の端面１０ｆを浸漬し、マスキングフィルムの穿孔部１６を通じて、ハニカム構造体１０にセラミックスラリー１３を導入、導入されたスラリ−が固化後に、ハニカム構造体１０をセラミックスラリー１３から抜き出し、乾燥させる。一方、ハニカム構造体の他端側を同様にマスキングフィルムの穿孔部１７を通じて、ハニカム構造体１０にセラミックスラリー１３を導入、導入されたスラリ−が固化後に、ハニカム構造体１０をセラミックスラリー１３から抜き出し、乾燥させた後、マスキングフィルム１４、１５を剥がす。このとき、ハニカム構造体のセラミックスラリーへの浸積深さを調整することにより、所望する目封止深さが得られる。その後、目封止材の焼成を行い、隔壁と目封止材を一体化せしめ、図１に示す排気ガスの流入側と流出側の所定の連通孔が目封止されたセラミックハニカム構造体を得る。
【００１３】
以下、図面を用いて、排気ガス浄化用触媒担体をディーゼルエンジンに適用した本発明の排ガス浄化装置について説明する。
本発明の排気ガス浄化装置をディーゼルエンジンに用いる場合は、図４に示すように、エンジン２１の排気通路２２に、上流側から酸化触媒２３、ＤＰＦ２４、ＳＣＲ触媒２５を設けて構成される。また、ＤＰＦ２４とＳＣＲ触媒２５との間の排気通路２２にアンモニアを噴出できる還元剤供給装置２６を設ける。
この酸化触媒２３は、本発明の排気ガス浄化用触媒担体にアルミナの触媒担持層をコーティングにより形成し、この担持層に白金Ｐｔ，バナジウムＰｄ等の触媒成分を担持させたものが使用される。このＤＰＦ２４は、多数の排気通路（セル）が互いに平行に形成されたコージェライト製のハニカムフィルタやアルミナ等のセラミックス不織布や繊維からなるフィルタ等を使用することができる。
また、このＳＣＲ触媒２５は、本発明のＳＣＲ装置用触媒担体上にＰｔ、Ａｌ2 Ｏ3 ，ＴｉＯ2 ，Ｖ2 Ｏ5 ，Ｆｅ2 Ｏ3 ，ＣｕＯ，Ｍｎ2 Ｏ3 ，Ｃｒ2 Ｏ3 ，ＭｏＯ3 等で形成する。そして、還元剤供給装置２６はアンモニア水や液体アンモニアや尿素水溶液の還元剤タンク２６ａからアンモニアを排気通路２２内に噴霧できる還元剤噴射弁２６ｂを備えて形成される。この還元剤供給装置２６は排ガスの温度がＳＣＲ触媒２５の触媒活性開始温度以上の時に、ＮＯｘ還元用の還元剤を供給する。
以上の構成によるディーゼルエンジンの排気ガス浄化装置は、排気通路２２のエンジン２１とＳＣＲ触媒２５の間に酸化触媒２３とフィルタ２４を直列に配置しているので、ディーゼルエンジン２１から排出されるＰＭは、下流側のフィルタ２４で捕集され、酸化触媒２３の強い酸化力によって酸化したＮＯ２にて燃焼除去することができる。また、窒素酸化物はＳＣＲ触媒により還元浄化できる。
【００１４】
【発明の実施の形態】
以下、本発明の実施の形態を詳細に説明する。
（実施例１）
カオリン、タルク、シリカ、水酸化アルミニウム、アルミナなどの粉末を調整して、質量比で、ＳｉＯ２：４７〜５３％、Ａｌ２Ｏ３：３２〜３８％、ＭｇＯ：１２〜１６％及びＣａＯ、Ｎａ２Ｏ、Ｋ２Ｏ、ＴｉＯ２、Ｆｅ２Ｏ３、ＰｂＯ、Ｐ２Ｏ５などの不可避的に混入する成分を全体で２．５％以下を含むようなコージェディエライト生成原料粉末に、成形助剤としてメチルセルロース及びヒドロキシプロピルメチルセルロース、および造孔剤として平均粒径４５ｍの樹脂粉末を添加し、規定量の水を注入して更に十分な混合を行い、ハニカム構造に押出成形可能な坏土を調整した。
そして、公知のハニカム構造体が得られる押出成形用金型を用い押出成形し、外周壁と、この外周壁の内周側で隔壁により囲まれた断面が四角形状の流通孔を有するハニカム構造の成形体を得、その後乾燥、切断、焼成を行うことにより、隔壁厚さ０．３ｍｍ、隔壁ピッチ１．５ｍｍ、隔壁の気孔率６５％、隔壁中の１０μｍ以上の細孔の表面積が０．１０ｍ２／ｇで、外径２６６．７ｍｍ、長さ３０４．８ｍｍのコージェライト質セラミックハニカム構造体を２ケ準備した。ここで、隔壁中の１０μｍ以上の総表面積は、Micromeritics社製のオートポアIII９４１０を使用し、水銀圧入法で測定した。
この中の、一方のコージェライト質セラミックハニカム構造体に対し、図３に示す方法で流通孔の開口端部に交互に長さ１０ｍｍの目封止部を形成し、排気ガスの流入側と流出側の所望の流通孔を目封止した試験ＮＯ.１の触媒担体とした。また、もう一方のコージェライト質セラミックハニカム構造体は、そのまま目封止部は形成せず、試験ＮＯ.２の触媒担体とした。
一方、カオリン、タルク、シリカ、水酸化アルミ、アルミナなどの粉末を調整して、質量比で、ＳｉＯ２：４７〜５３％、Ａｌ２Ｏ３：３２〜３８％、ＭｇＯ：１２〜１６％及びＣａＯ、Ｎａ２Ｏ、Ｋ２Ｏ、ＴｉＯ２、Ｆｅ２Ｏ３、ＰｂＯなどの不可避的に混入する成分を全体で２．５％以下を含むようなコーディエライト生成原料粉末に、成形助剤としてメチルセルロース及びヒドロキシプロピルメチルセルロースを添加し、規定量の水を注入して更に十分な混合を行い、ハニカム構造に押出成形可能な坏土を調整した。
そして、公知のハニカム構造体が得られる押出成形用金型を用い押出成形し、外周壁と、この外周壁の内周側で隔壁により囲まれた断面が四角形状の流通孔を有するハニカム構造の成形体を得、その後乾燥、切断、焼成を行うことにより、隔壁厚さ０.１ｍｍ、隔壁ピッチ１.０ｍｍ、隔壁の気孔率３５％、隔壁中の１０μｍ以上の細孔の表面積が０.０１ｍ２／ｇで、外径２６６.７ｍｍ、長さ３０４.８ｍｍのコージェライト質セラミックハニカム構造体からなる試験ＮＯ.３の触媒担体を準備した。ここで、気孔率を３５％としたのは、隔壁の厚さが、０.１ｍｍという薄壁構造であったため成形時のハニカム構造体の強度を確保するためでる。
【００１５】
これら３種類の試験ＮＯ.１〜３の触媒担体に対して、隔壁の幾何学的表面積、有効隔壁体積、有効隔壁重量、有効細孔表面積、触媒担持有効表面積、担体１ケ中の触媒担持有効表面積を下式により求めた結果を、表１に示す。下式の記号は表１で定義される内容とも同一である。
隔壁の密度；ρ（ｋｇ／ｍ３）＝２５００×（１−Ｐ／１００）
ここでコージェライトの真密度を２５００ｋｇ／Ｌとする。
幾何学的表面積；ＳＧ（ｍ２／Ｌ）＝４×（ｐ−ｔ）／ｐ2
両端面目封止の場合は上記数字の１／２
有効隔壁体積；Ｖ（ｍ３／Ｌ）＝（ｐ２−（ｐ−ｔ）２）／（１０００×ｐ２）
有効隔壁重量；Ｗ（ｋｇ／Ｌ）＝ρ×Ｖ
有効細孔表面積；Ｓｐ（ｍ２／Ｌ）＝１０００×Ｖ１０×Ｗ
触媒担持有効表面積；ＳＥ（ｍ２／Ｌ）＝ＳＧ＋ＳＰ
担体１ケ当たりの触媒担持有効表面積；Ｓ（ｍ２／ケ）＝ＳＥ×（（Ｄ０２×π／４）×Ｌ×１０−６）
ここでＰ；ハニカム構造体隔壁の気孔率（％）
ｔ；隔壁厚さ（ｍｍ）
ｐ；隔壁ピッチ（ｍｍ）
Ｖ１０；１０μｍ以上の細孔の総表面積（ｍ２／ｇ）
Ｄ０；ハニカム構造体の外径（ｍｍ）
ＬＴ；ハニカム構造体の全長（ｍｍ）
【００１６】
【表１】
更に上記試験ＮＯ.１〜ＮＯ.３の触媒担体に対し、ＴｉＯ２、ＷＯ３、Ｖ２Ｏ５粉末に、バインダとしてアルミナゾル、シリカゾル、及び水を加えてスラリー状としたものを、ウオッシュコートして触媒担体の有効表面積に換算して８ｇ／ｍ２のコート量に担持した。得られた試験ＮＯ.１〜ＮＯ.３の触媒担体に対し、排気ガス温度３００℃、ＮＯｘを４００ｐｐｍ含む排気ガスに対して、排気ガス中のＮＯｘ量と同量の尿素（Ｎ換算）を添加した結果、ハニカム構造体出口の排気ガス中のＮＯｘ量を比較し、ＮＯｘ浄化性能を調査した。ＮＯｘ浄化率が９０％以上であったものを（◎）、ＮＯｘ浄化率が７０％以上であったものを（○）、ＮＯｘ浄化率が７０％未満であったものを（×）として評価した。結果を併せて表１に示す。
表１から、本発明例である試験ＮＯ.１の触媒担体は、比較例である従来構造の試験ＮＯ.２及び３の触媒担体に比べて、隔壁内の細孔の表面積を有効に使えることから、単位体積当たりの有効表面積ＳＥ及び触媒担体１ケ当たりの有効表面積Ｓの値が桁違いに大きいことが判る。このためＮＯｘ浄化率の評価も（◎）であり、ＮＯｘ浄化性能の優れていることか判る。
【００１８】
（実施例２）
実施例１の試験ＮＯ.１と同様の方法を採用し、ハニカム構造体の切断長さのみを変更することにより、隔壁厚さ０.３ｍｍ、隔壁ピッチ１.５ｍｍ、隔壁の気孔率６５％、隔壁中の１０μｍ以上の細孔の総表面積が０.１０ｍ２／ｇで、外径２６６.７ｍｍ、長さ１５２.４ｍｍ及び７６.２ｍｍのコージェライト質セラミックハニカム構造体を準備した。そして、これらハニカム構造体に対し、実施例１と同様、図３に示す方法で流通孔の開口端部に交互に長さ１０ｍｍの目封止部を形成し、排気ガスの流入側と流出側の所望の流通孔を目封止した試験ＮＯ.４及びＮＯ.５の触媒担体とした。
一方、実施例１の試験ＮＯ.３と同様の方法を用い、隔壁厚さ０.１ｍｍ、隔壁ピッチ１.０ｍｍ、隔壁の気孔率３５％、隔壁中の１０μｍ以上の細孔の総表面積が０.０１ｍ２／ｇで、外径２６６.７ｍｍ、長さ６０９.６ｍｍのコージェライト質セラミックハニカム構造体からなる試験ＮＯ.６の触媒担体を準備した。
これら３種類の試験ＮＯ.４〜６の触媒担体に対して、隔壁の幾何学的表面積、有効隔壁体積、有効隔壁重量、有効細孔表面積、触媒担持有効表面積、担体１ケ中の触媒担持有効表面積を下式により求めた結果を、表２に示す。
更に上記試験ＮＯ.４〜ＮＯ.６の触媒担体に対し、ＴｉＯ２、ＷＯ３、Ｖ２Ｏ５粉末に、バインダとしてアルミナゾル、シリカゾル、及び水を加えてスラリー状としたものを、ウオッシュコートして８ｇ／ｍ２のコート量に担持した。得られたＮＯ.４〜ＮＯ.６の触媒担体に対し、排気ガス温度３００℃、ＮＯｘを４００ｐｐｍ含む排気ガスに対して、排気ガス中のＮＯｘ量と同量の尿素（Ｎ換算）を添加した結果、ハニカム構造体出口の排気ガス中のＮＯｘ量を比較し、ＮＯｘ浄化性能を調査した。
【００１９】
【表２】
表２の触媒担体はいずれも外径が２６６.７ｍｍの担体であるが、本発明例である試験ＮＯ.４及びＮＯ.５の触媒担体は、全長が１５２.４ｍｍ及び７６.２ｍｍで、ＮＯｘ浄化性能の評価が（○）となっているのに対し、本発明の比較例である従来構造の試験ＮＯ.６の触媒担体の場合は、ＮＯｘ浄化性能評価を（○）とするためには、表面積を確保するため６０９.６ｍｍという全長の長い触媒担体にする必要のあることが判る。このため本発明の触媒担体は、ＳＣＲ触媒の性能を発揮するための有効表面積を大きくしていることから、ＳＣＲ装置の効率を上げ、小型化することが可能となることが判る。
【００２１】
【発明の効果】
以上説明したように、本発明の排気ガス浄化装置は、外周壁と外周壁の内側で軸方向に隔壁により仕切られた多数の流通孔を有し、排気ガスの流入側と流出側の所望の流通孔を目封止することにより、排気ガスを前記隔壁を通過させるハニカム構造体からなる排気ガス浄化用触媒担体を備え、排気ガスを前記隔壁表面及び隔壁内の細孔を通過させて浄化する。更に、前記隔壁の気孔率が５０％〜８０％、細孔径が１０μm以上である細孔の総細孔表面積が０．０２ｍ２／ｇ以上としていることから、隔壁中の細孔の表面積を有効に活用することが出来るため、従来の外周壁と外周壁の内側で軸方向に隔壁により仕切られた多数の流通孔を有するハニカム構造の触媒担体に比べて、単位体積当たりの触媒反応に係わる表面積を大きくでき、浄化性能を低下させずに排気ガス浄化装置を小型化することができる。このため、かかる排気ガス浄化用触媒担体を用いたディーゼルエンジンの排気ガス浄化装置を小型化することも可能となる。
【図面の簡単な説明】
【図１】本発明の排気ガス浄化装置に備えられるハニカム構造体からなる排気ガス浄化用触媒担体の斜視図である。
【図２】本発明の排気ガス浄化装置に備えられるハニカム構造体からなる排気ガス浄化用触媒担体の模式断面図である
【図３】ハニカム構造体に目封止材を導入している状況を示す模式断面図である。
【図４】本発明の排気ガス浄化装置を示すディーゼルエンジンの排気系の構成図である。
【符号の説明】
１０、１１：ハニカム構造体からなる排気ガス浄化用触媒担体
１１ａ：外周壁
１１ｂ：隔壁
１１ｃ、１１ｅ：流通孔
１１ｄ：流入側端面
１１ｆ、１０ｆ：流出側端面
１２ａ：流入側目封止材
１２ｂ：流出側目封止材
１３：セラミックスラリー
１４、１５：マスキングフィルム
１６、１７：穿孔部
１８：スラリー容器
２１：エンジン
２２：排気通路
２３：酸化触媒
２４：ＤＰＦ
２５：ＳＣＲ触媒
２６：還元剤供給装置
２７：排気ガス
３０ａ：流入する排気ガス流
３０ｂ：流出する排気ガス流[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust gas purifying device for a diesel engine that purifies exhaust gas by utilizing catalytic action.
[0002]
[Prior art]
Demand for diesel engines is increasing mainly in Europe due to its high fuel efficiency. However, since particulate matter (PM) and nitrogen oxides (NOx) contained in exhaust gas from diesel engines have a great influence on human health, there are various technologies for reducing PM and NOx. It is being considered.
As one of the exhaust gas aftertreatment technologies for reducing PM and NOx in the exhaust gas, a continuous regeneration type DPF (Diesel Particle Filter) for PM purification and a SCR (SCR: SCR: A system that combines Selective Catalytic Reduction (selective reduction catalyst) is expected. In this system, a continuous regeneration type DPF is disposed upstream of the exhaust system, and an SCR is disposed downstream. In the continuous regeneration type DPF, as described in, for example, Patent Document 1, a partition wall of a honeycomb structure having an outer peripheral wall and a plurality of flow holes axially partitioned by a partition wall inside the outer peripheral wall upstream of the exhaust system Oxidation catalyst carrying Pt group metal on the surface, and a number of flow holes partitioned by partition walls in the axial direction inside the outer peripheral wall and the outer peripheral wall at the downstream, and desired flow on the exhaust gas inflow side and outflow side A DPF for collecting exhaust particulates with holes sealed is arranged, and NO (nitrogen monoxide) in the exhaust gas is changed to NO by the upstream oxidation catalyst.2(Nitrogen dioxide) The PM in the exhaust gas is collected by the downstream DPF, and the collected PM is generated by the oxidation catalyst.2 The PM on the DPF is removed by oxidizing the substrate.
On the other hand, in the NOx purification device represented by SCR arranged in the subsequent stage of the continuous regeneration type DPF, as disclosed in, for example, Patent Document 2, an aqueous ammonia solution, an aqueous urea solution, liquid ammonia, or the like is contained in high-temperature exhaust gas. After injecting the generated ammonia, it is contacted with a metal catalyst for denitration, and NOx is purified. Specifically, as shown in FIG. 4, a
[0003]
[Patent Document 1]
JP-A-1-318715
[Patent Document 2]
JP 2000-303826 A
[0004]
[Problems to be solved by the invention]
However, in the exhaust gas aftertreatment technology, the oxidation catalyst, the DPF, and the SCR catalyst are arranged in series in the exhaust gas passage, and all the devices are separated by the partition wall in the axial direction inside the outer peripheral wall and the outer peripheral wall. Since a honeycomb structure having a large number of partitioned circulation holes is used, there is a problem that the installation space becomes enormous, and a small and highly efficient exhaust gas purification device has been demanded.
An object of the present invention is to obtain a small and efficient exhaust gas purification device.
[0005]
[Means for Solving the Problems]
In order to reduce the size of the exhaust gas purification device, the present inventors have considered increasing the efficiency and reducing the size of a NOx purification device typified by an SCR device. Basically, since the exhaust gas purification device utilizes a catalytic reaction between exhaust gas and a catalyst, the surface area per unit volume of the catalyst carrier is increased to reduce the amount of catalyst supported on the catalyst carrier surface. If the catalytic reaction with the exhaust gas was promoted by increasing the amount, the same purification efficiency could be obtained with a smaller device than before. Therefore, the present inventors paid attention to a catalyst carrier used in a conventional SCR device. A conventionally used catalyst carrier is a honeycomb structure having an outer peripheral wall and a large number of flow holes axially partitioned by partition walls inside the outer peripheral wall, and the flow holes are not plugged. It was. Since the exhaust gas passes straight through a large number of flow holes opened without plugging the flow holes from the inflow side to the outflow side, the surface area per unit volume of the honeycomb structure is expressed by the following equation: expressed. Surface area per unit volume S = 4 × (P−t) / P2 (mm2/ mmThreeHere, P indicates the pitch (mm) of the partition walls, and t indicates the thickness (mm) of the partition walls. Therefore, in order to increase the surface area per unit volume of the honeycomb structure, it is necessary to use a so-called thin wall, high cell density honeycomb structure in which the partition wall thickness is thin or the partition wall pitch is small. It was. However, for example, when a honeycomb structure having a partition wall thickness of 0.1 mm or less, a partition wall pitch of 1.0 mm or less, and a high cell density is used, the opening area in the direction of the honeycomb structure flow path is reduced. It has been found that there is a problem that the pressure loss of the whole honeycomb structure increases because the pressure loss at the body inlet increases. Further, in the case of a catalyst support for a diesel engine, a large honeycomb structure having an outer diameter of 150 mm or more is usually used. Therefore, in a partition wall having a wall thickness of 0.1 mm or less, the partition wall is formed by its own weight at the time of molding. There is a problem that it is easy to deform and the isostatic strength is lowered, and it has been found that there is a limit to downsizing the SCR catalyst device by improving the conventional honeycomb structure. Thus, as a result of further investigations, the inventors of the present invention have developed a honeycomb structure having an outer peripheral wall used as a conventional SCR catalyst support and a large number of flow holes that are partitioned by partition walls in the axial direction inside the outer peripheral wall. By adopting plugging in the desired flow holes on the exhaust gas inflow side and outflow side with respect to the body, the exhaust gas is also passed through the partition wall to increase the chance of contact with the catalyst. The present inventors have found that the size can be reduced and have come up with the present invention. That is, the exhaust gas purification apparatus of the present invention isAn exhaust gas purification apparatus configured by providing an oxidation catalyst, a DPF, and an SCR catalyst from an upstream side in an exhaust passage of an engine, and a catalyst carrier used for the SCR catalyst includes:The partition wall has a plurality of flow holes that are partitioned by a partition wall in the axial direction inside the outer peripheral wall and the outer peripheral wall, and plugs the exhaust gas into the partition wall by plugging the desired flow holes on the exhaust gas inflow side and the outflow side. Catalyst carrier for purifying exhaust gas comprising a honeycomb structure through which gas passesThe catalyst carrier has an outer diameter of 150 mm or more, a porosity of the partition walls of 50% to 80%, and a total pore surface area of pores of 10 μm or more in the partition walls is 0.02 m. 2 / G or more, the plugging length is 3 to 20 mm,The exhaust gas is purified by passing through the partition wall surface and the pores in the partition wall. The exhaust gas purifying apparatus of the present invention isAn exhaust gas purification apparatus configured by providing an oxidation catalyst, a DPF, and an SCR catalyst from an upstream side in an exhaust passage of an engine, and a catalyst carrier used for the SCR catalyst includes:A plurality of flow holes that are axially partitioned by partition walls on the inner side of the outer peripheral wall and the outer peripheral wall, and plugging the desired flow holes on the exhaust gas inflow side and the outflow side to plug the exhaust gas into the partition wall Catalyst carrier for purifying exhaust gas having a honeycomb structure passing throughIsTherefore, the surface area per unit volume can be increased as compared with a conventional honeycomb structure having a large number of flow holes partitioned axially by partition walls inside the outer peripheral wall and the outer peripheral wall. This is because in the honeycomb structure of the conventional structure, the pores formed on the partition wall surface are used, the catalyst material is supported on the partition wall surface, and the exhaust gas is divided into a large number of flow holes partitioned by the partition walls in the axial direction. The surface area effective for the purification of exhaust gas is the geometric surface area of the partition wall because purification is performed by the action of the catalytic substance supported on the partition wall surface by passing straight from the exhaust gas inflow side to the outflow side. However, in addition to the exhaust gas purification action of the conventional honeycomb structure, the catalyst support of the honeycomb structure provided in the exhaust gas purification device of the present invention is configured to exhaust gas by plugging a desired portion of the flow hole. Can pass through the pores formed in the partition walls, so that the surface of the pores formed in the partition walls can be used effectively in addition to the partition wall surfaces constituting the flow holes. Chance of contact between Tanji catalyst material on the pore surface and the exhaust gas will be increase, it is possible to increase the effective surface area per unit volume as compared with the conventional honeycomb structure. As a result, the amount of catalyst that can be effectively used per unit volume can be increased compared to the conventional honeycomb structure, so that the exhaust gas purification catalyst carrier can be downsized without degrading the purification performance. The entire exhaust gas purification device can be reduced in size.
[0006]
FIG. 1 is a perspective view of an exhaust gas
The catalytic reaction with the exhaust gas in the exhaust gas
[0007]
The porosity of the partition walls of the exhaust gas purification catalyst carrier provided in the exhaust gas purification apparatus of the present invention is 50% to 80%, and the total pore surface area of the pores having pore diameters of 10 μm or more in the partition walls is 0.00. 02m2/ G or more is preferable because of the following reasons.
This is because if the porosity of the partition walls of the exhaust gas purification catalyst carrier is less than 50%, the ventilation resistance when the exhaust gas passes through the partition walls increases, so that the pressure loss of the exhaust gas purification catalyst carrier increases. . On the other hand, if the porosity exceeds 80%, the strength of the exhaust gas purifying catalyst carrier is lowered, and there is a risk of damage due to mechanical stress or vibration when used as an exhaust gas purifying device. The porosity of the partition walls of the exhaust gas purifying catalyst carrier is preferably 60 to 75%.
[0008]
Further, the total pore surface area of the pores having a pore diameter of 10 μm or more in the partition wall of the exhaust gas purification catalyst carrier is 0.02 m.2/ G or more is preferable because, for example, when the SCR catalyst material is supported on the exhaust gas purification device, the catalyst material blocks pores and increases pressure loss. That is, when the catalyst substance is coated on the surface of the pores formed in the partition walls, if the pore diameter is 10 μm or more, the pores can be blocked to prevent an increase in pressure loss. It is. The total pore surface area of the pores having a pore diameter of 10 μm or more is 0.02 m.2/ G or more makes it possible to obtain a three-dimensional connection with pores having a pore diameter of 10 μm or more in the partition wall, and plugging the desired flow holes on the exhaust gas inflow side and outflow side. It is possible to prevent an increase in pressure loss of the exhaust gas purification device including the exhaust gas purification catalyst carrier having the structure. The total pore surface area of pores having a pore diameter of 10 μm or more is 0.02 m.2If it is less than / g, the pressure loss of the exhaust gas purifier after supporting the SCR catalyst increases, which leads to a decrease in engine output. The total pore surface area of the pores having a pore diameter of 10 μm or more in the partition wall of the exhaust gas purification catalyst carrier is 0.07 m in order to reduce the increase in pressure loss.2/ G or more is more preferable. Here, the total pore surface area of pores having a porosity and pore diameter of 10 μm or more is measured by a mercury intrusion method.
[0009]
The partition wall thickness of the exhaust gas purification catalyst carrier provided in the exhaust gas purification apparatus of the present invention is preferably 0.1 to 0.5 mm, and the partition wall pitch is preferably 1.3 mm or more. If the partition wall thickness is less than 0.1 mm, the porosity of the partition wall is set in a high range of 50 to 80%, which is not preferable because the strength of the exhaust gas purifying catalyst carrier decreases. On the other hand, if the partition wall thickness exceeds 0.5 mm, no matter how high the partition wall has a high porosity, the flow resistance of the partition wall to the exhaust gas increases, so the pressure loss of the exhaust gas purification catalyst carrier increases. is there. A more preferable partition wall thickness is 0.2 to 0.4 mm. Further, if the partition wall pitch is less than 1.3 mm, the opening area of the through-hole inlet of the exhaust gas purifying catalyst carrier becomes small, and the pressure loss at the exhaust gas purifying catalyst carrier inlet becomes large.
In the exhaust gas purification apparatus of the present invention, the length in the flow path direction of the plugging
[0010]
As the material constituting the partition wall of the exhaust gas purification catalyst carrier, since the present invention is mainly used for purifying exhaust gas of a diesel engine, it is preferable to use a material having excellent heat resistance, It is preferable to use a ceramic material whose main crystal is at least one selected from the group consisting of cordierite, alumina, mullite, silicon nitride, silicon carbide and LAS. Among these, a honeycomb structure having cordierite as a main crystal is most preferable because it is inexpensive, excellent in heat resistance and corrosion resistance, and has low thermal expansion.
[0011]
Next, in the exhaust gas purifying apparatus of the present invention, an outer peripheral wall used for the exhaust gas purifying catalyst carrier and a ceramic honeycomb structure having a plurality of flow holes partitioned by partition walls in the axial direction inside the outer peripheral wall. An example of the manufacturing method will be described. First, an organic binder, a forming aid such as a lubricant, and a pore former are added to the ceramic raw material powder, and after mixing, a predetermined amount of water is injected, and mixing and kneading are performed to prepare a clay having plasticity. Thereafter, the kneaded material is extruded using a known honeycomb structure mold, so that the outer wall and the inner wall of the outer wall are surrounded by a partition wall in the axial direction, and the honeycomb having a square-shaped passage hole. A molded body having a structure is obtained, and then cut, dried, and fired at a predetermined length to obtain a ceramic honeycomb structure having a plurality of flow holes partitioned by a partition wall inside the outer peripheral wall and the outer peripheral wall. At this time, the porosity is 50 to 80%, and the total pore surface area of the pore having a pore diameter of 10 μm or more is 0.02 m.2/ G is selected, and the selection of the pore former and the addition amount are adjusted. Specifically, as the pore former, a material having an average particle diameter of 10 μm or more and a uniform particle diameter is selected, and if 10 parts by mass or more is added to 100 parts by mass of the ceramic raw material powder, the pore diameter is 10 μm or more. The total pore surface area of a certain pore is 0.02m2/ G or more.
In addition, after removing the outer peripheral wall of the ceramic fired body having a honeycomb structure after firing and the peripheral portion thereof, a coating material composed of a ceramic aggregate, an inorganic binder, an organic binder, and the like is applied to the removed outer peripheral surface. A method of forming a ceramic honeycomb structure having a plurality of through-holes formed by drying and curing to form an outer peripheral wall and partitioning the outer peripheral wall and the outer peripheral wall by partition walls may be adopted.
[0012]
Next, an example of a method for plugging a honeycomb structure having a plurality of flow holes axially partitioned by a partition wall inside the outer peripheral wall and inside the outer peripheral wall used in the exhaust gas purification apparatus of the present invention is shown. 3 will be described. FIG. 3 is a schematic cross-sectional view showing a situation where a plugging material is introduced into the
[0013]
Hereinafter, an exhaust gas purifying apparatus of the present invention in which an exhaust gas purifying catalyst carrier is applied to a diesel engine will be described with reference to the drawings.
When the exhaust gas purification apparatus of the present invention is used in a diesel engine, as shown in FIG. 4, an
As the
The
In the exhaust gas purifying apparatus for a diesel engine having the above-described configuration, the
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail.
Example 1
Adjust the powder of kaolin, talc, silica, aluminum hydroxide, alumina, etc.2: 47-53%, Al2O3: 32-38%, MgO: 12-16% and CaO, Na2O, K2O, TiO2, Fe2O3, PbO, P2O5A cordierite light generating raw material powder containing 2.5% or less of components inevitably mixed such as methylcellulose and hydroxypropylmethylcellulose as molding aids, and a resin powder having an average particle size of 45 m as a pore-forming agent Was added, and a specified amount of water was injected to perform further sufficient mixing to prepare a clay that can be extruded into a honeycomb structure.
Then, extrusion molding is performed using an extrusion mold for obtaining a known honeycomb structure, and a honeycomb structure having a peripheral wall and a circulation hole having a square cross section surrounded by partition walls on the inner peripheral side of the outer peripheral wall. By obtaining a molded body, followed by drying, cutting and firing, the partition wall thickness is 0.3 mm, the partition wall pitch is 1.5 mm, the partition wall porosity is 65%, and the surface area of the pores of 10 μm or more in the partition wall is 0.10 m.22 cordierite ceramic honeycomb structures having an outer diameter of 266.7 mm and a length of 304.8 mm were prepared. Here, the total surface area of 10 μm or more in the partition wall was measured by a mercury intrusion method using Autopore III9410 manufactured by Micromeritics.
Of these cordierite ceramic honeycomb structures, plugging portions having a length of 10 mm are alternately formed at the opening ends of the flow holes by the method shown in FIG. The catalyst carrier of Test No. 1 was plugged with the desired flow holes on the side. Further, the other cordierite ceramic honeycomb structure did not form a plugged portion as it was, and was used as a catalyst carrier of Test No. 2.
On the other hand, by adjusting the powder of kaolin, talc, silica, aluminum hydroxide, alumina, etc., by mass ratio, SiO2: 47-53%, Al2O3: 32-38%, MgO: 12-16% and CaO, Na2O, K2O, TiO2, Fe2O3To the cordierite-producing raw material powder containing 2.5% or less of components inevitably mixed such as PbO, methylcellulose and hydroxypropylmethylcellulose are added as molding aids, and a prescribed amount of water is injected. Further sufficient mixing was performed to prepare a clay that can be extruded into a honeycomb structure.
Then, extrusion molding is performed using an extrusion mold for obtaining a known honeycomb structure, and a honeycomb structure having a peripheral wall and a circulation hole having a square cross section surrounded by partition walls on the inner peripheral side of the outer peripheral wall. By obtaining a molded body, followed by drying, cutting, and firing, the partition wall thickness is 0.1 mm, the partition wall pitch is 1.0 mm, the partition wall porosity is 35%, and the surface area of the pores of 10 μm or more in the partition wall is 0.01 m.2A catalyst support of Test No. 3 comprising a cordierite ceramic honeycomb structure having an outer diameter of 266.7 mm and a length of 304.8 mm was prepared. Here, the reason why the porosity was set to 35% is to secure the strength of the honeycomb structure during molding because the partition wall had a thin wall structure of 0.1 mm.
[0015]
For these three types of catalyst supports of test Nos. 1 to 3, the geometric surface area of the partition walls, the effective partition wall volume, the effective partition wall weight, the effective pore surface area, the catalyst support effective surface area, and the catalyst support effective in one support Table 1 shows the results of the surface area obtained by the following formula. The symbols in the following formula are the same as those defined in Table 1.
Bulkhead density; ρ (kg / m3) = 2500 × (1-P / 100)
Here, the true density of cordierite is 2500 kg / L.
Geometric surface area; SG(M2/ L) = 4 × (pt) / p2
In the case of plugging both ends, 1/2 of the above number
Effective partition volume; V (m3/ L) = (p2-(Pt)2) / (1000 × p2)
Effective partition wall weight; W (kg / L) = ρ × V
Effective pore surface area; Sp(M2/ L) = 1000 × V10× W
Effective surface area of catalyst support; SE(M2/ L) = SG+ SP
Effective surface area of catalyst supported per carrier; S (m2/ Ke) = SE× ((D02 × π / 4) × L × 10-6)
Where P: porosity of the honeycomb structure partition wall (%)
t: partition wall thickness (mm)
p: partition wall pitch (mm)
V10The total surface area of pores of 10 μm or more (m2/ G)
D0; Outer diameter of honeycomb structure (mm)
LT; Overall length of honeycomb structure (mm)
[0016]
[Table 1]
Furthermore, TiO was used for the catalyst carriers of the above test Nos.2, WO3, V2O5A powder obtained by adding alumina sol, silica sol, and water as a binder to form a slurry is wash-coated and converted to an effective surface area of the catalyst support of 8 g / m2The amount of the coating was supported. The same amount of urea (N conversion) as the amount of NOx in the exhaust gas is added to the exhaust gas containing 300 ppm of NOx and the exhaust gas temperature of 300 ° C with respect to the obtained catalyst carriers of tests NO.1 to NO.3. As a result, the NOx amount in the exhaust gas at the outlet of the honeycomb structure was compared, and the NOx purification performance was investigated. The case where the NOx purification rate was 90% or more was evaluated as (◎), the case where the NOx purification rate was 70% or more (◯), and the case where the NOx purification rate was less than 70% was evaluated as (×). . The results are also shown in Table 1.
From Table 1, the catalyst carrier of test No. 1 as an example of the present invention can effectively use the surface area of pores in the partition wall as compared with the catalyst carrier of test No. 2 and 3 of the conventional structure as a comparative example. From the effective surface area S per unit volumeEIt can also be seen that the value of the effective surface area S per catalyst carrier is orders of magnitude greater. Therefore, the evaluation of the NOx purification rate is also (）), and it can be seen that the NOx purification performance is excellent.
[0018]
(Example 2)
By adopting the same method as test No. 1 in Example 1 and changing only the cut length of the honeycomb structure, the partition wall thickness was 0.3 mm, the partition wall pitch was 1.5 mm, the partition wall porosity was 65%, The total surface area of pores of 10 μm or more in the partition wall is 0.10 m2Cordierite ceramic honeycomb structures having an outer diameter of 266.7 mm, lengths of 152.4 mm, and 76.2 mm were prepared. Then, similarly to Example 1, for these honeycomb structures, plugging portions having a length of 10 mm were alternately formed at the opening end portions of the flow holes by the method shown in FIG. 3, and the exhaust gas inflow side and outflow side were formed. No. 4 and NO. 5 catalyst carriers in which desired flow holes were plugged.
On the other hand, using the same method as test No. 3 in Example 1, the partition wall thickness was 0.1 mm, the partition wall pitch was 1.0 mm, the partition wall porosity was 35%, and the total surface area of the pores of 10 μm or more in the partition wall was 0. .01m2A catalyst support of Test No. 6 comprising a cordierite ceramic honeycomb structure having an outer diameter of 266.7 mm and a length of 609.6 mm was prepared.
For these three kinds of catalyst supports of test Nos. 4 to 6, the geometric surface area of the partition walls, the effective partition wall volume, the effective partition wall weight, the effective pore surface area, the catalyst support effective surface area, and the catalyst support effective in one support Table 2 shows the results of the surface area obtained by the following formula.
Furthermore, TiO was used for the catalyst carriers of the above test Nos.2, WO3, V2O5The powder was made into a slurry by adding alumina sol, silica sol, and water as a binder, and was wash coated to 8 g / m.2The amount of the coating was supported. The same amount of urea (N conversion) as the amount of NOx in the exhaust gas was added to the obtained NO.4 to NO.6 catalyst carrier with respect to the exhaust gas having an exhaust gas temperature of 300 ° C and 400 ppm of NOx. As a result, the NOx amount in the exhaust gas at the honeycomb structure outlet was compared, and the NOx purification performance was investigated.
[0019]
[Table 2]
All of the catalyst carriers in Table 2 are carriers having an outer diameter of 266.7 mm, but the catalyst carriers of Test Nos. 4 and 5 which are examples of the present invention have total lengths of 152.4 mm and 76.2 mm, and NOx In the case of the catalyst carrier of test No. 6 of the conventional structure which is a comparative example of the present invention, while the evaluation of the purification performance is (◯), in order to make the NOx purification performance evaluation (◯) It can be seen that it is necessary to use a catalyst support having a long total length of 609.6 mm in order to secure the surface area. For this reason, the catalyst carrier of the present invention has an increased effective surface area for exerting the performance of the SCR catalyst, so that it can be seen that the efficiency of the SCR device can be increased and the size can be reduced.
[0021]
【The invention's effect】
As described above, the exhaust gas purifying apparatus of the present invention has a plurality of flow holes that are partitioned by the partition wall in the axial direction inside the outer peripheral wall and the outer peripheral wall, and has desired exhaust gas inflow and outflow side desired. By plugging the flow holes, an exhaust gas purification catalyst carrier made of a honeycomb structure that allows exhaust gas to pass through the partition walls is provided, and the exhaust gas is purified by passing through the partition wall surfaces and pores in the partition walls. . Further, the total pore surface area of the pores having a porosity of 50% to 80% and a pore diameter of 10 μm or more is 0.02 m.2/ G or more, the surface area of the pores in the partition walls can be effectively utilized, so that a honeycomb having a number of flow holes partitioned by partition walls in the axial direction inside the conventional outer peripheral wall and the outer peripheral wall. Compared with the catalyst carrier having the structure, the surface area related to the catalytic reaction per unit volume can be increased, and the exhaust gas purification device can be downsized without degrading the purification performance. For this reason, it becomes possible to reduce the size of the exhaust gas purification device for a diesel engine using such an exhaust gas purification catalyst carrier.
[Brief description of the drawings]
FIG. 1 is a perspective view of an exhaust gas purification catalyst carrier comprising a honeycomb structure provided in an exhaust gas purification apparatus of the present invention.
FIG. 2 is a schematic cross-sectional view of an exhaust gas purifying catalyst carrier comprising a honeycomb structure provided in the exhaust gas purifying apparatus of the present invention.
Fig. 3 is a schematic cross-sectional view showing a situation where a plugging material is introduced into a honeycomb structure.
FIG. 4 is a configuration diagram of an exhaust system of a diesel engine showing an exhaust gas purification device of the present invention.
[Explanation of symbols]
10, 11: Exhaust gas purification catalyst carrier comprising a honeycomb structure
11a: outer peripheral wall
11b: partition wall
11c, 11e: distribution hole
11d: Inflow side end face
11f, 10f: Outflow side end face
12a: Inflow side plugging material
12b: Outflow side plugging material
13: Ceramic slurry
14, 15: Masking film
16, 17: Perforated part
18: Slurry container
21: Engine
22: Exhaust passage
23: Oxidation catalyst
24: DPF
25: SCR catalyst
26: Reducing agent supply device
27: exhaust gas
30a: Inflowing exhaust gas flow
30b: Outflowing exhaust gas flow
Claims (1)
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| KR100794541B1 (en) * | 2004-06-30 | 2008-01-17 | 이비덴 가부시키가이샤 | Exhaust gas purification apparatus |
| JP4344684B2 (en) * | 2004-12-08 | 2009-10-14 | 英明 牧田 | Exhaust gas purification device for internal combustion engine |
| JP2006183507A (en) * | 2004-12-27 | 2006-07-13 | Mitsubishi Fuso Truck & Bus Corp | Exhaust emission control device for internal combustion engine |
| DE102005006262A1 (en) * | 2005-02-11 | 2006-08-24 | Emitec Gesellschaft Für Emissionstechnologie Mbh | Method for positioning a sensor in a honeycomb body, corresponding honeycomb body and motor vehicle |
| JP5409984B2 (en) * | 2005-07-20 | 2014-02-05 | 日野自動車株式会社 | Exhaust gas purification device using selective reduction catalyst |
| US8609581B2 (en) * | 2005-08-31 | 2013-12-17 | Ngk Insulators, Ltd. | Honeycomb structure and honeycomb catalytic body |
| JP5376805B2 (en) * | 2005-11-04 | 2013-12-25 | 日本碍子株式会社 | Honeycomb structure and honeycomb catalyst body |
| JP2007285295A (en) * | 2006-03-24 | 2007-11-01 | Ngk Insulators Ltd | Exhaust emission control system |
| US8105545B2 (en) | 2007-06-19 | 2012-01-31 | Hino Motors, Ltd. | Engine exhaust gas purifier |
| KR100882665B1 (en) | 2007-11-20 | 2009-02-06 | 현대자동차주식회사 | Diesel particulate filter |
| JP4920752B2 (en) * | 2010-01-05 | 2012-04-18 | 日本碍子株式会社 | Honeycomb structure |
| JP6633952B2 (en) * | 2016-03-28 | 2020-01-22 | 日本碍子株式会社 | Honeycomb structure |
| JP6802096B2 (en) | 2017-03-14 | 2020-12-16 | 日本碍子株式会社 | Sealed honeycomb structure |
| CN109707486B (en) * | 2019-02-12 | 2023-10-13 | 合肥宝发动力技术股份有限公司 | Engine tail gas aftertreatment device based on DPF/GPF bimodal technology |
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