【０００１】
【発明の属する技術分野】
本発明は、ディーゼルエンジンから排気される排気ガス等を浄化する集塵用フィルタ部材に関する。
【０００２】
【従来の技術】
ディーゼルエンジンから排出される粒子状物質（ＰＭ：パティキュレート・マター：以下ＰＭとする）の排出量は、ＮＯｘ，ＣＯそしてＨＣ等と共に年々規制が強化されてきており、規制の強化に伴いエンジンの改良のみでは、対応できなくなってきている。そこで、エンジンから排出されるＰＭをディーゼルパティキュレートフィルタ（ＤＰＦ：Ｄｉｅｓｅｌ Ｐａｒｔｉｃｕｌａｔｅ Ｆｉｌｔｅｒ ：以下ＤＰＦとする）と呼ばれるフィルタで捕集して、外部へ排出されるＰＭの量を低減する技術が開発され、直接、このＰＭを捕集するフィルタには、多孔質フィルタや繊維フィルタ等が使用されてきている。
【０００３】
しかし、多孔質フィルタは、セラミックスや金属の多孔材で形成され、主に、フィルタの表面における慣性さえぎり効果（ケーキろ過）でＰＭの捕集を行うが、慣性さえぎり効果が主となるため、球直径相当で１μｍ以下の微細なＰＭの捕集は困難であり、粒径の範囲が広いＰＭの微細な粒子が捕集できないという問題がある。
【０００４】
また、多孔質フィルタにおいて多孔材の表面に触媒を担持したフィルタは、表面の比表面積拡大の効果と触媒作用による酸化反応の促進効果でＰＭの吸着及び低温における燃焼除去を行うが、ＰＭの総量によってはフィルタ表面がＰＭで覆われてしまい捕集効率が低下するという問題がある。
【０００５】
そして、繊維フィルタは、セラミックス等の無機繊維をランダムに積層したフェルトを用いて形成され、フィルタ表面（表面ろ過）に加えてフィルタ内部の慣性さえぎり効果（深層ろ過）によってもＰＭの捕集を行うので、多孔質フィルタに比べて集塵容量が大きくなるが、ＰＭの微細な粒子の捕集効率は低いという問題がある。
【０００６】
この繊維フィルタにおいては、ＰＭの捕集効率を向上させるために、複数のフェルトで形成し、排気ガスの通過に関して上流側となるフェルトにおいては比較的太い無機繊維を不規則かつ粗に積層し、下流側となるフェルトにおいては比較的細い無機繊維を不規則かつ密に積層して、粗のフェルトの上流側に耐熱金網を、密のフェルトの下流側に織布をそれぞれ重ねて積層体を形成し、この積層体を周方向に蛇腹状に折り曲げて筒状のフィルタを形成したディーゼル機関の排気微粒子フィルタが提案されている（例えば、特許文献１参照。）。
【０００７】
この繊維フィルタの捕集形態は、フィルタ表面でＰＭを捕集し、この捕集されて堆積したＰＭにさらにＰＭが捕集される表面ろ過（ケーキろ過）と、フィルタ内部でＰＭが捕集される深層ろ過との２つの集塵形式を有しており、また、フィルタの空隙サイズの分布が広くなるように構成されているので、ＰＭの粒径分布に関して広い範囲で捕集できる。
【０００８】
しかし、環境改善の見地や排ガス規制対策を考えた場合、さらなるＰＭの捕集効率向上が求められており、その中でも粒径１０μｍ以下の浮遊粒子状物質（ＳＰＭ）や粒径が２．５μｍ以下のＰＭ２．５等のサブミクロン級の微細な粒子を捕集することが重要になってきている。
【０００９】
そのため、セラミックス又は耐熱金属からなる繊維積層構造等によって構成されたフィルタにおいて、フィルタを構成する固体部分のうち、排気ガス等の流体が接する表面部分にセラミックス又は耐熱金属からなる被膜をＣＶＤや有機ケイ素ポリマーの熱分解等により形成して、耐熱耐食性を高めると共に、この被膜にセラミックス又は耐熱金属微粒子を内包して凹凸部を形成してＰＭの捕集効率をアップさせるフィルタ材が提案されている（例えば、特許文献２参照。）。
【００１０】
しかしながら、このフィルタ材においては、セラミックス又は耐熱金属微粒子をＣＶＤや有機ケイ素ポリマーの熱分解により生成した被膜に内包する構成になっているため、ＣＶＤや熱分解等の加工行程が必要になり、製造コストが高いという問題がある。
【００１１】
その上、セラミックス微粒子は被膜の数ミクロンの瘤状粒子からなる凹凸部を形成するために使用され、被膜で包まれてしまうため、微小な凹凸の形成が困難であるという問題と、セラミックス微粒子のＰＭを吸着する性質を利用できないという問題がある。
【００１２】
【特許文献１】
特開２０００−１３０１５０号公報
【００１３】
【特許文献２】
特開２００２−３８９２１号公報
【００１４】
【発明が解決しようとする課題】
本発明は、上述の問題を解決するべくなされたものであり、その目的は、繊維フィルタの長所を保持したまま、ＰＭのサブミクロン級の微細な粒子も効率よく捕集でき、ＰＭの粒径分布の広い範囲において高い捕集効率を発揮できる集塵用フィルタ部材を提供することにある。
【００１５】
【課題を解決するための手段】
以上のような目的を達成するための本発明の集塵用フィルタ部材は、フェルト状の繊維フィルタ部材を有して構成される集塵用フィルタ部材において、前記繊維フィルタ部材の繊維の表面にガス中の微粒子状の物質を吸着捕集する超微粒子を担持して構成される。
【００１６】
ディーゼルエンジンの排気ガス中のＰＭや大気中の浮遊物質等の微粒子状の物質を吸着捕集する超微粒子は、粒径が０．００５μｍφ〜５μｍφの非常に小さい粒子であり、セラミックス系材料等で形成でき、表面活性に優れた高比表面積を有している。この超微粒子の粒径の大きいものは、ＰＭ中の比較的大きな粒子（例えば、０．５μｍφ〜１μｍφ：以下ＰＭ粒子という）を吸着し易く、粒径の小さいものは、ＰＭ中の比較的小さな粒子（例えば、０．１μｍφ以下：以下ＰＭ微細粒子という）を吸着し易いという性質を持っている。なお、この超微粒子の粒径が０．００５μｍφより小さいと製造が困難となり、５μｍφより大きいと比表面積が小さくなり、捕集効率が低下する。
【００１７】
また、この比較的大きな超微粒子を繊維上に担持させることにより、繊維表面において凹凸が形成され、この凹凸による慣性さえぎり効果が増大するので、慣性さえぎり機構で捕集され易い粒径０．５μｍより大きいＰＭ粒子の捕集効率を向上することができる。また、高比表面積の比較的小さな超微粒子を繊維上に担持させることにより、繊維の表面活性を大きくすることができるので、ブラウン拡散効果による吸着捕集機構が支配的となる粒径１μｍ以下のＰＭ微細粒子の捕集効率を向上することができる。
【００１８】
そして、上記の集塵用フィルタ部材において、超微粒子がセラミックス系材料でー形成され、超微粒子の平均粒径が繊維の直径の１／５〜１／３０００である場合、及び、超微粒子を担持した繊維フィルタ部材の比表面積が１ｍ２ ／ｇ〜２００ｍ２ ／ｇである場合に、特に、ＰＭの捕集効率を大きくすることができる。なお、このフィルタの比表面積とは、繊維フィルタ部材の繊維に超微粒子を担持させた状態でＪＩＳ規格のＲ１６２６に準拠して計測した比表面積のことをいう。
【００１９】
また、このセラミックス系超微粒子は、酸化アルミニウム（アルミナ）、酸化ケイ素、酸化チタニウム、ゼオライト等のセラミックス材料で形成される粒径が０．００５μｍφ〜５μｍφの超微粒子である。また、繊維は炭化ケイ素（ＳｉＣ）、窒化ケイ素（Ｓｉ３ Ｎ４ ）、アルミナ（Ａｌ２ Ｏ３ ）、ムライト等で形成できる。
【００２０】
上記の集塵用フィルタ部材において、超微粒子を担持した繊維フィルタ部材の上流側に慣性さえぎり効果により捕集する捕集部材を設けることにより、比較的大きなＰＭ粒子を予め上流側で慣性さえぎり効果により捕集できるので、下流側のセラミックス系超微粒子を担持した層では、慣性さえぎり効果では捕集しにくい比較的小さなＰＭ微細粒子を効率良く捕集できるようになる。なお、この慣性さえぎり効果により捕集する捕集部材としては、超微粒子を担持しない繊維フィルタ部材や多孔質フィルタや多孔体で構成されたハニカム構造体等がある。
【００２１】
あるいは、上記の集塵用フィルタ部材において、上流側に設ける繊維フィルタ部材を粗に形成し、下流側に設ける繊維フィルタ部材を密に形成すると共に、上流側の前記繊維フィルタ部材の繊維径を下流側の前記繊維フィルタ部材の繊維径よりも太くし、かつ、上流側の前記繊維フィルタ部材の繊維に担持される超微粒子の平均粒径を、下流側の前記繊維フィルタ部材の繊維に担持される超微粒子の平均粒径よりも大きくして構成する。
【００２２】
この構成によれば、上流側の繊維フィルタ部材では、比較的大きな超微粒子を担持した繊維層で主に慣性さえぎり機構により比較的大きなＰＭ粒子を捕集でき、下流側繊維フィルタ部材では、比較的小さな超微粒子を担持した繊維層で、吸着機構（ブラウン拡散効果）により比較的小さなＰＭ微細粒子を捕集できる。従って、ＰＭを広い粒径の範囲で効率よく捕集できる。
【００２３】
つまり、上流側では、比較的大きなＰＭ粒子を捕捉するため、下流側に到達するＰＭはＰＭ微細粒子が中心になるので、この部分を構成する繊維表面に表面活性の優れる高比表面積を有するセラミックス系超微粒子を担持することでＰＭ微細粒子の捕集効率をより向上できる。
【００２４】
また、上記の集塵用フィルタ部材において、繊維又は超微粒子の少なくとも一方に触媒粒子を担持することにより、担持した酸化触媒やＰＭ酸化触媒やＮＯｘ還元触媒等の触媒作用によって、ＰＭの低温燃焼を促進でき、また、ＮＯｘ等の排気ガス中の有害成分も浄化できるようになる。
【００２５】
そして、本発明の排気ガス浄化装置は、上記の集塵用フィルタ部材を有して構成され、ＰＭのサブミクロン級の微細な粒子も効率よく捕集でき、ＰＭの粒径分布の広い範囲において高い捕集効率を発揮できるようになる。
【００２６】
なお、ディーゼルエンジンの排気ガス等の高温ガスを浄化対象とする場合には、耐熱性に優れた無機繊維や金属繊維をフェルト状に積層した繊維フィルタ部材を用いるが、低温のガスを浄化対象とする場合には、自然素材や合成樹脂等の有機繊維をフェルト状に積層した繊維フィルタ部材を用いることもできる。
【００２７】
【発明の実施の形態】
以下、本発明に係る実施の形態の集塵用フィルタ部材と排気ガス浄化装置について、ディーゼルエンジンの排気ガスを浄化する浄化装置用の集塵用フィルタ部材と排気ガス浄化装置を例にして、図面を参照しながら説明する。
【００２８】
本発明の第１の実施の形態の集塵用フィルタ部材１０Ａは、図１及び図２に示すように、無機繊維１１からなるフェルト状の繊維フィルタ部材１２において、無機繊維１１の表面にＰＭを吸着捕集するセラミックス系材料で形成した超微粒子１３を担持させて形成される。
【００２９】
この繊維フィルタ部材１２は、炭化ケイ素（ＳｉＣ）、窒化ケイ素（Ｓｉ３ Ｎ４ ）、アルミナ（Ａｌ２ Ｏ３ ）、ムライト等の繊維径が５〜２０μｍφ程度の無機繊維１１をランダムに積層してフェルト状にして形成することができる。
【００３０】
また、この超微粒子１３は、酸化アルミニウム（アルミナ）、酸化ケイ素、酸化チタニウム、ゼオライト等のセラミックス系で形成されるが、同一材料だけの超微粒子１３を使用してもよく、幾つかの材料で形成された超微粒子１３を混合して使用してもよい。
【００３１】
そして、粒径が比較的大きい方の超微粒子１３Ａとしては、例えば、平均粒径が０．２μｍφのα−アルミナの超微粒子があり、粒径が比較的小さい方の超微粒子１３Ｂとしては、例えば、平均粒径が０．０３μｍφのγ−アルミナの超微粒子がある。また、無機繊維１１の引張強度の面から、この超微粒子１３の平均粒径は無機繊維１１の直径の１／５〜１／３０００であることが好ましい。
【００３２】
この超微粒子１３を繊維フィルタ部材１２を形成する無機繊維１１に担持させる。この超微粒子１３の担持は、繊維フィルタ部材１２を、エタノールとテトラエトキシシラン（ＴＥＳ）と蒸留水を重量比で０．５：６：３で混合した溶液中にセラミックス系超微粒子を１ｍａｓｓ％（１ｗｔ％）分散した担持溶液に浸漬した後、余分な溶液を除去してから大気中５５０℃で熱処理することにより行う。
【００３３】
なお、この超微粒子１３の担持によるＰＭの捕集効果を上げるためには、超微粒子１３を担持させた繊維フィルタ部材１２の比表面積が１〜２００ｍ２ ／ｇであることが好ましい。
【００３４】
そして、この繊維フィルタ部材１２を、一枚、又は複数枚積層して、両側を耐熱金網１４，１４で挟持して第１の実施の形態の集塵用フィルタ部材１０Ａを形成する。この集塵用フィルタ部材１０Ａを、図３及び図４に示すように、蛇腹状に折り曲げ加工した後に収納ケース２０に入れて、第１の実施の形態の排気ガス浄化装置１Ａを形成する。
【００３５】
この構成の集塵用フィルタ部材１０Ａ及びこれを用いた排気ガス浄化装置１Ａによれば、比較的大きな超微粒子を無機繊維上に担持させた場合には、繊維表面において凹凸が形成され、この凹凸による慣性さえぎり効果が増大するので、慣性さえぎり機構で捕集され易い粒径１μｍ以上のＰＭ粒子の捕集効率が向上し、高比表面積の比較的小さな超微粒子を無機繊維上に担持させた場合には、繊維の表面活性を大きくすることができるので、ブラウン拡散効果による吸着捕集機構が支配的となる粒径１μｍ以下のＰＭ微細粒子の捕集効率が向上する。従って、ＰＭのサブミクロン級の微細な粒子も効率よく捕集でき、ＰＭの粒径分布の広い範囲において高い捕集効率を発揮できる。
【００３６】
次に、第２の実施の形態の集塵用フィルタ部材１０Ｂについて説明する。この集塵用フィルタ部材１０Ｂは、図５に示すように、第１の実施の形態の集塵用フィルタ部材１０Ａの上流側に慣性さえぎり効果により捕集する捕集部材１５を設けて構成する。この慣性さえぎり効果の捕集部材１５としては、例えば、繊維径が１４μｍφの炭化ケイ素（ＳｉＣ）繊維１１Ａをフェルト状に積層して形成した粗の繊維フィルタ部材１２Ａを使用することができる。
【００３７】
そして、この粗の繊維フィルタ部材１２Ａを、第１の実施の形態の繊維フィルタ部材１２の上流側に積層して両側を金網１４，１４で挟持して、第２の実施の形態の集塵用フィルタ部材１０Ｂを形成する。この集塵用フィルタ部材１０Ｂを、図３及び図４に示すように、蛇腹状に折り曲げ加工した後に収納ケース２０に入れて、第２の実施の形態の排気ガス浄化装置１Ｂを形成する。
【００３８】
この構成の集塵用フィルタ部材１０Ｂ及びこれを用いた排気ガス浄化装置１Ｂによれば、超微粒子１３を担持した繊維フィルタ部材１２の上流側に慣性さえぎり効果により捕集する捕集部材１２Ａ（１５）を設けることにより、比較的大きなＰＭ粒子を予め上流側で慣性さえぎり効果により捕集できるので、下流側の繊維フィルタ部材１２では、慣性さえぎり効果では捕集しにくい比較的小さなＰＭ微細粒子を効率良く捕集できる。
【００３９】
次に第３の実施の形態の集塵用フィルタ部材１０Ｃについて説明する。この集塵用フィルタ部材１０Ｃは、図６に示すように、上流側に比較的大きな超微粒子１３Ａを担持した粗の繊維フィルタ部材１２Ａを、下流側に比較的小さな超微粒子１３Ｂを担持した密の繊維フィルタ部材１２Ｂを設けると共に、この上流側の粗の繊維フィルタ部材１２Ａの繊維径を、下流側の密の繊維フィルタ部材１２Ｂの繊維径よりも太くして形成する。
【００４０】
つまり、上流側に設ける繊維フィルタ部材１２Ａを粗に形成し、下流側に設ける繊維フィルタ部材１２Ｂを密に形成すると共に、上流側の繊維フィルタ部材１２Ａの繊維径を下流側の繊維フィルタ部材１２Ｂの繊維径よりも太くし、かつ、上流側の繊維フィルタ部材１２Ａの無機繊維１１Ａに担持される超微粒子１３Ａの平均粒径を、下流側の繊維フィルタ部材１２Ｂの無機繊維１１Ｂに担持される超微粒子１３Ｂの平均粒径よりも大きくする。
【００４１】
この集塵用フィルタ部材１Ｃにおいては、上流側の第１繊維フィルタ部材１２Ａは、繊維径が１４μｍφの炭化ケイ素繊維１１Ａをフェルト状に積層して形成され、下流側の密の第２繊維フィルタ部材１２Ｂは９μｍφの炭化ケイ素繊維１１Ｂをフェルト状に積層して形成される。
【００４２】
そして、第１繊維フィルタ部材１２Ａを、エタノールとテトラエトキシシラン（ＴＥＳ）と蒸留水を重量比で０．５：６：３で混合した溶液中に平均粒径が０．２μｍφのα−アルミナ等の比較的大きな径のセラミックス系超微粒子１３Ａを１ｍａｓｓ％（１ｗｔ％）分散した担持溶液に浸漬した後、余分な溶液を除去してから大気中５５０℃で熱処理して、超微粒子１３Ａを無機繊維１１Ａに担持させる。
【００４３】
また、第２繊維フィルタ部材１２Ｂを、エタノールとテトラエトキシシラン（ＴＥＳ）と蒸留水を重量比で０．５：６：３で混合した溶液中に平均粒径が０．０３μｍφのγ−アルミナ等の比較的小さな径のセラミックス系超微粒子１３Ｂを１ｍａｓｓ％（１ｗｔ％）分散した担持溶液に浸漬した後、余分な溶液を除去してから大気中５５０℃で熱処理して、超微粒子１３Ｂを無機繊維１１Ｂに担持させる。
【００４４】
この第１繊維フィルタ部材１２Ａに第２繊維フィルタ部材１２Ｂを積層して両側を金網１４，１４で挟持して、第３の実施の形態の集塵用フィルタ部材１０Ｃを形成する。この集塵用フィルタ部材１０Ｃを、図３及び図４に示すように、蛇腹状に折り曲げ加工した後に収納ケース２０に入れて、第３の実施の形態の排気ガス浄化装置１Ｃを形成する。
【００４５】
この集塵用フィルタ部材１０Ｃは、図７に模式的に示すように、第１繊維フィルタ部材１２Ａの表面ろ過領域Ｒ１と第１深層ろ過領域Ｒ２と、第２繊維フィルタ部材１２Ｂの第２深層ろ過領域Ｒ３とからなる３段階のろ過領域を有している。
【００４６】
この表面ろ過領域Ｒ１では、表面ろ過（ケーキろ過）により、フィルタ表面でＰＭを捕集し、この捕集されて堆積したＰＭ上にさらにＰＭが捕集される。そして、第１深層ろ過領域Ｒ２では、慣性さえぎりが主な捕集機構となり、粒径１μｍφ以上のＰＭ粒子を捕集するが、超微粒子１３Ａの担持による繊維表面の凹凸形成により、この慣性さえぎり効果が増大する。また、第２深層ろ過領域Ｒ３では、ブラウン拡散が主な捕集機構となり粒径１μｍφ以下のＰＭ微細粒子を捕集するが、高比表面積の超微粒子１３Ｂの担持により繊維１１Ｂの表面活性が大きくなり、ＰＭ微細粒子の捕集効果が著しく向上する。
【００４７】
従って、この構成の集塵用フィルタ部材１０Ｃ及びこれを用いた排気ガス浄化装置１Ｃによれば、上流側で、比較的大きなＰＭ粒子を捕捉し、下流側に到達するＰＭ微細粒子を、高比表面積を有する超微粒子１３Ｂを担持した第２繊維フィルタ部材１２Ｂの第２深層ろ過領域Ｒ３で効率よく捕集できる。
【００４８】
次に第４の実施の形態の集塵用フィルタ部材１０Ｄについて説明する。この集塵用フィルタ部材１Ｄでは、第３の実施の形態において、無機繊維１１Ａ，１１Ｂが担持する超微粒子１３Ａ，１３Ｂに白金等の触媒粒子１６を担持させる。
【００４９】
この第４の実施の形態の集塵用フィルタ部材１Ｄは、溶液浸漬、ウォッシュコート等の方法により第３の実施の形態における超微粒子１３Ａ，１３Ｂに白金等の触媒粒子１６を担持させた超微粒子１３Ｃ，１３Ｄを用意し、第３の実施の形態における超微粒子１３Ａ，１３Ｂの代りに、この超微粒子１３Ｃ，１３Ｄを用いて、第３の実施の形態の集塵用フィルタ部材１Ｃと同様な工程を経て作製される。
【００５０】
これにより、集塵用フィルタ部材１Ｄは、図８に示すように、白金等の触媒粒子１６を担持させた超微粒子１３Ｃ，１３Ｄを担持した無機繊維１１Ｃ，１１Ｄをフェルト状に積層した繊維フィルタ部材１２Ｃ，１２Ｄを有して構成されるようになる。ちなみに、触媒粒子１６の粒径は１〜１０ｎｍφ程度である。
【００５１】
この構成の集塵用フィルタ部材１０Ｅ及びこれを用いた排気ガス浄化装置１Ｅによれば、酸化触媒やＰＭ酸化触媒やＮＯｘ還元触媒等の触媒粒子１６の触媒作用によって、ＰＭの低温燃焼を促進でき、また、ＮＯｘ等の排気ガス中の有害成分も浄化できるようになる。
【００５２】
次に第５の実施の形態の集塵用フィルタ部材１０Ｅについて説明する。この集塵用フィルタ部材１Ｅでは、第３の実施の形態に加えて、無機繊維１１Ａ，１１Ｂと超微粒子１３Ａ，１３Ｂに白金等の触媒粒子１６を担持させる。
【００５３】
この第５の実施の形態の集塵用フィルタ部材１Ｅは、第３の実施の形態における繊維フィルタ部材１２Ａ，１２Ｂ又は集塵用フィルタ部材１Ｅを、触媒粒子１６の溶液に浸漬した後乾燥及び熱処理する等の方法により、無機繊維１１Ａ，１１Ｂと超微粒子１３Ａ，１３Ｂに白金等の触媒粒子１６を担持させることにより作製される。
【００５４】
これにより、集塵用フィルタ部材１Ｅは、図９に示すように、白金等の触媒粒子１６が超微粒子１３Ｃ，１３Ｄのみならず、無機繊維１１Ｃ，１１Ｄにも担持されるようになり、第４の実施の形態の集塵用フィルタ部材１Ｄと同様な効果を奏することができる。
【００５５】
次に第６の実施の形態の集塵用フィルタ部材１０Ｆについて説明する。この集塵用フィルタ部材１Ｆでは、第３の実施の形態に加えて、無機繊維１１Ａ，１１Ｂに白金等の触媒粒子１６を担持させる。
【００５６】
この第６の実施の形態の集塵用フィルタ部材１Ｆは、第３の実施の形態における繊維フィルタ部材１２Ａ，１２Ｂを、超微粒子１３Ａ，１３Ｂを担持させる前に、触媒粒子１６の溶液に浸漬した後乾燥及び熱処理する等の方法により、無機繊維１１Ａ，１１Ｂに白金等の触媒粒子１６を担持させる。この担持後に、第３の実施の形態と同じ工程で、超微粒子１３Ａ，１３Ｂを担持させる。
【００５７】
これにより、集塵用フィルタ部材１Ｆは、図１０に示すように、白金等の触媒粒子１６と超微粒子１３Ａ，１３Ｂが担持された無機繊維１１Ｅ，１１Ｆを積層した繊維フィルタ部材１２Ｅ，１２Ｆを有して構成されるようになり、第４の実施の形態の集塵用フィルタ部材１Ｄと同様な効果を奏することができる。
【００５８】
〔実施例〕
また、本発明のフィルタの効果を確認するために、以下に述べるような実施例１〜３の集塵用フィルタ部材と、比較のための比較例１，２の集塵用フィルタ部材を作製し、ＰＭ粒子の捕集試験等を行った。
【００５９】
実施例１の集塵用フィルタ部材は、ＰＭ粒子の中でも１μｍ以下の、特に粒径が１００ｎｍφ以下の超微細な粒子に対する捕集効率の向上を図って、粗繊維フィルタ部材と密繊維フィルタ部材を重ねて構成すると共に、下流側の密繊維フィルタ部材においては繊維に平均粒径が０．０３μｍφのγ−アルミナを担持させて構成した集塵用フィルタ部材であり、次のようにして作製された。
【００６０】
繊維径が１４μｍφの炭化ケイ素繊維をフェルト状に積層して形成した粗繊維フィルタ部材を、第１繊維フィルタ部材とし、繊維径９μｍφの炭化ケイ素繊維をフェルト状に積層して形成した密繊維フィルタを第２繊維フィルタ部材とし、この密繊維フィルタ部材を、エタノールとテトラエトキシシラン（ＴＥＳ）と蒸留水を重量比で０．５：６：３で混合した溶液中に平均粒径が０．０３μｍφのγ−アルミナを１ｍａｓｓ％（１ｗｔ％）分散した担持溶液に浸漬した後、余分な溶液を除去してから大気中５５０℃で熱処理して第２繊維フィルタ部材を作製した。
【００６１】
そして、第１繊維フィルタ部材に第２繊維フィルタ部材を積層して両側を金網で挟持して実施例１の集塵用フィルタ部材Ａを作製し、さらに、蛇腹状に折り曲げ加工した後に収納ケースに入れて排気ガス浄化用の実施例１の排気ガス浄化装置を形成した。
【００６２】
実施例２の集塵用フィルタ部材は、ＰＭ粒子の中でも特に粒径が０．５μｍφ〜１μｍφ前後と、更には０．５μｍφ以下、好ましくは０．１μｍφ以下の微細な粒子に対する捕集効率の向上を図って、粗と密の繊維フィルタ部材を重ねて構成すると共に、上流側の繊維フィルタ部材においては繊維に平均粒径が０．２μｍφのα−アルミナを担持させ、下流側の繊維フィルタ部材においては繊維に平均粒径が０．０３μｍφのγ−アルミナを担持させて構成したフィルタであり、次のようにして作製された。
【００６３】
繊維径が１４μｍφの炭化ケイ素繊維をフェルト状に積層して形成した粗繊維フィルタ部材を、エタノールとテトラエトキシシラン（ＴＥＳ）と蒸留水を重量比で０．５：６：３で混合した溶液中に平均粒径が０．２μｍφのα−アルミナを１ｍａｓｓ％（１ｗｔ％）分散した担持溶液に浸漬した後、余分な溶液を除去してから大気中５５０℃で熱処理して第１繊維フィルタ部材を作製した。
【００６４】
この第１繊維フィルタ部材に、実施例１の第２繊維フィルタ部材と同様にして作製した第２繊維フィルタ部材を積層して両側を金網で挟持して実施例２の集塵用フィルタ部材Ｂを作製し、更に、蛇腹状に折り曲げ加工した後に収納ケースに入れて排気ガス浄化用の実施例２の排気ガス浄化装置を作製した。
【００６５】
実施例３の集塵用フィルタ部材は、ＰＭの燃焼除去の促進を図って、実施例２の集塵用フィルタ部材の第１繊維フィルタ部材と第２繊維フィルタ部材のアルミナ粒子のそれぞれに白金を担持させて形成した第１繊維フィルタ部材と第２繊維フィルタ部材を積層して両側を金網で挟持して実施例３の集塵用フィルタ部材Ｃを作製し、更に、蛇腹状に折り曲げ加工した後に収納ケースに入れて排気ガス浄化用の実施例３の排気ガス浄化装置を作製した。
【００６６】
また、比較例１の集塵用フィルタ部材は、４００ｃｐｉのコージェライトハニカム構造のフィルタを実施例の容積と同じ容積にして形成し、これを収納ケースに入れて排気ガス浄化用の比較例１の排気ガス浄化装置を作製した。
【００６７】
また、比較例２の集塵用フィルタ部材は、繊維径１４μｍφの炭化ケイ素繊維を用いた粗繊維フィルタ部材と繊維径９μｍφの炭化ケイ素繊維を用いた密繊維フィルタ部材を積層して両側を金網で挟持して比較例２の集塵用フィルタ部材を作製し、更に、蛇腹状に折り曲げ加工した後に収納ケースに入れて排気ガス浄化用の比較例２の排気ガス浄化装置を作製した。
【００６８】
この比較例２の集塵用フィルタ部材は、表面ろ過（ケーキろ過）と深層ろ過との２つの集塵形式を有し、また、フィルタの空隙サイズの分布が広いので、ＰＭの粒径分布において広い範囲でＰＭを捕集でき、ディーゼル１３モードによるＰＭ捕集結果では捕集効率は７５〜８４％、ＰＭ２．５（２．５μｍ以下の浮遊粒子状物質）に関しても８０％近い捕集効率を示した。
【００６９】
なお、コージェライトハニカムの比較例１の集塵用フィルタ部材は初期の状態から捕集効率が高いが、初期圧力損失が高く、目詰まりし易い。一方、繊維フィルタの比較例２の集塵用フィルタ部材は初期の捕集効率は比較例１よりも５％程低いが、初期圧力損失も低い。
【００７０】
これらの比表面積を表１に示す。実施例１〜３の比表面積は、比較例１の比表面積に対して１５０〜２００倍で、比較例２の比表面積に対して１２０〜１５０倍となった。
【００７１】
【表１】
また、図１１にＰＭの捕集試験の結果であるＰＭの捕集効率（重量比）を示すが、これにより、実施例１〜３（Ａ，Ｂ，Ｃ）は、同じ繊維フィルタである比較例２（Ｙ）に対して高い捕集効率を示し、特に実施例２，３（Ｂ，Ｃ）はコージェライトハニカムの比較例１（Ｘ）と同等以上の捕集効率を示した。また、この捕集効率の試験は５００℃程度の排気ガス温度で行ったが、白金を担持した実施例３では試験中にフィルタの目詰まりが発生せず、白金がＰＭの燃焼を促す酸化触媒として十分に機能していることが分かった。
【００７２】
この図１１で、実施例１（Ａ）が比較例１（Ｘ）よりも捕集効率が低いのは、主に捕集の対象としているＰＭの範囲が、比較例１（Ｘ），実施例２（Ｂ），実施例３（Ｃ）は粒径５００ｎｍφ〜１μｍφ以上のＰＭ粒子であるのに対して、比較例２（Ｙ），実施例１（Ａ）は粒径１００ｎｍφ以下のＰＭ微細粒子であるため、比較例２（Ｙ），実施例１（Ａ）でＰＭ微細粒子を捕集しても、重量基準の捕集効率にはその効果が表れないためである。
【００７３】
また、図１２にＰＭの粒径５００ｎｍφより小さいＰＭ微細粒子の粒径別の捕集効率（粒子数）を測定した結果を示すが、これにより、ＰＭのうちの微細な粒子の捕集効率は実施例１〜３（Ａ，Ｂ，Ｃ）が比較例１，２（Ｘ，Ｙ）に比べて著しく向上していることが分かる。
【００７４】
そして、実施例１において、γアルミナの粒子径の平均粒子径（μｍ）を変化させた場合における比表面積（ｍ２ ／ｇ）を表２に示す。
【００７５】
【表２】
また、この比表面積をベースとしたＰＭの粒径別（３７〜４２０ｎｍφ）の捕集効率を図１３に示す。この図１３から、比表面積が大きくなる程、より微細な粒子の捕集効率が増加することが分かり、特に、比表面積で１ｍ２ ／ｇ以上、平均粒子径で０．５μｍ以下であれば大きな捕集効率となることが分かった。
【００７６】
また、実施例１において担持させる超微粒子の材料を変化させた場合における比表面積（ｍ２ ／ｇ）を表３に示し、ＰＭの粒径別捕集効率を図１４に示す。図１３と同様に比表面積が大きくなる程ＰＭ微細粒子の捕集効率が向上した。
【００７７】
【表３】
次に、図１５に「繊維表面に担持した粒子径／繊維径」をベースにした「繊維引張強度の変化率（％）」を示す。この図１５は、繊維径を１０μｍφに固定し、粒子径を０．０３〜２μｍφとした時の図であるが、この図１５より、繊維表面に担持した粒子径／繊維径が２μｍ／１０μｍつまり１／５を超えると繊維引張強度が急激に低下する結果となった。従って、繊維表面に担持する超微粒子の平均粒径は、繊維径の１／５以下にすることが好ましいことが分かる。
【００７８】
また、図１６に粒子径を０．０１μｍφ、繊維径を１０μｍφに固定し、繊維表面への粒子担持量（繊維１ｇ当たりの担持した粒子重量（ｍｇ））と担持繊維の比表面積の関係を示す。この図１６より粒子担持量を３５０ｍｇ／ｇ以上に増しても担持繊維の比表面積は２００ｍ２ ／ｇを大きく超えることはなかった。
【００７９】
従って、これらの実施例の試験結果から、担持するセラミックス系超微粒子の平均粒径は０．５μｍ以下、比表面積は１ｍ２ ／ｇ以上、「超微粒子の平均粒径／繊維径」は１／５以下が好ましいことが分かる。
【００８０】
なお、上記では、ディーゼルエンジンの排気ガス用の集塵用フィルタ部材として説明し、超微粒子を担持した無機繊維を積層した繊維フィルタ部材を金網で挟持したものを集塵用フィルタとしているが、本発明の集塵用フィルタ部材は、この形式の集塵用フィルタに限定されるものではなく、また、金網を構成要件とするものでもない。
【００８１】
また、集塵の対象もディーゼルパティキュレートフィルタに限定されるものではなく、これ以外の目的にも使用でき、集塵用フィルタ部材の使用条件に合わせて、繊維フィルタ部材に担持させる超微粒子の材料、担持する触媒の種類を選択できる。また、繊維フィルタ部材を構成する材料も集塵用フィルタ部材の使用条件に合わせて、種々選択できる。
【００８２】
【発明の効果】
以上に説明したように、本発明の集塵用フィルタ部材によれば、次のような効果を奏することができる。
【００８３】
本発明の集塵用フィルタ部材は、フェルト状の繊維フィルタ部材を有して構成される集塵用フィルタ部材において、繊維フィルタ部材の繊維の表面にＰＭを吸着捕集するセラミックス系超微粒子を担持させて形成されるので、この繊維に担持させるセラミックス系超微粒子を０．２μｍφ程度の比較的大きな超微粒子にすると、繊維表面に凹凸が形成され、この凹凸による慣性さえぎり効果が増大し、粒子径が１μｍ以上のＰＭ粒子の捕集効率を向上することができる。また、０．０３μｍφ程度の高比表面積の比較的小さな超微粒子にすると、繊維の表面活性を大きくしてブラウン拡散効果による吸着捕集効果を上げることができ、粒子径が１μｍ以下のＰＭ微細粒子の捕集効率を向上することができる。
【００８４】
また、上流側に慣性さえぎり効果により捕集する層を設けたり、上流側と下流側で繊維に担持される超微粒子の平均粒径を変化させたりすることにより、上流側では主に慣性さえぎり機構によりＰＭ中の比較的大きなＰＭ粒子を捕集し、下流側ではブラウン拡散効果による吸着捕集によりＰＭ中の比較的小さなＰＭ微細粒子を効率良く捕集できるようになる。従って、ＰＭを広い粒径の範囲で効率よく捕集できる。
【００８５】
そして、上記の集塵用フィルタ部材において、繊維又は超微粒子の少なくとも一方に触媒粒子を担持することにより、担持した酸化触媒やＰＭ酸化触媒やＮＯｘ還元触媒等の触媒作用によって、ＰＭの燃焼を促進でき、また、ＮＯｘ等の排気ガス中の有害成分も浄化できるようになる。
【図面の簡単な説明】
【図１】本発明に係る第１の実施の形態の集塵用フィルタ部材の構造を示す部分拡大図である。
【図２】図１の繊維フィルタ部材の繊維部分の拡大図である。
【図３】集塵用フィルタ部材の蛇腹状の折り曲げ状態を模式的に示す図である。
【図４】集塵用フィルタ部材を蛇腹状の折り曲げて収納ケースに収容した排気ガス浄化装置の構成を模式的に示す図である。
【図５】本発明に係る第２の実施の形態の集塵用フィルタ部材の構造を示す部分拡大図である。
【図６】本発明に係る第３の実施の形態の集塵用フィルタ部材の構造を示す部分拡大図である。
【図７】図６の集塵用フィルタ部材のＰＭ捕集機構を模式的に示す図である。
【図８】本発明に係る第４の実施の形態の集塵用フィルタ部材の構造を示す、繊維フィルタ部材の繊維部分の拡大図である。
【図９】本発明に係る第５の実施の形態の集塵用フィルタ部材の構造を示す、繊維フィルタ部材の繊維部分の拡大図である。
【図１０】本発明に係る第６の実施の形態の集塵用フィルタ部材の構造を示す、繊維フィルタ部材の繊維部分の拡大図である。
【図１１】実施例と従来例の集塵用フィルタ部材のＰＭ捕集率の経時変化を示す図である。
【図１２】実施例と従来例の集塵用フィルタ部材のＰＭ平均粒径と捕集効率の関係を示す図である。
【図１３】実施例１の集塵用フィルタ部材における、比表面積と捕集効率の関係をＰＭ平均粒径別に示す図である。
【図１４】実施例１の集塵用フィルタ部材における、ＰＭ平均粒径と捕集効率の関係を超微粒子の材料別に示す図である。
【図１５】実施例１の集塵用フィルタ部材における、超微粒子の平均粒径と繊維引張強度の変化率の関係を示す図である。
【図１６】実施例１の集塵用フィルタ部材における、繊維表面への粒子担持量と担持繊維の比表面積率の関係を示す図である。
【符号の説明】
１Ａ〜１Ｆ 排気ガス浄化装置
１０Ａ〜１０Ｆ 集塵用フィルタ部材
１１，１１Ａ〜１１Ｆ 無機繊維
１２，１２Ａ〜１２Ｆ 繊維フィルタ部材
１３，１３Ａ，１３Ｂ 超微粒子
１４ 金網（耐熱金網）
１６ 触媒粒子
２０ 収納ケース[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a dust collecting filter member for purifying exhaust gas or the like exhausted from a diesel engine.
[0002]
[Prior art]
Emissions of particulate matter (PM: particulate matter: hereinafter referred to as PM) emitted from diesel engines have been strengthened year by year along with NOx, CO and HC. Improvement alone has made it impossible to respond. Therefore, a technology has been developed to collect PM discharged from the engine with a filter called a diesel particulate filter (DPF: DPF) and reduce the amount of PM discharged to the outside. As a filter that directly collects PM, a porous filter, a fiber filter, or the like has been used.
[0003]
However, the porous filter is made of a ceramic or metal porous material and collects PM mainly by the inertia blocking effect (cake filtration) on the surface of the filter, but the inertia blocking effect is mainly used. It is difficult to collect fine PM having a diameter equivalent to 1 μm or less, and there is a problem that PM fine particles having a wide particle size range cannot be collected.
[0004]
In addition, a filter carrying a catalyst on the surface of a porous material in a porous filter performs adsorption of PM and combustion removal at a low temperature by the effect of expanding the specific surface area of the surface and the effect of the oxidation reaction by the catalytic action, but the total amount of PM In some cases, the filter surface is covered with PM and the collection efficiency is lowered.
[0005]
The fiber filter is formed using a felt in which inorganic fibers such as ceramics are randomly stacked, and collects PM not only by the filter surface (surface filtration) but also by the inertia blocking effect (depth filtration) inside the filter. Therefore, although the dust collection capacity is larger than that of the porous filter, there is a problem that the collection efficiency of the fine particles of PM is low.
[0006]
In this fiber filter, in order to improve the collection efficiency of PM, a plurality of felts are formed, and relatively thick inorganic fibers are laminated irregularly and roughly in the felt on the upstream side with respect to the passage of exhaust gas, In the felt on the downstream side, relatively thin inorganic fibers are laminated irregularly and densely, and a heat-resistant wire mesh is stacked on the upstream side of the coarse felt, and a woven fabric is stacked on the downstream side of the dense felt to form a laminate. An exhaust particulate filter for a diesel engine has been proposed in which the laminated body is bent into a bellows shape in the circumferential direction to form a cylindrical filter (see, for example, Patent Document 1).
[0007]
The collection form of this fiber filter is that the PM is collected on the filter surface, the surface filtration (cake filtration) where PM is further collected on the collected and deposited PM, and the PM is collected inside the filter. In addition, the filter can be collected in a wide range with respect to the particle size distribution of PM.
[0008]
However, considering the viewpoint of environmental improvement and countermeasures for exhaust gas regulations, further improvement in PM collection efficiency is required. Among them, suspended particulate matter (SPM) with a particle size of 10 μm or less and particle size of 2.5 μm or less It has become important to collect fine particles of submicron grade such as PM2.5.
[0009]
Therefore, in a filter constituted by a fiber laminate structure made of ceramics or a heat-resistant metal, a coating made of ceramics or a heat-resistant metal is applied to the surface part in contact with a fluid such as exhaust gas among the solid parts constituting the filter by CVD or organic silicon. A filter material has been proposed which is formed by thermal decomposition of a polymer to improve heat resistance and corrosion resistance, and includes a ceramic or heat resistant metal fine particles in the coating to form an uneven portion to improve PM collection efficiency ( For example, see Patent Document 2.)
[0010]
However, this filter material has a structure in which ceramics or refractory metal fine particles are encapsulated in a coating produced by CVD or pyrolysis of an organosilicon polymer, and therefore, a process such as CVD or pyrolysis is required, and manufacturing is performed. There is a problem that the cost is high.
[0011]
In addition, the ceramic fine particles are used to form irregularities made of a few micron-like particles of the coating, and are encased in the coating, which makes it difficult to form fine irregularities. There is a problem that the property of adsorbing PM cannot be used.
[0012]
[Patent Document 1]
JP 2000-130150 A
[0013]
[Patent Document 2]
JP 2002-38921 A
[0014]
[Problems to be solved by the invention]
The present invention has been made to solve the above-mentioned problems, and the object thereof is to efficiently collect fine PM submicron particles while maintaining the advantages of a fiber filter. An object of the present invention is to provide a dust collection filter member that can exhibit high collection efficiency in a wide range of distribution.
[0015]
[Means for Solving the Problems]
In order to achieve the above object, a dust collecting filter member of the present invention is a dust collecting filter member having a felt-like fiber filter member, and a gas is applied to the fiber surface of the fiber filter member. It is configured to carry ultrafine particles that adsorb and collect the fine particulate matter inside.
[0016]
Ultrafine particles that adsorb and collect particulate matter such as PM in exhaust gas of diesel engines and suspended substances in the atmosphere are very small particles with a particle size of 0.005 μmφ to 5 μmφ. It can be formed and has a high specific surface area with excellent surface activity. The ultrafine particles having a large particle size easily adsorb relatively large particles in PM (for example, 0.5 μmφ to 1 μmφ: hereinafter referred to as PM particles), and those having a small particle size are relatively small in PM. It has the property of easily adsorbing particles (for example, 0.1 μmφ or less: hereinafter referred to as PM fine particles). If the particle size of the ultrafine particles is smaller than 0.005 μmφ, the production becomes difficult. If the particle size is larger than 5 μmφ, the specific surface area becomes small, and the collection efficiency decreases.
[0017]
In addition, by supporting the relatively large ultrafine particles on the fiber, irregularities are formed on the fiber surface, and the inertia blocking effect due to the irregularities is increased. Therefore, the particle diameter is more than 0.5 μm which is easily collected by the inertia blocking mechanism. The collection efficiency of large PM particles can be improved. In addition, since the surface activity of the fiber can be increased by supporting ultrafine particles with a relatively small high specific surface area on the fiber, the particle size of 1 μm or less where the adsorption / collection mechanism by the Brown diffusion effect is dominant. The collection efficiency of PM fine particles can be improved.
[0018]
In the filter member for dust collection, when the ultrafine particles are formed of a ceramic material and the average particle size of the ultrafine particles is 1/5 to 1/3000 of the diameter of the fiber, the ultrafine particles are supported. The specific surface area of the finished fiber filter member is 1 m 2 / G-200m 2 In particular, when PM is / g, the PM collection efficiency can be increased. The specific surface area of the filter means a specific surface area measured in accordance with JIS standard R1626 in a state where ultra fine particles are supported on the fibers of the fiber filter member.
[0019]
The ceramic ultrafine particles are ultrafine particles having a particle diameter of 0.005 μmφ to 5 μmφ formed of a ceramic material such as aluminum oxide (alumina), silicon oxide, titanium oxide, and zeolite. The fibers are silicon carbide (SiC), silicon nitride (Si 3 N 4 ), Alumina (Al 2 O 3 ), Mullite or the like.
[0020]
In the filter member for dust collection described above, by providing a collecting member for collecting by the inertia blocking effect on the upstream side of the fiber filter member carrying the ultrafine particles, relatively large PM particles are previously upstream by the inertia blocking effect. Since it can be collected, the layer carrying the ceramic ultrafine particles on the downstream side can efficiently collect relatively small PM fine particles that are difficult to collect by the inertia blocking effect. Examples of the collecting member that collects by the inertia blocking effect include a fiber filter member that does not carry ultrafine particles, a porous filter, and a honeycomb structure composed of a porous body.
[0021]
Alternatively, in the above dust collecting filter member, the fiber filter member provided on the upstream side is roughly formed, the fiber filter member provided on the downstream side is formed densely, and the fiber diameter of the fiber filter member on the upstream side is set downstream. The fiber diameter of the fiber filter member on the downstream side is made larger than the fiber diameter of the fiber filter member on the side, and the average particle size of the ultrafine particles supported on the fibers of the fiber filter member on the upstream side is supported on the fibers of the fiber filter member on the downstream side. It is configured to be larger than the average particle size of the ultrafine particles.
[0022]
According to this configuration, in the upstream fiber filter member, relatively large PM particles can be collected mainly by the inertia blocking mechanism in the fiber layer carrying relatively large ultrafine particles, and in the downstream fiber filter member, With a fiber layer carrying small ultrafine particles, relatively small PM fine particles can be collected by an adsorption mechanism (Brown diffusion effect). Therefore, PM can be efficiently collected in a wide particle size range.
[0023]
In other words, in order to capture relatively large PM particles on the upstream side, the PM that reaches the downstream side is centered on fine PM particles, so ceramics having a high specific surface area with excellent surface activity on the surface of the fibers constituting this part. By supporting the system ultrafine particles, the collection efficiency of PM fine particles can be further improved.
[0024]
Further, in the filter member for dust collection described above, the catalyst particles are supported on at least one of the fibers or the ultrafine particles, so that the low temperature combustion of PM is caused by the catalytic action of the supported oxidation catalyst, PM oxidation catalyst, NOx reduction catalyst, and the like. It can be promoted, and harmful components in exhaust gas such as NOx can be purified.
[0025]
The exhaust gas purifying apparatus of the present invention is configured to have the above-described dust collecting filter member, and can efficiently collect fine PM submicron particles, and in a wide range of PM particle size distribution. High collection efficiency can be demonstrated.
[0026]
When high temperature gas such as exhaust gas from diesel engines is to be purified, a fiber filter member in which inorganic fibers and metal fibers excellent in heat resistance are laminated in a felt shape is used. In this case, a fiber filter member in which organic fibers such as natural materials and synthetic resins are laminated in a felt shape can be used.
[0027]
DETAILED DESCRIPTION OF THE INVENTION
DETAILED DESCRIPTION OF EMBODIMENTS Hereinafter, a dust collecting filter member and an exhaust gas purifying apparatus according to an embodiment of the present invention will be described with reference to an example of a dust collecting filter member and an exhaust gas purifying apparatus for a purifying apparatus that purifies exhaust gas of a diesel engine. Will be described with reference to FIG.
[0028]
As shown in FIGS. 1 and 2, the dust collecting filter member 10 </ b> A according to the first embodiment of the present invention is a felt-like fiber filter member 12 made of inorganic fibers 11, and PM is applied to the surface of the inorganic fibers 11. It is formed by supporting ultrafine particles 13 formed of a ceramic material to be adsorbed and collected.
[0029]
The fiber filter member 12 includes silicon carbide (SiC) and silicon nitride (Si 3 N 4 ), Alumina (Al 2 O 3 ), Inorganic fibers 11 having a fiber diameter of about 5 to 20 μmφ such as mullite can be randomly laminated to form a felt shape.
[0030]
The ultrafine particles 13 are formed of ceramics such as aluminum oxide (alumina), silicon oxide, titanium oxide, zeolite, etc., but the ultrafine particles 13 made of only the same material may be used. The formed ultrafine particles 13 may be mixed and used.
[0031]
The ultrafine particles 13A having a relatively large particle size include, for example, α-alumina ultrafine particles having an average particle size of 0.2 μmφ, and the ultrafine particles 13B having a relatively small particle size include, for example, There are ultrafine particles of γ-alumina having an average particle diameter of 0.03 μmφ. In view of the tensile strength of the inorganic fiber 11, the average particle diameter of the ultrafine particles 13 is preferably 1/5 to 1/3000 of the diameter of the inorganic fiber 11.
[0032]
The ultrafine particles 13 are supported on the inorganic fibers 11 forming the fiber filter member 12. The ultrafine particles 13 are supported by placing 1 mass% of the ceramic ultrafine particles in the fiber filter member 12 in a solution in which ethanol, tetraethoxysilane (TES), and distilled water are mixed at a weight ratio of 0.5: 6: 3. (1 wt%) After immersing in the dispersed support solution, the excess solution is removed and then heat treatment is performed at 550 ° C. in the atmosphere.
[0033]
In order to increase the PM collection effect by supporting the ultrafine particles 13, the specific surface area of the fiber filter member 12 supporting the ultrafine particles 13 is 1 to 200 m. 2 / G is preferable.
[0034]
Then, one or a plurality of the fiber filter members 12 are laminated, and both sides are sandwiched between the heat-resistant metal meshes 14 and 14, thereby forming the dust collection filter member 10A of the first embodiment. As shown in FIGS. 3 and 4, the dust collecting filter member 10A is bent into a bellows shape and then placed in the storage case 20 to form the exhaust gas purifying apparatus 1A of the first embodiment.
[0035]
According to the dust collecting filter member 10A having this configuration and the exhaust gas purifying apparatus 1A using the dust collecting filter member 10A, when relatively large ultrafine particles are supported on the inorganic fiber, unevenness is formed on the fiber surface. Since the inertia blocking effect due to is increased, the collection efficiency of PM particles with a particle size of 1 μm or more that are easily collected by the inertia blocking mechanism is improved, and ultra-fine particles having a relatively high specific surface area are supported on inorganic fibers. Since the surface activity of the fiber can be increased, the collection efficiency of PM fine particles having a particle diameter of 1 μm or less, in which the adsorption and collection mechanism by the Brown diffusion effect is dominant, is improved. Therefore, PM submicron fine particles can be collected efficiently, and high collection efficiency can be exhibited in a wide range of PM particle size distribution.
[0036]
Next, the dust collection filter member 10B of the second embodiment will be described. As shown in FIG. 5, the dust collection filter member 10B is configured by providing a collection member 15 that collects the inertia collection effect on the upstream side of the dust collection filter member 10A of the first embodiment. As the inertia blocking effect collecting member 15, for example, a coarse fiber filter member 12A formed by laminating silicon carbide (SiC) fibers 11A having a fiber diameter of 14 μmφ in a felt shape can be used.
[0037]
Then, the coarse fiber filter member 12A is laminated on the upstream side of the fiber filter member 12 of the first embodiment, and both sides are sandwiched between the metal meshes 14 and 14, thereby collecting the dust of the second embodiment. The filter member 10B is formed. As shown in FIGS. 3 and 4, the dust collecting filter member 10B is bent into a bellows shape and then placed in the storage case 20 to form the exhaust gas purifying apparatus 1B of the second embodiment.
[0038]
According to the dust collection filter member 10B having this configuration and the exhaust gas purification apparatus 1B using the dust collection filter member 10B, the collection member 12A (15) that collects the upstream side of the fiber filter member 12 carrying the ultrafine particles 13 by the inertia blocking effect. ), It is possible to collect relatively large PM particles in advance by the inertia blocking effect on the upstream side. Therefore, the downstream fiber filter member 12 can efficiently collect relatively small PM fine particles that are difficult to collect by the inertia blocking effect. It can be collected well.
[0039]
Next, a dust collection filter member 10C according to a third embodiment will be described. As shown in FIG. 6, the dust collecting filter member 10C has a coarse fiber filter member 12A carrying relatively large ultrafine particles 13A on the upstream side, and a dense fiber carrying relatively small ultrafine particles 13B on the downstream side. The fiber filter member 12B is provided, and the upstream coarse fiber filter member 12A has a fiber diameter larger than the fiber diameter of the downstream dense fiber filter member 12B.
[0040]
That is, the fiber filter member 12A provided on the upstream side is roughly formed, the fiber filter member 12B provided on the downstream side is formed densely, and the fiber diameter of the upstream fiber filter member 12A is set to that of the downstream fiber filter member 12B. The average particle diameter of the ultrafine particles 13A that are thicker than the fiber diameter and supported on the inorganic fibers 11A of the upstream fiber filter member 12A is set to be the ultrafine particles supported on the inorganic fibers 11B of the downstream fiber filter member 12B. It is larger than the average particle size of 13B.
[0041]
In the dust collecting filter member 1C, the upstream first fiber filter member 12A is formed by laminating felt-like silicon carbide fibers 11A having a fiber diameter of 14 μmφ, and the downstream dense second fiber filter member. 12B is formed by laminating 9 μmφ silicon carbide fibers 11B in a felt shape.
[0042]
Then, α-alumina having an average particle size of 0.2 μmφ in a solution in which the first fiber filter member 12A is mixed with ethanol, tetraethoxysilane (TES), and distilled water at a weight ratio of 0.5: 6: 3, etc. After immersing the ceramic ultrafine particles 13A having a relatively large diameter in a supporting solution in which 1% by mass (1 wt%) is dispersed, the excess solution is removed, and then heat treatment is performed at 550 ° C. in the atmosphere, so that the ultrafine particles 13A are inorganic fibers. It is carried on 11A.
[0043]
Further, the second fiber filter member 12B is a solution in which ethanol, tetraethoxysilane (TES), and distilled water are mixed at a weight ratio of 0.5: 6: 3, and γ-alumina having an average particle size of 0.03 μmφ. After immersing the ceramic-based ultrafine particles 13B having a relatively small diameter in a supporting solution in which 1 mass% (1 wt%) is dispersed, the excess solution is removed, and then heat treatment is performed at 550 ° C. in the atmosphere, so that the ultrafine particles 13B are inorganic fibers. It is carried on 11B.
[0044]
The second fiber filter member 12B is laminated on the first fiber filter member 12A and both sides are sandwiched between the metal meshes 14 and 14, thereby forming the dust collection filter member 10C of the third embodiment. As shown in FIGS. 3 and 4, the dust collecting filter member 10C is bent into a bellows shape and then placed in the storage case 20 to form the exhaust gas purifying apparatus 1C of the third embodiment.
[0045]
As schematically shown in FIG. 7, the dust collecting filter member 10C includes a surface filtration region R1, a first depth filtration region R2 of the first fiber filter member 12A, and a second depth filtration of the second fiber filter member 12B. It has a three-stage filtration region consisting of region R3.
[0046]
In the surface filtration region R1, PM is collected on the filter surface by surface filtration (cake filtration), and further PM is collected on the collected and deposited PM. In the first depth filtration region R2, inertia blocking is a main collection mechanism, and PM particles having a particle diameter of 1 μmφ or more are collected. However, this inertia blocking effect is achieved by forming irregularities on the fiber surface by supporting the ultrafine particles 13A. Will increase. Further, in the second depth filtration region R3, Brown diffusion is the main collection mechanism, and PM fine particles having a particle size of 1 μmφ or less are collected. However, the surface activity of the fibers 11B is increased by supporting the ultrafine particles 13B having a high specific surface area. Thus, the effect of collecting PM fine particles is remarkably improved.
[0047]
Therefore, according to the dust collecting filter member 10C having this configuration and the exhaust gas purification apparatus 1C using the dust collecting filter member 10C, on the upstream side, relatively large PM particles are captured, and the PM fine particles reaching the downstream side are reduced to a high ratio. It can be efficiently collected in the second depth filtration region R3 of the second fiber filter member 12B carrying the ultrafine particles 13B having a surface area.
[0048]
Next, a dust collection filter member 10D according to a fourth embodiment will be described. In the dust collecting filter member 1D, in the third embodiment, catalyst particles 16 such as platinum are supported on the ultrafine particles 13A and 13B supported by the inorganic fibers 11A and 11B.
[0049]
The dust collecting filter member 1D according to the fourth embodiment has ultrafine particles obtained by supporting catalyst particles 16 such as platinum on the ultrafine particles 13A and 13B according to the third embodiment by a method such as solution dipping or wash coating. 13C and 13D are prepared, and using the ultrafine particles 13C and 13D instead of the ultrafine particles 13A and 13B in the third embodiment, the same process as the dust collecting filter member 1C of the third embodiment is performed. It is produced through.
[0050]
Thereby, as shown in FIG. 8, the dust collecting filter member 1D is a fiber filter member in which inorganic fibers 11C and 11D carrying ultrafine particles 13C and 13D carrying catalyst particles 16 such as platinum are laminated in a felt shape. 12C and 12D are configured. Incidentally, the particle size of the catalyst particles 16 is about 1 to 10 nmφ.
[0051]
According to the dust collecting filter member 10E having this configuration and the exhaust gas purification apparatus 1E using the dust collecting filter member 10E, the low temperature combustion of PM can be promoted by the catalytic action of the catalyst particles 16 such as an oxidation catalyst, a PM oxidation catalyst, and a NOx reduction catalyst. In addition, harmful components in exhaust gas such as NOx can be purified.
[0052]
Next, a dust collection filter member 10E according to a fifth embodiment will be described. In the dust collecting filter member 1E, in addition to the third embodiment, catalyst particles 16 such as platinum are supported on the inorganic fibers 11A and 11B and the ultrafine particles 13A and 13B.
[0053]
The dust collecting filter member 1E of the fifth embodiment is dried and heat-treated after the fiber filter members 12A, 12B or the dust collecting filter member 1E of the third embodiment are immersed in the solution of the catalyst particles 16. In this way, the inorganic fibers 11A and 11B and the ultrafine particles 13A and 13B are made to carry catalyst particles 16 such as platinum.
[0054]
As a result, as shown in FIG. 9, the filter member 1E for dust collection is such that the catalyst particles 16 such as platinum are supported not only on the ultrafine particles 13C and 13D but also on the inorganic fibers 11C and 11D. The same effect as the dust collecting filter member 1D of the embodiment can be obtained.
[0055]
Next, a dust collection filter member 10F according to a sixth embodiment will be described. In the dust collection filter member 1F, in addition to the third embodiment, catalyst particles 16 such as platinum are supported on the inorganic fibers 11A and 11B.
[0056]
In the dust collecting filter member 1F of the sixth embodiment, the fiber filter members 12A and 12B in the third embodiment are immersed in a solution of the catalyst particles 16 before the ultrafine particles 13A and 13B are supported. The catalyst particles 16 such as platinum are supported on the inorganic fibers 11A and 11B by a method such as post-drying and heat treatment. After this loading, the ultrafine particles 13A and 13B are loaded in the same process as in the third embodiment.
[0057]
As a result, the filter member 1F for dust collection has fiber filter members 12E and 12F in which inorganic fibers 11E and 11F carrying catalyst particles 16 such as platinum and ultrafine particles 13A and 13B are laminated as shown in FIG. Thus, the same effect as the dust collecting filter member 1D of the fourth embodiment can be obtained.
[0058]
〔Example〕
Further, in order to confirm the effect of the filter of the present invention, the dust collecting filter member of Examples 1 to 3 as described below and the dust collecting filter member of Comparative Examples 1 and 2 for comparison were prepared. A PM particle collection test was conducted.
[0059]
The filter member for dust collection of Example 1 is intended to improve the collection efficiency for ultrafine particles having a particle diameter of 1 nm or less, particularly 100 nmφ or less, among the PM particles, and the coarse fiber filter member and the dense fiber filter member. A dust collecting filter member constructed by overlapping and forming a dense fiber filter member on the downstream side by supporting γ-alumina having an average particle diameter of 0.03 μmφ on the fiber, and was produced as follows. .
[0060]
A coarse fiber filter member formed by laminating silicon carbide fibers having a fiber diameter of 14 μmφ in a felt shape is used as a first fiber filter member, and a dense fiber filter formed by laminating silicon carbide fibers having a fiber diameter of 9 μmφ in a felt shape is provided. As the second fiber filter member, this dense fiber filter member has an average particle size of 0.03 μmφ in a solution in which ethanol, tetraethoxysilane (TES), and distilled water are mixed at a weight ratio of 0.5: 6: 3. After immersing γ-alumina in a supporting solution in which 1% by mass (1 wt%) was dispersed, the excess solution was removed, and then heat treatment was performed at 550 ° C. in the atmosphere to produce a second fiber filter member.
[0061]
Then, the second fiber filter member is laminated on the first fiber filter member, and both sides are sandwiched by a metal mesh to produce the dust collecting filter member A of Example 1, and after being bent into a bellows shape, The exhaust gas purification apparatus of Example 1 for exhaust gas purification was formed.
[0062]
The filter member for dust collection of Example 2 improves the collection efficiency for fine particles having a particle size of about 0.5 μmφ to about 1 μmφ, and further 0.5 μmφ or less, preferably 0.1 μmφ or less among PM particles. In the downstream fiber filter member, the fiber filter member on the upstream side carries α-alumina having an average particle diameter of 0.2 μmφ, and the fiber filter member on the upstream side carries a coarse and dense fiber filter member. Is a filter constructed by supporting γ-alumina having an average particle diameter of 0.03 μmφ on a fiber, and was produced as follows.
[0063]
A coarse fiber filter member formed by laminating silicon carbide fibers having a fiber diameter of 14 μmφ in a felt shape, in a solution in which ethanol, tetraethoxysilane (TES), and distilled water are mixed at a weight ratio of 0.5: 6: 3 After immersing α-alumina having an average particle diameter of 0.2 μmφ in a supporting solution in which 1 mass% (1 wt%) is dispersed, the excess solution is removed, and heat treatment is performed at 550 ° C. in the atmosphere to obtain the first fiber filter member. Produced.
[0064]
The second fiber filter member produced in the same manner as the second fiber filter member of Example 1 is laminated on this first fiber filter member, and both sides are sandwiched by a metal mesh, and the dust collection filter member B of Example 2 is used. The exhaust gas purification apparatus of Example 2 for purifying exhaust gas was manufactured after being manufactured and further bent into a bellows shape and then placed in a storage case.
[0065]
The filter member for dust collection of Example 3 promotes combustion removal of PM, and platinum is applied to each of the first fiber filter member of the filter member for dust collection of Example 2 and the alumina particles of the second fiber filter member. After the first fiber filter member and the second fiber filter member formed to be supported are laminated and both sides are sandwiched by a wire mesh, the filter member C for dust collection of Example 3 is manufactured, and further, after being bent into a bellows shape An exhaust gas purifying apparatus of Example 3 for purifying exhaust gas was prepared in a storage case.
[0066]
In addition, the filter member for dust collection of Comparative Example 1 is formed by forming a 400 cpi cordierite honeycomb structure filter having the same volume as that of the Example, and placing this in a storage case, and purifying the exhaust gas purifying of Comparative Example 1 An exhaust gas purification device was produced.
[0067]
Further, the dust collecting filter member of Comparative Example 2 is formed by laminating a coarse fiber filter member using a silicon carbide fiber having a fiber diameter of 14 μmφ and a dense fiber filter member using a silicon carbide fiber having a fiber diameter of 9 μmφ, and both sides are made of a metal mesh. The dust collecting filter member of Comparative Example 2 was produced by being sandwiched, and after being bent into a bellows shape, the filter member was placed in a storage case to produce the exhaust gas purifying apparatus of Comparative Example 2 for exhaust gas purification.
[0068]
The filter member for dust collection of Comparative Example 2 has two dust collection types of surface filtration (cake filtration) and depth filtration, and since the pore size distribution of the filter is wide, the PM particle size distribution is PM can be collected in a wide range, and the PM collection result by diesel 13 mode is 75 to 84%, and PM2.5 (floating particulate matter of 2.5 μm or less) is nearly 80%. Indicated.
[0069]
The filter member for dust collection of Comparative Example 1 of cordierite honeycomb has a high collection efficiency from the initial state, but has a high initial pressure loss and is easily clogged. On the other hand, the dust collection filter member of Comparative Example 2 of the fiber filter has an initial collection efficiency of about 5% lower than that of Comparative Example 1, but the initial pressure loss is also low.
[0070]
These specific surface areas are shown in Table 1. The specific surface areas of Examples 1 to 3 were 150 to 200 times that of Comparative Example 1 and 120 to 150 times that of Comparative Example 2.
[0071]
[Table 1]
Moreover, although the collection efficiency (weight ratio) of PM which is the result of the collection test of PM is shown in FIG. 11, Examples 1-3 (A, B, C) are comparisons which are the same fiber filters by this. Example 2 (Y) showed high collection efficiency, and in particular, Examples 2 and 3 (B, C) showed collection efficiency equal to or higher than that of Comparative Example 1 (X) of cordierite honeycomb. The collection efficiency test was performed at an exhaust gas temperature of about 500 ° C., but in Example 3 in which platinum was supported, the filter was not clogged during the test, and platinum was an oxidation catalyst that promoted PM combustion. It turns out that it works well.
[0072]
In FIG. 11, Example 1 (A) has a lower collection efficiency than Comparative Example 1 (X) because the range of PM that is mainly the target of collection is Comparative Example 1 (X). 2 (B) and Example 3 (C) are PM particles having a particle size of 500 nmφ to 1 μmφ or more, whereas Comparative Example 2 (Y) and Example 1 (A) are PM fine particles having a particle size of 100 nmφ or less. Therefore, even if PM fine particles are collected in Comparative Example 2 (Y) and Example 1 (A), the effect does not appear in the collection efficiency on a weight basis.
[0073]
FIG. 12 shows the results of measuring the collection efficiency (number of particles) of PM fine particles smaller than the particle diameter of PM of 500 nmφ by particle diameter, whereby the collection efficiency of fine particles in PM is It turns out that Examples 1-3 (A, B, C) are remarkably improved as compared with Comparative Examples 1 and 2 (X, Y).
[0074]
In Example 1, the specific surface area (m) when the average particle size (μm) of the particle size of γ-alumina was changed. 2 / G) is shown in Table 2.
[0075]
[Table 2]
Moreover, the collection efficiency according to the particle size (37 to 420 nmφ) of PM based on this specific surface area is shown in FIG. From FIG. 13, it can be seen that as the specific surface area increases, the collection efficiency of finer particles increases. In particular, the specific surface area is 1 m. 2 / G or more and an average particle size of 0.5 μm or less, it was found that the collection efficiency was large.
[0076]
Further, the specific surface area (m 2 / G) is shown in Table 3, and the collection efficiency by PM particle size is shown in FIG. As in FIG. 13, the collection efficiency of PM fine particles improved as the specific surface area increased.
[0077]
[Table 3]
Next, FIG. 15 shows “change rate (%) of fiber tensile strength” based on “particle diameter supported on fiber surface / fiber diameter”. FIG. 15 is a diagram when the fiber diameter is fixed to 10 μmφ and the particle diameter is 0.03 to 2 μmφ. From FIG. 15, the particle diameter / fiber diameter carried on the fiber surface is 2 μm / 10 μm. If it exceeded 1/5, the fiber tensile strength was abruptly reduced. Therefore, it can be seen that the average particle diameter of the ultrafine particles supported on the fiber surface is preferably 1/5 or less of the fiber diameter.
[0078]
FIG. 16 shows the relationship between the amount of particles supported on the fiber surface (particle weight supported per gram of fiber (mg)) and the specific surface area of the supported fibers, with the particle diameter fixed at 0.01 μmφ and the fiber diameter fixed at 10 μmφ. . FIG. 16 shows that the specific surface area of the supported fiber is 200 m even when the particle loading is increased to 350 mg / g or more. 2 / G was not greatly exceeded.
[0079]
Therefore, from the test results of these examples, the average particle size of the ceramic ultrafine particles to be supported is 0.5 μm or less and the specific surface area is 1 m. 2 It can be seen that the average particle size / fiber diameter of the ultrafine particles is preferably 1/5 or less.
[0080]
In the above description, the dust collecting filter member for exhaust gas of a diesel engine is described. A fiber filter member in which inorganic fibers carrying ultrafine particles are sandwiched by a wire mesh is used as a dust collecting filter. The dust collection filter member of the invention is not limited to this type of dust collection filter, and does not have a wire mesh as a constituent feature.
[0081]
In addition, the dust collection target is not limited to the diesel particulate filter, and can be used for other purposes. The material of the ultrafine particles supported on the fiber filter member according to the use conditions of the dust collection filter member. The type of catalyst to be supported can be selected. Moreover, the material which comprises a fiber filter member can also be variously selected according to the use conditions of the filter member for dust collection.
[0082]
【The invention's effect】
As described above, according to the filter member for dust collection of the present invention, the following effects can be obtained.
[0083]
The filter member for dust collection of the present invention is a filter member for dust collection configured to have a felt-like fiber filter member, and carries ceramic ultrafine particles that adsorb and collect PM on the fiber surface of the fiber filter member. Therefore, if the ceramic ultrafine particles supported on this fiber are made to be relatively large ultrafine particles of about 0.2 μmφ, irregularities are formed on the fiber surface, and the inertia blocking effect due to these irregularities is increased. Can improve the collection efficiency of PM particles having a particle size of 1 μm or more. In addition, if ultrafine particles with a relatively high specific surface area of about 0.03 μmφ are used, the surface activity of the fibers can be increased to increase the adsorption and collection effect by the Brown diffusion effect, and the PM fine particles having a particle diameter of 1 μm or less. The collection efficiency of can be improved.
[0084]
In addition, an inertia blocking mechanism is mainly used on the upstream side by providing a layer to collect by the inertia blocking effect on the upstream side, and changing the average particle size of the ultrafine particles supported on the fibers on the upstream side and the downstream side. Thus, relatively large PM particles in the PM can be collected, and relatively small PM fine particles in the PM can be efficiently collected on the downstream side by adsorption and collection due to the brown diffusion effect. Therefore, PM can be efficiently collected in a wide particle size range.
[0085]
In the dust collecting filter member, catalyst combustion is supported on at least one of the fibers or the ultrafine particles, thereby promoting the combustion of PM by the catalytic action of the supported oxidation catalyst, PM oxidation catalyst, NOx reduction catalyst, or the like. In addition, harmful components in exhaust gas such as NOx can be purified.
[Brief description of the drawings]
FIG. 1 is a partially enlarged view showing the structure of a filter member for dust collection according to a first embodiment of the present invention.
2 is an enlarged view of a fiber portion of the fiber filter member of FIG. 1. FIG.
FIG. 3 is a diagram schematically showing a bellows-like bent state of a dust collecting filter member.
FIG. 4 is a diagram schematically showing a configuration of an exhaust gas purifying apparatus in which a dust collecting filter member is bent in a bellows shape and accommodated in a storage case.
FIG. 5 is a partially enlarged view showing a structure of a dust collecting filter member according to a second embodiment of the present invention.
FIG. 6 is a partially enlarged view showing the structure of a filter member for dust collection according to a third embodiment of the present invention.
7 is a view schematically showing a PM collection mechanism of the dust collection filter member of FIG. 6. FIG.
FIG. 8 is an enlarged view of a fiber portion of a fiber filter member showing a structure of a filter member for dust collection according to a fourth embodiment of the present invention.
FIG. 9 is an enlarged view of a fiber portion of a fiber filter member showing a structure of a filter member for dust collection according to a fifth embodiment of the present invention.
FIG. 10 is an enlarged view of a fiber portion of a fiber filter member showing a structure of a dust collection filter member according to a sixth embodiment of the present invention.
FIG. 11 is a diagram showing a change with time of PM collection rate of a filter member for dust collection of an example and a conventional example.
FIG. 12 is a graph showing the relationship between the PM average particle diameter and the collection efficiency of the filter member for dust collection in Examples and Conventional Examples.
FIG. 13 is a graph showing the relationship between the specific surface area and the collection efficiency in the dust collection filter member of Example 1 for each PM average particle diameter.
14 is a graph showing the relationship between the PM average particle diameter and the collection efficiency in the dust collection filter member of Example 1 for each material of ultrafine particles. FIG.
15 is a graph showing the relationship between the average particle diameter of ultrafine particles and the rate of change in fiber tensile strength in the dust collection filter member of Example 1. FIG.
16 is a graph showing the relationship between the amount of particles supported on the fiber surface and the specific surface area ratio of the supported fibers in the dust collection filter member of Example 1. FIG.
[Explanation of symbols]
1A-1F Exhaust gas purification device
10A-10F Dust collection filter member
11, 11A-11F Inorganic fiber
12, 12A-12F Fiber filter member
13, 13A, 13B Ultrafine particles
14 Wire mesh (heat-resistant wire mesh)
16 catalyst particles
20 Storage case
