Process for decreasing content of particulate material contained in exhaust gas from lean burn engine or the like

Abstract

To decrease the content of a particulate material contained in an exhaust gas from a diesel engine or the like, the content of the particulate material is continuously decreased by generating plasma in the exhaust gas containing the particulate material to thereby produce a plurality of O( 1 D) radicals and subsequently produce a plurality of per-hydroxide excited species, and oxidizing the particulate material by the per-hydroxide excited species.

What is claimed is:  
     
         1 . A process for decreasing the content of a particulate material contained in an exhaust gas from a lean burn engine, comprising the steps of: generating plasma in the exhaust gas discharged from the lean burn engine and containing the particulate material, to thereby produce a plurality of O( 1 D) radicals and subsequently produce a plurality of per-hydroxide excited species; and oxidizing the particulate material by the per- hydroxide excited species.  
     
     
         2 . A process for decreasing the content of a particulate material contained in an exhaust gas from a lean burn engine or the like according to  claim 1 , wherein, in plasma generating conditions, an intensity E of an electric field is set at a value equal to or larger than 3.0 kV/mm, and a power density Dw is set at a value equal to or larger than 1 W/cm 3 .  
     
     
         3 . A process for decreasing the content of a particulate material contained in an exhaust gas from a lean burn engine or the like according to  claim 1  or  2 , wherein the surface of at least one of opposed electrodes which is opposed to the other electrode is covered with a dielectric.  
     
     
         4 . A process for decreasing the content of a particulate material contained in an exhaust gas from a lean burn engine or the like and comprising a carbon solid fraction and a soluble organic fraction covering the carbon solid fraction, the process comprising the steps of: subjecting the soluble organic fraction to the reaction with oxygen under the presence of a catalyst to oxidize the soluble organic fraction; generating plasma in the exhaust gas to produce plasma excited species; and oxidizing the carbon solid fraction by the plasma excited species.  
     
     
         5 . A process for decreasing the content of a particulate material contained in an exhaust gas from a lean burn engine or the like according to  claim 4 , wherein the catalyst is at least one selected from the group consisting of Pt, Pd, Rh, Cu Ag and Au.  
     
     
         6 . A process for decreasing the content of a particulate material contained in an exhaust gas from a lean burn engine or the like according to  claim 4  or  5 , wherein, in plasma generating conditions, an intensity E of electric field is set at a value equal to or larger than 3.0 kV/mm, and a power density Dw is set at a value equal to or larger than 1 W/cm 3 .  
     
     
         7 . A process for decreasing the content of a particulate material contained in an exhaust gas from a lean burn engine or the like according to  claim 4 ,  5  or  6 , wherein the surface of at least one of opposed electrodes which is opposed to the other electrode is covered with a dielectric.  
     
     
         8 . A process for decreasing the content of a particulate material contained in an exhaust gas from a lean burn engine or the like, comprising the steps of: generating plasma in the exhaust gas discharged from the lean burn engine and containing the particulate material to produce a plurality of nitrogen dioxide molecules and a plurality of ozone molecules; and oxidizing the particulate material by the nitrogen dioxide molecules and the ozone molecules.  
     
     
         9 . A process for decreasing the content of a particulate material contained in an exhaust gas from a lean burn engine, comprising the steps of: generating plasma in the exhaust gas discharged from the lean burn engine and containing the particulate material to produce a plurality of nitrogen dioxide molecules and a plurality of ozone molecules; oxidizing the particulate material by the nitrogen dioxide molecules and-the ozone molecules; and subjecting the particulate material to the reaction with the nitrogen dioxide molecules and the ozone molecules in the presence of a catalyst to oxidize the particulate material.  
     
     
         10 . A process for decreasing the content of a particulate material contained in an exhaust gas from a lean burn engine or the like according to  claim 9 , wherein the catalyst is at least one selected from the group consisting of Pt, Pd, Rh, Cu Ag and Au.  
     
     
         11 . A process for decreasing the content of a particulate material contained in an exhaust gas from a lean burn engine or the like according to  claim 8 ,  9  or  10 , wherein, in plasma generating conditions, an intensity E of electric field is set at a value equal to or larger than 3.0 kV/mm, and a power density Dw is set at a value equal to or larger than 1 W/cm 3 .  
     
     
         12 . A process for decreasing the content of a particulate material contained in an exhaust gas from a lean burn engine or the like according to  claim 8 ,  9 ,  10  or  11 , wherein the surface of at least one of opposed electrodes which is opposed to the other electrode is covered with a dielectric.