Regenerable catalyzed trap and apparatus, and method of using the same

Abstract

A method of at least periodically removing from a lean gaseous stream a sorbable component such as SO x includes passing the gaseous stream through a trap member having an oxidation catalyst combined with a sorbent material at a temperature within the sorbing temperature range of the sorbent material. The sorbed component is periodically removed by introducing a combustible component into the gaseous stream and oxidizing it on the trap member to thermally desorb the sorbed component. The amount of combustible component introduced is limited to maintain the gaseous stream composition lean, but is sufficient to increase the surface temperature of at least part of the trap member to above the bulk temperature of the gaseous stream. Sorbing and desorbing periods are alternated and a composition and an apparatus to carry out the process is provided.

What is claimed is:  
     
         1 . A method for removing a sorbable component from a lean gaseous stream containing the same, the method comprising: 
 (a) in a trapping period, passing the gaseous stream within a sorbing temperature range through a catalyzed trap member comprising a combination of a regenerable sorbent material and an oxidation catalyst, and sorbing at least some of the sorbable component into the sorbent material to thereby provide a sorbable component-depleted gaseous stream exiting the catalyzed trap member;    (b) in a desorbing period, introducing a combustible component into the gaseous stream upstream of the catalyzed trap member and combusting the combustible component in the presence of the oxidation catalyst, the combustible component being introduced in an amount which is limited in order to maintain the bulk composition of the gaseous stream lean but which is enough to heat at least a portion of the sorbent material to within a desorbing temperature range to thereby thermally desorb the sorbable component from the sorbent material and provide a sorbable component-enriched gaseous stream exiting the catalyzed trap member.    
     
     
         2 . The method of  claim 1  including controlling combustion during the desorbing period whereby to maintain at least portions of the surface of the catalyzed trap member at a temperature above the bulk temperature of the sorbable component-enriched gaseous stream.  
     
     
         3 . The method of  claim 1  or  claim 2  further comprising passing the sorbable component-depleted stream to a first zone and the sorbable component-enriched stream to a second zone.  
     
     
         4 . The method of  claim 3  wherein the sorbable component comprises So x  whereby the sorbable component-depleted stream comprises a SO x -depleted stream.  
     
     
         5 . The method of  claim 4  wherein the gaseous stream contains a pollutant component and the first zone comprises a catalytic treatment zone for abatement of the pollutant component.  
     
     
         6 . The method of  claim 5  wherein the pollutant component comprises NO x  and the first zone comprises a catalytic lean NO x  abatement zone.  
     
     
         7 . The method of  claim 6  wherein the catalytic NO x  abatement zone comprises a NO x  abatement catalyst having an effective operating temperature range below the desorbing temperature range of the SOX, and passing the SO x -depleted stream to the catalytic NO x  abatement zone at a temperature within the effective operating temperature range for lean NO x  reduction.  
     
     
         8 . The method of  claim 1  or  claim 2  wherein the sorbable component is selected from the group consisting of one or both of SO x  and PO x .  
     
     
         9 . The method of  claim 1  or  claim 2  wherein the sorbent material comprises at least one basic oxygenated compound and the oxidation catalyst comprises a catalyst selected from the group consisting of at least one platinum group metal catalytic component.  
     
     
         10 . The method of  claim 9  wherein the oxidation catalyst comprises a platinum catalytic component.  
     
     
         11 . The method of  claim 10  wherein the sorbent material is selected from the group consisting of one or more of metal oxides, metal carbonates, metal hydroxides and mixed metal oxides.  
     
     
         12 . The method of  claim 11  wherein the metals of the metal oxides, metal hydroxides and metal carbonates and at least one of the metals of the mixed metal oxides are selected from the group consisting of one or more of magnesium, calcium, strontium, barium and lanthanum.  
     
     
         13 . The method of  claim 11  wherein the sorbent material is selected from the group consisting of one or more oxides of cerium, praseodymium and elements of atomic numbers  22  through  29  inclusive.  
     
     
         14 . The method of  claim 11  wherein the sorbent material is selected from the group consisting of at least one compound selected from each of group A and group B wherein: group A consists of one or more of metal oxides, metal carbonates, metal hydroxides and mixed metal oxides, the metals of which (at least one metal of the mixed metal oxides) are selected from the group consisting of magnesium, calcium, strontium, barium and lanthanum; and group B consists of one or more oxides of cerium, praseodymium and elements of atomic numbers from 22 to 29 inclusive.  
     
     
         15 . The method of  claim 1  wherein the catalyzed trap member comprises a segregated combination of the oxidation catalyst and the sorbent.  
     
     
         16 . A thermally regenerable composition for sorbing a sorbable component from a gas stream, the composition comprising an oxidation catalyst and a regenerable sorbent material disposed in combination with each other on a common refractory carrier member; 
 the oxidation catalyst comprising at least one catalytic metal component dispersed on a first support material; and    the sorbent material comprising at least one basic oxygenated metal compound which is segregated from at least about 50 percent by weight of the first catalytic metal component, at least to the extent that (a) when the sorbent material is dispersed on a support material, the segregated catalytic metal component and the sorbent material are not dispersed on the same increment of support material, and (b) when the sorbent material is in bulk form, the segregated catalytic metal component is not incorporated into the bulk sorbent material.    
     
     
         17 . A thermally regenerable composition for sorbing a sorbable component from a gas stream, the composition comprising an oxidation catalyst and a regenerable sorbent material disposed in combination with each other on a common refractory carrier member; 
 the oxidation catalyst comprising at least one catalytic metal component dispersed on a first support material; and    the sorbent material is selected from the group consisting of at least one compound selected from each of group A and group B wherein: group A consists of one or more of metal oxides, metal carbonates, metal hydroxides and mixed metal oxides, the metals of which (at least one metal of the mixed metal oxides) are selected from the group consisting of magnesium, calcium, strontium, barium and lanthanum; and group B consists of one or more oxides of cerium, praseodymium and elements of atomic numbers from 22 to 29 inclusive.    
     
     
         18 . The composition of  claim 17  wherein the group A compounds comprise from about 50 to 95 percent by weight of the combined weight of the group A and group B compounds.  
     
     
         19 . The composition of  claim 16  or  claim 17  wherein the catalytic metal component comprises a platinum group metal catalytic component.  
     
     
         20 . The composition of  claim 19  wherein the catalytic metal component comprises a platinum metal component.  
     
     
         21 . The composition of  claim 16  or  claim 17  wherein the oxidation catalyst is disposed as a first discrete layer on the refractory carrier member and the sorbent material is disposed as a second discrete layer on the refractory carrier member.  
     
     
         22 . The composition of  claim 16  or  claim 17  wherein the sorbent material is selected from the group consisting of one or more of metal oxides, metal carbonates, metal hydroxides and mixed metal oxides.  
     
     
         23 . The composition of  claim 22  wherein the sorbent material comprises one or more group A compounds and one or more group B compounds, wherein the metals of the metal oxides, metal hydroxides and metal carbonates and at least one of the metals of the mixed metal oxides are, for the group A compounds, selected from the group consisting of one or more of magnesium, calcium, strontium and barium, and, for the group B compounds, selected from the group consisting of one or more of rare earth metal oxides and oxides of manganese, lanthanum, nickel and iron.  
     
     
         24 . The composition of  claim 23  wherein the group A compounds comprise from about 5 to 95 percent by weight of the combined weight of the group A compounds and the group B compounds.  
     
     
         25 . The composition of  claim 24  wherein one or more of the group A compounds and one or more of the group B compounds are present in bulk form and are admixed in the same layer of sorbent material.  
     
     
         26 . The composition of  claim 24  wherein one or more of the group A compounds and one or more of the group B compounds are supported on the same increment of support material.  
     
     
         27 . The composition of  claim 16  or  claim 17  further comprising a second oxidation catalytic metal moiety present in an amount to enhance the SO x  sorption capability of the sorbent material, the second oxidation catalytic metal moiety being in intimate contact with the sorbent material to the extent that (a) when the sorbent material is dispersed on a support material, the second catalytic metal moiety is dispersed on the same increment of support material as is the sorbent material, and (b) when the sorbent material is in bulk form, the second catalytic metal moiety is incorporated into the bulk sorbent material.  
     
     
         28 . The composition of  claim 27  wherein the second oxidation catalytic metal moiety comprises at least one platinum group metal component.  
     
     
         29 . The composition of  claim 27  wherein the second oxidation catalytic metal moiety comprises a platinum catalytic metal moiety.  
     
     
         30 . The composition of  claim 27  wherein the second oxidation catalytic metal moiety is present in an amount sufficient to promote the sorption function of the sorbent material.  
     
     
         31 . An apparatus for removing a sorbable component from a gaseous stream containing the same comprises: 
 (a) an inlet conduit dimensioned and configured for connection in flow communication to a source of a gaseous stream containing the first component;    (b) a catalyzed trap member having a trap inlet and a trap outlet, the trap inlet being connected in flow communication to the inlet conduit, the trap member comprising a segregated combination of a regenerable sorbent material and a catalyst material effective for promoting the oxidation of a combustible component in such gaseous stream;    (c) an outlet conduit connected to the trap outlet;    (d) combustible component inlet means connected in flow communication to the inlet conduit; and    (e) control means associated with the inlet conduit to permit intermittent injection of a combustible component into the inlet conduit.    
     
     
         32 . The apparatus of  claim 31  wherein the trap member comprises a SO x  trap material selected from the group consisting of one or more of metal oxides, metal carbonates, metal hydroxides and mixed metal oxides and the oxidation catalyst comprises a platinum group metal catalytic metal component dispersed on a suitable support material.  
     
     
         33 . The apparatus of  claim 31  or  claim 32  wherein the oxidation catalyst comprises a platinum metal catalytic component.