Reduction of gas phase reduced nitrogen species in partial burn FCC processes

Abstract

Reduced emissions of gas phase reduced nitrogen species in the off gas of an FCC regenerator operated in a partial or incomplete mode of combustion is achieved by contacting the off gas with an oxidative catalyst/additive composition having the ability to reduce gas phase nitrogen species to molecular nitrogen. Fluidizable particles of the oxidative catalyst/additives are circulated throughout the partial or incomplete burn FCC unit along with the FCC catalyst inventory. The flue gas having a reduced content of gas phase reduced nitrogen species and NO x is passed to a downstream CO boiler, preferably a low NO x CO boiler. In the CO boiler, as CO is oxidized to CO 2 , a reduced amount of gas phase reduced nitrogen species is oxidized to NO x , thereby providing an increase in the overall reduction of NO x emitted into the environment.

We claim:  
     
         1 . A process for reducing the content of gas phase reduced nitrogen species in the off gas derived from a regeneration zone of a fluid catalytic cracking unit (FCCU), said process comprising contacting under catalytic cracking conditions gas phase reduced nitrogen species contained in the regeneration zone off gas released from the regeneration zone of an FCCU during a FCC process, with a gas phase reduced nitrogen species oxidative catalyst/additive composition in an amount sufficient to reduce the content of gas phase reduced nitrogen species present in the off gas relative to the content of gas phase reduced nitrogen species present in the off gas absent the oxidation catalyst/additive composition, said oxidative catalyst/additive composition having a mean particle size of about 50 to about 200 μm and having the ability to oxidize gas phase reduced nitrogen species in the off gas to molecular nitrogen under catalytic cracking conditions.  
     
     
         2 . The process of  claim 1  wherein the oxidative catalyst/additive composition is circulated throughout the FCCU along with a circulating inventory of catalytic cracking catalyst.  
     
     
         3 . The process of  claim 2  wherein the residence time of the oxidative catalyst/additive composition in the regeneration zone of the FCCU relative to that of the inventory cracking catalyst is substantially the same as the catalytic cracking catalyst inventory.  
     
     
         4 . The process of  claim 3  wherein the residence time of the oxidative catalyst/additive composition in the regeneration zone of the FCCU relative to that of the cracking catalyst inventory is the same.  
     
     
         5 . The process of  claim 1  wherein the oxidative catalyst/additive composition has a mean particle size ranging from about 55 to about 150 μm.  
     
     
         6 . The process of  claim 1  wherein said regeneration zone is operated in a partial mode of combustion.  
     
     
         7 . The process of  claim 1  wherein said regeneration zone is operated in an incomplete mode of combustion.  
     
     
         8 . The process of  claim 1  further comprising passing said regeneration zone off gas having a reduced content of gas phase reduced nitrogen species to a CO boiler and releasing an off gas having a reduced content of NO x  emissions into the atmosphere.  
     
     
         9 . The process of  claim 1  wherein the gas phase reduced nitrogen species comprise ammonia.  
     
     
         10 . The process of  claim 1  wherein the gas phase reduced nitrogen species comprises hydrogen cyanide.  
     
     
         11 . The process of  claim 8  wherein the CO boiler is a low NO x  CO boiler.  
     
     
         12 . A process for reducing the content of gas phase reduced nitrogen species in the off gas derived from a regeneration zone of a fluid catalytic cracking unit (FCCU), said process comprising contacting an off gas containing gas phase reduced nitrogen species from an FCCU regenerator with a gas phase reduced nitrogen species oxidative catalyst/additive composition in an amount sufficient to reduce the content of gas phase reduced nitrogen species present in the off gas relative to the content of gas phase reduced nitrogen species present in the off gas absent the oxidative catalyst/additive composition, said oxidative catalyst/additive composition being circulated throughout the FCCU along with an inventory of cracking catalyst and having the ability to oxidize the gas phase reduced nitrogen species in the off gas to molecular nitrogen under catalytic cracking conditions.  
     
     
         13 . The process of  claim 12  wherein the oxidative catalyst/additive composition is circulated throughout the FCCU simultaneous with the cracking catalyst inventory.  
     
     
         14 . The process of  claim 12  wherein the residence time of the oxidative catalyst/additive composition in the FCCU regenerator relative to that of the cracking catalyst inventory is substantially the same.  
     
     
         15 . The process of  claim 12  wherein the residence time of the oxidative catalyst/additive composition in the FCCU regenerator relative to that of the cracking catalyst inventory is the same.  
     
     
         16 . The process of  claim 12  wherein the oxidative catalyst/additive composition has a particle size ranging from about 50 to about 200 μm.  
     
     
         17 . The process of  claim 16  wherein the oxidative catalyst/additive composition has a particle size ranging from about 55 to about 150 μm.  
     
     
         18 . The process of  claim 12  wherein said FCCU regenerator is operated in a partial or incomplete mode of combustion.  
     
     
         19 . The process of  claim 12  further comprising passing said regeneration zone off gas having a reduced content of gas phase reduced nitrogen species to a CO boiler and releasing an off gas having a reduced content of NO x  into the atmosphere.  
     
     
         20 . The process of  claim 18  further comprising passing said regeneration zone off gas having a reduced content of gas phase reduced nitrogen species to a CO boiler and releasing an off gas having a reduced content of NO x  into the atmosphere.  
     
     
         21 . The process of  claim 19  or  20  wherein the CO boiler is a low NO x  CO boiler.  
     
     
         22 . The process of  claim 12  wherein the gas phase reduced nitrogen species comprise ammonia.  
     
     
         23 . The process of  claim 12  wherein the gas phase reduced nitrogen species comprise hydrogen cyanide.  
     
     
         24 . A method of reducing NO x  emissions during catalytic cracking of hydrocarbon feedstocks into lower molecular weight components while operating the catalyst regeneration zone in a partial or incomplete mode of combustion, said method comprising (a) contacting an inventory of catalytic cracking catalyst circulating in a catalytic cracking unit with a gas phase reduced nitrogen species oxidative catalyst/additive, (b) circulating the cracking catalyst inventory and oxidative catalyst/additive composition throughout the fluid catalytic cracking unit between a hydrocarbon cracking zone and catalyst regeneration zone operated in a partial or incomplete mode of combustion to contact a regeneration zone off gas containing gas phase reduced nitrogen species to provide a regeneration off gas having a reduced content of gas phase reduced nitrogen species relative to the content of gas phase reduced nitrogen species present in the regeneration zone off gas without the oxidative catalyst/additive composition, (c) providing a CO boiler downstream of said regeneration zone, said CO boiler being operated in a manner effective to oxidize the regeneration zone off gas, and (d) passing the regeneration zone off gas to the CO boiler to provide an off gas having a reduced NO x  content into the atmosphere.  
     
     
         25 . The process of  claim 24  wherein said regeneration zone off gas is passed to a separations means wherein said cracking catalyst and oxidative catalyst/additive composition are separated in said separation means prior to passage to the CO boiler.  
     
     
         26 . The process of  claim 24  wherein the oxidative catalyst/additive composition is contacted with the regeneration zone off gas in an amount effective to reduce the content of gas phase reduced nitrogen species in the regeneration zone off gas.  
     
     
         27 . The process of  claim 24  wherein the gas phase reduced nitrogen species oxidative catalyst/additive composition comprises particles having a particle size sufficient to permit the catalyst/additive composition to be circulated throughout the catalytic cracking unit simultaneously with the cracking catalyst inventory.  
     
     
         28 . The process of  claim 24  wherein the residence time of the oxidative catalyst/additive composition in the regeneration zone relative to the residence time of the cracking catalyst inventory in the regeneration zone is substantially the same.  
     
     
         29 . The process of  claim 24  wherein the residence time of the oxidative catalyst/additive composition in the regeneration zone relative to the residence time of the cracking catalyst in the regeneration zone is the same.  
     
     
         30 . The process of  claim 27  wherein the oxidative catalyst/additive composition has a mean particle size of from about 50 to about 200 μm.  
     
     
         31 . The process of  claim 24  wherein the catalytic cracking process is a fluid catalytic cracking process.  
     
     
         32 . The process of  claim 24  wherein the gas phase reduced nitrogen species comprise ammonia.  
     
     
         33 . The process of  claim 24  wherein the gas phase reduced nitrogen species comprise hydrogen cyanide.  
     
     
         34 . The process of  claim 24  or  25  wherein the CO boiler is a low NO x  CO boiler.  
     
     
         35 . The process of claims  1 ,  12  or  24  wherein the gas phase reduced nitrogen species oxidative/additive composition comprises (a) at least 1 wt %, measured as the oxide, of an acidic metal oxide containing substantially no zeolite; (b) at least 0.5 wt % of metal component, measured as the oxide, selected from the group consisting of an alkali metal, an alkaline earth metal and mixtures thereof; (c) at least 0.1 wt %, measured as the oxide, of a rare earth or transition metal oxygen storage metal oxide component; and (d) at least 0.1 ppm, measured as the metal, of a noble metal component selected from the group consisting of Pt, Pd, Rh, Ir, Os, Ru, Re and mixtures thereof, all percentages expressed being based on the total weight of the oxidative catalyst/additive composition.  
     
     
         36 . The process of claims  1 ,  12  or  24  wherein the gas phase reduced nitrogen species oxidative/additive composition comprises (1) an acidic metal oxide support; (2) about 1-10 parts by weight, measured as metal oxide, of at least one alkali metal, alkaline earth metal or mixtures thereof; (3) at least 1 part by weight of CeO 2 ; and (4) about 0.01-5.0 parts by weight, measured as metal oxide, of Cu or Ag, all of said parts by weight of components (2)-(4) being per 100 parts by weight of said acidic oxide support material.  
     
     
         37 . The process of claims  1 ,  12  or  24  wherein the gas phase reduced nitrogen species oxidative/additive composition comprises at least one metal-containing spinel which includes a first metal and a second metal having a valence higher than the valence of said first metal, at least one component of a third metal other than said first and second metals and at least one component of a fourth metal other than said first, second and third metals, wherein said third metal is selected from the group consisting of Group Ib metals, Group IIB metals, Group VIA metals, the rare earth metals, the Platinum Group metals and mixtures thereof, and said fourth metal is selected from the group consisting of iron, nickel, titanium, chromium, manganese, cobalt, germanium, tin, bismuth, molybdenum, antimony, vanadium and mixtures thereof.  
     
     
         38 . The process of claims  1 ,  12  or  24  wherein the gas phase reduced nitrogen species oxidative/additive composition comprises (1) an acidic oxide support containing at least 50 wt % alumina; (2) 1-10 wt %, measured as the metal oxide, of an alkali metal, an alkaline earth metal or mixtures thereof; (3) at least 1 wt % CeO 2 ; and (4) 0.01-5.0 parts wt % palladium, all weight percentages of components (2)-(4) being based on the total weight of the acidic oxide support material.  
     
     
         39 . The process of claims  1 ,  12  or  24  wherein the gas phase reduced nitrogen species oxidative catalyst/additive is an additive particle separate from the catalytic cracking catalyst.  
     
     
         40 . The process of claims  1 ,  12 , or  24  wherein the gas phase reduced nitrogen species oxidative catalyst/additive is integrated into the catalytic cracking catalyst as a component thereof.