Process For Reducing The Quantity Of Carbon Dioxide Produced In A Fluid Catalytic Cracking Regeneration Off Gas

Abstract

The present invention relates to a process for the reduction of CO2 emissions from the flue gas of a cracking catalyst regenerator that is part of a fluidized catalytic cracking system which cracks petroleum feedstocks such as petroleum distillates of residual or crude oil which, when catalytically cracked, provide either a gasoline or a gas oil product. This process may also be utilized with regard to the cracking of synthetic feeds having boiling points of from 400° F. to about 1000 as exemplified by oils derived from coal or shale oil. By reducing the CO2 emissions in the regeneration step of catalytic cracking, the further goal of maximizing the production of CO in the flue gas is achieved, the CO being further utilized as a fuel in the refinery or further processed to produce hydrogen.

1 . A process for reducing the quantity of CO2 produced in a fluid catalytic cracking regeneration off gas that is derived from the combusting of coke on catalyst in a fluid catalytic cracking regeneration zone of a fluidized catalytic cracking unit, said process comprising carrying out the combustion of the coke on catalyst under regeneration conditions using a pure or relatively pure oxygen gas that is introduced in an amount sufficient to produce an off gas stream that contains at least 35 volume % of carbon monoxide. 
     
     
         2 . The process of  claim 1 , wherein the fluidized catalytic cracking unit comprises a hydrocarbon cracking zone and a catalyst regeneration zone and the catalyst utilized in the hydrocarbon cracking zone, once contacted with hydrocarbon in the cracking zone where a lower molecular hydrocarbon is produce and some coke deposited on the catalyst is circulated to the catalyst regeneration zone where the catalyst undergoes regeneration before being recycled back to the hydrocarbon cracking zone for further use. 
     
     
         3 . The process of  claim 1 , wherein the regeneration conditions comprise a temperature from about 500° C. to about 800° C. and a pressure from about 1 psig to about 100 psig 
     
     
         4 . The process of  claim 1 , wherein the purity of oxygen introduced to the combustion zone is from about volume 23% to about 99.9 volume %. 
     
     
         5 . The process of  claim 4 , wherein the amount of oxygen introduced is from about 80 volume % to about 99.5 volume %. 
     
     
         6 . The process of  claim 4 , wherein the carbon monoxide content in the off gas stream produced as a result of regeneration of the spent catalyst is at least 40 volume %. 
     
     
         7 . The process of  claim 4 , wherein the carbon monoxide content in the off gas stream produced as a result of regeneration of the spent catalyst is from 35 volume % to 65 volume %. 
     
     
         8 . The process of  claim 1 , wherein the off gas stream that contains at least 35 volume % of carbon monoxide is burned as fuel. 
     
     
         9 . The process of  claim 1 , wherein the off gas stream that contains at least 35 volume % of carbon monoxide is subjected to a water gas shift reaction that includes compressing the off gas stream, combining the compressed off gas stream with steam and then contacting the combined stream with a catalyst to produce water gas shift effluent that is high in hydrogen. 
     
     
         10 . The process of  claim 9 , wherein the hydrogen in the water gas shift effluent is further purified in a pressure swing adsorption unit to produce a high purity hydrogen stream and a pressure swing adsorption tail gas. 
     
     
         11 . The process of  claim 10 , wherein the pressure swing adsorption tail gas is burned to make steam and CO2. 
     
     
         12 . The process of  claim 9 , wherein the water gas shift effluent is subjected to an amine contactor to produce a pure CO2 stream and a high purity H2 stream, the pure CO2 stream being recycled to the fluid catalytic cracking regenerator to control the temperature in the regenerator. 
     
     
         13 . A process of minimizing carbon dioxide from a combustion off gas stream from a fluid catalytic cracking unit comprising a FCC reactor for converting a stream of petroleum feedstock in the presence of a fluidized bed of cracking catalyst into a stream of cracked product and a FCC regenerator for combusting coke buildup on the catalyst to thereby regenerate the catalyst and provide the combustion off gas stream, comprising the steps of combusting the coke buildup deposited on the spent catalyst in the FCC regenerator by contacting the spent catalyst with an amount of pure or relatively pure oxygen gas under regeneration conditions in order to minimize the conversion of carbon monoxide to carbon dioxide and thus form an off gas stream that contains at least 35 volume % of carbon monoxide wherein the amount of pure or relative pure oxygen ranges from about 40% to about 80% of the stoichiometric amount required to convert carbon into carbon dioxide. 
     
     
         14 . The process of  claim 13 , wherein the regeneration conditions comprise a temperature from about 500° C. to about 800° C. and a pressure from about 1 psig to about 99 psig. 
     
     
         15 . The process of  claim 13 , wherein the amount of oxygen introduced is from about 40 to 60%. 
     
     
         16 . The process of  claim 15 , wherein the amount of oxygen introduced is from about 45% to about 55_%. 
     
     
         17 . The process of  claim 16 , wherein the carbon monoxide content in the off gas stream produced as a result of regeneration of the spent catalyst is at least 40 volume %. 
     
     
         18 . The process of  claim 16 , wherein the carbon monoxide content in the off gas stream produced as a result of regeneration of the spent catalyst is from 35 volume % to 65 volume %. 
     
     
         19 . A process for cracking hydrocarbons in a cracking system employing a catalytic cracker, a catalyst regenerator having a dilute phase and an inventory of circulating particulate solids including cracking catalyst, wherein said hydrocarbons are cracked in contact with said cracking catalyst and coke is formed on said cracking catalyst at cracking conditions in said catalytic cracker and wherein said regeneration is carried out under regeneration conditions in the presence of pure or relatively pure oxygen to regenerate thus forming an off gas that contains at least 35.0% by volume of carbon monoxide. 
     
     
         20 . The process of  claim 19 , wherein the fluidized catalytic cracking unit comprises a hydrocarbon cracking zone and a catalyst regeneration zone and the catalyst utilized in the hydrocarbon cracking zone, once spent, is circulated to the fluid catalytic cracking regeneration zone where the spent catalyst undergoes regeneration before being recycled back to the hydrocarbon cracking zone for further use. 
     
     
         21 . The process of  claim 19 , wherein the regeneration conditions comprise a temperature from about 500° C. to about 800° C. and a pressure from about 1 psig to about 99 psig 
     
     
         22 . The process of  claim 19 , wherein the amount of oxygen introduced is from about 40% to about 60% of the stoichiometric amount required to convert carbon into carbon dioxide. 
     
     
         23 . The process of  claim 22 , wherein the amount of oxygen introduced is from about 45 to about 55%. 
     
     
         24 . The process of  claim 22 , wherein the carbon monoxide content in the off gas stream produced as a result of regeneration of the spent catalyst is at least 40 volume %. 
     
     
         25 . The process of  claim 22 , wherein the carbon monoxide content in the off gas stream produced as a result of regeneration of the spent catalyst is from 40 volume % to 65 volume %. 
     
     
         26 . The process of  claim 19 , wherein said cracking catalyst comprises a silica-alumina catalyst or a zeolite-containing catalyst. 
     
     
         27 . The process of  claim 26 , wherein said zeolite-containing catalyst is selected from the group consisting of an X zeolite and a Y zeolite. 
     
     
         28 . A process for reducing CO2 emissions during the cracking of hydrocarbons and catalyst regeneration comprising a cracking catalyst that is recycled between a hydrocarbon cracking zone and a catalyst regeneration zone operated at a temperature of from 1050° F. to about 1300° F. wherein the regeneration off-gas is formed by burning coke off said catalyst, in the presence of pure or relatively pure oxygen gas, at regeneration conditions, in said regeneration zone wherein during the coke-burning the pure or relatively pure oxygen is injected in an amount sufficient to minimize the conversion of carbon monoxide to carbon dioxide and thus form an off gas stream that contains at least 35 volume % of carbon monoxide. 
     
     
         29 . The process of  claim 28 , wherein the amount of pure or relative pure oxygen ranges from about 40% to about 60% of the stoichiometric amount required to convert carbon into carbon dioxide. 
     
     
         30 . The process of  claim 28 , wherein said catalyst inventory circulates between said hydrocarbon cracking and said regeneration zone and wherein said catalyst inventory is stripped, in the presence of steam, to remove hydrocarbons from said catalyst inventory. 
     
     
         31 . A process for regenerating a hydrocarbon cracking catalyst having coke deposits thereon in a FCC unit comprising a hydrocarbon cracking zone and a catalyst regeneration zone comprising the steps:
 (a) contacting the catalyst having coke deposits thereon with pure oxygen or relatively pure oxygen in the hydrocarbon cracking zone at an average temperature in the range of about 500° C. to about 800° C., the pure oxygen or relatively pure oxygen introduced into the catalyst regeneration zone in an amount from about 40% to about 60% of the stoichiometric amount required to convert carbon into carbon dioxide and introduced independently of the introduction of the spent catalyst into the catalyst regeneration zone, thereby combusting at least part of the coke on the catalyst and effectively minimizing the conversion of at least part of the carbon monoxide formed as a result of the combusting of the coke to carbon dioxide to produce an off gas having greater than 35 volume % of carbon monoxide.   
     
     
         32 . The process of  claim 31 , wherein said catalyst is in the fluidized state. 
     
     
         33 . The process of  claim 32 , wherein said catalyst is cycled between said catalyst regeneration zone and the hydrocarbon cracking zone. 
     
     
         34 . The process of  claim 33 , wherein said catalyst is selected from the group consisting of type X zeolites, type Y zeolites and mixtures of these. 
     
     
         35 . The process of  claim 1 , wherein at least part of the carbon monoxide in said combustion gas is converted to carbon dioxide by water-gas shift reaction. 
     
     
         36 . The process of  claim 1 , wherein said oxygen-inert gas mixture entering said combustion zone comprises oxygen and a gas selected from nitrogen, carbon dioxide or mixtures of these.