FIELD OF THE INVENTION:

The present invention relates to a catalyst which acts as a CO combustion promoter and a process for preparation thereof. Specifically, the present invention relates to a catalyst to be used in Fluid Catalytic Cracking (FCC) units to promote CO combustion.

BACKGROUND OF THE INVENTION:

Fluid Catalytic Cracking (FCC) is widely used in the petrochemical industry to convert high- molecular weight hydrocarbons into low molecular weight hydrocarbons. During the FCC process, there is always technical limitations with respect to complete combustion of coke to CO2 and compete combustion of CO. Generally, alumina support-based CO combustion promoter additives are used to enhance combustion of coke by promoting CO oxidation and to reduce after burning issues in the FCC units. Some of the known catalysts and the process to promote the CO combustion in FCC units are discussed in detail.

U.S. Pat. No. 3,696,025 discloses catalytic cracking by addition of titanium to catalyst. Further, the document discloses method to increase the regeneration temperature to 690° C to 760° C in the presence of high concentration of 02 in the regenerator, to enable complete combustion of coke to CO2 in the regeneration level. However, the metallurgical limitations do not permit the adoption of such a method with existing plants. Though, such a process helps in preventing afterburning, it does not provide a control in the CO2/CO ratio to the desired level.

U.S. Pat. No. 4,093,535 discloses impregnation of noble metals such as Pt and Pd in Y type zeolite, which is an active component of the FCC catalyst. Such catalysts with 25 ppm Pt and 25 ppm Pd significantly control CO2/CO ratio. However, these catalysts do not have flexibility such as addition of CO-combustion promoter cannot be terminated as and when required, or to increase/ decrease the CO2/CO ratio. U.S. Pat. No. 4,199,435 discloses NOx Control in cracking catalyst regeneration and discloses that the amount of NOx formed during regeneration of a cracking catalyst in the presence of a metallic carbon monoxide combustion catalyst is decreased without substantially adversely affecting the carbon monoxide combustion activity of the promoter by subjecting the combustion-promoting catalyst to steam treatment prior to employing it in the cracking catalyst regeneration operation. The document also discloses a combustion promoter selected from the metals, such as Pt, Pd, Ir, Os, Ru, Rh, Re, and copper on an inorganic support.

The U.S. Pat. No. 4,290,878 discloses that in regeneration of a cracking catalyst using platinum to catalyze combustion of CO, the amount of nitrogen oxides formed is decreased by employing a combustion promoter containing, for each part of platinum, from 0.01 to 1 part of iridium or rhodium.

Most of these CO combustion promoter additives are alumina based. However, such conventional used alumina-based CO combustion promoter additives require high demand of air supply to combust CO to CO2 during regeneration process. However, high supply amount of air to the regenerator is a limiting factor in the FCC units. Accordingly, there is a need for an improved catalysts which can promote CO combustion in FCC units under normal/ minimum air supply condition.

Further, it is also clear from the literature that with growing regulations on CO emission in the environment and for circumventing the problem of afterburning associated with the FCC technology, improved catalysts as well as improved methods are continuously in demand which provides efficient oxidation of CO in regenerator dense bed of FCC units.

SUMMARY OF THE INVENTION:

The present invention discloses a catalyst for promoting CO combustion in an FCC unit. The catalyst includes an alumina-cerium-zirconium support loaded with active metals. The alumina- cerium-zirconium support is micro spherical in shape. The active metals are selected from platinum group metals. Specifically, the active metals are selected from at least one metal from Platinum (Pt), Palladium (Pd), Ruthenium (Ru), or a combination thereof. The alumina- cerium-zirconium support is mainly made up of AI2O3 in 50 - 90 wt.%, ZrCh in 0.5-30 wt.%, and CeCh in 2-60 wt.%. Further, the catalyst consists of at least one metal selected from Platinum (Pt) which is in 100-1000 ppm, Palladium (Pd) which is in 100-1500 ppm, and Ruthenium (Ru) which is in 100-2000 ppm, or a combination of these metals.

The present invention also discloses a process for preparing a catalyst to promote CO combustion in an FCC unit. The process includes steps of synthesizing a cerium-zirconium solid hydroxide, wherein the cerium-zirconium solid hydroxide is synthesized by a precipitating reaction of a cerium precursor and a zirconium precursor. Then adding and mixing a high-density dispersible alumina binder solution in the cerium-zirconium solid hydroxide to make alumina-cerium- zirconium slurry. Wherein the high-density dispersible alumina binder solution includes an aluminium chlorohydrate solution, a pseudoboehmite alumina solution or a combination thereof.

Thereafter, a step of spray drying the alumina-cerium-zirconium slurry is completed to produce the alumina-cerium-zirconium support. The step of spray drying the alumina-cerium-zirconium slurry provides an alumina-cerium-zirconium support which is micro spherical in shape. Specifically, the step of spray drying of the alumina-cerium-zirconium slurry is completed in a cocurrent spray drying operation unit having an inlet temperature of 400°C and an outlet temperature of 170°C.

Thereafter, the said micro spherical alumina-cerium-zirconium support undergoes through a calcination step, wherein, the calcination is performed at a temperature range of 580°C to 620°C for a time period of 3 to 5 hours.

Finally loading of active metals on the said alumina-cerium-zirconium support is done, wherein, the active metals are selected from a platinum group metals (PGMs). Specifically, the platinum group metals (PGMs) are selected from at least one metal from Platinum (Pt), Palladium (Pd), Ruthenium (Ru), or a combination thereof. Further, the alumina- cerium-zirconium slurry is prepared by mixing a high-density dispersible alumina binder solution and the cerium-zirconium solid hydroxide in a demineralized water to produce a reaction mixture. Wherein, the high-density dispersible alumina is 50-95 wt.%, the cerium-zirconium solid hydroxide is 0.5-60 wt.%, and the formic acid is 1-10 wt.%. Then milling the reaction mixture to reduce a particle size of the reaction mixture below 5 micron and adding formic acid to the reaction mixture with continued stirring for 45-75 minutes.

The hydroxide of Ce-Zr is prepared by a precipitate reaction of a first reaction solution having a nitrate or a chloride salt of zirconium, a nitrate or a chloride salt of cerium and Millipore water, and a second reaction solution at a reaction temperature of 70°C to 90°C for a period of 40 minutes to 80 minutes in an autoclave by maintaining the pH of the reaction solution at a pH range of 8-10 to get a CeCh-ZrCh precipitate slurry. Then, the CeCh-ZrCh precipitate slurry is filtered and washed with a hot distilled water having temperature of 70°C to 80°C to obtain a precipitate of CeCh-ZrCh. Thereafter, drying the precipitates of CeCh-ZrCh at a drying temperature range of 90°C to 120°C for a period of 11-12 hours.

The first reaction solution consists of at least 0.3-1 moles of a nitrate or a chloride salt of zirconium, and 0.3-1 moles of a nitrate or a chloride salt of cerium. Specifically, the first reaction solution consists of at least one of a nitrate salt of zirconium such as zirconyl oxynitrate, the chloride salt of zirconium such as zirconyl oxychloride, the nitrate salt of cerium such as cerium nitrate hexahydrate, or a combination thereof.

The second reaction solution consists of a sodium hydroxide and distilled water, wherein, the sodium hydroxide is 2-2.5 moles.

The present invention also discloses a process for promoting the CO combustion in a Fluid Catalytic Cracking (FCC) unit, wherein the process includes using a catalyst for promoting CO combustion which acts as a CO combustion promoter additive along with a spent catalyst in the FCC unit. Wherein, the 1 weight percent of CO combustion promoter additive is mixed with 499 weight percent of spent catalyst to yield CO combustion above 95%. OBJECTIVES OF THE PRESENT INVENTION:

It is the primary objective of the present invention to provide a catalyst which acts as CO combustion promoter.

It is further objective of the present invention to provide a catalyst which can promote CO combustion in Fluid Catalytic Cracking (FCC) units under normal air supply condition.

It is further objective of the present invention to provide a catalyst which have higher oxygen storage capacity and thus efficiently convert CO to CO2 under normal air flow conditions.

It is further objective of the present invention to provide a process for preparing a catalyst to promote CO combustion in a Fluid Catalytic Cracking (FCC) unit.

DESCRIPTION OF THE INVENTION:

According to the main embodiment, the present invention provides a catalyst for promoting CO combustion in a Fluid Catalytic Cracking (FCC) unit, a process for preparing the said catalyst, and a process for promoting the CO combustion in a Fluid Catalytic Cracking (FCC) unit by using the said catalyst along with a spent catalyst.

Keeping the need of a catalyst which shows high conversion of CO to CO2, the present invention proposes a catalyst which have improved oxygen storage capacity. Hence, the said catalyst efficiently utilizes oxygen and convert CO to CO2 effectively.

In a specific embodiment, the present invention provides a catalyst for promoting CO combustion in a Fluid Catalytic Cracking (FCC) unit. The catalyst includes an alumina-cerium-zirconium support loaded with active metals. The alumina-cerium-zirconium support is micro spherical in shape having a particle size in a range of 20-300 micron.

The active metals are selected from a platinum group metals (PGMs). Specifically, the platinum group metals (PGMs) include at least one metal from Platinum (Pt), Palladium (Pd), Ruthenium (Ru), or a combination thereof. The alumina-cerium-zirconium support is mainly made up of AI2O3 in 50 - 95 wt.%, ZrCh in 0.5-30 wt.%, and CeCh in 2-60 wt.%. In another embodiment the alumina- cerium-zirconium support is mainly made up of AI2O3 in 50 - 90 wt.%, ZrCh in 0.5-20 wt.%, and CeCh in 2-20 wt.%. Further, the catalyst consists of at least one metal selected from Platinum (Pt) which is in 100-1000 ppm, Palladium (Pd) which is in 100-1500 ppm, and Ruthenium (Ru) which is in 100-2000 ppm, or a combination of these metals.

In an important embodiment, the present invention provides a process for preparing a catalyst to promote CO combustion in a Fluid Catalytic Cracking (FCC) unit. The process includes steps of synthesizing a cerium-zirconium solid hydroxide, wherein the cerium-zirconium solid hydroxide is synthesized by a precipitating reaction of a cerium precursor and a zirconium precursor. Then adding and mixing a high-density dispersible alumina binder solution in the cerium-zirconium solid hydroxide to make alumina-cerium-zirconium slurry. Wherein the high-density dispersible alumina binder solution includes an aluminium chlorohydrate solution, a pseudoboehmite alumina solution or a combination thereof.

Thereafter, a step of spray drying the alumina-cerium-zirconium slurry is completed to produce the alumina-cerium-zirconium support. The step of spray drying the alumina-cerium-zirconium slurry provides a micro spherical alumina-cerium-zirconium support having a particle size in the range of 20-150 micron. Specifically, the step of spray drying of the alumina-cerium-zirconium slurry is completed in a co-current spray drying operation unit having an inlet temperature of 400°C and an outlet temperature of 170°C.

Thereafter, the said micro spherical alumina-cerium-zirconium support undergoes through a calcination step, wherein, the calcination is performed at a temperature range of 580°C to 650°C for a time period of 3 to 5 hours.

Finally, loading of active metals on the said micro spherical alumina-cerium-zirconium support is done, wherein, the active metals are selected from a platinum group metals (PGMs). Specifically, the platinum group metals (PGMs) includes at least one metal from Platinum (Pt), Palladium (Pd), Ruthenium (Ru), or a combination thereof. Specifically, a desired concentration of the active metal solution is added slowly in a mixing vessel containing the said micro spherical alumina-cerium- zirconium support. Further, the temperature of the mixing vessel is maintained at 15°C-25°C to avoid the temperature shooting while adding the metal solution in the mixing vessel. After loading of active metals on the said alumina- cerium-zirconium support drying and calcination step are followed to obtain a final catalyst product used for promoting CO combustion or which act as a CO combustion promoter additive when used along with a spent catalyst.

The said catalyst for promoting CO combustion includes Alumina as AI2O3 in 50 - 95 wt.%, Zirconia as ZrO2 in 0.5-30 wt.%, Ceria as CeO2 in 2-60wt.%, and an active metal selected from one of Platinum as Pt in 100-1000 ppm, Palladium as Pd in 100-1500 ppm, Ruthenium as Ru 100- 2000 ppm, or a combination thereof. In another embodiment, said catalyst for promoting CO combustion include Alumina as AI2O3 in 50 - 90 wt.%, Zirconia as ZrO2 in 0.5-20 wt.%, and Ceria as CeO2 in 2-20 wt.%.

Further, in another important embodiment the alumina-cerium-zirconium slurry is prepared by mixing a high-density dispersible alumina and a hydroxide of Ce-Zr in a demineralized water to produce a reaction mixture. Wherein, the high-density dispersible alumina is 50-90 wt.%, the hydroxide of Ce-Zr is 0.5-60 wt.%, and the formic acid is 1-10 wt.%. Then milling the reaction mixture to reduce a particle size of the reaction mixture below 5 micron and adding formic acid to the reaction mixture with continued stirring for 45-75 minutes.

Further, in another important embodiment the hydroxide of Ce-Zr is prepared by a precipitate reaction of a first reaction solution having a nitrate or a chloride salt of zirconium, a nitrate or a chloride salt of cerium and Millipore water, and a second reaction solution at a reaction temperature of 70°C to 90°C for a period of 40 minutes to 80 minutes in an autoclave by maintaining the pH of the reaction solution at a pH range of 8-10 to get a CeCh-ZrCh precipitate slurry. Then, the CeCh-ZrCh precipitate slurry is filtered and washed with a hot distilled water having temperature 70°C to 80°C to obtain a precipitate of CeCh-ZrCh. Thereafter, drying the precipitates of CeCh-ZrCh at a drying temperature range of 90°C to 120°C for a period of 11-12 hours. The first reaction solution consists of at least 0.3-1 moles of the nitrate or the chloride salt of zirconium, and 0.3-1 moles of the nitrate or a chloride salt of cerium. Specifically, the first reaction solution consists of at least one of the nitrate salt of zirconium such as zirconyl oxynitrate, the chloride salt of zirconium such as zirconyl oxychloride, the nitrate salt of cerium such as cerium nitrate hexahydrate, or a combination thereof. The second reaction solution consists of sodium hydroxide and distilled water, wherein, the sodium hydroxide is 2-2.5 moles per liter of distilled water.

Further, the exemplary preparation method of the said cerium-zirconium solid hydroxide is explained herein below. Further, experiments were conducted to determine the efficacy of the catalyst as provided in the present disclosure with respect to similar catalyst compositions.

Example- 1:

Preparation of CeOz-ZrOz solid solution:

CeCh-ZrCh solid solution with 1: 1 mole ratio was prepared by a precipitation method using zirconyl oxynitrate or zirconyl oxychloride as source of zirconium and cerium nitrate hexahydrate as source cerium. Sodium hydroxide was used as hydrolyzing agent.

Specifically, 1815 g of zirconyl oxychloride, 1260 g of cerium nitrate hexahydrate and 10 L of Millipore water were mixed uniformly in 20 L vessel (and named as solution- 1 or first reaction solution). In another vessel, 950 g of sodium hydroxide and 10 L water were mixed uniformly in 20 L vessel to obtain clear solution (named as solution-2 or second reaction solution). Thereafter, 5 L of DM water was added to 25 L autoclave with continuous stirring at a temperature of 80°C. Further, the solution- 1 and solution-2 were added at constant flow rate simultaneously to the autoclave while maintaining the pH of the solution at 8-9 during addition of solution- 1 and solution-2. Further, the reaction temperature is maintained at 80°C during precipitation reaction. After the completion of addition of solution- 1 and solution-2, the stirring was continued for 1 hour to ensure complete homogeneity and to complete the hydrolysis and a CeOz-ZrCh precipitate slurry is produced. After 1 hour, the said slurry was filtered and washed repeatedly with hot DM water to obtain the CeOz-ZrOz precipitates without sodium ion. The CeOz-ZrOz precipitates was then dried at 100°C for 12 hours. The synthesized material is designated as hydroxide of Ce-Zr (1:1). Similarly, the CeCh-ZrCh solid solution with mole ratio of 0.3: 0.7 was prepared and marked as hydroxide of Ce-Zr (0.3:0.7). 2541 g of zirconyl oxychloride, 757 g of cerium nitrate hexahydrate was taken as zirconium and cerium source.

Similarly, the CeCh-ZrCh solid solution with mole ratio of 0.7: 0.3 were prepared and marked as hydroxide of Ce-Zr (0.7: 0.3). 1089 g of zirconyl oxychloride, 1766 g of cerium nitrate hexahydrate was taken as zirconium and cerium source.

Preparation of microsphere of CeOz-ZrOz-alumina support:

Example -2:

571 grams of hydroxide of Ce-Zr (1:1 mole ratio), and 517 grams of high-density dispersible alumina were added in 1550 grams of DM water to prepare an alumina-cerium- zirconium slurry. The mixture i.e., alumina- cerium-zirconium slurry was transferred to ball mill and milled for 4 hours to reduce the particle size to less than 5 microns. After milling, the said slurry was transferred to a vessel attached with a stirrer. In the said vessel, 30 g for formic acid was added and continued the stirring for 1 hours. Then in the said vessel, 800 grams of Aluminium chlorohydrate solution was added to the slurry and continued the stirring for 1 hour. The final slurry was spray dried at a co-current spray drying operation unit with inlet temperature of 400°C and outlet temperature of 170°C. The spray dried microsphere named as CeCh-ZrCh-alumina support was calcined at 600°C for 4 hours. After calcination, 500 ppm of Platinum (Pt) was impregnated on microspheres of CeO2-ZrO2-alumina support by an incipient wetness impregnation method. The said incipient wetness impregnation method includes adding a metal precursor containing solution to a microsphere shaped catalyst support for impregnation. The volume of the solution added is equal to the pore volume of the catalyst support. After impregnation, the catalyst was dried at 100°C for 8 hours and calcined at 600°C for 2 hours.

Example 3 & 4:

Similar to the above example-2, the hydroxide of Ce-Zr (0.3: 0.7), and the hydroxide of Ce-Zr (0.7: 0.3) were added to the alumina slurry for the preparation of microsphere and impregnated with 500 ppm Platinum (Pt) to form final catalyst additive respectively. Example-5:

533 g of zirconium hydroxide, and 517 g of high-density dispersible alumina were added in 1550 g of DM water to get a slurry mixture of alumina- zirconium. The slurry mixture was then transferred to a ball mill and milled for 4 hours to reduce the particle size less than 5 micron. After milling, the said alumina-cerium-zirconium slurry was transferred to a vessel attached with a stirrer. In the said vessel, 30 gram of formic acid was added and continued the stirring for 1 hour. Thereafter, 800 g of aluminium chlorohydrate solution was added to the said slurry mixture and continued the stirring for 1 hour. The final slurry was spray dried at a co-current spray drying operation unit with inlet temperature of 400°C and outlet temperature of 170°C. The spray drying produces a microsphere ZrCh-alumina support. The spray dried microsphere ZrCh-alumina support was calcined at 600°C for 4 hours. After calcination, 500 ppm of Platinum (Pt) was impregnated on the said microsphere ZrCh-alumina support by an incipient wetness impregnation method to produce a ZrCh-alumina catalyst. After impregnation, the said catalyst was dried at 100°C for 8 hours and calcined at 600°C for 2 hours.

Example-6:

615 g of cerium hydroxide, and 517 g of high-density dispersible alumina were added in 1550 g of DM water to get a slurry mixture of alumina-cerium. The slurry mixture was transferred to a ball mill and milled for 4 hours to reduce the particle size less than 5 microns. After milling, slurry was transferred to a vessel attached with a stirrer. In the said vessel, 30 g for formic acid was added and continued the stirring for 1 hours. Thereafter, 800 g of aluminium chlorohydrate solution was added to the said slurry mixture and continued the stirring for 1 hour. The final slurry was spray dried at a co-current spray drying operation unit with inlet temperature of 400°C and outlet temperature of 170°C. The spray drying produces a microsphere CeCh-alumina support. The spray dried microsphere CeCh-alumina support was calcined at 600°C for 4 hours. After calcination, 500 ppm of Platinum (Pt) was impregnated on the said microsphere CeCh-alumina support by an incipient wetness impregnation method to produce a CeCh-alumina catalyst. After impregnation, the catalyst was dried at 100°C for 8 hours and calcined at 600°C for 2 hours. Example-7:

308 g of cerium hydroxide, 267 g of zirconium hydroxide and 517 g of high-density dispersible alumina were added in 1550 g of DM water to get a slurry mixture. The slurry mixture was transferred to a ball mill and milled for 4 hours to reduce the particle size less than 5 microns. After milling, the said slurry was transferred to a vessel attached with a stirrer. In the said vessel, 30 g for formic acid was added and continued the stirring for 1 hour. Thereafter, 800 g of aluminium chlorohydrate solution was added to the slurry and continued the stirring for 1 hour. The final slurry was spray dried at a co-current spray drying operation unit with inlet temperature of 400°C and outlet temperature of 170°C. The spray drying produces a microsphere CeCh-ZrCh- alumina support. The spray dried microsphere CeCh-ZrCh-alumina support were calcined at 600°C for 4 hours. After calcination, 500 ppm of Platinum (Pt) was impregnated on the said microsphere by an incipient wetness impregnation method. After impregnation, the catalyst was dried at 100°C for 8 h and calcined at 600°C for 2 hours.

Example-8:

1034 g of high-density dispersible alumina were added in 1550 g of DM water to get an alumina slurry. The mixture was transferred to a ball mill and milled for 4 hours to reduce the particle size less than 5 microns. After milling, slurry was transferred to a vessel attached with a stirrer. In the said vessel, 30 g for formic acid was added and continued the stirring for 1 hour. Thereafter, 800 g of aluminium chlorohydrate solution was added to the said slurry and continued the stirring for 1 hour. The final slurry was spray dried at a co-current spray drying operation unit with an inlet temperature of 400°C and an outlet temperature of 170°C. The spray drying produces a microsphere alumina support. The spray dried microsphere alumina support was calcined at 600°C for 4 hours. After calcination, 500 ppm of Platinum (Pt) was impregnated on microsphere by incipient wetness impregnation method to produce an alumina catalyst. After impregnation, the said alumina catalyst was dried at 100°C for 8 hours and calcined at 600°C for 2 hours.

Example-9:

Physio-chemical characterization and performance of various catalysts as prepared hereinabove was determined. The physio-chemical properties such as apparent bulk density (ABD), ASTM D5757 attrition index (Al), chemical analysis, N2 adsorption analysis were carried for these catalysts and presented in below table -1.

Table-1: Physio-chemical characterization of CO combustion promoter additive

In another important embodiment, the present invention also discloses a process for promoting the CO combustion in a Fluid Catalytic Cracking (FCC) unit, wherein the process includes using a catalyst for promoting CO combustion which acts as a CO combustion promoter additive along with a spent catalyst in the FCC unit. Wherein, 1 weight percent of CO combustion promoter additive is mixed with 499 weight percent of spent catalyst. Reaction and results:

Further, each of the catalyst as prepared hereinabove was evaluated with respect to their efficiency as a CO combustion promoter additive. The said evaluation was carried out in a short contact time reactor testing (SCT-RT) unit. Wherein, 0.05 g of CO combustion promoter additive or the said CO combustion promoter catalyst was thoroughly mixed with 24.95 g of spent catalyst. The reaction temperature was kept at 690°C and air flow rate was maintained at 500 SCCM. The flue gas generated from the reaction was analyzed through online IR analyzer. The % of CO conversion was calculated from the ratio of difference between the amount of CO in without catalyst/additive and with the said catalyst/additive. The below table 2 represent the said performance evaluation results of CO combustion promoter catalyst/additive.

Table-2: Performance evaluation results of CO combustion promoter catalyst/additive

From the above experimental data, it is evident that the percentage of CO conversion by the catalyst as produced under example-2 is higher among the other similar catalysts.

Accordingly, it is evident that the ZrO2 stabilized CeO2 alumina microsphere provides improved average pore diameter, improved ABD and attrition properties with 100-2000 ppm active metals selected from at least one of platinum, palladium, Ruthenium or their combination. Further, the CeO2-ZrO2 mixed oxides provides outstanding oxygen storage capacity (OSC) and thermal stability. Further, the synergy between ZrCh and CeCh enhances the CO combustion in FCCU units.