Field of invention

The present invention relates to a fluidized catalytic cracking process for cracking hydrocarbon feed having organo-sulfur compound as an impurity. The present invention also relates to the use of heavy metal poisoned FCC/RFCC spent catalyst for maintaining the activity of the composite circulating catalyst and as a sulfur reducing agent in fluid catalytic cracking process for reduction of sulfur in products of catalytic cracking. Background of the invention Fluid catalytic cracking process is a well known since 1942. The history and the evolution of FCC process at various generations are detailed in the book "Fluid Catalytic Cracking Handbook by Reza Sadeghbeigi, Gulf publishing company", ''Fluid catalytic cracking by Wilson, and various other literatures.

Generally, cracking is defined as breaking down, hydrocarbons of higher molecular weight into lower molecular weight hydrocarbons. It can be carried out thermally or catalytically. In fluid catalytic cracking process, the catalyst is a fluidizable fine particle in the size range of 5-150 microns. The steps involved in the conventional FCC process are described below: a) Hydrocarbon feedstock is preheated to a temperature range of 150-400 ⁰ C to enhance the atomization/ vaporization of feed. b) The preheated feed is mixed with the steam at particular ratio and passed through a nozzle to disperse the feed into fine droplets inside an up-fiow riser. c) The dispersed feed gets contacted with the hot regenerated catalyst at the bottom of the riser, where the reactions are initiated to take place along the remaining length of the riser. d) The mixture of catalyst and products of catalytic cracking is separated by a termination device; further the entrained catalyst is separated from the product vapor by cyclone separators and transferred to the catalyst bed in the reactor stripper. e) The entrapped hydrocarbon components are removed from the separated catalyst by stripping using steam. f) The coke laden fluidizable catalyst, often referred as spent catalyst, is transferred to a regenerator through spent catalyst standpipe and spent catalyst slide valve. g) The deposited coke in the catalyst is burnt in the regenerator by means of hot compressed air and the hot regenerated catalyst is transferred to riser through regenerated catalyst standpipe and regenerated catalyst slide valve for the next cycle of operation. In this manner, FCC process is termed as a cyclic process where the reaction and regeneration takes place continuously in a riser - reactor and regenerator respectively. A particular amount of fresh catalyst is added to the circulating inventory in order to maintain the activity of the catalyst at same level while keeping the inventory at constant level. The regeneration of catalyst mentioned above only removes the coke that is deposited on the catalyst not the heavy metal poisons. The heavy metals present in the feedstock finally ends up in the coke which in turn deposits on the catalyst during reaction step. Each metal has its own effect on the FCC unit performance. Vanadium particularly deactivates the catalyst permanently by destructing the zeolite structure. Nickel promotes the dehydrogenation reactions facilitating the production of hydrogen and coke. Iron reduces the catalyst bottom cracking characteristics. It also increases SO _x emission and coke on regenerated catalyst (CRC) in partial burn units. As the cycle of FCC operation continues, these metals continuously deposits on the surface of catalyst and enhances its detrimental effects. Due to incremental deactivation by deposition of heavy metals on catalyst, addition of proportionately higher amount of catalyst is needed in order to maintain the activity of the circulating catalyst inventory. In order to keep the catalyst inventory at the desired level, a part of the catalyst is required to be withdrawn through which a portion of the heavy metals is disposed off from the circulating inventory.

In the present scenario, processing of heavy crudes in refinery becomes mandatory to increase the profit margin. As a result of this, there is a pressure to maximize the intake of vacuum residue or atmospheric residue in feed to FCC/RFCC unit. However, increase in concentration of heavy ends in FCC unit feed will have the deleterious effect as it contains higher concentration of heavy metals like nickel, vanadium, iron, etc. The effect of vanadium on zeolite destruction is well known from various literatures (See R.E. Roncolatto and Y. L. Lam, Effect of vanadium on the deactivation of FCC catalysts, Braz.Chem.Engg, VoI 15, No.2, June 1998, O'Connor et al, Deactivation and testing of hydrocarbon processing catalysts, ACS symposium series, 571(1995), etc.). The destruction of zeolite structure due to vanadium, increased dehydrogenation activity of nickel and iron poisoning make the catalyst less active affecting the unit performance owing to loss in conversion and product selectivity.

Deactivation of catalyst by coke is a temporary phenomenon. The activity of catalyst is restored by burning the coke on catalyst with the aid of air or any oxygen containing gas in regenerator. However, deactivation of catalyst by heavy metals is considered to be permanent processes in which the activity of catalyst cannot be restored within the reactor-regenerator section. The use of additives to trap the heavy metals within the reactor regenerator section has limited success, as it cannot rejuvenate the activity of the catalyst completely (See Kuei-Jung Chao et al, Vanadium Passivation of cracking catalysts by using secondary ion mass spectrometry, Appl. Cat A: 121(1995), 217-229, Guintar Luciano Baugis et al, The Luminescent Behaviour of the Steamed EUY Zeolite incorporated with Vanadium and rare earth passivators, Microporous and mesoporous materials 49 (2001) 179 - 187).

The only way to maintain particular activity of catalyst in circulating inventory is to remove a portion of equilibrium catalyst from the inventory and add the equivalent amount of fresh catalyst. Depending upon the activity to be maintained and the concentration of metals in feed, about 1-10 MT/day of heavy metal poisoned catalyst is removed and simultaneously, equivalent amount of fresh catalyst is added in the circulating inventory in order to maintain the regenerator inventory level and also unit catalyst activity at constant values. Conventionally, depending upon the hazardous nature, the spent catalyst removed from the circulating inventory of the unit is disposed for landfill operation and / or used as a raw material in the cement industries.

Various attempts made by researchers to rejuvenate the activity of the catalyst have limited success as the method of rejuvenation leads to energy intensive cum expensive route. For example, a detailed description of removal of metal poisons like vanadium, nickel and iron by Sang Ku Park et al, Ind. Eng. Chem. Res., 42 (2003), 736-742 on modified Demet III and Demet IV series of process claims the selective removal of heavy metal poisons by series of sulfidation, air oxidation and washing steps. US Patent No. 4,954,244 of Fu et al, claims the process of reactivation of spent heavy metal poisoned catalyst by treating the catalyst with ammonium, fluorine compound and a passivating agent preferably magnesium, calcium, boron, aluminium, phosphorous or antimony. Doctor Richard D in US Patent No. 5,250,482 proposes the benefication of FCC catalyst to different categories based on the nickel concentration by induced magnetic field and recycling the low concentration nickel contaminated catalyst to fluidized bed.

There are only limited numbers of proposals for direct use of heavy metal poisoned FCC catalyst. In US Patent No. 5,324,417, it is claimed that the hot spent catalyst is used for demetalization or deemulsification of heavy slop oils/refinery sludge etc. In US Patent No. 5,928,980, it is claimed that the metal poisoned spent FCC catalyst can be used along with new catalytic metal or metal salt to provide an attrition resistant catalyst or sorbent for different catalytic or absorption process. Although there are several disadvantages of vanadium and nickel in FCC/RFCC unit performance as discussed in various open literatures, Mystrad et al, discloses the advantage of vanadium metal in FCCU performance (see Effect of Nickel and Vanadium on Sulfur Reduction of FCC Naphtha, Applied catalysis A: General 192 (2000), 299-305). In this, it is given that fresh FCC catalyst with impregnated vanadium and nickel reduces the sulfur content in naphtha. The reference does not discuss about the effect of loss in conversion due to zeolite destruction by metal impregnation.

Due to strict environmental legislations on sulfur specifications, several attempts have been made by researchers and refiners to reduce the sulfur content in gasoline. As the major contribution of about 90% of sulfur in gasoline pool is from FCC gasoline, various attempts made to reduce FCC gasoline sulfur for the past 10 years.

One such attempt leads to the gasoline sulfur reduction additive technology in which the additive can be used along with FCC catalyst for the insitu reduction of gasoline sulfur (See Francisco Hernandez-Beltran et al, Sulfur Reduction in Cracked Naphtha by a commercial additive: Effect of feed and catalyst properties Appl. Cat. B: Environmental 34 (2001) 137-148", "Sulfur Reduction in FCC Gasoline with a Commercial Additive: A Microactivity Study, J. Earth. Res. Utilization, 21, Iss 7-8).

Several patents disclosed on additive for reduction of gasoline sulfur are US 5,376,608, US 5,525,210, US 6,635,168, US 6,635,169, US 6,846,403, US 6,852,214, US 6,923,903, US 6,974,787, and US 7,033,487. The claims in these differ primarily with respect to the composition and the type of metal used in the additive to perform the GSR function. In US2003/0034275, it is proposed that the impregnated vanadium with different concentration on alumina support, which leads to a freshly prepared pure vanadium, based GSR additive.

In US2004/0099573, it is claimed that the gasoline sulfur reduction in fluid catalytic cracking process can be accomplished by the addition of vanadium as liquid along with the feed. The vanadium compound was selected from the group comprising vanadium oxalate, vanadium sulfate, vanadium naphthanate, vanadium halides and mixtures thereof.

Along with the other impurities, the hydrocarbon feedstock contains organosulfur compounds as one of the impurities. Normally in FCC/RFCC processes, these organosulfur compounds, which are non-thiophenic get converted into H ₂ S and removed along with product vapour. The remaining sulfur compounds along with traces of non- thiophenic sulfur compounds, which actually formed during the cracking reaction, are distributed in the products of cracking. The distribution of sulfur compounds in the liquid products depends upon many parameters. Although there are several technologies available to reduce the sulfur content in FCC/RFCC gasoline, insitu reduction by means of additive technology found to be advantageous and hence preferable.

Although there are several patents available for FCC spent catalyst rejuvenation and gasoline sulfur reduction additive, none of them are related to reuse or direct use of external heavy metal poisoned spent or waste FCC/RFCC catalyst with high metal concentration to maintain the activity of FCC/RFCC circulating catalyst with low heavy metal concentration and as a gasoline sulfur reducing agent in FCC/RFCC circulating catalyst with low heavy metal concentration. By this the multiple advantage of disposal of heavy metal poisoned FCC/RFCC catalyst, maintaining the activity by overcoming the vanadium deactivation and gasoline sulfur reduction can be accomplished at a single stroke. Summary

The present invention relates to a fluidized catalytic cracking process for cracking hydrocarbon feed having organo-sulfur compound as an impurity. The process involves adding a heavy metal poisoned spent catalyst to an equilibrium catalyst in an amount to maintain the activity of the circulating catalyst and obtaining a fluidized catalytic cracked product. The present invention also relates to a fluidized catalytic cracking process for cracking hydrocarbon feed having organo-sulfur compound as an impurity, said process comprising: adding a heavy metal poisoned spent catalyst to an equilibrium catalyst to obtain a composite circulating catalyst, wherein the heavy metal poisoned spent catalyst is added in an amount to maintain the activity of the circulating catalyst, catalytically cracking a hydrocarbon feed in a reactor operating at catalytic cracking conditions with the circulating catalyst in a circulating inventory to obtain a reactor effluent, separating the reactor effluent into a vapour rich phase containing fluidized catalytic cracked product and a solid rich phase containing coke laden catalyst, and removing the vapour rich phase and fractionating the vapour rich phase to obtain fluidized catalytic cracked product.

The present invention further relates fluidized catalytic cracked product obtained by the process of the present invention.

These and other features, aspects, and advantages of the present subject matter will become better understood with reference to the following description and appended claims. This summary is provided to introduce a selection of concepts in a simplified form. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. Detailed Description of Invention The present invention provides a fluidized catalytic cracking process for cracking hydrocarbon feed having organo-sulfur compound as an impurity, said process comprising: adding a heavy metal poisoned spent catalyst to an equilibrium catalyst to obtain a composite circulating catalyst, wherein the metal poisoned spent catalyst is added in an amount to maintain the activity of the circulating catalyst; and obtaining a fluidized catalytic cracked product.

An embodiment of the present invention is the fluidized catalytic cracking process, wherein the hydrocarbon feed is selected from a group consisting of straight run hydrocarbon fractions and cracked hydrocarbon fractions or mixture thereof having carbon number 5 to 120 comprising at least one organo-sulfur compound. Yet another embodiment of the present invention is the fluidized catalytic cracking process, wherein the heavy metal poisoned spent catalyst comprises one or more metals selected from Pt, V, Ni, Fe, Co and Mo. Another embodiment of the present invention is the fluidized catalytic cracking process, wherein the heavy metal poisoned spent catalyst has metal concentration not less than 500 ppm.

Yet another embodiment of the present invention is the fluidized catalytic cracking process, wherein the heavy metal poisoned spent catalyst has metal concentration in the range of 500 ppm to 35,000 ppm.

Still another embodiment of the present invention is the fluidized catalytic cracking process, wherein the activity of the circulating catalyst is maintained by maintaining the vanadium concentration in the range of 550 ppm to 20,000 ppm. Further embodiment of the present invention is the fluidized catalytic cracking process, wherein the activity of the composite circulating catalyst is maintained by maintaining the increase in the vanadium concentration in the range of 550 ppm to 3000 ppm.

Yet another embodiment of the present invention is the fluidized catalytic cracking process, wherein the heavy metal concentration in the equilibrium catalyst is less than 20,000 ppm.

Further embodiment of the present invention is the fluidized catalytic cracking process, wherein the metal concentration in the equilibrium catalyst is in the range of 0 ppm to 20,000 ppm. The present invention also provides a fluidized catalytic cracking process for cracking hydrocarbon feed having organo-sulfur compound as an impurity, said process comprising: adding a heavy metal poisoned spent catalyst to an equilibrium catalyst to obtain a composite circulating catalyst, wherein the heavy metal poisoned spent catalyst is added in an amount to maintain the activity of the composite circulating catalyst, catalytically cracking a hydrocarbon feed in a reactor operating at catalytic cracking conditions with the composite circulating catalyst in a circulating inventory to obtain a reactor effluent, separating the reactor effluent into a vapour rich phase containing fluidized catalytic cracked product and a solid rich phase containing coke laden catalyst, and removing the vapour rich phase and fractionating the vapour rich phase to obtain fluidized catalytic cracked product.

An embodiment of the present invention is the fluidized catalytic cracking process, wherein the hydrocarbon feed is selected from a group consisting of straight run hydrocarbon fractions and cracked hydrocarbon fractions or mixture thereof having carbon number 5 to 120 comprising at least one organo-sulfur compound.

Another embodiment of the present invention is the fluidized catalytic cracking process, wherein the heavy metal poisoned spent catalyst comprises one or more metals selected from Pt, V, Ni, Fe, Co, Mo etc,.

Yet another embodiment of the present invention is the fluidized catalytic cracking process, wherein the heavy metal poisoned spent catalyst has heavy metal concentration not less than 500 ppm.

Another embodiment of the present invention is the fluidized catalytic cracking process, wherein the heavy metal poisoned spent catalyst has the metal concentration in the range of 500 ppm to 35,000ppm.

Still another embodiment of the present invention is the fluidized catalytic cracking process, wherein the activity of the composite circulating catalyst is maintained by maintaining the vanadium concentration in the range of 550 ppm to 20,000 ppm. Further embodiment of the present invention is the fluidized catalytic cracking process, wherein the activity of the composite circulating catalyst is maintained by maintaining the increase in the vanadium concentration in the range of 550 ppm to 3000 ppm.

Another embodiment of the present invention is the fluidized catalytic cracking process, wherein the heavy metal concentration in the equilibrium catalyst is less than 20,000 ppm.

The present invention provides fluidized catalytic cracked product obtained by the process of the present invention.

The present invention provides fluidized catalytic cracked product, wherein sulfur content is reduced by more than 20 % (wt/wt) when the cut point of the fluidized catalytic cracked product is C5-250°C.

In an embodiment of the present invention the fluidized catalytic cracked products having carbon number in the range of C5 to C15 the sulfur content is reduced by more than 20 % (wt/wt). In another embodiment of the present invention the fluidized catalytic cracked products having carbon number in the range of C5 to Cl 5 the sulfur content is reduced by more than 20 % (wt/wt) and upto 50% (wt/wt). An embodiment of the present invention the fluidized catalytic cracked products having cut point in the range of C5-250°C having the Research Octane Number (RON) increases by more than 1 unit.

The "Research octane number (RON)" is a parameter used to estimate the antiknocking characteristics of a fuel at low engine speeds (@600 rpm and 12O ⁰ F (49 ⁰ C) air temperature).

An embodiment of the present invention the added heavy metal poisoned spent catalyst improves the propylene yield by more than 0.25 wt% depending on the feed characteristics, host catalyst property and the process conditions. The present invention provides a fluidized catalytic cracking process for cracking hydrocarbon feed having organo-sulfur compound as an impurity, said process comprising, adding a requisite amount of heavy metal poisoned spent catalyst to the circulating catalyst inventory in such concentration to maintain the activity of the circulating catalyst even with the increase in heavy metal concentration and obtaining fluidized catalytic cracked products.

The feedstock used in the fluidized catalytic cracking process of present invention is any hydrocarbon feedstock, which contains atleast one organosulfur compounds. Some of the examples of the conventional FCC feedstocks are vacuum gas oil, hydrocracker bottoms, heavy vacuum gas oil, vacuum slop, cycle oils, slurry oils, atmospheric residue, vacuum residue, light straight run naphtha, heavy naphtha, coker gas oil, coker naphtha, etc. and mixtures thereof. The feed explained above may also contain the impurities like basic nitrogen, vanadium, nickel, iron, sulfur, etc. The impurities concentration may vary depending upon the source of crude.

Heavy metal poisoned spent FCC/RFCC catalyst and the actual host catalyst (fresh as well as equilibrium catalyst) are mixed in different proportions and tested in the laboratory. The effect of present invention is to remove the sulfur from cracked products, primarily gasoline by increasing the metal concentration of the circulating inventory without increasing the metal concentration on the actual host catalyst particles.

In an embodiment of the present invention the amount of the fresh catalyst to be added to the circulating catalyst is reduced by the addition of an equivalent amount of heavy metal poisoned spent catalyst.

Still another embodiment of the present invention is to provide a fluidized catalytic cracking process wherein the metal concentration in the circulatory catalyst inventory without adding a requisite amount of heavy metal poisoned spent catalyst is less than the metal concentration of the metal poisoned spent catalyst.

The continuous circulating catalyst inventory in the FCC/RFCC unit is referred as equilibrium catalyst (E-cat). It is to be noted that the withdrawn catalyst from the circulating catalyst inventory of the unit is referred as spent catalyst. The spent catalyst referred here is completely different from that of spent catalyst mentioned earlier, i.e., the coke laden fluidizable catalyst, which is transferred to regenerator through spent catalyst standpipe and spent catalyst slide valve. The preferred spent catalyst for the present invention is the heavy metal poisoned spent catalyst normally withdrawn from the unit inventory and disposed thereof.

In an embodiment of the present invention, an improved FCC/RFCC process where the spent heavy metal poisoned FCC/RFCC catalyst with higher concentration of heavy metals particularly vanadium and nickel is added separately or along with the fresh catalyst into the FCC/RFCC unit catalyst inventory, which has lower metal concentration. The addition provides the increase in heavy metal concentration in the composite circulating catalyst without increasing the host heavy metal concentration, which in turn reduces the sulfur content of the cracked products and also enhances the conversion and selectivity of the valuable products. The heavy metal poisoned FCC/RFCC catalyst can also be blended with any of the commercial FCC/RFCC catalyst cum additive system with desired concentration and can be added in FCCU/RFCCU. Examples of the said commercial additives are ZSM-5, SOx, NOx, Bottom cracking additive, Gasoline sulfur reduction additive, etc. The base catalyst and heavy metal poisoned FCC/RFCC catalyst used in the process is obtained from different refineries and also simulated in laboratories.

Yet another embodiment of the present invention is that there is an increase in C5- 220 ^υ C conversion with increased LPG and light olefins yield. It may be due to the effect of heavy metal poisoned catalyst, which has the ability to crack the feed components, which is not possible using commercial additive aiming towards gasoline sulfur reduction or incorporation of vanadium as liquid along with the feed. It is important to note here that the increased heavy metal concentration in the FCCU catalyst inventory does not lead to the host catalyst deactivation. This can be further explained in the following examples. The term activity means ASTM 3907 MAT activity

The term "conversion" means the sum of yields of gas products, liquid products with final true boiling point up to 22O ⁰ C and coke. An embodiment of the present invention is that the added external spent heavy metal poisoned FCC/RFCC catalyst reduces the sulfur content in the cracked products, primarily gasoline.

Since, another embodiment of the present invention is the reduction in sulfur content up to 50 wt% in the cracked products, primarily gasoline.

Another embodiment of the present invention is utilization of spent heavy metal poisoned FCC/RFCC catalyst, which is to be disposed off.

Yet another embodiment of the present invention is the addition of foreign spent heavy metal poisoned FCC/RFCC catalyst will not inhibit the host equilibrium catalyst in the circulating catalyst inventory of FCCU/RFCCU process.

The addition methodology of spent heavy metal poisoned FCC/RFCC catalyst favors the above-mentioned advantages.

Further embodiment of the present invention relates to addition of the spent catalyst to the host FCC unit circulating catalyst inventory, which can be performed independently through a separate line or by mixing with fresh host catalyst or by mixing with specific additives like ZSM-5, BCA, SOx and NOx additives, etc. Addition in all these cases can be in either intermittent or continuous.

Yet another embodiment of the present invention is that the reduction of metal concentration on spent heavy metal poisoned FCC/RFCC spent catalyst due to its addition to FCCU/RFCC unit inventory having low metal concentration, which makes the mixture catalyst less hazardous and enables its acceptance as raw materials in cement industry.

In an embodiment of the present invention, the addition of heavy metal poisoned FCC/RFCC catalyst in to the equilibrium catalyst inventory is unit specific. The term unit specific means the quantity of the addition depends upon various constraints/variables like system metal concentration, wet gas compressor capacity, unit-operating conditions, amount of sulfur to be removed, feed sulfur, coke burning capacity of the regenerator, etc. The spent catalyst can be mixed with host equilibrium catalyst by separate addition or by mixing with fresh catalyst or in combination with different additive system as stated earlier. EXAMPLES

The examples provided below are for illustration of the present invention and should not be construed to limit the scope of present disclosure. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are intended to provide further explanation of the claimed subject matter.

Catalyst testing and analysis of products

The fluidized catalytic cracking (FCC) process in accordance to the present invention was tested in a fixed fluidized bed catalyst ACE unit. The catalyst in the reactor is fluidized with a stream of nitrogen of 1 OOcc/min flow rate. The catalyst to oil ratio was varied by changing the amount of catalyst added. The feed rate and time on stream were kept constant. After reaction, the catalyst was stripped by nitrogen. The quantity of gaseous product was measured by water displacement method. Coke on catalyst was determined by in-situ regeneration with fluidized air.

The gaseous product obtained from ACE unit was analyzed by an online gas chromatographic technique. The liquid product was analyzed by using Simdist analyzer. The products in the process of the present invention are Dry gas (DG comprising Hydrogen disulfide, hydrogen and Cl & C2 hydrocarbons), Liquefied petroleum gas (LPG comprising C3 & C4 hydrocarbons), Gasoline (C5 tol 50°C), HCN (Heavy Cracked Naphtha, 150-220 ⁰ C), Light Cycle Oil (LCO: 220-370 ⁰ C) and Clarified oil (CLO: 370°C+). Carbon was analyzed by online Infra red analyzer.

The feed used in the following experiments was mixture of gas oil and once through Hydrocracker bottom (OHCUB) and it is designated as fresh feed. Two different feeds pertaining to two FCC units (Feed-A & Feed-B) were used, the properties of which are summarized in the Table- 1

Table-I : Characteristics of feed

Equilibrium catalysts (E-cat) and heavy metal poisoned spent catalysts from various commercial FCC units and laboratory simulated equilibrium catalyst and spent catalysts were taken for the study. In addition, one ZSM-5 based additive was also included. Physico-chemical properties of different catalysts used in the experiments are shown in the Table-2.

Table-2: Physico-chemical characteristics of catalysts

Example-1 Effect of external metal poisoned spent catalyst on FCC unit performance

External heavy metal poisoned spent catalyst from FCC unit - Catalyst-C was directly used to test its effect on FCC unit-A performance. The catalyst used in this experiment comprises 90 wt% Catalyst-A, the E-Cat from FCC unit-A and 10 wt% of Catalyst-C which is a heavy metal poisoned spent catalyst from FCC unit-C. The results of the experiment in fluidized based ACE unit using Feed-A are shown in Table-3.

It is interesting to note here that the conversion and the yields of both LPG & propylene yield increased with use of 10 wt% external heavy metal poisoned spent catalyst. The percentage gasoline sulfur reduction was found to be 27.62 wt%.

Additional set of experiments were conducted to re-examine the effect of external heavy metal poisoned spent catalyst on performance of another FCC unit-B using the corresponding E-Cat and the feed. Accordingly, the catalyst used in this experiment comprises 90 wt% Catalyst-B and 10 wt% of Catalyst-C. The feed for this experiment was changed corresponding to the unit and it is designated as Feed B. The results of the experiment in fluidized based ACE Micro-reactor unit are shown in Table-3.

From the data it is evident that use of external heavy metal poisoned spent catalyst surely reduces the sulfur in gasoline product. Further, the conversion, yields of LPG and propylene are in the increasing trend while using the 10 wt% of external heavy metal poisoned spent catalyst. The propylene selectivity improves with incorporation of 10 wt% Catalyst-C in the circulating inventory of Catalyst- A and Catalyst-B.

This shows that the performance of heavy metal poisoned catalyst with respect to enhanced conversion and sulfur reduction characteristics is independent of characteristics of host base catalyst.

Table-3: Experimental results on FCCU Performance

Example -2

Eixternal heavy metal poisoned spent catalyst from a FCC unit was directly used to test its effect on FCC unit performance. The catalyst used in this experiment comprises a mixture of 60 wt%, equilibrium catalyst having nickel and vanadium concentration of 3500 and 7000 ppm respectively and 40 wt% of spent heavy metal poisoned catalyst having nickel and vanadium concentration of 3400 and 9000 ppm respectively. The results of the experiment in fluidized based ACE unit using Feed-A are shown in Table-4.

It is evident from the data that the composite circulating catalyst obtained after adding the heavy metal poisoned spent catalyst to the equilibrium catalyst show 75.08 % of conversion. It is also evident that even after increase in vanadium concentration the activity of the catalyst is not got effected. The % yield of LPG is in the increasing trend.

TABLE 4

Example-3

External heavy metal poisoned spent catalyst from a FCC unit was directly used to test its effect on FCC unit performance. The catalyst used in this experiment comprises a mixture of 70 wt% equilibrium catalyst (E-Cat) having nickel and vanadium concentration of 3000 and 12000 ppm respectively and 30 wt% of heavy metal poisoned spent catalyst having nickel and vanadium concentration of 3000 and 20000 ppm respectively . The results of the experiment in fluidized based ACE unit using Feed-A are shown in Table-5.

It is evident from the data that the circulating catalyst obtained after adding the spent catalyst to the equilibrium catalyst show 63.05 % of conversion. It is also evident that even after increase in vanadium concentration the activity of the catalyst is not got effected. The % yield of LPG is in the increasing trend.

TABLE 5

Example-4

Vanadium migration from external heavy metal poisoned spent catalyst to host equilibrium catalyst

The purpose of this example is to verify whether the vanadium from the external heavy metal poisoned spent catalyst being directly included in the equilibrium catalyst inventory is migrating to the host FCC/RFCC equilibrium catalyst and thereby causing incremental destruction of zeolite leading to catalyst deactivation.

Catalyst-A was subjected to calcination followed by hydrothermal deactivation at 810 ⁰ C for 5 hours in presence of saturated steam under fluidized conditions.

In a similar way, a mixture of Catalyst-A and Catalyst-C in the ratio of 90: 10 (wt/wt) was subjected to calcination followed by hydrothermal deactivation at 81O ⁰ C for 5 hours in presence of saturated steam under fluidized conditions.

Further, Catalyst-C was calcined and hydro-thermally deactivated under same conditions and a mixture was prepared comprising 90 wt% of hydro-thermally deactivated Catalyst-A and 10 wt% of hydro-thermally deactivated Catalyst-C. It is to be noted that in this case, the hydrothermal deactivation using steam was carried out separately. The performance of the above catalyst / catalyst mixture was tested using Feed-A at specified operating conditions and the results are shown in Table-6. TabIe-6

Expectedly, conversion has decreased by 35.48 wt% with Catalyst-A after additional hydrothermal deactivation in the laboratory. However, it is interesting to note that when both catalyst-A & C are being hydrothermally deactivated together, the conversion drop is 28.5 wt%. If we compare the performance of the catalyst mixture comprising 90 wt% Catalyst-A and 10 wt% Catalyst-C before and after the said hydrothermal deactivation in the laboratory, there is a conversion drop of 29.07 wt% owing to additional deactivation, which is lower than the conversion drop realized with only catalyst-A. This establishes beyond doubt that the vanadium in the external heavy metal poisoned spent catalyst is not mobile and thereby, does not cause any additional deactivation to the host Catalyst-A. In fact, the conversion drop is the least in the case of combined deactivation of 90 wt% Catalyst-A and 10 wt% Catalyst-C. Further, both LPG and propylene selectivity are also higher in the case of the combined deactivation of 90 wt% Catalyst-A and 10 wt% Catalyst-C. Example-5 Catalyst deactivation by feed metal

As can be seen from the example 4, it is clear that the heavy metal poisoned catalyst will not affect or deactivate the host base catalyst. Further in order to confirm that vanadium will deactivate the catalyst provided the source of vanadium is from feed or from other source, fresh catalyst A was doped with vanadium and nickel to the level of 1 OOOppm and 2500 ppm respectively, which is relative to the concentration of vanadium and nickel when 10 wt% of external heavy metal poisoned catalyst-C is mixed with Catalyst-A. The metal doped catalyst was steam deactivated followed by performance evaluation study. The results are shown in Table 7. It is observed that at 1000 ppm vanadium concentration conversion decreases by 2.62 wt%. Dry gas and CLO increases significantly by 0.55 & 3.24 wt% respectively whereas LPG, gasoline, and TCO yield decreases by 0.98, 1.21 , &1.25 wt% respectively. It is clear that the conversion loss and CLO increase is due to the increase in vanadium concentration in the catalyst from feed deposition only and not by the addition of heavy metal poisoned catalyst.

TABLE-7

Example-6

Effect of laboratory deactivated heavy metal poisoned spent catalyst on sulfur reduction in FCC products In order to eliminate the interference or synergy, if any, contributed by any other catalyst / additive in the commercial unit Catalyst-C, experiment was conducted with simulated synthetic heavy metal poisoned FCC catalyst using the fresh catalyst corresponding to Catalyst-C. This is referred to as 'Simulated Catalyst-C.

Fresh FCC catalyst corresponding to Catalyst-C in the commercial unit was doped with the vanadium and nickel actuates. The amount of nickel and vanadium actuates was in accordance with the metal concentration on actual Catalyst-C. Therefore, the said fresh catalyst was doped with 8400 ppm of Vanadium and 2500 ppm of nickel. The metal concentration was measured using XRF technique. The metal doped catalyst was subjected to one cycle of hydrogen reduction and subsequently, it was steam deactivated to simulate the characteristics of actual spent catalyst.

About 10 wt% of 'Simulated Catalyst-C thus obtained in the laboratory was mixed with 90 wt% of Catalyst-B. The performance of the above catalyst mixture was tested using Feed-B at specified operating conditions in fluidized based ACE Micro- reactor unit and the results are provided in Table-8 It is observed that the LPG yield increases by +1.82 wt% and the percentage gasoline sulfur reduction was found to be 30.6 wt%. This study will clearly establishes that the direct use of external heavy metal poisoned catalyst reduces the sulfur in gasoline product and also it is evident that the effect is not due to synergy or contribution by any other catalyst/additive which might present in the commercial spent catalyst. TabIe-8

Example-7

Effect of external heavy metal poisoned spent catalyst on FCC unit performance using laboratory deactivated host catalyst

In order to eliminate the interference or synergy, if any, contributed by any other catalyst / additive in the commercial unit Catalyst-A, experiment was conducted with simulated synthetic deactivated FCC catalyst using the fresh catalyst corresponding to Catalyst-A.

Fresh FCC catalyst corresponding to Catalyst-A in the commercial unit was steam deactivated at 81O ⁰ C for 5 hrs using saturated steam in a fluidized bed tubular reactor to simulate the characteristics of actual Catalyst-A. This is referred to as 'Simulated Catalyst- A'. Experiments were conducted by using a catalyst mixture comprising 90 wt% of 'Simulated Catalyst-A' thus obtained in the laboratory and 10 wt% of Catalyst-C using Feed-A and the results are compared with those obtained with Catalyst-A at same operating conditions in Table-9. The percentage reduction of gasoline sulfur when compared to the base catalyst was found to be 29.4 wt%. In this case also, yields of LPG and propylene increase with incorporation of external heavy metal poisoned spent catalyst. Similarly, it is clear that there is no synergy or contribution by any other additive in the host equilibrium catalyst.

Table-9

Example-8

Behavior of heavy metal poisoned spent catalyst in presence of ZSM-5 additive In this study, a commercial ZSM-5 additive was included in order to explore its impact on the capability of maintaining the activity of composite circulating catalyst and sulfur reducing function of external heavy metal poisoned FCC spent catalyst. The additive was deactivated hydro thermal Iy at 81O ⁰ C for 5 hours using saturated steam in a fluidized bed tubular reactor prior to the use in the experiments. The base catalyst was Catalyst-B and the feed used was Feed-B. The experimental data as generated above at specified operating conditions in fluidized based ACE Micro-reactor unit are summarized in Table- 10.

With inclusion of 10 wt% of Catalyst-C in the mixture of 85 wt% Catalyst-B & 5 wt% ZSM-5 additive, the conversion and LPG yield is in the increasing trend and the percentage gasoline sulfur reduction was found to be 28.37 wt%. It shows that the heavy metal poisoned spent catalyst can perform its function along with any additive system.

Further, Catalyst-C was replaced by Catalyst-D obtained from other source in the above experiment, the result of which is included in the same Table-8. The result again follows the same trend as obtained with that of catalyst-C. This again clearly indicates that the FCC performance effect of addition of heavy metal poisoned spent catalyst does not depend upon the spent catalyst source and type. The heavy metal present in the spent catalyst is responsible for sulfur reduction. However, the performance in regard to the yield pattern may vary depending upon the type of spent catalyst. Table-10

ExampIe-9

Efficacy of external heavy metal poisoned spent catalyst in circulating fluidized bed pilot plant This example demonstrates the application of external heavy metal poisoned spent catalyst in maintaining the activity of composite circulating catalyst and reducing sulfur in FCC products while employing a circulating fluidized bed pilot plant. Feed-A, Catalyst-A and Catalyst-C considered in the ACE micro- reactor studies were taken for the pilot plant study. Pilot plant resembles the commercial scale FCC/RFCC unit and it can handle 160 liters feed per day.

The performance with 100% host catalyst-A is considered as base. In order to evaluate the performance of heavy metal poisoned catalyst with respect to gasoline sulfur reduction, yield pattern and vanadium migration cum deactivation effect, 10 wt% of total circulating inventory was replaced by Catalyst-C subsequently. Feed-A is processed continuously with the composite circulating catalyst inventory for about 170 hrs. The yield pattern obtained during these run are compared with base in Table- 1 1. The liquid samples collected from both the runs were fractionated to separate out the gasoline. The results of analysis of gasoline for both the runs are shown in Table-12. This example clearly demonstrates that even with the continuous operation for about 170 hrs that there is no deterioration in conversion, yield pattern etc, further it is seen that the conversion is enhanced by 6.86 wt% with significant increase in LPG yield and hence, it confirms that there is no vanadium migration or deactivation from heavy metal poisoned spent catalyst to base host catalyst. It is to be noted from the quality results that gasoline sulfur reduces by 42% with simultaneous increase in RON by 1 unit in case of processing feed with mixture of heavy metal poisoned spent Catalyst-C along with the host base catalyst, Catalyst-A.

Table-11

Table-12: Properties of gasoline

Abbreviations

FCC - Fluid Catalytic Cracking

RFCC - Resid Fluid Catalytic Cracking GSRA - Gasoline Sulfur Reduction Additive

E-Cat - Equilibrium Catalyst

BCA - Bottom Cracking Additive

MAI - Micro Activity Test

AS l M - American Society for Testing Machine C TO - Catalyst To Oil ratio

ACE - Advanced Cracking Evaluation

UCS - Unit Crystalline Size

APS - Average Particle Size

ABD - Apparent Bulk Density OHCUB - Once through hydrocracker bottom

IBP - Initial Boiling Point

FBP - Final Boiling Point

LPG - Liquified Petroleum Gas

I IN - Heavy Naphtha LCO - Light Cycle Oil

HCO- Heavy Cycle Oil

CLO - Clarified Oil

RON - Research Octane Number

Although the subject matter has been described in considerable detail with reference to certain preferred embodiments thereof, other embodiments are possible, As such, the spirit and scope of the appended claims should not be limited to the description of the preferred embodiment contained therein.