FCC process

Abstract

The present invention is a fluidized catalytic cracking process that incorporates a zoned riser reactor. The process provides an in-situ method for feed upgrading in a riser reactor. The process assists in the removal of undesirable contaminants, such as nitrogen, from FCC feedstocks.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This patent application claims benefit of U.S. provisional patent application serial No. 60/191,579 filed Mar. 23, 2000, serial No. 60/191,530 filed Mar. 23, 2000, and serial No. 60/246,317 filed Nov. 6, 2000.

BACKGROUND

[0002] The present invention relates to a fluidized catalytic cracking process that incorporates a zoned riser reactor.

[0003] Catalytic cracking is an established and widely used process in the petroleum refining industry for converting relatively high boiling products to more valuable lower boiling products including gasoline and middle distillates, such as kerosene, jet fuel and heating oil. The pre-eminent catalytic cracking process is the fluid catalytic cracking process (FCC) wherein a pre-heated feed contacts a hot cracking catalyst. During the cracking reactions, coke and hydrocarbons deposit on the catalyst particles, resulting in a loss of catalytic activity and selectivity. The coked catalyst particles, and associated hydrocarbon material, are stripped, usually with steam, to remove as much of the hydrocarbon material as technically and economically feasible. The stripped particles, containing non-strippable coke, pass from the stripper and to a regenerator. In the regenerator, the coked catalyst particles are regenerated by contacting them with air, or a mixture of air and oxygen, at elevated temperatures, resulting in the combustion of the coke—an exothermic reaction. The coke combustion removes the coke and heats the catalyst to the temperatures appropriate for the endothermic cracking reactions.

[0004] The process occurs in an integrated unit comprising the cracking reactor, the stripper, the regenerator, and the appropriate ancillary equipment. The catalyst is continuously circulated from the reactor or reaction zone, to the stripper and then to the regenerator and back to the reactor. The circulation rate is typically adjusted relative to the feed rate of the oil to maintain a heat balanced operation in which the heat produced in the regenerator is sufficient for maintaining the cracking reaction with the circulating, regenerated catalyst being used as the heat transfer medium.

[0005] There is a growing need to process heavier feeds containing contaminants such as nitrogen in FCC operations. Therefore, a need exists for a process that can perform in-situ upgrading of nitrogen-containing feeds that can effectively and efficiently minimize the problems caused by nitrogen-containing FCC feeds.

[0006] Additionally, an increased demand for high octane, low emissions fuels and hydrocarbons useful for olefin production has led to a desire to increase the light (C2-C4) olefin content is riser reactor products. Typical heavy oil, gas oil, or resid feeds for riser reactor processes generally contain at most small amounts of light olefins, if any. Catalytic cracking in the riser reactor produces light olefins; however, these products may be thermally cracked into undesirable products such as catalyst coke, diolefins, and dry gas (including methane). These products may also be saturated via hydrogen transfer reactions before they reach the end of the riser. Both activities reduce the concentrations of high-octane naphtha and light olefins.

SUMMARY

[0007] One embodiment of the present invention is a catalytic cracking process comprising (a) contacting a first portion of catalyst with a secondary feed in a first upstream zone wherein the secondary feed has a boiling range between about 25° C. and about 250° C.; (b) in a first primary feed conversion zone, contacting a primary feed comprising nitrogen contaminants with the first portion of catalyst passed from the first upstream zone, wherein the temperature in the first primary feed conversion zone is greater than about 450° C., thereby vaporizing a substantial portion of the primary feed; (c) passing the effluent from the first primary feed conversion zone to a secondary primary feed conversion zone and contacting the effluent from the first primary feed conversion zone with a second portion of catalyst under catalytic cracking conditions.

[0008] Another embodiment comprises a catalytic cracking process comprising (a) passing a first portion of regenerated catalyst to a FCC reactor configured to have a plurality of zones; (b) in a first upstream zone, contacting the first portion of regenerated catalyst with a secondary FCC feed, the secondary feed comprising steam and hydrocarbons boiling in the range of about 25° C. to about 250° C. wherein the residence time of the secondary feed in the first upstream zone is less than about 1.5 seconds; (c) in a first primary feed conversion zone downstream from the first upstream zone, contacting the effluent from the first upstream zone with a primary FCC feed, wherein the effluent of the first upstream zone has sufficient enthalpy to vaporize at least 50 wt % of the FCC primary feed, the primary FCC feed comprising hydrocarbons boiling in the range of between about 250° C. and about 575° C., wherein the residence time within the first primary feed conversion zone is between about 0.2 and about 2 seconds and the catalyst to oil weight ratio is between about 2:1 and about 5:1; (d) contacting a second portion of regenerated catalyst with a secondary FCC feed, the second portion of regenerated catalyst comprising a catalytic cracking catalyst, the secondary feed comprising steam and hydrocarbons boiling in the range of about 25° C. to about 250° C. and then passing the second portion of regenerated catalyst and partially converted secondary FCC feed to a second primary feed conversion zone positioned downstream from the first primary feed conversion zone; and, (e) in the second primary feed conversion zone, contacting the effluent of the first primary feed conversion zone with the second portion of regenerated catalyst wherein the residence time within the second primary feed conversion zone is less than about 10 seconds.

[0009] Another embodiment of the present invention comprises a catalytic cracking process comprising (a) passing a first portion of regenerated catalyst to a FCC reactor configured to have a plurality of zones; (b) in a first upstream zone, contacting the first portion of regenerated catalyst with a secondary FCC feed, the secondary feed comprising steam and hydrocarbons boiling in the range of about 25° C. to about 250° C. wherein the residence time of the secondary feed in the first upstream zone is less than about 1.5 seconds; (c) in a first primary feed conversion zone downstream from the first upstream zone, contacting the effluent from the first upstream zone with a primary FCC feed, wherein the effluent of the first upstream zone has sufficient enthalpy to vaporize at least 50 wt % of the FCC primary feed, the primary FCC feed comprising hydrocarbons boiling in the range of between about 250° C. and about 575° C., wherein the residence time within the first conversion zone is between about 0.2 and about 2 seconds and the catalyst to oil weight ratio is between about 2:1 and about 5:1; (d) in a second primary feed conversion zone downstream from the first primary feed conversion zone, contacting the effluent of the first primary feed conversion zone with a second portion of regenerated catalyst passed into the second conversion zone, the regenerated catalyst passed into the second conversion zone comprising a catalytic cracking catalyst wherein the residence time within the second primary feed conversion zone is less than about 10 seconds; and (e) in a third primary feed conversion zone downstream from the second primary feed conversion zone, contacting the effluent of the second primary feed conversion zone with a third portion of regenerated catalyst passed into the third conversion zone, the regenerated catalyst comprising a catalytic cracking catalyst, wherein the residence time in the third primary feed conversion zone is between about 0.2 and 1 second.

[0010] Another embodiment is a catalytic cracking process comprising (a) passing a first portion of regenerated catalyst to a FCC reactor configured to have a plurality of zones; (b) in a first upstream zone, contacting the first portion of regenerated catalyst with a secondary FCC feed, the secondary feed comprising steam and hydrocarbons boiling in the range of about 25° C. to about 250° C. wherein the residence time of the secondary feed in the first upstream zone is less than about 1.5 seconds; (c) in a first primary feed conversion zone downstream from the first upstream zone, contacting the effluent from the first upstream zone with a primary FCC feed, wherein the effluent of the first upstream zone has sufficient enthalpy to vaporize at least 50 wt % of the FCC primary feed, the primary FCC feed comprising hydrocarbons boiling in the range of between about 250° C. and about 575° C., wherein the residence time within the first conversion zone is between about 0.2 and about 2 seconds and the catalyst to oil weight ratio is between about 2:1 and about 5:1; (d) contacting a second portion of regenerated catalyst with a secondary FCC feed, the second portion of regenerated catalyst comprising a catalytic cracking catalyst, the secondary feed comprising steam and hydrocarbons boiling in the range of about 25° C. to about 250° C. and then passing the second portion of regenerated catalyst and partially converted secondary FCC feed to a second primary feed conversion zone; (e) in the second primary feed conversion zone, positioned downstream from the first primary feed conversion zone, contacting the effluent of the first primary feed conversion zone with the second portion of regenerated catalyst wherein the residence time within the second primary feed conversion zone is less than about 10 seconds; (f) contacting a third portion of regenerated catalyst with a secondary FCC feed, the third portion of regenerated catalyst comprising a catalytic cracking catalyst, the secondary feed comprising steam and hydrocarbons boiling in the range of about 25° C. to about 250° C. and then passing the third portion of regenerated catalyst and partially converted secondary FCC feed to a third primary feed conversion zone; and, (g) in the third primary feed conversion zone downstream from the second primary feed conversion zone, contacting the effluent of the second primary feed conversion zone with the third portion of regenerated catalyst wherein the residence time in the third primary feed conversion zone is between about 0.2 and about 1 second.

[0011] Another embodiment is a catalytic cracking process comprising (a) passing a first portion of catalyst to a FCC reactor configured to have a plurality of zones, the first portion of catalyst comprising a regenerated catalyst and an at least partially coked catalyst; (b) in a first primary feed conversion zone, contacting the first portion of catalyst with a primary FCC feed, wherein the first portion of catalyst has sufficient enthalpy to vaporize at least 50 wt % of the FCC primary feed, the primary FCC feed comprising hydrocarbons boiling in the range of between about 250° C. and about 575° C., wherein the residence time within the first primary feed conversion zone is between about 0.2 and about 2 seconds and the catalyst to oil weight ratio is between about 2:1 and about 5:1; (c) in a second primary feed conversion zone, positioned downstream from the first primary feed conversion zone, contacting the effluent of the first primary feed conversion zone with a second portion of catalyst wherein the residence time within the second primary feed conversion zone is less than about 10 seconds; and, (d) in a third primary feed conversion zone downstream from the second primary feed conversion zone, contacting the effluent of the second primary feed conversion zone with a third portion of catalyst wherein the residence time in the third primary feed conversion zone is between about 0.2 and about 1 seconds.

[0012] Another embodiment is catalytic cracking process comprising (a) passing a first portion of regenerated catalyst to a FCC reactor configured to have a plurality of zones; (b) in a first upstream zone, contacting the first portion of regenerated catalyst with a secondary FCC feed, the secondary feed comprising steam and hydrocarbons boiling in the range of about 25° C. to about 250° C. wherein the residence time of the secondary feed in the first upstream zone is less than about 1.5 seconds; and, (c) in a first primary feed conversion zone downstream from the first upstream zone, contacting the effluent from the first upstream zone with a primary FCC feed, wherein the effluent of the first upstream zone has sufficient enthalpy to vaporize at least 80 wt % of the FCC primary feed, the primary FCC feed comprising hydrocarbons boiling in the range of between about 250° C. and about 575° C.

[0013] Another embodiment is a process comprising: (a) passing a vacuum resid having boiling range greater than about 565° C. (about 1050° F.) to a resid processing unit; (b) separating a light resid fraction having boiling range between about 565° C. and about 650° C. (about 1200° F.) from the vacuum resid; (c) combining the light resid fraction with a FCC feed; (d) passing the combined FCC feed to a FCC unit configured to have a plurality of reaction zones; (e) in the FCC unit: (i) contacting a first portion of catalyst with a secondary feed in a first upstream zone, the secondary feed having a boiling range between about 25° C. and about 250° C.; (ii) in a first primary feed conversion zone, contacting the combined feed comprising nitrogen contaminants with the first portion of catalyst passed from the first upstream zone, wherein the temperature in the first primary feed conversion zone is greater than about 450° C., thereby vaporizing a substantial portion of the combined feed; and, (iii) passing the effluent from the first primary feed conversion zone to a secondary primary feed conversion zone and contacting the effluent from the first primary feed conversion zone with a second portion of catalyst under catalytic cracking conditions.

[0014] Another embodiment is a process comprising: (a) passing a atmospheric pipe still bottoms stream to a vacuum pipe still; (b) separating a vacuum gas oil having a boiling range between about 340° C. and about 565° C. from the bottoms stream, the remainder comprising a vacuum resid fraction; (c) passing at least a portion of the vacuum resid fraction to a short-path distillation unit; (d) in the short-path distillation unit, separating a lighter resid fraction having a boiling range between about 565° C. and about 650° C. (about 1200° F.); (e) combining the lighter resid fraction with the vacuum gas oil to form a FCC feed; (f) passing the FCC feed to a FCC unit configured to have a plurality of reaction zones; and, (e) in the FCC unit: (i) contacting a first portion of catalyst with a secondary feed in a first upstream zone, the secondary feed having a boiling range between about 25° C. and about 250° C.; (ii) in a first primary feed conversion zone, contacting the FCC feed comprising nitrogen contaminants with the first portion of catalyst passed from the first upstream zone, wherein the temperature in the first primary feed conversion zone is greater than about 450° C., thereby vaporizing a substantial portion of the FCC feed; and, (iii) passing the effluent from the first primary feed conversion zone to a secondary primary feed conversion zone and contacting the effluent from the first primary feed conversion zone with a second portion of catalyst under catalytic cracking conditions.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] FIG. 1 illustrates an embodiment of a riser used with the present process wherein the riser has three zones.

[0016] FIG. 2 illustrates an embodiment of a riser used with the present process wherein the riser has four zones.

[0017] FIG. 3 illustrates another embodiment of a riser used with the present process wherein the riser has four zones.

[0018] FIG. 4 illustrates an embodiment of a riser used with the present process wherein the riser has five zones.

DETAILED DESCRIPTION

[0019] Suitable FCC feeds for the process of the present invention include hydrocarbon oils boiling in the range of about 430° F. to about 1050° F. (220° C.-565° C.), such as gas oil, heavy hydrocarbon oils comprising materials boiling above 1050° F. (565° C.), heavy and reduced petroleum crude oil, petroleum atmospheric distillation bottoms, petroleum vacuum distillation bottoms, pitch, asphalt, bitumen, other heavy hydrocarbon residues, tar sand oils, shale oil, liquid products derived from coal liquefaction processes, and mixtures thereof. Small amounts (less than about 15 wt. %) of higher boiling fractions such as vacuum resids may be added to the feedstocks.

[0020] The invention is useful for riser reactor processes such as fluidized catalytic cracking (FCC) processes. The FCC process preferably occurs in an integrated unit comprising a riser reactor 500, a stripper, a regenerator, and appropriate ancillary equipment. The cracking catalyst continuously circulates from the reactor 500 to the stripper to the regenerator and back to the reactor 500.

[0021] In a conventional FCC process, a pre-heated feed contacts the regenerated cracking catalyst that cracks the heavier hydrocarbon components into more valuable products having a lower boiling point. During the cracking reactions, coke and hydrocarbons deposit on the catalyst particles, resulting in a loss of catalytic activity. The catalyst particles then separate from the vapor products in a solid/gas separator, such as a cyclone. The coked catalyst particles, and any associated hydrocarbon material, are stripped, usually with steam, to remove the strippable (volatile) components. The stripped components pass with the cracked products to a fractionator.

[0022] The stripped particles, containing non-strippable coke, pass from the stripper to the regenerator where the coked catalyst particles are regenerated by contacting air, or a mixture of air and oxygen, at elevated temperatures. Suitable regeneration conditions include a temperature from about 1100 to about 1500° F. (593° C.-816° C.), and a pressure ranging from about 0 to about 150 psig (101-1136 kPa). Regeneration burns at least a portion of the coke off the catalyst and heats the catalyst to the temperatures necessary for the endothermic cracking conditions in the reactor 500.

[0023] The catalytic cracking catalyst used in the present process may be any conventional FCC catalyst. Suitable catalysts include (a) amorphous solid acids, such as alumina, silica-alumina, silica-magnesia, silica-zirconia, silica-thoria, silica-beryllia, silica-titania, and the like, and (b) zeolite catalysts containing faujasite. Silica-alumina materials suitable for use in the present invention are amorphous materials containing about 10 to 40 wt. % alumina. Other promoters may or may not be added.

[0024] The catalyst may also comprise zeolite materials that are iso-structural to zeolite Y, including the ion-exchanged forms such as the rare-earth hydrogen and ultra stable (USY) form. The particle size of the zeolite may range from about 0.1 to 10 microns, preferably from about 0.3 to 3 microns. The zeolite is mixed with a suitable porous matrix material when used as a catalyst for fluid catalytic cracking. The catalyst may contain at least one crystalline aluminosilicate, also referred to herein as a large-pore zeolite, having an average pore diameter greater than about 0.7 nanometers (nm). The pore diameter, also sometimes referred to as effective pore diameter, is measured using standard adsorption techniques and hydrocarbons of known minimum kinetic diameters. See Breck, Zeolite Molecular Sieves, 1974 and Anderson et al., J. Catalysis 58, 114 (1979), both of which are incorporated herein by reference. Zeolites useful in the second catalytic cracking catalyst are described in the “Atlas of Zeolite Structure Types”, eds. W. H. Meier and D. H. Olson, Butterworth-Heineman, Third Edition, 1992, which is hereby incorporated by reference.

[0025] The large-pore zeolites may include “crystalline admixtures” which are thought to be the result of faults occurring within the crystal or crystalline area during the synthesis of the zeolites. The crystalline admixtures are themselves medium-pore-size, shape-selective zeolites and are not to be confused with physical admixtures of zeolites in which distinct crystals of crystallites of different zeolites are physically present in the same catalyst composite or hydrothermal reaction mixtures.

[0026] The catalytic cracking catalyst particles may contain metals such as platinum, promoter species such as phosphorous-containing species, clay filler, and species for imparting additional catalytic functionality such as bottoms cracking and metals passivation. Such an additional catalytic functionality may be provided, for example, by aluminum-containing species. In addition, individual catalyst particles may contain large-pore zeolite, amorphous species, other components described herein, and mixtures thereof.

[0027] Non-limiting porous matrix materials that may be used include alumina, silica-alumina, silica-magnesia, silica-zirconia, silica-thoria, silica-beryllia, silica-titania, and ternary compositions, such as silica-alumina-thoria, silica-alumina-zirconia, magnesia, and silica-magnesia-zirconia. The matrix may also be in the form of a cogel. The matrix itself may possess acidic catalytic properties and may be an amorphous material. The inorganic oxide matrix component binds the particle components together so that the catalyst particle product is hard enough to survive inter-particle and reactor wall collisions. The inorganic oxide matrix may be made according to conventional processes from an inorganic oxide sol or gel that is dried to bind the catalyst particle components together. Preferably, the inorganic oxide matrix is not catalytically active and comprises oxides of silicon and aluminum. Preferably, separate alumina phases may be incorporated into the inorganic oxide matrix. Species of aluminum oxyhydroxides, boehmite, diaspore, and transitional aluminas such as &agr;-alumina, &bgr;-alumina, &ggr;-alumina, &dgr;-alumina, &egr;-alumina, &kgr;-alumina, and &rgr;-alumina can be employed. The alumina species may be an aluminum trihydroxide such as gibbsite, bayerite, nordstrandite, or doyelite. The matrix material may also contain phosphorous or aluminum phosphate.

[0028] The catalyst of the present invention may also comprise one or more known nitrogen scavenger catalysts, including, but not limited to, amorphous aluminosilicates, acid clays, hydrogen or ammonium exchanged mordenite, clinoptilolite, chabazite, erionite, mineral acids or mineral acid precursors supported on a previously described matrix material, and Catapal alumina. Acid clays include kaolin, halloysite, sepiolite, and vermiculite. Mineral acids may include phosphoric acid, sulfuric acid, and boric acid. Mineral acid precursor refers to a compound that will form a mineral acid when subjected to FCC conditions.

[0029] Preferably, the nitrogen scavenger has a relatively low catalytic activity. If desired, in one embodiment, the nitrogen scavenger catalyst is less dense than the conventional FCC catalyst previously described. The difference in density provides at least two advantages. First, the lower density of the nitrogen scavenger catalyst decreases the lift gas 300 (steam) requirements for passing the catalyst up the riser. Second, by using a less dense nitrogen scavenger catalyst, selective catalyst separation may occur in the regenerator. Because the nitrogen scavenger is less dense, the fluidization of the regenerator bed causes: (a) the nitrogen scavenger to migrate to the top of the regenerator catalyst bed; and, (b) the conventional catalyst to migrate to the bottom of the regenerator catalyst bed. Accordingly, the nitrogen scavenger may be withdrawn at or near the top of the regenerator catalyst bed, and the conventional FCC catalyst may be withdrawn at or near the bottom of the regenerator catalyst bed. Of course, other suitable separation techniques may be employed if catalyst separation is desired.

[0030] When a nitrogen scavenger catalyst is incorporated into the present process, the nitrogen scavenger comprises all or a portion of the regenerated catalyst 400 passed into zone I if separation techniques are used. If no separation is used, the catalyst 400 passed to the upstream end of the reactor 500 comprises both the nitrogen scavenger and the conventional FCC catalyst.

[0031] Viewing FIG. 1, the present process incorporates a riser reactor 500 having one or more, preferably three zones I, II, III—although in some embodiments, the riser reactor may be configured to have four or five zones (zones IV and V). A first portion of the catalyst 400 from the regenerator (not shown) passes through a standpipe and enters the base of the riser reactor 500 by any conventional means. For example, FIG. 1 illustrates one configuration employing a J-bend where a lift gas 300, preferably steam, provides some of the lift necessary to flow the catalyst 400 up through reactor 500.

[0032] In an embodiment of the present process incorporating a riser reactor 500 with three zones—a first zone I, a second zone II downstream from zone I, and a third zone III downstream from zone II—a primary feed 100 passes into zone II and a secondary feed 200 passes upstream into zone I, also referred to herein as the first upstream zone.

[0033] The secondary feed 200 preferably comprises hydrocarbons having boiling point between 25° C. and 250° C. and includes, but is not limited to, light cat naphtha (LCN), heavy cat naphtha, light cycle oil, virgin naphtha, hydrocracked naphtha, coker naphtha, and/or combinations thereof. Secondary feed 200 preferably comprises LCN and additional steam. Secondary feed 200 passes into zone I of the riser reactor 500. LCN is a hydrocarbon stream having a final boiling point less than about 140° C. (300° F.) and comprises olefins in the C5-C9 range, single ring aromatics (C6-C9) and paraffins in the C5-C9 range. LCN passes into zone I together with about 2 to about 50 wt. % steam based on the total weight of LCN. Zone I is configured so that the LCN and steam passed into zone I have a vapor residence time less than about 1.5 sec., preferably less than about 1.0 sec. and more preferably between about 0.1 and about 1 sec. Cat/oil ratios range between about 30:1 and about 150:1 (wt.:wt.), pressures range between about 100 and about 400 kPa, and catalyst temperatures range from about 620° C. to about 775° C.

[0034] The injection of steam and LCN into zone I results in (a) increased C3 and C4 olefin yields by cracking C5-C9 olefins in the LCN, and (b) a reduced volume of naphtha that has an increased octane value. At least about 5 wt. % of the C5-C9 olefins are converted to C3 and C4 olefins. While not wanting to be bound by any theory, applicants believe that adjusting the LCN feed rate into zone I regulates the amount of coke formed on the zeolite component of the catalyst. Regulating the amount of coke on the zeolite enables a degree of control over the amount of catalytic conversion that occurs in the subsequent, downstream zone(s). Moreover, regulating the secondary feed 200 rate into zone I regulates the temperature and consequently, the conversion and adsorption of nitrogen-containing species in the subsequent downstream zone(s).

[0035] The effluent from zone I flows to a second zone II, also referred to herein as the first primary feed conversion zone. In zone II, a primary FCC feed 100 passes into the riser reactor 500 and contacts the up-flowing catalyst 400. Reaction conditions in zone II include initial catalyst temperature of from about 570° C. to about 725° C. at pressures of from about 100 to about 400 kPa and cat:oil ratios of about 2:1 to about 5:1 (wt.:wt.). Zone II is configured so that vapor residence times range from about 0.2 to about 2 seconds, preferably from about 0.2 to about 1 second, and more preferably from about 0.2 to about 0.5 seconds. Average temperatures in zone II largely depend on the boiling range of the primary FCC feed 100. Typically, the average temperature ranges from greater than about 450° C. to about 550° C., and preferably from about 480° C. to about 500° C. In one embodiment using a conventional heavy oil feed having a gravity of 20° API and a Watson characterization factor (“Kw”) of about 11.6, the catalyst exiting zone I has a temperature of at least 480° C., and preferably ranging from about 480° C. to about 500° C.

[0036] The effluent from zone I should have sufficient enthalpy to vaporize at least about 50 wt. % of the primary FCC feed 100, more preferably at least 80 wt. %, and more preferably at least about 90 wt. %, based on the total weight of the primary FCC feed 100. While not wishing to be bound by any theory or model, it is believed that when at least 80 wt. % of the primary FCC feed 100 is vaporized in zone II, a substantial portion of the nitrogen-containing impurities in the primary FCC feed 100 are irreversibly adsorbed onto the catalyst and converted to coke, thus removing at least a portion of the impurities from the primary FCC feed 100. This effect should increase as the molecular weight and basicity of the nitrogen-containing species increases. The bulk of the nitrogen removed leaves the reactor in the form of coke on catalyst, while a smaller fraction may yield ammonia.

[0037] Controlling the enthalpy of the effluent from zone I so that at least 80 wt. % of the primary FCC feed 100 is vaporized but so that there is not significant primary FCC conversion, leads to a relatively low catalyst to primary FCC feed ratio and a lower average temperature in zone II. Applicants believe that the lower average temperature in zone II favors adsorption by the catalyst of undesirable nitrogen-containing species in the primary FCC feed 100. Additionally, lower average temperatures result in reduced thermal cracking and consequently, improved selectivity to naphtha and light olefins.

[0038] Effluent from zone II may be further converted (catalytically cracked) in subsequent reaction zones in the riser 500 and passed to the cyclones and stripper as previously described.

[0039] In one embodiment of the present invention, the riser reactor 500 is configured to have a third zone III between zone II and riser reactor outlet. The conditions in zone III may be regulated to take advantage of the in-situ feed upgrading process previously described.

[0040] In zone III, also referred to herein as the second primary feed conversion zone, fresh regenerated catalyst 401, preferably comprising a conventional FCC catalyst, passes into the riser reactor 500 through one or more ports 250 in zone III to contact the upgraded primary FCC feed effluent from zone II, which includes catalyst 400. Catalyst 401 may pass into the reactor 500 in any conventional manner. Contacting the upgraded FCC feed with fresh regenerated catalyst 401 leads to substantially less coke and nitrogen deposition on the regenerated catalyst 401 passed into zone III, which leads to an effective increase in catalyst activity.

[0041] Catalyst to oil ratio in zone III may be adjusted by regulating the feed rates of the catalyst(s) passed into the first zone I and third zone III. Preferably, the amount of regenerated catalyst passed 401 into zone III (R3) exceeds the amount of catalyst 400 passed into zone I (R1). More preferably, the ratio of R3 to R1 ranges from about 1:2 to about 2:1.

[0042] Conditions in zone III are similar to those in a conventional FCC operation and include (i) temperatures from about 500° C. to about 650° C., preferably from about 500° C. to about 600° C.; (ii) hydrocarbon partial pressures from about 10 to about 40 psia (70-280 kPa), preferably from about 20 to about 35 psia (140-245 kPa); and, (iii) a catalyst to oil (wt:wt) ratio from about 3:1 to about 12:1, preferably from about 4:1 to about 10:1.

[0043] The increased availability of strong catalyst acid sites in zone III enables the attainment of the required feed conversion at relatively short contact (residence) times of less than ten seconds, more preferably between about 2 and about 5 seconds, and even more preferably less than 2 seconds. As used herein, contact time and residence time are synonymous and are used to designate the average residence time of the solids (catalyst) passing through a particular zone. Applicants believe that contacting freshly regenerated catalyst in zone III with upgraded feed passing from zone II leads to substantially less coke and nitrogen deposition on the catalyst. In turn, this results in an effective increase in catalyst conversion activity. Coke yields from zone III decrease due to reduced hydrogen transfer and enhanced primary cracking, thus allowing the option of constant coke operation via increased zone III cat to oil ratios.

[0044] FIG. 2 illustrates another embodiment of the present invention. Riser reactor 500 is configured to have a fourth zone IV, also referred to herein as a second upstream zone, positioned upstream from port(s) 250 (or port(s) 350 as described below). In zone IV, another stream of secondary feed 200, preferably LCN, contacts catalyst stream 401 before catalyst stream 401 passes through port(s) 250. The additional LCN injection occurs as previously described for zone I (and may include steam co-injection). Incorporating zone IV helps quench the temperature of the subsequent zones, minimizes thermal cracking and aromatics formation, and generates additional light olefins by conventional cracking. Zone IV also provides the option of increasing the cat to oil ratio without unwanted increases in the subsequent reaction zone temperatures. Operating conditions for the optional zone IV lie within those previously described for zone I.

[0045] Viewing FIG. 3, in another embodiment, the riser reactor 500 employs a fifth zone, zone V, also referred to herein as the third primary feed conversion zone. In an embodiment including zone V, which may or may not include zone IV, at least one additional regenerated catalyst inlet port(s) 350 are positioned downstream from zone III and a portion of regenerated catalyst 402 is directed through port(s) 350, although catalyst 402 may pass into zone V in any conventional manner. Port(s) 350 are configured in the same manner as described for port(s) 250, but port(s) 350 are positioned downstream from port(s) 250 so that the contact (residence) time of the catalyst to oil between the injection ports is between about 0.2 and about 1 second, preferably about 0.5 seconds. This configuration provides an additional stage of feed pretreatment. The catalyst-to-oil ratio (wt:wt) in zone V is between about 3:1 and about 12:1, and the temperature within zone V is between about 500° C. and about 650° C.

[0046] Zone V may be used in conjunction with an embodiment incorporating zones I-IV (see FIG. 4), or with an embodiment that incorporates only zones I-III (see FIG. 3). Regenerated catalyst 402 passing into zone V may also contact a secondary feed stream 200 to provide additional advantages as already set forth for zones I and IV. The secondary feed 200 may be contacted with a single catalyst stream that is thereafter separated into catalyst streams 401, 402, or the secondary feed 200 may be contacted with the catalyst streams 401, 402 separately. In some embodiments, the combined residence time within zones III and V is less than about 4 seconds.

[0047] In some embodiments, the weight ratio of catalyst stream 401 to catalyst stream 402 ranges between about 1:2 and about 1:1, and the weight ratio of catalyst stream 400 to the combined weight of catalyst streams 401 and 402 is between 1:1 and 1:2.

[0048] Coked catalyst particles and cracked hydrocarbon products exit the riser reactor 500 and pass the cyclones where the cracked products separate from coked catalyst particles. Coked catalyst particles from the cyclones pass to a stripping zone. The stripper removes and recovers the strippable hydrocarbons from coked catalyst particles. Stripped hydrocarbons pass with cracked hydrocarbon products for further processing. After the coked catalyst is stripped, it passes to the regenerator and eventually back to the riser reactor 500.

[0049] In other embodiments not shown in the Figures, it may be desirable to eliminate the step of pre-contacting one or more of the catalyst streams with a secondary feed 200. In such embodiments, the catalyst streams flowing to the reactor 500 would comprise an at least partially coked catalyst, preferably having a coke content of greater than 0.1 wt % based upon the total weight of the catalyst charge. In some embodiments, the catalyst would also comprise fully regenerated catalysts. For instance, in one embodiment, at least partially coked catalyst from the stripper may pass into the base of the riser reactor 500 alone or in combination with regenerated catalyst 400. In another embodiment, at least partially coked catalyst may pass into any of the zones discussed herein in place of or in combination with catalyst that to be pre-coked with a secondary feed 200, although applicants prefer pre-coking with secondary feed 200.

[0050] In yet another embodiment, a two-stage catalyst regenerator may be employed, and the catalyst 400 passed to the base of the riser may comprise a first portion of substantially regenerated catalyst passed from one stage of the regenerator and a second portion of only partially regenerated and at least partially coked catalyst that passed from another stage of the regenerator. Applicants believe that the use of the partially coked catalyst provides benefits similar to that found by using catalyst pre-coked by contact with LCN or other secondary feed 200.

[0051] In another embodiment of the present invention, the embodiments of the multi-zone riser may be used in conjunction with a resid upgrading unit or process, such as short-path distillation. In an embodiment employing short path distillation, high vacuum evaporation of volatile species from a thin liquid film spread on a heated surface is used. Evolved vapor is rapidly condensed on a closely adjacent cooled surface. Wiper blades on the heated and cooled surfaces operate continuously to facilitate heat and mass transport. Typically, two or more stages are employed. The overhead vapor is routed through an entrainment separator to minimize carryover of heavier components. Holdup is minimal and the short residence time acts to prevent thermal cracking of the overhead and bottoms streams. Short path distillation is also described in U.S. Pat. Nos. 5,415,764 and 4,925,558, which are incorporated herein by reference to the extent they do not conflict with the present disclosure. Short path distillation offers the potential to boost the 1050/1200° F. (565/650° C.) fraction of vacuum resid to the FCC without incurring the typical debits for high feed metals as well as rejecting the highest Conradson carbon 1200° F.+ (650° C.+) fraction.

[0052] Combining the short path distillation or other suitable process to capture a 1050/1200° F. (565/650° C.) fraction of vacuum reside with the multi-zone FCC riser results in a synergy to capture additional advantage from the lower coke selectivity of the multi-zone process. A particular benefit from the multi-zone riser is improved coke/bottoms selectivity, which can be exploited by increasing the final boiling point of the primary feed to the riser. Vacuum pipe still bottoms have an initial boiling point >1050° F. (°565° C.), and small increments of that stream elevate nickel and vanadium concentrations in the primary feed, resulting in higher coke and dry gas yields. The nickel and vanadium content of the primary feed is comparable to that of typical gas oil FCC feeds because the lighter vacuum resid fraction is typically low in metals. The nitrogen content and Conradson carbon content are greater than typical gas oil FCC feeds but well suited for the multi-zone FCC riser. The multi-zone riser can tolerate increased nitrogen concentrations, but the metals contamination debits remain. Short-path distillation of vacuum pipe still bottoms and blending the 1050/1200° F. (565/650° C.) fraction from the short-path distillation unit with the primary feed permits processing of the lower boiling fraction of the vacuum resid.

[0053] In a particular embodiment, a bottoms stream from an atmospheric pipe still is passed to a vacuum pipe still where a gas oil stream boiling in the about 650/1050° F. (about 340/565° C.) range is derived from a vacuum pipe still (distillation column). A vacuum resid fraction boiling above 1050° F. (565° C.) passes from the vacuum pipe still to a short-path distillation unit such as the VRSD process offered by Buss AG, or other suitable resid unit. Overhead streams, referred to herein as a lighter resid stream, having a boiling range of 1050/1200° F. (565/650° C.) taken from the resid unit are then combined with the 650/1050° F. (340/565° C.) gas oil fraction obtained from the vacuum pipe still (or other suitable FCC feed stream) and may be preheated for injection into the multi-zone riser as the primary FCC feed. Other suitable process(es), such as solvent deasphalting, may also be used to obtain a lower final boiling point cut of lighter vacuum resid.

[0054] Boiling ranges of various streams are measured by conventional methods, preferably ASTM distillation.

EXAMPLES 1-3

[0055] Examples 1-3 illustrate the nitrogen removal capabilities of the present invention. Examples 1-3 were conducted using a conventional FCC catalyst and a vacuum gas oil feed containing about 925 wppm total nitrogen. The catalyst was not lightly coked by cracking a secondary light feed. Results are therefore deemed conservative, in the sense that lightly coked catalyst would have been expected to further suppress conversion, without adversely affecting nitrogen removal efficiency.

[0056] Example 1 represents a base case at typical cat to oil ratio and reactor temperature. Operation at these conditions results in relatively high (430° F.−/221° C.−) conversion of 80 wt. %. The nitrogen removal from the collected liquid product was 83.3 wt. %.

[0057] Example 2 shows that reducing reactor temperature to about 944° F. (507° C.) and using a cat to oil of 3.15 (conditions that are within the range of operation of the zone II of the present invention) lowered conversion to 50.6 wt. %. However, a large percentage (62.1 wt. %) of the total feed nitrogen was removed. This is about 75% of the amount of nitrogen removed in Example 1, but only 41% of the catalyst was used.

[0058] Example 3 data was obtained by reducing contact time to 0.33 seconds, which is close to the lower end of the preferred contact times of the present invention for the conversion zone(s). Conditions otherwise were roughly comparable to those in Example 1. Lower contact time significantly reduced conversion to 65.5 wt. %, but nitrogen was still high at 71.7 wt. %. Table 1 illustrates the results from Examples 1-3. 1 TABLE 1 Total N Contact Reactor Wt. % Removal, Time, Temp. Cat to Oil (430° F.−) wt. % of Feed Example sec. ° C. Ratio Conversion N 1 1.8 541 7.73 80.0 83.3 2 2.0 507 3.15 50.6 62.1 3  0.33 541 7.02 65.6 71.7

EXAMPLES 4-5

[0059] Examples 4-5 were conducted with a conventional FCC catalyst and a vacuum gas oil containing about 1900 wppm total nitrogen. Reactor temperature was 557° C. in both cases.

[0060] Example 4 represents base case FCC operation with a captive fluid bed employing a typical FCC catalyst to oil ratio.

[0061] Example 5 is the combined result of two sequential steps performed in the captive fluid bed simulating the second and third zone of the present invention. The presence of a first zone was simulated by using a lightly coked (0.16 wt % coke) version of the base case catalyst in the second zone simulation by coking it with the base vacuum gas oil feed instead of a secondary light feed due to equipment constraints. Equipment constraints also mandated a reactor temperature of 557° C. Therefore, the results are conservative because the pre-coking with a lighter feed and lower reactor temperature would have been expected to increase the amount of nitrogen removed.

[0062] In the first step of Example 5, the vacuum gas oil feed was cracked at 2.5 catalyst to oil ratio over the lightly coked catalyst.

[0063] The lower nitrogen content liquid product as well as the more highly coked, but stripped catalyst produced in the first step, were collected for use in the second step. Nitrogen removal was about 46%.

[0064] Stripping of second zone catalyst would not occur in the actual process, but was required to fully material balance the stage-wise simulation. In the second step, the reactor was charged with a 1:1 weight ratio blend of regenerated catalyst with the same coke on regenerated catalyst as the base case (Example 4) and coked, stripped catalyst collected in step 1, for an overall catalyst to original base vacuum gas oil feed ratio of 4.9. Liquid product from the first step served as feed. Overall process yields were obtained by combining results of the two steps.

[0065] The results shown in Table 2 illustrate than despite the lower catalyst to oil ratio, the process of Example 5 resulted in a 2.9 wt % higher 430° F.− (221° C.−) conversion and significant improvement in selectivity as shown by the lower 650° F.+ (343° C.+) bottoms/coke yield ratio. 2 TABLE 2 Wt % 430 F.− 650 F.+ (343° C.) 650 F.+ (343° C.+) Catalyst to (221° C.) Coke Yield, Bottoms Yield, Bottoms/Coke Example Oil Ratio Conversion wt % wt % Yield Ratio 4 6.1 71.5 7.4 11.7 1.6 5 4.9 74.4 7.4  8.9 1.2

Claims

1. A catalytic cracking process comprising:

(a) contacting a first portion of catalyst with a secondary feed in a first upstream zone, the secondary feed having a boiling range between about 25° C. and about 250° C.;

(b) in a first primary feed conversion zone, contacting a primary feed comprising nitrogen contaminants with the first portion of catalyst passed from the first upstream zone, wherein the temperature in the first primary feed conversion zone is greater than about 450° C., thereby vaporizing a substantial portion of the primary feed;

(c) passing the effluent from the first primary feed conversion zone to a secondary primary feed conversion zone and contacting the effluent from the first primary feed conversion zone with a second portion of catalyst under catalytic cracking conditions.

2. The process according to

claim 1 wherein the secondary feed further comprises between about 2 and about 50 wt % steam based on the total weight of the secondary feed.

3. The process according to

claim 1 wherein the catalyst to secondary feed weight ratio in the first upstream zone is between about 30:1 and about 150:1.

4. The process according to

claim 1 wherein the residence time in the first upstream zone is between about 0.1 and 1 second.

5. The process according to

claim 1 wherein the residence time in the first primary feed conversion zone is less than 2 seconds.

6. The process according to

claim 1 wherein at least 50 wt. % of the primary feed is vaporized.

7. The process of

claim 1 wherein the effluent of the first upstream zone has sufficient enthalpy to vaporize at least 80 wt % of the FCC primary feed.

8. The process of

claim 1 wherein the effluent of the first upstream zone has sufficient enthalpy to vaporize at least 90 wt % of the FCC primary feed.

9. The process according to

claim 1 wherein the residence time in the second primary feed conversion zone is less than 2 seconds.

10. The process according to

claim 1 further comprising contacting a third portion of regenerated catalyst with a secondary FCC feed, the third portion of regenerated catalyst comprising a catalytic cracking catalyst, the secondary feed comprising steam and hydrocarbons boiling in the range of about 25° C. to about 250° C. and then passing the third portion of regenerated catalyst and partially converted secondary FCC feed to a third primary feed conversion zone.

11. The process according to

claim 10 further comprising in the third primary feed conversion zone downstream from the second primary feed conversion zone, contacting the effluent of the second primary feed conversion zone with the third portion of regenerated catalyst wherein the residence time in the third primary feed conversion zone is between about 0.2 and about 1 second.

12. The process according to

claim 11 wherein the weight ratio of the first portion of catalyst to the sum of the weights of the second and third portions of catalyst is between about 1:1 and about 1:2 and wherein the weight ratio of the second portion of catalyst to the third portion of catalyst is between about 1:2 and about 1:1.

13. A catalytic cracking process comprising:

(a) contacting a first portion of catalyst with a secondary feed in a first upstream zone, the secondary hydrocarbon feed having a boiling range between about 25° C. and about 250° C.;

(b) in a first primary feed conversion zone, contacting a primary feed comprising nitrogen contaminants with the first portion of catalyst passed from the first upstream zone, wherein the temperature in the first primary feed conversion zone is sufficient to vaporize at least 80 wt. % of the primary feed;

(c) passing the effluent from the first primary feed conversion zone to a secondary primary feed conversion zone and contacting the effluent from the first primary feed conversion zone with a second portion of regenerated catalyst under catalytic cracking conditions.

14. The process according to

claim 13 wherein the secondary feed further comprises between about 2 and about 50 wt % steam based on the total weight of the secondary feed.

15. The process according to

claim 13 wherein the catalyst to secondary feed weight ratio in the first upstream zone is between about 30:1 and about 150:1.

16. The process according to

claim 13 wherein the residence time in the first upstream zone is between about 0.1 and 1 second.

17. The process according to

claim 13 wherein the residence time in the first primary feed conversion zone is less than 2 seconds.

18. The process according to

claim 13 wherein the temperature in the first primary feed conversion zone is at least 450° C.

19. The process according to

claim 13 wherein the residence time in the second primary feed conversion zone is less than 2 seconds.

20. The process according to

claim 13 further comprising contacting a third portion of regenerated catalyst with a secondary FCC feed, the third portion of regenerated catalyst comprising a catalytic cracking catalyst, the secondary feed comprising steam and hydrocarbons boiling in the range of about 25° C. to about 250° C. and then passing the third portion of regenerated catalyst and partially converted secondary FCC feed to a third primary feed conversion zone.

21. The process according to

claim 20 further comprising in the third primary feed conversion zone downstream from the second primary feed conversion zone, contacting the effluent of the second primary feed conversion zone with the third portion of regenerated catalyst wherein the residence time in the third primary feed conversion zone is between about 0.2 and about 1 second.

22. The process according to

claim 21 wherein the weight ratio of the first portion of catalyst to the sum of the weights of the second and third portions of catalyst is between about 1:1 and about 1:2 and wherein the weight ratio of the second portion of catalyst to the third portion of catalyst is between about 1:2 and about 1:1.