IE43837B1 - Process for regenerating a coke-contaminated fluid catalytic cracking catalyst and catalytic conversion of co to co2 - Google Patents

Abstract

A process for initiating and controlling the regeneration of spent fluid catalytic cracking catalyst containing catalytically effective amounts of a C0 conversion promotor and for the essentially complete catalytic conversion of C0 to C02 both in a dense bed of catalyst maintained in an FCC regeneration zone. The process comprises (a) passing to a dense-phase catalyst bed in a regeneration zone said catalyst and fresh regeneration gas at a first flow rate sufficient to oxidize coke to produce partially spent regeneration gas, (b) oxidizing coke at first oxidizing conditions including a catalyst bed first temperature of from 399.degree.C to 677.degree.C to produce regenerated catalyst and partially spent regeneration gas containing C0, (c) increasing the catalyst bed temperature from said first temperature to a second temperature of from 677.degree.C to 760.degree.C, (d) passing to the catalyst bed fresh regeneration gas at a second flow rate stoichiometrically sufficient to essentially completely oxidize C0 to C02, (e) oxidizing in said catalyst bed, maintained at second oxidizing conditions including the presence of said C0 conversion promotor, C0 to produce spent regeneration gas, (f) analyzing spent regeneration gas to obtain a measured free-oxygen concentration and comparing the measured free-oxygen concentration to a predetermined free-oxygen concentration, and (g) thereafter regulating fresh regeneration gas at a third flow rate to maintain the measured free-oxygen concentration equal to the predetermined free-oxygen concentration thereby ensuring essentially complete conversion of C0 to C02. The process is generally distinguishable from the prior art in terms of the C0 conversion temperature employed. [CA1072527A]

Description

4383·? · - 2 - The field of art to which this invention pertains is hydrocarbon processing. More particularly, the invention relates to a regeneration process for the oxidative removal of coke from a spent, i.e. coke-5 contaminated catalyst which has been used in fluid catalyst cracking (FCC catalyst), and for the catalytic conversion of CO to C02> Regeneration techniques in which a fluidizable spent catalyst is regenerated in a regeneration zone 10 occupy a large segment of the chemical arts. The patents which have attempted to solve problems associated with regeneration of spent fluidizable catalyst have generally dealt with maximum removal of coke on catalyst while at the same time attempting to prevent or minimize the 15 conversion of carbon monoxide to carbon dioxide within any portion of the regeneration zone.

Specifically, it has been refinery practice to operate conventional regeneration zones to preclude essentially complete conversion of CO to C02 anywhere 20 within the regeneration zone and especially in the dilute-phase catalyst region where there is little catalyst present to absorb the heat of reaction and where heat damage to cyclones or other separation equipment can therefore result. Essentially complete CO conversion in 25 conventional regeneration zones was prevented quite _ 3 - 4383? simply by limiting the amount of fresh regeneration gas passing into the regeneration zone. Without sufficient oxygen present to support the reaction of CO to C02» after-burning simply cannot occur no matter 5 what the temperatures in the regeneration zone. As well, temperatures in the regeneration zone were generally limited to less than about 677°C. by the proper selection of hydrocarbon reaction zone operating conditions or fresh feed streams or recycle streams. At 10 these temperatures the rate of reaction of CO oxidation was considerably reduced so that should upsets occur more of an excess of fresh regeneration gas would be required for CO conversion than would be needed at temperatures higher than about 677°C. The flue gas 15 produced, containing several volume percent CO, was either vented directly to the atmosphere or used as fuel in a CO boiler located downstream of the regeneration zone.

Usual practice, familiar to those skilled in the 20 art of FCC processes, has been to initially manually regulate the flow of fresh regeneration gas to the regeneration zone in an amount sufficient to produce partially spent regeneration gas but insufficient to sustain essentially complete CO conversion while at the 25 same time limiting regeneration zone temperatures to about 677°C. This flow rate required was usually equivalent to about 8 to 12 pounds of air per pound of coke. When reasonable steady state control was achieved the flow rate of fresh regeneration gas was then typically 30 regulated directly responsive to a small temperature differential between the flue gas outlet temperature (or the dilute phase disengaging space temperature) and the dense bed temperature to maintain automatically this proper flow rate of fresh regeneration gas to preclude 35 essentially complete conversion of CO to C02 anywhere within the regeneration zone. As the temperature 4383? - 4 - difference increased beyond some predetermined temperature difference, indicating that more conversion of CO was taking place in the dilute phase, the amount of fresh regeneration gas was decreased to preclude 5 essentially complete conversion of CO to COj. This method of control is exemplified by Pohlenz O.S. Patents 3,161,583 and 3,206,393. While such method produces a small amount of 02 in the flue gas, generally in the range of D.l to 1 vol.% 02, it precludes essentially 10 complete conversion of CO to C02 within the regeneration zone.

Until the advent of zeolite-containing catalysts, there was little economic incentive for essentially complete conversion of CO to C02 within the regeneration 15 zone. The heat of combustion that might have been removed was simply not needed by the process; there was generally no feed preheat for the hydrocarbon reaction zone and the larger coke yield obtained with the amorphous, catalysts in the hydrocarbon conversion zone 20 was usually sufficient when burned in the regeneration zone to provide the heat required.for the overall process heat balance at the lower hydrocarbon conversion zone temperatures then employed without requiring such additional heat inputs as feed preheat. The use of the 25 zeolite-containing FCC catalysts with their lower coke-producing tendencies and the use of higher hydrocarbon conversion zone temperature, however, often made additional heat input into the FCC process necessary. Typically additional heat was provided by burning 30 external fuel such as torch oil in the regeneration zone or by preheating the FCC hydrocarbon feed in external preheaters. Thus heat was typically being added to and then later removed from the FCC process by two external installations, a feed preheater and a CO boiler, each 35 representing a substantial capital investment.

By the process of our invention, as is explained - 5 - 4383? and defined below, coke from a spent fluid catalytic cracking catalyst containing catalytically effective amounts of a CO conversion promoter is oxidized and essentially complete catalyst conversion of CO to C02 5 is initiated and controlled within a dense-phase fluid bed of catalyst in a regeneration zone. The recovery in the dense-phase catalyst bed of at least a portion of the heat of reaction of CO combustion permits either reduced feed preheat requirements or higher hydrocarbon 10 reaction zone temperatures without additional feed preheat while at the same time eliminating an air pollution problem without the need for an external CO boiler. More specifically, the use in our process of a fluid catalytic cracking catalyst containing catalytic-15 ally effective amounts of a CO conversion promoter permits either the same rate of CO conversion to occur at a temperature as much as 55°C. or more lower than that required with no CO conversion promotor or a faster rate of CO conversion to occur at a particular temperat-20 ure than that which would occur at the same temperature without the use of a CO conversion promotor. It is this latter advantage which is of particular commercial importance. Without a CO conversion promotor, uneven dispersion of fresh regeneration gas within the dense-25 phase catalyst bed often requires higher regeneration zone temperatures or higher fresh regeneration gas rates than desired to maintain a sufficiently fast rate of CO conversion so that essentially complete conversion of CO takee place within the regeneration zone. To increase 30 the regeneration zone temperature torch oil was burned in the regeneration zone or increased amounts of slurry oil were recycled back to the hydrocarbon reaction zone so that the spent catalyst would contain more coke which could be burned in the regeneration zone to 35 increase the temperature. Increased fresh regeneration gas rates, besides using blower capacity, often overloaded cyclone separation devices and produced higher 4383? ~ 6 - amounts of flue gas particulate emissions (catalyst) than allowed by air pollution regulations. The use of the CO conversion promotor permits the elimination of torch oil or increased slurry oil recycled rates and a 5 reduction in the amount of excess fresh regeneration gas and thus gives back to the refiner more FCC process flexibility.

While the prior art broadly teaches the use of temperatures greater than about 677°C. in regeneration 10 zones (see for example Bunn U.S. Patent 3,751,359? Iscol et al U.S. Patent 3,261,777? Pfeiffer et al U.S. Patent 3,563,911, and Lee et al U.S. Patent 3,769,203) and also broadly discloses control of air flow rates responsuve to oxygen in the flue gas (see for example 15 Thomas et al U.S. Patent 2,414,002 and Gerhold et al U.S. Patent 2,466,041), the process of our invention is distinguishable since it requires rather than avoids essentially complete conversion of CO to C02 within the regeneration zone. Our process furthermore recognizes 20 that oxidizing CO is not effected by the single factor of high temperature, that is, temperatures above about 677°C.? indeed, the process of our invention requires as a distinct step the passing of sufficient fresh regeneration gas to the dense bed to make possible the 25 essentially complete conversion of CO to C02. Without sufficient 02 present, temperatures higher than about 677°c. will neither initiate nor sustain after-burning A temperature of about 677°C. is initially required to provide a sufficiently fast rate of reaction, once CO 50 conversion is initiated, to ensure that it will be essentially completed within the dense bed of the regeneration zone. .

The use of CO conversion promotors in regeneration zones is disclosed in U.S. Patent 3,808,121. In the 15 process of that invention, coke and CO oxidation are 4283? - 7 - accomplished by employing two separate catalysts of different particle size and composition: a hydrocarbon conversion catalyst and a CO oxidation catalyst. Moreover, the CO oxidation catalyst is maintained within a 5 conventional-type regeneration zone and does not pass out of that zone to the hydrocarbon reaction zone as does the catalyst employed in the process of our invention.

It is a broad objective of the process of this 10 invention to provide a regeneration process for the oxidation of coke from a spent fluid catalytic cracking catalyst containing catalytically effective amounts of a CO conversion promotor and for the essentially complete catalytic conversion of CO to CO2 to produce regenerated 15 catalyst and spent regeneration gas in a manner such that at.least a portion of the heat of CO conversion is recovered within the regeneration zone.

According to the present invention there is provided a process for the regeneration of coke-contaminated fluid 20 catalytic cracking catalyst containing catalytically effective amounts of a CO conversion promotor and for the essentially complete catalytic conversion of carbon monoxide to carbon dioxide, which process comprises the steps of: (a) passing to a dense-phase fluid catalyst 25 bed in a regeneration zone said catalyst and fresh regeneration gas at a first flow rate sufficient to oxidize coke to produce partially spent regeneration gas; (b) oxidizing coke at first oxidizing conditions including a catalyst bed first temperature of from 30 399°C. to 677°C. to produce regenerated catalyst and partially spent regeneration gas containing CO; (c) increasing the catalyst bed temperature from said first temperature to a second temperature of from 677°C. to 760°C.; (d) passing to the catalyst bed fresh regenerat- 35 ion gas at a second flow rate stoichiometrically sufficient to essentially completely oxidize CO to co2; 4383^ - 8 - (e) oxidizing in said catalyst bed, maintained at second oxidizing conditions including a catalyst bed second temperature of from 677°C to 760°C. and the presence of said CO conversion promotor, CO to produce 5 spent regeneration gas; (f) analyzing spent regeneration gas to obtain a measured free-oxygen concentration and comparing the measured free-oxygen concentration to a predetermined free-oxygen concentration; and (g) thereafter regulating fresh regeneration 10 gas at a third flow rate to maintain the measured free-oxygen concentration equal to the predetermined free-oxygen concentration thereby ensuring essentially complete conversion of CO to COj.

The accompanying drawing depicts schematically 15 the side view of a regeneration zone suitable for carrying out the process of our invention, it is to be understood that the drawing is presented only in such detail as is necessary for an understanding of the invention and that minor items have been omitted there-20 from for the sake of simplicity. Referring to the drawing, spent FCC catalyst containing typically from about 0.5 to 1.5 wt.% coke passes from a hydrocarbon reaction zone (not shown) into regeneration zone 1 via line 9. Catalyst is maintained within regeneration zone 25 1 as a denSe-phase fluid bed 3. Freshly regenerated catalyst is removed from dense bed 3 and regeneration zone 1 via line 4 and returned back to the hydrocarbon reaction zone. Control valve 5, typically a slide valve, in line 4 is utilized to control the quantity of 30 regenerated catalyst leaving regeneration zone 1 and passing into the hydrocarbon reaction zone.

Line 14 may enter line 9 for the purpose of admitting one of several particular fluids. The fluid may be a stripping medium such as steam to cause the 35 removal of adsorbed and interstitial hydrocarbons from the spent catalyst before the catalyst is passed into *· 9 ^ 43837 regeneration zone 1. The fluid may be an aeration medium such as air or steam for the purpose of keeping the spent catalyst in line 9 in a fluidized state thereby ensuring an even flow of catalyst into the 5 regeneration zone. The fluid may also be a hydrocarbon liquid or gas added to the regeneration zone as an additional external fuel for the purpose of increasing the temperature within the regeneration zone.

Fresh regeneration gas is introduced via line 6 10 into dense bed 3. The fresh regeneration gas passes through distributing device 8 which allows the gas to be more readily dispersed within dense bed 3. Typically, the distributing device can be a metal plate containing holes or slots therein or a pipe grid arrangement both 15 of which are familiar to those skilled in the art. In the presence of sufficient fresh regeneration gas and at a dense bed temperature of at least 677°C. oxidation of coke and essentially complete afterburning of CO to C02 takes place in the dense bed to produce regenerated 20 catalyst and spent regeneration gas.

Spent regeneration gas, along with entrained regenerated catalyst passes out of dense bed 3 and into dilute phase region 2 which is positioned above and in communication with dense bed 3. Separation means 12, 25 typically a cyclone separating device, is located in dilute phase region 2 and is used to achieve a substantial separation of spent regeneration gas and entrained catalyst. Although the drawing shows only one such cyclone, it is anticipated that multiple cyclones 30 arranged for parallel or series flow of the gas and catalyst could be so positioned in dilute phase 2. As shown in this drawing the spent regeneration gas passes out of zone 1 via line 10 while substantially all the catalyst passing into the cyclone is recovered through 35 dipleg 13 which passes the catalyst downward toward or into dense bed 3. Spent regeneration gas passes out of - 10 - 43831? regeneration zone 1 via line 10 at a rate controlled by valve 11. Valve 11 in line 10 can be operated to maintain a given pressure within the regeneration zone or more preferably may be operated to maintain a given 5 pressure differential between the regeneration zone and the hydrocarbon reaction zone.

Line 15 which is connected to line 10 passes a sample of the spent regeneration gas to analyzing means 16. Analyzing means 16 is any instrument known in the art 10 by which the concentration of free-oxygen present in the spent regeneration gas can be measured.

Regulating means 7 is connected to fresh regeneration gas inlet line 6 and regulates the rate of regeneration gas passed into regeneration zone 1 based on the 15 measured free oxygen concentration determined by analyzing means 16. Specifically, in the particular apparatus shown in the drawing analyzing means 16 is connected to the regulating means via control means 19 which is connected to the regulating means 7 via means 18. Control 20 means 19 has a setpoint input signal corresponding to a predetermined free-oxygen concentration represented by line 20 and can receive an output signal from the analyzing means which is responsive to the quantity of free-oxygen passing through line 10. The control means 25 can compare this free-oxygen quantity with a setpoint or desired free-oxygen concentration and via means 18 can pass a control means output signal to the regulating means 7 to alter the flow of regeneration gas into the regeneration zone depending upon the deviation of the 30 measured free-oxygen concentration from the desired predetermined free-oxygen concentration in the spent regeneration gas.

Regulating means 7 can be any apparatus which can control the quantity of a gas stream passing through a 35 line. Specifically, the regulating means can include a ! 43837 - 11 - compressor which passes fresh regeneration gas through line 6 at a desired rate. The compressor can be altered in its operation to change the rate of flow of fresh regeneration gas passing through line 6 depending upon 5 the free-oxygen content in the spent regeneration gas passing through line 10. Other regulating means include valves to regulate the flow of regeneration gas through the line or combinations of flow control loops including an orifice connected to pressure controllers and control 10 valves in a manner which enables the regulation of a regeneration gas passing through line 6 into the regeneration zone 1.

Control means 19 is any apparatus which can generate an output signal which responds to a deviation 15 of an input Bignal fed to it from a desired set point value which the control means attempts to maintain. In normal operations an input signal fed to the control means via line 17 is read by the control means. The deviation, if any, of this signal from the setpoint input 20 signal represented by line 20 which is programmed into control means 19 is determined. An output signal passes via means 18 to the regulating means in accordance with the deviation of the input value to the control means.

The materials of construction of the regeneration 25 zone can be metal or other refractory materials which can withstand the high temperatures and the attrition conditions present in fluidized regeneration processes.

The term "afterburning" as generally understood by those skilled in the art means the incomplete oxidation of 30 CO to C02 within the regeneration zone or the flue gas line. Generally afterburning is characterized by a rapid temperature increase and occurs during periods of unsteady state operations or process "upset". It is, therefore, usually of short duration until steady state operations are 35 resumed. 4 383^ - 12 - In contrast to afterburning, the term "essentially complete conversion of CO” as used herein refers to the intentional, sustained, controlled, and essentially complete combustion of CO to COj within the regeneration 5 zone and more specifically within a densephase bed of catalyst maintained in the regeneration zone. "Essentially complete" means that the CO concentration in the spent regeneration gas (hereinafter defined) has been reduced to less than 1000 ppm and more preferably less than 500 10 ppm.

The term "spent catalyst" as used in this specification means catalyst withdrawn from a hydrocarbon conversion zone because of reduced activity caused by coke deposits. Spent catalyst passing into the dense-15 phase catalyst bad can contain anywhere from a few tenths up to 5 wt.% of coke, but typically in FCC operations spent catalyst will contain from 0.5 to 1.5 wt.% coke.

The term "regenerated catalyst" as used in this specification means catalyst from which at least a portion 20 of coke has been removed. Regenerated catalyst produced by the process according to the invention will generally contain less than 0.5 wt.% coke and more typically will contain from 0.01 to 0.15 wt.% coke.

The term "regeneration gas" as used in this 25 specification means, in a generic sense, any gas which is to contact catalyst or which has contacted catalyst within the regeneration zone. Specifically, the term "fresh regeneration gas" includes free-oxygen-aontaining gases such as air or oxygen enriched or deficient air which pass 30 into the dense-phase bed of the regeneration zone to allow oxidation of coke from the spent catalyst and essentially complete conversion of CO. Usually the fresh regeneration gas will be air. Free-oxygen refers to uncombined oxygen present in a regeneration gas.

The term "partially spent regeneration gas" refers 43837 - 13 - to regeneration gas which has contacted catalyst within the dense-phase bed and which contains a reduced quantity of free-oxygen as compared to fresh regeneration gas. Partially spent regeneration gas will generally 5 contain several volume percent each of nitrogen, free- oxygen, carbon monoxide, carbon dioxide, and water. More specifically, the partially spent regeneration gas will generally contain from 7 to 14 vol.% each of carbon monoxide and carbon dioxide.

The term "spent regeneration gas" means regeneration gas which contains a reduced concentration of CO as compared to partially spent regeneration gas. Preferably the spent regeneration gas will contain less than 1000 ppm of CO and more typically and preferably, less than 15 500 ppm. CO· Free oxygen, carbon dioxide, nitrogen, and water will also be present in the spent regeneration gas.

The free-oxygen concentration of the spent regeneration gas will generally be greater than 0.1 vol.% of the present regeneration gas.

The terms "dense-phase" and "dilute-phase" are commonly used terms in the art of FCC to generally characterize densities of the fluid catalyst bed in various parts of the regeneration zone. While the demarcation density is somewhat ill-defined, the term "dense-25 phase" as used herein generally refers to regions within the regeneration zone where the catalyst density is greater than 240 kg/m3 whereas "dilute-phase" generally refers to regions where the catalyst density is less than about 240 kg/m . Usually the dense-phase density will be 30 in the range of from 320 to 640 kg/m or more and the dilute-phase density will be much less than 240 kg/m and typically in the range of from 1.6 to 80 kg/m3. Catalyst densities within FCC vessels are commonly measured by measuring pressure or head differences across pressure 35 taps installed in the vessels and spaced at known distances apart. 4383? - 14 - In the process of the present invention coke oxidation and essentially complete catalyzed conversion of CO to CO2 are initiated and take place within a dense-phase fluid catalyst bed in the regeneration zone 5 and at least a portion of the heat of combustion of CO is recovered by the regenerated catalyst for use within the FCC process. Regenerated catalyst which passes to the hydrocarbon reaction zone is therefore at a higher temperature than regenerated catalyst produced by a non-10 CO-burning regeneration zone thereby permitting a reduction or elimination of external feed preheat. Additionally, the CO conversion is controlled to ensure essentially complete elimination of atmospheric CO pollution without the requirement of an external CO 15 boiler. Moreover the process of the invention is applicable to present-day regeneration units without extensive modifications or revamp.

Additionally it is a feature of the process that the essentially complete conversion of CO to CO2 is 20 catalyzed by catalytically effective amounts of a CO conversion promoter which passes as part of the fluid cracking catalyst through the FCC process. The rate of coke oxidation is not affected by employing a fluid catalytic cracking catalyst containing a CO conversion 25 promotor, nor is the conversion of hydrocarbons within the hydrocarbon conversion zone, but the rate of CO conversion is increased. With a CO conversion promotor the kinetic rate constant for the reaction CO + iOj + C02 may be increased typically from 2 to 5 times or more. 30 Thus a faster rate of CO conversion can be obtained in the presence of a CO conversion promotor at a given regeneration zone temperature and oxygen concentration than aan be obtained without the promotor. Since perfect dispersion and ideal mixing of the fresh 35 regeneration gas within the catalyst in the dense-phase bed are never achieved, it has often happened that the rate of reaction of CO oxidation must be increased to - 15 - » ο a Ο *7 kJOlJ ί ensure that essentially complete conversion of CO occurs within the dense bed. The rate of reaction has been increased by increasing the regeneration zone temperature or by increasing the fresh regeneration gas 5 (oxygen concentration). Regeneration zone temperatures were increased by such methods as burning torch oil in the regeneration zone, increasing the amount of slurry oil recycle to the hydrocarbon conversion zone thereby producing more coke to be burned, preheating the fresh 10 regeneration gas to the regeneration zone, preheating the feed to the hydrocarbon conversion zone or by a combination of such methods. Such methods generally increase the operating cosn of the FCC process and take away some of the flexibility of the FCC process.

Employing an FCC catalyst containing catalytically effective amounts of a CO conversion promotor permits a reduction or elimination of torch oil burning and slurry oil recycle, a reduction or elimination of fresh regeneration gas and feed preheat, and a reduction in 20 the amount of excess fresh regeneration gas required for essentially complete conversion of CO within the regeneration zone.

Suitable catalysts for use in the process of our invention can comprise any of the catalyst known to the 25 art of fluid catalytic cracking and containing catalytic-ally effective amounts of a CO conversion promotor. The term "catalytically effective amounts" generally means such amounts of a promotor as will increase the kinetic rate constant of CO conversion to C02· Such amounts can 30 be from a few weight parts per million up to about 20 wt.% or more of the FCC catalyst. More preferably such amounts will range from 100 wt. ppm. to lo wt.% of the FCC catalyst.

Suitable CO conversion promotors broadly comprise 35 one or more oxides selected from the transition metals and the rare earth metals. Particularly suitable CO 4 3 8 31; - 16 - conversion promotors comprise one or more oxides selected from the group consisting of vanadium oxide, chromium oxide, manganese oxide, iron oxide, cobalt oxide, nickel oxide, copper oxide, palladium oxide, platinum oxide, and rare earth metal oxides. The CO conversion promotors can be incorporated into amorphous PCC catalysts comprising silica and/or alumina or into any of the zeolite-containing FCC catalysts by any suitable method known to the catalyst manufacturing art 10 such as coprecipitation or cogelling or impregnation. Suitable zeolites include both naturally occuring and synthetic crystalline aluminosilicate materials known to the art such as faujasite, mordenite, chabazite, type X and type Y zeolites, and the so-called "ultrastable" 15 crystalline aluminosilicate materials.

In order to initiate and sustain essentially complete combustion of CO to C02 within the dense bed of a regeneration zone two requirements must be met: the dense bed temperature must be high enough to produce a 20 sufficiently fast rate of reaction of CO oxidation and. the quantity of fresh regeneration gas must be at least sufficient stoichiometrically for essentially complete CO oxidation.

The rate of reaction of CO oxidation must be 25 sufficiently fast to permit essentially complete combustion of CO within a reasonable gas residence time in the dense bed of the regeneration zone. If the rate of reaction is too slow, it is possible that all of the CO combustion will not be completed in the time interval 30 that partially spent regeneration gas is in the dense bed where there is sufficient catalyst density to absorb the heat of reaction. In this situation, CO conversion can then take place in the dilute phase region of the regeneration zone or in the flue gas line outside of the 35 regeneration zone where it is not desirable. Temperature above some minimum with or without the presence of a CO 4383? - 17 - conversion promotor is therefore important to ensure the proper rate of reaction.

The proper quantity of fresh regeneration gas is important because without sufficient oxygen present to 5 support the reaction of CO oxidation to C02, the reaction will not occur no matter what the temperature is in the regeneration zone. Furthermore, it is important that some excess of fresh regeneration be present beyond that stoichiometrically required to ensure the essentially 10 complete conversion of the CO.

It is generally recognized that fcc catalyst regeneration zone operation is essentially adiabatic.

While it is true that some heat is lost to the surroundings that amount of heat is a small fraction of the 15 total heat released. Since regeneration zone operation is essentially adiabatic, the regeneration zone temperature is a direct function of the amount of fuel burned in the regeneration zone. As the total amount of fuel increases the regeneration zone temperature increases.

Until intentional conversion of CO to C02 is initiated in the regeneration zone, the fuel is primarily coke on spent catalyst but will also include any adsorbed or interstitial hydrocarbons passing into the regeneration zone with the spent catalyst or any "torch oil" burned 25 in the regeneration zone. Indeed, during initial FCC process start-up the fuel is primarily torch oil until sufficient coke has been built up on the catalyst. When intentional conversion of CO to C02 is initiated then CO contributes significantly to the total fuel burned in the 30 regeneration zone.

Thus by controlling either the amount of fuel passed into the regeneration zone or the fresh regeneration gas which would allow the fuel to be burned, the regeneration zone temperature can be controlled at any temperature 35 from 399°C. uo to 760°C. The amount of coke can typically £333? - 18 - be controlled by varying the hydrocarbon reaction zone operating conditions such as temperature or by varying the composition of the feedstock to that reaction time.

\ Specifically, more coke is produced as the hydrocarbon 5 reaction conditions become more severe or as the feedstock becomes heavier, that is, as the Conradson carbon content increases.

It has been common practice to limit the operating temperatures of conventional (non-CO-burning) regeneration zones to about 677°C. On 3?CC processes employing 10 amorphous catalysts this was generally done by limiting the hydrocarbon reaction zone temperature to some maximum or by limiting the amount of coke-producing slurry oil recycled to the hydrocarbon reaction zone to some maximum. These maximums are determined, for any 15 particular feedstock, primarily by operating experience on the FCC process. With an FCC process employing zeolite-containing catalysts where less coke was produced it often became necessary to burn torch oil to maintain a regeneration zone temperature of about·677°C. A temperat-20 ure near 677°C was desired to produce the hottest possible regenerated catalyst yet the temperature was limited to a maximum of about 677°C. both for possible metallurgy limitations and because the rate of reaction of afterburning, should it occur during process upsets, 25 was relatively slow.

In the process of our invention spent catalyst containing catalytieally effective amounts of a CO conversion promotor and fresh regeneration gas are first passed to a dense-phase fluid catalyst bed. in the 30 regeneration zone. The fresh regeneration gas is initially passed into the dense bed at a first flow rate sufficient to oxidize coke to produce partially spent regeneration gas. This first flow rate is preferably in the range equivalent to 8 to 12 grams of air per gram of 35 coke entering the regeneration zone. Coke is then oxidized at first oxidizing conditions to produce regenerated catalyst and £3837 - 19 - partially spent regeneration gas.

The first oxidizing conditions include a dense bed temperature of from 399°c. to 677°C., not because of any metallurgical limitation but because the rate of 5 reaction of afterburning, should it occur during unsteady startup conditions, is relatively slow. During startup, torch oil will be burned in the regeneration zone until sufficient coke is deposited on the catalyst in the hydrocarbon reaction zone. Thereafter torch oil 10 will gradually be reduced or eliminated as the amount of coke on spent catalyst increases and tha dense bed temperature will be limited to about 677°C. by the methods described above, other first oxidizing conditions will generally include an operating pressure of from 15 atmospheric pressure to 4.4 atm. with the preferred range being from 2 to 3.7 atm. Additionally, superficial fresh regeneration gas velocities will be limited to the transport velocity, that is, the velocity past which the catalyst would be carried out of the dense bed upward 20 into the dilute phase region. Superficial gas velocities will therefore preferably be less than about 1 metre per second with 0.5 to 0.8 metre per second being the usual range.

After coke is being oxidized to produce regenerated 25 catalyst and partially spent regeneration gas the dense bed temperature is then increased to a second temperature of from 677°C. to 760°C. so that the rate of CO oxidation when it is allowed to occur will be sufficiently fast to ensure essentially complete convers-30 ion of CO to C02 within the dense bed. The temperature can be increased by any of several methods or combination of methode. The severity of operating conditions in the hydrocarbon reaction zone can be increased, thereby producing more coke on spent catalyst; the amount of 35 slurry oil recycle to the hydrocarbon reaction zone can be increased to produce more coke on spent catalyst; i- 43837 - 20 - torch oil can again be added or increased to the regeneration zone; stripping of spent catalyst can be reduced thereby allowing more combustible material to pass with the spent catalyst into the regeneration zone; 5 or, a heavier feedstock can be employed.

The fresh regeneration gas is next increased from the first flow rate to a second flow rate stoichio-metrically sufficient to permit essentially complete oxidation of CO to C02, thereby producing spent regenerat-10 ion gas. This second flow rate is preferably in the range equivalent to 12 to 16 grams of air per gram of coke entering the regeneration zone. Carbon monoxide ie then oxidized in the dense bed at second oxidizing conditions to produce spent regeneration gas. With the dense bed at 15 a temperature of from 677°C. to 760°C., essentially complete conversion of CO to C02 within the dense bed occurs essentially spontaneously as soon as the fresh regeneration gas rate is increased to the second flow rate. Since the oxidation of CO is exothermic it will 20 not be necessary,· once CO oxidation has been initiated to continue the measures that were employed to increase the dense bed temperature to the second temperature.

Second oxidizing conditions include a catalyst bed temperature from 677°C. to 760°C. and a superficial fresh 25 regeneration gas velocity limited as described above to the transport velocity. Operating pressure will generally be from atmospheric pressure to 4,4 atm. with the preferred range being from 2 to 3.7 atm. .

At this stage of regeneration zone operation, it is 30 possible that normal variations which occur in feedstock flow rate and particularly composition will result in intervals in which all of the CO is not essentially completely converted to COj. The flow rate of fresh regeneration gas at this state of operation is just 35 sufficient for essentially complete oxidation of CO to 4SS37 - 21 - COj with no provision for an excess. The CO concentration of the spent regeneration gas may increase during these intervale from a preferred concentration of less than 500 ppm. to several thousand ppm. CO. The process 5 of our invention includes steps to prevent this and to ensure the essentially complete combustion of CO to CO2 in spite of such variations.

Specifically in our process the spent regeneration gas is analyzed by analyzing means to obtain a measured 10 free-oxygen concentration and that measured concentration is then compared with a predetermined free-oxygen concentration. The predetermined free-oxygen concentration of the spent regenertation gas will represent, an amount of free-oxygen in excess of that stoichiometrically 15 required for CO oxidation. Thereafter/ the fresh regeneration gas rate is regulated at a third flow rate to maintain a measured free-oxygen concentration equal to the predetermined free-oxygen concentration thereby ensuring essentially complete conversion of CO to COg. The third 20 flow rate will therefore be higher than the second flow rate. Typically the third flow rate will be equivalent to 13 to 17 grams of air per gram of coke.

The free-oxygen concentration of the spent regeneration gas will generally be greater than 0.1 25 volume percent of the spent regeneration gas stream and more specifically can be from 0.1 vol.% free oxygen to 10 vol.% or more free oxygen. Preferably, the free-oxygen concentration will be from 0.2 vol% to 5 vol.% of the spent regeneration gas and more preferably will be 30 from 1 vol.% to 3 vol.%.

The analyzing means used in the process of this invention to measure the free oxygen concentration in the spent regeneration gas can include any apparatus capable of measuring the concentration of O2 in a gas 35 mixture comprising 02, CO, COj, K2, H2, and light hydro- 43837 - 22 - carbons in concentrations ranging from volume parts per million to many volume percent. Specifically included are Orsat, gas chromatographic, and mass spectrographic apparatus. Samples of flue gas may be periodically with-5 drawn manually from the process and manually analyzed or may be automatically withdrawn and analyzed continuously or at programmed time intervals by sampling and analyzing means.

After the measured free-oxygen concentration has 10 been determined and compared with the predetermined free-oxygen concentration a regulating means will be adjusted manually or automatically if necessary to pass more Or less fresh regeneration gas into the regeneration zone.

Typically, the regulating means will comprise a valve 15 for controlling flow or a control device which can control speed or discharge pressure of a fresh regeneration gas compressor to change the flow rate of fresh regeneration gas into the regeneration zone. In an automatic system, the analyzing means may generate and send 20 to a control means an output signal representing the measured free-oxygen concentration. The control means may typically connect the analyzing means to the regulating means or may be incorporated within the design of either and have a variable setpoint representing the 25 predetermined free-oxygen concentration. The control means receives the analyzing means output signal, compares, it to the setpoint value and if a differential exists, passes a signal to the regulating means to change the fresh regeneration gas rate into the regeneration zone 30 so that the measured free-oxygen concentration in the spent regeneration gas will equal the predetermined free-oxygen concentration. The analyzing means, control means, and, regulating means may all be connected by methods 1 known in the art and can be incorporated into a single 35 control unit. 4383? - 23 - The following examples are presented to illustrate some of the features and advantages of the process of our invention.

EXAMPLE X.

In this example coke and CO were oxidized in a regenerator operating at a dense bed temperature of about 732°C. and a pressure of about 3.7 atm. Approximately 945,000 kg/hr of spent catalyst containing about 0.8 wt.% coke was passed into the regenerator while the input of 10 air to the regenerator was maintained at a ratio of about 14.60 grams of air per gram of coke.

The air input rate to the regenerator was controlled to maintain a predetermined free-oxygen concentration in the spent regeneration gas to about 1-2 vol.%. The 15 conversion of CO to C02 was substantially complete and was maintained steadily and continuously within the dense bed of catalyst in the regenerator. The superificial gas velocity was about 0.85 metre/second.

By being able to control the conversion of CO in the 20 dense bed of the regenerator the reactor temperature was able to be raised to about 538°C. with no addition of feed preheat which increased conversion and the quantity of gasoline and lighter compounds produced.

EXAMPLE IX.

In this example, a comparison is made between the operations of a commercial FCC unit before and after essentially complete CO conversion was initiated and controlled. 43837 - 24 - TABLE I Commercial FCC Operation Before and After CO Conversion Without CO Conversion CO Conversion Taking Place Reactor Temperature, °C. 530 530 Regenerator Dense Phase Temp., °C. 677 732 Regenerator Dilute Phase Temp., °C. 699 734 Feed Preheat Temp. 363 260 Conversion, L.V. % 79.4 79.1 Coke Yield, wt, % 5.4 4.6 Gasoline Yield, L.V. % 63.2 65.6 CO in Flue Gas, Vol. % 10.1 0.0* C02 in Flue Gas, Vol. % 9.7 16.7 02 in Flue Gas, Vol. % 0.2 2.1 * Actual determination was 350 ppm.

The above data demonstrates the advantages of reduced feed preheat, higher conversion, and higher gasoline yield made possible by the process of our 5 invention. As well, CO pollution has essentially been eliminated without the requirement of an external CO boiler.

EXAMPLE XXI.

This example shows a comparison of operations 10 from a commercial FCC process before and after an FCC catalyst containing a CO conversion promotor was used in the regeneration zone where, for both operations, i S837 - 25 - essentially complete conversion of CO to C02 was taking place, Data are shown in Table 2.

TABLE 2 FCC Process Before and After CO Conversion Promoter Before After Reactor Temperature, °C, 535 533 Peed Rate, m3/hr. 185 178 Slurry Oil Recycle, m3/hr. 7.8 5.7 Peed Preheat, °C.

Regenerator Temperature, °C. 169 185 Cyclones 780 738 Dilute Phase 717 703 Dense Phase 715 703 Air Heater 169 185 Air Rate, m3/min. 2,040 1,810 Superficial Velocity, m/sec. 1.1 0.9 Spent Regen. Gas Analysis C02, vol.% 12.5 16.5 02, vol. % 4.4 1.2 CO, vol. ppm. <500 <500 4383*? -26- The comparison shows a significant reduction in air 3 3 rate of from 2,040 m /min to 1,810 m /min made possible by employing an FCC catalyst containing a CO conversion promotor. This reduction in air rate reduced the super-5 ficial velocity of the air in the regeneration zone from 1.1 m/sec to 0.9 m/sec and resulted in lower catalyst loss from the regeneration zone. Lower regeneration zone temperatures, a reduced slurry oil recycle, and a smaller excess of 02 in the spent regeneration gas are also shown 10 for the operation which employed catalyst containing a CO conversion promoter.

Claims (13)

4383? - 27 - CLAIM Si-

1. A process for the regeneration of coke-contaminated fluid catalytic cracking «atalyst containing catalytically effective amounts of a CO conversion 5 promotor and for the essentially complete catalytic conversion of carbon monoxide to carbon dioxide, which process comprises the steps of: a. passing to a dense-phase fluid catalyst bed in a regeneration zone said catalyst and fresh regeneration 10 gas at a first flow rate sufficient to oxidize coke to produce partially spent regeneration gas; b. oxidizing coke at first oxidising conditions including a catalyst bed first temperature of from 399°C. to 677°C. to produce regenerated catalyst and partially 15 spent regeneration gas containing CO; c. increasing the catalyst bed temperature from said first temperature to a second temperature of from 677°C. to 760°C.; d. passing to the catalyst bed fresh regeneration 20 gas at a second flow rate stoichiometrically sufficient to essentially completely oxidize CO to C02; e. oxidizing in said catalyst bed, maintained at second oxidizing conditions including a catalyst bed second temperature of from 677°C. to 760°C. and the 25 presence of said CO conversion promotor, CO to produce spent regeneration gas; f. analyzing spent regeneration gas to obtain a measured free-oxygen concentration and comparing the measured free-oxygen concentration to a predetermined 30 free-oxygen concentration; and, g. thereafter regulating fresh regeneration gas at a third flow rate to maintain the measured free-oxygen concentration equal to the predetermined free-oxygen concentration thereby ensuring essentially complete ^3837 - 28 - conversion of CO to C02·

2. The process of Claim 1 wherein said CO conversion promotor comprises one or more oxides selected from vanadium oxide, chromium oxide, manganese oxide, iron 5 oxide, cobalt oxide, nickel oxide, copper oxide, palladium oxide, platinum oxide, and rare earth metal oxides.

3. The process of Claim 1 or 2 wherein said regeneration zone comprises a dense-phase catalyst bed and a dilute-phase catalyst region superimposed over said bed.

4. The process of any of Claims 1 to 3 wherein said first flow rate of fresh regeneration gas is equivalent to 8 to 12 grams of air per gram of coke.

5. The process of any of Claims 1 to 4 wherein said second flow rate of fresh regeneration gas is 15 equivalent to 12 to 16 grams of air per gram of coke.

6. The process of any of Claims 1 to 5 wherein said partially spent regeneration gas contains from 7 to 14 vol.% each of CO and C02·

7. The process of any of Claims 1 to 6 wherein 20 said predetermined free-oxygen concentration is within the range of from 0.1 to 10 vol.% of the spent regeneration gas.

8. The process of Claim 7 wherein said predetermined free-oxygen concentration is within the range 25 of from 0.2 to 5 vol.% of the spent regeneration gas.

9. The process of any of claime 1 to 8 wherein said spent regeneration gas contains less than 1000 ppm. CO.

10. The process of Claim 9 wherein said spent 30 regeneration gas contains less than 500 ppm. CO.

11. The process of any of Claims 1 to 10 being operated within a pressure range of from 1 to 4.4 atmospheres.

12. A process for the regeneration of coke- 4383? - 29 - contaminated fluid catalytic cracking catalyst as claimed in Claim 1 and carried out substantially as described in any of the foregoing Examples.

13. A fluid catalytic cracking process wherein a 5 hydrocarbon feed is catalytically cracked in the presence of a fluid catalytic cracking catalyst containing catalytically effective amounts of a CO conversion promotor and when the catalyst has become contaminated with coke it is regenerated by a process according to 10 any of Claims 1 to 12 and reused in a fluid catalytic cracking process. F. R. KELLY & CO. AGENTS FOR THE APPLICANTS.