CA1046483A - Regeneration of cracking catalyst - Google Patents

Abstract

REGENERATION OF CRACKING CATALYST
(D#73,215-C2-F) ABSTRACT
A process for the regeneration of coke-contaminated fluidizable catalytic cracking catalyst wherein the regeneration flue gas having a reduced concentration of carbon monoxide and regenerated catalyst having a reduced residual carbon content are obtained. By this method a fluidized dense catalyst phase of coke-contaminated catalyst is regenerated with an excess amount of oxygen-containing regeneration gas at an elevated temperature such that there is a controlled afterburn of carbon monoxide to carbon dioxide in the dilute catalyst phase whereby a flue gas having a carbon monoxide content of from 0 to 500 ppm is obtained. The residence time of catalyst in the fluidized dense catalyst phase is adjusted to provide a low level of residual carbon-on-regenerated-catalyst.

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Description

~0~6~83 BACKGROUND OF THE INVENTION
This invention relates to an improved process for regenerating fluidizable catalytic cracking catalyst. In particular, it is related to a method of operating the regenerator of a fluid catalytic cracking unit (FCCU) having a single fluidized dense catalyst phase wherein coke-con-` taminated fluidizable catalytic cracking catalyst is con-tacted with an oxygen-containing regeneration gas in order to obtain a regenerated catalyst having a low carbon content while producing a regenerator effluent flue gas having a carbon monoxide content substantially lower than obtained -heretofore.
The fluidized catalytic cracking of hydrocarbons is well-known in the prior art and may be accomplished using a variety of continuous cyclic processes which employ fluid-ized solids techniques. In such fluid catalytic cracking `~
processes hydrocarbons are converted under conditions such ~; that substantial portions of a hydrocarbon feed are trans-formed into desirable products such as gasoline, liquefied petroleum gas, alkylation feedstocks and middle distillate blending stocks with concomitant by-product formation of an undesirable nature, such as gas and coke. When substantial amounts of coke deposition occur, reduction in catalyst . ~
activity and, particularly, catalyst selectivity results .i ,., ~1 thereby deterring hydrocarbon conversion, reducing gasoline ,, production and simultaneously increasing the production of less desired products. To overcome such catalyst deacti-vation through coke deposition, the catalyst is normally withdrawn from the reaction zone and passed to a stripping zone wherein entrained and absorbed hydrocarbons are ini-.~ i .
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10~6~3 tially displaced from the catalyst by means of stripping medium such as steam. The steam and hydrocarbonsare re~
moved and the stripped catalyst is passed to a regeneration zone where it is contacted with an oxygen-containing gas to effect combustion of at least a portion of the coke and thereby regenerate the catalystO Thereafter, the regenera-ted catalyst is reintroduced to the reaction zone and therein contacted with additional hydrocarbons.
Generally, regeneration processes provide a regenera-tion zone wherein the coke-contaminated catalyst is con-tacted with sufficient oxygen-containing regeneration gas at an elevated temperature to effect com~ustion of the coke deposits from the catalyst. Most common of the regeneration processes are those wherein the contacting is effected in a fluidized dense catalyst phase in a lower portion of the regeneration zone constituted by passing the oxygen-con-taining regeneration gas upwardly through the regeneration zone. The space above the fluidized dense catalyst phase contains partially spent regeneration gases and catalyst ;
entrained by the upward 10wing regeneration gas. This . .
portion of the regeneration zone is generally referred to as the dilute catalyst phase. The catalyst entrained in the i dilute catalyst phase is recovered by gas solid separation - cyclones located in the upper portions of the regeneration zone and is returned to the fluidized dense catalyst phase.
Flue gas comprising carbon monoxide, other by-product gases obtained from the combustion of the coke deposits, inert gases such as nitrogen and any unconverted oxygen is re-covered from the upper portion of the regeneration zone and a catalyst of reduced carbon content is recovered from a . ' ~
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~0~6483 lower portion of the regeneration zone.
In the regeneration of catalytic cracking catalyst, particularly high activity molecular sieve type cracking catalysts, it is desirable to burn a substantial amount of coke from the catalyst such that the residual caxbon content of the regenerated catalyst is very low. A carbon-on-regenerated-catalyst content of about 0.15 weight percent or less is desirable. Cracking catalysts with such a reduced carbon content enable higher conversion levels within the reaction zone of the FCC unit and improved selectivity to gasoline and other desirable hydrocarbon products.
Most of the prior art processes for regenerating fluid catalytic cracking catalyst generally involve contacting the coke-contaminated catalyst in the fluidized dense catalyst phase at a temperature of from about 1100F. to about 1200F.
for a sufficient period of time to reduce the carbon content ~-of the catalyst to the desired level. Such processes are undesirable in that the carbon content of the regenerated catalyst is generally reduced only to a level of from about 0.3 to about 0.5 weight percent and because a flue gas is obtained containing large amounts of carbon monoxide which must be treated prior to discharge into the atmosphere.
It is known that increasing the temperature of the fluidized dense catalyst phase will reduce the residual carbon level of the regenerated catalyst. However, pro-cesses in which the temperature of the fluidized dense catalyst phase exceeds about 1200F. generally involve elaborate modifications to counteract the effects of after-burning in the dilute catalyst phase. By after-burniny is meant the further oxidation of carbon monoxide -to carbon .
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~0464~3 dioxide in the dilute catalyst phase. Whenever after-burning occurs in the dilute catalyst phase, it is generally accompanied by a substantial increase in the temperature due to the large quantities of heat liberated. In such circum-stances the dilute phase temperature may exceed about 1500F. and, in severe cases, may increase to about 1800F.
or higher. Such high temperatures in the dilute catalyst phase are deleterious to the entrained catalyst present in the dilute catalyst phase and result in a permanent loss of catalytic activity, thu~ necessitating an inordinately high rate of catalyst addition or replacement to-the process in order to maintain a desired level of catalytic activity in the hydrocarbon reaction zone. Such high temperatures are "
. -additionally undesirable because of the damage which may result to the mechanical components of the regeneration -zone, particularly to cyclone separators employed to sepa-rate the entrained catalyst from the flue gas.
It is kno~^m that commonly employed catalytic cracXing catalysts such as amorphous silica-alumina, silica-alumina zeolitic molecular sieves, silica-alumina zeolitic molecular sieves ion-exchanged with divalent metal ions, rare earth metal ions, etc., and mixtures thereof, are adversely 'I affected by exposure to excessively high temperatures. At `~ temperatures of approximately 1500~F. and higher, the struc-ture of such catalytic cracking catalyst undergo physical -change, usually observeable as a reduction in the surface area with resulting substantial decrease in catalytic acti-- vity. Consequently, it is desirable to maintain the tem-peratures within the regeneration zone at levels below which `
there is any substantial physical damage to the catalyst.
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,' ' ~O~ 3 Known methods for regenerating fluid catalytic cracking catalysts to low carbon contents, while avoid excessively high dilute catalyst phase temperatures, are generally unsatisfactory. In some processes a cooling medium which may comprise steam, liquid water, unregenerated catalyst, hydrocarbon oil, flue gas, etc., is brought into heat ex-change contact with the dilute catalyst phase either to absorb the heat liberated by after-burning which may occur therein or to prevent the occurrence of after-burning. See, for example, U.S. Patents 2,382,382; 2,580,827; 2,454,373;

2,454,466; 2,374,660; 2,393,839; and 3,661,799.
Other methods employ multiple catalyst regen~ration zones to provide sufficient residence time for contacting the coke~rcontaminated catalyst with an oxygen-containing regeneration gas to burn the coke deposits therefrom at a temperature at which after-burning will not occur. See, for example, U.S. Patents 3,563,911; 2,477,345; 2,788,311;

3,494,858; 2,414,002; and 3,647,714. Still other methods such as those disclosed in U.S. Patents 2,831,800 and i~ 20 3,494,858 teach multiple zone regeneration of coke-con-taminated catalyst, but are silent with respect to control of dilute phase temperatures. Still another approach em-ployed involves indirect heat exchange such as steam gene-.
ration coils employed in the fluidized dense catalyst phase.
All of the above methods are unsatisfactory in that the processes involved cumbersome additional processing steps for absorbing h~at liberated due to after-burning in the : dilute catalyst phase or require expensive facilities for .
the treatment of the regeneration flue gas stream, because of the avoidance of after-burning in the regeneration zone ., ~
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and the resultant substantial carbon monoxide content in the flue gas, generally ranging from about 2 to about 6 volume percent, or higher.
Summary of the Invention ~ _ . . . ..
Now, according to the present invention, an improved method for regenerating a coke-contaminat~d cracking cata-lyst has been discovered wherein a regenerated catalyst ; having a low residual carbon content of about 0.15 weight percent or less is obtained and wherein the carbon monoxide content of the flue gas from the regeneration process may be maintained at about 500 ppm or less, and preferably 10 ppm or less.
The process of the present invention comprises con-tinously introducing a cok~-contaminated catalyst from a fluid catalytic cracking unit into a fluidized dense cata-lyst phase of a regeneration zone maintained at a tempera-ture of from about 1250F. to about 1350F., and contacting the coke-contaminated catalyst therein with an oxygen-containing regenera~ion gas in an amount in excess of that : . .
required for burning essentially all of the coke to carbon dioxide and to provide from about 1 to about 10 mol% oxygen - in the regeneration flue gas. The coke-contaminated cata-lyst is maintained within the dense phase fluidized bed for - a period of at least about 3 minutes, and up to about 10 ~ minutes, as required, to provide a regenerated catalyst with ;~ a residual carbon content of about 0.15 weight percent or less in a single regeneration step. - -By following the method of the present invention the amount of carbon monoxide contained in the partially spent regeneration gases leaving the fluidized dense catalyst .

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phase is maintained at a sufficiently low level such that the amount of after-burn in the dilute catalyst phase is ;
such that the temperatures obtained therein are maintained at less than about 1455F., and generally within a range of about 1375F. to about 1455F. This process affords re-generated catalysts at lower residual carbon contents than ~;
heretofore known, while maintaining regeneration zone tem-- peratures at levels below those at which the catalyst suf-fers any substantial loss of activity, or at which mecha-10 nical components of the regeneration zone are damaged. `-Moreover, the instant process has the further advantage of producing a regenerator flue gas having a carbon monoxide content of about 500 ppm or less without employing addition-al flue gas treating facilities. A still further benefit of the process of this invention resides in the substantially reduced inventory of catalyst required in the regeneration ~-zone, as contrasted with regeneration processes known in the art.
~ Detailed Description of the Invention ; 20 According to the process of this invention, a fluidiz-able catalytic cracking catalyst which has been partially deactivated by the deposition of carbonaceous deposits upon the surface thereof (hereinafter rsferred to as coke-con-taminated catalyst) in a fluidized catalytic cracking pro-cess is introduced into a fluidized dense catalyst phase of a regeneration zone wherein it is contacted with an oxygen-containing regeneration gas for the purpose of burning the carbonaceous deposits from the catalyst thereby to xestore its activity. The regeneration zone generally comprises a regeneration vessel in which there is a fluidized dense .

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~ ' ' ,, . ' ' ' ' ,;, , S~46~3 catalyst phase in the lower portion thereof and a dilute catalyst phase in the upper portion thereof. The oxygen-containing regeneration gas is introduced into the lower portion of the regeneration zone thereby to maintain the catalyst in a fluidized dense catalyst state. A flue gas is recovered from the top of the regeneration zone comprising carbon monoxide and other by-products of the combustion of the coke deposits contained on the coke-contaminated cata-lyst.
The fluidized dense catalyst phase is generally main-tained at a density of from about 10 to about 60 lb/ft3 and preferably at a density of from about 20 to about 40 lb/ft3 by the upward flow of the oxygen-containing regeneration gas, which is introduced at a lower portion in the regene-ration zone. The catalyst in the lower portion of the regeneration zone is maintained in a fluidized dense cata-lyst phase in order to obtain good heat transfer throughout the bed and to avoid localized hot spots and their conco-mitant high temperatures, which are known to adversely affect the catalyst. In order to maintain the catalyst in a -fluidized state, a superficial vapor velocity of the regenera-tion gas of from about 0.2 to about 6.0 ft/sec. is general-ly maintained. The regeneration vessel is generally sized to provide a superficial vapor velocity within the aforemen-,.~ . .
tioned range when operating with the desired residence timefor the catalyst in the regeneration æone and with the required amount of oxygen-containing regeneration gas to , effect the combustion of the coke from the catalyst in the ,...................................................................... ...
reaction zone. Additionally, it is possible to control the superficial vapor velocity within the desired range by em-', ' ~

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;i -8-, ~ - -6~3 ploying an operating pressure within the re~eneration zone within the range of from about 1 to about 50 psig, and ~ preferably from about 15 to about 45 psig. If, within these -~ operating parameters, there is nevertheless insufficient oxygen-containing regeneration gas to provide the desired superficial vapor velocities, steam or an inert diluent gas may be combined with the oxygen-containing regeneration gas to provide the desired superficial vapor velocity.
Surprisingly, it has been found that if the fluidized dense catalyst phase is maintained at a temperature in the range of from about 1275F to about 1350F., while con-tacting the coke-contaminated catalyst with an oxygen-containing regeneration gas in the desired amounts, there is obtained a regenerated catalyst with a residual carbon-on-regenerated-catalyst content of 0.15 weight percent or less, and a regeneration zone flue gas in which the carbon monox-ide content is approximately 500 ppm or less, and generally 10 ppm or less. These results are surprisingly, in that it is known that at regenerator temperatures of from about 1100F.
~0 to about 1200F. and higher, an a~terburn of the carbon monoxide contained the regeneration gases leaving the top of the fluidized dense catalyst phase is initiated and high temperatures of 1500F. and higher result in the dilute catalyst phase. It is known that temperatures above about 1500F. are detrimental to the catalyst. The essence of the instant invention resides in maintaining the fluidized dense catalyst phase at a temperature such that the after-burn of carbon monoxide to carbon dioxide is initiated in the fluidized dense catalyst phase and is completed in the di-lute catalyst phase with only a moderate increase in tem-~', .~
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~464~3 perature, such that the temperature in the dilute phase of the regeneration zone does not exceed about 1455F. This controlled afterburn is accomplished by controlling the amount of carbon monoxide in the regeneration gases leaving the fluidized dense catalyst phase, such that the tempera- :
ture in the dilute catalyst phase is in the range of from about 1375F. to about 1455F. and preferably from about 1400F. to about 1455F.
In view of the environmental considerations, it is im~
10 portant that the concentration of carbon monoxide, which is -known to be a severe air pollutant, be maintained at as low a level as possible in the regeneration flue gas. In the ;process of this invention carbon monoxide concentrations in the regeneration flue gas may be maintained at 500 ppm or less, and generally at 10 ppm or less, without additional treatment of the regeneration flue gas.
The amount of oxygen-containing regeneration gas necessary in the practice of the process of this invention will depend upon the amount of coke-contamination on the catalyst being introduced into the regeneration zone.
Generally, oxygen in provided in an amount sufficient to effect the complet~ combustion of coke from the catalys~ and to provide an oxygen concentration in the flue gas from the regeneration zone of from about 1 to about 10 mol% and preferably from about 3 to about 10 mol%. The oxygen-con- -taining regeneration gas is generally introduced into the lower portion of the regeneration zone, however, if desired, a portion of the oxygen-containing regeneration gas may be introduced into the dilute catalyst phase. It is by supply-ing this excess oxygen that it is possible to reduce the ...

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carbon monoxide content of the regeneration flue gas to the ., ~
low levels hereinbefore mentioned.
In one embodiment of the method of the present inven-tion still higher oxygen-containing regeneration gas rates are employed in order to provide temperature moderation in the fluidized dense catalyt phase and/or in the dilute catalyst phase of the regeneration zone.
The oxygen-containing regeneration gas which may be employed in practicing the process of this invention in-- 10 cludes gases which contain molecular oxygen in admixture with other inert gases. Air is a particularly suitable regeneration gas. Additional gases which may be employed include oxygen in combination with carbon dioxide and/or other inert gases. Additionally, if desirable, steam may be added as a part of the regeneration gas mixture.
In practicing the method of the present invention to obtain a regenerated catalyst having a carbon-on-regenera-ted-catalyst content of about 0.15 weight percent or less, it is necessary to maintain the coke-contaminated catalyst ~;
in the fluidized dense catalyst phase at the aforementioned conditions for a period of from about 3 to about 10 minutes.
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~ of course, longer residence times may be employed, although Q~, generally there is no advantage in so doing. It is an :
advantage of the process of the present invention that catalyst residence times in the regeneration zone may be substantially decreased over residence times employed in . .
other prior art processes. Thus, it is possible to operate ~, the process of this invention at a substantially reduced , catalyst inventory within the fluidized catalytic cracking unit. The residence time of the catalyst within the flu-: .

~0~6483 idized dense catalyst phase is maintained at the desired level by adjustment of the depth of the fluidized dense catalyst phase within the regeneration zone. ;
In general, the amount of coke contained on the coke-contaminated catalyst obtained from conventional fluid catalytic cracking operations will be in the range of from about 0.8 to about 1.0 pounds of coke per pound of catalyst.
This amount of coke, if burned to produce a regenerated catalyst with a carbon content of about 0.15 weight percent 10 or less, will provide sufficient heat in the regeneration -~
zone to maintain the fluidized dense catalyst phase at the desired temperature. However, if the coke content of the contaminated catalyst is too low to maintain the desired ~ . .
temperature in the fluidized dense catalyst phase of the ;~
regeneration zone, torch oil may be introduced into the fluidized dense catalyst phase to supply the necessary heat energy.
This invention will now be further illustrated in the -following examples which are not to be considered as a limitation on the scope of the invention.
EXAMPLE I
A continuous fluidized catalytic cracking process was operated in a pilot unit wherein hydrocarbon charge and fresh regenerated catalyst were combined in the lower por-, tion of a riser and wherein catalyst and hydrocarbon vapor - discharged from the top of said riser into a reaction ves-sel. In said reaction vessel, hydrocarbon vapor disenga~ed ' the used cracking catalyst and the cracking catalyst was maintained as a fluidized bed with the reaction vessel below the riser outlet by the action of primary stripping steam.
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~ 46~83 From the reaction vessel used catalyst was continuously withdrawn into a stripping section wherein strippable hy-drocarbon vapors were removed from the catalyst by the stripping action of steam. From the stripping section, used catalyst was continuously transferred into a reg~neration vessel. The regeneration vessel comprised an upright cylin-drical vessel having means for introducing used catalyst continuously thereto, means for withdrawing regenerated catalyst, a sparger near the bottom of the introduction of oxygen-containing regeneration gas, e.g., air, a cyclone separator near the top of said vessel for the separation of - catalyst from the flue gas resulting from the regeneration of the catalyst, and a vent pipe for removing flue gas from ; the regeneration vessel. The regeneration vessel was equip- '"
ped with valves, piping, thermocouples, pressure gauges, sample taps and flow measuring devices necessary to obtain the data shown in this example. In this example, used catalyst at a temperature of about 950F. was continuously added to the regeneration vessel through a catalyst entry nozzle. In the regeneration vessel, the catalyst was main-` tained in a dense fluidized bed employing air. The catalyst regeneration was operated at increasing dense phase tempera-tures. Orsat analysis of the flue gas and residual carbon analysis of regenerated catalyst were made at different operating conditions. The operating conditions and test , results are shown in Table 1 below.
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109~6~33 Run No. 1 2 3 4 5 6 7 8 Ai~ to re-generator, Dense Phase Temperature, F. 1245 1243 1252 1280 13301391 1491 1411 Flue Gas 10 Analysis(Orsat) - CO2,mol.% 11.8 12.0 12.0 13.0 14.816.4 12.0 12.0 O ,mol.% 0.6 0.4 0.2 0.2 0.8 1.4 5.4 6.2 C~,mol.% 7.8 7.6 6.4 5.6 1.8 0.0 0.6 0.0 Carbon on regenerated Catalyst, wt.%0.32 0.43 0.3 0.2 0.12 0.12 0.12 0.11 Coke Yield (% of fresh feed) - 7.53 7.26 7.70 7.16 7.37 6.19 6.68 As can be seen from the data tabulated in Table 1 above, as the dense phase catalyst bed temperature increased, the amount of carbon monoxide present in the flue gas de-creased. At about 1391F. (Run 6) the carbon monoxide content of the flue gas tested 0% by the Orsat analysis method. Substantially all the carbon monoxide from the combustion of coke was converted into carbon dioxide within the dense phase bed. Consequently, very little or no "after- ;
burning" occurred in the dilute phase. The results shown in column 6 of this experiment, wherein carbon monoxide in the ~ flue gas is substantially eliminated, wherein residual i, 30 carbon upon the regenerated catalyst is reduced to about 0.12 weight percent, and wherein after~burning of carbon monoxide in the dilute phase is not excessive, demonstrate ,~ the advantage of the present invention over regeneration processes known to the prior art.
EXAMPLE II
The process as described in Example I was operated to demonstrate the necessity for obtaining a sufficient tem-.. . .

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~ o~ s3 perature in the dense phase regenerator bed for substanti-ally reducing the Co content in the flue gas and reducing the residual carbon-on-regenerated-catalyst. The second run was operated at a constant regenerator temperature of about 1130F. The air rate was increased to provide substantial excess oxygen in the flue gas. However, as can be seen from the data shown in Table 2 below, the CO content of the flue gas was not substantially reduced and the residual carbon-on-regenerated-catalyst was not reduced.

Run No. 1 2 3 4 5 6 7 8 Air to Regenerator Dense Phase Temperature F. 1122 1106 1114 1036 1130 1116 1129 1132 Flue Gas Analysis (Orsat) 20 C02,mol.% 11.8 11.0 11.4 11.0 8.8 8.0 8.6 9.8 -O ,mol.% 0.6 0.8 0.9 1.0 3.2 3.0 4.4 5.0 ' C~,mol.% 4.6 6.2 5.2 6.0 6.0 5.0 6.0 5.0 Carbon on Regenerated Catalyst, wt.%0.16 0.12 0.45 0.45 0.13 0.20 0.23 0.17 Coke Yield (% of fresh feed) 4.84 5.07 5.29 5.79 5.44 5.47 6.05 5.99 The results of this experiment demonstrate that the 30 temperature of the regenerator dense phase catalyst bed must be increased above normally accepted fluid catal~st regenera-tion temperatures to promote substantially complete con-version of Co to CO2. Further, excess air at relatively low regeneration temperatures is not sufficient to convert substantially all the CO to CO2 within the regeneration . :
zone.

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464~33 EXAMPLE III
The fluidized catalytic cracking unit (FCCU) of Example I was operated to determine the feasibility of operating the FCCU regenerator with excess oxygen and dense phase catalyst bed temperatures sufficiently high to reduce the flue gas CO
concentration to about 10 ppm or less and reduce carbon-on-regenerated-catalyst tCORC) to a low value, preferably about -0.12 weight percent or less. Cracking runs on the FCCU were made on a once through gas-oil charge basis at constant charge rate. Reactor operating conditions (riser ou-tlet temperature, catalyst bed level, and regenerator air rates) were adjusted to obtain a range of regenerator temperatures and flue gas excess oxygen concentrations. Conclusions from - this example include: carbon monoxide concentrations in the flue gas of about 10 ppm or less were obtained without excessive after-burning of CO to CO2, when operating at , ,.
'~ regenerator bed temperature of about 1375F. and higher and with abou-t 1-5 mol.% excess oxygen in the flue gas; carbon-. on-regenerated-catalyst was decreased to less than 0.1 ` 20 ~ weight percent by operating at regenerator bed temperatures of about 1375F. and higher and with about 1-5 mol.% excess oxygen in the flue gas; coke yield was substantially reduced `t` at constant conversion by increasing regenerator tempera-.~ tures from the 1100-1250F. range to about 1375F. and - higher; and cracked naphtha octane values increased about 2 RON (clear) at constant conversion by increasing the regen-erator temperatures from the 1100-1250F. range to about 1375F. and higher.
~- Charge stock employed in this experiment was a refinery virgin gas oil FCCU charge. Properties of this charge stock ~"

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CHARGE STOCK EVALUATION
Description FCCU ~AS-OIL FEED
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Gravity, API 29.5 Aniline Point, F. 180.5 Sulfur, X-Ray wt.% 0.41 ASTM Distillation, F.

lO/20 540/5~4 ~`

Bromine Number Conradson Carbon Residue, wt.% 0.19 Aromatics, wt.% 40.2 Refr~ctive Index at 25C 1.486 20 Basic Nitrogen, wppm 199 Total Nitrogen, wppm 32 Viscosity, ~entistokes at 100F +80 W Absorbance at 285 ~. 4.41 `~
Pentane Insolubles, wt.% 0.07 -The two initial FCCU runs (2616A and 2616B) were made - :.
to determine the approximate minimum regenerator tempera~
- tures required to initiate burning of CO in the regenerator :
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dense phase bed as excess oxygen was added. For run 2616A

the reactor bed level and riser outlet temperature were ad-. ,:
justed to give a regenerator bed temperature of about 1120F. The regenerator air rates then were adjusted to obtain less than 1 vol.% 2 in the flue gas and were main~
- tained at this level for the first two hours of the run.
During these first two hours, carbon-on-regenerated-catalyst (CORC) was found to be in the range of 0.3-0.5 weight percent and flue gas CO2 to CO ratio ranged from 1.8/1 to ~;
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Lo~ 33 2.6/1. Thereafter, the regenerator air rate was increased : every two hours in increments of about 30-40 SCFH in an ; attempt to burn CO to C02 in the regenerator bed. Pertinent operating data and yields from run 2616A are shown in Tables 4A and 4B, following.

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`; ~L04~83 As can be seen in Table 4, carbon monoxide concentration in the flue gas was not reduced to low values - acceptable for pollution control during this run with low - regenerator bed temperatures, even though up -to 6.4 mol percent excess oxygen was present in the flue gas. The CO2 to CO rakio at the end of this run was lower than at the start of the run and no significant increase in regenerator bed temperatures was experienced as would be expected if additional CO had been burned to CO2 within the regenerator ~^~
bed. However, the CORC was improved to about 0.2 weight percenk as a result of a higher oxygen content within the regenerator bed. From this run, it is seen that the 1120F.
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regenerator bed temperature at the start of the run was too low for obtaining a CO burn within the regenerator bed.
The second run, 2516B, using the same procedure as for run 2616A, except reactor conditions (reactor bed level and riser outlet temperature) were adjusted to give a regenerator bed temperature of 1245F. at -the start of the run with less than 1.0 mol percent oxygen in the flue gas.
Thereafter, the air rate was increased in the increments of 40-50 SCFH to provide additional oxygen in the regenerator.
Operating conditions and yields for run 2615B are summarized in Table 5, following.

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' -~09~83 From Table 5, it is seen that as the air rate was increased there was a corresponding increase in the re-generator bed temperature, a decrease in the CO content of the flue gas, and a reduction in the level of carbon-on-regenerated-catalyst. The data indicate that at 1.4 mol percent oxygen in the flue gas and 1391F. regenerator bed temperature, substantially all CO was being consumed in the regenerator. Incremental increases in the regenerator air rate were continued until about 5 to 6 mol percent oxygen in the flue gas was obtained. As air rate increased the regenerator bed temperature to about 1410-1420F. where it lined out with very little CO in the flue gas. At this lined out condition, there was little or no after-burning, ~`
(i.e., burning of CO to CO2 in the dilute phase above the catalyst dense phase bed), indicating that essentially all CO was burned to CO2 in the regenerator dense phase catalyst bed.
From Table 5 it is seen that as the regenerator bed temperature increased from 1245F. to 1410F. during run 2616B, carbon-on-regenerated-catalyst (CORC) decreased from about 0.43 weight perceNt to about 0.04 weight percent; CO
content of the flue gas decreased substantially from about 7 mol percent to about 0.2 mol percent; and debutanized naphtha octane increased from about 90 Research Octane (clear) to about 93.7 Research Octance (clear). Further, from Table 5 it is seen that gas-oil conversion did not change significantly during the course of run 2616B, despite a significant decrease in catalyst to oil ratio.
As the regenerator temperature increased from 1245F.
to 1410F. in the course of run 2616B, it was necessary to ;

,:
. . :

~0~1~4~3 reduce catalyst circulation into the riser reaction zone in order to maintain a cons-tant riser outlet temperature.
Hydrocarbon charge rate was content, consequently the catalyst to oil weight ratio was reduced. In normal, low temperature regeneration, operation of fluid catalytic cracking processes, lower catalyst to oil ratios are ex-pected to result in lower fresh feed conversion values, other conditions being maintaine~ constant. Evidently, during run 2616B reduction of fresh ~eed conversion due to 10 lowering catalyst to oil ratios was offset by increased ;;
conversion due to increased effective catalyst activity as carbon-on-regenerated-catalyst decreased from 0.43 to 0.04 weight percent.
Run 2616B was successful in demonstrating that high temperature regeneration of fluid catalytic cracking cata-lyst could be accomplished at temperatures in the range of about 1245-1420F., with excess oxygen present in the re-generator wherein substantially all the CO was burned to CO2 in the regenerator dense phase bed and wherein no severe after-burning occurred in the regenerator dilute phase or in the flue gas line. However, CO content of the flue gas was indicated, by results of ORSAT analysis, to be in the 0-0.4 mol percent range. The range, 0-0.4 mol percent, of Yalues obtained for CO concentration in the flue gas was considered to be too large, considering stability of operations during run 2616B. Consequently, a program of testing the accuracy of ORSAT analysis of low CO concentrations in flue gas was undertaken. As a result o~ this testing, it was found that ORSAT analysis of flue gas for CO concentrations in the 0-0.4 mol percent range were highly inaccurate as compared to ' .

1~46a,L83 ' gas chromatographic techniques and results from MSA Model 47133 CO detector. Results from -the gas chromotograph and MSA detector supported each othe~r and indicated that CO
concentration in the flue gas was less than 10 ppm under conditions wherein the regenerator dense phase bed tempera-ture was in the range o 1380-1430F., and wherein 1.0 mol ; percent or more excess oxygen was present in the flue gas.
Conclusions, which may be drawn from the results obtained in run 2616B, and reported in Table 5, include that 10 for an FCCU regenerator operating at about 1250F. with a normal air supply (i.e., sufficient air to provide about 1/1 CO~/CO ratio in the flue gas), substantially all CO can be burned to CO2 within the regenerator dense phase catalyst bed with very little or no afterburn of C0 in the regenera-tor dilute phase by increasing air flow to the regenerator dense phase catalyst bed sufficiently to maintain at least about 1.0 mol percent oxygen, and preferably about 3.5 mol ~:~ percent oxygen, in the flue gas. Addi-tion of such excess oxygen to a regenerator dense phase catalyst bed operating s 20 at a temperature of at least about 1250F. initiates a CO
burn within the regenerator dense phase bed. Initiation of this CO burn causes the dense phase bed temperature to increase to a temperature in the range of about 1380-1420F.
whereupon essentially all the CO is burned to CO2 within the `~ regeneration dense phase catalyst bed and very little or no , afterburn of CO to CO2 occurs in the regenerator dilute phase. This result is unexpected for normal regenerator temperatures below about 1250F., an increase in air supply - to the regenerator results in initiation of a CO afterburn ', , "',;
,`~, ' ' :

~Oq~64~33 in the regenerator dilute phase.
As is well-known to those familiar with FCCU's, an afterburn is combustion of CO to C02 in the regenerator . ~
dilute phase, or in the flue gas line, above the dense phase catalyst bed. If not controlled, an afterburn can result in excessively high flue gas temperatures which can damage cyclones and other regenerator internal parts. An after-burn is normally controlled by, among other methods, mini-mizing air supply to the regenerator so that little or no excess oxygen is present in the dilute phase as combustion gases leave the dense phase catalyst bed.
; EXAMPLE IV
.4 ' ' .. . .
Upon completion of the fluidized catalytic cracking runs of Example III, demonstrating that essentially all CO
could be burned to Co2 in a regenerator dense phase catalyst bed at temperatures (1380-1430F.) compatible with molecular sieves cracking catalysts in the presence of excess oxygen, without initiation of severe afterburn in the regenerator -, dilute phase which might cause damage to the regenerator .,~ .
20 structural members or to the catalyst, additional fluid `
catalytic cracking runs were undertaken to demonstrate the advantage of such high temperature, low flue gas CO con-centration regeneration operations over more conventional, lower temperatures regeneration operations. In this ex-ample, four high temperatures regeneration test runs were made on the fluidized catalytic cracking unit of Example I
at successively higher fresh feed rates and successively lower FCCU regenerator catalyst inventories down to the minimum regenerator catalyst inventory attainable. For com-- 30 parison, two runs were made at more conventional FCCU low ... .
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104~4~33 temperature test runs and comparison runs demonstrate that for the high temperature, low flue gas CO concentration runs, reduction of regenerator datalyst inventories to about 4.6 lbs. catalyst per bbl. daily fresh feed capacity could be obtained without effecting the level of CO emissions (10 ppm in flue gas) or the low level of carbon-on-regenerated-catalyst (0.12 wt.%). Also, the high temperature, low flue gas CO regeneration operations result in higher debutanized naphtha yields with higher clear octane values, and lower 10 coke yields compared to more conventional regeneration operations at the same conversion and operating conditions.
Fresh charge stock used in this example was a FCCU gas oil feed obtained from a petroleum refinery. Test results on this fresh feed are shown in Table 6, following. Recycle feed comprised heavy cycle gas oil recovered from -the FCCU
cracked products. In all runs of this example, fresh feed and recycle were charged to a single riser of the FCCU.

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. TABLE 6 - FRESH CHARGE TEST RESULTS

: DESCRIPTION FCCU ~AS-OIL FEED

Gravity, API 27.9 ASTM Distillation, F(Vol.) :
Pour Point, F. ~65 Refractive Index at 25C 1.4874 ...
Sulfur, wt.% 0.49 Total Nitrogen, wppm 354 ;;-Basic Nitrogen, wppm 142 ' Aniline Point, F. 181.5 ;-Bromine Number 3 - Watson Aromatics, wt.% 42.6 W Absorbance at 285 m. 4.44 Conradson Carbon Residue, wt.~ 0.14 Catalyst employed in the runs of this example was an ion-exchanged silica-alumina zeolitic molecular sieve cata- `~
lyst as manufactured by Davison Chemical Co. under the ;~
tradename "CBZ-l". Equilibrium catalyst obtained from a commercial FCCU was employed at start-up of the FCCU, and fresh catalyst was added on a regular basis to maintain equilibrium activity.
Detailed data on operating conditions and product yields from the four high temperature, low CO regeneration test runs of this example and the two conventional regenera-. tion test runs are shown in Table 7, following.

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~0~6~83 The high temperature, low CO regeneration study com-prised four high temperature regeneration runs made at successively higher fresh feed rates and successively lower regenerator catalyst inventories, down to the minimum allow-able inventory (24.8 pounds). The 24.8 pounds regenerator catalyst inventory for runs 2623B and 2624A is significantly below the 100 lb. inventory used for comparison runs 2609C
and 2609F. From Table 7 it can be seen that regenerator bed temperature of about 1420-1445F. was maintained for the low 10 CO regeneration test runs and, as in the previous examples of high temperature regeneration, both CO concentration in the flue gas and carbon--on-regenerated-catalyst were at very low levels. As a result of increasing the fresh feed rate (and consequently the cataIyst circulation rate~ and re-ducing the regenerator catalyst inventory, the catalyst residence time in the regenerator was decreased from about `
9.8 minutes for run 2622H at the start of the study to 4.7 minutes for run 2624A and 2633B. At the same time, the specific coke burning rate (e.g., the weight of coke burned 20 per hour per weight of catalyst in the regenerator) in-creased from 0.068 to 0.149. Thus, lowering the regenerator residence time from g.8 to 4.7 minutes and increasing speci-fic coke burning rate from 0.068 to 0.149 lb/hr/lb. had not `
discernable detrimental effect on either carbon-on-regenera-ted-catalyst (CORC) or CO emissions in the regenerator flue s gas, thereby demonstrating utility of the process of the present invention over a wide range of FCCU regenerator operating conclitions. No afterburn of CO to CO2 was ex-perienced in the regenerator dilute phase under high tem-30 perature regeneration conditions, indicating essentially ... .
-32- ~

~cii464B3 complete conversion of CO to CO2 within the regenerator dense phase bed.
Comparison of the product yield data obtained from the - four high temperature regeneration runs of this example (runs 2622H; 2623A; 2623B and 2624A) with yield data from the conventional regeneration runs (2609C and 2609F) demon-strate further advantage of the process of the present invention. Coke yields for the high temperature regenera-tion runs are about 0.8 to 0.9 wt.% below coke yields for 10 conventional regeneration at the same conversion and opera- ;
ting conditions, which amounts to 14-15% reduction in coke yield. Total debutanized naphtha yield and octane are significantly higher for the high temperature low flue gas CO content regeneration method of the present invention, ;
compared to the conventional regeneration results. -~
EXAMPLE V
In this example three regeneration test runs were made on the fluidized catalytic cracking unit of Example I. The runs were made at fluidized dense catalyst phase tempera-tures of from about 1250F. to about 1375F. The purpose ofthese runs was to demonstrate that at intermediate fluidized dense catalyst phase temperatures in the regeneration zone within the range indicated, a regenerated catalyst could be obtained with a carbon-on-regenerated-catalyst (CORC) con-tent of about 0.15 wt.% or less and that the afterburn of `1 carbon monoxide in the dilute catalyst phase could be con-trolled such that the temperature in the dilute catalyst phase did not exceed about 1450F.
; The charge stock used in these runs was the same FCCU
, 30 gas-oil feed employed in Example III, the properties of ... . .
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~0~83 which are shown in Table 3. Detailed data on operating conditions and product yields from the test runs of this : example are shown in Table 8, following.

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:1046~33 As can be seen in Table 8 operation of the regene-ration process with a fluidized dense catalyst ph~se tempexature in the range of from approximately 1304F. to about 1355F. results in a "controlled afterburn" of carbon monoxide in the dilute catalyst phase wherein temperatures in the dilute catalyst phase range from about 1417F to about 1455F. In these runs the regeneration air rate was main-tained at a level such that the oxygen content of the flue ~ gas was in the range of from about 3.95 to about 5.5 mol%.
^- 10 In all runs a regenerated catalyst with a carbon-on-regene-rated catalyst (CORC) content of approximately 0.15 weight - percent or less was obtained.
The data from run 2609F (presented in Table 7) il-lustrates that considerable after-burning will occur if excess oxygen is present in the regeneration flue gas. In that run, the fluidized dense catalyst phase was maintained at a temperature of 1261F. and the afterburn was approxi-mately 113F with approximately 3 mol% oxygen in the ` regeneration flue gas. Nevertheless, the carbon monoxide content of the flue gas in that run was high (0.95 mol%), ; ':
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~ 0~6~3 indicating that a still higher air rate is reguired to burn substantially all of the carbon monoxide. Additionally, it may be noted that in runs 2616B (presented in Table 5) the data indicate that at a fluidized dense catalyst phase temperature of approximately 1275F. there is some after-burning as indicated by the slight drop in carbon monoxide content of the flue gas. Moreover, the data there presented show that at a fluidized dense catalyst phase temperature of ~ approximately 1315F. there is a considerable afterburn as - 10 evidenced by the still lower carbon monoxide content of the flue gas. However, in both these runs the oxygen content of the flue gas was low (less than 1 mol%) resulting in in-complete conversion of the carbon monoxide.
The afterburn obtained in the three runs, presented in Table 8~ ranged from approximately 11F. to 151F. and were obtained with excess oxygen present in the regeneration flue gas in an amount of from 3.95 to 5.53 mol%. A com- `~
parison of Run 2616H with Run 2616G2 ~roughly eguivalent fluidized dense catalyst phase temperatures) illustrates the .. ~.
20 effect of higher excPss oxygen rates on the reduction of ;~
carbon monoxide in the flue gas.
From the foregoing disclosure and examples, many modi-fications and variations will appear obvious to those skilled in the art. All such variations and modifications ~` are to be included in the present invention, and no limi-tations are intended except those included within the -`~
~; appended claims.

.

.;. . . . . . .

Claims (12)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In a process for the regeneration of a coke-contaminated fluidizable catalytic cracking catalyst which has been partially deactivated with carbonaceous deposits comprising continuously introducing the coke-contaminated catalyst into a dense catalyst phase of a regeneration zone comprising a single fluidized dense catalyst phase in the lower section of the regeneration zone maintained at a temperature sufficient to support combustion of the carbon-aceaus deposits and a dilute phase in the upper section of the regeneration zone, contacting the coke-contaminated catalyst in the regeneration zone with an upwardly flowing oxygen-containing regeneration gas thereby effecting combus-tion of the carbonaceous deposits from the coke-contaminated catalyst, recovering a flue gas comprising carbon monoxide and recovering a regenerated catalyst of reduced coke-contamination, the improvement comprising the steps of:
a) maintaining the fluidized dense catalyst phase of the regeneration zone at a temperature of from about 1275°F. to about 1350°F., b) maintaining the catalyst in the fluidized dense catalyst phase of the regeneration zone for a residence time of from about 3 to about 10 minutes, and c) contacting the coke-contaminated catalyst in the regeneration zone with an upwardly flowing oxygen-containing regeneration gas in an amount in excess of that required to effect combustion of coke to carbon dioxide and to provide in the range of from about 1 to about 10 mol%
oxygen in the flue gas, thereby to recover a flue gas from the regeneration zone comprising carbon monoxide in an amount of from about 0 to about 500 ppm, to recover a regenerated catalyst from the fluidized dense catalyst phase of the regeneration zone having a carbon content of not greater than about 0.15 weight percent, and to maintain the regeneration zone dilute catalyst phase at a temperature in the range of from about 1375°F. to about 1455°F.

2. The method of Claim 1 wherein the oxygen-containing regeneration gas is air.

3. The method of Claim 1 wherein the coke-contaminated catalyst is contacted in the regeneration zone with an oxygen-containing regeneration gas in an amount to provide from about 3 to about 10 mol% oxygen in the flue gas from the regeneration zone.

4. The method of Claim 1 wherein a regenerated catalyst is recovered from the regeneration zone having a carbon content of not greater than 0.12 weight percent.

5. The method of Claim 4 wherein a flue gas is recovered from the regeneration zone comprising carbon monoxide in an amount of not greater than about 10 ppm.

6. The method of Claim 1 wherein the fluidized dense catalyst phase of the regeneration zone is maintained at a temperature of from about 1300°F. to about 1350°F., and wherein the oxygen-containing regeneration gas is supplied in an amount in excess of that required to effect combustion of coke to carbon dioxide and to provide in the range of from 3 to about 10 mol% oxygen in the flue gas, thereby to maintain the regeneration zone dilute catalyst phase at a temperature in the range of from about 1400°F.
to about 1455°F.

7. In a process for the regeneration of a coke-contaminated fluidizable catalytic cracking catalyst which has been partially deactivated with carbonaceous deposits comprising continuously introducing the coke-contaminated catalyst into a dense catalyst phase of a regeneration zone comprising a single fluidized dense catalyst phase in the lower section of the regeneration zone maintained at a temperature sufficient to support combustion of the carbona-ceous deposits and a dilute phase in the upper section of the regeneration zone, contacting the coke-contaminated catalyst in the regeneration zone with an upwardly flowing oxygen-containing regeneration gas thereby effecting combustion of the carbonaceous deposits from the coke-contaminated catalyst, recovering a flue gas comprising carbon monoxide and recovering a regenerated catalyst of reduced coke-contamination, the improvement comprising the steps of:

a) maintaining the fluidized dense catalyst phase of the regeneration zone at a temperature of from about 1275°F. to about 1350°F.;
b) maintaining the catalyst in the fluidized dense catalyst phase of the regeneration zone for a residence time of from about 3 to about 10 minutes; and c) contacting the coke-contaminated catalyst in the fluidized dense catalyst phase of the regeneration zone with an upwardly flowing oxygen-containing regeneration gas in an amount in excess of that required to effect combustion of coke to carbon dioxide and to provide in the range of from about 1 to about 10 mol% oxygen in the flue gas, there-by to recover a flue gas from the regeneration zone comprising carbon monoxide in an amount of from about 0 to about 500 ppm, to recover a regenerated catalyst from the fluidized dense catalyst phase of the regeneration zone having a carbon content of not greater than about 0.15 weight percent, and to maintain the regeneration zone dilute catalyst phase at a temperature in the range of from about 1375°F. to about 1455°F.

8. The method of Claim 7 wherein the oxygen-containing regeneration gas is air.

9. The method of Claim 7 wherein the coke-contaminated catalyst is contacted in the fluidized dense catalyst phase of the regeneration zone with an oxygen-containing regeneration gas in an amount to provide from about 3 to about 10 mol% oxygen in the flue gas from the regeneration zone.

10. The method of Claim 7 wherein a regenerated catalyst is recovered from the regeneration zone having a carbon content of not greater than about 0.12 weight percent

11. The method of Claim 10 wherein a flue gas is recovered from the regeneration zone comprising carbon monoxide in an amount of not greater than about 10 ppm.

12. The method of Claim 7 wherein the fluidized dense catalyst phase of the regeneration zone is maintained at a temperature of from about 1300°F. to about 1350°F., and wherein the oxygen-containing regeneration gas is supplied in an amount in excess of that required to effect combustion of coke to carbon dioxide and to provide in the range of from about 3 to about 10 mol% oxygen in the flue gas, thereby to maintain the regeneration zone dilute catalyst phase at a temperature in the range of from about 1400°F. to about 1455°F.