NO770317L - PROCEDURES FOR THE REGENERATION OF COKEN - CONTAMINATED CATALYST WITH CONTINUOUS COMBUSTION OF CARBON MONOXIDE. - Google Patents

Description

Process for the regeneration of coked cata-

lysator during the simultaneous combustion of carbon monoxide

The present invention concerns the treatment of hydrocarbons and more particularly catalytic cracking. The invention relates to a method for regenerating coke-contaminated cracking catalysts with simultaneous regulated combustion of CO to C02 in the regeneration zone in a catalytic cracking process.

Regeneration techniques where coked catalyst is regenerated in a regeneration zone form a larger area of chemistry. Particularly used are regeneration methods for coked, fluidizable, catalytic cracking catalyst in the regeneration zone by fluid catalytic cracking (fluid catalytic cracking is FCC). Until recently, the technique in the area has mainly consisted of removing the largest possible amount of coke from used catalyst and at the same time preventing too high temperatures, which are the result of the conversion of carbon monoxide to carbon dioxide, in certain parts of the regeneration zone, especially in the catalyst zone which is in the "dilute phase", where there is little catalyst present that can absorb the heat of reaction and where cyclones or other processing or separation equipment can therefore be destroyed by the heat. Complete CO turnover in conventional regeneration zones was prevented simply by limiting the amount of fresh regeneration gas introduced into the regeneration zone. Without sufficient oxygen to support the oxidation of

CO to C02 such afterburning cannot take place regardless of the temperatures in the regeneration zone. The temperatures in the regeneration zone were also generally limited to below approx. 675° C by choosing such operating conditions or compositions of fresh feed and recycled streams or combinations of these that the amount of coke on used catalyst and thereby the amount of fuel burned in the regeneration zone was limited. The formed exhaust gases, which contained several percentages of CO by volume, were either taken directly to the pipe or used as fuel in

a CO boiler that was further down in the regeneration zone. Common practice in liquid catalytic cracking has consisted of first manually regulating the flow of fresh regeneration gas to the regeneration zone in an insufficient amount to maintain complete C0 conversion, while at the same time limiting the reaction zone temperature to a maximum of approx. 675° C. Once steady-state conditions had been achieved for this FCC process, the flow regulation of fresh regeneration gas was typically regulated by instruments that were directly controlled depending on a small temperature differential between the outlet gas temperature (or the temperature in the space around the diluted catalyst phase) and the temperature of the dense catalyst bed, thereby automatically maintaining the correct flow rate for fresh regeneration gas and ensuring that complete combustion of CO to CO2 did not occur anywhere in the regeneration zone.

When the temperature difference became greater than a certain value, which indicated that a greater conversion of CO was taking place in the diluted phase, the amount of fresh regeneration gas was reduced, thereby avoiding complete conversion of CO to CO.-,. This regulation method is described, for example, in US patents 3,161,583 and 3,206,393. Although the method releases a small amount of 02 in the exhaust gas, usually in the range of 0.1 to 1 vol% 02, it prevents the complete conversion of CO to C02.

Until the zeolite catalysts were introduced, there was little economic reason to seek complete conversion of CO

to the C02i regeneration zone. The use of zeolite-containing FCC catalysts, which are more stable in terms of temperature and have less tendency to coke deposits, and the use of higher turnover temperatures in the reaction zone, however, often required the introduction of additional heat to the FCC process. This additional heat was typically provided by burning external fuel such as blow-off oil in the regeneration zone or increasing

the preheating. In this way, heat was introduced into and later removed from the FCC process by two external facilities, namely a preheater for the feed and a CO boiler, both with considerable capital outlay. Catalyst regeneration methods described later have realized the advantages of substantially complete combustion of CO into C02 and recovery of at least part of the heat of combustion for CO, within the regeneration zone. Examples of such regeneration processes are US patent 3 844 973 and 3 909 392. The advantages of these methods are well known: they enable the reduction or elimination of the feed pre-heating, and avoid contamination of air by CO and the need for an external CO boiler is eliminated and, connected with modern hydrocarbon turnover zones, the method provides an improved yield of better products.

Regeneration processes that use accelerators or catalysts for the CO turnover are not new, previously known techniques for the regeneration of fluidizable coked cracking catalysts have used such accelerators or catalysts. For example, in liquid catalytic cracking as described in US patent 2,436,927 (1948), a physical mixture of individual particles of a cracking catalyst and individual particles of an oxidation catalyst for CO on the carrier material is used in a dense phase area in a regeneration zone to increase the CO turnover in the dense phase to thereby prevent "afterburning" in the dilution phase area in the regeneration zone. In the method described in US patent 3 364 136 (1968), a mixture of cracking catalyst and shape-selective crystalline aluminum oxide silicate containing oxidation catalyst in the pore structure is used to regulate the C02/CO ratio in the regeneration zone without affecting the reaction taking place in the reaction zone. According to. US patent 3 808 121 uses two separate catalysts with different particle size and composition, a cracking catalyst and a CO-oxidation catalyst, preferably on carrier material, in a lattice mass such as e.g. aluminum oxide spheres and monoliths. Furthermore, the CO oxidation catalyst on the carrier material is delimited within the regeneration zone and does not go out of this zone and into the hydrocarbon zone as the cracking catalyst otherwise does. Coke and CO are oxidized in the regeneration zone and the content of CO in the exhaust gas is reduced.

Thus, the prior regeneration techniques have used CO oxidation accelerators in one of two ways: (1) on single particles belonging to a particle mass or carrier material, which particles were mixed with the liquid cracking catalyst and (2) as a part of or component of the liquid cracking catalyst itself . Mixtures of cracking catalyst and CO oxidation accelerator on the carrier material tend to be uneven and can result in unacceptable CO concentrations in the exhaust gas. The use of cracking catalysts containing a certain concentration of CO oxidation accelerator makes it difficult to achieve an optimal concentration of oxidation accelerator in a certain regeneration zone, in order to achieve

the best turnover conditions in this regeneration zone, or possibilities for controlling a dependent process variable.

In the method of the present invention, a CO oxidation accelerator is added to the regeneration zone independently of the cracking catalyst, coke from used catalyst is oxidized to form regenerated catalyst and at the same time CO is converted to CO2 in the presence of the accelerator and regenerated catalyst in the regeneration zone. An accelerator for the oxidation of carbon monoxide can be precisely and easily introduced into the regeneration zone, and especially when it is a liquid", in quantities sufficient to regulate the CO concentration in the exhaust gas,

regulate the temperature in the regeneration zone or the amount of

residual carbon on regeneration catalyst. Addition of CO-oxidase ion accelerator according to the present method is therefore more economical than both using separator particles of CO-accelerator on the support material together with cracking catalyst or using cracking catalyst added with Co-turnover accelerator during the manufacturing process for the catalyst.

In addition, the present inventive method provides a new operating variable in a process which previously took place under unchanging conditions. One can thereby achieve better control and flexibility with the present invention. The procedure can be applied to all liquid catalytic cracking processes, new or existing.

It is therefore a main purpose of the invention to provide a method for the regeneration of coked catalyst while simultaneously carefully regulating the combustion of CO in a regeneration zone in a way that releases a regulated amount of heat which is used in the regeneration zone and for reducing the amount of CO in the exhaust gases. Another feature of the invention is that in a catalytic cracking process where coke-contaminated cracking catalyst and oxygen-containing regeneration gas are led to a regeneration zone which is maintained at oxidizing conditions for the coke while forming regenerated catalyst and exhaust gas containing CO and CO2, a method is used which is based on in situ combustion of CO to CO2 for regulating the operation of the regeneration zone. Other features of the invention consist of (1) a method for regulating the CO concentration in the exhaust gas within a specific CO concentration range, (2) a method for regulating the temperature in the regeneration zone within a specific range and (3) a method for regulating the residual carbon concentration on the regeneration catalyst within

a specific area.

A method according to the invention for the regeneration of coked catalyst during simultaneous regulated combustion of CO comprises the following steps: (a) introduction of coked catalyst into a regeneration zone, (b) supply of

CO oxidation accelerator to the regeneration zone independent of the coked catalyst, in such an amount as to achieve an acceleration of the combustion of CO to CO2, (c) introducing oxygen-containing regeneration gas into the regeneration zone in a quantity sufficient to burn off the coke from the coked catalyst and provide a sufficient excess of oxygen to achieve the desired CO combustion, (d) react a first portion of the oxygen-containing regeneration gas with the coked catalyst in the regeneration zone at oxidation conditions selected to remove coke from the coke-contaminated catalyst and form an off-gas which contains CO, and which is sufficient to sustain combustion of CO to C02 in the presence of the oxidation accelerator and (e) simultaneously contacting the exhaust gas and a second portion of the oxygen-containing regeneration gas with the CO oxidation ion accelerator in the regeneration zone in the presence of regenerated catalyst at said oxidation conditions such that one (i) releases a regulated amount of exothermic heat of reaction available for the operation of the regeneration zone and (ii) reduces the amount of CO in the exhaust gas.

From another point of view, a process for catalytic cracking of a hydrocarbon feed is provided in which coke-contaminated cracking catalyst and oxygen-containing regeneration gas are fed to a regeneration zone maintained at coke-oxidizing conditions and where coke is oxidized to form regenerated catalyst and an off-gas containing CO and C02, using the in situ combustion of CO to C02 for regulating the operation of the regeneration zone, which includes: (a) independently of the coke-contaminated catalyst, a CO oxidation accelerator is introduced into the regeneration zone in such an amount that a CO combustion is started and maintained in the zone in the presence of the regeneration catalyst and (b) then the amount of oxygen-containing regeneration gas introduced into the zone is regulated to a stoichiometrically sufficient amount to branch off the coke from the catalyst and convert at least part of the CO

to C02 so that (i) a regulated amount of exothermic heat available for the regeneration zone is released and (ii) the amount of CO in the exhaust gas is reduced.

Other features of the invention will be found in the following detailed description, where it will first be useful to define different terms.

"Reaction zone" or "hydrocarbon reaction zone"

is the part of an FFC plant' where an incoming stream of hydrocarbon (feed) is brought into contact with regenerated catalyst under cracking conditions to form a mixture of FFC products, coked (spent) catalyst and possibly unreacted feed. Typical product components after separation in subsequent equipment are: C2~ fuel gases, C3~ and C^ fractions, a gasoline fraction, recirculating residual oil and clarified slurry oil. After separation from the products, at least part of the spent catalyst is returned to the regeneration zone. "Coke-contaminated" catalyst, "coked catalyst" or "spent catalyst" are used interchangeably and refer to catalysts that are drained from the hydrocarbon conversion zone due to reduced activity due to coke deposits. Spent catalyst that enters the regeneration zone can contain anything from a few tenths and up to 5% by weight of coke, but the content of coke in typical FCC operation will be approx. 0.5 to 1.5% by weight.

The term "regeneration zone" means the part of the FCC plant where an oxygen-containing regeneration gas and at least a part of spent catalyst is introduced and where in it. at least part of the coke is removed from used catalyst by oxidation, forming regenerated catalyst and exhaust gas containing CO and CO,,. "Regenerated catalyst" means catalyst from which part of the coke has been removed by oxidation. Regenerated catalyst produced according to the present method generally contains less than approx. 0.3 wt% coke and more typically between 0.01 and 0.15 wt% coke. The term "regeneration gas" generally means any gas which is brought into contact with catalyst and which has been in contact with the catalyst in the regeneration zone. In particular, the term "oxygen-containing regeneration gas" denotes a regeneration gas containing free or unbound oxygen, for example air or oxygen-enriched or -depleted air, which is supplied to the regeneration zone for oxidation of the coke on used catalyst and conversion of CO. "Exhaust gas" means regeneration gas which has been in contact with catalyst in the regeneration zone and which has been led out of the zone. Exhaust gases will contain:: nitrogen, free oxygen, carbon monoxide, carbon dioxide and water. Because concentrations of CO and C02 are used for calculation of FCC processes, and since CO is a potential fuel that. can be burned in the regeneration zone or an external CO boiler or possibly both, and also because air pollution regulations apply to C0 gases, the exhaust gases will typically be characterized by the concentrations of CO and C02 or by the molar ratio C02/CO. Depending on the operating conditions in the regeneration zone, in particular the amount of oxygen-containing regeneration gas that is fed into the zone, the concentrations of CO in the gas can vary within a large area, from a few hundred m to approx. 15 vol% or more, and the concentration of C02 from 5 to approx. 20 vol%. When the regeneration zone is operated under conditions which essentially exclude oxidation of CO in the regeneration zone, concentrations of CO and C02 will be approximately equal, within the range of 7 to 15 vol%, and the C02/CO molar ratio will be in the range of 0.8 to 1.5. When the regeneration zone is maintained at conditions that provide more or less complete oxidation of CO, the concentration of CO will be lower than C02 and more particularly the C02/C0 molar ratio will typically lie between approx. 1.5 and 100. When the regeneration zone is maintained at conditions which provide substantially complete turnover of CO in the regeneration zone, the concentration of CO will typically be below 1000 ppm and typically below 500 ppm, and the C02/CO molar ratio will be greater than 100.

The terms "dense phase" and "dilute phase" are used in the field for the characterization of catalyst densities in different parts of the regeneration zone or the hydrocarbon conversion zone. Although the conditions are somewhat poorly chosen, "dense phase" is used in the present publication for areas where the catalyst density in the regeneration zone is greater than approx. 80 kg/m , and "diluted phase" refers to areas where the catalyst density is below approx. 80 kg/m<3>. Usually the dense phase density will be in the range of 80 to 560 kg/m 3 or more and the density in the dilute phase will be much lower than 80 kg/m<3>, namely in the range of 1.6 to 80 kg/m . Catalyst densities in the regeneration zone are most often measured by measuring the pressure differences across pressure valves that are inserted in the containers at a known distance.

The term "afterburning" denotes, as usual in the area, an unintended and unregulated oxidation of CO to C02 in the area with diluted phase in the regeneration zone or the exhaust line, where there is little catalyst present that can act as a heat collector. As the heat of reaction for CO oxidation is very high (approx. 2416 kgcal/kg CO oxidized), afterburning can seriously destroy the catalyst separation facilities found in the dilution phase. In general, the afterburning is characterized by rapid temperature rise and takes place under uneven operating conditions or "waiting periods". The burn-in periods are usually short until steady operating conditions are introduced.

In contrast to afterburning, the term "regulated conversion of CO" or "regulated oxidation of CO" refers to a sieved, regulated and limited operation of CO in the presence of sufficient catalyst to adsorb at least part of the heat of reaction while recovering at least part of the reaction heat and in such a way that the equipment in the area is not exposed to risk. Depending on the operating conditions used, the regulated oxidation of CO can be partial or essentially complete. "Partially" means that the CO concentration in the exhaust gas has been reduced so that the molar ratio C02/C0

in the gas is in the range 1.5 to 100. "Complete" conversion (or rather substantially complete conversion) of CO means that the CO concentration in the gas is reduced so that the C02/CO molar ratio is above approx. 100. Complete CO turnover will give concentrations of CO below 1000 ppm and preferably below 50 0 ppm.

The term "CO turnover accelerator" or "CO oxidation accelerator" or abbreviated "accelerator" denotes a substance that catalyzes the concentration of CO into CO2. With such an accelerator, the kinetic rate constant for the oxidation of CO to C02 will typically increase from 2 to 5 times or more. One can thereby achieve a higher conversion rate for CO under the same conversion conditions in the presence of a CO conversion accelerator than without an accelerator. Conversely, the same CO turnover rate can be achieved with conditions (e.g. temperature) that are much lower than without a CO accelerator.

The amount of CO oxidation accelerator added to the regeneration zone can be expressed as the amount necessary to achieve a desired change in a variable or can be expressed on the basis of circulating catalyst amount or rate or on the basis of replacement amounts of fresh cracking catalyst, or optionally on the basis of amount included feeding.. In the present description, the amount of accelerator is expressed as the amount necessary to achieve the desired change in a variable such as the temperature, the CO concentration or the residual carbon concentration, or development. read as weight ppm of circulating catalyst. "Circulating catalyst" refers to the amount of cracking catalyst in the FCC process that can be circulated from the regeneration zone to the hydrocarbon turnover zone and back again. It differs from the total amount of cracking catalyst because usually a part of the total amount of catalyst would be unavailable for circulation, for example a part of the total amount located in the conical part regeneration zone below the stirrer.

Based on these definitions, a typical existing FCC process is briefly discussed, with particular emphasis on the operation of the regeneration zone. Existing FCC processes have achieved a significant reduction in coke deposition through the extensive use of a cracking catalyst based on crystalline aluminum oxide silicate and the use of short contact times hydrocarbon catalyst in, for example, ladder cracking. Although these efforts have yielded higher yields of the valuable gaseous<p>g liquid products, the processes obviously reduced the amount of solid fuel available for combustion in the regeneration zone to supply the process' residual heat demand. Later known processes have taken into account that by burning CO formed by oxidation of coke in the regeneration zone and recovering at least part of the exothermic heat of reaction, a sufficient amount of heat is available to fulfill the remaining heat needs within a wide range of operating conditions and feeding - compositions. Such combustion of CO also enables further reduction of the coke deposit and feeds of gas yield and liquid yield, and enables the reduction or elimination of feed preheating while simultaneously solving CO pollution problems, without the need for an external CO boiler. Typical regeneration zones of recent construction consist of a single cylindrical vessel containing a dilute phase in the upper part which occupies the cyclone separator, and a dense phase in the lower part of the vessel. Spent catalyst falls in through the side or bottom of the container and fresh regeneration gas enters the bottom of the container and is dispersed in this phase through a tube grid or perforated plate. Coke is oxidized with the formation of regenerated catalyst and exhaust gas containing CO and CO2, and CO can be oxidized if sufficient catalyst is present to recover at least part of the combustion heat. Exhaust gas containing entrained catalyst exits the dense phase and into the dilution phase where the cyclone separation devices separate entrained catalyst and circulate this back to the dense phase and the separated exhaust gas is led out of the regeneration zone. Limitations with regard to the operation of the regeneration zone apply to the capacity of the air fan, limitations of the cyclone separator's effect, limitations with regard to the CO concentration in the exhaust gas and special gas concentrations in the exhaust gas and with regard to. container temperature. When the regeneration zone is in operation, the operator will mainly be concerned with controlling the degree of catalyst regeneration, the temperature of the regeneration zone and the concentration of CO and special components in the exhaust gas. In particular, it is typical refinery practice to withdraw catalyst samples at intervals and analyze these in known ways for residual carbon content, as a measure of the degree

of catalyst regeneration and an indication of the regenerated catalyst's cracking activity. The temperatures in the regeneration zone are routinely measured using thermocouples and the temperatures are recorded to detect operational changes and to ensure that limitations regarding the construction and metallurgy of the container are not exceeded. In addition, it is common practice to periodically or continuously take samples and analyze the exhaust gas with regard to concentrations of CO, C^, CO2 and particle content. The gas analyzes can be carried out in all known ways, including the orsat method, gas chromatographic methods and mass spectrometry. Measurement of the content of particulate material can be done by opacity measurements or other known analysis methods. The results of the gas analyzes can be used to calculate via the carbon-nitrogen-oxygen balance quantities such as coke composition, coke burning rate, need for oxygen-containing regeneration gas, the coke's burning rate and the amount of CO that can be burned in an external CO boiler or in the regeneration zone or possibly in both parts. Before the exhaust gas can be discharged directly into the atmosphere, the operator must also know the concentrations of CO and particles in order to determine whether the exhaust gas meets the local pollution requirements for CO and other gas concentrations. Concentrations of O 2 in the exhaust gas are important to ensure that the amount of oxygen-containing regeneration gas supplied to the regeneration zone is sufficient to promote the desired CO combustion, either partial or complete, but not in unnecessary excess.

It is a feature of the present invention in all embodiments that a CO oxidation accelerator is added to the regeneration zone independently of the cracking catalyst. The oxidation accelerators that can be used are metals from groups IB, IIB, VIB, IIB and VIII in the periodic table and their compounds. Representative metals are chromium, nickel, iron, molybdenum, cobalt, copper, zinc, manganese and vanadium and their compounds. Preferred oxidation accelerators are the noble metals and their compounds because it has been found that very small amounts of these accelerators are necessary to achieve the desired results. The term "precious metals" in the ordinary sense includes the metals gold, silver, mercury, platinum, palladium, iridium, rhodium, ruthenium and osmium. An accelerator can be added to the regeneration zone as a solid, for example a powder, or as shavings or beads or agglomerates, but the accelerator is preferably added in a liquid to facilitate handling and regulation. A liquid containing an accelerator can be introduced continuously or periodically by means of liquid regulating devices which are well known in the field. For example, a liquid containing an accelerator can be pushed out of a cylinder or "bomb" connected by pipes to an oil combustion nozzle or a probe introduced through a pressure valve and with flow regulation in the connecting pipe. Alternatively, the liquid could be pumped out of a container at a regulated speed, using a small displacement pump in the nozzle or probe. The CO turnover accelerator can be dispersible in the liquid as a colloidal dispersion or suspension or be dissolved in the liquid. Particularly preferred oxidation accelerators are noble metals or compounds in the form of soluble or dispersible substances in water or in liquid hydrocarbons. Suitable water-soluble metal compounds are metal halides, especially chlorides, nitrates, amine halides, oxides, sulphates, phosphates and other water-soluble inorganic salts. Special examples of water-soluble substances are chloroplatinic acid, palladium acid, palladium chloride, ruthenium tetrachloride, rhodium trichloride, rhodium nitrate and osmium trichloride. Optionally, a liquid hydrocarbon containing an oil-soluble or oil-dispersible CO oxidation accelerator can be added. Suitable liquid hydrocarbons include those types which are normally liquid at atmospheric temperatures and pressures, for example petrol and light oil. Oil-soluble or oil-dispersible compounds include metal diketonates, carbonyl compounds, metallocenes, olefin complexes, acetylene complexes, alkyl or arylphosphine complexes and carboxylates. Special examples are<p>latin acetylacetonate, palladium acetate, palladium naphthenate, triiodiridium (III) tri-carbonyl and u-cyclopentadienylethylenerhodium I. Among noble metals and their compounds, platinum and palladium and their compounds are preferred, especially those which are water-soluble as these seem to be easier to obtain than the compounds which are oil-soluble or oil-dispersible. Chloroplatinic acid and palladium acid are particularly preferred as water-soluble platinum and palladium compounds.

In order to be used technically in the best way, however, it is preferred that solutions of CO oxidation accelerators have a freezing point of 0° Cells lower so that they are still liquid at the coldest temperatures that one is likely to operate at in the field. Ideally, the solutions should have freezing points of approx. -34° C or lower. Solvents which form solutions with chloroplatinic acid or chloropalladium acid and with freezing points of 0° C or lower are alcohols selected from the group of saturated aliphatic alcohols with 2-8 carbon atoms per molecule and freezing points of 0° C or lower. Examples of such alcohols are together with their freezing points: methanol (-98.7° C), ethanol (-112° C), 1-propanol (-127° C), 2-propanol (-85.8° C) , 1-butanol (-89.2° C), 2-butanol (-89° C), 2,3-dimethyl-2-butanol (-14° C), 2-methyl-2-butanol (-14° C), 2-methyl-2-butanol (-11.9° C), 1-pentanol (-78.5° C), 1-hexanol (-51.6° C), 2-ethyl-l -hexanol (-70° C), 1-heptanol (-34.6° C), 4-heptanol (-41.5° C) and 1-octanol (-16.4° C).

Ideally, the solutions of CO oxidation accelerator should have freezing points of approx. -34° C or lower so that they are liquid at the coldest likely outdoor temperatures in the field. Better solvents will therefore be those which give solutions with chloroplatinic acid or chloropalladium acid with a desired freezing point of -34° C or lower. Such suitable solvents are selected from the group of saturated aliphatic alcohols with 2-8 carbon atoms per molecule and with freezing points of -34° C or lower. Examples are as above with the exception of 2,3-dimethyl-2-butanol, 2-methyl-2-butanol and 1-oct.ailiol, which three alcohols do not have freezing points of -34° C or lower.

In addition to a freezing point of -34° C or lower, solutions of preferred CO oxidation accelerators, namely chloroplatinic acid and chloropalladium acid, should be chemically stable so that no chemical change takes place, for example separation of another liquid phase or solid phase , during extensive storage periods. As an approximation to more extreme storage conditions that one might expect to encounter,

the solutions should be chemically stable for at least 30 days at a temperature of 63° C. Some of the above saturated aliphatic alcohols that give solutions that meet the pre-

o

drawn freezing point specifications of -34° C or lower do not give solutions that prove chemically stable or 30 days at 63° C. MethanoL, 2-propanol, 2-butanol and 2-methyl-2-propanol, for example, do not give solutions that were chemically stable over 30 days at 63° C. In addition, such known freezing point lowering agents as ethylene or propylene glycol were found to meet freezing point specifications but not chemical stability specifications. Solvents which gave solutions which met both the freezing point specification of -34° C and specifications regarding no detectable chemical change after 30 days at 63° C were alcohols selected from the group of saturated aliphatic primary alcohols of 2-8 carbon atoms per molecule and freezing points of -34° C or lower. Thus, these solvents are the preferred ones and 1-butanol and 2-ethyl-1-hexanol are particularly preferred. With the exception of methanol, it seemed that the chemical stability of the solutions was best when the solvent was a saturated aliphatic primary alcohol and worse when the solvent was a saturated aliphatic secondary or tertiary alcohol. Preferably used

therefore these saturated aliphatic primary alcohols with 2-8 carbon atoms per molecule and freezing points of -34° C or lower together with chloroplatinic acid or chloropalladium acid. Preferred concentrations of chloroplatinic or chloropalladium acid in a solution will be equivalent to 0.01 to 10% by weight Pt or Pd, preferably 0.01 to 5% by weight Pt or Pd.

To ensure maximum utilization of the very small amounts of accelerator that are required, limits are set for the addition of accelerator to the regeneration zone. By adding the accelerator directly to the regeneration zone where the CO oxidation takes place, immediate results are achieved with regard to operation and control of the regeneration zone, namely a regulated amount of exothermic heat of reaction and a reduction of the CO concentration in the exhaust gas. The CO conversion accelerator can be added to the dense catalyst phase or the dilute phase of the regeneration zone. Although the accelerator can be introduced at various locations in the regeneration zone, it has been found satisfactory to introduce the compound at only one location.

A container for typical regeneration processes has a number of pressure taps•and fuel nozzles which can all serve as introduction points and therefore little modification of the container itself is required before the present method can be put into use.

An embodiment according to the invention consists in a method for regeneration of coke-contaminated catalyst with simultaneous regulated combustion of CO. In this embodiment of the invention, coked catalyst is introduced into the regeneration zone and a Co-oxidation accelerator is introduced into the regeneration zone independently of the coked catalyst in an amount chosen so that the combustion of* CO to C02 is accelerated or accelerated. The added amount of accelerator is equivalent to approx. 0.1 to 25 wt ppm circulating catalyst based on elemental metal, preferably approx. 0.1 to 15 ppm by weight. Oxygen-containing regeneration gas is then introduced into the regeneration zone in sufficient quantity to fulfill the desired CO combustion. More specifically will. the introduced quantity of oxygen-containing regeneration gas corresponds to approx. 10 to 17 kg of air per kg of coke included in the regeneration zone per unit of time, depending on whether the CO combustion is partial or complete. The applicants have found it important that the accelerator is first introduced into the regeneration zone and then the oxygen-containing regeneration gas so that a smooth and regulated catalyzed conversion of CO can be initiated from the start and the risk of afterburning is made as small as possible. If the oxygen-containing regeneration gas is introduced first into the regeneration zone and the accelerator later, there is a risk that the afterburning will be started first rather than the desired regulated conversion of CO in the presence of the accelerator and regenerated catalyst. A first part of oxygen-containing regeneration gas will then react with pre-coked catalyst in the regeneration zone under oxidation conditions, removing coke from the catalyst and forming an off-gas that contains CO and is sufficient to accelerate the combustion of CO to C02 in the presence of an accelerator. Said oxidation conditions will, in addition to the presence of oxygen-containing regeneration gas as described above, involve a temperature in the range .590 to 790° C, and a pressure in the range from atmospheric pressure to approx. 4.5 atm. Under these conditions, the coke oxidation will be approximately spontaneous. At the same time (approximately at the same time), exhaust gas and a second part of the oxygen-containing regeneration gas will be brought into contact with the CO accelerator under the oxidation conditions described above so that a regulated amount of exothermic reaction heat is provided for operation of the regeneration zone and reduction of the amount of CO in the exhaust gas. The added amount of oxidation accelerator can be adjusted according to certain desired results, for example a desired CO concentration in the exhaust gas or a desired degree of catalyst regeneration or a desired catalyst temperature or a temperature in the regeneration zone. When CO oxidation accelerator is added to achieve such a result, the addition will usually take place in small portions and the desired dependent variable - either CO concentration

or the residual carbon concentration or a temperature - measured and compared to the desired result to determine if further addition of CO accelerator is necessary. If,

after adding a small portion of accelerator to the regeneration zone, the measured concentration of CO in the exhaust gas or

If the concentration of residual carbon on the regenerated catalyst or the temperature in the regenerated catalyst or the temperature in the regeneration zone does not lie within the specific range that applies to each measuring quantity, a new portion is added

accelerator and possibly further portions until the measured variables fall within the specified range. The addition of accelerator in several small portions over a relatively short period of a few minutes to a few hours enables the operator to achieve more careful regulation and control of the process. When the accelerator is added in several portions it will

total amount of accelerator fall within the ranges mentioned earlier. When the desired control variable is the temperature in the diluted phase, e.g. temperature in the exhaust gas, the CO oxidation accelerator can be added together with a quantity of dilution gas so that the temperature can be regulated below a certain level. The displacement gas will usually be oxygen-containing regeneration gas. When the measured variable is within the specified range for this variable, the accelerator will be added continuously or interrupted if necessary so that the variable remains within the range. While the amounts of accelerator required to maintain a variable within a certain range may vary somewhat from facility to facility and are best determined by experience in a particular facility, it has been found that the required amount of accelerator on a previous daily basis required to maintain this variable within a specific area will be equivalent to approx. 0.005 to 10 wt ppm of circulating catalyst amount on an elemental metal basis.

Other versions of the invention are specific and independent regulation methods to be put into use after starting the FCC process and after a reasonable level of equilibrium has been achieved in the process (steady-state). One embodiment of the invention consists in one process for catalytic cracking of a hydrocarbon feed where coke-contaminated catalyst and oxygen-containing regeneration gas are introduced into a regeneration zone which is maintained at oxidation conditions and coke is oxidized to regenerated catalyst and a waste gas containing C02 and CO, on which the relevant method is based on regulation of the CO concentration in the exhaust gas within a specific CO concentration range. In another embodiment, the present method in connection with the above-mentioned process is based on a regulation of the temperature in the regeneration zone within a specified area and in yet another embodiment, a method is used for regulating the concentration of residual carbon for regenerated catalyst within a specified area. Such regulation methods can be used by the operator independently of the others. methods. For example, a worker may be mainly interested in regulating the CO concentration in the exhaust gas, which must fall within a certain range, and if the regeneration zone's construction and metallurgy are such that assumed temperatures do not present any problem, he will accept the regeneration zone- temperatures and degree of regulation that result when the CO concentration is regulated. In other plants, one can mainly concentrate on the temperature in the regeneration zone due to limitations in terms of construction and metallurgy. In an embodiment of the invention, it is possible to regulate the temperature in the regulation zone within a certain area and one will then accept the concentration of CO found in the exhaust gas and the degree of regeneration that is the result of such regulation. With both control methods, a CO oxidation accelerator is first introduced into the regeneration zone and then oxygen-containing regeneration gas is supplied to the regeneration zone in a stoichiometrically sufficient amount to convert at least part of the CO into C02. As previously mentioned, the order of addition is important to avoid the risk of afterburning. At least one part of the amount of CO is converted by conversion conditions that include the presence of a CO oxidation accelerator and regenerated catalyst, to exhaust gases containing CO and C02- These conditions will include a temperature between 590 and 790° C and a pressure between atmospheric pressure and 4.5 atm. Depending on the regulation method, the exhaust gas will then be analyzed to determine its CO concentration which is compared to a given CO concentration range, or the temperature in the regeneration zone is measured and compared to the desired temperature, or the regenerated catalyst is analyzed to find the residual carbon concentration which then compared to a given desired area. Accelerator is then introduced into the regeneration zone in quantities that keep either the CO concentration or the temperature of the regeneration zone or the residual carbon concentration within the specified concentration ranges. The amount of accelerator that is initially added to the regeneration heat out- . preferably do small portions as described until the desired result is achieved. The portions in total will amount to approx. 0.1 to 25 wt ppm of the circulating catalyst based on elemental metal, preferably approx. 0.1 to 15 wt ppm of circulating catalyst. The amount of accelerator that is required on an average daily basis to keep a given measurement variable within a certain range will typically correspond to approx. 0.005 to 10 ppm by weight of the circulating elemental metal catalyst.

The type of cracking catalyst used in FCC processes using the method according to the invention is not decisive and can be any type of cracking catalyst that is in use or that can be used for FCC processes, including amorphous catalysts or crystalline aluminum silicate catalysts or mixtures thereof. Among these two large classes of cracking catalysts, crystalline aluminum silicates are preferred because these provide reduced coke deposition and increased product yield of gas and liquids compared to amorphous catalysts. Since CO is now oxidized as a fuel in addition to the coke in the regeneration zone and at least part of the heat of combustion for burning CO is recovered in the regeneration zone, the cracking system can now be as selective with respect to more valuable products as the conditions of the hydrocarbon turnover zone and the cracking catalyst make possible. The operating conditions of the hydrocarbon conversion zone will therefore be set with regard to maximum gas and liquid product yields and normally include a temperature range of 420 to 600° C and a pressure of between 1 and 4.5 atm., a catalyst/oil ratio of approx. 3 to 20 and a hydrocarbon residence time in contact with the catalyst of 1 to 30 sec., preferably 1 to 10 sec. Feeds used in FCC processes that use the method of the present invention need not be different from feeds that do not use the method and can include all feeds such as petrol, gas oils, light and medium distillates, residual oils and the like.

The following examples shall illustrate the invention and the choice of special accelerators, concentrations, operating conditions or methods of addition to the regeneration zone shall not be construed as limiting within the scope of the invention.

Example 1

The example describes experiments with FCC regeneration zones in pilot plants, carried out to determine the effect of a liquid addition containing a low concentration of. special accelerators for the regeneration zone in an FCC plant to reduce the CO concentration in the exhaust gas. The experiments were carried out in a vertical tube reactor whose upper and lower ends were provided with a stainless steel filter which, during the experiment, delimited the catalyst sample used in the container and whose lower end was connected to an inlet for fluidizing medium (nitrogen or air) and an inlet for liquid with accelerator. Devices were connected for heating the container to a constant temperature and. chromatographic equipment for sampling and analyzing exhaust gases from the container with regard to CO, CO2 and 02 and specifying the exact composition for characterizing reduced CO concentration.

Each experiment was carried out with a 500 g sample of used zeolite-containing cracking catalyst containing about 0.9% by weight of coke. The coke was deposited on the catalyst by passing a gas oil feed over a cleanly regenerated catalyst in a hydrocarbon conversion zone in a pilot plant under standard operating conditions and set up scheme for reaction stages. In test no. 1, no accelerator was added to the container during the test, the test was carried out to form a basis for comparison with the method according to the invention. A sample of 500 g of used catalyst was added to the container and fluidized with nitrogen which was introduced through the bottom of the container and the system heated to 593° C. At a specified time, the nitrogen was replaced with air which thereby started the oxidation of the coke. The exhaust gas from the container had CO concentrations as indicated by the chromatograph at various times after the introduction of air according to Table 1:

As shown above, the CO 2 /CO ratio remained during the experiment within the relatively narrow range of 2.5 to 3.0.

Experiment 2 was carried out in the same way as experiment 1, except that 15 seconds after the fluidization the nitrogen supply was switched with air supply and while the CO concentration was constantly increasing, a 30 ml sample of diluted chloroplatinic acid (I^PtClg) was introduced as a solution in - the container. The solution was prepared by diluting chloroplatinic acid which contained approx. 28.6 wt% Pt with distilled water to dilute chloroplatinic acid containing 0.1 mg Pt/ml. This amount of chloroplatinic acid is equivalent to approx. 6.0 wt ppm catalyst sample as Pt metal. From the instantaneous chromatograph readings, it was seen that the CO concentration was now reduced. As the experiment progressed, the exhaust gas had the following composition:

The concentration of carbon monoxide is greatly reduced and the C02/CO ratios are much higher than for experiment 1 at the same time. In order to find how quickly<p>latina lost its effect with regard to reducing the CO concentration, the regenerated catalyst from experiment 2 was used for several experiments in the reaction zone of the experimental plant and then in a regeneration zone without the addition of accelerator. After the further first three cycles through the hydrocarbon reaction zone and the regeneration zone, practically no CO formation was found when burning the coke, but from the fourth period a small amount of CO was formed in the exhaust gas, although this amount was considerably less than in experiment 1 without accelerator.

The same procedure was tried on a new 500 g of catalyst in experiment 3, except that a more dilute solution was used and that the liquid with accelerator was introduced into the container immediately before the fluidizing nitrogen was replaced with air. In this experiment, 25 ml of more strongly diluted chloroplatinic acid, equivalent to approx. 0.5 wt ppm catalyst as Pt metal added. The solution was prepared by diluting a portion of the same solution that was used in experiment 2 and. containing 0.1 mg Pt/ml with distilled water to a more dilute solution of chloroplatinic acid containing 0.01 mg Pt/ml. The exhaust gas concentrations for CO were as follows:

Although the reduced amount of accelerator used for the experiment seemed to give results about as good as with a higher concentration of accelerator in experiment 2, it turned out that the regenerated catalyst lost much of the accelerator's effect very quickly as subsequent periods showed the formation of some CO during the regeneration . After three periods, it turned out that the catalyst formed approx. two thirds of the amount of CO that was produced during experiment 1 during which no accelerator was added.

In experiment 4, 25 ml of a solution of chloropalladium acid in water containing 0.1 mg Pd/ml, equivalent to approx. 5 ppm by weight of the catalyst sample as Pd metal, injected into the container 15 seconds after the fluidizing nitrogen had been converted to air, which thereby started combustion. In the course of 2 minutes, the CO concentration in the exhaust gas had fallen to below 0.2 vol%.

Example 2

This example describes the conditions in a regeneration zone in a technical liquid catalysis cracking process shortly after the addition of small amounts of a liquid containing CO oxidation ion accelerator in the method of the invention without other operational changes.

The selected FCC plant treated about 124 m<J>/hour of a mixture of water and coke gas oil and had an amount of circulating catalyst of about 54,468 kg of zeolite catalyst. The plant was run under typical operating conditions without trials

on partial or complete reduction of the CO concentration in the exhaust gas and without the addition of a CO conversion accelerator in the regeneration zone. A summary of certain operating conditions before adding accelerator to the regeneration zone is shown in table 4 below. 2 liters of solution of chloroplatinic acid in water was then forced out of a cylinder and into the regeneration zone during 2 - 3 minutes through a tap in the regeneration zone. The dilute chloroplatinic acid solution was prepared by diluting 61.4 g of concentrated chloroplatinic acid (28.637 wt% Pt) to a 2 liter volume with distilled water. Introduction of this amount of solution into the regeneration zone corresponded to an addition of accelerator of about 0.32 weight p<p>m circulation catalyst as Pt metal. The regeneration zone reacted almost immediately to this addition: CO concen-

tration in the exhaust gas was reduced to approximately half the concentration before the addition and the temperature in the zone's dense catalyst phase rose approx. 25° C above the temperature before the addition. No other operational changes were made in the process. A summary of the operating conditions after this first addition of solution is also entered in table 4. Several hours later, a smaller amount of solution containing accelerator was equivalent to approx. 0.13 wt ppm circulation catalyst as Pt metal added to the regeneration zone in the same way as the first addition. Apart from the addition of an accelerator, no operational changes were made in the process. A summary of the operating conditions shortly after this second addition is also shown in Table 4.

As shown in Table 4, the CO concentration in the exhaust gas decreased from 10.5 vol% before the addition of accelerator to 5.9 vol% after the addition of the first amount of solution (0.32 wt ppm Pt) and to 1.4 vol% after the addition of the second amount of solution (0.13 wt ppm Pt). The amount of carbon on regenerated catalyst decreased from 0.30 wt% to 0.16 wt% after the addition of the first amount of solution and then to 0.06 wt% after the addition of the second amount of solution, while the temperature in the dense phase of the regeneration zone increased from 655 to 681 C and up to 713° C after additions of the respective amounts of solution. Other temperatures in the regeneration zone also increased but not as much as the temperature in the dense phase.

Example 3

This example describes the use of the invention in the same technical installation as in example 2 and indicates the advantages that can be achieved. Before the addition of the two portions of accelerator solution as in example 2, a fairly complete experiment, experiment 1, was carried out for comparison with later experiments when accelerator solution was added. During the day after the addition of the first two portions of accelerator solution, a further two portions of accelerator solution containing accelerator equivalent to approx. 0.13 and 0.32 weight ppm circulation catalyst as Pt metal were made as described above under example 2. This time, however, the amount of air was increased in relation to the regeneration zone to ensure sufficient oxygen for complete conversion of CO to CO2. Under equilibrium conditions, when CO was substantially completely burned in the regeneration zone in the presence of CO 2 conversion accelerator and regenerated catalyst, experiment 2 was carried out. At the time of trial 2, the total amount of dilute chloroplatinic acid added to the regeneration zone amounted to approx. 0.9 wt ppm oxidation accelerator based on circulating catalyst, and counted as Pt metal. Experiment 2 was carried out with the same feed rate, the same pressures in the regeneration zone and the hydrocarbon conversion zone as in experiment 1. Before starting experiment 2, no attempt was made to achieve the same degree of conversion as in experiment 1 or attempts to improve the flow rate of air with regard to complete CO turnover. Results of experiment 1 and experiment 2 can be found in table 5.

A comparison between these figures shows a reduction of the CO concentration in the exhaust gas from 10.5 vol% to less than 0.1 vol%, a reduction of carbon on regenerated catalyst from 0.28 wt% to 0.11 wt% ( indicating better catalyst regeneration)

and a general increase of the temperature in the regeneration zone on

38 to 44° C by using the method of the present invention. Although the temperatures in the hydrocarbon turnover zone are not exactly the same. Similarly, recovery of part of the CO combustion heat x the regeneration zone during experiment 2 has made it possible to reduce the temperature in the incoming feed. Although the turnover in experiment 2 was approx. 1.7% less than in trial 1

a comparison between the separate yields shows that a selective cracking to more valuable products was achieved in trial 2 than in trial 1. The coke deposition during trial 2 was 4.3 wt% compared to 5.4 wt% in trial 1 and although the turnover was 1 .7% less in trial 2 than in trial 1, the gasoline yield for trial 2 was 57.4 vol% compared to 57.6

vol% for experiment 1.

Later experience from the same technical facility showed that complete conversion of CO could be maintained by introducing into the • regeneration zone on an average daily basis a quantity of accelerator solution corresponding to approx. 0.12 weight ppm of circulating catalyst, calculated as Pt metal..

Platinum analysis of the catalyst samples from this technology

nic facilities indicate that a significant part of the accelerator is retained on the cracking catalyst. At a time when a total amount of chloroplatinic acid solution with accelerator corresponding to 75 g of Pt had been added to the technical plant, a sample of catalyst in equilibrium was taken from the unit and analyzed with regard to the Pt concentration. The sample showed 1.0 wt ppm,

Pt. If all 75 g of Pt that had been introduced into the plant were even

•distributed over 54,468 kg, you would get a concentration of 1.4

weight ppm Pt on the catalyst in equilibrium.

Example 4

The example generally illustrates the problem of chemical stability of the solution. More particularly, it illustrates the lack of chemical stability for a solution of chloroplatinum

acid in a mixture of water and a common freezing point depressant, ethylene glycol. Chloroplatinic acid containing 25.46

wt% Pt was dissolved in a mixture (1:1, by weight) of technical ethylene glycol and distilled or tap water into two solutions containing 0.045 wt% Pt. These two solutions were evaluated with regard to solubility properties at -2 9° C and with regard to temperature stability at 22,

43 and 63° C. The figures in table 6 below show that the solutions were liquid at -2 9° C but that they did not have the desired chemical stability over 30 days at 63° C, a black precipitate formed after approx. 11 days at 22° C

.and in only 0.7 days at 63° C. The black precipitate was separated by centrifugation, washed with water and analyzed to determine the Pt content. The content of elemental platinum in the black precipitate was found to be 94% and chemical analysis by electron spectroscopy showed mainly Pt° at approx. 5% PtO. Platinum recovery from the precipitate, the flasks and the clear solution was equal to 100.3%. The numbers indicate that the black precipitate is Pt o which indicates a reduction of Pt +4 in chloroplatinic acid Pt° and oxidation of the ethylene glycol. The oxidation product from ethylene glycol was not identified.

Example 5

This example reproduces figures for freezing point and chemical stability at selected temperatures of -36, 22, 63° C for ten solutions of chloroplatinic acid (CPA) in a concentration corresponding to 0.045 wt% Pt in various chemically pure primary, secondary or tertiary alcohols or mixtures thereof. A temperature of -36° C was chosen to simulate the coldest temperature encountered in the field, 22° C was chosen to simulate average conditions and 63° C to simulate average storage conditions (indoor and outdoor). The number of days before one observed black precipitation, the most likely visible Pt°, was recorded for each temperature. The figures can be found in table 7 below. Chemical stability for chloroplatinic acid is best in saturated aliphatic primary alcohols (with the exception of methyl alcohol) and worse for saturated aliphatic secondary and tertiary alcohols. In addition to the fact that the solutions are unsuitable for

due to poor chemical stability, the CPA-2-methyl-2-propanol solution was solid at -36° C. An arrangement of CP solutions in various solvents in order of decreasing chemical stability at 63° C is: 2- ethyl-l-hexanol (over 60 days), 1-propanol (over 58 days), 1-buta-

nol (59 days), ethanol and 1-hexanol (42 - 44 days), 2-methyl-2-prop.anol (13 days), 2-propanol and 2-butanol (1-2 days) and methanol (0 .25 days).

Example 6

This example describes experiments with regeneration zones on an experimental scale carried out to find the effect of a solution containing chloroplatinic acid in 1-butanol for reducing the CO concentration in the exhaust gas. The experiments were carried out with the same apparatus as in example 1. As in example 1, the apparatus could be heated to a constant temperature and chromatographic equipment was connected for continuous sampling and analysis of the exhaust gases with regard to CO, CO2 and 02. A chromatographic writes for the concentration of CO, C02 and 02

was connected so that one could take immediate readings of the CO combustion products during the test. A special one

ratio C02/C0, with the designation minimum ratio C02/C0, was calculated from the chromatographic investigations for each sample

by first determining the maximum CO concentration in the sample (which usually occurred within 2 to 3 minutes after the start of combustion), measuring the CO2 concentration at the maximum

model CO concentration and calculation of the C02/C0 ratio for the measured concentrations. The ratio is called the minimum ratio C02/C0 because it has been found after many such regeneration trials that if the instantaneous C02/CO ratios were set up as a curve against the time axis for each sample, a curve was obtained that would go through a minimum ratio C02/CO with a numerical value that

had the value calculated above. This minimum C02/CO ratio best characterizes the performance that can be achieved with solutions containing CO accelerator for catalysis of CO combustion.

The experiments were carried out with 500 g samples of zeolite-containing FCC catalyst set in equilibrium, which were first "used" by passing a gas oil feed over the catalyst sample in a hydrocarbon reaction zone in a test plant that was run at standard conditions and determined operating core. All catalyst samples used contained approx. 0.9 wt% coke.

Trial solution No. 1 contained no accelerator, the results were used as a basis for comparison for subsequent trials where the solution contained an accelerator. A 500 g sample of spent catalyst was applied to the reaction vessel and fluidized with nitrogen through the bottom of the vessel while the system was heated to 593° C. At a certain point, nitrogen was replaced with air which thereby initiated oxidation of the coke. The exhaust gas from the container was analyzed to find the content of C02, CO and O2 using chromatographic equipment, and from the figures for C02 and CO the minimum C02/CO ratio was calculated. To determine the reproducibility of these results, the experiments were repeated with separate samples of used catalyst four times. Minimum C02/CO ratios of between 2.5 and 3.3 are shown in Table 8 below.

Experiment 2 was carried out as experiment 1 except that immediately before switching the nitrogen flow to air, 25 g of a solution of chloroplatinic acid in 1-butanol was injected into the regeneration zone. The concentration of chloroplatinic acid in the sample corresponded to 0.008 wt% Pt and the amount of platinum in the sample was 2 mg Pt or 4 wt ppm of the catalyst sample of 500 g. A minimum CO2/CO ratio equal to 52.1 was measured and to find the rate at which the mixture of particles of accelerator and regenerated catalyst lost their effect with regard to reducing the CO concentration in the exhaust gas, the mixture was run through several periods or regeneration circuits. The mixture was "used" in the hydrocarbon reaction zone in the experimental plant as described above, and thereby separated for a new experimental period, and the regeneration experiment was repeated but without the addition of more accelerator solution. After the seventh circuit run, the minimum C02/CO was measured at 41.5, which indicated that the mixture had retained most of the Co-burning activity. The results from experiments 1 and 2 are summarized in table 8.

Claims (16)

1.. Method for the regeneration of coked catalyst during simultaneous regulated combustion of CO, comprising the following steps: (a) coke-contaminated catalyst is introduced into a regeneration zone, (b) a CO oxidation accelerator is introduced into the regeneration zone dependent on the coked catalyst in sufficient quantity to accelerate the combustion of CO to CO2, (c) oxygen-containing regeneration gas is introduced into the regeneration zone in a certain amount for burning off coke from the coke-contaminated catalyst and in <J> sufficient excess oxygen to sustain the desired CO combustion, (d) turnover of a first portion of the oxygen-containing regeneration gas with coke-contaminated catalyst in the regeneration zone at oxidation conditions chosen so that coke is removed from the coked catalyst with the formation of an off-c gas containing CO, and in sufficient quantity to burn ne CO to CO2 in the presence of the oxidation accelerator, and (e) simultaneously contacting the exhaust gas and a second part of the oxygen-containing regeneration gas with the CO oxidation accelerator in the regeneration zone in the presence of regenerated catalyst vec oxydas3cnsbetii.geiser so that one (i ) releases a regulated exothermic heat of reaction available for the operation of regeneration zone and (ii) reduces the amount of CO in the exhaust gas. 2. Method as stated in claim 1, characterized in that the CO oxidation accelerator in step (b) is added as a solution in a solvent. 3. Method as stated in claim 2, characterized in that the solvent is water or a liquid hydrocarbon. 4. Method as stated in claim 2, characterized in that the solvent is an alcohol selected from saturated aliphatic primary alcohols, with 2-8 carbon atoms per molecule and freezing points of 0° or lower. 5. Method as stated in claim 4, characterized in that the primary alcohol is 1-butanol or 2-ethyl-1-hexanol. 6. Method as stated in claims 1-5, characterized in that the CO oxidation accelerator added to the regeneration zone is adapted so that an exhaust gas containing CO is obtained in an amount equal to or less than a certain proportion. 7. Method as stated in claims 1-5, characterized in that the amount of CO oxidation accelerator that is added to the regeneration zone during step (b) is adjusted so that a reaction heat sufficient to raise the average combustion temperature in the zone to a temperature level that is effective for the production of regenerated catalyst containing less residual carbon than a certain limit. 8. Procedure as specified in claims 1-5, character- characterized in that the amount of CO oxidation accelerator added to the regeneration zone during step (b) is adjusted as follows that sufficient heat of reaction is released to raise the temperature in the regenerated catalyst to a certain level. 9. Method as stated in claims 1-5, characterized in that the amount of CO oxidation accelerator that is added to the regeneration zone during step (b) is adjusted so that practically all the heat given off by exothermic combustion of carbon monoxide is given off in the presence of a regenerated catalyst so that regulation of the temperature in the exhaust gas is achieved below a certain temperature. 10. Method as stated in claims 1-5, characterized in that the amount of CO oxidation accelerator that is added to the regeneration zone during step (b) is adjusted in such a way, together with an amount of dilution gas that is supplied to the zone, that the temperature of the exhaust gas is regulated to below a certain level. 11. Method as stated in claims 1-10, characterized in that the oxidation accelerator is selected from among the noble metals and their compounds. 12. Method as stated in claim 11, characterized in that the oxidation accelerator is selected from platinum, palladium and their compounds. 13. Method as stated in claims 6-10, characterized in that the oxidation accelerator introduced into the regeneration zone during step (b) corresponds to 0.1 to 15 ppm by weight of circulating catalyst mass calculated on the basis of elemental metal. 14. Method as stated in claims 6-10, characterized in that the amount of oxygen-containing regeneration gas is equivalent to 10 to 17 kg of air per kg of coke that is supplied to the regeneration zone per unit of time. 15. Method as stated in claims 6-10, characterized in that oxidation conditions in the regeneration zone comprise a temperature of 590 to 790° C and a pressure of between atmospheric pressure and 4.5 atmospheres. 16. Method as set forth in claims 6-10, characterized in that the amount of accelerator introduced into the regeneration zone is equivalent to 0.005 to 10 ppm by weight of circulating catalyst mass based on elemental metal, on average per day.