GB1575018A

GB1575018A - Catalytic cracking with reduced emission of noxious gases

Info

Publication number: GB1575018A
Application number: GB5275576A
Authority: GB
Original assignee: Standard Oil Co
Current assignee: Standard Oil Co
Priority date: 1975-12-19
Filing date: 1976-12-17
Publication date: 1980-09-17
Also published as: FR2335582B1; FR2433973A1; FR2335582A1; DE2654509A1; PL106573B1; JPS649046B2; AU502495B2; JPS5276305A; CS222233B2; CA1093050A; FR2433973B1; IT1076849B; GB1575019A; NL7613481A; AU1998776A

Description

(54) CATALYTIC CRACKING WITH REDUCED EMISSION OF NOXIOUS GASES (71) We, STANDARD OIL COMPANY, a corporation organized and existing under the laws of the State of Indiana, United States of America of 200 East Randolph Drive, Chicago, Illinois 60680, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to catalytic cracking with reduced emission of noxious gases and is particularly concerned with a cyclic fluidized catalytic cracking process which is suitable for use with sulfur-containing hydrocarbon feedstocks, and which involves a marked diminution in the emission of carbon monoxide and sulfur oxides in the regenerator stack gases.

Cracking catalyst which has become relatively inactive due to deposition of carbonaceous deposits, commonly called "coke," during the cracking of hydrocarbons in the reaction zone is continuously withdrawn from the reaction zone. Such spent catalyst from the reaction zone is passed to a stripping zone where strippable carbonaceous deposits, namely hydrocarbons are stripped from the catalyst which in turn is passed to a regeneration zone where the activity qf the catalyst is restored by removing the non-strippable carbonaceous deposits by burning the coke in oxygen-containing gas to form carbon monoxide and carbon dioxide. Hot regenerated catalyst is then continuously returned to the reactor to repeat the cycle.

In catalytic cracking, a problem arises from the incomplete combustion of carbon monoxide to carbon dioxide in the regeneration zone, leaving a significant amount of carbon monoxide in the regeneration zone flue gases. Apart from the undesirability of discharge of carbon monoxide to the atmosphere, carbon monoxide and residual oxygen in regeneration zone flue gases tend to react and thereby cause burning in ducts and flues in the plant and damage to such structures by excessive temperatures.

Further, when high-sulfur feedstocks, that is, petroleum hydrocarbon fractions containing organic sulfur compounds, are charged to a fluid-type catalytic cracking unit, the coke deposited on the catalyst contains sulfur. During regeneration of the coked, deactivated catalyst, the coke is burned from the catalyst surfaces; in this combustion process, the sulfur present is converted to sulfur dioxide, together with a minor proportion of sulfur trioxide, and thus included in the regeneration zone flue gas effluent stream. When cracking a high-sulfur feedstock, emissions of sulfur oxides are often in the region of substantially 1200 parts per million.

Pollution control standards have been developed for the emission of carbon monoxide and for particulate matter and are expected to be considered soon for other emissions, such as the sulfur oxides, particularly sulfur dioxide. Consequently, much attention is being devoted to reducing the level of emissions of various combustion products and particulates from regeneration zone effluent streams associated with petroleum cracking units. It is necessary that the method selected for reducing such emissions should be effective without lowering the activity and selectivity of the cracking catalyst. It is likewise necessary that the method selected should not overcome undesirable emission by presenting other problems, for example, an increase in particulate emission or operating costs. In view of these considerations, a highly desirable approach to a reduction in the emission of carbon monoxide and sulfur oxides from petroleum cracking units lies in the use of a cracking catalyst which is modified to minimize emissions of both carbon monoxide and sulfur oxides, while maintaining catalyst activity, stability, and resistance to attrition, under conventional cracking conditions in either existing or new cracking units.

With regard to carbon monoxide emissions, although metals are generally avoided in cracking catalysts and it is considered problematical to crack metal-containing stocks in the presence of a cracking catalyst, South African Patent No. 7924/72 and its later issued counterpart, U.S. Patent No. 3,909,392, discussed in greater detail below, disclose the use in conjunction with cracking catalysts of combustion catalysts or promoters within the regeneration zone, which include a metallic bar, mesh network, or screen in the combustion zone; and fluidizable- metal compounds, particularly powdered oxides of transition group metals, for example, ferric oxide, manganese dioxide, and rare earth oxides, which are added to the catalyst charge or confined within the regenerator vessel. Belgian Patent No. 826,266 (1975) discloses a method very similar to that of U.S. Patent No. 3,909,392 which involves a catalytic cracking catalyst in physical association with carbon monoxide-oxidation promoting catalyst of a metal having an atomic number of at least 20 and mentions metals from Groups IB, IIB, and III to VIII of the Periodic Table of the elements in particular, platinum, palladium, rhodium, molybdenum, tungsten, copper, chromium, nickel, manganese, cobalt, vanadium, iron, cerium, ytterbium, and uranium, as useful oxidation promoters. Further, U.S. Patent No. 3,808,121 discloses the regeneration of a cracking catalyst in the presence of a carbon monoxide oxidation catalyst which is retained in the regeneration zone.

Netherlands Patent Application No. 7,412,423 discloses that a cracking catalyst containing fewer than 100 parts per million, calculated as metal, based on total catalyst, of at least one metal component consisting of a metal from Periods 5 and 6 of Group VIII of the Periodic Chart, rhenium, and compounds thereof, showed particularly spectacular reductions in the carbon monoxide content in flue gases from catalytic cracking catalysts. This latter Patent also discloses a molecular sieve-type cracking catalyst-which is prepared in the sodium form, ion-exchanged with ammonium ions, and then impregnated with rare earth metals.

Further, with regard to sulfur oxide emissions, although various methods for processing flue gas have been devised, for example, washing or scrubbing, chemical absorption, neutral ization, and chemical reaction or conversion, all such methods for the removal of sulfur oxides require extensive and expensive auxiliary equipment, thus increasing both operating and capital costs. An approach set forth in U.S. Patent No. 3,699,037 contemplates the addition of at least a stoichiometric amount of a calcium or magnesium compound to the cracking cycle in relation to the amount of sulfur deposition on the catalyst. This added material is intended to react with sulfur oxides and then, being in a finely subdivided condition, exit from the cracking cycle as particulate matter in the regeneration zone flue gas stream. Continued addition of such material obviously increases operating costs. Similarly, U.S. Patents Nos. 3,303,300 and 3,030,314 disclose a catalytic cracking process which involves adding continuously to a moving bed cracking process cycle one or more compounds of boron, alkali metals and alkaline earth metals so as to provide catalyst particles which have increased resistance against impact breakage and surface abrasion, and which comprise a siliceous catalyst particle having a microporous, catalytically active core which is provided with an adherent, protective coating of a glaze comprising silica and one or more compounds of boron, alkali metal and alkaline earth metals.

U.S. Patent No. 3,835,031 discloses a cyclic, fluidized catalytic cracking process which provides reduced emissions of sulfur oxides in the regenerator stack gases. The method is operated with a catalyst which comprises a molecular sieve in a silica-alumina matrix and which is impregnated with one or more Group IIA metal oxides. U.S. Patents Nos.

3,388,077; 3,409,390 and 3,849,343, disclose a method for effecting the conversion of a noxious waste gas stream containing carbon monoxide and sulfur oxides, which comprises contacting the stream with a catalytic composite of a porous refractory carrier material, a catalytically active metallic component, for example, a platinium group metal, and an alkaline earth component consisting of calcium, barium or strontium.

According to our invention in its broadest aspect we provide a process for the cyclic, fluidized, catalytic cracking of a hydrocarbon feedstock containing organic sulfur compounds wherein (i) said feedstock is subjected to cracking in a reaction zone with fluidized solid particles of a molecular sieve-type cracking catalyst; (ii) catalyst particles, which are deactivated by sulfur-containing carbonaceous deposits, are separated from reaction zcne effluent and conveyed to a stripping zone wherein volatile deposits are removed from said deactivated catalyst by contact with a stripping gas; (iii) stripped catalyst particles are separated from stripping zone effluent and conveyed to a regeneration zone and regenerated by burning the non-strippable, sulfur-containing carbonaceous deposits from the stripped catalyst with an oxygen-containing gas; and (iv) regenerated catalyst particles are separated from regeneration zone effluent and recycled to the reaction zone a method for reducing emissions of carbon monoxide and sulfur oxides in the regeneration zone effluent gas which comprises,: (a) circulating the cracking catalyst through the process cycle in combination with a metallic reactant which reacts with sulfur oxides in the regeneration zone, the combination of catalyst and reactant consisting of fluidizable solid particles, the reactant being either incorporated into the particles of cracking catalyst or contained in a particulate solid other than the cracking catalyst, and the metallic reactant being a free or combined metallic element which is selected from sodium, magnesium, calcium, strontium, barium, scandium, titanium, chromium, molybdenum, manganese, iron, cobalt, nickel, antimony, copper, zinc, cadmium, lead a rare earth metal, or any mixture thereof; (b) cracking said feedstock at a temperature within the range of from 8500to 1,2000Fand in contact with the cracking catalyst and the metallic reactant; (c) stripping volatile deposits from the particles of said combination at a temperature within the range of from 850"F to 1,2000F with a stripping gas which contains steam, wherein the ratio by weight of steam to the catalyst is within the range of from 0.0005 to 0.025 per unit of time; (d) burning said sulfur-containing carbonaceous deposits from the stripped, solid particles at a temperature within the range of from 1,050 to 1 ,4500F in the presence of at least one free or combined metallic promotor selected from ruthenium, rhodium, palladium, osmium, iridium, platinum, vanadium, silver or rhenium, wherein the metallic promoter and the metallic reactant are present in sufficient amounts to effect absorption of a major portion of the sulfur oxides produced in said regeneration zone, and wherein the metallic promoter is present in sufficient amount to enhance said absorption of sulfur oxides and the conversion of carbon monoxide to carbon dioxide in the regeneration zone; (e) withdrawing an effluent gas containing molecular oxygen from the regeneration zone, said effluent gas having a reduced concentration of sulfur oxides; and (f) substantially withdrawing said absorbed sulfur oxides as a sulfur-containing material in the volatiles from the reaction and/or stripping zone.

In several embodiments, this invention also provides substantially complete combustion of carbon monoxide in the regeneration zone and absorption of the heat evolved during such combustion by solid particles which are circulated to the reaction zone and stripping zone before returning to the regeneration zone. Such solid particles comprise molecular sieve-type cracking catalyst and a metallic reactant and can also contain amorphous cracking catalyst, solids which are substantially inert to the cracking of hydrocarbons, and a metallic promoter.

Alternatively, the metallic promoter can be confined within the regeneration zone.

The metallic promoter and/or a metallic reactant can be incorporated into the molecular sieve-type cracking catalyst, amorphous cracking catalyst, and substantially inert solid and can be circulated through the cracking process cycle. Such incorporation can be achieved either before or after the particular substrate is introduced into the cracking process cycle.

Conditions are employed in the cracking process cycle such that a stable metal- and sulfurcontaining compound forms in the solid particles in the regeneration zone and a sulfurcontaining gas is withdrawn from the stripping zone.

The improvement of the invention comprises providing reduced emissions of carbon monoxide and sulfur oxides in regeneration zone flue gases by employing solid particles which comprise (1) a molecular sieve-type cracking catalyst comprising a cracking catalyst matrix containing crystalline aluminosilicate distributed throughout the matrix and (2) a metallic reactant which reacts with a sulfur oxide to form a metal- and a sulfur-containing compound in the solid particles; by employing a stripping gas which contains steam; by regenerating the stripped, deactivated cracking catalyst in the presence of the metallic oxidation promoter (for the oxidation of carbon monoxide and of sulfur oxide), at regeneration temperatures in the range where the metal- and sulfur-containing compound in the solid particles is stable; and by providing sufficient oxygen to the regeneration zone in the oxygen-containing regeneration gas stream so that flue gases containing molecular oxygen are withdrawn from the regeneration zone. Preferably, the solid particles comprise additionally the metallic promoter. Thus, the metallic promoter can be either confined within the regeneration zone or circulated in the solid particles throughout the catalytic cracking process cycle.

The cracking catalyst matrix of the molecular sieve-type cracking catalyst is preferably a combination of at least two materials consisting of silica, alumina, zirconia, titania. magnesia, thoria or boria, and more preferably is silica-alumina. This cracking catalyst matrix preferably contains from about 10 to about 65, more preferably from about 25 to about 60 weight percent of alumina; preferably from about 35 to about 90, more preferably from about 35 to about 70 weight percent of silica; and preferably from about 0.5 to about 50, more preferably from about 5 to about 50 weight percent of crystalline aluminosilicate. The molecular sieve-type cracking catalyst makes up preferably from about 10 to about 99.999, more preferably from about 30 to about 99.995, and most preferably from about 90 to about 99.995 weight percent of the solid particles.

The metallic promoter consists of at least one first metal from Periods 5 and 6 of Group VIII of the Periodic Chart, vanadium, silver, and rhenium; preferably from Periods 5 and 6 of Group VIII of the Periodic Chart and rhenium; and ideally consisting of platinum or palladium, their compounds, and mixtures thereof. The metallic reactant consists of at least one second metal preferably consisting of sodium, magnesium, calcium, strontium, barium, scandium, titanium, chromium, molybdenum, manganese, iron, cobalt, nickel, antimony, copper, zinc, cadmium, lead or rare earth metal, more preferably consisting of sodium, magnesium, calcium, strontium, barium,scandium, titanium, chromium, molybdenum, man- ganese, cobalt, nickel, copper, zinc, cadmium, antimony, lead or a rare earth metal; most preferably consisting of sodium, magnesium, calcium, strontium, barium, chromium, manganese, copper, zinc, cadmium, or a rare earth metal; and ideally consisting of sodium, magnesium, manganese or copper, their compounds, and mixtures thereof. The metallic reactant contains a second metal which is different from the first metal or metals in the metallic promoter.

The metallic promoter and metallic reactant are present in sufficient average amounts to provide reduced emissions of carbon monoxide and sulfur oxides in the regeneration zone flue gases. When a metal consisting of ruthenium, rhodium, palladiun, osmium, iridium, platinum, silver or rhenium is present, it is at an average level, calculated as the metal, in the range of from about 0.1 part per billion to about 0.1 weight percent, more preferably in the range of from about 0.1 part per billion to about 50 parts per million, and most preferably in the range of from about 0.1 part per million to about 10 parts per million of the solid particles.

When a metal consisting of vanadium or copper is present, it is at an average level, calculated as the metal, preferably in the range of from about 10 parts per million to about 10 weight percent, more preferably in the range of from about 50 parts per million to about 0.1 weight percent, and most preferably in the range of from about 50 parts per million to about 250 parts per million of the solid particles. When iron is present, it is at an average level, calculated as iron, preferably in the range of from about 50 parts per million to about 5 weight percent, more preferably in the range of from about .1 weight percent to about 1 weight percent and most preferably in the range of from about .3 weight percent to about 0.8 weight percent of the solid particles. When a metal consisting of magnesium, zinc, calcium, cadmium, manganese, strontium, barium, scandium or cobalt is present, it is at an average level, calculated as the metal, preferably in the range of from about 25 parts per million to about 7 weight percent, more preferably in the range of from about 0.01 weight percent to about 5 weight percent, and most preferably in the range of from about .01 weight percent to about 0.5 weight percent of the solid particles. When chromium, antimony or lead is present, it is at an average level, calculated as the metal, preferably in the range of from about 10 parts per million to about 1 weight percent, more preferably in the range of from about 0.01 weight percent to about 0.1 weight percent, and most preferably in the range of from about 0.01 weight percent to about 250 parts per million, of the solid particles. When sodium is present, it is at an average level, calculated as sodium, preferably in the range of from about 0.6 weight percent to about 3 weight percent, more preferably in the range of from about 0.8 weight percent to about 2 weight percent, and most preferably in the range of from about 0.85 weight percent to about 1.5 weight percent of the solid particles. When titanium is present, it is at an average level, calculated as titanium, preferably in the range of from about 10 parts per million to about 10 weight percent, more preferably in the range of from about 0.5 weight percent to about 1 weight percent, and most preferably in the range of from about 0.5 weight percent to about 0.8 weight percent, of the solid particles. When a rare earth metal is present, it is at an average level, calculated as the metal, preferably in the range of from about .2 weight percent to about 10 weight percent, more preferably in the range of from about 2 weight percent to about 6 weight percent, and most preferably in the range of from 2 weight percent to about 4 weight percent of the solid particles. When nickel is present, it is present at an average level, calculated as nickel, preferably in the range of from about 10 parts per million to about 10 weight percent, more preferably in the range of from about 50 parts per million to about 0.5 weight percent, and most preferably in the range of from about 50 parts per million to about 0.1 weight percent of the solid particles.

Certain individual solids in the solid particles of the method of this invention can contain an amount of at least one of the metallic promoter and metallic reactant which is greater than the average amount thereof in the solid particles, provided that such certain individual solids are admixed with other individual solids in the solid particles containing a smaller amount of at least one of the metallic promoter and metallic reactant such that the solid particles contain the above-mentioned average levels of the metallic promoter and metallic reactant.

The stripped, deactivated catalyst is regenerated at regeneration temperatures in the range where a stable metal- and sulfur-containing compound is formed in the solid particles from the metal in the metallic reactant and the sulfur oxide. The regeneration temperatures are preferably in the range of from about 1,050"F. to about 1,450"F. and more preferably in the range of from about 1,1800F. to about 1,350"F. The hydrocarbon feedstock is cracked at reaction temperatures in the range where the metal- and sulfur-containing compound in the solid particles reacts to form a sulfide of the metal in the metallic reactant. The cracking reaction temperature is preferably in the range of from about 850"F. to about 1,200"F., and more preferably in the range of from about 870"F. to about 1,100"F. The strippable disposits are stripped from the deactivated cracking catalyst with a steam-containing gas and at stripping temperatures in the range where the sulfide of the metal in the metallic reactant reacts with water to form hydrogen sulfide gas. The stripping temperatures are preferably in the range of from about 850"F. to about 1,200"F., and more preferably in the range of from about 870"F. to about 1,100"F. The weight ratio of steam-to-molecular sieve-type cracking catalyst being supplied to the stripping zone is preferably in the range of from about 0.0005 to about 0.025, and more preferably in the range of from about 0.0015 to about 0.0125. The regeneration zone flue gases contain preferably at least 0.01 volume percent and more preferably at least 0.5 volume percent of oxygen in order for the desired reduction of emissions of noxious gases to be achieved.

In one embodiment of this invention, at least one of the metallic promoter and metallic reactant is incorporated into the molecular sieve-type cracking catalyst. In such case, at least one of the metallic promoter and metallic reactant is incorporated into either the crystalline aluminosilicate or the matrix in the molecular sieve-type cracking catalyst. In another embodiment of this invention, the solid particles comprise additionally at least one material consisting of a solid which is substantially inert to the cracking of hydrocarbon feedstock or an amorphous cracking catalyst; and at least one of the metallic promoter and metallic reactant is incorporated into such material. In still another embodiment of this invention, at least one of the metallic promoter and metallic reactant is itself a solid in the solid particles. Our copending application 25455/79 (Serial No. 1575019) which has been divided from the present application) describes and claims various catalyst compositions suitable for use in the present invention.

The metallic promoter or metallic reactant or both can be incorporated into the solid particles either outside or within the catalytic cracking process cycle, which comprises the cracking reaction zone, the stripping zone and the regeneration zone. If incorporated during the catalytic cracking process cycle, then at least one of the metallic promoter and metallic reactant can be introduced into the fluid catalytic cracking process cycle as an oil- or water-soluble or -dispersible compound of the metal or metals in the metallic promoter and/or metallic reactant in the form of a solid, liquid, or gas, and can be incorporated in situ into the solid particles. Preferably, such compound consists of a metal diketonate, metal carbonyl, metallocene, metal olefin complex of from 2 to 20 carbon atoms, metal acetylene complex, metal complex of alkyl or aryl phosphines or metal carboxylate having from 1 to 20 carbon atoms. More preferably, one of such compounds is platinum acetylacetonate.

This invention relates to an improved fluid catalytic cracking process, including an improved process for the regeneration of cracking catalyst employed in fluid catalytic conversion and an improved process for reducing emissions of carbon monoxide and sulfur oxides in cracking catalyst regeneration zone effluent gas, involving the conversion of sulfur-containing hydrocarbon feedstocks wherein the cracking catalyst is deactivated by the deposition of sulfur-containing coke on the cracking catalyst surface. The solid particles of the method of this invention, comprising molecular sieve-type cracking catalyst. are circulated in well-dispersed physical association with one another throughout the cracking process cycle, which comprises the cracking zone, the stripping zone and the regeneration zone. The conditions employed effect reduction of carbon monoxide and sulfur oxides in the regeneration zone flue gases.

The cracking catalyst,metallic promoter, and metallic reactant of the method of this invention serve separate and essential functions. The cracking catalyst serves to catalyse the cracking reaction, which the metallic promoter and metallic reactant are substantially inert toward the cracking reaction and have little, if any, adverse effect on the catalytic conversion operation under the conditions employed. With regard to the combustion of carbon monoxide, all metals and their compounds which can serve suitably as the metallic promoter catalyse the oxidation of carbon monoxide to carbon dioxide within the regeneration zone. With regard to the reduction of sulfur oxides in the regeneration zone flue gas, the solid particles adsorb sulfur oxides in the regeneration zone. The molecular sieve-type cracking catalyst itself often serves as an adsorbent for sulfur oxides. The metallic promoter catalyses the oxidation of sulfur oxide or of a sulfur oxide group in a metal compound, and the metallic reactant reacts with the adsorbed sulfur oxides to form a metal- and sulfur-containing compound, in particular, a metal sulfate, in the solid particles. Provided that such metal- and sulfur-containing compound is stable under the operating conditions in the regeneration zone, it is carried on the surface of the solid particles to the reaction zone and stripping zone where it is reduced and separated as a sulfur-containing gas, in particular, as hydrogen sulfide.

It is understood that the activity in reducing the emission of carbon monoxide and of sulfur oxides in the regeneration zone flue gases may vary from metal to metal in the classes of those which may serve as a metal in the metallic promoter or metallic reactant. Similarly, many of the specific metals which may serve as a metal in the metallic promoter or metallic reactant do not necessarily yield equivalent results when compared with other specific metals which may be used in the metallic promoter or metallic reactant, respectively, or when utilized under varying conditions.

The solid particles of the method of this invention are finely divided and have, for example, an average particle size in the range of from about 20 microns or less to about 150 microns, such that they are in a form suitable for fluidization. Suitable cracking catalyst matrices include those containing silica and/or alumina. Other refractory metal oxides may be employed, limited only by their ability to be effectively regenerated under the chosen conditions. Admixtures of clay-extended aluminas may also be employed. Preferred catalysts include combinations of silica and alumina, admixed with "molecular sieves", also known as zeolites of crystalline aluminosilicates. Suitable cracking catalysts contain a sufficient amount of crystalline alumino silicate materially to increase the cracking activity of the catalyst. limited only by their ability to be effectively regenerated under the chosen conditions. The crystalline aluminosilicates usually have silica-to-alumina mole ratios of at least about 2:1, for instance about 2 to 12:1, preferably from about 4 to about 6: 1. Cracking catalysts with silica bases having a major proportion of silica, for example, from about 35 to about 90 weight percent silica and from about 10 to 65 weight percent alumina are suitable. Such catalysts may be prepared by any suitable method, such as milling, co-gelling, and the like, subject only to provision of the finished catalyst in a physical form capable of fluidization.

Suitable molecular sieves include both naturally occurring and synthetic aluminosilicate materials such as faujasite, chabazite, X-type and Y-type aluminosilicate nlaterials, and ultrastable, large-pore crystalline aluminosilicate materials. When admixed with, for example, silica-alumina to provide a petroleum cracking catalyst, the molecular sieve content of the fresh finished catalyst particles is suitably within the range of from about 0.5 to about 50 weight percent, desirably from about 5 to about 50. An equilibrium molecular sieve cracking catalyst may contain as lit of lighter materials or coke. The weight ratio of total cracking catalyst-to-oil in the riser reactor may vary within the range of from about 2 to about 20 in order that the fluidized dispersion will have a density within the range of from about 1 to about 20 pounds per cubic foot. Desirably, the catalyst-to-oil ratio is maintained within the range of from about 3 to about 20, preferably 3 to about 7. The fluidizing velocity in the riser reactor may range from about 10 to about 100 feet per second. The riser reactor generally has a ratio of length-to average diameter of about 25. For production of a typical naphtha product, the bottom section mixing temperature within the riser reactor is advantageously maintained at from about 1,000"F. to about 1,100"F. for vaporization of the oil feed, and so that the top section exit temperature will be about 950"F. For cracking residues and synthetic fuels, substantially higher temperatures would be necessary. Under these conditions, including provision for a rapid separation of spent catalyst from effluent oil vapour, a very short period of contact between the catalyst and oil will be established. Contact time within the riser reactor will generally be within the range of from about 1 to about 15 seconds, and preferably within the range of from about 3 to about 10 seconds. Short contact times are preferred because most of the hydrocarbon cracking occurs during the initial increment of contact time, and undesirable secondary reactions are avoided. This is especially important if higher product yield and selectivity, including lesser coke production, are to be realized.

Short contact time between catalyst particles and oil vapours may be achieved by various means. For example, catalyst may be injected at one or more points along the length of a lower, or bottom, section of the riser. Similarly, oil feed may be injected at all the points along the length of the lower section of the riser reactor, and a different injection point may be employed for fresh and recycle feed streams. The lower section of the riser reactor may, for this purpose, include up to about 80 percent of the total riser length in order to provide extremely short effective contact times inducive to optimum conversion of petroleum feeds.

Where a dense catalyst bed is employed, provision may also be made for injection of catalyst particles and/or oil feed directly into the dense-bed zone.

While the conversion conditions set forth above are directed to the production of gasoline as fuel for spark-ignition internal combustion engines, the processing scheme may be suitably varied to permit maximum production of heavier hydrocarbon products such as jet fuel, diesel fuel, heating oil and chemicals, in particular, olefins and aromatics.

In the catalytic process, some non-volatile carbonaceous material, or "coke", is deposited on the catalyst particles. Coke comprises highly condensed aromatic hydrocarbons which generally contain a minor amount of hydrogen, say from about 4 to about 10 weight percent.

When the hydrocarbon feedstock contains organic sulfur compounds, the coke also contains sulfur. As coke builds up on the catalyst, the activity of the catalyst for cracking and the selectivity of the catalyst for producing gasoline blending stocks diminish. The catalyst particles may recover a major porportion of their original capabilities by removal of most of the coke therefrom in a suitable regeneration process.

The spent catalyst from the petroleium conversion reactor is stripped prior to entering the regenerator. The stripping vessel for use in fluidized bed catalytic cracking unit may suitably be maintained essentially at conversion reactor temperature in the range of from about 850 to about 1,200 F. and desirably will be maintained above about 870"F. The preferred stripping gas is steam, although steam-conditioning nitrogen or other steam-containing inert or flue gas, may also be employed. The stripping gas is introduced at a pressure of generally at least about 10, preferably about 35 pounds per square inch gauge, suitable to effect substantially complete removal of volatile compounds from the spent conversion catalyst.

The method of this invention can be employed with any conventional cracking catalyst regeneration scheme but is advantageously employed with a regeneration system involving at least one dense-bed and at least one dilute-phase zone. Stripped spent catalyst particles may enter the dense-bed section of the regenerator vessel through suitable lines evolving from the stripping vessel. Entry may be from the bottom or from the side, desirably near the top of the dense-bed fluidized zone. Entry may also be from the top of the regenerator where catalyst has first been contacted with substantially spent regeneration gas in a restricted dilute-phase zone.

Catalyst regeneration is accomplished by burning the coke deposits from the catalyst surface with a molecular oxygen-containing gas, such as air. Many regeneration techniques are practised commercially whereby a significant restoration of catalyst activity is achieved in response to the degree of coke removal. As coke is progressively removed from the catalyst, removal of the remaining coke becomes most difficult and, in practice, an intermediate level of restored catalyst activity is accepted as an economic compromise.

The burning of coke deposits from the catalyst requires a large volume of oxygen or air.

Although the disclosed invention is not to be limited thereby, it is believed that oxidation of coke may be characterized in a simplified manner as the oxidation of carbon and represented by the following chemical equations: (a) C + 02 z CO2 (b) 2C + 2 < 2CO (c) 2CO + O2 z 2CO2 Reactions (a) and (b) both occur under typical catalyst regeneration conditons wherein the catalyst temperature may range from about 1050C to about 1450"F. and are exemplary of gas-solid chemical interactions when regenerating catalyst at temperatures within this range.

The effect of any increase in temperature is reflected in an increased rate of combustion of carbon and a more complete removal of carbon, or coke, from the catalyst particles. As the increased rate of combustion is accompanied by an increased evolution of heat, whenever sufficient free or molecular oxygen is present, the gas-phase reaction (c) may occur. This latter reaction is initiated and propagated by free radicals and can be catalysed.

The burning of sulfur-containing coke deposits from the catalyst also results in the formation of sulfur oxides; and, although the disclosed invention is not to be limited thereby, this burning mav be reDresented bv the following chemical eauations:

Reactions (d) and (e) also occur under typical cracking catalyst regeneration conditions.

While reaction (d) is fast, reaction (e) is relatively slow. Reaction (e) can be catalysed by any catalyst which catalyses reaction (c) above. Molecular sieves adsorb sulfur oxides, and therefore reaction (e) can occur on the cracking catalyst in the solid particles of the method of this invention. Other components of the solid particles can also adsorb sulfur oxides. The resulting sulfur trioxide can then react with a suitable metal, or more particularly an oxide of the metal in the metallic reactant, to form a stable metal sulfate in the solid particles. When the solid particles are separated from the regeneration zone flue gases, the metal sulfate in the solid particles is circulated to the reaction zone. Thus, the sulfur is rendered unavilable for exit as gaseous sulfur oxides in the regeneration zone flue gas.

The sulfate remains on the solid particles as they pass to the cracking reaction zone and, in the reducing atmosphere therein, is converted to the sulfide of the metal in the metallic reactant and possibly to hydrogen sulfide. Upon stripping with a steam-containing stripping gas in the stripping zone, the sulfur is converted to hydrogen sulfide and exits in the stripping zone effluent stream. The metallic reactant is thereby regenerated and made available again for reaction with sulfur oxides in the next pass through the regeneration zone. Hydrogen sulfide can then be recovered with the cracking products from the stripping zone, separated and converted to elemental sulfur in conventional facilities.

Although the disclosed invention is not to be limited thereby, it is believed that these reactions can be summarized as follows: Regenerator MxO +SO2 + 1/202 o MxO + S03 z MxSO4 Reactor MxSO4 + 4H2 < MxS + 4H20 < MxO + ll2S + 3H2O Stripper MxS + H20 o MxO + H2S where x is the ratio of the oxidation state of the oxide ion to the oxidation state of the metal in the metallic reactant when combined with oxygen.

These reactions are made possible by the molecular sieve-type cracking catalyst, metallic promoter and metallic reactant of the method of this invention. The high cracking activity normally present in the molecular sieve catalyst remains substantially unaffected by the presence of either the metallic promoter or metallic reactant so that the anticipated conversion of feedstock and yield of cracked products are realized together with the diminution of emission of carbon monoxide and sulfur oxides.

The metallic promoter can be a solid which is confined within the regeneration zone. The metallic promoter or metallic reactant or both can also be in a finely divided form, such as a powder, separate from the molecular sieve-type cracking catalyst or any other support. The metallic promoter or metallic reactant or both may be a powder which is admixed with the hydrocarbon cracking catalyst and circulated through the catalytic cracking process cycle.

Generally, such powdered metallic promoter or metallic reactant or both is advantageously in that a powder is easy to charge to, and handle in, a fluidized catalytic cracking process system.

The particle size of the powder should be chosen so as to avoid segregation of the particles at the fluidizing velocities. Desirably, the particles in such powder are not so minute that problems occur such as excessive emission with the gases from the bed as entrained particulate matter; however, filters, cyclones, precipitators, and the like are usually employed in conjunction with fluidized catalytic cracking operations to recover most of the entrained particulate matter and return it to the system to abate losses. The powder should be sufficiently strong for excessive attrition and degradation of the sized powder to be avoid.

Frequently, the average particle size of the powdered metallic promoter or metallic reactant or both is from about 0.5 or 1 to 100 microns, preferably less than about 50 microns, in diameter. It has been noted that microsized particles, that is, having an average particle size of less than about 1 micron, for instance, about 0.01 to 0.5 micron, may tend to form aggregates of larger size which may beneficially be employed in the process of fhis invention. Illustrative of powdered metallic promoters and metallic reactants which may be employed are ferric oxide, ferrous oxide, zinc oxide, manganese dioxide, cerium oxide and the like, dolomite and Trimex ((Trade Mark) manufactured by Trimex Corp. and described in U.S. Patent No.

3,630,696;.

Alternatively, the metallic promoter or metallic reactant or both can be incorporated onto a suitable support. The metallic promoter and metallic reactant can be incorporated into the substrate simultaneously or at different times and by the same or different methods of incorporation. Such support can be an amorphous cracking catalyst or a solid which is substantially inert to the cracking reaction and can, for example, be ceramic in nature. In such case, the supported metallic promoter or metallic reactant or both are then admixed with the molecular sieve-type cracking catalyst. Desirably, the support is porous and frequently has a surface area, including the area of the pores on the surface, of at least about 10, preferably at least about 50, square meters per gram. Illustrative of the supports are silica, alumina, silica-alumina and the like. Alternatively, the metallic promoter or metallic reactant or both can be incorporated into the molecular sieve-type cracking catalyst, or portion thereof, in the solid particles in the method of this invention. In such case, the metallic promoter or metallic reactant or both can be introduced into the cracking catalyst matrix during the catalyst manufacture or can be impregnated on the cracking catalyst structure. In such case, care should be taken in choice of the method of incorporation so that the cracking activity and selectivity of the cracking catalyst are not adversely affected. It is preferred that, if the cracking catalyst is of the type having ion-exchanged sites, the ion-exchange should be completed prior to incorporation of the metallic promoter and/or metallic reactant.

In any of the above cases, the precise manner in which the metal or metals of the metallic promoter or metallic reactant or both are incorporated into the molecular sieve-type cracking catalyst, amorphous cracking catalyst, or substantially inert substrate is not known with absolute certainty. The metals may enter into a complex combination with the carrier material and other components of the solid particles of this invention. Therefore, it is understood that the use of the terms "metallic promoter" or "metallic reactant" and "incorporated" into the substrate connotes the metals of such components existing on the carrier material in a combined form and/or in the elemental state.

The metallic promoter and/or metallic reactant may be incorporated into the substrate by ion exchange, by impregnation, or by other means, by contacting the substrate or a component thereof with a solution or solutions of a compound or compounds of the metal or metals in the metallic promoter or metallic reactant or both in an appropriate amount necessary to provide the desired concentration of the metallic promoter or metallic reactant or both within the scope of the invention.

The metallic promoter and/or metallic reactant may be combined with the substrate either in any step during preparation of the substrate or after the substrate has been prepared. One manner of incorporation is to subject the substrate to ion-exchange. For example, it is preferred to ion-exchange a crystalline aluminosilicate with a solution or solutions of a compound or compounds of the metal or metals in the metallic promoter or metallic reactant or both, and then to composite the ion-exchanged product with a porous cracking catalyst matrix. Also useful is the ion-exchanging of siliceous solids or clays with a solution or solutions of a compound or compounds of the metal or metals in the metallic promoter or metallic reactant or both. Suitable compounds for this purpose include the metal halides, preferably chlorides, nitrates, amine halides, oxides, sulfates, phosphates and other watersoluble inorganic salts; and also the metal carboxylates of from 1 to 5 carbon atoms, and alcoholates. Specific examples include palladium chloride, chloroplatinic acid, ruthenium penta-amine chloride, osmium chloride, perrhenic acid, diox obis(ethylenediamine)rhenium(V) chloride, rhodium chloride and the like.

Another method of preparing the metallic promoter or metallic reactant or both for use in the present invention is by impregnation of a suitable support with a water- or organic solvent-soluble or -dispersible compound or compounds or the metal or metals in the metallic promoter and/or metallic reactant. The impregnation may be practised in any way which will not destroy the structure of the substrate. The metallic promoter or metallic reactant or both may be impregnated onto a support inert to the hydrocarbon cracking, the molecular sieve-type cracking catalyst, or an amorphous cracking catalyst.

Impregnation differs from cation-exchange. Impregnation results in greater deposition and a primarily physical association on the surface of the substrate, while ion exchange results in a primarily chemical association and a greater diffusion and therefore less surface deposition.

In impregnation, the metal is deposited and no significant ion exchange occurs between the metal and the substrate. In impregnating a substrate, the metal or metals in the metallic promoter or metallic reactant or both can be present in or as a water- or organic solventsoluble or -dispersible compound or compounds in water or an organic solvent, in an amount or amounts sufficient to contain the quantity of metal or metals desired on the substrate, and the substrate is contacted therewith. The composite may be dried to remove the solvent, leaving the metallic promoter or metallic reactant or both deposited on the substrate.

Preferably, water-soluble nitrate salts are employed in the impregnating solution since residue from the thermal decomposition of nitrate salts is relatively innocuous to the activity of the hydrocarbon cracking catalyst. The halogen and sulfate salts of the metal to be impregnated may also be employed; however, since halogen or sulfide may be evalved during thermal degradation of the salt and may be deleterious to the activity of the hydrocarbon cracking catalyst, these salts are most often employed when depositing the metallic promoter or metallic reactant or both on substrates which are substantially inert to the cracking reaction and which do not significantly adversely affect the hydrocarbon cracking reaction.

Another method of physically depositing the metallic promoter or metallic reactant or both on a substrate, particularly porous substrates such as crystalline aluminosilicates, is adsorption of a fluid decomposable compound or compounds of the metal or metals in the metallic promoter or metallic reactant or both on the substrate followed by thermal or chemical decomposition of the compound or compounds. The substrate may be activated by heating to remove any adsorbed water and then contacted with a fluid decomposable compound or compounds of the metal or metals in the metallic promoter or metallic reactant or both, thereby adsorbing the compound or compounds onto the substrate. Typical of such compounds are the metal carbonyls, metal alkyls, volatile metal halides and the like. The adsorbed compound or compounds may then be reduced thermally or chemically to its active state thus leaving uniformly dispersed on the substrate an active metallic promoter or metallic reactant or both. Thermal reduction may be effected, for example, in the regeneration vessel during the regeneration process.

Both impregnation and adsorption can be performed with a substrate before it is introduced into the cracking process cycle. However, it is also advantageous to introduce a compound or compounds of the metal or metals in the metallic promoter or metallic reactant or- both into the cracking process cycle and incorporate it in situ into the substrate. Such compound or compounds can be introduced in either oil- or water-soluble or -dispersible form and in the solids, liquid, or gaseous state at any stage of the cracking process cycle so that wide distribution in the solid particles is achieved. For example, such compound or compounds can be admixed with the feedstock or fluidizing gas in the reaction zone, with the regeneration gas, torch oil, or water in the regeneration zone, or with the stripping gas in the stripping zone, or can be introduced as a separate stream. Suitable compounds for in situ incorporation include metal salts, organo-metallic compounds, metal diketonates, carbonyls, metallocenes, olefin complexes of 2 to 20 carbons, acetylene complexes, alkyl or aryl phosphine complexes and carboxylates of 1 to 20 carbons. Specific examples of these are platinum acetylacetonate, tris(acetylacetonato)- rhodium(III), triiodoridium(III) tricarbonyl, cyclopentadienylrhenium(I) tricarbonyl, ruthenocene, cyclopentadienyl sodium(I) dicarnonyl dimer, dichlor(ethylene)palladium(II) dimer, (cyclopen tadienyl) (ethylene)rhodium(I), diphenyl acetylenebis(triphenylphosphino)-platinum(O), bromoethylbis- (triethylphosphino)paladium(II), tetrakis(triphenylphosphine)palladium(O), chlorocarbonyl-bis-(triphenylphosphine)iridium(I), palladium acetate, palladium naphthenate, zinc dimethyl and zinc diethyl.

The key features of activity and stability are more easily attainable by introducing at least one of the metallic promoter and metallic reactant for producing reduced emissions of carbon monoxide and sulfur oxides into the cracking process cycle and incorporating it into the solid particles in situ, rather than compositing it with the cracking catalyst during manufacture of the cracking catalyst. Introducing at least one of the metallic promoter and metallic reactant into the cracking process cycle and incorporating it in situ as opposed to compositing it with the cracking catalyst during cracking catalyst preparation has been found to result in greater reduction in emissions of carbon monoxide and sulfur oxides in regeneration zone flue gases.

Incorporating at least one of the metallic promoter and metallic reactant during the cracking cycle is also advantageous in that a larger degree of control is maintained over any potential deleterious effect of such metallic promoter and/ or metallic reactant on the cracking reaction as the rate and/or amount of such metallic promoter and/ or metallic reactant introduced into the cracking cycle can be varied. Also, such metallic promoter and/or metallic reactant previously composited with the cracking catalyst before introduction of the catalyst into the cracking process cycle can be lost as fines during attrition of the cracking catalyst. Adding the metallic promoter and/or metallic reactant to the cracking cycle and incorporating it into the solid particles in situ allows for maintenance of a desired amount of metallic promoter and/ or metallic reactant on the outside or accessible portions of the solid particles.

A further method involves incorporating the metallic promoter or metallic reactant or both with a substrate precursor, for instance a silica gel or silica-alumina gel, prior to spray drying or other physical formation process, and drying the precursor to prepare the substrate. The resultant substrate body may be calcined to form the active material. Alternatively, heat treatment may be effected in the cracking cycle.

In a preferred embodiment of the invention, the metallic reactant is primarily in physical association with the molecular sieve-type cracking catalyst and consists of sodium, a rare earth metal or a compound or mixture thereof. In the practice of this embodiment, the metal or metals of the metallic reactant may be combined with the molecular sieve-type cracking catalyst by any method which does not result in a substantial chemical incorporation of such metal or metals into the crystalline aluminosilicate portion of the cracking catalyst. Consequently, in this embodiment, the metallic reactant cannot be incorporated into the molecular sieve-type cracking catalyst by ion exchange. With the exception of ion exchange on the molecular sieve-type cracking catalyst, however, the aforementioned techniques for incorporation of the metallic reactant into the substrate are generally suitable for use in the practice of this embodiment.

A major benefit from the process of this invention relates to the unusually low carbon monoxide content in the effluent gas stream from the regenerator which may be obtained.

Whereas flue gas from conventional regeneration of cracking catalysts usually contains from about 6 to 10 percent carbon monoxide, a similar amount of carbon dioxide and very little oxygen, the carbon monoxide content of the flue gas from this novel regeneration process may be maintained at less than about 0.2 volume percent, for example, about 500 to 1000 parts per million by volume (ppmv). Advantageously, the content is even lower, for example, within the range of from 0 to about 500 ppmv. This low concentration of carbon monoxide in the flue-gas stream permits the direction release of effluent gases to the atmosphere while meeting ambient air quality standards. If required, any remaining carbon monoxide may suitably be burned in the exhaust from the regenerator flue gas stack. This advantage of the invention additionally permits the elimination of capital expenditures otherwise required for installation of carbon monoxide boilers and associated turbine-type devices or other means for partial recovery of energy produced by the subsequent oxidation of the carbon monoxide while still meeting the existing standards for ambient air quality for carbon monoxide emissions.

The method of this invention provides additional benefits. Such benefits relate to the problem of after-burning and heat balance. A major problem often encountered and sought to be avoided in the practice, particularly of fluid catalyst regeneration, is the phenomenon known as "afterburning", described, for example, in Hengstebeck, Petroleum Processing, McGraw-Hill Book Co., 1959, at pages 160 and 175 and discussed in Oil and Gas Journal, Volume 53 (No. 3), 1955, at pages 93-94. This term is descriptive of the further combustion of carbon monoxide to carbon dioxide, as represented by reaction (c) above, which is highly exothermic. Afterburning has been vigorously avoided in catalyst regeneration processes because it was felt it could lead to very high temperatures which might damage equipment and cause permanent deactivation of cracking catalyst particles. Many fluid catalyst regenerator operations have experienced afterburning, and a very substantial body of art has developed around numerous means for controlling regeneration techniques so as to avoid afterburning. More recently, it has been sought to raise regenerator temperatures for various reasons; elaborate arrangements have also been developed for control of regenerator temperatures at the point of incipient afterburning by suitable means for control of the oxygen supply to the regenerator vessel as set forth, for example, in U.S. Patents Nos. 3,161,583 and 3,206,393, as well as in U.S. Patent No. 3,513,087. In typical contemporary practice accordingly, with avoidance of afterburning, the flue gas from catalyst regenerators usually' contains very little oxygen and a substantial quantity of carbon monoxide and carbon dioxide in nearly equimolar amounts.

Further combustion of carbon monoxide to carbon dioxide is an attractive source of heat energy because reaction (c) is highly exothermic. Afterburning can proceed at temperatures above about 1100 F. and liberates approximately 4350 BTU per pound of carbon monoxide oxidized. This typically represents about one-fourth of the total heat evolution realizable by combustion of coke. The combustion of carbon monoxide can be performed controllably in a separate zone or carbon monoxide boiler, after separation of effluent gas from catalyst, as described in, for example, U.S. Patent No. 2,753,925, with the released heat energy being employed in various refinery operations such as the generation of high pressure steam. Other uses of such heat energy have been described in U.S. Patents Nos. 3,012,962 and 3,137,133 (turbine drive) and U.S. Patent No. 3,363,993 (preheating of petroleum feedstock). Such heat recovery processes require separate and elaborate equipment but do serve to minimize the discharge of carbon monoxide into the atmosphere as a component of effluent gases, and, hence, serve to avoid a potentially serious pollution hazard.

Moreover, silica-alumina catalysts, employed conventionally for many years in various processes for the cracking of petroleum hydrocarbons, are not particularly sensitive to the level of residual coke on catalyst provided that the coke level be no greater than about 0.5 weight percent. However, silica-alumina catalysts have been largely supplanted by catalysts additionally incorporating a crystalline aluminosilicate component and known as zeolites or molecular sieves. The molecular sieve-containing catalysts are much more sensitive to the residual coke level, being greatly affected both with regard to catalyst activity and to catalyst - selectivity for conversion of feed to the desired product or products. Due to the difficulties encountered in conventional catalyst regeneration techniques for removal of the last increments of residual carbon, the practical coke level usually corresponds to a residual coke content on regenerated catalyst within the range of from 0.2 to about 0.3 weight percent.

Since enhanced activity and selectivity are achievable with sieve-type cracking catalysts at low coke levels, an attractive incentive is provided for discovering a means for reducing residual coke levels still further. Coke levels below about 0.05 weight percent are greatly desired but usually cannot be achieved by commercially practicable means. Considerations- such as larger regeneration vessels, greater catalyst inventory, greater heat losses, and the like, all serve to discourage attainment of such ideal equilibrium catalyst activity levels.

Preferred embodiments of the method of this invention involve operation in conjunction with the regeneration scheme of U.S. Patent No. 3,909,392. U.S. Patent No. 3,909,392 is directed to an improved catalytic cracking process, including an improved process for the regeneration of catalysts employed in fluid catalytic conversion of hydrocarbon feedstocks wherein the catalyst is deactivated by the deposition of coke on the catalytic surfaces. The process enables the coke level on regenerated catalyst to be maintained at an extremely low level while simultaneously maintaining a favourable heat balance in the conversion unit and providing a flue gas stream having an extremely low carbon monoxide content. Heat from the combustion of carbon monoxide is absorbed by the regenerated catalyst and provides part of the process heat required in the hydrocarbon conversion zone. In one embodiment of the process of the latter U.S. Patent, the combustion of carbon monoxide to carbon dioxide is carried substantially to completion within the regeneration vessel in a relatively dilute secondary catalyst regeneration zone advantageously at a temperature between about 1200 and 1500"F., desirably between about 1205 and 1450"F. The temperature of the secondary zone may be about 50 or 100"F. higher than that of the first regeneration zone. Partially regenerated catalyst from a relatively dense primary catalyst regeneration zone can be controllably flowed through the secondary zone in an amount and at a rate sufficient to absorb substantially all of the heat released by the combustion occurring in the secondary zone. Although most of the coke is burned from the catalyst in the primary zone, additional coke is burned from the partially regenerated catalyst while present in the secondary zone, and catalyst substantially free of coke may be recovered by recycle to the hydrocarbon conversion level.

In a second embodiment of the process of U.S. Patent No. 3,909,392, substantially all of the combustion, including both the oxidation of coke or carbon on the catalyst and the oxidation of carbon monoxide, occurs within a single, relatively dense phase regeneration zone in response to the proper control of, principally, the regeneration temperature and the gas velocity.

Similarly, when the process of the present invention is operated in embodiments involving the regeneration scheme of U.S. Patent No. 3,909,392, the major amount of heat liberated from the combustion of carbon monoxide in the regeneration zone is absorbed by the solid particles of this invention which include the cracking catalyst, and provides part of the heat required in the cracking zone. Beneficially, in such embodiments, the process of the present invention enables considerable coke and carbon monoxide to be combusted in the densephase zone, if one is present, wherein a substantially increased amount of solid particles is present, as compared with the dilute-phase zone, if one is present, to disperse the heat evolved therefrom. As the portion of combustion occurring in the dense-phase zone is increased, the evolution of heat in the dilute-phase zone is substantially reduced, and, hence, the need to provide rapid turnover of solid particles in the dilute-phase zone to absorb the evolved heat is reduced or eliminated.

In such embodiments, the process includes the use of the solid particles of this invention which comprise molecular sieve- type cracking catalyst and can also comprise the metallic promoter and metallic reactant of this method, in a system which supports substantially. complete combustion of carbon monoxide. The low catalyst coke levels achieved are less than about 0.2 weight percent, preferably less than about 0.05 weight percent. This process can result in flue gas having carbon monoxide levels of less than about 0.2 volume percent, for example about 500 to 1000 parts per million, and as low as from 0 to about 500 parts per million. The process also includes provision for recovery of evolved heat by transfer directly to the solid particles within the regeneration vessel.

In such embodiments, the fluidizing gas in the dense zone of the regenerator may have a velocity, for example, in the range of from about 0.2 to 4 feet per second, desirably about'0.5 to 3 feet per second. The regeneration gas serving to fluidize the dense-bed contains free or molecular oxygen, and the oxygen is charged to the generator in an amount somewhat in excess of that required for complete combustion of coke (carbon and hydrogen) to carbon dioxide and steam. The amount of oxygen in excess of that required for complete combustion of the coke may vary from about 0.1 to about 25 or more percent of the theoretical stoichiometric oxygen requirement for complete combustion of the coke, but advantageously need not be greater than about 10 percent. For example, when air is employed as the regeneration gas, a 10 percent excess of air provides only about 2 volume percent of oxygen in the effluent spent gas stream. Advantageously, the concentration of molecular or free oxygen and carbon monoxide at any point within the regenerator is maintained outside of the explosive range under those conditions, and preferably, the concentration of carbon monoxide is below the explosive range under those conditions, to eliminate any risk of detonation.

The regeneration gas, in addition to free or molecular oxygen, may contain inert, or diluent, gas such as nitrogen, steam, etc., recycle gas from the regenerator effluent, and the like. Frequently, the oxygen concentration of the regeneration gas at the inlet to the regenerator is from about 2 to 30 volume percent, preferably from about 5 to 25 volume percent. Since air is conveniently employed as a source of oxygen, a major portion of the inert gas may be nitrogen. The inert gas may serve to dissipate excessive heat from the combustion of coke from the catalyst. A source of hot, inert gas is the effluent from the regenerator, and a portion of this gas may be recycled to the regenerator and, for instance, combined with sufficient incoming air or other oxygen-containing gas, including essentially pure oxygen, to provide the desired oxygen content. Thus, the recycle gas may be employed in direct heat exchange to increase the temperature of the regeneration gas to provide even further heat economies in the system.

Solid particles within the dilute-phase may partially be carried into the separation zone, usually comprising cyclone separators in a plurality of stages, from which solid particles can be returned directly through dip-legs to the dense-bed zone, and spent regeneration and combustion gases are collected in a plenum, and finally discharged for suitable recovery of heat energy contained therein. Recovery processes for heat from flue gas include steam regeneration, spent catalyst stripping, indirect heat exchange with various refinery streams such as feed to the particular conversion process, and employment in various drying or evaporation arrangements.

The accompanying drawings, Figures 1 and 2, provide elevational views, partly in section, of embodiments of apparatus suitable for catalyst regeneration according to embodiments of the process of this invention involving the regeneration scheme of U.S. Patent No. 3,909,392.

Indeed, such embodiments may be employed beneficially in many existing petroleum hydrocarbon cracking process units particularly fluid catalytic cracking units having a variety of spatial arrangements of cracking, stripping and regeneration sections thereof.

Figure 1 is illustrative of one such embodiment of this invention employing bottom entry of stripped, spent catalyst passing from the cracking reactor (not shown) to the regenerator.

Solid particles containing spent catalyst impregnated with a metallic promoter and a metallic reactant from a stripping zone associated with the catalyst exit from the reactor, enter from the bottom of a regeneration vessel 1. The solid particles flow upwardly through inlet lines 2 and 3 and discharge into the dense bed through discharge heads 4 and 5. The dense-phase bed is maintained within the lower section 6 of the regenerator vessel and extends upwardly to the phase interface 7. Solid particles within the dense-phase bed are fluidized by the flow of combustion air through a line 8, valve 9 and line 10 to an air ring 11. Substantially balanced air flow patterns through the regeneration zone may be achieved by the use of additional air rings (not shown), as required. Combustion of coke contained on the spent catalyst with air is initiated within the dense-phase bed. Higher temperatures may be achieved by temporarily burning a stream of torch oil, for example a decanted oil, within the bed. Torch oil may be added by passage through a line 12, valve 13 and line 14 which terminates in a nozzle located above the air ring 11. Fluidizing air velocities continuously carry some of the solid particles upwardly into the dilute-phase zone which occupies the upper section 15 of the regenerator vessel; that is, the section above the phase interface 7. Combustion of coke continues in the dilute-phase zone and the largely spent combustion gas together with entrained solid particles is withdrawn into first-stage cyclone separators 20 and 21. Most of the solid particles are separated in the first-stage cyclones and discharged downwardly through dip-legs 22 and 23 into the dense-phase zone. Gases and remaining solid particles are passed through interstage cyclone lines 24 and 25 to second-stage cyclone separators 26 and 27 where substantially all of the remaining solid particles are separated and passed downwardly through dip-legs 28 and 29 into the dense-phase bed. Substantially spent combustion gas then passes through lines 30 and 31 into a plenum 32 and finally is discharged from the regenerator vessel through a line 33. This effluent may be suitably heat-exchanged (not shown) with refinery steam or for the production of process steam. Solid particles containing regenerated catalyst from the dense bed is withdrawn through standpipes 34 and 35, fitted with collector heads 36 and 37, respectively, for return to the cracking reactor.

Although the supply of combustion air provides an excess of oxygen over the amount required to effect complete combustion of the coke on the catalyst particles to steam and carbon dioxide, combustion of coke may not be completed in the dense-phase bed in one embodiment of this invention which employes the regeneration scheme of U.S. Patent No.

3,909,392. In this situation, the combustion gases rising from the dense bed zone thus contain a substantial quantity of carbon monoxide as well as carbon dioxide and oxygen. The remaining coke on catalyst and the carbon monoxide are substantially completely burned in the dilute phase zone with evolution of much heat. When carbon monoxide burns in the dilute phase, a high temperature zone will usually be present throughout much of the dilute phase zone and particularly at approximately the location indicated by X and can readily be viewed through a window (not shown) in that horizontal plane. Control of regeneration temperature within the dilute phase zone is effected in part through absorption of heat by the mass of solid particles either carried upwardly by the rising combustion gas stream or educted upwardly from the dense-bed through an eductor tube 40 and solid distributor head 41 where a rain, or fountain, of solid particles disperse into the dilute phase zone. Solid particles can be educted by means of air, steam or other inert gas entering through a line 42, valve 43 and jet tube 44 which extends a short distance into the lower end of the eductor tube 40. Excessive temperature levels in the top section of the regenerator may be further controlled by distribution of steam, for example through lines 45 and 46, a valve 47 and a line 48 to a steam pod 49.

Temperatures in the vicinity of the plenum may also be controlled with steam fed through a line 50, valve 51 and line 52 to a steam ring 53 which surrounds the plenum 32. Additional cooling, if desired, may be provided by the use of a water spray, (not shown), which may advantageously be directed within the region of the interstage cyclone lines 24 and 25. Such lower temperatures favour the formation of stable metal- and sulfur-containing compounds in the regeneration zone.

Figure 2 is illustrative of another embodiment of this invention employing the regeneration scheme of U.S. Patent No. 3,909,392, with side entry of the solid particles containing stripped, spent catalyst and metallic promoter and metallic reactant, from the cracking reactor to the regenerator. Solid particles containing spent catalyst impregnated with the metallic promoter and metallic reactant, enter a regeneration vessel 101 flowing downwardly through an inlet line 102 located on the side of the regeneration vessel to provide entry into the dense-phase bed maintained within a bottom section 106 a short distance below the phase interface 107. Fluidization of the solid particles is effected by combustion air passing through a line 108, valve 109 and line 110 to an air ring 111. Additional air rings (not shown) may be employed as desired for the further balancing of air flow patterns through the regeneration zones. As described in Figure 1 above, the combustion of coke on the spent catalyst particles is initiated within the dense-phase zone where higher temperatures as desired may be achieved by temporary burning of a torch oil stream within the zone. Such torch oil may be added through a line 112, valve 113 and line 114 terminating in a nozzle.

Fluidizing air velocity may be controlled so as continuously to carry solid particles upwardly for the purposes of heat absorption into the dilute-phase zone which occupies the upper section 115 of the regenerator vessel; that is, the section above the phase interface 107.

Combustion of coke as well as of carbon monoxide may continue in the dilute-phase zone and the largely spent combustion gas together with the entrained portion of solid particles is withdrawn into first-stage cyclone separators 120 and 121. Most of these solid particles are separated in the first-stage cyclones and discharged downwardly through dip-legs 122 and 123 into the dense-phase zone. Gases and remaining solid particles subsequently pass through interstage cyclone lines 124 and 125 to second-stage cyclone separators 126 and 127 where substantially all of the remaining solid particles are separated and passed downwardly through dip-legs 128 and 129 into the dense-phase bed. Substantially spent combustion gas then passes through lines 130 and 131 into a plenum 132 and finally is discharged from the regenerator vessel through a line 133. Solid particles containing regenerated catalyst from the dense bed are withdrawn through standpipes 134 and 135, fitted with collector heads 136 and 137, respectively, for return to the catalytic cracking reactor.

As described for the embodiment of Figure 1, carbon monoxide burns in the dilute phase providing a high temperature zone throughout much of the dilute phase zone and particularly at aprroximately the location indicated by X. Control of regeneration temperature within the dilute-phase zone is effected largely through absorption of heat by the mass of solid particles carried upwardly by the rising combustion gas stream. Temperatures in the vicinity of the plenum, cyclone and connecting lines may, as required, be reduced with steam fed through a line 150, valve 151 and line 152 to a steam ring 153, which surrounds the plenum 132. Water spray means (not shown) may similarly be employed.

In other, particularly preferred embodiments of this invention, the apparatus shown in Figure 1 or 2 is employed with a significant change in operating parameters as compared with the above-described embodiments. In these embodiments, gas velocity and solid particles input are adjusted so that essentially complete combustion of coke and carbon monoxide is completed within the dense phase and the heat is dispersed throughout the bed.

In all of these embodiments, the stabilization of the combustion reaction is particularly enhanced by the employment of the metallic promoter and the regenerator is thereby operable at lower temperatures, or so as to combust greater quantities of carbon monoxide and thus to regenerate more cracking catalyst at the same temperature. Such lower temperatures favour the formation of stable metal- and sulfur-containing compounds in the regenerator.

When the system is operated according to either of the embodiments described above with reference to Figures 1 and 2, recovery of the heat released by the essentially complete combustion of coke and carbon monoxide is by absorption in solid particles in both phases, and return of the solid particles to the dense phase serves also to secure maintenance of the suitably high temperatures within the dense-phase zone. The returned solid particles may carry with them additional heat to serve to raise the temperature of the dense-phase zone to a temperature which favours combustion of additional increments of coke deposits thereon and such that the combustion of the final increments of coke becomes substantially complete.

When the system is operated so that essentially all combustion is completed within the dense catalyst phase, the heat is dispersed throughout that phase as it is absorbed by the fluidized solid particles and final increments of coke are combusted. Accordingly, in all such embodiments, solid particles containing the regenerated catalyst passing from the regenerator back to the cracking reactor suitably contain from about 0.01 to about 0.10 weight percent, desirably 0.01 to 0.05 weight percent, and preferably from about 0.1 to about 0.03 weight percent, of carbon or coke on catalyst, and can be withdrawn from the regenerator at an advantageous temperature for use in the cracking reactor.

An outstanding advantage of these embodiments of this invention lies in providing a regenerated catalyst generally possessing enhanced activity and selectivity characteristics more closely approaching those of fresh conversion catalyst, particularly for use in conversions effected in very short contact times in riser reactors. The cracking activity of sievecontaining catalysts and their selectivity for converting hydrocarbon feeds to desired products are both dramatically affected in a favourable direction by the increased elimination of residual carbon or coke on the catalyst during regeneration. The low coke level on the regenerated catalyst is especially preferred with fluid cracking catalysts containing catalytically active, crystalline aluminosilicates. Accordingly, higher conversion of feedstock and higher yields of desirable conversion products may be achieved. The metallic promoter in this method assists in stabilizing regenerator control by controlling the oxidation of carbon monoxide. Moreover, the risk of extinguishing the oxidation of the carbon monoxide through a drop in temperature, increase in gas velocity which may cause blowout, or reduction in carbon monoxide content, is substantially abated since the oxidation of the carbon monoxide is promoted. The metallic promoter also results in lower regeneration temperatures and thus favours the formation of a stable metal- and sulfur-containing compound in the regeneration zone.

In those cracking processes using a lower dense-phase zone and an upper dilute-phase zone in the regeneration zone, the oxidation of the carbon monoxide to carbon dioxide may be accomplished to a major extent, often at least about 60 percent, and frequently about 65 to 95 percent or more, to completion in the dense phase of the regenerator. The oxidation of carbon monoxide to carbon dioxide in the dense phase provides heat to aid in sustaining the combustion of the coke deposits from the fluid catalyst. Furthermore, with a substantial portion of the carbon monoxide being oxidized in the dense phase, a lesser amount of carbon monoxide is present for combustion in the upper phase of the fluid catalyst in the regenerator, and thus "afterburning" and high temperatures due to uncontrolled excessive carbon monoxide combustion in the upper portion of the regenerator which may deleteriously affect materials employed to construct the reactor, the waste gas flue and the collectors for any particulate materials in the waste gas, for example, cyclones, and which may impair catalyst activity, may be substantially reduced or avoided.

Solid particles containing the regenerated catalyst particles having unusually low residual coke contents are recovered from the dense phase and passed at substantially the dense-bed temperature through a standpipe to the cracking reactor for contacting with fresh hydrocarbon feed or mixture thereof with recycle hydrocarbon fractions. Since the promoted oxidation of the carbon monoxide evolved from the combustion of the coke deposits on the catalyst may occur to a major extent in the dense phase and, in the preferred embodiments, essentially completely occurs in the dense phase, the regenerated catalyst can be returned to the cracking reactor at a much higher temperature as well as a higher activity than in heretofore conventional operations.

Many fluid cracking units are operated on the "heat balance" principle, depending upon combustion of coke for the evolution of heat required in the process. Such units, however, have not been able fully to utilize the benefits of the cracking catalysts, particularly zeolite catalysts, which can especially be achieved in a riser reactor where contact times between catalyst and oil vapours may be extremely short. The type of operation which affords high conversion coupled with high selectivity, favours a low ratio of catalyst-to-oil in the riser reactor which leads to less coke being available to generage heat from combustion in the regenerator. Accordingly, an external heat source such as a feed preheat furnace, is frequently added to increase the temperature of the catalyst or, alternatively, the unit may be operated at a lower temperature of fresh feed. Such undesirable features may be avoided or minimized by the method of this invention which permits efficient recovery of additional heat by the solid particles for transfer to the riser reactor. The heat of combustion of coke in conventional operations is about 12,000 BTU per pound. The method of this invention may increase available heat by combustion of the coke to about 17,000 or more BTU's per pound.

This higher heat of combustion tends to raise the regenerator temperature, lower the level of coke on the regenerated catalyst, and lower the circulation rate of solid particles while providing improved yields at a given conversion level.

In the following Examples, Examples 1 to 21 describe the preparation of cracking catalysts and supports which carry a metallic reactant and/or promoter which may be utilised in the present invention; Examples 22 to 50 describe bench scale tests which indicate the utility in the present invention of various cracking catalysts and supports which carry a metallic reactant and/or promoter; and Examples 51 to 60 represent full-scale tests either in a pilot plant or a commercial fluid catalytic cracking unit, and of these, Examples 51, 53 and 57 are control experiments whilst the others represent embodiments of the present ivention.

EXAMPLE 1 Two hundred grams of a calcined, equilibrium, commercially available, molecular sievetype cracking catalyst containing 5.3 percent of hydrogen and rare earth ion-exchanged, Y-type crystalline aluminosilicate and silica-alumina, which contained 30 weight percent of alumina, were impregnated with 3.90 grams of a 50 weight percent manganese nitrate solution and 210 milliliters of water. About 80 weight percent of the catalyst was in the 20 to 75 micron range in size. The impregnated catalyst particles were recovered and dried at 250"F., followed by calcination for 3 hours at 12500F. The resulting catalyst contained 0.3 weight percent of manganese.

EXAMPLE 2 The procedure of Example 1 was repeated, except that 1.265 grams of uranyl nitrate dissolved in 210 milliliters of water were employed as the impregnating solution. The impregnated catalyst was dried at 250"F. and then calcined for 3 hours at 1200"F. The catalyst contained 0.3 weight percent of uranium.

EXAMPLE 3 The procedure of Example 1 was repeated, except that 0.82 gram of ammonium metatungstate dissolved in 210 milliliters of water was employed as the impregnating solution. The catalyst was dried at 250"F., then calcined for 3 hours at 12000F. The resulting catalyst contained 0.3 weight percent of tungsten.

EXAMPLE 4 The procedure of Example 1 was repeated, except that 2.35 grams of ceric ammonium nitrate dissolved in 200 milliliters of water were employed as the impregnating solution. The catalyst was dried and calcined as in Example 1 and contained 0.3 weight percent of cerium.

EXAMPLE 5 The procedure of Example 1 was repeated, except that 2.73 grams of zinc nitrate hexahydrate dissolved in 200 milliliteres of water were employed as the impregnating solution. The catalyst was dried and calcined as in Example 1 and contained 0.3 weight percent of zinc.

EXAMPLE 6 The procedure of Example 1 was repeated, except that 4.35 grams of ferric nitrate dissolved in 200 milliliters of water were employed as the impregnating solution. The impregnated catalyst was dried and calcined as in Example 1 and contained 0.3 percent of iron.

EXAMPLE 7 The procedure of Example 1 was repeated, except that 1.1 grams of ammonium molybate in a 210 milliliter aqueous solution were employed as the impregnating solution. The impregnated catalyst was dried at 250"F. for three hours, and then calcined at 12000F. for three hours. The resulting catalyst contained 0.3 weight percent of molybdenum.

EXAMPLE 8 The procedure of Example 1 was repeated, except that 5.0 grams of titanium sulfate dissolved in 25 milliliters of an aqueous 30 percent solution of hydrogen peroxides which was diluted to 200 milliliters with water, were employed as the impregnating solution. The solution was heated until the titanium salt was fully dissolved. The catalyst was dried, at 250"F. and then calcined for 3 hours at 12000F. The resulting catalyst contained 0.3 weight percent of titanium.

EXAMPLE 9 The procedure of Example 1 was repeated, except that 1.2 grams of chromic oxide dissolved in 200 milliliters of water were employed as the impregnating solution. The impregnated catalyst was dried for 3 hours at 2500F. and then calcined for 3 hours at 12000F.

The resulting catalyst contained 0.6 weight percent of chromium.

EXAMPLE 10 The procedure of Example 1 was repeated, except that 2.12 grams of zirconyl chloride dissolved in 200 milliliters of water were employed as the impregnating solution. The impregnated catalyst was dried at 2500F. for 3 hours and then calcined for 3 hours at 12000F.

The resulting catalyst contained 0.3 weight percent of zirconium.

EXAMPLE 11 The procedure of Example 1 was repeated, except that 0.2506 gram of a 50 percent manganese nitrate solution and 200 milliliters of water were employed as the impregnating solution. The impregnated catalyst was dried at 2500F. for 3 hours and then calcined for 3 hours at ID= repeated until the magnesium, zinc, and phosphorus contents of the catalyst reached the levels of 1100, 703, and 59 parts per million, respectively. Zinc and phosphorus were inherently present in the lubricating oil additive.

EXAMPLE 19 The procedure of Example 18 was repeated, except that the cracking-purgingregeneration cycle was repeated with a 10g solution containing 6.5g of the oil and 3.5g of a lube oil additive containing 1.6wt. % Zn, 1.3 wt. % P, and 4.6 wt. % Mg until the magnesium, zinc, and phosphorus contents of the catalyst reached 2400,1200, and 1097 parts per million, respectively.

EXAMPLE 20 The procedure of Example 19 was repeated, except that an equilibrium, commercially available cracking catalyst which contained 3.3 weight percent of molecular sieve in a silica-alumina matrix, and had also been withdrawn from a commercial fluid catalytic cracking unit and calcined, was employed, and the cracking-purging-regeneration cycle was repeated until the magnesium, zinc, and phosphorus contents of the catalyst reached 4600, 304, and 1,136 parts per million, respectively.

EXAMPLE 21 A lubricating oil additive in the amount of 7.3 grams and containing 8.2 percent of magnesium, distributed as magnesium carbonate, magnesium hydroxide, and magnesium polypropylbenzene sulfonate, and a sufficient volume of xylene, was used to wet 2000 grams of an equilibrium, commercially available cracking catalyst which had been withdrawn from a commercial catalytic cracking unit and calcined, and which contained 2.5 weight percent of molecular sieve in a silica-alumina matrix and about 0.6 weight percent of sodium. The wetted catalyst was dried at 400"F. for 3 hours and calcined at 1000"F. for 20 hours. The catalyst contained 3000 parts per million of magnesium.

EXAMPLES 22-27 A bench-scale laboratory regeneration unit was used to test the potency of a number of the impregnated catalysts of Examples 1-21 for providing reduced emissions of carbon monoxide in regeneration zone flue gases. A synthetic flue gas comprising 4 volume percent of each of carbon monoxide, oxygen, and water vapour, and 88 volume percent of nitrogen was passed at a rate of about 1,000 milliliters (measured at 600F.) through a fixed fluidized bed of the molecular sieve-type cracking catalyst impregnated with a metal, which was maintained in a glass regenerator surrounded by a furnace to provide the desired regeneration temperature of 1,200"F. The temperature of the catalyst was measured by thermocouples. A cyclone was used to separate entrained catalyst from the gas exiting from the regenerator and to return the catalyst to the catalyst bed. The time during which the regenerator was operated under a given set of conditions ranged from about 40 to about 90 minutes in order to allow sufficient time to establish the oxidation state of the metal on the catalyst in an actual fluid catalytic cracking unit operation.

The gas exiting from the regenerator was analysed with a gas chromatograph for oxygen, nitrogen, carbon monoxide and carbon dioxide. The amount of carbon monoxide converted was determined as the difference between the carbon monoxide contents of the fresh synthetic gas mixture and of the gas exiting from the regenerator.

In Examples 22-26, the impregnated catalysts produced in Examples 1,4, 5,6, and 10 were used, and the volume percent of carbon monoxide converted was 65, 72, 55, 75 and 65,respectively. In Example 27, which employed the unimpregnated catalyst used in Examples 1, 4, 5, 6, and 10, the volume percent of carbon monoxide converted was 31.

EXAMPLES 28-31 Several of the above catalysts were tested according to standard uniform test methods used in the industry in a microfluidized catalytic unit to determine the desired selectivity for catalytic cracking. As a basis, in Example 28, the unimpregnated cracking catalyst used in Example 1 had a relative micro-activity of 154, a coke factor of 1.0, and a hydrogen-tomethane mole percent ratio of 0.64: 1. In Example 29, the impregnated catalyst produced in Example 1 was employed and showed a relative micro-activity of 147, a coke factor of 1.1, and a hydrogen-to-methane mole percent ratio of about 1.1:1 - 1.2:1. In Example 30, the impregnated catalyst produced in Example 4 was used and demonstrated a relative microactivity of 150, a coke factor of 1.1, and a hydrogen-to-methane mole percent ratio of 0.9:1 1.1:1. In Example 31, the catalyst produced in Example 6 was used and showed a relative activity of 134, a coke factor of 2.0, and a hydrogen-to-methane mole percent ratio of 6.5:1.

EXAMPLES 32-38 The procedure of Examples 22-27 was repeated, except that powdered metal oxides having a particle size of 5 microns and finer, in admixture with the unimpregnated catalyst used in Example 1, were used instead of the impregnated catalysts. The powdered metal oxides, the amounts thereof, and the volume percentages of carbon monoxide converted to carbon dioxide in Examples 32-35, as well as in comparative Example 36, which employed no metal oxide but was carried out under otherwise identical conditions, are shown in Table 1 below. Similar data for Example 37 and its comparative Example 38, which employed no metal oxide under otherwise identical conditions, are also shown in Table 1.

TABLE I Example Metallic Oxide Weight percentage Volume of Metal Oxide in Percentage Catalyst of Carbon Monoxide Converted 32 manganese dioxide 1.0 46 33 manganese dioxide 2.0 51 34 iron oxide 0.3 34 35 iron oxide 1.0 35 36 none - 28 37 rare earth oxides 1 65 38 none - 33 EXAMPLES 39-40 The procedure of Examples 22-27 was repeated, except that a synthetic flue gas made up of 1500 parts per million of sulfur dioxide in a mixture of 4 volume percent of each of oxygen and steam in nitrogen at 12500F. was passed through the regenerator at 1,500 milliliters per minute (measured at 600F) and an ultra-violet analyser was used to measure continuously the sulfur dioxide content of the effluent gas. Comparative tests were run using the unimpregnated catalyst used in Example 16 and the impregnated catalyst produced in Example 16.

Example 39 involved the unimpregnated catalyst, while Example 40 involved the impregnated catalyst. The volume percentages of sulfur dioxide removed from the regeneration zone flue gas are shown in Table 2 bwlow as a function of elapsed time after the beginning of the experiment. The volume percentage removed decreased with time as the catalyst surface became saturated. In Example 39, the sulfur level in the form of soluble sulfate on the catalyst was 55 parts per million before the experiment and 368 parts per million afterwards, corresponding to recovery on the catalyst of 76 weight percent of the sulfur removed from the regeneration gas. In Example 40, the sulfur level in the form of soluble sulfate on the catalyst was 111 parts per million before the experiment and 733 parts per million afterwards, corresponding to a recovery on the catalyst of 91 weight percent of the sulfur removed from the regeneration zone.

TABLE 2 Example Volume Percentage of Sulfur Dioxide Removed Time 39 40 41 42 43 44 45 46 47 0-10 86-70 98 100 82 78-63 85-82 92-91 36-24 60-49 10-20 70-52 98-95 100 57 63-43 82-78 91-89 24-16 49-39 20-30 52-43 95-85 100 48 43-32 78-74 89-88 16-14 39-33 30-40 43-35 85-76 100 43 32-27 74-70 88-87 14-13 33-30 EXAMPLES 41-42 The procedure of Examples 39-40 was repeated in comparative tests using mixtures of a molecular sieve-type cracking catalyst and different amounts of the vanadium and copperimpregnated alumina produced in Example 17. In Example 41, 10 grams of the vanadiumand copper-impregnated alumina were mixed with 90 grams of an equilibrium, commercially available cracking catalyst which contained 3.3 weight percent of molecular sieve and which had been withdrawn from a commercial fluid catalytic cracking unit and calcined at 1000"F. for 5 hours. The flow rate of the synthetic flue gas was 854 cubic centimeters/minute (measured at 600F).

In Example 42, 0.5 gram of the vanadium- and copper-impregnated alumina of Example 17 was mixed with 49.5 grams of the same calcined, equilibrium commercial cracking catalyst used in Example 41. The flow rate of the synthetic flue gas was 513 cubic centimeters/minute (measured at 600F). The volume percentages of sulfur dioxide removed from the flue gas for Examples 41-42 are shown in Table 2.

EXAMPLES 43-47 The procedure of Examples 39-40 was repeated using a regeneration temperature of 12500F. Example 43 was a comparative test using a flow rate of the synthetic flue gas mixture of 1084 milliliters per minute and the unimpregnated equilibrium catalyst used in Examples 18-19, while Examples 44-45 involved the impregnated catalyst produced in Examples 18-19, repsectively, and flow rates for the synthetic flue gas mixture of 989 and 1,014 milliliters per minute, respectively. Example 46 was a comparative test using the unimpregnated catalyst of Examples 20, 41 and 42 and a flow rate of the synthetic flue gas mixture of 891 milliliters per minute.

Example 47 involved the impregnated catalyst produced in Example 20 and a flow rate of the synthetic flue gas mixture of 992 milliliters per minute. The volume percentages of sulfur dioxide removed from the flue gas for Examples 43-47 are shown in Table 2.

EXAMPLES 48-50 Bench-scale laboratory fluid catalytic cracking tests were conducted with a gas oil feed containing 2.4 weight percent of sulfur in the form of organic sulfur compounds, In comparative cracking tests at constant cracking severity in Examples 48-50, with the calcined, unimpregnated equilibrium catalyst used in Example 13 and with the impregnated catalysts produced in Examples 13 and 14, respectively, the amounts of sulfur dioxide liberated from the stripped, deactivated catalysts upon subsequent regeneration were measured and calculated as parts per million by weight of sulfur on catalyst. The sulfur removable in Example 48 from the catalyst with no magnesium was 134 parts per million by volume. The sulfur removable in Example 49 from the catalyst containing 1 weight percent of magnesium was 52 parts per million, a reduction of 61 percent. The sulfur removable in Example 50 from the catalyst containing 0.5 weight percent of magnesium was 73 parts per million, a reduction cif 46 percent.

EXAMPLES 51-52 Comparative tests were performed involving cracking a gas oil containing 2.54 weight percent sulfur in a continuous cracking-regeneration unit of the type described in U.S. Patent No. 3,502,574, using the unimpregnated catalyst of Example 21 and the impregnated catalyst produced in Example 21. Example 51 involved the unimpregnated catalyst, while Example 52 involved the impregnated catalyst. The operating conditions and composition of the regenerator flue gas are shown in Table 3 below.

EXAMPLES 53-54 Pilot-plant cyclic fluid cracking tests were conducted with a gas oil feed, having a sulfur content of 2.4 weight percent, employing the unimpregnated catalyst used in Example 15 and the impregnated catalyst used in Example 15 and the impregnated catalyst produced in Example 15. Examples 53 and 54 involved the unimpregnated and impregnated catalysts,. respectively. The operating conditions and regeneration zone flue gas composition are shown in Table 3. The impregnated catalyst led to a reduction of 57.5 percent in emission of sulfur dioxide in the regenerator flue gas. Conversion and product yields were essentially identical with each catalyst.

TABLE 3 Example 51 52 53 54 55 56 57 58 598 60 Cracking conditions: Cracking temperature, F. 1000 1000 968 971 974 970 920 925 948 930 Total Feed rate, barrels/ dya 1.21 1.21 23.81 23.41 49,200 46,800 23,150 24,970 54,040 48,100 Throughput ratio 1.0 1.0 1.0 1.0 1.07 1.25 1.12 1.11 1.07 1.01 Catalyst circulation rate, tons/min. 8.31 8.31 2681 2591 29.1 26.4 18 18 24.9 26.7 Catalyst-to-oil weight ratio 7 7 5.3 5.2 7.2 6.7 4.2 5.2 Stripping conditions: Stripping temperature, F. 1000 1000 966 969 970 965 915 875 954 926 Steam lbs./ton catalyst 20 20 18.6 19.3 8.6 9.4 9.2 11 8.2 8.2 Regeneration conditions: Dense bed Temperature, F. 1200 1200 1086 1089 1270 1305 1195 1145 1301 1325 Combustion air rate, lbs./hr. 0.76 0.76 18.9 19.2 412,000 487,000 183,000 179,000 393,000 455,000 Composition of regeneration zone effluent gas: CO2, mole percent 10.0 10.5 3.9 4.5 13.0 14.0 11.8 11.0 17.4 15.8 CO, mole percent 1.4 1.3 2.6 2.2 5.0 5.6 7.3 5.2 0.1 0.8 O2, mole percent 2.5 2.5 5.1 5.1 0.5 2.0 0.5 2.6 1.0 2.4 Sulfur dioxide, ppmv 480 210 520 220 580 60 184 34 795 627 Footnotes 1 : Pounds per hour.

EXAMPLES 55-56 In Example 55, a gas oil feed having a sulfur content of 1.67 weight percent was cracked in a commercial fluid catalytic cracking unit having a riser reactor. Conventional regeneration was employed. A commercial equilibrium molecular sieve-type cracking catalyst containing 2.5 weight percent of molecular sieve and about 0.6 weight percent of sodium was used. In Example 56, a second gas oil feed having a sulfur content of 1.68 weight percent was cracked in the same commercial unit using the same regeneration scheme and the same cracking catalyst, but, additionally, the catalyst was impregnated with magnesium and zinc. The magnesium and zinc were deposited on the catalyst by introducing into the reaction zone small concentrations of magnesium sulfonate and zinc dialkyldithiophosphate in the form of lubricating oil additive in the feedstock. After several hours of addition in this manner, levels of magnesium of 0.3 weight percent and a zinc of 0.1 weight percent were built up on the cracking catalyst. The operating conditions and composition of the regeneration zone flue gases are shown in Table 3.

EXAMPLES 57-58 A gas oil feed having a sulfur content of 0.26 weight percent was cracked in a commercial fluid catalytic cracking unit having a riser reactor and employing conventional regeneration.

In Example 58, a commercial, equilibrium, molecular sieve-type fluid cracking catalyst containing 2.5 weight percent of molecular sieve and 1.01 weight percent of sodium was used.

The sodium was deposited on the catalyst by introducing with the feedstock an aqueous solution of sodium chloride. Comparative Example 57 involved cracking a gas oil having a sulfur content of 0.28 weight percent in the presence of the same catalyst used in Example 58, but not impregnated with sodium, under conditions which were otherwise substantially the same. The operating conditions and composition of the regeneration zone flue gases are shown in Table 3.

EXAMPLES 59-60 In Example 59, a gas oil feed having a sulfur content of 0.81 weight percent was cracked in a commercial fluid catalytic cracking unit having a riser reactor and a regenerator of the type shown in Figure 2. Regeneration was performed in accordance with the regeneration scheme of U.S. Patent No. 3,909,392. A commercial, equilibrium, molecular sieve-type fluid cracking catalyst containing 4.5 weight percent molecular sieve, 0.64 weight percent of iron, 56 parts per million of copper and 0.22 weight percent of sodium was used. In Example 60 a second gas oil feed having a sulfur content of 1.14 weight percent was cracked in the same commercial unit using the same regeneration scheme and using a commercial equilibrium molecular sieve-type fluid cracking catalyst containing 2.5 weight percent of molecular sieve, 0.52 weight percent of iron, 34 parts per million of copper, 0.22 weight percent of sodium, and 0.09 part per million of platinum. There were 300 tons of this catalyst in the unit, and the platinum was deposited on the catalyst by introducing into the reaction zone with the feedstock a solution of platinum acetylacetonate in benzene. A total of 20 grams of platinum metal was introduced at an average rate of 3 grams of platinum metal per day. For both catalysts, the sodium was inherently present in the catalyst, and the iron and copper were introduced into the cracking process cycle as components in the feedstock. The operating conditions and composition of the regeneration zone flue gases are shown in Table 3.

The results indicate that the addition of platinum to the cracking catalyst produced lower emissions of sulfur oxides even when the hydrocarbon feed contained larger amounts of sulfur. Further, the emission of carbon monoxide in each case was substantially less than the 8-10 mole percent which is typical of conventional regeneration in the absence of a platinum-promoted catalyst. The increase in the amount of carbon monoxide in the regeneration zone flue gas, when the platinum-promoted cracking catalyst was used was a reflection of a higher combustion air rate in that instance. The temperature at the inlet of the first cyclone in Example 59 was 1439"F. and in Example 60 was 1368"F. The decrease in the temperature at tbe cyclone inlet, the increase in the bed temperature, and the decrease in the difference between the temperatures of the bed and cyclone inlet, when using the platinum-promoted cracking catalyst, indicates a significant increase in the extent of combustion of carbon monoxide in the dense bed.

Claims

WHAT WE CLAIM IS:

1. In a process for the cyclic, fluidized, catalytic cracking of a hydrocarbon feedstock containing organic sulfur compounds wherein (i) said feedstock is subjected to cracking in a reaction zone with fluidized solid particles of a molecular sieve-type cracking catalyst; (ii) catalyst particles, which are deactivated by sulfur-containing carbonaceous deposits, are separated from reaction zone effluent and conveyed to a stripping zone wherein volatile deposits are removed from said deactivated catalyst by contact with a stripping gas; (iii) stripped catalyst particles are separated from stripping zone effluent and conveyed to a regeneration zone and regenerated by burning the non-strippable, sulfur-containing, carbonaceous deposits from the stripped catalyst with an oxygen-containing gas; and (iv) regenerated catalyst particles are separated from regeneration zone effluent and recycled to the reaction zone, a method for reducing emissions of carbon monoxide and sulfur oxides in the regeneration zone effluent gas which comprises: (a) circulating the cracking catalyst through the process cycle in combination with a metallic reactant which reacts with sulfur oxides in the regeneration zone, the combination of catalyst and reactant consisting of fluidizable solid particles, the reactant being either incorporated into the particles of cracking catalyst or contained in a particulate solid other than the cracking catalyst and the metallic reactant being a free or combined metallic element which is selected from sodium, magnesium, calcium, strontium, barium, scandium, titanium, chromium, molybdenum, manganese, iron, cobalt, nickel, antimony, copper, zinc, cadmium, lead, a rare earth metal, or any mixture thereof; (b) cracking said feedstock at a temperature within the range of from 850"F and in contact with the cracking catalyst and the metallic reactant; (c) stripping volatile deposits from the particles of said combination at a temperature within the range of from 850" to 1,200"F with a stripping gas which contains steam, wherein the ratio by weight of steam to the catalyst is within the range of from 0.0005 to 0.025 per unit of time; (d) burning said sulfur-containing carbonaceous deposits from the stripped, solid particles at a temperature within the range of from 1,050 to 1,4500F in the presence of at least one free or combined metallic promoter selected from ruthenium, rhodium, palladium, osmium, iridium, platinum, vanadium, silver or rhenium, wherein the metallic promoter and the metallic reactant are present in sufficient amounts to effect absorption of a m-ajor portion of the sulfur oxides produced in said regeneration zone, and wherein the metallic promoter is present in sufficient amount to enhance said absorption of sulfur oxides and the conversion of carbon monoxide to carbon dioxide in the regeneration zone; (e) withdrawing an effluent gas containing molecular oxygen from the regeneration zone, said effluent gas having a reduced concentration of sulfur oxides; and (f) substantially withdrawing said absorbed sulfur oxides as a sulfur-containing material in the volatiles from the reaction and/or stripping zone.

2. A method as claimed in claim 1, wherein the promoter consists of ruthenium, rhodium, palladium, osmium, iridium, platinum or rhenium or any compound thereof or any mixture thereof or of any compound thereof, and wherein the amount of the promoter is within the range of from 0.1 part per million to 10 parts per million, inclusive, calculated as the metal and based on the weight of the particles of the said combination.

3. A method as claimed in claim 2, wherein the promoter consists of platinum or palladium or any compounds thereof or any mixtures thereof or of any compounds thereof.

4. A method as claimed in claim 1 wherein the promoter consists of vanadium or a compound thereof or any mixtures of compounds thereof, and wherein the amount of the promoter is within the range of from 10 parts per million to 10 weight percent, inclusive, calculated as the metal and based on the weight of said particles of said combination.

5. A method as claimed in any of claims 1 to 4, wherein said metallic reactant consists of sodium, magnesium, calcium, strontium, barium, chromium, manganese, copper, zinc or cadmium, or a rare earth metal or any compounds thereof or any mixture thereof or of any compounds thereof.

6. A method as claimed in claim 5 wherein said metallic reactant consists of sodium, magnesium, manganese or copper or any compounds thereof, or of any mixture thereof or of any compound thereof.

7. A method as claimed in any of claims 1 to 4 wherein said metallic reactant consists of sodium, magnesium, calcium, strontium, barium, scandium, titanium, chromium, molybdenum, manganese, iron, cobalt, nickel, antimony, copper, zinc, cadmium or lead, or a rare earth metal or any oxide thereof, or of any mixture thereof or of any oxides thereof.

8. A method as claimed in claim 7 wherein said metallic reactant consisting of sodium, magnesium, manganese or copper or any oxide thereof, or any mixture thereof or of any oxides thereof.

9. A method as claimed in any of claims 1 to 8, wherein the regeneration zone effluent gas stream contains at least 0.5 volume percent of molecular oxygen.

10. A method as claimed in any of claims 1 to 9, wherein the particles of said combination comprise fluidizable particles of said molecular sieve-type cracking catalyst in admixture with - fluidizable particles which contain said metallic reactant.

11. A method as claimed in claim 10, wherein the particles which contain said metallic reactant comprise a support into or onto which is incorporated said metallic reactant, and wherein said support comprises at least one amorphous cracking catalyst and/or at least one solid which is substantially inert to the cracking of said feedstock.

12. A method as claimed in claim 11, wherein said support comprises silica or alumina or any mixture thereof.

13. A method as claimed in any of claims 10 to 12, wherein said promoter is additionally incorporated into the particles which contain said metallic reactant.

14. A method as claimed in any of claims 1 to 13, wherein the particles of said combination comprise particles of said molecular sieve-type cracking catalyst into or onto which has been incorporated the metallic reactant.

15. A method as claimed in claim 14, wherein said promoter is additionally incorporated into or onto the particles of the molecular sieve-type cracking catalyst.

16. A method as claimed in claim 15, wherein the amount of said molecular sieve-type cracking catalyst is within the range of from 90 to 99.995 weight percent of said combination of catalyst,- promoter and metallic reactant.

17. A method as claimed in claim 15 or 16, wherein at least one of said promoter and metallic reactant is incorporated into said particles of molecular sieve-type cracking catalyst by introducing into the process cycle at least one oil- or water-soluble or -dispersible compound of the metallic element or elements of said promoter or metallic reactant.

18. A method as claimed in claim 17, wherein said oil- or water-soluble or -dispersible compound consists of a metal diketonate, metal carbonyl, metallocene, metal olefin complex of 2 to 20 carbon atoms, metal acetylene complex, metal complex of an alkyl or aryl phosphine, or metal carboxylate having from 1 to 20 carbon atoms, or any mixture thereof.

19. A method as claimed in claim 17 or 18, wherein said oil- or water-soluble or -dispersible compound is platinium acetylacetonate.

20. A method as claimed in claim 1, wherein said oxidation promoter is incorporated into or onto a support, and wherein said support consists of at least one amorphous cracking catalyst and/or solid which is substantially inert to the cracking of said feedstock.

21. A method as claimed in claim 20, wherein said support consists of silica or alumina or any mixture thereof.

22. A method as claimed in claim 1, wherein the oxidation promoter is confined in the regeneration zone.

23. A method as claimed in claim 1, wherein the particles of said combination are regenerated at a temperature within the range of from 1,180 to about 1,350"F, inclusive,

24. A method as claimed in claim 1, wherein said promoter is a fluidizable powder which is circulated through the catalytic cracking process cycle.

25. A method as claimed in claim 1, wherein the metallic reactant is primarily in physical association with the molecular sieve-type cracking catalyst; wherein the metallic reactant consists of sodium, a rare earth metal, a compound thereof or any mixture thereof or of any compound thereof.

26. A method as claimed in claim 25, wherein said metallic reactant is an oxide of an element consisting of sodium or at least one rare earth metal or any mixture thereof:

27. A cyclic fluidized catalytic cracking process according to claim 1 substantially as herein described with reference to the- accompanying drawings and/or any of Examples 52, 54, 55, 56, 58, 59 and 60.