Regeneration method for gravity-flowing deactivated catalyst particles
APPLICABILITY OF INVENTION 
     Movable beds of particulate solids are currently employed in, or are applicable to a wide variety of systems. It is to such systems -- i.e. those containing a bed of solids movable therethrough via gravity-flow -- that the inventive concept of the present invention is applicable. More specifically, our invention is directed toward a system for the catalytic conversion of hydrocarbonaceous material, in which system deactivated catalyst particles are regenerated in a zone, or chamber through which the particles are downwardly movable via gravity-flow. 
     Relatively recent developments within the petroleum industry have resulted in hydrocarbon conversion processes wherein the reactants contact one or more zones of catalyst particles downwardly movable therethrough via gravity-flow. This operating technique has been proposed for a wide variety of hydrocarbon conversion processes, including catalytic reforming, fixed-bed alkylation, hydrorefining, hydrocracking, dehydrogenation, hydrogenation, steam reforming, etc. Although the present catalyst regeneration technique is applicable to all the foregoing processes, in the interest of brevity the same will be further described in conjunction with the well-known catalytic reforming process. 
     Historically, the catalytic reforming process has utilized a catalytic composite of a Group VIII noble metal component and a halogen component combined with a refractory inorganic oxide, and has been effected in a non-regenerative, fixed-bed system consisting of a plurality of reaction zones in side-by-side relation. When the catalytic composite is deactivated to the extent that continued operation is no longer economically feasible, the entire unit is shut down, and the catalyst regenerated in situ. After several such regenerations, the catalyst is replaced with fresh catalyst and the deactivated catalyst subjected either to an exotic reconditioning technique, or to an involved method for the recovery of the precious noble metal. Of more recent vintage is the so-called &#34;swing-bed&#34; system in which an extra reactor is substituted for one which is due to be placed off-stream for regeneration purposes. 
     Still more recently, a &#34;stacked&#34; reactor system has been provided in which the catalyst particles flow, via gravity, downwardly from one annular-form catalyst zone to another. Ultimately, the catalyst is transferred to a suitable regeneration system also functioning with a downwardly-moving bed of catalyst. In effect, the catalyst particles are maintained within the reaction system, and continuously transferred from one section to another in a manner such that the flow is continuous, at frequent intervals, or at extended intervals, the movement thereof being controlled by the quantity of catalyst withdrawn from the last in the series of individual reaction zones. 
     It is to this type of system -- gravity-flowing catalyst particles -- to which our invention is intended to be applied. More particularly, the present regeneration method is directed toward those catalytic composites which have become deactivated as a result of the deposition of carbonaceous matter thereon and the loss of a halogen component therefrom. 
     OBJECTS AND EMBODIMENTS 
     A principal object of our invention is to provide an improved method for continuously regenerating deactivated hydrocarbon conversion catalyst particles. A corollary objective involves a method for regenerating deactivated catalyst particles, comprising a Group VIII noble metal component and a halogen component in combination with a refractory inorganic oxide, in a regeneration zone through which said catalyst particles are movable via gravity-flow. 
     Another object of our invention is to afford a more economical technique for regenerating catalyst particles which have been deactivated by deposition of carbonaceous matter thereon and loss of halogen therefrom. 
     Therefore, in one embodiment, our invention is directed toward a method for continuously regenerating hydrocarbon conversion catalyst particles comprising a Group VIII metal component and a halogen component in combination with a refractory inorganic oxide carrier material, and which have become deactivated (1) by deposition of carbonaceous matter thereon and, (2) through loss of halogen therefrom, in a regeneration zone through which said catalyst particles are downwardly movable via gravity-flow, which regeneration method comprises the inter-related steps of: (a) introducing (i) deactivated catalyst particles, (ii) a first air stream from an external source and, (iii) a halogen, or halogen-containing compound, into an upper carbon-burning/halogenation first section; (b) maintaining said catalyst particles within said first section for a time sufficient to (i) remove substantially all of said carbonaceous matter therefrom and, (ii) increase the halogen content thereof; (c) introducing (i) the catalyst particles from said carbon-burning/halogenation section, via gravity-flow, and, (ii) a second air stream from an external source into a lower drying second section, and maintaining said catalyst particles within said second section for a time sufficient to remove substantially all the water therefrom; and, (d) withdrawing substantially water-free, regenerated catalyst particles from said regeneration zone. 
     In another embodiment, the temperature in the carbon-burning/halogenation section is maintained in the range of about 750° F. to about 1050° F. Generally, the temperature in the lower drying section will be from about 830° F. to about 1000° F. 
     Other objects and embodiments of our invention will become evident from the following more detailed description thereof. In one such other embodiment, the first air stream is introduced into the carbon-burning/halogenation section through the same locus through which the halogen, or halogen-containing compound is introduced. 
     PRIOR ART 
     U.S. Pat. No. 3,470,090 (Cl. 208-138) illustrates a side-by-side reaction system having intermediate heating of the reactant stream. Catalyst withdrawn from an individual reaction zone is transported to suitable regeneration facilities. This particular type of system can be modified such that the catalyst withdrawn from a given reaction zone is sent to the next succeeding reaction zone, while that catalyst withdrawn from the last reaction zone is transported to regeneration facilities. This latter technique is illustrated by U.S. Pat. Nos. 3,647,680 (Cl. 208-65) and 3,785,963 (Cl. 208-171). The catalytic reforming configuration is shown as a two-stage &#34;stacked&#34; system having an integrated regeneration facility which receives the catalyst particles withdrawn from the bottom reaction chamber. As illustrated, both techniques utilize a downwardly-moving bed of catalyst particles through the stacked reaction zones and through the regeneration chamber. 
     U.S. Pat. No. 3,652,231 (Cl. 23-288G) describes a reconditioning, or regeneration system for a moving column of reforming catalyst. It is to this type of regeneration system that our invention is particularly directed, and affords a distinct improvement therein. 
     A regeneration technique for gravity-flowing catalyst particles is disclosed in U.S. Pat. No. 3,981,824 (Cl. 252-415), issued Sept. 21, 1976. Three distinct stages of regeneration are employed: (1) a carbon-burning zone, into which the catalyst particles are initially introduced; (2) a halogenation section, or zone; and, (3) a lowermost catalyst-drying section. Flue gas vapors from the carbon-burning section are at least in part recycled thereto. Likewise, vapors from the drying and halogenation sections are recycled to the halogenation section. Obviously, at least a portion of the effluent vapors from the halogenation section are caused to bypass the recycle conduit and enter the carbon-burning section. A portion of substantially dry air is introduced into a heater and therefrom into the lower drying section. A second portion of the air stream is combined with the recycled flue gas for introduction therewith into the carbon-burning section. Steam and halogen, in admixture with effluent vapors from the drying and halogenation sections, are introduced into a second heater and therefrom into the halogenation section. The main thrust of this described technique involves a three-stage regeneration accompanied by split air flow to the drying and carbon-burning sections. 
     The technique encompassed by our inventive concept differs from the foregoing three-stage regeneration method in several important aspects which lead to significant advantages and/or benefits. Initially, there exists a simplification of the regeneration tower design in addition to the complete elimination of one entire flue gas recycle loop, including the heater. Total residence time of the catalyst particles, within the regeneration tower is reduced; thus, changes in regeneration are more quickly observed at the various sample points and especially in the reactor section itself. Start-up procedures become much more simplified; the time required for the start-up procedure is reduced from about twenty-four hours to about sixteen hours, and this greatly lessens the risk of catalyst damage. Simultaneous carbon-burning and halogenation maintains a relatively constant catalyst halide level, thus reducing the likelihood of noble metal agglomeration; thus, the metallic components retain their active, dispersed state. 
     SUMMARY OF INVENTION 
     As hereinbefore set forth, our invention is intended to effect the regeneration of deactivated hydrocarbon conversion catalyst particles comprising a Group VIII noble metal component and halogen component combined with a refractory inorganic oxide. In accordance with the Periodic Table of the Elements, E. H. Sargent &amp; Co., 1964, the term &#34;Group VIII noble metal component&#34; is intended to include ruthenium, rhodium, palladium, osmium, iridium, platinum, and mixtures thereof. Furthermore, our regeneration method is applicable to the recently-developed bi-, tri- and tetra-metallic catalysts in which metallic components other than those of the Group VIII noble metals are incorporated therewith. Such other metallic components include technetium, rhenium, gallium, vanadium, cobalt, nickel, gold, germanium, tin, lead, bismuth, etc. Generally, the quantity of the Group VIII noble metal components within the final catalytic composite is small compared to the quantities of the other components combined therewith, and will be present in an amount of about 0.01% to about 2.0% by weight of the final catalytic composite, calculated on an elemental basis. Similarly, with respect to the multi-metallic catalysts, the other metallic components, hereinabove set forth will be present in an amount in the range of about 0.01% to about 5.0%, again calculated on an elemental basis. 
     Another ingredient of the type of catalytic composites regenerated by the present method is a halogen component. Although the precise form of the chemistry of the association of this component with the other components of the catalyst is not known with accuracy, it is customary in the art to refer thereto as combined halogen. This may be either fluorine, chlorine, iodine, bromine, or mixtures thereof, with fluorine and particularly chlorine being preferred. The halogen component will be present within the catalyst in an amount within the range of about 0.1% to about 5.0%, and generally from about 0.5% to about 1.5% by weight, calculated on an elemental basis. One or more of the foregoing metallic components and the halogen component is combined with a suitable refractory inorganic oxide carrier material. With respect to the latter, many compositions have been employed, including alumina, silica, zirconia, hafnia, boria, thoria, mixtures thereof, etc.; however, with respect to the catalytic reforming of hydrocarbons, alumina in and of itself, is generally preferred. 
     The foregoing is presented to describe the general type of hydrocarbon conversion catalyst particles to which the regeneration method of the present invention is particularly directed. It is understood that the precise chemical and/or physical make-up of the catalytic composite is not essential to the present invention, nor is the particular technique selected for the manufacture of the catalyst particles. In short, our invention is concerned solely with a method for continuously regenerating deactivated hydrocarbon conversion catalyst particles comprising a Group VIII noble metal component and a halogen component in combination with a refractory inorganic oxide. Further, our method is intended for utilization in those hydrocarbon conversion systems wherein catalyst particles are regenerated in a regeneration zone through which they are movable via gravity-flow. 
     It is generally conceded, by those possessing the requisite skill in the appropriate art, that the principal cause of observed deactivation or instability of catalytic composites employed in hydrocarbon conversion processes is associated with the formation of coke or carbonaceous matter throughout the catalyst particles. The conditions utilized in these hydrocarbon conversion processes, to effect the desired reactions, typically result in the formation of heavy, black carbonaceous matter which deposits on the catalyst and gradually reduces its activity by shielding the active sites from the reactants. With many hydrocarbon conversion catalysts, removal of the carbonaceous matter by burning in air, via one or more suitable techniques, generally suffices to reactivate the catalyst to an acceptable degree. However, when considering dual-function catalysts, or those containing a Group VIII noble metal component and a halogen component, carbon removal in and of itself does not result in an acceptable reactivated catalyst. These catalysts, and their capability to function as intended, are acutely sensitive to the loss of the combined halogen both during the processing of the selected hydrocarbon stream and the carbon-burning. technique. Therefore, any successful regeneration procedure must recognize the attendant difficulty of restoring a uniform distribution of the halogen component within the catalyst particles. Furthermore, a comparison of fresh catalyst with deactivated catalyst indicates a substantial change in the character of the Group VIII noble metal component associated therewith. Generally, such a comparison indicates that the noble metal component, for example platinum, is no longer thoroughly and uniformly dispersed throughout the catalyst particles, but has been caused to agglomerate. These difficulties become more pronounced in regeneration techniques involving the bi-, tri- and tetra-metallic catalytic composites. As exemplified by U.S. Pat. No. 3,751,379 (Cl. 252-415) these problems appear to have been successfully solved with respect to batch reconditioning, or in situ regeneration of a fixed-bed of catalytic particles. 
     With the advent of continuous hydrocarbon processing, utilizing catalyst particles movable through the various reaction zones via gravity-flow, and having an integrated regeneration facility through which the catalyst particles also flow via gravity, the specter surrounding reconditioning problems is once again in evidence. While it may be that the catalyst particles which the regenerator &#34;sees&#34; initially have a lesser quantity of carbonaceous matter to be removed, and a lesser quantity of halogen to be replaced, the mere fact that the particles are continuously in motion through some part of the regeneration zone necessitates judiciously selected techniques in order to provide a continuous reconditioning method resulting in catalyst particles suitable for re-utilization in the reaction zone, or zones. One technique is that proposed for use with the reconditioning system illustrated in U.S. Pat. No. 3,652,231 (Cl. 23-288G). The regeneration zone is shown as having an upper carbon-burning section, an intermediate halogenation section and a lower drying section. Catalyst particles are introduced initially into the top of the regeneration zone, pass downwardly through the carbon-burning section into the halogenation section and finally into the lower drying section. All the air required for reconditioning is introduced into the lower drying section and passes upwardly therefrom into the halogenation section, and therethrough into the carbon-burning section. Halogen and steam are introduced into the intermediate halogenation section, and any excess is recycled in admixture with fresh steam and halogen. Furthermore, combustion vapors from the carbon-burning section are introduced into a caustic scrubbing facility, and thereafter recycled to the carbon-burning section. Another three-stage regeneration technique is that set forth in the previously described U.S. Pat. No. 3,981,824 (Cl. 252-415); however, the aspect of split air flow is incorporated therein. 
     Our catalyst regeneration technique is intended to improve significantly both of the above-described techniques. To reiterate briefly, the regeneration technique is accomplished in two discrete zones, or sections, as contrasted to the three zones of the prior art. In accordance with our inventive concept, substantially dry air is introduced to the lower drying section and undried air to the upper carbon-burning/halogenation section. With respect to the latter, the undried air is admixed with the halogen and recycled flue gas, and introduced therewith into this dual-function zone. The mole ratio of air introduced into the carbon-burning section, to that introduced into the drying section is at least 1.0:1.0, and generally in the range of about 1.0:1.0 to about 9.0:1.0. Preferably, the quantity (or proportion) of air introduced into the drying section will be the minimum sufficient to accomplish the necessary drying. Furthermore, the flue gas from the carbon-burning/halogenation section is recycled without any intermediate treatment, excepting the cooling thereof. The relative rates of the total air input and flue gas recycle are maintained to control the oxygen concentration at a level in the range of about 0.2% to 2.0%, on a molal basis, and preferably from about 0.5% to about 1.5%. 
     The upper section of the regeneration tower essentially serves two principal functions; first, the coke and/or carbonaceous material must be removed from the catalyst particles and, secondly, the halogen content must be increased while the metallic components are properly dispersed. One consequence of split air flow, introducing from about 10.0% to about 50.0% of the required air into the lower section, is to maintain the necessary partial pressure of halogen in the upper section with less fresh halogen addition. Furthermore, combining the halogenation and carbon-burning functions alleviates noble metal agglomeration normally occurring when the carbonaceous material is removed from the catalyst particles. Assuming a fresh catalyst halogen content of about 1.0% by weight (as combined halide), which is reduced to a level of about 0.75% when the catalyst is deactivated, the concentration will be about 1.1% by weight following halogenation and carbon-burning, and about 1.0% by weight following the drying step. 
     In further describing our invention, reference will be made to the accompanying diagrammatic sketch. This is presented for the sole purpose of illustration, and not with the intent of limiting our invention beyond the scope and spirit of the appended claims. Miscellaneous appurtenances, not required for a clear understanding, have been eliminated. 
    
    
     DESCRIPTION OF DRAWING 
     With specific reference now to the drawing, there is illustrated a regenerating tower 1, having an upper carbon-burning/halogenation section 2 and a lower catalyst drying section 3. Although the various structural elements may take any suitable tubular form, sound engineering principles and techniques dictate that the same be substantially circular in cross-section. Catalyst particles which have been withdrawn from the lower terminus of a reaction zone, through which they are movable via gravity-flow, are transported to regenerating tower 1 by way of lift line 8 and are introduced thereby into disengaging hopper 9. Catalyst particles are disengaged from dust-like catalyst fines which are removed from the regeneration facility by way of conduit 10. Separated catalyst particles flow downwardly through a plurality of inlet conduits 11, generally numbering from about four to sixteen, and into annular-form space 13. The latter is formed by a perforated centerpipe 6 and an outer catalyst-retaining screen 5, through which the reconditioning vapors pass. 
     The catalyst particles, at a temperature of about 210° F., initially traverse carbon-burning/halogenation section 2 which functions in the temperature range of about 830° F. (443° C.) to about 1050° F. (565° C.). Catalyst-burning/halogenation section 2 is that portion of the regenerating tower which extends from top plate 12 to terminal end 7 of centerpipe 6. Substantially coke-free catalyst particles flow via gravity into lower drying section 3, being that portion of regenerating tower 1 between the terminal end 7 of centerpipe 6 and the bottom of frusto-conical section 14. Drying section 3 functions at a temperature range of about 830° F. (443° C.) to about 1000° F. (538° C.); that is, substantially dry air introduced into frusto-conical section 14, by way of line 30, is at a temperature of about 1000° F. (538° C.), while catalyst particles emanating from the regenerating tower, via outlet port 15 and line 16, are at a temperature of about 830° F. (443° C.). Dried, reconditioned catalyst particles are subjected to hydrogen reduction either in a separate vessel prior to being transported to the reaction zone, or in a vessel which is an integral part of the reaction zone. 
     At least a portion of the effluent vapors, flue gas, emanating from the carbon-burning/halogenation section of the regeneration zone, are recycled thereto. Through this technique, the oxygen concentration within this upper section is regulated and maintained in the preferred range of about 0.5% to about 1.5%. Furthermore, dilution of the halogen atmosphere within the halogenation section is effected by the vapors emanating from the drying section. This relatively severe oxidizing atmosphere facilitates the redistribution of the noble metal component. 
     The remainder of the drawing will be described in conjunction with a commercially-scaled regenerator designed to process about 500 lbs/hr. (227 kg/hr.) of deactivated catalyst particles containing about 0.90% by weight of combined chloride and about 5.2% by weight of carbonaceous matter (coke). About 12.76 moles/hr. of air from a suitable external source, are introduced by way of line 22. Approximately 50.0% is diverted through line 26 into air dryer 4, through line 28 and an electric heater 29. The temperature thereof is increased to about 1000° F. (538° C.), and the heated air is introduced into drying section 3 via line 30. About 0.22 moles/hr. of water are removed from the catalyst particles in the drying section. 
     Halogen, or a halogen-containing compound is introduced by way of line 23, admixed with recycled flue gas from line 20, the mixture passing into carbon-burning/halogenation zone 2 by way of blower 24 and conduit 25. This halogen-containing stream is at a temperature of about 830° F. (443° C.). The halogen, for example chlorine, may be employed in its elemental state, or as a compound such as hydrogen chloride, ethylene dichloride, propylene dichloride, tertiary butyl chloride, etc. In the present illustration, the halogen addition will take the form of ethylene dichloride; about 0.018 moles/hr. is injected. 
     Effluent vapors from section 2, at a temperature of about 930° F. (498° C.), are withdrawn through the extension of centerpipe 6 and outlet port 17; these are introduced, by way of line 18, into cooler 19, wherein the temperature is decreased to about 840° F. (449° C.). Thus cooled vapors are withdrawn via line 20, and about 400 moles/hr. continue therethrough, admixed with about 6.4 moles/hr. of undried air from line 22, and introduced into blower 24 by way of conduit 23. The remaining portion of the cooled flue gas vapors are vented from the system through conduit 21. 
     The catalyst particles introduced into the regeneration zone from disengaging hopper 9, contain about 27.4 lbs/hr. (12.4 kg/hr.) of coke and about 0.90% by weight of combined chloride. When these leave the carbon-burning/halogenation section, they are substantially coke-free; the halogen content has been increased to about 1.1% by weight, and the catalyst particles contain about 0.90% by weight of water. The latter is removed in the drying section, and the dried catalyst particles are withdrawn from the regeneration zone containing 1.0% by weight of halogen. The upper carbon-burning/halogenation section and the lower drying section, of the regeneration zone 1, are sized and designed to provide an effective residence time, of the catalyst particles passing through each section, of from one to about three hours. 
     The foregoing illustrates the regeneration technique of the present invention wherein the regenerating tower consists of two stages as contrasted to the three-stage technique of the prior art. As a principal result, there is afforded an approximate three-fold increase in coke-burning capacity. Other benefits and advantages will become apparent to those possessing the requisite skill in the appropriate art.