Temperature controlled catalytic demetallization of hydrocarbons
BACKGROUND OF THE INVENTION 
     This invention relates to catalytic hydrocarbon processing, and particularly to hydrocarbon hydroprocessing, such as the process involving catalyzing the reaction of hydrogen with organosulfur, organonitrogen, and organometallic compounds. More particularly, this invention is directed to a process for hydrodemetallizing hydrocarbon liquids. 
     During the course of a typical process involving the catalytic refining of hydrocarbons, portions of contaminant metals and sulfur components contained in a hydrocarbon oil ordinarily are deposited on a porous particulate catalyst, causing a loss of catalytic activity and stability. Residual petroleum oil fractions, such as the heavy fractions produced in atmospheric and vacuum crude distillation columns, are especially undesirable as feedstocks for such catalytic refining processes due to their high contaminant metals and/or sulfur content. Economic considerations have recently provided new incentives for catalytic conversion of the heavy fractions to more marketable products. However, the presence of high concentrations of sulfur and contaminant metals precludes the effective use of residua as feedstocks for cracking, hydrocracking, and similar catalytic refining operations. 
     Methods are available to reduce the sulfur and metals content of residua. One such method is hydrodesulfurization, a process wherein a residuum contacts a catalyst usually containing hydrogenation metals on a porous refractory oxide support under conditions of elevated temperature and pressure and in the presence of hydrogen, such that sulfur components are converted to hydrogen sulfide, nitrogen components are converted to ammonia, while the contaminant metals are simultaneously deposited on the catalyst. The most common contaminant metals found in such hydrocarbon fractions include nickel, vanadium and iron. The extent of deactivation of the catalyst typically is a function of the amount of deposition of contaminant metals on the catalyst surface and in its pores, i.e., the usefulness of the catalyst steadily decreases as the amount of deposited metals increases with continued treatment of the residuum. Increased metals deposition as well as high coke deposition, may cause plugging of catalyst beds resulting in premature replacement of catalyst beds in the hydrocarbon refining reactors. 
     It has been recognized that hydrodesulfurization of hydrocarbons may involve removing a substantial proportion of contaminant metals prior to downstream removal of sulfur and nitrogen. For example in U.S. Pat. No. 4,431,526, contaminant metals are removed by contact with a relatively large pore first catalyst and then sulfur and additional contaminant metals are subsequently removed by a relatively small pore downstream catalyst. Another typical example of a demetallization process is disclosed in U.S. Pat. No. 4,548,710 wherein a relatively large pore demetallization catalyst accumulates (deposits) its own fresh weight in contaminant metals. Such a demetallization process allows the refiner to subsequently pass a feedstock having a substantially reduced metals content over a high surface area desulfurization catalyst such as that prepared in accordance with U.S. Pat. No. 3,980,552. 
     Catalytic removal of metals from hydrocarbons involving multiple reaction zones provides only limited improvement to such problems as catalyst activity before undesirable characteristics such as catalyst stability (i.e. catalyst life) are adversely affected. A need still exists for an improved process for depositing contaminant metals on a particulate catalyst. 
     It is, therefore, a major object of the present invention to provide a process for removing contaminant metals from a hydrocarbon oil, and more specifically to provide a catalytic hydrodemetallization process while simultaneously removing a substantial proportion of sulfur and Conradson carbon from a hydrocarbon oil. 
     It is another object of the invention to provide a multi-reaction zone process for the catalytic hydrodemetallization of a hydrocarbon oil, and more specifically to provide a process for substantially hydrodemetallizing a heavy hydrocarbon oil prior to substantially hydrodesulfurizing the oil. 
     A further object of the invention is to provide hydrocarbon products of reduced metals content so as to extend the life of downstream refining catalysts. 
     These and other objects and advantages of the invention will become apparent from the following description. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a process for removing contaminant metals from a hydrocarbon oil by successively contacting at least two portions of a particulate catalyst with the oil under demetallization conditions and wherein the weighted average catalyst bed temperature of an upstream portion of the particulate catalyst is lower than the weighted average catalyst bed temperature of a downstream second portion of the particulate catalyst. In a multi-reaction zone process for catalytically processing hydrocarbon oils, a large pore hydrodemetallization catalyst is employed in at least two reaction zones wherein the first reaction zone has a lower weighted average catalyst bed temperature than that of the second reaction zone. The product hydrocarbon from the second reaction zone contains a hydrocarbon oil having a substantially reduced contaminant metals content and, in one embodiment, such an oil then contacts a hydrodesulfurization catalyst in a third reaction zone to produce a product hydrocarbon having a substantially reduced sulfur and metals content. 
     In a multi-reactor demetallization process, a lower weighted average catalyst bed temperature in an upstream reactor provides a uniform deposition of contaminant metals on the hydrodemetallization catalyst located in upstream and downstream reactors. Although the hydrocarbon oil contacting the hydrodemetallization catalyst in an upstream reactor contains substantially more contaminant metals than the effluent hydrocarbon oil from the upstream reactor which contacts the hydrodemetallization catalyst in the downstream reactor, the process of the invention provides substantial contaminant metals deposition on the hydrodemetallization catalyst located in the downstream reactor as compared to that in the upstream reactor. As compared to a process employing two reactors at the same temperature, the process of the invention provides unusual improvement in sulfur and Conradson carbon removal in addition to the uniform deposition of contaminant metals on the particulate catalyst. 
     DETAILED DESCRIPTION OF THE INVENTION 
     A hydrocarbon oil is catalytically treated in a reaction zone containing a catalyst bed capable of having temperatures maintained in upstream portions of the bed that are at least 5° F. lower than those in downstream portions of the bed. A hydrocarbon oil may also be treated serially in two or more reaction zones containing the same particulate catalyst. The upstream reaction zones have a lower weighted average catalyst bed temperature than the weighted average catalyst bed temperatures of the downstream reaction zones. The process of the invention is particularly well suited for hydrodemetallization of a hydrocarbon oil containing a high content of contaminant metals and sulfur and most particularly for a multireaction zone hydrodesulfurization process emphasizing demetallization in upstream zones and desulfurization in downstream zones. Furthermore, the process of the invention is highly effective for simultaneous hydrodemetallization and hydrodesulfurization of hydrocarbons and for simultaneous hydrodemetallization and Conradson carbon removal from hydrocarbon oils. 
     The invention is directed to a process for utilization of particulate catalysts, and more preferably, of hydroprocessing catalysts comprising hydrogenation metals on a support, and more preferably still of a hydrodemetallization catalyst or a hydrodesulfurization catalyst containing Group VIII and Group VIB metal components on a support material typically containing a porous amorphous refractory oxide. Porous refractory oxides useful in the particulate catalyst of the invention includes silica, magnesia, silica-magnesia, zirconia, silica-zirconia, titania, silica-titania, alumina, silica-alumina, and the like. Mixtures of the foregoing oxides are also contemplated especially when prepared as homogeneously as possible. The preferred refractory oxide material comprises aluminum and is usually selected from the group consisting of alumina and silica-alumina. For either hydrodemetallization or hydroesulfurization, a support material containing gamma alumina is most highly preferred. 
     Contemplated for treatment by the process of the invention are hydrocarbon-containing oils, including broadly all liquid and liquid/vapor hydrocarbon mixtures such as crude petroleum oils and synthetic crudes. Among the typical hydrocarbon oils contemplated are top crudes, vacuum and atmospheric residual fractions, vacuum and atmospheric gas oils, creosote oils, shale oils, oils from bituminous sands, coal-derived oils, and blends thereof, which contain sulfur and one or more contaminant metals such as vanadium, nickel, iron, sodium, zinc, titanium and copper. The hydrocarbon oil finding particular use within the scope of this invention is any heavy hydrocarbonaceous oil, at least 15 volume percent and preferably 50 volume percent of which boils above 1,000° F. and which has greater than about 10 ppmw, preferably greater than about 50 ppmw and most preferably greater than 100 ppmw of nickel plus vanadium contaminant metals. A typical residuum oil for treatment herein is high boiling (i.e., at least 95 percent of its constituents boil above about 400° F.), often contains undesirable proportions of nitrogen, usually in a concentration between about 0.2 and 1.0 weight percent, calculated as N, and contains undesirable portions of sulfur typically between about 1 and 8 weight percent of sulfur, calculated as S. 
     The particulate catalyst is typically employed in a fixed bed of particulates in a suitable reactor vessel wherein the oils to be treated are introduced and subjected to elevated conditions of pressure and temperature, and ordinarily a substantial hydrogen partial pressure, so as to effect the desired degree of demetallization of the oil. The particulate catalyst is maintained as a fixed bed with the oil passing upwardly or downwardly therethrough, and most usually downwardly therethrough. Such catalysts employed in the process of the invention may be activated by being sulfided prior to use (in which case the procedure is termed &#34;presulfiding&#34;). Presulfiding may be accomplished by passing a sulfiding gas or sulfur-containing liquid hydrocarbon over the catalyst in the calcined form; however, since the hydrocarbon oils treated in the invention ordinarily contain sulfur impurities one may also accomplish the sulfiding in situ. 
     In one embodiment of the invention, a catalyst bed of particulate catalyst is contacted by a hydrocarbon oil fed from an upstream inlet location, through a single reactor containing the catalyst bed, to a downstream outlet location. The single reactor contains means for effecting different temperatures upon one or more upstream portions of the catalyst bed or upon one or more downstream portions of the bed during processing. Such temperature controlling means include quench or heating gas streams selectively positioned along upstream and downstream portions of the catalyst bed, and heat exchangers positioned along the bed. It is preferred that the particulate catalyst be utilized in two or more reactors, such as in a multiple train reactor system having one or two reactors loaded with one type of particulate catalyst and the remaining reactors with one or more other particulate catalysts. In either the single reactor system or the multiple reactor system, the individual reactors are generally operated under an independent set of demetallizing and/or desulfurizing conditions selected from those shown in the following TABLE A: 
     
                       TABLE A                                                     
______________________________________                                    
Operating Conditions                                                      
                Suitable Range                                            
                            Preferred Range                               
______________________________________                                    
Temperature, °F.                                                   
                500-900     600-850                                       
Hydrogen Pressure, p.s.i.g.                                               
                  500-3,000 1,000-2,500                                   
Space Velocity, LHSV                                                      
                0.05-3.0    0.1-1.5                                       
Hydrogen Recycle Rate,                                                    
                 1,000-15,000                                             
                             2,000-10,000                                 
scf/bbl                                                                   
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     In a single reactor embodiment, the upstream and downstream portions of the catalyst bed are contacted by a metals-containing hydrocarbon oil at demetallizing conditions including temperatures determined from the concentrations of contaminant metals in the respective portions of the oil contacting the upstream and downstream portions of the catalyst. In general, an upstream portion of the catalyst bed is maintained at a temperature lower than the temperature of a downstream portion of the catalyst bed. The temperatures of downstream portions of the catalyst bed are inversely related to the concentrations of contaminant metals contacting the corresponding downstream portions of the oil based on kinetic considerations including catalyst activity and operating conditions other than temperature. The temperature of an upstream portion of the catalyst bed is determined from the concentration of contaminant metals in the portion of the oil that contacts the upstream portion of the catalyst bed and must be sufficient to provide catalytic activity to remove a selected amount of contaminant metals from that portion of the oil. The temperature of a downstream portion of the catalyst bed is determined from the concentration of the portion of the oil that contacts the downstream portion of the catalyst bed and must be sufficiently higher than the temperature of an equivalent upstream portion of the catalyst bed so as to remove a second selected amount of contaminant metals from that portion of the oil contacting the downstream portion of the catalyst bed. 
     The selected amount of contaminant metals removed from a hydrocarbon oil, particularly the amount removed by the most upstream portion of the catalyst bed, depends upon such factors as the metals-accumulating capacity of the catalyst, the activity of the catalyst, the concentration of contaminant metals in the oil contacting the catalyst, operating conditions, and the like. In the present invention, the selected amount of contaminant metals removed in a downstream portion of the catalyst bed from a product hydrocarbon resulting from the contact of a hydrocarbon oil with the upstream portion of the catalyst bed is generally at least 25 percent, preferably about 75 percent to about 125 percent, and most preferably about 90 percent to about 110 percent of the selected amount of metals removed from the hydrocarbon oil having previously been contacted by an equivalent upstream portion of the catalyst bed. For instance, if a hydrocarbon oil containing 100 ppmw of contaminant metals contacts equal adjacent portions of a particulate catalyst in a catalyst bed, the temperature of the downstream portion of the catalyst bed is maintained at a temperature sufficient to remove at least about 10 ppmw, preferably about 30 ppmw to about 50 ppmw, and most preferably about 36 ppmw to about 44 ppmw of metals (i.e., the desired amount of contaminant metals) from the effluent obtained from the contacting of the upstream portion of the catalyst bed at a temperature sufficient to remove about 40 ppmw of metals from the initial hydrocarbon oil. 
     In a preferred embodiment of the invention, hydrocarbon oil is successively passed through at least two reaction zones, i.e. an upstream first zone and a downstream second zone, each zone containing a hydrodemetallization catalyst, at demetallizing conditions including a temperature of about 500° F. to about 900° F. and at a space velocity (LHSV) of about 0.05 to about 3.0 and in the presence of hydrogen at a partial pressure of about 500 to about 3,000 p.s.i.g., employed at a recycle rate of about 1,000 to about 15,000 scf/bbl. Preferably, the product hydrocarbon obtained from the first reaction zone is directly and rapidly passed into the second reaction zone, thus a connective relationship exists between the zones. In this connective relationship, the pressure between the zones is maintained such that there is no substantial loss of hydrogen partial pressure. 
     An unusual feature of the two-reaction zone embodiment of the invention involves intentionally lowering the weighted average catalyst bed temperature in the upstream first reaction zone as compared to the weighted average bed temperature of the downstream second reaction zone at the start of a processing run. Alternatively the weighted average bed temperature of the second reaction zone may be raised as compared to the weighted average bed temperature of the first reaction zone. Typically throughout a demetallizing run, the difference between the weighted average bed temperatures in the first and second reaction zones is at least 5° F., preferably at least 10° F., and ordinarily in the range from about 5° F. to about 100° F., and preferably about 10° F. to about 50° F. 
     The weighted average catalyst bed temperature for a typical commercial tubular reactor having a constant catalyst density and a linear temperature increase through the length of the bed is the average of the temperatures of the hydrocarbon oil at the inlet and outlet of the reactor. When the temperature increase through a catalyst bed is not linear, the temperatures of the weighted portions of the catalyst at selected bed locations must be averaged in accordance with the equation (WABT)=ΣTΔW/W wherein WABT is the weighted average catalyst bed temperature, W is the weight to the catalyst, ΔW is the weight of a portion of the catalyst bed having a given average temperature T. (When the catalyst reactor bed has a constant catalyst density, then ΣTΔW/W =ΣTΔL/L wherein L is the reactor bed length and ΔL is the length of a portion of the catalyst bed having a given average temperature T.) For example, a tubular reactor having a 15 foot catalyst bed with constant catalyst density and having a reactor inlet temperature of 700° F. and a reactor outlet temperature of 750°  F. has a weighted average catalyst bed temperature of 716.7° F. when the temperatures are 705° F. and 720° F. at the 5 and 10 ft. catalyst bed positions, respectively. 
     The demetallization of hydrocarbon oils may typically include exothermic reactions and the heat generated from such reactions may be used to increase the temperature of downstream portions of a catalyst bed. However, such an uncontrolled transfer of heat downstream along a single catalyst bed, as in a single bed adiabatic reactor, is not within the scope of the present invention that provides a selected temperature sufficient to deposit a specified amount of contaminant metals onto the catalyst at a particular contacting location on the catalyst bed. 
     In the process of the invention at a particular downstream location in the catalyst bed, an uncontrolled transfer of heat downstream is either supplemented with the heat from an outside source (such as recirculated heating gas) or reduced by cooling means (such as fresh hydrogen quench gas) so as to conform to the selected temperature that is inversely related to the concentration of contaminant metals at the particular downstream contacting location. 
     Although a substantial amount of contaminant metals are removed in the first reaction zone, the higher temperature in the second reaction zone provides substantial reduction of contaminant metals in the second reaction zone as well. Such a substantial metals removal in the second reaction zone is evidenced by the weight percent of contaminant metals deposited on the particulate catalyst located in the second reaction zone. Anytime after the beginning of a processing run and typically after at least 120 days of contacting the particulate catalyst in the first and second reaction zones, the weight percent of contaminant metals, calculated on a fresh catalyst basis, deposited on the particulate catalyst in the first reaction zone is in a ratio less than about 4 to 1 as compared to the weight percent of contaminant metals deposited on the particulate catalyst in the second reaction zone. Preferably, such a ratio is less than about 2 to 1, and more preferably less than about 1.5 to 1 and the most suitable results being with ratios in the range between about 0.75 to 1 and about 1.25 to 1, and most preferably between about 0.9 to 1 and about 1.1 to 1. In a similar manner, after 175 days a ratio of less than 1.5 to 1 is evidenced. 
     In addition to effective contaminant metals removal, the invention provides unusually effective simultaneous hydrodesulfurization and/or Conradson carbon removal from a hydrocarbon oil. When the temperatures of downstream reaction zones are elevated relative to the upstream zones, the overall process of the invention results in significantly superior catalytic desulfurization of the oil as compared to an overall process employing the same catalyst in upstream and downstream reaction zones having a temperature intermediate to those of the reaction zones of the invention. Furthermore, in such a demetallization-desulfurization process of the invention, the desulfurization activity of the particulate catalyst is maintained for a considerably longer period of time than in the process operated at the intermediate temperature. In the same comparison as with desulfurization, the process of the invention provides unusually effective removal of Conradson carbon from an oil in addition to imparting long-term demetallization stability. Moreover, in comparison to a process operated at essentially a 1-tier intermediate temperature in multiple reaction zones, the overall multi-tier temperature process of the invention provides for demetallization of hydrocarbons with simultaneous improvement in nitrogen removal, asphaltene conversion, and bottoms conversion (including vacuum tower bottoms, VTB, and atmospheric tower bottoms, ATB). Ordinarily, the invention provides for improvement in the stability of any hydrocarbon conversion reaction involved in refining hydrocarbons and also for improvement in conversion of any hydrocarbon conversion reaction that has an activation energy higher than that for the conversion of the organometallic compounds converted in the demetallization process. 
     In a preferred embodiment involving multiple reactions zones, a relatively large pore hydrodemetallization catalyst and a relatively small pore hydrodesulfurization catalyst are successively contacted in three or more reactions zones with a hydrocarbon oil initially containing at least about 50 ppmw of nickel plus vanadium contaminant metals and at least about 1.0 weight percent of sulfur. The hydrodemetallization catalyst has an average pore diameter from about 120 to about 220 angstroms and is contacted with the hydrocarbon oil in the first two or more upstream reaction zones. The hydrodesulfurization catalyst has an average pore diameter from about 40 to about 110 angstroms and is contacted in one or more downstream reaction zones with the product hydrocarbon obtained from the &#34;most downstream&#34; reaction zone containing the hydrodemetallization catalyst. During the processing, the weighted average catalyst bed temperature of each of the successive reaction zones containing the hydrodemetallization catalyst is elevated by at least 5° F., and preferably at least 10° F., relative to the weighted average catalyst bed temperature of the preceding reaction zone. 
    
    
     The invention is further illustrated by the following examples which are illustrative of specific modes of practicing the invention and are not intended as limiting the scope of the invention as defined in the appended claims. 
     EXAMPLE I 
     A hydrodemetallization catalyst (A) and a hydrodesulfurization catalyst (B) are loaded into a series of five cylindrical, vertical hydrocarbon refining reactors. The reactors are connected in series such that no substantial loss of hydrogen partial pressure is affected between the reactors. Also, the effluent from each reactor is passed continuously to the following reactor. 
     The first and second reactors (Reactors 1 and 2), contain hydrodemetallization Catalyst A that is prepared in the same manner as that disclosed in U.S. Pat. No. 4,548,710 and has an average pore diameter of about 180 angstroms. The third, fourth and fifth reactors (Reactors 3, 4 and 5) contain hydrodesulfurization Catalyst B that is prepared in the same manner as that disclosed in U.S. Pat. No. 3,980,552 and has an average pore diameter of about 70 angstroms. Both the hydrodemetallization and hydrodesulfurization catalyst have a nominal composition as follows 12.0 weight percent of molybdenum components, calculated as MoO 3 , 4.0 weight percent of cobalt components, calculated as CoO, with the balance containing gamma alumina. The volume ratio of Catalyst A to Catalyst B is 1 to 4. Catalysts A and B are conventionally presulfided and then contacted for ten (10) months with different atmospheric residuum feedstocks having characteristics shown in TABLE II and under hydrodemetallization and hydrodesulfurization conditions (overall process) summarized in TABLE III. 
     
                       TABLE II                                                    
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Atmospheric Resid                                                         
Feedstock Properties                                                      
                    Range      Average                                    
______________________________________                                    
Contam. Metals (Ni + V) ppmw                                              
                     10 to 130 50 to 60                                   
Sulfur, (S) wt. percent                                                   
                    1.7 to 4.5 3.0 to 3.5                                 
Carbon Residue D-189 wt. percent                                          
                     4.5 to 11.5                                          
                               7.0 to 7.5                                 
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                       TABLE III                                                   
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Operating Conditions                                                      
                 Range       Average                                      
______________________________________                                    
Space Velocity (LHSV)                                                     
                 0.1 to 0.4  0.2                                          
Hydrogen Recycle (scf/bbl)                                                
                 3,000 to 8,000                                           
                             4,500 to 5,500                               
Hydrogen Pressure (p.s.i.g.)                                              
                 1,500 to 2,500                                           
                             1,900 to 2,100                               
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     A portion of the feedstock is passed downwardly through each reactor and contacted with the described uniformly loaded catalysts in a single pass system with recycled hydrogen such that the effluent sulfur and contaminant metals concentrations in the effluent from the fifth reactor are maintained at less than 0.3 weight percent and less than 10 ppmw, respectively. Volume percentages of the product hydrocarbons (effluent from the fifth reactor) at the start of the ten month run (SOR) and at the end (EOR) of the ten month run are summarized in TABLE IV as follows: 
     
                       TABLE IV                                                    
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Product Hydrocarbons  SOR    EOR                                          
______________________________________                                    
naphtha               0.5%    4%                                          
(350° F. minus b.p.), vol. %                                       
light gas oil         3.5%   16%                                          
(350° F.-550° F. b.p.), vol. %                              
heavy gas oil           2%   10%                                          
(550° F.-650° F. b.p.), vol. %                              
bottoms                94%   70%                                          
(650° F. plus b.p.), vol. %                                        
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     The weighted average catalyst bed temperatures in each of the five reactors at the start and end of the ten month run are summarized in TABLE V as follows: 
     
                       TABLE V                                                     
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       SOR           EOR                                                  
Reactor No.                                                               
         Temp., °F.                                                
                   WABT, °F.                                       
                             Temp., °F.                            
                                     WABT, °F.                     
______________________________________                                    
1    inlet   664       667.5   702     702.5                              
     outlet  673               703                                        
2    inlet   667       680     711     726                                
     outlet  693               741                                        
3    inlet   637       648.5   689     713.5                              
     outlet  660               738                                        
4    inlet   642       649.5   714     727                                
     outlet  657               740                                        
5    inlet   646       649.5   727     733.5                              
     outlet  653               740                                        
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     The weighted average catalyst bed temperature of Reactors 1 and 2 are controlled throughout the run to maintain at least a 10° F. higher weighted average catalyst bed temperature in Reactor 2 than in Reactor 1. 
     After the ten month run, two separate portions of hydrodemetallization Catalyst A and hydrodesulfurization Catalyst B in Reactors 1 to 5 are analyzed to determine the weight percent of contaminant metals deposited on the catalyst, calculated on a fresh catalyst basis. The weight percents of contaminant metals deposited on Catalyst A in the catalyst beds from Reactors 1 and 2 and on Catalyst B in the catalyst beds from Reactors 3, 4 and 5 in two separate analysis of two representative portions of catalyst samples removed after the ten month run are summarized in TABLE VI as follows: 
     
                       TABLE VI                                                    
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Deposition of Ni Plus V on Catalyst                                       
             Analysis 1   Analysis 2                                      
Reactor Source                                                            
             wt. % (Ni + V)                                               
                          wt. % (Ni + V)                                  
______________________________________                                    
1 Cat A      15.3         27.1                                            
2 Cat A      39.4         27.8                                            
3 Cat B      6.0          3.5                                             
4 Cat B      2.2          1.2                                             
5 Cat B      1.3          0.9                                             
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     In view of the data in TABLE VI relative to weight percent of contaminant metals deposited on Catalyst A in Reactors 1 and 2, the contaminant metals are uniformly deposited on the catalyst in the catalyst beds containing Catalyst A. In Analysis 1, the weight percent of metals deposited on Catalyst A in Reactor 1 is in a ratio of about 0.39 to 1 as compared to the weight percent of contaminant metals deposited on Catalyst A in Reactor 2. In Analysis 2, the aforementioned ratio is about 0.97 to 1. 
     EXAMPLE II 
     Two equal volumes of the hydrodemetallization Catalyst A in Example I (8773 cu. feet) are loaded into fixed beds in single reactor vessels. One vessel (Reactor X) contains a single fixed bed of hydrodemetallization Catalyst A. The other (Reactor Y) contains a fixed bed divided into ten equal volume sections of demetallization Catalyst A with means for controlling the temperature of each of the ten sections of the bed. 
     The catalyst is presulfided and utilized to demetallize a Heavy Arabian Atmospheric Resid feedstock (12.5° API gravity and containing 141 ppmw of nickel plus vanadium contaminant metals) under the conditions of 2,000 p.s.i.g. total pressure and a hydrogen rate of 10,000 scf/bbl. A portion of the feedstock is passed downwardly through the reactors at a liquid hourly space velocity (LHSV) of 0.8 (30,000 bbl/day) and contacted with the catalyst in a single stage, single pass system with once-through hydrogen such that the effluent contaminant metals concentrations are maintained at about 52.5 ppmw over 300 day runs, i.e. equivalent to about 62.8 percent demetallization. 
     The calculated desired rate constant of an entire bed (Reactor X) of particulate catalyst that provides initial activity sufficient to convert the feedstock from 141 ppmw metals to 52.5 ppmw metals over the 300 day period and to deposit 80.8 weight percent of (Ni+V) contaminant metals is 0.08607. Hydrodemetallization Catalyst A has a known initial rate constant (1.5 order kinetics at 700° F.) at the start of the run (SOR) of 0.0618. The required weighted average catalyst bed temperature for the entire bed at SOR is 720° F. to attain the desired conversion. 
     The following TABLE VII summarizes (1) the calculated desired rate constants of ten sections (Reactor Y) particulate catalyst providing initial activity sufficient to convert the feedstock from 141 ppmw metals to 52.5 ppmw metals over the 300 day run and to deposit 80.8 weight percent of (Ni+V) contaminant metals (calculated on a fresh catalyst basis) onto the catalyst in each section, (2) the corresponding initial weighted average catalyst bed temperatures of each of the ten sections of the catalyst bed and (3) the corresponding inlet and outlet concentrations of contaminant metals for each of the ten sections of the catalyst bed. 
     
                                           TABLE VII                               
__________________________________________________________________________
Section      1    2    3    4    5    6    7    8    9    10              
__________________________________________________________________________
Inlet Metals Concent.,                                                    
             141  132.1                                                   
                       123.2                                              
                            114.3                                         
                                 105.4                                    
                                      96.5 87.6 78.7 69.8 60.9            
ppmw (Ni + V)                                                             
Outlet Metals Concent.,                                                   
             132.1                                                        
                  123.2                                                   
                       114.3                                              
                            105.4                                         
                                 96.5 87.6 78.7 69.8 60.9 52.0            
ppmw (Ni + V)                                                             
Desired Rate Constant,                                                    
             0.0447                                                       
                  .0494                                                   
                       .0551                                              
                            .0619                                         
                                 .0703                                    
                                      .0807                               
                                           .0941                          
                                                .1115                     
                                                     .1352                
                                                          .1685           
hr.sup.-1 ppmw.sup.-0.5                                                   
WABT, °F.                                                          
             681.0                                                        
                  686.9                                                   
                       693.2                                              
                            700.1                                         
                                 707.7                                    
                                      716.1                               
                                           725.5                          
                                                736.1                     
                                                     748.4                
                                                          762.8           
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     At the start of the 300 day run (SOR), Reactor X containing the single bed of catalyst, has a weighted average catalyst bed temperature of 720° F. During the course of the 300 day run, the weighted average catalyst bed temperatures of each reactor are increased to maintain the desired degree of conversion. An increase in temperature of Reactor Y includes corresponding increases in each of the ten sections of the catalyst bed. 
     After the 300 day runs, Catalyst A is unloaded from Reactors X and Y and analyzed to determine the profile of the contaminant metals deposited along the catalyst beds in each reactor. The weight percentages of contaminant metals deposited on Catalyst A (on a fresh catalyst basis) in Reactors X and Y at comparative positions along the catalyst bed are summarized below in TABLE VIII. (Section 1 of Reactor Y corresponds to bed location of 1-10 wt.% of Catalyst A in Reactor X, Section 2 of Reactor Y corresponds to bed location of 11-20 wt.% of Catalyst A in Reactor X, etc.) 
     
                                           TABLE VIII                              
__________________________________________________________________________
Metals on Catalyst vs. Catalyst Bed Position                              
__________________________________________________________________________
Bed Location, wt. % of                                                    
               1-10                                                       
                   11-20 21-30                                            
                              31-40 41-50                                 
                                        51-60                             
                                            61-70                         
                                                 71-80                    
                                                     81-90                
                                                          91-100          
fresh Cat A. (Reactor X)                                                  
Cat. A. wt. % of Ni + V                                                   
              170-138                                                     
                   138-116                                                
                         116-100                                          
                              100-82                                      
                                    82-72                                 
                                        72-65                             
                                            65-55                         
                                                 55-46                    
                                                     46-40                
                                                         40-37            
(Reactor X)                                                               
Section (Reactor Y)                                                       
              1    2     3    4     5   6   7    8   9   10               
Cat. A. wt % of Ni + V                                                    
              82-78                                                       
                   82-78 82-78                                            
                              82-78 82-78                                 
                                        82-78                             
                                            82-78                         
                                                 82-78                    
                                                     82-78                
                                                         82-78            
(Reactor Y)                                                               
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     In view of TABLE VIII, the profile of metals deposited along the bed of demetallization Catalyst A in Reactor Y of the invention is substantially more uniform than that in the single Reactor X. The upstream portions of the catalyst bed in Reactor X tend to plug and the downstream portions are substantially below the metals accumulating capacity of Catalyst A. 
     EXAMPLE III 
     Forty-five and fifty-five volume percent of fresh hydrodemetallization Catalyst A used in EXAMPLE I is loaded into the first and second fixed beds, respectively, of two interconnected reactor vessels (Process 1-T, reference process), and tested for overall desulfurization, demetallization and removal of Conradson carbon from a hydrocarbon oil. A second two-reactor system (Process 2-T of the invention), identical to Process 1-T except for operating temperatures in the individual reactors, is also tested for the same above-mentioned conversions of an equivalent portion of the same hydrocarbon oil. 
     The two-reactor processes are utilized in separate runs to hydrodesulfurize, hydrodemetallize and to remove Conradson carbon from Hondo atmospheric residua feedstocks having the characteristics shown in TABLE IX below under the following overall conditions: 2,000 p.s.i.g. total pressure and a hydrogen rate of 10,000 scf/bbl. The liquid hourly space velocity (LHSV) of the first reactor is 1.1, of the second reactor is 0.92 and the overall LHSV is 0.5. 
     
                       TABLE IX                                                    
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Feed Properties                                                           
Feed Description  Hondo Atmospheric Residua                               
______________________________________                                    
Gravity °API                                                       
                  12.3                                                    
Nitrogen (kjel), wt %                                                     
                  0.714                                                   
Sulfur, wt %      5.07                                                    
Nickel, ppmw      91                                                      
Vanadium, ppmw    222                                                     
Carbon Residue, D-189, wt %                                               
                  10.6                                                    
Asphaltenes, wt % 21.3                                                    
Distillation, Mod. Vac. Engler                                            
x-650 F. (vol. %) 21.3                                                    
650-850 F.        19.1                                                    
850-1,000 F.      13.3                                                    
1,000-1,050 F.    4.3                                                     
1,050+ F.         42.0                                                    
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     A portion of the feedstock is passed downwardly through each reactor and contacted with Catalyst A in a single-pass system with once-through hydrogen such that the effluent metals concentration of nickel and vanadium contaminant metals, calculated as Ni+V, from the second reactor is controlled in both Process 1-T and 2-T to 20 ppmw, i.e., greater than 90 percent demetallization. After an initial period in each run to increase the temperatures and establish the high stability period of Catalyst A&#39;s life for demetallization (i.e., both Process 1-T and Process 2-T attained essentially 0.0° F./day temperature increase requirement (TIR) values), each run is continued for 20 more days to determine the relative activities and TIR values of Catalyst A for desulfurization and Conradson carbon removal from the Hondo atmospheric residua. During Catalyst A&#39;s period of high demetallization stability (Days 1-20) the upstream reactor and the downstream reactor in Process 1-T are operated at a weighted average catalyst bed temperature of about 760° F. During the same period in Process 2-T of the invention, the upstream reactor is operated at a weighted average catalyst bed temperature of about 748° F. and the downstream reactor is operated at a weighted average catalyst bed temperature of about 779° F. 
     Giving the catalyst employed at day 1 in the reference process an arbitrary activity of 100, relative activities of Catalyst A employed in the invention compared to Catalyst A employed in the reference process are determined by calculation and tabulated in TABLE X. These determinations are based on a comparison of the reaction rates for desulfurization or Conradson carbon removal obtained from the data of the experiment according to the following standard equation which assumes second order kinetics for desulfurization or Conradson carbon removal: ##EQU1## where C fr  and C pr  are the respective concentrations of sulfur or Conradson carbon in the feed and product obtained with the catalyst employed in the reference process and C f  and C p  are the respective concentrations of sulfur or Conradson carbon in the feed and product obtained with a catalyst being compared to the reference. 
     The TIR determinations are based upon calculation by a relatively simple formula. TIR may be determined by dividing the difference between two operating temperatures required to give a specific product on two given days in a run by run length interval between these days. 
     
                       TABLE X                                                     
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Relative Activity and Stability for                                       
Hydrodesulfurization and Conradson Carbon                                 
Removal During Stable Hydrodemetallization                                
       Relative Activity                                                  
Process  Day 1      Day 21   Stability, °F./day                    
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Hydrodesulfurization                                                      
1-T      100         85      0.60                                         
2-T      146        126      0.45                                         
Conradson carbon                                                          
1-T      100         96      0.1                                          
2-T      148        148      0.0                                          
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     The data summarized in TABLE X indicate that the temperature increase requirement (TIR) calculated in ° F/day for both desulfurization and Conradson carbon removal is substantially lower for Catalyst A in the process of the invention (Process 2-T) as compared to Catalyst A of the reference process ((Process 1-T) The desulfurization deactivation rate of Catalyst A when employed in the reference process is 1.33 times greater than is the case when Catalyst A is employed in the process of the invention. The deactivation rate for Conradson carbon removal essentially parallels that for demetallization, having a TIR of essentially 0.0° F./day, i.e., high stability. In addition to this superiority in stability when employed in the process of the invention, Catalyst A also exhibits substantially improved activity for both desulfurization and Conradson carbon removal compared to Catalyst A in the reference process. 
     While particular embodiments of the invention have been described, it will be understood, of course, that the invention is not limited thereto since many obvious modifications can be made, and it is intended to include within this invention any such modifications as will fall within the scope of the appended claims.