CA1126190A - Catalytic cracking of metal contaminated mineral oil fractions - Google Patents
Catalytic cracking of metal contaminated mineral oil fractionsInfo
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- CA1126190A CA1126190A CA323,553A CA323553A CA1126190A CA 1126190 A CA1126190 A CA 1126190A CA 323553 A CA323553 A CA 323553A CA 1126190 A CA1126190 A CA 1126190A
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Abstract
CATALYTIC cracking OF METAL CONTAMINATED
MINERAL OIL FRACTIONS
ABSTRACT OF THE DISCLOSURE
Metal contaminated heavy oils such as residual fractions from petroleum distillation are economically converted to gasoline and other light products in catalytic cracking by practice of a novel catalyst makeup policy of adding controlled proportions of both an active cracking catalyst and a substantially inert, large pore solid to replace the amount of catalyst withdrawn from the inventory of a continuous cracking unit wherein catalyst inventory is continuously circulated between a reactor for cracking charge hydrocarbons and a regenerator for burning off the carbonaceous deposit laid down on catalyst in the cracking reaction.
MINERAL OIL FRACTIONS
ABSTRACT OF THE DISCLOSURE
Metal contaminated heavy oils such as residual fractions from petroleum distillation are economically converted to gasoline and other light products in catalytic cracking by practice of a novel catalyst makeup policy of adding controlled proportions of both an active cracking catalyst and a substantially inert, large pore solid to replace the amount of catalyst withdrawn from the inventory of a continuous cracking unit wherein catalyst inventory is continuously circulated between a reactor for cracking charge hydrocarbons and a regenerator for burning off the carbonaceous deposit laid down on catalyst in the cracking reaction.
Description
The invention is concerned wi~h increasing the portion of heavy petroleum crudes which can be utilized as catal-ytic cracking feedstock to produce premium petroleum products, particularly motor gasoline of high octane number. The heavy ends of many crudes are high in Conradson Carbon and metals which are undesirable in catalytic cracking feedstocks. The present invention provides an economically attractive method for utilizing the residues of atmospheric and vacuum distillations, commonly called atmospheric and vacuum residua or "resids." The undesirable CC (for Conradson Carbon) and metal bearing compounds present in the crude tend to be concentrated i~ the resids because most of them are o~ high boiling point.
When catalytic cracking was first introduced to the petroleum industry in the 1930's, the process constituted a major advance in its advantages over the previous technique for increasing the yield of motor gasoline from petroleum to meet a fast-growing demand for that premium product. The catalytic process produces abundant yields of high octane naphtha from petroleutn fractions boilLng above the gasoline range, upwards of about ~}00F. Catalytic cracking has been greatly improved by intensive research and development efforts and plant capacity has expanded rapidly to a present-day status :ln which the catalytic cracker is the dominant unit, the workhorse"
oE a petrole~lm reflnery.
25~8 Lnstalled cayaci~y oE catalytic crackLng has Lncreasecl, there has been Lncreaslng pressure to charge to those unlts greater proportlons oE the crude enterlng the refinery. 'L~o very efEectlve restraLnts oppose that pressure, name:Ly Conradson Carbon and metals content of the feed. ~s these values rlse, capaclty and eEflciency of the catalytic cracker have been adversely affected.
i ''~
, - 2 -::' 1 The effect of higher Conradson Carbon is to increase the portion of the charge converted to "coke" deposited on the catalyst.
As coke builds up on the catalyst, the active surface of the catalyst is masked and rendered inactive ~or the desired conversion.
It has been conventional to burn off the inactivating coke with air to "regenerate" the active surfaces, after which the catalyst is returned in cyclic fashion to the reaction stage for contact with and conversion of additional charge. The heat generated in -the burning regeneration stage is recovered and used, at least in part, to supply heat of vaporization of the charge and endothermic heat of the cracking reaction. The regeneration stage operates under a maximum temperature limitation to avoid heat damage of the catalyst.
Since the rate of coke burning is a function of temperature, it follows that any regeneration stage has a limit of coke which can be burned in unit time. As CC of the charge stock is increased, coke burning capacity becomes a bottleneck which forces reduction in the rate of charging feed to the unit. This is in addition to the disadvantage that part of the charge has been diverted to an undesirable reaction product.
~etal bearing fractions contain, inter alia, nickel and - vanadium which are potent catalysts for production of coke and hydrogen.
These metals, when present in the charge, are deposited on the catalyst as the mo:Lecule6 ln w~llch they occur are crackecl and tencl to buL:Lcl up to leve:ls whlch become very trouble60tne. The adver~e efeects O.e increa~ed coke are as revlewed above. The lighter end~ o~ the cracked product, butcme and llghter, are processed through fractlonatlon equlpment to separate components of value greater than fuel to furnaces, prlmarily propane, butane and the olefins of llke carbon number. ~Iydrogen, being incondensible in the "gas plant", occupies ~pace as a gas in the compression and fractionation 1 train and can easily overload the system when excessive amounts are produced by high metal content catalyst, causing reduction in charge rate to maintain the FCC unit and auxiliaries operative.
These problems have long been recognized in the art and many expedients have been proposed. Thermal conversions of resids produce large quantities of solid fuel (coke) and the pertinent processes are characterized as coking, of ~hich two varieties are presently practiced commercially. In delayed colcing, the feed is heated in a furnace and passed to large drums maintained at 780 to 840F. During the long residence time at this temperature, the charge is converted to coke and distillate products taken off the top of the drum for recovery of "coker gasoline", "coker gas oil"
and gas. The other coking process now in use employs a fluidized bed of coke in the form of small granules at about 900 to 1050F.
The resid charge undergoes conversion on the surface of the coke particles during a residence time on the order of two minutes, depositing additional coke on the surfaces of particles in the fluidized bed. Coke particles are transferred to a bed fluidized by air to burn some of the coke at temperatures upwards of 1100F., thus heating the residual coke whlch is then returned to the coking vessel for conversion of additional charge.
These coking processes are known to induce extensive cracking of components which would be valuable for catalytic crackLng charge, resultLng in gaGollne of lower octaine number (Erol~ thermal cracklrlg) I:han woul~ be obtaLnecl by catalytLc ; crackLng of the same componellts. The gas olls produced are oleflnic, i containing slgnLeLcanl: amounts of cZ:Lole~:Lns which are prone to degradat:Lon to colce ln furnace tubes and on cracking catalysts.
It :Is often desirable to treat the gas oils by expensive hydro-genation techniques before charging to catalytlc cracking. Coking ~6~
1 does reduce metals and Conradson Carbon but still leaves an inferior gas oil for charge to catalytic cracking.
Catalytic charge stock may also be prepared from resids by "deasphalting" in which an asphalt precipitant such as liquid propane is mixed with the oil. Metals and Conradson Car~on are drastically reduced but at low yield of deasphalted oil.
Solvent extractions and various other techniques have been proposed for preparation of FCC charge stock from resids. Solvent extraction, in common with propane deasphalting, functions by selection on chemical type, rejecting from the charge stcck the ~ aromatic compounds which can crack to yield high octane components ;~ of cracked naphtha. Low temperature, liquid phase sorption on catalytically inert silica gel is proposed by Shuman and Brace, ; OIL AND GAS JOURNAL, April 16, 1~53, Page 113.
Of the types of catalytic cracking systems, the one of greatest present interest in Fluid Catalytic Cracking (FCC). The installed plants of this type are characterist-Lcally large, and usually designed to process from about 5,000 to 135,000 bbls/day of fresh feed. Briefly, the catalyst section of the plant consists of a cracking section where a heavy charge stock is cracked in contact with fluidized cracking catalyst, and a regenerator section where fluidized catalyst coked in the cracking operation is regenerated by burning with air. ~11 of the plants utilize a relatively large Lnventory of cracking catalyst whlch ls contin1l0usly ci.rcu:Latlng between the cracklng and regenerator ~ectLons. Tlle s:lze of thia clrcll:LatLng lnventory ln exlstlng plants is withln the range of 50 to 600 tons, the newer plants belng ~es:Lgned for short tlme rlser cracklng w:Lth smaller catalyst inventory than that ln old~r plants.
Because the catalytlc activLty of the clrculatlng inventory of catalyst tends to decrease with age, fresh makeup catalyst usually 5 _ ''~
~;
,, ~..f~
1 amounting to about one to two percent of the circulating inventory, which corresponds to about 0.1 to 0.25 lbs. per bbl. of fresh feed, is added per day to maintain optimal catalyst activity, with daily withdrawal plus losses of about like amount o aged circulating inventory, commonly referred to as "equilibrium" catalyst. The considerations which are involved in setting catalyst makeup policy are adequately reviewed in "Dynamic Optimi~ation of Catalyst Make-Up Rate for Catalytic Cracking Systems" W. Lee, Ind. Eng. Chem. Process Des. Development, Vol. 9, No. 1, pp. 154-158 (Jan. 1970). That article pro~ides equations of state and an algorithm for optimizing the makeup rate.
In general, the oils fed to this process are principally the petroleum distillates commonly known as gas oils, which boil in the temperature range of about 650F. to 1000F~, supplemented at times by coker gas oil, vacuum tower overhead, etc. These oils generally have an API gravity in the range of about 15 to ~5 and are substantially free of metal contaminants.
The charge stoc~, which term herein is used to refer to the total fresh feed made up of one or more oils, is cracked in the reactor section in a reaction zone maintained at a temperature of about 800F. to 1200F., a pressure of about 1 to 5 atmospheres, and with a usual residence time for the oil of from about one to ten seconds with a modern short contact time riser design. The catalyst residence tLme 1~ from about one to flfteen seconds. 'rhe crackecl product~3 are separated Erom the coked catalyst and passed to a maln dLstillatlon tower where separatlon of gases and recovery oE gasoline, fuel oll, and recycle stock Ls efEected.
Petroleum refiners usually pay close attention in the fluld catalytic cracking process (hereinafter referred to as the i -6-i'';~'l .
1 FCC process) to supplying feedstocks substantially free oE metal contaminants. The reason for this is that the ~etals present in the charge stock are deposited along with the coke on the cracking catalyst. Unlike the coke, however, they are not removed by regeneration and thus they accumulate on the circulating inventory.
The metals so deposited act as a catalyst poison and, depending on the concentration of metals on the catalyst, more or less adversely affect the efficiency of the process by decreasing the catalyst activity and increasing the production of coke, hydrogen and dry gas at the expense of gasoline and/or fuel oil. Excessive accumula-tion of metals can cause serious problems in the usual ~CC operation.
For example, the amount of gas produced may exceed the capacity of the downstream gas plant, or excessive coke loads may result in regenerator temperatures above the metallurgical limits. In such cases the refiner must resort to reducing the feed rate with attendant economic penalty. Thus, a catalyst inventory that contains excessive deposits of metal is normally regarded as highly undesirable.
The principal metal contaminants in crude petroleum oils are nickel and vanadium, although iron and small amounts of copper also may be present. Additionally, trace amounts of zinc and sodium are sometimes found. It is known that almost all of the nickel and vanad:ium in crude oils is assoclated with very large nonvolatile hyclrocrlrbon mol.ecules, suctl as metrl:L porphyrln~ ~md rlsphalteneo.
~5 Crude c;l:ls, oE course, vary Ltl metaL conten~, but usua:Lly thLs cOnteQt Ls Elubstantial. An Arrlb Light whole crude, for example, n~ay assay 3.2 ppm (l.e. parts by weL~,ht of metal per m^llLlon parts of crude) of nickel and 13 ppm of vanadLum. A typlcal K~ait whole crude, generally considered oE average metals content~ may assay 6.3 ppm of nickel and 22.5 ppm of vanadium. Regardless of ~6~
1 the crude source, however, it is known that distillates produced from the crude are almost free of the metal contaminants which concentrate in the residual oil fractions.
Petroleum engineers concerned with the FCC process have several ways for referring to the metal content of a charge stock.
One of these is by reference to a "metals factor", designated F .
The factor may be expressed in equation form as follows:
F = ppm Fe + ppm V ~ 10 (ppm Ni f ppm Cu) A charge stock having a metals factor greater t~an 2.5 is 10 considered indicative of one which will poison cracking catalyst to a significant degree. This factor takes into account that the adverse effect of nickel is substantially more than that of vanadium -` and iron present in equal concentrations with the nickel.~ ;
; Another way of expressing the metals content of a char~e stock is as "ppm Nickel Equivalent" which is defined as ppm Nickel Equi~alent = ppm nickel + 0.25 ppm .~
vanadium ;, For the purpose of this specification, the value of ppm Nickel Equivalent will be used in discussing metals content of metal-contaminated oils, distillate stocks, and catalysts. As shown above, no mention is made of copper because this metal usually is not present to any significant extent. Eowever, it is to be understood herein that i~ it is present in significant concentration, it is to be included :Ln the comp~ltation of Nickel Equivalent and weighted as nickel.
~ 25 It lf~ current practlce Ln FCC technology to control the ! I metals content of the charge stock so that it does not exceed about 0.25 ppm Nickel Equivalent. Catalyst makeup is managed to control the activity of the circulating inventory. With thls practice, for example, in a plant utilizing 50,000 bbl/day of fresh feed, and an equilibrium catalyst withdrawal of 9 tons per day, the withdrawn :.
~ - 8 -," .
: :.: . : , : : -- :, - . .. .
1 catalyst under steady state conditions will contain about 300 ppm Nickel Equivalent of metals, taking into account that the fresh catalyst contributes 70 ppm to this value. Thus, the circulating inventory is maintained at about 300 ppm Nickel Equivalents of metal, which is considered tolerable, the usual range being at about 200 to 600 ppm, with preferred operation being at about 200 to ~00 ppm.
It is to be understood, of course, that the metals content of the charge stock may vary from day to day without serious disruption, provided that the weighted average of the metals content does not exceed about 0.25 ppm nickel equivalent of metal.
It is important, for the purpose of the present invention, to understand that all references to the metals content of an oil, or of a charge stock, refer to the time weighted average taken over a substantial period of time such as one month, for example. ~ecause of the large inventory of cata~yst relative to the total metals introduced into the system by the charge stock in one day, for example, the metals content of the catalyst changes little each day with fluctuations in the quality of the charge stock. However, a persistent increase in the metals content of the latter will in time result in a well-defined, calculatable increase in the metals content of the circulating inventory of catalyst, which determines the performance of the FCC unit. In fact, it is evident that the circulating inventDry of cataLyst, by its metal content, provides a tLme-nverage value Oe the meta1s content Oe the charge stock. tt is ln thls context, thenl that the phrase "metals content of the charge stock" ls ~Isecl herein.
For the purpose oE thls In~ent:Lon, char~e stocks t:o the FCG
process that contain up to about 0.~0 ppm Nickel Equivalent of metal contamlnants will be regarded as substantially free of metal contami-nants. Charge stocks that contain at least about 0.50 ppm Nickel ~ _ 9 _ .: .
1 Equivalents of metal will include those charge stocks referred to as metal-contaminated.
The effects oE nickel9 vanadium and other heavy metals on - activity and selectivity of FCC catalysts are discussed in detail by Cimbalo, Foster and Wachtel in a paper presented at the 37th midyear meeting to the API Division of Refining under the title "Deposited Metals Poison FCC Catalyst" and published at pages 113 - 122 of the Oil and Gas Jourllal for May 15, 1972. Those authors show that metal contaminants of cracking catalyst decline in poisoning activity through repeated cycles of oxidation and reduction and propose a value of "effective metals" determined by multiplication of actual metal concentration by a fraction related to the rate of fresh catalyst makeup as percent of catalyst inventory. -~
Although the authors note that different cracking catalysts may respond difEerently to metal poisoning and that differences in operation of the regenerator may affect rate of metal deactivation, they establish a single standard for determination of "effective metal" values to be applied generally, presumably having regard to specific catalyst and operating conditions.
The residual fraction of single stage atmospheric distillation or two stage atmospheric/vacuum distillation also contains the bulk of the crude components which deposit as resinous or tar-like bodies on crackLng catalysts without substantial conversion.
These are Ereq~ently reEerred to as "Conradson Carbon" Eroln the nnnLytical technique oE deterlnirling theLr concentratLon -Ln petroLe~lm Eractlons. The CLmbalo article above cited classLELes colce on spent catalyst in four groups: catalytic coke resulting Erom craclcing oE
charge components; cat-to-oil, related to reactor strlpper efElciency;
carbon residue (Conradson) as just discussed; and contaminant coke --10~
., ;
: '''~i ~:
. .
::
l derived from dehydrogenation reactions promoted by the heavy metal poisons nickel, vanadium, etc. The resldual stocks not only provide metal poisoning of the catalyst but also show high Conradson Carbon values which are reflected by coke of that class very nearly equal to the Conradson Carbon Number. It will be seen that the increment of Conradson Coke results from deposition on the catalyst of non-volatile hydrocarbons in the charge without significant change in nature of the deposited hydrocarbons.
With very limited exceptions, residual oils have not been successfully included in the charge stocks to the FCC process. The reasons for this are not fully understood, although from the foregoing discussion it is apparent that their high metals content is certainly a major contributing factor, as is the typically high Conradson Carbon.
~There has been interest in using them, however. The reason for this - 15 interest becomes apparent when we consider, for example, that typically only about 26 volume % of an Arab light whole crude is the 650-1000F.
gas oil fraction, while the total 650F. plus resid constitutes about 43 volume %. Thus, were it feasible to efficiently operate with residual oil fractions, a very substantial increase in the amount of gasoline plus fuel oil derivable from a barrel of crude could be obtained. In some refineries, the vacuum resid remaining after the distillation of the gas oil is coked and the coker gas oil is included in the ~CC charge stock. Ilowever, it is generally recognized that coker gas oLI, because oE lts higtl unsaturated ancl high aromatics content, is a poor quallty Eeed.
-Lt has been proposed Ln t~e pr:Lor art to hydrotrelt residual o:Lls uncler such condltions that the metals content is brought into the range commonly assocLated with gas olls. Such hydro~reated residual oils, substantially free of metal contaminants, may then be used as charge stock or a component thereof for the FCC process.
1 Processes to achieve such metals and sulEur reduction are disclosed in U.S. Patent 3,891,541~ issued June 24, 1975 and U.S. Patent 3,876,523, issued April 8, 1975, for example. The combination of hydrotreating to reduce metals and sulfur content followed by cracking also is disclosed in a publication by Hildebrand et al. in the Oil and Gas Journal, pp. 112-124, December 10, 1973. However, no installation is known which has adopted the proposed scheme, probably because the cost and severity associated with the operation involves a heavy economic penalty.
The concurrent problems of heavy metal and Conradson Carbon content oE heavy stocks have been approached by the ex~edient of catalyst modification. Patent 3,944,482 proposes a cracking catalyst of active aluminosilicate zeolite dispersed in a matrix of large pore refractory inorganic oxide. The patentee suggests that the tendency ~; 15 of the metals to deposit in large pore structures renders the matrix a sacrificial componellt which protects the active zeolite cracking surfaces of the zeolite from metal contamination. The eEfectiveness of large pore structures in adsorbing and/or converting metal bearing ; components oE crude is widely recognized. Many hydrotreating catalysts are preferably prepared by deposit of a ~roup VI metal with nickel or cobalt on a large pore alumina or the like. See also Patent 3,947,347 on demetallizing petroleum fractions in admixture with ; hydrogen over a large pore catalyst without added hydrogerlatlon meta]
catalysts and patenta 2,472,723 and ~,006,077.
Whether or not the charge stock contains heavy metaLs, activLty oE the catalyst ad~led as makeup has a proEound eefect on operatLon of an FCC Unit and Ls arl important eactor consLdered by the reElner in order to accomplish his ob~ectives. tt is usual to ' .. ~.
< 1 consider crack:ing catalysts in terms of capability to produce gasoline.
This takes no account of the very significant proportion of catalytic cracking capacity in refineri.es producing only minor gasoline yields.
In a market having a small. demand for gasoline as compared with the 5 demand for light distillate fuels (No. 2 heating oil, jet fuel, diesel fl~el, kerosene) FCC Units are opera~ed to minimize gasoline and maximize the distillates boiling above gasoline. Such units will genera].ly employ a catalyst of rela-tively low activity. To meet the demand for catalysts of various activity levels, catalyst manufacturers stand 10 prepared to deliver different grades of catalyst over a range of activities. One way to accomplish this without conducting manufacturing ~ operations in accordance with a large number of schemes is to manu-: facture one or a few different catalysts of differing activity. Inter-mediate grades are conveniently achieved by blending substantially inert 15 particles of like ~luidization properties with an active fluid catalyst to thereby provide a total catalyst of lower activity than the active portions. By all these techniques including blending as in patent
When catalytic cracking was first introduced to the petroleum industry in the 1930's, the process constituted a major advance in its advantages over the previous technique for increasing the yield of motor gasoline from petroleum to meet a fast-growing demand for that premium product. The catalytic process produces abundant yields of high octane naphtha from petroleutn fractions boilLng above the gasoline range, upwards of about ~}00F. Catalytic cracking has been greatly improved by intensive research and development efforts and plant capacity has expanded rapidly to a present-day status :ln which the catalytic cracker is the dominant unit, the workhorse"
oE a petrole~lm reflnery.
25~8 Lnstalled cayaci~y oE catalytic crackLng has Lncreasecl, there has been Lncreaslng pressure to charge to those unlts greater proportlons oE the crude enterlng the refinery. 'L~o very efEectlve restraLnts oppose that pressure, name:Ly Conradson Carbon and metals content of the feed. ~s these values rlse, capaclty and eEflciency of the catalytic cracker have been adversely affected.
i ''~
, - 2 -::' 1 The effect of higher Conradson Carbon is to increase the portion of the charge converted to "coke" deposited on the catalyst.
As coke builds up on the catalyst, the active surface of the catalyst is masked and rendered inactive ~or the desired conversion.
It has been conventional to burn off the inactivating coke with air to "regenerate" the active surfaces, after which the catalyst is returned in cyclic fashion to the reaction stage for contact with and conversion of additional charge. The heat generated in -the burning regeneration stage is recovered and used, at least in part, to supply heat of vaporization of the charge and endothermic heat of the cracking reaction. The regeneration stage operates under a maximum temperature limitation to avoid heat damage of the catalyst.
Since the rate of coke burning is a function of temperature, it follows that any regeneration stage has a limit of coke which can be burned in unit time. As CC of the charge stock is increased, coke burning capacity becomes a bottleneck which forces reduction in the rate of charging feed to the unit. This is in addition to the disadvantage that part of the charge has been diverted to an undesirable reaction product.
~etal bearing fractions contain, inter alia, nickel and - vanadium which are potent catalysts for production of coke and hydrogen.
These metals, when present in the charge, are deposited on the catalyst as the mo:Lecule6 ln w~llch they occur are crackecl and tencl to buL:Lcl up to leve:ls whlch become very trouble60tne. The adver~e efeects O.e increa~ed coke are as revlewed above. The lighter end~ o~ the cracked product, butcme and llghter, are processed through fractlonatlon equlpment to separate components of value greater than fuel to furnaces, prlmarily propane, butane and the olefins of llke carbon number. ~Iydrogen, being incondensible in the "gas plant", occupies ~pace as a gas in the compression and fractionation 1 train and can easily overload the system when excessive amounts are produced by high metal content catalyst, causing reduction in charge rate to maintain the FCC unit and auxiliaries operative.
These problems have long been recognized in the art and many expedients have been proposed. Thermal conversions of resids produce large quantities of solid fuel (coke) and the pertinent processes are characterized as coking, of ~hich two varieties are presently practiced commercially. In delayed colcing, the feed is heated in a furnace and passed to large drums maintained at 780 to 840F. During the long residence time at this temperature, the charge is converted to coke and distillate products taken off the top of the drum for recovery of "coker gasoline", "coker gas oil"
and gas. The other coking process now in use employs a fluidized bed of coke in the form of small granules at about 900 to 1050F.
The resid charge undergoes conversion on the surface of the coke particles during a residence time on the order of two minutes, depositing additional coke on the surfaces of particles in the fluidized bed. Coke particles are transferred to a bed fluidized by air to burn some of the coke at temperatures upwards of 1100F., thus heating the residual coke whlch is then returned to the coking vessel for conversion of additional charge.
These coking processes are known to induce extensive cracking of components which would be valuable for catalytic crackLng charge, resultLng in gaGollne of lower octaine number (Erol~ thermal cracklrlg) I:han woul~ be obtaLnecl by catalytLc ; crackLng of the same componellts. The gas olls produced are oleflnic, i containing slgnLeLcanl: amounts of cZ:Lole~:Lns which are prone to degradat:Lon to colce ln furnace tubes and on cracking catalysts.
It :Is often desirable to treat the gas oils by expensive hydro-genation techniques before charging to catalytlc cracking. Coking ~6~
1 does reduce metals and Conradson Carbon but still leaves an inferior gas oil for charge to catalytic cracking.
Catalytic charge stock may also be prepared from resids by "deasphalting" in which an asphalt precipitant such as liquid propane is mixed with the oil. Metals and Conradson Car~on are drastically reduced but at low yield of deasphalted oil.
Solvent extractions and various other techniques have been proposed for preparation of FCC charge stock from resids. Solvent extraction, in common with propane deasphalting, functions by selection on chemical type, rejecting from the charge stcck the ~ aromatic compounds which can crack to yield high octane components ;~ of cracked naphtha. Low temperature, liquid phase sorption on catalytically inert silica gel is proposed by Shuman and Brace, ; OIL AND GAS JOURNAL, April 16, 1~53, Page 113.
Of the types of catalytic cracking systems, the one of greatest present interest in Fluid Catalytic Cracking (FCC). The installed plants of this type are characterist-Lcally large, and usually designed to process from about 5,000 to 135,000 bbls/day of fresh feed. Briefly, the catalyst section of the plant consists of a cracking section where a heavy charge stock is cracked in contact with fluidized cracking catalyst, and a regenerator section where fluidized catalyst coked in the cracking operation is regenerated by burning with air. ~11 of the plants utilize a relatively large Lnventory of cracking catalyst whlch ls contin1l0usly ci.rcu:Latlng between the cracklng and regenerator ~ectLons. Tlle s:lze of thia clrcll:LatLng lnventory ln exlstlng plants is withln the range of 50 to 600 tons, the newer plants belng ~es:Lgned for short tlme rlser cracklng w:Lth smaller catalyst inventory than that ln old~r plants.
Because the catalytlc activLty of the clrculatlng inventory of catalyst tends to decrease with age, fresh makeup catalyst usually 5 _ ''~
~;
,, ~..f~
1 amounting to about one to two percent of the circulating inventory, which corresponds to about 0.1 to 0.25 lbs. per bbl. of fresh feed, is added per day to maintain optimal catalyst activity, with daily withdrawal plus losses of about like amount o aged circulating inventory, commonly referred to as "equilibrium" catalyst. The considerations which are involved in setting catalyst makeup policy are adequately reviewed in "Dynamic Optimi~ation of Catalyst Make-Up Rate for Catalytic Cracking Systems" W. Lee, Ind. Eng. Chem. Process Des. Development, Vol. 9, No. 1, pp. 154-158 (Jan. 1970). That article pro~ides equations of state and an algorithm for optimizing the makeup rate.
In general, the oils fed to this process are principally the petroleum distillates commonly known as gas oils, which boil in the temperature range of about 650F. to 1000F~, supplemented at times by coker gas oil, vacuum tower overhead, etc. These oils generally have an API gravity in the range of about 15 to ~5 and are substantially free of metal contaminants.
The charge stoc~, which term herein is used to refer to the total fresh feed made up of one or more oils, is cracked in the reactor section in a reaction zone maintained at a temperature of about 800F. to 1200F., a pressure of about 1 to 5 atmospheres, and with a usual residence time for the oil of from about one to ten seconds with a modern short contact time riser design. The catalyst residence tLme 1~ from about one to flfteen seconds. 'rhe crackecl product~3 are separated Erom the coked catalyst and passed to a maln dLstillatlon tower where separatlon of gases and recovery oE gasoline, fuel oll, and recycle stock Ls efEected.
Petroleum refiners usually pay close attention in the fluld catalytic cracking process (hereinafter referred to as the i -6-i'';~'l .
1 FCC process) to supplying feedstocks substantially free oE metal contaminants. The reason for this is that the ~etals present in the charge stock are deposited along with the coke on the cracking catalyst. Unlike the coke, however, they are not removed by regeneration and thus they accumulate on the circulating inventory.
The metals so deposited act as a catalyst poison and, depending on the concentration of metals on the catalyst, more or less adversely affect the efficiency of the process by decreasing the catalyst activity and increasing the production of coke, hydrogen and dry gas at the expense of gasoline and/or fuel oil. Excessive accumula-tion of metals can cause serious problems in the usual ~CC operation.
For example, the amount of gas produced may exceed the capacity of the downstream gas plant, or excessive coke loads may result in regenerator temperatures above the metallurgical limits. In such cases the refiner must resort to reducing the feed rate with attendant economic penalty. Thus, a catalyst inventory that contains excessive deposits of metal is normally regarded as highly undesirable.
The principal metal contaminants in crude petroleum oils are nickel and vanadium, although iron and small amounts of copper also may be present. Additionally, trace amounts of zinc and sodium are sometimes found. It is known that almost all of the nickel and vanad:ium in crude oils is assoclated with very large nonvolatile hyclrocrlrbon mol.ecules, suctl as metrl:L porphyrln~ ~md rlsphalteneo.
~5 Crude c;l:ls, oE course, vary Ltl metaL conten~, but usua:Lly thLs cOnteQt Ls Elubstantial. An Arrlb Light whole crude, for example, n~ay assay 3.2 ppm (l.e. parts by weL~,ht of metal per m^llLlon parts of crude) of nickel and 13 ppm of vanadLum. A typlcal K~ait whole crude, generally considered oE average metals content~ may assay 6.3 ppm of nickel and 22.5 ppm of vanadium. Regardless of ~6~
1 the crude source, however, it is known that distillates produced from the crude are almost free of the metal contaminants which concentrate in the residual oil fractions.
Petroleum engineers concerned with the FCC process have several ways for referring to the metal content of a charge stock.
One of these is by reference to a "metals factor", designated F .
The factor may be expressed in equation form as follows:
F = ppm Fe + ppm V ~ 10 (ppm Ni f ppm Cu) A charge stock having a metals factor greater t~an 2.5 is 10 considered indicative of one which will poison cracking catalyst to a significant degree. This factor takes into account that the adverse effect of nickel is substantially more than that of vanadium -` and iron present in equal concentrations with the nickel.~ ;
; Another way of expressing the metals content of a char~e stock is as "ppm Nickel Equivalent" which is defined as ppm Nickel Equi~alent = ppm nickel + 0.25 ppm .~
vanadium ;, For the purpose of this specification, the value of ppm Nickel Equivalent will be used in discussing metals content of metal-contaminated oils, distillate stocks, and catalysts. As shown above, no mention is made of copper because this metal usually is not present to any significant extent. Eowever, it is to be understood herein that i~ it is present in significant concentration, it is to be included :Ln the comp~ltation of Nickel Equivalent and weighted as nickel.
~ 25 It lf~ current practlce Ln FCC technology to control the ! I metals content of the charge stock so that it does not exceed about 0.25 ppm Nickel Equivalent. Catalyst makeup is managed to control the activity of the circulating inventory. With thls practice, for example, in a plant utilizing 50,000 bbl/day of fresh feed, and an equilibrium catalyst withdrawal of 9 tons per day, the withdrawn :.
~ - 8 -," .
: :.: . : , : : -- :, - . .. .
1 catalyst under steady state conditions will contain about 300 ppm Nickel Equivalent of metals, taking into account that the fresh catalyst contributes 70 ppm to this value. Thus, the circulating inventory is maintained at about 300 ppm Nickel Equivalents of metal, which is considered tolerable, the usual range being at about 200 to 600 ppm, with preferred operation being at about 200 to ~00 ppm.
It is to be understood, of course, that the metals content of the charge stock may vary from day to day without serious disruption, provided that the weighted average of the metals content does not exceed about 0.25 ppm nickel equivalent of metal.
It is important, for the purpose of the present invention, to understand that all references to the metals content of an oil, or of a charge stock, refer to the time weighted average taken over a substantial period of time such as one month, for example. ~ecause of the large inventory of cata~yst relative to the total metals introduced into the system by the charge stock in one day, for example, the metals content of the catalyst changes little each day with fluctuations in the quality of the charge stock. However, a persistent increase in the metals content of the latter will in time result in a well-defined, calculatable increase in the metals content of the circulating inventory of catalyst, which determines the performance of the FCC unit. In fact, it is evident that the circulating inventDry of cataLyst, by its metal content, provides a tLme-nverage value Oe the meta1s content Oe the charge stock. tt is ln thls context, thenl that the phrase "metals content of the charge stock" ls ~Isecl herein.
For the purpose oE thls In~ent:Lon, char~e stocks t:o the FCG
process that contain up to about 0.~0 ppm Nickel Equivalent of metal contamlnants will be regarded as substantially free of metal contami-nants. Charge stocks that contain at least about 0.50 ppm Nickel ~ _ 9 _ .: .
1 Equivalents of metal will include those charge stocks referred to as metal-contaminated.
The effects oE nickel9 vanadium and other heavy metals on - activity and selectivity of FCC catalysts are discussed in detail by Cimbalo, Foster and Wachtel in a paper presented at the 37th midyear meeting to the API Division of Refining under the title "Deposited Metals Poison FCC Catalyst" and published at pages 113 - 122 of the Oil and Gas Jourllal for May 15, 1972. Those authors show that metal contaminants of cracking catalyst decline in poisoning activity through repeated cycles of oxidation and reduction and propose a value of "effective metals" determined by multiplication of actual metal concentration by a fraction related to the rate of fresh catalyst makeup as percent of catalyst inventory. -~
Although the authors note that different cracking catalysts may respond difEerently to metal poisoning and that differences in operation of the regenerator may affect rate of metal deactivation, they establish a single standard for determination of "effective metal" values to be applied generally, presumably having regard to specific catalyst and operating conditions.
The residual fraction of single stage atmospheric distillation or two stage atmospheric/vacuum distillation also contains the bulk of the crude components which deposit as resinous or tar-like bodies on crackLng catalysts without substantial conversion.
These are Ereq~ently reEerred to as "Conradson Carbon" Eroln the nnnLytical technique oE deterlnirling theLr concentratLon -Ln petroLe~lm Eractlons. The CLmbalo article above cited classLELes colce on spent catalyst in four groups: catalytic coke resulting Erom craclcing oE
charge components; cat-to-oil, related to reactor strlpper efElciency;
carbon residue (Conradson) as just discussed; and contaminant coke --10~
., ;
: '''~i ~:
. .
::
l derived from dehydrogenation reactions promoted by the heavy metal poisons nickel, vanadium, etc. The resldual stocks not only provide metal poisoning of the catalyst but also show high Conradson Carbon values which are reflected by coke of that class very nearly equal to the Conradson Carbon Number. It will be seen that the increment of Conradson Coke results from deposition on the catalyst of non-volatile hydrocarbons in the charge without significant change in nature of the deposited hydrocarbons.
With very limited exceptions, residual oils have not been successfully included in the charge stocks to the FCC process. The reasons for this are not fully understood, although from the foregoing discussion it is apparent that their high metals content is certainly a major contributing factor, as is the typically high Conradson Carbon.
~There has been interest in using them, however. The reason for this - 15 interest becomes apparent when we consider, for example, that typically only about 26 volume % of an Arab light whole crude is the 650-1000F.
gas oil fraction, while the total 650F. plus resid constitutes about 43 volume %. Thus, were it feasible to efficiently operate with residual oil fractions, a very substantial increase in the amount of gasoline plus fuel oil derivable from a barrel of crude could be obtained. In some refineries, the vacuum resid remaining after the distillation of the gas oil is coked and the coker gas oil is included in the ~CC charge stock. Ilowever, it is generally recognized that coker gas oLI, because oE lts higtl unsaturated ancl high aromatics content, is a poor quallty Eeed.
-Lt has been proposed Ln t~e pr:Lor art to hydrotrelt residual o:Lls uncler such condltions that the metals content is brought into the range commonly assocLated with gas olls. Such hydro~reated residual oils, substantially free of metal contaminants, may then be used as charge stock or a component thereof for the FCC process.
1 Processes to achieve such metals and sulEur reduction are disclosed in U.S. Patent 3,891,541~ issued June 24, 1975 and U.S. Patent 3,876,523, issued April 8, 1975, for example. The combination of hydrotreating to reduce metals and sulfur content followed by cracking also is disclosed in a publication by Hildebrand et al. in the Oil and Gas Journal, pp. 112-124, December 10, 1973. However, no installation is known which has adopted the proposed scheme, probably because the cost and severity associated with the operation involves a heavy economic penalty.
The concurrent problems of heavy metal and Conradson Carbon content oE heavy stocks have been approached by the ex~edient of catalyst modification. Patent 3,944,482 proposes a cracking catalyst of active aluminosilicate zeolite dispersed in a matrix of large pore refractory inorganic oxide. The patentee suggests that the tendency ~; 15 of the metals to deposit in large pore structures renders the matrix a sacrificial componellt which protects the active zeolite cracking surfaces of the zeolite from metal contamination. The eEfectiveness of large pore structures in adsorbing and/or converting metal bearing ; components oE crude is widely recognized. Many hydrotreating catalysts are preferably prepared by deposit of a ~roup VI metal with nickel or cobalt on a large pore alumina or the like. See also Patent 3,947,347 on demetallizing petroleum fractions in admixture with ; hydrogen over a large pore catalyst without added hydrogerlatlon meta]
catalysts and patenta 2,472,723 and ~,006,077.
Whether or not the charge stock contains heavy metaLs, activLty oE the catalyst ad~led as makeup has a proEound eefect on operatLon of an FCC Unit and Ls arl important eactor consLdered by the reElner in order to accomplish his ob~ectives. tt is usual to ' .. ~.
< 1 consider crack:ing catalysts in terms of capability to produce gasoline.
This takes no account of the very significant proportion of catalytic cracking capacity in refineri.es producing only minor gasoline yields.
In a market having a small. demand for gasoline as compared with the 5 demand for light distillate fuels (No. 2 heating oil, jet fuel, diesel fl~el, kerosene) FCC Units are opera~ed to minimize gasoline and maximize the distillates boiling above gasoline. Such units will genera].ly employ a catalyst of rela-tively low activity. To meet the demand for catalysts of various activity levels, catalyst manufacturers stand 10 prepared to deliver different grades of catalyst over a range of activities. One way to accomplish this without conducting manufacturing ~ operations in accordance with a large number of schemes is to manu-: facture one or a few different catalysts of differing activity. Inter-mediate grades are conveniently achieved by blending substantially inert 15 particles of like ~luidization properties with an active fluid catalyst to thereby provide a total catalyst of lower activity than the active portions. By all these techniques including blending as in patent
2,455,915 and the inert, large pore matrix of patent 3,9447482, the refiner has at hand a catalyst of fixed activ:ity which he adds to ; 20 his unit in order to maintain an equilibrium activity according to the equation:
AF = AE(5+K) where ~ i8 activity of fresh catalyst 25~ Ls equ:llibrlulll activlty o:~ the total cal:alyst inventory l.n the ~n~:Lt S :l.~ the rate o:E makellp :Ln percentage of total inve.ntory per clay 1~ is a constant representing rate of catalyst deactl.vation 30This is essentially equation (15) of the Lee article cited above, which see for derivation and more detalled explanat.ion of terms.
~ .
1 It will be apparent that activity is a relative term, the absolute value of which is dependent on the test procedure. In this specification, "activity" refers to the value determined by a micro-activity test (MAT) conducted by cracking a Mid-Continent Gas Oil of the following properties:
Gravity, API 27.9 CCR, Wt. % 0.23 ~ :
Sulfur, W~. % 0.6 Initial Boiling Point, F. 482 50% Point 749 90% Point 979 The cracking test is conducted by contacting 1.2 grams of -~
the gas oil with 6.0 grams of catalyst (c/o = 5) at 910F. and feed time of 96 seconds for WES~ of 7.5. The liquid product is distilled and "conversion" is reported as 100 minus weight per cent based on 15 feed of liquid product boiling above 421~F. Activity is then calculated !
as = conversion 00 - conversion Methods are known to the art for preparing cracking catalysts of very low activities such as severely steamed amorphous silica-alumina , 20 of activity at 1 or less to very high activ:Lties above 20 such as highly active alumino-silicate zeolites. See patent 3,493,519. Such catalysts of very high activity have not come to the market because existing equipment for catalytic cracking is not capable of utilizing the activity, I hence no refiner wlll pay the higher price whlch must be charged in view i 25 o~ the hlgh production cost.
In .summary, the refiner who presently wishefl to charge residual tocks is compelled to ad~ust hls operatlon~ to the opt:Lon3 avallable to hlm. The catalyst makeup rate to his ca~alytic cracker is determined by the activi.ty considerations spelled out in the Lee article. To avoid adverse effects of metals deposited on the catalyst, the refiner ,`, ~ - 14 -., ; :.
~6~
.
hydrotreacs the resid, sends it to a coker or deasphalter or lives with the problem of metal on cracking caealyst of whatever fr~sh activity he selects.
SU~ RY OF T~IE, INVE~TION
A techniqlJe for operation of catalytic cracking equipment is now provided whieh decouples ~intenanee of equilibrium activity from management of the metals problem. This is accomplished by a catal~;st makeup policy for concurrent addition to the unit of two inventory eomponents, namely an active cracking catalyst and a large pore inert solid for selective acceptance of the large molecules characteristic of metal and Conradson Carbon content of the charge.
Instead of following the eonventional teehniques of calculating the amount of fresh catalyst required for maintenance of equilibrium activity or as modified by Lee to consider deaetivation rate of catalyst, the system of this invention is based on determination o~ a makeup rate whicll wlll maintain a desired metals level on total inventory inelu~ing fresh catalyst, partially deactivated eatalyst, eompletely deactivated catalyst (essentially inert porous solids of small pore si~e) and catalytically inert material of large pore size character-istie of praetiee of the inven~ion. When charging residual stocks, the ma~eup rate so determined will be unconventionally high, say upwards of 10~ of inventory per day. The aetivity of eatalyst required to maintain equi]ibrium aetivity is then ealeulated by the equation ahove. 'I'he mLt i9 then supplit-.d wi~h a q~lantlty of aetive e~talyst alld a quantLty Oe large pore Lnert solid such ~.hat blend of the two exhibits the desiretl ~etlvlty and quantity of the two satisfles the malcellp ra~e for metals leveL mnlntenanee.
Thus, in aeeorclanee wlth the present invention there :Ls provided in a proeess for catalytie eraeking of a meta]-eontaining hydroearbon ~harge by contacting the eharge at eracking temperature with a particle form solid craeking eatalyst whereby components of the charge .
- ~5 ~?
., .
:-. , - ' ' : ' are converted to lower boiling hydrocarbons with concurrent deposition on the catalyst of metals from the charge and of an inactivating carbonaceous contamlnant, regenerating catalytic cracking activity of the contaminated catalyst by burning carbonaceous deposit therefrom while retaining metals deposited on the catalyst, and contacting catalyst so regencrated with additional such charge, whereby the catalyst accumulates metal to detriment of the cracking reaction and declines .~ in re~enerated activity over repeated cycles of charge contact and regeneration; the average activity and metals content of the catalyst inventory being maintained at substantially constant equilibrium values : by replacing a portion of the catalyst inventory with fresh ca~alyst of activity above and metals content belo~ said equilibrium values;
the improvement whereby said equilibrium values of activity and metals content are decoupled for separate -~ control which comprises replacing a portion of said catalyst as aforesaid by fresh active cracking catalyst and a large pore inert solid at a rate to maintain said equilibrium metal value, the total quantity of said resh catalyst and said inert solid per unit of time being substantially equivalent to total metal input with said charge per unit of time divided by said equilibrium metal value, said total quantity having a cracking activity ~F determined by the equation, AF = ~E(S~K) S
where ~E ls saLd activity equilibrium value S ls sa.id total qu;ltltity per urllt oE tlme., ancl :Ls a constant represel~ting rate of decay of catalytic activity;.
the fraction of said fresh catalyst in said total quantity bei~g substantially equivalent to ~ divided by the activity of said fresh catalyst.
- 15a ' ' . , ~L26~
DESCRIPTION OF SPECIFIC EMBODIMENTS
The p~ocess of this invention contemplates an embodiment in which an FCC Unit is operated at unconventionally high levels of metal .i, :
~ , :
;
'''~' :
' ,:
::
- 15b ''',"','1:
,~
,. , - . , . ~ :
, . - , ~:
r~
1 on the circulating inventory of catalyst and inert material, herein-after called "catalyst inventory" for simplicity despiLe the Eact that it contains a high proportion of material not usually considered to be catalyst. Alternatively, the metals content of the catalyst inventory may be held at leve]s more usual in the art. ~tUS the invention makes available to the refiner a broad scope of operation from metals levels in the neighborhood of 2 wt % on catalyst (20,000 ppm) or above down to any lower level desired. It will be recogniæed that level~ of nickel, copper, vanadium and the like approximating 2% are high enough that withdrawn catalyst is an ore rich enough to justify hydrometalurgical processing to recover metal values and restore the mixture of porous inert particies and inactivated catalyst to a state suitable for reuse :~
as the inert component of FCC makeup in accordance with the invention.
Suitable hydrometallurgy may be treatment with sulfur dioxide and ~;, 15 water leach followed by liquid liquid ion exchange of the leach - solution. ~t will be noted that the metal enrlched catalyst is unusually ~ well suited to hydrometallurgy since the metal values are on surfaces - rather than combined with silica and the like in the body of the "ore" as is the case with marly natural ores.
Whether the metals level on catalyst is held at a value permitting use of withdrawn catalyst as ore or held to a lower number such that withdrawn catalyst is discarded, operation of the catalytic cracklng unlt is improved by addition of makeup constituted by acti~e caka:Lyst and a Large pore inert soLld ln proportions ca:Lculated ln accordance wlth prLnclples of the lnvent:Lon when cracklng metal conta~llnated heavy stocks such as atmospherlc or vacuum resldue, shale o:lls, tar sand liqulds, coal llqulds such as solvent reflned coal and the like.
For practice of the -lnvention, the operator of a catalytic
AF = AE(5+K) where ~ i8 activity of fresh catalyst 25~ Ls equ:llibrlulll activlty o:~ the total cal:alyst inventory l.n the ~n~:Lt S :l.~ the rate o:E makellp :Ln percentage of total inve.ntory per clay 1~ is a constant representing rate of catalyst deactl.vation 30This is essentially equation (15) of the Lee article cited above, which see for derivation and more detalled explanat.ion of terms.
~ .
1 It will be apparent that activity is a relative term, the absolute value of which is dependent on the test procedure. In this specification, "activity" refers to the value determined by a micro-activity test (MAT) conducted by cracking a Mid-Continent Gas Oil of the following properties:
Gravity, API 27.9 CCR, Wt. % 0.23 ~ :
Sulfur, W~. % 0.6 Initial Boiling Point, F. 482 50% Point 749 90% Point 979 The cracking test is conducted by contacting 1.2 grams of -~
the gas oil with 6.0 grams of catalyst (c/o = 5) at 910F. and feed time of 96 seconds for WES~ of 7.5. The liquid product is distilled and "conversion" is reported as 100 minus weight per cent based on 15 feed of liquid product boiling above 421~F. Activity is then calculated !
as = conversion 00 - conversion Methods are known to the art for preparing cracking catalysts of very low activities such as severely steamed amorphous silica-alumina , 20 of activity at 1 or less to very high activ:Lties above 20 such as highly active alumino-silicate zeolites. See patent 3,493,519. Such catalysts of very high activity have not come to the market because existing equipment for catalytic cracking is not capable of utilizing the activity, I hence no refiner wlll pay the higher price whlch must be charged in view i 25 o~ the hlgh production cost.
In .summary, the refiner who presently wishefl to charge residual tocks is compelled to ad~ust hls operatlon~ to the opt:Lon3 avallable to hlm. The catalyst makeup rate to his ca~alytic cracker is determined by the activi.ty considerations spelled out in the Lee article. To avoid adverse effects of metals deposited on the catalyst, the refiner ,`, ~ - 14 -., ; :.
~6~
.
hydrotreacs the resid, sends it to a coker or deasphalter or lives with the problem of metal on cracking caealyst of whatever fr~sh activity he selects.
SU~ RY OF T~IE, INVE~TION
A techniqlJe for operation of catalytic cracking equipment is now provided whieh decouples ~intenanee of equilibrium activity from management of the metals problem. This is accomplished by a catal~;st makeup policy for concurrent addition to the unit of two inventory eomponents, namely an active cracking catalyst and a large pore inert solid for selective acceptance of the large molecules characteristic of metal and Conradson Carbon content of the charge.
Instead of following the eonventional teehniques of calculating the amount of fresh catalyst required for maintenance of equilibrium activity or as modified by Lee to consider deaetivation rate of catalyst, the system of this invention is based on determination o~ a makeup rate whicll wlll maintain a desired metals level on total inventory inelu~ing fresh catalyst, partially deactivated eatalyst, eompletely deactivated catalyst (essentially inert porous solids of small pore si~e) and catalytically inert material of large pore size character-istie of praetiee of the inven~ion. When charging residual stocks, the ma~eup rate so determined will be unconventionally high, say upwards of 10~ of inventory per day. The aetivity of eatalyst required to maintain equi]ibrium aetivity is then ealeulated by the equation ahove. 'I'he mLt i9 then supplit-.d wi~h a q~lantlty of aetive e~talyst alld a quantLty Oe large pore Lnert solid such ~.hat blend of the two exhibits the desiretl ~etlvlty and quantity of the two satisfles the malcellp ra~e for metals leveL mnlntenanee.
Thus, in aeeorclanee wlth the present invention there :Ls provided in a proeess for catalytie eraeking of a meta]-eontaining hydroearbon ~harge by contacting the eharge at eracking temperature with a particle form solid craeking eatalyst whereby components of the charge .
- ~5 ~?
., .
:-. , - ' ' : ' are converted to lower boiling hydrocarbons with concurrent deposition on the catalyst of metals from the charge and of an inactivating carbonaceous contamlnant, regenerating catalytic cracking activity of the contaminated catalyst by burning carbonaceous deposit therefrom while retaining metals deposited on the catalyst, and contacting catalyst so regencrated with additional such charge, whereby the catalyst accumulates metal to detriment of the cracking reaction and declines .~ in re~enerated activity over repeated cycles of charge contact and regeneration; the average activity and metals content of the catalyst inventory being maintained at substantially constant equilibrium values : by replacing a portion of the catalyst inventory with fresh ca~alyst of activity above and metals content belo~ said equilibrium values;
the improvement whereby said equilibrium values of activity and metals content are decoupled for separate -~ control which comprises replacing a portion of said catalyst as aforesaid by fresh active cracking catalyst and a large pore inert solid at a rate to maintain said equilibrium metal value, the total quantity of said resh catalyst and said inert solid per unit of time being substantially equivalent to total metal input with said charge per unit of time divided by said equilibrium metal value, said total quantity having a cracking activity ~F determined by the equation, AF = ~E(S~K) S
where ~E ls saLd activity equilibrium value S ls sa.id total qu;ltltity per urllt oE tlme., ancl :Ls a constant represel~ting rate of decay of catalytic activity;.
the fraction of said fresh catalyst in said total quantity bei~g substantially equivalent to ~ divided by the activity of said fresh catalyst.
- 15a ' ' . , ~L26~
DESCRIPTION OF SPECIFIC EMBODIMENTS
The p~ocess of this invention contemplates an embodiment in which an FCC Unit is operated at unconventionally high levels of metal .i, :
~ , :
;
'''~' :
' ,:
::
- 15b ''',"','1:
,~
,. , - . , . ~ :
, . - , ~:
r~
1 on the circulating inventory of catalyst and inert material, herein-after called "catalyst inventory" for simplicity despiLe the Eact that it contains a high proportion of material not usually considered to be catalyst. Alternatively, the metals content of the catalyst inventory may be held at leve]s more usual in the art. ~tUS the invention makes available to the refiner a broad scope of operation from metals levels in the neighborhood of 2 wt % on catalyst (20,000 ppm) or above down to any lower level desired. It will be recogniæed that level~ of nickel, copper, vanadium and the like approximating 2% are high enough that withdrawn catalyst is an ore rich enough to justify hydrometalurgical processing to recover metal values and restore the mixture of porous inert particies and inactivated catalyst to a state suitable for reuse :~
as the inert component of FCC makeup in accordance with the invention.
Suitable hydrometallurgy may be treatment with sulfur dioxide and ~;, 15 water leach followed by liquid liquid ion exchange of the leach - solution. ~t will be noted that the metal enrlched catalyst is unusually ~ well suited to hydrometallurgy since the metal values are on surfaces - rather than combined with silica and the like in the body of the "ore" as is the case with marly natural ores.
Whether the metals level on catalyst is held at a value permitting use of withdrawn catalyst as ore or held to a lower number such that withdrawn catalyst is discarded, operation of the catalytic cracklng unlt is improved by addition of makeup constituted by acti~e caka:Lyst and a Large pore inert soLld ln proportions ca:Lculated ln accordance wlth prLnclples of the lnvent:Lon when cracklng metal conta~llnated heavy stocks such as atmospherlc or vacuum resldue, shale o:lls, tar sand liqulds, coal llqulds such as solvent reflned coal and the like.
For practice of the -lnvention, the operator of a catalytic
3 cracker will maintaln a stock of two diEEerent solld materlals having ,~ .~ - .
1 physical characteristics (si~e, density, porosity, etc.~ suited to operation of the type of unit. One stock is constituted by cracking catalyst of any desired type, preferably a catalyst of high activity.
The catalyst is the more expensive component to be added as makeup and it now becomes feasible in practice of the present inven~ion for the refiner to justify the higher cost of more active catalyst. Thus cracking ca~alysts of fresh MAT activity above 10 will be found useful and catalysts of fresh ~T activity as high as 20 or above will show economic advantage despite the high cost of such catalysts. The invention can utilize the older amorphous silica-alumina ca-talysts, but preference is noted for the more active catalysts constituted by rare earth and/or hydrogen forms of crystalline ~eolites such as those having the crystalline structure faujasite in a matrix of silica-alumina or the like. Such catalysts are described in patents 3,140,2~ and 3,140,253. Many techniques and compositions for high activity have been described. Although it is preferred to employ catalysts of high activity, the particular means adopted to achieve that high activity is not of particular significance and reference to knowledge ln the art will suffice for the preser~t purposes.
The large pore inert material to be added wLth active catalyst constitutes the real distinction from knowledge of catalyst components normally taken into account by those responsible for operation of catalytic cracking units. As noted above, dilution o~ crackLn~ catalyst wLth lnert sollds :ls a convenLent mealls by whlch a catalyst supplLer can malce ~everal act:lvity Levels avaLlable w-ltt relatLvely Eewer methods oE catalyst ~lanufacture. Such blends are sold on the basls oE overa:L:I actlvlty, se:l.ectlvlty and phys:lcal propertles such as hardness, tendency to erode equipment and ~he llke.
DLlutiorl, if any, is a matter of llttle concern to the purchaser except as it res-llts in reduced cost of the catalyst blend.
1 The large pore material is essentially inert in the sense that it induces minimal cracking of heavy hydrocarbons by the standard micro-activity test. Conversion by that test will be less than 20, preferably about 10, representing essentially thermal cracking.
The microspheres of calcined kaolin clay yreferably used in the process of the invention are known in the art and are employed as a chemical reactant with a sodium hydroxide in the manufacture of fluid zeolitic cracking catalysts as described in U.S. 3,647,718 to Haden et al. In practice of the instant invention, in contrast, the microspheres of calcined kaolin clay are no~ used as a chemical reactant. Thus the chemical composition of the microspheres of calcined clay used in practice of this invention corresponds to that of a dehydrated kaolin ; clay. Typically the calcined microspheres analqze about 51% to 53% (wt.) - SiO2, 41 to 45% A1203, and from 0 to 1% H20, the balance being minor amounts of indigenous impurities, notably iron, titanium and alkaline -~ earth metaLs. Generally, iron content (expressed as ~e203) is about 1/2% by weight and titanium (expressed as TiO2) is approximately 2%.
The microspheres are preferably produced by spray drying an aqueous suspension of kaolin clay. The term "kaolin clay" as used herein embraces clays, the predominating mineral constituent of which is kaolinite, halloysite, nacrite, dickite, anauxite and mixtures thereof. Preferably a fine particle size plastic hydrated clay, i.e., a clay containing a substantial amount of submicron size particles, L~s used ln order to prod~lce mlcrospheres hav:Lng adequate nlechanLcal strength.
~ rO facLlLtate ~pray drylng, the powdered hydrated clay pre~erabLy d:Lspersed Ln ~ater Ln ~he presence oE a deE:Locculating agen~ e~emp:Lifled by sodium silicate or a sodium condensed phosphate salt such as tetrasodium pyrophosphate. By employing a deflocculating agent, spray drying may be carried out at higher solids levels and 1 harder products are usually obtained. ~ten a deflocculating agent is employed, slurries containing about 55 to 60% soLids may be prepared and these high solids slurries are preferred to the 40 to 50% slurries which do not contain a deflocculating agent.
Several procedures can be followed in mixing the ingredients to form the slurry. One procedure, by way of example, is to dry blend the finely divided solids, add the water and then incorporate the def]occulating agent. The components can be mechanically worked together or individually to produce slurries of desired viscosity characteristics.
Spray dryers with countercurrent, cocurrent or mixed counter-current and cocurrent flow of slurry and hot air can be employed to produce the microspheres. The air may be heated electrically or by other indirect means. Combustion gases obtained by burning hydrocarbon fuel in air can be used.
Using a cocurrent dryer, air inlet temperatures to 1200~F. may be used when the clay feed is charged at a rate sufficient to produce an air outlet temperature within the range of 250 to 600~F. At these temperatures, free moistu~e is removed from the slurry without removing water of hydration (water of crystallization~ from the raw clay ingredient. Dehydration of some or all of the raw clay during spray drying is contemplated. The spray dryer discharge may be fractionated ; to recover microspheres of desired particle size. Typically particles having a diameter in the range of 20 to 150 microns are preferably recovered Eor calcinatLon.
Whlle It :Ls preEerabLe ln some cases ~o ca:Lcine the microspheres at temperatures 1~l the range oE about 1600 to 2100F.
:ln order to produce particles of maximtlm hardlless, lt ls possible to dehydrate the mlcro~spheres by calcinat~on at lower temperatures; Eor example7 te[nperatures in the range of 1000 to 1600~F., thereby converting the clay into the material known as "metakaolin". After .~
.
:' .
,. , ,: - , 1 calcination the microspheres should be cooled and fractionated, if necessary, to recover the portion which is in desired si~e range.
Pore volume of the microspheres will vary slightly with the calcination temperature and duration of calcination. Pore size distribution analysis of a representative sample was obtained by a conventional nitrogen desorption technique. Most of the pores were found to have diameters in the range of 150 to 600 Angstrom units, o primarily 300 to 600 A . In general, the inert materials used in accordance with the invention will have a majority of pores (determined as pores constituting more than half the total pore volume) of at least 100 Angstrom units diameter.
The surface area of the calcined microspheres is usually within the range of 10 to lS m /g~. as measured by the well-known B.E.T. method using nitrogen absorption. It is noted that the surface areas of commercial fluid zeolite catalysts is coniderably higher, generally exceeding values of 100 m /g. as measured by the B.E.T.
method.
Qther solids of low catalytic activity and of lilce pore diameter and particle size may be employed. In general, solids of low cost are recommended since it is contemplated that the high makeup rate charac~eristic of the inventi.on is offset by low net cost of the catalyst plus inert material to be added.
'Lhe :Lnvention ls appl.ied to a catalyt.lc cracker for which a precleterm:lned act.lvlty and metcl~.s level have been es~:abl:Lslled. These may vary w:lthln rather wide ranges dependlng primarlly on nature o:E the charge stoclc and the product slate dictated by market demancl. Thus a craclcer :In a re~l.nery serv:l.ng a market whLch demc.mds re:lat:Lvely large quantity of diesel fuel and dlstil.late Euel olls wil:L operate with a catalyst of relati~ely low activlty as compared with one serving a market of high gasoline demand. Predetermined metals level on '~
~2~
1 catalyst will normally be higher when practicing the present invention than would be the case with cracking catalysts of the prior art. The greater proportion of metals in the large pcre inert solid easily penetrated by the large metal bearing molecules, results in a level of metal on the active cracking catalyst well below the average metal content of the inventory circulated in the un-it. It is that latter value of average metal content which is determined by analysis and is the predetermined value which is to be held constant.
~rom observation of unit behavior and monitoring of charge stock analyses, it is determined at what rate catalyst activity declines and at what rate metals are deposited on the total inventory of catalyst and inert materials. With this information, the refiner derives a rate of metal deposition and thus maintains the metal level constant at about the predetermined value. The rate of replacement will be a value in per cent of circulating inventory per day which is readily converted to tons of makeup per day having regard to the weight of inventory in the circulating catalyst. In the preferred type of operation charging a residual stock of at least 10 Nickel ~quivalents of metal, the rate of makeup is simply obtained by dlviding total metal input with charge by the predetermined metals level on inventory in weight percent.
Having established a makeup rate in terms of tons per day or percent of inventory per day, the activity level of active catalyst pluA Inerts to be added 18 cletermlnecl by l,ee~s equatloll ln the form:
~F ~
g where ~ = actlvLty o~ makeup bLend = equlllbrium (prede~ermined) actlvlty of inventory in the unlt S ~ make rate determlned as above . .
1 K = a constant related to catalyst deactlvation determined as explained by Lee In the preferred embodiments of the invention using makeup rates oE 10%
of inventory per day and higher, the makeup rate S is so high compared with the constant K that the latter becomes relatively unimportant to the calculation. Having determined the activity AF for the makeup blend of active catalyst and inerts, the proportion of the makeup components is derived from the known activity of active catalyst A by dividing the desired blend activity by A thus ~F/A = fraction oE active catalyst in blend. The two components may be premixed in the required proportions and added to the unit intermittently or continuously at the rate S in tons per day. Concurrently, there will be an amount of equilibrium ; catalyst withdrawn from the ~mit to maintain a constant inventory, i.e. an amount of so withdrawn catalyst equal to the amount of makeup blend less losses of catalyst due to attrition and the like. At high metal contents in the neighborhood of 2%, the withdrawn catalyst becomes a valuable "ore"
for hydrowinning of nickel, vanadiurn, copper, etc.
Alternatively, the components of the makeup blend may be added separately to the unit for mixing as the inventory i~ circulated. This is particularly effective in FCC operations where any added material is very quickly and very thoroughly mixed with the inventory being circulated.
The invention is best utilized ln units which provide short contact tLme oE catalyst ancl charge stock in order that the two components Oe the makeup b:Lend may act with maxLmum eEEectLveness. The deslrecl resuLt appears to be depos:Lt on the inert sollcl oE metAls and Conradson Carbon (adclltLve coke) ancl c~ackLng on the actlve catalyst oE other components of the charge stock. Th.Ls effect is advantageously achieved at contac~ times less than 20 seconds, preEerably 2 seconds or less.
The fresh catalyst should have high activity, ~ T of at least ~ ' 1 1.5, preferably 4 or greater. These high activities of thc active catalyst component of the blend make possible high proportions of large pore inert material, upwards of 50%, preferably more than 75%.
The combination of short contact time, high proportion of large pore inert material, and high activity of the active catalyst component of the blend provide further advantages in management of coke make in the reactor and control of temperature in the regenerator of an FCC unit. The active catalyst component acquires coke which i5 primarily due to catalytic cracking. Coke due to dehydrogenation by contaminant metals is at a low-level for these short contact times.
Most of the Conradson Carbon coke (additive coke) is deposited on the large pore inert component. Regenerator temperatures may be reduced in this system of operation.
In general, the makeup rate according to the invention will be in excess of 3% of inventory per day and in excess of 0.3 lb./
catalyst blend with inerts per barrel of feed, up to 20% of inventory per day, with recommended levels of about 10% of inventory per day for most operations in cracking of metal con-taminated resids.
,,
1 physical characteristics (si~e, density, porosity, etc.~ suited to operation of the type of unit. One stock is constituted by cracking catalyst of any desired type, preferably a catalyst of high activity.
The catalyst is the more expensive component to be added as makeup and it now becomes feasible in practice of the present inven~ion for the refiner to justify the higher cost of more active catalyst. Thus cracking ca~alysts of fresh MAT activity above 10 will be found useful and catalysts of fresh ~T activity as high as 20 or above will show economic advantage despite the high cost of such catalysts. The invention can utilize the older amorphous silica-alumina ca-talysts, but preference is noted for the more active catalysts constituted by rare earth and/or hydrogen forms of crystalline ~eolites such as those having the crystalline structure faujasite in a matrix of silica-alumina or the like. Such catalysts are described in patents 3,140,2~ and 3,140,253. Many techniques and compositions for high activity have been described. Although it is preferred to employ catalysts of high activity, the particular means adopted to achieve that high activity is not of particular significance and reference to knowledge ln the art will suffice for the preser~t purposes.
The large pore inert material to be added wLth active catalyst constitutes the real distinction from knowledge of catalyst components normally taken into account by those responsible for operation of catalytic cracking units. As noted above, dilution o~ crackLn~ catalyst wLth lnert sollds :ls a convenLent mealls by whlch a catalyst supplLer can malce ~everal act:lvity Levels avaLlable w-ltt relatLvely Eewer methods oE catalyst ~lanufacture. Such blends are sold on the basls oE overa:L:I actlvlty, se:l.ectlvlty and phys:lcal propertles such as hardness, tendency to erode equipment and ~he llke.
DLlutiorl, if any, is a matter of llttle concern to the purchaser except as it res-llts in reduced cost of the catalyst blend.
1 The large pore material is essentially inert in the sense that it induces minimal cracking of heavy hydrocarbons by the standard micro-activity test. Conversion by that test will be less than 20, preferably about 10, representing essentially thermal cracking.
The microspheres of calcined kaolin clay yreferably used in the process of the invention are known in the art and are employed as a chemical reactant with a sodium hydroxide in the manufacture of fluid zeolitic cracking catalysts as described in U.S. 3,647,718 to Haden et al. In practice of the instant invention, in contrast, the microspheres of calcined kaolin clay are no~ used as a chemical reactant. Thus the chemical composition of the microspheres of calcined clay used in practice of this invention corresponds to that of a dehydrated kaolin ; clay. Typically the calcined microspheres analqze about 51% to 53% (wt.) - SiO2, 41 to 45% A1203, and from 0 to 1% H20, the balance being minor amounts of indigenous impurities, notably iron, titanium and alkaline -~ earth metaLs. Generally, iron content (expressed as ~e203) is about 1/2% by weight and titanium (expressed as TiO2) is approximately 2%.
The microspheres are preferably produced by spray drying an aqueous suspension of kaolin clay. The term "kaolin clay" as used herein embraces clays, the predominating mineral constituent of which is kaolinite, halloysite, nacrite, dickite, anauxite and mixtures thereof. Preferably a fine particle size plastic hydrated clay, i.e., a clay containing a substantial amount of submicron size particles, L~s used ln order to prod~lce mlcrospheres hav:Lng adequate nlechanLcal strength.
~ rO facLlLtate ~pray drylng, the powdered hydrated clay pre~erabLy d:Lspersed Ln ~ater Ln ~he presence oE a deE:Locculating agen~ e~emp:Lifled by sodium silicate or a sodium condensed phosphate salt such as tetrasodium pyrophosphate. By employing a deflocculating agent, spray drying may be carried out at higher solids levels and 1 harder products are usually obtained. ~ten a deflocculating agent is employed, slurries containing about 55 to 60% soLids may be prepared and these high solids slurries are preferred to the 40 to 50% slurries which do not contain a deflocculating agent.
Several procedures can be followed in mixing the ingredients to form the slurry. One procedure, by way of example, is to dry blend the finely divided solids, add the water and then incorporate the def]occulating agent. The components can be mechanically worked together or individually to produce slurries of desired viscosity characteristics.
Spray dryers with countercurrent, cocurrent or mixed counter-current and cocurrent flow of slurry and hot air can be employed to produce the microspheres. The air may be heated electrically or by other indirect means. Combustion gases obtained by burning hydrocarbon fuel in air can be used.
Using a cocurrent dryer, air inlet temperatures to 1200~F. may be used when the clay feed is charged at a rate sufficient to produce an air outlet temperature within the range of 250 to 600~F. At these temperatures, free moistu~e is removed from the slurry without removing water of hydration (water of crystallization~ from the raw clay ingredient. Dehydration of some or all of the raw clay during spray drying is contemplated. The spray dryer discharge may be fractionated ; to recover microspheres of desired particle size. Typically particles having a diameter in the range of 20 to 150 microns are preferably recovered Eor calcinatLon.
Whlle It :Ls preEerabLe ln some cases ~o ca:Lcine the microspheres at temperatures 1~l the range oE about 1600 to 2100F.
:ln order to produce particles of maximtlm hardlless, lt ls possible to dehydrate the mlcro~spheres by calcinat~on at lower temperatures; Eor example7 te[nperatures in the range of 1000 to 1600~F., thereby converting the clay into the material known as "metakaolin". After .~
.
:' .
,. , ,: - , 1 calcination the microspheres should be cooled and fractionated, if necessary, to recover the portion which is in desired si~e range.
Pore volume of the microspheres will vary slightly with the calcination temperature and duration of calcination. Pore size distribution analysis of a representative sample was obtained by a conventional nitrogen desorption technique. Most of the pores were found to have diameters in the range of 150 to 600 Angstrom units, o primarily 300 to 600 A . In general, the inert materials used in accordance with the invention will have a majority of pores (determined as pores constituting more than half the total pore volume) of at least 100 Angstrom units diameter.
The surface area of the calcined microspheres is usually within the range of 10 to lS m /g~. as measured by the well-known B.E.T. method using nitrogen absorption. It is noted that the surface areas of commercial fluid zeolite catalysts is coniderably higher, generally exceeding values of 100 m /g. as measured by the B.E.T.
method.
Qther solids of low catalytic activity and of lilce pore diameter and particle size may be employed. In general, solids of low cost are recommended since it is contemplated that the high makeup rate charac~eristic of the inventi.on is offset by low net cost of the catalyst plus inert material to be added.
'Lhe :Lnvention ls appl.ied to a catalyt.lc cracker for which a precleterm:lned act.lvlty and metcl~.s level have been es~:abl:Lslled. These may vary w:lthln rather wide ranges dependlng primarlly on nature o:E the charge stoclc and the product slate dictated by market demancl. Thus a craclcer :In a re~l.nery serv:l.ng a market whLch demc.mds re:lat:Lvely large quantity of diesel fuel and dlstil.late Euel olls wil:L operate with a catalyst of relati~ely low activlty as compared with one serving a market of high gasoline demand. Predetermined metals level on '~
~2~
1 catalyst will normally be higher when practicing the present invention than would be the case with cracking catalysts of the prior art. The greater proportion of metals in the large pcre inert solid easily penetrated by the large metal bearing molecules, results in a level of metal on the active cracking catalyst well below the average metal content of the inventory circulated in the un-it. It is that latter value of average metal content which is determined by analysis and is the predetermined value which is to be held constant.
~rom observation of unit behavior and monitoring of charge stock analyses, it is determined at what rate catalyst activity declines and at what rate metals are deposited on the total inventory of catalyst and inert materials. With this information, the refiner derives a rate of metal deposition and thus maintains the metal level constant at about the predetermined value. The rate of replacement will be a value in per cent of circulating inventory per day which is readily converted to tons of makeup per day having regard to the weight of inventory in the circulating catalyst. In the preferred type of operation charging a residual stock of at least 10 Nickel ~quivalents of metal, the rate of makeup is simply obtained by dlviding total metal input with charge by the predetermined metals level on inventory in weight percent.
Having established a makeup rate in terms of tons per day or percent of inventory per day, the activity level of active catalyst pluA Inerts to be added 18 cletermlnecl by l,ee~s equatloll ln the form:
~F ~
g where ~ = actlvLty o~ makeup bLend = equlllbrium (prede~ermined) actlvlty of inventory in the unlt S ~ make rate determlned as above . .
1 K = a constant related to catalyst deactlvation determined as explained by Lee In the preferred embodiments of the invention using makeup rates oE 10%
of inventory per day and higher, the makeup rate S is so high compared with the constant K that the latter becomes relatively unimportant to the calculation. Having determined the activity AF for the makeup blend of active catalyst and inerts, the proportion of the makeup components is derived from the known activity of active catalyst A by dividing the desired blend activity by A thus ~F/A = fraction oE active catalyst in blend. The two components may be premixed in the required proportions and added to the unit intermittently or continuously at the rate S in tons per day. Concurrently, there will be an amount of equilibrium ; catalyst withdrawn from the ~mit to maintain a constant inventory, i.e. an amount of so withdrawn catalyst equal to the amount of makeup blend less losses of catalyst due to attrition and the like. At high metal contents in the neighborhood of 2%, the withdrawn catalyst becomes a valuable "ore"
for hydrowinning of nickel, vanadiurn, copper, etc.
Alternatively, the components of the makeup blend may be added separately to the unit for mixing as the inventory i~ circulated. This is particularly effective in FCC operations where any added material is very quickly and very thoroughly mixed with the inventory being circulated.
The invention is best utilized ln units which provide short contact tLme oE catalyst ancl charge stock in order that the two components Oe the makeup b:Lend may act with maxLmum eEEectLveness. The deslrecl resuLt appears to be depos:Lt on the inert sollcl oE metAls and Conradson Carbon (adclltLve coke) ancl c~ackLng on the actlve catalyst oE other components of the charge stock. Th.Ls effect is advantageously achieved at contac~ times less than 20 seconds, preEerably 2 seconds or less.
The fresh catalyst should have high activity, ~ T of at least ~ ' 1 1.5, preferably 4 or greater. These high activities of thc active catalyst component of the blend make possible high proportions of large pore inert material, upwards of 50%, preferably more than 75%.
The combination of short contact time, high proportion of large pore inert material, and high activity of the active catalyst component of the blend provide further advantages in management of coke make in the reactor and control of temperature in the regenerator of an FCC unit. The active catalyst component acquires coke which i5 primarily due to catalytic cracking. Coke due to dehydrogenation by contaminant metals is at a low-level for these short contact times.
Most of the Conradson Carbon coke (additive coke) is deposited on the large pore inert component. Regenerator temperatures may be reduced in this system of operation.
In general, the makeup rate according to the invention will be in excess of 3% of inventory per day and in excess of 0.3 lb./
catalyst blend with inerts per barrel of feed, up to 20% of inventory per day, with recommended levels of about 10% of inventory per day for most operations in cracking of metal con-taminated resids.
,,
Claims (9)
1. In a process for catalytic cracking of a metal-containing hydrocarbon charge by contacting the charge at cracking temperature with a particle form solid cracking catalyst whereby components of the charge are converted to lower boiling hydrocarbons with concurrent deposition on the catalyst of metals from the charge and of an inactivating carbonaceous contaminant, regenerating catalytic cracking activity of the contaminated catalyst by burning carbonaceous deposit therefrom while retaining metals deposited on the catalyst, and contacting catalyst so regenerated with additional such charge, whereby the catalyst accumulates metal to detriment of the cracking reaction and declines in regenerated activity over repeated cycles of charge contact and regeneration; the average activity and metals content of the catalyst inventory being maintained at substantially constant equilibrium values by replacing a portion of the catalyst inventory with fresh catalyst of activity above and metals content below said equilibrium values;
the improvement whereby said equilibrium values of activity and metals content are decoupled for separate control which comprises replacing a portion of said catalyst as aforesaid by fresh active cracking catalyst and a large pore inert solid at a rate to maintain said equilibrium metal value, the total quantity of said fresh catalyst and said inert solid per unit of time being substantially equivalent to total metal input with said charge per unit of time divided by said equilibrium metal value, said total quantity having a cracking activity AF determined by the equation, where AE is said activity equilibrium value S is said total quantity per unit of time, and K is a constant representing rate of decay of catalytic activity;
the fraction of said fresh catalyst in said total quantity being substantially equivalent to AF divided by the activity of said fresh catalyst.
the improvement whereby said equilibrium values of activity and metals content are decoupled for separate control which comprises replacing a portion of said catalyst as aforesaid by fresh active cracking catalyst and a large pore inert solid at a rate to maintain said equilibrium metal value, the total quantity of said fresh catalyst and said inert solid per unit of time being substantially equivalent to total metal input with said charge per unit of time divided by said equilibrium metal value, said total quantity having a cracking activity AF determined by the equation, where AE is said activity equilibrium value S is said total quantity per unit of time, and K is a constant representing rate of decay of catalytic activity;
the fraction of said fresh catalyst in said total quantity being substantially equivalent to AF divided by the activity of said fresh catalyst.
2. A process according to claim 1 wherein said inert solid is characterized by at least 50% of pore volume constituted by pores of at least 100 Angstrom Units diameter.
3. A process according to claim 1 wherein said inert solid is characterized by at least 50% of pore volume constituted by pores of 150 to 600 Angstrom Units.
4. A process according to claim 1 wherein said inert solid is characterized by at least 50% of pore volume constituted by pores of 300 to 600 Angstrom Units.
5. A process according to claim 1 wherein said inert solid comprises a major portion of said total quantity.
6. A process according to claim 1 wherein said fresh catalyst has a MAT activity greater than 4.
7. A process according to claim 1 wherein the time of contact of said charge with said cracking catalyst is less than 20 seconds.
8. A process according to claim 1 wherein the time of contact of said charge with said cracking catalyst is less than 2 seconds.
9. In a process for catalytic cracking of a metal-containing hydrocarbon charge by contacting the charge at cracking temperature with a particle form solid cracking catalyst whereby components of the charge are converted to lower boiling hydrocarbons with concurrent deposition on the catalyst of metals from the charge and of an inactivating carbonaceous contaminant, regenerating catalytic cracking activity of the contaminated catalyst by burning carbonaceous deposit therefrom while retaining metals deposited on the catalyst, and contacting catalyst so regenerated with additional such charge, whereby the catalyst accumulates metal to detriment of the cracking reaction and declines in regenerated activity over repeated cycles of charge contact and regeneration; the average activity and metals content of the catalyst inventory being maintained at substantially constant equilibrium values by replacing a portion of the catalyst inventory with fresh catalyst of activity above and metals content below said equilibrium values;
the improvement whereby said equilibrium values of activity and metals content are decoupled which comprises replacing a portion of said catalyst as aforesaid by adding part of such replacement as catalyst of activity above and metals content below said equilibrium values and the remainder as inert porous solid particles of metals content below said equilibrium value and physical characteristics like that of said catalyst and varying the ratio between fresh catalyst and inert particles for separate control of said equilibrium value.
the improvement whereby said equilibrium values of activity and metals content are decoupled which comprises replacing a portion of said catalyst as aforesaid by adding part of such replacement as catalyst of activity above and metals content below said equilibrium values and the remainder as inert porous solid particles of metals content below said equilibrium value and physical characteristics like that of said catalyst and varying the ratio between fresh catalyst and inert particles for separate control of said equilibrium value.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US93589078A | 1978-08-23 | 1978-08-23 | |
| US935,890 | 1978-08-23 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1126190A true CA1126190A (en) | 1982-06-22 |
Family
ID=25467848
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA323,553A Expired CA1126190A (en) | 1978-08-23 | 1979-03-16 | Catalytic cracking of metal contaminated mineral oil fractions |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1126190A (en) |
-
1979
- 1979-03-16 CA CA323,553A patent/CA1126190A/en not_active Expired
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