US2737474A - Catalytic conversion of residual oils - Google Patents

Description

2,737,474 CATALYTI CONVERSION .oF RESIDUAL OILS Application'January '23, 1952, SerialNo. 267,706

Claims. (Cl. 196-49) This invention-relates to a multi-stage process' for catalytically converting :heavy hydrocarbon oils into lower boiling "products. More particularly, it relates 'to:-a proc- :ess wherein 'a residual petroleum oil is catalytically cracked in two stages with intermediate distillation in the presence of a densefiuidized bed composed ofxcatalytica'l- 1y inert'solids. Still more'specifically, in the first' stage the feed is catalytically cracked in liquid phase at relatively low temperature and low conversionand the ratio of catalyst to oil is so chosen that the amount of coke produced will completely or almost completely deactivate the catalyst by thetime the desired conversion is reached. This coke-deactivated catalyst then "behaves like an inert'solid and may be usedas the fiuidlz d mediurn inth'e distillation zone without tianger'orevercracking.

-'l"he'presentinvention is an improvement of a related conversion process previously described in our cop'endi'ng'patent application Serial No. 232,523, filed JuheZO,

The desire has frequently been expressed for afeasible process for the direct catalytic cracking of "petroleum residua or similar heavy hydrocarb'onfeeds.

The jc'hl'ef deterrent to catalytic cracking of residua by'c'onventional "means has beenthe severe catalyst contamination that occurs'and that leads to poor product distribution-and other- ,United St nt F .V

wise reduces the desired effectiveness of the catalyst.

Consequently, two-stage vapor phase catalytic processes have been proposed in theory according to which the eoke and other contaminants are supposed to be depositedon a catalyst'in a first stage intended to minimize the adverse effect of the contaminants, and the resulting puri fied feed is only thereafter subjected to a second cataly- =tic cracking stage wherein the main conversion iss'upposed to be accomplished. However, the difficulty with this type of operation has been that there'was' no'wholly successful process for carrying out the first catalytic cracking step at sufliciently low conversions, with the result that the feed was principally converted inth'e first sta'g'eun der conditions wherein the 'etfectiveness of the catalyst was severelylimited, similarly as in aone stage process. The difiiculty lay largely in the 'fact that in order to achieve the complete vaporization necessary in a vapor phase catalytic cracking process, such astonventional fluid catalytic cracking, highconversion of the residua accompanied by high contamination of catalyst was unavoidable. v I if aly's't contamination, this in turn resulted in undesirably highyields of coke and gas, at the expense of more 'va'li uable distillate'fractions.

More recent attempts to work out a practicalpro'cess for converting heavy residua have all but abando'ned the idea of direct catalytic cracking. Instead, the trend has been toward first coking the residua in the presence of inerts'olids and subjecting only the liberated distillate'to a catalytic conversion step. Of course, this also has'm'eant considerably poorer product distribution and poorerproduct quality than in an all-catalytic conversion.

Asa result of this high degree of cat-- 2,737,474 Patented Mar. 6, 1956 -Thus,-.it is the main object of this inventionto'provide a commercially practical, all-catalytic process for con- ,verting heavy-hydrocarbons. A more specific object is form=of-apparatus wherein the novel process "may be conveniently conducted.

The feeds to the present process preferably comprise vacuum residua which are obtained by :the'yacuumtdistillationof crude petroleum oils and may have API gravities in the range of about 0 to 16, Conradsoncarbon contents in the-range of about 5 to 35 wt. per cent, an initialatmospheric boiling point above about '1000 -F., and viscosities aboveabout 200 seconds Saybolt Furolat 210 F. However, other feeds may be employed such as atmospheric residua, whole crude oils, tars and:pitches from various refining operations, as well as gas oils, especially theiheavy gas oils.

Referring to 'the drawing, residuum fe'e'd having an .APIgravity of about 7 .5", aConradson carbon of about '20 weight per cent, and aninitial boiling ipointabov'e 11.050" Fmat atmospheric pressure, preferably preheated to about 500 to "650 F., is introduced into the system *throu'ghline'10 wherein it is mixed with a finely divided "cracking catalyst or'with-a mixture of catalyst-containing powdered solids introduced through line 16. The fee'd is diluted with about an equal volume'of naphtha "from line 12. In addition, one may also run: the feed with heavier-streams recycled within the process such -as the distillation bottoms shown in line 14, which may also contain'catalyst fines from the'sec'o'nd catalytic stagedescribed later.

The purpose of the diluent naptha is to decrease the viscosity-of 'the'res'iduu'm. This aids in obtaining high it-urbulence in subsequent heating and conversion-zones and thus tends to prevent fouling of the-reaction ve'ss'el wallsand the deposition of coke thereon. However, the

"diluent naphtha maybe omitted when the "feed itself is not unduly viscous, or steam may be used in "place of entirely omitted. When desired, hues of relatively high grade catalyst may be recovered from the recycle oil before it is mixed with the residuum feed.

vInstead of using diluents, or in addition thereto, high turbulencemay also be obtained in coil 20 and 'soaker -22 bysuitable'design and by other means such as mechanical agitation in soaker 22. Also instead of using a single isoaker 22, a plurality of vessels may be used if desired.

"The catalyst introduced by line 16 may be any "contact cracking catalyst having fluidizableparticle siz'e characteristics, that is, a particle size ranging up to about 4(l0 lmicrons, preferably between 20 and microns. Suitable catalysts include acid treated clays, synthetic composites of silicia and alumina, silica and mag- 'ne'sia, 'alumina and boria, aluminum fluoride, and so '"Catalyst that hasbeen previously used in the second cracking stage of the present process or in other "fluid processesf or the catalytic cracking offgas oils and the "like is 's'atisfacto'ry'for use in the first cracking stage herein.

'Ihe'niixtur'e'of hydrocarbon feed and catalyst is passed vaporized from its burden of spent catalyst.

from line 10 through a first cracking stage constituted by heated coil 20 and soaker 22 where it is maintained under reaction conditions for a sufficient time to achieve the desired conversion. Such reaction conditions in zones 20 and 22 may comprise temperatures between about 700 to 900 F., preferably 750 to 850 F., and pressures sufficient to maintain the major portion of the oil in liquid phase. Depending partly on the amount of added naphtha or similar relatively volatile constituents present, the reaction pressure may range from about 500 to 3000 p. s. i. g., higher concentration of volatile constituents requiring relatively greater pressures for keeping the reaction mixture in liquid phase. The combined residence time in zones 20 and 22 may vary from about 2 to 60 minutes, preferably about 10 to 30 minutes above 650 F.

To achieve the main purposes of the present invention, it is desirable to keep the formation of dry gas (up to and including C3) in the first cracking stage below about 5 weight percent, preferably between about 1 to 3 weight percent based on residuum feed. This conversion in the presence of catalyst has been found to cause sufiicient cracking of the large residuum molecules to convert them into high quality products capable of vaporization in a subsequent non-catalytic distillation zone without further appreciable decomposition. At the same time, such a conversion has been found low enough to keep non-catalytic decomposition of the feed in the first stage at a negligible minimum.

The amount of active catalyst used in the first cracking stage may vary between about 20 to 200 lbs., preferably 50 to 120 lbs. per barrel of residuum feed. Within these limits, the optimum amount of catalyst varies with the type of feed used and with the activity level of the catalytic solids. It is best chosen so as to give at least some catalytic effect during the entire cracking stage, while the catalyst is being covered with non-catalytic contaminants, principally coke. Consequently, a relatively large amount of catalyst is required when a feed having high coke-forming tendencies is being processed and also when the catalyst-containing solids have relatively low catalytic activity, and vice versa. At the same time, it is essential to the purposes of this invention to choose the amount of catalyst so that the amount of coke laid down thereon by the end of the first cracking stage substantially completely deactivates the catalyst. For instance, about to 60 weight percent of coke based on catalyst may be deposited in this stage depending on the initial activity level of the catalytic solids used.

Of course, some of the advantages of the present invention may also be obtained if inert solids such as coke are used in the first stage instead of catalyst, as more particularly described in our aforesaid patent application Serial No. 232,523. However, in such a case, poorer product distribution and quality are obtained, and larger equipment may be necessary to compensate for the larger holding time required if the first stage is non-catalytic.

The converted reaction mixture containing the substantially completely spent or deactivated catalyst is passed from soaker 22 through line 24 and pressurerelease device 26 and sprayed or flashed into the upper disperse phase of distillation zone 30, where the oil is rapidly Since the catalyst entering distillation zone 30 through line 24 is substantially deactivated by coke, the mass of fluidized solid formed therefrom in the lower part of zone 30 is also substantially inert and incapable of causing further significant conversion of the oil during the relatively short residence time of the oil in the distillation zone. An inert gas such as steam may be introduced into the bottom portion of distillation zone 30 in amounts ranging. from about 1 to 20 weight percent on residuum feed. Such addition of steam is usually desirable both for the purpose of stripping oil vapors from the fluidized solids and to aid in maintaining proper fluidization, since the volatile hydrocarbons vaporized in the distillation are usually insufiicient ,to give velocities high enough for good fluidization. As

is well known, good fluidization usually requires that the total linear superficial gas velocity in the fluidized bed be between about 0.5 and 5 ft./sec., or preferably between 1 and 3 ft./sec.

The pressure in distillation zone 30 may be substantially atmospheric, that is, between about 15 and 50 p. s. i. absolute, although vacuum or moderate pressures may be used. The temperature in the distillation zone may be from about 850 to 1050 F., preferably 900 to 950 F., but not high enough to cause appreciable thermal decomposition of the oil being distilled.

A portion of the coke-bearing catalyst, preferably after stripping, may be withdrawn from distillation zone 30 by line 32 and the coke thereon burned in coil 34 which may be embedded in the dense bed in zone 30 in order to supply the required heat thereto; the outlet of coil 34 may enter regenerator 40 described hereafter. Alternative means of heating distillation zone 30 may be employed also. The remainder of the coke-bearing catalyst is removed from zone 30 by line 36 at a rate sufficient to maintain the upper surface of the dense turbulent bed in zone 30 at a constant level. This removed catalyst is then suspended in an oxygen-containing gas such as air and introduced into a regenerator 40 where substantially all of the coke may be burned off while the catalyst is again maintained as a dense turbulent bed. Regenerated catalyst is finally withdrawn from regenerator 40 and recirculated to line 10 by aforementioned line 16. If a higher solids recirculation rate through line 16 or lower catalytic activity in reactor coil 20 is desired, the catalyst may be only partially regenerated in vessel 40. Also when'using a feed of relatively low coke forming tendency, it may be impractical to deposit enough coke on the catalyst to accomplish the high degree of catalyst deactivation desired in the first conversion stage. Consequently, in

. such a case partial regeneration would be of value, leaving say 3 to 8 weight percent coke on the catalyst being recycled from regenerator 40 to line 10 through line 16. Regeneration temperatures in zone 40 are kept below the deactivation temperature of the catalyst, which deactivation temperature may be between about 1100 and about 1200 or 1250 F. depending on the particular catalyst used; Where necessary or desirable, heat may be recovered from regenerator 40 by means of steam generating coils 42 or by equivalent means.

The oil vaporized in distillation zone 30 may be passed therefrom by lines 44 and 45 to fractionator 50 where it can be separated, for instance, into gas, naphtha, heating oil, gas oil, and oil bottoms containing some entrained catalyst which, as mentioned earlier, may be recycled to line 10 by line 14 if desired. A part of the naphtha may also be recycled to line 10 by line 12 and serve therein as the aforementioned diluent. The remaining naphtha and heating oil fractions may be recovered as products and the gas oil fraction may be passed from fractionator 50 by lines 52 and 53 to a conventional catalyst cracking zone 54. In zone 54 this gas oil can be efliciently cracked over a clean and therefore selective catalyst under otherwise known conditions including fairly high conversions to give about 50 to 75 weight percent of430 F. end point gasoline based on the gas oil feed. As a result, high yields of good quality gasoline and heating oil are produced in addition to the like fractions catalytically produced in the first conversion stage. Of course, instead of fractionating the first-stage products into the several fractions mentioned, they may all be fed directly to the catalytic cracking zone 54 by lines 44, 46 and 53.

The cracked vapors from cracking zone 54 pass by line 56 into line 45 where they may join the vapors from the first cracking Zone and then enter common fractionator 50. However, at other times, it may be preferred to fractionate the first-stage products separately from the second-stage products in order to permit individual recovery of the various fractions. For instance, the naphtha from the second stage may have a different octane rating than that from the first stage. Also, it may be prefer- 60by combustion with air as otherwise well known. -called Fluid catalytic reactors and regenerators as illusrimaran 5 able to avoid recycling of the gas 'oil'from *thCSCCO'Il'd stage if otheruses are available.

The crac'kingcatalyst in zone 54 is ofrclatively good I quality 'and high' activity, and is maintained therein I at a lowdegree of contamination, for instance, up to about lLO weight percentof coke on catalyst and a negligible amount of mineral contaminants. -Consequently, much higher'se- -lectivity to gasoline, and a gasoline of better anti-knock *qualities, can usually beobtained in'zone 54 than in the first cracking stage.

Spent catalyst is withdrawn from conversion zone 54 and regenerated in aseparate vessel :trated in the drawing are preferred, though other conversion systems'employing the catalyst in the formof fixed or moving beds may be substituted for zone '54 illustrated inthe drawing.

mixed feed. The crackingucatalyst comprised a synthetic silica alumina .composite containing about 13% alumina,

and .was partially deactivated .by previous service Jfor cracking gas .oils .during which it became contaminated with .about0.5 weight percent .of inorganic impurities including iron oxide and its surface area was reduced to about 100 square meters per gram. The mixed feed containing catalyst was introduced into heating coil 20 and soaker 22 where it was heated to about 775 F. at a pressure of about 1200 p. s. i. g. Turbulence was provided in soaker 22 by means of mechanical agitation. The residence time in coil 20 and soaker 22 at temperatures above about 760 F. was about 30 minutes. Under these conditions the residual oil was substantially converted to coke and distillable products without fouling of the vessel walls. The coke deposited upon the catalyst in coil 20 and soaker 22 amounted to about 23 pounds per barrel of mixed feed or about 47 weight percent on catalyst. This amount of coke substantially deactivated thecatalyst so that it was incapable of promoting any significant additional amount of cracking during the short residence time of the oil in the subsequent distillation zone 30.

The cracked products containing coke-bearing catalyst were introduced into fluid solids distillation zone 30 containing a fluidized bed of coke-deactivated catalyst maintained at about 950 F. and about p. s. i. g. Steam amounting to about 20 weight percent of the oil feed was introduced into distillation zone 30 to maintain the cokedeactivated catalyst in a fluidized condition and to aid in the distillation process. The oil feed rate to distillation zone 30 was about weight per hour per weight of coke-deactivated catalyst present in zone 30. As the cracked oil was introduced into zone 30 it was rapidly vaporized and removed overhead by line 44 Without substantial further conversion in zone 30 while the coke-deactivated catalyst entering zone 30 with the oil feed remained in this zone and became a part of the fluidized mass therein until withdrawn at the bottom. The oil vaporized in zone 30 was fractionated in tower 50 (in the absence of second-stage products) and the following yields of products were recovered for each barrel of mixed naphtha and residuum feed: 1) about 2.5 lbs. of dry gas, (2) about 24.2 gal. of gasoline cut boiling below about 430 F. (including the naphtha introduced in the feed as diluent), (3) about 4.3 gal. of heating oil boiling in the range of about 430 to 650 F., (4) about 9.6 gal. of gas oil boiling in the range of about 650 to 1000" F., and

s -about 2ll gal. of higher boiling bottoms =s'uitablefor fuel oil or for-recycling to the first conversion stage. The isolated gas oil was then catalyticallycracked furtherin Fluid zone 54 and an addit'ionahvolume of valuable gasoline and other products was obtained.

in summary, it is seen from the foregoing description and example that the present invention provides for a conversion just about high enough to permit vaporizationof the residuum in the presence of a'relatively contaminated catalyst in a firststage, followed by extensive conversion over a relatively non-contaminated, selective catalyst in a second stage. Thus, high over-all selectivities favoring formation of'the most desired products are assured. Vari- 'ous modifications not specifically described herein'may become apparent to those skilled in the'art, without departing from the spirit of the present invention for which patentprotection is desired within the-full scope-of the appended claims.

The claims:

1. In a process for crackingheavy residual oils having a Conradson carbon of about '5 to weight per cent and an atmospheric boiling range substantially above 1000 F., the improvement which comprises'mixing the heavy residual oil with 20 to 200 lbs. of finely divided cracking catalyst per barrel-of residual oil, passing the mixture through a conversion zone at 700 to 900 F.-andat a pressure between 500 to 3000 p. s. i. g. which is suflicient to maintain a major portion of the residual oil in liquid phase, keeping the niixture'under the said reaction conditions for a residence time between about 210 60 minutes to produce a conversion correspondingto not more than S Weightper cent of dry gas formation based on"resid-ual feed and until thecatalyst is :just substantially completely deactivated by deposited coke, releasing the pressure on the converted mixture and passing the mixture into a distillation zone containing a dense fluidized bed of inert solids in the lower part thereof whereby the coke-bearing catalyst becomes part of the fluidized bed, maintaining the distillation zone at substantially atmospheric pressure and at a temperature between about 850 to 1050 F. and high enough to vaporize the converted oil without substantial decomposition, removing the converted oil vapors from an overhead portion of the distillation zone and withdrawing solids from the bottom of the distillation zone.

2. A process according to claim 1 wherein the residual oil feed is diluted with 15 to gallons of naphtha per barrel of feed and wherein the temperature in the conversion zone is between 750 and 850 F.

3. A process according to claim 1 wherein the residence time of the reaction mixture in the conversion zone is between 10 and 30 minutes and produces a conversion corresponding to about 1 to 3 weight per cent dry gas formation based on residual oil feed.

4. A process according to claim 1 wherein the catalyst concentration in the reaction mixture is between 50 and pounds per barrel of residuum and results in deposition of about 10 to 60 weight per cent of coke on catalyst at the end of the conversion.

5. A process according to claim 1 wherein an inert fluidizing gas is introduced at the bottom of the distillation zone at a rate suflicient to produce a total superficial gas velocity of about 0.5 to 5 feet per second in the dense fluidized bed.

coke is burned off at 1100 to 1250" F. and below the deactivation temperature of the catalyst, and the resulting regenerated catalyst is recycled for mixing with further amounts of fresh residual oil.

8. A process according to claim 1 wherein the oil vapors removed from the distillation zone are fractionated in a fractionation zone to give a naphtha cut, a gas oil out and a bottoms cut, and wherein the bottoms cut is mixed with fresh residual oil feed in a proportion of 1 to 30 volume per cent based on the residual oil.

9. A process according to claim 8 wherein the separated gas oil cut is passed under cracking conditions through a second conversion zone containing selective cracking catalyst and wherein the cracked hydrocarbon products from the second conversion zone are mixed with the vaporized oil removed from the distillation zone prior to passing the resulting hydrocarbon mixture jointly to the fractionation zone.

10. In a process for cracking heavy residual oils having a Conradson carbon of about to 35 weight per cent and an atmospheric boiling range substantially above 1000 F., the improvement which comprises mixing the heavy residual oil with 20 to 200 lbs. of finely divided cracking catalyst per barrel of residual oil, passing the mixture through a first conversion zone at 700 to 900 F. and at a pressure between 500 and 3000 p. s. i. g. which is sufficient to maintain a major portion of the residual oil in liquid phase, keeping the mixture under the said reaction conditions for a residence time between about 2 to 60 minutes to produce a conversion corresponding to not more than 5 weight per cent of dry gas fraction based on the residual feed and until the catalyst is just substantially completely deactivated by deposited coke,

releasing the pressure on the converted mixture and passing the mixture into a distillation zone containing a dense, fluidized'bed of inert solids in the lower part thereof whereby the coke-bearing catalyst becomes part of the fluidized bed, maintaining the distillation zone at substantially atmospheric pressure and at a temperature between about 850 to 1050 F. and high enough to vaporize the converted oil without substantial decomposition, removing the converted oil vapors from an overhead portion of the distillation zone, withdrawing solids from the bottom of the distillation zone, fractionating the oil vapors to give a naphtha cut, a gas oil cut and a bottoms cut, admixing the bottoms cut with fresh residual oil feed in a proportion of 1 to 30 volume per cent based on the residual oil, cracking the gas oil cut in a second conversion zone with finely divided cracking catalyst, removing spent catalyst overhead from the second conversion zone with cracked hydrocarbon vapors and admixing the spent catalyst with fresh residual oil being fed to the first conversion zone.

References Cited in the file of this patent UNITED STATES PATENTS 2,156,591 Jacobson May 2, 1939 2,315,192 Egloft Mar. 30, 1943 2,378,531 Becker June 19, 1945 2,388,055 Hernminger Oct. 30, 1945 2,419,427 Teter Apr. 22, 1947 2,432,744 Gary Dec. 16, 1947 2,485,315 Rex Oct. 18, 1949 2,517,900 Loy Aug. 8, 1950 2,571,342 Crowley Oct. 16, 1951 2,598,058 Hunter May 27, 1952

Claims (1)

1. IN A PROCESS FOR CRACKING HEAVY RESIDUAL OILS HAVING A CONRADSON CARBON OF ABOUT 5 TO 35 WEIGHT PER CENT AND AN ATMOSPHERIC BOILING RANGE SUBSTANTIALLY ABOVE 1000* F., THE IMPROVEMENT WHICH COMPRISES MIXING THE HEAVY RESIDUAL OIL WITH 20 TO 200 LBS. OF FINELY DIVIDED CRACKING CATALYST PER BARREL OF RESIDUAL OIL, PASSING THE MIXTURE THROUGH A CONVERSION ZONE AT 700 TO 900* F. AND AT A PRESSURE BETWEEN 500 TO 3000 P.S.I.G. WHICH IS SUFFICIENT TO MAINTAIN A MAJOR PORTION OF THE RESIDUAL OIL IN LIQUID PHASE, KEEPING THE MIXTURE UNDER THE SAID REACTION CONDITIONS FOR A RESIDENCE TIME BETWEEN ABOUT 2 TO 60 MINUTES TO PRODUCE A CONVERSION CORRESPONDING TO NOT MORE THAN 5 WEIGHT PER CENT OF DRY GAS FORMATION BASED ON RESIDUAL FEED AND UNTIL THE CATALYST IS JUST SUBSTANTIALLY COMPLETELY

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