US 2651601 A
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. W. TAFF ET AL PREPARATION OF FEED MATERIAL FOR Filed Jan. 3, 1949 THE CONVERSION OF HYDROCARBONS mw .dmvmdg Sept. 8, 1953 FMJPDO |10 w11@ 'wzfrfed o.
Patented Sept. 8, 1953 PREPARATION OF FEED MATERIAL FOR THE CONVERSION OF HYDROCARBONS Wilfred O.k Taff, Cranford, and John Weikarty Elizabeth, N. J., assignors tol Standard Oil Development Company, a. corporation of Delaware Application January 3, 1949, Serial No. 68,938
This invention pertains to a method of converting hydrocarbon materialsV and particularly to the conversion of residual stocks in order to form substantial quantities of high quality feed for catalytic cracking operations.
In order to prepare'feed stocks for catalytic cracking operations it is common practice in the art to subject petroleum crude oil to an atmospheric distillation in order to obtain a gas oil fraction, generally boiling between about 430 F. and about 800-900 F., and a higher boiling residuum which will normally-equal about up to about -30 vol."% of the original feed. This residuum does not represent a satisfactory catalytic cracking stock and accordingly efforts have been made to convert it or obtain additional amounts of gas oil therefrom which would be suitable as feed stocks for a catalytic cracking system. The method of converting this higher boiling residual stock ordinarily is a thermal cracking or visbreaking operation. It has been found however that the gas oil produced in the normal visbreaking operation is a poor catalytic cracking feed stock. The terms "visbreaking and visbreaker used herein are synonymous with the terms viscosity breaking and viscosity breaker respectively.V 1
It is the object of this invention to lprovide the art with an improved method for treating higher boiling residual stocks from the atmospheric distillation of petroleum crude oils.
It is a further object of this invention to provide the art with a method for treating higher boiling residual stocks from the atmospheric distillation of petroleum crude oils which increases the quantity and improves the quality of the gas oil formed to make it suitable as a feed stock to a catalytic crackingoperation. These and other objects will appear more clearly from the detailed specification and claims which follow.
It has now been found that the foregoing objects can be fulfilled if the residual stock is passed into a tower maintained substantially below atmospheric pressure and which has its bottom section divided into two sections by means of a dam or partition. The residue from the atmospheric distillation is supplied to one of the sections in the bottom of the vacuum tower wherein it is further reduced, or additional amounts of gas oil are stripped therefrom. The stripped residue is thensubjected to a visbreaking operation.v The visbreaker is preferably of the coil-only type where relatively high temperatures and short contact times can be ems ployed. However, the coil and drum type or a coil and swinging drum visbreaker could be used in which latter case all of the cracked bottoms are recycled and the drums allowed to cake. The reaction products from the visbreaker are fractionated in an atmospheric fractionating tower to separate visbreaker gas and gasoline and a visbreaker residuum. This residuum is recycled to the vacuum tower preferably to the other of the two sections in the bottom of the tower where it is stripped of gas oil formed in the visbreaking operation whereupon the visbreaker gas oil is combined with the gas oil from the virgin residuum and passed'to a catalytic cracking unit. The stripped visbreaker residuum is withdrawn from the second section of the vacuum tower partly as a purgestream and partly to be combined with the stripped virgin residuum and recycled to the visbreaker.
Reference is made to the accompanying drawing wherein a schematic flow diagram of the process of the present invention is shown.
In the drawing, I0 is a supply line through which virgin residuum from an atmospheric distillation of a petroleum crude oil is passed, at elevated temperatures into vacuum' tower II. A partition or dam I2 is arranged in the bottom of vacuum tower II in order to divide the bottom portion of the tower into two sections I3 and I4. The virgin residuum is supplied to section I3 and because of the low oil partial pressure maintained in thel tower because of the vacuum and stripping steam, further quantities of gas oil are vaporized and taken overhead from the lvacuum tower II through outlet line I5.
An outlet line I6 is arranged at the bottom of the tower II for the withdrawal of stripped residuum from section I3. The stripped residuum withdrawn from section I3 is then pumped through linev I'I which passes through furnace I8 wherein the stripped virgin residuum is heated to conventionalY visbreaking temperatures of about 800-950 F. at the coil outlet. If a coil and drum type of visbreaking operation is employed, the temperature at the coil outlet will ordinarily be between 800 and 900 F.
The visbreakerA products are discharged through line I9 into atmospheric distillation co1. umn 20 from which visbreaker gasand gasoline are taken overhead through'line 2| while a residuum is withdrawn from the bottom of column 20 and passed through line 22 into section I4 in the bottomv of vacuum tower Il wherein it is vacuum stripped of gas oil formed in the visbreaking step. The kvisbreaker gas oil is with ash and carbon residue content of the cracked residuum it is preferable to remove a portion of this stream from the system )through `purgeline 24 for use as fuel oil.
The present process is applicable to any residfual stocks obtained by theatrnospheric distillation of crude petroleum goil. .a rule the residuum will comprise at most about 21o-,30 vol. percent of the original oil and will have a boiling range above about 800-900 F. The residualVA stocks as withdrawn from the atmospheric distillation operation will ordinarily, be at a tem.- perature ofatleastabout 600 F. If the oil is too .cool to dash off appreciable cpiantitie s oi gas oil when, .placed under reduced pressure the vacuum tower, the residuum can be subjected Yto .a preheating operation to bring its temperature upto the .desired operating level of about 600 ,to..about 800.,F. The. pressure maintained in 'the vacuum tower .H is ordinarily below aboutV 50 mm. Hg. Inorder l toreducethe oil partialpressure in the vacuum tower. -tobelowlabout mm. Hg, further stripping steam .may be introduced through steam inlets25 in the `bottom oithevacuuin tower l i..
The stripped virgin residuum is heated in .furnace i8 .to the.maximum temperature permissible without dposition of jcoke on the coils. Ordinarily.,the coil outlet'te'mperatuie in a coilonly visbreaker is between 90W-925 F., vwhile with `other .typesof visbreakers, the temperature level is generally )about '50 F. lower.
The .following example will' serve'to illustrate the imrvirov'en'ient in yield and quality' as a rfeed lstock for .acatalytic lcracking operation of gas oils obtainable from a residual stock in accordance with the present invention.
A 16 %,residuu1n obtained from thefatmospheric distillation oa West Texascrude having a .gravity of about 10 A..P..I., a;Conradson Carbori .of aboutl wt. percent and agviscosityof 12,50 Saybolt Universal secondsfat 210, jwas subjected to vacuumdistillation at Vabout Lfininl-Ig and a temperature of 770.Q F. The residue .from 'this vvacuum distillation was then thermally cracked and thegas .and gasoline :formed in this thermal cracking operation were separated Vfrom thel visbreake'r residuum The latteruwas subjected to vacuum distillation under the saine conditions ,as -applied to the virgin Yresiduuni. The gas oil .separated from the visbreakerv residuum was combined with the virgin gasoil vacuum stripped from the original residuumwand the mixture was .then" .catalyti ca1ly cracked by contacting'it Nwith a silica-aluminacracking catalyst at 975 F. .to a conversion of 55%. n
Another portion of .thesame 1,6%Mresiduum was Vsubjected directly. 'to a ,thermalkcracking operation. The gasand gasoline formedgwere separated from thereaction product andthe residuum wassubjected to vacuum distillation at abou Hg .and a temperature oi 77o F. The gas oil obtained was then catalytically cracked under the vsame conditions as the mix- 4 ture of virgin and thermally cracked gas oil as described above. The results obtained are summarized in the following table:
Table Dvlum. f.: is ation h vis'brenkmg Vbrfkmg Residuum Treatment and Vacuum imD- tgluum Distinauon of '1 'of Visbreaker Visbrcaker R Residue esidue Gas Gil for Cat. Cracking.- Percent on Qriginal Residuum: `V1rginl percent.. 48. 8
Thermally Cracked-. .do-. 22. 5 57 6 Vacuum Still Bottoms:
Percent on Rcsiduum 26, 2 30.0
Speciiic Gravity 1. 12 l. 1l v .Softening Point ..F 260 240 Gig.: Cracking 'Yields (Based on Gas Gasoline, Vol. percent 45. 9 41. 0 Excess Butane-Butylene, Vol. 3. 4 6.3
percent. Dry Gas (C4 free) wnpercentl-.. 8. 3 Y .8. 0 Carbon, wt. percent d. 0 7. 4 Conversion 55. 0 55. 00 Gasoline Yields, Vol. percent ased on Residuum 32. 7 23. 6
These data showthat afsubstantial increase in gas oil is obtained by the process in accordance with the present invention and that it is abetter .catalytic cracking feed stock as shown Vby the Ahiglnergasoline yields based not "only on the residuum .but also on the gasoil charged, and 4kshowed substantially less carbon formation.
It maybe seen from the foregoing description that the process in accordance with .thepr'esent invention makes it possible to avoid thermal cracking and/or degradation of any virgi'ngas oil that is capable of being vacuum stripped .from the original residuum .and permits the vacuum flashing of the virgin lresiduurn'and visbreaker .residuum in al single lvacuum tower without contamination `of) thelstripped virgin residuum. i The foregoing description contains a limited number of embodiments of the'present invention. vIt will be understood that numerous variations are possible without departing .from the scope vof the following claims. l
What is claimed'is;
ll. A process for theprodu'cti'on of high .quality feed for .catalytic cracking fromresidualstocks which comprises s ubjectinga petroleum crude oil tov distillationVv at atmospheric pressure to separate light .constituents and a .gas .oil Afraction boiling from about 5130?'1 F. to Slm-900" F. forming higher boiling virginresidual stock constitutf mg atentan-30% or the originaipetroieum'crude oil, passing said virgin residualfstock to a primary stripping `zone maintained at a pressure'substantially below atmospheric4 pressure .inforder to remove further quantities "of virgin gas oil 'therefrom, .subjecting .the 'stripped virgin residual 'stock to visbreaking, subjecting the reaction Aproduct from `the visbreaking step to atmospheric distillationhto separate visbreakeri'gas and gasoline from visbreaker'residue, .passing the visbreaker residue to a separate compartment of the' primary strippingzone in order tostr'ip visbreaker'gas oil from the visbreaker residue, combining'the visbreaker gas oil with .the gas oils'tr'ippe'd from said virginresidualstock, recycling apart ofthe stripped visbreaker residue 'to .the visbreaking step, and removing a 'suflicient aifno'u'nt ofthe stripped visbreake'r residue from the system to prevent excessive accumulation of ash andcarbon residues therein.
2. A process for the production of high quality feed for catalytic cracking from residual stocks which comprises passing virgin residual stock, from a distillation operation wherein lighter products including a gas oil fraction boiling up to 800 to 900 F. has been removed, to a primary 5 stripping zone under substantially subatmospheric pressure to remove as much additional gas oil as possible from said virgin residual stock, passing the stripped residual stock to a visbreaker and subjecting to mild vis-breaking treatment for a short Contact time to produce further gas oil and lighter products, passing the vis-broken stock to an atmospheric distillation zone to strip said lighter products, passing the stripped stock to a sub-atmospheric separating zone operating under essentially the same conditions as said primary stripping zone to separate gas oil therefrom, combining said separated gas oil with the above mentioned additional gas oil, withdrawing the bottoms from said separating zone, removing part of said bottoms from the system and recycling the remainder of said bottoms to the vis-breaker, atmospheric distillation and separating zones, to maximize gas oil yield with a minimum of cracking of said gas oil in the vis-breaking operation.
WILFRED O. TAFF. JOHN WEIKART.
References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 1,981,842 Keith Nov. 20, 1934 1,997,675 Bahlke et al Apr. 16, 1935 2,105,935 Swanson Jan. 18, 1938 2,160,286 Ruthruif May 30, 1939 2,166,176 Peterkin July 18, 1939 2,185,222 Nofsinger et al Jan. 2, 1940 2,219,345 Thiele et al Oct. 29, 1940 2,312,445 Ruthruff Mar. 2, 1943 2,368,704A Carlson Feb. 6, 1945 2,374,338 Dunham Apr. 24, 1945 OTHER REFERENCES Nelson: Petroleum Renery Engineering,
page 205, 3rd edition, 1949, McGraw-Hill Book Co., New York.