US 2873245 A
Description (OCR text may contain errors)
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Charles E. Thompson Joseph Stewart Inventors Arthur W. Longer, Jr.
By M JwAttorneyg `deficient heavy oil such as a United States Patent() HEAVY OIL CONVERSION PROCESS Charles E. Thompson, Fanwood, Joseph Stewart, Cranford, and Arthur W. Langer, Jr., Nixon, N. J., assignors to Esso Research and Engineering Company, a corporation of Delaware Application December 15, 1954, Serial No. 475,484 2 Claims. ('Cl. 208-56) The present invention relates generally to the conversion of hydrocarbon oils. It pertains particularly to a process for converting petroleum oils to lighter and more valuable products combining the steps of catalysis and hydrogen donor diluent cracking.
There recently has been introduced into the art of residua upgrading a process termed hydrogen donor diluent cracking (HDDC). ln this process a hydrogen vacuum residuum is upgraded by admixing it with a relatively inexpensive `hydrogen donor material, aromatic-naphthenicin nature, and thermally cracking the resulting mixture. The donor diluent is advantageously a normally surplusage refinery material, such as a thermal tar obtained from thermal cracking of catalytic cycle stock having the ability to take up hydrogen in a hydrogenation zone and to readily release it to hydrogen deficient oils in a thermal cracking zone. In this process, the selected hydrogen donor material is recovered and is partially hydrogenated before being recycled by conventional methods using, preferably, a sulfur insensitive catalyst such as molybdenum sulfide or nickel tungsten sulfide. In this manner of hydrocracking oils, the heavy oil being upgraded is not contacted directly with the hydrogenation catalyst and does not, therefore, impair its activity by contamination. This technique of HDDC is more fully depicted in co-pending application entitled, Upgrading of Heavy Hydrocarbon Oils, S. N. 365,335, tiled July l, 1953, now abandoned, by A. W. Langer, Ir., a co-inventor of the present invention.
One of the principal applications of the hydrogen donor diluent process has been in the preparation of gas oils suitable as catalytic cracking feed stocks from heavy, low value petroleum oils. `The previously proposed HDDC processes, however, have used principally a diluent boiling in the range of about 700-900 F. The use of a diluent of this boiling range conflicts with the production of the gasoil for catalytic cracking as it is gas oils in this boiling range that are used in catalytic cracking. When using a diluent of this boiling range, there is a loss of available gas oil product for catalytic cracking operations because some of the gas oil produced must necessarily be recycled with the diluent. There is an adidtional disadvantage in that the gas oil product boiling above and below this range is contaminated somewhat with polycyclic aromatics from the hy drogen donor diluent. These polycyclic aromatics from the diluent whichare carried into the gas oil cut decrease its value as a catalytic cracking feed stock because of their refractory nature and high carbon-forming tendency.
According to the present invention, when a low boiling `hydrogen donor diluent is used, e. g., a partially hydrogenated thermal tar boiling in the range within the limits of 400 to 700 F., the above difficulty is avoided and the quality of the gas oil product from the process is unexpectedly improved.V The use of a diluent in this boiling range, besides unexpectedly increasing the gas oil yields from the hydrogen donor cracking operation, also gives higher yields of gasoline.
It is, accordingly, an object of this invention to present to the art a combination process for the conversion of hydrocarbon oils. More particularly, it .is an object of this invention to prepare naphthas of motor fuel quality in a process comprising the steps of hydrogen donor diluent cracking of a heavy oil and catalytically cracking the gas oil therefrom.
Further objects and advantages will more clearly appear from the attached drawings, depicting schematically preferred embodiments of this invention and forming a part of this specification. The drawings are presented by way of illustration only and the invention is not to be limited thereto.
Fig. 1 illustrates the essential steps of this process.
Fig. 2 depicts a prefererd embodiment wherein a two-step HDDC process is used to upgrade hydrogen deficient oils to naphthas and gas oils of catalytic cracking quality.
In brief compass the present invention comprises a conversion process wherein a heavy oil is admixed with a hydrogen donor diluent boiling in a range within the limits of 400 to 700 F., e. g., 430.to 650 F., and cracking the resulting mixture under hydrogen donor diluent cracking conditions. The cracked mixture is then separated to obtain the spent donor diluent and heavier gas oils. The spent diluent is partially hydrogenated, as is customary, to regenerate it and is returned to the cracking step. The heavy gas oils are subjected to catalytic cracking to secure naphthas of motor fuel quality and to secure additional amounts of the hydrogen donor precursor.
As will appear in the description of preferred embodi ments of this invention, the donor diluent, or portions thereof, is secured from the catalytic cracking step and the bottoms or residue from the catalytic cracking unit are returned to the HDDC step to be further treated therein.
The heavy oils that may be upgraded according to the present invention comprise those oils customarily charged to previously described HDDC processes. Suchheavy oils include whole crudes7 and heavy distillate and residual fractions therefrom, and may also broadly include hydrogen deficient oils such as shale oils, asphalte., tars, pitches, coal tars, heavy synthetic oils, etc. In the present invention there may be charged to the catalytic cracking step, besides the gas oil obtained from the HDDC step, other gas oils customarily charged to such a process.
It is preferred to use a fluidized solids catalytic cracking process, well known in the art, using a silicaalumina type catalyst in the practice of this invention. Other catalytic conversion processes may be used, however, if desired, including fixed and gravitating beds processes and processes using catalysts such as activated carbon, magnesia-silica, etc.
The pertinent operating conditions applicable to the attached Fig. 1 are conveniently sumarized in Table 1, presented hereinafter. Referring particularly now to Fig. l, a heavy oil, such as a vacuum residuum, enters the process via line 1 and is admixed with 0.1 to 2 volumes of diluent, supplied by line 2, boiling in the range within the limits ot 430 to 650 F. Various recycle streams may in addition be mixed with the feed as will later be described. rhe resulting mixture is then heated in furnace 3 to `a temperature in the range of 700 to l000 F. The heated mixture is then held at this temperature for a period of time suliicient to secure the desired degree of cracking and of hydrogen transfer. For the coil 3 and drum 4 arrangement shown, feed rates of the mixture will be in the range of 0.25 to l5 v./v./hr.
Conversions based on fresh feed are held in the HDDC zone within the limits of 40 tor70% on a 1000 F. basis. It has been found that it the conversion exceeds this when using a low boiling donor diluent. then recycle operation becomes difcult, it not impossible, because the heavy recycle stream is not sufficiently solubilized or peptized bythe light donor diluent. Also, during recycle operation the Conradson carbon content of the recycle stream will build up to a. maximum level. if this level becomes too high, then it greatly affects product quality and distribution. it is preferred in the single step HDDC process illustrated to maintain the Conradson carbon of the recycle bottoms fraction below 60 Wt. percent. The embodiment depicted in Fig. 2 is directed to an alternative processing scheme that circumvents this diiiiculty.
After-the thermal treatment, the mixture is transferred by line 5 to a separation system o. As many fractions may be obtained at this point as desired. As illustrated, light gases are removed overhead by line 7 and naphthas are removed by line 8. The Spent diluent boiling in a range within the limits of 400 to 650 F. is Withdrawn by line 9 and transferred to a hydrogenation vessel 12. The heavier gas oils are removed by line 10 and transferred to the catalytic cracking unit 20. The bottoms boiling above a temperature in the range of about 950 `to 1100a F. are removed by line 11i. A portion of these bottoms may be removed as residual fuel by line 13 and the remainder can be recycled by line 14 for further treatment.
The gas oils in line 10 may be adniixed with recycle streams from the catalytic cracking unit and passed by line 'l5 to unit 20. Extraneous gas oils may be supplied to the process if desired by line 16. These gas oils may conveniently comprise virgin gas oils obtained from the separation of `the whole crude wherein the vacuum residuurn of the example, supplied to the process by line 1, is obtained.
A conventional fluid catalytic cracking unit with external regeneration means (not shown) Iis used for the purposes of this illustration. Conventional catalytic cracking conditions are maintained in unit 20. Fluidizing gas, e. g., steam, is admitted to the base o the unit by line 17 as is customary. The converted oils are withdrawn overhead by line 2l `and transferred to separation zone 22.
Light gases are removed by line 23 from fractionator 22 and naplitbas are removed by line 24. Heating oils boiling above about 430 F. up to about 700 F. are removed by line 25. A portion of these heating oils may conveniently be used to supply makeup diluent to the HDDC step. Thus, line 26 can transfer material boiling in a diluent boiling range to hydrogenator 12.
To remove materials from this heating oil (makeup diluent) fraction that do not contribute to its hydrogen donor characteristics, this stream may conveniently be subjected to thermal cracking to crack out non-donors such as paraihns, or to extraction processes such as phenol extraction to concentrate the aromatics.
Hear/ier gas oils separated 'from the catalytic cracking elliuent are removed from the pro-cess by line 27. As is customary in heart cut recycle" operations, a major portion of these gas oils can be recycled to the catalytic unit via lines 2S and l5. The bottoms from this separation step may be withdrawn as residual fuel via line 29 or may conveniently be transferred by line 30 to the HDDC stepto be upgraded therein. K
The spent donor diluent and makeup fraction are transestacas ferred to the hydrogenator 12 via line 31. Hydrogen is supplied to the vessel via line 355, and the spent gas is removed by line Se, a major portion ot which may be recycled. Conventional hydrogenation conditions are used. Preferably the hydrogenation zone contains a fixed bed of a relatively sulfurainsensitive catalyst such as nickel tungsten salti-de, molybdenum sullide, cobalt molybdate on alumina, etc. The diluent traction is only partially hydrogenated as substantially complete hydrogenation will greatly reduce or eliminate its effectiveness as a donor diluent. For a donor diluent boiling in the range of 430 to 650 F., the introduction into the diluent of 200 to 2000, preferably 300 to 700 standard cubic it. (s. c. f.) of hydrogen per barrel of diiuent will achieve the desired degree of hydrogenation. The regenerated donor diluent is recycled to the feed inlet line via line 2.
For many types of oils, it has been found that the process may be substantially unconsuming as to the bydrogen donor diluent. ln fact, excess donor diluent may be produced by the process. This is true apparently because crude oils contain many molecules of an aromaticnaphthenic nature or molecules that will upon cracking readily reduce to aromatic-naphthenes, and lthus the feed `streams to the process itself will supply a substantial part, if not all, of the desired aromatic-naphthenic ring structures necessary for the hydrogen transfer.
In some cases, however, some of the donor diluent will be cracked out of the desired boiling range and materials such as paraiiins not suitable as donor diluents will be cracked into the diluent boiling range. lt is desirable, therefore, in some cases to bleed from the process via line 32 a portion of the diluent stream in order to maintain its effective aromaticity. Alternatively, the concentration of the desired aromatic-naphthenes may be increased by various means including mild thermal cracking of the diluent stream, aromatization of the diluent, or solvent extracting the diluent. In the present example makeup diluent is supplied via line 26 as previously described although extraneous diluent sources may be resorted to. Besides extracts and thermal tars from catalytic cycle oils, donor diluents may be obtained from cracked beating oils, certain naturally occurring sources such as Coastal heating oil, etc.
Table 1 presents the operating conditions applicable to the process described with reference to Fig. l. Table 2 presents the products obtainable from this process from the feed stocks indicated when it is operated in accordance with the example of Table l.
Table 1 Range Example HDDC Conditions (Coil nud/or Drum):
Temperature, F Pressure, p. s. i. g Throughput, v./v./hr Dilucnt/oil ratio (Inc. recycle) Diluent Boiling Range, F 1,000 F. Conversion per pass,1
vol. percent. Catalytic Cracking Conditions, Fluid Unit.
Catalyst Temperature, F Pressure, p. s. i. g Feed rate, W./hr./ Catalyst/oil ratio 430 F. Conversion per pass,s Y `701. percent. Hydrogcnation Conditions:
Catalyst Temperature, F
Pressure, p. s. l. g...
Hz Consumed, s. e.
Hi Furity, percent 850 to l,000 930 0 to 5 Nickel Tungsten Sultlde. 650.
50 to l00 is defined as: vol. percent feed minus vol.
l 1,000 F.-Conversion above 1,000" F., excluding coke, based on fresh perzcnt products boiling 2 430 F.-Conversicn ls defined as: 100 vol. pereentieed minus vol. percent products boiling above 430 F., excluding coke, based on fresh feed.
1 gevaarte Heating oil, 430650 F Gas oilI 050 to 1,000 F Residual fuel, 1,000 F.+
Internal flows, percent on fresh fcedi 57 vol.- percent.
46 8 vol ercent...
"zzble2 HDDC Unit Feed Inspections: H/C atomic ratio 1.39
API gravity 3.8 Sulfur, wt. perceut 4.54 Oonradson carbon wt. Percent- 24.6 softening point, 155
Products: HDDC Unit, Catalytic Unit,
percent on ropercent on gas slduum l oil from HDDC unit at g conversion to `430" F.- Gases, Gg 6.7 wt. percent.. 5.8 Wt. percent. Naphtha, (J4-430 F.-. 33.9 vol. percent... 35.3 vol. percent.
34.0 vol. percent. 26.0 vol.` percent. i
4.9 Wt. percent (on catalyst).
To illustrate the advantages of this invention, particularly that increased yields ofl gas oils are obtained, Table 3 is presented. In Table 3, the product yields are shown when a 27% Hawkins vacuum residuum was cracked using the low boiling di' lent of this invention and when a higher boiling diluent boiling in the range of 700 to 900 F. was used. The Hawkins residuum had the following inspections:
Conradson carbon..` 24.6 wt. percent. Initial boiling point 1000* F. Gravity 3.8 API. Sulfur 4.54 wt. percent.
Table 3 Diluont boilin ran e 700- 430 g g 900 F G50" F Conv. to 1000 F., Vol. percent on Rosld 53. 2 51. 3 Coke, Wt. percent- 0. 1 U. 2 Ca, Wt. percent.. 3. 6 C4, Vol. percent 2. 2 l1; C-430 F., Vol. perce 2i. 4 230.0 430-050 F., Diluent Recovery Vol. percent e5. 6 430700 F., Vol. percent 37. l) 70D-900 F., Vol. percent, Diluent Recovery Vol.
percent 70. 2
650-1,000 F., Vol. percslm 900-1,000 F., Vol. percent. 1000 F., Vol. percent It is to be noted that the lower boiling donor diluent resulted in a 9 vol. percent increase in gas oil (430- 1000 F., less diluent) yield.
With reference to Fig. 2, a process that avoids the difficulty of recycle operation previously referred to and results in higher conversion of the heavy oil feed will be described. The heavy oil is admitted to the process via line 51 and in this caseis separately preheated to a temperature in the rangev of 600 to 800 F. by furnace 52 before it is mixed with the donor diluent. The donor diluent is heated in furnace 53 to a temperature in the range of 700 to 900 F. and is supplied to the preheated feed in line S4 by line 5S. The resulting mixture is transferred to a soaking drum 56 to allow time for the cracking reaction to occur. The thermally treated mixture is then transferred by line 57 to fractionating system 58 which can include an atmospheric fractionator and a vacuum distillation unit. Light gases are sepv arated and removed from the mixture by lines 59 and 60 respectively. A diluent fraction boiling in the range of 430 to 650 F. is removed by line 61 and a portion of it may be bled from the process. The remainder is transferred to hydrogenator 63 by line 62. Makeup diluent from the previously described sources can be supplied to the process by line 64. Gas oils are separated and recovered by line 65 and are transferred to the catalytic cracking step previously described. The heavy bottoms which are not amenable to further cracking using a light diluent are transferred by line 66 to a second HDDC step that uses a higher boiling diluent. The use of a higher boiling diluent permits these heavy bottoms to be more readily converted because the solu bility and peptizing action of a heavy diluent is better.
The lighter diluent in the first step of the process is regenerated in hydrogenator 63 as previously described, the regenerated diluent 'being returned by line 64 to heater 53.
The bottoms fraction in line 66 is heated in furnace 67 and mixed with a diluent boiling in the range within the limits of 700 to 1l50 F., e. g., 700-900 F., and then transferred by line 68 to soaking drum 69. It is preferred to maintain the temperature of' the reaction mixture within the limits of 750 to 950 F. for reaction times within the limits of 0.1 to 1.0 hours. Preferably, 0.2 to 1 volume of the heavier diluent are used perl vol ume of the bottoms fraction. After the thermal treatment, the mixture is transferred by line 70 to fractionator 71. Gases and naphthas are removed from the fractionator by lines 72 and 73 respectively. A heating oil fraction `boiling above about 430 F. up to the diluent boiling range is removed by line 74 and may be transferred to the catalytic cracking unit as shown or may be removed as product. The diluent fraction is transferred by line' 75 to hydrogenation vessel 76. A portion of this diluent may be bled from the process by line 77 and makeup diluent may be supplied by line 78. This diluent fraction is partially hydrogenated as previously described. In some applications it may be convenient to partially hydrogenate the light and heavy diluent fractions in a commonhydrogenation zone and then to separate the light and heavy fractions and return them to their respective HDDC steps. As shown, however, the regenerated heavy diluent is removed from hydrogenator 76 by line 79, reheated in furnace 80 to a temperature n the range of 700 to 950 F. and passed to the feed stream by line 81.
Having described preferred embodiments of this invention, what is sought to be protected by Letters Patent is succinctly set forth in the following claims.
What is claimed is:
l. A heavy oil conversion process which comprises the Q7 steps of: thermally cracking in the absence of a solid catalyst a heavy oil admixed with a light hydrogen donor diluent boiling in a range within the limits 400 to 700 f F., at 1000o F. conversions in the range of 40 to 70 vol.
percent so as to produce gas oils, separating the cracked mixture to obtain naphthas, spent light diluent, heavier gas oils and residue, subjecting said residue to a second stage of thermal cracking in the absence of a solid catalyst in admixture with a heavy hydrogen donor diluent boiling in a range within the limits of 700 to'1l5'0 F., separating the etiluent from the second stage toobtain further amounts of naphthas, gas oils boiling below :saidj heavy diluent and spent heavy diluent, catalytically ,crack ing said gas oils to obtain naphthasof motor fuel quality and cycle stocks, regenerating said light and h'eavyhydrogen donor diluents by partially catalytically hydrogenating portions'of said spent light and heavy'y dilnents along with make-up diluent obtained from said cycle stocks, and repeating the process.
I l 2. The process of claim 1 wherein 0.2 to l volume of heavy diluent per volume of residua is introduced into said second stage of thermal cracking, and a reaction time of 0.1 to 1.0 hour is employed in said second stage.
References Cited in the leofthis patent UNITED STATES PATENTS 2,381,522 Stewart Aug. 7, 1945 2,426,929- Greensfelder Sept. 2, 1947 2,584,378 Beam Feb. 5, 1952 2,620,293 Blue et al. Dec. 2, 1952 2,772,214v Langer Nov. 27,1956 2,772,218 'Martin Nov. 27, 1956 2,772,221Y 1956 yStewart et al. .Q- Nov. 27,