US 3622502 A
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United States Patent  Inventors Ralph B. Mason ABSTRACT: Hydrocarbon residua boiling mostly 1,000 F. Denham Springs; and above are catalytically hydrocracked under liquid phase l Baton 98 boul conditions and novel recycle ratios to obtain a product which  Am. N 840,935 is predominantly an aromatic gas oil which is eminently suita-  Filed July 1 ble either as a solvent or as feed to commercial hydrocracking Patented 1 1971 operations. Although the upper boiling limit of this gas oil may  Assignee E850 R searc an Eng n ring mp y be in the range of 600-800 F the process is illustrated with separation into fractions boiling 650 F. and 650 F.+. An amount of the low-boiling and high-boiling fractions are recy-  CRACKING HYDROCARBON RESIDUA cled so that the feed mixture to the reaction zone contains 10 Claims 1 Drawing percent of the low-boiling fraction, percent of the high-  11.8. (I 208/112 boiling fraction, and 40 percent of fresh feed while the high-  lm. Cl. Clog 13/02 iling fra i n i recycled to extinction at a rate such that the Field of Search 208/112, amount present in the feed mixture to the reactor is equal to 123, 145 the amount in the product. 1-25 percent of an acyclic hydrocarbon modifier is added to the reaction mixture to act (defences Cited as a free radical acceptor under such conditions that is has a FOREIGN PATENTS residence time of 1 hour or less as compared to l to 6 hours 1,007,327 10/1965 Great Britain 208/111 f F Primary Examiner-Delbert E. Gantz Assistant ExaminerG. E. Schmitkons Attorneys-Pearlman and Stahl and C. D. Stores 43o s5oF l8 l'ims PRODUCTS RECYCLE GAS a /3 (H AND GASEOUS g MODIFIER) r 9 g 8 a CONDENSER AND GAS SEPARATOR FLASH CHAMBER LIQUID PHASE DRAW OFF HYDROCRACKER 5 2 RECYCLE D R REs|nuE I4 \I 6 I5 20 ssom CRACKING HYDROCARBON RESIDUA BACKGROUND OF THE INVENTION This invention relates to the catalytic conversion of hydrocarbon residua and more particularly relates to the hydrocracking of heavy residua under conditions of extinction recycle.
It is expected that steam cracking facilities will expand in the future, particularly in Europe. This will require means for easily disposing of the considerable amounts of tar which are a concomitant part of the steam cracking process. One obvious method is to upgrade these tars as well as other residues by thermally treating the tars with a hydrogen donor diluent material. The donor diluent is a hydrogen-containing material, aromatic-naphthenic in nature, that has the ability to take up hydrogen in a hydrogenation zone and readily release it to a hydrogen-deficient oil in a thennal cracking zone. Unfortunately, however, there is often undesired coke deposition at hot spots and preheater zones, leading to plugging of the equipment.
In Ser. No. 839,220 filed July 7, 1969 (now abandoned) for the present applicants it was shown that residual materials could be hydrodepolymerized in a liquid-phase operation in which that portion of the product boiling above 650 F. is recycled to extinction and the amount of material (including recycle) in the feed boiling below 650 F. is maintained between 20 and 50 percent of the total composition fed to the reaction zone in which the amount of 650 F. recycle and the amount of 650 F. in the product are kept at about the same level and yields of 95 volume-percent gas oil obtained particularly in the additional presence of an acyclic hydrocar bon acting as a free radical acceptor.
SUMMARY OF THE INVENTION ln accordance with the present invention it has been found that results equally as good or better than those obtained in Ser. No. 839,220 (supra) can be obtained by subjecting residual materials to catalytic hydrocracking in the liquid phase in operation in which the 650 F. material is recycled to extinction and the amount of 650 F. material and the amount of 650 F. material and the amount of fresh feed fed to the reactor zone is maintained in a ratio of approximately 40:20:40 weight-percent and the amount of 650 F. material recycled to extinction and the amount of 650 F. in the product are kept at about the same level, i.e. leveling ofi at about 40 percent. Where desired the recycle stream may be further processed in a coking operation to produce coke or binder oil. Yields of 95 volume-percent of 650 F. can easily be obtained. The presence of the 650 F. material provides solvency which permits mobility and moderate temperatures and thus minimizes coke make.
It is also a feature of this invention that acyclic hydrocarbons both straight-chain and branched and both saturated and unsaturated when present in amounts of 1-25 percent,
preferably l percent, acting as free radical acceptors increase product yields. To achieve maximum byproduct utilization from, the added acyclic free-radical acceptors, it is preferred that the residence time of the acceptor be maintained relatively short, i.e. 1 hour or less.
BRIEF DESCRIPTION OF THE DRAWING The drawing represents in diagrammatic form a preferred method for carrying out the process of this invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawing, a hydrocarbon residue, having a Conradson carbon number between and 40 and a substantial amount boiling at 1,000 F. and above such as thermal tar from steam cracking, reduced crude, shale oil residue, liquified coal fractions, and the like is slurried with 0.5 to 5 weight-percent a catalyst such as Harshaw nickel and is fed by line 1 and mixed with lower-boiling material, such as gas oil,
preferably recycled from a later stage of the process which enters through line 2, mixed with 500-5 ,000 SCF of hydrogen or a nonoxidizing gas per barrel of feed introduced by line 3. Gas oil or the like acts as a solvent for the tar and pennits easy pumping at moderate temperatures and prevents coking at hot spots in the system. The mixture is passed by line 4 into the bottom of hydrocracker 5 where the mixture is maintained at a temperature of 700900 F., (preferably 750-775 F.) and under sufficient pressure to maintain it in the liquid phase, e.g. 50-1000 p.s.i.g. A free-radical acceptor or modifier,
preferably an acyclic hydrocarbon, which may be a parafiin or iso-parafim of four to 20 carbon atoms per molecule, or an olefin or iso-olefin of two to 20 carbon atoms per molecule or mixtures thereof is added by lines 6 and 7. Suitable hydrocarbons include n-heptane; n-pentane; 2,2,4-trimethyl pentane; 2,2,4-trimethyl pentane-l; 2,4,4-trimethyl pentane-2, low-octane unsaturated naptha fractions, a normal C -C virgin naphtha, catalytic heavy naphtha, heavy alkylates, a l00- l 65 F. hydroformate fraction, the 2l0-400 F. fraction may be made by polymerizing propylenes and butylenes with l-I PO on kieselguhr, and the like. These hydrocarbons are added in amounts of about 1 to 25 percent based on tar feed and are sprayed, jetted of otherwise passed through the liquid tar phase in hydrocracker 5, into the vapor phase and removed overhead through line 8. The residence time of the modifier added through line 7 should range from about 5 minutes to l hour. The presence of the hydrocarbon modifiers at such short residence times results in reduced coke and gas loss. However some of the modifier is consumed in the process. When n-heptane is the modifier the degradation products are predominately normal hydrocarbons, namely, n-butane n-pentane, n-hexane, etc. whereas when iso-octane is used the degradation products are predominately branched, i.e., isobu tane, isopentane and branched C and C, paraffins. The use of 2,2,4-trimethylpentane and olefins of a similar skeletal structure results in the production of the importing blending agent, triptane. Without intending to limit the invention to any theory of what occurs, it is believed that the mechanism is one in which the modifier is being consumed with accompanying hydrogen exchange, demethanation, alkylation, isomerization, aromatic disproportionation and probably every known hydrocarbon reaction. The most plausible explanation is a free radical mechanism in which the condensed ring aromatic components of the tar depolymerize with the formation of free radicals which attach themselves to the modifier as a sink. In doing so the modifier in turn forms free radicals involving stepwise degradation and rearrangement reactions leading to gaseous products, coke, etc.
From the above it appears that conditions of short residence times for the modifier (less than 1 hour) coupled with fairly long residence times for the tar feed (1 to 6 hours) is important for best results.
The modifier leaving hydrocracker 5 through line 8 is passed to separator 9 from which hydrogen and uncondensed gas is recycled by line 10. Condensate from separator 9 is passed by line 11 to fractionator 12 from which low-boiling products are removed by line 13 and unreacted modifier and entrained higher-boiling components by line 14. This unreacted modifier is recycled to depolymerizer 5 by lines 15 and 7.
. Liquid products are withdrawn from hydrocracker 5 by line 16 and passed through filter 22 where catalyst, coke and/or other solid contaminants are removed and then passed and recycled to hydrocracker 5 by line 23. If desired the solids from filter 22 may be passed to a burner where carbonaceous material is removed and thence a hydrocarbon reduction zone to provide a reduced metal and/or sulfide suitable for recycling to the hydrocracker as catalyst therein. Liquid products are passed to flash chamber 17 where they are separated into products boiling above and below 650 F. Those boiling below 650 F. are either drawn off as make products through lines 18 and 21 or are recycled to hydrocracker 5 by line 18, 2 and 4. Products boiling above 650 F. are recycled by lines 20, 15, and 7.
The amount of products boiling below and above 650 F. recycled is critical, and must be in the ratio of 40 percent 650 F. :20 percent 650' F. :40 percent fresh feed. This control is made possible by withdrawing an amount of 650 F. material from the system by line 21 necessary to maintain the proper recycle ratio. The product drawn off through line 21 is suitable as such, as solvent for use in the chemical industry or may be further fractionated to separate out desired solvent and aromatic fractions and if desired with recycle of the highboiling material.
The recycle of the 650 F. material on the otherhand is also controlled so that the amount of this material fed to the hydrocracker based on total feed will be substantially the same as the amount of 650 F. material found in the product, based on tar blend. Generally this is between 35 and 45 percent preferably 39-41 percent. While it is not limited to be bound by any theory as to mechanism involved, it is believed that the beneficial results obtained are due to an equilibrium phenomenon in which an equilibrium exists between the condensed ring aromatic-containing 650 F. fraction and the lower-boiling 650 F. hydrocracked fraction. Excessive amounts of the 650 F. fraction will retard the hydrocracking, limit throughput of the depolymerization feed and incur excessive handling costs.
The following examples are included to illustrate the effectiveness of the instant process for the depolymerization of tars without, however, limiting the same.
EXAMPLE 1 A steam-cracked tar consisting of 35.7 percent material boiling 430-650 F 34.3 percent boiling 6501000 F., and
' 30 percent boiling 1000 F. was subjected to several cycles of hydrodepolymerization for 4 hours each at 775 F. under 1000 p.s.i.g. hydrogen pressure while about percent n-heptane, based on tar was thoroughly agitated with the liquid. The following data were obtained:
Run No. 68 70 72 Grams of Catalyst 20.8 20.4 20.0 Tar Feed, Grams 424.9 376.5 464.6 Wt. b Tar 39.7 37.3 38.5 Wt. i 650 F.-- Recycle 19.1 19.4 20.5 Wt. 650' F.+ Recycle 41.2 43.3 41.0 n-Heptane Employed,
' Grains 51.0 50.0 50.0 Operating conditions Avg. Temperature, F. 775 775 775 775 Hours of Run 4 4 2' 2 Pressure, p.s.i.g.
A! Star! L000 1,000 1,000 1.000 Maximum 1,500 1,520 1,200 1,000 Recoveries, Grams n-Heptane 34.8 29.2 32.5 Total Solids 18.8 21.6 19.7
Iv Carbon 14.64 29.5 k Hydrogen 0.92 [.42 I: Nickel 58.] 55.0 Liquid 6: Gas ex. n-
Heptane C -Gas 20.0 24 19.5 C,221 F. Cut, Grams 3.2 2.6 2.3 221-375 F. Cut, Grams 9.8 9.2 9.2 375-430" F. Cut. Grams l2.8 14.1 l9.0
430-650 F. Cut, Grams 214.4 170.9 239.0
650 F.+ Portion 175.9 162.3 188.5
Coke 2.9 6.7
Coke Gas, Wt.
Based on Fresh Tar 1.3 1.3 1.3 Est. Vol. 650 F. on
Recycle to Extinction 104 I04 104 After 2 hours at 775.F. temperature was cooled to 600 F. and pressure was reduced to 200 p.s.i.g. by venting through cooled traps. Pressure was brought to 1,000 p.s.i.g. with hydrogen addition and temperature was brought to 775 F. for 2 additional hours. Hydrogen additions were made during both periods on heat to compensate for hydrogen uptake.
The above data show that recycle of the 650 F. material to extinction can be obtained with only minor losses to coke and gas when employing a catalytic system and in which the ratio of fresh feedz650 F. recyclez650 F. recycle is maintained at 40:20:40, approximately.
The nature of the present invention having thus been fully set forth and specific examples of the same given what is claimed as new, useful and unobvious and desired to be secured by Letters Patent is:
l. A process for the catalytic hydrocracking of hydrocarbon residua having Conradson carbon numbers between 5 and 40 which comprises heating said residua in the presence of hydrogen and a particulate hydrogenenation catalyst under a pressure sufficient to maintain the residua in the liquid phase and at a temperature between 700 and 900 F. in the additional presence of l to 25 percent of an acyclic hydrocarbon modifier, having two to 20 carbon atoms, removing reacted residua and separating it into a low-boling fraction boiling below 650 F. and a high-boiling fraction boiling above 650 F. and recycling an amount of low-boiling fraction such that the ratio of fresh feed to high-boiling recycle to low-boiling recycle is maintained at about 40:20:40 percent.
2. The process of claim 1 in which the residence time of the acyclic hydrocarbon modifier is 1 hour or less and that of the residua-recycle mixture is 1 to 6 hours and the catalyst is pulverized Harshaw nickel.
3. The process of claim 2 in which the modifier is n-heptane.
4. The process of claim 2 in which the modifier is n-pentane.
5. The process of claim 2 in which the modifier is 2,2,4- trimethyl pentane.
6. The process of claim 2 in which the modifier is 2,2,4- trimethyl pentanel 7. The process of claim 2 in which the modifier is 2,4,4- trimethyl pentane-2.
8. The process of claim 2 in which the modifier is a normal C -C virgin naphtha.
9. The process of claim 2 in which the modifier is a l00-l 6 5 F. hydroformate.
10. The process of claim 2 in which the modifier is the 2l0-400 F. fraction made by polymerizing propylenes and butylenes with H PO on kieselguhr.
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