US2925376A - Hydrocarbon conversion - Google Patents

Description

Unite t res i may be obtained. it

g'et'her with recycle. hydrocarbons,

Thisrv inyention relates doth catalytic conversidn. hydrocarbon fractions and more particularly to ,a process atent ri'ice a I 2,925,376 Patented Feb. 16, 1960 soil; "of the gas toil'is solvent extracted to yield a raffinate irme l tt ll l crac ng res du oils whe e nv an n.- creased yieldofgasoline and valuable aromatic fractions 7 While residual crude oils a rei not-:favored as;the charg to a; catalytic cracking operation sincethey contain large amounts of coke-formers. and' catalysti-deactiyating metal ednipounds; inIa'reas where heavy fuel is in t yelf-supply, tand;

s bm f u l stsv r i tstn f n 'escn m v 4 point, "to crack such'stocks; and ,commercialgprocesses,

'suchasthe; Houdresid process; have been 'developed toj processr' ed1.1c ed c'rudes In; such proc esses fthe crude, to I e d l n t ajcbnsiderablelquaritity ofsteam, wh chjserves to reduce the partial ressure; of the? hydrocarbons and lessen coke depositiomfto areactor'inwhich the'hydrocar bons are contacted at temperatures of from about 850 F.- to 1000. F., with; a cracking catalyst such asbauxite, acti ven which; atpresent'market prices, is'worth'more. than t gasoline and abettorns product valuable as carbon black vated clay or syntheticsilica-alumina gel; The' products from thef-cracking foperation fare thenl'fractionated-r to produce a C and lighter'cut, agasoline out, and higher.

boiling hydrocarbons, This higher but contains themore refractory components ofth 'el charge and cannot be: re-.

cycled in its entirety to thejcrackingloperationsince excessive' amounts of coke i'r/Io'uld belaid down on theacatalystf-l'eading to. rapidfd'activation thereof. in oraetn o make the cracking process economically attractive, how 3 over, some of 'thishigher 'boiling must ibefiecycled; othersoldas lowpriced fuel oilsif wis some 60, ,percenfoff he cracked products must" be One presently operatlng commercial process 'is olveisl bo fpofl ns, higher than gasoline into a fraction bo ling in the 400- t the problem by fr'actio nating' thefh which. is recycled 'to 'the-catalytic c1 ackingstep, aridan' extractewhich. is thermally. cracked Anotherprior art;

' t proposal is :torsblventzextract-all of; the crackedproductsfl boiling abovegasolineiresulting fr mthe cataIytic'crack- I v fii'ng of :a'; gas oil, torecycle the rafi'inate' to the' catalytic j 1 I :cracking-step', and to send theektractgto'thermalcracking;

a lhe present' invention is also conc erned with a p'roc'ess in whichaportion of the cracked :productsisulting froin' the? catalyticrcrackingi :of a: hydrocarbon: feed sto clt iti solvent 'extracted with the rafiihate being returned to the cracking step, but is;limited to aprocesstin'which the I hydrocarbon feed is a reduced crude., In-accordance with the invention, the cracked products are fractionated-to v yieldi a gasoline fractiomia fraction; boiling in the 400- 500" F. range, a gas oil fraction, and a bottoms'fraction co'mprisi'ngfrom;aboutj25% to 35% by volume of. the 1 feedto thet crackentandboilingtlargely above'-7 50.,F-.'

The; 4004-500 fraction is, a, light-colored; stable productvaluable asaiNo; ;2' fuel oil component. The gas oil fraction-is recycled to the; cracker without further :treatment and willusually-comprise about-15m 25 percent of theffe'ed.thereto;;1-; The bottoms, fraction is solvent'exitracted to, remove about 25; to 3 5i percent thereof as ex:

tractg'andj the raffinateisgreturned to the cracker as a, feed componen -g T qext al t mayytb be r r a y tilledrt yield, ,as an overhead product an aromaticsola r r @The process of. the 1 present invention distinguishes from the prior. art in many respects. First, no products oflow value are produced, such asthe-heavy fuel oil produced in the, commercial process described above, ,or

the tars produced in the prior art process described above.

Second, a stable No. 2 fuel oilis produced. This fraction is largely lost in processesin which the'light gas oil is recycledto catalytic cracking, 1 since it is of-relatively low'mo-lecular'weight, andsince cracking catalysts direct splitting of-the moleule toward the center, products or: cracking; this fraction], are largely coke and normally gaseous hydrocarbons '-A third point of differentiation ijthat onlyasmallfportion of the cracked products, in.-

V and also to produce a valuable aromatic solvent and a I carbon black oil from the highest boiling components fraction boiling largely between 600 F. and 800", E,

which is recycled to the crackingtstep, and la highly re-.

fractory bottoms; boiling largel'y above SOOPF. which is I useful only for sal'e as}low-prRiedheayysfuel"oil; By 7 'such fractionation, about 10%'ofthecrackedprodu "ts are burn the carbon ofl the catalyst.

formers, which deposit anexcessive amount of coke dun ing the cracking operation, necessitating the provision of ,overly large catalyst regeneration facilities in order to Proposals have also been made for treating cracked products boiling above gasoline-by solvent extraction to" remove aromatics and thus re'ducethe coke-formers 'in oil fraction, and a tar bottoms; or the heavier pereluding all the highest boiling components, is extracted;

By proceeding according to they present, invention, it is.

possible to minimize the-size of the extraction equipment,

of the cracked products; Neither ofthese productst'are produced in the-prior artprocesses v a c llow sheetof the processw eed 'vvhichji s emaciated The mixed feed, in the amount of 12,300 b./d., is then 925 F, and thence through line 3'10 a reactor 4, in

which itiis contacted. with a-silica-alumina catalyst and steam: in a manner well known to the art atatemperature ofabout925" F.

Conversion products are taken through line 5 to fractionating tower 6, from which 1840 b./d. of C and lighterhydrocarbons are taken overhead for further procrder t atthoserskilled in the art may more fullyr natured-my inv i na d the m t od f;

,an example will be more fullyi described g: with ,the accompanying drawing which is l and with 24 6O,'.b.[d."ofia distillaterecyclestream obtained I from a later stage of the process as hereinafter described.

essing through line 7. A side stream of 4220 b./d. of gasoline boiling from 110-430 F. is recovered through line 8; 650b./d.. ofa side stream boiling from 390 F. to 525 F. are taken off through line 9 for sale as No.2 fuel oil; and 2460 b./d. of recycle gas oil are removed from a lower point in the column and are passed through line 10 to admixture with the incoming fresh feed.

Bottoms amounting to 3790 b./d. is removed from 1 fractionator 6 through line 11 and is passed to a furfural extraction plant 12 in which it is separated into 2740 b./d. of a 20. A.P.I. rafiinate, which is cycled through line 13 to admixture with incoming fresh feed, and 1050 b./d. of aromatic extract of 1 A.P.I. gravity. Furfural extraction plant 12 consists of a contacting tower or other contacting means, together with solvent recovery facilities. purpose would be served by describing them in detail herein.

- The extract, which is over 90% aromatic, is taken through line 14 to a fractionating tower 15, in which it is separated into 760 b./d. of an aromatic solvent and 290 b./d. of a high-grade carbon black oil.

' The improvement in results obtainable by my new process over those obtained in conventional cracking of residual stocks without solvent extraction may be seen from the following table, in which column A shows the productdistribution, in percentages of the total feed to .thecatalytic cracker, obtained by proceeding according to present-day commercial practice, that is, by recycling 5200 b./d. of distillate gas oil to the process "to make up a total of 12,300 b./d. of feed to the cracker. Column B shows the results obtained when operating according to the procedure of the foregoing example. In column A, coke formation and dry gas formation were the limiting factors, whereas, in column B, conditions were adjusted to give about 35% gasoline yield per pass.

Table I Product-Percent of Feed Dry Gas and lower) Butyleues Pentanes and Butanes Cs+Gasoline No.2 Fuel.

Carbon Black Oil Total Recovery, 04 and higher. Coke make, lb./hr

to H

s weps psm e-es ore-GenocmoWboMoMo i dry gas have been considerably reduced, low-priced heavy fuel oil has been eliminated as a product, and total recovery of C and higher hydrocarbons has been increased by 2.2%. Reduction in coke yield is particularly important in those installations in which catalyst regeneration capacity is the limiting factor, since with lower coke make, a larger amount of feed hydrocarbons may be processed in the same equipment.

Since such facilities are well known to the art, no

4 I claim: 1. A process for the conversion of residual petroleum 7 fractions which comprises mixing a reduced crude feed stock with a recycle gas oil fraction and a recycle raflinate fraction, both of said latter fractions being recovered from a later stage of the process; contacting the mixture with a cracking catalyst in a cracking zone at cracking temperatures; recovering an'effiuent from the cracking zone; subjecting the eflluent to fractional distillation to recover as separate streams a C and lower fraction, a gasoline fraction, a No. 2 fuel oil fraction boiling in the 400-500 F. range, a recycle gas oil fraction, and a bottoms fraction amounting to about 25 to 35 volume percent of the total feed tothe cracking zone and boiling largely above 750 F.; recycling the recycle gas oil fraction to admixture with the reduced crude feed stock; contacting the bottoms fraction with a solvent selective for the extraction of aromatic hydrocarbons;.recoverin'g a solvent-free rafiinate of reduced aromaticity as compared "to the bottoms fraction, in an amount equal to from about to volume percent of the bottoms; recycling the raffinate to admixture with the reduced crude feed stock; recovering a solvent-free extract from the solvent extraction step, subjecting the extract to fractional distillation, recovering as an overhead fraction an aromatic solvent oil, and recovering a carbon black oil as a bottoms fraction. Y I a 2. A process for the conversion of residualipetroleurn fractions which comprises charging a feed stock comprising a reduced crude fraction, a recycle gas oil 'frac tion, and arecycle raflinate fraction, the latter two free tions being recovered from a later stage of the process to a cracking zone, contacting the feed therein with a cracking catalyst at cracking temperatures, recovering an effluent from the cracking zone, subjecting the effiuent to fractional distillation to recover hydrocarbons boiling below about 500 F., a gas oil fraction boiling abojve 500 F., and a bottoms fraction in volume equalling about 25 to 35 volume percent of the feed to the cracking zone and boiling largely above 750 F., recycling the gas oil fraction to the cracking zone, contacting the bottoms fraction with a solvent selective for the extraction of aromatic hydrocarbons, recovering a solvent-free raffinate of reduced aromaticity as compared to the bottoms fraction in an amount equal to from about 65% to 75% of the bottoms, recycling the rafiinate to the cracking zone, recovering a solvent-free extract from the solvent extraction step, subjecting the extract to fractional distillation, recovering as an overhead fraction anaromatic solvent oil, and recovering a carbon black oil as a bottoms fraction.

References Cited in the file of this patent UNITED STATES PATENTS

Claims (1)

1. IN A PROCESS FOR THE CONVERSION OF RESIDUAL PETROLEUM FRACTIONS WHICH COMPRISES MIXING A REDUCED CRUDE FEED STOCK WITH A RECYCLE GAS OIL FRACTION AND A RECYCLE RAFFINATE FRACTION, BOTH OF SAID LATTER FRACTIONS BEING RECOVERED FROM A LATER STAGE OF THE PROCESS, CONTACTING THE MIXTURE WITH A CRACKING CATALYST IN A CRACKING ZONE AT CRACKING TEMPERATURES, RECOVERING AN EFFLUENT FROM THE CRACKLING ZONE, SUBJECTING THE EFFLUENT TO FRACTIONAL DISTILLATION TO RECOVER AS SEPARATE STREAMS A C4 AND LOWER FRACTION, A GASOLINE FRACTION, A NO. 2 FUEL OIL FRACTION BOILING IN THE 400-500* F. RANGE, A RECYCLE GAS OIL FRACTION, AND A BOTTOMS FRACTION AMOUNTING TO ABOUT 25 TO 35 VOLUME PERCENT OF THE TOTAL FEED TO THE CRACKING ZONE AND BOILING LARGELY ABOVE 750* F., RECYCLING THE RECYCLE GAS OIL FRACTION TO ADMIXTURE WITH THE REDUCED CRUDE FEED STOCK, CONTACTING THE BOTTOMS FRACTIONS WITH A SOLVENT SELECTIVE FOR THE EXTRACTION OF AROMATIC HYDROCARBONS, RECOVERING A SOLVENT-FREE RAFFINATE OF REDUCED ARMOTICITY AS COMPARED TO THE BOTTOMS FRACTION, IN AN AMOUNT EQUAL TO FROM ABOUT 65 TO 75 VOLUME PERCENT OF THE BOTTOMS, RECYCLING THE RAFFINATE TO ADMIXTURE WITH THE REDUCED CRUDE FEED STOCK, RECOVERING A SOLVENT-FREE EXTRACT FROM THE SOLVENT EXTRACTION STEP, SUBJECTING THE EXTRACT TO FRACTIONAL DISTILLATION, RECOVERING AS AN OVERHEAD FRACTION AN AROMATIC SOLVENT OIL, AND RECOVERING A CARBON BLACK OIL AS A BOTTOMS FRACTION.

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