US3080311A - Gas oil hydrocracking process to produce a high octane gasoline - Google Patents

Description

March 5, 1963 T; S. MERTES GAS OIL HYDROCRACKING PROCESS TO PRODUCE A HIGH OCTANE GASOLINE Filed Sept. 15, 1960 Catalytic Straight Run Gas Oil Gas Oil H2 l0 ll Makeup I2 30 \A i Fr ction /35 Extraction mma a Naphthene Makeup l3 '6 Saturate g Fraction 3l\ Temperature //32 H2 Cracking t/l'l Si lice ous Catalyst with l4 Hydrogenating Temperature component Cracking 2o 24 (AlBr -HBr) 36 H Recycle HBr 37 Distillation Distillation Residuum R O -L|ghter Hydrocarbons Hydrocarbons Above Gasoline u \m Fraction -Isobutane G Naphthene 39 W 0 -6 Paraffins Heavy Gasoline Fraction High Antiknock Gasoline INVENTOR. THOMAS S. MERTES ATTORNEY United States Patent Qfifice 3,080,311 Phtented Mar. 5, 1963 Jersey Filed Sept. 15, 1960,.Ser. No. 56,198 2 Claims. (Cl. 208-78) This invention relates to a combination process for producing high antiknock gasoline from both straight run and catalytic gas oils by hydrocracking.

In application Serial No. 25,509, filed April 29*, 1960, now abandoned, a process is described which is capable of converting high boiling saturate hydrocarbons, such as the staurate portion of gas oils, substantially completely into saturate hydrocarbons boiling in the gasoline range. These product hydrocarbons, which are mainly C -C isopar-afiins and C and higher naphthenes, have high antiknock values and are suitable as components of high antiknock gasolines. The process'involves hydrocracking at relatively low temperature utilizing AlBr -HBr =as catalyst, and the reaction must be carried out in the presence of a substantial amount of one or more naphthenes of the C -C range. The reaction system is homogeneous and the reaction proceeds cleanly without any sludge forma tion.

One drawback to the process described in said application is that the charge stock must be essentially free of aromatics, since these hydrocarbons form sludges with the catalyst and prevent it from functioning in the manner desired. This circumstance necessitates the use of a feed preparation step for removal of essentially all of the mo matics from the gas oil feed stock. Since the resultin aromatic product generally would have to be sold as residual fuel oil at relatively low value compared to gasoline, this procedure, in effect, results in a downgrading of a portion of the gas oil stock.

The present invention involves a manner of utilizing the foregoing process advantageously in a combination system for converting both straight run gas oil and catalytic gas oil into high antiknock gasoline. Catalytic gas oils, which typically may have aromatic contents in the range of 3060% by volume, are not suitable charge stocks for the above-discussed process in view of the cost of separating the relatively high proportion of aromatics from the saturates and the low value of the aromatic portion. They are also not suitable charge stocks for conventional catalytic cracking processes because of the refractory character of the aromatics. However they can be cracked effectively into high octane gasoline by hydrocracking under conditions involving the use of a large proportion of hydrogen and a siliceous cracking catalyst containing a hydrogenating component.

A process of this type is described in Scott United States Patent No. 2,944,006. It involves the use of a catalyst containing a hydrogenating component, which is either nickel sulfide or cobalt sulfide, supported on an active siliceous cracking catalyst such as silica-alumina, silicarnagnesia, silica-zirconia and acid activated clays. The process is operated at temperatures between 350 and 700 F., with at least 1500 s.c.f. of H per barrel of con- Version product boiling below the charge and hydrogen partial pressure generally in the range of 500-2000 p.s.ig. The antiknock value of the gasoline product increases as the aromatic content of the charge increases. Normally the operation effects a conversion of 50-70% per pass and the material which boils higher than the desired gasoline product is totally recycled- Another process for hydrocracking catalytic gas oils is described in Hansford United States Patent No. 2,885 ,349. This process utilizes an acidic oxide cracking catalyst, such as silica-alumina, containing a hydrogenating component which is chromium sulfide derived by reduction of chromium sulfate. Conditions of operation include temperatures in the range of 7 50-1050 F., hydrogen input of 1000-10000 s.c.f. per barrel of feed and hydrogen pressures in the range of 500-5000 p.s.i.g.

In the present invention processes of the types mentioned in the above-discussed patent application and patents are utilized in a combination operation wherein both straight run gas oil and catalytic gas oil are converted to gasoline in the most eflicacious manner. According to the invention the straight run gas oil stock is treated in a manner to separate essentially all of the aromatics from the saturate fraction. The aromatics are then blended with the catalytic gas oil stock and the mixture is subjected to catalytic hydrocra-cking conditions in the presence of hydrogen and a siliceous cracking catalyst containing a hydrogenating component to produce catalytic gasoline. The saturate fraction is blended with a naphthene or mixture of naphthenes having 7-9 carbon atoms to form a blend containing 25-90% by Weight of the naphthene, and AlBr is dissolved in the mixturein amount of 25- by weight based on the total hydrocarbons. The mixture is then contacted in the presence of HBr with hydrogen under a partial pressure of 25-500 p.s.i. and at a temperature in the range of 0-100 C. for a time sufiicient to convert at least a major portion of the charge saturate content to hydrocarbons boiling in the gasoline range. In this reaction the C -C naphthene remains largely unconverted and can be separated from the reaction product and recycled. Also the hydrocarbons boiling above the gasoline range can be totally recycled, so that no material boiling above gasoline results from the operation.

The invention is described more specifically in conjunction with the accompanying drawing which is a schematic illustration of the present process. Referring to the drawing, straight run and catalytic gas oils enter the system, respectively, through lines 10 and 11. The straight run gas oil first goes to an extraction zone 12 wherein the aromatics are substantially completely separated from the saturates. While the extraction step could be carried out by solvent extraction utilizing an aromatic-selective solvent, e.g. furfural, and sufficiently efiicient extraction conditions to attain the necessary degree of separation, this would be costly in view of'the fact that the saturate product needs to be essentially aromatic-free. A distinctly better way of eiiecting the separation is by selective adsorption by means of silica gel. A particularly suitable selective adsorption process for this step is the Arosorb Process which is operated in cyclic manner as described on pages 109-113 of Petroleum Refiner, vol. 31, No. 5

(May 1952 issue). In such process, the charge stock, preferably diluted with a low boiling saturate solvent such as pentane, is passed through a bed of silica gel until the capacity of the bed for adsorbing charge aromatics is largely but not entirely depleted, after which a sufficient quantity of desorbent to desorb the charge aromatics completely is passed through the bed. The desorbent, which preferably comprises a component of high adsorbability such as benzene together with a component of low adsorbability such as pentane, is so selected that its boiling range is sutiiciently below the boiling range of the charge stock to enable easy separation of charge and desorbent components by distillation.

The efiluent from the adsorbent case, during each cycle of operation, is collected in two or more portions, one of which comprises charge saturates and desorbent, and another ofwhich comprises charge aromatics and desorbent. These portions are then separately subjected to fractional distillation in order to recover a charge saturate fraction, a charge aromatics fraction, and desorbent for recycle .to the process. For the present purpose the selective adsorption step is most economically operated under conditions such that the saturate fraction obtained is essentially aromatic-free while the aromatic fraction contains a substantial proportion of saturates, e.g. 20% by volume.- This allows the separation to be effected more readi ly than would be the case if a pure aroma-tic fraction also were to be produced. The saturates in the aromatic fraction are not reduced in value since they are readily cracked to gasoline in the subsequent hydrocracking of the aromatic fraction.

The aromatic-free saturate fraction obtained from extraction zone 12 is sent through line 13 to a low temperature cracking zone 14. Prior to entering this zone the saturate fraction is admixed with a recycle stream from line 15 which stream contains one or more naphthenes of the C -C range (indicated in the drawing as O; naphthene). A small amount of make-up C naphthene can be added to the system through line 16. The proportion of the hydrocarbon streams should be such that the C -C naphthene content of the mixture is in the range of 25-90% by weight, more preferably, 30-50%. Any naphthene of the C -C range can be used for this purpose. While it remains mainly unconverted in the sys tem, its presence in reaction zone 14 is important for obraining a clean reaction and avoiding sludge formation.

The catalyst used in reaction Zone 14 is AlBr in combination with HBr. The amount of AlBr present should be 25-l00% based on the weight of total hydrocarbons in zone 14. The amount of HBr used is not particularly important as long as at least a small amount is present, for example, 025% by weight based on the hydrocarbons. Hydrogen is fed into reaction zone 14 through line 17 and the amount so introduced should be sufiicient to maintain a hydrogen partial pressure in the range of 25-500 psi. The reaction temperature should be maintained in the range of -100 C., more preferably 25-75 C., and the reaction mixture should be agitated continuously to effect intimate contact with the hydrogen. The reaction mixture is homogeneous, and under the conditions specified essentially no sludge formation occurs. A sufiicient residence time in the reactor should be allowed to convert at least a major portion of the gas oil saturates to hydrocarbons boiling in the gasoline range.

The reaction mixture from zone 14 passes through line 18 to a distillation zone indicated diagrammatically at 19. I-lBr is first stripped from the mixture and passes back to cracking zone 14 through line 20. Isobutane, which is invariably produced in substantial yield, is removed next as indicated by line 21 and can be utilized in another process such as alkylation. The C -C parafiin products, which are preponderantly isoparaflins of high antiknock value, are removed as indicated by line 22. Then the C naphthene (or if desired a mixture of C -C naphthenes) can be recovered as indicated by line 23 and a part or all of this material is recycled through lines 24 and to cracking Zone 14 to maintain the necessary naphthene content of the reaction mixture. Only a small amount of the naphthene originally used is converted to other products in the reaction and hence in no event is any large make-up of naphthene through line 16 required. In fact, when only a C naphthene such as methylcyclohexane is originally used, not only is the extent of disappearance of the C naphthene small but C and C naphthenes generally are produced in substantial amounts from the gas oil saturates. Hence sufiicient C -C naphthene can be recycled to maintain the desired naphthene content in zone 14 and no make-up whatever is required through line 16.

A heavy gasoline fraction, which boils above the cut point of the naphthene cut, is distilled and removed through line 25, leaving as residue hydrocarbons boiling above the gasoline range with AlBr dissolved therein or both dissolved and dispersed therein depending on AlBr concentration and the temperature. of the stream. This material is recycled through lines 24 and 15 for re-use of the AlBr and further conversion of the hydrocarbons to gasoline. The heavy gasoline fraction is composed essentially entirely of naphthenes boiling above the cut point of the recycle naphthene fraction together with isoparaffins, and it also has a high antiknock value.

Referring back to the aromatic fraction which is obtained from extraction zone 12 via line 30, this material is blended with the catalytic gas oil from line it and with recycle material from line 31 and the material is fed to cracking zone 32 which operates at considerably higher temperature than is used in cracking zone 14. The proper temperature level in zone 32 depends to considerable extent upon the particular catalyst being used but in any event falls within the general range of 350-1050 F. The catalyst is composed of a hydrogenating component deposited on an active siliceous cracking catalyst support, such as described in the aforementioned United States Patent No. 2,944,006 and Patent No. 2,885,349 wherein the hydrogenating components are nickel sulfide, cobalt sulfide or chromium sulfide. Other hydrogenating components that can be used are the sulfides of iron, molybdenum and tungsten, the oxides of iron, nickel, chromium, molybdenum and tungsten, platinum, rubidium and rhodiurn. Hydrogen in amount of 1000-2500 s.c.f. per barrel of mixed hydrocarbon feed is introduced through line 33 into cracking zone 32 and a hydrogen partial pressure in the range of 500-5000 p.s.i. is maintained therein. The hydrogen stream is composed of recycle hydrogen from line 34 together with make-up hydrogen admitted from line 35.

The efiluent which leaves cracking zone 32. via line 36 is passed through suitable separating means (not shown) for recovering the excess hydrogen and then into distillation zone 37. The hydrocarbons are fractionated to remove C, and lighter hydrocarbons as indicated by line 33 and a debutanized gasoline as shown by line 39. The residuum, composed of hydrocarbons boiling above the gasoline range, can all be withdrawn through line 40 as a fuel oil product but preferably is at least mainly recycled through line 3-1 for further conversion to gasoline. The gasoline fraction from line 39 can be blended with the C -C paratfins from line 22 and the heavy gasoline fraction from lines 25 and 41 to yield a high quality gasoline product.

In order to illustrate advantages of the present process, the following comparison is made between a process operated according to the aforesaid application Serial No. 25,509 for the purpose of processing 10,000 bbls./ day of straight run gas oil and the present process operated to hydrocrack a total of 10,000 bbls./ day of gas oils comprising 6,667 hbls/day of straight run gas oil and 3,333 bbls/day of catalytic gas oil. It is assumed that the straight run and catalytic gas oils have aromatic contents of 20% and 40% by volume, respectively.

The following data show the processing capacities required for the two operations and the products obtained:

From the data presented it can be seen that the present process requires less total plant capacity and produces a considerably larger volume of gasoline without any production of fuel oil. Also the gasoline produced has an appreciably higher antiknock value.

I claim:

1. A process for cracking straight run gas oil and catalytic gas oil which comprises contacting a straight run gas oil stock With silica gel to obtain an aromatic fraction and a saturate fraction essentially free of aromatics, blending said aromatic fraction with a catalytic gas oil stock, subjecting the blend of aromatic fraction and catalytic gas oil stock to catalytic hydrocracking conditions in the presence of hydrogen and a siliceous cracking catalyst containing a hydrogenating component at 35 0-105 0 F. to form catalytic gasoline, forming a reaction mixture comprising said saturate fraction and 25-90% by weight, based on the total hydrocarbon content of the reaction mixture, of monocyclic naphthene having 7-9 carbon atoms yer molecule, said reaction mixture also containing 25-100% by weight, based on the hydrocarbon content, of AlBr contacting the reaction mixture in the presence of HBr with hydrogen under a partial pressure of hydrogen at 25-500 p.s.i. at a temperature in the range of 0100 C. for a time sufiicient to convert at least a major portion of said saturate fraction in the reaction mixture to hydrocarbons boiling in the gasoline range, and blending said catalytic gasoline and said hydrocarbons boiling in the gasoline range to yield a gasoline product of high anti-knock value.

2. A process according to claim 1 wherein said hydrogenating component is selected from the group consisting of nickel sulfide, cobalt sulfide, and chromium sulfide.

References Cited in the file of this patent UNITED STATES PATENTS 2,326,627 Eglofi et al Aug. 10, 1943 2,627,495 Lanning Feb. 3, 1953 2,885,349 Hansford May 5, 1959 2,908,628 Schneider et -al i Oct. 13, 1959

Claims (1)

1. A PROCESS FOR CRACKING STRAIGHT RUN GAS OIL AND CATALYTIC GAS OIL WHICH COMPRISES CONTACTING A STRAIGHT RUN GAS OIL STOCK WITH SILICA GEL TO OBTAIN AN AROMATIC FRACTION AND A SATURATE FRACTION ESSENTIALLY FREE OF AROMATICS, BLENDING SAID AROMATIC FRACTION WITH A CATALYTIC GAS OIL STOCK, SUBJECTING THE BLEND OF AROMATIC FRACTION AND CATALYTIC GAS OIL STOCK TO CATALYTIC HYDROCRACKING CONDITIONS IN THE PRESENCE OF HYDROGEN AND A SILICEOUS CRACKING CATALYST CONTAINING A HYDROGENATING COMPONENT AT 350-1050*F. TO FORM CATALYTIC GASOLINE, FORMING A REACTION MIXTURE COMPRISING SAID SATURATE FRACTION AND 25-90% BY WEIGHT, BASED ON THE TOTAL HYDROCARBON CONTENT OF THE REACTION MIXTURE, OF MONOCYCLIC NAPHTHENE HAVING 7-9 CARBON ATOMS PER MOLECULE, SAID REACTION MIXTURE ALSO CONTAINING 25-100% BY WEIGHT, BASED ON THE HYDROCARBON CONTENT, OF ALBR3, CONTACTING THE REACTION MIXTURE IN THE

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