US3023158A - Increasing the yield of gasoline boiling range product from heavy petroleum stocks - Google Patents

Description

Feb. 27, 1962 c. H. WATKlNS 3,023,158

INCREASING THE YIELD OF GASOLINE BOILING RANGE PRODUCT FROM HEAVY PETROLEUM STOCKS Filed March 21, 1960 Charge Stoc/r I l Hydrogen Hydrorefining Zone 5 7 NH3 f SeparoI/on 7 Zone v n s 6 26 :9 H Light, Gaseous Hydrocarbons Aromatic Extracting Zone /2 -/4 '26 /3\ I //5 Extract Raff/note Recovery Recovery Zone Zone Hi h Boi/in /6\ Grac%ed Pro act /77 Hydrogen /8 fag Hydrocrac/ring gf g I Zone Zone,

20 3/ 2/ f 32 Separation Separation 7 Zone 1 Zone Light Gases Light Gases liVVE/VTOR: 27 v 25 Char/es H, Watkins I i B).- Jet Fuel Products Gasoline Products 5% A rromvgys 3,023,158 IN CREAING TIE YIELD F GASOLINE BQILHJG RANGE PRGDUCT FRSM HEAVY PETROLEUM SEOCKS Charies H. Watkins, Arlington Heights, ill, assignor to Universal Gil XQHS Company, Des Plaines, 11L, a corporation of Delaware Filed Mar. 21, was, Ser. No. 16,312 9 Claims. (Ci. 20889} This invention relates to a process for converting high boiiing hydrocarbon stocks into a gasoline boiling range product by a combination process in which each of the several stages are peculiarly adapted to convert the particular class of components present in the charge stock into desirable gasoline components, effecting such conversion of the separated components at the most economical and practical conditions suited to these components. More specifically, this invention relates to a combination process in which the aromatic components of a high boiling petroleum fraction are recovered therefrom and separately hydrocracked in a process involving a catalyst particularly adapted to the conversion of the aromatic components and separately converting the parafinic, aliphatic components of the feed stock in a catalytic cracking stage and at conversion conditions adapted to the production of gasoline boiling range products and thereafter blending the gasoline fractions of each of the hydrocrack-' ing and catalytic cracking stages to form a motor fuel product.

Extensive study of the problem of converting high boiling petroleum charge stocks into more useful gasoline boiling range materials has indicated that the hydrocracking process is especially suitable for yielding a motor fuel boiling range product of high quality. The termhydrocracking is a descriptive term of the art which characterizes a conversion process in which the hydrocarbon charge stock, boiling above the gasoline boiling range and comprising a mixture of relatively long chain hydrocarbons containing 12 or more carbon atoms per molecule is subjected to reaction conditions in which the hydrocarbon components of the charge stock tend to undergo scission or cracking in the presence of hydrogen at a superatomospheric pressure, any olefinic or aromatic components involved in the process being simultaneously converted into their naphthenic and/or paraifinic analogs of substantially shorter chain length than the hydrocarbons comprising the charge stock and involved in the convere sion. The reaction is carried out in the presence of a catalyst comprising a cracking component, usually an acid-actin g support, such as a calcined silica-alumina composite, and a hydrogenating component, usually a metal selected from the elements of group VIII of the periodic table, such as palladium or platinum. It is also known that the long chain aliphatic components of the charge stock may be more conveniently or economically converted to shorter chain hydrocarbons boiling in the gasoline range by cracking these hydrocarbons directly in the presence of a cracking catalyst, such as the aforementioned silica-alumina composite. It has been found, however, that the aromatic components which generally accompany the aliphatic compounds present in high boiling hydrocarbon feed stocks do not readily undergo cracking reactions in the presence of a catalyst containing only cracking components but, instead, are converted in large measure into carbon and'light, non-condensable gases, such as hydrogen, methane, ethane, etc. The aromatic components, if separated from the feed stock, however, can be conveniently and economically converted into gasoline boiling range products in a separate hydrocracking reaction without significant production of carbon and/or light hydrocarbon gases. By thus separating the and nitrogenous contaminants which comprises hydroc l i aromatic and aliphatic portions of the high boiling charge stock in a preliminary step, a process for handling such charge stocks whereby optimum yields and products of optimum quality boiling in the gasoline range are obtained The present invention. provides a combination process wherein the separated alifrom each stage of the process.

These detrimental effects are usually evidenced by a marked reduction in the catalytic activity of the cracking and hydrocracking catalysts, necessitating the use of. more severe conversion conditions in both stages of the process. Accompanying such higher conversion temperatures, both stages of the process yield an excessive proportion of light hydrocarbon gases which are the uneconomical end products of the cracking and hydrocracking reactions. bus, the presence of the nitrogenous and sulfur-containing contaminants in the feed stock rapidly reduces the capacity of the catalyst to effect the desired cracking reaction, requiring the use of ever increasing temperatures in order to overcome the loss in cracking activity of the catalyst. The net effect of such nitrogen and sulfur-containing contaminants in the feed stock is a reduction in the net yield of the desired gasoline boiling range product from a given quantity of charge stock and the requirement of more frequent reactivation of the catalyst by virtue of the deposition of carbonaceous residues on the catalyst which accumulate and accelerate the deactivation of the catalysts. In order to recover at least part of the activity of the catalyst the reactor must be shut down and the catalyst removed or reactivated in place by passing through the catalyst bed a stream of an oxygencontaining gas. These procedures necessitate additional plant equipment and frequent costly interruptions of the process, as well as hastening the ultimate complete, irretrievable deactivation of the catalyst.

in accordance with the present combination process, the nitrogen and sulfur-containing contaminants present in the high boiling feed stock are removed prior to the cracking and extraction stages of the process in a preliminary hydrorefining treatment wherein the charge stock, together with an atmosphere of hydrogen, is passed at hydrorefining conversion conditions through a bed of catalyst of particular composition especially adapted to the conversion of the nitrogen and sulfur-bearing contaminants present in the feed stock into ammonia and hydrogen sulfide which can be separately removed in a treatment preceding the extraction stage of the present process.

The objective of the present combination of process steps, therefore, is to economically convert high boiling charge stocks derived from petroleum and containing organically-bound nitrogen and sulfur compounds into an ultimate gasoline boiling range product of high quality for motor fuel use. Another object of this invention is to provide a means of converting a high boiling hydrocarbon charge stock into a gasoline product and maxi: mizing such conversion.

In one of its embodiments this invention relates to a process for converting a petroleum stock boiling above the gasoline range and containing aromatic components Patented Feb. 27, 1962 extract separate from a non-aromatic railinate, catalytically hydrocracking said aromatic extract in the presence of a catalyst containing hydrogenating and cracking catalyst components, catalytically cracking said railinate, and blending the gasoline boiling range fractions of the cracked and hydrocraclted products.v

Specific embodiments of this invention relate to particular process conditions and to specific methods of recycling certain fractions of the product, such as the residualbottoms of the hydrocracked product, after separation of the gasoline boiling range fraction from the hydrocracked product, to the inlet of the hydrocracking stage or to the inlet of the extraction stage of the process.

The flow diagram of the process involved in the present invention is diagrammatically illustrated in the accompanying drawing to which reference is hereby made for further description of the invention. The charging stock to the present process, herein referred to generally as a petroleum fraction boiling above the gasoline boiling range fraction, is charged into the process fiow through line 1 of the diagram. Typcial of the charge stocks boiling above gasoline are the so-called gas oil fractions which includes the upper end of the gasoline boiling range fraction, kerosene, and the higher boiling cuts of petroleu 1., such as the lubricating oil fractions having a top boiling range limit of about 900 F. These charge stoc is may be derived from any suitable source, although highly aromatic and condensed ring hydrocarbon fractions are particularly adapted for use as charge stock herein. In the event that a stock boihngin the lube oil range is charged to the present process, it is desirably diluted with a relatively light parafiin diluent, such as hexane, heptane or a small amount of a gasoline boiling range fraction in order to reduce the viscosity of the stock, particularly during the stages of the process operated at relatively low temperatures.

The charge stock, together with hydrogen introduced through line 2, enter hydrorelining zone 3, containing a hydrorefining catalyst maintained at hydrorefining reaction conditions. Hydrogen at a pressure preferably above 500. lbs. per square inch, up to about 3000 lbs. per square inch, and more preferably from about 1000 to about 2000 lbs. per square inch enters zone 3, at a rate equal to at least 500 standard cubic feet per barrel ofliquid' charge stock. The catalyst provided in zone 3-, is a supported hydrogenation catalyst comprising a metal of group VIII of the periodic table, such as one of'the iron group metals, including nickel, cobalt or iron or one of the platinum group metals, such as palladium, platinum, iridium, or ruthenium on a support consisting of one or more refractory, inert metal oxides. The iron group metals are preferably combined with a metal or oxide of a metal selected from group VI of the periodic table, preferably molybdenum in the metallic state or in the form of a compound of molybdenum. The refractory metal oxide support for the hydrogcnating component of the catalyst is an oxide inert in the reaction, such as'alumina, zirconia, thorium oxide, magnesia, mixed metal oxides such as alumina-zirconia, alumina-magnesia or a clay, in which the composition of the mixture of oxides may be varied within rather wide ranges to provide operable catalyst composites. The preferred metal oxide base is alumina. The hydrorefining conversion provided in zone 3 is preferably eifected at a temperature within the range of from about 600 to about 900 F. and more preferably from about 650 to about 800 F; The actual conditions maintained in zone 3 will depend to some extent upon the type of nitrogenous compound contaminating the charge stock and. the diificulty encountered in converting this compound to free ammonia to the extent required to form a liquid reaction product containing less than about 5 ppm. of total nitrog As previously indicated, the nitrogen content of the liquid portion of the hydrorefined product has a pronounced effect upon the, activity of the hydrocracking and cracking catalysts utilized in the subsequent stages" of the process. Thus, it has been found that by reducing the nitrogen content of the feed stock to the hydrocracking and cracking stages of the process to less than 5 p.p.m. total nitrogen (from a nitrogen content in the charge stock of generally above about 1500 ppm.) the cracking and hydrocracking stages may be operated for long periods of time without regeneration of the catalyst and without significant reduction in the activity of the catalyst for the desired cracking and hydrocracking purposes. It is therefore essential for the proper operation of the cracking and hydrocracking stages of the present process that the nitrogen content of the liquid portion of the hydrorefined product be reduced to less than 5 p.p.m., and preferably to less than 1 ppm. in order to effect the cracking and hydrocracking stages of the process with the accompanying aforementioned advantages.

The mixed phase reaction product of hydrorefining zone 3 is withdrawn therefrom through line 4, and discharged into separation zone 5 wherein the normally gaseous and normally liquid portion of the hydrorefined products are separated for further processing in accordance with the present invention. The mixture of gaseous and normally liquid products present in the product of the hydrorefining reaction charged into separation zone 5, is generally separated into a light, normally gaseous fraction comprising ammonia, hydrogen sulfide (formed by the reaction of hydrogen with the sulfur compounds normally present in the feed stock), unconconverted hydrogen and light hydrocarbon gases, such as methane, ethane, etc. Ammonia may ordinarily be removed from the light gaseous fraction by washing the latter with a dilute aqueous solution of a m'neral acid, such as sulfuric acid, or by passing the mixture of gases over a cationic, ion-exchange resin, the ammonia being removed through line 6, from zone 5. Hydrogen sulfide is generally recovered from the recycle hydrogen gas by solvent extraction with an organic solvent, such as ethylene or diethylene glycol and removed from the process flow through line 7. The residual light gases, comprising generally a mixture of hydrogen and methane, are recovered from the hydrogen sulfide extractor and desirably recycled to the hydrorefining zone, being charged into the inlet of the hydrogen stream thereto through line 8, connecting line 7 with line 2. The re maining light gaseous hydrocarbons, generally containing C to C paraffins, olefins and diolefins, is removed fromseparation zone 5, through line 9, and discharged from the process.

At the foregoing preferred hydrorefining reaction conditions, maintained in the hydrorefining reaction zone 5 util'zing hydrogen at a high pressure and a catalyst which effects the hydrorefining conversion at relatively low temperatures, the yield of undesired light gaseous hydrocarbons produced in the hydrorefining conversion is low and a large proportion of the charge stock is retained as liquid, non cracked, paraffinic and naphthenic hydrocarbons.

. The normally liquid portion of the hydrorefined product, after separation of ammonia, light gaseous hydrocarbons, hydrogenand hydrogen sulfide therefrom is re' traction procedure with either a liquid solvent or a solidadsorbent which preferentially extracts the aromatic components from the liquid hydrorefined stock. By

aoasnaa extraction is meant to include any form of separation procedure for recovering aromatic components from a mixture of hydrocarbons, including extraction by adsorp tion of the aromatic hydrocarbons on a solid adsorbent, liquid-liquid solvent extraction, extractive distillation, molecular'sieve separation, or urea or thiourea clatharation procedures. The wide variety of methods and procedures utilized by the prior art for recovery of aromatic components from liquid hydrocarbon mixtures are contemplated herein as suitable extraction methods and are within the scope of the term extraction as utilized herein. One of the preferred procedures, for separately recovering the aromatic and non-aromatic hydrocarbon components of the hydrorefined product is the liquid-liquid solvent extraction process wherein the liquid portion of the hydrorefined product is contacted, preferably under countercurrent liquid-liquid flow conditions, in a suitable contacting tower with a solvent which is selec tively miscible with the aromatic components of the feed stock, thereby producing a rich solvent streamcontaining the dissolved aromatic components of the feed stock and a separate non-aromatic rafiina'te phase which is removed overhead from the solvent extraction zone and separately treated in accordance with the process of this invention. The rafiinate removed from the extraction zone is desirably water-washed to remove the normally small amount of solvent that dissolves in the hydrocarbon stream by virtue of the contact in the solvent extraction tower. The rich solvent stream comprising the aromatic components of the feed stock dissolved in the liquid phase solvent solution is removed from aromatic extraction zone 11, through line 12, into extract recovery zone 13, wherein the dissolved aromatic components of both monoand polycyclic structure are recovered from v the rich solvent for example, by stripping. Most solvents utilized for solvent extraction purposes in the recovery of aromat c components from hydrocarbon stocks contain water, the stripping operation being primarily steam stripping which is effectively accomplished by merely heating the rich solvent stream to a temperature above the boiling point of the rich solvent, While introducing steam, if desired, into the bottom of the extract recovery zone.

Another effective method of recovering components of the hydrocarbon feed stock, pecially preferred when the charge stock is a viscous, high boiling point oil which is diluted with a light naphtha to reduce viscosity, is the method referred to as adsorption in which the stock is passed through a stationary bed of solid adsorbent, such as silica gel partcles or charcoal, the aromatic components being retained by the adsorbent and the non-sorbed raffinate passing through the column as efiluent. In the latter adsorption method, the extracted aromatic components retained on the solid adsorbent are generally removed therefrom by means of heat supplied to the extract recovery zone as the sensible heat of a heated inert gaseous desorbent or as a hot liquid desorbent such as a light parafiin naphtha heated, for example, to above about 100 R, up to 400 F.

The non-aromatc raflinate is recovered from extraction zone 11 through line 14, the raffiuate efiluent being discharged into zone 15 wherein any residual solvent contained in the raftinate stream is removed therefrom, for example, by distillation or by washing with water. The raffinate thus recovered in zone 15 is dscharged therefrom through line 17.

Suitable solvents for use in the aromatic extraction zone may be selected from a wide variety of organic compounds, such as the alcohols, the glycols, the polyglycols, the phenols, the amines, the ethers, etc. One of the preferred solvents for aromatic extraction is an aqueous solution of a polyglycol, such as diethylene or triethylene glycol, with or without added quantities of dipropylene or tripropylene glycol in admixture therewith the aromatic a method csand containing from 1.0 to about 15 percent by weight of water.

In accordance with the process herein provided, the aromatic extract recovered from the hydrorefined feed stock is separately subjected to hydrocracking and the parafiinic raifinate portion of the hydrorefined feed stock is separately subjected to catalytic cracking, each of the reactions being effected in separate zones in order to obtain maximum conversion of each of the fractions to gasoline boiling range products of high quality for motor fuel use. Hydrocracking of the aromatic extract, however, is feasible only if and when the nitrogen-containing contaminants present in the original charge stock and inherently transferred into the aromatic extract during the extraction stage, are removed prior to the extraction stage to a nitrogen level less than 5 ppm. The hydrorefining stage ofthe present combination process is designed, when operated at'sufiiciently severe conditions,

to convert all of the nitrogenous compounds originally present in the feed stock into ammonia which when stripped from the hydrorefined stock will reduce the total nitrogen content of the stripped stock to less than 5 ppm. of nitrogen. Only when the nitrogen content of the feed to the hydrocracking step is reduced to 5 ppm. or less will the catalyst used in the hydrocracking step remain active for a sufilcient period of on-stream use to be practically feasible.

Hydrocracking is effected in zone 18 in the presence of a catalyst comprising a cracking component and a hydrogenating component, both components of the catalyst acting simultaneously to etfect the intended conversion. Suitable hydrocracking catalysts contain from about 0.5 to about 15 percent by weight of the hydrogenating component, selected from the metals, sulfides and oxides of the elements of group VIII of the periodic table, particularly nickel and/or cobalt, composited with a cracking catalyst base and preferably containing from about 4 to 20 percent by weight of molybdenum or a molybdenum compound such as the molybdate or thiomolybdate salts of the iron group metal. Other group VIII metals suitable as the hydrogenating compounds of the hydrocracking catalyst are platinum, palladium and ruthenium which are present in the catalyst in amounts of from about 0.01 to about 5 percent by weight, composited with the cracking catalyst base. The base may consist of a composite of silica-alumina, silica-zirconia, silica-alumina-zirconia, alumina-b-oria, silica-magnesia or an alumina support containing from 0.1 percent to about 5 percent by weight of combined halogen, selected from either or both fluorine and chlorine. It has been found through comparative tests of various catalysts that one of the preferred hydrocracking catalysts is a composite of palladium on a cracking catalyst base consisting of silica-alumina and containing from about 0.2 to about 0.8 percent by weight of palladium.

In the hydrocracking stage of the process, the aromatic extract at a temperature of from about 600 F. to about 900 F., together with hydrogen at a pressure of from about 500 lbs. to about 3000 lbs. per square inch is passed into hydrocracking zone 18, containing the hydrocracking catalyst at a space velocity of from about 0.2 to about 2.5 volumes of liquid feed stock per volume of catalyst per hour. At the indicated reaction conditions and particularly, when the residence time of the aromatic extract with the hydrocarcking catalyst in zone 18 is sufficient, the aromatics undergo hydrogenation and at substantially the same time, the resulting ring compounds split into smaller molecular weight fragments of aliphatic structure, boiling within the gasoline and/or kerosene range, constituting the desired end products of the present process.

The mixed phase product of the hydrocracking process is removed from zone 18 through line 19, into separation zone 20 wherein the light gaseous portion of the product is separated into the desired fractions, for example, by

hydrogen supply line 23 which feeds into hydrocracking zone 18. The fraction of the hydrocracked products boiling above the butanes, up to about 400 1 comprising gasoline boiling range material, one of the desired end products of the process is removed from zone through line 24 into line 25 leading to product blending and storage. A fraction boiling above the end point of the gasoline fraction comprising terosene and fuel oil fractions may be separately recovered for jet fuel use or recycled in the process and subjected to further hydrcracking or solvent extraction, as desired. The latter fraction is removed from separation zone 20 through line 26- and either discharged from the process as product through line 2?, diverted from line 26 into line 28, which in turn connects with line is, feeding into hydrocracliing zone 18, or conveyed by line 26 into line leading into aromatic extraction zone i1 wherein the aromatic components normally present in the bottoms fraction of the hydrocracking products are recovered therefrom by the present solvent extraction step.

Referring again to the raflinate portion of the extraction stage, removed from zone through line 17, this predominantly parafiinic fraction is subjected to catalytic cracking in zone 29 in the presence of an acidic cracking catalyst which ruptures the long chain hydrocarbons present in the rafiinatc fraction into smaller fragments boiling within the gasoline or kerosene range, depending upon the particular temperature and pressure conditions maintained in the reactor. Cracking zone 29 contains a cracking catalyst distributed therein, in fixed bed, fluidized, or moving bed relationship to the incoming charge. The rafiinate charge is catalytically cracked in zone 29 by passing the raffinate at a temperature of from about 750 to about 1100 F., and more preferably at a emperature of from about 800 to about 1000 F. into contact with the cracking catalyst at a pressure of from 10 to about 1000 lbs. per square inch and at a rate equivalent to a liquid hourly space velocity of from about 0.5 to about 2.5 volumes of liquid feed stock per volume of catalyst per hour. Fluidizcd catalytic cracking is generally the preferred method of contacting the catalyst with the charge stock and preferably at temperatures of from about 8' to about 1000" F. and at pressures of from about 10 to about 100 p.s.i.g.

Suitable cracking catalysts are Well-known in the art, including generally certain acid-acting composites of refractory metal oxides, such as silica-alumina, silica-zirconia, silica-magnesia, alumina-boria, alumina-silica-magnesia, siliea-alumina-zirconia and other acid-acting mixtures of refractory metal oxides containing from about 2 to about percent by weight of silica and/ or boria.

Although the product of the cracking reaction in the case of the present raifinate stock is primarily a liquid material boiling in the gasoline range, certain gaseous products are also likely to be formed, such as the low molecular weight hydrocarbon gases, including methane, ethane, propylene, and the butanes. In order to separate the various fractions of the catalytically cracked product, the reaction effluent from zone 29 is passed through line 30 into separation Zone 31 wherein the desired fractionation and separation is effected. A light, normally gaseous overhead is fractionally distilled from the catalytic crackingreaction product in zone 31, being removed therefrom through line 32 and discharged from the process. A gasoline boiling range fraction, including the components boiling above C ,-up to about 400 F. end point is separated in zone 31 as an intermediate boiling range fraction which is removed through line 33 and discharged into line 25 for blending to form the gasoline product of the present process.

The bottomsresidue boiling above the 400 F. end point of the desired gasoline fraction is separated from the cracked products in zone 31 and recycled through line 3d to the inlet of hydrocracking zone 18, line 16. The high boiling residual bottoms recovered from the catalytically cracked products, is generally rich in arcmatic and olefinic hydrocarbons and is a suitable feed stock to the hydroerackingzone. In this manner, the initial feed-stock in its entirety is converted into the desired gasoline boiling range product.

The present invention is illustrated with respect to several of its specific embodiments in the following ex-- the scope of the invention necessarily in accordance 7 to the cracking reactor.

therewith.

Example I A Mid-Continent virgin gas oil stock, having a boiling range of from about 560 F. to about 930 F. containing 31 percent by weight of polynuclear aromatic components and 1200 ppm. of nitrogen as naturally-occurring nitrogenous contaminants is catalytically cracked, using an alumina-silica cracking catalyst containing 12 percent by weight of silica. In this run, the charge stock, at a pressure of 900 lbs. per square inch and at a temperature of 875 F. is charged into a fixed bed of the.

cracking catalyst at a space velocity of 1.5 volumes of iquid charge per volume of catalyst per hour. The normally liquid portion of the products is fractionated to separate a gasoline boiling range fraction having an end boiling point of 400 F. from a liquid bottoms residue (23 percent by volume of charge) which is recycled The net conversion to gasoline boiling range product is about 62 percent by weight of the material charged, 8 percent by weight of the original feed is separated as a liquid tar from the distillate bot-v toms and about 3450 s.c.f./bbl. of charge, consisting of light, non-condensable gaseous hydrocarbons and hydrogen are produced in the conversion. The catalyst re-.

quires regeneration after 56' hours on stream and replacement afiter two-regenerations.

In the following run the identical charge stock speci-v ficd in the above catalytic cracking run is first subjected to hydrorefining by passing the charge stock, together with hydrogen (2000 standard cubic feet per barrel of charge stock) and at a pressure of 3000 lbs. per squarev inch gauge over a hydrorefining catalyst consisting of 2 percent by weight of nickel, 12 percent by weight of molybdenum and'3 percent by weight of cobalt on an alumina base, the catalyst being maintained in the hydrorefining zone as a fixed bed of precalcined pellets. The charge stock is passed through the hydrorefining catalyst at a temperature of 725 F. and at a liquid hourly space velocity of 0.5 volumes of liquid per volume of catalyst per hour. The exit gas from the top of the reactor contains substantially all of the ammonia formed during the hydrorelining conversion and is passed through a countercurrent acid wash stream to remove the ammonia. hydrorefined products is stripped at atmospheric pressure to remove the normally gaseous hydrocarbons from the liquid portion of the product; 51 s.c.f. of gaseous.

hydrocarbons per barrel of charge stock is separated. The conversion results in a net consumption of hydrogen.

The stabilized liquid portion of the hydrorefined prodnot is thereafter subjected to extraction for the removal of aromatic components by passing the liquid product The liquid portion of the.

begin to appear in the efiluent stream, 'the feed stock is diverted to a second adsorption tower containing reactivated silica gel adsorbent. The first tower is thereafter reactivated and the aromatic components of the charge stock recovered from the adsorbent by passing a paraffinic naphtha boiling from about 300 to about 350 F. downwardly through the column of spent adsorbent at a temperature of about 300 F. and removing the efiluent in liquid phase from the bottom of the adsorption tower. The desorbed efiiuent is thereafter fractionated to recover the aromatic component as bottoms from the liquid efiluent and to distill overhead the paraffinic naphtha desorbent.

As soon as aromatic components begin to appear in the eflluent of the second column, a similar desorption is carried out on the second column as fresh hydrorefined charge stock is charged into the first adsorption column. Aromatics are recovered from the liquid portion of the hydrorefined product in this manner to provide a yield of 31 volume percent of the hydrorefined product. The aromatics thus recovered are reserved for use in the subsequent hydrocracking stage of the process. The nitrogen content of both the raiiinate and extract portions of the hydrorefined product is reduced to less than 0.5 ppm. total nitrogen.

The rafiinate portion of the hydroreiined product (adsorber eluate) is catalytically cracked in a separate fluidized catalytic cracking reactor containing a silica-alumina cracking catalyst (containing 12 percent silica). The rafiinate preheated to 930 F. and at a pressure of 900 lbs./in. is charged at a rate of 1.3 liquid hourly space velocity into the fiuidized bed of cracking catalyst. The products of the cracking reaction are first stripped at the reactor pressure and thereafter fractional'ly distilled, separating a light normally gaseous overhead from the cracked products, (1090 s.c.f./bbi. of charge), an intermediate gasoline fraction boiling up to 400 F. end point (68 percent by weight of the charge) from the remaining liquid portion of the product and a liquid bottoms residue (21 percent by weight of the initial rafiinate out) which is thereafter mixed with the aromatic extract recovered from the hydrorefined product and charged to the hydrocracking reactor hereinafter described. The gasoline boiling range cut is reserved for subsequent blending with the similar boiling range cut of the hydrocracking reaction product.

The mixed liquid bottoms of the cracking reaction product and the aromatic extract recovered from the adsorber are charged into a hydrocracking reactor at a liquid hourly space velocity of 0.8 volumes of liquid/ volume of catalyst/hour, together with hydrogen at a rate of 1000 standard cubic feet per barrel of charge stock at a pressure of 3000 lbs/in. and at a temperature of 725 F. The hydrocracking catalyst, consisting of 0.4 percent palladium on a silica-alumina cracking catalyst base, is maintained as a fixed bed in the reactor. The hydrocracking conversion products are first passed into a high pressure separation zone wherein the noncondensable gases are separated from the condensed liquid portion of the product at the particular pressure maintained in the hydrocracking reaction zone. The non-condensable gas fraction, consisting mostly of hydrogen, is recycled to the hydrocracking zone. Thereafter, the light hydrocarbon gases, up to and including nbutane, are separated from the liquid portion of the high pressure condenser. An intermediate cut boiling from C to 400 F. and point is separated from the hydrocracked products and reserved as the gasoline boiling range fraction for blending with the gasoline product of the catalytic cracking zone. The gasoline boiling range fraction of the hydrocracked product represents 10' a conversion of 78 percent basedupon the charge stock to the hydrocracking reactor. The liquid bottoms fraction representing the material of the hydrocrackedprodnot boiling above the end point of gasoline and containing 21 percent by "weight of aromatic components is recycled to the inlet of the aromatic extraction zone hereinbefore referred to. The hydrocracking zone, operated at the above conditions, is capable of on-stream use for a period of over 800 hours before the conversion falls below 75 percent; thereafter the temperature of the hydrocracking zone may be increased an additional 25 F. to restore the catalyst to its initial conversion rate. In this manner the hydrocracking catalyst may be continuously utilized for the hydrocracking conversion for a period of over 4000 hours before reactivation is required.

The net conversion of the virgin gas oil feed stock to gasoline boiling range product is over 89-percent and the product has a clear octane number of 90.3.

I claim as my invention:

1. A process for converting a petroleum stock boiling above the gasoline range and containing aromatic components and nitrogenous contaminants which comprises hydrorefining said stock in the presence of a hydrorefining catalyst at a temperature, pressure and time of contact of the'stock with the catalyst sufficient to convert the nitrogen of said nitrogenous contaminants into ammonia, removing ammonia rom the liquid portion of the hydrorefined stock to a nitrogen content not substantially in excess of 5 p.p.m., extracting the aromatic components from said liquid hydrorefined stock and recovering an aromatic extract separate from a nonaromatic raifinate, catalytically hydrocracking said aromatic extract in the presence of a catalyst containing hydrogenating and cracking catalyst components, catalytically cracking said raffinate and separating from the resultant products a fraction boiling in the gasoline range and a heavier residual fraction rich in aromatic and olefinic hydrocarbons, supplying said residual fraction to the hydrocracking step, and blending the gasoline boiling range fractions of the cracked and hydrocracked products.

2. The process of claim 1 further characterized in that said aromatic extraction is effected in the presence of a solid adsorbent for aromatic hydrocarbons and said aromatic extract is recovered from the solid sorbent.

3. The process of claim 1 further characterized in that said cracking catalyst component of the hydrocracking catalyst is a composite of silica and alumina.

4. The process of claim 3 further characterized in that said hydrogenating component of said hydrocracking catalyst is palladium.

5. The process of claim 1 further characterized in that said hydrorefining catalyst comprises a metal of group VIII of the periodic table composited with a base comprising alumina.

6. The process of claim 5 further characterized in that said group VIII metal is selected from the group consisting of nickel and cobalt and said catalyst base is alumina containing a molybdenum compound.

7. The process of claim 1 further characterized in that said hydrorefining reaction is elfected in the presence of hydrogen and at a pressure of from about 1000 to about 3000 lbs. per square inch, a temperature of from about 650 to about 850 F. and a liquid hourly space velocity of from about 0.5 to about 1.5 volumes of liquid hydrocarbon charge stock per volume of catalyst per hour.

8. The process of claim 1 further characterized in that the liquid portion of the hydrocracked product is separated into a gasoline boiling range fraction and a residue boiling above said gasoline boiling range fraction and recycling said residue to the aromatic extraction stage of the process.

9;. The process of claim 1 further characterized inthat the, residue from the liquid precinct of the hydro cracking reaction is. recycled to the inlet of the hydrocraekingstep, mixed with said extract of the, aromatic extraction step, and the resulting combined feed charged 5 into the hydrocracking reaction. v

References Cited in the file of this patent UNITED "STATES PATENTS Gleirn Sept. 22, 1959

Claims (1)

1. A PROCESS FOR CONVERTING A PETROLEUM STOCK BOILING ABOVE THE GASOLINE RANGE AND CONTAINING AROMATIC COMPONENTS AND NITROGENOUS CONTAMINANTS WHICH COMPRISES HYDROREFINING SAID STOCK IN THE PRESENCE OF A HYDROREFINING CATALYST AT A TEMPERATURE, PRESSURE AND TIME OF CONTACT OF THE STOCK WITH THE CATALYST SUFFICIENT TO CONVERT THE NITROGEN OF SAID NITROGENOUS CONTAMINANTS INTO AMMONIA, REMOVING AMMONIA FROM THE LIQUID PORTION OF THE HYDROREFINED STOCK TO A NITROGEN CONTENT NOT SUBSTANTIALLY IN EXCESS OF 5 P.P.M., EXTRACTING THE AROMATIC COMPONENTS FROM SAID LIQUID HYDROREFINED STOCK AND RECOVERING AN AROMATIC EXTRACT SEPARATE FROM A NONAROMATIC RAFFINATE, CATALYTICALLY HYDROCRACKING SAID AROMATIC EXTRACT IN THE PRESENCE OF A CATALYST CONTAINING

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