Abstract: For producing three effluents which are respectively rich in straight chain paraffins, in mono-branched paraffins, and in di-branched and tri-branched paraffins possibly with naphthenic and/or aromatic compounds, from C5-C8 cuts or intermediate cuts (C5-C7, C6-C8, C7-C8, C6-C7, C7 or C8), comprising paraffic and possibly naphthenic, aromatic and olefinic hydrocarbons, the separation process of the invention uses at least two separation units operating either by adsorption or by permeation. It is of particular application when coupled with a hydro-isomerization process, which selectively recycles straight chain and mono-branched paraffins, necessary with paraffins containing more than 7 carbon atoms.

Abstract: Hydrocarbon fluid catalytic cracking (FCC) plants are debottlenecked by subjecting part or all of the wet gas stream leaving the main fractionator overhead receiver to pressure swing adsorption to remove methane and hydrogen from this gas stream prior to its introduction into the wet gas compressor. This allows debottlenecking of the compressor system. It can allow the reduction in pressure in the system back to the catalyst regenerator. The reduction in pressure in the catalyst regenerator makes it possible to increase the rate of regeneration of catalyst. Consequently, the rate of hydrocarbon throughput in the FCC plant can be increased.

Abstract: An apparatus and method for treating a liquid hydrocarbon stream useful as a precursor for transportation fuel and which contains an unacceptably high level of heteroatom compounds is provided for the removal of a significant portion of the heteroatom compounds from the hydrocarbon stream. The method and apparatus employ an adsorbent which is brought into countercurrent contact with a hydrocarbon stream in an adsorption zone to form a product hydrocarbon stream and a spent adsorbent stream. The adsorbent is recirculated to a desorption zone and is thereafter brought into cross-current contact with a reactivating medium, such as hydrocarbon gas, at elevated temperatures to form a reactivated adsorbent stream and a hydrogen/heteroatom stream. The regenerated adsorbent is recirculated back to the adsorption zone to form the adsorbent stream.

Abstract: Distillate or hydrotreated distillate effluent is separated into an aromatics rich permeate and an aromatics lean retentate by use of a permselective membrane with the aromatic rich permeate being sent to a hydrotreater, thereby increasing the quantity of reduced aromatics content product.

Abstract: The yield and quality of products secured from cracking units is increased by the process of subjecting the product stream secured from such cracking unit to a selective aromatics removal process and recycling the recovered aromatics lean (saturates rich) stream to the cracking unit whereby such saturates rich stream is subjected to increased conversion to higher value desired products.

Abstract: A method of removing contaminants from a hydrocarbon stream which involves contacting the hydrocarbon stream containing a heavy-metal contaminant with a porous material under conditions suitable for adsorption of the contaminant by the porous material. A process for preparing an adsorbent which involves forming a mixture of metal oxide powder and support powder, shaping the mixture into an aggregate, and reducing the aggregate to transform the metal oxide to the metallic state.

Abstract: Hydrocarbon oils such as diesel fuels, turbine fuels and intermediate distillates may be subjected to quantitative analysis of their saturate, aromatic and polar components by supercritical fluid chromatography using carbon dioxide as the solvent. A sample of the oil is passed into a packed column of silica or the like whereby the respective fractions are separated and retained on the column. Supercritical carbon dioxide at selected pressure and temperature conditions is passed through the column to extract, separately, each of the fractions retained on the column. The extracted fraction and solvent are passed through a restrictor and expanded down to a pressure which will allow the solvent to evaporate and to permit retention or collection of the extracted fraction in a collector arrangement including a selector valve and plural collection containers.

Abstract: The present invention is a process for reducing the smoke emissions from a jet fuel engine by combusting a jet fuel range hydrocarbon in a jet engine wherein prior to combusting the jet fuel in the engine the jet fuel is treated by the following process: (a) contacting the jet fuel with at least one adsorbent in at least one adsorbent bed under suitable process conditions such that the smoke point of the jet fuel is increased and (b) recovering the jet fuel.

Abstract: This invention is a method for reducing the particulate emissions tendency of diesel fuel. Also the piston ring sticking, and deposit formation tendency of diesel fuel on the injector and combustion chamber of an internal combustion diesel fuel are reduced. The diesel fuel under the method of this invention is fed to at least one adsorbent bed in which the diesel fuel is contacted with one or more adsorbents under suitable process conditions such that there is a reduction in content of impurities in the fuel which cause the particulate emission causing tendency, piston ring sticking, and deposit formation tendency of the diesel fuel on the injector and/or combustion chamber.

Abstract: A method for removing arsenic and/or phosphorus from a petroleum charge with a retaining material comprising:(a) from 60 to 97% of a carrier containing, by weight, from 1.5 to 60% of oxide of at least one metal A selected from the group consisting of Mg, Ca, Sr, Ba, Mn, Fe, Co, Ni, Cu and Zn, dissolved in alumina in the form of aluminate, and from 40 to 98.5% of at least one alumina,(b) from 3 to 40% of nickel oxide, with which the carrier is impregnated by exchange or depositing, and(c) possibly from 0 to 1% of platinum and/or palladium oxide with which the carrier is impregnated.

Abstract: This invention provides a process to remove aromatic color bodies, particularly oxygen or sulfur containing aromatics from a C.sub.8-11 aromatic hydrocarbon stream having a boiling range between about 160.degree.-460.degree. F. The process involves contacting the hydrocarbon stream with a neutral attapulgite clay for a time sufficient to adsorb the aromatic color bodies. The process is effective in reducing the APHA color value of the subject hydrocarbon stream from an initial 850-1100 value to about 400 or less.

Abstract: A process for separation and removal of stable polycyclic aromatic dimer foulants from refinery process streams by selectively adsorbing the foulants while eluting non-fouling smaller-ringed aromatics. Synchronous Scanning Fluorescence may be used in the identification and monitoring of the stable polycyclic aromatic dimers.

Abstract: A hydrocarbon feedstock is simultaneously distilled into two or more fractions while trace concentrations of contaminants in the feedstock are absorbed onto a sorbent packing material during distillation operation. The sorbent packings contain active metal components supported on porous refractory oxides. Such sorbent packings provide surfaces for mass transfer in the distillation process and concurrently absorb contaminants. Product boiling fractions from the absorption-distillation process are further processed over contaminant-sensitive catalysts such as reforming or isomerization catalyst.

Abstract: A process for purifying linear paraffins in which a hydrocarbon feedstream containing linear paraffins contaminated with aromatics, sulfur-, nitrogen-, and oxygen-containing compounds, and color bodies, and also containing up to about 5 wt % desorbent from effluent recycle, is contacted with a solid adsorbent such as a NaX zeolite or zeolite MgY; after adsorption the adsorbent is desorbed with an alkyl-substituted aromatic desorbent, such as toluene. As the adsorent bed is being desorbed, the initial effluent from the adsorption cycle will contain levels of desorbent and may be recycled to the hydrocarbon feedstream. Previous to the removal of impurities from the adsorbent by desorption, the desorbent displaces interstitial linear paraffins which are also recycled to the hydrocarbon feedstream.

Abstract: Process for reducing the metal content of a hydrocarbon feed mixture by reverse osmosis, comprising contacting the feed mixture substantially boiling in the range between about 100.degree. and about 350.degree. C. and containing at most about 1000 parts per billion by weight (ppbw) of metal(s) with a metal-selective membrane to give a hydrocarbon permeate stream having a metal content which is less.

Abstract: An improved adsorption-desorption process is disclosed for separating low octane components from field natural gasoline and virgin naphthas. The low octane materials may be further separated into chemical feed stocks, fluid catalytic cracking feed stocks, steam active reforming feed stocks, paraffinic solvents, and diesel and jet fuel blend stocks by conventional fractionation and/or solvent extraction processes. The remaining higher octane materials make excellent reformer feed and/or gasoline blend stocks.

Abstract: Fused polynuclear aromatic compounds (PNAs) are continuously removed from a recycle oil stream in a hydrocracking process. An adsorption bed removes the PNAs from the recycle oil, a desorbing reagent removes the PNAs from the bed, and a regenerating agent regenerates the bed, all steps being performed simultaneously and continuously.

Abstract: The present invention relates to a new and integrated process involving the utilization of a primary adsorption bed containing a regenerable, physical adsorbent and an auxiliary sorption bed containing a chemisorbent for the removal of sulfur compounds from a fluid stream, which process provides for higher yields, higher purity and lower costs. A system for removing sulfur compounds in accordance with the above process is also disclosed.

Abstract: A process for treating catalytic particles in a vertical chamber is disclosed. The catalytic particles comprise spent catalysts from such hydroprocesses as hydrocracking and hydroreforming. The process comprises suspending the catalytic particles in a gaseous atmosphere of a vertical chamber for a time sufficient to remove the waste products from the catalytic particles. The process can be used to remove carbonaceous and sulfur deposits from the surface of the particles as well as volatile hydrocarbons and hydrates.

Abstract: A process for purifying linear paraffins in which a hydrocarbon stream containing linear paraffins contaminated with aromatics, sulfur-, nitrogen-, and oxygen-containing compounds, and color bodies, but essentially free of olefins, is contacted with a solid absorbent such as a NaX zeolite or zeolite MgY. After adsorption the adsorbent is desorbed with an alkyl- substituted aromatic desorbent, such as tuluene. The initial effluent from the adsorb cycle, which will contain a high concentration of residual desorbent, is recycled to a desorbent recovery system. The level of desorbent in the adsorber effluent is monitored on a real time basis until the desorbent level of the adsorber effluent declines from a plateau level, i.e., a 100% plateau level, that correlates with the level of impurities, particularly the aromatic impurities in the feed, which is an indication of aromatics breakthrough, thereby signaling the need to switch the adsorbent beds.

Abstract: The invention relates to a method for removing RCS from off-spec white mineral oil prepared by catalytic hydrogenation by filtering the off-spec white mineral oil through a bleaching clay, such as a smectite clay, particularly an acid treated montmorillonite clay, such as bentonite or attapulgite.

Abstract: A method for removing a tertiary halide from an olefin hydrocarbon stream which comprises contacting the hydrocarbon stream with activated alumina at a temperature of about -40.degree. to about 120.degree. C.

Abstract: The present invention is a concentration swing adsorption process for separating a liquid phase feedstock comprising a more adsorbable component (A) and a less adsorbable component (B) with respect to an adsorbent. The process is operated in a system comprising a single or a plurality of adsorption columns containing the adsorbent which are operated in cycle in a predetermined sequence. The following operational steps are performed in the order recited in each of the adsorption columns in its turn. Feedstock is passed through the adsorbent and the more adsorbable component (A) is selectively adsorbed while a stream enriched in component (B) is discharged from the adsorption column. The adsorbent is rinsed in a direction co-current to the feedstock with the more adsorbable component (A) whereby the less adsorbable component (B) is displaced from the adsorbent and a stream comprising a mixture of the more adsorbable component (A) and the less adsorbable component (B) is withdrawn from the adsorption column.

Abstract: Aromatic hydrocarbons are readily recovered from aqueous solutions by contacting the aqueous solution with an oxidized activated carbon having a low concentration of acidic oxides.The novel oxidized activated carbon is produced by contacting activated carbon with an acidic oxidizing agent which is used in low concentrations.The process can be employed to reduce aromatic hydrocarbons such as benzene from aqueous solutions such as industrial effluents or potable water supplies to levels permissible by environmental protection regulations.

Abstract: Processes are disclosed for the separation of light hydrocarbons from a feedstream containing hydrogen, light hydrocarbons and heavy hydrocarbons. The processes employ thermal swing adsorption zone to adsorb heavy hydrocarbons and a pressure swing adsorption zone to remove the remaining light hydrocarbons. At least a portion of the product from the pressure swing adsorption zone is used to purge the thermal swing adsorption zone. Specific applications of the process of the present invention are disclosed with relation to hydrodealkylation processes and dehydrocyclodimerization processes.

Abstract: A process of separating the ortho, meta and para isomers of ethyltoluene. One aspect employs a ferrierite absorbent which separates the para isomer from a mixture of the same and at least one of the meta and ortho isomers. A second aspect employs a silicalite absorbent which separates the ortho isomer from a mixture of the same and the meta isomer. A third aspect combines the ferrierite and silicalite absorbents in sequence to separate a mixture of the ortho, meta and para isomers into the essentially pure compounds.

Abstract: A process for the selective separation of alkenes and/or alkynes from gases obtained by cracking of petroleum products comprising: (a) treating said gases containing at least one alkene and/or at least one alkyne with a macroporous strongly acidic cation exchange resin in its hydrogen form to selectively adsorb said at least one alkene and/or said at least one alkyne; and (b) introducing water, oxygen or an acid in vapor form to simultaneously desorb said at least one alkene and/or said at least one alkyne and to form at least one alcohol, aldehyde, oxide or ester.

Abstract: The invention relates to a method of operating an adsorption system using only two adsorption beds, for control of output quality of a gas containing a hydrocarbon. In the method before complete changeover of one bed A from adsorption to regeneration and of the other bed B from adsorption to regeneration, the adsorption feed gas flow is split into two streams of equal flow rate in the embodiment described, flowing in parallel through the beds and recombining the gas from the adsorbing bed A and the regenerating bed.

Abstract: A two step process for the obtainment of white oils, using hydrocarbons which are heavy alkylates obtained as a by product in the manufacture of detergent range linear alkylbenzene (9-15 carbon atom paraffin chains) as the raw material is described.The first step consists of pretreatment (of an absorbent nature) of the feed, with an activated magnesium silicate in order to eliminate the heaviest components. In a second stage, the resulting treated product acts as a feed in a hydrogenation process to produce white oils, in a presence of a hydrogenation catalyst formed by a metallic component of the group of iron and/or nickel upon a refractory inorganic oxide support.The catalytic hydrogenation process is carried out in a fix bed reactor with down flow.It is useful in the pharmaceutical and food industries.

Abstract: A catalytic hydrocracking process which comprises: (a) contacting a hydrocarbonaceous feedstock having a propensity to form 11.sup.+ ring heavy polynuclear aromatic compounds and a liquid recycle stream in a hydrocracking zone with added hydrogen and a metal promoted hydrocracking catalyst at elevated temperature and pressure sufficient to convert a substantial portion of the feedstock to lower boiling hydrocarbon products; (b) partially condensing the hydrocarbon effluent from the hydrocracking zone to produce a gaseous hydrocarbon stream comprising hydrogen, and an unconverted hydrocarbon stream having components boiling above about 400.degree. F. (204.degree. C.) and comprising trace quantities of 11.sup.

Abstract: Treatment of diesel or jet fuel with a non-ionic, macroreticular, cross-linked, acrylic aliphatic ester resin reduces polar impurities and (diesel) color.

Abstract: Disclosed herein is a process for removing contaminating mercury from hydrocarbon streams, gas or liquid, wherein the stream is contacted with a molecular sieve pretreated with an alkali polysulfide. The pretreatment consists of saturating the sieve with an aqueous solution of the polysulfide and subsequently drying the saturated sieve under conditions calculated to dry but not decompose the polysulfide present.

Abstract: A solid adsorbent for an unsaturated hydrocarbon comprising (a) (i) a silver or copper(I) halide or (ii) a silver or copper(I) halide and the halide of a bivalent metal, or (iii) a silver or copper(I) halide and an aluminum halide, and (b) polystyrene or a derivative thereof.This solid adsorbent can effectively adsorb an unsaturated hydrocarbon such as ethylene from a gas mixture by contacting the gas mixture therewith at a temperature of -40.degree. C. to 140.degree. C. under normal pressures.

Abstract: The present invention relates to a process for removing arsine from a light olefin to containing hydrocarbon feedstock, said process comprising the steps of (a) passing said feedstock over an absorbent material comprising nickel deposited on a support material wherein nickel is present as both nickel oxide and metallic nickel; and (b) recovering a stream having a substantially reduced arsine content.

Abstract: This invention relates to a process for increasing the octane of a refinery gasoline pool by segregating components which are increased in value by isomerization from those which are diminished in octane value by isomerization. The preferred feed stream of this process comprises di-branched paraffins, mono-methyl-branched paraffins and normal paraffins from which mono-methyl-branched and normal paraffins are selectively captured by a shape-selective molecular sieve. The preferred separatory shape-selective molecular sieve has a pore size of 5.5.times.5.5 to 4.5.times.4.5A but excluding 4.5.times.4.5A. Mono-methyl-branched paraffins and normal paraffins are removed from the shape-selective molecular sieve and isomerized in an isomerization zone to form di-methyl branched paraffins. An isomerization zone effluent stream is produced comprising unisomerized normal paraffins, mono-methyl-branched paraffins and di-branched paraffins.

Abstract: The invention relates to a method of preparing a stationary silica phase for the purpose of packing a chromatographic column intended for the liquid-phase separation of components. There are thus effected a first grafting with functional groups of the amine type, a complete hydrolysis of the stationary phase so grafted, and finally a further grafting with functional groups of the alkyl type, optionally substituted. A chromatographic column packed with the stationary silica phase can be used to separate the constituents of a petroleum product.

Abstract: A process and apparatus for converting light hydrocarbons, such as waste organic solvents, to a useful fuel having a high flash point. A mixture of light hydrocarbon and heavy oil, wherein the ratio of light hydrocarbon to heavy oil preferably lies in the range from about 10:1 to about 1:4, is forced at a pressure of preferably at least about 500 psi through a porous substrate having a catalytically effective amount of an active oxide of hexavalent group 6b metal, such as chromium, thereon. The porous substrate may comprise a sintered powder stainless steel material having an average pore size in the range from about 20 to about 2000 microns. The catalyst is prepared by wetting the porous substrate with a solution of a salt of the group 6b metal and heating the wetted substrate until a catalytically active oxide of hexavalent group 6b metal is formed thereon.

Abstract: An improved catalytic reforming process. The process is operated at high severity in order to obtain a reformate product having an enhanced octane rating. Higher octane reformate is required to compensate for the reduction or total elimination of lead-based additives used in motor gasoline for increasing octane rating, since reformate is a primary component of motor gasoline. High severity operation results in the formation of quantities of polycyclic aromatic compounds whose presence is highly undesirable. These compounds are removed from the vaporous products of the catalytic reforming process by adsorption on an appropriate material. It was totally unexpected to find that these very high molecular weight compounds are present in vapor streams comprised of hydrogen and light normally-gaseous hydrocarbons such as methane, ethane, and propane.

Abstract: A process for hydrotreating a hydrocarbonaceous charge stock having hydrogenatable hydrocarbonaceous compounds which process comprises the steps of: (a) contacting said hydrocarbonaceous charge stock in the presence of hydrogen with a hydrogenation catalyst in a hydrotreating reaction zone; (b) contacting said hydrotreating reaction zone effluent with an aqueous scrubbing solution; (c) introducing a resulting admixture of said reaction zone effluent and said aqueous scrubbing solution into a separation zone to provide a hydrotreated hydrocarbonaceous stream having trace quantities of hydrogenatable hydrocarbonaceous compounds and a spent aqueous stream; and (d) contacting said hydrotreated hydrocarbonaceous stream with an adsorbent to remove at least a portion of said trace quantities of hydrogenatable hydrocarbonaceous compounds from said hydrotreated hydrocarbonaceous stream.

Abstract: This invention comprises a process for separating the minor dinitrotoluene isomers, 2,3-dinitrotoluene and 3,4-dinitrotoluene from a feed mixture comprising 2,4- and 2,6-dinitrotoluene, and the minor isomers, which process comprises contacting the mixtures at adsorption conditions with an adsorbent comprising a Y type, or dealuminated Y type, zeolite, cation exchanged with Na, Ca or H, thereby selectively adsorbing the 2,3- and 3,4- isomers or 2,4- and 2-6 isomers, respectively. The remainder of the feed mixture is removed from the adsorbent and the minor isomers are recovered by desorption at desorption conditions with a desorbent material comprising an alcohol, ketone or an ester.

Abstract: A process is disclosed for removing color or color inducing impurities to petroleum derived wax by means of an adsorbent comprising a refined inorganic oxide having a pore distribution such that at least 60% of the pores possess a size of less than 350 Angstroms. Preferably, at least 90% of the pores possess a size of less than 350 Angstroms. The preferred inorganic oxide is an aluminum oxide and preferably has a surface area between 200 square meters per gram and 500 square meters per gram. A process is also disclosed for wax finishing utilizing multiple beds of refined alumina which may be operated in a swing bed fashion to intimately regenerate the refined alumina absorbent by such procedural steps as naphtha soaking, steam treating and heating in air.

Abstract: A process is described for separating and identifying organic sulphur compounds in petroleum distillates which comprises subjecting an aromatic-containing fraction to chromatography in a dual packed silica gel-alumina column employing pentane-ethyl acetate as a solvent to obtain a sulphur-containing eluate and analyzing the sulphur-containing eluate by gas chromatography and mass spectrometry. The aromatic-containing fraction is usually a naphtha fraction or a light gas oil fraction, with the gas oil fraction being subjected to chromatography on a silica gel column to obtain an aromatic fraction which is then subjected to the chromatography in the above silica gel-alumina column.

Abstract: The useful life of a deactivated inorganic pillared clay catalyst or an inorganic pillared clay sorbent saturated with a steam-distillable organic sorbate is extended by adding a small amount of ammonia to the regeneration gas or to the regeneration steam.

Abstract: A process for catalytically cracking a hydrocarbon-containing feed stream, preferably having an API.sup.60 gravity of about 5-30, wherein at least a portion of off-gases is treated so as to remove C.sub.2 -C.sub.4 olefins therefrom, and the off-gas stream having a reduced olefin content is then recycled to the catalytic cracking zone.

Abstract: A process is disclosed for deactivating or removing aromatic compounds from a kerosene or gas oil, which aromatics are coke precursors in a steam cracking process (conducted in the absence of a catalyst) to convert the hydrocarbons contained in the kerosene or gas oil to hydrocarbons of smaller molecules. The excising occurs by contacting the kerosene or gas oil, before admission to the steam cracking zone, with particulate size activated carbon of 4 mesh to 50 mesh size and physically removing the activated carbon (with at least a portion of the aromatic content of the coke derived from the kerosene or gas oil absorbed thereon) from the slurry before passage of the kerosene or gas oil to the steam cracking furnace.

Abstract: A major portion, preferably a substantial portion, of the coke precursors may be removed from atmospheric and vacuum resids having a Conradson carbon residue of at least about 10 wt. % by selectively removing the components of said feedstock which have an overall Hildebrand solubility parameter greater than 9.0 and a complexing solubility parameter greater than 1.3, such that there results a coke precursor rich fraction containing components having the requisite solubility parameters and a coke precursor depleted fraction. Each fraction may then be processed separately. Segregation of coke precursors by removing the components having the requisite solubility parameters also results in an enhanced yield of useable liquid hydrocarbons relative to that obtained using conventional separation processes.

Abstract: Normal paraffins present in high concentrations in light naphtha streams are separated from non-normal paraffins in a four or more bed adsorption system employing, on a cyclic basis, the processing steps of (1) cocurrent purge/adsorption, (2) cocurrent feed/adsorption, (3) countercurrent purge and (4) countercurrent displacement. A processing sequence is employed wherein the cocurrent purge/adsorption and countercurrent purge steps are carried out on a discontinuous basis, while cocurrent feed/adsorption and countercurrent displacement steps are carried out in overlapping sequence.

Abstract: The instant invention is directed to a process for the continuous manufacturing of carbon molecular sieves having average effective pore diameters of from 2 to 15 Angstroms which comprises continuously feeding a charred naturally occurring substrate to a means for heating said substrate and heating said substrate under non-activation conditions, without the use of an externally added pore blocking substance, at a temperature range of about 900.degree. F. (482.degree. C.) to 2000.degree. F. (1093.degree. C.) for a time period of about 5 to 90 minutes.The instant invention is also directed to a carbon molecular sieve, useful for separating gas or liquid mixtures containing components of at least two different molecular diameters, molecular weights or molecular shapes which has the following physical characteristics:(a) an apparent density of from 0.60 to 0.70 g/cc,(b) an oxygen diffusivity (X 10.sup.-8) of from 500 to 900 cm.sup.2 /sec,(c) an oxygen/nitrogen selectivity ratio of from 5.0 to 8.

Abstract: An improved process for separating ortho aromatic isomers from a feed stream containing a mixture of aromatics by contacting the feed stream with a bed of the crystalline aluminophosphate adsorbent AlPO.sub.4 -5. The adsorbed ortho aromatic isomers is removed from the adsorbent by desorption.

Abstract: A method is disclosed for hydrocracking a hydrocarbon feedstock having a propensity to form polynuclear aromatic compounds without excessively fouling the processing unit. The hydrocracking method includes contacting the hydrocarbon feedstock with a crystalline zeolite hydrocracking catalyst, contacting at least a portion of the resulting unconverted hydrocarbon oil containing polynuclear aromatic compounds with an adsorbent which selectively retains polynuclear aromatic compounds and recycling unconverted hydrocarbon oil having a reduced concentration of polynuclear aromatic compounds to the hydrocracking zone.