US3592759A - Multiple stage hydrocracking process - Google Patents

Abstract

A SULFUROUS CHARGE STOCK, CONTAINING NITROGENOUS COMPOUNDS AND AROMATIC HYDROCARBONS, IS CONVERTED INTO LOWER-BOILING HYDROCARBON PRODUCTS OF PREDETERMINED END BOILING POINTS. THE CHARGE STOCK, IN ADMIXTURE WITH A PREVIOUSLY HYDROCRACKED, SUBSTANTIALLY DESULFURIZED STREAM, IS SUBJECTED TO A CLEAN-UP OPERATION AT RELATIVELY LOW OPERATING SEVERITIES FOR THE REMOVAL OF NITROGENOUS COMPOUNDS WITHOUT INCURRING THE FORMATION OF APPRECIABLE QUANTITIES OF POLYNUCLEAR AROMATICS. FOLLOWING SEPARATION, A PORTION OF THE SUBSTANTIALLY NITROGEN-FREE PRODUCT IS THEN SUBJECTED TO HYDROCRACKING WITHOUT INCURRING RAPID CATALYST DEACTIVATION NORMALLY RESULTING FROM THE PRESENCE OF CONDENSED RING, POLYNUCLEAR AROMATICS.

Description

y 13, 1971 E. L. POLLITZER 3,592,759

MULTIPLE STAGE HYDROCRACKING PROCESS Filed April 18. 1969 Reactor Product Separation //Vl E/V TOR: E rnesf L. Poll/'rzer Q/zidzur- 4 2 AZQ'M ATTORNEYS United States Patent 3,592,759 MULTIPLE STAGE HYDROCRACKING PROCESS Ernest L. Pollitzer, Skokie, Ill., assignor to Universal Oil Products Company, Des Plaines, Ill. Filed Apr. 18, 1969, Ser. No. 817,533 Int. Cl. Cg 23/00 U.S. Cl. 208-89 6 Claims ABSTRACT OF THE DISCLOSURE APPLICABILITY OF INVENTION In its broad sense, the present invention involves the conversion of hydrocarbonaceous mixtures into lowerboiling hydrocarbon products. More specifically, the inventive concept herein described encompasses a process for hydrocracking hydrocarbonaceous mixtures containing aromatic hydrocarbons and contaminated by sulfurous and nitrogenous compounds. Through the utilization of my invention, the interference, with catalytic activity, experienced as a result of the simultaneous presence of sulfur, nitrogen and aromatic hydrocarbons is significantly decreased.

Suitable charge stocks, to the processing and conversion of which the present invention is applicable, are generally classified into a variety of categories. These include gasoline boiling range fractions, both light naphtha and heavy naphtha, kerosene fractions, gas oil fractions, heavy vacuum gas oil distillates, and even heavier hydrocarbonaceous material boiling up to a temperature of about 1050 F. The quality of the desired lower-boiling hydrocarbon product is generally dependent upon the character of the charge stock. For example, light naphtha and other gasoline boiling range distillates will often be converted into substantial quantities of LPG (liquefied petroleum gas). Light and heavy gas oils are generally processed to produce gasoline or middle-distillate boiling range fractions. As is well-known to those having expertise in petroleum refining techniques, various combinations of product streams may be desired depending upon the particular locale and marketing needs and demands. For example, a heavy charge stock, boiling from about 850 F. to about 1050 P. will often be processed in a manner which produces maximum quantities of both LPG and a gasoline boiling range fraction. It is understood that the present invention is not considered to be limited to a particular charge stock from which it is desired to produce a particular product slate.

The charge stocks processed in accordance with the 3,592,759 Patented July 13, 1971 ice present invention contain condensed ring aromatics, simpler, mononuclear aromatics, or their partially hydrogenated derivatives, as well as alkyl-substituted aromatic hydrocarbons. Depending upon the boiling range of the particular charge stock, the quantity of aromatic hydrocarbons can vary from about 5.0% to about 60.0% by volume. Likewise, those charge stocks intended for conversion into lower-boiling hydrocarbon products contain substantial quantities of sulfurous compounds, often ranging as high as 5.0% by weight, calculated as elemental sulfur. The quantity of nitrogenous compounds will generally vary as the boiling range of the charge stock and its source, and can be as low as about 25 p.p.m., and as high as about 6,000 ppm, calculated as nitrogen by weight. Prior to becoming suitable for their intended use, the lower-boiling products must necessarily be substantially, completely free from nitrogen and sulfur. A common practice is to subject such material to a hydrotreating unit (often referred to as hydrofining) in order to prepare a substantially clean charge stock for subsequent processing in a hydrocracking unit. These hydrotreating or hydrorefining processes are generally conducted catalytically at temperatures of about 700 F. to about 800 F, as measured at the inlet to the catalyst bed. It has been found that excellent nitrogen and sulfur removal results, even with heavier charge stocks, but the severity of operation leads to considerable formation of polynuclear aromatics which are effective catalyst poisons in any subsequent hydrocracking operation. Indications also exist that the nitrogenous compounds actually foster the formation of polynuclear aromatics such that an effective clean-up operation results in additional polynuclear aromatics being charged to the hydrocracking reaction zone. The anomaly is obvious: the desired product must be substantially sulfur and nitrogen free; nitrogen and aromatic hydrocarbons should not co-exist within the process in an atmosphere conducive to the formation of polynuclear aromatics; and, at least a substantial portion of the virgin aromatics present in the fresh feed charge stock should be hydrogenated. These aromatics interfere, and are otherwise detrimental to hydrocracking in several ways. Condensed ring aromatics actually serve as a catalyst poison to the extent that the desired hydrocracking reactions are inhibited to an undesirable degree. Furthermore, the mononuclear aromatics, or their partially hydrogenated derivatives, can condense to produce additional polynuclear compounds. It should also be noted that the hydrogenation of aromatic hydrocarbons involves a high heat of reaction which in turn favors the undesired condensation side reactions.

Briefly, the process encompassed by the present invention involves the initial removal of nitrogenous compounds at relatively low severities which are not as conducive to the formation of polynuclear aromatics, hydrocracking at an elevated operating severity and desulfurization at an intermediate operating severity.

OBJECTS AND EMBODIMENTS An object of the present invention is to convert a hydrocarbon charge stock into lower-boiling hydrocarbon products. A corollary objective involves hydrocracking a sulfurous charge stock containing nitrogenous compounds and aromatic hydrocarbons, into lower-boiling hydrocarbon products, without incurring the rapid deactivation of the catalytic composite otherwise resulting from the simultaneous presence of nitrogenous compounds and aromatic hydrocarbons.

Another object of my invention is to provide a multiple-stage, fixed-bed catalytic system in which the hydrocracking of hydrocarbonaceous material is facilitated.

Therefore, in one embodiment, my invention provides a catalytic process for converting a sulfurous charge stock, containing nitrogeous compounds and aromatic hydrocarbons, into lower-boiling hydrocarbon products of a predetermined end boiling point, which process comprises the steps of: (a) reacting a substantially nitrogen-free portion of said charge stock, and hydrogen in a first reaction zone, in contact with a first catalytic composite, at conversion conditions including a maximum catalyst bed temperature of 800 F. to about 900 F.; (b) introducing the resulting first zone effluent into a second reaction zone, and reacting the same, in contact with a second catalytic composite, at desulfurization conditions including a maximum catalyst bed temperature of 700 F. to about 800 F.; (c) introducing said charge stock and the resulting second zone efiluent into a third reaction zone, and reacting the same and hydrogen, in contact with a third catalytic composite, at conditions including a maximum catalyst bed temperature of about 650 F. to about 725 F., and selected to convert nitrogenous compounds; (d) separating the third reaction zone efiiuent to provide a hydrogen-rich vaporous phase, to recover said lower-boiling products and to provide a normally liquid hydrocarbon stream boiling above said predetermined end boiling point and containing said nitrogen-free portion of said charge stock; and, (e) reacting said normally liquid stream in said first reaction zone.

Other objects and embodiments of my invention will become evident from the following, more detailed description thereof. These involve preferred catalytic composites, operating conditions and various operating techniques.

SUMMARY OF INVENTION As hereinbefore set forth, the present invention is directed toward a multiple-stage hydrocracking process wherein the charge stock contains aromatic hydrocarbons, nitrogenous compounds and sulfurous compounds. The hydrocracking process, encompassed by my invention, is a catalytic process, preferably conducted in a fixed-bed system. The particular choice of catalyst forms no essential part of my invention, and a greatly detailed discussion thereof is not necessary to a clear understanding of the manner in which the present process is effected. There are, however, certain aspects relative to the catalytic composites which are distinctly preferred. For example, although the catalytic composite may be the same in all three of the reaction zones, in view of the fact that the functions serve thereby are distinctly different one from the other, a preferred method utilizes catalysts having similar, but different characteristics. In general, the process makes use of catalytic composites having a hydrogenation/dehydrogenation function, coupled with a cracking function. Dual-function catalysts are thoroughly described in the literature, and are utilized for the purpose of promoting a wide variety of hydrocarbon conversion reactions. It is generally thought that the cracking function is associated with an acid-acting carrier material of a porous, adsorptive, refractory inorganic oxide type. The carrier material is utilized as the support for one or more heavy metal components, generally the metals or compounds of metals of Groups V through VIII of the Periodic Table.

It is well-known to those skilled in the art, that the principal cause of catalytic deactivation, or instability, of such dual-function catalysts is principally associated with the fact that coke forms on the surface of the catalyst during the course of the reaction. The coke stems from the formation of heavy, high molecular weight, solid or semi-solid, hydrogen-poor carbonaceous material which reduces the effectiveness of the catalyst by shielding the active sites from the material being processed. This difficulty is further compounded by the simultaneous presence of aromatic hydrocarbons and nitrogeous compounds in the fresh feed charge stock. As hereinbefore set forth, the mononuclear aromatics, or their partially hydrogenated derivatives, can undergo condensation to produce polynuclear compounds, the latter actually functioning as a catalyst poison.

Catalytic composites suitable for use in the process of the present invention constitute a carrier material of the crystalline aluminas known as gamma-, eta-, and thetaalumina, and which generally contain other refractory inorganic oxides such as silica, zirconia, magnesia, etc. In general, the carrier preferably constitutes a mixture of alumina and one of the aforementioned oxides. Thus, the carrier material may comprise alumina containing from about 10% to about 90% by weight of silica. At the operating conditions utilized, the carrier material employed in the hydrocracking reaction zone will contain a greater percentage of silica; similarly, the carrier material utilized in the denitrification reaction zone will contain a somewhat lesser quantity of silica, but greater than that utilized in the carrier material within the desulfurization reaction zone. The carrier material may be characterized as amorphous or zeolitic, the latter including mordenite, faujasite, type A or type U molecular sieves, etc. With respect to the hydrocracking reaction zone, a particularly preferred carrier material is a crystalline 'aluminosilicate of which at least about 90.0% by weight is zeolitic. The carrier material may be prepared in any suitable manner, and may be activated prior to use by one or more treatments including drying, calcination, steaming, etc. Although generally existing in some combined form, the concentration of the catalytically active metallic components is calculated on the basis of the elemental metals. Suitable hydrocracking catalysts will contain from about 0.01% to about 30.0% by weight of one or more metals, or compounds thereof, from the groups of vanadium, chromium, iron, cobalt, nickel, niobium, molybdenum, technetium, ruthenium, rhodium, palladium, tantalum, tungsten, rhenium, osmium, iridium and platinum. Another constituent of hydrocracking catalysts, suitable for use in the process of the present invention is a halogen component. While the precise form of association of the halogen component of the carrier material is not accurately known, it is customary in the art to refer to the halogen component as being combined with the carrier, or with the other ingredients of the catalyst therein. Combined halogen may be either fluorine, chlorine, iodine, bromine or mixtures thereof; of these, fluorine and chlorine are particularly preferrd. The halogen will be composited with the carrier material in such a manner as results in a final catalytic composite containing from about 0.1% to about 2.0% by weight of a halogen component, calculated as the element.

The metallic components may be incorporated within the catalytic composite in any suitable manner including co-precipitation or co-gellation with the carrier, ionexchange, or impregnation of the carrier, and either after or before calcination. Following the incorporation of the metallic components, the carrier material is dried and subjected to a high temperature calcination or oxidation technique at a temperature of about 750 F. to about 1300 F. When a crystalline aluminosilicate is utilized as the carrier material, the upper limit for the calcination step is about 1000 F.

One particularly preferred catalyst preparation technique involves the water-free reduction of the calcined composite. This particular step is designed to insure a more uniform and finely divided dispersion of the metallic components throughout the carrier material. Substantially pure and dry hydrogen, containing less than 30.0 volume ppm. of water is utilized as the reducing agent. The reduced catalytic composite is then subjected to a presulfiding technique to incorporate from about 0.05% to about 0.50% by weight of sulfur, on an elemental basis, within the final catalytic composite.

With respect to the desulfurization catalyst, the carrier material contains an excess of alumina with respect to silica, for example, 88.0% by weight of alumina and 12.0% by weight of silica. For effective desulfurization, this carrier material may then be combined with 11.3% by weight of molybdenum, 4.2% by weight of nickel and 0.05% by weight of cobalt.

With respect to the denitrification catalyst, the quantity of silica is generally increased, for example, 63.0% by weight of alumina and 37.0% by Weight of silica. A suitable catalyst, utilizing this carrier material, would include 2.0% by weight of nickel and 16.0% by Weight of molybdenum. In many instances, depending upon the concentration of nitrogenous compounds, calculated as nitrogen, within the fresh feed charge stock, the catalyst in the denitrification zone will be prepared from a carrier material also containing boron phosphate in amounts from about 2.0% to about 25.0% by weight.

As hereinbefore stated, the hydrocracking catalyst contains the greater percentage of silica in the carrier material. Thus, one suitable hydrocracking catalyst comprises a carrier material of 75.0% by weight of silica and 25 .0% by weight of alumina, with which is combined 5.0% by weight of nickel. Another suitable catalyst utilizing the 75/25 silica alumina carrier material, has impregnated thereon about 0. 4% by weight of platinum. A particularly preferred hydrocracking catalyst consists of about 5.0% by weight of nickel on a high silica faujasite, crystalline aluminosilicate, of Which at least about 90.0% by weight is zeolitic.

The operating conditions, under which the process is conducted, will vary according to the physical and chemical characteristics of the charge stock, as well as the desired end result. With the exception of the catalyst bed temperature, these operating conditions may be the same in each of the three reaction zones, or entirely different one from the other. The various reactions, hydrocracking, desulfurization and denitrification, are effected at elevated pressures in the range of from about 500 to about 5,000 p.s.i.g., and preferably at some intermediate level of about 800 to about 3,500 p.s.i.g. A preferred technique constitues serial flow through the three reaction zones, starting with the hydrocracking reactor, and, therefore, the hydrocracking reactor will normally function at a higher pressure level than the other reaction zones. The latter will function at a slightly lower pressure due to the pressure drop experienced as a result of fluid flow through the system. As utilized herein, operating temperature alludes to the maximum temperature of the catalyst within the reaction zone; this is also commonly referred to as the reactor outlet temperature. Since the principal reactionsbeing effected are exothermic in nature, an increasing temperature gradient is experienced as the material flows through the catalyst bed, with the result that the outlet temperature is higher than that at the inlet to the catalyst bed. A preferred technique limits the temperature increase to 100 F., or less, and this may be readily accomplished through the use of conventional quench streams, either normally liquid or normally gaseous, being introduced at one or more intermediate loci of the reaction zone. The maximum catalyst bed temperature within the hydrocarcking reaction zone is within the range of about 800 F. to about 900 F., and higher than that in either of the other two reaction zones. The maximum catalyst bed temperature within the desulfurization, or second, reaction zone is within the range of about 700 F. to about 800 F., and higher than the maximum catalyst bed temperature Within the third, or denitrification reaction zone. The latter has a maximum catalyst bed temperature confined Within the range of about 650 F. to about 725 :F. At these conditions, nitrogenous compounds contained within the charge stock are converted to hydrocarbons and ammonia, with some conversion of sulfurous compounds to hydrogen sulfide and hydrocarbons. Furthermore, at least partial saturation of aromatic hydrocarbons is eifected. The normally liquid product effluent, substantially free from nitrogenous compounds, is subjected to hydrocracking Without incurring the detrimental effect of the simultaneous presence of nitrogenous compounds and aromatic hydrocarbons. The hydrocracked product effluent, containing high-boiling sulfurous compounds, is then subjected to desulfurization, the desulfurized normally liquid product effluent being admixed with the charge stock for introduction into the denitrification reaction zone.

Liquid hourly space velocities (defined as volumes of hydrocarbon charge per hour per volume of catalyst disposed in the reaction zone) of from about 0.25 to about 10.0 are suitable, the lower range generally being considered necessary for the heavier stocks. Hydrogen circulation rate will be at least about 3,000 standard cubic feet per barrel, having an upper limit of about 50,000 standard cubic feet per barrel, based upon fresh feed. For the majority of feed stocks, hydrogen concentrations in the range of 5,000 to 20,000 standard cubic feet per barrel will sufiice. As hereinafter indicated in the description of the accompanying drawing, the overall process is facilitated since the hydrogen circulation constitutes series-flow, starting with the hydrocracking reaction zone. The overall process is further facilitated by the fact that the second and third reaction zones can be stacked with the fresh feed charge stock being introduced at a locus therebetween. This in effect provides a quench stream for the material which has passed through the desulfurization zone, and which is at a temperature higher than that desirable in the denitrification reaction zone.

Other operating conditions and processing techniques will be presented in the following description of the accompanying drawing.

DESCRIPTION OF DRAWING In the drawing, only those vessels and lines necessary for a clear understanding of the present process are presented. Various valves, control valves, knock-out pots, compressors, heat-exchangers, and start-up lines have been eliminated from the drawing. These as 'well as other miscellaneous appurtenances are well within the purview of one possessing expertise in the art of petroleum refining. Further, the drawing will be described in conjunction with a commercially-scaled unit processing a blend of gas oils in an amount of 8,500 barrels per day. The intended object is to produce maximum quantities of a heptane-3 F. gasoline boiling range product.

The blended charge stock is a mixture of a virgin gas oil, a heavy vacuum gas oil, a light cycle oil and a heavy cycle oil having the following gravities in API 37.6, 25.7, 22.5, and 17.4, respectively. Pertinent properties of the blended material are a gravity of 32.7 API, an initial boiling point of 374 F., at 50.0% volumetric distillation temperature of 524 F. and an end boiling point of 791 F. The blended charge is contaminated by the presence of 3,150 p.p.m. of sulfur, 51 p.p.m. of nitrogen and constitutes about 29.1% by volume aromatic hydrocarbons.

A hydrocracked product effluent is Withdrawn from reactor 14, containing catalyst bed 15, by way of line 16, at a temperature of about 850 F. The catalytic composite disposed within reactor 14 constitutes 5.0% by weight of nickel combined with a carrier material of 75.0% by Weight of silica and 25.0% by weight of alumina. Following its use as a heat-exchange medium, to decrease its temperature to a level of about 650 F., the hydrocracked product efiluent continues through line 16, being introduced thereby into reactor 2. Reactor 2 is under an imposed pressure of about 1,450 p.s.i.g. and contains a catalyst bed 3 of 11.3% by weight of molybdenum, 4.2% by weight of nickel and 0.05% by weight of cobalt combined with a carrier material of 88.0% by Weight of alumina and 12.0% by weight of silica. Catalyst bed 3 is in an amount such that the liquid hourly space velocity of the material flowing therethrough is about 2.4. The outlet temperature of catalyst bed 3 is about 750 F., and is quenched by the fresh feed charge stock entering by way of line 1, to a temperature of about 575 F. It should be noted that reactor 2 contains separate and distinct beds of catalyst 3 and 4, and in a stacked position. The charge stock in line 1 is introduced therebetween by way of locus 5. The particular manner by which catalyst beds 3 and 4 are separated in reactor 2, and the internal means by which the charge stock in line 1 and the product effluent from catalyst bed 3 are intimately admixed, are not considered to be essential features of my invention.

Catalyst bed 4, the primary function of which is to effect the denitrification of the charge stock entering line 1, and partial desulfurization, especially of the lowerboiling components, constitutes a carrier material of 63.0% by weight of alumina and 37.0% by weight of silica, with which is combined 2.0% by weight of nickel and 16.0% by weight of molybdenum. The catalyst employed is in a quantity such that the liquid hourly space velocity, based upon the 8,500 barrels per day of fresh feed charge stock only is about 2.4. The product eflluent emanating from catalyst bed 4 by way of line 6 is at a temperature of 675 F. Following its use as a heatexchange medium, and further cooled to a temperature of about 110 F., the efiluent continues through line 6 into cold separator 7. Cold separator 7 serves to provide a principally vaporous phase rich in hydrogen, withdrawn by way of line 8, and a normally liquid product effiuent indicated as being withdrawn by way of line 9. Although not indicated in the drawing, the ammonia, resulting from the conversion of nitrogenous compounds, may be readily removed from the product effluent of line 6 by the well-known technique of injecting water therein prior to introducing the same into cold separator 7. Cold separator 7 is then equipped with a water dip-leg from which the sour water containing ammonia is removed and transported to suitable waste facilities. Thus, the normally liquid portion of the product effluent in line 9 is substantially free from absorbed ammonia. The hydrogen-rich vaporous phase in line 8 may be suitably treated by any well-known means for the purpose of removing therefrom hydrogen sulfide resulting from the conversion of the lower-boiling sulfurous compounds in the charge stock. Lower-boiling sulfurous compounds are considered to be those boiling within the gasoline boiling rangei.e. at temperatures below about 400 F. Following the removal of hydrogen sulfide, the hydrogen-enriched vaporous phase is introduced into reactor 14 by compressive means not indicated in the drawing. Reactor 14 is maintained at a pressure of about 1,500 p.s.i.g. by way of a pressure control valve also not indicated. Make-up hydrogen, required to compensate for that consumed in the process and removed by way of dissolution in the product streams, may be added at any point, and from any suitable source such as a hydrogen-producing process. Convenience dictates that the make-up hydrogen enter the process by way of line 8, in an amount such that the hydrogen circulation through reactor 14 is in an amount of about 8,400 standard cubic feet per barrel. Catalyst bed 15 is utilized in an amount such that the liquid hourly space velocity therethrough is of the order of about 0.65.

The normally liquid product eflluent from cold separator 7 continues through line 9 into product separation facility 10. Product separation facility 10 will obviously be designed to conform to the recovery of one or more desired product streams. As indicated in the drawing, hydrocarbonaceous material boiling below heptane is removed by way of line 11 as an overhead stream. The stream may be further separated to provide a C /C concentrate suitable for use in motor fuel blending. The desired product, gasoline boiling from heptane to about 380 F., is removed by way of line 12. A bottoms stream, comprising that portion of the product efi'luent boiling TABLE.PRODUCT YIELD AND DISTRIBUTION Weight, Volume, Component percent percent Ammonia Of interest is the fact that the foregoing product yield and distribution was obtained with a total chemical consumption of hydrogen of only 1,617 standard cubic feet per barrel (2.84% by weight). Of further interest is the fact that the 18.36% by volume butanes produced constituted 70.0% iso-butane. The total pentane/ hexane fraction has a gravity of about 833 API and a research octane rating (clear) of 85, the research octane rating (3 ml. TEL.) of 99. The desired gasoline fraction indicates a gravity of 53.2 API, a research octane rating (clear) of 64, a research octane rating (3 ml. TEL.) of 82, and consists of about 36.0% by volume parafiins, 52.0% by volume naphthenes and 12.0% by volume aromatics. It will be recognized that this type of gasoline boiling range fraction forms an excellent charge for a catalytic reforming unit in order to increase the octane rating thereof.

The foregoing specification, and particularly the example integrated into the description of the drawing, clearly illustrates the method of effecting the process of the present invention, and indicates the benefits to be afforded through the utilization thereof.

I claim as my invention:

1. A catalytic process for converting a sulfurous charge stock, containing nitrogenous compounds and aromatic hydrocarbons, into lower-boiling hydrocarbon products of predetermined end boiling point, which process comprises the steps of:

(a) reacting a substantially nitrogen-free portion of said charge stock, and hydrogen in a first reaction zone, in contact with a first catalytic composite, at conversion conditions including a maximum catalyst bed temperature of 800 F. to about 900 F.;

(b) introducing the resulting first zone eflluent into a second reaction zone, and reacting the same and hydrogen, in contact with a desulfurization second catalytic composite, at desulfurization conditions including a maximum catalyst bed temperature of 700 F. to about 800 F.;

(c) introducing said charge stock and the resulting total second zone effluent into a third reaction zone, and reacting the same and hydrogen, in contact with a third catalytic composite, at conditions including a maximum catalyst bed temperature of about 650 F.

to about 725 F and selected to convert nitrogenous compounds;

(d) separating the third reaction zone eflluent to provide a hydrogen-rich vaporous phase, to recover said lower-boiling products and to provide a normally liquid stream boiling above said predetermined end boiling point and containing said nitrogen-free porton of said charge stock; and, (e) reacting said normally liquid stream in said first reaction zone. 2. The process of claim 1 further characterized in that said first catalytic composite contains a Group VIII metal component combined with a siliceous carrier material.

3. The process of claim 1 further characterized in that said and third catalytic composites contain at least one metal component from the metals of Groups VI-B and the Iron-group.

4. The process of claim 1 further characterized in that said first catalytic composite contains a Group VIII metal component combined with a crystalline aluminosilicate carrier material.

5. The process of claim 1 further characterized in that the maximum catalyst bed temperature is lower in said third reaction zone than in said second reaction zone.

6. The process of claim 1 further characterized in that said hydrogen flows serially through said first, second and third reaction zones.

References Cited UNITED STATES PATENTS 6/1966 Hass et al. 20889 8/1967 Wood 208-97 U.S. Cl. X.R.

Images