US3475322A - Hydrocracking process - Google Patents

Description

/NVE/V'TOR' Don B. Carson A rroR/vfys D. B. CARSON HYDROCRACKING PROCESS Filed Aug'. l. 1966 Oct. 2s, 1969 United States Patent O U.S. Cl. 208-89 6 Claims ABSTRACT OF THE DISCLOSURE Method for hydrocracking hydrocarbons using a plural stage reactor system and efiiuent-heat exchange for reactor temperature control. A hydrogenation conditioning zone is utilized prior to the hydrocracking zone. Gasoline boiling range materials are obtained as product from distillate and residual oils.

This invention relates to a method for converting hydrocarbons into lower boiling hydrocarbon products. It particularly relates to a catalytic hydrocracking method for converting hydrocarbons into lower molecular weight products. It specifically relates to an improved method for achieving thermal balance within a catalytic hydrocracking process.

Hydrocracking or destructive hydrogenation, as distinguished from the relatively simple addition of hydrogen to unsaturated bonds between carbon atoms, effects definite changes in the molecular structure of hydrocarbons. It is of significant commercial interest since hydrocracking offers unique advantages over conventional catalytic cracking operations. Therefore, hydrocracking may be designated as a conversion process wherein not only are lower molecular weight or lower boiling products produced, but these conversion products resulting therefrom are substantially more saturated than when hydrogen or material supplying hydrogen is not present. Typically, hydrocracking processes are employed for the conversion of various coals, tars, and heavy residual oils into lower boiling, more saturated and, in most cases, more valuable products. t

Although many of the prior art processes may be conducted on a strictly thermal basis, the preferred processing technique involves the utilization of a catalytic mass possessing a high degree of hydrocracking activity. By use of proper catalysis, the hydrocracking reaction can selectively convert a wide variety of feedstocks to lower boiling distillates with significantly less gas and coke yield and higher yields of good quality liquid products than are usually produced by catalytic cracking.

Much of the effort on the part of the prior art has been to develop processing schemes to increase the selectivity of the catalytic mass used for the hydrocracking reaction. However, since this reaction is strongly exothermic in nature, there has been only a small effort on the part of the prior art to improve on the utility and capital costs for a conventional hydrocracking process.

Therefore, it is an object of this invention to provide a method for converting a hydrocarbon feedstock to lower boiling hydrocarbons. It is another object of this invention to provide an improved method for converting nitrogen-contaminated hydrocarbons into lower boiling hydrocarbons substantially free from nitrogenous compounds. It is a particular object of this invention to provide an improved method of achieving thermal balance in a catalytic hydrocracking process which uses plural stage reactors.

These and other objects will be achieved by the invention particularly described hereinbelow and illustrated by reference to the appended drawing which is schematic 3,475,322 Patented Oct. 28, 1969 flow diagram of one specified embodiment of the invention.

According to the present invention, a method for converting a hydrocarbon feedstock containing less than 1,000 p.p.m. total nitrogen to lower boiling hydrocarbons comprises subjecting said feedstock to conditioning treatment in the presence of a hydrogenation catalyst and added hydrogen under conditions sufficient to convert at least part of said nitrogen to ammonia without substantial conversion of the feedstock hydrocarbons to lower boiling hydrocarbons; passing the total conditioned efiiuent, including said ammonia, into a first catalyst bed of a plural catalyst bed conversion zone under conditions, including a first conversion temperature, suicient to convert feedstock hydrocarbons to lower boiling hydrocarbons; withdrawing a first reaction product stream from said first bed at a temperature substantially above said first conversion temperature; quenching the first reaction product stream to substantially said first conversion temperature by indirect heat exchange with a portion of said feedstock; passing said quenched reaction product stream directly to a second catalyst bed of said zone under conditions, including a second conversion temperature, sufiicient to convert at least part of the feedstock hydrocarbons to lower boiling hydrocarbons; withdrawing a second reaction product stream from said second bed at a temperature substantially above said second conversion temperature; quenching the second reaction product stream to at least said second conversion temperture by indirect heat exchange with another portion of said feedstock; and, recovering lower boiling hydrocarbons from the final reaction product from said conversion zone.

A more particular embodiment of this invention relates to an improved method for a process of converting nitrogen contaminated hydrocarbons, having a boiling range from 500 F. to about 1,0007 F., into lower boiling hydrocarbons substantially free from nitrogenous compounds by catalytic hydrocracking using plural stage reactors which comprises passing preheated said nitrogencontaminated hydrocarbons, as hereinbelow specified, into a hydrorefining zone under conditions sufiicient to convert nitrogenous compounds to ammonia without substantial cracking of said hydrocarbons; cracking the normally liquid products from the hydrorefining zone in the presence of added hydrogen in a first reactor stage of a plural stage conversion zone containing catalyst maintained at hydrocracking conditions, including a conversion temperature, by passing said liquid products through the reactor in a radial flow path; withdrawing from the first reactor stage a first conversion produ-ct stream at a temperature substantially above said conversion temperature; quenching the first conversion product stream to substantially said conversion temperature by indirect heat exchange with a portion of the nitrogen-contaminated hydrocarbons thereby preheating same as specified; cracking additional liquid hydrocarbons in said first product stream into lower boiling hydrocarbons n a second reactor stage of said conversion zone maintained at hydrocracking conditions, by passing said first conversion product stream through the reactor in a radial flow path; withdrawing from the second reactor stage a second conversion product stream at a temperature above said conversion temperature; quenching the second conversion product stream to at least said conversion temperature by indirect heat exchange with another portion of said nitrogen-contaminated hydrocarbons thereby preheating same as specified; and, recovering lower boiling hydrocarbons substantially free from nitrogenous compounds.

A critical feature of the present invention is that the method must be operated in plu-ral stages by hydrocracking, for to do otherwise would not permit the achieving of thermal balance as uniquely obtained by the inventive method. Those skilled in the art recognize that the hydrocracking reaction is substantially exothermic in nature. Therefore, the heat generated by the reaction must be removed in a controlled manner if selective hydrocracking is to be achieved. Most of the prior art processes utilize a quenching medium which is injected in physical admixture with the reactor eluent in order to absorb the excess heat of reaction prior to the next stage of the reaction. The use of the injection method has the disadvantage of requiring substantially larger reactor sizes and requiring substantially more catalyst in order to handle the additional material through the reactors. In any event, the prior art processes experience considerable pressure drop through the catalyst bed, thereby necessitating extremely high capacity pumping means and also requiring the operation of the process at a substantially elevated pressure in order to overcome the pressure drop through the reaction. Additionally, the use of the injection method inceases heat and power requirements for the operating unit.

It is noted from the discussion above that one embodiment of the present invention contemplates the use of a radial tlow reactor design. Typically, such a design is represented in U.S. Patent No. 2,634,194 to H. J. Nebeck, and has the advantage of minimizing pressure drop through the reactor. Therefore, one of the basic principles involved in this embodiment of the present invention is the utilization of radial ow reactors whereby the additional pressure drop experienced through indirect heat exchange means does not become objectionable. On the other hand, it is to be noted that the prior art processes, having extremely large pressure drops through the reactor, could not tolerate the additional pressure drop from using indirect heat exchange on the reactor eluent as a quenching means without significantly increasing capital costs for pumps, reactors, etc.

Suitable charge stocks for the practice of the present invention include kerosene fractions, gas oil fractions, lubricating oil and white oil stocks, cycle stocks, fuel oil stocks, reduced crudes, various high boiling bottoms fractions including vacuum residium, and other sources of hydrocarbons having a depreciated market demand due to the high boiling points of these hydrocarbons accompanied by the usual presence of asphaltic and other heavy residues. The present invention is particularly directed toward processing the heavier of the aforementioned hydrocarbon feedstocks; namely, vacuum gas oil fractions, heavy cycle stocks, reduced crudes, etc., that is, those hydrocarbons having an initial boiling point in excess of 650 F., preferably having a boiling range from 650 F. to about 1,000F. Generally, all of these sources of hydrocarbon feedstocks contain nitrogenous compounds, and it is distinctly preferably for the practice of this invention, however, to limit the total nitrogen content of the feedstock to less than 1,000 ppm. total nitrogen.

The catalyst used in the practice of the present invention may be any hydrcracking catalyst known to those skilled in the art as being selective for the hydrocracking reaction in the presence of nitrogenous compounds, such as ammonia, Thus, in regard to nitrogen-insensitive catalyst, the term metallic component or catalytically active metallic component is intended to encompass those catalytic components which are employed for their hydrocracking activity, or for their propensity for the destructive removal of the nitrogenous compounds, as the case may be, and which components are selected from the metals and compounds of Groups VI-A and VIII of the Periodic Table. In this manner, the metallic catalytic components are distinguished from those components which are employed as the solid support, or carrier material, or the acidic cracking component. The metallic component of the catalyst which may be employed in the practice of this invention may comprise two or more of such metals. Thus, the catalyst employed in the present method may comprise chromium, molybdenum, tungsten, iron, cobalt, nickel, palladium, platinum, ruthenium, rhodium, osmium, iridium, and mixtures of two or more including nickel-molybdenum, nickel-chromium, molybdenum-platinum, cobalt-nickel-molybdenum, molybdenum-palladium, chromium-platinum, chromiumpalladium, molybdenum-nickel-palladium, etc.

As hereinafter set forth in greater detail with respect to the embodiment of the present invention represented by the appended drawing, the method of the present invention must be composed of two or more separate, but integrated, reaction stages representing a plural stage conversion zone containing catalyst. Each stage may contain a distinct catalytic composite of the same composition in each stage, or any combinations and mixtures of catalyst depending upon the needs of the business situation experienced by those skilled in the art.

Regardless of the particular catalytically active component or components, these are composited with a suitable solid carrier material which may be either naturally occurring or which may be synthetically prepared by means known to those in the art. Naturally occurring carrier materials include various aluminum silicates, particularly when acid treated to increase the activity thereof, various alumina-containing clays, sands, earths and the like. Typically, the synthetically prepared components include at least a portion of both silica and alumina. Other suitable carrier material components which may, in particular instances, be combined as an integral portion of the hydrocracking catalyst include zirconia, magnesia, thoria, boria, titania, strontia, hafnia, etc., with the preferred cracking component consisting essentially of the composite of silica and alumina.

Since the various embodiments of the present invention utilize a hydrocarbon feedstock containing nitrogenous compounds, but having preferably less than 1,000 p.p.m. total nitrogen, it is distinctly preferable to practice the present invention as a combination process which utilizes as a first step of the combination method, a hydroretining reaction, in order to convert the nitrogenous compounds into ammonia. By operating in this manner, the ammonia can be easily removed from the tinal reaction product from the subsequent hydrocracking conversion zone by, say, water washing, thereby leaving behind lower boiling hydrocarbons substantially free from nitrogenous compounds. The hydrorening treatment preferably is operated as an integral part of the overall hydrocracking process, i.e., the entire hydrorener eluent is passed directly through the first hydrocracking stage without intervening condensation or purification.

The hydrorening operation may be conducted either adiabatically or isothermally, and generally is practiced at a temperature from 600 F. to 850 F.. preferably from 650 F. to 750 F.; a pressure from 500 to 3,000 p.s.i.g., preferably from 800 to 2,000 p.s.i.g.; liquid hourly space velocity (LHSV) from 0.5 to 10, preferably from 0.75 to 5; and a hydrogen-to-oil ratio from 500 to 20,000 s.c.f./b., preferably from 1,000 to 10,000 s.c.f./b. r[hose skilled in the art know how to suitably adjust these conditions in order to convert at least part of the total nitrogen present to ammonia without substantial conversion of the feedstock hydrocarbons to lower boiling hydrocarbons.

Referring now to the drawing, the hydrocarbon charge stock, contaminated by a substantial quantity of nitrogenous compounds on the order of from 300 to 500 ppm. total nitrogen, enters the process from line 10, continuing into line 11 where it is admixed with hydrogen which is introduced by recycle via line 42. Although indicated as having a boiling range from an initial boiling point of 650 F. to about 1,000 F., the hydrocarbon charge in line 10 is not intended to be limited thereto although the method of the present invention is especially adaptable to the processing of nitrogen-contaminated hydrocarbons boiling in excess of 650 F.

In any event the mixture of hydrogen and hydrocarbon in line 11 entering exchanger 12 is such that the hydrogen is present in an amount Within the range of from 500 to 20,000 standard cubic feet per liquid barrel of charge. Typically, the hydrogen is present in an amount of approximately 8,000 s.c.f./b. The mixture is raised to about 500 F. in exchanger 12 by indirect heat exchange with the final reactor effluent and is passed through line 13 in split flow arrangement through heat exchangers 16 and 17, respectively, utilizing lines 14 and 15, respectively. In other Words, separate portions of the nitrogen-contaminated hydrocarbon pass in indirect heat exchange with the reactor effluent leaving hydrocracking reactors 25 and 27, more fully discussed hereinafter, and wherein the combined feed hydrocarbons plus hydrogen are heated to a temperature of approximately 725 F. in line 18. The preheated hydrocarbons are passed from line 18 into the first hydrorefining reactor 19. The hydrorefining conditions, which are sufficient to convert nitrogenous compounds to ammonia without substantial conversion of the feed hydrocarbons to lower boiling hydrocarbons, are those specified hereinabove, but typically include a temperature of 725 F., a pressure of 1500 p.s.i.g., and a LHSV of 0.75. The partially hydrorefined product is removed from reactor 19 via line 20 and passed in admixture with additional hydrogen introduced through line 38 into a cleanup hydrorefining reactor 22 via line 21. The conditions maintained in reactor 22 are substantially the same as for reactor 19.

Under these hydrorefning conditions and in the presence of a catalyst, the organically bound nitrogenous compounds are separated at the nitrogen-hydrogen bonds to form ammonia which is released in a free form from the Ireaction media. The total reactor effluent which has now been conditioned for the hydrocracking reaction, is removed from cleanup reactor 22 through line 23 into the first reactor stage 25 Without intervening separation or purification.

In order to maximize the production of distillate fractions from the hydrocracking reaction, the undesired heavy hydrocarbons are normally recycled to the reactor; therefore, additional hydrogen gas and recycle oil in line 39 are admixed with the conditioned hydrorefined efliuent in line 24 for passage through the plural catalyst bed conversion zone as hereinafter discussed.

The conditioned hydrofined effluent, together with heavy recycle oil and hydrogen is passed into the first hydrocracking reactor 25, the precise operating conditions of which will be dependent upon the various physical and/ or chemical characteristics of the particular hydrocarbons being processed. Generally, this first stage reactor will be maintained at a conversion temperature of from 650 F. to 900 F., preferably about 725 F. and under an imposed pressure within the range of 300 to 3,000 p.s.i.g., preferably about 1500 p.s.i.g. Higher pressures appear to favor the destructive removal of any remaining nitrogenous compounds as Well as the conversion of those hydrocarbons boiling in excess of about 650 F. The total hydrocarbons in the feedstock to hydrocracking reactor 25 will contact the particular catalyst employed at a liquid hourly space velocity within the range of about 0.5 to about 10, preferably about 1.5.

The catalyst deposed within this first catalyst bed serves a dual function: that is the catalyst is nonsensitive to the presence of nitrogenous compounds While, at the same time, it is capable of effecting the destructive removal thereof, and also effects conversion of at least a portion of those hydrocarbons boiling at a temperature in excess of about 650 F. to 700 F. The process conditions are adjusted in reactor 25 to provide preferably, about to 60% by volume conversion to lower boiling hydrocarbons per pass.

Since the hydrocracking reaction is exothermic in nature, the etliuent from reactor 2S is withdrawn at a temperature substantially above the conversion temperature, e.g. 800 F., through line 26 and passed into exchanger 17 wherein the reactor 25 effluent is quenched to a temperature substantially equal to the conversion temperature maintained in reactor 25, to wit: about 725 F., by indirect heat exchange with a portion of the feed hydrocarbons as hereinabove discussed. The quenched efiiuent stream is passed via line 26 into a second catalyst bed 27 which is maintained under substantially the same conditions as were imposed on the first catalyst bed 25.

In some cases, it may be desirable to impose a different set of conditions on the second catalyst bed depending upon the nature of the feedstock and the desirable products to be produced. In other words, the amount of quenching which is performed in heat exchanger 17 can be adjusted so that the temperature of the hydrocarbons in line 26 may be either greater or less than the temperature used in reactor 25. Preferably however, the temperature of the hydrocarbons in line 26 is substantially the same as the conversion temperature used in reactor 25. Thus, the effluent is passed through the catalyst bed 27 whereby additional cracking of hydrocarbons occurs. Again, due to the exothermic nature of the reaction, the effluent from the second catalyst bed 27 is removed therefrom at a temperature substantially in excess of the conversion temperature used in catalyst bed 27; that is, the effluent is Withdrawn in line 2S at a temperature of about 800 F.

The eiiuent from the second catalyst bed at its elevated temperature is passed through heat exchanger 16 where it is quenched to a temperature substantially equal to the conversion temperature maintained in the second catalyst bed 27 by indirect heat exchange with another portion of the feedstock hydrocarbons as hereinbefore discussed. The quenched eiuent is removed from exchanger 16 and passed into the third bed of the conversion zone via line 28. In the third bed 29 additional hydrocracking takes place such that the total conversion of hydrocarbons to lower boiling hydrocarbons will be as high as by volume. The total reaction product is removed from the conversion Zone via line 30 and cooled from its elevated temperature of, say 800 F. to for exP ample, 600 F. in heat exchange-r 31 and, then, to 300 F. for example in exchanger 12 from whence it passes into separator 32.

In separator 32 the hydrogen-containing gas is removed via line 37 and recycled in part to the hydrorening step of the process via line 38, in part to the heavy oil recycle stream in line 39, via lines 40 and 41, and in part to admixture with the feedstock hydrocarbons in line 11 via lines 40 and 42. The relative amounts of hydrogen recycle, which are directed into each of the aforementioned portions, is not critical. Those skilled in the art can determine the hydrogen partial pressures desirable in each step of this operation from a knowledge of its behavior. Makeup hydrogen, as needed to the system, is added via line 39.

Referring again to separator 32, the normally liquid products are removed from separator 32 and passed into fractionating column 34 wherein the desired lower boiling hydrocarbons are removed to storage via line 36, and the undesired heavy hydrocarbons, i.e., those boiling in excess of 650 F., are recycled to the process through line 35 as hereinabove discussed. It is noted that additional economies in the thermal balance of the process are achieved by recycling the heavier oil through exchanger 31 in order to partly cool the final reaction product, and by the passage of the feedstock hydrocarbons plus hydrogen recycle through exchanger 12 for additional cooling of the final reaction product, thereby add-ing preheat to the feedstock hydrocarbons as hereinabove mentioned.

The gaseous ammonia formed and acid gases, such as hydrogen sulfide, are removed from the total reactor efiiuent in any suitable means not shown. For example, the total reactor efiiuent may be admixed with water and thereafter by be subjected to separation such that the ammonia will be absorbed within the water phase, or as another example, the total reaction zone efiiuent may be passed into a separate separation zone counter-currently to a suitable liquid absorbent whereby the ammonia, hydrogen sulfide, etc., are effectively removed therefrom.

Since it is desired that the few light parafiinic hydrocarbons, such as methane, ethane, and propane, are also removed from the efiiuent, separation zone 32 may comprise a low temperature flash chamber Where-by the ammonia and light parainic hydrocarbons are removed as a gas phase. These light parafiinic hydrocarbons, along with a small amount of normally liquid hydrocarbons, may be passed into a separate fractionation column, not shown, whereby the light parafiinic hydrocarbons are removed from the system, thereby also purifying the hydrogen gas for recycle following the removal of ammonia from the effluent of the latter fractionating column.

As hereinbefore set forth, regardless of the particular separating means employed, the resulting normally liquid hydrocarbons having a lower molecular weight than the feedstock hydrocarbons and boiling within the range of 100 F. to about 700 F., will contain some residual nitrogenous compounds. Therefore, alternatively the normally liquid hydrocarbons may be distilled in a sidecut fractionator under such conditions as will yield a heartcut of lower boiling hydrocarbons having a boiling range of about 400 F. to about 650 F., which is substantially free from nitrogenous compounds. As mentioned previously, the hydrocarbon fraction boiling in excess of about 650 F., may be recycled to combine with the charge stock to the hydrocracking conversion zone.

It is understood that the broad scope of the present invention is not to be unduly limited to a particular catalyst or to a particular means for manufacturing the catalyst, since each of these is conventional and wellknown to those skilled in the art. The choice of a particular catalytic composite, as well as the operating conditions for each stage of the process, will of necessity yield results which are vastly different when compared to another. Therefore, the present invention is not necessarily predicated on a particular set of operating conditions or catalyst. However, an essential feature of the present invention, as pointed out hereinabove, is the plural stage catalytic conversion zone having integrally connected therewith a charge stock heat exchanger system whereby the efiiuent from each stage is effectively quenched and the feedstock is effectively preheated. It follows, therefore,that from a judicious choice of operation conditions the feedstock can be preheated via the heat exchange system disclosed, such that no external heat need be supplied to achieve, for example, the conditioning or hydrofining operating temperature.

Preferably, the operation of the present invention is accomplished utilizing a radial fiow path for effectuating the contact between the reactants and the hydrocracking catalyst. It is to be understood that the radial fiow may be accomplished in either upflow or downfiow, either infiow or outflow, or any combination of these desired by those skilled in the art. It follows also that the operation of the present invention is not applicable to those of the moving bed type or suspensoid type of operation in which the catalyst and hydrocarbons are passed as a slurry through the reaction zone.

Therefore, from the discussion presented herein, another broad embodiment of the present invention relates to an improved method for converting a hydrocarbon feedstock having a boiling range from 650 F. to about l,000 F., into lower boiling hydrocarbons by catalytic hydrocracking in a fixed bed reactor which comprises cracking preheated feedstock, as hereinbelow specified, in the presence of added hydrogen in a reactor containing hydrocracking catalyst maintained at hydro-cracking conditions, including conversion temperature, by passing said feedstock through the reactor in a radial flow path; withdrawing from said reactor a conversion product stream containing lower boiling hydrocarbons at a temperature above said conversion temperature; quenching said conversion product stream to at least conversion temperature by indirect heat exchange with said feedstock thereby preheating same as specified; and, recovering said lower boiling hydrocarbons.

The invention claimed:

1. Method for converting a hydrocarbon feedstock containing less than 1000 p.p.m. total nitrogen to lower boiling hydrocarbons which comprises:

(a) subjecting hereinafter specified combined portions of preheated feedstock to conditioning treatment in the presence of a hydrogenation catalyst and added hydrogen under conditions sufficient to convert at least part of said nitrogen to ammonia without substantial conversion of the feedstock hrydrocarbons to lower boiling hydrocarbons;

(b) passing the total conditioned efiiuent including said ammonia into and through a first catalyst bed of a plural catalyst bed conversion zone in a radial flow path under conditions, including a first conversion temperature and a first pressure, sufficient to convert feedstock hydrocarbons to lower boiling hydrocarbons;

(c) withdrawing a first reaction product stream from said first bed at a temperature substantially above said first conversion temperature;

(d) quenching the first reaction product stream to substantially said rst conversion temperature by indirect heat exchange with a portion of said feedstock thereby preheating said portion of feedstock;

(e) passing said quenched reaction product without compression to and through a second catalyst bed of said zone in a radial iiow path under conditions, including a second conversion temperature and a second pressure no higher than said first pressure, sufficient to convert at least part of the feedstock hydrocarbons to lower boiling hydrocarbons;

(f) withdrawing a second reaction product stream from said second bed at a temperature substantially above said second conversion temperature;

(g) quenching the second reaction product stream to at least said second conversion temperature by indirect heat exchange with another portion of said feedstock thereby preheating said another portion of said feedstock;

(h) recovering lower boiling hydrocarbons from the final reaction product from said conversion zone; and

(i) said method being characterized in that no external heat is supplied for the conditioning zone and conversion zone subsequent to start-up of ,said method.

2. Method according to claim 1 wherein said conditions for the conditioning treatment include temperature from 600 F. to 850 F. and a pressure from 500 to 3000 p.s.i.g.; and said conditions for said conversion zone include a temperature from 650 F. to 900 F. and a pressure from 300 to 3000 p.s.i.g.

3. In a process for converting nitrogen contaminated hydrocarbons, having a boiling range of from 650 F. to about 1000 F., into lower boiling hydrocarbons substantially free from nitrogenous compounds, by catalytic hydrocracking using plural stage reactors, the improvement which comprises:

(a) passing preheated said nitrogen-contaminated hydrocarbons, as hereinbelow specified, into a hydrorefining Zone under conditions sufficient to convert nitrogenous compounds to ammonia without substantial cracking of said hydrocarbons;

(b) cracking the normally liquid products from the hydrorefining zone in the presence of added hydrogen in a rst reactor stage of a plural stage conversion zone containing catalyst maintained at hydrocracking conditions, including a conversion temperature and conversion pressure by passing said liquid products through the first reactor in a radial ow path;

(c) withdrawing from the first reactor stage a rst conversion product stream at a temperature substantially above said conversion temperature;

(d) quenching the first conversion product stream to substantially said conversion temperature by indirect heat exchange with a portion of said nitrogencontaminated hydrocarbons thereby preheating same as specified;

(e) cracking additional liquid hydrocarbons in said first product stream into lower boiling hydrocarbons in a second reactor stage of said conversion zone maintained at hydrocracking conditions including a temperature substantially the same as said first stage temperature and a pressure no higher than said first stage pressure by passing said first conversion product stream without compression through the second reactor in a radial fiow path;

(f) withdrawing from the second reactor stage a second conversion product stream at a temperature above said conversion temperature;

(g) quenching the second conversion product stream to at least said conversion temperature by indirect heat exchange with another portion of said nitrogencontaminated hydrocarbons thereby preheating same as specified;

(h) recovering lower-boiling hydrocarbons substantially free from nitrogenous compounds; and

(i) said process ybeing characterized in that no external heat is supplied for the hydrorefining zone and conversion zone subsequent to start-up of said process.

4. Improvement according to claim 3 wherein said hydrorefining conditions include a temperature from 600 F. to 850 F. and a pressure from 300 to 3000 p.s.i.g.; and said hydrocracking conditions include a temperature from 650 F. to 900 F. and a pressure from 300 to 3000 p.s.i.g.

5. Method for converting a hydrocarbon feedstock boiling in excess of 650 F. and containing nitrogenous compounds into lower boiling hydrocarbons which comprises:

(a) heating said yfeedstock by hereinafter specified indirect heat exchange means to a temperature from 600 F. to 850 F.;

y(b) reacting the heated feedstock with hydrogen in a reaction zone by contact with a hydrorefining catalyst under conditions sufficient to convert nitrogenous compounds into ammonia without substantial conversion of the feedstock hydrocarbons to lower boiling hydrocarbons;

(c) withdrawing from the first reaction zone a reaction product stream containing ammonia and the feedstock hydrocrabons;

(d) cracking said reaction product stream in a first catalyst bed of a plural catalyst `bed conversion zone in the presence of added hydrogen and a hereinafter specified hydrocarbon recycle stream by passing said reaction product stream at an inlet temperature from 650 F. to 900 F. and a pressure from 300 p.s.i.g. to 3000 p.s.i.g. through the first catalyst bed in a radial flow path;

(e) withdrawing from the first catalyst bed a first conversion product stream containing lower boiling hydrocarbons at a temperature substantially above said inlet temperature;

(f) quenching the first conversion product stream to said inlet temperature by indirect heat exchange with at least a portion of said hydrocarbon feedstock thereby heating same as above specified;

(g) reacting said quenched first conversion product stream with hydrogen in a second catalyst bed of said conversion zone by passing said conversion product stream without compression and at substantially said inlet temperature and a pressure no higher than said first bed pressure through the second bed in a radial flow path;

(h) withdrawing from the second catalyst bed a second conversion product stream containing lower boiling hydrocarbons at a temperature substantially a-bove said inlet temperature;

(i) quenching the second conversion product stream v to at least said inlet temperature by indirect heat exchange with at least a portion of said hydrocarbon feedstock thereby heating same as above specified;

(j) removing a total reaction effluent from said conversion zone and cooling said efiiuent by indirect heat exchange with hereinafter specified hydrocarbon recycle stream;

(k) separating said eiiiuent into at least a first fraction comprising said lower boiling hydrocarbons, a second Ifraction comprising higher boiling hydrocarbons, and a third fraction containing hydrogen;

(l) recycling said second fraction as the hereinabove specified hydrocarbon recycle stream;

(m) recycling a portion of said third fraction to the first reaction zone;

(n) recycling a portion of said third fraction to the conversion zone in admixture with said second fraction;

(o) recovering lower boiling hydrocarbons substantially free of nitrogenous compounds; and

(p) said method being characterized in that no external heat is supplied for the reaction zone and confversion zone subsequent to start-up of said method.

6. Method according to claim 5 wherein said quenched second conversion product stream is further cracked in the presence of hydrogen in a third catalyst bed of said conversion zone by passing said second stream at substantially said inlet temperature through the bed in a radial flow path.

References Cited UNITED STATES PATENTS 2,120,715 6/1938 Seguy 196-62 2,634,194 10/1951 Nebeck 23--288 3,256,177 6/ 1966 Tulleners et al. 208--89 DELBERT E. GANTZ, Primary Examiner T. H. YOUNG, Assistant Examiner

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