US 3132087 A
Description (OCR text may contain errors)
A. E. KELLEY ETAL MANUFACTURE OF GASOLINE AND JET FUEL. BY HYDROCRACKING Filed Aug. 30, 1961 May 5, 1964 United States Patent C) 3,132,687 MANUECTURE @lil GASQLENE AND KET FUEL BY HYDRRACKING This invention relates to the manufacture of both gaso- To measure the luminosity of iiaines produced by various fuels, the CFR Luminometer has recently been developed. In this instrument, a fuel sample is burned in line and high quality jet fuel by multi-stage catalytic hyl drocrackng. VMore specifically, the invention relates to low pressure hydrocracking at below about 3,600 p.s.i.g., wherein the feedstock is iirst subjected to hydrocracking in the presence of nitrogen base contaminants, and the vmaterial not convertedito gasoline in the first hydrocracking stage is then subjected to hydrocracking in the substantial absence of nitrogen compounds in a second stage. The product from the second stage is then fractionated separately from the first-stage product, to recover second-stage gasoline, a high quality jet fuel, and optionally a diesel fraction which may 'oe withdrawn from the process or recycled for further hydrocracking in the second hydrocracking stage. It has been found that, despitethe fact that the product from the second hydrocracking stage has been subjected to more total cracking than the lirst stage product, which seemingly might reduce the proportionvof high-quality jet fuel hydrocarbons (paraffins, naphthenes, etc.), the jet fuel fraction recovered from the second stage product contains more paraffins, and exhibits better overall jet fuel characteristics, than does the corresponding jet fuel fraction recovered from the first stage hydrocracking product. It has been found moreover, that a similar difference in jet fuel quality occurs even when the rst hydrocracking stage is preceded by an'integral hydroiining operation (which would presumably increase the total proportion of saturated hydrocarbons). The gasoline fractions recovered from the respective firstand second hydrocracking stages are preferably subjectedjto catalytic reforming to improvetheir octane ratings, and it has been found thatv the first-stage gasoline has a higher initial octane number than the second-stage, gasoline, and hence the second-stage gasoline is preferably subjected to a more lsevere reforming treatment than the first-stage gasoline. The development of modern jet engines has resulted in the promulgation of many and various specifications for jet fuels.` Among such specifications are qualifica- Vtions relating to freezing point, volatility, stability, corrosiveness to polysuliide-type synthetic rubbers, odor, etc. In addition to these physical and chemical qualitcations, various other specifications have been set forth with respect to actual burning qualities, c g., heat content per pound, smoke point, luminosity of the flame, and the like. Flaine luminosity appears to be emerging as one of the more important specifications with reference to burning Y qualities. lA fuel which burns incompletely and produces much smoke will normally generate less usable power per pound than will a fuel which bums with a smokeless' arne. Moreover, smoke-producing flames are linherently quite luminous because of the incandescent carbon particles produced during burning. These luminous. flames produce relatively more radiant heat with resultant heating of the combustion chamber liner of the jet engine .to higher temperatures than would prevail if the engine were operated at the same power output with a nonluminous iiame. It has beenvfound in fact that, at the same power output, the engine liner temperature may be as much as 500 F. higher when operating with a luminous flame than when operating with a flame of minimal luminosity. Y
a combustion chamber at the saine level of vluminosity as a reference fuel, and its heat release at that luminosity level is then compared with that of the reference fuel. Thus, a high luminometer number means thatra given fuel will produce large amounts of heat at a given flame luminosity, while a low luminosity number means that the fuel will release relatively less heat at that luminosity level. On the CFR Luminometerscale, tetralin has a luminosity number of O and isooctane, l00.V For an even wider scale, normal heptane can be used, its luminosity number being 220. ln general it can be said that the paraffin hydrocarbonshave Vluminosity numbers ranging from 10() to240, naphthenes and oleiins from 40 to 130, and aromatics from -15 to 20.- It will thus be noted that the hydrocarbons most desirable in reciprocating piston engines are the least desirable for jet fuels, at least insofar as burning qualities are concerned.
The principal purpose of this invention is to provide an integrated hydrocracking process designed mainly for the production of gasoline, but which can be easily regulated to produce a high-quality jet fuel boiling for eX- ample in the SSN-550 F. range. A further objective is to minimize the total reforming capacity required to convert hydrocracked gasoline derived from multi-stage hydrocracking, into high octane gasoline. Another objective is to provide maximum exibility in a multi-stage hydrocracking process, which will permit the` refiner to shift readily from jet fuel to gasoline as his market may require; 1t is a specific object of this invention to provide a hydrocracking process for producing a 350-550 F; boiling-range jet fuel fraction which will have a luminosity number above about 70. Other objects will be apparent from themore detailed description which follows. j
In the succeeding description of process conditionsand catalysts to be employed in the various conversion units, it will be understood that the prescribed conditions are set out in order to define an integrated hydrocracking process wherein the jet fuel fraction recovered from the second stage of hydrocracking will inherently be of higher burning quality than the corresponding jet fuel fraction produced in the first hydrocracking stage. In defining these conditions, account is taken of the many complex variables involved, ie., relative hydi'ogenating and cracking activity of the catalysts used, temperatures, hydrogen pressures, and the degree of conversion to gasoline-boiling-range materials in each of the two hydrocracking stages. It is perhaps not surprising that high-quality jet fuel fractions can oe produced during a hydrogenative cracking process, but in View of the complexity of the variables involved, it was not apparent at the outset that the kinetics of the liydrogenation and cracking reactions occurring in the respective `hydrocracking stages, and under the conditions prescribed, would be such that the second stage jet fuel product would be superior to tlie first stage jet fuel product. Furthermore, inasmuch as the feedV to the first hydrocracking stage usually contains basic nitrogen compounds, which are known to inhibit the crackingactivity of hydrocracking catalysts relatively.'
reactor, using appropriate 'Ibis includes straight-run gas-oils, coker distillate gas oils, deasphalted crude cils, cycle oils derived from catalytic or thermal cracking operations and the like. These fractions may be derived from petroleum crude oils, shale oils, tar sand oils, coal hydrogeuation products and the like. Specifically, it is preferred to employ feedstocks boiling between about 400 and 900 F., having an API gravity of 20 to 35, .and containing at least about 20% by volume of acid-soluble components `(aromatics-l-oleins). Such oils may also contain from about 0.1% to of sulfur and from :about 0.01% to 2% by weight of nitrogen.
Reference is now made to the attached drawing, which is fa owsheet illustrating the invention in one of its most comprehensive aspects. In the succeeding description, it be understood that the drawing has been simplified by the omission of certain conventional elements such as valves, pumps, compressors, and the like. Where heaters or coolers are indicated, it will be understood that these are merely symbolical, and in actual practice many of these will .be combined into banks of heat exchangers and fired heaters, according to standard engineering practice. 'Phe fra-ctionating equipment is merely illustrative of a system providing for flexibility in handling different feedstocks; in acual practice, different feedstocks would require modifications in the fractionating equipment for economy.
In the drawing, the initial feedstock is brought in via line 2, mixed with recycle and makeup hydrogen from line 4, preheated to incipient hydroining temperature in heater 6, and then passed `directly into hydrofiner 8, where hydrofining proceeds under substantially conventional conditions. Suitable hydroiining catalysts include for example mixftures of the oxides and/or sulfdes of cobalt and molybdenum, or of nickel and tungsten, preferably supported on a carrier such as alumina, or alumina containing a small amount of coprecipitated silica gel. Other suitable catalysts include in general the oxides and/ or suliides of the group VIB and for `group VIII metals,`
preferably supported on adsorbent oxide `carriers such as alumina, silica, titania, and the like. The hydrofining operation may be conducted either adiabatically or isothermally, and under the following general condition:
HY DROHNING CONDI'I'EIONS Operative Preferred 60o-850 650-750 500-3, 000 SOO-2, 000 0. 5-10 1-5 50G-15, 000 1, OOO-10, 000
The above conditions are suitably adjusted so as to reduce the nitrogen content of the feed to below about 25 parts per million, and preferably below about 10 parts per million.
'Ihe total hydroned product from hydroner 8 is withdrawn via line and transferred via heat exchanger 12 to first-stage hydrocracker 14, 'Without intervening condensation or separation of products. Heat exchanger 12 is .for the purpose of suitably adjusting the temperature of feed to hyd-rocracker 14; this may require either cooling or heating, depending upon the respective hydrolning and hydrocracking temperatures employed. Inasmuch as first-stage hydrocracker 14 and hydro-finer I8 are preferably operated at essentially the same pressure, it is entirely feasible to enclose both contacting zones within a single temperature control means.
The catalyst employed in reactor 14 may consist of any desired combination of a refractory crackin-g base with a suitable hydrogenating component. Suitable cracking bases include for example mixtures of two or more refractory oxides such as silica-alumina, silca-magnesia, silicazirconia, falumina-boria, silioa-titania, silica-zirconia-titania, acidv treated clays and the like. Acidic metal phosphates such aluminum phosphate may also be used.
The preferred cracking bases comprise composites of silica and :alumina containing .about 50%-9'0% silica; coprecipitated composites of silica, titania, and zirconia containing between 5% and 75% lof each component; partially dehydrated, zeolitic, crystalline molecular sieves, eig., of the X cr Y crystal types, having relatively unform pore diameters of about 8 to 14 angstroms, and comprising silica, alumina and one or more exchangeable zeolitic cations.
'I'lle foregoing molecular sieve type crackingbases, when compounded with a hydrogenating metal, are particularly useful for hydrocracking at relatively low temperatures of 500-700 F., Iand relatively low pressures of 50G-1,500 psi-g. It is preferred to employ molecular sieves having a relatively high SiOz/AlzOf, ratio, eg., between about 2.5 and 61.10. The most active forms are those wherein the exchangeable zeolitic cations are hydrogen 'and/or a divalent metal such as magnesium, calcium or zinc. In particular, the Y molecular sieves, wherein the no2/A1203 ratio is about 5, are preferred, either in their hydrogen form, or a divalent metal form. Norm-ally, such molecular sieves are prepared nrst in the sodium or potassium form, and the monovalent metal is ion-exchanged out with a divalent metal, or where the hydrogen form is desired, Iwith an ammonium salt followed by heating to decompose the zeolitic ammonium ion `and leave a hydrogen ion. It is not necessary to exchange out all of the monovalent metal; the tin-al compositions may contain up to about 4% by weight of NazO, or equivalent amounts of other monovalent metals. t
As in the case of the X molecular sieves, the Y sieves also contain pores of relatively uniform `diameter in the individual crystals. In the case of X sieves, the pore diameters may range .between about `6 and \14 A., and this is likewise the case in the Y sieves, although the latter usually are found to have crystal pores of about 9 to l0 A. in diameter.
"Iable l below shows the X-ray powder diffraction pattern of the Y sieve. In obtaining the diffraction pattern, standard techniques were employed, utilizing as the radiation source the Koe doublet of cobalt (7\=l.7889 A.). and a Geiger counter spectrometer with a strip chart peu recorder. The peak heights, I, and the value of the respective Bragg angles were read from the spectrometer chart. From these, the relative intensities, I/I1, 'were estimated l(strongest pealc=`100) and the interplaner spacings d (A.) were calculated from the equation, \=2d sin 6, being the wave length of the source, 0 the Bragg angle, and
a' the interplaner spacing in angstroms.
TABLE 1 dot.) I/Ir dot.) I/I,
Any of the foregoing cracking bases may be further promoted by the addition Vof small amounts, eg., 1 to 10% by Weight, of halides such as iluon'ne, boron trifluoride or silicon tetrafluoride.
The foregoing cracking bases are compounded, as by impregnation, with from about 0.5% to 25% (based on free metal) of a group VIB or group VIII metal promoter, eg., an oxide or sulfide of chromium, tungsten, cobalt, nickel, or the corresponding free metals, or any combination thereof. Alternatively, even smaller proportions, between about 0.05% and 2% of the metals platinum, palladium, rhodium or iridium may be employed. The oxides and sultldes of other transitional metals may also be used, but to less 'advantage than the foregoing.
In the case of the molecular sieve type catalysts, it is desirable to distribute the hydrogenating metal preferentially in the internal pore areas thereof. This can be accomplished either by forming the sieve crystals in an aqueous medium containing an appropriate, alkalistable complex lof the hydrogenating metal, or by i011- exchanging the hydrogenating metal onto the sieve and reducing to form the free metal and redistribute it into thepores. Y l
A particularly lysts is composed of about 75-95% 'by weight of a cosuitable class of hydrocracking cata- Y precipitated base containing 5-75% SiO2, 5-75% Z102,
and 5-75% Ti02, and incorporated therein from about 5-25%, based on free metal, of a group VIII metal or metal sulfide, e.g., nickel or nickel sulfide.
The process conditions in hydrocracker la are suitably adjusted so as to provide about `20-50% conversion to gasoline per pass, while at the' same time permitting relatively long runs between regenerations, i.e., from about 2 to 8 months. For these purposes, it will be understood that temperatures in the high range will be used in connection with pressures in the high range, while the lower temperatures will normally be used in conjunction with lower pressures. The range of operative conditions contemplated for reactor I4 are as follows:
FIRST-STAGE HYDROCRACKING CONDITIONS Operative Preferred Temperature, F 60G-850 G50-800 Pressure, p.s.i.ff-. 50G-3, 000 80G-2, 000 LHSV, v./v./hr 0. 5-10 1-5 Hg/oil ratio, s.c.f./b. 50G-15, 000 1,000-10, 000
The eflluentV from hydrocracker 14 is Withdrawn via line I6, condensed in condenser l, then mixed with wash water injected via linel 20 into line 22, and the entire mixture is then transferred to high-pressure sepa- .purpose of recovering Cq-lgasoline for reforming, and
a gas-oil feed for the second-stage hydrocracker. Light gasoline, boiling, up to the C5 range is normally not subjected to reforming, and is hence removed as overhead via line 40. The Cq-lgasoline for reforming is withdrawn as a iirst side-cut via line 42. In many cases,
` the entire remaining heavy ends from column 3S may be recovered as bottoms and sent to the second-stage hydrocracker. Normally however it is preferable to withdraw a heavy bottoms fraction from the system in order to prevent buildupdof heavy materials boiling above about 700 F. In the modification illustrated, a second side-cut, boiling substantially in the jet fuel range (eg, 350-550 F.) is removed via line 44 and transferred to sideecut stripper 46, from which gasoline-boiling-range hydrocarbons are stripped out and returned to column SS'via line 48. The remaining bottoms from stripper 46 constitute the primary feedstock for the second-stage hydrocracking, and is withdrawn via line 50 for that purpose. The bottoms fraction from column 38 may be withdrawn from the system via line 52 and utilized for example as diesel fuel blending stock, or alternatively it may be diverted Vin part or in whole via lines 54 and 56 to second stage hydrocracker feed line 50 for further conversion to jet fuel and gasoline. The choice of for the various products involved.
The total second-stage feedstock'in line 50 is then mixed with recycle and makeup hydrogen from line 58 preheated to incipient hydrocracking temperatures in heater 60, and passed into second-stage hydrocracker 62. This feedstock differs considerably from the feed to the irst-stage hydrocracker, in that it is substantially free of nitrogen compounds and has a higher gravity. The feedstock is also substantially free of sulfur compounds, and hence the second stage hydrocracker may be operated entirely sweet if desired by simply removing hydrogen sulfide from the recycle gas to that stage. Ordinarily, it is preferred to operate the second stage sweet, in order to maintain the hydrogenating component on the catalyst in a metallic state, the metallic state normally being the most active form .forhydrogenation Moreover, due to the substantialV absence of nitrogen compounds, lower temperatures and higher conversion levels can be maine tained in hydrocracker 62. The process conditions in hydrocracker 62 are preferably adjusted so as to provide from Sil-70% conversion to gasoline per pass. Further, the conversion to gasoline in hydrocracker 62 may be substantially higher, e.g., at least about 10% higher, than in irst-stage hydrocracker ld. To achieve these objectives, the hydrocracking conditions should be suitably correlated within the following general ranges:
SECOND-STAGE HYDROCRACKING CONDITIONS The catalyst for use in hydrocracker 62 may be of the same general type as previously described for use in hydrocracker I4, except that as noted, it is preferred to maintain the hydrogenating component in the metallic state in hydrocracker 62. At the conversion levels and conditions prescribed for the second-stage hydrocracker, the run length between regenerations can be adjusted to coincide substantially with the run length in reactor 14, e.g., between about 2 and 8 months. In extended runs such as these, it is normally preferable to maintain substantially constant conversion in each stage by incrementally raising the temperature as the activity of the catalyst declines. The rate of catalyst activity decline in reactors i4 and 62 under the' prescribed conditions is such that constant conversion in both reactors can be obtained by raising the respective temperatures between about 0.1 and `3 F. per day, on the average. The average temperature in hydrocracker 62 will normally be about 25 l25 F. lower than the average temperature in hydrocracker 14.
The total effluent from hydrocracker 62 is withdrawn via line 64, condensed inrcooler 66 and transferred into f high pressure separator 68, from which recycle hydrogen is withdrawn via line 70. The condensed hydrocarbons in separator 68 are then flashed via line '72 into low pressure separator 74, from which flash gases are withdrawn via line-76. The liquid hydrocarbon product in separator 74 is withdrawn via line 7S and transferred to secondstage product fractionation column 80, wherein it is fractionated into various gasoline and jet fuel fractions as in column 38. Light gasoline blending stock is withdrawn facilities.A Alternatively, a portion of the jet fuel product from line 94, may be diverted via line 96 and recycled to second-stage hydrocracker 62 via lines 55 and 50. Also, all or a portion of the diesel fraction Withdrawn as bottoms via line 86 may be recycled via lines 98, 56 and 50 to hydrocracker 52. Again it will be understood that the choice of the various alternatives depends largely upon the desired renery balance and market demands.
The second-stage Cq-lgasoline in line 84';- requires a more severe reforming treatment to raise it to a given octane level, in comparison to the first-stage Cq-igasoline removed from column 38 vial ine 42. While these two fractions can be blended together and reformed in the same unit, it is preferable where economics permit to treat them separately in order to avoid the loss in liquid yield resulting from overtreating the higher octane product in line 42. This objective may be accomplished by using separate reformers at different' temperature levels, space velocities, etc., but in the modification illustrated, a differential space velocity is provided. The low octane gasoline in line 84 is mixed with fresh and recycle hydrogen from line 100, preheated to incipient reforming temperatures in heater 102 and passed through a small pre-reforming unit 104. The higher octane gasoline in line 42 is blended with fresh and recycle hydrogen from line 106, preheated to reforming tempeartures in heater.' 108, and then blended with the eflluent from reformer 104l in line 110. The entire blend is then passed into main reformer 112 wherein reforming to the desired octane level is completed. The conditions of reforming in units 104 and 112 are substantially conventional and hence will not be described in detail. Generally the temperatures will range between about 850 and 950 F., pressures between about 300 and 800 p.s.i.g., and the catalysts may comprise a conventional platinum-alumina reforming catalyst, or alternatively other noble metals such as rhodium or palladium on alumina or other carriers may be used. Overall space velocities may range between about 0.5 and 5.0, but preferably the gasoline from line 84 is treated at a space velocity which is being about 0.1 and 0.5 lower than the total space velocity at which the product from line 42 is treated, other treating conditions being the same.
The total eflluent from reformer 112 is removed Via line 114, condensed in cooler 116, and transferred to high-pressure separator 118, from which hydrogen recycle gas is withdrawn via line 120. The liquid product in separator 118 is flashed via line 122 into low pressure separator 124, from which flash gases are Withdrawn via line 126. Gasoline reformate is withdrawn via line 128, and may be sent to blending and storage facilities not shown, where it may be blended with the high octane light gasoline recovered via line 40 and 82.`
The following example is cited to illustrate the operation and results of the process as above described in connection with the drawing. This example should not however be construed as limiting in scope:
Example l In this example, a blend of coker distillate and thermally cracked gas oils derived from California crude oils is utilized as feed. The treatment comprises aninitial catalytic hydroning, with the total hydroning elluent passing to the first stage of hydrocracking. The firststage hydrocracking effluent is Water-washed and fractionated to recover a Cry-385 F. gasoline fraction, a S60-510 F. jet fuel fraction and a bottoms fraction, the latter two fractions being fed to the second stage of hydrocracking. The effluent from the second hydrocracking stage is condensed and separately fractionated to recover a C7-385 F. gasoline fraction, a S60-510 F. jet fuel fraction and a bottoms fraction, the latter two fractions being in part (75%) withdrawn from the process as jet fuel and diesel fuel products respectively, and in part (25%) recycled to the second stage of hydrocracking.
The signicant conditions, specifications and results of the process are as follows: Initial feedstock:
Boiling range, F 400-750 Acid-solubles, vol. percent 65 `Gravity, API 23.0 Nitrogen, wt. percent 0.36
Sulfur, wt. percent 2.1 Hydrofning conditions:
Catalyst-3% COO, 15% M003 on 5% SiOZ, A1203 carrier; catalyst presulfided.
Temperature, `average bed, F. 705
Pressure, p.s.i.g 1,500
H2/oi1 ratio, s.c.f./b 5,000 First-stage hydnocracking conditions:
Catalyst 20% Ni supported on coprecipitated composite of 20% SiOg, 30% ZrO2,
50% TiOZ; finalcatalyst in sulded form. Temperature, laverage bed, F. 800 Pressure, p.s.i.g. 1,500
. LHSV 1.5 Hz/oil ratio, s.c.f./b. 8,000 Conversion .per pass to 0-3'85" F. gasoline,
vol. percent 25 Second-stage hydrocracking conditions:
Catalyst-Same as first stage, except in nonsuhided form.
Temperature, average bed, F. 715 Pressure, p.s.i.g 1,500 LHSV 1.5 Hz/oil ratio, s.c.f./b 8,000 Conversion per pass to 0-385 F. gasoline,
vol. percent 42 Cq-385" F. gasoline products:
First Second Stage Stage Research octane number, clear 64. 5 59. 5 +3 m1. TEL s3. s so. 1
360510 F. jet fuel products:
First Second Stage Stage Aniline p0int, F 122 143 V01. percent saturates (non-aromatics) 74 93 CFR Lumnometer N o 47 71 Second-stage diesel fuel product:
Boiling range, F. 500-670 Cetane number 58 Approximate material balances (per bbls. fresh feed): Ultimate products- Barrels O-,CG 19 C7--385 F. gasoline:
First stage 27 Second stage 32 360-510 F. jet fuel 25 50G-670 F. diesel fuel 12 The leaded octane numbers of the respective rst and second stage C17-385 F. gasoline products can be raised to the 100 level by reforming `at 925 F. and `600 p.s.i.g. over a conventional 0.5% platinum on alumina catalyst. To accomplish this, the second-stage gasoline is preferably reformed at a total space velocity (Ll-ISV) of about 1.5, While the first-stage gasoline is reformed at 1.8 space velocity.
' Example II Another run was carried out by the same two-stage technique described in Example I, but using a 600 F. end- (4) Vsubjecting said `point coker gas-oi las feed, and a 0.5% palladium-loaded magnesium Y molecular sieve in each hydrocracking stage. l
'Ilhe operating conditions were as follows:
[llo 400 E. end-point gasoline. Y' V bTo 525 F.--minus material; about 21% conversion per pass fto 400 F. end-pointV gasoline.
The 372-528 F. boiling range jet fuel `recovered from Y the second stageV contained only 1% aromaties and 99% Vsatunates. Its luminometer number was 80. 'The correspending jet fuel fraction-from the -iirst hydrocracking stage was of much lower quality.
Results lanalogous to those indicatedy in the foregoing examples are obtained when yother hydrocracking catalysts and conditions, other feedstocks and other hydroining conditions within thebroad purview of the above disclosure are employed. It is hence not intended to limit the invention to the details of the example or the drawing, but only broadly as dened in the following claims.
We claim: Y f
1. Aprocess for the manufacture of gasoline and highquality jet fuel by the hydrocracking ot nitrogen-contami-` Y nated feedstocks, which comprises:
i (1)Y subjecting a gas oil gasoline range and containing at least about'50 parts per million of nitrogen inthe form of organic nitrogen compounds to catalytic hydroning with added hydrogen to eifect decomposition of said organic nitrogen compounds without substantial cracking of hydrocarbons; f V(2) subjecting ammonia-containing eluent from said hydroning, without intervening condensation or separation,V to a -rst stage of catalytic hydrocracking in the presence' of a group VIII metal sulde hydroicrackingV catalyst, at a temperature between about 600 and 850 F. Vand under conditions adjusted to give a 20-50% conversion per pass to 400 end.
point gasoline; l (3) treating the V,effluent from said first-stage hydro-- cracking to separate out a first-stage gasoline product, ammonia, and a hydrocarbon residue boiling above said first-stage gasolineboiling range, said residue containing less than about v25 parts per million of nitrogen and comprising a substantial proportion of i `hydrocarbons boiling in the jet fuel range;
feedstockboiling above the hydrocarbon residue plus added hydrogen to a second stage of catalytic hydrocracking in the presence of a group VllI free metal hydrocracking catalyst, at a temperature between about 400 and 800 F. underconditionsadjusted to give a conversion per pass to 400 F. end-point gasoline which is (a) between about 30% and 70% by volurne, and (b) higher than the conversion to gasoline maintained in said rst hydrocracking stage;
(5) lfractionating the effluent from said second-stage hydrocracking separately from said irststage hydrocracking effluent, to separate out a second-stage gasoline product and a jet fuel fraction boiling between about 350 and 550 F.; Y I(6) withdrawingat least a portion of said jet fuel fraction las product and recycling any remaining portion thereof'to said second hydrocracking stage;
(7) subjecting the C7+ fraction of said second-stage gasoline to catalytic reforming in the presence of added hydrogen;
(8) subjecting the C7+ fraction of said first-stage gasoline to catalytic reforming in the presence of added hydrogen, but under less severe reforming conditions than the conditions employed for reforming said second-stage gasoline; and wherein ing Vstages are carriedv out at pressures between about 500 and 3,000 p.s.i.g.
2.' A process as delined in claim 1 wherein the hydrocracking in said second-stage hydrocr-acking is conducted at 'a temperature between about 25. and 125 F. lower than the temperature of said first-stage hydrocracking.
3. A process as defined in claim 1 wherein the initial feedstock to said hydroiining step is a cracked gas-oil boiling between about 400 and 900 F., and containing at least about 20%v by volume of acid-soluble components.
4. A process as defined in claim 1 wherein the hydrocracking catalyst in each of said hydrocracking stages contains between about 5% and 25% by weight of nickel, the remainder being made up of a coprecipitated composite of silica, Zirconia, and titania 5. A process as defined in claim 1 wherein the hydro- ReferencesjCited in the le of this patent UNITED STATES` PATENTS 2,956,002` Folkins -V oct. 11, 1960 Y 2,983,670 sentore May 9,1961
y3,008,895 Hansford etal 1 1 Nov, 14, 1961A` (9) said hydroining step and each of said hydrocrack`