US3092567A - Low temperature hydrocracking process - Google Patents

Description

United States Patent Ofificc 3,092,567 Patented June 4, 1963 3,092,567 LOW TEMPERATURE HYDROCRACKING PROCESS Robert H. Kozlowski and Harold F. Mason, Berkeley,

and John W. Scott, Jr., Ross, Calif., assignors to California Research Corporation, San Francisco, Cali, a corporation of Delaware No Drawing. Filed Jan. 14, 1960, Ser. No. 2,363 4 Claims. (Cl. 208-57) This invention relates to a method for the catalytic conversion of hydrocarbon distillate fractions to lower boiling products. In essence, it is directed to a unitary process involving a sequence of steps wherein a hydrocarbon feed stream incorporating aromatic compounds having at least 9 carbon atoms in the molecule and which is extremely low in nitrogen-containing compounds, is hydrogenated under conditions favoring saturation of the aromatic compounds and is then hydrocracked at relatively low temperatures to produce a synthetic product stream having an extremely high ratio of iso to non mal paraffins in the C -C range. Moreover, in the case of many feed stocks, the product so formed tends to be unusually rich in those cyclic hydrocarbons containing from six to eight carbon atoms in the molecule which are of particular utility for gasoline blending purposes.

In line with known methods for the hydrocracking of petroleum fractions wherein the feed is first hydrofined to clfect removal of nitrogenand sulfur-contain ing impurities and is then passed, along with hydrogen, over a catalyst incorporating hydrogenating and active cracking components, it is found that the aromatic compounds present in the feed tend to be converted to primary products having but one, two, and in some cases three fewer carbon atoms than the corresponding precursor compounds. Thus, to take a typical example wherein a heavy naphtha boiling over a range of from about 360 to 450 F. and containing approximately 40% aromatics is subjected to a sequence of hydrofining and hydrocracking steps, it is found that the synthetic product fractions boiling below about 360 F. are rich in C aromatic components and contain relatively smaller amounts of compounds such as benzene, toluene, and xylene (or their naphthenic equivalents) which constitute preferred gasoline blending stocks from both the octane and volatility standpoints.

The present invention is supported by the finding that when an aromatics saturation step is interposed between the hydrofining step and one of hydrocracking conducted at low temperatures of from about 300 to 700 F., cyclic compounds present in the feed which contain 9 or more carbon atoms in the molecule are converted in large part to cyclic product compounds, principally naphthenes, which contain four less carbon atoms than the corresponding precursor compounds. Thus, in the case discussed above wherein a naphtha is employed as feed, the use of a sequence of hydrofining, aromatics saturation and low temperature 'hydrocracking steps can be expected to give a synthetic product which is relatively rich in C and C naphthenes. It was also found that a practice of the present method not only affords a substantial increase in the amounts of C -C parafiins produced during the hydrocracking step and a reduction in C -C paraffins, but also effects a qualitative change in that the ratio of iso to normal compounds in said paraflins is many times greater than that which is observed in processes omitting the aromatics saturation step.

It is also a feature of the present invention that the product obtained following hydrocracking is very low in aromatic content. Accordingly, all portions of this product which boil in the proper range are well adapted to be used for jet and other non-gasoline fuel purposes.

On the other hand, part of the product can be diverted to gasoline usage, with the higher boiling product fractions either being used for non-gasoline purposes or recycled to the hydrocracking zone for further conversion to gasoline products. Still another method for working up the efiluent from the hydrocracking step is to recover said lower boiling fractions for gasoline, with the next higher boiling fraction such, for example, as one boiling from about 350 to 575 F., being utilized for jet, diesel or stove fuels and with the still higher boiling bottoms fractions then being recycled to the hydrocracking zone for further conversion to lower boiling products. It is contemplated that those fractions of the recovered gasoline stream which contain cyclic components preferably be passed through a catalytic reformer under reforming conditions so as to convert naphthene compounds present to the corresponding aromatics inasmuch as the latter compounds constitute preferred gasoline blending stocks.

The feeds which are usefully employed in the practice of this invention are hydrocarbon distillates which contain aromatic compounds having at least 9 carbon atoms in the molecule, and which boil above about 300 F. Representative feeds are those generally defined as heavy naphthas boiling in a range from about 300 to 475 F., kerosenes, light and heavy gas oils, light and heavy coker distillates, and light and heavy catalytic cycle oils and the like. Various of these 'feeds are of straight run origin, while others are recovered as distillate product fractions from various processing units such as cokers or other cracking units of the thermal or catalytic variety. Other appropriate feed stocks comprise the efiluent portions boiling above about 300325 F. as obtained from a catalytic reforming unit, such stocks being conventionally produced by passing straight run, thermally cracked and/or catalytically cracked naphthas, along with added hydrogen, over a platinum-o-n-alumina or a molybdenualumina catalyst under reforming conditions. Still other suitable feed stocks include concentrates rich in aromatic hydrocarbons, as obtained by the extraction of various hydrocarbon fnactions with sulfur dioxide, furfural, mixtures of various polyethylene and polypropylene glycols or the like.

While the invention finds particular utility in connection with the treatment of distillate fractions derived either directly from crude petroleum or from process units working with petroleum hydrocarbons, it is also within the scope of the present invention to employ distillate feed stocks derived from other sources such as shale, gilsonite, coal, or the like. In general, it is preferred to employ feed stocks wherein at least the ASTM D86, D-l58, or D-l160 10% and distillation points fall within a range of from about 350 to 950 F.

Reference has been made above to the fact that the present invention is practiced with feeds which contain aromatic components. The content of the latter compounds is not critical, and the invention finds utility with stocks, as exemplified by those set forth above, wherein the content of aromatics ranges all the way from about 1 to volume percent.

Feeds of the type described above normally contain a substantial proportion of nitrogen-containing impurities, along with those of sulfurous character. Accordingly, as the first step in the process when dealing with feeds of this character, the feed is subjected to a hydrofining treatment to reduce the nitrogen content thereof, preferably to a level of from 0 to 10 p.p.m. expressed as total nitrogen. This can be effected by contacting the feed, along with at least 500 s.c.f. of hydrogen per barrel thereof, with a sulfur-resistant hydrogenation catalyst at temperatures of from about 450 to 800 F., pressures of at least 300 p.s.i.g., and liquid hourly space velocities (LHSV) of from about 0.3 to 5. As is conventional in hydrofining operations having as their objective the removal of nitrogen-containing and sulfur-containing ingredients, the conditions of the hydrofining step are so chosen that saturation of aromatic components is generally limited, and so that little cracking of the feed takes place other than that of the nitrogen-and sulfur-containing compounds present. Any of the known sulfur-resistant hydrogenation catalysts may be used in the present process. The preferred catalysts of this category have as their main active ingredient one or more oxides or sulfides of the transition metals such as cobalt, molybdenum, nickel, and tungsten, or of their reduced counterparts. These materials may be used in a variety of combinations with or without the use of various known stabilizers and promoters. Morever, these catalysts may be employed either alone or in combination with various conventional supporting materials such as charcoal, fullers earth, kieselguhr, silica gel, alumina, bauxite, or magnesia. A representative effective hydrofining catalyst for use in the present invention is one embodying an alumina support and containing molybdenum and/ or tungsten in the sulfide or oxide form, in the amount of about 5 to 25% expressed as Mo or W, together with oxides or sulfides of cobalt and/or nickel, the latter materials being present in the amounts of from about 1 to expressed as Ni or Co.

The effiuent obtained from the hydrofining step is treated, in accordance with methods presently known in the art, so to remove ammonia and some hydrogen sulfide which may be present. A preferred removal method involves injecting water into the total eflluent from the hydrofining unit and then passing the resulting mixture into a high pressure separator operating under such conditions of temperature and pressure (for example, 100 F. and 950 p.s.i.g.) that a gaseous overhead is removed that is predominantly hydrogen but which normally contains some hydrogen sulfide and light hydrocarbons. This overhead (following a clean-up treatment to remove any nitrogen and sulfur-containing compounds, if desired), can be recycled to the hydrofining unit along with makeup hydrogen. Two liquid phases are formed in the separator, an upper hydrocarbon phase and a lower aqueous phase which contains essentially all of the ammonia present and some hydrogen sulfide in the form of ammonium sulfide. The aqueous phase is removed from the system and discarded.

The hydrocarbon layer is then preferably passed into a stripper or distillation column from which any remaining hydrogen sulfide, ammonia and water are removed overhead.

As the next step in the process, the portion of the hydrofined efiluent to be hydrocracked is passed, along with added hydrogen, over a hydrogenation catalyst under elevated conditions of temperature and pressure effective to saturate a substantial portion of the aromatics present in the feed, the process in most operations effecting saturation of at least 50% of the aromatic compounds present. Hydrogen is supplied along with the feed in an amount at least sufficient to effect said saturation, and preferably an excess of hydrogen is used so as to supply at least a portion of that required during the ensuing hydrocracking step, which is also consumptive of hydrogen. This permits the entire efiluent from the saturation zone to be passed directly to the hydrocracking zone, if this method of processing is adopted. For most feed stocks, the dual requirements of aromatics saturation and of saturation of cracked products can be met by adding to the feed passed to the aromatics saturation zone at least 2000 s.c.f./H per barrel of said feed, and preferably at least 3000 s.c.f./H per barrel are so used.

The conditions employed in the aromatics saturation zone are generally similar to those employed in the hydrofining step except that here the temperatures employed are somewhat lower, being of the order of 300 to 700 F., with a preferred range being from 400 to 650 F. The

catalyst used in this second stage may be a sulfuractive catalyst of the type used in the first, or hydrofining stage, or it may consist of supported metals and/or metal oxides of groups VI, VII and VIII elements of the periodic system. Thus, Raney nickel can be employed, while other suitable catalysts comprise molybdenum oxide, platinum, palladium, rhodium, rhenium, nickel or cobalt and the like supported on alumina, silica gel, kieselguhr or other similar carriers of low cracking activity and high surface area. A preferred catalyst for use in effecting aromatics saturation comprises one containing about 0.1 to 20% or more of metallic platinum supported on an alumina base. These catalysts may also contain from 0.1 to 2%, by Weight, of halogen components such as fluorine or chlor rine, thus including those platinum reforming and other catalysts of the type presently employed in catalytic reforming operations.

The effluent from the aromatics saturation (i.e., hydrogenation) step can be handled in a variety of ways. Thus, it can be passed to a gas liquid separator to recover a hydrogen-rich gaseous stream which can be recycled back over the hydrogenation catalyst along with fresh makeup hydrogen. The remainder of the effluent can then be sent to storage for later processing over the hydrocracking catalyst. Alternatively, said remainder can be fractionated to recover particular product cuts, with the balance of the material then being passed along with added hydrogen, to the hydrocracking unit. In thus carrying out the process, the hydrogenation catalyst will normally be supported in its own reactor vessel. However, in the preferred practice of the invention, the entire effluent from the hydrogenation catalyst is passed directly, along with added amounts of hydrogen, where required, over the hydrocracking catalyst. This permits the hydrogenation catalyst to be supported in the same reactor shell as the hydrocracking catalyst but in a position such that necessary aromatics saturation is accomplished within said shell prior to passing the stream over the hydrocracking catalyst. On the other hand, it will be obvious to those skilled in the art that in this method of operation, as in that referred to above, the hydrogenation catalyst may be supported in a reactor unit which is separate from that used to contain the hydrocracking catalyst.

The catalyst employed in the hydrocracking unit is an acidic material having hydrogenating characteristics and high cracking activity. It is made up of a hydrogenating component together with a material having a high degree of cracking activity either per se or when combined with the material employed to provide a hydrogenating component of the catalyst. In this connection, the term high cracking activity is employed herein to designate those catalysts having activity equivalent to a cat. A value of at least 25 or a quinoline number of at least 20 (Journal Am. Chem. Society, 72, 1554, (1950)). In the case of catalysts not adapted to withstand the conditions employed in such tests, generally comparable, minimal cracking activity values can be determined by other methods known in the art.

Broadly speaking, the hydrogenating component of the catalyst may comprise one or more of the metals, and compounds of said metals, in groups I(B), II(B), V, VI, VII, and VIII of the periodic table. However, when, as in the preferred embodiment of the present invention, it is desired to provide a synthetic product fraction from the hydrocracking zone having a ratio of iso to normal paraffinic components which is far above the theoretical thermodynamic equilibrium values at the temperatures employed, the hydrogenating component of the catalyst is selected from one or more of the various compounds of metals falling within the aforesaid groups which are not readily reduced to the corresponding metal form under the reducing conditions prevailing in the hydrocracking zone. Thus, while the invention is operable with catalysts such as those having platinum or a compound such as nickel oxide or cobalt oxide which is readily reduced to the corresponding metal form in the hydrocracking zone, it is preferred to use compounds not readily reduced such as an oxide or sulfide of molybdenum, tungsten, chromiurrr, rhenuim, or zinc, or a sulfide of cobalt, nickel, copper, or cadmium; other hydrogenating materials falling within this preferred category are complexes of the various metals of the defined groups such, for example, as cobalt-chromium and nickel chromium. Representative preparations of this character are described in US. Patent No. 2,899,287. If desired, more than one hydrogenating component may be present. The amount of the hydrogenating component may be varied within relatively Wide limits of from about 0.1 to 35% or more, based on the weight of the entire catalyst composition.

The remaining, or cracking component of the hydrocracking catalyst may be selected from a variety of solid or liquid materials of the type having good cracking activity. Among solid compositions which can be used are the various siliceous cracking catalysts, those wherein alumina is chemically bonded to aluminum chloride, fluorided magnesium oxide, and aluminum chloride, particularly when contained within the pores of a support such as charcoal so as to reduce vaporization of the AlCl Representative liquid catalysts having a high degree of cracking activity are hydrogen fluoride-boron trifluoride compositions, titanium trichloride, and aluminum chloride as contained in a suitable hydrocarbon vehicle along with HCl.

In general it is preferred to employ a solid siliceous material as the cracking component of the catalyst. For example, there may be used composites of silica-alumina, silica-magnesium, silica-alumina-zirconia, acid treated clays and the like, as well as synthetic metal aluminum silicates (including synthetic chabazites normally referred to as molecular sieves) which have *been found to impart the necessary degree of cracking activity to the catalyst. Particularly preferred siliceous catalyst components are synthetically prepared silica-alumina compositions having a silica content in the range of from about 40 to 99% by weight.

Particularly good results from the standpoint of high per-pass conversion, even at relatively low operating temperatures, coupled with high iso/normal ratios and the ability to withstand repeated regeneration with but relatively minor decreases in activity, are obtained with catalysts comprising a total of from about 0.1 to 35 wt. percent of at least one compound selected from the group consisting of cobalt sulfide and nickel sulfide, said compounds being deposited on the aforementioned synthetically prepared silica-alumina composites. Of these catalysts, those containing nickel sulfide are found to have the highest activity.

The following hydrocracking catalysts are representative of those which are adapted to be used in a practice of the present invention, the support in each case being a synthetically prepared silica-alumina composite containing about 87-90% silica and having a cat. A value of 46.

Nickel sulfide (3.6% Ni) on silica-alumina: This catalyst (No. 425-2) was prepared by impregnating 11 liters of a crushed silica-alumina aggregate with 2896.9 grams of Ni(NO '6H O, dissolved in enough water to make 8800 milliliters total solution, following which the beads were held for 24 hours at 70 F. The catalyst was then dried for hours at 250 F. and thereafter calcined at 1000 F. for 10 hours. The calcined material was reduced in an atmosphere of hydrogen at 580 F. and 1200 p.s.i.g., following which the resulting nickel-bearing catalyst was sulfided in an atmosphere containing 8% H 8 in hydrogen at 1200 p.s.i.g. and 580 F., thereby converting essentially all the nickel to nickel sulfide.

Nickel sulfide (2.5% Ni) on silica-alumina: This catalyst (No. 316) was prepared by impregnating 11 liters of a crushed silica-alumina aggregate with a solution prepared by mixing 1500 milliliters Water and 500 milliliters of ammonium hydroxide solution with 1082 grams of ethylenediamine tetraacetic acid (EDTA) and 469 grams of nickel carbonate, the solution being made up to a total of 4000 milliliters with water. The impregnated material was held for a period of 24 hours at 70 F., following which it was centrifuged and calcined for 10 hours at 1000 F. in air to convert the nickel chelate to nickel oxide. The catalyst was then reduced in an atmosphere of hydrogen at 650 F. and 1200 p.s.i.g. and sulfided in situ in the reactor by the use of a feedstream made up of a catalytic cycle oil (49 volume percent aromatics) to which 0.1% by volume of dimethyl disulfide had been added, at a pressure of 1200 p.s.i.g., and in the presence of approximately 6500 s.c.f. H per barrel of feed.

Nickel sulfide (2.5 Ni) on silica-alumina: This catalyst (No. 353) was prepared by impregnating approximately 7.5 liters of a crushed SiO -A1 O aggregate which had been dried in air for 24 hours at 400 F., with 2183.7 grams of Ni(NO -6H O dissolved in water and made up to a total of 7760 milliliters The impregnated base material was then held for 24 hours at 70 F. and calcined for 10 hours at 1000 F. The catalyst was then sulfided by treatment in an atmosphere of hydrogen containing 8% hydrogen sulfide at 1200 p.s.i.g. and 580 F.

Cobalt sulfide (4% Co) on silica-alumina: This catalyst (No. 248-2) was prepared by impregnating 2000 milliliters of a crushed SiO Al O aggregate with 1500 milliliters of an aqueous solution containing 172.5 milliliters ammonium hydroxide solution and 373 grams EDTA along with 168 grams cobalt carbonate, the solution being heated until bubbling ceased before being added to the silica-alumina material which, in turn, had previously been dried for 24 hours at 400 F. Following impregnation, the catalyst was centrifuged and calcined for four hours at 1000 F., thus yielding a material having an amount of cobalt oxide equivalent to 2.2% weight percent Co. A second impregnating solution was then made up as above, using 150.2 grams cobalt carbonate, 334 grams EDTA and 154 milliliters of ammonium hydroxide and added to the catalyst. Following a holding period of 24 hours at 70 F., the catalyst was centrifuged and calcined for 10 hours at 1000 F. The calcined product so obtained was then alternately reduced in hydrogen and oxide in air (repeating the cycle 5 times) at 1000 F. and 1200 p.s.i.g. The catalyst was then sulfided by treatment with an excess of a mixture comprising 10% by volume of dimethyl disulfide in mixed hexanes at 1200 p.s.i.g. and 675 F., hydrogen also being present in the amount of about 6500 s.c.f. per barrel of feed.

Cobalt sulfide (2% Co) and chromium sulfide (3.53% Cr) on silica-alumina: This catalyst (No. 1745) was prepared by forming an aqueous slurry with 1130 grams of the chelate of chromium and EDTA, to which slurry was added 196 grams of cobalt carbonate, the solution being then stirred until bubbling action ceased and made up to 1779 milliliters. This solution was warmed to F. and added to 2280 milliliters of the crushed SiO Al O aggregate. The resulting material was then held for 24 hours at 140 F., following which it was centriguged and calcined 10 hours at 1000 F. The calcined product was reduced in an atmosphere of hydrogen at 1200 p.s.i.g. and 675 F., following which the cobalt and chromium metals present were converted to sulfides by treatment with an excess of a solution comprising 10% by volume of dimethyl disulfide in mixed hexanes at 1200 p.s.i.g. and 675 F., hydrogen also being present in the amount of 6500 s.c.f. per barrel of feed.

Molybdenum sulfide (2% Mo) on silica-alumina: This catalyst (No. 226) was prepared by forming 530 milliliters of an ammoniacal solution containing 41.4 grams of ammonium molybdate. This solution was then added to the crushed SiO -Al O aggregate, previously dried for 24 hours at 400 F., in an amount sufiicient to yield a dried product containing the equivalent of 2 weight percent Mo. After being held for 24 hours at 70 F., the impregnated material was centrifuged and calcined for hours at 1000 F. It was then reduced in an atmosphere of hydrogen at 1200 p.s.i.g. and 650 F., following which it was sulfided in situ by treatment under these same conditions of temperature and hydro gen pressure with a hydrofined cycle oil (49% aromatics) containing 1% by volume .dimethyl disulfide.

Nickel sulfide (1% Ni) and molybdenum sulfide (1% Mo) on silica-alumina: This catalyst (No. 296) was prepared in the following manner. 28.6 milliliters of ammonia were mixed with 80 milliliters water and added to 49.3 grams EDTA, and to this solution was added 22.3 grams of nickel carbonate. After being heated to evolve carbon dioxide, this solution was mixed with another solution prepared by dissolving 78.7 grams of ammonium molybdate in a mixture of 80 milliliters of ammonia hydroxide and 80 milliliters of water. The resulting solution, on being made up to 480 milliliters by the addition of Water, was then used to impregnate 600 milliliters of the crushed SiO -Al O aggregate. The impregnated material, after being held for 24 hours at 70 F., was centrifuged and calcined for a period of hours at 1000 F. It was then reduced in an atmosphere of hydrogen at 1200 p.s.i.g. and 650 F., following which it was sulfided under these same conditions of temperature and hyddrogen pressure with a solution containing 10 volume percent dimethyl disulfide in mixed hexanes.

Returning now to a general teaching of the present invention, it is to be noted that whatever the nature of the previous hydrofining and saturation steps, the resulting saturated, low nitrogen feed stock is passed, in admixture with at least 500 s.c.f. of hydrogen per barrel of total feed (including both fresh as well as recycle feed) over the hydrocracking catalyst at temperatures of from about 350 to 700 F. and at pressures of at least 400 p.s.i.g. At least 250 s.c.f. and normally from about 500 to 1500 s.c.f. of hydrogen are consumed in the hydrocracking re action zone per barrel of total feed converted to synthetic products, i.e., those boiling below the initial boiling point of the feed to this zone.

As indicated above, the pressures employed in the hydrocracking zone are in excess of 400 p.s.i.g., and they may range upwardly to as high as 3000 p.s.i.g. or more, with a preferred range being from about 500 to 2000 p.s.1.g.

Generally, the feed may be introduced into the hydrocracking zone at a liquid hourly space velocity (LHSV) of from about 0.2 to 5 volumes of hydrocarbon (calculated as liquid) per superficial volume of catalyst, with a preferred rate being from about 0.5 to 3 LHSV.

One of the most advantageous aspects of the subject process is that the average reaction temperature over the hydrocracking catalyst is maintained below about 700 F. The importance of such low temperature operations is reflected in long on-stream periods extending over many hundreds of hours in the production of extremely low yields of C C light gases, and in the formation of a synthetic product having iso to normal parafiin ratios far in excess of thermodynamic equilibrium values. In the preferred practice of this invention, the temperature at which the hydrocracking reaction is initiated when placing a fresh charge of catalyst on-stream should be as low as possible (commensurate with the maintenance of adequate per-pass conversion levels) since the lower the starting temperature the longer will be the duration of the said on-stream period. For any given conversion, the permissible starting temperature is a function of catalyst activity inasmuch as the more active catalysts (i.e., those capable of effecting a relatively high per-pass conversion under given operating conditions) permit the unit to be placed on-stream at lower starting temperatures than would otherwise be the case. Preferred initiating temperatures are in the range of from about 350 to 650 F., it being noted that the saturated feed stocks produced herein are less refractory than those which have not been previously saturated, and thus can be hydrocracked at significantly lower temperatures than would otherwise be possible.

The effiuent from the hydrocracking reactor may be worked up in any convenient fashion. Thus, a gas recycle stream rich in hydrogen is customarily separated in a high pressure gas-liquid separation zone, which stream can be recycled for admixture with the feed passing over the hydrofining, hydrogenation or hydrocracking catalysts. Alternatively, part or all of said hydrogen can be injected at one or more points in the reactor shells employed to contain any one or more of said catalysts for quench, or temperature control purposes. Thereafter, C C or C -C products are separated in a gas-liquid separation zone operated at lower pressures, thus leaving a normally liquid effluent portion from which fractions boiling in the gasoline range can be recovered. Said fractions may be used as gasoline components, or more preferably, their octane ratings can be greatly improved by passing appropriate portions thereof (e.g., one boiling from about 180 to 400 F.) through a catalytic reformer under reforming conditions. Products in the hydrocracking effluent boiling above the desired end point of the gasoline fractions can be employed in whole or in part for jet or other fuel purposes, or they may be recycled back over the hydrocracking catalyst or over both the hydrogenation and the hydrocracking catalysts. Thus, in one embodiment of the invention, fractions boiling below about 300-375 F. are recovered as gasoline blending stocks, a next higher boiling fraction having an end point of about 550 to 600 F. is diverted for jet fuel purposes, and any remaining bottoms are recycled through the aromatics saturation and hydrocracking zones.

The advantages to be obtained by a practice of the present invention are illustrated by the data of the following examples:

EXAMPLE I In order to show the difference between the nature of the products obtained when hydrocracking an aromatic compound of representative molecular weight as compared with those obtained in a similar operation wherein the same compound is first saturated and then hydrocracked, hexamethylbenzene (nitrogen-free) was passed over a hydrocracking catalyst comprising nickel sulfide (3.6 wt. percent Ni) on a synthetically prepared silicaalumina support at an average temperature of 650 F" pressure of 1200 p.s.i.g., and a LHSV of 8.0, along with 6700 s.c.f. H per barrel of feed. The per-pass conver- SlOl'l in this operation was 97.8% to products boiling below the initial boiling point of the feed compound. As shown by the data presented in Table I below, a large proportion of the feed was converted to C and C aromatic compounds.

A similar operation was then conducted using the corresponding saturated compound (hexamethylcyclohexane) as the starting compound. Here the nitrogen-free feed was passed at a pressure of 1185 p.s.i.g., a temperature of 550 F., and an LHSV of 8, along with 6533 s.c.f./H per barrel of feed, over a hydrocracking catalyst containing nickel sulfide (6 wt. percent Ni) on the synthetic silica-alumina cracking support. This catalyst was somewhat more active than that employed in the conversion of hexamethylbenzene, such activity being significant, as regards the data of comparative runs here being described, only in that it permitted temperatures to be reduced from 650 to 550 F. while maintaining other conditions, including per-pass conversion, substantially the same. The conversion in this operation was 99.8% per pass, and Table I below shows the product distribution obtained.

Table I Feed Moles of Product per 100 Moles of Feed Hexamethyl- Hexamethylbenzene cyclohexaue Methane l0. 3 0. 14 Ethane 4. 0t 16 Propane 7.7 7. 80 Isobutane. 37. 3 58. 68 n-Butane 5. 9 2. 28 Isopentane 11. 8 22. 75 n-Pentano 1. 4 0. 39 Isohexanes 7.0 13.28 n-Kexane 0. 5 D. 23 C Naphthencs- 4. 2 3. 62 C Naphthenes. 8.8 17. 86 C Naphthenes. 15. 7 62. 26 Cr Naphthenes 8. 4 3. 71 On; Naphthenes. 2. 2 none Cu Naphthenes 0.8 none 019 Naphthenes. 0. 1 none Xy1enes- 0. 2 none Mesityiene. 0. 9 none Pseudocu mane 3. 4 none Hemirnellitene 0. 7 none Durene, Isodurene 21. 2 none Prohnitone 2. 7 none C10 Aromatic 0. 5 none Pentamethylbenzen 19. 3 none Hexamethylbenzene... 2. 2 none From the data of the above table, it is evident that saturation of an aromatic compound prior to hydrocracking the same enables the resulting naphthene to be hydrocraoked in major portion to a naphthene containing 4 fewer carbon atoms than the feed compound. It will also be observed from said data that the saturated feed stock provides a much higher yield of the desired light isoparaflin compounds containing from 4 to 6 carbon atoms in the molecule, while at the same time effecting a corresponding reduction in the amounts of undesired lighter gases and normal C -C parafiins formed. In this latter connection, it is to be observed from the date of Table II given below, which derives from that shown in Table I, shows that the ratio of iso to normal components in the case of the saturated feed stock is many times higher than that obtained using hexamethylbenzene and is far above the iso/normal ratio as calculated from thermodynamic equilibrium considerations.

Table II Equilibrium Values Hexamethyl- Hexarnethyh benzene, cyclohexane,

650 F. 650 F. 550 F. 650 F.

iCi/IXCi 0. 96 0.8 6 25.7 iC /nC 2. 2.3 9 58.3 ice/n0 1 2. 7 2. 4 14 57. 7

Based on single-branched species, such being the type produced during the hydroeracking step.

EXAMPLE II In this operation there was employed as feed a catalytic cycle oil as obtained from a catalytic cracking unit operating with a California crude, said feed having the following specifications.

End point 549 The foregoing feed was hydrofined by passing the same, along with 3000 set". Hg/bbi. feed, at 720 p.s.i.g, 730 F., and 1.0 LHSV over a hydrofining catalyst comprising 104 wt. percent molybdenum oxide and 3.6 wt. percent cobalt oxide, the balance being alumina. The resulting material was thereafter treated so as to remove hydrogen, hydrogen sulfide, ammonia, other gases and watersoluble compounds, leaving a hydrofind stock having the following specifications.

Gravity, API 29.5

Aniline point, "F 86 Nitrogen content, total ppm 2.1 Aromatic content, vol. percent 55 Paraflins, vol. percent 12 Naphthcnes, vol. percent 33 Freezing point, F -29 Pour point, F -41 ASTM distillation D158, F

Start 380 10% 436 50% 470 90% 506 End point 522 The above hydrofincd stock. was then split into two portions, with one portion being saturated and then hydrocracked, and the other portion being only hydrocrackcd. The first of these samples was hydrogenated by passing the same, along with 6500 s.c.f. Hg/bbl. feed, over an alumina-supported platinum catalyst (0.75 Wt. percent Pt, 0.8 wt. percent halogen) at 650 F., 1200 p.s.i.-g. and 20 LHSV. This saturation operation, which entailed a hydrogen consumption of about 1 s.c.f./b bl. feed, yielded a product having the following inspections:

Gravity, API 36.5 Aniline point, F 147 Panaflins+naphthenes, vol. percent 90 Aromatics, vol. percent 10 Freezing point, F 35 Smoke point, nun 21 The hydrogenated product was then hydrocracked by passing the same, along with 12,000 s.c.f. H /bbl. feed, over a catalyst comprising nickel sulfide (2.6% Ni) on a synthetic silica (90%)-alumina cracking support, at an average temperature of 534 F., a pressure of 1200 p.s.i.g., and a LHSV of 1.1, under which conditions the conversion to product boiling below 360 F. was approximately 59 volume percent pro-pass. In this operation, the yields were as follows:

C wt. percent 0.0 C wt. percent 0.3 C wt. percent 0.9 iC wt. percent 6.3 nC wt. percent 0.7 C -l80 F. out, wt. percent 9.9 360 F. cut, wt. percent 42.7 360 F.+ 40.3

Hydrogen consumption s.c.f./bbl. feed converted 663 The 180360' F. cut, which contained 4% aromatics, 77% naphthenes, and 19% paraffins represented a gasoline blending stock which could be upgraded to a leaded octane value of from 100 to 103 by passage through a catalytic reformer. The 360 F.+ cut represented a good jet stock blending component and had the following inspections:

Gravity, API 41.1

Aniline point, F 152 Freezing point, F -31 Pour point, F 40 Smoke point, mm 24 Aromatic content, vol. percent 5 When, in a companion operation, the same operation as described above was repeated, but using the catalyst of Example I and without the practice of a hydrogenation step, it was found that the temperature of the hydrocracking catalyst, other conditions remaining the same, had to be raised to approximately 569 F. to get a comparable per-pass conversion. The product yields in this operation were as follows:

C wt. percent C wt. percent 0.8 C wt. percent 1.7 iC wt. percent 4.4 nC wt. percent 2.1 C .-,-l80 F. cut, wt. percent 11.2

180360 F. cut, wt. percent 42.01 360 F.+ fraction, wt. percent 40.1 Hydrogen consumption, s.c.f./bbl. feed converted- 1423 It will be noted that the ratio of iC to nC products is far lower here than the value shown above in connection with the hyrdrogenated stock.

The inspections on the 360 F.+ portion of the product from the hydrocracking zone were as follows.

Gravity, API 38.6 Aniline point, F 125 Composition, vol. percent:

Paraffins-t-naphthenes 71 Aromatics 29 Freezing point, F 27 Smoke point, mm 16 Due to its high content of aromatic components, this stock is not adapted for use as a jet fuel component.

EXAMPLE III In this operation, the feed employed was a catalytic cycle oil having the same specification as that described in Example I]. Here the feed was hydrofined in two stages; in the first stage the feed was passed, along with 6000 s.c.f. H /bbl. feed at 675 F. and 1.0 LHSV, over a catalyst comprising 25.4% molybdenum and 7.5% cobalt oxide on alumina. In the second stage, the operation of the first stage was repeated, but at 1.5 LHSV and a temperature of 685" F. Total hydrogen consumption was 500 s.c.f./bbl. of feed and the hydrofined product had the following inspections.

Gravity, API 30.2 Aniline point, F 90.0

Parafiins+naphthenes, vol percent 49 Aromatics, vol. percent 51 Total nitrogen, p.p.m 0.15 ASTM distillation D-158, F.:

Start 324 435 30% 455 50% 467 70% 482 90% 505 End point 557 The hydrofined feed was then processed by alternative methods. In the first method the feed was hydrogenated and then hydrocraeked. In the second, the feed was only hydrocracked. In both cases, the operation was one of extinction recycle, with all portions of the product from the hydrocracking unit boiling above 400 F. being recycled to said unit.

In the first method, the hydrofined feed was hydrogenated by passing the same, along with 6500 s.c.f. H /bbl. feed, at 1200 p.s.i.g., 500 F. and 3.0 LHSV over a catalyst comprising 2.0 wt. percent platinum on an activated alumina support, the hydrogen consumption 12 in this operation being 1000 s.c.f./bbl. of feed. The hydrogenated product had the following inspections.

Gravity, API 37.2 Aniline point, F 156.0 Paraflins, vol. percent 16 Naphthenes, vol. percent 84 Aromatics, vol. percent 0 ASTM distillation D-15B, F.:

Start 375 10% 414 30% 430 50% 445 70% 462 495 End point 539 The foregoing hydrogenated product was then hydrocracked by passing the same, along with 6500 s.c.f. H /bbl. feed, at 1200 p.s.i.g., 479 F. and 0.8 LHSV, over a catalyst comprising nickel sulfide (6 wt. percent Ni) on a synthetic silica-alumina cracking support containing about 90% silica, said support being in the shape of small beads /s" diameter) and having a cat. A value in excess of 40 at the time of being impregnated with the hydrogenating component and before being thereafter calcined and sulfided. Under these conditions, there was obtained a per-pass conversion of 62.3% to synthetic products boiling below 400 F. The wt. percent yield of such products, based on the feed converted thereto, was as follows, it being noted that the operation was consumptive of 1670 s.c.f. H /bbl. feed converted to synthetic product:

C 0.0 C 0.03 C 0.8 i-C 9.4 n-C C F. cut 17. 180400 F. cut 74.9

From the above data, it will be observed that the ratio of iso to normal 0., product was extremely high, being 13.4. Moreover, losses to C -C gases were insignificant. The 180400 F. cut referred to above had the following inspections.

Gravity, API 49,7 Aniline point, F 137 Parafiins, vol. percent 22 Naphthenes, vol. percent 78 ASTM distillation D-158, F.:

Start 221 10% 241 30% 268 50% 291 70% 333 90% 374 End point 400 In the comparison run, made without the practice of the hydrogenation step, the hydrofined feed was hydrocracked at the same conditions as described above, except that, in order to obtain a 60% per-pass conversion to product boiling below 400 F., it was found to be necessary to raise the catalyst temperature from the value of 479 F. noted above, to one of 555 F. Hydrogen consumption in this run was 1720 s.c.f. per barrel of converted feed, while the wt. percent yield of synthetic product, based on converted feed, was as follows:

C1 0.0 C2 0.1 c, 2.6 i-C 8.1 II'C4 3.1 c, 1s0 F. cut 19.0

l80400 F. cut 70.0

13 From the foregoing data, it will be noted that the hydrocracking operation conducted without preliminary hydrogenation resulted in considerably more light gas make. Moreover, the iso to normal C ratio was but 2.6 instead of 13.4.

The 180-400 F. cut had the following inspections, it being noted that due to relatively high aromatic content shown, this product would not be suitable for jet fuel blending process.

Gravity, API 47.1

EXAMPLE IV In this operation light catalytic cycle oil of California origin boiling over a range of 410 to 549 F. and, containing 900 p.p.m. total nitrogen and 55 volume percent aromatics, was hydrofined in the general manner shown in Example II to reduce the total nitrogen content to 2.1 ppm. The resulting product, along with 12,000 s.c.f. H per barrel of feed, was then passed at a pressure of 1200 p.s.i.g. and a LHSV of 3.0, first over one and then over another of separate catalysts. The first of said beds contained the hydrogenating catalyst shown in Example II, and the feed stream was admitted thereto at a temperature of approximately 500 F. The total eflluent stream from said bed, now at a temperature of approximately 670 F. due to the exothermic nature of the hydrogenation reaction taking place over the catalyst, was then passed over the catalyst in the second bed, said catalyst being a hydrocracking catalyst having the same composition as that of Example II. This operation was conducted once-through, and resulted in a 59.7% perpass conversion of the feed to synthetic product boiling below 360 F. Based on total feed to the reactor, a product stream was obtained having the following composition:

Wt. percent C, 0.0 C: 0.06 C 1.3 i-C 6.7 l'l-Cq 1.4 C --180 F. cut 13.4 180360 F. cut 42.5 360 F.+ cut 38.1

The respective cuts shown above had the following in- In this operation a heavy catalytic cycle oil of California origin boiling from 38 0 to 783 F. and containing 900 ppm. total nitrogen was hydrofined to a nitrogen level of 0.2 ppm. by passage, at 745 F., 1200 p.s.i.g.,

14 and 1.3 LHSV, along with 5700 s.c.f. H /bbl., over a catalyst comprising molybdena (19.1% Mo) and cobalt oxide (5.9% Co) on an alumina support. The hydrofined product had an aromatic content of 14 vol. percent. The hydrofined feed was then hydrogenated by passing the same at 1200 p.s.ig., 500 F. and 3.0 LHSV, along with 6500 set. H /bbL, over a catalyst comprising 2% platinum on alumina. In this hydrogenation step, which was consumptive of approximately 300 s.c.f. Hg/bbL, of feed, the feed was converted to an aromatics-free product. The hydrogenated product was then hydrocracked by passage, along with 6500 s.c.f. H /bhh, over the hydrocracking catalyst shown in Example III hereof at 1200 p.s.ig., 480 F. and 0.8 LHSV. The portion of the eflluent from the hydrocracking zone boiling above 525 F. was recycled to said zone, and the efiluent portion boiling below 525 F., obtained in a per-pass yield of 57.7%,

had the following composition:

The feed and the above cuts had the following inspections:

Feed Ci -180 F. ISO-360 F. BSD-525 F.

Gravity, API 34. 0 84. 4 est. 55.1 39. 9 Aniline point, F 179 142 Paraifins, Vol. percent..- 24 79 32 29 Naphthenes, Vol. percent 76 21 68 71 Aromatics, Vol. percent.. 0 0 0 0 Freezing point, F 27 Smoke point, mm 23 In addition to the advantages discussed above and obtained by a practice of this invention, it may also be observed that hydrogenating the feed prior to hydrocracking the same permits the hydrocracking zone to be operated at significantly lower pressures than would otherwise be the case, this without any increase in the fouling rate. Thus, for example, it has been found that by saturating the aromatics present therein, a typical catalytic cycle stock can be hydrocraclted at pressures of from about 600 to 800 p.s.ig. without raising the catalyst fouling rate over that otherwise obtained from pressures of about 1200-1500 p.s.ig in operations conducted without preliminary saturation of the aromatics in the feed prior to hydrocracking.

We claim:

1. A process for the conversion of a hydrocarbon distillate feed boiling above about 300 F., and containing nitrogen compounds and 1 to volume percent of aromatic compounds, to produce superior quality fuel products, which comprises:

a. hydrofining said feed by contacting said feed and at least 500 s.c.f. of hydrogen per barrel thereof with a sulfur-resistant hydrofining catalyst at a temperature of from about 450 to 800 R, a pressure of at least 300 p.s.i.g., and a liquid hourly space velocity of from about 0.3 to 50 whereby the nitrogen content of said feed is substantially reduced, with no more than a minor amount of aromatics saturation.

b. passing the resulting hydrofined product and at least 2000 s.c.f of hydrogen per barrel thereof into contact with an aromatics hydrogenation catalyst at a temperature of from about 300 to 700 F., a pressure of at least 300 p.s.i.g., and a liquid hourly space velocity of about 0.3 to 50, whereby at least 50% of the aromatics present are saturated.

0. passing the resulting hydrofined and hydrogenated product and at least 500 s.c.f. of hydrogen per barrel of total feed into contact with a hydrocracking catalyst at a temperature of from about 350 to 700 F. and a pressure of at least 400 p.s.i.g., whereby at least 50 volume percent of the resulting hydrocracked products boil below the initial boiling point of the feed, and

d. recovering from the hydrocracking step a product characterized by a low aromatics content, a high naphthene content, and a ratio of isoparatfins to normal paraflins that is higher than the theoretical thermodynamic equilibrium ratio.

2. A process as in claim 1 wherein said hydrocarbon distillate feed contains in excess of 10 ppm. total N, the nitrogen content is reduced in the hydrofining step to less than 10 ppm. total nitrogen, and the resulting hydrofined product is contacted in the aromatics hydrogenation step with an alumina supported platinum aromatics-saturation catalyst.

3. A process as in claim 1 wherein the temperature in the aromatics-saturation step is about from 400 to 650 F.

4. A process as in claim 2, wherein the temperature in the aromatics-saturation step is about from 400 to 650 F.

References Cited in the file of this patent UNITED STATES PATENTS 2,450,316 Voorhies et al. Sept. 28, 1948 2,459,465 Smith Jan. 18, 1949 2,697,684 Hemminger et a1 Dec. 21, 1954 2,727,853 Hennig Dec. 20, 1955 2,884,371 Kirshenbaum Apr. 28, 1959 2,888,397 Burton et a1 May 26, 1959 2,914,461 Ciapetta Nov. 24, 1959 2,945,802 Ciapetta et a1. July 19, 1960 2,956,002 Folkins Oct. 11, 1960 2,965,564 Kirshenbaum et al Dec. 20, 1960 3,006,843 Archibald Oct. 31, 1961 3,008,895 Hansford et al Nov. 14, 1961

Claims (1)

1. A PROCESS FOR THE CONVERSION OF A HYDROCARBON DISTILLATE FEED BOILING ABOVE ABOUT 300*F., AND CONTAINING NITROGEN COMPOUNDS AND 1 TO 100 VOLUME PERCENT OF AROMATIC COMPOUNDS, TO PRODUCE SUPERIOR QUALITY FUEL PRODUCTS, WHICH COMPRISES: A. HYDROFINING SAID FEED BY CONTACTING SAID FEED AND AT LEAST 500 S.C.F. OF HYDROGEN PER BARREL THEREOF WITH A SULFUR-RESISTANT HYDROFINING CATALYST AT A TEMPERATURE OF FROM ABOUT 450* TO 800*F., A PRESSURE OF AT LEAST 300 P.S.I.G., AND A LIQUID HOURLY SPACE VELOCITY OF FROM ABOUT 0.3 TO 5.0 WHEREBY THE NITROGEN CONTENT OF SAID FEED IS SUBSANTIALLY REDUCED, WITH NO MORE THAN A MINOR AMOUNT OF AROMATICS SATURATION. B. PASSING THE RESULTING HYDROFINED PRODUCT AND AT LEAST 2000 S.C.F OF HYDROGEN PER BARREL THEREOF INTO CONTACT WITH AN AROMATICS HYDROGENATION CATALYST AT A TEMPERATURE OF FROM ABOUT 300* TO 700* F., A PRESSURE OF AT LEAST 300 P.S.I.G., AND A LIQUID HOURLY SPACE VELOCITY OF ABOUT 0.3 TO 5.0, WHEREBY AT LEAST 50% OF THE AROMATICS PRESENT ARE SATURATED. C. PASSING THE RESULTING HYDROFINED AND HYDROGENATED PRODUCT AND AT LEAST 500 S.C.F. OF HYDROGEN PER BARREL OF TOTAL FEED INTO CONTACT WITH A HYDROCRACKING CATALYST AT A TEMPERATURE FROM ABOUT 350* TO 700* F. AND A PRESSURE OF AT LEAST 400 P.S.I.G., WHEREBY AT LEAST 50 VOLUME PERCENT OF HE RESULTING HYDROCRACKED PRODUCTS BOIL BELOW THE INITIAL BOILING POING OF THE FEED, AND D. RECOVERING FROM THE HYDROCRACKING STEP A PRODUCT CHARACTERIZED BY A LOW AROMATIC CONTENT, A HIGH NAPHTHENE CONTENT, AND A RATIO OF ISOPARAFFINS TO NORMAL PARAFFINS THAT IS HIGHER THAN THE THEORETICAL THERMODYNAMIC EQUILIBRIUM RATIO.