CATALYTIC CRACKING AND HYDROTREATING PROCESS FOR PRODUCING GASOLINE FROM HYDROCARBON FEEDSTOCKS CONTAINING SULFUR

Abstract: A gas oil or other sulfur containing hydrocarbon feedstock is catalytically cracked in a first stage to produce a cat cracked naphtha product of high olefin content (10-60%), and an intermediate or high boiling component thereof or both is recracked as a feed in a second stage over a zeolite catalyst to saturate the olefins, and hydrodenitrogenate and hydrodesulfurize said cat cracked naphtha. The recracked cat cracked naphtha is then hydrotreated or hydrofined at low to mild severities to provide either a low sulfur gasoline blending component for a gasoline blending pool or a feed suitable for a subsequent catalytic reforming (hydroforming) step in which high octane gasoline is produced. Hydrodesulfurized cat cracked naphtha produced in this process.

Description: EXXON RESFARCH AND ENG@NEERING COMPANY FATENT SPECIFICATION CATALYTIC CRACKING AND HYDROTREATING PROCESS FOR GASOLINE PRODUCTION FROM SULFUR - CONTAINING HYDROCARBON FEEDSTOCKS The present invention relates to a catalytic cracking and hydrotreating process for gasoline production from sulfur - containing hydrocarbon feedstocks. Cracking processes, both thermal and catalytic, have conscizuted the hear of petroleum refining operations for several decades. The purpose of both types of process is the same, i.e., co break heavy molecular feed components into lower boiling, more valuable components. The thermal process, which has now been largely replaced by the more effective catalytic process, accomplishes this result by heat, whereas the catalyLic process breaks the large molecules by contact between a heavy fed and an active catalyst at lower temperatures than used in thermal processes. The reactions which occur in the catalytic cracking operation are complex including, not only carbon-carbon bond scission but isomerization, alkylation, dehydrogenation, etc., and a carbonaceous material, or coke, is inevitably deposited on the catalyst. The catalyst, in such unit, is regenerated in a separate vessel, i.e., a regenerator, by burning off the coke to restore its activity. Commonly, the catalyst is continuously cycled between che reactor and regenerator as a moving bed without shutdown of either unit. The economics of the ca@alytic cracking unit ins a refinery, because ot its high degree of flexibility, to a large excent, determines the produce slate which will be produced by a refinery. Products from the catalytic crackling unit thus provide feed for other units, e.g., alkylacion and polymarization units. Cat cycie stocks are used to make lubes, and gas is employed as fuel in the refinery. However, a major portion of the product of che catalytic cracking unics of a given refinery are blended direccly in gasoline blending pools which serve as supplies of motor gasoline. With the phaseouc of lead anti-knock compounds it continues a formidable challenge for the refiner to maincain gasoline pools at the octane levels demanded; and, the problem is aggravated by the depletion of conventional petroleum supplies which creates an increased need to process heavy feedstocks such as residua, uncon- ventional heavy crudes and the like for conversion to gasoline. Cat cracking feed stocks are provided by atmospheric and vacuum stills, phenol extraction plancs and hydrotreaters. The usual feed to a comtnercial catalytic cracking unit is comprised of a gas oil boiling below about 1050 F (1050 F-), typically a virgin gas oil boiling between about 600 F and 1050 F. In addition, thermally cracked materials are often used as cat cracking feeds While various conventional types of processing; e.g., cat naphtha reforming and cat naphtha extraction, might be employed to upgrade cat naphcha octanes and increase the supply of high octane gasoline in the gasoline pool as lead is phased out of gasoline, most: are quite expensive; particularly cat naphtha reforming -which requires initial hydrotreating of the feed so that it can meet reformer feed specifications. The bulk of the sulfur in a gasoline blending pool is contributed by cat naphtha3 or product of the cat cracking units. The addition of.large amounts of sulfur ro a gasoline blending pool raises acute problems, particularly in view of the presence requirements in many countries to neet emission standards for hydrccarbons (HC) and carbon monoxide (CO). Thus automobiles are now equipped with catalytic converters for the purpose of lowering emissions of CO and HC, but the new standards will also impose restrictions on N0x emissions, as well as added restrictions on CO and HC emissions. Sulfur, however, is a known poison for the more useful, and active "three-way" catalysts contemplated by the auto industry for use in catalytic converters to meec the 1980's standards. Consequently, the activity and activitymaintenance of the catalysts are suppressed due co the presence of sulfur. Moreover, ic has been found that, due to the presence of the sulfur, the catalytic converters emit sulfate, either as a sulfuric acid aerosol or as parciculates caused by sulfuric acid corrosion of the metal portions of the exhaust train. The sulfur in gasoline, which is cypically present in zmouncs of about 300 ppm, is oxidized in the combustion chamber of the engine to sulfur dioxide. The catalytic converter, which is required for lowering the emissions of CO and HC, is thus responsible for the oxidation of sulfur dioxide in the exhaust gas to produce sulfur trioxide which immediately hydrates due to the presence of water vapor, one of the combustion products, to form a sulfuric acid aerosol or acid particulates, neither of which is environmentally acceptable. Whereas cat napththa hydrofinin; might be employed to produce low sulfur gasoline or a naphtha which can meec reformer feed specifications such treatment would be very expensive or such processes should require considerable hydrogen comsumption, and hydrogen is a rather expensive ccròdity. Hydrogen constitutes a major cost in hydrotreating a cat naphtha because typically from about 20 to 40 percent and perhaps 60 percent and higher of che feed is olefinic, and a considerable amount of hydrogen is required for saturation of the olefins. The olefins must be vircually completely saturated before the cat naphtas can be reformed over a platinum or promoted platinum catalyst, chis requiring generally from about 200 to 40G SCF/B of hydrogen to saturate the olefins typically concained in an intermediate boiling range cat naphtha. moreover, in addition to the restrictive olefins specifications imposed on a cat naphcha feed, such feed also contains considerable amounts of sulfur and nitrogen, and far more severe hydrotreating of the cat naphcha co bring it in line with sulfur and nitrogen reformer feed specifications is required than even is necessary in hydro treating virgin naphtha. In fact, in cat naphtha hydrofining mercaptan reversion reactions, or reactions wherein the hydrogen sulfide by-product reacts with cat naphcha olefins to form mercaptans is a troublesome problem; for mercapcans cannot be tolerated in significant amounts within the feed. Mercaptans must thus be eliminated by hydrofining, or hydrotreating the cat naphtha at sever condiions. While the degree of olefins saturation with resultant octane loss can be diminished by proper selection of hydrotreating operating variables1 and catalyst type, refiners cannot tolerate even small reductions in cat naphtha octane ratings, particularly now when lead is being phased out of gasoline blending pools; much less the loss in naphtha octane racings caused by further increased olefin sacuration resultant from the high severities which now appear necessary in order to lower gasoline sulfur limits within the ranges required. It is the primary objective of the present invention to provide an improved process which will at least in part overcome these and other disadvantages of presence catalytic cracking processes, and in face provide a new and novel multiple stage catalytic cracking process for the cracking of gas oils. This objective and others are achieved in accordance with the present invention embodying a process, an essential feature of which comprises recracking G cracked naphtha feed containing up co about 60 percent1 suitably from about 20 to about 40 percent olefins, over a crystalline aluminosilicate zeolite catalyst to further crack che naphtha and saturate at least about 50 percent of the olefins, preferably from about 80 percent to about 100 percent of the olefins, based on the weight of said cracked naphcha feed. Suitably, the cracked naphtha feed is contacted and reacted over the catalyst, without dilution of said feed, at temperature ranging from about 8000F to about 1100 F, preferably from about 900 F- co about 1030 F, and ac pressure ranging from about 0 to about 50 pounds per square inch gauge (psig), preferably from about 5 psig co about 20 psig. Reaction at such conditions not only produces significant saturation of the olefins, but also significant hydrodeni trogenation and hydrodesulfurization of said cat naphtha feed. In its preferred aspects the process is one wherein a conventional sulfur-bearing cat cracker feed, suitably a gas oil, i.s catalytically cracked, at conventional conditions, in an initial or first stage to provide a cat naphtha product containing generally fron about 10 to about 60 percent, preferably from about 20 co about 40 percent olefins. The cat naphtha produce in whole or in part is then re cracked, as an undiluted feed, in a subsequent or second catalytic cracking zone over a crystalling aluminosilicate zeolite catalyst Preferably, the cat naphtha product of the initial or first stage is split into fractions inclu sive of a low octane, highly olefinic intermediate fraction having a i c; ; end boiling point ranging from about 120 F, to 250 F preferably from about 180 F to about 220 F, and a high end boiling point ranging from about 250 F to about 380 F, pre ferably from about 270 F to about 350 F. A higher boiling fraction having a low end boiling point range from about 250 F to about 380 F, preferably from about 270 F to about 350 F, and a higher end boiling point range from about 350 F to about 450 F, preferably from about 400GF to about 4300F can also be obtained. The intermediate or high boiling fraction, or z composition which includes both, may be ucilized as feed and further catalytically cracked, or recracked, in a subsequent stage over a crystalline aluminosilicate zeolite catalyst suficient to produce significant saturation of the olefins, and hydrodenitrogenation and hydrodesulfurization of said cat cracked naphtha fraction, or fractions. The recracked product is then hydrotreated, or hydrofined, at mild hydrotreating conditions to provide a low sulfur gasoline of improved octane. Alternatively, che higher boiling fraction or fraction typically having a low end boiling point ranging from about 250 F to about 380 F and a high end boiling point ranting from about 350 F to about 450 F is not recracked because ic is generally of relatively high octane nd upgrading of this fracclon is not required. The intermediate fraction per se, preferably, is utilized as a feed and further cacalytically cracked, ar recracked, in a subsequent stage over a crystalline aluminosilicate zeolite catalyst suf ficient to produce significant saturation of the olefins, and hydrodenitrogenation and hydrodesulfurization of said of said cat cracked naphtha fraction. The recracked product thereof, is then hydrotreated, or hydrofined, at mild hydrotreating conditions, and chen reformed over a conventional catalyst at conventional reforming (hydroforming) conditions to provide a low olefin gasoline of improved octane. It has been found, quite surprisingly, that the recracking of an undiluted cracked naphtha, notably the intermediate of high boiling fractions, over a zeolite catalyst at rather low or mild conditions significantly increases the octane number while reducing the olefin content of the cracked naphtha by saturation cf the olefins, without direct hydrogen addition. This reduction of olefn content while increasing octane number is indeed surprising. This recracking not only virtually eliminates any necessity of hydrotreating the cracked naphtha to reduce its olefin content, but also sitnificancly reduces the nitrogen and sulfur concent of the cracked naphtha. In particular, it has been found that recracking reduces the sulfur content of the feed by up to about 75 percent, or higher, based on the weight of the sulfur in the cat cracked naphtha. Thereafter, only a mild hydrotreatment of the cat cracked naphtha product is required to eliminate residual sulfur and thereby render the product susceptable co reforming, if desired, over highly sulfur--sensitive catalysts to further improve the octane number. This, of course, significantly reduces the capital cost of the required hydrotreater (or hydrofiner) and direct high costs of hydrotreating a cracked naphtha to reforming feed specifications. Further- more, recracking of the cracked naphcha in this manner prior co hydrotreatment of the cracked naphcha to eliminate olefins minimizes mercapcan reversion reactions wherein olefins normally react wich by-product hydrogen sulfide to form mercaptans, any significant amount of which simply cannot be tolerated in a reformer feed. Various cracking catalysts can be used in cracking the gas oil feed, or feed to the first stage catalytic cracker. Suitable cracking catalyscs include conventional silica-based materials. Exemplary of such catalysts are, e.g., amorphous silica-alumina; silica-magnesia; silicazirconia; conventional clay cracking cacalysts, and the like, The amorphous gel silica-metal oxide cracking catalyst may further be composited with kaolin in amounts of about 10 to 40 wt. % (based on total weight of the composited catalyst) and up to -20 wt. % or more crystalline alumino- silicate zeolite, such as faujasite. A cryscalline alumino- silicate zeolite catalyst is required in the second stage catalytic cracker, i.e., for cracking he cat cracked naphtha, or fraction chereof, from the firs stage. These catalysts are well known and commercially available. Preferably, the catalyst utilized, particularly in the second stage catalytic cracker is an amorphous silica-alumina catalyst containing from about 5 to 16 weight percent y-type faujasite, and, optionally 15 to 40 percent kaolin. Generally, the first and second stage catalytic crackers are operated at about che same absolute conditions of temperature, pressure, space velocity, and catalyst/oil racio, che runs being initiated by adjusting the ieed and catalyst rates, and the temperature and pressure of the reactor to operating conditions. The catalytic cracking operation in boch stages of cracking is concinued ac con editions by adjustment of the major process variables, within the ranges described below: Major Operating Typical Process Preferred Process Variables Conditions Conditions Pressure, Psig 0-50 5-20 Reactor Temp., F 800-1100 900-1050 Space Velocity, W/W/Hr 2-200 5-150 Catalyst/Oil Ratio, (Instantaneous Vol. O- Reactor Space) lbs./per lb. of oil 2-12 4-8 The product of the first stage catalytic cracker, suitably a cat cracked naphtha obtained by cracking a gas oil, is characterized as a cracked naphtha having an olefin content ranging from about 10 percent co about 60 percent, more typically from about 20 percent to about 40 percent (by weight) and boiling within the gasoline range, typically from about 65 F to about 430 F (i.e., C5/430 F). All or a portion of the cat cracked naptha, preferably an inter- mediate or heavy fraccion, or composition which includes both fractions, as previously defined, is splic from the product of said first stage, fed into, and recracked, without dilution, over the crystalline aluminosilicate zeolite catalyst in the second stage catalytic cracker. The recracked product is then subjecced to a mild hydrotreatment by contact, with a catalyst comprising a composite of an inorganic oxide base, suitably alumina, and a Group VI-B or Group VIII metal, or borh, e.g., a cobalt moly/alumina catalyst, at conditions given as follows, to provide a gasoline suitable for addition co a gasoline blending pool, co wit: : Typical Preferred Process Variable Process ConditionsProcess Conditions Pressure, psIg 60-500 80-200 Temperature, OF 400-800 300-600 Feed Rate, LHSV 1-80 5-20 Hydrogen Rate, SCFjBbl 200-4000 800-2000 Alternacively, che recracked product is subjected to. the following mild hydrocreacing conditions so as to provide a naphtha suitable as a feed to a reforming process: : Typical Preferred Process Variable Process Conditions Process Conditions Pressure, psig 100-2000 200-300 Temperature, F 400-800 500-600 Feed Rate, LHSV 1-25 2-6 Hydrogen Rate, SCF/Bbl 200-3000 200-500 The product from the hydrofiner is subjected. to reforming, at reforming conditions, by contact wich a sulfur-sensitive, noble metal reforming catalyst co produce a satisfactory high@octane gasoline. Suitably, the reforming run is initiated by injection of hydrogen into the reforming reactor (or zone) with the feed at the desired hydrogen and fed rates, with adjustment of the temperature and pressure co operating conditions. The run is continued at optimum reforming conditions by adjustment of the major process variables, within the ranges described below: Major Operating Typical Process Preferred Process Variables Conditions Conditions Pressure, Psig 50-750 100-300 Reactor Temp., F 750-1100 850-1000 Gas Rate, SCF/B 1500-10,000 2000-7000 (Incl. Recycle Gas) Feed Rates W/W/Hr 0.5-10 1-3 The catalyst employed in reforming is one comprising a refractory or inorganic oxide support material, particularly alumina, which is composited with a Group VIII noble metal hydrogenation-dehydrogenation component, notably platinum, to which may be added an additional metal, or metals, to promote the activity and selectivity of the catalysts, particularly iridium or rhenium, or both, or component selected from the Group IV metals, Group VI metals, Group VII metals, ana Group VIII metals, e.g., germanium, tin, lead,osmium, ruthenium, rhodium or the like. A hologen component, suitably chlorine, is generally added co provide the desired acidicy. These components can be added to a support by any of the conventional methods, e,g., by impregnation prior co, following or simultaneously with the impregnation of the noble metal, or halogen components. The metal hydrogenation-dehydrogenation components, or promoters are added to a support in concentration ranging about 0.01 to 3 percent, preferably from about 0.05 to about 1 percent, based on the weight of the catalyst. A suitable support can contain, e.g., one or more of alumina, bentonite, clay, diatomaceous earth, zeolite, silica, activated carbon, magnesia, zirconia, thoria, and the like; though the most preferred support is alumina to which, if desired, can be added a suitable amount of ocher refractory carrier materials such as silica, zirconia, magnesia, titania, etc., usually in a range of about 1 to 20 percent, based on the weight of the sport. A preferred support is one having a surface area of -ore can 50 m2/g, preferably from about 100 to about 300 m2/g, a bulk density of about 0.3 co 1.0 g;nl, preferably about 0.4 LO 0.8 g/ml, an average pore volume of about 0.2 to 1.1 ml/g, preferably about 0.3 to 0.8 ml/g, and an average pore diameter of about 30 to 300A. The invention will be more fully understood by reference to the following nonlimiting demonstrations and examples which, present comparative data which illustrate its more salient features. All parts are given in terms of weight unless otherwise specified. In a first step, a 155 F/413 F cat naphtha fraction was obtained by catalycically cracKing a virgin gas oil at conventional conditions over a conventional catalyst co obtain a cat cracked naphtha, hereinafter referred co as Feedstock A, the complete feedstock inspeccions of which are given in Table I, below. Table I Feedstock A 155 F/415 F Cat Naphtha Sulfur, @ppm 572 Nitrogen, wppn 30 Br. No., cc/gm 24.8 Octane RONC 82.8 MONC 75.2 FIA, Vol. % Arom. 33.6 Gle-fins 15.3 Saturates 51.0 ASTM D-86 F IB@/5@ 155/194 10/20 207/228 30/40 245/262 D0/60 2S0/300 70/80 320/337 90/95 365/383 F3P 413 EXAMPLE 1 Feedstock A was hydrofined in a reactor at 40U psig, and 800 SCF/B over a cobalt moly-on-alumina catalyst to produce a low sulfur gasoline blending component having a Bromine number of about 5 and 20 wppm sulfur, this requiring about 96.5% hydrodesulfurization. The produce has a research octane number (RONC) at 77.3 and a motor octane number (MONC) of 73.0, this representing a loss of 5.5 RONC and a 2.2 loss of MONC as a result of the hydrofining. EXAMPLE 2 Feedstock A was recracked in a reactor at 93G F, 14.7 psia, 13.7 WHSV and ac a catalyst/oil ratio of 9.2 over a conventional commercial zeolite cracking ccalyse containing crystalline aluminosilicate zeolice, silica alumina gel and clays, and the product then fractionated to provide a light ends cut, and three fractions, i.e., a low boiling 65/200 F fraction, any intermediate 200/430 F fraction and a high boiling 430 F+ fraction, the low boiling and intermediate boiling fractions being characterized in Table II. Table II 65/200 F 200/430 F Vol. % on Feed 24.9 55.9 Sulfur, wppm 42 244 Br. No. 20.0 3.0 Octane RONC 85.0 90.4 MONC 80.0 80.9 The 200/430 F fraction is then hydrofined at 550 F, 400 psig, 800 SCF/Bbl over a cobalt moly-onalumina catalyst as in Example 1 to produce a low sulfur gasoline blending component having a Bromine No. of about 1 and containing 11 wppm sulfur, chis requiring about 95.5% hydrodesulfurization. The resulting product has octane ratings cf 89.4 RONC and 8G.9 MONC. Thus, , the loss in octane rating for chis low sulfur gasoline blending component is nil as relates co the motor octane number rat- ing, and only 1 octane number as relates to research octane number. When the recracked 65/200 F and 200/430 F recracked, hydrofined fractions are combined, the resultant product has an occane number of 88.7 RONC and 80.6 MONC, contains only 20 wppm of sulfur, anj represents 80.8 vol. percent recovered product, based on the original feed. Occane loss as a result of hydrofining is estimated ac about 0.5 RONC, or less. The following example demonstrates a more preferred embodiment wherein an intermediate fraction only is recracked. EXAMPLE 3 Feedscock A was splic into three fractions, a 65/200 F fraction, a 200/330 F fraction, and a 330 F+ fraction as defined in Table III. Table III 65/200 F 200/330 F 330 F+ Vol. % on Feed 17.2 @ 61.9 20.9 Sulfur, wppm 100 226 1,841 Br. No. 54.6 24.6 7.8 Octane RONC 87.5 81.6 82.5 MONC 79.2 75.3 75.0 The 65/200 F fraction is then treated in a Merox process, after admixture with light ends from the 200/330 F fraction which Is recracked as defined hereafter, co produce a product of 87.5 RONC and 79.2 MONC with 50 ppm sulfur, The 200/330 F fraction is recracked in a reactor at 930 F, 14.7 psia, 13.7 WHSV at a catalyst/oil ratio of 9.2 over a conventional commercial zeolite, silica-alumina gel and clays, and the produce then fraccionaced to provide a 65/200 F fraction which is blended with the 65/200 F fraction to Merox, a 200/430 f fraction, and a 430 F+ fraction. The 65/200 F and 200/430 F fractions are characterized in 'lable IV. Table IV 65/200 F 200/450 F Vol. % on Feed 10.7 39.3 Sulfur, wppm 67 88 Br. No. 20.4 2.7 Octane RONC 87.3 89.6 MONC 80.0 80.2 The 330 F+ fraction, characterized in Table III, is combined with the 200/430 F and 430 F+ recracked fractions then hydrofined over a cobalt moly-on-alumina catalyst at 550 F, 400 psig and 800 SCF/B. The feed entering the hydrofiner (H/F Feed), the product therefrom (H/F Product), and che final product formed by blending che hydrofined pro- duct and product from MEROX is characterized in Table V Table V Final H/F Feed H/F Product Product Voi. % on Feed 60.2 88.1 Sulfur, wppm 711 8@2 20 Br. No. 4.5 1.1 Octane RONC 88.5 87.5 87.5 MONC 78.4 78.4 78.7 These data show that the octane loss due co hydrofining the final produce is ccnsiderably improved as contrasted with hydrofining the original feed, and that octane loss as a result of the hydrofining approximates only 008 RON, with no loss in MON octane value Naphtha yield is considerably improved with no greacer octane loss due to hydrofining as contrasted with recracking the whole naphtha EXAMPLE 4 Feedstock A was recracked in a reactor at 930 F, 14.7 psia, 13.7 WHSV and at a catalyst/oil ratio of 9.2 over a conventional commercial zeolite cracking catalyst containing crystalline aluminosilicate zeolice, silica alumina gel and clays, and the product then fractionated to provide three fractions, i.e., a low boiling 65/200 F fraction, an intermediate 200/350 F fraction and a high boiling 350!4300F fraction, as characterized in Table VI. Table VI 65/200 F 200/350 F 350/430 F Vol. % on Feed 21.6 48.6 9.7 Sulfur, wppm 42 91 893 Nitrogen, wppm 2 2 9.2 Br. No. cc/gm 20.3 3.3 1.41 Octane RONC 85.1 89.7 93.8 MONC 80.0 80.5 82.9 FIA, Vol. % Arom. 3.8 50 74.7 Olefins 11.6 0.6 0.1 Saturates 84.6 49.4 25.1 The 200/350 F fraction is than hydrofined over a cobalt moly-on-alumina catalyst at conditions just sufficient to produce a suitable reforming feed, this, requiring 98.9% hydrodesulfurization, 50% hydrodenitrogenation, and 70% saturation of the olefins to provide a produce of 89 RONG with less than 1 ppm sulfur, less than 1 ppm nitrogen and a bromine number of less than 1. In forming this product a hydrogen consumption of 2C SCF/Bbl is required. The hydrofined fraction is then reformed over an iridium-promoted platinum catalyst at 930 F, 1.0 W/Hr/W, 200 psig at a hydrogen rate of 4800 SCF/Bbl co produce 160 RONC gasoline. In sharp contrast, when Feedscock A was split into fractions without recracking, che composicions given in Table VII ere obtained, ,o wic: Table VII 65/200 F 200/350 F 350/430 F Vol. % on Feed 17.2 61.9 18.9 Sulfur, wppm 100 226 1084.8 Nitrogen, wppm 1.2 17.0 62.0 Br. No. cc/gm 54.6 24.6 7.8 Octane RONC 87.5 81.6 82.0 MONC 79.2 75.3 75.1 FIA, Vol. % Arom. 4.7 39.4 59.2 Olefins 33.1 8.4 5.7 Saturates 62.2 52.2 35.1 These fractions are thus hIghly unsaturated as contrasted with similar fractions obtained by recracking Feedstock A, and contain considerably more sulfur and nitrogen. By way of f@rther contrast, however, a portion of the 200/350 F fraction (Table VII) is then hydrofined over the hydrofining catalyst previously defined at conditions just sufficient to achieve 99.6% hydrodesulfurization, 94.1% hydrodenitrogena tion end 96% saturation of the olefins to produce a product suitable for reforming to 100 RONC, i.e., one which contained less than 1 ppm sulfur, less than 1 ppm nitrogen and a bromine number of less than 1. This produced a product of 75 RONC and required over 150 SCF/Bbl of hydrogen, well over seen times the amount of hydrogen required to hydrofine the recracked product. The recracking of Feedstock A is thus shown to drastically reduce the amount of hydrotreating required to produce a reformer feed, and ic achieves this at far less severity and with far less consumption of hydrogen. Moreover, assuming first order desulfurization kinetics, 20% less reactor volume is required to achieve 98.8% hydrodesulfuriza- tion for the intermediate fraction of recracked Feedstock A than is required to produce 99.6% hydrodesulfurization for che intermediate fraction of raw Feedstock A. It also reduces reforming severicy, or the severity required to produce 100 RONC gasoline. The following example demonstrates a more preferred embodiment wherein an intermediate fraction only is recracked. EXAMPLE 5 Another portion of che 200/350 F fraction split from Feedstock A, as characterized in Table VII, was recracked at 930 F, 14.7 psiag, 14.3 WHSV and at a catalyst/oil ratio of 9.1. The produce was then split into three fractions, a 65/200 F fraction, a 200/350 F fraction, and a 350/430 F fraction as defined in Table VIII. Table VIII 65/200 F 200/350 F 350/430 F Vol. % on Feed 17.3 60.8 2.7 Sulfur, wppm 67 83' 186 Nitrogen, wppm 1.0 3.0 17 Br. No. cc/gm 20.4 2.7 3.5 Octane RONC 87.4 89.6 - MONG -- 80.2 - FIA, Vol. Arom. 0 45.4 97.5 Olefins 10.2 2.6 1.0 Saturates 89.8 52.1 1.5 The 200/350 F fraction is chen hydrofined over a cobalt moly-on-alumina catalyst at conditions just sufficient to produce a suitable reforming feed, this requiring 98.8% hydrodesulfurization, 67% hydrodenitrogenation, and 63% saturation of the olefins to provide a product of 89.6 RONC with less than 1 ppm sulfur, less than 1 ppm nitrogen and a bromine number of less than one. In forming this produce, a hydrogen consumption of 20 to 30 SCF/Bbl is required. The hydrofined fraction is then reformed over an iridium promoted platinum catalyst at 930 F, 1.0 W/Hr/W, 200 psig ac a hydrogen rate of 4800 SCB/Bbl to produce 100 RONC gasoline. These data thus show that recracking the intermediate fraction of 2 cat naphtha offers definite advantages over recracking the whole cat cracked naphtha. In comparing Example 5 with Example 4 it is thus shown that 85.6 percent of a C5 /430 0F product is obtained in recracking an intermediate fraction vis-a-vis the 7909 percent of C5/4300F product obtained in recracking the whole of Feedstock A. Wioreover, 60.8 percent of a 200/350 F product is obtained in recracking the intermediate fraction vis-a-vis the 48. 6 percent of a 200/350 F producc obtained in recracking the whole of Feedstock A. This fraction is particularly suitable as - reformer feed. The preferred enbodiment, as represented by Example 5, also provides higher selectivity for other relatively high value products vis-a-vis the embodiment of Example 4; or, conversely, lower selectivity for products of lesser value vis-a-vis the embodiment of Example 4. The data given in Table IX presents comparative daca illustrative of the product of such relatively low value by-products as coke, light gases, inclusive of hydrogen and C1 and C2 hydrocarbons, and 430 F+ hydrocarbons, in the preceding runs wherein, as in Example 4, ne whole of Feedstock A is recracked, and in Example 5 an intermediate boiling feedstock is recracked. The Table also presents the yields of C3 and C4 hydrocarbons which were obtained, these products being nearly as valuable as gasoline. The first column of Table ix identifies the by-product, the second column gives the percent yield of che by-product, based on the amount of recracked feed which was treated, and the third column gives the percent yield, based on the amount of original Feedstock A. Table IX Yield, Based on Yield, Based on Recracked Feed Feedstock A Product Example 4 Example 5 Example 4 Example 5 Coke, Wt. % 1.31 0.86 1.31 0.53 Hydrogen, Wt. % 0.0073 0.0067 0.0073 0.0041 C1, Wt. % 0.13 0.10 0.1 0.062 C2, Wt. % 0.70 0.53 0.70 0.33 C3, Wt. % 5.10 4.87 5.1 3.01 C4, Vol. % 11.00 13.4 11.0 8.3 430. F+, Vol. % 3.5 1.9 3.5 1.2 The advantages of recracking an intermediate out vis-a-vis 2 whole feed are apparent. In considering these data it is noted in particular that the 430 F+ product is of low API gravity, is not desirable or use as heating oil, and is unsuitable for use as diesel fuel or jet fuel. Only small levels of this 430+ product can be tolerated In gasoline for it contains multi-ring aromatics which cause serious engine deposits. Table X presents data which illustrates that the pre Ferred embodiment produces higher yields of che C3= and C, hydrocarbons, which material is a potentially valuable alkylate feed. Analysis of to the C3 and C4 hydrocarbons thus shows the following yield of C3= and C4= (and i-C4) hydrocarbons, based on recracked feed. Table X Yield, Based on Recracked Feed Product Example 4 Example 5 C3=, Wt. % 3.90 3.6 C4=, Vol. % 3.61 4.54 i-C4, Vol. % 6.21 7.24 The advantages of recracking an intermediate boiling feed are therefore demonstrated, However, the recracking of a heavier fraction, e.g., a 200/430 F fraction, is preferable to recracking a whole fraction, i.e., the 65/430 F fraction for obviously, inter alia, the cracking of a 65/200 F fraction will produce little 200/350 F product for reforming, if any. It is apparent that various modifications and changes can be made without departing the spirit and scope of the invention. Conversions of Units Temperatures expressed in F are converted to C by subtracting 32 and deviding by 1.8. Gas Volumes in Sta.ldard Cubic Feet (SCF) arc converted to litres by multiplying by 28.32. Liquid Volumes in Barrels (B or Bbl) are converted to litres by multiplying by 159.0 Mass in pounds (lbs) is converted to kilograms by dividing by 2.20462. Pressures in pounds per Square inch (psi) are converted to kg/cm2 by multiplying by 0.07031. Note "psia" denotes absolute pressure in psi and "psig" denotes gauge pressure in psi.

Claims: CLAIMS 1. A process for the production of a high octane ga@eline characterized by the following steps in combination: (a) cracking a sulfur-bearing hydrocarbon feed in a first cracking zone over a cracking catalyst at conditions sufficient to obtain a cat cracked naphtha product containing in the range of from 10 percent to 60 percent olefins, based on the weight of said product, (b) withdrawing said cat cracked naphtha as a product frown said first cracking zone, (c) recracking said cat cracked naphtha product or one or more fractions therof, without dilution with other hydrocarbons, over a crystalline aluminosilicate zeolite catalyst in a second cracking zone to desulfurize said feed and saturate at least 50 percent of said olefins, based on the weight of said cat cracked naphtha, and (d) hydrotreating or hydrofining the product cf said second crack- ing zcne over a hydrogenation catalyst at hydrofining conditions in a hydrore2ting or hydrofining zone to hydrodesulfurize said produc and reduce the olefin content of said product. 2. A process according to claim characterized in that at leat one of the said fractions of said cat cracked naphtha, product comprises an intermediate fraction having a low end boiling point in the range of from 150 F (65.50C) to 2500F (i2l.l0C) and a high end boiling point in the range of from 250 F (121.10C) to 3800F (193, 30 C). 3. A process according to claim 1 or claim 2 characterized in that at least one of said fractions of said cat cracked naphtha product comprises a fraction having a low end boiling point in the range of from 180 F (82,20± to 2200F (104.40C) and a high end boiling point in the range of from. 4000F (204.40C) to 4300F (221.100). 4. A process according to any one of claims ]-3 characterized in that the said hyrotreating or hydrofining conditions of step (d) are selected to result in a product suitable for addition to a gasoline blending pool. 5. A process according to any one of claims 1-3 characterized in that the said hydrotreating or hydrofining conditions of step (d) are selected to result in a product suitable as a feed for reforming over a sulfursensitive noBle metal reforming catalyst. 6. A process according to any one of claims 1-5 characterized in that the stilfur-bearing hydrocarbon feed introduced into said first cracking zene is a gas oil boiling below 10500F (565.50C)' 7. A process according to any one of claims 1-6 characterizcd in that from 80 to 100 percent of the olefins of the cat cracked naphtha feed introduced into the second cracking zone are saturated during the reactions In the second cracking zone. 8. A process according to any one of claims 1-7 characterized in that the cat cracked naphtha feed introduced into the second cracking zone is reacted at temperature in the range of from 8000F (26.60C) to 11000F (593.3 C) and at a pressure in the range of from 0 to 50 psig (0 to 3.5155 kg/cm2 gauge). 9. A hydrodesulfurized cat cracked naphta product whenever produced by the process of any one of claims 1-8.

Inventors: SCHUETTE, WILLIAM LEE, WINTER, WILLIAM EDWARD
Applicants: EXXON RESEARCH AND ENGINEERING COMPANY
Application year: 1979
Main classification: C10G69
IPC codes: C10G69, C10G51