WO1993022402A1 - Craquage catalytique de charges distillees - Google Patents

Craquage catalytique de charges distillees Download PDF

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Publication number
WO1993022402A1
WO1993022402A1 PCT/US1993/004088 US9304088W WO9322402A1 WO 1993022402 A1 WO1993022402 A1 WO 1993022402A1 US 9304088 W US9304088 W US 9304088W WO 9322402 A1 WO9322402 A1 WO 9322402A1
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Prior art keywords
riser
catalyst
feed
quench
cracking
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PCT/US1993/004088
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English (en)
Inventor
Peter Martin Adornato
David Lee Johnson
Hartley Owen
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Mobil Oil AS
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Mobil Oil AS
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Publication date
Application filed by Mobil Oil AS filed Critical Mobil Oil AS
Publication of WO1993022402A1 publication Critical patent/WO1993022402A1/fr
Anticipated expiration legal-status Critical
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Classifications

    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10G—CRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
    • C10G11/00—Catalytic cracking, in the absence of hydrogen, of hydrocarbon oils
    • C10G11/14—Catalytic cracking, in the absence of hydrogen, of hydrocarbon oils with preheated moving solid catalysts
    • C10G11/18—Catalytic cracking, in the absence of hydrogen, of hydrocarbon oils with preheated moving solid catalysts according to the "fluidised-bed" technique

Definitions

  • the invention relates to catalytic cracking of distilled hydrocarbon feeds.
  • FCC fluid catalytic cracking
  • Gas oils and vacuum gas oils, which are obtained by distillation, are preferred feeds for FCC. They have less contaminants and make less coke during cracking than heavier hydrocarbons which are left behind in distillation columns as residual fractions.
  • the FCC process can produce large quantities of gasoline and, in most FCC units operating for maximum gasoline production, roughly 50 LV % of the feed is converted into gasoline.
  • the FCC gasoline has high octane, and most of it can be added to the refinery gasoline blending pool. There is, however, a
  • FCC heavy naphtha is one fraction of FCC gasoline and which often has too much sulfur and is too heavy (too high an end point, or sometimes a 90 or 95% boiling point) to permit all of it to be added to the gasoline blending pool.
  • Legislation in many countries restricts the amount of sulfur and/or aromatics which may be present in gasoline and puts additional constraints on the volatility of the gasoline boiling range materials. Sulfur levels can be reduced by hydrotreating, but this requires considerable capital and operating expense and also saturates olefins, which reduces octane.
  • the FCC process itself can be used to reprocess naphtha produced by the FCC unit.
  • U.S. 4,832,825 teaches recycling FCC light naphtha to the base of an FCC riser to meet hot regenerated catalyst and reports that naphtha recycle doubles the
  • Table III shows multiple examples of cracking FCC naphtha in a riser pilot plant, to produce a gasoline product having 76.7 to 99.3 vol % aromatics.
  • the octane number and the yield of the gasoline product can simultaneously be increased by raising the temperature in the base of the FCC riser and then injecting a quench fluid at a specific distance along the riser.
  • U.S. 4,818,372 discloses the injection of a quench fluid in an FCC process but in combination with a resid-containing feed where the problems addressed are the the vaporization and conversion of the heavy products.
  • FCC units cracking distilled feeds have no problem vaporizing the feed.
  • the present invention resides a catalytic
  • catalyst/vaporized feed mixture in at least one quench zone within said riser reactor downstream of the base section thereof and more than 15% of the length of the riser upstream of the riser outlet, to lower the temperature in the riser by at least 6oC (10oF) and thereby reduce thermal cracking, without terminating catalytically cracking, of the quenched mixture;
  • the quench fluid is a heavy naphtha fraction including hydrocarbons boiling in the range 150 to 200°C (300 to 400°F) separated from the cracked product.
  • crude, oil flows via line 1 to an atmospheric distillation column 10, where the crude is distilled to produce streams ranging from light overhead vapor products removed via line 6, light overhead liquid products removed via line 3, to a naphtha fraction removed via line 4, and a gas oil fraction removed via line 2.
  • the resid fraction 5 is charged to a vacuum column, not shown, to produce a vacuum gas oil fraction and a vacuum resid. This produces more distilled feed for the FCC unit, and reduces the size of the resid stream, while preserving the principle of sending only distilled feeds to the FCC. In most units there is some contamination of the distilled feed, either due to entrainment in the fractionator, or because a minor amount of residual material is blended with the distilled feed.
  • the FCC unit comprises FCC riser 10, a separator 20, a regenerator 30, and FCC main column 40.
  • the gas oil from the atmospheric distillation column 10 and the vacuum gas oil from the vacuum column are charged to the base of riser reactor 10, where it contacts hot regenerated catalyst which is fed from regenerator 30 via line 32 to the base of the riser 10.
  • a quench stream preferably a recycled heavy naphtha from line 45, is added to one or more quench points via lines 63 or 65 at various elevations in the riser.
  • the optimum quench point, and number of quench points can vary based on product demands, unit constraints, and catalyst activity.
  • Hot cracked product withdrawn from vessel 20 passes via line 26 to the base of the FCC main column 40, which operates conventionally. Trays or packing fractionate the cracked product vapor into a main column bottom stream 42, sometimes called a slurry oil, one or more cycle oil products, such as a light cycle oil or LCO product withdrawn via line 55, a heavy naphtha stream withdrawn via line 48, a light naphtha stream withdrawn via line 43, and an overhead vapor stream withdrawn via line 46. Light liquid reflux returns to the column via line 58.
  • a main column bottom stream 42 sometimes called a slurry oil
  • one or more cycle oil products such as a light cycle oil or LCO product withdrawn via line 55, a heavy naphtha stream withdrawn via line 48, a light naphtha stream withdrawn via line 43, and an overhead vapor stream withdrawn via line 46.
  • Light liquid reflux returns to the column via line 58.
  • the heavy naphtha fraction withdrawn via line 48 may be removed as a product via line 47, but
  • FCC heavy naphtha is recycled via line 45 to one or more quench points in the FCC riser reactor. Cracking a distilled feed, followed by quenching with an FCC heavy naphtha produces a number of
  • the temperature in the base of the riser can be increased so as to promote the cracking
  • the conditions in the base of the riser are very similar to conventional FCC riser cracking conditions, but the temperature is preferably 6 to 30oC (10 to 50oF) hotter than that normally employed.
  • the mix temperature at the base of the riser is 510-590oC (950-1100oF), and catalyst:oil ratios is from 1:1 to 10:1, preferably greater than 4:1.
  • Atomizing feed nozzle(s) which produce droplets of oil having an average particle size below 2000 microns, preferably below 1000 microns, and most preferably below 500 microns, are desirable. Nozzle exit velocities above 15 m/s (50 fps), preferably above 30 m/s (100 fps), and most preferably above 61 m/s (200 fps) should be used.
  • the nozzles preferably vaporize the distilled feed in the riser within less than 10 meters of travel, and more preferably within 1 to 5 meters of riser travel or even less.
  • riser top temperatures 480 to 565oC (900 to 1050oF) will be satisfactory in many instances.
  • Quenching can be effected rapidly after feed injection, that is within less than a second or even within 0.5 seconds or less of feed injection.
  • rapid quenching requires large amount of quench fluid, that is sufficient quench fluid to reduce temperatures by 6 to 56°C (10 to 100°F), and preferably by 11 to 42°C (20 to 75°F), presuming all streams are well mixed and that quench is instantaneous.
  • the drawback of adding such large amounts of quench fluid is loss of plant capacity or loss of selectivity due to increased pressure.
  • Recycled liquid hydrocarbon quench streams unload to some extent the wet gas compressor but can load up the riser and even flood the main column.
  • quenching at the following fractional riser locations may be considered. In general, it is believe that quick quenching should occur no inore than 1/2 way up the riser, and preferably around 1/10 to 5/10 of the way up the riser. Quenching about 2/10 to 4/10 of the way up the riser will be optimum in many installations.
  • Quenching with modest amounts of quench fluid will usually occur after at least a second of vapor residence time in the base of the riser, and preferably after 1.5 seconds of residence time, and most preferably after 2.0 seconds of residence time.
  • quenching at the following fractional riser locations may be considered.
  • delayed quenching should occur at least 50% of the way up the riser, and preferably around 60 to less than 85% of the way up the riser. Quenching about 75% up the riser will be optimum in many installations.
  • quench fluids such as cold solids, water, steam, or inert vaporizable liquids, such as light cycle oil, heavy cycle oil, slurry oils, or other aromatic. rich streams, may be used. All such quench fluids will remove heat. Preferably liquids are used so that more heat can be removed from a given weight of fluid added. Use of a reactive quench liquid, such as the heavy naphtha fraction, which further promotes endothermic reactions, may be
  • the amount of quench fluid used is related to the quench point. Delayed quench, with only 7 wt % water, can work about as well as quick quenching with twice as much water. For units not limited by pressure, sour water or other constraints, it will be usually be preferred to use more quench fluid and. quench near the mid point of the riser.
  • the preferred quench fluid is FCC heavy naphtha, which is defined herein as that portion of the FCC cracked product having an initial boiling point of 100 to 160°C (220 to 325°F), a 5% boiling point of 120 to 150 °C (250 to 300°F), a 95% boiling point from 200 to 280oC (400 to 500°F) and an end boiling point of 220 to 270 °C (425°F to 525oF).
  • the heavy naphtha is the fraction intermediate the FCC light naphtha (C5+ to the end point for light naphtha) and light cycle oil. Considerable variation in boiling ranges of all these materials is possible, due both to local product specifications and fractionator constraints. There is usually considerable overlap between the end point of the heavy naphtha and the initial boiling point of the light cycle oil because of imperfect fractionation.
  • Heavy naphtha is the preferred quench fluid because it is always available downstream of an FCC unit and its use increases FCC conversion and gasoline octane without adding to sour water production or significantly increasing dry gas production. Also, quite unexpectedly, using heavy naphtha as a quench fluid in the process of the invention reduces its sulfur content.
  • Heavy naphtha quench may be used in an amount equal to 2.5 to 25 wt %, preferably 5 to 15 wt %, of the fresh feed. When used in these amounts, increased conversion of feed, an increase in both gasoline yield and octane number will be achieved.
  • the mid point, and the 90% point, of a finished gasoline product made from a blend of FCC light naphtha, and hydrotreated heavy naphtha can usually be reduced from 3 to 6°C (5 to 10°F) or more.
  • FCC catalyst can be used in the process of the invention, although it is preferred to employ highly active catalysts, with high zeolite contents, in particular high amounts of large pore zeolite cracking catalyst, such as zeolite Y.
  • large pore zeolite contents of the fresh makeup catalyst, exclusive of any additive catalyst, of 10 to 80 wt % are suitable, with 30 to 60% being preferred, and 35 to 55 wt % considered optimum.
  • Catalyst activities should be at least 55 MAT, more preferably at least 60 to 65 MAT, and most preferably above 70 or even 75 MAT.
  • the MAT test is well known, and more details of it may be found in ASTM test method D3907.
  • Thermal cracking produces olefinic (and highly reactive) gasoline of good octane number, but usually in poor yield. Thermal cracking of light ends of the feed, and re-cracking of cracked products is especially undesirable. It is therefore important to limit thermal cracking and ensure that catalytic cracking is the predominant reaction in the riser. For this reason it is important to restrict the feed to distilled materials, since resids are more susceptible to thermal cracking.
  • additive catalysts which may either be incorporated into the conventional FCC catalyst or added to the circulating inventory in the form of separate particles of additive.
  • High silica, shape selective additives, such as zeolites having a Constraint Index of 1 - 12, and silica:alumina ratios above 12 are preferred.
  • Silica:alumina ratios of 50:1, 100:1, 200:1, 300:1, 400:1, 500:1 or higher may be used. Details of the Constraint Index test procedures are provided in J. Catalysis 67, 218-222 (1981) and in U.S. 4,711,710 (Chen et al.).
  • Preferred shape selective zeolites are
  • ZSM-5 exemplified by ZSM-5, ZSM-11, ZSM-12, ZSM-23, ZSM-35, ZSM-48, ZSM-57 and similar materials.
  • ZSM-5 is especially preferred.
  • ZSM-5 is described in U.S. 3,702,886, U.S.
  • ZSM-23 is described in U.S. 4,076,842.
  • ZSM-35 is described in U.S. 4,016,245.
  • the optimum quench point will shift closer to the riser outlet, because the ZSM-5 retains catalytic activity long after the large pore cracking catalyst has lost most of its activity.
  • ZSM-5 plus matrix ZSM-5 plus matrix
  • 3.0 wt % ZSM-5 3.0 wt % ZSM-5
  • the present invention works with all distillable FCC feedstocks such as gas oils or vacuum gas oils. Modern fractionation technology has allowed deeper cuts to be made of feedstocks, and distilled feeds with end points in excess of 1000oF may readily be produced. Despite their high end points, such feeds were vaporized in a distillation column, are readily vaporized in an FCC riser, and are ideal for use in the process of the present invention. Such distilled feeds are essentially free of, or contain greatly reduced amounts of, all or most of the asphaltics, or Conradson Carbon Residue. These residual materials, which are troublesome to handle and difficult to vaporize, are preferably excluded from the process of the present invention.
  • Light cycle oil, heavy cycle oil, or slurry oil may be present. Recycle of such streams is common in FCC.
  • liquid yield refers to those liquid yields obtained with consistent operation of the fractionator to produce on specification products or streams having a specified boiling range and suitable for use a gasoline blending component.
  • the first experiment reported represents a test conducted at a commercial refinery processing a distilled feed.
  • the commercial scale FCC riser reactor had a throughput of about 12720 m 3 /day (80,000 BPD) and an initial riser diameter of about 1.1 m (3.5 feet), expanding to about 2.3 m (7.5 feet) at the riser outlet, and an overall length of about 47.2 m (155 feet). Quench nozzles for the test were installed in ports which were available. The ports were
  • the total residence time in the riser reactor was 4 seconds.
  • the heavy feed was a sour gas oil having the following properties:
  • the catalyst was an equilibrium catalyst having 66 FAI.
  • the equilibrium catalyst was estimated to have an average catalyst composition of 11 wt % USY on a Si-Al matrix, with 2.8 wt % rare earths.
  • the fresh make-up catalyst had more than 30 wt % USY content. Natural aging or steaming of the makeup catalyst in the FCC unit reduced the 30+ wt % USY zeolite of the fresh catalyst to the 11 wt % USY content of the equilibrium catalyst.
  • the naphtha is hydrofinished to meet a target of 0.20-0.22 wt % sulfur for the blended gasoline.
  • gasoline distillation showed an unexpected improvement in production of relatively lighter gasoline.
  • Most of the increased gasoline yield was in C 5 -280 TBP or C -320 TBP.
  • the model was used to predict yields for cracking the LETGO feed for a base case (no quench) and for a case with 10% quench.
  • the model was based on a total riser height of 46.9m (154 feet), with quench
  • the LETGO feed has no heavy ends, nor non-distillables, and yet its conversion in an FCC riser reactor is considerably enhanced by addition of 10 wt% quench.

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  • Chemical & Material Sciences (AREA)
  • Oil, Petroleum & Natural Gas (AREA)
  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • General Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Production Of Liquid Hydrocarbon Mixture For Refining Petroleum (AREA)

Abstract

Procédé de craquage catalytique servant à convertir une charge distillée d'hydrocarbures lourds en produits plus légers et comprenant le mélange de ladite charge et d'un courant chaud de catalyseur de craquage régénéré provenant d'un régénérateur de catalyseur (30) dans la section de base du réacteur à tuyau montant (10). Au moins 95 % en poids de ladite charge distillée est vaporisée en 0,24 seconde du temps de séjour de la vapeur dans ledit réacteur (10), la quantité et la température du catalyseur chaud régénéré étant suffisantes pour effectuer à la fois le craquage catalytique et thermique de ladite charge distillée et vaporisée dans la section de base dudit tuyau montant (10). Un fluide de refroidissement est injecté sur le mélange catalyseur/charge vaporisée dans une zone de refroidissement (63) ou (65) située dans ledit réacteur à tuyau montant (10) en aval de sa section de base et sur plus de 15 % de la longueur du tuyau en amont de sa sortie, de façon à faire descendre la température dans le tuyau d'au moins 6 °C.
PCT/US1993/004088 1992-05-04 1993-04-30 Craquage catalytique de charges distillees Ceased WO1993022402A1 (fr)

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US87791492A 1992-05-04 1992-05-04
US877,914 1992-05-04

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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3758403A (en) * 1970-10-06 1973-09-11 Mobil Oil Olites catalytic cracking of hydrocarbons with mixture of zsm-5 and other ze
US4356338A (en) * 1979-07-27 1982-10-26 Mobil Oil Corporation Extending catalyst life by treating with phosphorus and/or steam
US4764268A (en) * 1987-04-27 1988-08-16 Texaco Inc. Fluid catalytic cracking of vacuum gas oil with a refractory fluid quench
US4818372A (en) * 1985-07-10 1989-04-04 Compagnie De Raffinage Et De Distribution Total France Process and apparatus for the catalytic cracking of hydrocarbon feedstocks with reaction-temperature control

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3758403A (en) * 1970-10-06 1973-09-11 Mobil Oil Olites catalytic cracking of hydrocarbons with mixture of zsm-5 and other ze
US4356338A (en) * 1979-07-27 1982-10-26 Mobil Oil Corporation Extending catalyst life by treating with phosphorus and/or steam
US4818372A (en) * 1985-07-10 1989-04-04 Compagnie De Raffinage Et De Distribution Total France Process and apparatus for the catalytic cracking of hydrocarbon feedstocks with reaction-temperature control
US4764268A (en) * 1987-04-27 1988-08-16 Texaco Inc. Fluid catalytic cracking of vacuum gas oil with a refractory fluid quench

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