US3775305A - Hydrodesulfurization process for producing a heavy asphaltic fuel oil - Google Patents

Hydrodesulfurization process for producing a heavy asphaltic fuel oil Download PDF

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US3775305A
US3775305A US00206083A US3775305DA US3775305A US 3775305 A US3775305 A US 3775305A US 00206083 A US00206083 A US 00206083A US 3775305D A US3775305D A US 3775305DA US 3775305 A US3775305 A US 3775305A
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sulfur
percent
line
oil
stage
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J Mckinney
J Paraskos
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Chevron USA Inc
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Gulf Research and Development Co
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    • 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
    • C10G65/00—Treatment of hydrocarbon oils by two or more hydrotreatment processes only
    • C10G65/02—Treatment of hydrocarbon oils by two or more hydrotreatment processes only plural serial stages only
    • C10G65/04—Treatment of hydrocarbon oils by two or more hydrotreatment processes only plural serial stages only including only refining steps
    • 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
    • C10G2300/00—Aspects relating to hydrocarbon processing covered by groups C10G1/00 - C10G99/00
    • C10G2300/10—Feedstock materials
    • C10G2300/107—Atmospheric residues having a boiling point of at least about 538 °C

Definitions

  • This invention relates to a process for the production of crude or residual oils having an especially low sulfur content. More particularly, this invention relates to a hydrodesulfurization process for producing an asphaltic fuel oil having a low sulfur content.
  • Asphalt is a generally low-grade material that has been isolated from the crude oil and utilized in road construction.
  • asphalt has been proposed to treat the asphaltic fraction of crude oil in some manner so as to upgrade this material into a more valuable product such as a fuel oil.
  • asphalt when isolated, is highly viscous and is diicult to process over a catalyst.
  • asphalt consists of large molecules of fused, aromatic rings and contains the greatest amount of the total sulfur content of the full range crude on a relative basis.
  • Afurther problem is that some of the sulfur content of the asphalt is tied up in the interior of the ⁇ large molecules thereof, rendering the asphalt especially'diicult to desulfurize.
  • asphalt contains metals, principally nickel and vanadium, which readily deposit on desulfurization catalysts tending to deactivate the catalyst. The cumulative effect of such factors is that much more severe conditions in the form of higher temperatures and pressures are required as well as a different type of catalyst in'order to remove the sulfur-from heavy, asphaltic oils as compared with desulfurization of a distillate oil.
  • VSulfur is a major lcontributor to vair pollution. Accordingly, certain municipalities, both local and foreign, have placed an upper limit on the sulfur content of fuel oils. Inthe past, such locales ⁇ haveplaced a one percent by weight sulfur limit on heavy fuel oils, but the trend has been to a lower maximum sulfur content, such as 0.5 weight percent. Such limitations have provided a major impediment to the use of heavy asphaltic hydrocarbon oil fractions as fuel oil, since an asphaltic fuel oil having an 0.5 percent sulfur content is not easily obtained from some high sulfur crudes merely by passing the crude oil over a ⁇ desulfurization catalyst.
  • the sulfur content of a particular asphaltic crude or reduced oil could be reduced to one percent sulfur in a hydrodesulfurization zone, but if the sulfur level was to be reduced below one percent, the desulfurization temperature had to be increased to a point at which excessive hydrocracking to lower boiling materials resulted.
  • the sulfur level of such residual oils from 4 to l percent by weight of sulfur without incurring excessive cracking of the feed, it is substantially more diicult for a majority of typical feeds to remove more than about percent of the sulfur without excessive hydrocracking.
  • Excessive hydrocracking is undesirable since it unnecessarily consumes hydrogen and produces undesired light products and coke on the desulfurization catalyst.
  • the nature of the resulting product can be altered to the extent that it is not a heavy fuel oil whereas heavy oils generally have a higher heating value than lighter oils.
  • a particular heavy fuel oil containing an asphalt fraction may be produced having a sulfur content below one percent by weight of means of the present invention which comprises a process which involves passing an asphalt-containing or asphaltic, hydrocarbon oil, such as a crude oil or residual oil (a reduced crude) containing more than about one percent sulfur to a first hydrodesulfurization zone under an average hydrogen partial pressure, Pav, withdrawing a first effluent from the rst hydrodesulfurization zone having a reduced sulfur content relative to the feedstock, said first eflluent comprising hydrogen sulde, a light gas fraction, an oil fraction containing aromatics and saturates, and a higher boiling asphaltic fraction.
  • hydrocarbon oil such as a crude oil or residual oil (a reduced crude) containing more than about one percent sulfur
  • Pav average hydrogen partial pressure
  • the oil fraction is referred to as light oil to contrast it to the higher boiling asphaltic fraction.
  • the hydrogen sulfide, the light gas fraction, and a low boiling portion of the light oil fraction are separated from the first ellluent, and the remaining portion of the rst effluent comprising the asphaltic fraction and a higher boiling portion of the oil fraction is passed to a second hydrosulfurization zone and is desulfurized under an average hydrogen partial pressure, Pzav.
  • Each hydrodesulfurization zone is provided with a hydrodesulfurization catalyst that is disposed on a non-cracking support.
  • a second eflluent is withdrawn from the second hydrodesulfurization Zone which provides a heavy, asphaltic fuel oil containing less than one percent by weight sulfur.
  • the average hydrogen partial pressure, Pav is maintained above the hydrogen partial pressure value at which the reaction rate constant for the lirst zone 4would have the same value as the reaction rate constant for the second zone, but sufficiently low that not less than 40 percent by weight of said second efuent boils above the I.B.P. of the feed to said rst hydrodesulfurization zone.
  • PIBV PZIV wherein P18, is the average hydrogen partial pressure in the first hydrodesulfurization zone
  • P2M is the average hydrogen partial pressure in the second hydrodesulfurization zone.
  • the removal of the light oil fraction inherently removes substantially all the hydrogen sulfide and light hydrocarbons produced in the first stage so that this material does not enter the second stage.
  • One modification of the present invention involves a process which comprises passing an asphaltic, hydrocarbon Ifeed containing more than about one percent sulfur to a hydrosulfurization zone in the presence of hydrogen and Ia light oil fraction comprising aromatics and saturates having a boiling point below the asphaltic portion of the feedstock to said hydrodesulfurization zone, and controling the amount of said light oil, and thus the amount of aromatics and saturates that are passed to the hydrodesulfurization zone to increase the desulfurization rate and permit the recovery of a heavy, asphaltic hydrocarbon fuel containing less than about one percent sulfur.
  • the present invention provides an asphalt-containing heavy fuel oil, which is practically sulfur free, without the need for blending the asphaltic fuel 'oil with a sulfur-free middle distillate oil in order to obtained an oil having a low sulfur content, although such blending is not precluded in accordance with the present invention.
  • a still further modification of the present invention relates to a process .for controlling the hydrodesulfurization of an asphaltic, heavy oil, which process comprises passing crude oil or residual oil, for example, which oil contains an asphaltic fraction, through a hydrodesulfurization zone in the presence of hydrogen, the oil increasing in aromatic hydrocarbon content as it passes through the hydrodesulfurization zone, controlling the aromatic content of the oil as the oil passed through said hydrodesulfurization zone, and then withdrawing the oil from said hydrodesulfurization zone at substantially the point 'at which the aromatic content of the oil no longer increases.
  • asphalt or asphaltic as employed in the present specification is intended to include the resins and asphaltenes present in crude oil.
  • Asphalt can constitute approximately 5 to 30 percent by volume or more of crude oil and has an initial boiling point of about l040 F. It is obtained in refineries by a propane deasphaltng process (solvent extraction), or from the residues obtained from distillation.
  • Asphaltenes are highly aromatic and consist of large molecules of fused aromatic rings and normally contain the greatest sulfur concentration of any constituent of the full range crude. Unlike other crude fractions, asphalt also contains metals, principally nickel and vanadium.
  • the asphaltenes and resins may be distinguished from the remainder of the crude oil, which material comprises saturates and aromatics, by virtue of the solubility of these aromatics and saturates in propane and the insolubility of the asphaltenes and resins in propane.
  • the propane-soluble aromatics include benzenes, naphthalenes, thiophenes, benzothiophene, and dibenzothiophenes las the predominant molecular species, while the saturates include the non-aromatic, propane-soluble species, such as the naphthenes, e.g., cyclohexanes, andthe parafiins, e.g., dodecane, and sulfur-containing compounds, such as s-butyl mercaptan.
  • the material commonly referred to as asphalt comprises the residue of a propane extraction.
  • resins and asphaltenes are themselves separable by a pentane extraction, by virtue of the fact that asphaltenes are insoluble in pentane, while both resins and oils are soluble in pentane.
  • the point at which the sulfur remaining in the crude oil becomes refractory may vary with the nature of the particular type of crude oil. This point may be easily determined experimentally.
  • the asphaltenes consist of large molecules of fused aromatic rings and contain sulfur in the interior of the large molecules, thereby rendering the sulfur extremely diicult to remove.
  • the asphalt contains all of the metals, such as nickel and vanadium that are present in the crude, and these metals readily deposit on the catalyst tending to deactivate the catalyst and reduce its effectiveness.
  • FIG. 1 is a ow diagram illustrating the desulfurization of an asphaltic, reduced crude in two stages
  • FIG. 2 graphically illustrates the effect of hydrogen partial pressure in each desulfurization stage upon the desulfurization reaction rate constant
  • FIG. 3 illustrates graphically thepercent yield of materials boiling above the initial boiling point of the feed to a desulfurization reactor as the average reactor temperature increases
  • FIG. 4 graphically illustrates the change in concentration of the aromatic, saturate, asphaltene and resin fractions of an asphalt-containing reduced crude as the degree of desulfurization increases;
  • FIG. 5 graphically illustrates volume percentages of aromatics and saturates that are removed at various interstage flash points
  • FIGS. 6 to 10 are diagrammatic schemes for obtaining a low sulfur, light aromatic-rich fraction from one portion of the feedstock to solublize and reduce the viscosity of the solution of asphaltenes and resins present in the residual portion of the feed prior to desulfurization of the asphaltenes and resins.
  • FIG. 1l graphically illustrates the reaction rate advantage of a two-stage hydrodesulfurization system as contrasted with a single stage operation.
  • a reduced crude such as a 50 percent reduced Kuwait crude which contains the entire asphalt content of the full crude and therefore also contains all of the nickel and ⁇ vanadium and most refractory sulfurvcontent of the full crude is charged to the process through line and is pumped through line 14, preheater 16, line 18, solids filter and line 22 to drum 24. From drum 24 the liquid oil charge is passed through line 26 to feed pump 30.
  • Liquid from pump 30 is admixed with hydrogen from line 32 and passed through line 34, valve 36, line 38 and furnace 40.
  • Liquid flow valve 36 is disposed in a nonfully preheated liquid hydrocarbon line.
  • Recycled hydrogen along with make-up hydrogen (if desired) are introduced into the liquid charge to the reactor prior to the preheating thereof.
  • Recycled hydrogen is passed through line 42 and valve 44, while makeup hydrogen may be charged through line 46, compressor 48 and valve 50.
  • the recycled hydrogen and any make-up hydrogen are introduced to the relatively cool liquid charge through line 32.
  • a preheated mixture of liquid charge and hydrogen in line 54 may be passed through a guard reactor (not shown), if desired.
  • An eluent stream from the guard reactor is charged to the main reactor 60 containing catalyst beds 62, 64 and 66. This stream may have a 650 F.
  • the hydrodesulfurization catalyst employed in the process of theI present invention is conventional and comprises, for example, Group VI and Group VIII metals on a non-cracking support.
  • the catalyst may comprise nickel-cobalt-molybdenum or cobalt-molybdenum on an alumina support.
  • the alumina may be stabilized with 1 to 5 percent by weight of silica.
  • the preferred catalyst is' ⁇ a nickel-cobalt-molybdenum lon alumina containing less than 1 percent silica which catalyst may or may not be sulided.
  • Magnesia is also a non-cracking support.
  • An especially preferred catalyst comprises a particulate catalyst comprising particles between about lo and 1/40 inch in diameter, such as described in U.S. Pat. 3,562,800 to Carlson et al., which patent is hereby incorporated by reference.
  • the same or a different hydrodesulfurization catalyst can be employed in each stage.
  • ⁇ An essential feature of the present invention is that the catalyst is provided on a non-cracking support, since the process of the present invention is essentially a noncracking process in that vary little material is produced having a boiling point below the initial boiling point of the feed. However, high 'boiling material in the feed may be cracked to produce lower boiling products still in the boiling range of the feed.
  • prior processes have employed techniques involving, for example, high silica-containing catalysts, e.g.
  • the process of the present invention involves mainly the severance of carbon-sulfur bonds of the asphaltenes and resins inorder to desulfun'ze the diicultly desulfurizable asphalt, rather than cracking carbon-carbon bonds, which results in lower molecular weight materials.
  • sulfur is removed from oils during the present process, but this type of sulfur removal is relatively easy to accomplish.
  • the cracking of carbon-carbon bonds as in ⁇ prior processes employing cracking produces a material other than a heavy fuel oil and is outside the scope of the present invention.
  • a relatively minor amount of material is produced having a boiling point below the initial boiling point of the feed to the hydrodesulfurization unit.
  • hydrogen is introduced along with the feedstock by means of line 32.
  • Conventional reaction conditions in the hydrodesulfurization reactor are employed, for example, a hydrogen partial pressure of 1000 to 5000 pounds per square inch, preferably 1000 to 3000 pounds per square inch, is employed.
  • a hydrogen partial pressure of 1500 to 2500 pounds per square inch is especially preferred.
  • the gas circulation rate may be between about 200 and 20,000 standard cubic feet per barrel, generally, or preferably about 3000 to 10,000 standard cubic feet per barrel of feed, and preferably containing 85 percent or more of hydrogen.
  • the mol ratio of hydrogen to oil may be between about 8:1 and 80:1.
  • an essential feature of the present invention is the employment of a predetermined, average hydrogen partial pressure in each of the two hydrodesulfurization zone which will permit the desulfurization of the asphaltic oil of the present invention to the necessary extent without undue conversion of the asphaltenes and resins. It is necessary to employ a sufliciently high hydrogen partial pressure, particularly in the second hydrodesulfurization stage where the removal of the highly refractory, asphaltic sulfur takes place, in order to provide hydrogen to the reactive surface of the asphaltene molecule. It is the chemical activity as expressed in the partial pressure of hydrogen, rather than total reactor pressure, which determines hydrodesulfurization activity.
  • Sp pounds of sulfur per pound of oil in the product
  • Sf pounds of sulfur per pound of oil in the feed
  • LHSV volume of oil per hour per volume of catalyst.
  • the solid line curve of FIG. 2 shows the effect of hydrogen partial pressure upon the reaction rate constant in a second stage following a 650 F. ash (corresponding to atmospheric pressure) of hydrogen sulfide, light gases and a light fraction of the aromatics and saturates
  • FIG. 2 illustrates the advantage of employing increasing hydrogen partial pressures
  • a point is reached, in one example, at a hydrogen partial pressure of 2200 p.s.i. where the hydrogen partial pressure becomes significantly high that excessive hydrocracking occurs, since high hydrogen partial pressures induce hydrocracking.
  • the upper hydrogen partial pressure must not exceed 2200 p.s.i. for the system illustrated in FIG. 2. Otherwise, the process becomes a cracking process, rather than a non-cracking process, and with all the attendant disadvantages thereof.
  • the average hydrogen partial pressure of the first and second hydrodesulfurization stages must be sufficiently low that not less than 40 percent by weight of the effluent from the second stage boils above the I.B.P. of the feed to the first hydrodesulfurization stage.
  • the process of the present invention provides a yield of not less than 40 or 50 and up to 80 and 90 percent by weight of material having a boiling point greater than the initial boiling point (I.B.P.) of the feed to the first desulfurization reactor.
  • I.B.P. initial boiling point
  • the feed to the hydrodesulfurization reactor can have an I.B.P. of not less than 375 F., and will preferably have an I.B.P. of at least 620 or 650 F.
  • the amount of material obtained from the second hydrodesulfurization stage whose boiling point is lower than 375 F., 620 F., or 650 F. will not exceed 50 or 60 percent by weight, generally or preferably 10 or 20 weight percent.
  • a feed having an I.B.P. greater than 650 F. e.g. vacuum tower bottoms having an I.B.P. in the range of 750 to 900 F. or more, may be employed in the process of the present invention.
  • the amount of material obtained from the second hydrodesulfurization zone whose boiling point is below 650 F. will not exceed l0 or 20 weight percent.
  • the fuel oil product from each hydrodesulfurization unit has a total asphaltenes plus resins content of at least l or 20 and can have 30 or 40 up to 80 percent by weight of that present in the feed to the first hydrodesulfurization unit.
  • the fuel oil product from the second hydrodesulfurization unit has a preferred total content of resins plus asphaltenes of at least 40-50 or 70 up to 90 percent by weight of that present in the feed to second hydrodesulfurization zone. This is a further indication that the resins, and particularly asphaltenes may be desulfurized without their complete destruction as was previously proposed.
  • the point of intersection of the stage I and stage II curves of FIG. 2 will vary depending upon the catalyst and the feedstock that undergoes hydrodesulfurization. With some catalysts and/ or feedstocks, the point of intersection may be as low as 1000 p.s.i., so that effective twostage operation can occur between 1000 p.s.i. and 2200 p.s.i. Likewise, the point at which excessive hydrocracking occurs may vary both below and above 2200 p.s.i., e.g. 2500, 3000 or 3500 p.s.i.
  • the data for FIG. 2 was obtained by charging a 4.1 weight percent sulfur-containing Kuwait reduced crude to a first stage to reduce the sulfur content to one percent, and the eflluent is flashed at 650 F.+ based on atmospheric pressure. The sulfur content is reduced to 0.5 weight percent in the second stage.
  • the catalyst in each stage is a nickel-cobalt-molybdenum on alumina catalyst.
  • the hydrogen partial pressure in the first stage may be substantially the same as that employed in the second stage, if desired.
  • Hydrodesulfurization reactor temperatures may range between about 650 and about 900 F., and preferably between about 680 and 800 F.
  • each succeeding catalyst bed 62, 64 and 66 may have a larger volume than the bed just prior to it. If desired, .there may be 4to 6 catalyst beds in the reactor and, if desired, eachvreactor bed may have 25 percent, 50 percent, 100 percent Ior more catalyst than the bed just prior'to it.
  • the process of the present invention permits the eflicient removal of greater than 75 percent sulfur from an asphaltic oil and overcomes the refractory nature of such oils.
  • the eflluent in line 88 is passed to a high pressure flash chamber 90 wherein light hydrocarbon gases, hydrogen sulfide, hydrogen and a controlled portion of the relatively highly desulfurized saturates and aromatics are removed by means of line 92.
  • This interstage flash chamber 90 constitutes a critical feature of the present invention.
  • the sulfur becomes refractory to further desulfurization so that further desulfurization is accompanied by a loss in aromatics and a sharp increase in saturates. Both of these factors are detrimental in regard to removing further sulfur and overcoming the refractory nature of the oil at this point, since at the 75 percent sulfur-removal level most of the unremoved sulfur is concentrated in the resins and asphaltenes. Thus, a loss of aromatics deprives the viscous resins and asphaltenes of some solvation, while the formation of saturates imparts an excessive dispersion to the system tending to excessively dilute the remaining sulfur and thereby lower the reaction rate.
  • the aromatic content of the oil can be measured as it passes through the reactor, and the oil should be Withdrawn from the reactor when the aromatic content of the oil is no longer increased. This was the situation at 75 percent desulfurization in FIG. 3.
  • the aromatic content can increase 25 to 40 percent by Weight or more as it passes'through the reactor. Even a small increase in aromatics concentration is beneficial, e.g. 2 to 5 or 10 percent by weight. Of course, the aromatics concentration should not increase to such a great extent that it unduly dilutes the sulfur Wh'ich is to be removed.
  • a compromise must ,be reached wherein sufficient aromatics ⁇ are charged along with the feed to the second hydrodesulfurization stage so that the resins and asphaltenes are adequately solvated in order to permit proper desulfurization of the resins and asphaltenes, without the quantity of aromatics being so high that the total aromatics and saturates fed to the second stage will excessively dilute and disperse the sulfur to be removed and thereby reduce the reaction rate.
  • the volume 10 of aromatics and saturates, respectively, which may be removed at a given flash point is shown in FIG. 4.
  • an analysis of the saturate and aromatic content of the first sulfur removal stage eilluent is shown for various flash points when measured at atmospheric pressure.
  • the interstage flash point is 500 F.
  • all of the aromatics boiling above 500 F. will enter the second stage and will be available for solvating the resins and asphaltenes.
  • the stream comprises about 81 percent by volume saturates and about 19 percent by volume aromatics. This amount of aromatics together with the even greater amount of saturates which necessarily accompany it, might excessively dilute the asphaltic compounds and thereby lower the reaction rate.
  • the interstage flash point is as high as 800 F.
  • the oil fed to the second stage will have a higher ratio of aromatics to saturates which is desirable in order to accomplish high solvation with minimum diueunt.
  • the total amount of aromatics which enter the second stage may not be great enough to disolve the resins and asphaltenes and to sufliciently lower their viscosity to permit desulfurization. Accordingly, a proper balance of aromatics to saturates must be employed in order to obtain optimum desulfurization. This point may be easily experimentally determined for a particular stream undergoing desulfurization. For example, employing as a feed the residue represented by the overhead designated by the solid lines of FIG.
  • the dashed lines of FIG. 4 designate another possible overhead saturates and aromatics distribution in which aromatics begin to predominate in a 550 F. overhead fraction. However, since a 550 F. flash includes all the lighter material, the total overhead will still predominate in saturates over aromatics.
  • a predetermined amount of lliquid is flashed and removed by means of line 92.
  • the flashed material in line 92 may contain, for example, between about 5 and about 60 percent by Weight of the liquid eflluent from the desulfurization reactor 60, preferably between about l0 and about 3'5 percent by weight.
  • Suitable flash temperatures include, for example, between about 500 and about 800 F., preferably between about 600" and about 700 F. (These temperatures refer to atmospheric pressure and of course will be different at the process pressure).
  • An especially preferred flash point for the interstage flash is 650 F.
  • the most desirable amount of liquid to be flashed or otherwise separated from the desulfurization effluent stream may be easily determined experimentally.
  • the flashed material in line 92 is passed to a high pressure flash chamber unit 94 wherein hydrogen, hydrogen sulfide and light hydrocarbon gases are separated from a liquid hydrocarbon fraction.
  • the gases are withdrawn by means of line 96 and are'subjected to purification and separation, including various scrubbing operations and the like in recycle gas recovery unit 97. Subsequently, all of the hydrogen sulfide that it produced in reactor 60 is removed by means of line 93.
  • Hydrogen now free from hydrogen sulfide and light hydrocarbon gases is recovered from unit 97 and is passed by means of line 99 to recycle gas compressor 101 and recycled for utilization in the process by means of line 103.
  • the non-flashed liquid fraction is discharged from flash unit 94 by means of line 98.
  • the bottoms fraction from the ash unit 90 is discharged by means of line 100 and is admixed with makeup hydrogen, which is provided by means of line 102, valve 105 and line 107.
  • makeup hydrogen may be added to the make-up hydrogen in line 107 from line 103 by means of line 109, valve 115 and line 113.
  • make-up hydrogen may be passed from line 103 directly to line 108 by appropriate valving (not shown).
  • the combined stream may be charged to a furnace 106 in order to raise the temperature of this stream if desired.
  • furnace 106 is optional, as the stream 104 may be already at the desired desulfurization temperature for introduction by means of line 108 to the second hydrodesulfurization reactor 110.
  • the temperatures and pressures employed in reactor 110 may be the same as those described for the hydrodesulfurization reactor 60.
  • the desulfun'zation catalyst which is employed in reactor 110 may be identical to that described previously for reactor 60. It is noted at this point that the hydrodesulfurization catalyst is even more active for removal of nickel and vanadium than it is for removal of sulfur. Most of these metals will be removed in the rst hydrodesulfurization reactor 60. The heaviest laydown of such metals is at the inlet to reactor 60.
  • the second desulfurization reactor 110 will act as a metals clean-up stage, and the catalyst therein will not collect as much metals as does the catalyst in reactor 60. Hence, the lirst stage catalyst will remove most of the metals and will become deactivated by metals much faster than the second stage catalyst.
  • the desulfurized ellluent from reactor 110 is discharged by means of line 114 and is passed to a flash unit 116 for removal of light gases including hydrogen, hydrogen sulfide and light hydrocarbons.
  • This gaseous stream is sent by means of line 118 to high pressure flash unit 94.
  • a bottoms fraction including the asphaltic product stream of the present invention is passed by means of line 120 to a distillation column 122.
  • a sulfur containing stream comprising sour gas and sour water is removed from column 122 by means of line 124.
  • This stream is passed to a gas treatment plant (by a means not shown) to recover sulfur therefrom.
  • a naphtha fraction is withdrawn from the column 122 by means of line 132.
  • This naphtha stream may be employed as a wash liquid for the separation of the light hydrocarbons from the hydrogen in line 96 (by a means not shown).
  • a furnace oil or heavier fraction may be withdrawn through line 133 and be employed in a manner hereinafter described to provide additional aromatics to the second stage desulfurization reactor 110.
  • a product stream 134 is discharged from the distillation column 122.
  • This desulfurized oil stream contains asphaltenes and resins, and is especially useful, without further blending, as a fuel oil, particularly since less than one percent by weight sulfur is contained therein.
  • this heavy, asphaltic fuel oil contains, for example, between about 0.3 and about 0.5 percent by weight sulfur or less, which is well within the requirements of even the strictest ordinances for sulfur content of heavy fuel oils.
  • FIG. 6 is a simplified schematic diagram.
  • a reduced crude oil is introduced
  • the asphalt-containing bottoms fraction 226 is passed to a vacuum distillation unit 228 wherein additional light oil is discharged by means of line 230 and is admixed with the lighter fraction in line 224 and introduced along with hydrogen from line 233 into a hydrodesulfurization zone 232 by means of the line 234.
  • Zone 232 may be operated with a conventional gas oil desulfurization catalyst but at a lower temperature and hydrogen pressure (e.g., below 1000 p.s.i.) than are employed for the desulfurization of an asphaltic oil.
  • the asphalt-free distillate is easily completely desulfurized in the zone 232 and is discharged by means of line 236 and passed to distillation unit 238 from which an overhead fraction containing hydrogen, hydrogen sulfide and light gases is removed by line 240 and processed as previously described to recover hydrogen and light hydrocarbons.
  • An aromatic-rich, furnace oil and higher fraction is discharged from the distillation unit 238 by means of line 244.
  • an asphalt-containing oil is withdrawn from the vacuum distillation unit 228 by means of a line 246.
  • This stream may have, for example, an initial boiling point of about 1000 F. and contain about 5.5 percent by weight sulfur.
  • the stream 246 is passed through a blending zone 250 wherein the asphalt-containing stream is admixed with a controlled portion of the aromatic-rich fraction from the line 244 in order to 0btain the desired viscosity and solvency for the asphaltenes and resins contained in the stream.
  • hydrogen is added through line 248.
  • the heaviest product from distillation unit 242 can be blended with the product 268, if desired.
  • the asphaltic fraction containing solubilized resins and asphaltenes is passed by means of line 252 to a irst hydrodesulfurization zone 254 and subjected to desulfurization under the conditions previously described in regard to the reactor 60 of FIG. 1.
  • the eflluent from zone 254 has a reduced sulfur content and is passed by means of line 256 to an interstage ash unit 258 wherein hydrogen, hydrogen sulfide, light hydrocarbon gases, and a controlled portion of aromatics and saturates is discharged by means of line 260.
  • a ash point is selected so as to optimize the amount of aromatic solvent available for solubilizing the asphaltenes and resins in the feed to the second hydrodesulfurization zone.
  • An eluent stream 262 is discharged from the ash unit 258 and is admixed with hydrogen which is introduced by means of line 264.
  • the combined hydrogen-oil stream is passed to a second hydrodesulfurization unit 266 wherein the sulfur content of the asphaltic oil is reduced to below one percent by Weight.
  • the heavy oil product stream is discharged from the second hydrodesulfurization unit 266, which unit is operated in the manner described for unit 110 in FIG. l, and is withdrawn by means of the line 268 and treated as previously described for separation of hydrogen sulfide, light gases and the like.
  • the system of FIG. 6 provides a parallel mode of operation wherein an initially-separated lighter portion of the crude is desulfurized and is utilized to provide the desired viscosity and solvency for desulfurization of the heavy, asphaltic portion of the crude oil.
  • FIG. 7 Another modification of the FIG. 1 process is illustrated in FIG. 7.
  • an asphaltic oil is introduced by means of line 320 to a distillation unit 322 for separation into an aromatic-poor fraction on which is withdrawn from unit 322 by means of line 324 and an aromatic-rich fraction containing 4 percent sulfur.
  • An aromatic-rich asphaltic oil is discharged from unit 322 by means of a line 326.
  • distillation unit 322 may be operated to provide an asphaltic fraction having an initial boiling point of about 650 F.
  • the asphaltic stream in line 326 is admixed with hydrogenv which is introduced by means of line 328 and the combined stream is pased by means of line 330 into a 1 of 800 F.l is discharged means of the line 340.
  • the etlluent from zone 346 is removed by means of line 348 and is introduced into distillation unit 350 where an aromatic-rich fraction is separated and recovered by means of line 352.
  • a controlled portion of the material in stream 352 is recycled by means of line 342 for adrnixture with the asphaltic stream in line 340 as previously described.
  • the light gases are discharged from distillation unit 350 by means of line 354, while a substantially sulfur-free, asphaltic, heavy fuel oil is recovered from line 356.
  • Substantially all of the'asphaltenes and resins fed to distillation unit 350 are recovered in line 356 with the asphaltic fuel oil.
  • the recycle stream 342 is devoid of asphaltenes.
  • asphaltenes are not recycled to the rst hydrodesulfurization zone, since they would deactivate the catalyst prematurely. They are not recycled to the second hydrodesulfurization zone, since they have already been desulfurized, such recycle would serve no useful purpose.
  • FIG. 8 Still another modification of the present invention is shown in FIG. 8, wherein an sphaltic feed stream is introduced Iby means of a line 420 to a distillation unit 422 to reduce the feed and prepare a hydrodesulfurization feed for passage through line 426.
  • the asphaltic fraction is discharged by means of the line 426 from um't 422 and is admixed with a controlled portion of an aromatic-rich stream which is introduced by means of line 428.
  • the stream inline 428 can be an aromatic-rich fraction boiling within the range of between about 400 and about 1050 F., preferably between about 650 F. and about 900 F.
  • the combined stream is admixed with hydrogen, which is introduced by means of line 430, and a stream having a boiling point of about 650 R+ and containing about 4 percent by weight sulfur is introduced by means of line 432 into hydrodesulfurization zone 434.
  • This unit may be operated at a temperature of 690- 790 or 800 F.
  • An eluent stream having a sulfur content of about one percent by weight sulfur is introduced by means of line 436 into flash unit 438.
  • a light oil and gas fraction containing substantially all of the hydrogen sulde produced is flashed from the unit 438 and discharged by means of the line 440, which stream may have, for example, a 650 F. EP.
  • An asphaltic stream having a boiling point of, for example, 650 R+ is admixed with hydrogen which is introduced by means of line 442 and introduced by means of line 442 and introduced by means of line 444 into second hydrodesulfurization zone 446, which may be also operated at about 690 to 790 or 800 F.
  • the eiiiuent from the second desulfurization zone 446 has a sulfur content of less than one percent and is passed by means of line 448 to distillation unit 450.
  • An aromatics-rich fraction is withdrawn from unit 450 by means of line 452 and is recycled by means of line 428 for admixture to the asphaltic oil feedstock to the first desulfurization zone 434.
  • Hydrogen sulfide and light gases are withdrawn from the distillation unit 450 by means of line 454, While a low sulfur asphaltic fuel oil is recovered by means of line 456. Excess from stream 452vnot recycled can be from the flash unit 336 by blended with product in line 456 to reduce the sulfur content of the product.
  • FIG. 8 utilizes a low sulfur aromatic-rich product stream for solubilizing the asphaltenes and resins in a heavy desulfurization feedstock having a relatively high I.B.P.
  • FIG. 9 A modification of the system of FIG. 8 is shown in FIG. 9.
  • FIG. 8 The process of FIG. 8 is similar to FIG. 9, however, as shown in FIG. 9, the eiiiuent from flash unit 438 that is withdrawn by means of line 440 is passed to a flash unit which is provided with cooling coils. Hydrogen sulfide and light gases are removed in this lower temperature flash, which gases are withdrawn by means of line 443. The remaining heavier effluent is withdrawn from the flash unit 441 by means of the line 445 and is passed by means of pump 447 for admixture with stream 444 for introduction into the second stage desulfurization unit 446.
  • the mode of operation of FIG. 9 permits the employment of a iiash temperature for unit 438, which temperature may be the same as that employed in the hydrodesulfurization units 434 and 446.
  • the lower temperature flash unit 441 which is provided with cooling coils permits the separation of hydrogen sulfide and light gases and the reintroduction of a material having the optimum aromatics content and initial boiling int. poThus, for example, if it were determined that the optimum interstage ash temperature corresponded to 650 F. at atmospheric pressure and the desulfurization units 434 and 446 are being operated at about 700 F., the flash unit 438 may also be operated at 700 F. However, the lower temperature flash unit 441 is operated at 650 F. and thus permits the return by means of the 650 R+ material by means of line 449.
  • the modiiication of FIG. 9 avoids the need for reducing the temperature of the stream in line 436 and. the reheating of stream 444.
  • an asphaltic, sulfur-containing, hydrocarbon oil is introduced by means of line 520 to distillation unit 522 for separation of the feed into light gases, which are withdrawn by means of line 524, and an aromatic-rich fraction, which is discharged by line 526, which is to be employed in a manner hereinafter described.
  • This aromatic-rich fraction may have a 650 F. E.P.
  • An asphaltic bottoms fraction having an initial boiling point of, for example, about 650 F. is discharged by means of line 528 and is admixed with hydrogen from line 530 prior to introduction into iirst desulfurization zone 532.
  • the desulfurized eiiiuent from zone 538 is introduced by means of line 534 into flash unit 536.
  • the optimum flash point has been previously determined and a light oil fraction containing saturates and aromatics is ashed off along with light gases and hydrogen sulfide by means of line 538.
  • the asphaltic oil is passed from the flash unit 536 and mixed with hydrogen from line 540 and introduced by means of line 542 to the second stage desulfurization zone 546.
  • the asphaltic feed to the zone 546 is admixed with the aromatic-rich stream 526.
  • the distillation operation unit 522 is conducted under conditions so that the stream 52'6 has a selected boiling range and aromatics content which provides maximum solvation for the asphaltenes present in the feed to the second desulfurization zone 546.
  • the effluent from zone 546 is discharged by means of the line 548 and is passed t to distillation unit 550 for separation of the asphaltic 15 tion for the same total degree of desulfurization as a function of time. As illustrated in FIG.
  • Table I clearly illustrates the criticaldesulfurization constant is maintained above that 0f the ity of providing suicient aromatics 1n the asphaltic single stage process for each stage of the two-stage process. stream in order to solubilize the resins and asphaltenes
  • the average twoand to deagglomerate any asphaltene aggregates so as stage catalyst aging rate is about two units per day as to permit desulfurization thereof.
  • this Table compared with a single stage aging rate of about 3.5 shows the criticality of avoiding an excess of liquid inunits per day.
  • Catalyst aging is evidenced by the amount cluding aromatics, especially saturates, beyond what is of temperature increase required to produce a constant required to contribute a solubilizing effect, since such an desulfurization, as metals and code increasingly coat the excess of low-sulfur liquid will only tend to disperse and catalyst surface with time. dilute the sulfur-containing resins, resins and asphaltenes The following examples are presented to further illuS- and diminish their chance of contact with the catalyst. trate the invention.
  • the aromatic content of EXAMPLE 1 the feed to the second stage is richer in aromatics, i.e., 60.45 weight percent than is the feed to the rst stage, bAn pghaltcntammg reud rd 011 contalmmg i.e., 55.45 weight percent. This is due, in part to the 650 Ouctl Welghtererlu .ur .an y mgen ar.e.mtro ⁇ F. interstage flashing which removes saturates in much llc; 1 migo!
  • a lybo es unzaitlondfone ontammg a greater proportion relative to the aromatics present in mc'lfco alt'mpy enum (,a 5Std lposf fmt? non' the flashed, light oil stream.
  • the weight cra?. mg. aunm iuppotrt e t y ro fes) ulzsboizo; ratio of aromatics to resins plus asphaltenes to accomga 10g 1s geg uc e atfenpera res lf) 230311 d plish solvation should be at least 1 to 1 and is preferably th' an t.
  • y roglnlar la tpesllreo h d tp's'tlg an 1.5 or 2 to l, and can be 4 or 5 to 1.
  • the aromatics can e res mg as? a c maoena 1S as e a a empera' be present in the feed, can be introduced by recycle or ture corresponding to 650 F.
  • the distribution of sulfur in each of the various fractions of the oil undergoing 40 A 22 percent reduced Kuwait crude containing an desulfurization is set forth in Table I, below: asphalt fraction and 5.43 percent by weight sulfur is TABLE I Feed to first HDS Feed to second HDS zone zone Fuel oil product Sulfur in Sulfur in Sulfur in Fraction fraction Fraction fraction Fraction fraction (percent (percent (percent (percent (percent (percent (percent (percent (percent (percent (percent (percent (percent (percent (percent (percent (percent (percent (percent (percent (percent (percent (percent (percent (percent (percent (percent (percent (percent (percent (percent (percent (percent (percent (percent (percent (percent (percent (percent (percent (percent (percent (percent (percent (percent (percent (
  • Sulfur, percent by wt Boiling range, F Desulfimzation, percent API I.B.P. is 514 and the boiling range extends to 1400 As desulfurization continues, and the sulfur content is reduced to 1.41, the I.B.P. is 509 with the boiling range extending to 1400 R+. However, when the sulfur content is reduced to 0.83, the I.B.P. drops F. to 466 F. with the boiling range extending to 1400 R+.
  • hydrocrackng begins to predominate over hydrodesulfurization, i.e., carbon-carbon bonds are becoming severed, rather than carbon-sulfur bonds, beyond 74 percent sulfur removal.
  • Feedstock percent bg Composition change durln wt. desnlfurization (percent by wt.
  • EXAMPLE 4 In order to determine the effect of adequate, as contrasted to excessive solubilization of an asphalt-containing feed, a residual, high-boiling feed having au initial boiling point of about 800 F. is charged to a hydrodesulfurization process, and 76.2 percent by weight desulfurization is accomplished. Next, a second sample of the feed is diluted with 30 volume percent of a lower boiling gas oil which had been previously desulfurized to the extent of to 95 percent by weight. The addition of the gas oil, which comprises a high proportion of aromatics, increases the desnlfurization to 80.3 percent by weight.
  • EXAMPLE 5 A test is performed utilizing in the iirst and second stages a one-thirty-second inch nickel-cobalt-molybdenum on alumina catalyst.
  • the catalyst In the iirst stage the catalyst exhibits a six month life with a start-of-run temperature of 690 F. and an end-of-run temperature of about 790 F. in hydrodesulfurizing a Kuwait reduced crude from 4 to 1 weight percent sulfur at a LHSV of about 0.8.
  • the catalyst life in the second stage is even longer.
  • the one weight percent sulfur etlluent from the iirst stage is flashed to remove 650 F.
  • the first and second stages of this invention can operate for 3, 4, 5, 6 or even 7, 8 or l2 months at a LHSV generally ranging between 0.1 and 10 or preferably between 0.3 and 1.25.
  • the life of the second stage catalyst is longer than the life of the first stage catalyst.
  • a process for the hydrodesulfurization at a hydrogen partial pressure between 1,000 and 5,000 p.s.i. in a twozone reaction of a heavy asphaltic feed oil to produce a heavy asphaltic fuel oil product containing propaneand pentane-insoluble asphaltenes and propane-insoluble resins but pentane-soluble resins comprising passing a sulfur-containing asphaltic hydrocarbon oil feed downfiow with hydrogen through a first zone containing at least one bed of hydrodesulfurization catalyst particles y2() to 1/40 inch in diameter at a temperature between 680 and 800 F., the temperature being increased during the reaction to compensate for loss of hydrodesulfurization reaction rate due to catalyst aging, said catalyst particles comprising a Group VI and a Group VIII metal on alumina containing less than one percent silica, withdrawing a first effluent stream from said first hydrodesulfurization zone having a reduced sulfur content, said first eliiuent stream comprising a light gas fraction including hydrogen sulfide, a light oil fraction
  • said second Zone catalyst comprising a Group VI and a Group VIII metal on alumina containing less than one percent silica, operating the catalyst in said first and second zones for at least three months at a liquid hourly space velocity between 0.1 and 10, maintaining the average hydrogen partial pressure in each of said zones sufficiently high that the average hydrodesulfur-ization reaction rate constant is improved by said two zones of operation and accomplishing a degree of desulfurization with less catalyst as compared with a single zone of operation accomplishing the same degree of desulfurization, withdrawing a second efiiuent stream from said second hydrodesulfur-ization zone comprising
  • resins and asphaltenes comprise 5 to 30 percent or more of the feed.
  • liquid hourly space velocity is between 0.3 and 1.25.

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Cited By (4)

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US3893909A (en) * 1971-12-27 1975-07-08 Universal Oil Prod Co Fuel oil production by blending hydrodesulfurized vacuum gas oil and hydrodesulfurized deasphalted residuum
US4565620A (en) * 1984-05-25 1986-01-21 Phillips Petroleum Company Crude oil refining
US4713221A (en) * 1984-05-25 1987-12-15 Phillips Petroleum Company Crude oil refining apparatus
US5968347A (en) * 1994-11-25 1999-10-19 Kvaerner Process Technology Limited Multi-step hydrodesulfurization process

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US3775304A (en) * 1971-12-08 1973-11-27 Gulf Research Development Co Increasing the ratio of aromatics to saturates in hydrodesulfurization of heavy asphaltic feed oil

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US3429801A (en) * 1965-12-06 1969-02-25 Universal Oil Prod Co Two-stage hydrorefining of asphaltene-containing oils
US3409538A (en) * 1967-04-24 1968-11-05 Universal Oil Prod Co Multiple-stage cascade conversion of black oil
US4165064A (en) * 1978-03-13 1979-08-21 Fip, S.A. De C.V. Gate valve
JPS5547077A (en) * 1978-09-01 1980-04-02 Ippei Tamai Water feeding apparatus in use of float formed with aperture

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Publication number Priority date Publication date Assignee Title
US3893909A (en) * 1971-12-27 1975-07-08 Universal Oil Prod Co Fuel oil production by blending hydrodesulfurized vacuum gas oil and hydrodesulfurized deasphalted residuum
US4565620A (en) * 1984-05-25 1986-01-21 Phillips Petroleum Company Crude oil refining
US4713221A (en) * 1984-05-25 1987-12-15 Phillips Petroleum Company Crude oil refining apparatus
US5968347A (en) * 1994-11-25 1999-10-19 Kvaerner Process Technology Limited Multi-step hydrodesulfurization process

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