US3464915A - Desulfurization and blending of heavy fuel oil - Google Patents

Description

Sept. 2, 1969 N. J. PATERSON ET Al. 39,464,915

DESULFURIZATION ANI) BLENDING OF HEAYY FUEL OIL Filed March lO, 1967 NORMA/V J, PATE/QSON RONALD R. ROSEL/US Low SULFUR CRUDE /l ATTORNES Unted States Patient 3,464,915 DESULFURIZATION AND BLENDING OF HEAVY FUEL OIL Norman J. Paterson, San Rafael, and Ronald R. Roselius, Point Richmond, Calif., assignors to Chevron Research Company, San Francisco, Calif., a corporation of Delaware Filed Mar. 10, 1967, Ser. No. 622,289 Int. Cl. C10g 31/14 U.S. Cl. 208-218 3 Claims ABSTRACT F THE DISCLOSURE BACKGROUND OF THE INVENTION This invention relates to catalytic hydroconversion processes for purifying hydrocarbon oils, and more particularly it is concerned with catalytic hydrosulfurization of heavy oils to product low sulfur content fuel oil.

Due to its predominant position in the expanding energy market, fuel oil, particularly residual-type fuels having viscosities of 5-10 centistokes and higher, has come under close scrutiny by air pollution agencies throughout the World where this commodity serves as an important energy source. Sulfur limitations have been proposed, and adopted in some areas, generally limiting the sulfur content of fuel oils burned in large quantities to about 2 weight percent or less. The supply of crude petroleum from which residual fuel oil meeting these requirements is recoverable directly is limited, and these crudes command a high price. High sulfui content crude oils, i.e. oils in which the residual components boiling above about 650 F. have sulfur contents in excess of 2 weight percent, are more abundantly available and at a lower price.

Accordingly, various approaches have been studied by reners to desulfurize such high sulfur content residua. Desulfurization of the entire petroleum residue boiling above 650 F. becomes expensive and diiiicult to accomplish, particularly where the residua contain substantial amounts of metallic compound contaminants. It has been proposed to separate the residuum into nonasphaltic gas oil such as vacuum gas oil or solvent deasphalted oil, and a heavy asphaltic bottoms, desulfurize the gas oil, and blend the desulfurized gas oil back with the heavy asphaltic bottoms or a portion thereof. Obviously, the blend of desulfurized vacuum or deasphalted gas oil with the sulfur-containing asphaltic bottoms will have an intermediate sulfur content determined by the relative proportions used.

Unfortunately, certain other properties of a fuel oil blend are not so predictable. Pour point, in particular, cannot be calculated based on the pour points of the constituents to be blended. For example, it is well known that when atmospheric residuum is distilled under vacuum, the vacuum gas oil and the vacuum residuum may both have higher points than the original atmospheric residuum. If

3,464,915 Patented Sept. 2, 1969 'ice the vacuum gas oil and vacuum residuum are recombined, the original lower pour point is reestablished. On the other hand, however, when low sulfur content heavy fuel oil is produced from high sulfur content petroleum atmospheric residua by separating the high sulfur petroleum residue boiling above about 650 F. into an asphaltic vacuum residuum fraction and a nonasphaltic vacuum gas oil fraction, subjecting the vacuum gas oil fraction to a catalytic hydrodesulfurization treatment, and blending the desulfurized gas oil fraction boiling -above about 650 F. with the asphaltic residuum fraction to form low sulfur content heavy fuel oil, the resulting blended fuel oil often has a higher pour point than the original petroleum residue had. Spectifically, in a previously-reported operation wherein vacuum gas oil from atmospheric residuum was hydrodesulfurized 90 percent using cobalt-molybdate catalyst, net hydrocracking to below 650 F. was reported as 20 percent, and on reblending of the desulfurized 650-| F. gas oil with only 40 percent of the vacuum residuum a pour point of F was reported whereas the original atmospheric residuum had a lower pour point of -|65 F. (See U.S. Patent No. 3,155,607). In most cases, to obtain -acceptable pour point in the blend, light distillate fuels of greater value must also be blended into the lower value heavy fuel oil. This often results in too great a lowering of the fuel oil viscosity. Also, the yield of the 650+ F. desulfurized nonasphaltic fraction is sometimes lowered by the desulfurization to the extent that not all of the asphaltic fraction can be blended therewith because of incompatibility and/or too high a sulfur content resulting. The excess asphaltic fraction then has to be disposed of in some other way, which, in view of the restrictions on burning of high sulfur content materials, becomes particularly troublesome.

SUMMARY OF THE INVENTION It has now been found that low sulfur content heavy fuel oil of acceptable pour point and Viscosity can be formed directly by blending the desulfurized nonasphaltic fraction with the asphaltic fraction, if the desulfurization of the nonasphaltic fraction is carried out in admixture with light distillate boiling at least partly in the kerosene boiling range, between about 300 F. and 700 F., separating light distillate boiling below about 700 F. from desulfurized nonasphaltic fraction boiling above about 650 F. in the desulfurized admixture, and blending the thus desulfurized nonasphaltic fraction with the asphaltic fraction.

The previously-noted adverse effect of desulfurization on blended fuel oil pour point is theorized to result from hydrocracking, during the desulfurization, of components in the nonasphaltic fraction which were pour point depressants or were needed for blending compatibility with the asphaltic fraction. The presence of the light distillate in the present invention appears to have a synergistic effect in enhancing the desulfurization and inhibiting hydrocracking of the heavier nonasphaltic fraction. The blending compatibility of the nonasphaltic fraction with the asphaltic fraction is thereby preserved, yield is improved, and the blend of the desulfurized nonasphaltic fraction with the asphaltic fraction has improved pour point and viscosity characteristics.

At the same time, the light distillate, if sulfur-bearing, is also desulfurized with practically no increase in processing cost. Desirably the light distillate comprises hydrocarbons boiling in the kerosene and light diesel fuel boiling ranges. Thus, separate hydroning units which might otherwise have to be provided for hydrogenating the kerosene and for hydrofinishing the diesel fuel can be dispensed with. As mentioned, the distillate is present in an amount effective to substantially inhibit hydrocracking of the nonasphaltic fraction during the hydrodesulfurization, and it appears that this effect can be achieved over a broad range of compositions wherein the distillate may comprise from to 90 volume percent of the admixture subjected to desulfurization.

Superior results are achieved by employing in the hydrodesulfurization as the effective catalytic agent an aluminasilica composite carrier, having an A1203/ SOZ weight ratio of from 3 to 5, promoted with molybdenum and a Group VIII metal, preferably nickel, or their oxides 0r sulfides. When this type of catalyst is employed in the process, a relatively low hydrogen partial pressure can be used in hydrodesulfurization, below about 1500 p.s.i.a. and frequently below about 1000 p.s.i.a., for a long time without catalyst regeneration. Also, temperatures above 700 F. can be used for rapid conversion of organic sulfur compounds to HZS without excessive hydrocracking of the heavy oil.

It is not essential, or even desirable, that the hydrodesulfurization of the nonasphaltic fraction lower its pour point by any measurable amount to achieve the benefits of the present invention. The hydrogen treating conditions needed to achieve substantial pour point lowering of the heavy non-asphaltic fraction are generally so severe as to result in an undesirable amount of 'hydrocracking oc curring. Also, when the pour point of the nonasphaltic fraction is lowered by severe hydrogen treating causing hydrocracking, the lower pour point is often not reected in the fuel oil blend with the asphaltic fraction. As previously point out, the pour point of a mixture is not a property which can be readily predicted on the basis of the corresponding properties of the constitutents of the mixture.

In the present invention, hydrocracking is limited so that desirably no more than about l0 percent of the heavy nonasphaltic fraction boiling above 650 F. is converted to distillates boiling below 650 F. in the hydrodesulfurization in admixture with a light fraction.

BRIEF DESCRIPTION OF THE DRAWING In the attached drawing the single ligure is a schematic ow diagram showing flow paths and treating sequences usable in one embodiment of the invention wherein a low sulfur content crude and a high sulfur content crude are separately distilled, a vacuum gas oil from the high sulfur content crude is desulfurized in admixture with kerosene and diesel boiling range distillates, desulfurized kerosene and diesel fuel are separated from the desulfurized admixture, and a low sulfur content heavy fuel oil is formed by combining the desulfurized vacuum gas oil with the high sulfur content vacuum bottoms and with the lmoderately low sulfur content atmospheric residue of the low sulfur crude oil. Further reference to the drawing will be made hereafter.

DETAILED DESCRIPTION AND DESCRIPTION OF PREFERRED EMBODIMENTS The starting material or feedstock treated in accordance with the present invention is a high sulfur content residuum of petroleum or like hydrocarbonaceous material, boiling essentially entirely above about 650 F. In general, the residuum will be at least as heavy as the undistilled material remaining after atmospheric distillation 0f crude petroleum, and will include the asphaltic components and any metalliferous contaminants. The sulfur concentration in this residuum will be above 2 weight percent and generally at least 3 weight percent or higher.

The heavy fuel oil to ybe produced from this starting material will contain a major portion of components boiling in this residuum range, i.e. substantially entirely above about 650o F. The fuel oils are classied under various grades, generally in terms 0f a specified viscosity range and maximum pour point. For example, bunker fuel oils may have viscosities in the neighborhood of 260 centistokes at 122 F. or the equivalent in Engler degrees, Redwood seconds, etc., and are kept in a hot condition to maintain fluidity. Lighter grades of fuel oil may have viscosities in the range 70-200 centistokes at 122 F., but will still contain the highest boiling portions of the petroleum from which produced. For the lighter grades of fuel oil an upper pour point of about F. may be specified, or a requirement of a uidity at +32o F. A maximum sulfur content may be specified to apply to al the grades of fuel oil, and will dep-end on the local situation. For purposes of the present invention, the low sulfur content to be achieved in the heavy fuel oil product is in the neighborhood of 2 weight percent or lower.

In accordance with the invention the high sulfur content petroleum residuum is first separated into an asphaltic fraction comprising the highest boiling materials therein, and a nonasphaltic fraction substantially free of asphaltenes and metal contaminants. The separation may be accomplished lby distillation of the residua boiling above 650 F. under vacuum to obtain a heavy vacuum gas oil as the nonasphaltic fraction and a vacuum residuum as the asphaltic fraction. Equivalent means such as pitch stripping or combined visbreaking and pitch stripping may be used in place of or in addition to vacuum distillation. Similarly, the residuum starting material or the asphaltic vacuum residuum may be subjected to solvent deasphalting to obtain an additional portion of nonasphaltic fraction. The nonasphaltic fraction thus will boil substantially entirely above about 650 F., though there may be a small amount of overlapping materials boiling below 650 F. present therein due to the vagaries of conventional distillation procedures.

The nonasphaltic fraction is subjected to catalytic hydrodesulfurization in admixture with light distillate boiling at least partly in the kerosene boiling range. Various techniques for carrying out the catalytic hydrodesulfurization are feasible, all involving contacting the oil with free hydrogen While in contact with a sulfactive hydrogenation catalyst in a reaction zone, at hydrodesulfurization reaction conditions. 'This may be done using -uidized catalyst particles, slurried catalyst particles, or fixed beds of catalyst particles; flowing the oil and hydrogen concurrently upwards or downwards or countercurrently through the reaction zone containing the catalyst. Most conveniently, the oil and hydrogen are passed concurrently downwards through one or more xed beds of catalyst particles at a pressure in the range ZOO-4000 p.s.i.g., temperature in the range G-900 F., with flow rate of oil relative to catalyst of 0.2-20 LHSV, and using hydrogen-rich gas to oil ratios of from 1000 to 20,000 s.c.f. per barrel. The oil and gas mixture efuent of the reaction zone is cooled to condense the normally liquid oil therein and separate hydrogen-rich gas for recycling through the reaction zone with makeup hydrogen of relatively higher purity. The separated liquid oil may then be distilled and/or stripped to remove dissolved light hydrocarbons and to separate middle distillate and lower boiling fractions from the material boiling in the heavy fuel oil range, i.e. above about 650 F.

The catalyst employed in the hydrosulfurization is a sulfactive hydrogenation catalyst comprising a Group VI metal and a Group VIII metal, or compounds thereof such as the oxides or suldes, associated with a porous inorganic oxide carrier. As mentioned, superior results are obtained employing as the effective catalytic agent an alumina-silica composite carrier, having an alumina to silica ratio of from 3 to 5, promoted with molybdenum as the Group VI metal and nickel as the Group VIII metal. With this type of catalyst more preferred operating conditions in the range 500-2000 p.s.i.g., frequently 500-1000 p.s.i.g., and temperatures of 650-850 F., frequently 700-800 F., can be used with high space velocities of 1-10 LHSV based von the gross oil feed to the reactor. The catalysts have superior desulfurization activity coupled with only moderate hydrocracking activity and are highly resistant to deactivation or activity loss at low hydrogen partial pressures and moderately elevated temperatures. Catalysts employing tungsten rather than molybdenum as the Group VI metal component tend to have higher hydrocracking activity than desired as do those catalysts containing too much silica, i.e. with an A1203/ SiOz weight ratio below 3. Catalysts containing too little silica, i.e. with an Al2O3/Si02 weight ratio above 5, tend to have lower activity or to lose activity during use more rapidly than the preferred catalysts, which is also the case with catalysts containing too little nickel and molybdenum. Desirably these metal components make up from 15-50 weight percent of the catalyst when calculated as present in the oxide forms. Methods for preparing suitable catalysts are numerous and well known.

The light distillate, which is combined with the nonasphaltic fraction fed to the hydrodesulfurization, boils between about 300 F. and about 700 F, and includes material boiling at least partly in the kerosene boiling range. The kerosene boiling range extends from below about 325 F. to above about 550 F., and thus overlaps at the lower boiling end with heavy naphtha fractions and at the upper boiling end with light diesel boiling range fractions. The diesel boiling range is from below about 450 F. to above about 650 F., and thus will overlap at the low end with the kerosene boiling range and at the upper end with the vacuum gas oils. Generally, the light distillate mixed with the heavier nonasphaltic fraction for desulfurization will always boil over a range of at least about 50 F. and will include some material boiling between 400 F. and 500 F. Advantageously, the light distillate is a sulfur-bearing distillate needing hydrodesulfurization.

The added sulfur-bearing distillate may amount to from to 90 percent of the total feed to the hydrodesulfurization, the nonasphaltic fraction boiling above about 650 F. making up the remainder. More usually, the heavy nonasphaltic fraction will make up more than 30 percent of the mixture, and the amount of added distillate need be only suiiicient to have a substantial inhibiting effect on hydrocracking of the nonasphaltic fraction which would otherwise occur during hydrodesulfurization. It appears that the minimum amount of light distillate needed is about 10 volume percent of the gross feed.

The desulfurized oil mixture leaving the hydrodesulfurization zone, after separating off hydrogen-rich recycle gas, is treated as by distillation and/or stripping to separate the desulfurized distillates boiling below 700 F. from the desulfurized heavier nonasphaltic fraction boiling above about 650 F. As indicated, the end boiling point of the light distillate'fraction or fractions may overlap the initial boiling point of the heavier nonasphaltic fraction due to the imprecise nature of distillation techniques. When the thus-desulfurized nonasphaltic fraction is combined by blending with the asphaltic fraction, which had not been subjected to catalytic desulfurization, the blended heavy fuel oil thereby formed is characterized by an improved pour point relative to the blend which is formed when the nonasphaltic fraction is desulfurized in the absence of the added distillate fraction.

It is contemplated, and one advantage of the present invention resides therein, thatall of the asphaltic fraction can be utilized in forming heavy fuel oil if desired, by mixing with the desulfurized nonasphaltic fraction and other low sulfur content fractions suitable for use in fuel oil. In some cases there may be other uses for a portion of the asphaltic fraction such as in asphalt manufacture. Thus, one advantage of the invention is that it enables disposing of in heavy fuel oil, if necessary, all of the high sulfur content asphaltic fraction, which becomes possible because of the improved pour point and desirable viscosity adjusting techniques usable when a substantial portion of the blended fuel oil is made up of the nonasphaltic fraction desulfurized in accordance with the teachings herein.

It is customary, as is Iwell known to those skilled in the art, to adjust the viscosity and/or pour point of heavy fuel oils into the ranges needed to satisfy the specifications for the various particular grades, by blending in various cutter stocks, generally middle distillate fractions boiling in the range above about 350 F. Since these materials generally represent salable light distillate fuels of greater value than the heavy fuel oil, it is advantageous to minimize the amount of viscosity and pour point adjusting cutter used for this purpose. Frequently, moreover, difficulties are encountered in that in attempting to lower the pour point of heavy fuel oil to meet the specications for a particular grade, so much distillate cutter must be added that the viscosity of the fuel oil iS lowered excessively. By avoiding hydrocracking of the nonasphaltic fraction boiling above 650 F., in the desulfurization, the desirable viscosity and pour point enhancing characteristics are preserved such that less cutter stock is needed to obtain the desired pour point, and the viscosity is not unduly lowered.

It will further be recognized that the ultimate fuel oil product may contain any other heavy oil fractions meeting the sulfur specification and compatible for blending therein to arrive at desired viscosity and pour point. It will further be recognized, that where blending is contemplated with low sulfur content, high pour point, residua derived from crude oils not requiring desulfudization, the use therein of fuel oil prepared in accordance with the present invention can become particularly important in permitting the use of higher pour point cutter stocks ywithout exceeding the pour point specified for the blend and while still maintaining the desired viscosity characteristics.

The sulfur-bearing distillate fraction, boiling in the range between 300 F. and 700 F. may represent the atmospheric gas oil middle distillates derived from the original high sulfur content oil in the atmospheric distillation thereof to obtain the petroleum residue boiling above 650 F. In a special case, the present invention involves separating from a high sulfur content original crude petroleum, by two-stage distillation, those materials which boil below the kerosene boiling range as the overhead fraction from atmospheric distillation, and those materials boiling above the heavy vacuum gas oil boiling range as the bottoms from vacuum distillation of the atmospheric distillation bottoms. The remaining material, comprising the atmospheric gas oil and the vacuum gas oil, boiling over a range from below about 400 F. to above about 1000 F., is subjected to the catalytic hydrodesulfurization treatment in admixture to form a broad boiling range desulfurized oil. The broad boiling range desulfurized oil is then separated into one or more low sulfur content middle distillate fractions boiling below 700 F. and a low sulfur content heavy gas oil fraction boiling above 650 F. The desulfurized heavy gas oil fraction is blended with the materials boiling above the heavy vacuum gas oil boiling range to form the desired heavy fuel oil of acceptable sulfur content for burning. A p0rtion of the low sulfur content middle distillate fraction may be utilized as cutter stock in the heavy fuel oil, if cutter stock is needed.

Referring now to the attached drawing, by way of i1- lustration, a high sulfur content crude oil feed containing about 3 weight percent sulfur is passed via line 11 to atmospheric distillation facilities 12 from which there is shown being withdrawn a light gaseous overhead stream comprising butane and lighter hydrocarbons in line 13, a naphtha fraction comprising C5 and heavier hydrocarbons boiling up to about 350 F. in line 14, and a middle distillate atmospheric gas oil fraction in line 15, boiling from about 350 F. to 650 F. The atmospheric residuum or reduced crude bottoms, boiling substantially entirely above about 650 F., is withdrawn from atmospheric distillation facilities 12 through line 16 and passed to vacuum distillation facilities 17. In the vacuum distillation facilities the atmospheric reduced crude is separated into heavy vacuum gas oil boiling from about 650 F. to about 1000 F. or higher, in line 18, and vacuum reduced crude referred to herein as vacuum residuum, boiling substantially entirely above about 1000 F., in line 19. The vacuum gas oil of line 18 is a nonasphaltic fraction in that the asphaltic constituents of the crude are concentrated in the vacuum residuum of line 19, which is accordingly an asphaltic fraction.

The middle distillate of line 15 and the vacuum gas oil of line 18 in the illustrated embodiment are combined and passed via lines 20 and 21 to hydrodesulfurization reaction zone 22. Additional fractions may be combined with the middle distillate and vacuum gas oil fractions, such as vacuum gas oil from distillation of another high sulfur content crude, or a kerosene boiling range fraction shown as added via line 23, a diesel fuel boiling range shown as added via line 45, or other middle distillate fractions. The combined hydrocarbon fractions, hydrogen-rich recycle gas of line 24, and makeup hydrogen of line are passed preheated and at elevated pressure to the hydrodesulfurization reaction zone 22 wherein they pass through fixed beds of sulfactive hydrogenation catalyst particles comprising nickel and molybdenum impregnated on an alumina-silica carrier comprising about 75 percent alumina and about 25 percent silica. .At typical hydrodesulfurization reaction conditions as previously described, for example 700-750 F., SOO-1500 p.s.i.g., 1-5 LHSV, and 2000-10,000 s.c.f. hydrogen-rich gas per barrel of oil, the combined hydrocarbon oil fractions are nearly completely desulfurized by conversion of the 0rganic sulfur compounds therein to HZS.

The hot mixture of oil and hydrogen-rich gas effluent of the reaction zone in line 26 is cooled to a temperature in the range 70-200 F. and passed to separator 27, from which the hydrogen-rich recycle gas of line 24 is withdrawn, and the normally liquid hydrogen oil, containing some dissolved light gases, is withdrawn via line 28. The oil passes Via line 28 to atmospheric distillation facilities shown as zone 29 from which there is withdrawn overhead a light gaseous fraction comprising butane and lighter hydrocarbons and the HZS formed, in line 30, a light naphtha fraction in line 31, a kerosene boiling range fraction in line 32, and a diesel fuel boiling range fraction in line 33. The bottoms from distillation facilities 29 withdrawn via line 34 boils substantially entirely above 650 F., corresponding closely in boiling range to the vacuum gas oil of line 18.

The desulfurized 650 F.-{ nonasphaltic fraction of line 34 is combined with the asphaltic Vacuum residuum of line 19 to form a fuel oil of acceptably low sulfur content for burning, in tank 35. In addition there will generally be blended into the low sulfur content fuel oil other crude residua of acceptable sulfur content and also cutter stocks where needed to adjust the viscosity and/or pour point to meet the specifications of a particular desired fuel oil grade. As illustrated in the drawing, representing a preferred combined embodiment of the invention, this is done by distilling a low sulfur content crude oil, comprising a Far Eastern crude such as Sumatran, a North African crude such as Libyan, or a West African crude such as Nigerian, in line 36 in atmospheric distillation facilities shown as zone 37. Similarly as in the case of atmospheric distillation of the high sulfur content crude oil in zone 12, there is withdrawn from zone 37 a light gaseous overhead fraction in line 38, a light naphtha fraction in line 39, a kerosene boiling range fraction in line 40, and a diesel fuel boiling range fraction in line 41. As indicated, the naphtha fraction of line 39 may be combined with the naphtha fractions of lines 14 and 31 to form a single low sulfur content naphtha fraction in line 42. Similarly, all or a portion of the kerosene fraction of line 40 may be combined with all or a portion of the kerosene fraction of line 32 to form a low sulfur content kerosene product in line 43; and all or a portion of the diesel fraction in line 41 may be combined with all or a portion of the diesel fraction in line 33 to form a low sulfur content diesel product in line 44. As further indicated, all or a portion of the kerosene fraction of line 40 and all or a portion of the diesel fraction of line 41 may pass respectively via lines 23 and 45 to the hydrodesulfurization reactor 22, said fractions then serving as all or a portion of the required distillate boiling between 300 and 700 F. for er1- hancing desulfurization and inhibiting hydrocracking of the vacuum gas oil fraction in the desulfurization.

More commonly, portions of the kerosene fraction in line 43 and the diesel fuel fraction in line 44 are passed Via line 49 for blending with the high sulfur content low sulfur content heavy fuel oil. As further indicated, the atmospheric residuum from distillation of the low sulfur content crude oil is withdrawn from Zone 37 and passed via line 49 for blending with the high sulfur content vacuum residuum of line 19 and the low sulfur content desulfurized vacuum gas oil of line 34 to form with the cutter stocks of line 48 the low sulfur content heavy fuel oil of tank 35.

The following example compares the fuel oil yield and quality obtainable by (a) the prior art method of blending atmospheric residua with a viscosity and pour point reducing cutter stock, (b) the prior art method of hydrodesulfurizing vacuum gas oil and blending the desulfurized gas oil with residua and cutter, and (c) an embodiment of the present invention wherein vacuum gas oil is hydrodesulfurized in admixture with a middle distillate fraction, and the desulfurized vacuum gas oil is blended with residua and cutter.

Example 1 In a particular case, in a fuel oil consuming market area, there were available 33 volumes of low sulfur content crude oil and 110 volumes of high sulfur content crude oil, from which it was desired to recover the naphtha and middle distillate fractions and to form heavy fuel oil from the high boiling remainder.

(a) By atmospheric distillation of the mixed crudes there are obtained 82 volumes of 650-}- F. atmospheric residua, 26 volumes of naphtha and lighter material boiling below 350 F., and 35 volumes of middle distillate boiling from 350 to 650 F. The 650| F. atmospheric residua has too high a viscosity and pour point for use directly as fuel oil. volumes of fuel oil having a viscosity of 75 centistokes at 122 F. and a pour point of +60 F. are obtainable by blending the 82 volumes of 650-l- F. residua with 18 volumes of the 350-650 F. middle distillate as cutter. The sulfur content of the fuel oil blend is undesirably high, above 3 weight percent.

(b) When the crude oils were separately distilled at atmospheric pressure and the atmospheric residuum of the high sulfur content crude oil was subjected to vacuum distillation, there were obtained 28 volumes of 650-1000 F. vacuum gas oil. When, in accordance with the prior art, this vacuum gas oil was subjected to catalytic hydrodesulfurization, and the desulfurized 650+ F. vacuum gas oil was blended back with the low sulfur content atmospheric residuum and the high sulfur content vacuum residuum, only about 76 volumes of 650 F. fuel oil were formed. No more than 18 volumes of 350-650 F. middle distillate cutter stock could be blended in to obtain a viscosity of 75 centistokes in a total of only 94 volumes of fuel oil. The sulfur concentration in the fuel oil blend was satisfactory, but the pour point of the blend was higher, +75 F.

(c) In accordance with an embodiment of the present invention, the crudes were separately distilled at atmospheric pressure and the atmospheric residuum of the high sulfur crude was distilled under vacuum. The 28 volumes of 650-1000 F. vacuum gas oil were subjected to catalytic hydrodesulfurization in admixture with 26 volumes of the S50-650 F. middle distillate. After separating materials boiling below 650 F. (28 volumes) from the hydrodesulfurized admixture, there remained 26 volumes of 650-l000 F. desulfurized vacuum gas oil for blending with the low sulfur content atmospheric residuum and the high sulfur content vacuum residuum, giving 80 volumes of 650+ F. fuel oil. To this could be added 19.5 volumes of the BSO-650 F. middle distillate cutter stock to obtain the desired viscosity of 75 centistokes at 122 F., and the 99.5 volumes of fuel oil thus formed had a pour point of only +60 F. and a satisfactory low sulfur content as well. In addition, there are separately recovered 27 volumes of naphtha and lighter materials boiling below 350 F. and 17.7 volumes of S50-650 F. middle distillate, and the middle distillate thas a lower sulfur content as compared to case (a). The foregoing data are summarized in the following Table I.

TABLE I Sulfur, Vols in Blend- Gravity, Wt. per- API cent (a) (b) (c) Low sulfur atmospheric resid. 27. 0. 1 20 19 20 High sulfur atmospheric resid.... 11. 5 4. 5 62 High sulfur vacuum resid 5. 2 5. 6 34 34 Desulfurized vacuum gas oil. 26-27. 5 0.4 23. 5 26 Cutter Stock 37. 5 0. 1 18 17. 5 19. 5

Total 100 94. 0 99. 5 Blend:

Viscosity, c.s. at 122 F 75 75 75 Pour point, F +60 +75 +60 Sulfur, wt. percent.. 3.0 2. 4 2. 3 Gravity, API 18.9 20.1 20.4

Pour point depressing additives commonly added to middle distillate fractions have not been effective in heavy fuel oils, but these as well as other additives may advantageously be incorporated in the fuel oil prepared in accordance with the present invention. Improved response to pour depressants of the type comprising alkenyl succinamic acids and long chain polymers such as ethylenepropylene copolymers, but especially mixtures of such acids and copolymers, is manifested in fuel oil comprising a blend of heavy gas oil boiling from 350 F. to 1000 F., i.e. vacuum gas oil desulfurized in the presence of light distillate as described herein, with high sulfur content vacuum residuum and high pour point atmospheric residuum and straight run middle distillate cutter derived from low sulfur content, waxy, crude. Thus, for example, the pour point of the above blend prepared in case (c) can be lowered by -30 F. by incorporating in the fuel oil from 400 to 800 p.p.m. of a mixed additive of the type described. As a result, more of the low sulfur content, high pour point, waxy residuum can be incorporated in the fuel oil.

The following example further illustrates advantages of the middle distillate fraction being present in admixture with a vacuum gas oil fraction in the catalytic hydrodesulfurization.

Example 2 A vacuum gas oil derived from high sulfur content crude oil was subjected to catalytic hydrodesulfurization at two temperature levels, about 700 F. and about 750 F. in runs (a) and (b); and in a comparison run (c) the vacuum gas oil was subjected to the catalytic hydrodesulfurization in admixture with kerosene and diesel fuel distillate fractions at an intermediate temperature of about 725 F. and a higher total space velocity. The operating conditions and the yields and sulfur contents of product fractions produced are shown in the following table.

TABLE II Desulfurization of Desulfurization of Vacuum Gas Vacuum Gas Oil plus Distillates (e) (b) (c) Temperature. F 749 701 724 Pressure, p.s.i.g 885 885 1, 070 Space Velocity, LHSV---.. 2. 0 2. 0 3. 0 H1 recycle gas, scf/bbl 1, 460 1, 400 1, 560 Hg consumption, s.e.f./bb1 380 340 400 Liquid Feed Products Feed Products (a) (b) (c) Vol ./hr./100 vol. catalyst 199 203 300 300 Cta-350 F 2 1 6. 6 8.1 S50-450 F. Kerosene.. 23.1 21. 6 Wt. percent S 0.22 0. 003

l l 42 45o-650 F. Diesel 2 16 3 52. 8 64.5 Wt. percent S.. 0 04 0. 16 1. 6 0.08 d-1,000 F. Gas 160 217. 5 205. 8 Wt. percent 8..... 2 9 0.14 0.4 3. 1 0.35

l350-650u F. fraction. 2 8 vol. percent of 525-650 F. overlap in nominal 650-1 ,000 F. gas 0101. 3 Includes 6 volumes (2%) 525-650 F. overlap in nominal G50-1,000 F As can be seen from the above data, when the vacuum gas oil was hydrodesulfurized in admixture with the keroserie and diesel fractions, instead of separately, there was less hydrocracking of the vacuum gas oil fraction while still achieving the desired degree of desulfurization, and in addition the kerosene and diesel fractions were nearly completely desulfurized. In run (c) hydrodesulfurization of the vacuum gas oil did not measurably change its pour point, which was +95 F. in the 6501000 F. portion of the feed and product. However, on blending the 01000 F. portion of the desulfurized gas oil all of the 1000+ F. vacuum residuum, having I+120 F. pour is the same pour point as the original atmospheric residuum had.

In the above Examples 1 and 2, the catalyst employed in the hydrodesulfurization was a sulded composite of compounds of nickel, molybdenum, alumina and silica prepared by impregnating a previously formed silicaalumina carrier comprising percent A1203 and 25 percent SiO2 with -compounds of nickel and molybdenum, calcining, and sulding. The calcined catalyst contained about 8 percent nickel oxide and 26 percent molybdenum oxide. As an indication of the influence of catalyst selection in the hydrodesulfurization, a comparison run was made with another somewhat similar catalyst as in the following example.

Example 3 The 650- F. vacuum gas oil described in Example 2 was subjected to hydrodesulfurization at conditions similar to those in run (a) of said example, namely at 747 F., 890 p.s.i.g., 2.0 LHSV, with 1850 s.c.f. H2 recycle gas per barrel using .a catalyst comprising an aluminasilica carrier which was about 10 percent Si02 and 90 percent Al203, promoted with about 4 percent nickel and 11 percent molybdenum Net hydrocracking of the 650+ F. vacuum gas oil to distillates boiling below 650 F. was only 11 percent, but only 45 percent of the sulfur was removed from the vacuum gas oil. The 650+ F. product still contained 1.6 percent sulfur, and only a minor portion of the asphaltic vacuum residuum can be blended with this partially desulfurized gas oil to form fuel oil of acceptable low sulfur content. To obtain a low enough sulfur content in the desulfurized vacuum gas oil to permit, on a calculated basis, blending with all of the asphaltic fraction, the hydrodesulfurization conditions with this catalyst have to be so severe that substantially more hydrocracking occurs. Then, there is no longer obtained the calculated amount of vacuum gas oil assumed available, and the pour point sepcication is not met in the blend with the asphaltic fraction.

In contrast, it will be noted that using the higher silicaand molybdenum-content catalyst at essentially the same conditions as above, in run (a) of Example 2, thhe vacuum gas oil was much more completely desulfurized. Also, as shown in run (c) of Example 2, with the added light distillate desulfurization of the vacuum gas oil was more complete at a higher space velocity .and lower temperature, as compared to Example 3.

It will be apparent to those skilled in the art that the degree of desulfurization of nonasphaltic fraction needed depends on the sulfur content of the crude feed and the sulfur limitation imposed on the heavy fuel oil product. Similarly the yield of heavy nonasphaltic fraction which needs to be separated from the crude residue starting material, so as to limit the amount of asphaltic residue remaining, and the means which must be employed to obtain a needed yield, will depend on the sulfur content and other properties of the crude residue. In .an extreme case where it appears desirable to make the asphaltic residue a minimum, the whole crude or topped crude may be subjected to the desulfurization, in which case the desulfurization, yield, and product pour point may be improved by carrying out the desulfurization in admixture with added light distillate derived from another source, such as another crude.

We claim: l. A process for producing low sulfur content heavy fuel oil from high sulfur content petroleum residua boiling above about 650 F. which comprises:

separating said residua into an asphaltic fraction and a heavy nonasphaltic fraction boiling above about 650 F.,

mixing said nonasphaltic fraction with a light hydrocarbon distillate boiling between about 300 and 700 F.,

hydrodesulfurizing said mixture with a desulfurizing catalyst comprising an alumina-silica composite carrier having an Al2O3/Si02 weight ratio of from 3 to 5 and promoted with molybdenum and nickel or their oxides or suldes, said reaction being carried out at a hydrocracking conversion of no more than 10 volume percent of said nonasphaltic fraction to products boiling below 650 F.,

seprating from the desulfurized effluent of said reaction a rst light distillate fraction boiling below about 700 F. and a second fraction boiling above 650 F., and blending said second fraction with said asphaltic fraction, thereby forming low :sulfur content heavy fuel oil of improved pour point.

2. A process in accordance with claim 1 which includes separating from low sulfur content crude petroleum a fraction boiling between .about 300 F. and about 700 F. and adding a portion of said fraction to the catalytic hydrodesulfurization reaction; and blending another portion of said fraction boiling between 300 F and 700 F. into the heavy fuel oil as cutter stock.

3. A process in accordance with claim 1 which includes blending a fraction boiling above the atmospheric gas oil boiling range into said heavy fuel oil, said fraction being separated from a low sulfur content waxy crude.

References Cited UNITED STATES PATENTS 6/1961 Inwood 20S-211 1l/1964 Friess 208-211 U.S. C1. X.R. 208-212, 216, 211

UNITED STATES PATENT OFFICE CERTIFICATE oF CORRECTION Patent No. 3,464 ,915 September` 2 1969 Norman J. Paterson et al.

It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 7, line 43, "normally liquid hydrogen oil" should read normally liquid hydrocarbon oil Column 8, line 19, "via line 49 for blending with the high sulfur content" should read via lines 46, 47 and 48 to tank 35 as cutter stock for the Column l0, line 39, after "+l20 F. pour" insert point, a blended pour point of +55 F. is obtained,

Signed and sealed this 5th day of May 1970.

(SEAL) Attest:

Edward M. Fletcher, Jr. WILLIAM E. SCHUYLER, YJR.

Attesting Officer Commissioner of Patents

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