US2951807A - Hydro-treating a blend of straight-run fuel oil and thermally cracked gasoline - Google Patents

Description

Septv 6,1950 E. .1.4 KlRlaERc` 2,951,801

HYDRO-TREATING A BLEND OF STRAIGHT-RUN FUEL'OIL AND THERMALLY CRACKED GAsoLlNE Filed sept. 19, 1955 nited States HYDRO-TREATING A BLEND OF 'STRAIGHT-RUN FUEL DIL AND THERMALLY CRACKED GASO- LINE Emil J. Kirberg, Pittsburgh, Pa., assignor to Gulf Oil Corporation, Pittsburgh, Pa., a corporation of Pennsyl- This invention relates to the improvement of straight run distillate fuel oils and thermally cracked gasoline both of which contain sulfur compounds.

It is well known to subject certain petroleum fractions to desulfurization treatment in the presence of hydrogen to remove sulfur compounds. 'Ihe desulfurization treatment ordinarily has Vinvolved treatment with hydrogen in the presence of hydrogenation catalyst at elevated pressures and temperatures. It has furthermore been known to subject sulfur-containing gasoline to a similar desulfurization treatment and to then subject the hydrodesulfurized gasoline to reforming in the presence of hydrogen in order to improve the octane number of the gasoline.

This invention has for its object to provide improved procedure for simultaneously hydrodesulfurizing a thermally cracked gasoline and a straight run distillate fuel oil, both of which contain sulfur compounds in harmful amounts. Another object is to provide procedure whereby the reaction temperature during hydrodesulfurization of a thermallyV cracked gasoline may be controlled so that the temperature may be retained within optimum conditions in all portions of the catalyst bed and so that an improved desulfurized gasoline is obtained. A further object is to provide an improved procedure for hydrodesulfurizing and hydrogen reforming a thermally cracked gasoline.

Another object is to provide procedure for simultaneously improving a straight run distillate fuel oil and thermally cracked gasoline or naphtha. Other objects will appear hereinafter.

These and other objects are accomplished by my invention which includes subjecting a thermally cracked gasoline and a straight run `distillate fuel oil to treatment with hydrogen in the presence of a hydrogenation catalyst at a temperature between yabout 650 and 850 F. at a pressure between about 500 and 1000 p.s.i.g., at a space velocity between about 1 and 18 and fractionating the resultant hydrocarbon mixture to separate the distillate fuel oil fraction and the gasoline fraction.

lf Ia thermally cracked naphtha or gasoline is subjected alone to hydrodesulfurization under the above described conditions, it will be found that the tempera ture of reaction is relatively erratic and difficult to control, especially in localized areas of the catalyst bed. Also the quality of the desulfun'zed thermally cracked naphtha is not as satisfactory as it would be if the process were carried out in accordance with the present invention. It is presumed that the deterioration in product quality and temperature uctuat-ion are due to the fact that the thermally cracked naphtha contains relatively large amounts of olefns which are hydrogenated under the above describedconditions and heat is released since the reaction is exothermic. However, when operating in accordance` with the present invention, the straight run distillate fuel oil, which absorbs relatively little hydro- -gen and therefore gives olf relatively little heat during atent O ICC the reaction, acts to control the temperature. As a result the characteristics of both components are markedly improved. Although the straight run distillate fuel oil is present during the hydrogenation, it does not exert a harmful effect on the hydrogenation of the thermally cracked naphtha so that the olens in the gasoline are converted into paraflinic or more saturated hydrocarbons. Therefore the treated gasoline or naphtha product is an excellent charge stock for a catalytic hydrogen reforming operation. It is probable that under the above described conditions a portion of the distillate fuel oil charge stock is in liquid phase. By operating with the above described mixture, it has been found that the gasoline acts to maintain the furnace oil more completely in vapor phase. Therefore the difficult problem of distributing liquid evenly on a catalyst bed is minimized and the desulfurization of the distillate fuel oil is improved.

In the following examples and description I have set forth several of the preferred embodiments of my invention, but it is to be understood that they are given by way of illustration and not in limitation thereof.

The distillate fuel oil employed. in my invention may be `derived from any crude petroleum which contains sulfur compounds which are distilled with the fuel oil and are present in the fuel oil in harmful amounts. I prefer to employ a straight run fuel oil which distills predominantly between 425 and 650 F. Fuel oils usually distill over a rather broad range. However, I

may use either narrow boiling or full range boiling fuel,

oils. Also fuel oils frequently contain small amounts of component boiling below 425 F. (to give higher flash points) or boiling about 650 F. and such fuel oils may be used. In general any straight run fuel oil in the` kerosene range up to, but not including, the lubricating oil range may be used. I prefer to employ la full range type fuel oil and also prefer to employ a No. 2 fuel oil. The thermally cracked gasoline or naphtha employed in the process of my invention may be derived from any conventional thermal cracking process as well -as from visbreaking, delayed coking, etc. The thermally cracked gasoline should preferably have an end. point below about 425 F. and an end point of about 400 is ordinarily preferred. Thermal cracking is frequently employed to convert crudes or fractions thereof which contain relatively large amounts of sulfur, and this sulfur is present in the thermally cracked gasoline in harmful amounts and requires separation. Also these thermally cracked gasolines have a relatively low octane number under present day standards and improvement thereof is desirable. Thermally cracked `gasolines frequently have a low initial boiling point since they contain gaseous materials such as butanes or butenes. The presence of such gaseous materials or the utilization of thermally cracked naphthas or gasolines hav-ing low initial boiling points is entirely feasible. Mixtures containing 5 to 50 percent thermal gasoline and to 50 percent distillate fuel oil may be treated :in accordance with my invention.

The catalyst employed in the desulfurization step may be any type of hydrogenation catalyst which functions in the presence of sulfur, for instance, sulfide or oxide catalysts such as sulfides or oxides of tungsten, molybdenum, chromium, vanadium, etc. may be employed. A preferred type of catalyst is a mixture or chemical combination of an oxide or sulfide of an iron group metal with the oxide or sulde of a metal of group VI, lefthand column of the periodic table, such as a mixture of the oxide or sulfide of nickel or cobalt with theV oxide or sulfide of tungsten or molybdenum. l especially prefer to use a catalyst comprising a mixture or chemical combination of an oxide or sulfide of cobalt with molybdenum oxide or suliide. It is preferred to employ the catalyst on a porous carrier such as activated alumina, alumina stabilized with a small amount of silica or a silica-alumina cracking catalyst type carrier. It is preferred to employ a carrier which contains only a small amount of silica since the objective is to avoid substantial cracking of the distillate fuel oil or the naphtha. If a carrier containing a large amount of silica, such as a silica-alumina cracking catalyst is used, it is preferred that the cracking activity be reduced by steam treatment. The hydrogenating component usually will be about 2 to 20 percent and preferably about 5 to 15 percent of the catalyst. Y

Temperatures below 650 F. give an insuiiicient rate of desulfurization and hydrogenation whereas temperatures above 850 F. result in a fuel oil having poorer characteristics and in thermal decomposition of both the fuel oil and naphtha. A temperature .of 675 to 750 F. is preferred. The use fof pressures below 500 pounds gives insufficient rates of desulfurization or incomplete desulfurization within reasonable reaction times. ,Pressures above 1000 p.s.i.g. may be employed, but it is a distinct advantage of the .present invention that moderate pressures below about 1000 pounds can be used to obtain rapid desulfurization and hydrogenation. By using these more moderate pressures it is possible to avoid the utilization of expensive high pressure equipment and excessive consumption of hydrogen. Also the reforming characteristics of the gasoline are improved. A pressure. of about 550 to 700 p.s.i.g. is preferred.

The space velocity employed will depend upon the amount of sulfur present in the charge stocks and the degree of desulfurization desired. As the space velocity increases, desulfurization decreases. The same is largely true with respect to the saturation of the olefins present in the thermally cracked naphtha. A space velocity of between about .2 and 4 will be found to be most satisfactory for mixtures commonly treated. A space velocity below about 12 is preferred since with higher space velocities the reforming quality of the thermal gasoline tends to decrease.

The throughput between regenerations does not affect desulfurization or hydrogenation to a marked extent, and `the throughput used will depend upon the nature of the charge stocks especially the boiling point of the straight run distillaterfuel oil. Also the temperature of treatment plays Yan important part. Hydrogenation reactions are favored at low temperatures, At lL'gh temperatures, dehydrogenation reactions and coke formation occur which shorten the useful catalyst life and make inferior products. The product from treating cracked gasoline .alone where high local temperatures obtain is inferior to the product from mixture treating and catalyst life lis shorter. The limiting factor is the amount of carbon deposited upon the catalyst, and of course the higher the `boiling point of the fuel oil and the higher the temperature, the greater the amount of carbon deposited and therefore the more frequent the regeneration. When treating a mixture iof No. 2 furnace oil having an end point of about 650 F. and naphtha with a cobalt molybdate catalyst onV an alumina carrier, a throughput of 3400 volumes or more of the mixed charge stock per volume of catalyst has been obtained before regeneration is required. A throughput `of about 8 to 3400 will generally be satisfactory. The regeneration is accomplished in conventional fashion by subjecting the catalyst to combustion with an oxygen-containing gas such asV airrto burn off the deposited carbon. When a molybdenum-containing catalyst is used, it is best to avoid regeneration temperatures that are above about 1100 F. Y The hydrogen employed in my process may contain considerable amounts of impurities such as gaseous hydrocarbons. It is preferred to employ as fresh hydrogen the oif gas from a hydrogen reforming operation. Such a gas contains about 65 to 85 percent hydrogen, and such a hydrogen mixture may be employed although pure hydrogen may be utilized where it is available at competitive prices. The hydrogen is preferably recycled at a rate of between about 1000 and 4000 standard cubic feet per barrel. A higher hydrogen or lower recycle rate may be employed without materially affecting the desulfurization and hydrogenation. expensive and the increased benefits are ordinarily not sufficient to justify recycle rates above 4000. One Vof the advantages of my invention is that it enables the use of lower hydrogen recycle rates. Thus recycle hydrogen has been commonly used to remove the exothermic heat of the hydrogenation 'reaction and if pure or undiluted thermally cracked gasoline is treated, -a relatively high hydrogen recycle rate would be required to remove this exothermic heat. However, by treating a mixture as in my invention, the problem is overcome without usinghigh recycle rates. The recycledlhydrogen should have a purity such that when mixed with make-up hydrogen, the mixture will benabout 65 o r more percent hydrogen.

After subjecting themixture of straight run fuel oil and thermally cracked gasoline to the above described treatment, the reaction mixture is separated from the hydrogen and is fractionated to separate the desulfurized fuel oil from the naphtha. This can be accomplished by conventional fractionation. The presence of the gasoline has an advantage in that while it is being removed by fractionation, the hydrogen-sulfide gas absorbed in the hydrocarbon mixture distills off with the gasoline. Therefore the fuel oil can be directly obtained practically sulfur free by an ordinary distillation. Also the presence of the gasoline permits the use of lower temperatures during the distillation. By avoiding higher temperatures during distillation, the quality of the fuel oil is further improved. The fuel oil from the fractionation is in prime condition for utilization. It has been found that the added gasoline promotes such complete hydrogen sulfide removal that the fuel oil need not be caustic washed, which adds water to the fuel oil and must be removed in a subsequent drying stage. The fuel oil thus remains dry and ready for sale :and the troublesome caustic wash and drying steps are eliminated. The gasoline may be separated from the reiiux drum employed in the fractionation while hydrogen sulfide, propane and lighter material is taken as overhead. The gasoline from the reflux drum of the fractionation then may be stabilized to remove hydrogen sulfide and hydrocarbons boiling below butane. During this stabilization the hydrocarbon gases `assist in removal of hydrogen sulfide absorbed in the gasoline.

This desulfurized gasoline has a lower octane number than the starting material. However, because it is free ofsulfur and has a lower bromine number, it yields an excellent gasoline when subjected to hydrogen reforming. Hydrogen reforming is well known in the art, and the process per se forms no part of this invention. Reference is made -to Progress for Petroleum Technology, August 7, 1951, pages 39 to 76, for a more complete description of several conventional reforming processes which may be employed for improving the octane number of the desulfurized naphtha.

It is known that in certain types of hydrogen reforming operations, it is desirable to utilize a charge stock which is free of sulfur and nitrogen. The process of my invention provides an admirable charge stock for this purpose in that it is substantially free of sulfur and nitrogen. Furthermore it is desirable that -the chargerstock for a hydrogen reforming process should be relatively free of aromatics and olens. A thermally cracked naphtha containsV only smlall Yamounts of aromfatics, and the'olens are largely saturated in the first step of my invention. A

In the accompanying drawing I have illustrated diagrammatically apparatus in which my invention may be carried out. Referring to the drawing, numeral V2. desig- However, recycling is agencer hates a conduit through which a mixture of straight run fuel oil and thermally cracked gasoline is introduced into heater 4. Numeral 8 designates a conduit for introducing fresh or make-up hydrogen under reaction pressure into heater 4. The mixture of hydrogen, straight run fuel oil and thermally cracked gasoline is heated in heater 4 to about reaction temperature and is then introduced by way of conduit 10 into reactor 12 which contains and the mixture was subjected to hydrodesulfurization by contacting with a cobalt molybdate catalyst (3 percent lcobalt oxide and percent molybdenum oxide) deposited upon activated alumina in the presence of hydrogen at a temperature of about 680 F., a pressure of 600 p.s.i.g., a space velocity of 3.97 vol./hr./vol. and at a hydrogen recycle rate of 4000 s.c.f./bbl. The properties of the charge stocks and products are shown in a bed of hydrogenation catalyst such yas described above. Table l.-

Table I Gasoline Furnace Oil Streams Charge Product Charge Product Yield, Percent by Vol. o Charge 18.0 18. 3 82. 0 82.2 Inspection Data:

Gravity, API 53. 58. 6 38. 8 40. 7 ulfur, L, percent 10. 95 0. 07 Sulfur, GRM 1123, percent 1.08 0.13 Brornine No., ASTM D 1159-51T l 75 3. 0 9.0 Aniline Point, F.: ASTM D 611-50A--, 105 156 Nitrogen. Total, p.p.1n'. 134 3 Nitrogen, Basic, p.p.m 5 Flash P-M, F.: ASTM D 98-46 168 104 Carbon Residue, Conradson on 10% Bottoms, percent: ASTM D 1823-52...- 0.06 Distillation: ASTM D 86-46 D 86-46 D 158e52 D 158-52 Over Point, 165 146 37 404 End, 416 364 642 612 10% at, F 210 200 433 442 0 283 267 510 503 90 371 322 602 593 CFR Calculated Cetane Tndex 55.8 58. S

1 Estimated from individual gasoline components.

The mixture of hydrogen and hydrocarbons iiows downwardly through the reactor where conversion of sulfur compounds into hydrogen sullide and hydrogenation of olefins takes place. The mixture then iiows out of the reactor through conduit 14, passes through cooler 16 and thence into high pressure separator 18. Here liquids are separated from gases. The gas is primarily hydrogen :and is removed through conduit 20 partly vented through conduit 21 to maintain required purity and the balance compressed by compressor 22 to reaction pressure and recycled through conduit 24.' The liquid from high pressure separator 18 is removed through conduit 26 and is introduced into fractionator 23. gasoline, hydrogen suliide, small amounts of hydrogen, hydrocarbon gases, water, etc., 'are taken overhead through conduit and the higher boiling portion is condensed in reflux drum 32. A portion of this condensed liquid is returned as reflux via conduit 34 and the balance is removed through conduit 36 and stabilized by fractionation in stablizer 38. Stabilized gasoline which may contain C4 hydrocarbons is removed through conduit 40.

During fractionation in fractionator 28 the vaporization of the gasoline assists in.carryng out or removing the hydrogen sulfide absorbed in the product. Therefore a practically sulfur-free fuel oil is removed as a heavier or bottoms fraction from fractionator 28. A similar effect takes place in stabilizer 38. Gases separated in reflux drum 32 and stabilizer 38` are removed from the system through conduits 39 and 42 respectively and may be processed for the recovery of their components, primarily hydrogen sulfide, hydrogen and propane.

The gasoline removed from conduit 40 then may be combined with hydrogen and subjected to hydrogen reforming as conventionally practiced. The gasoline will be substantially free of hydrogen sulfide if stabilizer 38 is operated so that a small amount of hydrocarbon `gases goes off through conduit 42. Thus removal of 0.5 to l percent gases in this manner will yield a gasoline which is relatively free of hydrogen sulfide.

EXAMPLE During fractionation A kuwait straight run furnace oil was mixed with 18 I The bromine number, nitrogen content and sulfur content indicate Ithat the gasoline would be Very satisfactory for catalytic hydrogen reforming. The furnace oil product did not require caustic washing, was doctor sweet, gave no copper strip` corrosion and had a carbon residue on l0 percent bottoms of .0l percent or less. It gave no precipitate in an accelerated stability test involving heating to 212 F. for 64 hours. It also gave no precipitate on storage at room temperature for six months.

I claim:

1. The process for desulfurizing a straight run fuel oil distillate and a thermally cracked distillate boiling in the gasoline range and for improving the reforming characteristics of the thermally cracked gasoline which comprises contacting a mixture of straight run fuel oil and thermally cracked gasoline with a hydrogenation catalyst composited with a porous carrier at a temperature between about 650 F. and 850 F. at a pressure between about 500 and 1000 p.s'.i.g., at a space velocity between about l and 18 liquid volumes of mixed charge stock per hour per volume of hydrogenation catalyst, whereby the olens contained in the thermally cracked distillate are substantially hydrogenated and the fuel oil distillate and thermally cracked distillate are substantially desulfurized and fractionating the resulting hydrocarbon mixture to separate the fuel oil from the gasoline.

2. The process for desulfurizing a straight run furnace oil distillate boiling between kerosene and lubricating oil and a thermally cracked distillate boiling in the gasoline range and for improving the reforming characteristics of the thermally cracked gasoline which comprises contacting a mixture of the straight run furnace oil and thermally cracked gasoline with a cobalt oxide-molybdenurn oxide catalyst composited with an. activated alumina carrier at a temperature between about 650 F. and 850 F. at a pressure between about 500 and 1000 p.s.i.g., at a space velocity between about 2 and 4 liquid rvolumes of mixed charge stock per hour per volume of catalyst at a hydrogen recycle rate of vbetween about 1000 and 4000 s.c.f./bbl. and at a throughput of between about 8 and 3400 volumes of the mixed charge stock per` volume of catalyst, whereby the oleiins contained in the thermally cracked distillate are substantially hydrogenated and the furnace oil distillate and Ithermally cracked distillate are substantially desulfun'zed and fractionating the `resulting hydrocarbon mixture to separate the furnace oil from the gasoline.

3. The process for desulfurizing a straight run furnace oil distillate distilling between about 425 and 690 F. and a thermally cracked distillate boiling in the gasoline range and for improving fthe reforming characteristics of the thermally cracked gasoline which comprises contacting a mixture of straight run furnace oil and thermally cracked gasoline with a cobalt oxide-molybdenum oxide catalyst composited with an activated alumina carrier at a temperature between about 675 F. and 750 F. at a pressure between about 550 and 700 p.s.i.g., at a space Velocity between about 2 and 8 -liquid volumes of mixed charge stock per hour per volume of catalyst at a hydrogen recycle rate of between about 1000 and 4000 s.c;f./bb1. and at a throughput of between about 8 and 3400 volumes of the mixed charge stock per volume of catalyst whereby the olens contained in the thermally cracked distillate are substantially hydrogenated and t-he furnace oil distillate and thermally cracked distillate are subs-tmtially desulfurized, fractionating the resulting hydrocarbon mixture to separate the furnace oil substantially free of hydrogen sulfide as bottoms and the gasoline, hydrogen sulde and hydrocarbon gases as overhead, and vaporizing the hydrocarbon gases and hydrogen sulfide from fthe gasoline.

4. The process for desulfurizing a straight run furnace o'il' and a thermally cracked distillate boiling in the gasoline range and for improving the reforming characteristics of the thermally cracked gasoline which comprises subjecting a sulfur-containing crude petroleum to distillation toi separate a furnace oil boiling between about 425 and 650 F., subjecting this furnace oil together with a sulfur-containing thermally cracked gasoline to treatment with hydrogen by contacting the furnace oil and the thermally Vcracked gasoline with a cobalt oxidemolybdenum oxide hydrogenation catalyst composited with a porous carrier at a temperature between about 650 and 850 F. at a pressure ybetween about 500 and 1000 psig., at a space velocity between about 2 and 8 liquid volumes of mixed charge stock per hour per volume of catalyst and at a recycle rate of 1000 to 4000 standard cubic feet per barrel of mixed charge stock, whereby the olens contained in the thermally cracked distillate are substantially hydrogenated, the lthernrally cracked dis.- tillate is converted into a superior reforming charge stock and the furnace oil and the thermally cracked distillate are substantially desulfurized, subjecting the resultant product to fractionation ,to separate a desulfurized furnace loil fraction and a desulfurized thermally cracked gasoline andsubjecting the desulfurized gasoline to reforming in the presence of hydrogen and a dehydrogenation catalyst.

5. The process for desulfurizing a straight run furnace `oil and a thermally cracked distillate boiling in the gasoline range and for improving the reforming characteristics of the thermally cracked gasoline which comprises subjecting a sulfur-containing crude petroleum to distillation to separate a furnace oil boiling over approximately the full range of 425 to 650 F., subjecting this furnace oil together with a sulfur-containing thermally cracked gasoline to treatment with hydrogen by contacting the furnace oil and the thermally cracked gasoline with a cobalt oxide-molybdenum oxide hydrogenation catalyst composited with a porous carrier at a temperature between about 650 and 850 F. at a pressure between about 500 and 100.0 p.s.i.g., at a space velocity between about 2 and 8 liquid volumes of mixed charge stock per hour per volume of catalyst and at a recycle rate of 1000 to 4000 standard cubic feet per barrel of mixed charge stock, whereby the olens contained in the thermally cracked distillate are substantially hydrogenated, the thermally cracked distillate is converted into a superior reforming charge stock and the furnace oil and the thermally cracked distillate are substantially desulfurized, subjecting the resultant product to fractionation to separate a desulfurized furnace oil fraction and a desulfurized thermally cracked gasoline and subjecting the desulfurized gasoline to reforming in the presence of hydrogen and a dehydrogenation catalyst.

' References Cited in the tile of this patent UNTED STATES PATENTS Belgium Feb. 14, 1953

Claims (1)

1. THE PROCESS FOR DESULFURIZING A STRAIGHT RUN FUEL OIL DISTILLATE AND A THERMALLY CRACKED DISTILLATE BOILING IN THE GASOLINE RANGE AND FOR IMPROVING THE REFORMING CHARCTERISTICS OF THE THERMALLY CRACKED GASOLINE WHICH COMPRISES CONTACTING A MIXTURE OF STRAIGHT RUN FUEL OIL AND THERMALLY CRACKED GASOLINE WITH A HYDROGENATION CATALYST COMPOSITED WITH A POROUS CARRIER AT A TEMPERATURE BETWEEN ABOUT 650*F. AND 850*F. AT A PRESSURE BETWEEN ABOUT 500 AND 1000 P.S.I.G., AT A SPACE VELOCITY BETWEEN ABOUT 1 AND 18 LIQUID VOLUMES OF MIXED CHARGE STOCK PER HOUR PER VOLUME OF HYDROGENATION CATALYST, WHEREBY THE OLEFINS CONTAINED IN THE THERMALLY CRACKED DISTILLATE ARE SUBSTANTIALLY HYDROGENATED AND THE FUEL OIL DISTILLATE AND THERMALLY CRACKED DISTILLATE ARE SUBSTANTIALLY DESULFURIZED AND FRACTIONATING THE RESULTING HYDROCARBON MIXTURE TO SEPARATE THE FUEL OIL FROM THE GASOLINE.

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