METHOD FOR HYDROCRACKING HEAVY FRACTION OIL

Abstract: A method for hydrocracking a heavy fraction oil characterized by cracking a heavy fraction oil in the presence of a hydrogen donating solvent and hydrogen gas and circulating a fraction having a specific boiling range as the circulating solvent through the cracking reactor whereby the formation of carbonaceous substances is greatly inhibited, the supply of a makeup hydrogen donating solvent is dispensed with and the concentration of tetralin in the circulating solvent is maintained at a fixed or higher level.

Description: The present invention relates to a process for hydrocracking a heavy fraction oil, particularly one containing at least 1.0 wt.% of asphaltene, using a hydrogen donating solvent. The hydrogenolysis of a heavy fraction oil is used increasingly. Thus, there have been proposed many hydrogenolysis methods for thermocracking, catalytic cracking etc. The term "cracking" used herein to indicate hydrocracking to obtain light fraction oils including naphtha, gasoline, kerosene and gas oil fractions from heavy fraction oil. The most serious and troublesome problems raised by the cracking of a heavy fraction oil are, in general, the formation of carbonaceous substances and the clogging of various parts of an apparatus used for the cracking by carbonaceous substances. Further, a serious problem caused by catalytic cracking of a heavy fraction oil is the decrease in catalytic activity of a catalyst used. Still further, the cracking of a heavy fraction oil raises an economic problem because of the amount of hydrogen consumed. These problems become more serious the heavier the fraction oil to be cracked is, with the concomitant need for the cracking to proceed farther. One of the methods for solving these problems is a method comprising the use of a hydrogen donating solvent (For example, U.S. Patent No. 4,430,197). It is well known that compounds, such as tetralin (tetrahydronaphthalene), obtained by hydrogenating polycyclic aromatic compounds, serve as a hydrogen donor and that catalysts are not necessarily required for the hydrogenolysis of a heavy fraction oil with the use of such a hydrogen donating solvent, and this reaction proceeds under a comparatively low hydrogen pressure (For example, U.S. Patent No. 4,294,686 and Oil & Gas Journal, Nov. 22, 1982, pp. 111-116). Attempts have often been made to use the above methods industrially (For example, U.S. Patent No. 2,953,513). It is indeed known generally for such hydrogen donating substances to be present in the thermocracked oils, catalytically cracked oils and hydrocracked oils in general where they function, per se, as an effective hydrogen donor (For example, U.S. Patent No. 3,970,545). These known methods, however, will not produce fully stable cracked products and will give rise to problems as to the formation of carbonaceous substances, and the like. In order to solve these problems, it is known to be effective to have a suitable catalyst coexist with a hydrogen donating solvent (Japanese Pat. Appln. Laid-Open Gazettes Nos. 61-62591, 61-130394 and 61-136591 and US-A-4,640,765. It has been found by the present inventors that the combined use of a hydrogen donating solvent such as tetralin, and a catalyst capable of hydrogenolysis will provide the following advantages. (1) The formation of carbonaceous substances is inhibited. The formation of carbonaceous substances will be inhibited even by the use of a hydrogen donating solvent only. If a suitable catalyst, however, is used in combination with said solvent, the resulting cracked products will be hydrogenated and therefore stabilized with the formation of carbonaceous substances being greatly inhibited and with problems which may otherwise be caused due to the clogging of a hydrocracking apparatus with the carbonaceous substances bing reduced. (2) A decrease in catalytic activity of the catalyst is reduced. The most serious problem occurring in the cracking of a heavy fraction oil using a suitable catalyst is a decrease in catalytic activity of the catalyst. In general, a heavy fraction oil contains asphaltene in which are contained heavy metals such as vanadium and nickel. When the heavy fraction oil is cracked, these heavy metals and carbonaceous substances will adhere to the surface of the catalyst whereby its catalytic activity drops. The coexistence of a hydrogen donating solvent such as tetralin, will greatly reduce the decrease in catalytic activity of the catalyst. If the catalyst used is highly susceptible to adhesion of heavy metals thereto at this point, the effects of the hydrogen donating solvent will be particularly beneficial (3) The cracking reaction may be carried out at lower pressures. It is normally necessary to use a high hydrogen pressure, generally 100 atm. to 200 atm., in order to mainly avoid decrease in catalytic activity of the catalyst when cracking a heavy fraction oil in the presence of a suitable catalyst only. It is unnecessary, however, to use a high hydrogen pressure since hydrogen is supplied from a hydrogen donating solvent if the hydrogen donating solvent, such as tetralin, coexists in the system; in this case, 30 atm. to 150 atm. is sufficient as the hydrogen pressure. (4) The amount of hydrogen consumed may be decreased. According to the results of experiments made by the present inventors, it has been found that the cracking of a heavy fraction oil in the presence of a catalyst without a hydrogen donating solvent leads to different and hydrogenating reactions taking place in the cracking from those when cracking the same heavy fraction oil in the presence of the hydrogen donating solvent without the catalyst, and that both cracking techniques are greatly different from each other in the amount of hydrogen consumed even in cases where the same cracking ratio or rate is obtained by each of said two cracking reactions. The combined use of the hydrogen donating solvent and the catalyst enables effective hydrogenolysis to be attained with a minimum amount of hydrogen consumed and without unnecessary hydrogenation. It is also known that, in general, a fraction containing hydrogen donating solvents is recovered from a distillate from fractionation and the fraction so recovered is used for recirculation (Japanese Pat. Appln. Laid-Open Gazettes Nos. 61-62591 and 61-130394). The methods proposed in these Gazettes, however, raise the following problems. (1) The starting oil is cracked, and the resulting hydrocarbon having the same boiling point as the circulating solvent is incorporated into the circulating solvent and accumulated therein whereby the concentration of hydrogenating solvent in the circulating solvent decreases. (2) In a case where a heavy fraction oil is cracking using tetralin, the tetralin and naphthalene which are present are partly lost when carrying out distillation operation for recovering the circulating solvent. Further, the tetralin is converted to decalin, methylindane, methylnaphthalene, butylbenzene and the like during the cracking operation. The compounds produced by the conversion are discharged from the system, resulting in a partial loss of tetralin. The total amount of tetralin lost due to the distillation operation and the conversion will be reduced in part but not completely, by suitable selection of a catalyst and cracking reaction conditions used. Accordingly, if tetralin or naphthalene (to be converted to tetralin by hydrogenation) is not produced form the starting oil during the cracking operation, the amount of tetralin or naphthalene originally existing in the system will gradually decrease. To compensate for this decrease, the amount of makeup tetralin or naphthalene supplied from outside of the system will be large. An object of the present invention is to provide a method for cracking heavy fraction oil containing at least 1.0 wt.% of asphaltene in the presence of a hydrogen donating solvent, in which the formation of carbonaceous substances is greatly inhibited and problems as to the circulation of the hydrogen donating solvent are solved. According to this invention there is provided a method of hydrocracking a heavy fraction oil which comprises the steps of: A) cracking a heavy fraction oil containing 1 wt.% up to 30 wt.% of asphaltene and at least 50 wt.% of a fraction boiling at at least 350°C. in the presence of a circulating flow comprising a hydrogen donating solvent and which is employed in an amount expressed by a ratio of 0.1-2.0 (wt/wt starting oil), hydrogen gas and a catalyst capable of hydrogenation in a cracking reactor at a temperature of 380°C. - 470°C., at a pressure of 30-150kg/cm²; B) hydrogenating the fractions obtained by the cracking of said heavy fraction oil, in the presence of a hydrogenating catalyst in a hydrogenating reactor at a temperature of 320°C-440°C. and a pressure of 30-150kg/cm²; C) separating the thus hydrogenated fractions into liquid and gaseous phases in a separator, fractionating the thus separated liquid phase in a distillation apparatus to obtain a specific fraction in which at least 90wt.% boils in the range of 150°C-250°C., at least 60wt.% boils in the range of 190°C-230°C. and at least 30wt.% is tetralin, and D) circulating said specific fraction as the circulating solvent through said cracking reactor, in the absence of added hydrogen donating solvent The present inventors made various studies and made the following observations which are embodied in the method of this invention. (1) As one of the characteristics, tetralin and naphthalene are formed as cracking products in cases where a heavy fraction oil is cracked in the presence of a catalyst capable of hydrogenation, a hydrogen donating solvent and hydrogen gas. Although tetralin and naphthalene are still produced even in the absence of a catalyst, they will be produced in greater amounts in the presence of the catalyst. (2) The hydrocarbons (produced by the cracking and hereinafter referred to as "other hydrocarbons") incorporated in the circulating solvent are further cracked, treated in a fractionating apparatus and then discharged as a light fraction oil from the system. (3) There exists an equilibrium concentration at which the amount of "other hydrocarbons" incorporated in the circulating solvent is equal to the amount of light fraction oil produced by cracking the "other hydrocarbons" and discharged from the circulating solvent. (4) When the boiling range of the circulating solvent is allowed to be wide, the concentration of the "other hydrocarbons" in the circulating solvent becomes large, whereas the concentration of tetralin therein conversely becomes small. (5) By limiting the boiling range of the circulating solvent, the concentration of tetralin therein is kept at a high level. (6) When the cracking is carried out while maintaining the concentration of tetralin in the circulating solvent at a fixed level, the loss of tetralin caused by its discharge from the system is compensated for by tetralin and naphthalene produced from the starting heavy fraction oil by cracking, resulting in no apparent loss of tetralin. It has thus been found that when the heavy fraction oil is cracked using a catalyst capable of hydrogenation in the presence of a hydrogen donating solvent and hydrogen gas and a fraction having a specific boiling range is circulated, the formation of carbonaceous substances is greatly inhibited, the supply of a makeup hydrogen donating solvent can be dispensed with and the concentration of tetralin in the circulating solvent is maintained at a fixed or higher level. The starting heavy fraction oils used in the present invention are those containing 1.0 to 30 wt.%, preferably 5-30 wt.%, of asphaltene and at least 50 wt.% of a fraction boiling at 350°C or higher, and they include residual oils obtained by the distillation of crude oils at atmospheric or reduced pressure, oils obtained from coal, oil sand, oil shale, bitumen or the like, and mixtures of said various heavy fraction oils. The hydrogen donating solvents used in the present invention may be hydrogenation products of polycyclic aromatic hydrocarbons. The polycyclic aromatic hydrocarbons include bicyclic to hexacyclic, preferably bicyclic to tetracyclic, aromatic hydrocarbons and derivatives thereof such as naphthalene, anthracene, phenanthrene, pyrene, naphthacene, chrysene, benzopyrene, perylene, picene and derivatives thereof, which may be used individually or jointly. In addition, the hydrides of hydrocarbon oils boiling in the range of 150-500°C and containing at least 20 wt.% of said polycyclic aromatic hydrocarbons, may also be used as such hydrogen donating solvents, and the hydrocarbon oils include cycle oils in an apparatus for catalytic cracking (FCC), bottom oils in a catalytic reforming apparatus, bottom oils in a thermocracking apparatus and other oil products obtained from petroleum refining plants, as well as coal-derived products such as tar oil, anthracene oil, creosote oil, coal liquefied oil, and products obtained from tar sand, oil shale and bitumen. The hydrocarbon oils used in the present invention preferably include FCC cycle oils containing naphthalene, anthracene and the like, and bottoms obtained by thermocracking and reforming naphtha. In the present invention, although such polycyclic aromatic hydrocarbons and hydrocarbon oils may be hydrogenated prior to being charged into the reactor, this is not necessarily required since the hydrocarbons and oils are otherwise hydrogenated to produce hydrogen donating solvents because of the presence of hydrogen gas and catalysts in the reactor. In addition, in the present invention, if a circulating solvent containing hydrogen donating solvents is stored in a circulating solvent storage tank the circulating solvent may be used as the hydrogen donating solvent. The catalysts in the cracking reactor used in the present invention are not particularly limited, but it is desirable that they have a demetallizing function and should preferably be such that they will show comparatively little degradation of catalytic activity due to the accumulation of heavy metals such as vanadium and nickel. These catalysts include the oxides and sulfides of Group VIII metals of the Periodic Table such as nickel and cobalt as well as of Group VIB metals of the Periodic Table such as molybdenum and tungsten, each carried on alumina, silica, silica-alumina, alumina-boria, silica-alumina-magnesia, silica-alumina-titania and inorganic substances such as natural and synthetic zeolites. The solid catalyst particles are required to have such a shape that they will not accompany the flow of the liquid discharged from the cracking reactor. They may be spherical or elongate in shape and may be formed by extrusion molding or compression molding. It is desirable that these catalysts have a particle size of 0.1-10 mm, preferably 0.2-5 mm. A better understanding of the method of the present invention may be had from a consideration of the following detailed description, taken in conjunction with the accompanying drawings, in which: Fig. 1 is a block diagram illustrating a method for cracking heavy fraction oils according to the present invention; Fig. 2 is a schematic diagram showing the longitudinal section of a cracking reactor used in the present invention; Fig. 3 illustrates the distillation curves of circulating solvents; Fig. 4 illustrates changes in concentration of tetralin in circulating solvents with the lapse of time in the course of cracking operation; and Fig. 5 illustrates changes in amount of tetralin in the course of cracking operation. Referring now to Fig. 1, a starting heavy fraction oil 1, a hydrogen-containing gas 2 and a circulating solvent 12 containing a hydrogen donating solvent, are introduced into a cracking reactor 3. The cracking reactor 3 holds therein a solid catalyst in the form of a catalyst-filled layer and is maintained at a reaction temperature of 380-470°C, preferably 390-440°C, and a reaction pressure of 30-150 Kg/cm², preferably 40-100 Kg/cm². The heavy fraction oil 1 is cracked in the cracking reactor 3, during which at least 50 wt.% of heavy metals such as vanadium and nickel contained in the heavy fraction oil is removed therefrom by attaching the metals to the solid catalyst in the cracking reactor. The hydrocracked oil obtained from the heavy fraction oil, the hydrogen-containing gas and the circulating solvent containing the hydrogen donating solvent, are introduced from the cracking reactor 3, without any separation treatment, via a pipe 4 into a hydrogenating reactor 5. The hydrogenating reactor 5 holds therein a solid catalyst in the form of a filled layer and is maintained at a reaction temperature of 320-440°C and a reaction pressure of 30-150 Kg/cm². In the hydrogenating reactor, the cracking reaction still proceeds, but the main reactions include the hydrogenation, desulfurization and denitrification of the cracked oils from the cracking reactor 3, the hydrogenation of the used hydrogen donating solvents, and the hydrogenation of carbon precursors produced in the cracking reactor 3. The carbon precursor is hydrogenated in the hydrogenating reactor 5 to be converted to a toluene-soluble substance, resulting in the production of substantially no carbonaceous substances. The liquid and gases from the hydrogenating reactor 5 are separated into the liquid and the gases in a liquid-gas separator 6. The gases so separated containing hydrogen sulfide, ammonium sulfide and the like are subjected to appropriate washing or scrubbing treatment, after which a part of the washed gases is discharged from the system while another part thereof is reused as the circulating gas. The liquid 8 which has been separated from the gases 7 in the liquid-gas separator 6, is introduced into a fractionating apparatus 9 where a circulating solvent fraction 12 is separated from a light fraction oil 10 and a heavy fraction oil 11 and then circulated again to the cracking reactor 3. A solvent storage tank may be provided in the passage of said circulating solvent fraction. This circulating solvent fraction is required to be such that at least 90 wt.% of the solvent fraction is a hydrocarbon fraction boiling in the range of 150-250°C, at least 60 wt.% of the solvent fraction is a hydrocarbon fraction boiling in the range of 190-230°C and at least 30 wt.% of the solvent fraction is tetralin. The amount of circulating solvent fraction circulated is that expressed by a ratio of 0.1-2.0 (wt./wt. starting oil), particularly preferably 0.1-1.2 (wt./wt. starting oil). If the amount of circulating solvent fraction circulated is smaller than that so expressed, the formation of carbonaceous substances will be significant and give rise to problems such as the clogging of the hydrocracking apparatus with the carbonaceous substances and the increased reduction in catalytic activity of the catalyst. If, on the other hand, the amount of liquid circulated is too great, the apparatus will be required to be a large in its capacity and the amount of heat required for heating will be large, this being economically undesirable. A starting heavy fraction oil is cracked in the presence of a hydrogen donating solvent, a hydrogen-containing gas and a catalyst capable of hydrogenation according to the present invention, whereby tetralin, naphthalene and the like are produced from the starting oil in a total amount of at least 0.5 wt.% thereof. The amount of these hydrogen donating solvents produced from the starting oil may be adjusted by changing the cracking reaction conditions and fractionator conditions, and it will also vary depending on the kind of starting oil used. In the present invention, it is generally unnecessary to replenish hydrogen donating solvents from outside the system since the loss of the solvents caused by discharging to outside the system can be compensated by forming hydrogen donating solvents such as tetralin and naphthalene as the cracked products obtained from a starting heavy fraction oil and circulating a fraction boiling in the specific ranges (this fraction so circulated being a circulating solvent fraction). Depending on the kind of starting heavy fraction oil, the starting oil may be incorporated with hydrogen donating solvents in an amount of not more than 0.7 wt.%, preferably not higher than 0.5 wt.%, of the starting oil. In the cracking reactor used in the method of the present invention, the tetralin evolves hydrogen therefrom and is partly converted to naphthalene and some of the tetraline is converted to decalin, methylindane, methylnaphthalene and the like as by-products. These by-products may be inhibited from forming by using appropriate cracking reaction conditions so that they will not accumulate in the circulating solvents. The naphthalene in the circulating solvents may be limited to 5 wt.% or lower in concentration since it is hydrogenated under the action of the catalysts and converted to tetralin in the cracking reactor and hydrogenating reactor. It is necessary that a catalyst capable of hydrogenation be present in the cracking reactor used in the present invention. The catalyst may usually be a solid one. In a case where a solid catalyst is used in the present invention, it is not desirable for the catalyst to be discharged together with the flow of the liquid from the reactors since it is difficult to recover the thus discharged catalyst at the subsequent stages and maintain the catalyst concentration at a desired high level whereby the effective use of the catalyst is not attained. It is effective to use a fixed bed, moving bed, fluid bed (dense fluid bed) or the like in order to retain a solid catalyst in the reactors. In cases where the fixed or moving bed is used, it is effective to maintain a liquid linear velocity of at least 2 cm/sec. Further, it is particularly effective to employ an internal natural liquid circulation system as indicated in Japanese Pat. Appln. Laid-Open Gazette No. 61-235492. The internal natural circulation system will be explained below with reference to Fig. 2. A liquid flow 1 of starting oil and a hydrogen donating solvent and a hydrogen-containing gas 2 are introduced through an introduction pipe 101 provided on the lower part of the cracking reactor 3. The interior of the cracking reactor 3 is vertically divided into two parts by a cylindrical partition 102 including a solid catalyst 103 housed therein, and the aforesaid two parts communicate with each other on the upper and lower parts of the partition 102. It is preferable for the introduced hydrogen-containing gas 2 to be introduced toward the inner part of the cylindrical partition 102 so as not to flow into the outside portion of the partition 102. The same applies to the heavy fraction oil and the hydrogen donating solvent. The foamy hydrogen-containing gas 2 ascends the interior of the partition 102. With such construction, the fluid in the cracking reactor 3 is circulated in the direction of an arrow shown in the figure due to the intra-reactor pressure unbalance caused by the small specific gravity of a region in which the hydrogen-containing gas 2 is present. A part of the above-described circulating fluid is capable of passing through the solid catalyst-housed partition 102 from the exterior of the partition 102 where the hydrogen-containing gas 2 is substantially absent to the inside thereof where gas 2 is present in the diection shown by arrows represented by broken lines. The amount of the fluid passed changes depending on the void ratio of the catalyst-filled partition or the pressure difference between the exterior and interior of the partition 102. The void ratio of the partition 102 preferably ranges from 5 to 95 % in general. The void ratio used herein is the proportion of the space existing in unit volume to the unit volume. By arranging a cylinder as the partition 102 in the cracking reactor 3, it is possible to yield a circulating flow inside the reactor, assure a required flow velocity, and avoid any blocking in the cracking reactor 3 caused by carbonaceous substances therein. The hydrogen-containing gas 2 ascends in the cylindrical partition 102 and is discharged from the outlet pipe 104, while the fluid circulates in the cracking reactor 3 and, after a prescribed residence time, is discharged from the outlet pipe 104. Accordingly, the fluid which resides for a prescribed period of time under prescribed temperature and pressure conditions can be cracked and lighter fractions obtained therefrom. The partition for housing a solid catalyst in practising the method of the present invention is porous as a whole, a part or the whole of the porous partition being composed of the solid catalyst having a hydrogenation function. The partition is generally a porous plain plate- or curved plate-shaped body. A part or the whole of the plate is formed by an assembly of solid catalyst particles having a hydrogenation function. The partition may be illustrated by those prepared by housing at least one kind of particulate catalyst selected from extrusion molded catalyst, spherical catalyst and compression molded catalyst, in a container made of a metal mesh, punched metal or the like, and may also be illustrated by an assembly of catalyst particles bonded to each other with a binder. The thickness of the partition for housing a solid catalyst is 1/100 to 2/5, preferably 1/10 to 1/3, of the inner diameter of the reaction reactor. The sizes of openings of the metal mesh and punched metal for housing a solid catalyst are such that solid catalyst particles do not pass through the openings and the fluid may sufficiently contact with catalyst particles. The amount of catalyst used in the present invention ranges from 1/100 to 1/1.5, preferably 1/50 to 1/2, of the internal volume of the cracking reactor. The solid catalyst used is not particularly limited; it is merely necessary that it have hydrogenation function, such as hydrocracking, hydrodemetallization, hydrodesulfurization or hydrodenitrification. But, from the viewpoint of long-term operation, a preferred catalyst is one which will not significantly undergo loss of activity due to vanadium, nickel and the like present in starting oils, even if it has originally low activity. For example, there can be used a catalyst of the type employed in a heavy fraction oil treating process such as hydrocracking, hydrodemetallization or hydrodesulfurization for heavy fraction oils. One can also employ used catalysts. In addition, it is possible to add a small quantity of a fresh catalyst to the above-described catalysts or to use catalysts having relatively low activity instead of the above-described used catalysts. The solid catalysts include the oxides or sulfides of a Group VIII metal such as nickel or cobalt or of a Group VI B metal such as molybdenum or tungsten, the metal oxides or sulfides being carried on an inorganic substance such as alumina, silica, silica-alumina, alumina-boria, silica-alumina-magnesia, silica-alumina-titania, or natural or synthetic zeolite. The solid catalyst is not particularly limited in shape. For example an extrusion molded catalyst, a spherical catalyst or a compression molded catalyst may be used. The diameters of the catalyst particles range from 0.1 to 10 mm, preferably 0.2 to 5 mm. The operating conditions used in the present invention are as follows: reaction temperature, 380 to 470°C; reaction pressure, 30 to 150 kg/cm², varying depending on the kind of a hydrogen-containing gas used; residence time of starting heavy fraction oil in the cracking reactor, preferably 0.2 to 10 hours; circulating flow speed of the fluid in the cracking reactor, at least 1 cm/sec., preferably 5 to 100 cm/sec. The hydrogenating reactor used in the method of the present invention is usually in the form of a generally fixed bed, and the flow of the fluid in said reactor may be either an ascending one or a descending one. In the hydrogenating reactor, the cracking reaction still proceeds, but the main reactions include hydrogenation, desulfurization and denitrification of the cracked oils as well as hydrogenation of the hydrogen donating solvents and carbon precursors (expressed as toluene-insolubles) to solubilize the precursors. Thus, the catalysts used in the hydrogenating reactor are required to have a hydrogenation function and may have the same shape as those generally used in fixed-bed reactors. In addition, they may generally have the same composition as those used in hydrogenating treatments such as hydrolysis and hydrodesulfurization. In order to separate the circulating solvent fraction from the resulting reaction products, a conventional fractionator may be used. The fractionation may be carried out using two (first and second) fractionators, the first fractionator being used for separation of lighter fraction oils and the second one for separation of heavy fraction oils, or may be carried out using a single fractionator, a circulating solvent fraction being withdrawn from halfway along the single fractionator. The effects obtainable by the practice of the present invention are as follows. In cases where a heavy fraction oil is cracked in the presence of a hydrogen donating solvent, a hydrogen-containing gas and a catalyst capable of hydrogenation as indicated in the hydrocracking method of the present invention, the formation of carbonaceous substances is greatly inhibited, and the loss of the hydrogen donating solvent caused by the discharge thereof from the system is inhibited whereby the replenishment of makeup solvent is dispensed with. The present invention will be better understood by the following Examples and Comparative Examples. Example 1 An Arabian reduced-pressure heavy residual oil having the properties indicated in Table 1 was cracked by the method of Fig. 1 and under the conditions indicated in Table 2. Tetralin was used as the main hydrogen donating solvent. The cracking reactor used was of internal natural circulation type (Refer to US-A 4,640,765 for detailed information), the hydrogenating reactor used was of the downward current fixed bed type. Fractionators of the double-stage type were used to separate the lighter fraction oil at the first stage and to separate the heavy fraction oil at the second stage while recovering, at the second-stage the top circulating solvent fraction boiling in the range shown in Fig. 3. The catalyst used in the cracking reactor was one in which cobalt (4.0 wt.%) and molybdenum (11.5 wt.%) were supported on a silica-alumina carrier (porosity 53 c.c./g, surface area 190 m²/g, average pore radius 58 Å (5.8 nm) and extrusion molded to form 1/16 inch (1.5mm) extrusion molded catalyst particles which were housed in an annular cylindrical punched metal housing. The catalyst used in the hydrogenating reactor was 1/32 inch (0.75mm) extrusion molded catalyst particles in which cobalt (4.1 wt.%) and molybdenum (13.0 wt.%) were supported on a silica-alumina carrier (porosity 49 c.c./g, surface area 212 m²/g, average pore radius 58 Å (5.8 nm). The operation was continued at a cracking rate of 85 wt.% for 25 days to find changes in composition of the circulating solvent (Fig. 4) and changes in amount of the tetralin in the system (Fig. 5). Comparative Example 1 The procedure of Example 1 was followed except that the circulating solvent herein used had a boiling range which was different from that of the circulating solvent used in Example 1. The properties of the starting oil and hydrocracked oils are indicated in Table 1, the reaction conditions used in the cracking and hydrogenating reactors are indicated in Table 2, and the distillation curves of the circulating solvents, in comparison with that of Example 1, are shown in Fig. 3. In addition, Fig. 4 indicates the changes in tetralin concentration with the elapse of time of operation in the circulating solvents, and Fig. 5 shows the changes in tetralin concentration with the elapse of time of operation in the system in comparison with those exhibited in Example 1. Comparative Example 2 The procedure of Example 1 was followed except that the circulating solvent used herein had the same boiling range as that used in Comparative Example 1 and the cracking reactor contained no catalyst. The test results are shown, in comparison with those in Example 1 and Comparative Example 1, in Tables 1 and 2. Properties of Starting Oil and Product Oil Starting Oil Product Oil Ex.1 Com.Ex.1 Com.Ex.2 Specific gravity (d 15 / 4) 1.030 0.930 0.933 0.935 Viscosity (cSt) 145.3 (@160°C) 28.31 (@50°C) 30.15 (@50°C) 37.25 (@50°C) Residual carbon (wt.%) 22.52 8.35 8.71 9.13 Softening point (°C) 43.4 - - - Asphaltene (wt.%) (Pentane-insolubles) 13.3 3.0 3.2 6.1 Elemental analysis (wt.%) S 4.79 0.71 0.73 1.37 N 0.4 0.14 0.15 0.21 C 84.5 86.9 87.1 85.8 H 10.3 11.9 12.02 11.0 H/C (Atomic ratio) 1.46 1.64 1.66 1.54 Metal (ppm) V 143 21 22 70 Ni 46 15 15 31 Cracking ratio (wt.%) - 84.9 83.7 82.5 Item Cracking reactor Hydrogenating reactor Ex.1 Com. Ex.1 Com. Ex.2 Ex.1 Com. Ex.1 Com. Ex.2 Reaction temp. (°C) 437 437 437 370 370 370 Reaction pressure (kg/cm²) 80 80 80 80 80 80 LHSV (hr⁻¹) 0.4 0.4 0.4 0.25 0.25 0.25 Amount of fluid circulated (wt./wt. starting oil) 1.1 1.1 1.1 1.1 1.1 1.1 Amount of residual oil fed (g/hr) 700 700 700 - - - The information obtained from Figs. 3-5 is as follows. In cases where a circulating solvent having a broad boiling range is used (Comparative Examples 1 and 2), the tetralin concentration will gradually decrease with the elapse of time of operation, whereas in cases where a circulating solvent having a narrow boiling range is used (Example 1), the tetralin concentration in the solvent will decrease at the initial stage and then become constant. This indicates that in the case of the narrow boiling range, the amount of "other hydrocarbons" which invade to the circulating (or recycle) solvent is small and consequently an equilibrium concentration at which the amount of "other hydrocarbons" incorporated in the circulating solvent is equal to the amount of lighter hydrocarbons exhausted by further cracking the "other hydrocarbons" becomes low (equilibrium concentration of tetralin becoming high). It can be seen that the equilibrium concentration of tetralin in the circulating (or recycle) solvent is about 70 wt.% in Example 1. On the other hand, in the case of the broad boiling range, the tetralin concentration in the circulating solvent will continue to decrease since the equilibrium concentration is kept at a low level (Fig. 4). Further, the amount of tetralin in the system will not decrease in Example 1 and Comparative Example 1, but it will decrease with the lapse of time of operation in Comparative Example 2. In Example 1 and Comparative Example 1, tetralin and naphthalene are produced from the starting oil in an amount enough to make up for the amount of tetralin and naphthalene discharged as the loss from the system since the starting oil is cracked in the presence of both the hydrogen donating solvent and the catalyst, with the result that the amount of tetralin in the system decreases during a short time just after the start of the cracking operation and does not decrease after the elapse of the short time. In Comparative Example 2, on the other hand, tetralin and naphthalene are produced in less amount than in Example 1 and Comparative Example 1 since the crack is carried out in the presence of the hydrogen donating solvent only. In cases where a heavy fraction oil is cracked in the presence of both the catalyst and tetralin as mentioned above, it is possible to maintain the tetralin concentration in the circulating solvent at a predetermined level without decreasing the amount of tetralin in the system by using a circulating solvent having its boiling range narrowed to a certain extent. This enables the application of a hydrogen donating solvent to be employed with petroleum-based heavy fraction oils, which has heretofore been considered difficult.

Claims: A process of hydrocracking a heavy fraction oil which comprises the steps of: A) cracking a heavy fraction oil containing 1 wt.% up to 30 wt.% of asphaltene and at least 50 wt.% of a fraction boiling at at least 350°C. in the presence of a circulating flow comprising a hydrogen donating solvent and which is employed in an amount expressed by a ratio of 0.1-2.0 (wt/wt starting oil), hydrogen gas and a catalyst capable of hydrogenation in a cracking reactor at a temperature of 380°C. - 470°C., at a pressure of 30-150kg/cm²; B) hydrogenating the fractions obtained by the cracking of said heavy fraction oil, in the presence of a hydrogenating catalyst in a hydrogenating reactor at a temperature of 320°C-440°C. and a pressure of 30-150kg/cm²; C) separating the thus hydrogenated fractions into liquid and gaseous phases in a separator, fractionating the thus separated liquid phase in a distillation apparatus to obtain a specific fraction in which at least 90wt.% boils in the range of 150°C-250°C., at least 60wt.% boils in the range of 190°C-230°C. and at least 30wt.% is tetralin, and circulating said specific fraction as the circulating solvent through said cracking reactor, in the absence of added hydrogen donating solvent. The process according to claim 1, wherein said catalyst in the cracking reactor is a solid catalyst capable of demetallization. The process according to claim 1 or 2, wherein said catalyst in the cracking reactor and said catalyst in the hydrogenating reactor are both used in the form of a packed bed.

Inventors: KUBO, JUNICHI, SUZUKI, KENJI
Applicants: NIPPON OIL CO. LTD.
Application year: 1988
Main classification: C10G65
IPC codes: B01D3, C10G65, B01J23