METHOD FOR HYDROCRACKING HEAVY FRACTION OILS

Abstract: A method for hydrocracking a heavy fraction oil which comprises cracking a heavy fraction oil in the coexistence of a catalyst and a hydrogen donating solvent such as tetralin while adding a hydrogen-containing gas to the cracking reactor thereby inhibiting the formation of carbonaceous substances and precursors thereof and then hydrogenating the reaction products in the presence of a solid catalyst while adding a hydrogen-containing gas to the hydrogenating reactor thereby to convert the toluene-insoluble carbonaceous substances and precursors thereof to toluene-soluble ones, thus causing no clogging in an apparatus used.

Description: The present invention relates to a method for hydrocracking heavy fraction oils, particularly those containing at least 1.0 wt.% of asphaltene, that is, pentane-insoluble ingredients, using a hydrogen donating solvent. The hydrogenolysis of heavy fraction oils has recently been carried out to an increasing extent. Thus, there have been proposed many methods for thermal cracking, catalytic cracking, hydrogenolysis, etc. The heavy fraction oils used are hydrocarbon oils containing at least 50 wt.% of a fraction boiling at 350°C or higher, particularly heavy fraction oils containing at least 1.0 wt.% of pentane-insoluble ingredients, and they include residual oils obtained by the atmospheric or reduced pressure distillation of crude oils, and oils obtained from coal, oil shale, oil sand, bitumen and superheavy crude oils. The term "cracking" used herein is intended to indicate processes which give light fraction oils including naphtha, gasoline, kerosene and gas oil fractions by hydrocracking the heavy fraction oils. The most serious and troublesome problems raised by the cracking of heavy fraction oils are, in general, the formation of carbonaceous materials and the clogging of various parts of an apparatus for the cracking with the carbonaceous materials. Further, a serious problem caused by the catalytic cracking of the heavy fraction oils is a decrease in catalytic activity of the catalyst used. Still further, the cracking of the heavy fraction oils raises a problem as to an increase in amount of hydrogen consumed. These problems are rendered more serious the heavier the fraction oils to be cracked are. One of 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 obtained by hydrogenating polycyclic aromatic compounds, for instance, tetralin (tetrahydronaphthalene), serve as a hydrogen donor and that catalysts are not necessarily required for the hydrogenolysis of heavy fraction oils with the use of such a hydrogen donating solvent. 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 industrially this method (For example, U.S. Patent No. 2,953,513). It is also known that such hydrogen donating substances are contained in thermocracked oils, catalytically cracked oils, hydrocracked oils and the like and function, per se, as an effective hydrogen donating solvent (For example, U.S. Patent No. 3,970,545). In these known methods, since the cracking reaction takes place effectively only at comparatively high temperatures, the carbonaceous substances or precursors thereof are produced at the time of the cracking and clog the various parts of an apparatus for the cracking thereby hindering the long-term safe operation of the apparatus, this being the most serious problem. Further, Japanese Pat. Appln. Laid-Open Gazette No. 61-235492 which corresponds to EP-A-0 176 795 discloses the use of partitions made from a solid catalyst in a reaction tower to generate natural circulation of a liquid thereby obtaining the necessary liquid flow velocity to avoid clogging and the like with carbonaceous substances and that not only cracking reactions are effectively carried out, but also that the formation of carbonaceous substances is greatly reduced owing to the presence or use of a catalyst capable of hydrogenation in the reaction tower. The above techniques so disclosed enable the formation of carbonaceous substances and precursors thereof to be greatly inhibited, but they still permit small amounts of the carbonaceous substances and precursors thereof to be produced thereby raising problems as to clogging of the devices and piping used downstream of the reaction tower. The object of the present invention is to provide a method for effectively cracking heavy fraction oils containing at least 1.0 wt.% of asphaltene in the presence of a hydrogen donating solvent while inhibiting the formation of carbonaceous substances and lessening the clogging of the apparatus used for the cracking. The present inventors made various researches in the formation of carbonaceous substances at the time of cracking of heavy fraction oils and then found the following. (1) It is most effective to have a hydrogen donating solvent and a suitable catalyst coexist in a cracking reactor in order to inhibit formation of carbonaceous substances in the cracking reactor. (2) It is effective at the time of cracking that the amount of the catalyst present in the cracking reactor be larger than a certain amount to inhibit the formation of carbonaceous substances. (3) It is necessary that the catalyst used be high in catalytic activity and be capable of hydrogenation to attain effective inhibition. (4) It is possible to inhibit the formation of carbonaceous substances by maintaining at lower than a certain level the ratio of the amount of the starting heavy fraction oils treated to the amount of the catalyst used in the cracking reactor, the ratio being set in terms of liquid hourly space velocity (LHSV). (5) It is effective to increase the linear velocity of the liquid passing through the catalyst in the cracking reactor in order to avoid the clogging with the carbonaceous substances therein. (6) It is most suitable that the catalyst be filled to form a fixed bed in the cracking reactor. (7) The formation of the carbonaceous substances and precursors thereof in the cracking reactor will be inhibited by meeting the above various requirements; however, small amounts of the carbonaceous substances and precursors thereof still produced will be converted to toluene-soluble substances by a downstream fixed bed hydrogenating reactor maintained under suitable conditions. (8) The conditions under which the hydrogenating reactor is maintained are suitably such that the catalyst is present in at least a certain amount by volume relative to the volume of the reactor, the LHSV is kept suitably low, the hydrogenating activity of the catalyst is high and the temperature thereof is low as compared with that of the cracking reactor. The present invention is based on the above findings. More particularly, the above findings were utilized and a reactor was designed from the view-point of economy to accomplish the present invention. The method for cracking a heavy fraction oil according to the present invention, comprises (1) introducing a heavy fraction oil containing at least 1 wt.% of asphaltene (pentane-insoluble ingredients), a hydrogen donating solvent and a hydrogen-containing gas into (i) a cracking reactor in which at least one partition holding therein a solid catalyst in a total amount of at least 20% by volume of the interior of the cracking reactor is provided dividing the interior of the reactor into at least two parts, the divided parts communicate with each other at the upper and lower ends of the interior of the reactor, and the liquid (the oil and solvent) interiorly circulates at a linear speed of at least 2 cm/sec. around the at least one partition in the reactor or (ii) a cracking reactor in which a solid catalyst is held in an amount of at least 20% by volume of the interior of the cracking reactor and in the form of an upstream fixed bed, and recycled liquid (oil and solvent) is circulated externally of the reactor so that the liquid to be reacted passes through the fixed bed at a linear velocity of at least 2 cm/sec., (2) cracking the starting heavy fraction oil at a temperature in the range of from 380-470°C, at a pressure of from 30-150 Kg/cm².G and at a LHSV of not higher than 1 (hr⁻¹) (oil/catalyst) while adding hydrogen in such an amount that the amount of hydrogen consumed is at least 1 Nm³/kℓ-starting oil/%-cracking conversion so as to inhibit the formation of toluene-insoluble carbonaceous substances and precursors thereof in the cracking reactor (i) or (ii), (3) (i) passing the liquid and gases from the cracking reactor (i) to a hydrogenating reactor holding therein at least 50 vol.%, based on the interior of the hydrogenating reactor, of a solid catalyst in the form of a filler layer and maintained at a lower temperature than the cracking reactor or (ii) recycling a part of the liquid from the reactor (ii) and passing the remaining liquid and the gases from the reactor (ii) to the hydrogenating reactor, and then (4) hydrogenating the thus passed materials at a temperature in the range of from 330-440°C and 10 to 80°C lower than the temperature in the cracking, at a pressure of from 30 to 150 Kg/cm².G and at a LHSV of not higher than 0.5 (hr⁻¹) (oil/catalyst) while adding hydrogen to the hydrogenating reactor in such an amount that the amount of hydrogen consumed is at least 3 Nm³/kℓ-starting oil/%-cracking conversion thereby to convert the toluene-insoluble carbonaceous substances and precursors thereof to toluene-soluble ones. 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 is a block diagram illustrating another method for cracking heavy fraction oils according to the present invention; and Fig. 4 shows graphically the relationships between the cracking conversion and the content of toluene-insoluble ingredients in Example 1 and Comparative Examples 1-2. Referring now to Fig. 1, a starting heavy fraction oil l, a hydrogen donating solvent 2 and a hydrogen-containing gas 3 are introduced into a cracking reactor 4a. The cracking reactor 4a holds a solid catalyst in an amount of at least 20% by volume of the interior of the reactor. The cracked heavy fraction oil, hydrogen donating solvent and hydrogen-containing gas in the cracking reactor are then introduced, as the reaction mixture 5 and without being separated, into a hydrogenating reactor 6. The reactor 6 holds a catalyst in an amount of at least 50% by volume of the interior of the reactor 6. Carbonaceous substances and precursors thereof are inhibited from being formed in the cracking reactor 4a owing to the coexistence of the hydrogen donating solvent and the catalyst, but they are still formed in a small amount. The carbonaceous substances and precursors thereof which are still formed are hydrogenated for solubilization in the hydrogenating reactor 6. Thus, the resulting hydrogenation reaction mixture 7 substantially lacks such carbonaceous substances and precursors thereof. In industrial apparatuses, such a hydrogenation reaction mixture 7 is generally fractionated to obtain various fractions and recover the hydrogen donating solvent for recycled use. The hydrogenating reactor 6 used is of the usual type which holds therein a solid catalyst in the form of a filler layer. With reference to Fig. 2, a starting heavy fraction oil, a hydrogen donating solvent and a hydrogen-containing gas are introduced into a cracking reactor at the inlet 101 and through a distributor 102. The interior of the cracking reactor is divided vertically into two portions by a hollow cylindrical or annular partition 105 formed of a solid catalyst 104 held by a punched metal housing 103, the two portions communicating with each other at the upper and lower ends of the partition. It is necessary that the introduced hydrogen-containing gas flow through the inner portion of the cylindrical partition 105 without flowing outwardly through the partition. The same holds for the starting oil and hydrogen donating solvent. Bubbles of the hydrogen-containing gas ascend through the inner portion of the partition 105. Thus the zone in which the hydrogen-containing gas is present has a low specific gravity, thus causing pressure imbalance in the cracking reactor, and, therefore, a part of the liquid in the cracking reactor is circulated in the direction indicated by the arrow 107 in the reactor. In addition, a part 106 of the circulated liquid can pass through the partition 105 holding the catalyst 104 from the outside thereof (where the hydrogen-containing gas is absent) to the inside (where the hydrogen-containing gas is present). The said direction is indicated by the dotted arrow line. In this manner, a circulating flow is caused to occur and the necessary liquid flow velocity is ensured by providing the partition 105 in the cracking reactor. The hydrogen-containing gas ascends through the inner part of the cylindrical partition 105 and discharges out of the cracking reactor at the outlet 108, while the liquid circulates for a predetermined residence time and then discharges out of the reactor at the outlet 108. The partition holding the solid catalyst therein, is a porous body overall, and a part or the whole of the porous body is made of a solid catalyst. The partition is, as a whole, in the form of a thin porous flat or curved body which may be regarded as a sheet, and a part or the whole of the body is constituted of solid catalyst particles. The mesh size of punching metal sheet or wire mesh in which the solid catalyst is held, may be such that the solid catalyst is just not able to pass the mesh and the liquid is allowed to satisfactorily contact the solid catalyst particles. With reference to Fig. 3, a starting heavy fraction oil 1, a hydrogen donating solvent 2 and a hydrogen-containing gas 3 are introduced into a cracking reactor 4b. The cracking reactor 4b holds a solid catalyst in an amount of at least 20% by volume of the interior of the reactor. A part of the liquid cracked here, carbonaceous substances produced here and the hydrogen-containing gas pass, as cracked reaction mixture 5 and without being separated, into a hydrogenating reactor 6. The remainder of the liquid cracked in the cracking reactor 4b is, directly or preferably after separation of the hydrogen-containing gas from the liquid, re-introduced, as the circulating liquid (9), into the cracking reactor 4b by, for example, a circulation pump 8. When a small amount of the hydrogen-containing gas coexists with the liquid, it is not necessary to separate the gas from the liquid. The cracking reactor 4b is of a type in which a usual fixed bed holding a solid catalyst is provided so that the gas-liquid mixture flows upward. In addition, a reactor of the type disclosed in Japanese, Pat. Appln. Laid-Open Gazette No. 61-235492 (EP-A-0 176 795) may also be used. In the present invention, the amount of catalyst used in the cracking reactor is at least 20%, preferably 30-95% and more preferably 50-70%, by volume of the interior of the reactor. The use of the catalyst in an amount of less than 20 vol.% will have the catalyst exhibiting unsatisfactory catalytic effects and unsatisfactory inhibitory effects on the formation of carbonaceous substances in the cracking reactor. On the other hand, the amount of the catalyst used in the hydrogenating reactor is at least 50%, preferably 60-95% by volume of the interior of the reactor. The use of the catalyst in an amount of less than 50 vol.% will fail to make the best use of the volume of the hydrogenating reactor, this being undesirable from the economical view-point. In the present invention, it is necessary to maintain the linear velocity of the liquid at at least 2 cm/sec., preferably at least 3.5 cm/sec. in order to prevent the pressure loss from increasing in the cracking reactor. This may be attained by causing an internal circulating liquid flow to occur in the interior of the cracking reactor as indicated in Fig. 1 or by causing an external circulating liquid flow to take place as shown in Fig. 3. The internal circulating liquid flow is detailed in Japanese Pat. Appln. Laid-Open Gazette No. 61-235492 (EP-A-0 176 795) and it may be naturally generated by provision of the partition in the cracking reactor as mentioned above and outlined in Fig. 2 or may also be forcibly generated by provision of a pump or the like at the distributor located in the lower part of the partition. The most serious problem which occurs when heavy fraction oils are cracked is the formation of carbonaceous substances and the consequent clogging. The problem may be somewhat solved by the use of the hydrogen donating solvent, but carbonaceous substances are still formed whereby the reactor, other devices and piping are clogged, this hindering the operation of stable cracking. In general, the cracking is effected without the use of the catalyst in a case where the hydrogen donating solvent is used. In this case, however, the formation of carbonaceous substances and precursors thereof is greatly inhibited by using a hydrogenating catalyst. It is preferable that the hydrogenating catalyst used herein be a catalyst capable of hydrogenation and demetallization. By using such a preferable catalyst, heavy metals, such as vanadium and nickel, contained in a heavy fraction oil are removed and attached to the catalyst while cracking the oil, whereby the amount of the heavy metals being brought into the next hydrogenating reactor decreases, thus greatly preventing the catalyst in the hydrogenating reactor from undergoing deterioration in catalytic activity. Further, it is necessary that the catalyst used in the cracking reactor have catalytic activity above a certain level. Inhibition of the formation of carbonaceous substances is attained as a result of the catalyst being present in a comparatively large amount in the cracking reactor and the ratio of the amount of the oil treated to that of the catalyst in the reactor, that is a LHSV, being low. When the catalyst used is a presently commercially available one, it is necessary that the LHSV in the cracking reactor be 1 (hr⁻¹) or lower, preferably 0.1-0.8 (hr⁻¹), and that in the hydrogenating reactor it be 0.5 (hr⁻¹) or lower. It is the amount of hydrogen consumed that indicates how far or to what extent the formation of carbonaceous substances is inhibited in the present invention. This is because consumption of a large amount of hydrogen means that the cracked products are hydrogenated and thereby stabilized. This may be considered to express the function of the catalyst. In general, the carbonaceous substances and precursors thereof are expressed in terms of toluene-insoluble ingredients (wt.%). Assuming that the amount of toluene-insoluble ingredients contained in the liquid at the outlet of the cracking reactor should be up to 1 wt.% and that in the liquid at the outlet of the hydrogenating reactor it should be up to 0.05 wt.% to allow an apparatus used in the present invention to operate stably without raising any problem as to the clogging of the apparatus with carbonaceous substances formed, the amount of hydrogen consumed in the cracking reactor should be at least 1 Nm³/kℓ-starting oil/%-cracking conversion (the amount of hydrogen consumed per cracking conversion 1%), preferably 1.2-10 Nm³/kℓ-starting oil/%-cracking conversion, and that in the hydrogenating reactor should be at least 3 Nm³/kℓ-starting oil/%-cracking conversion, preferably 5-150 Nm³/kℓ-starting oil/%-cracking conversion. In other words, it is necessary for the above purpose that the amounts of hydrogen corresponding to those consumed as indicated above be supplied respectively to the cracking and hydrogenating reactors. The term "cracking conversion" used herein is defined as follows: In principle, the catalyst in the cracking reactor may be fluidized in order to prevent clogging in the apparatus for cracking, but a complicated apparatus is required for this purpose and catalyst concentration decreases, this being undesirable. When the heavy fraction oil is cracked in the presence of both the hydrogen donating solvent and the catalyst, carbonaceous substances and precursors thereof will be produced in the form of fine particles and they will be easily carried away by the flow of the liquid. It is accordingly unnecessary to fluidize the catalyst particles in order to avoid the clogging in the cracking reactor, and the clogging may be avoided by maintaining the linear velocity of the liquid at 2 cm/sec. or higher in the cracking reactor. The carbonaceous substances and precursors thereof so carried away from the cracking reactor are subjected to hydrogenation treatment for solubilization in the subsequent hydrogenating reactor. The above is an important finding which the present inventors have experimentally made and is due to the fact that the preceding cracking is effected in the presence of both the hydrogen donating solvent and the catalyst. This finding according to the present invention enables the formation of carbonaceous substances, which has heretofore been inevitable at the time of cracking heavy fraction oils, to be substantially prevented. When the cracking is carried out in the presence of both the hydrogen donating solvent and the catalyst, it will proceed at comparatively low temperatures and pressures although conventional cracking in the presence of only the hydrogen donating solvent requires high temperatures. In the method of the present invention, the temperature of the cracking reactor is to be in the range of 380-470°C to effect the cracking. In addition, very high hydrogen pressures are not necessary for the cracking, and pressures of 30-150 Kg/cm².G are satisfactory therefor because of the presence of the hydrogen donating solvent and are to be used. On the other hand, it is necessary that the hydrogenating reactor be maintained at a lower temperature, 10-80°C lower, than the cracking reactor. The reason for this is that a small amount of carbonaceous substances and precursors thereof produced in the cracking reactor is hydrogenated for solubilization and the formation of such carbonaceous materials is prevented in the hydrogenating reactor. The temperature and pressure used in the hydrogenating reactor are 330-440°C and 30-150 Kg/cm².G, respectively. In the present invention, the hydrogen donating solvent may be added in a ratio of the solvent/the starting oil by weight of 0.3-3, preferably 0.5-2. In the subsequent hydrogenating reactor, the hydrogenation of the cracked products and hydrogen donating solvent is mainly carried out. In this hydrogenating reaction the carbonaceous substances and precursors thereof produced by the preceding cracking reaction are hydrogenated for solubilization and the cracked oil products are simultaneously subjected to hydrofining such as hydrodesulfurization and hydrodenitrification. The hydrogen donating solvents used in the present invention may be hydrocarbons containing at least 30 wt.% of hydrogenated polycyclic aromatic hydrocarbon. 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. In addition, compounds boiling in the range of 150-500°C and containing at least 30 wt.% of hydrogenated polycyclic aromatic hydrocarbons, may also be used as a hydrogen donating solvent. These solvents include recycle oils in an apparatus for catalytic cracking (FCC), bottom oils in catalytic reforming apparatus, bottom oils in an apparatus for thermocracking naphtha, and other oil products obtained from petroleum refining apparatuses, 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, bitumen and the like. The catalysts used in the present invention are not particularly limited and may be usual ones, but the catalysts used in the cracking reactor are required to have a hydrodemetallizing function and should preferably be such that they will be comparatively little degraded in catalytic activity when heavy metals, such as vanadium and nickel, are attached to them. The catalysts used in the hydrogenating reactor are required to have a hydrodesulfurization function and may therefore be desulfurizing catalysts. These catalysts of solid form include the oxides and sulfides of Group VIII metals of the Periodic Table such as nickel and cobalt as well as of Group VIB Group 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 not particularly limited in shape. They may be spherical in shape and may be formed by extrusion molding or compression molding. It is desirable that these catalysts have a particle size of 0.01-10 mm, preferably 0.1-5 mm. The hydrogen-containing gas used in the present invention is preferably a gas containing at least 70 wt.% of hydrogen, and is, for example, a hydrogen-containing gas from reforming apparatuses. This invention will be better understood by the following Examples and Comparative Examples. Example 1 An experiment was carried out in accordance with Fig. 1 to hydrocrack Arabian Heavy reduced-pressure residual oils. The cracking reactor used in this Example was internal natural circulation liquid flow-type reactor (Japanese Pat. Appln. Laid-Open No. 61-235492-EP-A-0 176 795) as shown in Fig. 2. This reactor is of the type in which the interior is partitioned into two parts (inner and outer parts) by the catalyst annularly held in a perforated metal sheet and the internal natural circulation of the liquid is caused to take place by passing the hydrogen-containing gas only through the inner (or central) part. The properties of the starting oils, the shape and size of the cracking and hydrogenating reactors, and the operational conditions are indicated in Tables 1, 2 and 3, respectively. The hydrogen donating solvent used was tetralin. The starting oil and tetralin were charged in a ratio by weight of 1:1 into the cracking reactor. The resulting reaction products were recovered, freed of the tetralin and then had their properties determined. The operation was successively carried out for 720 hours without increasing the pressure loss. The properties of the products at the outlets of the cracking and hydrogenating reactors, together with those of the starting, are indicated in Table 1. The amounts (wt.%) of the carbonaceous substances are difficult to measure and are therefore indicated in terms of those of those ingredients which are toluene-insoluble. The catalyst used was a commercially available extrusion molded type catalyst (particle size: 1/32 inch (0.08 mm)) consisting of cobalt and molybdenum carried on silica-alumina. After the completion of the experiment, the apparatus used was opened for inspection with the result that no carbonaceous substances were found deposited in the reactors and piping. Comparative Example 1 The procedure of Example 1 was followed except that no catalyst was present in the cracking reactor and only the hydrogen donating solvent (tetralin) was present therein for cracking. One hundred and twenty (120) hours after the start of the cracking operation, clogging took place in the pipe at the outlet of the cracking reactor and in the catalyst layer of the hydrogenating reactor thereby increasing the pressure drop, and, therefore, the experiment was stopped. The properties of the products present at the outlets of the cracking reactor and hydrogenating reactor are shown in Table 1. After the end of the experiment, the apparatus used was opened for inspection with the result that carbonaceous substances were found deposited even in the piping downstream of the hydrogenating reactor. Comparative Example 2 The procedure of Example 1 or Comparative Example 1 was followed except that the catalyst was placed in the cracking reactor in an amount of 10% by volume of the interior thereof, and the catalyst was fluidized by the internal natural circulating liquid flow. In addition, experiments were carried out in which the LHSV relative to the catalyst in the cracking reactor was varied by changing the amount of the starting heavy fraction oil charged. The results of these experiments are indicated in Fig. 4. This figure shows the amounts (wt.%/starting oil) of the toluene-insoluble ingredients plotted with respect to the cracking rates (545°C base) at the outlet of the cracking reactor for different LHSV values. This figure, thus shows the results of Example 1 for comparison and also the properties of the products obtained by selecting a LHSV of 1.0. Example 2 An experiment was made to thermocrack Arabian Heavy reduced-pressure residual oils in accordance with the process as shown in Fig. 3. The cracking reactor used had an upstream fixed bed therein and an external circulating liquid flow, and the hydrogenating reactor had a downstream fixed bed therein. The properties of the starting oil, the shape and size of the reactors and the operational conditions, are indicated respectively in Tables 1, 2 and 3. Tetralin was used as the hydrogen donating solvent. The starting oil and tetralin were charged in a ratio by weight of 1:1 into the cracking reactor. The resulting reaction products were recovered, freed of the tetralin and then were evaluated. Operation was continuously performed for 680 hours without increasing the pressure loss. Table 1 shows the properties of the products at the outlets of the cracking and hydrogenating reactors, together with the properties of the starting oil. The carbonaceous substances were difficult to measure and were therefore expressed in terms of toluene-insoluble ingredients. In addition, the catalyst used was the same as used in Example 1. After the end of the experiment, the apparatus used was opened for inspection with the result that no carbonaceous substances were found to have deposited in the reactors and piping. Comparative Example 3 The procedure of Example 2 was followed except that no catalyst was used in the cracking reactor and the cracking was carried out in the presence of the hydrogen donating solvent only. After the operation had been performed for 100 hours, clogging took place in the cracking reactor, in the pipe at the outlet of the cracking reactor and in the catalyst layer of the hydrogenating reactor thereby increasing the pressure loss and stopping the experiment. The properties of the products at the outlets of the cracking and hydrogenating reactors are shown in Table 1. Further, after the end of the experiment, the apparatus was opened for inspection with the result that carbonaceous substances were found to have deposited even in the cracking reactor, in the piping downstream of the hydrogenating reactor. Comparisons between Example 1 and Comparative Examples 1, 2 and between Example 2 and Comparative Example 3 show the following. (1) Hydrogenation of cracked products is accelerated and the formation of toluene-insoluble ingredients (carbonaceous substances and precursors thereof) is greatly inhibited in the cracking reactor by using the hydrogen donating solvent and the catalyst in combination, increasing the ratio of volume of the catalyst present in the cracking reactor and keeping LHSV (starting heavy fraction oil (g/hr)/catalyst (g)) at a low level. More specifically, as is apparent from Table 1 and Fig. 4, the amounts (wt.%) of the toluene-insoluble ingredients formed are greater in the following increasing order: Example 1 < Comparative Example 2 < Comparative Example 1, and, in addition, Example 2 < Comparative Example 3. As is shown in Fig. 4, the amount of toluene-insoluble ingredients formed will increase if LHSV used increases at the same cracking conversion. (2) The toluene-insoluble ingredients will decrease in amount by introducing the reaction products into the subsequent hydrogenating reactor for hydrogenation. As is apparent from Table 1, the amounts of toluene-insoluble ingredients at the outlet of the hydrogenating reactor decrease as compared with those at the outlet of the cracking reactor in Examples 1-2 and Comparative Examples 1-3. (3) By means of the hydrocracking process of the present invention, it is possible to inhibit the formation of carbonaceous substances and precursors thereof in the cracking reactor and reduce toluene-insoluble ingredients to zero at the outlet of the hydrogenating reactor (Table 1). (4) A small amount of carbonaceous substances and precursors thereof is still produced in the cracking reactor, but the pressure loss in the cracking reactor will not be increased by maintaining the linear velocity of the liquid at 2 cm/sec. or higher (the results of Examples 1-2). (5) The pressure loss will not increase in the hydrogenating reactor. More particularly, the pressure loss in the hydrogenating reactor will not increase since the formation of the carbonaceous substance is inhibited in the cracking reactor and the carbonaceous substances and precursors thereof are solubilized in the hydrogenating reactor. As is clear from the above results, the cracking method of the present invention is capable of inhibiting the carbonaceous substances, eliminating the problem of clogging and rendering possible the long-term stable operation of the apparatus for cracking. The effects obtained by the practice of the present invention are summarized as follows. (1) The formation of carbonaceous substances and precursors thereof is inhibited. As previously mentioned, the combined use of the hydrogen donating solvent and the catalyst, the use of the catalyst in an amount larger than a certain one and the maintenance of LHSV at a low level, will enable the carbonaceous substances and precursors thereof to be formed in a reduced amount which is lower than 1/10 of the amount formed in the case of non-use of the catalyst. (2) Clogging is avoided in the cracking reactor. As previously mentioned, an increase in the pressure loss will be avoided by maintaining the linear velocity of the liquid at 2 cm/sec. or higher since the carbonaceous substances and precursors thereof are formed in a small amount in the cracking reactor and they have a fine particle size. (3) Clogging of the piping and devices provided between the cracking reactor and the hydrogenating reactor is avoided. It has been necessary to remove solid particles (carbonaceous substances) downstream of the cracking reactor in conventional cracking methods. In the method of the present invention, however, it is not necessarily required to remove the solid particles unlike the conventional methods since the carbonaceous substances and precursors thereof may be introduced in the subsequent hydrogenating reactor. For this reason, the piping between the cracking reactor and the hydrogenating reactor can be simplified whereby clogging is avoided. (4) No clogging takes place in the hydrogenating reactor. The catalyst is held in the form of a fixed bed in the hydrogenating reactor. The pressure loss will not increase in the hydrogenating reactor since the carbonaceous substances and precursors thereof are solubilized in said reactor in the present invention although an increase in pressure loss in the catalyst layer raises a problem in the conventional methods. (5) There is no problem of clogging of the apparatus and piping provided downstream of the hydrogenating reactor. As mentioned before, substantially no solid matter is present in the piping and devices provided downstream of the hydrogenating reactor since the carbonaceous substances and precursors thereof are solubilized in the reactor. Accordingly, the hitherto serious problem as to the clogging has been solved by the practice of the present invention.

Claims: A method for hydrocracking a heavy fraction oil which comprises the steps of: (1) introducing said heavy fraction oil containing at least 1 wt.% of asphaltene (pentane-insoluble ingredients), a hydrogen donating solvent and a hydrogen-containing gas into a cracking reactor in which at least one partition holding therein a solid catalyst in a total amount of at least 20% by volume of the interior of the cracking reactor is provided thereby dividing the interior of the reactor into at least two parts, the thus divided parts communicating with each other at the upper and lower ends of the interior of the reactor, and the liquid comprising said oil and solvent interiorly circulates at a linear velocity of at least 2 cm/sec. around the partition holding therein a solid catalyst, (2) cracking said heavy fraction oil at a temperature in the range of from 380-470°C, at a pressure of from 30-150 Kg/cm².G and at a LHSV of not higher than 1 (hr⁻¹) (oil/catalyst) while adding hydrogen in such an amount that the amount of hydrogen consumed is at least 1 Nm³/kℓ-starting oil/%-cracking conversion thereby to inhibit the formation of toluene-insoluble carbonaceous substances and precursors thereof in the cracking reactor, (3) passing the liquid and gases from the cracking reactor to a hydrogenating reactor holding therein at least 50 vol.%, based on the interior of the hydrogenating reactor, of a solid catalyst in the form of a filler layer and maintained at a lower temperature than the cracking reactor and then (4) hydrogenating the thus passed materials at a temperature in the range of from 330-440°C and 10-80°C lower than the temperature in the cracking at a pressure of from 30 to 150 Kg/cm².G and at a LHSV of not higher than 0.5 (hr⁻¹) (oil/catalyst) while adding hydrogen to the hydrogenating reactor in such an amount that the amount of hydrogen consumed is at least 3Nm³/kℓ-starting oil/%-cracking conversion thereby to convert the toluene-insoluble carbonaceous substances and precursors thereof to toluene-soluble ones. A method for hydrocracking a heavy fraction oil which comprises, the steps of: (1) introducing said heavy fraction oil containing at least 1 wt.% of asphaltene (pentane-insoluble ingredients), a hydrogen donating solvent and a hydrogen-containing gas into a cracking reactor in which a solid catalyst is held in an amount of at least 20% by volume of the interior of the cracking reactor and in the form of an upstream fixed bed, and recycled liquid comprising oil and solvent is circulated externally of the reactor so that the liquid to be reacted passes through the fixed bed at a linear velocity of at least 2 cm/sec., (2) cracking said heavy fraction oil at a temperature in the range of from 380 to 470°C and a pressure of from 30-150Kg/cm².G and at a LHSV of not higher than 1 (hr⁻¹) (oil/catalyst) while adding hydrogen in such an amount that the amount of hydrogen consumed is at least 1 Nm³/kℓ-starting oil/%-cracking conversion thereby to inhibit the formation of toluene-insoluble carbonaceous substances and precursors thereof in the cracking reactor, (3) recycling a part of the liquid from the cracking reactor and passing the remaining liquid and the gases from the cracking reactor to a hydrogenating reactor and then (4) hydrogenating the thus passed materials at a temperature in the range of from 330-440°C and 10-80°C lower than the temperature in the cracking, at a pressure of from 30 to 150Kg/cm².G and at a LHSV of not higher than 0.5 (hr⁻¹) (oil/catalyst) while adding hydrogen to the hydrogenating reactor in such an amount that the amount of hydrogen consumed is at lest 3 Nm³/kℓ-starting oil/%-cracking conversion thereby to convert the toluene-insoluble carbonaceous substances and precursors thereof to toluene-soluble ones. A method according to claim 1 or 2, wherein the hydrogen donating solvent is a hydrogenated polycyclic aromatic compound. A method according to any preceding claim, wherein the hydrogen donating solvent is boiling at 150-500°C and is the hydride of a hydrocarbon oil containing aromatic hydrocarbons in an amount of at least 30 wt.%. A method according to any preceding claim, wherein the catalyst held in the cracking reactor has a hydrodemetallizing function. A method according to any preceding claim, wherein the catalyst held in the hydrogenating reactor has a hydrodesulfurizing function.

Inventors: KATO, HIROSHI, KATO, KIYOSHI, KUBO, JUNICHI, SATO, MASARU, YAMASHITA, TADAKAZU
Applicants: NIPPON OIL CO. LTD.
Application year: 1987
Main classification: C10G65
IPC codes: C10G47, C10G65