BE737036A - Removal of nitrogen compounds from hydrocarbons - before hydrocracking - Google Patents

Abstract

Hydrocarbon charges containing nitrogen compounds and condensed polycyclic aromatic compounds are treated to improve their quality by initially passing the hydrocarbon charge in contact with a hydrogenation catalyst, and then in contact with a hydrogenolysis catalyst having an appreciable cracking activity. The elimination of nitrogen from the hydrocarbon charge, and the hydrogenation of the polycyclic aromatic compounds is effected by means of the hydrogenation catalyst, under hydrogenation conditions with a decreasing temp. profile selected in a manner to assure complete hydrogenation of the polycyclic aromatic compounds after the elimination of the combined nitrogen of the charge. Hydrogenation is pref. carried out in two stages, the first stage eliminating nitrogen from the charge, and the second state, which is preferred at a lower temp. hydrogenating the polycyclic aromatic compounds. The product is then subjected to hydrocracking in the presence of a hydrocracking catalyst sensitive to nitrogen.

Description

  

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  Multi-stage catalytic process for the improvement by hydrocracking of a hydrocarbon feed containing sulfur and nitrogen compounds.



   Hydrocracking is useful for converting relatively refractory foods containing high boiling polycyclic aromatic compounds and other high boiling point hydrocarbons to lower boiling products. , such as gasoline and middle distillates. These refractory feeds with a high boiling point, when they are admitted to catalytic cracking carried out in the appreciable absence of hydrogen, cause an abundant deposit.

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 of coke on the catalyst and therefore greatly diminishes its activity and its ability to maintain production.

   Current hydrocracking processes generally involve two or more catalytic treatment zones comprising a first zone for the preliminary hydrogenation of the feed and one or more zones for hydrogenolysis of the hydrocarbons. The combination of the prior hydrogenation with the subsequent hydrogenolysis of the hydrocarbons is generally called hydrocracking. Further, the pre-hydrogenation is often referred to as "pre-treatment" and the hydrogenolyses of hydrocarbons are often referred to as "hydrocracking". Consequently, by "hydrocracking" is meant in the literature not only the overall operation, but also the operations which follow the prior hydrogenation. For the purposes of the invention, the term "hydrocracking" is used in the latter sense.



   Prehydrogenation is normally carried out with a view to reducing the sulfur and nitrogen content of the feed by converting compounds containing these elements to hydrogen sulfide and ammonia, respectively. It has been found that the nitrogen-containing compounds which commonly exist in relatively heavy hydrocracking feeds have the unfavorable effect of lowering the cracking activity of most hydrocracking catalysts and often accelerating the cracking activity of most hydrocracking catalysts. deactivation of the catalyst. When this is so, frequent regenerations become necessary for the maintenance of a required hydrocarbon conversion rate during hydrocracking.

   The deleterious effects of nitrogen, sulfur and carbonaceous residue are particularly evident when an amorphous or non-crystalline based hydrocracking catalyst is used for the hydrocracking operations. Hydrocracking catalysts comprising crystalline aluminosilicate are less severely affected by nitrogen and carbon compounds.

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 sulfur feed as amorphous based hydrocracking catalysts, but many hydrocracked petroleum fractions contain organic nitrogen compounds in high amounts which have a significant adverse effect on the activity of these various catalysts.

   Therefore, the hydrocarbon feed which is to come into contact with a hydrocracking catalyst containing a crystalline aluminosilicate must also undergo prior hydrogenation lowering the sulfur and nitrogen concentrations to low. required value allowing the best exploitation of the catalyst.



   A hydrocracking catalyst containing a crystalline aluminosilicate generally exhibits more cracking activity for relatively large fractions of a hydrocarbon feed and better conversion selectivity than an amorphous based catalyst. These properties of hydrocracking catalysts containing a crystalline aluminosilicate have favored their use for hydrocracking.



  However, catalysts containing crystalline aluminosilicate suffer from the disadvantage that their cracking ability of relatively high molecular weight polycyclic hydrocarbons and especially condensed polycyclic aromatic and hydroaromatic hydrocarbons is poorer than that of hydrocracking catalysts based. amorphous. This is probably so due to the limitations to interparticle diffusion resulting from the relatively small pore size of crystalline aluminosilicates.

   Thus, when a hydrocracking catalyst containing a crystalline aluminosilicate is used, the pores of which have a diameter of 6 to 15 and when all or part of the unconverted heavy hydrocarbons are recycled from a single pass operation to depletion or when carrying out a new conversion of these hydrocarbons in a

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 As a separate conversion zone, it is necessary to control the concentration of polycyclic aromatic hydrocarbons in the feed coming into contact with a crystalline aluminosilicate catalyst, especially in the hydrocracking zone.



  Otherwise, the concentration of polycyclic hydrocarbons steadily increases in the recycle stream in the hydrocracking zone and, upon recycle, has an additional adverse effect on the selectivity and cracking activity of the based catalyst. crystalline aluminosilicate.



  In the case of hydrocracking catalysts with an amorphous base, their activity, on the other hand, is affected more unfavorably than that of catalysts based on crystalline aluminosilicate under the conditions of hydrocracking by excessive concentrations of nitrogen compounds. in hydrocarbons.



   The accumulation of polycyclic aromatic hydrocarbons containing, for example, three condensed rings or more at the hydrocracking stage results in an acceleration of the aging of one catalyst or the other and requires more frequent regeneration of the catalyst. On the other hand, the catalyst used in the pre-hydrogenation zone for the removal of sulfur and nitrogen compounds is deactivated by nitrogen compounds and condensed polycyclic aromatic hydrocarbons from the feed, when it is used under certain selected pre-treatment conditions, much less rapidly than a hydrocracking catalyst based on amorphous, crystalline aluminosilicate based or based on a mixture of such catalysts, used under the conditions hydrocracking.

   catalysts for pretreatment do not need to be regenerated as frequently as hydrocracking catalysts, but since pretreatment and hydrocracking are carried out successively, these operations should be discontinued when the catalyst needed for one 'between them must

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 be regenerated. Consequently, regeneration of the catalyst for only one of the operations results in economic disadvantages: because it is necessary to stop the operation of the installation. The efficiency of the operations is greater and the economy greater if the regeneration of the prior hydrogenation catalyst and that of the hydrocracking catalyst are simultaneous, because the service time is better exploited.

   To improve the efficiency of the operations, it is therefore advantageous to reduce the rate of aging of the hydrocracking or hydrogenolysis catalyst so that it becomes close to that of the prior hydrogenation catalyst.



   Currently, the rate of aging of a hydrocracking catalyst is improved by choosing feeds with a limited concentration of polycyclic aromatic hydrocarbons. This choice of feed, however, results in many drawbacks, because the flexibility of application of the method for the convection of many feeds is limited. Further, since the activity of the hydrocracking catalyst decreases with service life, its ability to convert polycyclic aromatic hydrocarbons is significantly reduced and the amount of polycyclic aromatic hydrocarbons allowable in the feed varies with time. on duty.

   The hydrocracking catalyst may initially be active enough to convert feed hydrocarbons other than polycyclic aromatics, but this activity is rapidly attenuated by condensed polycyclic aromatics resulting in undesirable build-up of underconverted hydrocarbons and polycyclic aromatic hydrocarbons in the recycle stream. It then becomes necessary to regenerate the hydrocracking catalyst more often than desired in order to maintain its activity for the conversion of hydrocarbons comprising aromatic compounds.

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 polycondensed.



   The invention relates to improving the quality of a hydrocarbon feed of petroleum boiling at about 204 to 593 C and containing sulfur compounds, nitrogen compounds and polycyclic compounds with three condensed rings or more. . In the process of the invention, the hydrocarbon feed is passed successively through a zone for the preliminary hydrogenation of the feed under conditions specified below where the concentration of sulfur and nitrogen compounds is reduced to a desired value which is less than about 100 ppm and preferably less than about 10 ppm nitrogen and wherein the polycyclic compounds are hydrogenated, the feed then entering one or more hydrocracking zones in the presence of a suitable hydrocracking catalyst.



  The effluent from the pretreatment zone is fractionated into a hydrocarbon feed containing less than 100 ppm and preferably at most 5 ppm of nitrogen and, on the other hand, unchanged hydrogen, ammonia, water and sulfur dioxide. 'hydrogen. Larger amounts of nitrogen remaining in the effluent are permissible when using crystalline aluminosilicate rather than amorphous hydrocracking catalysts. The collected and purified hydrogen-rich gas can be recycled if desired.

   The hydrocarbon stream from the pretreatment, having an acceptable sulfur and nitrogen content and containing more hydrogenated polycyclic compounds, is then brought to hydrocracking in one or more separate hydrocracking zones. As a more particular aspect of the invasion, sulfur and nitrogen are removed from the hydrocarbon feed at a relatively high temperature, i.e. above about 385 C, and the more complete hydrogenation of the polycyclic compounds of the feed is carried out at a lower hydrogenation temperature which is

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 less than about 371 C,

   but preferably greater than about 260 ° C. The hydrogenation of the polycyclic compounds is carried out at temperatures defined below, which are lower than those required for the removal of sulfur and nitrogen from the hydrocarbon feed when a pre-hydrogenation catalyst is used which has relatively little or no cracking activity. It is preferable during the pretreatment of the feed to limit the conversion to products whose boiling point falls below the initial boiling point of the feed to about 20% or more lower.

   The effluent obtained by hydrocracking the feed thus treated beforehand is separated under conditions which allow the isolation of the lower boiling point products which may be required, such as gasoline and a middle distillate, from a stream. A higher boiling point hydrogenated hydrocarbon comprising hydrocarbons which must be further converted and in particular insufficiently converted polycyclic compounds. This insufficiently converted hydrocarbon stream separated from the effluent from the hydrocracking can be subjected to a new hydrocracking during a new hydrocarbon conversion using the same or different catalyst or it can be subjected to a new hydrocracking. recycled before treatment or hydrocracking.

   For example, this insufficiently converted hydrocarbon stream can be combined with the hydrocarbon effluent from the pretreatment to form a hydrocarbon feed admitted to the first of the hydrocracking zones. It is, however, preferable that this insufficiently converted recycle stream is subjected to a further hydrogenation treatment under conditions which advance the hydrogenation of the insufficiently converted compounds, in particular the polycyclic compounds, before they have undergone. a new sensible conversion.

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   The effluent from the preliminary hydrogenation, the recycled stream from the hydrocracking and the fresh feed arriving at the pretreatment can be observed substantially continuously or alternatively intermittently for the determination of the aromatic hydrocarbon concentration. condensed polycyclic of more than 2 and preferably about 3 to 7 condensed unsaturated rings. The results of the measurements make it possible to adjust the conditions at the stage of the preliminary hydrogenation of the feed, so as to ensure a more complete hydrogenation of the polycyclic aromatic hydrocarbons which reach the hydrocracking.

   The concentration of polycyclic aromatic compounds, as can be measured by locating the predominant maximum of the absorption spectrum in the visible and ultraviolet between about 3000 and 5000, can be limited in the hydro-carbon stream reaching the initial hydrocracking zone at values falling within the intervals below. If this stream contains condensed polycyclic aromatic compounds which substantially absorb light between about 4000 and 5000, the concentration of these compounds is limited to a maximum of 350 p.p.m, and preferably to a maximum of about 100 p.p.m.



  On the other hand, if the stream does not contain polycyclic aromatic compounds which substantially absorb light between about 4000 and 5000, the concentration of condensed polycyclic aromatics substantially absorbing light between about 3000 and 4000 is used for regulation. and is limited to a maximum value of 10,000 p. p.m. and preferably at a minimum value of about 1000 p.p.m.



   Details of light absorption by aromatic compounds warrant the details given for accuracy in the discussion below. For example, phenylperylene, which is a polycyclic aromatic compound,

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 contains 6 aromatic rings of which 5 are condensed (i.e. contain at least 2 carbon atoms in common with one another) and one of which is not condensed (i.e. is a ring united to one other but without a common carbon atom). This compound absorbs light (1) as an aromatic compound comprising 5 condensed rings and (2) as a monocyclic aromatic compound.



  However, it does not absorb light in the vicinity of the wavelength at which the corresponding aromatic compounds of 6 condensed rings absorb light. In absorption spectroscopy, a reference to an aromatic polycyclic compound therefore does not identify the precise number of condensed rings. A reference to a polycyclic compound of X rings, on the other hand, indicates only that the compound comprises X condensed rings, but not that it comprises only the X rings in question, since the number of rings can be. equal to or greater than X.



   It should be noted that the pre-hydrogenation zone and the hydrocracking zones involved in the process of the invention can be housed in two or more reactors and that devices are provided for removing the H2S and the NH3. formed from the feed which has undergone the pretreatment, either before or after a more complete hydrogenation of the polycyclic constituents and before the admission of the feed to the catalytic hydrocracking in the presence of a catalyst more sensitive to nitrogen.



   It has been found that by subjecting the feed to a preliminary hydrogenation to limit the amount of nitrogen of the feed admitted to hydrocracking to a value less than about 100 ppm and preferably less than about 10 or even sometimes 5 ppm and by carrying out together the more complete hydrogenation of the polycyclic aromatic compounds of 3 or more condensed rings in the hydrocarbon stream arriving at the hydrocracking, the catalyst can be used.

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 more efficient hydrocracking for the conversion of hydrocarbons to the desired lower boiling point products.



  Further, by controlling the severity of the prior hydrogenation and hydrogenation of the polycyclic compounds, according to the invention, a convenient method is provided for imparting a more favorable value to the rate. aging of the hydrocracking catalyst without having an adverse effect on the production rate.



   The pre-hydrogenation catalyst used in the process of the invention comprises a hydrogenation component dispersed on a suitable carrier exhibiting relatively moderate or else little or no cracking activity compared to that of a catalyst. Hydrocracking, amorphous or containing crystalline aluminosilicate, but exhibiting very substantial or great hydrogenation activity. Depending on the hydrogenation activity of the pre-hydrogenation catalyst, the reaction in the pre-hydrogenation zone can be dictated by the hydrogenation-dehydrogenation equilibrium or by the rate constants.

   For a pressure and for a determined contact time in the preliminary hydrogenation zone, the hydrogenation of the polycyclic compounds in this zone and therefore the concentration of the polycyclic aromatic hydrocarbons in the effluent depends (1) on the temperature and (2 ) because the reaction in the pre-hydrogenation zone is dictated by the reaction rate or the hydrogenation-dehydrogenation equilibrium. In such a system, when the reaction is dictated by the rate constants, the concentration of polycyclic aromatic hydrocarbons can be lowered either by increasing the temperature or by decreasing the space speed.

   When the reaction is imposed by the hydrogenation-dehydrogenation equilibrium on the other hand, the concentration of polycyclic aromatic hydrocarbons in

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 the effluent from the hydrogenation zone can be lowered by lowering the temperature. When the reaction is imposed by rate constants or by equilibrium, the concentration of polycyclic aromatic hydrocarbons in the effluent from the hydrogenation stage can be lowered by increasing the partial pressure of hydrogen and / or by reduction of the partial oil pressure in the pre-hydrogenation zone. When the reaction is dictated by the rate constants, a decrease in temperature causes a decrease in the rate of conversion of the polycyclic aromatics.

   This phenomenon is undesirable because the concentration of polycyclic aromatic hydrocarbons then increases. Furthermore, when the reaction is at equilibrium, an increase in temperature is undesirable because it results in an increase in the concentration of polycyclic aromatic hydrocarbons. Consequently, for a partial pressure of hydrogen and for a determined contact time, working at the lowest possible temperature at which the reaction is defined by equilibrium results in a reduction to a minimum of the con- centration of polycyclic hydrocarbons in the effluent from the prior hydrogenation.



   As indicated, the concentration of polycyclic aromatic hydrocarbons comprising 3 or more condensed rings found in the effluent from the pre-hydrogenation can be lowered by increasing the partial pressure of the hydrogen. hydrogen during hydrogenation.



  However, prehydrogenation reactors are built to withstand a certain maximum pressure which is usually imposed by the economy of the process and the advantages which may result from an increase in pressure should be considered in comparison with the price. building a

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 reactor and accessories with greater strength. Therefore, within the design limits of an installation, the partial pressure of the hydrogen during the preliminary hydrogenation can be advantageously increased by increasing the rate of circulation of the hydrogen therein.

   In addition, the concentration of polycyclic aromatic hydrocarbons in the effluent can be substantially lowered by controlling the temperature and the space velocity as indicated above. According to the invention, it is also possible to act on the concentration of polycyclic aromatic hydrocarbons in the fresh feed arriving at the preliminary hydrogenation, together with the specified operating limitations, which consists in applying the concept of regulation. feed forward.



   The amorphous base hydrogenation and pretreatment catalyst used in the process of the invention comprises one or more hydrogenation components dispersed in an amorphous base material having relatively low cracking activity. or zero and having a pore size of more than about 20 and preferably about 30 to 500. Useful hydrogenation constituents include the metals of Group VIB and Group VIII of the Periodic Table of the Elements as well as their oxides, sulphides and mixtures thereof.



  Useful Group VIB metals are especially chromium, molybdenum and tungsten, while suitable Group VIII metals are especially iron, nickel, cobalt, metals of platinum mine, namely platinum, iridium and osmium, metals from the illadium mine, namely palladium, rhodium and ruthenium, as well as their mixtures. Among the preferred hydrogenation constituents, there may be mentioned nickel-tungsten sulfide, nickel sulfide, cobalt-molybdenum sulfide, nickel-cobalt-molybdenum sulfide, platinum and palladium.

   Basic subjects

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 Suitable amorphous compounds include oxides of the metals of
Groups IIA, IIIA and IVB of the Periodic Table of the Elements, alone or in combination with silica for the formation of mixtures. Examples of such amorphous base materials are alumina, silica-alumina, silica-zirconia, silica-zirconia-alumina, silica-magnesia, silica, etc. The amorphous base materials used are those having a limited cracking activity index falling in the range of about 15 to 45 and preferably about 20 to 35, as can be measured by the "Cat A" test described by Alexander and Shimp in National Petroleum News, 36, page R-537 (August 2, 1944),

   these characteristics being measured before the catalyst has come into contact with ammonia or nitrogenous organic compounds under the conditions of hydrocracking.



   The metal hydrogenation component of the pre-hydrogenation catalyst and the hydrogenation catalyst is used in amounts and under conditions ensuring substantial removal of sulfur and nitrogen and more selective hydrogenation, ie. that is, sufficient hydrogenation to convert a substantial majority of any organic nitrogen and sulfur compounds in the feed to ammonia and hydrogen sulfide, respectively. It is important for the purposes of the invention that the hydrogenation activity is sufficient for a more complete hydrogenation of a substantial proportion of the condensed polycyclic aromatics of the corresponding saturated feed.

   The amount of hydrogenation component involved in the pre-hydrogenation catalyst depends on the hydrogenation activity of this component and can range from about 0.1 to 45% of the weight of the amorphous base material. cracking. When nickel or metals such as platinum or palladium are used, 0.1 to 6% is preferably taken and more preferably about

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 0.2 to 2%, based on the weight of the amorphous base material. When the hydrogenation component is not nickel, platinum or palladium, it is preferable to take about 8 to 50% thereof, in metal oxides, based on the weight of the amorphous base material.

   The hydrogenation component can be introduced into the amorphous base material by impregnation or by co-precipitation on the surface of the base material, by mixing, e.g. ion exchange or other conventional techniques.



   During the preliminary hydrogenation, the temperature is generally maintained in the range of about 316 to 482 C, and preferably above about 385 C for the removal of sulfur and nitrogen from the gas. hydrocarbon feed, but less than 371 C for the required hydrogenation of the condensed polycyclic aromatic compounds. A partial pressure of hydrogen of about 70 to 246 and preferably about 105 to 176 kg / cm 2 is taken on a pressure gauge, with a liquid hourly space velocity of about 0.2 to 5 volumes per hour and by volume and a hydrogen flow rate of about 178 to 3560 and preferably about 890 to 1780 volumes per volume of oil.



   The hydrocracking catalysts used may also comprise one or more hydrogenation constituents in combination with a support having considerable cracking activity, such as a support, for example based on amorphous silica-alumina or based. siliceous, crystalline aluminosilicates having the required cracking activity or mixtures of such agents having the desired hydrogenation and cracking activity being suitable. It should be noted that the crystalline aluminosilicate cracking component can be used alone or as the sole carrier of the hydrogenation component, but that it is also suitable in combination with an amorphous siliceous cracking base.

   The ratio of the amount of crystalline aluminosilicate to amorphous base material of

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 cracking can vary widely depending on the activity of the two components and can range from about 0 to 100% and preferably. about 3 to 80%.



   The crystalline aluminosilicate cracking component of the hydrocracking catalyst is structurally distinguished by uniformly sized pores consisting of tetrahedra of alumina and silica. For the purposes of the invention, it is desirable to use crystalline aluminosilicates having a pore size of about 6 to 15.



   Both natural and synthetic crystalline aluminosilicates can be used. Among the useful aluminosilicates, mention should be made of synthetic products, such as zeolites X, Y, B, L and T, and products of natural origin, such as faujasite, mordenite, chabazite, erionite, l 'offer, etc.



  These aluminosilicates are preferably used in a form having a low sodium or alkali metal content, i.e. less than about 5% by weight, more preferably only about 2% by weight, expressed as alkali metal oxide, based on the weight of the aluminosilicate.



   These products are prepared by base exchange with a fluid containing metal ions which can be exchanged for sodium ions and other alkali metal ions, as described by Plank et al. In U.S. Patents Nos. 3,140,249 and 3,140,253, as well as by other authors, for the formation of a high activity selective cracking catalyst. Among the metal cations which can be introduced in this way to improve the cracking activity of aluminosilicates, mention should be made of those from Groups IB to VIII of the periodic table of the elements, as well as rare earth metals.

   In addition, the alkali metal can also be removed from the aluminosilicate by base exchange with cations containing hydrogen, such as ammonium or tetra cations.

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 alkylammonium, followed by treatment to form the catalyst in the hydrogen form. In addition, the aluminosilicate can undergo a base exchange aimed at replacing the alkali metal cations with a mixture of the above metal cations or with a mixture of the above metal cations and hydrogen cations.

   The preferred forms of crystalline aluminosilicate are those containing cations of rare earth metals and hydrogen cations, palladium or nickel ions and hydrogen ions, palladium or nickel ions and cations of rare earth metals, palladium ions. or nickel and ions of the rare earth metals and hydrogen ions because these forms of the catalysts have high catalytic activity and good selectivity. The residual alkali metal content, expressed as metal oxides, should be less than about 5% and is preferably less than about 2% by weight in order for the cracking activity and selectivity to have the required values.



   The amorphous base material of the hydrocracking catalyst is distinguished by the fact that it has a higher hydrocracking activity than that of the prehydrogenation catalyst, that it comprises pores of a size greater than about 20 and preferably about 30 to 500!. Amorphous basal cracking materials which can be used include the oxides of the metals of Groups IIA, IIIA and IVB of the Periodic Table of the Elements, in addition to si lica, and mixtures thereof. Examples of suitable amorphous siliceous cracking base materials include silica-alumina, silica-zirconia, silica-zirconia-alumina, silica-magnesia, silica,

  alumina and so on. The amorphous base materials used are those having a cracking activity index of about 20 to 60 and preferably at least about 30, as can be measured by the "Cat A" test described by Alexander and Shimp in National Petroleum News, 36, page R-537 (August 2, 1944).



   The metal hydrogenation component of the catalyst

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 hydrocracking can be used in amounts of about 0.1 to
45% by weight of the cracking component depending on the nature of the cracking component and that of the metal hydrogenating component. The hydrogenation component can be introduced into the cracking component by ion exchange, impregnation, physical mixing or any other known process.



   Nickel and metals such as platinum or palladium are used in amounts of preferably about 0.1 to.
6% and more preferably about 0.2 to 3% of the weight of the zeolite base material. When the metal hydrogenation component is other than nickel, platinum or palladium, it is preferably taken in an amount of about 6 to 30%, as metal oxides by weight of the cracking base material consisting crystalline aluminosilate, or in an amount of about 8 to 50% metal oxides, by weight of the amorphous cracking base material. Hydrogenation constituents, such as mixtures of nickel sulfide and sodium sulfide. tungsten, in amounts of about 5 to 15% by weight of nickel and tungsten,

   platinum in amounts of about 0.1 to 5% by weight, associated with an X zeolite or a Y zeolite containing cations of rare earth metals, hydrogen cations or a mixture of cations of rare earth metals and Hydrogen cations in combination with a siliceous cracking feedstock form very effective hydrocracking catalysts.



   The conversion conditions for the hydrocracking are chosen so as to cause a conversion of the hydrocarbon feed of about 20 to 80% by volume per pass to products boiling below about 204 C. In general, the conditions maintained are the following :

   from about 232 to 482 C and preferably from about 288 to 399 C, partial pressure of hydrogen from about 35 to 210 kg / cm at a gauge and preferably from about 70 to 175 kg / cm2 pressure gauge, space velocity of about 0.1 to 10 volumes per hour per volume and preferably about 1 to

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 5 volumes per hour per volume and rate of hydrogen circulation of about 178 to 3560 volumes per volume of oil and preferably about 534 to 1424 volumes per volume of oil.



   The hydrocarbon feeds which can be treated by the process of the invention with advantage are relatively high boiling point distillates and in particular those boiling from about 204 to 593 C or residual fractions. which are relatively and preferably completely free of ash and asphaltic constituents. Useful hydrocarbon feeds are in particular heavy virgin vacuum distillation gas oils, coking gas oils, catalytic cracking gas oils, heavy aromatic extracts obtained by furfural extraction of high boiling point hydrocarbons, such as light, medium and heavy virgin gas oils, cracked gas oils and their mixtures.



   The temperature has been particularly indicated as a variable allowing the control of the process in the description above, but the space velocity, the rate of hydrogen circulation and the abundance of the polycyclic aromatic compounds condensed in the feed brought to. pre-hydrogenation are also variables which can be used simultaneously for regulation.



   In the combined operations described, the feed to the pre-hydrogenation stage usually has a good organic combined oxygen, nitrogen and sulfur content. stroke higher than that permitted for any subsequent hydocracking operation. These nitrogen compounds (and the ammonia which comes out of the pretreatment apparatus) bind to the catalyst (probably at the aciues sites) and deactivate it. Some deactivation of the hydrogenation-dehydrogenation sites of the catalyst also takes place by absorption of compounds containing sulfur and / or nitrogen.

   By con-

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 sequent, the pretreatment is carried out so as to provide a relatively low hydrocracking conversion which is generally less than about 20%, on a weight basis, and this conversion relates mainly to the ring-opening hydrogenolysis of heterocyclic compounds containing. nitrogen, oxygen and sulfur and, to a limited extent, hydrogenolysis by hydrocracking of other hydrocarbons. The temperatures necessary to achieve the above desired hydrogenation conversions using the prior hydrogenation catalyst can vary widely with the activity of the catalyst and the nature of the hydrocarbon feed.

   At the relatively high temperatures involved in the removal of nitrogen and sulfur during pretreatment, the hydrogenation activity of the pretreatment catalyst is usually very high, but the magnitude of the hydrogenation is usually limited by thermodynamic equilibrium. This situation is favored for the hydrogenation of polycyclic compounds by lowering the temperature below about 371 ° C. in order to relax the thermodynamic limitations.



  Thus, the hydrogenation of the aromatic compounds and that of the unsaturated compounds which provide the required removal of sulfur and nitrogen to below about 100 ppm and preferably to 5 or 10. ppm of nitrogen remaining in the hydrocarbon feed are the main reactions at the preliminary hydrogenation stage, but the results detailed below show the advantages of the successive operations in accordance with the invention and show that these reactions are the main beneficial reactions during pretreatment.



   During hydrocracking, on the other hand, the concentration of nitrogen and sulfur compounds, which are catalyst deactivating poisons, is deliberately kept low, for example from 0.1 to. 100 and preferably less

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 of approximately 50 or 10 p.p.m. of nitrogen in the feed instead of 100 to 2000 p.p.m. or more in the feed allowed upon pre-hydrogenation. Therefore, if the same catalyst is used for the hydrocracking as for the prehydrogenation, the relatively high conversion of hydrocarbons required during hydrocracking is generally obtained at a lower temperature than that prevailing during hydrocracking. previous generation.

   In principle, the pretreatment is carried out by means of a much less active cracking catalyst, but having a high hydrogenation activity, at temperatures somewhat higher than those used for the subsequent hydrocracking, for which A catalyst having a much higher effective activity is taken under the reaction conditions.



   When carrying out the process of the invention, the amount of polycyclic aromatic compounds condensed in the fresh feed and / or in the recycle stream is observed to regulate one or more of the variables intervening in the operations, such as temperature, the space speed, the rate of hydrogen circulation and the conversion per pass, so that the hydrocracking catalyst does not exceed the required aging rate, as can be expressed in C per day or in service life of the catalyst of at least 10,000 hours of use.



  If the concentration of polycyclic aromatics in these two streams is determined by visible and ultraviolet absorption spectroscopy, then the polycyclic aromatics considered are those with 3 to 7 condensed rings.



   Fig. 1 showing on the abscissa the temperature at the first stage in C and on the ordinate, on the left, the relative concentration of polycyclic aromatic compounds condensed from 5 to 7 cycles in the effluent of the first stage, as indicated by ab -

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 sorption of light with a wavelength of 4480, the unit being the absorption factor to be multiplied by 1000, and on the right, the nitrogen content of the effluent from the preliminary hydrogenation, in p.p.m.

   on a weight basis, and shows the influence of the operating temperature of the reactor during the pretreatment on the content of polycyclic aromatic compounds and on the nitrogen content of the effluent from this operation, the conditions being a pressure of 140 kg / cm2 at a pressure gauge, a fresh feed liquid hourly space velocity at
1000 p.p.m. of nitrogen of 1.2 with a gas recycle rate of 1246 volumes of gas per volume of oil without liquid recycle.



   Fig. 2, showing on the abscissa the relative concentration of polycyclic aromatic compounds condensed from 5 to 7 rings in the effluent of the first stage, as indicated by the absorption of light with a wavelength of 4480, the unit being the absorption factor to be multiplied by 1000, and in ordinates the rate of aging of the catalyst in the second stage in C per day, the conditions being a pressure of 114 kg / cm2 at a pressure gauge with an hourly space velocity liquid 0.90 for total feed, and 0.54 for fresh feed, at 1 ppm

   of nitrogen, a per pass conversion of 60% by volume, a gas recycle rate of 979 volumes of gas-per volume of oil with product recycle rising to over 199 C, indicates the relationship between the state of operation of the pretreatment reactor and the rate of aging of the hydrocracking catalyst occurring during the subsequent hydrocracking.



   The results on which the present invention is based were obtained by treating a hydrocarbon feed boiling at about 288 to 510 C and comprising a mixture of coking gas oils, catalytic cracking recycle oils and aromatic fraction obtained by furfural extraction of heavy catalytic cracking recycle oils. This

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 The hydrocarbon feed contains about 1000 ppm by weight of organically combined nitrogen and is subjected to a treatment on a preliminary hydrogenation catalyst, at 140 kg / cm2 at the total pressure gauge, with a liquid hourly space velocity of 1.2 and with a hydrogen recycling rate of 1246 volumes of gas per volume of feed oil.

   The catalyst for the pretreatment or pretreatment of the feed for the removal of sulfur and nitrogen and for the hydrogenation of the polycyclic aromatic compounds is a commercially available catalyst which com - takes a hydrogenation component, such as nickel-tungsten distributed in basic amorphous silica-alumina having a relatively low cracking activity. Many other catalysts allow the judicious pretreatment of the feed as described herein. The object of the invention is therefore a process for carrying out the preliminary hydrogenation rather than the particular catalyst which is used for this purpose.

   During the pretreatment of the hydrocarbon feed, the operation is essentially a hydrogenation aimed at eliminating the sulfur and nitrogen compounds, even at the cost of a moderate conversion of the admitted hydrocarbons, namely from 10 to 20% by volume, under the effect of the prior hydrogenation catalyst which has a limited cracking activity. In any case, even if the catalyst for the preliminary hydrogenation is capable of deactivation by the compounds of nitrogen and sulfur, it must retain a hydrogenation activity allowing the realization of the above hydrogenation, as well as hydrogenation of polycyclic aromatic compounds in food.



   As mentioned, Fig.l indicates the effect of the temperature of the reactor on the content of polycyclic aromatic compounds and on the nitrogen content of the effluent obtained after the preliminary hydrogenation. Line "A" shows that

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 as the temperature increases during the preliminary hydrogenation, the amount of nitrogen in the effluent can be lowered to the point that at a temperature of about 399 C the amount of nitrogen remaining in the effluent is less than about 1 ppm and in fact little more than 0.5 ppm on a weight basis. On the other hand, at temperatures below about 393 ° C, the amount of nitrogen remaining in the effluent after pre-hydrogenation is greater than about 1 p.p.m. by weight.

   This value clearly shows that there is no one-to-one relationship between the content of condensed polycyclic aromatic compounds and the content of organically combined nitrogen in the effluent from the pre-hydrogenation stage. Rather, it emerges that for a given concentration of condensed polycyclic aromatic compounds, two different nitrogen contents can be found depending on whether the effluent was held at a temperature falling to the right or to the left of that corresponding to the minimum trough. of curve "B".

   Curve "B", which is representative of the concentration of aromatic compounds remaining in the stream after the preliminary hydrogenation as a function of the temperature of the reactor, shows that at 399 C the concentration reaches 75 ppm for the polycyclic aromatic compounds. from 5 to 7 cycles, as indicated by the absorption of light, and that this concentration of aromatic compounds can be greatly reduced by lowering the pre-treatment temperature to a value below that necessary to eliminate nitrogen from the feed. The lower point of curve "B" in FIG. 1 indicates the lowest temperature at which the hydrogenation-dehydrogenation equilibrium is reached for the catalyst involved.

   When the pre-hydrogenation reactor operates so that the reaction rate is the determining factor, the temperature-concentration relationship is represented by the branch of the curve "B" to the left of the

 <Desc / Clms Page number 24>

 minimum point. Under such working conditions, the concentration of condensed polycyclic aromatic compounds can be attenuated either by an increase in temperature or by a decrease in space velocity. On the other hand, when the reaction in the preliminary hydrogenation reactor is imposed by the hydrogenation-dehydrogenation equilibrium, the temperature-concentration relationship is represented by the branch of the curve "B" to the right of the line. aforementioned lower point.

   Under such working conditions and according to the invention, the concentration of condensed polycyclic aromatic compounds can be lowered by lowering the temperature. Fig. 1 therefore clearly demonstrates the advantages of removing sulfur and nitrogen at elevated temperatures and then carrying out the hydrogenation of the condensed polycyclic aromatics at a lower temperature. It should be noted, however, that the relationship and shape of the curves depend on the nature of the catalyst and its rate of aging.



  It should be noted that due to the nitrogen sensitivity of amorphous based hydrocracking catalysts compared to the sensitivity of a crystalline aluminosilicate, the preliminary hydrogenation cannot be carried out effectively outside of!, interval delimited by the dotted line in the lower area of FIG. 1, if it is desired to use an amorphous-based hydrocracking catalyst which relates to FIG. 2 in the second stage.



   Fig. 2 specifies in the case of two different hydrocracking catalysts "A" and "B" the effect of the working conditions in the reduction of the condensed polycyclic aromatic compounds and therefore the rate of aging of the two catalysts used. at a second stage intended mainly to ensure hydrocracking.



   It should be noted that the slope of the two lines is

 <Desc / Clms Page number 25>

 fortuitously almost the same, but it should be noted that this relationship between the curves can change a lot for different catalysts. However, it is more important to note that the catalysts age more quickly as the concentration of polycyclic aromatic compounds increases in the effluent from the pre-hydrogenation stage. It is, however, believed that it was unexpected and unpredictable that catalyst "B" comprising a mixture of crystalline aluminosilicate and amorphous silica-alumina as the hydrocracking base material had an aging rate lower than. that of the amorphous-based catalyst "A".

   It is therefore quite obvious that the method of carrying out the preliminary hydrogenation aimed at limiting the concentration of insufficiently hydrogenated aromatic compounds and of nitrogen in the feed coming into contact with the hydrocracking catalyst is of very great importance. for hydrocracking and in particular for the rate of aging of the catalysisw 'hydrocracking. As already stated, FIG. 2 Indicates the concentration of polycyclic aromatic compounds of 5 to 7 rings condensed in the effluent from the pre-hydrogenation stage (as shown by the absorption of light of a wavelength of 4480 by this effluent) that can be obtained by means of each of the catalysts.

   The feeds used for this purpose are all liquid effluents which have undergone preliminary hydrogenation and contain approximately
1 p.p.m. by weight of organically combined nitrogen, obtained under the pre-hydrogenation conditions identifiable by means of FIG. 1. The temperature at which the power supplies for FIG. 2 values are obtained varies with the age of the prehydrogenation catalyst (eg, the service life of the prehydrogenation reactor and / or the degree of deactivation of the catalyst). Depending on this temperature, the power supplies to which FIG. 2 have a different content of aroma-

 <Desc / Clms Page number 26>

 condensed polycyclic ticks, but they still have an organically combined nitrogen content of 1 p.p.m.



   It is therefore obvious that the specification of the nitrogen content of the liquid effluent from the pre-hydrogenation reactor alone is not sufficient to guarantee perfect control of the rate of aging of the catalyst during catalytic hydrocracking. ulterior. In particular, it has been shown that for a determined nitrogen content in the effluent from the prior hydrogenation reactor, the aging of the catalyst during the subsequent hydrocracking is independent of this content, but that it is a function of the content of polycyclic aromatic compounds in the feed admitted for hydrocracking.



   To illustrate the invention more clearly, one can assume that it is desired that the rate of aging of the catalyst does not exceed 0.165 ° C. per day in the hydrocracking stages of the process. From Fig. 2 it can be deduced that it is necessary to carry out the preliminary hydrogenation so as to obtain an effluent product which contains about 22 ppm of polycyclic aromatic compounds of 5 to 7 rings, as indicated by the light absorption in the case of uses an amorphous-based catalyst to which FIG. 2 for the hydrocracking stages of the process and a maximum of about 60 p.p.m. of polycyclic aromatic compounds of 5 to 7 condensed rings if the mixed crystalline-amorphous base catalyst referred to in FIG. 2 also for the hydrocracking stages in the process.

   It can be assumed that the amorphous-based catalyst is used in the hydrocracking stages of the process. We then deduce from FIG. 1 that a satisfactory effluent can be obtained from the preliminary hydrogenation at temperatures of 357 to 379 ° C. under the conditions specified in FIG. 1 by means of the catalyst to which FIG. 1 for the degree of aging of the catalyst which has been determined

 <Desc / Clms Page number 27>

 under the conditions which led to the results shown in FIG. 1.However, when the catalyst to which FIG. 1 ages further, the line representing nitrogen content in FIG.

   1 moves to the right and the descending branch of the U-shaped curve representative of the content of polycyclic aromatic compounds expressed by the light absorption moves to the right, while the ascending branch of this curve remains fixed, the consequence being that the minimum value for the content of polycyclic aromatic compounds slowly increases. Therefore, as the prehydrogenation catalyst ages, the lower limit for the temperature range corresponding to satisfactory prehydrogenation increases, while the upper limit remains constant, so that the interval for prehydrogenation satisfactory shrinks in proportion.



   It is therefore evident that the numerical values to which FIG. 1 evolve as the pre-hydrogenation catalyst ages and therefore cannot be used as such to ensure the production of a suitable pre-hydrogenation effluent throughout the service life of the pre-hydrogenation catalyst . However, the qualitative aspects of the results to which FIG. 1 identify the field of the invention and the process it relates to for producing a pre-hydrogenation effluent, the quality and composition of which, at least as regards the combined concentrations of nitrogen and of condensed polycyclic aromatic compounds, are tolerated for the hydro-cracking stages.



   The quantitative, but not qualitative, character of the correlations in Figs. 1 and 2 vary with working conditions, such as pressure, space velocities, recycling rate

 <Desc / Clms Page number 28>

 of hydrogen and the conversion rates which have been kept constant for the establishment of the data referred to in Figs. 1 and 2. The quantitative aspects of the correlations also vary from catalyst to catalyst and for the correlation of FIG. 2, this is directly representative. The correlation of FIG. 1 emerges from the table which makes it possible to compare the service qualities of two different prior hydrogenation catalysts available commercially for a degree of aging which is also substantially low at 402.2 ° C. under the defined working conditions to which FIG. 1.

   The data for catalyst "A" in the table is taken from FIG. 1.



   In the combination of operations described herein, the feed fed to the prehydrogenation usually has a much higher organically combined oxygen, nitrogen and sulfur content than the feed accepted in the hydrochloric stages. subsequent cracking. These nitrogen compounds (and the ammonia which comes from them in the pre-hydrogenation reactor) absorb onto the catalyst (probably at the acid sites) and deactivate it. Some deactivation of the hydrogenation-dehydrogenation sites of the catalyst also takes place by absorption of nitrogen and / or sulfur compounds at these sites.

   Therefore, the preliminary hydrogenation is carried out in such a way as to ensure a relatively weak hydrocracking, compatible mainly with the hydrogenolysis by opening of the ring of the heretocyclic compounds of nitrogen, oxygen and sulfur and with limited hydrocracking of the compounds. hydrocarbons. The temperature required for such a conversion using the deactivated catalyst from the prehydrogenation stage is much higher than that which would be required with the relatively unactivated, high activity hydrocracking stage catalyst.

   At the relatively high temperature of

 <Desc / Clms Page number 29>

 pre-hydrogenation, the hydrogenation activity of the deactivated pre-treatment catalyst is very high, therefore hydrogenation of aromatics and unsaturated compounds is the main reaction of hydrocarbons during hydrogenation preliminary and the results presented here show that it can thus be the main advantageous reaction as-urea during the preliminary hydrogenation.



   During hydrocracking, on the other hand, the concentration of poisons containing nitrogen and sulfur which deactivate the catalyst is deliberately kept low, for example at a value of 0.1. at 50 ppm of nitrogen and preferably at most 5 or 10 ppm in the feed instead of 100 to 2000 ppm of nitrogen in the feed admitted to the prior hydrogenation. Therefore, if the same catalyst is used for the hydrocracking and for the prehydrogenation, even the relatively high conversion of hydrocarbons desired for the hydrocracking stages is generally achieved at a temperature lower than that used. for the relatively low conversion desired for the prehydrogenation catalyst which is poisoned by nitrogen compounds.

   Essentially, the prehydrogenation is carried out using a deactivated catalyst at a somewhat higher temperature than that of the subsequent hydrocracking where the catalyst exhibits higher activity.



   There are circumstances in which it may be advantageous to carry out a one-stage process in which the prehydrogenation and hydrocracking are carried out together under substantially the same conditions. For the application of the principle of the invention in this case, the pre-hydrogenation catalyst is housed upstream of the hydrocracking catalyst and the temperature is kept lower in the region of the neighboring pre-hydrogenation catalyst. cataly-

 <Desc / Clms Page number 30>

 hydrocracking sor than in that close to the reactor inlet.



   BOARD
EFFECT OF THE CATALYST ON THE CONTENT OF AROMATIC COMPOUNDS
AND NITROGEN FROM PRIOR HYDROGENATION EFFLUENT (1300 p.p.m. by weight in feed)
 EMI30.1
 
<tb> Job <SEP> conditions <SEP>
<tb>
<tb>
<tb>
<tb>
<tb> Rate <SEP> of <SEP> circulation <SEP> of <SEP> H2 <SEP> 1246 <SEP> vol <SEP> gas / vol <SEP> oil
<tb>
<tb>
<tb>
<tb> Temperature, <SEP> C <SEP> 402.2
<tb>
<tb>
<tb>
<tb>
<tb> Speed <SEP> spatial <SEP> hourly <SEP> liquid <SEP> 1,2
<tb>
<tb>
<tb>
<tb>
<tb> Pressure, <SEP> kg / cm2 <SEP> (pressure gauge)

   <SEP> 140
<tb>
<tb>
<tb>
<tb>
<tb> Nature <SEP> of the <SEP> catalyst <SEP> for prior hydrogenation <SEP> <SEP> A <SEP> B
<tb>
<tb>
<tb>
<tb>
<tb> Effluent <SEP> from <SEP> prior hydrogenation <SEP>
<tb>
<tb>
<tb>
<tb>
<tb> Concentration <SEP> relative <SEP> in <SEP> compounds
<tb>
<tb>
<tb> aromatics <SEP> polycyclic <SEP> s <SEP> from <SEP> 5 <SEP> to <SEP> 7
<tb>
<tb>
<tb> condensed <SEP> cycles, <SEP> determined <SEP> by
<tb>
<tb>
<tb> absorption <SEP> to <SEP> 4480 <SEP> A <SEP> (UV)
<tb>
<tb>
<tb> absorption factor <SEP> <SEP> x <SEP> 10 <SEP> 3 <SEP> 10.9 <SEP> 9.0
<tb>
<tb>
<tb> Nitrogen <SEP> combined <SEP> organically,
<tb>
<tb>
<tb> p.p.m.

   <SEP> in <SEP> weight <SEP> 0.25 <SEP> 0.8
<tb>
 
Although various embodiments and details of embodiments have been described to illustrate the invention, it goes without saying that the latter is susceptible of numerous variations and modifications without departing from its scope.

 

Claims (1)

CLAIMS 1.- Process for improving the quality of a hydrocarbon feed comprising nitrogen compounds and condensed polycyclic aromatic compounds, characterized in that the hydrocarbon feed is passed initially in contact with a catalyst having mainly an activity of hydrogenation and then in contact with a hydrogenolysis catalyst having substantial cracking activity and the removal of nitrogen from the hydrocarbon feed and hydrogenation of the polycyclic aromatic compounds is carried out by means of this catalyst having mainly an activity. of hydrogenation under the conditions of the hydrogenation with a decreasing temperature profile chosen so as to ensure the more complete hydrogenation of the polycyclic aromatic compounds of the feed after the required removal of the combined nitrogen of the load. 2. - Improved process for refining a hydrocarbon feed comprising nitrogen compounds and polycyclic aromatic compounds, firstly by removing nitrogen from the feed during a first step of catalytic contact and secondly by hydrogenolysis of the feed during at least one second stage of catalytic contact, characterized in that another stage of hydrogenating catalytic contact is carried out between the first stage and the second, at a temperature lower than that applied for the first stage and chosen in such a way in ensuring mainly the hydrogenation of the polycyclic aromatic compounds remaining in the hydrocarbon feed collected on leaving the first stage of catalytic contact. 3. - Improved process for improving the quality of a hydrocarbon feed containing nitrogen compounds and condensed polycyclic aromatic compounds converted to lower boiling point constituents comprising gasoline, <Desc / Clms Page number 32> characterized in that the hydrocarbon feed is subjected to a preliminary hydrogenating treatment by means of a hydrogenation catalyst having a relatively low cracking activity at a temperature sufficiently high to cause the substantial elimination of the nitrogen from the gas. charge, then another contact of the feed is carried out at a lower temperature suitable for ensuring a more complete hydrogenation of the condensed polycyclic aromatic compounds and the hydrocarbon feed is then subjected to the conditions of hydrocracking in the presence of a d catalyst. 'nitrogen sensitive hydrocracking .. 4. A process according to claim 3, characterized in that the nitrogen is removed from the feed at a temperature above about 385 C and the polycyclic aromatic compounds condensed at a lower temperature are more completely hydrogenated. 5. A process according to claim 3, characterized in that the hydrogenation of the polycyclic compounds is carried out at a temperature of 260 to 371 C. 6. - Process according to claim 3, characterized in that the hydrocracking of the load is carried out by means of a hydrocracking catalyst containing a crystalline aluminosilicate at a temperature above about 260 C. 7. A process according to claim 3, characterized in that the rate of conversion of the hydrocarbon feedstock into products having a lower boiling point falling in the gasoline boiling range is maintained. to a value not exceeding about 20% during the removal of nitrogen from the feed. 8. - Process according to claim 3, characterized in that the nitrogen content of the hydrocarbon feed supplied to the hydrocracking is higher when using a hydrocracking catalyst containing a crystalline aluminosilicate than when using a amorphous based hydrocracking catalyst. <Desc / Clms Page number 33> 9. A method according to claim 3, characterized in that the hydrocracking catalyst comprises a mixture @ntime of a crystalline aluminosilicate having undergone an exchange against rare earth ions and an amorphous silica-alumina base in association with a or more hydrogenation constituents suitable for improving the hydrogenating cracking of the hydrocarbon feedstock.